Vol. 78 Tuesday, 

No. 10 January 15, 2013 

Part II 

Environmental Protection Agency 

40 CFR Parts 50, 51, 52 et al. 

National Ambient Air Quality Standards for Particulate Matter; Final Rule 


tkelley on DSK3SPTVN1PROD with 
3086 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Parts 50, 51, 52, 53 and 58 

[EPA–HQ–OAR–2007–0492; FRL–9761–8] 

RIN 2060–AO47 

National Ambient Air Quality 

Standards for Particulate Matter 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Final rule. 

SUMMARY: Based on its review of the air 

quality criteria and the national ambient 

air quality standards (NAAQS) for 

particulate matter (PM), the EPA is 

making revisions to the suite of 

standards for PM to provide requisite 

protection of public health and welfare 

and to make corresponding revisions to 

the data handling conventions for PM 

and to the ambient air monitoring, 

reporting, and network design 

requirements. The EPA also is making 

revisions to the prevention of significant 

deterioration (PSD) permitting program 

with respect to the NAAQS revisions. 

With regard to primary (health-based) 

standards for fine particles (generally 

referring to particles less than or equal 

to 2.5 micrometers (mm) in diameter, 

PM2.5), the EPA is revising the annual 

PM2.5 standard by lowering the level to 

12.0 micrograms per cubic meter (mg/ 

m3) so as to provide increased 

protection against health effects 

associated with long- and short-term 

exposures (including premature 

mortality, increased hospital admissions 

and emergency department visits, and 

development of chronic respiratory 

disease), and to retain the 24-hour PM2.5

standard at a level of 35 mg/m3. The EPA 

is revising the Air Quality Index (AQI) 

for PM2.5 to be consistent with the 

revised primary PM2.5 standards. With 

regard to the primary standard for 

particles generally less than or equal to 

10 mm in diameter (PM10), the EPA is 

retaining the current 24-hour PM10

standard to continue to provide 

protection against effects associated 

with short-term exposure to thoracic 

coarse particles (i.e., PM10-2.5). With 

regard to the secondary (welfare-based) 

PM standards, the EPA is generally 

retaining the current suite of secondary 

standards (i.e., 24-hour and annual 

PM2.5 standards and a 24-hour PM10

standard). Non-visibility welfare effects 

are addressed by this suite of secondary 

standards, and PM-related visibility 

impairment is addressed by the 

secondary 24-hour PM2.5 standard. 

DATES: The final rule is effective on 

March 18, 2013. 

ADDRESSES: Section X.B requests 

comments on an information collection 

request regarding changes to the 

monitoring requirements. Submit your 

comments, identified by Docket ID No. 

EPA–HQ–OAR–2007–0492, to the EPA 

by one of the following methods: 

• www.regulations.gov: Follow the 

on-line instructions for submitting 

comments. 

• Email: a-and-r-Docket@epa.gov. 

• Fax: 202–566–9744. 

• Mail: Docket No. EPA–HQ–OAR– 

2007–0492, Environmental Protection 

Agency, Mail code 6102T, 1200 

Pennsylvania Ave. NW., Washington, 

DC 20460. Please include a total of two 

copies. 

• Hand Delivery: Docket No. EPA– 

HQ–OAR–2007–0492, Environmental 

Protection Agency, EPA West, Room 

3334, 1301 Constitution Ave. NW., 

Washington, DC. Such deliveries are 

only accepted during the Docket’s 

normal hours of operation, and special 

arrangements should be made for 

deliveries of boxed information. 

Instructions: Direct your comments to 

Docket ID No. EPA–HQ–OAR–2007– 

0492. The EPA’s policy is that all 

comments received will be included in 

the public docket without change and 

may be made available online at 

www.regulations.gov, including any 

personal information provided, unless 

the comment includes information 

claimed to be Confidential Business 

Information (CBI) or other information 

whose disclosure is restricted by statute. 

Do not submit information that you 

consider to be CBI or otherwise 

protected through www.regulations.gov 

or email. The www.regulations.gov Web 

site is an ‘‘anonymous access’’ system, 

which means the EPA will not know 

your identity or contact information 

unless you provide it in the body of 

your comment. If you send an email 

comment directly to the EPA without 

going through www.regulations.gov your 

email address will be automatically 

captured and included as part of the 

comment that is placed in the public 

docket and made available on the 

Internet. If you submit an electronic 

comment, the EPA recommends that 

you include your name and other 

contact information in the body of your 

comment and with any disk or CD–ROM 

you submit. If the EPA cannot read your 

comment due to technical difficulties 

and cannot contact you for clarification, 

the EPA may not be able to consider 

your comment. Electronic files should 

avoid the use of special characters, any 

form of encryption, and be free of any 

defects or viruses. For additional 

information about EPA’s public docket 

visit the EPA Docket Center homepage 

at http://www.epa.gov/epahome/ 

dockets.htm. Comments on this 

information collection request should 

also be sent to the Office of Management 

and Budget (OMB). See section X.B 

below for additional information 

regarding submitting comments to OMB. 

Docket: The EPA has established a 

docket for this action under Docket No. 

EPA–HQ–OAR–2007–0492. All 

documents in the docket are listed on 

the www.regulations.gov Web site. This 

includes documents in the rulemaking 

docket (Docket ID No. EPA–HQ–OAR– 

2007–0492) and a separate docket, 

established for 2009 Integrated Science 

Assessment (Docket No. EPA–HQ– 

ORD–2007–0517), that has have been 

incorporated by reference into the 

rulemaking docket. All documents in 

these dockets are listed on the 

www.regulations.gov Web site. Although 

listed in the index, some information is 

not publicly available, e.g., CBI or other 

information whose disclosure is 

restricted by statute. Certain other 

material, such as copyrighted material, 

is not placed on the Internet and may be 

viewed, with prior arrangement, at the 

EPA Docket Center. Publicly available 

docket materials are available either 

electronically in www.regulations.gov or 

in hard copy at the Air and Radiation 

Docket and Information Center, EPA/ 

DC, EPA West, Room 3334, 1301 

Constitution Ave. NW., Washington, 

DC. The Public Reading Room is open 

from 8:30 a.m. to 4:30 p.m., Monday 

through Friday, excluding legal 

holidays. The telephone number for the 

Public Reading Room is (202) 566–1744 

and the telephone number for the Air 

and Radiation Docket and Information 

Center is (202) 566–1742. For additional 

information about EPA’s public docket 

visit the EPA Docket Center homepage 

at: http://www.epa.gov/epahome/ 

dockets.htm. 

FOR FURTHER INFORMATION CONTACT: Ms. 

Beth M. Hassett-Sipple, Health and 

Environmental Impacts Division, Office 

of Air Quality Planning and Standards, 

U.S. Environmental Protection Agency, 

Mail code C504–06, Research Triangle 

Park, NC 27711; telephone: (919) 541– 

4605; fax: (919) 541–0237; email: 

hassett-sipple.beth@epa.gov. 

SUPPLEMENTARY INFORMATION: 

General Information 

Availability of Related Information 

A number of the documents that are 

relevant to this rulemaking are available 

through the EPA’s Office of Air Quality 

Planning and Standards (OAQPS) 

Technology Transfer Network (TTN) 

Web site at http://www.epa.gov/ttn/ 

naaqs/standards/pm/s_pm_index.html. 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3087 

These documents include the Plan for 

Review of the National Ambient Air 

Quality Standards for Particulate Matter 

(U.S. EPA, 2008a), available at http:// 

www.epa.gov/ttn/naaqs/standards/pm/ 

s_pm_2007_pd.html, the Integrated 

Science Assessment for Particulate 

Matter (U.S. EPA, 2009a), available at 

http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_isa.html, the 

Quantitative Health Risk Assessment for 

Particulate Matter (U.S. EPA, 2010a), 

available at http://www.epa.gov/ttn/ 

naaqs/standards/pm/ 

s_pm_2007_risk.html, the Particulate 

Matter Urban-Focused Visibility 

Assessment (U.S. EPA 2010b), available 

at http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_risk.html, 

and the Policy Assessment for the 

Review of the Particulate Matter 

National Ambient Air Quality 

Standards (U.S. EPA, 2011a), available 

at http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_pa.html. 

These and other related documents are 

also available for inspection and 

copying in the EPA docket identified 

above. 

Table of Contents 

The following topics are discussed in this 

preamble: 

I. Executive Summary 

A. Purpose of This Regulatory Action 

B. Summary of Major Provisions 

C. Costs and Benefits 

II. Background 

A. Legislative Requirements 

B. Review of the Air Quality Criteria and 

Standards for PM 

1. Previous PM NAAQS Reviews 

2. Litigation Related to the 2006 PM 

Standards 

3. Current PM NAAQS Review 

C. Related Control Programs To Implement 

PM Standards 

D. Summary of Proposed Revisions to the 

PM NAAQS 

E. Organization and Approach to Final PM 

NAAQS Decisions 

III. Rationale for Final Decisions on the 

Primary PM2.5 Standards 

A. Background 

1. General Approach Used in Previous 

Reviews 

2. Remand of Primary Annual PM2.5

Standard 

3. General Approach Used in the Policy 

Assessment for the Current Review 

B. Overview of Health Effects Evidence 

C. Overview of Quantitative 

Characterization of Health Risks 

D. Conclusions on the Adequacy of the 

Current Primary PM2.5 Standards 

1. Introduction 

a. Evidence- and Risk-based Considerations 

in the Policy Assessment 

b. CASAC Advice 

c. Administrator’s Proposed Conclusions 

Concerning the Adequacy of the Current 

Primary PM2.5 Standards 

2. Comments on the Need for Revision 

3. Administrator’s Final Conclusions 

Concerning the Adequacy of the Current 

Primary PM2.5 Standards 

E. Conclusions on the Elements of the 

Primary Fine Particle Standards 

1. Indicator 

2. Averaging Time 

3. Form 

a. Annual Standard 

b. 24-Hour Standard 

4. Level 

a. General Approach for Considering 

Standard Levels 

b. Proposed Decisions on Level 

i. Consideration of Alternative Standard 

Levels in the Policy Assessment 

ii. CASAC Advice 

iii. Administrator’s Proposed Decisions on 

the Primary PM2.5 Standard Levels 

c. Comments on Standard Levels 

i. Annual Standard Level 

ii. 24-Hour Standard Level 

d. Administrator’s Final Conclusions on 

the Primary PM2.5 Standard Levels 

F. Administrator’s Final Decisions on the 

Primary PM2.5 Standards 

IV. Rationale for Final Decision on Primary 

PM10 Standard 

A. Background 

1. Previous Reviews of the PM NAAQS 

a. Reviews Completed in 1987 and 1997 

b. Review Completed in 2006 

2. Litigation Related to the 2006 Primary 

PM10 Standards 

3. General Approach Used in the Current 

Review 

B. Health Effects Related to Exposure to 

Thoracic Coarse Particles 

C. Consideration of the Current and 

Potential Alternative Standards in the 

Policy Assessment 

1. Consideration of the Current Standard in 

the Policy Assessment 

2. Consideration of Potential Alternative 

Standards in the Policy Assessment 

D. CASAC Advice 

E. Administrator’s Proposed Conclusions 

Concerning the Adequacy of the Current 

Primary PM10 Standard 

F. Public Comments on the Administrator’s 

Proposed Decision To Retain the Primary 

PM10 Standard 

G. Administrator’s Final Decision on the 

Primary PM10 Standard 

V. Communication of Public Health 

Information 

VI. Rationale for Final Decisions on the 

Secondary PM Standards 

A. Background 

1. Approaches Used in Previous Reviews 

2. Remand of 2006 Secondary PM2.5

Standards 

3. General Approach Used in the Policy 

Assessment for the Current Review 

B. Proposed Decisions on Secondary PM 

Standards 

1. PM-related Visibility Impairment 

a. Nature of PM-related Visibility 

Impairment 

i. Relationship Between Ambient PM and 

Visibility 

ii. Temporal Variations of Light Extinction 

iii. Periods During the Day of Interest for 

Assessment of Visibility 

iv. Exposure Durations of Interest 

v. Periods of Fog and Rain 

b. Public Perception of Visibility 

Impairment 

c. Summary of Proposed Conclusions 

i. Adequacy 

ii. Indicator 

iii. Averaging Time 

iv. Form 

v. Level 

vi. Administrator’s Proposed Conclusions 

vii. Related Technical Analysis 

2. Other (Non-Visibility) PM-related 

Welfare Effects 

a. Evidence of Other Welfare Effects 

Related to PM 

b. CASAC Advice 

c. Summary of Proposed Decisions 

Regarding Other Welfare Effects 

C. Comments on Proposed Rule 

1. Comments on Proposed Secondary PM 

Standard for Visibility Protection 

a. Overview of Comments 

b. Indicator 

i. Comments on Calculated vs. Directly 

Measured Light Extinction 

ii. Comments on Specific Aspects of 

Calculated Light Extinction Indicator 

c. Averaging Time 

d. Form 

e. Level 

i. Comments on Visibility Preference 

Studies 

ii. Specific Comments on Level 

f. Need for a Distinct Secondary Standard 

g. Legal Issues 

h. Relationship With Regional Haze 

Program 

2. Comments on the Proposed Decision 

Regarding Non-Visibility Welfare Effects 

D. Conclusions on Secondary PM 

Standards 

1. Conclusions Regarding Secondary PM 

Standards To Address Non-Visibility 

Welfare Effects 

2. Conclusions Regarding Secondary PM 

Standards for Visibility Protection 

E. Administrator’s Final Decisions on 

Secondary PM Standards 

VII. Interpretation of the NAAQS for PM 

A. Amendments to Appendix N: 

Interpretation of the NAAQS for PM2.5

1. General 

2. Monitoring Considerations 

3. Requirements for Data Use and 

Reporting for Comparison With the 

NAAQS for PM2.5

4. Comparisons with the PM2.5 NAAQS 

B. Exceptional Events 

C. Updates for Data Handling Procedures 

for Reporting the Air Quality Index 

VIII. Amendments to Ambient Monitoring 

and Reporting Requirements 

A. Issues Related to 40 CFR Part 53 

(Reference and Equivalent Methods) 

1. PM2.5 and PM10-2.5 Federal Equivalent 

Methods 

2. Use of Chemical Speciation Network 

(CSN) Methods to Support the Proposed 

New Secondary PM2.5 Visibility Index 

NAAQS 

B. Changes to 40 CFR Part 58 (Ambient Air 

Quality Surveillance) 

1. Terminology Changes 

2. Special Considerations for 

Comparability of PM2.5 Ambient Air 

Monitoring Data to the NAAQS 


tkelley on DSK3SPTVN1PROD with 
3088 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

a. Revoking Use of Population-Oriented as 

a Condition for Comparability of PM2.5

Monitoring Sites to the NAAQS 

b. Applicability of Micro- and Middle-scale 

Monitoring Sites to the Annual PM2.5

NAAQS 

3. Changes to Monitoring for the National 

Ambient Air Monitoring System 

a. Background 

b. Primary PM2.5 NAAQS 

i. Addition of a Near-road Component to 

the PM2.5 Monitoring Network 

ii. Use of PM2.5 Continuous FEMs at 

SLAMS 

c. Revoking PM10-2.5 Speciation 

Requirements at NCore Sites 

d. Measurements for the Proposed New 

PM2.5 Visibility Index NAAQS 

4. Revisions to the Quality Assurance 

Requirements for SLAMS, SPMs, and 

PSD 

a. Quality Assurance Weight of Evidence 

b. Quality Assurance Requirements for the 

Chemical Speciation Network 

c. Waivers for Maximum Allowable 

Separation of Collocated PM2.5 Samplers 

and Monitors 

5. Revisions To Probe and Monitoring Path 

Siting Criteria 

a. Near-road Component to the PM2.5

Monitoring Network 

b. CSN Network 

c. Reinsertion of Table E–1 to Appendix E 

6. Additional Ambient Air Monitoring 

Topics 

a. Annual Monitoring Network Plans and 

Periodic Assessment 

b. Operating Schedules 

c. Data Reporting and Certification for CSN 

and IMPROVE Data 

d. Requirements for Archiving Filters 

IX. Clean Air Act Implementation 

Requirements for the PM NAAQS 

A. Designation of Areas 

1. Overview of Clean Air Act Designations 

Requirements 

2. Proposed Designations Schedules 

3. Comments and Responses 

4. Final Intended Designations Schedules 

B. Section 110(a)(2) Infrastructure SIP 

Requirements 

C. Implementing the Revised Primary 

Annual PM2.5 NAAQS in Nonattainment 

Areas 

D. Prevention of Significant Deterioration 

and Nonattainment New Source Review 

Programs for the Revised Primary 

Annual PM2.5 NAAQS 

1. Prevention of Significant Deterioration 

a. Transition Provision (Grandfathering) 

i. Proposal 

ii. Comments and Responses 

iii. Final Action 

b. Modeling Tools and Guidance 

Applicable to the Revised Primary 

Annual PM2.5 NAAQS 

c. PSD Screening Tools: Significant 

Emissions Rates, Significant Impact 

Levels, and Significant Monitoring 

Concentration 

d. PSD Increments 

e. Other PSD Transition Issues 

2. Nonattainment New Source Review 

E. Transportation Conformity Program 

F. General Conformity Program 

X. Statutory and Executive Order Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

B. Paperwork Reduction Act 

C. Regulatory Flexibility Act 

D. Unfunded Mandates Reform Act 

E. Executive Order 13132: Federalism 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

and Safety Risks 

H. Executive Order 13211: Actions that 

Significantly Affect Energy Supply, 

Distribution, or Use 

I. National Technology Transfer and 

Advancement Act 

J. Executive Order 12898: Federal Actions 

To Address Environmental Justice in 

Minority Populations and Low-Income 

Populations 

K. Congressional Review Act 

References 

I. Executive Summary 

A. Purpose of This Regulatory Action 

Sections 108 and 109 of the Clean Air 

Act (CAA) govern the establishment, 

review, and revision, as appropriate, of 

the national ambient air quality 

standards (NAAQS) to protect public 

health and welfare. The CAA requires 

periodic review of the air quality 

criteria—the science upon which the 

standards are based—and the standards 

themselves. This rulemaking is being 

done pursuant to these statutory 

requirements. The schedule for 

completing this review is established by 

a court order. 

In 2006, the EPA completed its last 

review of the PM NAAQS. In that 

review, the EPA took three principal 

actions: (1) With regard to fine particles 

(generally referring to particles less than 

or equal to 2.5 micrometers (mm) in 

diameter, PM2.5), at that time, the EPA 

revised the level of the primary 24-hour 

PM2.5 standard from 65 to 35 mg/m3 and 

retained the level of the primary annual 

PM2.5 standard; (2) With regard to the 

primary standards for particles less than 

or equal to 10 mm in diameter (PM10), 

the EPA retained the primary 24-hour 

PM10 standard to continue to provide 

protection against effects associated 

with short-term exposure to thoracic 

coarse particles (i.e., PM10-2.5) and 

revoked the primary annual PM10

standard; and (3) the EPA also revised 

the secondary standards to be identical 

in all respects to the primary standards. 

In subsequent litigation, the U.S. 

Court of Appeals for the District of 

Columbia Circuit remanded the primary 

annual PM2.5 standard to the EPA 

because the Agency had failed to 

explain adequately why the standard 

provided the requisite protection from 

both short- and long-term exposures to 

fine particles, including protection for 

at-risk populations such as children. 

The court remanded the secondary 

PM2.5 standards to the EPA because the 

Agency failed to explain adequately 

why setting the secondary standards 

identical to the primary standards 

provided the required protection for 

public welfare, including protection 

from PM-related visibility impairment. 

The EPA initiated this review in June 

2007. Between 2007 and 2011, the EPA 

prepared draft and final Integrated 

Science Assessments, Risk and 

Exposure Assessments, and Policy 

Assessments. Multiple drafts of all of 

these documents were subject to review 

by the public and were peer reviewed 

by the EPA’s Clean Air Scientific 

Advisory Committee (CASAC). The EPA 

proposed revisions to the primary and 

secondary PM NAAQS on June 29, 2012 

(77 FR 38890). This final rulemaking is 

the final step in the review process. 

In this rulemaking, the EPA is 

revising the suite of standards for PM to 

provide requisite protection of public 

health and welfare. The EPA is revising 

the PSD permitting regulations to 

address the changes in the PM NAAQS. 

In addition, the EPA is updating the 

AQI for PM2.5 and making changes in 

the data handling conventions for PM 

and ambient air monitoring, reporting, 

and network design requirements to 

correspond with the changes to the PM 

NAAQS. 

B. Summary of Major Provisions 

With regard to the primary standards 

for fine particles, the EPA is revising the 

annual PM2.5 standard by lowering the 

level from 15.0 to 12.0 mg/m3 so as to 

provide increased protection against 

health effects associated with long-and 

short-term exposures. The EPA is 

retaining the level (35 mg/m3) and the 

form (98th percentile) of the 24-hour 

PM2.5 standard to continue to provide 

supplemental protection against health 

effects associated with short-term 

exposures. This action provides 

increased protection for children, older 

adults, persons with pre-existing heart 

and lung disease, and other at-risk 

populations against an array of PM2.5- 

related adverse health effects that 

include premature mortality, increased 

hospital admissions and emergency 

department visits, and development of 

chronic respiratory disease. The EPA 

also is eliminating spatial averaging 

provisions as part of the form of the 

annual standard to avoid potential 

disproportionate impacts on at-risk 

populations. 

The final decisions for the primary 

annual and 24-hour PM2.5 standards are 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3089 

within the ranges that CASAC advised 

the Agency to consider. These decisions 

are based on an integrative assessment 

of an extensive body of new scientific 

evidence, which substantially 

strengthens what was known about 

PM2.5-related health effects in the last 

review, including extended analyses of 

key epidemiological studies, and 

evidence of health effects observed at 

lower ambient PM2.5 concentrations, 

including effects in areas that likely met 

the current standards. The revised suite 

of PM2.5 standards also reflects 

consideration of a quantitative risk 

assessment that estimates public health 

risks likely to remain upon just meeting 

the current and various alternative 

standards. Based on this information, 

the Administrator concludes that the 

current primary PM2.5 standards are not 

requisite to protect public health with 

an adequate margin of safety, as 

required by the CAA, and that these 

revisions are warranted to provide the 

appropriate degree of increased public 

health protection. 

With regard to the primary standard 

for thoracic coarse particles (PM10-2.5), 

the EPA is retaining the current 24-hour 

PM10 standard, with a level of 150 mg/ 

m3 and a one-expected exceedance 

form, to continue to provide protection 

against effects associated with shortterm exposure to PM10-2.5 including 

premature mortality and increased 

hospital admissions and emergency 

department visits. In reaching this 

decision, the Administrator concludes 

that the available health evidence and 

air quality information for PM10-2.5, 

taken together with the considerable 

uncertainties and limitations associated 

with that information, suggests that a 

standard is needed to protect against 

short-term exposure to all types of 

PM10-2.5 and that the degree of public 

health protection provided against 

short-term exposures to PM10-2.5 does 

not need to be increased beyond that 

provided by the current PM10 standard. 

With regard to the secondary PM 

standards, the Administrator is retaining 

the current suite of secondary PM 

standards, except for a change to the 

form of the annual PM2.5 standard. 

Specifically, the EPA is retaining the 

current secondary 24-hour PM2.5 and 

PM10 standards, and is revising only the 

form of the secondary annual PM2.5

standard to remove the option for 

spatial averaging consistent with this 

change to the primary annual PM2.5

standard. This suite of secondary 

standards addresses PM-related nonvisibility welfare effects including 

ecological effects, effects on materials, 

and climate impacts. With respect to 

PM-related visibility impairment, the 

Administrator has identified a target 

degree of protection, defined in terms of 

a PM2.5 visibility index (based on 

speciated PM2.5 mass concentrations 

and relative humidity data to calculate 

PM2.5 light extinction), a 24-hour 

averaging time, and a 90th percentile 

form, averaged over 3 years, and a level 

of 30 deciviews (dv), which she judges 

to be requisite to protect public welfare 

with regard to visual air quality (VAQ). 

The EPA’s analysis of monitoring data 

provides the basis for concluding that 

the current secondary 24-hour PM2.5

standard would provide sufficient 

protection, and in some areas greater 

protection, relative to this target 

protection level. Adding a distinct 

secondary standard to address visibility 

would not affect this protection. Since 

sufficient protection from visibility 

impairment will be provided for all 

areas of the country without adoption of 

a distinct secondary standard, and 

adoption of a distinct secondary 

standard will not change the degree of 

over-protection of VAQ provided for 

some areas of the country by the 

secondary 24-hour PM2.5 standard, the 

Administrator judges that adoption of a 

distinct secondary standard, in addition 

to the current suite of secondary 

standards, is not needed to provide 

requisite protection for both visibility 

and non-visibility related welfare 

effects. 

The revisions to the PM NAAQS 

trigger a process under which states 

(and tribes, if they choose) will make 

recommendations to the Administrator 

regarding designations, identifying areas 

of the country that either meet or do not 

meet the revised NAAQS. States will 

also review, modify and supplement 

their existing state implementation 

plans (SIPs), as needed. With regard to 

these implementation-related activities, 

the EPA intends to promulgate a 

separate implementation rule on a 

schedule that provides timely clarity to 

the states, tribes, and other parties 

responsible for NAAQS 

implementation. The NAAQS revisions 

also affect the applicable air permitting 

requirement, but cause no significant 

change to the transportation conformity 

and general conformity processes. The 

EPA is revising its PSD regulations to 

provide limited grandfathering from the 

requirements that result from the 

revised PM NAAQS. 

On other topics, the EPA is changing 

the AQI for PM2.5 to be consistent with 

the revised primary PM2.5 NAAQS. The 

EPA also is revising the data handling 

procedures for PM2.5 consistent with the 

revised PM2.5 NAAQS including the 

computations necessary for determining 

when the standards are met and the 

measurement data that are appropriate 

for comparison to the standards. With 

regard to monitoring-related activities, 

the EPA is updating several aspects of 

the monitoring regulations and 

specifically requiring that a small 

number of PM2.5 monitors be relocated 

to be collocated with measurements of 

other pollutants (e.g., nitrogen dioxide, 

carbon monoxide) in the near-road 

environment. 

C. Costs and Benefits 

In setting the NAAQS, the EPA may 

not consider the costs of implementing 

the standards. This was confirmed by 

the United States Supreme Court in 

Whitman v. American Trucking 

Associations, 531 U.S. 457, 465–472, 

475–76 (2001), as noted in section II.A 

of this rule. As has traditionally been 

done in NAAQS rulemaking, the EPA 

has conducted a Regulatory Impact 

Analysis (RIA) to provide the public 

with information on the potential costs 

and benefits of attaining several 

alternative PM2.5 standards. In NAAQS 

rulemaking, the RIA is done for 

informational purposes only, and the 

final decisions on the NAAQS in this 

rulemaking are not in any way based on 

consideration of the information or 

analyses in the RIA. The RIA fulfills the 

requirements of Executive Orders 13563 

and 12866. The summary of the RIA, 

which is discussed in more detail below 

in section X.A, estimates benefits 

ranging from $4,000 million to $9,100 

million at a 3 percent discount rate and 

$3,600 million to $8,200 million at a 7 

percent discount rate in 2020 and costs 

ranging from $53 million to $350 

million per year at a 7 percent discount 

rate. 

II. Background 

A. Legislative Requirements 

Two sections of the CAA govern the 

establishment, review and revision of 

the NAAQS. Section 108 (42 U.S.C. 

7408) directs the Administrator to 

identify and list certain air pollutants 

and then to issue air quality criteria for 

those pollutants. The Administrator is 

to list those air pollutants that in her 

‘‘judgment, cause or contribute to air 

pollution which may reasonably be 

anticipated to endanger public health or 

welfare;’’ ‘‘the presence of which in the 

ambient air results from numerous or 

diverse mobile or stationary sources;’’ 

and ‘‘for which * * * [the 

Administrator] plans to issue air quality 

criteria * * *’’ Air quality criteria are 

intended to ‘‘accurately reflect the latest 

scientific knowledge useful in 

indicating the kind and extent of all 

identifiable effects on public health or 


tkelley on DSK3SPTVN1PROD with 
3090 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

1The legislative history of section 109 indicates 

that a primary standard is to be set at ‘‘the 

maximum permissible ambient air level * * * 

which will protect the health of any [sensitive] 

group of the population,’’ and that for this purpose 

‘‘reference should be made to a representative 

sample of persons comprising the sensitive group 

rather than to a single person in such a group.’’ S. 

Rep. No. 91–1196, 91st Cong., 2d Sess. 10 (1970). 

2Welfare effects as defined in section 302(h) (42 

U.S.C. 7602(h)) include, but are not limited to, 

‘‘effects on soils, water, crops, vegetation, manmade materials, animals, wildlife, weather, 

visibility and climate, damage to and deterioration 

of property, and hazards to transportation, as well 

as effects on economic values and on personal 

comfort and well-being.’’ 3The CASAC PM Review Panel is comprised of 

the seven members of the chartered CASAC, 

supplemented by fifteen subject-matter experts 

appointed by the Administrator to provide 

additional scientific expertise relevant to this 

review of the PM NAAQS. Lists of current CASAC 

members and review panels are available at: http:// 

yosemite.epa.gov/sab/sabproduct.nsf/WebCASAC/ 

CommitteesandMembership?OpenDocument. 

Members of the CASAC PM Review Panel are listed 

in the CASAC letters providing advice on draft 

assessment documents (Samet, 2009a–f, 2012a–d). 

4Particulate matter is the generic term for a broad 

class of chemically and physically diverse 

substances that exist as discrete particles (liquid 

droplets or solids) over a wide range of sizes, such 

that the indicator for a PM NAAQS has historically 

been defined in terms of particle size ranges. 

welfare which may be expected from the 

presence of [a] pollutant in the ambient 

air * * *’’ 42 U.S.C. 7408(b). Section 

109 (42 U.S.C. 7409) directs the 

Administrator to propose and 

promulgate ‘‘primary’’ and ‘‘secondary’’ 

NAAQS for pollutants for which air 

quality criteria are issued. Section 

109(b)(1) defines a primary standard as 

one ‘‘the attainment and maintenance of 

which in the judgment of the 

Administrator, based on such criteria 

and allowing an adequate margin of 

safety, are requisite to protect the public 

health.’’ 1 A secondary standard, as 

defined in section 109(b)(2), must 

‘‘specify a level of air quality the 

attainment and maintenance of which, 

in the judgment of the Administrator, 

based on such criteria, is requisite to 

protect the public welfare from any 

known or anticipated adverse effects 

associated with the presence of [the] 

pollutant in the ambient air.’’ 2

The requirement that primary 

standards provide an adequate margin 

of safety was intended to address 

uncertainties associated with 

inconclusive scientific and technical 

information available at the time of 

standard setting. It was also intended to 

provide a reasonable degree of 

protection against hazards that research 

has not yet identified. See Lead 

Industries Association v. EPA, 647 F.2d 

1130, 1154 (D.C. Cir 1980); American 

Petroleum Institute v. Costle, 665 F.2d 

1176, 1186 (D.C. Cir. 1981); American 

Farm Bureau Federation v. EPA, 559 F. 

3d 512, 533 (D.C. Cir. 2009); Association 

of Battery Recyclers v. EPA, 604 F. 3d 

613, 617–18 (D.C. Cir. 2010). Both kinds 

of uncertainties are components of the 

risk associated with pollution at levels 

below those at which human health 

effects can be said to occur with 

reasonable scientific certainty. Thus, in 

selecting primary standards that provide 

an adequate margin of safety, the 

Administrator is seeking not only to 

prevent pollution levels that have been 

demonstrated to be harmful but also to 

prevent lower pollutant levels that may 

pose an unacceptable risk of harm, even 

if the risk is not precisely identified as 

to nature or degree. The CAA does not 

require the Administrator to establish a 

primary NAAQS at a zero-risk level or 

at background concentration levels, see 

Lead Industries v. EPA, 647 F.2d at 1156 

n.51, but rather at a level that reduces 

risk sufficiently so as to protect public 

health with an adequate margin of 

safety. 

In addressing the requirement for an 

adequate margin of safety, the EPA 

considers such factors as the nature and 

severity of the health effects involved, 

the size of at-risk population(s), and the 

kind and degree of the uncertainties that 

must be addressed. The selection of any 

particular approach to providing an 

adequate margin of safety is a policy 

choice left specifically to the 

Administrator’s judgment. See Lead 

Industries Association v. EPA, 647 F.2d 

at 1161–62; Whitman v. American 

Trucking Associations, 531 U.S. 457, 

495 (2001). 

In setting standards that are 

‘‘requisite’’ to protect public health and 

welfare, as provided in section 109(b), 

the EPA’s task is to establish standards 

that are neither more nor less stringent 

than necessary for these purposes. In so 

doing, the EPA may not consider the 

costs of implementing the standards. 

See generally, Whitman v. American 

Trucking Associations, 531 U.S. 457, 

465–472, 475–76 (2001). Likewise, 

‘‘[a]ttainability and technological 

feasibility are not relevant 

considerations in the promulgation of 

national ambient air quality standards.’’ 

American Petroleum Institute v. Costle, 

665 F. 2d at 1185. 

Section 109(d)(1) requires that ‘‘not 

later than December 31, 1980, and at 5- 

year intervals thereafter, the 

Administrator shall complete a 

thorough review of the criteria 

published under section 108 and the 

national ambient air quality standards 

* * * and shall make such revisions in 

such criteria and standards and 

promulgate such new standards as may 

be appropriate * * *’’ Section 109(d)(2) 

requires that an independent scientific 

review committee ‘‘shall complete a 

review of the criteria * * * and the 

national primary and secondary ambient 

air quality standards * * * and shall 

recommend to the Administrator any 

new * * * standards and revisions of 

existing criteria and standards as may be 

appropriate. * * *’’ Since the early 

1980’s, this independent review 

function has been performed by the 

CASAC.3

B. Review of the Air Quality Criteria and 

Standards for PM 

1. Previous PM NAAQS Reviews 

The EPA initially established NAAQS 

for PM under section 109 of the CAA in 

1971. Since then, the Agency has made 

a number of changes to these standards 

to reflect continually expanding 

scientific information, particularly with 

respect to the selection of indicator4 and 

level. Table 1 provides a summary of the 

PM NAAQS that have been promulgated 

to date. These decisions are briefly 

discussed below. 

TABLE 1—SUMMARY OF NATIONAL AMBIENT AIR QUALITY STANDARDS PROMULGATED FOR PM 1971–2006 a

Final rule Indicator Averaging 

time Level Form 

1971—36 FR 8186 April 30, 

1971.

TSP .......... 24-hour .... 260 μg/m3 (primary) ..................

150 μg/m3 ..................................

(secondary) ................................

Not to be exceeded more than once per year. 

Annual ..... 75 μg/m3 ....................................

(primary) ....................................

Annual average. 

1987—52 FR 24634 July 1, 

1987.

PM10 ........ 24-hour .... 150 μg/m3 .................................. Not to be exceeded more than once per year on 

average over a 3-year period. 

Annual ..... 50 μg/m3 .................................... Annual arithmetic mean, averaged over 3 years. 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3091 

5See 40 CFR parts 50, 53, and 58 for more 

information on reference and equivalent methods 

for measuring PM in ambient air. 

6Monitoring stations sited to represent 

community-wide air quality would typically be at 

the neighborhood or urban-scale; however, where a 

population-oriented micro or middle-scale PM2.5

monitoring station represents many such locations 

throughout a metropolitan area, these smaller scales 

might also be considered to represent communitywide air quality [40 CFR part 58, appendix D, 

4.7.1(b)]. 

7Population-oriented monitoring (or sites) means 

residential areas, commercial areas, recreational 

areas, industrial areas where workers from more 

than one company are located, and other areas 

where a substantial number of people may spend 

a significant fraction of their day (40 CFR 58.1). 

TABLE 1—SUMMARY OF NATIONAL AMBIENT AIR QUALITY STANDARDS PROMULGATED FOR PM 1971–2006 a—Continued 

Final rule Indicator Averaging 

time Level Form 

1997—62 FR 38652 July 18, 

1997.

PM2.5 ........ 24-hour .... 65 μg/m3 .................................... 98th percentile, averaged over 3 years.b

Annual ..... 15.0 μg/m3 ................................. Annual arithmetic mean, averaged over 3 

years.c d

PM10 ........ 24-hour .... 150 μg/m3 .................................. Initially promulgated 99th percentile, averaged 

over 3 years; when 1997 standards for PM10

were vacated, the form of 1987 standards remained in place (not to be exceeded more 

than once per year on average over a 3-year 

period). 

Annual ..... 50 μg/m3 .................................... Annual arithmetic mean, averaged over 3 years. 

2006—71 FR 61144 October 

17, 2006.

PM2.5 ........ 24-hour ....

Annual .....

35 μg/m3 ....................................

15.0 μg/m3 .................................

98th percentile, averaged over 3 years.b

Annual arithmetic mean, averaged over 3 

years.c e

PM10 ........ 24-hour .... 150 μg/m3 .................................. Not to be exceeded more than once per year on 

average over a 3-year period. 

aWhen not specified, primary and secondary standards are identical. 

bThe level of the 24-hour standard is defined as an integer (zero decimal places) as determined by rounding. For example, a 3-year average 

98th percentile concentration of 35.49 μg/m3 would round to 35 μg/m3 and thus meet the 24-hour standard and a 3-year average of 35.50 μg/m3

would round to 36 and, hence, violate the 24-hour standard (40 CFR part 50, appendix N). cThe level of the annual standard is defined to one decimal place (i.e., 15.0 μg/m3) as determined by rounding. For example, a 3-year average 

annual mean of 15.04 μg/m3 would round to 15.0 μg/m3 and, thus, meet the annual standard and a 3-year average of 15.05 μg/m3 would round 

to 15.1 μg/m3 and, hence, violate the annual standard (40 CFR part 50, appendix N). dThe level of the standard was to be compared to measurements made at sites that represent ‘‘community-wide air quality’’ recording the highest level, or, if specific requirements were satisfied, to average measurements from multiple community-wide air quality monitoring sites (‘‘spatial 

averaging’’). eThe EPA tightened the constraints on the spatial averaging criteria by further limiting the conditions under which some areas may average 

measurements from multiple community-oriented monitors to determine compliance (See 71 FR 61165 to 61167, October 17, 2006). 

In 1971, the EPA established NAAQS 

for PM based on the original air quality 

criteria document (DHEW, 1969; 36 FR 

8186, April 30, 1971). The reference 

method specified for determining 

attainment of the original standards was 

the high-volume sampler, which 

collects PM up to a nominal size of 25 

to 45 mm (referred to as total suspended 

particles or TSP). The primary standards 

(measured by the indicator TSP) were 

260 mg/m3, 24-hour average, not to be 

exceeded more than once per year, and 

75 mg/m3, annual geometric mean. The 

secondary standard was 150 mg/m3, 24- 

hour average, not to be exceeded more 

than once per year. 

In October 1979, the EPA announced 

the first periodic review of the criteria 

and NAAQS for PM, and significant 

revisions to the original standards were 

promulgated in 1987 (52 FR 24634, July 

1, 1987). In that decision, the EPA 

changed the indicator for PM from TSP 

to PM10, the latter including particles 

with an aerodynamic diameter less than 

or equal to a nominal 10 mm, which 

delineates thoracic particles (i.e., that 

subset of inhalable particles small 

enough to penetrate beyond the larynx 

to the thoracic region of the respiratory 

tract). The EPA also revised the primary 

standards by (1) replacing the 24-hour 

TSP standard with a 24-hour PM10

standard of 150 mg/m3 with no more 

than one expected exceedance per year 

and (2) replacing the annual TSP 

standard with a PM10 standard of 50 mg/ 

m3, annual arithmetic mean. The 

secondary standard was revised by 

replacing it with 24-hour and annual 

PM10 standards identical in all respects 

to the primary standards. The revisions 

also included a new reference method 

for the measurement of PM10 in the 

ambient air and rules for determining 

attainment of the new standards. On 

judicial review, the revised standards 

were upheld in all respects. Natural 

Resources Defense Council v. EPA, 902 

F. 2d 962 (D.C. Cir. 1990). 

In April 1994, the EPA announced its 

plans for the second periodic review of 

the criteria and NAAQS for PM, and 

promulgated significant revisions to the 

NAAQS in 1997 (62 FR 38652, July 18, 

1997). Most significantly, the EPA 

determined that although the PM 

NAAQS should continue to focus on 

thoracic particles (PM10), the fine and 

coarse fractions of PM10 should be 

considered separately. New standards 

were added, using PM2.5 as the indicator 

for fine particles. The PM10 standards 

were retained for the purpose of 

regulating the coarse fraction of PM10

(referred to as thoracic coarse particles 

or PM10-2.5).5 The EPA established two 

new PM2.5 standards: an annual 

standard of 15.0 mg/m3, based on the 3- 

year average of annual arithmetic mean 

PM2.5 concentrations from single or 

multiple monitors sited to represent 

community-wide air quality6 and a 24- 

hour standard of 65 mg/m3, based on the 

3-year average of the 98th percentile of 

24-hour PM2.5 concentrations at each 

population-oriented monitor7 within an 

area. Also, the EPA established a new 

reference method for the measurement 

of PM2.5 in the ambient air and rules for 

determining attainment of the new 

standards. To continue to address 

thoracic coarse particles, the annual 

PM10 standard was retained, while the 

form, but not the level, of the 24-hour 

PM10 standard was revised to be based 

on the 99th percentile of 24-hour PM10

concentrations at each monitor in an 

area. The EPA revised the secondary 

standards by making them identical in 

all respects to the primary standards. 

Following promulgation of the revised 

PM NAAQS in 1997, petitions for 

review were filed by a large number of 


tkelley on DSK3SPTVN1PROD with 
3092 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

8 In recognition of an alternative view expressed 

by most members of the CASAC PM Panel, the 

Agency also solicited comments on a subdaily (4- 

to 8-hour averaging time) secondary PM2.5 standard 

to address visibility impairment, considering 

alternative standard levels within a range of 20 to 

30 mg/m3 in conjunction with a form within a range 

of the 92nd to 98th percentile (71 FR 2685, January 

17, 2006). 

parties, addressing a broad range of 

issues. In May 1998, a three-judge panel 

of the U.S. Court of Appeals for the 

District of Columbia Circuit issued an 

initial decision that upheld the EPA’s 

decision to establish fine particle 

standards, holding that ‘‘the growing 

empirical evidence demonstrating a 

relationship between fine particle 

pollution and adverse health effects 

amply justifies establishment of new 

fine particle standards.’’ American 

Trucking Associations v. EPA, 175 F. 3d 

1027, 1055–56 (D.C. Cir. 1999), 

rehearing granted in part and denied in 

part, 195 F. 3d 4 (D.C. Cir. 1999), 

affirmed in part and reversed in part, 

Whitman v. American Trucking 

Associations, 531 U.S. 457 (2001). The 

panel also found ‘‘ample support’’ for 

the EPA’s decision to regulate coarse 

particle pollution, but vacated the 1997 

P.M.10 standards, concluding, in part, 

that PM10 is a ‘‘poorly matched 

indicator for coarse particulate 

pollution’’ because it includes fine 

particles. Id. at 1053–55. Pursuant to the 

court’s decision, the EPA removed the 

vacated 1997 P.M.10 standards from the 

CFR (69 FR 45592, July 30, 2004) and 

deleted the regulatory provision (at 40 

CFR 50.6(d)) that controlled the 

transition from the pre-existing 1987 

P.M.10 standards to the 1997 P.M.10

standards. The pre-existing 1987 P.M.10

standards remained in place (65 FR 

80776, December 22, 2000). The court 

also upheld the EPA’s determination not 

to establish more stringent secondary 

standards for fine particles to address 

effects on visibility (175 F. 3d at 1027). 

More generally, the panel held (over 

a strong dissent) that the EPA’s 

approach to establishing the level of the 

standards in 1997, both for the PM and 

for the ozone NAAQS promulgated on 

the same day, effected ‘‘an 

unconstitutional delegation of 

legislative authority.’’ Id. at 1034–40. 

Although the panel stated that ‘‘the 

factors EPA uses in determining the 

degree of public health concern 

associated with different levels of ozone 

and PM are reasonable,’’ it remanded 

the rule to the EPA, stating that when 

the EPA considers these factors for 

potential non-threshold pollutants 

‘‘what EPA lacks is any determinate 

criterion for drawing lines’’ to 

determine where the standards should 

be set. Consistent with the EPA’s longstanding interpretation and D.C. Circuit 

precedent, the panel also reaffirmed its 

prior holdings that in setting NAAQS, 

the EPA is ‘‘not permitted to consider 

the cost of implementing those 

standards.’’ Id. at 1040–41. 

On EPA’s petition for rehearing, the 

panel adhered to its position on these 

points. American Trucking Associations 

v. EPA, 195 F. 3d 4 (D.C. Cir. 1999). The 

full Court of Appeals denied the EPA’s 

request for rehearing en banc, with five 

judges dissenting. Id. at 13. Both sides 

filed cross appeals on these issues to the 

United States Supreme Court, which 

granted certiorari. In February 2001, the 

Supreme Court issued a unanimous 

decision upholding the EPA’s position 

on both the constitutional and cost 

issues. Whitman v. American Trucking 

Associations, 531 U.S. 457, 464, 475–76. 

On the constitutional issue, the Court 

held that the statutory requirement that 

NAAQS be ‘‘requisite’’ to protect public 

health with an adequate margin of safety 

sufficiently cabined the EPA’s 

discretion, affirming the EPA’s approach 

of setting standards that are neither 

more nor less stringent than necessary. 

The Supreme Court remanded the case 

to the Court of Appeals for resolution of 

any remaining issues that had not been 

addressed in that court’s earlier rulings. 

Id. at 475–76. In March 2002, the Court 

of Appeals rejected all remaining 

challenges to the standards, holding 

under the statutory standard of review 

that the EPA’s PM2.5 standards were 

reasonably supported by the 

administrative record and were not 

‘‘arbitrary and capricious.’’ American 

Trucking Association v. EPA, 283 F. 3d 

355, 369–72 (D.C. Cir. 2002). 

In October 1997, the EPA published 

its plans for the next periodic review of 

the air quality criteria and NAAQS for 

PM (62 FR 55201, October 23, 1997). 

After CASAC and public review of 

several drafts, the EPA’s National Center 

for Environmental Assessment (NCEA) 

finalized the Air Quality Criteria 

Document for Particulate Matter 

(henceforth, AQCD or the ‘‘Criteria 

Document’’) in October 2004 (U.S. EPA, 

2004) and OAQPS finalized an 

assessment document, Particulate 

Matter Health Risk Assessment for 

Selected Urban Areas (Abt Associates, 

2005), and the Review of the National 

Ambient Air Quality Standards for 

Particulate Matter: Policy Assessment of 

Scientific and Technical Information, in 

December 2005 (henceforth, ‘‘Staff 

Paper,’’ U.S. EPA, 2005). In conjunction 

with its review of the Staff Paper, 

CASAC provided advice to the 

Administrator on revisions to the PM 

NAAQS (Henderson, 2005a). In 

particular, most CASAC PM Panel 

members favored revising the level of 

the primary 24-hour PM2.5 standard 

within the range of 35 to 30 mg/m3 with 

a 98th percentile form, in concert with 

revising the level of the primary annual 

PM2.5 standard within the range of 14 to 

13 mg/m3 (Henderson, 2005a, p.7). For 

thoracic coarse particles, the Panel had 

reservations in recommending a primary 

24-hour PM10-2.5 standard, and agreed 

that there was a need for more research 

on the health effects of thoracic coarse 

particles (Henderson, 2005b). With 

regard to secondary standards, most 

Panel members strongly supported 

establishing a new, distinct secondary 

PM2.5 standard to protect urban 

visibility (Henderson, 2005a, p. 9). 

On January 17, 2006, the EPA 

proposed to revise the primary and 

secondary NAAQS for PM (71 FR 2620) 

and solicited comment on a broad range 

of options. Proposed revisions included: 

(1) Revising the level of the primary 24- 

hour PM2.5 standard to 35 mg/m3; (2) 

revising the form, but not the level, of 

the primary annual PM2.5 standard by 

tightening the constraints on the use of 

spatial averaging; (3) replacing the 

primary 24-hour PM10 standard with a 

24-hour standard defined in terms of a 

new indicator, PM10-2.5, which was 

qualified so as to include any ambient 

mix of PM10-2.5 dominated by particles 

generated by high-density traffic on 

paved roads, industrial sources, and 

construction sources, and to exclude 

any ambient mix of particles dominated 

by rural windblown dust and soils and 

agricultural and mining sources (71 FR 

2667 to 2668), set at a level of 70 mg/ 

m3 based on the 3-year average of the 

98th percentile of 24-hour PM10-2.5

concentrations; (4) revoking the primary 

annual PM10 standard; and (5) revising 

the secondary standards by making 

them identical in all respects to the 

proposed suite of primary standards for 

fine and coarse particles.8 Subsequent to 

the proposal, CASAC provided 

additional advice to the EPA in a letter 

to the Administrator requesting 

reconsideration of CASAC’s 

recommendations for both the primary 

and secondary PM2.5 standards as well 

as the standards for thoracic coarse 

particles (Henderson, 2006a). 

On October 17, 2006, the EPA 

published revisions to the PM NAAQS 

to provide increased protection of 

public health and welfare (71 FR 

61144). With regard to the primary and 

secondary standards for fine particles, 

the EPA revised the level of the primary 

24-hour PM2.5 standard to 35 mg/m3, 

retained the level of the primary annual 

PM2.5 standard at 15.0 mg/m3, and 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3093 

9CASAC specifically identified input provided 

by the American Medical Association, the 

American Thoracic Society, the American Lung 

Association, the American Academy of Pediatrics, 

the American College of Cardiology, the American 

Heart Association, the American Cancer Society, 

the American Public Health Association, and the 

National Association of Local Boards of Health 

(Henderson et al., 2006b, p. 2). 

10See workshop materials available at: http:// 

www.regulations.gov/search/Regs/home.html#home 

Docket ID numbers EPA–HQ–OAR–2007–0492–008; 

EPA–HQ–OAR–2007–0492–009; EPA–HQ–OAR– 

2007–0492–010; and EPA–HQ–OAR–2007–0492– 

012. 

11The process followed in this review varies from 

the NAAQS review process described in section 1.1 

of the Integrated Review Plan (U.S. EPA, 2008a). On 

May 21, 2009, Administrator Jackson called for key 

changes to the NAAQS review process including 

reinstating a policy assessment document that 

contains staff analyses of the scientific bases for 

alternative policy options for consideration by 

senior Agency management prior to rulemaking. In 

conjunction with this change, the EPA will no 

longer issue a policy assessment in the form of an 

advance notice of proposed rulemaking (ANPR) as 

Continued 

revised the form of the primary annual 

PM2.5 standard by adding further 

constraints on the optional use of spatial 

averaging. The EPA revised the 

secondary standards for fine particles by 

making them identical in all respects to 

the primary standards. With regard to 

the primary and secondary standards for 

thoracic coarse particles, the EPA 

retained the level and form of the 24- 

hour PM10 standard (such that the 

standard remained at a level of 150 mg/ 

m3 with a one-expected exceedance 

form and retained the PM10 indicator) 

and revoked the annual PM10 standard. 

The EPA also established a new Federal 

Reference Method (FRM) for the 

measurement of PM10-2.5 in the ambient 

air (71 FR 61212 to 13). Although the 

standards for thoracic coarse particles 

were not defined in terms of a PM10-2.5

indicator, the EPA adopted a new FRM 

for PM10-2.5 to facilitate consistent 

research on PM10-2.5 air quality and 

health effects and to promote 

commercial development of Federal 

Equivalent Methods (FEMs) to support 

future reviews of the PM NAAQS (71 FR 

61212/2). 

Following issuance of the final rule, 

CASAC articulated its concern that the 

‘‘EPA’s final rule on the NAAQS for PM 

does not reflect several important 

aspects of the CASAC’s advice’’ 

(Henderson et al., 2006b, p. 1). With 

regard to the primary PM2.5 annual 

standard, CASAC expressed serious 

concerns regarding the decision to 

retain the level of the standard at 15 mg/ 

m3. Specifically, CASAC stated, ‘‘It is 

the CASAC’s consensus scientific 

opinion that the decision to retain 

without change the annual PM2.5

standard does not provide an ‘adequate 

margin of safety * * * requisite to 

protect the public health’ (as required 

by the Clean Air Act), leaving parts of 

the population of this country at 

significant risk of adverse health effects 

from exposure to fine PM’’ (Henderson 

et al., 2006b, p. 2). Furthermore, CASAC 

pointed out that its recommendations 

‘‘were consistent with the mainstream 

scientific advice that EPA received from 

virtually every major medical 

association and public health 

organization that provided their input to 

the Agency’’ (Henderson et al., 2006b, p. 

2).9 With regard to EPA’s final decision 

to retain the 24-hour PM10 standard for 

thoracic coarse particles, CASAC had 

mixed views with regard to the decision 

to retain the 24-hour standard and the 

continued use of PM10 as the indicator 

of coarse particles, while also 

recognizing the need to have a standard 

in place to protect against effects 

associated with short-term exposures to 

thoracic coarse particles (Henderson et 

al., 2006b, p. 2). With regard to the 

EPA’s final decision to revise the 

secondary PM2.5 standards to be 

identical in all respects to the revised 

primary PM2.5 standards, CASAC 

expressed concerns that its advice to 

establish a distinct secondary standard 

for fine particles to address visibility 

impairment was not followed and 

emphasized ‘‘that continuing to rely on 

the primary standard to protect against 

all PM-related adverse environmental 

and welfare effects assures neglect, and 

will allow substantial continued 

degradation, of visual air quality over 

large areas of the country’’ (Henderson 

et al, 2006b, p. 2). 

2. Litigation Related to the 2006 PM 

Standards 

Several parties filed petitions for 

review following promulgation of the 

revised PM NAAQS in 2006. These 

petitions addressed the following issues: 

(1) Selecting the level of the primary 

annual PM2.5 standard; (2) retaining 

PM10 as the indicator of a standard for 

thoracic coarse particles, retaining the 

level and form of the 24-hour PM10

standard, and revoking the PM10 annual 

standard; and (3) setting the secondary 

PM2.5 standards identical to the primary 

standards. On February 24, 2009, the 

U.S. Court of Appeals for the District of 

Columbia Circuit issued its opinion in 

the case American Farm Bureau 

Federation v. EPA, 559 F. 3d 512 (D.C. 

Cir. 2009). The court remanded the 

primary annual PM2.5 NAAQS to the 

EPA because the EPA failed to 

adequately explain why the standard 

provided the requisite protection from 

both short- and long-term exposures to 

fine particles, including protection for 

at-risk populations such as children. 

American Farm Bureau Federation v. 

EPA, 559 F. 3d 512, 520–27 (D.C. Cir. 

2009). With regard to the standards for 

PM10, the court upheld the EPA’s 

decisions to retain the 24-hour PM10

standard to provide protection from 

thoracic coarse particle exposures and 

to revoke the annual PM10 standard. 

American Farm Bureau Federation v. 

EPA, 559 F. 2d at 533–38. With regard 

to the secondary PM2.5 standards, the 

court remanded the standards to the 

EPA because the Agency’s decision was 

‘‘unreasonable and contrary to the 

requirements of section 109(b)(2)’’ of the 

CAA. The court further concluded that 

the EPA failed to adequately explain 

why setting the secondary PM standards 

identical to the primary standards 

provided the required protection for 

public welfare, including protection 

from visibility impairment. American 

Farm Bureau Federation v. EPA, 559 F. 

2d at 528–32. 

The decisions of the court with regard 

to these three issues are discussed 

further in sections III.A.2, IV.A.2, and 

VI.A.2 below. The EPA is responding to 

the court’s remands as part of the 

current review of the PM NAAQS. 

3. Current PM NAAQS Review 

The EPA initiated the current review 

of the air quality criteria for PM in June 

2007 with a general call for information 

(72 FR 35462, June 28, 2007). In July 

2007, the EPA held two ‘‘kick-off’’ 

workshops on the primary and 

secondary PM NAAQS, respectively (72 

FR 34003 to 34004, June 20, 2007).10

These workshops provided an 

opportunity for a public discussion of 

the key policy-relevant issues around 

which the EPA would structure this PM 

NAAQS review and the most 

meaningful new science that would be 

available to inform our understanding of 

these issues. 

Based in part on the workshop 

discussions, the EPA developed a draft 

Integrated Review Plan outlining the 

schedule, process, and key policyrelevant questions that would guide the 

evaluation of the air quality criteria for 

PM and the review of the primary and 

secondary PM NAAQS (U.S. EPA, 

2007a). On November 30, 2007, the EPA 

held a consultation with CASAC on the 

draft Integrated Review Plan (72 FR 

63177, November 8, 2007), which 

included the opportunity for public 

comment. The final Integrated Review 

Plan (U.S. EPA, 2008a) incorporated 

comments from CASAC (Henderson, 

2008) and the public on the draft plan 

as well as input from senior Agency 

managers.11 12


tkelley on DSK3SPTVN1PROD with 
3094 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

discussed in the Integrated Review Plan (U.S. EPA, 

2008a, p. 3). For more information on the overall 

process followed in this review including a 

description of the major elements of the process for 

reviewing NAAQS see Jackson (2009). 12All written comments submitted to the Agency 

are available in the docket for this PM NAAQS 

review (EPA–HQ–OAR–2007–0429). Transcripts of 

public meetings and teleconferences held in 

conjunction with CASAC’s reviews are also 

included in the docket. 

A major element in the process for 

reviewing the NAAQS is the 

development of an Integrated Science 

Assessment. This document provides a 

concise evaluation and integration of 

the policy-relevant science, including 

key science judgments upon which the 

risk and exposure assessments build. As 

part of the process of preparing the PM 

Integrated Science Assessment, NCEA 

hosted a peer review workshop in June 

2008 on preliminary drafts of key 

Integrated Science Assessment chapters 

(73 FR 30391, May 27, 2008). CASAC 

and the public reviewed the first 

external review draft Integrated Science 

Assessment (U.S. EPA, 2008b; 73 FR 

77686, December 19, 2008) at a meeting 

held on April 1 to 2, 2009 (74 FR 2688, 

February 19, 2009). Based on CASAC 

(Samet, 2009e) and public comments, 

NCEA prepared a second draft 

Integrated Science Assessment (U.S. 

EPA, 2009b; 74 FR 38185, July 31, 

2009), which was reviewed by CASAC 

and the public at a meeting held on 

October 5 and 6, 2009 (74 FR 46586, 

September 10, 2009). Based on CASAC 

(Samet, 2009f) and public comments, 

NCEA prepared the final Integrated 

Science Assessment titled Integrated 

Science Assessment for Particulate 

Matter, December 2009 (U.S. EPA, 

2009a; 74 FR 66353, December 15, 

2009). 

Building upon the information 

presented in the PM Integrated Science 

Assessment, the EPA prepared Risk and 

Exposure Assessments that provide a 

concise presentation of the methods, 

key results, observations, and related 

uncertainties. In developing the Risk 

and Exposure Assessments for this PM 

NAAQS review, OAQPS released two 

planning documents: Particulate Matter 

National Ambient Air Quality 

Standards: Scope and Methods Plan for 

Health Risk and Exposure Assessment 

and Particulate Matter National 

Ambient Air Quality Standards: Scope 

and Methods Plan for Urban Visibility 

Impact Assessment (henceforth, Scope 

and Methods Plans, U.S. EPA, 2009c,d; 

74 FR 11580, March 18, 2009). These 

planning documents outlined the scope 

and approaches that staff planned to use 

in conducting quantitative assessments 

as well as key issues that would be 

addressed as part of the assessments. In 

designing and conducting the initial 

health risk and visibility impact 

assessments, the Agency considered 

CASAC comments (Samet 2009a,b) on 

the Scope and Methods Plans made 

during an April 2009 consultation (74 

FR 7688, February 19, 2009) as well as 

public comments. CASAC and the 

public reviewed two draft assessment 

documents, Risk Assessment to Support 

the Review of the PM2.5 Primary 

National Ambient Air Quality 

Standards: External Review Draft, 

September 2009 (U.S. EPA, 2009e) and 

Particulate Matter Urban-Focused 

Visibility Assessment—External Review 

Draft, September 2009 (U.S. EPA, 2009f) 

at a meeting held on October 5 and 6, 

2009 (74 FR 46586, September 10, 

2009). Based on CASAC (Samet 

2009c,d) and public comments, OAQPS 

staff revised these draft documents and 

released second draft assessment 

documents (U.S. EPA, 2010d,e) in 

January and February 2010 (75 FR 4067, 

January 26, 2010) for CASAC and public 

review at a meeting held on March 10 

and 11, 2010 (75 FR 8062, February 23, 

2010). Based on CASAC (Samet, 

2010a,b) and public comments on the 

second draft assessment documents, the 

EPA revised these documents and 

released final assessment documents 

titled Quantitative Health Risk 

Assessment for Particulate Matter, June 

2010 (henceforth, ‘‘Risk Assessment,’’ 

U.S. EPA, 2010a) and Particulate Matter 

Urban-Focused Visibility Assessment— 

Final Document, July 2010 (henceforth, 

‘‘Visibility Assessment,’’ U.S. EPA, 

2010b) (75 FR 39252, July 8, 2010). 

Based on the scientific and technical 

information available in this review as 

assessed in the Integrated Science 

Assessment and Risk and Exposure 

Assessments, the EPA staff prepared a 

Policy Assessment. The Policy 

Assessment is intended to help ‘‘bridge 

the gap’’ between the relevant scientific 

information and assessments and the 

judgments required of the Administrator 

in reaching decisions on the NAAQS 

(Jackson, 2009, attachment, p. 2). 

American Farm Bureau Federation v. 

EPA, 559 F. 3d at 521. The Policy 

Assessment is not a decision document; 

rather it presents the EPA staff 

conclusions related to the broadest 

range of policy options that could be 

supported by the currently available 

information. A preliminary draft Policy 

Assessment (U.S. EPA, 2009g) was 

released in September 2009 for 

informational purposes and to facilitate 

discussion with CASAC at the October 

5 and 6, 2009 meeting on the overall 

structure, areas of focus, and level of 

detail to be included in the Policy 

Assessment. The EPA considered 

CASAC’s comments on this preliminary 

draft in developing a first draft Policy 

Assessment (U.S. EPA, 2010c; 75 FR 

4067, January 26, 2010) that built upon 

the information presented and assessed 

in the final Integrated Science 

Assessment and second draft Risk and 

Exposure Assessments. The EPA 

presented an overview of the first draft 

Policy Assessment at a CASAC meeting 

on March 10, 2010 (75 FR 8062, 

February 23, 2010) and it was discussed 

during public CASAC teleconferences 

on April 8 and 9, 2010 (75 FR 8062, 

February 23, 2010) and May 7, 2010 (75 

FR 19971, April 16, 2010). 

The EPA developed a second draft 

Policy Assessment (U.S. EPA, 2010f; 75 

FR 39253, July 8, 2010) based on 

CASAC (Samet, 2010c) and public 

comments on the first draft Policy 

Assessment. CASAC reviewed the 

second draft document at a meeting on 

July 26 and 27, 2010 (75 FR 32763, June 

9, 2010). The EPA staff considered 

CASAC (Samet, 2010d) and public 

comments on the second draft Policy 

Assessment in preparing a final Policy 

Assessment titled Policy Assessment for 

the Review of the Particulate Matter 

National Ambient Air Quality 

Standards, April, 2011 (U.S. EPA, 

2011a; 76, FR 22665, April 22, 2011). 

This document includes final staff 

conclusions on the adequacy of the 

current PM standards and alternative 

standards for consideration. 

The schedule for the rulemaking in 

this review is subject to a court order in 

a lawsuit filed in February 2012 by a 

group of plaintiffs who alleged that the 

EPA had failed to perform its mandatory 

duty, under section 109(d)(1), to 

complete a review of the PM NAAQS 

within the period provided by statute. 

American Lung Association and 

National Parks Conservation 

Association v. EPA, D.D.C. No. 12–cv– 

00243 (consol. with No. 12–cv–00531) 

Court orders in that case provide that 

the EPA sign a notice of proposed 

rulemaking concerning its review of the 

PM NAAQS no later than June 14, 2012 

and a notice of final rulemaking no later 

than December 14, 2012. 

On June 14, 2012, the EPA issued its 

proposed decision to revise the NAAQS 

for PM (77 FR 38890, June 29, 2012) 

(henceforth ‘‘proposal’’). In the 

proposal, the EPA identified revisions to 

the standards, based on the air quality 

criteria for PM, and to related data 

handling conventions and ambient air 

monitoring, reporting, and network 

design requirements. The EPA proposed 

revisions to the PSD permitting program 

with respect to the proposed NAAQS 

revisions. The Agency also proposed 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3095 

13For ease of reference, these studies will be 

referred to as ‘‘new’’ studies or ‘‘new’’ science, 

using quotation marks around the word new. 

Referring to studies that were published too 

recently to have been included in the 2009 

Integrated Science Assessment as ‘‘new’’ studies is 

intended to clearly differentiate such studies from 

those that have been published since the last review 

and which are included in the Integrated Science 

Assessment (these studies are sometimes referred to 

as new (without quotation marks) or more recent 

studies, to indicate that they were not included in 

the Integrated Science Assessment and thus are 

newly available in this review). 

changes to the AQI for PM2.5, consistent 

with the proposed primary PM2.5

standards. The proposal solicited public 

comments on alternative primary and 

secondary standards and related 

matters. The proposal is summarized in 

section II.D below. 

The EPA held two public hearings to 

receive public comment on the 

proposed revisions to the PM NAAQS 

(77 FR 39205, July 2, 2012). One hearing 

took place in Philadelphia, PA on July 

17, 2012 and a second hearing took 

place in Sacramento, CA on July 19, 

2012. At these public hearings, the EPA 

heard testimony from 168 individuals 

representing themselves or specific 

interested organizations. 

The EPA received more than 230,000 

comments from members of the public 

and various interest groups on the 

proposed revisions to the PM NAAQS 

by the close of the public comment 

period on August 31, 2012. Major issues 

raised in the public comments are 

discussed throughout the preamble of 

this final action. A more detailed 

summary of all significant comments, 

along with the EPA’s responses 

(henceforth ‘‘Response to Comments’’) 

can be found in the docket for this 

rulemaking (Docket No. EPA–HQ–OAR– 

2007–0492) (U.S. EPA, 2012a). 

In the proposal, the EPA recognized 

that there were a number of new 

scientific studies on the health effects of 

PM that had been published since the 

mid-2009 cutoff date for inclusion in the 

Integrated Science Assessment.13 As in 

the last PM NAAQS review, the EPA 

committed to conduct a provisional 

review and assessment of any 

significant ‘‘new’’ studies published 

since the close of the Integrated Science 

Assessment, including studies 

submitted to the EPA during the public 

comment period. The purpose of the 

provisional science assessment was to 

ensure that the Administrator was fully 

aware of the ‘‘new’’ science that has 

developed since 2009 before making 

final decisions on whether to retain or 

revise the current PM NAAQS. The EPA 

screened and surveyed the recent health 

literature, including studies submitted 

during the public comment period, and 

conducted a provisional assessment 

(U.S. EPA, 2012b) that places the results 

of those studies of potentially greatest 

policy relevance in the context of the 

findings of the Integrated Science 

Assessment (U.S. EPA, 2009a). This 

provisional assessment, including a 

summary of the key conclusions, can be 

found in the rulemaking docket (EPA– 

HQ–OAR–2007–0492). 

The provisional assessment found 

that the ‘‘new’’ studies expand the 

scientific information considered in the 

Integrated Science Assessment and 

provide important insights on the 

relationship between PM exposure and 

health effects. The provisional 

assessment also found that the ‘‘new’’ 

studies generally strengthen the 

evidence that long- and short-term 

exposures to fine particles are 

associated with a wide range of health 

effects. Some of the ‘‘new’’ 

epidemiological studies report effects in 

areas with lower PM2.5-concentrations 

than those in earlier studies considered 

in the Integrated Science Assessment. 

‘‘New’’ toxicological and 

epidemiological studies continue to link 

various health effects with a range of 

fine particle sources and components. 

With regard to thoracic coarse particles, 

the provisional assessment recognized 

that a limited number of ‘‘new’’ studies 

provide evidence of an association with 

short-term PM10-2.5 exposures and 

increased asthma-related emergency 

department visits in children, but 

continue to provide no evidence of an 

association between long-term PM10-2.5

exposure and mortality. Further, the 

provisional assessment found that the 

results reported in ‘‘new’’ studies do not 

materially change any of the broad 

scientific conclusions regarding the 

health effects of PM exposure made in 

the Integrated Science Assessment. 

The EPA believes it was important to 

conduct a provisional assessment in this 

proceeding, so that the Administrator 

would be aware of the science that 

developed too recently for inclusion in 

the Integrated Science Assessment. 

However, it is also important to note 

that the EPA’s review of that science to 

date has been limited to screening, 

surveying, and preparing a provisional 

assessment of these studies. Having 

performed this limited provisional 

assessment, the EPA must decide 

whether to consider the ‘‘new’’ studies 

in this review and to take such steps as 

may be necessary to include them in the 

basis for the final decision, or to reserve 

such action for the next review of the 

PM NAAQS. 

As in prior NAAQS reviews, the EPA 

is basing its decision in this review on 

studies and related information 

included in the Integrated Science 

Assessment, Risk and Exposure 

Assessment, and Policy Assessment, 

which have undergone CASAC and 

public review. The studies assessed in 

the Integrated Science Assessment, and 

the integration of the scientific evidence 

presented in that document, have 

undergone extensive critical review by 

the EPA, CASAC, and the public during 

the development of the Integrated 

Science Assessment. The rigor of that 

review makes these studies, and their 

integrative assessment, the most reliable 

source of scientific information on 

which to base decisions on the NAAQS. 

NAAQS decisions can have profound 

impacts on public health and welfare, 

and NAAQS decisions should be based 

on studies that have been rigorously 

assessed in an integrative manner not 

only by the EPA but also by the 

statutorily-mandated independent 

advisory committee, CASAC, and have 

been subject as well to the public review 

that accompanies this process. As 

described above, the provisional 

assessment did not and could not 

provide that kind of in-depth critical 

review. 

This decision is consistent with the 

EPA’s practice in prior NAAQS reviews. 

Since the 1970 amendments, the EPA 

has taken the view that NAAQS 

decisions are to be based on scientific 

studies and related information that 

have been assessed as a part of the 

pertinent air quality criteria. See e.g., 36 

FR 8186 (April 30, 1971) (the EPA based 

original NAAQS for six pollutants on 

scientific studies discussed in air 

quality criteria documents and limited 

consideration of comments to those 

concerning validity of scientific basis); 

38 FR 25678, 25679–25680 (September 

14, 1973) (the EPA revised air quality 

criteria for sulfur oxides to provide basis 

for reevaluation of secondary NAAQS). 

This longstanding interpretation was 

strengthened by new legislative 

requirements enacted in 1977, which 

added section 109(d)(2) of the CAA 

concerning CASAC review of air quality 

criteria. The EPA has consistently 

followed this approach. 52 FR 24634, 

24637 (July 1, 1987) (after review by 

CASAC, the EPA issued a post-proposal 

addendum to the PM Air Quality 

Criteria Document, to address certain 

new scientific studies not included in 

the 1982 Air Quality Criteria 

Document); 61 FR 25566, 25568 (May 

22, 1996) (after review by CASAC, the 

EPA issued a post-proposal supplement 

to the 1982 Air Quality Criteria 

Document to address certain new health 

studies not included in the 1982 Air 

Quality Criteria Document or 1986 


tkelley on DSK3SPTVN1PROD with 
3096 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

Addendum). The EPA reaffirmed this 

approach in its decision not to revise 

the ozone NAAQS in 1993, as well as in 

its final decision on the PM NAAQS in 

the 1997 and 2006 reviews. 58 FR 

13008, 13013 to 13014 (March 9, 1993) 

(ozone review); 62 FR 38652, 38662 

(July 18, 1997) and 71 FR 61141, 61148 

to 61149 (October 17, 2006) (PM 

reviews) (The EPA conducted a 

provisional assessment but based the 

final PM decisions on studies and 

related information included in the air 

quality criteria that had been reviewed 

by CASAC). 

As discussed in the EPA’s 1993 

decision not to revise the NAAQS for 

ozone, ‘new’ studies may sometimes be 

of such significance that it is 

appropriate to delay a decision on 

revision of NAAQS and to supplement 

the pertinent air quality criteria so the 

‘‘new’’ studies can be taken into account 

(58 FR, 13013 to 13014, March 9, 1993). 

In this proceeding, the provisional 

assessment of recent studies concludes 

that, taken in context, the ‘‘new’’ 

information and findings do not 

materially change any of the broad 

scientific conclusions regarding the 

health effects of PM exposure made in 

the Integrated Science Assessment (U.S. 

EPA, 2012b). For this reason, reopening 

the air quality criteria review would not 

be warranted even if there were time to 

do so under the court order governing 

the schedule for this rulemaking. 

Accordingly, the EPA is basing the final 

decisions in this review on the studies 

and related information included in the 

PM air quality criteria that have 

undergone CASAC and public review. 

The EPA will consider the ‘‘new’’ 

published studies for purposes of 

decision making in the next periodic 

review of the PM NAAQS, which will 

provide the opportunity to fully assess 

them through a more rigorous review 

process involving the EPA, CASAC, and 

the public. 

C. Related Control Programs To 

Implement PM Standards 

States are primarily responsible for 

ensuring attainment and maintenance of 

NAAQS once the EPA has established 

them. Under section 110 of the CAA and 

related provisions, states are to submit, 

for the EPA’s approval, SIPs that 

provide for the attainment and 

maintenance of such standards through 

control programs directed to sources of 

the pollutants involved. The states, in 

conjunction with the EPA, also 

administer the PSD permitting program 

(CAA sections 160 to 169). In addition, 

federal programs provide for nationwide 

reductions in emissions of PM and other 

air pollutants through the federal motor 

vehicle and motor vehicle fuel control 

program under title II of the Act (CAA 

sections 202 to 250) which involves 

controls for emissions from mobile 

sources and controls for the fuels used 

by these sources, and new source 

performance standards (NSPS) for 

stationary sources under section 111 of 

the CAA. 

Currently, there are 35 areas in the 

U.S. that are designated as 

nonattainment for the current annual 

PM2.5 standard and 32 areas in the U.S. 

that are designated as nonattainment for 

the current 24-hour PM2.5 standards. 

With the revisions to the PM NAAQS 

that are being finalized in this rule, the 

EPA will work with the states to 

conduct a new area designation process. 

Those states with new nonattainment 

areas will be required to develop SIPs to 

attain the standards. In developing their 

attainment plans, states will have to 

take into account projected emission 

reductions from federal and state rules 

that have already been adopted at the 

time of plan submittal. A number of 

significant emission reduction programs 

that will lead to reductions of PM and 

its precursors are in place today or are 

expected to be in place by the time any 

new SIPs will be due. Examples of such 

rules include regulations for onroad and 

nonroad engines and fuels, the utility 

and industrial boilers toxics rules, and 

various other programs already adopted 

by states to reduce emissions from key 

emissions sources. States will then 

evaluate the level of additional emission 

reductions needed for each 

nonattainment area to attain the 

standards ‘‘as expeditiously as 

practicable’’ and adopt new state 

regulations, as appropriate. Section IX 

includes additional discussion of 

designation and implementation issues 

associated with the revised PM NAAQS. 

D. Summary of Proposed Revisions to 

the PM NAAQS 

For reasons discussed in the proposal, 

the Administrator proposed to revise the 

current primary and secondary PM 

standards. With regard to the primary 

PM2.5 standards, the Administrator 

proposed to revise the level of the 

annual PM2.5 standard from 15.0 mg/m3

to a level within a range of 12.0 to 13.0 

mg/m3 and to retain the level of the 24- 

hour PM2.5 standard at 35 mg/m3. The 

Administrator also proposed to 

eliminate spatial averaging provisions as 

part of the form of the annual standard 

to avoid potential disproportionate 

impacts on at-risk populations. The EPA 

proposed to revise the AQI for PM2.5, 

consistent with the proposed primary 

PM2.5 standards. 

With regard to the primary coarse 

particle standard, the EPA proposed to 

retain the current 24-hour PM10

standard to continue to provide 

protection against effects associated 

with short-term exposure to thoracic 

coarse particles (i.e., PM10-2.5). 

With regard to the secondary PM 

standards, the EPA proposed to revise 

the suite of secondary PM standards by 

adding a distinct standard for PM2.5 to 

address PM-related visibility 

impairment. The separate secondary 

standard was proposed to be defined in 

terms of a PM2.5 visibility index, which 

would use speciated PM2.5 mass 

concentrations and relative humidity 

data to calculate PM2.5 light extinction, 

translated to the deciview (dv) scale, 

similar to the Regional Haze Program; a 

24-hour averaging time; a 90th 

percentile form averaged over 3 years; 

and a level set at one of two options— 

either 30 or 28 dv. The EPA also 

proposed to retain the current secondary 

standards generally to address nonvisibility welfare effects. 

The EPA also proposed to revise the 

data handling procedures consistent 

with the revised primary and secondary 

standards for PM2.5 including the 

computations necessary for determining 

when these standards are met and the 

measurement data that are appropriate 

for comparison to the standards. With 

regard to monitoring-related activities, 

the EPA proposed to update several 

aspects of the monitoring regulations 

and specifically to require that a small 

number of PM2.5 monitors be relocated 

to be collocated with measurements of 

other pollutants (e.g., nitrogen dioxide, 

carbon monoxide) in the near-road 

environment. 

E. Organization and Approach to Final 

PM NAAQS Decisions 

This action presents the 

Administrator’s final decisions on the 

review of the current primary and 

secondary PM2.5 and PM10 standards. 

Consistent with the decisions made by 

the EPA in the last review and with the 

conclusions in the Integrated Science 

Assessment and Policy Assessment, fine 

and thoracic coarse particles continue to 

be considered as separate subclasses of 

PM pollution. Primary standards for fine 

particles and for thoracic coarse 

particles are addressed in sections III 

and IV, respectively. Changes to the AQI 

for PM2.5, consistent with the revised 

primary PM2.5 standards, are addressed 

in section V. Secondary standards for 

fine and coarse particles are addressed 

in section VI. Related data handling 

conventions and exceptional events are 

addressed in section VII. Updates to the 

monitoring regulations are addressed in 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3097 

14Nonetheless, the Administrator recognizes the 

importance of all studies, including international 

studies, in the Integrated Science Assessment’s 

considerations of the weight of the evidence that 

informs causality determinations. 

section VIII. Implementation activities, 

including PSD-related actions, are 

addressed in section IX. Section X 

addresses applicable statutory and 

executive order reviews. 

Today’s final decisions addressing 

standards for fine and coarse particles 

are based on a thorough review in the 

Integrated Science Assessment of 

scientific information on known and 

potential human health and welfare 

effects associated with exposure to these 

subclasses of PM at levels typically 

found in the ambient air. These final 

decisions also take into account: (1) 

Staff assessments in the Policy 

Assessment of the most policy-relevant 

information in the Integrated Science 

Assessment as well as a quantitative 

health risk assessment and urbanfocused visibility assessment based on 

that information; (2) CASAC advice and 

recommendations, as reflected in its 

letters to the Administrator, its 

discussions of drafts of the Integrated 

Science Assessment, Risk and Exposure 

Assessments, and Policy Assessment at 

public meetings, and separate written 

comments prepared by individual 

members of the CASAC PM Review 

Panel; (3) public comments received 

during the development of these 

documents, both in connection with 

CASAC meetings and separately; and (4) 

extensive public comments received on 

the proposed rulemaking. 

III. Rationale for Final Decisions on the 

Primary PM2.5 Standards 

This section presents the 

Administrator’s final decision regarding 

the need to revise the current primary 

PM2.5 standards and, more specifically, 

regarding revisions to the level and form 

of the existing primary annual PM2.5

standard in conjunction with retaining 

the existing primary 24-hour PM2.5

standard. As discussed more fully 

below, the rationale for the final 

decision is based on a thorough review, 

in the Integrated Science Assessment, of 

the latest scientific information, 

published through mid-2009, on human 

health effects associated with long- and 

short-term exposures to fine particles in 

the ambient air. The final decisions also 

take into account: (1) Staff assessments 

of the most policy-relevant information 

presented and assessed in the Integrated 

Science Assessment and staff analyses 

of air quality and human risks presented 

in the Risk Assessment and the Policy 

Assessment, upon which staff 

conclusions regarding appropriate 

considerations in this review are based; 

(2) CASAC advice and 

recommendations, as reflected in 

discussions of drafts of the Integrated 

Science Assessment, Risk Assessment, 

and Policy Assessment at public 

meetings, in separate written comments, 

and in CASAC’s letters to the 

Administrator; (3) the multiple rounds 

of public comments received during the 

development of these documents, both 

in connection with CASAC meetings 

and separately; and (4) extensive public 

comments received on the proposal. 

In developing this final rule, the 

Administrator recognizes that the CAA 

requires her to reach a public health 

policy judgment as to what standards 

would be requisite—neither more nor 

less stringent than necessary—to protect 

public health with an adequate margin 

of safety, based on scientific evidence 

and technical assessments that have 

inherent uncertainties and limitations. 

This judgment requires making 

reasoned decisions as to what weight to 

place on various types of evidence and 

assessments, and on the related 

uncertainties and limitations. Thus, in 

selecting the final standards, the 

Administrator is seeking not only to 

prevent fine particle concentrations that 

have been demonstrated to be harmful 

but also to prevent lower fine particle 

concentrations that may pose an 

unacceptable risk of harm, even if the 

risk is not precisely identified as to 

nature or degree. 

As discussed below, as well as in 

more detail in the proposal, a 

substantial amount of new research has 

been conducted since the close of the 

science assessment in the last review of 

the PM2.5 NAAQS (U.S. EPA, 2004), 

with important new information coming 

from epidemiological studies, in 

particular. This body of evidence 

includes hundreds of new 

epidemiological studies conducted in 

many countries around the world. In its 

assessment of the evidence judged to be 

most relevant to making decisions on 

elements of the primary PM2.5

standards, the EPA has placed greater 

weight on U.S. and Canadian studies 

using PM2.5 measurements, since studies 

conducted in other countries may reflect 

different demographic and air pollution 

characteristics.14

The newly available research studies 

as well as the earlier body of scientific 

evidence presented and assessed in the 

Integrated Science Assessment have 

undergone intensive scrutiny through 

multiple layers of peer review and 

opportunities for public review and 

comment. In developing this final rule, 

the EPA has drawn upon an integrative 

synthesis of the entire body of evidence 

concerning exposure to ambient fine 

particles and a broad range of health 

endpoints (U.S. EPA, 2009a, Chapters 2, 

4, 5, 6, 7, and 8) focusing on those 

health endpoints for which the 

Integrated Science Assessment 

concludes that there is a causal or likely 

causal relationship with long- or shortterm PM2.5 exposures. The EPA has also 

considered health endpoints for which 

the Integrated Science Assessment 

concludes there is evidence suggestive 

of a causal relationship with long-term 

PM2.5 exposures. 

The EPA has also drawn upon a 

quantitative risk assessment based upon 

the scientific evidence described and 

assessed in the Integrated Science 

Assessment. These analyses, discussed 

in the Risk Assessment (U.S. EPA, 

2010a) and Policy Assessment (U.S. 

EPA, 2011a, chapter 2), have also 

undergone intensive scrutiny through 

multiple layers of peer review and 

multiple opportunities for public review 

and comment. 

Although important uncertainties 

remain in the qualitative and 

quantitative characterizations of health 

effects attributable to ambient fine 

particles, progress has been made in 

addressing these uncertainties in this 

review. The EPA’s review of this 

information has been extensive and 

deliberate. This intensive evaluation of 

the scientific evidence and quantitative 

assessments has provided a 

comprehensive and adequate basis for 

regulatory decision making at this time. 

This section describes the integrative 

synthesis of the evidence and technical 

information contained in the Integrated 

Science Assessment, the Risk 

Assessment, and the Policy Assessment 

with regard to the current and 

alternative standards. The EPA notes 

that the final decision for retaining or 

revising the current primary PM2.5

standards is a public health policy 

judgment made by the Administrator. 

The Administrator’s final decision 

draws upon scientific information and 

analyses related to health effects and 

risks; judgments about uncertainties that 

are inherent in the scientific evidence 

and analyses; CASAC advice; and 

comments received in response to the 

proposal. 

In presenting the rationale for the 

final decisions on the primary PM2.5

standards, this section begins with a 

summary of the approaches used in 

setting the initial primary PM2.5 NAAQS 

in 1997 and in reviewing and revising 

those standards in 2006 (section III.A.1). 

The DC Circuit Court of Appeals 

remand of the primary annual PM2.5

standard in 2009 is discussed in section 

III.A.2. Taking into consideration this 


tkelley on DSK3SPTVN1PROD with 
3098 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

15The term ‘‘evidence-based’’ approach or 

consideration generally refers to using the 

information in the scientific evidence to inform 

judgments on the need to retain or revise the 

NAAQS. The term ‘‘risk-based’’ generally refers to 

using the quantitative information in the Risk 

Assessment to inform such judgments. 

16 In so doing, the EPA noted that because an 

annual standard would focus control programs on 

annual average PM2.5 concentrations, it would not 

only control long-term exposure levels, but would 

also generally control the overall distribution of 24- 

hour exposure levels, resulting in fewer and lower 

24-hour peak concentrations. Alternatively, a 24- 

hour standard that focused controls on peak 

concentrations could also result in lower annual 

average concentrations. Thus, the EPA recognized 

that either standard could provide some degree of 

protection from both short- and long-term 

exposures, with the other standard serving to 

address situations where the daily peaks and 

annual averages are not consistently correlated (62 

FR 38669, July 18, 1997). In the circumstances 

presented in that review, the EPA determined that 

it was appropriate to focus on the annual standard 

as the standard best suited to control both annual 

and daily air quality distributions (62 FR 38670). 

history, section III.A.3 describes the 

EPA’s general approach used in the 

current review for considering the need 

to retain or revise the current suite of 

fine particle standards, taking into 

account public comment on the 

proposed approach. 

The scientific evidence and 

quantitative risk assessment were 

presented in sections III.B and III.C of 

the proposal, respectively (77 FR 38906 

to 38917, June 29, 2012) and are 

outlined in sections III.B and III.C 

below. Subsequent sections of this 

preamble provide a more complete 

discussion of the Administrator’s 

rationale, in light of key issues raised in 

public comments, for concluding that it 

is appropriate to revise the suite of 

current primary PM2.5 standards 

(section III.D), as well as a more 

complete discussion of the 

Administrator’s rationale for retaining 

or revising the specific elements of the 

primary PM2.5 standards, namely the 

indicator (section III.E.1); averaging time 

(section III.E.2); form (section III.E.3); 

and level (section III.E.4). A summary of 

the final decisions to revise the suite of 

primary PM2.5 standards is presented in 

section III.F. 

A. Background 

There are currently two primary PM2.5

standards providing public health 

protection from effects associated with 

fine particle exposures. The annual 

standard is set at a level of 15.0 mg/m3, 

based on the 3-year average of annual 

arithmetic mean PM2.5 concentrations 

from single or multiple monitors sited to 

represent community-wide air quality. 

The 24-hour standard is set at a level of 

35 mg/m3, based on the 3-year average of 

the 98th percentile of 24-hour PM2.5

concentrations at each populationoriented monitor within an area. 

The past and current approaches for 

reviewing the primary PM2.5 standards 

described below are all based most 

fundamentally on using information 

from epidemiological studies to inform 

the selection of PM2.5 standards that, in 

the Administrator’s judgment, protect 

public health with an adequate margin 

of safety. Such information can be in the 

form of air quality distributions over 

which health effect associations have 

been observed in scientific studies or in 

the form of concentration-response 

functions that support quantitative risk 

assessment. However, evidence- and 

risk-based approaches using information 

from epidemiological studies to inform 

decisions on PM2.5 standards are 

complicated by the recognition that no 

population threshold, below which it 

can be concluded with confidence that 

PM2.5-related effects do not occur, can 

be discerned from the available 

evidence.15 As a result, any general 

approach to reaching decisions on what 

standards are appropriate necessarily 

requires judgments about how to 

translate the information available from 

the epidemiological studies into a basis 

for appropriate standards. This includes 

consideration of how to weigh the 

uncertainties in the reported 

associations across the distributions of 

PM2.5 concentrations in the studies and 

the uncertainties in quantitative 

estimates of risk, in the context of the 

entire body of evidence before the 

Agency. Such approaches are consistent 

with setting standards that are neither 

more nor less stringent than necessary, 

recognizing that a zero-risk standard is 

not required by the CAA. 

1. General Approach Used in Previous 

Reviews 

The general approach used to 

translate scientific information into 

standards in the previous PM NAAQS 

reviews focused on consideration of 

alternative standard levels that were 

somewhat below the long-term mean 

PM2.5 concentrations reported in key 

epidemiological studies (U.S. EPA, 

2011a, section 2.1.1). This approach 

recognized that the strongest evidence 

of PM2.5-related associations occurs 

where the bulk of the data exists, which 

is over a range of concentrations around 

the long-term (i.e., annual) mean. 

In setting primary PM2.5 annual and 

24-hour standards for the first time in 

1997, the Agency relied primarily on an 

evidence-based approach that focused 

on epidemiological evidence, especially 

from short-term exposure studies of fine 

particles judged to be the strongest 

evidence at that time (U.S. EPA, 2011a, 

section 2.1.1.1). The EPA selected a 

level for the annual standard that was at 

or below the long-term mean PM2.5

concentrations in studies providing 

evidence of associations with short-term 

PM2.5 exposures, placing greatest weight 

on those short-term exposure studies 

that reported clearly statistically 

significant associations with mortality 

and morbidity effects. Further 

consideration of long-term mean PM2.5

concentrations associated with mortality 

and respiratory effects in children did 

not provide a basis for establishing a 

lower annual standard level. The EPA 

did not place much weight on 

quantitative risk estimates from the very 

limited risk assessment conducted, but 

did conclude that the risk assessment 

results confirmed the general 

conclusions drawn from the 

epidemiological evidence that a serious 

public health problem was associated 

with ambient PM levels allowed under 

the then current PM10 standards (62 FR 

38665/1, July 18, 1997). 

The EPA considered the 

epidemiological evidence and data on 

air quality relationships to set an annual 

PM2.5 standard that was intended to be 

the ‘‘generally controlling’’ standard; 

i.e., the primary means of lowering both 

long- and short-term ambient 

concentrations of PM2.5.16 In 

conjunction with the annual standard, 

the EPA also established a 24-hour 

PM2.5 standard to provide supplemental 

protection against days with high peak 

concentrations, localized ‘‘hotspots,’’ 

and risks arising from seasonal 

emissions that might not be well 

controlled by an annual standard (62 FR 

38669/3). 

In 2006, the EPA used a different 

evidence-based approach to assess the 

appropriateness of the levels of the 24- 

hour and annual PM2.5 standards (U.S. 

EPA, 2011a, section 2.1.1.2). Based on 

an expanded body of epidemiological 

evidence that was stronger and more 

robust than that available in the 1997 

review, including additional studies of 

both short- and long-term exposures, the 

EPA decided that using evidence of 

effects associated with periods of 

exposure that were most closely 

matched to the averaging time of each 

standard was the most appropriate 

public health policy approach for 

evaluating the scientific evidence to 

inform selecting the level of each 

standard. Thus, the EPA relied upon 

evidence from the short-term exposure 

studies as the principal basis for 

revising the level of the 24-hour PM2.5

standard from 65 to 35 mg/m3 to protect 

against effects associated with shortterm exposures. The EPA relied upon 

evidence from long-term exposure 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3099 

17By utilizing this approach, the Agency also is 

responsive to the remand of the 2006 standard. As 

noted in section III.A.2, the D.C. Circuit, in 

remanding the 2006 primary annual PM2.5 standard, 

concluded that the Administrator had failed to 

Continued 

studies as the principal basis for 

retaining the level of the annual PM2.5

standard at 15 mg/m3 to protect against 

effects associated with long-term 

exposures. This approach essentially 

took the view that short-term studies 

were not appropriate to inform 

decisions relating to the level of the 

annual standard, and long-term studies 

were not appropriate to inform 

decisions relating to the level of the 24- 

hour standard. With respect to 

quantitative risk-based considerations, 

the EPA determined that the estimates 

of risks likely to remain upon 

attainment of the 1997 suite of PM2.5

standards were indicative of risks that 

could be reasonably judged important 

from a public health perspective and, 

thus, supported revision of the 

standards. However, the EPA judged 

that the quantitative risk assessment had 

important limitations and did not 

provide an appropriate basis for 

selecting the levels of the revised 

standards in 2006 (71 FR 61174/1–2, 

October 17, 2006). 

2. Remand of Primary Annual PM2.5

Standard 

As noted above in section II.B.2, 

several parties filed petitions for review 

in the U.S. Court of Appeals for the 

District of Columbia Circuit following 

promulgation of the revised PM NAAQS 

in 2006. These petitions challenged 

several aspects of the final rule 

including the level of the primary PM2.5

annual standard. The primary 24-hour 

PM2.5 standard was not challenged by 

any of the litigants and, thus, was not 

considered in the court’s review and 

decision. 

On judicial review, the D.C. Circuit 

remanded the primary annual PM2.5

NAAQS to the EPA on grounds that the 

Agency failed to adequately explain 

why the annual standard provided the 

requisite protection from both shortand long-term exposures to fine 

particles including protection for at-risk 

populations. American Farm Bureau 

Federation v. EPA, 559 F. 3d 512 (D.C. 

Cir. 2009). With respect to human 

health protection from short-term PM2.5

exposures, the court considered the 

different approaches used by the EPA in 

the 1997 and 2006 p.m. NAAQS 

decisions, as summarized in section 

III.A.1 above. The court found that the 

EPA failed to adequately explain why a 

primary 24-hour PM2.5 standard by itself 

would provide the protection needed 

from short-term exposures and 

remanded the primary annual PM2.5

standard to the EPA ‘‘for further 

consideration of whether it is set at a 

level requisite to protect the public 

health while providing an adequate 

margin of safety from the risk of shortterm exposures to PM2.5.’’ American 

Farm Bureau Federation v. EPA, 559 F. 

3d at 520–24. 

With respect to protection from longterm exposure to fine particles, the court 

found that the EPA failed to adequately 

explain how the primary annual PM2.5

standard provided an adequate margin 

of safety for children and other at-risk 

populations. The court found that the 

EPA did not provide a reasonable 

explanation of why certain morbidity 

studies, including a study of children in 

Southern California showing lung 

damage associated with long-term PM2.5

exposure (Gauderman et al., 2000) and 

a multi-city study (24-Cities Study) 

evaluating decreased lung function in 

children associated with long-term 

PM2.5 exposures (Raizenne et al., 1996), 

did not warrant a more stringent annual 

PM2.5 standard. Id. at 522–23. 

Specifically, the court found that: 

EPA was unreasonably confident that, even 

though it relied solely upon long-term 

mortality studies, the revised standard would 

provide an adequate margin of safety with 

respect to morbidity among children. Notably 

absent from the final rule, moreover, is any 

indication of how the standard will 

adequately reduce risk to the elderly or to 

those with certain heart or lung diseases 

despite (a) the EPA’s determination in its 

proposed rule that those subpopulations are 

at greater risk from exposure to fine particles 

and (b) the evidence in the record supporting 

that determination. Id. at 525. 

In addition, the court held that the 

EPA had not adequately explained its 

decision to base the level of the annual 

standard essentially exclusively on the 

results of long-term studies and the 24- 

hour standard level essentially 

exclusively on the results of short-term 

studies. See 559 F. 3d at 522 (‘‘[e]ven if 

the long-term studies available today are 

useful for setting an annual standard 

* * * it is not clear why the EPA no 

longer believes it useful to look as well 

to short-term studies in order to design 

the suite of standards that will most 

effectively reduce the risks associated 

with short-term exposure’’); see also Id. 

at 523–24 (holding that the EPA had not 

adequately explained why a standard 

based on levels in short-term exposure 

studies alone provided appropriate 

protection from health effects associated 

with short-term PM2.5 exposures given 

the stated need to lower the entire air 

quality distribution, and not just peak 

concentrations, in order to control 

against short-term effects). 

In remanding the primary annual 

PM2.5 standard for reconsideration, the 

court did not vacate the standard, Id. at 

530, so the standard remains in effect 

and is therefore the standard considered 

by the EPA in this review. 

3. General Approach Used in the Policy 

Assessment for the Current Review 

This review is based on an assessment 

of a much expanded body of scientific 

evidence, more extensive air quality 

data and analyses, and a more 

comprehensive quantitative risk 

assessment relative to the information 

available in past reviews, as presented 

and assessed in the Integrated Science 

Assessment and Risk Assessment and 

discussed in the Policy Assessment. As 

a result, the EPA’s general approach to 

reaching conclusions about the 

adequacy of the current suite of PM2.5

standards and potential alternative 

standards that are appropriate to 

consider was broader and more 

integrative than in past reviews. Our 

general approach also reflected 

consideration of the issues raised by the 

court in its remand of the primary 

annual PM2.5 standard as discussed in 

section III.A.2 above, since decisions 

made in this review, and the rationales 

for those decisions, will comprise the 

Agency’s response to the remand. 

The EPA’s general approach took into 

account both evidence-based and riskbased considerations and the 

uncertainties related to both types of 

information, as well as advice from 

CASAC (Samet, 2010c,d) and public 

comments on the first and second draft 

Policy Assessments (U.S. EPA, 2010c,f). 

In so doing, the EPA staff developed a 

final Policy Assessment (U.S. EPA, 

2011a) which provided as broad an 

array of policy options as was supported 

by the available information, 

recognizing that the selection of a 

specific approach to reaching final 

decisions on the primary PM2.5

standards will reflect the judgments of 

the Administrator as to what weight to 

place on the various approaches and 

types of information available in the 

current review. 

The Policy Assessment concluded it 

was most appropriate to consider the 

protection against PM2.5-related 

mortality and morbidity effects, 

associated with both long- and shortterm exposures, afforded by the annual 

and 24-hour standards taken together, as 

was done in the 1997 review, rather 

than to consider each standard 

separately, as was done in the 2006 

review (U.S. EPA, 2011a, section 

2.1.3).17 As the EPA recognized in 1997, 


tkelley on DSK3SPTVN1PROD with 
3100 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

adequately explain why an annual standard was 

sufficiently protective in the absence of 

consideration of the long-term mean PM2.5

concentrations in short-term exposure studies as 

well, and likewise had failed to explain why a 24- 

hour standard was sufficiently protective in the 

absence of consideration of the effect of an annual 

standard on reducing the overall distribution of 24- 

hour average PM2.5 concentrations. 559 F. 3d at 

520–24. 

18 In confirmation, a number of studies have 

presented analyses excluding higher PM 

concentration days and reported a limited effect on 

the magnitude of the effect estimates or statistical 

significance of the association (e.g., Dominici, 

2006b; Schwartz et al., 1996; Pope and Dockery, 

1992). 

there are various ways to combine two 

standards to achieve an appropriate 

degree of public health protection. The 

extent to which these two standards are 

interrelated in any given area depends 

in large part on the relative levels of the 

standards, the peak-to-mean ratios that 

characterize air quality patterns in an 

area, and whether changes in air quality 

designed to meet a given suite of 

standards are likely to be of a more 

regional or more localized nature. 

In considering the combined effect of 

annual and 24-hour standards, the 

Policy Assessment recognized that 

changes in PM2.5 air quality designed to 

meet an annual standard would likely 

result not only in lower annual average 

PM2.5 concentrations but also in fewer 

and lower peak 24-hour PM2.5

concentrations. The Policy Assessment 

also recognized that changes designed to 

meet a 24-hour standard would result 

not only in fewer and lower peak 24- 

hour PM2.5 concentrations but also in 

lower annual average PM2.5

concentrations. Thus, either standard 

could be viewed as providing protection 

from effects associated with both shortand long-term exposures, with the other 

standard serving to address situations 

where the daily peak and annual 

average concentrations are not 

consistently correlated. 

In considering the currently available 

evidence, the Policy Assessment 

recognized that the short-term exposure 

studies were primarily drawn from 

epidemiological studies that associated 

variations in area-wide health effects 

with monitor(s) that measured the 

variation in daily PM2.5 concentrations 

over the course of several years. The 

strength of the associations in these data 

was demonstrably in the numerous 

‘‘typical’’ days within the air quality 

distribution, not in the peak days. See 

also 71 FR 61168, October 17, 2006 and 

American Farm Bureau Federation v. 

EPA, 559 F. 3d at 523, 524 (making the 

same point). The quantitative risk 

assessments conducted for this and 

previous reviews demonstrated the 

same point; that is, much, if not most of 

the aggregate risk associated with shortterm exposures results from the large 

number of days during which the 24- 

hour average concentrations are in the 

low-to mid-range, below the peak 24- 

hour concentrations (U.S. EPA, 2011a, 

section 2.2.2; U.S. EPA, 2010a, section 

3.1.2.2). In addition, there was no 

evidence suggesting that risks associated 

with long-term exposures were likely to 

be disproportionately driven by peak 

24-hour concentrations.18

For these reasons, the Policy 

Assessment concluded that strategies 

that focused primarily on reducing peak 

days were less likely to achieve 

reductions in the PM2.5 concentrations 

that were most strongly associated with 

the observed health effects. 

Furthermore, the Policy Assessment 

concluded that a policy approach that 

focused on reducing peak exposures 

would most likely result in more 

uneven public health protection across 

the U.S. by either providing inadequate 

protection in some areas or 

overprotecting in other areas (U.S. EPA, 

2011a, p. 2–9; U.S. EPA, 2010a, section 

5.2.3). This is because, as discussed 

above, reductions based on control of 

peak days are less likely to control the 

bulk of the air quality distribution. 

The Policy Assessment concluded 

that a policy goal of setting a ‘‘generally 

controlling’’ annual standard that will 

lower a wide range of ambient 24-hour 

PM2.5 concentrations, as opposed to 

focusing on control of peak 24-hour 

PM2.5 concentrations, was the most 

effective and efficient way to reduce 

total population risk and so provide 

appropriate protection. This approach, 

in contrast to one focusing on a 

generally controlling 24-hour standard, 

would likely reduce aggregate risks 

associated with both long- and shortterm exposures with more consistency 

and would likely avoid setting national 

standards that could result in relatively 

uneven protection across the country, 

due to setting standards that are either 

more or less stringent than necessary in 

different geographical areas (U.S. EPA, 

2011a, p. 2–9). 

The Policy Assessment also 

concluded that an annual standard 

intended to serve as the primary means 

for providing protection from effects 

associated with both long- and shortterm PM2.5 exposures cannot be 

expected to offer sufficient protection 

against the effects of all short-term PM2.5

exposures. As a result, in conjunction 

with a generally controlling annual 

standard, the Policy Assessment 

concluded it was appropriate to 

consider setting a 24-hour standard to 

provide supplemental protection, 

particularly for areas with high peak-tomean ratios possibly associated with 

strong local or seasonal sources, or 

PM2.5-related effects that may be 

associated with shorter-than-daily 

exposure periods (U.S. EPA, 2011a, p. 

2–10). 

The Policy Assessment’s 

consideration of the protection afforded 

by the current and alternative suites of 

standards focused on PM2.5-related 

health effects associated with long-term 

exposures for which the magnitude of 

quantitative estimates of risks to public 

health generated in the risk assessment 

was appreciably larger in terms of 

overall incidence and percent of total 

mortality or morbidity effects than for 

short-term PM2.5-related effects. 

Nonetheless, the EPA also considered 

health effects and estimated risks 

associated with short-term exposures. In 

both cases, the Policy Assessment 

placed greatest weight on health effects 

that had been judged in the Integrated 

Science Assessment to have a causal or 

likely causal relationship with PM2.5

exposures, while also considering 

health effects judged to be suggestive of 

a causal relationship or evidence that 

focused on specific at-risk populations. 

The Policy Assessment placed relatively 

greater weight on statistically significant 

associations that yielded relatively more 

precise effect estimates and that were 

judged to be robust to confounding by 

other air pollutants. In the case of shortterm exposure studies, the Policy 

Assessment placed greatest weight on 

evidence from large multi-city studies, 

while also considering associations in 

single-city studies. 

In translating information from 

epidemiological studies into the basis 

for reaching staff conclusions on the 

adequacy of the current suite of 

standards, the Policy Assessment 

considered a number of factors. As an 

initial matter, the Policy Assessment 

considered the extent to which the 

currently available evidence and related 

uncertainties strengthens or calls into 

question conclusions from the last 

review regarding associations between 

fine particle exposures and health 

effects. The Policy Assessment also 

considered evidence of health effects in 

at-risk populations and the potential 

impacts on such populations. Further, 

the Policy Assessment explored the 

extent to which PM2.5-related health 

effects had been observed in areas 

where air quality distributions extend to 

lower concentrations than previously 

reported or in areas that would likely 

have met the current suite of standards. 

In translating information from 

epidemiological studies into the basis 

for reaching staff conclusions on 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3101 

19The epidemiological studies evaluated in the 

Integrated Science Assessment that examined the 

shape of concentration-response relationships and 

the potential presence of a threshold focused on 

cardiovascular-related hospital admissions and 

emergency department visits associated with shortterm PM10 exposures and premature mortality 

associated with long-term PM2.5 exposure (U.S. 

EPA, 2009a, sections 6.5, 6.2.10.10 and 7.6). 

Overall, the Integrated Science Assessment 

concluded that the studies evaluated support the 

use of a no-threshold, log-linear model but 

recognized that ‘‘additional issues such as the 

influence of heterogeneity in estimates between 

cities, and the effect of seasonal and regional 

differences in PM on the concentration-response 

relationship still require further investigation’’ (U.S. 

EPA, 2009a, section 2.4.3). 

20This is distinct from confidence intervals 

around concentration-response relationships that 

are related to the magnitude of effect estimates 

generated at specific PM2.5 concentrations (i.e., 

point-wise confidence intervals) and that are 

relevant to the precision of the effect estimate 

across the air quality distribution, rather than to our 

confidence in the existence of a continuing 

concentration-response relationship across the 

entire air quality distribution on which a reported 

association was based. 

21Using the term ‘‘composite monitor’’ does not 

imply that the EPA can identify one monitor that 

represents the air quality evaluated in a specific 

study area. Rather, the composite monitor 

concentration represents the average concentration 

across monitors within each area with more than 

one monitor included in a given study as typically 

reported in epidemiological studies. For multi-city 

studies, this metric reflects concentrations averaged 

across multiple monitors or from single monitors 

within each area and then averaged across study 

areas for an overall study mean PM2.5 concentration. 

This is consistent with the epidemiological 

evidence considered in other NAAQS reviews. 

22 In the PM NAAQS review completed in 2006, 

the Staff Paper similarly recognized that the 

evidence of an association in any epidemiological 

study is ‘‘strongest at and around the long-term 

average where the data in the study are most 

concentrated. For example, the interquartile range 

of long-term average concentrations within a study 

[with a lower bound of the 25th percentile] or a 

range within one standard deviation around the 

study mean, may reasonably be used to characterize 

the range over which the evidence of association is 

strongest’’ (U.S. EPA, 2005, p. 5–22). A range of one 

standard deviation around the mean represents 

approximately 68 percent of normally distributed 

data, and below the mean falls between the 25th 

and 10th percentiles. 

standard levels for consideration (U.S. 

EPA, 2011a, sections 2.1.3 and 2.3.4), 

the Policy Assessment first recognized 

the absence of discernible thresholds in 

the concentration-response functions 

from long- and short-term PM2.5

exposure studies (U.S. EPA, 2011a, 

section 2.4.3).19 In the absence of any 

discernible thresholds, the Agency’s 

general approach for identifying 

appropriate standard levels for 

consideration involved characterizing 

the range of PM2.5 concentrations over 

which we have the most confidence in 

the associations reported in 

epidemiological studies. In so doing, the 

Policy Assessment recognized that there 

is no single factor or criterion that 

comprises the ‘‘correct’’ approach, but 

rather there are various approaches that 

are reasonable to consider for 

characterizing the confidence in the 

associations and the limitations and 

uncertainties in the evidence. 

Identifying the implications of various 

approaches for reaching conclusions on 

the range of alternative standard levels 

that is appropriate to consider can help 

inform the final decisions to either 

retain or revise the standards. Today’s 

final decisions also take into account 

public health policy judgments as to the 

degree of health protection that is to be 

achieved. 

In reaching staff conclusions on the 

range of annual standard levels that was 

appropriate to consider, the Policy 

Assessment focused on identifying an 

annual standard that provided requisite 

protection from effects associated with 

both long- and short-term exposures. In 

so doing, the Policy Assessment 

explored different approaches for 

characterizing the range of PM2.5

concentrations over which our 

confidence in the nature of the 

associations for both long- and shortterm exposures is greatest, as well as the 

extent to which our confidence is 

reduced at lower PM2.5 concentrations. 

First, the Policy Assessment 

recognized that the approach that most 

directly addressed this issue considered 

studies that analyzed confidence 

intervals around concentration-response 

relationships and in particular, analyses 

that averaged across multiple 

concentration-response models rather 

than considering a single concentrationresponse model.20 The Policy 

Assessment explored the extent to 

which such analyses had been 

published for studies of health effects 

associated with long- or short-term 

PM2.5 exposures. Such analyses could 

potentially be used to characterize a 

concentration below which uncertainty 

in a concentration-response relationship 

substantially increases or is judged to be 

indicative of an unacceptable degree of 

uncertainty about the existence of a 

continuing concentration-response 

relationship. The Policy Assessment 

concluded that identifying this area of 

uncertainty in the concentrationresponse relationship could be used to 

inform identification of alternative 

standard levels that are appropriate to 

consider. 

Further, the Policy Assessment 

explored other approaches that 

considered different statistical metrics 

from epidemiological studies. The 

Policy Assessment first took into 

account the general approach used in 

previous PM reviews which focused on 

consideration of alternative standard 

levels that were somewhat below the 

long-term mean PM2.5 concentrations 

reported in epidemiological studies 

using air quality distributions based on 

composite monitor concentrations.21

This approach recognized that the 

strongest evidence of PM2.5-related 

associations occurs at concentrations 

around the long-term (i.e., annual) 

mean. In using this approach, the Policy 

Assessment placed greatest weight on 

those long- and short-term exposure 

studies that reported statistically 

significant associations with mortality 

and morbidity effects. 

In extending this approach, the Policy 

Assessment also considered information 

beyond a single statistical metric of 

PM2.5 concentrations (i.e., the mean) to 

the extent such information was 

available. Pursuant to an express 

comment from CASAC (Samet 2010d, p. 

2), the Policy Assessment utilized 

distributional statistics (i.e., statistical 

characterization of an entire distribution 

of data) to identify the broader range of 

PM2.5 concentrations that had the most 

influence on the calculation of relative 

risk estimates in both long- and shortterm exposure epidemiological studies. 

Thus, the Policy Assessment considered 

the part of the distribution of PM2.5

concentrations in which the data 

analyzed in the study (i.e., air quality 

and population-level data, as discussed 

below) were most concentrated, 

specifically, the range of PM2.5

concentrations around the long-term 

mean over which our confidence in the 

magnitude and significance of 

associations observed in the 

epidemiological studies was greatest. 

The Policy Assessment then focused on 

the lower part of the distribution to 

characterize where the data became 

appreciably more sparse and, thus, 

where our understanding of the 

magnitude and significance of the 

associations correspondingly became 

more uncertain. The Policy Assessment 

recognized there was no single 

percentile value within a given 

distribution that was most appropriate 

or ‘‘correct’’ to use to characterize where 

our confidence in the associations 

becomes appreciably lower. The Policy 

Assessment concluded that the range 

from the 25th to 10th percentiles is a 

reasonable range to consider as a region 

where we had appreciably less 

confidence in the associations observed 

in epidemiological studies.22

In considering distributional statistics 

from epidemiological studies, the final 

Policy Assessment focused on two types 

of population-level metrics that CASAC 

advised were most useful to consider in 

identifying the PM2.5 concentrations 


tkelley on DSK3SPTVN1PROD with 
3102 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

23The second draft Policy Assessment focused on 

the distributions of ambient PM2.5 concentrations 

and associated population data across areas 

included in several multi-city studies for which 

such data were available in seeking to identify the 

most influential range of concentrations (U.S. EPA, 

2010f, section 2.3.4.1). In its review of the second 

draft Policy Assessment, CASAC advised that it 

‘‘would be preferable to have information on the 

concentrations that were most influential in 

generating the health effect estimates in individual 

studies’’ (Samet, 2010d, p.2). Therefore, in the final 

Policy Assessment, the EPA considered populationlevel data (i.e., area-specific health event data and 

study area population data) along with 

corresponding PM2.5 concentrations to generate a 

cumulative distribution of the population-level data 

relative to long-term mean PM2.5 concentrations to 

determine the most influential part of the air quality 

distribution (U.S. EPA, 2011a, Figure 2–7 and 

associated text). 

24Statistical metrics (e.g., means) based on 

composite monitor distributions may be identical to 

or below the same statistical metrics based on 

maximum monitor distributions. For example, some 

areas may have only one monitor, in which case the 

composite and maximum monitor distributions will 

be identical in those areas. Other areas may have 

multiple monitors that may be very close to the 

monitor measuring the highest concentrations, in 

which case the composite and maximum monitor 

distributions could be similar in those areas. As 

noted in Hassett-Sipple et al. (2010), for studies 

involving a large number of areas, the composite 

and maximum concentrations are generally within 

5 percent of each other (77 FR 38905, fn. 30). Still 

other areas may have multiple monitors that may 

be separately impacted by local sources in which 

case the composite and maximum monitor 

distributions could be quite different (U.S. EPA, 

2011a, p. 2–14). See further discussion of this issue 

in section III.E.4.c.i below. 

25 Design values are the metrics (i.e., statistics) 

that are compared to the NAAQS levels to 

determine compliance. 

most influential in generating the health 

effect estimates reported in the 

epidemiological studies.23 Consistent 

with CASAC advice, the most relevant 

information was the distribution of 

health events (e.g., deaths, 

hospitalizations) occurring within a 

study population in relation to the 

distribution of PM2.5 concentrations. 

However, in recognizing that access to 

health event data can be restricted, the 

Policy Assessment also considered the 

number of study participants within 

each study area as an appropriate 

surrogate for health event data. 

The Policy Assessment recognized 

that an approach considering analyses 

of confidence intervals around 

concentration-response functions was 

intrinsically related to an approach that 

considered different distributional 

statistics. Both of these approaches 

could be employed to understand the 

broader distribution of PM2.5

concentrations which correspond to the 

health events reported in 

epidemiological studies. In applying 

these approaches, the Policy 

Assessment, consistent with CASAC 

advice (Samet, 2010d, p. 3), considered 

PM2.5 concentrations from long- and 

short-term PM2.5 exposure studies using 

composite monitor distributions. 

In reaching staff conclusions on 

alternative standard levels that were 

appropriate to consider, the Policy 

Assessment also included a broader 

consideration of the uncertainties and 

limitations of the current scientific 

evidence. Most notably, these 

uncertainties are related to the 

heterogeneity observed in the 

epidemiological studies in the eastern 

versus western parts of the U.S., the 

relative toxicity of PM2.5 components, 

and the potential role of co-pollutants 

(U.S. EPA, 2011a, pp. 2–25 to 2–26). 

The limitations and uncertainties 

associated with the currently available 

scientific evidence, including the 

availability of fewer studies toward the 

lower range of alternative annual 

standard levels being considered in this 

proposal, are summarized in section 

III.B below and further discussed in 

section III.B.2 of the proposal. 

The Policy Assessment recognized 

that the level of protection afforded by 

the NAAQS relies both on the level and 

the form of the standard. The Policy 

Assessment concluded that a policy 

approach that used data based on 

composite monitor distributions to 

identify alternative standard levels, and 

then compared those levels to 

concentrations at maximum monitors to 

determine whether an area meets a 

given standard, inherently has the 

potential to build in some margin of 

safety (U.S. EPA, 2011a, p. 2–14).24 This 

conclusion was consistent with 

CASAC’s comments on the second draft 

Policy Assessment, in which CASAC 

expressed its preference for focusing on 

an approach using composite monitor 

distributions ‘‘because of its stability, 

and for the additional margin of safety 

it provides’’ when ‘‘compared to the 

maximum monitor perspective’’ (Samet, 

et al., 2010d, pp. 2 to 3). 

In reaching staff conclusions on 

alternative 24-hour standard levels that 

are appropriate to consider for setting a 

24-hour standard intended to 

supplement the protection afforded by a 

generally controlling annual standard, 

the Policy Assessment considered 

currently available short-term PM2.5

exposure studies. The evidence from 

these studies informed our 

understanding of the protection afforded 

by the suite of standards against effects 

associated with short-term exposures. In 

considering the short-term exposure 

studies, the Policy Assessment 

evaluated both the distributions of 24- 

hour PM2.5 concentrations, with a focus 

on the 98th percentile concentrations (to 

the extent such data were available) to 

match the form of the current 24-hour 

PM2.5 standard, as well as the long-term 

mean PM2.5 concentrations reported in 

these studies. In addition to considering 

the epidemiological evidence, the Policy 

Assessment also considered air quality 

information based on county-level 24- 

hour and annual design values 25 to 

understand the policy implications of 

the alternative standard levels 

supported by the underlying science. In 

particular, the Policy Assessment 

considered the extent to which different 

combinations of alternative annual and 

24-hour standards would support the 

policy goal of focusing on a generally 

controlling annual standard in 

conjunction with a 24-hour standard 

that would provide supplemental 

protection. In so doing, the Policy 

Assessment discussed the roles that 

each standard might be expected to play 

in the protection afforded by alternative 

suites of standards. 

Beyond these evidence-based 

considerations, the Policy Assessment 

also considered the quantitative risk 

estimates and the key observations 

presented in the Risk Assessment. This 

assessment included an evaluation of 15 

urban case study areas and estimated 

risk associated with a number of health 

endpoints associated with long- and 

short-term PM2.5 exposures (U.S. EPA, 

2010a). As part of the risk-based 

considerations, the Policy Assessment 

considered estimates of the magnitude 

of PM2.5-related risks associated with 

recent air quality levels and air quality 

simulated to just meet the current and 

alternative suites of standards using 

alternative simulation approaches. The 

Policy Assessment also characterized 

the risk reductions, relative to the risks 

remaining upon just meeting the current 

standards, associated with just meeting 

alternative suites of standards. In so 

doing, the Policy Assessment 

recognized the uncertainties inherent in 

such risk estimates, and took such 

uncertainties into account by 

considering the sensitivity of the ‘‘core’’ 

risk estimates to alternative assumptions 

and methods likely to have substantial 

impact on the estimates. In addition, the 

Policy Assessment considered 

additional analyses characterizing the 

representativeness of the urban study 

areas within a broader national context 

to understand the roles that the annual 

and 24-hour standards may play in 

affording protection against effects 

related to both long- and short-term 

PM2.5 exposures. 

Based on the approach discussed 

above, the Policy Assessment reached 

conclusions related to the primary PM2.5

standards that reflected an 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3103 

26The term ‘‘likely causal association’’ was used 

in the 2004 Criteria Document to summarize the 

strength of the available evidence available in the 

last review for PM2.5. However, this terminology 

was not based on a formal framework for evaluating 

evidence for inferring causation. Since the last 

review, the EPA has developed a more formal 

framework for reaching causal determinations with 

standardized language to express evaluation of the 

evidence (U.S. EPA, 2009a, section 1.5). 

27The causal framework draws upon the 

assessment and integration of evidence from across 

epidemiological, controlled human exposure, and 

toxicological studies, and the related uncertainties 

that ultimately influence our understanding of the 

evidence. This framework employs a five-level 

hierarchy that classifies the overall weight of 

evidence and causality using the following 

categorizations: causal relationship, likely to be 

causal relationship, suggestive of a causal 

relationship, inadequate to infer a causal 

relationship, and not likely to be a causal 

relationship (U.S. EPA, 2009a, Table 1–3). The 

development of the causal framework reflects 

considerable input from CASAC and the public, 

with CASAC concluding that, ‘‘The five-level 

classification of strength of evidence for causal 

inference has been systemically applied [for PM]; 

this approach has provided transparency and a 

clear statement of the level of confidence with 

regard to causation, and we recommend its 

continued use in future ISAs’’ (Samet, 2009f, p. 1). 

28These causal inferences are based not only on 

the more expansive epidemiological evidence 

available in this review but also reflect 

consideration of important progress that has been 

made to advance our understanding of a number of 

potential biologic modes of action or pathways for 

PM-related cardiovascular and respiratory effects 

(U.S. EPA, 2009a, chapter 5). 

understanding of both evidence-based 

and risk-based considerations to inform 

two overarching questions related to: (1) 

The adequacy of the current suite of 

PM2.5 standards and (2) revisions to the 

standards that were appropriate to 

consider in this review to protect 

against health effects associated with 

both long- and short-term exposures to 

fine particles. When evaluating the 

health protection afforded by the 

current or any alternative suites of 

standards considered, the Policy 

Assessment took into account the four 

basic elements of the NAAQS: The 

indicator, averaging time, form, and 

level. 

The general approach for reviewing 

the primary PM2.5 standards described 

above provided a comprehensive basis 

that helped to inform the 

Administrator’s judgments in reaching 

her proposed and final decisions to 

revise the current suite of primary fine 

particle NAAQS and in responding to 

the remand of the 2006 primary annual 

PM2.5 standard. 

B. Overview of Health Effects Evidence 

This section outlines the key 

information presented in section III.B of 

the proposal (77 FR 38906 to 38911, 

June 29, 2012) and discussed more fully 

in the Integrated Science Assessment 

(Chapters 2, 4, 5, 6, 7, and 8) and the 

Policy Assessment (Chapter 2) related to 

health effects associated with fine 

particle exposures. Section III.B. of the 

proposal discusses available 

information on the health effects 

associated with exposures to PM2.5, 

including the nature of such health 

effects (section III.B.1) and associated 

limitations and uncertainties (section 

III.B.2), at-risk populations (section 

III.B.3), and potential PM2.5-related 

impacts on public health (section 

III.B.4). As was true in the last two 

reviews, evidence from epidemiological, 

controlled human exposure and animal 

toxicological studies played a key role 

in the Integrated Science Assessment’s 

evaluation of the scientific evidence. 

The 2006 PM NAAQS review 

concluded that there was ‘‘strong 

epidemiological evidence’’ for linking 

long-term PM2.5 exposures with 

cardiovascular-related and lung cancer 

mortality and respiratory-related 

morbidity and for linking short-term 

PM2.5 exposures with cardiovascularrelated and respiratory-related mortality 

and morbidity (U.S. EPA, 2004, p. 9–46; 

U.S. EPA, 2005, p. 5–4). Overall, the 

evidence from epidemiological, 

toxicological, and controlled human 

exposure studies supported ‘‘likely 

causal associations’’ between PM2.5 and 

both mortality and morbidity from 

cardiovascular and respiratory diseases, 

based on ‘‘an assessment of strength, 

robustness, and consistency in results’’ 

(U.S. EPA, 2004, p. 9–48).26

In this review, based on the expanded 

body of evidence, the EPA finds that: 

(1) In looking across the extensive new 

scientific evidence available in this review, 

our overall understanding of health effects 

associated with fine particle exposures has 

been greatly expanded. The currently 

available evidence is largely consistent with 

evidence available in the last review and 

substantially strengthens what is known 

about the effects associated with fine particle 

exposures. 

(2) A number of large multi-city 

epidemiological studies have been conducted 

throughout the U.S., including extended 

analyses of long-term exposure studies that 

were important to inform decision-making in 

the last review. The body of currently 

available scientific evidence has also been 

expanded greatly by the publication of a 

number of new multi-city, time-series studies 

that have used uniform methodologies to 

investigate the effects of short-term PM2.5

exposures on public health. This body of 

evidence provides a more expansive data 

base and considers multiple locations 

representing varying regions and seasons that 

provide evidence of the influence of different 

air pollution mixes on PM2.5-associated 

health effects. These studies provide more 

precise estimates of the magnitude of effects 

associated with short-term PM2.5 exposure 

than most smaller-scale single-city studies 

that were more commonly available in the 

last review. These studies have reported 

consistent increases in morbidity and/or 

premature mortality related to ambient PM2.5

concentrations, with the strongest evidence 

reported for cardiovascular-related effects. 

(3) In addition, the findings of new 

toxicological and controlled human exposure 

studies greatly expand and provide stronger 

support for a number of potential biological 

mechanisms or pathways for cardiovascular 

and respiratory effects associated with longand short-term PM exposures. These studies 

provide coherence and biological plausibility 

for the effects observed in epidemiological 

studies. 

(4) Using a more formal framework for 

reaching causal determinations than used in 

prior reviews,27 the EPA concludes that a 

causal relationship exists between both longand short-term exposures to PM2.5 and 

premature mortality and cardiovascular 

effects and a likely causal relationship exists 

between long- and short-term PM2.5

exposures and respiratory effects. Further, 

there is evidence suggestive of a causal 

relationship between long-term PM2.5

exposures and other health effects, including 

developmental and reproductive effects (e.g., 

low birth weight, infant mortality) and 

carcinogenic, mutagenic, and genotoxic 

effects (e.g., lung cancer mortality).28

(5) The newly available evidence 

significantly strengthens the link between 

long- and short-term exposure to PM2.5 and 

premature mortality, while providing 

indications that the magnitude of the PM2.5- 

mortality association with long-term 

exposures may be larger than previously 

estimated. The strongest evidence comes 

from recent studies investigating long-term 

exposure to PM2.5 and cardiovascular-related 

mortality. The evidence supporting a causal 

relationship between long-term PM2.5

exposure and mortality also includes 

consideration of new studies that 

demonstrated an improvement in community 

health following reductions in ambient fine 

particles. 

(6) Several new studies have examined the 

association between cardiovascular effects 

and long-term PM2.5 exposures in multi-city 

studies conducted in the U.S. and Europe. 

While studies were not available in the last 

review with regard to long-term exposure and 

cardiovascular-related morbidity, recent 

studies have provided new evidence linking 

long-term exposure to PM2.5 with an array of 

cardiovascular effects such as heart attacks, 

congestive heart failure, stroke, and 

mortality. This evidence is coherent with 

studies of short-term exposure to PM2.5 that 

have observed associations with a continuum 

of effects ranging from subtle changes in 

indicators of cardiovascular health to serious 

clinical events, such as increased 

hospitalizations and emergency department 

visits due to cardiovascular disease and 

cardiovascular mortality. 

(7) Extended analyses of studies available 

in the last review as well as new 

epidemiological studies conducted in the 

U.S. and abroad provide stronger evidence of 

respiratory-related morbidity effects 

associated with long-term PM2.5 exposure. 

The strongest evidence for respiratory-related 


tkelley on DSK3SPTVN1PROD with 
3104 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

29A copollutant meets the criteria for potential 

confounding in PM-health associations if: (1) It is 

a potential risk factor for the health effect under 

study; (2) it is correlated with PM; and (3) it does 

not act as an intermediate step in the pathway 

between PM exposure and the health effect under 

study (U.S. EPA, 2004, p. 8–10). 

30The quantitative risk assessment conducted for 

this review is more fully described and presented 

in the Risk Assessment (U.S. EPA, 2010a) and 

summarized in detail in the Policy Assessment 

(U.S. EPA, 2011a, sections 2.2.2. and 2.3.4.2). The 

scope and methodology for this risk assessment 

were developed over the last few years with 

considerable input from CASAC and the public as 

described in section II.B.3 above. 

31The Risk Assessment concluded that these 15 

urban study areas were generally representative of 

urban areas in the U.S. likely to experience 

relatively elevated levels of risk related to ambient 

PM2.5 exposure with the potential for better 

characterization at the higher end of that 

distribution (U.S. EPA, 2011a, p. 2–42; U.S. EPA, 

2010a, section 4.4, Figure 4–17). The 

representativeness analysis also showed that the 15 

urban study areas do not capture areas with the 

highest baseline morality risks or the oldest 

populations (both of which can result in higher 

PM2.5-related mortality estimates). However, some 

of the areas with the highest values for these 

attributes had relatively low PM2.5 concentrations 

(e.g., urban areas in Florida) and, consequently, the 

Risk Assessment concluded failure to include these 

areas in the set of urban study areas was unlikely 

to exclude high PM2.5-risk locations (U.S. EPA, 

2010a, section 4.4.1). 

effects is from studies that evaluated 

decrements in lung function growth, 

increased respiratory symptoms, and asthma 

development. The strongest evidence from 

short-term PM2.5 exposure studies has been 

observed for increased respiratory-related 

emergency department visits and hospital 

admissions for chronic obstructive 

pulmonary disease (COPD) and respiratory 

infections. 

(8) The body of scientific evidence is 

somewhat expanded from the 2006 review 

but is still limited with respect to 

associations between long-term PM2.5

exposures and developmental and 

reproductive effects as well as cancer, 

mutagenic, and genotoxic effects. The 

strongest evidence for an association between 

PM2.5 and developmental and reproductive 

effects comes from epidemiological studies of 

low birth weight and infant mortality, 

especially due to respiratory causes during 

the post-neonatal period (i.e., 1 month–12 

months of age). With regard to cancer effects, 

‘‘[m]ultiple epidemiologic studies have 

shown a consistent positive association 

between PM2.5 and lung cancer mortality, but 

studies have generally not reported 

associations between PM2.5 and lung cancer 

incidence’’ (U.S. EPA 2009a p. 2–13). 

(9) Efforts to evaluate the relationships 

between PM composition and health effects 

continue to evolve. While many constituents 

of PM2.5 can be linked with differing health 

effects, the evidence is not yet sufficient to 

allow differentiation of those constituents or 

sources that may be more closely related to 

specific health outcomes nor to exclude any 

individual component or group of 

components associated with any source 

categories from the fine particle mixture of 

concern. 

(10) Specific groups within the general 

population are at increased risk for 

experiencing adverse health effects related to 

PM exposures. The currently available 

evidence expands our understanding of 

previously identified at-risk populations (i.e., 

children, older adults, and individuals with 

pre-existing heart and lung disease) and 

supports the identification of additional atrisk populations (e.g., persons with lower 

socioeconomic status, genetic differences). 

Evidence for PM-related effects in these atrisk populations has expanded and is 

stronger than previously observed. There is 

emerging, though still limited, evidence for 

additional potentially at-risk populations, 

such as those with diabetes, people who are 

obese, pregnant women, and the developing 

fetus. 

(11) The population potentially affected by 

PM2.5 is large. In addition, large subgroups of 

the U.S. population have been identified as 

at-risk populations. While individual effect 

estimates from epidemiological studies may 

be small in size, the public health impact of 

the mortality and morbidity associations can 

be quite large given the extent of exposure. 

Taken together, this suggests that exposure to 

ambient PM2.5 concentrations can have 

substantial public health impacts. 

(12) While the currently available scientific 

evidence is stronger and more consistent 

than in previous reviews, providing a strong 

basis for decision making in this review, the 

EPA recognizes that important uncertainties 

and limitations in the health effects evidence 

remain. Epidemiological studies evaluating 

health effects associated with long- and 

short-term PM2.5 exposures have reported 

heterogeneity in responses between cities 

and geographic regions within the U.S. This 

heterogeneity may be attributed, in part, to 

differences in the fine particle composition 

or related to exposure measurement error, 

which can introduce bias and increased 

uncertainty in associated health effect 

estimates. Variability in the associations 

observed across PM2.5 epidemiological 

studies may be due in part to exposure error 

related to measurement-related issues, the 

use of central fixed-site monitors to represent 

population exposure to PM2.5, models used 

in lieu of or to supplement ambient 

measurements, and our limited 

understanding of factors that may influence 

exposures (e.g., topography, the built 

environment, weather, source characteristics, 

ventilation usage, personal activity patterns, 

photochemistry). In addition, where PM2.5

and other pollutants (e.g., ozone, nitrogen 

dioxide, and carbon monoxide) are 

correlated, it can be difficult to distinguish 

the effects of the various pollutants in the 

ambient mixture (i.e., co-pollutant 

confounding).29

While uncertainties and limitations 

still remain in the available health 

effects evidence, the Administrator 

judges the currently available scientific 

data base to be stronger and more 

consistent than in previous reviews 

providing a strong basis for decision 

making in this review. 

C. Overview of Quantitative 

Characterization of Health Risks 

In addition to a comprehensive 

evaluation of the health effects evidence 

available in this review, the EPA 

conducted an expanded quantitative 

risk assessment for selected health 

endpoints to provide additional 

information and insights to inform 

decisions on the primary PM2.5

NAAQS.30 As discussed in section III.C 

of the proposal, the approach used to 

develop quantitative risk estimates 

associated with PM2.5 exposures was 

built on the approach used and lessons 

learned in the last review and focused 

on improving the characterization of the 

overall confidence in the risk estimates, 

including related uncertainties, by 

incorporating a number of 

enhancements, in terms of both the 

methods and data used in the analyses. 

The goals of this quantitative risk 

assessment were largely the same as 

those articulated in the risk assessment 

conducted for the last review. These 

goals included: (1) To provide estimates 

of the potential magnitude of premature 

mortality and/or selected morbidity 

effects in the population associated with 

recent ambient levels of PM2.5 and with 

simulating just meeting the current and 

alternative suites of PM2.5 standards in 

15 selected urban study areas,31

including, where data were available, 

consideration of impacts on at-risk 

populations; (2) to develop a better 

understanding of the influence of 

various inputs and assumptions on the 

risk estimates to more clearly 

differentiate among alternative suites of 

standards; and (3) to gain insights into 

the distribution of risks and patterns of 

risk reductions and the variability and 

uncertainties in those risk estimates. In 

addition, the quantitative risk 

assessment included nationwide 

estimates of the potential magnitude of 

premature mortality associated with 

long-term exposure to recent ambient 

PM2.5 concentrations to more broadly 

characterize this risk on a national scale 

and to support the interpretation of the 

more detailed risk estimates generated 

for selected urban study areas. 

The expanded and updated risk 

assessment conducted in this review 

included estimates of risk for: (1) Allcause, ischemic heart disease-related, 

cardiopulmonary-related, and lung 

cancer-related mortality associated with 

long-term PM2.5 exposure; (2) nonaccidental, cardiovascular-related, and 

respiratory-related mortality associated 

with short-term PM2.5 exposure; and (3) 

cardiovascular-related and respiratoryrelated hospital admissions and asthmarelated emergency department visits 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3105 

32The evidence available for these selected health 

effect endpoints generally focused on the entire 

population, although some information was 

available to support analyses that considered 

differences in estimated risk for at-risk populations 

including older adults and persons with preexisting cardiovascular and respiratory diseases. 

33 Variability refers to the heterogeneity of a 

variable of interest within a population or across 

different populations. Uncertainty refers to the lack 

of knowledge regarding the actual values of inputs 

to an analysis (U.S. EPA, 2010a, p. 3–63). 

34The extent to which key sources of potential 

variability were (or were not) fully captured in the 

design of the risk assessment are discussed in 

section 3.5.2 of the Risk Assessment (U.S. EPA, 

2010a, pp. 3–67 to 3–69). 

associated with short-term PM2.5

exposure.32

The Risk Assessment included a core 

set of risk estimates supplemented by an 

alternative set of risk results generated 

using single-factor and multi-factor 

sensitivity analyses. The core set of risk 

estimates was developed using the 

combination of modeling elements and 

input data sets identified in the Risk 

Assessment as having higher confidence 

relative to inputs used in the sensitivity 

analyses. The results of the sensitivity 

analyses provided information to 

evaluate and rank the potential impacts 

of key sources of uncertainty on the core 

risk estimates. In addition, the 

sensitivity analyses represented a set of 

reasonable alternatives to the core set of 

risk estimates that fell within an overall 

set of plausible risk estimates 

surrounding the core estimates. 

The EPA recognized that there were 

many sources of variability and 

uncertainty inherent in the inputs to its 

quantitative risk assessment.33 The 

design of the risk assessment included 

a number of elements to address these 

issues in order to increase the overall 

confidence in the risk estimates 

generated for the 15 urban study areas, 

including using guidance from the 

World Health Organization (WHO, 

2008) as a framework for characterizing 

uncertainty in the analyses.34

With respect to the sources of 

variability, the Risk Assessment 

considered those that contributed to 

differences in risk across urban study 

areas, but did not directly affect the 

degree of risk reduction associated with 

the simulation of just meeting current or 

alternative standard levels (e.g., 

differences in baseline incidence rates, 

demographics and population behavior). 

The Risk Assessment also focused on 

factors that not only introduced 

variability into risk estimates across 

study areas, but also played an 

important role in determining the 

magnitude of risk reductions upon 

simulation of just meeting current or 

alternative standard levels (e.g., peak-tomean ratios of ambient PM2.5

concentrations within individual urban 

study areas and the nature of the 

rollback approach used to simulate just 

meeting the current or alternative 

standards). Key sources of potential 

variability that were likely to affect 

population risks included the following: 

(1) Intra-urban variability in ambient 

PM2.5 concentrations, including PM2.5

composition; (2) variability in the 

patterns of reductions in PM2.5

concentrations associated with different 

rollback approaches when simulating 

just meeting the current or alternative 

standards; (3) co-pollutant exposures; 

(4) factors related to demographic and 

socioeconomic status; (5) behavioral 

differences across urban study areas 

(e.g., time spent outdoors); (6) baseline 

incidence rates; and (7) longer-term 

temporal variability in ambient PM2.5

concentrations reflecting meteorological 

trends as well as future changes in the 

mix of PM2.5 sources, including changes 

in air quality related to future regulatory 

actions. 

With regard to uncertainties, single 

and multi-factor sensitivity analyses 

were combined with a qualitative 

analysis to assess the impact of potential 

sources of uncertainty on the core risk 

estimates. Key sources of uncertainty 

included: (1) Characterizing intra-urban 

population exposure in the context of 

epidemiological studies linking PM2.5 to 

specific health effects; (2) statistical fit 

of the concentration-response functions 

for short-term exposure-related health 

endpoints; (3) shape of the 

concentration-response functions; (4) 

specifying the appropriate lag structure 

for short-term exposure studies; (5) 

transferability of concentration-response 

functions from study locations to urban 

study area locations for long-term 

exposure-related health endpoints; (6) 

use of single-city versus multi-city 

studies in the derivation of 

concentration-response functions; (7) 

impact of historical air quality on 

estimates of health risk associated with 

long-term PM2.5 exposures; and (8) 

potential variation in effect estimates 

reflecting compositional differences in 

PM2.5. 

Beyond characterizing uncertainty 

and variability, a number of design 

elements were included in the risk 

assessment to increase the overall 

confidence in the risk estimates 

generated for the 15 urban study areas 

(U.S. EPA, 2011a, pp. 2–38 to 2–41). 

These elements included: (1) Use of a 

deliberative process for specifying 

components of the risk model that 

reflects consideration of the latest 

research on PM2.5 exposure and risk 

(U.S. EPA, 2010a, section 5.1.1); (2) 

integration of key sources of variability 

into the design as well as the 

interpretation of risk estimates (U.S. 

EPA, 2010a, section 5.1.2); (3) 

assessment of the degree to which the 

urban study areas are representative of 

areas in the U.S. experiencing higher 

PM2.5-related risk (U.S. EPA, 2010a, 

section 5.1.3); and (4) identification and 

assessment of important sources of 

uncertainty and the impact of these 

uncertainties on the core risk estimates 

(U.S. EPA, 2010a, section 5.1.4). 

Further, additional analyses examined 

potential bias and overall confidence in 

the risk estimates. Greater confidence is 

associated with risk estimates based on 

simulated annual mean PM2.5

concentrations that are within the 

region of the air quality distribution 

used in deriving the concentrationresponse functions where the bulk of 

the data reside (e.g., within one 

standard deviation around the long-term 

mean PM2.5 concentration) (U.S. EPA, 

2011a, p. 2–38). 

Key observations and insights from 

the PM2.5 risk assessment, together with 

important caveats and limitations, were 

discussed in section III.C.3 of the 

proposal. In general, in considering the 

set of quantitative risk estimates and 

related uncertainties and limitations 

related to long- and short-term PM2.5

exposure together with consideration of 

the health endpoints which could not be 

quantified, the Policy Assessment 

concluded this information provided 

strong evidence that risks estimated to 

remain upon simulating just meeting the 

current suite of PM2.5 standards are 

important from a public health 

perspective, both in terms of severity 

and magnitude of effects. Patterns of 

increasing estimated risk reductions 

were generally observed as either the 

annual or 24-hour standard level, or 

both, were reduced over the ranges 

considered in the Risk Assessment. 

The magnitude of both long- and 

short-term exposure-related risk 

estimated to remain upon just meeting 

the current suite of standards as well as 

alternative standard levels was strongly 

associated with the simulated change in 

annual mean PM2.5 concentrations. 

Although long- and short-term 

exposure-related mortality rates have 

similar patterns in terms of the subset of 

urban study areas experiencing risk 

reductions for the current suite of 

standard levels, the magnitude of risk 

remaining is higher for long-term 

exposure-related mortality and 

substantially lower for short-term 

exposure-related mortality. Short-term 

exposure-related morbidity risk 

estimates were greater for 

cardiovascular-related than respiratoryrelated events and emergency 


tkelley on DSK3SPTVN1PROD with 
3106 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

35Based on the consideration of both the 

qualitative and quantitative assessments of 

uncertainty, the Risk Assessment concluded that it 

is unlikely that the estimated risks are over-stated, 

particularly for premature mortality related to longterm PM2.5 exposures. In fact, the Policy 

Assessment and the Risk Assessment concluded 

that the core risk estimates for this category of 

health effects may well be biased low based on 

consideration of alternative model specifications 

evaluated in the sensitivity analyses (U.S. EPA, 

2011a, p. 2–41; U.S. EPA, 2010a, p. 5–16; Figures 

4–7 and 4–8). In addition, the Policy Assessment 

recognized that the currently available scientific 

information included evidence for a broader range 

of health endpoints and at-risk populations beyond 

those included in the quantitative risk assessment, 

including decrements in lung function growth and 

respiratory symptoms in children as well as 

reproductive and developmental effects (U.S. EPA, 

2011a, section 2.2.1). 

36Evidence-based considerations include the 

assessment of epidemiological, toxicological, and 

controlled human exposure studies evaluating longor short-term exposures to PM2.5, with supporting 

evidence related to dosimetry and potential 

pathways/modes of action, as well as the 

integration of evidence across each of these 

disciplines, as assessed in the Integrated Science 

Assessment (U.S. EPA, 2009a) and focus on the 

policy-relevant considerations as discussed in 

section III.B above and in the Policy Assessment 

(U.S. EPA, 2011a, section 2.2.1). Risk-based 

considerations draw from the results of the 

quantitative analyses presented in the Risk 

Assessment (U.S. EPA, 2010a) and focus on the 

policy-relevant considerations as discussed in 

section III.C above and in the Policy Assessment 

(U.S. EPA, 2011a, section 2.2.2). 

37The study periods referred to in the Policy 

Assessment (U.S. EPA, 2011a) and in this final rule 

reflect the years of air quality data that were 

included in the analyses, whereas the study periods 

identified in the Integrated Science Assessment 

(U.S. EPA, 2009a) reflect the years of health event 

data that were included. 

department visits for asthma-related 

events were significant: Furthermore, 

most of the aggregate risk associated 

with short-term exposures was not 

primarily driven by the small number of 

days with PM2.5 concentrations in the 

upper tail of the air quality distribution, 

but rather by the large number of days 

with PM2.5 concentrations at and around 

the mean of the distribution, that is, the 

24-hour average concentrations that are 

in the low- to mid-range, well below the 

peak 24-hour concentrations (U.S. EPA, 

2011a, p. 2–3). 

With regard to characterizing 

estimates of PM2.5-related risk 

associated with simulation of alternative 

standards, the Policy Assessment 

recognized that greater overall 

confidence was associated with 

estimates of risk reduction than for 

estimates of absolute risk remaining 

(U.S. EPA, 2011a, p. 2–94). 

Furthermore, the Policy Assessment 

recognized that estimates of absolute 

risk remaining for each of the alternative 

standard levels considered, particularly 

in the context of long-term exposurerelated mortality, may be 

underestimated.35 In addition, the 

Policy Assessment observed that in 

considering the overall confidence 

associated with the quantitative 

analyses, the Risk Assessment 

recognized that: (1) Substantial 

variability existed in the magnitude of 

risk remaining across urban study areas 

and (2) in general, higher confidence 

was associated with risk estimates based 

on PM2.5 concentrations near the mean 

PM2.5 concentrations in the underlying 

epidemiological studies providing the 

concentration-response functions (e.g., 

within one standard deviation of the 

mean PM2.5 concentration reported). 

Furthermore, although the Risk 

Assessment estimated that the 

alternative 24-hour standard levels 

considered (when controlling) would 

result in additional estimated risk 

reductions beyond those estimated for 

alternative annual standard levels alone, 

these additional estimated reductions 

were highly variable. Conversely, the 

Risk Assessment recognized that 

alternative annual standard levels, when 

controlling, resulted in more consistent 

risk reductions across urban study areas, 

thereby potentially providing a more 

consistent degree of public health 

protection (U.S. EPA, 2010a, p. 5–17). 

D. Conclusions on the Adequacy of the 

Current Primary PM2.5 Standards 

1. Introduction 

The initial issue to be addressed in 

the current review of the primary PM2.5

standards is whether, in view of the 

advances in scientific knowledge and 

other information reflected in the 

Integrated Science Assessment, the Risk 

Assessment, and the Policy Assessment, 

the existing standards should be 

retained or revised. In considering the 

adequacy of the current suite of PM2.5

standards, the Administrator has 

considered the large body of evidence 

presented and assessed in the Integrated 

Science Assessment (U.S. EPA, 2009a), 

the quantitative assessment of risks, 

staff conclusions and associated 

rationales presented in the Policy 

Assessment, views expressed by 

CASAC, and public comments. The 

Administrator has taken into account 

both evidence- and risk-based 

considerations 36 in developing final 

conclusions on the adequacy of the 

current primary PM2.5 standards. 

a. Evidence- and Risk-based 

Considerations in the Policy Assessment 

In considering the available 

epidemiological evidence in this review, 

the Policy Assessment took a broader 

approach than was used in the last 

review. This approach reflected the 

more extensive and stronger body of 

evidence available since the last review 

on health effects related to both longand short-term exposure to PM2.5. As 

discussed in section III.A.3 above, this 

broader approach focused on setting the 

annual standard as the ‘‘generally 

controlling’’ standard for lowering both 

short- and long-term PM2.5

concentrations and so providing 

requisite protection to public health. In 

conjunction with such an annual 

standard, this approach focused on 

setting the 24-hour standard to provide 

supplemental protection against days 

with high peak PM2.5 concentrations. 

In addressing the question whether 

the evidence now available in this 

review supports consideration of 

standards that are more protective than 

the current PM2.5 standards, the Policy 

Assessment considered whether: (1) 

Statistically significant health effects 

associations with long- or short-term 

exposures to fine particles occur in 

areas that would likely have met the 

current PM2.5 standards [see American 

Trucking Associations, 283 F. 3d at 369, 

376 (revision of level of PM NAAQS 

justified when health effects are 

observed in areas meeting the existing 

standard)], and (2) associations with 

long-term exposures to fine particles 

extend down to lower air quality 

concentrations than had previously 

been observed. With regard to 

associations observed in long-term PM2.5

exposure studies, the Policy Assessment 

recognized that extended follow-up 

analyses of the ACS and Harvard Six 

Cities studies provided consistent and 

stronger evidence of an association with 

mortality at lower air quality 

distributions than had previously been 

observed (U.S. EPA, 2011a, pp. 2–31 to 

2–32). The original and reanalysis of the 

ACS study reported positive and 

statistically significant effects associated 

with a long-term mean PM2.5

concentration of 18.2 mg/m3 across 50 

metropolitan areas for 1979 to 1983 

(Pope et al., 1995; Krewski et al., 

2000).37 In extended analyses, positive 

and statistically significant effects of 

approximately similar magnitude were 

associated with declining PM2.5

concentrations, from an aggregate longterm mean in 58 metropolitan areas of 

21.2 mg/m3 in the original monitoring 

period (1979 to 1983) to 14.0 mg/m3 for 

116 metropolitan areas in the most 

recent years evaluated (1999–2000), 

with an overall average across the two 

study periods in 51 metropolitan areas 

of 17.7 mg/m3 (Pope et al., 2002; 

Krewski et al., 2009). With regard to the 

Harvard Six Cities Study, the original 

and reanalysis reported positive and 

statistically significant effects associated 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3107 

38Aggregate mean concentration provided by 

study author (personal communication from Dr. 

Francine Laden, 2009). 

39The Policy Assessment noted that in 

comparison to other long-term exposure studies, the 

Miller et al. (2007) study was more limited in that 

it was based on only one year of air quality data 

(U.S. EPA, 2011a, p. 2–82). The proposal further 

noted that the air quality data considered were 

extrapolated from that one single year of air quality 

data (2000) to the whole study, and that the air 

quality data post-dated the years of health events 

considered (i.e., 1994 to 1998) (77 FR 38918, fn 62). 

40Zeger et al. (2008) also reported positive and 

statistically significant effects for the central region, 

with an aggregate long-term mean PM2.5

concentration of 10.7 mg/m3. However, in contrast 

to the eastern and western risk estimates, the 

central risk estimate increased with adjustment for 

COPD (used as a proxy for smoking status). Due to 

the potential for confounding bias influencing the 

risk estimate for the central region, the Policy 

Assessment did not focus on the results reported in 

the central region to inform the adequacy of the 

current suite of standards or alternative annual 

standard levels (U.S. EPA, 2011a, p. 2–32). 

41See American Farm Bureau Federation v. EPA, 

559 F. 3d at 525 (noting the importance of these 

studies, as well as EPA’s failure to properly take 

them into account). 

with a long-term mean PM2.5

concentration of 18.0 mg/m3 for 1980 to 

1985 (Dockery et al., 1993; Krewski et 

al., 2000). In an extended follow-up of 

this study, the aggregate long-term mean 

concentration across all years evaluated 

was 16.4 mg/m3 for 1980 to 1988 38

(Laden et al., 2006). In an additional 

analysis of the extended follow-up of 

the Harvard Six Cities study, 

investigators reported that the 

concentration-response relationship was 

linear and ‘‘clearly continuing below the 

level’’ of the current annual standard 

(U.S. EPA, 2009a, p. 7–92; Schwartz et 

al., 2008). 

Cohort studies conducted since the 

last review provided additional 

evidence of mortality associated with air 

quality distributions that are generally 

lower than those reported in the ACS 

and Harvard Six Cities studies, with 

effect estimates that were similar or, in 

some studies, significantly greater in 

magnitude than in the ACS and Harvard 

Six Cities studies (see also, section 

III.D.1.a of the proposal, 77 FR 38918 to 

28919; U.S. EPA, 2011a, pp. 2–32 to 2– 

33). The Women’s Health Initiative 

(WHI) study reported positive and most 

often statistically significant 

associations between long-term PM2.5

exposure and cardiovascular-related 

mortality as well as morbidity effects, 

with much larger relative risk estimates 

for mortality than in the ACS and 

Harvard Six Cities studies, at an 

aggregate long-term mean PM2.5

concentration of 12.9 mg/m3 for 2000 

(Miller et al., 2007).39

Using the Medicare cohort, Eftim et 

al. (2008) reported somewhat higher 

effect estimates than in the ACS and 

Harvard Six Cities studies with 

aggregate long-term mean 

concentrations of 13.6 mg/m3 and 14.1 

mg/m3, respectively, for 2000 to 2002. 

Zeger et al. (2008) reported associations 

between long-term PM2.5 exposure and 

mortality for the eastern region of the 

U.S. at an aggregated long-term PM2.5

median concentration of 14.0 mg/m3, 

although no association was reported for 

the western region with an aggregate 

long-term PM2.5 median concentration 

of 13.1 mg/m3 (U.S. EPA, 2009a, p. 7– 

88).40

Premature mortality in children 

reported in a national infant mortality 

study as well as mortality in a cystic 

fibrosis cohort including both children 

and adults reported positive but 

statistically nonsignificant effects 

associated with long-term aggregate 

mean concentrations of 14.8 mg/m3 and 

13.7 mg/m3, respectively (Woodruff et 

al., 2008; Goss et al., 2004). 

With respect to respiratory morbidity 

effects associated with long-term PM2.5

exposure, the across-city mean of 2- 

week average PM2.5 concentrations 

reported in the initial Southern 

California Children’s Health Study was 

approximately 15.1 mg/m3 (Peters et al., 

1999). These results were found to be 

consistent with results of cross-sectional 

analyses of the 24-Cities Study (Dockery 

et al., 1996; Raizenne et al., 1996), 

which reported a long-term cross-city 

mean PM2.5 concentration of 14.5 mg/ 

m3.41 In this review, extended analyses 

of the Southern California Children’s 

Health Study provide stronger evidence 

of PM2.5-related respiratory effects, at 

lower air quality concentrations than 

had previously been reported, with a 

four-year aggregate mean concentration 

of 13.8 mg/m3 across the 12 study 

communities (McConnell et al., 2003; 

Gauderman et al., 2004, U.S. EPA, 

2009a, Figure 7–4). 

In also considering health effects for 

which the Integrated Science 

Assessment concluded evidence was 

suggestive of a causal relationship, the 

Policy Assessment noted a limited 

number of birth outcome studies that 

reported positive and statistically 

significant effects related to aggregate 

long-term mean PM2.5 concentrations 

down to approximately 12 mg/m3 (U.S. 

EPA, 2011a, p. 2–33). 

Collectively, the Policy Assessment 

concluded that currently available 

evidence provided support for 

associations between long-term PM2.5

exposure and mortality and morbidity 

effects that extend to distributions of 

PM2.5 concentrations that are lower than 

those that had previously been 

associated with such effects, with 

aggregate long-term mean PM2.5

concentrations extending to well below 

the level of the current annual standard. 

The Policy Assessment also 

considered the long-term mean PM2.5

concentrations in short-term exposure 

studies in assessing the appropriateness 

of the level of the current annual 

standard. See American Farm Bureau 

Federation v. EPA, 559 F. 3d at 522, 

523–24 (remanding 2006 standard 

because the EPA had not adequately 

explained its choice not to consider 

long-term means of short-term exposure 

studies in assessing adequacy of 

primary annual PM2.5 standard). In light 

of the mixed findings reported in singlecity, short-term exposure studies, the 

Policy Assessment placed 

comparatively greater weight on the 

results from multi-city studies in 

considering the adequacy of the current 

suite of standards (U.S. EPA, 2011a, pp. 

2–34 to 2–35). 

With regard to associations reported 

in short-term PM2.5 exposure studies, 

the Policy Assessment recognized that 

long-term mean concentrations reported 

in new multi-city U.S. and Canadian 

studies provided evidence of 

associations between short-term PM2.5

exposure and mortality at similar air 

quality distributions to those that had 

previously been observed in an 8-cities 

Canadian study (Burnett and Goldberg, 

2003; aggregate long-term mean PM2.5

concentration of 13.3 mg/m3). In a multicity time-series analysis of 112 U.S. 

cities, Zanobetti and Schwartz (2009) 

reported a positive and statistically 

significant association with all-cause, 

cardiovascular-related (e.g., heart 

attacks, stroke), and respiratory-related 

mortality and short-term PM2.5

exposure, in which the aggregate longterm mean PM2.5 concentration was 13.2 

mg/m3 (U.S. EPA, 2009a, Figure 6–24). 

Furthermore, city-specific effect 

estimates indicated the association 

between short-term exposure to PM2.5

and total mortality and cardiovascularand respiratory-related mortality was 

consistently positive for an 

overwhelming majority (99 percent) of 

the 112 cities across a wide range of air 

quality concentrations (long-term mean 

concentrations ranging from 6.6 mg/m3

to 24.7 mg/m3; U.S. EPA, 2009a, Figure 

6–24, p. 6–178 to 179). The EPA staff 

noted that for all-cause mortality, cityspecific effect estimates were 

statistically significant for 55 percent of 

the 112 cities, with long-term city-mean 

PM2.5 concentrations ranging from 7.8 

mg/m3 to 18.7 mg/m3 and 24-hour PM2.5

city-mean 98th percentile 

concentrations ranging from 18.4 to 64.9 


tkelley on DSK3SPTVN1PROD with 
3108 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

42Single-city Bayes-adjusted effect estimates for 

the 112 cities analyzed in Zanobetti and Schwartz 

(2009) were provided by the study authors 

(personal communication with Dr. Antonella 

Zanobetti, 2009; see also U.S. EPA, 2009a, Figure 

6–24). 

43This sub-analysis was not included in the 

original publication (Dominici et al., 2006a). The 

study authors provided sub-analysis results for the 

Administrator’s consideration as a letter to the 

docket following publication of the proposed rule 

in January 2006 (personal communication with Dr. 

Francesca Dominici, 2006b). As noted in section 

III.A.3, this study is part of the basis for the 

conclusion that there is no evidence suggesting that 

risks associated with long-term exposures are likely 

to be disproportionately driven by peak 24-hour 

concentrations. 

44Based on analyses of the representativeness of 

the 15 urban study areas in the broader national 

context, the Policy Assessment concludes that these 

study areas are generally representative of urban 

areas in the U.S. likely to experience relatively 

elevated levels of risk related to ambient PM2.5

exposures (U.S. EPA, 2011a, p. 2–42). 

45Premature mortality for all causes attributed to 

PM2.5 exposure was estimated to be on the order of 

tens of thousands of deaths per year on a national 

scale based on 2005 air quality data (U.S. EPA, 

2010a, Appendix G, Table G–1). 

mg/m3 (personal communication with 

Dr. Antonella Zanobetti, 2009).42

With regard to cardiovascular and 

respiratory morbidity effects, in the first 

analysis of the Medicare cohort 

conducted by Dominici et al. (2006a) 

across 204 U.S. counties, investigators 

reported a statistically significant 

association with hospitalizations for 

cardiovascular and respiratory diseases 

and short-term PM2.5 exposure, in which 

the aggregate long-term mean PM2.5

concentration was 13.4 mg/m3. 

Furthermore, a sub-analysis restricted to 

days with 24-hour average 

concentrations of PM2.5 at or below 35 

mg/m3 indicated that, in spite of a 

reduced statistical power from a smaller 

number of study days, statistically 

significant associations were still 

observed between short-term exposure 

to PM2.5 and hospital admissions for 

cardiovascular and respiratory diseases 

(Dominici, 2006b).43 In an extended 

analysis of this cohort, Bell et al. (2008) 

reported a positive and statistically 

significant increase in cardiovascular 

hospitalizations associated with shortterm PM2.5 exposure, in which the 

aggregate long-term mean PM2.5

concentration was 12.9 mg/m3. These 

results, along with the observation that 

approximately 50 percent of the 204 

county-specific mean 98th percentile 

PM2.5 concentrations in the study 

aggregated across all years were below 

the 24-hour standard of 35 mg/m3, not 

only indicated that effects are occurring 

in areas that would meet the current 

standards but also suggested that the 

overall health effects observed across 

the U.S. are not primarily driven by the 

higher end of the PM2.5 air quality 

distribution (Bell, 2009a, personal 

communication from Dr. Michelle Bell 

regarding air quality data for Bell et al., 

2008 and Dominici et al., 2006a). 

Collectively, the Policy Assessment 

concluded that the findings from shortterm PM2.5 exposure studies provided 

evidence of PM2.5-associated health 

effects occurring in areas that would 

likely have met the current suite of 

PM2.5 standards (U.S. EPA, 2011a, p. 2– 

35). These findings were further 

bolstered by evidence of statistically 

significant PM2.5-related health effects 

occurring in analyses restricted to days 

in which 24-hour average PM2.5

concentrations were below 35 mg/m3

(Dominici, 2006b). 

In evaluating the currently available 

scientific evidence, as summarized in 

section III.B of the proposal, the Policy 

Assessment first concluded that there 

was stronger and more consistent and 

coherent support for associations 

between long- and short-term PM2.5

exposures and a broad range of health 

outcomes than was available in the last 

review, providing the basis for fine 

particle standards at least as protective 

as the current PM2.5 standards (U.S. 

EPA, 2011a, p. 2–26). Having reached 

this initial conclusion, the Policy 

Assessment addressed the question of 

whether the available evidence 

supported consideration of standards 

that were more protective than the 

current standards. In so doing, the 

Policy Assessment considered whether 

there was now evidence that health 

effect associations have been observed 

in areas that likely met the current suite 

of PM2.5 standards. As discussed above, 

long- and short-term PM2.5 exposure 

studies provided evidence of 

associations with mortality and 

cardiovascular and respiratory effects 

both at lower ambient PM2.5

concentrations than had been observed 

in the previous review and at 

concentrations allowed by the current 

standards (U.S. EPA, 2011a, p. 2–35). 

In reviewing this information, the 

Policy Assessment recognized that 

important limitations and uncertainties 

associated with this expanded body of 

scientific evidence, as discussed in 

section III.B.2 of the proposal, needed to 

be carefully considered in determining 

the weight to be placed on the body of 

studies available in this review. Taking 

these limitations and uncertainties into 

consideration, the Policy Assessment 

concluded that the currently available 

evidence clearly calls into question 

whether the current suite of primary 

PM2.5 standards protects public health 

with an adequate margin of safety from 

effects associated with long- and shortterm exposures. Furthermore, the Policy 

Assessment concluded this evidence 

provides strong support for considering 

fine particle standards that would afford 

increased protection beyond that 

afforded by the current standards (U.S. 

EPA, 2011a, p. 2–35). 

In addition to evidence-based 

consideration, the Policy Assessment 

also considered the extent to which 

health risks estimated to occur upon 

simulating just meeting the current 

PM2.5 standards may be judged to be 

important from a public health 

perspective, taking into account key 

uncertainties associated with the 

quantitative health risk estimates. In so 

doing, the Policy Assessment first noted 

that the quantitative risk assessment 

addresses: (1) The core PM2.5-related 

risk estimates; (2) the related 

uncertainty and sensitivity analyses, 

including additional sets of reasonable 

risk estimates generated to supplement 

the core analysis; (3) an assessment of 

the representativeness of the urban 

study areas within a national context; 44

and (4) consideration of patterns in 

design values and air quality monitoring 

data to inform interpretation of the risk 

estimates, as discussed in section III.C 

above. 

In considering the health risks 

estimated to remain upon simulation of 

just meeting the current suite of 

standards and considering both the 

qualitative and quantitative assessment 

of uncertainty completed as part of the 

assessment, the Policy Assessment 

concluded these risks are important 

from a public health standpoint and 

provided strong support for 

consideration of alternative standards 

that would provide increased protection 

beyond that afforded by the current 

PM2.5 (U.S. EPA, 2011a, pp. 2–47 to 2– 

48). This conclusion reflected 

consideration of both the severity and 

the magnitude of the effects. For 

example, the Risk Assessment indicated 

the possibility that premature deaths 

related to ischemic heart disease 

associated with long-term PM2.5

exposure alone would likely be on the 

order of thousands of deaths per year in 

the 15 urban study areas upon 

simulating just meeting the current 

standards 45 (U.S. EPA, 2011a, pp. 2–46 

to 2–47). Moreover, additional risks 

were anticipated for premature 

mortality related to cardiopulmonary 

effects and lung cancer associated with 

long-term PM2.5 exposure as well as 

mortality and cardiovascular- and 

respiratory-related morbidity effects 

(e.g., hospital admissions, emergency 

department visits) associated with shortterm PM2.5 exposures. Based on the 

consideration of both qualitative and 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3109 

46The EPA notes that this increased confidence 

in the long- and short-term associations generally 

reflects less uncertainty as to the likely causal 

nature of such associations, but does not address 

directly the question of the extent to which such 

associations remain toward the lower end of the 

range of ambient PM2.5 concentrations. This 

question is central to the Agency’s evaluation of the 

relevant evidence to determine appropriate 

standards levels, as discussed below in section 

III.E.4. 

quantitative assessments of uncertainty 

completed as part of the quantitative 

risk assessment, the Risk Assessment 

concluded that it was unlikely that the 

estimated risks are over-stated, 

particularly for mortality related to longterm PM2.5 exposure, and may well be 

biased low based on consideration of 

alternative model specifications 

evaluated in the sensitivity analyses 

(U.S. EPA, 2010a, p. 5–16; U.S. EPA, 

2011a, p. 2–41). Furthermore, the 

currently available scientific 

information summarized in section III.B 

of the proposal provided evidence for a 

broader range of health endpoints and 

at-risk populations beyond those 

included in the quantitative risk 

assessment (U.S. EPA, 2011a, p. 2–47). 

b. CASAC Advice 

The CASAC, based on its review of 

drafts of the Integrated Science 

Assessment, the Risk Assessment, and 

the Policy Assessment, provided an 

array of advice both with regard to 

interpreting the scientific evidence and 

quantitative risk assessment, as well as 

with regard to consideration of the 

adequacy of the current PM2.5 standards 

(Samet, 2009a,b,c,d,e,f; Samet 

2010a,b,c,d). With regard to the 

adequacy of the current standards, 

CASAC concluded that the ‘‘currently 

available information clearly calls into 

question the adequacy of the current 

standards’’ (Samet, 2010d, p. i) and that 

the current standards are ‘‘not 

protective’’ (Samet, 2010d, p. 1). 

Further, in commenting on the first draft 

Policy Assessment, CASAC noted: 

With regard to the integration of evidencebased and risk-based considerations, CASAC 

concurs with EPA’s conclusion that the new 

data strengthens the evidence available on 

associations previously considered in the last 

round of the assessment of the PM2.5

standard. CASAC also agrees that there are 

significant public health consequences at the 

current levels of the standard that justify 

consideration of lowering the PM2.5 NAAQS 

further (Samet, 2010c, p. 12). 

c. Administrator’s Proposed Conclusions 

Concerning the Adequacy of the Current 

Primary PM2.5 Standards 

At the time of the proposal, in 

considering the body of scientific 

evidence, the Administrator concluded 

there was stronger and more consistent 

and coherent support for associations 

between long- and short-term PM2.5

exposure and a broader range of health 

outcomes than was available in the last 

review, providing the basis for fine 

particle standards at least as protective 

as the current PM2.5 standards. In 

particular, the Administrator recognized 

in section III.D.4 of the proposal that the 

Integrated Science Assessment 

concluded that the results of 

epidemiological and experimental 

studies form a plausible and coherent 

data set that supports a causal 

relationship between long- and shortterm PM2.5 exposures and mortality and 

cardiovascular effects and a likely 

causal relationship between long- and 

short-term PM2.5 exposures and 

respiratory effects. Furthermore, the 

Administrator reflected that effects had 

been observed at lower ambient PM2.5

concentrations than what had been 

observed in the last review, including at 

ambient PM2.5 concentrations in areas 

that likely met the current PM2.5

NAAQS. With regard to the results of 

the quantitative risk assessment, the 

Administrator noted that the Risk 

Assessment concluded that the risks 

estimated to remain upon simulation of 

just meeting the current standards were 

important from a public health 

standpoint in terms of both the severity 

and magnitude of the effects. 

At the time of the proposal, in 

considering whether the current suite of 

PM2.5 standards should be revised to 

provide requisite public health 

protection, the Administrator carefully 

considered the staff conclusions and 

rationales presented in the Policy 

Assessment, the advice and 

recommendations from CASAC, and 

public comments to date on this issue. 

In so doing, the Administrator placed 

primary consideration on the evidence 

obtained from the epidemiological 

studies and provisionally found the 

evidence of serious health effects 

reported in long- and short-term 

exposure studies conducted in areas 

that would have met the current 

standards to be compelling, especially 

in light of the extent to which such 

studies are part of an overall pattern of 

positive and frequently statistically 

significant associations across a broad 

range of studies that collectively 

represent a strong and robust body of 

evidence. 

As discussed in the Integrated Science 

Assessment and Policy Assessment, the 

Administrator recognized that much 

progress has been made since the last 

review in addressing some of the key 

uncertainties that were important 

considerations in establishing the 

current suite of PM2.5 standards. For 

example, progress made since the last 

review provides increased confidence in 

the long- and short-term exposure 

studies as a basis for considering 

whether any revision of the annual 

standard is appropriate and increased 

confidence in the short-term exposure 

studies as a basis for considering 

whether any revision of the 24-hour 

standard is appropriate.46

Based on her consideration of these 

conclusions, as well as consideration of 

CASAC’s conclusion that the evidence 

and risk assessment clearly called into 

question the adequacy of the public 

health protection provided by the 

current PM2.5 NAAQS and public 

comments on the proposal, the 

Administrator provisionally concluded 

that the current primary PM2.5

standards, taken together, were not 

requisite to protect public health with 

an adequate margin of safety and that 

revision was needed to provide 

increased public health protection. The 

Administrator provisionally concluded 

that the scientific evidence and 

information on risk provided strong 

support for consideration of alternative 

standards that would provide increased 

public health protection beyond that 

afforded by the current PM2.5 standards. 

2. Comments on the Need for Revision 

This section addresses general 

comments based on relevant facts that 

either support or oppose any change to 

the current suite of primary PM2.5

standards. Comments on specific longand short-term exposure studies that 

relate to consideration of the 

appropriate levels of the annual and 24- 

hour standards are addressed in section 

III.E.4 below. Many public comments 

asserted that the current PM2.5 standards 

are insufficient to protect public health 

with an adequate margin of safety and 

that revisions to the standards are 

therefore appropriate, indeed 

necessitated. 

Among those calling for revisions to 

the current standards were the 

Children’s Health Protection Advisory 

Committee (CHPAC); major medical and 

public health groups including the 

American Heart Association (AHA), 

American Lung Association (ALA), 

American Public Health Association 

(APHA), American Thoracic Society 

(ATS); the Physicians for Social 

Responsibility (PSR); major 

environmental groups such as the Clean 

Air Council, Clean Air Task Force, 

Earthjustice, Environmental Defense 

Fund (EDF), National Resources Defense 

Council (NRDC), and Sierra Club; many 

environmental justice organizations as 


tkelley on DSK3SPTVN1PROD with 
3110 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

well as medical doctors, academic 

researchers, health professionals, and 

many private citizens. For example, the 

American Heart Association and other 

major national public health and 

medical organizations stated that, ‘‘[o]ur 

organizations are keenly aware of the 

public health and medical threats from 

particulate matter’’ and called on the 

EPA to ‘‘significantly strengthen’’ both 

the annual and 24-hour PM2.5 standards 

‘‘to help us protect the health of our 

patients and our nation’’ (AHA et al., 

2012, pp. 1 and 13). AHA et al. and ALA 

et al., as well as a group of more than 

350 physicians, environmental health 

researchers, and public health and 

medical professionals articulated 

similar comments on the available 

evidence: 

Ample scientific evidence supports 

adopting tighter standards to protect the 

health of people who are most susceptible to 

the serious health effects of these pollutants. 

More than 10,000 peer-reviewed scientific 

studies have been published since 1997 

when EPA adopted the current annual 

standard. These studies validate and extend 

earlier epidemiologic research linking both 

acute and chronic fine particle pollution with 

serious morbidity and mortality. The newer 

research has also expanded our 

understanding of the range of health 

outcomes associated with PM and has 

identified adverse respiratory and 

cardiovascular health effects at lower 

exposure levels than previously reported. As 

discussed and interpreted in the EPA’s 2009 

Integrated Science Assessment for Particulate 

Matter, the new evidence reinforces already 

strong existing studies and supports the 

conclusion that PM2.5 is causally associated 

with numerous adverse health effects in 

humans at exposure levels far below the 

current standard. Such a conclusion 

demands prompt action to protect human 

health. (AHA et al., 2012, pp. 1 to 2; ALA et 

al., pp. 4 to 5; similar comment submitted by 

Rom et al., 2012, p. 1). 

All of these medical and public health 

commenters stated that the current 

PM2.5 standards need to be revised, and 

that even more protective standards 

than those proposed by the EPA are 

needed to adequately protect public 

health, particularly for at-risk 

populations. Many environmental 

justice organizations and individual 

commenters also expressed such views. 

The National Association of Clean Air 

Agencies (NACAA), the Northeast States 

for Coordinated Air Use Management 

(NESCAUM), and many State and local 

air agencies and health departments 

who commented on the PM2.5 standards 

supported revision of the suite of 

current PM2.5 standards, as did five state 

attorneys general (Schneiderman et al., 

2012) and the National Tribal Air 

Association (NTAA). 

These commenters based their views 

chiefly on the body of evidence and 

technical analyses presented and 

discussed in the Integrated Science 

Assessment, the Risk Assessment, and 

the Policy Assessment finding the 

available scientific information to be 

stronger and more compelling than in 

the last review. These commenters 

generally placed much weight on 

CASAC’s recommendation to revise the 

PM2.5 standards to provide increased 

public health protection and on the EPA 

staff conclusions presented in the final 

Policy Assessment. 

Some of these commenters 

specifically mentioned extended 

analyses of seminal long-term exposure 

studies—the ACS (Krewski et al., 2009), 

Harvard Six Cities (Laden et al., 2006), 

and Southern California Children’s 

Health (Gauderman et al., 2004) studies. 

These commenters also highlighted the 

availability of additional long-term 

exposure studies in this review, 

specifically a study of premature 

mortality in older adults (Eftim et al., 

2008) and the WHI study of 

cardiovascular morbidity and mortality 

effects in women (Miller et al., 2007) 

providing stronger evidence of mortality 

and morbidity effects associated with 

long-term PM2.5 exposures at lower 

concentrations than had previously 

been observed, including studies of 

effects in at-risk populations. For 

example, some commenters asserted: 

Evidence during the last review showed 

clearly that the annual average standard 

needed to be much lower than the standard 

of 15 mg/m3 that was first set in 1997. The 

evidence has only grown since then. 

Multiple, multi-city studies over long periods 

of time have shown clear evidence of 

premature death, cardiovascular and 

respiratory harm as well as reproductive and 

developmental harm at contemporary 

concentrations far below the level of the 

current (annual) standard (ALA et al., 2012, 

p. 39; AHA et al., 2012, p. 10). 

These commenters also highlighted 

the availability of a number of shortterm PM2.5 exposure studies as 

providing evidence of mortality and 

morbidity effects at concentrations 

below the level of the current 24-hour 

PM2.5 standard. Specifically, these 

commenters made note of multi-city 

studies of premature mortality 

(Zanobetti and Schwartz, 2009) and 

increased hospitalizations for 

cardiovascular and respiratory-related 

effects in older adults (Bell et al., 2008). 

These commenters also asserted the 

importance of many of the single-city 

studies, arguing that these studies 

‘‘provide valuable information regarding 

impacts on susceptible populations and 

on health risk in areas with high peak 

to mean concentration ratios’’ (ALA, et 

al., 2012, p. 65). Collectively, 

considering the multi- and single-city 

short-term exposure studies, these 

commenters asserted ‘‘the record clearly 

supports a more stringent 24-hour 

standard of 25 mg/m3 to provide uniform 

protection in all regions of the country 

particularly from short-term spikes in 

pollution and from the sub-daily 

exposures that trigger heart attacks and 

strokes’’ (ALA et al., 2012, p. 62). A 

group of more than 350 physicians, 

environmental health researchers, and 

public health and medical professionals 

argued, ‘‘[s]tudies of short-term 

exposure demonstrate that PM2.5 air 

pollution increases the risk of hospital 

admissions for heart and lung problems 

even when you exclude days with 

pollution concentrations at or above the 

current daily standard of 35 mg/m3. 

Daily concentrations must be capped at 

lower levels to protect against peak 

exposure days that occur due to local 

and seasonal sources of emissions’’ 

(Rom et al., 2012, p. 2). 

In addition, many of these 

commenters generally concluded that 

progress had been made in reducing 

many of the uncertainties identified in 

the last review, in better understanding 

mechanisms by which PM2.5 may be 

causing the observed health effects, and 

in improving our understanding of atrisk populations. Further, a number of 

commenters argued that by making the 

standards more protective, the PM2.5

NAAQS would be more consistent with 

other existing standards (e.g., 

California’s annual average standard of 

12 mg/m3) (CARB, 2012; CA OEHHA, 

2012). Other commenters argued that 

revising the primary PM2.5 standards 

would be more consistent with the 

recommendations of the World Health 

Organization (WHO) and/or Canada 

(e.g., ALA et al., 2012, p. 62; ISEE, 2012, 

p. 2; MOE-Ontario, 2012, p. 1). 

With regard to the scope of the 

literature reviewed for PM2.5-related 

health effects, some commenters 

asserted that the EPA inappropriately 

narrowed the scope of the review by 

excluding a number of categories of 

relevant studies, specifically related to 

studies of diesel pollution and trafficrelated pollution (ALA, et al., 2012, p. 

17). These commenters argued that, 

based upon the exclusion of these types 

of studies, the Integrated Science 

Assessment ‘‘came to the erroneous 

conclusion that the causal relationship 

between PM and cancer is merely 

suggestive. This conclusion does not 

square with the International Agency 

Research on Cancer (IARC) finding that 

diesel emissions are a known human 

carcinogen nor with the conclusions of 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3111 

47 In developing the second draft Integrated 

Science Assessment, the EPA reexamined the 

controlled human exposure and toxicological 

studies of fresh diesel and gasoline exhaust. This 

information, in addition to other considerations, 

supported a change in the causal determinations for 

ultrafine particles. Specifically, in reevaluating the 

causal determinations for short-term ultrafine 

particle exposures and cardiovascular and 

respiratory effects, the EPA changed the 

classification from ‘‘inadequate’’ to ‘‘suggestive’’ for 

both categories of health outcomes (Vandenberg, 

2009, p. 3). CASAC agreed with the EPA’s rationale 

for revising these causal determinations (Samet, 

2009f, p. 10). 

the extended analyses of the [Harvard] 

Six Cities and ACS cohort studies that 

report positive and statistically 

significant associations between PM2.5

and lung cancer.’’ Id. 

Some of these commenters also noted 

the results of the EPA’s quantitative risk 

assessment, concluding that it showed 

that the risks estimated to remain when 

the current standards are met are large 

and important from a public health 

perspective and warrant increased 

protection. For example, ALA et al., 

noted that the Risk Assessment 

indicated the quantitative risk analyses 

likely underestimated PM2.5-related 

mortality (U.S. EPA, 2010a, p. 5–16) and 

argued that ‘‘the measurements of risk 

should be treated conservatively’’ (ALA, 

et al., 2012, p. 73). These commenters 

also summarized an expanded analysis 

of alternative PM2.5 standard levels that 

they argued documented the need for 

more protective standards (McCubbin, 

2011). 

In general, all of these commenters 

agreed on the importance of results from 

the large body of scientific studies 

reviewed in the Integrated Science 

Assessment and on the need to revise 

the suite of PM2.5 standards as 

articulated in the EPA’s proposal, while 

generally differing with the EPA’s 

proposed judgments about the extent to 

which the standards should be revised 

based on this evidence, specifically for 

providing protection for at-risk 

populations. 

The EPA generally agrees with these 

commenters’ conclusion regarding the 

need to revise the current suite of PM2.5

standards. The scientific evidence noted 

by these commenters was generally the 

same as that assessed in the Integrated 

Science Assessment and the Policy 

Assessment, and the EPA agrees that 

this evidence provides a strong basis for 

concluding that the current PM2.5

standards, taken together, are not 

requisite to protect public health with 

an adequate margin of safety, and they 

need to be revised to provide increased 

protection. For reasons discussed in 

section III.E.4.c below, however, the 

EPA disagrees with aspects of these 

commenters’ views on the level of 

protection that is appropriate. 

The EPA disagrees with these 

commenters’ views that diesel exhaust 

studies were excluded from the 

Integrated Science Assessment and were 

not considered when making the 

causality determination for cancer, 

mutagenicity, and genotoxicity. As 

discussed in section 7.5 of the 

Integrated Science Assessment, diesel 

exhaust studies were integrated within 

the broader body of scientific evidence 

that was considered in reaching the 

causality determination for these health 

endpoints. Additionally, as discussed in 

section 1.5.3 of the Integrated Science 

Assessment, the evidence from diesel 

exhaust studies was also considered as 

part of the collective evidence evaluated 

when making determinations for other, 

noncancer health outcomes (e.g., 

cardiovascular and respiratory 

effects).47 Specifically, when evaluating 

this evidence, the focus was on 

understanding the effects of diesel 

exhaust particles. 

It is important to recognize that the 

Integrated Science Assessment focused 

on experimental studies of diesel 

exhaust that evaluated exposures that 

were relevant to ambient 

concentrations, i.e., ‘‘within one or two 

orders of magnitude of ambient PM 

concentrations’’ (U.S. EPA, 2009a, 

section 1.3). The causal determination 

for cancer, mutagenicity, and 

genotoxicity presented in the Integrated 

Science Assessment represents an 

integration of experimental and 

observational evidence of exposures to 

ambient PM concentrations. The EPA 

fully considered the findings of studies 

that assessed these and other health 

effects associated with exposure to 

diesel particles in reaching causality 

determinations regarding health 

outcomes associated with PM2.5

exposures. Furthermore, CASAC 

supported the EPA’s change to the 

causal determination for cancer and 

long-term PM2.5 concentrations from 

‘‘inadequate’’ to ‘‘suggestive’’ (Samet, 

2009f, p. 2). 

With regard to traffic studies, the EPA 

disagrees with the commenters’ views 

that traffic studies that focused on 

exposure indicators such as distance to 

roadways should have been included in 

the Integrated Science Assessment. 

These studies were excluded from 

consideration because they did not 

measure ambient concentrations of 

specific air pollutants, including PM2.5, 

but instead were studies evaluating 

exposure to the undifferentiated ‘‘traffic 

related air pollution’’ mixture (ALA et 

al., 2012, p. 17) (U.S. EPA, 2009a, 

section 1.3). As a result, these studies do 

not add to the collective body of 

evidence on the relationship between 

long- or short-term exposure to ambient 

concentrations of PM2.5 and health 

effects. 

Some of these commenters also 

identified ‘‘new’’ studies that were not 

included in the Integrated Science 

Assessment as providing further support 

for the need to revise the primary PM2.5

standards. As discussed in section II.B.3 

above, the EPA notes that, as in past 

NAAQS reviews, the Agency is basing 

the final decisions in this review on the 

studies and related information 

included in the PM air quality criteria 

that have undergone CASAC and public 

review and will consider the ‘‘new’’ 

studies for purposes of decision making 

in the next PM NAAQS review. 

Nonetheless, in provisionally evaluating 

commenters’ arguments (see Response 

to Comments document), the EPA notes 

that its provisional assessment of ‘‘new’’ 

science found that such studies did not 

materially change the conclusions in the 

Integrated Science Assessment (U.S. 

EPA, 2012b). 

Another group of commenters 

opposed revising the current PM2.5

standards. These views were most 

extensively presented in comments from 

the Utility Air Regulatory Group 

(UARG), representing a group of electric 

generating companies and organizations 

and several national trade associations; 

the American Petroleum Institute (API) 

representing more than 500 oil and 

natural gas companies; the National 

Association of Manufacturers (NAM), 

the American Chemistry Council (ACC), 

the American Fuel & Petroleum 

Manufacturers (AFPM), the Alliance of 

Automobile Manufacturers (AAM), and 

other manufacturing associations; the 

Electric Power Research Institute (EPRI); 

and the Texas Commission on 

Environmental Quality (Texas CEQ). 

These commenters generally mentioned 

many of the same studies that were 

cited by the commenters who supported 

revising the standards, as well as other 

studies, but highlighted different 

aspects of these studies in reaching 

substantially different conclusions 

about their strength and the extent to 

which progress has been made in 

reducing uncertainties in the evidence 

since the last review. Furthermore, they 

asserted that the evidence that has 

become available since the last review 

does not establish a more certain risk or 

a risk of effects that are significantly 

different in character to those that 

provided a basis for the current 

standards, nor does the evidence 

demonstrate that the risk to public 

health upon attainment of the current 

standards would be greater than was 


tkelley on DSK3SPTVN1PROD with 
3112 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

48The EPA notes that the same concerns about 

the causal determinations presented in the 

Integrated Science Assessment were raised in 

comments to CASAC on the draft Integrated Science 

Assessments (e.g., UARG, 2009; API, 2009; ACC, 

2012, Appendix B). CASAC, therefore, had the 

opportunity to consider these comments in reaching 

consensus conclusions on this issue. 

49Statistical significance is an indicator of the 

precision of a study’s results, which is influenced 

by a variety of factors including, but not limited to, 

the size of the study, exposure and measurement 

error, and statistical model specifications. Studies 

typically calculate ‘‘p-values’’ to determine whether 

the study results are statistically significant or 

whether the study results are likely to occur simply 

by chance. In general practice, effects are 

considered statistically significant if p values are 

less than 0.05. 

50For example, Rothman (1998) stated, ‘‘Many 

data analysts appear to remain oblivious to the 

qualitative nature of significance testing [and that] 

* * * statistical significance is itself only a 

dichotomous indicator. As it has only two values, 

significant or not significant * * *. Nevertheless, pvalues still confound effect size with study size, the 

two components of estimation that we believe need 

to be reported separately.’’ As a result, Rothman 

recommended that p-values be omitted as long as 

point and interval estimates are available. 

understood when the EPA established 

the current standards in 2006. 

These commenters generally 

expressed the view that the current 

standards provide the requisite degree 

of public health protection. In 

supporting their view, these 

commenters generally argued that the 

EPA’s conclusions are inconsistent with 

the current state of the science and 

questioned the underlying scientific 

evidence including the causal 

determinations reached in the Integrated 

Science Assessment. More specifically, 

this group of commenters argued that: 

(1) The EPA did not apply its framework 

for causal determination consistently 

across studies or health outcomes and, 

in the process, the EPA relied on a 

selective group of long- and short-term 

exposure studies to reach conclusions 

regarding causality; (2) toxicological and 

controlled human exposure studies do 

not provide supportive evidence that 

the health effects observed in 

epidemiological studies are biologically 

plausible; (3) uncertainties in the 

underlying health science are as great or 

greater than in 2006; (4) there is no 

evidence of greater risk since the last 

review to justify tightening the current 

annual PM2.5 standard; and (5) ‘‘new’’ 

studies not included in the Integrated 

Science Assessment continue to 

increase uncertainty about possible 

health risks associated with exposure to 

PM2.5. These comments are discussed in 

turn below. 

(l) Some of these commenters asserted 

that the EPA did not apply its 

framework for causal determinations 

consistently across studies or health 

outcomes (e.g., ACC, 2012, Attachment 

A, pp. 1 to 2; API, 2012, Attachment 1, 

p. 30; NAM et al., 2012, pp. 22 to 25; 

Texas CEQ, 2012, pp 2 to 3).48 These 

commenters argued that the EPA 

downplayed epidemiological studies 

with null or inconsistent results, 

inappropriately used the Hill criteria 

when evaluating the epidemiological 

evidence, and used the same study and 

the same underlying database to 

conclude that there was a causal 

association between mortality and 

multiple criteria pollutants. 

The EPA disagrees with these 

commenters’ views. First, the EPA 

recognizes that the evaluation of the 

scientific evidence and its application of 

the causal framework used in the 

current PM NAAQS review was the 

subject of exhaustive and detailed 

review by CASAC and the public. As 

summarized in section II.B.3 above, 

prior to finalizing the Integrated Science 

Assessment, two drafts were released for 

CASAC and public review to evaluate 

the scientific integrity of the documents. 

Evidence related to the substantive 

issues raised by CASAC and public 

commenters with regard to the content 

of the first and second draft Integrated 

Science Assessments were discussed at 

length during these public CASAC 

meetings and considered in developing 

the final Integrated Science Assessment. 

CASAC supported the development of 

the EPA’s causality framework and its 

use in the current PM NAAQS review 

and concluded: 

The five-level classification of strength of 

evidence for causal inference has been 

systematically applied; this approach has 

provided transparency and a clear statement 

of the level of confidence with regard to 

causation, and we recommend its continued 

use in future Integrated Science Assessments 

(Samet 2009f, p. 1). 

These commenters asserted that 

during the application of the causal 

framework the EPA inappropriately 

relied on a selective group of long- and 

short-term exposure studies in reaching 

causal inferences (API, 2012, pp 12 to 

17; ACC, 2012, Attachment A, pp 1 to 

2; NAM et al., 2012, pp. 22 to 25; Texas 

CEQ, 2012, pp 2 to 3). Additionally, 

these commenters expressed the view 

that the EPA focused on a subset of 

epidemiological studies that reported 

positive and statistically significant 

results while ignoring other studies, 

especially those that reported no 

statistically significant associations, 

those that reported potential thresholds, 

or those that highlighted uncertainties 

and limitations in study design or 

results. Furthermore, some of these 

commenters argued that 

epidemiological studies are 

observational in nature and cannot 

provide evidence of a causal 

association. 

The EPA disagrees with these 

commenters’ views on assessing the 

health effects evidence and on the 

conclusions regarding the causality 

determinations reached in the Integrated 

Science Assessment. In conducting a 

comprehensive evaluation of the 

evidence in the Integrated Science 

Assessment, the EPA recognized the 

distinction between the evaluation of 

the relative scientific quality of 

individual study results and the 

evaluation of the pattern of results 

within the broader body of scientific 

evidence and considered both in 

reaching causality determinations. The 

more detailed characterizations of 

individual studies included an 

assessment of the quality of the study 

based on specific criteria as described in 

the Integrated Science Assessment (U.S. 

EPA, 2009a, section 1.5.3). 

In developing an integrated 

assessment of the health effects 

evidence for PM, the EPA emphasized 

the importance of examining the pattern 

of results across various studies and did 

not focus solely on statistical 

significance 49 as a criterion of study 

strength. This approach is consistent 

with views clearly articulated 

throughout the epidemiological and 

causal inference literature, specifically, 

that it is important not to focus on 

results of statistical tests to the 

exclusion of other information.50 The 

concepts underlying the EPA’s approach 

to evaluating statistical associations 

have been discussed in numerous 

publications, including a report by the 

U.S. Surgeon General on the health 

consequences of smoking (Centers for 

Disease Control and Prevention, 2004). 

This report cautions against overreliance on statistical significance in 

evaluating the overall evidence for an 

exposure-response relationship. Criteria 

characterized by Hill (1965) also 

addressed the value, or lack thereof, of 

statistical tests in the determination of 

cause: 

No formal tests of significance can answer 

those [causal] questions. Such tests can, and 

should, remind us of the effects the play of 

chance can create, and they will instruct us 

in the likely magnitude of those effects. 

Beyond that, they contribute nothing to the 

‘proof’ of our hypothesis (Hill, 1965, p. 299). 

The statistical significance of 

individual study findings has played an 

important role in the EPA’s evaluation 

of the study’s results and the EPA has 

placed greater emphasis on studies 

reporting statistically significant results. 

However, in the broader evaluation of 

the evidence from many 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3113 

epidemiological studies, and 

subsequently during the process of 

forming causality determinations in 

integrating evidence across 

epidemiological, controlled human 

exposure, and toxicological studies, the 

EPA has emphasized the pattern of 

results across epidemiological studies, 

and whether the effects observed were 

coherent across the scientific disciplines 

for drawing conclusions on the 

relationship between PM2.5 and different 

health outcomes. Thus, the EPA did not 

limit its focus or consideration to just 

studies that reported positive 

associations or where the results were 

statistically significant. 

In addition, some commenters 

asserted that the EPA inappropriately 

used the Hill criteria by failing to 

consider the limitations of studies with 

weak associations, thereby overstating 

the consistency of the observed 

associations (API, 2012, Attachment 1, 

pp. 30 to 35). These commenters argued 

that risk estimates greater than 3 to 4 

reflect strong associations supportive of 

a causal link, while smaller risk 

estimates (i.e., 1.5 to 3) are considered 

to be weak and require other lines of 

evidence to demonstrate causality. 

As discussed in section 1.5.3 of the 

Integrated Science Assessment, the EPA 

thoroughly considered the limitations of 

all studies during its evaluation of the 

scientific literature (U.S. EPA,, 2009a, p. 

1–14). This collective body of evidence, 

including known uncertainties and 

limitations of the studies evaluated, 

were considered during the process of 

forming causality determinations as 

discussed in chapters 6 and 7 of the 

Integrated Science Assessment. For 

example, the EPA concluded that ‘‘a 

causal relationship exists between shortterm PM2.5 exposure and cardiovascular 

effects,’’ however, in reaching this 

conclusion, the Agency recognized and 

considered limitations of the current 

evidence that still requires further 

examination (U.S. EPA, 2009a., in 

section 6.2.12.1). Therefore, the EPA 

disagrees with these commenters’ views 

that the Hill criteria were 

inappropriately used in that the 

limitations of studies were not 

considered. 

The EPA also disagrees with the 

commenters’ assertion that the 

magnitude of the association must be 

large to support a determination of 

causality. As discussed in the Integrated 

Science Assessment, the strength of the 

observed association is an important 

aspect to aid in judging causality and 

‘‘while large effects support causality, 

modest effects therefore do not preclude 

it’’ (U.S. EPA, 2009a, Table 1–2, section 

1.5.4). The weight of evidence approach 

used by the EPA encompasses a 

multitude of factors of which the 

magnitude of the association is only one 

component (U.S. EPA, 2009a, Table 1– 

3). An evaluation of the association 

across multiple investigators and 

locations supports the ‘‘reproducibility 

of findings [which] constitutes one of 

the strongest arguments for causality’’ 

(U.S. EPA, 2009a, Table 1–2). Even 

though the risk estimates for air 

pollution studies may be modest, the 

associations are consistent across 

hundreds of studies as demonstrated in 

the Integrated Science Assessment. 

Furthermore, the causality 

determinations rely on different lines of 

evidence, by integrating evidence across 

disciplines, including animal 

toxicological studies and controlled 

human exposure studies. 

Furthermore, as summarized in 

section III.B above and discussed more 

fully in section III.B.3 of the proposal, 

the EPA recognizes that the population 

potentially affected by PM2.5 is 

considerable, including large subgroups 

of the U.S. population that have been 

identified as at-risk populations (e.g., 

children, older adults, persons with 

underlying cardiovascular or respiratory 

disease). While individual effect 

estimates from epidemiological studies 

may be modest in size, the public health 

impact of the mortality and morbidity 

associations can be quite large given 

that air pollution is ubiquitous. Indeed, 

with the large population exposed, 

exposure to a pollutant causally 

associated at a population level with 

mortality and serious illness has 

significant public health consequences, 

virtually regardless of the relative risk. 

Taken together, this information 

indicates that exposure to ambient PM2.5

concentrations has substantial public 

health impacts. 

In addition, these commenters 

believed that the EPA downplayed null 

or inconsistent findings in numerous 

long-term mortality studies with 

reported PM2.5 concentrations above 

and below the level of the current 

annual standard. The EPA disagrees that 

studies with null or inconsistent 

findings were not accurately presented 

and considered in the Integrated 

Science Assessment. For example, as 

discussed throughout section 7.6 and 

depicted in Figures 7–6 and 7–7 of the 

Integrated Science Assessment, the EPA 

presented the collective evidence from 

all studies that examined the association 

between long-term PM2.5 exposure and 

mortality. Overall, across these studies 

there was evidence of consistent 

positive associations in different 

cohorts. That evidence, in combination 

with the biological plausibility provided 

by experimental and toxicological 

studies evaluated in sections 7.1 and 7.2 

of the Integrated Science Assessment, 

supported a causal relationship exists 

between long-term PM2.5 exposure and 

mortality. 

Lastly, some of these commenters 

argued that in some cases, the EPA used 

the same study and the same underlying 

database to conclude that there is a 

causal association between mortality 

and multiple criteria pollutants. These 

commenters argued, ‘‘[i]n doing so, EPA 

attributes the cause of the mortality 

effects observed to whichever criteria 

pollutant it is reviewing at the time’’ 

(API, 2012, pp. 14 to 16). 

The EPA strongly disagrees that the 

Agency ‘‘attributes the cause of 

mortality effects observed to whichever 

criteria pollutant it is reviewing at the 

time.’’ The EPA consistently recognizes 

that other pollutants are also associated 

with health outcomes, as is reflected in 

the fact that the EPA has established 

regulations to limit emissions of 

particulate criteria pollutants as well as 

other gaseous criteria pollutants. 

Epidemiological studies often examine 

the association between short- and longterm exposures to multiple air 

pollutants and mortality within a 

common dataset in an attempt to 

identify the air pollutant(s) of the 

complex mixture most strongly 

associated with mortality. In evaluating 

these studies, the EPA employs specific 

study selection criteria to identify those 

studies most relevant to the review of 

the NAAQS. In its assessment of the 

health evidence regarding PM2.5, the 

EPA has carefully evaluated the 

potential for confounding, effect 

measure modification, and the role of 

PM2.5 as a component of a complex 

mixture of air pollutants (U.S. EPA, 

2009a, p. 1–9). The EPA used a rigorous 

weight of evidence approach to inform 

causality that evaluated consistency 

across studies within a discipline, 

evidence for coherence across 

disciplines, and biological plausibility. 

Additionally, during this process, the 

EPA assessed the limitations of each 

study in the context of the collective 

body of evidence. It was the collective 

evidence, not one individual study that 

ultimately determined whether a causal 

relationship exists between a pollutant 

and health outcome. In the Integrated 

Science Assessment, the combination of 

epidemiological and experimental 

evidence formed the basis for the 

Agency concluding for the first time that 

a causal relationship exists between 

short- or long-term exposure to a criteria 

pollutant and mortality (U.S. EPA, 2009, 

sections 2.3.1.1 and 2.3.1.2). 


tkelley on DSK3SPTVN1PROD with 
3114 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

51See American Trucking Associations v. EPA, 

175 F. 3d 1027, 1055–56 (DC Cir. 1999) reversed in 

part and affirmed in part sub nom, Whitman v. 

American Trucking Associations, 531 U.S. 457 

(2001) holding that the EPA could establish NAAQS 

without identifying a biological mechanism (‘‘To 

begin with, the statute itself requires no such proof. 

The Administrator may regulate air pollutants 

‘‘emissions of which, in his judgment, cause or 

contribute to air pollution which may reasonably be 

anticipated to endanger public health or welfare.’’ 

(emphasis added by the court). Moreover, this court 

has never required the type of explanation 

petitioners seek from EPA. In fact, we have 

expressly held that EPA’s decision to adopt and set 

air quality standards need only be based on 

‘reasonable extrapolations from some reliable 

evidence’* * *. Indeed, were we to accept 

petitioners’ view, EPA (or any agency for that 

matter) would be powerless to act whenever it first 

recognizes clear trends of mortality or morbidity in 

areas dominated by a particular pathogen.’’). 

53For example, the EPA excludes from its 

controlled human exposure studies involving 

exposure to PM2.5 any individual with a significant 

risk factor for experiencing adverse effects from 

such exposure. Thus, the EPA excludes a priori the 

following categories of persons: those with a history 

of angina, cardiac arrhythmias, and ischemic 

myocardial infarction or coronary bypass surgery; 

those with a cardiac pacemaker; those with 

uncontrolled hypertension (greater than 150 

systolic and 90 diastolic); those with neurogenetive 

diseases; those with a history of bleeding diathesis; 

those taking beta-blockers; those using oral 

anticoagulants; those who are pregnant, attempting 

to become pregnant, or breastfeeding; those who 

Additionally, while the EPA has 

evaluated some of the studies used to 

inform the causality determination for 

PM in the Integrated Science 

Assessments for other criteria air 

pollutants, the Agency has done so in 

the context of examining the collective 

body of evidence for each of the 

respective criteria air pollutants. As 

such, the body of evidence to inform 

causality has varied from pollutant to 

pollutant resulting in the association 

between each criteria air pollutant and 

mortality being classified at a different 

level of the five-level hierarchy used to 

inform causation (e.g., U.S. EPA, 2008e, 

U.S. EPA, 2008f, U.S. EPA, 2010k). 

The EPA notes that the final causality 

determinations presented in the 

Integrated Science Assessment reflected 

CASAC’s recommendations on the 

second draft Integrated Science 

Assessment (Samet, 2009f, pp. 2 to 3). 

Specifically, CASAC supported the 

EPA’s changes (in the second versus 

first draft Integrated Science 

Assessment) from ‘‘likely causal’’ to 

‘‘causal’’ for long-term exposure to PM2.5

and cardiovascular effects and for 

cancer and PM2.5 (from ‘‘inadequate’’ to 

‘‘suggestive’’). Id. Furthermore, CASAC 

recommended ‘‘upgrading’’ the causal 

classification for PM2.5 and total 

mortality to ‘‘causal’’ for both the shortand long-term timeframes. Id. With 

regard to mortality, the ‘‘EPA carefully 

reevaluated the body of evidence, 

including the collective evidence for 

biological plausibility for mortality 

effects, and determined that a causal 

relationship exists for short- and longterm exposure to PM2.5 and mortality, 

consistent with the CASAC comments’’ 

(Jackson, 2010). 

(2) With regard to toxicological and 

controlled human exposure studies, 

these commenters argued that the 

available evidence does not provide 

coherence or biological plausibility for 

health effects observed in 

epidemiological studies (API, 2012, pp. 

21 to 22, Attachment 1, pp. 25 to 29; 

AAM, 2012, pp. 15 to 16; Texas CEQ, 

2012, p. 3). With regard to the issue of 

mechanisms, these commenters noted 

that although the EPA recognizes that 

new evidence is now available on 

potential mechanisms and plausible 

biological pathways, the evidence 

provided by toxicological and 

controlled human exposure studies still 

does not resolve all questions about how 

PM2.5 at ambient concentrations could 

produce the mortality and morbidity 

effects observed in epidemiological 

studies. More specifically, for example, 

some of these commenters argued that: 

A review of the Integrated Science 

Assessment, however, suggests that the 

experimental evidence is inconsistent and 

not coherent with findings in epidemiology 

studies. Specifically, the findings of mild and 

reversible effects in most experimental 

studies conducted at elevated exposures are 

not consistent with the more serious 

associations described in epidemiology 

studies (e.g., hospital admissions and 

mortality). Also, both animal studies and 

controlled human exposure studies have 

identified no effect levels for acute and 

chronic exposure to PM and PM constituents 

at concentrations considerably above ambient 

levels. EPA should consider the experimental 

findings in light of these higher exposure 

levels and what the relevance may be for 

ambient exposures (API, 2012, Attachment 1, 

p. 25). 

The EPA notes that in the review 

completed in 1997, the Agency 

considered the lack of demonstrated 

biological mechanisms for the varying 

effects observed in epidemiological 

studies to be an important caution in its 

integrated assessment of the health 

evidence upon which the standards 

were based (71 FR 61157, October 17, 

2006). In the review completed in 2006, 

the EPA recognized the findings from 

additional research that indicated that 

different health responses were linked 

with different particle characteristics 

and that both individual components 

and complex particle mixtures appeared 

to be responsible for many biologic 

responses relevant to fine particle 

exposures. Id. Since that review, there 

has been a great deal of research 

directed toward advancing our 

understanding of biologic mechanisms. 

While this research has not resolved all 

questions, and further research is 

warranted (U.S. EPA, 2011a, section 

2.5), it has provided important insights 

as discussed in section III.B.1 of the 

proposal (77 FR at 38906 to 38909) and 

discussed more fully in the Integrated 

Science Assessment (U.S. EPA, 2009a, 

Chapter 5). 

As noted in the proposal, 

toxicological studies provide evidence 

to support the biological plausibility of 

cardiovascular and respiratory effects 

associated with long- and short-term PM 

exposures observed in epidemiological 

studies (77 FR 38906) and provide 

supportive mechanistic evidence that 

the cardiovascular morbidity effects 

observed in long-term exposure 

epidemiological studies are coherent 

with studies of cardiovascular-related 

mortality (77 FR 38907). The Integrated 

Science Assessment concluded that the 

new evidence available in this review 

‘‘greatly expands’’ upon the evidence 

available in the last review ‘‘particularly 

in providing greater understanding of 

the underlying mechanisms for PM2.5

induced cardiovascular and respiratory 

effects for both short- and long-term 

exposures’’ (U.S. EPA, 2009a, p. 2–17). 

The mechanistic evidence now 

available, taken together with newly 

available epidemiological evidence, 

increases the Agency’s confidence that a 

causal relationship exists between longand short-term exposure to PM2.5 and 

cardiovascular effects and mortality.51

In addition, CASAC supported the 

Integrated Science Assessment approach 

and characterization of potential 

mechanisms or modes of action (Samet, 

2009e, pp. 7 to 8; Samet, 2009f, p. 11), 

as well as the findings of a causal 

relationship at the population level 

between exposure to PM2.5 and 

mortality and cardiovascular effects 

(Samet, 2009f, pp. 2 to 3).52

Additionally, the EPA disagrees with 

commenters that the mild and reversible 

effects observed in controlled human 

exposure studies are inconsistent with 

the more serious effects observed in 

epidemiological studies. Ethical 

considerations regarding the types of 

studies that can be performed with 

human subjects generally limit the 

effects that can be evaluated to those 

that are transient, reversible, and of 

limited short-term consequence. The 

relatively small number of subjects 

recruited for controlled exposure 

studies should also be expected to have 

less variability in health status and risk 

factors than occurring in the general 

population.53 Consequently, the severity 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3115 

have experienced a respiratory infection within four 

weeks of exposure; those experiencing eye or 

abdominal surgery within six weeks of exposure; 

those with active allergies; those with a history of 

chronic illnesses such as diabetes, cancer, 

rheumatologic diseases, immunodeficiency state, 

known cardiovascular disease, or chronic 

respiratory diseases; smokers. The EPA 

‘‘Application for Independent Review Board 

Approval of Human Subjects Research: 

Cardiopulmonary Effects of healthy Older GSTM1 

Null and Sufficient individuals to Concentrated 

Ambient Air Particles (CAPTAIN)’’, Nov. 9, 2011, 

p. 9. 

54The Integrated Science Assessment defines 

confounding as ‘‘a confusion of effects. Specifically, 

the apparent effect of the exposure of interest is 

distorted because the effect of an extraneous factor 

is mistaken for or mixed with the actual exposure 

effect (which may be null) (Rothman and 

Greenland, 1998)’’ (U.S. EPA, 2009a, p. 1–16). 

Epidemiological analyses attempt to adjust or 

control for these characteristics (i.e., potential 

confounders) that differ between exposed and nonexposed individuals (U.S. EPA, 2009a, section 

1.5.3). Not all risk factors can be controlled for 

within a study design/model and are termed 

‘‘unmeasured confounders.’’ An unmeasured 

confounder is a confounder that has not previously 

been measured and therefore is not included in the 

study design/model. 

of health effects observed in controlled 

human exposure studies evaluating the 

effects of PM should be expected to be 

less than observed in epidemiologic 

studies. Nonetheless, that effects are 

observed in relatively healthy 

individuals participating in controlled 

exposure studies serves as an indicator 

that PM is initiating health responses 

and that more severe responses may 

reasonably be expected in a more 

diverse population. 

It should also be noted that there is a 

small body of toxicological evidence 

demonstrating mortality in rodents 

exposed to PM (e.g., Killingsworth et al. 

1997). Overall it is not surprising that 

lethality is not induced in more 

toxicological research, as these types of 

studies do not readily lend themselves 

to this endpoint. Epidemiological 

studies have observed associations 

between PM and mortality in 

communities with populations in the 

range of many thousands to millions of 

people. Clearly, it is not feasible to 

expose hundreds (if not thousands) of 

animals to ambient PM (potentially over 

many years) in a laboratory setting to 

induce enough lethalities to distinguish 

between natural deaths and those 

attributable to PM. Furthermore, the 

heterogeneous human populations 

sampled in epidemiological studies are 

comprised of individuals with different 

physical, genetic, health, and 

socioeconomic backgrounds which may 

impact the outcome. However, in 

toxicological studies, the rodent groups 

are typically inbred, such that interindividual variability is minimized. 

Thus, if the rodent strain used is quite 

robust, PM-induced effects may not be 

observed at low exposure 

concentrations. 

(3) In asserting that the uncertainties 

in the underlying health science are as 

great or greater than in the last review 

and therefore do not support revision to 

the standards at this time, commenters 

in this group variously discussed a 

number of issues related to: (a) 

Confounding, (b) heterogeneity in risk 

estimates, (c) exposure measurement 

error, (d) model specification, (e) the 

shape of the concentration-response 

relationship, and (f) understanding the 

relative toxicity of components within 

the mixture of fine particles. Each of 

these issues is addressed below and 

some are discussed in more detail in the 

Response to Comments document. 

In summary, these commenters 

concluded that the substantial 

uncertainties present in the last review 

have not been resolved and/or that the 

uncertainty about the possible health 

risks associated with PM2.5 exposure has 

not diminished. As discussed below, the 

EPA believes that the overall 

uncertainty about possible health risks 

associated with both long- and shortterm PM2.5 exposure has diminished to 

an important degree since the last 

review. While the EPA agrees that 

important uncertainties remain, and that 

future research directed toward 

addressing these uncertainties is 

warranted, the EPA disagrees with 

commenters’ views that the remaining 

uncertainties in the scientific evidence 

are too great to warrant revising the 

current PM2.5 NAAQS. 

(a) Confounding 

Some commenters have criticized the 

EPA for not adequately addressing the 

issue of confounding in both long- and 

short-term exposure studies of mortality 

and morbidity. This includes 

confounding due to copollutants, as 

well as unmeasured confounding.54

With regard to copollutant 

confounding, these commenters asserted 

that the EPA has not adequately 

interpreted the results from studies that 

examined the effect of copollutants on 

the relationship between long- and 

short-term PM2.5 exposures and 

mortality and morbidity outcomes. 

These commenters contend that the EPA 

has inappropriately concluded that 

PM2.5-related mortality and morbidity 

associations are generally robust to 

confounding. The commenters stated 

that statistically significant PM2.5

associations in single-pollutant models 

in epidemiological studies do not 

remain statistically significant in 

copollutant models. 

The loss of statistical significance or 

the reduction in the magnitude of the 

effect estimate when a co-pollutant 

model is used may be the result of 

factors other than confounding. These 

changes do not prove either the 

existence or absence of confounding. 

These impacts must be evaluated in a 

broader context that considers the entire 

body of evidence. The broader 

examination of this issue in the 

Integrated Science Assessment included 

a focus on evaluating the stability of the 

size of the effect estimates in 

epidemiological studies conducted by a 

number of research groups using singleand copollutant models (U.S. EPA, 

2009a, sections 6.2.10.9, 6.3.8.5, and 

6.5, Figures 6–5, 6–9, and 6–15). This 

examination found that, for most 

epidemiological studies, there was little 

change in effect estimates based on 

single- and copollutant models, 

although the Integrated Science 

Assessment recognized that in some 

cases, the PM2.5 effect estimates were 

markedly reduced in size and lost 

statistical significance. Additionally, the 

EPA notes that these comments do not 

adequately reflect the complexities 

inherent in assessing the issue of 

copollutant confounding. As discussed 

in the proposal (77 FR 38907, 38909, 

and 38910) and more fully in the 

Integrated Science Assessment 

(U.S.EPA, 2009a, sections 6.2, 6.3, and 

6.5), although copollutant models may 

be useful tools for assessing whether 

gaseous copollutants may be potential 

confounders, such models alone cannot 

determine whether copollutants are in 

fact confounders. Interpretation of the 

results of copollutant models is 

complicated by correlations that often 

exist among air pollutants, by the fact 

that some pollutants play a role in the 

atmospheric reactions that form other 

pollutants such as secondary fine 

particles, and by the statistical power of 

the studies in question inherent in the 

study methodology. For example, the 

every-third or sixth-day sampling 

schedule often employed for PM2.5

measurements compared to daily 

measurements of gaseous copollutants 

drastically reduces the overall sample 

size to assess the effect of copollutants 

on the PM2.5-morbidity or mortality 

relationship, such that the reduced 

sample size can lead to less precise 

effect estimates (e.g., wider confidence 

intervals). 

The EPA recognizes that when PM2.5

is correlated with gaseous pollutants it 

can be difficult to identify the effect of 

individual pollutants in the ambient 

mixture (77 FR 38910). However, based 

on the available evidence, the EPA 


tkelley on DSK3SPTVN1PROD with 
3116 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

55 In its evaluation of Janes et al. (2007) in the 

Integrated Science Assessment, the EPA did not 

identify limitations in the statistical methods used 

per se (U.S. EPA, 2009a, p. 7–88) and included the 

results of the national-scale analyses in that study 

in the body of evidence that supported the 

determination that there is a causal relationship 

between long-term PM2.5 exposure and mortality. 

56Though not directly comparable, the national 

effect estimates for mortality reported by Janes et al. 

(2007) and Greven et al. (2011) are coincidentally 

similar in magnitude to those previously reported. 

It is important to note that previous cohort studies 

have focused on identifying spatial differences in 

PM2.5 concentrations between cities, while Janes et 

al. (2007) and Greven et al. (2011) focus primarily 

on temporal differences in PM2.5 concentrations. In 

fact, Greven et al. (2011) state ‘‘We do not focus 

here on a third type [of statistical approach] used 

in cohort studies, measuring the association 

between average PM2.5 levels and average ageadjusted mortality rates across cities (purely spatial 

or cross-sectional association).’’ 

57Some commenters argued that there were flaws 

in the criticisms offered by Pope and Burnett (2007) 

on the paper by Janes et al. (2007) (UARG, 2012, 

Attachment A, pp. 19 to 23). The EPA responds to 

each of these specific comments in the Response to 

Comments document. 

58As noted above, however, Janes et al. (2007) 

and Greven et al. (2011) focused on temporal 

variability and other studies of long-term exposure 

to PM2.5 and mortality focus on spatial variability. 

concludes epidemiological studies 

continue to support the conclusion that 

PM2.5 associations with mortality and 

morbidity outcomes are robust to the 

inclusion of gaseous copollutants in 

statistical models. The EPA evaluated 

the potential confounding effects of 

gaseous copollutants and, although it is 

recognized that uncertainties and 

limitations still remain, the Agency 

concluded the collective body of 

scientific evidence is ‘‘stronger and 

more consistent than in previous 

reviews providing a strong basis for 

decision making in this review’’ (77 FR 

38910/1). 

Several commenters offered detailed 

comments on the long-term PM2.5

exposure studies arguing that 

associations from mortality studies are 

subjected to unmeasured confounding 

and as a result are not appropriately 

characterized as providing evidence of a 

causal relationship between long-term 

PM2.5 exposure and mortality (e.g., 

UARG, 2012, pp. 10 to 11, Attachment 

A, pp. 17 to 23; API, 2012, pp. 13 to 14, 

Attachment 1, pp. 11 to 14, Attachment 

7, pp. 2–10; ACC, 2012, p. 18 to 21; 

AFPM, 2012, p. 8; Texas CEQ, 2012, p. 

4). Specifically, commenters cited two 

studies (i.e., Janes et al., 2007 and 

Greven et al., 2011) that used a new type 

of statistical analysis to examine 

associations between annual (long-term) 

and monthly (sub-chronic) PM2.5

exposure and mortality. The 

commenters interpreted the results of 

these analyses as evidence of 

unmeasured confounding in the longterm PM2.5 exposure-mortality 

relationship. These commenters 

interpreted these studies as raising 

fundamental questions regarding the 

EPA’s determination that a causal 

relationship exists between long-term 

PM2.5 exposure and mortality. In 

addition to the commenters mentioned 

above, all of the authors of the 

publications by Janes et al. (2007) and 

Greven et al. (2011) (i.e., Francesca 

Dominici, Scott Zeger, Holly Janes, and 

Sonja Greven) submitted a joint 

comment to the public docket in order 

to clarify specific points regarding these 

two studies (Dominici et al., 2012). 

The first study, Janes et al. (2007), was 

evaluated in the Integrated Science 

Assessment (U.S. EPA, 2009a, p. 7–88). 

The second study, Greven et al. (2011), 

an extension of the Janes et al. (2007) 

study adding three more years of data, 

is a ‘‘new’’ study discussed in the 

Provisional Science Assessment (U.S. 

EPA, 2012). Both studies used 

nationwide Medicare mortality data to 

examine the association between 

monthly average PM2.5 concentrations 

over the preceding 12 months and 

monthly mortality rates in 113 U.S. 

counties and examined whether 

community-specific trends in monthly 

PM2.5 concentrations and mortality 

declined at the same rate as the national 

rate. The investigators examined this by 

decomposing the association between 

PM2.5 and mortality into two 

components: (1) National trends, 

defined as the association between the 

national average trend in monthly PM2.5

concentrations averaged over the 

previous 12 months and the national 

average trend in monthly mortality 

rates, and (2) local trends, defined as 

county-specific deviations in monthly 

PM2.5 concentrations and monthly 

mortality rates from national trends. 

The EPA does not question the results 

of the national trends analyses 

conducted by Janes et al. (2007) and 

Greven et al. (2011).55 Both Janes et al. 

(2007) and Greven et al. (2011) observed 

positive and statistically significant 

associations between long-term 

exposure to PM2.5 and mortality in their 

national analyses. However, Janes et al. 

(2007) and Greven et al. (2011) 

eliminated all of the spatial variation in 

air pollution and mortality in their data 

set when estimating the national effect, 

focusing instead on both chronic 

(yearly) and sub-chronic (monthly) 

temporal differences in the data 

(Dominici et al. 2012). Janes et al. (2007) 

(Table 1) highlighted that over 90 

percent of the variance in the data set 

used for the analyses conducted by both 

Janes et al. (2007) and Greven et al. 

(2011) was attributable to spatial 

variability, which the authors chose to 

discard. As noted above, the focus of the 

analyses by Janes et al. (2007) and 

Greven et al. (2011) was on two 

components: (1) A temporal or time 

component, i.e., the ‘‘national’’ trends 

analysis, which examined the 

association between the national 

average trend in monthly PM2.5

concentrations averaged over the 

previous 12 months and the national 

average trend in monthly mortality rates 

and (2) a space-by-time component, i.e., 

the ‘‘local’’ trends analysis, which 

examined county-specific deviations in 

monthly PM2.5 concentrations and 

monthly mortality rates from national 

trends. These two components 

combined comprised less than 10 

percent of the variance in the data set. 

The authors included a focus on the 

space-by-time component, which 

represented approximately 5 percent of 

the variance in the data set, in an 

attempt to identify, absent confounding, 

if PM2.5 was associated with mortality at 

this unique exposure window. Thus, 

these studies are not directly 

comparable to other cohort studies 

investigating the relationship between 

long-term exposure to PM2.5 and 

mortality, which make use of spatial 

variability in air pollution and mortality 

data.56 This point was highlighted by 

the study authors who stated that 

‘‘when one considers that this wealth of 

information is not accounted for in 

[Janes 2007], it is not as surprising that 

* * * vastly different estimates of the 

PM2.5/mortality relationship [were 

observed] than in other studies that do 

exploit that variability’’ (Dominici et al., 

2012, p. 2). 

The EPA notes that the results of the 

local trends analyses conducted by 

Janes et al. (2007) and Greven et al. 

(2011) are limited by the monthly 

timescale used in these analyses. This 

view is consistent with comments on 

the Janes et al. (2007) study articulated 

in Pope and Burnett (2007),57 which 

noted that an important limitation of the 

local scale analysis conducted by Janes 

et al. (2007) and subsequently by 

Greven et al. (2011) was the subchronic 

exposure window considered in these 

analyses. Both studies used annual 

average PM2.5 concentrations to 

characterize long-term national trends 

which was consistent with exposure 

windows considered in other studies of 

long-term exposure to PM2.5 and 

mortality.58 However, the local scale 

analyses used monthly average PM2.5

concentrations to characterize countyspecific deviations from national trends 

(the local scale). The use of monthly 

average data likely does not provide 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3117 

59Further, the EPA notes that Janes et al. (2007) 

and Greven et al. (2011) provide no information 

relevant to examining confounding in studies of 

short-term exposure to PM2.5. 

60The EPA notes that the EPA’s conclusion with 

regard to interpretation of the results from Janes et 

al. (2007) and Greven et al. (2012) is supported by 

the study authors’ conclusion that ‘‘[o]ur results do 

not invalidate previous epidemiological studies’’ 

(Dominici, 2012, p. 1 (emphasis original)). 

enough exposure contrast to observe 

temporal changes in mortality at the 

local scale. It also represents a different 

exposure window than considered in 

the large body of evidence of health 

effects related to short-term (from less 

than one day to up to several days) and 

chronic (one or more years) measures of 

PM2.5.

Furthermore, the EPA disagrees with 

commenters that studies by Janes et al. 

(2007) and Greven et al. (2011) provide 

evidence that other studies of long-term 

exposure to PM2.5 and mortality are 

affected by unmeasured confounding. 

As noted above, the design of the 

studies conducted by Janes et al. (2007) 

and Greven et al. (2011) are 

fundamentally different than those used 

in other studies of long-term exposure to 

PM2.5 and mortality, including the ACS 

cohort and the Harvard Six Cities study. 

Studies, such as the ACS and Harvard 

Six Cities studies, used the spatial 

variation between cities to measure the 

effect of long-term (annual) exposures to 

PM2.5 on mortality risk, and did not 

conduct any analyses relying on the 

temporal variation in PM2.5. The 

opposite is true of the Janes et al. (2007) 

and Greven et al. (2011) studies which 

first removed the spatial variability in 

PM2.5 and then examined the temporal 

variation at both the national and local 

scale to measure the effects of temporal 

differences in PM2.5 on mortality risk. 

Janes et al. (2007) and Greven et al. 

(2011) focus on changes in PM2.5

concentrations over time and, therefore, 

control for confounders would be based 

on including variables that vary over 

time rather than over space. As a result, 

any evidence of potential confounding 

of the PM2.5-mortality risk relationship 

derived from Janes et al. (2007) and 

Greven et al. (2011) cannot be 

extrapolated to draw conclusions 

related to potential spatial confounding 

in studies based on the spatial variation 

in PM2.5 concentrations. 

As detailed in the Integrated Science 

Assessment (U.S. EPA, 2009a, section 

7.6), and recognized by the authors of 

Janes et al. (2007) and Greven et al. 

(2011), the cohort studies that informed 

the causality determination for longterm PM2.5 exposure and mortality 

‘‘have developed approaches to adjust 

for measured and unmeasured 

confounders’’ (Dominici et al., 2012, p. 

2). These approaches were specifically 

designed to adjust for spatial 

confounding. The hypothesis that the 

authors of Janes et al. (2007) and Greven 

et al. (2011) chose to examine was that 

differences in the local and national 

effects indicated unmeasured temporal 

confounding in either the local or 

national effect estimate. This hypothesis 

was specific to these two studies that 

examined temporal variability in 

exposure to air pollution and did not 

include known potential confounders at 

either the national or local scale as timevarying covariates in the statistical 

model. The authors acknowledged that 

the interpretation of either the national 

or local estimates needs to occur with 

an appreciation of the potential 

confounding effects of national and 

local scale covariates that were omitted 

from the model (Dominici et al., 2012). 

It is important to recognize that 

because Janes et al. (2007) and Greven 

et al. (2011) focused on variations in 

PM2.5 over time and not space, the 

results from these two studies do not 

provide any indication that other 

studies of long-term exposure to PM2.5

and mortality exhibit spatial 

confounding, or that PM2.5 does not 

cause mortality.59 The authors of Janes 

et al. (2007) and Greven et al. (2011) 

recognized that ‘‘it is entirely possible 

that these papers are looking for an 

association at a timescale for which no 

association truly exists’’ (Dominici et 

al., 2012, p. 3). Furthermore, as 

highlighted in the Integrated Science 

Assessment and discussed by Pope and 

Burnett (2007), the conclusions of Janes 

et al. (2007) ‘‘are overstated * * * 

[T]heir analysis tells us little or nothing 

about unmeasured confounding in those 

and related studies because the 

methodology of Janes et al. largely 

excludes the sources of variability that 

are exploited in those other studies. By 

using monthly mortality counts and 

lagged 12-month average pollution 

concentrations, the authors eliminate 

the opportunity to exploit short-term or 

day-to-day variability.’’ 

In conclusion, the EPA interprets the 

results of the analyses conducted by 

Janes et al. (2007) and Greven et al. 

(2011) as being consistent with prior 

knowledge of examining associations 

with long-term exposure to PM2.5 at the 

national scale using long-term average 

PM2.5 concentrations. For the reasons 

presented above and discussed in more 

detail in the Response to Comments 

document, the Agency disagrees with 

the commenters’ assumption that the 

results of Janes et al. (2007) and Greven 

et al. (2011) indicate unmeasured 

confounding in the results of other 

cohort studies of long-term exposure to 

PM2.5 and mortality. Therefore, the EPA 

concludes that these studies do not 

invalidate the large body of 

epidemiological evidence that supports 

the EPA’s determination that a causal 

relationship exists between long-term 

PM2.5 exposure and mortality.60

(b) Heterogeneity in Risk Estimates 

Some commenters argued that the 

heterogeneity in risk estimates observed 

in multi-city epidemiological studies 

and the lack of statistical significance in 

many regional or seasonal estimates 

highlights a potential bias associated 

with combined multi-city 

epidemiological study results (e.g., API, 

2012, Attachment 1, pp. 15 to 19). These 

commenters further argued that more 

refined intra-urban exposure estimates 

conducted for two of the largest cities 

included in the ACS study, Los Angeles 

and New York City, based on land-use 

regression models and/or kriging 

methods (Krewski et al., 2009) 

‘‘underscore the importance of 

considering city-specific health 

estimates, which may account for 

heterogeneity in PM2.5 concentrations or 

other differences among cities, rather 

than relying on pooled nationwide 

results from multi-city studies’’ (API, 

2012, Attachment 1, p. 17). 

With respect to understanding the 

nature and magnitude of PM2.5-related 

risks, the EPA agrees that 

epidemiological studies evaluating 

health effects associated with long- and 

short-term PM2.5 exposures have 

reported heterogeneity in responses 

between cities and effect estimates 

across geographic regions of the U.S. 

(U.S. EPA, 2009a, sections 6.2.12.1, 

6.3.8.1, 6.5.2, and 7.6.1; U.S. EPA, 

2011a, p. 2–25). For example, when 

focusing on short-term PM2.5 exposure, 

the Integrated Science Assessment 

found that multi-city studies that 

examined associations with mortality 

and cardiovascular and respiratory 

hospital admissions and emergency 

department visits demonstrated greater 

cardiovascular effects in the eastern 

versus the western U.S. (Dominici, et 

al., 2006a; Bell et al., 2008; Franklin et 

al. (2007, 2008)). 

In addition, the Integrated Science 

Assessment evaluated studies that 

provided some evidence for seasonal 

differences in PM2.5 risk estimates, 

specifically in the northeast. The 

Integrated Science Assessment found 

evidence indicating that individuals 

may be at greater risk of dying from 

higher exposures to PM2.5 in the warmer 

months, and at greater risk of PM2.5

associated hospitalization for 


tkelley on DSK3SPTVN1PROD with 
3118 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

cardiovascular and respiratory diseases 

during colder months of the year. The 

limited influence of seasonality on PM 

risk estimates in other regions of the 

U.S. may be due to a number of factors 

including varying PM composition by 

season, exposure misclassification due 

to regional tendencies to spend more or 

less time outdoors and air conditioning 

usage, and the prevalence of infectious 

diseases during the winter months (U.S. 

EPA, 2009a, p. 3–182). 

Overall, the EPA took note in the 

proposal that uncertainties still remain 

regarding various factors that contribute 

to heterogeneity observed in 

epidemiological studies (77 FR 38909/ 

3). Nonetheless, the EPA recognizes that 

this heterogeneity could be attributed, at 

least in part, to differences in PM2.5

composition across the U.S., as well as 

to exposure differences that vary 

regionally such as personal activity 

patterns, microenvironmental 

characteristics, and the spatial 

variability of PM2.5 concentrations in 

urban areas (U.S. EPA, 2009a, section 

2.3.2; 77 FR 38910). 

As recognized in the Policy 

Assessment, the current epidemiological 

evidence and the limited amount of 

city-specific speciated PM2.5 data do not 

allow conclusions to be drawn that 

specifically differentiate effects of PM2.5

in different locations (U.S. EPA, 2011a, 

p. 2–25). Furthermore, the Integrated 

Science Assessment concluded ‘‘that 

many constituents of PM2.5 can be 

linked with multiple health effects, and 

the evidence is not yet sufficient to 

allow differentiation of those 

constituents or sources that are more 

closely related to specific health 

outcomes’’ (U.S. EPA, 2009a, p. 2–17). 

CASAC thoroughly reviewed the EPA’s 

presentation of the scientific evidence 

indicating heterogeneity in PM2.5 effect 

estimates in epidemiological studies 

and concurred with the overall 

conclusions presented in the Integrated 

Science Assessment. 

(c) Exposure Measurement Error 

Some commenters argued that the 

EPA did not adequately consider 

exposure measurement error, which 

they asserted is an important source of 

bias in epidemiological studies that can 

bias effect estimates in either direction 

(e.g., API, 2012, Attachment 1, pp. 19 to 

20). 

The EPA agrees that exposure 

measurement error is an important 

source of uncertainty and that the 

variability in risk estimates observed in 

multi-city studies could be attributed, in 

part, to exposure error due to 

measurement-related issues (77 FR 

38910). However, the Agency disagrees 

with the commenters’ assertion that 

exposure measurement error was not 

adequately considered in this review. 

The Integrated Science Assessment 

included an extensive discussion that 

addresses issues of exposure 

measurement error (U.S. EPA, 2009a, 

sections 2.3.2 and 3.8.6). Exposure 

measurement error may lead to bias in 

effect estimates in epidemiological 

studies. A number of studies evaluated 

in the last review (U.S. EPA, 2004, 

section 8.4.5) and in the current review 

(U.S. EPA, 2009a, section 3.8.6) have 

discussed the direction and magnitude 

of bias resulting from specified patterns 

of exposure measurement error 

(Armstrong 1998; Thomas et al. 1993; 

Carroll et al. 1995) and have generally 

concluded ‘‘classical’’ (i.e., random, 

within-person) exposure measurement 

error can bias effect estimates towards 

the null. Therefore, consistent with 

conclusions reached in the last review, 

the Integrated Science Assessment 

concluded ‘‘in most circumstances, 

exposure error tends to bias a health 

effect estimate downward’’ (U.S. EPA, 

2009a, sections 2.3.2 and 3.8.6) 

(emphasis added). Thus, the EPA has 

both considered and accounted for the 

possibility of exposure measurement 

error, and the possible bias would make 

it more difficult to detect true 

associations, not less difficult. 

(d) Model Specification 

Commenters contended that the EPA 

did not account for the fact that 

‘‘selecting an appropriate statistical 

model for epidemiologic studies of air 

pollution involves several choices that 

involve much ambiguity, scant 

biological evidence, and a profound 

impact on analytic results, given that 

many estimated associations are weak’’ 

(ACC, 2012, p. 5). For short-term 

exposure studies, the EPA recognizes, as 

summarized in the HEI review panel 

commentary that selecting a level of 

control to adjust for time-varying 

factors, such as temperature, in timeseries epidemiological studies involves 

a trade-off (HEI, 2003). For example, if 

the model does not sufficiently adjust 

for the relationship between the health 

outcome and temperature, some effects 

of temperature could be falsely ascribed 

to the pollution variable. Conversely, if 

an overly aggressive approach is used to 

control for temperature, the result 

would possibly underestimate the 

pollution-related effect and compromise 

the ability to detect a small but true 

pollution effect (U.S. EPA, 2004, p. 8– 

236; HEI, 2003, p. 266). The selection of 

approaches to address such variables 

depends in part on prior knowledge and 

judgments made by the investigators, for 

example, about weather patterns in the 

study area and expected relationships 

between weather and other time-varying 

factors and health outcomes considered 

in the study. As demonstrated in section 

6.5 of the Integrated Science 

Assessment, the EPA thoroughly 

considered each of these issues and the 

overall effect of different model 

specifications on the association 

between short-term PM2.5 exposure and 

mortality. Regardless of the model 

employed, consistent positive 

associations were observed across 

studies that controlled for the potential 

confounding effects of time and weather 

using different approaches (U.S. EPA 

2009a, Figure 6–27). The EPA also 

considered the influence of model 

specification in the examination of longterm PM2.5 exposure studies. For 

example, in section 7.6 of the Integrated 

Science Assessment, Figures 7–6 and 7– 

7 summarize the collective evidence 

that evaluated the association between 

long-term PM2.5 exposure and mortality. 

Regardless of the model used, these 

studies collectively found evidence of 

consistent positive associations between 

long-term PM2.5 exposure and mortality. 

The EPA, therefore, disagrees with 

commenters that model specification 

was not considered when evaluating the 

epidemiological evidence used to form 

causality determinations. The EPA 

specifically points out that the process 

of assessing the scientific quality and 

relevance of epidemiological studies 

includes examining ‘‘important 

methodological issues (e.g., lag or time 

period between exposure and effects, 

model specifications, thresholds, 

mortality displacement) related to 

interpretation of the health evidence 

(U.S. EPA, 2009, p. 1–9).’’ Consistent 

with the conclusions of the 2004 PM Air 

Quality Criteria Document, the EPA 

recognizes that there is still no clear 

consensus at this time as to what 

constitutes appropriate control of 

weather and temporal trends in shortterm exposure studies, and that no 

single statistical modeling approach is 

likely to be most appropriate in all cases 

(U.S. EPA, 2004, p. 8–238). However, 

the EPA believes that the available 

evidence interpreted in light of these 

remaining uncertainties does provide 

increased confidence relative to the last 

review in the reported associations 

between short- and long-term PM2.5

exposures and mortality and morbidity 

effects, alone and in combination with 

other pollutants. 

(e) Concentration-Response 

Relationship 

Additionally, commenters questioned 

the interpretation of the shape of the 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3119 

61While epidemiological analyses have not 

identified a population threshold in the range of air 

quality concentrations evaluated in these studies, 

the EPA recognizes that it is possible that such 

thresholds exist towards the lower end of these 

ranges (or below these ranges). 

concentration-response relationship, 

specifically stating that multiple studies 

have demonstrated that there is a 

threshold in the PM-health effect 

relationship and that the log-linear 

model is not biologically plausible (API, 

2012, Attachment 9; ACC, 2012, 

Appendix A, pp. 7 to 8). The EPA 

disagrees with this assertion due to the 

number of studies evaluated in the 

Integrated Science Assessment that 

continue to support the use of a nothreshold, log-linear model to most 

appropriately represent the PM 

concentration-response relationship 

(U.S. EPA, 2009a, section 2.4.3). While 

recognizing that uncertainties remain, 

the EPA believes that our understanding 

of this issue for both long- and shortterm exposure studies has advanced 

since the last review. As discussed in 

the Integrated Science Assessment, both 

long- and short-term exposure studies 

have employed a variety of statistical 

approaches to examine the shape of the 

concentration-response function and 

whether a threshold exists. While the 

EPA recognizes that there likely are 

individual biological thresholds for 

specific health responses, the Integrated 

Science Assessment concluded the 

overall evidence from existing 

epidemiological studies does not 

support the existence of thresholds at 

the population level, for effects 

associated with either long-term or 

short-term PM exposures within the 

ranges of air quality observed in these 

studies (U.S. EPA, 2009a, section 

2.4.3).61 The Integrated Science 

Assessment concluded that this 

evidence collectively supported the 

conclusion that a no-threshold, loglinear model is most appropriate (U.S. 

EPA, 2009a, sections 6.2.10.10, 6.5.2.7, 

and 7.6.4). CASAC likewise advised that 

‘‘[a]lthough there is increasing 

uncertainty at lower levels, there is no 

evidence of a threshold’’ (Samet, 2010d, 

p. ii). 

The EPA recognizes that some shortterm exposure studies have examined 

the PM2.5 concentration-response 

relationship in individual cities or on a 

city-to-city basis and observed 

heterogeneity in the shape of the 

concentration-response curve across 

cities. As discussed in (b) above, these 

findings are a source of uncertainty that 

the EPA agrees requires further 

investigation. Nonetheless, the 

Integrated Science Assessment 

concluded that ‘‘the studies evaluated 

further support the use of a nothreshold, log-linear model, but 

additional issues such as the influence 

of heterogeneity in estimates between 

cities and the effects of seasonal and 

regional differences in PM on the 

concentration-response-relationship still 

require further investigation’’ (U.S. EPA, 

2009a, p. 2–25). 

(f) Relative Toxicity of PM2.5

Components 

Some commenters highlighted 

uncertainties in understanding the role 

of individual constituents within the 

mix of fine particles. These commenters 

asserted that a mass-based standard may 

not be appropriate due to the growing 

body of evidence indicating that certain 

PM2.5 components may be more closely 

related to specific health outcomes (e.g., 

EC and OC) (EPRI, 2012, p. 2). 

With regard to questions about the 

role of individual constituents within 

the mix of fine particles, as a general 

matter, the EPA recognizes that 

although new research directed toward 

this question has been conducted since 

the last review, important questions 

remain and the issue remains an 

important element in the Agency’s 

ongoing research program. At the time 

of the last review, the Agency 

determined that it was appropriate to 

continue to control fine particles as a 

group, as opposed to singling out any 

particular component or class of fine 

particles (71 FR 61162 to 61164, October 

17, 2006). This distinction was based 

largely on epidemiological evidence of 

health effects using various indicators of 

fine particles in a large number of areas 

that had significant contributions of 

differing components or sources of fine 

particles, together with some limited 

experimental studies that provided 

some evidence suggestive of health 

effects associated with high 

concentrations of numerous fine particle 

components. 

In this review, as discussed in the 

proposal (77 FR 38922 to 38923) and in 

section III.E.1 below, while most 

epidemiological studies continue to be 

indexed by PM2.5 mass, several recent 

epidemiological studies included in the 

Integrated Science Assessment have 

used PM2.5 speciation data to evaluate 

health effects associated with fine 

particle exposures. In the Integrated 

Science Assessment, the EPA 

thoroughly evaluated the scientific 

evidence that examined the effect of 

different PM2.5 components and sources 

on a variety of health outcomes (U.S. 

EPA, 2009a, section 6.6) and observed 

that the available information continues 

to suggest that many different chemical 

components of fine particles and a 

variety of different types of source 

categories are all associated with, and 

probably contribute to, effects 

associated with PM2.5. The Integrated 

Science Assessment concluded that the 

current body of scientific evidence 

indicated that ‘‘many constituents of PM 

can be linked with differing health 

effects and the evidence is not yet 

sufficient to allow differentiation of 

those constituents or sources that are 

more closely related to specific health 

outcomes’’ (U.S. EPA, 2009a, p. 2–26 

and 6–212). Furthermore, the Policy 

Assessment concluded that the evidence 

is not sufficient to support eliminating 

any component or group of components 

associated with any specific source 

categories from the mix of fine particles 

included in the PM2.5 indicator (U.S. 

EPA, 2009a, p. 2–56). CASAC agreed 

that it was reasonable to retain PM2.5 as 

an indicator for fine particles in this 

review as ‘‘[t]here was insufficient peerreviewed literature to support any other 

indicator at this time’’ (Samet, 2010c, p. 

12). 

This information is relevant to the 

Agency’s decision to retain PM2.5 as the 

indicator for fine particles as discussed 

in section III.E.1 below. The EPA also 

believes that it is relevant to the 

Agency’s conclusion as to whether 

revision of the suite of primary PM2.5

standards is appropriate. While there 

remain uncertainties about the role and 

relative toxicity of various components 

of fine PM, the current evidence 

continues to support the view that fine 

particles should be addressed as a group 

for purposes of public health protection. 

In summary, in considering the above 

issues related to uncertainties in the 

underlying health science, on balance, 

the EPA believes that the available 

evidence interpreted in light of these 

remaining uncertainties does provide 

increased confidence relative to the last 

review in the reported associations 

between long- and short-term PM2.5

exposures and mortality and morbidity 

effects, alone and in combination with 

other pollutants, and supports stronger 

inferences as to the causal nature of the 

associations. The EPA also believes that 

this increased confidence, when taken 

in context of the entire body of available 

health effects evidence and in light of 

the evidence from epidemiological 

studies of associations observed in areas 

meeting the current primary PM2.5

standards, specifically in areas meeting 

the current primary annual PM2.5

standard, adds support to its conclusion 

that the current suite of PM2.5 standards 

needs to be revised to provide increased 

public health protection. 

(4) In asserting that there is no 

evidence of greater risk since the 2006 


tkelley on DSK3SPTVN1PROD with 
3120 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

review to justify lowering the current 

annual PM2.5 standard, some 

commenters argued that, ‘‘if the current 

primary PM2.5 annual standard of 15 mg/ 

m3 was considered to be adequately 

protective of public health in 2006, 

given relative risk estimates that EPA 

was using at that time, then that 

standard would surely still be 

adequately protective of the public 

health if relative risk estimates remain 

at the same level (or lower)’’ (UARG, 

2012, Attachment 1, p. 24). These 

commenters compared risk coefficients 

used for mortality in the EPA’s risk 

assessment done in the last review with 

those from the Agency’s core risk 

assessment done as part of this review, 

and they concluded that ‘‘the entire 

range of the core relative risk for longterm mortality is lower now than it was 

in the prior review’’ (UARG, 2012, 

Attachment 1, p. 24). These commenters 

used this conclusion as the basis for a 

claim that there is no reason to revise 

the current annual PM2.5 standard. 

The EPA believes that this claim is 

fundamentally flawed. In comparing the 

scientific understanding of the risk 

presented by exposure to PM2.5 between 

the last and current reviews, one must 

examine not only the quantitative 

estimate of risk from those exposures 

(e.g., the numbers of premature deaths 

or increased hospital admissions at 

various concentrations), but also the 

degree of confidence that the Agency 

has that the observed health effects are 

causally linked to PM2.5 exposure at 

those concentrations. As documented in 

the Integrated Science Assessment and 

in the recommendations and 

conclusions of CASAC, the EPA 

recognizes significant advances in our 

understanding of the health effects of 

PM2.5, based on evidence that is stronger 

than in the last review. As a result of 

these advances, the EPA is now more 

certain that fine particles, alone or in 

combination with other pollutants, 

present a significant risk to public 

health at concentrations allowed by the 

current primary PM2.5 standards. From 

this more comprehensive perspective, 

since the risks presented by PM2.5 are 

more certain, similar or even somewhat 

lower relative risk estimates would not 

be a basis to conclude that no revision 

to the suite of PM2.5 standards is 

‘‘requisite’’ to protect public health with 

an adequate margin of safety. This also 

ignores that the relative risk estimate is 

only one factor considered by the 

Administrator, e.g. it ignores that 

epidemiological studies since the last 

review indicate associations between 

PM2.5 and mortality and morbidity in 

areas meeting the current annual 

standard. 

In any case, the commenters’ reliance 

on the flawed 2006 review is misplaced. 

As discussed in section III.A.2 above, 

the D.C. Circuit remanded 

Administrator Johnson’s 2006 decision 

to retain the primary annual PM2.5

standard because the Agency failed to 

adequately explain why the annual 

standard provided the requisite 

protection from both short- and longterm exposure to fine particles 

including protection for at-risk 

populations. The 2006 standard was 

also at sharp odds with CASAC advice 

and recommendations as to the requisite 

level of protection (Henderson, 

2006a,b). In other words, the 2006 

primary annual PM2.5 standard is not an 

appropriate benchmark for comparison. 

(5) Some of these commenters also 

identified ‘‘new’’ as well as older 

studies that had been included in prior 

reviews as providing additional 

evidence that the causality 

determinations presented in the 

Integrated Science Assessment did not 

consider the totality of the scientific 

literature, further supporting their view 

that a revision of the PM2.5 is 

unwarranted. As discussed in section 

II.B.3 above, the EPA notes that, as in 

past NAAQS reviews, the Agency is 

basing the final decisions in this review 

on the studies and related information 

included in the Integrated Science 

Assessment that have undergone 

CASAC and public review, and will 

consider newly published studies for 

purposes of decisionmaking in the next 

PM NAAQS review. In provisionally 

evaluating commenters’ arguments (see 

Response to Comments document), the 

EPA notes that its provisional 

assessment of ‘‘new’’ science found that 

such studies did not materially change 

the conclusions reached in the 

Integrated Science Assessment (U.S. 

EPA, 2012b). 

3. Administrator’s Final Conclusions 

Concerning the Adequacy of the Current 

Primary PM2.5 Standards 

Having carefully considered the 

public comments, as discussed above, 

the Administrator believes the 

fundamental scientific conclusions on 

the effects of PM2.5 reached in the 

Integrated Science Assessment, and 

discussed in the Policy Assessment, are 

valid. In considering whether the suite 

of primary PM2.5 standards should be 

revised, the Administrator places 

primary consideration on the evidence 

obtained from the epidemiological 

studies. The Administrator believes that 

this literature, combined with the other 

scientific evidence discussed in the 

Integrated Science Assessment, 

collectively represents a strong and 

generally robust body of evidence of 

serious health effects associated with 

both long- and short-term exposures to 

PM2.5. As discussed in the Integrated 

Science Assessment and Policy 

Assessment, the EPA believes that much 

progress has been made since the last 

review in reducing some of the major 

uncertainties that were important 

considerations in establishing the 

current suite of PM2.5 standards. In that 

context, the Administrator finds the 

evidence of serious health effects 

reported in exposure studies conducted 

in areas with long-term mean 

concentrations ranging from 

approximately at or above the level of 

the annual standard to long-term mean 

concentrations significantly below the 

level of the annual standard to be 

compelling, especially in light of the 

extent to which such studies are part of 

an overall pattern of positive and 

frequently statistically significant 

associations across a broad range of 

studies. The information in the 

quantitative risk assessment lends 

support to this conclusion. 

There has been extensive critical 

review of this body of evidence, the 

quantitative risk assessment, and related 

uncertainties, including review by 

CASAC and the public. The public 

comments on the basis for the EPA’s 

proposed decision to revise the suite of 

primary PM2.5 standards have identified 

a number of issues about which 

different parties disagree including 

issues for which additional research is 

warranted. Having weighed all 

comments and the advice of CASAC, the 

Administrator believes that since the 

last review the overall uncertainty about 

the public health risks associated with 

both long- and short-term exposure to 

PM2.5 has been diminished to an 

important degree. The remaining 

uncertainties in the available evidence 

do not diminish confidence in the 

associations between exposure to fine 

particles and mortality and serious 

morbidity effects. Based on her 

increased confidence in the association 

between exposure to PM2.5 and serious 

public health effects, combined with 

evidence of such an association in areas 

that would meet the current standards, 

the Administrator agrees with CASAC 

that revision of the current suite of 

PM2.5 standards to provide increased 

public health protection is necessary. 

Based on these considerations, the 

Administrator concludes that the 

current suite of primary PM2.5 standards 

is not sufficient, and thus not requisite, 

to protect public health with an 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3121 

62Ultrafine particles, generally including 

particles with a mobility diameter less than or equal 

to 0.1 mm, are emitted directly to the atmosphere 

or are formed by nucleation of gaseous constituents 

in the atmosphere (U.S. EPA, 2009a, p. 3–3). 

adequate margin of safety, and that 

revision is needed to increase public 

health protection. 

It is important to note that this 

conclusion, and the reasoning on which 

it is based, do not resolve the question 

of what specific revisions are 

appropriate. That requires looking 

specifically at the current 24-hour and 

annual PM2.5 standards, including their 

indicator, averaging times, forms, and 

levels, and evaluating the scientific 

evidence and other information relevant 

to determining the appropriate revision 

of the suite of standards. 

E. Conclusions on the Elements of the 

Primary Fine Particle Standards 

1. Indicator 

In initially setting standards for fine 

particles in 1997, the EPA concluded it 

was appropriate to control fine particles 

as a group, rather than singling out any 

particular component or class of fine 

particles. The EPA noted that 

community health studies had found 

significant associations between various 

indicators of fine particles, and that 

health effects in a large number of areas 

had significant mass contributions of 

differing components or sources of fine 

particles. In addition, a number of 

toxicological and controlled human 

exposure studies had reported health 

effects associations with high 

concentrations of numerous fine particle 

components. It was also not possible to 

rule out any component within the mix 

of fine particles as not contributing to 

the fine particle effects found in the 

epidemiologic studies (62 FR 38667, 

July 18, 1977). In establishing a sizebased indicator in 1977 to distinguish 

fine particles from particles in the 

coarse mode, the EPA noted that the 

available epidemiological studies of fine 

particles were based largely on PM2.5

and also considered monitoring 

technology that was generally available. 

The selection of a 2.5 mm size cut 

reflected the regulatory importance of 

defining an indicator that would more 

completely capture fine particles under 

all conditions likely to be encountered 

across the U.S., especially when fine 

particle concentrations and humidity 

are likely to be high, while recognizing 

that some small coarse particles would 

also be captured by current methods to 

monitor PM2.5 (62 FR 38666 to 38668, 

July 18, 1997). In the last review, based 

on the same considerations, the EPA 

again recognized that the available 

information supported retaining the 

PM2.5 indicator and remained too 

limited to support a distinct standard 

for any specific PM2.5 component or 

group of components associated with 

any source categories of fine particles 

(71 FR 61162 to 61164, October 17, 

2006). 

In this current review, the same 

considerations continue to apply for 

selection of an appropriate indicator for 

fine particles. As an initial matter, the 

Policy Assessment recognizes that the 

available epidemiological studies 

linking mortality and morbidity effects 

with long- and short-term exposures to 

fine particles continue to be largely 

indexed by PM2.5. For the same reasons 

discussed in the last two reviews, the 

Policy Assessment concluded that it 

was appropriate to consider retaining a 

PM2.5 indicator to provide protection 

from effects associated with long- and 

short-term fine particle exposures (U.S. 

EPA, 2011a, p. 2–50). 

The Policy Assessment also 

considered the expanded body of 

evidence available in this review to 

consider whether there was sufficient 

evidence to support a separate standard 

for ultrafine particles 62 or whether there 

was sufficient evidence to establish 

distinct standards focused on regulating 

specific PM2.5 components or a group of 

components associated with any source 

categories of fine particles (U.S. EPA, 

2011a, section 2.3.1). 

A number of studies available in this 

review have evaluated potential health 

effects associated with short-term 

exposures to ultrafine particles. As 

noted in the Integrated Science 

Assessment, the enormous number and 

larger, collective surface area of 

ultrafine particles are important 

considerations for focusing on this 

particle size fraction in assessing 

potential public health impacts (U.S. 

EPA, 2009a, p. 6–83). Per unit mass, 

ultrafine particles may have more 

opportunity to interact with cell 

surfaces due to their greater surface area 

and their greater particle number 

compared with larger particles (U.S. 

EPA, 2009a, p. 5–3). Greater surface area 

also increases the potential for soluble 

components (e.g., transition metals, 

organics) to adsorb to ultrafine particles 

and potentially cross cell membranes 

and epithelial barriers (U.S. EPA, 2009a, 

p. 6–83). In addition, evidence available 

in this review suggests that the ability 

of particles to enhance allergic 

sensitization is associated more strongly 

with particle number and surface area 

than with particle mass (U.S. EPA, 

2009a, p. 6–127). 

New evidence, primarily from 

controlled human exposure and 

toxicological studies, expands our 

understanding of cardiovascular and 

respiratory effects related to short-term 

ultrafine particle exposures. However, 

the Policy Assessment concluded that 

this evidence was still very limited and 

largely focused on exposure to diesel 

exhaust, for which the Integrated 

Science Assessment concluded it was 

unclear whether the effects observed are 

due to ultrafine particles, larger 

particles within the PM2.5 mixture, or 

the gaseous components of diesel 

exhaust (U.S. EPA, 2009a, p. 2–22). In 

addition, the Integrated Science 

Assessment noted uncertainties 

associated with the controlled human 

exposure studies using concentrated 

ambient particle systems which have 

been shown to modify the composition 

of ultrafine particles (U.S. EPA, 2009a, 

p. 2–22, see also section 1.5.3). 

The Policy Assessment recognized 

that there are relatively few 

epidemiological studies that have 

examined potential cardiovascular and 

respiratory effects associated with shortterm exposures to ultrafine particles 

(U.S. EPA, 2011a, p. 2–51). These 

studies have reported inconsistent and 

mixed results (U.S. EPA, 2009a, section 

2.3.5). 

Collectively, in considering the body 

of scientific evidence available in this 

review, the Integrated Science 

Assessment concluded that the 

currently available evidence was 

suggestive of a causal relationship 

between short-term exposures to 

ultrafine particles and cardiovascular 

and respiratory effects. Furthermore, the 

Integrated Science Assessment 

concluded that evidence was inadequate 

to infer a causal relationship between 

short-term exposure to ultrafine 

particles and mortality as well as longterm exposure to ultrafine particles and 

all outcomes evaluated (U.S. EPA, 

2009a, sections 2.3.5, 6.2.12.3, 6.3.10.3, 

6.5.3.3, 7.2.11.3, 7.3.9, 7.4.3.3, 7.5.4.3, 

and 7.6.5.3; Table 2–6). 

With respect to our understanding of 

ambient ultrafine particle 

concentrations, at present, there is no 

national network of ultrafine particle 

samplers; thus, only episodic and/or 

site-specific data sets exist (U.S. EPA, 

2009a, p. 2–2). Therefore, the Policy 

Assessment recognized a national 

characterization of concentrations, 

temporal and spatial patterns, and 

trends was not possible at this time, and 

the availability of ambient ultrafine 

measurements to support health studies 

was extremely limited (U.S. EPA, 2011a, 

p. 2–51). In general, measurements of 

ultrafine particles are highly dependent 

on monitor location and, therefore, more 

subject to exposure error than 


tkelley on DSK3SPTVN1PROD with 
3122 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

63Most studies considered between 7 to 20 

ambient PM2.5 constituents, with elemental carbon, 

organic carbon, sulfates, nitrates, and metals most 

commonly measured. Many of the studies grouped 

the constituents with various factorization or source 

apportionment techniques to examine the 

relationship between the grouped constituents and 

various health effects. However, not all studies 

labeled the constituent groupings according to their 

presumed source and a small number of controlled 

human exposure and toxicological studies did not 

use any constituent grouping. These differences 

across studies substantially limit any integrative 

interpretation of these studies (U.S. EPA, 2009a, p. 

6–203). 

64To expand our understanding of the role of 

specific PM2.5 components and sources with respect 

to the observed health effects, researchers have 

expressed a strong interest in having access to PM2.5

speciation measurements collected more frequently 

(U.S. EPA, 2011a, p. 2–53, including footnote 47). 

accumulation mode particles (U.S. EPA, 

2009a, p. 2–22). Furthermore, the 

number of ultrafine particles generally 

decreases sharply downwind from 

sources, as ultrafine particles may grow 

into the accumulation mode by 

coagulation or condensation (U.S. EPA, 

2009a, p. 3–89). Limited studies of 

ambient ultrafine particle measurements 

have suggested that these particles 

exhibit a high degree of spatial and 

temporal heterogeneity driven primarily 

by differences in nearby source 

characteristics (U.S. EPA, 2009a, p. 3– 

84). Internal combustion engines and, 

therefore, roadways are a notable source 

of ultrafine particles, so concentrations 

of these particles near roadways are 

generally expected to be elevated (U.S. 

EPA, 2009a, p. 2–3). Concentrations of 

ultrafine particles have been reported to 

drop off much more quickly with 

distance from roadways than fine 

particles (U.S. EPA, 2009a, p. 3–84). 

In considering both the currently 

available health effects evidence and the 

air quality data, the Policy Assessment 

concluded that this information was 

still too limited to provide support for 

consideration of a distinct PM standard 

for ultrafine particles (U.S. EPA, 2011a, 

p. 2–52). 

In addressing the issue of particle 

composition, the Integrated Science 

Assessment concluded that, ‘‘[f]rom a 

mechanistic perspective, it is highly 

plausible that the chemical composition 

of PM would be a better predictor of 

health effects than particle size’’ (U.S. 

EPA, 2009a, p. 6–202). Heterogeneity of 

ambient concentrations of PM2.5

constituents (e.g., elemental carbon, 

organic carbon, sulfates, nitrates) 

observed in different geographical 

regions as well as regional heterogeneity 

in PM2.5-related health effects reported 

in a number of epidemiological studies 

are consistent with this hypothesis (U.S. 

EPA, 2009a, section 6.6). 

With respect to the availability of 

ambient measurement data for fine 

particle components in this review, the 

Policy Assessment noted that there were 

now more extensive ambient PM2.5

speciation measurement data available 

through the Chemical Speciation 

Network (CSN) than in previous reviews 

(U.S. EPA, 2011a, section 1.3.2 and 

Appendix B, section B.1.3). The 

Integrated Science Assessment observed 

that data from the CSN provided further 

evidence of spatial and seasonal 

variation in both PM2.5 mass and 

composition among cities and 

geographic regions (U.S. EPA, 2009a, 

pp. 3–50 to 3–60; Figures 3–12 to 3–18; 

Figure 3–47). Some of this variation may 

be related to regional differences in 

meteorology, sources, and topography 

(U.S. EPA, 2009a, p. 2–3). 

The currently available 

epidemiological, toxicological, and 

controlled human exposure studies 

evaluated in the Integrated Science 

Assessment on the health effects 

associated with ambient PM2.5

constituents and categories of fine 

particle sources used a variety of 

quantitative methods applied to a broad 

set of PM2.5 constituents, rather than 

selecting a few constituents a priori 

(U.S. EPA, 2009a, p. 2–26). 

Epidemiological studies have used 

measured ambient PM2.5 speciation 

data, including monitoring data from 

the CSN, while all of the controlled 

human exposure and most of the 

toxicological studies have used 

concentrated ambient particles and 

analyzed the constituents therein (U.S. 

EPA, 2009a, p. 6–203).63 The CSN 

provides PM2.5 speciation 

measurements generally on a one-inthree or one-in-six day sampling 

schedule and, thus, does not capture 

data every day at most sites.64

The Policy Assessment recognized 

that several new multi-city studies 

evaluating short-term exposures to fine 

particle constituents are now available. 

These studies continued to show an 

association between mortality and 

cardiovascular and/or respiratory 

morbidity effects and short-term 

exposures to various PM2.5 components 

including nickel, vanadium, elemental 

carbon, organic carbon, nitrates, and 

sulfates (U.S. EPA, 2011a, section 2.3.1; 

U.S. EPA, 2009a, sections 6.5.2.5 and 

6.6). 

Limited evidence is available to 

evaluate the health effects associated 

with long-term exposures to PM2.5

components (U.S. EPA, 2009a, section 

7.6.2). The Policy Assessment noted the 

most significant new evidence was 

provided by a study that evaluated 

multiple PM2.5 components and an 

indicator of traffic density in an 

assessment of health effects related to 

long-term exposure to PM2.5 (Lipfert et 

al., 2006a). Using health data from a 

cohort of U.S. military veterans and 

PM2.5 measurement data from the CSN, 

Lipfert et al. (2006a) reported positive 

associations between mortality and 

long-term exposures to nitrates, 

elemental carbon, nickel, and vanadium 

as well as traffic density and peak ozone 

concentrations (U.S. EPA, 2011a, p. 2– 

54; U.S. EPA, 2009a, pp. 7–89 to 7–90). 

With respect to source categories of 

fine particles potentially associated with 

a range of health endpoints, the 

Integrated Science Assessment reported 

that the currently available evidence 

suggests associations between 

cardiovascular effects and a number of 

specific PM2.5-related source categories, 

including oil combustion, wood or 

biomass burning, motor vehicle 

emissions, and crustal or road dust 

sources (U.S. EPA, 2009a, section 6.6; 

Table 6–18). In addition, a few studies 

have evaluated associations between 

PM2.5-related source categories and 

mortality. For example, one study 

reported an association between 

mortality and a PM2.5 coal combustion 

factor (Laden et al., 2000), while other 

studies linked mortality to a secondary 

sulfate long-range transport PM2.5

source (Ito et al., 2006; Mar et al., 2006) 

(U.S. EPA, 2009a, section 6.6.2.1). Other 

studies have looked at different 

components of particulate matter. There 

was less consistency in associations 

observed between selected sources of 

fine particles and respiratory health 

endpoints, which may be partially due 

to the fact that fewer studies have 

evaluated respiratory-related outcomes 

and measures. However, there was some 

evidence for PM2.5-related associations 

with secondary sulfate and decrements 

in lung function in asthmatic and 

healthy adults (U.S. EPA, 2009a, p. 6– 

211; Gong et al., 2005; Lanki et al., 

2006). A couple of studies have 

observed an association between 

respiratory endpoints in children and 

adults with asthma and surrogates for 

the crustal/soil/road dust and traffic 

sources of PM (U.S. EPA, 2009a, p. 6– 

205; Gent et al., 2009; Penttinen et al., 

2006). 

Recent studies have shown that 

source apportionment methods have the 

potential to add useful insights into 

which sources and/or PM constituents 

may contribute to different health 

effects. Of particular interest are several 

epidemiological studies that compared 

source apportionment methods and 

reported consistent results across 

research groups (U.S. EPA, 2009a, p. 6– 

211; Hopke et al., 2006; Ito et al., 2006; 

Mar et al., 2006; Thurston et al., 2005). 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3123 

65No public comments were submitted regarding 

the use of a different size cut for fine particles. 

These studies reported associations 

between total mortality and secondary 

sulfate in two cities for two different lag 

times. The sulfate effect was stronger for 

total mortality in Washington, DC and 

for cardiovascular-related mortality in 

Phoenix (U.S. EPA, 2009a, p. 6–204). 

These studies also found some evidence 

for associations with mortality and a 

number of source categories (e.g., 

biomass/wood combustion, traffic, 

copper smelter, coal combustion, sea 

salt) at various lag times (U.S. EPA, 

2009a, p. 6–204). Sarnat et al. (2008) 

compared three different source 

apportionment methods and reported 

consistent associations between 

emergency department visits for 

cardiovascular diseases with mobile 

sources and biomass combustion as well 

as increased respiratory-related 

emergency department visits associated 

with secondary sulfate (U.S. EPA, 

2009a, pp. 6–204 and 6–211). 

Collectively, in considering the 

currently available evidence for health 

effects associated with specific PM2.5

components or groups of components 

associated with any source categories of 

fine particles as presented in the 

Integrated Science Assessment, the 

Policy Assessment concluded that 

additional information available in this 

review continues to provide evidence 

that many different constituents of the 

fine particle mixture as well as groups 

of components associated with specific 

source categories of fine particles are 

linked to adverse health effects (U.S. 

EPA, 2011a, p. 2–55). However, as noted 

in the Integrated Science Assessment, 

while ‘‘[t]here is some evidence for 

trends and patterns that link particular 

ambient PM constituents or sources 

with specific health outcomes * * * 

there is insufficient evidence to 

determine whether these patterns are 

consistent or robust’’ (U.S. EPA, 2009a, 

p. 6–210). Assessing this information, 

the Integrated Science Assessment 

concluded that ‘‘the evidence is not yet 

sufficient to allow differentiation of 

those constituents or sources that are 

more closely related to specific health 

outcomes’’ (U.S. EPA, 2009a, pp. 2–26 

and 6–212). Therefore, the Policy 

Assessment concluded that the 

currently available evidence is not 

sufficient to support consideration of a 

separate indicator for a specific PM2.5

component or group of components 

associated with any source category of 

fine particles. Furthermore, the Policy 

Assessment concluded that the evidence 

is not sufficient to support eliminating 

any component or group of components 

associated with any source categories of 

fine particles from the mix of fine 

particles included in the PM2.5 indicator 

(U.S. EPA, 2011a, p. 2–56). 

The CASAC agreed with the EPA staff 

conclusions presented in the Policy 

Assessment and concluded that it is 

appropriate to consider retaining PM2.5

as the indicator for fine particles and 

further asserted, ‘‘There [is] insufficient 

peer-reviewed literature to support any 

other indicator at this time’’ (Samet, 

2010c, p. 12). CASAC expressed a strong 

desire for the EPA to ‘‘look ahead to 

future review cycles and reinvigorate 

support for the development of evidence 

that might lead to newer indicators that 

may correlate better with the health 

effects associated with ambient air 

concentrations of PM * * *’’ (Samet, 

2010c, p 2). 

Consistent with the staff conclusions 

presented in the Policy Assessment and 

CASAC advice, the Administrator 

proposed to retain PM2.5 as the indicator 

for fine particles. Further, the 

Administrator provisionally concluded 

that currently available scientific 

information does not provide a 

sufficient basis for supplementing massbased, primary fine particle standards 

with standards using a separate 

indicator for ultrafine particles or a 

separate indicator for a specific PM2.5

component or group of components 

associated with any source categories of 

fine particles. In addition, the 

Administrator also provisionally 

concluded that the currently available 

scientific information did not provide a 

sufficient basis for eliminating any 

individual component or group of 

components associated with any source 

categories from the mix of fine particles 

included in the PM2.5 mass-based 

indicator. 

The EPA received comparatively few 

public comments on issues related to 

the indicator for fine particles.65 Some 

commenters emphasized the need to 

conduct additional research to more 

fully understand the effect of specific 

PM2.5 components and/or sources on 

public health. These commenters 

expressed views about the importance 

of evaluating health effect associations 

with various fine particle components 

and types of source categories as a basis 

for focusing ongoing and future research 

to reduce uncertainties in this area and 

for considering whether alternative 

indicator(s) may be appropriate to 

consider in future PM NAAQS reviews 

for standards intended to protect against 

the array of health effects that have been 

associated with fine particles as indexed 

by PM2.5. For example, the PSR 

encouraged more research and 

monitoring related to PM2.5 components 

and noted the importance of 

components associated with coal 

combustion (PSR, 2012, pp. 5 to 6). EPRI 

asserted that ‘‘new’’ studies support 

focusing on EC and OC and encouraged 

the EPA to seriously consider the massbased approach (EPRI, 2012, p. 2). 

Likewise, Georgia Mining Association 

supported additional monitoring and 

research efforts related to PM2.5

composition and specifically 

encouraged the evaluation of using 

particle number (e.g., particle count) 

(GMA, 2012, pp. 2 to 3). 

The Administrator agrees with 

CASAC as well as these commenters 

that the results of additional research 

and monitoring efforts will be helpful 

for informing future PM NAAQS 

reviews. Information from such studies 

could also help inform the development 

of strategies that emphasize control of 

specific types of emission sources so as 

to address particles of greatest concern 

to public health. However, based upon 

the scientific information considered in 

the Integrated Science Assessment as 

well as the public comments 

summarized above, the Administrator 

continues to take note there is evidence 

that many different constituents of the 

fine particle mixture as well as groups 

of components associated with specific 

sources of fine particles are linked to 

adverse health effects. Furthermore, she 

recognizes that the evidence is not yet 

sufficient to differentiate those 

constituents or sources that are most 

closely related to specific health 

outcomes nor to exclude any PM2.5

components or sources of fine particles 

from the mix of particles included in the 

PM2.5 indicator. 

Having considered the public 

comments on this issue, the 

Administrator concurs with the Policy 

Assessment conclusions and CASAC 

recommendations and concludes that it 

is appropriate to retain PM2.5 as the 

indicator for fine particles. 

2. Averaging Time 

In 1997, the EPA initially set both an 

annual standard, to provide protection 

from health effects associated with both 

long- and short-term exposures to PM2.5, 

and a 24-hour standard to supplement 

the protection afforded by the annual 

standard (62 FR 38667 to 38668, July, 

18, 1997). In the last review, the EPA 

retained both annual and 24-hour 

averaging times (71 FR 61164, October 

17, 2006). These decisions were based, 

in part, on evidence of health effects 

related to both long-term (from a year to 

several years) and short-term (from less 

than one day to up to several days) 

measures of PM2.5. 


tkelley on DSK3SPTVN1PROD with 
3124 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

66Spatial averaging as part of the form of the 

annual PM2.5 standard is unique to this standard 

and is not used with other PM standards nor with 

other NAAQS. 

The overwhelming majority of studies 

conducted since the last review 

continue to utilize annual (or multiyear) and 24-hour averaging times, 

reflecting the averaging times of the 

current PM2.5 standards. These studies 

continue to provide evidence that health 

effects are associated with annual and 

24-hour averaging times. Therefore, the 

Policy Assessment concluded it is 

appropriate to retain the current annual 

and 24-hour averaging times to provide 

protection from effects associated with 

both long- and short-term PM2.5

exposures (U.S. EPA, 2011a, p. 2–57). 

In considering whether the 

information available in this review 

supports consideration of different 

averaging times for PM2.5 standards 

specifically with regard to considering a 

standard with an averaging time less 

than 24 hours to address health effects 

associated with sub-daily PM2.5

exposures, the Policy Assessment noted 

there continues to be a growing body of 

studies that provide additional evidence 

of effects associated with exposure 

periods less than 24-hours (U.S. EPA, 

2011a, p. 2–57). Relative to information 

available in the last review, recent 

studies provide additional evidence for 

cardiovascular effects associated with 

sub-daily (e.g., one to several hours) 

exposure to PM, especially effects 

related to cardiac ischemia, vasomotor 

function, and more subtle changes in 

markers of systemic inflammation, 

hemostasis, thrombosis and coagulation 

(U.S. EPA, 2009a, section 6.2). Because 

these studies have used different 

indicators (e.g., PM2.5, PM10, PM10-2.5, 

ultrafine particles), averaging times (e.g., 

1, 2, and 4 hours), and health outcomes, 

it is difficult to draw conclusions about 

cardiovascular effects associated 

specifically with sub-daily exposures to 

PM2.5. 

With regard to respiratory effects 

associated with sub-daily PM2.5

exposures, the currently available 

evidence was much sparser than for 

cardiovascular effects and continues to 

be very limited. The Integrated Science 

Assessment concluded that for several 

studies of hospital admissions or 

medical visits for respiratory diseases, 

the strongest associations were observed 

with 24-hour average or longer 

exposures, not with less than 24-hour 

exposures (U.S. EPA, 2009a, section 

6.3). 

Collectively, the Policy Assessment 

concluded that this information, when 

viewed as a whole, is too unclear, with 

respect to the indicator, averaging time 

and health outcome, to serve as a basis 

for consideration of establishing a 

primary PM2.5 standard with an 

averaging time shorter than 24-hours at 

this time (U.S. EPA, 2011a, p. 2–57). 

With regard to health effects 

associated with PM2.5 exposure across 

varying seasons in this review, Bell et 

al. (2008) reported higher PM2.5 risk 

estimates for hospitalization for 

cardiovascular and respiratory diseases 

in the winter compared to other seasons. 

In comparison to the winter season, 

smaller statistically significant 

associations were also reported between 

PM2.5 and cardiovascular morbidity for 

spring and autumn, and a positive, but 

statistically non-significant association 

was observed for the summer months. In 

the case of mortality, Zanobetti and 

Schwartz (2009) reported a 4-fold higher 

effect estimate for PM2.5-associated 

mortality for the spring as compared to 

the winter. Taken together, these results 

provided emerging but limited evidence 

that individuals may be at greater risk 

of dying from higher exposures to PM2.5

in the warmer months and may be at 

greater risk of PM2.5-associated 

hospitalization for cardiovascular and 

respiratory diseases during colder 

months of the year (U.S. EPA, 2011a, p. 

2–58). 

Overall, the Policy Assessment 

observed that there are few studies 

presently available to deduce a general 

pattern in PM2.5-related risk across 

seasons. In addition, these studies 

utilized 24-hour exposure periods 

within each season to assess the PM2.5- 

associated health effects and do not 

provide information on health effects 

associated with a season-long exposure 

to PM2.5. Due to these limitations in the 

currently available evidence, the Policy 

Assessment concluded that there was no 

basis to consider a seasonal averaging 

time separate from a 24-hour averaging 

time. 

Based on the above considerations, 

the Policy Assessment concluded that 

the currently available information 

provided strong support for 

consideration of retaining the current 

annual and 24-hour averaging times but 

does not provide support for 

considering alternative averaging times 

(U.S. EPA, 2011a, p. 2–58). In addition, 

CASAC considered it appropriate to 

retain the current annual and 24-hour 

averaging times for the primary PM2.5

standards (Samet, 2010c, pp. 2 to 3). At 

the time of the proposal, the 

Administrator concurred with the staff 

conclusions and CASAC advice and 

proposed that the averaging times for 

the primary PM2.5 standards should 

continue to include annual and 24-hour 

averages to protect against health effects 

associated with long- and short-term 

exposures. Furthermore, the 

Administrator provisionally concluded, 

consistent with conclusions reached in 

the Policy Assessment and by CASAC, 

that the currently available information 

was too limited to support consideration 

of alternative averaging times to 

establish a national standard with a 

shorter-than 24-hour averaging time or 

with a seasonal averaging time. 

The EPA received no significant 

public comments on the issue of 

averaging time for the PM2.5 primary 

standards. The Administrator concurs 

with recommendations made by CASAC 

and the staff conclusions presented in 

the Policy Assessment and concludes, 

as proposed, that it is appropriate to 

retain the current annual and 24-hour 

averaging times for the primary PM2.5

standards to protect against health 

effects associated with long- and shortterm exposure periods. 

3. Form 

The ‘‘form’’ of a standard defines the 

air quality statistic that is to be 

compared to the level of the standard in 

determining whether an area attains the 

standard. In this review, the EPA 

considers whether currently available 

information supports retaining or 

revising the forms for the annual or 24- 

hour PM2.5 standards. 

a. Annual Standard 

In 1997, the EPA established the form 

of the annual PM2.5 standard as an 

annual arithmetic mean, averaged over 

3 years, from single or multiple 

community-oriented monitors. This 

form was intended to represent a 

relatively stable measure of air quality 

and to characterize longer-term areawide PM2.5 concentrations, in 

conjunction with a 24-hour standard 

designed to provide adequate protection 

against localized peak or seasonal PM2.5

concentrations. The level of the 

standard was to be compared to 

measurements made at each 

community-oriented monitoring site, or, 

if specific criteria were met, 

measurements from multiple 

community-oriented monitoring sites 

could be averaged (i.e., spatial 

averaging) 66 (62 FR 38671 to 38672, 

July 18, 1997). The constraints were 

intended to ensure that spatial averaging 

would not result in inequities in the 

level of protection provided by the 

standard (62 FR 38672, July 18, 1997). 

This approach was consistent with the 

epidemiological studies on which the 

PM2.5 standard was primarily based, in 

which air quality data were generally 

averaged across multiple monitors in an 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3125 

67As discussed in section VIII.B.1 below, the EPA 

is revising several terms associated with PM2.5

monitor placement. Specifically, the EPA is 

revoking the term ‘‘community-oriented’’ and 

replacing it with the term ‘‘area-wide’’ monitoring. 

68As discussed in section VIII.B.2.b below, the 

EPA concludes that PM2.5 monitoring sites at microand middle-scale locations are comparable to the 

annual standard if the monitoring site has been 

approved by the Regional Administrator as 

representing an area-wide location. 

area or were taken from a single monitor 

that was selected to represent 

community-wide exposures. 

In the last review, the EPA tightened 

the criteria for use of spatial averaging 

to provide increased protection for 

vulnerable populations exposed to 

PM2.5. This change was based in part on 

an analysis of the potential for 

disproportionate impacts on potentially 

at-risk populations, which found that 

the highest concentrations in an area 

tend to be measured at monitors located 

in areas where the surrounding 

population is more likely to have lower 

education and income levels and higher 

percentages of minority populations (71 

FR 61166/2, October 17, 2006; U.S. EPA, 

2005, section 5.3.6.1). 

In this review, as outlined in section 

III.B above and discussed more fully in 

section III.B.3 of the proposal, there now 

exist more health data such that the 

Integrated Science Assessment has 

identified persons from lower 

socioeconomic strata as an at-risk 

population (U.S. EPA, 2009a, section 

8.1.7; U.S. EPA, 2011a, section 2.2.1). 

Moreover, there now exist more years of 

PM2.5 air quality data than were 

available in the last review. 

Consideration in the Policy Assessment 

of the spatial variability across urban 

areas that was revealed by this 

expanded data base has raised questions 

as to whether an annual standard that 

allows for spatial averaging, even within 

specified constraints as narrowed in 

2006 (71 FR 61165 to 61167, October 17, 

2006), would provide appropriate 

public health protection. 

In considering the potential for 

disproportionate impacts on at-risk 

populations, the Policy Assessment 

considered an update of an air quality 

analysis conducted for the last review 

(U.S. EPA, 2011a, pp. 2–59 to 60; 

Schmidt, 2011, Analysis A). This 

analysis focused on determining 

whether the spatial averaging 

provisions, as modified in 2006, could 

introduce inequities in protection for atrisk populations exposed to PM2.5. 

Specifically, the Policy Assessment 

considered whether persons of lower 

socioeconomic status, minority groups, 

or different age groups (i.e., children or 

older adults) are more likely than the 

general population to live in areas in 

which the monitors recording the 

highest air quality values in an area are 

located. Data used in this analysis 

included demographic parameters 

measured at the Census Block or Census 

Block Group level, including percent 

minority population, percent minority 

subgroup population, percent of persons 

living below the poverty level, percent 

of persons 18 years of age or older, and 

percent of persons 65 years of age and 

older. In each candidate geographic 

area, data from the Census Block(s) or 

Census Block Group(s) surrounding the 

location of the monitoring site (as 

delineated by radii buffers of 0.5, 1.0, 

2.0, and 3.0 miles) in which the highest 

air quality value was monitored were 

compared to the average of monitored 

values in the area. This analysis looked 

beyond areas that would meet the 

current spatial averaging criteria and 

considered all urban areas (i.e., Core 

Based Statistical Areas or CBSAs) with 

at least two valid annual design value 

monitors (Schmidt, 2011, Analysis A). 

Recognizing the limitations of such 

cross-sectional analyses, the Policy 

Assessment observed that the highest 

concentrations in an area tend to be 

measured at monitors located in areas 

where the surrounding populations are 

more likely to live below the poverty 

line and to have higher percentage of 

minorities (U.S. EPA, 2011a, p. 2–60). 

Based upon the analysis described 

above, the Policy Assessment concluded 

that the existing constraints on spatial 

averaging, as modified in 2006, may be 

inadequate to avoid substantially greater 

exposures in some areas, potentially 

resulting in disproportionate impacts on 

at-risk populations of persons with 

lower SES levels as well as minorities. 

Therefore, the Policy Assessment 

concluded that it was appropriate to 

consider revising the form of the annual 

PM2.5 standard such that it did not allow 

for the use of spatial averaging across 

monitors. In doing so, the level of the 

annual PM2.5 standard would be 

compared to measurements made at the 

monitoring site that represents areawide air quality recording the highest 

PM2.5 concentrations 67 (U.S. EPA, 

2011a, p. 2–60). 

The CASAC agreed with staff 

conclusions that it was ‘‘reasonable’’ for 

the EPA to eliminate the spatial 

averaging provisions (Samet, 2010d, p. 

2). Further, in CASAC’s comments on 

the first draft Policy Assessment, it 

noted, ‘‘Given mounting evidence 

showing that persons with lower SES 

levels are a susceptible group for PMrelated health risks, CASAC 

recommends that the provisions that 

allow for spatial averaging across 

monitors be eliminated for the reasons 

cited in the (first draft) Policy 

Assessment’’ (Samet, 2010c, p. 13). In 

its review of the second draft Policy 

Assessment, CASAC recognized 

‘‘although much of the epidemiological 

research has been conducted using 

community-wide averages, several key 

studies reference the nearest 

measurement site, so that some risk 

estimates are not necessarily biased by 

the averaging process. Further, the 

number of such studies is likely to 

expand in the future’’ (Samet, 2010d, 

pp. 1 to 2). 

Only two areas in the country used 

the initial spatial averaging provisions 

for demonstrating attainment with the 

primary annual PM2.5 standard set in 

1997 (70 FR 19847, April 14, 2005; U.S. 

EPA, 2006c). Since these provisions 

were tightened in 2006, no area has 

used spatial averaging to demonstrate 

attainment. No areas in the country are 

currently using the spatial averaging 

provisions to demonstrate attainment 

with the current primary annual PM2.5

standard. 

In considering the Policy 

Assessment’s conclusions based on the 

results of the analysis discussed above 

and concern over the evidence of 

potential disproportionate impacts on 

at-risk populations as well as CASAC 

advice, the Administrator proposed to 

revise the form of the annual PM2.5

standard to eliminate the use of spatial 

averaging. Thus, the Administrator 

proposed revising the form of the 

annual PM2.5 standard to compare the 

level of the standard with measurements 

from each ‘‘appropriate’’ monitor in an 

area 68 with no allowance for spatial 

averaging. Thus, for an area with 

multiple monitors, the appropriate 

reporting monitor with the highest 

design value would determine the 

attainment status for that area. 

Of the commenters noted in section 

III.D.2 above who supported a more 

stringent annual PM2.5 standard, those 

who commented on the form of the 

annual PM2.5 standard supported the 

EPA’s proposal to eliminate the spatial 

averaging provisions. These commenters 

contended that the EPA’s analyses of the 

potential impacts of spatial averaging, 

discussed above and in the proposal (77 

FR 38924), demonstrated that the 

current form results in uneven public 

health protection leading to 

disproportionate impacts on at-risk 

populations. Specifically, the ALA and 

other environmental and public health 

commenters contended that ‘‘spatial 

averaging allows exposure of people to 

unhealthy levels of pollution at specific 

locales even within an area meeting the 

standard’’ (ALA et al., 2012, p. 23). 


tkelley on DSK3SPTVN1PROD with 
3126 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

69This is in contrast to the 24-hour standard 

which is designed to provide supplemental 

protection, addressing peak exposures that might 

not otherwise be addressed by the annual standard. 

Consistent with this, monitors are not required to 

be representative of area-wide air quality to be 

compared to the 24-hour standard. 

These commenters particularly focused 

on the importance for low-income and 

minority populations of eliminating the 

spatial averaging provisions. They 

concluded that spatial averaging ‘‘is an 

environmental justice concern because 

poor people are more likely to live near 

roads, depots, factories, ports, and other 

pollution sources.’’ Id. p. 24. 

Other commenters (e.g., AAM, 2012; 

Dow, 2012) also supported the 

elimination of spatial averaging in order 

to ‘‘avoid potential disproportionate 

impacts on at-risk populations’’ and to 

maximize ‘‘the benefits to public health 

of reducing the annual PM2.5 standard.’’ 

However, these groups expressed 

concern that the elimination of spatial 

averaging, in combination with the 

requirement for near road monitors (as 

discussed in section VIII.B.3.b.i of the 

proposal), would effectively and 

inappropriately increase the stringency 

of the annual PM2.5 standard. 

This concern was also shared by other 

commenters who disagreed with the 

elimination of spatial averaging. For 

example, the Class of ’85 RRG 

emphasized concerns about increasing 

the stringency of the standard while 

providing few health benefits if spatial 

averaging is eliminated, particularly in 

combination with the requirement for 

near-road monitors. These commenters 

contended that ‘‘[b]ecause EPA proposes 

to use the readings from the highest 

single worst case monitor (rather than 

the average of all community area 

monitors), and since roadway 

monitoring locations will likely be 

worst case monitors, the proposed 

NAAQS will become more stringent 

without targeting the PM2.5 species most 

harmful to human health’’ (Class of ’85 

RRG, 2012, p. 6). 

Several commenters also maintained 

that because spatial averaging is 

consistent with how air quality data are 

considered in the underlying 

epidemiological studies, such averaging 

should not be eliminated. Specifically, 

commenters including NAM et al., 

AFPM, and ACC pointed out that PM2.5

epidemiological studies use spatially 

averaged multi-monitor concentrations, 

rather than the single highest monitor, 

when evaluating health effects. 

Therefore, these commenters contended 

that allowing spatial averaging would 

make the PM2.5 standard more 

consistent with the approaches used in 

the epidemiological studies upon which 

the standard is based. In addition, some 

commenters also contended that the 

EPA failed to consider whether 

modifying, rather than eliminating, the 

constraints on spatial averaging would 

have been sufficient to protect the 

public health. If so, these commenters 

argued that ‘‘elimination of spatial 

averaging would go beyond what is 

requisite to protect the public health’’ 

(NAM et al., 2012, p. 20). 

In considering the public comments 

on the form of the annual standard, the 

EPA recognizes a number of 

commenters agreed with the basis for 

the EPA’s proposal to eliminate spatial 

averaging. While other commenters 

expressed disagreement or concern with 

the proposed decision to eliminate the 

spatial averaging provisions, the Agency 

notes that these commenters did not 

challenge the analyses or considerations 

that provided the fundamental basis for 

the Administrator’s proposed decision. 

Rather, these commenters generally 

raised concerns that eliminating the 

option for spatial averaging would 

increase the stringency of the standard, 

especially in light of additional 

monitoring sites in near-road 

environments (as discussed in section 

VIII.B.3.b.1 below). 

The EPA does not agree with the 

comment that siting some monitors in 

near roadway environments makes the 

standard more stringent or 

impermissibly more stringent. As 

discussed in section VIII.B.3.b.i below, 

a significant fraction of the population 

lives in proximity to major roads, and 

these exposures occur in locations that 

represent ambient air. Monitoring in 

such areas does not make the standard 

more stringent than warranted, but 

rather affords the intended protection to 

the exposed populations, among them 

at-risk populations, exposed to fine 

particles in these areas. Thus, in cases 

where monitors in near roadway 

environments are deemed to be 

representative of area-wide air quality 

they would be compared to the annual 

standard (as discussed more fully in 

section VIII below). The 24-hour and 

annual NAAQS are designed to protect 

the public with an adequate margin of 

safety, and this siting provision is fully 

consistent with providing the protection 

the standard is designed to provide and 

does not make the standard more 

stringent or more stringent than 

necessary. 

Monitors that are representative of 

area-wide air quality may be compared 

to the annual standard. This is 

consistent with the use of monitoring 

data in the epidemiological studies that 

provide the primary basis for 

determining the level of the annual 

standard. In addition, the EPA notes 

that the annual standard is designed to 

protect against both long- and shortterm exposures through controlling the 

broad distribution of air quality across 

an area over time.69 It is fully consistent 

with the protection the standard is 

designed to provide for near road 

monitors to be compared to the annual 

standard if the monitor is representative 

of area-wide air quality. This does not 

make the standard either more stringent 

or impermissibly more stringent. 

In further considering these 

comments, the EPA notes that the 

stringency or level of protection 

provided by each NAAQS is not based 

solely on the form of the standard; 

rather, the four elements of the standard 

that together serve to define each 

standard (i.e., indicator, averaging time, 

form, and level) must be considered 

collectively in evaluating the protection 

afforded by each standard. Therefore, 

the EPA considers these comments are 

also appropriate to discuss collectively 

with other issues related to the 

appropriate level for annual standard, 

and are discussed below in sections 

III.E.4.c–d. 

In reaching a final decision on the 

form of the annual standard, the 

Administrator considers the available 

analyses, CASAC advice, and public 

comments on form as discussed above. 

She also considers related issues in the 

public comments on the level of the 

annual standard as discussed in section 

III.E.4.c below. She notes that even 

when the annual PM2.5 standard was 

first set in 1997, the spatial averaging 

provisions included constraints 

intended to ensure that inequities in the 

level of protection would not result. 

These constraints on spatial averaging 

were tightened in the last review, based 

on an analysis showing the potential for 

spatial averaging to allow higher PM2.5

concentrations in locations where 

subgroups within the general 

population were potentially 

disproportionately exposed and hence, 

at disproportionate risk (e.g., low 

income and minority communities). The 

Administrator notes that in proposing to 

eliminate spatial averaging altogether in 

this review, she has relied on further 

analyses in the current review (Schmidt, 

2011, Analysis A). As discussed above 

and in the proposal (77 FR 38924), these 

analyses showed that the current 

constraints on spatial averaging may be 

inadequate in some areas to avoid 

substantially greater exposures for 

people living near monitors recording 

the highest PM2.5 concentrations. Such 

exposures could result in 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3127 

70Section VIII.B.3.b.i below discusses public 

comments specifically related to the proposed 

requirement for near-road monitors. 

71 In reaching this final decision, the EPA 

recognized a technical problem associated with a 

potential bias in the method used to calculate the 

98th percentile concentration for this form. The 

EPA adjusted the sampling frequency requirement 

in order to reduce this bias. Accordingly, the 

Agency modified the final monitoring requirements 

such that areas that are within 5 percent of the 

standards are required to increase the sampling 

frequency to every day (71 FR 61164 to 61165, 

October 17, 2006). 

72See ATA III, 283 F.3d at 374–376 which 

concludes that it is legitimate for the EPA to 

consider overall stability of the standard and its 

resulting promotion of overall effectiveness of 

NAAQS control programs in setting a standard that 

is requisite to protect the public health. 

disproportionate impacts to at-risk 

populations, including low-income 

populations as well as minority groups. 

On this basis, the Administrator 

concludes that public health would not 

be protected with an adequate margin of 

safety in all locations, as required by 

law, if disproportionately higher 

exposure concentrations in at-risk 

populations such as low income 

communities as well as minority 

communities were averaged together 

with lower concentrations measured at 

other sites in a large urban area. See 

ALA v. EPA, 134 F. 3d 388, 389 (D.C. 

Cir., 1998) (‘‘this court has held that 

‘NAAQS must protect not only average 

healthy individuals, but also sensitive 

citizens such as children,’ and ‘if a 

pollutant adversely affects the health of 

these sensitive individuals, EPA must 

strengthen the entire national 

standard’’’) and Coalition of Battery 

Recyclers Association v. EPA, 604 F 3d. 

613, 617 (D.C. Cir., 2010) (‘‘Petitioners’ 

assertion that the revised lead NAAQS 

is overprotective because it is more 

stringent than necessary to protect the 

entire population of young U.S. children 

ignores that the Clean Air Act allows 

protection of sensitive 

subpopulations.’’) In reaching this 

conclusion, the Administrator further 

notes that her concern over possible 

disproportionate PM2.5-related health 

impacts in at-risk populations extends 

to populations living near important 

sources of PM2.5, including the large 

populations that live near major 

roadways.70

In light of all of the above 

considerations, including consideration 

of available analyses, CASAC advice, 

and public comments, the 

Administrator concludes that the 

current form of the annual PM2.5

standard should be revised to eliminate 

spatial averaging provisions. Thus, the 

level of the revised annual PM2.5

standard established with this rule will 

be compared with measurements from 

each appropriate monitor in an area, 

with no allowance for spatial averaging. 

The Administrator’s conclusions with 

regard to the appropriate level of the 

annual PM2.5 standard to set in 

conjunction with this form are 

discussed below in section III.E.4.d. 

b. 24-Hour Standard 

In 1997, the EPA established the form 

of the 24-hour PM2.5 standard as the 

98th percentile of 24-hour 

concentrations at each populationoriented monitor within an area, 

averaged over three years (62 FR at 

38671 to 38674, July 18, 1997). The 

Agency selected the 98th percentile as 

an appropriate balance between 

adequately limiting the occurrence of 

peak concentrations and providing 

increased stability which, when 

averaged over 3 years, facilitated 

effective health protection through the 

development of more stable 

implementation programs. By basing the 

form of the standard on concentrations 

measured at population-oriented 

monitoring sites, the EPA intended to 

provide protection for people residing 

in or near localized areas of elevated 

concentrations. In the last review, in 

conjunction with lowering the level of 

the 24-hour standard, the EPA retained 

this form based in part on a comparison 

with the 99th percentile form.71

In revisiting the stability of a 98th 

versus 99th percentile form for a 24- 

hour standard intended to provide 

supplemental protection for a generally 

controlling annual standard, an analysis 

presented in the Policy Assessment 

considered air quality data reported in 

2000 to 2008 to update our 

understanding of the ratio between 

peak-to-mean PM2.5 concentrations. 

This analysis provided evidence that the 

98th percentile value was a more stable 

metric than the 99th percentile (U.S. 

EPA, 2011a, Figure 2–2, p. 2–62). 

At the time of the proposal, the 

Agency recognized that the selection of 

the appropriate form of the 24-hour 

standard includes maintaining adequate 

protection against peak 24-hour 

concentrations while also providing a 

stable target for risk management 

programs, which serves to provide for 

the most effective public health 

protection in the long run.72 As in 

previous reviews, the EPA recognized 

that a concentration-based form, 

compared to an exceedance-based form, 

was more reflective of the health risks 

posed by elevated pollutant 

concentrations because such a form 

gives proportionally greater weight to 

days when concentrations are well 

above the level of the standard than to 

days when the concentrations are just 

above the level of the standard. Further, 

the Agency provisionally concluded 

that a concentration-based form, when 

averaged over three years, provided an 

appropriate balance between limiting 

peak pollutant concentrations and 

providing a stable regulatory target, thus 

facilitating the development of more 

stable implementation programs. 

In considering the information 

provided in the Policy Assessment and 

recognizing that the degree of public 

health protection likely to be afforded 

by a standard is a result of the 

combination of the form and the level of 

the standard, the Administrator 

proposed to retain the 98th percentile 

form of the 24-hour standard. The 

Administrator provisionally concluded 

that the 98th percentile form represents 

an appropriate balance between 

adequately limiting the occurrence of 

peak concentrations and providing 

increased stability relative to an 

alternative 99th percentile form. 

Few public commenters commented 

specifically on the form of the 24-hour 

standard. None of the public 

commenters raised objections to 

continuing the use of a concentrationbased form for the 24-hour standard. 

Many of the individuals and groups 

who supported a more stringent 24-hour 

PM2.5 standard noted in section III.D.2 

above, however, recommended a more 

restrictive concentration-based 

percentile form, specifically a 99th 

percentile form. The limited number of 

these commenters who provided a 

specific rationale for this 

recommendation generally expressed 

their concern that the 98th percentile 

form could allow too many days where 

concentrations exceeded the level of the 

standard, and thus fail to adequately 

protect public health. Other public 

commenters representing state and local 

air agencies and industry groups 

generally supported retaining the 

current 98th percentile form. In most 

cases, these groups expressed the 

overall view that the current 24-hour 

PM2.5 standard, including the form of 

the current standard, should be 

retained. 

The EPA notes that the viewpoints 

represented in this review are similar to 

comments submitted in the last review 

and through various NAAQS reviews. 

The EPA recognizes that the selection of 

the appropriate form includes 

maintaining adequate protection against 

peak 24-hour values while also 

providing a stable target for risk 

management programs, which serves to 

provide for the most effective public 


tkelley on DSK3SPTVN1PROD with 
3128 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

73As just noted above, it is legitimate for the EPA 

to consider promotion of overall effectiveness of 

risk management programs designed to attain the 

NAAQS, including their overall stability, in setting 

a standard that is requisite to protect the public 

health. The context for the court’s discussion in 

ATA III is identical to that here; whether to adopt 

a 98th percentile form for a 24-hour standard 

intended to provide supplemental protection for a 

generally controlling annual standard. 

74Throughout this section, the annual standard 

levels are denoted as integer values for simplicity, 

although, as noted above in section II.B.1, Table 1, 

the annual standard level is defined to one decimal 

place, such that the current annual standard level 

is 15.0 mg/m3. Alternative annual standard levels 

discussed in this section are similarly defined to 

one decimal place. 

health protection in the long run.73

Nothing in the commenters’ views has 

provided a reason to change the 

Administrator’s previous conclusion 

regarding the appropriate balance 

represented in the proposed form of the 

24-hour PM2.5 standard. Therefore, the 

Administrator concurs with staff 

conclusions presented in the Policy 

Assessment and CASAC 

recommendations and concludes that it 

is appropriate to retain the 98th 

percentile form for the 24-hour PM2.5

standard. 

4. Level 

In the last review, the EPA selected 

levels for the annual and the 24-hour 

PM2.5 standards using evidence of 

effects associated with periods of 

exposure that were most closely 

matched to the averaging time of each 

standard. Thus, as discussed in section 

III.A.1, the EPA relied upon evidence 

from long-term exposure studies as the 

principal basis for selecting the level of 

the annual PM2.5 standard that would 

protect against effects associated with 

long-term exposures. The EPA relied 

upon evidence from the short-term 

exposure studies as the principal basis 

for selecting the level of the 24-hour 

PM2.5 standard that would protect 

against effects associated with shortterm exposures. As summarized in 

section III.A.2 above, the 2006 decision 

to retain the level of the annual PM2.5

standard at 15 mg/m3 74 was challenged 

and on judicial review, the DC Circuit 

remanded the primary annual PM2.5

standard to the EPA, finding that EPA’s 

explanation for its approach to setting 

the level of the annual standard was 

inadequate. 

a. General Approach for Considering 

Standard Levels 

Building upon the lessons learned in 

the previous PM NAAQS reviews, in 

considering alternative standard levels 

supported by the currently available 

scientific information, the Policy 

Assessment used an approach that 

integrated evidence-based and riskbased considerations, took into account 

CASAC advice, and considered the 

issues raised by the court in remanding 

the primary annual PM2.5 standard. 

Following the general approach 

outlined in section III.A.3 above, for the 

reasons discussed below, the Policy 

Assessment concluded it was 

appropriate to consider the protection 

afforded by the annual and 24-hour 

standards taken together against 

mortality and morbidity effects 

associated with both long- and shortterm PM2.5 exposures. This was 

consistent with the approach taken in 

the review completed in 1997 rather 

than considering each standard 

separately, as was done in the review 

completed in 2006. 

Beyond looking directly at the 

relevant epidemiologic evidence, the 

Policy Assessment considered the 

extent to which specific alternative 

PM2.5 standard levels were likely to 

reduce the nature and magnitude of 

both long-term exposure-related 

mortality risk and short-term exposurerelated mortality and morbidity risk 

(U.S. EPA, 2011a, section 2.3.4.2; 

U.S.EPA, 2010a, section 4.2.2). As noted 

in section III.C above, patterns of 

increasing estimated risk reductions 

were generally observed as either the 

annual or 24-hour standard, or both, 

were reduced below the level of the 

current standards (U.S. 2011a, Figures 

2–11 and 2–12; U.S. EPA, 2010a, 

sections 4.2.2, 5.2.2, and 5.2.3). 

Based on the quantitative risk 

assessment, the Policy Assessment 

observed, as discussed in section III.A.3, 

that analyses conducted for this and 

previous reviews demonstrated that 

much, if not most, of the aggregate risk 

associated with short-term exposures 

results from the large number of days 

during which the 24-hour average 

concentrations are in the low-to midrange, below the peak 24-hour 

concentrations (U.S. EPA, 2011a, p. 2– 

9). Furthermore, as discussed in section 

III.C above and in section III.C.3 of the 

proposal, the Risk Assessment observed 

that alternative annual standard levels, 

when controlling, resulted in more 

consistent risk reductions across urban 

study areas, thereby potentially 

providing a more consistent degree of 

public health protection (U.S. EPA, 

2010a, pp. 5–15 to 5–16). In contrast, 

the Risk Assessment noted that the 

results of simulating alternative suites of 

PM2.5 standards including different 

combinations of alternative annual and 

24-hour standard levels suggested that 

an alternative 24-hour standard level 

can produce additional estimated risk 

reductions beyond that provided by an 

alternative annual standard alone. 

However, the degree of estimated risk 

reduction provided by alternative 24- 

hour standard levels was highly 

variable, in part due to the choice of 

rollback approached used (U.S. EPA, 

2010a, p. 5–17). 

Based on its review of the second 

draft Policy Assessment, CASAC agreed 

with the EPA staff’s general approach 

for translating the available 

epidemiological evidence, risk 

information, and air quality information 

into the basis for reaching conclusions 

on alternative standards for 

consideration. Furthermore, CASAC 

agreed ‘‘that it is appropriate to return 

to the strategy used in 1997 that 

considers the annual and the short-term 

standards together, with the annual 

standard as the controlling standard, 

and the short-term standard 

supplementing the protection afforded 

by the annual standard’’ and ‘‘considers 

it appropriate to place the greatest 

emphasis’’ on health effects judged to 

have evidence supportive of a causal or 

likely causal relationship as presented 

in the Integrated Science Assessment 

(Samet, 2010d, p. 1). 

Therefore, the Policy Assessment 

concluded, consistent with specific 

CASAC advice, that it was appropriate 

to set a ‘‘generally controlling’’ annual 

standard that will lower a wide range of 

ambient 24-hour concentrations. The 

Policy Assessment concluded this 

approach would likely reduce aggregate 

risks associated with both long- and 

short-term exposures with more 

consistency than a generally controlling 

24-hour standard and would be the most 

effective and efficient way to reduce 

total PM2.5-related population risk and 

so provide appropriate protection. The 

staff believed this approach, in contrast 

to one focusing on a generally 

controlling 24-hour standard, would 

likely reduce aggregate risks associated 

with both long- and short-term 

exposures with more consistency and 

would likely avoid setting national 

standards that could result in relatively 

uneven protection across the country 

due to setting standards that were either 

more or less stringent than necessary in 

different geographical areas. 

The Policy Assessment recognized 

that an annual standard intended to 

serve as the primary means for 

providing protection against effects 

associated with both long- and shortterm PM2.5 exposures cannot be 

expected to offer an adequate margin of 

safety against the effects of all shortterm PM2.5 exposures. As a result, in 

conjunction with a generally controlling 

annual standard, the Policy Assessment 

concluded it was appropriate to 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3129 

consider setting a 24-hour standard to 

provide supplemental protection, 

particularly for areas with high peak-tomean ratios possibly associated with 

strong local or seasonal sources, or 

PM2.5-related effects that may be 

associated with shorter-than-daily 

exposure periods. 

At the time of the proposal, the 

Administrator agreed with the approach 

discussed in the Policy Assessment as 

summarized in section III.A.3 above, 

and supported by CASAC, of 

considering the protection afforded by 

the annual and 24-hour standards taken 

together for mortality and morbidity 

effects associated with both long- and 

short-term exposures to PM2.5. 

Furthermore, based on the evidence and 

quantitative risk assessment, the 

Administrator provisionally concluded 

it was appropriate to set a ‘‘generally 

controlling’’ annual standard that will 

lower a wide range of ambient 24-hour 

concentrations, with a 24-hour standard 

focused on providing supplemental 

protection, particularly for areas with 

high peak-to-mean ratios possibly 

associated with strong local or seasonal 

sources, or PM2.5-related effects that 

may be associated with shorter-than 

daily exposure periods. The 

Administrator provisionally concluded 

this approach would likely reduce 

aggregate risks associated with both 

long- and short-term exposures more 

consistently than a generally controlling 

24-hour standard and would be the most 

effective and efficient way to reduce 

total PM2–5-related population risk. 

The Administrator is mindful that 

considering what standards are requisite 

to protect public health with an 

adequate margin of safety requires 

public health policy judgments that 

neither overstate nor understate the 

strength and limitations of the evidence 

or the appropriate inferences to be 

drawn from the evidence. At the time of 

the proposal, in considering how to 

translate the available information into 

appropriate standard levels, the 

Administrator weighed the available 

scientific information and associated 

uncertainties and limitations. For the 

purpose of determining what standard 

levels were appropriate to propose, the 

Administrator recognized, as did the 

EPA staff in the Policy Assessment, that 

there was no single factor or criterion 

that comprised the ‘‘correct’’ approach 

to weighing the various types of 

available evidence and information, but 

rather there were various approaches 

that were appropriate to consider. The 

Administrator further recognized that 

different evaluations of the evidence 

and other information before the 

Administrator could reflect placing 

different weight on the relative strengths 

and limitations of the scientific 

information, and different judgments 

could be made as to how such 

information should appropriately be 

used in making public health policy 

decisions on standard levels. This 

recognition led the Administrator to 

consider various approaches to 

weighing the evidence so as to identify 

appropriate standard levels to propose. 

In so doing, the Administrator 

encouraged extensive public comment 

on alternative approaches to weighing 

the evidence and other information so 

as to inform her public health policy 

judgments before reaching final 

decisions on appropriate standard 

levels. 

b. Proposed Decisions on Standard 

Levels 

i. Consideration of the Alternative 

Standard Levels in the Policy 

Assessment 

In recognizing the absence of a 

discernible population threshold below 

which effects would not occur, the 

Policy Assessment’s general approach 

for identifying alternative annual 

standard levels that were appropriate to 

consider focused on characterizing the 

part of the distribution of PM2.5

concentrations in which we had the 

most confidence in the associations 

reported in the epidemiological studies 

and conversely where our confidence in 

the association became appreciably 

lower. The most direct approach to 

address this issue, consistent with 

CASAC advice (Samet, 2010c, p. 10), 

was to consider epidemiological studies 

reporting confidence intervals around 

concentration-response relationships 

(U.S. EPA, 2011a, p. 2–63). Based on a 

thorough search of the available 

evidence, the Policy Assessment 

identified only one study (Schwartz et 

al., 2008) that conducted a multi-model 

analysis to characterize confidence 

intervals around the estimated 

concentration-response relationship. 

The Policy Assessment concluded that 

this single relevant analysis was too 

limited to serve as the principal basis 

for identifying alternative standard 

levels in this review (U.S. EPA, 2011a, 

p. 2–70). 

The Policy Assessment explored other 

approaches to characterize the part of 

the distributions of long-term mean 

PM2.5 concentrations that were most 

influential in generating health effect 

estimates in long- and short-term 

epidemiological studies, and placed 

greatest weight on those studies that 

reported positive and statistically 

significant associations (U.S. EPA, 

2011a, p. 2–63). First, as discussed in 

section III.A.3 above, the Policy 

Assessment considered the statistical 

metric used in previous reviews. This 

approach recognized the EPA’s views 

that the strongest evidence of 

associations occurs at concentrations 

around the long-term mean 

concentration. Thus, in earlier reviews, 

the EPA focused on identifying standard 

levels that were somewhat below the 

long-term mean concentrations reported 

in PM2.5 epidemiological studies. The 

long-term mean concentrations 

represented air quality data typically 

used in epidemiological analyses and 

provided a direct link between PM2.5

concentrations and the observed health 

effects. Further, these data were 

available for all long- and short-term 

exposure studies analyzed and, 

therefore, represented the data set 

available for the broadest set of 

epidemiological studies. 


tkelley on DSK3SPTVN1PROD with 
3130 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

75While CASAC expressed the view that it would 

be most desirable to have information on 

concentration-response relationships, they 

recognized that it would also be ‘‘preferable to have 

information on the concentrations that were most 

influential in generating the health effect estimates 

in individual studies’’ (Samet, 2010d, p. 2). 

76 In the last review, staff believed it was 

appropriate to consider a level for an annual PM2.5

standard that was somewhat below the averages of 

the long-term concentrations across the cities in 

each of the key long-term exposures studies, 

recognizing that the evidence of an association in 

any such study was strongest at and around the 

long-term average where the data in the study are 

most concentrated. For example, the interquartile 

range of long-term average concentrations within a 

study and a range within one standard deviation 

around the study mean were considered reasonable 

approaches for characterizing the range over which 

the evidence of association is strongest (U.S. EPA, 

2005, pp. 5–22 to 5–23). In this review, the Policy 

Assessment noted the interrelatedness of the 

distributional statistics and a range of one standard 

deviation around the mean which contains 

approximately 68 percent of normally distributed 

data, in that one standard deviation below the mean 

falls between the 25th and 10th percentiles (U.S. 

EPA, 2011a, p. 2–71). 

77The distributional statistical analysis of 

population-level data built upon an earlier analysis 

that evaluated the distributions of air quality and 

associated population data for three long-term 

exposure studies and three short-term exposure 

studies (Schmidt et al., 2010, Analysis 2). 

78Additional studies presented and assessed in 

the Integrated Science Assessment report effects at 

higher long-term mean PM2.5 concentrations (e.g., 

U.S. EPA, 2009a, Figures 2–1, 2–2, 7–6, and 7–7). 

79The long-term mean PM2.5 concentrations 

reported by the study authors for the Miller et al. 

(2007) and Lipfert et al. (2006a) studies are 

discussed more fully in the Response to Comments 

document (U.S. EPA, 2012a). 

However, consistent with CASAC’s 

comments on the second draft Policy 

Assessment 75 (Samet, 2010d, p. 2), in 

preparing the final Policy Assessment, 

the EPA staff explored ways to take into 

account additional information from 

epidemiological studies, when available 

(Rajan et al., 2011). These analyses 

focused on evaluating different 

statistical metrics, beyond the long-term 

mean concentration, to characterize the 

part of the distribution of PM2.5

concentrations in which staff continued 

to have confidence in the associations 

observed in epidemiological studies and 

below which there was a comparative 

lack of data such that the staff’s 

confidence in the relationship was 

appreciably less. This would also be the 

part of the distribution of PM2.5

concentrations which had the most 

influence on generating the health effect 

estimates reported in epidemiological 

studies. As discussed in section III.A.3 

above, the Policy Assessment 

recognized there was no one percentile 

value within a given distribution that 

was the most appropriate or ‘‘correct’’ 

way to characterize where our 

confidence in the associations becomes 

appreciably lower. The Policy 

Assessment concluded that focusing on 

concentrations within the lower quartile 

of a distribution, such as the range from 

the 25th to the 10th percentile, was 

reasonable to consider as a region 

within which we begin to have 

appreciably less confidence in the 

associations observed in 

epidemiological studies.76 In the EPA 

staff’s view, considering lower PM2.5

concentrations, down to the lowest 

concentration observed in a study, 

would be a highly uncertain basis for 

selecting alternative standard levels 

(U.S. EPA, 2009a, p. 2–71). 

As outlined in section III.A.3 above, 

the Policy Assessment recognized that 

there were two types of population-level 

information to consider in identifying 

the range of PM2.5 concentrations which 

have the most influence on generating 

the health effect estimates reported in 

epidemiological studies. The most 

relevant information to consider was the 

number of health events (e.g., deaths, 

hospitalizations) occurring within a 

study population in relation to the 

distribution of PM2.5 concentrations 

likely experienced by study 

participants. However, in recognizing 

that access to health event data may be 

restricted, and consistent with advice 

from CASAC (Samet 2010d, p. 2), EPA 

staff also considered the number of 

participants within each study area, in 

relation to the distribution of PM2.5

concentrations (i.e., study population 

data), as a surrogate for health event 

data. 

In applying this approach, the Policy 

Assessment focused on identifying the 

part of the distribution of PM2.5

concentrations which had the most 

influence on generating health effect 

estimates in epidemiological studies, as 

discussed in section III.A.3 above. As 

discussed below, in working with study 

investigators, the EPA staff was able to 

obtain health event data for three large 

multi-city studies (Krewski et al., 2009; 

Zanobetti and Schwartz, 2009; Bell et 

al., 2008) and population data for the 

same three studies and one additional 

long-term exposure study (Miller et al., 

2007), as documented in a staff 

memorandum (Rajan et al., 2011).77 For 

the three studies for which both health 

event and study population data were 

available, the EPA staff analyzed the 

reliability of using study population 

data as a surrogate for health event data. 

Based on these analyses, the EPA staff 

recognized that the 10th and 25th 

percentiles of the health event and 

study population distributions are 

nearly identical and concluded that the 

distribution of population data can be a 

useful surrogate for event data, 

providing support for consideration of 

the study population data for Miller et 

al. (2007), for which health event data 

were not available (Rajan et al., 2011, 

Analysis 1 and Analysis 2, in particular, 

Table 1 and Figures 1 and 2). 

With regard to the long-term mean 

PM2.5 concentrations which are relevant 

to the first approach, Figures 1 through 

3 (U.S. EPA, 2011a, Figures 2–4, 2–5, 2– 

6, and 2–8) summarize data available for 

multi-city, long- and short-term 

exposure studies that evaluated 

endpoints classified in the Integrated 

Science Assessment as having evidence 

of a causal or likely causal relationship 

or evidence suggestive of a causal 

relationship, showing the studies with 

long-term mean PM2.5 concentrations 

below 17 mg/m3.78 As discussed in more 

detail in section III.E.4.b of the proposal, 

Figures 1 and 3 summarize the health 

outcomes evaluated, relative risk 

estimates, air quality data, and 

geographic scope for long- and shortterm exposure studies, respectively, that 

evaluated mortality (evidence of a 

causal relationship); cardiovascular 

effects (evidence of a causal 

relationship); and respiratory effects 

(evidence of a likely causal relationship) 

in the general population, as well as in 

older adults, an at-risk population. 

Figure 2 provides this same summary 

information for long-term exposure 

studies that evaluated respiratory effects 

(evidence of a likely causal relationship) 

in children, an at-risk population, as 

well as developmental effects (evidence 

suggestive of a causal relationship). 


tkelley on DSK3SPTVN1PROD with 

ER15JA13.000</GPH>tkelley on DSK3SPTVN1PROD with 

Figure 1. Summary of Effect Estimates (per 10 Ilg/m3) and Air Quality Distributions for Multi-City, Lon

Studies of the General Population and Older Adults 79 

YursofAir Air Qualilv Data 

StudJ Cite QuaII1y Endpoint Author Rtported DatI 

Data Meani-;S· RqI 

AIIevD 

WHI Milet at at (2007) 36UScilie& 2000 IncidentMl 12:9" 102 3.4-28.3 RevascuIa!izati 

SbnIIe. 

CSVD 

... 

11.8-15.9 CystIc FIbrosis GeIss etaL (2004)" 2000 131 9.5 (lOR) 

MorIaIily-iiD Acs.ReanaJp1s II (2(M)9) 1999-2000 14.0 11.0 .5.8-22 MorWIy-CPD 

t.bfaIity-lung caooer 

VA etaL (2IlOO) tli!99-2001 1'.btaIIy4 cause 14.3 11.3 5.0-1 

MorIaIty-CV 

!,aden etal. (200&) 1979"1_ 16 .• 10.8 10-22 

OfderA.dt* 

10.+185 MCAPS-wutem US Ztger et at (2008) 62US 00UIIIies 2.000-2005 MortaII;y4 cause 13.1d . (lOR} 

Mecllcare-ACS Ellin et at (2008) 51USMSM 2.000-2002 MortaII;y4 cause 13.8 10B tto.25.1 

12.3-15.3 Zeger et aI. (2OOtl) 421 US QOI.IIlies 2.000-2005 MutaIy4 cause 14.00 - (ICIR) 

MedIcare .sea E1II'il et at (2001) BOOGIes 2.000-2002 MoItIIy-aI cause 14.1 11.0 9.6-19.1 

"'lIefetlll (2001) PMo.a4ala included ill CUrl. 2OQ9 

OCoIlortifldu4ed1 andokl\et. mean .: 18.4)Q 

'EsIimated fIOmdaia proIIided by 8I\idy author (I..aden. 2009) "Median (IQR: In!erq\IIa.tilutlhge); <MlI81II.IS repo!Ied median (IQR.) of 13.2 f.9m" (11.144.9. 

Source: U.S. EPA, 20lla, Figure 2-4 

Effect Estimate !

, 

I 

, 

, • • : . 

I 

. 

I • 

• 

. • • 

I 

· • i • I-· • I 

I 

· , • • ,.* , 

I .-- • 

,-I , 

• 

I • 

------

I 

, , 

: • 

, 

II! 

, , . 

I 

:. 

• 

. 

, ....... 

os 1 1.2 1.4 

ER15JA13.001</GPH>tkelley on DSK3SPTVN1PROD with 

Figure 2. Summary of Effect Estimates (per 10 Jlglm3) and Air Quality Distributions for Multi-City, Long

Studies of Children 

Children 

Study Cite Geographic Years of Air QuaJity Endpoint Air Quality Data (pgIm3) Area Data Mean Mean- Effect Estimat

1SD Range 

I 

Belletal. 199&-2002 Low Birth Weight 10.3 I GT,MA 11.9" I (2007) I • 

I 

IUGR -1nd !rimester I r---

I 

Uuetal. IUGR -2M trimester I 

(2007) 3 Canadian cities 1.985-1999 12.2 - 0.3-15 :-

I 

IUGR - Jrdtrimester I r---

I 

Pal1<erand 10.9-16.1. I I COntinental US 2000-2003 Low arrth Weight - paR) ----,-- I 

I 

McConneDet 12GOOlmunmes - Bronchilic I SCACHS 1996-1999 13.8 6.1 6,.29 1 al. (2003) seA symptoms I • I 

I 

24 COIJ1rnunmes- I 24-Cities 198&-1991 Bronchitis 14:5 10.3 5.&-20.7 I (1 1 us, Canada I • I" 

I 

Wootlrulf at ai. 96 US counties 1999-2002 Infant mortatity 14.9b 12.0-18Jl I {2008} - (IQR) .--- I 

'Ges!ationaI.lTII!aII 

ilMedian for all cause mmtali\y; median (IQR:interquarlile range) forSUtviVOlS = 14.8 (11.7 -18.7) pglm3• Exposure period was first 2 months of life. (J.B 1 1.2 1.4 1.6 

Source: U.S. EPA, 20lla, Figure 2-5 
With regard to consideration of 

additional information from relevant to the second approach, the 

epidemiological studies which was 

range of PM

EPA staff compiled a summary of the 

2.5 concentrations 


ER15JA13.002</GPH>tkelley on DSK3SPTVN1PROD with 

Figure 3. Summary of Effect Estimates (per 10 Jlg/m3) and Air Quality Distributions for Multi-City, Sh

Studies of the General Population and Older Adults 

Years of 

Study/Cite Geographic AirQualily Endpoint Area Data 

Burnett at aI. (2004) 12 Carman Cities 1981-1999 NonaccidenIaI 

Zaoobe!ti & SdlwW: (2009) 112 US coonties 1999-2005 

Bumett& Goldberg (2003) 8 Garman Cities 1986-1986 Nonaooidenlal moIWrty 

Halvard and Mason 

6USciIies 

(Nodheast/ 1979-1988 

MKMesI) 

Franldfn et al. (2008) 25 US 2000-2005 NonacckIenIaI oomllU1ilies lI'ICfIaIiIy 

Franldfn et at (2007) 1991-2002 

CVOHA 

MCAPSIBeII et aI. (2008) 202 US counties 1999-2005 RespHA 

IHOHA 

GHFHA 

Dysrhythmia HA 

MCAPSJDominici etal. 2006 204 US counties 1999-2002 CBVDHA 

PVDHA 

COPDHA 

RfIHA 

O' Connor (2008) 7USCities 1998-2001 Wheeze/Cough 

- - --- - ---_ ... _-_ .. _----------------_._--------- - - -- --- ---- - ---- -- ------- -_ .. _--

oEahl11ed from deta provided by study author or publi!lhed study 

loQIiml11ed from coefficient of varielion reported in original wdy by Burnett lit .1. (2000) 

<Mean value not reported In eIiIdy. median presented from original sIudy by Schwartz eI al. (1996) 

"MCAPS cohort i'lc:kIded adulls;;, 65 J!S; O'Connor (2(08) cohort ineluded !:himn. mean age: 7.7 yr,I 

lOR: inillrquarlile range 

Air QualitY Data (ulll'm!) E1fect Estimate 

A.uthor Reported Data 

Mean 1';- Range 

General Population 

12.8 - - 38.0 

13.2- 10.30 6.6-24.7 34.3 

13.3 3.91 . 38.9" 

-

9-23 14.7· · (lOR) . 

---

14.80 · 9.9-27.'" 43.0 

-

15.6- - 8.8-23.9 45.8 

Older AduIIsfCIIiIdre. 

12.9- 102- 4-20 342 

-

f--. 

f--o--

13 .• 10,50 4-23 34.8 

-

14.0 · - 39.0-

-------------

OwU 0_ ... t '

Source: U.S. EPA, 20lla, Figure 2-6 
3134 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

80The EPA staff obtained health event data (e.g., 

number of deaths, hospitalizations) occurring in a 

study population for three multi-city studies 

(Krewski et al., 2009; Zanobetti and Schwartz, 2009; 

Bell et al., 2008) and study population data were 

obtained for the same three studies and one 

additional study (Miller et al., 2007) (U.S. EPA, 

2011a, p. 2–71). If health event or study population 

data were available for additional studies, the EPA 

could employ distributional statistics to identify the 

broader range of PM2.5 concentrations that were 

most influential in generating health effect 

estimates in those studies. 

81Long- and short-term exposure studies 

considered ‘‘key’’ studies for consideration are 

summarized in Figure 4 and include those studies 

observing effects for which the evidence supported 

a causal or likely causal association. This figure 

represents the subset of multi-city studies included 

in Figures 1 through 3 that provided evidence of 

positive and generally statistically significant 

effects associated in whole or in part with more 

recent air quality data, generally representing health 

effects associated with lower PM2.5 concentrations 

than had previously been considered in the last 

review. The EPA notes that many of these studies 

evaluated multiple health endpoints, and not all of 

the effects evaluated provided evidence of positive 

and statistically significant effects. For purposes of 

informing the Administrator’s decision on the 

appropriate standard levels, the Agency considers 

the full body of scientific evidence and focuses on 

those aspects of the key studies that provided 

evidence of positive and generally statistically 

significant effects. 

82The long-term mean PM2.5 concentrations 

reported by the study authors for the Miller et al. 

(2007) and Lipfert et al. (2006a) studies are 

discussed more fully in the Response to Comments 

document (U.S. EPA, 2012a). 

corresponding with the 25th to 10th 

percentiles of health event or study 

population data from the four multi-city 

studies, for which distributional 

statistics are available 80 (U.S. EPA, 

2011a, Figure 2–7; Rajan et al., 2011, 

Table 1). By considering this approach, 

one could focus on the range of PM2.5

concentrations below the long-term 

mean ambient concentrations over 

which we continue to have confidence 

in the associations observed in 

epidemiological studies (e.g., above the 

25th percentile) where commensurate 

public health protection could be 

obtained for PM2.5-related effects and, 

conversely, identify the range in the 

distribution below which our 

confidence in the associations is 

appreciably less, to identify alternative 

annual standard levels. 

The mean PM2.5 concentrations 

associated with the studies summarized 

in Figures 1, 2, and 3 and with the 

distributional statistics analyses (Rajan 

et al., 2011) are based on concentrations 

averaged across ambient monitors 

within each area included in a given 

study and then averaged across study 

areas to calculate an overall study mean 

concentration, as discussed above. 

Figure 4, discussed in more detail in 

section III.E.4.a of the proposal, 

summarizes statistical metrics for those 

key studies 81 included in Figures 1, 2, 

and 3 that provide evidence of positive 

and generally statistically significant 

PM2.5-related effects, which are relevant 

to the two approaches for translating 

epidemiological evidence into potential 

standard levels as discussed above. The 

top of Figure 4 includes information for 

long-term exposure studies evaluating 

health outcomes classified as having 

evidence of a causal or likely causal 

relationship with PM2.5 exposures (longterm mean PM2.5 concentrations 

indicated by diamond symbols). The 

middle of Figure 4 includes information 

for short-term exposure studies 

evaluating health outcomes classified as 

having evidence of a causal or likely 

causal relationship with PM2.5

exposures (long-term mean PM2.5

concentrations indicated by triangle 

symbols). The bottom of Figure 4 

includes information for long-term 

exposures studies evaluating health 

outcomes classified as having evidence 

suggestive of a causal relationship 

(long-term mean PM2.5 concentrations 

indicated by square symbols). Figure 4 

also summarizes the range of PM2.5

concentrations corresponding with the 

25th (indicated by solid circles) to 10th 

(indicated by open circles) percentiles 

of the health event or study population 

data from the four multi-city studies 

(highlighted in bold text) for which 

distributional statistics are available. 


tkelley on DSK3SPTVN1PROD with 
In considering the evidence, the 

provide requisite protection, neither 

NAAQS are standards set so as to 

Policy Assessment recognized that 

judgment, ultimately made by the 

adequate margin of safety. This 

to protect public health, with an 

more nor less stringent than necessary 

that evidence. Therefore, depending on 

inherent uncertainties and limitations of 

strength of the evidence and the 

Administrator, involves weighing the 


ER15JA13.003</GPH>tkelley on DSK3SPTVN1PROD with 

Figure 4. Translating Epidemiological Evidence from Multi-City Exposure Studies into a

Standard82 

Causal / likely Causa! - Long-Term Exposure Studies 

Miller et al., 2007 (WHI, 36 cities) 

Eltim 200$ (MCAP$oAC$ $Ite$. 110 _nIIe$) 

GOA et aI •• 2004 (Cydo Flbfosis) 

McCon ..... et aI. 2003; Oaudenna" et ..... 2004 (S CA CHS. 12 comm ... llies) 

Krewsklillt aI., 2009 (ACS-Reanaly$ls II. 116 MSAs) 

Zeger <It at. 2008 (MCAP&Ea&I, 421 counlle$) 

Eftim et aI •• 2008 {MCAPS-HaMVd Six 0II:ie$ 1IiIe$} 

\.ipfeIt <It .... 2008 study) 

et 81 .. RoIinnne <It aI .. 19V!1 (2+CiIiiII$ study 

Laden "I 81.. 2006 (Harvard Six CiIies) 

Causal/Likely Causal - Short· Term Exposure Studies 

IIumeIt et ..... 2004 (12 Ca_ CiIies) 

Bel, .. al •• 2008 {MCAPS. 202 counties, 

ZtU10betti & SChWartz, 2009 (112 cities) 

Sumett " Goldberg. 2003 (8 Cal1OOdia" cities} 

DominICi et 81 .. 2008 (MCAPS. 204 ¢OunIIe$j 

Klemm & Mason, 2003 (HlllVllrd Sloe Ci!ies) 

Franldin et aL. 2008 (25 us cities> FllInkIin 2IlO7 (27 US ..... ) 

SUggestive· Long-Term Exposure Sludies 

Bell et at. 2007 {low 

IJI.t 2007 (lUGRl 

WoodruII <It at .. 2008 (lnNnt moIlaIity) 

-AddItional studies report effecls at higher long-term mean concentrations -More limited and mixed evidence is available from single-Oty, $lhort-tann exposure studies with Iong..tenn maen concentrations below 15 \.Ig/IW 

""' 

v 

9 10 

- 4 ....., 

• • • • • • • • 

.. 

- j 

- .. 

.. 

A 

.& 

.. 

.& 

• I. 

I • 

11 12 13 14 15 

Long-term mean PM2.5 concentration (lJglm3) 

Source: U.S. EPA, 20lla, Figure 2-8 

Level of c

.. 

• 

16 17 
3136 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

the weight placed on different aspects of 

the evidence and inherent uncertainties, 

consideration of different alternative 

standard levels could be supported. 

Given the currently available 

evidence discussed in more detail in 

section III.E.4.b of the proposal and 

considering the various approaches 

discussed above, the Policy Assessment 

concluded it was appropriate to focus 

on an annual standard level within a 

range of about 12 to 11 mg/m3 (U.S. EPA, 

2011a, pp. 2–82, 2–101, and 2–106). As 

illustrated in Figure 4, the Policy 

Assessment recognized that a standard 

level of 12 mg/m3, at the upper end of 

this range, was somewhat below the 

long-term mean PM2.5 concentrations 

reported in all the multi-city, long- and 

short-term exposure studies that 

provided evidence of positive and 

statistically significant associations with 

health effects classified as having 

evidence of a causal or likely causal 

relationship, including premature 

mortality and hospitalizations and 

emergency department visits for 

cardiovascular and respiratory effects as 

well as respiratory effects in children. 

Further, a level of 12 mg/m3 would 

reflect consideration of additional 

population-level information from such 

epidemiological studies in that it 

generally corresponded with 

approximately the 25th percentile of the 

available distributions of health events 

data in the studies for which 

population-level information was 

available. In addition, a level of 12 mg/ 

m3 would reflect some consideration of 

studies that provided more limited 

evidence of reproductive and 

developmental effects, which were 

suggestive of a causal relationship, in 

that it was about at the same level as the 

lowest long-term mean PM2.5

concentrations reported in such studies 

(see Figure 4). 

Alternatively the Policy Assessment 

recognized that an annual standard level 

of 11 mg/m3, at the lower end of this 

range, was well below the lowest longterm mean PM2.5 concentrations 

reported in all multi-city long- and 

short-term exposure studies that provide 

evidence of positive and statistically 

significant associations with health 

effects classified as having evidence of 

a causal or likely causal relationship. A 

level of 11 mg/m3 would reflect placing 

more weight on the distributions of 

health event and population data, in 

that this level was within the range of 

PM2.5 concentrations corresponding to 

the 25th and 10th percentiles of all the 

available distributions of such data. In 

addition, a level of 11 mg/m3 was 

somewhat below the lowest long-term 

mean PM2.5 concentrations reported in 

reproductive and developmental effects 

studies that are suggestive of a causal 

relationship. Thus, a level of 11 mg/m3

would reflect an approach to translating 

the available evidence that places 

relatively more emphasis on margin of 

safety considerations and less certain 

causal relationships than would a 

standard set at a higher level. Such a 

policy approach would tend to weigh 

uncertainties in the evidence in such a 

way as to avoid potentially 

underestimating PM2.5-related risks to 

public health. Further, recognizing the 

uncertainties inherent in identifying any 

particular point at which our confidence 

in reported associations becomes 

appreciably less, the Policy Assessment 

concluded that the available evidence 

did not provide a sufficient basis to 

consider alternative annual standard 

levels below 11 mg/m3 (U.S. EPA, 2011a, 

p. 2–81). 

The Policy Assessment also 

considered the extent to which the 

available evidence provided a basis for 

considering alternative annual standard 

levels above 12 mg/m3. As discussed 

below, the Policy Assessment 

concluded that it could be reasonable to 

consider a standard level up to 13 mg/ 

m3 based on a policy approach that 

weighed uncertainties in the evidence 

in such a way as to avoid potentially 

overestimating PM2.5-related risks to 

public health, especially to the extent 

that primary emphasis was placed on 

long-term exposure studies as a basis for 

an annual standard level. A level of 13 

mg/m3 was somewhat below the longterm mean PM2.5 concentrations 

reported in all but one of the long-term 

exposure studies providing evidence of 

positive and statistically significant 

associations with PM2.5-related health 

effects classified as having a causal or 

likely causal relationship. As shown in 

Figure 4, the one long-term exposure 

study with a long-term mean PM2.5

concentration just below 13 mg/m3 was 

the Miller et al., (2007) study. However, 

as noted in section III.D.1.a of the 

proposal and discussed in more detail 

in the Response to Comments 

document, the Policy Assessment 

observed that in comparison to other 

long-term exposure studies, the Miller et 

al. study was more limited in that it was 

based on only one year of air quality 

data and the one year was after the 

health outcomes were reported (U.S. 

EPA, 2011a, pp. 2–81 to 2–82). Thus, to 

the extent that less weight was placed 

on the Miller et al. study than on other 

long-term exposure studies with more 

robust air quality data, a level of 13 mg/ 

m3 could be considered as being 

protective of long-term exposure related 

effects classified as having a causal or 

likely causal relationship. In also 

considering short-term exposure 

studies, however, the Policy Assessment 

noted that a level of 13 mg/m3 was below 

the long-term mean PM2.5

concentrations reported in most but not 

all such studies. In particular, two 

studies—Burnett et al. (2004) and Bell et 

al. (2008)—reported long-term mean 

PM2.5 concentrations of 12.8 and 12.9 

mg/m3, respectively. In considering 

these studies, the Policy Assessment 

found no basis to conclude that these 

two studies were any more limited or 

uncertain than the other short-term 

exposure studies shown in Figures 3 

and 4 (U.S. EPA, 2011a, p. 2–82). On 

this basis, as discussed below, the 

Policy Assessment concluded that 

consideration of an annual standard 

level of 13 mg/m3 would have 

implications for the degree of protection 

that would need to be provided by the 

24-hour standard, in order that the suite 

of PM2.5 standards, taken together, 

would provide appropriate protection 

from effects on public health related to 

short-term exposure to PM2.5 (U.S. EPA, 

2011a, p. 2–82). 

The Policy Assessment also noted that 

a standard level of 13 mg/m3 would 

reflect a judgment that the uncertainties 

in the epidemiological evidence as 

summarized in section III.B above and 

discussed in more detail in section 

III.B.2 of the proposal, including 

uncertainties related to the 

heterogeneity observed in the 

epidemiological studies in the eastern 

versus western parts of the U.S., the 

relative toxicity of PM2.5 components, 

and the potential role of co-pollutants, 

are too great to warrant placing any 

weight on the distributions of health 

event and population data that extend 

down below the long-term mean 

concentrations into the lower quartile of 

the data. This level would also reflect a 

judgment that the evidence from 

reproductive and developmental effects 

studies that is suggestive of a causal 

relationship was too uncertain to 

support consideration of any lower 

level. 

Beyond evidence-based 

considerations, the Policy Assessment 

also considered the extent to which the 

quantitative risk assessment supported 

consideration of these alternative 

standard levels or provided support for 

lower levels. In considering simulations 

of just meeting alternative annual 

standard levels within the range of 13 to 

11 mg/m3 (in conjunction with the 

current 24-hour standard level of 35 mg/ 

m3), the Policy Assessment concluded 

that important public health 

improvements are associated with risk 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3137 

reductions estimated for standard levels 

of 13 and 12 mg/m3 and noted that the 

level of 11 mg/m3 was not included in 

the quantitative risk assessment. The 

Policy Assessment noted that the overall 

confidence in the quantitative risk 

estimates varied for the different 

alternative standard levels evaluated 

and was stronger for the higher levels 

and substantially lower for the lowest 

level evaluated (i.e., 10 mg/m3). Based 

on the above considerations, the Policy 

Assessment concluded that the 

quantitative risk assessment provided 

support for considering alternative 

annual standard levels within a range of 

13 to 11 mg/m3, but did not provide 

strong support for considering lower 

alternative standard levels (U.S. EPA, 

2011a, pp. 2–102 to 2–103). 

Taken together, the Policy Assessment 

concluded that consideration of 

alternative annual standard levels in the 

range of 13 to 11 mg/m3 may be 

appropriate. Furthermore, the Policy 

Assessment concluded that the 

currently available evidence most 

strongly supported consideration of an 

alternative annual standard level in the 

range of 12 to 11 mg/m3 (U.S. EPA, 

2011a, p. 2–82). The Policy Assessment 

concluded that an alternative level 

within the range of 12 to 11 mg/m3

would more fully take into 

consideration the available information 

from all long- and short-term PM2.5

exposure studies, including studies of 

at-risk populations, than would a higher 

level. This range also reflected placing 

weight on information from studies that 

helped to characterize the range of PM2.5

concentrations over which we continue 

to have confidence in the associations 

observed in epidemiological studies, as 

well as the extent to which our 

confidence in the associations was 

appreciably less at lower 

concentrations. 

As recognized in sections III.A.3 and 

III.E.4.a above, an annual standard 

intended to serve as the primary means 

for providing protection from effects 

associated with both long- and shortterm PM2.5 exposures is not expected to 

provide appropriate protection against 

the effects of all short-term PM2.5

exposures (unless established at a level 

so low as to undoubtedly provide more 

protection than necessary for long-term 

exposures). Of particular concern are 

areas with high peak-to-mean ratios 

possibly associated with strong local or 

seasonal sources, or PM2.5-related effects 

that may be associated with shorterthan-daily exposure periods. As a result, 

the Policy Assessment concluded that it 

was appropriate to consider alternative 

24-hour PM2.5 standard levels that 

would supplement the protection 

provided by an annual standard. 

As outlined in section III.A.3 above, 

the Policy Assessment considered the 

available evidence from short-term 

PM2.5 exposure studies, as well as the 

uncertainties and limitations in that 

evidence, to assess the degree to which 

alternative annual and 24-hour PM2.5

standards can be expected to reduce the 

estimated risks attributed to short-term 

fine particle exposures. In considering 

the available epidemiological evidence, 

the Policy Assessment took into account 

information from multi-city studies as 

well as single-city studies. The Policy 

Assessment considered the distributions 

of 24-hour PM2.5 concentrations 

reported in short-term exposure studies, 

focusing on the 98th percentile 

concentrations to match the form of the 

24-hour standard as discussed in section 

III.E.3.b above. In recognizing that the 

annual and 24-hour standards work 

together to provide protection from 

effects associated with short-term PM2.5

exposures, the Policy Assessment also 

considered information on the long-term 

mean PM2.5 concentrations from these 

studies. 

In addition to considering the 

epidemiological evidence, the Policy 

Assessment considered air quality 

information, specifically peak-to-mean 

ratios using county-level 24-hour and 

annual design values, to characterize air 

quality patterns in areas possibly 

associated with strong local or seasonal 

sources. These patterns helped in 

understanding the extent to which 

different combinations of annual and 

24-hour standards would be consistent 

with the policy goal of setting a 

generally controlling annual standard 

with a 24-hour standard that provides 

supplemental protection especially for 

areas with high peak-to-mean ratios 

(U.S. EPA, 2011a, p. 2–14). 

In considering the information 

provided by the short-term exposure 

studies, the Policy Assessment 

recognized that to the extent these 

studies were conducted in areas that 

likely did not meet one or both of the 

current standards, such studies did not 

help inform the characterization of the 

potential public health improvements of 

alternative standards set at lower levels. 

Therefore, in considering the short-term 

exposure studies to inform staff 

conclusions regarding levels of the 24- 

hour standard that are appropriate to 

consider, the Policy Assessment placed 

greatest weight on studies conducted in 

areas that likely met both the current 

annual and 24-hour standards. 

With regard to multi-city studies that 

evaluated effects associated with shortterm PM2.5 exposures, as summarized in 

Figure 3 above and discussed in more 

detail in section III.E.4.c of the proposal, 

the Policy Assessment noted that, to the 

extent air quality distributions were 

reduced to reflect just meeting the 

current 24-hour standard, additional 

protection would be anticipated for the 

effects observed in the three multi-city 

studies with 98th percentile values 

greater than 35 mg/m3 (Burnett et al., 

2004; Burnett and Goldberg, 2003; 

Franklin et al., 2008). In the three 

additional studies with 98th percentile 

values below 35 mg/m3, specifically 98th 

percentile concentrations of 34.2, 34.3, 

and 34.8 mg/m3, the Policy Assessment 

noted that these studies reported longterm mean PM2.5 concentrations of 12.9, 

13.2, and 13.4 mg/m3, respectively (Bell 

et al., 2008; Zanobetti and Schwartz, 

2009; Dominici et al., 2006a). To the 

extent that consideration was given to 

revising the level of the annual 

standard, as discussed in section 

III.E.4.b of the proposal, the Policy 

Assessment recognized that potential 

changes associated with meeting such 

an alternative annual standard would 

result in lowering risks associated with 

both long- and short-term PM2.5

exposures. Consequently, in considering 

a 24-hour standard that would operate 

in conjunction with an annual standard 

to provide appropriate public health 

protection, the Policy Assessment noted 

that to the extent that the level of the 

annual standard was revised to within 

a range of 13 to 11 mg/m3, in particular 

in the range of 12 to 11 mg/m3, 

additional protection would be 

provided for the long-term effects 

observed in these multi-city studies 

(U.S. EPA, 2011a, p. 2–84). 

Based on this information, the Policy 

Assessment concluded that the multicity, short-term exposure studies 

generally provided support for retaining 

the 24-hour standard level at 35 mg/m3

so long as the standard is in conjunction 

with an annual standard level revised to 

within a range of 12 to 11 mg/m3 (U.S. 

EPA, 2011a, p. 2–84). Alternatively, in 

conjunction with an annual standard 

level of 13 mg/m3, the Policy Assessment 

concluded that the multi-city studies 

provided limited support for revising 

the 24-hour standard level somewhat 

below 35 mg/m3, such as down to 30 mg/ 

m3, based on one study (Bell et al., 

2008) that reported positive and 

statistically significant effects with an 

overall 98th percentile value below the 

level of the current 24-hour standard 

and an overall long-term mean 

concentration slightly less than 13 mg/ 

m3 (Figure 3; U.S. EPA, 2011a, p. 2–84). 

In reaching staff conclusions 

regarding alternative 24-hour standard 

levels that were appropriate to consider, 


tkelley on DSK3SPTVN1PROD with 
3138 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

the Policy Assessment also took into 

account relevant information from 

single-city studies that evaluated effects 

associated with short-term PM2.5

exposures. The Policy Assessment 

recognized that these studies may 

provide additional insights regarding 

impacts on at-risk populations and/or 

on areas with isolated peak 

concentrations. 

As discussed in more detail in section 

III.E.4.c of the proposal, although a 

number of single-city studies reported 

effects at appreciably lower PM2.5

concentrations than multi-city shortterm exposure studies, the uncertainties 

and limitations associated with the 

single-city studies were considerably 

greater than those associated with the 

multi-city studies and, thus, the Policy 

Assessment concluded there was less 

confidence in using these studies as a 

basis for setting the level of a standard. 

Therefore, the Policy Assessment 

concluded that the multi-city short-term 

exposure studies provided the strongest 

evidence to inform decisions on the 

level of the 24-hour standard, and the 

single-city studies did not warrant 

consideration of 24-hour standard levels 

different from those supported by the 

multi-city studies (U.S. EPA, 2011a, p. 

2–88). 

In addition to considering the 

epidemiological evidence, the Policy 

Assessment took into account air quality 

information based on county-level 24- 

hour and annual design values to 

understand the public health 

implications of the alternative standard 

levels supported by the currently 

available scientific evidence, as 

discussed in this section. Consistent 

with the general approach discussed in 

section III.A.3 above, the Policy 

Assessment considered the extent to 

which different combinations of 

alternative annual and 24-hour standard 

levels based on the evidence would 

support the policy goal of lowering 

annual and 24-hour air quality 

distributions by using the annual 

standard to be the ‘‘generally 

controlling’’ standard in conjunction 

with setting the 24-hour standard to 

provide supplemental protection (U.S. 

EPA, 2011a, pp 2–88 to 2–91, Figure 2– 

10). 

Using information on the relationship 

of the 24-hour and annual design 

values, the Policy Assessment examined 

the implications of three alternative 

suites of PM2.5 standards identified as 

appropriate to consider based on the 

currently available scientific evidence, 

as discussed above. The Policy 

Assessment concluded that an 

alternative suite of PM2.5 standards that 

would include an annual standard level 

of 11 or 12 mg/m3 and a 24-hour 

standard with a level of 35 mg/m3 (i.e., 

11/35 or 12/35) would result in the 

annual standard being the generally 

controlling standard in most areas 

although the 24-hour standard would 

continue to be the generally controlling 

standard in the Northwest (U.S. EPA, 

2011a, pp. 2–89 to 2–91 and Figure 2– 

10). These Northwest counties generally 

represented areas where the annual 

mean PM2.5 concentrations have 

historically been low but where 

relatively high 24-hour concentrations 

occur, often related to seasonal wood 

smoke emissions. Alternatively, 

combining an alternative annual 

standard of 13 mg/m3 with a 24-hour 

standard of 30 mg/m3 would result in 

many more areas across the country in 

which the 24-hour standard would 

likely become the controlling standard 

(the standard driving air quality 

distributions lower) than if an 

alternative annual standard of 12 or 11 

mg/m3 were paired with the current 

level of the 24-hour standard (i.e., 35 mg/ 

m3). 

The Policy Assessment concluded 

that consideration of retaining the 24- 

hour standard level at 35 mg/m3 would 

reflect placing greatest weight on 

evidence from multi-city studies that 

reported positive and statistically 

significant associations with health 

effects classified as having a causal or 

likely causal relationship. In 

conjunction with lowering the annual 

standard level, especially within a range 

of 12 to 11 mg/m3, this alternative 

recognized additional public health 

protection against effects associated 

with short-term PM2.5 exposures which 

would be provided by lowering the 

annual standard such that revision to 

the 24-hour standard would not be 

warranted (U.S. EPA, 2011a, p. 2–91). 

Beyond evidence-based 

considerations, the Policy Assessment 

also considered the extent to which the 

quantitative risk assessment supported 

consideration of retaining the current 

24-hour standard level or provided 

support for lower standard levels. In 

considering simulations of just meeting 

the current 24-hour standard level of 35 

mg/m3 or alternative levels of 30 or 25 

mg/m3 (in conjunction with alternative 

annual standard levels within a range of 

13 to 11 mg/m3), the Policy Assessment 

noted that the overall confidence in the 

quantitative risk estimates varied for the 

different standard levels evaluated and 

was stronger for the higher levels and 

substantially lower for the lowest level 

evaluated (i.e., 25 mg/m3). Based on this 

information, the Policy Assessment 

concluded that the quantitative risk 

assessment provided support for 

considering a 24-hour standard level of 

35 or 30 mg/m3 (in conjunction with an 

alternative standard level within a range 

of 13 to 11 mg/m3) but did not provide 

strong support for considering lower 

alternative 24-hour standard levels (U.S. 

EPA, 2011a, pp. 2–102 to 2–103). 

Taken together, the Policy Assessment 

concluded that while it was appropriate 

to consider an alternative 24-hour 

standard level within a range of 35 to 30 

mg/m3, the currently available evidence 

most strongly supported consideration 

for retaining the current 24-hour 

standard level at 35 mg/m3 in 

conjunction with lowering the level of 

the annual standard within a range of 12 

to 11 mg/m3 (U.S. EPA, 2011a, p. 2–92). 

ii. CASAC Advice 

Based on its review of the second 

draft Policy Assessment, CASAC agreed 

with the general approach for 

translating the available epidemiological 

evidence, risk information, and air 

quality information into the basis for 

reaching conclusions on alternative 

standards for consideration. 

Furthermore, CASAC agreed ‘‘that it is 

appropriate to return to the strategy 

used in 1997 that considers the annual 

and the short-term standards together, 

with the annual standard as the 

controlling standard, and the short-term 

standard supplementing the protection 

afforded by the annual standard’’ and 

‘‘considers it appropriate to place the 

greatest emphasis’’ on health effects 

judged to have evidence supportive of a 

causal or likely causal relationship as 

presented in the Integrated Science 

Assessment (Samet, 2010d, p. 1). 

CASAC concluded that the range of 

levels presented in the second draft 

Policy Assessment (i.e., alternative 

annual standard levels within a range of 

13 to 11 mg/m3 and alternative 24-hour 

standard levels within a range of 35 to 

30 mg/m3) ‘‘are supported by the 

epidemiological and toxicological 

evidence, as well as by the risk and air 

quality information compiled’’ in the 

Integrated Science Assessment, Risk 

Assessment, and second draft Policy 

Assessment. CASAC further noted that 

‘‘[a]lthough there is increasing 

uncertainty at lower levels, there is no 

evidence of a threshold (i.e., a level 

below which there is no risk for adverse 

health effects)’’ (Samet, 2010d, p. ii). 

Although CASAC supported the 

alternative standard level ranges 

presented in the second draft Policy 

Assessment, it did not express support 

for any specific levels or combinations 

of standards. Rather, CASAC 

encouraged the EPA to develop a clearer 

rationale in the final Policy Assessment 

for staff conclusions regarding annual 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3139 

and 24-hour standards that were 

appropriate to consider, including 

consideration of the combination of 

these standards supported by the 

available information (Samet, 2010d, p. 

ii). Specifically, in commenting on a 

distributional statistical analysis of air 

quality and associated population data 

presented in the second draft Policy 

Assessment, CASAC encouraged staff to 

focus on information related to the 

concentrations that were most 

influential in generating the health 

effect estimates in individual studies to 

inform alternative standard levels. 

CASAC urged that the EPA redo that 

analysis using health event or study 

population data (Samet, 2010d, p. 2). 

CASAC also commented that the 

approach presented in the second draft 

Policy Assessment to identify 

alternative 24-hour standard levels 

which focused on peak-to-mean ratios 

was not relevant for informing the 

actual level (Samet 2010d, p. 4). 

Further, they expressed the concern that 

the combinations of annual and 24-hour 

standard levels discussed in the second 

draft Policy Assessment (i.e., in the 

range of 13 to 11 mg/m3 for the annual 

standard, in conjunction with retaining 

the current 24-hour PM2.5 standard level 

of 35 mg/m3; alternatively, revising the 

level of the 24-hour standard to 30 mg/ 

m3 in conjunction with an annual 

standard level of 11 mg/m3) ‘‘may not be 

adequately inclusive’’ and ‘‘[i]t was not 

clear why, for example a daily standard 

of 30 mg/m3 should only be considered 

in combination with an annual level of 

11 mg/m3’’ (Samet, 2010d, p. ii). CASAC 

encouraged the EPA to more clearly 

explain its rationale for identifying the 

24-hour/annual combinations that are 

appropriate for consideration (Samet 

2010d, p. ii). 

In considering CASAC’s advice as 

well as public comment on the second 

draft Policy Assessment, the EPA staff 

conducted additional analyses and 

modified their conclusions regarding 

alternative standard levels that were 

appropriate to consider. The staff 

conclusions in the final Policy 

Assessment (U.S. EPA, 2011a, section 

2.3.4.4) differed somewhat from the 

alternative standard levels discussed in 

the second draft Policy Assessment 

(U.S. EPA, 2010f, section 2.3.4.3), upon 

which CASAC based its advice. Changes 

made in the final Policy Assessment 

were primarily focused on improving 

and clarifying the approach for 

translating the epidemiological evidence 

into a basis for staff conclusions on the 

broadest range of alternative standard 

levels supported by the available 

scientific information and more clearly 

articulating the rationale for the staff’s 

conclusions (Wegman, 2011, pp. 1 to 2). 

Consistent with CASAC’s advice to 

consider more information from 

epidemiological studies, as discussed in 

section III.E.4.b.1 above, the EPA 

analyzed additional population-level 

data obtained from several study 

authors (Rajan et al., 2011). In 

transmitting the final Policy Assessment 

to CASAC, the Agency notified CASAC 

that the final staff conclusions reflected 

consideration of CASAC’s advice and 

that those staff conclusions were based, 

in part, on the specific distributional 

analysis that CASAC had urged the EPA 

to conduct (Wegman, 2011, p.2). Thus, 

CASAC had an opportunity to comment 

on the final Policy Assessment, but 

chose not to provide any additional 

comments or advice after receiving it. 

iii. Administrator’s Proposed Decisions 

on the Primary PM2.5 Standard Levels 

In reaching her conclusions regarding 

appropriate alternative standard levels 

to consider, the Administrator 

considered the epidemiological and 

other scientific evidence, estimates of 

risk reductions associated with just 

meeting alternative annual and/or 24- 

hour standards, air quality analyses, 

related limitations and uncertainties, 

staff conclusions as presented in the 

Policy Assessment, and the advice of 

CASAC. As an initial matter, the 

Administrator agreed with the general 

approach discussed in the Policy 

Assessment as summarized in sections 

III.A.3 and III.E.4.a above, and 

supported by CASAC, of considering the 

protection afforded by the annual and 

24-hour standards taken together for 

mortality and morbidity effects 

associated with both long- and shortterm exposures to PM2.5 (77 FR 38939). 

Furthermore, based on the evidence and 

quantitative risk assessment, the 

Administrator provisionally concluded 

it is appropriate to set a ‘‘generally 

controlling’’ annual standard that will 

lower a wide range of ambient 24-hour 

concentrations, with a 24-hour standard 

focused on providing supplemental 

protection, particularly for areas with 

high peak-to-mean ratios possibly 

associated with strong local or seasonal 

sources, or PM2.5-related effects that 

may be associated with shorter-than 

daily exposure periods. The 

Administrator provisionally concluded 

this approach would likely reduce 

aggregate risks associated with both 

long- and short-term exposures more 

consistently than a generally controlling 

24-hour standard and would be the most 

effective and efficient way to reduce 

total PM2.5-related population risk. Id. 

In reaching decisions on alternative 

standard levels to propose, the 

Administrator judged that it was most 

appropriate to examine where the 

evidence of associations observed in the 

epidemiological studies was strongest 

and, conversely, where she had 

appreciably less confidence in the 

associations observed in the 

epidemiological studies. Based on the 

characterization and assessment of the 

epidemiological and other studies 

presented and assessed in the Integrated 

Science Assessment and the Policy 

Assessment, the Administrator 

recognized the substantial increase in 

the number and diversity of studies 

available in this review including 

extended analyses of the seminal 

studies of long-term PM2.5 exposures 

(i.e., ACS and Harvard Six Cities 

studies) as well as important new longterm exposure studies (as summarized 

in Figures 1 and 2). Collectively, the 

Administrator noted that these studies, 

along with evidence available in the last 

review, provided consistent and 

stronger evidence of an association with 

premature mortality, with the strongest 

evidence related to cardiovascularrelated mortality, at lower ambient 

concentrations than previously 

observed. The Administrator also 

recognized the availability of stronger 

evidence of morbidity effects associated 

with long-term PM2.5 exposures, 

including evidence of cardiovascular 

effects from the WHI study and 

respiratory effects, including decreased 

lung function growth, from the extended 

analyses for the Southern California 

Children’s Health Study. Furthermore, 

the Administrator recognized new U.S. 

multi-city studies that greatly expanded 

and reinforced our understanding of 

mortality and morbidity effects 

associated with short-term PM2.5

exposures, providing stronger evidence 

of associations at ambient 

concentrations similar to those 

previously observed (as summarized in 

Figure 3). Id. at 38939–40. 

The newly available scientific 

evidence built upon the previous 

scientific data base to provide evidence 

of generally robust associations and to 

provide a basis for greater confidence in 

the reported associations than in the last 

review. The Administrator recognized 

that the weight of evidence, as evaluated 

in the Integrated Science Assessment, 

was strongest for health endpoints 

classified as having evidence of a causal 

relationship. These relationships 

included those between long- and shortterm PM2.5 exposures and mortality and 

cardiovascular effects. She recognized 

that the weight of evidence was also 


tkelley on DSK3SPTVN1PROD with 
3140 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

83The EPA notes that the Miller et al., (2007) 

study provides strong evidence of cardiovascular 

related effects associated with long-term PM2.5

exposures. At the time of the proposal, the EPA 

recognized the limited nature of the air quality data 

considered in this study (77 FR 38918, fn. 62). The 

EPA has reviewed those limitations, in conjunction 

with consideration of public comments received on 

the proposal as discussed in section III.E.4.c, in 

conjunction with reaching a final decision on the 

level of the annual standard. 

84With respect to suggestive evidence related to 

cancer, mutagenic, and genotoxic effects, the PM2.5

concentrations reported in studies generally 

included ambient concentrations that are equal to 

or greater than ambient concentrations observed in 

studies that reported mortality and cardiovascular 

and respiratory effects (U.S. EPA, 2009a, section 

7.5), such that in selecting alternative standard 

levels that provide protection from mortality and 

cardiovascular and respiratory effects, it is 

reasonable to anticipate that protection will also be 

provided for carcinogenic effects. 

strong for health endpoints classified as 

having evidence of a likely causal 

relationship, which included those 

between long- and short-term PM2.5

exposures and respiratory effects. In 

addition, the Administrator made note 

of the much more limited evidence for 

health endpoints classified as having 

evidence suggestive of a causal 

relationship, including developmental, 

reproductive and carcinogenic effects. 

Id. at 38940. 

Based on information discussed and 

presented in the Integrated Science 

Assessment, the Administrator 

recognized that health effects may occur 

over the full range of concentrations 

observed in the long- and short-term 

epidemiological studies and that no 

discernible threshold for any effects can 

be identified based on the currently 

available evidence (U.S. EPA, 2009a, 

section 2.4.3). She also recognized, in 

taking note of CASAC advice and the 

distributional statistics analysis 

discussed in section III.E.4.b.i above and 

in the Policy Assessment, that there was 

significantly greater confidence in 

observed associations over certain parts 

of the air quality distributions in the 

studies, and conversely, that there was 

significantly diminished confidence in 

ascribing effects to concentrations 

toward the lower part of the 

distributions. 

Consistent with the general approach 

summarized in section III.A.3 above, 

and supported by CASAC as discussed 

in section III.E.4.a above, the 

Administrator generally agreed that it 

was appropriate to consider a level for 

an annual standard that was somewhat 

below the long-term mean PM2.5

concentrations reported in long- and 

short-term exposure studies. In 

recognizing that the evidence of an 

association in any such study was 

strongest at and around the long-term 

average where the data in the study are 

most concentrated, she understood that 

this approach did not provide a bright 

line for reaching decisions about 

appropriate standard levels. The 

Administrator noted that long-term 

mean PM2.5 concentrations were 

available for each study considered and, 

therefore, represented the most robust 

data set to inform her decisions on 

appropriate annual standard levels. She 

also noted that the overall study mean 

PM2.5 concentrations were generally 

calculated based on monitored 

concentrations averaged across monitors 

in each study area with multiple 

monitors, referred to as a composite 

monitor concentration, in contrast to the 

highest concentration monitored in each 

study area, referred to as a maximum 

monitor concentration, which are used 

to determine whether an area meets a 

given standard. In considering such 

long-term mean concentrations, the 

Administrator understood that it was 

appropriate to consider the weight of 

evidence for the health endpoints 

evaluated in such studies in giving 

weight to this information. Id. 

Based on the information summarized 

in Figure 4 above and presented in more 

detail in the Policy Assessment (U.S. 

EPA, 2011a, chapter 2) for effects 

classified in the Integrated Science 

Assessment as having a causal or likely 

causal relationship with PM2.5

exposures, the Administrator observed 

an overall pattern of statistically 

significant associations reported in 

studies of long-term PM2.5 exposures 

with long-term mean concentrations 

ranging from somewhat above the 

current standard level of 15 mg/m3 down 

to the lowest mean concentration in 

such studies of 12.9 mg/m3 (in Miller et 

al., 2007).83 She observed a similar 

pattern of statistically significant 

associations in studies of short-term 

PM2.5 exposures with long-term mean 

concentrations ranging from around 15 

mg/m3 down to 12.8 mg/m3 (in Burnett 

et al., 2004). With regard to effects 

classified as providing evidence 

suggestive of a causal relationship, the 

Administrator observed a small number 

of long-term exposure studies related to 

developmental and reproductive effects 

that reported statistically significant 

associations with overall study mean 

PM2.5 concentrations down to 11.9 mg/ 

m3 (in Bell et al., 2007).84 Id. 

The Administrator also considered 

additional information from 

epidemiological studies, consistent with 

CASAC advice, to take into account the 

broader distribution of PM2.5

concentrations and the degree of 

confidence in the observed associations 

over the broader air quality distribution. 

In considering this additional 

information, she understood that the 

Policy Assessment presented 

information on the 25th and 10th 

percentiles of the distributions of PM2.5

concentrations available from four 

multi-city studies to provide a general 

frame of reference as to the part of the 

distribution in which the data become 

appreciably more sparse and, thus, 

where her confidence in the 

associations observed in 

epidemiological studies would become 

appreciably less. 

As summarized in Figure 4 above, the 

Administrator took note of additional 

population-level data that were 

available for four studies (Krewski et al., 

2009; Miller et al., 2007; Bell et al., 

2008; Zanobetti and Schwartz, 2009), 

each of which reported statistically 

significant associations with health 

endpoints classified as having evidence 

of a causal relationship. In considering 

the long-term PM2.5 concentrations 

associated with the 25th percentile 

values of the population-level data for 

these four studies, she observed that 

these values ranged from somewhat 

above to somewhat below 12 mg/m3. The 

Administrator recognized that these 

studies include some of the strongest 

evidence available within the overall 

body of scientific evidence and noted 

that three of these studies (Krewski et 

al., 2009; Bell et al., 2008; Zanobetti and 

Schwartz, 2009) were used as the basis 

for concentration-response functions 

used in the quantitative risk assessment 

(U.S. EPA, 2010a, section 3.3.3). 

In considering this information, the 

Administrator noted that CASAC 

advised that information about the longterm PM2.5 concentrations that were 

most influential in generating the health 

effect estimates in epidemiological 

studies can help to inform selection of 

an appropriate annual standard level. 

However, the Administrator also 

recognized that additional populationlevel data were available for only these 

four studies and, therefore, she believed 

that these studies comprised a more 

limited data set than one based on longterm mean PM2.5 concentrations for 

which data were available for all studies 

considered, as discussed above. 

The Administrator recognized, as 

summarized in section III.B above, that 

important uncertainties remain in the 

evidence and information considered in 

this review of the primary fine particle 

standards. These uncertainties are 

generally related to understanding the 

relative toxicity of the different 

components in the fine particle mixture, 

the role of PM2.5 in the complex ambient 

mixture, exposure measurement errors 

inherent in epidemiological studies 

based on concentrations measured at 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3141 

fixed monitor sites, and the nature, 

magnitude, and confidence in estimated 

risks related to increasingly lower 

ambient PM2.5 concentrations. 

Furthermore, the Administrator noted 

that epidemiological studies have 

reported heterogeneity in responses 

both within and between cities and 

geographic regions across the U.S. She 

recognized that this heterogeneity may 

be attributed, in part, to differences in 

fine particle composition in different 

regions and cities. The Administrator 

also recognized that there are additional 

limitations associated with evidence for 

reproductive and developmental effects, 

identified as being suggestive of a causal 

relationship with long-term PM2.5

exposures, including: the limited 

number of studies evaluating such 

effects; uncertainties related to 

identifying the relevant exposure time 

periods of concern; and limited 

toxicological evidence providing little 

information on the mode of action(s) or 

biological plausibility for an association 

between long-term PM2.5 exposures and 

adverse birth outcomes. Id. at 38941. 

The Administrator was mindful that 

considering what standards were 

requisite to protect public health with 

an adequate margin of safety required 

public health policy judgments that 

neither overstated nor understated the 

strength and limitations of the evidence 

or the appropriate inferences to be 

drawn from the evidence. In considering 

how to translate the available 

information into appropriate standard 

levels, the Administrator weighed the 

available scientific information and 

associated uncertainties and limitations. 

For the purpose of determining what 

standard levels were appropriate to 

propose, the Administrator recognized, 

as did EPA staff in the Policy 

Assessment, that there was no single 

factor or criterion that comprised the 

sole ‘‘correct’’ approach to weighing the 

various types of available evidence and 

information, but rather there were 

various approaches that are appropriate 

to consider. The Administrator further 

recognized that different evaluations of 

the evidence and other information 

before the Administrator could reflect 

placing different weight on the relative 

strengths and limitations of the 

scientific information, and different 

judgments could be made as to how 

such information should appropriately 

be used in making public health policy 

decisions on standard levels. This 

recognition led the Administrator to 

consider various approaches to 

weighing the evidence so as to identify 

appropriate standard levels to propose. 

In so doing, the Administrator 

encouraged extensive public comment 

on alternative approaches to weighing 

the evidence and other information so 

as to inform her public health policy 

judgments before reaching final 

decisions on appropriate standard 

levels. 

In considering the available 

information, the Administrator noted 

the advice of CASAC that the currently 

available scientific information, 

including epidemiological and 

toxicological evidence as well as risk 

and air quality information, provided 

support for considering an annual 

standard level within a range of 13 to 11 

mg/m3 and a 24-hour standard level 

within a range of 35 to 30 mg/m3. In 

addition, the Administrator recognized 

that the Policy Assessment concluded 

that the available evidence and riskbased information support 

consideration of annual standard levels 

in the range of 13 to 11 mg/m3, and that 

the Policy Assessment also concluded 

that the evidence most strongly 

supported consideration of an annual 

standard level in the range of 12 to 11 

mg/m3. In considering how the annual 

and 24-hour standards work together to 

provide appropriate public health 

protection, the Administrator observed 

that CASAC did not express support for 

any specific levels or combinations of 

standards within these ranges. Nor did 

CASAC choose to comment on 

additional information and analyses 

presented in the final Policy Assessment 

prepared in response to CASAC’s 

recommendations on the second draft 

Policy Assessment (Wegman, 2011). 

In considering the extent to which the 

currently available evidence and 

information provided support for 

specific standard levels within the 

ranges identified by CASAC and the 

Policy Assessment as appropriate for 

consideration, the Administrator 

initially considered standard levels 

within the range of 13 to 11 mg/m3 for 

the annual standard. In so doing, the 

Administrator first considered the longterm mean PM2.5 concentrations 

reported in studies of effects classified 

as having evidence of a causal or likely 

causal relationship, as summarized in 

Figure 4 above and discussed more 

broadly above. She noted that a level at 

the upper end of this range would be 

below most but not all the overall study 

mean concentrations from the multi-city 

studies of long- and short-term 

exposures, whereas somewhat lower 

levels within this range would be below 

all such overall study mean 

concentrations. In considering the 

appropriate weight to place on this 

information, the Administrator again 

noted that the evidence of an 

association in any such study was 

strongest at and around the long-term 

average where the data in the study are 

most concentrated, and that long-term 

mean PM2.5 concentrations were 

available for each study considered and, 

therefore, represented the most robust 

data set to inform her decisions on 

appropriate annual standard levels. 

Further, she was mindful that this 

approach did not provide a bright line 

for reaching decisions about appropriate 

standard levels. Id. 

In considering the long-term mean 

PM2.5 concentrations reported in studies 

of effects classified as having evidence 

suggestive of a causal relationship, as 

summarized in Figure 4 for reproductive 

and developmental effects, the 

Administrator noted that a level at the 

upper end of this range would be below 

the overall study mean concentration in 

one of the three studies, while levels in 

the mid- to lower part of this range 

would be below the overall study mean 

concentrations in two or three of these 

studies. In considering the appropriate 

weight to place on this information, the 

Administrator noted the very limited 

nature of this evidence of such effects 

and the additional uncertainties in these 

epidemiological studies relative to the 

studies that provide evidence of causal 

or likely causal relationships. 

The Administrator also considered 

the distributional analyses of 

population-level information that were 

available from four of the 

epidemiological studies that provide 

evidence of effects identified as having 

a causal relationship with long- or shortterm PM2.5 concentrations for annual 

standard levels within the same range of 

13 to 11 mg/m3. In so doing, the 

Administrator first noted that a level in 

the mid-part of this range generally 

corresponds with approximately the 

25th percentile of the distributions of 

health events data available in three of 

these studies. The Administrator also 

noted that standard levels toward the 

upper part of this range would reflect 

placing substantially less weight on this 

information, whereas standard levels 

toward the lower part of this range 

would reflect placing substantially more 

weight on this information. In 

considering this information, the 

Administrator noted that there was no 

bright line that delineates the part of the 

distribution of PM2.5 concentrations 

within which the data become 

appreciably more sparse and, thus, 

where her confidence in the 

associations observed in 

epidemiological studies became 

appreciably less. 

In considering mean PM2.5

concentrations and distributional 


tkelley on DSK3SPTVN1PROD with 
3142 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

analyses from the various sets of 

epidemiological studies noted above, 

the Administrator was mindful, as noted 

above, that such studies typically report 

concentrations based on composite 

monitor distributions, in which 

concentrations may be averaged across 

multiple ambient monitors that may be 

present within each area included in a 

given study. Thus, a policy approach 

that used data based on composite 

monitors to identify potential 

alternative standard levels would 

inherently build in a margin of safety of 

some degree relative to an alternative 

standard level based on measurements 

at the monitor within an area that 

records the highest concentration, or the 

maximum monitor, since once a 

standard was set, concentrations at 

appropriate maximum monitors within 

an area were generally used to 

determine whether an area meets a 

given standard. 

The Administrator also recognized 

that judgments about the appropriate 

weight to place on any of the factors 

discussed above should reflect 

consideration not only of the relative 

strength of the evidence but also on the 

important uncertainties that remained 

in the evidence and information being 

considered in this review. The 

Administrator noted that the extent to 

which these uncertainties influenced 

judgments about appropriate annual 

standard levels within the range of 13 to 

11 mg/m3 would likely be greater for 

standard levels in the lower part of this 

range which would necessarily be based 

on fewer available studies than would 

higher levels within this range. 

Based on the above considerations, 

the Administrator concluded that it was 

appropriate to propose to set a level for 

the primary annual PM2.5 standard 

within the range of 12 to 13 mg/m3. The 

Administrator provisionally concluded 

that a standard set within this range 

would reflect alternative approaches to 

appropriately placing the most weight 

on the strongest available evidence, 

while placing less weight on much more 

limited evidence and on more uncertain 

analyses of information available from a 

relatively small number of studies. 

Further, she provisionally concluded 

that a standard level within this range 

would reflect alternative approaches to 

appropriately providing an adequate 

margin of safety for the populations at 

risk for the serious health effects 

classified as having evidence of a causal 

or likely causal relationship, depending 

in part on the emphasis placed on 

margin of safety considerations. The 

Administrator recognized that setting an 

annual standard level at the lower end 

of this range would reflect an approach 

that placed more emphasis on the entire 

body of the evidence, including the 

analysis of the distribution of air quality 

concentrations most influential in 

generating health effect estimates in the 

studies, and on margin of safety 

considerations, than would setting a 

level at the upper end of the range. 

Conversely, an approach that would 

support a level at the upper end of this 

range would generally support a view 

that the uncertainties remaining in the 

evidence are such that the evidence 

does not warrant setting a lower annual 

standard level. Id. at 38942. 

At the time of the proposal, while the 

Administrator recognized that CASAC 

advised, and the Policy Assessment 

concluded, that the available scientific 

information provided support for 

considering a range that extended down 

to 11 mg/m3, she concluded that 

proposing such an extended range 

would reflect a public health policy 

approach that placed more weight on 

relatively limited evidence and more 

uncertain information and analyses than 

she considered appropriate at this time. 

Nonetheless, the Administrator solicited 

comment on a level down to 11 mg/m3

as well as on approaches for translating 

scientific evidence and rationales that 

would support such a level. Such an 

approach might reflect a view that the 

uncertainties associated with the 

available scientific information warrant 

a highly precautionary public health 

policy response that would incorporate 

a large margin of safety. 

The Administrator recognized that 

potential air quality changes associated 

with meeting an annual standard set at 

a level within the range of 12 to 13 mg/ 

m3 will result in lowering risks 

associated with both long- and shortterm PM2.5 exposures. However, the 

Administrator recognized that such an 

annual standard intended to serve as the 

primary means for providing protection 

from effects associated with both longand short-term PM2.5 exposures would 

not by itself be expected to offer 

requisite protection with an adequate 

margin of safety against the effects of all 

short-term PM2.5 exposures. As a result, 

in conjunction with proposing an 

annual standard level in the range of 12 

to 13 mg/m3, the Administrator 

provisionally concluded that it was 

appropriate to continue to provide 

supplemental protection by means of a 

24-hour standard set at the appropriate 

level, particularly for areas with high 

peak-to-mean ratios possibly associated 

with strong local or seasonal sources, or 

for PM2.5-related effects that may be 

associated with shorter-than-daily 

exposure periods. 

Based on the approach discussed in 

section III.A.3 above, at the time of the 

proposal the Administrator relied upon 

evidence from the short-term exposure 

studies as the principal basis for 

selecting the level of the 24-hour 

standard. In considering these studies as 

a basis for the level of a 24-hour 

standard, and having selected a 98th 

percentile form for the standard, the 

Administrator agreed with the focus in 

the Policy Assessment of looking at the 

98th percentile values, as well as at the 

long-term mean PM2.5 concentrations in 

these studies. 

In considering the information 

provided by the short-term exposure 

studies, the Administrator recognized 

that to the extent these studies were 

conducted in areas that likely did not 

meet one or both of the current 

standards, such studies did not help 

inform the characterization of the 

potential public health improvements of 

alternative standards set at lower levels. 

By reducing the PM2.5 concentrations in 

such areas to just meet the current 

standards, the Administrator anticipated 

that additional public health protection 

would occur. Therefore, the 

Administrator focused on studies that 

reported positive and statistically 

significant associations in areas that 

would likely have met both the current 

24-hour and annual standards. She also 

considered whether or not these studies 

were conducted in areas that would 

likely have met an annual standard level 

of 12 to 13 mg/m3 to inform her decision 

regarding an appropriate 24-hour 

standard level. As discussed in section 

III.E.4.a, consistent with the Policy 

Assessment, the Administrator 

concluded that multi-city, short-term 

exposure studies provided the strongest 

data set for informing her decisions on 

appropriate 24-hour standard levels. 

The Administrator viewed the singlecity, short-term exposure studies as a 

much more limited data set providing 

mixed results and, therefore, she had 

less confidence in using those studies as 

a basis for setting the level of a 24-hour 

standard. With regard to the limited 

number of single-city studies that 

reported positive and statistically 

significant associations for a range of 

health endpoints related to short-term 

PM2.5 concentrations in areas that would 

likely have met the current suite of 

PM2.5 standards, the Administrator 

recognized that many of those studies 

had significant limitations (e.g., limited 

statistical power, limited exposure data) 

or equivocal results (mixed results 

within the same study area) that made 

them unsuitable to form the basis for 

setting the level of a 24-hour standard. 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3143 

With regard to multi-city studies that 

evaluated effects associated with shortterm PM2.5 exposures, the Administrator 

observed an overall pattern of positive 

and statistically significant associations 

in studies with 98th percentile values 

averaged across study areas in the range 

of 45.8 to 34.2 mg/m3 (Burnett et al., 

2004; Zanobetti and Schwartz, 2009; 

Bell et al., 2008; Dominici et al., 2006a, 

Burnett and Goldberg, 2003; Franklin et 

al., 2008). The Administrator noted that, 

to the extent air quality distributions 

were reduced to reflect just meeting the 

current 24-hour standard, additional 

protection would be anticipated for the 

effects observed in the three multi-city 

studies with 98th percentile values 

greater than 35 mg/m3 (Burnett et al., 

2004; Burnett and Goldberg, 2003; 

Franklin et al., 2008). In the three 

additional studies with 98th percentile 

values below 35 mg/m3, specifically 98th 

percentile concentrations of 34.2, 34.3, 

and 34.8 mg/m3, the Administrator noted 

that these studies reported long-term 

mean PM2.5 concentrations of 12.9, 13.2, 

and 13.4 mg/m3, respectively (Bell et al., 

2008; Zanobetti and Schwartz, 2009; 

Dominici et al., 2006a). 

In proposing to revise the level of the 

annual standard to within the range of 

12 to 13 mg/m3, as discussed above, the 

Administrator recognized that 

additional protection would be 

provided for the short-term effects 

observed in these multi-city studies in 

conjunction with an annual standard 

level of 12 mg/m3, and in two of these 

three studies in conjunction with an 

annual standard level of 13 mg/m3. She 

noted that the study-wide mean 

concentrations were based on averaging 

across monitors within study areas and 

that compliance with the standard 

would be based on concentrations 

measured at the monitor reporting the 

highest concentration within each area. 

The Administrator believed it would be 

reasonable to conclude that revision to 

the 24-hour standard would not be 

appropriate in conjunction with an 

annual standard within this range. 

Based on the above considerations 

related to the epidemiological evidence, 

the Administrator provisionally 

concluded that it was appropriate to 

retain the level of the 24-hour standard 

at 35 mg/m3, in conjunction with a 

revised annual standard level in the 

proposed range of 12 to 13 mg/m3. 

In addition to considering the 

epidemiological evidence, the 

Administrator also took into account air 

quality information based on countylevel 24-hour and annual design values 

to understand the public health 

implications of retaining the 24-hour 

standard level at 35 mg/m3 in 

conjunction with an annual standard 

level within the proposed range of 12 to 

13 mg/m3. She considered whether these 

suites of standards would meet a public 

health policy goal which included 

setting the annual standard to be the 

‘‘generally controlling’’ standard in 

conjunction with setting the 24-hour 

standard to provide supplemental 

protection to the extent that additional 

protection is warranted. As discussed 

above, the Administrator provisionally 

concluded that this approach was the 

most effective and efficient way to 

reduce total population risk associated 

with both long- and short-term PM2.5

exposures, resulting in more uniform 

protection across the U.S. than the 

alternative of setting the 24-hour 

standard to be the controlling standard. 

In considering the air quality 

information, the Administrator first 

recognized that there was no annual 

standard within the proposed range of 

levels, when combined with a 24-hour 

standard at the proposed level of 35 mg/ 

m3, for which the annual standard 

would be the generally controlling 

standard in all areas of the country. She 

further observed that such a suite of 

PM2.5 standards with an annual 

standard level of 12 mg/m3 would result 

in the annual standard as the generally 

controlling standard in most regions 

across the country, except for certain 

areas in the Northwest, where the 

annual mean PM2.5 concentrations have 

historically been low but where 

relatively high 24-hour concentrations 

occur, often related to seasonal wood 

smoke emissions (U.S. EPA, 2011a, pp. 

2–89 to 2–91, Figure 2–10). Although 

not explicitly delineated on Figure 2–10 

in the Policy Assessment, an annual 

standard of 13 mg/m3 would be 

somewhat less likely to be the generally 

controlling standard in some regions of 

the U.S. outside the Northwest in 

conjunction with a 24-hour standard 

level of 35 mg/m3. 

Taking the above considerations into 

account, the Administrator proposed to 

revise the level of the primary annual 

PM2.5 standard from 15.0 mg/m3 to 

within the range of 12.0 to 13.0 mg/m3

and to retain the 24-hour standard level 

at 35 mg/m3. In the Administrator’s 

judgment, such a suite of primary PM2.5

standards and the rationale supporting 

such levels could reasonably be judged 

to reflect alternative approaches to the 

appropriate consideration of the 

strength of the available evidence and 

other information and their associated 

uncertainties and the advice of CASAC. 

The Administrator recognized that the 

final suite of standards selected from 

within the proposed range of annual 

standard levels, or the broader range of 

annual standard levels on which public 

comment was solicited, must be clearly 

responsive to the issues raised by the 

DC Circuit’s remand of the 2006 primary 

annual PM2.5 standard. Furthermore, at 

the time of the proposal, she recognized 

that the final suite of standards will 

reflect her ultimate judgment in the 

final rulemaking as to the suite of 

primary PM2.5 standards that would be 

requisite to protect the public health 

with an adequate margin of safety from 

effects associated with fine particle 

exposures. The final judgment to be 

made by the Administrator will 

appropriately consider the requirement 

for a standard that is neither more nor 

less stringent than necessary and will 

recognize that the CAA does not require 

that primary standards be set at a zerorisk level, but rather at a level that 

reduces risk sufficiently so as to protect 

public health with an adequate margin 

of safety. 

At the time of the proposal, having 

reached her provisional judgment to 

propose revising the annual standard 

level from 15.0 to within a range of 12.0 

to 13.0 mg/m3 and to propose retaining 

the 24-hour standard level at 35 mg/m3, 

the Administrator solicited public 

comment on this range of levels and on 

approaches to considering the available 

evidence and information that would 

support the choice of levels within this 

range. The Administrator also solicited 

public comment on alternative annual 

standard levels down to 11 mg/m3 and 

on the combination of annual and 24- 

hour standards that commenters may 

believe is appropriate, along with the 

approaches and rationales used to 

support such levels. In addition, given 

the importance the evidence from 

epidemiologic studies played in 

considering the appropriate annual and 

24-hour levels, the Administrator 

solicited public comment on issues 

related to translating epidemiological 

evidence into standards, including 

approaches for addressing the 

uncertainties and limitations associated 

with this evidence. 

c. Comments on Standard Levels 

This section addresses comments that 

relate to consideration of the 

appropriate levels of the primary annual 

and 24-hour PM2.5 standards, including 

comments on the general approach used 

by the EPA to translate the available 

scientific information into standard 

levels and how specific PM2.5 exposure 

studies should be considered as a basis 

for the standard levels. These comments 

on standard levels expand upon the 

more general comments that either 

supported or opposed any change to the 

current suite of primary PM2.5


tkelley on DSK3SPTVN1PROD with 
3144 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

85Specific comments on the forms of the annual 

and 24-hour standards are addressed in section 

III.E.3.a and III.E.3.b, respectively. 

86The commenter indicated that this analysis was 

based on monitoring data for every core based 

statistical area (CBSA) in the EPA’s Air Quality 

System (AQS) database. 

87The design value is the air quality statistic that 

is compared to the level of the NAAQS to determine 

the attainment status of a given area. 

standards, which are addressed above in 

section III.D.2.85 As explained there, one 

group of commenters generally opposed 

any change to the current primary PM2.5

standards and more specifically 

disagreed with the basis for the EPA’s 

proposal to revise the annual standard 

level. Another group of commenters 

supported revising the current suite of 

primary PM2.5 standards to provide 

increased public health protection. 

Some commenters in this second group 

argued that both the annual and 24-hour 

standard levels should be lowered while 

other commenters in this group agreed 

with the EPA’s proposal to retain the 

level of the 24-hour standard in 

conjunction with revising the level of 

the annual standard. While generally 

supporting the EPA’s proposal to lower 

the level of the annual standard, many 

commenters in this group disagreed that 

a level within the EPA’s proposed range 

was adequately protective and 

supported a level of 11 mg/m3 or below. 

i. Annual Standard Level 

The group of commenters opposed to 

any change to the current suite of 

primary PM2.5 standards generally 

raised questions regarding the 

underlying scientific evidence, 

including the causal determinations 

reached in the Integrated Science 

Assessment, and focused strongly on the 

uncertainties they saw in the scientific 

evidence as a basis for their conclusion 

that no changes to the current standard 

levels were warranted. In commenting 

on the proposed standard levels, these 

commenters typically relied on the 

arguments summarized and addressed 

above in section III.D.2 as to why they 

believed it was inappropriate for the 

EPA to make any revisions to the suite 

of primary PM2.5 standards. That is, they 

asserted that the EPA’s causal 

determinations were not adequately 

supported by the underlying scientific 

information; the biological plausibility 

of health effects observed in 

epidemiological studies has not been 

demonstrated in controlled human 

exposure and toxicological studies; 

uncertainties in the underlying health 

science are as great or greater than in 

2006; there is no evidence of greater risk 

since the last review to justify tightening 

the current annual PM2.5 standard; and 

‘‘new’’ studies not included in the 

Integrated Science Assessment continue 

to increase uncertainty about possible 

health risks associated with exposure to 

PM2.5. 

With regard to the level of the annual 

standard, these commenters strongly 

disagreed with the Agency’s proposed 

decision to revise the level to within a 

range of 12 to 13 mg/m3 and argued that 

the current standard level of 15 mg/m3

should be retained. For example, UARG, 

API, and other commenters in this 

group raised a number of issues that 

they asserted called into question the 

EPA’s interpretation of the 

epidemiological evidence to support 

revising the annual standard level. 

These commenters raised specific 

questions related to the general 

approach used by the EPA to translate 

the air quality and other information 

from specific epidemiological studies 

into standard levels, including: (1) The 

EPA’s approach for using composite 

monitor air quality distributions 

reported in epidemiological studies to 

select a standard level that would be 

compared to measurements at the 

monitor recording the highest value in 

an area to determine compliance with 

the standard; (2) the appropriate 

exposure period for effects observed in 

long-term exposure mortality studies; 

and (3) the use of the EPA’s analysis of 

distributions of underlying populationlevel data (i.e., health event and study 

population data) for those 

epidemiological studies for which such 

information was available. These 

commenters also raised questions 

regarding the EPA’s consideration of 

specific scientific evidence as a basis for 

setting a standard level, including: (4) 

evidence of respiratory morbidity effects 

in long-term exposure studies and (5) 

more limited evidence of health effects 

which have been categorized in the 

Integrated Science Assessment as 

suggestive of a causal relationship (i.e., 

developmental and reproductive 

outcomes). These comments are 

discussed in turn below. 

(1) Some commenters in this group 

argued that one reason why they believe 

there is no basis for setting a standard 

level below 15 mg/m3 is that the air 

quality metric from epidemiological 

studies that the EPA relied on in the 

proposal is not the same metric that will 

be compared to the level of the standard 

to determine compliance with the 

standard. That is, commenters noted 

that the long-term mean PM2.5

concentrations that the EPA considered, 

shown in Figure 4 above, are composite 

monitor mean concentrations (i.e., 

concentrations averaged across multiple 

monitors within areas with more than 

one monitor), whereas the PM2.5

concentrations that will be compared to 

the level of the standard are maximum 

monitor concentrations (i.e., the 

concentration measured by the monitor 

within an area reporting the highest 

concentration). This comment was 

presented most specifically in UARG’s 

comments (UARG, 2012, Attachment 1, 

pp. 2 to 6), which raised two 

overarching issues as discussed below. 

First, the commenter noted that the 

EPA’s approach of considering 

composite monitor mean PM2.5

concentrations in selecting a standard 

level, and then comparing the maximum 

monitor mean PM2.5 concentration in 

each area to the standard level when the 

standard is implemented, was 

characterized in the proposal as 

inherently having the potential to build 

in a margin of safety (UARG, 2012, 

Attachment 1, p. 4, citing 77 FR 38905). 

The commenter asserted that the 

Administrator is ignoring this 

distinction between composite and 

maximum monitor concentrations, and 

that this approach creates an 

unwarranted case for lowering the 

standard level, since in the commenter’s 

view, it would result in a margin of 

safety that would be arbitrary, not based 

on evidence, and unquantified (UARG, 

2012, Attachment 1, p. 4). In support of 

this view, the commenter asserted that 

there is a significant difference between 

composite monitor mean PM2.5

concentrations and maximum monitor 

mean PM2.5 concentrations. The 

commenter asserted that the maximum 

monitor value will always be higher 

than the composite monitor value 

(except in areas that contain only a 

single monitor), such that when an area 

just attains the NAAQS, that area’s 

composite monitor long-term mean 

PM2.5 concentration will be lower than 

the level of the standard (UARG, 2012, 

Attachment 1, p. 3). 

Second, the commenter asserted that 

a more ‘‘reasoned and consistent 

approach would be to decide on a mean 

composite monitor PM2.5 level that 

should be achieved and then identify 

the maximum monitor level that would 

result in that composite value’’ (UARG, 

2012, Attachment 1, p. 4). The 

commenter conducted an analysis of 

maximum monitor versus composite 

monitor annual mean PM2.5

concentrations using monitoring data 86

from 2006 to 2008 and presented results 

averaged across areas within two groups 

(i.e., those with design values 87 above 

the current standard level and those 

with design values just below the 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3145 

88As discussed above in section III.E.3.a. 

89The average difference between the maximum 

and composite design value among the 123 CBSAs 

with two or more monitors is 0.8 mg/m3 and the 

median difference is 0.6 mg/m3. The 25th and 75th 

percentiles are 0.3 and 1.0 mg/m3, respectively 

(Frank, 2012a, p. 4). 

current standard level) to illustrate their 

suggested alternative approach. The 

commenter interpreted this analysis as 

showing that the composite monitor 

long-term mean PM2.5 concentrations 

from the subset of the epidemiological 

studies shown in Figure 4 (of the 

proposal and above) that the commenter 

considered to be an appropriate focus 

for this analysis would be achieved 

across the U.S. if the current annual 

NAAQS of 15 mg/m3 is retained and 

attained. The commenter considered the 

subset of epidemiological studies that 

included only long-term exposures 

studies of effects for which the evidence 

is categorized as causal or likely causal, 

but did not consider short-term 

exposure studies. On this basis, the 

commenter asserted that attaining the 

current annual PM2.5 standard would 

result in composite monitor long-term 

mean concentrations in all areas that 

would be generally within or below the 

range of the composite monitor longterm mean concentrations from such 

studies and, as a result, there is no 

reason to lower the level of the current 

annual NAAQS. 

In considering the first issue related to 

the EPA’s approach, the EPA notes that 

in proposing to revise both the form and 

level of the annual standard, the 

Administrator clearly took into account 

the distinction between the composite 

monitor long-term mean PM2.5

concentrations from the epidemiological 

studies, considered as a basis for 

selecting an annual standard level, and 

maximum monitor long-term mean 

PM2.5 concentrations. In deciding to 

focus on the composite monitor longterm mean concentrations in selecting 

the standard level, and on the maximum 

monitor concentrations in selecting the 

form of the standard (i.e., consistent 

with proposing to eliminate the option 

for spatial averaging across monitors 

within an area when implementing the 

standard 88), the Administrator 

reasonably considered the distinction 

between these metrics in a manner that 

was consistent with advice from CASAC 

(Samet et al., 2010d, pp. 2 to 3). 

As noted above in section III.A.3, the 

EPA recognizes that a statistical metric 

(e.g., the mean of a distribution) based 

on maximum monitor concentrations 

may be identical to or above the same 

statistical metric based on composite 

monitor concentrations. More 

specifically, many areas have only one 

monitor, in which case the composite 

and maximum monitor concentrations 

are identical. Based on the most recent 

data from the EPA’s AQS from 2009 to 

2011 in the 331 CBSAs in which valid 

PM2.5 data are available, as discussed in 

Frank (2012a, Table 5), there were 208 

such areas (with design values ranging 

up to about 15 mg/m3). Frank (2012a) 

also observed that other areas have 

multiple monitors with composite and 

maximum monitor mean PM2.5

concentrations that were the same or 

relatively close, with 57 areas in which 

the maximum monitor mean 

concentration was no more than 0.5 mg/ 

m3 higher than the composite monitor 

mean concentration and 56 areas in 

which the difference was between 0.6 

and 2 mg/m3. Further, there were only a 

few other areas in which the maximum 

monitor mean concentration was 

appreciably higher than the composite 

monitor mean concentration, such as 

areas in which some monitors may be 

separately impacted by local sources. 

There were only 10 such areas in the 

country in which the maximum monitor 

mean concentration was between 2 to 6 

mg/m3 higher than the composite 

monitor concentration (Frank, 2012a, 

Table 4).89 Thus, the EPA does not agree 

that there is a significant difference 

between composite monitor mean PM2.5

concentrations and maximum monitor 

mean PM2.5 concentrations in the large 

majority of areas across the country. 

In proposing to revise the form of the 

annual PM2.5 standard, as discussed 

above in section III.E.3.a, the EPA noted 

that when an annual PM2.5 standard was 

first set in 1997, the form of the 

standard included the option for 

averaging across measurements at 

appropriate monitoring sites within an 

area, generally consistent with the 

composite monitor approach used in 

epidemiological studies, with some 

constraints intended to ensure that 

spatial averaging would not result in 

inequities in the level of protection for 

communities within large metropolitan 

areas. In the last review the EPA 

tightened the constraints on spatial 

averaging, and in this review has 

eliminated the option altogether, on the 

basis of analyses in each review that 

showed that such constraints may be 

inadequate to avoid substantially greater 

exposures for people living in locations 

around the monitors recording the 

highest PM2.5 concentrations in some 

areas, potentially resulting in 

disproportionate impacts on at-risk 

populations of persons with lower SES 

levels as well as minorities. In light of 

these analyses, and consistent with the 

Administrator’s decision to revise the 

form of the annual PM2.5 standard by 

eliminating the option for spatial 

averaging, the EPA continues to 

conclude that a standard level based on 

consideration of long-term mean 

concentrations from composite 

monitors, and applied at each monitor 

within an area including the monitor 

measuring the highest concentration, is 

the appropriate approach to use in 

setting a standard that will protect 

public health, including the health of atrisk populations, with an adequate 

margin of safety, as required by the 

CAA. 

The EPA acknowledges that at 

proposal, the Agency characterized the 

approach of using maximum monitor 

concentrations to determine compliance 

with the standard, while selecting the 

standard level based on consideration of 

composite monitor concentrations, as 

one that inherently had the potential to 

build in a margin of safety (77 FR 

38905), and CASAC reiterated that view 

in supporting the EPA’s approach 

(Samet, 2010d, p. 3). Nonetheless, in 

light of the discussion above, the EPA 

more specifically recognizes that this 

approach does not build in any margin 

of safety in the large number of areas 

across the country with only one 

monitor. Further, based on the analyses 

done to inform consideration of the 

form of the standard (Schmidt, 2011, 

Analysis A), the EPA concludes that this 

approach does not provide a margin of 

safety for the at-risk populations that 

live around the monitor measuring the 

highest concentration, such as in those 

few areas in which the maximum 

monitor concentration is appreciably 

higher than the composite monitor 

concentration. Rather, this approach 

properly treats those at-risk populations 

the same way it does the broader 

populations that live in areas with only 

one monitor, by providing the same 

degree of protection for those at-risk 

populations that would otherwise be 

disproportionately impacted as it does 

for the broader populations in other 

areas, While the EPA recognizes that 

this approach can result in some 

additional margin of safety for the 

subset of areas with multiple monitors 

in which at-risk populations may not be 

disproportionately represented in areas 

around the maximum monitor, which 

may be the case in areas with relatively 

small differences between the maximum 

and composite monitor concentrations, 

the EPA notes that this margin would be 

relatively small in such areas. 

Based on the above considerations, 

the EPA does not agree that the 

Agency’s approach of using maximum 

monitor concentrations to determine 

compliance with the standard, while 


tkelley on DSK3SPTVN1PROD with 
3146 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

90For the first group of areas (which included 33 

areas), this analysis calculated an average across the 

areas of maximum monitor annual mean PM2.5

concentrations, averaged over 3 years, of 17.2 mg/ 

m3 compared to an average of composite monitor 

concentrations of 14.3 mg/m3. For the second group 

of areas (which included 11 areas), this analysis 

calculated an average across the areas of maximum 

monitor annual mean concentrations, averaged over 

3 years, of 14.8 mg/m3 compared to an average of 

composite monitor concentrations of 13.6 mg/m3

(UARG, 2012, Attachment 1, Table 1). 

91The EPA notes that the Frank (2012a) analysis 

is similar to an earlier EPA staff analysis (HassettSipple et al., 2010), which used air quality data 

from EPA’s AQS database to compare maximum 

versus composite monitor long-term mean PM2.5

concentrations across the study areas in six selected 

multi-city epidemiological studies. 

92The EPA’s analysis was intended to repeat the 

commenter’s analysis, but using only valid air 

quality data (from 2006 to 2008). For the first group 

of areas (which included 21 areas with valid data), 

the EPA’s analysis calculated an average across the 

areas of maximum monitor annual mean 

concentrations, averaged of 3 years, of 16.8 mg/m3

compared to an average of composite monitor 

concentrations of 14.8 mg/m3. For the second group 

of areas (which included 10 areas with valid data), 

the EPA’s analysis calculated an average across the 

areas of maximum monitor annual mean 

concentrations, averaged over 3 years, of 14.8 mg/ 

m3 compared to an average of composite monitor 

concentrations of 14.2 mg/m3 (Frank, 2012a, Table 

3). 

selecting the standard level based on 

consideration of composite monitor 

concentrations creates an unwarranted 

case for lowering the standard level 

based on a margin of safety that would 

be arbitrary, not based on evidence, or 

lack quantification. The EPA recognizes 

that setting a standard to protect public 

health, including the health of at-risk 

populations, with an adequate margin of 

safety, depends upon selecting a 

standard level sufficiently below where 

the EPA has found the strongest 

evidence of health effects so as to 

provide such protection, and that the 

EPA’s approach regarding consideration 

of composite and maximum monitor 

concentrations is intended to, and does, 

serve to address this requirement as part 

of and not separate from the selection of 

an appropriate standard level based on 

the health effects evidence. 

In considering the second issue 

related to the commenter’s suggested 

alternative approach, the EPA strongly 

disagrees with the commenter’s view 

that a more ‘‘reasoned and consistent 

approach would be to decide on a mean 

composite monitor PM2.5 level that 

should be achieved and then identify 

the maximum monitor level that would 

result in that composite value’’ (UARG, 

2012, Attachment 1, p. 4). As discussed 

above, the EPA notes that for areas with 

only one monitor, or with multiple 

monitors that measure concentrations 

that are very close in magnitude, the 

maximum monitor level that would 

limit the composite monitor PM2.5 level 

to be no greater than the level that 

should be achieved to protect public 

health with an adequate margin of 

safety, would essentially be the same as 

that composite monitor level. Further, 

as discussed above, even for areas in 

which the maximum monitor 

concentration is appreciably higher than 

other monitor concentrations within the 

same area, public health would not be 

protected with an adequate margin of 

safety if the disproportionately higher 

exposures of at-risk, susceptible 

populations around the monitor 

measuring the highest concentration 

were in essence averaged away with 

measurements from monitors in other 

locations within large urban areas. 

Further, the commenter’s suggested 

approach would be based on annual 

average PM2.5 concentrations that have 

been measured over some past time 

period. Such an approach would reflect 

the air quality that existed in the past, 

but it would not necessarily provide 

appropriate constraints on the range of 

concentrations that would be allowed 

by such a standard in the future, when 

relationships between maximum and 

composite monitor concentrations in 

areas across the country may be 

different. For these reasons, the EPA 

fundamentally rejects the commenter’s 

suggested approach because in the 

EPA’s view it would not protect public 

health, including providing protection 

for at-risk populations, with an adequate 

margin of safety in areas across the 

country. 

More specifically, in further 

considering the commenter’s analysis of 

design values based on maximum 

versus composite monitor annual mean 

PM2.5 concentrations using monitoring 

data from 2006 to 2008 which they 

assert supports retaining the current 

standard level of 15 mg/m3, the EPA 

finds flaws with the numerical results 

and the scope of the analysis, as well as 

flaws in the commenter’s translation of 

the analysis results into the basis for 

selecting an annual standard level. 

In considering the commenter’s 

analysis, the EPA notes that the analysis 

compared maximum versus composite 

monitor annual mean PM2.5

concentrations, averaged over 3 years, 

for two groups of areas: (1) Areas with 

design values that exceed the current 

annual standard level (i.e., greater than 

15.0 mg/m3) and (2) areas with design 

values that are just attaining the current 

annual standard (i.e., between 14.5 and 

15.0 mg/m3).90 The commenter indicated 

that they used the full body of PM2.5

monitoring data from the EPA’s AQS 

database (UARG, 2012, Attachment 1, p. 

4), In attempting to reproduce the 

commenter’s results, the EPA repeated 

the calculations using only valid air 

quality data (i.e., data that meet data 

completeness and monitor siting 

criteria) from the AQS database for the 

same time period (Frank, 2012a).91

Based on this corrected analysis, the 

EPA finds that the composite monitor 

concentrations averaged across the areas 

within each group are somewhat higher 

than those calculated by the commenter, 

and the average differences between the 

maximum and composite monitor 

concentrations are somewhat smaller 

(Frank, 2012a, Table 3).92 Notably, the 

difference between the maximum and 

composite monitor average 

concentrations for the second group of 

areas is substantially reduced in the 

corrected analysis, such that the 

difference (averaged across the 10 areas 

with valid data in the second group) is 

approximately 0.5 mg/m3, not 1.2 mg/m3

as in the commenter’s analysis. In 

addition, the commenter’s analysis 

compared the average of the composite 

monitors to the average of the maximum 

monitors for each subset of areas. This 

comparison of averages across all the 

areas in each subset masks the fact that 

the large majority of areas across the 

country have only one monitor, with the 

composite monitor and maximum 

monitor values the same for such areas, 

and many other areas have a maximum 

monitor value that is close to the 

composite monitor value. As discussed 

above, these circumstances have a major 

impact on the protection that would be 

achieved by the approach suggested by 

the commenter. 

With regard to the scope of the 

commenter’s analysis, the EPA finds 

that by limiting the scope to a small 

subset of areas with design values above 

or just below the current annual 

standard level of 15 mg/m3, the analysis 

ignores the large number of areas across 

the country with lower design values 

that are relevant to consider in light of 

the epidemiological evidence of serious 

health effects at lower concentrations, 

well below the level of the current 

standard. 

In translating the analysis results into 

the basis for selecting an annual 

standard level, the commenter’s 

translation is premised on the view that 

the ‘‘natural focal point’’ for setting an 

annual PM2.5 standard level should be 

somewhere within the range of the longterm mean PM2.5 concentrations from 

the subset of epidemiological studies 

that included only long-term exposure 

studies of effects for which the evidence 

is categorized as causal or likely causal, 

but not for effects categorized as 

suggestive of causality, nor did it 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3147 

93The commenter suggests that the EPA should 

not place significant reliance on the long-term mean 

concentrations from short-term exposure studies 

because ‘‘[T]he short-term studies did not use the 

annual average of PM2.5 to develop their 

associations; they used the daily 24-hour averages 

of PM2.5. Thus, short-term studies do not provide 

a natural indicator for the appropriate level of an 

annual standard * * *.’’ (UARG, 2012, Attachment 

1, p. 3). The EPA finds this argument unpersuasive. 

Quite simply, effects were observed in these studies 

with an air quality distribution that can 

meaningfully be characterized by these long-term 

mean concentrations. Indeed, in remanding the 

2006 standard, the D.C. Circuit discussed at length 

the interrelationship of the long- and short-term 

standards and studies, and remanded the 2006 

standard to the EPA, in part, for ignoring those 

relationships without adequate explanation. 

American Farm Bureau Federation v. EPA. 559 F. 

3d at 522–24. 

include short-term exposure studies 

(which are included in Figure 4 of the 

proposal notice and above). Such a view 

is not consistent with setting a standard 

that would provide sufficient protection 

from the serious health effects reported 

even in the limited subset of studies 

considered by the commenter, including 

protecting public health with an 

adequate margin of safety. As discussed 

below, the EPA does not agree with the 

commenter’s view as to the appropriate 

focal point for selecting the level of an 

annual PM2.5 standard, or with the 

limited set of studies considered by the 

commenter as a basis for selecting the 

level of the annual PM2.5 standard. 

Regarding an appropriate focal point 

for selecting the level of the annual 

standard, as discussed in the proposal 

and as advised by CASAC, the EPA has 

focused on PM2.5 concentrations 

somewhat below the lowest long-term 

mean concentrations from each of the 

key studies of both long- and short-term 

exposures of effects for which the 

evidence is causal or likely causal, as 

considered by the EPA (i.e., the first two 

sets of studies shown in Figure 4). If the 

level of the annual standard was set just 

somewhere within the range of the longterm mean concentrations from the 

various long-term exposure studies, 

then one or more of the studies would 

have a long-term mean concentration 

below the selected level of the standard. 

Absent some reason to ignore or 

discount these studies, which the 

commenter does not provide (and of 

which the EPA is unaware), setting such 

a standard would allow that level of air 

quality, where the evidence of health 

effects is strongest, and its associated 

risk of PM2.5-related mortality and/or 

morbidity effects to continue. Selecting 

such a standard level could not be 

considered sufficient to protect the 

public health with an adequate margin 

of safety. 

Further, focusing on just the longterm mean PM2.5 concentrations in the 

key epidemiological studies—even the 

lowest long-term mean concentration 

from the set of key studies—is not 

appropriate. Concentrations at and 

around the long-term mean 

concentrations represent the part of the 

air quality distribution where the data 

in any given study are most 

concentrated and, thus, where the 

confidence in the magnitude and 

significance of an association in such 

study is strongest. However, the 

evidence of an association with adverse 

health effects in the studies is not 

limited to the PM2.5 concentrations just 

at and around the long-term mean, but 

rather extends more broadly to a lower 

part of the distribution, recognizing that 

no discernible population-level 

threshold for any such effects can be 

identified based on the available 

evidence. This broader region of the 

distribution of PM2.5 concentrations 

should be considered to the extent 

relevant information is available, 

recognizing that the degree of 

confidence in the association identified 

in a study would become lower as one 

moves below concentrations at and 

around the long-term mean 

concentration in any given study. The 

commenter’s approach ignores this 

fundamental consideration. 

Regarding the set of studies that is 

appropriate to inform the selection of 

the level of the annual PM2.5 standard, 

the EPA finds that limiting 

consideration only to the long-term 

exposure studies, as this commenter 

suggests, would be tantamount to 

ignoring the short-term exposure 

studies,93 which provide some of the 

strongest evidence from the entire body 

of epidemiological studies. Thus, 

selecting an annual standard level using 

the limited set of studies suggested by 

the commenter would fail to provide a 

degree of protection that would be 

sufficient to protect public health with 

an adequate margin of safety. 

For all the reasons discussed above, 

the EPA finds the commenter’s concerns 

with the EPA’s approach to considering 

composite and maximum monitor PM2.5

concentrations in selecting the level of 

the annual PM2.5 standard to be without 

merit. Further, the EPA finds no support 

in the commenter’s analysis for their 

suggested alternative approach. 

(2) With respect to the appropriate 

exposure period for mortality effects 

observed in long-term exposure studies, 

some commenters in this group 

generally expressed views consistent 

with comments from UARG that argued 

that these studies ‘‘are most likely 

detecting health risk from earlier, higher 

PM2.5 levels and misattributing those 

risks to more recent, lower PM2.5 levels’’ 

(UARG, 2012, Attachment 1, p 7). 

Further, this commenter asserted that 

‘‘there is no knowledge or evidence 

indicating whether premature deaths are 

the result of PM2.5 exposures in the most 

recent year; or due to physical damages 

incurred from PM2.5 exposures much 

earlier in life (with the impact on 

lifespan only emerging later in life); or 

due to total accumulated PM2.5 exposure 

over many years.’’ Id. In addition, the 

commenter asserted that the long-term 

exposure studies of mortality are central 

to the EPA’s basis for proposing to set 

a lower annual standard level, since 

most of the estimated benefits 

associated with a lower annual PM2.5

standard are based on reductions in 

mortality related to long-term exposures 

to PM2.5. 

As an initial matter, the EPA has 

recognized the challenge in 

distinguishing between PM2.5-associated 

effects due to past and recent long-term 

exposures, and in identifying the 

relevant latency period for long-term 

exposure to PM and resultant health 

effects (U.S. EPA, 2009a, section 7.6.4; 

77 FR 38941/1). While the EPA has 

acknowledged that there remain 

important uncertainties related to 

characterizing the most relevant 

exposure periods in long-term exposure 

studies, the assertion that there is ‘‘no 

knowledge or evidence’’ that helps to 

inform this issue is not correct, as 

discussed below. 

Both in the last review and in the 

current review, the EPA has assessed 

studies that used different air quality 

periods for estimating long-term 

exposure and tested associations with 

mortality for the different exposure 

periods (U.S. EPA, 2004, section 8.2.3.5; 

U.S. EPA 2009a, section 7.6.4). In this 

review, the Integrated Science 

Assessment discussed studies available 

since the last review that have assessed 

the relationship between long-term 

exposure to PM2.5 and mortality to 

explore the issue of the latency period 

between exposure to PM2.5 and death 

(U.S. EPA, 2009a, section 7.6.4). 

Notably, in a recent analysis of the 

extended Harvard Six Cities Study, 

Schwartz et al. (2008) used model 

averaging (i.e., multiple models were 

averaged and weighted by probability of 

accuracy) to assess exposure periods 

prospectively (77 FR 38907/1–2). The 

exposure periods were estimated across 

a range of unconstrained distributed lag 

models (i.e., same year, one year prior, 

two years prior to death). In comparing 

lags, the authors reported that the effects 

of changes in exposure to PM2.5 on 

mortality were strongest within a 2-year 

period prior to death (U.S. EPA, 2009a, 

p. 7–92, Figure 7–9). Similarly, a large 


tkelley on DSK3SPTVN1PROD with 
3148 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

94Nonetheless, the EPA notes that the Krewski et 

al. (2009) and Miller et al. (2007) studies provide 

strong evidence of mortality and cardiovascularrelated effects associated with long-term PM2.5

exposures to inform causality determinations 

reached in the Integrated Science Assessment (U.S. 

EPA, 2009a, sections 7.2.11 and 7.6). 

multi-city study of the elderly found 

that the mortality risk associated with 

long-term exposure to PM10 reported 

cumulative effects that extended over 

the years that deaths were observed in 

the study population (i.e., the follow-up 

period) and for the 3-year period prior 

to death (Zanobetti et al., 2008). 

Further, in a study of two locations 

that experienced an abrupt decline in 

PM2.5 concentrations (i.e., Utah Steel 

Strike, coal ban in Ireland), Ro ̈o ̈ sli et al. 

(2005) reported that approximately 75 

percent of health benefits were observed 

in the first 5 years (U.S. EPA, 2009a, 

Table 7–9). Schwartz et al. (2008) and 

Puett et al. (2008) found, in a 

comparison of exposure periods ranging 

from 1 month to 48 months prior to 

death, that exposure to PM10 24 months 

prior to death exhibited the strongest 

association, and the weakest association 

was reported for exposure in the time 

period of 1 month prior to death. 

Overall, the EPA notes that the 

available evidence for determining the 

exposure period that is causally related 

to the mortality effects of long-term 

PM2.5 exposures, as discussed above, 

cannot specifically disentangle the 

effects observed in long-term exposure 

studies associated with more recent air 

quality measurements from effects that 

may have been associated with earlier, 

and most likely higher, PM2.5 exposures. 

While the evidence suggests that a 

latency period of up to five years would 

account for the majority of deaths, it 

does not provide a basis for concluding 

that it is solely recent PM2.5

concentrations that account for the 

mortality risk observed in such studies. 

Nonetheless, the more recent air quality 

data does well at explaining the 

relationships observed between longterm exposures to PM2.5 and mortality, 

with the strongest association observed 

in the two years prior to death. Further, 

the EPA recognizes that there is no 

discernible population-level threshold 

below which effects would not occur, 

such that it is reasonable to consider 

that health effects may occur over the 

full range of concentrations observed in 

the epidemiological studies, including 

the lower concentrations in the latter 

years. 

In light of this evidence and these 

considerations, the EPA concludes that 

it is appropriate to consider air quality 

concentrations that are generally 

contemporaneous with the collection of 

health event data (i.e., collected over the 

same time period) as being causally 

associated with at least some proportion 

of the deaths assessed in a long-term 

exposure study. This would include 

long-term mean PM2.5 concentrations 

from most of the key long-term exposure 

studies of effects with causal or likely 

causal evidence shown in Figure 4 

above, which reported long-term mean 

PM2.5 concentrations ranging from 13.6 

mg/m3 to 14.3 mg/m3. These studies 

include studies of mortality by Eftim et 

al. (2008), which separately analyzed 

the ACS and Harvard Six City sites, 

Zeger et al. (2008), and Lipfert et al. 

(2006a), as well as studies of morbidity 

endpoints by Goss et al. (2004), 

McConnell et al. (2003) and Gauderman 

et al. (2004), and Dockery et al. (1996) 

and Razienne et al. (1996). The EPA 

acknowledges that uncertainty in the 

relevant exposure period is most notable 

in two other long-term exposure studies 

of mortality. The Miller et al. (2007) 

reported a long-term mean PM2.5

concentration for a 1-year exposure 

period that post-dated the follow-up 

period in which health event data were 

collected by two years. Also, the 

Krewski et al. (2009) study reported a 

long-term mean PM2.5 concentration for 

an exposure period that included only 

the last two years of the 18-year followup period. Based on these 

considerations, the EPA does not now 

consider it appropriate to put weight on 

the reported long-term mean 

concentrations from these two studies 

for the purpose of translating the 

information from the long-term 

mortality studies into a basis for 

selecting the level of the annual PM2.5

standard.94

In addition, the EPA acknowledges 

that exposure periods that extend at 

least a couple years prior to the followup period in which health event data 

were collected would likely more fully 

capture the PM-related deaths in such 

studies. To explore how much higher 

the long-term mean PM2.5

concentrations would likely have been 

had air quality data prior to the followup years of the studies been included, 

the EPA conducted a sensitivity analysis 

of long-term mean PM2.5 concentrations 

(Schmidt, 2012a) particularly 

considering studies that only included 

deaths from a relatively recent followup period. As examples of such studies, 

this analysis considered the Eftim et al. 

(2008) study of mortality in the ACS 

sites and the Harvard Six Cities sites, as 

well as sites in the eastern region in the 

Zeger et al. (2008) study. Using data 

from the EPA’s AQS database, the 

analysis added the two years of air 

quality data just prior to the follow-up 

period in each study, which was 2000 

to 2002 in Eftim et al. (2008) and 2000 

to 2005 in Zeger et al. (2008). The 

analysis then calculated the extended 

long-term mean PM2.5 concentration for 

each study. As discussed in Schmidt 

(2012a), in each case the long-term 

mean PM2.5 concentration averaged over 

the extended exposure period was less 

than 0.4 mg/m3 higher than the longterm mean PM2.5 concentration averaged 

over the follow-up period. The EPA 

finds it reasonable to conclude that such 

a relatively small difference in longterm mean PM2.5 concentrations would 

likely apply for other long-term 

exposure studies that used similarly 

recent follow-up periods as well (e.g., 

Goss et al., 2004; Lipfert et al., 2006a). 

Based on the above considerations, 

the EPA concludes that it is appropriate 

to consider the available air quality 

information from the long-term 

exposure studies, while taking into 

account the uncertainties in the relevant 

long-term exposure periods in weighing 

the information from these studies. The 

EPA recognizes that considering such 

information in selecting an appropriate 

annual standard level has the potential 

to build in some margin of safety. The 

EPA further concludes that it is 

appropriate to consider the air quality 

information from the set of long-term 

exposure studies discussed above in the 

context of the broader array of 

epidemiological studies that inform the 

EPA’s consideration of the level of the 

annual PM2.5 standard. 

The EPA also notes that while the 

long-term exposure studies are an 

important component of the 

epidemiological evidence that informs 

the Agency’s consideration of the level 

of the annual standard, they do not 

provide the only relevant information, 

nor are they the set of studies for which 

the relevant long-term mean PM2.5

concentrations are the lowest. As 

discussed in the proposal, the EPA also 

considers the long-term mean PM2.5

concentrations from the short-term 

mortality and morbidity studies as 

providing important information in 

considering the level of the annual 

standard. As discussed above, a large 

proportion of the aggregate risk 

associated with short-term exposures 

results from the large number of days 

during which the 24-hour average 

concentrations are in the low- to midrange of the concentrations observed in 

the studies. Thus, setting the level of the 

annual standard based on long-term 

mean concentrations, as well as the 

distribution of concentrations below the 

mean, in the short-term exposure 

studies is the most effective and 

efficient way to reduce total PM2.5- 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3149 

95As noted above, the EPA is not placing weight 

on the reported long-term mean concentrations 

from the Miller et al. (2007) study for the purpose 

of translating the information from the long-term 

mortality studies into a basis for selecting the level 

of the annual PM2.5 standard. 

96Health event data and study population data 

were available from two short-term exposure 

studies (Bell et al. 2008; Zanobetti and Schwartz, 

2009) and one long-term exposure study (Krewski 

et al., 2009). Only study population data were 

available from another long-term exposure study 

(Miller et al., 2007). 

related risk from the broad array of 

mortality and morbidity effects 

associated with short-term exposures. 

Further, the EPA notes that the 

relevant exposure period for the shortterm exposure studies is the period 

contemporaneous with the collection of 

health event data, and that this exposure 

period is not subject to the uncertainties 

discussed above related to the long-term 

exposure studies. Recognizing that the 

long-term mean PM2.5 concentrations 

from several of the multi-city short-term 

exposure studies shown in Figure 4 are 

below the long-term mean PM2.5

concentrations from the long-term 

exposure studies (with the exception of 

Miller et al., 2007).95 It is reasonable 

that in selecting the level of the annual 

standard primary consideration should 

be given to the information from this set 

of short-term exposure studies. There is 

no reasonable basis to discount the longterm mean concentrations of the shortterm exposure studies for purposes of 

setting the level of the annual standard. 

Thus, the commenter is incorrect in 

asserting that the long-term exposure 

studies, not the short-term exposure 

studies, would be central in the 

Administrator’s decision on the level of 

the annual standard. The standard is 

ultimately intended to protect not just 

against the single type of effect that 

contributes the most to quantitative 

estimates of risk to public health, but 

rather to the broad array of effects, 

including mortality and morbidity 

effects from long- and short-term 

exposures across the range of at-risk 

populations impacted by PM2.5-related 

effects. 

(3) With regard to the EPA’s analysis 

of distributions of underlying 

population-level data (i.e., health event 

and study population data) and 

corresponding air quality data from each 

study area in certain key multi-city 

epidemiological studies (Rajan et al., 

2011), some commenters in this group 

raised a number of issues related to this 

analysis (API, 2012, Attachment 1 pp. 5 

to 6; McClellan, 2012, pp.2 to 4). Some 

commenters noted the limited number 

of studies for which health event and 

study population data were available, 

and questioned whether these 

distributions would apply to other 

studies. Commenters expressed 

concerns that this analysis had not been 

formally reviewed by CASAC and was 

not published in the peer-review 

literature. Based on such concerns, 

some commenters asserted that the EPA 

should not consider this information as 

a basis for selecting a standard level. 

As an initial matter, as discussed in 

section III.E.4.b above, the EPA agrees 

with CASAC’s advice that it is 

appropriate to consider additional data 

beyond the mean PM2.5 concentrations 

in key multi-city studies to help inform 

selection of the level of the annual PM2.5

standard. As both the EPA and CASAC 

recognize, in the absence of a 

discernible threshold, health effects may 

occur over the full range of 

concentrations observed in the 

epidemiological studies. Nonetheless, 

the EPA recognizes that confidence in 

the magnitude and significance of an 

association is highest at and around the 

long-term mean PM2.5 concentrations 

reported in the studies and the degree 

of confidence becomes lower at lower 

concentrations within any given study. 

Following CASAC’s advice (Samet, 

2010d, p.2), the EPA used additional 

population-level and air quality data 

made available by study authors to 

conduct an analysis of the distributions 

of such data, to help inform 

consideration of how the degree of 

confidence in the magnitude and 

significance of observed associations 

varies across the range of long-term 

mean PM2.5 concentrations in study 

areas within key multi-city 

epidemiological studies. In the EPA’s 

view, such consideration is important in 

selecting a level for an annual standard 

that will protect public health with an 

adequate margin of safety. 

With regard to the number of multicity studies for which an analysis of the 

distributions of population-level data 

across the study areas and the 

corresponding annual mean PM2.5

concentrations was done, the EPA noted 

at proposal that data for such an 

analysis were made available from study 

authors for four studies, including two 

long-term exposure studies and two 

short-term exposure studies.96 The EPA 

recognized that access to health event 

data can be restricted due to 

confidentiality issues, such that it is not 

reasonable to expect that such 

information could be made available 

from all studies. In considering the 

information from these four studies, the 

EPA has further taken into 

consideration uncertainties discussed in 

response to the above comment related 

to the appropriate exposure period for 

long-term exposure studies. Based on 

these considerations, as noted above, 

the EPA concludes that such 

uncertainties are an important factor in 

evaluating the usefulness of the air 

quality information from the two longterm exposure studies in this analysis 

(Krewski et al., 2009; Miller et al., 2007) 

and that it would not be appropriate to 

place weight on the distributional 

analysis of health event and air quality 

data from these two studies specifically 

for the purpose of translating the 

information from the long-term 

mortality studies into a basis for 

selecting the level of the annual PM2.5

standard. Such uncertainties are not 

relevant to the short-term exposure 

studies, and thus, the Agency focuses on 

the two short-term exposure studies in 

this analysis (Bell et al., 2008; Zanobetti 

and Schwartz, (2009). 

In focusing on these two short-term 

exposure studies, the EPA first notes 

that these studies are key multi-city 

studies that reported positive and 

statistically significant associations 

between mortality and cardiovascularrelated hospital admissions across a 

large number of areas throughout the 

U.S. (112 U.S. cities in Zanobetti and 

Schwartz, 2009; 202 U.S. counties in 

Bell et al., 2008) using relatively recent 

air quality and health event data (i.e., 

1999 through 2005 in both studies). The 

EPA considers this to be a modest but 

important data set to use for this 

distributional analysis to help inform 

consideration of how much below the 

long-term mean PM2.5 concentrations in 

key multi-city long- and short-term 

exposure studies the annual PM2.5

standard level should be set. While the 

EPA acknowledges that having such 

data available from more studies would 

have been useful, the Agency finds the 

information from this limited set of 

studies to be an important consideration 

in selecting an annual standard level, 

consistent with CASAC advice to 

consider such information. 

In considering the results of this 

distributional analysis, as discussed 

more fully in the Response to Comments 

document, the EPA considers PM2.5

concentrations between the 25th and 

10th percentiles of the distribution of 

health events to be a reasonable range 

for providing a general frame of 

reference for that part of the distribution 

in which confidence in the magnitude 

and significance of the association may 

be appreciably lower than confidence at 

and around the long-term mean 

concentration. For the two short-term 

exposure studies included in this 

analysis, the EPA notes that the PM2.5

concentrations corresponding to the 

25th percentiles of the distributions of 


tkelley on DSK3SPTVN1PROD with 
3150 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

97Clinical significance was defined as an FEV1

below 80 percent of the predicted value, a criterion 

commonly used in clinical settings to identify 

persons at increased risk for adverse respiratory 

conditions (U.S. EPA, 2009a, p. 7–29 to 7–30). The 

primary NAAQS for sulfur dioxide (SO2) also 

included this interpretation for FEV1 (75 FR 35525, 

June 22, 2010). 

98 Gauderman et al. (2004) clearly stated 

throughout their analysis that NO2 was one 

component of a highly correlated mixture that 

contains PM2.5. Gauderman et al. (2004) did not 

present the results from copollutants models but 

stated ‘‘two-pollutant models for any pair of 

health events were 12.5 mg/m3 and 11.5 

mg/m3, respectively, for Zanobetti and 

Schwartz (2009) and for Bell et al. 

(2008), with the 10th percentiles being 

lower by approximately 2 mg/m3 in each 

study (Rajan et al., 2011, Table 1). In 

considering this information, the EPA 

recognizes, however, that there is no 

clear dividing line or single percentile 

within a given distribution (including 

both above and below the 25th 

percentile) provided by the scientific 

evidence that is most appropriate or 

‘correct’ to use to characterize where the 

degree of confidence in the associations 

warrants setting the annual standard 

level. The decision as to the appropriate 

standard level below the long-term 

mean concentrations of the key studies 

is largely a public health policy 

judgment to be made by the 

Administrator, taking into account all of 

the evidence and its related 

uncertainties, as discussed in section 

III.E.4.d below. 

In response to concerns that this 

analysis was not reviewed by CASAC 

nor published in the peer-reviewed 

literature, the EPA notes that this 

analysis was conducted to directly 

respond to advice from CASAC, as 

discussed in section III.E.4.b.i above, in 

conjunction with their review of the 

Policy Assessment. The EPA notes that 

the same type of distributional analysis 

was presented in the second draft Policy 

Assessment based on air quality data, as 

well as population-weighted air quality 

data, rather than health event or study 

population data. In considering that 

distributional information, CASAC 

urged that the EPA redo the analysis 

using health event or study population 

data, which is exactly what the EPA did 

and presented in the final Policy 

Assessment. The EPA provided CASAC 

with the final Policy Assessment and 

communicated how the final staff 

conclusions reflected consideration of 

its advice and that those staff 

conclusions were based in part on the 

specific distributional analysis that 

CASAC had urged the EPA to conduct 

(Wegman, 2011, Attachment p. 2). 

CASAC did not choose to provide any 

additional comments or advice after 

receiving the final Policy Assessment. 

The EPA considers this distributional 

analysis to be the product of the peer 

review conducted by CASAC of the 

Policy Assessment, and thus does not 

agree with commenters’ characterization 

that the analysis lacked appropriate peer 

review. The EPA’s final analysis was 

based on the comments provided by 

CASAC, the peer review committee 

established pursuant to the CAA, on the 

draft analysis, such that the final 

analysis stems directly from CASAC’s 

advice and the EPA’s response to its 

comments. 

Based on the above considerations, 

the EPA continues to conclude that its 

analysis of distributions of health event 

and air quality data from two key multicity epidemiological studies provides 

important information related to 

understanding the associations between 

health events observed in each city (e.g., 

deaths, hospitalizations) and the 

corresponding long-term mean PM2.5

concentrations observed in the studies. 

While recognizing that this is a 

relatively modest data set, the EPA 

further concludes that such information 

can appropriately help to inform the 

selection of the level of an annual 

standard that will protect public health 

with an adequate margin of safety from 

these types of health effects which are 

causally related to long- and short-term 

exposures to PM2.5. 

(4) Some commenters in this group 

asserted there were limitations in the 

long-term exposure studies of 

morbidity, including studies evaluating 

respiratory effects in children. For 

example, one commenter (UARG, 2012, 

p. 12, Attachment 1, pp. 14 to 16) 

asserted there were serious limitations 

in the long-term exposure studies of 

respiratory morbidity in each of the 

studies considered by the EPA 

(including McConnell et al., 2003; 

Gauderman et al., 2004; Dockery et al., 

1996; Raizenne et al., 1996; and Goss et 

al., 2004) and argued that this evidence 

provides only a ‘‘weak association’’ with 

PM2.5 exposures. This commenter 

asserted that many of these long-term 

exposure studies evaluating respiratory 

effects were considered at the time the 

EPA reaffirmed the current annual 

standard level of 15 mg/m3 in 2006, that 

the Administrator in the last review 

determined that the information they 

provided ‘‘was too limited to serve as 

the basis for setting a level of a national 

standard,’’ and that they should be 

given little weight in setting the level of 

the annual standard in this review 

(UARG, 2012, Attachment 1, p. 14). 

More specifically, this commenter 

asserted that the McConnell et al. (2003) 

and Gauderman et al. (2004) studies 

reported mixed results for associations 

with PM2.5 and stronger associations 

with NO2 (API, 2012, Attachment 1, pp. 

14 to 15). Similarly, this commenter 

argued that the Dockery et al. (1996) and 

Raizenne et al. (1996) studies showed 

stronger associations with acidity than 

with fine particles (measured as PM2.1). 

Id. pp. 15 to 16. With regard to the 

cystic fibrosis study, this commenter 

noted that the association between 

pulmonary exacerbations and PM2.5 in 

this study was no longer statistically 

significant when the model adjusted for 

each individual’s baseline lung 

function. The commenters referred to 

the data on lung function as an 

‘‘important explanatory variable,’’ and 

suggested that the EPA should rely on 

results from the model that included 

individual baseline lung function 

information. Id. p. 16. For the reasons 

discussed below and in more detail in 

the Response to Comments document, 

the EPA disagrees with the commenters’ 

interpretation of these studies. 

As an initial matter, the EPA notes 

that three of these studies (McConnell et 

al., 2003; Dockery et al., 1996; Raizenne 

et al., 1996) as well as the initial studies 

from the Southern California Children’s 

Health Study (Peters et al., 1999; 

McConnell et al., 1999; Gauderman et 

al., 2000, 2002; Avol et al., 2001) were 

discussed and considered in the 2004 

Air Quality Criteria Document (U.S. 

EPA, 2004) and, thus, considered within 

the air quality criteria supporting the 

EPA’s final decisions in the review 

completed in 2006. Two additional 

studies (Gauderman et al., 2004; Goss et 

al., 2004) were discussed and 

considered in the provisional science 

assessment conducted for the last 

review (U.S. EPA, 2006a). The EPA 

concluded that ‘‘new’’ studies 

considered in the provisional 

assessment completed in 2006 did not 

materially change any of the broad 

scientific conclusions regarding the 

health effects of PM exposure made in 

the Criteria Document (71 FR 61148 to 

61149, October 17, 2006). All of these 

studies were considered in the 

Integrated Science Assessment that 

informs the current review (U.S. EPA, 

2009a). 

With regard to the Southern California 

Children’s Health Study, extended 

analyses considered in the Integrated 

Science Assessment provided evidence 

that clinically important deficits in lung 

function 97 associated with long-term 

exposure to PM2.5 persist into early 

adulthood (U.S. EPA, 2009a, p. 7–27; 

Gauderman et al., 2004). These effects 

remained positive in copollutant 

models.98 Additional analyses of the 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3151 

pollutants did not provide a significantly better fit 

to the data than the corresponding single-pollutant 

models.’’ 

99The 24-City study conducted by Dockery et al. 

(1996) included 18 sites in the U.S. and 6 sites in 

Canada. The Raizenne et al. (1996) study 

considered 22 of these 24 study areas. Athens, OH 

and South Brunswick, NJ were not included in this 

study. 

Southern California Children’s Health 

Study cohort reported an association 

between long-term PM2.5 exposure and 

bronchitic symptoms (U.S. EPA, 2009a, 

p. 7–23 to 7–24; McConnell et al., 2003, 

long-term mean concentration of 13.8 

mg/m3) that remained positive in copollutant models, with the PM2.5 effect 

estimates increasing in magnitude in 

some models and decreasing in others, 

and a strong modifying effect of PM2.5

on the association between lung 

function and asthma incidence (U.S. 

EPA, 2009a, 7–24; Islam et al., 2007). 

The outcomes observed in the more 

recent reports from the Southern 

California Children’s Health Study, 

including evaluation of a broader range 

of endpoints and longer follow-up 

periods, were larger in magnitude and 

more precise than reported in the initial 

version of the study. Supporting these 

results were new longitudinal cohort 

studies conducted by other researchers 

in varying locations using different 

methods (U.S. EPA, 2009a, section 

7.3.9.1). The EPA, therefore, disagrees 

with the commenters that the studies by 

McConnell et al. (2003) and Gauderman 

et al. (2004) are flawed and should not 

be used in the PM NAAQS review 

process. 

The 24-City study 99 by Dockery et al. 

(1996) (long-term mean concentration of 

14.5 mg/m3) was considered in the 

current as well as two previous reviews 

(U.S. EPA, 2009a; U.S. EPA, 2004; U.S. 

EPA, 1996). This study observed that 

PM, specifically ‘‘particle strong 

acidity’’ and sulfate particles (indicators 

of fine particles), were associated with 

reports of bronchitis in the previous 

year. Similarly, the magnitude of the 

associations between bronchitis and 

PM10 and PM2.1 were similar to those for 

acidic aerosols and sulfate particles, 

though the confidence intervals for the 

PM10 and PM2.1 associations were 

slightly wider and the associations were 

not statistically significant. Acid 

aerosols, sulfate, and fine particles are 

formed in secondary reactions of the 

emissions from incomplete combustion 

and these pollutants have similar 

regional and temporal distributions. As 

noted by the study authors, ‘‘the strong 

correlations of several pollutants in this 

study, especially particle strong acidity 

with sulfate (r=0.90) and PM2.1 (r=0.82), 

make it difficult to distinguish the agent 

of interest’’ (Dockery et al., 1996, p. 

505). Overall, Dockery et al. (1996) (and, 

similarly, Raizenne et al., 1996) 

observed similar associations between 

respiratory health effects and acid 

aerosols, sulfate, PM10 and PM2.1

concentrations. The commenters noted 

that the associations with particle 

acidity were sensitive to the inclusion of 

the six Canadian sites. The EPA notes 

that none of these Canadian cities were 

in the ‘‘sulfate belt’’ where particle 

strong acidity was highest. Thus, the 

change in the effect estimate when the 

six Canadian cities were excluded from 

the analysis is likely due to the lower 

prevalence of bronchitis and the lower 

concentrations of acid aerosols in these 

cities, and not due to some difference in 

susceptibility to bronchitis between the 

U.S. and Canadian populations that is 

not due to air pollution, as suggested by 

the commenters (UARG, 2012, 

Attachment 1, p. 15). In fact, contrary to 

the statements made by the commenters, 

the authors did not observe any 

subgroups that appeared to be markedly 

more susceptible to the risk of 

bronchitis. 

The Goss et al. (2004) study 

considered a U.S. cohort of cystic 

fibrosis patients and provided evidence 

of association between long-term PM2.5

exposures and exacerbations of 

respiratory symptoms resulting in 

hospital admissions or use of home 

intravenous antibiotics (U.S. EPA, 

2009a, p. 7–25; long-term mean 

concentration of 13.7 mg/m3). The 

commenters noted that the association 

between pulmonary exacerbations and 

PM2.5 in this study was no longer 

statistically significant when the model 

adjusted for each individual’s baseline 

lung function. The commenters referred 

to the data on lung function as an 

‘‘important explanatory variable,’’ and 

suggested that the EPA should rely on 

results from the model that included 

individual baseline lung function 

information. The EPA disagrees with the 

commenters’ interpretation of this 

study. The Agency concludes it is 

unlikely that lung function is a potential 

confounder or an important explanatory 

variable in this study. In fact, the 

authors noted that ‘‘it is more likely that 

lung function decline may be intimately 

associated with chronic exposure to air 

pollutants and may be part of the causal 

pathway in worsening prognosis in CF 

[cystic fibrosis]; in support of this 

explanation, we found both crosssectional and longitudinal strong 

inverse relationships between FEV1 and 

PM levels’’ (Goss et al., 2004, p. 819). 

The EPA notes that adjusting for a 

variable that is on the causal pathway 

can lead to overadjustment bias, which 

is likely to attenuate the association 

(Schisterman et al. 2009); this is likely 

what was observed by the authors. 

Thus, the EPA continues to believe it is 

appropriate to focus on the results 

reported in Goss et al. (2004) that did 

not include individual baseline lung 

function in the model. 

In addition, the EPA disagrees with 

commenters’ reliance solely on 

statistical significance when 

interpreting the study results from 

individual study results and the 

collective evidence across studies. As 

discussed in section III.D.2 above, 

statistical significance of individual 

study findings has played an important 

role in the EPA’s evaluation of the 

study’s results and the EPA has placed 

greater emphasis on studies reporting 

statistically significant results. However, 

in the broader evaluation of the 

evidence from many epidemiological 

studies, and subsequently during the 

process of forming causality 

determinations in the Integrated Science 

Assessment by integrating evidence 

from across epidemiological, controlled 

human exposure, and toxicological 

studies, the EPA has emphasized the 

pattern of results across epidemiological 

studies and whether the effects observed 

were coherent across the scientific 

disciplines for drawing conclusions on 

the relationship between PM2.5 and 

different health outcomes. 

As noted in section III.B.1.a of the 

proposal, with regard to respiratory 

effects, the Integrated Science 

Assessment concluded that extended 

analyses of studies available in the last 

review as well as new epidemiological 

studies conducted in the U.S. and 

abroad provided stronger evidence of 

respiratory-related morbidity associated 

with long-term PM2.5 exposure (77 FR 

38918). The strongest evidence for 

respiratory-related effects available in 

this review was from epidemiological 

studies that evaluated decrements in 

lung function growth in children and 

increased respiratory symptoms and 

disease incidence in adults (U.S. EPA, 

2009a, sections 2.3.1.2, 7.3.1.1, and 

7.3.2.1). 

In considering the collective evidence 

from epidemiological, toxicological, and 

controlled human exposure studies, 

including the studies discussed above, 

the EPA recognizes that the Integrated 

Science Assessment concluded that a 

causal relationship is likely to exist 

between long-term PM2.5 exposures and 

respiratory effects (U.S. EPA, 2009a, p. 

2–12, pp. 7–42 to 7–43). CASAC 

concurred with this causality 

determination (Samet, 2009f, p.9). 


tkelley on DSK3SPTVN1PROD with 
3152 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

100As discussed in section II.A above, the 

requirement that primary standards provide an 

adequate margin of safety was intended to address 

uncertainties associated with inconclusive 

scientific and technical information available at the 

time of standard setting. I was also intended to 

provide a reasonable degree of protection against 

hazards that research has not yet identified. This 

certainly encompasses consideration of effects for 

which there is evidence suggestive of a causal 

relationship. 

101As discussed in section III.E.4.c.ii, many of 

these commenters also supported lowering the level 

of the primary 24-hour PM2.5 standard. 

The commenter’s assertion that the 

EPA should adhere to its assessment of 

these studies as it did in the review 

completed in 2006 is significantly 

mistaken. Most obviously, the EPA’s 

final decision in the last review was 

held to be deficient by the DC Circuit in 

remanding the 2006 primary annual 

PM2.5 standard. As discussed in section 

III.A.2 above, the DC Circuit specifically 

held that the EPA did not provide a 

reasonable explanation of why certain 

morbidity studies, including an earlier 

study from the Southern California 

Children’s Health Study (Gauderman et 

al., 2000, long-term mean PM2.5

concentration approximately 15 mg/m3) 

and the 24-Cities Study (Raizenne et al., 

1996, long-term mean concentrations 

approximately 14.5 mg/m3) did not 

warrant a more stringent annual PM2.5

standard when the long-term mean 

PM2.5 concentrations reported in those 

studies were at or lower than the level 

of the annual standard. American Farm 

Bureau Federation v. EPA. 559 F. 3d at 

525. Indeed, the court found that, 

viewed together, the Gauderman et al. 

(2000) and Raizenne et al., (1996) 

studies ‘‘are related and together 

indicate a significant public health risk 

* * * On this record, therefore, it 

appears the EPA too hastily discounted 

the Gauderman and 24-Cities studies as 

lacking in significance.’’ Id. 

In this review, the EPA recognizes a 

significant amount of evidence beyond 

these two studies that expands our 

understanding of respiratory effects 

associated with long-term PM2.5

exposures. This body of scientific 

evidence includes an extended and new 

analyses from the Southern California 

Children’s Health Study (Gauderman et 

al., 2004; Islam et al., 2007; Stanojevic 

et al., 2008) as well as additional studies 

that examined these health effects (Kim 

et al., 2004; Goss et al., 2004). Thus, 

even more so than in the last review, the 

evidence indicates a ‘‘significant public 

health risk’’ to children from long-term 

PM2.5 exposures at concentrations below 

the level of the current annual standard. 

A standard that does not reflect 

appropriate consideration of this 

evidence would not be requisite to 

protect public health with an adequate 

margin of safety. 

(5) With regard to the use of studies 

of health effects for which the EPA finds 

the evidence to be ‘‘suggestive’’ of a 

causal relationship, some commenters 

argued that such studies ‘‘do not merit 

any weight in the setting of the annual 

NAAQS’’ (e.g., UARG, 2012, Appendix 

1, p. 3). 

The EPA disagrees with the 

commenter’s view that studies of health 

effects for which the evidence is 

suggestive of a causal relationship, 

rather than studies of health effects for 

which the evidence supports a causal or 

likely causal relationship, merit no 

weight at all in setting the NAAQS. To 

place no weight at all on such evidence 

would in essence treat such evidence as 

though it had been categorized as ‘‘not 

likely to be a causal relationship.’’ To do 

so would ignore the important 

distinctions in the nature of the 

evidence supporting these different 

causality determinations in the 

Integrated Science Assessment. It would 

also ignore the CAA requirement that 

primary standards are to be set to 

provide protection with an adequate 

margin of safety, including providing 

protection for at-risk populations. Thus, 

ignoring this information in making 

decisions on the appropriate standard 

level would not be appropriate.100

Nonetheless, in considering studies of 

health effects for which the evidence is 

suggestive of a causal relationship, the 

EPA does believe that it is appropriate 

to place less weight on such studies 

than on studies of health effects for 

which there is evidence of a causal or 

likely causal relationship. 

A second group of commenters 

supported revising the suite of primary 

PM2.5 standards to provide increased 

public health protection. These 

commenters found the available 

scientific information and technical 

analyses to be stronger and more 

compelling than in the last review. 

These commenters generally placed 

substantial weight on CASAC advice 

and on the EPA staff analyses presented 

in the final Policy Assessment, which 

concluded that the evidence most 

strongly supported an annual standard 

level within a range of 11 to 12 mg/m3

(U.S. EPA, 2011a, p. 2–206). While some 

of these commenters felt that the level 

should be set within the proposed range 

(12 to 13 mg/m3), most of these 

commenters advocated a level of 11 mg/ 

m3.101 For example, ALA et al., 

asserted: 

The EPA’s proposed PM2.5 standards, 

while a step in the right direction are 

insufficient to protect public health, 

including the health of susceptible 

populations, with an adequate margin of 

safety as required by the Clean Air Act 

* * *we will discuss the enormous gap in 

public health protection afforded by an 

annual standard of 13 mg/m3, at the upper 

end of the proposed range, compared to the 

more protective 11 mg/m3, as advocated by 

our organizations (ALA et al., 2012, p. 6). 

In general, these commenters 

expressed the view that given the 

strength of the available scientific 

evidence, the serious nature of the 

health effects associated with PM2.5

exposures, the large size of the at-risk 

populations, the risks associated with 

long- and short-term PM2.5 exposures, 

and the important uncertainties 

inherently present in the evidence, the 

EPA should follow a highly 

precautionary policy response by 

selecting an annual standard level that 

incorporates a large margin of safety. 

More specifically, these commenters 

offered a range of comments related to 

the general approach used by the EPA 

to select standard levels, including: (1) 

The EPA’s approach for setting a 

generally controlling annual standard; 

(2) the importance of the greatly 

expanded and stronger overall scientific 

data base; (3) consideration of the 

distributional statistical analysis 

conducted by the EPA and other 

approaches for translating the air quality 

information from specific 

epidemiological studies into standard 

levels; and (4) the significance of the 

PM2.5-related public health impacts, 

especially potential impacts on at-risk 

populations, including children, in 

reaching judgments on setting standards 

that provide protection with an 

adequate margin of safety. These 

comments are discussed in turn below. 

(1) Some of these commenters 

disagreed with the EPA’s approach for 

setting a ‘‘generally controlling’’ annual 

standard in conjunction with a 24-hour 

standard providing supplemental 

protection particularly for areas with 

high peak-to-mean ratios. These 

commenters argued this approach 

would lead to ‘‘regional inequities’’ as 

demonstrated in the EPA’s analyses 

contained in Appendix C of the Policy 

Assessment (ALA et al., pp. 26 to 27). 

Specifically, these commenters argued: 

There is no basis in the Clean Air Act for 

such a determination. The Clean Air Act 

requires only that the NAAQS achieve public 

health protection with an adequate margin of 

safety. It is well-documented that both longand short-term exposures to PM2.5 have 

serious and sometimes irreversible health 

impacts. There is no health protection reason 

to argue that one standard should be 

‘‘controlling’’ as a matter of policy without 

regard to the health consequences of such a 

policy. To adopt such a policy ignores the 

obligation to provide equal protection under 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3153 

102 In confirmation, a number of studies have 

presented analyses excluding higher PM 

concentration days and reported a limited effect on 

the magnitude of the effect estimates or statistical 

significance of the association (e.g., Dominici, 

2006b; Schwartz et al., 1996; Pope and Dockery, 

1992). 

the law to all Americans because it would 

result in uneven protection from air pollution 

in different localities and regions of the 

country (ALA et al., 2012, p. 26). 

The EPA believes these commenters 

misunderstood the basis for the EPA’s 

policy goal of setting a ‘‘generally 

controlling’’ annual standard. This 

approach relates exclusively to setting 

standards that will provide requisite 

protection against effects associated 

with both long- and short-term PM2.5

exposures. It does so by lowering the 

overall air quality distributions across 

an area, recognizing that changes in 

PM2.5 air quality designed to meet an 

annual standard would likely result not 

only in lower annual mean PM2.5

concentrations but also in fewer and 

lower peak 24-hour PM2.5

concentrations. As discussed in section 

III.A.3 in the proposal and above, the 

EPA recognizes that there are various 

ways to combine the two primary PM2.5

standards to achieve an appropriate 

degree of public health protection. 

Furthermore, the extent to which these 

two standards are interrelated in any 

given area depends in large part on the 

relative levels of the standards, the 

peak-to-mean ratios that characterize air 

quality patterns in an area, and whether 

changes in air quality designed to meet 

a given suite of standards are likely to 

be of a more regional or more localized 

nature. 

In focusing on an approach of setting 

a generally controlling annual standard, 

the EPA’s intent is in fact to avoid the 

potential ‘‘regional inequities’’ that are 

of concern to the commenters. The EPA 

judges that the most appropriate way to 

set standards that provide more 

consistent public health protection is by 

using the approach of setting a generally 

controlling annual standard. This 

judgment builds upon information 

presented in the Policy Assessment as 

discussed in section III.A.3 above. More 

specifically, the Policy Assessment 

recognized that the short-term exposure 

studies primarily evaluated daily 

variations in health effects with 

monitor(s) that measured the variation 

in daily PM2.5 concentrations over the 

course of several years. The strength of 

the associations observed in these 

epidemiological studies was 

demonstrably in the numerous ‘‘typical’’ 

days within the air quality distribution, 

not in the peak days (U.S. EPA, 2011a, 

p. 2–9). In addition, the quantitative risk 

assessments conducted for this and 

previous reviews demonstrated the 

same point, that is, much, if not most, 

of the aggregate risk associated with 

short-term PM2.5 exposures results from 

the large number of days during which 

the 24-hour average concentrations are 

in the low-to mid-range, below the peak 

24-hour concentrations (U.S. EPA, 

2011a, section 2.2.2; U.S. EPA, 2010a, 

section 3.1.2.2). In addition, there was 

no evidence suggesting that risks 

associated with long-term exposures 

were likely to be disproportionately 

driven by peak 24-hour 

concentrations.102

For these reasons, the Policy 

Assessment concluded that strategies 

that focused primarily on reducing peak 

days were less likely to achieve 

reductions in the PM2.5 concentrations 

that were most strongly associated with 

the observed health effects. 

Furthermore, the Policy Assessment 

concluded that an approach that 

focused on reducing peak exposures 

would most likely result in more 

uneven public health protection across 

the U.S. by either providing inadequate 

protection in some areas or 

overprotecting in other areas (U.S. EPA, 

2011a, p. 2–9; U.S. EPA, 2010a, section 

5.2.3). This is because reductions based 

on control of peak days are less likely 

to control the bulk of the air quality 

distribution. 

As a result, the EPA believes an 

approach that focuses on a generally 

controlling annual standard would 

likely reduce aggregate risks associated 

with both long- and short-term 

exposures more consistently than a 

generally controlling 24-hour standard 

and, therefore, would be the most 

effective and efficient way to reduce 

total PM2.5-related population risk. The 

CASAC agreed with this approach and 

considered it was ‘‘appropriate to return 

to the strategy used in 1997 that 

considers the annual and the short-term 

standards together, with the annual 

standard as the controlling standard, 

and the short-term standard 

supplementing the protection afforded 

by the annual standard’’ (Samet, 2010d, 

p. 1). For the reasons discussed above, 

the EPA disagrees with the comments 

that this approach will result in the 

concerns raised by the commenters; 

rather the EPA concludes that this 

approach will help to address these 

concerns. 

(2) Many of these commenters 

asserted that the currently available 

scientific information is greatly 

expanded and stronger compared to the 

last review. Some of these commenters 

highlighted the availability of multiple, 

multi-city long- and short-term exposure 

studies providing ‘‘repeated, consistent 

evidence of effects below the current 

annual standard level’’ (ALA et al., 

2012, pp. 39 to 49) and, more 

specifically, ‘‘significant evidence of 

harm with strong confidence well below 

EPA’s proposed annual standard range 

of 12–13 mg/m3’’ (AHA et al., 2012, pp. 

10 to 12). 

The EPA recognizes that in setting 

standards that are requisite to protect 

public health with an adequate margin 

of safety, the Administrator must weigh 

the various types of available scientific 

information in reaching public health 

policy judgments that neither overstate 

nor understate the strength and 

limitations of this information or the 

appropriate inferences to be drawn from 

the available science. 

In general, the EPA agrees with these 

commenters’ views that the currently 

available scientific evidence is stronger 

‘‘because of its breadth and the 

substantiation of previously observed 

health effects’’ (77 FR 38906/2) and 

provides ‘‘greater confidence in the 

reported associations than in the last 

review’’ (77 FR 38940/1). The EPA also 

agrees with the commenters’ position 

that it is appropriate to consider the 

regions within the broader air quality 

distributions where we have the 

strongest confidence in the associations 

reported in epidemiological studies in 

setting the level of the annual standard. 

However, as discussed in section 

III.E.4.d below, in weighing the 

available evidence and technical 

analyses, as well as the associated 

uncertainties and limitations in that 

information, the EPA disagrees with the 

commenters’ views regarding the extent 

to which the available scientific 

information provides support for 

considering an annual standard level 

below the proposed range (i.e., below 12 

to 13 mg/m3). In particular, the EPA 

disagrees with the degree to which these 

commenters place more weight on the 

relatively more uncertain evidence that 

is suggestive of a causal relationship 

(e.g., low birth weight). Consistent with 

CASAC advice (Samet, 2010d, p. 1), the 

Agency concludes it is appropriate and 

reasonable to place the greatest 

emphasis on health effects for which the 

Integrated Science Assessment 

concluded there is evidence of a causal 

or likely causal relationship and to 

place less weight on the health effects 

that provide evidence that is only 

suggestive of a causal relationship. 

(3) With regard to using the air quality 

information from epidemiological 

studies to inform decisions on standard 

levels, commenters in this group 

generally supported the EPA’s efforts to 

explore different statistical metrics from 


tkelley on DSK3SPTVN1PROD with 
3154 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

epidemiological studies to inform the 

Administrator’s decisions. These 

commenters argued that by considering 

different analytic measures—either 

concentrations one standard deviation 

below the long-term means reported in 

the epidemiological studies or the EPA’s 

distributional statistical analysis of 

population-level data that extends the 

approach used in previous PM NAAQS 

reviews to consider information beyond 

a single statistical metric—‘‘the annual 

standard must be significantly lower 

than EPA has proposed’’ (ALA et al., 

2012, pp. 50 to 61). Furthermore, with 

regard to characterizing the PM2.5 air 

quality at which associations have been 

observed, some of these commenters 

highlighted CASAC’s recommendation 

that ‘‘[f]urther consideration should be 

given to using the 10th percentile as a 

level for assessing various scenarios of 

levels for the PM NAAQS’’ (Samet, 

2010c, p. 11) (ALA et al., 2012, p. 55). 

Other commenters urged that the EPA 

extend the distributional analysis to 

include additional studies. For example, 

CHPAC urged the EPA to also conduct 

distributional analysis for children’s 

health studies to better inform standards 

that would protect both children and 

adults from adverse health outcomes 

(CHPAC, 2012, p. 3). 

The EPA agrees with these 

commenters’ views that it is appropriate 

to take into account different statistical 

metrics from epidemiological studies to 

inform the decisions on standard levels 

that are appropriate to consider in 

setting a standard that will protect 

public health with an adequate margin 

of safety. In the development of the 

Policy Assessment, the EPA staff 

explored various approaches for using 

information from epidemiological 

studies in setting the standards. The 

general approach used in the final 

Policy Assessment, discussed in 

sections III.A.3 and III.E.4.a above, 

reflects consideration of CASAC advice 

(Samet, 2010c, d) and public comments 

on multiple drafts of the Policy 

Assessment. 

With regard to using the distributional 

statistical analysis to characterize the 

confidence in the associations, the EPA 

emphasizes that there is no clear 

dividing line provided by the scientific 

evidence, and that choosing how far 

below the long-term mean 

concentrations from the epidemiological 

studies is appropriate to identify a 

standard level that will provide 

protection for the public health with an 

adequate margin of safety is largely a 

public health policy judgment. The EPA 

considers the region from approximately 

the 25th to 10th percentiles to be a 

reasonable range for providing a general 

frame of reference as to the part of the 

distribution over which our confidence 

in the magnitude and significance of the 

associations observed in 

epidemiological studies is appreciably 

lower. Based on these considerations, 

the EPA concludes that it is not 

appropriate to place as much confidence 

in the magnitude and significance of the 

associations over the lower percentiles 

of the distributions in each study as at 

and around the long-term mean 

concentrations. Thus, the EPA disagrees 

with the commenters’ views that this 

analysis compels placing more 

emphasis on the lower part of this range 

in selecting a level for an annual 

standard that will protect public health 

with an adequate margin of safety. The 

EPA recognizes that this information 

comes primarily from two short-term 

exposure studies, a relatively modest 

data set. In light of the limited nature of 

this information, and in recognition of 

more general uncertainties inherent in 

the epidemiological evidence, the 

Administrator deems it reasonable not 

to place more emphasis on 

concentrations in the lower part of this 

range, as discussed below in section 

III.E.4.d. 

With regard to the scope of the 

distributional statistical analysis, the 

EPA requested additional populationlevel data from the study authors for a 

group of six multi-city studies for which 

previous air quality analyses had been 

conducted (Hassett-Sipple et al., 2010; 

Schmidt et al., 2010, Analysis 2). These 

six studies were originally selected 

because they considered multiple 

locations representing varying 

geographic regions across multiple 

years. Thus, these studies provided 

evidence on the influence of different 

particle mixtures on health effects 

associated with long- and short-term 

PM2.5 exposures. In addition, these 

multi-city studies considered relatively 

more recent health events and air 

quality conditions (1999 to 2005). As 

discussed in section III.E.4.b.i above, the 

EPA received and analyzed populationlevel data for four of the six studies 

(Rajan et al., 2011). Three of these four 

studies (Krewski et al., 2009; Bell et al., 

2008; Zanobetti and Schwartz, 2009) 

served as the basis for the 

concentration-response functions used 

to develop the core risk estimates (U.S. 

EPA, 2010a, section 3.3.3). While, the 

EPA agrees that it would be useful to 

have such data from more studies, the 

Agency believes that the additional data 

that was requested and received from 

study authors provide useful 

information to help inform the 

Administrator’s selection of the annual 

standard level. 

(4) Many commenters in this group 

highlighted PM2.5-related impacts on atrisk populations, including potential 

impacts on children, older adults, 

persons with pre-existing heart and lung 

disease, and low-income populations, to 

support their views that the annual 

standard should be revised to a level of 

11 mg/m3 or lower (CHPAC, 2012; AHA 

et al., 2012; ALA, 2012, pp. 29 to 38; 

Rom et al., 2012; Air Alliance Houston, 

et al., 2012). These commenters urged 

the EPA to adopt a policy approach that 

placed less weight on the remaining 

uncertainties and limitations in the 

evidence and placed more emphasis on 

margin of safety considerations, 

including providing protection against 

effects for which there is more limited 

scientific evidence. For example, 

CHPAC urged the EPA ‘‘to place the 

same weight on studies examining 

impacts on children’s health as that of 

adult studies. * * * The fact that there 

may be stronger evidence from adult 

studies does not mean that standards 

based on adult studies will be protective 

for children and consequently will meet 

the standard requisite to protect public 

health with an adequate margin of 

safety’’ (CHPAC, 2012 p. 3). 

Furthermore, with regard to the EPA’s 

approach for weighing uncertainties, 

some of these commenters stated that 

‘‘we find no justification in the 

preamble for an annual standard level as 

high as 13 mg/m3, other than the vague 

assertion that uncertainties increase at 

lower concentrations. Further, the final 

proposal completely failed to address 

the Policy Assessment 

recommendations that if 13 mg/m3 was 

proposed, the 24-hour standard should 

be strengthened as well’’ (ALA et al., p. 

7). 

The EPA has carefully evaluated and 

considered evidence of effects in at-risk 

populations. With regard to effects 

classified as having evidence of a causal 

or likely causal relationship with longor short-term PM2.5 exposures (i.e., 

premature mortality, cardiovascular 

effects, and respiratory effects), the 

Agency takes note that it considered the 

full range of studies evaluating these 

effects, including studies of at-risk 

populations, to inform its review of the 

primary PM2.5 standards. Specific multicity studies summarized in Figures 1, 2, 

and 3 above highlight evidence of 

effects observed in two different 

lifestages—children and older adults— 

that have been identified as at-risk 

populations. Thus, the EPA places as 

much weight on studies that explored 

effects in children for which the 

evidence is causal or likely causal in 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3155 

nature as on studies of such effects in 

adults, including older adults. As 

discussed above in responses to 

commenters supporting the retention of 

the current standards, in setting the 

standard, the EPA has focused on 

considering PM2.5 concentrations 

somewhat below the lowest long-term 

mean concentrations from each of the 

key studies of both long- and short-term 

exposures of effects for which the 

evidence supports a causal or likely 

causal relationship (i.e., the first two 

sets of studies shown in Figure 4). 

Absent some reason to ignore or 

discount these studies, which the 

commenter does not provide (and of 

which the EPA is unaware), the EPA 

considers the available evidence of 

effects in children as well as other atrisk populations. 

With respect to the EPA’s 

consideration of more limited studies 

providing evidence suggestive of a 

causal relationship (e.g., developmental 

and reproductive effects), as noted 

above in responding to comments from 

the first group of commenters, the 

Agency agrees that it is important to 

place some weight on this body of 

evidence in setting standards that 

provide protection for at-risk 

populations, as required by the CAA. 

However, the Agency does not agree 

that the same weight must be placed on 

this information as on the body of 

scientific information for which there is 

evidence of a causal or likely causal 

relationship. To do so would ignore the 

difference in the breadth and strength of 

the evidence supporting the different 

causality determinations reached in the 

Integrated Science Assessment. 

With regard to weighing the 

uncertainties and limitations remaining 

in the evidence and technical analyses, 

as discussed in section II.A above, the 

EPA recognizes that in setting a primary 

NAAQS that provides an adequate 

margin of safety, the Administrator must 

consider a number of factors including 

the nature and severity of the health 

effects involved, the size of sensitive 

population(s) at risk, and the kind and 

degree of the uncertainties that remain. 

As discussed in section III.E.4.d below, 

the Agency agrees with these 

commenters that, in weighing the 

available evidence and technical 

analyses including the uncertainties and 

limitations in this scientific 

information, there is no justification for 

setting a primary PM2.5 annual standard 

level as high as 13 mg/m3. 

Finally, some commenters in both 

groups also identified ‘‘new’’ studies 

that were not included in the Integrated 

Science Assessment as providing further 

support for their views on the level of 

the annual standard. As discussed in 

section II.B.3 above, the EPA completed 

a provisional review and assessment of 

‘‘new’’ studies published since the close 

of the Integrated Science Assessment, 

including ‘‘new’’ studies submitted by 

commenters (U.S. EPA, 2012b). The 

provisional assessment found that the 

‘‘new’’ studies expand the scientific 

information considered in the Integrated 

Science Assessment and provide 

important insights on the relationship 

between PM2.5 exposure and health 

effects of PM (U.S. EPA, 2012b). 

However, the EPA notes that the 

provisional assessment found that the 

‘‘new’’ science did not materially 

change the conclusions reached in the 

Integrated Science Assessment. The 

EPA notes that, as in past NAAQS 

reviews, the Agency is basing the final 

decisions in this review on the studies 

and related information included in the 

Integrated Science Assessment that have 

undergone CASAC and public review, 

and will consider newly published 

studies for purposes of decision making 

in the next PM NAAQS review. 

ii. 24-Hour Standard Level 

With respect to the level of the 24- 

hour standard, the EPA received 

comments on the proposal from two 

distinct groups of commenters. One 

group that included virtually all 

commenters representing industry 

associations, businesses, and many 

States agreed with the Agency’s 

proposed decision to retain the level of 

the 24-hour PM2.5 standard. The other 

group of commenters included many 

medical groups, numerous physicians 

and academic researchers, many public 

health organizations, some State and 

local agencies, five State Attorneys 

General, and a large number of 

individual commenters. These 

commenters disagreed with the 

Agency’s proposed decision and argued 

that EPA should lower the level of the 

24-hour standard to 30 or 25 mg/m3. 

Comments from these groups on the 

level of the 24-hour PM2.5 standard are 

addressed below and in the Response to 

Comments Document. 

As noted above, of the public 

commenters who addressed the level of 

the 24-hour PM2.5 standard, all industry 

commenters and most State and local 

commenters supported the proposed 

decision to retain the current level of 35 

mg/m3. In many cases, these groups 

agreed with the rationale supporting the 

Administrator’s proposed decision to 

retain the current 24-hour PM2.5

standard, including her emphasis on the 

annual standard as the generally 

controlling standard with the 24-hour 

standard providing supplementary 

protection, and her conclusion that 

multi-city, short-term exposure studies 

provide the strongest data set for 

informing decisions on the appropriate 

24-hour standard level. Many of these 

commenters agreed with the 

Administrator’s view that the singlecity, short-term studies provided a 

much more limited data set (e.g., limited 

statistical power, limited exposure data) 

and more equivocal results (e.g., mixed 

results within the same study area), 

making them an unsuitable basis for 

setting the level of the 24-hour standard. 

While these commenters agreed with 

the EPA’s proposed decision to retain 

the current 24-hour PM2.5 standard, 

some did not agree with the EPA’s 

approach to considering the evidence 

from short-term multi-city studies. For 

example, a commenter representing 

UARG pointed out that the 98th 

percentile concentrations reported in 

the proposal for multi-city studies 

reflect the averages of 98th percentile 

concentrations across the cities 

included in those studies (UARG, 2012; 

Attachment 1; p. 25). This commenter 

contended that such averaged 98th 

percentile PM2.5 concentrations do not 

provide information that can 

appropriately inform a decision on the 

adequacy of the public health protection 

provided by the current or alternative 

24-hour standards. 

While the EPA agrees that there is 

uncertainty in linking effects reported in 

multi-city studies to specific air quality 

concentrations (U.S. EPA, 2011a, 

section 2.3.4.1), the EPA disagrees with 

this commenter’s view that such 

uncertainty precludes the use of 

averaged 98th percentile PM2.5

concentrations to inform a decision on 

the appropriateness of the protection 

provided by the 24-hour PM2.5 standard. 

In particular, the EPA notes that 

averaged 98th percentile concentrations 

do provide information on the extent to 

which study cities contributing to 

reported associations would likely have 

met or violated the current 24-hour 

PM2.5 standard during the study period. 

As evidence of this, the EPA notes the 

three multi-city studies specifically 

highlighted by this commenter as 

having averaged 98th percentile 24-hour 

PM2.5 concentrations below 35 mg/m3

(Dominici et al., 2006a; Bell et al., 2008; 

Zanobetti and Schwartz, 2009). Based 

on the 98th percentiles of 24-hour PM2.5

concentrations in the individual cities 

evaluated in these studies, the EPA 

notes that the majority of these study 

cities would likely have met the current 

standard during the study periods 

(Hassett-Sipple et al., 2010). Therefore, 

regardless of whether the averaged 98th 

percentile concentrations or the 98th 


tkelley on DSK3SPTVN1PROD with 
3156 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

103This is not to say that the EPA’s decision on 

whether to revise the 24-hour PM2.5 standard 

should be based on or only be informed by 

considerations of whether studies reported 

associations with mortality or morbidity in areas 

with averaged 98th percentile PM2.5 concentrations 

less than 35 mg/m3. As discussed below, in 

reaching a decision in this final notice on the most 

appropriate approach to strengthen the suite of 

PM2.5 standards, the Administrator considers the 

degree of public health protection provided by the 

combination of the annual and 24-hour standards 

together. 

104Commenters also highlighted associations 

with short-term PM2.5 concentrations reported in 

sub-analyses restricted to days with 24-hour 

concentrations at or below 35 mg/m3 (Dominici, 

2006b). These sub-analyses were not included in 

the original publication by Dominici et al. (2006a). 

Authors provided results of sub-analyses for the 

Administrator’s consideration in a letter to the 

docket following publication of the proposed rule 

in January 2006 (personal communication with Dr. 

Francesca Dominici, 2006b). As noted in section 

III.A.3, these sub-analyses are part of the basis for 

the conclusion that there is no evidence suggesting 

that risks associated with long-term exposures are 

likely to be disproportionately driven by peak 24- 

hour concentrations. Because the sub-analyses did 

not present long-term average PM2.5 concentrations, 

it is not clear whether they reflected PM2.5 air 

quality that would have been allowed by the 

revised annual PM2.5 standard being established in 

this rule. 

105 It is also the case that additional protection is 

anticipated in locations with 98th percentile 24- 

hour PM2.5 concentrations above 35 mg/m3, even if 

long-term concentrations are below 12 mg/m3. As 

noted in the proposal and in the Policy Assessment 

(U.S. EPA, 2011a, Figure 2–10), parts of the 

northwestern U.S. are more likely than other parts 

of the country to violate the 24-hour standard and 

meet the revised annual standard. 

percentile concentrations in each city 

are considered, these studies provide 

evidence for associations between shortterm PM2.5 and mortality or morbidity 

across a large number of U.S. cities, the 

majority of which would likely have 

met the current 24-hour PM2.5 standard 

during study periods. In their review of 

the PM Policy Assessment, CASAC 

endorsed the conclusions drawn from 

analyses of averaged 98th percentile 24- 

hour PM2.5 concentrations, and the EPA 

continues to conclude that this type of 

information can appropriately inform 

the Administrator’s decision on the 

current 24-hour PM2.5 standard.103

Another group of commenters argued 

that the 24-hour standard level should 

be lowered. Many of these commenters 

supported setting the level of the 24- 

hour PM2.5 standard at either 25 or 30 

mg/m3. In support of their position, the 

ALA et. al., AHA et al., five state 

Attorneys General, and a number of 

additional groups pointed to 98th 

percentile PM2.5 concentrations in 

locations of multi-city and single-city 

epidemiological studies. For example, 

the ALA and others pointed to multicity studies by Dominici et al. (2006a), 

Zanobetti and Schwartz (2009), Burnett 

et al. (2000), and Bell et al. (2008) as 

providing evidence for associations with 

mortality and morbidity in study 

locations with averaged (i.e., averaged 

across cities) 98th percentile 24-hour 

PM2.5 concentrations below 35 mg/m3. 

These commenters also pointed to 

several single-city and panel studies 

reporting associations between shortterm PM2.5 and mortality or morbidity in 

locations with relatively low 24-hour 

PM2.5 concentrations. Because some of 

these multi- and single-city studies have 

reported associations with health effects 

in locations with 98th percentile PM2.5

concentrations below 35 mg/m3, 

commenters maintained that the current 

24-hour PM2.5 standard (i.e., with its 

level of 35 mg/m3) does not provide an 

appropriate degree of protection in all 

areas. 

In further support of their position 

that the level of the current 24-hour 

standard should be lowered, these 

commenters pointed out the variability 

across the U.S. in ratios of 24-hour to 

annual PM2.5 concentrations. They 

noted that some locations, including 

parts of the northwestern U.S., 

experience relatively low annual PM2.5

concentrations but can experience 

relatively high 24-hour concentrations 

at certain times of the year. In order to 

provide protection against effects 

associated with short-term PM2.5

exposures, especially in locations with 

high ratios of 24-hour to annual PM2.5

concentrations, these commenters 

advocated setting a lower level for the 

24-hour standard. 

The EPA agrees with these 

commenters that it is appropriate to 

maintain a 24-hour PM2.5 standard in 

order to supplement the protection 

provided by the revised annual 

standard, particularly in locations with 

relatively high ratios of 24-hour to 

annual PM2.5 concentrations. However, 

in highlighting 98th percentile PM2.5

concentrations in study locations 

without also considering the impact of 

a revised annual standard on short-term 

concentrations, these commenters 

ignore the fact that many areas would be 

expected to experience decreasing shortand long-term PM2.5 concentrations in 

response to a revised annual standard. 

In considering the specific multi-city 

studies highlighted by public 

commenters who advocated a more 

stringent 24-hour standard, the EPA 

notes that such studies have reported 

consistently positive and statistically 

significant associations with short-term 

PM2.5 exposures in locations with 

averaged 98th percentile PM2.5

concentrations ranging from 45.8 to 34.2 

mg/m3 and long-term mean PM2.5

concentrations ranging from 13.4 to 12.9 

(Burnett and Goldberg, 2003; Burnett et 

al., 2004; Dominici et al., 2006a; Bell et 

al., 2008; Franklin et al., 2008; Zanobetti 

and Schwartz, 2009).104 The EPA notes 

that to the extent air quality 

distributions are reduced to meet the 

current 24-hour standard with its level 

of 35 mg/m3 and/or the revised annual 

standard with its level of 12 mg/m3, 

additional protection would be 

anticipated against the effects reported 

in these short-term, multi-city studies. 

Put another way, to attain an annual 

standard with a level below the longterm means in the locations of these 

short-term studies (as EPA is adopting 

here), the overall air quality 

distributions in the majority of study 

cities will necessarily be reduced, 

resulting in lower daily PM2.5 ambient 

concentrations. We therefore expect that 

the revised annual standard will result 

in 98th percentile PM2.5 concentrations 

in these cities that are lower than those 

measured in the studies, and that the 

overall distributions of PM2.5

concentrations will be lower than those 

reported to be associated with health 

effects. Thus, even for effects reported 

in multi-city studies with averaged 98th 

percentile concentrations below 35 mg/ 

m3, additional protection from the risks 

associated with short-term exposures is 

anticipated from the revised annual 

standard, without revising the 24-hour 

standard, because long-term average 

PM2.5 concentrations in multi-city study 

locations were above the level of the 

revised annual standard (i.e., 12 mg/ 

m3).105 As discussed above, reducing 

the annual standard is the most efficient 

way to reduce the risks from short-term 

exposures identified in these studies, as 

the bulk of the risk comes from the large 

number of days across the bulk of the 

air quality distribution, not the 

relatively small number of days with 

peak concentrations. 

In considering the single-city studies 

highlighted by public commenters who 

advocated a more stringent 24-hour 

standard, the EPA first notes that, 

overall, these single-city studies 

reported mixed results. Specifically, 

some studies reported positive and 

statistically significant associations with 

PM2.5, some studies reported positive 

but non-significant associations, and 

several studies reported negative 

associations or a mix of positive and 

negative associations with PM2.5. In 

light of these inconsistent results, the 

proposal noted that the overall body of 

evidence from single-city studies is 

mixed, particularly in locations with 

98th percentiles of 24-hour 

concentrations below 35 mg/m3. 

Therefore, although some single-city 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3157 

106This section focuses on the 24-hour standard. 

Section III.E.4.c.i above also discusses these 

commenters’ recommendations within the context 

of the annual PM2.5 standard. 

studies reported effects at appreciably 

lower PM2.5 concentrations than shortterm multi-city studies, the 

uncertainties and limitations associated 

with the single-city studies were noted 

to be greater. In light of these greater 

uncertainties and limitations, the 

Administrator concluded in the 

proposal that she had less confidence in 

using these studies as a basis for setting 

the level of the standard (77 FR 38943). 

Given the considerations and 

conclusions noted above, in the 

proposal the Administrator concluded 

that the short-term multi-city studies 

provide the strongest evidence to inform 

decisions on the level of the 24-hour 

standard. Further, she viewed singlecity, short-term exposure studies as a 

much more limited data set providing 

mixed results, and she had less 

confidence in using these studies as a 

basis for setting the level of a 24-hour 

standard (77 FR 38942). In highlighting 

specific single-city studies, public 

health, environmental, and State and 

local commenters appear to have 

selectively focused on studies reporting 

associations with PM2.5 and to have 

overlooked studies that reported more 

equivocal results (e.g., Ostro et al., 2003; 

Rabinovitch et al., 2004; Slaughter et al., 

2005; Villeneuve et al., 2006) (U.S. EPA, 

2011, Figure 2–9). As such, these 

commenters have not presented new 

information that causes the EPA to 

reconsider its decision to emphasize 

multi-city studies over single-city 

studies when identifying the 

appropriate level of the 24-hour PM2.5

standard. 

In further considering the single-city 

studies highlighted by public 

commenters, the EPA notes that some 

commenters advocating for a lower level 

for the 24-hour PM2.5 standard also 

discussed short-term studies that have 

been published since the close of the 

Integrated Science Assessment. These 

recent studies were conducted in single 

cities or in small panels of volunteers. 

As in prior NAAQS reviews and as 

discussed above in more detail (section 

II.B.3), the EPA is basing its decisions in 

this review on studies and related 

information assessed in the Integrated 

Science Assessment. The studies 

assessed in the Integrated Science 

Assessment, and the conclusions based 

on those studies, have undergone 

extensive critical review by the EPA, 

CASAC, and the public. The rigor of 

that review makes the studies assessed 

in the Integrated Science Assessment, 

and the conclusions based on those 

studies, the most reliable source of 

scientific information on which to base 

decisions on the NAAQS. 

However, as discussed above (section 

II.B.3), the EPA recognizes that ‘‘new 

studies’’ may sometimes be of such 

significance that it is appropriate to 

delay a decision on revision of a 

NAAQS and to supplement the 

pertinent air quality criteria so the 

studies can be taken into account. In the 

present case, the EPA’s provisional 

consideration of ‘‘new studies’’ 

concludes that, taken in context, the 

‘‘new’’ information and findings do not 

materially change any of the broad 

scientific conclusions made in the air 

quality criteria regarding the health 

effects of PM2.5 (U.S. EPA, 2012b). 

For this reason, reopening the air 

quality criteria review would not be 

warranted, even if there were time to do 

so under the court order governing the 

schedule for completing this review. 

Accordingly, the EPA is basing its final 

decisions in this review on the studies 

and related information included in the 

PM Integrated Science Assessment (i.e., 

the air quality criteria) that has 

undergone CASAC and public review. 

The EPA will consider the ‘‘new 

studies’’ in the next periodic review of 

the PM NAAQS, which will provide an 

opportunity to fully assess these studies 

through a more rigorous review process 

involving the EPA, CASAC, and the 

public. 

Some public health, medical, and 

environmental commenters also 

criticized the EPA’s interpretation of 

PM2.5 risk results. These commenters 

presented risk estimates for 

combinations of annual and 24-hour 

standards using more recent air quality 

data than that used in the EPA’s Risk 

Assessment (U.S. EPA, 2010a). Based on 

these additional risk analyses, the ALA 

and other commenters contended that 

public health benefits could continue to 

increase as annual and 24-hour standard 

levels decrease below 13 mg/m3 and 35 

mg/m3, respectively. 

The EPA agrees with commenters that 

important public health benefits are 

expected as a result of revising the level 

of the annual standard to 12 mg/m3, as 

is done in this rule, rather than 13 mg/ 

m3. The Agency also acknowledges that 

estimated PM2.5-associated health risks 

continue to decrease with annual 

standard levels below 12 mg/m3 and/or 

with 24-hour standard levels below 35 

mg/m3. However, the EPA disagrees with 

the commenters’ views regarding the 

extent to which risk estimates support 

setting standard levels below 12 mg/m3

(annual standard) and 35 mg/m3 (24- 

hour standard).106

The CAA charges the Administrator 

with setting NAAQS that are ‘‘requisite’’ 

(i.e., neither more nor less stringent than 

necessary) to protect public health with 

an adequate margin of safety. In setting 

such standards the Administrator must 

weigh the available scientific evidence 

and information, including associated 

uncertainties and limitations. As 

described above, in reaching her 

proposed decisions on the PM2.5

standards that would provide 

‘‘requisite’’ protection, the 

Administrator carefully considered the 

available scientific evidence and risk 

information, making public health 

policy judgments that, in her view, 

neither overstated nor understated the 

strengths and limitations of that 

evidence and information. In contrast, 

as discussed more fully above, public 

health, medical, and environmental 

commenters who recommended levels 

below 35 mg/m3 for the 24-hour PM2.5

standard have not provided new 

information or analyses to suggest that 

such standard levels are appropriate, 

given the uncertainties and limitations 

in the available health evidence, 

particularly uncertainties in studies 

conducted in locations with 98th 

percentile 24-hour PM2.5 concentrations 

below 35 mg/m3 and long-term average 

concentrations below 12 mg/m3. 

d. Administrator’s Final Conclusions on 

the Primary PM2.5 Standard Levels 

In reaching her conclusions regarding 

appropriate standard levels, the 

Administrator has considered the 

epidemiological and other scientific 

evidence, estimates of risk reductions 

associated with just meeting alternative 

annual and/or 24-hour standards, air 

quality analyses, related limitations and 

uncertainties, the advice of CASAC, and 

extensive public comments on the 

proposal. After careful consideration of 

all of these, the Administrator has 

decided to revise the level of the 

primary annual PM2.5 standard from 

15.0 mg/m3 to 12.0 mg/m3 and to retain 

the level of the primary 24-hour 

standard at 35 mg/m3. 

As an initial matter, the Administrator 

agrees with the approach supported by 

CASAC and discussed in the Policy 

Assessment as summarized in sections 

III.A.3 and III.E.4.a above, of 

considering the annual and 24-hour 

standards together in determining the 

protection afforded against mortality 

and morbidity effects associated with 

both long- and short-term exposures to 

PM2.5. This approach is consistent with 

the approach taken in the review 


tkelley on DSK3SPTVN1PROD with 
3158 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

107See 71 FR 61148 and 61168, October 17, 2006. 

completed in 1997, in contrast to the 

approach used in the review completed 

in 2006 where each standard was 

considered independently of the other 

(i.e., only data from long-term exposure 

studies were used to inform the level of 

the annual standard and only data from 

short-term exposure studies were used 

to inform the level of the 24-hour 

standard).107

Based on the evidence and 

quantitative risk assessment, the 

Administrator concludes that it is 

appropriate to set an annual standard 

that is generally controlling, which will 

lower the broad distribution of 24-hour 

average concentrations in an area as 

well as the annual average 

concentration, so as to provide 

protection from both long- and shortterm PM2.5 exposures. In conjunction 

with this, it is appropriate to set a 24- 

hour standard focused on providing 

supplemental protection, particularly 

for areas with high peak-to-mean ratios 

of 24-hour concentrations, possibly 

associated with strong local or seasonal 

sources, and for PM2.5-related effects 

that may be associated with shorter-than 

daily exposure periods. The 

Administrator concludes this approach 

will reduce aggregate risks associated 

with both long- and short-term 

exposures more consistently than a 

generally controlling 24-hour standard 

and is the most effective and efficient 

way to reduce total PM2.5-related 

population risk and to protect public 

health with an adequate margin of 

safety. 

In selecting the level of the annual 

PM2.5 standard, based on the 

characterization and assessment of the 

epidemiological and other studies 

presented and assessed in the Integrated 

Science Assessment and the Policy 

Assessment, the Administrator 

recognizes the substantial increase in 

the number and diversity of studies 

available in this review. This expanded 

body of evidence includes extended 

analyses of the seminal studies of longterm PM2.5 exposures (i.e., ACS and 

Harvard Six Cities studies) as well as 

important new long-term exposure 

studies (as summarized in Figures 1 and 

2). Collectively, the Administrator notes 

that these studies, along with evidence 

available in the last review, provide 

consistent and stronger evidence than 

previously observed of an association 

between long-term PM2.5 exposures and 

premature mortality in areas with lower 

long-term ambient concentrations than 

previously observed, with the strongest 

evidence related to cardiovascularrelated mortality. The Administrator 

also recognizes the availability of 

stronger evidence of morbidity effects 

associated with long-term PM2.5

exposures, including evidence of 

respiratory effects such as decreased 

lung function growth, from the extended 

analyses for the Southern California 

Children’s Health Study and evidence of 

cardiovascular effects from the WHI 

study. Furthermore, the Administrator 

recognizes new U.S. multi-city studies 

that greatly expand and reinforce our 

understanding of mortality and 

morbidity effects associated with shortterm PM2.5 exposures, providing 

stronger evidence of associations in 

areas with ambient concentrations 

similar to those previously observed in 

short-term exposure studies considered 

in the previous review (as summarized 

in Figure 3). 

The Administrator recognizes the 

strength of the scientific evidence for 

evaluating health effects associated with 

fine particles, noting that the newly 

available scientific evidence builds 

upon the previous scientific data base to 

provide evidence of generally robust 

associations and a basis for greater 

confidence in the reported associations 

than in the last review. She notes the 

conclusion of the Integrated Science 

Assessment that this body of evidence 

supports a causal relationship between 

long- and short-term PM2.5 exposures 

and mortality and cardiovascular effects 

and a likely causal relationship between 

long- and short-term PM2.5 exposures 

and respiratory effects. In addition, the 

Administrator notes additional, but 

more limited evidence, for a broader 

range of health endpoints including 

evidence suggestive of a causal 

relationship for developmental and 

reproductive effects as well as for 

carcinogenic effects. 

Based on information discussed and 

presented in the Integrated Science 

Assessment, the Administrator 

recognizes that health effects may occur 

over the full range of concentrations 

observed in the epidemiological studies 

of both long-term and short-term 

exposures, since no discernible 

population-level threshold for any such 

effects can be identified based on the 

currently available evidence (U.S. EPA, 

2009a, section 2.4.3). To inform her 

decisions on an appropriate level for the 

annual standard that will protect public 

health with an adequate margin of 

safety, in the absence of any discernible 

population-level thresholds, the 

Administrator judges that it is 

appropriate to consider the relative 

degree of confidence in the magnitude 

and significance of the associations 

observed in epidemiological studies 

across the range of long-term PM2.5

concentrations in such studies. Further, 

she recognizes, in taking note of CASAC 

advice and the distributional statistics 

analysis discussed in the Policy 

Assessment and in section III.E.4.a 

above, that there is significantly greater 

confidence in the magnitude and 

significance of observed associations for 

the part of the air quality distribution 

corresponding to where the bulk of the 

health events evaluated in each study 

have been observed, generally at and 

around the long-term mean 

concentrations. Conversely, she also 

recognizes that there is significantly 

diminished confidence in the 

magnitude and significance of observed 

associations in the lower part of the air 

quality distribution corresponding to 

where a relatively small proportion of 

the health events were observed. 

Further, the Administrator recognizes 

that the long-term mean concentrations, 

or any other specific point in the air 

quality distribution of each study, do 

not represent a ‘‘bright line’’ at and 

above which effects have been observed 

and below which effects have not been 

observed. 

In considering the long-term mean 

concentrations reported in 

epidemiological studies, the 

Administrator recognizes that in 

selecting a level of the annual standard 

that will protect public health with an 

adequate margin of safety, it is not 

sufficient to focus on a concentration 

generally somewhere within the range 

of long-term mean concentrations from 

the key long-term and short-term 

exposure studies that reported lower 

concentrations than had been observed 

in earlier reviews. These key studies 

provide information for various types of 

serious health endpoints (including 

mortality and morbidity effects), 

different study populations (which may 

include at-risk populations such as 

children and older adults), and different 

air quality distributions that are specific 

to each study. A level somewhere 

within the range of long-term mean 

concentrations of the full set of key 

studies would be higher than the longterm mean of at least one of the studies 

being considered and therefore would 

not provide a sufficient degree of 

protection against the health effects 

observed in that study. Absent some 

reasoned basis to place less weight on 

the evidence in the epidemiological 

study with the lowest long-term mean 

concentration among these key studies, 

this approach would not be consistent 

with the requirement to set a standard 

that will protect public health with an 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3159 

108See American Farm Bureau Federation v. 

EPA, 559 F. 3d 512, 525–26 (D.C. Cir. 2009). 

109 In the case of Miller et al. (2007), the mean 

concentration is based on a single year of air quality 

data which post-dated by two years the period for 

which the health events data were collected. In the 

case of Krewski et al. (2009), the air quality data 

were based on the last two years of the 18-year 

period for which the health event data were 

collected. 

110Nonetheless, as noted above, the EPA notes 

that the Krewski et al. (2009) and Miller et al. 

(2007) studies provide strong evidence of mortality 

and cardiovascular-related effects associated with 

long-term PM2.5 exposures to inform causality 

determinations reached in the Integrated Science 

Assessment (U.S. EPA, 2009a, sections 7.2.11 and 

7.6). 

111As summarized in section III.E.4.a, 

population-level data were provided to the EPA for 

four studies. These four studies represent some of 

the strongest evidence showing associations 

between health effects and PM2.5 within the overall 

body of scientific evidence and include three 

studies (Krewski et al., 2009; Bell et al., 2008; and 

Zanobetti and Schwartz, 2009) that were used as the 

basis for concentration-response functions in the 

quantitative risk assessment (U.S. EPA, 2010a, 

section 3.3.3). The Administrator recognizes that 

the additional population-level data available for 

these four multi-city studies represents a more 

limited data set compared to the set of long-term 

mean PM2.5 concentrations which were available in 

the published literature for all studies considered 

in the Integrated Science Assessment. 

adequate margin of safety.108 Thus, the 

Administrator recognizes it is important 

to protect against the serious effects 

observed in each of these studies so as 

to protect public health with an 

adequate margin of safety. In so doing, 

she looks to identify the study with the 

lowest long-term mean concentration 

within the full set of key studies to help 

inform her decision of the appropriate 

standard level which will provide 

protection for the broad array of health 

outcomes observed in all of the studies, 

including effects observed in at-risk 

populations. 

Further, consistent with the general 

approach summarized in section 

III.E.4.a above and supported by CASAC 

as discussed in section III.E.4.b.ii above, 

the Administrator recognizes that it is 

appropriate to consider a level for an 

annual standard that is not just at but 

rather is somewhat below the long-term 

mean PM2.5 concentrations reported in 

each of the key long- and short-term 

exposure studies. In so doing, she 

focuses especially on multi-city studies 

that evaluated health endpoints for 

which the associations are causal or 

likely causal (i.e., mortality and 

cardiovascular and respiratory effects 

associated with both long- and shortterm PM2.5 exposures). As discussed 

above, the importance of considering a 

level somewhat below the lowest longterm mean concentrations in this set of 

key studies is to establish a standard 

that would be protective against the 

observed effects in all of the studies, 

and that takes into account the relative 

degree of confidence in the magnitude 

and significance of observed 

associations across the air quality 

distributions in these studies. 

The Administrator recognizes that 

there is no clear way to identify how 

much below the long-term mean 

concentrations of key studies to set a 

standard that would provide requisite 

protection with an adequate margin of 

safety. She therefore must use her 

judgment to weigh the available 

scientific and technical information, 

and associated uncertainties, to reach a 

final decision on the appropriate 

standard level. In considering the 

information in Figures 1–4 for effects 

classified as having evidence of a causal 

or likely causal relationship with longor short-term PM2.5 exposures, she 

observes a cluster of short-term 

exposure studies with long-term mean 

concentrations within a range of 13.4 

mg/m3 down to 12.8 mg/m3 (Dominici et 

al., 2006a; Burnett and Goldberg, 2003; 

Zanobetti and Schwartz, 2009; Bell et 

al., 2008; Burnett et al., 2004). She also 

observes a cluster of long-term exposure 

studies with long-term mean 

concentrations within a range of 14.5 

mg/m3 to 13.6 mg/m3 (Dockery et al., 

1996; Lipfert et al., 2006a; Zeger et al., 

2008; McConnell et al., 2003; Goss et al., 

2004; Eftim et al., 2008). For the reasons 

discussed in response to public 

comments in section III.E.4.c above, the 

Administrator is less influenced by the 

long-term mean PM2.5 concentrations 

from the Miller et al. (2007) and 

Krewski et al. (2009) studies with 

reported long-term mean PM2.5

concentrations of 12.9 and 14.0 mg/m3, 

respectively. In each case, the most 

relevant exposure periods would likely 

have had higher mean PM2.5

concentrations than those reported in 

the studies.109 Thus, the Administrator 

considers the long-term mean PM2.5

concentrations from these two studies to 

be a highly uncertain basis for informing 

her selection of the annual standard 

level.110

To help guide her judgment of the 

appropriate level below the long-term 

mean concentrations in the 

epidemiological studies at which to set 

the standard, the Administrator 

considered additional information from 

epidemiological studies concerning the 

broader distribution of PM2.5

concentrations which correspond to the 

health events observed in these studies 

(e.g., deaths, hospitalizations). The 

Administrator observes that the 

development and use of this 

information in considering standard 

levels is consistent with CASAC’s 

advice, as discussed in section 

III.E.4.b.ii above, to focus on 

understanding the concentrations that 

were most influential in generating the 

health effect estimates in individual 

studies (Samet, 2010d, p. 2). 

In considering this additional 

population-level information, the 

Administrator recognizes that, in 

general, the confidence in the 

magnitude and significance of an 

association identified in a study is 

strongest at and around the long-term 

mean concentration for the air quality 

distribution, as this represents the part 

of the distribution in which the data in 

any given study are generally most 

concentrated. She also recognizes that 

the degree of confidence decreases as 

one moves towards the lower part of the 

distribution. Consistent with the 

approach used in the Policy 

Assessment, the Administrator believes 

that the range from approximately the 

25th to 10th percentiles is a reasonable 

range for providing a general frame of 

reference as to the part of the 

distribution in which her confidence in 

the associations observed in 

epidemiological studies is appreciably 

lower. However, as noted above, it is 

important to emphasize that there is no 

clear dividing line or single percentile 

within a given distribution provided by 

the scientific evidence that is most 

appropriate or ‘correct’ to use to 

characterize where the degree of 

confidence in the associations warrants 

setting the annual standard level. The 

decision of the appropriate standard 

level below the long-term mean 

concentrations of the key studies, which 

in conjunction with the other elements 

of the standard would protect public 

health with an adequate margin of 

safety, is largely a public health policy 

judgment, taking into account all of the 

evidence and its related uncertainties. 

As discussed in section III.E.4.b, the 

Administrator takes note of additional 

population-level data that were made 

available to the EPA by study 

authors.111 In considering this 

information, the Administrator 

particularly focuses on the analysis of 

the distributions of the health event data 

for each area within these studies and 

the corresponding air quality data for 

the two short-term exposure studies 

(Zanobetti and Schwartz, 2009; Bell et 

al., 2008). These short-term exposure 

studies evaluate the relationship 

between daily changes (one or more 

days) in PM2.5 concentrations and daily 

changes in health events (e.g., deaths, 

hospitalizations), such that the air 

quality concentrations that comprise the 

most relevant exposure periods in these 


tkelley on DSK3SPTVN1PROD with 
3160 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

112Nonetheless, as explained in section III.E.1, 

the currently available evidence is not sufficient to 

support replacing or supplementing the PM2.5

indicator with any other indicator defined in terms 

of a specific fine particle component or group of 

components associated with any source categories 

of fine particles. Furthermore, the evidence is not 

sufficient to support eliminating any component or 

group of components associated with any source 

categories of fine particles from the mix of fine 

particles included in the PM2.5 indicator. 

studies are contemporaneous with the 

health event data. In addition, these 

studies considered more recent air 

quality data, representing generally 

lower PM2.5 concentrations, in a large 

number of study areas across the U.S. 

Thus, such studies provide the most 

useful evidence for an analysis 

evaluating the distribution of health 

event data and the corresponding longterm mean PM2.5 concentrations across 

the areas included in each multi-city 

study. 

The Administrator also considered 

the additional population-level data that 

were made available to EPA for two 

long-term exposure studies (Krewski et 

al., 2009; Miller et al., 2007). She 

recognizes that in long-term exposure 

studies investigators follow a specific 

group of study participants (i.e., cohort) 

over time and across urban study areas, 

and evaluate how PM2.5 concentrations 

averaged over a period of years are 

associated with specific health 

endpoints (e.g., deaths) across cities. As 

discussed in response to public 

comments in section III.E.4.c, 

disentangling the effects observed in 

long-term exposure studies associated 

with more recent air quality 

measurements from effects that may 

have been associated with earlier, and 

most likely higher, PM2.5 exposures 

introduces some uncertainty with regard 

to understanding the appropriate 

exposure window associated with the 

observed effects. This is in contrast to 

the short-term exposure studies where 

the relevant exposure period is 

contemporaneous to the period for 

which the health data were collected. In 

light of these considerations, as noted 

above, the Administrator considers the 

analysis of air quality concentrations 

that correspond to the distribution of 

population-level data in these two 

studies to be a highly uncertain basis for 

informing her selection of the annual 

standard level. 

Based on the above considerations, 

the Administrator views the additional 

population-level data for the two shortterm exposure studies as appropriate to 

help inform her judgment of how much 

below the long-term mean 

concentrations to set the level of the 

annual standard. The Administrator 

notes that the long-term mean PM2.5

concentrations corresponding with 

study areas contributing to the 25th 

percentiles of the distribution of deaths 

and cardiovascular-related 

hospitalizations in these two short-term 

exposure studies were 12.5 mg/m3 and 

11.5 mg/m3, respectively, for Zanobetti 

and Schwartz (2009) and for Bell et al. 

(2008), with the 10th percentiles being 

lower by approximately 2 mg/m3 in each 

study. 

The Administrator recognizes, as 

summarized in section III.B above and 

discussed more fully in section III.B.2 of 

the proposal, that important 

uncertainties remain in the evidence 

and information considered in this 

review of the primary fine particle 

standards. These uncertainties are 

generally related to understanding the 

relative toxicity of the different 

components in the fine particle mixture, 

the role of PM2.5 in the complex ambient 

mixture, exposure measurement errors, 

and the nature and magnitude of 

estimated risks related to increasingly 

lower ambient PM2.5 concentrations. 

Furthermore, the Administrator notes 

that epidemiological studies have 

reported heterogeneity in responses 

both within and between cities and 

geographic regions across the U.S. She 

recognizes that this heterogeneity may 

be attributed, in part, to differences in 

fine particle composition in different 

regions and cities.112

With regard to evidence for 

reproductive and developmental effects 

identified as being suggestive of a causal 

relationship with long-term PM2.5

exposures, the Administrator recognizes 

that there are a number of limitations 

associated with this body of evidence 

including: the limited number of studies 

evaluating such effects; uncertainties 

related to identifying the relevant 

exposure time periods of concern; and 

limited toxicological evidence providing 

little information on the mode of 

action(s) or biological plausibility for an 

association between long-term PM2.5

exposures and adverse birth outcomes. 

Nonetheless, the Administrator believes 

that this more limited body of evidence 

provides some support for considering 

that serious effects may be occurring in 

a susceptible population at 

concentrations lower than those 

associated with effects classified as 

having a causal or likely causal 

relationship with long-term PM2.5

exposures (i.e., mortality, 

cardiovascular, and respiratory effects). 

Overall, the Administrator believes 

that the available evidence interpreted 

in light of the remaining uncertainties, 

as summarized above and discussed 

more fully in the Integrated Science 

Assessment and the Policy Assessment, 

provides increased confidence relative 

to information available in the last 

review and provides a strong basis for 

informing her final decisions in the 

current review. The Administrator is 

mindful that considering what 

standards are requisite to protect public 

health with an adequate margin of safety 

requires public health policy judgments 

that neither overstate nor understate the 

strength and limitations of the evidence 

or the appropriate inferences to be 

drawn from the evidence. In considering 

how to translate the available 

information into appropriate standard 

levels, the Administrator weighs the 

available scientific information and 

associated uncertainties and limitations. 

For the purpose of determining what 

annual standard level is appropriate the 

Administrator recognizes that there is 

no single factor or criterion that 

comprises the ‘‘correct’’ approach to 

weighing the various types of available 

evidence and information. 

In considering this information, the 

Administrator notes the advice of 

CASAC that ‘‘there are significant 

public health consequences at the 

current levels of the standards that 

justify consideration of lowering the 

PM2.5 NAAQS further’’ (Samet, 2010c, p. 

12). In addition, she recognizes that 

CASAC concluded, ‘‘although there is 

increasing uncertainty at lower levels, 

there is no evidence of a threshold (i.e., 

a level below which there is no risk for 

adverse effects)’’ (Samet, 2010d, p.ii) 

and that the final decisions on standard 

levels must reflect a judgment of the 

available scientific information with 

respect to her interpretation of the 

CAA’s requirement to set primary 

standards that provide requisite 

protection to public health with an 

adequate margin of safety (Samet, 

2010d, p. 4). The Administrator 

recognizes CASAC’s advice that the 

currently available scientific 

information provided support for 

considering an annual standard level 

within a range of 13 to 11 mg/m3 and a 

24-hour standard level within a range of 

35 to 30 mg/m3. In considering how the 

annual and 24-hour standards work 

together to provide appropriate public 

health protection, the Administrator 

observes that CASAC did not express 

support for any specific levels or 

combinations of standards within these 

ranges. She also notes that CASAC 

encouraged the EPA staff to consider 

additional data from epidemiological 

studies to help quantify the 

characterization of the PM2.5

concentrations that were most 

influential in generating the health 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3161 

113With respect to cancer, mutagenic, and 

genotoxic effects, the Administrator observes that 

the PM2.5 concentrations reported in studies 

evaluating these effects generally included ambient 

concentrations that are equal to or greater than 

ambient concentrations observed in studies that 

reported mortality and cardiovascular and 

respiratory effects (U.S. EPA, 2009a, section 7.5). 

Therefore, the Administrator concludes that in 

selecting alternative standard levels that provide 

protection from mortality and cardiovascular and 

respiratory effects, it is reasonable to anticipate that 

Continued 

effect estimates in these studies (Samet, 

2010d, p. 2). 

In response to CASAC’s advice, the 

Administrator recognizes that the EPA 

staff acquired additional data from 

authors of key epidemiological studies 

and analyzed these data to characterize 

the distribution of PM2.5 concentrations 

in relation to health events data to better 

understand the degree of confidence in 

the associations observed in the studies 

as discussed above. The Administrator 

recognizes that the final Policy 

Assessment included consideration of 

these additional analyses in reaching 

final staff conclusions with regard to the 

broadest range of alternative standard 

levels supported by the science. She 

takes note that the final Policy 

Assessment concluded that while 

alternative standard levels within the 

range of 13 to 11 mg/m3 were 

appropriate to consider, the evidence 

most strongly supported consideration 

of an annual standard level in the range 

of 12 to 11 mg/m3. The Administrator is 

aware that, in transmitting the final 

Policy Assessment to CASAC, the 

Agency notified CASAC that the final 

staff conclusions reflected consideration 

of CASAC’s advice and that those staff 

conclusions were based, in part, on the 

specific distributional analysis that 

CASAC had urged the EPA to conduct 

(Wegman, 2011). Thus, CASAC had an 

opportunity to comment on the final 

Policy Assessment, but chose not to 

provide any additional comments or 

advice after receiving it. 

In selecting the annual standard level, 

the Administrator has considered many 

factors including the nature and severity 

of the health effects involved, the 

strength of the overall body of scientific 

evidence as considered in reaching 

causality determinations, the size of the 

at-risk populations, and the estimated 

public health impacts. She has also 

considered the kind and degree of the 

uncertainties that remain in the 

available scientific information. She 

recognizes that the association between 

PM2.5 and serious health effects is well 

established, including at concentrations 

below those allowed by the current 

standard. Further, she recognizes the 

CAA requirement that requires primary 

standards to provide an adequate 

margin of safety was intended to 

address uncertainties associated with 

inconclusive scientific and technical 

information as well as to provide a 

reasonable degree of protection against 

hazards that research has not yet 

identified. In considering the currently 

available evidence, as summarized and 

discussed more broadly above, the 

information on risk, CASAC advice, the 

conclusions of the Policy Assessment, 

and public comments on the proposal, 

the Administrator strongly believes that 

a lower annual standard level is needed 

to protect public health with an 

adequate margin of safety. 

In reaching her final decision on the 

appropriate annual standard level to set, 

the Administrator is mindful that the 

CAA does not require that primary 

standards be set at a zero-risk level, but 

rather at a level that reduces risk 

sufficiently so as to protect public 

health, including the health of at-risk 

populations, with an adequate margin of 

safety. On balance, the Administrator 

concludes that an annual standard level 

of 12 mg/m3 would be requisite to 

protect the public health with an 

adequate margin of safety from effects 

associated with long- and short-term 

PM2.5 exposures, while still recognizing 

that uncertainties remain in the 

scientific information. 

In the Administrator’s judgment, an 

annual standard of 12 mg/m3

appropriately reflects placing greatest 

weight on evidence of effects for which 

the Integrated Science Assessment 

determined there is a causal or likely 

causal relationship with long- and shortterm PM2.5 exposures. An annual 

standard level of 12 mg/m3 is below the 

long-term mean PM2.5 concentrations 

reported in each of the key multi-city, 

long- and short-term exposures studies 

providing evidence of an array of 

serious health effects (e.g., premature 

mortality, increased hospitalization for 

cardiovascular and respiratory effects). 

As noted above, the importance of 

considering a level somewhat below the 

lowest long-term mean concentration in 

the full set of studies considered is to 

set a standard that would provide 

appropriate protection against the 

observed effects in all such studies. 

In reaching her decision, the 

Administrator has taken into account 

that at and around the mean PM2.5

concentration in any given study 

represents a part of the air quality 

distribution in which the health event 

data in that study are generally most 

concentrated. Furthermore, in 

identifying an appropriate annual 

standard level below the long-term 

mean concentrations, she recognizes 

that there is no evidence to support the 

existence of any discernible threshold, 

and, therefore, she has a high degree of 

confidence that the observed effects are 

associated with concentrations not just 

at but extending somewhat below the 

long-term mean concentration. To 

further inform her judgment in setting 

the annual standard level so as to 

protect public health with an adequate 

margin of safety, the Administrator has 

placed weight on additional populationlevel information available from a 

subset of these epidemiological studies, 

consistent with CASAC advice. In 

particular, she has drawn from two 

short-term exposure studies, which 

provide the most relevant information 

for evaluating the distribution of health 

events and corresponding long-term 

PM2.5 concentrations. As explained 

above, this helps inform her judgment 

as to the degree of confidence in the 

observed associations in the 

epidemiological studies. In this regard, 

the Administrator generally judges the 

region around the 25th percentile as a 

reasonable part of the distribution to 

help guide her decision on the 

appropriate standard level. Since this 

evidence comes primarily from two 

studies, a relatively modest data set, the 

Administrator deems it reasonable not 

to draw further inferences from air 

quality and health event data in the 

lower part of the distribution for the 

purpose of setting a standard level. The 

Administrator notes that the long-term 

mean PM2.5 concentrations around the 

25th percentile of the distributions of 

deaths and cardiovascular-related 

hospitalizations were approximately 

around 12 mg/m3 in these two studies. 

The Administrator views this 

information as helpful in guiding her 

determination as to where her 

confidence in the magnitude and 

significance of the associations is 

reduced to such a degree that a standard 

set at a lower level would not be 

warranted to provide requisite 

protection that is neither more nor less 

than needed to provide an adequate 

margin of safety. 

The Administrator also recognizes 

that a level of 12 mg/m3 places some 

weight on studies which provide 

evidence of reproductive and 

developmental effects (e.g., infant 

mortality, low birth weight). These 

studies were identified in the Integrated 

Science Assessment as having evidence 

suggestive of a causal relationship with 

long-term PM2.5 concentrations. A level 

of 12 mg/m3 is approximately the same 

level as the lowest long-term mean 

concentration reported in such studies 

(Figures 2 and 4; 11.9 mg/m3 for Bell et 

al., 2007).113 While the Administrator 


tkelley on DSK3SPTVN1PROD with 
3162 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

protection will also be provided for carcinogenic 

effects. 

114The Administrator is mindful that, in 

reviewing the 2006 final PM NAAQS decisions, the 

D.C. Circuit Court of Appeals concluded that the 

EPA failed to adequately explain why that annual 

standard provided requisite protection from effects 

associated with both long- and short-term exposures 

or from morbidity effects in children and other atrisk populations when long-term means of 

important short-term studies were below the level 

the Administrator selected for the annual standard. 

See American Farm Bureau v. EPA. 559 F. 3d 512, 

524–26. There is no reasonable basis to discount 

these two studies for purposes of setting the level 

of the annual standard. 

acknowledges that this evidence is 

limited, she believes it is appropriate to 

place some weight on these studies in 

order to set a standard that provides 

protection with an adequate margin of 

safety, including providing protection 

for at-risk populations, as required by 

the CAA. Due to the limited nature of 

this evidence, she has determined it is 

not necessary to set a standard below 

the lowest long-term mean 

concentration in these studies. 

In reflecting on extensive public 

comments received on the proposal as 

discussed in section III.E.4.c above, the 

Administrator recognizes that some 

commenters have offered different 

evaluations of the evidence and other 

information available in this review and 

would make different judgments about 

the weight to place on the relative 

strengths and limitations of the 

scientific information and about how 

such information could be used in 

making public health policy decisions 

on the annual standard level. One group 

of such commenters who supported a 

higher annual standard level (e.g., above 

13 mg/m3) would place greater weight on 

the remaining uncertainties in the 

evidence as a basis for supporting a 

higher standard level than the 

Administrator judges to be appropriate. 

Such an approach is based on these 

commenters’ judgment that the 

uncertainties remaining in the evidence 

are too great to warrant setting an 

annual standard below the current level. 

The Administrator does not agree. 

As an initial matter, an annual 

standard level of 13 mg/m3 or higher 

would be above the long-term mean 

concentrations reported in two wellconducted, multi-city short-term 

exposure studies reporting positive and 

statistically significant associations of 

serious effects (Burnett et al., 2004 and 

Bell et al., 2008). These important 

studies are fully consistent with the 

pattern of evidence presented by the 

large body of evidence in this review. 

As the Administrator recognized in the 

proposal, and as advised by CASAC, the 

appropriate focus for selecting the level 

of the annual PM2.5 standard is on 

concentrations somewhat below the 

lowest long-term mean concentrations 

from the set of key studies of both longterm and short-term PM2.5 exposures 

considered by the EPA (i.e., as shown in 

Figure 4). Thus, a standard level set at 

13 mg/m3 or higher would clearly not 

provide protection for the effects 

observed in the full set epidemiological 

studies and, therefore, this standard 

level could not be judged to be requisite 

with an adequate margin of safety.114

In addition, as noted above, in 

recognizing that there is no evidence to 

support the existence of a discernible 

threshold below which an effect would 

not occur, the Administrator is mindful 

that effects occur around and below the 

long-term mean concentrations reported 

in both the short-term and long-term the 

epidemiological studies. A standard 

level of 13 mg/m3 or higher would not 

appropriately take into account 

evidence from the two well-conducted, 

multi-city, short-term exposure studies 

reporting serious effects with long-term 

mean concentrations below 13 mg/m3

noted above (Burnett et al, 2004; Bell et 

al., 2008). Such a standard level would 

also not appropriately take into account 

additional population-level data from a 

limited number of epidemiological 

studies. This approach would ignore 

CASAC’s advice to consider such 

information in order to better 

understand the concentrations over 

which there is a high degree of 

confidence regarding the magnitude and 

significance of the associations observed 

in individual epidemiological studies 

and where there is appreciably less 

confidence. 

Furthermore, a standard level of 13 

mg/m3 or higher would not 

appropriately take into account the 

more limited evidence of effects in some 

at-risk populations (e.g., low birth 

weight). In the Administrator’s view, a 

standard set at this level would not 

provide protection with an adequate 

margin of safety, including providing 

protection for at-risk populations. The 

Administrator is mindful that the CAA 

requirement that primary standards 

provide an adequate margin of safety, 

discussed in section II.A above, was 

intended to address uncertainties 

associated with inconclusive scientific 

and technical information available at 

the time of standard setting as well as 

to provide a reasonable degree of 

protection against hazards that research 

has not yet identified. 

In light of the entire body of evidence 

as discussed above, the Administrator 

judges that an annual standard level set 

above 12 mg/m3 would not be sufficient 

to protect public health with an 

adequate margin of safety from the 

serious health effects associated with 

long- and short-term exposure to PM2.5.

The Administrator also recognizes 

that a second group of commenters 

supported a lower annual standard level 

(e.g., no higher than 11 mg/m3). Such a 

standard level would reflect placing 

essentially as much weight on the 

relatively more limited data providing 

evidence suggestive of a causal 

relationship for effects observed in some 

at-risk populations (e.g., low birth 

weight) as on more certain evidence of 

effects classified as having a causal or 

likely causal relationship with PM2.5

exposures. In the Administrator’s view, 

while it is important to place some 

weight on such suggestive evidence, it 

would not be appropriate to place as 

much weight on it as the commenters 

would do. 

An annual standard level of 11 mg/m3

would also reflect these commenters’ 

judgment that it is appropriate to focus 

on a lower part of the distributions of 

health event data from the small number 

of epidemiological studies for which 

this information was made available 

than the Administrator believes is 

warranted. In the Administrator’s view, 

using this type of information to set a 

standard level of 11 mg/m3 or below 

would assume too high a degree of 

confidence in the magnitude and 

significance of the associations observed 

in the lower part of the distributions of 

health events observed in these studies. 

Given the uncertainties in the evidence 

and the limited set of studies for which 

the EPA has information on the 

distribution of health event data and 

corresponding air quality data, the 

Administrator believes it is not 

appropriate to focus on the lower part 

of the distributions of health events 

data. 

On balance, the Administrator finds 

that the available evidence interpreted 

in light of the remaining uncertainties 

does not justify a standard level set 

below 12 mg/m3 as necessary to protect 

public health with an adequate margin 

of safety. 

After carefully considering the above 

considerations and the public comments 

summarized in section III.E.4.c above, 

the Administrator has decided to set the 

level of the primary annual PM2.5

standard at 12 mg/m3. In her judgment, 

a standard set at this level provides the 

requisite degree of public health 

protection, including the health of atrisk populations, with an adequate 

margin of safety and is neither more nor 

less stringent than necessary for this 

purpose. 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3163 

115As noted in section II.B.1, Table 1 and section 

III.E.4.a above, the annual standard level is defined 

to one decimal place. Throughout this section, the 

annual standard levels discussed have been 

Continued 

As discussed above, the 

Administrator concludes that an 

approach that focuses on setting a 

generally controlling annual standard is 

the most effective and efficient way to 

reduce total population risk associated 

with both long- and short-term PM2.5

exposures. Such an approach would 

result in more uniform protection across 

the U.S. than the alternative of setting 

the levels of the 24-hour and annual 

standard such that the 24-hour standard 

would generally be the controlling 

standard in areas across the country (see 

section III.A.3). 

The Administrator recognizes that 

potential air quality changes associated 

with meeting an annual standard level 

of 12.mg/m3 will result in lowering risks 

associated with both long- and shortterm PM2.5 exposures by lowering the 

overall air quality distribution. 

However, the Administrator recognizes 

that such an annual standard alone 

would not be expected to offer sufficient 

protection with an adequate margin of 

safety against the effects of short-term 

PM2.5 exposures in all parts of the 

country. As a result, in conjunction with 

an annual standard level of 12 mg/m3, 

the Administrator concludes that it is 

appropriate to continue to provide 

supplemental protection by means of a 

24-hour standard set at the appropriate 

level, particularly for areas with high 

peak-to-mean ratios possibly associated 

with strong local or seasonal sources 

and for areas with PM2.5-related effects 

that may be associated with shorterthan-daily exposure periods. 

In selecting the level of a 24-hour 

standard meant to provide such 

supplemental protection, the 

Administrator relies upon evidence and 

air quality information from key shortterm exposure studies. In considering 

these studies, the Administrator notes 

that to the extent air quality 

distributions in the study areas 

considered are reduced to meet the 

current 24-hour standard (at a level of 

35 mg/m3) or to meet the revised annual 

standard discussed above (at a level of 

12 mg/m3), additional protection would 

be anticipated against the effects 

observed in these studies. In light of 

this, when selecting the appropriate 

level for the 24-hour standard, the 

Administrator considers both the 98th 

percentiles of 24-hour PM2.5

concentrations and the long-term mean 

PM2.5 concentrations in the locations of 

the short-term exposure studies. She 

notes that such consideration of both 

short- and long-term PM2.5

concentrations can inform her decision 

on the extent to which a given 24-hour 

standard, in combination with the 

revised annual standard established in 

this rule, would provide protection 

against the health effects reported in 

short-term studies. 

As discussed in section III.E.4.a 

above, the Administrator concludes that 

multi-city short-term exposure studies 

provide the strongest data set for 

informing her decisions on appropriate 

24-hour standard levels. With regard to 

the limited number of single-city studies 

that reported positive and statistically 

significant associations for a range of 

health endpoints related to short-term 

PM2.5 concentrations in areas that would 

likely have met the current suite of 

PM2.5 standards, the Administrator 

recognizes that many of these studies 

had significant limitations (e.g., limited 

statistical power, limited exposure data) 

or equivocal results (mixed results 

within the same study area) that make 

them unsuitable to form the basis for 

setting the level of a 24-hour standard. 

With regard to multi-city studies that 

evaluated effects associated with shortterm PM2.5 exposures, the Administrator 

observes an overall pattern of positive 

and statistically significant associations 

in studies with 98th percentile 24-hour 

values averaged across study areas 

within the range of 45.8 to 34.2 mg/m3

(Burnett et al., 2004; Zanobetti and 

Schwartz, 2009; Bell et al., 2008; 

Dominici et al., 2006a, Burnett and 

Goldberg, 2003; Franklin et al., 2008). 

The Administrator notes that, to the 

extent air quality distributions are 

reduced to reflect just meeting the 

current 24-hour standard, additional 

protection would be provided for the 

effects observed in the three multi-city 

studies with 98th percentile values 

greater than 35 mg/m3 (Burnett et al., 

2004; Burnett and Goldberg, 2003; 

Franklin et al., 2008). In the three 

additional multi-city studies with 98th 

percentile values below 35 mg/m3, 

specifically 98th percentile 

concentrations of 34.2, 34.3, and 34.8 

mg/m3, the Administrator notes that 

these studies reported long-term mean 

PM2.5 concentrations of 12.9, 13.2, and 

13.4 mg/m3, respectively (Bell et al., 

2008; Zanobetti and Schwartz, 2009; 

Dominici et al., 2006a). In revising the 

level of the annual standard to 12 mg/ 

m3, as discussed above, the 

Administrator recognizes that additional 

protection would be provided for the 

short-term effects observed in these 

multi-city studies such that revision to 

the 24-hour standard would not be 

warranted. That is, by lowering the level 

of the annual standard to 12 mg/m3, the 

98th percentile of the distribution 

would be lowered as well such that 

additional protection from effects 

associated with short-term exposures 

would be afforded. Therefore, the 

epidemiological evidence supports a 

conclusion that it is appropriate to 

retain the level of the 24-hour standard 

at 35 mg/m3, in conjunction with a 

revised annual standard level of 12 mg/ 

m3. 

In addition to considering the 

epidemiological evidence, the 

Administrator also has taken into 

account air quality information based on 

county-level 24-hour and annual design 

values to understand the implications of 

revising the annual standard level from 

15 to 12 mg/m3 in conjunction with 

retaining the 24-hour standard level at 

35 mg/m3. She has considered this 

information to evaluate the public 

health protection provided by the two 

standards in combination and to 

evaluate the most appropriate means of 

developing a suite of standards 

providing requisite public health 

protection with an adequate margin of 

safety. 

In considering the air quality 

information, the Administrator observes 

that a suite of PM2.5 standards that 

includes an annual standard level of 12 

mg/m3 and a 24-hour standard level of 

35 mg/m3 would result in the annual 

standard as the generally controlling 

standard in most regions across the 

country, except for certain areas in the 

Northwest, where the annual mean 

PM2.5 concentrations have historically 

been low but where relatively high 24- 

hour concentrations occur, often related 

to seasonal wood smoke emissions (U.S. 

EPA, 2011a, pp. 2–89 to 2–91, Figure 2– 

10). In fact, these are the type of areas 

for which the supplemental protection 

afforded by the 24-hour standard is 

intended, such that the two standards 

together provide the requisite degree of 

protection. The Administrator 

concludes the current 24-hour standard 

at a level of 35 mg/m3, in conjunction 

with a revised annual standard level of 

12 mg/m3, will provide appropriate 

protection from effects observed in 

studies in such areas in which the longterm mean concentrations were below 

12 mg/m3 and the 98th percentile 24- 

hour concentrations were above 35 mg/ 

m3 (e.g., areas in the Northwest U.S.). 

After carefully taking the public 

comments and above considerations 

into account, the Administrator has 

decided to retain the current level of the 

primary PM2.5 24-hour standard at 35 

mg/m3 in conjunction with revising the 

annual standard level from 15.0 mg/m3

to 12.0 mg/m3.115 In the Administrator’s 


tkelley on DSK3SPTVN1PROD with 
3164 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

denoted as integer values (e.g., 12 mg/m3) for 

simplicity. 

116The Administrator also judges that this suite 

of standards addresses the issues raised by the D.C. 

Circuit’s remand of the 2006 primary annual PM2.5

standard by appropriately revising that standard. 

117Throughout this section of the preamble, we 

are using the terms ‘‘thoracic coarse particles’’, 

‘‘inhalable coarse particles’’, and ‘‘PM10-2.5’’ 

synonymously. 

judgment, this suite of primary PM2.5

standards and the rationale supporting 

these levels appropriately reflects 

consideration of the strength of the 

available evidence and other 

information and its associated 

uncertainties as well as the advice of 

CASAC and consideration of public 

comments. In the Administrator’s 

judgment, this suite of primary PM2.5

standards is sufficient but not more 

protective than necessary to protect the 

public health, including at-risk 

populations, with an adequate margin of 

safety from effects associated with longand short-term exposures to fine 

particles. This suite of standards will 

provide significant protection from 

serious health effects including 

premature mortality and cardiovascular 

and respiratory morbidity effects that 

are causally or likely causally related to 

long- and short-term PM2.5 exposures. 

These standards will also provide an 

appropriate degree of protection against 

other health effects for which there is 

more limited evidence of effects and 

causality, such as reproductive and 

developmental effects. This judgment by 

the Administrator appropriately 

considers the requirement for a standard 

that is requisite to protect public health 

but is neither more nor less stringent 

than necessary.116

D. Administrator’s Final Decisions on 

Primary PM2.5 Standards 

For the reasons discussed above, and 

taking into account the information and 

assessments presented in the Integrated 

Science Assessment, Risk Assessment, 

and Policy Assessment, the advice and 

recommendations of CASAC, and public 

comments to date, the Administrator 

revises the current suite of primary 

PM2.5 standards. Specifically, the 

Administrator revises: (1) The level of 

the primary annual PM2.5 standard to 

12.0 mg/m3 and (2) the form of the 

primary annual PM2.5 standard to one 

based on the highest appropriate areawide monitor in an area, with no option 

for spatial averaging. In conjunction 

with revising the primary annual PM2.5

standard to provide protection from 

effects associated with long- and shortterm PM2.5 exposures, the Administrator 

retains the level of 35 mg/m3 and the 

98th percentile form of the primary 24- 

hour PM2.5 standard to continue to 

provide supplemental protection for 

areas with high peak PM2.5

concentrations. The Administrator is 

not revising the current PM2.5 indicator 

or the annual and 24-hour averaging 

times for the primary PM2.5 standards. 

The Administrator concludes that this 

suite of standards would be requisite to 

protect public health with an adequate 

margin of safety against health effects 

potentially associated with long- and 

short-term PM2.5 exposures. 

IV. Rationale for Final Decision on 

Primary PM10 Standard 

This section presents the rationale for 

the Administrator’s final decision to 

retain the current 24-hour primary PM10

standard in order to continue to provide 

public health protection against shortterm exposures to inhalable particles in 

the size range of 2.5 to 10 mm (i.e., 

PM10-2.5 or thoracic coarse particles). 

These are particles capable of reaching 

the most sensitive areas of the lung, 

including the trachea, bronchi, and deep 

lungs. The current standard uses PM10

as the indicator for thoracic coarse 

particles, and thus is referred to as a 

PM10 standard.117

As discussed more fully in the 

proposal and below, this rationale is 

based on a thorough review of the latest 

scientific evidence, published through 

mid-2009 and assessed in the Integrated 

Science Assessment (U.S. EPA, 2009a), 

evaluating human health effects 

associated with long- and short-term 

exposures to thoracic coarse particles. 

The Administrator’s final decision also 

takes into account: (1) The EPA staff 

analyses of air quality information and 

health evidence and staff conclusions 

regarding the current and potential 

alternative standards, as presented in 

the Policy Assessment for the PM 

NAAQS (U.S. EPA, 2011a); (2) CASAC 

advice and recommendations, as 

reflected in discussions at public 

meetings of drafts of the Integrated 

Science Assessment and Policy 

Assessment, and in CASAC’s letters to 

the Administrator; (3) the multiple 

rounds of public comments received 

during the development of the 

Integrated Science Assessment and 

Policy Assessment, both in connection 

with CASAC meetings and separately; 

and (4) public comments (including 

testimony at the public hearings) 

received on the proposal. 

In presenting the rationale for the 

final decision to retain the current 

primary PM10 standard, this section 

discusses the EPA’s past reviews of the 

PM NAAQS and the general approach 

taken to review the current standard 

(section IV.A), the health effects 

associated with exposures to ambient 

PM10-2.5 (section IV.B), the consideration 

of the current and potential alternative 

standards in the Policy Assessment 

(section IV.C), CASAC 

recommendations regarding the current 

and potential alternative standards 

(section IV.D), the Administrator’s 

proposed decision to retain the current 

primary PM10 standard (section IV.E), 

public comments received in response 

to the Administrator’s proposed 

decision (section IV.F), and the 

Administrator’s final decision to retain 

the current primary PM10 standard 

(section IV.G). 

A. Background 

The following sections discuss 

previous reviews of the PM NAAQS 

(section IV.A.1), the litigation of the 

EPA’s 2006 decision on the PM10

standards (section IV.A.2), and the 

general approach taken to review the 

primary PM10 standard in the current 

review (section IV.A.3). 

1. Previous Reviews of the PM NAAQS 

a. Reviews Completed in 1987 and 1997 

The PM NAAQS have always 

included some type of a primary 

standard to protect against effects 

associated with exposures to thoracic 

coarse particles. In 1987, when the EPA 

first revised the PM NAAQS, the EPA 

changed the indicator for PM from TSP 

to focus on inhalable particles, those 

which can penetrate into the trachea, 

bronchi, and deep lungs (52 FR 24634, 

July 1, 1987). In that review, the EPA 

changed the PM indicator to PM10 based 

on evidence that the risk of adverse 

health effects associated with particles 

with a nominal mean aerodynamic 

diameter less than or equal to 10 mm 

was significantly greater than risks 

associated with larger particles (52 FR 

24639, July 1, 1987). 

In the 1997 review, in conjunction 

with establishing new fine particle (i.e., 

PM2.5) standards (discussed above in 

sections II.B.1 and III.A.1), the EPA 

concluded that continued protection 

was warranted against potential effects 

associated with thoracic coarse particles 

in the size range of 2.5 to 10 mm. This 

conclusion was based on particle 

dosimetry, toxicological information, 

and on limited epidemiological 

evidence from studies that measured 

PM10 in areas where the coarse fraction 

was likely to dominate PM10 mass (62 

FR 38677, July 18, 1997). The EPA 

concluded there that a PM10 standard 

could provide requisite protection 

against effects associated with particles 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3165 

118With regard to the 24-hour PM10 standard, the 

EPA retained the indicator, averaging time, and 

level (150 mg/m3), but revised the form (i.e., from 

one-expected-exceedance to the 99th percentile). 

119The PM Staff Paper (U.S. EPA, 2005) also 

presented results of a quantitative assessment of 

health risks for PM10-2.5. However, staff concluded 

that the nature and magnitude of the uncertainties 

and concerns associated with this risk assessment 

weighed against its use as a basis for recommending 

specific levels for a thoracic coarse particle 

standard (U.S. EPA, 2005, p. 5–69). 

in the size range of 2.5 to 10 mm.118

Although the EPA considered a more 

narrowly defined indicator for thoracic 

coarse particles in that review (i.e., 

PM10-2.5), the EPA concluded that it was 

more appropriate, based on existing 

evidence, to continue to use PM10 as the 

indicator. This decision was based, in 

part, on the recognition that the only 

studies of clear quantitative relevance to 

health effects most likely associated 

with thoracic coarse particles used 

PM10. These were two studies 

conducted in areas where the coarse 

fraction was the dominant fraction of 

PM10, and which substantially exceeded 

the 24-hour PM10 standard (62 FR 

38679). In addition, there were only 

very limited ambient air quality data 

then available specifically for PM10-2.5, 

in contrast to the extensive monitoring 

network already in place for PM10. 

Therefore, the EPA considered it more 

administratively feasible to use PM10 as 

an indicator. The EPA also stated that 

the PM10 standards would work in 

conjunction with the PM2.5 standards by 

regulating the portion of particulate 

pollution not regulated by the then 

newly adopted PM2.5 standards. 

In May 1998, a three-judge panel of 

the U.S. Court of Appeals for the District 

of Columbia Circuit found ‘‘ample 

support’’ for the EPA’s decision to 

regulate coarse particle pollution, but 

vacated the 1997 PM10 standards, 

concluding that the EPA had failed to 

adequately explain its choice of PM10 as 

the indicator for thoracic coarse 

particles American Trucking 

Associations v. EPA, 175 F. 3d 1027, 

1054–56 (D.C. Cir. 1999). In particular, 

the court held that the EPA had not 

explained the use of an indicator under 

which the allowable level of coarse 

particles varied according to the amount 

of PM2.5 present, and which, moreover, 

potentially double regulated PM2.5. The 

court also rejected considerations of 

administrative feasibility as justification 

for use of PM10 as the indicator for 

thoracic coarse PM, since NAAQS (and 

their elements) are to be based 

exclusively on health and welfare 

considerations. Id. at 1054. Pursuant to 

the court’s decision, the EPA removed 

the vacated 1997 PM10 standards from 

the CFR (69 FR 45592, July 30, 2004) 

and deleted the regulatory provision (at 

40 CFR 50.6(d)) that controlled the 

transition from the pre-existing 1987 

PM10 standards to the 1997 PM10

standards (65 FR 80776, December 22, 

2000). The pre-existing 1987 PM10

standards thus remained in place. Id. at 

80777. 

b. Review Completed in 2006 

In the review of the PM NAAQS that 

concluded in 2006, the EPA considered 

the growing, but still limited, body of 

evidence supporting associations 

between health effects and thoracic 

coarse particles measured as PM10-2.5.119

The new studies available in the 2006 

review included epidemiological 

studies that reported associations with 

health effects using direct 

measurements of PM10-2.5, as well as 

dosimetric and toxicological studies. In 

considering this growing body of 

PM10-2.5 evidence, as well as evidence 

from studies that measured PM10 in 

locations where the majority of PM10

was in the PM10-2.5 fraction (U.S. EPA, 

2005, section 5.4.1), staff concluded that 

the level of protection afforded by the 

existing 1987 PM10 standard remained 

appropriate (U.S. EPA, 2005, p. 5–67) 

but recommended that the indicator for 

the standard be revised. Specifically, 

staff recommended replacing the PM10

indicator with an indicator of urban 

thoracic coarse particles in the size 

range of 10–2.5 mm (U.S. EPA, 2005, pp. 

5–70 to 5–71). The agency proposed to 

retain a standard for a subset of thoracic 

coarse particles, proposing a qualified 

PM10-2.5 indicator to focus on the mix of 

thoracic coarse particles generally 

present in urban environments. More 

specifically, the proposed revised 

thoracic coarse particle standard would 

have applied only to an ambient mix of 

PM10-2.5 dominated by resuspended dust 

from high-density traffic on paved roads 

and/or by industrial and construction 

sources. The proposed revised standard 

would not have applied to any ambient 

mix of PM10-2.5 dominated by rural 

windblown dust and soils. In addition, 

agricultural sources, mining sources, 

and other similar sources of crustal 

material would not have been subject to 

control in meeting the standard (71 FR 

2667 to 2668, January 17, 2006). 

The Agency received a large number 

of comments overwhelmingly and 

persuasively opposed to the proposed 

qualified PM10-2.5 indicator (71 FR 

61188 to 61197, October 17, 2006). After 

careful consideration of the scientific 

evidence and the recommendations 

contained in the 2005 Staff Paper, the 

advice and recommendations from 

CASAC, and the public comments 

received regarding the appropriate 

indicator for coarse particles, and after 

extensive evaluation of the alternatives 

available to the Agency, the 

Administrator decided it would not be 

appropriate to adopt the proposed 

qualified PM10-2.5 indicator, or any 

qualified indicator. Underlying this 

determination was the Administrator’s 

decision that it was requisite to provide 

protection from exposure to all thoracic 

coarse PM, regardless of its origin. The 

Administrator thus rejected arguments 

that there are no health effects from 

community-level exposures to coarse 

PM in non-urban areas (71 FR 61189). 

The EPA concluded that dosimetric, 

toxicological, occupational and 

epidemiological evidence supported 

retention of a primary standard for 

short-term exposures that included all 

thoracic coarse particles (i.e., particles 

of both urban and non-urban origin), 

consistent with the Act’s requirement 

that primary NAAQS must be requisite 

to protect the public health and provide 

an adequate margin of safety. At the 

same time, the Agency concluded that 

the standard should target protection 

toward urban areas, where the evidence 

of health effects from exposure to 

PM10-2.5 was strongest (71 FR at 61193, 

61197). The proposed indicator was not 

suitable for that purpose. Not only did 

it inappropriately provide no protection 

at all to many areas, but it failed to 

identify many areas where the ambient 

particle mix was dominated by coarse 

particles contaminated with urban/ 

industrial types of coarse particles for 

which evidence of health effects was 

strongest (71 FR 61193). 

The Agency ultimately concluded that 

the existing indicator, PM10, was most 

consistent with the evidence. Although 

PM10 includes both coarse and fine PM, 

the Agency concluded that it remained 

an appropriate indicator for thoracic 

coarse particles because, as discussed in 

the PM Staff Paper (U.S. EPA, 2005, p. 

2–54, Figures 2–23 and 2–24), fine 

particle levels are generally higher in 

urban areas and, therefore, a PM10

standard set at a single unvarying level 

will generally result in lower allowable 

concentrations of thoracic coarse 

particles in urban areas than in nonurban areas (71 FR 61195–96). The EPA 

considered this to be an appropriate 

targeting of protection given that the 

strongest evidence for effects associated 

with thoracic coarse particles came from 

epidemiological studies conducted in 

urban areas and that elevated fine 

particle concentrations in urban areas 

could result in increased contamination 

of coarse fraction particles by PM2.5, 


tkelley on DSK3SPTVN1PROD with 
3166 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

120Thus, the standard is met when a 24-hour 

average PM10 concentration of 150 mg/m3 is not 

exceeded more than one day per year, on average 

over a three-year period. As noted above, the 1987 

PM10 standard was not adopted solely to control 

thoracic coarse particles. However, when reviewing 

this standard in the 2006 review, EPA determined 

that the level and form of the standard being 

reviewed (i.e., the 1987 PM10 standard) provided 

requisite protection with an adequate margin of 

safety from short-term exposures to thoracic coarse 

particles. 121As noted below, however, with this rule the 

EPA is revoking the requirement for PM10-2.5

speciation at NCore monitoring sites due to 

technical issues related to the development of 

appropriate monitoring methods (section VIII.B.3.c). 

The requirement for PM10-2.5 mass measurements at 

NCore sites is being retained. 

122Studies that have characterized the 

concentration-response relationships for PM 

exposures have evaluated PM10, which includes 

potentially increasing the toxicity of 

thoracic coarse particles in urban areas 

(id.). Given the evidence that the 

existing (i.e., 1987) PM10 standard was 

established at a level and form which 

afforded requisite protection with an 

adequate margin of safety, the Agency 

retained the level and form of the 24- 

hour PM10 standard.120

The Agency also revoked the annual 

PM10 standard, in light of the 

conclusion in the PM Criteria Document 

(U.S. EPA, 2004, p. 9–79) that the 

available evidence does not suggest an 

association with long-term exposure to 

PM10-2.5 and the conclusion in the Staff 

Paper (U.S. EPA, 2005, p. 5–61) that 

there is no quantitative evidence that 

directly supports retention of an annual 

standard. This decision was consistent 

with CASAC advice and 

recommendations (Henderson, 2005a,b). 

In the same rulemaking, the EPA also 

included a new FRM for the 

measurement of PM10-2.5 in the ambient 

air (71 FR 61212 to 61213, October 17, 

2006). Although the standard for 

thoracic coarse particles does not use a 

PM10-2.5 indicator, the new FRM for 

PM10-2.5 was established to provide a 

basis for approving FEMs and to 

promote the gathering of scientific data 

to support future reviews of the PM 

NAAQS (71 FR 61202/3, October 17, 

2006).121

2. Litigation Related to the 2006 Primary 

PM10 Standards 

A number of groups filed suit in 

response to the final decisions made in 

the 2006 review. See American Farm 

Bureau Federation v. EPA, 559 F. 3d 

512 (D.C. Cir. 2009). Among the 

petitions for review were challenges 

from industry groups on the decision to 

retain the PM10 indicator and the level 

of the PM10 standard and from 

environmental and public health groups 

on the decision to revoke the annual 

PM10 standard. The court upheld both 

the decision to retain the 24-hour PM10

standard and the decision to revoke the 

annual standard. 

First, the court upheld the EPA’s 

decision for a standard to encompass all 

thoracic coarse PM, both of urban and 

non-urban origin. The court rejected 

arguments that the evidence showed 

there are no risks from exposure to nonurban coarse PM. The court further 

found that the EPA had a reasonable 

basis not to set separate standards for 

urban and non-urban coarse PM, namely 

the inability to reasonably define what 

ambient mixes would be included under 

either ‘urban’ or ‘non-urban;’ and the 

evidence in the record that supported 

the EPA’s appropriately cautious 

decision to provide ‘‘some protection 

from exposure to thoracic coarse 

particles * * * in all areas.’’ 559 F. 3d 

at 532–33. Specifically, the court stated, 

Although the evidence of danger from 

coarse PM is, as EPA recognizes, 

‘‘inconclusive,’’ (71 FR 61193, October 17, 

2006), the agency need not wait for 

conclusive findings before regulating a 

pollutant it reasonably believes may pose a 

significant risk to public health. The 

evidence in the record supports the EPA’s 

cautious decision that ‘‘some protection from 

exposure to thoracic coarse particles is 

warranted in all areas.’’ Id. As the court has 

consistently reaffirmed, the CAA permits the 

Administrator to ‘‘err on the side of caution’’ 

in setting NAAQS. 559 F. 3d at 533. 

The court also upheld the EPA’s 

decision to retain the level of the 

standard at 150 mg/m3 and to use PM10

as the indicator for thoracic coarse 

particles. In upholding the level of the 

standard, the court referred to the 

conclusion in the Staff Paper that there 

is ‘‘little basis for concluding that the 

degree of protection afforded by the 

current PM10 standards in urban areas is 

greater than warranted, since potential 

mortality effects have been associated 

with air quality levels not allowed by 

the current 24-hour standard, but have 

not been associated with air quality 

levels that would generally meet that 

standard, and morbidity effects have 

been associated with air quality levels 

that exceeded the current 24-hour 

standard only a few times.’’ 559 F. 3d 

at 534. The court also rejected 

arguments that a PM10 standard 

established at an unvarying level will 

result in arbitrarily varying levels of 

protection given that the level of coarse 

PM would vary based on the amount of 

fine PM present. The court agreed that 

the variation in allowable coarse PM 

was in accord with the strength of the 

evidence: Typically less coarse PM 

would be allowed in urban areas (where 

levels of fine PM are typically higher), 

in accord with the strongest evidence of 

health effects from coarse particles. 559 

F. 3d at 535–36. In addition, such 

regulation would not impermissibly 

double regulate fine particles, since any 

additional control of fine particles 

(beyond that afforded by the primary 

PM2.5 standard) would be for a different 

purpose: To prevent contamination of 

coarse particles by fine particles. 559 F. 

3d at 535, 536. These same explanations 

justified the choice of PM10 as an 

indicator and provided the reasoned 

explanation for that choice lacking in 

the record for the 1997 standard. 559 F. 

3d at 536. 

With regard to the challenge from 

environmental and public health 

groups, the court upheld the EPA’s 

decision to revoke the annual PM10

standard. The court rejected the 

argument that the EPA is required by 

law to have an annual PM10 standard, 

holding that section 109(d)(1) of the Act 

allows the EPA to revoke a standard no 

longer warranted by the current 

scientific understanding. 559 F. 3d at 

538. The court further held that the 

EPA’s decision to revoke the annual 

standard was supported by the science: 

The EPA reasonably decided that an 

annual coarse PM standard is not necessary 

because, as the Criteria Document and the 

Staff Paper make clear, the latest scientific 

data do not indicate that long-term exposure 

to coarse particles poses a health risk. The 

CASAC also agreed that an annual coarse PM 

standard is unnecessary. 559 F. 3d at 538–39. 

3. General Approach Used in the 

Current Review 

The approach taken to considering the 

existing and potential alternative 

primary PM10 standards in the current 

review builds upon the approaches used 

in previous PM NAAQS reviews. This 

approach is based most fundamentally 

on using information from 

epidemiological studies and air quality 

analyses to inform the identification of 

a range of policy options for 

consideration by the Administrator. The 

Administrator considers the 

appropriateness of the current and 

potential alternative standards, taking 

into account the four elements of the 

NAAQS: Indicator, averaging time, 

form, and level. 

Evidence-based approaches to using 

information from epidemiological 

studies to inform decisions on PM 

standards are complicated by the 

recognition that no population 

threshold, below which it can be 

concluded with confidence that PMrelated effects do not occur, can be 

discerned from the available evidence 

(U.S. EPA, 2009a, sections 2.4.3 and 

6.5.2.7).122 As a result, any approach to 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3167 

both coarse and fine particles, and PM2.5 (U.S. EPA, 

2009a, sections 2.4.3 and 6.5.2.7). 

123 It should also be noted that CASAC endorsed 

the approach adopted in the Integrated Science 

Assessment, which draws weight-of-evidence 

conclusions for PM2.5 and PM10-2.5, but not for PM10

(Samet, 2009f). 

124The statistical significance of effect estimates 

provides important information on their statistical 

precision. However, when a group of studies report 

effect estimates that are similar in direction and 

magnitude, such a pattern of results warrants 

consideration of those studies even if not all 

reported statistically significant associations in 

single- or co-pollutant models (section III.D.2, 

above). In considering the PM10-2.5 epidemiologic 

studies below, the Administrator considers both the 

pattern of results across studies and the statistical 

significance of those results. 

125The causal framework draws upon the 

assessment and integration of evidence from across 

epidemiological, controlled human exposure, and 

toxicological studies, and the related uncertainties 

that ultimately influence our understanding of the 

evidence. This framework employs a five-level 

hierarchy that classifies the overall weight-ofevidence using the following categorizations: 

Causal relationship, likely to be causal relationship, 

suggestive of a causal relationship, inadequate to 

infer a causal relationship, and not likely to be a 

causal relationship (U.S. EPA, 2009a, Table 1–3). In 

the case of a ‘‘suggestive’’ determination, ‘‘the 

evidence is suggestive of a causal relationship with 

relevant pollutant exposures, but is limited because 

chance, bias and confounding cannot be ruled out. 

For example, at least one high-quality 

epidemiologic study shows an association with a 

given health outcome but the results of other 

studies are inconsistent’’ (U.S. EPA, 2009a, Table 1– 

3). 

reaching decisions on what standards 

are appropriate requires judgments 

about how to translate the information 

available from the epidemiological 

studies into a basis for appropriate 

standards, which includes consideration 

of how to weigh the uncertainties in 

reported associations across the 

distributions of PM concentrations in 

the studies. The approach taken to 

informing these decisions in the current 

review recognizes that the available 

health effects evidence reflects a 

continuum consisting of ambient levels 

at which scientists generally agree that 

health effects are likely to occur through 

lower levels at which the likelihood and 

magnitude of the response become 

increasingly uncertain. Such an 

approach is consistent with setting 

standards that are neither more nor less 

stringent than necessary, recognizing 

that a zero-risk standard is not required 

by the CAA. 

Because the purpose of the PM10

standard is to protect against exposures 

to PM10-2.5, it is most appropriate to 

focus on PM10-2.5 health studies when 

considering the degree of public health 

protection provided by the current PM10

standard. Compared to health studies of 

PM10, studies that evaluate associations 

with PM10-2.5 provide clearer evidence 

for health effects following exposures to 

thoracic coarse particles. In contrast, it 

is difficult to interpret PM10 studies 

within the context of a standard meant 

to protect against exposures to PM10-2.5

because PM10 is comprised of both fine 

and coarse particles, even in locations 

with the highest concentrations of 

PM10-2.5 (U.S. EPA, 2011a, Figure 3–4). 

Therefore, the extent to which PM10

effect estimates reflect associations with 

PM10-2.5 versus PM2.5 can be highly 

uncertain. In light of this uncertainty, it 

is preferable to consider PM10-2.5 studies 

when such studies are available. Given 

the availability in this review of a 

number of studies that evaluated 

associations with PM10-2.5, and given 

that the Integrated Science Assessment 

weight-of-evidence conclusions for 

thoracic coarse particles were based on 

studies of PM10-2.5, in this review the 

EPA focuses primarily on studies that 

have specifically evaluated PM10-2.5.123

As discussed in more detail in the 

Risk Assessment (U.S. EPA, 2010a, 

Appendix H), the EPA did not conduct 

a quantitative assessment of health risks 

associated with PM10-2.5. The Risk 

Assessment concluded that limitations 

in the monitoring network and in the 

health studies that rely on that 

monitoring network, which would be 

the basis for estimating PM10-2.5 health 

risks, would introduce significant 

uncertainty into a PM10-2.5 risk 

assessment such that the risk estimates 

generated would be of limited value in 

informing review of the standard. 

Therefore, it was judged that a 

quantitative assessment of PM10-2.5 risks 

is not supportable at this time (U.S. 

EPA, 2010a, p. 2-6). This decision does 

not indicate that health effects are not 

associated with exposure to thoracic 

coarse particles. Rather, as noted above, 

it reflects the conclusion that limitations 

in the available health studies and air 

quality information would introduce 

significant uncertainty into a 

quantitative assessment of PM10-2.5 risks 

such that the risk estimates generated 

would be of limited value in informing 

review of the standard. 

B. Health Effects Related to Exposure to 

Thoracic Coarse Particles 

This section briefly outlines the key 

information presented in section IV.B of 

the proposal (77 FR 38947 to 38951, 

June 29, 2012), and discussed more fully 

in the Integrated Science Assessment 

(U.S. EPA, 2009a, Chapters 2, 4, 5, 6, 7, 

and 8) and the Policy Assessment (U.S. 

EPA, 2011a, Chapter 3), related to health 

effects associated with thoracic coarse 

particle exposures. In looking across the 

new scientific evidence available in this 

review, our overall understanding of 

health effects associated with thoracic 

coarse particle exposures has been 

expanded, though important 

uncertainties remain. Some highlights of 

the key policy-relevant scientific 

evidence available in this review 

include the following: 

(1) A number of multi-city and single-city 

epidemiological studies have evaluated 

associations between short-term PM10-2.5 and 

mortality, cardiovascular effects (e.g., 

including hospital admissions and 

emergency department visits), and/or 

respiratory effects. Despite differences in the 

approaches used to estimate ambient PM10-2.5

concentrations, the majority of these studies 

have reported positive, though often not 

statistically significant, associations with 

short-term PM10-2.5 concentrations. Most 

PM10-2.5 effect estimates remained positive in 

co-pollutant models that included either 

gaseous or particulate co-pollutants. In U.S. 

study locations likely to have met the current 

PM10 standard during the study period, a few 

PM10-2.5 effect estimates were statistically 

significant and remained so in co-pollutant 

models.124

(2) A small number of controlled human 

exposure studies have reported alterations in 

heart rate variability or increased pulmonary 

inflammation following short-term exposure 

to PM10-2.5, providing some support for the 

associations reported in epidemiological 

studies. Toxicological studies that have 

examined the effects of PM10-2.5 have used 

intratracheal instillation and, because these 

studies do not directly mirror any real-world 

mode of exposure, they provide only limited 

evidence for the biological plausibility of 

PM10-2.5-induced effects. 

(3) Using a more formal framework for 

reaching causal determinations than used in 

previous reviews, the Integrated Science 

Assessment concluded that the existing 

evidence is ‘‘suggestive’’ of a causal 

relationship between short-term PM10-2.5

exposures and mortality, cardiovascular 

effects, and respiratory effects (U.S. EPA, 

2009a, section 2.3.3).125 In contrast, the 

Integrated Science Assessment concluded 

that available evidence is ‘‘inadequate’’ to 

infer a causal relationship between long-term 

PM10-2.5 exposures and various health effects. 

(4) There are several at-risk populations 

that may be especially susceptible or 

vulnerable to PM-related effects, including 

effects associated with exposures to coarse 

particles. These groups include those with 

preexisting heart and lung diseases, specific 

genetic differences, and lower socioeconomic 

status as well as the lifestages of childhood 

and older adulthood. Evidence for PMrelated effects in these at-risk populations 

has expanded and is stronger than previously 

observed. There is emerging, though still 

limited, evidence for additional potentially 

at-risk populations, such as those with 

diabetes, people who are obese, pregnant 

women, and the developing fetus. 

(5) The Integrated Science Assessment 

concludes that currently available evidence 

is insufficient to draw distinctions in particle 

toxicity based on composition and notes that 

recent studies have reported that PM (both 

PM2.5 and PM10-2.5) from a variety of sources, 


tkelley on DSK3SPTVN1PROD with 
3168 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

126As noted above, the EPA’s decision not to 

conduct a quantitative risk assessment reflects 

uncertainty regarding the value of such an 

assessment, but does not indicate that health effects 

are not associated with exposure to thoracic coarse 

particles. 

including sources likely to be present in 

urban and non-urban locations, is associated 

with adverse health effects. 

Although new PM10-2.5 scientific 

studies have become available since the 

last review and have expanded our 

understanding of the association 

between PM10-2.5 and adverse health 

effects (see above and U.S. EPA, 2009a, 

Chapter 6), important uncertainties 

remain. These uncertainties, and their 

implications for interpreting the 

scientific evidence, include the 

following: 

(1) The potential for confounding by cooccurring pollutants, especially PM2.5, has 

been addressed with co-pollutant models in 

only a relatively small number of PM10-2.5

epidemiological studies (U.S. EPA, 2009a, 

section 2.3.3). This is a particularly 

important limitation given the relatively 

small body of experimental evidence (i.e., 

controlled human exposure and animal 

toxicological studies) available to support the 

associations between PM10-2.5 and adverse 

health effects. The net impact of such 

limitations is to increase uncertainty in 

characterizations of the extent to which 

PM10-2.5 itself, rather than one or more cooccurring pollutants, is responsible for the 

mortality and morbidity effects reported in 

epidemiological studies. 

(2) There is greater spatial variability in 

PM10-2.5 concentrations than PM2.5

concentrations, resulting in increased 

exposure error for PM10-2.5 (U.S. EPA, 2009a, 

p. 2–8). Available measurements do not 

provide sufficient information to adequately 

characterize the spatial distribution of 

PM10-2.5 concentrations (U.S. EPA, 2009a, 

section 3.5.1.1). The net effect of these 

uncertainties on PM10-2.5 epidemiological 

studies is to bias the results of such studies 

toward the null hypothesis. That is, as noted 

in the Integrated Science Assessment, these 

limitations in estimates of ambient PM10-2.5

concentrations ‘‘would tend to increase 

uncertainty and make it more difficult to 

detect effects of PM10-2.5 in epidemiologic 

studies’’ (U.S. EPA, 2009a, p. 2–21). 

(3) Only a relatively small number of 

PM10-2.5 monitoring sites are currently 

operating and such sites have been in 

operation for a relatively short period of time, 

limiting the spatial and temporal coverage for 

routine measurement of PM10-2.5

concentrations. Given these limitations in 

routine monitoring, epidemiological studies 

have employed different approaches for 

estimating PM10-2.5 concentrations. Given the 

relatively small number of PM10-2.5

monitoring sites, the relatively large spatial 

variability in ambient PM10-2.5 concentrations 

(see above), the use of different approaches 

to estimating ambient PM10-2.5 concentrations 

across epidemiological studies, and the 

limitations inherent in such estimates, the 

distributions of thoracic coarse particle 

concentrations over which reported health 

outcomes occur remain highly uncertain 

(U.S. EPA, 2009a, sections 2.2.3, 2.3.3, 2.3.4, 

and 3.5.1.1). 

(4) There is relatively little information on 

the chemical and biological composition of 

PM10-2.5 and the effects associated with the 

various components (U.S. EPA, 2009a, 

section 2.3.4). Without more information on 

the chemical speciation of PM10-2.5, the 

apparent variability in associations with 

health effects across locations is difficult to 

characterize (U.S. EPA, 2009a, section 

6.5.2.3). 

(5) One of the implications of the 

uncertainties and limitations discussed above 

is that the Risk Assessment concluded it 

would not be appropriate to conduct a 

quantitative assessment of health risks 

associated with PM10-2.5. The lack of a 

quantitative PM10-2.5 risk assessment in the 

current review adds to the uncertainty in any 

conclusions about the extent to which 

revision of the current PM10 standard would 

be expected to improve the protection of 

public health, beyond the protection 

provided by the current standard.126

C. Consideration of the Current and 

Potential Alternative Standards in the 

Policy Assessment 

The following sections discuss the 

Policy Assessment’s consideration of 

the current and potential alternative 

standards to protect against exposures to 

thoracic coarse particles (U.S. EPA, 

2011a, chapter 3). Section IV.C.1 

discusses the consideration of the 

current standard while section IV.C.2 

discusses the consideration of potential 

alternative standards in terms of the 

basic elements of a standard: Indicator, 

averaging time, form, and level. 

1. Consideration of the Current Standard 

in the Policy Assessment 

As discussed above the 24-hour PM10

standard is meant to protect the public 

health against exposures to thoracic 

coarse particles (i.e., PM10-2.5). In 

considering the adequacy of the current 

PM10 standard, the Policy Assessment 

considered the health effects evidence 

linking short-term PM10-2.5 exposures 

with mortality and morbidity (U.S. EPA, 

2009a, chapters 2 and 6), the ambient 

PM10 concentrations in PM10-2.5 study 

locations (U.S. EPA, 2011a, section 

3.2.1), the uncertainties and limitations 

associated with this health evidence 

(U.S. EPA, 2011a, section 3.2.1), and the 

consideration of these uncertainties and 

limitations as part of the weight of 

evidence conclusions in the Integrated 

Science Assessment (U.S. EPA, 2009a). 

In considering the health evidence, air 

quality information, and associated 

uncertainties as they relate to the 

current PM10 standard, the Policy 

Assessment noted that a decision on the 

adequacy of the public health protection 

provided by that standard is a public 

health policy judgment in which the 

Administrator weighs the evidence and 

information, as well as its uncertainties. 

Therefore, depending on the emphasis 

placed on different aspects of the 

evidence, information, and 

uncertainties, consideration of different 

conclusions on the adequacy of the 

current standard could be supported. 

For example, the Policy Assessment 

noted that one approach to considering 

the evidence, information, and its 

associated uncertainties would be to 

place emphasis on the following (U.S. 

EPA, 2011a, section 3.2.3): 

(1) While most of PM10-2.5 effect estimates 

reported for mortality and morbidity were 

positive, many were not statistically 

significant, even in single-pollutant models. 

This includes effect estimates reported in 

study locations with PM10 concentrations 

above those allowed by the current 24-hour 

PM10 standard. 

(2) The number of epidemiological studies 

that have employed co-pollutant models to 

address the potential for confounding, 

particularly by PM2.5, remains limited. 

Therefore, the extent to which PM10-2.5 itself, 

rather than one or more co-pollutants, 

contributes to reported health effects remains 

uncertain. 

(3) Only a limited number of experimental 

studies provide support for the associations 

reported in epidemiological studies, resulting 

in further uncertainty regarding the 

plausibility of a causal link between PM10-2.5

and mortality and morbidity. 

(4) Limitations in PM10-2.5 monitoring and 

the different approaches used to estimate 

PM10-2.5 concentrations across 

epidemiological studies result in uncertainty 

as to the ambient PM10-2.5 concentrations at 

which the reported effects occur. 

(5) The chemical and biological 

composition of PM10-2.5, and the effects 

associated with the various components, 

remains uncertain. Without more information 

on the chemical speciation of PM10-2.5, the 

apparent variability in associations across 

locations is difficult to interpret. 

(6) In considering the available evidence 

and its associated uncertainties, the 

Integrated Science Assessment concluded 

that the evidence is ‘‘suggestive’’ of a causal 

relationship between short-term PM10-2.5

exposures and mortality, cardiovascular 

effects, and respiratory effects. These weightof-evidence conclusions contrast with those 

for the relationships between PM2.5

exposures and adverse health effects, which 

were judged in the Integrated Science 

Assessment to be either ‘‘causal’’ or ‘‘likely 

causal’’ for mortality, cardiovascular effects, 

and respiratory effects. 

The Policy Assessment concluded 

that, to the extent a decision on the 

adequacy of the current 24-hour PM10

standard were to place emphasis on the 

considerations noted above, it could be 

judged that, although it remains 

appropriate to maintain a standard to 

protect against short-term exposures to 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3169 

thoracic coarse particles, the available 

evidence suggests that the current 24- 

hour PM10 standard appropriately 

protects public health and provides an 

adequate margin of safety against effects 

that have been associated with PM10-2.5

exposures. Although such an approach 

to considering the adequacy of the 

current standard would recognize the 

positive, and in some cases statistically 

significant, associations between all 

types of PM10-2.5 and mortality and 

morbidity, it would place relatively 

greater emphasis on the limitations and 

uncertainties noted above, which tend 

to complicate the interpretation of that 

evidence. 

In addition, the Policy Assessment 

noted the judgment that, given the 

uncertainties and limitations in the 

PM10-2.5 health evidence and air quality 

information, it would not have been 

appropriate to conduct a quantitative 

assessment of health risks associated 

with PM10-2.5 (U.S. EPA, 2011a, p. 3–6; 

U.S. EPA, 2010a, pp. 2–6 to 2–7, 

Appendix H). As discussed above, the 

lack of a quantitative PM10-2.5 risk 

assessment adds to the uncertainty 

associated with any characterization of 

potential public health improvements 

that would be realized with a revised 

standard. 

The Policy Assessment also noted an 

alternative approach to considering the 

evidence and its uncertainties would 

place emphasis on the following (U.S. 

EPA, 2011a, section 3.2.3): 

(1) Several multi-city epidemiological 

studies conducted in the U.S., Canada, and 

Europe, as well as a number of single-city 

studies, have reported generally positive, and 

in some cases statistically significant, 

associations between short-term PM10-2.5

concentrations and adverse health endpoints 

including mortality and cardiovascularrelated and respiratory-related hospital 

admissions and emergency department visits. 

(2) Both single-city and multi-city analyses, 

using different approaches to estimate 

ambient PM10-2.5 concentrations, have 

reported positive PM10-2.5 effect estimates in 

locations that would likely have met the 

current 24-hour PM10 standard. In a few 

cases, these PM10-2.5 effect estimates were 

statistically significant. 

(3) While limited in number, studies that 

have evaluated co-pollutant models have 

generally reported that PM10-2.5 effect 

estimates remain positive, and in a few cases 

statistically significant, when these models 

include gaseous pollutants or fine particles. 

(4) Support for the plausibility of the 

associations reported in epidemiological 

studies is provided by a small number of 

controlled human exposure studies reporting 

that short-term (i.e., 2-hour) exposures to 

PM10-2.5 decrease heart rate variability and 

increase markers of pulmonary inflammation. 

This approach to considering the 

health evidence, air quality information, 

and the associated uncertainties would 

place substantial weight on the 

generally positive PM10-2.5 effect 

estimates that have been reported for 

mortality and morbidity, even those 

effect estimates that are not statistically 

significant. The Policy Assessment 

concluded that this could be judged 

appropriate given that consistent results 

have been reported across multiple 

studies using different approaches to 

estimate ambient PM10-2.5

concentrations and that exposure 

measurement error, which is likely to be 

larger for PM10-2.5 than for PM2.5, tends 

to bias the results of epidemiological 

studies toward the null hypothesis, 

making it less likely that associations 

will be detected. Such an approach 

would place less weight on the 

uncertainties and limitations in the 

evidence that resulted in the Integrated 

Science Assessment conclusions that 

the evidence is only suggestive of a 

causal relationship. 

Given all of the above, the Policy 

Assessment concluded that it would be 

appropriate to consider either retaining 

or revising the current 24-hour PM10

standard, depending on the approach 

taken to considering the available 

evidence, air quality information, and 

the uncertainties and limitations 

associated with that evidence and 

information (U.S. EPA, 2011a, section 

3.2.3). 

2. Consideration of Potential Alternative 

Standards in the Policy Assessment 

Given the conclusion that it would be 

appropriate to consider either retaining 

or revising the current PM10 standard, 

the Policy Assessment also considered 

what potential alternative standards, if 

any, could be supported by the available 

scientific evidence in order to increase 

public health protection against 

exposures to PM10-2.5. The Policy 

Assessment considered such potential 

alternative standards defined in terms of 

the elements of a standard (i.e., 

indicator, averaging time, form, and 

level). Key conclusions from the Policy 

Assessment regarding indicator, 

averaging time, and form included the 

following: 

(1) A PM10 indicator would continue to 

appropriately target protection against 

thoracic coarse particle exposures to those 

locations where the evidence is strongest for 

associations with adverse health effects (i.e., 

urban areas). 

(2) The available evidence supports the 

importance of maintaining a standard that 

protects against short-term exposures to all 

thoracic coarse particles. Given that the 

majority of this evidence is based on 24-hour 

average thoracic coarse particle 

concentrations, consideration of a 24-hour 

averaging time remains appropriate. 

(3) Given the limited body of evidence 

supporting PM10-2.5-related effects following 

long-term exposures, which resulted in the 

Integrated Science Assessment conclusion 

that the available evidence is ‘‘inadequate’’ to 

infer a causal relationship between long-term 

PM10-2.5 exposures and a variety of health 

effects, consideration of an annual thoracic 

coarse particle standard is not supported at 

this time. 

(4) To the extent it is judged appropriate 

to revise the current 24-hour PM10 standard, 

it would be appropriate to consider revising 

the form to the 3-year average of the 98th 

percentile of the annual distribution of 24- 

hour PM10 concentrations. 

In considering the available evidence 

and air quality information within the 

context of identifying potential 

alternative standard levels for 

consideration (assuming a decision were 

made that it is appropriate to amend the 

standard), the Policy Assessment first 

noted that a standard level as high as 

about 85 mg/m3, for a 24-hour PM10

standard with a 98th percentile form, 

could be supported. Based on 

considering air quality concentrations in 

study locations, the Policy Assessment 

noted that such a standard level would 

be expected to maintain PM10 and 

PM10-2.5 concentrations below those 

present in U.S. locations of single-city 

studies where PM10-2.5 effect estimates 

have been reported to be positive and 

statistically significant and below those 

present in some locations where singlecity studies reported PM10-2.5 effect 

estimates that were positive, but not 

statistically significant. These include 

some locations likely to have met the 

current PM10 standard during the study 

periods (U.S. EPA, 2011a, section 3.3.4). 

The Policy Assessment also noted 

that, based on analysis of the number of 

people living in counties that could 

violate the current and potential 

alternative PM10 standards, a 24-hour 

PM10 standard with a 98th percentile 

form and a level between 75 and 80 mg/ 

m3 would provide a level of public 

health protection that is generally 

equivalent, across the U.S., to that 

provided by the current standard. Given 

this, the Policy Assessment concluded 

that it would be appropriate to consider 

standard levels in the range of 

approximately 75 to 80 mg/m3 (with a 

98th percentile form), to the extent 

population counts were emphasized in 

comparing the public health protection 

provided by the current and potential 

alternative standards and to the extent 

it was judged appropriate to set a 

revised standard providing at least the 

level of public health protection that is 

provided by the current standard, based 

on such population counts (U.S. EPA, 

2011a, section 3.3.4). 


tkelley on DSK3SPTVN1PROD with 
3170 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

127Nonetheless, CASAC endorsed the Integrated 

Science Assessment weight of evidence conclusions 

for PM10-2.5 (i.e., that the evidence is only 

‘‘suggestive’’ of a causal relationship between shortterm exposures and mortality, respiratory effects, 

and cardiovascular effects) (Samet, 2009e; Samet, 

2009f). 

The Policy Assessment also 

concluded that alternative approaches 

to considering the evidence could lead 

to consideration of standard levels 

below 75 mg/m3 for a standard with a 

98th percentile form. For example, a 

number of single-city epidemiological 

studies have reported positive, though 

not statistically significant, PM10-2.5

effect estimates in locations with 98th 

percentile PM10 concentrations below 

75 mg/m3. Given that exposure error is 

particularly important for PM10-2.5

epidemiological studies and can bias the 

results of these studies toward the null 

hypothesis (see section IV.B above), the 

Policy Assessment noted that it could be 

judged appropriate to place more weight 

on positive associations reported in 

these epidemiological studies, even 

when those associations are not 

statistically significant. In addition, the 

Policy Assessment noted that multi-city 

averages of 98th percentile PM10

concentrations in the locations 

evaluated by U.S. multi-city studies of 

thoracic coarse particles (Zanobetti and 

Schwartz, 2009; Peng et al., 2008) were 

near or below 75 ppb. Despite 

uncertainties in the extent to which 

effects reported in multi-city studies are 

associated with the short-term air 

quality in any particular location, the 

Policy Assessment noted that emphasis 

could be placed on these multi-city 

averaged concentrations. The Policy 

Assessment concluded that, to the 

extent more weight is placed on singlecity studies reporting positive, but not 

statistically significant, PM10-2.5 effect 

estimates and on multi-city studies, it 

could be appropriate to consider 

standard levels as low as 65 mg/m3 with 

a 98th percentile form (U.S. EPA, 2011a, 

section 3.3.4). 

In considering potential alternative 

standard levels below 65 mg/m3, the 

Policy Assessment noted that the overall 

body of PM10-2.5 health evidence is 

relatively uncertain, with somewhat 

stronger support in U.S. studies for 

associations with PM10-2.5 in locations 

with 98th percentile PM10

concentrations above 85 mg/m3 than in 

locations with 98th percentile PM10

concentrations below 65 mg/m3. In light 

of the limitations in the evidence for a 

relationship between PM10-2.5 and 

adverse health effects in locations with 

relatively low PM10 concentrations, 

along with the overall uncertainties in 

the body of PM10-2.5 health evidence as 

described above and in the Integrated 

Science Assessment, the Policy 

Assessment concluded that 

consideration of standard levels below 

65 mg/m3 was not appropriate (U.S. 

EPA, 2011a, section 3.3.4). 

D. CASAC Advice 

Following their review of the first and 

second draft Policy Assessments, 

CASAC provided advice and 

recommendations regarding the current 

and potential alternative standards for 

thoracic coarse particles (Samet, 

2010c,d). With regard to the existing 

PM10 standard, CASAC concluded that 

‘‘the current data, while limited, is 

sufficient to call into question the level 

of protection afforded the American 

people by the current standard’’ (Samet, 

2010d, p. 7). In drawing this conclusion, 

CASAC noted the positive associations 

in multi-city and single-city studies, 

including in locations with PM10

concentrations below those allowed by 

the current standard. In addition, 

CASAC gave ‘‘significant weight to 

studies that have generally reported that 

PM10-2.5 effect estimates remain positive 

when evaluated in co-pollutant models’’ 

and concluded that ‘‘controlled human 

exposure PM10-2.5 studies showing 

decreases in heart rate variability and 

increases in markers of pulmonary 

inflammation are deemed adequate to 

support the plausibility of the 

associations reported in epidemiologic 

studies’’ (Samet, 2010d, p. 7).127 Given 

all of the above conclusions CASAC 

recommended that ‘‘the primary 

standard for PM10 should be revised’’ 

(Samet, 2010d, p. ii and p. 7). In 

discussing potential revisions, while 

CASAC noted that the scientific 

evidence supports adoption of a 

standard at least as stringent as the 

current standard, they recommended 

revising the current standard in order to 

increase public health protection. In 

considering potential alternative 

standards, CASAC drew conclusions 

and made recommendations in terms of 

the major elements of a standard: 

indicator, averaging time, form, and 

level. 

The CASAC agreed with the EPA 

staff’s conclusions that the available 

evidence supports consideration in the 

current review of retaining the current 

PM10 indicator and the current 24-hour 

averaging time (Samet, 2010c, Samet, 

2010d). Specifically, with regard to 

indicator, CASAC concluded that 

‘‘[w]hile it would be preferable to use an 

indicator that reflects the coarse PM 

directly linked to health risks (PM10-2.5), 

CASAC recognizes that there is not yet 

sufficient data to permit a change in the 

indicator from PM10 to one that directly 

measures thoracic coarse particles’’ 

(Samet, 2010d, p. ii). In addition, 

CASAC ‘‘vigorously recommends the 

implementation of plans for the 

deployment of a network of PM10-2.5

sampling systems so that future 

epidemiological studies will be able to 

more thoroughly explore the use of 

PM10-2.5 as a more appropriate indicator 

for thoracic coarse particles’’ (Samet, 

2010d, p. 7). 

The CASAC also agreed that the 

evidence supports consideration of a 

potential alternative form. Specifically, 

CASAC ‘‘felt strongly that it is 

appropriate to change the statistical 

form of the PM10 standard to a 98th 

percentile’’ (Samet, 2010d, p.7). In 

reaching this conclusion, CASAC noted 

that ‘‘[p]ublished work has shown that 

the percentile form has greater power to 

identify non-attainment and a smaller 

probability of misclassification relative 

to the expected exceedance form of the 

standard’’ (Samet, 2010d. p. 7). 

With regard to standard level, in 

conjunction with a 98th percentile form, 

CASAC concluded that ‘‘alternative 

standard levels of 85 and 65 mg/m3

(based on consideration of 98th 

percentile PM10 concentration) could be 

justified’’ (Samet, 2010d, p.8). However, 

in considering the evidence and 

uncertainties, CASAC recommended a 

standard level from the lower part of the 

range discussed in the Policy 

Assessment, recommending a level 

‘‘somewhere in the range of 75 to 65 mg/ 

m3’’ (Samet, 2010d, p. ii). 

In making this recommendation, 

CASAC noted that the number of people 

living in counties with air quality not 

meeting the current standard is 

approximately equal to the number 

living in counties that would not meet 

a 98th percentile standard with a level 

between 75 and 80 mg/m3. CASAC used 

this information as the basis for their 

conclusion that a 98th percentile 

standard between 75 and 80 mg/m3

would be ‘‘comparable to the degree of 

protection afforded to the current PM10

standard’’ (Samet, 2010d, p. ii). Given 

this conclusion regarding the 

comparability of the current and 

potential alternative standards, as well 

as their conclusion on the public health 

protection provided by the current 

standard (i.e., that available evidence is 

sufficient to call it into question), 

CASAC recommended a level within a 

range of 75 to 65 mg/m3 in order to 

increase public health protection, 

relative to that provided by the current 

standard (Samet 2010d, p. ii). 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3171 

E. Administrator’s Proposed 

Conclusions Concerning the Adequacy 

of the Current Primary PM10 Standard 

In considering the evidence and 

information as they relate to the 

adequacy of the current 24-hour PM10

standard, the Administrator first noted 

in the proposal that this standard is 

meant to protect the public health 

against effects associated with shortterm exposures to PM10-2.5. In the last 

review, it was judged appropriate to 

maintain such a standard given the 

‘‘growing body of evidence suggesting 

causal associations between short-term 

exposure to thoracic coarse particles 

and morbidity effects, such as 

respiratory symptoms and hospital 

admissions for respiratory diseases, and 

possibly mortality’’ (71 FR 61185, 

October 17, 2006). Given the continued 

expansion in the body of scientific 

evidence linking short-term PM10-2.5 to 

health outcomes such as premature 

death and hospital visits, discussed in 

detail in the Integrated Science 

Assessment (U.S. EPA, 2009a, Chapter 

6) and summarized in the proposal, the 

Administrator provisionally concluded 

that the available evidence continued to 

support the appropriateness of 

maintaining a standard to protect the 

public health against effects associated 

with short-term (e.g., 24-hour) 

exposures to all PM10-2.5. In drawing 

provisional conclusions in the proposal 

as to whether the current PM10 standard 

remains requisite (i.e., neither more nor 

less stringent than necessary) to protect 

public health with an adequate margin 

of safety against such exposures, the 

Administrator considered the following: 

(1) The extent to which it is appropriate to 

maintain a standard that provides some 

measure of protection against all PM10-2.5, 

regardless of composition or source of origin; 

(2) The extent to which it is appropriate to 

retain a PM10 indicator for a standard meant 

to protect against exposures to ambient 

PM10-2.5; and 

(3) The extent to which the current PM10

standard provides an appropriate degree of 

public health protection. 

With regard to the first point, the 

proposal noted the conclusion from the 

last review that dosimetric, 

toxicological, occupational, and 

epidemiological evidence supported 

retention of a primary standard to 

provide some measure of protection 

against short-term exposures to all 

thoracic coarse particles, regardless of 

their source of origin or location, 

consistent with the Act’s requirement 

that primary NAAQS provide requisite 

protection with an adequate margin of 

safety (71 FR 61197). In that review, the 

EPA concluded that PM from a number 

of source types, including motor vehicle 

emissions, coal combustion, oil burning, 

and vegetative burning, are associated 

with health effects (U.S. EPA, 2004). 

This information formed part of the 

basis for the D.C. Circuit’s holding that 

it was appropriate for the thoracic 

coarse particle standard to provide 

‘‘some protection from exposure to 

thoracic coarse particles * * * in all 

areas’’ (American Farm Bureau 

Federation v. EPA, 559 F. 3d at 532–33). 

In considering this issue in the 

proposal, the Administrator judged that 

the expanded body of scientific 

evidence in this review provides even 

more support for a standard that 

protects against exposures to all thoracic 

coarse particles, regardless of their 

location or source of origin. Specifically, 

the Administrator noted that 

epidemiological studies have reported 

positive associations between PM10-2.5

and mortality or morbidity in a large 

number of cities across North America, 

Europe, and Asia, encompassing a 

variety of environments where PM10-2.5

sources and composition are expected to 

vary widely. See 77 FR 38959. In 

considering this evidence, the Integrated 

Science Assessment concluded that 

‘‘many constituents of PM can be linked 

with differing health effects’’ (U.S. EPA, 

2009a, p. 2–26). While PM10-2.5 in most 

of these study areas is of largely urban 

origin, the Administrator noted that 

some recent studies have also linked 

mortality and morbidity with relatively 

high ambient concentrations of thoracic 

coarse particles of non-urban crustal 

origin. In considering these studies, she 

noted the Integrated Science 

Assessment’s conclusion that ‘‘PM (both 

PM2.5 and PM10-2.5) from crustal, soil or 

road dust sources or PM tracers linked 

to these sources are associated with 

cardiovascular effects’’ (U.S. EPA, 

2009a, p. 2–26). 

In light of this body of available 

evidence reporting PM10-2.5-associated 

health effects across different locations 

with a variety of sources, as well as the 

Integrated Science Assessment’s 

conclusions regarding the links between 

adverse health effects and PM sources 

and composition, the Administrator 

provisionally concluded in the proposal 

that it is appropriate to maintain a 

standard that provides some measure of 

protection against exposures to all 

thoracic coarse particles, regardless of 

their location, source of origin, or 

composition (77 FR 38959–60). 

With regard to the second point, in 

considering the appropriateness of a 

PM10 indicator for a standard meant to 

provide such public health protection, 

the Administrator noted that the 

rationale used in the last review to 

support the unqualified PM10 indicator 

(see above) remains relevant in the 

current review. Specifically, as an initial 

consideration, she noted that PM10 mass 

includes both coarse PM (PM10-2.5) and 

fine PM (PM2.5). As a result, the 

concentration of PM10-2.5 allowed by a 

PM10 standard set at a single level 

declines as the concentration of PM2.5

increases. At the same time, the 

Administrator noted that PM2.5

concentrations tend to be higher in 

urban areas than in rural areas (U.S. 

EPA, 2005, p. 2–54, and Figures 2–23 

and 2–24) and, therefore, a PM10

standard will generally allow lower 

PM10-2.5 concentrations in urban areas 

than in rural areas. 77 FR 38960. 

In considering the appropriateness of 

this variation in allowable PM10-2.5

concentrations, the Administrator 

considered the relative strength of the 

evidence for health effects associated 

with PM10-2.5 of urban origin versus nonurban origin. She specifically noted 

that, as described above and similar to 

the scientific evidence available in the 

last review, the large majority of the 

available evidence for thoracic coarse 

particle health effects comes from 

studies conducted in locations with 

sources more typical of urban and 

industrial areas than of rural areas. 

Although as just noted, associations 

with adverse health effects have been 

reported in some study locations where 

PM10-2.5 is largely non-urban in origin 

(i.e., in dust storm studies), particle 

concentrations in these study areas are 

typically much higher than reported in 

study locations where the PM10-2.5 is of 

urban origin. Therefore, the 

Administrator noted that the strongest 

evidence for a link between PM10-2.5 and 

adverse health impacts, particularly for 

such a link at relatively low particle 

concentrations, comes from studies 

where exposure is to PM10-2.5 of urban 

or industrial origin. 77 FR 38960. 

The Administrator also noted that 

chemical constituents present at higher 

levels in urban or industrial areas, 

including byproducts of incomplete 

combustion (e.g. polycyclic aromatic 

hydrocarbons) emitted as PM2.5 from 

motor vehicles as well as metals and 

other contaminants emitted from 

anthropogenic sources, can contaminate 

PM10-2.5 (U.S. EPA, 2004, p. 8–344; 71 

FR 2665). While the Administrator 

acknowledged the uncertainty 

expressed in the Integrated Science 

Assessment regarding the extent to 

which, based on available evidence, 

particle composition can be linked to 

health outcomes, she also considered 

the possibility that PM10-2.5

contaminants typical of urban or 

industrial areas could increase the 


tkelley on DSK3SPTVN1PROD with 
3172 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

toxicity of thoracic coarse particles in 

urban locations (77 FR 38960). 

Given that the large majority of the 

evidence for PM10-2.5 toxicity, 

particularly at relatively low particle 

concentrations, comes from study 

locations where thoracic coarse particles 

are of urban origin, and given the 

possibility that PM10-2.5 contaminants in 

urban areas could increase particle 

toxicity, the Administrator provisionally 

concluded in the proposal that it 

remains appropriate to maintain a 

standard that targets public health 

protection to urban locations. 

Specifically, she concluded at proposal 

that it is appropriate to maintain a 

standard that allows lower ambient 

concentrations of PM10-2.5 in urban 

areas, where the evidence is strongest 

that thoracic coarse particles are linked 

to mortality and morbidity, and higher 

concentrations in non-urban areas, 

where the public health concerns are 

less certain. Id. 

Given all of the above considerations 

and conclusions, the Administrator 

judged that the available evidence 

supported retaining a PM10 indicator for 

a standard that is meant to protect 

against exposure to thoracic coarse 

particles. In reaching this initial 

judgment, she noted that, to the extent 

a PM10 indicator results in lower 

allowable concentrations of thoracic 

coarse particles in some areas compared 

to others, lower concentrations will be 

allowed in those locations (i.e., urban or 

industrial areas) where the science has 

shown the strongest evidence of adverse 

health effects associated with exposure 

to thoracic coarse particles and where 

we have the most concern regarding 

PM10-2.5 toxicity. Therefore, the 

Administrator provisionally concluded 

that the varying amounts of coarse 

particles that are allowed in urban vs. 

non-urban areas under the 24-hour PM10

standard, based on the varying levels of 

PM2.5 present, appropriately reflect the 

differences in the strength of evidence 

regarding coarse particle effects in urban 

and non-urban areas (77 FR 38960). 

In reaching this provisional 

conclusion, the Administrator also 

noted that, in their review of the second 

draft Policy Assessment, CASAC 

concluded that ‘‘[w]hile it would be 

preferable to use an indicator that 

reflects the coarse PM directly linked to 

health risks (PM10-2.5), CASAC 

recognizes that there is not yet sufficient 

data to permit a change in the indicator 

from PM10 to one that directly measures 

thoracic coarse particles’’ (Samet, 

2010d, p. ii). In addition, CASAC 

‘‘vigorously recommends the 

implementation of plans for the 

deployment of a network of PM10-2.5

sampling systems so that future 

epidemiological studies will be able to 

more thoroughly explore the use of 

PM10-2.5 as a more appropriate indicator 

for thoracic coarse particles’’ (Samet, 

2010d, p. 7). Given this 

recommendation, the Administrator 

further judged that, although current 

evidence is not sufficient to identify a 

standard based on an alternative 

indicator that would be requisite to 

protect public health with an adequate 

margin of safety across the United 

States, consideration of alternative 

indicators (e.g., PM10-2.5) in future 

reviews is desirable and could be 

informed by additional research, as 

described in the Policy Assessment 

(U.S. EPA, 2011a, section 3.5). 

With regard to the third point, in 

evaluating the degree of public health 

protection provided by the current PM10

standard, the Administrator noted that 

the Policy Assessment discussed two 

different approaches to considering the 

scientific evidence and air quality 

information (U.S. EPA, 2011a, section 

3.2.3). These different approaches, 

which are described above (section 

IV.C.1), lead to different conclusions 

regarding the appropriateness of the 

degree of public health protection 

provided by the current PM10 standard. 

The Administrator further noted that the 

primary difference between the two 

approaches lies in the extent to which 

weight is placed on the following (U.S. 

EPA, 2011a, section 3.2.3): 

(1) The PM10-2.5 weight-of-evidence 

classifications presented in the Integrated 

Science Assessment concluding that the 

existing evidence is suggestive of a causal 

relationship between short-term PM10-2.5

exposures and mortality, cardiovascular 

effects, and respiratory effects (a 

classification supported by CASAC); 

(2) Individual PM10-2.5 epidemiological 

studies reporting associations in locations 

that meet the current PM10 standard, 

including associations that are not 

statistically significant; 

(3) The limited number of PM10-2.5

epidemiological studies that have evaluated 

co-pollutant models; 

(4) The limited number of PM10-2.5

controlled human exposure studies; 

(5) Uncertainties in the PM10-2.5 air quality 

concentrations reported in epidemiological 

studies, given limitations in PM10-2.5

monitoring data and the different approaches 

used across studies to estimate ambient 

PM10-2.5 concentrations; and 

(6) Uncertainties and limitations in the 

evidence that tend to call into question the 

presence of a causal relationship between 

PM10-2.5 exposures and mortality/morbidity. 

In evaluating the different possible 

approaches to considering the public 

health protection provided by the 

current PM10 standard, the 

Administrator first noted that when the 

available PM10-2.5 scientific evidence 

and its associated uncertainties are 

considered, the Integrated Science 

Assessment concluded that the evidence 

is suggestive of a causal relationship 

between short-term PM10-2.5 exposures 

and mortality, cardiovascular effects, 

and respiratory effects. As discussed in 

section IV.B.1 above and in more detail 

in the Integrated Science Assessment 

(U.S. EPA, 2009a, section 1.5), a 

suggestive determination is made when 

the ‘‘[e]vidence is suggestive of a causal 

relationship with relevant pollutant 

exposures, but is limited because 

chance, bias and confounding cannot be 

ruled out.’’ In contrast, the 

Administrator noted that she proposed 

to strengthen the annual fine particle 

standard based on a body of scientific 

evidence judged sufficient to conclude 

that a causal relationship exists (i.e., 

mortality, cardiovascular effects) or is 

likely to exist (i.e., respiratory effects) 

(section III.B). 77 FR 38961. The 

suggestive judgment for PM10-2.5 reflects 

the greater degree of uncertainty 

associated with this body of evidence, 

as discussed above (sections IV.B and 

IV.C) and summarized below. 

In the proposal (77 FR 38961), the 

Administrator noted that the important 

uncertainties and limitations associated 

with the scientific evidence and air 

quality information raise questions as to 

whether public health benefits would be 

achieved by revising the existing PM10

standard. Such uncertainties and 

limitations include the following: 

(1) While PM10-2.5 effect estimates reported 

for mortality and morbidity were generally 

positive, most were not statistically 

significant, even in single-pollutant models. 

This includes effect estimates reported in 

some study locations with PM10

concentrations above those allowed by the 

current 24-hour PM10 standard. 

(2) The number of epidemiological studies 

that have employed co-pollutant models to 

address the potential for confounding, 

particularly by PM2.5, remains limited. 

Therefore, the extent to which PM10-2.5 itself, 

rather than one or more co-pollutants, 

contributes to reported health effects is less 

certain. 

(3) Only a limited number of experimental 

studies (i.e., controlled human exposure and 

animal toxicological) provide support for the 

associations reported in epidemiological 

studies, resulting in further uncertainty 

regarding the plausibility of the associations 

between PM10-2.5 and mortality and morbidity 

reported in epidemiological studies. 

(4) Limitations in PM10-2.5 monitoring data 

and the different approaches used by 

epidemiological study researchers to estimate 

PM10-2.5 concentrations across 

epidemiological studies result in uncertainty 

in the ambient PM10-2.5 concentrations at 

which the reported effects occur, increasing 

uncertainty in estimates of the extent to 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3173 

128There are similarities with the conclusions 

drawn by the Administrator in the last review. 

There, the Administrator concluded that there was 

no basis for concluding that the degree of protection 

afforded by the current PM10 standards in urban 

areas is greater than warranted, since potential 

mortality effects have been associated with air 

quality levels not allowed by the current 24-hour 

Continued 

which changes in ambient PM10-2.5

concentrations would likely impact public 

health. 

(5) The lack of a quantitative PM10-2.5 risk 

assessment further contributes to uncertainty 

regarding the extent to which any revisions 

to the current PM10 standard would be 

expected to improve the protection of public 

health, beyond the protection provided by 

the current standard (see section III.B.5 

above). 

(6) The chemical and biological 

composition of PM10-2.5, and the effects 

associated with the various components, 

remains uncertain. Without more information 

on the chemical speciation of PM10-2.5, the 

apparent variability in associations across 

locations is difficult to interpret. 

In considering these uncertainties and 

limitations, the Administrator noted in 

particular the considerable degree of 

uncertainty in the extent to which 

health effects reported in 

epidemiological studies are due to 

PM10-2.5 itself, as opposed to one or 

more co-occurring pollutants. As 

discussed above, this uncertainty 

reflects the fact that there are a 

relatively small number of PM10-2.5

studies that have utilized co-pollutant 

models, particularly co-pollutant 

models that have included PM2.5, and a 

very limited body of controlled human 

exposure evidence supporting the 

biological plausibility of a causal 

relationship between PM10-2.5 and 

mortality and morbidity at ambient 

concentrations. The Administrator 

noted that these important limitations in 

the overall body of health evidence 

introduce uncertainty into the 

interpretation of individual 

epidemiological studies, particularly 

those studies reporting associations 

with PM10-2.5 that are not statistically 

significant. Given this, the 

Administrator reached the provisional 

conclusion in the proposal that it is 

appropriate to place relatively little 

weight on epidemiological studies 

reporting associations with PM10-2.5 that 

are not statistically significant in singlepollutant and/or co-pollutant models. 

Id. 

With regard to this provisional 

conclusion, the Administrator noted 

that, for single-city mortality studies 

conducted in the United States where 

ambient PM10 concentration data were 

available for comparison to the current 

standard, positive and statistically 

significant PM10-2.5 effect estimates were 

only reported in study locations that 

would likely have violated the current 

PM10 standard during the study period 

(U.S. EPA, 2011a, Figure 3–2). In U.S. 

study locations that would likely have 

met the current standard, PM10-2.5 effect 

estimates for mortality were positive, 

but not statistically significant (U.S. 

EPA, 2011a, Figure 3–2). In considering 

U.S. study loc‘ations where single-city 

morbidity studies were conducted, and 

which would likely have met the 

current PM10 standard during the study 

period, the Administrator noted that 

PM10-2.5 effect estimates were both 

positive and negative, with most not 

statistically significant (U.S. EPA, 

2011a, Figure 3–3). 

In addition, in considering single-city 

analyses for the locations evaluated in a 

large U.S. multi-city mortality study 

(Zanobetti and Schwartz, 2009), the 

Administrator noted that associations in 

most of the study locations were not 

statistically significant and that this was 

the only study to estimate ambient 

PM10-2.5 concentrations as the difference 

between county-wide PM10 and PM2.5

mass. As discussed in the Policy 

Assessment and in the proposal, it is not 

clear how computed PM10-2.5

measurements, such as those used by 

Zanobetti and Schwartz (2009), compare 

with the PM10-2.5 concentrations 

obtained in other studies either by 

direct measurement or by calculating 

the difference using co-located samplers 

(U.S. EPA, 2009a, section 6.5.2.3). For 

these reasons, in the proposal the 

Administrator noted that ‘‘there is 

considerable uncertainty in interpreting 

the associations in these single-city 

analyses’’ (77 FR 38961–62). 

The Administrator acknowledged that 

an approach to considering the available 

scientific evidence and air quality 

information that emphasizes the above 

considerations differs from the approach 

taken by CASAC. Specifically, in its 

review of the draft Policy Assessment 

CASAC placed a substantial amount of 

weight on individual studies, 

particularly those reporting positive 

health effects associations for PM10-2.5 in 

locations that met the current PM10

standard during the study period. In 

emphasizing these studies, as well as 

the limited number of supporting 

studies that have evaluated co-pollutant 

models and the small number of 

supporting experimental studies, 

CASAC concluded that ‘‘the current 

data, while limited, is sufficient to call 

into question the level of protection 

afforded the American people by the 

current standard’’ (Samet, 2010d, p. 7) 

and recommended revising the current 

PM10 standard (Samet, 2010d). 

The Administrator carefully 

considered CASAC’s advice and 

recommendations. She noted that in 

making its recommendation on the 

current PM10 standard, CASAC did not 

discuss its approach to considering the 

important uncertainties and limitations 

in the health evidence, and did not 

discuss how these uncertainties and 

limitations were reflected in its 

recommendation. Nor did CASAC 

discuss uncertainties in the reported 

concentrations of PM10-2.5 in the 

epidemiological studies, or how 

reported concentrations in the various 

studies relate to one another when 

differing measurement methodologies 

are used. As discussed above, such 

uncertainties and limitations 

contributed to the conclusions in the 

Integrated Science Assessment that the 

PM10-2.5 evidence is only suggestive of a 

causal relationship, a conclusion that 

CASAC endorsed (Samet, 2009e,f). 

Given the importance of these 

uncertainties and limitations to the 

interpretation of the evidence, as 

reflected in the weight of evidence 

conclusions in the Integrated Science 

Assessment and as discussed above, the 

Administrator judged it appropriate to 

consider and account for them when 

drawing conclusions about the potential 

implications of individual PM10-2.5

health studies for the current standard. 

In light of the above approach to 

considering the scientific evidence, air 

quality information, and associated 

uncertainties, the Administrator reached 

the following provisional conclusions in 

the proposal: 

(1) When viewed as a whole the available 

evidence and information suggests that the 

degree of public health protection provided 

against short-term exposures to PM10-2.5 does 

not need to be increased beyond that 

provided by the current PM10 standard. This 

provisional conclusion noted the important 

uncertainties and limitations associated with 

the overall body of health evidence and air 

quality information for PM10-2.5, as discussed 

above and as reflected in the Integrated 

Science Assessment weight-of-evidence 

conclusions; that PM10-2.5 effect estimates for 

the most serious health effect, mortality, were 

not statistically significant in U.S. locations 

that met the current PM10 standard and 

where coarse particle concentrations were 

either directly measured or estimated based 

on co-located samplers; and that PM10-2.5

effect estimates for morbidity endpoints were 

both positive and negative in locations that 

met the current standard, with most not 

statistically significant. 

(2) The degree of public health protection 

provided by the current standard is not 

greater than warranted. This provisional 

conclusion noted that positive and 

statistically significant associations with 

mortality were reported in single-city U.S. 

study locations likely to have violated the 

current PM10 standard.128


tkelley on DSK3SPTVN1PROD with 
3174 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

standard, but have not been associated with air 

quality levels that would generally meet that 

standard, and morbidity effects have been 

associated with air quality levels that exceeded the 

current 24-hour standard only a few times (71 FR 

61202). In addition, the Administrator concluded 

that there was a high degree of uncertainty in the 

relevant population exposures implied by the 

morbidity studies suggesting that there is little basis 

for concluding that a greater degree of protection is 

warranted. Id. The D.C. Circuit in American Farm 

Bureau Federation v EPA explicitly endorsed this 

reasoning. 559 F. 3d at 534. 

In reaching these provisional 

conclusions, the Administrator noted 

that the Policy Assessment also 

discussed the potential for a revised 

PM10 standard (i.e., with a revised form 

and level) to be ‘‘generally equivalent’’ 

to the current standard, but to better 

target public health protection to 

locations where there is greater concern 

regarding PM10-2.5-associated health 

effects (U.S. EPA, 2011a, sections 3.3.3 

and 3.3.4). In considering such a 

potential revised standard, the Policy 

Assessment discussed the large amount 

of variability in PM10 air quality 

correlations across monitoring locations 

and over time (U.S. EPA, 2011a, Figure 

3–7) and the regional variability in the 

relative degree of public health 

protection that could be provided by the 

current and potential alternative 

standards (U.S. EPA, 2011a, Table 3–2). 

In light of this variability, the 

Administrator noted the Policy 

Assessment conclusion that no single 

revised PM10 standard (i.e., with a 

revised form and level) would provide 

public health protection equivalent to 

that provided by the current standard, 

consistently over time and across 

locations (U.S. EPA, 2011a, section 

3.3.4). That is, a revised standard, even 

one that is meant to be ‘‘generally 

equivalent’’ to the current PM10

standard, could increase protection in 

some locations while decreasing 

protection in others (77 FR 38962). 

In considering the appropriateness of 

revising the current PM10 standard in 

this way, the Administrator noted the 

following: 

(1) Positive PM10-2.5 effect estimates for 

mortality were not statistically significant in 

U.S. locations that met the current PM10

standard and where coarse particle 

concentrations were either directly measured 

or estimated based on co-located samplers, 

while positive and statistically significant 

associations with mortality were reported in 

locations likely to have violated the current 

PM10 standard. 

(2) Effect estimates for morbidity endpoints 

in locations that met the current standard 

were both positive and negative, with most 

not statistically significant. 

(3) Important uncertainties and limitations 

associated with the overall body of health 

evidence and air quality information for 

PM10-2.5, as discussed above and as reflected 

in the Integrated Science Assessment weightof-evidence conclusions, call into question 

the extent to which the type of quantified 

and refined targeting of public health 

protection envisioned under a revised 

standard could be reliably accomplished. 

Given all of the above considerations, 

the Administrator noted that there is a 

large amount of uncertainty in the 

extent to which public health would be 

improved by changing the locations to 

which the PM10 standard targets 

protection. Therefore, she reached the 

provisional conclusion that the current 

PM10 standard should not be revised in 

order to change that targeting of 

protection. 

In considering all of the above, 

including the scientific evidence, the air 

quality information, the associated 

uncertainties, and CASAC’s advice, the 

Administrator reached the provisional 

conclusion that the current 24-hour 

PM10 standard is requisite (i.e., neither 

more protective nor less protective than 

necessary) to protect public health with 

an adequate margin of safety against 

effects that have been associated with 

PM10-2.5. In light of this provisional 

conclusion, the Administrator proposed 

to retain the current PM10 standard in 

order to protect against health effects 

associated with short-term exposures to 

PM10-2.5 (77 FR 38963). 

The Administrator recognized that her 

proposed conclusions and decision to 

retain the current PM10 standard 

differed from CASAC’s 

recommendations, stemming from the 

differences in how the Administrator 

and CASAC considered and accounted 

for the evidence and its limitations and 

uncertainties. In light of CASAC’s views 

and recommendation to revise the 

current PM10 standard, the 

Administrator welcomed the public’s 

views on these different approaches to 

considering and accounting for the 

evidence and its limitations and 

uncertainties, as well as on the 

appropriateness of revising the primary 

PM10 standard, including revising the 

form and level of the standard. In doing 

so, the Administrator solicited comment 

on all aspects of the proposed decision, 

including her rationale for reaching the 

provisional conclusion that the current 

PM10 standard is requisite to protect 

public health with an adequate margin 

of safety and the provisional conclusion 

that it is not appropriate to revise the 

current PM10 standard by setting a 

‘‘generally equivalent’’ standard with 

the goal of better targeting public health 

protection. 

F. Public Comments on the 

Administrator’s Proposed Decision To 

Retain the Primary PM10 Standard 

This section discusses the major 

public comments received on the 

Administrator’s proposed decision to 

retain the primary PM10 standard. 

Additional comments are addressed in 

the Response to Comments Document 

(U.S. EPA, 2012a). 

Many public commenters agreed with 

the Administrator’s proposed decision 

to retain the current 24-hour primary 

PM10 standard. Among those expressing 

a position on this proposed decision, 

industry groups and most State and 

Local commenters endorsed the 

Administrator’s proposed rationale for 

retaining the current primary PM10

standard, including her consideration of 

the available scientific evidence and 

associated uncertainties and her 

consideration of CASAC 

recommendations. 

Although industry commenters 

generally agreed with the 

Administrator’s proposed decision to 

retain the current primary PM10

standard, some also contended that the 

current standard is ‘‘excessively 

precautionary’’ (NMA and NCBA, 2012, 

p. 4) and a few expressed support for a 

less stringent standard for coarse 

particles that are comprised largely of 

crustal material. For example, the 

Coarse Particulate Matter Coalition 

(CPMC) (2012) and several other 

industry commenters recommended that 

the final decision allow application of a 

98th percentile form for the current 

standard (i.e. with its level of 150 mg/ 

m3) in cases where coarse particles 

consist primarily of crustal material. 

Such an approach would allow more 

yearly exceedances of the existing 

standard level than are allowed with the 

current one-expected-exceedance form. 

These industry commenters contended 

that a 98th percentile form applied in 

this way would provide appropriate 

regulatory relief for areas where the 

evidence for coarse particle-related 

health effects is relatively uncertain. 

In reaching her conclusion that the 

current primary PM10 standard is 

requisite to protect public health with 

an adequate margin of safety, the 

Administrator considered the degree of 

public health protection provided by the 

current standard as a whole, including 

all elements of that standard (i.e., 

indicator, averaging time, form, level). 

As discussed above and in the following 

section, this conclusion reflects the 

Administrator’s judgments that (1) the 

current standard appropriately provides 

some measure of protection against 

exposures to all thoracic coarse 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3175 

129Based on regression analyses presented in the 

PA (U.S. EPA, 2011a, Figures 3–7 and 3–8), PM10

one-expected-exceedance concentration-equivalent 

design values were between approximately 175 and 

300 mg/m3 at monitoring locations recording 3-year 

averages of 98th percentile 24-hour PM10

concentrations around 150 mg/m3 (i.e., the level of 

the current standard). This suggests that, depending 

on the location, a 24-hour PM10 standard with a 

98th percentile form in conjunction with the 

current level (i.e., as recommended by these 

commenters) could be ‘‘generally equivalent’’ to a 

24-hour PM10 standard with a one-expectedexceedance form and a level as high as 

approximately 300 mg/m3. Based on this analysis, a 

24-hour PM10 standard with a 98th percentile form 

and a level of 150 mg/m3 would be markedly less 

health protective than the current standard. 

particles, regardless of their location, 

source of origin, or composition and (2) 

the current standard appropriately 

allows lower ambient concentrations of 

PM10-2.5 in urban areas, where the 

evidence is strongest that thoracic 

coarse particles are linked to mortality 

and morbidity, and higher 

concentrations in non-urban areas, 

where the public health concerns are 

less certain. 

Because the considerations that led to 

these judgments, and to the conclusion 

that the current primary PM10 standard 

is requisite to protect public health, took 

into account the degree of public health 

protection provided by the standard as 

a whole, it would not be appropriate to 

consider revising one element of the 

standard (e.g., the form, as suggested by 

commenters in this case) without 

considering the extent to which the 

other elements of the standard should 

also be revised. The change in form 

requested by industry commenters, 

without also lowering the level of the 

standard, would markedly reduce the 

public health protection provided 

against exposures to thoracic coarse 

particles.129 However, industry 

commenters have not presented new 

evidence or analyses to support their 

conclusion that an appropriate degree of 

public health protection could be 

achieved by allowing the use of an 

alternative form (i.e., 98th percentile) 

for some coarse particles, while 

retaining the other elements of the 

current standard. Nor have these 

commenters presented new evidence or 

analyses challenging the basis for the 

conclusion in the proposal that the 

varying amounts of coarse particles 

allowed in urban versus non-urban 

areas under the current 24-hour PM10

standard, based on the varying levels of 

PM2.5 present, appropriately reflect the 

differences in the strength of evidence 

regarding coarse particle effects in urban 

and non-urban areas. In light of this, 

EPA does not believe that a reduction in 

public health protection, such as that 

requested by industry commenters, is 

warranted. 

In further considering these 

comments, it is to be remembered that 

epidemiologic studies have not 

demonstrated that coarse particles of 

non-urban origin do not cause health 

effects, and commenters have not 

provided additional evidence on this 

point. While there are fewer studies of 

non-urban coarse particles than of urban 

coarse particles, several studies have 

reported positive and statistically 

significant associations between coarse 

particles of crustal, non-urban origin 

and mortality or morbidity (Ostro et al., 

2003; Bell et al., 2008; Chan et al., 2008; 

Middleton et al., 2008; Perez et al., 

2008). These studies formed part of the 

basis for the PM Integrated Science 

Assessment conclusion that ‘‘recent 

studies have suggested that PM (both 

PM2.5 and PM10-2.5) from crustal, soil or 

road dust sources or PM tracers linked 

to these sources are associated with 

cardiovascular effects’’ (U.S. EPA, 

2009a, p. 2–26). Moreover, crustal 

coarse particles may be contaminated 

with toxic trace elements and other 

components from previously deposited 

fine PM from ubiquitous sources such as 

mobile source engine exhaust, as well as 

by toxic metals from smelters or other 

industrial activities, animal waste, or 

pesticides (U.S. EPA, 2004, p. 8–344). In 

the proposal, the Administrator 

acknowledged the potential for this type 

of contamination to increase the toxicity 

of coarse particles of crustal, non-urban 

origin (77 FR 38960; see also 71 FR 

61190). 

In suggesting a change in the form of 

the current standard, industry 

commenters also did not address the 

manifold difficulties noted above, and 

in the last review, associated with 

developing an indicator that could 

reliably identify ambient mixes 

dominated by particular types of 

sources of coarse particles. See above 

and 71 FR 61193. Yet such an indicator 

would be a prerequisite of the type of 

standard these commenters request. 

For all of the reasons discussed above, 

the EPA does not agree with industry 

commenters who recommended 

allowing the application of a 98th 

percentile form for the current standard 

in cases where coarse particles consist 

primarily of crustal material. 

Some industry commenters 

contended that the uncertainties and 

limitations that precluded a quantitative 

risk assessment also preclude revising 

the PM10 standard. Although the EPA 

agrees that there are important 

uncertainties and limitations in the 

extent to which the quantitative 

relationships between ambient PM10-2.5

and health outcomes can be 

characterized in risk models, the 

Agency does not agree that such 

limitations alone preclude the option of 

revising a NAAQS. As noted above, the 

lack of a quantitative PM10-2.5 risk 

assessment in the current review adds 

uncertainty to conclusions about the 

extent to which revision of the current 

PM10 standard would be expected to 

improve the protection of public health, 

beyond the protection provided by the 

current standard. However, the EPA 

does not agree that such uncertainties 

necessarily preclude revision of a 

NAAQS. Indeed, with respect to 

thoracic coarse particles, the DC Circuit 

noted that ‘‘[a]lthough the evidence of 

danger from coarse PM is, as the EPA 

recognizes, ‘inconclusive’, the agency 

need not wait for conclusive findings 

before regulating a pollutant it 

reasonably believes may pose a 

significant risk to public health.’’ 559 F. 

3d at 533. Thus, the Administrator’s 

conclusion that the current 24-hour 

PM10 standard provides requisite 

protection of public health relies on her 

consideration of the broad body of 

evidence, rather than solely on the 

uncertainties that led to the decision not 

to conduct a quantitative assessment of 

PM10-2.5 health risks. 

Commenters representing a number of 

environmental groups and medical 

organizations disagreed with the 

Administrator’s proposal to retain the 

current primary PM10 standard. These 

commenters generally requested that the 

EPA revise the PM10 standard to 

increase public health protection, 

consistent with the recommendations 

from CASAC. 

As discussed above and in the 

proposal, in reaching provisional 

conclusions in the proposal regarding 

the current standard, the Administrator 

carefully considered CASAC’s advice 

and recommendations. She specifically 

noted that in making its 

recommendation on the current PM10

standard, CASAC did not discuss its 

approach to considering the important 

uncertainties and limitations in the 

health evidence, and did not discuss 

how these uncertainties and limitations 

were reflected in its recommendations. 

Such uncertainties and limitations 

contributed to the conclusions in the 

Integrated Science Assessment that the 

PM10-2.5 evidence is only suggestive of a 

causal relationship, a conclusion that 

CASAC endorsed (Samet, 2009e,f). 

These commenters also did not address 

the important uncertainties in the 

epidemiologic studies on which their 

comments are based. Given the 

importance of these uncertainties and 

limitations to the interpretation of the 


tkelley on DSK3SPTVN1PROD with 
3176 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

130Although EPA relied in the 1997 review on 

evidence from PM10 studies, EPA did so out of 

necessity (i.e., there were as yet no reliable studies 

measuring PM10-2.5). In the 2006 review, EPA placed 

primary reliance on epidemiologic studies 

measuring or estimating PM10-2.5, although there 

were comparatively few such studies. In this 

review, a larger body of PM10-2.5 studies are 

available. EPA regards these studies as the evidence 

to be given principal weight in reviewing the 

adequacy of the PM10 standard. 

131The D.C. Circuit agreed. See 559 F. 3d at 532– 

33. 

132 Indeed, CASAC recommended making the 

standard for all types of thoracic coarse PM more 

stringent (Samet, 2010d). 

evidence, as reflected in the weight of 

evidence conclusions in the Integrated 

Science Assessment and as discussed in 

the proposal, the Administrator judges 

that it is appropriate to consider and 

account for them when drawing 

conclusions about the implications of 

individual PM10-2.5 health studies for the 

current standard. Commenters have not 

provided new information that would 

change the Administrator’s views on the 

evidence and uncertainties. 

In recommending that the PM10

standard be revised, some commenters 

supported their conclusions by 

referencing studies that evaluated PM10, 

rather than PM10-2.5. These commenters 

contended that ‘‘[t]he most relevant 

studies to the setting of a PM10 standard 

are the thousands of studies that have 

reported adverse effects associated with 

PM10 pollution’’ (ALA et al., 2012). 

As discussed in the Policy 

Assessment, the proposal, and above, 

since the establishment of the primary 

PM2.5 standards, the purpose of the 

primary PM10 standard has been to 

protect against health effects associated 

with exposures to PM10-2.5. PM10 is the 

indicator, not the target pollutant. With 

regard to the appropriateness of 

considering PM10 health studies for the 

purpose of reaching conclusions on a 

standard meant to protect against 

exposures to PM10-2.5, the proposal 

noted that PM10 includes both fine and 

coarse particles, even in locations with 

the highest concentrations of PM10-2.5. 

Therefore, the extent to which PM10

effect estimates reflect associations with 

PM10-2.5 versus PM2.5 can be highly 

uncertain and it is often unclear how 

PM10 health studies should be 

interpreted when considering a standard 

meant to protect against exposures to 

PM10-2.5. Given this uncertainty and the 

availability of a number of PM10-2.5

health studies in this review, the 

Integrated Science Assessment 

considered PM10-2.5 studies, but not 

PM10 studies, when drawing weight-ofevidence conclusions regarding the 

coarse fraction.130 In light of the 

uncertainty in ascribing PM10-related 

health effects to the coarse or fine 

fractions, indicating that the best 

evidence for effects associated with 

exposures to PM10-2.5 comes from 

studies evaluating PM10-2.5 itself, and 

given CASAC’s support for the approach 

adopted in the Integrated Science 

Assessment, which draws weight-ofevidence conclusions for PM2.5 and 

PM10-2.5 but not for PM10 (Samet, 2009f), 

the EPA continues to conclude that it is 

appropriate to focus on PM10-2.5 health 

studies when considering the degree of 

public health protection provided by the 

current primary PM10 standard, a 

standard intended exclusively to 

provide protection against exposures to 

PM10-2.5. 

G. Administrator’s Final Decision on the 

Primary PM10 Standard 

In reaching a final decision on the 

primary PM10 standard, the 

Administrator takes into account the 

available scientific evidence, and the 

assessment of that evidence, in the 

Integrated Science Assessment; the 

analyses and staff conclusions presented 

in the Policy Assessment; the advice 

and recommendations of CASAC; and 

public comments on the proposal. In 

particular, as in the proposal, the 

Administrator places emphasis on her 

consideration of the following issues: 

(1) The extent to which it is appropriate to 

maintain a standard that provides some 

measure of protection against all PM10-2.5, 

regardless of composition or source of origin; 

(2) The extent to which it is appropriate to 

retain a PM10 indicator for a standard meant 

to protect against exposures to ambient 

PM10-2.5; and 

(3) The extent to which the current PM10

standard provides an appropriate degree of 

public health protection. 

Each of these issues is discussed 

below. 

With regard to the first issue, as in the 

proposal the Administrator judges that 

the expanded body of scientific 

evidence available in this review 

provides ample support for a standard 

that protects against exposures to all 

thoracic coarse particles, regardless of 

their location or source of origin. There 

was already ample evidence for this 

position in the previous review,131 and 

that evidence has since increased. 

Specifically, the Administrator notes 

that epidemiological studies have 

reported positive associations between 

PM10-2.5 and mortality or morbidity in a 

large number of cities across North 

America, Europe, and Asia, 

encompassing a variety of environments 

where PM10-2.5 sources and composition 

are expected to vary widely. In 

considering this evidence, the Integrated 

Science Assessment concludes that 

‘‘many constituents of PM can be linked 

with differing health effects’’ (U.S. EPA, 

2009a, p. 2–26). Although PM10-2.5 in 

most of these study areas is of largely 

urban origin, the Administrator notes 

that some recent studies have also 

linked mortality and morbidity with 

relatively high ambient concentrations 

of particles of non-urban crustal origin. 

In considering these studies, she notes 

the Integrated Science Assessment’s 

conclusion that ‘‘PM (both PM2.5 and 

PM10-2.5) from crustal, soil or road dust 

sources or PM tracers linked to these 

sources are associated with 

cardiovascular effects’’ (U.S. EPA, 

2009a, p. 2–26). The Administrator 

likewise notes CASAC’s emphatic 

advice that a standard remains needed 

for all types of thoracic coarse PM.132 In 

light of this body of available evidence 

reporting PM10-2.5-associated health 

effects across different locations with a 

variety of sources, the Integrated 

Science Assessment’s conclusions 

regarding the links between adverse 

health effects and PM sources and 

composition, and CASAC’s advice, the 

Administrator concludes in the current 

review that it is appropriate to maintain 

a standard that provides some measure 

of protection against exposures to all 

thoracic coarse particles, regardless of 

their location, source of origin, or 

composition. 

With regard to the second issue, in 

considering the appropriateness of a 

PM10 indicator for a standard meant to 

provide such public health protection, 

the Administrator notes that the 

rationale used in the last review to 

support the unqualified PM10 indicator 

remains relevant in the current review. 

Specifically, as an initial consideration, 

she notes that PM10 mass includes both 

coarse PM (PM10-2.5) and fine PM 

(PM2.5). As a result, the concentration of 

PM10-2.5 allowed by a PM10 standard set 

at a single level declines as the 

concentration of PM2.5 increases. At the 

same time, the Administrator notes that 

PM2.5 concentrations tend to be higher 

in urban areas than rural areas (U.S. 

EPA, 2005, p. 2–54, and Figures 2–23 

and 2–24) and, therefore, a PM10

standard will generally allow lower 

PM10-2.5 concentrations in urban areas 

than in rural areas. 

In considering the appropriateness of 

this variation in allowable PM10-2.5

concentrations, the Administrator 

considers the relative strength of the 

evidence for health effects associated 

with PM10-2.5 of urban origin versus nonurban origin. She specifically notes that, 

as discussed in the proposal, the large 

majority of the available evidence for 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3177 

133As discussed in the proposal, the 

Administrator recognizes that this relationship is 

qualitative. That is, the varying coarse particle 

concentrations allowed under the PM10 standard do 

not precisely correspond to the variable toxicity of 

thoracic coarse particles in different areas (insofar 

as that variability is understood). Although 

currently available information does not allow any 

more precise adjustment for relative toxicity, the 

Administrator believes the standard will generally 

ensure that the coarse particle levels allowed will 

be lower in urban areas and higher in non-urban 

areas. Addressing this qualitative relationship, the 

DC Circuit held that ‘‘[i]t is true that the EPA relies 

on a qualitative analysis to describe the protection 

the coarse PM NAAQS will provide. But the fact 

that the EPA’s analysis is qualitative rather than 

quantitative does not undermine its validity as an 

acceptable rationale for the EPA’s decision.’’ 559 F. 

3d at 535. 

134The D.C. Circuit agreed with similar 

conclusions in the last review and held that this 

rationale reasonably supported use of an 

unqualified PM10 indicator for thoracic coarse 

particles. American Farm Bureau Federation v. 

EPA, 559 F. 3d at 535–36. 

135 In addition, CASAC ‘‘vigorously recommends 

the implementation of plans for the deployment of 

a network of PM10-2.5 sampling systems so that 

future epidemiological studies will be able to more 

thoroughly explore the use of PM10-2.5 as a more 

appropriate indicator for thoracic coarse particles’’ 

(Samet, 2010d, p. 7). Consideration of alternative 

indicators (e.g., PM10-2.5) in future reviews could be 

informed by additional research, as described in the 

Policy Assessment (U.S. EPA, 2011a, section 3.5). 

thoracic coarse particle health effects 

comes from studies conducted in 

locations with sources more typical of 

urban and industrial areas than rural 

areas. While associations with adverse 

health effects have been reported in 

some study locations where PM10-2.5 is 

largely non-urban in origin (i.e., in dust 

storm studies), particle concentrations 

in these study areas are typically much 

higher than reported in study locations 

where the PM is of urban origin. 

Therefore, the Administrator notes that 

the strongest evidence for a link 

between PM10-2.5 and adverse health 

impacts, particularly for such a link at 

relatively low particle concentrations, 

comes from studies of urban or 

industrial PM10-2.5. 

The Administrator also notes that 

chemical constituents present at higher 

levels in urban or industrial areas, 

including byproducts of incomplete 

combustion (e.g. polycyclic aromatic 

hydrocarbons) emitted as PM2.5 from 

motor vehicles as well as metals and 

other contaminants emitted from 

anthropogenic sources, can contaminate 

PM10-2.5 (U.S. EPA, 2004, p. 8–344; 71 

FR 2665, January 17, 2006). While the 

Administrator acknowledges the 

uncertainty expressed in the Integrated 

Science Assessment regarding the extent 

to which particle composition can be 

linked to health outcomes based on 

available evidence, she also considers 

the possibility that PM10-2.5

contaminants typical of urban or 

industrial areas could increase the 

toxicity of thoracic coarse particles in 

urban locations. 

Given that the large majority of the 

evidence for PM10-2.5 toxicity, 

particularly at relatively low particle 

concentrations, comes from study 

locations where thoracic coarse particles 

are of urban origin, and given the 

possibility that PM10-2.5 contaminants in 

urban areas could increase particle 

toxicity, the Administrator concludes 

that it remains appropriate to maintain 

a standard that provides some 

protection in all areas but targets public 

health protection to urban locations. 

Specifically, she concludes that it is 

appropriate to maintain a standard that 

allows lower ambient concentrations of 

PM10-2.5 in urban areas, where the 

evidence is strongest that thoracic 

coarse particles are linked to mortality 

and morbidity, and higher 

concentrations in non-urban areas, 

where the public health concerns are 

less certain. 

Given all of the above considerations 

and conclusions, the Administrator 

judges that the available evidence 

supports retaining a PM10 indicator for 

a standard that is meant to protect 

against exposures to thoracic coarse 

particles. In reaching this judgment, she 

notes that, to the extent a PM10 indicator 

results in lower allowable 

concentrations of thoracic coarse 

particles in some areas compared to 

others, lower concentrations will be 

allowed in those locations (i.e., urban or 

industrial areas) where the science has 

shown the strongest evidence of adverse 

health effects associated with exposure 

to thoracic coarse particles and where 

we have the most concern regarding 

PM10-2.5 toxicity. Therefore, the 

Administrator concludes that the 

varying amounts of coarse particles that 

are allowed in urban vs. non-urban 

areas under the 24-hour PM10 standard, 

based on the varying levels of PM2.5

present, appropriately reflect the 

differences in the strength of evidence 

regarding coarse particle effects in urban 

and non-urban areas.133 134

In reaching this conclusion, the 

Administrator also notes that, in their 

review of the second draft Policy 

Assessment, CASAC concluded that 

‘‘[w]hile it would be preferable to use an 

indicator that reflects the coarse PM 

directly linked to health risks (PM10-2.5), 

CASAC recognizes that there is not yet 

sufficient data to permit a change in the 

indicator from PM10 to one that directly 

measures thoracic coarse particles’’ 

(Samet, 2010d, p. ii). Thus, consistent 

the considerations presented above and 

with CASAC advice, the Administrator 

concludes that it is appropriate to retain 

PM10 as the indicator for thoracic coarse 

particles.135

With regard to the third issue, in 

evaluating the degree of public health 

protection provided by the current PM10

standard, the Administrator first notes 

that when the available PM10-2.5

scientific evidence and its associated 

uncertainties were considered, the 

Integrated Science Assessment 

concluded that the evidence is 

suggestive of a causal relationship 

between short-term PM10-2.5 exposures 

and mortality, cardiovascular effects, 

and respiratory effects. As discussed 

above and in more detail in the 

Integrated Science Assessment (U.S. 

EPA, 2009a, section 1.5), a suggestive 

determination is made when the 

‘‘[e]vidence is suggestive of a causal 

relationship with relevant pollutant 

exposures, but is limited because 

chance, bias and confounding cannot be 

ruled out.’’ In contrast, the 

Administrator notes that she is 

strengthening the annual fine particle 

standard based on a body of scientific 

evidence judged sufficient to conclude 

that a causal relationship exists (i.e., 

mortality, cardiovascular effects) or is 

likely to exist (i.e., respiratory effects). 

The suggestive judgment for PM10-2.5

reflects the greater degree of uncertainty 

associated with this body of evidence, 

as discussed above and in more detail 

in the proposal, and as summarized 

below. 

The Administrator notes that the 

important uncertainties and limitations 

associated with the scientific evidence 

and air quality information raise 

questions as to whether public health 

benefits would be achieved by revising 

the existing PM10 standard. Such 

uncertainties and limitations include 

the following: 

(1) While PM10-2.5 effect estimates reported 

for mortality and morbidity were generally 

positive, most were not statistically 

significant, even in single-pollutant models. 

This includes effect estimates reported in 

some study locations with PM10

concentrations above those allowed by the 

current 24-hour PM10 standard. 

(2) The number of epidemiological studies 

that have employed co-pollutant models to 

address the potential for confounding, 

particularly by PM2.5, remains limited. 

Therefore, the extent to which PM10-2.5 itself, 

rather than one or more co-pollutants, 

contributes to reported health effects remains 

uncertain. 

(3) Only a limited number of experimental 

studies provide support for the associations 

reported in epidemiological studies, resulting 

in further uncertainty regarding the 

plausibility of the associations between 

PM10-2.5 and mortality and morbidity 

reported in epidemiological studies. 


tkelley on DSK3SPTVN1PROD with 
3178 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

136The Administrator acknowledges that this 

approach to interpreting the evidence differs in 

emphasis from the approach she has adopted for the 

evidence relating to PM2.5. As discussed above in 

section III.E.4, for fine particles the Administrator 

has considered not only whether study results are 

statistically significant (or remain so after 

application of co-pollutant models), but she also 

places emphasis on the overall pattern of results 

across the epidemiological literature. This includes 

giving some credence to studies that reported 

statistically non-significant associations. This 

difference in emphasis stems from the much 

stronger overall body of evidence available for fine 

particles, compared to coarse particles. As 

discussed above, when the available PM2.5 scientific 

evidence and its associated uncertainties were 

considered, the Integrated Science Assessment 

concluded that the evidence was sufficient to 

conclude that causal relationships exist with 

mortality and cardiovascular effects, and that a 

causal relationship is likely to exist with respiratory 

effects. In contrast, the Integrated Science 

Assessment concluded that the evidence is 

suggestive of a causal relationship between shortterm PM10-2.5 exposures and mortality, 

cardiovascular effects, and respiratory effects. A 

suggestive determination is made when the 

‘‘[e]vidence is suggestive of a causal relationship 

with relevant pollutant exposures, but is limited 

because chance, bias and confounding cannot be 

ruled out’’ (U.S. EPA, 2009a, section 1.5). The 

suggestive judgment for PM10-2.5 reflects the greater 

degree of uncertainty associated with this body of 

evidence. 

(4) Limitations in PM10-2.5 monitoring data 

and the different approaches used to estimate 

PM10-2.5 concentrations across 

epidemiological studies result in uncertainty 

in the ambient PM10-2.5 concentrations at 

which the reported effects occur, increasing 

uncertainty in estimates of the extent to 

which changes in ambient PM10-2.5

concentrations would likely impact public 

health. 

(5) The lack of a quantitative PM10-2.5 risk 

assessment further contributes to uncertainty 

regarding the extent to which any revisions 

to the current PM10 standard would be 

expected to improve the protection of public 

health, beyond the protection provided by 

the current standard (see section III.B.5 

above). 

(6) The chemical and biological 

composition of PM10-2.5, and the effects 

associated with the various components, 

remains uncertain. Without more information 

on the chemical speciation of PM10-2.5, the 

apparent variability in associations across 

locations is difficult to characterize. 

In considering these uncertainties and 

limitations, the Administrator notes in 

particular the considerable degree of 

uncertainty in the extent to which 

health effects reported in 

epidemiological studies are due to 

PM10-2.5 itself, as opposed to one or 

more co-occurring pollutants. As 

discussed above, this uncertainty 

reflects the fact that there are a 

relatively small number of PM10-2.5

studies that have evaluated co-pollutant 

models, particularly co-pollutant 

models that have included PM2.5, and a 

very limited body of controlled human 

exposure evidence supporting the 

plausibility of a causal relationship 

between PM10-2.5 and mortality and 

morbidity at ambient concentrations. 

The Administrator notes that these 

important limitations in the overall 

body of health evidence introduce 

uncertainty into the interpretation of 

individual epidemiological studies, 

particularly those studies reporting 

associations with PM10-2.5 that are not 

statistically significant. Given this, the 

Administrator reaches the conclusion 

that it is appropriate to place relatively 

little weight on epidemiological studies 

reporting associations with PM10-2.5 that 

are not statistically significant in singlepollutant and/or co-pollutant models.136

With regard to this conclusion, the 

Administrator notes that, for single-city 

mortality studies conducted in the 

United States where ambient PM10

concentration data were available for 

comparison to the current standard, 

positive and statistically significant 

PM10-2.5 effect estimates were only 

reported in study locations that would 

likely have violated the current PM10

standard during the study period (U.S. 

EPA, 2011a, Figure 3–2). In U.S. study 

locations that would likely have met the 

current standard, PM10-2.5 effect 

estimates for mortality were positive, 

but not statistically significant (U.S. 

EPA, 2011a, Figure 3–2). In considering 

U.S. study locations where single-city 

morbidity studies were conducted, and 

which would likely have met the 

current PM10 standard during the study 

period, the Administrator notes that 

PM10-2.5 effect estimates were both 

positive and negative, with most not 

statistically significant (U.S. EPA, 

2011a, Figure 3–3). 

In addition, in considering single-city 

analyses for the locations evaluated in a 

large U.S. multi-city mortality study 

(Zanobetti and Schwartz, 2009), the 

Administrator notes that associations in 

most of the study locations were not 

statistically significant and that this was 

the only study to estimate ambient 

PM10-2.5 concentrations as the difference 

between county-wide PM10 and PM2.5

mass. As discussed in the proposal, the 

Administrator notes that it is not clear 

how computed PM10-2.5 measurements, 

such as those used by Zanobetti and 

Schwartz (2009), compare with the 

PM10-2.5 concentrations obtained in 

other studies either by direct 

measurement by calculating the 

difference using co-located samplers 

(U.S. EPA, 2009a, section 6.5.2.3). For 

these reasons, as in the proposal, the 

Administrator notes that there is 

considerable uncertainty in interpreting 

the associations, and especially the 

concentrations at which such 

associations may have occurred, in 

these single-city analyses. 

The Administrator acknowledges that 

an approach to considering the available 

scientific evidence and air quality 

information that emphasizes the above 

considerations differs from the approach 

taken by CASAC. Specifically, CASAC 

placed a substantial amount of weight 

on individual studies, particularly those 

reporting positive health effects 

associations in locations that met the 

current PM10 standard during the study 

period. In emphasizing these studies, as 

well as the limited number of 

supporting studies that have evaluated 

co-pollutant models and the small 

number of supporting experimental 

studies, CASAC concluded that ‘‘the 

current data, while limited, is sufficient 

to call into question the level of 

protection afforded the American 

people by the current standard’’ (Samet, 

2010d, p. 7) and recommended revising 

the current PM10 standard (Samet, 

2010d). 

The Administrator has carefully 

considered CASAC’s advice and 

recommendations. She notes that in 

making its recommendation on the 

current PM10 standard, CASAC did not 

discuss its approach to considering the 

important uncertainties and limitations 

in the health evidence, and did not 

discuss how these uncertainties and 

limitations are reflected in its 

recommendation. As discussed above, 

such uncertainties and limitations 

contributed to the conclusions in the 

Integrated Science Assessment that the 

PM10-2.5 evidence is only suggestive of a 

causal relationship, a conclusion that 

CASAC endorsed (Samet, 2009e,f). 

Given the importance of these 

uncertainties and limitations to the 

interpretation of the evidence, as 

reflected in the weight of evidence 

conclusions in the Integrated Science 

Assessment and as discussed above, the 

Administrator judges that it is 

appropriate to consider and account for 

them when drawing conclusions about 

the potential implications of individual 

PM10-2.5 health studies for the current 

standard. 

In light of the above approach to 

considering the scientific evidence, air 

quality information, and associated 

uncertainties, the Administrator reaches 

the following conclusions: 

(1) When viewed as a whole the available 

evidence and information suggests that the 

degree of public health protection provided 

against short-term exposures to PM10-2.5

should be maintained but does not need to 

be increased beyond that provided by the 

current PM10 standard. This conclusion 

emphasizes the important uncertainties and 

limitations associated with the overall body 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3179 

137This is not to say that the EPA could not adopt 

or revise a standard for a pollutant for which the 

evidence is suggestive of a causal relationship. 

Indeed, with respect to thoracic coarse particles 

itself, the DC Circuit noted that ‘‘[a]lthough the 

evidence of danger from coarse PM is, as the EPA 

recognizes, ‘inconclusive’, the agency need not wait 

for conclusive findings before regulating a pollutant 

it reasonably believes may pose a significant risk to 

public health.’’ American Farm Bureau Federation 

v EPA 559 F. 3d at 533. As explained in the text 

above, it is the Administrator’s judgment that 

significant uncertainties presented by the evidence 

and information before her in this review, both as 

to causality and as to concentrations at which 

effects may be occurring, best support a decision to 

retain rather than revise the current primary 24- 

hour PM10 standard. 

138There are similarities with the conclusions 

drawn by the Administrator in the last review. 

There, the Administrator concluded that there was 

no basis for concluding that the degree of protection 

afforded by the current PM10 standards in urban 

areas is greater than warranted, since potential 

mortality effects have been associated with air 

quality levels not allowed by the current 24-hour 

standard, but have not been associated with air 

quality levels that would generally meet that 

standard, and morbidity effects have been 

associated with air quality levels that exceeded the 

current 24-hour standard only a few times. 71 FR 

61202. In addition, the Administrator concluded 

that there was a high degree of uncertainty in the 

relevant population exposures implied by the 

morbidity studies suggesting that there is little basis 

for concluding that a greater degree of protection is 

warranted. Id. The D.C. Circuit in American Farm 

Bureau Federation v EPA explicitly endorsed this 

reasoning. 559 F. 3d at 534. 

139As discussed in detail above (section IV.C.2.d) 

and in the Policy Assessment (U.S. EPA, 2011a, 

sections 3.3.3 and 3.3.4), a revised standard that is 

generally equivalent to the current PM10 standard 

could provide a degree of public health protection 

that is similar to the degree of protection provided 

by the current standard, across the United States as 

a whole. However, compared to the current PM10

standard, such a generally equivalent standard 

would change the degree of public health protection 

provided in some specific areas, providing 

increased protection in some locations and 

decreased protection in other locations. 

140See http://www.airnow.gov/. 

141 In 1976, the EPA established a nationally 

uniform air quality index, then called the Pollutant 

Standard Index (PSI), for use by State and local 

agencies on a voluntary basis (41 FR 37660, 

September 7, 1976). In August 1999, the EPA 

adopted revisions to this air quality index (64 FR 

42530, August 4, 1999) and renamed the index the 

AQI. 

of health evidence and air quality 

information for PM10-2.5, as discussed above 

and as reflected in the Integrated Science 

Assessment weight-of-evidence conclusions; 

that PM10-2.5 effect estimates for the most 

serious health effect, mortality, were not 

statistically significant in U.S. locations that 

met the current PM10 standard and where 

coarse particle concentrations were either 

directly measured or estimated based on colocated samplers; and that PM10-2.5 effect 

estimates for morbidity endpoints were both 

positive and negative in locations that met 

the current standard, with most not 

statistically significant.137

(2) The degree of public health protection 

provided by the current standard is not 

greater than warranted. This conclusion 

notes that positive and statistically 

significant associations with mortality were 

reported in single-city U.S. study locations 

likely to have violated the current PM10

standard.138

In reaching these conclusions, the 

Administrator notes that the Policy 

Assessment also discussed the potential 

for a revised PM10 standard (i.e., with a 

revised form and level) to be ‘‘generally 

equivalent’’ to the current standard, but 

to better target public health protection 

to locations where there is greater 

concern regarding PM10-2.5-associated 

health effects (U.S. EPA, 2011a, sections 

3.3.3 and 3.3.4).139 In considering such 

a potential revised standard, the Policy 

Assessment discusses the large amount 

of variability in PM10 air quality 

correlations across monitoring locations 

and over time (U.S. EPA, 2011a, Figure 

3–7) and the regional variability in the 

relative degree of public health 

protection that could be provided by the 

current and potential alternative 

standards (U.S. EPA, 2011a, Table 3–2). 

In light of this variability, the 

Administrator notes the Policy 

Assessment conclusion that no single 

revised PM10 standard (i.e., with a 

revised form and level) would provide 

public health protection equivalent to 

that provided by the current standard, 

consistently over time and across 

locations (U.S. EPA, 2011a, section 

3.3.4). That is, a revised standard, even 

one that is meant to be ‘‘generally 

equivalent’’ to the current PM10

standard, could increase protection in 

some locations while decreasing 

protection in other locations. 

In considering the appropriateness of 

revising the current PM10 standard in 

this way, the Administrator notes the 

following: 

(1) As discussed above, positive PM10-2.5

effect estimates for mortality were not 

statistically significant in U.S. locations that 

met the current PM10 standard and where 

coarse particle concentrations were either 

directly measured or estimated based on colocated samplers, while positive and 

statistically significant associations with 

mortality were reported in locations likely to 

have violated the current PM10 standard. 

(2) Also as discussed above, effect 

estimates for morbidity endpoints in 

locations that met the current standard were 

both positive and negative, with most not 

statistically significant. 

(3) Important uncertainties and limitations 

associated with the overall body of health 

evidence and air quality information for 

PM10-2.5, as discussed above and as reflected 

in the Integrated Science Assessment weightof-evidence conclusions, call into question 

the extent to which the type of quantified 

and refined targeting of public health 

protection envisioned under a revised 

standard could be reliably accomplished. 

Given all of the above considerations, 

the Administrator notes that there is a 

large amount of uncertainty in the 

extent to which public health would be 

improved by changing the locations to 

which the PM10 standard targets 

protection. Therefore, she reaches the 

conclusion that the current PM10

standard should not be revised in order 

to change that targeting of protection. 

In considering all of the above, 

including the scientific evidence, the air 

quality information, the associated 

uncertainties, CASAC’s advice, and 

public comments received on the 

proposed rule, the Administrator 

reaches the conclusion in the current 

review that the existing 24-hour PM10

standard, with its one-expected 

exceedance form and a level of 150 mg/ 

m3, is requisite (i.e., neither more 

protective nor less protective than 

necessary) to protect public health with 

an adequate margin of safety against 

effects that have been associated with 

PM10-2.5. In light of this conclusion, with 

this rule the Administrator retains the 

current PM10 standard. 

V. Communication of Public Health 

Information 

Sections 319(a)(1) and (3) of the CAA 

require the EPA to establish a uniform 

air quality index for reporting of air 

quality. These sections specifically 

direct the Administrator to ‘‘promulgate 

regulations establishing an air quality 

monitoring system throughout the 

United States which utilizes uniform air 

quality monitoring criteria and 

methodology and measures such air 

quality according to a uniform air 

quality index’’ and ‘‘provides for daily 

analysis and reporting of air quality 

based upon such uniform air quality 

index * * *’’ In 1979, the EPA 

established requirements for index 

reporting (44 FR 27598, May 10, 1979). 

The requirement for State and local 

agencies to report the AQI appears in 40 

CFR 58.50, and the specific 

requirements (e.g., what to report, how 

to report, reporting frequency, 

calculations) are in appendix G to 40 

CFR part 58. 

Information on the public health 

implications of ambient concentrations 

of criteria pollutants is currently made 

available primarily by AQI reporting 

through EPA’s AIRNow Web site.140 The 

current AQI has been in use since its 

inception in 1999.141 It provides 

accurate, timely, and easily 

understandable information about daily 

levels of pollution (40 CFR 58.50). The 

AQI establishes a nationally uniform 

system of indexing pollution levels for 

ozone, carbon monoxide, nitrogen 


tkelley on DSK3SPTVN1PROD with 
3180 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

142Currently, we are cautioning members of 

sensitive groups at the AQI value of 100 at 35 mg/ 

m3, 24-hour average, consistent with more recent 

guidance from the EPA with regard to the 

development of State emergency episode 

contingency plans (Harnett, 2009, Attachment B). 

dioxide, PM, and sulfur dioxide. The 

AQI is also recognized internationally as 

a proven tool to effectively 

communicate air quality information to 

the public. 

The AQI converts pollutant 

concentrations in a community’s air to 

a number on a scale from 0 to 500. 

Reported AQI values enable the public 

to know whether air pollution levels in 

a particular location are characterized as 

good (0–50), moderate (51–100), 

unhealthy for sensitive groups (101– 

150), unhealthy (151–200), very 

unhealthy (201–300), or hazardous 

(301–500). The AQI index value of 100 

typically corresponds to the level of the 

short-term (e.g., daily or hourly 

standard) NAAQS for each pollutant. 

Below an index value of 100, an 

intermediate value of 50 was defined 

either as the level of the annual 

standard if an annual standard has been 

established (e.g., PM2.5, nitrogen 

dioxide), or as a concentration equal to 

one-half the value of the short-term 

standard used to define an index value 

of 100 (e.g., carbon monoxide). An AQI 

value greater than 100 means that a 

pollutant is in one of the unhealthy 

categories (i.e., unhealthy for sensitive 

groups, unhealthy, very unhealthy, or 

hazardous) on a given day. An AQI 

value at or below 100 means that a 

pollutant concentration is in one of the 

satisfactory categories (i.e., moderate or 

good). The underlying health 

information that supports the NAAQS 

review also supports the selection of the 

AQI ‘‘breakpoints’’—the ambient 

concentrations that delineate the 

various AQI categories for each 

pollutant. 

Historically, state and local agencies 

have primarily used the AQI to provide 

general information to the public about 

air quality and its relationship to public 

health. For more than a decade, many 

states and local agencies, as well as the 

EPA and other Federal agencies, have 

been developing new and innovative 

programs and initiatives to provide 

more information to the public in a 

more timely way. These initiatives, 

including air quality forecasting, realtime data reporting through the AirNow 

Web site, and state and local air quality 

action day programs, can serve to 

provide useful, up-to-date, and timely 

information to the public about air 

pollution and its effects. Such 

information will help individuals take 

actions to avoid or to reduce exposures 

to ambient pollution at levels of concern 

to them. Thus, these programs have 

significantly broadened the ways in 

which state and local agencies can meet 

the nationally uniform AQI reporting 

requirements and contribute to state and 

local efforts to provide community 

health protection. 

With respect to an AQI value of 50, 

the historical approach is to set it at the 

same level of the annual primary 

standard, if there is one. This is 

consistent with the previous AQI subindex for PM2.5, in which the AQI value 

of 50 was set at 15 mg/m3 in 1999, 

consistent with the level of the annual 

PM2.5 standard at that time. In 

recognition of the proposed change to 

the annual PM2.5 standard summarized 

in section III.F of the proposal, the EPA 

proposed a conforming change to the 

PM2.5 sub-index of the AQI to be 

consistent with the proposed change to 

the annual standard. As discussed 

below, no state or local agencies, or 

their organizations (e.g., NACAA), that 

commented on the proposed changes to 

the AQI disagreed with our proposed 

approach. Based on these comments, the 

EPA continues to see no basis for 

deviating from this approach in this 

review. Thus, the EPA is taking final 

action to set an AQI value of 50 at 12.0 

mg/m3, 24-hour average, consistent with 

the final decision on the annual PM2.5

standard level (section III.F). 

With respect to an AQI value of 100, 

which is the basis for advisories to 

individuals in sensitive groups, in the 

proposal we described two general 

approaches that could be used to select 

the associated PM2.5 level. By far the 

most common approach, which has 

been used with all of the other subindices, is to set an AQI value of 100 at 

the same level as the short-term 

standard. In the proposal, the EPA 

recognized that some state and local air 

quality agencies have expressed a strong 

preference that the Agency set an AQI 

value of 100 equal to any short-term 

standard (77 FR 38964). These agencies 

typically express the view that this 

linkage is useful for the purpose of 

communicating with the public about 

the standard, as well as providing 

consistent messages about the health 

impacts associated with daily air 

quality. The EPA proposed to use this 

approach to set the AQI value of 100 at 

35 mg/m3, 24-hour average, consistent 

with the proposed decision to retain the 

current 24-hour PM2.5 standard. Id. 

An alternative approach discussed in 

the proposal (77 FR 38964), was to 

directly evaluate the health effects 

evidence to select the level for an AQI 

value of 100. This was the approach 

used in the 1999 rulemaking to set the 

AQI value of 100 at a level of 40 mg/m3, 

24-hour average,142 when the 24-hour 

standard level was 65 mg/m3. This 

alternative approach was used in the 

case of the PM2.5 sub-index, because the 

annual and 24-hour PM2.5 standards set 

in 1997 were designed to work together, 

and the intended degree of health 

protection against short-term risks was 

not defined by the 24-hour standard 

alone, but rather by the combination of 

the two standards working in concert. 

Indeed, at that time, the 24-hour 

standard was set to provide 

supplemental protection relative to the 

principal protection provided by the 

annual standard. In the proposal, the 

EPA solicited comment on this 

alternative approach in recognition that, 

as proposed, the 24-hour PM2.5 standard 

is intended to continue to provide 

supplemental protection against effects 

associated with short-term exposures of 

PM2.5 by working in conjunction with 

the annual standard to reduce 24-hour 

exposures to PM2.5. The EPA recognized 

that in the past, some state and local air 

quality agencies have expressed support 

for this alternative approach. Using this 

alternative approach could have 

resulted in consideration of a lower 

level for an AQI value of 100, based on 

the discussion of the health information 

pertaining to the level of the 24-hour 

standard in section III.E.4 of the 

proposal. The EPA encouraged state and 

local air quality agencies to comment on 

both the approach and the level at 

which to set an AQI value of 100 

together with any supporting rationale. 

Of the state or local agencies, or their 

organizations (e.g., NACAA), that 

commented on the proposed changes to 

the AQI, only one organization, 

NESCAUM, expressed some support for 

this approach. In its comments, 

NESCAUM expressed support for a 24- 

hour standard set at 30 mg/m3, 24-hour 

average. NESCAUM also expressed the 

view that EPA should carefully consider 

how to set the breakpoint for an AQI 

value of 100. NESCAUM expressed the 

view that if the EPA were to keep the 

24-hour PM2.5 standard at 35 mg/m3, the 

annual standard would be controlling, 

and a 24-hour breakpoint at that level 

(35 mg/m3) would not be very effective 

for the purposes of public health 

messaging. However, other agencies, 

such as Georgia Department of Natural 

Resources (Georgia DNR), expressed the 

view that linkage between the shortterm standard and the AQI of 100 is 

useful for the purpose of 

communicating with the public about 

the standard as well as providing 

consistent messages about the health 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3181 

143We note that this level is consistent with the 

level recommended in the more recent EPA 

guidance (Harnett, 2009, Attachment B), which is 

in use by many State and local agencies. 

144As discussed in section VII.C below, the EPA 

is also updating the data handling procedures for 

reporting the AQI and corresponding updates for 

other AQI-sub-indices presented in Table 2 of 

appendix G of 40 CFR part 58. 

impacts associated with the daily air 

quality. Based on these comments, the 

EPA sees no basis for deviating from the 

approach proposed in this review. Thus, 

the EPA is taking final action to set an 

AQI value of 100 at 35 mg/m3, 24-hour 

average, consistent with the final 

decision on the 24-hour PM2.5 standard 

level (section III.F). 

With respect to an AQI value of 150, 

this level is based upon the same health 

effects information that informs the 

selection of the level of the 24-hour 

standard and the AQI value of 100. The 

AQI value of 150 was set in the 1999 

rulemaking at a level of 65 mg/m3, 24- 

hour average. In considering what level 

to propose for an AQI value of 150, we 

stated the view that the health effects 

evidence indicates that the level of 55 

mg/m3, 24-hour average, is appropriate 

to use 143 in conjunction with an AQI 

value of 100 set at the level of 35 mg/ 

m3. The Agency’s approach to selecting 

the levels at which to set the AQI values 

of 100 and 150 inherently recognizes 

that the epidemiological evidence upon 

which these decisions are based 

provides no evidence of discernible 

thresholds, below which effects do not 

occur in either sensitive groups or in the 

general population, at which to set these 

two breakpoints. Therefore, the EPA 

concluded the use of a proportional 

adjustment would be appropriate. 

Commenters did not comment on this 

proposed approach to revising the AQI 

value of 150; thus, the EPA is taking 

final action to set an AQI value of 150 

at 55 mg/m3, 24-hour average. 

Based on the air quality and health 

considerations discussed in section V of 

the proposal, the EPA concluded that it 

was appropriate to propose to retain the 

current level of 500 mg/m3, 24-hour 

average, for the AQI value of 500. In 

addition, the EPA solicited comment on 

alternative levels and approaches to 

setting a level for the AQI value of 500, 

as well as supporting information and 

rationales for such alternative levels. 

The EPA also solicited any additional 

information, data, research or analyses 

that may be useful to inform a final 

decision on the appropriate level to set 

the AQI value of 500. Receiving no 

information with which to inform 

alternative approaches to setting an AQI 

value of 500, the EPA is taking final 

action to retain the current level of 500 

mg/m3, 24-hour average, for the AQI 

value of 500. 

For the intermediate breakpoints in 

the AQI between the values of 150 and 

500, the EPA proposed PM2.5

concentrations that generally reflected a 

linear relationship between increasing 

index values and increasing PM2.5

values (77 FR 38965). The available 

scientific evidence of health effects 

related to population exposures to PM2.5

concentrations between the level of the 

24-hour standard and an AQI value of 

500 suggested a continuum of effects in 

this range, with increasing PM2.5

concentrations being associated with 

increasingly larger numbers of people 

likely to experience such effects. The 

generally linear relationship between 

AQI values and PM2.5 concentrations in 

this range is consistent with the health 

evidence. This also is consistent with 

the Agency’s practice of setting 

breakpoints in symmetrical fashion 

where health effects information does 

not suggest particular levels. 

Table 2 below summarizes the 

finalized breakpoints for the PM2.5 subindex.144 Table 2 shows the 

intermediate breakpoints for AQI values 

of 200, 300 and 400 based on a linear 

interpolation between the proposed 

levels for AQI values of 150 and 500. If 

a different level were to be set for an 

AQI value of 150 or 500, intermediate 

levels would be calculated based on a 

linear relationship between the selected 

levels for AQI values of 150 and 500. 

TABLE 2—BREAKPOINTS FOR PM2.5 SUB-INDEX

AQI category Index values 

Proposed breakpoints 

(μg/m3, 24-hour 

average) 

Good .................................................................................................................................................. 0–50 0.0–(12.0) 

Moderate ............................................................................................................................................ 51–100 (12.1)–35.4 

Unhealthy for Sensitive Groups ......................................................................................................... 101–150 35.5–55.4 

Unhealthy ........................................................................................................................................... 151–200 55.5–150.4 

Very Unhealthy .................................................................................................................................. 201–300 150.5–250.4 

Hazardous .......................................................................................................................................... 301–400 

401–500 

250.5–350.4 

350.5–500.4 

In retaining the 500 level for the AQI 

as described above, we note that the 

EPA is not establishing a Significant 

Harm Level (SHL) for PM2.5. The SHL is 

an important part of air pollution 

Emergency Episode Plans, which are 

required for certain areas by CAA 

section 110(a)(2)(G) and associated 

regulations at 40 CFR 51.150, under the 

Prevention of Air Pollution Emergency 

Episodes program. The Agency believes 

that air quality responses established 

through an Emergency Episode Plan 

should be developed through a 

collaborative process working with State 

and Tribal air quality, forestry and 

agricultural agencies, Federal land 

management agencies, private land 

managers and the public. Therefore, if 

in future rulemaking the EPA proposes 

revisions to the Prevention of Air 

Pollution Emergency Episodes program, 

the proposal will include a SHL for 

PM2.5 that is developed in collaboration 

with these organizations. As discussed 

in the 1999 Air Quality Index Reporting 

Rule (64 FR 42530), if a future 

rulemaking results in a SHL that is 

different from the 500 value of the AQI 

for PM2.5, the AQI will be revised 

accordingly. 

The EPA also received more general 

comments on AQI reporting, comments 

that did not pertain to setting specific 

breakpoints. One set of commenters 

(e.g., API and UARG), expressed the 

view that changes to the AQI are not 

appropriate. They noted that air quality 

is getting better, and in fact is better 

than when EPA established the AQI. 

These commenters stated that the 

proposed changes to the annual 

standard and the AQI would mean that 

the public would hear less often that air 

quality is good, and thereby would 

receive apparently inconsistent or 

misleading messages that air quality is 


tkelley on DSK3SPTVN1PROD with 
3182 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

worse. The AQI has been revised several 

times in conjunction with revisions to 

the standards. State and local air quality 

agencies and organizations are 

proficient at communicating with the 

public about the reasons for changes to 

the AQI. Therefore, the EPA strongly 

disagrees with these commenters that 

the public will receive inconsistent or 

misleading messages. Recognizing the 

importance of the AQI as a 

communication tool that allows the 

public to take exposure reduction 

measures when air quality may pose 

health risks, the EPA agrees with state 

and local air quality agencies and 

organizations that favored revising the 

AQI at the same time as the primary 

standard. 

A few state and local air quality 

agencies and organizations 

recommended against using nearroadway PM2.5 monitors for AQI 

reporting. In support of this comment, 

they expressed the following views, that 

near-roadway monitors are sourceoriented, represent micro-scale 

conditions, and the agencies don’t have 

experience using them for AQI 

reporting. The EPA disagrees with the 

comment in that these monitors will be 

sited at existing near-road stations sited 

to be representative of area-wide PM2.5

concentrations indicative of general 

population exposure. Accordingly, data 

from these near-road monitors should be 

included in the AQI since they provide 

information about PM2.5 levels that 

millions of people, who work, live and 

go to school near busy roadways, are 

exposed to. The stations are 

representative of somewhat elevated 

concentrations in near-road 

environments, but since these stations 

represent many such locations 

throughout a metropolitan area, they are 

appropriate for characterizing exposure 

in typical portions of major urban areas. 

The EPA is committed to helping air 

quality agencies develop appropriate 

ways to report PM2.5 levels from these 

monitors using the AQI. 

VI. Rationale for Final Decisions on the 

Secondary PM Standards 

This section presents the 

Administrator’s final decisions 

regarding the need to revise the current 

suite of secondary PM2.5 and PM10

standards to address visibility 

impairment and other welfare effects 

considered in this review. Specifically, 

this section describes the 

Administrator’s final decision to retain 

the current suite of secondary PM 

standards to address PM-related 

visibility impairment as well as other 

PM-related welfare effects, including 

ecological effects, effects on materials, 

and climate impacts. This suite of 

standards includes an annual PM2.5

standard of 15 mg/m3, a 24-hour PM2.5

standard of 35 mg/m3, and a 24-hour 

PM10 standard of 150 mg/m3. The 

Administrator is revising only the form 

of the secondary annual PM2.5 standard 

to remove the option for spatial 

averaging consistent with this change to 

the primary annual PM2.5 standard. 

Contrary to what was proposed, the 

Administrator has decided not to 

establish a distinct standard to address 

PM-related visibility impairment. The 

rationale for this decision is presented 

below. 

The Administrator’s final decisions 

on the secondary standards are based on 

a thorough review of the latest scientific 

information published through mid2009 on welfare effects associated with 

fine and coarse particles in the ambient 

air, as presented in the Integrated 

Science Assessment. The final decisions 

also take into account: (1) Staff 

assessments of the most policy-relevant 

information presented and assessed in 

the Integrated Science Assessment and 

staff analyses of air quality and visibility 

effects presented in the Visibility 

Assessment and the Policy Assessment, 

upon which staff conclusions regarding 

appropriate considerations in this 

review are based; (2) CASAC advice and 

recommendations, as reflected in 

discussions of drafts of the Integrated 

Science Assessment, Visibility 

Assessment, and Policy Assessment at 

public meetings, in separate written 

comments, and in CASAC’s letters to 

the Administrator; (3) the multiple 

rounds of public comments received 

during the development of these 

documents, both in connection with 

CASAC meetings and separately; and (4) 

public comments received on the 

proposal. 

In particular, this section presents 

background information on the EPA’s 

previous and current reviews of the 

secondary PM standards (section VI.A), 

a summary of the proposed decisions 

regarding the secondary PM standards 

(section VI.B), a discussion of 

significant public comments received on 

those proposed decisions (section VI.C), 

and the Administrator’s final decisions 

on the secondary PM standards (section 

VI.D). 

A. Background 

The current suite of secondary PM 

standards is identical to the suite of 

primary PM standards set in 2006, 

including 24-hour and annual PM2.5

standards and a 24-hour PM10 standard. 

The current secondary PM2.5 standards 

are intended to provide protection from 

PM-related visibility impairment, 

whereas the entire suite of secondary 

PM standards is intended to provide 

protection from other PM-related effects 

on public welfare, including effects on 

sensitive ecosystems, materials damage 

and soiling, and climatic and radiative 

processes. 

The approach used for reviewing the 

current suite of secondary PM standards 

built upon and broadened the 

approaches used in previous PM 

NAAQS reviews. The following 

discussion focuses particularly on the 

current secondary PM2.5 standards 

related to visibility impairment and 

provides a summary of the approaches 

used to review and establish secondary 

PM2.5 standards in the last two reviews 

(section VI.A.1); judicial review of the 

2006 standards that resulted in the 

remand of the secondary annual and 24- 

hour PM2.5 NAAQS to the EPA (section 

VI.A.2); and the approach used in this 

review for evaluating the secondary 

PM2.5 standards (section VI.A.3). 

1. Approaches Used in Previous 

Reviews 

The original secondary PM2.5

standards were established in 1997, and 

a revision to the 24-hour standard was 

made in 2006. The approaches used in 

making final decisions on secondary 

standards in those reviews, as well as 

the current review, utilized different 

ways to consider the underlying body of 

scientific evidence. They also reflected 

an evolution in EPA’s understanding of 

the nature of the effect on public welfare 

from PM-related visibility impairment, 

from an approach that focused only on 

Federal Class I area visibility impacts to 

a more multifaceted approach that also 

considered PM-related impacts on 

visibility in non-Federal Class I areas, 

such as in urban areas. This evolution 

occurred in conjunction with the 

expansion of available PM data and 

information from visibility-related 

studies of public perception, valuation, 

and personal comfort and well-being. 

In 1997, the EPA revised the PM 

NAAQS in part by establishing new 

identical primary and secondary PM2.5

standards. In revising the secondary 

standards, the EPA recognized that PM 

produces adverse effects on visibility 

and that impairment of visibility was 

being experienced throughout the U.S., 

in multi-state regions, urban areas, and 

remote mandatory Federal Class I areas 

alike. However, in considering an 

appropriate level for a secondary 

standard to address adverse effects of 

PM2.5 on visibility, the EPA concluded 

that the determination of a single 

national level was complicated by 

important regional differences 

influenced by factors such as 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3183 

145 In 1977, Congress established as a national 

goal ‘‘the prevention of any future, and the 

remedying of any existing, impairment of visibility 

in mandatory Federal Class I areas which 

impairment results from manmade air pollution,’’ 

section 169A(a)(1) of the CAA. The EPA is required 

by section 169A(a)(4) of the CAA to promulgate 

regulations to ensure that ‘‘reasonable progress’’ is 

achieved toward meeting the national goal. 

background and current levels of PM2.5, 

composition of PM2.5, and average 

relative humidity. Variations in these 

factors across regions could thus result 

in situations where attaining an 

appropriately protective concentration 

of fine particles in one region might or 

might not provide adequate protection 

in a different region. The EPA also 

determined that there was insufficient 

information at that time to establish a 

level for a national secondary standard 

that would represent a threshold above 

which visibility conditions would 

always be adverse and below which 

visibility conditions would always be 

acceptable. 

Based on an assessment of the 

potential visibility improvements that 

would result from reaching attainment 

with the new primary standards for 

PM2.5, the EPA concluded that 

attainment of the annual and 24-hour 

PM2.5 primary standards would lead to 

visibility improvements in the eastern 

U.S. at both urban and regional scales, 

but little or no change in the western 

U.S., except in and near certain urban 

areas. 

The EPA also considered the potential 

effectiveness of a regional haze program, 

required by sections 169A and 169B of 

the CAA 145 to address those effects of 

PM on visibility that would not be 

addressed through attainment of the 

primary PM2.5 standards. The regional 

haze program would be designed to 

address the widespread, regionally 

uniform type of haze caused by a 

multitude of sources. The structure and 

requirements of sections 169A and 169B 

of the CAA provide for visibility 

protection programs that can be more 

responsive to the factors contributing to 

regional differences in visibility than 

can programs addressing the kinds of 

nationally applicable secondary NAAQS 

considered in the 1997 review. The 

regional haze visibility goal is more 

protective than a secondary NAAQS 

since the goal is to eliminate any 

anthropogenic impairment rather than 

to provide a level of protection from 

visibility impairment that is requisite to 

protect the public welfare. Thus, an 

important factor considered in the 1997 

review was whether a regional haze 

program, in conjunction with secondary 

standards set identical to the suite of 

PM2.5 primary standards, would provide 

appropriate protection for visibility in 

non-Federal Class I areas. The EPA 

concluded that the two programs and 

associated control strategies should 

provide such protection due to the 

regional approaches needed to manage 

emissions of pollutants that impair 

visibility in many of these areas. 

For these reasons, in 1997 the EPA 

concluded that a national regional haze 

program, combined with a nationally 

applicable level of protection achieved 

through secondary PM2.5 standards set 

identical to the primary PM2.5 standards, 

would be more effective for addressing 

regional variations in the adverse effects 

of PM2.5 on visibility than would be 

national secondary standards for PM 

with levels lower than the primary 

PM2.5 standards. The EPA further 

recognized that people living in certain 

urban areas may place a high value on 

unique scenic resources in or near these 

areas and as a result might experience 

visibility problems attributable to 

sources that would not necessarily be 

addressed by the combined effects of a 

regional haze program and PM2.5

secondary standards. The EPA 

concluded that in such cases, state or 

local regulatory approaches, such as 

past action in Colorado to establish a 

local visibility standard for the City of 

Denver, would be more appropriate and 

effective in addressing these special 

situations because of the localized and 

unique characteristics of the problems 

involved. Visibility in an urban area 

located near a mandatory Federal Class 

I area could also be improved through 

state implementation of the then-current 

visibility regulations, by which 

emission limitations can be imposed on 

a source or group of sources found to be 

contributing to ‘‘reasonably 

attributable’’ impairment in the 

mandatory Federal Class I area. 

Based on these considerations, in 

1997 the EPA set secondary PM2.5

standards identical to the primary PM2.5

standards, that would work in 

conjunction with the Regional Haze 

Program to be established under 

sections 169A and 169B of the CAA, as 

the most appropriate and effective 

means of addressing the public welfare 

effects associated with visibility 

impairment. Together, the two programs 

and associated control strategies were 

expected to provide appropriate 

protection against PM-related visibility 

impairment and enable all regions of the 

country to make reasonable progress 

toward the national visibility goal. 

In 2006, the EPA revised the suite of 

secondary PM2.5 standards to address 

visibility impairment by making the 

suite of secondary standards identical to 

the revised suite of primary PM2.5

standards. The EPA’s decision regarding 

the need to revise the suite of secondary 

PM2.5 standards reflected a number of 

new developments that had occurred 

and sources of information that had 

become available following the 1997 

review. First, the EPA promulgated a 

Regional Haze Program in 1999 (65 FR 

35713, July 1, 1999) which required 

states to establish goals for improving 

visibility in Federal Class I areas and to 

adopt control strategies to achieve these 

goals. Second, extensive new 

information from visibility and fine 

particle monitoring networks had 

become available, allowing for updated 

characterizations of visibility trends and 

PM concentrations in urban areas, as 

well as Federal Class I areas. These new 

data allowed the EPA to better 

characterize visibility impairment in 

urban areas and the relationship 

between visibility and PM2.5

concentrations. Finally, additional 

studies in the U.S. and abroad provided 

the basis for the establishment of 

standards and programs to address 

specific visibility concerns in a number 

of local areas. These studies (Denver, 

Phoenix, and British Columbia) utilized 

photographic representations of 

visibility impairment and produced 

reasonably consistent results in terms of 

the visual ranges found to be generally 

acceptable by study participants. The 

EPA considered the information 

generated by these studies useful in 

characterizing the nature of particleinduced haze and for informing 

judgments about the acceptability of 

various levels of visual air quality in 

urban areas across the U.S. Based 

largely on this information, the 

Administrator concluded that it was 

appropriate to revise the secondary 

PM2.5 standards to provide increased 

protection from visibility impairment 

principally in urban areas, in 

conjunction with the regional haze 

program for protection of visual air 

quality in Federal Class I areas. 

In so doing, the Administrator 

recognized that PM-related visibility 

impairment is principally related to fine 

particle concentrations and that 

perception of visibility impairment is 

most directly related to short-term, 

nearly instantaneous levels of visual air 

quality. Thus, in considering whether 

the then-current suite of secondary 

standards would provide the 

appropriate degree of protection, he 

concluded that it was appropriate to 

focus on just the 24-hour secondary 

PM2.5 standard to provide requisite 

protection. 

The Administrator then considered 

whether PM2.5 mass remained the 

appropriate indicator for a secondary 


tkelley on DSK3SPTVN1PROD with 
3184 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

standard to protect visibility, primarily 

in urban areas. The Administrator noted 

that PM-related visibility impairment is 

principally related to fine particle 

levels. Hygroscopic components of fine 

particles, in particular sulfates and 

nitrates, contribute disproportionately 

to visibility impairment under high 

humidity conditions. Particles in the 

coarse mode generally contribute only 

marginally to visibility impairment in 

urban areas. With the substantial 

addition to the air quality and visibility 

data made possible by the national 

urban PM2.5 monitoring networks, an 

analysis conducted for the 2006 review 

found that, in urban areas, visibility 

levels showed far less difference 

between eastern and western regions on 

a 24-hour or shorter time basis than 

implied by the largely non-urban data 

available in the 1997 review. In 

analyzing how well PM2.5

concentrations correlated with visibility 

in urban locations across the U.S., the 

2005 Staff Paper concluded that clear 

correlations existed between 24-hour 

average PM2.5 concentrations and 

calculated (i.e., reconstructed) light 

extinction, which is directly related to 

visual range (U.S. EPA, 2005, p. 7–6). 

These correlations were similar in the 

eastern and western regions of the U.S. 

These correlations were less influenced 

by relative humidity and more 

consistent across regions when PM2.5

concentrations were averaged over 

shorter, daylight time periods (e.g., 4 to 

8 hours) when relative humidity in 

eastern urban areas was generally lower 

and thus more similar to relative 

humidity in western urban areas. The 

2005 Staff Paper noted that a standard 

set at any specific PM2.5 concentration 

would necessarily result in visual 

ranges that vary somewhat in urban 

areas across the country, reflecting the 

variability in the correlations between 

PM2.5 concentrations and light 

extinction. The 2005 Staff Paper 

concluded that it was appropriate to use 

PM2.5 as an indicator for standards to 

address visibility impairment in urban 

areas, especially when the indicator is 

defined for a relatively short period 

(e.g., 4 to 8 hours) of daylight hours 

(U.S. EPA, 2005, p. 7–6). Based on their 

review of the Staff Paper, most CASAC 

Panel members also endorsed such a 

PM2.5 indicator for a secondary standard 

to address visibility impairment 

(Henderson, 2005a, p. 9). Based on the 

above considerations, the Administrator 

concluded that PM2.5 should be retained 

as the indicator for fine particles as part 

of a secondary standard to address 

visibility protection, in conjunction 

with averaging times from 4 to 24 hours. 

In considering what level of 

protection against PM-related visibility 

impairment would be appropriate, the 

Administrator took into account the 

results of the public perception and 

attitude surveys regarding the 

acceptability of various degrees of 

visibility impairment in the U.S. and 

Canada, state and local visibility 

standards within the U.S., and visual 

inspection of photographic 

representations of several urban areas 

across the U.S. In the Administrator’s 

judgment, these sources provided useful 

but still quite limited information on the 

range of levels appropriate for 

consideration in setting a national 

visibility standard primarily for urban 

areas, given the generally subjective 

nature of the public welfare effect 

involved. Based on photographic 

representations of varying levels of 

visual air quality, public perception 

studies, and local and state visibility 

standards, the 2005 Staff Paper had 

concluded that 30 to 20 mg/m3 PM2.5

represented a reasonable range for a 

national visibility standard primarily for 

urban areas, based on a sub-daily 

averaging time (U.S. EPA, 2005, p. 7– 

13). The upper end of this range was 

below the levels at which illustrative 

scenic views are significantly obscured, 

and the lower end was around the level 

at which visual air quality generally 

appeared to be good based on 

observation of the illustrative views. 

This concentration range generally 

corresponded to median visual ranges in 

urban areas within regions across the 

U.S. of approximately 25 to 35 km, a 

range that was bounded above by the 

visual range targets selected in specific 

areas where state or local agencies 

placed particular emphasis on 

protecting visual air quality. In 

considering a reasonable range of forms 

for a PM2.5 standard within this range of 

levels, the 2005 Staff Paper had 

concluded that a concentration-based 

percentile form was appropriate, and 

that the upper end of the range of 

concentration percentiles for 

consideration should be consistent with 

the 98th percentile used for the primary 

standard and that the lower end of the 

range should be the 92nd percentile, 

which represented the mean of the 

distribution of the 20 percent most 

impaired days, as targeted in the 

regional haze program (U.S. EPA, 2005 

pp. 7–11 to 7–13). While recognizing 

that it was difficult to select any specific 

level and form based on then-currently 

available information (Henderson, 

2005a, p. 9), the CASAC Panel was 

generally in agreement with the ranges 

of levels and forms presented in the 

2005 Staff Paper. 

The Administrator also considered 

the level of protection that would be 

afforded by the proposed suite of 

primary PM2.5 standards (71 FR 2681, 

January 17, 2006), on the basis that 

although significantly more information 

was available than in the 1997 review 

concerning the relationship between 

fine PM levels and visibility across the 

country, there was still little available 

information for use in making the 

relatively subjective value judgment 

needed in selecting the appropriate 

degree of protection to be afforded by 

such a standard. In so doing, the 

Administrator compared the extent to 

which the proposed suite of primary 

standards would require areas across the 

country to improve visual air quality 

with the extent of increased protection 

likely to be afforded by a standard based 

on a sub-daily averaging time. Based on 

such an analysis, the Administrator 

observed that the predicted percent of 

counties with monitors not likely to 

meet the proposed suite of primary 

PM2.5 standards was actually somewhat 

greater than the predicted percent of 

counties with monitors not likely to 

meet a sub-daily secondary standard 

with an averaging time of 4 daylight 

hours, a level toward the upper end of 

the range recommended in the 2005 

Staff Paper, and a form within the 

recommended range. Based on this 

comparison, the Administrator 

tentatively concluded that revising the 

secondary 24-hour PM2.5 standard to be 

identical to the proposed revised 

primary PM2.5 standard (and retaining 

the then-current annual secondary PM2.5

standard) was a reasonable policy 

approach to addressing visibility 

protection primarily in urban areas. In 

proposing this approach, the 

Administrator also solicited comment 

on a sub-daily (4- to 8-hour averaging 

time) secondary PM2.5 standard (71 FR 

2675 to 2781, January 17, 2006). 

In commenting on the proposed 

decision, the CASAC requested that a 

sub-daily standard to protect visibility 

‘‘be favorably reconsidered’’ 

(Henderson, 2006a, p.6). The CASAC 

noted three cautions regarding the 

proposed reliance on a secondary PM2.5

standard identical to the proposed 24- 

hour primary PM2.5 standard: (1) PM2.5

mass measurement is a better indicator 

of visibility impairment during daylight 

hours, when relative humidity is 

generally low; the sub-daily standard 

more clearly matches the nature of 

visibility impairment, whose adverse 

effects are most evident during the 

daylight hours; using a 24-hour PM2.5

standard as a proxy introduces error and 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3185 

uncertainty in protecting visibility; and 

sub-daily standards are used for other 

NAAQS and should be the focus for 

visibility; (2) CASAC and its monitoring 

subcommittees had repeatedly 

commended EPA’s initiatives promoting 

the introduction of continuous and 

near-continuous PM monitoring and 

recognized that an expanded 

deployment of continuous PM2.5

monitors would be consistent with 

setting a sub-daily standard to protect 

visibility; and (3) the analysis showing 

a similarity between percentages of 

counties not likely to meet what the 

CASAC Panel considered to be a lenient 

4- to 8-hour secondary standard and a 

secondary standard identical to the 

proposed 24-hour primary standard was 

a numerical coincidence that was not 

indicative of any fundamental 

relationship between visibility and 

health. The CASAC Panel further stated 

that ‘‘visual air quality is substantially 

impaired at PM2.5 concentrations of 35 

mg/m3’’ and that ‘‘[i]t is not reasonable 

to have the visibility standard tied to the 

health standard, which may change in 

ways that make it even less appropriate 

for visibility concerns’’ (Henderson, 

2006a, pp. 5 to 6). 

In reaching a final decision, the 

Administrator focused on the relative 

protection provided by the proposed 

primary standards based on the abovementioned similarities in percentages of 

counties meeting alternative standards 

and on the limitations in the 

information available concerning 

studies of public perception and 

attitudes regarding the acceptability of 

various degrees of visibility impairment 

in urban areas, as well as on the 

subjective nature of the judgment 

required. In so doing, the Administrator 

concluded that caution was warranted 

in establishing a distinct secondary 

standard for visibility impairment and 

that the available information did not 

warrant adopting a secondary standard 

that would provide either more or less 

protection against visibility impairment 

in urban areas than would be provided 

by secondary standards set equal to the 

proposed primary PM2.5 standards. 

2. Remand of 2006 Secondary PM2.5

Standards 

As noted above in section II.B.2 

above, several parties filed petitions for 

review challenging EPA’s decision to set 

the secondary NAAQS for fine PM 

identical to the primary NAAQS. On 

judicial review, the D.C. Circuit 

remanded to the EPA for 

reconsideration the secondary NAAQS 

for fine PM because the Agency’s 

decision was unreasonable and contrary 

to the requirements of section 109(b)(2). 

American Farm Bureau Federation v. 

EPA, 559 F. 3d 512 (D.C. Cir., 2009). 

The petitioners argued that the EPA’s 

decision lacked a reasoned basis. First, 

they asserted that the EPA never 

determined what level of visibility was 

‘‘requisite to protect the public welfare.’’ 

They argued that the EPA unreasonably 

rejected the target level of protection 

recommended by its staff, while failing 

to provide a target level of its own. The 

court agreed, stating that ‘‘the EPA’s 

failure to identify such a level when 

deciding where to set the level of air 

quality required by the revised 

secondary fine PM NAAQS is contrary 

to the statute and therefore unlawful. 

Furthermore, the failure to set any target 

level of visibility protection deprived 

the EPA’s decision-making of a reasoned 

basis.’’ 559 F. 3d at 530. 

Second, the petitioners challenged 

EPA’s method of comparing the 

protection expected from potential 

standards. They contended that the EPA 

relied on a meaningless numerical 

comparison, ignored the effect of 

humidity on the usefulness of a 

standard using a daily averaging time, 

and unreasonably concluded that the 

primary standards would achieve a level 

of visibility roughly equivalent to the 

level the EPA staff and CASAC deemed 

‘‘requisite to protect the public welfare.’’ 

The court found that the EPA’s 

equivalency analysis based on the 

percentages of counties exceeding 

alternative standards ‘‘failed on its own 

terms.’’ The same table showing the 

percentages of counties exceeding 

alternative secondary standards, used 

for comparison to the percentages of 

counties exceeding alternative primary 

standards to show equivalency, also 

included six other alternative secondary 

standards within the recommended 

CASAC range that would be more 

‘‘protective’’ under EPA’s definition 

than the adopted primary standards. 

Two-thirds of the potential secondary 

standards within the CASAC’s 

recommended range would be 

substantially more protective than the 

adopted primary standards. The court 

found that the EPA failed to explain 

why it looked only at one of the few 

potential secondary standards that 

would be less protective, and only 

slightly less so, than the primary 

standards. More fundamentally, 

however, the court found that the EPA’s 

equivalency analysis based on 

percentages of counties demonstrated 

nothing about the relative protection 

offered by the different standards, and 

that the tables offered no valid 

information about the relative visibility 

protection provided by the standards. 

559 F. 3d at 530–31. 

Finally, the Staff Paper had made 

clear that a visibility standard using 

PM2.5 mass as the indicator in 

conjunction with a daily averaging time 

would be confounded by regional 

differences in humidity. The court 

noted that the EPA acknowledged this 

problem, yet did not address this issue 

in concluding that the primary 

standards would be sufficiently 

protective of visibility. 559 F. 3d at 530. 

Therefore, the court granted the petition 

for review and remanded for 

reconsideration the secondary PM2.5

NAAQS. 

3. General Approach Used in the Policy 

Assessment for the Current Review 

The approach used in this review 

broadened the general approaches used 

in the last two PM NAAQS reviews by 

utilizing, to the extent available, 

enhanced tools, methods, and data to 

more comprehensively characterize 

visibility impacts. As such, the EPA 

took into account considerations based 

on both the scientific evidence 

(‘‘evidence-based’’) and a quantitative 

analysis of PM-related impacts on 

visibility (‘‘impact-based’’) to inform 

conclusions related to the adequacy of 

the current secondary PM2.5 standards 

and alternative standards that were 

appropriate for consideration in this 

review. As in past reviews, the EPA also 

considered that the secondary NAAQS 

should address PM-related visibility 

impairment in conjunction with the 

Regional Haze Program, such that the 

secondary NAAQS would focus on 

protection from visibility impairment 

principally in urban areas in 

conjunction with the Regional Haze 

Program that is focused on improving 

visibility in Federal Class I areas. The 

EPA again recognized that such an 

approach remains the most appropriate 

and effective means of addressing the 

public welfare effects associated with 

visibility impairment in areas across the 

country. 

The Policy Assessment drew from the 

qualitative evaluation of all studies 

discussed in the Integrated Science 

Assessment (U.S. EPA, 2009a). 

Specifically, the Policy Assessment 

considered the extensive new air quality 

and source apportionment information 

available from the regional planning 

organizations, long-standing evidence of 

PM effects on visibility, and limited 

public preference study information 

from four urban areas (U.S. EPA, 2009a, 

chapter 9), as well as the integration of 

evidence across disciplines (U.S. EPA, 

2009a, chapter 2). In addition, limited 

information that had become available 

regarding the characterization of public 

preferences in urban areas provided 


tkelley on DSK3SPTVN1PROD with 
3186 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

146As used in the Regional Haze Program, the 

term bext refers to light extinction due to PM2.5, 

PM10-2.5, and ‘‘clean’’ atmospheric gases. In the 

Policy Assessment, in focusing on light extinction 

due to PM2.5, the deciview values include only the 

effects of PM2.5 and the gases. The ‘‘Rayleigh’’ term 

associated with clean atmospheric gases is 

represented by the constant value of 10 Mm¥1. 

Omission of the Rayleigh term would create the 

possibility of negative deciview values when the 

PM2.5 concentration is very low. 

147The algorithm is referred to as the IMPROVE 

algorithm because it was developed specifically to 

use the aerosol monitoring data generated at 

network sites and with equipment specifically 

designed to support the IMPROVE program and was 

evaluated using IMPROVE optical measurements at 

the subset of sites that make those measurements 

(Malm et al., 1994). 

some new perspectives on the 

usefulness of this information in 

informing the selection of target levels 

of urban visibility protection. On these 

bases, the Policy Assessment again 

focused assessments on visibility 

conditions in urban areas. 

The conclusions in the Policy 

Assessment reflected EPA staff’s 

understanding of both evidence-based 

and impact-based considerations to 

inform two overarching questions 

related to (1) the adequacy of the current 

suite of PM2.5 standards and (2) what 

potential alternative standards, if any, 

should be considered in this review to 

provide appropriate protection from 

PM-related visibility impairment. In 

addressing these broad questions, the 

discussions in the Policy Assessment 

were organized around a series of more 

specific questions reflecting different 

aspects of each overarching question 

(U.S. EPA, 2011a, Figure 4–1). When 

evaluating the visibility protection 

afforded by the current or any 

alternative standards considered, the 

Policy Assessment took into account the 

four basic elements of the NAAQS: 

indicator, averaging time, level, and 

form. 

B. Proposed Decisions on Secondary PM 

Standards 

At the time of proposal, the 

Administrator proposed to revise the 

suite of secondary PM standards by 

adding a distinct standard for PM2.5 to 

address PM-related visibility 

impairment, focused primarily on 

visibility in urban areas. This proposed 

standard was to be defined in terms of 

a PM2.5 visibility index, which would 

use measured PM2.5 mass concentration, 

in combination with speciation and 

relative humidity data, to calculate 

PM2.5 light extinction, translated into 

the deciview (dv) scale; a 24-hour 

averaging time; a 90th percentile form, 

averaged over 3 years; and a level of 28– 

30 dv. To address other non-visibility 

welfare effects, the Administrator 

proposed to retain the current suite of 

secondary PM standards generally, 

while revising only the form of the 

secondary annual PM2.5 standard to 

remove the option for spatial averaging 

consistent with this proposed change to 

the primary annual PM2.5 standard. Each 

of these proposed decisions is described 

in more detail in the proposal and 

below. 

1. PM-Related Visibility Impairment 

As discussed in Section VI.B of the 

proposal, the Administrator’s proposed 

decision regarding a distinct secondary 

standard to provide protection from 

visibility impairment reflected careful 

consideration of the following: (1) The 

latest scientific information on visibility 

effects associated with PM as described 

in the Integrated Science Assessment 

(U.S. EPA, 2009a); (2) insights gained 

from assessments of correlations 

between ambient PM2.5 and visibility 

impairment prepared by EPA staff in the 

Visibility Assessment (U.S. EPA, 

2010b); and (3) specific conclusions 

regarding the need for revisions to the 

current standards (i.e., indicator, 

averaging time, form, and level) that, 

taken together, would be requisite to 

protect the public welfare from adverse 

effects on visual air quality. This section 

summarizes key information from the 

proposal regarding the nature of 

visibility impairment, including the 

relationship between ambient PM and 

visibility, temporal variations in light 

extinction, periods during the day of 

interest for assessing visibility 

conditions, and exposure durations of 

interest (section VI.B.1.a); limited public 

perceptions and attitudes about 

visibility impairment and the impacts of 

visibility impairment on public welfare 

(section VI.B.1.b); CASAC advice 

regarding the need for, and design of, 

secondary standards to protect visibility 

(section VI.B.1.c); and the 

Administrator’s proposed conclusions 

regarding setting a distinct standard to 

address visibility impairment (section 

VI.B.1.d). 

a. Nature of PM-Related Visibility 

Impairment 

As noted at the time of proposal, the 

fundamental science characterizing the 

contribution of PM, especially fine 

particles, to visibility impairment is 

well understood. This science provides 

the basis for the Integrated Science 

Assessment designation of the 

relationship between PM and visibility 

impairment as causal. New research 

available in this review, discussed in 

chapter 9 of the Integrated Science 

Assessment, continues to support and 

refine EPA’s understanding of the effect 

of PM on visibility and the source 

contributions to that effect in rural and 

remote locations. This research provides 

new insights regarding the regional 

source contributions to urban visibility 

impairment and better characterization 

of the increment in PM concentrations 

and visibility impairment that occur in 

many cities (i.e., the urban excess) 

relative to conditions in the surrounding 

rural areas (i.e., regional background). 

Ongoing urban PM2.5 speciated and 

aggregated mass monitoring has 

produced new information that has 

allowed for updated characterization of 

current visibility levels in urban areas. 

i. Relationship Between Ambient PM 

and Visibility 

Visibility impairment is caused by the 

scattering and absorption of light by 

suspended particles and gases in the 

atmosphere. When PM is present in the 

air, its contribution to light extinction 

typically greatly exceeds that of gases. 

The combined effect of light scattering 

and absorption by both particles and 

gases is characterized as light 

extinction, i.e., the fraction of light that 

is scattered or absorbed in the 

atmosphere. Light extinction can be 

quantified by a light extinction 

coefficient with units of 1/distance, 

which is often expressed as 1/(1 million 

meters) or inverse megameters 

(abbreviated Mm–1) or in terms of an 

alternative scale known as the deciview 

scale, defined by the following 

equation: 146

Deciview (dv) = 10 ln (bext/ 10 Mm-1) 

The deciview scale is frequently used in 

the scientific literature on visibility, as 

well as in the Regional Haze Program. 

In particular, the deciview scale is used 

in the public perception studies that 

were considered in the past and current 

reviews to inform judgments about an 

appropriate degree of protection to be 

provided by a secondary NAAQS. 

The amount of light extinction 

contributed by PM depends on the 

particle concentration as well as on the 

particle size distribution and 

composition and also on the relative 

humidity. As described in detail in 

section VI.B.1.a of the proposal, 

visibility scientists have developed an 

algorithm, known as the IMPROVE 

algorithm,147 to estimate light extinction 

using routinely monitored fine particle 

(PM2.5) speciation and coarse particle 

mass (PM10-2.5) data, as well as data on 

relative humidity. There is both an 

original and a revised version of the 

IMPROVE algorithm (Pitchford et al., 

2007). The revised version was 

developed to address observed biases in 

the predictions using the original 

algorithm under very low and very high 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3187 

148These biases were detected by comparing light 

extinction estimates generated from the IMPROVE 

algorithm to direct optical measurements in a 

number of rural Federal Class I areas. 

149The IMPROVE algorithm does not explicitly 

separate the light-scattering and light-absorbing 

effects of elemental carbon. 

150 In either version of the IMPROVE algorithm, 

the concentration of each of the major aerosol 

components is multiplied by a dry extinction 

efficiency value and, for the hygroscopic 

components (i.e., ammoniated sulfate and 

ammonium nitrate), also multiplied by an 

additional factor to account for the water growth to 

estimate these components’ contribution to light 

extinction. Both the dry extinction efficiency and 

water growth terms have been developed by a 

combination of empirical assessment and 

theoretical calculation using typical particle size 

distributions associated with each of the major 

aerosol components. 

151The relative contributions of sulfate, nitrate, 

and organic mass concentrations to visibility 

impairment with the revised algorithm are different 

than with the original algorithm due to the 

combination of the dry extinction coefficient and 

f(RH) functions for derived concentrations of small 

and large particles. The apportionment of the total 

fine particle concentration of each of the three PM2.5

components into the concentrations of the small 

and large size fractions was empirically developed 

for remote areas. The fraction of the fine particle 

component that is in the large mode is estimated 

by dividing the total concentration of the 

component by 20 mg/m3. If the total concentration 

of a component exceeds 20 mg/m3, all of it is 

assumed to be in the large mode. 

152The revised IMPROVE algorithm uses a 

multiplier of 1.8 for rural areas instead of 1.4 as 

used in the original algorithm for the mean ratio of 

organic mass to organic carbon. 

light extinction conditions.148 These 

IMPROVE algorithms are routinely used 

to calculate light extinction levels on a 

24-hour basis in Federal Class I areas 

under the Regional Haze Program. 

In either version of the IMPROVE 

algorithm, the concentration of each of 

the major aerosol components is 

multiplied by a dry extinction efficiency 

value and, for the hygroscopic 

components (i.e., ammoniated sulfate 

and ammonium nitrate), also multiplied 

by an additional factor to account for 

the water growth to estimate these 

components’ contribution to light 

extinction. Summing the contribution of 

each component gives the estimate of 

total light extinction per unit distance 

denoted as the light extinction 

coefficient (bext), as shown below for the 

original IMPROVE algorithm. 

bext ≈ 3 × f(RH) × [Sulfate] 

+ 3 × f(RH) x [Nitrate] 

+ 4 × [Organic Mass] 

+ 10 × [Elemental Carbon] 

+ 1 × [Fine Soil] 

+ 0.6 × [Coarse Mass] 

+ 10 

Light extinction (bext) is in units of 

Mm-1, the mass concentrations of the 

components indicated in brackets are in 

units of mg/m3, and f(RH) is the unitless 

water growth term that depends on 

relative humidity. The final term of 10 

Mm-1 is known as the Rayleigh 

scattering term and accounts for light 

scattering by the natural gases in 

unpolluted air. Despite the simplicity of 

this algorithm, it performs reasonably 

well and permits the contributions to 

light extinction from each of the major 

components (including the water 

associated with the sulfate and nitrate 

compounds) to be separately 

approximated. Inspection of the PM 

component-specific terms in the simple 

original IMPROVE algorithm shows that 

most of the PM2.5 components 

contribute 5 times or more light 

extinction than a similar concentration 

of PM10-2.5.

The f(RH) term in the original 

algorithm reflects the increase in light 

scattering caused by particulate sulfate 

and nitrate under conditions of high 

relative humidity. Particles with 

hygroscopic components (e.g., 

particulate sulfate and nitrate) 

contribute more light extinction at 

higher relative humidity than at lower 

relative humidity because they change 

size in the atmosphere in response to 

ambient relative humidity conditions. 

For relative humidity below 40 percent 

the f(RH) value is 1, but it increases to 

2 at approximately 66 percent, 3 at 

approximately 83 percent, 4 at 

approximately 90 percent, 5 at 

approximately 93 percent, and 6 at 

approximately 95 percent relative 

humidity. The result is that both 

particulate sulfate and nitrate are more 

efficient per unit mass in light 

extinction than any other aerosol 

component for relative humidity above 

approximately 85 percent where their 

total light extinction efficiency exceeds 

the 10 m2/g associated with elemental 

carbon (EC). PM containing elemental or 

black carbon (BC) absorbs light as well 

as scattering it, making it the component 

with the greatest light extinction 

contributions per unit of mass 

concentration, except for the 

hygroscopic components under these 

high relative humidity conditions.149

As noted above, subsequent to the 

development of the original IMPROVE 

algorithm, an alternative algorithm 

(variously referred to as the ‘‘revised 

algorithm’’ or the ‘‘new algorithm’’ in 

the literature) was developed. The 

revised IMPROVE algorithm is different 

from the original algorithm in several 

important ways. First, the revised 

algorithm employs a more complex 

split-component mass extinction 

efficiency to correct biases believed to 

be related to particle size 

distributions.150 Specifically, the 

revised algorithm incorporates terms to 

account for particles representing the 

different dry extinction and water 

uptake from two size modes of sulfate, 

nitrate and organic mass.151 Second, the 

revised algorithm uses a different 

multiplier for organic carbon for 

purposes of estimating organic 

carbonaceous material to better 

represent aged aerosol found in remote 

areas.152 In addition, the revised 

algorithm includes a term for 

hygroscopic sea salt that can be 

important for remote coastal areas, and 

site-specific Rayleigh light scattering 

terms in place of a universal Rayleigh 

light scattering value. As noted in 

section VI.B.1.a of the proposal, the 

revised IMPROVE algorithm can yield 

higher estimates of current light 

extinction levels in urban areas on days 

with relatively poor visibility as 

compared to the original algorithm 

(Pitchford, 2010). This difference is 

primarily attributable to the splitcomponent mass extinction efficiency 

treatment in the revised algorithm. This 

revised algorithm was evaluated at 21 

remote locations and is generally used 

by RPOs and States for implementation 

of the Regional Haze Rule. 

ii. Temporal Variations of Light 

Extinction 

Particulate matter concentrations and 

light extinction in urban environments 

vary from hour to hour throughout the 

24-hour day due to a combination of 

diurnal changes in meteorological 

conditions and systematic changes in 

emissions activity (e.g., rush hour 

traffic). Various factors combine to make 

early morning the most likely time for 

peak urban light extinction; although 

the net effects of the systematic urbanand larger-scale variations mean that 

peak daytime PM light extinction levels 

can occur any time of day, in many 

areas they occur most often in early 

morning hours (U.S. EPA, 2010b, 

sections 3.4.2 and 3.4.3; Figures 3–9, 3– 

10, and 3–12). This temporal pattern in 

urban areas contrasts with the general 

lack of a strong diurnal pattern in PM 

concentrations and light extinction in 

most Federal Class I areas, reflective of 

a relative lack of local sources as 

compared to urban areas. The use in the 

Regional Haze Program of 24-hour 

average concentrations in the IMPROVE 

algorithm is consistent with this general 

lack of a strong diurnal pattern in 

Federal Class I areas. 

iii. Periods During the Day of Interest for 

Assessment of Visibility 

As noted in sections VI.B.1.b and 

VI.B.1.c of the proposal, daytime 

visibility has dominated the attention of 


tkelley on DSK3SPTVN1PROD with 
3188 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

those who have studied the visibility 

effects of air pollution, particularly in 

urban areas. The EPA recognizes, 

however, that physically PM light 

extinction behaves the same at night as 

during the day and can contribute to 

nighttime visibility effects by enhancing 

the scattering of anthropogenic light, 

contributing to the ‘‘skyglow’’ within 

and over populated areas, adding to the 

total sky brightness, and contributing to 

the reduction in contrast of stars against 

the background. However, little research 

has been conducted on nighttime 

visibility, and the state of the science is 

not comparable to that associated with 

daytime visibility impairment, 

particularly in terms of the impact on 

human welfare. The Policy Assessment 

notes that the science is not available at 

this time to support adequate 

characterization specifically of 

nighttime PM light extinction 

conditions and the related effects on 

public welfare (U.S. EPA, 2011a, p. 4– 

18). Therefore the EPA has focused its 

assessments of PM visibility impacts in 

urban areas on daylight hours during 

this review. 

iv. Exposure Durations of Interest 

As noted in section VI.B.1.d of the 

proposal, the roles that exposure 

duration and variations in visual air 

quality within any given exposure 

period play in determining the 

acceptability or unacceptability of a 

given level of visual air quality have not 

been investigated via preference studies. 

In the preference studies available for 

this review, subjects were simply asked 

to rate the acceptability or 

unacceptability of each image of a hazeobscured scene, without being provided 

any suggestion of assumed duration or 

of assumed conditions before or after 

the occurrence of the scene presented. 

Preference and/or valuation studies 

show that atmospheric visibility 

conditions can be quickly assessed and 

preferences determined. The EPA is 

unaware of any studies that characterize 

the extent to which different frequencies 

and durations of exposure to visibility 

conditions contribute to the degree of 

public welfare impact that occurs. 

The Policy Assessment considered a 

variety of circumstances that are 

commonly expected to occur in 

evaluating the potential impact of 

visibility impairment on the public 

welfare based on available information 

(U.S. EPA, 2011a, pp. 4–19 to 4–20). In 

some circumstances, such as infrequent 

visits to scenic vistas in natural or urban 

environments, people are motivated 

specifically to take the opportunity to 

view a valued scene and are likely to do 

so for many minutes to hours to 

appreciate various aspects of the vista 

they choose to view. However, the 

public has many more opportunities to 

notice visibility conditions on a daily 

basis in settings associated with 

performing daily routines (e.g., during 

commutes and while working, 

exercising, or recreating outdoors). As 

noted in the Policy Assessment, 

information regarding the fraction of the 

public that has only one or a few 

opportunities to experience visibility 

during the day, or on the role the 

duration of the observed visibility 

conditions has on wellbeing effects 

associated with those visibility 

conditions, is not available (U.S. EPA, 

2011a, p. 4–20). However, it is possible 

that people with limited opportunities 

to experience visibility conditions on a 

daily basis would receive the entire 

impact of the day’s visual air quality 

based on the visibility conditions that 

occur during the short time period when 

they can see it. Since this group could 

be affected on the basis of observing 

visual air quality conditions for periods 

as short as one hour or less, and because 

during each daylight hour there are 

some people outdoors, commuting, or 

near windows, the Policy Assessment 

judged that it would be appropriate to 

use the maximum hourly value of PM 

light extinction during daylight hours 

for each day for purposes of evaluating 

the adequacy of the current suite of 

secondary standards. Other observers 

may have access to visibility conditions 

throughout the day. For this group, it 

might be that an hour with poor or 

‘‘unacceptable’’ visibility can be offset 

by one or more other hours with clearer 

conditions. Therefore, the proposal 

acknowledged that it might also be 

appropriate to consider a multi-hour 

daylight exposure period. 

v. Periods of Fog and Rain 

As discussed in section VI.C of the 

proposal, the EPA also recognized that 

it is appropriate to give special 

treatment to periods of fog and rain 

when considering whether current PM2.5

standards adequately protect public 

welfare from PM-related visibility 

impairment. Visibility impairment 

occurs during periods with fog or 

precipitation irrespective of the 

presence or absence of PM. Therefore, it 

is logical that periods with naturally 

impaired visibility due to fog or 

precipitation should not be treated as 

having PM-impaired visibility. There 

are multiple ways to adjust visibility 

data to reduce the effects of fog and 

precipitation. In the Visibility 

Assessment, following the advice of 

CASAC, the EPA evaluated the effect of 

excluding daylight hours for which 

relative humidity was greater than 90 

percent from analyses in order to avoid 

precipitation and fog confounding 

estimates of PM visibility impairment. 

For the 15 urban areas included in the 

Visibility Assessment, the EPA found 

that a 90 percent relative humidity 

cutoff criterion was effective in that on 

average less than 6 percent of the 

daylight hours were removed from 

consideration, yet those hours had on 

average ten times the likelihood of rain, 

six times the likelihood of snow/sleet, 

and 34 times the likelihood of fog 

compared with hours with 90 percent or 

lower relative humidity. In the Regional 

Haze program, the EPA utilizes monthly 

average relative humidity values based 

on 10 years of climatological data to 

reduce the effect of fog and 

precipitation. This approach focuses on 

longer-term averages for each 

monitoring site and thereby eliminates 

the effect of very high humidity 

conditions on visibility at those 

locations. 

b. Public Perception of Visibility 

Impairment 

As described in section VI.B.2 of the 

proposal, there are two main types of 

studies that evaluate the public 

perception of urban visibility 

impairment: urban visibility preference 

studies and urban visibility valuation 

studies. As noted in the Integrated 

Science Assessment, ‘‘[b]oth types of 

studies are designed to evaluate 

individuals’ desire (or demand) for good 

visual air quality (VAQ) where they live, 

using different metrics to evaluate 

demand. Urban visibility preference 

studies examine individuals’ demand by 

investigating what amount of visibility 

degradation is unacceptable while 

economic studies examine demand by 

investigating how much one would be 

willing to pay to improve visibility’’ 

(U.S. EPA, 2009a, p. 9–66). Because of 

the limited number of new studies on 

urban visibility valuation, the Integrated 

Science Assessment cites to the 

discussion in the 2004 Criteria 

Document of the various methods one 

can use to determine the economic 

valuation of changes in visibility, which 

include hedonic valuation, contingent 

valuation and contingent choice, and 

travel cost. 

Contingent valuation studies are a 

type of stated preference study that 

measures the strength of preferences 

and expresses that preference in dollar 

values. Contingent valuation studies 

often include payment vehicles that 

require respondents to consider 

implementation costs and their ability 

to pay for visibility improvements in 

their responses. This study design 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3189 

153 In the regulatory impact analysis (RIA) 

accompanying this rulemaking, the EPA describes 

a revised approach to estimate urban residential 

visibility benefits that applies the results of several 

contingent valuation studies. The EPA is unable to 

apply the public perception studies to estimate 

benefits because they do not provide sufficient 

information on which to develop monetized 

benefits estimates. Specifically, the public 

perception studies do not provide preferences 

expressed in dollar values, even though they do 

provide additional evidence that the benefits 

associated with improving residential visibility are 

not zero. As previously noted in this preamble, the 

RIA is done for informational purposes only, and 

the proposed decisions on the NAAQS in this 

rulemaking are not in any way based on 

consideration of the information or analyses in the 

RIA. 

154By ‘‘characteristics of the scene’’ the EPA 

means the distance(s) between the viewer and the 

object(s) of interest, the shapes and colors of the 

objects, the contrast between objects and the sky or 

other background, and the inherent interest of the 

objects to the viewer. Distance is particularly 

important because at a given value of light 

extinction, which is a property of air at a given 

point(s) in space, more light is actually absorbed 

and scattered when light passes through more air 

between the object and the viewer. 

aspect is critical because the EPA 

cannot consider implementations costs 

in setting either primary or secondary 

NAAQS. Therefore in considering the 

information available to help inform the 

standard-setting process, the EPA has 

focused on the public perception 

studies that do not embed consideration 

of implementation costs. Nonetheless, 

the EPA recognizes that valuation 

studies do provide additional evidence 

that the public is experiencing losses in 

welfare due to visibility impairment.153

The public perception studies are 

described in detail below. 

In order to identify levels of visibility 

impairment appropriate for 

consideration in setting secondary PM 

NAAQS to protect the public welfare, 

the Visibility Assessment 

comprehensively examined information 

that was available in this review 

regarding people’s stated preferences 

regarding acceptable and unacceptable 

visual air quality. 

Light extinction is an atmospheric 

property that by itself does not directly 

translate into a public welfare effect. 

Instead, light extinction becomes 

meaningful in the context of the impact 

of differences in visibility on the human 

observer. This has been studied in terms 

of the acceptability or unacceptability 

expressed for the visibility impact of a 

given level of light extinction by a 

human observer. The perception of the 

visibility impact of a given level of light 

extinction occurs in conjunction with 

the associated characteristics and 

lighting conditions of the viewed 

scene.154 Thus, a given level of light 

extinction may be perceived differently 

by observers looking at different scenes 

or the same scene with different lighting 

characteristics. Likewise, different 

observers looking at the same scene 

with the same lighting may have 

different preferences regarding the 

associated visual air quality. When 

scene and lighting characteristics are 

held constant, the perceived appearance 

of a scene (i.e., how well the scenic 

features can be seen and the amount of 

visible haze) depends only on changes 

in light extinction. This has been 

demonstrated using the WinHaze model 

(Molenar et al., 1994) that uses image 

processing technology to apply userspecified changes in light extinction 

values to the same base photograph with 

set scene and lighting characteristics. 

Much of what is known about the 

acceptability of levels of visibility 

comes from survey studies in which 

participants were asked questions about 

their preference or the value they place 

on various visibility levels as displayed 

to them in scenic photographs and/or 

WinHaze images with a range of known 

light extinction levels. The Visibility 

Assessment (U.S. EPA, 2010b, chapter 

2) reviewed the limited number of urban 

visibility preference studies currently 

available (i.e., four studies) to assess the 

light extinction levels judged by the 

participant to have acceptable visibility 

for those particular scenes. 

The reanalysis of urban preference 

studies conducted in the Visibility 

Assessment for this review included 

three completed western urban visibility 

preference survey studies plus a pair of 

smaller focus studies designed to 

explore and further develop urban 

visibility survey instruments. The three 

western studies included one in Denver, 

Colorado (Ely et al., 1991), one in the 

lower Fraser River valley near 

Vancouver, British Columbia (BC), 

Canada (Pryor, 1996), and one in 

Phoenix, Arizona (BBC Research & 

Consulting, 2003). A pilot focus group 

study was also conducted for 

Washington, DC (Abt Associates Inc., 

2001). In response to an EPA request for 

public comment on the Scope and 

Methods Plan (74 FR 11580, March 18, 

2009), comments were received (Smith, 

2009) about the results of a new focus 

group study of scenes from Washington, 

DC, that had been conducted on subjects 

from both Houston, Texas, and 

Washington, DC, using scenes, methods 

and approaches similar to the method 

and approach employed in the EPA 

pilot study (Smith and Howell, 2009). 

When taken together, these studies from 

the four different urban areas included 

a total of 852 individuals, with each 

individual responding to a series of 

questions while viewing a set of images 

of various urban visual air quality 

conditions. 

The approaches used in the four 

studies were similar and were all 

derived from the method first developed 

for the Denver urban visibility study. In 

particular, the studies all used a similar 

group interview type of survey to 

investigate the level of visibility 

impairment that participants described 

as ‘‘acceptable.’’ In each preference 

study, participants were initially given 

a set of ‘‘warm up’’ exercises to 

familiarize them with how the scene in 

the photograph or image appears under 

different VAQ conditions. The 

participants next were shown 25 

randomly ordered photographs (images), 

and asked to rate each one based on a 

scale of 1 (poor) to 7 (excellent). They 

were then shown the same photographs 

or images again, in the same order, and 

asked to judge whether each of the 

photographs (images) would violate 

what they would consider to be an 

appropriate urban visibility standard 

(i.e. whether the level of impairment 

was ‘‘acceptable’’ or ‘‘unacceptable’’). 

The term ‘‘acceptable’’ was not defined, 

so that each person’s response was 

based on his/her own values and 

preferences for VAQ. However, when 

answering this question, participants 

were instructed to consider the 

following three factors: (1) The standard 

would be for their own urban area, not 

a pristine national park area where the 

standards might be stricter; (2) The level 

of an urban visibility standard violation 

should be set at a VAQ level considered 

to be unreasonable, objectionable, and 

unacceptable visually; and (3) 

Judgments of standards violations 

should be based on visibility only, not 

on health effects. While the results 

differed among the four urban areas, 

results from a rating exercise show that 

within each preference study, 

individual survey participants 

consistently distinguish between photos 

or images representing different levels 

of light extinction, and that more 

participants rate as acceptable images 

representing lower levels of light 

extinction than they do images 

representing higher levels. 

Given the similarities in the 

approaches used, the EPA staff 

concluded that it was reasonable to 

compare the results to identify overall 

trends in the study findings and to 

conclude that this comparison can 

usefully inform the selection of a range 

of levels for use in further analyses. 

However, the staff also noted that 

variations in the specific materials and 

methods used in each study introduce 

uncertainties that should also be 

considered when interpreting the results 


tkelley on DSK3SPTVN1PROD with 
3190 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

155Only 47 percent of the British Columbia 

participants rated a 19.2 dv photograph as 

acceptable. 156 In the 2001 Washington, DC study, a 30.9 dv 

image was used as a repeated slide. The first time 

it was shown 56 percent of the participants rated 

it as acceptable, but only 11 percent rated it as 

acceptable the second time it was shown. The same 

visual air quality level was rated as acceptable by 

4 percent of the participants in the 2009 study (Test 

1). All three points are shown in Figure 5. 157Top scale shows light extinction in inverse 

megameter units; bottom scale in deciviews. Logit 

analysis estimated response functions are shown as 

the color-coded curved lines for each of the four 

urban areas. 

158At present, data is only available for four 

urban areas, as presented in Figure 5 and discussed 

throughout this section. Additional research could 

help inform whether the range identified by 

combining the results of the studies depicted in 

Figure 5 is more broadly representative. 

of these comparisons. Key differences 

between the studies include the 

following: (1) Scene characteristics; (2) 

image presentation methods (e.g., 

projected slides of actual photos, 

projected images generated using 

WinHaze (a significant technical 

advance in the method of presenting 

visual air quality conditions), or use of 

a computer monitor screen; (3) number 

of participants in each study; (4) 

participant representativeness of the 

general population of the relevant 

metropolitan area; and (5) specific 

wording used to frame the questions 

used in the group interview process. 

In the Visibility Assessment, each 

study was evaluated separately and 

figures developed to display the 

percentage of participants that rated the 

visual air quality depicted in each 

photograph as ‘‘acceptable.’’ Ely et al. 

(1991) introduced a ‘‘50% acceptability’’ 

criterion analysis of the Denver 

preference study results. The 50 percent 

acceptability criterion is designed to 

identify the visual air quality level 

(defined in terms of deciviews or light 

extinction) that best divides the 

photographs into two groups: Those 

with a visual air quality rated as 

acceptable by the majority of the 

participants, and those rated not 

acceptable by the majority of 

participants. The Visibility Assessment 

adopted this criterion as a useful index 

for comparison between studies. The 

results of each analysis were then 

combined graphically to allow for visual 

comparison. This information was then 

carried forward into the Policy 

Assessment. Figure 5 presents the 

graphical summary of the results of the 

studies in the four cities and draws on 

results previously presented in Figures 

2–3, 2–5, 2–7, and 2–11 of chapter 2 in 

the Visibility Assessment. Figure 5 also 

contains lines at 20 dv and 30 dv that 

generally identify a range where the 50 

percent acceptance criteria occur across 

all four of the urban preference studies 

(U.S. EPA, 2011a, p. 4–24). Out of the 

114 data points shown in Figure 5, only 

one photograph (or image) with a visual 

air quality below 20 dv was rated as 

acceptable by less than 50 percent of the 

participants who rated that 

photograph.155 Similarly, only one 

image with a visual air quality above 30 

dv was rated acceptable by more than 50 

percent of the participants who viewed 

it.156

As Figure 5 above shows, each urban 

area has a separate and unique response 

curve that appears to indicate that it is 

distinct from the others.158 These curves 

are the result of a logistical regression 

analysis using a logit model of the 

greater than 19,000 ratings of haze 

images as acceptable or unacceptable. 

The model results can be used to 

estimate the visual air quality in terms 

of dv values where the estimated 

response functions cross the 50 percent 

acceptability level, as well as any 

alternative criteria levels. Selected 

examples of these are shown in Table 4– 


tkelley on DSK3SPTVN1PROD with ER15JA13.004</GPH>
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3191 

159These values were rounded from 74 Mm¥1

and 201 Mm¥1 to avoid an implication of greater 

precision than is warranted. Note that the middle 

value of 25 dv when converted to light extinction 

is 122 Mm¥1 is rounded to 120 Mm¥1 for the same 

reason. Assessments conducted for the Visibility 

Assessment and the first and second drafts of the 

Policy Assessment used the unrounded values. The 

Policy Assessment considered the results of 

assessment using unrounded values to be 

sufficiently representative of what would result if 

the rounded values were used that it was 

unnecessary to redo the assessments. That is why 

some tables and figures in the Policy Assessment 

reflected the unrounded values. 

160Rayleigh scatter is light scattering by 

atmospheric gases which is on average about 10 

Mm¥1. 

161The first preference study using WinHaze 

images of a scenic vista from Washington, DC was 

conducted in 2001 using subjects who were 

residents of Washington, DC. More recently, Smith 

and Howell (2009) interviewed additional subjects 

using the same images and interview procedure. 

The additional subjects included some residents of 

the Washington, DC area and some residents of the 

Houston, Texas area. 

162 In order to examine this issue, an effort would 

have to be made to see if scenes in such areas could 

be found that would be generally comparable to the 

western scenes (e.g., scenes that contain valued 

scenic elements at more sensitive distances than 

that used in the eastern study). This is only one of 

a family of issues concerning how exposure to 

urban scenes of varying sensitivity affects public 

perception for which no preference study 

information is currently available. 

1 of the Policy Assessment (U.S. EPA, 

2011a; U.S. EPA, 2010b, Table 2–4). 

This table shows that the logit model 

results also support the upper and lower 

ends of the range of 50th percentile 

acceptability values (e.g., near 20 dv for 

Denver and near 30 dv for Washington, 

DC) already identified in Figure 5. 

Based on the composite results and 

the effective range of 50th percentile 

acceptability across the four urban 

preference studies shown in Figure 5 

and Table 4–1 of the Policy Assessment, 

benchmark levels of (total) light 

extinction were selected in a range from 

20 dv to 30 dv (75 to 200 Mm¥1) 159 for 

the purpose of provisionally assessing 

whether visibility conditions would be 

considered acceptable (i.e., less than the 

low end of the range), unacceptable (i.e., 

greater than the high end of the range), 

or potentially acceptable (within the 

range) based on the very limited public 

preference information. A midpoint of 

25 dv (120 Mm¥1) was also selected for 

use in the assessment. This level is also 

very near to the 50th percentile criterion 

value from the Phoenix study (i.e., 24.2 

dv), which is by far the best of the four 

studies in terms of the fit of the data to 

the response curve and the 

representativeness of study participants. 

Based on the currently available 

information, the Policy Assessment 

concluded that the use of 25 dv to 

represent the middle of the distribution 

of results seemed well supported (U.S. 

EPA, 2011a, p. 4–25). 

These three benchmark values 

provide a low, middle, and high set of 

light extinction conditions that are used 

to provisionally define daylight hours 

with urban haze conditions that have 

been judged unacceptable by at least 50 

percent of the participants in one or 

more of these preference studies. As 

discussed above, PM light extinction is 

taken to be (total) light extinction minus 

the Rayleigh scatter,160 such that the 

low, middle, and high levels correspond 

to PM light extinction levels of about 65 

Mm¥1, 110 Mm¥1, and 190 Mm¥1. In 

the Visibility Assessment, these three 

light extinction levels were called 

Candidate Protection Levels (CPLs). 

This term was also used in the Policy 

Assessment and in the proposal notice. 

It is important to note, however, that the 

degree of protection provided by a 

secondary NAAQS is not determined 

solely by any one component of the 

standard but by all the components (i.e., 

indicator, averaging time, form, and 

level) being applied together. Therefore, 

the Policy Assessment noted that the 

term CPL is meant only to indicate 

target levels of visibility within a range 

that the EPA staff felt appropriate for 

consideration that could, in conjunction 

with other elements of the standard, 

including indicator, averaging time, and 

form, potentially provide an appropriate 

degree of visibility protection. 

In characterizing the Policy 

Assessment’s confidence in each CPL 

and across the range, a number of issues 

were considered (U.S. EPA, 2011a, p. 4– 

26). Looking first at the two studies that 

define the upper and lower bounds of 

the range, the Policy Assessment 

considered whether they represent a 

true regional distinction in preferences 

for urban visibility conditions between 

western and eastern U.S. There was 

little information available to help 

evaluate the possibility of a regional 

distinction especially given that there 

have been preference studies in only 

one eastern urban area. Smith and 

Howell (2009) found little difference in 

preference response to Washington, DC, 

haze photographs between the study 

participants from Washington, DC, and 

those from Houston, Texas.161 This 

provides some limited evidence that the 

value judgment of the public in different 

areas of the country may not be an 

important factor in explaining the 

differences in these study results. 

In further considering what factors 

could explain the observed differences 

in preferences across the four urban 

areas, the Policy Assessment noted that 

the urban scenes used in each study had 

different characteristics (U.S. EPA, 

2011a, p. 4–26). For example, each of 

the western urban visibility preference 

study scenes included mountains in the 

background while the single eastern 

urban study did not. It is also true that 

each of the western scenes included 

objects at greater distances from the 

camera location than in the eastern 

study. There is no question that objects 

at a greater distance have a greater 

sensitivity to perceived visibility 

changes as light extinction is changed 

compared to otherwise similar scenes 

with objects at a shorter range. This 

alone might explain the difference 

between the results of the eastern study 

and those from the western urban 

studies. Having scenes with the object of 

greatest intrinsic value nearer and hence 

less sensitive in the eastern urban area 

compared with more distant objects of 

greatest intrinsic value in the western 

urban areas could further explain the 

difference in preference results. 

Another question considered was 

whether the high CPL value that is 

based on the eastern preference results 

is likely to be generally representative of 

urban areas that do not have associated 

mountains or other valued objects 

visible in the distant background. Such 

areas would include the middle of the 

country, many areas in the eastern U.S., 

and possibly some areas in the western 

U.S. as well.162 Based on the currently 

available information, the Policy 

Assessment concluded that the high end 

of the CPL range (30 dv) is an 

appropriate level to consider (U.S. EPA, 

2011a, p. 4–27). 

With respect to the low end of the 

range, the Policy Assessment considered 

factors that might further refine its 

understanding of the robustness of this 

level. The Policy Assessment concluded 

that additional urban preference studies, 

especially with a greater variety in types 

of scenes, could help evaluate whether 

the lower CPL value of 20 dv is 

generally supportable (U.S. EPA, 2011a, 

p. 4–27). Further, the reason for the 

noisiness in data points around the 

curves apparent in both the Denver and 

British Columbia results compared to 

the smoother curve fit of Phoenix study 

results could be explored. One possible 

explanation discussed in the Policy 

Assessment is that these older studies 

use photographs taken at different times 

of day and on different days to capture 

the range of light extinction levels 

needed for the preference studies. In 

contrast, the use of WinHaze in the 

Phoenix (and Washington, DC) study 

reduced variations that affect scene 

appearance preference rating and 

avoided the uncertainty inherent in 

using ambient measurements to 


tkelley on DSK3SPTVN1PROD with 
3192 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

163 ‘‘CASAC has also identified needs for the next 

review cycle in terms of further research on a 

number of topics related to urban visibility; * * *. 

In particular, there is a need for the Agency to 

conduct additional urban visibility preference 

studies over a broad range of urban areas and 

viewing conditions, to further evaluate and refine 

the range of visibility levels considered to be 

acceptable in the current assessment.’’ (Samet, 

2010a) 

164PM-related light extinction is used here to 

refer to the light extinction caused by PM regardless 

of particle size; PM10 light extinction refers to the 

contribution by particles sampled through an inlet 

with a particle size 50 percent cutpoint of 10 mm 

diameter; and PM2.5 light extinction refers to the 

contribution by particles sampled through an inlet 

with a particle size 50 percent cutpoint of 2.5 mm 

diameter. 

165The 15 urban areas are Tacoma, Fresno, Los 

Angeles, Phoenix, Salt Lake City, Dallas, Houston, 

St. Louis, Birmingham, Atlanta, Detroit, Pittsburgh, 

Baltimore, Philadelphia, and New York. 

166Comments on the second draft Visibility 

Assessment from those familiar with the monitoring 

sites in St. Louis indicated that the site selected to 

provide continuous PM10 monitoring, although less 

than a mile from the site of the PM2.5 data, was not 

representative of the urban area and resulted in 

unrealistically large PM10-2.5 values. The EPA staff 

considered these comments credible and set aside 

the St. Louis assessment results for PM10 light 

extinction. Thus, results and statements in the 

Policy Assessment regarding PM10 light extinction 

applied to only the other 14 areas. However, results 

regarding PM2.5 light extinction in most cases 

applied to all 15 study areas because the St. Louis 

estimates for PM2.5 light extinction were not 

affected by the PM10 monitoring issue. 

167Phoenix and Salt Lake City met the current 

PM2.5 NAAQS under current conditions and 

required no reduction. 

represent sight path-averaged light 

extinction values. Reducing these 

sources of noisiness and uncertainty in 

the results of future studies of sensitive 

urban scenes could provide more 

confidence in the selection of a low CPL 

value. 

Based on the above considerations, 

and recognizing the limitations in the 

currently available information, the 

Policy Assessment concluded that it is 

reasonable to consider a range of CPL 

values including a high value of 30 dv, 

a mid-range value of 25 dv, and a low 

value of 20 dv (U.S. EPA, 2011a, p. 4– 

27). Based on its review of the second 

draft Policy Assessment, CASAC also 

supported this set of CPLs for 

consideration by the EPA in this review. 

CASAC noted that these CPL values 

were based on all available visibility 

preference data and that they bound the 

study results as represented by the 50 

percent acceptability criteria. While 

recommending that further visibility 

preference studies be conducted to 

reduce remaining uncertainties,163

CASAC concluded that this range of 

levels was ‘‘adequately supported by the 

evidence presented’’ (Samet, 2010d, p. 

iii). 

c. Summary of Proposed Conclusions 

i. Adequacy of the Current Standards for 

PM-Related Visibility Impairment 

At the time of proposal, the 

Administrator provisionally concluded 

that the current suite of secondary PM 

standards is not sufficiently protective 

of visual air quality, and that 

consideration should be given to an 

alternative secondary standard that 

would provide additional protection 

against PM-related visibility 

impairment, with a focus primarily in 

urban areas. This proposed conclusion 

was based on the information presented 

in the proposal with regard to the nature 

of PM-related visibility impairment, the 

results of public perception surveys on 

the acceptability of varying degrees of 

visibility impairment in urban areas, 

analyses of the number of days that are 

estimated to exceed a range of candidate 

protection levels under conditions 

simulated to just meet the current 

standards, and the advice of CASAC. 

This section summarizes key points 

from section VI.C of the proposal 

regarding visibility under current 

conditions, the degree of protection 

afforded by the current standards, and 

CASAC’s advice regarding the adequacy 

of the current standards. 

As discussed in section VI.C.1 of the 

proposal, to evaluate visibility under 

current conditions the Visibility 

Assessment and Policy Assessment 

estimated PM-related light extinction164

levels for 15 urban areas165 in the 

United States. Consistent with the 

emphasis in this review on the hourly 

or multi-hour time periods that might 

reasonably characterize the visibility 

effects experienced by various segments 

of the population, these analyses 

focused on using maximum 1-hour and 

4-hour values of PM light extinction 

during daylight hours for purposes of 

evaluating the degree of visibility 

impairment. Hourly average PM-related 

light extinction was analyzed in terms 

of both PM10 and PM2.5 light extinction. 

For reasons discussed above, hours with 

relative humidity greater than 90 

percent were excluded from 

consideration. Recent visibility 

conditions in these urban areas were 

then compared to the CPLs identified 

above. The Visibility Assessment, which 

focused on PM10 light extinction in 14 

of the 15 urban areas during the 2005 to 

2007 time period,166 found that all 14 

areas had daily maximum hourly PM10

light extinction values estimated to 

exceed even the highest CPL some of the 

days. Except for the two Texas areas and 

the non-California western urban areas, 

all of the other urban areas were 

estimated to have maximum hourly 

PM10 concentrations that exceeded the 

high CPL on about 20 percent to over 60 

percent of the days. All 14 of the urban 

areas were estimated to have maximum 

hourly PM10 concentrations that 

exceeded the low CPL on about 40 

percent to over 90 percent of the days. 

In general, areas in the East and in 

California tend to have a higher 

frequency of hourly visibility conditions 

estimated to be above the high CPL 

compared with those in the western 

U.S. 

The Policy Assessment repeated the 

Visibility Assessment-type modeling 

based on PM2.5 light extinction and data 

from the more recent 2007 to 2009 time 

period for the same 15 study areas 

(including St. Louis). While the 

estimates of the percentage of daily 

maximum hourly PM2.5 light extinction 

values exceeding the CPLs were 

somewhat lower than for PM10 light 

extinction, the patterns of these 

estimates across the study areas was 

found to be similar. More specifically, 

except for the two Texas and the nonCalifornia western urban areas, all of the 

other urban areas were estimated to 

have maximum hourly PM2.5

concentrations that exceeded the high 

CPL on about 10 percent up to about 50 

percent of the days based on PM2.5 light 

extinction, while all 15 areas were 

estimated to have maximum hourly 

PM2.5 concentrations that exceeded the 

low CPL on over 10 percent to over 90 

percent of the days. 

To evaluate how PM-related visibility 

would be affected by just meeting the 

current suite of PM2.5 secondary 

standards, the Policy Assessment 

applied the proportional rollback 

approach described in section VI.C.2 of 

the proposal to all the PM2.5 monitoring 

sites in each study area.167 After 

adjusting for composition, the Policy 

Assessment applied the original 

IMPROVE algorithm to calculate the 

PM10 light extinction, using ‘‘rolled 

back’’ PM2.5 component concentrations, 

the current conditions PM10-2.5

concentration for the day and hour, and 

relative humidity for the day and hour. 

In these analyses, the Policy 

Assessment estimated both PM2.5 and 

PM10 light extinction in terms of both 

daily maximum 1-hour average values 

and multi-hour (i.e., 4-hour) average 

values for daylight hours. Figure 4–7 

and Table 4–6 of the Policy Assessment 

displayed the results of the rollback 

procedures as a box and whisker plot of 

daily maximum daylight 1-hour PM2.5

light extinction and the percentage of 

daily maximum hourly PM2.5 light 

extinction values estimated to exceed 

the CPLs when just meeting the current 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3193 

suite of PM2.5 secondary standards for 

all 15 areas considered in the Visibility 

Assessment (including St. Louis) 

(excluding hours with relative humidity 

greater than 90 percent). These displays 

showed that the daily maximum 1-hour 

average PM2.5 light extinction values in 

all of the study areas other than the 

three western non-California areas were 

estimated to exceed the high CPL on 

about 8 percent up to over 30 percent 

of the days and to exceed the middle 

CPL on about 30 percent up to about 70 

percent of the days, while all areas 

except Phoenix were estimated to have 

daily maximum 1-hour average PM2.5

light extinction values that exceeded the 

low CPL on over 15 percent to about 90 

percent of the days. Figure 4–8 and 

Table 4–7 of the Policy Assessment 

present results based on daily maximum 

4-hour average values. These displays 

show that the daily maximum 4-hour 

average PM2.5 light extinction values in 

all of the study areas other than the 

three western non-California areas and 

the two areas in Texas were estimated 

to exceed the high CPL on about 4 

percent up to over 15 percent of the 

days and to exceed the middle CPL on 

about 15 percent up to about 45 percent 

of the days, while all areas except 

Phoenix were estimated to have daily 

maximum 4-hour average PM2.5 light 

extinction values that exceeded the low 

CPL on over 10 percent to about 75 

percent of the days. A similar set of 

figures and tables were developed in 

terms of PM10 light extinction (U.S. 

EPA, 2011a, Figures 4–5 and 4–6, Tables 

4–4 and 4–5). 

Taking the results of these analyses 

focusing on 1-hour and 4-hour 

maximum light extinction values into 

account, the Policy Assessment 

concluded that the available 

information in this review clearly called 

into question the adequacy of the 

current suite of PM2.5 standards in the 

context of public welfare protection 

from visibility impairment, primarily in 

urban areas, and supported 

consideration of alternative standards to 

provide appropriate protection (U.S. 

EPA, 2011a, p. 4–39). This conclusion 

was based in part on the large 

percentage of days, in many urban areas, 

that were estimated to have maximum 

1-hour or 4-hour light extinction values 

that exceed the range of CPLs identified 

for consideration under simulations of 

conditions that would just meet the 

current suite of PM2.5 secondary 

standards. In particular, for air quality 

that was simulated to just meet the 

current PM2.5 standards, greater than 10 

percent of the days were estimated to 

have peak light extinction values that 

exceed the highest, least protective CPL 

of 30 dv in terms of PM2.5 light 

extinction for 9 of the 15 urban areas, 

based on 1-hour average values, and 

would thus likely fail to meet a 90th 

percentile-based standard at that level. 

For these areas, the percent of days 

estimated to have maximum 1-hour 

values that exceed the highest CPL 

ranged from over 10 percent to over 30 

percent. Similarly, when the middle 

CPL of 25 dv was considered, greater 

than 30 percent up to approximately 70 

percent of the days were estimated to 

have peak light extinction that exceeded 

that CPL in terms of PM2.5 light 

extinction, for 11 of the 15 urban areas, 

based on 1-hour average values. Based 

on a 4-hour averaging time, 5 of the 

areas were estimated to have at least 10 

percent of the days with peak light 

extinction exceeding the highest CPL in 

terms of PM2.5 light extinction, and 8 of 

the areas were estimated to have at least 

30 percent of the days with peak light 

extinction exceeding the middle CPL in 

terms of PM2.5 light extinction. For the 

lowest CPL of 20 dv, the percentages of 

days with 4-hour maximum light 

extinction estimated to exceed that CPL 

are even higher for all cases considered. 

Based on all of the above, the Policy 

Assessment concluded that PM light 

extinction estimated to be associated 

with just meeting the current suite of 

PM2.5 secondary standards in many 

areas across the country exceeded levels 

and percentages of days that could 

reasonably be considered to be 

important from a public welfare 

perspective (U.S. EPA, 2011a, p. 4–40). 

Further, the Policy Assessment 

concluded that use of the current 

indicator of PM2.5 mass, in conjunction 

with the current 24-hour and annual 

averaging times, is clearly called into 

question for a national standard 

intended to protect public welfare from 

PM-related visibility impairment (U.S. 

EPA, 2011a, p. 4–40). This is because 

such a standard is inherently variable in 

the degree of protection provided 

because of regional differences in 

relative humidity and species 

composition of PM2.5, which are critical 

factors in the relationship between the 

mix of fine particles in the ambient air 

and the associated impairment of 

visibility. The Policy Assessment noted 

that this concern was one of the 

important elements in the court’s 

decision to remand the PM2.5 secondary 

standards set in 2006 to the Agency. 

Thus, in addition to concluding that 

the available information clearly calls 

into question the adequacy of the 

protection against PM-related visibility 

impairment afforded by the current 

suite of PM2.5 standards, the Policy 

Assessment also concluded that it 

clearly calls into question the 

appropriateness of each of the current 

standard elements: indicator, averaging 

time, form, and level (U.S. EPA, 2011a, 

p. 4–40). 

After reviewing the information and 

analysis in the second draft Policy 

Assessment, CASAC concluded that the 

‘‘currently available information clearly 

calls into question the adequacy of the 

current standards and that consideration 

should be given to revising the suite of 

standards to provide increased public 

welfare protection’’ (Samet, 2010d, p. 

iii). CASAC noted that the detailed 

estimates of hourly PM light extinction 

associated with just meeting the current 

standards ‘‘clearly demonstrate that 

current standards do not protect against 

levels of visual air quality which have 

been judged to be unacceptable in all of 

the available urban visibility preference 

studies.’’ Further, CASAC stated, with 

respect to the current suite of secondary 

PM2.5 standards, that ‘‘[T]he levels are 

too high, the averaging times are too 

long, and the PM2.5 mass indicator could 

be improved to correspond more closely 

to the light scattering and absorption 

properties of suspended particles in the 

ambient air’’ (Samet, 2010d, p. 9). 

After considering the available 

evidence and the advice of CASAC, the 

Administrator concluded at the time of 

proposal that such information did 

provide an appropriate basis to inform 

a conclusion as to whether the current 

standards afford adequate protection 

against PM-related visibility impairment 

in urban areas. The Administrator took 

into account the information discussed 

above with regard to the nature of PMrelated visibility impairment, the results 

of public perception surveys on the 

acceptability of varying degrees of 

visibility impairment in urban areas, 

analyses of the number of days on 

which peak 1-hour or 4-hour light 

extinction values are estimated to 

exceed a range of candidate protection 

levels under conditions simulated to 

just meet the current standards, and the 

advice of CASAC. She noted the clear 

causal relationship between PM in the 

ambient air and impairment of 

visibility, the evidence from the 

visibility preference studies, and the 

rationale for determining a range of 

candidate protection levels based on 

those studies. She also noted the 

relatively large number of days when 

maximum 1-hour or 4-hour light 

extinction values were estimated to 

exceed the three candidate protection 

levels, including the highest level of 30 

dv, under the current standards. While 

recognizing the limitations in the 

available information on public 


tkelley on DSK3SPTVN1PROD with 
3194 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

perceptions of the acceptability of 

varying degree of visibility impairment 

and the information on the number of 

days estimated to exceed the CPLs, she 

concluded that such information 

provided an appropriate basis to inform 

a conclusion as to whether the current 

standards provide adequate protection 

against PM-related visibility impairment 

in urban areas. Based on these 

considerations, and placing great 

importance on the advice of CASAC, the 

Administrator provisionally concluded 

that the current standards are not 

sufficiently protective of visual air 

quality, and that consideration should 

be given to an alternative secondary 

standard that would provide additional 

protection against PM-related visibility 

impairment, with a focus primarily in 

urban areas. 

Having reached this conclusion, the 

Administrator also stated at the time of 

proposal that the current indicator of 

PM2.5 mass, in conjunction with the 

current 24-hour and annual averaging 

times, is not well suited for a national 

standard intended to protect public 

welfare from PM-related visibility 

impairment. As noted in the proposal, 

the current standards do not incorporate 

information on the concentrations of 

various species within the mix of 

ambient particles, nor do they 

incorporate information on relative 

humidity, both of which play a central 

role in determining the relationship 

between the mix of PM in the ambient 

air and impairment of visibility. Such 

considerations were reflected both in 

CASAC’s advice to set a distinct 

secondary standard that would more 

directly reflect the relationship between 

ambient PM and visibility impairment 

and in the court’s remand of the current 

secondary PM2.5 standards. Based on the 

above considerations, at the time of 

proposal the Administrator 

provisionally concluded that the current 

secondary PM2.5 standards, taken 

together, are neither sufficiently 

protective nor suitably structured to 

provide an appropriate degree of public 

welfare protection from PM-related 

visibility impairment, primarily in 

urban areas. This led the EPA to 

consider alternative standards by 

looking at each of the elements of the 

standards—indicator, averaging time, 

form, and level—as discussed below. 

ii. Indicator 

At the time of proposal, the EPA 

considered three alternative indicators 

for a PM2.5 standard designed to protect 

against visibility impairment: The 

current PM2.5 mass indicator; directly 

measured PM2.5 light extinction; and 

calculated PM2.5 light extinction. 

Directly measured PM2.5 light extinction 

is a measurement (or combination of 

measurements) of the light absorption 

and scattering caused by PM2.5 under 

ambient conditions. Calculated PM2.5

light extinction uses the IMPROVE 

algorithm to calculate PM2.5 light 

extinction using measured PM2.5 mass, 

speciated PM2.5 mass, and measured 

relative humidity. The Policy 

Assessment evaluated each of these 

alternatives, finally concluding that 

consideration should be given to 

establishing a new calculated PM2.5 light 

extinction indicator (U.S. EPA, 2011a, p. 

4–51). 

As discussed in section VI.D.1 of the 

proposal, the Policy Assessment 

concluded that consideration of the use 

of either directly measured PM2.5 light 

extinction or calculated PM2.5 light 

extinction as an indicator is justified 

because light extinction is a physically 

meaningful measure of the characteristic 

of ambient PM2.5 that is most relevant 

and directly related to PM-related 

visibility effects (U.S. EPA, 2011a, p. 4– 

41). Further, as noted above, PM2.5 is the 

component of PM responsible for most 

of the visibility impairment in most 

urban areas. In these areas, the 

contribution of PM10-2.5 is a minor 

contributor to visibility impairment 

most of the time. The Policy Assessment 

also indicated that the available 

evidence demonstrated a strong 

correspondence between calculated 

PM2.5 light extinction and PM-related 

visibility impairment, as well as the 

significant degree of variability in 

visibility protection across the U.S. 

allowed by a PM2.5 mass indicator. The 

Policy Assessment recognized that 

while in the future it would be 

appropriate to consider a direct 

measurement of PM2.5 light extinction it 

was not an appropriate option in this 

review because a suitable specification 

of the equipment and associated 

performance verification procedures 

cannot be developed in the time frame 

for this review. 

(a) PM2.5 Mass 

In terms of utilizing a PM2.5 mass 

indicator, the proposal noted that PM2.5

mass monitoring methods are in 

widespread use, including the FRM 

involving the collection of periodic 

(usually 1-day-in-6 or 1-day-in-3) 24- 

hour filter samples. However, these 

routine monitoring activities do not 

include measurement of the full water 

content of the ambient PM2.5 that 

contributes, often significantly, to 

visibility impacts. Further, the PM2.5

mass concentration monitors do not 

provide information on the composition 

of the ambient PM2.5, which plays a 

central role in the relationship between 

PM-related visibility impairment and 

ambient PM2.5 mass concentrations. 

Additional analyses discussed in the 

proposal that looked at the contribution 

of PM2.5 to total PM-related light 

extinction (defined in terms of hourly 

PM10 calculated light extinction) 

indicate that there is a poor correlation 

between hourly PM10 light extinction 

and hourly PM2.5 mass principally due 

to the impact of the water content of the 

particles on light extinction, which 

depends on both the composition of the 

PM2.5 and the ambient relative 

humidity. Both composition and 

especially relative humidity vary during 

a single day, as well as from day-to-day, 

at any site and time of year. Also, there 

are systematic regional and seasonal 

differences in the distribution of 

ambient humidity and PM2.5

composition conditions that make it 

impossible to select a PM2.5

concentration that generally would 

correspond to the same PM-related light 

extinction levels across all areas of the 

nation. Analyses discussed in the 

proposal quantify the projected uneven 

protection that would result from the 

use of 1-hour average PM2.5 mass as the 

indicator. 

(b) Directly Measured PM2.5 Light 

Extinction 

PM light extinction has a nearly oneto-one relationship to light extinction, 

unlike PM2.5 mass concentration. As 

explained above, PM2.5 is the 

component responsible for the large 

majority of PM light extinction in most 

places and times. PM2.5 light extinction 

can be directly measured using several 

instrumental methods, some of which 

have been used for decades to routinely 

monitor the two components of PM2.5

light extinction (light scattering and 

absorption) or to jointly measure both as 

total light extinction (from which 

Rayleigh scattering is subtracted to get 

PM2.5 light extinction). As noted at the 

time of proposal, there are a number of 

advantages to direct measurements of 

light extinction for use in a secondary 

standard relative to estimates of PM2.5

light extinction calculated using PM2.5

mass and speciation data. These include 

greater accuracy of direct measurements 

with shorter averaging times and overall 

greater simplicity when compared to the 

need for measurements of multiple 

parameters to calculate PM light 

extinction. 

In evaluating whether direct 

measurement of PM2.5 or PM10 light 

extinction is appropriate to consider in 

the context of this PM NAAQS review, 

the EPA solicited comment from the 

Ambient Air Monitoring and Methods 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3195 

168About 200 sites in the CSN routinely measure 

24-hour average PM2.5 chemical components using 

filter-based samplers and chemical analysis in a 

laboratory, on either a 1-day-in-3 or 1-day-in-6 

schedule (U.S. EPA, 2011a, Appendix B, section 

B.1.3). 

169As noted at the time of proposal, the sheer size 

of the ambient air quality, meteorological, and 

chemical transport modeling data files involved 

with the Visibility Assessment approach would 

make it very difficult for state agencies or any 

interested party to consistently apply such an 

approach on a routine basis for the purpose of 

implementing a national standard defined in terms 

of the Visibility Assessment approach. 

170 If the revised IMPROVE algorithm were used 

to define the calculated PM2.5 mass-based indicator, 

it would not be possible to algebraically reduce the 

revised algorithm to a two-factor version as 

described above and in Appendix F of the Policy 

Assessment for the simplified approaches. Instead, 

five component fractions would be determined from 

each day of speciated sampling, and then either 

applied to hourly measurements of PM2.5 mass on 

the same day or averaged across a month and then 

applied to measurements of PM2.5 mass on each day 

of the month. 

171An organic carbon (OC)-to-organic mass (OM) 

multiplier of 1.6 was used for the assessment, 

which was found to produce a value of OM 

comparable to the one derived with the original, 

albeit more complex, Visibility Assessment method. 

172Filter-based FRMs are designed to adequately 

quantify the amount of PM2.5 collected over 24- 

hours. They cannot be presumed to be appropriate 

for quantifying average concentrations over 1-hour 

or 4-hour periods. 

Subcommittee (AAMMS) of CASAC. 

The CASAC AAMMS recommended 

that consideration of direct 

measurement should be limited to PM2.5

light extinction, and that although 

instruments suitable for this purpose are 

commercially available at present, 

research is expected to produce even 

better instruments in the near term. The 

CASAC AAMMS advised against 

choosing any currently available 

commercial instrument, or even a 

general measurement approach, as an 

FRM because to do so could discourage 

development of other potentially 

superior approaches. Instead, the 

CASAC AAMMS recommended that the 

EPA develop performance-based 

approval criteria for direct measurement 

methods in order to put all approaches 

on a level playing field. 

At the present time, the EPA has not 

undertaken to develop and test such 

performance-base approval criteria. The 

EPA anticipates that if an effort were 

begun it would take at least several 

years before such criteria would be 

ready for regulatory use. Thus, the 

Policy Assessment concluded that while 

in the future it would be appropriate to 

consider a direct measurement of PM2.5

light extinction, or the sum of separate 

measurements of light scattering and 

light absorption, as the indicator for the 

secondary PM2.5 standard, this is not an 

appropriate option in this review 

because a suitable specification of the 

equipment or appropriate performancebased verification procedures cannot be 

developed in the time frame for this 

review (U.S. EPA, 2011a, p. 4–51, –52). 

(c) Calculated PM2.5 Light Extinction 

For the reasons discussed above, the 

Policy Assessment concluded that a 

calculated PM2.5 light extinction 

indicator would be the preferred 

approach. PM2.5 light extinction can be 

calculated from PM2.5 mass, combined 

with speciated PM2.5 mass concentration 

data plus relative humidity data, as is 

presently routinely done on a 24-hour 

average basis under the Regional Haze 

Program using data from the rural 

IMPROVE monitoring network. This 

same calculation procedure, using a 24- 

hour average basis, could be used for a 

NAAQS focused on protecting against 

PM-related visibility impairment 

primarily in urban areas. This approach 

would use the type of data that is 

routinely collected from the urban 

CSN 168 in combination with monthly 

average relative humidity data based on 

long-term climatological means as used 

in the Regional Haze Program (U.S. 

EPA, 2011a, Appendix G, section G.2). 

The proposal discussed the complex 

approach utilized in the Visibility 

Assessment for calculating hourly PM2.5

light extinction 169 and discussed 

various simplified approaches for 

calculating these hourly values that 

were analyzed in the Policy Assessment. 

The Policy Assessment concluded that 

each of these simplified approaches 

provided reasonably good estimates of 

PM2.5 light extinction and each would 

be appropriate to consider as the 

indicator for a distinct hourly or multihour secondary standard (U.S. EPA, 

2011a, p. 4–48). The proposal also 

recognized that the Policy Assessment 

identified a number of variations on 

these simplified approaches that it 

would be appropriate to consider, 

including: 

(1) The use of the split-component mass 

extinction efficiency approach from the 

revised IMPROVE algorithm170

(2) The use of more refined value(s) for the 

organic carbon multiplier 171

(3) The use of the reconstructed 24-hour 

PM2.5 mass (i.e., the sum of the five PM2.5

components from speciated monitoring) as a 

normalization value for the hourly 

measurements from the PM2.5 instrument as 

a way of better reflecting ambient nitrate 

concentrations 

(4) The use of historical monthly or 

seasonal, or regional, speciation averages 

Overall, the analyses conducted for 

the Visibility Assessment and Policy 

Assessment indicated that the use of a 

calculated PM2.5 light extinction 

indicator would provide a much higher 

degree of uniformity in terms of the 

degree of protection from visibility 

impairment across the country than a 

PM2.5 mass indicator, because a 

calculated PM2.5 light extinction 

indicator would directly incorporate the 

effects of humidity and PM2.5

composition differences between 

various regions. Further, the proposal 

noted that the Policy Assessment 

concluded that consideration could be 

given to defining a calculated PM2.5

light extinction indicator on either a 24- 

hour or a sub-daily basis (U.S. EPA, 

2011a, p. 4–52). However, the Policy 

Assessment noted that approval of 

continuous FEM monitors has been 

based only on 24-hour average, not 

hourly, PM2.5 mass. In addition, there 

are mixed results of data quality 

assessments on a 24-hour basis for these 

monitors, as well as the near absence of 

performance data for sub-daily 

averaging periods. Thus, while it is 

possible to utilize data from PM2.5

continuous FEMs on a 1-hour or multihour (e.g., 4-hour) basis, these factors 

increase the uncertainty of utilizing 

continuous methods to support 1-hour 

or 4-hour PM2.5 mass measurements as 

an input to the light extinction 

calculation. Therefore, as noted at the 

time of proposal, until issues regarding 

the comparability of 24-hour PM2.5 mass 

values derived from continuous FEMs 

and filter-based FRMs 172 are resolved, 

there is reason to be cautious about 

relying on a calculation procedure that 

uses hourly PM2.5 mass values reported 

by continuous FEMs in combination 

with speciated PM2.5 mass values from 

24-hour filter-based samplers. 

(d) CASAC Advice 

In reviewing the second draft Policy 

Assessment, CASAC stated that it 

‘‘overwhelmingly * * * would prefer 

the direct measurement of light 

extinction,’’ recognizing it as the 

property of the atmosphere that most 

directly relates to visibility effects 

(Samet, 2010d, p. iii). CASAC noted that 

‘‘[I]t has the advantage of relating 

directly to the demonstrated harmful 

welfare effect of ambient PM on human 

visual perception.’’ However, CASAC 

also concluded that the calculated PM2.5

light extinction indicator ‘‘appears to be 

a reasonable approach for estimating 

hourly light extinction’’ (Samet, 2010d, 

p. 11). Further, based on CASAC’s 

understanding of the time that would be 

required to develop an FRM for this 

indicator, CASAC agreed with the staff 

preference presented in the second draft 

Policy Assessment for a calculated PM2.5

light extinction indicator. CASAC noted 

that ‘‘[I]ts reliance on procedures that 


tkelley on DSK3SPTVN1PROD with 
3196 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

173 In commenting on the second draft Policy 

Assessment, CASAC did not have an opportunity to 

review the assessment of continuous PM2.5 FEMs 

compared to collocated FRMs (Hanley and Reff, 

2011) as presented and discussed in the final Policy 

Assessment (U.S. EPA, 2011a, p. 4–50). 

have already been implemented in the 

CSN and routinely collected continuous 

PM2.5 data suggest that it could be 

implemented much sooner than a 

directly measured indicator’’ (Samet, 

2010d, p. iii).173

(e) Administrator’s Proposed 

Conclusions on Indicator 

At the time of proposal, while 

agreeing with CASAC that a directly 

measured PM light extinction indicator 

would provide the most direct link 

between PM in the ambient air and PMrelated light extinction, the 

Administrator provisionally concluded 

that this was not an appropriate option 

in this review because a suitable 

specification of currently available 

equipment or performance-based 

verification procedures cannot be 

developed in the time frame of this 

review. Taking all of the above 

considerations and CASAC advice into 

account, the Administrator 

provisionally concluded that a new 

calculated PM2.5 light extinction 

indicator, similar to that used in the 

Regional Haze Program (i.e., using an 

IMPROVE algorithm as translated into 

the deciview scale), was the appropriate 

indicator to replace the current PM2.5

mass indicator. Such an indicator, 

referred to as a PM2.5 visibility index, 

would appropriately reflect the 

relationship between ambient PM and 

PM-related light extinction, based on 

the analyses discussed in the proposal 

and incorporation of factors based on 

measured PM2.5 speciation 

concentrations and relative humidity 

data. In addition, selection of this type 

of indicator would address, in part, the 

issues raised in the court’s remand of 

the 2006 p.m.2.5 standards. The 

Administrator also noted that such a 

PM2.5 visibility index would afford a 

relatively high degree of uniformity of 

visual air quality protection in areas 

across the country by virtue of directly 

incorporating the effects of differences 

in PM2.5 composition and relative 

humidity across the country. 

Based on these above considerations, 

the Administrator proposed to set a 

distinct secondary standard for PM2.5

defined in terms of a PM2.5 visibility 

index (i.e., a calculated PM2.5 light 

extinction indicator, translated into the 

deciview scale) to protect against PMrelated visibility impairment primarily 

in urban areas. The Administrator 

proposed that such an index be based 

on the original IMPROVE algorithm in 

conjunction with monthly average 

relative humidity data based on longterm climatological means as used in 

the Regional Haze Program. The EPA 

solicited comment on all aspects of the 

proposed indicator, especially: 

(1) The proposed use of a PM2.5 visibility 

index rather than a PM10 visibility index 

which would include an additional term for 

coarse particles; 

(2) Using the revised IMPROVE algorithm 

rather than the original IMPROVE algorithm; 

(3) The use of alternative values for the 

organic carbon multiplier in conjunction 

with either the original or revised IMPROVE 

algorithm; 

(4) The use of historical monthly, seasonal, 

or regional speciation averages; 

(5) Alternative approaches to determining 

relative humidity; and 

(6) Simplified approaches to generating 

hourly PM2.5 light extinction values for 

purposes of calculating an hourly or multihour indicator. 

iii. Averaging Times 

In this review, as discussed in section 

VI.D.2 of the proposal, consideration of 

appropriate averaging times for use in 

conjunction with a PM2.5 visibility 

index was informed by information 

related to the nature of PM visibility 

effects and the nature of inputs to the 

calculation of PM2.5 light extinction, as 

discussed above. The EPA considered 

both sub-daily (1- and 4-hour averaging 

times) and 24-hour averaging times. In 

considering sub-daily averaging times, 

the EPA has also considered what 

diurnal periods and ambient relative 

humidity conditions would be 

appropriate to consider in conjunction 

with such an averaging time. 

As an initial matter, the Policy 

Assessment considered sub-daily 

averaging times. Taking into account 

what is known from available studies 

concerning how quickly people 

experience and judge visibility 

conditions, the possibility that some 

fraction of the public experiences 

infrequent or short periods of exposure 

to ambient visibility conditions, and the 

typical rate of change of the pathaveraged PM light extinction over urban 

areas, the initial analyses conducted as 

part of the Visibility Assessment 

focused on a 1-hour averaging time. In 

its review of the first draft Policy 

Assessment, CASAC agreed that a 1- 

hour averaging time would be 

appropriate to consider, noting that PM 

effects on visibility can vary widely and 

rapidly over the course of a day and 

such changes are almost instantaneously 

perceptible to human observers (Samet, 

2010c, p. 19). The Policy Assessment 

noted that this view related specifically 

to a standard defined in terms of a 

directly measured PM light extinction 

indicator, in that CASAC also noted that 

a 1-hour averaging time is well within 

the instrument response times of the 

various currently available and 

developing optical monitoring methods. 

However, CASAC also advised that if 

a PM2.5 mass indicator were to be used, 

it would be appropriate to consider 

‘‘somewhat longer averaging times—2 to 

4 hours—to assure a more stable 

instrumental response’’ (Samet, 2010c, 

p. 19). In considering this advice, the 

Policy Assessment concluded that since 

a calculated PM2.5 light extinction 

indicator relies in part on measured 

PM2.5 mass, it would be appropriate to 

consider a multi-hour averaging time on 

the order of a few hours (e.g. 4-hours). 

A multi-hour averaging time might 

reasonably characterize the visibility 

effects experienced by the segment of 

the population who have access to 

visibility conditions often or 

continuously throughout the day. For 

this segment of the population, it may 

be that their perception of visual air 

quality reflects some degree of offsetting 

an hour with poor visual air quality 

with one or more hours of clearer visual 

conditions. Further, the Policy 

Assessment recognized that a multihour averaging time would have the 

effect of averaging away peak hourly 

visibility impairment, which can change 

significantly from one hour to the next 

(U.S. EPA, 2011a, p. 4–53; U.S. EPA, 

2010b, Figure 3–12). 

In considering either 1-hour or multihour averaging times, the Policy 

Assessment recognized that no data are 

available with regard to how the 

duration and variation of time a person 

spends outdoors during the daytime 

impacts his or her judgment of the 

acceptability of different degrees of 

visibility impairment. As a 

consequence, it is not clear to what 

degree, if at all, the protection levels 

found to be acceptable in the public 

preference studies would change for a 

multi-hour averaging time as compared 

to a 1-hour averaging time. Thus, the 

Policy Assessment concluded that it is 

appropriate to consider a 1-hour or 

multi-hour (e.g., 4-hour) averaging time 

as the basis for a sub-daily standard 

defined in terms of a calculated PM2.5

light extinction indicator (U.S. EPA, 

2011a, p. 4–53). 

In addition, as discussed above, some 

data quality uncertainties have been 

observed with regard to hourly data 

collected by FEMs. Specifically, as part 

of the review of data from all 

continuous FEM PM2.5 instruments 

operating at state/local monitoring sites, 

the Policy Assessment noted that the 

occurrence of questionable outliers in 1- 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3197 

174Similarly questionable hourly data were not 

observed in the 2005 to 2007 continuous PM2.5 data 

used in the Visibility Assessment, all of which 

came from early-generation continuous instruments 

that had not been approved as FEMs. However, only 

15 sites and instruments were involved in the 

Visibility Assessment analyses, versus about 180 

currently operating FEM instruments submitting 

data to AQS. Therefore, there were more 

opportunities for very infrequent measurement 

errors to be observed in the larger FEM data set. 

175These analyses are also based on the use of a 

90th percentile form, averaged over 3 years, as 

discussed below in section VI.D.3 and in section 

4.3.3 of the Policy Assessment (U.S. EPA, 2011a). 

176The EPA staff noted that the R2 value (0.44) 

for Houston was notably lower than for the other 

cities. 

hour data submitted to AQS from 

continuous FEM PM2.5 instruments had 

been observed at some of these sites 

(Evangelista, 2011). Some of these 

outliers were questionable simply by 

virtue of their extreme magnitude, as 

high as 985 mg/m3, whereas other values 

were questionable because they were 

isolated to single hours with much 

lower values before and after, a pattern 

that is much less plausible than if the 

high concentrations were more 

sustained.174 The Policy Assessment 

noted that any current data quality 

problems might be resolved in the 

normal course of monitoring program 

evolution as operators become more 

adept at instrument operation and 

maintenance and data validation or by 

improving the approval criteria and 

testing requirements for continuous 

instruments. Regardless, the Policy 

Assessment noted that multi-hour 

averaging of FEM data could serve to 

reduce the effects of such outliers 

relative to the use of a 1-hour averaging 

time. 

The Policy Assessment noted that 

there are significant reasons to consider 

using PM2.5 light extinction calculated 

on a 24-hour basis to reduce the various 

data quality concerns described above 

with respect to relying on continuous 

PM2.5 monitoring data. However, the 

Policy Assessment recognized that 24 

hours is far longer than the hourly or 

multi-hour time periods that might 

reasonably characterize the visibility 

effects experienced by various segments 

of the population, including both those 

who do and do not have access to 

visibility conditions often or 

continuously throughout the day. Thus, 

the Policy Assessment concluded that 

the appropriateness of considering a 24- 

hour averaging time would depend 

upon the extent to which PM-related 

light extinction calculated on a 24-hour 

average basis would be a reasonable and 

appropriate surrogate for PM-related 

light extinction calculated on a subdaily basis. 

To examine this relationship, the EPA 

conducted comparative analyses of 24- 

hour and 4-hour averaging times in 

conjunction with a calculated PM2.5

indicator. For these analyses, 4-hour 

average PM2.5 light extinction was 

calculated based on using the Visibility 

Assessment approach. The 24-hour 

average PM2.5 light extinction was 

calculated using the original IMPROVE 

algorithm and long-term relative 

humidity conditions to calculate PM2.5

light extinction. Based on these 

analyses,175 which are presented and 

discussed in Appendix G of the Policy 

Assessment, scatter plots comparing 24- 

hour and 4-hour calculated PM2.5 light 

extinction were constructed for each of 

the 15 cities included in the Visibility 

Assessment and for all 15 cities pooled 

together (U.S. EPA, 2011a, Figures G–4 

and G–5). Though there was some 

scatter around the regression line for 

each city because the calculated 4-hour 

light extinction values included dayspecific and hour-specific influences 

that are not captured by the simpler 24- 

hour approach, these analyses generally 

showed good correlation between 24- 

hour and 4-hour average PM2.5 light 

extinction, as evidenced by reasonably 

high city-specific and pooled R2 values, 

generally in the range of over 0.6 to over 

0.8.176 This suggested that PM2.5 light 

extinction calculated on a 24-hour basis 

is a reasonable and appropriate 

surrogate to PM2.5 light extinction 

calculated on a sub-daily basis. 

Taking the above considerations and 

CASAC’s advice into account, the Policy 

Assessment concluded that it would be 

appropriate to consider a 24-hour 

averaging time, in conjunction with a 

calculated PM2.5 light extinction 

indicator and an appropriately specified 

standard level, as discussed below. By 

using site-specific daily data on PM2.5

composition and site-specific long-term 

relative humidity conditions, this 24- 

hour average indicator would provide 

more consistent protection from PM2.5- 

related visibility impairment than 

would a secondary PM2.5 NAAQS based 

only on 24-hour or annual average PM2.5

mass. In particular, this approach would 

account for the systematic difference in 

humidity conditions between most 

eastern states and most western states. 

The Policy Assessment also concluded 

that it would also be appropriate to 

consider a multi-hour, sub-daily 

averaging time, for example a period of 

4 hours, in conjunction with a 

calculated PM2.5 light extinction 

indicator and with further consideration 

of the data quality issues discussed 

above. Such an averaging time, to the 

extent that data quality issues can be 

appropriately addressed, would be more 

directly related to the short-term nature 

of the perception of visibility 

impairment, short-term variability in 

PM-related visual air quality, and the 

short-term nature (hourly to multiple 

hours) of relevant exposure periods for 

segments of the viewing public. Such an 

averaging time would still result in an 

indicator that is less sensitive than a 1- 

hour averaging time to short-term 

instrument variability with respect to 

PM2.5 mass measurement. In 

conjunction with consideration of a 

multi-hour, sub-daily averaging time, 

the Policy Assessment concluded that 

consideration should be given to 

including daylight hours only and to 

applying a relative humidity screen of 

approximately 90 percent to remove 

hours in which fog or precipitation is 

much more likely to contribute to the 

observed visibility impairment (U.S. 

EPA, 2011a, p. 4–58). Recognizing that 

a 1-hour averaging time would be even 

more sensitive to data quality issues, 

including short-term variability in 

hourly data from currently available 

continuous monitoring methods, the 

Policy Assessment concluded that it 

would not be appropriate to consider a 

1-hour averaging time in conjunction 

with a calculated PM2.5 light extinction 

indicator in this review (U.S. EPA, 

2011a, p. 4–58). 

As noted above, in its review of the 

first draft Policy Assessment, CASAC 

concluded that PM effects on visibility 

can vary widely and rapidly over the 

course of a day and such changes are 

almost instantaneously perceptible to 

human observers (Samet, 2010c, p. 19). 

Based in part on this consideration, 

CASAC agreed that a 1-hour averaging 

time would be appropriate to consider 

in conjunction with a directly measured 

PM light extinction indicator, noting 

that a 1-hour averaging time is well 

within the instrument response times of 

the various currently available and 

developing optical monitoring methods. 

At that time, CASAC also advised that 

if a PM2.5 mass indicator were to be 

used, it would be appropriate to 

consider ‘‘somewhat longer averaging 

times—2- to 4-hours—to assure a more 

stable instrumental response’’ (Samet, 

2010c, p. 19). Thus, CASAC’s advice on 

averaging times that would be 

appropriate for consideration was 

predicated in part on the capabilities of 

monitoring methods that were available 

for the alternative indicators discussed 

in the draft Policy Assessment. 

CASAC’s views on a multi-hour 

averaging time would also apply to the 

calculated PM2.5 light extinction 

indicator since hourly PM2.5 mass 

measurements are also required for this 


tkelley on DSK3SPTVN1PROD with 
3198 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

indicator when calculated on a subdaily basis. 

It is important to note that at the time 

it provided advice on suitable averaging 

times, CASAC did not have the benefit 

of EPA’s subsequent assessment of the 

data quality issues associated with the 

use of continuous FEMs as the basis for 

hourly PM2.5 mass measurements. 

Furthermore, since CASAC only 

commented on the first and second 

drafts of the Policy Assessment, neither 

of which included discussion of a 

calculated PM2.5 indicator based on a 

24-hour averaging time, CASAC did not 

have a basis to offer advice regarding a 

24-hour averaging time. In addition, the 

24-hour averaging time is not based on 

consideration of 24-hours as a relevant 

exposure period, but rather as a 

surrogate for a sub-daily period of 4 

hours, which is consistent with 

CASAC’s advice concerning an 

averaging time associated with the use 

of a PM2.5 mass indicator. 

Taking into account the information 

discussed above with regard to analyses 

and conclusions presented in the final 

Policy Assessment the Administrator 

recognized that hourly or sub-daily, 

multi-hour averaging times, within 

daylight hours and excluding hours 

with relative humidity above 

approximately 90 percent, are more 

directly related than a 24-hour averaging 

time to the short-term nature of the 

perception of PM-related visibility 

impairment and the relevant exposure 

periods for segments of the viewing 

public. On the other hand, she 

recognized that data quality 

uncertainties have recently been 

associated with currently available 

instruments that would be used to 

provide the hourly PM2.5 mass 

measurements that would be needed in 

conjunction with an averaging time 

shorter than 24-hours. As a result, while 

the Administrator recognized the 

desirability of a sub-daily averaging 

time, she had strong reservations about 

proposing to set a standard at this time 

in terms of a sub-daily averaging time. 

In considering the information and 

analyses related to consideration of a 

24-hour averaging time, the 

Administrator recognized that the 

Policy Assessment concluded that PM2.5

light extinction calculated on a 24-hour 

averaging basis is a reasonable and 

appropriate surrogate for sub-daily 

PM2.5 light extinction calculated on a 4- 

hour average basis. In light of this 

finding and the views of CASAC based 

on its reviews of the first and second 

drafts of the Policy Assessment, the 

Administrator proposed to set a distinct 

secondary standard with a 24-hour 

averaging time in conjunction with a 

PM2.5 visibility index. 

iv. Form 

As discussed in section VI.D.3 of the 

proposal, the ‘‘form’’ of a standard 

defines the air quality statistic that is to 

be compared to the level of the standard 

in determining whether the standard is 

achieved. The form of the current 24- 

hour PM2.5 NAAQS is such that the 

level of the standard is compared to the 

3-year average of the annual 98th 

percentile value of the measured 

indicator. The purpose in averaging for 

three years is to provide stability from 

the occasional effects of inter-annual 

meteorological variability that can result 

in unusually high pollution levels for a 

particular year. The use of a multi-year 

percentile form, among other things, 

makes the standard less subject to the 

possibility of transient violations caused 

by statistically unusual indicator values, 

thereby providing more stability to the 

air quality management process that 

may enhance the practical effectiveness 

of efforts to implement the NAAQS. 

Also, a percentile form can be used to 

take into account the number of times 

an exposure might occur as part of the 

judgment on protectiveness in setting a 

NAAQS. For all of these reasons, the 

Policy Assessment concluded it would 

be appropriate to consider defining the 

form of a distinct secondary standard in 

terms of a 3-year average of a specified 

percentile air quality statistic (U.S. EPA, 

2011a, p. 4–58). 

The urban visibility preference 

studies that provided results leading to 

the range of CPLs being considered in 

this review offer no information that 

addresses the frequency of time that 

visibility levels should be below those 

values. Given this lack of information, 

and recognizing that the nature of the 

public welfare effect is one of aesthetics 

and/or feelings of well-being, the Policy 

Assessment concluded that it would not 

be appropriate to consider eliminating 

all exposures above the level of the 

standard and that allowing some 

number of hours/days with reduced 

visibility can reasonably be considered 

(U.S. EPA, 2011a, p. 4–59). In the 

Visibility Assessment, 90th, 95th, and 

98th percentile forms were assessed for 

alternative PM light extinction 

standards (U.S. EPA, 2010b, section 

4.3.3). In considering these alternative 

percentiles, the Policy Assessment 

noted that the Regional Haze Program 

targets the 20 percent most impaired 

days for improvements in visual air 

quality in Federal Class I areas. If 

improvement in the 20 percent most 

impaired days were similarly judged to 

be appropriate for protecting visual air 

quality in urban areas, a percentile well 

above the 80th percentile would be 

appropriate to increase the likelihood 

that all days in this range would be 

improved by control strategies intended 

to attain the standard. A focus on 

improving the 20 percent most impaired 

days suggests that the 90th percentile, 

which represents the median of the 

distribution of the 20 percent worst 

days, would be an appropriate form to 

consider. Strategies that are 

implemented so that 90 percent of days 

have visual air quality that is at or 

below the level of the standard would 

reasonably be expected to lead to 

improvements in visual air quality for 

the 20 percent most impaired days. 

Higher percentile values within the 

range assessed could have the effect of 

limiting the occurrence of days with 

peak PM-related light extinction in 

urban areas to a greater degree. In 

considering the limited information 

available from the public preference 

studies, the Policy Assessment found no 

basis to conclude that it would be 

appropriate to consider limiting the 

occurrence of days with peak PMrelated light extinction in urban areas to 

a greater degree. 

Another aspect of the form discussed 

in the proposal for a sub-daily averaging 

time was whether to include all daylight 

hours or only the maximum daily 

daylight hour(s). The maximum daily 

daylight 1-hour or multi-hour form 

would be most directly protective of the 

welfare of people who have limited, 

infrequent or intermittent exposure to 

visibility during the day (e.g., during 

commutes), but spend most of their time 

without an outdoor view. For such 

people a view of poor visibility during 

their morning commute may represent 

their perception of the day’s visibility 

conditions until the next time they 

venture outside during daylight, which 

may be hours later or perhaps the next 

day. Other people have exposure to 

visibility conditions throughout the day. 

For those people, it might be more 

appropriate to include every daylight 

hour in assessing compliance with a 

standard, since it is more likely that 

each daylight hour could affect their 

welfare. 

The Policy Assessment did not have 

information regarding the fraction of the 

public that has only one or a few 

opportunities to experience visibility 

during the day, nor did it have 

information on the role the duration of 

the observed visibility conditions has on 

wellbeing effects associated with those 

visibility conditions. However, it is 

logical to conclude that people with 

limited opportunities to experience 

visibility conditions on a daily basis 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3199 

177 In 2009, the DC Circuit remanded the 

secondary PM2.5 standards to the EPA in part 

because the Agency failed to identify a target level 

of protection, even though EPA staff and CASAC 

had identified a range of target levels of protection 

that were appropriate for consideration. The court 

determined that the Agency’s failure to identify a 

target level of protection as part of its final decision 

was contrary to the statute and therefore unlawful, 

and that it deprived EPA’s decision-making of a 

reasoned basis. See 559F. 3d at 528–31; see also 

section VI.A.2 above and the Policy Assessment, 

section 4.1.2. 

would experience the entire impact 

associated with visibility based on their 

short-term exposure. The impact of 

visibility for those who have access to 

visibility conditions often or 

continuously during the day may be 

based on varying conditions throughout 

the day. 

In light of these considerations, the 

analyses conducted as part of the 

Visibility Assessment analyses included 

both the maximum daily hour and the 

all daylight hours forms. The Policy 

Assessment noted that there is a close 

correspondence between the level of 

protection afforded for all 15 urban 

areas by a maximum daily daylight 1- 

hour approach using the 90th percentile 

form and an all daylight hours approach 

combined with the 98th percentile form 

(U.S. EPA, 2010b, section 4.1.4). This 

suggested that reductions in visibility 

impairment required to meet either form 

of the standard would provide 

protection to both fractions of the public 

(i.e., those with limited opportunities 

and those with greater opportunities to 

view PM-related visibility conditions). 

CASAC generally supported 

consideration of both types of forms 

without expressing a preference based 

on its review of information presented 

in the second draft Policy Assessment 

(Samet, 2010d, p. 11). 

In conjunction with a calculated PM2.5

light extinction indicator and alternative 

24-hour or sub-daily (e.g., 4-hour) 

averaging times, based on the above 

considerations, and given the lack of 

information on and the high degree of 

uncertainty over the impact on public 

welfare of the number of days with 

visibility impairment over a year, the 

Policy Assessment concluded that it 

would be appropriate to give primary 

consideration to a 90th percentile form, 

averaged over three years (U.S. EPA, 

2011a, p. 4–60). Further, in the case of 

a multi-hour, sub-daily alternative 

standard, the Policy Assessment 

concluded that it would be appropriate 

to give primary consideration to a form 

based on the maximum daily multi-hour 

period in conjunction with the 90th 

percentile form (U.S. EPA, 2011a, p. 4– 

60). This sub-daily form would be 

expected to provide appropriate 

protection for various segments of the 

population, including those with 

limited opportunities during a day and 

those with more extended opportunities 

over the daylight hours to experience 

PM-related visual air quality. 

Though CASAC did not provide 

advice as to a specific form that would 

be appropriate, it took note of the 

alternative forms considered in that 

document and encouraged further 

analyses in the final Policy Assessment 

that might help to clarify a basis for 

selecting from within the range of forms 

identified. In considering the available 

information and the conclusions in the 

final Policy Assessment in light of 

CASAC’s comments, at the time of 

proposal the Administrator concluded 

that a 90th percentile form, averaged 

over 3 years, is appropriate, and 

proposed such a form in conjunction 

with a PM2.5 visibility index and a 24- 

hour averaging time. 

v. Level 

As discussed in section VI.D.4 of the 

proposal, in considering appropriate 

levels for a 24-hour standard defined in 

terms of a PM2.5 visibility index and an 

90th percentile form, averaged over 3 

years, the Policy Assessment took into 

account the evidence- and impact-based 

considerations discussed above, with a 

focus on the results of public perception 

and attitude surveys related to the 

acceptability of various levels of visual 

air quality and on the important 

limitations in the design and scope of 

such available studies. The Policy 

Assessment considered a variety of 

approaches for identifying appropriate 

levels for such a standard, including 

utilizing both adjusted and unadjusted 

CPLs derived from the visibility 

preference studies. 

The Policy Assessment interpreted 

the results from the visibility 

preferences studies conducted in four 

urban areas to define a range of low, 

middle, and high CPLs for a sub-daily 

standard (e.g., 1- to 4-hour averaging 

time) of 20, 25, and 30 dv, which are 

approximately equivalent to PM2.5 light 

extinction of values of 65, 110, and 190 

Mm¥1. The CASAC generally supported 

this approach, noting that the ‘‘EPA 

staff’s approach for translating and 

presenting the technical evidence and 

assessment results is logically conceived 

and clearly presented. The 20–30 

deciview range of levels chosen by EPA 

staff as ‘Candidate Protection Levels’ is 

adequately supported by the evidence 

presented’’ (Samet, 2010d, p. 11).177 The 

Policy Assessment also recognized that 

to define a range of alternative levels 

that would be appropriate to consider 

for a 24-hour calculated PM2.5 light 

extinction standard, it would be 

appropriate to consider whether some 

adjustment to these CPLs is warranted 

since these preference studies cannot be 

directly interpreted as applying to a 24- 

hour exposure period (as noted above 

and in Policy Assessment section 4.3.1). 

Considerations related to such 

adjustments are more specifically 

discussed below. 

In considering alternative levels for a 

sub-daily standard based directly on the 

four preference study results, the Policy 

Assessment noted that the individual 

low and high CPLs are in fact generally 

reflective of the results from the Denver 

and Washington, DC studies 

respectively, and the middle CPL is very 

near to the 50th percentile criteria result 

from the Phoenix study, which was by 

far the best of the studies, providing 

somewhat more support for the middle 

CPL. 

In considering the results from the 

four visibility preference studies, the 

Policy Assessment recognized that 

currently available studies are limited in 

that they were conducted in only four 

areas, three in the U.S. and one in 

Canada. Further, the Policy Assessment 

recognized that available studies 

provide no information on how the 

duration and variation of time a person 

spends outdoors during the daytime 

may impact their judgment of the 

acceptability of different degrees of 

visibility impairment. As such, there is 

a relatively high degree of uncertainty 

associated with using the results of 

these studies to inform consideration of 

a national standard for any specific 

averaging time. Nonetheless, the Policy 

Assessment concluded, as did CASAC, 

that these studies are appropriate to use 

for this purpose (U.S. EPA, 2011a, p. 4– 

61). 

Using approaches described in section 

VI.C.4 of the proposal, the Policy 

Assessment explored various 

approaches to adjusting the CPLs 

derived from the preference studies to 

inform alternative levels for a 24-hour 

standard. These various approaches, 

based on analyses of 2007–2009 data 

from the 15 urban areas assessed in the 

Visibility Assessment, focused on 

estimating CPLs for a 24-hour standard 

that would provide generally equivalent 

protection as that provided by a 4-hour 

standard with CPLs of 20, 25, and 30 dv. 

In conducting these analyses, staff 

initially expected that the values of 24- 

hour average PM2.5 light extinction and 

daily maximum daylight 4-hour average 

PM2.5 light extinction would differ on 

any given day, with the shorter term 

peak value generally being larger. This 

would mean that, in concept, the level 

of a 24-hour standard should include a 


tkelley on DSK3SPTVN1PROD with 
3200 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

178Note that the city-specific ranges shown in 

Table G–6, Appendix G of the Policy Assessment 

are incorrectly stated for Approaches C and E. 

Drawing from the more detailed and correct results 

for Approaches C and E presented in Tables G–7 

and G–8, respectively, the city-specific ranges in 

Table G–6 for Approach C should be 17–21 dv for 

the CPL of 20 dv; 21–25 dv for the CPL of 25 dv; 

and 24–30 dv for the CPL of 30 dv; the city-specific 

ranges in Table G–6 for Approach E should be 17– 

21 dv for the CPL of 20 dv; 21–26 dv for the CPL 

of 25 dv; and 25–31 dv for the CPL of 30 dv. In 

the EPA’s reanalysis comparing 4- vs. 24-hour 

values, Frank et al. (2012b) recreated Table G–6 

using the correct values from Tables G–7 and G–8. 

179As discussed in more detail in Appendix G of 

the Policy Assessment, some days have higher 

values for 24-hour average light extinction than for 

daily maximum 4-hour daylight light extinction, 

and consequently an adjusted ‘‘equivalent’’ 24-hour 

CPL can be greater than the original 4-hour CPL. 

This can happen for two reasons. First, the use of 

monthly average historical RH data will lead to 

cases in which the f(RH) values used for the 

calculation of 24-hour average light extinction are 

higher than all or some of the four hourly values 

of f(RH) used to determine daily maximum 4-hour 

daylight light extinction on the same day. Second, 

PM2.5 concentrations may be greater during nondaylight periods than during daylight hours. 

downward adjustment compared to the 

level of a 4-hour standard to provide 

generally equivalent protection. As 

discussed more fully in section G.5 of 

Appendix G and summarized below, 

this initial expectation was not found to 

be the case across the range of CPLs 

considered. In fact, as shown in Tables 

G–7 and G–8 of Appendix G and in the 

corrected version of Table G–6 found in 

Frank et al. (2012b),178 in considering 

estimates aggregated or averaged over all 

15 cities as well as the range of cityspecific estimates for the various 

approaches considered, these analyses 

indicated that the generally equivalent 

24-hour levels ranged from somewhat 

below the 4-hour level to just above the 

4-hour level for each of the CPLs.179 In 

all cases, the range of city-specific 

estimates of generally equivalent 24- 

hour levels included the 4-hour level for 

each of the CPLs of 20, 25, and 30 dv. 

As noted in the proposal, looking more 

broadly at these results could support 

consideration of using the same CPL for 

a 24-hour standard as for a 4-hour 

standard, recognizing that there is no 

one approach that can most closely 

identify a generally equivalent 24-hour 

standard level in each urban area for 

each CPL. The use of such an 

unadjusted CPL for a 24-hour standard 

would place more emphasis on the 

relatively high degree of spatial and 

temporal variability in relative humidity 

and fine particle composition observed 

in urban areas across the country, so as 

to reduce the potential of setting a 24- 

hour standard level that would require 

more than the intended degree of 

protection in some areas. 

In considering the appropriate level of 

a secondary standard focused on 

protection from PM-related urban 

visibility impairment based on either a 

24-hour or a multi-hour, sub-daily (e.g., 

4-hour) averaging time, the EPA has 

been mindful of the important 

limitations in the available evidence 

from public preference studies. These 

uncertainties and limitations are due in 

part to the small number of stated 

preference studies available for this 

review; the relatively small number of 

study participants and the extent to 

which the study participants may not be 

representative of the broader study area 

population in some of the studies; and 

the variations in the specific materials 

and methods used in each study such as 

scene characteristics, the range of VAQ 

levels presented to study participants, 

image presentation methods and 

specific wording used to frame the 

questions used in the group interviews. 

In addition the EPA has noted that the 

scenic vistas available on a daily basis 

in many urban areas across the country 

generally may not have the inherent 

visual interest or the distance between 

viewer and object of greatest intrinsic 

value as in the Denver and Phoenix 

preference studies, and that there is the 

possibility that there could be regional 

differences in individual preferences for 

VAQ. 

It is also important to note that as in 

past reviews, the EPA is considering a 

national visibility standard in 

conjunction with the Regional Haze 

Program as a means of achieving 

appropriate levels of protection against 

PM-related visibility impairment in 

urban, non-urban, and Federal Class I 

areas across the country. The EPA 

recognizes that programs implemented 

to meet a national standard focused 

primarily on the visibility problems in 

urban areas can be expected to improve 

visual air quality in surrounding nonurban areas as well, as would programs 

now being developed to address the 

requirements of the Regional Haze 

Program established for protection of 

visual air quality in Federal Class I 

areas. The EPA also believes that the 

development of local programs, such as 

those in Denver and Phoenix, can 

continue to be an effective and 

appropriate approach to provide 

additional protection, beyond that 

afforded by a national standard, for 

unique scenic resources in and around 

certain urban areas that are particularly 

highly valued by people living in those 

areas. 

The Policy Assessment concluded 

that it is appropriate to give primary 

consideration to alternative standard 

levels toward the upper end of the 

ranges identified above for 24-hour and 

sub-daily standards, respectively (U.S. 

EPA, 2011a, p. 4–63). Thus, the Policy 

Assessment concluded it is appropriate 

to consider the following alternative 

levels: A level of 28 dv or somewhat 

below, down to 25 dv, for a standard 

defined in terms of a calculated PM2.5

light extinction indicator, a 90th 

percentile form, and a 24-hour averaging 

time; and a standard level of 30 dv or 

somewhat below, down to 25 dv, for a 

similar standard but with a 4-hour 

averaging time (U.S. EPA, 2011a, p. 4– 

63). The Policy Assessment judged that 

such standards would provide 

appropriate protection against PMrelated visibility impairment primarily 

in urban areas. The Policy Assessment 

noted that CASAC generally supported 

consideration of the 20–30 dv range as 

CPLs and, more specifically, that 

support for consideration of the upper 

part of the range of the CPLs derived 

from the public preference studies was 

expressed by some CASAC Panel 

members during the public meeting on 

the second draft Policy Assessment. The 

Policy Assessment concluded that such 

a standard would be appropriate in 

conjunction with the Regional Haze 

Program to achieve appropriate levels of 

protection against PM-related visibility 

impairment in areas across the country 

(U.S. EPA, 2011a, p. 4–63). 

Based on the considerations discussed 

above and in section VI.D.4 of the 

proposal, and taking into account the 

advice of CASAC, at the time of 

proposal the Administrator concluded 

that it would be appropriate to establish 

a target level of protection—for a 

standard defined in terms of a PM2.5

visibility index; a 90th percentile form 

averaged over 3 years; and a 24-hour 

averaging time—equivalent to the 

protection afforded by such a sub-daily 

(i.e., 4-hour) standard at a level of 30 dv, 

which is the upper end of the range of 

CPLs identified in the Policy 

Assessment and generally supported by 

CASAC. More specifically, the 

Administrator provisionally concluded 

that a 24-hour level of either 30 dv or 

28 dv could be construed as providing 

such a degree of protection, and that 

either level was supported by the 

available information and was generally 

consistent with the advice of CASAC. 

Thus, the EPA proposed two options for 

the level of a new 24-hour standard 

(defined in terms of a PM2.5 visibility 

index and a 90th percentile form, 

averaged over 3 years) to provide 

appropriate protection from PM-related 

visibility impairment: Either 30 dv or 28 

dv. As noted in the proposal, the option 

of setting such a 24-hour standard at a 

level of 30 dv would reflect recognition 

that there is considerable spatial and 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3201 

temporal variability in the key factors 

that determine the value of the PM2.5

visibility index in any given urban area, 

such that there is a relatively high 

degree of uncertainty as to the most 

appropriate approach to use in selecting 

a 24-hour standard level that would be 

generally equivalent to a specific 4-hour 

standard level. Selecting a 24-hour 

standard level of 30 dv would reflect a 

judgment that such substantial degrees 

of variability and uncertainty should be 

reflected in a higher standard level than 

would be appropriate if the underlying 

information were more consistent and 

certain. Alternatively, the option of 

setting such a 24-hour standard at a 

level of 28 dv would reflect placing 

more weight on statistical analyses of 

aggregated data from across the study 

cities and not placing as much emphasis 

on the city-to-city variability as a basis 

for determining an appropriate degree of 

protection on a national scale. 

The information available for the 

Administrator to consider when setting 

the secondary PM standard raises a 

number of uncertainties. While CASAC 

supported moving forward with a new 

standard on the basis of the available 

information, CASAC also recognized 

these uncertainties, referencing the 

discussion of key uncertainties and 

areas for future research in the second 

draft of the Policy Assessment. In 

discussing areas of future research, 

CASAC stated that: ‘‘The range of 50% 

acceptability values discussed as 

possible standards are based on just four 

studies (Figure 4–2), which, given the 

large spread in values, provide only 

limited confidence that the benchmark 

candidate protection levels cover the 

appropriate range of preference values. 

Studies using a range of urban scenes 

(including, but not limited to, iconic 

scenes—‘‘valued scenic elements’’ such 

as those in the Washington, DC study), 

should also be considered’’ (Samet, 

2010d, p. 12). The EPA solicited 

comment on how the Administrator 

should weigh those uncertainties as 

well as any additional comments and 

information to inform her consideration 

of these uncertainties. 

In addition, the EPA solicited 

comment on a number of other issues 

related to the level of the standard, 

including: 

(1) Both of the proposed levels and the 

various approaches to identifying generally 

equivalent levels upon which the alternative 

proposed levels are based. 

(2) A broader range of levels down to 25 

dv in conjunction with a 24-hour averaging 

time. 

(3) A range of alternative levels from 30 to 

25 dv in conjunction with a sub-daily (e.g., 

4-hour) averaging time. 

(4) The strengths and limitations associated 

with the public preference studies and the 

use of these studies to inform the selection 

of a range of levels that could be used to 

provide an appropriate degree of public 

welfare protection when combined with the 

other elements of the standard (i.e. indicator, 

form and averaging time). 

(5) Specific aspects of the public 

preference studies, including the extent to 

which the 50 percent acceptability criterion 

is an appropriate basis for establishing target 

protection levels in the context of 

establishing a distinct secondary NAAQS to 

address PM-related visibility impairment in 

urban areas; how the variability among 

preference studies in the extent to which 

study participants may be representative of 

the broader study area population should be 

weighed in the context of considering these 

studies in reaching proposed conclusions on 

a distinct secondary NAAQS; and the extent 

to which the ranges of VAQ levels presented 

to participants in each of the studies may 

have influenced study results and on how 

this aspect of the study designs should 

appropriately be weighed in the context of 

considering these studies in the context of 

this review. 

vi. Administrator’s Proposed 

Conclusions Regarding PM Standards 

To Protect Visibility 

At the time of proposal, based on the 

considerations described above, the 

Administrator proposed to revise the 

suite of secondary PM standards by 

adding a distinct standard for PM2.5 to 

address PM-related visibility 

impairment, focused primarily on 

visibility in urban areas. This proposed 

visibility standard was to be defined in 

terms of a PM2.5 visibility index, which 

would use measured PM2.5 mass, 

combined with PM2.5 speciation data 

and relative humidity data, to calculate 

PM2.5 light extinction, translated into 

the deciview (dv) scale; a 24-hour 

averaging time; a 90th percentile form, 

averaged over 3 years; and a level of 28– 

30 dv. 

vii. Related Technical Analysis 

At the time of proposal, the EPA 

conducted a two-pronged technical 

analysis of the relationships between 

the proposed PM2.5 visibility index 

standard and the current 24-hour PM2.5

mass-based standard (Kelly, et al., 

2012a). This analysis was designed to 

provide technical information to inform 

key issues related to implementing a 

distinct secondary standard for visibility 

as proposed. Specifically, the EPA 

recognized that significant technical 

issues were likely to arise for new or 

modified emissions sources conducting 

air quality analyses for purposes of 

demonstrating that they would not 

cause or contribute to a violation of the 

visibility standard under the Prevention 

of Significant Deterioration (PSD) 

program. Such a demonstration for the 

proposed secondary PM2.5 visibility 

index standard could require each PSD 

applicant to predict, via air quality 

modeling, the increase in visibility 

impairment, in terms of the proposed 

PM2.5 visibility index, that would result 

from the proposed source’s emissions in 

conjunction with an assessment of 

existing air quality (visibility 

impairment) conditions in terms of the 

proposed PM2.5 visibility index. The 

EPA noted that if this demonstration 

were to be attempted using the six-step 

procedure that the EPA proposed to use 

for calculating PM2.5 visibility index 

design values from monitored air 

concentrations of PM2.5 components, 

significant technical issues with the 

modeling procedures could arise. 

To address these technical issues, the 

EPA sought to explore whether sources 

that met the requirements pertaining to 

the 24-hour mass-based standard of 35 

mg/m3 would also meet the requirements 

pertaining to the proposed visibility 

index standard. As described in Kelly et 

al. (2012a), the first prong of the 

analysis addressed aspects of a PSD 

significant impact analysis by 

evaluating whether an individual 

source’s impact resulting in a small 

increase in the ambient PM2.5

concentration would produce a 

comparably small increase in visibility 

impairment. This analysis included 

estimates of PM2.5 speciation profiles 

based on direct PM2.5 emission profiles 

for a broad range of source categories 

and for theoretical upper and lower 

bound scenarios. 

The second prong of the analysis 

addressed aspects of a PSD cumulative 

impact analysis by exploring the 

relationship between the three-year 

design values for the existing 24-hour 

PM2.5 standard and coincident design 

values for the proposed PM2.5 visibility 

index standard based on recent air 

quality data. This aspect of the analysis 

indicated that increases in 24-hour 

PM2.5 design values generally 

correspond to increases in visibility 

index design values, and vice-versa. The 

analysis further explored the 

appropriateness of using a 

demonstration that a source does not 

cause or contribute to a violation of the 

24-hour PM2.5 standard as a surrogate 

for a demonstration that a source does 

not cause or contribute to a violation of 

the proposed secondary PM2.5 visibility 

index standard. This analysis was based 

on 2008 to 2010 air quality data, and 

compared the proposed level of 35 mg/ 

m3 for the 24-hour PM2.5 standard and 

for illustrative purposes an alternative 

standard level of 12 mg/m3 for the 

annual PM2.5 standard with the 


tkelley on DSK3SPTVN1PROD with 
3202 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

180 Kelly et al. (2012a) also noted that ‘‘Regional 

reductions in sulfate PM2.5 due to emission controls 

planned as part of national rules as well as emission 

reductions associated with potential annual 

standard violations are expected to improve 

visibility in this region’’ (p. 17). 

181The analysis also showed that attaining the 24- 

hour PM2.5 standard level of 35 mg/m3 would result 

in achieving a lower PM2.5 visibility index level in 

certain areas of the country, largely western areas, 

than would be achieved in other areas of the 

country. This is due to differences in the 

composition of ambient PM2.5 and the lower relative 

humidity in those areas. 

182Atmospheric PM is referred to as aerosols in 

the remainder of this section to be consistent with 

the Integrated Science Assessment. 

proposed levels of 28 or 30 dv for the 

secondary PM2.5 visibility index 

standard with a 24-hour averaging time 

and a 90th percentile form. The results 

indicated that all (for the 30 dv level) or 

nearly all (for the 28 dv level) areas in 

attainment of the 24-hour PM2.5

standard would also have been in 

attainment of the proposed secondary 

PM2.5 visibility index standard. 

Based on this technical analysis, the 

EPA proposed that there is sufficient 

evidence that a demonstration that a 

source does not cause or contribute to 

a violation of the mass-based 24-hour 

PM2.5 standard serves as a suitable 

surrogate for demonstrating that a 

source does not cause or contribute to 

a violation of the proposed secondary 

24-hour PM2.5 visibility index standard 

under the PSD program. As such, the 

EPA proposed to conclude that many or 

all sources undergoing PSD review for 

PM2.5 could rely upon their analysis for 

demonstrating that they do not cause or 

contribute to a violation of the massbased 24-hour PM2.5 standard to also 

show that they do not cause or 

contribute to a violation of the proposed 

secondary PM2.5 visibility index 

standard, if a distinct visibility standard 

were finalized. 

Although this proposed ‘‘surrogacy 

policy’’ was designed to address an 

implementation-related issue, the 

second prong of the technical analysis 

addresses the broader technical question 

of the relationship between the existing 

24-hour PM2.5 standard and the 

proposed PM2.5 visibility index standard 

in terms of the degree of protection 

likely to be afforded by each standard. 

Specifically, the analysis indicated that 

depending on the level of the proposed 

PM2.5 visibility index standard, the 

existing 24-hour PM2.5 mass-based 

standard would be as protective or in 

some areas more protective of visibility 

than a distinct secondary standard set 

within the range of levels proposed. 

Commenters on the proposed PM2.5

visibility index explored the 

implications of this analysis at length, 

as discussed further below in section 

VI.C.1.f. For this reason, the analysis is 

described in some detail here. 

Kelly et al. (2012a) noted that the 

relationship between design values for 

the 24-hour PM2.5 standard and the 

proposed secondary visibility index 

standard is not obvious a priori because 

of differences in design value 

calculations for the standards. However, 

closer examination of this relationship 

indicated that increases or decreases in 

24-hour PM2.5 design values correspond, 

respectively, to increases or decreases in 

visibility index values. Specifically, 

based on measurements from 102 sites 

with complete data from 2008–2010, 

Kelly et al. (2012a) found linear 

correlations between the 24-hour PM2.5

design values and the visibility index 

design values with r2 values ranging 

from 0.65 to 0.98 across these sites, with 

an average r2 value of 0.75 across all 

U.S. sites. Moreover, the data indicated 

that no design value existed where the 

visibility index design value exceeded 

30 dv, but the 24-hour PM2.5 standard 

level of 35 mg/m3 was attained. 

Visibility index design values for certain 

sites in the Industrial Midwest were 

shown to exceed 28 dv despite the fact 

that the 24-hour PM2.5 design values for 

these sites were below 35 mg/m3. This 

was attributed to the combination of 

high nitrate and sulfate fractions, 

substantial RH adjustment factors, and 

PM2.5 distribution characteristics that 

led to relatively high visibility index 

design values for a given 24-hour PM2.5

design value for counties in the 

Industrial Midwest.180 Kelly et al. 

(2012a) concluded that the ‘‘overall, 

design values based on 2008–2010 data 

suggest that counties that attain 24-hour 

PM2.5 NAAQS level of 35 mg/m3 would 

attain the proposed secondary PM2.5

visibility index NAAQS level of 30 dv 

and generally attain the level of 28 dv’’ 

(pp. 17–18). In addition, the Kelly et al. 

analysis indicated that at sites that 

violated both the 24-hour PM2.5 level 

and the proposed visibility index 30 dv 

level, the proposed level of 30 dv would 

likely be attained if PM2.5

concentrations were reduced such that 

the 24-hour PM2.5 level of 35 mg/m3 was 

attained (Kelly et al., 2012a, p.15).181 A 

key implication of this analysis, 

therefore, was that within the range of 

levels proposed by the EPA for a 

visibility index standard (28–30 dv), the 

24-hour PM2.5 standard of 35 mg/m3

would be controlling in almost all (at 28 

dv) or all (at 30 dv) instances. 

2. Other (Non-Visibility) PM-related 

Welfare Effects 

In the 2006 review, the EPA 

concluded that there was insufficient 

information to consider a distinct 

secondary standard based on PM-related 

impacts to ecosystems, materials 

damage and soiling, and climatic and 

radiative processes (71 FR 61144, 

October 17, 2006). Specifically, there 

was a lack of evidence linking various 

non-visibility welfare effects to specific 

levels of ambient PM. In that review, to 

provide a level of protection for these 

welfare-related effects, the secondary 

standards were set equal to the revised 

primary standards to directionally 

improve the level of protection afforded 

vegetation, ecosystems, and materials 

(71 FR 61210, October 17, 2006). 

This section briefly outlines key 

conclusions discussed more fully in 

section VI.E of the proposal regarding 

the non-visibility welfare effects of PM. 

These conclusions relate to the climate, 

ecological (including effects on plants, 

soil and nutrient cycling, wildlife and 

water) and materials damage effects of 

PM. For all of these effects, the Policy 

Assessment concluded that there is 

insufficient information at this time to 

revise the current suite of secondary 

standards. It is important to note that 

the Policy Assessment explicitly 

excluded discussion of the effects 

associated with deposited particulate 

matter components of NOX and SOx and 

their transformation products which are 

addressed fully in the joint review of the 

secondary NO2 and SO2 NAAQS. 

a. Evidence of Other Welfare Effects 

Related to PM 

With regard to the role of PM in 

climate, the proposal noted that there is 

considerable ongoing research focused 

on understanding aerosol contributions 

to changes in global mean temperature 

and precipitation patterns. The 

Integrated Science Assessment 

concluded ‘‘that a causal relationship 

exists between PM and effects on 

climate, including both direct effects on 

radiative forcing and indirect effects 

that involve cloud feedbacks that 

influence precipitation formation and 

cloud lifetimes’’ (U.S. EPA, 2009a, 

section 9.3.10). These effects are 

discussed in more detail in section 

VI.E.1 of the proposal, which provides 

information on the major aerosol 

components of interest for climate 

processes, including black carbon (BC), 

organic carbon (OC), sulfates, nitrates, 

and mineral dusts, and the nature, 

magnitude, and direction (e.g., cooling 

vs. warming) of various aerosol impacts 

on climate.182 The Policy Assessment 

concluded that aerosols alter climate 

processes directly through radiative 

forcing and by indirect effects on cloud 

brightness, changes in precipitation, and 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3203 

183This conclusion would apply for both the 

secondary (welfare-based) and the primary (healthbased) standards. 

possible changes in cloud lifetimes (U.S. 

EPA, 2011a, p. 5–10). Further, the 

Policy Assessment noted that the major 

aerosol components that contribute to 

climate processes (i.e. BC, OC, sulfate, 

nitrate and mineral dusts) vary in their 

reflectivity, forcing efficiencies and 

even in the direction of climate forcing, 

though there is an overall net climate 

cooling associated with aerosols in the 

global atmosphere (U.S. EPA, 2009a, 

section 9.2.10). The Policy Assessment 

concluded that the current mass-based 

PM2.5 and PM10 secondary standards 

were not an appropriate or effective 

means of focusing protection against 

PM-associated climate effects due to 

these differences in components (U.S. 

EPA, 2011a, p. 5–11). In addition, in 

light of the significant uncertainties in 

current scientific information and the 

lack of sufficient data, the Policy 

Assessment concluded it is not 

currently feasible to conduct a 

quantitative analysis for the purpose of 

informing revisions of the current 

secondary PM standards based on 

climate (U.S. EPA, 2011a, p. 5–11). 

Overall the Policy Assessment 

concluded that there is insufficient 

information at this time to base a 

national ambient standard on climate 

impacts associated with current ambient 

concentrations of PM or its constituents 

(U.S. EPA, 2011a, p. 5–11, –12).183

With regard to ecological effects, the 

proposal noted that several ecosystem 

components (e.g., plants, soils and 

nutrient cycling, wildlife and water) are 

impacted by PM air pollution, which 

may alter the services provided by 

affected ecosystems. Ecological effects 

include both direct effects due to 

deposition (e.g., wet, dry or occult) to 

vegetation surfaces and indirect effects 

occurring via deposition to ecosystem 

soils or surface waters where the 

deposited constituents of PM then 

interact with biological organisms. 

Some of the ecological effects 

considered in this review include direct 

effects to metabolic processes of plant 

foliage; contribution to total metal 

loading resulting in alteration of soil 

biogeochemistry and microbiology, and 

plant and animal growth and 

reproduction; and contribution to total 

organics loading resulting in 

bioaccumulation and biomagnification 

across trophic levels. Section VI.E.2 of 

the proposal summarizes key findings 

related to: 

(1) Impacts on plants and the ecosystem 

services they provide due to deposition of 

PM to vegetative surfaces, which alters the 

radiation received by the plant, and uptake 

of deposited PM components by plants from 

soil or foliage, which can lead to stress and 

decreased photosynthesis; 

(2) Impacts on ecosystem support services 

such as nutrient cycling, products such as 

crops and the regulation of flooding and 

water quality; 

(3) Impacts on wildlife, especially due to 

biomagnification of heavy metals (especially 

Hg) up the food chain and bioconcentration 

of POPs and PBDEs; and 

(4) Impacts of deposited PM, especially 

metals and organics, on the ecosystem 

services provided by water bodies, including 

primary production, provision of fresh water, 

regulation of climate and floods, recreational 

fishing and water purification. 

The proposal noted that the Integrated 

Science Assessment had concluded that 

ecological evidence is sufficient to 

conclude that a causal relationship is 

likely to exist between deposition of PM 

and a variety of effects on individual 

organisms and ecosystems (U.S. EPA, 

2009a, sections 2.5.3 and 9.4.7), and 

also noted that vegetation and other 

ecosystem components are affected 

more by particulate chemistry than size 

fraction. However, the proposal also 

pointed to the Integrated Science 

Assessment conclusion that it is 

generally difficult to characterize the 

nature and magnitude of effects and to 

quantify relationships between ambient 

concentrations of PM and ecosystem 

response due to significant data gaps 

and uncertainties as well as 

considerable variability that exists in 

the components of PM and their various 

ecological effects. There are few studies 

that link ambient PM concentrations to 

observed effect. Most direct ecosystem 

effects associated with particulate 

pollution occur in severely polluted 

areas near industrial point sources 

(quarries, cement kilns, metal smelting) 

(U.S. EPA, 2009a, sections 9.4.3 and 

9.4.5.7). 

Based on the evidence available at 

this time, the proposal noted the 

following key conclusions in the Policy 

Assessment: 

(1) A number of significant environmental 

effects that either have already occurred or 

are currently occurring are linked to 

deposition of chemical constituents found in 

ambient PM. 

(2) Ecosystem services can be adversely 

impacted by PM in the environment, 

including supporting, provisioning, 

regulating and cultural services. 

(3) The lack of sufficient information to 

relate specific ambient concentrations of 

particulate metals and organics to a degree of 

impairment of a specific ecological endpoint 

hinders the identification of a range of 

appropriate indicators, levels, forms and 

averaging times of a distinct secondary 

standard to protect against associated effects. 

(4) Data from regionally-based ecological 

studies can be used to establish probable 

local, regional and/or global sources of 

deposited PM components and their 

concurrent effects on ecological receptors. 

The proposal noted that the Policy 

Assessment had concluded that the 

currently available information is 

insufficient for purposes of assessing the 

adequacy of the protection for 

ecosystems afforded by the current suite 

of PM secondary standards or 

establishing a distinct national standard 

for ambient PM based on ecosystem 

effects of particulates not addressed in 

the NOX/SOX secondary review (e.g., 

metals, organics) (U.S. EPA, 2011a, p. 5– 

24). Furthermore, the Policy Assessment 

had concluded that in the absence of 

information providing a basis for 

specific standards in terms of particle 

composition, the observations continue 

to support retaining an appropriate 

degree of control on both fine and 

coarse particles to help address effects 

to ecosystems and ecosystem 

components associated with PM (U.S. 

EPA, 2011a, p. 5–24). 

With regard to materials damage, the 

proposal discussed effects associated 

with deposition of PM, including both 

physical damage (materials damage 

effects) and impaired aesthetic qualities 

(soiling effects). As with the other 

categories of welfare effects discussed 

above, the Integrated Science 

Assessment concluded that evidence is 

sufficient to support a causal 

relationship between PM and effects on 

materials (U.S. EPA, 2009a, sections 

2.5.4 and 9.5.4). The deposition of PM 

can physically affect materials, adding 

to the effects of natural weathering 

processes, by potentially promoting or 

accelerating the corrosion of metals, by 

degrading paints and by deteriorating 

building materials such as stone, 

concrete and marble (U.S. EPA, 2009a, 

section 9.5). In addition, the deposition 

of ambient PM can reduce the aesthetic 

appeal of buildings and objects through 

soiling. The Policy Assessment made 

the following observations: 

(1) Materials damage and soiling that occur 

through natural weathering processes are 

enhanced by exposure to atmospheric 

pollutants, most notably sulfur dioxide and 

particulate sulfates. 

(2) While ambient particles play a role in 

the corrosion of metals and in the weathering 

of materials, no quantitative relationships 

between ambient particle concentrations and 

rates of damage have been established. 

(3) While soiling associated with fine and 

course particles can result in increased 

cleaning frequency and repainting of 

surfaces, no quantitative relationships 

between particle characteristics and the 

frequency of cleaning or repainting have been 

established. 

(4) Limited new data on the role of 

microbial colonizers in biodeterioration 


tkelley on DSK3SPTVN1PROD with 
3204 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

184As summarized in section VI.A and Table 1 

above, the current suite of secondary PM standards 

includes annual and 24-hour PM2.5 standards and 

a 24-hour PM10 standard. 

processes and contributions of black crust to 

soiling are not sufficient for quantitative 

analysis. 

(5) While several studies in the PM 

Integrated Science Assessment and NOX/SOX

Integrated Science Assessment suggest that 

particles can promote corrosion of metals 

there remains insufficient evidence to relate 

corrosive effects to specific particulate levels 

or to establish a quantitative relationship 

between ambient PM and metal degradation. 

With respect to damage to calcareous stone, 

numerous studies suggest that wet or dry 

deposition of particles and dry deposition of 

gypsum particles can enhance natural 

weathering processes. 

The Policy Assessment concluded 

that none of the new evidence in this 

review called into question the 

adequacy of the current standards for 

protecting against material damage 

effects, that such effects could play no 

quantitative role in determining 

whether revisions to the secondary PM 

NAAQS are appropriate at this time, 

and that observations continue to 

support retaining an appropriate degree 

of control on both fine and coarse 

particles to help address materials 

damage and soiling associated with PM 

(U.S. EPA, 2011a, p. 5–29). 

b. CASAC Advice 

In advising the EPA regarding the 

non-visibility welfare effects, CASAC 

stated that it ‘‘concurs with the Policy 

Assessment’s conclusions that while 

these effects are important, and should 

be the focus of future research efforts, 

there is not currently a strong technical 

basis to support revisions of the current 

standards to protect against these other 

welfare effects’’ (Samet, 2010c). More 

specifically, with regard to climate 

impacts, CASAC concluded that while 

there is insufficient information on 

which to base a national standard, the 

causal relationship is established and 

the risk of impacts is high, so further 

research on a regional basis is urgently 

needed (Samet, 2010c, p. 5). CASAC 

also noted that reducing certain aerosol 

components could lead to increased 

radiative forcing and regional climate 

warming while having a beneficial effect 

on PM-related visibility. As a 

consequence, CASAC noted that a 

secondary standard directed toward 

reducing PM-related visibility 

impairment has the potential to be 

accompanied by regional warming if 

light scattering aerosols are 

preferentially targeted. 

With regard to ecological effects, 

CASAC concluded that the published 

literature is insufficient to support a 

national standard for PM effects on 

ecosystem services (Samet, 2010c, p.23). 

CASAC noted that the best-established 

effects are related to particles containing 

nitrogen and sulfur, which are being 

considered in the EPA’s ongoing review 

of the secondary NAAQS for NOX/SOX. 

With regard to PM-related effects on 

materials, CASAC concluded that the 

published literature, including literature 

published since the last review, is 

insufficient either to call into question 

the current level of the standard or to 

support any specific national standard 

for PM effects on materials (Samet, 

2010c, p.23). Nonetheless, with regard 

to both types of effects, CASAC noted 

the importance of maintaining an 

appropriate degree of control of both 

fine and coarse particles to address such 

effects, even in the current absence of 

sufficient information to develop a 

standard. 

c. Summary of Proposed Decisions 

Regarding Other Welfare Effects 

Based on the above considerations 

and the advice of CASAC, at the time of 

proposal the Administrator 

provisionally concluded that it would 

not be appropriate to establish any 

distinct secondary PM standards to 

address other non-visibility PM-related 

welfare effects, including ecological 

effects, effects on materials, and climate 

impacts. Nonetheless, the Administrator 

concurred with the conclusions of the 

Policy Assessment and CASAC advice 

that it is important to maintain an 

appropriate degree of control of both 

fine and coarse particles to address such 

effects. Noting that there is an absence 

of information that would support any 

different standards, the Administrator 

proposed generally to retain the current 

suite of secondary PM standards 184 to 

address non-visibility welfare effects. 

Specifically, the Administrator 

proposed to retain all aspects of the 

current secondary 24-hour PM2.5 and 

PM10 standards. With regard to the 

secondary annual PM2.5 standard, the 

Administrator proposed to retain the 

level of the current standard and to 

revise the form of the standard by 

removing the option for spatial 

averaging consistent with this change to 

the primary annual PM2.5 standard. 

C. Public Comments on Proposed 

Decisions Regarding Secondary PM 

Standards 

The EPA received a large number of 

comments on its proposed decisions 

with regard to secondary PM standards, 

with the large majority of those 

comments focusing on the proposal to 

set a distinct standard to protect against 

visibility impairment, discussed below 

in section VI.C.1. Very few commenters 

addressed the proposal to retain the 

existing secondary standards for nonvisibility welfare effects, discussed 

below in section VI.C.2. As discussed in 

section VI.D. below, the Administrator 

has decided to retain the current suite 

of secondary PM standards generally, 

while revising only the form of the 

secondary annual PM2.5 standard to 

remove the option for spatial averaging 

consistent with this change to the 

primary annual PM2.5 standard. The 

Administrator has also decided, 

contrary to what was proposed, not to 

establish a distinct secondary standard 

to address PM-related visibility 

impairment. This section discusses 

EPA’s responses to the comments EPA 

received on its proposal, and the 

rationale behind the Administrator’s 

final decisions is discussed in section 

VI.D. below. 

1. Comments on Proposed Secondary 

Standard for Visibility Protection 

a. Overview of Comments 

Among those commenting on the 

proposal to set a distinct secondary 

PM2.5 visibility index standard, a large 

majority of commenters, including more 

than 25 state and local agencies; 

regional organizations such as NACAA, 

NESCAUM, and WESTAR; and industry 

commenters, such as ACC, API, BP, 

EPRI, NCBA, NEDA–CAP, NMA, 

NSSGA, and UARG, opposed setting a 

distinct secondary standard for visibility 

at this time. Many commenters in this 

group expressed the view that such a 

standard was not needed, primarily on 

the basis that adequate protection was 

provided by the existing 24-hour 

secondary PM2.5 standard. Some of these 

commenters also expressed legal 

concerns with the nature of the 

proposed standard. Other commenters 

in this group supported a distinct 

secondary standard for visibility in 

concept, but expressed the view that it 

was premature to set such a standard 

pending collection of additional 

visibility preference study data and the 

resolution of a number of key technical 

issues. Support for setting such a 

distinct secondary standard for visibility 

at this time came from a second group 

of commenters, including the 

Department of the Interior (National 

Park Service), several states, the MidAtlantic/Northeast Visibility Union 

(MANE–VU), the National Tribal Air 

Association (NTAA), environmental 

organizations such as the Appalachian 

Mountain Club, National Parks 

Conservation Association, Earthjustice 

(AMC, et al.) and the League of Women 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3205 

185Comments pertaining to implementation 

issues, which the Administrator may not consider 

in making decisions about setting national ambient 

air quality standards, are discussed in the Response 

to Comments document, as are comments regarding 

monitoring issues related to the proposed distinct 

visibility index standard. 

186Some commenters expressed concern about 

the omission of other contributors to visibility 

impairment from the visibility index, as discussed 

in the Response to Comments document. 

Voters of Texas. These commenters 

argued that the existing secondary 

standards are not sufficiently protective 

of visual air quality, and that a distinct 

secondary standard similar to the 

proposed visibility index standard is 

both necessary and appropriate to 

ensure adequate protection of visibility. 

Commenters in both groups expressed 

concerns about various aspects of the 

proposed distinct secondary standard, 

including the indicator, averaging time, 

level, and form. In addition, a large 

number of commenters, including 

commenters from both groups, 

expressed concern and/or confusion 

over the relationship between the 

Regional Haze Program and the 

proposed distinct secondary standard 

for visibility, raising issues such as 

analytical differences in methods 

between the programs, monitoring 

issues, and other implementation 

challenges. 

A discussion of the significant 

comments outlined above, including 

EPA’s responses to the comments, is 

presented here, with more detailed 

discussion in the Response to 

Comments document. Comments 

relating to the specific elements of the 

proposed standard—indicator, averaging 

time, form and level—are discussed in 

sections VI.C.1.b-e, respectively. 

Comments related to the need for a 

distinct secondary standard at this time 

are discussed in section VI.C.f. Legal 

issues raised by commenters opposed to 

setting a secondary standard based on 

the proposed visibility index are 

discussed in section VI.C.g. Finally, 

comments related to the relationship 

between a distinct secondary standard 

and the Regional Haze Program are 

discussed in section VI.C.h.185 While 

the EPA concludes in section VI.D 

below to retain the current suite of 

secondary PM2.5 standards, the 

appropriateness of the protection that 

would be provided by the proposed 

PM2.5 visibility index standard, and the 

relationship between this degree of 

protection and that provided by the 

current secondary 24-hour secondary 

PM2.5 standard, are key elements in the 

Administrator’s decision, and are 

discussed below. 

b. Indicator 

Numerous commenters, both those 

supporting a distinct secondary 

standard and those opposed to setting 

such a standard, expressed views on the 

suitability of utilizing a PM2.5 calculated 

light extinction indicator for the 

standard as proposed. While these 

groups of commenters differed in terms 

of their views on the appropriateness of 

using calculated PM2.5 light extinction 

as the basis for the indicator rather than 

relying on direct measurements of PM2.5

light extinction, commenters from both 

groups expressed concern over specific 

elements of the proposed method of 

calculating PM2.5 light extinction. In 

particular, commenters expressed 

differing views on which IMPROVE 

algorithm should be utilized; whether it 

is appropriate to exclude coarse 

particles from the indicator; and 

whether the proposed protocols for 

incorporating data on relative humidity 

and PM2.5 species are appropriate.186

i. Comments on Calculated vs. Directly 

Measured Light Extinction 

The majority of commenters in both 

groups noted the uncertainties 

associated with relying on a calculated 

light extinction indicator and stated a 

preference for utilizing direct light 

extinction measurements. However, 

recognizing the limitations on applying 

direct measurements at present, 

commenters supporting the proposal to 

set a distinct standard argued that 

relying on ‘‘calculated light extinction is 

a reasonable first approach’’ (DOI, p. 2). 

These commenters pointed to the advice 

of CASAC, which had acknowledged 

that it was not possible for the EPA to 

develop an FRM for direct measurement 

of light extinction within the time frame 

of this review and had concluded that 

relying on a calculated PM2.5 light 

extinction indicator represented a 

reasonable approach that could be 

implemented sooner than a directly 

measured indicator. These commenters 

generally supported the proposal to 

adopt a calculated PM2.5 light extinction 

indicator, at least as an interim 

approach. 

Commenters opposed to setting a 

distinct standard generally argued that it 

was inappropriate to rely on a 

calculated light extinction indicator 

rather than direct measurements. Some 

of these commenters argued that the 

proposed calculated light extinction 

indictor is ill suited for a bright line 

standard because the method uses 

average humidity and a reconstructed 

visibility measurement calculated from 

PM2.5 speciation filter analysis, rather 

than measuring what is actually 

observed by individuals. A number of 

commenters advocated postponing 

setting a distinct standard until an 

approach based on direct light 

extinction measurements can be 

adopted. Many of these commenters 

stated that relying on direct light 

extinction measurements would enable 

a standard to be based on a shorter 

averaging time, either 1-hour or subdaily (4 to 6 hours), consistent with the 

more instantaneous nature of 

perceptions of visual air quality and the 

advice of CASAC in this review. 

The EPA generally agrees with 

commenters that an indicator based on 

directly measured light extinction 

would provide the most direct link 

between PM in the ambient air and PMrelated light extinction. However, as 

noted at the time of proposal and in 

accordance with the advice of CASAC, 

the EPA has concluded that this is not 

an appropriate option in this review 

because a suitable specification of 

currently available equipment or 

performance-based verification 

procedures could not be developed in 

the time frame of this review. Moreover, 

CASAC concluded that relying on a 

calculated PM2.5 light extinction 

indicator based on PM2.5 chemical 

speciation and relative humidity data 

represented a reasonable approach. The 

inputs that are necessary include 

measurements that are available through 

existing monitoring networks and 

approved protocols. Thus, the EPA 

remains confident that the available 

evidence demonstrates that a strong 

correspondence exists between 

calculated PM2.5 light extinction and 

PM-related visibility impairment. 

Furthermore, CASAC agreed, noting that 

the proposed calculated PM2.5 light 

extinction indicator based on the 

original IMPROVE algorithm ‘‘appears 

to be a reasonable approach for 

estimating hourly light extinction’’ 

(Samet, 2010d, p. 11) and ‘‘its reliance 

on procedures that have already been 

implemented in the CSN and routinely 

collected continuous PM2.5 data suggest 

that it could be implemented much 

sooner than a directly measured 

indicator’’ (Samet, 2010d, p. iii). Thus it 

would not be appropriate to postpone 

setting a distinct secondary standard 

until an approach based on direct light 

extinction measurements could be 

adopted. 

ii. Comments on Specific Aspects of 

Calculated Light Extinction Indicator 

Some commenters, even those 

supporting the adoption of a calculated 

light extinction indicator, also 

expressed concern over specific aspects 

of the proposed indicator. First, a 


tkelley on DSK3SPTVN1PROD with 
3206 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

187Specifically, the revised IMPROVE algorithm 

incorporates additional terms to account for 

particles representing the different dry extinction 

and water uptake (f(RH)) from two size modes of 

sulfate, nitrate and organic mass, as well as adding 

a term for hygroscopic sea salt. There are also 

adjustments for the calculation of OM as 1.8*OC 

compared to 1.4*OC in the original algorithm to 

better account for the more aged PM organic 

components found in remote areas. 

188Starting in 2007, the CSN adopted the 

IMPROVE monitoring protocol for the measurement 

of organic and elemental carbon using the 

IMPROVE analytical method and an IMPROVE-like 

sampler. The transition was completed in 2009. 

(See ‘‘Modification of Carbon Procedures in the 

Speciation Network,’’ http://www.epa.gov/ttn/ 

amtic/files/ambient/pm25/spec/faqcarbon.pdf.) 

number of commenters expressed 

concern over the proposal to use the 

original IMPROVE algorithm as the 

basis for the calculated light extinction 

indicator. These commenters noted that 

the original IMPROVE algorithm has 

been shown to have consistent biases at 

both low and high levels of light 

extinction. In particular, these 

commenters expressed concern with the 

algorithm’s bias at higher levels of light 

extinction, which they pointed out were 

the conditions that might be 

encountered on hazier days in urban 

areas. 

Some commenters supported use of 

the revised IMPROVE algorithm. These 

commenters noted that the revised 

equation has been through a peer review 

which confirmed that it is based on the 

best science and corrects the biases 

inherent in the original algorithm. 

Commenters also noted that this revised 

algorithm has been widely incorporated 

into Regional Haze plans, and urged the 

EPA to use this same equation in the 

visibility index for the sake of 

consistency: ‘‘EPA approved this 

approach for regional haze and does not 

dispute its greater accuracy. Therefore, 

a national secondary ambient air quality 

standard based on criteria that 

accurately reflect the latest scientific 

knowledge logically should not revert to 

the original IMPROVE algorithm’’ 

(Oklahoma DEQ, p. 2). Other 

commenters noted that both the original 

and the revised IMPROVE algorithms 

were designed in support of the 

Regional Haze Program which is 

focused on largely rural Class I areas, 

and that neither algorithm is necessarily 

suitable for urban areas. Noting that the 

EPA has not thoroughly evaluated the 

applicability of either IMPROVE 

algorithm in urban areas, these 

commenters urged additional research 

to evaluate the suitability of either 

algorithm (or an alternative approach) in 

urban areas. 

Second, a number of commenters 

argued that exclusion of coarse PM from 

the calculated light extinction indicator 

was inappropriate. These commenters 

noted that coarse particulate matter is 

an important contributor to visibility 

impairment in many areas, particularly 

in the western U.S., and that the levels 

of ‘‘acceptable’’ visual air quality 

derived from the visibility preference 

studies reflected total light extinction 

due to the full mix of particles 

(including coarse PM) in ambient air. A 

few commenters noted that due to the 

exclusion of coarse particles, a 

‘‘deciview’’ calculated for purposes of 

the proposed PM2.5 visibility index is 

inconsistent with the unit as 

conventionally defined under the 

Regional Haze Program. Other 

commenters, however, supported the 

proposal to exclude coarse PM from the 

calculated light extinction indicator, 

noting the important role that PM2.5

plays in urban visibility and arguing it 

would be more difficult to control the 

contribution of coarse particle sources 

such as wind-blown dust to urban 

visibility impairment. 

Third, some commenters questioned 

why the EPA was proposing to rely on 

monthly average relative humidity 

(f(RH)) values when hourly humidity 

data are widely available, particularly in 

urban areas. One commenter argued that 

the EPA’s proposed approach involves 

‘‘guessing relative humidity’’ rather than 

relying on accurate, readily available 

measurements (Oklahoma DEQ, p. 1). 

The commenter stated that since relative 

humidity is highly variable and weather 

dependent, the proposed approach 

‘‘effectively undermines the capacity of 

the prescribed monitoring regime to 

identify periods when PM2.5 adversely 

affects visibility.’’ Other commenters 

supported this view, noting that relative 

humidity can vary substantially even 

within a 24-hour period, and that light 

extinction can be very sensitive to these 

changes. These commenters 

recommended that hourly or daily 

humidity measurements should be 

utilized in place of the proposed 

monthly average f(RH) values. 

Some commenters also recommended 

that the EPA should utilize a 90 percent 

relative humidity screen rather than 95 

percent cap for purposes of eliminating 

periods in which visibility impairment 

is due to rain or fog. These commenters 

claimed that under a 95 percent cap, 

both the average f(RH) values and the 

PM2.5 visibility index values could be 

inflated in locations frequently affected 

by fog and/or precipitation. These 

commenters preferred the approach of 

excluding hours with relative humidity 

above 90 percent on the grounds that 

this approach would eliminate foggy/ 

rainy hours irrespective of the frequency 

of occurrence. 

The EPA does not agree with 

commenters who advocated using the 

revised IMPROVE algorithm. Both the 

original and the revised IMPROVE 

algorithms have been evaluated by 

comparing the calculated estimates of 

light extinction with coincident optical 

measurements. As discussed above in 

section VI.B.1.a.i, the revised algorithm 

was developed to address observed 

biases in the predictions using the 

original algorithm under very low and 

very high light extinction conditions, 

with further modifications and 

additions to better account for 

differences in particle composition and 

aging in remote areas.187 However, the 

EPA does not believe that these same 

modifications and additions would 

necessarily be appropriate for 

calculating light extinction in urban 

areas. Instead, the EPA considers the 

original algorithm to be suitable for 

purposes of calculating urban lightextinction, although some adjustments 

may be appropriate for urban 

environments as well. The reasons why 

the original algorithm is suited to urban 

environments are discussed further 

below, along with adjustments that the 

EPA believes are likely appropriate 

based on the current (limited) state of 

knowledge. 

First, the EPA considers that the 

multiplier of 1.8 used to convert OC to 

OM in the revised IMPROVE algorithm 

is too high for urban environments. The 

EPA is aware that there has been 

considerable debate within the research 

community about the appropriate 

multiplier to use to best represent urban 

environments. As discussed in 

Appendix F of the Policy Assessment 

(U.S. EPA, 2011a), the EPA used the 

SANDWICH mass closure approach 

(Frank, 2006) in the Urban Focused 

Visibility Assessment (U.S. EPA, 2010b) 

for purposes of calculating maximum 

daylight hourly PM2.5 light extinction 

and evaluated which multiplier would 

produce 24-hour results most similar to 

the SANDWICH approach using 24-hour 

PM2.5 organic carbon derived from the 

new Chemical Speciation Network 

(CSN) carbon monitoring protocol 

established in 2007.188 Analyses 

presented in Appendix F of the Policy 

Assessment indicate that a multiplier of 

1.6 is most appropriate for purposes of 

comparing the hourly PM2.5 light 

extinction with calculated 24-hour 

extinction (see Appendix F, section F.6 

for a full explanation). The EPA also 

considers this higher multiplier to be a 

better approach for urban CSN 

monitoring sites where the new 

measurements of organic carbon tend to 

be lower than those produced by the 

older NIOSH-type monitoring protocol 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3207 

189The difference between higher PM2.5 mass in 

urban areas compared to surrounding regions, 

known as the urban excess, is largely attributed to 

organic mass (U.S. EPA, 2004b). 

190The implications of this shift to a 1.6 

multiplier for OC in urban areas for decisions about 

averaging time, level, and need for a distinct 

secondary standard are discussed further below in 

sections VI.C.1.c, VI.C.1.e, and VI.C.1.f, 

respectively. 

(Malm, 2011). A multiplier of 1.6 is now 

used to calculate OM from OC 

measurements at CSN sites. 

At the time of proposal, the EPA 

proposed to use the original IMPROVE 

algorithm with its 1.4 multiplier for 

converting OC to OM, but requested 

comment on whether this value was 

appropriate. Comments received by the 

Agency generally indicate that the OCto-OM multiplier of 1.4 used in the 

original IMPROVE algorithm is too low 

for urban areas. Based on the analyses 

presented in Appendix F of the Policy 

Assessment, the EPA agrees with these 

commenters. However, the EPA also 

believes that it would be inappropriate 

to use a multiplier as high as 1.8 to 

convert OC to OM in urban areas. As 

noted by commenters, the organic mass 

contribution to visibility impairment 

can be large, and generally OM is 

significantly larger in urban areas 

compared to surrounding rural areas.189

Because a large portion of the organic 

component of urban PM results from 

nearby emissions sources, the total OM 

mass is generally closer to the measured 

OC from which it is derived. This means 

it is appropriate to use a smaller 

multiplier to convert OC to OM in urban 

areas as compared to the value of 1.8 

used in the revised algorithm, which is 

tailored to remote areas. The CASAC 

noted that urban OM includes fresh 

emissions and the EPA concluded in the 

Visibility Assessment that ‘‘the original 

version is considered more 

representative of urban situations when 

emissions are still fresh rather than aged 

as at remote IMPROVE sites’’ (U.S. EPA, 

2010b, p. 3–19). Although the revised 

algorithm represents the best science of 

estimating extinction in remote areas 

with its aged aerosol, the commenters 

did not address how the EPA should 

modify the revised algorithm to best 

represent the more complex and 

different urban aerosol, particularly for 

OM. In light of all of these 

considerations, in particular the 

analyses the EPA conducted for 

Appendix F of the Policy Assessment 

and the fact that the monitoring method 

for organic carbon has recently changed 

in the CSN network, the EPA judges that 

a multiplier of 1.6 for urban areas would 

be most appropriate for purposes of 

calculating PM2.5 light extinction in 

urban areas.190 In formulating this 

judgment, the EPA recognizes that 

neither the original nor the revised 

IMPROVE algorithm has been tested for 

suitability in urban areas and that 

additional research is necessary to 

reduce the uncertainties about the most 

appropriate value for the OC to OM 

multiplier in urban environments. With 

regard to other changes between the 

original and revised IMPROVE 

algorithms, the EPA also does not 

believe that it would be appropriate to 

include a term for hygroscopic sea salt 

for urban light extinction, or to 

differentiate between different size 

modes of sulfate, nitrate, and organic 

mass as empirically defined by the 

revised IMPROVE algorithm. Unlike in 

some remote coastal locations, sea salt 

is not major contributor to light 

extinction in urban areas. Moreover, 

urban sources of salt include sanding of 

roads during the winter and those reentrained particles are mostly in the 

coarse size range. 

Like in remote areas, small and large 

size modes of sulfate, nitrate and 

organic mass would exist in the urban 

environment. However, the 

apportionment of the total fine particle 

concentration of each of the three PM2.5

components into the concentrations of 

the small and large size fractions would 

likely need a different approach than 

that used for remote areas. This is 

because of the closer proximity of urban 

sources to their emissions. This is a 

particular concern not only for organic 

mass, which as explained previously 

has a large contribution from nearby 

urban emission sources, but also for 

PM2.5 nitrate whose concentrations are 

also higher in urban areas compared to 

the surrounding regions. Thus, a higher 

portion of the total urban concentration 

may be in the small mode compared to 

remote areas and thus a different 

apportionment algorithm would be 

needed. 

Finally, the EPA does not consider it 

necessary to employ site-specific 

Rayleigh light scattering terms in place 

of a universal Rayleigh light scattering 

value for purposes of calculating light 

extinction in urban areas for purposes of 

calculating the 90th percentile values. 

The site-specific Rayleigh value is most 

important to accurately estimate 

extinction on the best visibility days 

which is an essential metric for the 

regional haze program. 

For all of these reasons, the EPA 

considers the original IMPROVE 

algorithm better suited to the task of 

calculating urban light extinction than 

the revised IMPROVE algorithm. 

However, the EPA does consider it 

appropriate to make certain adjustments 

to the original algorithm for purposes of 

calculating urban light extinction. As 

discussed above, the EPA believes it is 

appropriate to use a 1.6 multiplier to 

convert OC to OM in urban areas. In 

addition, the EPA believes it is 

appropriate to exclude the term for 

coarse particles from the equation. The 

EPA does not agree with commenters 

who suggested that coarse particles 

should be included in the calculated 

light extinction indicator. As noted in 

the proposal, PM2.5 is the component of 

PM responsible for most of the visibility 

impairment in most urban areas. 

Currently available data suggest that 

PM10-2.5 is a minor contributor to 

visibility impairment most of the time, 

although at some locations (U.S. EPA, 

2010b, Figure 3–13 for Phoenix) PM10-2.5

can be a major contributor to urban 

visibility effects. While it is reasonable 

to assume that other urban areas in the 

desert southwestern region of the 

country may have conditions similar to 

the conditions shown for Phoenix, in 

fact few urban areas conduct continuous 

PM10-2.5 monitoring. This significantly 

increases the difficulty of assessing the 

role of coarse particles in urban 

visibility impairment. For example, 

among the 15 urban areas assessed in 

this review, only four areas had 

collocated continuous PM10 data 

allowing calculation of hourly PM10-2.5

data for 2005 to 2007. In addition, 

PM10-2.5 is generally less homogenous in 

urban areas than PM2.5 in that coarse 

particle concentrations exhibit greater 

temporal variability and a steeper 

gradient across urban areas than fine 

particles (U.S. EPA, 2009a, p. 3–72). 

This makes it more challenging to select 

sites that would adequately represent 

urban visibility conditions. Thus, while 

it would be possible to include a 

PM10-2.5 light extinction term in a 

calculated light extinction indicator, as 

was done in the Visibility Assessment, 

there is insufficient information 

available at this time to assess the 

impact and effectiveness of such a 

refinement in providing public welfare 

protection in areas across the country 

(U.S. EPA, 2011a, pp. 4–41 to 4–42). 

Therefore, the EPA concludes that it is 

not appropriate to set a standard based 

on a calculated light extinction 

indicator that includes coarse particles 

at this time, and the calculated indicator 

should be based on PM2.5 light 

extinction. 

With regard to the suggestion by some 

commenters that the calculated light 

extinction indicator should be 

calculated using hourly humidity data, 


tkelley on DSK3SPTVN1PROD with 
3208 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

the EPA disagrees that concurrent 

humidity measurements should be used. 

The use of longer-term averages for each 

monitoring site adequately captures the 

seasonal variability of relative humidity 

and its effects of visibility impairment, 

and this approach focuses more on the 

underlying aerosol contributions to 

visibility impairment and less on the 

day-to-day variations in humidity. This 

provides a more stable indicator for 

comparison to the NAAQS and one that 

is more directly related to the 

underlying emissions that contribute to 

visibility impairment. 

With regard to the comments 

advocating the use of a 90 percent 

humidity screen as opposed to a 95 

percent humidity cap, the EPA believes 

that relying on monthly average relative 

humidity values based on 10 years of 

climatological data appropriately 

reduces the effect of fog and 

precipitation. Although the approach of 

using a 95 percent humidity cap, as in 

the Regional Haze Program, includes 

some hours with relative humidity 

between 90–95 percent, the general 

approach of using a longer-term average 

for each monitoring site effectively 

eliminates the effect of very high 

humidity conditions on visibility at 

those locations. 

Therefore, taking all of the above 

considerations and CASAC advice into 

account, the EPA continues to conclude 

that a calculated PM2.5 light extinction 

indicator, similar to that used in the 

Regional Haze Program (i.e., using an 

IMPROVE algorithm as translated into 

the deciview scale), would be the most 

appropriate indicator to replace the 

current PM2.5 mass indicator for a 

distinct secondary standard. Moreover, 

the EPA continues to conclude that this 

calculated indicator should based on the 

original IMPROVE algorithm, adjusted 

to use a 1.6 OC multiplier and exclude 

the term for coarse particles, in 

conjunction with monthly average 

relative humidity data (i.e., f(RH) 

values) based on long-term 

climatological means as used in the 

Regional Haze Program. A PM2.5

visibility index defined in this way 

would appropriately reflect the 

relationship between ambient PM and 

PM-related light extinction, based on 

the analyses discussed in the proposal 

and reflecting the aerosol and relative 

humidity contributions to visibility 

impairment by incorporation of factors 

based on measured PM2.5 speciation 

concentrations and climatological 

average relative humidity data. In 

addition, this type of indicator would 

address, in part, the issues raised in the 

court’s remand of the 2006 PM2.5

standards. Such a PM2.5 visibility index 

would afford a relatively high degree of 

uniformity of visual air quality 

protection in areas across the country by 

virtue of directly incorporating the 

effects of differences in PM2.5

composition and relative humidity 

across the country. 

c. Averaging Time 

Few commenters specifically 

addressed the issue of averaging time. 

Those who did generally expressed the 

view that an hourly or sub-daily 

averaging time would be the most 

appropriate approach, as supported by 

CASAC and the EPA’s own analyses in 

this review. These comments were 

generally consistent with the emphasis 

among all commenters on the 

desirability of adopting a directly 

measured light extinction indicator that 

could be measured on an hourly or subdaily time scale. Some commenters 

noted that a standard based on a 4–6 

hour averaging time would better 

capture peak daily light extinction 

while allowing stable signal quality; 

others urged EPA to adopt a 1-hour 

averaging time in conjunction with 

direct measurements. Commenters 

pointed to significant limitations 

associated with using a 24-hour 

averaging time, including the 

uncertainties in translating hourly or 

sub-daily visibility index values into 24- 

hour equivalent values. Some 

commenters criticized the analysis 

presented in the Policy Assessment 

comparing the 24-hour calculated light 

extinction values to the maximum 

daylight 4-hour calculated light 

extinction values. These commenters 

stated that the scatter plots and 

regressions presented in the Policy 

Assessment indicate there is 

considerable variation in the 24-hour vs. 

4-hour relationship, and interpreted this 

to mean that 24-hour light extinction 

values are a poor surrogate for 4-hour 

values. For example, several industry 

commenters cited an analysis which 

noted that the correlation coefficient 

between the 24-hour and 4-hour values 

was as low as r2 = 0.42 in Houston, and 

stated that the EPA was being overly 

‘‘optimistic’’ in concluding that cityspecific and pooled r2 values in the 

range of 0.6 to 0.8 showed good 

correlation (UARG, Attachment 2, p. 

27). 

In addition, some commenters 

expressed concern over potential bias 

and greater uncertainty introduced by 

the inclusion of nighttime hours, noting 

that because relative humidity tends to 

be higher at night, inclusion of these 

hours could cause areas to ‘‘record 

NAAQS exceedances that have no 

corresponding visibility impairment 

value’’ (UARG, p. 36). Commenters also 

emphasized the poor fit of a 24-hour 

averaging time with the near 

instantaneous judgments about visibility 

impairment reflected in the visibility 

preference studies. Commenters also 

noted that there is greater hourly 

variation in PM concentrations and 

resulting visibility conditions in urban 

areas than in Class I areas; thus, while 

the Regional Haze Program uses 24-hour 

IMPROVE data, the commenters stated 

that a shorter averaging time is needed 

for an urban-focused PM2.5 visibility 

standard. Some commenters objected to 

a 24-hour averaging time as 

unsupported by the record in this 

review: ‘‘Because the science the 

Administrator relies on for the other 

elements of the proposed visibility 

standard is tied to short-term exposures 

to visibility impairment, the EPA has no 

basis for promulgating a standard that 

uses a 24-hour averaging time’’ (API, p. 

43). These commenters claimed that 

while the EPA may not have the 

information or infrastructure in place to 

allow the Agency to set a standard based 

on a 1-hour or other sub-daily averaging 

time, this does not justify moving to a 

24-hour averaging time. 

Among commenters supporting the 

proposed distinct secondary standard 

for visibility, many commenters 

recognized the limitations on 

monitoring methods and currently 

available data that led to the EPA’s 

proposal to adopt a standard based on 

a 24-hour averaging time. Most of these 

commenters acknowledged that the lack 

of reliable hourly speciation data means 

that a 24-hour averaging time is the only 

workable approach for a standard based 

on calculated light extinction. 

Commenters advocating a distinct 

secondary standard for visibility 

therefore generally supported the 

proposal to adopt a 24-hour averaging 

time, at least as an interim approach 

until a directly measured light 

extinction indicator could be adopted in 

the future. This approach was also 

supported by a few industry 

commenters who noted that since a 

visibility index standard would be 

based on data from the IMPROVE and 

CSN monitors, which operate on a 24- 

hour basis with 1-in-3 (or 1-in-6) day 

sampling, ‘‘it is imperative that EPA 

retain a 24-hour averaging time if a 

secondary visibility standard is 

promulgated’’ (API, Attachment 2, p. 9). 

In response to comments supporting a 

1-hour or sub-daily (4- to 6- hour) 

averaging time in conjunction with a 

direct light extinction measurements, 

the EPA notes that, as discussed above 

in the response to comments on 

indicator, the Agency has concluded 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3209 

that a directly measured light extinction 

indicator is not an appropriate option in 

this review, independent of the decision 

on averaging time. Having reached the 

conclusion that a calculated PM2.5 light 

extinction indicator would be most 

appropriate, the EPA has next 

considered what averaging time would 

be most desirable for such an indicator. 

As noted in the proposal, the EPA has 

recognized that hourly or sub-daily (4- 

to 6-hour) averaging times, within 

daylight hours and excluding hours 

with high relative humidity, are more 

directly related than a 24-hour averaging 

time to the short-term nature of the 

perception of PM-related visibility 

impairment and the relevant exposure 

periods for segments of the viewing 

public. Thus, the Agency agrees with 

commenters’ general point that, as a 

starting premise, a sub-daily averaging 

time would generally be preferable. 

However, as noted at the time of 

proposal and discussed above in section 

VI.B.1.c, important data quality 

uncertainties have recently been 

identified in association with currently 

available instruments that would be 

used to provide the hourly PM2.5 mass 

measurements that would be needed in 

conjunction with an averaging time 

shorter than 24 hours. As a result, at this 

time the Agency has strong technical 

reservations about a secondary standard 

that would be defined in terms of a subdaily averaging time. The data quality 

issues which have been identified, 

including short-term variability in 

hourly data from currently available 

continuous monitoring methods, 

effectively preclude adoption of a 1- 

hour averaging time in this review, 

given the sensitivity of a 1-hour 

averaging time to these data quality 

limitations. Even with regard to multihour averaging times, the EPA continues 

to conclude that the data quality 

concerns preclude adoption of a subdaily averaging time. 

Moreover, analyses conducted for the 

Policy Assessment indicate that PM2.5

light extinction calculated on a 24-hour 

average basis would be a reasonable and 

appropriate surrogate for PM2.5 light 

extinction calculated on a 4-hour basis. 

The scatter plots comparing 24-hour and 

4-hour calculated PM2.5 light extinction 

in the Policy Assessment (U.S. EPA, 

2011a, Figures G–4 and G–5) do show 

some scatter around the regression line 

for each city. This was to be expected, 

since the calculated 4-hour light 

extinction includes day-specific and 

hour-specific influences that are not 

captured by the simpler 24-hour 

approach. Overall, however, in the 

EPA’s view, both the city-specific and 

pooled 15-city 24-hour vs. 4-hour 

comparisons show strong correlation 

between the two averaging times. 

Moreover, the 90th percentile design 

values calculated for 4-hour vs. 24-hour 

light extinction are much more closely 

correlated than are the values for 

individual days in particular urban 

areas calculated using these two 

approaches. Thus, while the EPA agrees 

with commenters who pointed out the 

relatively low correlation between 4- 

and 24-hour values in cities such as 

Houston, the Agency points out that the 

correlations of 90th percentile values 

are much higher, particularly when one 

considers the average values across 

urban areas. In general, the 90th 

percentile values line up better and 

demonstrate closer to a one-to-one 

relationship. 

The EPA has conducted a reanalysis 

(Frank et al., 2012b) of the relationships 

between estimated 24-hour and 4-hour 

visibility impairment based on the 

variety of metrics discussed in 

Appendix G of the Policy Assessment 

that further supports this finding. The 

reanalysis more appropriately 

considered the uncertainty of the 

calculated 4-hour values. It also 

considered the effect of changing the OC 

to OM multiplier used in urban areas 

with the new CSN monitoring protocol 

from 1.4 to 1.6. The revised analysis 

shows that the 24-hour values are 

generally closer to the 4-hour values 

than originally estimated. 

Since conclusions in the proposal 

about the relationship between 4-hour 

and 24-hour values were drawn not just 

on the basis of the city-specific results 

but also on the more robust 90th 

percentile values, the EPA disagrees 

with commenters who state that the 

Agency was overly optimistic in 

considering 24-hour values an 

appropriate surrogate for 4-hour values. 

Also, it is appropriate to focus on the 

90th percentile design value comparison 

since the design values would 

determine attainment status and the 

degree of improvement in air quality 

that could be expected in areas 

instituting controls to meet the NAAQS. 

Therefore the EPA does not agree with 

commenters who state that a 24-hour 

averaging time cannot serve as an 

appropriate surrogate for sub-daily 

periods of visibility impairment. On the 

contrary, the EPA continues to 

conclude, on the basis of this analysis, 

that PM2.5 light extinction calculated on 

a 24-hour basis is a reasonable and 

appropriate surrogate for sub-daily 

PM2.5 light extinction calculated on a 4- 

hour basis. 

The EPA recognizes that the effect of 

adopting a 24-hour averaging time may 

be to smooth out some of the hour-byhour variability in visibility index 

values. (Indeed, this is true if we 

compare a 4-hour averaging time to a 1- 

hour averaging time as well.) Hourspecific influences which would be 

evident if an hourly or sub-daily 

averaging time were to be used will be 

masked to some extent when those 

hours are averaged together with other 

hours. This means, in part, that a 24- 

hour averaging time may effectively 

reduce peak values by means of 

averaging them together with other 

hours, which may have lower values. 

However, given the well documented 

variability in hourly visibility 

conditions, especially in urban areas, as 

noted by commenters, it is reasonable to 

assume that in some cases peak hours 

may be significantly influenced by 

atypical conditions, making it 

appropriate to adopt an averaging time 

that is sufficiently long to ensure that 

hour-specific influences are balanced 

against more typical conditions. Perhaps 

even more important is the concern that 

many peak hourly measurements may 

be significantly influenced by atypical 

instrument performance; this reinforces 

the conclusion that it is appropriate to 

adopt a longer averaging time, to ensure 

that hour-specific uncertainties are 

balanced against more robust 

measurements. 

Thus, in agreement with commenters 

who supported a daily averaging time, 

the EPA concludes that a 24-hour 

averaging time would be appropriate for 

a distinct secondary standard based on 

a calculated PM2.5 light extinction 

indicator. 

d. Form 

The EPA received very few comments 

with regard to the proposal to adopt a 

90th percentile form, averaged over 3- 

years, in conjunction with a PM2.5

visibility index and a 24-hour averaging 

time. One commenter stated that it was 

inappropriate to use a 90th percentile 

form, noting that this would result in 

the exclusion of a minimum of 36 days 

of data annually. The commenter 

expressed particular concern that this 

proposed approach, in combination 

with a 24-hour standard based on an 

unadjusted CPL, would not capture the 

worst visibility impairment and that this 

would undermine ‘‘the intent of setting 

a meaningful secondary visibility 

standard’’ (AMC, et al., p. 2). Another 

commenter argued that the EPA had 

provided no scientific basis for why the 

90th percentile form was suitable, and 

claimed that the Agency was making ‘‘a 

somewhat arbitrary judgment that 

people’s welfare would be affected only 

if adverse urban visibility were to occur 


tkelley on DSK3SPTVN1PROD with 
3210 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

more than 10 percent of the time’’ (API, 

Attachment 2, p. 4). 

On other hand, a few commenters 

who appeared to generally support the 

proposal to use a 90th percentile form 

advocated averaging the 90th percentile 

values over longer time periods, arguing 

that averaging over only 3 years would 

not provide a stable assessment of visual 

air quality in the West because this time 

period is insufficient to properly 

account for western drought and fire 

cycles. These commenters pointed to 

the approach in the Regional Haze 

Program of averaging visibility 

impairment over 5 years, and noted that 

even within this longer time period data 

can be significantly influenced by high 

emissions during significant fire years. 

The EPA disagrees with all of these 

comments. With regard to the comment 

opposing the 90th percentile form as 

inappropriately excluding the worst 

visibility days, the EPA notes that there 

is a significant lack of information on, 

and a high degree of uncertainty 

regarding, the impact on public welfare 

of the number of days with visibility 

impairment over the course of a year. 

For example, the visibility preference 

studies used to derive the range of CPLs 

considered in this review offered no 

information regarding the frequency of 

time that visibility levels should be 

below those values. Based on this 

limitation, the EPA concluded in the 

Policy Assessment that it would not be 

appropriate to consider eliminating all 

exposures above the level of the 

standard and that it was reasonable to 

consider allowing some number of days 

with reduced visibility. Recognizing 

that the Regional Haze Program focuses 

attention on the 20 percent worst 

visibility days (i.e., those at or above the 

80th percentile of visibility 

impairment), the EPA continues to 

believe, as noted in the proposal, that a 

percentile well above the 80th 

percentile would be appropriate to 

increase the likelihood that all days in 

this range would be improved by 

control strategies intended to help areas 

attain the standard. Focusing on the 

90th percentile, which represents the 

median of the distribution of the 20 

percent worst visibility days, could be 

reasonably expected to lead to 

improvements in visual air quality on 

the 20 percent most impaired days. 

Thus, the EPA has made a reasoned 

judgment based on a full consideration 

of the upper end of the distribution of 

visibility impairment conditions and 

continues to conclude that it is 

appropriate to focus on the 90th 

percentile of visibility impairment 

values. 

With regard to comments requesting 

the EPA adopt a longer multi-year 

averaging period for the 90th percentile 

values, the EPA disagrees that it would 

be appropriate to average the 90th 

percentile values over periods longer 

than 3 years. The EPA recognizes that a 

multi-year percentile form offers greater 

stability to the air quality management 

process by reducing the possibility that 

statistically unusual indicator values 

will lead to transient violations of the 

standard. Utilizing a 3-year average form 

provides stability from the occasional 

effects of inter-annual meteorological 

variability that can result in unusually 

high pollution levels for a particular 

year. The Agency has adopted this 

approach in other NAAQS, including 

the current secondary 24-hour PM2.5

NAAQS, which has a 98th percentile 

form averaged over 3 years. However, 

adopting a multi-year averaging period 

longer than 3 years would increase the 

number of days with visibility 

impairment above the target level of 

protection and would therefore reduce 

the protectiveness of the standard. 

Based on this the EPA does not believe 

it would be appropriate to average 90th 

percentile values over a period as long 

as five years. Therefore, the EPA 

continues to conclude that a 90th 

percentile form, averaged over 3 years, 

would be appropriate, in conjunction 

with a calculated PM2.5 light extinction 

indicator and a 24-hour averaging time. 

e. Level 

With regard to level, commenters 

focused on two main themes. First, a 

large number of commenters addressed 

the information available from the 

public preference studies with regard to 

the acceptability of various levels of 

visual air quality. These comments, 

which are discussed in subsection 

VI.C.1.e.i below, address the EPA’s use 

of visibility preference studies as the 

basis for the selection of a range of 

appropriate levels for the Administrator 

to consider. Many commenters 

challenged the use of these studies as 

the basis for setting a distinct secondary 

standard, arguing that limitations in 

these studies rendered them an 

unsuitable and insufficient basis on 

which to establish such a standard. 

Second, commenters expressed different 

views as to what level(s) of a distinct 

secondary standard would be 

appropriate, if the EPA were to set such 

a standard. These comments reflected 

consideration of the results of the public 

preference studies as well as analyses 

conducted in the Visibility Assessment 

and the Policy Assessment, as discussed 

in the proposal. Comments addressing 

the appropriateness of specific levels are 

discussed in subsection VI.C.1.e.ii 

below. 

i. Comments on Visibility Preference 

Studies 

A majority of commenters expressed 

the view that the existing preference 

studies provide an insufficient basis for 

selection by the Administrator of an 

appropriate level of public welfare 

visibility protection for a national 

standard. These commenters 

highlighted a number of limitations and 

uncertainties (enumerated below) 

associated with these studies as support 

for this view. In contrast, other 

commenters felt that despite certain 

limitations, these studies do provide a 

sufficient basis on which the 

Administrator can select an appropriate 

level of a standard to provide national 

public welfare visibility protection. The 

remainder of this section organizes and 

discusses these comments under four 

broad topic areas, including: (a) 

Limitations and uncertainties associated 

with the visibility preference studies; (b) 

preference study methods and design; 

(c) use of preference study results for 

determining adversity; (d) the 

appropriateness of using regionally 

varying preference study results to 

select a single level for a national 

standard. 

(a) Preference Study Limitations and 

Uncertainties 

A large and diverse number of 

limitations and uncertainties associated 

with the visibility preference studies 

have been identified and discussed in 

the public comments. Many of these 

same limitations and uncertainties were 

also identified and discussed by the 

EPA in the various documents 

developed throughout this review. The 

most important and fundamental 

limitations and uncertainties will be 

discussed here in the preamble, while 

more specific, unique or detailed 

comments will be addressed in the 

Response to Comments document. 

The primary or most frequent 

limitation cited by many commenters 

relates to the small number of 

preference studies that are available in 

this review. In particular, some 

commenters note that these preference 

studies cover just four locations, only 

three of which occur in the U.S., that 

the two studies conducted in 

Washington, DC were pilot studies, not 

full preference studies, and/or that three 

of the preference studies were 

conducted in the West, while only one 

was conducted in the East, providing 

only limited geographic coverage. 

Typically, these same commenters also 

pointed out that taken together, these 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3211 

limited studies only included a total of 

852 participants, which they claimed 

was too small a sample size and 

unrepresentative nationally. These 

commenters thus concluded that there 

is insufficient information, both 

geographically and demographically, 

upon which to select a national level of 

a visibility index for purposes of 

visibility protection. 

In contrast, several commenters stated 

support for using the preference studies, 

concluding they provide an adequate 

basis, in spite of their limited nature. In 

particular, AMC et al. state: 

We believe that these studies provide 

sufficient results to inform setting a national 

visibility standard. While the number of 

studies is small, they do incorporate spatial 

variation and, in the case of Denver and 

Phoenix, varied populations* * *. EPA 

should have confidence, rather than 

uncertainty, in the fact that these studies 

used different methods and respondents and 

yield a range of 20–24 dv, with one outlier 

of 29. (AMC, et al., pp. 6–7) 

Regarding the first group of 

commenters, the EPA notes that it is 

well aware of the limited nature of the 

information, which it has described in 

great detail in the Integrated Science 

Assessment, Visibility Assessment, and 

Policy Assessment, as well as in section 

VI.B.2 of the proposed rule (77 FR 

38973). The EPA further notes, however, 

that limited information does not 

preclude the Administrator from making 

judgments based on the best available 

science, taking into account the existing 

uncertainties and limitations associated 

with that available science. Thus, in 

reaching judgments based on the 

science, the Administrator appropriately 

weighs the associated uncertainties. The 

CASAC supported this view and 

concluded that the available 

information provided a sufficient basis 

on which the Administrator could form 

a judgment about requisite PM-related 

public welfare visibility protection. 

Specifically, CASAC stated ‘‘[t]he 20–30 

deciview range of levels chosen by EPA 

staff as ‘Candidate Protection Levels’ is 

adequately supported by the evidence 

presented’’ (Samet, 2010b, p. iii). As 

discussed in the proposed rule (77 FR 

38990), the Administrator recognized 

and explicitly took into account the 

uncertainties and limitations in the 

science in determining an appropriate 

degree of protection when she proposed 

a level at the upper end of the 

recommended range. As discussed 

below, the Administrator continues to 

be mindful of these uncertainties and 

limitations in reaching her final 

determination regarding what 

constitutes an appropriate degree of 

protection with respect to PM-related 

visibility impairment. 

With respect to the comments of AMC 

et al., the EPA agrees that these studies 

provide a sufficient basis to inform the 

Administrator’s judgments regarding an 

appropriate level of protection from PMrelated visibility impairment, but she 

recognizes that these studies, which are 

the only studies before her, are a limited 

source of information. However, the 

EPA does not agree that the Washington, 

DC, results represent an outlier, and 

thus the EPA believes these results are 

appropriately included in the range 

identified for the Administrator to 

consider. 

Some commenters made the point 

that the EPA relied on much of this 

same evidence to reach the conclusion 

in 2006 that the information was too 

limited to allow selection of a national 

standard. For example, API stated: 

[T]he bulk of the VAQ preference studies 

were available during the previous PM 

NAAQS review and were considered by the 

Agency in its establishment of the 2006 p.m. 

secondary NAAQS * * *. The Proposed Rule 

does not mention this fact and does not 

explain why many of these same studies now 

compel EPA to propose this new secondary 

NAAQS * * *. The Proposed Rule notes in 

passing that, since the last review of the PM 

NAAQS, ‘limited information that has 

become available regarding the 

characterization of public preferences in 

urban areas has provided some new 

perspectives on the usefulness of this 

information in informing the selection of 

target levels of urban visibility protection.’ 77 

Fed. Reg. at 38969/2. It is a serious oversight 

that the Proposed Rule makes no attempt to 

explain what that information is or how it 

affects the interpretation of the VAQ 

preference studies. This ‘limited information’ 

is an apparent reference to information 

provided by Dr. Anne Smith. (API, p. 37) 

The EPA disagrees with these 

commenters. First, the EPA disagrees 

that it failed to distinguish between 

studies that were available in the 

previous review and the current review. 

The discussion in section VI.A.1 of the 

proposal specifically identifies the 

studies from Denver, Phoenix and 

British Columbia (77 FR 38967/2) as 

being considered in the last review. The 

EPA further disagrees with the 

implication that it is being circumspect 

about identifying the ‘‘limited 

information that has become available 

regarding the characterization of public 

preferences in urban areas.’’ Beginning 

in section VI.A.3 of the proposed rule 

(77 FR 38969), the EPA was clear about 

what information, both preexisting and 

new, it relied upon in this review to 

inform its views and provide the basis 

for its proposal. In section VI.B.2, the 

EPA elaborates on the specific 

information, tools, methods and data 

which are considered in relation to the 

public preference studies, including the 

new information available since the last 

review. 

As noted above and in the proposal, 

in addition to the substantial PM urban 

air quality information and analyses 

new to this review, there are three other 

sources of information that have 

specifically ‘‘provided some new 

perspectives on the usefulness of’’ the 

preference studies ‘‘in informing the 

selection of target levels of urban 

visibility protection’’ (77 FR 38969). 

They include: (1) Results from 

additional urban visibility preference 

study experiments conducted for 

Washington, DC by Smith and Howell 

(2009) which added to the preference 

data for that location and shed light on 

the role of location in preference 

responses; (2) a review and reanalysis 

(Stratus Consulting, 2009) of the urban 

visibility public preference studies from 

the four urban areas, including the 

newly available Smith and Howell 

(2009) experiments which examined the 

similarities and differences between the 

studies and evaluated the potential 

significance of those differences on the 

study results; and (3) additional 

analyses, including most importantly a 

logit analysis (Deck and Lawson, 2010, 

as discussed in Chapter 2 and Appendix 

J of the Visibility Assessment), which 

was requested and reviewed by CASAC, 

which showed that each city’s responses 

represented unique and statistically 

different curves. Taken together, these 

sources contributed to the EPA’s current 

knowledge and understanding of each 

survey study’s results, the 

appropriateness of comparing each 

study’s results to the others, and the key 

uncertainties relevant to data 

interpretation. In addition, in the last 

review the decision to not adopt a 

distinct secondary standard was 

remanded as contrary to law and failing 

to provide a reasoned explanation for 

the decision. As such it is not 

appropriate for purposes of comparison 

with the Administrator’s judgment and 

reasoning in this review. 

(b) Preference Study Methods and 

Design 

In addition to the limitations and 

uncertainties noted above, many 

comments also asserted the 

methodologies used in the preference 

studies are fundamentally flawed. Many 

commenters cited some of the same 

issues that have already been identified 

by the EPA as sources of uncertainty 

and potential factors in producing the 

statistically different study results (see 

section VI.B.1.b above). As noted above, 


tkelley on DSK3SPTVN1PROD with 
3212 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

the EPA is well aware of the issues 

raised regarding the adequacy of the 

preference studies to serve as a basis for 

a secondary NAAQS (see 77 FR 38975) 

and solicited comment on how these 

uncertainties should be considered (see 

77 FR 38990). Most of these same 

commenters also pointed to an 

assessment of the preference studies 

methodology provided by Smith and 

Howell (2009) as the basis for their 

views, as indicated by the following 

comments: 

Smith and Howell (2009) show that VAQ 

preference study outcomes are malleable and 

depend entirely on the design of the study. 

Accordingly, such studies do not identify any 

meaningful threshold of acceptable visibility 

conditions. Despite Smith and Howell’s 

conclusions, EPA continues to assert that the 

VAQ preference studies can be used to 

identify minimally acceptable visibility 

conditions even though the Agency has never 

provided any valid scientific basis for 

discounting the Smith and Howell (2009) 

results. (API, p. 38) 

Well-controlled preference studies 

discussed by Anne Smith of Charles River 

Associates at the March 2010 CASAC 

meeting demonstrated that the judgment of 

panel members was affected by the order in 

which photographs were presented and 

tendency to identify the middle of the range 

of visibility degredation as a threshold of 

acceptability. This points to a potential flaw 

in these studies and that artifacts caused by 

these tendencies may have influenced study 

results. Dismissing these inherent flaws in 

the existing preference studies and then 

using these studies to set a secondary 

NAAQS is arbitrary and capricious. (API, 

Attachment 2, p. 12) 

EPA also fails to acknowledge that the only 

study conducted since the last review rebuts 

the validity of the VAQ preference studies 

previously conducted. (UARG, Attachment 2, 

p. 28) 

As is explained in a more detailed 

discussion in the Response to 

Comments document, the EPA disagrees 

that the study conducted by Smith and 

Howell (2009) supports the conclusion 

that the preference study methodologies 

were fundamentally flawed; however, 

the EPA notes that their experiments do 

identify areas where additional research 

would be useful to further inform our 

limited understanding of public 

preferences in urban areas. The EPA 

views the Smith and Howell 

experiments as increasing the EPA’s 

knowledge and understanding of the 

findings of the 2001 Washington, DC 

focus group pilot study (Abt, 2001) in 

several important ways, although this 

information still remains limited 

overall. Specifically, the Smith and 

Howell results suggest: (1) The 2001 

results, while based on a small sample 

size of 9, were consistent with results 

from a larger sample of the general 

Washington, DC population; (2) an 

individual’s preferences for visibility in 

one location may not depend on 

whether they live in that location; and 

(3) presentation method (i.e., changing 

from slide projection to computer 

monitor) did not appear to affect the 

reported preferences. 

(c) Preference Study Results and 

Adversity 

A number of comments were received 

regarding the EPA’s use of preference 

study results to make the determination 

that adverse PM2.5-related visibility 

effects on the public welfare are 

occurring. In this context, several 

commenters questioned whether the 

EPA had made the case that 

unacceptable levels of visual air quality 

based on preference study results alone 

can be equated with an adverse public 

welfare effect. These commenters 

suggested that unless preference study 

information is linked to personal 

comfort and well-being or other 

associated welfare effects, it cannot form 

the basis of a determination of adversity. 

For example, Kennecott Utah Copper 

LLC stated that: 

Thus, EPA seemingly was building the 

foundation for a determination of what 

constitutes an adverse effect on visibility in 

the context of public welfare. However * * * 

EPA subsequently veered toward an 

oversimplified focus on public acceptance of 

visibility conditions * * *. EPA’s discussion 

of visibility in the Policy Assessment and its 

proposed rule in the Federal Register focuses 

entirely on ‘‘acceptable’’ and ‘‘unacceptable’’ 

visual air quality and make no mention of an 

‘‘adverse effect’’ in the context of visibility. 

EPA’s reliance on only 3 urban preference 

studies represents a paucity of data and a 

wholesale abandonment of any effort to seek 

a scientifically measurable adverse effect. 

(Kennecott Utah Copper LLC, p. 26) 

In response, the EPA first notes that 

the definition of effects on welfare 

included in section 302(h) of the CAA 

identifies both visibility and the broader 

category of effects on personal comfort 

and well-being as effects on welfare. In 

setting a secondary standard to address 

visibility impairment, the EPA 

considers the effect on the public from 

impairment of visibility as a separate 

and distinct welfare effect in its own 

right. The EPA is not required to 

translate this into terms of personal 

comfort and well-being, as visibility 

impairment is designated explicitly by 

Congress as an effect on welfare. While 

there may be a large degree of overlap 

among these different welfare effects, 

the EPA properly focuses on evaluating 

all of the information before the Agency 

on the effect visibility impairment has 

on the public, whether or not this 

impairment would also be categorized 

as having an adverse effect on personal 

comfort and well-being. It is in the 

context of all of this information that the 

EPA makes the judgment as to the 

appropriate degree of protection from 

known and anticipated adverse effects 

on the public from visibility 

impairment. The EPA recognizes that 

there is uncertainty about the degree of 

adversity to the public welfare 

associated with PM-related visibility 

impairment. However a secondary 

standard is designed to provide 

protection from ‘‘known or anticipated’’ 

adverse effects, and a bright line 

determination of adversity is not 

required in judging the requisite degree 

of protection under section 109(b)(2). 

Furthermore, the EPA disagrees that it 

has abandoned its consideration of 

visibility-related impacts on the welfare 

effect of personal comfort and wellbeing, as is made clear in the following 

quote: 

Research has demonstrated that people are 

emotionally affected by low visual air 

quality, that perception of pollution is 

correlated with stress, annoyance, and 

symptoms of depression, and that visual air 

quality is deeply intertwined with a ‘‘sense 

of place,’’ affecting people’s sense of the 

desirability of a neighborhood (U.S. EPA, 

2009a, section 9.2.4). Though it is not known 

to what extent these emotional effects are 

linked to different periods of exposure to 

poor visual air quality, providing additional 

protection against short-term exposures to 

levels of visual air quality considered 

unacceptable by subjects in the context of the 

preference studies would be expected to 

provide some degree of protection against the 

risk of loss in the public’s ‘‘sense of wellbeing.’’ (77 FR 38973/1, emphasis added) 

The approach taken to address such 

qualitative, but policy-relevant, 

information in this review is the same 

as in other NAAQS reviews. The review 

is initiated with a comprehensive 

assessment of all possible public health 

and welfare effects associated with PM 

in the Integrated Science Assessment. 

Then policy-relevant effects for which 

there is sufficient quantitative 

information to allow a determination of 

the change in risks associated with 

incremental changes in air quality are 

assessed (in this review, in the Visibility 

Assessment) and used to provide a 

quantitative basis to inform the 

selection of an appropriate range of 

levels for further consideration in the 

Policy Assessment. In the Policy 

Assessment, the EPA considers all 

important policy-relevant evidence and 

information, both quantitative and 

qualitative, in making recommendations 

regarding the range of policy options 

appropriate for the Administrator to 

consider. It is in the context of all of this 

information that the Administrator 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3213 

makes her final judgment as to the 

appropriate degree of protection from 

known and anticipated adverse effects 

on the public from visibility 

impairment. 

Another issue raised in the comments 

regarding adversity is the EPA’s 

decision to use the 50 percent 

acceptability criterion from the public 

preference studies in determining 

candidate protection levels of visibility 

impairment for the selection of a 

national level of visibility protection. 

For example, AMC et al. recommended 

‘‘a 75% acceptability criterion as a target 

that is in line with protecting the 

broader public from the negative effects 

of visibility impairment’’ (AMC, et al., 

p. 9). 

In the Visibility Assessment, the EPA 

noted that the use of the 50 percent 

acceptance level for urban visibility was 

first presented in Ely et al. (1991) (U.S. 

EPA, 2010b, p. 2–5). Ely discussed the 

use of the 50 percent acceptability 

criterion as a reasonable basis for setting 

an urban visibility standard. 

The standard was determined based on a 

50% acceptability criterion, that is, the 

standard was set at the level of extinction 

that would divide the slides into two groups: 

those judged acceptable and those judged 

unacceptable by a majority of the people in 

the study. The criterion is politically 

reasonable because it defines the point where 

a majority of the study participants begin to 

judge slides as representing unacceptable 

visibility. It is also consistent with 

psychological scaling theory which indicates 

that a ‘‘true score’’ exceeds a standard when 

more than 50% of the ‘‘observed scores’’ 

exceed that standard. (Ely et al., 1991, p. 11) 

As Ely described, the 50 percent 

acceptability criterion and the 

preference study conducted by Ely were 

used as the basis for setting the level of 

the Denver Visibility Standard in 1990. 

That same criterion was judged 

appropriate and selected for use in the 

Phoenix preference study (BBC 

research, 2003) and as the basis for 

setting the level of the Phoenix 

Visibility Standard in 2003. Most 

recently, the 50 percent acceptability 

criterion has been recommended by the 

British Columbia Visibility Coordinating 

Committee as the basis for the visibility 

standard currently under consideration 

by British Columbia, Canada. 

Furthermore, CASAC supported this 

approach, while recognizing the 

uncertainty associated with this issue. 

Specifically, CASAC agreed that ‘‘the 

50th percentile for the acceptability 

criteria is logical, given the noted 

similarities in methodologies employed 

in the 4 study areas. * * * In terms of 

choosing a specific percentile from the 

preference studies, we note that there 

may not be a ‘‘preferred’’ one, but in 

assessing preference studies to propose 

a PM secondary NAAQS, the 50th 

percentile is sufficient, as it is the basis 

for existing visibility indexes used in 

the Denver/Colorado Front Range and 

Phoenix metropolitan areas’’ (Samet, 

2009c, pp. 8–9). Therefore, after 

considering the information that served 

as the original basis for its selection as 

described in Ely et al., 1991, and given 

its acceptance and use in existing 

visibility programs, the EPA continues 

to conclude, consistent with the advice 

of CASAC, that it is reasonable to use 

the 50 percent acceptability criterion in 

determining target levels of protection 

from visibility impairment. 

(d) Appropriateness of using 

regionally varying preference study 

results to select a single level for a 

national standard. 

A number of commenters raised 

concerns regarding the bases for and 

implications of the differences observed 

in the preference study results, 

concluding that these results were due 

to regionally varying factors and thus 

could not be used to set a national 

standard. For example, some 

commenters asserted that because the 

confidence intervals around the four 50 

percent acceptability levels do not 

overlap at all, and because there are 

variations in preference study designs 

and inherent differences in the visual 

setting among cities and panels, the four 

preference curves and their associated 

50 percent dv values are city-specific 

and statistically different. The 

commenters concluded, therefore, that it 

was inappropriate to aggregate the 50th 

percentile dv values from multiple 

studies and that they should instead be 

evaluated individually. 

Other commenters expressed the 

related view that the preference study 

results cannot be used to set a national 

standard for visibility impairment 

because the results show that visibility 

preferences vary regionally. For 

example, API stated that: 

The ‘one-size-fits-all’ approach * * * is 

not viable because it does not account for 

regional and city-specific factors that have 

been made evident in the disparity of 

preference study data * * *. It is well 

known, for example, that the level of light 

extinction to which people in different areas 

of the country are accustomed, as well as the 

urban setting, are the primary factors that 

affect a person’s visual perception of an 

urban vista. Thus, the degree to which 

extinction threshold can be related to human 

welfare is inevitably regionally-dependent. 

(API, Attachment 2, p. 4) 

Some of these commenters argued that 

because acceptable visual air quality is 

regionally dependent, it would be more 

appropriate to develop distinct visibility 

standards at the state or local level. 

Others pointed out that areas which lack 

‘‘important visibility vistas’’ might not 

need standards at all, since flat areas 

without significant terrain have a 

limited maximum visual range (NEDA/ 

CAP, p. 3). 

Other commenters stated that due to 

regionally varying factors, such as 

relative humidity, it is not possible to 

select a single level for a national 

standard to protect visibility across the 

United States. In particular, these 

commenters pointed to differences 

between Eastern and Western areas, 

arguing that a single national standard 

could not offer the appropriate degree of 

protection in locations with distinct 

characteristics. For example: 

[T]he proposed method falls short because 

it is not temporally or geographically 

representative enough to have any meaning 

* * *. The uncertainty evidenced in these 

studies and the non-uniformity between the 

western and eastern vistas makes it 

impossible at this time to set an acceptable 

light extinction value that would 

appropriately address visibility concerns in 

non-Class I areas. (New York DOH/DEC, pp. 

5–6) 

The EPA agrees that the preference 

curves and the 50 percent dv levels are 

separate and distinct data points 

representing four different VAQ 

preference curves for four unique urban 

scenes. However, the EPA does not 

consider the fact that the four curves are 

distinct as a weakness of the approach 

or a reason that the results cannot be 

compared. In addition, the EPA does not 

agree that the study results necessarily 

support a conclusion that preferences 

are regionally dependent. In particular, 

the EPA notes that the results of Smith 

and Howell (2009) which show that 

participants in Houston and 

Washington, DC did not have 

significantly different views on 

acceptable air quality in Washington, 

DC, provide limited support for the 

conclusion that people’s preferences 

differ less because of where they live 

and more because of the scene they are 

viewing. 

On the other hand, the existing 

literature indicates that people’s 

preferences for VAQ depend in large 

part on the characteristics and 

sensitivity of the scene being viewed. 

The EPA understands there is a wide 

variety or range of urban scenes within 

the United States. These sensitive urban 

scenes include those with natural vistas 

such as the Colorado Rocky Mountains 

as well as those with iconic man-made 

urban structures like the Washington 

Monument. The EPA believes that the 

scenes presented in the four urban areas 


tkelley on DSK3SPTVN1PROD with 
3214 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

include important types of sensitive 

valued urban scenes and therefore, 

when considered together, can inform 

the selection of a level of acceptable 

urban VAQ at the national scale, taking 

into account the variation across the 

country evidenced in the studies. This 

is discussed further in the next section, 

below. 

The EPA does agree with commenters 

that there are regionally varying factors 

that are important to take into account 

when setting a national standard for 

visibility protection. Section VI.A above 

regarding the history of the secondary 

PM NAAQS review discusses the 

evolution of the EPA’s understanding 

regarding the regional differences in PM 

concentrations, relative humidity and 

other factors. As a result, the current 

review has gone to great lengths to 

address these factors, leading to the 

EPA’s proposal to use the IMPROVE 

algorithm to calculate light extinction in 

order to take into account the varying 

effects of relative humidity and 

speciated PM. While this approach does 

not result in a uniform level of ambient 

PM2.5, it does ensure a nationally 

uniform level of visibility protection. 

The EPA refers the reader to other 

sections of the final rule, including 

sections VI.B.1.a, VI.B.1.c, VI.C.1.b and 

VI.C.1.f, and the Response to Comments 

document for a more detailed response 

as to how it is taking these variables into 

account. 

ii. Specific Comments on Level 

The EPA received relatively few 

comments endorsing a specific level for 

a distinct secondary standard for 

visibility. In general, commenters who 

opposed setting a distinct secondary 

standard at this time did not address the 

question of what level would be 

appropriate if the EPA were to set a 

distinct secondary standard for 

visibility; similarly, commenters who 

supported adopting a distinct secondary 

standard at this time generally did not 

recommend a specific level. However, a 

few commenters did provide comments 

in support of a specific level or range of 

levels, with some commenters 

advocating standards at the upper end 

of the range of proposed levels (i.e., 30 

dv), while others supported levels 

below the lower end of the proposed 

range (i.e., below 28 dv). 

As discussed above, a large number of 

commenters argued that the currently 

available data are insufficient to 

determine what constitutes a standard 

that would be neither more nor less 

protective than necessary and that no 

standard should be set at this time. 

These commenters pointed to the 

limitations and uncertainties in the 

preference studies discussed above as 

the basis for this claim. These 

commenters pointed to significant 

variation in the results of the preference 

studies in support of their arguments 

that the studies should not be used to 

derive a level for a distinct secondary 

standard for visibility. For example, one 

consultant cited by several industry 

commenters argued that the proposed 

level of 28 or 30 dv did not reflect the 

substantial difference in visibility 

preferences between the East and the 

West reflected in the preference studies 

(UARG, Attachment 2, p. 11), and that 

it did not reflect the full range of 

preferences (i.e., potential 50 percent 

acceptability levels) likely to exist 

nationwide (UARG, Attachment 2, p. 

19). This commenter further objected to 

the EPA’s proposal for a level of 28 or 

30 dv on the grounds that the EPA had 

inaccurately adjusted 4-hour values into 

24-hour values. Based on his analysis, 

the consultant concluded that ‘‘a range 

of adjusted values from 28 to 32 dv is 

needed’’ to account for the majority of 

the spread between the 4-hour vs. 24- 

hour equivalent values at the upper end 

of the distribution of values. 

A number of commenters questioned 

whether the proposed range of levels 

was appropriate. One industry 

commenter claimed that the EPA had 

not explicitly justified why a standard 

within the proposed range was 

requisite, stating that ‘‘EPA makes no 

attempt to explain how the proposed 

level of the standard is neither lower 

nor higher than necessary to protect 

public welfare’’ (NSSGA, p. 15). Arizona 

DEQ noted that since the proposed 

calculated light extinction indicator 

excluded coarse particles and Rayleigh 

scattering, the proposed levels of 28 or 

30 dv were inconsistent with the 

visibility preference studies, which 

considered total light extinction. Noting 

these perceived problems with the 

proposed range of levels, a few 

commenters noted that if the EPA were 

to set a distinct secondary standard, the 

level should be set no lower than 30 dv, 

‘‘to account for inconsistent value 

judgments, a great deal of spatial and 

temporal variability, and a very high 

level of uncertainty’’ (Texas CEQ, p. 7). 

In contrast, some commenters 

supporting the EPA’s proposal for a 

distinct secondary standard for visibility 

stated that the proposed range of levels 

from 28–30 dv was insufficiently 

protective based on a 24-hour averaging 

time, and recommended a lower level 

for the visibility index standard. These 

commenters expressed the view that the 

proposed levels of 28 or 30 dv 

represented neither adequate surrogates 

for equivalent 4-hour values, as the EPA 

claimed, nor sufficiently protective 

levels based on recent air quality data. 

Several commenters stated that the 

EPA’s own analyses suggested that a 

standard set at a level of 28 or 30 dv was 

insufficiently protective based on a 24- 

hour averaging time. One commenter 

emphasized that the Policy Assessment 

had indicated a level between 25–28 dv 

was appropriate for a standard 

calculated on a 24-hour average, and 

encouraged the EPA to adopt a standard 

level of 25 dv. Several environmental 

groups provided comments stating that 

a 24-hour average would underestimate 

a 4-hour value by 13–42 percent and 

certain areas of the country— 

particularly the Northeast—would be 

affected disproportionately. These 

commenters suggested that a 24-hour 

PM2.5 visibility index standard should 

be set at a level of 18.6–20 dv. The 

Department of the Interior pointed to 

recent air quality data indicating that 

visibility on the 20% worst days in 

several large metropolitan areas, 

including Birmingham, Fresno, New 

York City, Phoenix, and Washington, 

DC was below 29 dv. While noting that 

these calculations were based on 

IMPROVE calculations which include 

contributions from coarse PM mass, DOI 

expressed the view that the proposed 

level of 28 to 30 dv would not provide 

adequate visibility protection compared 

to the current 24-hour PM2.5 standard of 

35 mg/m3 and recommended that the 

standard be set at a level of 25 dv 

consistent with the results of the 

Phoenix visibility preference study. 

In contrast, the states of Arizona and 

Colorado submitted comments arguing 

that the visibility preference studies 

conducted in Phoenix and Denver, 

respectively, were designed to address a 

specific local problem and that the 

results of these studies were not an 

appropriate basis for selecting the level 

of a national standard. For example, 

Arizona DEQ noted: 

The cited studies were conducted 

considering total light extinction; including 

extinction resulting from particulate matter 

and Rayleigh scattering. Visibility 

impairment due to coarse particulate matter 

can be an important contributor in Arizona, 

specifically in the Phoenix area where 

ongoing measurements have been made. 

Therefore, ADEQ believes that the proposed 

levels of the secondary visibility standard are 

inconsistent with applicable urban studies. 

(Arizona DEQ, p. 2) 

Similarly, the Colorado Department of 

Public Health and the Environment 

noted that the Denver visibility standard 

was designed to address ‘‘brown 

clouds’’, i.e., strong inversions that 

occur in the Denver metropolitan area, 

and that this standard ‘‘is based on a 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3215 

191 In particular, EPA staff expressed a preference 

for Approach B in the Policy Assessment. However, 

in light of the additional information provided by 

the other approaches explored in Appendix G of the 

Policy Assessment and the reanalysis in Frank, et 

al. (2012b), the EPA judges it more appropriate to 

consider the range of values resulting from all five 

analytical approaches for purposes of informing 

decisions about the equivalent level of a 24-hour 

standard. 

192Approach E as presented in the Policy 

Assessment is based on the median values for each 

city; these results are not affected by the regression 

analyses. Therefore, Approach E was not included 

in the reanalysis, and the results remain unchanged 

from those reported in the corrected Table G–6 as 

reported in Frank, et al., 2012b. 

193 In Appendix G of the Policy Assessment, a 24- 

hour adjusted CPL of 28 dv was estimated to be 

equivalent to a 4-hour value of 30 dv under 

Approach B (annual 90th percentile values 

regression). 

194 In Appendix G of the Policy Assessment, 

under Approach C (all-days city-specific 

regression), a 24-hour adjusted CPL of 27 dv was 

estimated to be equivalent to a 4-hour CPL of 30 dv 

when averaged across cities, while city-specific 

values were estimated to range from 24–30 dv. 

195 In the reanalysis, Approach D (all days pooled 

regression) generated results of 28 dv for the 24- 

hour CPL equivalent to a 4-hour value of 30 dv as 

compared to a value of 27 dv in the original 

analysis described in Appendix G. 

196The analysis in Appendix G of the Policy 

Assessment used the 4-hour light extinction value 

treated as the independent (x-axis) variable in an 

ordinary least squares regression. The EPA now 

concludes that this regression approach was not the 

most appropriate approach because that variable 

has error and in fact may be more uncertain than 

the calculated 24-hour extinction values. The Frank 

et al. (2012b) reanalysis uses an orthogonal 

regression instead of ordinary least squares 

regression and results in slopes closer to the 1:1 line 

for all the results, particularly for Dallas, TX. 

Furthermore, consistent with the EPA’s conclusion 

that a higher multiplier for converting OC to OM 

would be appropriate (see section VI.C.1.b.ii above), 

the reanalysis substitutes a 1.6 multiplier for 

converting OC to OM in the calculation of 24-hour 

values instead of the value of 1.4 that was used in 

calculating 24-hour values for Appendix G. The 

higher multiplier is more consistent with the 

SANDWICH approach used to calculate the 4-hour 

values found in Appendix G. See Frank et al. 

(2012b) for a more detailed explanation. 

specific view of Denver’’ associated 

with particular sight paths and direct 

measurement methods. The commenter 

stated that this standard ‘‘is applicable 

only to this location,’’ and that these 

limitations make it potentially 

unsuitable for application as ‘‘a national 

secondary standard, particularly a 

proposed standard that does not use a 

direct measurement method’’ (Colorado 

DPHE, p. 2). 

While acknowledging the 

uncertainties and limitations associated 

with the visibility preference studies as 

discussed above, the EPA continues to 

conclude, as did CASAC, that the 

preference studies are appropriate to use 

as the basis for selecting a target level 

of protection from visibility impairment. 

However, the EPA agrees with 

commenters who emphasize the high 

degree of variability in visibility 

conditions and the potential variability 

in visibility preferences across different 

parts of the country. In light of the 

associated uncertainty, as noted in the 

proposal, the Administrator judged it 

appropriate to establish a target level of 

protection equivalent to the upper end 

of the range of Candidate Protection 

Levels (CPLs) identified in the Policy 

Assessment and generally supported by 

CASAC. Thus, the EPA proposed to set 

a 24-hour visibility index standard that 

would provide protection equivalent to 

the protection afforded by a 4-hour 

standard set at a level of 30 dv. In light 

of the comments received on the 

proposal, in particular comments 

emphasizing the uncertainty and 

variability in the results of the public 

preference studies, the EPA continues to 

conclude that this approach is 

warranted, and that it is appropriate to 

set a target level of protection equivalent 

to the protection that would be afforded 

by a 4-hour, 30 dv visibility index 

standard. 

Moreover, the EPA disagrees with 

commenters who argued that the EPA’s 

approach for translating 4-hour CPLs 

into equivalent 24-hour values was 

inappropriate. In adjusting 4-hour 

values for purposes of defining an 

appropriate level for a 24-hour standard, 

the EPA noted at the time of proposal 

that there were multiple approaches for 

estimating generally equivalent levels 

on a city-specific or national basis. 

While expressing the view that it was 

appropriate to consider the two 

approaches with the highest r2 values 

(Approaches A and B in Appendix G of 

the Policy Assessment),191 which used 

regressions of 90th percentile light 

extinction values, the EPA determined it 

would also be appropriate to consider 

the city-specific estimates resulting from 

Approaches C and E which showed 

greater variability than the aggregated 

estimates. Approaches C and E 

generated a range of city-specific 

estimates of generally equivalent 24- 

hour levels that encompassed the range 

of levels considered appropriate for 4- 

hour CPLs, including the CPL of 30 dv 

at the upper end of that range. This 

information provided support for using 

the same CPL for a 24-hour standard as 

for a 4-hour standard, since no single 

approach could generate an equivalent 

24-hour standard level in each urban 

area for each CPL. The EPA continues 

to conclude, as it did at the time of 

proposal, that using an unadjusted 4- 

hour CPL for purposes of establishing a 

target level of protection for a 24-hour 

standard is appropriate because this 

approach places more emphasis on the 

relatively high degree of spatial and 

temporal variability in relative humidity 

and fine particle composition observed 

in urban areas across the country, 

consistent with EPA’s reanalysis 

discussed below. 

The EPA has conducted a reanalysis 

(Frank et al., 2012b) of the relationships 

between estimated 24-hour and 4-hour 

visibility impairment based on the 

variety of metrics discussed in 

Appendix G of the Policy Assessment. 

The reanalysis has more appropriately 

considered the uncertainty of the 

calculated 4-hour values. The revised 

analysis shows that the 24-hour 

equivalent level is generally closer to 

the 4-hour value at the upper end of the 

range of CPLs than originally estimated, 

as can be seen in the results for 

Approaches B, C, and D.192 For 

example, the reanalysis indicates that 

Approach B yields an adjusted 24-hour 

CPL of 29 dv193 as generally being 

equivalent to a 4-hour CPL of 30 dv, 

while Approach C yields a 24-hour 

equivalent CPL of 29 dv averaged across 

cities and a range of city-specific values 

from 25–36 dv.194 195 Not only are the 

90th percentile and pooled average 

values closer to the 4-hour CPL of 30 dv, 

the range of city-specific results shows 

a wider spread that clearly encompasses 

the unadjusted 4-hour value of 30 dv 

near the midpoint of the city-specific 

range. This provides support for 

concluding that the EPA’s approach to 

translating of 4-hour CPLs into 

equivalent 24-hour values was 

appropriate, and that it is appropriate to 

use unadjusted 4-hour values for 

purposes of selecting a level for a 

standard based on a 24-hour averaging 

time.196

Moreover, the EPA disagrees with 

commenters who argue that the 

currently available evidence is sufficient 

to justify establishing a target level of 

protection at 25 dv or below. The EPA 

recognizes that 25 dv represents the 

middle of the range of 50 percent 

acceptability levels from the 4 cities 

studied, and represents the 50 percent 

acceptability level from the Phoenix 

study, which the Agency has 

acknowledged as the best of the four 

studies in terms of having the least 

noise in the preference study results and 

the most representative selection of 

participants. The EPA also notes the 

caveats discussed in the proposal 

regarding whether it would be 

appropriate to interpret results from the 

western studies as generally 

representative of a broader range of 

scenic vistas in urban areas across the 

country. The Policy Assessment noted 

significant differences in the 


tkelley on DSK3SPTVN1PROD with 
3216 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

characteristics of the urban scenes used 

in each study, with western urban 

visibility preference study scenes 

including mountains in the background 

and objects at greater distances, while 

scenes in the eastern study did not. 

Since objects at a greater distance have 

a greater sensitivity to perceived 

visibility changes as light extinction 

changes compared to otherwise similar 

scenes with objects at a shorter range, 

this likely explains part of the difference 

between the results of the eastern study 

and results of the western studies. In the 

proposal, the EPA noted that the scenic 

vistas available on a daily basis in many 

urban areas across the country generally 

do not have the inherent visual interest 

or the distance between viewer and 

object of greatest intrinsic value as in 

the Denver and Phoenix preference 

studies. Also, the Agency takes note of 

the caution expressed by Colorado and 

Arizona about using the results of the 

Denver and Phoenix preference studies, 

which were aimed at addressing specific 

local visibility problems, to inform the 

choice of level for a national standard. 

Therefore, the Agency considers it 

reasonable to conclude, especially in 

light of the significant uncertainties, 

that it is appropriate to place less weight 

on the western preference results and 

that the high CPL value (30 dv) that is 

based on the eastern preference results 

is likely to be more representative of 

urban areas that do not have associated 

mountains or other valued objects 

visible in the distant background. These 

areas would include the middle of the 

country and many areas in the eastern 

U.S., as well as some western areas. As 

a result, the EPA concludes that it is 

more appropriate to establish a target 

level of protection at the upper end of 

the range of 24-hour CPLs considered, 

recognizing that no one level will be 

‘‘correct’’ for every urban area in the 

country. 

In considering the upper end of this 

range, the EPA must identify a target 

level of protection that is considered 

requisite to protect public welfare from 

a national perspective, recognizing that 

the same target level would apply in all 

locations. Making this judgment 

requires a balancing of the risks to the 

public welfare and the substantial 

uncertainties surrounding appropriate 

levels of visibility protection. As 

acknowledged in the proposal, the EPA 

recognizes that setting a target level of 

protection for a 24-hour standard at 30 

dv would reflect a judgment that the 

current substantial degrees of variability 

and uncertainty inherent in the public 

preference studies should be reflected in 

a higher target protection level than 

would be appropriate if the underlying 

information were more consistent and 

certain. Also, a 24-hour visibility index 

at a level of 30 dv would reflect 

recognition that there is considerable 

spatial and temporal variability in the 

key factors that determine the value of 

the PM2.5 visibility index in any given 

urban area, such that there is a relatively 

high degree of uncertainty as to the most 

appropriate approach to use in selecting 

a 24-hour standard level that would be 

generally equivalent to a specific 4-hour 

standard level. In light of these 

uncertainties, the EPA continues to 

believe that it is appropriate to establish 

a target level of protection for visual air 

quality of 30 dv, averaged over 24- 

hours, with a form as discussed above. 

In reaching this conclusion, the EPA 

notes that any national ambient air 

quality standard for visibility would be 

designed to work in conjunction with 

the Regional Haze Program as a means 

of achieving appropriate levels of 

protection against PM-related visibility 

impairment in all areas of the country, 

including urban, non-urban, and 

Federal Class I areas. While the Regional 

Haze Program is focused on improving 

visibility in Federal Class I areas and a 

secondary visibility index NAAQS 

would focus on protecting visual air 

quality principally in urban areas, both 

programs could be expected to provide 

benefits in surrounding areas. In 

addition, the development of local 

programs, such as those in Denver and 

Phoenix, can continue to be an effective 

and appropriate approach to provide 

additional protection, beyond that 

afforded by a national standard, for 

unique scenic resources in and around 

certain urban areas that are particularly 

highly valued by people living in those 

areas. With regard to comments from the 

Department of Interior noting that many 

large metropolitan areas have 24-hour 

IMPROVE values below 30 dv on the 

worst 20 percent of days already, the 

EPA notes that the purpose of 

establishing NAAQS is to ensure 

adequate protection of public welfare 

everywhere, not to mandate continuous 

improvements in areas that may already 

be relatively clean. In fact, the evidence 

from the IMPROVE program that many 

urban areas have total 24-hour PMrelated light extinction below 29 dv on 

the 20 percent worst visibility days 

suggests that many areas have relatively 

good visual air quality already. 

f. Need for a Distinct Secondary 

Standard To Protect Visibility 

Numerous commenters questioned 

whether a distinct secondary standard 

for visibility is necessary in light of the 

analysis described in section VI.B.1.c.vii 

above (Kelly et al., 2012a) which 

indicated that a 24-hour mass-based 

PM2.5 standard of 35 mg/m3 would 

protect against visibility impacts 

exceeding the range of levels considered 

in the proposal (28–30 dv). While this 

analysis was conducted in support of 

proposed implementation requirements 

for a distinct secondary standard 

(specifically, the modeling 

demonstrations that would be required 

under the PSD program), the second 

prong of the analysis showed that 

within the range of levels proposed by 

the EPA for the visibility index NAAQS 

(28–30 dv), the 24-hour PM2.5 standard 

of 35 mg/m3 would generally be 

controlling. Kelly et al. (2012a) 

concluded that ‘‘overall, design values 

based on 2008–2010 data suggest that 

counties that attain 24-hour PM2.5

NAAQS level of 35 mg/m3 would attain 

the proposed secondary PM2.5 visibility 

index NAAQS level of 30 dv and 

generally attain the level of 28 dv’’ (pp. 

17–18). 

Citing this conclusion, many state and 

local agencies and industry commenters 

argued that a visibility index standard 

in the range proposed (28–30 dv) would 

provide no additional protection beyond 

that afforded by the existing secondary 

24-hour PM2.5 NAAQS, and therefore no 

distinct visibility standard was 

necessary. These commenters advocated 

retaining the current 24-hour PM2.5

mass-based standard to protect against 

visibility effects. ‘‘Since the 24-hour 

PM2.5 standard already protects the 

welfare the 24-hour PM2.5 visibility 

standard is designed to protect, the new 

standard is duplicative and 

unnecessary’’ (South Dakota DENR, p. 

2). Furthermore, a number of state 

commenters objected to the additional 

resource burden associated with 

implementing a standard which had, in 

their view, no practical effect: ‘‘If the 24- 

hour PM2.5 mass standard has the same 

effect as the visibility standard, crafting 

complex regulations to implement 

another standard seems redundant’’ 

(South Carolina DHEC, p. 3). Other 

states agreed: ‘‘A PM2.5-related Visibility 

Index appears redundant since the 

benefits achieved from the current 

primary and secondary annual and 24- 

hour PM2.5 standards already provide 

reductions that would improve 

visibility. Establishing a new PM2.5

secondary standard for visibility would 

be an additional complication and 

burden to the states that is not 

warranted’’ (Indiana DEM, p. 5). 

In addition, several commenters 

submitted additional analyses 

supporting their position that a 35 mg/ 

m3 24-hour PM2.5 standard would 

provide at least equivalent protection to 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3217 

a distinct 24-hour visibility standard 

within the range of levels proposed 

(API, Attachment 2, p. 8 and 

Attachment 3, p. 1). 

In responding to these comments 

stating that a distinct visibility standard 

is not needed, the EPA notes as an 

initial matter that the Administrator 

provisionally concluded at the time of 

proposal that the current PM standards 

were not sufficiently protective of visual 

air quality, and that consideration 

should be given to an alternative 

secondary standard that would provide 

additional protection against PM-related 

visibility impairment, especially in 

urban areas. This provisional 

conclusion was based on the results of 

public preference surveys on the 

acceptability of varying degrees of 

visibility impairment in urban areas, 

analyses of the number of days on 

which peak 1-hour or 4-hour light 

extinction values were estimated to 

exceed a range of CPLs under conditions 

simulated to just meet the current 

standards, and the advice of CASAC. 

The Administrator also noted that the 

current indicator of PM2.5 mass, in 

conjunction with the current 24-hour 

and annual averaging times, was not 

well suited for purposes of protecting 

visibility, since it does not incorporate 

species composition or relative 

humidity, both of which play a central 

role in determining the impact of 

ambient PM on visibility. Taking into 

account the advice of CASAC and the 

court’s remand of the current secondary 

PM2.5 standards, the Administrator 

provisionally concluded that the current 

secondary standards were neither 

sufficiently protective nor suitably 

structured to provide an appropriate 

degree of public welfare protection from 

PM-related visibility impairment. As a 

result, the EPA proposed a new, distinct 

secondary standard that was designed to 

address these deficiencies. 

The EPA notes that in critiquing the 

proposed secondary standard, 

commenters generally did not advocate 

that the form of the existing mass-based 

PM2.5 standards was better suited 

scientifically to the task of protecting 

against visibility impairment. Rather, 

the commenters’ position that a distinct 

secondary standard was not needed for 

purposes of protecting visibility was 

based almost entirely on the relative 

degree of protection likely to be afforded 

by the existing standards (in particular, 

the existing 24-hour PM2.5 standard) as 

compared to the proposed visibility 

index, along with the relatively large 

uncertainties associated with the latter. 

Thus, for all the reasons discussed in 

the proposal with regard to the scientific 

appropriateness of an indicator that 

takes into account both species 

composition and relative humidity, the 

EPA continues to conclude that the 

proposed standard based on a visibility 

index would be appropriate 

scientifically to provide targeted 

protection of visibility, since it would 

provide a measure of PM-related light 

extinction that directly takes into 

account the factors (i.e., species 

composition and relative humidity) that 

influence the relationship between 

PM2.5 in the ambient air and PM-related 

visibility impairment. 

Furthermore, the EPA disagrees with 

commenters who stated that 

implementation concerns, in particular 

the additional resource burden 

associated with implementing a distinct 

secondary standard, should alter the 

Agency’s decision making with regard 

to a standard to protect visibility. The 

EPA may not take the costs of 

implementation into account in setting 

or revising the NAAQS. 

However, in light of the results of the 

Kelly et al. (2012a) analysis and the 

views expressed by commenters on the 

implications of this analysis for 

conclusions regarding the adequacy of 

the current secondary 24-hour PM2.5

standard, the EPA has reconsidered 

some of the conclusions drawn at the 

time of proposal, in particular with 

regard to the degree of protection that 

would be provided by the current 

secondary standard. Based on a review 

of comments related to indicator, 

averaging time, form and level, the 

Agency has concluded that (as 

described in sections VI.C.1b-e above) a 

standard defined in terms of a PM2.5

visibility index (based on speciated 

PM2.5 mass concentrations and relative 

humidity data to calculate PM2.5 light 

extinction), a 24-hour averaging time, 

and a 90th percentile form, averaged 

over 3 years, and a level of 30 dv, would 

provide sufficient but not more than 

necessary protection of the public 

welfare with regard to visual air quality. 

Having identified this target level of 

protection, the EPA is now in a position 

to compare it specifically to the existing 

secondary 24-hour PM2.5 standard of 35 

mg/m3 for purposes of determining 

whether it would provide more, the 

same, or less protection from visibility 

impairment. The EPA must consider 

both whether the existing secondary 24- 

hour PM2.5 standard of 35 mg/m3 is 

sufficient (i.e. not under-protective) and 

whether it is more stringent than 

necessary (i.e. over-protective). 

With regard to the degree to which the 

existing secondary 24-hour PM2.5

standard provides sufficient but not 

more than necessary protection for 

visibility, the EPA first notes that the 

kind of area-specific analysis conducted 

in Kelly et al. (2012a) is essential for 

addressing the court remand of the 2006 

secondary standards. In the case of the 

2006 secondary standards, the EPA had 

argued that the 35 mg/m3 24-hour PM2.5

standard was requisite because one part 

of the proposed range for a distinct 

secondary standard the Agency had 

considered would affect the attainment 

status of a somewhat fewer counties 

than the 35 mg/m3 24-hour PM2.5

standard. The court rejected this kind of 

rough balancing, finding that the EPA’s 

equivalency analysis based on 

percentages of counties demonstrated 

nothing about the relative protection 

offered by the different standards. Based 

on this, an area-by-area evaluation of the 

relative degree of protection offered by 

different standards should be conducted 

to the extent air quality data is available. 

Kelly et al. (2012a) performed such an 

evaluation. Based on 2008–2010 data, 

there are no areas that would have 

exceeded a 30 dv, 24-hour visibility 

index standard that would not also have 

exceeded a 24-hour PM2.5 standard of 35 

mg/m3. Stated another way, all areas that 

met the 24-hour PM2.5 standard of 35 

mg/m3 would have had visual air quality 

at least as good as 30 dv (24-hour 

average, based on 90th percentile form 

averaged over 3 years). The Kelly 

(2012a) analysis also showed that for 

some areas, particularly in the West, 

areas that would have met a 24-hour 

PM2.5 standard of 35 mg/m3 would have 

had visual air quality better than 30 dv 

for the PM2.5 visibility index standard, 

and that at sites that violated both the 

24-hour level and the visibility index 30 

dv level, the visibility index level of 30 

dv would likely be attained if PM2.5

concentrations were reduced such that 

the 24-hour PM2.5 level of 35 mg/m3 was 

attained. 

The EPA has conducted a reanalysis 

(Kelly et al., 2012b) to update the areaby-area analysis in the original Kelly et 

al. (2012a) analysis in three respects. 

First, noting that the original Kelly at al. 

(2012a) analysis used a 1.4 multiplier to 

convert OC to OM at those monitors not 

using the new CSN monitoring protocol, 

the EPA recalculated the visibility index 

design values for 2008–2010 using a 

higher multiplier for converting OC to 

OM at monitors not already using the 

new CSN monitoring protocol 

SANDWICH approach, consistent with 

the Agency’s view that it is more 

appropriate to use a multiplier of 1.6 at 

such monitors as compared to 1.4, as 

described in section VI.C.1.a.ii, 


tkelley on DSK3SPTVN1PROD with 
3218 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

197Some of the OC measurements were produced 

with CSN’s newer monitoring protocol and did not 

require a change in the computed OM. 

198The 2011 air quality data were not yet 

available at the time of proposal. 

above.197 The recomputed visibility 

design index values for 2008–2010 show 

the same overall relationship to 24-hour 

PM2.5 design values as presented in 

Kelly et al., 2012a. 

Second, the EPA repeated the 

calculations comparing visibility index 

design values with 24-hour PM2.5 design 

values using 2009–2011 data, the most 

recent three years of air quality 

information currently available.198

Third, the EPA modified the area-byarea evaluation to ensure consistency 

with the data completeness criteria of 40 

CFR part 50, Appendix N, including the 

removal of data approved by EPA as 

exceptional events, for the current 24- 

hour PM2.5 standard and the proposed 

visibility index standard. 

The results of this reanalysis, as 

presented in Kelly et al. (2012b), show 

a similar pattern to that described in the 

original Kelly memo. Specifically, the 

analysis indicates that there were no 

areas with visibility impairment above 

30 dv that did not also exceed the 24- 

hour PM2.5 standard of 35 mg/m3. The 

updated memo concludes that the 

results for 2009–2011 corroborate the 

findings for 2008–2010. 

Based on these analyses (Kelly et al., 

2012a; 2012b), the EPA concludes with 

a high degree of confidence that having 

air quality that meets the 24-hour PM2.5

standard of 35 mg/m3 would be 

sufficient to ensure areas would not 

exceed 30 dv. The EPA notes that this 

conclusion from Kelly et al. (2012a) is 

supported by two analyses submitted by 

industry commenters (API, Attachments 

2 and 3). 

At the time of proposal, the EPA had 

reached a different conclusion, 

specifically that the 35 mg/m3 24-hour 

PM2.5 standard was not sufficiently 

protective. This conclusion was based, 

in part, on the analyses conducted for 

the Visibility Assessment and Policy 

Assessment regarding 1- to 4-hour peak 

light extinction values based on 2007– 

2009 data. For the reasons outlined 

above in sections VI.B.1.c and VI.C.1.c, 

the EPA originally focused on hourly or 

sub-daily timeframes for evaluating 

visibility conditions. However, data 

quality concerns effectively precluded 

adoption of a 1-hour or sub-daily 

averaging time in this review, and 

ultimately the EPA has concluded that 

a 24-hour averaging time can serve as an 

appropriate surrogate. In reaching this 

conclusion, the EPA has recognized that 

adopting a 24-hour averaging time will 

likely smooth out some of the hour-byhour variability in visibility index 

values, and will effectively reduce peak 

values by averaging them together with 

other hours. In concluding it is 

appropriate to adopt a 24-hour 

averaging time, which limits the impact 

of hour-specific influences, the Agency 

is now placing less weight on the results 

of the 1-hour and 4-hour analyses 

presented in the Visibility Assessment 

and the Policy Assessment which 

focused on identifying the percent of 

days with peak hourly light extinction 

above various CPLs. In light of the 

Agency’s conclusion that a 24-hour 

averaging time would be appropriate, 

the Agency has determined to place 

more weight on analyses of visibility 

conditions over a 24-hour time period, 

especially the results in Kelly et al. 

(2012a and 2012b). In addition, the EPA 

notes that the Kelly et al. analyses 

reflects updated air quality information 

from more recent years of data (2008– 

2010 for Kelly et al., 2012a; 2009–2011 

for Kelly et al. 2012b) as compared to 

the air quality information used in the 

Visibility Assessment and Policy 

Assessment. 

In light of all of these considerations, 

including the results of the Kelly et al. 

(2012a; 2012b) analyses, and the 

supporting comments provided by a 

broad range of public commenters, the 

EPA now concludes that the 24-hour 

PM2.5 standard of 35 mg/m3 provides 

sufficient protection in all areas against 

the effects of visibility impairment. The 

EPA concludes that the existing 24-hour 

PM2.5 standard would provide at least 

the target level of protection for visual 

air quality defined by a visibility index 

set at 30 dv, as described above, which 

the EPA judges appropriate. 

However, the EPA also recognizes that 

it is important to evaluate whether such 

a standard would be over-protective (i.e. 

more stringent than necessary to protect 

public welfare). The analyses presented 

in Kelly et al. (2012a; 2012b) indicates 

that the 24-hour PM2.5 standard of 35 

mg/m3 would achieve more than the 

target level of protection of visual air 

quality (30 dv) in some areas. That is, 

when meeting a mass-based standard of 

35 mg/m3, some areas would have levels 

of PM-related visibility impairment far 

below 30 dv. Thus, when considered by 

itself and without consideration of the 

secondary standards adopted for 

purposes of non-visibility welfare 

effects, the 24-hour PM2.5 standard of 35 

mg/m3 would be over-protective of 

visibility in some areas. However, it is 

important to note that as long as the 

current secondary 24-hour PM2.5

standard of 35 mg/m3 remains in effect, 

this overprotection for visibility would 

occur, regardless of whether a distinct 

secondary standard based on a visibility 

index set at 30 dv were adopted. These 

issues are discussed more fully in 

section VI.D, which outlines the 

Administrator’s final conclusions on the 

secondary PM standards, below. 

g. Legal Issues 

Some commenters opposed the 

proposal to establish a distinct 

secondary standard that would be 

defined in terms of a PM2.5 visibility 

index. The proposed standard would 

use measured PM2.5 mass concentration, 

in combination with speciated PM2.5

mass concentration and relative 

humidity data, to calculate PM2.5 light 

extinction, translated to the deciview 

(dv) scale. The standard would also be 

defined in terms of a specified averaging 

time and form, and a level for the PM2.5

visibility index set at one of two 

options—either 30 dv or 28 dv. The 

commenters argued that the entire 

approach proposed by the EPA is 

inconsistent with the requirements of 

CAA section 109(b). They pointed to a 

number of different aspects of the 

proposal which in their view made it 

incompatible with the CAA. For 

example, the Utility Air Resources 

Group (UARG) stated: 

In the past, EPA has always used a measure 

of PM mass as the indicator for both primary 

and secondary PM NAAQS. Such a standard 

is, as a general matter, consistent with the 

directive in the CAA that the NAAQS 

‘‘specify a level of air quality’’ and targets for 

control the listed criteria air pollutant. CAA 

§ 109(b)(2). The standard contained in EPA’s 

proposed rule does neither of these things. 

Instead, it would (1) regulate relative 

humidity, which is not a criteria pollutant; 

(2) fail to ‘‘specify a level of air quality’’ as 

required by section 109(b)(2) of the CAA; and 

(3) result in a standard necessitating 

nationally variable PM concentrations 

instead of a standard establishing a 

nationally uniform, minimally acceptable PM 

concentration. (UARG, p. 22–23) 

Other commenters raised similar or 

related issues, arguing that the EPA 

improperly set a visibility standard, and 

not a PM2.5 standard, and that NAAQS 

can only be set in terms of a level or 

concentration of the air pollutant. 

Commenters also argued that an 

endangerment finding and air quality 

criteria would be needed before the EPA 

could set a standard based on PM 

components. Each of these comments is 

discussed below. 

As an initial matter, the commenters 

argued that the proposed standard is 

unlawful because it is ‘‘not a PM2.5

standard at all, but rather a visibility 

standard, and visibility is neither an air 

pollutant nor a criteria pollutant for 

which a NAAQS may be promulgated’’ 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3219 

(NMA/NCBA, p. 21). According to these 

commenters, the CAA requires that 

NAAQS be established as limits on the 

concentration of an air pollutant in 

ambient air, not limits on the 

‘‘identifiable effects’’ caused by that air 

pollutant. These commenters claimed 

that reduced visibility due to light 

extinction is not an air pollutant but 

instead is an effect, noting that ‘‘the 

Act’s definition of ‘air pollutant’ speaks 

in terms of specific substances or matter 

in the ambient air’’ (NSSGA, p. 8). The 

commenters pointed to the use of the 

term ‘‘air pollutant’’ in sections 

109(a)(1)(A) and (b)(2) as support for 

their argument, as these provisions refer 

to setting standards for the ‘‘air 

pollutant’’ to address the effects 

associated with the presence of the air 

pollutant in the ambient air. They 

likewise pointed to section 108(a)(2)’s 

reference to the presence of the air 

pollutant in the ambient air. Since 

reduced visibility is not an air pollutant, 

they argue the EPA cannot set a NAAQS 

that is a standard for visibility. They 

argue that the proposed secondary 

standard it is not a PM2.5 standard as it 

does not limit the concentration of PM2.5

or any other fraction of particulate 

matter in the ambient air and therefore 

is not an ‘‘ambient air quality standard’’ 

for any pollutant. 

One commenter argued that the EPA 

is required to ‘‘specify a level of air 

quality’’ under section 109(b)(2), which 

Congress intended as an acceptable 

concentration level of the air pollutant 

in the ambient air, noting that 

specification of acceptable visibility 

conditions is not the same as an 

acceptable air pollution concentration 

level. Citing American Farm Bureau v. 

EPA, 559 F.3d at 516, one commenter 

claimed that the court had affirmed that 

‘‘the NAAQS—whether primary or 

secondary—is a mass-based standard’’ 

(Nevada DEP, p. 5). Commenters also 

refer to the legislative history of the 

1970 amendments, referring to NAAQS 

as setting the ‘‘maximum permissible 

ambient air level’’ for an air pollutant. 

The commenters argue that the 

proposed standard is improper because 

it does not limit the concentration of 

PM2.5 or any fraction of PM in ambient 

air, but improperly sets a limit on 

visibility effects. 

With regard to humidity, these 

commenters argued that the proposed 

standard improperly regulates relative 

humidity because it is included in the 

calculation to determine the value of the 

visibility index. According to these 

commenters, the CAA allows the EPA to 

control criteria air pollutants through 

the NAAQS program, but not other 

various substances. The commenters 

stated that the EPA recognized this in 

the last review, treating humidity as a 

confounding factor and considering 

addressing it by measuring PM2.5 massbased concentration over the midday 

hours, when humidity would have the 

least effect. This would target the effects 

caused by PM, and not by humidity. 

Referring to American Farm Bureau v. 

EPA, 559 F.3d 512, 528 (DC Cir. 2009) 

and 77 FR at 38979 n.153. UARG 

contested the proposed calculated 

visibility index as it does not approach 

relative humidity as a confounding 

factor but instead ‘‘embraces it and 

treats it as if it were a PM effect’’ (UARG 

p. 24). 

The commenters also stated that the 

use of a calculated visibility index, and 

the failure to exclude the effects of 

humidity, would result in acceptable 

PM concentrations that vary across the 

nation. These commenters claimed that 

such a standard is inconsistent with the 

requirements of the CAA because the 

proposed approach fails to establish a 

nationally uniform PM concentration 

standard. For example, API argued that 

the proposed visibility index approach 

is ‘‘essentially specifying levels—not a 

level—of air quality’’ (API, p. 29). UARG 

agreed, and stated that the Act ‘‘requires 

that criteria pollutant concentrations 

throughout the nation reach, at the least, 

a single, specified ambient 

concentration level’’ (UARG, p. 25, 

emphasis in original). The commenters 

argue that a PM2.5 visibility index 

standard cannot provide equal 

protection nationwide due to geographic 

variation in key factors such as relative 

humidity that affect level of particles 

allowed in different areas. The 

commenters noted that establishing a 

single national level for the PM2.5

visibility index would necessarily result 

in unequal acceptable PM2.5 levels in 

different areas of the country, with 

lowest allowable PM2.5 levels in urban 

areas in the Southeast and highest 

allowable levels in the arid West. UARG 

recognized that under section 108 the 

air quality criteria are to ‘‘address those 

variable factors (including atmospheric 

conditions) which of themselves or in 

combination with other factors may 

alter the effects on public health or 

welfare of such air pollutant,’’ but stated 

that while section 108 ‘‘allows’’ this, it 

has no bearing on this issue. Instead, the 

commenter stated that the EPA may take 

such information into account in setting 

a permissible concentration of the 

pollutant that is uniform and national 

(UARG, p. 25). 

In addition, some commenters 

opposed to the proposed distinct 

secondary standard argued that in order 

to base a standard on measured levels of 

several speciated substances, the EPA 

must first make an endangerment 

finding and issue air quality criteria for 

each of the speciated substances 

included in the calculation of PM2.5

light extinction. According to these 

commenters, ‘‘EPA cannot use NAAQS 

to indirectly regulate multiple 

substances which are not criteria 

pollutants under the guise of 

establishing a visibility standard’’ 

(NMA/NCBA, p. 21). Noting that air 

quality criteria for particulate matter 

were issued in 1969, NMA/NCBA 

argued that the 1969 Criteria Document 

‘‘did not establish air quality criteria for 

individual constituents that occur in 

particle form, instead it established 

criteria for particulate matter as a 

whole’’ (p. 27). In light of the fact that 

criteria have never been issued for 

‘‘individual speciated components of 

particulate matter,’’ these commenters 

argued, ‘‘if EPA wishes to promulgate a 

rule such as its secondary visibility 

NAAQS, it first must make a finding 

that the speciated components listed in 

Appendix N endanger public health or 

welfare and then issue an air quality 

criteria document for those 

components’’ (NMA/NCBA, p. 29). 

According to these commenters, the 

approach the EPA adopted in 

promulgating a NAAQS for lead 

supports this view: 

When EPA promulgated a NAAQS for lead, 

an individual substance in particle form, it 

did not assert that an endangerment finding 

or criteria document for lead was 

unnecessary because lead was already 

covered by the PM Criteria Document. 

Instead, EPA complied with the Section 108 

and 109 NAAQS prerequisites for lead, just 

as it must do for Appendix N substances if 

it intends to promulgate a NAAQS for those 

substances. * * * [In 1976], EPA listed lead 

as an air pollutant that adversely affected 

public health or welfare, issued an air quality 

criteria document for lead, and promulgated 

a NAAQS for lead. 43 FR 46246 (Oct. 5, 

1976). (NMA/NCBA, p. 29) 

Finally, UARG argued that the EPA 

has in the past recognized that the 

secondary NAAQS is an inappropriate 

vehicle for regulating PM-related 

visibility, referring to 62 FR at 38680, 

including fn 49. UARG claimed the 

same situation continues, and the EPA 

has not provided a valid basis for 

changing this conclusion. 

The EPA disagrees with the points 

raised by these commenters. While the 

EPA is not adopting the proposed 

secondary standard, as explained below, 

this decision is not based on concern 

over the EPA’s authority to adopt a 

secondary standard such as the one 

proposed. 

The proposed distinct secondary 

standard is a standard for PM2.5, and is 


tkelley on DSK3SPTVN1PROD with 
3220 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

199 In a provision that is not part of the CAA, in 

1990 Congress required EPA to request a report 

from the National Academy of Sciences on the role 

of secondary national ambient air quality standards, 

including information on the ‘‘effects on welfare 

and the environment which are caused by ambient 

concentrations of pollutants’’ listed under section 

108, and the ‘‘ambient concentrations of each such 

pollutant which would be adequate to protect 

welfare and the environment from such effects.’’ 

Section 817(a) of the CAA Amendments of 1990, 

Pub. L. 101–549. 

not a ‘‘visibility standard.’’ The 

proposed secondary standard is based 

on the mass concentration of PM2.5 in 

the ambient air. The standard is defined 

in terms of calculated PM2.5 light 

extinction which is based on the 

measurement of the mass concentration 

of ambient PM2.5 over a 24-hour period. 

The measured mass concentration is 

adjusted based on information on the 

speciated mass components of the PM2.5

and the relative humidity, resulting in a 

calculated visibility index. The level of 

the visibility index, combined with the 

form of the standard and averaging time, 

identifies whether a level of ambient 

mass concentration of PM2.5 achieves 

the standard or not. Given any specific 

mass concentration of ambient PM2.5, 

combined with information on 

speciation and relative humidity, it can 

be determined whether the specific 

mass concentration of ambient PM2.5

achieved the NAAQS. Hence, the 

proposed secondary NAAQS specifies 

acceptable levels of ambient mass 

concentration of PM2.5. 

The combination of indicator, 

averaging time, form, and level of the 

proposed NAAQS is designed to 

provide the appropriate degree of 

protection from visibility impairment 

caused by ambient levels of PM2.5. It 

does this by calculating the light 

extinction associated with ambient 

concentrations of PM2.5 and specifying 

the level of acceptable PM2.5 mass 

concentration in terms of this 

calculation. However this does not 

change the fact that the standard is for 

the air pollutant PM2.5, and defines 

acceptable ambient levels of this air 

pollutant. It does not transform the 

standard into a ‘‘visibility standard’’ and 

not a standard for PM2.5. While the 

commenters had additional concerns 

over the use of relative humidity in the 

calculation, and the variation around 

the country of acceptable mass 

concentrations, those issues are separate 

and do not change the fact that the 

proposed standard defined in terms of 

calculated PM2.5 light extinction is 

based on measurement of PM2.5

concentration in the ambient air, and is 

a NAAQS for PM2.5. 

With regard to the contention that 

section 109(b) limits the EPA to setting 

a standard that is based on the 

concentration of the pollutant in the 

ambient air, we note that the term 

‘‘concentration’’ typically means some 

measure of relative content. For 

example, this would include relative 

measures such as mass per unit of 

volume or parts per million. The EPA 

has often used such metrics to define 

the NAAQS, largely because the 

scientific evidence of health or welfare 

effects supporting the NAAQS typically 

use such metrics in air pollution 

studies. For example, the current 

secondary standards for PM are defined 

in terms of the concentration of PM2.5

and PM10 in the ambient air, measured 

as the dried mass of the particulate 

matter per unit of air. However section 

109(b) does not require that a NAAQS 

be defined this way. 

Sections 109(a) and (b) both use the 

general term ‘‘air quality’’ when 

discussing the EPA’s obligation to set 

NAAQS. The NAAQS are clearly 

national ambient ‘‘air quality’’ standards 

under section 109(b), which specifies 

that the primary NAAQS ‘‘shall be 

ambient air quality standards’’ and the 

secondary NAAQS ‘‘shall specify a level 

of air quality.’’ Both the primary and 

secondary NAAQS are to be based on 

the ‘‘air quality criteria,’’ which are to 

accurately reflect the latest scientific 

knowledge on the effects on public 

health and welfare associated with ‘‘the 

presence of such air pollutant in the 

ambient air, in varying quantities.’’ 

Section 109(b), 108(a)(2). Congress 

spoke in broad terms, tasking the EPA 

with assessing the latest scientific 

knowledge about the public health and 

welfare associated with the presence of 

the pollutant in the air, without limiting 

this to consideration of only those 

effects associated with one or more 

measures of concentration of the air 

pollutant. Congress referred to any and 

all effects associated with the presence 

of the pollutant in the ambient air, not 

just the effects associated with the 

concentration of the pollutant in the 

ambient air. Based on this knowledge, 

the EPA is required to set standards for 

the quality of the air that will provide 

the appropriate degree of protection 

from these health and welfare effects, 

without limitation on how to measure or 

define air quality. While concentration 

in the air has typically been an 

appropriate way to set a standard to 

achieve these requirements, the more 

general terms used in section 108(a) and 

109(b) do not limit the EPA to using 

concentration as the only way to 

measure air quality for purposes of 

setting a NAAQS. The EPA is charged 

with setting air quality standards, and 

has the discretion under section 109(b) 

to choose the metric for defining air 

quality that is appropriate to address the 

health or welfare effect at issue. 

Congress did refer to ‘‘concentration’’ 

in certain situations. In section 109(c) 

Congress required the EPA to set a 

primary NAAQS for NO2 concentration 

over 3 hours. This addressed Congress’ 

concern over whether the then current 

NO2 standard, which used 

concentration as a metric, provided 

adequate protection. Congress also 

called on CASAC to advise the 

Administrator on the relative 

contribution to ‘‘air pollution 

concentrations’’ of natural and 

anthropogenic sources, under section 

109(d)(2)(C)(iii). This information is in 

addition to the advice CASAC is 

required to provide concerning 

appropriate revisions to the ‘‘air quality 

criteria’’ and to the NAAQS under 

section 109(d)(2)(B).199 While these 

provisions refer to ambient 

concentrations of pollutants, this 

reflects the EPA’s standard practice to 

date in setting NAAQS, and none of 

them change or limit the range of 

discretion provided under section 

109(b) in setting NAAQS. They do not 

change the fact that the EPA is to set 

‘‘air quality’’ standards, and is not 

limited to ‘‘air concentration’’ 

standards. The reference in the 

legislative history to a maximum 

permissible ambient air level for the 

pollutant also does not limit the EPA to 

a level of air pollutant concentration, as 

compared to a different metric for 

specifying the level of air quality, if that 

is judged to be appropriate. 

The text of sections 108 and 109 does 

not support the limited interpretation 

commenters suggest. Instead these 

provisions provide the EPA with 

significant discretion in determining the 

metric for air quality that is appropriate 

to achieve the required degree of 

protection of public welfare. The 

commenters’ interpretation would 

improperly limit this discretion, 

interfering with achieving the goals of 

section 109(b). 

For example, in this review the EPA 

considered whether it would be 

appropriate to base a secondary NAAQS 

on direct measurement of the light 

extinction caused by PM2.5. See 77 FR 

38890, 38980–1 (June 29, 2012). There 

are several instrumental methods that 

directly measure PM2.5 light 

extinction—the amount of light 

extinction caused by the presence of 

PM2.5 in the ambient air. This is not a 

measure of the concentration of PM2.5 in 

the air, but a measure of the light 

extinction caused by PM2.5. This is 

clearly an effect associated with the 

presence of PM2.5 in the ambient air, 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3221 

200UARG recognizes these provisions, but argues, 

as above, that this is limited by the requirement that 

the EPA set a NAAQS based solely on ambient 

concentration. 

201According to the Integrated Science 

Assessment, ‘‘Confounding is ‘* * * a confusion of 

effects. Specifically, the apparent effect of the 

exposure of interest is distorted because the effect 

of an extraneous factor is mistaken for or mixed 

with the actual exposure effect (which may be 

null) ’ (Rothman and Greenland, 1998, 086599)’’ 

(U.S. EPA, 2009a, p. 1–16). 

and this atmospheric property is 

directly related to visibility effects. 

Unlike PM2.5 mass concentration, there 

is a close scientific relationship between 

directly measured PM2.5 light extinction 

and visibility effects. 

It would appear straightforward to say 

that PM2.5 light extinction is a quality of 

the ambient air, and a secondary 

NAAQS that specified an acceptable 

level of PM2.5 based on directly 

measured PM2.5 light extinction would 

be an ‘‘ambient air quality standard’’ for 

the air pollutant that specifies a ‘‘level 

of air quality’’ designed to provide 

protection against visibility impairment. 

Unlike directly measured PM2.5 light 

extinction, the mass concentration of 

PM2.5 does not have the same direct 

relationship to light extinction, and 

specifying an acceptable level of mass 

concentration of PM2.5 would be a more 

indirect and less effective way to 

provide protection from visibility 

impairment caused by the presence of 

PM2.5 in the ambient air. Under the 

commenters’ interpretation, the EPA 

would be precluded from specifying a 

level of air quality in terms of directly 

measured PM2.5 light extinction, the 

more scientifically appropriate and 

direct measure of the effect PM2.5 has on 

visibility. Instead the EPA would be 

limited to the more indirect and less 

effective specification of a level of 

concentration of PM2.5. 

The commenters also objected to the 

inclusion of relative humidity as an 

adjustment factor in the calculation of 

PM2.5 light extinction. Contrary to the 

claims of these commenters, the use of 

calculated PM2.5 light extinction does 

not regulate relative humidity. The 

proposed secondary standard would 

define acceptable levels of ambient 

PM2.5, not acceptable levels of relative 

humidity. In addition, section 108 

explicitly requires that the air quality 

criteria include information on the 

atmospheric conditions that can alter 

the effects of the air pollutant on public 

health or welfare, and relative humidity 

certainly has this kind of impact. 

Section 109(b) requires that the standard 

be based on the air quality criteria, 

indicating that this information can and 

should be taken into account in setting 

the standard. Including relative 

humidity as an adjustment factor in the 

calculation of PM2.5 light extinction is a 

reasonable and straightforward way to 

use the scientific information in the air 

quality criteria in establishing a 

standard to provide protection from 

visibility impairment.200

Some commenters pointed to the 

EPA’s position in the last review, stating 

that the EPA properly treated relative 

humidity as a confounding factor, and 

in this review improperly moves away 

from that position. See 77 FR at 38979, 

71 FR 61144, 61205 (October 17, 2006). 

In the last review the EPA considered a 

distinct PM2.5 mass-based secondary 

standard. In that context, limiting the 

measurement of PM2.5 mass 

concentration to the mid-day hours 

when relative humidity had the least 

impact would promote the correlation 

between measured PM2.5 mass 

concentration and light extinction, 

which would promote achievement of a 

relatively consistent degree of visibility 

protection across the country. However 

in this rulemaking the proposed 

calculated PM2.5 light extinction 

standard achieves a consistent degree of 

visibility protection by directly 

accounting for humidity, in a 

scientifically defensible manner. The 

goal has not changed—achieving the 

desired degree of protection across the 

country. What has changed is that 

calculated PM2.5 light extinction is a 

more direct and scientifically 

appropriate way to achieve that result. 

Finally, it should be made clear that 

water is not a separate compound from 

PM2.5 that confounds the impact PM2.5

has on light extinction. As described in 

the Integrated Science Assessment, ‘‘PM 

is the generic term for a broad class of 

chemically and physically diverse 

substances that exist as discrete 

particles (liquid droplets or solids) over 

a wide range of sizes’’ (U.S. EPA, 2009a, 

p. 1–4). ‘‘Particles composed of water 

soluble inorganic salts (i.e., ammoniated 

sulfate, ammonium nitrate, sodium 

chloride, etc.) are hygroscopic in that 

they absorb water as a function of 

relative humidity to form a liquid 

solution droplet. Aside from the 

chemical consequences of this water 

growth, the droplets become larger 

when relative humidity increases, 

resulting in increased light scattering. 

Hence, the same PM dry concentration 

produces more haze’’ (U.S. EPA, 2009a, 

p. 9–6). Thus water is not a compound 

that is separate and apart from the 

particle that acts as an extraneous 

confounding factor.201 The effect of 

relative humidity occurs after the water 

becomes part of the particle. Certain 

water soluble salts absorb water and the 

resulting particle is larger in size and 

scatters more light, increasing the 

visibility impact of the particle. But the 

particle is still a PM2.5 particle. The fact 

that the PM NAAQS traditionally uses 

a measurement of the dried mass of the 

particles as the metric for the standard 

does not change the fact that the 

particles in the air include liquid 

droplets and particles that have 

increased in size because of absorption 

of water. These ambient PM2.5 particles 

are what is in the air and impacting 

visibility, not just the dried mass of 

PM2.5 that is measured in the laboratory 

and is currently used as the indicator for 

the PM NAAQS. Thus the commenters 

improperly claimed that the proposed 

secondary standard regulates water or 

relative humidity, and not PM2.5, when 

in fact the proposed secondary standard 

accounts in a scientific manner for the 

fact that some PM2.5 particles are larger 

in size and have a greater impact on 

light extinction when the relative 

humidity increases. 

The commenters also raised concerns 

that a standard based on calculated 

PM2.5 light extinction, compared to a 

standard based on just PM2.5 mass 

concentration, improperly results in 

variable levels of acceptable PM2.5 mass 

concentrations across the country. This 

stems from the adjustments in the 

calculation for speciated components of 

PM2.5 and relative humidity. According 

to commenters, this is improper as 

section 109(b) requires that the NAAQS 

set a single, specified ambient 

concentration that is nationally uniform 

across the country. 

As discussed above, the text of section 

109(b) does not specify this limitation of 

a single national acceptable 

concentration. Instead the secondary 

NAAQS is to specify a level of air 

quality that achieves the appropriate 

degree of protection. The proposed 

secondary standard would do just that— 

specify a level of air quality, defined in 

terms of calculated PM2.5 light 

extinction, that would achieve the 

desired degree of protection. The fact 

that this results in varying allowable 

levels of PM2.5 mass concentrations is 

not inconsistent with the Act. The DC 

Circuit recently approved such a result. 

In the last review of the PM10 primary 

NAAQS, the court approved the EPA’s 

choice of an indicator that was designed 

to allow varying levels of acceptable 

coarse PM. The court stated that: 

The industry petitioners next argue that the 

150 mg/m3 standard for PM10 will result in 

arbitrarily varying levels of coarse PM, and 

that the agency should instead have used a 

PM10-2.5 indicator. The EPA does not dispute 


tkelley on DSK3SPTVN1PROD with 
3222 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

that using the PM10 indicator will result in 

coarse PM levels that vary within the limit 

of 150 mg/m3. As the EPA explains: ‘‘Because 

the PM10 indicator includes both coarse PM 

(PM10-2.5) and fine PM (PM2.5), the 

concentration of PM10-2.5 allowed by a PM10

standard set at a single level declines as the 

concentration of PM2.5 increases. Thus, the 

level of coarse particles allowed varies 

depending on the level of fine particles 

present.’’ Id. at 61,195. 

Although the EPA acknowledges that a 

PM10 indicator will result in varying coarse 

PM levels, it does not agree that the variance 

will be arbitrary. The EPA agrees with the 

industry petitioners that protection from 

coarse particles should be targeted at urban 

areas, where coarse particles have been 

shown to pose the greatest danger. Id. at 

61,194. But the agency argues that targeting 

of urban areas is effectively accomplished by 

using an indicator that permits the varying 

levels that the industry petitioners challenge. 

* * * Id. at 61,195–96 (citations omitted). In 

other words: ‘‘The varying levels of coarse 

particles allowed by a PM10 indicator will 

therefore target protection in urban and 

industrial areas where the evidence of 

adverse health effects associated with 

exposure to coarse particles is strongest.’’ Id. 

The EPA also offers a further rationale for 

tying the stringency of coarse PM regulation 

to increases in the level of PM2.5.* * * EPA 

argues that it is ‘‘logical to allow lower levels 

of coarse particles when fine particle 

concentrations are high.* * * [I]nclusion of 

PM2.5 in the PM10 indicator for purposes of 

coarse particle protection would 

appropriately reflect the contribution that 

contaminants emitted in fine particle form 

can make to the overall health risk posed by 

coarse particles.’’ Id. 

In sum, we find that the EPA has provided 

a reasonable explanation for its decision[ ] 

* * * to utilize a standard that allows 

targeted variance in coarse PM levels in an 

inverse relationship to the amount of fine PM 

in the air. American Farm Bureau v. EPA, 

559 F.3d 512, 534–5 (D.C. Cir. 2009). 

A similar result applies here. Under 

the proposed secondary standard there 

would be a single level of air quality 

specified for the NAAQS. The standard 

would apply across the nation; it would 

not be a regional standard. The 

proposed standard would be the same 

standard everywhere—the acceptable 

level of mass concentration of PM2.5

would be defined the same way across 

the nation, using the same method of 

calculating the allowable concentration 

of PM2.5. The same degree of protection 

from visibility impairment would apply 

across the country. While the allowable 

amount of PM2.5 could vary, this would 

be a reasoned way to achieve the 

desired degree of protection from 

visibility impairment. The requirements 

of section 109(b) would be satisfied. 

Commenters also objected that the 

EPA could not set a NAAQS for the 

separate components of PM2.5 without 

listing the components of PM2.5 under 

section 108, based on an endangerment 

finding, and issuing air quality criteria 

for these components. They argued that 

the issuance of air quality criteria for 

particulate matter starting in 1969 did 

not provide a lawful basis for a 

proposed secondary standard that is 

based on components of PM, as the 1969 

air quality was for particulate matter ‘‘as 

a whole,’’ defining PM as particles 

smaller than 500 micrometers (NMA/ 

NCBA, p. 27). However, as discussed 

above, the proposed standard sets the 

allowable limit on ambient 

concentrations of PM2.5. Information on 

both the speciated components of PM2.5

and the relative humidity affect how 

much light extinction is associated with 

any specific level of PM2.5, but the 

standard is for PM2.5. The D.C. Circuit 

has made it clear that PM2.5, just like 

PM10 and TSP before that, is an 

appropriate subset of PM for the EPA to 

focus on in setting the NAAQS based on 

the scientific evidence before the EPA. 

This focus of the NAAQS does not make 

the subset a new pollutant that requires 

listing and new air quality criteria under 

section 108 before setting a NAAQS. 

American Trucking Association et al. v. 

EPA, 175 F.3d 1027, 1055 (D.C. Cir. 

1999). Commenters’ interpretation 

would apply to PM2.5 as well as to 

components of PM2.5, and is 

inconsistent with the ATA decision. In 

addition, it is clear that the current air 

quality criteria do address the scientific 

basis for calculating PM2.5 light 

extinction as the EPA proposed (U.S. 

EPA, 2009a, pp. 9–5 to 9–8). 

Finally, at least one commenter 

argued that the EPA has concluded in 

prior reviews that the secondary 

NAAQS program is an inappropriate 

vehicle for regulating PM related 

visibility impairment (UARG, p. 26). 

UARG mischaracterized the EPA’s past 

decision-making. In past reviews the 

EPA has been clear that the EPA should 

take into account the existence of the 

visibility program under section 169A, 

the regional haze program, when 

considering a secondary NAAQS and 

should not treat the secondary NAAQS 

as the sole mechanism to address 

visibility impairment across the 

country. That is the approach the EPA 

has taken in this and prior reviews. See 

77 FR at 38990. 

h. Relationship With Regional Haze 

Program 

A large number of commenters 

expressed confusion and concern over 

differences between the proposed 

visibility index standard and the 

Regional Haze Program. This included 

commenters who supported setting a 

distinct secondary standard to protect 

visibility as well as those opposed to 

setting such a standard. A number of 

these commenters noted that visibility 

impairment would be assessed 

differently under the two approaches 

due to differences in the way light 

extinction is calculated, including 

different IMPROVE equations and 

differences in the inclusion and 

weighting of specific species and 

components. The commenters argued it 

would be inappropriate to have two 

different regimes for managing visibility 

impairment in the exact same location. 

These commenters claimed that since 

data from the IMPROVE monitoring 

network would inform nonattainment 

designations, as well as an area’s 

obligations under the Regional Haze 

Program, there could be considerable 

confusion over how to draw 

nonattainment boundaries and what 

requirements would affect large sources 

in rural areas. These commenters also 

noted the resource burden associated 

with maintaining two different 

programs aimed at protecting visibility 

in the same geographic area. Some 

commenters argued that a visibility 

NAAQS should not apply to rural areas. 

The Department of the Interior 

requested that the EPA clearly define 

the geographic area to which the 

visibility index standard would be 

applicable, and suggested that Class I 

and Class II areas should generally be 

excluded from the standard. As 

discussed above, commenters 

questioned the need for a distinct 

visibility standard, arguing that the 

existing primary PM standards 

combined with the Regional Haze 

Program ensured adequate protection of 

visibility, even in urban areas. 

In response to these comments 

relating to the overlap between the 

Regional Haze program and a distinct 

secondary standard designed to protect 

visibility principally in urban areas, the 

EPA notes that the objectives of each 

program are distinct. While the Regional 

Haze program is designed to eliminate 

man-made impairment of visibility in 

Federal Class I areas over the course of 

several decades, a distinct secondary 

standard for PM-related visibility 

impairment would be focused on 

providing a nationally applicable level 

of protection for all areas, particularly 

urban areas which do not receive 

targeted protection under the Regional 

Haze Program. Moreover, the metric 

used to assess visibility impairment 

differs between the two programs 

precisely because each program is 

aimed at a different aspect of the 

problem. Recognizing the importance of 

fresh emissions for urban visibility, the 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3223 

202As summarized in section VI.A and Table 1 

above, the current suite of secondary PM standards 

includes annual and 24-hour PM2.5 standards and 

a 24-hour PM10 standard. 

Visibility Assessment focused on 

visibility impairment as measured by 

the original IMPROVE equation because 

‘‘the original version is considered more 

representative of urban situations when 

emissions are still fresh rather than aged 

as at remote IMPROVE sites’’ (U.S. EPA, 

2010b, p. 3–19). The Regional Haze 

Program, on the other hand, has shifted 

to a revised IMPROVE algorithm more 

suited to remote locations. While this 

difference is discussed in more detail in 

section VI.C.1.b above, the result is that 

each program would appropriately 

measure those aspects of visibility 

impairment most closely related to the 

problem the program is trying to 

prevent. Since the same data can be 

used to calculate both visibility 

impairment under the Regional Haze 

approach and the proposed visibility 

index, the additional calculation burden 

for state and local agencies would be 

light. Also, to the extent that there is 

any difference in terms of the emissions 

control obligations the two different 

programs would impose upon state and 

local areas, this is likely appropriate 

given the extent and nature of visibility 

impairment in those areas. The EPA 

notes that in general, there is likely to 

be substantial overlap in the control 

strategies a state or local area would 

pursue under either program. Thus, the 

EPA disagrees with commenters who 

stated that a distinct visibility standard 

as proposed would inherently conflict 

with the Regional Haze Program or that 

it would be appropriate to draw 

geographical distinctions that would 

explicitly exclude some areas (e.g., Class 

I areas) from the NAAQS. The EPA 

notes that the CAA requires that 

NAAQS be national in scope, and that 

the specific requirements laid out in the 

proposal for the distinct secondary 

standard would ensure that the 

protection it afforded would be 

appropriately targeted toward urban 

areas so that it could work in 

conjunction with—not be in conflict 

with—the Regional Haze Program under 

sections 169A and 169B of the CAA. 

2. Comments on the Proposed Decision 

Regarding Non-Visibility Welfare Effects 

Relatively few commenters addressed 

the proposal to retain the existing suite 

of secondary PM standards to address 

non-visibility welfare effects. A couple 

of states, including Mississippi and 

South Dakota, offered brief 

endorsements of the proposal. A few 

other commenters offered more 

extensive comments on the proposal to 

retain the existing secondary standards, 

and these commenters opposed this 

aspect of the proposal for one of two 

reasons. First, some commenters 

opposed the proposal to retain the 

current secondary annual PM2.5

standard of 15 mg/m3 in light of the 

proposal to revise the level of the 

primary annual PM2.5 standard to a level 

between 12–13 mg/m3. Expressing 

concern over the implications of this 

decision for the air quality planning 

obligations of states, these commenters 

argued that the EPA should revise the 

secondary PM2.5 standards to be 

equivalent in all respects to the primary 

PM2.5 standards. For example, the 

American Association of State Highway 

and Transportation Officials (AASHTO) 

supported ‘‘retaining secondary 

standards that are consistent with the 

primary standards in order to reduce the 

complexity of the transportation and air 

quality planning processes, as well as 

the transportation conformity process’’ 

(AASHTO, p. 3). Thus, if the EPA were 

to adopt a lower level for the primary 

annual PM2.5 standard, the commenters 

recommended that the EPA adopt this 

same lower level for the primary 

secondary PM2.5 standard as well. 

In response to these comments, the 

EPA notes that the Agency lacks an 

appropriate scientific basis for revising 

the level of the secondary annual PM2.5

standard. As noted above in section 

VI.B.2, there is an absence of 

information that would support any 

different secondary standards for PM. 

Comments related to the 

implementation challenges associated 

with distinct primary and secondary 

standards are not relevant to the 

Administrator’s final decisions 

regarding what standards are requisite 

to protect the public welfare. Therefore, 

the EPA continues to conclude that it 

would be appropriate to retain the 

current suite of secondary PM 

standards 202 to address non-visibility 

welfare effects, while revising only the 

form of the secondary annual PM2.5

standard to remove the option for 

spatial averaging consistent with this 

change to the primary annual PM2.5

standard, as proposed. 

Other commenters focused on the 

impacts of particulate matter on climate. 

One commenter cited a number of 

recent studies that considered mobile 

source black carbon emissions and 

associated climate impacts, and urged 

the EPA to protect the public welfare by 

setting ‘‘higher standards for gasoline 

quality’’ (Urban Air Initiative, p. 4). This 

commenter did not, however, advocate 

specific secondary NAAQS to address 

climate impacts of PM. More extensive 

comments on this same subject were 

provided by the Center for Biological 

Diversity (CBD), which urged the EPA to 

‘‘set a separate limit for black carbon 

within the overall PM2.5 standard’’ to 

ensure that public welfare is fully 

protected ‘‘from the serious climate 

impacts of black carbon’’ (CBD, p. 2). 

This commenter argued that 

‘‘[p]recaution is required for secondary 

NAAQS,’’ citing American Trucking 

Associations, Inc. v. EPA, 283 F.3d 355, 

369 (D.C. Cir. 2002): 

[N]othing in the Clean Air Act requires 

EPA to wait until it has perfect information 

before adopting a protective secondary 

NAAQS. Rather, the Act mandates 

promulgation of secondary standards 

requisite to protect public welfare from any 

‘‘anticipated adverse effects associated with’’ 

regulated pollutants, 42 U.S.C. 7409(b)(2) 

(emphasis added), suggesting that EPA must 

act as soon as it has enough information 

(even if crude) to ‘‘anticipate[]’’ such 

effects[.] 

The commenter stressed the growing 

scientific evidence regarding the 

impacts of black carbon on climate, and 

argued that the EPA’s proposal ignores 

important research studies published 

within the last five years which provide 

improved estimates of the radiative 

forcing associated with black carbon, 

and the effects of black carbon on snow 

and ice, the Arctic climate, water 

availability and climate ‘‘tipping 

points.’’ The commenter also noted that 

reductions in cooling aerosol species, 

particularly sulfate, due to pollution 

control programs are leading to an 

‘‘unmasking’’ of the true extent of 

warming due to the accumulation of 

greenhouse gases in the atmosphere. 

The commenter argued that this 

unmasking effect can be offset by 

ensuring ‘‘that sufficient black carbon 

reductions accompany reductions in 

overall aerosol pollution’’ (CBD, p. 10). 

The commenter also argued that the 

EPA did not consider the negative 

impacts of climate change on public 

health adequately in the proposal. 

The commenter stated that the EPA 

had an obligation to address the impacts 

of black carbon in the PM NAAQS, 

despite the remaining uncertainties. The 

commenter pointed to the EPA’s report 

to Congress on Black Carbon (U.S. EPA, 

2012c), stating that the ‘‘report shows 

that EPA is aware of the climate science 

and public health information that point 

to the importance of addressing black 

carbon pollution. EPA must use this 

information in its relevant 

decisionmaking’’ (CBD, p. 13). The 

commenter also noted that the U.S. 

participates in a number of international 

forums that have recognized the need to 

take action on black carbon, and argued 


tkelley on DSK3SPTVN1PROD with 
3224 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

that the U.S. has ‘‘an obligation under 

the Gothenburg Protocol to address 

black carbon pollution.’’ The 

commenter challenged the uncertainties 

cited by EPA with regard to the climate 

impacts of aerosols generally, arguing 

that they ‘‘do not apply to the regulation 

of black carbon’’ (CBD, p. 14). 

Specifically, the commenter stated that 

‘‘there are significant anthropogenic 

sources of black carbon that contribute 

a large proportion of total black carbon 

emissions’’; that ‘‘there is enough 

information related to black carbon’s 

impact to know that global temperatures 

will rise due to black carbon 

emissions’’; that spatial and temporal 

heterogeneity in black carbon emissions 

do not matter for estimating likely 

climate effects; that ‘‘[b]lack carbon’s 

negative climate impacts do not depend 

upon details of cloud interactions with 

aerosols’’; and that the EPA does not 

need to be able to quantify the health or 

climate benefits precisely to know that 

it is appropriate to control black carbon 

as a specific component of PM under 

the CAA (CBD, pp. 14–15). 

As a result, the commenter concluded 

that the current size-based PM mass 

standard ‘‘is insufficient to fully protect 

health and welfare,’’ and that the EPA 

was obligated to establish a specific 

limit on black carbon as a component of 

PM. The commenter argued that ‘‘Black 

carbon must be regulated separately and 

in addition to PM2.5 because absent 

separate standards sulfates and nitrates 

may be more likely to be mitigated than 

the black carbon component of PM’’ 

(CBD, p. 17). To support this point, the 

commenter cited the conclusion in the 

Policy Assessment that: 

The current standards that are defined in 

terms of aggregate size mass cannot be 

expected to appropriately target controls on 

components of fine and coarse particles that 

are related to climate forcing effects. Thus, 

the current mass-based PM2.5 and PM10

secondary standards are not an appropriate 

or effective means of focusing protection 

against PM-associated climate effects due to 

these differences in components. (U.S. EPA, 

2011a, p. 5–11) 

The commenter also noted that 

existing regulations on diesel engines, 

which are the largest source of black 

carbon in the United States, do not 

affect existing engines and vehicles, and 

stated that ‘‘The NAAQS program is one 

of the few opportunities to reduce black 

carbon from existing engines, industrial 

and biofuel sources within the United 

States and rapidly reduce emissions 

from this pollutant’’ (CBD, p. 18). 

The EPA agrees with the commenters’ 

assertion that the scientific information 

about the impacts of aerosol species on 

climate is developing rapidly, and that 

understanding of the magnitude of 

aerosol effects on climate and the 

contribution of individual aerosol 

components to those effects has 

improved substantially over the past 

decade. The EPA also agrees that certain 

species, in particular black carbon, play 

a significant role in multiple aspects of 

climate. The Policy Assessment 

recognized that ‘‘Aerosols can impact 

glaciers, snowpack, regional water 

supplies, precipitation and climate 

patterns,’’ and may contribute to the 

melting of ice and snow, a decrease in 

surface albedo, and climate impacts in 

the Arctic and other locations (U.S. 

EPA, 2011a, p. 5–9). The contribution of 

black carbon to these effects is 

discussed in detail in the EPA’s recent 

Report to Congress on Black Carbon 

(U.S. EPA, 2012c). In particular, black 

carbon plays an important role in 

heating the lower atmosphere by 

absorbing incoming solar radiation and 

outgoing terrestrial radiation, i.e. via 

‘‘direct’’ radiative forcing. 

However, the EPA disagrees that there 

is sufficient information available at this 

time to establish a NAAQS to protect 

against the climate impacts associated 

with current ambient concentrations of 

black carbon or other PM constituents. 

While the Integrated Science 

Assessment concluded that ‘‘a causal 

relationship exists between PM and 

effects on climate, including both direct 

effects on radiative forcing and indirect 

effects that involve cloud feedbacks that 

influence precipitation formation and 

cloud lifetime’’ (U.S. EPA, 2009a, 

section 9.3.10), it also identified 

substantial remaining uncertainties with 

regard to the contribution of individual 

aerosol species to these climate effects. 

The contribution of individual aerosol 

components to total aerosol direct 

radiative forcing is more uncertain than 

the global average (U.S. EPA, 2009a, 

section 9.3.6.6), and the indirect effects 

of aerosols and aerosol components 

remain highly uncertain, in particular 

with regard to their complex 

interactions with clouds. 

With regard to black carbon, for 

example, the EPA disagrees with CBD’s 

claims that ‘‘black carbon’s negative 

climate impacts do not depend upon 

details of cloud interactions with 

aerosols’’ and that the uncertainties 

associated with climate impacts of 

aerosols generally do not apply to black 

carbon. In fact, the EPA has pointed to 

cloud interactions as the area of greatest 

uncertainty with regard to black carbon: 

recognizing that black carbon affects 

cloud reflectivity (albedo), lifetime, and 

stability as well as precipitation, the 

Report to Congress on Black Carbon 

noted that ‘‘few quantitative estimates of 

these effects are available, and 

significant uncertainty remains. Due to 

all of the remaining gaps in scientific 

knowledge, it is difficult to place 

quantitative bounds on the forcing 

attributable to [black carbon] impacts on 

clouds at present’’ (U.S. EPA, 2012c, p. 

4). The Report acknowledged that ‘‘most 

estimates of the forcing from aerosol 

indirect effects are based on all aerosol 

species (e.g. total PM) and are not 

estimated for individual species (e.g, BC 

alone)’’ (U.S. EPA, 2012c, p. 40). The 

Report concluded that it remains 

unclear the extent to which black 

carbon contributes to the overall aerosol 

indirect effect, and did not assign any 

central estimate or even a range of 

possible values to the role of black 

carbon in the overall aerosol indirect 

effect. With regard to black carbon’s net 

contribution to climate, therefore, the 

Report concluded: 

The direct and snow/ice albedo effects of 

BC are widely understood to lead to climate 

warming. However, the globally averaged net 

climate effect of BC also includes the effects 

associated with cloud interactions, which are 

not well quantified and may cause either 

warming or cooling. Therefore, though most 

estimates indicate that BC has a net warming 

influence, a net cooling effect cannot be ruled 

out. It is also important to note that the net 

radiative effect of all aerosols combined 

(including sulfates, nitrates, BC and OC) is 

widely understood to be negative (cooling) 

on a global average basis. (U.S. EPA, 2012c, 

p. 3) 

Given the remaining uncertainties 

about the impact of aerosols on climate, 

there is even greater uncertainty with 

regard to how aerosol-induced climate 

change will affect public health. At this 

time, it is not possible to estimate the 

extent to which aerosols in general, let 

alone particular aerosol components, 

contribute to the occurrence or 

exacerbation of adverse health outcomes 

due to climate change. The EPA 

therefore disagrees with CBD’s claim 

that the EPA should pursue black 

carbon reductions for purposes of 

reducing the impacts of climate change 

on public health. 

The Report to Congress on Black 

Carbon also stressed the importance of 

considering co-emitted PM species, 

such as SO2 and NOX, in evaluating the 

benefits of black carbon mitigation 

options. Noting that many of these coemitted particles and gases have a 

cooling influence on climate, the Report 

noted the difficulty of estimating the net 

effect of various mitigation measures on 

net radiative forcing or other climate 

variables. The EPA concluded that the 

location and timing of emissions 

reductions would be critically important 

for achieving climate benefits, and that 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3225 

203This conclusion applies for both the secondary 

(welfare-based) and the primary (health-based) 

standards. 

‘‘more research is needed on the 

benefits of individual control measures 

in specific locations to support policy 

decisions made at the national level’’ 

(U.S. EPA, 2012c, p. 140). Thus, the 

EPA disagrees with CBD’s claim that 

spatial and temporal heterogeneity in 

black carbon emissions do not matter for 

estimating likely climate effects, and 

continues to believe that being able to 

quantify the climate impacts of various 

aerosol species, alone and in 

combination, is essential for informing 

any possible revisions to the current 

secondary PM standards based on 

climate. 

Furthermore, while the EPA agrees 

with the commenter that a large 

percentage of black carbon emissions 

come from anthropogenic sources, 

including diesel engines and vehicles, 

the EPA notes that existing regulations 

on mobile diesel engines are already 

reducing these emissions substantially. 

Between 1990 and 2005, new engine 

requirements resulted in a 32 percent 

reduction in black carbon emissions 

from mobile sources, and a further 86 

percent reduction from 2005 levels is 

projected to occur by 2030 as vehicles 

and engines meeting existing 

regulations are phased into the fleet 

(U.S. EPA, 2012c, p. 175). Long-term 

historic data indicate that there has been 

a dramatic overall decline in black 

carbon emissions over the past century, 

due to changes in fuel use, more 

efficient combustion practices, and 

implementation of PM controls. 

Therefore, the EPA disagrees with CBD’s 

claim that a distinct black carbon 

NAAQS is necessary to achieve 

reductions in black carbon emissions. 

Clearly, U.S. emissions of black carbon 

are already declining substantially, 

suggesting that the existing mass-based 

PM standards, though not targeting 

black carbon specifically, have been 

effective in achieving black carbon 

emissions reductions in practice. As 

acknowledged in the Report to Congress 

on Black Carbon, ‘‘While [black carbon] 

is not the direct target of existing 

programs, it has been reduced through 

controls aimed at reducing ambient 

PM2.5 concentrations and/or direct 

particle emissions’’ (U.S. EPA, 2012c, p. 

161). The EPA has acknowledged the 

need to encourage PM mitigation 

strategies that focus on reducing directly 

emitted PM2.5 for purposes of reducing 

black carbon, and this is reflected in 

U.S. commitments under the 

Gothenburg Protocol: the new 

provisions in the Protocol pertaining to 

PM encourage parties to develop 

national inventories and projections for 

black carbon, and to ‘‘give priority’’ to 

black carbon when implementing 

measures to control PM. However, the 

EPA notes that the U.S. has not yet 

ratified the PM amendments to the 

Gothenburg Protocol, and furthermore, 

these amendments do not require action 

specifically to reduce black carbon, but 

rather encourage countries to take such 

actions voluntarily within the context of 

their broader PM reduction strategies. 

Thus the EPA disagrees with the 

commenter that the U.S. has an 

‘‘obligation’’ to reduce black carbon 

under the Gothenburg Protocol, or that 

it has ‘‘agree[d] to choose mitigation 

options for particulate matter that focus 

on black carbon reductions’’ under the 

Protocol (CBD, p. 13). 

In sum, the EPA notes the substantial 

remaining the uncertainties and gaps 

with regard to the climate impacts of 

PM components, including black 

carbon. These include the uncertainties 

associated with the spatial and temporal 

heterogeneity of PM components that 

contribute to climate forcing; the 

uncertainties associated with 

measurement of aerosol components; 

the inadequate consideration of aerosol 

impacts in climate modeling; and the 

currently insufficient data on local and 

regional microclimate variations and the 

heterogeneity of cloud formations. As a 

result, the EPA continues to conclude 

that it is not currently feasible to 

conduct a quantitative analysis for the 

purpose of informing revisions of the 

current secondary PM standards based 

on climate, and that there is insufficient 

information at this time to base a 

national ambient standard on climate 

impacts associated with current ambient 

concentrations of PM or any of its 

constituents.203

D. Conclusions on Secondary PM 

Standards 

This section describes the 

Administrator’s conclusions regarding 

the secondary PM standards and the 

rationale leading to the Administrator’s 

final decision to retain the current suite 

of secondary PM standards, including 

an annual PM2.5 standard of 15 mg/m3 a 

24-hour PM2.5 standard of 35 mg/m3, and 

a 24-hour PM10 standard of 150 mg/m3, 

to address PM-related visibility 

impairment as well as other PM-related 

welfare effects, including ecological 

effects, effects on materials, and climate 

impacts. Specifically, this section 

explains the Administrator’s decision, 

consistent with the proposal, to retain 

the current suite of secondary PM 

standards generally, while revising only 

the form of the secondary annual PM2.5

standard to remove the option for 

spatial averaging consistent with this 

change to the primary annual PM2.5

standard. It also explains the 

Administrator’s decision, contrary to 

what was proposed, not to establish a 

distinct standard to address PM-related 

visibility impairment. 

In reaching conclusions regarding the 

need to revise the secondary PM 

standards for both visibility and nonvisibility welfare effects, the 

Administrator has taken into account 

several key factors, including: (1) The 

latest scientific information on both 

visibility and non-visibility welfare 

effects associated with PM, as 

previously described; (2) the advice of 

CASAC; and (3) the comments received 

during the public comment period, as 

discussed above. Based on this 

information, the Administrator has 

reached final conclusions about the 

secondary PM standards and made final 

decisions about those standards, as 

outlined below. Because the 

Administrator’s final conclusions with 

regard to the need to establish a distinct 

secondary standard to protect against 

visibility impairment reflect, in part, her 

conclusions on secondary PM standards 

for non-visibility welfare effects, section 

VI.D.1 first outlines her conclusions 

regarding secondary PM standards to 

address non-visibility welfare effects. 

This is followed by section VI.D.2 

which outlines her conclusions 

regarding a secondary PM standard to 

address PM-related visibility 

impairment. Finally, section VI.D.3 

summarizes the Administrator’s final 

decisions with regard to the secondary 

PM standards for both visibility and 

non-visibility welfare effects. 

1. Conclusions Regarding Secondary PM 

Standards To Address Non-Visibility 

Welfare Effects 

With regard to the secondary PM 

standards to address non-visibility 

welfare effects, the Administrator 

concludes that it is generally 

appropriate to retain the existing 

secondary standards and that it is not 

appropriate to establish any distinct 

secondary PM standards to address nonvisibility PM-related welfare effects. 

This conclusion is based on the 

considerations discussed above in 

section VI.B.2, including the latest 

scientific information and the advice of 

CASAC, and the public comments 

received on the proposal, as discussed 

above in section VI.C.2. The 

Administrator concurs with the advice 

of CASAC and the conclusions 

expressed at the time of proposal that it 

is important to maintain an appropriate 


tkelley on DSK3SPTVN1PROD with 
3226 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

204This focus on the 24-hour PM2.5 standard 

reflects the Administrator’s judgments that PMrelated visibility impairment is principally related 

to fine particle concentrations and that perception 

of visibility impairment is most directly related to 

short-term levels of visual air quality. 

degree of control of both fine and coarse 

particles to address non-visibility 

welfare effects, including ecological 

effects, effects on materials, and climate 

impacts. In the absence of information 

that would support any different 

standards the Administrator concludes 

that it is appropriate to retain the 

existing suite of secondary standards to 

address non-visibility welfare effects, as 

proposed. More specifically, the 

Administrator concludes it is 

appropriate to retain all aspects of the 

current 24-hour PM2.5 and PM10

standards. With regard to the secondary 

annual PM2.5 standard, the 

Administrator concludes that it is 

appropriate to retain a level of 15.0 mg/ 

m3 for this standard while revising only 

the form of the secondary annual PM2.5

standard to remove the option for 

spatial averaging consistent with this 

change to the primary annual PM2.5

standard. In reaching this conclusion, 

the Administrator notes that no areas in 

the country are currently using the 

option for spatial averaging to 

demonstrate attainment with the 

secondary annual PM2.5 standard. 

2. Conclusions Regarding Secondary PM 

Standards for Visibility Protection 

Having reached the conclusion that it 

is generally appropriate to retain the 

existing secondary standards to protect 

against non-visibility welfare effects, the 

Administrator next considered the target 

level of protection that would be 

requisite to protect public welfare with 

regard to visual air quality. The 

Administrator then determined whether 

to adopt a distinct secondary standard 

to achieve this target level of protection. 

In making this decision, the 

Administrator compared the degree of 

protection for visibility that would be 

provided by such a distinct secondary 

standard to the degree of protection 

provided by the existing secondary 

standards, focusing specifically on the 

secondary 24-hour PM2.5 standard of 35 

mg/m3.204

Based on the considerations discussed 

above in section VI.B and VI.C, the 

Administrator first concludes that a 

target level of protection for a secondary 

standard is most appropriately defined 

in terms of a PM2.5 visibility index as 

proposed, since it would provide a 

measure of PM-related light extinction 

that directly takes into account the 

factors (i.e., species composition and 

relative humidity) that influence the 

relationship between PM2.5 in the 

ambient air and PM-related visibility 

impairment. Such a PM2.5 visibility 

index standard would afford a relatively 

high degree of uniformity of visual air 

quality protection in areas across the 

country by virtue of directly 

incorporating the effects of differences 

in PM2.5 composition and relative 

humidity across the country. 

In defining a target level of protection 

based on a PM2.5 visibility index, the 

Administrator has considered specific 

aspects of such an index, including the 

appropriate indicator, averaging time, 

level, and form. First, with regard to 

indicator, the Administrator notes the 

conclusion of CASAC that relying on a 

calculated PM2.5 light extinction 

indicator based on PM2.5 chemical 

speciation and relative humidity data 

represented a reasonable approach. 

Based on the analyses conducted in 

support of this rulemaking, as described 

above, as well as the advice of CASAC, 

the Administrator concludes that a 

calculated PM2.5 light extinction 

indicator that utilizes the original 

IMPROVE algorithm, adjusted to use a 

1.6 OC multiplier and exclude the term 

for coarse particles, in conjunction with 

monthly average relative humidity data 

(i.e., f(RH) values) based on long-term 

climatological means would be the most 

appropriate indicator for a PM2.5

visibility index standard. 

With regard to averaging time, the 

Administrator notes that both CASAC 

and EPA staff have concluded that 

hourly or sub-daily (4- to 6-hour) 

averaging times, within daylight hours 

and excluding hours with high relative 

humidity, are more directly related than 

a 24-hour averaging time to the shortterm nature of the perception of PMrelated visibility impairment and the 

relevant exposure periods for segments 

of the viewing public. However, in light 

of the important data quality 

uncertainties that have recently been 

identified in association with currently 

available instruments that would be 

used to provide the hourly PM2.5 mass 

measurements that would be needed in 

conjunction with an averaging time 

shorter than 24 hours, the Administrator 

concludes it would not be appropriate at 

this time to set a standard based on a 

sub-daily averaging time. Moreover, the 

Administrator notes that analyses 

conducted by the EPA during this 

review clearly indicate that PM2.5 light 

extinction calculated on a 24-hour 

average basis would be a reasonable and 

appropriate surrogate for PM2.5 light 

extinction calculated on a 4-hour basis. 

Thus, the Administrator concludes that 

a 24-hour averaging time would be 

appropriate for a PM2.5 visibility index. 

The Administrator recognizes that a 24- 

hour averaging time would effectively 

reduce the influence of peak hours of 

visibility impairment on visibility index 

values, but concludes that in light of the 

concern that peak hourly measurements 

may be significantly influenced by 

atypical conditions and/or atypical 

instrument performance, it is 

appropriate to adopt a longer averaging 

time to ensure that hour-specific 

influences and uncertainties are 

balanced against more robust 

measurements. 

With regard to form, the 

Administrator notes that consistent with 

the approach taken in other NAAQS, 

including the current 24-hour PM2.5

NAAQS, a multi-year percentile form 

offers greater stability to the air quality 

management process by reducing the 

possibility that statistically unusual 

indicator values will lead to transient 

violations of the standard. Utilizing a 

three-year average form provides 

stability from the occasional effects of 

inter-annual meteorological variability 

that can result in unusually high 

pollution levels for a particular year. 

Moreover, considering the lack of 

information on and the high degree of 

uncertainty regarding the impact on 

public welfare of the number of days 

with visibility impairment over the 

course of a year, the Administrator 

considers it reasonable to focus on the 

90th percentile, which represents the 

median of the distribution of the 20 

percent worst visibility days, a key 

focus of the Regional Haze program. The 

Administrator concludes that ensuring 

that 90 percent of days have visual air 

quality that is at or below the target 

level of protection could be reasonably 

expected to lead to improvements in 

visual air quality on the 20 percent most 

impaired days, and that the limited 

information available in this review 

provides no basis for adopting a 

different form which would limit the 

occurrence of days with peak PMrelated light extinction in urban areas to 

a greater degree. Therefore, the 

Administrator concludes that a 90th 

percentile form, averaged over 3 years, 

is appropriate, for purposes of 

establishing a target level of protection 

in terms of a 24-hour PM2.5 visibility 

index. 

With regard to level, the 

Administrator concludes that in light of 

the uncertainty associated with the high 

degree of variability in visibility 

conditions and the potential variability 

in visibility preferences across different 

parts of the country, it is appropriate to 

establish a target level of protection 

based on the upper end of the range of 

Candidate Protection Levels (CPLs) 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3227 

identified in the Policy Assessment (i.e., 

20–30 dv) and generally supported by 

CASAC. Thus, the Administrator 

concludes that it would be appropriate 

to set a target level of protection in 

terms of a PM2.5 visibility index with a 

24-hour averaging time that would 

provide protection equivalent to the 

protection afforded by a 4-hour PM2.5

visibility index with a level of 30 dv. 

Furthermore, the Administrator notes 

that the approaches used to estimate 

generally equivalent levels for a 24-hour 

PM2.5 visibility index generated 90th 

percentile 24-hour values similar to the 

4-hour values and a range of cityspecific estimates of generally 

equivalent 24-hour levels that 

encompassed the range of levels 

considered appropriate for 4-hour CPLs, 

including the CPL of 30 dv at the upper 

end of that range. The Administrator 

thus concludes that it would be 

appropriate to use an unadjusted 4-hour 

CPL for purposes of establishing a target 

level of protection in terms of a 24-hour 

PM2.5 visibility index. 

In considering the alternative levels 

proposed for a 24-hour standard, either 

28 dv or 30 dv, the Administrator 

concludes that the current substantial 

degrees of variability and uncertainty 

inherent in the public preference 

studies should be reflected in a higher 

target protection level than would be 

appropriate if the underlying 

information were more consistent and 

certain. In addition, she concludes that, 

in light of the significant uncertainties, 

it is appropriate to place less weight on 

the results of western visibility 

preference studies and that the CPL 

value (30 dv) that is based on the 

eastern preference study results is likely 

to be more representative of urban areas 

that do not have associated mountains 

or other valued objects visible in the 

distant background For all of these 

reasons, the Administrator concludes 

that it is appropriate to set a target level 

of protection in terms of a 24-hour PM2.5

visibility index at 30 dv. 

In summary, in light of all the 

information available in this review, the 

Administrator concludes that the 

protection provided by a standard 

defined in terms of a PM2.5 visibility 

index (based on speciated PM2.5 mass 

concentrations and relative humidity 

data to calculate PM2.5 light extinction), 

a 24-hour averaging time, and a 90th 

percentile form, averaged over 3 years, 

set at a level of 30 dv, would be 

requisite to protect public welfare with 

regard to visual air quality. 

In reaching this conclusion, the 

Administrator notes that any national 

ambient air quality standard to address 

PM-related visibility impairment would 

be designed to work in conjunction with 

the Regional Haze Program as a means 

of achieving appropriate levels of 

protection against PM-related visibility 

impairment in all areas of the country, 

including urban, non-urban, and 

Federal Class I areas. While the Regional 

Haze Program is focused on improving 

visibility in Federal Class I areas and a 

secondary NAAQS to address PMrelated visibility impairment would 

focus on protecting visual air quality 

principally in urban areas, both 

programs could be expected to provide 

benefits in surrounding areas. In 

addition, the development of local 

programs, such as those in Denver and 

Phoenix, could continue to be an 

effective and appropriate approach to 

provide additional protection, beyond 

that afforded by a national standard, for 

unique scenic resources in and around 

certain urban areas that are particularly 

highly valued by people living in those 

areas. 

Having concluded that the protection 

provided by a standard defined in terms 

of a PM2.5 visibility index, with a 24- 

hour averaging time, and a 90th 

percentile form, averaged over 3 years, 

set at a level of 30 dv, would be 

requisite to protect public welfare with 

regard to visual air quality, the 

Administrator next has to determine 

whether to adopt such a visibility index 

as a distinct secondary standard. This 

determination requires considering such 

a secondary standard not in isolation 

but in the context of the full suite of 

secondary standards. As discussed 

above, the Administrator has 

determined to retain the current suite of 

secondary PM standards to address nonvisibility welfare effects (except for the 

form of the annual standard). A distinct 

secondary standard to address visibility 

impairment is properly considered in a 

context where there is also a 24-hour 

PM2.5 standard of 35 mg/m3. 

In this context, the Administrator has 

considered the degree of protection from 

visibility impairment afforded by the 

existing secondary PM2.5 standards. The 

Administrator has considered both 

whether the existing 24-hour PM2.5

standard of 35 mg/m3 is sufficient (i.e. 

not under-protective) and whether it is 

not more stringent than necessary (i.e. 

not over-protective). 

As discussed above in section 

VI.C.1.f, the results of the Kelly et al. 

(2012a; 2012b) analyses indicate that 

based on 2008–2010 and 2009–2011 

data, all areas meeting the 24-hour PM2.5

standard of 35 mg/m3 had visual air 

quality at least as good as 30 dv (24- 

hour average, based on 90th percentile 

form averaged over 3 years). This means 

that it is highly likely that the secondary 

24-hour PM2.5 standard of 35 mg/m3

would be controlling relative to a 24- 

hour standard based on a PM2.5

visibility index set at a level of 30 dv, 

and highly unlikely that areas would 

exceed the target level of protection for 

visibility of 30 dv without also 

exceeding the existing secondary 24- 

hour standard. On the basis of this 

evidence, and the supporting public 

comments, the Administrator judges 

that the 24-hour PM2.5 standard of 35 

mg/m3 provides sufficient protection in 

all areas against the effects of visibility 

impairment—i.e., that the existing 24- 

hour PM2.5 standard would provide at 

least the target level of protection for 

visual air quality of 30 dv which the 

Administrator judges appropriate. 

The Administrator also recognizes 

that the analyses presented in Kelly et 

al. (2012a; 2012b) indicate that the 24- 

hour PM2.5 standard of 35 mg/m3 also 

would likely achieve more than the 

target level of protection of visual air 

quality (30 dv) in some areas. That is, 

when meeting a mass-based standard of 

35 mg/m3, some areas would have levels 

of PM-related visibility impairment 

below 30 dv. Thus, the 24-hour PM2.5

standard of 35 mg/m3 would be overprotective in some areas (i.e. more 

stringent than necessary) relative to the 

target level of protection for visibility. 

This is not surprising, as the current 

mass-based standard does not account 

for variation in particle species and 

relative humidity. The 24-hour PM2.5

standard of 35 mg/m3 would provide 

more than the necessary protection in 

the areas where this would be expected, 

for example western areas with lower 

relative humidity. 

In light of the Administrator’s 

conclusion that it is appropriate to 

retain the current secondary 24-hour 

PM2.5 standard of 35 mg/m3 for nonvisibility welfare effects, the 

Administrator notes that this standard 

will remain in place regardless of 

whether she elects to set a distinct 

secondary standard in terms of a PM2.5

visibility index. The issue is not 

whether to adopt a PM2.5 visibility index 

standard when viewed in isolation, but 

whether such a distinct secondary 

standard should be adopted in addition 

to the current secondary 24-hour PM2.5

standard of 35 mg/m3. The EPA notes 

that adoption of such a distinct 

secondary standard is not needed to 

provide sufficient protection from 

visibility impairment with respect to the 

target level of protection determined 

above. In addition, adoption of such a 

distinct secondary standard would not 

change the fact that the current 

secondary 24-hour PM2.5 standard of 35 

mg/m3 would result in over-protection 


tkelley on DSK3SPTVN1PROD with 
3228 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

from visibility impairment in certain 

areas of the country. Such overprotection will occur whether or not 

such a distinct secondary standard is 

adopted. In effect, adopting such a 

distinct secondary standard would have 

no impact on the degree of protection 

provided from visibility impairment. 

Since sufficient protection from 

visibility impairment would be 

provided for all areas of the country 

without adoption of a distinct secondary 

standard, and adoption of a distinct 

secondary standard will not change the 

degree of over-protection provided for 

some areas of the country, the 

Administrator judges that adoption of 

such a distinct secondary standard is 

not needed to provide requisite 

protection for both visibility and nonvisibility related welfare effects. 

It is important to note that this 

conclusion is based on the specific 

target level of protection determined 

above, and the specific set of current 

secondary standards. The 

Administrator’s conclusion with regard 

to the sufficiency of the protection 

provided by the current suite of 

secondary standards is based on 

comparing the a 30 dv target level of 

protection for a PM2.5 visibility index 

standard against the degree of protection 

provided by the current secondary 24- 

hour PM2.5 standard of 35 mg/m3. It is 

the combination of the specific target 

level of protection and the current suite 

of secondary standards that is the basis 

for the decision not to adopt a distinct 

secondary standard in terms of a PM2.5

visibility index at this time. 

The EPA recognizes that, as in the last 

review, the final decision is to not adopt 

a distinct secondary standard to address 

visibility impairment. While the DC 

Circuit remanded the decision on a 

secondary standard in the last review, 

the EPA’s decision in this review has 

addressed the issues raised in the 

court’s remand. Here the EPA has 

clearly identified the target degree of 

protection (defined in terms of a PM2.5

visibility index at a level of 30 dv based 

on a 24-hour averaging time, and a 90th 

percentile form, averaged over 3 years) 

that would be requisite to protect public 

welfare with regard to visual air quality. 

The EPA has carefully compared this 

degree of protection with that provided 

by the current secondary 24-hour PM2.5

standard of 35 mg/m3, based on an areaspecific analysis of recent air quality 

data and concluded that the degree of 

protection from visibility impairment 

provided by the current secondary 

standard is sufficient to protect public 

welfare consistent with section 

109(b)(2). This provides a clear basis for 

judging that the current secondary 24- 

hour PM2.5 standard of 35 mg/m3 would 

provide sufficient protection. The 

analysis also shows that the current 

secondary 24-hour PM2.5 standard 

would provide more protection than is 

needed in some areas, largely because it 

does not take into account variable 

factors such as relative humidity. 

However, the EPA has recognized that 

adoption of a distinct secondary 

standard to address visibility, in 

addition to retaining the current 

secondary standard, would not change 

this result. The EPA has therefore 

concluded that adoption of such a 

distinct secondary standard, in addition 

to the current suite of secondary PM 

standards, is not needed to provide 

requisite protection for both visibility 

and non-visibility related welfare 

effects. Thus the EPA’s decision has 

carefully considered and accounted for 

the views of the court in the remand of 

the 2006 NAAQS. 

E. Administrator’s Final Decisions on 

Secondary PM Standards 

To address PM-related welfare effects, 

including ecological effects, effects on 

materials, climate impacts, and 

visibility impairment, the Administrator 

is retaining the current suite of 

secondary PM standards, except for a 

change to the form of the annual 

standard. Specifically, to address PMrelated non-visibility welfare effects 

including ecological effects, effects on 

materials, and climate impacts, the EPA 

is retaining the current secondary 24- 

hour PM2.5 and PM10 standard and is 

revising only the form of the secondary 

annual PM2.5 standard to remove the 

option for spatial averaging consistent 

with this change to the primary annual 

PM2.5 standard. With respect to PMrelated visibility impairment, the 

Administrator has identified a target 

degree of protection, defined in terms of 

a PM2.5 visibility index (based on 

speciated PM2.5 mass concentrations 

and relative humidity data to calculate 

PM2.5 light extinction), a 24-hour 

averaging time, and a 90th percentile 

form, averaged over 3 years, and a level 

of 30 deciviews (dv), which she judges 

to be requisite to protect public welfare 

with regard to visual air quality. The 

EPA’s analysis of monitoring data 

provides the basis for concluding that 

the current secondary 24-hour PM2.5

standard would provide sufficient 

protection, and in some areas greater 

protection, relative to this target 

protection level. Adding a distinct 

secondary standard to address PMrelated visibility impairment would not 

affect this protection. Since sufficient 

protection from visibility impairment 

will be provided for all areas of the 

country without adoption of a distinct 

secondary standard, and adoption of a 

distinct secondary standard will not 

change the degree of over-protection of 

visual air quality provided for some 

areas of the country by the secondary 

24-hour PM2.5 standard, the 

Administrator judges that adoption of a 

distinct secondary standard, in addition 

to the current suite of secondary 

standards, is not needed to provide 

requisite protection for both visibility 

and non-visibility related welfare 

effects. 

VII. Interpretation of the NAAQS for 

PM 

This section discusses the EPA 

Administrator’s final decisions on the 

revisions proposed to the data handling 

procedures for the primary and 

secondary PM2.5 standards. Appendix N 

to 40 CFR part 50 describes the 

computations necessary for determining 

when the PM2.5 standards are met and 

also addresses which measurement data 

are appropriate for comparison to the 

standards; as well, it specifies 

associated data reporting protocols, data 

completeness criteria, and rounding 

conventions. The EPA is modifying 

appendix N to conform to the revised 

PM2.5 standards; most notably, the EPA 

is amending the appendix N procedures 

by removing the option for spatial 

averaging. In addition to making 

changes to appendix N that correspond 

to the changes in the annual standard 

form and the revised primary annual 

standard level, the EPA is also finalizing 

additional proposed revisions to the 

appendix in order to codify existing 

practices currently included in guidance 

documents or implemented as EPA 

standard operating procedures; better 

align appendix N language and 

requirements with changes in PM2.5

ambient monitoring and reporting 

requirements; provide greater clarity 

and transparency in the provisions; and 

enhance consistency with data handling 

protocols utilized for other pollutants. 

A. Revised Amendments to Appendix N: 

Interpretation of the NAAQS for PM2.5

As discussed in sections III and VI 

above, the EPA Administrator has 

decided to: (1) Revise the form and level 

of the primary annual PM2.5 standard, 

and retain the current primary 24-hour 

PM2.5 standard (section III.F) and (2) 

retain the current secondary 24-hour 

PM2.5 standard, and revise the form and 

retain the level of the secondary annual 

PM2.5 standard (for visibility and nonvisibility-related welfare protection) 

(section VI.E). Appendix N is being 

revised to conform to those changes to 

the standards. In the proposal, the EPA 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3229 

recommended additional data handling 

procedures to appendix N for the 

proposed distinct secondary standard to 

address PM2.5-related visibility 

impairment. However, as discussed in 

section VI.E, the Administrator has 

decided not to establish the proposed 

distinct secondary standard to address 

visibility impairment, and therefore, the 

associated proposed data handling 

procedures related to that proposed 

standard are not included in the final 

revised appendix N. 

In addition to the changes to 

appendix N necessitated by the annual 

NAAQS form and level revisions 

(discussed in depth in sections III and 

VI above), the EPA is also finalizing 

additional revisions to appendix N in 

order to: (1) Better align appendix N 

language and requirements with 

changes in the PM2.5 ambient 

monitoring and reporting requirements 

as discussed in section VIII below; (2) 

enhance consistency with recently 

codified changes in data handling 

procedures for other criteria pollutants; 

(3) codify existing practices currently 

included in guidance documents or 

implemented as the EPA standard 

operating procedures; and (4) provide 

enhanced clarity and consistency in the 

articulation and application of appendix 

N provisions. Key elements of the 

finalized revisions to appendix N are 

summarized in sections VII.A.1 through 

VII.A.4 below which correspond to the 

similarly numbered sections in 

appendix N. The proposed potential 

new fifth section of appendix N dealt 

with the proposed distinct PM2.5-related 

visibility secondary standard that was 

not finalized by the Administrator and 

thus the proposed appendix N section 5 

is not included in the final appendix N. 

Furthermore, proposed changes to 

sections 1 through 4 of appendix N that 

also dealt with the proposed secondary 

visibility index standard (e.g., term 

definitions, rounding conventions, etc.) 

are also omitted from the final revised 

appendix. 

1. General 

As proposed, the EPA is finalizing 

modifications to section 1.0 of appendix 

N to provide additional clarity regarding 

the scope and interpretation of the PM2.5

NAAQS. This appendix section now 

references the finalized revisions of the 

primary annual PM2.5 standard (40 CFR 

50.18) and the retained secondary PM2.5

NAAQS. With regard to the appendix N 

term definitions which are delineated in 

this initial section, the EPA has added, 

modified, and eliminated term 

definitions, as appropriate, in 

accordance with the final data handling 

rule revisions such as the modification 

of terms that referenced spatial 

averaging. Additional term definitions 

were also added to reference otherwise 

unchanged appendix N content in an 

effort to streamline the appendix text, 

enhance clarity and thus improve 

readability and understanding. In 

particular, the definition of data 

substitution tests was shortened, and a 

definition for ‘‘test design value’’ (TDV) 

was added for completeness and for 

further clarity. This term was previously 

part of the data substitution definition 

and now it is more explicitly defined. 

The EPA notes that there were no 

substantive public comments received 

with regard to this section. 

2. Monitoring Considerations; Spatial 

Averaging 

As proposed, the EPA has finalized 

revisions to section 2.0 of appendix N 

consistent with the concurrent 

modification of the form of the primary 

annual PM2.5 standard that removes the 

option for spatial averaging. As 

described in more detail in section 

III.E.3.a above, the EPA decided to 

remove this option as part of the form 

of the primary annual PM2.5 standard in 

light of analysis that indicates that the 

existing constraints on spatial averaging, 

as modified in 2006, may be inadequate 

to avoid substantially greater exposures 

in some areas, potentially resulting in 

disproportionate impacts on susceptible 

populations (Schmidt 2011a, Analysis 

A). 

With respect to the form of the 

secondary annual PM2.5 standard, as 

discussed in section VI.E above, the 

EPA has decided to retain the current 

secondary annual PM2.5 standard to 

provide protection for welfare effects. In 

the proposal, the EPA believed it would 

be reasonable and appropriate to align 

the data handling procedures for the 

primary and secondary annual PM2.5

standards and remove the option for 

spatial averaging for the secondary 

annual PM2.5 standard to be consistent 

with the revised form of the primary 

annual PM2.5 standard (FR 77 39000, 

June 29, 2012). The EPA noted that no 

areas in the country are currently using 

the option for spatial averaging to 

demonstrate attainment with the 

secondary annual PM2.5 standard. There 

were no comments on the proposed 

change and the EPA has therefore 

concluded it appropriate to remove the 

option for spatial averaging for the 

secondary annual PM2.5 standard from 

Appendix N. 

Consistent with the revised form of 

the primary and secondary annual PM2.5

standards, the levels of both standards 

will be compared to measurements from 

each appropriate (i.e., ‘‘eligible’’) 

monitoring site in an area, as specified 

in 40 CFR 58.30, with no allowance for 

spatial averaging. Thus, for an area with 

multiple eligible monitoring sites, the 

site with the highest design value would 

determine the attainment status for that 

area. As a result of the decision to 

eliminate the spatial averaging option 

for both the primary and secondary 

annual standards, the EPA omitted all 

references to the spatial averaging 

option in the finalized version of 

appendix N. See section III.E.3.a above 

for a discussion of EPA’s response to 

received public comment on the issue of 

removal of the spatial averaging option. 

3. Requirements for Data Use and 

Reporting for Comparisons With the 

NAAQS for PM2.5

In the proposal, the EPA suggested 

changes to section 3.0 of appendix N to 

correspond to the proposed new 

secondary standard to address PMrelated visibility impairment. Since the 

EPA is not finalizing the proposed 

distinct secondary standard to address 

visibility impairment, none of these 

proposed changes are necessary and are 

not being made. The EPA is, however, 

finalizing proposed changes to improve 

consistency with procedures used for 

other NAAQS as well as to improve 

consistency with current standard 

operating procedures. Specifically, the 

EPA proposed revisions to this section 

regarding: (1) Clarification of monitoring 

data appropriate to compare to the PM2.5

NAAQS; (2) clarification of procedures 

for combining monitoring data from 

collocated instruments into a single 

‘‘combined site’’ record; and (3) 

codification of the current standard 

operating procedure whereby the EPA 

uses data for which the certification 

deadline has passed but the monitoring 

agency has not requested certification of 

the data to determine compliance with 

the PM2.5 NAAQS provided the data are 

complete and accurate (thus making 

appendix N consistent with data 

handling appendices for other criteria 

pollutants). In the final revision to 

appendix N, the EPA is incorporating all 

the above noted modifications to section 

3 of appendix N. Additional details 

describing the incorporated 

modifications are provided below. 

With regard to clarification of which 

monitoring data are appropriate for 

comparison to the PM2.5 NAAQS, the 

proposal acknowledged important data 

quality concerns associated with the 

PM2.5 measurements collected by 

continuous PM2.5 FEMs and referenced 

a subsequent preamble proposal section 

that discussed the issue in more depth 

and put forward a solution to mitigate 

the data quality concerns. The revised 


tkelley on DSK3SPTVN1PROD with 
3230 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

205The EPA also allows use of alternative 

methods where explicitly stated in the monitoring 

methodology requirements (appendix C of 40 CFR 

part 58), such as PM2.5 Approved Regional Methods 

(ARMs) which can be used to determine 

compliance with the NAAQS. Monitoring agencies 

identifying ARMs that are not providing data of 

sufficient quality will also be allowed to exclude 

these data in making comparisons to the PM2.5

NAAQS. Currently, there are no designated ARMs 

for PM2.5. 

206 Data for a combined site record originates by 

default from the designated ‘‘primary’’ monitor at 

the site location and is then augmented with data 

from collocated FRM or FEM monitors whenever 

valid data are not generated by the primary monitor. 

Samples in the combined site record are deemed 

‘‘creditable’’ or ‘‘extra’’ according to the required 

sampling frequency for a specific monitoring site 

(i.e., ‘‘site-level sampling frequency’’) which, by 

default, is defined to be the same as the sampling 

frequency required of the primary monitor. Samples 

in the combined site data record that correspond to 

scheduled days according to the site-level sampling 

frequency are deemed ‘‘creditable’’ and, thus, are 

considered for determining whether or not a 

specific monitoring site meets data completeness 

requirements. These samples also determine which 

daily value in the ranked list of daily values for a 

year represents the annual 98th percentile 

concentration. Samples that are not deemed 

‘‘creditable’’ are classified as ‘‘extra’’ samples. 

These samples do not count towards data 

completeness requirements and do not affect which 

daily values represent the annual 98th percentile 

concentration; ‘‘extra’’ samples, however, are 

candidates for selection as the 98th percentile. 

207Before the introduction of continuous FEMs, 

when two or more samplers were collocated at the 

same site, monitoring agencies typically identified 

the sampler that operated on the more frequent 

sampling schedule as the ‘‘primary’’ monitor for 

developing a single site record. However, due to 

concerns regarding the comparability of FEMs to 

FRMs operated in some monitoring agency 

networks, and as briefly discussed above and in 

more detail in section VIII.B.3.b.iii below, many 

monitoring agencies have kept the FRM as the 

‘‘primary’’ monitor and delegated the continuous 

FEM (which samples more frequently, except in 

cases where the FRM operates on an ‘‘every day’’ 

schedule) to be the ‘‘supplemental’’ (non-primary) 

collocated monitor. In such cases, FEM 

measurements reported on the FRM ‘‘off’’ days were 

technically considered ‘‘extra.’’ In light of this 

practice, EPA modified standing operating 

procedures whereby supplemental collocated FEM 

samples reported on the FRM ‘‘off’’ days would be 

considered ‘‘scheduled’’ and ‘‘creditable.’’ Thus, 

collocated FEM samples would count towards data 

capture rates (actually, increasing both the 

numerator and the denominator in the capture rate 

equation), and also would count towards 

identifying annual 98th percentile concentrations. 

Further, if data from a supplemental collocated 

FEM are missing on an FRM ‘‘off’’ day (and no 

unscheduled FRM data are reported that day), the 

EPA proposed not to identify these as ‘‘scheduled’’ 

days consistent with current practice, and thus, 

reported data generated from the supplemental 

collocated continuous FEMs can only help increase 

data capture rates (77 FR 39001, June 29, 2012)). 

208 Data substitution tests are supplemental data 

completeness assessments that use estimates of 24- 

hour average concentrations to fill in for missing 

data (i.e., ‘‘data substitution’’). 

monitoring rule, promulgated today in 

conjunction with the PM NAAQS 

revision, includes, as proposed, 

language allowing monitoring agencies 

to identify PM2.5 FEMs that are not 

providing data of sufficient 

comparability to the FRM and, with 

EPA approval, to allow such data to be 

deemed ineligible for comparisons with 

the PM2.5 NAAQS 205; see detailed 

discussion of this decision in section 

VIII.A.1 below. Rule language for the 

definition of ‘‘suitable monitors’’ in 

section 1.0 of the finalized revised 

appendix N accommodates and 

references this monitoring rule revision 

codified in 40 CFR 58.11. 

With respect to the procedures for 

combining monitored data from 

collocated instruments into a single 

‘‘combined site’’ data record, the EPA 

proposed to revise the current 

methodology in situations where an 

FRM monitor operating on a non-daily 

schedule is collocated with a 

continuous FEM monitor (that has 

acceptable comparability with an FRM). 

As noted in the proposal, the EPA was 

not advocating a change to the actual 

procedures for constructing a combined 

site record but rather a modification to 

the subsequent evaluation of whether 

the specific measurements were 

considered ‘‘creditable’’ or ‘‘extra’’ 

samples.206 The language clarification 

proposed is currently standard 

operating procedure in Agency design 

value computations so the language 

modification in appendix N merely 

proposed to modify actual practices.207

The revised appendix N finalized in 

today’s action incorporates the 

modification as proposed. The EPA 

notes that there were no substantive 

public comments received regarding 

this change. 

4. Comparisons with the PM2.5 NAAQS 

Section 4.0 of appendix N specifies 

the procedures for comparing monitored 

data to the PM2.5 standards. The EPA 

proposed revisions to section 4.0 of 

appendix N to: (1) Provide consistency 

with the proposed primary and 

secondary annual PM2.5 standards; (2) 

expand the data completeness 

assessments to be consistent with 

current guidance and standard operating 

procedures; and (3) simplify the 

procedure for calculating annual 98th 

percentile concentrations when using an 

approved seasonal sampling schedule. 

Consistent with the proposed 

decisions to revise the level of the 

primary annual PM2.5 standard (section 

III.E.4.b.iii) and to retain the current 

level of the secondary annual PM2.5

standard (section VI.B.1.c.vi), the EPA 

proposed to modify section 4.1(a) of 

appendix N to separately list the levels 

of the primary and secondary annual 

PM2.5 standards. The final revised 

appendix N incorporates this proposed 

change; this appendix N section now 

references the revised primary annual 

standard level of 12.0 mg/m3 and the 

retained secondary annual standard 

level of 15.0 mg/m3. However, as 

discussed above with respect to the final 

decision to not establish a distinct 

secondary standard to provide 

protection for visibility impairment, the 

final appendix N now explicitly 

references all PM2.5 secondary standard 

protection (that is, protection from 

visibility impairment and non-visibilityrelated welfare effects) to be provided 

by the revised annual standard with 

retained level of 15.0 mg/m3 and the 

retained 24-hour standard with retained 

level of 35 mg/m3. Consistent with the 

final decisions to remove the option for 

spatial averaging for the primary annual 

PM2.5 standard (section III.F), as well as 

for the secondary annual PM2.5 standard 

(section VII.A.2), the EPA amended 

section 4.4 of appendix N to remove 

equations and associated instructions 

relating to spatial averaging. 

With regard to assessments of data 

completeness, the EPA proposal 

included two additional data 

substitution tests 208 (making a total of 

three data substitution tests) into 

appendix N for validating annual and 

24-hour PM2.5 design values otherwise 

deemed incomplete (via the 75 percent 

and 11 creditable sample minimum 

quarterly data completeness 

requirements). The EPA proposed to 

add these tests in order to codify 

existing practices currently included in 

guidance documents (U.S. EPA, 1999) 

and implemented as EPA standard 

operating procedures, and further, to 

make the data handling procedures for 

PM2.5 more consistent with the 

procedures used for other NAAQS. 

While the need for data substitution will 

lessen as more continuous PM2.5

monitors continue to be deployed in 

PM2.5 networks, the EPA believes that 

these substitution procedures are 

important to ensure that available data, 

if incomplete, can be confidently used 

to make comparisons to the NAAQS. As 

noted in the EPA proposal, data 

substitution tests are diagnostic in 

nature; that is; they are only used in an 

illustrative manner to show that the 

NAAQS status based on incomplete data 

is reasonable. As codified in section 4 

of Appendix N, data are substituted for 

missing data to produce a ‘‘test design 

value’’ which is compared to the level 

of the NAAQS. If the test design value 

passes the diagnostic test, the 

‘‘incomplete’’ design value (without the 

data substitutions) is then considered a 

valid design value. If an ‘‘incomplete’’ 

design value does not pass any data 

substitution test, then the original 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3231 

209Slightly incomplete is defined as less than 75 

percent but at least 50 percent quarterly data 

capture. 

210Appendix N states that when the data 

substitution tests are satisfied, then the NAAQS 

design values derived from reported PM2.5 data 

which otherwise would be considered to be 

incomplete shall be considered valid for 

comparisons to the PM2.5 NAAQS. 

211A balanced data record has the same 

proportion of ambient measurements (with respect 

to the total number of days in the sampling period) 

in the ‘‘high’’ season as in the ‘‘low’’ season. 

design value is still considered 

incomplete (and not valid for NAAQS 

comparisons). Previously, section 4.1(c) 

of appendix N specified only one data 

substitution test for validating an 

otherwise incomplete design value. That 

diagnostic test only applied to the 

primary and secondary annual PM2.5

standard and only applies in instances 

of a violation; this test is referred to as 

the ‘‘minimum quarterly value’’ test and 

is used to determine if the NAAQS has 

not been met. The two proposed 

additional data substitution tests were 

to be applicable for making comparisons 

to the primary and secondary annual 

and 24-hour PM2.5 standards, 

specifically to show that the NAAQS 

had been met. One of these proposed 

tests uses collocated PM10 data to fill in 

‘‘slightly incomplete’’ 209 data records, 

and the other uses quarter-specific 

maximum values to fill in slightly 

incomplete data records; these two test 

are referred to as the ‘‘collocated PM10

test’’ and the ‘‘maximum quarterly value 

test’’, respectively. Both tests are 

designed to confirm that the PM2.5

design value is valid and is less than the 

level of the NAAQS. 

The EPA received several comments 

on the proposed addition of the two 

data substitution tests to determine that 

the NAAQS was met. The majority of 

comments generally supported the 

proposed addition of data substitution 

tests. However, one commenter 

questioned the general philosophy of all 

appendix N data substitution tests (i.e., 

the existing ‘‘over NAAQS’’ test and the 

two proposed ‘‘under NAAQS’’ tests) by 

suggesting that there were more 

appropriate techniques for filling in for 

missing data that would result in better 

estimates of true design value level. The 

EPA believes that the data substitution 

tests provided in the finalized appendix 

N are all very conservative approaches 

to verify that the NAAQS standards are 

either met or not met, and that the test 

design values are not to be used as the 

best estimators of the design value 

concentration.210

Another commenter questioned, and 

argued against, the use of collocated 

PM10 data in PM2.5 data substitution 

tests. The commenter stressed that this 

type of test is not consistent with those 

established for other pollutants. The 

commenter further argued that while 

PM10 and PM2.5 are both measurements 

of particulate matter, they are 

essentially different pollutants with 

different sources and different 

dispersion characteristics, and further, 

that the ratio of PM2.5 to PM10 varies 

spatially and temporally. In general, the 

commenter claimed that the EPA had 

offered no explanation of why PM10 data 

were valid for a PM2.5 data substitution 

test. At the time of proposal, the EPA 

believed that PM10 data would be 

appropriate for a PM2.5 data substitution 

test. After consideration of public 

comments and additional air quality 

analyses, the EPA has decided that a 

collocated PM10 test is largely 

redundant with the maximum quarterly 

value test and thus not necessary to 

include it in Appendix N. The EPA has 

analyzed the most recent three years of 

PM2.5 and PM10 data (2009–2011) and 

assessed the separate benefit of the PM10

substitution routine compared to the 

maximum quarterly value test (Schmidt, 

2012b). In this assessment of 2009–2011 

PM2.5 design values which did not meet 

the nominal data completeness 

requirements, the EPA found that the 

collocated PM10 test was almost entirely 

redundant with the maximum quarterly 

value test. It was also very infrequently 

needed as a separate test. For the annual 

NAAQS, the maximum quarter value 

test in 100 cases resulted in a test design 

value (TDVmax) less than or equal to 12.0 

mg/m3. There were only two additional 

cases (i.e. 2 percent) when TDVmax was 

greater than 12.0 mg/m3 but the TDV 

associated with the collocated PM10 test 

was less than 12.0 mg/m3. Similarly for 

the 24-hour NAAQS, the maximum 

quarter value test in 116 cases resulted 

in a test design value (TDVmax) less than 

or equal to 35 mg/m3 and again only 2 

additional sites (less than 2 percent) 

passed the collocated PM10 test but not 

the maximum quarterly value test. 

Furthermore, the maximum quarterly 

value tests allowed the annual and 24- 

hour design value to be validated 

approximately 5 times more often than 

through the use of the collocated PM10

test. Accordingly, the EPA has decided 

to not include the collocated PM10 data 

substitution tests in Appendix N, and 

thereby further simplify the data 

handling procedures for making 

comparisons to the annual and daily 

NAAQS. 

With regard to identifying annual 

98th percentile concentrations for 

comparison to the primary and 

secondary 24-hour PM2.5 standards, the 

EPA suggested in the proposal to 

simplify the procedures used with an 

approved seasonal sampling schedule. 

Specifically, the EPA proposed to 

eliminate the use of a special formula 

for calculating annual 98th percentile 

concentrations with a seasonal sampling 

schedule and thereby proposed to use 

only one method for calculating annual 

98th percentile concentrations for all 

sites (77 FR 39002, June 29, 2012). 

The proposal explained that with an 

approved seasonal sampling schedule, a 

site is typically required to sample 

during periods of the year when the 

highest concentrations are expected to 

occur, but less frequently during periods 

of the year when lower concentrations 

are expected to occur (77 FR 39002, 

June 29, 2012). This type of sampling 

schedule generally leads to an 

unbalanced data record; that is, a data 

record with proportionally more 

ambient measurements (with respect to 

the total number of days in the sampling 

period) in the ‘‘high’’ season and 

proportionally fewer ambient 

measurements in the ‘‘low’’ season. In 

the last review, the EPA revised section 

4.5 of appendix N to include a special 

formula for computing annual 98th 

percentile values when a site operates 

on an approved seasonal sampling 

schedule. This special formula 

accounted for an unbalanced data 

record and was consistent with 

guidance documentation (US EPA, 

1999), and, where appropriate, with 

official OAQPS design value 

calculations (71 FR 61211, October 17, 

2006). In cases where there is a 

balanced 211 (or near-balanced) data 

record, the special formula yields the 

same result as the regular procedure for 

calculating annual 98th percentile 

concentrations. 

To qualify for a seasonal sampling 

schedule, monitoring agencies are 

required to co-locate a continuous PM2.5

instrument with the seasonal sampling 

FRM. Since the last review, there has 

been considerable deployment of 

continuous PM2.5 FEM monitors. In 

situations where a PM2.5 FRM monitor 

operating on a non-daily periodic 

schedule (such as a 1-day-in-3 or a 1- 

day-in-6 schedule) is collocated with a 

continuous PM2.5 FEM monitor, data are 

combined based on procedures stated in 

section 3.0 of appendix N as modified, 

as discussed in section VII.A.3 above. 

Combining collocated FRM and FEM 

data effectively results in a site which 

samples everyday and results in a 

balanced data record. In such a case, if 

a site used a seasonal sampling schedule 

regime for the FRM monitor, these data 

would be balanced by the every-day 


tkelley on DSK3SPTVN1PROD with 
3232 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

212References to ‘‘air agencies’’ are meant to 

include state, local, and tribal air agencies 

responsible for implementing the Exceptional 

Events Rule. 

213The EPA released draft exceptional events 

guidance documents (U.S. EPA, 2012e) for public 

comment via a Notice of Availability in the Federal 

Register on July 6, 2012 (77 FR 39959). 

FEM data and there would be no need 

for the special formula for calculating 

annual 98th percentile concentrations 

on the combined site data. 

As EPA noted in the proposal, there 

are very few PM2.5 FRM monitors that 

operated on an approved seasonal 

sampling schedule (only 15 sites out of 

approximately 1,000 total sites in 2010) 

and that for almost half of those sites, 

the collocated continuous instrument 

was a PM2.5 FEM (77 FR 39002, June 29, 

2012). The proposal stated that for the 

3-year period 2008 to 2010, the annual 

98th percentile concentrations 

calculated with the special formula at 

those 15 sites were approximately five 

percent lower than if the regular 

procedure was used. The EPA also 

noted in the proposal that, in the last 

review, the Agency modified the 

monitoring requirements for areas with 

an FRM operating on a non-daily 

schedule such that, when the design 

values were within five percent of the 

24-hour PM2.5 NAAQS, those areas 

would be required to increase the 

frequency of sampling to every day (40 

CFR 58.12(d)(1); 71 FR 61165, October 

17, 2006; 71 FR 61249, October 17, 

2006). In consideration of these facts, 

the EPA proposed to simplify the data 

handling procedures for sites operating 

on a seasonal sampling schedule by 

eliminating the special formula and all 

references to it for the following 

reasons: (1) The small difference 

between 98th percentile concentrations 

calculated using the special formula 

versus the regular procedure and the 

small number of sites currently using 

the special formula; (2) the EPA requires 

every day sampling in areas with design 

values that are within five percent of the 

24-hour PM2.5 NAAQS; and (3) FRMs 

operating on an approved seasonal 

sampling schedule are required to be 

collocated with a continuous PM2.5

instrument (and if that instrument were 

an FEM, the resulting combined site 

record would tend to be balanced over 

the year and thus the special formula 

would be superfluous) (77 FR 39002, 

June 29, 2012). Thus, the EPA proposal 

included only one method for 

calculating annual 98th percentile 

concentrations, the ‘‘regular’’ table lookup method specified in section 4.5(a)(1) 

of appendix N. 

In light of the rationale provided 

above and because EPA received no 

significant negative comments regarding 

the proposal, the EPA concludes it is 

appropriate to eliminate the special 

seasonal sampling 98th percentile 

identification procedure from appendix 

N. The final revised appendix N 

specifies only one method for 

identifying annual 98th percentile 

concentrations; the table look-up 

method is now the only permitted 

technique for identifying annual 98th 

percentile concentrations. 

B. Exceptional Events 

The EPA is finalizing primary annual 

PM2.5-specific deadlines in 40 CFR 

50.14 by which air agencies 212 must flag 

ambient air quality data that they 

believe have been affected by 

exceptional events and submit initial 

descriptions of those events. The EPA is 

also finalizing the deadlines by which 

air agencies must submit detailed 

exceptional events documentation to 

support the exclusion of those data from 

the EPA’s monitoring-based 

determinations of attainment or 

nonattainment with the revised primary 

annual PM2.5 NAAQS. The final 

exceptional events-related schedule is 

aligned with the designations schedule, 

discussed in greater detail in section IX, 

and is promulgated as proposed and as 

supported by multiple commenters. 

Without revisions to 40 CFR 50.14, an 

air agency may not be able to flag and 

submit documentation for some relevant 

data either because the generic 

deadlines may have already passed by 

the time the new or revised NAAQS is 

promulgated or because the generic 

deadlines require documentation 

submission at least 12 months prior to 

the date that the EPA must make a 

regulatory decision. 

The EPA acknowledges the concern 

raised by a few commenters that 

numerous wildfires occurred between 

2010 and 2012 that air agencies may 

determine influenced ambient air 

quality concentrations potentially 

affecting compliance with the revised 

primary annual PM2.5 NAAQS, and that 

air agencies may want to submit 

detailed exceptional events 

documentation associated with multiple 

wildfires. Commenters further noted 

that 1 year to provide documentation of 

these potential exceptional events may 

not be sufficient. The EPA believes that 

the promulgated schedules provide 

sufficient time for air agencies to submit 

information related to the annual 

standard and for the EPA to fully 

consider and act on the submitted 

information during the initial area 

designation process. The EPA recently 

released draft exceptional events 

guidance that clarifies key provisions of 

the 2007 Exceptional Events Rule, 

provides examples of best practices, and 

streamlines the documentation 

development process. The guidance 

provides approaches that are broadly 

applicable to all event/pollutant 

combinations and would apply to many 

PM events, including wildfire/PM 

combinations. Additionally, the EPA 

has posted several concurred upon 

wildfire/PM exceptional event 

demonstration packages on its Web site 

at: http://www.epa.gov/ttn/analysis/ 

exevents.htm. Considered together, the 

EPA believes this guidance will help air 

agencies submit information in a timely 

manner.213 The EPA notes that under 

the promulgated schedule, except for 

events that occur in December 2012, air 

agencies will have more than 1 year to 

provide documentation for these 

potential events. The EPA intends to 

work with potentially affected areas to 

identify, screen, and prioritize events 

potentially influencing compliance with 

the primary annual PM2.5 NAAQS and 

associated area designations. 

Also in response to comments, the 

EPA is clarifying that this preamble 

language and the associated 

promulgated exceptional events 

schedules apply only to the NAAQS 

that the EPA is newly promulgating or 

revising in this action, that is, the 

revised primary annual PM2.5 NAAQS. 

The promulgated exceptional event 

schedule revisions do not apply to the 

retained PM standards (i.e., secondary 

PM standards, primary 24-hour PM10, 

primary 24-hour PM2.5). Further, the 

revised/extended exceptional event 

schedules apply only to those data the 

EPA will use to establish initial area 

designations for the revised primary 

annual PM2.5 NAAQS. 

The ‘‘Treatment of Data Influenced by 

Exceptional Events; Final Rule’’ (72 FR 

13560, March 22, 2007), known as the 

Exceptional Events Rule and codified at 

40 CFR 50.14, contains generic 

deadlines for an air agency to submit to 

the EPA specified information about 

exceptional events and associated air 

pollutant concentration data. As 

discussed in the proposal, without 

revisions to 40 CFR 50.14, an air agency 

may not be able to flag and submit 

documentation for some relevant data 

because the generic deadlines may have 

already passed by the time the new or 

revised NAAQS is promulgated. 

Similarly, revisions to 40 CFR 50.14 are 

needed because air agencies may not be 

able to flag and submit documentation 

for events that occurred in December of 

2013 by 1 year before the designations 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3233 

are made in 2014 as is required by the 

existing generic schedule requires. 

To support appropriate consideration 

of exceptional event data influencing 

ambient air quality concentrations 

potentially affecting compliance with 

the revised primary annual PM2.5

NAAQS, the EPA is adopting revisions 

to 40 CFR 50.14 to change the 

submission dates for claimed 

exceptional events information affecting 

PM2.5 data considered during the initial 

area designations process under the 

promulgated revised primary annual 

PM2.5 NAAQS. As proposed, for air 

quality data collected in 2010 or 2011, 

the EPA is extending to July 1, 2013 the 

otherwise applicable generic deadlines 

of July 1, 2011 and July 1, 2012, 

respectively, for flagging data and 

providing an initial description of an 

event (40 CFR 50.14(c)(2)(iii)). The EPA 

is retaining the existing generic deadline 

in the Exceptional Events Rule of July 

1, 2013 for flagging data and providing 

an initial description of events 

occurring in 2012. Similarly, the EPA is 

revising to December 12, 2013, the 

deadline for submitting documentation 

to justify exceptional events occurring 

in 2010 through 2012 and potentially 

influencing compliance with the revised 

primary annual PM2.5 NAAQS. The EPA 

believes these revisions/extensions will 

provide adequate time for air agencies to 

review potential PM2.5 exceptional 

events influencing compliance with the 

revised primary annual PM2.5 NAAQS 

from 2010 to 2012, to notify the EPA by 

flagging the relevant data and providing 

an initial description in AQS, and to 

submit documentation to support claims 

for exceptional events. These schedule 

revisions will also allow the EPA to 

fully consider and act on the submitted 

information during the initial area 

designation process. 

If an air agency intends the EPA to 

consider in the revised primary annual 

PM2.5 designations decisions whether 

PM2.5 data collected during 2013 

influence compliance with the primary 

annual PM2.5 NAAQS, then the air 

agency must flag these data by the 

generic Exceptional Event Rule deadline 

of July 1, 2014. The EPA is finalizing 

August 1, 2014, as the deadline for 

submitting documentation to justify 

PM2.5-related exceptional events 

occurring in 2013 and potentially 

influencing compliance with the revised 

primary annual PM2.5 NAAQS. The EPA 

believes that these deadlines provide air 

agencies with adequate time to review 

and identify potential exceptional 

events that occur in calendar year 2013 

and for the EPA to fully consider and 

act on the submitted information during 

the initial area designation process. 

While the EPA will make every effort 

to designate areas for the primary 

annual PM2.5 NAAQS on a 2 year 

schedule, the EPA recognizes that it 

may need up to an additional year for 

the designations process to ensure that 

states/tribes and the EPA base 

designations decisions on complete and 

sufficient information. If the EPA 

announces at a later date that it is 

extending the designations schedule 

beyond 2 years based on unavailability 

of data, the EPA will consider extending 

the 2013 exceptional event 

documentation submission schedule by 

promulgating additional revisions to 40 

CFR 50.14. 

Therefore, using the authority 

provided in CAA section 319(b)(2) and 

in the Exceptional Events Rule at 40 

CFR 50.14 (c)(2)(vi), the EPA is 

finalizing the schedule for data flagging 

and submission of demonstrations for 

PM2.5 exceptional events data 

potentially influencing compliance with 

the revised primary annual PM2.5

NAAQS considered for initial area 

designations under the promulgated 

primary annual PM2.5 NAAQS as 

presented in Table 3. 

TABLE 3—REVISED SCHEDULE FOR EXCEPTIONAL EVENT FLAGGING AND DOCUMENTATION SUBMISSION FOR DATA TO BE

USED IN INITIAL AREA DESIGNATIONS FOR THE 2012 PM2.5 NAAQS 

NAAQS Pollutant/standard/(level)/promulgation date 

Air quality data 

collected for 

calendar year 

Event flagging & 

initial description 

deadline 

Detailed 

documentation 

submission deadline 

PM2.5/Primary Annual Standard (12.0 μg/m3) Promulgated December 14, 2012 ....... 2010 and 2011 July 1, 2013 ...... December 12, 2013. 

2012 ................. July 1, 2013a .... December 12, 2013. 

2013 ................. July 1, 2014a .... August 1, 2014. 

aThis date is the same as the general schedule in 40 CFR 50.14. 

Note: The table of revised deadlines only applies to data the EPA will use to establish the initial area designations for the revised primary annual PM2.5 NAAQS. The general schedule applies for all other purposes, most notably, for data used by the EPA for redesignations to 

attainment. 

C. Updates for Data Handling 

Procedures for Reporting the Air Quality 

Index 

There were no comments regarding 

the proposed updates for data handling 

procedures for reporting the AQI. 

However, two table footnotes that were 

part of the existing rule were 

inadvertently omitted from the 

proposal. The inadvertently dropped 

footnotes were footnotes 3 and 4 of 

Table 2 (‘‘Breakpoints for the AQI’’) of 

appendix G (‘‘Uniform Air Quality 

Index (AQI) and Daily Reporting’’) to 

Part 58. Since the footnotes are still 

applicable, the EPA has included them 

in the final rule. The final rule also 

codifies all changes identified in the 

EPA proposal regarding data handling 

procedures for the AQI. 

VIII. Amendments to Ambient 

Monitoring and Reporting 

Requirements 

The EPA is finalizing a number of 

changes to the ambient air monitoring, 

reporting, and network design 

requirements associated with the PM 

NAAQS. Ambient PM monitoring data 

are used to meet a variety of monitoring 

objectives including determining 

whether an area is in violation of the 

PM NAAQS. Ambient PM monitoring 

data are collected by state, local, and 

tribal monitoring agencies (‘‘monitoring 

agencies’’) in accordance with the 

monitoring requirements contained in 

40 CFR parts 50, 53, and 58. This 

section discusses the monitoring 

changes that the EPA is finalizing to 

support the revised PM NAAQS 

summarized in sections III.F, IV.F, and 

VI.F above. 

The monitoring changes being 

finalized primarily relate to the revised 

primary PM2.5 NAAQS. Several 

monitoring changes were proposed 

specifically in support of a potential 

distinct secondary PM2.5 visibility index 

standard; however, as explained in 

Section VI, EPA is not finalizing a 

distinct secondary standard using a 

visibility index and therefore is not 

finalizing the monitoring changes that 

would have been necessary to support 

it. The EPA did not propose any 

monitoring changes associated with the 


tkelley on DSK3SPTVN1PROD with 
3234 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

214Class III refers to those methods for PM2.5 or 

PM10-2.5 that are employed to provide PM2.5 or 

PM10-2.5 ambient air measurements representative of 

one-hour or less integrated PM2.5 or PM10-2.5

concentrations, as well as 24-hour measurements 

determined as, or equivalent to, the mean of 24 onehour consecutive measurements. 

215Class II refers to those methods for PM2.5 or 

PM10-2.5 in which integrated samples are taken by 

filtration and subjected to a subsequent filter 

conditioning process followed by a gravimetric 

mass determination, but which is not a Class I 

equivalent methods because of substantial 

deviations from the design specification of the 

sampler specified for reference methods in 

appendix L or O (as applicable) of part 50 of the 

CFR. 

216At the recent National Air Quality Conference 

in May of 2012, a training session on ‘‘Best 

Practices for Operating PM2.5 Continuous FEMs’’ 

was conducted. Presentations from this session are 

publically available on EPA’s web site at: http:// 

www.epa.gov/ttn/amtic/2012present.html. 

PM10 NAAQS and is not adopting any 

in this final rule. 

A. Issues Related to 40 CFR Part 53 

(Reference and Equivalent Methods) 

To be used in a determination of 

compliance with the PM NAAQS, PM 

data are typically collected using 

samplers or monitors employing an 

FRM or FEM. The EPA also allows use 

of alternative methods where explicitly 

stated in the monitoring methodology 

requirements (appendix C of 40 CFR 

part 58), such as PM2.5 ARMs which can 

be used to determine compliance with 

the NAAQS. The EPA prescribes testing 

and approval criteria for FRM and FEM 

methods in 40 CFR part 53. 

1. PM2.5 and PM10-2.5 Federal Equivalent 

Methods 

As described in the proposal, the EPA 

continues to believe that an effective 

PM2.5 monitoring strategy includes the 

use of both filter-based FRM samplers 

and well-performing continuous PM2.5

monitors. Well-performing continuous 

PM2.5 monitors would include both nondesignated continuous PM2.5 monitors 

and designated Class III 214 continuous 

FEMs that meet the performance criteria 

described in table C–4 of 40 CFR part 53 

when comparing to a collocated FRM 

operated by the monitoring agency. 

Only designated methods (i.e., FRMs, 

FEMs, and ARMs) are approved to be 

used in comparison to the NAAQS; 

however, non-designated methods may 

be useful to meet other monitoring 

objectives (e.g., reporting the AQI). The 

use of Class III continuous FEMs at 

SLAMS is described in more detail in 

section VIII.B.3.b.ii below. Monitoring 

agencies are encouraged to evaluate the 

quality of data being generated by FEMs 

and, where appropriate, to reduce the 

use of manual, filter-based samplers to 

improve operational efficiency and to 

lower overall operating costs. To 

encourage such a strategy, the EPA is 

working with numerous stakeholders 

including the monitoring committee of 

NACAA, instrument manufacturers, and 

monitoring agencies to support national 

data analyses of continuous PM2.5 FEM 

performance, and where such 

performance does not meet data quality 

objectives, to develop and institute a 

program of best practices to improve the 

quality and consistency of resulting 

data. 

The EPA believes that progress is 

being made to implement well 

performing PM2.5 continuous FEMs 

across the nation. As noted in the 

proposal, the first few steps involved 

the EPA developing and approving the 

testing and performance criteria which 

were finalized in 2006, followed by 

instrument companies performing field 

testing and submitting applications to 

the EPA, and the EPA review and 

approval, as appropriate, of Class III 

FEMs. In the current step, monitoring 

agencies are testing and assessing the 

data comparability from continuous 

PM2.5 FEMs. 

While EPA did not propose any 

changes to the performance or testing 

criteria in 40 CFR part 53 used to 

approve PM2.5 continuous FEMs, the 

EPA did propose an administrative 

change to part 53.9—‘‘Conditions of 

designations.’’ See 77 FR 39006. This 

section describes a number of 

conditions that must be met by a 

manufacturer as a condition of 

maintaining designation of an FRM or 

FEM. Subsection (c) of this section 

reads, ‘‘Any analyzer, PM10 sampler, 

PM2.5 sampler, or PM10-2.5 sampler 

offered for sale as part of a FRM or FEM 

shall function within the limits of the 

performance specifications referred to in 

40 CFR 53.20(a), 53.30(a), 53.50, or 

53.60, as applicable, for at least 1 year 

after delivery and acceptance when 

maintained and operated in accordance 

with the manual referred to in 40 CFR 

53.4(b)(3).’’ The EPA’s intent in this 

requirement is to ensure that monitoring 

methods work within performance 

criteria, which includes methods for 

PM2.5 and PM10-2.5; however, there was 

no specific reference to performance 

criteria for Class II 215 and III PM2.5 and 

PM10-2.5 methods. The EPA proposed to 

link the performance criteria referred to 

in 40 CFR part 53.35 associated with 

Class II and III PM2.5 and PM10-2.5

methods with this requirement for 

maintaining designation of approved 

FEMs. The specific performance criteria 

identified in 40 CFR 53.35 for PM2.5 and 

PM10-2.5 methods are available in table 

C–4 to subpart C of 40 CFR part 53. 

All comments received on this 

proposed change were supportive and 

EPA is finalizing this change. The 

implication of this change is that 

instrument manufacturers and air 

agencies operating the equipment will 

have a shared responsibility for 

approved FEMs to meet required 

performance criteria for at least the first 

12 months of operation, which is the 

typical warranty period for an 

instrument. By having a shared 

responsibility for an FEM to meet the 

performance criteria, instrument 

companies and air agencies will both be 

motivated to ensure the best practices 

for installing, operating, and servicing 

an instrument are carried out according 

to the instrument company’s operating 

manual and other readily available 

materials 216 in support of each method. 

2. Use of Chemical Speciation Network 

(CSN) Methods To Support the 

Proposed New Secondary PM2.5

Visibility Index NAAQS 

The EPA had proposed to use CSN 

methods to support the proposed new 

secondary PM2.5 visibility index 

NAAQS; however, as explained in 

Section VI of this final rule, EPA is not 

finalizing the new secondary PM2.5

visibility index NAAQS and therefore 

has no need to finalize the CSN methods 

to support such a standard. 

Despite our decision not to finalize 

formal requirements for CSN methods, 

this network remains a critical 

component in our PM monitoring 

program. The EPA, monitoring agencies, 

and external scientists and policy 

makers use PM2.5 data from the CSN to 

support several important monitoring 

objectives such as: Development of 

modeling tools and the application of 

source apportionment modeling for 

control strategy development to 

implement the NAAQS; health effects 

and exposure research studies; 

assessment of the effectiveness of 

emission reductions strategies through 

the characterization of air quality; and 

development of SIPs. The use of the 

CSN to support all of these objectives 

will continue. 

B. Changes to 40 CFR Part 58 (Ambient 

Air Quality Surveillance) 

1. Terminology Changes 

The EPA proposed to revise several 

terms associated with PM2.5 monitor 

placement to ensure consistency with 

other NAAQS and to conform with longstanding practices in siting of 

equipment by monitoring agencies (77 

FR 39007). 

The EPA proposed to revoke the term 

‘‘community-oriented’’ and replace it 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3235 

217Monitoring Planning Area (MPA) means a 

contiguous geographic area with well established, 

well defined boundaries, such as a CBSA, county 

or State, having a common areas that is used for 

planning monitoring locations for PM2.5. 

218These are found in 40 CFR 58.30 (Special 

considerations for data comparisons to the 

NAAQS). 

219See 40 CFR part 50. 

220See, e.g., 40 CFR 58.1 (defining ‘‘federal 

reference method’’ as ‘‘a method for sampling and 

analyzing the ambient air for an air pollutant 

* * *’’) 

with the term ‘‘area-wide.’’ The term 

‘‘community-oriented,’’ while used 

within the description of the design 

criteria for PM2.5, is not defined and has 

not been used in the design criteria for 

other NAAQS pollutants. Appendix D to 

40 CFR part 58 presents a functional 

usage of the term where sites at the 

neighborhood and urban scale area are 

considered to be ‘‘community-oriented.’’ 

In addition, population-oriented, microor middle-scale PM2.5 monitoring may 

also be considered ‘‘communityoriented’’ when determined by the 

Regional Administrator to represent 

many such locations throughout a 

metropolitan area. The EPA proposed to 

replace this usage of ‘‘communityoriented’’ with the term ‘‘area-wide’’ in 

the text of the PM2.5 network design 

criteria and to define it in 40 CFR 58.1 

to provide a more consistent usage of 

this concept throughout appendix D of 

40 CFR part 58. Specifically, the EPA 

proposed that the terminology would 

read—‘‘Area-wide means all monitors 

sited at neighborhood, urban, and 

regional scales, as well as those 

monitors sited at either micro-or 

middle-scale that are representative of 

many such locations in the same 

CBSA.’’ 

The EPA proposed to revoke the term 

‘‘Community Monitoring Zone’’ (CMZ) 

and to remove references to it in 40 CFR 

part 58. Community monitoring zone is 

currently defined as ‘‘an optional 

averaging area with established, well 

defined boundaries, such as county or 

census block, within an MPA 217 that 

has relatively uniform concentrations of 

annual PM2.5 as defined by appendix N 

of 40 CFR part 50 of this chapter. Two 

or more community oriented state and 

local air monitoring stations (SLAMS) 

monitors within a CMZ that meet 

certain requirements as set forth in 

appendix N of 40 CFR part 50 may be 

averaged for making comparisons to the 

annual PM2.5 NAAQS.’’ The EPA 

proposed to revoke this term and 

references to it since, as discussed in 

section VII.A.2 above, the EPA proposed 

to eliminate all references to the nowrevoked spatial averaging option 

throughout appendix N. 

The one comment directly addressing 

the proposed rule changes (from a state 

air agency) supported the proposal. A 

few industry commenters noted the 

change in the context of how monitoring 

data are used to compare to the NAAQS, 

but did not address the proposed 

specific terminology changes. However, 

as explained in section III.E.3.a, several 

industry commenters did provide 

comments critical of EPA’s proposal to 

revoke spatial averaging which is 

related to revoking the term 

‘‘Community Monitoring Zone’’. 

For the reasons explained above, the 

EPA is finalizing its proposed change to 

revoke the term ‘‘community-oriented’’ 

and to replace it with the term ‘‘areawide.’’ The EPA is also finalizing its 

proposal to revoke the term 

‘‘Community Monitoring Zone’’ (CMZ) 

and references to it in 40 CFR part 58. 

2. Special Considerations for 

Comparability of PM2.5 Ambient Air 

Monitoring Data to the NAAQS 

In general, ambient monitors must 

meet a basic set of requirements before 

the resulting data can be used for 

comparison to the NAAQS. These 

requirements include the presence and 

implementation of an approved quality 

assurance project plan; the use of 

methods that are reference, equivalent, 

or other approved method as described 

in appendix C to 40 CFR part 58; and 

compliance with the probe and siting 

path criteria as described in appendix E 

to 40 CFR part 58. While these 40 CFR 

part 58 requirements apply to any 

monitor that provides data for 

comparison to the NAAQS, there are 

certain additional restrictions that apply 

only to PM2.5 monitoring.218 These 

additional restrictions provide that sites 

must be ‘‘population-oriented’’ for 

comparison to either the 24-hour or 

annual NAAQS, and specifically for 

comparison to the annual NAAQS, sites 

must be sited to represent area-wide 

locations. There is a related provision 

that provides for comparing sites at 

micro- or middle-scales to the annual 

PM2.5 NAAQS when the site is 

determined by the Regional 

Administrator to represent a larger 

region of localized high ambient PM2.5

concentration. 

These provisions have been in the 

monitoring regulations since the 

inception of the PM2.5 NAAQS. 

Nonetheless, these provisions and the 

fact that such monitoring requirements 

are not found in the requirements for all 

other criteria pollutants have created 

areas of uncertainty for the EPA and 

state, local, and tribal agencies that base 

implementation decisions on 

monitoring requirements through 

programs such as dispersion modeling, 

SIP planning, and the calculation of 

transportation conformity budgets. For 

example, in developing modeling 

guidance to support near-road 

transportation conformity modeling, the 

EPA struggled to determine how the 

identification of acceptable PM2.5

receptor locations can be reconciled 

with the PM2.5 monitoring regulations 

that reference potentially acceptable (or 

unacceptable) monitoring locations that 

may, or may not, be considered unique 

for purposes of comparing to the annual 

PM2.5 NAAQS. Accordingly, the EPA 

proposed to revise these particular PM2.5

requirements for consistency with longstanding practices in all other NAAQS 

pollutant monitoring networks, and to 

ensure that interpretation of the 

monitoring rules does not cause 

ambiguity in implementation examples 

that also include the treatment of 

unmonitored areas (see 77 FR 39007– 

009). Each of these topics is described 

below. 

a. Eliminating the Term ‘‘Population 

Oriented’’ From Section 58.30 

The EPA proposed to remove the term 

‘‘population oriented’’ from section 

58.30 so that there would no longer be 

an explicit requirement that PM2.5

monitoring sites be ‘‘populationoriented’’ for comparison to the PM2.5

NAAQS. The EPA noted that this 

requirement is not entirely consistent 

with the definition of ‘‘ambient’’ used in 

the NAAQS. The EPA’s definition of 

ambient air is specified in 40 CFR 

50.1—‘‘Ambient air means that portion 

of the atmosphere, external to buildings, 

to which the general public has access.’’ 

The EPA’s definition of ‘‘populationoriented’’ is provided in 40 CFR 58.1— 

‘‘Population-oriented monitoring (or 

sites) means residential areas, 

commercial areas, recreational areas, 

industrial areas where workers from 

more than one company are located, and 

other areas where a substantial number 

of people may spend a significant 

fraction of their day.’’ The NAAQS are 

standards for concentrations ‘‘in the 

ambient air’’ 219—i.e., air to which 

members of the public could be 

exposed— and all monitors used for 

NAAQS regulatory purposes must be 

representative of ambient air 

concentrations.220 Consistent with this 

requirement and the long-standing 

practice of monitoring agencies locating 

ambient monitors, the EPA’s experience 

is that PM2.5 monitors are placed in 

areas that are representative of 

population exposures. There are no 

PM2.5 monitors currently operating as 


tkelley on DSK3SPTVN1PROD with 
3236 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

221Examples include dispersion modeling to 

support NAAQS attainment planning, associated 

SIP development, and the calculation of 

transportation conformity budgets. 

222The last known non population-oriented site 

at Sun Metro in El Paso Texas (AQS ID: 48–141– 

0053), was shut down in October 2010 and is in the 

process of being moved to a nearby neighborhood. 

‘‘non-population oriented’’ and the EPA 

does not believe that the requirement for 

near-road monitoring (discussed in 

detail further below) will result in 

monitors that are not representative of 

population exposures. At the same time, 

the specification that certain PM2.5

monitors must be ‘‘population-oriented’’ 

in the rules has created substantial 

confusion in how to treat potential 

locations of exposure for NAAQSrelated regulatory requirements other 

than monitoring network design, such 

as in applying modeling as part of a PSD 

or SIP exercise.221

The EPA’s intention in proposing to 

remove the term ‘‘population oriented’’ 

from section 58.30 was to remove a 

potential source of inconsistency in the 

monitoring rules as they apply for all 

the NAAQS. As noted earlier, the 

NAAQS provide protection for the 

public health and welfare in areas 

where the public can be exposed. For all 

other criteria pollutants, the monitoring 

requirements have no such restriction 

on the comparability of a monitor. In the 

case of PM2.5 however, the additional 

restriction of monitors being required to 

be ‘‘population-oriented’’ for 

comparability to the NAAQS has 

existed. The term ‘‘population oriented’’ 

has lacked a quantitative definition (e.g., 

the interpretation of ‘‘substantial 

number’’ in the definition of 

‘‘population-oriented’’), therefore 

monitoring agencies and those 

stakeholders who based implementation 

strategies and decisions on monitoring 

regulations have been uncertain about 

which locations would meet 

requirements described in § 58.30, 

which do not exist for any other 

NAAQS. Monitoring agencies are also 

not in a position to precisely forecast 

where future residential, commercial, or 

recreational development may occur, 

therefore requiring that PM2.5 monitors 

that are to be compared to the NAAQS 

can only be located where ‘‘substantial 

numbers of people’’ live, work, or play 

(i.e., in the present tense) represents an 

unwise limitation on the flexibility of 

monitoring agencies to revise their PM2.5

networks to account for anticipated 

changes in demographics or 

development as well as a contradiction 

with the inherent applicability of the 

NAAQS in ambient air locations where 

the public has access (e.g., in any 

location outside the perimeter of a 

industrial facility). From an operational 

standpoint, we note that revoking this 

term would not change the requirements 

in the PM2.5 network design criteria. To 

the extent that the phrase ‘‘populationoriented’’ served to emphasize the need 

for micro- or middle-scale monitors to 

be representative of locations with 

population exposure to be comparable 

to the annual NAAQS, the definition of 

ambient air, together with the 

requirement in revised section 58.30 

that such sites must be ‘‘area-wide’’ to 

be comparable to the annual NAAQS, 

adequately serves the same purpose. By 

revising the PM2.5 monitoring rules to 

ensure consistency with the longstanding definition of ambient air 

applied to the other NAAQS pollutants, 

the EPA will be able to more clearly 

define how to treat potential exposure 

receptors for other NAAQS regulatory 

requirements, regardless of whether 

monitoring exists or not. 

Public comments on this issue were 

supported by air agencies and public 

health and environmental groups. Two 

commenters from state agencies 

supported the proposed change, with 

one noting further that regardless of a 

change it is still the air agency’s 

responsibility to plan a network with 

sites that are appropriate for comparison 

to the NAAQS. Several public health 

and environmental groups supported 

revoking ‘‘population oriented’’ as a 

condition for comparability of PM2.5

monitoring sites to the NAAQS stating 

that retaining such a policy is 

inconsistent with the text, purpose and 

intent of the Clean Air Act. Most 

industry commenters did not support 

revoking ‘‘population-oriented’’ as a 

condition for comparison to the 

NAAQS. Most of these comments raised 

concerns with using data from an area 

where potentially no one is exposed. 

In considering these comments, the 

EPA agrees that it is appropriate for 

individual air agencies to provide a 

recommendation in the annual 

monitoring network plan regarding 

whether any site may or may not be 

appropriate for comparison to the PM2.5

(or any) NAAQS. The roles of the air 

agency and the EPA in this process of 

identifying whether a site is, or is not, 

consistent with the network plan 

requirements for a NAAQS are specified 

in the already-established monitoring 

requirements of § 58.10. In this approval 

process, the air agency initiates the 

recommendations and the EPA has the 

responsibility to approve, as 

appropriate, any plans that provide for 

changes to the network. 

EPA disagrees with the industry 

comments. As noted above, monitors 

(including those for PM2.5) must already 

meet the test of being representative of 

ambient air to be compared to the 

NAAQS, and thus such monitors 

meeting this test will be sited in 

locations where people are already 

located, or where they could be 

exposed, whether or not the term 

‘‘population oriented’’ appears in 

section 58.30. Moreover, as discussed 

below, comparisons to the annual PM2.5

NAAQS can be only be from monitors 

‘‘that are representative of area-wide air 

quality.’’ ‘‘Area-wide’’ monitors are 

those at the neighborhood scale or 

larger, or at smaller scales if they are 

representative of many such locations in 

the same CBSA. The EPA anticipates 

that a monitor that is sited as 

representative of ambient air at the 

neighborhood scale or larger (or of 

ambient air at many smaller areas) will 

be representative of population 

exposure. This conclusion is further 

supported by the fact that all current 

monitors used for comparison with the 

PM2.5 NAAQS are designated as 

‘‘population-oriented.’’ 222

After consideration of the public 

comments, the EPA is finalizing its 

decision to revoke use of ‘‘populationoriented’’ as a condition for 

comparability of PM2.5 monitoring sites 

to the NAAQS. The EPA concludes that 

the ‘‘population-oriented’’ language is 

unnecessary and inconsistent with other 

monitoring rules, and should therefore 

be removed. 

b. Applicability of Micro- and MiddleScale Monitoring Sites to the Annual 

PM2.5 NAAQS 

The EPA proposed language in 40 

CFR section 58.30 to clarify when data 

from PM2.5 monitoring sites at microand middle-scale locations can be 

compared to the annual PM2.5 NAAQS. 

The EPA’s intent was to provide 

consistency and predictability in the 

interpretation of the monitoring 

regulations. The EPA’s current rules 

state that ‘‘PM2.5 data that are 

representative, not of area-wide but 

rather, of relatively unique populationoriented micro-scale, or localized hot 

spot, or unique population-oriented 

middle-scale impact sites are only 

eligible for comparison to the 24-hour 

PM2.5 NAAQS. For example, if the PM2.5

monitoring site is adjacent to a unique 

dominating local PM2.5 source or can be 

shown to have average 24-hour 

concentrations representative of a 

smaller than neighborhood spatial scale, 

then data from a monitor at the site 

would only be eligible for comparison to 

the 24-hour PM2.5 NAAQS.’’ We 

proposed clarifying language to 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3237 

223NCore is a multi-pollutant network that 

integrates several advanced measurements for 

particles, gases and meteorology (U.S. EPA, 2011a, 

Appendix B, section B.4). Measurements required at 

NCore include PM2.5 mass and speciation, PM10-2.5

mass, ozone, CO, SO2, NO, NOy, and basic 

meteorology. 

explicitly state that measuring PM2.5 in 

micro- and middle-scale environments 

near emissions of mobile sources, such 

as a highway, does not constitute being 

impacted by a ‘‘unique’’ source and so 

could be compared to the annual PM2.5

NAAQS. We explained that mobile 

sources are rather ubiquitous and there 

are many locations throughout an urban 

area where elevated exposures 

attributable to such sources could occur. 

Therefore, we proposed that in most 

cases the potential location for a PM2.5

monitoring site, including micro- and 

middle-scale sites near roadways, would 

be eligible for comparison to the annual 

NAAQS. We further noted that the 

existing definition of ‘‘middle scale’’ in 

appendix D to part 58 already indicates 

that traffic corridors can be middle 

scale, and hence not unique, and 

therefore comparable to the annual 

PM2.5 NAAQS (as well as to the 24-hour 

PM2.5 NAAQS) (77 FR 39008). 

Air agencies that commented on this 

part of the proposed rule offered a 

variety of positions. One air agency 

stated that sites at these smaller scales 

should not be compared to the annual 

NAAQS. Another air agency stated that 

these sites should be considered for 

comparison with the annual PM2.5

NAAQS only when the air agency 

initiates a decision that such sites at 

these smaller scales are area-wide. A 

different air agency offered that all 

micro- and middle-scale sites should be 

compared to the annual NAAQS since 

the wording of the provision is 

problematic and will be difficult for 

agencies to implement. 

Industry commenters were largely 

against finalizing such a provision. The 

major concern raised was that such a 

provision combined with other related 

provisions represented an unwarranted 

tightening of the NAAQS. Some 

industry commenters pointed out that 

there are examples of unique locations 

in near road environments and as such 

EPA should not presume that PM2.5

monitors in these locations should be 

applicable to the annual PM2.5 NAAQS. 

In considering comments on this part 

of the rule, the EPA notes that there are 

already examples of where the States 

and EPA have determined certain 

micro- and middle-scale locations as 

applicable to the annual NAAQS and 

others where they were determined as 

not applicable to the annual PM2.5

NAAQS. These cases exist where a State 

proposed and the Regional 

Administrator determined that either 

the micro-scale or middle-scale site did 

or did not represent many similar areas 

in a CBSA (40 CFR 58.30 and section 4.7 

to Appendix D, part 58). The EPA also 

notes that the existing descriptions of 

the types of micro- and middle-scale 

sites which are unique and cited in 

§ 58.30 are not being amended and that 

data from these types of sites would 

remain as not comparable to the annual 

PM2.5 NAAQS. Accordingly, PM2.5 data 

that are representative, not of area-wide 

but rather, of relatively unique 

population-oriented microscale, or 

localized hot spots, or unique middle 

scale impact sites will only be eligible 

for comparison to the 24-hour NAAQS. 

Our proposal was to clarify language to 

explicitly state that measuring PM2.5 in 

micro- and middle-scale environments 

near emissions of mobile sources, such 

as a highway, does not constitute being 

impacted by a ‘‘unique’’ source and so 

the site could be compared to the 

annual PM2.5 NAAQS. However, in light 

of public comments pointing out that 

there are cases where near-road 

environments can be considered a 

unique location; EPA is not finalizing 

this part of the rule language. Examples 

of such locations that are considered 

unique and should therefore not be 

considered applicable to the annual 

PM2.5 NAAQS are explained later in 

section VIII.B.3.b.i. As noted in the 

preamble to the proposed rule (77 FR 

39008–09), air agencies and the EPA 

will use the annual monitoring network 

plan described in 40 CFR 58.10 for 

identification and approval of sites that 

are suitable and sites that are not 

suitable for comparison with the annual 

PM2.5 NAAQS. 

The EPA disagrees with those 

comments that asserted that the 

proposed change would have 

represented a tightening of the NAAQS. 

As explained in section III.E.3.a on the 

form of the annual NAAQS, the EPA 

carefully considered that areas such as 

traffic corridors were potential high 

exposure areas, since a significant 

fraction of the population, including atrisk populations, live in proximity to 

major roads and should be afforded the 

degree of protection intended by the 

revisions to the form and level of the 

annual PM2.5 standard being adopted. 

Monitoring in such areas as traffic 

corridors does not make the annual 

standard more stringent than intended, 

but rather affords the populations of 

such middle- and micro-scale areas 

(where determined to represent areawide air quality) the requisite level of 

protection from long-term exposure to 

PM2.5. 

3. Changes to Monitoring for the 

National Ambient Air Monitoring 

System 

a. Background 

As described in appendix D to 40 CFR 

part 58, the ambient air monitoring 

networks must be designed to meet 

three basic monitoring objectives: 

(a) Provide air pollution data to the 

general public in a timely manner. Data 

can be presented to the public in a 

number of attractive ways including 

through air quality maps, newspapers, 

Internet sites, and as part of weather 

forecasts and public advisories. 

(b) Support compliance with ambient 

air quality standards and emissions 

strategy development. Data from FRM, 

FEM, and ARM monitors for NAAQS 

pollutants will be used for comparing an 

area’s air pollution levels against the 

NAAQS. Data from monitors of various 

types can be used in the development of 

attainment and maintenance plans. 

SLAMS, and especially National Core 

Monitoring Network (NCore) 223 station 

data, will be used to evaluate the 

regional air quality models used in 

developing emission strategies and to 

track trends in air pollution abatement 

control measures’ impact on improving 

air quality. In monitoring locations near 

major air pollution sources, sourceoriented monitoring data can provide 

insight into how well industrial sources 

are controlling their pollutant 

emissions. 

(c) Support for air pollution research 

studies. Air pollution data from the 

NCore network can be used to 

supplement data collected by 

researchers working on health effects 

assessments and atmospheric processes 

or for monitoring methods development 

work. 

To support the air quality 

management work indicated in the three 

basic air monitoring objectives, a 

network must be designed with a variety 

of types of monitoring sites. Monitoring 

sites must be capable of informing 

managers about many things including 

the peak air pollution levels, typical 

levels in populated areas, air pollution 

transported into and outside of a city or 

region, and air pollution levels near 

specific sources. Following is a listing of 

six general site types: (a) Sites located 

to determine the highest concentrations 

expected to occur in the area covered by 

the network (highest concentration); (b) 


tkelley on DSK3SPTVN1PROD with 
3238 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

224For example, the emissions used for the PM 

NAAQS RIA modeling show that nationwide onroad primary PM2.5 emissions are expected to be 

reduced by 63% between 2007 and 2020. 

Additionally, the elemental carbon portion of the 

on-road emissions is expected to drop by 81 percent 

between 2007 and 2020. Therefore, we expect that 

measured near-road PM2.5 gradients will be much 

lower in the future as elemental carbon is a large 

fraction of the gradient, due to future impacts of 

existing mobile source controls. 

225EPA Regional Administrator approval would 

be required prior to the discontinuation of SLAMS 

monitors, based on the criteria described in 40 CFR 

58.14(c). 

226NO2, CO, and now PM2.5 measurements are all 

expected to be collocated at near-road monitoring 

stations. 

sites located to measure typical 

concentrations in areas of high 

population density (population 

oriented); (c) sites located to determine 

the impact of significant sources or 

source categories on air quality (source 

impact or source oriented); (d) sites 

located to determine general 

background concentration levels 

(general background); and (e) sites 

located to determine the extent of 

regional pollutant transport among 

populated areas (regional transport); and 

in support of secondary standards 

(welfare related impacts). 

b. Primary PM2.5 NAAQS 

The EPA proposed to add a near-road 

component to the PM2.5 network design 

criteria and to clarify the use of 

approved PM2.5 continuous FEMs at 

SLAMS. 

ii. Addition of a Near-Road Component 

to the PM2.5 Monitoring Network 

The EPA proposed to add a near-road 

component to the PM2.5 monitoring 

network (77 FR 39009). The EPA 

explained that there are gradients in 

near-roadway PM2.5 that are most likely 

to be associated with heavily travelled 

roads (particularly those with 

significant heavy-duty diesel activity), 

and that the largest numbers of 

impacted populations are located in the 

largest CBSAs in the country 

(Ntziachristos et al., 2007; Ross et al., 

2007; Yanosky et al., 2009; Zwack et al., 

2011). The EPA further noted that by 

adding a modest number of PM2.5

monitoring sites that are leveraged with 

measurements of other pollutants in the 

near-road environment, a number of key 

monitoring objectives will be supported, 

including collection of NAAQS 

comparable data in the near-road 

environment, support for long-term 

health studies investigating adverse 

effects on people, providing a better 

understanding of pollutant gradients 

impacting neighborhoods that parallel 

major roads, availability of data to 

validate performance of models 

simulating near-road dispersion, 

characterization of areas with 

potentially elevated concentrations and/ 

or poor air quality, implementation of a 

multi-pollutant paradigm as stated in 

the NO2 NAAQS proposed rule (74 FR 

34442, July 15, 2009), and monitoring 

goals consistent with existing objectives 

noted in the specific design criteria for 

PM2.5 described in appendix D, 4.7.1(b) 

to 40 CFR part 58. 

The monitoring methods that are 

appropriate for this purpose are an 

FRM, FEM, or ARM. The EPA 

recognized that there are limitations in 

the ability of some of these methods to 

accurately measure PM2.5 mass due to 

the incomplete retention of semivolatile material on the sampling 

medium (U.S. EPA, 2009a, section 

3.4.1.1). This limitation is relevant to 

the near-road environment as well as to 

other environments where PM is 

expected to have semi-volatile 

components. The EPA also recognized 

that continuous PM2.5 FEMs, which 

provide mass concentration data on an 

hourly basis, are better suited to 

accomplish the goals of near-road 

monitoring as they will complement the 

time resolution of the other air quality 

measurements and traffic data collected 

at the same sites. In this regard, 

particular PM2.5 FEMs are generally 

better suited for near-road monitoring 

than FRMs. However, filter-based FRMs 

do offer some advantages which may be 

highly desirable for near-road 

monitoring, such as readily available 

filters for later chemical analysis such as 

for elemental composition by x-ray 

fluorescence and black carbon (BC) by 

transmissometry. As a result of these 

tradeoffs, monitoring agencies are 

encouraged to select one or more PM2.5

methods for deployment at near-road 

monitoring stations that best meet their 

agencies monitoring objectives while 

ensuring that at least one of those 

methods is appropriate for comparison 

to the NAAQS (i.e., a FRM, FEM, or 

ARM). The EPA believes that by 

allowing monitoring agencies to choose 

the FRM, FEM, or ARM method(s) that 

best fits their needs, whether filterbased or continuous, the data will still 

be able to meet the objectives cited 

above while ensuring maximum 

flexibility for the monitoring agencies in 

the operation of their network. 

The EPA believes that requiring a 

modest network of near-road 

compliance PM2.5 monitors is necessary 

to provide characterization of 

concentrations in near-road 

environments including for comparison 

to the NAAQS. These long-term 

monitors will supplement shorter-term 

networks to support the tracking of 

long-term trends 224 of near-road PM2.5

mass concentrations and other 

pollutants in near-road environments 

where people are exposed. Therefore, 

the EPA proposed to require nearroadway monitoring of PM2.5 at one 

location within each CBSA with a 

population of one million persons or 

greater. The EPA believes that this 

network will be adequate to support the 

NAAQS since the largest CBSAs are 

likely to have greater numbers of 

exposed populations, a higher 

likelihood of elevated near-road PM2.5

concentrations, and a wide range of 

diverse situations with regard to traffic 

volumes, traffic patterns, roadway 

designs, terrain/topography, 

meteorology, climate, surrounding land 

use and population characteristics. 

Given the latest population data 

available, the proposed requirement 

would result in approximately 52 

required near-road PM2.5 monitors 

across the country. An indirect benefit 

of this network design is that 

monitoring agencies in these largest 

CBSAs are more likely to already have 

redundant monitors that could be 

relocated to the near-road environment, 

reducing costs for equipment and 

ongoing operation.225 While only a 

single near-road PM2.5 monitor is 

required within each of the CBSAs, 

agencies may elect to add additional 

PM2.5 monitoring sites in near-road 

environments. 

While the EPA recognized that the 

location of maximum concentration of 

PM2.5 exposure from roadway sources 

might differ from the maximum location 

of NO2 or other pollutants, the EPA 

proposed to require that near-road PM2.5

monitors be collocated with the planned 

NO2 monitors. The NO2 network design 

considers multiple factors that are also 

relevant for PM2.5 concentrations (i.e., 

average annual daily traffic, fleet mix, 

roadway design, congestion patterns, 

terrain, and meteorology) and 

significant thought and review has 

already gone into its design, including 

pilot studies at five locations, and the 

development of a technical assistance 

document in conjunction with the 

affected monitoring agencies and the 

CASAC AAMMS (Russell and Samet, 

2010b) to support deployment. Further, 

this collocation will allow multiple 

pollutants to be tracked in the near-road 

environment. To the extent that air 

agencies are still determining the 

optimum location for their multipollutant 226 near-road monitoring 

stations, EPA encourages consideration 

of sites that best reflect measurement of 

maximum concentrations associated 

with exposure of people living in areas 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3239 

227The EPA has proposed a revised timeline for 

deployment of the near-road NO2 monitors, where 

all CBSAs with one million or more people are to 

have their first near-road NO2 station operational by 

January 1, 2014 (77 FR 64244, October 19, 2012). 

228One study identified that 45 million 

Americans live within 300 feet of a major roadway 

or other source of mobile emissions. The 

commenters’ information is based on the American 

Housing Survey, which is available on the Web at: 

Continued 

that parallel major roads, to maximize 

the value of the data for use later in 

health studies. Therefore, while 

compromises may be necessary when 

siting a multi-pollutant near road 

monitoring station, on balance, the EPA 

believes this is the most efficient and 

beneficial approach for deployment of 

this component of the network. 

The EPA notes that the planned 52 

near-road monitors represent a small 

number of the total approximate 900 

operating PM2.5 monitoring stations 

across the country. The EPA could have 

proposed more near-road sites, however, 

the addition of sites in lower population 

CBSAs is not expected to lead to much 

if any difference in characterization of 

air quality since the bump in PM2.5

concentration associated with near-road 

environments in lower population 

CBSAs, which typically have 

correspondingly less travelled roads, is 

expected to be very small. The EPA 

could also have proposed multiple sites 

in larger CBSAs; however, State 

monitoring programs are already 

working towards representative nearroad monitoring stations and there is a 

synergistic value in ensuring these 

measurements are collocated with 

multiple other measurements to serve 

the monitoring objectives noted above. 

Since EPA has already finalized 

requirement of CO monitoring at nearroad stations in CBSA’s with a 

population of 1 million or more at sites 

that are collocated with NO2, there 

would be less value in requiring any 

more than 52 PM2.5 monitors as any 

more stations will not have CO for use 

in multi-pollutant monitoring objectives 

(e.g., health studies and model 

evaluation). 

Ideally, near-road sites would be 

located at the elevation and distance 

from the road where maximum PM2.5

levels occur in this environment, 

representing locations where 

populations are exposed; for example, 

in apartments and other housing; 

schools located along major roadways; 

industrial parks where workers exposed; 

and in recreational areas such as 

greenways, bikeways, and other park 

facilities that are often developed along 

roads. Specific to probe and siting 

criteria for near-road PM2.5 monitors, 

which is explained later in this section, 

EPA did not set additional criteria on 

what the elevation and distance 

requirements should be, beyond what is 

already defined for PM2.5 or near-road 

NO2 monitors for reasons explained 

above. Also, the EPA did not propose 

that the near-road PM2.5 monitors be 

located within a specific distance of 

other area-wide sites; however, 

monitoring agencies are encouraged to 

consider that a near-road site selected in 

accordance with monitoring 

requirements and also located in 

proximity to a robust area-wide site, 

such as an NCore station, would provide 

useful information in characterizing the 

near-road contribution to multiple 

pollutants, including PM2.5 and tracking 

the decreasing trend that is expected in 

the PM2.5 near-road gradient over time, 

due to future impacts of existing mobile 

source controls. 

The timeline to implement the nearroad PM2.5 monitors should be as 

minimally disruptive to on-going 

operations of monitoring agency 

programs as possible recognizing 

monitoring agency resource constraints, 

while still meeting the need to collect 

for near-road PM2.5 data in a timely 

fashion. Since the near-road PM2.5

monitors were proposed to be collocated 

with the emerging near-road NO2

network that was scheduled to be 

operational by January 1, 2013,227 the 

EPA believes it is appropriate to wait 

until after the near-road NO2 network is 

established before implementing the 

near-road PM2.5 monitors. Therefore, the 

EPA proposed that each PM2.5 monitor 

planned for collocation with a near-road 

NO2 monitoring site be implemented no 

later than January 1, 2015. 

The EPA received comments from a 

number of air agencies, industrial 

groups, and environmental and public 

health organizations on its proposal to 

require PM2.5 monitoring in near-road 

environments. 

Among comments from air agencies, 

several commenters did not support the 

addition of near road monitoring citing 

the challenges of siting these stations 

and the additional cost it would require 

to operate the monitors. Several air 

agencies recognized the value of adding 

monitors to provide better 

characterization of exposures in nearroad environments, but recommended a 

slower deployment of the PM2.5

monitors so that it can be phased in over 

a multi-year period. Several air agencies 

recommended that the PM2.5 monitoring 

in the near-road environment be 

deployed on a phased-in schedule with 

the first such monitors being required 

no sooner than one year after 

deployment of the NO2 sites. These air 

agencies stated that phasing in of the 

PM2.5 monitors in the near road 

environment would allow more time to 

learn and share information on what 

worked best in deploying the NO2

monitors at near-road monitoring 

stations, since NO2 is the first pollutant 

required to be monitored at near-road 

stations. A few air agencies identified a 

need to more clearly support or require 

the maintenance of as much of the 

existing network of neighborhood scale 

PM2.5 monitoring sites as possible in 

regulatory text. These neighborhood 

scale PM2.5 sites were identified by 

commenters as the most broadly 

representative sites for characterizing 

CBSA wide exposures that are 

supportive of a number of monitoring 

objectives. A few air agencies also 

identified a need for flexibility in the 

proposed network design requirement 

that PM2.5 near-road monitors must be 

collocated with the NO2 monitors in the 

near-road environment. The 

commenters suggested allowing 

flexibility for air agencies to meet the 

requirement for PM2.5 in a near-road 

environment by siting at a different 

near-road location where PM2.5

concentrations are expected to be high. 

Most industry commenters did not 

support the addition of near-road 

monitoring for PM2.5, again arguing that 

using data from such monitors, for 

comparison to the NAAQS, combined 

with other changes (i.e., elimination of 

‘‘population-oriented’’ as a criteria for 

comparison to the NAAQS and the 

elimination of spatial averaging) would 

represent, in their judgement, a 

tightening of the PM2.5 NAAQS. A few 

of these commenters asserted that 

monitoring in the near-road 

environment is not representative of 

ambient air exposures. A few industry 

comments noted that if the EPA 

required PM2.5 monitoring in the nearroad environment, any data collected 

should not be used for comparison to 

the NAAQS. One commenter stated it 

had no problem with monitoring in the 

near-road environment, so long as any 

such monitoring used to compare to the 

PM2.5 annual NAAQS is population– 

oriented. One commenter stated that the 

decision to co-locate with NO2 monitors 

was based on convenience and the 

intent of the NO2 near-road monitoring 

is to find the highest micro-scale 

concentrations within a few meters of 

the most heavily travelled expressways, 

representing a unique situation. 

Environmental and public health 

groups strongly support the addition of 

PM2.5 monitoring to the near-road 

environment. Commenters cited the 

large number of people that live in 

proximity to major roadways 228 in their 


tkelley on DSK3SPTVN1PROD with 
3240 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

http://www.census.gov/housing/ahs/data/ 

ahs2009.html. The survey provides an estimate of 

the county’s housing units in the U.S. that are 

located with 300 feet of a highway with four or 

more lanes, or a railroad, or an airport. 

229See the Near-road NO2 Monitoring Technical 

Assistance Document at: http://www.epa.gov/ttn/ 

amtic/files/nearroad/NearRoadTAD.pdf. 

support for adding these monitors, that 

such protection of people in these 

environments is long overdue, and that 

such data therefore be used for 

comparison to the NAAQS. 

Regarding comments from air 

agencies that the near-road monitors are 

challenging to site and that there is 

additional cost in operating these 

monitors, the EPA maintains that the 

major challenges in siting would already 

be accomplished by implementing the 

required NO2 monitoring stations in 

near-road environments since the EPA 

fully expects that the PM2.5 monitors 

will be placed at the NO2 near roadway 

stations and has revised the PM2.5

monitoring requirements consistent 

with that expectation. The EPA also 

points out that the requirements for the 

minimum number of PM2.5 monitors is 

unchanged and that in most cases the 

addition of near-road PM2.5 monitors 

can be accomplished by relocating an 

existing monitor, with no net increase in 

monitors. Thus, while we are requiring 

a new component of the PM2.5

monitoring network, the overall size of 

the network is expected to remain about 

the same, and we expect that air 

agencies can meet this requirement by 

relocating existing lower-priority 

monitors. In considering comments 

from air agencies on a schedule for 

implementing PM2.5 monitors at near 

road monitoring stations, the EPA is 

persuaded by commenters from air 

agencies who stated that a phased 

deployment of the PM2.5 monitors 

would be a better approach as it would 

allow agencies to learn from the 

deployment of the NO2 monitors and a 

first phase of PM2.5 monitors. Phasing in 

the deployment of monitors is also 

consistent with previous CASAC advice 

(Russell and Samet, 2010b) on a 

schedule for deployment of near-road 

NO2 monitors. 

Regarding comments from air 

agencies on maintaining the 

neighborhood scale monitoring stations 

as the largest part of the network as 

these sites are the most broadly 

representative of exposures across 

CBSAs, the EPA supports such a goal. 

Neighborhood scale monitoring sites 

remain the backbone of the PM2.5

monitoring network and they will 

continue to represent over two thirds of 

the operating network following the 

deployment of the near-road monitors. 

The EPA expects that each CBSA 

required to monitor for PM2.5 will 

maintain its existing highest 

concentration area-wide monitoring site 

(referred to as the design value site) and 

not attempt to move such sites to nearroad environments. Maintaining the 

area-wide and largely neighborhood 

scale design value sites is critical to the 

long-standing goal of using data to 

support a variety of monitoring 

objectives. The EPA also recognizes that 

while every PM2.5 monitor has value in 

some capacity at its current location, air 

agencies are expected to recommend 

relocation of monitors that are relatively 

low in priority to meet the near-road 

requirement. 

Regarding comments from air 

agencies on the need for flexibility in 

the network design requirement that 

PM2.5 near-road monitors must be 

collocated with the NO2 monitors in the 

near-road environment, the EPA points 

out that it prefers to maintain this 

requirement so that the multi-pollutant 

data are available to support the 

monitoring objectives cited above. 

However, the EPA also recognizes there 

may be cases where an air agency 

recommends siting their near-road PM2.5

monitor in another high concentration 

near-road environment. The EPA 

believes such cases will be very limited, 

but that these situations can be 

supported in one of two ways. First, 

EPA and the air agency can use their 

discretion to site two near-road PM2.5

monitors in the area. Second, the EPA 

can use its discretion in approving a 

deviation from the PM2.5 monitoring 

requirements as already exists in the 

network design criteria. Such deviations 

are to be approved by the Regional 

Administrator as described in section 

4.7.1 of Appendix D to part 58. 

Regarding the comment that PM2.5

monitors in near-road environments 

were sited for convenience, which due 

to siting with NO2 monitors a few 

meters from the road presents a unique 

situation, the EPA disagrees that these 

monitors were sited solely for 

convenience or that they would 

represent a unique situation within an 

urban area. On the initial point, the EPA 

believes that the characterization of 

representative maximum PM2.5

concentrations due to on-road mobile 

sources and the appropriate location of 

such PM2.5 monitors will be the same 

approximate locations that are the focus 

of the near-road NO2 network. This is 

due to the fact that PM2.5, like NOX, is 

disproportionately influenced by heavy 

duty (HD) vehicles which are 

predominantly diesel fueled, when 

compared to light duty (LD) vehicles 

which are primarily gasoline fueled. 

Specifically, for both PM2.5 and NOX, 

HD vehicles emit more of these two 

pollutants and their precursors on a per 

vehicle basis than LD vehicles. The EPA 

recognized this fact in the near-road 

NO2 network by requiring states to 

consider the fleet mix of candidate road 

segments where near-road monitoring 

might occur. In the design of the NO2

near-road network where the PM2.5

monitors will be installed, states were 

instructed to place a higher priority on 

those highly trafficked roads which 

have more diesel fueled vehicles using 

a metric called the fleet equivalent 

average annual daily traffic.229 As such, 

the Agency believes it is appropriate 

that required near-road PM2.5 monitors 

would be located with near-road NO2

monitors as they are similarly 

influenced not only by fleet mix but also 

by total traffic count, congestion 

patterns, roadway design, terrain, and 

meteorology. On the second point with 

regard to such sites representing a 

unique situation within an urban area, 

EPA points out that the determination of 

a near-road micro- or middle-scale site 

being considered to represent ‘‘areawide’’ air quality or ‘‘unique’’ will be 

made on a case by case basis with the 

monitoring agency providing such 

recommendations in their annual 

monitoring network plans described in 

§ 58.10. Examples of such ‘‘unique’’ 

micro- and middle-scale locations are 

provided later in this section. 

We do not accept the comment that 

siting some monitors in near roadway 

environments makes the standard 

impermissibly more stringent. A 

significant fraction of the population 

lives in proximity to major roads. These 

exposures occur in locations that 

represent ambient air for which the 

agency has a responsibility to ensure the 

public is protected with an adequate 

margin of safety. Ignoring monitoring 

results from such areas (or not 

monitoring at all) would abdicate this 

responsibility. Put another way, 

monitoring in such areas does not make 

the standard more stringent, but rather 

affords requisite protection to the 

populations, among them at-risk 

populations, exposed to fine particulate 

in these areas. Thus, the EPA has made 

a determination to protect all area-wide 

locations, including those locations 

with populations living near major 

roads that are representative of many 

such locations throughout an area. As 

discussed above, EPA concludes that 

the requirement to locate monitors to 

represent ambient air, along with other 

siting requirements, will ensure that 

monitors represent PM2.5 concentrations 

in areas of potential public exposure. 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3241 

230The incremental one-time cost of moving the 

52 monitors required to be located in the near-road 

environment is described in section X.B— 

Paperwork Reduction Act. 

231 76 FR 54294, August 31, 2011. 

232The EPA maintains a list of approved 

Reference and Equivalent Methods on its Web site 

at: http://www.epa.gov/ttn/amtic/criteria.html. 

We do recognize, however, the 

possibility that some near-road 

monitoring stations may be 

representative of relatively unique 

locations versus the more representative 

area-wide situation mentioned above. 

This could occur because an air agency 

made a siting decision based on NO2

criteria that resulted in the 

characterization of a microscale 

environment that is not considered areawide for PM2.5; for example, due to 

proximity to a unique source like a 

tunnel entrance, nearby major point 

source, or other relatively unique 

microscale hot spot. In these types of 

scenarios, air agencies would identify 

the site as a unique monitor comparable 

only to the 24-hour PM2.5 NAAQS per 

the language in section 58.30, and not 

comparable to the annual NAAQS, 

through the Annual Monitoring 

Network Plan process described earlier. 

Although EPA expects most near-road 

PM2.5 monitors to be sited to represent 

area-wide conditions, since a vast 

majority of the near-road stations have 

yet to be installed, we believe that 

providing such clarity and flexibility in 

siting and NAAQS comparability is 

warranted. 

After careful consideration of the 

public comments, the EPA is finalizing 

its decision to add PM2.5 monitors to the 

near-road monitoring stations. The EPA 

is finalizing this decision as the nearroad environment is an area where 

significant public exposure can occur, 

recognizing that this is a gap in the 

current PM2.5 monitoring networks, and 

because these PM2.5 monitors will be 

collocated with NO2 monitors in the 

near-road environment, there will not be 

a significant additional burden on the 

air agencies.230 However, in recognition 

of the comments from air agencies 

above, EPA is finalizing a revised and 

phased schedule for deployment of the 

PM2.5 monitors at near-road stations. A 

minimum of one PM2.5 monitor in each 

CBSA with a population greater than or 

equal to 2.5 million is to be collocated 

at a near-road NO2 monitoring station 

and must to be operational by January 

1, 2015. The remaining CBSAs (i.e., 

those CBSAs with populations greater 

than or equal to 1M, but less than 2.5M) 

must be operational by January 1, 2017. 

This schedule will ensure that air 

agencies have sufficient time to learn 

from deployment of the NO2 monitors in 

near-road environments, that the highest 

population CBSAs begin operating their 

PM2.5 monitors in near-road 

environments first, and that the 

remaining PM2.5 monitors are deployed 

on the same schedule as the CO 

monitors (also, required by January 1, 

2017).231 In consideration of the 

comments regarding maintaining 

neighborhood scale monitoring sites as 

the largest portion of the network, the 

EPA is revising the wording of a 

requirement that requires at least one 

site to be in an area-wide location of 

expected maximum concentration, to 

wording that states that such sites must 

be in an area-wide location of expected 

maximum concentration while also 

being at the neighborhood or larger scale 

of representation. 

iii. Use of PM2.5 Continuous FEMs at 

SLAMS 

The EPA proposed that each agency 

specify its intention and rationale to use 

or not use data from continuous PM2.5

FEMs that are eligible for comparison to 

the NAAQS as part of its annual 

monitoring network plan due to the 

applicable EPA Region Office by July 1 

each year. The proposal also provided 

that the EPA Regional Administrator 

would be responsible for approving 

annual monitoring network plans where 

agencies have provided a 

recommendation that certain PM2.5

FEMs be considered ineligible for 

comparison to the NAAQS. 

In 2006, the EPA finalized new 

performance criteria for approval of 

continuous PM2.5 monitors as either 

Class III FEMs or ARMs. At the time of 

proposal, the EPA had already approved 

six PM2.5 continuous FEMs 232 and there 

are nearly 200 of these monitors already 

operating in State, local, and Tribal 

networks. Monitoring agencies have 

been deploying and field-testing these 

units over the last couple of years and 

the EPA recently compiled an 

assessment of the FEM data in 

relationship to collocated FRMs (Hanley 

and Reff, 2011; U.S. EPA, 2011a, pp. 4– 

50 to 4–51). As described in the 

proposal (FR 38983), the EPA found that 

some sites with continuous PM2.5 FEMs 

have an acceptable degree of 

comparability with collocated FRMs, 

while others had poor data 

comparability that would not meet the 

performance criteria used to approve the 

FEMs (71 FR 61285–61286, Table C–4, 

October 17, 2006). The EPA is 

encouraging use of the FEM data from 

those sites with acceptable data 

comparability including for purposes of 

comparison to the NAAQS. For sites 

with unacceptable data comparability, 

the EPA is working closely with the 

monitoring committee of the NACAA, 

instrument manufacturers, and 

monitoring agencies to document best 

practices on these methods to improve 

the comparability and consistency of 

resulting data wherever possible. The 

EPA believes that the performance of 

many of these continuous PM2.5 FEMs at 

locations with poor data comparability 

can be improved to a point where the 

acceptance criteria noted above can be 

met. 

Given the varying data comparability 

of continuous PM2.5 FEMs noted above, 

we believe that a need exists for 

flexibility in the approaches for how 

such data are used, particularly for the 

objective of determining NAAQS 

compliance. Accordingly, we proposed 

that monitoring agencies address the use 

of data from PM2.5 continuous FEMs in 

their annual monitoring network plans 

due to the applicable EPA Regional 

Office by July 1 of each year for any 

cases where the agency believes that the 

data generated by PM2.5 continuous 

FEMs in their network should not to be 

compared to the NAAQS. The annual 

network plans would include 

assessments such as comparisons of 

continuous FEMs to collocated FRMs, 

and analyses of whether the resulting 

statistical performance would meet the 

established approval criteria. Based on 

these quantitative analyses, monitoring 

agencies would have the option of 

requesting that data from continuous 

FEMs be excluded from NAAQS 

comparison subject to EPA approval; 

however, these data could still be 

utilized for other objectives such as AQI 

reporting. 

The issue exists of whether such data 

use provisions should be prospective 

only (i.e., future NAAQS comparability 

excluded based on an analysis of recent 

past performance) or a combination of 

retrospective and prospective (i.e., the 

implications of unacceptable FEM 

performance impacting usage of 

previously collected data as well as 

future data). In the proposal, the EPA 

stated that in most cases, monitoring 

agencies should be restricted to 

addressing prospective data issues to 

provide stability and predictability in 

the long-term PM2.5 data sets used for 

supporting attainment decisions. 

However, in the first year after this 

proposed option would become 

effective, we indicated it would be 

appropriate to provide monitoring 

agencies with a one-time opportunity to 

review already reported continuous 

PM2.5 FEM data and request that data 

with unacceptable performance be 

restricted (retrospectively) from NAAQS 


tkelley on DSK3SPTVN1PROD with 
3242 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

233 Data from any PM2.5 monitor being used to 

meet minimum monitoring requirements could not 

be restricted from NAAQS comparability. 

comparability. Accordingly, in the first 

year after this rule becomes effective, we 

proposed that monitoring agencies have 

the option of requesting in their annual 

monitoring network plans that a portion 

or all of the existing continuous PM2.5

FEM data, as applicable, as well as 

future data, be restricted from NAAQS 

comparability for the period of time that 

the plan covers.233 In the proposal we 

stated that annual monitoring network 

plans in subsequent years would only 

need to cover new data for the period 

of time that the plan covers. 

As noted above, in cases where an 

agency is operating a PM2.5 continuous 

FEM that is not meeting the expected 

performance criteria used to approve the 

FEMs (71 FR 61285 to 61286, Table C– 

4, October 17, 2006) when compared to 

their collocated FRMs, an agency can 

recommend that the data not be used for 

comparison to the NAAQS. However, all 

required SLAMS would still be required 

to have an operating FRM (or other well 

performing FEM) to ensure a data record 

is available for comparison to the 

NAAQS. In cases where a PM2.5

continuous FEM was not meeting the 

expected performance criteria, and the 

Regional Administrator has approved a 

recommendation that the FEM data not 

be considered eligible for comparison to 

the NAAQS, the data would still be 

required to be loaded to AQS; however, 

these data would be identified distinctly 

from data used for comparison to the 

NAAQS. 

The goal of proposing to allow 

monitoring agencies the opportunity to 

recommend not having data from PM2.5

continuous FEMs as comparable to the 

NAAQS is to ensure that only high 

quality data (i.e., data from FRMs which 

are already well established and new 

continuous FEMs that meet the 

performance criteria used to approve 

FEMs when compared to collocated 

FRMs operated in each agencies 

network) are used when comparing data 

to the PM2.5 NAAQS. Under the current 

monitoring regulations, a monitoring 

agency can identify a PM2.5 continuous 

FEM as an SPM, which allows the 

monitor to be operated for up to 24 

months without its data being used in 

comparison to the NAAQS. While 24 

months should be sufficient time to 

operate the monitor across all seasons, 

assess the data quality, and in some 

cases resolve operational issues with the 

instrument, it may still leave some 

agencies with monitors whose data are 

not sufficiently comparable to data from 

their FRMs. In these cases there may be 

a disincentive to continue operating the 

PM2.5 continuous FEM, especially in 

networks where the monitoring data are 

near the level of the NAAQS. With the 

proposed provision, where a monitoring 

agency can recommend not having data 

from PM2.5 continuous FEMs be 

comparable to the NAAQS, a monitoring 

agency can continue to operate their 

PM2.5 continuous FEM to support other 

monitoring objectives (e.g., diurnal 

characterization of PM2.5, AQI 

forecasting and reporting), while 

working through options for improved 

data comparability while still providing 

data for comparison to the NAAQS from 

an FRM. 

The EPA believes that an assessment 

of FEM performance should include 

several elements based on the original 

performance criteria. The Agency also 

believes that certain modifications to 

the performance criteria are appropriate 

in recognition of the differences 

between how monitoring agencies 

operate routine monitors and how 

instrument manufacturers conduct 

required FRM and FEM testing 

protocols. The details below summarize 

these issues. 

The EPA proposed to use the 

performance criteria used to approve the 

FEMs (71 FR 61285 to 61286, Table C– 

4, October 17, 2006) for those agencies 

that recommend not having data from 

PM2.5 continuous FEMs be comparable 

to the NAAQS. To accommodate how 

routine monitoring networks operate, 

the EPA proposed that agencies seeking 

to demonstrate insufficient data 

comparability base their assessment 

mainly on collocated data from FRMs 

and continuous FEMs at monitoring 

stations in their network. The EPA does 

not believe it is practical to utilize the 

requirement in table C–4 of 40 CFR part 

53 for having multiple FRMs and FEMs 

at each site since such arrangements are 

not typically found in monitoring 

agency networks. Accordingly, the 

requirement for assessing intra-method 

replicate precision would be 

inapplicable. Another consideration is 

the range of 24-hour data 

concentrations, for instance, the 

performance criteria in table C–4 of 40 

CFR part 53, provides for an acceptable 

concentration range of 3 to 200 mg/m3. 

However, the EPA notes that during an 

evaluation of data quality from two 

FEMs (U.S. EPA, 2011a, p. 4–50), the 

Agency found that including low 

concentration data was helpful for 

understanding whether an intercept or 

slope was driving a potential bias in an 

instrument. Therefore, the EPA 

proposed that agencies may include low 

concentration data (i.e., below 3 mg/m3) 

for purposes of evaluating the data 

comparability of continuous FEMs. 

With regard to the minimum number of 

samples needed for the assessment, the 

EPA notes that a minimum of 23 sample 

pairs are specified for each season in 

table C–4 of 40 CFR part 53. Having 23 

sample pairs per season should be easily 

obtainable within one year for sites with 

a FRM operating on at least a 1 in 3 day 

sample frequency and we proposed that 

this requirement be applicable to the 

assessments being discussed here. For 

sites on a one in 6 day sampling 

frequency, two years of data may be 

necessary to meet this requirement. The 

EPA recognizes that it would be best to 

assess the data based on the most 

recently available information; however, 

having data across all seasons in 

multiple years will provide a more 

robust data set for use in the data 

comparability assessment; therefore, the 

EPA proposed that data quality 

assessments be permitted to utilize up 

to the last three years of data for 

purposes of recommending not having 

data from PM2.5 continuous FEMs be 

comparable to the NAAQS. 

The EPA recognizes that only a 

portion of continuous PM2.5 FEMs will 

be collocated with FRMs, and it would 

be impractical to restrict the 

applicability of data comparability 

assessments to only those sites that had 

collocated FRM and FEM monitors. In 

these cases, the monitoring agency will 

be permitted to group the sites that are 

not collocated with an FRM with 

another similar site that is collocated 

with an FRM for purposes of 

recommending that the data are not 

eligible for use in comparison to the 

NAAQS. Monitoring agencies may 

recommend having PM2.5 continuous 

FEM data eligible for comparison to the 

NAAQS from locations where the 

method has been demonstrated to 

provide acceptable data comparability, 

while also recommending not having it 

eligible in other types of areas where the 

method has not been demonstrated to 

meet data comparability criteria. For 

example, a rural site may be more 

closely associated with aged particles 

where volatilization issues are 

minimized resulting in acceptable data 

comparability between filter-based and 

continuous methods, while a highly 

populated urban site with fresh 

emissions with higher volatility may 

result in higher readings on the PM2.5

continuous FEM that would not meet 

the expected performance criteria as 

compared to a collocated FRM. In all 

cases where a monitoring agency chose 

to group sites for purposes of identifying 

a subset of PM2.5 continuous FEMs that 

would not be comparable to the 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3243 

234Through the annual monitoring network plan 

explained in § 58.10. 

235The EPA has had a long-standing policy of 

allowing PM2.5 continuous data to be statistically 

correlated and corrected to use in AQI reporting. A 

report is available on this: See ‘‘Data Quality 

Objectives (DQOs) for Relating Federal Reference 

Method (FRM) and Continuous PM2.5

Measurements to Report an Air Quality Index 

(AQI), EPA–454/B–02–002, November 2002’’. 

NAAQS, the assessment submitted with 

the annual monitoring network plan 

would have to provide sufficient detail 

to support the identification of which 

combinations of method and sites 

would, and would not, be comparable to 

the NAAQS, as well as the rationale and 

quantitative basis for the grouping and 

recommendation. 

Most comments received on this issue 

were from air agencies. All air agencies 

either supported the proposal or 

supported it with a recommendation to 

continue to allow for retrospective 

assessments to be used such that data 

would not be compared to the NAAQS, 

if such an assessment showed that the 

data were not of sufficient comparability 

to a collocated FRM such that the 

continuous FEM should not be 

compared to the NAAQS. One air 

agency supported the proposal, except 

though it had reservations about how to 

best group sites together when a 

particular PM2.5 continuous FEM is not 

collocated with a FRM. 

The EPA notes the support by air 

agencies to finalize this provision. EPA 

also notes that all commenters who 

offered input on the retrospective use of 

assessments were supportive of 

allowing continued retrospective 

assessments in annual monitoring 

networks plans so that data may be 

recommended as excluded from 

comparison to the NAAQS under 

certain provisions. However, the EPA 

has some reservations about how and 

under what circumstances such an 

allowance should be made. The EPA 

notes the concern expressed from one 

agency about how to best group sites 

together when considering an 

assessment. 

On the issue of whether to allow data 

collected to be retrospectively excluded 

from comparison to the NAAQS, the 

EPA notes there are a number of 

considerations, including that several 

air agencies support such a policy. The 

EPA has evaluated how this issue can be 

achieved and believes that some 

consideration should be allowed, but 

also wants to ensure there is a 

consistent and easily recognizable 

interpretation of such cases where air 

agencies recommend excluding already 

collected and reported data. To help 

illustrate the possible outcomes of how 

this could work consider the following 

examples. Example 1: An agency finds 

that the bias between a collocated PM2.5

continuous FEM and FRM are 

acceptable, but near the limit of that 

acceptability and then finds a year later 

that the assessment indicates that the 

bias is just outside the limit of that 

acceptability. Such relatively small 

changes where an assessment indicates 

flipping in or out of the acceptable bias 

are in themselves acceptable since the 

overall Data Quality Objectives (DQOs) 

can still be met. The overall DQOs can 

still be met since there are a number of 

other factors that feed into the DQOs 

such as precision, data completeness, 

and especially sample frequency, which 

when operating a continuous FEM is a 

daily sample. Daily sampling provides 

less uncertainty than sampling at the 

one-in-three day or one-in-six day 

sampling frequencies, which are 

routinely employed by filter-based FRM 

samplers. Therefore, in this example the 

existing data should still be compared to 

the NAAQS, but the air agency should 

thoughtfully consider whether to 

recommend 234 and the EPA will 

consider whether to approve that any 

new data from PM2.5 continuous FEMs 

are used in comparison to the NAAQS. 

If an air agency recommends to not use 

a PM2.5 continuous FEM for comparison 

to the NAAQS, it would need to ensure 

another approved method (i.e., a filterbased FRM/FEM or other continuous 

FEM which is performing within 

acceptable performance criteria) is 

operating at the site or sites of interest. 

This would be expected for all SLAMS, 

but at a minimum the design value 

monitoring station for the area of 

interest would be required to have 

another approved PM2.5 method (i.e., an 

FRM, other filter-based FEM, or other 

continuous FEM or ARM with 

acceptable data comparability) operating 

on the required sample frequency or 

more often for that location. Example 2: 

A PM2.5 continuous FEM operated by an 

air agency is found to have a significant 

bias compared to a collocated FRM. If 

the air agency finds cause to invalidate 

the data (e.g., a flow sensor is found to 

be outside of acceptable limits), then it 

should invalidate the relevant data (i.e., 

data from the period going back to the 

last successful flow check or audit or 

other information that points to a cause 

that the flow sensor is not meeting its 

performance criteria) for all data uses 

and there is no follow-up issue of 

retrospective analysis. A case of finding 

cause to invalidate data would be based 

on validation criteria found in an air 

agencies approved quality assurance 

project plan (QAPP). Example 3: A 

PM2.5 continuous FEM operated by an 

air agency and previously identified as 

appropriate to compare to the NAAQS, 

is found to have a significant and 

unacceptable bias compared to a 

collocated FRM and there is no other 

reason to invalidate the data. That is, all 

other information points to the data 

being valid; however, there has been a 

significant shift in the comparability of 

the PM2.5 continuous FEM compared to 

a collocated FRM (which itself is found 

to be operating correctly and data are 

valid). A significant shift in the 

comparability would be noticeable by 

comparing assessments for a site from 

one year to the next and seeing a 

significant and unacceptable change in 

one of the key statistical metrics used in 

the evaluation (i.e., additive or 

multiplicative bias). Such a case of 

retrospectively recommending not using 

PM2.5 continuous FEM data should also 

take into account all other available 

information that can help inform 

approving such a recommendation as 

part of an annual monitoring network 

plan. For example, do data from the 

PM2.5 performance evaluation program 

data also suggest an unacceptable bias 

for a specific period of interest with this 

method as used in the air agencies 

network? Note: This type of assessment 

is often limited by the small number of 

samples taken in the PEP program 

relative to the large number of 

collocated samples expected when an 

FRM and PM2.5 continuous FEM are 

collocated. In this type of example, the 

air agency might want to recommend 

not using the continuous FEM data for 

comparison to the NAAQS; however, 

the continuous FEM data could be 

appropriate for use in reporting the Air 

Quality Index (AQI) or other data uses 

either as is or if statistically 

correlated 235 and corrected back to the 

collocated FRM. So in this last example, 

the PM2.5 continuous FEM data would 

be stored separately in the EPA’s data 

system so that they are eligible for use 

in AQI calculations, but not used in 

comparison to the NAAQS, if approved 

by the EPA. Again, the air agency 

should thoughtfully consider and state 

its position and rationale in the annual 

monitoring network plan on whether 

any future data should be compared to 

the NAAQS. 

Another issue to consider is the 

transparent and consistent use of PM2.5

continuous FEM data from a method 

where one air agency recommends using 

the data for comparison to the NAAQS 

and another specifically recommends to 

not use it for comparison to the NAAQS. 

The use of the annual monitoring plans 

ensures that the process is transparent; 

however, it may not ensure a consistent 


tkelley on DSK3SPTVN1PROD with 
3244 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

236Approval of an annual monitoring network 

plan is subject to approval of the EPA Regional 

Administrator as provided for in § 58.10(a)(2). 

approach if one agency recommends 

exclusion of data and another agency 

does not. For example, consider two 

adjacent air agencies operating the same 

make and model of a PM2.5 continuous 

FEM, where one air agency recommends 

using data and the other air agency 

recommends not using it for comparison 

to the NAAQS. While on its face it may 

seem straightforward that a method with 

acceptable comparability to a collocated 

FRM should perform similarly in other 

air agency networks where they have 

similar aerosol composition and 

climate, in practice there are a number 

of other variables that affect data 

comparability. Such factors that lead to 

differences in comparability might 

include differences in installation, 

training, development of SOPs, control 

of shelter conditions, maintenance of 

the continuous FEM, and performance 

of the FRMs which are being used as the 

basis of comparison to the continuous 

FEM. Also, there may be cases where 

the concentration levels are so far away 

from the level of the NAAQS (either 

substantially higher or lower) that it 

would not matter if the data are 

excluded or not, the same NAAQS 

determination would result. The EPA 

has considered these issues and in 

general believes that it would still be 

acceptable for one agency to use data for 

comparison to the NAAQS, while 

another agency does not, even if it’s the 

same method used in adjacent air 

agency networks. 

On the issue of grouping sites for 

purposes of allowing monitors that are 

not collocated to be included when 

recommending a method should not be 

compared to the NAAQS, the EPA 

believes that it is not necessary to 

provide specific details on what criteria 

are necessary to group sites as air 

agencies are in the best position to 

determine a recommendation of when 

such sites should or should not be 

grouped. However, to illustrate 

examples of possible ways to group 

sites, the air agency could take into 

account factors such as whether the 

sites are all in either a rural or urban 

location, since urban locations tend to 

be impacted more directly by fresh 

emissions which are known to be more 

volatile, or whether there is consistency 

in the climate for the sites of interest as 

might be the case for sites near a large 

water body or at a high altitude. The 

EPA will consider these issues when 

evaluating air agency requests for 

approval. 

The EPA is finalizing its proposal to 

allow each air agency to specify its 

intention to use or not use data from 

continuous PM2.5 FEMs that are eligible 

for comparison to the NAAQS as part of 

their annual monitoring network plan 

due to the applicable EPA Region Office 

by July 1 each year where adequate FRM 

data are available. The EPA’s approval 

of an annual monitoring network 

plan 236 as a whole, or in part, will 

constitute concurrence with an air 

agency’s recommendation to use or not 

use data from continuous PM2.5 FEMs as 

eligible for comparison to the NAAQS, 

unless otherwise noted in the approval 

of the plan. The absence of an air agency 

statement specifying a position on use 

of data from a continuous PM2.5 FEM for 

comparison to the NAAQS will be 

interpreted as meaning that all such 

data are applicable for comparison to 

the NAAQS following the provisions in 

Part 50, Appendix N on data handling 

and Part 58 on the monitoring 

requirements. In finalizing this decision 

the EPA will ensure, as proposed, that 

air agencies can identify already 

collected data from PM2.5 continuous 

FEMs that should not be used for 

comparison to the NAAQS. After 

considering comments in support of 

allowing additional retrospective 

assessments, the EPA is also finalizing 

an approach of allowing for the 

continued use of retrospective 

assessments to inform when already 

collected data should not be compared 

to the NAAQS, if there has been a 

significant change in the assessment of 

that data from previous years. 

c. Revoking PM10-2.5 Speciation 

Requirements at NCore Sites 

The EPA proposed to revoke the 

requirement for PM10-2.5 speciation 

monitoring as part of the current suite 

of NCore monitoring requirements. The 

requirement to monitor for PM10-2.5 mass 

(total) at all NCore multi-pollutant sites 

remains. PM10-2.5 mass monitoring 

commenced on January 1, 2011 as part 

of the nationwide startup of the NCore 

network (U.S. EPA, 2011a, p. 1–15). 

As part of the process to further 

define appropriate techniques for 

PM10-2.5 speciation monitoring, a public 

consultation with the CASAC AAMMS 

on monitoring issues related to PM10-2.5

speciation was held in February 2009 

(74 FR 4196, January 23, 2009). The 

subcommittee noted the lack of 

consensus on appropriate sampling and 

analytical methods for PM10-2.5

speciation and expressed concern that 

the Agency’s commitment to launch the 

PM10-2.5 monitoring network without 

sufficient time to analyze the data from 

a planned pilot project was premature 

(Russell, 2009). Based on the noted lack 

of consensus on PM10-2.5 speciation 

monitoring techniques, the Agency did 

implement a small pilot monitoring 

project to evaluate the available 

monitoring and analytical technologies. 

The EPA pilot monitoring project was 

completed in 2011, with plans to 

analyze the data and prepare a final 

report on findings and 

recommendations in 2013. At that time, 

the EPA will consider what PM10-2.5

speciation sampling techniques, 

analytical methodologies, and 

monitoring design strategies would be 

most appropriate as part of a potential 

nation-wide monitoring deployment. 

Such a deployment could be based on 

the NCore multi-pollutant framework or 

some other strategy that allows 

flexibility and targets measurements in 

areas with higher levels of coarse 

particles. 

All comments received from air 

agencies and multi-state organizations 

were supportive of the removal of the 

PM10-2.5 speciation requirement. 

A few industry commenters raised 

concerns about the availability of 

PM10-2.5 speciation data for research 

purposes. One environmental group 

opposed revoking the PM10-2.5

speciation requirement and expressed 

the need for PM10-2.5 data to support 

health effects research and future 

regulatory efforts. 

The EPA has considered the 

comments from air agencies that were 

all supportive of revoking the 

requirement, as well as the industry and 

environmental groups concerns that 

PM10-2.5 speciation data will not be 

available for research. In considering 

these comments, the EPA recognizes the 

importance of efforts to develop and 

evaluate speciation monitoring 

approaches for PM10-2.5 given that there 

is relatively little information available 

on the chemical and biological 

composition of PM10-2.5 and on the 

health effects associated with the 

various components (U.S. EPA, 2009a, 

section 2.3.4). Without more 

information on the chemical speciation 

of PM10-2.5, the apparent variability in 

associations with health effects across 

locations is difficult to characterize 

(U.S. EPA, 2009a, section 6.5.2.3). 

However, the EPA believes that until a 

final report on the findings from the 

pilot study is completed in 2013 and the 

results of the study can be considered, 

PM10-2.5 speciation is not ready for 

nationwide deployment. Therefore, the 

EPA is finalizing its decision to revoke 

the PM10-2.5 speciation requirement at 

NCore stations. Given the continued 

importance of characterizing PM10-2.5

species, and given that ongoing and 

future research will likely further 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3245 

inform the development of speciation 

methods, the appropriateness of 

requiring speciation monitoring for 

PM10-2.5 will be revisited in future 

reviews. 

d. Measurements for the Proposed New 

PM2.5 Visibility Index NAAQS 

The EPA proposed requirements for 

sampling of PM2.5 chemical speciation 

in states with large CBSAs. However, as 

explained in section VI, the EPA is not 

finalizing the proposed secondary PM2.5

visibility index NAAQS and therefore is 

not finalizing the proposed monitoring 

changes associated with that standard. 

4. Revisions to the Quality Assurance 

Requirements for SLAMS, SPMs, and 

PSD 

a. Quality Assurance Weight of 

Evidence 

The EPA proposed to use a weight-ofevidence approach for determining 

whether the quality of data is 

appropriate for regulatory decisionmaking purposes. While the EPA 

believes that it is essential to require a 

minimum set of checks and procedures 

in appendix A to support the successful 

implementation of a quality system, the 

success or failure of any one check or 

series of checks should not preclude the 

EPA from determining that data are of 

acceptable quality to be used for 

regulatory decision-making purposes. 

Accordingly, the EPA proposed to 

include additional wording in appendix 

A to clarify the role that appendix A 

generated data quality indicators have 

in the overall quality system that 

supports ambient air monitoring 

activities. 

The EPA received eight comments on 

the weight of evidence approach with 

the majority of commenters endorsing 

the approach. One commenter felt that 

the ‘‘paragraph, as written, undermines 

the importance of the quality control/ 

quality assurance system dictated in 

Part 58.’’ Some that supported the 

approach also provided a word of 

caution that ‘‘while a common sense 

approach to the assessment of quality 

data is important, minimum 

requirements are necessary to ensure 

scientifically-defensible data is being 

used in decision making’’. The EPA 

agrees with the commenter’s points that 

data should be subject to a minimum set 

of requirements for data collection, 

reporting and quality. In developing the 

weight of evidence approach, the EPA is 

not attempting to diminish the 

requirements of appendix A but rather 

ensure that other elements of a quality 

system that air agencies implement and 

are documented in their QAPP can also 

be used when judging whether data are 

valid for a particular monitoring 

objective. While the EPA considers the 

appendix A requirements the minimum 

for reporting, it is not the only data that 

the EPA and the air agencies use to 

judge quality. Therefore, if an appendix 

A requirement for some reason is not 

complete, the EPA concludes that it 

should not necessarily be the sole 

reason to declare the data invalid or 

unusable. One commenter who felt that 

the approach may be appropriate also 

suggested that the language of the 

proposal was vague and may weaken 

the ability of air monitoring agencies to 

validate their own data and instead 

allows the EPA to make decisions 

regarding data validity. In the majority 

of cases when the quality of ambient air 

data is called into question, the EPA 

Regions and air agencies work together 

and reach consensus on data usability. 

The EPA agrees that the air agencies 

know more about their data and it is the 

air agencies responsibility to certify the 

data as valid. In most cases, the EPA 

and the air agencies will be in 

agreement on the validity and usability 

of this data. However, since the EPA is 

responsible for making final regulatory 

decisions concerning the NAAQS, in 

rare cases it may ultimately have to 

make a validity decision that the air 

agencies may not agree with. After 

consideration of the general support 

received, the EPA will finalize the 

language as proposed. For the reasons 

explained above, the EPA concludes 

that this will not undermine the quality 

assurance system, but rather strengthen 

it. 

A few commenters, although 

supporting the weight of evidence 

approach, also commented that 

appendix A minimum requirements 

should not only apply to all air quality 

data collected by state, local, and tribal 

agencies, but also to ‘‘secondary’’ data 

collected by other monitoring efforts. 

The EPA understands that this term is 

used by these commenters to either 

represent the Chemical Speciation and 

IMPROVE Network data being used to 

calculate light extinction for the 

secondary PM2.5 visibility index 

NAAQS, or for criteria pollutant data 

collected by entities other than the state, 

local or tribal monitoring organizations. 

The EPA agrees with the comments that 

the appendix A requirements must 

apply to the CSN and IMPROVE data, if 

the data were being used for comparison 

to the secondary NAAQS, and included 

the term ‘‘PM2.5 CSN’’ to refer to both 

networks. However, since as explained 

in Section VI, the secondary PM2.5

visibility index NAAQS is not being 

finalized, the EPA will be removing any 

text related to the CSN and IMPROVE 

requirements from appendix A. If the 

term is being used by commenters to 

refer to criteria pollutant data collected 

by entities other than the state, local or 

tribal monitoring organizations then the 

appendix A requirements, as has always 

been the case, apply to those monitors. 

b. Quality Assurance Requirements for 

the Chemical Speciation Network 

The EPA proposed to include 

requirements for flow rate verifications 

and flow rate audits for the PM2.5 CSN. 

Air agencies currently perform these 

audits even though they are not 

currently required. Thus, although they 

would be considered a new 

requirement, they are not new 

implementation activities. In addition, 

the CSN already includes six collocated 

sites which the EPA proposes to include 

in the 40 CFR part 58 appendix A 

requirements. The EPA proposed that 

PSD sites would not be required to 

collocate a second set of instruments for 

speciated PM2.5 mass monitoring. 

There were no comments that 

specifically addressed the addition of 

collocation and flow rate requirements 

in appendix A for the chemical 

speciation network (CSN). Since these 

flow rates have historically been 

included in the Agencies’ CSN Network 

Quality Assurance Project Plan and 

implemented for many years, air 

agencies may not have considered them 

any additional burden on the program. 

However, as explained in Section VI, 

the secondary PM2.5 visibility index 

NAAQS is not being finalized; therefore, 

the EPA will not include these QA 

requirements into appendix A since the 

networks will not produce data to be 

used for NAAQS decisions. 

c. Waivers for Maximum Allowable 

Separation of Collocated PM2.5 Samplers 

and Monitors 

The EPA proposed to allow waivers, 

when approved by the EPA Regional 

Administrator, for collocation of PM2.5

samplers and monitors of up to 10 

meters so long as the site is at a 

neighborhood scale or larger. The EPA 

proposed to allow waivers for the 

maximum allowable distance associated 

with collocated PM2.5 samplers and 

monitors. Ensuring PM2.5 continuous 

FEMs and PM2.5 FRMs meet collocation 

requirements (i.e., 1 to 4 meters for 

PM2.5 samplers with flow rates of less 

than 200 liters/minute) can be 

challenging, since in some cases 

multiple instruments, FEMs installed in 

the shelter and FRMs installed on a 

platform, are being sited at the same 

station. The EPA believes that 


tkelley on DSK3SPTVN1PROD with 
3246 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

237See Table E–1 in Appendix E to Part 58 for 

defining the scale of representation of a PM sampler 

based on its distance to the nearest traffic lane and 

average daily traffic count. 

instruments spaced farther apart could 

be maintained within the operational 

precision of the instruments, especially 

at sites located at larger scales of 

representation (e.g., neighborhood scale 

and larger). 

All comments received responded in 

support of the requirement allowing up 

to 10 meter horizontal spacing for sites 

at a neighborhood or larger scale of 

representation. The EPA received no 

negative comments on this part of the 

proposal. During stakeholder 

presentations of the proposal, the EPA 

received a verbal comment that air 

agencies were also having difficulty 

meeting the one meter vertical criteria 

since PM2.5 FEMs are typically housed 

in shelters with inlets extending 

through shelter roofs while the 

collocated FRM monitors are placed 

outside, usually on platforms somewhat 

lower to the ground. After considering 

this comment, and further discussion 

with EPA Office of Research and 

Development on spacing requirements, 

the agency will amend the appendix A 

requirements to allow for a 1–3 meter 

vertical spacing which may be approved 

by the Regional Administrator for sites 

at a neighborhood or larger scale of 

representation. In addition, the language 

will be amended to allow for waiver 

approvals during annual network plan 

approval processes. Alternatively, the 

existing waiver provision outlined in 

paragraph 10 of Appendix E may be 

used. 

5. Revisions to Probe and Monitoring 

Path Siting Criteria 

a. Near-Road Component to the PM2.5

Monitoring Network 

The EPA proposed that the probe and 

siting criteria for the near-road 

component of the PM2.5 monitoring 

network design follow the same probe 

and siting criteria as the NO2 near-road 

monitoring sites. These requirements 

would provide that the monitoring 

probe be sited ‘‘* * * as near as 

practicable to the outside nearest edge 

of the traffic lanes of the target road 

segments; but shall not be located at a 

distance greater than 50 meters, in the 

horizontal, from the outside nearest 

edge of the traffic lanes of the target 

road segment’’ (section 6.4 of appendix 

E to 40 CFR part 58). 

The EPA received comments from 

several stakeholders on the probe and 

siting criteria for PM2.5 monitors in the 

near-road environment. One public 

health group offered detailed comments 

on the probe and siting criteria for PM2.5

monitors in near-road environments. 

While the commenter offered support 

for collocating the PM2.5 monitors with 

NO2 monitors in the near-road 

environment, there was concern 

expressed regarding allowing monitors 

at sites of more than 15 meters from the 

traffic corridor which is the source of 

the air quality concern. The commenter 

points out that the EPA’s existing rules 

for siting localized hot spot sites in 

areas of highest concentration require 

sites at microscale locations which 

provide for a distance of no more than 

15 meters from a major roadway. 

Several air agencies offered consistent 

comments that the inlet of the PM2.5

monitors should be the same as that of 

the near-roadway NO2 monitors; 

however, one of the commenters 

suggested that the requirements for 

distance to the nearest vertical wall or 

obstruction should match the 

requirements for current micro and 

middle scale installations of PM2.5

monitors. The concern expressed is that 

a wall or obstruction may disrupt the 

normal downwind flow across a 

roadway. 

In reviewing comments on probe and 

monitoring path criteria for PM2.5

monitors in near road environments, 

and whether to make any changes, the 

EPA has several issues to consider. One 

of the most important things to consider 

is what the intended network design of 

these monitors should be. As stated in 

the proposal our goal is to ‘‘better 

understand the health impacts of these 

(near-road PM2.5) exposures,’’ that a 

number of monitoring objectives can be 

supported by having near-road PM2.5

monitors, and that while it might be that 

the location of maximum concentration 

of PM2.5 exposure from near-roadway 

sources might differ from the maximum 

location of NO2 or other pollutants, we 

proposed to require that the near-road 

PM2.5 monitors be collocated with the 

planned NO2 monitors. The EPA did not 

propose to change the distance from 

obstructions for PM2.5 monitors in its 

proposal. 

As we stated in the proposal, the 

planned NO2 monitors are using several 

relevant factors that are also relevant for 

siting of PM2.5 (e.g., average annual 

daily traffic and fleet mix [accounting 

for heavy duty vehicles] by road 

segment) and that significant thought 

and review are going into the design of 

the near-road stations. Therefore, the 

EPA is not persuaded that we should 

provide any additional constraints to 

the siting of the station (i.e., the distance 

from the roadway) than is already 

provided for in the NO2 near-road 

monitor probe and monitoring path 

siting criteria. The EPA is concerned 

that additional constraints (i.e., to 

require sites within 15 meters of the 

road), might have some advantages, but 

also might unnecessarily eliminate 

otherwise useful near-road locations 

that on balance might be a better 

candidate location. 

The EPA recognizes that there may be 

cases where the physical location of a 

near-road monitoring station is farther 

than 15 meters, but no greater than 50 

meters from the roadway, but such cases 

are presumed to still be the most useful 

location for the siting of the NO2

monitors, which we then proposed to 

collocate with PM2.5. Regardless of the 

actual distance of the inlet for the PM2.5

monitor at the near-road monitoring 

station, so long as it is collocated with 

the approved near-road station for NO2

and meets existing criteria, the EPA will 

consider this site to be appropriate as a 

near-road PM2.5 monitoring station. As 

explained in the proposal, there are a 

number of reasons to collect multipollutant data in the near-road 

environment. The EPA believes that 

these sites will be sufficient as 

representative maximum concentration 

sites for NO2 and PM2.5 in the near-road 

environment. As noted above, where an 

air agency believes a different location 

is a more appropriate site for a near-road 

PM2.5 monitor, the EPA can use its 

discretion in approving a deviation from 

the PM2.5 monitoring requirements as 

already exists in the network design 

criteria. A deviation would be 

appropriate for consideration where, for 

example, a state provides quantitative 

evidence demonstrating that peak 

ambient PM2.5 concentrations would 

occur in a near-road location which 

meets siting criteria but is not a nearroad NO2 monitoring site. Such 

deviations are to be approved by the 

Regional Administrator as described in 

section 4.7.1 of Appendix D to part 58. 

While it is still desirable for the nearroad stations to be as close to the road 

as practical, there may be differences in 

the scale of representation of the nearroad PM2.5 monitor from one location to 

another, while the NO2 near-road 

monitors are at the same scale of 

representation (i.e., micro-scale) in 

different locations. This is a result of the 

scale of representation being based on 

the pollutant at a location and not the 

location alone. Therefore, in cases 

where the station is 20 meters from a 

major road, the NO2 measurement may 

still be micro-scale, while the PM2.5

measurement would be middle-scale if 

the average daily traffic count were 

sufficiently large enough.237 If a site 

with both measurements were 10 meters 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3247 

238The EPA provides a link to these assessments 

on EPA’s Web site at: http://www.epa.gov/ttn/ 

amtic/plans.html. A detailed description of the 

requirements for the assessments is described in 40 

CFR 58.10. 

239Comments on the substantive question of 

whether to revoke references to community 

monitoring zones were addressed in section 

VIII.B.1. 

from a major road they would both be 

expected to be micro-scale sites. 

In considering the comment on 

distance from obstructions, the EPA 

notes that a monitoring station with 

multiple measurements is effectively 

considered collocated for those 

measurements, even though the actual 

location of the inlets is slightly different 

from each other within the station. For 

example, a gas monitor (e.g., for carbon 

monoxide) may be pulling ambient air 

from a manifold with an inlet located on 

one part of a station roof, while a PM 

monitor is pulling air directly from its 

inlet located a few meters away on the 

same roof. The EPA believes it is 

appropriate and consistent with the 

public comment above on distance from 

obstructions to maintain the existing 

requirements for distance from 

obstructions on a pollutant by pollutant 

basis, even if they are different for PM2.5

and NO2 monitors that will be at the 

same station. Air agencies will need to 

consider these distances from 

obstructions for each pollutant inlet 

probe (i.e., >1 meter for NO2 monitors 

and >2 meters for PM2.5 monitors) in 

locating monitors at the station. 

The EPA is maintaining the existing 

probe and siting criteria for PM2.5

monitors; however, we are finalizing the 

provision that the required near-road 

component of the PM2.5 monitoring 

network design shall be collocated with 

a required NO2 monitor at near-road 

monitoring station. These near-road NO2

monitoring stations are to be sited 

‘‘* * * as near as practicable to the 

outside nearest edge of the traffic lanes 

of the target road segments; but shall not 

be located at a distance greater than 50 

meters, in the horizontal, from the 

outside nearest edge of the traffic lanes 

of the target road segment’’ (section 6.4 

of appendix E to 40 CFR part 58). The 

EPA is retaining the existing 

requirement that PM2.5 inlets, including 

those at near road stations, must be >2 

meters from obstructions. 

b. CSN Network 

As explained in Section VI, the EPA 

is not finalizing the proposed secondary 

standard based on a PM2.5 visibility 

index and therefore will not be 

finalizing probe and siting criteria 

associated with the use of CSN 

measurements. 

c. Reinsertion of Table E–1 to Appendix 

E 

The EPA proposed to reinsert table E– 

1 to appendix E of 40 CFR part 58. This 

table presents the minimum separation 

distance between roadways and probes 

or monitoring paths for monitoring 

neighborhood and urban scale ozone 

(O3) and oxides of nitrogen (NO, NO2, 

NOX, NOy). This table was inadvertently 

removed during a previous CFR revision 

process. 

The only comments received on this 

topic were supportive of the reinsertion 

of table E–1; therefore, the EPA is 

finalizing the reinsertion of this table, 

unchanged from its prior iteration, back 

into the CFR. 

6. Additional Ambient Air Monitoring 

Topics 

a. Annual Monitoring Network Plan and 

Periodic Assessment 

In October of 2006, the EPA finalized 

new requirements for each state, or 

where applicable, local agency to 

perform and submit to their EPA 

Regional Offices an Assessment of the 

Air Quality Surveillance System (40 

CFR 58.10). This assessment is required 

every five years. The first required five 

year assessments were due to EPA 

Regional Offices by July 1, 2010. The 

assessments are intended to provide a 

comprehensive look at each monitoring 

agency’s ambient air monitoring 

network to ensure that the network is 

meeting the minimum monitoring 

objectives defined in appendix D to 40 

CFR part 58, whether new sites are 

needed, whether existing sites are no 

longer needed and can be terminated, 

and whether new technologies are 

appropriate for incorporation into the 

ambient air monitoring network.238

Since each agency has completed its 

first required five-year assessment, and 

several monitoring rule requirements 

have either been added or changed since 

this requirement was added in 2006, the 

EPA thought it was appropriate to 

review this requirement and solicit 

comment on any possible changes the 

EPA should consider that may improve 

the usefulness of the assessments. 

Specifically, the EPA solicited comment 

on ways to either streamline or add 

additional criteria for future 

assessments. 

The EPA also proposed to remove 

references to ‘‘community monitoring 

zones’’ and ‘‘spatial averaging’’ in the 

annual monitoring network plans due to 

EPA Regional Offices by July 1 of each 

year. The Agency proposed to remove 

these references since, as discussed in 

section VII.A.2 above, the EPA proposed 

to remove all references to the spatial 

averaging option throughout 40 CFR 

part 50 appendix N. Consistent with 

these changes, the EPA also proposed to 

remove references to community 

monitoring zones under the annual 

monitoring network plans described in 

40 CFR 58.10. 

The EPA received comments from 

several air agencies on the five year 

assessments. Most comments on the five 

year assessments focused on the type 

and usefulness of assessment tools made 

available to air agencies during the last 

review. Of specific note were concerns 

that assessment tools used to evaluate 

networks on a regional or national basis 

do not provide the spatial resolution 

necessary to adequately assess state 

networks on a scale most useful to air 

agencies. This is especially true when 

attempting to evaluate smaller scale 

monitoring or pollutant gradients 

associated with near-road and source 

oriented monitoring. Suggestions for 

improvement identified the need for the 

EPA to work closely with air agencies 

early in the next cycle of assessments 

(due in 2015) so that any tools 

developed can be of benefit to the 

questions air agencies need to address 

for their programs. The EPA did not 

receive any comments on removing 

references to community monitoring 

zones specifically as it pertains to their 

listing in the annual monitoring 

network plans described in 40 CFR 

58.10.239

The EPA took comment on potential 

improvements to the five year 

assessments. All the recommendations 

received focused on the types of 

assessments to perform and ensuring 

that the EPA works closely with air 

agencies so that assessments will be of 

benefit to the air agencies. No specific 

recommendations were made to add or 

remove any of the requirements of the 

five year assessments and consequently 

the EPA is not making any changes. The 

EPA intends to work with air agencies 

to ensure future tools are as helpful as 

practicable. 

Consistent with the decision to end 

the practice of spatial averaging, the 

EPA is finalizing the removal of 

language that references ‘‘community 

monitoring zones’’ and ‘‘spatial 

averaging’’ in the annual monitoring 

network plans due to EPA Regional 

Offices by July 1 of each year. 

b. Operating Schedules 

The EPA generally requires PM2.5

SLAMS to operate on at least a 1-dayin-3 sampling schedule, unless a 

reduced sampling frequency is 

approved such as might be the case with 


tkelley on DSK3SPTVN1PROD with 
3248 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

240All NCore stations must operate on at least a 

one-in-three day sample frequency for filter-based 

PM sampling. 

241This and all subsequent references to ‘‘air 

agency’’ are meant to include state, local and tribal 

agencies responsible for the implementation of a 

PM2.5 control program. 

a site that has a collocated continuous 

operating PM2.5 monitor.240 However, in 

the 2006 monitoring rule amendments, 

the EPA finalized a new requirement for 

the operating schedule of PM2.5 SLAMS 

sites (40 CFR 58.12). The new 

requirement stated that sites with a 

design value within plus or minus five 

percent of the 24-hour PM2.5 NAAQS 

must have an FRM or FEM operating on 

a daily sampling schedule. This 

requirement was included to minimize 

any statistical error associated with the 

form of the 24-hour PM2.5 NAAQS (i.e., 

the 98th percentile). In section III.F, the 

Administrator is finalizing revisions to 

the level of the primary annual PM2.5

NAAQS. Accordingly, possible changes 

to sampling frequency requirements 

were also considered. 

The EPA had previously considered 

how sample frequency affects the Data 

Quality Objectives in a consultation 

with the CASAC AAMMS in September 

of 2005 (70 FR 51353 to 51354, August 

30, 2005). As a result of that 

consultation, the EPA proposed (71 FR 

2710 to 2808, January 17, 2006) and 

finalized (71 FR 61236 to 61328, 

October 17, 2006) changes to the sample 

frequency requirements as part of the 

monitoring rule changes in 2006. In that 

work, the EPA demonstrated that having 

a higher sample count is generally more 

useful to minimize uncertainty for a 

percentile standard than an annual 

average. Given the decision to 

strengthen the primary annual PM2.5

NAAQS and the known burden of 

performing daily sampling using the 

filter-based samplers that are still a 

mainstay in monitoring agency 

networks, the issue of needing daily 

sampling for sites that have design 

values close to the level of the 24-hour 

PM2.5 standard was reconsidered if the 

site already has a design value above the 

level of the primary annual PM2.5

NAAQS. 

In a related issue, since the EPA 

finalized the requirement for daily 

sampling at sites within 5 percent of the 

24-hour PM2.5 NAAQS in 2006, there 

has been confusion over the procedures 

for adjusting sample frequencies, where 

necessary, to account for variations in 

year-to-year design values. Therefore, 

the EPA proposed to revise this 

requirement in the following ways: (1) 

The EPA proposed that monitors would 

only be required to operate on a daily 

schedule if their 24-hour design values 

were within five percent of the 24-hour 

PM2.5 NAAQS and the site had a design 

value that was not above the level of the 

annual PM2.5 NAAQS. (2) The EPA 

proposed that review of data for 

purposes of determining applicability of 

this requirement at a minimum be 

included in each agency’s annual 

monitoring network plan described in 

40 CFR 58.10 based on the three most 

recent years of ambient data that were 

certified as of the May 1 annual 

deadline. However, monitoring agencies 

may request changes to sample 

frequency at any time of the year by 

submitting such a request to their 

applicable EPA Regional Office. 

Changes in sampling frequency are 

expected to take place by January 1 of 

the following year. Increased sampling 

is expected to be conducted for at least 

three years, unless a reduction in 

sampling frequency has been approved 

in a subsequent annual monitoring 

network plan or otherwise approved by 

the Regional Administrator. 

Comments received on the sample 

frequency requirements for PM2.5 were 

from air agencies, who were generally 

supportive of the EPA’s proposed 

approach. 

The EPA is finalizing its proposal to 

modify the sample frequency 

requirements for triggering daily 

sampling so that only those areas with 

24-hour design values within five 

percent of the 24-hour PM2.5 NAAQS 

and where the design value site is not 

above the level of the annual PM2.5

NAAQS would be required to operate 

on a daily sample frequency. The EPA 

is also finalizing all other aspects of this 

part of the proposal. 

c. Data Reporting and Certification for 

CSN and IMPROVE Data 

The EPA is not finalizing its proposal 

on minor changes to reporting and 

certification of data associated with CSN 

and IMPROVE networks since as 

explained in Section VI, EPA is not 

finalizing a secondary standard to 

support visibility impairment that 

would have used CSN and IMPROVE 

data. 

d. Requirements for Archiving Filters 

The EPA proposed to extend the 

requirement for archival of PM2.5, PM10, 

and PM10-2.5 filters from manual lowvolume samplers (samplers with a flow 

rate of less than 200 liters/minute) at 

SLAMS from one year after data 

collection to five years after data 

collection. The archive of low-volume 

PM filters is an important resource for 

on-going research and development of 

emission control strategies and for use 

in health and epidemiology research. 

During a workshop on Ambient Air 

Quality Monitoring and Health Research 

in 2008, retaining filters for laboratory 

analysis was identified as a key 

recommendation to provide daily 

measurements of metals and elements 

(U.S. EPA, 2008d, pp. 17 to 21). The 

EPA’s previous requirement of one-year 

is not sufficiently long for retrospective 

analysis of important episodes and for 

use in long-term epidemiology research. 

Since initially requiring filter archival of 

low-volume PM filters in 1997, the EPA 

has always recommended longer 

archiving of filters and most agencies 

are already doing so. However, a small 

number of agencies have reported 

discarding older filters, despite the 

minimal cost of storing these filters. 

Since cold storage of a large number of 

filters may be cost prohibitive and of 

little benefit in retaining key aerosol 

species in the x-ray fluorescence (XRF) 

analyses, the EPA proposed to minimize 

the costs of retaining filters by only 

requiring cold storage during the first 

year after sample collection. 

All comments received on this issue 

were from air agencies, which were 

largely supportive of such a change to 

this requirement. One air agency did 

report that it would present a hardship 

to store filters for such a long period of 

time as they did not have the room to 

support such a requirement. 

The EPA is finalizing the requirement 

for archival of PM2.5, PM10, and PM10-2.5

filters from manual low-volume 

samplers (samplers with a flow rate of 

less than 200 liters/minute) at SLAMS 

for a minimum of five years after data 

collection, with cold storage only 

required for the first 12 months of 

archiving. The EPA will work closely 

with air agencies through its EPA 

Regional Offices and laboratories to 

support any air agency unable to store 

filters for the new five year requirement. 

IX. Clean Air Act Implementation 

Requirements for the PM NAAQS 

This section of the preamble discusses 

the general approach for air agencies 241

to meet certain CAA requirements for 

implementing the revised primary 

annual PM2.5 NAAQS as part of the 

revised suite of NAAQS for PM. In 

accordance with CAA section 107(d), 

the PM NAAQS revisions trigger a 

process under which states must and 

tribes may make recommendations to 

the Administrator regarding area 

designations, and the EPA will take 

final action on those designations. 

Under section 110 of the CAA and 

related provisions, states are also 

required to submit, for the EPA’s 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3249 

242While the CAA says ‘‘designating’’ with 

respect to the Governor’s list, in the full context of 

the CAA section it is clear that the Governor 

actually makes a recommendation to which the EPA 

must respond via a specified process if the EPA 

does not accept it. 

approval, SIPs that provide for the 

attainment and maintenance of the 

revised NAAQS through control 

programs directed at sources of direct 

PM2.5 and precursor emissions. If a state 

fails to adopt and implement the 

required SIPs by the time periods 

provided in the CAA, the EPA has 

responsibility under the CAA to adopt 

a Federal Implementation Plan (FIP) to 

assure that areas attain the NAAQS in 

an expeditious manner. Additionally, 

emissions sources and air agencies must 

address the revised PM NAAQS in the 

context of preconstruction air 

permitting requirements and the 

transportation conformity and general 

conformity processes. 

In addition to today’s revisions to the 

primary annual PM2.5 NAAQS, the EPA 

is taking final action on a PSD 

implementation provision. To facilitate 

timely implementation of the PSD 

requirements resulting from the revised 

NAAQS, which would otherwise 

become applicable to all PSD permit 

applications upon the effective date of 

this final PM NAAQS rule, the EPA is 

finalizing a grandfathering provision for 

pending permit applications. This final 

rule incorporates revisions to the PSD 

regulations that provide for 

grandfathering of PSD permit 

applications that have been determined 

to be complete on or before December 

14, 2012 or for which public notice of 

a draft permit or preliminary 

determination has been published as of 

the effective date of today’s revised 

PM2.5 NAAQS. Accordingly, for projects 

eligible under the grandfathering 

provision, sources must meet the 

requirements associated with the prior 

primary annual PM2.5 NAAQS rather 

than the revised primary annual PM2.5

NAAQS. 

The EPA also proposed to implement 

a surrogacy approach for addressing 

PSD requirements associated with the 

proposed distinct secondary visibility 

index NAAQS. As described in section 

VI, the EPA is not finalizing a distinct 

secondary visibility index standard at 

this time and therefore the proposed 

surrogacy approach for implementing 

such a standard under the PSD program 

is unnecessary. Additionally, as 

discussed in section IV, today’s final 

rule does not include any changes to the 

existing PM10 NAAQS. Accordingly, 

this section of the preamble does not 

include any discussion of 

implementation specifically related to 

the PM10 NAAQS. 

Under the schedule in section 

107(d)(1) of the CAA, as confirmed in 

this action, state Governors and tribes, 

if they choose, are required to submit 

their initial designation 

recommendations for the revised 

primary annual PM2.5 NAAQS to the 

EPA no later than 1 year following 

promulgation of the revised NAAQS 

(i.e., by December 13, 2013). The EPA 

will provide designation guidance to air 

agencies shortly after today’s final 

NAAQS rule to assist them in 

formulating their designation 

recommendations. The EPA intends to 

complete initial designations for the 

revised primary annual PM2.5 NAAQS 

by December 12, 2014 using available 

air quality data from the current PM2.5

monitoring networks. 

In addition to describing the PSD 

grandfathering provision being finalized 

in today’s rule and responding to 

associated public comments, this 

section of the preamble describes the 

EPA’s future plans for addressing the 

remaining aspects of implementation, 

such as infrastructure SIP submittals 

and nonattainment area planning. In the 

proposed rule, the EPA solicited 

preliminary comment on some of the 

issues that the Agency anticipates will 

need to be addressed in future guidance 

or regulatory actions related to 

implementation of the revised PM2.5

NAAQS. The EPA received comments 

on a few of these issues and, as 

explained in greater detail later in this 

section, the EPA either has considered 

or will consider, as appropriate, all 

substantive comments received as future 

guidance and proposed rules are 

developed. 

A. Designation of Areas 

1. Overview of Clean Air Act 

Designations Requirements 

After the EPA establishes or revises a 

NAAQS, the CAA requires the EPA and 

states to take steps to ensure that the 

new or revised NAAQS is met. The first 

step, known as the initial area 

designations, involves identifying areas 

of the country that either meet or do not 

meet the new or revised NAAQS along 

with the nearby areas contributing to 

violations. Section 107(d)(1) of the CAA 

states that, ‘‘By such date as the 

Administrator may reasonably require, 

but not later than 1 year after 

promulgation of a new or revised 

national ambient air quality standard for 

any pollutant under section 109, the 

Governor of each state shall * * * 

submit to the Administrator a list of all 

areas (or portions thereof) in the State’’ 

that designates those areas as 

nonattainment, attainment, or 

unclassifiable.242 Section 107(d)(1)(B)(i) 

further provides, ‘‘Upon promulgation 

or revision of a NAAQS, the 

Administrator shall promulgate the 

designations of all areas (or portions 

thereof) * * * as expeditiously as 

practicable, but in no case later than 2 

years from the date of promulgation. 

Such period may be extended for up to 

one year in the event the Administrator 

has insufficient information to 

promulgate the designations.’’ The term 

‘‘promulgation’’ has been interpreted by 

the courts with respect to the NAAQS 

to be signature and widespread 

dissemination of a rule. By no later than 

120 days prior to promulgating 

designations, the EPA is required to 

notify states of any intended 

modifications to their 

recommendations, including area 

boundaries, that the EPA may deem 

necessary. States then have an 

opportunity to demonstrate why the 

EPA’s intended modification is 

inappropriate. Whether or not a state 

provides a recommendation, the EPA 

must timely promulgate the designation 

that it deems appropriate. While section 

107 of the CAA specifically addresses 

states, the EPA intends to follow the 

same process for tribes that choose to 

make a recommendation to the extent 

practicable, pursuant to section 301(d) 

of the CAA regarding tribal authority, 

and the Tribal Authority Rule (63 FR 

7254, February 12, 1998). To provide 

clarity and consistency in doing so, the 

EPA issued a 2011 guidance 

memorandum on working with tribes 

during the designations process (Page, 

2011). 

2. Proposed Designations Schedules 

When the EPA proposed the new and 

revised PM NAAQS on June 29, 2012, 

the EPA indicated an intention to follow 

the standard 2-year schedule for initial 

area designations for both the revised 

primary annual PM2.5 standard and the 

proposed secondary PM visibility index 

standard, noting that promulgating 

initial area designations for these 

standards on the same schedule would 

provide early regulatory certainty for 

states. Under this approach, the EPA 

intended to complete initial 

designations for both the revised 

primary annual PM2.5 NAAQS and the 

secondary PM visibility index NAAQS 

by December 2014 using available air 

quality data from the current PM2.5 and 

speciation monitoring networks using 

the most recent 3 consecutive years of 

certified air quality monitoring data 

(i.e., most likely data from 2011–2013). 


tkelley on DSK3SPTVN1PROD with 
3250 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

243The remainder of the near-road monitors in 

CBSAs with populations between 1 million but less 

than 2.5 million will be deployed by January 1, 

2017. 

244The EPA has used area-specific information to 

support boundary determinations by evaluating 

factors such as air quality data, emissions and 

emissions-related data, meteorology, geography/ 

topography, and existing jurisdictional boundaries. 

This may include, as appropriate, information from 

non-FRM/FEM/ARM monitors and air quality 

modeling, where available, to help define an 

appropriate boundary for areas contributing to 

FRM/FEM/ARM-based monitored violations. 

245While the EPA intends to make every effort to 

designate areas for the primary annual PM2.5

NAAQS on a 2-year schedule, the EPA recognizes 

that new information may later arise that justifies 

the need for additional time, up to 1 additional year 

available based on insufficiency of data, to 

complete the process. Any subsequent change to the 

designations schedule would be announced. 

The EPA’s June 29, 2012 notice 

proposed new requirements for 

establishing near-road PM2.5 monitors in 

certain cities (section VIII.B.3.b.i of the 

proposal) and new requirements for 

each state with a CBSA over 1 million 

in population to add or relocate an 

existing CSN (or IMPROVE) monitoring 

site in at least one of its CBSAs to 

collect speciated PM2.5 data to support 

implementation of the proposed 

secondary standard to address visibility 

impairment (section VIII.A.2 of the 

proposal). The EPA anticipated that 3 

consecutive years of air quality data 

from any near-road monitoring sites or 

newly placed CSN (or IMPROVE) PM2.5

speciated monitoring site would not be 

available until 2018. The timing for both 

of these proposed monitoring changes 

would preclude the use of the collected 

data in initial area designations, and 

therefore, the EPA stated in the proposal 

that initial area designations would not 

take into account monitoring data from 

any newly established near-road 

monitoring sites, nor from newly 

established speciation monitoring sites. 

3. Comments and Responses 

The EPA received numerous 

comments on the proposed designations 

schedules from states, state 

organizations, local air pollution control 

agencies, regional organizations, 

industry, environmental organizations, 

and health-related organizations. Most 

commenters expressed support for a 

standard 2-year schedule for initial area 

designations for the primary annual 

standard. Several commenters also 

encouraged the EPA to consider an 

additional year for initial area 

designations associated with the 

proposed secondary PM visibility index 

standard due to the lag in obtaining data 

from speciation monitoring networks, 

the variability in monitored relative 

humidity data, and the ‘‘unique’’ nature 

of the proposed secondary standard. For 

the reasons stated in section VI.D.2, the 

Administrator has decided not to 

establish the proposed distinct 

secondary standard to address visibility 

impairment, and therefore, the EPA will 

not promulgate initial area designations 

for a secondary PM visibility index 

standard. Because data are currently 

available from numerous existing PM2.5

mass monitoring sites to determine 

compliance with the revised primary 

annual PM2.5 NAAQS, the EPA believes 

it is appropriate to pursue a standard 

2-year schedule for initial area 

designations for the primary annual 

PM2.5 NAAQS. 

The EPA also received numerous 

comments related to the use of data 

from the proposed new near-road 

monitors in the designations process. 

Several commenters asked the EPA to 

clarify whether these data will be used 

if available for initial area designations. 

Others asked the EPA to provide 

guidance related to establishing 

boundaries for areas containing 

violating near-road monitors. One 

commenter suggested that the EPA 

conduct dispersion modeling around 

transportation facilities in accordance 

with the EPA’s transportation 

conformity hotspot modeling guidance 

and use concentrations to determine 

attainment status for designations 

process. This same commenter also 

supported using modeling for 

unmonitored areas, e.g., communities 

near roadways. 

As previously stated, the EPA does 

not believe that data from the new nearroad monitors will be available for the 

EPA to consider within the timeframe 

for initial area designation provided by 

the CAA. Section 107(d)(1)(B) of the 

CAA requires the EPA to designate areas 

no later than 2 years following 

promulgation of a new or revised 

NAAQS, or by December 2014. (The 

CAA provides the Agency an additional 

third year from promulgation should 

there be insufficient information on 

which to make compliance 

determinations). For initial area 

designations for the primary annual 

PM2.5 NAAQS, the EPA relies 

exclusively on monitoring data to 

identify areas to be designated 

nonattainment due to violations of the 

standards and then uses other 

information to identify areas 

contributing to violations in those areas. 

See Catawba County v. EPA, 571 F.3d 

12–13 (D.C. Cir. 2009). As indicated in 

the proposal, the initial set of nearroadway PM2.5 monitors will be fully 

deployed by January 2015, with the 

requisite 3 years of air quality data 

available in 2018.243 The EPA intends to 

proceed with initial area designations 

using 3 years of consecutive air quality 

data from the existing, area-wide FRM/ 

FEM/ARM PM2.5 monitoring sites to 

complete designations by December 

2014. Consistent with previous area 

designations processes used in 

informing boundary decisions, the EPA 

would then analyze a variety of areaspecific information 244 in determining 

which nearby areas contribute to a 

violation. As previously indicated, the 

EPA relies on monitoring data to 

identify areas to be designated 

nonattainment due to violations of the 

standards and does not intend to 

conduct or use dispersion modeling 

around transportation facilities or in 

unmonitored areas to determine 

whether an area is violating the primary 

annual PM2.5 NAAQS for purposes of 

establishing nonattainment areas as this 

is not required by the statute. See 

Catawba County v. EPA, 571 F.3d 12– 

13 (D.C. Cir. 2009). The EPA intends to 

address the use of area-specific 

information and the boundary setting 

process, including the presumptive 

starting area boundary, in the 

designation guidance to the states, 

expected to be available shortly after 

promulgation of the PM NAAQS. 

4. Intended Designations Schedules 

In this final rule, the EPA is setting a 

revised, more protective primary annual 

PM2.5 NAAQS. After considering the 

public comments and for the reasons 

discussed above, the EPA intends to 

designate areas for the primary annual 

PM2.5 NAAQS on a 2-year schedule from 

signature of this final PM NAAQS rule, 

as prescribed in CAA section 107.245

Under the schedule in section 107(d)(1) 

of the CAA, as confirmed in this action, 

state Governors and tribes, if they 

choose, are required to submit their 

initial designation recommendations for 

the revised primary annual PM2.5

NAAQS to the EPA no later than 1 year 

following promulgation of the revised 

NAAQS (i.e., by December 13, 2013). 

These recommendations should be 

based on air quality data from the years 

2010 to 2012. If the EPA intends to 

make any modifications to a state’s or 

tribe’s recommendations, the EPA is 

required to notify the state or tribe no 

later than 120 days prior to finalizing 

the designation; this would be no later 

than August 14, 2014. States and tribes 

will then have an opportunity to 

demonstrate why the EPA’s intended 

modification is inappropriate before the 

EPA makes the final designation 

decisions. Prior to the EPA’s signing a 

final rule by December 12, 2014, 

promulgating the initial area 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3251 

designations for the 2012 primary 

annual PM2.5 NAAQS, data from 2013 

may be available. If so, the EPA’s 

designations decisions will be based on 

air quality data from the years 2011 to 

2013. States and tribes may update their 

recommendations when these new data 

become available. 

In the proposal, the EPA stated its 

intention to provide technical 

information and guidance to states 

shortly after promulgation of the 

NAAQS to assist states and tribes in the 

development of their designation 

recommendations. The EPA 

understands that developing 

recommendations on appropriate 

nonattainment area boundaries is a 

significant effort for states, especially for 

states with little or no experience in 

PM2.5 air quality planning. Therefore, 

the EPA plans to assist states throughout 

the designations process on technical 

and policy-related issues through 

outreach efforts that will provide 

information and data sources relevant to 

making designations decisions. The EPA 

will include such information for the 

revised primary annual PM2.5 NAAQS 

on the general PM2.5 designations Web 

site at http://www.epa.gov/ 

pmdesignations. The EPA also 

encourages states and tribes to consult 

with their EPA regional office as they 

develop their area recommendations. 

B. Section 110(a)(2) Infrastructure SIP 

Requirements 

The proposal described the CAA 

requirements for air quality 

management infrastructure SIPs that 

states must submit to the EPA within 3 

years after promulgation of a new or 

revised primary standard. As discussed 

in the proposal, while the CAA allows 

the EPA to set a shorter time for 

submission of these SIPs, the EPA does 

not currently intend to do so. In the 

proposal, the EPA solicited comment on 

infrastructure SIP submittal timing, in 

addition to ‘‘all aspects’’ of 

infrastructure SIPs, for the Agency to 

consider in developing future guidance. 

The EPA received comments 

recommending that the EPA provide 

states an additional 18 months to submit 

SIPs for any revised secondary standard, 

but because the Agency is not revising 

the secondary NAAQS in this rule, the 

issue of whether or not to allow states 

extra time to submit infrastructure SIPs 

for the secondary NAAQS is now moot. 

The EPA received several comments on 

other aspects of infrastructure SIPs, 

which are being considered in the 

development of a forthcoming guidance 

document on section 110 infrastructure 

SIP requirements that will apply to all 

NAAQS, including the revised PM2.5

NAAQS. In addition, the EPA may issue 

supplemental infrastructure SIP 

guidance specific to the revised PM2.5

NAAQS if needed. 

C. Implementing the Revised Primary 

Annual PM2.5 NAAQS in Nonattainment 

Areas 

In the proposal, the EPA described the 

basic CAA requirements that govern SIP 

submittals for nonattainment areas (77 

FR 38890, June 29, 2012 at 39019–21). 

The Agency did not propose any 

particular approach for implementing 

any revised PM2.5 standards, but rather 

indicated its intent to carry out a noticeand-comment rulemaking to propose 

and issue a final implementation rule 

that would spell out the implementation 

requirements for the revised primary 

annual PM2.5 NAAQS and the revised 

monitoring regulations. The EPA 

acknowledges that several states and 

industry groups commented on the need 

for the EPA to issue an implementation 

rule, either in proposed or final form, 

simultaneous with this final PM 

NAAQS rule. Other commenters 

commented that the EPA should consult 

with states and local air agencies to 

develop the future implementation rule 

and to do so expeditiously, while 

another state commenter requested that 

the EPA commit to firm deadlines for 

issuing the future implementation rule 

and guidance related to infrastructure 

SIPs, among other things. 

The EPA acknowledges states’ need 

for timely guidance on how to 

implement the revised NAAQS. 

However, due to the number of unique 

and complex issues associated with the 

PM NAAQS proposal and uncertainty 

about the outcome of the final NAAQS, 

the EPA is not able to propose an 

implementation rule or finalize any 

aspect of the implementation program 

beyond the PSD grandfathering 

provision discussed later in this section 

at this time. Because we agree that it is 

beneficial to engage with air agencies 

early in the rule development process, 

however, we have initiated such 

discussions to inform the upcoming 

proposed rule. The EPA intends to 

finalize the implementation rule around 

the time the initial area designations 

process is finalized. 

One particular implementationrelated issue that the EPA sought 

preliminary comment on in the proposal 

was the concept of a transition period 

during which any changes in 

monitoring requirements would not 

affect attainment plans and maintenance 

plans for the 1997 and 2006 PM2.5

NAAQS. The EPA received a range of 

comments both in support of and in 

opposition to such a concept. Upon 

further analysis of the potential effect of 

monitoring requirement changes, and in 

consideration of comments received, we 

believe that it will not be necessary to 

provide for such a transition period in 

the future implementation rule because 

the changes in monitoring requirements 

included in this final rule would not 

automatically affect attainment plans 

and maintenance plans for the 1997 or 

2006 PM2.5 NAAQS. Specifically, there 

are currently approximately ten PM2.5

air quality monitors that have been 

identified as not comparable to the 

annual standards as part of the annual 

state monitoring plan revision process. 

If a state chooses to revise the status of 

one of these monitors in order to make 

it comparable to the annual standards 

because it is determined to be 

representative of many other similar 

locations, it would propose a change in 

status for that monitor in the next 

revision of the state PM2.5 monitoring 

plan (state revisions are due in June of 

each year). The EPA would then review 

and take action on the state’s proposed 

change. The EPA believes that the 

monitoring plan revision process 

provides adequate procedural steps for 

identifying which monitors are to be 

comparable to the annual PM2.5

standards. Thus for this reason, there is 

no need to include any ‘‘transition 

period’’ in a future rule. 

The EPA appreciates the input 

received from commenters on 

implementation issues and will take it 

into consideration as we continue to 

work with air agencies to develop our 

proposed implementation rule. In 

developing the future implementation 

rule proposal, the EPA also plans to 

address any potential impact of the 

monitoring requirement changes being 

finalized in this rule, particularly on 

attainment planning and development 

of attainment demonstrations by states, 

and in doing so, we will consider the 

preliminary comments received on this 

topic. 

D. Prevention of Significant 

Deterioration and Nonattainment New 

Source Review Programs for the Revised 

Primary Annual PM2.5 NAAQS 

The CAA requires states to include 

SIP provisions that address the 

preconstruction review of new 

stationary sources and the modification 

of existing sources. The preconstruction 

review of each new and modified source 

generally applies on a pollutant-specific 

basis and the requirements for each 

pollutant vary depending on whether 

the area is designated attainment (or 

unclassifiable) or nonattainment for that 

pollutant. Parts C and D of title I of the 

CAA contain specific requirements for 


tkelley on DSK3SPTVN1PROD with 
3252 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

246Under various provisions of the CAA, PSD 

requirements are applicable to each pollutant 

subject to regulation under the CAA, excluding 

hazardous air pollutants. The definition of 

‘‘regulated NSR pollutant’’ also includes pollutants 

subject to any standard under section 111 of the 

CAA or any Class I or II substance subject to title 

VI of the CAA. 

247 It should be noted that on October 25, 2012, 

the definition of ‘‘regulated NSR pollutant’’ was 

revised to remove the requirement that condensable 

PM be included when considering ‘‘particulate 

matter emissions.’’ Accordingly, the definition now 

requires condensable PM to be counted for PM10

emissions and PM2.5 emissions, and for ‘‘particulate 

matter emissions’’ only when required by the 

applicable New Source Performance Standard or 

SIP. (See 77 FR 65107.) 

the preconstruction review and 

permitting of new major stationary 

sources and major modifications, 

referred to as the PSD program and the 

nonattainment new source review 

(NNSR) program, respectively. 

Collectively, those permit requirements 

are commonly referred to as the ‘‘major 

NSR program’’ because of their 

applicability to new major stationary 

sources and major modifications. 

Today’s final rule revising the 

primary annual PM2.5 NAAQS will 

affect PSD permitting requirements as of 

the effective date of today’s final rule, 

March 18, 2013, which is also the 

effective date of the revised PM2.5

NAAQS. In addition, certain NNSR 

permitting requirements related to the 

revised PM2.5 NAAQS will take effect on 

and after the effective date of any 

nonattainment area designation for 

PM2.5. In order to minimize potential 

delays for pending PSD permit 

applications and to provide a reasonable 

transition, the EPA is finalizing a 

grandfathering provision for PSD permit 

applications that have reached a 

specified milestone in the permitting 

process. This final rule incorporates 

revisions to the PSD regulations that 

provide for grandfathering of PSD 

permit applications for which the 

reviewing authority has determined the 

application to be complete on or before 

December 14, 2012 or for which the 

reviewing authority has first published 

public notice that a draft permit or 

preliminary determination for the 

permit has been issued prior to the 

effective date of today’s revised PM 

NAAQS. Accordingly, projects eligible 

under the grandfathering provision must 

meet the requirements associated with 

the prior primary annual PM2.5 NAAQS 

rather than the revised primary annual 

PM2.5 NAAQS. As discussed in more 

detail in the following sections, the EPA 

is not now making any changes to the 

PM2.5 increments, nor are we revising 

any of the screening tools that are now 

used to implement the major NSR 

program for PM2.5. These screening tools 

include the significant emission rate 

(‘‘SER’’), used as a threshold for 

determining whether a given project is 

subject to major NSR permitting 

requirements under both PSD and 

NNSR; the significant impact levels 

(‘‘SILs’’), used to determine the scope of 

the required air quality analysis that 

must be carried out in order to 

demonstrate that the source’s emissions 

will not cause or contribute to a 

violation of any NAAQS or increment 

under the PSD program; and the 

significant monitoring concentration 

(‘‘SMC’’), a screening tool used to 

determine whether it may be 

appropriate to exempt a proposed 

source from the requirement to collect 

preconstruction ambient monitoring 

data as part of the required air quality 

analysis. 

1. Prevention of Significant 

Deterioration 

The PSD requirements set forth under 

part C (sections 160 through 169) of the 

CAA apply to new major stationary 

sources and major modifications 

locating in areas designated as 

‘‘attainment’’ or ‘‘unclassifiable’’ with 

respect to the NAAQS for a particular 

pollutant. The EPA regulations 

addressing the statutory requirements 

under part C for a PSD permit program 

can be found at 40 CFR 51.166 

(containing the PSD requirements for an 

approved SIP) and 40 CFR 52.21 (the 

federal PSD permit program). For PSD, 

a ‘‘major stationary source’’ is one with 

the potential to emit 250 tons per year 

(tpy) or more of any air pollutant, unless 

the source or modification is classified 

under a list of 28 source categories 

contained in the statutory definition of 

‘‘major emitting facility’’ in section 

169(1) of the CAA. For those 28 listed 

source categories, a ‘‘major stationary 

source’’ is one with the potential to emit 

100 tpy or more of any air pollutant. A 

‘‘major modification’’ is a physical 

change or a change in the method of 

operation of an existing major stationary 

source that results in a significant 

emissions increase and a significant net 

emissions increase of a regulated NSR 

pollutant. Under PSD, new major 

sources and major modifications must 

apply best available control technology 

(BACT) for each applicable pollutant 

and conduct an air quality analysis to 

demonstrate that the proposed source or 

project will not cause or contribute to a 

violation of any NAAQS or PSD 

increments (see CAA section 165(a)(3); 

40 CFR 51.166(k); 40 CFR 52.21(k)). PSD 

requirements also include in 

appropriate cases an analysis of 

potential adverse impacts on Class I 

areas (see sections 162 and 165 of the 

CAA). 

PSD permitting requirements 

generally first became applicable to 

PM2.5 in 1997, on the effective date of 

the NAAQS for PM2.5 (Seitz, 1997). The 

EPA’s regulations define the term 

‘‘regulated NSR pollutant’’ to include 

any pollutant for which a NAAQS has 

been promulgated or that is otherwise 

identified as a constituent or precursor 

to a NAAQS pollutant (40 CFR 

51.166(b)(49); 40 CFR 52.21(b)(50)).246

In addition, on May 16, 2008, the EPA 

amended its regulations to identify 

certain PM2.5 precursors (SO2 and NOX) 

as regulated NSR pollutants and adopt 

other provisions, such as a significant 

emissions rate for PM2.5, to facilitate 

implementation of PSD and NNSR 

program requirements for PM2.5 (73 FR 

28321).247 Air agencies were required to 

revise their SIPs by May 16, 2011, to 

incorporate the required elements of the 

2008 final rule. 

On October 20, 2010, the EPA again 

amended the PSD regulations at 40 CFR 

51.166 and 52.21 to add PSD increments 

as well as two screening tools for 

PM2.5—SILs and SMC (75 FR 64864). 

The October 2010 final rule became 

effective on December 20, 2010. The 

EPA indicated that the SILs and SMC 

for PM2.5, while useful tools for program 

implementation, are not considered 

mandatory elements of an approvable 

SIP; thus, no schedule was imposed on 

states for addressing those screening 

tools in their PSD rules. For the portions 

of the rule that addressed the PSD 

increments for PM2.5, states were 

required to submit the necessary SIP 

revisions (at least as stringent as the 

PSD requirements at 40 CFR 51.166) to 

the EPA for approval within 21 months 

from the date on which the EPA 

promulgated the new PM2.5

increments—by July 20, 2012. The 

schedule for developing and submitting 

the revisions specifically for the 

adoption of new PSD increments in 

state PSD programs is prescribed by the 

CAA section 166(b). As of October 20, 

2011, sources for which PSD permits 

have been issued pursuant to the federal 

PSD program at 40 CFR 52.21 have been 

required, where applicable, to 

determine their impact on the PM2.5

increments. 

The PSD program currently regulates 

emissions of PM using several 

indicators of particles, including 

‘‘particulate matter emissions’’ (as 

regulated under various new source 

performance standards under 40 CFR 

part 60), ‘‘PM10 emissions,’’ and ‘‘PM2.5

emissions.’’ The latter two emission 

indicators are designed to be consistent 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3253 

248The EPA is also revising the form of the 

annual primary standard by removing the option for 

spatial averaging. However, this provision has 

played no role in PSD so its removal has no 

implications for PSD. 

249Section 165(a)(3) of the CAA generally 

requires that no major emitting facility may be 

constructed unless the owner or operator 

demonstrates that emissions from construction or 

operation of such facility will not cause or 

contribute to a violation of any NAAQS or PSD 

increment. Section 165(c) of the CAA requires that 

the EPA grant or deny any completed permit 

application not later than one year after the date of 

filing of such complete application. Section 301 of 

the CAA authorizes the EPA to prescribe such 

regulations as are necessary to carry out the 

functions under the CAA. 

with the ambient air indicators for PM 

that the EPA currently uses to define the 

PM NAAQS. As already noted, the PSD 

program also limits PM2.5

concentrations by regulating emissions 

of gaseous pollutants that result in the 

secondary formation of particulate 

matter. Those pollutants, known as 

PM2.5 precursors, generally include SO2

and NOX. 

In addition to the NAAQS revisions 

contained in today’s final rule, the EPA 

is finalizing certain clarifications to the 

existing monitoring regulations codified 

at 40 CFR 58.30 (Special considerations 

for data comparisons to the NAAQS). 

These clarifications are presented in 

detail in section VIII.B.2 of this 

preamble. The monitoring regulations 

provide a basis for determining whether 

specific monitoring sites are comparable 

to specific NAAQS. By extension, the 

EPA has also used the principles for 

making these determinations for 

monitoring sites to guide permitting 

authorities in assessing the 

comparability of specific receptor 

locations involved in PSD air quality 

analyses. Receptors are used in PSD 

modeling analyses to predict potential 

air quality impacts in the vicinity of the 

proposed new or modified facility and 

in some cases also at more distant Class 

I areas. Since the EPA interprets the 

regulation at 40 CFR 58.30 to apply in 

this context, the EPA will continue to 

use the principles in the revised 

regulations in guiding PSD modeling 

analysis design. Accordingly, the EPA 

recommends that specific receptor 

locations used in PSD air quality 

analyses are evaluated consistent with 

the final monitoring regulations, as 

amended by today’s rule. 

a. Transition Provision (Grandfathering) 

i. Proposal 

As discussed previously in this 

preamble, today’s final rule establishes 

a revised level of the primary annual 

PM2.5 NAAQS.248 Longstanding EPA 

policy interprets the CAA and 40 CFR 

52.21(k)(1) and 51.166(k)(1) to generally 

require that PSD permit applications 

include a demonstration that new major 

stationary sources and major 

modifications will not cause or 

contribute to a violation of any NAAQS 

that is in effect as of the date the PSD 

permit is issued (Page, 2010a; Seitz, 

1997). Thus, as a result of today’s final 

rule, any proposed major new and 

modified sources with permits pending 

at the time the PM2.5 NAAQS changes 

take effect would be expected to 

demonstrate compliance with the 

revised standard, absent some type of 

transition provision exempting such 

applications from the new requirements. 

In order to provide for a reasonable 

transition into the new PSD permitting 

requirements that will result from the 

revision of the primary annual PM2.5

NAAQS (primarily the requirement to 

demonstrate that emissions will not 

cause or contribute to a violation of the 

revised NAAQS) and the changes to the 

monitoring requirements discussed 

earlier, the EPA proposed to add a 

grandfathering provision to the federal 

PSD program codified at 40 CFR 52.21 

that would apply to certain PSD permit 

applications that are pending on the 

effective date of the revised PM2.5

NAAQS. Specifically, the EPA proposed 

to amend the federal PSD regulations at 

40 CFR 52.21 to grandfather pending 

permit applications for which the 

Administrator or delegated air agency 

has published a public notice on the 

draft permit prior to the effective date of 

the revised PM2.5 NAAQS. Qualifying 

applications could continue being 

processed in accordance with the PSD 

requirements applicable to the preexisting suite of PM NAAQS at the time 

the public notice on the draft permit 

was first published. The EPA also 

proposed that air agencies that issue 

PSD permits under their own SIPapproved PSD permit program should 

have the discretion to ‘‘grandfather’’ 

proposed PSD permits in the same 

manner under these same 

circumstances. Thus, the EPA also 

proposed to revise section 40 CFR 

51.166 to provide a comparable 

exemption applicable to SIP-approved 

PSD programs. 

In the preamble to the proposal, the 

EPA provided a detailed rationale and 

legal basis for the proposed 

grandfathering provision, also citing 

examples in which the EPA previously 

recognized that the CAA provides 

discretion for the EPA to grandfather 

PSD permit applications from 

requirements that become applicable 

while the application is pending (45 FR 

52683, Aug. 7, 1980; 52 FR 24672, July 

1, 1987; U.S. EPA, 2011c, pp. 54 to 61). 

In summary, when read in combination, 

sections 165(a)(3), 165(c) and 301 249 of 

the CAA provide the EPA with the 

discretion to promulgate regulations to 

grandfather pending permit applications 

from having to address a revised 

NAAQS where necessary to achieve a 

balance between the CAA objectives in 

order to protect the NAAQS on the one 

hand, and to avoid delays in processing 

PSD permit applications on the other. 

The EPA has also construed section 

160(3) of the CAA, which states that a 

purpose of the PSD program is to 

‘‘insure that economic growth will occur 

in a manner consistent with the 

preservation of existing clean air 

resources,’’ to call for a balancing of 

economic growth and protection of air 

quality (70 FR 59582, Oct. 12, 2005 at 

59587 to 59588). The reasoning of those 

prior EPA actions is also applicable to 

the promulgation of revised PM 

NAAQS. 

In developing the proposed 

grandfathering provision, the EPA 

considered whether such a provision 

should include a sunset clause. A sunset 

clause would add a time limit beyond 

which an otherwise eligible permit 

application would no longer be 

grandfathered from specified new PSD 

permitting requirements. Consistent 

with past grandfathering actions 

described above, the EPA did not 

propose to include a sunset clause for 

the proposed grandfathering provision. 

ii. Comments and Responses 

The majority of commenters, 

including all industry and state agency 

representatives, supported the EPA’s 

proposal to adopt a grandfathering 

provision based on the purpose and 

rationale described in the preamble to 

the proposal. These commenters agreed 

that grandfathering certain pending PSD 

permit applications was reasonable to 

balance the CAA objectives to protect 

the NAAQS on one hand, and to avoid 

delays in processing PSD permit 

applications on the other. They also 

agreed grandfathering provides a 

reasonable transition into the PSD 

requirements associated with the 

revised NAAQS. Industry commenters 

also indicated that such a provision was 

important to economic growth and 

recovery, and was consistent with the 

purposes of the PSD program, i.e., to 

ensure that economic growth will occur 

in a manner consistent with 

preservation of air quality. Several state 

commenters pointed out that finalizing 

the revised PM2.5 NAAQS without a 

grandfathering provision would result 


tkelley on DSK3SPTVN1PROD with 
3254 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

in a significant additional resource 

burden on both permit applicants and 

air agencies, which would have to 

reopen pending permit applications that 

have reached advanced stages in 

processing to address the revised 

standard. The commenters further noted 

that there would likely be little if any 

environmental benefit afforded by such 

a process. One state agency commenter 

performed a preliminary review of 

recent PSD permitting actions and 

determined that in all cases, the 

proposed primary annual PM2.5

standard would not have led to tighter 

permit restrictions or reduced 

emissions, and that a re-noticing of the 

preliminary permit decisions would 

accomplish nothing more than to 

change the margins of compliance. In 

other words, re-noticing would have led 

to project delays with no reduction in 

PM2.5 impacts. 

Four environmental group 

commenters (one representing a 

coalition of a health advocacy group and 

several environmental groups) opposed 

the proposed grandfathering provision 

based either on concerns about further 

delay in implementation of the revised 

PM NAAQS or on a position that the 

proposed grandfathering provision 

exceeds the EPA’s statutory authority 

and is unlawful. Commenters 

challenging the EPA’s legal authority to 

implement the proposed grandfathering 

provision contended that CAA sections 

165 and 301 do not confer any authority 

on the EPA to grandfather PSD permit 

applications. The commenters asserted 

that CAA section 165(a) forecloses the 

EPA’s proposed approach, specifically 

citing CAA section 165(a)(3)(B) which 

provides that no major emitting facility 

‘‘may be constructed’’ unless the 

facility’s owner or operator 

demonstrates emissions from the facility 

will not cause or contribute to the 

violation of ‘‘any * * * national 

ambient air quality standard in any air 

quality control region.’’ These 

commenters further claimed that 

because Congress limited the 

applicability of the new PSD 

requirements in several ways, including 

specific grandfathering relief for sources 

constructed before the enactment of the 

1977 Amendments to the CAA, the EPA 

is not authorized to waive otherwise 

applicable statutory requirements (citing 

Andrus v. Glover Constr. Co., 446 U.S 

608, 616–17 (1980)). 

A subset of commenters also stated 

that the EPA’s proposed grandfathering 

approach undermines the policy choices 

made by Congress in adopting the PSD 

program that (1) it is preferable to 

prevent air pollution from becoming a 

problem in the first place, and (2) 

controls should be installed when new 

sources are being constructed rather 

than as retrofits on existing sources. 

One commenter asserted that there is 

no conflict between CAA sections 165(a) 

and 165(c) as the EPA had implied; 

therefore, there is no need for the EPA 

to invoke the regulatory authority of 

CAA section 301. This commenter also 

concluded that the EPA’s rationale of 

balancing of economic growth and the 

protection of air quality pursuant to 

CAA section 160(3) was unlawful, and 

that the EPA had not adequately 

explained the considerations it sought 

to balance and how the proposal would 

achieve its goals. The same commenter 

questioned the EPA’s authority to 

leverage principles of equity and 

fairness in proposing the grandfathering 

provision. The commenter also objected 

to the EPA’s rationale for choosing the 

public notice date of a draft permit as 

the milestone triggering the 

grandfathering provision, stating that 

the approach was contrary to statute 

because it would deprive interested 

persons of their statutory right to 

comment on elements of the application 

related to the current NAAQS. 

The EPA does not agree with the 

interpretations of the CAA offered by 

the commenters opposing the proposed 

grandfathering provision. The EPA has 

previously exercised this discretion to 

establish grandfathering provisions in 

regulations. Indeed, the EPA has done 

so where provisions of the CAA 

contradict each other, citing the 

authority under section 301(a)(1) ‘‘to set 

transitional rules which accommodate 

reasonably the purpose and concerns 

behind the two contradictory 

provisions’’ (45 FR 52676, August 7, 

1980 at 52683). Furthermore, the EPA 

has noted and continues to recognize 

that even in the absence of a conflict 

between sections of the Act, ‘‘EPA 

would have the authority under section 

301(a)(1) to exempt those projects in 

order to phase-in new requirements on 

a reasonable schedule.’’ Id. at 52683 n. 

5. 

There is a conflict or tension between 

certain provisions of the CAA that the 

EPA must reconcile in situations where 

the ability of air agencies to complete 

action on a permit application within 

the statutory one-year deadline is likely 

to be impeded if a new or revised 

NAAQS becomes applicable during the 

permit application review process. We 

do not agree with the commenters’ 

arguments to the contrary. The CAA 

does not provide clear direction 

concerning how the EPA should apply 

section 165(a)(3) of the Act to NAAQS 

that become effective in circumstances 

where efforts to update a permit 

application to address the new or 

revised NAAQS would be time 

consuming and impede compliance 

with the CAA obligation to take action 

on the application within one year after 

the completeness determination. Since 

Congress has not precisely spoken to 

this issue, the EPA has the discretion to 

apply a permissible interpretation of the 

Act that balances the requirements in 

the Act to make a decision on a permit 

application within one year and to 

ensure that new and modified sources 

will only be authorized to construct 

after showing they can meet the 

substantive permitting criteria. Chevron, 

U.S.A., Inc. v. Natural Res. Def. Council, 

Inc., 467 U.S. 837, 843–44 (1984). 

Targeted grandfathering applicable to 

a specific NAAQS does not waive the 

statutory requirements in section 

165(a)(3), as some commenters assert. 

Rather, the grandfathering provision 

makes clear which NAAQS are covered 

by this provision of the Act when it is 

applied to a permit application that has 

reached a specific stage in the review 

process (i.e., the date the application is 

determined to be complete or the first 

date of publication of a public notice on 

the draft permit or preliminary 

determination) before a specified date. 

Grandfathering resolves the question of 

how the EPA and other permitting 

authorities should interpret and apply 

section 165(a)(3) of the Act in the case 

of today’s PM NAAQS revisions 

considering the requirement of section 

165(c) of the Act that reviewing 

authorities make a decision on a permit 

application within one year of the date 

the application was determined 

complete. This is not a question of 

whether section 165(a)(3) applies; it is a 

question of which NAAQS this 

requirement should cover in the case of 

a pending PSD permit. 

The EPA agrees that as a general rule, 

section 165(a)(3) applies to ‘‘any 

NAAQS’’ that is effective as of the date 

a final PSD permit is initially issued 

(before any administrative appeal 

proceeding commences). However, 

these provisions cannot be read in 

isolation and should be construed in the 

context of other provisions in section 

165 of the Act, such as section 165(c). 

Since the EPA is required to give effect 

to all provisions of the Act, in those 

circumstances where a strict reading of 

sections 165(a)(3) would frustrate 

congressional intent that the EPA and 

other implementing air agencies act in 

a timely manner, the Agency has the 

discretion to interpret the reach of 

section 165(a)(3) to be limited to 

particular NAAQS that were proposed 

or effective prior to significant 

milestones in the permitting process. 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3255 

Thus, the EPA does not agree with the 

view expressed by some commenters 

that section 165(a)(3) must be read 

strictly in all circumstances to apply to 

all NAAQS in effect on the date the EPA 

issues a final permit decision, regardless 

of other circumstances or other 

requirements of the CAA. Such a 

reading fails to acknowledge or give 

meaning to section 165(c) of the Act. 

Legislative history illustrates 

congressional intent to avoid delays in 

permit processing. S. Rep. No. 94–717, 

at 26 (1976) (‘‘nothing could be more 

detrimental to the intent of this section 

and the integrity of this Act than to have 

the process encumbered by bureaucratic 

delay’’). 

The EPA is also not persuaded that 

the presence of a grandfathering 

provision in section 168(b) precludes 

the EPA from establishing 

grandfathering exemptions in other 

circumstances. The commenter’s 

reference to the Supreme Court’s 

observation that when ‘‘Congress 

expressly enumerates certain exceptions 

to a general prohibition, additional 

exceptions are not to be implied in the 

absence of evidence of a contrary 

legislative intent,’’ Andrus, 446 U.S. at 

616–17, is not persuasive here. The 

Court applied this principle in a 

circumstance where there was a 

provision of law ‘‘expressly relating to 

contracts of the sort at issue here.’’ Id. 

These are not the circumstances here. 

Section 168(b) of the Act does not 

expressly relate to the application of 

PSD permitting requirements to an 

application pending at the time of the 

promulgation of a new or revised 

NAAQS. Section 168(b) exempted 

facilities that were subject to permitting 

requirements under an earlier version of 

the PSD program created solely by the 

EPA regulation prior to the enactment of 

section 165 of the CAA and other 

provisions that expressly authorized 

and established the requirements of the 

PSD permitting program applicable 

today. This exemption operated to 

continue existing requirements for 

certain sources after a fundamental 

change in the statutory and regulatory 

regime under which such sources were 

required to obtain authorization to 

construct or modify major stationary 

sources of air pollutants. Such an 

exemption does not expressly relate to 

the incorporation of a new requirement 

into the PSD program, under existing 

statutory authority, when the EPA 

promulgates a regulation that creates 

such a requirement. In this case, the 

EPA is not grandfathering permit 

applications from the general 

prohibition in section 165(a) against 

commencing construction in the 

absence of a permit issued ‘‘in 

accordance with the requirements of 

this part.’’ The CAA does not contain 

any express exemptions to the phrase 

‘‘the requirements of this part’’ or from 

section 165(a)(3) of the Act that apply 

when the EPA promulgates a new or 

revised NAAQS. Furthermore, section 

168(b) applied to sources that had 

commenced construction before new 

provisions of the CAA were enacted, 

whereas the grandfathering that the EPA 

proposed for purposes of the revised PM 

NAAQS is applicable to changes in 

regulatory requirements prior to the 

issuance of a permit. Thus, the adoption 

of a one-time grandfather provision 

upon enactment of the statutory PSD 

program is clearly different from 

grandfathering when the EPA 

promulgates a new or revised NAAQS, 

which the Act does not address. The 

fact that Congress expressly enumerated 

an exemption in section 168 intended to 

ease transition upon enactment of the 

PSD provisions in the Act does not 

constrain the Agency with respect to 

offering reasonable transitional 

exemption provisions when EPA 

regulations create new PSD program 

requirements under those statutory 

provisions. 

The EPA agrees that the PSD program 

is based on the goals of preventing air 

pollution and installing controls when 

new sources are being constructed, but 

section 160(3) of the Act also states that 

a purpose of the PSD program is to 

‘‘insure that economic growth will occur 

in a manner consistent with the 

preservation of existing clean air 

resources.’’ The EPA continues to 

construe this provision to call for a 

balancing of economic growth and 

protection of air quality. See 70 FR 

59582, October 12, 2005 at 59587–88. 

Legislative history illustrates 

Congressional intent to avoid a 

moratorium on construction and delays 

in permit processing. The House 

Committee report describes how ‘‘the 

committee went to extraordinary lengths 

to assure that this legislation and the 

time needed to develop and implement 

regulations would not cause current 

construction to be halted or clamp even 

a temporary moratorium on planned 

industrial and economic development.’’ 

H.R. Rep. No. 95–294, 95th Cong., 1st 

Sess., at 171 (1977). As an illustration of 

the lengths to which the committee 

went, the report lists five elements of 

the legislation, including the following 

statement: ‘‘To prevent disruption of 

present or planned sources, the 

committee has authorized extensive 

‘grandfathering’ of both existing and 

planned sources.’’ Id. Furthermore, the 

Senate Committee report specifically 

discusses concerns about delays in 

program implementation. S. Rep. No. 

94–717, at 26 (1976) (‘‘nothing could be 

more detrimental to the intent of this 

section and the integrity of this Act than 

to have the process encumbered by 

bureaucratic delay’’). 

In the 1980 PSD regulation, the EPA 

sought to strike a balance between 

competing goals of the CAA (45 FR 

52683). The EPA explained that 

delaying certain construction ‘‘by 

imposing new PSD requirements could 

frustrate economic development’’ and 

noted that the grandfathered projects 

‘‘have a relatively minor effect on air 

quality.’’ Id. As a result, the EPA 

adopted a grandfathering provision that 

‘‘would strike a rough balance between 

the benefits and costs of applying PSD 

to those projects.’’ Id. Although the EPA 

used issuance of permits previously 

required under the SIP in that case to 

determine eligibility for grandfathering, 

this precedent does not preclude the 

EPA from using another milestone in 

the permit process to determine 

eligibility in order to strike the 

appropriate balance in a different 

situation. The interests behind section 

165 include both protection of air 

quality and timely decision-making on 

pending permit applications. The EPA 

is seeking here to balance the 

requirements in the Act to make a 

decision on a permit application within 

one year and to ensure that new and 

modified sources will only be 

authorized to construct after showing 

they can meet the substantive 

permitting criteria. 

Moreover, this action is not based on 

an assertion of equitable power to 

disregard or override law, but rather on 

an interpretation of our statutory 

authority. In so doing, the EPA has in 

this case determined which regulatory 

requirements are covered by the 

statutory requirements that apply to an 

application that has reached a specified 

milestone when the regulatory 

requirement was established. The EPA 

does not dispute that administrative 

agencies only have the powers conferred 

by statute. However, the EPA may 

interpret the statutory requirements 

consistent with Congressional intent 

and exercise its discretion in a 

thoughtful way in doing so. Thus, while 

an administrative agency in the 

executive branch does not have the 

equitable powers of a court, this does 

not necessarily mean an administrative 

agency cannot interpret its statutory 

authority to achieve equitable outcomes 

consistent with Congressional intent. 


tkelley on DSK3SPTVN1PROD with 
3256 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

Based on the foregoing, the EPA 

believes it has adequately explained its 

consideration of the CAA requirements 

related to both NAAQS protection and 

timely decision-making on permit 

applications in designing the proposed 

grandfathering provision. As described 

below, the EPA is finalizing a 

grandfathering provision that applies to 

two categories of PSD permit 

applications: (1) Those that the 

reviewing authority has determined to 

be complete on or before December 14, 

2012, or (2) those for which the 

reviewing authority has first published 

a public notice that a draft permit or 

preliminary determination had been 

prepared prior to the effective date of 

the revised PM NAAQS. In the proposal, 

the EPA proposed to grandfather only 

the latter category, based on publication 

of a public notice on a draft permit or 

preliminary determination by the 

effective date of the final PM NAAQS. 

However, as described later in this 

section, based on consideration of 

public comments received on the 

proposal, the EPA decided to augment 

the grandfathering provision to include 

applications that had been determined 

to be complete on or before December 

14, 2012, the date of signature of the 

final rule. Permit applications 

qualifying under the final 

grandfathering provision must 

demonstrate that a qualifying new or 

modified source will not cause or 

contribute to a violation of the PM2.5

NAAQS and increments in effect as of 

the date the permit application is 

determined to be complete by the 

reviewing authority or as of the date the 

reviewing authority first publishes 

public notice of the draft permit or 

preliminary determination, depending 

on which prong of the grandfathering 

provision is applicable. 

The grandfathering provision does not 

apply to any other applicable PSD 

requirements related to PM2.5. Sources 

with projects qualifying under the 

grandfathering provision will be 

required to install BACT for PM2.5

emissions, demonstrate that project 

emissions will not cause or contribute to 

a violation of the PSD increments for 

PM2.5 or the PM2.5 NAAQS in effect at 

the time the permit application is 

determined to be complete or the public 

notice is first published on the draft 

permit or preliminary determination, 

and address Class I and additional 

impacts in accordance with the PSD 

regulatory requirements. Accordingly, 

the EPA does not expect that the 

grandfathering provision being finalized 

in today’s rule will result in 

significantly different air quality 

impacts than would occur absent any 

type of grandfathering or transition 

provision. One commenter has 

submitted an analysis to support this 

conclusion. 

As described in the proposal and 

some of the comments received from 

state agencies, if the EPA and other 

reviewing authorities were to require 

permit applicants to demonstrate that 

they will not cause or contribute to a 

violation of the revised PM NAAQS 

after the public comment period has 

begun, this would unduly delay the 

processing of the permit application by 

potentially requiring an additional 

public comment period and increased 

demand on the limited resources of the 

reviewing authority. The EPA disagrees 

with commenters who contend that 

grandfathering is contrary to statute 

because it would preclude public 

comment on elements of the application 

related to the current NAAQS. With 

respect to an application grandfathered 

under the new provisions provided by 

today’s rule, interested persons will 

have the opportunity to comment on all 

aspects of PSD review for PM2.5,

including the air quality impacts 

associated with the revised NAAQS that 

became effective after the application 

was determined to be complete or after 

a public notice was published on the 

draft permit or preliminary 

determination, depending on which 

prong of the grandfathering provision 

applies. Section 165(a)(2) of the CAA 

and section 51.166(q)(2)(v) require an 

opportunity for the public to comment 

on ‘‘the air quality impact of the source’’ 

and ‘‘other appropriate considerations.’’ 

The grandfathering provision does not 

necessarily take away the ability of the 

public to comment on the impact the 

source may have on the revised NAAQS 

(including the standard proposed 

several months earlier) or the discretion 

of the permitting authority to consider 

these comments. However, as provided 

by the grandfathering provision 

established today in the EPA’s PSD 

regulations, a permit applicant is not 

required to complete an analysis after 

the date of the applicable grandfathering 

milestone to demonstrate that it will not 

cause or contribute to a violation of the 

NAAQS that became effective after that 

date to obtain a permit. Thus, consistent 

with CAA section 165(a)(2), ‘‘the 

required analysis’’ will have ‘‘been 

conducted in accordance with 

regulation promulgated by the 

Administrator’’ and made available for 

public comment. 

Several of the commenters supporting 

the proposed grandfathering provision 

in general recommended that the EPA 

establish the grandfathering milestone 

as the date that a complete permit 

application is submitted (or that a 

submitted permit application is deemed 

complete by the reviewing agency) 

rather than the publication date of 

public notice for a draft permit or 

preliminary determination as proposed. 

These commenters pointed out the 

significant level of effort, resources and 

time involved in preparing all of the 

information necessary for a complete 

permit application, including a BACT 

analysis, air quality analysis, additional 

impacts analyses, and a Class I area 

impact analysis. They claimed that it 

would be unfair to establish a 

grandfathering milestone past the 

complete application date because the 

processes and timeframes involved in 

generating the draft permit or 

preliminary determination materials 

and publishing the public notice are 

largely out of the control of the permit 

applicant and vary from agency to 

agency. They further stated that 

requiring reevaluation of a proposed 

project to assess impacts with respect to 

the revised NAAQS after a permit 

application has been deemed complete 

would result in significant additional 

cost and delay. One industry commenter 

pointed out that the EPA’s proposed 

grandfathering approach could place 

considerable pressure on permit 

authorities to expedite review of 

publication of draft permits or decisions 

before adequate internal review was 

completed, which could result in 

subsequent withdrawal of the permit. 

Several commenters cited prior EPA 

grandfathering provisions that relied 

upon that milestone, including the 1987 

PM10 NAAQS (52 FR 24672, July 1, 

1987) and the 1988 NO2 increments (53 

FR 40656, October 17, 1998), and 

contended that the EPA had not 

justified the use of an alternative date 

for purposes of the proposed revisions 

to the PM2.5 NAAQS. 

Some state commenters also indicated 

that the proposed draft permit public 

notice date milestone could result in 

additional resource burden on the 

agency to expedite completion of draft 

permit packages and process public 

notices. Other state commenters 

supported the EPA’s proposed draft 

permit or preliminary determination 

public notice date as the appropriate 

grandfathering eligibility milestone, 

indicating that this approach would 

provide states and industry certainty on 

the NAAQS demonstration required 

during the PM2.5 NAAQS transition 

period. 

The EPA acknowledges the comments 

raising concerns about an approach 

based solely on the public notice 

milestone date, and agrees that they 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3257 

warrant consideration of a different 

milestone date. Further, we agree that 

an alternate milestone for 

grandfathering based on the date a 

permit application is determined 

complete would address many of these 

concerns. Therefore, the EPA has 

modified its proposed approach to 

address these concerns. In particular, 

the EPA agrees with commenters that a 

substantial portion of the level of effort, 

resource investment, and time involved 

in the PSD permit process occurs during 

the process of preparing a PSD permit 

application and obtaining a 

completeness determination from the 

reviewing authority. Of particular 

importance is the issue of the time delay 

and the effect on permitting authorities 

to meet permit issuance deadlines, as 

previously noted. Commenters have 

persuaded the EPA that reevaluation of 

a proposed project to assess impacts 

with respect to the revised NAAQS after 

a permit application has been deemed 

complete would result in significant 

additional delay, thus frustrating the 

statutory requirement to complete 

action on a permit application within 

one year of the completeness date. 

We also agree with commenters that 

after the permit application 

completeness determination stage in the 

permitting process, the applicant must 

have completed all of the required 

technical demonstrations (including a 

BACT analysis, air quality analysis, 

additional impacts analyses, and Class I 

area impact analyses), and that the final 

stages of the permitting process prior to 

public notice (i.e., developing the draft 

permit or preliminary determination, 

developing supporting materials and 

publishing the public notice) are under 

the control of the permitting authority. 

Given the variable practices and 

timelines of permitting authorities in 

processing these final steps between 

permit application completeness and 

publication of a public notice on the 

draft permit or preliminary 

determination pointed out by 

commenters, we agree that the proposed 

grandfathering approach could result in 

inequitable and burdensome outcomes 

in some circumstances. 

The EPA has therefore concluded 

based on public comments that it 

should add an additional grandfathering 

milestone to avoid substantial 

additional burden and delay for permit 

applications that have reached a stage in 

the review process by which significant 

resources have been expended to 

complete fundamental PSD analyses 

and demonstrations that would have to 

be redone. After a PSD permit 

application has been determined 

complete, it may be time consuming for 

the applicant to amend its permit 

application to address new or revised 

NAAQS promulgated after that date. 

The time required to both amend the 

application and review the amended 

application would impose unreasonable 

additional burden and delay upon the 

applicant and the reviewing authority. 

As a result, if the EPA and other 

reviewing authorities were to require 

permit applicants to demonstrate that 

they will not cause or contribute to a 

violation of the revised PM NAAQS 

after the permit application is 

determined to be complete, or any later 

stage in the permitting process, this 

would unduly delay the processing of 

the permit application and place 

increased demand on the limited 

resources of the reviewing authority at 

a time when it should be focused on 

preparing the draft permit and 

supporting materials, preparing a public 

notice, considering public comments 

and preparing a final permit decision in 

order to conclude its review of a permit 

application in a timely manner. 

The EPA also agrees with 

commenters’ concerns that the proposed 

grandfathering approach, based solely 

on the date of publication of a public 

notice on a draft permit or preliminary 

determination, could in some cases 

result in pressure on permitting 

authorities to expedite review of 

publication of draft permits, resulting in 

additional burden on such permitting 

authorities and other potential adverse 

consequences. We note that expediting 

review is consistent with the 

requirement of section 165(c) of the 

CAA to process permit applications in 

a timely manner. We also observe that 

using the milestone of a completeness 

determination to determine eligibility 

for grandfathering could simply shift 

this pressure back to the stage in which 

a permitting authority is reviewing an 

application to determine if it is 

complete. A significant distinction, 

however, is that the one-year deadline 

for completing action on a permit does 

not begin to run until the date that a 

permit application is determined 

complete. 

Based on the comments received and 

the EPA’s consideration of those 

comments described above, the EPA has 

decided to modify the proposed 

grandfathering approach by adding a 

second category of applications to the 

proposed qualifying criteria. 

Specifically, the EPA is finalizing a 

grandfathering provision that extends 

grandfathering to permit applications 

that the reviewing authority has 

determined, on or before December 14, 

2012 (the signature date of the final 

rule), to be complete. We are adding this 

category to our originally proposed 

category: Permit applications for which 

the permitting authority has first 

published a public notice that the draft 

permit or preliminary determination has 

been prepared prior to the effective date 

of the revised PM NAAQS. 

We are adding eligibility criteria 

rather than wholly replacing what we 

proposed for two reasons. First, the EPA 

understands that there may be some 

permitting authorities that do not issue 

formal determinations that an 

application is complete. Applications in 

these jurisdictions that may in fact have 

been complete and far enough along in 

the review process that a public notice 

could be issued before the effective date 

of the revised NAAQS could be 

significantly delayed if the EPA 

removed the eligibility criteria based on 

the publication of the public notice. 

Second, given that the EPA proposed to 

establish eligibility for grandfathering 

based on the timing of the public notice, 

some permitting authorities and 

applicants may have anticipated that 

they had more time to take action to 

qualify for grandfathering and may have 

not acted as promptly as they could 

have to submit additional information 

or make a completeness determination. 

Retaining the proposed eligibility 

criteria avoids prejudice to parties that 

may have relied on the proposed rule in 

such a manner. 

For the second eligibility criterion 

added in this final rule, the EPA chose 

to use the date an application is 

determined complete, as requested by 

several commenters. In several existing 

provisions in sections 51.166(i) and 

52.21(i) of the EPA’s regulations, a 

pending application was able to quality 

for grandfathering if it was submitted 

before the applicable date but 

subsequently determined complete after 

that date. However, this historic 

approach can be cumbersome to 

implement and can lead to inconsistent 

implementation and potential abuse. 

These concerns stem from the fact that 

there is a time lag between submittal 

and the completeness determination 

during which there are typically 

additional data requests by the 

permitting authority and supplemental 

application material submittals by the 

applicant. Therefore, it can be difficult 

to determine the specific date that the 

submitted application actually became 

complete; since this date could range 

from the initial submittal date, through 

a number of supplemental submittal 

dates, to the date the permitting 

authority formally determines the 

application to be complete. The EPA has 

chosen to use the date an application is 

determined complete because this date 


tkelley on DSK3SPTVN1PROD with 
3258 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

250 In one extraordinary case where the EPA had 

not previously adopted a grandfathering provision 

in regulations and had significantly exceeded the 

deadline in section 165(c) of the CAA, the EPA has 

taken the position that it may grandfather a specific 

source through adjudication, thus interpreting its 

regulations, as well as other authorities, to allow 

grandfathering in that extraordinary circumstance 

(U.S. EPA, 2011c, pp. 67 to 71). Although 

grandfathering without a specific exemption in 

regulations was justified based on the particular 

facts in that specific instance, the preferred 

approach is to enable grandfathering through 

express regulatory exemptions of the type being 

finalized in this action (U.S. EPA, 2011c, p. 68). 

is easier to identify and apply. For PSD 

permits issued under 40 CFR 52.21, the 

EPA’s regulations in 40 CFR part 124 

define the effective date of an 

application as the date the permitting 

authority notifies the applicant that the 

application is complete. 40 CFR 

124.3(f). 

The EPA chose to base the second 

eligibility criterion on the date this rule 

has been signed by the Administrator to 

avoid creating pressure on permitting 

authorities to determine applications 

complete. Such pressure could lead to 

premature findings of completeness and 

grandfathering of a larger number of 

applications than is warranted to avoid 

undue delays, thus increasing the air 

quality impact of the grandfathering 

provision. Notably, the one-year 

deadline for completing action on a 

permit does not begin to run until the 

date that a permit application is 

determined complete. While Congress 

desired timely action on a permit 

application, the statute gives permitting 

authorities leeway to ensure they have 

all the necessary information to proceed 

expeditiously on a permit application 

before the clock starts running. The goal 

of protecting air quality can thus be 

fulfilled without compromising 

Congressional intent for timely action 

by conducting a careful review of an 

application to determine that it is 

complete. Applications that have not yet 

been determined complete may be 

supplemented to ensure the proposed 

source does not cause or contribute to 

a violation of the revised NAAQS 

without compromising compliance with 

the one-year deadline in section 165(c). 

The EPA thus selected the signature 

date of the final rule to ensure the 

integrity of completeness 

determinations issued after the rule is 

signed and to limit the number of 

additional sources eligible for 

grandfathering. 

The final grandfathering provision 

appropriately balances the objectives of 

CAA section 165 to protect air quality 

and ensure timely decision-making on 

permit applications, while also 

addressing concerns about resource 

burdens raised by commenters. In 

addition, as pointed out by commenters, 

the final grandfathering provision also 

provides an approach that is more 

consistent with prior EPA 

grandfathering actions, e.g., in the 1987 

PM10 NAAQS, wherein the EPA selected 

the date of application completeness for 

grandfathering projects from 

requirements associated with the new 

NAAQS. 

Regarding the need for a sunset clause 

for the grandfathering provision, the 

majority of commenters supported, as 

proposed, not including such a clause, 

and no commenters specifically 

recommended that a sunset clause be 

established. Commenters pointed out 

that permit applicants and reviewing 

authorities already have strong 

incentives to issue final permits in a 

timely manner following the public 

notice stage, and that a sunset clause 

would not add any meaningful 

incentive to expedite the permitting 

process, rather potentially causing 

additional delays. One commenter 

stated that permitting authorities have 

ample discretion, which they routinely 

use, to refuse to issue a draft permit if 

additional information is requested 

during a comment period or the agency 

itself wants additional information 

following publication of a draft permit 

or preliminary determination. The same 

commenter indicated that permitting 

authorities also have sufficient 

discretion to reopen permit proceedings 

if they consider information in an 

application to be stale. 

The EPA agrees with commenters that 

the addition of a sunset clause to the 

proposed grandfathering provision 

would not add meaningful additional 

incentive for sources or permitting 

authorities to expedite permitting 

processes. The EPA also agrees that a 

sunset clause could in fact result in 

further delays for permit actions that 

qualify for the proposed grandfathering 

provision in circumstances where 

unrelated and not reasonably avoidable 

factors cause final permit issuance to 

lapse beyond the sunset date. In such 

cases, the already delayed permit action 

would necessarily be further delayed to 

address PSD permitting requirements 

associated with the revised PM2.5

NAAQS, potentially triggering a domino 

effect of newly applicable requirements. 

As such, the EPA believes a sunset 

clause would diminish the value of the 

grandfathering provision and likely 

introduce additional complexities in 

relation to specific permit actions. 

A few industry commenters 

suggested, as an alternative to our 

proposed approach, that the EPA should 

effectively grandfather PSD permit 

actions from meeting requirements 

associated with the revised PM NAAQS 

by extending the effective date of the 

NAAQS by one year. These commenters 

argued that such an approach is 

preferable because it would address 

potential concerns about the inability of 

state agencies to implement the 

proposed grandfathering provision prior 

to rule adoption and SIP approval. 

Several industry groups and 

representatives also commented that the 

EPA should not eliminate state 

discretion to grandfather individual 

permits even without an express 

exemption. 

The EPA disagrees with extending the 

effective date of the revised PM NAAQS 

by one year because this approach 

would entirely defer the important 

health benefits associated with the 

revised PM NAAQS. Further, as 

discussed in the proposal, the EPA does 

not anticipate any issues related to 

implementation of the grandfathering 

provision in SIP approved state/local 

jurisdictions. The EPA proposed and is 

finalizing a revision to 40 CFR 51.166 to 

provide a comparable exemption 

applicable to SIP-approved PSD 

programs, and air agencies that issue 

PSD permits under an EPA-approved 

PSD permit program should have the 

discretion to ‘‘grandfather’’ proposed 

PSD permits consistent with these final 

rule provisions. Even absent an express 

grandfathering provision in state rules, 

states have the discretion to permit 

grandfathering consistent with the 

federal regulations if the particular 

state’s laws and regulations may be 

interpreted to provide such 

discretion.250 However, state SIPs may 

not be less stringent than federal 

requirements. Accordingly, the EPA 

believes that such discretion must be 

limited to applying grandfathering 

consistent with the federal rule 

provisions. 

iii. Final Action 

For the reasons articulated above, the 

EPA is finalizing a grandfathering 

provision under the PSD regulations 

that provides that qualifying sources 

and modifications shall not be required 

to demonstrate that their proposed 

emissions will not cause or contribute to 

a violation of the revised primary 

annual PM2.5 NAAQS but instead shall 

demonstrate that such emissions will 

not cause or contribute to the PM2.5

NAAQS in effect on the date the 

reviewing authority determines the 

permit application to be complete or the 

date the public notice on the draft 

permit or preliminary determination is 

first published, depending on which 

prong of the grandfathering provision is 

applicable. Under the final 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3259 

251There may be application completeness 

determinations or draft permits/preliminary 

determinations for which a public notice was 

issued prior to October 20, 2011, which is the date 

that PM2.5 increments became applicable 

requirements for any newly issued federal PSD 

permits under 40 CFR 52.21. It is not the EPA’s 

intention that the final grandfathering provision 

should relieve such a permit from the requirement 

to demonstrate compliance with those new PM2.5

increments, for which the EPA did not adopt any 

grandfathering provisions but deferred 

implementation in accordance with the 

requirements of the CAA. 

252The presentation on this draft guidance was 

posted on the EPA Web site at: http://www.epa.gov/ 

ttn/scram/10thmodconf.htm. 

253The PSD rules provide that a source that 

would emit major amounts of any regulated NSR 

pollutant must undergo review for that pollutant as 

well as any other regulated NSR pollutant that the 

source would emit in significant amounts. 

grandfathering provision, qualifying 

sources and modifications are those for 

which the reviewing authority has 

determined that the permit application 

is complete on or before December 14, 

2012 or the permitting authority has 

first published a public notice that a 

draft permit or preliminary 

determination has been prepared prior 

to the effective date of today’s final 

revisions to the PM NAAQS.251 The 

relevant public notice requirements for 

EPA and delegated agency issued 

permits are those in 40 CFR 

124.10(c)(2), and the corresponding 

provisions for implementation-plan 

approved agency permits are those in 40 

CFR 51.166(q)(2)(iii). The 

grandfathering provision is being 

incorporated into the regulations at 40 

CFR 52.21 and 51.166 to provide the 

same transition for the EPA, delegated 

jurisdictions, and implementation planapproved jurisdictions. The EPA is not 

establishing a sunset date for this 

grandfathering provision. 

b. Modeling Tools and Guidance 

Applicable to the Revised Primary 

Annual PM2.5 NAAQS 

Today’s final rule revising the level of 

the primary annual PM2.5 NAAQS from 

15.0 mg/m3 to 12.0 mg/m3 generally will 

require proposed new major stationary 

sources and modifications to take these 

changes into account as part of the 

required air quality analysis to 

demonstrate that the proposed 

emissions increase will not cause or 

contribute to a violation of the PM 

NAAQS. Upon the effective date of 

today’s final revisions to the PM 

NAAQS, proposed new major stationary 

sources and major modifications that are 

not grandfathered from the new 

requirements (as described in section 

IX.D.1.a) will be required to 

demonstrate compliance with the suite 

of PM NAAQS, including the revised 

primary annual PM2.5 NAAQS. 

PSD applicants are currently required 

to demonstrate compliance with the 

existing primary and secondary annual 

and 24-hour PM2.5 NAAQS and will 

need to consider the impact of their 

proposed emissions increases on the 

revised primary annual PM2.5 NAAQS. 

To assist sources and permitting 

authorities in carrying out the required 

air quality analysis for PM2.5 under the 

existing standards, the EPA issued, on 

March 23, 2010, a guidance 

memorandum that recommends certain 

interim procedures to address the fact 

that compliance with the 24-hour PM2.5

NAAQS is based on a particular 

statistical form, and that there are 

technical complications associated with 

the ability of existing models to estimate 

the impacts of secondarily formed PM2.5

resulting from emissions of PM2.5

precursors (Page, 2010b). For the latter 

issue, the EPA recommended that 

special attention be given to the 

evaluation of monitored background air 

quality data, since such data readily 

account for the contribution of both 

primary and secondarily formed PM2.5

from existing sources affecting the area. 

To provide more detail and to address 

potential issues associated with the 

modeling of direct and precursor 

emissions of PM2.5, the EPA is now 

developing additional permit modeling 

guidance that will recommend 

appropriate technical approaches for 

conducting a PM2.5 NAAQS compliance 

demonstration, which includes more 

adequate accounting for contributions 

from secondary formation of ambient 

PM2.5 resulting from a proposed new or 

modified source’s precursor emissions. 

To this end, the EPA discussed this 

draft guidance in March 2012 at the 

EPA’s 10th Modeling Conference.252

Based on its review of comments 

received through the conference and 

further technical analyses, the EPA 

intends to issue final guidance by the 

end of calendar year 2012, prior to the 

effective date of today’s final PM 

NAAQS revisions. 

The EPA also received a number of 

industry and state comments on the 

PM2.5 NAAQS proposal related to PM2.5

air quality impact analyses and 

associated existing modeling tools and 

procedures. In general, commenters 

identified the lack of approved air 

quality modeling tools and procedures 

to predict the impacts of single source 

emissions on PM2.5 concentration in 

ambient air as well as limitations 

associated with existing PM2.5 modeling 

tools and guidance. Commenters 

recommended the EPA address these 

existing issues and provide updated 

guidance through an open stakeholder 

process and preferably through noticeand-comment rulemaking. As described 

above, the EPA intends to issue revised 

PM2.5 modeling guidance prior to the 

effective date of today’s revised PM 

NAAQS to assist permit applicants and 

reviewing authorities in performing 

required air quality impact analyses. 

The EPA expects that this revised 

guidance will address all or most of the 

remaining issues related to PM2.5 air 

quality impact demonstrations under 

the PSD program, at least on an interim 

basis, until the EPA takes additional 

steps to improve existing regulatory 

models and procedures. To that end, the 

EPA is also pursuing regulatory updates 

to the Guideline on Air Quality Models 

(40 CFR part 51 Appendix W) to 

formalize new models and techniques as 

appropriate. The EPA recently granted a 

petition for rulemaking to specifically 

evaluate whether to incorporate into the 

Guideline new analytical techniques or 

models for secondary PM2.5 (McCarthy, 

2012). The EPA anticipates that this 

rulemaking will be proposed by the end 

of calendar year 2014 or early in 

calendar year 2015. 

c. PSD Screening Tools: Significant 

Emissions Rates, Significant Impact 

Levels, and Significant Monitoring 

Concentration 

The EPA has historically allowed the 

use of screening tools to help facilitate 

the implementation of the NSR program 

by reducing the permit applicant’s 

burden and streamlining the permitting 

process for circumstances where 

emissions or concentrations could be 

considered de minimis. These screening 

tools, which all provide de minimis 

thresholds of some kind, include SERs, 

SILs, and a SMC. The EPA promulgated 

a SER for PM2.5 in the 2008 final rule 

on NSR implementation as part of the 

first phase of NSR amendments to 

address PM2.5 (74 FR 28333, May 16, 

2008). The PM2.5 SER is used to 

determine whether any proposed major 

stationary source or major modification 

will emit sufficient amounts of PM2.5 to 

require review under the PSD 

program.253 Under the terms of the 

existing EPA regulations, the applicable 

SER for PM2.5 is 10 tpy of direct PM2.5

emissions (including condensable PM) 

and, for precursors, 40 tpy of SO2 and 

40 tpy of NOX emissions. 40 CFR 

51.166(b)(23); 40 CFR 52.21(b)(23). This 

SER applies to permitting requirements 

based on both the annual and 24-hour 

PM2.5 NAAQS. The SERs are pollutantspecific but not specific to the averaging 


tkelley on DSK3SPTVN1PROD with 
3260 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

254Page, 2010c; Page, 2010d. The EPA provided 

similar advice before it finalized the proposed PM2.5

SILs (Page, 2010b). See also, In re Mississippi Lime 

Co., PSD Permit Appeal 11–01, Slip. Op. at 34–41 

(EAB August 9, 2011) and U.S. EPA, 2012d. 

time of any NAAQS for a particular 

pollutant. 

Once it is determined that emissions 

resulting from the proposed new source 

or modification are significant for PM2.5, 

the permit applicant must complete an 

air quality analysis. 40 CFR 

51.166(m)(1)(i); 40 CFR 52.21(m)(1)(i). 

The SIL helps to determine the scope of 

the required air quality analysis that 

must be carried out in order to 

demonstrate that the source’s emissions 

will not cause or contribute to a 

violation of any NAAQS or increment. 

The EPA promulgated SILs for PM2.5 in 

2010 under a final rule that established 

increments, SILs, and a SMC for PM2.5

(75 FR 64864, October 20, 2010 at 64890 

to 64894). 

Historically, the EPA and other 

permitting authorities have allowed 

permit applicants to determine the 

scope of analysis required to satisfy 

section 165(a)(3) of the CAA by 

modeling their proposed emissions 

increase to predict ambient air quality 

impacts associated with that emissions 

increase, and by comparing this 

predicted increase in ambient 

concentration of PM2.5 to the applicable 

SIL, which is also expressed as an 

ambient PM2.5 concentration over a 

prescribed averaging time consistent 

with the NAAQS and increments. The 

EPA notes that the current PM2.5 SILs 

are the subject of a petition that 

challenges the EPA’s legal authority 

under the CAA to develop and 

implement those SILs, and also alleges 

that the PM2.5 SILs established by the 

EPA have not been adequately 

demonstrated to represent de minimis 

values. Sierra Club v. EPA, No. 10–1413 

(D.C. Cir. filed Dec. 17, 2010). In the 

course of this litigation, the EPA has 

recognized the need to correct the text 

addressing the use of the PM2.5 SILs in 

the PSD regulations (40 CFR 

51.166(k)(2); 40 CFR 52.21(k)(2)), and 

the EPA has asked the court to vacate 

and remand those provisions so that the 

EPA may correct them. However, the 

EPA does not believe this corrective 

action would preclude appropriate use 

of the PM2.5 SILs in the interim. The 

EPA has not asked the court to vacate 

the SILs in section 51.165(b) of its 

regulations. Furthermore, SILs that are 

not reflected in rules may be used if the 

permitting record provides adequate 

support that the values reflect a de 

minimis impact on air quality, 

consistent with the principles described 

in EPA memoranda establishing interim 

SILs for the one-hour SO2 and NO2

NAAQS.254 The revisions to the primary 

annual PM2.5 NAAQS do not affect the 

continued used of the PM2.5 SILs. 

Finally, the SMC, also measured as an 

ambient pollutant concentration 

(mg/m3), is a screening tool used to 

determine whether it may be 

appropriate to exempt a proposed 

source from the requirement to collect 

pre-construction ambient monitoring 

data as part of the required air quality 

analysis for a particular pollutant. The 

EPA promulgated the existing SMC for 

PM2.5 in 2010 on the basis of the defined 

minimum detection limit for PM2.5 and 

the current information at that time 

concerning the physical capabilities of 

the PM2.5 FRM samplers. In that 

rulemaking, the EPA addressed 

uncertainties introduced into the 

measurement of PM2.5 due to variability 

in the mechanical performance of the 

PM2.5 samplers and micro-gravimetric 

analytical balances that weigh filter 

samples. Like the PM2.5 SILs, the SMC 

was challenged by the Sierra Club in the 

same petition, and is currently under 

review by the Court. 

In the proposal, the EPA did not 

propose any changes to the existing 

PM2.5 SERs, SILs and SMC, but solicited 

preliminary comment on whether any 

such changes would be appropriate. The 

EPA also indicated that any changes to 

the PM2.5 screening values would be 

addressed in a subsequent rulemaking 

that would specifically address various 

PSD implementation issues. 

The EPA received several comments 

from industry and state agencies 

regarding the existing PSD screening 

tools and the potential need to adjust 

associated values based on the revised 

primary annual PM2.5 NAAQS. The 

majority of these commenters supported 

retaining the existing SERs, SILs and 

SMC for PM2.5 (and PM2.5 precursors in 

the case of the SERs), indicating that 

there was no compelling technical 

reason for revision based on the 

proposed revision to the primary PM2.5

NAAQS. One industry commenter 

indicated that there might be a need to 

revise the annual PM2.5 SILs based on 

the approach used in establishing the 

current value. However, this commenter 

and others recommended that any 

revisions to the PSD screening levels for 

PM2.5 be accomplished through a 

separate notice-and-comment 

rulemaking. Several state commenters 

that supported retention of the current 

PM2.5 SILs also urged the EPA to 

provide guidance on the use of those 

existing SILs. 

One set of collaborative comments 

from health and environmental 

advocacy groups stated that the EPA’s 

proposal to leave in place the PSD 

screening tools adopted with the 

previous PM NAAQS had no rational 

basis and was contrary to statutory 

requirements. These commenters 

claimed that the EPA has no statutory 

authority to establish SILs and SMC for 

PM2.5, which is the subject of current 

litigation in Sierra Club v. EPA, No. 10– 

1413 (D.C. Cir. filed Dec. 17, 2010). The 

EPA’s argument in support of the 

existing PSD screening tools is 

contained in a brief filed in that case, 

which is included in the docket for the 

final rule. Id., Brief of Respondent at 

26–56 (June 26, 2012). These same 

commenters and one additional 

collaborative comment letter from 

academic researchers also stated that the 

EPA should revise the current PM2.5

SERs, SILs and SMC to reflect the 

revised NAAQS and true de minimis 

levels. 

The EPA did not propose to make and 

is not finalizing any changes to the 

existing PM2.5 SERs, SILs and SMC as 

part of this final rule. The EPA intends 

to consider the need for any future 

changes to these values in light of 

today’s revision of the primary annual 

PM2.5 NAAQS and considering public 

comments received. The EPA will 

address any changes to the PM2.5 SERs, 

SILs and SMC in a subsequent PSD 

implementation rulemaking if deemed 

necessary or appropriate. The EPA will 

determine the need for, and develop 

such rulemaking expeditiously, and any 

such forthcoming rulemaking will 

provide an additional opportunity for 

public comment on specific proposed 

revisions to the PSD screening tool 

values for PM2.5. Until any rulemaking 

to amend existing regulations is 

completed, permitting decisions should 

continue to be based on the SERs for 

PM2.5 (and its precursors) and the SILs 

and SMC for PM2.5 in existing 

regulations. 

d. PSD Increments 

Section 166(a) of the CAA requires the 

EPA to promulgate ‘‘regulations to 

prevent the significant deterioration of 

air quality’’ for pollutants covered by 

the NAAQS. Among other things, the 

EPA has implemented this requirement 

through promulgation of PSD 

increments. The EPA promulgated PM2.5

increments in 2010 to prevent 

significant air quality deterioration with 

regard to the primary and secondary 

annual and 24-hour PM2.5 NAAQS (75 

FR 64864, October 20, 2010). The 

revision to the primary annual PM2.5

NAAQS raises the question of whether 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3261 

255A United States District Court has upheld the 

EPA’s interpretation. See Order Granting 

Defendant’s Motion to Dismiss Mandatory Duty 

Claim, Wildearth Guardians v. Jackson, Case No. 

11–cv–5651–YGR (N.D. Cal. May 7, 2012). An 

appeal of this decision is now pending with the 

United States Court of Appeals for the Ninth 

Circuit. 

the EPA should consider revising the 

annual PM2.5 increments. The EPA does 

not interpret section 166(a) of the Act to 

require that the EPA revise existing 

increments whenever the EPA revises a 

NAAQS for the same pollutant and 

averaging time,255 but the Agency 

interprets the Act to afford the EPA the 

discretion to do so. In the proposal, the 

EPA did not propose to revise the PM2.5

increments. In the meantime, the 

current PM2.5 increments remain in 

effect, and PSD permitting should 

continue pursuant to the current 

increments, with a minimum of 

disruption to the permitting process 

when the revised NAAQS take effect. 

The EPA received few comments on 

whether there was any need or 

justification to revise the existing PSD 

increments for PM2.5. Industry and state 

agency commenters generally supported 

retaining the existing increments. 

Commenters again recommended that 

any revisions to the PSD increments for 

PM2.5 be accomplished through a 

separate notice-and-comment 

rulemaking. 

The EPA did not propose to make and 

is not finalizing any changes to the 

existing PSD increments for PM2.5 as 

part of this final rule. The EPA will 

consider whether it is appropriate to 

propose any revised PSD increments for 

PM2.5 in the future. Any such 

forthcoming rulemaking will provide an 

additional opportunity for public 

comment on specific proposed revisions 

to the PSD increments for PM2.5. Until 

any rulemaking to amend existing 

regulations is completed, permitting 

decisions should continue to be based 

on the PSD increments for PM2.5 in 

existing regulations. 

e. Other PSD Transition Issues 

Several industry commenters 

expressed concern that a permitting 

problem would result from the fact that, 

upon promulgation of the revised PM2.5

NAAQS, ambient air quality monitoring 

data would show that for some areas, 

PM2.5 concentrations exceed the revised 

NAAQS, although those areas would not 

be formally designated as 

‘‘nonattainment’’ until a later date 

pursuant to the designation process 

provided by the CAA. The commenters 

noted that sources locating in such areas 

would be required to obtain a PSD 

permit in order to construct or modify, 

but could not do so because the 

requirement that the new or modified 

source must demonstrate that it will not 

cause or contribute to a NAAQS 

violation, even though the area would 

technically already be in nonattainment. 

The commenters further noted that once 

the nonattainment designation is made, 

section 173 of the Act provides a 

nonattainment area permit program that 

specifies conditions under which a 

permit will be issued, including 

obtaining offsetting reductions in 

emissions rather than demonstrating 

through modeling or other analysis that 

the source will not cause or contribute 

to a violation of the NAAQS as required 

in PSD. Thus, the commenters urged the 

EPA to offer an interim approach that 

would avoid the imposition of an 

effective construction ban on such areas 

until such time as the nonattainment 

area designations and the nonattainment 

NSR offset requirements are in place 

instead of the PSD requirements. Some 

of the commenters specifically 

requested that the EPA provide either a 

surrogacy approach based on showing 

compliance with the pre-existing annual 

PM2.5 NAAQS or a PSD offset approach 

to avoid a construction moratorium in 

such areas. 

The commenters are correct in that 

areas already in violation of the revised 

annual PM2.5 NAAQS upon the effective 

date of such NAAQS may not be 

formally designated nonattainment for 

two years or potentially longer in 

accordance with the statutory 

procedures for promulgating such area 

designations. In addition, it is the EPA’s 

longstanding policy that new and 

revised NAAQS must be implemented 

through the permitting process as of the 

NAAQS effective date (except for earlier 

projects that would qualify for any EPAauthorized grandfathering). 

Accordingly, new major stationary 

sources and major modifications for 

which permits will be issued on or after 

the effective date of the revised annual 

PM2.5 NAAQS must comply with the 

PSD requirement to demonstrate 

compliance with that and any other 

applicable NAAQS. 

We disagree, however, with the 

commenters’ conclusion that such 

circumstances will result in ‘‘the 

imposition of an effective construction 

ban on such areas.’’ First, as already 

described, the EPA is promulgating a 

grandfathering provision that allows 

certain proposed new and modified 

sources to proceed with the permit 

process based on the requirements that 

were in effect previously, provided the 

permitting authority either has 

determined on or before December 14, 

2012 that the permit application is 

complete or has proposed the permit 

(i.e., the draft permit or preliminary 

determination has been noticed for 

public comment) prior to the date the 

revised PM standards become effective, 

which is 60 days after publication in the 

Federal Register. The grandfathering 

provision thus will enable some sources 

to avoid issues associated with potential 

violations of the revised annual PM2.5

NAAQS. 

Second, for those sources that are not 

eligible to be grandfathered under the 

new provision, permitting authorities 

have the discretion to consider 

offsetting emissions reductions at other 

sources as part of a demonstration that 

an individual source seeking a permit 

will not cause or contribute to violation 

of the NAAQS. See, Page (2010c). The 

EPA has historically recognized in 

regulations and through other actions 

that sources applying for PSD permits 

may utilize offsets as part of the 

required PSD demonstration, even 

though the PSD provisions of the Clean 

Air Act do not expressly reference 

offsets in the same manner as the 

nonattainment NSR provisions of the 

Act. See, In re Interpower of New York, 

Inc., 5 E.A.D. 130, 141 (EAB 1994) 

(describing an EPA Region 2 PSD permit 

that relied in part on offsets to 

demonstrate the source would not cause 

or contribute to a violation of the 

NAAQS). 

Existing EPA regulations provide a 

procedure by which major stationary 

sources and major modifications 

locating in an area designated as 

attainment or unclassifiable for any 

NAAQS, and found to cause or 

contribute to a NAAQS violation in any 

area, may utilize offsets to address such 

adverse impacts and ultimately be 

issued a permit. See 40 CFR 51.165(b). 

Specifically, paragraph (b)(3) of those 

regulations provides that the required 

permit program may include a provision 

allowing a proposed major source or 

major modification to reduce the impact 

of its emissions on air quality by 

obtaining sufficient emissions 

reductions to, at a minimum, 

compensate for its adverse ambient 

impact where the source or modification 

would otherwise cause or contribute to 

a violation of any NAAQS. On October 

20, 2010, the EPA amended the 

requirements at 40 CFR 51.165(b) to 

define a significant impact with regard 

to the PM2.5 NAAQS. See 75 FR 64864 

at 64902. 

As noted by some of the commenters, 

the EPA addressed this same issue in 

1987 when it promulgated a new set of 

NAAQS for PM10 and revised 40 CFR 

51.165(b) of the regulations. See 52 FR 

24672 (July 1, 1987) at 24684, 24686–87, 


tkelley on DSK3SPTVN1PROD with 
3262 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

256 In 1980, the EPA had determined that the 

statutory requirement under CAA section 

165(a)(3)(B), providing that a proposed new or 

modified PSD source must demonstrate that it will 

not cause or contribute to a violation of any 

NAAQS, taken together with the requirements of 

section 110(a)(2)(D) of the CAA required all major 

stationary sources locating outside a nonattainment 

area but causing or contributing to a NAAQS 

violation to reduce the impact on air quality so as 

to assure attainment and maintenance of the 

NAAQS. In a footnote, the EPA further indicated 

that this offset requirement must apply to sources 

causing or contributing to a newly discovered 

NAAQS violation until the area is designated 

nonattainment. See 45 FR 31307 (May 13, 1980) at 

31310. In this 1980 rule, EPA adopted section 

51.18(k), which was later renumbered section 

51.165(b). EPA revised 51.165(b) in 1987 to 

expressly authorize an offset program to meet the 

requirements of section 110(a)(2)(D)(i), but this 

provision may also be interpreted to apply to 

section 165(a)(3)(B) of the CAA, consistent with 

EPA’s reading of section 51.18(k) in 1980. 

257 In some cases, however, the CAA and the 

EPA’s regulations define ‘‘major stationary source’’ 

for nonattainment area NSR in terms of a lower 

emissions rate dependent on the pollutant. For 

PM10, for example, a source having the potential to 

emit at least 70 tpy of PM10 is considered ‘‘major’’ 

if the source is located in a nonattainment area 

classified as a ‘‘Serious Area.’’ 

258However, transportation conformity 

requirements discussed in section IX.E below are 

dependent upon the averaging period(s) for which 

an area is designated nonattainment. 

24698. For PM10, the EPA made it clear 

that when a proposed PSD source was 

found to cause or contribute to violation 

of the PM10 NAAQS, the source would 

be required satisfy the requirements of 

40 CFR 51.165(b) ‘‘to obtain, at a 

minimum, sufficient PM10 emission 

offsets to compensate for the source’s 

ambient impact in the area of the 

violation.’’ Such offsets were considered 

to satisfy the ‘‘cause or contribute to’’ 

language under section 165(a)(3)(B) of 

the CAA. Id. at 24698.256 In response to 

comments concerning the appropriate 

criteria for applying this offset 

requirement for PSD purposes, the EPA 

also stated that any emissions offsets 

used for PSD purposes must meet 

applicability criteria that are at least as 

stringent as the offset criteria set forth 

in the nonattainment NSR requirements 

for offsets under 40 CFR 51.165(a)(3). Id. 

at 24684. 

We continue to believe that the 40 

CFR 51.165(a)(3) criteria provide the 

most appropriate guide for determining 

the creditability of PSD offsets, 

including any offsets obtained to satisfy 

the PSD requirements for the revised 

PM2.5 NAAQS prior to any anticipated 

designation of any area as 

nonattainment with that NAAQS. Since 

the purpose for using offsets in PSD is 

to show that additional emissions from 

the proposed construction will not 

cause or contribute to a violation, the 

EPA has not codified a requirement that 

such offsets necessarily must meet the 

same criteria that apply to offsets under 

the nonattainment NSR program. In fact, 

the EPA has previously observed that, in 

the context of PSD, it may not be 

necessary for a permit applicant to fully 

offset the proposed emissions increase if 

an emissions reduction of lesser 

quantity will be sufficient to mitigate 

the proposed source’s adverse air 

quality impact on a modeled violation. 

Page (2010c); 44 FR 3274, January 16, 

1979, at 3278 (‘‘Although full emission 

offsets are not required, such a source 

must obtain emission offsets sufficient 

to compensate for its air quality impact 

where the violation occurs.’’). This may 

be particularly true where anticipated 

reductions from existing air quality 

regulations may mitigate the impacts of 

a proposed source’s emissions by the 

time the source begins operating in an 

area that is expected to be designated 

nonattainment. This would need to be 

evaluated on a case-by-case basis. To the 

extent that any permit applicants may 

experience difficulties making the 

NAAQS compliance showing required 

to obtain a PSD permit in areas and as 

set forth in the Memorandum noted 

above, the EPA is committed to working 

with permitting authorities and 

applicants to identify ways to apply 

offsets under the PSD program as 

necessary to meet PSD requirements. 

2. Nonattainment New Source Review 

Part D of Title I of the CAA pertains 

to the preconstruction review and 

permitting requirements for new major 

stationary sources and major 

modifications locating in areas 

designated ‘‘nonattainment’’ for a 

particular pollutant. Those requirements 

are commonly referred to as the NNSR 

program. The EPA regulations for the 

NNSR program are contained at 40 CFR 

51.165, 52.24 and part 51, appendix S. 

For NNSR, ‘‘major stationary source’’ 

is generally defined as a source with the 

potential to emit at least 100 tpy or more 

of a pollutant for which an area has 

been designated ‘‘nonattainment.’’ The 

NNSR program applies only to 

pollutants for which the EPA has 

promulgated NAAQS. Because the EPA 

has defined the PM NAAQS, and has 

established area designations for PM, in 

terms of two separate indicators—PM10

and PM2.5—each indicator is regulated 

separately for purposes of NNSR 

applicability. That is, for PM10, a ‘‘major 

stationary source’’ for NNSR 

applicability generally is a source that is 

located in a PM10 nonattainment area 

and has the potential to emit at least 100 

tpy of PM10 emissions.257 For PM2.5, a 

‘‘major stationary source’’ for NNSR 

applicability is a source that is located 

in a PM2.5 nonattainment area and has 

the potential to emit at least 100 tpy of 

direct PM2.5 (‘‘PM2.5 emissions’’) or any 

individual precursor of PM2.5. 

For a major modification, the NNSR 

regulations rely upon SERs described 

previously in the PSD discussion in 

section IX.D.1. For NNSR, a major 

modification is a physical change or a 

change in the method of operation of an 

existing stationary source that is major 

for the nonattainment pollutant and 

results in a significant emissions 

increase and a significant net emissions 

increase of that nonattainment pollutant 

or any individual precursor of that 

pollutant. As described earlier, the EPA 

will be evaluating the existing SERs for 

PM2.5 and PM2.5 precursors, and will 

determine whether there is any basis for 

proposing changes to any of the existing 

values. Any decision to propose 

changing the existing SERs in a future 

rulemaking would also apply to their 

use in the NNSR program requirements. 

The EPA has designated 

nonattainment areas for the existing 

primary annual and 24-hour PM2.5

NAAQS independently, and the EPA 

also approves redesignations to 

attainment separately for the two 

averaging periods. Thus, an area may be 

nonattainment for the annual standard 

and unclassifiable/attainment or 

attainment for the 24-hour standard. In 

the proposal, the EPA indicated that no 

formal policy has yet been developed to 

address this situation, but that the EPA 

presently believes that it is reasonable to 

require that only NNSR (and not PSD) 

applies for PM2.5 in any area that is 

nonattainment for either averaging 

period.258 The same situation would 

have existed with respect to the 

proposed secondary visibility index 

standard, had the EPA elected to 

finalize such a standard. Accordingly, 

the EPA indicated in the proposal that 

it intends to address this issue in a 

future NSR rulemaking, but invited 

preliminary comment on whether it is 

appropriate to apply the NNSR program 

requirements for any pollutant that is 

designated nonattainment for at least 

one averaging period or at least one 

primary or secondary NAAQS for a 

particular pollutant. 

New major stationary sources or major 

modifications that trigger NNSR based 

on PM2.5 emissions (or emissions of a 

PM2.5 precursor) in a PM2.5

nonattainment area must install 

technology that meets the lowest 

achievable emission rate (LAER); secure 

appropriate emissions reductions to 

offset the proposed emissions increases; 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3263 

and perform other analyses as required 

under section 173 of the CAA. 

Following the promulgation of any 

revised NAAQS for PM2.5, some new 

nonattainment areas for PM2.5 may 

result. Where a state does not have any 

NNSR program or the current NNSR 

program does not apply to PM2.5, that 

state will be required to submit the 

necessary SIP revisions to ensure that 

new major stationary sources and major 

modifications for PM2.5 undergo 

preconstruction review pursuant to the 

NNSR program. Under section 172(b) of 

the CAA, the Administrator may 

provide states up to 3 years from the 

effective date of nonattainment area 

designations to submit the necessary SIP 

revisions meeting the applicable NNSR 

requirements. Nevertheless, permits 

issued to sources in nonattainment areas 

must satisfy the applicable requirements 

for nonattainment areas as of the 

effective date of the specific 

nonattainment designation; therefore, 

states whose existing NNSR program 

requirements, if any, cannot be 

interpreted to apply to the revised 

primary annual PM2.5 NAAQS at that 

time will be allowed to issue the 

necessary permits in accordance with 

the applicable nonattainment permitting 

requirements contained in the 

Emissions Offset Interpretative Ruling at 

40 CFR part 51, appendix S, which 

would apply to the revised PM2.5

NAAQS upon its effective date (see 73 

FR 38321, May 16, 2008 at 28340). The 

EPA did not propose any type of PM2.5

grandfathering provision at this time for 

purposes of NNSR. 

Several industry commenters 

recommended that the EPA establish a 

grandfathering provision for NNSR as 

was proposed under the PSD program. 

A subset of these commenters 

recommended that grandfathering be 

accomplished by establishing an 

effective date for designations one year 

after initial publication in the Federal 

Register. However, no commenters 

provided any rationale or supporting 

basis for such a grandfathering 

provision or the underlying need for a 

transition into NNSR permitting for the 

revised PM2.5 NAAQS. 

The EPA disagrees with commenters 

that recommended a grandfathering 

provision for NNSR requirements 

associated with the revised PM2.5

NAAQS. As described in the proposal, 

the timetable for adopting new 

provisions under a state’s NNSR 

program will not apply with regard to 

the revised NAAQS for PM2.5 until such 

time that an area is designated 

nonattainment for a particular standard. 

Major NSR permits for PM2.5 issued in 

areas newly designated as 

nonattainment for the revised primary 

annual PM2.5 NAAQS must, as of the 

effective date of such designation, meet 

the applicable NNSR requirements for 

PM2.5 (Seitz, 1991). As such, there may 

be cases where applicants with PSD 

permit applications for PM2.5 in progress 

will be required to revise their 

applications to address NNSR 

requirements for a newly designated 

PM2.5 nonattainment area, and such 

revisions could result in additional 

resource burden and permit delays. 

However, the EPA believes at this time 

that such cases will be very limited, and 

in addition there is a substantial lead 

time between the effective date of the 

revised PM2.5 NAAQS and the effective 

date of any associated new 

nonattainment designations for permit 

applicants and air agencies to anticipate 

when the NNSR requirements will 

apply. Therefore, the EPA is not 

inclined at this time to pursue a 

rulemaking to establish a grandfathering 

provision for the revised PM2.5 NAAQS 

under the NNSR program. The EPA will 

independently, and in consultation with 

other reviewing authorities, work with 

permit applicants on specific projects 

requiring additional measures to 

achieve a workable transition into 

NNSR permitting requirements. The 

EPA will also continue to consider 

whether regulatory grandfathering may 

become necessary for NNSR, and if 

determined to be, will undertake any 

such action as part of a subsequent NSR 

implementation rulemaking with 

additional opportunity for public 

comment. 

A few industry and state commenters 

addressed the issue of potential dual 

review (applying NNSR and PSD 

simultaneously) based on distinct 

designations for separate averaging 

times of the PM2.5 NAAQS. These 

commenters generally agreed with the 

EPA’s conclusion that it was reasonable 

to apply only the NNSR permitting 

requirements to such situations and not 

PSD. Regarding the issue of potential 

dual review for multiple averaging times 

of the PM2.5 NAAQS, since the proposal, 

the EPA has determined that existing 

regulations resolve this issue in favor of 

the conclusion suggested in the 

proposed rule. Based on the express 

terms of existing regulations, only the 

NNSR permit requirements, and not 

PSD, apply for the pollutant PM2.5 in 

cases where the area is designated 

nonattainment for at least one averaging 

time of the PM2.5 NAAQS. The federal 

PSD regulations provide that the PSD 

requirements (the requirements of 

paragraphs (j) through (r) of each 

section) ‘‘do not apply to a major 

stationary source or major modification 

with respect to a particular pollutant if 

the owner or operator demonstrates that, 

as to that pollutant, the source or 

modification is located in an area 

designated as nonattainment under 

section 107 of the Act.’’ 40 CFR 

52.21(i)(2) and 40 CFR 51.166(i)(2) 

(emphasis added). Thus, this provision 

expressly excludes from PSD any 

pollutant for which an area is 

designated nonattainment, without 

reference to a particular averaging 

period. For a number of years, it was the 

EPA’s practice to establish a single 

designation in an area for a particular 

pollutant. Accordingly, if the area was 

not meeting the NAAQS for a particular 

averaging period, the area was 

designated nonattainment—even though 

the area was likely meeting the NAAQS 

for one or more averaging periods for 

the same pollutant. The EPA’s statement 

in the proposal that we had not yet 

established a policy on the dual review 

question for PM2.5 was based on the fact 

that we had only recently begun 

establishing designations for each 

averaging time in the case of the PM2.5

NAAQS. However, at the time of the 

proposal, the EPA had not closely 

examined the applicability of the 

language in sections 51.166(i)(2) and 

52.21(i)(2) in this context. After closer 

inspection prompted by the comments 

on this issue, we do not read these 

provisions to authorize application of 

PSD to a pollutant when an area may be 

designated nonattainment for a 

particular averaging time, while also 

designated attainment or unclassifiable 

for a different averaging time for the 

same pollutant. 

As proposed, the EPA is not finalizing 

any changes under the NNSR program 

regulations as part of this final NAAQS 

rule. The EPA will consider the need for 

any changes to the NNSR program 

provisions and will implement any such 

changes as part of a future NSR 

implementation rule and/or guidance. 

E. Transportation Conformity Program 

Transportation conformity is required 

under CAA section 176(c) to ensure that 

transportation plans, transportation 

improvement programs (TIPs) and 

federally supported highway and transit 

projects will not cause new air quality 

violations, worsen existing violations, or 

delay timely attainment of the relevant 

NAAQS or interim reductions and 

milestones. Transportation conformity 

applies to areas that are designated 

nonattainment and maintenance for 

transportation-related criteria 

pollutants: Carbon monoxide, ozone, 

NO2, and PM2.5, and PM10. 

Transportation conformity for any 


tkelley on DSK3SPTVN1PROD with 
3264 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

revised NAAQS for PM2.5 does not 

apply until 1 year after the effective date 

of the nonattainment designation for 

that revised NAAQS (see CAA section 

176(c)(6) and 40 CFR 93.102(d)). The 

EPA’s Transportation Conformity Rule 

(40 CFR part 51, subpart T, and 40 CFR 

part 93, subpart A) establishes the 

criteria and procedures for determining 

whether transportation activities 

conform to the SIP. The EPA is not 

making any changes to the 

transportation conformity rule in this 

rulemaking. The EPA notes that the 

transportation conformity rule already 

addresses the PM2.5 and PM10 NAAQS. 

The EPA will review whether there is a 

need to issue new or revised 

transportation conformity guidance in 

light of this final rule. In developing 

new or revised guidance the EPA will 

consider the comments related to 

implementation of the transportation 

conformity rule that were received in 

response to the proposal. 

As discussed in section VIII above, 

the EPA finalized certain clarifying 

changes to PM2.5 air quality monitoring 

regulations. These changes are designed 

to align different elements of the 

monitoring regulations for consistency. 

Due to these changes to the 

monitoring regulations, the EPA will 

update its guidance on conformity 

quantitative PM2.5 hot-spot analyses as 

appropriate to make it consistent with 

the revised monitoring requirements 

(U.S. EPA, 2010j). The EPA intends that 

the current quantitative PM2.5 hot-spot 

guidance continues to apply to any 

quantitative PM2.5 hot-spot analysis that 

was begun before the effective date of 

these revisions to the monitoring 

regulations. Revised guidance for 

quantitative PM2.5 hot-spot analyses 

would apply to any quantitative PM2.5

hot-spot analysis begun after the 

effective date of the revised monitoring 

regulations. Nonattainment and 

maintenance areas are encouraged to 

use their interagency consultation 

processes to determine whether an 

analysis for a given project was started 

before the effective date of changes to 

the monitoring requirements. Applying 

the current guidance to PM2.5 analyses 

that had begun before the effective date 

of changes to the monitoring regulations 

is consistent with how the conformity 

rule and guidance address the 

transitional period for new emissions 

factor models or local planning 

assumptions (40 CFR 93.110(a) and 

93.111(b) and (c)). In both of those 

cases, analyses begun before the new 

model or data became available can be 

completed using the data and/or model 

that were available when the analyses 

began. The EPA rules allow this in order 

to conserve state resources by not 

making transportation planning 

agencies redo analyses simply because a 

model has been revised, new data have 

become available, or in this case, the 

EPA has revised its regulations for PM2.5

monitoring. 

F. General Conformity Program 

General conformity is required by 

CAA section 176(c). This section 

requires that actions by federal agencies 

do not cause new air quality violations, 

worsen existing violations, or delay 

timely attainment of the relevant 

NAAQS or interim reductions and 

milestones. General conformity applies 

to any federal action (e.g., funding, 

licensing, permitting, or approving), 

other than projects that are Federal 

Highway Administration (FHWA)/ 

Federal Transit Administration (FTA) 

projects as defined in 40 CFR 93.101 

(which are covered under transportation 

conformity described above), if the 

action takes place in a nonattainment or 

maintenance area for ozone, PM, NO2, 

carbon monoxide, lead, or SO2. General 

conformity also applies to a federal 

highway and transit project if it does not 

involve either Title 23 or 49 funding, 

but does involve FHWA or FTA 

approval such as is required for a 

connection to an Interstate highway or 

for a deviation from applicable design 

standards per 40 CFR 93.101. (The 

FHWA and FTA actions described here 

as not subject to general conformity are 

subject to transportation conformity.) 

General conformity for the revised PM 

NAAQS will not apply until 1 year after 

the effective date of a nonattainment 

designation for that NAAQS. The EPA’s 

General Conformity Rule (40 CFR 

93.150 to 93.165) establishes the criteria 

and procedures for determining if a 

federal action conforms to the SIP. With 

respect to the revised PM NAAQS, 

federal agencies are expected to 

continue to estimate emissions for 

conformity analyses in the same manner 

as they are estimated for conformity 

analyses for the 1997 and 2006 p.m. 

NAAQS. The EPA’s existing general 

conformity regulations include the basic 

requirement that a federal agency’s 

general conformity analysis be based on 

the latest and most accurate emissions 

estimation techniques available (40 CFR 

93.159(b)), and the EPA expects that this 

same principle will be followed for 

analyses needed for these revised PM 

NAAQS. When updated and improved 

emissions estimation techniques 

become available, the EPA expects the 

federal agency to use those techniques. 

With this final rule, the EPA is making 

no changes to the general conformity 

rule as it already addresses the PM2.5

and PM10 NAAQS. As noted in the 

proposal, the EPA will review the need 

to issue guidance describing how the 

current conformity rule applies in 

nonattainment and maintenance areas 

for the final revised primary annual 

PM2.5 NAAQS. 

X. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

Under section 3(f)(1) of Executive 

Order 12866 (58 FR 51735, October 4, 

1993), this action is an ‘‘economically 

significant regulatory action’’ because it 

is likely to have an annual effect on the 

economy of $100 million or more. The 

$100 million threshold can be triggered 

by either costs or benefits, or a 

combination of them. Accordingly, the 

EPA submitted this action to the Office 

of Management and Budget (OMB) for 

review under Executive Orders 12866 

and 13563 (76 FR 3821, January 21, 

2011), and any changes made in 

response to OMB recommendations 

have been documented in the docket for 

this action. 

The EPA prepared an analysis of the 

potential costs and benefits associated 

with this action. This analysis is 

contained in Regulatory Impact 

Analysis for the Final Revisions to the 

National Ambient Air Quality 

Standards for Particulate Matter, EPA 

452/R–12–003. A copy of the analysis is 

available in Docket No. EPA–HQ–OAR– 

2010–0955. 

The estimates in the RIA are 

associated with the revised standard 

and alternative standard levels (in mg/ 

m3) of the primary annual PM2.5

standards including: 13, 12, and 11. 

Table 4 provides a summary of the 

estimated costs, monetized benefits, and 

net benefits associated with full 

attainment of these alternative 

standards. 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3265 

TABLE 4—TOTAL COSTS, MONETIZED BENEFITS AND NET BENEFITS IN 2020 (MILLIONS OF 2010$) 

FULL ATTAINMENT a

Alternative 

PM2.5

annual 

standards 

(μg/m3) 

Total costs b Monetized benefits d Net benefits 

3% Discount 

rate c

7% Discount 

rate 3% Discount rate 7% Discount rate 3% Discount rate d 7% Discount rate 

13 .................. $11 to $100 ...... $11 to $100 ...... $1,300 to $2,900 .... $1,200 to $2,600 .... $1,200 to $2,900 .... $1,100 to $2,600 

12 .................. $53 to $350 ...... $53 to $350 ...... $4,000 to $9,100 .... $3,600 to $8,200 .... $3,700 to $9,000 .... $3,300 to $8,100 

11 .................. $320 to $1,700 $320 to $1,700 $13,000 to $29,000 $12,000 to $26,000 $11,000 to $29,000 $10,000 to $26,000 

aThese estimates reflect incremental emissions reductions from an analytical baseline that gives an ‘‘adjustment ’’ to the San Joaquin and 

South Coast areas in California for NOX emissions reductions expected to occur between 2020 and 2025, when those areas are expected to 

demonstrate attainment with the revised standards. Full benefits of the revised standards in those two areas will not be realized until 2025. bThe two cost estimates do not represent lower and upper bound estimates, but represent estimates generated by two different methodologies. The lower estimate is generated using the fixed-cost methodology, which assumes that technological change and innovation will result in 

the availability of additional controls by 2020 that are similar in cost to the higher end of the cost range for current, known controls. The higher 

estimate is generated using the hybrid methodology, which assumes that while additional controls may become available by 2020, they become 

available at an increasing cost and the increasing cost varies by geographic area and by degree of difficulty associated with obtaining the needed emissions reductions. c Due to data limitations, we were unable to discount compliance costs for all sectors at 3%. See section 7.2.2 of the RIA for additional details 

on the data limitations. As a result, the net benefit calculations at 3% were computed by subtracting the costs at 7% from the monetized benefits 

at 3%. dThe reduction in premature deaths each year accounts for over 90% of total monetized benefits. Mortality risk valuation assumes discounting 

over the SAB-recommended 20-year segmented lag structure. Not all possible benefits or disbenefits are quantified and monetized in this analysis. B is the sum of all unquantified benefits. Data limitations prevented us from quantifying these endpoints, and as such, these benefits are inherently more uncertain than those benefits that we were able to quantify. The range of benefits reflects the range of the central estimates from 

two mortality cohort studies (i.e., Krewski et al. (2009) to Lepeule et al. (2012)). 

B. Paperwork Reduction Act 

The information collection 

requirements in this final rule have been 

submitted for approval to the OMB 

under the Paperwork Reduction Act, 44 

U.S.C. 3501 et seq. The information 

collection requirements are not 

enforceable until OMB approves them. 

The Information Collection Request 

(ICR) document prepared by the EPA for 

these revisions to part 58 has been 

assigned EPA ICR number 0940.26. The 

information collected under 40 CFR part 

53 (e.g., test results, monitoring records, 

instruction manual, and other 

associated information) is needed to 

determine whether a candidate method 

intended for use in determining 

attainment of the NAAQS in 40 CFR 

part 50 will meet the design, 

performance, and/or comparability 

requirements for designation as an FRM 

or FEM. The EPA does not expect the 

number of FRM or FEM determinations 

to increase over the number that is 

currently used to estimate burden 

associated with PM10, PM2.5, or PM10-2.5

FRM/FEM determinations provided in 

the current ICR for 40 CFR part 53 (EPA 

ICR numbers 0940.24). As such, no 

change in the burden estimate for 40 

CFR part 53 has been made as part of 

this rulemaking. 

The information collected and 

reported under 40 CFR part 58 is needed 

to determine compliance with the 

NAAQS, to characterize air quality and 

associated health impacts, to develop 

emissions control strategies, and to 

measure progress for the air pollution 

program. The amendments finalized in 

this rule will revise the network design 

requirements for PM2.5 monitoring sites, 

resulting in the movement of 21 

monitors to established near-road 

monitoring stations by January 1, 2015. 

The incremental burden associated with 

moving these 21 monitors that are 

required in 40 CFR part 58 (this is a onetime cost of relocating the monitors) is 

$28,570. Burden is defined at 5 CFR 

1320.3(b). State, local, and Tribal 

entities are eligible for state assistance 

grants provided by the federal 

government under the CAA which can 

be used for monitors and related 

activities. An agency may not conduct 

or sponsor, and a person is not required 

to respond to, a collection of 

information unless it displays a 

currently valid OMB control number. 

The OMB control numbers for the EPA’s 

regulations in 40 CFR are listed in 40 

CFR part 9. 

To comment on the Agency’s need for 

this information, the accuracy of the 

provided burden estimates, and any 

suggested methods for minimizing 

respondent burden, the EPA has 

established a public docket for this rule, 

which includes this ICR, under Docket 

ID number EPA–HQ–OAR–2007–0492. 

Submit any comments related to the ICR 

to the EPA and OMB. Send comments 

to the EPA at the Air and Radiation 

Docket and Information Center Docket 

in the EPA Docket Center (EPA/DC), 

EPA West, Room 3334, 1301 

Constitution Ave. NW., Washington, 

DC. The EPA Docket Center Public 

Reading Room is open from 8:30 a.m. to 

4:30 p.m., Monday through Friday, 

excluding legal holidays. The telephone 

number for the Reading Room is (202) 

566–1744, and the telephone number for 

the Air and Radiation Docket and 

Information Center Docket is (202) 566– 

1742. An electronic version of the 

public docket is available at 

www.regulations.gov. Send comments to 

OMB at the Office of Information and 

Regulatory Affairs, Office of 

Management and Budget, 725 17th 

Street NW., Washington, DC 20503, 

Attention: Desk Office for EPA. Since 

OMB is required to make a decision 

concerning the ICR between 30 and 60 

days after January 15, 2013, a comment 

to OMB is best assured of having its full 

effect if OMB receives it by February 14, 

2013. 

C. Regulatory Flexibility Act 

The Regulatory Flexibility Act (RFA) 

generally requires an agency to prepare 

a regulatory flexibility analysis of any 

rule subject to notice and comment 

rulemaking requirements under the 

Administrative Procedure Act or any 

other statute unless the agency certifies 

that the rule will not have a significant 

economic impact on a substantial 

number of small entities. Small entities 

include small businesses, small 

organizations, and small governmental 

jurisdictions. 

For purposes of assessing the impacts 

of this rule on small entities, small 

entity is defined as: (1) A small business 

that is a small industrial entity as 

defined by the Small Business 

Administration’s (SBA) regulations at 13 

CFR 121.201; (2) a small governmental 


tkelley on DSK3SPTVN1PROD with 
3266 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

jurisdiction that is a government of a 

city, county, town, school district or 

special district with a population of less 

than 50,000; and (3) a small 

organization that is any not-for-profit 

enterprise which is independently 

owned and operated and is not 

dominant in its field. 

After considering the economic 

impacts of this final rule on small 

entities, I certify that this action will not 

have a significant economic impact on 

a substantial number of small entities. 

This final rule will not impose any 

requirements on small entities. Rather, 

this rule establishes national standards 

for allowable concentrations of 

particulate matter in ambient air as 

required by section 109 of the CAA. See 

also American Trucking Associations v. 

EPA. 175 F.3d at 1044–45 (NAAQS do 

not have significant impacts upon small 

entities because NAAQS themselves 

impose no regulations upon small 

entities). We continue to be interested in 

the potential impacts of the proposed 

rule on small entities and welcome 

comments on issues related to such 

impacts. 

D. Unfunded Mandates Reform Act 

This action contains no Federal 

mandates under the provisions of Title 

II of the Unfunded Mandates Reform 

Act of 1995 (UMRA), 2 U.S.C. 1531– 

1538 for state, local, or tribal 

governments or the private sector. The 

action imposes no enforceable duty on 

any state, local or tribal governments or 

the private sector beyond those duties 

already established in the CAA. 

Therefore, this action is not subject to 

the requirements of sections 202 or 205 

of the UMRA. 

This action is also not subject to the 

requirements section 205 of the UMRA 

because it contains no regulatory 

requirements that might significantly or 

uniquely affect small governments. This 

action imposes no new expenditure or 

enforceable duty on any state, local, or 

tribal governments or the private sector, 

and the EPA has determined that this 

rule contains no regulatory 

requirements that might significantly or 

uniquely affect small governments. 

Furthermore, in setting a NAAQS, the 

EPA cannot consider the economic or 

technological feasibility of attaining 

ambient air quality standards although 

such factors may be considered to a 

degree in the development of state plans 

to implement the standards. See also 

American Trucking Associations v. 

EPA, 175 F. 3d at 1043 (noting that 

because the EPA is precluded from 

considering costs of implementation in 

establishing NAAQS, preparation of a 

Regulatory Impact Analysis pursuant to 

the Unfunded Mandates Reform Act 

would not furnish any information 

which the court could consider in 

reviewing the NAAQS). The EPA 

acknowledges, however, that any 

corresponding revisions to associated 

SIP requirements and air quality 

surveillance requirements, 40 CFR part 

51 and 40 CFR part 58, respectively, 

might result in such effects. 

Accordingly, the EPA will address, as 

appropriate, unfunded mandates if and 

when it proposes any revisions to 40 

CFR parts 51 or 58. 

E. Executive Order 13132: Federalism 

This action does not have federalism 

implications. It will not have substantial 

direct effects on the states, on the 

relationship between the national 

government and the states, or on the 

distribution of power and 

responsibilities among the various 

levels of government, as specified in 

Executive Order 13132. The rule does 

not alter the relationship between the 

Federal government and the states 

regarding the establishment and 

implementation of air quality 

improvement programs as codified in 

the CAA. Under section 109 of the CAA, 

the EPA is mandated to establish and 

review NAAQS; however, CAA section 

116 preserves the rights of states to 

establish more stringent requirements if 

deemed necessary by a state. 

Furthermore, this final rule does not 

impact CAA section 107 which 

establishes that the states have primary 

responsibility for implementation of the 

NAAQS. Finally, as noted in section D 

(above) on UMRA, this rule does not 

impose significant costs on state, local, 

or Tribal governments or the private 

sector. Thus, Executive Order 13132 

does not apply to this action. 

However, as also noted in section D 

(above) on UMRA, the EPA recognizes 

that states will have a substantial 

interest in this rule and any 

corresponding revisions to associated 

air quality surveillance requirements, 40 

CFR part 58. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

Executive Order 13175, entitled 

‘‘Consultation and Coordination with 

Indian Tribal Governments’’ (65 FR 

67249, November 9, 2000), requires the 

EPA to develop an accountable process 

to ensure ‘‘meaningful and timely input 

by tribal officials in the development of 

regulatory policies that have tribal 

implications.’’ This rule concerns the 

establishment of national standards to 

address the health and welfare effects of 

particulate matter. Historically, the 

EPA’s definition of ‘‘tribal implications’’ 

has been limited to situations in which 

it can be shown that a rule has impacts 

on the tribes’ ability to govern or 

implications for tribal sovereignty. 

Based on this historic definition, this 

action does not have Tribal 

implications, as specified in Executive 

Order 13175 (65 FR 67249, November 9, 

2000), i.e. because it does not have a 

substantial direct effect on one or more 

Indian tribes, since tribes are not 

obligated to adopt or implement any 

NAAQS. Nevertheless, we were aware 

that many tribes would be interested in 

this rule and we undertook a number of 

outreach activities to inform tribes about 

the PM NAAQS review and offered to 

two consultations with tribes. 

Although Executive Order 13175 does 

not apply to this rule, the EPA 

undertook a consultation process 

including: Prior to proposal on March 

29, 2012 we sent letters to tribal 

leadership inviting consultation on the 

rule and then sent a second round of 

letters offering consultation after the 

proposal was issued on June 29, 2012. 

No tribe requested a formal consultation 

with the EPA. We conducted outreach 

and information calls to tribal 

environmental staff on May 9, 2012; 

June 15, 2012; and August 1, 2012. We 

also participated on the National Tribal 

Air Association call on June 28, 2012. 

As a result we received comments 

from the National Tribal Air 

Association, the Southern Ute Mountain 

Ute Tribe, and the Navajo Nation EPA. 

In general, these tribal organizations 

were supportive of the EPA’s proposal. 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

and Safety Risks 

This action is subject to Executive 

Order 13045 (62 FR 19885, April 23, 

1997) because it is an economically 

significant regulatory action as defined 

by Executive Order 12866, and the EPA 

believes that the environmental health 

or safety risk addressed by this action 

may have a disproportionate effect on 

children. Accordingly, we have 

evaluated the environmental health or 

safety effects of PM exposures on 

children. The protection offered by 

these standards is especially important 

for children because childhood 

represents a lifestage associated with 

increased susceptibility to PM-related 

health effects. Because children have 

been identified as an at-risk population, 

we have carefully evaluated the 

environmental health effects of 

exposure to PM pollution among 

children. Discussions of the results of 

the evaluation of the scientific evidence 

and policy considerations pertaining to 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3267 

259A list of designated reference and equivalent 

methods is available on EPA’s Web site at: http:// 

www.epa.gov/ttn/amtic/criteria.html. 

children are contained in sections III.B, 

III.D, III.E, IV.B, and IV.C of this 

preamble. The revised primary PM2.5

NAAQS discussed above will provide 

greater public health protection, 

including increased protection for atrisk populations such as children. 

H. Executive Order 13211: Actions That 

Significantly Affect Energy Supply, 

Distribution or Use 

This action is not a ‘‘significant 

energy action’’ as defined in Executive 

Order 13211 (66 FR 28355, May 22, 

2001), because it is not likely to have a 

significant adverse effect on the supply, 

distribution, or use of energy. The 

purpose of this action concerns the 

review of the NAAQS for PM. The 

action does not prescribe specific 

pollution control strategies by which 

these ambient standards will be met. 

Such strategies are developed by states 

on a case-by-case basis, and the EPA 

cannot predict whether the control 

options selected by states will include 

regulations on energy suppliers, 

distributors, or users. 

I. National Technology Transfer and 

Advancement Act 

Section 12(d) of the National 

Technology Transfer and Advancement 

Act of 1995 (NTTAA), Public Law 104– 

113, section 12(d) (15 U.S.C. 272 note) 

directs the EPA to use voluntary 

consensus standards in its regulatory 

activities unless to do so would be 

inconsistent with applicable law or 

otherwise impractical. Voluntary 

consensus standards are technical 

standards (e.g., materials specifications, 

test methods, sampling procedures, and 

business practices) that are developed or 

adopted by voluntary consensus 

standards bodies. The NTTAA directs 

the EPA to provide Congress, through 

OMB, explanations when the Agency 

decides not to use available and 

applicable voluntary consensus 

standards. 

This final rulemaking involves 

technical standards for environmental 

monitoring and measurement. 

Specifically, the EPA proposes to retain 

the indicators for fine (PM2.5) and coarse 

(PM10) particles. The indicator for fine 

particles is measured using the 

Reference Method for the Determination 

of Fine Particulate Matter as PM2.5 in the 

Atmosphere (appendix L to 40 CFR part 

50), which is known as the PM2.5 FRM, 

and the indicator for coarse particles is 

measured using the Reference Method 

for the Determination of Particulate 

Matter as PM10 in the Atmosphere 

(appendix J to 40 CFR part 50), which 

is known as the PM10 FRM. 

To the extent feasible, the EPA 

employs a Performance-Based 

Measurement System (PBMS), which 

does not require the use of specific, 

prescribed analytic methods. The PBMS 

is defined as a set of processes wherein 

the data quality needs, mandates or 

limitations of a program or project are 

specified, and serve as criteria for 

selecting appropriate methods to meet 

those needs in a cost-effective manner. 

It is intended to be more flexible and 

cost effective for the regulated 

community; it is also intended to 

encourage innovation in analytical 

technology and improved data quality. 

Though the FRM defines the particular 

specifications for ambient monitors, 

there is some variability with regard to 

how monitors measure PM, depending 

on the type and size of PM and 

environmental conditions. Therefore, it 

is not practically possible to fully define 

the FRM in performance terms to 

account for this variability. 

Nevertheless, our approach in the past 

has resulted in multiple brands of 

monitors being approved as FRM for 

PM, and we expect this to continue. 

Also, the FRMs described in 40 CFR 

part 50 and the equivalency criteria 

described in 40 CFR part 53, constitute 

a performance-based measurement 

system for PM, since methods that meet 

the field testing and performance 

criteria can be approved as FEMs. Since 

finalized in 2006 (71 FR, 61236, October 

17, 2006) the new field and performance 

criteria for approval of PM2.5 continuous 

FEMs has resulted in the approval of six 

approved FEMs.259 In summary, for 

measurement of PM2.5 and PM10, the 

EPA relies on both FRMs and FEMs, 

with FEMs relying on a PBMS approach 

for their approval. The EPA is not 

precluding the use of any other method, 

whether it constitutes a voluntary 

consensus standard or not, as long as it 

meets the specified performance 

criteria. 

J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations 

Executive Order 12898 (59 FR 7629, 

February 16, 1994) establishes federal 

executive policy on environmental 

justice. Its main provision directs 

federal agencies, to the greatest extent 

practicable and permitted by law, to 

make environmental justice part of their 

mission by identifying and addressing, 

as appropriate, disproportionately high 

and adverse human health or 

environmental effects of their programs, 

policies, and activities on minority 

populations and low-income 

populations in the United States. 

The EPA maintains an ongoing 

commitment to ensure environmental 

justice for all people, regardless of race, 

color, national origin, or income. 

Ensuring environmental justice means 

not only protecting human health and 

the environment for everyone, but also 

ensuring that all people are treated 

fairly and are given the opportunity to 

participate meaningfully in the 

development, implementation, and 

enforcement of environmental laws, 

regulations, and policies. We conducted 

an outreach and information call with 

environmental justice organizations on 

August 9, 2012. 

The EPA has identified potential 

disproportionately high and adverse 

effects on minority and/or low-income 

populations related to PM2.5 exposures. 

In addition, the EPA has identified 

persons from lower socioeconomic 

strata as an at-risk population for PMrelated health effects. As a result, the 

EPA has carefully evaluated the 

potential impacts on low-income and 

minority populations as discussed in 

section III.E.3.a of this preamble. Based 

on this evaluation and consideration of 

public comments on the proposal, the 

EPA is eliminating the spatial averaging 

provisions as part of the form of the 

primary annual PM2.5 standard to avoid 

potential disproportionate impacts on 

at-risk populations. The Agency expects 

this final rule will lead to the 

establishment of uniform NAAQS for 

PM. The Integrated Science Assessment 

and Policy Assessment contain the 

evaluation of the scientific evidence and 

policy considerations that pertain to 

these populations. These documents are 

available as described in the 

Supplementary Information section of 

this preamble and copies of all 

documents have been placed in the 

public docket for this action. 

K. Congressional Review Act 

The Congressional Review Act, 5 

U.S.C. 801 et seq., as added by the Small 

Business Regulatory Enforcement 

Fairness Act of 1996, generally provides 

that before a rule may take effect, the 

agency promulgating the rule must 

submit a rule report, which includes a 

copy of the rule, to each House of the 

Congress and to the Comptroller General 

of the United States. The EPA will 

submit a report containing this rule and 

other required information to the U.S. 

Senate, the U.S. House of 

Representatives, and the Comptroller 

General of the United States prior to 

publication of the rule in the Federal 


tkelley on DSK3SPTVN1PROD with 
3268 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

Register. A major rule cannot take effect 

until 60 days after it is published in the 

Federal Register. This action is a ‘‘major 

rule’’ as defined by 5 U.S.C. 804(2). This 

rule will be effective March 18, 2013. 

References 

AAM (2012). Comments of the Alliance of 

Automobile Manufacturers on National 

Ambient Air Quality Standards for 

Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9475. August 31, 2012. 

AASHTO (2012). Comments of the American 

Association of State Highway and 

Transportation Officials on National 

Ambient Air Quality Standards for 

Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9506. August 31, 2012. 

Abt Associates Inc. (2001). Assessing Public 

Opinions on Visibility Impairment Due 

to Air Pollution: Summary Report. 

Available: http://www.epa.gov/ttn/ 

oarpg/t1/reports/vis_rpt_final.pdf. 

Abt Associates (2005). Particulate Matter 

Health Risk Assessment for Selected 

Urban Areas. Final Report. Bethesda, 

MD. Prepared for the Office of Air 

Quality Planning and Standards, U.S. 

Environmental Protection Agency, 

Contract No. 68–D–03–002. EPA 452/R– 

05–007A. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/ 

data/PMrisk20051220.pdf. 

ACC (2012). Comments of the American 

Chemistry Council on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Docket No. EPA– 

HQ–OAR–2007–0492–9295/August 29, 

2012. 

AFPM (2012). Comments of the American 

Fuel & Petrochemical Manufacturers on 

National Ambient Air Quality Standards 

for Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9573. August 31, 2012. 

AHA et al. (2012). American Heart 

Association; American Lung Association; 

American Public Health Association; 

American Thoracic Society; Asthma and 

Allergy Foundation of America; Health 

Care Without Harm; March of Dimes; 

National Association of County and City 

Health Officials; Trust for America’s 

Health (2012). Letter to EPA 

Administrator Lisa P. Jackson re: 

Comments on the Proposed National 

Ambient Air Quality Standards for 

Particulate Matter. August 31, 2012. 

Docket ID number EPA–HQ–OAR–2007– 

0492–9512. 

Air Alliance Houston et al., (2012). Air 

Alliance Houston, Alliance for 

Affordable Energy, Alliance for Health 

Promotion, American Bottom 

Conservancy; Center for Biological 

Diversity; Chelsea Board of Health; 

Clelsea Collaborative; Citizens for 

Pennsylvania’s Future; Clean Air 

Carolina; Clean Air Task Force; Clean 

Air Watch; Clean Water Action; Clean 

Water Action Michigan; Clean Water 

Action Rhode Island; Communities for a 

Better Environment; Conservation Law 

Foundation; Environment & Human 

Health, Inc.; Environment Illinois; 

Environment Northeast; Environmental 

and Energy Study Institute; 

Environmental Defense Fund; Fresh 

Energy; Green For All; Greenpeace USA; 

Hoosier Environmental Council; 

Improving Kids’ Environment; Kentucky 

Resources Council; Massachusetts 

Climate Action Network; Midwest 

Environmental Advocates; Mining 

Impact Coalition of Wisconsin; Moms 

Clean Air Force; Mothers & Others for 

Clean Air; NAACP; National Resources 

Defense Council; National Wildlife 

Federation; New York Public Interest 

Research Group; Powder River Basin 

Resource Council; Respiratory Health 

Association; Safe Air for Everyone; Save 

Our Sky Blue Waters; Save the Dunes; 

Sierra Club; Southern Alliance for Clean 

Energy; Uranium Watch; US Climate 

Action Network; Valley Watch; Wasatch 

Clean Air Coalition; Western 

Environmental Law Center. Letter to EPA 

Administrator Lisa P. Jackson. 

Comments on the Proposed National 

Ambient Air Quality Standards for 

Particulate Matter. August 31, 2012. 

Docket ID number EPA–HQ–OAR–2007– 

0492–9402. 

ALA et al. (2012). Comments of the American 

Lung Association, Clean Air Council, 

Clean Air Task Force, Earthjustice, 

Environmental Defense Fund, Natural 

Resources Defense Council, Sierra Club 

on EPA’s Proposed Revisions to the 

Primary National Ambient Air Quality 

Standards for Particulate Matter. Docket 

No. EPA–HQ–OAR–2007–0492–9826. 

August 31, 2012. 

AMC, et al. (2012). Comments of the 

Appalachian Mountain Club, the 

National Parks Conservation Association, 

and Earthjustice on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Docket No. EPA– 

HQ–OAR–2007–0492–9562. August 31, 

2012. 

API (2009). Comments of the American 

Petroleum Institute on the Integrated 

Science Assessment for Particulate 

Matter—Second External Review Draft. 

Docket No. EPA–HQ–ORD–2007–0517– 

0079. October 13, 2009. 

API (2012). Comments of the American 

Petroleum Institute on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Docket No. EPA– 

HQ–OAR–2007–0492–9530. August 31, 

2012. 

Armstrong BG. Effect of measurement error 

on epidemiological studies of 

environmental and occupational 

exposures. Occup Environ Med 1998, 55: 

651–6. 

Arizona DEQ (2012). Comments of the 

Arizona Department of Environmental 

Quality on National Ambient Air Quality 

Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9492. August 31, 2012. 

Avol E; Gauderman WG; Tan SM; London SJ; 

Peters JM (2001). Respiratory effects of 

relocating to areas of differing air 

pollution levels. Am. J. Respir. Crit. Care 

Med. 164: 2067–2072. 

BBC Research & Consulting (2003). Phoenix 

Area Visibility Survey. Draft Report. 

Available: http://www.azdeq.gov/ 

environ/air/download/vis_021903f.pdf. 

Accessed 9/16/2008. 

Bell ML, Ebisu K, Belanger K (2007). 

Ambient air pollution and low birth 

weight in Connecticut and 

Massachusetts. Environ Health Perspect, 

115: 1118–24. 

Bell ML; Ebisu K; Peng RD; Walker J; Samet 

JM; Zeger SL; Dominic F (2008). 

Seasonal and regional short-term effects 

of fine particles on hospital admissions 

in 202 U.S. counties, 1999–2005. Am J 

Epidemiol, 168: 1301–1310. 

Bell ML (2009a). Personal communication 

with Dr. Michelle Bell. Annual PM2.5

levels used in Dominici et al. 2006 and 

Bell et al. 2008. December 7, 2009. 

Docket No. EPA–HQ–ORD–2007–0517– 

0087. 

Bell ML, Ebisu K, Peng R, Samet J, Dominici 

F (2009b). Hospital Admissions and 

Chemical Composition of Fine Particle 

Air Pollution. Am J Respir Crit Care 

Med, 179: 1115–1120. 

Burnett RT; Brook J et al. (2000). Association 

between particulate- and gas-phase 

components of urban air pollution and 

daily mortality in eight Canadian cities. 

Inhal. Toxicol. 12 Suppl 4: 15–39. 

Burnett RT, Goldberg MS (2003). Sizefractionated particulate mass and daily 

mortality in eight Canadian cities. In: 

Revised analyses of time-series studies of 

air pollution and health. Special report. 

May 2003. Boston, MA: Health Effects 

Institute; pp. 85–90. Available: http:// 

www.healtheffects.org/news.htm. 

Burnett RT, Stieb D, Brook JR, Cakmak S, 

Dales R, Raizenne M, Vincent R, Dann T 

(2004). Associations between short-term 

changes in nitrogen dioxide and 

mortality in Canadian cities. Arch 

Environ Occup Health, 59: 228–236. 

CARB (2012). Comments of the California Air 

Resources Board on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Docket No. EPA– 

HQ–OAR–2007–0492–1694. July 18, 

2012. 

CA OEHHA (2012). Comments of the 

California Environmental Protection 

Agency, Office of Environmental Health 

Hazard Assessment on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Docket No. EPA– 

HQ–OAR–2007–0492–9882. August 28, 

2012. 

Carroll RJ, Ruppert D, Stefanski LA (1995). 

Measurement error in nonlinear models. 

London, UK: Chapman and Hall Ltd. 

CBD (2012). Comments of the Center for 

Biological Diversity on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Docket No. EPA– 

HQ–OAR–2007–0492–9894. August 31, 

2012. 

CDC (2004) Introduction and approach to 

causal inference. In: The health 

consequences of smoking: a report of the 

Surgeon General. Atlanta, GA: U.S. 

Department of Health and Human 

Services, Centers for Disease Control and 

Prevention, National Center for Chronic 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3269 

Disease Prevention and Health 

Promotion, Office on Smoking and 

Health. Available: http://www.cdc.gov/

tobacco/data_statistics/sgr/2004/pdfs/ 

tableofcontents.pdf. 

Chan CC; Chuang KJ; Chen WJ; Chang WT; 

Lee CT; Peng CM (2008). Increasing 

cardiopulmonary emergency visits by 

long-range transported Asian dust storms 

in Taiwan. Environ Res, 106: 393–400. 

Chock DP; Winkler SL; Chen C. (2000). A 

study of the association between daily 

mortality and ambient air pollutant 

concentrations in Pittsburgh, 

Pennsylvania. J Air Waste Manag Assoc, 

50: 1481–1500. 

CHPAC (2012). Comments of the Children’s 

Health Protection Advisory Committee 

on National Ambient Air Quality 

Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9944. September 10, 

2012. 

Class of ’85 RRG (2012). Comments of the 

Class of ’85 Regulatory Response Group 

on National Ambient Air Quality 

Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9435. August 31, 2012. 

Colorado DPHE (2012). Comments of the 

Colorado Department of Public Health 

and the Environment on National 

Ambient Air Quality Standards for 

Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9353. August 31, 2012. 

CPMC (2012). Comments of the Coarse 

Particulate Matter Coalition on National 

Ambient Air Quality Standards for 

Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9491. August 31, 2012. 

Deck L; Lawson M (2010). Statistical analysis 

of existing urban visibility preference 

studies. Memorandum to Vicki 

Sandiford, U.S. EPA/Office of Air 

Quality Planning and Standards from 

Leland Deck and Megan Lawson, Stratus 

Consulting Inc. February 3, 2010. Docket 

ID no. EPA–HQ–OAR–2007–0492-0089. 

DHEW (1969). Air Quality Criteria for 

Particulate Matter. U.S. Department of 

Health, Education, and Welfare. Public 

Health Service, Environmental Health 

Service, National Air Pollution Control 

Administration, Washington, DC January 

1969. 

Dockery DW, Pope CA III, Xu X, Spengler JD, 

Ware JH, Fay ME, Ferris BG Jr, Speizer 

FE (1993). An association between air 

pollution and mortality in six U.S. cities. 

N Engl J Med, 329: 1753–1759. 

Dockery DW, Cunningham J, Damokosh AI, 

Neas LM, Spengler JD, Koutrakis P, Ware 

JH, Raizenne M, Speizer FE (1996). 

Health effects of acid aerosols on North 

American children: respiratory 

symptoms. Environ Health Perspect, 

104(5):500–5. 

DOI (2012). Comments of the United States 

Department of the Interior on National 

Ambient Air Quality Standards for 

Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

7970. August 23, 2012. 

Dominici F, Peng RD, Bell ML, Pham L, 

McDermott A, Zeger SL, Samet JM 

(2006a). Fine particulate air pollution 

and hospital admission for 

cardiovascular and respiratory diseases. 

JAMA, 295: 1127–1134. 

Dominici F (2006b). Letter from Dr. 

Francesca Dominici, Associate Professor 

of Biostatistics, Bloomberg School of 

Public Health, Johns Hopkins University, 

comments to the proposed rule. Docket 

ID number OAR–2001–0017–0988. 

March 21, 2006. 

Dominici F, Peng RD, Zeger SL, White RH, 

Samet JM (2007). Particulate air 

pollution and mortality in the United 

States: did the risks change from 1987 to 

2000? Am J Epidemiol, 166: 880–8. 

Dominici F; Zeger SL; Janes H; Greven S 

(2012). Memo from Francesca Dominici, 

Harvard School of Public Health; Scott L. 

Zeger, The Johns Hopkins University; 

Sonja Greven, Ludwig-MaximiliansUniversitat Munchen; and Holly Janes, 

University of Washington to Bryan 

Hubbell and Jason Sacks, U.S. EPA. 

Additional information to EPA for Janes 

et al. (2007) and Greven et al. (2011). 

November 28, 2012. 

Dow (2012). Comments of the Dow Chemical 

Company on National Ambient Air 

Quality Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–8424. August 28, 2012. 

Eftim SE., Samet JM, Janes H, McDermott A, 

Dominici F (2008). Fine Particulate 

Matter and Mortality: A Comparison of 

the Six Cities and American Cancer 

Society Cohorts With a Medicare Cohort. 

Epidemiology, 19: 209- 216. 

Ely DW; Leary JT; Stewart TR; Ross DM 

(1991). The establishment of the Denver 

Visibility Standard. Presented at 84th 

annual meeting & exhibition of the Air 

& Waste Management Association; June; 

Vancouver, British Columbia. Pittsburgh, 

PA: Air & Waste Management 

Association; paper no. 91–48.4. 

EPRI (2012). Comments of the Electric Power 

Research Institute on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Docket No. EPA– 

HQ–OAR–2007–0492–9396. August 31, 

2012. 

Frank N (2006). Retained Nitrate, Hydrated 

Sulfates, and Carbonaceous Mass in 

Federal Reference Method Fine 

Particulate Matter for Six Eastern U.S. 

Cities. J Air Waste Manage Assoc., 56: 

500–511. 

Frank N (2012a). Differences between 

maximum and composite monitor 

annual PM2.5 design values by CBSA. 

Memorandum to the PM NAAQS review 

docket. Docket number EPA–HQ–OAR– 

2007–0492. December 2012. Available: 

http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_td.html. 

Frank N (2012b). Reanalysis of the 

relationship between 24-hour and 4-hour 

visibility index levels. Memorandum to 

the PM NAAQS review docket. Docket 

number EPA–HQ–OAR–2007–0492. 

December 2012. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/

s_pm_2007_td.html. 

Franklin M; Zeka A; Schwartz J (2007). 

Association between PM2.5 and all-cause 

and specific-cause mortality in 27 U.S. 

communities. J Expo Sci Environ 

Epidemiol, 17: 279–287. 

Franklin M; Koutrakis P; Schwartz J (2008). 

The role of particle composition on the 

association between PM2.5 and mortality. 

Epidemiology, 19: 680–689. 

Gauderman WJ; McConnell R; Gilliland F; 

London S; Thomas D; Avol E; Vora H; 

Berhane K; Rappaport EB; Lurmann F; 

Margolis HG; Peters J (2000). Association 

between air pollution and lung function 

growth in southern California children. 

Am J Respir Crit Care Med, 162: 1383– 

1390. 

Gauderman WJ; Gilliland GF; Vora H; Avol 

E; Stram D; McConnell R; Thomas D; 

Lurmann F; Margolis HG; Rappaport EB; 

Berhane K; Peters JM (2002). Association 

between air pollution and lung function 

growth in southern California children: 

results from a second cohort. Am J 

Respir Crit Care Med, 166: 76–84. 

Gauderman WJ; Avol E; Gilliland F; Vora H; 

Thomas D; Berhane K; McConnell R; 

Kuenzli N; Lurmann F; Rappaport E; 

Margolis H; Bates D; Peters J (2004). The 

effect of air pollution on lung 

development from 10 to 18 years of age. 

NEJM, 351: 1057–67. 

Gent JF, Koutrakis P, Belanger K, Triche E, 

Holford TR, Bracken MB, Leaderer BP 

(2009) Symptoms and medication use in 

children with asthma and traffic-related 

sources of fine particle pollution. 

Environ Health Perspect, 117: 1168–74. 

Georgia DNR (2012). Comments of the 

Georgia Department of Natural Resources 

on National Ambient Air Quality 

Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9444. August 31, 2012. 

GMA (2012). Comments of the Georgia 

Mining Association on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Docket No. EPA– 

HQ–OAR–2007–0492–3678. August 5, 

2012. 

Gong H Jr; Linn WS; Clark KW; Anderson 

KR; Geller MD; Sioutas C (2005). 

Respiratory responses to exposures with 

fine particulates and nitrogen dioxide in 

the elderly with and without COPD. 

Inhal Toxicol, 17(3):123–32. 

Goodman SN. (1993). P values, hypothesis 

tests, and likeli-hood: implications for 

epidemiology of a neglected historical 

debate. American Journal of 

Epidemiology 137:485–496. 

Goodman SN. (1999). Towards evidencebased medical statistics. 1: the P value 

fallacy. Annals of Internal Medicine 

130:995–1004. 

Goss CH; Newsom SA; Schildcrout JS; 

Sheppard L; Kaufman JD (2004). Effect of 

ambient air pollution on pulmonary 

exacerbations and lung function in cystic 

fibrosis. Am J Respir Crit Care Med, 169: 

816–821. 

Greenland, S. (1998) Meta-analysis. In: 

Rothman, K. J.; Greenland, S., eds. 

Modern epidemiology. Philadelphia, PA: 

Lippincott Williams & Wilkins; pp. 643– 

673. 

Greven S; Dominici F; Zeger S (2011). An 

Approach to the Estimation of Chronic 


tkelley on DSK3SPTVN1PROD with 
3270 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

Air Pollution Effects Using SpatioTermporal Information. Journal of the 

American Statistical Association. Vol. 

106, No. 494. 396–406. 

Hanley T and Reff A (2011). Assessment of 

PM2.5 FEMs compared to collocated 

FRMs. Memorandum to PM NAAQS 

review. Docket ID number EPA–HQ– 

OAR–2007–0492–0332. April 7, 2011. 

Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/s_pm_bar;2007_

td.html. 

Harnett WT (2009). Guidance on SIP 

Elements Required Under Sections 

110(a)(1) and (2) for the 2006 24-Hour 

Fine Particle (PM2.5) National Ambient 

Air Quality Standards (NAAQS). 

September 25, 2009. Docket ID number 

EPA–HQ–OAR–2007–0492–0341. 

Available: http://www.epa.gov/ttn/ 

oarpg/t1/memoranda/20090925

_harnett_pm25_sip_110a12.pdf. 

Hassett-Sipple B; Rajan P; Schmidt M (2010). 

Analyses of PM2.5 Data for the PM 

NAAQS Review. Memorandum to the 

PM NAAQS review docket. Docket ID 

number EPA–HQ–OAR–2007–0492– 

0077. March 29, 2010. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/

s_pm_2007_td.html. 

HEI (2003). Commentary on revised analyses 

of selected studies. In: Revised analyses 

of time-series studies of air pollution and 

health. Special report. Boston, MA: 

Health Effects Institute; pp. 255–290. 

Available: http://www.healtheffects.org/

Pubs/TimeSeries.pdf. October 18, 2004. 

Henderson R (2005a). Letter from Dr. Rogene 

Henderson, Chair, Clean Air Scientific 

Advisory Committee to Honorable 

Stephen L. Johnson, Administrator, U.S. 

EPA. CASAC PM Review Panel’s Peer 

Review of the Agency’s Review of the 

National Ambient Air Quality Standards 

for Particulate Matter: Policy Assessment 

of Scientific and Technical Information 

(Second Draft PM Staff Paper, January 

2005). June 6, 2005. EPA–SAB–CASAC– 

05–007. Docket ID number EPA–HQ– 

OAR–2001–0017–0393. Available: http:// 

www.epa.gov/sab/pdf/casac-05-007.pdf. 

Henderson R (2005b). Clean Air Scientific 

Advisory Committee (CASAC) Review of 

the EPA Staff Recommendations 

Concerning a Potential Thoracic Coarse 

PM Standard in the Review of the 

National Ambient Air Quality Standards 

for Particulate Matter: Policy Assessment 

of Scientific and Technical Information 

(Final PM OAQPS Staff Paper, EPA–452/ 

R–05–005, June 2005). September 15, 

2005. EPA–SAB–CASAC–05–012. 

Docket ID number EPA–HQ–OAR–2001– 

0017–0477. Available: http:// 

yosemite.epa.gov/sab/sabproduct.nsf/

3562FF25F05133FC85257084000B1B77/ 

$File/sab-casac-05-012.pdf. 

Henderson R (2005c). Letter from Dr. Rogene 

Henderson, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Stephen L. Johnson, Administrator, U.S. 

EPA. Clean Air Scientific Advisory 

Committee (CASAC) Advisory on 

Implementation Aspects of the Agency’s 

Final Draft National Ambient Air 

Monitoring Strategy (NAAMS) 

(December 2004). April 20, 2005. EPA– 

SAB–CASAC–05–006. Available: http:// 

yosemite.epa.gov/sab/sabproduct.nsf/

FA9EBA6E90F17D

BC8525700B005520A5/$File/SABCASAC-05-006_unsigned.pdf. 

Henderson R. (2006a). Letter from Dr. Rogene 

Henderson, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Stephen L. Johnson, Administrator, U.S. 

EPA. Clean Air Scientific Advisory 

Committee Recommendations 

Concerning the Proposed National 

Ambient Air Quality Standards for 

Particulate Matter. March 21, 2006. EPA– 

CASAC–LTR–06–002. Docket ID number 

EPA–HQ–OAR–2001–0017–1452. 

Available: http://www.epa.gov/sab/pdf/

casac-ltr-06-002.pdf. 

Henderson R; Cowling E; Crapo JD; Miller FJ; 

Poirot RL; Speizer F; Zielinski B (2006b). 

Letter from Clean Air Scientific Advisory 

Committee to the Honorable Stephen L. 

Johnson, Administrator, U.S. EPA. Clean 

Air Scientific Advisory Committee 

Recommendations Concerning the Final 

National Ambient Air Quality Standards 

for Particulate Matter. September 29, 

2006. EPA–CASAC–LTR–06–003. Docket 

ID number EPA–HQ–OAR–2007–0492– 

0051. Available: http://yosemite.epa.gov/ 

sab/sabproduct.nsf/1C69E987731CB7

75852571FC00499A10/$File/casac-ltr06-003.pdf. 

Henderson R (2008). Letter from Dr. Rogene 

Henderson, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Stephen L. Johnson, Administrator, U.S. 

EPA. Clean Air Scientific Advisory 

Committee Particulate Matter Review 

Panel’s Consultation on EPA’s Draft 

Integrated Review Plan for the National 

Ambient Air Quality Standards for 

Particulate Matter. January 3, 2008. EPA– 

CASAC–08–004. Docket ID number 

EPA–HQ–OAR–2007–0492–0018. 

Available: 

http://yosemite.epa.gov/sab/ 

sabproduct.nsf/264cb1227d55e02c85257

402007446a4/76D069B819138

1DA852573C500688E74/$File/EPACASAC-08-004-unsigned.pdf. 

Herman SA, Perciasepe R (1999). State 

Implementation Plans: Policy Regarding 

Excess Emissions During Malfunctions, 

Startup, and Shutdown. Memorandum 

from Steven A. Herman, Assistant 

Administrator for Enforcement and 

Compliance Assurance, and Robert 

Perciasepe, Assistant Administrator for 

Air and Radiation to Regional 

Administrators, Regions I–X. September 

20, 1999. 

Hill AB (1965). The environment and 

disease: Association or causation? Proc. 

R. Soc. Med. 58: 295–300. 

Hopke PK; Ito K; Mar T; Christensen WF; 

Eatough DJ; Henry RC; Kim E; Laden F; 

Lall R; Larson TV; Liu H; Neas L; Pinto 

J; Stolzel M; Suh H; Paatero P; Thurston 

GD (2006). PM source apportionment 

and health effects: 1 Intercomparison of 

source apportionment results. J Expo Sci 

Environ Epidemiol, 16: 275–286. 

Indiana DEM (2012). Comments of the 

Indiana Department of Environmental 

Management on National Ambient Air 

Quality Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9398. August 31, 2012. 

ISEE (2012). Comments on EPA’s proposal to 

revise the Air Quality Standards for 

Particle Pollution (Particulate Matter). 

Letter from Annette Peters, President, 

International Society for Environmental 

Epidemiology to EPA Administrator Lisa 

P. Jackson. Docket No. EPA–HQ–OAR– 

2007–0492–9234. August 30, 2012. 

Islam T; Gauderman WJ; Berhane K; 

McConnell R; Avol E; Peters JM; 

Gilliland FD (2007). The relationship 

between air pollution, lung function and 

asthma in adolescents. Thorax, 62: 957– 

963. 

Ito K; Christensen WF; Eatough DJ; Henry RC; 

Kim E; Laden F; Lall R; Larson TV; Neas 

L; Hopke PK; Thurston GD (2006). PM 

source apportionment and health effects: 

2 An investigation of intermethod 

variability in associations between 

source-apportioned fine particle mass 

and daily mortality in Washington, DC. 

J Expo Sci Environ Epidemiol, 16: 300– 

310. 

Jackson L (2009). Memo from Administrator 

Lisa P. Jackson to Elizabeth Craig, Acting 

Assistant Administrator for OAR and Lek 

Kadeli, Acting Assistant Administrator 

for ORD. Process for Reviewing the 

National Ambient Air Quality Standards. 

May 21, 2009. Available: http:// 

www.epa.gov/ttn/naaqs/pdfs/

NAAQSReviewProcessMemo52109.pdf. 

Jackson L J (2010). Letter from Administrator 

Lisa P. Jackson to Dr. Jonathan M. Samet, 

Chairman, Clean Air Scientific Advisory 

Committee. February 25, 2010. Docket ID 

number EPA–HQ–ORD–2007–0517– 

0127. 

Janes H; Dominici F; Zeger SL (2007). Trends 

in Air Pollution and Mortality: An 

Approach to the Assessment of 

Unmeasured Confounding. 

Epidemiology, 18: 416–423. 

Kelly J; Schmidt M; Frank N; Timin B; 

Solomon D; Rao V (2012a). Technical 

Analyses to Support Surrogacy Policy for 

Proposed Secondary PM2.5 NAAQS 

under NSR/PSD Program. Memorandum 

to EPA Docket No. EPA–HQ–OAR–2007– 

0492 through Richard Wayland, Director, 

Air Quality Assessment Division, U.S. 

EPA Office of Air Quality Planning and 

Standards. June 14, 2012. Available: 

http://www.epa.gov/ttn/naaqs/

standards/pm/s_pm_2007_td.html. 

Kelly J; Schmidt M; Frank N (2012b). 

Updated comparison of 24-hour PM2.5

design values and visibility index design 

values. Memorandum to EPA Docket No. 

EPA–HQ–OAR–2007–0492. Available: 

http://www.epa.gov/ttn/naaqs/

standards/pm/s_pm_2007_td.html. 

Kennecott Utah Copper (2012). Comments of 

the Kennecott Utah Copper LLC on 

National Ambient Air Quality Standards 

for Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9442. August 31, 2012. 

Killingsworth CR; Alessandrini F; Krishna 

Murthy GG; Catalano PJ; Paulauskis JD; 

Godleski JJ (1997). Inflammation, 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3271 

chemokine expression, and death in 

monocrotaline-treated rats following fuel 

oil fly ash inhalation. Inhalation 

Toxicology. 9: 541–565. 

Kim JJ; Smorodinsky S; Lipsett M; Singer BC; 

Hodgson AT; Ostro B (2004). Trafficrelated air pollution near busy roads: 

The East Bay Children’s Respiratory 

Health Study. Am J Respir Crit Care 

Med, 170: 520–526. 

Klemm RJ; Mason R (2003). Replication of 

reanalysis of Harvard Six-City mortality 

study. In HEI Special Report: Revised 

Analyses of Time-Series Studies of Air 

Pollution and Health, Part II (pp. 165– 

172). Boston, MA: Health Effects 

Institute. 

Klemm RJ; Lipfert FW; Wyzga RE; Gust C 

(2004). Daily mortality and air pollution 

in Atlanta: Two years of data from 

ARIES. Inhal Toxicol, 16 Suppl 1: 131– 

141. 

Krewski D; Burnett RT; Goldberg MS; Hoover 

K; Siemiatycki J; Jerrett M; 

Abrahamowicz M; White WH (2000). 

Reanalysis of the Harvard Six Cities 

Study and the American Cancer Society 

Study of particulate air pollution and 

mortality. A special report of the 

Institute’s particle epidemiology 

reanalysis project. Cambridge, MA: 

Health Effects Institute. Available: 

http://pubs.healtheffects.org/

view.php?id=6. 

Krewski D; Jerrett M; Burnett RT; Ma R; 

Hughes E; Shi Y; Turner MC; Pope AC 

III; Thurston G; Calle EE; Thun MJ 

(2009). Extended Follow-Up and Spatial 

Analysis of the American Cancer Society 

Study Linking Particulate Air Pollution 

and Mortality. HEI Research Report 140, 

Health Effects Institute, Boston, MA. 

Available: http://pubs.healtheffects.org/

view.php?id=315. 

Laden F; Neas LM; Dockery DW; Schwartz J 

(2000). Association of fine particulate 

matter from different sources with daily 

mortality in six U.S. cities. Environ 

Health Perspect, 108: 941–947. 

Laden F; Schwartz J; Speizer FE; Dockery DW 

(2006). Reduction in fine particulate air 

pollution and mortality: Extended 

follow-up of the Harvard Six Cities 

Study. Am. J. Respir. Crit. Care Med. 

173: 667–672. 

Laden F (2009). Personal communication 

with Dr. Francine Laden: Annual PM2.5

levels used in the update of the Harvard 

Six Cities Study. May 21, 2009. Docket 

No. EPA–HQ–OAR–2007–0492–0122. 

Lanki T; Pekkanen J; Aalto P; Elosua R; 

Berglind N; D’Ippoliti D; Kulmala M; 

Nyberg F; Peters A; Picciotto S; Salomaa 

V; Sunyer J; Tiittanen P; Von Klot S; 

Forastiere F (2006). Associations of 

traffic-related air pollutants with 

hospitalization for first acute myocardial 

infarction: The HEAPSS study. Occup 

Environ Med, 63: 844–851. 

League of Women Voters (2012). Comments 

of the League of Women Voters on 

National Ambient Air Quality Standards 

for Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9505. 

Lepeule J, Laden F, Dockery D, Schwartz .J 

(2012). Chronic Exposure to Fine 

Particles and Mortality: An Extended 

Follow-Up of the Harvard Six Cities 

Study from 1974 to 2009. Environ Health 

Perspect. 120: 965–970. 

Lipfert, FW; Wyzga RE; Baty JD; Miller JP 

(2006a). Traffic density as a surrogate 

measure of environmental exposures in 

studies of air pollution health effects: 

Long-term mortality in a cohort of U.S. 

veterans. Atmospheric Environment 40: 

154–169. 

Lipfert FW; Baty JD; Miller JP; Wyzga RE 

(2006b). PM2.5 constituents and related 

air quality variables as predictors of 

survival in a cohort of U.S. military 

veterans. Inhalation Toxicology. 18: 645– 

657. 

Lipfert FW; Baty JD; Miller JP; Wyzga RE 

(2006). PM2.5 constituents and related air 

quality variables as predictors of survival 

in a cohort of U.S. military veterans. 

Inhal Toxicol, 18: 645–657. 

Liu S; Krewski D; Shi Y; Chen Y; Burnett R 

(2007). Association between maternal 

exposure to ambient air pollutants 

during pregnancy and fetal growth 

restriction. J Expo Sci Environ 

Epidemiol, 17: 426–432. 

Malm WC; Sisler JF; Huffman D; Eldred RA; 

Cahill TA (1994). Spatial and Seasonal 

Trends in Particle Concentration and 

Optical Extinction in the United States, 

Journal of Geophysical Research 

(Atmospheres), 99:. 1347–1370. 

Malm WC; Schichtel BA; Pitchford ML 

(2011). Uncertainties in PM2.5

gravimetric and speciation 

measurements and what we can learn 

from them. J Air Waste Manag Assoc, 

61(11): 1131–49. 

MANE–VU (2012). Comments of the MidAtlantic North East Visibility Union on 

National Ambient Air Quality Standards 

for Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9364. 

Mar TF; Ito K; Koenig JQ; Larson TV; Eatough 

DJ; Henry RC; Kim E; Laden F; Lall R; 

Neas L; Sto ̈lzel M; Paatero P; Hopke PK; 

Thurston GD (2006). PM source 

apportionment and health effects. 3. 

Investigation of inter-method variations 

in associations between estimated source 

contributions of PM2.5 and daily 

mortality in Phoenix, AZ. J Expo Sci 

Environ Epidemiol, 16:. 311–20. 

McCarthy, R. (2012). Letter from the 

Assistant Administrator, EPA Office of 

Air and Radiation to Mr. Robert Ukeiley. 

Subject: Petition to Initiate Rulemaking 

to Designate Air Quality Models. January 

4, 2012. Available: 

McClellan R (2012). Comments of Roger O 

McClellan, Advisor, Toxicology and 

Human Health Risk Analysis on National 

Ambient Air Quality Standards for 

Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9409. August 31, 2012. 

McConnell R; Berhane K; Gilliland F; London 

SJ; Vora H; Avol E; Gauderman WJ; 

Margolis HG; Lurmann F; Tomas DC; 

Peters JM (1999). Air pollution and 

bronchitic symptoms in southern 

California children with asthma. 

Environ. Health Perspect. 107: 757–760. 

McConnell R; Berhane K; Gilliland F; Molitor 

J; Thomas D; Lurmann F; Avol E; 

Gauderman WJ; Peters JM (2003). 

Prospective study of air pollution and 

bronchitic symptoms in children with 

asthma. Am J Respir Crit Care Med, 168: 

790–797. 

McCubbin D (2011). Health Benefits of 

Alternative PM2.5 Standards. July 2011. 

Middleton N; Yiallouros P; Kleanthous S; 

Kolokotroni O; Schwartz J; Dockery DW; 

Demokritou P; Koutrakis P (2008). A 10- 

year time-series analysis of respiratory 

and cardiovascular morbidity in Nicosia, 

Cyprus: The effect of short-term changes 

in air pollution and dust storms. Environ 

Health, 7: 39. 

Miller KA; Siscovick DS; Sheppard L; 

Shepherd K; Sullivan JH; Anderson GL; 

Kaufman JD (2007). Long-term exposure 

to air pollution and incidence of 

cardiovascular events in women. N Engl 

J Med, 356: 447–458. 

MOE-Ontario (2012). Comments of the 

Ministry of the Environment for the 

Province of Ontario, Canada on National 

Ambient Air Quality Standards for 

Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9409. August 31, 2012. 

Molenar JV; Malm WC; Johnson CE (1994). 

Visual air quality simulation techniques. 

Atmos Environ, 28(5): 1055–1063. 

NACAA (2012). Comments of the National 

Association of Clean Air Agencies on 

National Ambient Air Quality Standards 

for Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9397. August 31, 2012. 

NAM et al. (2012). Comments of the National 

Association of Manufacturers, 

Aluminum Association, American 

Chemistry Council, American Coke & 

Coal Chemicals Institute, American 

Forest & Paper Association, American 

Foundry Society, American Iron & Steel 

Institute, American Petroleum Institute, 

American Wood Council, BCCA Appeal 

Group, Brick Industry Association, 

Council of Industrial Boiler Owners, 

Corn Refiners Association, Hardwood 

Plywood and Veneer Association, 

Industrial Energy Consumers of America, 

Motor & Equipment Manufacturers 

Association, National Association for 

Surface Finishing, National Federation of 

Independent Business, National Oilseed 

Processors Association, National Mining 

Association, North American Die Casting 

Association, Rubber Manufacturers 

Association, U.S. Chamber of Commerce, 

and Wisconsin Manufacturers & 

Commerce on National Ambient Air 

Quality Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9425. August 31, 2012. 

NEDA/CAP (2012). Comments of the 

National Environmental Development 

Association’s Clean Air Project on 

National Ambient Air Quality Standards 

for Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9421. August 31, 2012. 

NESCAUM (2012). Comments of the 

Northeast States for Coordinated Air Use 

Management on National Ambient Air 


tkelley on DSK3SPTVN1PROD with 
3272 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

Quality Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9366. August 31, 2012. 

Nevada DEP (2012). Comments of the Nevada 

Division of Environmental Protection, 

Department of Conservation and Natural 

Resources, on National Ambient Air 

Quality Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9410. August 31, 2012. 

New York DOH/DEC (2012). Comments of 

the New York State Departments of 

Health and Environmental Conservation 

on National Ambient Air Quality 

Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9352. August 28, 2012. 

NTAA (2012). Comments of the National 

Tribal Air Association on National 

Ambient Air Quality Standards for 

Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9926. August 31, 2012. 

Ntziachristos L; Ning Z; Geller MD; Sheesley 

RJ; Schauer JJ; Sioutas C (2007). Fine, 

ultrafine and nanoparticle trace element 

compositions near a major freeway with 

a heavy-duty diesel fraction. 

Atmospheric Environment, 41 (2007): 

5684–5696. 

NMA/NCBA (2012). Comments of the 

National Mining Association and the 

National Cattlemen’s Beef Association on 

National Ambient Air Quality Standards 

for Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9382. August 31, 2012. 

NSSGA (2012). Comments of the National 

Stone, Sand & Gravel Association on 

National Ambient Air Quality Standards 

for Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9345. August 30, 2012. 

O’Connor GT; Neas L; Vaughn B; Katan M; 

Mitchell H; Crain EF; Evans R 3rd; 

Gruchalla R; Morgan W; Stout J; Adams 

GK; Lippmann M (2008). Acute 

respiratory health effects of air pollution 

on children with asthma in U.S. inner 

cities. J Allergy Clin Immunol, 121: 

1133–1139. 

Oklahoma DEQ (2012). Comments of the 

Oklahoma Department of Environmental 

Quality on National Ambient Air Quality 

Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9373. August 30, 2012. 

Ostro BD; Broadwin R; Lipsett, MJ (2003). 

Coarse particles and daily mortality in 

Coachella Valley, California. In: Revised 

analyses of time-series studies of air 

pollution and health. Special report. 

Boston, MA: Health Effects Institute; pp. 

199–204. Available: http:// 

pubs.healtheffects.org/getfile.php?u=21. 

Page S (2010a). Applicability of the Federal 

Prevention of Significant Deterioration 

Permit Requirements to New and 

Revised National Ambient Air Quality 

Standards. Memorandum from Stephen 

D. Page, Director, U.S. EPA Office of Air 

Quality Planning and Standards to Air 

Division Directors and Deputies, Regions 

I–X. April 1, 2010. Available: http:// 

www.epa.gov/region07/air/nsr/ 

nsrmemos/psdnaaqs.pdf. 

Page S (2010b). Modeling Procedures for 

Demonstrating Compliance with PM2.5

NAAQS. Memorandum from Stephen D. 

Page, Director, U.S. EPA Office of Air 

Quality Planning and Standards. March 

23, 2010. Available: http://www.epa.gov/ 

region7/air/nsr/nsrmemos/ 

pm25memo.pdf. 

Page S (2010c). Guidance Concerning the 

Implementation of the 1-hour NO2

NAAQS for the Prevention of Significant 

Deterioration Program. Memorandum 

from Stephen D. Page, Director, U.S. EPA 

Office of Air Quality Planning and 

Standards to Air Division Directors. June 

29, 2010. Includes 2 attachments. 

Available: http://www.epa.gov/region07/ 

air/nsr/nsrmemos/appwno2.pdf. 

Page S (2010d). Guidance Concerning the 

Implementation of the 1-hour SO2

NAAQS for the Prevention of Significant 

Deterioration Program. Memorandum 

from Stephen D. Page, Director, U.S. EPA 

Office of Air Quality Planning and 

Standards to Air Division Directors. 

August 23, 2010. Includes 2 attachments. 

Available: http://www.epa.gov/region7/ 

air/nsr/nsrmemos/appwso2.pdf. 

Page S (2011). Guidance to Regions for 

Working with Tribes during the National 

Ambient Air Quality Standards 

(NAAQS) Designations Process. 

Memorandum from Stephen D. Page, 

Director, EPA OAQPS to Regional 

Administrators, Regions I–X. December 

20, 2011. Available: http://www.epa.gov/ 

ttn/oarpg/t1/memoranda/ 

20120117naaqsguidance.pdf. 

Page S (2012). Timely Processing of 

Prevention of Significant Deterioration 

(PSD) Permits when EPA or a PSDDelegated Air Agency Issues the Permit. 

Memorandum from Stephen D. Page, 

Director, U.S. EPA Office of Air Quality 

Planning and Standards to Regional Air 

Division Directors. October 15, 2012. 

Available: http://www.epa.gov/region7/ 

air/nsr/nsrmemos/timely.pdf. 

Parker JD; Woodruff TJ; Basu R; Schoendorf 

KC (2005). Air pollution and birth 

weight among term infants in California. 

Pediatrics, 115: 121–128. 

Parker JD; Woodruff TJ (2008). Influences of 

study design and location on the 

relationship between particulate matter 

air pollution and birthweight. Paediatr 

Perinat Epidemiol, 22: 214–227. 

Penttinen P; Vallius M; Tiittanen P; 

Ruuskanen J; Pekkanen J (2006). Sourcespecific fine particles in urban air and 

respiratory function among adult 

asthmatics. Inhal Toxicol, 18: 191–198. 

Perez L; Tobias A; Querol X; Kunzli N; Pey 

J; Alastuey A; Viana M; Valero N; 

Gonzalez-Cabre M; Sunyer J (2008). 

Coarse particles from Saharan dust and 

daily mortality. Epidemiology, 19: 800– 

807. 

Peters A; Dockery DW; Muller JE; Mittleman 

MA (2001). Increased particulate air 

pollution and the triggering of 

myocardial infarction. Circulation, 103: 

2810–2815. 

Peters J; Avol E; Gauderman WJ; Linn WS; 

Navidi W; London S; Margolis H; 

Rappaport E; Vora H; Gong H Jr; Thomas 

DC (1999). A study of twelve southern 

California communities with differing 

levels and types of air pollution II Effects 

on pulmonary function. Am J Respir Crit 

Care Med, 159: 768–775. 

Pitchford M; Maim W; Schichtel B; Kumar N; 

Lowenthal D; Hand J (2007). Revised 

algorithm for estimating light extinction 

from IMPROVE particle speciation data. 

J Air Waste Manag Assoc, 57: 1326–36. 

Pitchford M (2010). Assessment of the Use of 

Speciated PM2.5 Mass-Calculated Light 

Extinction as a Secondary PM NAAQS 

Indicator of Visibility. Memorandum to 

PM NAAQS review docket. November 

17, 2010. Docket ID number EPA–HQ– 

OAR–2007–0492–0337. Available: 

http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_td.html. 

Pope CA 3rd; Dockery DW (1992). Acute 

health effects of PM10 pollution on 

symptomatic and asymptomatic 

children. Am Rev Respir Dis, 145(5): 

1123–8. 

Pope CA 3rd; Thun MJ; Namboodiri MM; 

Dockery DW; Evans JS; Speizer FE; 

Heath CW (1995). Particulate air 

pollution as a predictor of mortality in a 

prospective study of U.S. adults. Am J 

Respir Crit Care Med, 151: 669–674. 

Pope CA 3rd; Burnett RT; Thun MJ; Calle EE; 

Krewski D; Ito K; Thurston GD (2002). 

Lung cancer, cardiopulmonary mortality, 

and long-term exposure to fine 

particulate air pollution. JAMA, 287: 

1132–1141. 

Pope CA; Burnett RT (2007). Commentary: 

Confounding in Air Pollution 

Epidemiology: The Broader Context. 

Epidemiology, 18: 424–426. 

Pryor SC (1996). Assessing public perception 

of visibility for standard setting 

exercises. Atmos Environ, 30: 2705– 

2716. 

PSR (2012). Comments on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Submitted on 

behalf of Physicians for Social 

Responsibility by Alan H. Lockwood, 

Andrew S. Kanter, Catherine 

Thomasson, and Barbara Gottlieb. Docket 

No. EPA–HQ–OAR–2007–0492–5763. 

August 13, 2012. 

Puett RC; Schwartz J; Hart JE; Yanosky JD; 

Speizer FE; Suh H; Paciorek CJ; Neas 

LM; Laden F (2008). Chronic particulate 

exposure, mortality, and coronary heart 

disease in the nurses’ health study. Am 

J Epidemiol, 168: 1161–1168. 

Rabinovitch N; Zhang LN; Murphy JR; Vedal 

S; Dutton SJ; Gelfand EW (2004). Effects 

of wintertime ambient air pollutants on 

asthma exacerbations in urban minority 

children with moderate to severe 

disease. J Allergy Clin Immunol, 114: 

1131–1137. 

Raizenne M; Neas LM; Damokosh AI; 

Dockery DW; Spengler JD; Koutrakis P; 

Ware JH; Speizer FE (1996). Health 

effects of acid aerosols on North 

American children: Pulmonary function. 

Environ Health Perspect, 104: 506–514. 

Rajan P, Schmidt M, Hassett-Sipple B (2011). 

PM2.5 Distributional Statistical Analyses. 

Memorandum to PM NAAQS review 

docket. April 7, 2011. Docket ID number 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3273 

EPA–HQ–OAR–2007–0492–0333. 

Available: http://www.epa.gov/ttn/

naaqs/standards/pm/s_pm_2007_td.

html. 

Rom W (2012). Letter from Dr. William N. 

Rom and more than 350 doctors, nurses, 

scientists, and public health and medical 

professionals to EPA Administrator Lisa 

P. Jackson providing comments on the 

proposed revision of the PM NAAQS, 

August 31, 2012. Docket No. EPA–HQ– 

OAR–2007–0492–9755. August 31, 2012. 

Roosli M; Kunzli N; Braun-Farlander C; Egger 

M (2005). Years of life lost attributable to 

air pollution in Switzerland: Dynamic 

exposure-response model. Int J 

Epidemiol, 34:1029–1035. 

Ross Z; Jerrertt M; Ito K; Tempalski B; 

Thurston GD (2007). A land use 

regression for predicting fine particulate 

matter concentrations in the New York 

City region. Atmospheric Environment 

41 (2007) 2255–2269. 

Rothman, KJ; Greenland S., eds. (1998). 

Modern epidemiology. 2nd ed. 

Philadelphia, PA: Lippincott-Raven 

Publishers. 

Royall, RM (1997). Statistical Evidence: A 

Likelihood Paradigm. London: Chapman 

and Hall. 

Russell, A (2009). Letter from the Clean Air 

Science Advisory Committee (CASAC) 

Ambient Air Monitoring and Methods 

Subcommittee (AAMMS) to the 

Honorable Lisa P, Jackson, 

Administrator, U.S. EPA. Subject: 

Consultation on Monitoring Issues 

Related to the NAAQS for Particulate 

Matter. March 6, 2009. EPA–CASAC–09– 

006. Docket ID number EPA–HQ–OAR– 

2007–0492–0088. Available: http:// 

yosemite.epa.gov/sab/sabproduct.nsf/ 

C446E60A1156E2DF8525757100780CF4/ 

$File/EPA-CASAC-09-006-unsigned.pdf. 

Russell, A; Samet, J.M. (2010b). Letter from 

the Clean Air Science Advisory 

Committee (CASAC) Ambient Air 

Monitoring and Methods Subcommittee 

(AAMMS) to the Honorable Lisa P, 

Jackson, Administrator, U.S. EPA. 

Review of the ‘‘Near-road Guidance 

Document-Outline’’ and ‘‘Near-road 

Monitoring Pilot Study Objectives and 

Approach.’’ November 24, 2010. EPA– 

CASAC–11–001. Docket ID number. 

EPA–HQ–OAR–2007–0492–XXXX 

Available: http://yosemite.epa.gov/sab/ 

sabproduct.nsf/ACD1BD26412312DC8

52577E500591B37/$File/EPA-CASAC11-001-unsigned.pdf. 

Savitz, DA; Tolo KA; Poole C (1994). 

Statistical significance testing in the 

American Journal of Epidemiology, 

1970–1990. American Journal of 

Epidemiology 139:1047–1052. 

Samet J (2009a). Letter from Dr. Jonathan M. 

Samet, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Lisa P. Jackson, Administrator, U.S. EPA. 

Consultation on EPA’s Particulate Matter 

National Ambient Air Quality Standards: 

Scope and Methods Plan for Health Risk 

and Exposure Assessment. May 21, 2009. 

EPA–CASAC–09–009. Docket ID 

number. EPA–HQ–OAR–2007–0492– 

0024. Available: http://yosemite.epa.gov/ 

sab/sabproduct.nsf/723FE644C5D758DF

852575BD00763A32/$File/EPA-CASAC09-009-unsigned.pdf. 

Samet, J (2009b). Letter from Dr. Jonathan M. 

Samet, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Lisa P. Jackson, Administrator, U.S. EPA. 

Consultation on EPA’s Particulate Matter 

National Ambient Air Quality Standards: 

Scope and Methods Plan for Urban 

Visibility Impact Assessment. EPA– 

CASAC–09–010. Docket ID number. 

EPA–HQ–OAR–2007–0492–0026. May 

21, 2009. Available: http://yosemite.

epa.gov/sab/sabproduct.nsf/0F63D7995

F5850D5852575BD0077869C/$File/EPACASAC-09-010-unsigned.pdf. 

Samet J (2009c). Letter from Dr. Jonathan M. 

Samet, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Lisa P. Jackson, Administrator, U.S. EPA. 

Review of Risk Assessment to Support 

the Review of the Particulate Matter (PM) 

Primary National Ambient Air Quality 

Standards—External Review Draft 

(September 2009). November 24, 2009. 

Docket ID number EPA–HQ–OAR–2007– 

0492–0065. Available: http:// 

yosemite.epa.gov/sab/sabproduct.nsf/ 

BC1ECC5D539EF72385257678006

D5754/$File/EPA-CASAC-10-003- 

unsigned.pdf. 

Samet J (2009d). Letter from Dr. Jonathan M. 

Samet, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Lisa P. Jackson, Administrator, U.S. EPA. 

Review of Particulate Matter UrbanFocused Visibility Assessment (External 

Review Draft, September 2009). 

November 24, 2009. Docket ID number 

EPA–HQ–OAR–2007–0492–0064. 

Available: http://yosemite.epa.gov/sab/ 

sabproduct.nsf/15872217938041F6852

57678006A26E3/$File/EPA-CASAC-10- 

002-unsigned.pdf. 

Samet J (2009e). Letter from Dr. Jonathan M. 

Samet, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Lisa P. Jackson, Administrator, U.S. EPA. 

CASAC Review of EPA’s Integrated 

Science Assessment for Particulate 

Matter—First External Review Draft 

(December 2008). May 21, 2009. EPA– 

CASAC–09–008. Docket ID number 

EPA–HQ–ORD–2007–0517–0120. 

Available: http://yosemite.epa.gov/sab/ 

sabproduct.nsf/264cb1227d55e02c

85257402007446a4/73ACCA

834AB44A10852575BD0064346B/$File/ 

EPA-CASAC-09-008-unsigned.pdf. 

Samet J (2009f). Letter from Dr. Jonathan M. 

Samet, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Lisa P. Jackson, Administrator, U.S. EPA. 

CASAC Review of EPA’s Integrated 

Science Assessment for Particulate 

Matter—Second External Review Draft 

(July 2009). November 24, 2009. Docket 

ID number. EPA–HQ–ORD–2007–0517– 

0121. Available: http://yosemite.epa.gov/ 

sab/sabproduct.nsf/264cb1227d55e02c

85257402007446a4/151B1F83B02314558

5257678006836B9/$File/EPA-CASAC10-001-unsigned.pdf. 

Samet J (2010a). Letter from Dr. Jonathan M. 

Samet, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Lisa P. Jackson, Administrator, U.S. EPA. 

CASAC Review of Quantitative Health 

Risk Assessment for Particulate Matter— 

Second External Review Draft (February 

2010). April 15, 2010. Docket ID number 

EPA–HQ–OAR–2007–0492–0109. 

Available: http://yosemite.epa.gov/sab/ 

sabproduct.nsf/BC4F6E77

B6385155852577070002F09F/$File/EPACASAC-10-008-unsigned.pdf. 

Samet J (2010b). Letter from Dr. Jonathan M. 

Samet, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Lisa P. Jackson, Administrator, U.S. EPA. 

CASAC Review of Particulate Matter 

Urban-Focused Visibility Assessment— 

Second External Review Draft (January 

2010). April 20, 2010. Docket ID number 

EPA–HQ–OAR–2007–0492–0110. 

Available: http://yosemite.epa.gov/sab/ 

sabproduct.nsf/0D5CB76AFE7FA77C85

25770D004EED55/$File/EPA-CASAC-10- 

009-unsigned.pdf. 

Samet J (2010c). Letter from Dr. Jonathan M. 

Samet, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Lisa P. Jackson, Administrator, U.S. EPA. 

CASAC Review of Policy Assessment for 

the Review of the PM NAAQS—First 

External Review Draft (March 2010). May 

17, 2010. Docket ID number EPA–HQ– 

OAR–2007–0492–0113. Available: 

http://yosemite.epa.gov/sab/ 

sabproduct.nsf/264cb1227d

55e02c85257402007446a4/E504EE327

6D87A9E8525772700647AFB/$File/EPACASAC-10-011-unsigned.pdf. 

Samet J (2010d). Letter from Dr. Jonathan M. 

Samet, Chair, Clean Air Scientific 

Advisory Committee to the Honorable 

Lisa P. Jackson, Administrator, U.S. EPA. 

CASAC Review of Policy Assessment for 

the Review of the PM NAAQS—Second 

External Review Draft (June 2010). 

September 10, 2010. Docket ID number 

EPA–HQ–OAR–2007–0492–0256. 

Available: http://yosemite.epa.gov/sab/ 

sabproduct.nsf/264cb1227

d55e02c85257402007446a4/CCF9F4C05

00C500F8525779D0073C593/$File/EPACASAC-10-015-unsigned.pdf. 

Sarnat J; Marmur A; Klein M; Kim E; Russell 

AG; Sarnat SE; Mulholland JA; Hopke 

PK; Tolbert PE (2008). Fine particle 

sources and cardiorespiratory morbidity: 

An application of chemical mass balance 

and factor analytical sourceapportionment methods. Environ Health 

Perspect, 116: 459–466. 

Sato M; Hansen J; Koch D; Lucis A; Ruedy 

R; Dubovik O; Holben B; Chin M; 

Novakov T (2003). Global atmospheric 

black carbon inferred from AAEONET. 

Presented at Proceedings of the National 

Academy of Science. 

Schisterman EF, Cole SR, Platt RW (2009). 

Overadjustment bias and unnecessary 

adjustment in epidemiologic studies. 

Epidemiology 20(4): 488–495. 

Schmidt M; Hassett-Sipple B; Rajan P (2010) 

PM2.5 Air Quality Analyses. 

Memorandum for the PM NAAQS 

Review (Docket EPA–HQ–OAR–2007– 

0492). July 22, 2010. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/ 

s_pm_2007_td.html. 


tkelley on DSK3SPTVN1PROD with 
3274 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

Schmidt M (2011). PM2.5 Air Quality 

Analyses—Update: Memorandum to the 

PM NAAQS Review Docket. April 15, 

2011. Docket ID number EPA–HQ–OAR– 

2007–0492–0340. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/ 

s_pm_2007_td.html. 

Schmidt M (2012a). Sensitivity Analysis of 

Long-term Mean PM2.5 Concentrations 

for Selected Long-term Exposure 

Epidemiological Studies. Memorandum 

to PM NAAQS Review Docket No. EPA– 

HQ–OAR–2007–0492. December 2012. 

Available: http://www.epa.gov/ttn/

naaqs/standards/pm/

s_pm_2007_td.html. 

Schmidt M (2012b). Evaluation of the PM2.5

Collocated PM10 Data Substitution 

Routine, 2009–2011. Memorandum to 

PM NAAQS Review Docket No. EPA– 

HQ–OAR–2007–0492, December 2012. 

Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/ 

s_pm_2007_td.html. 

Schneiderman ET; Myers MJ; Wilson L; 

Biden JR; King G; Kilmartin PF; Sorrell 

WH (2012). Comments of the State 

Attorneys General of New York, 

Delaware, New Mexico, Rhode Island, 

and Vermont on National Ambient Air 

Quality Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9385. August 31, 2012. 

Schwartz J; Dockery DW; Neas LM (1996). Is 

daily mortality associated specifically 

with fine particles? J Air Waste Manage 

Assoc, 46: 927–939. 

Schwartz J; Coull B; Laden F; Ryan L (2008). 

The effect of dose and timing of dose on 

the association between airborne 

particles and survival. Environ Health 

Perspect, 116: 64–69. 

Seitz J (1991). New Source Review Program 

Transitional Guidance. Memorandum 

from John S. Seitz, Director, EPA Office 

of Air Quality Planning and Standards. 

Available: http://www.epa.gov/region07/ 

air/nsr/nsrmemos/trnsguid.pdf. 

Seitz J (1997). Memorandum on the Interim 

Implementation of New Source Review 

Requirements for PM2.5. Memorandum 

from John S. Seitz, Director, EPA Office 

of Air Quality Planning and Standards. 

EPA Reference OZPMRH–2–97. 

Available: http://www.epa.gov/ttn/caaa/ 

t1/memoranda/pm25.pdf. 

Sheppard L; Levy D; Norris G; Larson TV; 

Koenig JQ (2003). Effects of ambient air 

pollution and nonelderly asthma 

hospital admissions in Seattle, 

Washington, 1987–1994. Epidemiology, 

10: 23–30. 

Slaughter JC; Kim E; Sheppard L; Sullivan 

JH; Larson TV; Claiborn C (2005). 

Association between particulate matter 

and emergency room visits, hospital 

admissions and mortality in Spokane, 

Washington. J Expo Sci Environ 

Epidemiol, 15: 153–159. 

Smith A (2009). Comments to CASAC on 

Particulate Matter National Ambient Air 

Quality Standards: Scope and Methods 

Plan for Urban Visibility Impact 

Assessment. Anne E. Smith, CRA 

International. Washington, DC. March 

24, 2009. Prepared at the request of the 

Utility Air Regulatory Group. Docket ID 

number EPA–HQ–OAR–2007–0492– 

0015, Attachment I. 

Smith AE; Howell S (2009). An assessment 

of the robustness of visual air quality 

preference study results. CRA 

International. Washington, DC. http:// 

yosemite.epa.gov/sab/sabproduct.nsf/ 

B55911DF9796E5E385257592006FB737/ 

$File/CRA+VAQ+Pref+

Robustness+Study+3+30+09+final.pdf. 

South Carolina DHEC (2012). Comments of 

the South Carolina Department of Health 

and Environmental Control on National 

Ambient Air Quality Standards for 

Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9469. August 31, 2012. 

South Dakota DENR (2012). Comments of the 

South Dakota Department of 

Environment and Natural Resources on 

National Ambient Air Quality Standards 

for Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9360. August 31, 2012. 

Southern Company (2012). Comments of the 

Southern Company on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Docket No. EPA– 

HQ–OAR–2007–0492–9365. August 31, 

2012. 

Stanojevic S; Wade A; Stocks J; Hankinson J; 

Coates AL; Pan H; Rosenthal M; Corey 

M; Lebecque P; Cole TJ (2008). Reference 

ranges for spirometry across all ages: a 

new approach. Am J Respir Crit Care 

Med. 177: 253–260. 

Stratus Consulting (2009). Review of Urban 

Visibility Public Preference Studies: 

Final Report. Docket ID No. EPA–HQ– 

OAR–2007–0492–0042. 

Texas CEQ (2012). Comments of the Texas 

Commission on Environmental Quality 

on National Ambient Air Quality 

Standards for Particulate Matter; 

Proposed Rule. Docket No. EPA–HQ– 

OAR–2007–0492–9522. August 31, 2012. 

Thomas D, Stram D, Dwyer J (1993). 

Exposure measurement error: influence 

on exposure-disease. Relationships and 

methods of correction. Annu Rev Public 

Health, 14: 69–93. 

Thurston G; Ito K; Mar T; Christensen WF; 

Eatough DJ; Henry RC; Kim E; Laden F; 

Lall R; Larson TV; Liu H; Neas L; Pinto 

J; Stolzel M; Suh H; Hopke PK (2005). 

Results and implications of the 

workshop on the source apportionment 

of PM health effects. Epidemiology, 16: 

S134–S135. 

UARG (2009). Comments of the Utility Air 

Resources Group on the Integrated 

Science Assessment for Particulate 

Matter—Second External Review Draft. 

Docket No. EPA–HQ–ORD–2007–0517– 

0077. October 13, 2009. 

UARG (2012). Comments of the Utility Air 

Resources Group on National Ambient 

Air Quality Standards for Particulate 

Matter; Proposed Rule. Docket No. EPA– 

HQ–OAR–2007–0492–9483. August 31, 

2012. 

Urban Air Initiative (2012). Comments on 

National Ambient Air Quality Standards 

for Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9538. August 30, 2012. 

U.S. EPA (1996). Air Quality Criteria for 

Particulate Matter. U.S. Environmental 

Protection Agency. Research Triangle 

Park, NC. EPA/600/P–95/001. April 

1996. Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/s_pm_cr_cd.html. 

U.S. EPA (1997). Guidance for Network 

Design and Optimum Site Exposure for 

PM2.5 and PM10. U.S. Environmental 

Protection Agency, Office of Air Quality 

Planning and Standards, Research 

Triangle Park, NC 27711; EPA–454/R– 

99–022. December 1997. Available: 

http://www.epa.gov/ttn/amtic/files/ 

ambient/pm25/network/r-99–022.pdf. 

U.S. EPA (1999). Guideline on Data Handling 

Conventions for the PM NAAQS; EPA– 

454/R–99–008. 

U.S. EPA (2003). Guidance for Tracking 

Progress Under the Regional Haze Rule. 

U.S. Environmental Protection Agency, 

Office of Air Quality Planning and 

Standard, Research Triangle Park, NC 

27711. Report No. EPA–454/B–03–004. 

September 2003. Available: http:// 

www.epa.gov/ttn/oarpg/t1/memoranda/

rh_tpurhr_gd.pdf. 

U.S. EPA (2004a). Air Quality Criteria for 

Particulate Matter. National Center for 

Environmental Assessment, Office of 

Research and Development, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC 27711; 

Report No. EPA/600/P–99/002aF and 

EPA/600/P–99/002bF. October 2004. 

Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/s_pm_cr_cd.html. 

U.S. EPA (2004b). The Particle Pollution 

Report: Current Understanding of Air 

Quality and Emissions through 2003. 

Office of Air Quality Planning and 

Standards, Research Triangle Park, NC. 

Report No. EPA 454–R–04–002. 

December 2004. Available: http:// 

www.epa.gov/airtrends/aqtrnd04/ 

pmreport03/report_2405.pdf. 

U.S. EPA (2005). Review of the National 

Ambient Air Quality Standards for 

Particulate Matter: Policy Assessment of 

Scientific and Technical Information, 

OAQPS Staff Paper. Research Triangle 

Park, NC 27711: Office of Air Quality 

Planning and Standards. Report No. 

EPA–452/R–05–005a. December 2005. 

Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/s_pm_cr_sp.html. 

U.S. EPA (2006a). Provisional Assessment of 

Recent Studies on Health Effects of 

Particulate Matter Exposure. National 

Center for Environmental Assessment, 

Office of Research and Development, 

U.S. Environmental Protection Agency, 

Research Triangle Park, NC. Report No. 

EPA 600/R–06/063. July 2006. Available: 

http://cfpub.epa.gov/ncea/cfm/ 

recordisplay.cfm?deid=151826. 

U.S. EPA (2006b). Air Quality Criteria for 

Lead—Final Report. U.S. Environmental 

Protection Agency, Washington, DC, 

EPA/600/R–05/144aF–bF, October 2006. 

Available: http://www.epa.gov/ttn/ 

naaqs/standards/pb/s_pb_cr_cd.html. 

U.S. EPA (2006c). Report on Air Quality in 

Nonattainment Areas for 2003–2005 

Covering Ozone, Particulate Matter, 

Carbon Monoxide, Sulfur Dioxide, 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3275 

Nitrogen Dioxide, and Lead: Technical 

Summary. U.S. Environmental 

Protection Agency, Research Triangle 

Park, NC. Office of Air Quality Planning 

and Standards. November 2006, revised 

February 14, 2007. Available: http:// 

www.epa.gov/airtrends/pdfs/ 

20070214_aq_na_2003–2005.pdf. 

U.S. EPA (2007a). Draft Integrated Review 

Plan for the National Ambient Air 

Quality Standards for Particulate Matter. 

National Center for Environmental 

Assessment and Office of Air Quality 

Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. Report No. 

EPA 452/P–08–006. October 2007. 

Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/ 

s_pm_2007_pd.html. 

U.S. EPA (2007b). Ambient Air Monitoring 

Network Assessment Guidance, 

Analytical Techniques for Technical 

Assessments of Ambient Air Monitoring 

Networks. EPA 454/d–07–001. February 

2007. Available: http://www.epa.gov/ttn/ 

amtic/files/ambient/pm25/datamang/ 

network-assessment-guidance.pdf. 

U.S. EPA (2008a). Integrated Review Plan for 

the National Ambient Air Quality 

Standards for Particulate Matter. 

National Center for Environmental 

Assessment and Office of Air Quality 

Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. Report No. 

EPA 452/R–08–004. March 2008. 

Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/ 

s_pm_2007_pd.html. 

U.S. EPA (2008b). Integrated Science 

Assessment for Particulate Matter: First 

External Review Draft. National Center 

for Environmental Assessment—RTP 

Division, Office of Air Quality Planning 

and Standards, Research Triangle Park, 

NC. EPA/600/R–08/139 and 139A. 

December 2008. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/ 

s_pm_2007_isa.html. 

U.S. EPA (2008c). U.S. EPA. Integrated 

Science Assessment (ISA) for Oxides of 

Nitrogen and Sulfur Ecological Criteria 

(Final Report). U.S. Environmental 

Protection Agency, Washington, DC, 

EPA/600/R–08/082F, December 2008. 

Available: http://www.epa.gov/ttn/ 

naaqs/standards/no2so2sec/cr_isi.html. 

U.S. EPA (2008d). Ambient Air Quality 

Monitoring and Health Research: 

Summary of April 16–17, 2008. 

Workshop to Discuss Key Issues. 

December 2008. EPA–452/S–08–001. 

Available: http://epa.gov/airscience/pdf/ 

FINAL-April-2008-AQ-Health-ResearchWorkshop-Summary-Dec-2008.pdf. 

U.S. EPA (2008e). Integrated Science 

Assessment for Oxides of Nitrogen— 

Health Criteria (Final Report). U.S. 

Environmental Protection Agency, 

Washington, DC, EPA/600/R–08/071. 

July 2008. Available: http:// 

www.epa.gov/ttn/naaqs/standards/nox/ 

s_nox_cr_isi.html. 

U.S. EPA (2008f). Integrated Science 

Assessment (ISA) for Sulfur Oxides— 

Health Criteria (Final Report). U.S. 

Environmental Protection Agency, 

Washington, DC, EPA/600/R–08/047F, 

2008. Available: http://www.epa.gov/ttn/ 

naaqs/standards/so2/s_so2_cr_isa.html. 

U.S. EPA (2009a). Integrated Science 

Assessment for Particulate Matter: Final 

Report. National Center for 

Environmental Assessment—RTP 

Division, Office of Research and 

Development, Research Triangle Park, 

NC. EPA/600/R–08/139F. December 

2009. Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/ 

s_pm_2007_isa.html. 

U.S. EPA (2009b). Integrated Science 

Assessment for Particulate Matter: 

Second External Review Draft. National 

Center for Environmental Assessment— 

RTP Division, Office of Research and 

Development, Research Triangle Park, 

NC. EPA/600/R–08/139B. July 2009. 

Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/ 

s_pm_2007_isa.html. 

U.S. EPA (2009c). Particulate Matter National 

Ambient Air Quality Standards: Scope 

and Methods Plan for Health Risk and 

Exposure Assessment. Office of Air 

Quality Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA–452/P– 

09–002. February 2009. Available: 

http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_pd.html. 

U.S. EPA (2009d). Particulate Matter National 

Ambient Air Quality Standards: Scope 

and Methods Plan for Urban Visibility 

Impact Assessment. Office of Air Quality 

Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA–452/P– 

09–001. February 2009. Available: 

http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_pd.html. 

U.S. EPA (2009e). Risk Assessment to 

Support the Review of the PM Primary 

National Ambient Air Quality 

Standards—External Review Draft. Office 

of Air Quality Planning and Standards, 

U.S. Environmental Protection Agency, 

Research Triangle Park, NC. EPA–452/P– 

09–006. September 2009. Available: 

http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_risk.html. 

U.S. EPA (2009f). Particulate Matter UrbanFocused Visibility Assessment—External 

Review Draft. Office of Air Quality 

Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA–452/P– 

09–005. September 2009. Available: 

http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_risk.html. 

U.S. EPA (2009g). Policy Assessment for the 

Review of the Particulate Matter National 

Ambient Air Quality Standards— 

Preliminary Draft. Office of Air Quality 

Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA–452/P– 

09–007. September 2009. Available: 

http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_pa.html. 

U.S. EPA (2009h). Risk and Exposure 

Assessment for Review of the Secondary 

National Ambient Air Quality Standards 

for Oxides of Nitrogen and Oxides of 

Sulfur. (Final Report). U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC, EPA–452/R– 

09–008a. Available: http://www.epa.gov/ 

ttn/naaqs/standards/no2so2sec/ 

cr_rea.html. 

U.S. EPA (2010a). Quantitative Health Risk 

Assessment for Particulate Matter—Final 

Report. Office of Air Quality Planning 

and Standards, U.S. Environmental 

Protection Agency, Research Triangle 

Park, NC. EPA–452/R–10–005. June 

2010. Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/ 

s_pm_2007_risk.html. 

U.S. EPA (2010b). Particulate Matter UrbanFocused Visibility Assessment—Final 

Report. Office of Air Quality Planning 

and Standards, U.S. Environmental 

Protection Agency, Research Triangle 

Park, NC. EPA–452/R–10–004. July 2010. 

Available: http://www.epa.gov/ttn/ 

naaqs/standards/pm/ 

s_pm_2007_risk.html. 

U.S. EPA (2010c). Policy Assessment for the 

Review of the Particulate Matter National 

Ambient Air Quality Standards—First 

External Review Draft. Office of Air 

Quality Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA 452/P– 

10–003. March 2010. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/ 

s_pm_2007_pa.html. 

U.S. EPA (2010d). Quantitative Risk 

Assessment for Particulate Matter— 

Second External Review Draft. Office of 

Air Quality Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA–452/P– 

10–001. February 2010. Available: 

http://www.epa.gov/ttn/naaqs/ 

standards/pm/s_pm_2007_risk.html. 

U.S. EPA (2010e). Particulate Matter UrbanFocused Visibility Assessment—Second 

External Review Draft. Office of Air 

Quality Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA–452/P– 

10–002. January 2010. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/ 

s_pm_2007_risk.html. 

U.S. EPA (2010f). Policy Assessment for the 

Review of the Particulate Matter National 

Ambient Air Quality Standards—Second 

External Review Draft. Office of Air 

Quality Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA 452/P– 

10–007. June 2010. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/ 

s_pm_2007_pa.html. 

U.S. EPA (2010h). Risk and Exposure 

Assessment for Review of the Secondary 

National Ambient Air Quality Standards 

for Oxides of Nitrogen and Oxides of 

Sulfur. Office of Air Quality Planning 

and Standards, U.S. Environmental 

Protection Agency, Research Triangle 

Park, NC. EPA 452/R–09–008a/b. 

September 2009. Available: http:// 

www.epa.gov/ttn/naaqs/standards/ 

no2so2sec/cr_rea.html. 

U.S. EPA (2010i). White Paper regarding 

Draft Near-road Guidance Document— 


tkelley on DSK3SPTVN1PROD with 
3276 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

Outline and Draft Near-road Monitoring 

Pilot Study Objectives & Approach. 

Office of Air Quality Planning and 

Standards, U.S. Environmental 

Protection Agency, Research Triangle 

Park, NC. August 24. 1010. Available: 

http://yosemite.epa.gov/sab/ 

sabproduct.nsf/0/ 

9E0F3E9D727323C18525778900596432/ 

$File/Review+Document+for+Sept.+29+- 

+30,+2010+AAMMS+Meeting.pdf. 

U.S. EPA (2010j). Transportation Conformity 

Guidance for Quantitative Hot-spot 

Analyses in PM2.5 and PM10

Nonattainment and Maintenance Areas. 

U.S. EPA Office of Transportation and 

Air Quality, Transportation and Regional 

Programs Division. December 2010. 

EPA–420–B–10–040. Available: http:// 

www.epa.gov/otaq/stateresources/ 

transconf/policy/420b10040.pdf. 

U.S. EPA (2010k). Integrated Science 

Assessment for Carbon Monoxide (Final 

Report). U.S. Environmental Protection 

Agency, Washington, DC, EPA/600/R– 

09/019F, January 2010. Available: 

http://cfpub.epa.gov/ncea/cfm/ 

recordisplay.cfm?deid=218686. 

U.S. EPA (2011a). Policy Assessment for the 

Review of the Particulate Matter National 

Ambient Air Quality Standards. Office of 

Air Quality Planning and Standards, U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA 452/R– 

11–003. April 2011. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/ 

s_pm_2007_pa.html. 

U.S. EPA (2011b). Policy Assessment for the 

Review of the Secondary National 

Ambient Air Quality Standards for 

Oxides of Nitrogen and Oxides of Sulfur. 

Office of Air Quality Planning and 

Standards, U.S. Environmental 

Protection Agency, Research Triangle 

Park, NC, EPA–452/R–11–005a, b. 

February 2011. Available: http:// 

www.epa.gov/ttn/naaqs/standards/ 

no2so2sec/cr_pa.html. 

U.S. EPA (2011c). Responses to Public 

Comments on the Proposed Prevention 

of Significant Deterioration Permit for 

the Avenal Energy Project. U.S. 

Environmental Protection Agency. May 

2011. 

U.S. EPA (2011d). Integrated Science 

Assessment of Ozone and Related 

Photochemical Oxidants (Second 

External Review Draft). U.S. 

Environmental Protection Agency, 

Washington, DC, EPA/600/R–10/076B, 

2011. September 2011. Available: 

http://www.epa.gov/ttn/naaqs/ 

standards/ozone/s_o3_2008_isa.html. 

U.S. EPA (2012a). Responses to Significant 

Comments on the 2012 Proposed Rule on 

the National Ambient Air Quality 

Standards for Particulate Matter (June 29, 

2012; 77 FR 38890). Docket Number 

EPA–HQ–OAR–2007–0492. U.S. 

Environmental Protection Agency. 

December 2012. Available: http:// 

www.epa.gov/ttn/naaqs/standards/pm/ 

s_pm_index.html. 

U.S. EPA (2012b). Provisional Assessment of 

Recent Studies on Health Effects of 

Particulate Matter Exposure. U.S. 

Environmental Protection Agency. Office 

of Research and Development, National 

Center for Environmental Assessment. 

EPA/600/R–12/056A. December 2012. 

U.S. EPA (2012c). Report to Congress on 

Black Carbon. Office of Air and 

Radiation, Office of Air Quality Planning 

and Standards, U.S. Environmental 

Protection Agency, Research Triangle 

Park, NC, EPA–450/R–12–001. March 

2012. Available: http://www.epa.gov/ 

blackcarbon/. 

U.S. EPA (2012d). Order Partially Granting 

and Partially Denying the Petition for 

Objection to Permit for CF&I Steel, L.P. 

(EVRAZ Rocky Mountain Steel). U.S. 

Environmental Protection Agency. May 

31, 2012. Available: http://www.epa.gov/ 

region07/air/title5/petitiondb/petitions/ 

evraz_response2011.pdf. 

U.S. EPA (2012e). Draft Guidance to 

Implement Requirements for the 

Treatment of Air Quality Monitoring 

Data Influenced by Exceptional Events. 

U.S. Environmental Protection Agency. 

June 2012. Available: http:// 

www.epa.gov/ttn/analysis/exevents.htm. 

Vandenberg J (2009). CASAC Review of 

Integrated Science Assessment for 

Particulate Matter: Second External 

Review Draft. Memorandum from John 

Vandenberg, Director, National Center 

for Environmental Assessment, Research 

Triangle Park Division, U.S. EPA to 

Holly Stallworth, Designated Federal 

Officer, Clean Air Scientific Advisory 

Committee, EPA Science Advisory Board 

Staff Office. August 5, 2009. Docket ID 

no. EPA–HQ–ORD–2007–0517–0125. 

Wegman L (2011). Transmittal of Policy 

Assessment for the Review of the 

Particulate Matter National Ambient Air 

Quality Standards—Final Document. 

Memorandum from Lydia N. Wegman, 

Director, Health and Environmental 

Impacts Division, Office of Air Quality 

Planning and Standards, U.S. EPA to 

Holly Stallworth, Designated Federal 

Officer, Clean Air Scientific Advisory 

Committee, EPA Science Advisory Board 

Staff Office. April 20, 2011. Docket ID 

no. EPA–HQ–OAR–2007–0492–0338. 

WESTAR (2012). Comments of the Western 

States Air Resources Council on National 

Ambient Air Quality Standards for 

Particulate Matter; Proposed Rule. 

Docket No. EPA–HQ–OAR–2007–0492– 

9374. August 31, 2012. 

WHO (2008). Part 1: Guidance Document on 

Characterizing and Communicating 

Uncertainty in Exposure Assessment, 

Harmonization Project Document No. 6. 

Published under joint sponsorship of the 

World Health Organization, the 

International Labour Organization and 

the United Nations Environment 

Programme. WHO Press, World Health 

Organization, 20 Avenue Appia, 1211 

Geneva 27, Switzerland. 

Woodruff TJ; Darrow LA; Parker JD (2008). 

Air pollution and postneonatal infant 

mortality in the United States, 1999– 

2002. Environ Health Perspect, 116: 110– 

115. 

Yanosky JD; Paciorek CJ; Suh HH (2009). 

Predicting Chronic Fine and Coarse 

Particulate Exposures Using 

Spatiotemporal Models for the 

Northeastern and Midwestern United 

States. EHP, 117(4): 522–529. 

Zanobetti A; Schwartz J (2009). The effect of 

fine and coarse particulate air pollution 

on mortality: A national analysis. 

Environ Health Perspect, 117: 898–903. 

Zanobetti A. (2009). Personal communication 

with Dr. Antonella Zanobetti; email to 

Jason Sacks, U.S. EPA, NCEA. June 1, 

2009. Docket No. EPA–HQ–ORD–2007– 

0517–0064. 

Zeger S; Dominici F; McDermott A; Samet J 

(2008). Mortality in the Medicare 

population and chronic exposure to fine 

particulate air pollution in urban centers 

(2000–2005). Environ Health Perspect, 

116: 1614. 

Zwack LM; Paciorek CJ; Spengler JD; Levy JI 

(2011). Characterizing local traffic 

contributions to particulate air pollution 

in street canyons using mobile 

monitoring techniques. Atomspheric 

Environment 45 (2011), 2507–2514. 

List of Subjects 

40 CFR Part 50 

Environmental protection, Air 

pollution control, Carbon monoxide, 

Lead, Nitrogen dioxide, Ozone, 

Particulate matter, Sulfur oxides. 

40 CFR Part 51 

Environmental protection, 

Administrative practices and 

procedures, Air pollution control, 

Intergovernmental relations. 

40 CFR Part 52 

Environmental protection, 

Administrative practices and 

procedures, Air pollution control, 

Incorporation by reference, 

Intergovernmental relations. 

40 CFR Part 53 

Environmental protection, 

Administrative practice and procedure, 

Air pollution control, Intergovernmental 

relations, Reporting and recordkeeping 

requirements. 

40 CFR Part 58 

Environmental protection, 

Administrative practice and procedure, 

Air pollution control, Intergovernmental 

relations, Reporting and recordkeeping 

requirements. 

Dated: December 14, 2012. 

Lisa P. Jackson, 

Administrator. 

For the reasons set forth in the 

preamble, chapter I of title 40 of the 

Code of Federal Regulations is amended 

as follows: 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3277 

PART 50—NATIONAL PRIMARY AND 

SECONDARY AMBIENT AIR QUALITY 

STANDARDS 

■ 1. The authority citation for part 50 

continues to read as follows: 

Authority: 42 U.S.C. 7401 et seq. 

■ 2. Section 50.3 is revised to read as 

follows: 

§ 50.3 Reference conditions. 

All measurements of air quality that 

are expressed as mass per unit volume 

(e.g., micrograms per cubic meter) other 

than for particulate matter (PM2.5) 

standards contained in §§ 50.7, 50.13, 

and 50.18, and lead standards contained 

in § 50.16 shall be corrected to a 

reference temperature of 25 (deg) C and 

a reference pressure of 760 millimeters 

of mercury (1,013.2 millibars). 

Measurements of PM2.5 for purposes of 

comparison to the standards contained 

in §§ 50.7, 50.13, and 50.18, and of lead 

for purposes of comparison to the 

standards contained in § 50.16 shall be 

reported based on actual ambient air 

volume measured at the actual ambient 

temperature and pressure at the 

monitoring site during the measurement 

period. 

■ 3. Table 1 in § 50.14(c)(2)(vi) is 

revised to read as follows: 

§ 50.14 Treatment of air quality monitoring 

data influenced by exceptional events. 

* * * * * 

(c) * * * 

(2) * * * 

(vi) * * * 

TABLE 1—SPECIAL SCHEDULES FOR EXCEPTIONAL EVENT FLAGGING AND DOCUMENTATION SUBMISSION FOR DATA TO BE

USED IN INITIAL DESIGNATIONS FOR NEW OR REVISED NAAQS 

NAAQS pollutant/ 

standard/(level)/ 

promulgation date 

Air quality data 

collected 

for calendar year 

Event flagging & initial 

description deadline 

Detailed 

documentation 

submission deadline 

PM2.5/24-Hr Standard (35 μg/m3) 

Promulgated October 17, 2006.

2004–2006 .................................... October 1, 2007 ............................ April 15, 2008. 

Ozone/8-Hr Standard (0.075 ppm) 

Promulgated March 12, 2008.

2005–2007 ....................................

2008 ..............................................

2009 ..............................................

June 18, 2009 ...............................

June 18, 2009 ...............................

60 days after the end of the calendar quarter in which the 

event occurred or February 5, 

2010, whichever date occurs 

first. 

June 18, 2009. 

June 18, 2009. 

60 days after the end of the calendar quarter in which the 

event occurred or February 5, 

2010, whichever date occurs 

first. 

NO2/1-Hr Standard (100 ppb) Promulgated February 9, 2010.2008 ..............................................

2009 ..............................................

2010 ..............................................

July 1, 2010 ..................................

July 1, 2010 a ................................

April 1, 2011 .................................

January 22, 2011. 

January 22, 2011. 

July 1, 2011. 

SO2/1-Hr Standard (75 ppb) Promulgated June 22, 2010.2008 ..............................................

2009 ..............................................

2010 ..............................................

2011 ..............................................

October 1, 2010 ............................

October 1, 2010 ............................

June 1, 2011 .................................

60 days after the end of the calendar quarter in which the 

event occurred or March 31, 

2012, whichever date occurs 

first.

June 1, 2011. 

June 1, 2011. 

June 1, 2011. 

60 days after the end of the calendar quarter in which the 

event occurred or March 31, 

2012, whichever date occurs 

first. 

PM2.5/Primary Annual Standard 

(12 μg/m3) Promulgated December 14, 2012.

2010 and 2011 .............................

2012 ..............................................

2013 ..............................................

July 1, 2013 ..................................

July 1, 2013 a ................................

July 1, 2014 a ................................

December 12, 2013. 

December 12, 2013. 

August 1, 2014. 

aThis date is the same as the general schedule in 40 CFR 50.14. 

Note: The table of revised deadlines only applies to data EPA will use to establish the initial area designations for new or revised NAAQS. The 

general schedule applies for all other purposes, most notably, for data used by the EPA for redesignations to attainment. 

* * * * * 

■ 4. Add § 50.18 to read as follows: 

§ 50.18 National primary ambient air 

quality standards for PM2.5. 

(a) The national primary ambient air 

quality standards for PM2.5 are 12.0 

micrograms per cubic meter (mg/m3) 

annual arithmetic mean concentration 

and 35 mg/m3 24-hour average 

concentration measured in the ambient 

air as PM2.5 (particles with an 

aerodynamic diameter less than or equal 

to a nominal 2.5 micrometers) by either: 

(1) A reference method based on 

appendix L to this part and designated 

in accordance with part 53 of this 

chapter; or 

(2) An equivalent method designated 

in accordance with part 53 of this 

chapter. 

(b) The primary annual PM2.5

standard is met when the annual 

arithmetic mean concentration, as 

determined in accordance with 

appendix N of this part, is less than or 

equal to 12.0 mg/m3. 

(c) The primary 24-hour PM2.5

standard is met when the 98th 

percentile 24-hour concentration, as 

determined in accordance with 

appendix N of this part, is less than or 

equal to 35 mg/m3. 

■ 5. Appendix N to part 50 is revised to 

read as follows: 

Appendix N to Part 50—Interpretation 

of the National Ambient Air Quality 

Standards for PM2.5

1.0 General 

(a) This appendix explains the data 

handling conventions and computations 

necessary for determining when the national 

ambient air quality standards (NAAQS) for 

PM2.5 are met, specifically the primary and 

secondary annual and 24-hour PM2.5 NAAQS 

specified in § 50.7, 50.13, and 50.18. PM2.5 is 

defined, in general terms, as particles with an 

aerodynamic diameter less than or equal to 

a nominal 2.5 micrometers. PM2.5 mass 

concentrations are measured in the ambient 

air by a Federal Reference Method (FRM) 

based on appendix L of this part, as 

applicable, and designated in accordance 

with part 53 of this chapter; or by a Federal 

Equivalent Method (FEM) designated in 

accordance with part 53 of this chapter; or by 

an Approved Regional Method (ARM) 

designated in accordance with part 58 of this 

chapter. Only those FRM, FEM, and ARM 

measurements that are derived in accordance 

with part 58 of this chapter (i.e., that are 

deemed ‘‘suitable’’) shall be used in 

comparisons with the PM2.5 NAAQS. The 

data handling and computation procedures to 

be used to construct annual and 24-hour 


tkelley on DSK3SPTVN1PROD with 
3278 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

NAAQS metrics from reported PM2.5 mass 

concentrations, and the associated 

instructions for comparing these calculated 

metrics to the levels of the PM2.5 NAAQS, are 

specified in sections 2.0, 3.0, and 4.0 of this 

appendix. 

(b) Decisions to exclude, retain, or make 

adjustments to the data affected by 

exceptional events, including natural events, 

are made according to the requirements and 

process deadlines specified in §§ 50.1, 50.14 

and 51.930 of this chapter. 

(c) The terms used in this appendix are 

defined as follows: 

Annual mean refers to a weighted 

arithmetic mean, based on quarterly means, 

as defined in section 4.4 of this appendix. 

The Air Quality System (AQS) is EPA’s 

official repository of ambient air data. 

Collocated monitors refers to two or more 

air measurement instruments for the same 

parameter (e.g., PM2.5 mass) operated at the 

same site location, and whose placement is 

consistent with § 53.1 of this chapter. For 

purposes of considering a combined site 

record in this appendix, when two or more 

monitors are operated at the same site, one 

monitor is designated as the ‘‘primary’’ 

monitor with any additional monitors 

designated as ‘‘collocated.’’ It is implicit in 

these appendix procedures that the primary 

monitor and collocated monitor(s) are all 

deemed suitable for the applicable NAAQS 

comparison; however, it is not a requirement 

that the primary and monitors utilize the 

same specific sampling and analysis method. 

Combined site data record is the data set 

used for performing calculations in appendix 

N. It represents data for the primary monitors 

augmented with data from collocated 

monitors according to the procedure 

specified in section 3.0(d) of this appendix. 

Creditable samples are daily values in the 

combined site record that are given credit for 

data completeness. The number of creditable 

samples (cn) for a given year also governs 

which value in the sorted series of daily 

values represents the 98th percentile for that 

year. Creditable samples include daily values 

collected on scheduled sampling days and 

valid make-up samples taken for missed or 

invalidated samples on scheduled sampling 

days. 

Daily values refer to the 24-hour average 

concentrations of PM2.5 mass measured (or 

averaged from hourly measurements in AQS) 

from midnight to midnight (local standard 

time) from suitable monitors. 

Data substitution tests are diagnostic 

evaluations performed on an annual PM2.5

NAAQS design value (DV) or a 24-hour PM2.5

NAAQS DV to determine if those metrics, 

which are judged to be based on incomplete 

data in accordance with 4.1(b) or 4.2(b) of 

this appendix shall nevertheless be deemed 

valid for NAAQS comparisons, or 

alternatively, shall still be considered 

incomplete and not valid for NAAQS 

comparisons. There are two data substitution 

tests, the ‘‘minimum quarterly value’’ test 

and the ‘‘maximum quarterly value’’ test. 

Design values (DVs) are the 3-year average 

NAAQS metrics that are compared to the 

NAAQS levels to determine when a 

monitoring site meets or does not meet the 

NAAQS, calculated as shown in section 4. 

There are two separate DVs specified in this 

appendix: 

(1) The 3-year average of PM2.5 annual 

mean mass concentrations for each eligible 

monitoring site is referred to as the ‘‘annual 

PM2.5 NAAQS DV’’. 

(2) The 3-year average of annual 98th 

percentile 24-hour average PM2.5 mass 

concentration values recorded at each 

eligible monitoring site is referred to as the 

‘‘24-hour (or daily) PM2.5 NAAQS DV’’. 

Eligible sites are monitoring stations that 

meet the criteria specified in § 58.11 and 

§ 58.30 of this chapter, and thus are approved 

for comparison to the annual PM2.5 NAAQS. 

For the 24-hour PM2.5 NAAQS, all site 

locations that meet the criteria specified in 

§ 58.11 are approved (i.e., eligible) for 

NAAQS comparisons. 

Extra samples are non-creditable samples. 

They are daily values that do not occur on 

scheduled sampling days and that cannot be 

used as make-up samples for missed or 

invalidated scheduled samples. Extra 

samples are used in mean calculations and 

are included in the series of all daily values 

subject to selection as a 98th percentile 

value, but are not used to determine which 

value in the sorted list represents the 98th 

percentile. 

Make-up samples are samples collected to 

take the place of missed or invalidated 

required scheduled samples. Make-up 

samples can be made by either the primary 

or the collocated monitor. Make-up samples 

are either taken before the next required 

sampling day or exactly one week after the 

missed (or voided) sampling day. 

The maximum quarterly value data 

substitution test substitutes actual ‘‘high’’ 

reported daily PM2.5 values from the same 

site (specifically, the highest reported nonexcluded quarterly value(s) (year nonspecific) contained in the combined site 

record for the evaluated 3-year period) for 

missing daily values. 

The minimum quarterly value data 

substitution test substitutes actual ‘‘low’’ 

reported daily PM2.5 values from the same 

site (specifically, the lowest reported 

quarterly value(s) (year non-specific) 

contained in the combined site record for the 

evaluated 3-year period) for missing daily 

values. 

98th percentile is the smallest daily value 

out of a year of PM2.5 mass monitoring data 

below which no more than 98 percent of all 

daily values fall using the ranking and 

selection method specified in section 4.5(a) 

of this appendix. 

Primary monitors are suitable monitors 

designated by a state or local agency in their 

annual network plan (and in AQS) as the 

default data source for creating a combined 

site record for purposes of NAAQS 

comparisons. If there is only one suitable 

monitor at a particular site location, then it 

is presumed to be a primary monitor. 

Quarter refers to a calendar quarter (e.g., 

January through March). 

Quarterly data capture rate is the 

percentage of scheduled samples in a 

calendar quarter that have corresponding 

valid reported sample values. Quarterly data 

capture rates are specifically calculated as 

the number of creditable samples for the 

quarter divided by the number of scheduled 

samples for the quarter, the result then 

multiplied by 100 and rounded to the nearest 

integer. 

Scheduled PM2.5 samples refers to those 

reported daily values which are consistent 

with the required sampling frequency (per 

§ 58.12 of this chapter) for the primary 

monitor, or those that meet the special 

exception noted in section 3.0(e) of this 

appendix. 

Seasonal sampling is the practice of 

collecting data at a reduced frequency during 

a season of expected low concentrations. 

Suitable monitors are instruments that use 

sampling and analysis methods approved for 

NAAQS comparisons. For the annual and 24- 

hour PM2.5 NAAQS, suitable monitors 

include all FRMs, and all FEMs/ARMs except 

those specific continuous FEMs/ARMs 

disqualified by a particular monitoring 

agency network in accordance with 

§ 58.10(b)(13) and approved by the EPA 

Regional Administrator per § 58.11(e) of this 

chapter. 

Test design values (TDV) are numerical 

values that used in the data substitution tests 

described in sections 4.1(c)(i), 4.1(c)(ii) and 

4.2(c)(i) of this appendix to determine if the 

PM2.5 NAAQS DV with incomplete data are 

judged to be valid for NAAQS comparisons. 

There are two TDVs: TDVmin to determine if 

the NAAQS is not met and is used in the 

‘‘minimum quarterly value’’ data substitution 

test and TDVmax to determine if the NAAQS 

is met and is used in the ‘‘maximum 

quarterly value’’ data substitution test. These 

TDV’s are derived by substituting historically 

low or historically high daily concentration 

values for missing data in an incomplete 

year(s). 

Year refers to a calendar year. 

2.0 Monitoring Considerations 

(a) Section 58.30 of this chapter provides 

special considerations for data comparisons 

to the annual PM2.5 NAAQS. 

(b) Monitors meeting the network technical 

requirements detailed in § 58.11 of this 

chapter are suitable for comparison with the 

NAAQS for PM2.5. 

(c) Section 58.12 of this chapter specifies 

the required minimum frequency of sampling 

for PM2.5. Exceptions to the specified 

sampling frequencies, such as seasonal 

sampling, are subject to the approval of the 

EPA Regional Administrator and must be 

documented in the state or local agency 

Annual Monitoring Network Plan as required 

in § 58.10 of this chapter and also in AQS. 

3.0 Requirements for Data Use and Data 

Reporting for Comparisons With the NAAQS 

for PM2.5

(a) Except as otherwise provided in this 

appendix, all valid FRM/FEM/ARM PM2.5

mass concentration data produced by 

suitable monitors that are required to be 

submitted to AQS, or otherwise available to 

EPA, meeting the requirements of part 58 of 

this chapter including appendices A, C, and 

E shall be used in the DV calculations. 

Generally, EPA will only use such data if 

they have been certified by the reporting 

organization (as prescribed by § 58.15 of this 

chapter); however, data not certified by the 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3279 

reporting organization can nevertheless be 

used, if the deadline for certification has 

passed and EPA judges the data to be 

complete and accurate. 

(b) PM2.5 mass concentration data 

(typically collected hourly for continuous 

instruments and daily for filter-based 

instruments) shall be reported to AQS in 

micrograms per cubic meter (mg/m3) to at 

least one decimal place. If concentrations are 

reported to one decimal place, additional 

digits to the right of the tenths decimal place 

shall be truncated. If concentrations are 

reported to AQS with more than one decimal 

place, AQS will truncate the value to one 

decimal place for NAAQS usage (i.e., for 

implementing the procedures in this 

appendix). In situations where suitable PM2.5

data are available to EPA but not reported to 

AQS, the same truncation protocol shall be 

applied to that data. In situations where 

PM2.5 mass data are submitted to AQS, or are 

otherwise available, with less precision than 

specified above, these data shall nevertheless 

still be deemed appropriate for NAAQS 

usage. 

(c) Twenty-four-hour average 

concentrations will be computed in AQS 

from submitted hourly PM2.5 concentration 

data for each corresponding day of the year 

and the result will be stored in the first, or 

start, hour (i.e., midnight, hour ‘0’) of the 24- 

hour period. A 24-hour average concentration 

shall be considered valid if at least 75 

percent of the hourly averages (i.e., 18 hourly 

values) for the 24-hour period are available. 

In the event that less than all 24 hourly 

average concentrations are available (i.e., less 

than 24, but at least 18), the 24-hour average 

concentration shall be computed on the basis 

of the hours available using the number of 

available hours within the 24-hour period as 

the divisor (e.g., 19, if 19 hourly values are 

available). Twenty-four-hour periods with 

seven or more missing hours shall also be 

considered valid if, after substituting zero for 

all missing hourly concentrations, the 

resulting 24-hour average daily value is 

greater than the level of the 24-hour PM2.5

NAAQS (i.e., greater than or equal to 35.5 mg/ 

m3). Twenty-four hour average PM2.5 mass 

concentrations that are averaged in AQS from 

hourly values will be truncated to one 

decimal place, consistent with the data 

handling procedure for the reported hourly 

(and also 24-hour filter-based) data. 

(d) All calculations shown in this appendix 

shall be implemented on a site-level basis. 

Site level concentration data shall be 

processed as follows: 

(1) The default dataset for PM2.5 mass 

concentrations for a site shall consist of the 

measured concentrations recorded from the 

designated primary monitor(s). All daily 

values produced by the primary monitor are 

considered part of the site record; this 

includes all creditable samples and all extra 

samples. 

(2) Data for the primary monitors shall be 

augmented as much as possible with data 

from collocated monitors. If a valid daily 

value is not produced by the primary monitor 

for a particular day (scheduled or otherwise), 

but a value is available from a collocated 

monitor, then that collocated value shall be 

considered part of the combined site data 

record. If more than one collocated daily 

value is available, the average of those valid 

collocated values shall be used as the daily 

value. The data record resulting from this 

procedure is referred to as the ‘‘combined site 

data record.’’ 

(e) All daily values in a combined site data 

record are used in the calculations specified 

in this appendix; however, not all daily 

values are given credit towards data 

completeness requirements. Only creditable 

samples are given credit for data 

completeness. Creditable samples include 

daily values in the combined site record that 

are collected on scheduled sampling days 

and valid make-up samples taken for missed 

or invalidated samples on scheduled 

sampling days. Days are considered 

scheduled according to the required 

sampling frequency of the designated 

primary monitor with one exception. The 

exception is, if a collocated continuous FEM/ 

ARM monitor has a more intensive sampling 

frequency than the primary FRM monitor, 

then samples contributed to the combined 

site record from that continuous FEM/ARM 

monitor are always considered scheduled 

and, hence, also creditable. Daily values in 

the combined site data record that are 

reported for nonscheduled days, but that are 

not valid make-up samples are referred to as 

extra samples. 

4.0 Comparisons With the Annual and 24- 

Hour PM2.5 NAAQS 

4.1 Annual PM2.5 NAAQS 

(a) The primary annual PM2.5 NAAQS is 

met when the annual PM2.5 NAAQS DV is 

less than or equal to 12.0 mg/m3 at each 

eligible monitoring site. The secondary 

annual PM2.5 NAAQS is met when the annual 

PM2.5 NAAQS DV is less than or equal to 15.0 

mg/m3 at each eligible monitoring site. 

(b) Three years of valid annual means are 

required to produce a valid annual PM2.5

NAAQS DV. A year meets data completeness 

requirements when quarterly data capture 

rates for all four quarters are at least 75 

percent. However, years with at least 11 

creditable samples in each quarter shall also 

be considered valid if the resulting annual 

mean or resulting annual PM2.5 NAAQS DV 

(rounded according to the conventions of 

section 4.3 of this appendix) is greater than 

the level of the applicable primary or 

secondary annual PM2.5 NAAQS. 

Furthermore, where the explicit 75 percent 

data capture and/or 11 sample minimum 

requirements are not met, the 3-year annual 

PM2.5 NAAQS DV shall still be considered 

valid if it passes at least one of the two data 

substitution tests stipulated below. 

(c) In the case of one, two, or three years 

that do not meet the completeness 

requirements of section 4.1(b) of this 

appendix and thus would normally not be 

useable for the calculation of a valid annual 

PM2.5 NAAQS DV, the annual PM2.5 NAAQS 

DV shall nevertheless be considered valid if 

one of the test conditions specified in 

sections 4.1(c)(i) and 4.1(c)(ii) of this 

appendix is met. 

(i) An annual PM2.5 NAAQS DV that is 

above the level of the NAAQS can be 

validated if it passes the minimum quarterly 

value data substitution test. This type of data 

substitution is permitted only if there are at 

least 30 days across the three quarters of the 

three years under consideration (e.g., 

collectively, quarter 1 of year 1, quarter 1 of 

year 2 and quarter 1 of year 3) from which 

to select the quarter-specific low value. Data 

substitution will be performed in all quarter 

periods that have less than 11 creditable 

samples. 

Procedure: Identify for each deficient 

quarter (i.e., those with less than 11 

creditable samples) the lowest reported daily 

value for that quarter, looking across those 

three months of all three years under 

consideration. If after substituting the lowest 

reported daily value for a quarter for (11¥ 

cn) daily values in the matching deficient 

quarter(s) (i.e., to bring the creditable number 

for those quarters up to 11), the procedure 

yields a recalculated annual PM2.5 NAAQS 

test DV (TDVmin) that is greater than the level 

of the standard, then the annual PM2.5

NAAQS DV is deemed to have passed the 

diagnostic test and is valid, and the annual 

PM2.5 NAAQS is deemed to have been 

violated in that 3-year period. 

(ii) An annual PM2.5 NAAQS DV that is 

equal to or below the level of the NAAQS can 

be validated if it passes the maximum 

quarterly value data substitution test. This 

type of data substitution is permitted only if 

there is at least 50 percent data capture in 

each quarter that is deficient of 75 percent 

data capture in each of the three years under 

consideration. Data substitution will be 

performed in all quarter periods that have 

less than 75 percent data capture but at least 

50 percent data capture. If any quarter has 

less than 50 percent data capture then this 

substitution test cannot be used. 

Procedure: Identify for each deficient 

quarter (i.e., those with less than 75 percent 

but at least 50 percent data capture) the 

highest reported daily value for that quarter, 

excluding state-flagged data affected by 

exceptional events which have been 

approved for exclusion by the Administrator, 

looking across those three quarters of all 

three years under consideration. If after 

substituting the highest reported daily PM2.5

value for a quarter for all missing daily data 

in the matching deficient quarter(s) (i.e., to 

make those quarters 100 percent complete), 

the procedure yields a recalculated annual 

PM2.5 NAAQS test DV (TDVmax) that is less 

than or equal to the level of the standard, 

then the annual PM2.5 NAAQS DV is deemed 

to have passed the diagnostic test and is 

valid, and the annual PM2.5 NAAQS is 

deemed to have been met in that 3-year 

period. 

(d) An annual PM2.5 NAAQS DV based on 

data that do not meet the completeness 

criteria stated in 4(b) and also do not satisfy 

the test conditions specified in section 4(c), 

may also be considered valid with the 

approval of, or at the initiative of, the EPA 

Administrator, who may consider factors 

such as monitoring site closures/moves, 

monitoring diligence, the consistency and 

levels of the daily values that are available, 

and nearby concentrations in determining 

whether to use such data. 

(e) The equations for calculating the annual 

PM2.5 NAAQS DVs are given in section 4.4 

of this appendix. 


tkelley on DSK3SPTVN1PROD with 
3280 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

4.2 Twenty-four-hour PM2.5 NAAQS 

(a) The primary and secondary 24-hour 

PM2.5 NAAQS are met when the 24-hour 

PM2.5 NAAQS DV at each eligible monitoring 

site is less than or equal to 35 mg/m3. 

(b) Three years of valid annual PM2.5 98th 

percentile mass concentrations are required 

to produce a valid 24-hour PM2.5 NAAQS DV. 

A year meets data completeness requirements 

when quarterly data capture rates for all four 

quarters are at least 75 percent. However, 

years shall be considered valid, 

notwithstanding quarters with less than 

complete data (even quarters with less than 

11 creditable samples, but at least one 

creditable sample must be present for the 

year), if the resulting annual 98th percentile 

value or resulting 24-hour NAAQS DV 

(rounded according to the conventions of 

section 4.3 of this appendix) is greater than 

the level of the standard. Furthermore, where 

the explicit 75 percent quarterly data capture 

requirement is not met, the 24-hour PM2.5

NAAQS DV shall still be considered valid if 

it passes the maximum quarterly value data 

substitution test. 

(c) In the case of one, two, or three years 

that do not meet the completeness 

requirements of section 4.2(b) of this 

appendix and thus would normally not be 

useable for the calculation of a valid 24-hour 

PM2.5 NAAQS DV, the 24-hour PM2.5 NAAQS 

DV shall nevertheless be considered valid if 

the test conditions specified in section 

4.2(c)(i) of this appendix are met. 

(i) A PM2.5 24-hour mass NAAQS DV that 

is equal to or below the level of the NAAQS 

can be validated if it passes the maximum 

quarterly value data substitution test. This 

type of data substitution is permitted only if 

there is at least 50 percent data capture in 

each quarter that is deficient of 75 percent 

data capture in each of the three years under 

consideration. Data substitution will be 

performed in all quarters that have less than 

75 percent data capture but at least 50 

percent data capture. If any quarter has less 

than 50 percent data capture then this 

substitution test cannot be used. 

Procedure: Identify for each deficient 

quarter (i.e., those with less than 75 percent 

but at least 50 percent data capture) the 

highest reported daily PM2.5 value for that 

quarter, excluding state-flagged data affected 

by exceptional events which have been 

approved for exclusion by the Regional 

Administrator, looking across those three 

quarters of all three years under 

consideration. If, after substituting the 

highest reported daily maximum PM2.5 value 

for a quarter for all missing daily data in the 

matching deficient quarter(s) (i.e., to make 

those quarters 100 percent complete), the 

procedure yields a recalculated 3-year 24- 

hour NAAQS test DV (TDVmax) less than or 

equal to the level of the standard, then the 

24-hour PM2.5 NAAQS DV is deemed to have 

passed the diagnostic test and is valid, and 

the 24-hour PM2.5 NAAQS is deemed to have 

been met in that 3-year period. 

(d) A 24-hour PM2.5 NAAQS DV based on 

data that do not meet the completeness 

criteria stated in section 4(b) of this appendix 

and also do not satisfy the test conditions 

specified in section 4(c) of this appendix, 

may also be considered valid with the 

approval of, or at the initiative of, the EPA 

Administrator, who may consider factors 

such as monitoring site closures/moves, 

monitoring diligence, the consistency and 

levels of the daily values that are available, 

and nearby concentrations in determining 

whether to use such data. 

(e) The procedures and equations for 

calculating the 24-hour PM2.5 NAAQS DVs 

are given in section 4.5 of this appendix. 

4.3 Rounding Conventions. For the 

purposes of comparing calculated PM2.5

NAAQS DVs to the applicable level of the 

standard, it is necessary to round the final 

results of the calculations described in 

sections 4.4 and 4.5 of this appendix. Results 

for all intermediate calculations shall not be 

rounded. 

(a) Annual PM2.5 NAAQS DVs shall be 

rounded to the nearest tenth of a mg/m3

(decimals x.x5 and greater are rounded up to 

the next tenth, and any decimal lower than 

x.x5 is rounded down to the nearest tenth). 

(b) Twenty-four-hour PM2.5 NAAQS DVs 

shall be rounded to the nearest 1 mg/m3

(decimals 0.5 and greater are rounded up to 

the nearest whole number, and any decimal 

lower than 0.5 is rounded down to the 

nearest whole number). 

4.4 Equations for the Annual PM2.5 NAAQS. 

(a) An annual mean value for PM2.5 is 

determined by first averaging the daily values 

of a calendar quarter using equation 1 of this 

appendix: 

Where: 

X ̄ q,y = the mean for quarter q of the year y; 

nq = the number of daily values in the 

quarter; and 

xi q,y = the ith value in quarter q for year y. 

(b) Equation 2 of this appendix is then 

used to calculate the site annual mean: 

Where: 

X ̄ y = the annual mean concentration for year 

y (y = 1, 2, or 3); and 

X ̄ q,y = the mean for quarter q of year y (result 

of equation 1). 

(c) The annual PM2.5 NAAQS DV is 

calculated using equation 3 of this appendix: 

Where: 

X ̄ = the annual PM2.5 NAAQS DV; and 

X ̄ y = the annual mean for year y (result of 

equation 2) 

(d) The annual PM2.5 NAAQS DV is 

rounded according to the conventions in 

section 4.3 of this appendix before 

comparisons with the levels of the primary 

and secondary annual PM2.5 NAAQS are 

made. 

4.5 Procedures and Equations for the 24- 

Hour PM2.5 NAAQS 

(a) When the data for a particular site and 

year meet the data completeness 

requirements in section 4.2 of this appendix, 

calculation of the 98th percentile is 

accomplished by the steps provided in this 

subsection. Table 1 of this appendix shall be 

used to identify annual 98th percentile 

values. 

Identification of annual 98th percentile 

values using the Table 1 procedure will be 

based on the creditable number of samples 

(as described below), rather than on the 

actual number of samples. Credit will not be 

granted for extra (non-creditable) samples. 

Extra samples, however, are candidates for 

selection as the annual 98th percentile. [The 

creditable number of samples will determine 

how deep to go into the data distribution, but 

all samples (creditable and extra) will be 

considered when making the percentile 

assignment.] The annual creditable number 

of samples is the sum of the four quarterly 

creditable number of samples. 

Procedure: Sort all the daily values from a 

particular site and year by descending value. 

(For example: (x[1], x[2], x[3], * * *, x[n]). 

In this case, x[1] is the largest number and 

x[n] is the smallest value.) The 98th 

percentile value is determined from this 

sorted series of daily values which is ordered 

from the highest to the lowest number. Using 

the left column of Table 1, determine the 

appropriate range for the annual creditable 

number of samples for year y (cny) (e.g., for 

120 creditable samples per year, the 

appropriate range would be 101 to 150). The 

corresponding ‘‘n’’ value in the right column 

identifies the rank of the annual 98th 

percentile value in the descending sorted list 

of site specific daily values for year y (e.g., 

for the range of 101 to 150, n would be 3). 

Thus, P0.98, y = the nth largest value (e.g., for 

the range of 101 to 150, the 98th percentile 

value would be the third highest value in the 

sorted series of daily values. 


tkelley on DSK3SPTVN1PROD with ER15JA13.005</GPH> ER15JA13.006</GPH> ER15JA13.007</GPH>
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3281 

TABLE 1 

Annual number of creditable samples for year y (cny) 

The 98th percentile for year y 

(P0.98,y), is the nth maximum 

24-hour average value for the 

year where n is the listed number 

1 to 50 ........................................................................................................................................................................ 1 

51 to 100 .................................................................................................................................................................... 2 

101 to 150 .................................................................................................................................................................. 3 

151 to 200 .................................................................................................................................................................. 4 

201 to 250 .................................................................................................................................................................. 5 

251 to 300 .................................................................................................................................................................. 6 

301 to 350 .................................................................................................................................................................. 7 

351 to 366 .................................................................................................................................................................. 8 

(b) The 24-hour PM2.5 NAAQS DV is then 

calculated by averaging the annual 98th 

percentiles using equation 4 of this appendix: 

P0.98,y

Where: 

P ̄ 0.98 = the 24-hour PM2.5 NAAQS DV; and 

P0.98, y = the annual 98th percentile for year 

y 

(c) The 24-hour PM2.5 NAAQS DV is 

rounded according to the conventions in 

section 4.3 of this appendix before a 

comparison with the level of the primary and 

secondary 24-hour NAAQS are made. 

PART 51—REQUIREMENTS FOR 

PREPARATION, ADOPTION, AND 

SUBMITTAL OF IMPLEMENTATION 

PLANS 

■ 6. The authority citation for part 51 

continues to read as follows: 

Authority: 23 U.S.C. 101; 42 U.S.C. 7401– 

7671q. 

Subpart I—[Amended] 

■ 7. In § 51.166, add paragraph (i)(10) to 

read as follows: 

§ 51.166 Prevention of significant 

deterioration of air quality. 

* * * * * 

(i) * * * 

(10) The plan may provide that the 

requirements of paragraph (k)(1) of this 

section shall not apply to a stationary 

source or modification with respect to 

the national ambient air quality 

standards for PM2.5 in effect on March 

18, 2013 if: 

(i) The reviewing authority has 

determined a permit application subject 

to this section to be complete on or 

before December 14, 2012. Instead, the 

requirements in paragraph (k)(1) of this 

section shall apply with respect to the 

national ambient air quality standards 

for PM2.5 in effect at the time the 

reviewing authority determined the 

permit application to be complete; or 

(ii) The reviewing authority has first 

published before March 18, 2013 a 

public notice of a preliminary 

determination for the permit application 

subject to this section. Instead, the 

requirements in paragraph (k)(1) of this 

section shall apply with respect to the 

national ambient air quality standards 

for PM2.5 in effect at the time of first 

publication of a public notice on the 

preliminary determination. 

* * * * * 

PART 52—APPROVAL AND 

PROMULGATION OF 

IMPLEMENTATION PLANS 

■ 8. The authority citation for part 52 

continues to read as follows: 

Authority: 42 U.S.C. 7401, et seq. 

■ 9. In § 52.21, add paragraph (i)(11) to 

read as follows: 

§ 52.21 Prevention of significant 

deterioration of air quality. 

* * * * * 

(i) * * * 

(11) The requirements of paragraph 

(k)(1) of this section shall not apply to 

a stationary source or modification with 

respect to the national ambient air 

quality standards for PM2.5 in effect on 

March 18, 2013 if: 

(i) The Administrator has determined 

a permit application subject to this 

section to be complete on or before 

December 14, 2012. Instead, the 

requirements in paragraph (k)(1) of this 

section shall apply with respect to the 

national ambient air quality standards 

for PM2.5 in effect at the time the 

Administrator determined the permit 

application to be complete; or 

(ii) The Administrator has first 

published before March 18, 2013 a 

public notice that a draft permit subject 

to this section has been prepared. 

Instead, the requirements in paragraph 

(k)(1) of this section shall apply with 

respect to the national ambient air 

quality standards for PM2.5 in effect on 

the date the Administrator first 

published a public notice that a draft 

permit has been prepared. 

* * * * * 

PART 53—AMBIENT AIR MONITORING 

REFERENCE AND EQUIVALENT 

METHODS 

■ 10. The authority citation for part 53 

continues to read as follows: 

Authority: Section 301(a) of the CAA (42 

U.S.C. sec. 1857g(a)), as amended by sec. 

15(c)(2) of Pub. L. 91–604, 84 Stat. 1713, 

unless otherwise noted. 

■ 11. In § 53.9, revise paragraph (c) to 

read as follows: 

§ 53.9 Conditions of designation. 

* * * * * 

(c) Any analyzer, PM10 sampler, PM2.5

sampler, or PM10-2.5 sampler offered for 

sale as part of an FRM or FEM shall 

function within the limits of the 

performance specifications referred to in 

§ 53.20(a), § 53.30(a), § 53.35, § 53.50, or 

§ 53.60, as applicable, for at least 1 year 

after delivery and acceptance when 

maintained and operated in accordance 

with the manual referred to in 

§ 53.4(b)(3). 

* * * * * 

PART 58—AMBIENT AIR QUALITY 

SURVEILLANCE 

■ 12. The authority citation of part 58 

continues to read as follows: 

Authority: 42 U.S.C. 7403, 7405, 7410, 

7414, 7601, 7611, 7614, and 7619. 

■ 13. Section 58.1 is amended by adding 

in alphabetical order a definition for 

‘‘Area-wide’’ and by removing the 

definition for ‘‘Community monitoring 

zone (CMZ)’’ to read as follows: 

§ 58.1 Definitions. 

* * * * * 

Area-wide means all monitors sited at 

neighborhood, urban, and regional 


tkelley on DSK3SPTVN1PROD with ER15JA13.008</GPH>
3282 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

scales, as well as those monitors sited at 

either micro- or middle-scale that are 

representative of many such locations in 

the same CBSA. 

* * * * * 

■ 14. Section 58.10 is amended as 

follows: 

■ a. By revising paragraph (a)(2). 

■ b. By adding paragraph (a)(8). 

■ c. By adding paragraph (b)(13). 

■ d. By revising paragraph (c). 

■ e. By revising paragraph (d). 

§ 58.10 Annual monitoring network plan 

and periodic network assessment. 

(a) * * * 

(2) Any annual monitoring network 

plan that proposes SLAMS network 

modifications (including new 

monitoring sites, new determinations 

that data are not of sufficient quality to 

be compared to the NAAQS, and 

changes in identification of monitors as 

suitable or not suitable for comparison 

against the annual PM2.5 NAAQS) is 

subject to the approval of the EPA 

Regional Administrator, who shall 

provide opportunity for public comment 

and shall approve or disapprove the 

plan and schedule within 120 days. If 

the State or local agency has already 

provided a public comment opportunity 

on its plan and has made no changes 

subsequent to that comment 

opportunity, and has submitted the 

received comments together with the 

plan, the Regional Administrator is not 

required to provide a separate 

opportunity for comment. 

* * * 

(8)(i) A plan for establishing near-road 

PM2.5 monitoring sites in CBSAs having 

2.5 million or more persons, in 

accordance with the requirements of 

appendix D to this part, shall be 

submitted as part of the annual 

monitoring network plan to the EPA 

Regional Administrator by July 1, 2014. 

The plan shall provide for these 

required monitoring stations to be 

operational by January 1, 2015. 

(ii) A plan for establishing near-road 

PM2.5 monitoring sites in CBSAs having 

1 million or more persons, but less than 

2.5 million persons, in accordance with 

the requirements of appendix D to this 

part, shall be submitted as part of the 

annual monitoring network plan to the 

EPA Regional Administrator by July 1, 

2016. The plan shall provide for these 

required monitoring stations to be 

operational by January 1, 2017. 

(b) * * * 

(13) The identification of any PM2.5

FEMs and/or ARMs used in the 

monitoring agency’s network where the 

data are not of sufficient quality such 

that data are not to be compared to the 

NAAQS. For required SLAMS where the 

agency identifies that the PM2.5 Class III 

FEM or ARM does not produce data of 

sufficient quality for comparison to the 

NAAQS, the monitoring agency must 

ensure that an operating FRM or filterbased FEM meeting the sample 

frequency requirements described in 

§ 58.12 or other Class III PM2.5 FEM or 

ARM with data of sufficient quality is 

operating and reporting data to meet the 

network design criteria described in 

appendix D to this part. 

(c) The annual monitoring network 

plan must document how state and local 

agencies provide for the review of 

changes to a PM2.5 monitoring network 

that impact the location of a violating 

PM2.5 monitor. The affected state or 

local agency must document the process 

for obtaining public comment and 

include any comments received through 

the public notification process within 

their submitted plan. 

(d) The state, or where applicable 

local, agency shall perform and submit 

to the EPA Regional Administrator an 

assessment of the air quality 

surveillance system every 5 years to 

determine, at a minimum, if the network 

meets the monitoring objectives defined 

in appendix D to this part, whether new 

sites are needed, whether existing sites 

are no longer needed and can be 

terminated, and whether new 

technologies are appropriate for 

incorporation into the ambient air 

monitoring network. The network 

assessment must consider the ability of 

existing and proposed sites to support 

air quality characterization for areas 

with relatively high populations of 

susceptible individuals (e.g., children 

with asthma), and, for any sites that are 

being proposed for discontinuance, the 

effect on data users other than the 

agency itself, such as nearby states and 

tribes or health effects studies. The 

state, or where applicable local, agency 

must submit a copy of this 5-year 

assessment, along with a revised annual 

network plan, to the Regional 

Administrator. The assessments are due 

every five years beginning July 1, 2010. 

* * * * * 

■ 15. Section 58.11 is amended by 

adding paragraph (e) to read as follows: 

§ 58.11 Network technical requirements. 

* * * * * 

(e) State and local governments must 

assess data from Class III PM2.5 FEM and 

ARM monitors operated within their 

network using the performance criteria 

described in table C–4 to subpart C of 

part 53 of this chapter, for cases where 

the data are identified as not of 

sufficient comparability to a collocated 

FRM, and the monitoring agency 

requests that the FEM or ARM data 

should not be used in comparison to the 

NAAQS. These assessments are required 

in the monitoring agency’s annual 

monitoring network plan described in 

§ 58.10(b) for cases where the FEM or 

ARM is identified as not of sufficient 

comparability to a collocated FRM. For 

these collocated PM2.5 monitors the 

performance criteria apply with the 

following additional provisions: 

(1) The acceptable concentration 

range (Rj), mg/m3 may include values 

down to 0 mg/m3. 

(2) The minimum number of test sites 

shall be at least one; however, the 

number of test sites will generally 

include all locations within an agency’s 

network with collocated FRMs and 

FEMs or ARMs. 

(3) The minimum number of methods 

shall include at least one FRM and at 

least one FEM or ARM. 

(4) Since multiple FRMs and FEMs 

may not be present at each site; the 

precision statistic requirement does not 

apply, even if precision data are 

available. 

(5) All seasons must be covered with 

no more than thirty-six consecutive 

months of data in total aggregated 

together. 

(6) The key statistical metric to 

include in an assessment is the bias 

(both additive and multiplicative) of the 

PM2.5 continuous FEM(s) compared to a 

collocated FRM(s). Correlation is 

required to be reported in the 

assessment, but failure to meet the 

correlation criteria, by itself, is not 

cause to exclude data from a continuous 

FEM monitor. 

■ 16. Section 58.12 is amended by 

revising paragraph (d)(1)(iii) and by 

removing and reserving paragraph (f)(2) 

to read as follows: 

§ 58.12 Operating schedules. 

* * * * * 

(d) * * * 

(1) * * * 

(iii) Required SLAMS stations whose 

measurements determine the 24-hour 

design value for their area and whose 

data are within plus or minus 5 percent 

of the level of the 24-hour PM2.5 NAAQS 

must have an FRM or FEM operate on 

a daily schedule if that area’s design 

value for the annual NAAQS is less than 

the level of the annual PM2.5 standard. 

A continuously operating FEM or ARM 

PM2.5 monitor satisfies this requirement 

unless it is identified in the monitoring 

agency’s annual monitoring network 

plan as not appropriate for comparison 

to the NAAQS. 

* * * * * 

(f) * * * 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3283 

(2) [Reserved] 

* * * * * 

■ 17. Section 58.13 is amended by 

adding paragraph (f) to read as follows: 

§ 58.13 Monitoring network completion. 

* * * * * 

(f) PM2.5 monitors required in nearroad environments as described in 

appendix D to this part, must be 

physically established and operating 

under all of the requirements of this 

part, including the requirements of 

appendices A, C, D, and E to this part, 

no later than: 

(1) January 1, 2015 for PM2.5 monitors 

in CBSAs having 2.5 million persons or 

more; or 

(2) January 1, 2017 for PM2.5 monitors 

in CBSAs having 1 million or more, but 

less than 2.5 million persons. 

■ 18. Section 58.16 is amended by 

revising paragraphs (a) and (f) to read as 

follows: 

§ 58.16 Data submittal and archiving 

requirements. 

(a) The state, or where appropriate, 

local agency, shall report to the 

Administrator, via AQS all ambient air 

quality data and associated quality 

assurance data for SO2; CO; O3; NO2; 

NO; NOy; NOX; Pb-TSP mass 

concentration; Pb-PM10 mass 

concentration; PM10 mass concentration; 

PM2.5 mass concentration; for filterbased PM2.5 FRM/FEM the field blank 

mass, sampler-generated average daily 

temperature, and sampler-generated 

average daily pressure; chemically 

speciated PM2.5 mass concentration 

data; PM10-2.5 mass concentration; 

meteorological data from NCore and 

PAMS sites; average daily temperature 

and average daily pressure for Pb sites 

if not already reported from sampler 

generated records; and metadata records 

and information specified by the AQS 

Data Coding Manual (http:// 

www.epa.gov/ttn/airs/airsaqs/manuals/ 

manuals.htm). The state, or where 

appropriate, local agency, may report 

site specific meteorological 

measurements generated by onsite 

equipment (meteorological instruments, 

or sampler generated) or measurements 

from the nearest airport reporting 

ambient pressure and temperature. Such 

air quality data and information must be 

submitted directly to the AQS via 

electronic transmission on the specified 

quarterly schedule described in 

paragraph (b) of this section. 

* * * * * 

(f) The state, or where applicable, 

local agency shall archive all PM2.5, 

PM10, and PM10-2.5 filters from manual 

low-volume samplers (samplers having 

flow rates less than 200 liters/minute) 

from all SLAMS sites for a minimum 

period of 5 years after collection. These 

filters shall be made available for 

supplemental analyses, including 

destructive analyses if necessary, at the 

request of EPA or to provide 

information to state and local agencies 

on particulate matter composition. 

Other Federal agencies may request 

access to filters for purposes of 

supporting air quality management or 

community health—such as biological 

assay—through the applicable EPA 

Regional Administrator. The filters shall 

be archived according to procedures 

approved by the Administrator, which 

shall include cold storage of filters after 

post-sampling laboratory analyses for at 

least 12 months following field 

sampling. The EPA recommends that 

particulate matter filters be archived for 

longer periods, especially for key sites 

in making NAAQS-related decisions or 

for supporting health-related air 

pollution studies. 

* * * * * 

■ 19. Section 58.20 is amended by 

revising paragraph (c) to read as follows: 

§ 58.20 Special purpose monitors (SPM). 

* * * * * 

(c) All data from an SPM using an 

FRM, FEM, or ARM which has operated 

for more than 24 months are eligible for 

comparison to the relevant NAAQS, 

subject to the conditions of §§ 58.11(e) 

and 58.30, unless the air monitoring 

agency demonstrates that the data came 

from a particular period during which 

the requirements of appendix A, 

appendix C, or appendix E to this part 

were not met, subject to review and EPA 

Regional Office approval as part of the 

annual monitoring network plan 

described in § 58.10. 

* * * * * 

■ 20. The heading for Subpart D is 

revised to read as follows: 

Subpart D—Comparability of Ambient 

Data to the NAAQS 

■ 21. Section 58.30 is amended by 

revising paragraph (a) to read as follows: 

§ 58.30 Special considerations for data 

comparisons to the NAAQS. 

(a) Comparability of PM2.5 data. The 

primary and secondary annual and 24- 

hour PM2.5 NAAQS are described in part 

50 of this chapter. Monitors that follow 

the network technical requirements 

specified in § 58.11 are eligible for 

comparison to the NAAQS subject to the 

additional requirements of this section. 

PM2.5 measurement data from all 

eligible monitors are comparable to the 

24-hour PM2.5 NAAQS. PM2.5

measurement data from all eligible 

monitors that are representative of areawide air quality are comparable to the 

annual PM2.5 NAAQS. Consistent with 

appendix D to this part, section 4.7.1, 

when micro- or middle-scale PM2.5

monitoring sites collectively identify a 

larger region of localized high ambient 

PM2.5 concentrations, such sites would 

be considered representative of an areawide location and, therefore, eligible for 

comparison to the annual PM2.5

NAAQS. PM2.5 measurement data from 

monitors that are not representative of 

area-wide air quality but rather of 

relatively unique micro-scale, or 

localized hot spot, or unique middlescale impact sites are not eligible for 

comparison to the annual PM2.5

NAAQS. PM2.5 measurement data from 

these monitors are eligible for 

comparison to the 24-hour PM2.5

NAAQS. For example, if a micro- or 

middle-scale PM2.5 monitoring site is 

adjacent to a unique dominating local 

PM2.5 source, then the PM2.5

measurement data from such a site 

would only be eligible for comparison to 

the 24-hour PM2.5 NAAQS. Approval of 

sites that are suitable and sites that are 

not suitable for comparison with the 

annual PM2.5 NAAQS is provided for as 

part of the annual monitoring network 

plan described in § 58.10. 

* * * * * 

■ 22. Appendix A to part 58 is amended 

as follows: 

■ a. By redesignating the existing 

introductory paragraph in section 1 as 

paragraph (b) in section 1, and revising 

newly redesignated paragraph (b). 

■ b. By adding paragraph (a) to section 

1. 

■ c. By revising paragraphs 3.2.5.6, and 

3.2.6.3. 

■ d. By revising Table A–1. 

The revisions and additions read as 

follows: 

Appendix A to Part 58—Quality 

Assurance Requirements for SLAMS, 

SPMs and PSD Air Monitoring 

* * * * * 

1. * * * 

(a) Each monitoring organization is 

required to implement a quality system that 

provides sufficient information to assess the 

quality of the monitoring data. The quality 

system must, at a minimum, include the 

specific requirements described in this 

appendix of this subpart. Failure to conduct 

or pass a required check or procedure, or a 

series of required checks or procedures, does 

not by itself invalidate data for regulatory 

decision making. Rather, monitoring agencies 

and EPA shall use the checks and procedures 

required in this appendix in combination 

with other data quality information, reports, 

and similar documents showing overall 

compliance with part 58. Accordingly, EPA 


tkelley on DSK3SPTVN1PROD with 
3284 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

and monitoring agencies shall use a ‘‘weight 

of evidence’’ approach when determining the 

suitability of data for regulatory decisions. 

The EPA reserves the authority to use or not 

use monitoring data submitted by a 

monitoring organization when making 

regulatory decisions based on the EPA’s 

assessment of the quality of the data. 

Generally, consensus built validation 

templates or validation criteria already 

approved in Quality Assurance Project Plans 

(QAPPs) should be used as the basis for the 

weight of evidence approach. 

(b) This appendix specifies the minimum 

quality system requirements applicable to 

SLAMS air monitoring data and PSD data for 

the pollutants SO2, NO2, O3, CO, Pb, PM2.5, 

PM10 and PM10-2.5 submitted to EPA. This 

appendix also applies to all SPM stations 

using FRM, FEM, or ARM methods which 

also meet the requirements of appendix E of 

this part, unless alternatives to this appendix 

for SPMs have been approved in accordance 

with § 58.11(a)(2). Monitoring organizations 

are encouraged to develop and maintain 

quality systems more extensive than the 

required minimums. The permit-granting 

authority for PSD may require more frequent 

or more stringent requirements. Monitoring 

organizations may, based on their quality 

objectives, develop and maintain quality 

systems beyond the required minimum. 

Additional guidance for the requirements 

reflected in this appendix can be found in the 

‘‘Quality Assurance Handbook for Air 

Pollution Measurement Systems’’, Volume II 

(see reference 10 of this appendix) and at a 

national level in references 1, 2, and 3 of this 

appendix. 

* * * * * 

3.2.5* * * 

3.2.5.6 The two collocated monitors must 

be within 4 meters of each other and at least 

2 meters apart for flow rates greater than 200 

liters/min or at least 1 meter apart for 

samplers having flow rates less than 200 

liters/min to preclude airflow interference. A 

waiver allowing up to 10 meters horizontal 

distance and up to 3 meters vertical distance 

(inlet to inlet) between a primary and 

collocated sampler may be approved by the 

Regional Administrator for sites at a 

neighborhood or larger scale of 

representation. This waiver may be approved 

during the annual network plan approval 

process. Calibration, sampling, and analysis 

must be the same for all the collocated 

samplers in each agency’s network. 

* * * * * 

3.2.6 * * * 

3.2.6.3 The two collocated monitors must 

be within 4 meters of each other and at least 

2 meters apart for flow rates greater than 200 

liters/min or at least 1 meter apart for 

samplers having flow rates less than 200 

liters/min to preclude airflow interference. A 

waiver allowing up to 10 meters horizontal 

distance and up to 3 meters vertical distance 

(inlet to inlet) between a primary and a 

collocated sampler may be approved by the 

Regional Administrator for sites at a 

neighborhood or larger scale of 

representation taking into consideration 

safety, logistics, and space availability. This 

waiver may be approved during the annual 

network plan approval process. Calibration, 

sampling, and analysis must be the same for 

all the collocated samplers in each agency’s 

network. 

* * * * * 

TABLE A–1 OF APPENDIX A TO PART 58—DIFFERENCE AND SIMILARITIES BETWEEN SLAMS AND PSD REQUIREMENTS

Topic SLAMS PSD 

Requirements ..................................................... 1. The development, documentation, and implementation of an approved quality system.Same as SLAMS. 

2. The assessment of data quality.

3. The use of reference, equivalent, or approved methods.

4. The use of calibration standards traceable 

to NIST or other primary standard.

5. The participation in EPA performance evaluations and the permission for EPA to conduct system audits.Same as SLAMS 

Monitoring and QA Responsibility ..................... State/local agency via the ‘‘primary quality assurance organization’’.Source owner/operator. 

Monitoring Duration ........................................... Indefinitely ........................................................ Usually up to 12 months. 

Annual Performance Evaluation (PE) ................ Standards and equipment different from those 

used for spanning, calibration, and 

verifications. Prefer different personnel.

Personnel, standards and equipment different 

from those used for spanning, calibration, 

and verifications. 

PE audit rate: 

—Automated ............................................... 100% per year .................................................. 100% per quarter. 

—Manual .................................................... Varies depending on pollutant. See Table A–2 

of this appendix.

100% per quarter. 

Precision Assessment: 

—Automated ............................................... One-point QC check biweekly but data quality 

dependent.

One point QC check biweekly. 

—Manual .................................................... Varies depending on pollutant. See Table A–2 

of this appendix.

One site: 1 every 6 days or every third day for 

daily monitoring (TSP and Pb). 

Reporting 

—Automated ............................................... By site—EPA performs calculations annually .. By site—source owner/operator performs calculations each sampling quarter. 

—Manual .................................................... By reporting organization—EPA performs calculations annually.By site—source owner/operator performs calculations each sampling quarter. 

* * * * * 

■ 23. Appendix D to part 58 is amended 

as follows: 

■ a. By revising paragraphs 4.7.1(b) and 

4.7.1(c)(1). 

■ b. By removing paragraph 4.7.5. 

■ c. By removing and reserving 

paragraph 4.8.2. 

Appendix D to Part 58—Network 

Design Criteria for Ambient Air Quality 

Monitoring 

* * * * * 

4.7.1 * * * 

(b) Specific Design Criteria for PM2.5. The 

required monitoring stations or sites must be 

sited to represent area-wide air quality. These 

sites can include sites collocated at PAMS. 

These monitoring stations will typically be at 

neighborhood or urban-scale; however, 

micro-or middle-scale PM2.5 monitoring sites 

that represent many such locations 

throughout a metropolitan area are 

considered to represent area-wide air quality. 

(1) At least one monitoring station is to be 

sited at neighborhood or larger scale in an 

area of expected maximum concentration. 

(2) For CBSAs with a population of 

1,000,000 or more persons, at least one PM2.5

monitor is to be collocated at a near-road NO2


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3285 

station required in section 4.3.2(a) of this 

appendix. 

(3) For areas with additional required 

SLAMS, a monitoring station is to be sited in 

an area of poor air quality. 

(4) Additional technical guidance for siting 

PM2.5 monitors is provided in references 6 

and 7 of this appendix. 

(c) * * * 

(1) Micro-scale. This scale would typify 

areas such as downtown street canyons and 

traffic corridors where the general public 

would be exposed to maximum 

concentrations from mobile sources. In some 

circumstances, the micro-scale is appropriate 

for particulate sites. SLAMS sites measured 

at the micro-scale level should, however, be 

limited to urban sites that are representative 

of long-term human exposure and of many 

such microenvironments in the area. In 

general, micro-scale particulate matter sites 

should be located near inhabited buildings or 

locations where the general public can be 

expected to be exposed to the concentration 

measured. Emissions from stationary sources 

such as primary and secondary smelters, 

power plants, and other large industrial 

processes may, under certain plume 

conditions, likewise result in high ground 

level concentrations at the micro-scale. In the 

latter case, the micro-scale would represent 

an area impacted by the plume with 

dimensions extending up to approximately 

100 meters. Data collected at micro-scale 

sites provide information for evaluating and 

developing hot spot control measures. 

* * * * * 

4.8 * * * 

4.8.2 [Reserved] 

* * * * * 

■ 24. Appendix E to part 58 is amended 

as follows: 

■ a. By adding table E–1 to paragraph 6 

above paragraph 6.1. 

■ b. By revising table E–4. 

Appendix E to Part 58—Probe and 

Monitoring Path Siting Criteria for 

Ambient Air Quality Monitoring 

* * * * * 

6. * * * 

TABLE E–1 TO APPENDIX E OF PART

58—MINIMUM SEPARATION DISTANCE BETWEEN ROADWAYS AND

PROBES OR MONITORING PATHS

FOR MONITORING NEIGHBORHOOD

AND URBAN SCALE OZONE (O3) AND

OXIDES OF NITROGEN (NO, NO2, 

NOX, NOy) 

Roadway 

average daily 

traffic, 

vehicles per 

day 

Minimum 

distance 1

(meters) 

Minimum 

distance 1 2

meters) 

≤ 1,000 .......... 10 10 

10,000 ........... 10 20 

15,000 ........... 20 30 

20,000 ........... 30 40 

40,000 ........... 50 60 

70,000 ........... 100 100 

≥ 110,000 ...... 250 250 

1 Distance from the edge of the nearest traffic lane. The distance for intermediate traffic 

counts should be interpolated from the table 

values based on the actual traffic count. 2Applicable for ozone monitors whose 

placement has not already been approved as 

of December 18, 2006. 

* * * * * 

11. * * * 

TABLE E–4 OF APPENDIX E TO PART 58—SUMMARY OF PROBE AND MONITORING PATH SITING CRITERIA

Pollutant 

Scale (maximum monitoring path length, meters) 

Height from ground to 

probe, inlet or 80% of 

monitoring path 1 (meters) 

Horizontal and vertical 

distance from supporting 

structures 2 to probe, inlet 

or 90% of monitoring 

path1 (meters) 

Distance from trees to 

probe, inlet or 90% of 

monitoring path 1 (meters) 

Distance from roadways 

to probe, inlet or monitoring path 1 (meters) 

SO2 3456 .......................... Middle (300 m) Neighborhood Urban, and Regional (1 km).2–15 ................................ >1 .................................... >10 .................................. N/A. 

CO 457 ............................. Micro [downtown or 

street canyon sites], 

micro [near-road sites], 

middle (300 m) and 

Neighborhood (1 km).

2.5–3.5; 2–7; 2–15 ......... >1 .................................... >10 .................................. 2–10 for downtown areas 

or street canyon 

microscale; ≤50 for 

near-road microscale; 

see Table E–2 of this 

appendix for middle 

and neighborhood 

scales. 

O 3

345 ............................... Middle (300 m) Neighborhood, Urban, and Regional (1 km).

2–15 ................................ >1 .................................... >10 .................................. See Table E–1 of this 

appendix for all scales. 

NO2 345 ............................ Micro (Near-road [50– 

300 m]).

2–7 (micro); .................... >1 .................................... >10 .................................. ≤50 for near-road microscale. 

Middle (300 m) ............... 2–15 (all other scales).

Neighborhood, Urban, 

and Regional (1 km).

......................................... ......................................... ......................................... See Table E–1 of this 

appendix for all other 

scales. 

Ozone precursors (for 

PAMS) 345.

Neighborhood and Urban 

(1 km).

2–15 ................................ >1 .................................... >10 .................................. See Table E–4 of this 

appendix for all scales. 

PM, Pb 34568 ................... Micro, Middle, Neighborhood, Urban and Regional.2–7 (micro); 2–7 (middle 

PM10-2.5); 2–7 for nearroad; 2–15 (all other 

scales).

>2 (all scales, horizontal 

distance only).

>10 (all scales) ............... 2–10 (micro); see Figure 

E–1 of this appendix 

for all other scales. 

≤50 for near-road. 

N/A—Not applicable. 

1 Monitoring path for open path analyzers is applicable only to middle or neighborhood scale CO monitoring, middle, neighborhood, urban, and regional scale NO2

monitoring, and all applicable scales for monitoring SO2, O3, and O3 precursors. 2When probe is located on a rooftop, this separation distance is in reference to walls, parapets, or penthouses located on roof.

3Should be greater than 20 meters from the dripline of tree(s) and must be 10 meters from the dripline when the tree(s) act as an obstruction. 4 Distance from sampler, probe, or 90 percent of monitoring path to obstacle, such as a building, must be at least twice the height the obstacle protrudes above the 

sampler, probe, or monitoring path. Sites not meeting this criterion may be classified as middle scale (see text). 5 Must have unrestricted airflow 270 degrees around the probe or sampler; 180 degrees if the probe is on the side of a building or a wall. 6The probe, sampler, or monitoring path should be away from minor sources, such as furnace or incineration flues. The separation distance is dependent on the 

height of the minor source’s emission point (such as a flue), the type of fuel or waste burned, and the quality of the fuel (sulfur, ash, or lead content). This criterion is 

designed to avoid undue influences from minor sources. 7For micro-scale CO monitoring sites, the probe must be >10 meters from a street intersection and preferably at a midblock location. 


tkelley on DSK3SPTVN1PROD with 
3286 Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 

8 Collocated monitors must be within 4 meters of each other and at least 2 meters apart for flow rates greater than 200 liters/min or at least 1 meter apart for samplers having flow rates less than 200 liters/min to preclude airflow interference, unless a waiver is in place as approved by the Regional Administrator pursuant to section 3 of Appendix A. 

* * * * * 

■ 25. Appendix G to part 58 is amended 

as follows: 

■ a. By revising section 9. 

■ b. By revising section 10. 

■ c. By revising paragraphs 12.1 

introductory text and 12.1.a, and table 2. 

■ d. By revising section 13. 

Appendix G to Part 58—Uniform Air 

Quality Index (AQI) and Daily 

Reporting 

* * * * * 

9. How does the AQI relate to air 

pollution levels? 

For each pollutant, the AQI 

transforms ambient concentrations to a 

scale from 0 to 500. The AQI is keyed 

as appropriate to the national ambient 

air quality standards (NAAQS) for each 

pollutant. In most cases, the index value 

of 100 is associated with the numerical 

level of the short-term standard (i.e., 

averaging time of 24-hours or less) for 

each pollutant. The index value of 50 is 

associated with the numerical level of 

the annual standard for a pollutant, if 

there is one, at one-half the level of the 

short-term standard for the pollutant, or 

at the level at which it is appropriate to 

begin to provide guidance on cautionary 

language. Higher categories of the index 

are based on increasingly serious health 

effects and increasing proportions of the 

population that are likely to be affected. 

The index is related to other air 

pollution concentrations through linear 

interpolation based on these levels. The 

AQI is equal to the highest of the 

numbers corresponding to each 

pollutant. For the purposes of reporting 

the AQI, the sub-indexes for PM10 and 

PM2.5 are to be considered separately. 

The pollutant responsible for the 

highest index value (the reported AQI) 

is called the ‘‘critical’’ pollutant. 

10. What monitors should I use to get 

the pollutant concentrations for 

calculating the AQI? 

You must use concentration data from 

State/Local Air Monitoring Station 

(SLAMS) or parts of the SLAMS 

required by 40 CFR 58.10 for each 

pollutant except PM. For PM, calculate 

and report the AQI on days for which 

you have measured air quality data (e.g., 

from continuous PM2.5 monitors 

required in Appendix D to this part). 

You may use PM measurements from 

monitors that are not reference or 

equivalent methods (for example, 

continuous PM10 or PM2.5 monitors). 

Detailed guidance for relating nonapproved measurements to approved 

methods by statistical linear regression 

is referenced in section 13 below. 

* * * * * 

12. How do I calculate the AQI? 

i. The AQI is the highest value 

calculated for each pollutant as follows: 

a. Identify the highest concentration 

among all of the monitors within each 

reporting area and truncate as follows: 

(1) Ozone—truncate to 3 decimal places 

PM2.5—truncate to 1 decimal place 

PM10—truncate to integer 

CO—truncate to 1 decimal place 

SO2—truncate to integer 

NO2—truncate to integer 

(2) [Reserved] 

* * * * * 

TABLE 2—BREAKPOINTS FOR THE AQI 

These breakpoints Equal these AQI’s 

O3 (ppm) 8-hour O3 (ppm) 1- 

hour1

PM2.5 (μg/m3) 

24-hour 

PM10 (μg/ 

m3) 24-hour 

CO (ppm) 

8-hour 

SO2 (ppb) 

1-hour 

NO2 (ppb) 

1-hour AQI Category 

0.000–0.059 ....... .................... 0.0–12.0 0–54 0.0–4.4 0–35 0–53 0–50 Good. 

0.060–0.075 ....... .................... 12.1–35.4 55–154 4.5–9.4 36–75 54–100 51–100 Moderate. 

0.076–0.095 ....... 0.125–0.164 35.5–55.4 155–254 9.5–12.4 76–185 101–360 101–150 Unhealthy for 

Sensitive 

Groups. 

0.096–0.115 ....... 0.165–0.204 3 55.5–150.4 255–354 12.5–15.4 4 186–304 361–649 151–200 Unhealthy. 

0.116–0.374 ....... 0.205–0.404 3 150.5–250.4 355–424 15.5–30.4 4 305–604 650–1249 201–300 Very Unhealthy. 

(2) ....................... 0.405–0.504 3 250.5–350.4 425–504 30.5–40.4 4 605–804 1250–1649 301–400 Hazardous. 

(2) ....................... 0.505–0.604 3 350.5–500.4 505–604 40.5–50.4 4 805–1004 1650–2049 401–500 

1Areas are generally required to report the AQI based on 8-hour ozone values. However, there are a small number of areas where an AQI 

based on 1-hour ozone values would be more precautionary. In these cases, in addition to calculating the 8-hour ozone index value, the 1-hour 

ozone index value may be calculated, and the maximum of the two values reported. 2 8-hour O3 values do not define higher AQI values (≥301). AQI values of 301 or greater are calculated with 1-hour O3 concentrations. 3 If a different SHL for PM2.5 is promulgated, these numbers will change accordingly. 4 1-hr SO2 values do not define higher AQI values (≥ 200). AQI values of 200 or greater are calculated with 24-hour SO2 concentrations. 

* * * * * 

13. What additional information should 

I know? 

The EPA has developed a computer 

program to calculate the AQI for you. 

The program prompts for inputs, and it 

displays all the pertinent information 

for the AQI (the index value, color, 

category, sensitive group, health effects, 

and cautionary language). The EPA has 

also prepared a brochure on the AQI 

that explains the index in detail (The 

Air Quality Index), Reporting Guidance 

(Technical Assistance Document for the 

Reporting of Daily Air Quality—the Air 

Quality Index (AQI)) that provides 

associated health effects and cautionary 

statements, and Forecasting Guidance 

(Guideline for Developing an Ozone 

Forecasting Program) that explains the 

steps necessary to start an air pollution 

forecasting program. You can download 

the program and the guidance 

documents at www.airnow.gov. 

Reference for relating non-approved PM 

measurements to approved methods 

(Eberly, S., T. Fitz-Simons, T. Hanley, L. 

Weinstock., T. Tamanini, G. Denniston, 

B. Lambeth, E. Michel, S. Bortnick. Data 

Quality Objectives (DQOs) For Relating 

Federal Reference Method (FRM) and 

Continuous PM2.5 Measurements to 

Report an Air Quality Index (AQI). U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA–454/ 

B–02–002, November 2002) can be 

found on the Ambient Monitoring 

Technology Information Center 


tkelley on DSK3SPTVN1PROD with 
Federal Register / Vol. 78, No. 10 / Tuesday, January 15, 2013 / Rules and Regulations 3287 

(AMTIC) Web site, http://www.epa.gov/ 

ttnamti1/. 

[FR Doc. 2012–30946 Filed 1–14–13; 8:45 am] 

BILLING CODE 6560–50–P 


tkelley on DSK3SPTVN1PROD with