Vol. 80 Monday, 

No. 206 October 26, 2015 

Part II 

Environmental Protection Agency 

40 CFR Part 50, 51, 52, et al. 

National Ambient Air Quality Standards for Ozone; Final Rule 

mstockstill on DSK4VPTVN1PROD with RULES2

65292 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

ENVIRONMENTAL PROTECTION 

AGENCY 

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

[EPA–HQ–OAR–2008–0699; FRL–9933–18– 

OAR] 

RIN 2060–AP38 

National Ambient Air Quality 

Standards for Ozone 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Final rule. 

SUMMARY: Based on its review of the air 

quality criteria for ozone (O3) and 

related photochemical oxidants and 

national ambient air quality standards 

(NAAQS) for O3, the Environmental 

Protection Agency (EPA) is revising the 

primary and secondary NAAQS for O3

to provide requisite protection of public 

health and welfare, respectively. The 

EPA is revising the levels of both 

standards to 0.070 parts per million 

(ppm), and retaining their indicators 

(O3), forms (fourth-highest daily 

maximum, averaged across three 

consecutive years) and averaging times 

(eight hours). The EPA is making 

corresponding revisions in data 

handling conventions for O3 and 

changes to the Air Quality Index (AQI); 

revising regulations for the prevention 

of significant deterioration (PSD) 

program to add a transition provision 

for certain applications; and 

establishing exceptional events 

schedules and providing information 

related to implementing the revised 

standards. The EPA is also revising the 

O3 monitoring seasons, the Federal 

Reference Method (FRM) for monitoring 

O3 in the ambient air, Federal 

Equivalent Method (FEM) analyzer 

performance requirements, and the 

Photochemical Assessment Monitoring 

Stations (PAMS) network. Along with 

exceptional events schedules related to 

implementing the revised O3 standards, 

the EPA is applying this same schedule 

approach to other future new or revised 

NAAQS and removing obsolete 

regulatory language for expired 

exceptional events deadlines. The EPA 

is making minor changes to the 

procedures and time periods for 

evaluating potential FRMs and 

equivalent methods, including making 

the requirements for nitrogen dioxide 

(NO2) consistent with the requirements 

for O3, and removing an obsolete 

requirement for the annual submission 

of Product Manufacturing Checklists by 

manufacturers of FRMs and FEMs for 

monitors of fine and coarse particulate 

matter. For a more detailed summary, 

see the Executive Summary below. 

DATES: The final rule is effective on 

December 28, 2015. 

ADDRESSES: EPA has established a 

docket for this action (Docket ID No. 

EPA–HQ–OAR–2008–0699) and a 

separate docket, established for the 

Integrated Science Assessment (ISA) 

(Docket No. EPA–HQ–ORD–2011–0050), 

which has been incorporated by 

reference into the rulemaking docket. 

All documents in the docket are listed 

on the www.regulations.gov Web site. 

Although listed in the docket index, 

some information is not publicly 

available, e.g., confidential business 

information 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, WJC West Building, 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. 

Susan Lyon Stone, 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– 

1146; fax: (919) 541–0237; email: 

stone.susan@epa.gov. 

SUPPLEMENTARY INFORMATION: 

General Information 

Availability of Related Information 

A number of the documents that are 

relevant to this action are available 

through the EPA’s Office of Air Quality 

Planning and Standards (OAQPS) 

Technology Transfer Network (TTN) 

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

naaqs/standards/ozone/s_o3_

index.html). These documents include 

the Integrated Science Assessment for 

Ozone (U.S. EPA, 2013), available at 

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

standards/ozone/s_o3_2008_isa.html; 

the Health Risk and Exposure 

Assessment and the Welfare Risk and 

Exposure Assessment for Ozone, Final 

Reports (HREA and WREA, respectively; 

U.S. EPA, 2014a, 2014b), available at 

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

standards/ozone/s_o3_2008_rea.html; 

and the Policy Assessment for the 

Review of the Ozone National Ambient 

Air Quality Standards (PA; U.S. EPA, 

2014c), available at http://www.epa.gov/ 

ttn/naaqs/standards/ozone/s_o3_2008_

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: 

Executive Summary 

I. Background 

A. Legislative Requirements 

B. Related Control Programs 

C. Review of Air Quality Criteria and 

Standards for O3

D. Ozone Air Quality 

E. Summary of Proposed Revisions to the 

O3 Standards 

F. Organization and Approach to Decisions 

in This O3 NAAQS Review 

II. Rationale for Decision on the Primary 

Standard 

A. Introduction 

1. Overview of Health Effects Evidence 

2. Overview of Human Exposure and 

Health Risk Assessments 

B. Need for Revision of the Primary 

Standard 

1. Basis for Proposed Decision 

2. Comments on the Need for Revision 

3. Administrator’s Conclusions on the 

Need for Revision 

C. Conclusions on the Elements of a 

Revised Primary Standard 

1. Indicator 

2. Averaging Time 

3. Form 

4. Level 

D. Decision on the Primary Standard 

III. Communication of Public Health 

Information 

A. Proposed Revisions to the AQI 

B. Comments on Proposed Revisions to the 

AQI 

C. Final Revisions to the AQI 

IV. Rationale for Decision on the Secondary 

Standard 

A. Introduction 

1. Overview of Welfare Effects Evidence 

2. Overview of Welfare Exposure and Risk 

Assessment 

3. Potential Impacts on Public Welfare 

B. Need for Revision of the Secondary 

Standard 

1. Basis for Proposed Decision 

2. Comments on the Need for Revision 

3. Administrator’s Conclusions on the 

Need for Revision 

C. Conclusions on Revision of the 

Secondary Standard 

1. Basis for Proposed Revision 

2. Comments on Proposed Revision 

3. Administrator’s Conclusions on Revision 

D. Decision on the Secondary Standard 

V. Appendix U: Interpretation of the Primary 

and Secondary NAAQS for O3

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65293 

A. Background 

B. Data Selection Requirements 

C. Data Reporting and Data Handling 

Requirements 

D. Exceptional Events Information 

Submission Schedule 

VI. Ambient Monitoring Related to O3

Standards 

A. Background 

B. Revisions to the Length of the Required 

O3 Monitoring Seasons 

1. Proposed Changes to the Length of the 

Required O3 Monitoring Seasons 

2. Comments on the Length of the Required 

O3 Monitoring Seasons 

3. Final Decisions on the Length of the 

Required O3 Monitoring Seasons 

C. Revisions to the PAMS Network 

Requirements 

1. Network Design 

2. Speciated VOC Measurements 

3. Carbonyl Measurements 

4. Nitrogen Oxides Measurements 

5. Meteorology Measurements 

6. PAMS Season 

7. Timing and Other Implementation Issues 

D. Addition of a New FRM for O3

1. Proposed Changes to the FRM for O3

2. Comments on the FRM for O3

E. Revisions to the Analyzer Performance 

Requirements 

1. Proposed Changes to the Analyzer 

Performance Requirements 

2. Comments on the Analyzer Performance 

Requirements 

VII. Grandfathering Provision for Certain PSD 

Permits 

A. Summary of the Proposed 

Grandfathering Provision 

B. Comments and Responses 

C. Final Action and Rationale 

VIII. Implementation of the Revised O3

Standards 

A. NAAQS Implementation Plans 

1. Cooperative Federalism 

2. Additional New Rules and Guidance 

3. Background O3

4. Section 110 State Implementation Plans 

5. Nonattainment Area Requirements 

B. O3 Air Quality Designations 

1. Area Designation Process 

2. Exceptional Events 

C. How do the New Source Review (NSR) 

requirements apply to the revised O3

NAAQS? 

1. NSR Requirements for Major Stationary 

Sources for the Revised O3 NAAQS 

2. Prevention of Significant Deterioration 

(PSD) Program 

3. Nonattainment NSR 

D. Transportation and General Conformity 

1. What are Transportation and General 

Conformity? 

2. When would Transportation and General 

Conformity apply to areas designated 

nonattainment for the revised O3

NAAQS? 

3. Impact of a Revised O3 NAAQS on a 

State’s Existing Transportation and/or 

General Conformity SIP 

E. Regional and International Pollution 

Transport 

1. Interstate Transport 

2. International Transport 

IX. 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 & 

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 (CRA) 

References 

Executive Summary 

This section summarizes information 

about the purpose of this regulatory 

action, the major provisions of this 

action, and provisions related to 

implementation. 

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 NAAQS to protect public health and 

welfare. The CAA requires the EPA to 

periodically review the air quality 

criteria—the science upon which the 

standards are based—and the standards 

themselves. This rulemaking is being 

conducted pursuant to these statutory 

requirements. The schedule for 

completing this review is established by 

a federal court order, which requires 

that the EPA make a final determination 

by October 1, 2015. 

The EPA completed its most recent 

review of the NAAQS for O3 in 2008. As 

a result of that review, EPA took four 

principal actions: (1) Revised the level 

of the 8-hour primary standard to 0.075 

ppm; (2) expressed the standard to three 

decimal places; (3) revised the 8-hour 

secondary standard by making it 

identical to the revised primary 

standard; and (4) made conforming 

changes to the AQI. 

In subsequent litigation, the U.S. 

Court of Appeals for the District of 

Columbia Circuit (DC Circuit) upheld 

the EPA’s 2008 primary standard but 

remanded the 2008 secondary standard 

(Mississippi v. EPA, 744 F. 3d 1334 

[D.C. Cir. 2013]). With respect to the 

primary standard, the court held that 

the EPA reasonably determined that the 

existing primary standard, set in 1997, 

did not protect public health with an 

adequate margin of safety and required 

revision. In upholding the EPA’s revised 

primary standard, the court dismissed 

arguments that the EPA should have 

adopted a more stringent standard. The 

court remanded the secondary standard 

to the EPA after finding that the EPA’s 

justification for setting the secondary 

standard identical to the revised 8-hour 

primary standard violated the CAA 

because the EPA had not adequately 

explained how that standard provided 

the required public welfare protection. 

In remanding the 2008 secondary 

standard, the court did not vacate it. 

The EPA has addressed the court’s 

remand with this final action. 

This final action reflects the 

Administrator’s conclusions based on a 

review of the O3 NAAQS that began in 

September 2008, and also concludes the 

EPA’s reconsideration of the 2008 

decision that it initiated in 2009 and 

subsequently consolidated with the 

current review. In conducting this 

review, the EPA has carefully evaluated 

the currently available scientific 

literature on the health and welfare 

effects of O3, focusing particularly on 

the new literature available since the 

conclusion of the previous review in 

2008. Between 2008 and 2014, the EPA 

prepared draft and final versions of the 

Integrated Science Assessment, the 

Health and Welfare Risk and Exposure 

Assessments, and the Policy 

Assessment. Multiple drafts of these 

documents were subject to public 

review and comment, and, as required 

by the CAA, were peer-reviewed by the 

Clean Air Scientific Advisory 

Committee (CASAC), an independent 

scientific advisory committee 

established pursuant to the CAA and 

charged with providing advice to the 

Administrator. 

The EPA proposed revisions to the 

primary and secondary O3 NAAQS on 

December 17, 2014 (79 FR 75234), and 

provided a 3-month period for 

submission of comments from the 

public. In addition to written comments 

submitted to EPA, comments were also 

provided at public hearings held in 

Washington, DC, and Arlington, Texas, 

on January 29, 2015, and in Sacramento, 

California, on February 2, 2015. After 

consideration of public comments and 

the advice from the CASAC, the EPA 

has developed this final rulemaking, 

which is the final step in the review 

process. 

In this rulemaking, the EPA is 

revising the suite of standards for O3 to 

provide requisite protection of public 

health and welfare. In addition, the EPA 

is updating the AQI, and making 

changes in the data handling 

conventions and ambient air 

monitoring, reporting, and network 

mstockstill on DSK4VPTVN1PROD with RULES2

65294 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

design requirements to correspond with 

the changes to the O3 NAAQS. 

Summary of Major Provisions 

With regard to the primary standard, 

the EPA is revising the level of the 

standard to 0.070 ppm to provide 

increased public health protection 

against health effects associated with 

long- and short-term exposures. The 

EPA is retaining the indicator (O3), 

averaging time (8-hour) and form 

(annual fourth-highest daily maximum, 

averaged over 3 years) of the existing 

standard. This action provides increased 

protection for children, older adults, 

and people with asthma or other lung 

diseases, and other at-risk populations 

against an array of adverse health effects 

that include reduced lung function, 

increased respiratory symptoms and 

pulmonary inflammation; effects that 

contribute to emergency department 

visits or hospital admissions; and 

mortality. 

The decisions on the adequacy of the 

current standard and the appropriate 

level for the revised standard are based 

on an integrative assessment of an 

extensive body of new scientific 

evidence, which substantially 

strengthens what was known about O3- 

related health effects in the last review. 

The revised standard 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 O3 standard is not 

requisite to protect public health with 

an adequate margin of safety, as 

required by the CAA, and that revision 

of the level to 0.070 ppm is warranted 

to provide the appropriate degree of 

increased public health protection for 

at-risk populations against an array of 

adverse health effects. In concluding 

that a revised primary standard set at a 

level of 0.070 ppm is requisite to protect 

public health with an adequate margin 

of safety, the Administrator relies on 

several key pieces of information, 

including: (a) A level of 0.070 ppm is 

well below the O3 exposure 

concentration shown to cause the 

widest range of respiratory effects (i.e., 

0.080 ppm) and is below the lowest O3

exposure concentration shown to cause 

the adverse combination of decreased 

lung function and increased respiratory 

symptoms (i.e., 0.072 ppm); (b) a level 

of 0.070 ppm will eliminate, or nearly 

eliminate, repeated occurrence of these 

O3 exposure concentrations (this is 

important because the potential for 

adverse effects increases with frequency 

of occurrence); (c) a level of 0.070 ppm 

will protect the large majority of the 

population, including children and 

people with asthma, from lower 

exposure concentrations, which can 

cause lung function decrements and 

airway inflammation in some people 

(i.e., 0.060 ppm); and (d) a level of 0.070 

ppm will result in important reductions 

in the risk of O3-induced lung function 

decrements as well as the risk of O3- 

associated hospital admissions, 

emergency department visits, and 

mortality. In addition, the revised level 

of the primary standard is within the 

range that CASAC advised the Agency 

to consider. 

The EPA is also revising the level of 

the secondary standard to 0.070 ppm to 

provide increased protection against 

vegetation-related effects on public 

welfare. The EPA is retaining the 

indicator (O3), averaging time (8-hour) 

and form (annual fourth-highest daily 

maximum, averaged over 3 years) of the 

existing secondary standard. This 

action, reducing the level of the 

standard, provides increased protection 

for natural forests in Class I and other 

similarly protected areas against an 

array of vegetation-related effects of O3. 

The Administrator is making this 

decision based on judgments regarding 

the currently available welfare effects 

evidence, the appropriate degree of 

public welfare protection for the revised 

standard, and currently available air 

quality information on seasonal 

cumulative exposures that may be 

allowed by such a standard. 

In making this decision on the 

secondary standard, the Administrator 

focuses on O3 effects on tree seedling 

growth as a proxy for the full array of 

vegetation-related effects of O3, ranging 

from effects on sensitive species to 

broader ecosystem-level effects. Using 

this proxy in judging effects to public 

welfare, the Administrator has 

concluded that the requisite protection 

will be provided by a standard that 

generally limits cumulative seasonal 

exposures to 17 ppm-hours (ppm-hrs) or 

lower, in terms of a 3-year W126 index. 

Based on air quality analyses which 

indicate such control of cumulative 

seasonal exposures will be achieved 

with a standard set at a level of 0.070 

ppm (and the same indicator, averaging 

time, and form as the current standard), 

the Administrator concludes that a 

standard revised in this way will 

provide the requisite protection. In 

addition to providing protection of 

natural forests from growth-related 

effects, the revised standard is also 

expected to provide increased 

protection from other effects of potential 

public welfare significance, including 

crop yield loss and visible foliar injury. 

Thus, based on all of the information 

available in this review, the 

Administrator concludes that the 

current secondary O3 standard is not 

requisite to protect public welfare as 

required by the CAA, and that this 

revision will provide appropriate 

protection against known or anticipated 

adverse effects to the public welfare. 

Provisions Related to Implementation 

As directed by the CAA, reducing 

pollution to meet NAAQS always has 

been a shared task, one involving the 

federal government, states, tribes and 

local air agencies. This partnership has 

proved effective since the EPA first 

issued O3 standards more than three 

decades ago, and is evidenced by 

significantly lower O3 levels throughout 

the country. To provide a foundation 

that helps air agencies build successful 

strategies for attaining new O3

standards, the EPA will continue to 

move forward with federal regulatory 

programs, such as the final Tier 3 motor 

vehicle emissions standards. To 

facilitate the development of CAAcompliant implementation plans and 

strategies to attain new standards, the 

EPA intends to issue timely and 

appropriate implementation guidance 

and, where appropriate and consistent 

with the law, new rulemakings to 

streamline regulatory burdens and 

provide flexibility in implementation. 

Given the regional nature of O3 air 

pollution, the EPA will continue to 

work with states to address interstate 

transport of O3 and O3 precursors. The 

EPA also intends to work closely with 

states to identify locations affected by 

high background concentrations on high 

O3 days due to stratospheric intrusions 

of O3, wildfire O3 plumes, or long-range 

transport of O3 from sources outside the 

U.S. and ensure that the appropriate 

CAA regulatory mechanisms are 

employed. To this end, the EPA will be 

proposing revisions to the 2007 

Exceptional Events Rule and related 

draft guidance addressing the effects of 

wildfires. 

In addition to revising the primary 

and secondary standards, this action is 

changing the AQI to reflect the revisions 

to the primary standard and also making 

corresponding revisions in data 

handling conventions for O3, extending 

the O3 monitoring season in 33 states, 

revising the requirements for the PAMS 

network, and revising regulations for the 

PSD permitting program to add a 

provision grandfathering certain 

pending permits from certain 

requirements with respect to the revised 

standards. The preamble also provides 

schedules and information related to 

implementing the revised standards. 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65295 

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.’’ 

3As used here with regard to human populations, 

and similarly throughout this document, the term 

‘‘population’’ refers to people having a quality or 

characteristic in common, including a specific preexisting illness or a specific age or lifestage. 

4Lists of CASAC members and of members of the 

CASAC Ozone Review Panel are accessible from: 

http://yosemite.epa.gov/sab/sabpeople.nsf/Web

Committees/CASAC. 

The rule also contains revisions to the 

schedules associated with exceptional 

events demonstration submittals for the 

revised O3 standards and other future 

revised NAAQS, and makes minor 

changes related to monitoring for other 

pollutants. 

I. Background 

A. Legislative Requirements 

Two sections of the CAA govern the 

establishment 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 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 Mississippi v. 

EPA, 744 F. 3d 1334, 1353 (D.C. Cir. 

2013); 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 concentrations, see Lead 

Industries v. EPA, 647 F.2d at 1156 n.51; 

Mississippi v. EPA, 744 F. 3d at 1351, 

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, the size of 

sensitive population(s) 3 at risk, and the 

kind and degree of the uncertainties that 

must be addressed. The selection of any 

particular approach for 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; Mississippi, 744 F. 3d at 

1353. 

In setting primary and secondary 

standards that are ‘‘requisite’’ to protect 

public health and welfare, respectively, 

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, the CASAC4 has performed this 

independent review function. 

B. Related Control Programs 

States are primarily responsible for 

ensuring attainment and maintenance of 

NAAQS once the EPA has established 

them. The EPA performs an oversight 

function, and as necessary takes actions 

to ensure CAA objectives are achieved. 

Under section 110 of the CAA, and 

related provisions, states submit, for the 

EPA’s approval, state implementation 

plans (SIPs) that provide for the 

attainment and maintenance of such 

standards through control programs 

directed to sources of the relevant 

pollutants. The states, in conjunction 

with the EPA, also administer the PSD 

program (CAA sections 160 to 169) 

which is a pre-construction permit 

program designed to prevent significant 

deterioration in air quality. In addition, 

federal programs provide for nationwide 

reductions in emissions of O3 precursors 

and other air pollutants through new 

source performance standards for 

stationary sources under section 111 of 

the CAA and the federal motor vehicle 

and motor vehicle fuel control program 

under title II of the CAA (sections 202 

mstockstill on DSK4VPTVN1PROD with RULES2

65296 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

5The Cross-State Air Pollution Rule was upheld 

by the Supreme Court in Environmental Protection 

Agency v. EME Homer City Generation, L.P., 134 S. 

Ct. 1584 (2014), and remanded to the D.C. Circuit 

for further proceedings. The D.C. Circuit issued its 

decision on remand from the Supreme Court on 

July 28, 2015, remanding CSAPR to EPA, without 

vacating the rule, for EPA to reconsider certain 

emission budgets for certain States (EME Homer 

City Generation, L.P. v. Environmental Protection 

Agency, No. 11–1302, 2015 WL 4528137 [D.C. Cir. 

July 28, 2015]). 

6Although the level of the 2008 O3 standards are 

specified in the units of ppm (i.e., 0.075 ppm), O3

concentrations are described using the units of parts 

per billion (ppb) in several sections of this notice 

(i.e., sections II, III, IV and VI) for consistency with 

the common convention for information discussed 

in those sections. In ppb, 0.075 ppm is equivalent 

to 75. 

to 250), which involves controls for 

emissions from mobile sources and 

controls for the fuels used by these 

sources. For some stationary sources, 

the national emissions standards for 

hazardous air pollutants under section 

112 of the CAA may provide ancillary 

reductions in O3 precursors. 

After the EPA establishes a new or 

revised NAAQS, the CAA directs the 

EPA and the states to take steps to 

ensure that the new or revised NAAQS 

are met. One of the first steps, known 

as the initial area designations, involves 

identifying areas of the country that are 

not meeting the new or revised NAAQS 

along with the nearby areas that contain 

emissions sources that contribute to the 

areas not meeting the NAAQS. For areas 

designated ‘‘nonattainment,’’ the 

responsible states are required to 

develop SIPs to attain the standards. In 

developing their attainment plans, states 

first take into account projected 

emission reductions from federal and 

state rules that have been already 

adopted at the time of plan submittal. A 

number of significant emission 

reduction programs that will lead to 

reductions of O3 precursors are in place 

today or are expected to be in place by 

the time revised SIPs will be due. 

Examples of such rules include the 

Nitrogen Oxides (NOX) SIP Call and 

Cross-State Air Pollution Rule 

(CSAPR),5 regulations controlling onroad and non-road engines and fuels, 

hazardous air pollutant rules for utility 

and industrial boilers, 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 O3 standards ‘‘as 

expeditiously as practicable,’’ and adopt 

new state regulations as appropriate. 

Section VIII of this preamble includes 

additional discussion of designation and 

implementation issues associated with 

the revised O3 NAAQS. 

C. Review of Air Quality Criteria and 

Standards for O3

The EPA first established primary and 

secondary NAAQS for photochemical 

oxidants in 1971 (36 FR 8186, April 30, 

1971). The EPA set both primary and 

secondary standards at 0.08 ppm,6 as a 

1-hour average of total photochemical 

oxidants, not to be exceeded more than 

one hour per year. The EPA based the 

standards on scientific information 

contained in the 1970 Air Quality 

Criteria for Photochemical Oxidants 

(AQCD; U.S. DHEW, 1970). The EPA 

initiated the first periodic review of the 

NAAQS for photochemical oxidants in 

1977. Based on the 1978 AQCD (U.S. 

EPA, 1978), the EPA published 

proposed revisions to the original 

NAAQS in 1978 (43 FR 26962, June 22, 

1978) and final revisions in 1979 (44 FR 

8202, February 8, 1979). At that time, 

the EPA revised the level of the primary 

and secondary standards from 0.08 to 

0.12 ppm and changed the indicator 

from photochemical oxidants to O3, and 

the form of the standards from a 

deterministic (i.e., not to be exceeded 

more than one hour per year) to a 

statistical form. This statistical form 

defined attainment of the standards as 

occurring when the expected number of 

days per calendar year with maximum 

hourly average concentration greater 

than 0.12 ppm equaled one or less. 

Following the EPA’s decision in the 

1979 review, the city of Houston 

challenged the Administrator’s decision 

arguing that the standard was arbitrary 

and capricious because natural O3

concentrations and other physical 

phenomena in the Houston area made 

the standard unattainable in that area. 

The U.S. Court of Appeals for the 

District of Columbia Circuit (D.C. 

Circuit) rejected this argument, holding 

(as noted above) that attainability and 

technological feasibility are not relevant 

considerations in the promulgation of 

the NAAQS. The court also noted that 

the EPA need not tailor the NAAQS to 

fit each region or locale, pointing out 

that Congress was aware of the difficulty 

in meeting standards in some locations 

and had addressed this difficulty 

through various compliance related 

provisions in the CAA. See API v. 

Costle, 665 F.2d 1176, 1184–6 (D.C. Cir. 

1981). 

In 1982, the EPA announced plans to 

revise the 1978 AQCD (47 FR 11561; 

March 17, 1982), and, in 1983, the EPA 

initiated the second periodic review of 

the O3 NAAQS (48 FR 38009; August 

22, 1983). The EPA subsequently 

published the 1986 AQCD (U.S. EPA, 

1986) and the 1989 Staff Paper (U.S. 

EPA, 1989). Following publication of 

the 1986 AQCD, a number of scientific 

abstracts and articles were published 

that appeared to be of sufficient 

importance concerning potential health 

and welfare effects of O3 to warrant 

preparation of a Supplement (U.S. EPA, 

1992). In August of 1992, under the 

terms of a court order, the EPA 

proposed to retain the existing primary 

and secondary standards based on the 

health and welfare effects information 

contained in the 1986 AQCD and its 

1992 Supplement (57 FR 35542, August 

10, 1992). In March 1993, the EPA 

announced its decision to conclude this 

review by affirming its proposed 

decision to retain the standards, without 

revision (58 FR 13008, March 9, 1993). 

In the 1992 notice of its proposed 

decision in that review, the EPA 

announced its intention to proceed as 

rapidly as possible with the next review 

of the air quality criteria and standards 

for O3 in light of emerging evidence of 

health effects related to 6- to 8-hour O3

exposures (57 FR 35542, August 10, 

1992). The EPA subsequently published 

the AQCD and Staff Paper for the review 

(U.S. EPA, 1996a,b). In December 1996, 

the EPA proposed revisions to both the 

primary and secondary standards (61 FR 

65716, December 13, 1996). With regard 

to the primary standard, the EPA 

proposed to replace the then-existing 1- 

hour primary standard with an 8-hour 

standard set at a level of 0.08 ppm 

(equivalent to 0.084 ppm based on the 

proposed data handling convention) as 

a 3-year average of the annual thirdhighest daily maximum 8-hour 

concentration. The EPA proposed to 

revise the secondary standard either by 

setting it identical to the proposed new 

primary standard or by setting it as a 

new seasonal standard using a 

cumulative form. The EPA completed 

this review in 1997 by setting the 

primary standard at a level of 0.08 ppm, 

based on the annual fourth-highest daily 

maximum 8-hour average concentration, 

averaged over three years, and setting 

the secondary standard identical to the 

revised primary standard (62 FR 38856, 

July 18, 1997). In reaching her decision 

on the primary standard, the 

Administrator identified several reasons 

supporting her decision to reject a 

potential alternate standard set at 0.07 

ppm, including first the fact that no 

CASAC panel member supported a 

standard level lower than 0.08 ppm and 

her consideration of the scientific 

uncertainties with regard to the health 

effects evidence for exposure 

concentrations below 0.08 ppm. In 

addition to those reasons, the 

Administrator noted that a standard set 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65297 

at a level of 0.07 ppm would be closer 

to peak background concentrations that 

infrequently occur in some areas due to 

nonanthropogenic sources of O3

precursors (62 FR 38856, 38868; July 18, 

1997). 

On May 14, 1999, in response to 

challenges by industry and others to the 

EPA’s 1997 decision, the D.C. Circuit 

remanded the O3 NAAQS to the EPA, 

finding that section 109 of the CAA, as 

interpreted by the EPA, effected an 

unconstitutional delegation of 

legislative authority. American Trucking 

Assoc. vs. EPA, 175 F.3d 1027, 1034– 

1040 (D.C. Cir. 1999) (‘‘ATA I’’). In 

addition, the court directed that, in 

responding to the remand, the EPA 

should consider the potential beneficial 

health effects of O3 pollution in 

shielding the public from the effects of 

solar ultraviolet (UV) radiation, as well 

as adverse health effects. Id. at 1051–53. 

In 1999, the EPA petitioned for 

rehearing en banc on several issues 

related to that decision. The court 

granted the request for rehearing in part 

and denied it in part, but declined to 

review its ruling with regard to the 

potential beneficial effects of O3

pollution. 195 F. 3d 4, 10 (D.C Cir., 

1999) (‘‘ATA II’’). On January 27, 2000, 

the EPA petitioned the U.S. Supreme 

Court for certiorari on the constitutional 

issue (and two other issues), but did not 

request review of the ruling regarding 

the potential beneficial health effects of 

O3. On February 27, 2001, the U.S. 

Supreme Court unanimously reversed 

the judgment of the D.C. Circuit on the 

constitutional issue. Whitman v. 

American Trucking Assoc., 531 U. S. 

457, 472–74 (2001) (holding that section 

109 of the CAA does not delegate 

legislative power to the EPA in 

contravention of the Constitution). The 

Court remanded the case to the D.C. 

Circuit to consider challenges to the O3

NAAQS that had not been addressed by 

that court’s earlier decisions. On March 

26, 2002, the D.C. Circuit issued its final 

decision on remand, finding the 1997 O3

NAAQS to be ‘‘neither arbitrary nor 

capricious,’’ and so denying the 

remaining petitions for review. 

American Trucking Associations, Inc. v. 

EPA, 283 F.3d 355, 379 (D.C Cir., 2002) 

(‘‘ATA III’’). 

Specifically, in ATA III, the D.C. 

Circuit upheld the EPA’s decision on 

the 1997 O3 standard as the product of 

reasoned decision making. With regard 

to the primary standard, the court made 

clear that the most important support 

for EPA’s decision to revise the standard 

was the health evidence of insufficient 

protection afforded by the then-existing 

standard (‘‘the record is replete with 

references to studies demonstrating the 

inadequacies of the old one-hour 

standard’’), as well as extensive 

information supporting the change to an 

8-hour averaging time (283 F. 3d at 378). 

The court further upheld the EPA’s 

decision not to select a more stringent 

level for the primary standard noting 

‘‘the absence of any human clinical 

studies at ozone concentrations below 

0.08 [ppm]’’ which supported the EPA’s 

conclusion that ‘‘the most serious health 

effects of ozone are ‘less certain’ at low 

concentrations, providing an eminently 

rational reason to set the primary 

standard at a somewhat higher level, at 

least until additional studies become 

available’’ (283 F. 3d at 378, internal 

citations omitted). The court also 

pointed to the significant weight that 

the EPA properly placed on the advice 

it received from CASAC (283 F. 3d at 

379). In addition, the court noted that 

‘‘although relative proximity to peak 

background O3 concentrations did not, 

in itself, necessitate a level of 0.08 

[ppm], the EPA could consider that 

factor when choosing among the three 

alternative levels’’ (283 F. 3d at 379). 

Independently of the litigation, the 

EPA responded to the court’s remand to 

consider the potential beneficial health 

effects of O3 pollution in shielding the 

public from effects of UV radiation. The 

EPA provisionally determined that the 

information linking changes in patterns 

of ground-level O3 concentrations to 

changes in relevant patterns of 

exposures to UV radiation of concern to 

public health was too uncertain, at that 

time, to warrant any relaxation in 1997 

O3 NAAQS. The EPA also expressed the 

view that any plausible changes in UV– 

B radiation exposures from changes in 

patterns of ground-level O3

concentrations would likely be very 

small from a public health perspective. 

In view of these findings, the EPA 

proposed to leave the 1997 primary 

standard unchanged (66 FR 57268, Nov. 

14, 2001). After considering public 

comment on the proposed decision, the 

EPA published its final response to this 

remand in 2003, re-affirming the 8-hour 

primary standard set in 1997 (68 FR 

614, January 6, 2003). 

The EPA initiated the fourth periodic 

review of the air quality criteria and 

standards for O3 with a call for 

information in September 2000 (65 FR 

57810, September, 26, 2000). The 

schedule for completion of that review 

was ultimately governed by a consent 

decree resolving a lawsuit filed in 

March 2003 by plaintiffs representing 

national environmental and public 

health organizations, who maintained 

that the EPA was in breach of a 

nondiscretionary duty to complete 

review of the O3 NAAQS within a 

statutorily mandated deadline. In 2007, 

the EPA proposed to revise the level of 

the primary standard within a range of 

0.075 to 0.070 ppm (72 FR 37818, July 

11, 2007). The EPA proposed to revise 

the secondary standard either by setting 

it identical to the proposed new primary 

standard or by setting it as a new 

seasonal standard using a cumulative 

form. Documents supporting these 

proposed decisions included the 2006 

AQCD (U.S. EPA, 2006a) and 2007 Staff 

Paper (U.S. EPA, 2007) and related 

technical support documents. The EPA 

completed the review in March 2008 by 

revising the level of the primary 

standard from 0.08 ppm to 0.075 ppm, 

and revising the secondary standard to 

be identical to the revised primary 

standard (73 FR 16436, March 27, 2008). 

In May 2008, state, public health, 

environmental, and industry petitioners 

filed suit challenging the EPA’s final 

decision on the 2008 O3 standards. On 

September 16, 2009, the EPA 

announced its intention to reconsider 

the 2008 O3 standards, and initiated a 

rulemaking to do so. At the EPA’s 

request, the court held the consolidated 

cases in abeyance pending the EPA’s 

reconsideration of the 2008 decision. 

On January 2010, the EPA issued a 

notice of proposed rulemaking to 

reconsider the 2008 final decision (75 

FR 2938, January 19, 2010). In that 

notice, the EPA proposed that further 

revisions of the primary and secondary 

standards were necessary to provide a 

requisite level of protection to public 

health and welfare. The EPA proposed 

to revise the level of the primary 

standard from 0.075 ppm to a level 

within the range of 0.060 to 0.070 ppm, 

and to revise the secondary standard to 

one with a cumulative, seasonal form. 

At the EPA’s request, the CASAC 

reviewed the proposed rule at a public 

teleconference on January 25, 2010 and 

provided additional advice in early 

2011 (Samet, 2010, 2011). After 

considering comments from CASAC and 

the public, the EPA prepared a draft 

final rule, which was submitted for 

interagency review pursuant to 

Executive Order 12866. On September 

2, 2011, consistent with the direction of 

the President, the Administrator of the 

Office of Information and Regulatory 

Affairs, Office of Management and 

Budget (OMB), returned the draft final 

rule to the EPA for further 

consideration. In view of this return and 

the fact that the Agency’s next periodic 

review of the O3 NAAQS required under 

CAA section 109 had already begun (as 

announced on September 29, 2008), the 

EPA decided to consolidate the 

mstockstill on DSK4VPTVN1PROD with RULES2

65298 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

7This rulemaking concludes the reconsideration 

process. Under CAA section 109, the EPA is 

required to base its review of the NAAQS on the 

current air quality criteria, and thus the record and 

decision for this review also serve for the 

reconsideration. 

8The court cautioned, however, that ‘‘perhaps 

more [clinical] studies like the Adams studies will 

yet reveal that the 0.060 ppm level produces 

significant adverse decrements that simply cannot 

be attributed to normal variation in lung function,’’ 

and further cautioned that ‘‘agencies may not 

merely recite the terms ‘substantial uncertainty’ as 

a justification for their actions.’’ Id. at 1350, 1357 

(internal citations omitted). 

9As of this review, the document developed in 

NAAQS reviews to document the air quality 

criteria, previously the AQCD, is the ISA, and the 

document describing the OAQPS staff evaluation, 

previously the Staff Paper, is the PA. These 

documents are described in the IRP. 

10See http://yosemite.epa.gov/sab/sabproduct.

nsf/WebProjectsbyTopicCASAC!OpenView for more 

information on CASAC activities related to the 

current O3 NAAQS review. 

11The PA is prepared by the OAQPS staff. 

Formerly known as the Staff Paper, it presents a 

staff evaluation of the policy implications of the key 

scientific and technical information in the ISA and 

REAs for the EPA’s consideration. The PA provides 

a transparent evaluation, and staff conclusions, 

regarding policy considerations related to reaching 

judgments about the adequacy of the current 

standards, and if revision is considered, what 

revisions may be appropriate to consider. The PA 

is intended to help ‘‘bridge the gap’’ between the 

agency’s scientific assessments presented in the ISA 

reconsideration with its statutorily 

required periodic review.7

In light of the EPA’s decision to 

consolidate the reconsideration with the 

current review, the D.C. Circuit 

proceeded with the litigation on the 

2008 final decision. On July 23, 2013, 

the court upheld the EPA’s 2008 

primary O3 standard, but remanded the 

2008 secondary standard to the EPA 

(Mississippi v. EPA, 744 F. 3d 1334). 

With respect to the primary standard, 

the court first held that the EPA 

reasonably determined that the existing 

standard was not requisite to protect 

public health with an adequate margin 

of safety, and consequently required 

revision. Specifically, the court noted 

that there were ‘‘numerous 

epidemiologic studies linking health 

effects to exposure to ozone levels 

below 0.08 ppm and clinical human 

exposure studies finding a causal 

relationship between health effects and 

exposure to ozone levels at and below 

0.08 ppm’’ (Mississippi v. EPA, 744 F. 

3d at 1345). The court also specifically 

endorsed the weight of evidence 

approach utilized by the EPA in its 

deliberations (Mississippi v. EPA, 744 F. 

3d at 1344). 

The court went on to reject arguments 

that the EPA should have adopted a 

more stringent primary standard. 

Dismissing arguments that a clinical 

study (as properly interpreted by the 

EPA) showing effects at 0.06 ppm 

necessitated a standard level lower than 

that selected, the court noted that this 

was a single, limited study (Mississippi 

v. EPA, 744 F. 3d at 1350). With respect 

to the epidemiologic evidence, the court 

accepted the EPA’s argument that there 

could be legitimate uncertainty that a 

causal relationship between O3 and 8- 

hour exposures less than 0.075 ppm 

exists, so that associations at lower 

levels reported in epidemiologic studies 

did not necessitate a more stringent 

standard (Mississippi v. EPA, 744 F. 3d 

at 1351–52).8

The court also rejected arguments that 

an 8-hour primary standard of 0.075 

ppm failed to provide an adequate 

margin of safety, noting that margin of 

safety considerations involved policy 

judgments by the agency, and that by 

setting a standard ‘‘appreciably below’’ 

the level of the current standard (0.08 

ppm), the agency had made a reasonable 

policy choice (Mississippi v. EPA, 744 F. 

3d at 1351–52). Finally, the court 

rejected arguments that the EPA’s 

decision was inconsistent with the 

CASAC’s scientific recommendations 

because the CASAC had been 

insufficiently clear in its 

recommendations whether it was 

providing scientific or policy 

recommendations, and the EPA had 

reasonably addressed the CASAC’s 

policy recommendations (Mississippi v. 

EPA, 744 F. 3d at 1357–58). 

With respect to the secondary 

standard, the court held that the EPA’s 

justification for setting the secondary 

standard identical to the revised 8-hour 

primary standard violated the CAA 

because the EPA had not adequately 

explained how that standard provided 

the required public welfare protection. 

The court thus remanded the secondary 

standard to the EPA (Mississippi v. EPA, 

744 F. 3d at 1360–62). 

At the time of the court’s decision, the 

EPA had already completed significant 

portions of its next statutorily required 

periodic review of the O3 NAAQS. This 

review was formally initiated in 2008 

with a call for information in the 

Federal Register (73 FR 56581, Sept. 29, 

2008). On October 28–29, 2008, the EPA 

held a public workshop to discuss the 

policy-relevant science, which informed 

identification of key policy issues and 

questions to frame the review. Based in 

part on the workshop discussions, the 

EPA developed a draft Integrated 

Review Plan (IRP) outlining the 

schedule, process,9 and key policyrelevant questions that would guide the 

evaluation of the air quality criteria for 

O3 and the review of the primary and 

secondary O3 NAAQS. A draft of the IRP 

was released for public review and 

comment in September 2009 and was 

the subject of a consultation with the 

CASAC on November 13, 2009 (74 FR 

54562; October 22, 2009).10 After 

considering the comments received 

from that consultation and from the 

public, the EPA completed and released 

the IRP for the review in 2011 (U.S. 

EPA, 2011a). 

In preparing the first draft ISA, the 

EPA’s National Center for 

Environmental Assessment (NCEA) 

considered CASAC and public 

comments on the IRP, and also 

comments received from a workshop 

held on August 6, 2010, to review and 

discuss preliminary drafts of key ISA 

sections (75 FR 42085, July 20, 2010). In 

2011, the first draft ISA was released for 

public comment and for review by 

CASAC at a public meeting on May 19– 

20, 2011 (U.S. EPA, 2011b; 76 FR 10893, 

February 28, 2011; 76 FR 23809, April 

28, 2011). Based on CASAC and public 

comments, NCEA prepared a second 

draft ISA, which was released for public 

comment and CASAC review (U.S. EPA, 

2011c; 76 FR 60820, September 30, 

2011). The CASAC reviewed this draft 

at a January 9–10, 2012, public meeting 

(76 FR 236, December 8, 2011). Based 

on CASAC and public comments, NCEA 

prepared a third draft ISA (U.S. EPA, 

2012; 77 FR 36534, June 19, 2012), 

which was reviewed at a CASAC 

meeting in September 2012. The EPA 

released the final ISA in February 2013 

(U.S. EPA, 2013). 

The EPA presented its plans for 

conducting Risk and Exposure 

Assessments (REAs) for health risk and 

exposure (HREA) and welfare risk and 

exposure (WREA) in two documents 

that outlined the scope and approaches 

for use in conducting quantitative 

assessments, as well as key issues to be 

addressed as part of the assessments 

(U.S. EPA, 2011d, e). The EPA released 

these documents for public comment in 

April 2011, and consulted with CASAC 

on May 19–20, 2011 (76 FR 23809, April 

28, 2011). The EPA considered CASAC 

advice and public comments in further 

planning for the assessments, issuing a 

memo that described changes to 

elements of the REA plans and brief 

explanations regarding them (Samet, 

2011; Wegman, 2012). 

In July 2012, the EPA made the first 

drafts of the Health and Welfare REAs 

available for CASAC review and public 

comment (77 FR 42495, July 19, 2012; 

77 FR 51798, August 27, 2012). The first 

draft PA was made available for CASAC 

review and public comment in August 

2012 (77 FR 42495, July 19, 2012; 77 FR 

51798, August 27, 2012).11 The first 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65299 

and REAs, and the judgments required of the EPA 

Administrator in determining whether it is 

appropriate to retain or revise the NAAQS. 

draft REAs and PA were the focus of a 

CASAC public meeting in September 

2012 (Frey and Samet, 2012a, 2012b). 

The second draft REAs and PA, 

prepared with consideration of CASAC 

advice and public comments, were 

made available for public comment and 

CASAC review in January 2014 (79 FR 

4694, January 29, 2014). These 

documents were the focus of a CASAC 

public meeting on March 25–27, 2014 

(Frey, 2014a; Frey, 2014b; Frey, 2014c). 

The final versions of these documents 

were developed with consideration of 

the comments and recommendations 

from CASAC, as well as comments from 

the public on the draft documents, and 

were released in August 2014 (U.S. EPA 

2014a; U.S. EPA, 2014b; U.S. EPA, 

2014c). 

The proposed decision (henceforth 

‘‘proposal’’) on this review of the O3

NAAQS was signed on November 25, 

2014, and published in the Federal 

Register on December 17, 2014. The 

EPA held three public hearings to 

provide direct opportunity for oral 

testimony by the public on the proposal. 

The hearings were held on January 29, 

2015, in Arlington, Texas, and 

Washington, DC, and on February 2, 

2015, in Sacramento, California. At 

these public hearings, the EPA heard 

testimony from nearly 500 individuals 

representing themselves or specific 

interested organizations. Transcripts 

from these hearings and written 

testimony provided at the hearings are 

in the docket for this review. 

Additionally, approximately 430,000 

written comments were received from 

various commenters during the public 

comment period on the proposal, 

approximately 428,000 as part of mass 

mail campaigns. Significant issues 

raised in the public comments are 

discussed in the preamble of this final 

action. A summary of all other 

significant comments, along with the 

EPA’s responses, can be found in a 

separate document (henceforth 

‘‘Response to Comments’’) in the docket 

for this review. 

The schedule for completion of this 

review is governed by a court order 

resolving a lawsuit filed in January 2014 

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 O3

NAAQS within the period provided by 

statute. The court order that governs this 

review, entered by the court on April 

30, 2014, provides that the EPA will 

sign for publication a notice of final 

rulemaking concerning its review of the 

O3 NAAQS no later than October 1, 

2015. 

As in prior NAAQS reviews, the EPA 

is basing its decision in this review on 

studies and related information 

included in the ISA, REAs and PA, 

which have undergone CASAC and 

public review. The studies assessed in 

the ISA and PA, and the integration of 

the scientific evidence presented in 

them, have undergone extensive critical 

review by the EPA, the CASAC, and the 

public. 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, decisions that 

all parties recognize as of great import. 

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, as well as the 

public review that accompanies this 

process. Some commenters have 

referred to and discussed individual 

scientific studies on the health and 

welfare effects of O3 that were not 

included in the ISA (USEPA, 2013) 

(‘‘ ‘new’ studies’’). In considering and 

responding to comments for which such 

‘‘new’’ studies were cited in support, 

the EPA has provisionally considered 

the cited studies in the context of the 

findings of the ISA. The EPA’s 

provisional consideration of these 

studies did not and could not provide 

the kind of in-depth critical review 

described above. 

The decision to rely on studies and 

related information included in the ISA, 

REAs and PA, which have undergone 

CASAC and public review, is consistent 

with the EPA’s practice in prior NAAQS 

reviews and its interpretation of the 

requirements of the CAA. 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, and the EPA has 

consistently followed this approach. 

This longstanding interpretation was 

strengthened by new legislative 

requirements enacted in 1977, which 

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

concerning CASAC review of air quality 

criteria. See 71 FR 61144, 61148 

(October 17, 2006) (final decision on 

review of NAAQS for particulate matter) 

for a detailed discussion of this issue 

and the EPA’s past practice. 

As discussed in the EPA’s 1993 

decision not to revise the NAAQS for 

O3, ‘‘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 (58 FR 

at 13013–13014, March 9, 1993). 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 regarding the 

health and welfare effects and exposure 

pathways of ambient O3 made in the air 

quality criteria. 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 O3 air quality criteria 

that have undergone CASAC and public 

review. The EPA will consider the 

‘‘new’’ studies for purposes of decision 

making in the next periodic review of 

the O3 NAAQS, which the EPA expects 

to begin soon after the conclusion of this 

review and which will provide the 

opportunity to fully assess these studies 

through a more rigorous review process 

involving the EPA, CASAC, and the 

public. Further discussion of these 

‘‘new’’ studies can be found in the 

Response to Comments document, 

which is in the docket for this 

rulemaking and also available on the 

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

standards/ozone/s_o3_index.html). 

D. Ozone Air Quality 

Ozone is formed near the earth’s 

surface due to chemical interactions 

involving solar radiation and precursor 

pollutants including volatile organic 

compounds (VOCs) and NOX. Over 

longer time periods, methane (CH4) and 

carbon monoxide (CO) can also lead to 

O3 formation at the global scale. The 

precursor emissions leading to O3

formation can result from both manmade sources (e.g., motor vehicles and 

electric power generation) and natural 

sources (e.g., vegetation and wildfires). 

Occasionally, O3 that is created 

naturally in the stratosphere can also 

contribute to O3 levels near the surface. 

Once formed, O3 near the surface can be 

transported by winds before eventually 

being removed from the atmosphere via 

chemical reactions or deposition to 

surfaces. In sum, O3 concentrations are 

influenced by complex interactions 

between precursor emissions, 

meteorological conditions, and surface 

characteristics (U.S. EPA, 2014a). 

mstockstill on DSK4VPTVN1PROD with RULES2

65300 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

12A design value is a statistic that describes the 

air quality status of a given location relative to the 

level of the NAAQS. 

13These modeling studies are based on coupled 

global climate and regional air quality models and 

are designed to assess the sensitivity of U.S. air 

quality to climate change. A wide range of future 

climate scenarios and future years have been 

modeled and there can be variations in the expected 

response in U.S. O3 by scenario and across models 

and years, within the overall signal of higher 

summer O3 concentrations in a warmer climate. 

14Without global greenhouse gas mitigation 

efforts, climate change is projected to dramatically 

increase the area burned by wildfires across most 

of the contiguous U.S., especially in the West (U.S. 

EPA, 2015 p. 72). 

In order to continuously assess O3 air 

pollution levels, state and local 

environmental agencies operate O3

monitors at various locations and 

subsequently submit the data to the 

EPA. At present, there are 

approximately 1,400 monitors across the 

U.S. reporting hourly O3 averages 

during the times of the year when local 

O3 pollution can be important (U.S. 

EPA, 2014c, Section 2.1). Much of this 

monitoring is focused on urban areas 

where precursor emissions tend to be 

largest, as well as locations directly 

downwind of these areas, but there are 

also over 100 sites in rural areas where 

high levels of O3 can also be measured. 

Based on data from this national 

network, the EPA estimates that, in 

2013, approximately 99 million 

Americans lived in counties where O3

design values 12 were above the level of 

the existing health-based (primary) 

NAAQS of 0.075 ppm. High O3 values 

can occur almost anywhere within the 

contiguous 48 states, although the 

poorest O3 air quality in the U.S. is 

typically observed in California, Texas, 

and the Northeast Corridor, locations 

with some of the most densely 

populated areas in the country. From a 

temporal perspective, the highest daily 

peak O3 concentrations generally tend to 

occur during the afternoon within the 

warmer months due to higher solar 

radiation and other conducive 

meteorological conditions during these 

times. The exceptions to this general 

rule include 1) some rural sites where 

transport of O3 from upwind areas of 

regional production can occasionally 

result in high nighttime levels of O3, 2) 

high-elevation sites episodically 

influenced by stratospheric intrusions 

which can occur in other months, and 

3) certain locations in the western U.S. 

where large quantities of O3 precursors 

emissions associated with oil and gas 

development can be trapped by strong 

inversions associated with snow cover 

during the colder months and efficiently 

converted to O3 (U.S. EPA, 2014c, 

Section 2.3). 

One of the challenging aspects of 

developing plans to address high O3

concentrations is that the response of O3

to precursor reductions is nonlinear. In 

particular, NOX emissions can lead to 

both increases and decreases of O3. The 

net impact of NOX emissions on O3

concentrations depends on the local 

quantities of NOX, VOC, and sunlight 

which interact in a set of complex 

chemical reactions. In some areas, such 

as certain urban centers where NOX

emissions typically are high compared 

to local VOC emissions, NOX can 

suppress O3 locally. This phenomenon 

is particularly pronounced under 

conditions associated with low O3

concentrations (i.e., during cool, cloudy 

weather and at night when 

photochemical activity is limited or 

nonexistent). However, while NOX

emissions can initially suppress O3

levels near the emission sources, these 

same NOX emissions ultimately react to 

form higher O3 levels downwind when 

conditions are favorable. Photochemical 

model simulations suggest that, in 

general, reductions in NOX emissions in 

the U.S. will slightly increase O3

concentrations on days with lower O3

concentrations in close proximity to 

NOX sources (e.g., in urban core areas), 

while at the same time decreasing the 

highest O3 concentrations in downwind 

areas. See generally, U.S. EPA, 2014a 

(section 2.2.1). 

At present, both the primary and 

secondary NAAQS use the annual 

fourth-highest daily maximum 8-hour 

concentration, averaged over 3 years, as 

the form of the standard. An additional 

metric, the W126 exposure index, is 

often used to assess impacts of O3

exposure on ecosystems and vegetation. 

W126 is a cumulative seasonal aggregate 

of weighted hourly O3 values observed 

between 8 a.m. and 8 p.m. As O3

precursor emissions have decreased 

across the U.S., annual fourth-highest 

8-hour O3 maxima have concurrently 

shown a modest downward trend. The 

national average change in annual 

fourth-highest daily maximum 8-hour 

O3 concentrations between 2000 and 

2013 was an 18% decrease. The national 

average change in the annual W126 

exposure index over the same period 

was a 52% decrease. Air quality model 

simulations estimate that O3 air quality 

will continue to improve over the next 

decade as additional reductions in O3

precursors from power plants, motor 

vehicles, and other sources are realized. 

In addition to being affected by 

changing emissions, future O3

concentrations may also be affected by 

climate change. Modeling studies in the 

EPA’s Interim Assessment (U.S. EPA, 

2009a) that are cited in support of the 

2009 Endangerment Finding under CAA 

section 202(a) (74 FR 66496, Dec. 15, 

2009) as well as a recent assessment of 

potential climate change impacts (Fann 

et al., 2015) project that climate change 

may lead to future increases in summer 

O3 concentrations across the contiguous 

U.S.13 While the projected impact is not 

uniform, climate change has the 

potential to increase average 

summertime O3 concentrations by as 

much as 1–5 ppb by 2030, if greenhouse 

gas emissions are not mitigated. 

Increases in temperature are expected to 

be the principal factor in driving any O3

increases, although increases in 

stagnation frequency may also 

contribute (Jacob and Winner, 2009). If 

unchecked, climate change has the 

potential to offset some of the 

improvements in O3 air quality, and 

therefore some of the improvements in 

public health, that are expected from 

reductions in emissions of O3

precursors. 

Another challenging aspect of this air 

quality issue is the impact from sources 

of O3 and its precursors beyond those 

from domestic, anthropogenic sources. 

Modeling analyses indicate that 

nationally the majority of O3

exceedances are predominantly caused 

by anthropogenic emissions from within 

the U.S. However, observational and 

modeling analyses have concluded that 

O3 concentrations in some locations in 

the U.S. on some days can be 

substantially influenced by sources that 

cannot be addressed by domestic 

control measures. In particular, certain 

high-elevation sites in the western U.S. 

are impacted by a combination of nonU.S. sources like international transport, 

or natural sources such as stratospheric 

O3, and O3 originating from wildfire 

emissions.14 Ambient O3 from these 

non-U.S. and natural sources is 

collectively referred to as background 

O3. See generally section 2.4 of the PA 

(U.S. EPA, 2014c). The analyses suggest 

that, at these locations, there can be 

episodic events with substantial 

background contributions where O3

concentrations approach or exceed the 

level of the current NAAQS (i.e., 75 

ppb). These events are relatively 

infrequent, and the EPA has policies 

that allow for the exclusion of air 

quality monitoring data from design 

value calculations when they are 

substantially affected by certain 

background influences. 

E. Summary of Proposed Revisions to 

the O3 Standards 

For reasons discussed in the proposal, 

the Administrator proposed to revise the 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65301 

current primary and secondary 

standards for O3. With regard to the 

primary standard, the Administrator 

proposed to revise the level from 75 ppb 

to a level within a range from 65 to 70 

ppb. The EPA proposed to revise the 

AQI for O3, consistent with revision to 

the primary standard. 

With regard to the secondary 

standard, the Administrator proposed to 

revise the level of the current secondary 

standard to within the range of 0.065 to 

0.070 ppm, which air quality analyses 

indicate would provide cumulative, 

seasonal air quality or exposure values, 

in terms of 3-year average W126 index 

values, at or below a range of 13–17 

ppm-hours. 

The EPA also proposed to make 

corresponding revisions in data 

handling conventions for O3; to revise 

regulations for the PSD permitting 

program to add a provision 

grandfathering certain pending permits 

from certain requirements with respect 

to the proposed revisions to the 

standards; and to convey schedules and 

information related to implementing 

any revised standards. In conjunction 

with proposing exceptional event 

schedules related to implementing any 

revised O3 standards, the EPA also 

proposed to extend the new schedule 

approach to other future NAAQS 

revisions and to remove obsolete 

regulatory language associated with 

expired exceptional event deadlines for 

historical standards for both O3 and 

other pollutants for which NAAQS have 

been established. The EPA also 

proposed to make minor changes to the 

procedures and time periods for 

evaluating potential FRMs and 

equivalent methods, including making 

the requirements for NO2 consistent 

with the requirements for O3, and 

removing an obsolete requirement for 

the annual submission of 

documentation by manufacturers of 

certain particulate matter monitors. 

F. Organization and Approach to 

Decisions in This O3 NAAQS Review 

This action presents the 

Administrator’s final decisions in the 

current review of the primary and 

secondary O3 standards. The final 

decisions addressing standards for O3

are based on a thorough review in the 

ISA of scientific information on known 

and potential human health and welfare 

effects associated with exposure to O3 at 

levels typically found in the ambient 

air. These final decisions also take into 

account the following: (1) Staff 

assessments in the PA of the most 

policy-relevant information in the ISA 

as well as a quantitative health and 

welfare exposure and risk assessments 

based on that information; (2) CASAC 

advice and recommendations, as 

reflected in its letters to the 

Administrator and its discussions of 

drafts of the ISA, REAs, and PA at 

public meetings; (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. 

The primary standard is addressed in 

section II. Corresponding changes to the 

AQI are addressed in section III. The 

secondary standard is addressed in 

section IV. Related data handling 

conventions and exceptional events are 

addressed in section V. Updates to the 

monitoring regulations are addressed in 

section VI. Implementation activities, 

including PSD-related actions, are 

addressed in sections VII and VIII. 

Section IX addresses applicable 

statutory and executive order reviews. 

II. Rationale for Decision on the 

Primary Standard 

This section presents the 

Administrator’s final decisions 

regarding the need to revise the existing 

primary O3 standard and the 

appropriate revision to the level of that 

standard. Based on her consideration of 

the full body of health effects evidence 

and exposure/risk analyses, the 

Administrator concludes that the 

current primary standard for O3 is not 

requisite to protect public health with 

an adequate margin of safety. In order to 

increase public health protection, she is 

revising the level of the primary 

standard to 70 ppb, in conjunction with 

retaining the current indicator, 

averaging time and form. The 

Administrator concludes that such a 

revised standard will be requisite to 

protect public health with an adequate 

margin of safety. As discussed more 

fully below, the rationale for these final 

decisions draws from the thorough 

review in the ISA (U.S. EPA, 2013) of 

the available scientific evidence, 

generally published through July 2011, 

on human health effects associated with 

the presence of O3 in the ambient air. 

This rationale also takes into account: 

(1) Analyses of O3 air quality, human 

exposures to O3, and O3-associated 

health risks, as presented and assessed 

in the HREA (U.S. EPA, 2014a); (2) the 

EPA staff assessment of the most policyrelevant scientific evidence and 

exposure/risk information in the PA 

(U.S. EPA, 2014c); (3) CASAC advice 

and recommendations, as reflected in 

discussions of drafts of the ISA, REA, 

and PA at public meetings, in separate 

written comments, and in CASAC’s 

letters to the Administrator; (4) public 

input received during the development 

of these documents, either in 

connection with CASAC meetings or 

separately; and (5) public comments on 

the proposal notice. 

Section II.A below summarizes the 

information presented in the proposal 

regarding O3-associated health effects, 

O3 exposures, and O3-attributable health 

risks. Section II.B presents information 

related to the adequacy of the current 

primary O3 standard, including a 

summary of the basis for the 

Administrator’s proposed decision to 

revise the current standard, public 

comments received on the adequacy of 

the current standard, and the 

Administrator’s final conclusions 

regarding the adequacy of the current 

standard. Section II.C presents 

information related to the elements of a 

revised primary O3 standard, including 

information related to each of the major 

elements of the standard (i.e., indicator, 

averaging time, form, level). Section II.D 

summarizes the Administrator’s final 

decisions on the primary O3 standard. 

A. Introduction 

As discussed in section II.A of the 

proposal (79 FR 75243–75246, 

December 17, 2014), the EPA’s approach 

to informing decisions on the primary 

O3 standard in the current review builds 

upon the general approaches used in 

previous reviews and reflects the 

broader body of scientific evidence, 

updated exposure/risk information, and 

advances in O3 air quality modeling 

now available. This approach is based 

most fundamentally on using the EPA’s 

assessment of the available scientific 

evidence and associated quantitative 

analyses to inform the Administrator’s 

judgments regarding a primary standard 

for O3 that is ‘‘requisite’’ (i.e., neither 

more nor less stringent than necessary) 

to protect public health with an 

adequate margin of safety. Specifically, 

it is based on consideration of the 

available body of scientific evidence 

assessed in the ISA (U.S. EPA, 2013), 

exposure and risk analyses presented in 

the HREA (U.S. EPA, 2014a), evidenceand exposure-/risk-based considerations 

and conclusions presented in the PA 

(U.S. EPA, 2014c), advice and 

recommendations received from CASAC 

(Frey, 2014a, c), and public comments. 

Section II.A.1 below summarizes the 

information presented in the proposal 

regarding O3-associated health effects. 

Section II.A.2 summarizes the 

information presented in the proposal 

regarding O3 exposures and O3- 

attributable health risks. 

mstockstill on DSK4VPTVN1PROD with RULES2

65302 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

15 In determining that a causal relationship exists 

for O3 with specific health effects, the EPA has 

concluded that ‘‘[e]vidence is sufficient to conclude 

that there is a causal relationship with relevant 

pollutant exposures’’ (U.S. EPA, 2013, p. lxiv). 

16 In determining a ‘‘likely to be a causal’’ 

relationship exists for O3 with specific health 

effects, the EPA has concluded that ‘‘[e]vidence is 

sufficient to conclude that a causal relationship is 

likely to exist with relevant pollutant exposures, 

but important uncertainties remain’’ (U.S. EPA, 

2013, p. lxiv). 

1. Overview of Health Effects Evidence 

The health effects of O3 are described 

in detail in the ISA (U.S. EPA, 2013). 

Based on its assessment of the health 

effects evidence, the ISA determined 

that a ‘‘causal’’ relationship exists 

between short-term exposure to O3 in 

ambient air and effects on the 

respiratory system 15 and that a ‘‘likely 

to be causal’’ relationship exists 

between long-term exposure to O3 in 

ambient air and respiratory effects 16

(U.S. EPA, 2013, pp. 1–6 to 1–7). The 

ISA summarizes the longstanding body 

of evidence for O3 respiratory effects as 

follows (U.S. EPA, 2013, p. 1–5): 

The clearest evidence for health effects 

associated with exposure to O3 is provided 

by studies of respiratory effects. Collectively, 

a very large amount of evidence spanning 

several decades supports a relationship 

between exposure to O3 and a broad range of 

respiratory effects (see Section 6.2.9 and 

Section 7.2.8). The majority of this evidence 

is derived from studies investigating shortterm exposures (i.e., hours to weeks) to O3, 

although animal toxicological studies and 

recent epidemiologic evidence demonstrate 

that long-term exposure (i.e., months to 

years) may also harm the respiratory system. 

Additionally, the ISA determined that 

the relationships between short-term 

exposures to O3 in ambient air and both 

total mortality and cardiovascular 

effects are likely to be causal, based on 

expanded evidence bases in the current 

review (U.S. EPA, 2013, pp. 1–7 to 

1–8). The ISA determined that the 

currently available evidence for 

additional endpoints is ‘‘suggestive’’ of 

causal relationships with short-term 

(central nervous system effects) and 

long-term exposures (cardiovascular 

effects, reproductive and developmental 

effects, central nervous system effects 

and total mortality) to ambient O3. 

Consistent with emphasis in past 

reviews on O3 health effects for which 

the evidence is strongest, in this review 

the EPA places the greatest emphasis on 

studies of health effects that have been 

determined in the ISA to be caused by, 

or likely to be caused by, O3 exposures 

(U.S. EPA, 2013, section 2.5.2). This 

preamble section summarizes the 

evidence for health effects attributable 

to O3 exposures, with a focus on 

respiratory morbidity and mortality 

effects attributable to short- and longterm exposures, and cardiovascular 

system effects (including mortality) and 

total mortality attributable to short-term 

exposures (from section II.B in the 

proposal, 79 FR 75246–75271). 

The information highlighted here is 

based on the assessment of the evidence 

in the ISA (U.S. EPA, 2013, Chapters 4 

to 8) and consideration of that evidence 

in the PA (U.S. EPA, 2014c, Chapters 3 

and 4) on the known or potential effects 

on public health which may be expected 

from the presence of O3 in the ambient 

air. This section summarizes: (1) 

Information available on potential 

mechanisms for health effects associated 

with exposure to O3 (II.A.1.a); (2) the 

nature of effects that have been 

associated directly with both short- and 

long-term exposure to O3 and indirectly 

with the presence of O3 in ambient air 

(II.A.1.b); (3) considerations related to 

the adversity of O3-attributable health 

effects (II.A.1.c); and (4) considerations 

in characterizing the public health 

impact of O3, including the 

identification of ‘‘at risk’’ populations 

(II.A.1.d). 

a. Overview of Mechanisms 

This section briefly summarizes the 

characterization of the key events and 

pathways that contribute to health 

effects resulting from O3 exposures, as 

discussed in the proposal (79 FR 75247, 

section II.B.1) and in the ISA (U.S. EPA, 

2013, section 5.3). 

Experimental evidence elucidating 

modes of action and/or mechanisms 

contributes to our understanding of the 

biological plausibility of adverse O3- 

related health effects, including 

respiratory effects and effects outside 

the respiratory system (U.S. EPA, 2013, 

Chapters 6 and 7). Evidence indicates 

that the initial key event is the 

formation of secondary oxidation 

products in the respiratory tract (U.S. 

EPA, 2013, section 5.3). This mainly 

involves direct reactions with 

components of the extracellular lining 

fluid (ELF). Although the ELF has 

inherent capacity to quench (based on 

individual antioxidant capacity), this 

capacity can be overwhelmed, 

especially with exposure to elevated 

concentrations of O3 (U.S. EPA 2014c, at 

3–3, 3–9). The resulting secondary 

oxidation products transmit signals to 

the epithelium, pain receptive nerve 

fibers and, if present, immune cells 

involved in allergic responses. The 

available evidence indicates that the 

effects of O3 are mediated by 

components of ELF and by the multiple 

cell types in the respiratory tract. 

Oxidative stress is an implicit part of 

this initial key event. 

Secondary oxidation products initiate 

numerous responses at the cellular, 

tissue, and whole organ level of the 

respiratory system. These responses 

include the activation of neural reflexes 

which leads to lung function 

decrements; initiation of pulmonary 

inflammation; alteration of barrier 

epithelial function; sensitization of 

bronchial smooth muscle; modification 

of lung host defenses; airways 

remodeling; and modulation of 

autonomic nervous function which may 

alter cardiac function (U.S. EPA, 2013, 

section 5.3, Figure 5–8). 

Persistent inflammation and injury, 

which are observed in animal models of 

chronic and quasi-continuous exposure 

to O3, are associated with airways 

remodeling (see section 7.2.3 of the ISA, 

U.S. EPA, 2013). Chronic quasicontinuous exposure to O3 has also been 

shown to result in effects on the 

developing lung and immune system. 

Systemic inflammation and vascular 

oxidative/nitrosative stress are also key 

events in the toxicity pathway of O3

(U.S. EPA, 2013, section 5.3.8). 

Extrapulmonary effects of O3 occur in 

numerous organ systems, including the 

cardiovascular, central nervous, 

reproductive, and hepatic systems (U.S. 

EPA, 2013, sections 6.3 to 6.5 and 

sections 7.3 to 7.5). 

Responses to O3 exposure are variable 

within the population. Studies have 

shown a large range of pulmonary 

function (i.e., spirometric) responses to 

O3 among healthy young adults, while 

responses within an individual are 

relatively consistent over time. Other 

responses to O3 have also been 

characterized by a large degree of 

interindividual variability, including 

airways inflammation. The mechanisms 

that may underlie the variability in 

responses seen among individuals are 

discussed in the ISA (U.S. EPA, 2013, 

section 5.4.2). Certain functional genetic 

polymorphisms, pre-existing conditions 

or diseases, nutritional status, lifestages, 

and co-exposures can contribute to 

altered risk of O3-induced effects. 

Experimental evidence for such O3- 

induced changes contributes to our 

understanding of the biological 

plausibility of adverse O3-related health 

effects, including a range of respiratory 

effects as well as effects outside the 

respiratory system (e.g., cardiovascular 

effects) (U.S. EPA, 2013, Chapters 6 and 

7). 

b. Nature of Effects 

This section briefly summarizes the 

information presented in the proposal 

on respiratory effects attributable to 

short-term exposures (II.A.1.b.i), 

respiratory effects attributable to longmstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65303 

17CASAC concurred that these were ‘‘the kinds 

of identifiable effects on public health that are 

expected from the presence of ozone in the ambient 

air’’ (Frey 2014c, p. 3). 

18Table 6–1 of the ISA includes descriptions of 

the activity levels evaluated in controlled human 

exposure studies (U.S. EPA, 2013). 

19Adams (2006); (2002) both provide data for an 

additional group of 30 healthy subjects that were 

exposed via facemask to 60 ppb O3 for 6.6 hours 

with moderate exercise. These subjects are 

described on page 133 of Adams (2006) and pages 

747 and 761 of Adams (2002). The facemask 

exposure is not expected to affect the FEV1

responses relative to a chamber exposure. 

20For the 60 ppb target exposure concentration, 

Schelegle et al. (2009) reported that the actual mean 

exposure concentration was 63 ppb. 

21Adams (2006) did not find effects on FEV1 at 

60 ppb to be statistically significant. In an analysis 

of the Adams (2006) data, Brown et al. (2008) 

addressed the more fundamental question of 

whether there were statistically significant 

differences in responses before and after the 6.6 

hour exposure period and found the average effect 

on FEV1 at 60 ppb to be small, but highly 

statistically significant using several common 

statistical tests, even after removal of potential 

outliers. Schelegle et al. (2009) reported that, 

compared to filtered air, the largest change in FEV1

for the 60 ppb protocol occurred after the sixth (and 

final) exercise period. 

22As noted above, for the 70 ppb exposure group, 

Schelegle et al. (2009) reported that the actual mean 

exposure concentration was 72 ppb. 

23The ISA notes that by considering responses 

uncorrected for filtered air exposures, during which 

lung function typically improves (which would 

increase the size of the change, pre-and postexposure), 10% is an underestimate of the 

proportion of healthy individuals that are likely to 

experience clinically meaningful changes in lung 

function following exposure for 6.6 hours to 60 ppb 

O3 during quasi-continuous moderate exertion (U.S. 

EPA, 2012, section 6.2.1.1). 

24One of these models, the McDonnell-StewartSmith (MSS) model (McDonnell et al. 2012) was 

used to estimate the occurrences of lung function 

decrements in the HREA. 

term exposures (II.A.1.b.ii), 

cardiovascular effects attributable to 

short-term exposures (II.A.1.b.iii), and 

premature mortality attributable to 

short-term exposures (II.A.1.b.iv) (79 FR 

75247, section II.B.2). 

i. Respiratory Effects—Short-term 

Exposure 

Controlled human exposure, animal 

toxicological, and epidemiologic studies 

available in the last review provided 

clear, consistent evidence of a causal 

relationship between short-term O3

exposure and respiratory effects (U.S. 

EPA, 2006a). Recent studies evaluated 

since the completion of the 2006 AQCD 

support and expand upon the strong 

body of evidence available in the last 

review (U.S. EPA, 2013, section 6.2.9). 

Key aspects of this evidence are 

discussed below with regard to (1) lung 

function decrements; (2) pulmonary 

inflammation, injury, and oxidative 

stress; (3) airway hyperresponsiveness; 

(4) respiratory symptoms and 

medication use; (5) lung host defense; 

(6) allergic and asthma-related 

responses; (7) hospital admissions and 

emergency department visits; and (8) 

respiratory mortality.17

Lung Function Decrements 

Lung function decrements are 

typically measured by spirometry and 

refer to reductions in the maximal 

amount of air that can be forcefully 

exhaled. Forced expiratory volume in 1 

second (FEV1) is a common index used 

to assess the effect of O3 on lung 

function. The ISA summarizes the 

currently available evidence from 

multiple controlled human exposure 

studies evaluating changes in FEV1

following 6.6-hour O3 exposures in 

young, healthy adults engaged in 

moderate levels of physical activity 18

(U.S. EPA, 2013, section 6.2.1.1, Figure 

6–1). Exposures to an average O3

concentration of 60 ppb results in group 

mean decrements in FEV1 ranging from 

1.8% to 3.6% (Adams, 2002; Adams, 

2006; 19 Schelegle et al., 2009; 20 Kim et 

al., 2011). The weighted average group 

mean decrement was 2.7% from these 

studies. In some analyses, these group 

mean decrements in lung function were 

statistically significant (Brown et al., 

2008; Kim et al., 2011), while in other 

analyses they were not (Adams, 2006; 

Schelegle et al., 2009).21 Prolonged 

exposure to an average O3 concentration 

of 72 ppb results in a statistically 

significant group mean decrement in 

FEV1 of about 6% (Schelegle et al., 

2009).22 There is a smooth doseresponse curve without evidence of a 

threshold for exposures between 40 and 

120 ppb O3 (U.S. EPA, 2013, Figure 6– 

1). When these data are taken together, 

the ISA concludes that ‘‘mean FEV1 is 

clearly decreased by 6.6-hour exposures 

to 60 ppb O3 and higher concentrations 

in [healthy, young adult] subjects 

performing moderate exercise’’ (U.S. 

EPA, 2013, p. 6–9). 

As described in the proposal (79 FR 

75250), the ISA focuses on individuals 

with >10% decrements in FEV1 because 

(1) it is accepted by the American 

Thoracic Society (ATS) as an abnormal 

response and a reasonable criterion for 

assessing exercise-induced 

bronchoconstriction, and (2) some 

individuals in the Schelegle et al. (2009) 

study experienced 5–10% FEV1

decrements following exposure to 

filtered air. The proportion of healthy 

adults experiencing FEV1 decrements 

>10% following prolonged exposures to 

80 ppb O3 while at moderate exertion 

ranged from 17% to 29% and following 

exposures to 60 ppb O3 ranged from 3% 

to 20%. The weighted average 

proportion (i.e., based on numbers of 

subjects in each study) of young, 

healthy adults with >10% FEV1

decrements is 25% following exposure 

to 80 ppb O3 and 10% following 

exposure to 60 ppb O3, for 6.6 hours at 

moderate exertion (U.S. EPA, 2013, page 

6–18 and 6–19).23 Responses within an 

individual tend to be reproducible over 

a period of several months, reflecting 

differences in intrinsic responsiveness. 

Given this, the ISA concludes that 

‘‘[t]hough group mean decrements are 

biologically small and generally do not 

attain statistical significance, a 

considerable fraction of exposed 

individuals [in the clinical studies] 

experience clinically meaningful 

decrements in lung function’’ when 

exposed for 6.6 hours to 60 ppb O3

during quasi-continuous, moderate 

exertion (U.S. EPA, 2013, section 

6.2.1.1, p. 6–20). 

This review has marked an advance in 

the ability to make reliable quantitative 

predictions of the potential lung 

function response to O3 exposure, and, 

thus, to reasonably predict the degree of 

interindividual response of lung 

function to that exposure. McDonnell et 

al. (2012) and Schelegle et al. (2012) 

developed models, described in more 

detail in the proposal (79 FR 75250), 

that included mathematical approaches 

to simulate the potential protective 

effect of antioxidants in the ELF at 

lower ambient O3 concentrations, and 

that included a dose threshold below 

which changes in lung function do not 

occur. The resulting empirical models 

can estimate the frequency distribution 

of individual responses and summary 

measures of the distribution such as the 

mean or median response and the 

proportions of individuals with FEV1

decrements >10%, 15%, and 20%.24

The predictions of the models are 

consistent with the observed results 

from the individual controlled human 

exposure studies of O3-induced FEV1

decrements (79 FR 75250–51, see also 

U.S. EPA, 2013, Figures 6–1 and 6–3). 

CASAC agreed that these models mark 

a significant technical advance over the 

exposure-response modeling approach 

used for the lung function risk 

assessment in the last review and 

explicitly found that ‘‘[t]he MSS model 

to be scientifically and biologically 

defensible’’ (Frey, 2014a, pp. 8, 2). 

CASAC also stated that ‘‘the comparison 

of the MSS model results to those 

obtained with the exposure-response 

model is of tremendous importance. 

Typically, the MSS model gives a result 

about a factor of three higher . . . for 

school-age children, which is expected 

because the MSS model includes 

mstockstill on DSK4VPTVN1PROD with RULES2

65304 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

25Reversible loss of lung function in combination 

with the presence of symptoms meets ATS criteria 

for adversity (ATS, 2000a). 

26Panel studies include repeated measurements 

of health outcomes, such as respiratory symptoms, 

at the individual level (U.S. EPA, 2013, p. 1x). 

27CASAC also addressed this issue: ‘‘The CASAC 

believes that these modest changes in FEV1 are 

usually associated with inflammatory changes, such 

as more neutrophils in the bronchoalveolar lavage 

fluid. Such changes may be linked to the 

pathogenesis of chronic lung disease’’ (Frey, 2014a 

p. 2). 

28When evaluated, these studies have also 

reported O3-induced respiratory symptoms in 

asthmatics. Specifically, Scannell et al. (1996), 

Basha et al. (1994), and Vagaggini et al. (2001, 2007) 

reported increased symptoms in addition to 

inflammation. 

responses for a wider range of exposure 

protocols’’ (Frey, 2014a, pp. 8, 2). 

Epidemiologic studies have 

consistently linked short-term increases 

in ambient O3 concentrations with lung 

function decrements in diverse 

populations and lifestages, including 

children attending summer camps, 

adults exercising or working outdoors, 

and groups with pre-existing respiratory 

diseases such as asthmatic children 

(U.S. EPA, 2013, section 6.2.1.2). Some 

of these studies reported O3-associated 

lung function decrements accompanied 

by respiratory symptoms 25 in asthmatic 

children. In contrast, studies of children 

in the general population have reported 

similar O3-associated lung function 

decrements but without accompanying 

respiratory symptoms (79 FR 75251; 

U.S. EPA, 2013, section 6.2.1.2). As 

noted in the PA (EPA, 2014c, pp. 4–70 

to 4–71), additional research is needed 

to evaluate responses of people with 

asthma and healthy people in the 40 to 

70 ppb range. Further epidemiologic 

studies and meta-analyses of the effects 

of O3 exposure on children will help 

elucidate the concentration-response 

functions for lung function and 

respiratory symptom effects at lower O3

concentrations. 

Several epidemiologic panel studies 26

reported statistically significant 

associations with lung function 

decrements at relatively low ambient O3

concentrations. For outdoor recreation 

or exercise, associations were reported 

in analyses restricted to 1-hour average 

O3 concentrations less than 80 ppb, 

down to less than 50 ppb. Among 

outdoor workers, Brauer et al. (1996) 

found a robust association with daily 1- 

hour max O3 concentrations less than 40 

ppb. Ulmer et al. (1997) found a robust 

association in schoolchildren with 30- 

minute maximum O3 concentrations 

less than 60 ppb. For 8-hour average O3

concentrations, associations with lung 

function decrements in children with 

asthma were found to persist at 

concentrations less than 80 ppb in a 

U.S. multicity study (Mortimer et al., 

2002) and less than 51 ppb in a study 

conducted in the Netherlands (Gielen et 

al., 1997). 

As described in the proposal (79 FR 

75251), several epidemiologic panel 

studies provided information on 

potential confounding by copollutants 

and most O3 effect estimates for lung 

function were robust to adjustment for 

temperature, humidity, and copollutants 

such as particulate matter with mass 

median aerodynamic diameter less than 

or equal to 2.5 micrometers (PM2.5), 

particulate matter with mass median 

aerodynamic diameter less than or equal 

to 10 micrometers (PM10), NO2, or sulfur 

dioxide (SO2) (Hoppe et al., 2003; 

Brunekreef et al., 1994; Hoek et al. 1993; 

U.S. EPA, 2013, pp. 6–67 to 6–69). 

Although examined in only a few 

epidemiologic studies, O3 also remained 

associated with decreases in lung 

function with adjustment for pollen or 

acid aerosols (79 F 75251; U.S. EPA, 

2013, section 6.2.1.2). 

Pulmonary Inflammation, Injury and 

Oxidative Stress 

As described in detail in section 

II.B.2.a.ii of the proposal (79 FR 75252), 

O3 exposures can result in increased 

respiratory tract inflammation and 

epithelial permeability. Inflammation is 

a host response to injury, and the 

induction of inflammation is evidence 

that injury has occurred. Oxidative 

stress has been shown to play a key role 

in initiating and sustaining O3-induced 

inflammation. As noted in the ISA (U.S. 

EPA, 2013, section 6.2.3), O3 exposures 

can initiate an acute inflammatory 

response throughout the respiratory 

tract that has been reported to persist for 

at least 18–24 hours after exposure. 

Inflammation induced by exposure of 

humans to O3 can have several potential 

outcomes, ranging from resolving 

entirely following a single exposure to 

becoming a chronic inflammatory state, 

as described in detail in section 

II.B.2.a.ii of the proposal (79 FR 75252) 

and in the ISA (U.S. EPA, 2013, section 

6.2.3). Continued cellular damage due to 

chronic inflammation ‘‘may alter the 

structure and function of pulmonary 

tissues’’ (U.S. EPA, 2013, p. 6–161). 

Lung injury and the resulting 

inflammation provide a mechanism by 

which O3 may cause other more serious 

morbidity effects (e.g., asthma 

exacerbations) (U.S. EPA, 2013, section 

6.2.3).27

Building on the last review, recent 

studies continue to support the 

evidence for airway inflammation and 

injury with new evidence for such 

effects following exposures to lower 

concentrations than had been evaluated 

previously. These studies include recent 

controlled human exposure and 

epidemiologic studies and are discussed 

more below. 

An extensive body of evidence from 

controlled human exposure studies, 

described in section II.B.2.a.ii of the 

proposal, indicates that short-term 

exposures to O3 can cause pulmonary 

inflammation and increases in 

polymorphonuclear leukocyte (PMN) 

influx and permeability following 80– 

600 O3 ppb exposures, eosinophilic 

inflammation following exposures at or 

above 160 ppb, and O3-induced PMN 

influx following exposures of healthy 

adults to 60 ppb O3, the lowest 

concentration that has been evaluated 

for inflammation. A meta-analysis of 21 

controlled human exposure studies 

(Mudway and Kelly, 2004) using varied 

experimental protocols (80–600 ppb O3

exposures; 1–6.6 hours exposure 

duration; light to heavy exercise; 

bronchoscopy at 0–24 hours post-O3

exposure) reported that PMN influx in 

healthy subjects is linearly associated 

with total O3 dose. 

As with FEV1 responses to O3, 

inflammatory responses to O3 are 

generally reproducible within 

individuals, with some individuals 

experiencing more severe O3-induced 

airway inflammation than indicated by 

group averages. Unlike O3-induced 

decrements in lung function, which are 

attenuated following repeated exposures 

over several days, some markers of O3- 

induced inflammation and tissue 

damage remain elevated during repeated 

exposures, indicating ongoing damage 

to the respiratory system (79 FR 75252). 

Most controlled human exposure 

studies have reported that asthmatics 

experience larger O3-induced 

inflammatory responses than nonasthmatics.28

In the previous review (U.S. EPA, 

2006a), the epidemiologic evidence of 

O3-associated changes in airway 

inflammation and oxidative stress was 

limited (79 FR 75253). Since then, as a 

result of the development of less 

invasive test methods, there has been a 

large increase in the number of studies 

assessing ambient O3-associated changes 

in airway inflammation and oxidative 

stress, the types of biological samples 

collected, and the types of indicators. 

Most of these recent studies have 

evaluated biomarkers of inflammation 

or oxidative stress in exhaled breath, 

nasal lavage fluid, or induced sputum 

(U.S. EPA, 2013, section 6.2.3.2). These 

recent studies form a larger database to 

establish coherence with findings from 

controlled human exposure and animal 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65305 

studies that have measured the same or 

related biological markers. Additionally, 

results from these studies provide 

further biological plausibility for the 

associations observed between ambient 

O3 concentrations and respiratory 

symptoms and asthma exacerbations. 

Airway Hyperresponsiveness (AHR) 

A strong body of controlled human 

exposure and animal toxicological 

studies, most of which were available in 

the last review of the O3 NAAQS, report 

O3-induced AHR after either acute or 

repeated exposures (U.S. EPA, 2013, 

section 6.2.2.2). People with asthma 

often exhibit increased airway 

responsiveness at baseline relative to 

healthy control subjects, and asthmatics 

can experience further increases in 

responsiveness following exposures to 

O3. Studies reporting increased airway 

responsiveness after O3 exposure 

contribute to a plausible link between 

ambient O3 exposures and increased 

respiratory symptoms in asthmatics, and 

increased hospital admissions and 

emergency department visits for asthma 

(section II.B.2.a.iii, 79 FR 75254; U.S. 

EPA, 2013, section 6.2.2.2). 

Respiratory Symptoms and Medication 

Use 

Respiratory symptoms are associated 

with adverse outcomes such as 

limitations in activity, and are the 

primary reason for people with asthma 

to use quick relief medication and to 

seek medical care. Studies evaluating 

the link between O3 exposures and such 

symptoms allow a direct 

characterization of the clinical and 

public health significance of ambient O3

exposure. Controlled human exposure 

and toxicological studies have described 

modes of action through which shortterm O3 exposures may increase 

respiratory symptoms by demonstrating 

O3-induced AHR (U.S. EPA, 2013, 

section 6.2.2) and pulmonary 

inflammation (U.S. EPA, 2013, section 

6.2.3). 

The link between subjective 

respiratory symptoms and O3 exposures 

has been evaluated in both controlled 

human exposure and epidemiologic 

studies, and the link with medication 

use has been evaluated in epidemiologic 

studies. In the last review, several 

controlled human exposure studies 

reported respiratory symptoms 

following exposures to O3

concentrations at or above 80 ppb. In 

addition, one study reported such 

symptoms following exposures to 60 

ppb O3, though the increase was not 

statistically different from filtered air 

controls. Epidemiologic studies reported 

associations between ambient O3 and 

respiratory symptoms and medication 

use in a variety of locations and 

populations, including asthmatic 

children living in U.S. cities (U.S. EPA, 

2013, pp. 6–1 to 6–2). In the current 

review, additional controlled human 

exposure studies have evaluated 

respiratory symptoms following 

exposures to O3 concentrations below 

80 ppb and recent epidemiologic studies 

have evaluated associations with 

respiratory symptoms and medication 

use (U.S. EPA, 2013, sections 6.2.1, 

6.2.4). 

As noted in section II.B.2.a.iv in the 

proposal (79 FR 75255), the findings for 

O3-induced respiratory symptoms in 

controlled human exposure studies, and 

the evidence integrated across 

disciplines describing underlying 

modes of action, provide biological 

plausibility for epidemiologic 

associations observed between shortterm increases in ambient O3

concentration and increases in 

respiratory symptoms (U.S. EPA, 2013, 

section 6.2.4). 

Most epidemiologic studies of O3 and 

respiratory symptoms and medication 

use have been conducted in children 

and/or adults with asthma, with fewer 

studies, and less consistent results, in 

non-asthmatic populations (U.S. EPA, 

2013, section 6.2.4). The 2006 AQCD 

(U.S. EPA, 2006a; U.S. EPA, 2013, 

section 6.2.4) concluded that the 

collective body of epidemiologic 

evidence indicated that short-term 

increases in ambient O3 concentrations 

are associated with increases in 

respiratory symptoms in children with 

asthma. A large body of single-city and 

single-region studies of asthmatic 

children provides consistent evidence 

for associations between short-term 

increases in ambient O3 concentrations 

and increased respiratory symptoms and 

asthma medication use in children with 

asthma (U.S. EPA, 2013, Figure 6–12, 

Table 6–20, section 6.2.4.1). 

Methodological differences, described 

in section II.B.2.a.iv of the proposal, 

among studies make comparisons across 

recent multicity studies of respiratory 

symptoms difficult. 

Available evidence indicates that O3- 

associated increases in respiratory 

symptoms are not confounded by 

temperature, pollen, or copollutants 

(primarily PM) (U.S. EPA, 2013, section 

6.2.4.5; Table 6–25). However, 

identifying the independent effects of 

O3 in some studies was complicated due 

to the high correlations observed 

between O3 and PM or different lags and 

averaging times examined for 

copollutants. Nonetheless, the ISA 

noted that the robustness of associations 

in some studies of individuals with 

asthma, combined with findings from 

controlled human exposure studies for 

the direct effects of O3 exposure, 

provide substantial evidence supporting 

the independent effects of short-term 

ambient O3 exposure on respiratory 

symptoms (U.S. EPA, 2013, section 

6.2.4.5). 

In summary, both controlled human 

exposure and epidemiologic studies 

have reported respiratory symptoms 

attributable to short-term O3 exposures. 

In the last review, the majority of the 

evidence from controlled human 

exposure studies in young, healthy 

adults was for symptoms following 

exposures to O3 concentrations at or 

above 80 ppb. Although studies that 

have become available since the last 

review have not reported increased 

respiratory symptoms in young, healthy 

adults following exposures with 

moderate exertion to 60 ppb, one recent 

study did report increased symptoms 

following exposure to 72 ppb O3. As 

was concluded in the last review, the 

collective body of epidemiologic 

evidence indicates that short-term 

increases in ambient O3 concentration 

are associated with increases in 

respiratory symptoms in children with 

asthma (U.S. EPA, 2013, section 6.2.4). 

Recent studies of respiratory symptoms 

and medication use, primarily in 

asthmatic children, add to this 

evidence. In a smaller body of studies, 

increases in ambient O3 concentration 

were associated with increases in 

respiratory symptoms in adults with 

asthma. 

Lung Host Defense 

The mammalian respiratory tract has 

a number of closely integrated defense 

mechanisms that, when functioning 

normally, provide protection from the 

potential health effects of exposures to 

a wide variety of inhaled particles and 

microbes. Based on toxicological and 

human exposure studies, in the last 

review EPA concluded that available 

evidence indicates that short-term O3

exposures have the potential to impair 

host defenses in humans, primarily by 

interfering with alveolar macrophage 

function. Any impairment in alveolar 

macrophage function may lead to 

decreased clearance of microorganisms 

or nonviable particles. Compromised 

alveolar macrophage functions in 

asthmatics may increase their 

susceptibility to other O3 effects, the 

effects of particles, and respiratory 

infections (U.S. EPA, 2006a). 

Relatively few studies conducted 

since the last review have evaluated the 

effects of O3 exposures on lung host 

defense. As presented in section 

II.B.2.a.v of the proposal (79 FR 75256), 

mstockstill on DSK4VPTVN1PROD with RULES2

65306 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

29Epidemiologic associations for O3 are more 

robust during the warm season than during cooler 

months (e.g., smaller measurement error, less 

potential confounding by copollutants). The 

rationale for focusing on warm season 

epidemiologic studies for O3 can be found at 72 FR 

37838–37840. 

30The consideration of ambient O3

concentrations in the locations of these 

epidemiologic studies are discussed in sections 

II.D.1.b and II.E.4.a below, for the current standard 

and for alternative standards, respectively. 

31The ISA concluded that, ‘‘[o]verall, recent 

studies provide copollutant results that are 

consistent with those from the studies evaluated in 

the 2006 O3 AQCD [(U.S. EPA, 2006[a]), Figure 7– 

12, page 7–80 of the 2006 O3 AQCD], which found 

that O3 respiratory hospital admissions risk 

estimates remained robust to the inclusion of PM 

in copollutant models (U.S. EPA, 2013, pp. 6–152 

to 6–153). 

32Premature mortality is discussed in more detail 

below in section II.A.1.b.iv. 

when the available evidence is taken as 

a whole, the ISA concludes that acute 

O3 exposures impair the host defense 

capability of animals, primarily by 

depressing alveolar macrophage 

function and perhaps also by decreasing 

mucociliary clearance of inhaled 

particles and microorganisms. Coupled 

with limited evidence from controlled 

human exposure studies, this suggests 

that humans exposed to O3 could be 

predisposed to bacterial infections in 

the lower respiratory tract. 

Allergic and Asthma Related Responses 

Evidence from controlled human 

exposure and epidemiologic studies 

available in the last review indicates 

that O3 exposure skews immune 

responses toward an allergic phenotype 

and could also make airborne allergens 

more allergenic, as discussed in more 

detail in the proposal (79 FR 75257). 

Evidence from controlled human 

exposure and animal toxicology studies 

available in the last review indicates 

that O3 may also increase AHR to 

specific allergen triggers (75 FR 2970, 

January 19, 2010). When combined with 

NO2, O3 has been shown to enhance 

nitration of common protein allergens, 

which may increase their allergenicity 

(Franze et al., 2005). 

Hospital Admissions and Emergency 

Department Visits 

The 2006 AQCD concluded that ‘‘the 

overall evidence supports a causal 

relationship between acute ambient O3

exposures and increased respiratory 

morbidity resulting in increased 

emergency department visits and 

[hospital admissions] during the warm 

season’’ 29 (U.S. EPA, 2006a). This 

conclusion was ‘‘strongly supported by 

the human clinical, animal 

toxicologic[al], and epidemiologic 

evidence for [O3-induced] lung function 

decrements, increased respiratory 

symptoms, airway inflammation, and 

airway hyperreactivity’’ (U.S. EPA, 

2006a). 

The results of recent studies largely 

support the conclusions of the 2006 

AQCD (U.S. EPA, 2013, section 6.2.7). 

Since the completion of the 2006 AQCD, 

relatively fewer studies, conducted in 

the U.S., Canada, and Europe, have 

evaluated associations between shortterm O3 concentrations and respiratory 

hospital admissions and emergency 

department visits, with a growing 

number of studies conducted in Asia. 

This epidemiologic evidence is 

discussed in detail in the proposal (79 

FR 75258) and in the ISA (U.S. EPA, 

2013, section 6.2.7).30

In considering this body of evidence, 

the ISA focused primarily on multicity 

studies because they examine 

associations with respiratory-related 

hospital admissions and emergency 

department visits over large geographic 

areas using consistent statistical 

methodologies (U.S. EPA, 2013, section 

6.2.7.1). The ISA also focused on singlecity studies that encompassed a large 

number of daily hospital admissions or 

emergency department visits, included 

long study-durations, were conducted in 

locations not represented by the larger 

studies, or examined populationspecific characteristics that may impact 

the risk of O3-related health effects but 

were not evaluated in the larger studies 

(U.S. EPA, 2013, section 6.2.7.1). When 

examining the association between 

short-term O3 exposure and respiratory 

health effects that require medical 

attention, the ISA distinguishes between 

hospital admissions and emergency 

department visits because it is likely 

that a small percentage of respiratory 

emergency department visits will be 

admitted to the hospital; therefore, 

respiratory emergency department visits 

may represent potentially less serious, 

but more common outcomes (U.S. EPA, 

2013, section 6.2.7.1). 

The collective evidence across studies 

indicates a mostly consistent positive 

association between O3 exposure and 

respiratory-related hospital admissions 

and emergency department visits. 

Moreover, the magnitude of these 

associations may be underestimated to 

the extent members of study 

populations modify their behavior in 

response to air quality forecasts, and to 

the extent such behavior modification 

increases exposure misclassification 

(U.S. EPA, 2013, Section 4.6.6). Studies 

examining the potential confounding 

effects of copollutants have reported 

that O3 effect estimates remained 

relatively robust upon the inclusion of 

PM and gaseous pollutants in twopollutant models (U.S. EPA, 2013, 

Figure 6–20, Table 6–29). Additional 

studies that conducted copollutant 

analyses, but did not present 

quantitative results, also support these 

conclusions (Strickland et al., 2010; 

Tolbert et al., 2007; Medina-Ramon et 

al., 2006; U.S. EPA, 2013, section 

6.2.7.5).31

In the last review, studies had not 

evaluated the concentration-response 

relationship between short-term O3

exposure and respiratory-related 

hospital admissions and emergency 

department visits. As described in the 

proposal in section II.B.2.a.vii (79 FR 

75257) and in the ISA (U.S. EPA, 2013, 

section 6.2.7.2), a preliminary 

examination of this relationship in 

studies that have become available since 

the last review found no evidence of a 

deviation from linearity when 

examining the association between 

short-term O3 exposure and asthma 

hospital admissions (Silverman and Ito, 

2010; Strickland et al., 2010). In 

addition, an examination of the 

concentration-response relationship for 

O3 exposure and pediatric asthma 

emergency department visits found no 

evidence of a threshold at O3

concentrations as low as 30 ppb (for 

daily maximum 8-hour concentrations) 

(U.S. EPA, 2013, section 6.2.7.3). 

However, in these studies there is 

uncertainty in the shape of the 

concentration-response curve at the 

lower end of the distribution of O3

concentrations due to the low density of 

data in this range. Further studies at 

low-level O3 exposures might reduce 

this uncertainty. 

Respiratory Mortality 

Evidence from experimental studies 

indicates multiple potential pathways of 

respiratory effects from short-term O3

exposures, which support the 

continuum of respiratory effects that 

could potentially result in respiratoryrelated mortality in adults (U.S. EPA, 

2013, section 6.2.8).32 The evidence in 

the last review was inconsistent for 

associations between short-term O3

concentrations and respiratory mortality 

(U.S. EPA, 2006a). New epidemiologic 

evidence for respiratory mortality is 

discussed in detail in the ISA (U.S. EPA, 

2013, section 6.6) and summarized 

below. The majority of recent multicity 

studies have reported positive 

associations between short-term O3

exposures and respiratory mortality, 

particularly during the summer months 

(U.S. EPA, 2013, Figure 6–36). 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65307 

Recent multicity studies from the U.S. 

(Zanobetti and Schwartz, 2008), Europe 

(Samoli et al., 2009), Italy (Stafoggia et 

al., 2010), and Asia (Wong et al., 2010), 

as well as a multi-continent study 

(Katsouyanni et al., 2009), reported 

associations between short-term O3

concentrations and respiratory mortality 

(U.S. EPA, 2013, Figure 6–37, page 6– 

259). With respect to respiratory 

mortality, summer-only analyses were 

consistently positive and most were 

statistically significant. All-year 

analyses had more mixed results, but 

most were positive. 

Of the studies evaluated, only two 

studies analyzed the potential for 

copollutant confounding of the O3- 

respiratory mortality relationship 

(Katsouyanni et al., (2009); Stafoggia et 

al., (2010)). Based on the results of these 

analyses, the O3 respiratory mortality 

risk estimates appear to be moderately 

to substantially sensitive (e.g., increased 

or attenuated) to inclusion of PM10. 

However, in the APHENA study 

(Katsouyanni et al., 2009), the mostly 

every-6th-day sampling schedule for 

PM10 in the Canadian and U.S. datasets 

greatly reduced their sample size and 

limits the interpretation of these results 

(U.S. EPA, 2013, sections 6.2.8 and 

6.2.9). 

The evidence for associations between 

short-term O3 concentrations and 

respiratory mortality has been 

strengthened since the last review, with 

the addition of several large multicity 

studies. The biological plausibility of 

the associations reported in these 

studies is supported by the 

experimental evidence for respiratory 

effects. 

ii. Respiratory Effects—Long-Term 

Exposure 

Since the last review, the body of 

evidence indicating the occurrence of 

respiratory effects due to long-term O3

exposure has been strengthened. This 

evidence is discussed in detail in the 

ISA (U.S. EPA, 2013, Chapter 7) and 

summarized below for new-onset 

asthma and asthma prevalence, asthma 

hospital admissions, pulmonary 

structure and function, and respiratory 

mortality. 

Asthma is a heterogeneous disease 

with a high degree of temporal 

variability. The onset, progression, and 

symptoms can vary within an 

individual’s lifetime, and the course of 

asthma may vary markedly in young 

children, older children, adolescents, 

and adults. In the previous review, 

longitudinal cohort studies that 

examined associations between longterm O3 exposures and the onset of 

asthma in adults and children indicated 

a direct effect of long-term O3 exposures 

on asthma risk in adults and effect 

modification by O3 in children. Since 

then, additional studies have evaluated 

associations with new onset asthma, 

further informing our understanding of 

the potential gene-environment 

interactions, mechanisms, and 

biological pathways associated with 

incident asthma. 

In children, the relationship between 

long-term O3 exposure and new-onset 

asthma has been extensively studied in 

the Children’s Health Study (CHS), a 

long-term study that was initiated in the 

early 1990’s which has evaluated effects 

in several cohorts of children. For this 

review, recent studies from the CHS 

provide evidence for gene-environment 

interactions in effects on new-onset 

asthma by indicating that the lower 

risks associated with specific genetic 

variants are found in children who live 

in lower O3 communities. Described in 

detail in the proposal (79 FR 75259) and 

in the ISA (U.S. EPA, 2013, section 

7.2.1), these studies indicate that the 

risk for new-onset asthma is related in 

part to genetic susceptibility, as well as 

behavioral factors and environmental 

exposure. Cross-sectional studies by 

Akinbami et al. (2010) and Hwang et al. 

(2005) provide further evidence relating 

O3 exposures with asthma prevalence. 

Gene-environment interactions are 

discussed in detail in Section 5.4.2.1 in 

the ISA (U.S. EPA, 2013). 

In the 2006 AQCD (U.S. EPA, 2006a), 

studies on O3-related hospital 

discharges and emergency department 

visits for asthma and respiratory disease 

mainly looked at short-term (daily) 

metrics. Recent studies continue to 

indicate that there is evidence for 

increases in both hospital admissions 

and emergency department visits in 

children and adults related to all 

respiratory outcomes, including asthma, 

with stronger associations in the warm 

months. 

In the 2006 AQCD (U.S. EPA, 2006a), 

few epidemiologic studies had 

investigated the effect of chronic O3

exposure on pulmonary function. As 

discussed in the proposal, 

epidemiologic studies of long-term 

exposures in both children and adults 

provide mixed results about the effects 

of long-term O3 exposure on pulmonary 

function and the growth rate of lung 

function. 

Long-term studies in animals allow 

for greater insight into the potential 

effects of prolonged exposure to O3 that 

may not be easily measured in humans, 

such as structural changes in the 

respiratory tract. Despite uncertainties, 

epidemiologic studies observing 

associations of O3 exposure with 

functional changes in humans can attain 

biological plausibility in conjunction 

with long-term toxicological studies, 

particularly O3-inhalation studies 

performed in non-human primates 

whose respiratory systems most closely 

resemble that of the human. An 

important series of studies, discussed in 

section 7.2.3.2 of the ISA (U.S. EPA, 

2013), have used nonhuman primates to 

examine the effect of O3 alone, or in 

combination with an inhaled allergen, 

house dust mite antigen, on morphology 

and lung function. Animals exhibit the 

hallmarks of allergic asthma defined for 

humans (NHLBI, 2007). These studies 

and others have demonstrated changes 

in pulmonary function and airway 

morphology in adult and infant 

nonhuman primates repeatedly exposed 

to environmentally relevant 

concentrations of O3 (U.S. EPA, 2013, 

section 7.2.3.2). As discussed in more 

detail in the proposal, the studies 

provide evidence of an O3-induced 

change in airway resistance and 

responsiveness and provide biological 

plausibility of long-term exposure, or 

repeated short-term exposures, to O3

contributing to the effects of asthma in 

children. 

Collectively, evidence from animal 

studies strongly suggests that chronic O3

exposure is capable of damaging the 

distal airways and proximal alveoli, 

resulting in lung tissue remodeling and 

leading to apparent irreversible changes. 

Potentially, persistent inflammation and 

interstitial remodeling play an 

important role in the progression and 

development of chronic lung disease. 

Further discussion of the modes of 

action that lead to O3-induced 

morphological changes and the 

mechanisms involved in lifestage 

susceptibility and developmental effects 

can be found in the ISA (U.S. EPA, 

2013, section 5.3.7, section 5.4.2.4). The 

findings reported in chronic animal 

studies offer insight into potential 

biological mechanisms for the suggested 

association between seasonal O3

exposure and reduced lung function 

development in children as observed in 

epidemiologic studies (U.S. EPA, 2013, 

section 7.2.3.1). Further research could 

help fill in the gaps in our 

understanding of the mechanisms 

involved in lifestage susceptibility and 

developmental effects in children of 

seasonal or long-term exposure to O3. 

A limited number of epidemiologic 

studies have assessed the relationship 

between long-term exposure to O3 and 

mortality in adults. The 2006 AQCD 

concluded that an insufficient amount 

of evidence existed ‘‘to suggest a causal 

relationship between chronic O3

exposure and increased risk for 

mstockstill on DSK4VPTVN1PROD with RULES2

65308 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

mortality in humans’’ (U.S. EPA, 2006a). 

Though total and cardio-pulmonary 

mortality were considered in these 

studies, respiratory mortality was not 

specifically considered. 

In a recent follow-up analysis of the 

American Cancer Society cohort (Jerrett 

et al., 2009), cardiopulmonary deaths 

were separately subdivided into 

respiratory and cardiovascular deaths, 

rather than combined as in the Pope et 

al. (2002) work. Increased O3 exposure 

was associated with the risk of death 

from respiratory causes, and this effect 

was robust to the inclusion of PM2.5. 

Additionally, a recent multicity time 

series study (Zanobetti and Schwartz, 

2011), which followed (from 1985 to 

2006) four cohorts of Medicare enrollees 

with chronic conditions that might 

predispose to O3-related effects, 

observed an association between longterm (warm season) exposure to O3 and 

elevated risk of mortality in the cohort 

that had previously experienced an 

emergency hospital admission due to 

chronic obstructive pulmonary disease 

(COPD). A key limitation of this study 

is the inability to control for PM2.5, 

because data were not available in these 

cities until 1999. 

iii. Cardiovascular Effects—Short-Term 

Exposure 

A relatively small number of studies 

have examined the potential effect of 

short-term O3 exposure on the 

cardiovascular system. The 2006 AQCD 

(U.S. EPA, 2006a, p. 8–77) concluded 

that ‘‘O3 directly and/or indirectly 

contributes to cardiovascular-related 

morbidity,’’ but added that the body of 

evidence was limited. This conclusion 

was based on a controlled human 

exposure study that included 

hypertensive adult males; a few 

epidemiologic studies of physiologic 

effects, heart rate variability, 

arrhythmias, myocardial infarctions, 

and hospital admissions; and 

toxicological studies of heart rate, heart 

rhythm, and blood pressure. 

More recently, the body of scientific 

evidence available that has examined 

the effect of O3 on the cardiovascular 

system has expanded. There is an 

emerging body of animal toxicological 

evidence demonstrating that short-term 

exposure to O3 can lead to autonomic 

nervous system alterations (in heart rate 

and/or heart rate variability) and 

suggesting that proinflammatory signals 

may mediate cardiovascular effects. 

Interactions of O3 with respiratory tract 

components result in secondary 

oxidation product formation and 

subsequent production of inflammatory 

mediators, which have the potential to 

penetrate the epithelial barrier and to 

initiate toxic effects systemically. In 

addition, animal toxicological studies of 

long-term exposure to O3 provide 

evidence of enhanced atherosclerosis 

and ischemia/reperfusion (I/R) injury, 

corresponding with development of a 

systemic oxidative, proinflammatory 

environment. Recent experimental and 

epidemiologic studies have investigated 

O3-related cardiovascular events and are 

summarized in the ISA (U.S. EPA, 2013, 

section 6.3). 

Controlled human exposure studies 

discussed in previous reviews have not 

demonstrated any consistent 

extrapulmonary effects. In this review, 

evidence from controlled human 

exposure studies suggests 

cardiovascular effects in response to 

short-term O3 exposure (U.S. EPA, 2013, 

section 6.3.1) and provides some 

coherence with evidence from animal 

toxicology studies. Controlled human 

exposure studies also support the 

animal toxicological studies by 

demonstrating O3-induced effects on 

blood biomarkers of systemic 

inflammation and oxidative stress, as 

well as changes in biomarkers that can 

indicate the potential for increased 

clotting following O3 exposures. 

Increases and decreases in high 

frequency heart rate variability (HRV) 

have been reported. These changes in 

cardiac function observed in animal and 

human studies provide preliminary 

evidence for O3-induced modulation of 

the autonomic nervous system through 

the activation of neural reflexes in the 

lung (U.S. EPA, 2013, section 5.3.2). 

Overall, the ISA concludes that the 

available body of epidemiologic 

evidence examining the relationship 

between short-term exposures to O3

concentrations and cardiovascular 

morbidity is inconsistent (U.S. EPA, 

2013, section 6.3.2.9). 

Despite the inconsistent evidence for 

an association between O3 concentration 

and cardiovascular disease (CVD) 

morbidity, mortality studies indicate a 

consistent positive association between 

short-term O3 exposure and 

cardiovascular mortality in multicity 

studies and in a multi-continent study. 

When examining mortality due to CVD, 

epidemiologic studies consistently 

observe positive associations with shortterm exposure to O3. Additionally, there 

is some evidence for an association 

between long-term exposure to O3 and 

mortality, although the association 

between long-term ambient O3

concentrations and cardiovascular 

mortality can be confounded by other 

pollutants (U.S. EPA, 2013). The ISA 

(U.S. EPA, 2013, section 6.3.4) states 

that taken together, the overall body of 

evidence across the animal and human 

studies is sufficient to conclude that 

there is likely to be a causal relationship 

between relevant short-term exposures 

to O3 and cardiovascular system effects. 

iv. Premature Mortality—Short-Term 

Exposure 

The 2006 AQCD concluded that the 

overall body of evidence was highly 

suggestive that short-term exposure to 

O3 directly or indirectly contributes to 

nonaccidental and cardiopulmonaryrelated mortality in adults, but 

additional research was needed to more 

fully establish underlying mechanisms 

by which such effects occur (U.S. EPA, 

2006a; U.S. EPA, 2013, p. 2–18). In 

building on the evidence for mortality 

from the last review, the ISA states (U.S. 

EPA, 2013, p. 6–261): 

The evaluation of new multicity studies 

that examined the association between shortterm O3 exposures and mortality found 

evidence that supports the conclusions of the 

2006 AQCD. These new studies reported 

consistent positive associations between 

short-term O3 exposure and all-cause 

(nonaccidental) mortality, with associations 

persisting or increasing in magnitude during 

the warm season, and provide additional 

support for associations between O3 exposure 

and cardiovascular and respiratory mortality. 

The 2006 AQCD reviewed a large 

number of time-series studies of 

associations between short-term O3

exposures and total mortality including 

single- and multicity studies, and metaanalyses. Available studies reported 

some evidence for heterogeneity in O3

mortality risk estimates across cities and 

across studies. Studies that conducted 

seasonal analyses reported larger O3

mortality risk estimates during the 

warm or summer season. Overall, the 

2006 AQCD identified robust 

associations between various measures 

of daily ambient O3 concentrations and 

all-cause mortality, which could not be 

readily explained by confounding due 

to time, weather, or copollutants. With 

regard to cause-specific mortality, 

consistent positive associations were 

reported between short-term O3

exposure and cardiovascular mortality, 

with less consistent evidence for 

associations with respiratory mortality. 

The majority of the evidence for 

associations between O3 and causespecific mortality were from single-city 

studies, which had small daily mortality 

counts and subsequently limited 

statistical power to detect associations. 

The 2006 AQCD concluded that ‘‘the 

overall body of evidence is highly 

suggestive that O3 directly or indirectly 

contributes to nonaccidental and 

cardiopulmonary-related mortality’’ 

(U.S. EPA, 2013, section 6.6.1). 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65309 

33 ‘‘In drawing the distinction between adverse 

and nonadverse reversible effects, this committee 

recommended that reversible loss of lung function 

in combination with the presence of symptoms 

should be considered as adverse’’ (ATS, 2000a). 

34These include, for example, the transient and 

reversible effects demonstrated in controlled human 

exposure studies, such as lung function decrements 

or respiratory symptoms. 

Recent studies have strengthened the 

body of evidence that supports the 

association between short-term O3

concentrations and mortality in adults. 

This evidence includes a number of 

studies reporting associations with 

nonaccidental as well as cause-specific 

mortality. Multi-continent and multicity 

studies have consistently reported 

positive and statistically significant 

associations between short-term O3

concentrations and all-cause mortality, 

with evidence for larger mortality risk 

estimates during the warm or summer 

months (79 FR 75262; U.S. EPA, 2013 

Figure 6–27; Table 6–42). Similarly, 

evaluations of cause-specific mortality 

have reported consistently positive 

associations with O3, particularly in 

analyses restricted to the warm season 

(79 FR 75262; U.S. EPA, 2013 Fig. 6–37; 

Table 6–53). 

In the previous review, multiple 

uncertainties remained regarding the 

relationship between short-term O3

concentrations and mortality, including 

the extent of residual confounding by 

copollutants; characterization of the 

factors that modify the O3-mortality 

association; the appropriate lag 

structure for identifying O3-mortality 

effects; and the shape of the O3- 

mortality concentration-response 

function and whether a threshold exists. 

Many of the studies, published since the 

last review, have attempted to address 

one or more of these uncertainties and 

are described in more detail in the 

proposal (79 FR 75262 and in the ISA 

(U.S. EPA, 2013, section 6.6.2). 

In particular, recent studies have 

evaluated different statistical 

approaches to examine the shape of the 

O3-mortality concentration-response 

relationship and to evaluate whether a 

threshold exists for O3-related mortality. 

These studies are detailed in the 

proposal (79 FR 75262) and in the ISA 

(U.S. EPA, 2013, p. 2–32). The ISA 

reaches the following overall 

conclusions that the epidemiologic 

studies identified in the ISA indicated 

a generally linear C–R function with no 

indication of a threshold but that there 

is a lack of data at lower O3

concentrations and therefore, less 

certainty in the shape of the C–R curve 

at the lower end of the distribution (U.S. 

EPA, 2013, p. 2–32). 

c. Adversity of Effects 

In making judgments as to when 

various O3-related effects become 

regarded as adverse to the health of 

individuals, in previous NAAQS 

reviews, the EPA has relied upon the 

guidelines published by the ATS and 

the advice of CASAC. In 2000, the ATS 

published an official statement on 

‘‘What Constitutes an Adverse Health 

Effect of Air Pollution?’’ (ATS, 2000a), 

which updated and built upon its earlier 

guidance (ATS, 1985). The earlier 

guidance defined adverse respiratory 

health effects as ‘‘medically significant 

physiologic changes generally 

evidenced by one or more of the 

following: (1) Interference with the 

normal activity of the affected person or 

persons, (2) episodic respiratory illness, 

(3) incapacitating illness, (4) permanent 

respiratory injury, and/or (5) progressive 

respiratory dysfunction,’’ while 

recognizing that perceptions of 

‘‘medical significance’’ and ‘‘normal 

activity’’ may differ among physicians, 

lung physiologists and experimental 

subjects (ATS, 1985). The more recent 

guidance concludes that transient, 

reversible loss of lung function in 

combination with respiratory symptoms 

should be considered adverse.33

However, the committee also 

recommended ‘‘that a small, transient 

loss of lung function, by itself, should 

not automatically be designated as 

adverse’’ (ATS, 2000a, p. 670). 

There is also a more specific 

consideration of population risk in the 

2000 guidance. Specifically, the 

committee considered that a shift in the 

risk factor distribution, and hence the 

risk profile of the exposed population, 

should be considered adverse, even in 

the absence of the immediate 

occurrence of frank illness (ATS, 2000a, 

p. 668). For example, a population of 

asthmatics could have a distribution of 

lung function such that no individual 

has a level associated with clinically 

important impairment. Exposure to air 

pollution could shift the distribution to 

lower levels of lung function that still 

do not bring any individual to a level 

that is associated with clinically 

relevant effects. However, this would be 

considered to be adverse because 

individuals within the population 

would already have diminished reserve 

function, and therefore would be at 

increased risk to further environmental 

insult (ATS, 2000a, p. 668). 

The ATS also concluded in its 

guidance that elevations of biomarkers 

such as cell numbers and types, 

cytokines, and reactive oxygen species 

may signal risk for ongoing injury and 

more serious effects or may simply 

represent transient responses, 

illustrating the lack of clear boundaries 

that separate adverse from nonadverse 

events. More subtle health outcomes 

also may be connected mechanistically 

to health effects that are clearly adverse, 

so that small changes in physiological 

measures may not appear clearly 

adverse when considered alone, but 

may be part of a coherent and 

biologically plausible chain of related 

health outcomes that include responses 

that are clearly adverse, such as 

mortality (U.S. EPA, 2014c, section 

3.1.2.1). 

Application of the ATS guidelines to 

the least serious category of effects 34

related to ambient O3 exposures, which 

are also the most numerous and, 

therefore, are also important from a 

public health perspective, involves 

judgments about which medical experts 

on CASAC panels and public 

commenters have in the past expressed 

diverse views. To help frame such 

judgments, in past reviews, the EPA has 

defined gradations of individual 

functional responses (e.g., decrements 

in FEV1 and airway responsiveness) and 

symptomatic responses (e.g., cough, 

chest pain, wheeze), together with 

judgments as to the potential impact on 

individuals experiencing varying 

degrees of severity of these responses. 

These gradations were used by the EPA 

in the 1997 O3 NAAQS review and 

slightly revised in the 2008 review (U.S. 

EPA, 1996b, p. 59; U.S. EPA, 2007, p. 

3–72; 72 FR 37849, July 11, 2007). These 

gradations and impacts are summarized 

in Tables 3–2 and 3–3 in the 2007 O3

Staff Paper (U.S. EPA, 2007, pp. 3–74 to 

3–75). 

For the purpose of estimating 

potentially adverse lung function 

decrements in active healthy people, the 

CASAC panel in the 2008 O3 NAAQS 

review indicated that a focus on the mid 

to upper end of the range of moderate 

levels of functional responses is most 

appropriate (e.g., FEV1 decrements 

≥15% but <20%) (Henderson, 2006; U.S. 

EPA, 2007, p. 3–76). In this review, 

CASAC reiterated that the ‘‘[e]stimation 

of FEV1 decrements of ≥15% is 

appropriate as a scientifically relevant 

surrogate for adverse health outcomes in 

active healthy adults’’ (Frey, 2014c, p. 

3). 

For the purpose of estimating 

potentially adverse lung function 

decrements in people with lung disease, 

the CASAC panel in the 2008 O3

NAAQS review indicated that a focus 

on the lower end of the range of 

moderate levels of functional responses 

is most appropriate (e.g., FEV1

decrements ≥10%) (Henderson, 2006; 

U.S. EPA, 2007, p. 3–76). In their letter 

mstockstill on DSK4VPTVN1PROD with RULES2

65310 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

35As noted above, the ATS recommended ‘‘that 

a small, transient loss of lung function, by itself, 

should not automatically be designated as adverse’’ 

(ATS, 2000a, p. 670). 

36Lifestages, which in this case includes 

childhood and older adulthood, are experienced by 

most people over the course of a lifetime, unlike 

other factors associated with at-risk populations. 

advising the Administrator on the 

reconsideration of the 2008 final 

decision, CASAC stated that ‘‘[a] 10% 

decrement in FEV1 can lead to 

respiratory symptoms, especially in 

individuals with pre-existing 

pulmonary or cardiac disease. For 

example, people with chronic 

obstructive pulmonary disease have 

decreased ventilatory reserve (i.e., 

decreased baseline FEV1) such that a ≥ 

10% decrement could lead to moderate 

to severe respiratory symptoms’’ (Samet, 

2011). In this review, CASAC provided 

similar advice, stating that ‘‘[a]n FEV1

decrement of ≥ 10% is a scientifically 

relevant surrogate for adverse health 

outcomes for people with asthma and 

lung disease’’, and that such decrements 

‘‘could be adverse for people with lung 

disease’’ (Frey, 2014c, pp. 3, 7). 

In judging the extent to which these 

impacts represent effects that should be 

regarded as adverse to the health status 

of individuals, in previous NAAQS 

reviews, the EPA has also considered 

whether effects were experienced 

repeatedly during the course of a year or 

only on a single occasion (U.S. EPA, 

2007). While some experts would judge 

single occurrences of moderate 

responses to be a ‘‘nuisance,’’ especially 

for healthy individuals, a more general 

consensus view of the adversity of such 

moderate responses emerges as the 

frequency of occurrence increases. In 

particular, not every estimated 

occurrence of an O3-induced FEV1

decrement will be adverse.35 However, 

repeated occurrences of moderate 

responses, even in otherwise healthy 

individuals, may be considered to be 

adverse since they could set the stage 

for more serious illness (61 FR 65723). 

The CASAC panel in the 1997 NAAQS 

review expressed a consensus view that 

these ‘‘criteria for the determination of 

an adverse physiological response were 

reasonable’’ (Wolff, 1995). In the review 

completed in 2008, as in the current 

review (II.B, II.C below), estimates of 

repeated occurrences continued to be an 

important public health policy factor in 

judging the adversity of moderate lung 

function decrements in healthy and 

asthmatic people (72 FR 37850, July 11, 

2007). 

d. Ozone-Related Impacts on Public 

Health 

The currently available evidence 

expands the understanding of 

populations that were identified to be at 

greater risk of O3-related health effects 

at the time of the last review (i.e., people 

who are active outdoors, people with 

lung disease, children and older adults 

and people with increased 

responsiveness to O3) and supports the 

identification of additional factors that 

may lead to increased risk (U.S. EPA, 

2006a, section 6.3; U.S. EPA, 2013, 

Chapter 8). Populations and lifestages 

may be at greater risk for O3-related 

health effects due to factors that 

contribute to their susceptibility and/or 

vulnerability to O3. The definitions of 

susceptibility and vulnerability have 

been found to vary across studies, but in 

most instances ‘‘susceptibility’’ refers to 

biological or intrinsic factors (e.g., 

lifestage, sex, preexisting disease/

conditions) while ‘‘vulnerability’’ refers 

to non-biological or extrinsic factors 

(e.g., socioeconomic status [SES]) (U.S. 

EPA, 2013, p. 8–1; U.S. EPA, 2010, 

2009b). In some cases, the terms ‘‘atrisk’’ and ‘‘sensitive’’ have been used to 

encompass these concepts more 

generally. In the ISA, PA, and proposal, 

‘‘at-risk’’ is the all-encompassing term 

used to define groups with specific 

factors that increase their risk of O3- 

related health effects. 

There are multiple avenues by which 

groups may experience increased risk 

for O3-induced health effects. A 

population or lifestage 36 may exhibit 

greater effects than other populations or 

lifestages exposed to the same 

concentration or dose, or they may be at 

greater risk due to increased exposure to 

an air pollutant (e.g., time spent 

outdoors). A group with intrinsically 

increased risk would have some 

factor(s) that increases risk through a 

biological mechanism and, in general, 

would have a steeper concentration-risk 

relationship, compared to those not in 

the group. Factors that are often 

considered intrinsic include preexisting asthma, genetic background, 

and lifestage. A group of people could 

also have extrinsically increased risk, 

which would be through an external, 

non-biological factor, such as 

socioeconomic status (SES) and diet. 

Some groups are at risk of increased 

internal dose at a given exposure 

concentration, for example, because of 

breathing patterns. This category would 

include people who work or exercise 

outdoors. Finally, there are those who 

might be placed at increased risk for 

experiencing greater exposures by being 

exposed to higher O3 concentrations. 

This would include, for example, 

groups of people with greater exposure 

to ambient O3 due to less availability or 

use of home air conditioners such that 

they are more likely to be in locations 

with open windows on high O3 days. 

Some groups may be at increased risk of 

O3-related health effects through a 

combination of factors. For example, 

children tend to spend more time 

outdoors when O3 levels are high, and 

at higher levels of activity than adults, 

which leads to increased exposure and 

dose, and they also have biological, or 

intrinsic, risk factors (e.g., their lungs 

are still developing) (U.S. EPA, 2013, 

Chapter 8). An at-risk population or 

lifestage is more likely to experience 

adverse health effects related to O3

exposures and/or, develop more severe 

effects from exposure than the general 

population. The populations and 

lifestages identified by the ISA (U.S. 

EPA, 2013, section 8.5) identified that 

have ‘‘adequate’’ evidence for increased 

O3-related health effects are people with 

certain genotypes, people with asthma, 

younger and older age groups, people 

with reduced intake of certain nutrients, 

and outdoor workers. These at-risk 

populations and lifestages are described 

in more detail in section II.B.4 of the 

proposal (79 FR 75264–269). 

One consideration in the assessment 

of potential public health impacts is the 

size of various population groups for 

which there is adequate evidence of 

increased risk for health effects 

associated with O3-related air pollution 

exposure (U.S. EPA, 2014c, section 

3.1.5.2). The factors for which the ISA 

judged the evidence to be ‘‘adequate’’ 

with respect to contributing to increased 

risk of O3-related effects among various 

populations and lifestages included: 

Asthma; childhood and older 

adulthood; diets lower in vitamins C 

and E; certain genetic variants; and 

working outdoors (U.S. EPA, 2013, 

section 8.5). No statistics are available to 

estimate the size of an at-risk population 

based on nutritional status or genetic 

variability. 

With regard to asthma, Table 3–7 in 

the PA (U.S. EPA, 2014c, section 

3.1.5.2) summarizes information on the 

prevalence of current asthma by age in 

the U.S. adult population in 2010 

(Schiller et al. 2012; children—Bloom et 

al., 2011). Individuals with current 

asthma constitute a fairly large 

proportion of the population, including 

more than 25 million people. Asthma 

prevalence tends to be higher in 

children than adults. Within the U.S., 

approximately 8.2% of adults have 

reported currently having asthma 

(Schiller et al., 2012) and 9.5% of 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65311 

37As noted below (II.C.3.a.ii), asthmatics can 

experience larger O3-induced respiratory effects 

than non-asthmatic, healthy adults. The 

responsiveness of asthmatics to O3 exposures could 

depend on factors that have not been well-evaluated 

such as asthma severity, the effectiveness of asthma 

control, or the prevalence of medication use. 

38The O*NET program is the nation’s primary 

source of occupational information. Central to the 

project is the O*NET database, containing 

information on hundreds of standardized and 

occupation-specific descriptors. The database, 

which is available to the public at no cost, is 

continually updated by surveying a broad range of 

workers from each occupation. http://www.

onetcenter.org/overview.html. http://www.

onetonline.org/find/descriptor/browse/Work_

Context/4.C.2/. 

39The HREA uses the Community Multi-scale Air 

Quality (CMAQ) photochemical model 

instrumented with the higher order direct 

decoupled method (HDDM) to estimate O3

concentrations that would occur with the 

achievement of the current and alternative O3

standards (U.S. EPA, 2014a, Chapter 4). 

40The urban study areas assessed are Atlanta, 

Baltimore, Boston, Chicago, Cleveland, Dallas, 

Denver, Detroit, Houston, Los Angeles, New York, 

Philadelphia, Sacramento, St. Louis, and 

Washington, DC. 

41Exposure and risk analyses for most of the 

urban study areas focus on reducing U.S. 

anthropogenic NOX emissions alone. The 

exceptions are Chicago and Denver. Exposure and 

risk analyses for Chicago and Denver are based on 

reductions in emissions of both NOX and VOC (U.S. 

EPA, 2014a, section 4.3.3.1; Appendix 4D). 

42These estimates thus reflect design values—8 

hour values using the form of the NAAQS that meet 

the level of the current or alternative standards. 

These simulations are illustrative and do not reflect 

any consideration of specific control programs 

designed to achieve the reductions in emissions 

required to meet the specified standards. Further, 

these simulations do not represent predictions of 

when, whether, or how areas might meet the 

specified standards. 

43 It is important to note that sensitivity analyses 

in the HREA indicate that the increases in low O3

concentrations are smaller when NOX and VOC 

emissions are reduced than when only NOX

emissions are reduced (U.S. EPA, 2014a, Appendix 

4–D, section 4.7). 

children have reported currently having 

asthma (Bloom et al., 2011).37

With regard to lifestages, based on 

U.S. census data from 2010 (Howden 

and Meyer, 2011), about 74 million 

people, or 24% of the U.S. population, 

are under 18 years of age and more than 

40 million people, or about 13% of the 

U.S. population, are 65 years of age or 

older. Hence, a large proportion of the 

U.S. population (i.e., more than a third) 

is included in age groups that are 

considered likely to be at increased risk 

for health effects from ambient O3

exposure. 

With regard to outdoor workers, in 

2010, approximately 11.7% of the total 

number of people (143 million people) 

employed, or about 16.8 million people, 

worked outdoors one or more days per 

week (based on worker surveys).38 Of 

these, approximately 7.4% of the 

workforce, or about 7.8 million people, 

worked outdoors three or more days per 

week. 

While it is difficult to estimate the 

total number of people in groups that 

are at greater risk from exposure to O3, 

due to the overlap in members of the 

different at-risk population groups, the 

proportion of the total population at 

greater risk is large. The size of the atrisk population combined with the 

estimates of risk of different health 

outcomes associated with exposure to 

O3 can give an indication of the 

magnitude of O3 impacts on public 

health. 

2. Overview of Human Exposure and 

Health Risk Assessments 

To put judgments about health effects 

into a broader public health context, the 

EPA has developed and applied models 

to estimate human exposures to O3 and 

O3-associated health risks. Exposure and 

risk estimates that are output from such 

models are presented and assessed in 

the HREA (U.S. EPA, 2014a). Section 

II.C of the proposal discusses the 

quantitative assessments of O3

exposures and O3-related health risks 

that are presented in the HREA (79 FR 

75270). Summaries of these discussions 

are provided below for the approach 

used to adjust air quality for 

quantitative exposure and risk analyses 

in the HREA (II.A.2.a), the HREA 

assessment of exposures to ambient O3

(II.A.2.b), and the HREA assessments of 

O3-related health risks (II.A.2.c). 

a. Air Quality Adjustment 

As discussed in section II.C.1 of the 

proposal (79 FR 75270), the HREA uses 

a photochemical model to estimate 

sensitivities of O3 to changes in 

precursor emissions in order to estimate 

ambient O3 concentrations that would 

just meet the current and alternative 

standards (U.S. EPA, 2014a, Chapter 

4).39 For the 15 urban study areas 

evaluated in the HREA,40 this modelbased adjustment approach estimates 

hourly O3 concentrations at each 

monitor location when modeled U.S. 

anthropogenic precursor emissions (i.e., 

NOX, VOC) 41 are reduced. The HREA 

estimates air quality that just meets the 

current and alternative standards for the 

2006–2008 and 2008–2010 periods.42

As discussed in Chapter 4 of the 

HREA (U.S. EPA, 2014a), this approach 

to adjusting air quality models the 

physical and chemical atmospheric 

processes that influence ambient O3

concentrations. Compared to the 

quadratic rollback approach used in 

previous reviews, it provides more 

realistic estimates of the spatial and 

temporal responses of O3 to reductions 

in precursor emissions. Because 

ambient NOX can contribute both to the 

formation and destruction of O3 (U.S. 

EPA, 2014a, Chapter 4), the response of 

ambient O3 concentrations to reductions 

in NOX emissions is more variable than 

indicated by the quadratic rollback 

approach. This improved approach to 

adjusting O3 air quality is consistent 

with recommendations from the 

National Research Council of the 

National Academies (NRC, 2008). In 

addition, CASAC strongly supported the 

new approach as an improvement and 

endorsed the way it was utilized in the 

HREA, stating that ‘‘the quadratic 

rollback approach has been replaced by 

a scientifically more valid Higher-order 

Decoupled Direct Method (HDDM)’’ and 

that ‘‘[t]he replacement of the quadratic 

rollback procedure by the HDDM 

procedure is important and supported 

by the CASAC’’ (Frey, 2014a, pp. 1 and 

3). 

Within urban study areas, the modelbased air quality adjustments show 

reductions in the O3 levels at the upper 

ends of ambient concentrations and 

increases in the O3 levels at the lower 

ends of those distributions (U.S. EPA, 

2014a, section 4.3.3.2, Figures 4–9 and 

4–10).43 Seasonal means of daily O3

concentrations generally exhibit only 

modest changes upon model 

adjustment, reflecting the seasonal 

balance between daily decreases in 

relatively higher concentrations and 

increases in relatively lower 

concentrations (U.S. EPA, 2014a, 

Figures 4–9 and 4–10). The resulting 

compression in the seasonal 

distributions of ambient O3

concentrations is evident in all of the 

urban study areas evaluated, though the 

degree of compression varies 

considerably across areas (U.S. EPA, 

2014a, Figures 4–9 and 4–10). 

As discussed in the PA (U.S. EPA, 

2014c, section 3.2.1), adjusted patterns 

of O3 air quality have important 

implications for exposure and risk 

estimates in urban case study areas. 

Estimates influenced largely by the 

upper ends of the distribution of 

ambient concentrations (i.e., exposures 

of concern and lung function risk 

estimates, as discussed in sections 3.2.2 

and 3.2.3.1 of the PA) will decrease with 

model-adjustment to the current and 

alternative standards. In contrast, 

seasonal risk estimates influenced by 

the full distribution of ambient O3

concentrations (i.e., epidemiology-based 

risk estimates, as discussed in section 

3.2.3.2 of the PA) either increase or 

decrease in response to air quality 

adjustment, depending on the balance 

between the daily decreases in high O3

mstockstill on DSK4VPTVN1PROD with RULES2

65312 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

44 In addition, because epidemiology-based risk 

estimates use ‘‘area-wide’’ average O3

concentrations, calculated by averaging 

concentrations across multiple monitors in urban 

case study areas (section 3.2.3.2 below), risk 

estimates on a given day depend on the daily 

balance between increasing and decreasing O3

concentrations at individual monitors. 45This was the case for all of the urban study 

areas evaluated, with the exception of New York 

(U.S. EPA, 2014a, Appendix 4–D, section 4.7). In 

this analysis, emissions of NOX and VOC were 

reduced by equal percentages, a scenario not likely 

to reflect the optimal combination for reducing 

risks. In most of the urban study areas the inclusion 

of VOC emissions reductions did not alter the NOX

emissions reductions required to meet the current 

or alternative standards. The exceptions are Chicago 

and Denver, for which the HREA risk estimates are 

based on reductions in both NOX and VOC (U.S. 

EPA, 2014a, section 4.3.3.1). 

46 In addition, the range of modeled personal 

exposures to ambient O3 provide an essential input 

to the portion of the health risk assessment based 

on exposure-response functions (for lung function 

decrements) from controlled human exposure 

studies. The health risk assessment based on 

exposure-response information is discussed below 

(II.C.3). 

47See 79 FR 75269 ‘‘The activity pattern of 

individuals is an important determinant of their 

exposure. Variation in O3 concentrations among 

various microenvironments means that the amount 

of time spent in each location, as well as the level 

of activity, will influence an individual’s exposure 

to ambient O3. Activity patterns vary both among 

and within individuals, resulting in corresponding 

variations in exposure across a population and over 

time’’ (internal citations omitted). 

48 In this review, the term ‘‘exposure of concern’’ 

is defined as a personal exposure, while at 

moderate or greater exertion, to 8-hour average 

ambient O3 concentrations at and above specific 

benchmarks levels. As discussed below, these 

benchmark levels represent exposure 

concentrations at which O3-induced health effects 

are known to occur, or can reasonably be 

anticipated to occur, in some individuals. 

concentrations and increases in low O3

concentrations.44

To evaluate uncertainties in air 

quality adjustments, the HREA assessed 

the extent to which the modeled O3

response to reductions in NOX

emissions appropriately represent the 

trends observed in monitored ambient 

O3 following actual reductions in NOX

emissions, and the extent to which the 

O3 response to reductions in precursor 

emissions could differ with emissions 

reduction strategies that are different 

from those used in HREA to generate 

risk estimates. 

To evaluate the first issue, the HREA 

conducted a national analysis 

evaluating trends in monitored ambient 

O3 concentrations during a time period 

when the U.S. experienced large-scale 

reductions in NOX emissions (i.e., 2001 

to 2010). Analyses of trends in 

monitored O3 indicate that over such a 

time period, the upper end of the 

distribution of monitored O3

concentrations (i.e., indicated by the 

95th percentile) generally decreased in 

urban and non-urban locations across 

the U.S. (U.S. EPA, 2014a, Figure 8–29). 

During this same time period, median 

O3 concentrations decreased in 

suburban and rural locations, and in 

some urban locations. However, median 

concentrations increased in some large 

urban centers (U.S. EPA, 2014a, Figure 

8–28). As discussed in the HREA, these 

increases in median concentrations 

likely reflect the increases in relatively 

low O3 concentrations that can occur 

near important sources of NOX upon 

reductions in NOX emissions (U.S. EPA, 

2014a, section 8.2.3.1). These patterns of 

monitored O3 during a period when the 

U.S. experienced large reductions in 

NOX emissions are qualitatively 

consistent with the modeled responses 

of O3 to reductions in NOX emissions. 

To evaluate the second issue, the 

HREA assessed the O3 air quality 

response to reducing both NOX and 

VOC emissions (i.e., in addition to 

assessing reductions in NOX emissions 

alone) for a subset of seven urban study 

areas. As discussed in the PA (U.S. EPA, 

2014c, section 3.2.1), the addition of 

VOC reductions generally resulted in 

larger decreases in mid-range O3

concentrations (25th to 75th percentiles) 

(U.S. EPA, 2014a, Appendix 4D, section 

4.7).45 In addition, in all seven of the 

urban study areas evaluated, the 

increases in low O3 concentrations were 

smaller for the NOX/VOC scenarios than 

the NOX alone scenarios (U.S. EPA, 

2014a, Appendix 4D, section 4.7). This 

was most apparent for Denver, Houston, 

Los Angeles, New York, and 

Philadelphia. Given the impacts on total 

risk estimates of increases in low O3

concentrations (discussed below), these 

results suggest that in some locations 

optimized emissions reduction 

strategies could result in larger 

reductions in O3-associated mortality 

and morbidity than indicated by HREA 

estimates. 

b. Exposure Assessment 

As discussed in section II.C.2 of the 

proposal, the O3 exposure assessment 

presented in the HREA (U.S. EPA, 

2014a, Chapter 5) provides estimates of 

the number and percent of people 

exposed to various concentrations of 

ambient O3 while at specified exertion 

levels. The HREA estimates exposures 

in the 15 urban study areas for four 

study groups, all school-age children 

(ages 5 to 18), asthmatic school-age 

children, asthmatic adults (ages 19 to 

95), and all older adults (ages 65 to 95), 

reflecting the evidence indicating that 

these populations are at increased risk 

for O3-attributable effects (U.S. EPA, 

2013, Chapter 8; II.A.1.d, above). An 

important purpose of these exposure 

estimates is to provide perspective on 

the extent to which air quality adjusted 

to just meet the current O3 NAAQS 

could be associated with exposures to 

O3 concentrations reported to result in 

respiratory effects.46 These analyses of 

exposure assessment incorporate 

behavior patterns, including estimates 

of physical exertion, which are critical 

in assessing whether ambient 

concentrations of O3 may pose a public 

health risk.47 In particular, exposures to 

ambient or near-ambient O3

concentrations have only been shown to 

result in potentially adverse effects if 

the ventilation rates of people in the 

exposed populations are raised to a 

sufficient degree (e.g., through physical 

exertion) (U.S. EPA, 2013, section 

6.2.1.1). Estimates of such ‘‘exposures of 

concern’’ provide perspective on the 

potential public health impacts of 

O3-related effects, including effects that 

cannot currently be evaluated in a 

quantitative risk assessment.48

The HREA estimates 8-hour exposures 

at or above benchmark concentrations of 

60, 70, and 80 ppb for individuals 

engaged in moderate or greater exertion 

(i.e., to approximate conditions in the 

controlled human exposure studies on 

which benchmarks are based). 

Benchmarks reflect exposure 

concentrations at which O3-induced 

respiratory effects are known to occur in 

some healthy adults engaged in 

moderate, quasi-continuous exertion, 

based on evidence from controlled 

human exposure studies (U.S. EPA, 

2013, section 6.2; U.S. EPA, 2014c, 

section 3.1.2.1). The amount of weight 

to place on the estimates of exposures 

at or above specific benchmark 

concentrations depends in part on the 

weight of the scientific evidence 

concerning health effects associated 

with O3 exposures at those benchmark 

concentrations. It also depends on 

judgments about the importance, from a 

public health perspective, of the health 

effects that are known or can reasonably 

be inferred to occur as a result of 

exposures at benchmark concentrations 

(U.S. EPA, 2014c, sections 3.1.3, 3.1.5). 

In considering estimates of O3

exposures of concern at or above 

benchmarks of 60, 70, and 80 ppb, the 

PA focuses on modeled exposures for 

school-age children (ages 5–18), 

including asthmatic school-age 

children, which are key at-risk 

populations identified in the ISA (U.S. 

EPA, 2014c, section 3.1.5). The 

percentages of children estimated to 

experience exposures of concern are 

considerably larger than the percentages 

estimated for adult populations (i.e., 

approximately 3-fold larger across urban 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65313 

49HREA exposure estimates for all children and 

asthmatic children are virtually indistinguishable, 

in terms of the percent estimated to experience 

exposures of concern (U.S. EPA, 2014a, Chapter 5). 

Consistent with this, HREA analyses indicate that 

activity data for people with asthma is generally 

similar to non-asthmatic populations (U.S. EPA, 

2014a, Appendix 5G, Tables 5G2-to 5G–5). 

50Estimates for each urban case study area were 

averaged for the years evaluated in the HREA (2006 

to 2010). Ranges reflect the ranges across urban 

study areas. Estimates smaller than 0.05% were 

rounded downward to zero (from U.S. EPA, 2014a, 

Tables 5–11 and 5–12). Numbers in parentheses 

reflect averages across urban study areas, as well as 

over the years evaluated in the HREA. 51Numbers of children exposed in each urban 

case study area were averaged over the years 2006 

to 2010. These averages were then summed across 

urban study areas. Numbers were rounded to 

nearest thousand unless otherwise indicated. 

Estimates smaller than 50 were rounded downward 

to zero (from U.S. EPA, 2014a, Appendix 5F Table 

5F–5). 

52As discussed in section 4.3.3 of the HREA, the 

model-based air quality adjustment approach used 

to estimate exposures and lung function decrements 

associated with the current and alternative 

standards was unable to estimate the distribution of 

ambient O3 concentrations in New York City upon 

just meeting an alternative standard with a level of 

60 ppb. Therefore, for the 60 ppb standard level, the 

numbers of children and asthmatic children, and 

the ranges of percentages, reflect all of the urban 

study areas except New York. 

53As noted below (II.C.3.a.ii), in the case of 

asthmatics, responsiveness to O3 could depend on 

factors that have not been well-evaluated, such as 

asthma severity, the effectiveness of asthma control, 

or the prevalence of medication use. 

54The exception to this is lung function 

decrements, as discussed below (and in U.S. EPA, 

2014c, section 3.2.3.1). 

study areas) 49 (U.S. EPA, 2014a, section 

5.3.2 and Figures 5–5 to 5–8). The larger 

exposure estimates for children are due 

primarily to the larger percentage of 

children estimated to spend an 

extended period of time being 

physically active outdoors when O3

concentrations are elevated (U.S. EPA, 

2014a, sections 5.3.2 and 5.4.1). 

Although exposure estimates differ 

between children and adults, the 

patterns of results across the urban 

study areas and years are similar among 

all of the populations evaluated (U.S. 

EPA, 2014a, Figures 5–5 to 5–8). 

Therefore, while the PA highlights 

estimates in children, including 

asthmatic school-age children, it also 

notes that the patterns of exposures 

estimated for children represent the 

patterns estimated for adult asthmatics 

and older adults. 

Table 1 of the proposal (79 FR 75272 

to 75273) summarizes key results from 

the exposure assessment. This table is 

reprinted below. 

TABLE 1—SUMMARY OF ESTIMATED EXPOSURES OF CONCERN IN ALL SCHOOL-AGE CHILDREN FOR THE CURRENT AND

ALTERNATIVE O3 STANDARDS IN URBAN STUDY AREAS

Benchmark concentration Standard level 

(ppb) 

Average % 

children 

exposed 50

Average number of 

children exposed 

[average number of 

asthmatic children] 51

% Children—worst 

year and worst 

area 

One or more exposures of concern per season 

≥ 80 ppb ......................................................................... 75 0–0.3 (0.1) 27,000 [3,000] 1.1 

70 0–0.1 (0) 3,700 [300] 0.2 

65 0 (0) 300 [0] 0 

60 0 (0) 100 52 [0] 0 

≥ 70 ppb ......................................................................... 75 0.6–3.3 (1.9) 362,000 [40,000] 8.1 

70 0.1–1.2 (0.5) 94,000 [10,000] 3.2 

65 0–0.2 (0.1) 14,000 [2,000] 0.5 

60 0 (0) 1,400 [200] 0.1 

≥ 60 ppb ......................................................................... 75 9.5–17 (12.2) 2,316,000 [246,000] 25.8 

70 3.3–10.2 (6.2) 1,176,000 [126,000] 18.9 

65 0–4.2 (2.1) 392,000 [42,000] 9.5 

60 0–1.2 (0.4) 70,000 [8,000] 2.2 

Two or more exposures of concern per season 

≥ 80 ppb ......................................................................... 75 0 (0) 600 [100] 0.1 

70 0 (0) 0 [0] 0 

65 0 (0) 0 [0] 0 

60 0 (0) 0 [0] 0 

≥ 70 ppb ......................................................................... 75 0.1–0.6 (0.2) 46,000 [5,000] 2.2 

70 0–0.1 (0) 5,400 [600] 0.4 

65 0 (0) 300 [100] 0 

60 0 (0) 0 [0] 0 

≥ 60 ppb ......................................................................... 75 3.1–7.6 (4.5) 865,000 [93,000] 14.4 

70 0.5–3.5 (1.7) 320,000 [35,000] 9.2 

65 0–0.8 (0.3) 67,000 [7,500] 2.8 

60 0–0.2 (0) 5,100 [700] 0.3 

Uncertainties in exposure estimates 

are summarized in section II.C.2.b of the 

proposal (79 FR 75273). For example, 

due to variability in responsiveness, 

only a subset of individuals who 

experience exposures at or above a 

benchmark concentration can be 

expected to experience health effects.53

In addition, not all of these effects will 

be adverse. Given the lack of sufficient 

exposure-response information for most 

of the health effects that informed 

benchmark concentrations, estimates of 

the number of people likely to 

experience exposures at or above 

benchmark concentrations generally 

cannot be translated into quantitative 

estimates of the number of people likely 

to experience specific health effects.54

The PA views health-relevant exposures 

as a continuum with greater confidence 

and less uncertainty about the existence 

of adverse health effects at higher O3

exposure concentrations, and less 

confidence and greater uncertainty as 

one considers lower exposure 

concentrations (e.g., U.S. EPA, 2014c, 

mstockstill on DSK4VPTVN1PROD with RULES2

65314 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

55 ‘‘The CASAC further notes that clinical studies 

do not address sensitive subgroups, such as 

children with asthma, and that there is a scientific 

basis to anticipate that the adverse effects for such 

subgroups are likely to be more significant at 60 

ppb than for healthy adults’’ (Frey 2014a, p. 7). 

56See EPA 2014a pp. 5–53 to 54 describing EPA’s 

sensitivity analysis regarding impacts of potential 

averting behavior for school-age children on the 

exposure and lung function decrement estimate, 

and see also section B.2.a.i below. 

57Estimates of O3-associated respiratory mortality 

are based on the study by Jerrett et al. (2009). This 

study used seasonal averages of 1-hour daily 

maximum O3 concentrations to estimate long-term 

concentrations. 

58Analysis of this issue in the HREA is based on 

risk estimates in Los Angeles for 2006 unadjusted 

air quality. The HREA shows that more than 90% 

of daily instances of FEV1 decrements ≥10% occur 

when 8-hr average ambient concentrations are 

above 40 ppb for this modeled scenario. The HREA 

notes that the distribution of responses will be 

different for different study areas, years, and air 

quality scenarios (U.S. EPA, 2014c, Chapter 6). 

sections 3.1 and 4.6). This view draws 

from the overall body of available health 

evidence, which indicates that as 

exposure concentrations increase, the 

incidence, magnitude, and severity of 

effects increases. 

Another important uncertainty is that 

there is very limited evidence from 

controlled human exposure studies, 

which provided the basis for health 

benchmark concentrations for both 

exposures of concern and lung function 

decrements, related to clinical responses 

in at-risk populations. Compared to the 

healthy young adults included in the 

controlled human exposure studies, 

members of at-risk populations could be 

more likely to experience adverse 

effects, could experience larger and/or 

more serious effects, and/or could 

experience effects following exposures 

to lower O3 concentrations.55

There are also uncertainties 

associated with the exposure modelling. 

These are described most fully, and 

their potential impact characterized, in 

section 5.5.2 of the HREA (U.S. EPA, 

2013, pp. 5–72 to 5–79). These include 

interpretation of activity patterns set 

forth in diaries which do not typically 

distinguish the basis for activity 

patterns and so may reflect averting 

behavior,56 and whether the HREA 

underestimates exposures for groups 

spending especially large proportion of 

time being active outdoors during the O3

season (outdoor workers and especially 

active children). 

c. Quantitative Health Risk Assessments 

As discussed in section II.C.3 of the 

proposal (79 FR 75274), for some health 

endpoints, there is sufficient scientific 

evidence and information available to 

support the development of quantitative 

estimates of O3-related health risks. In 

the current review, for short-term O3

concentrations, the HREA estimates 

lung function decrements; respiratory 

symptoms in asthmatics; hospital 

admissions and emergency department 

visits for respiratory causes; and allcause mortality (U.S. EPA, 2014a). For 

long-term O3 concentrations, the HREA 

estimates respiratory mortality (U.S. 

EPA, 2014a).57 Estimates of O3-induced 

lung function decrements are based on 

exposure modeling using the MSS 

model (see section II.1.b.i.(1) above, and 

79 FR 75250), combined with exposureresponse relationships from controlled 

human exposure studies (U.S. EPA, 

2014a, Chapter 6). Estimates of O3- 

associated respiratory symptoms, 

hospital admissions and emergency 

department visits, and mortality are 

based on concentration-response 

relationships from epidemiologic 

studies (U.S. EPA, 2014a, Chapter 7). As 

with the exposure assessment discussed 

above, O3-associated health risks are 

estimated for recent air quality and for 

ambient concentrations adjusted to just 

meet the current and alternative O3

standards, based on 2006–2010 air 

quality and adjusted precursor 

emissions. The following sections 

summarize the discussions from the 

proposal on the lung function risk 

assessment (II.A.2.c.i) and the 

epidemiology-based morbidity and 

mortality risk assessments (II.A.2.c.ii). 

i. Lung Function Risk Assessment 

The HREA estimates risks of lung 

function decrements in school-aged 

children (ages 5 to 18), asthmatic 

school-aged children, and the general 

adult population for the 15 urban study 

areas. The results presented in the 

HREA are based on an updated dosethreshold model that estimates FEV1

responses for individuals following 

short-term exposures to O3 (McDonnell 

et al., 2012), reflecting methodological 

improvements since the last review 

(II.B.2.a.i (1), above; U.S. EPA, 2014a, 

section 6.2.4). The impact of the dose 

threshold is that O3-induced FEV1

decrements result primarily from 

exposures on days with average ambient 

O3 concentrations above about 40 ppb 

(U.S. EPA, 2014a, section 6.3.1, Figure 

6–9).58

Table 2 in the proposal (79 FR 75275), 

and reprinted below, summarizes key 

results from the lung function risk 

assessment. Table 2 presents estimates 

of the percentages of school-aged 

children estimated to experience O3- 

induced FEV1 decrements >10, 15, or 

20% when air quality was adjusted to 

just meet the current and alternative 8- 

hour O3 standards. Table 2 also presents 

the numbers of children, including 

children with asthma, estimated to 

experience such decrements. 

TABLE 2—SUMMARY OF ESTIMATED O3-INDUCED LUNG FUNCTION DECREMENTS FOR THE CURRENT AND POTENTIAL

ALTERNATIVE O3 STANDARDS IN URBAN CASE STUDY AREAS

Lung function decrement Alternative 

standard level 

Average % 

children 59

Number of children (5 to 

18 years) [number of 

asthmatic children] 60

% Children worst 

year and area 

One or more decrements per season 

≥10% .............................................................................. 75 14–19 3,007,000 [312,000] 22 

70 11–17 2,527,000 [261,000] 20 

65 3–15 1,896,000 [191,000] 18 

60 5–11 611,404,000 [139,000] 13 

≥15% .............................................................................. 75 3–5 766,000 [80,000] 7 

70 2–4 562,000 [58,000] 5 

65 0–3 356,000 [36,000] 4 

60 1–2 225,000 [22,000] 3 

≥20% .............................................................................. 75 1–2 285,000 [30,000] 2.8 

70 1–2 189,000 [20,000] 2.1 

65 0–1 106,000 [11,000] 1.4 

60 0–1 57,000 [6,000] 0.9 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65315 

59Estimates in each urban case study area were 

averaged for the years evaluated in the HREA (2006 

to 2010). Ranges reflect the ranges across urban 

study areas. 

60Numbers of children estimated to experience 

decrements in each study urban case study area 

were averaged over 2006 to 2010. These averages 

were then summed across urban study areas. 

Numbers are rounded to nearest thousand unless 

otherwise indicated. 

61As discussed in section 4.3.3 of the HREA, the 

model-based air quality adjustment approach used 

to estimate risks associated with the current and 

alternative standards was unable to estimate the 

distribution of ambient O3 concentrations in New 

York City upon just meeting an alternative standard 

with a level of 60 ppb. Therefore, for the 60 ppb 

standard level, the numbers of children and 

asthmatic children experiencing decrements, and 

the ranges of percentages of such children across 

study areas, reflect all of the urban study areas 

except New York City. Because of this, in some 

cases (i.e., when New York City provided the 

smallest risk estimate), the lower end of the ranges 

in Table 2 are higher for a standard level of 60 ppb 

than for a level of 65 ppb. 

62The 12 urban areas evaluated are Atlanta, 

Baltimore, Boston, Cleveland, Denver, Detroit, 

Houston, Los Angeles, New York, Philadelphia, 

Sacramento, and St. Louis. 

63 In the epidemiologic studies that provide the 

health basis for HREA risk assessments, 

concentration-response relationships are based on 

daytime O3 concentrations, averaged across 

multiple monitors within study areas. These daily 

averages are used as surrogates for the spatial and 

temporal patterns of exposures in study 

populations. Consistent with this approach, the 

HREA epidemiologic-based risk estimates also 

utilize daytime O3 concentrations, averaged across 

monitors, as surrogates for population exposures. In 

this notice, we refer to these averaged 

concentrations as ‘‘area-wide’’ O3 concentrations. 

Area-wide concentrations are discussed in more 

detail in section 3.1.4 of the PA (U.S. EPA, 2014c). 

TABLE 2—SUMMARY OF ESTIMATED O3-INDUCED LUNG FUNCTION DECREMENTS FOR THE CURRENT AND POTENTIAL

ALTERNATIVE O3 STANDARDS IN URBAN CASE STUDY AREAS—Continued 

Lung function decrement Alternative 

standard level 

Average % 

children 59

Number of children (5 to 

18 years) [number of 

asthmatic children] 60

% Children worst 

year and area 

Two or more decrements per season 

≥10% .............................................................................. 75 7.5–12 1,730,000 [179,000] 14 

70 5.5–11 1,414,000 [145,000] 13 

65 1.3–8.8 1,023,000 [102,000] 11 

60 2.1–6.4 741,000 [73,000] 7.3 

≥15% .............................................................................. 75 1.7–2.9 391,000 [40,000] 3.8 

70 0.9–2.4 276,000 [28,000] 3.1 

65 0.1–1.8 168,000 [17,000] 2.3 

60 0.2–1.0 101,000 [10,000] 1.4 

≥20% .............................................................................. 75 0.5–1.1 128,000 [13,000] 1.5 

70 0.3–0.8 81,000 [8,000] 1.1 

65 0–0.5 43,000 [4,000] 0.8 

60 0–0.2 21,000 [2,000] 0.4 

Uncertainties in estimates of lung 

function risks are summarized in 

section II.C.3.a.ii of the proposal (79 FR 

75275). In addition to the uncertainties 

noted for exposure estimates, an 

uncertainty which impacts lung 

function risk estimates stems from the 

lack of exposure-response information 

in children. In the near absence of 

controlled human exposure data for 

children, risk estimates are based on the 

assumption that children exhibit the 

same lung function response following 

O3 exposures as healthy 18 year olds 

(i.e., the youngest age for which 

controlled human exposure data is 

generally available) (U.S. EPA, 2014a, 

section 6.5.3). This assumption is 

justified in part by the findings of 

McDonnell et al. (1985), who reported 

that children (8–11 years old) 

experienced FEV1 responses similar to 

those observed in adults (18–35 years 

old) (U.S. EPA, 2014a, p. 3–10). In 

addition, as discussed in the ISA (U.S. 

EPA, 2013, section 6.2.1), summer camp 

studies of school-aged children reported 

O3-induced lung function decrements 

similar in magnitude to those observed 

in controlled human exposure studies 

using adults. In extending the risk 

model to children, the HREA thus fixes 

the age term in the model at its highest 

value, the value for age 18. 

Notwithstanding the information just 

summarized supporting this approach, 

EPA acknowledges the uncertainty 

involved, and notes that the approach 

could result in either over- or 

underestimates of O3-induced lung 

function decrements in children, 

depending on how children compare to 

the adults used in controlled human 

exposure studies (U.S. EPA, 2014a, 

section 6.5.3). 

A related source of uncertainty is that 

the risk assessment estimates of 

O3-induced decrements in asthmatics 

used the exposure-response relationship 

developed from data collected from 

healthy individuals. Although the 

evidence has been mixed (U.S. EPA, 

2013, section 6.2.1.1), several studies 

have reported statistically larger, or a 

tendency toward larger, O3-induced 

lung function decrements in asthmatics 

than in non-asthmatics (Kreit et al., 

1989; Horstman et al., 1995; Jorres et al., 

1996; Alexis et al., 2000). On this issue, 

CASAC noted that ‘‘[a]sthmatic subjects 

appear to be at least as sensitive, if not 

more sensitive, than non-asthmatic 

subjects in manifesting O3-induced 

pulmonary function decrements’’ (Frey, 

2014c, p. 4). To the extent asthmatics 

experience larger O3-induced lung 

function decrements than the healthy 

adults used to develop exposureresponse relationships, the HREA could 

underestimate the impacts of O3

exposures on lung function in 

asthmatics, including asthmatic 

children. The implications of this 

uncertainty for risk estimates remain 

unknown at this time (U.S. EPA, 2014a, 

section 6.5.4), and could depend on a 

variety of factors that have not been 

well-evaluated, including the severity of 

asthma and the prevalence of 

medication use. However, the available 

evidence shows responses to O3

increase with severity of asthma 

(Horstman et al., 1995) and 

corticosteroid usage does not prevent O3

effects on lung function decrements or 

respiratory symptoms in people with 

asthma (Vagaggini et al., 2001, 2007). 

ii. Mortality and Morbidity Risk 

Assessments 

As discussed in section II.C.3.b of the 

proposal (79 FR 75276), the HREA 

estimates O3-associated risks in 12 

urban study areas 62 using 

concentration-response relationships 

drawn from epidemiologic studies. 

These concentration-response 

relationships are based on ‘‘area-wide’’ 

average O3 concentrations.63 The HREA 

estimates risks for the years 2007 and 

2009 in order to provide estimates of 

risk for a year with generally higher O3

mstockstill on DSK4VPTVN1PROD with RULES2

65316 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

64The CASAC also concluded that ‘‘[i]n light of 

the potential nonlinearity of the C–R function for 

long-term exposure reflecting a threshold of the 

mortality response, the estimated number of 

premature deaths avoidable for long-term exposure 

reductions for several levels need to be viewed with 

caution’’ (Frey, 2014a, p. 3). 

65There is also uncertainty about the extent to 

which mortality estimates based on the long-term 

metric used in the study by Jerrett et al. (2009) (i.e., 

seasonal average of 1-hour daily maximum 

concentrations) reflects associations with long-term 

average O3 versus repeated occurrences of elevated 

short-term concentrations. 

66A related uncertainty is the existence, or not, 

of a threshold. The HREA addresses this issue for 

long-term O3 by evaluating risks in models that 

include potential thresholds (II.D.2.c). 

concentrations (2007) and a year with 

generally lower O3 concentrations 

(2009) (U.S. EPA, 2014a, section 7.1.1). 

In considering the epidemiologybased risk estimates, the proposal 

focuses on mortality risks associated 

with short-term O3 concentrations. The 

proposal considers estimates of total 

risk (i.e., based on the full distributions 

of ambient O3 concentrations) and 

estimates of risk associated with O3

concentrations in the upper portions of 

ambient distributions. Both estimates 

are discussed to provide information 

that considers risk estimates based on 

concentration-response relationships 

being linear over the entire distribution 

of ambient O3 concentrations, and thus 

have the greater potential for morbidity 

and mortality to be affected by changes 

in relatively low O3 concentrations, as 

well as risk estimates that are associated 

with O3 concentrations in the upper 

portions of the ambient distribution, 

thus focusing on risk from higher O3

concentrations and placing greater 

weight on the uncertainty associated 

with the shapes of concentrationresponse curves for O3 concentrations in 

the lower portions of the distribution. 

These results for O3-associated mortality 

risk are summarized in Table 3 in the 

proposal (79 FR 75277). 

Important uncertainties in 

epidemiology-based risk estimates, 

based on their consideration in the 

HREA and PA, are discussed in section 

II.C.3.b.ii of the proposal (79 FR 75277). 

Compared to estimates of O3 exposures 

of concern and estimates of O3-induced 

lung function decrements (discussed 

above), the HREA conclusions reflect 

lower confidence in epidemiologicbased risk estimates (U.S. EPA, 2014a, 

section 9.6). In particular, the HREA 

highlights the heterogeneity in effect 

estimates between locations, the 

potential for exposure measurement 

errors, and uncertainty in the 

interpretation of the shape of 

concentration-response functions at 

lower O3 concentrations (U.S. EPA, 

2014a, section 9.6). The HREA also 

concludes that lower confidence should 

be placed in the results of the 

assessment of respiratory mortality risks 

associated with long-term O3, primarily 

because that analysis is based on only 

one study, though that study is welldesigned, and because of the 

uncertainty in that study about the 

existence and identification of a 

potential threshold in the concentrationresponse function (U.S. EPA, 2014a, 

section 9.6).64,65 This section further 

discusses some of the key uncertainties 

in epidemiologic-based risk estimates, 

as summarized in the PA (U.S. EPA, 

2014c, section 3.2.3.2), with a focus on 

uncertainties that can have particularly 

important implications for the 

Administrator’s consideration of 

epidemiology-based risk estimates. 

The PA notes that reducing NOX

emissions generally reduces O3- 

associated mortality and morbidity risk 

estimates in locations and time periods 

with relatively high ambient O3

concentrations and increases risk 

estimates in locations and time periods 

with relatively low concentrations (II.A, 

above). When evaluating uncertainties 

in epidemiologic risk estimates, the PA 

considered (1) the extent to which the 

modeled O3 response to reductions in 

NOX emissions appropriately represents 

the trends observed in monitored 

ambient O3 following actual reductions 

in NOX emissions, (2) the extent to 

which the O3 response to reductions in 

precursor emissions could differ with 

emissions reduction strategies that are 

different from those used in HREA to 

generate risk estimates, and (3) the 

extent to which estimated changes in 

risks in urban study areas are 

representative of the changes that would 

be experienced broadly across the U.S. 

population. The first two of these issues 

are discussed in section II.A.2.c above. 

The third issue is discussed below. 

The HREA conducted national air 

quality modeling analyses that 

estimated the proportion of the U.S. 

population living in locations where 

seasonal averages of daily O3

concentrations are estimated to decrease 

in response to reductions in NOX

emissions, and the proportion living in 

locations where such seasonal averages 

are estimated to increase. Given the 

close relationship between changes in 

seasonal averages of daily O3

concentrations and changes in seasonal 

mortality and morbidity risk estimates, 

this analysis informs consideration of 

the extent to which the risk results in 

urban study areas represent the U.S. 

population as a whole. This 

‘‘representativeness analysis’’ indicates 

that the majority of the U.S. population 

lives in locations where reducing NOX

emissions would be expected to result 

in decreases in warm season averages of 

daily maximum 8-hour ambient O3

concentrations. Because the HREA 

urban study areas tend to 

underrepresent the populations living in 

such areas (e.g., suburban, smaller 

urban, and rural areas), risk estimates 

for the urban study areas are likely to 

understate the average reductions in O3- 

associated mortality and morbidity risks 

that would be experienced across the 

U.S. population as a whole upon 

reducing NOX emissions (U.S. EPA, 

2014a, section 8.2.3.2). 

Section 7.4 of the HREA also 

highlights some additional uncertainties 

associated with epidemiologic-based 

risk estimates (U.S. EPA, 2014a). This 

section of the HREA identifies and 

discusses sources of uncertainty and 

presents a qualitative evaluation of key 

parameters that can introduce 

uncertainty into risk estimates (U.S. 

EPA, 2014a, Table 7–4). For several of 

these parameters, the HREA also 

presents quantitative sensitivity 

analyses (U.S. EPA, 2014a, sections 

7.4.2 and 7.5.3). Of the uncertainties 

discussed in Chapter 7 of the HREA, 

those related to the application of 

concentration-response functions from 

epidemiologic studies can have 

particularly important implications for 

consideration of epidemiology-based 

risk estimates, as discussed below. 

An important uncertainty is the shape 

of concentration-response functions at 

low ambient O3 concentrations (U.S. 

EPA, 2014a, Table 7–4).66 In recognition 

of the ISA’s conclusion that certainty in 

the shape of O3 concentration-response 

functions decreases at low ambient 

concentrations, the HREA provides 

estimates of epidemiology-based 

mortality risks for entire distributions of 

ambient O3 concentrations, as well as 

estimates of total mortality associated 

with various ambient O3 concentrations. 

The PA considers both types of risk 

estimates, recognizing greater public 

health concern for adverse O3- 

attributable effects at higher ambient O3

concentrations (which drive higher 

exposure concentrations, section 3.2.2 

of the PA (U.S. EPA, 2014c)), as 

compared to lower concentrations. 

A related consideration is associated 

with the public health importance of the 

increases in relatively low O3

concentrations following air quality 

adjustment. There is uncertainty that 

relates to the assumption that the 

concentration response function for O3

is linear, such that total risk estimates 

are equally influenced by decreasing 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65317 

high concentrations and increasing low 

concentrations, when the increases and 

decreases are of equal magnitude. Even 

on days with increases in relatively low 

area-wide average concentrations, 

resulting in increases in estimated risks, 

some portions of the urban study areas 

could experience decreases in high O3

concentrations. To the extent adverse 

O3-attributable effects are more strongly 

supported for higher ambient 

concentrations (which, as noted above, 

are consistently reduced upon air 

quality adjustment), the impacts on risk 

estimates of increasing low O3

concentrations reflect an important 

source of uncertainty. In addition to the 

uncertainties discussed above, the 

proposal also notes uncertainties related 

to (1) using concentration-response 

relationships developed for a particular 

population in a particular location to 

estimate health risks in different 

populations and locations; (2) using 

concentration-response functions from 

epidemiologic studies reflecting a 

particular air quality distribution to 

adjusted air quality necessarily 

reflecting a different (simulated) air 

quality distribution; (3) using a national 

concentration-response function to 

estimate respiratory mortality associated 

with long-term O3; and (4) unquantified 

reductions in risk that could be 

associated with reductions in the 

ambient concentrations of pollutants 

other than O3, resulting from control of 

NOX (79 FR 75277 to 75279). 

B. Need for Revision of the Primary 

Standard 

The initial issue to be addressed in 

the current review of the primary O3

standard is whether, in view of the 

advances in scientific knowledge and 

additional information, it is appropriate 

to revise the existing standard. This 

section presents the Administrator’s 

final decision on whether it is 

‘‘appropriate’’ to revise the current 

standard within the meaning of section 

109 (d)(1) of the CAA. Section II.B.1 

contains a summary discussion of the 

basis for the proposed conclusions on 

the adequacy of the primary standard. 

Section II.B.2 discusses comments 

received on the adequacy of the primary 

standard. Section II.B.3 presents the 

Administrator’s final conclusions on the 

adequacy of the current primary 

standard. 

1. Basis for Proposed Decision 

In evaluating whether it is appropriate 

to retain or revise the current standard, 

the Administrator’s considerations build 

upon those in the 2008 review, 

including consideration of the broader 

body of scientific evidence and 

exposure and health risk information 

now available, as summarized in 

sections II.A to II.C (79 FR 75246– 

75279) of the proposal and section II.A 

above. 

In developing conclusions on the 

adequacy of the current primary O3

standard, the Administrator takes into 

account both evidence-based and 

quantitative exposure- and risk-based 

considerations. Evidence-based 

considerations include the assessment 

of evidence from controlled human 

exposure, animal toxicological, and 

epidemiologic studies for a variety of 

health endpoints. The Administrator 

focuses on health endpoints for which 

the evidence is strong enough to support 

a ‘‘causal’’ or a ‘‘likely to be causal’’ 

relationship, based on the ISA’s 

integrative synthesis of the entire body 

of evidence. The Administrator’s 

consideration of quantitative exposure 

and risk information draws from the 

results of the exposure and risk 

assessments presented in the HREA. 

The Administrator’s consideration of 

the evidence and exposure/risk 

information is informed by the 

considerations and conclusions 

presented in the PA (U.S. EPA, 2014c). 

The purpose of the PA is to help ‘‘bridge 

the gap’’ between the scientific and 

technical information assessed in the 

ISA and HREA, and the policy decisions 

that are required of the Administrator 

(U.S. EPA, 2014c, Chapter 1); see also 

American Farm Bureau Federation, 559 

F. 3d at 516, 521 (‘‘[a]lthough not 

required by the statute, in practice EPA 

staff also develop a Staff Paper, which 

discusses the information in the Criteria 

Document that is most relevant to the 

policy judgments the EPA makes when 

it sets the NAAQS’’). The PA’s 

evidence-based and exposure-/riskbased considerations and conclusions 

are briefly summarized below in 

sections II.B.1.a (evidence-based 

considerations), II.B.1.b (exposure- and 

risk-based considerations), and II.B.1.c 

(PA conclusions on the current 

standard). Section II.B.1.d summarizes 

CASAC advice to the Administrator and 

public commenter views on the current 

standard. Section II.B.1.e presents a 

summary of the Administrator’s 

proposed conclusions concerning the 

adequacy of the public health protection 

provided by the current standard, and 

her proposed decision to revise that 

standard. 

a. Evidence-Based Considerations From 

the PA 

In considering the available scientific 

evidence, the PA evaluates the O3

concentrations in health effects studies 

(U.S. EPA, 2014c, section 3.1.4). 

Specifically, the PA characterizes the 

extent to which health effects have been 

reported for the O3 exposure 

concentrations evaluated in controlled 

human exposure studies, and effects 

occurring over the distributions of 

ambient O3 concentrations in locations 

where epidemiologic studies have been 

conducted. These considerations, as 

they relate to the adequacy of the 

current standard, are presented in detail 

in section 3.1.4 of the PA (U.S. EPA, 

2014c) and are summarized in the 

proposal (79 FR 75279–75287). The 

PA’s considerations are summarized 

briefly below for controlled human 

exposure, epidemiologic panel studies, 

and epidemiologic population-based 

studies. 

Section II.D.1.a of the proposal 

discusses the PA’s consideration of the 

evidence from controlled human 

exposure and panel studies. This 

evidence is assessed in section 6.2 of the 

ISA (U.S. EPA, 2013) and is summarized 

in section 3.1.2 of the PA (U.S. EPA, 

2014c). A large number of controlled 

human exposure studies have reported 

lung function decrements, respiratory 

symptoms, air inflammation, airway 

hyperresponsiveness, and/or impaired 

lung host defense in young, healthy 

adults engaged in moderate quasicontinuous exertion, following 6.6-hour 

O3 exposures. These studies have 

consistently reported such effects 

following exposures to O3

concentrations of 80 ppb or greater. In 

addition to lung function decrements, 

available studies have evaluated 

respiratory symptoms or airway 

inflammation following exposures to O3

concentrations below 75 ppb. Table 3– 

1 in the PA highlights the group mean 

results of individual controlled human 

exposure studies that evaluated 

exposures to O3 concentrations below 

75 ppb. These studies observe the 

combination of lung function 

decrements and respiratory symptoms 

following exposures to O3

concentrations as low as 72 ppb, and 

lung function decrements and airway 

inflammation following exposures to O3

concentrations as low as 60 ppb (based 

on group means). 

Based on this evidence, the PA notes 

that controlled human exposure studies 

have reported a variety of respiratory 

effects in young, healthy adults 

following exposures to a wide range of 

O3 concentrations for 6.6 hours, 

including exposures to concentrations 

below 75 ppb. In particular, the PA 

further notes that a recent controlled 

human exposure study reported the 

combination of lung function 

decrements and respiratory symptoms 

in healthy adults engaged in quasimstockstill on DSK4VPTVN1PROD with RULES2

65318 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

67As noted above (section II.A.1.B.i), the ISA 

concludes that studies that examined the potential 

confounding effects of copollutants found that O3

effect estimates remained relatively robust upon the 

inclusion of PM and gaseous pollutants in twopollutant models (U.S. EPA, 2013, section 6.2.7.5). 

68Unlike for the studies of short-term O3, the 

available U.S. and Canadian epidemiologic studies 

evaluating long-term ambient O3 concentration 

metrics have not been conducted in locations likely 

to have met the current 8-hour O3 standard during 

the study period, and have not reported 

concentration-response functions that indicate 

confidence in health effect associations at O3

concentrations meeting the current standard (U.S. 

EPA, 2014c, section 3.1.4.3). 

continuous, moderate exertion 

following 6.6 hour exposures to 72 ppb 

O3, a combination of effects that have 

been classified as adverse based on ATS 

guidelines for adversity (ATS, 2000a). In 

addition, a recent study has also 

reported lung function decrements and 

pulmonary inflammation following 

exposure to 60 ppb O3. Sixty ppb is the 

lowest exposure concentration for 

which inflammation has been evaluated 

and reported to occur, and corresponds 

to the lowest exposure concentration 

demonstrated to result in lung function 

decrements large enough to be judged 

an abnormal response by ATS (ATS, 

2000b). The PA also notes, and CASAC 

agreed, that these controlled human 

exposure studies were conducted in 

healthy adults, while at-risk groups 

(e.g., children, people with asthma) 

could experience larger and/or more 

serious effects. Therefore, the PA 

concludes that the evidence from 

controlled human exposure studies 

provide support that the respiratory 

effects experienced following exposures 

to O3 concentrations lower than 75 ppb 

would be adverse in some individuals, 

particularly if experienced by members 

of at-risk populations (e.g., people with 

asthma, children). 

The PA also notes consistent results 

in some panel studies of O3-associated 

lung function decrements. In particular, 

the PA notes that epidemiologic panel 

studies in children and adults 

consistently indicate O3-associated lung 

function decrements when on-site, 

ambient monitored concentrations were 

below 75 ppb (although the evidence 

becomes less consistent at low O3

concentrations, and the averaging 

periods involved ranged from 10 

minutes to 12 hours (U.S. EPA, 2014c, 

section 3.2.4.2)). 

Section II.D.1.b of the proposal 

summarizes the PA’s analyses of 

monitored O3 concentrations in 

locations of epidemiologic studies. 

While the majority of the epidemiologic 

study areas evaluated would have 

violated the current standard during 

study periods, the PA makes the 

following observations with regard to 

health effect associations at O3

concentrations likely to have met the 

current standard: 

(1) A single-city study reported 

positive and statistically significant 

associations with asthma emergency 

department visits in children and adults 

in Seattle, a location that would have 

met the current standard over the entire 

study period (Mar and Koenig, 2009). 

(2) Additional single-city studies 

support associations with respiratory 

morbidity at relatively low ambient O3

concentrations, including when 

virtually all monitored concentrations 

were below the level of the current 

standard (Silverman and Ito, 2010; 

Strickland et al., 2010). 

(3) Canadian multicity studies 

reported positive and statistically 

significant associations with respiratory 

morbidity or mortality when the 

majority of study cities, though not all 

study cities, would have met the current 

standard over the study period in each 

of these studies (Cakmak et al., 2006; 

Dales et al., 2006; Katsouyanni et al., 

2009; Stieb et al., 2009). 

(4) A U.S. multicity study reported 

positive and statistically significant 

associations with mortality when 

ambient O3 concentrations were 

restricted to those likely to have met the 

current O3 standard (Bell et al., 2006). 

The PA also takes into account 

important uncertainties in these 

analyses of air quality in locations of 

epidemiologic study areas. These 

uncertainties are summarized in section 

II.D.1.b.iii of the proposal. Briefly, they 

include the following: (1) Uncertainty in 

conclusions about the extent to which 

multicity effect estimates reflect 

associations with air quality meeting the 

current standard, versus air quality 

violating that standard; (2) uncertainty 

regarding the potential for thresholds to 

exist, given that regional heterogeneity 

in O3 health effect associations could 

obscure the presence of thresholds, 

should they exist; (3) uncertainty in the 

extent to which the PA appropriately 

recreated the air quality analyses in the 

published study by Bell et al. (2006); 

and (4) uncertainty in the extent to 

which reported health effects are caused 

by exposures to O3 itself, as opposed to 

other factors such as co-occurring 

pollutants or pollutant mixtures, 

particularly at low ambient O3

concentrations.67

In considering the analyses of 

monitored O3 air quality in locations of 

epidemiologic studies, as well as the 

important uncertainties in these 

analyses, the PA concludes that these 

analyses provide support for the 

occurrence of morbidity and mortality 

associated with short-term ambient O3

concentrations likely to meet the current 

O3 standard.68 In considering the 

evidence as a whole, the PA concludes 

that (1) controlled human exposure 

studies provide strong support for the 

occurrence of adverse respiratory effects 

following exposures to O3

concentrations below the level of the 

current standard and (2) epidemiologic 

studies provide support for the 

occurrence of adverse respiratory effects 

and mortality under air quality 

conditions that would meet the current 

standard. 

b. Exposure- and Risk-Based 

Considerations in the PA 

In order to further inform judgments 

about the potential public health 

implications of the current O3 NAAQS, 

the PA considers the exposure and risk 

assessments presented in the HREA 

(U.S. EPA, 2014c, section 3.2). 

Overviews of these exposure and risk 

assessments, including brief summaries 

of key results and uncertainties, are 

provided in section II.A.2 above. 

Section II.D.2 of the proposal 

summarizes key observations from the 

PA related to the adequacy of the 

current O3 NAAQS, based on 

consideration of the HREA exposure 

assessment, lung function risk 

assessment, and mortality/morbidity 

risk assessments (79 FR 75283). 

Section II.D.2.a of the proposal 

summarizes key observations from the 

PA regarding estimates of O3 exposures 

of concern (79 FR 75283). Given the 

evidence for respiratory effects from 

controlled human exposure studies, the 

PA considers the extent to which the 

current standard would be estimated to 

protect at-risk populations against 

exposures of concern to O3

concentrations at or above the health 

benchmark concentrations of 60, 70, and 

80 ppb (i.e., based on HREA estimates 

of one or more and two or more 

exposures of concern). In doing so, the 

PA notes the CASAC conclusion that 

(Frey, 2014c, p. 6): 

The 80 ppb-8hr benchmark level represents 

an exposure level for which there is 

substantial clinical evidence demonstrating a 

range of ozone-related effects including lung 

inflammation and airway responsiveness in 

healthy individuals. The 70 ppb-8hr 

benchmark level reflects the fact that in 

healthy subjects, decreases in lung function 

and respiratory symptoms occur at 

concentrations as low as 72 ppb and that 

these effects almost certainly occur in some 

people, including asthmatics and others with 

low lung function who are less tolerant of 

such effects, at levels of 70 ppb and below. 

The 60 ppb-8hr benchmark level represents 

the lowest exposure level at which ozonemstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65319 

69As discussed in section II.C.2.b of the proposal, 

due to variability in responsiveness, only a subset 

of individuals who experience exposures at or 

above a benchmark concentration can be expected 

to experience adverse health effects. 

related effects have been observed in clinical 

studies of healthy individuals. 

For exposures of concern at or above 

60 ppb, the proposal highlights the 

following key observations for air 

quality adjusted to just meet the current 

standard: 

(1) On average over the years 2006 to 

2010, the current standard is estimated 

to allow approximately 10 to 18% of 

children in urban study areas to 

experience one or more exposures of 

concern at or above 60 ppb. Summing 

across urban study areas, these 

percentages correspond to almost 2.5 

million children experiencing 

approximately 4 million exposures of 

concern at or above 60 ppb during a 

single O3 season. Of these children, 

almost 250,000 are asthmatics.69

(2) On average over the years 2006 to 

2010, the current standard is estimated 

to allow approximately 3 to 8% of 

children in urban study areas to 

experience two or more exposures of 

concern to O3 concentrations at or above 

60 ppb. Summing across the urban 

study areas, these percentages 

correspond to almost 900,000 children 

(including almost 90,000 asthmatic 

children). 

(3) In the worst-case years (i.e., those 

with the largest exposure estimates), the 

current standard is estimated to allow 

approximately 10 to 25% of children to 

experience one or more exposures of 

concern at or above 60 ppb, and 

approximately 4 to 14% to experience 

two or more exposures of concern at or 

above 60 ppb. 

For exposures of concern at or above 

70 ppb, the PA highlights the following 

key observations for air quality adjusted 

to just meet the current standard: 

(1) On average over the years 2006 to 

2010, the current standard is estimated 

to allow up to approximately 3% of 

children in urban study areas to 

experience one or more exposures of 

concern at or above 70 ppb. Summing 

across urban study areas, almost 

400,000 children (including almost 

40,000 asthmatic children) are estimated 

to experience O3 exposure 

concentrations at or above 70 ppb 

during a single O3 season. 

(2) On average over the years 2006 to 

2010, the current standard is estimated 

to allow less than 1% of children in 

urban study areas to experience two or 

more exposures of concern to O3

concentrations at or above 70 ppb. 

(3) In the worst-case location and 

year, the current standard is estimated 

to allow approximately 8% of children 

to experience one or more exposures of 

concern at or above 70 ppb, and 

approximately 2% to experience two or 

more exposures of concern, at or above 

70 ppb. 

For exposures of concern at or above 80 

ppb, the PA highlights the observation 

that the current standard is estimated to 

allow about 1% or fewer children in 

urban study areas to experience 

exposures of concern at or above 80 

ppb, even in years with the highest 

exposure estimates. 

Uncertainties in exposure estimates 

are summarized in section II.C.2.b of the 

proposal (79 FR 75273), and discussed 

more fully in the HREA (U.S. EPA, 

2014a, section 5.5.2) and the PA (U.S. 

EPA, 2014c, section 3.2.2). Key 

uncertainties include the variability in 

responsiveness following O3 exposures, 

resulting in only a subset of exposed 

individuals experiencing health effects, 

adverse or otherwise, and the limited 

evidence from controlled human 

exposure studies conducted in at-risk 

populations. In addition, there are a 

number of uncertainties in the exposure 

modelling approach used in the HREA, 

contributing to overall uncertainty in 

exposure estimates. 

Section II.D.2.b of the proposal 

summarizes key observations from the 

PA regarding the estimated risk of O3- 

induced lung function decrements (79 

FR 75283 to 75284). With respect to the 

lung function decrements that have 

been evaluated in controlled human 

exposure studies, the PA considers the 

extent to which standards with revised 

levels would be estimated to protect 

healthy and at-risk populations against 

one or more, and two or more, moderate 

(i.e., FEV1 decrements ≥10% and ≥15%) 

and large (i.e., FEV1 decrements ≥20%) 

lung function decrements. As discussed 

in section 3.1.3 of the PA (U.S. EPA, 

2014c), although some experts would 

judge single occurrences of moderate 

responses to be a nuisance, especially 

for healthy individuals, a more general 

consensus view of the adversity of 

moderate lung function decrements 

emerges as the frequency of occurrence 

increases. 

With regard to decrements ≥10%, the 

PA highlights the following key 

observations for air quality adjusted to 

just meet the current standard: 

(1) On average over the years 2006 to 

2010, the current standard is estimated 

to allow approximately 14 to 19% of 

children in urban study areas to 

experience one or more lung function 

decrements ≥10%. Summing across 

urban study areas, this corresponds to 

approximately 3 million children 

experiencing 15 million O3-induced 

lung function decrements ≥10% during 

a single O3 season. Of these children, 

about 300,000 are asthmatics. 

(2) On average over the years 2006 to 

2010, the current standard is estimated 

to allow approximately 7 to 12% of 

children in urban study areas to 

experience two or more O3-induced 

lung function decrements ≥10%. 

Summing across the urban study areas, 

this corresponds to almost 2 million 

children (including almost 200,000 

asthmatic children) estimated to 

experience two or more O3-induced 

lung function decrements greater than 

10% during a single O3 season. 

(3) In the worst-case years, the current 

standard is estimated to allow 

approximately 17 to 23% of children in 

urban study areas to experience one or 

more lung function decrements ≥10%, 

and approximately 10 to 14% to 

experience two or more O3-induced 

lung function decrements ≥10%. 

With regard to decrements ≥15%, the 

PA highlights the following key 

observations for air quality adjusted to 

just meet the current standard: 

(1) On average over the years 2006 to 

2010, the current standard is estimated 

to allow approximately 3 to 5% of 

children in urban study areas to 

experience one or more lung function 

decrements ≤15%. Summing across 

urban study areas, this corresponds to 

approximately 800,000 children 

(including approximately 80,000 

asthmatic children) estimated to 

experience at least one O3-induced lung 

function decrement ≤15% during a 

single O3 season. 

(2) On average over the years 2006 to 

2010, the current standard is estimated 

to allow approximately 2 to 3% of 

children in urban study areas to 

experience two or more O3-induced 

lung function decrements ≤15%. 

(3) In the worst-case years, the current 

standard is estimated to allow 

approximately 4 to 6% of children in 

urban study areas to experience one or 

more lung function decrements ≤15%, 

and approximately 2 to 4% to 

experience two or more O3-induced 

lung function decrements ≤15%. 

With regard to decrements ≤20%, the 

PA highlights the following key 

observations for air quality adjusted to 

just meet the current standard: 

(1) On average over the years 2006 to 

2010, the current standard is estimated 

to allow approximately 1 to 2% of 

children in urban study areas to 

experience one or more lung function 

decrements ≥20%. Summing across 

mstockstill on DSK4VPTVN1PROD with RULES2

65320 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

70As discussed above (II.C.1), in locations and 

time periods when NOX is predominantly 

contributing to O3 formation (e.g., downwind of 

important NOX sources, where the highest O3

concentrations often occur), model-based 

adjustment to the current and alternative standards 

decreases estimated ambient O3 concentrations 

compared to recent monitored concentrations (U.S. 

EPA, 2014a, section 4.3.3.2). In contrast, in 

locations and time periods when NOX is 

predominantly contributing to O3 titration (e.g., in 

urban centers with high concentrations of NOX

emissions, where ambient O3 concentrations are 

often suppressed and are thus relatively low), 

model-based adjustment increases ambient O3

concentrations compared to recent monitored 

concentrations (U.S. EPA, 2014a, section 4.3.3.2). 

Changes in epidemiology-based risk estimates 

depend on the balance between the daily decreases 

in high O3 concentrations and increases in low O3

concentrations following the model-based air 

quality adjustment. Commenting on this issue, 

CASAC noted that ‘‘controls designed to reduce the 

peak levels of ozone (e.g., the fourth-highest annual 

MDA8) may not be effective at reducing lower 

levels of ozone on more typical days and may 

actually increase ozone levels on days where ozone 

concentrations are low’’ (Frey 2014a, p. 2). CASAC 

further noted that risk results ‘‘suggest that the 

ozone-related health risks in the urban cores can 

increase for some of the cities as ozone NAAQS 

alternatives become more stringent. This is because 

reductions in nitrogen oxides emissions can lead to 

less scavenging of ozone and free radicals, resulting 

in locally higher levels of ozone’’ (Frey 2014c, p. 

10). 

71For the 2009 adjusted year (i.e., the year with 

generally lower O3 concentrations), changes in risk 

were generally smaller than in 2007 (i.e., most 

changes about 2% or smaller). Increases were 

estimated for Houston, Los Angeles, and New York 

City. 

72Risk estimates for respiratory mortality 

associated with long-term O3 exposures are based 

on the study by Jerrett et al. (2009) (U.S. EPA, 

2014a, Chapter 7). As discussed above (II.B.2.b.iv) 

and in the PA (U.S. EPA, 2014c, section 3.1.4.3), 

Jerrett et al. (2009) reported that when seasonal 

averages of 1-hour daily maximum O3

concentrations ranged from 33 to 104 ppb, there 

was no statistical deviation from a linear 

concentration-response relationship between O3

and respiratory mortality across 96 U.S. cities (U.S. 

EPA, 2013, section 7.7). However, the authors 

reported ‘‘limited evidence’’ for an effect threshold 

at an O3 concentration of 56 ppb (p=0.06). In 

communications with EPA staff (Sasser, 2014), the 

study authors indicated that it is not clear whether 

a threshold model is a better predictor of respiratory 

mortality than the linear model, and that 

‘‘considerable caution should be exercised in 

accepting any specific threshold.’’ 

urban study areas, this corresponds to 

approximately 300,000 children 

(including approximately 30,000 

asthmatic children) estimated to 

experience at least one O3-induced lung 

function decrement ≥20% during a 

single O3 season. 

(2) On average over the years 2006 to 

2010, the current standard is estimated 

to allow less than 1% of children in 

urban study areas to experience two or 

more O3-induced lung function 

decrements ≥20%. 

(3) In the worst-case years, the current 

standard is estimated to allow 

approximately 2 to 3% of children to 

experience one or more lung function 

decrements ≥20%, and less than 2% to 

experience two or more O3-induced 

lung function decrements ≥20%. 

Uncertainties in lung function risk 

estimates are summarized in section 

II.C.3.a of the proposal, and discussed 

more fully in the HREA (U.S. EPA, 

2014a, section 6.5) and the PA (U.S. 

EPA, 2014c, section 3.2.3.1). In addition 

to the uncertainties noted above for 

exposure estimates, the key 

uncertainties associated with estimates 

of O3-induced lung function decrements 

include the paucity of exposureresponse information in children and in 

people with asthma. 

Section II.D.2.c of the proposal 

summarizes key observations from the 

PA regarding risk estimates of O3- 

associated mortality and morbidity (79 

FR 75284 to 75285). With regard to total 

mortality or morbidity associated with 

short-term O3, the PA notes the 

following for air quality adjusted to just 

meet the current standard: 

(1) When air quality was adjusted to 

the current standard for the 2007 model 

year (the year with generally ‘‘higher’’ 

O3-associated risks), 10 of 12 urban 

study areas exhibited either decreases or 

virtually no change in estimates of the 

number of O3-associated deaths (U.S. 

EPA, 2014a, Appendix 7B). Increases 

were estimated in two of the urban 

study areas (Houston, Los Angeles)70

(U.S. EPA, 2014a, Appendix 7B).71

(2) In focusing on total risk, the 

current standard is estimated to allow 

thousands of O3-associated deaths per 

year in the urban study areas. In 

focusing on the risks associated with the 

upper portions of distributions of 

ambient concentrations (area-wide 

concentrations ≤ 40, 60 ppb), the current 

standard is estimated to allow hundreds 

to thousands of O3-associated deaths per 

year in the urban study areas. 

(3) The current standard is estimated 

to allow tens to thousands of O3- 

associated morbidity events per year 

(i.e., respiratory-related hospital 

admissions, emergency department 

visits, and asthma exacerbations). 

With regard to respiratory mortality 

associated with long-term O3, the PA 

notes the following for air quality 

adjusted to just meet the current 

standard: 

(1) Based on a linear concentrationresponse function, the current standard 

is estimated to allow thousands of O3- 

associated respiratory deaths per year in 

the urban study areas. 

(2) Based on threshold models, HREA 

sensitivity analyses indicate that the 

number of respiratory deaths associated 

with long-term O3 concentrations could 

potentially be considerably lower (i.e., 

by more than 75% if a threshold exists 

at 40 ppb, and by about 98% if a 

threshold exists at 56 ppb) (U.S. EPA, 

2014a, Figure 7–9).72

Compared to the weight given to 

HREA estimates of exposures of concern 

and lung function risks, and the weight 

given to the evidence, the PA places 

relatively less weight on epidemiologicbased risk estimates. In doing so, the PA 

notes that the overall conclusions from 

the HREA likewise reflect less 

confidence in estimates of 

epidemiologic-based risks than in 

estimates of exposures and lung 

function risks. The determination to 

attach less weight to the epidemiologicbased estimates reflects the 

uncertainties associated with mortality 

and morbidity risk estimates, including 

the heterogeneity in effect estimates 

between locations, the potential for 

exposure measurement errors, and 

uncertainty in the interpretation of the 

shape of concentration-response 

functions at lower O3 concentrations 

(U.S. EPA, 2014a, section 9.6). 

Uncertainty in the shape of 

concentration-response functions at 

lower O3 concentrations is particularly 

important to interpreting risk estimates 

given the approach used to adjust air 

quality to just meet the current 

standard, and potential alternative 

standards, and the resulting 

compression in the air quality 

distributions (i.e., decreasing high 

concentrations and increasing low 

concentrations) (II.A.2.a, above). Total 

risk estimates in the HREA are based on 

the assumption that the concentration 

response function for O3 is linear, such 

that total risk estimates are equally 

influenced by decreasing high 

concentrations and increasing low 

concentrations, when the increases and 

decreases are of equal magnitude. 

However, consistent with the PA’s 

consideration of risk estimates, in the 

proposal the Administrator notes that 

the overall body of evidence provides 

stronger support for the occurrence of 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65321 

O3-attributable health effects following 

exposures to O3 concentrations 

corresponding to the upper ends of 

typical ambient distributions (II.E.4.d of 

the proposal). In addition, even on days 

with increases in relatively low areawide average concentrations, resulting 

in increases in estimated risks, some 

portions of the urban study areas could 

experience decreases in high O3

concentrations. Therefore, to the extent 

adverse O3-attributable effects are more 

strongly supported for higher ambient 

concentrations (which, as noted above, 

are consistently reduced upon air 

quality adjustment), the PA notes that 

the impacts on risk estimates of 

increasing low O3 concentrations reflect 

an important source of uncertainty. 

c. PA Conclusions on the Current 

Standard 

Section II.D.3 of the proposal 

summarizes the PA conclusions on the 

adequacy of the existing primary O3

standard (79 FR 75285). As an initial 

matter, the PA concludes that reducing 

precursor emissions to achieve O3

concentrations that meet the current 

standard will provide important 

improvements in public health 

protection. This initial conclusion is 

based on (1) the strong body of scientific 

evidence indicating a wide range of 

adverse health outcomes attributable to 

exposures to O3 concentrations 

commonly found in the ambient air and 

(2) estimates indicating decreased 

occurrences of O3 exposures of concern 

and decreased health risks upon 

meeting the current standard, compared 

to recent air quality. 

In particular, the PA concludes that 

strong support for this initial conclusion 

is provided by controlled human 

exposure studies of respiratory effects, 

and by quantitative estimates of 

exposures of concern and lung function 

decrements based on information in 

these studies. Analyses in the HREA 

estimate that the percentages of children 

(i.e., all children and children with 

asthma) in urban study areas 

experiencing exposures of concern, or 

experiencing abnormal and potentially 

adverse lung function decrements, are 

consistently lower for air quality that 

just meets the current O3 standard than 

for recent air quality. The HREA 

estimates such reductions consistently 

across the urban study areas evaluated 

and throughout various portions of 

individual urban study areas, including 

in urban cores and the portions of urban 

study areas surrounding urban cores. 

These reductions in exposures of 

concern and O3-induced lung function 

decrements reflect the consistent 

decreases in the highest O3

concentrations following reductions in 

precursor emissions to meet the current 

standard. Thus, populations in both 

urban and non-urban areas would be 

expected to experience important 

reductions in O3 exposures and O3- 

induced lung function risks upon 

meeting the current standard. 

The PA further concludes that 

support for this initial conclusion is also 

provided by estimates of O3-associated 

mortality and morbidity based on 

application of concentration-response 

relationships from epidemiologic 

studies to air quality adjusted to just 

meet the current standard. These 

estimates are based on the assumption 

that concentration-response 

relationships are linear over entire 

distributions of ambient O3

concentrations, an assumption which 

has uncertainties that complicate 

interpretation of these estimates 

(II.A.2.c.ii). However, risk estimates for 

effects associated with short- and longterm O3 exposures, combined with the 

HREA’s national analysis of O3

responsiveness to reductions in 

precursor emissions and the consistent 

reductions estimated for the highest 

ambient O3 concentrations, suggest that 

O3-associated mortality and morbidity 

would be expected to decrease 

nationwide following reductions in 

precursor emissions to meet the current 

O3 standard. 

After reaching the initial conclusion 

that meeting the current primary O3

standard will provide important 

improvements in public health 

protection, and that it is not appropriate 

to consider a standard that is less 

protective than the current standard, the 

PA considers the adequacy of the public 

health protection that is provided by the 

current standard. In considering the 

available scientific evidence, exposure/ 

risk information, advice from CASAC 

(II.B.1.d, below), and input from the 

public, the PA reaches the conclusion 

that the available evidence and 

information clearly call into question 

the adequacy of public health protection 

provided by the current primary 

standard. In reaching this conclusion, 

the PA notes that evidence from 

controlled human exposure studies 

provides strong support for the 

occurrence of adverse respiratory effects 

following exposures to O3

concentrations below the level of the 

current standard. Epidemiologic studies 

provide support for the occurrence of 

adverse respiratory effects and mortality 

under air quality conditions that would 

likely meet the current standard. In 

addition, based on the analyses in the 

HREA, the PA concludes that the 

exposures and risks projected to remain 

upon meeting the current standard are 

indicative of risks that can reasonably 

be judged to be important from a public 

health perspective. Thus, the PA 

concludes that the evidence and 

information provide strong support for 

giving consideration to revising the 

current primary standard in order to 

provide increased public health 

protection against an array of adverse 

health effects that range from decreased 

lung function and respiratory symptoms 

to more serious indicators of morbidity 

(e.g., including emergency department 

visits and hospital admissions), and 

mortality. In consideration of all of the 

above, the PA draws the conclusion that 

it is appropriate for the Administrator to 

consider revision of the current primary 

O3 standard to provide increased public 

health protection. 

d. CASAC Advice 

Section II.D.4 of the proposal 

summarizes CASAC advice regarding 

the adequacy of the existing primary O3

standard. Following the 2008 decision 

to revise the primary O3 standard by 

setting the level at 0.075 ppm (75 ppb), 

CASAC strongly questioned whether the 

standard met the requirements of the 

CAA. In September 2009, the EPA 

announced its intention to reconsider 

the 2008 standards, issuing a notice of 

proposed rulemaking in January 2010 

(75 FR 2938). Soon after, the EPA 

solicited CASAC review of that 

proposed rule and in January 2011, 

solicited additional advice. This 

proposal was based on the scientific and 

technical record from the 2008 

rulemaking, including public comments 

and CASAC advice and 

recommendations. As further described 

above (I.D), in the fall of 2011, the EPA 

did not revise the standard as part of the 

reconsideration process but decided to 

defer decisions on revisions to the O3

standards to the next periodic review, 

which was already underway. 

Accordingly, in this section we describe 

CASAC’s advice related to the 2008 

final decision and the subsequent 

reconsideration, as well as its advice on 

this current review of the O3 NAAQS 

that was initiated in September 2008. 

In April 2008, the members of the 

CASAC Ozone Review Panel sent a 

letter to EPA stating ‘‘[I]n our mostrecent letters to you on this subject— 

dated October 2006 and March 2007— 

the CASAC unanimously recommended 

selection of an 8-hour average Ozone 

NAAQS within the range of 0.060 to 

0.070 parts per million [60 to 70 ppb] 

for the primary (human health-based) 

Ozone NAAQS’’ (Henderson, 2008). In 

2010, in response to the EPA’s 

solicitation of advice on the EPA’s 

mstockstill on DSK4VPTVN1PROD with RULES2

65322 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

73CASAC provided similar advice in their letter 

to the Administrator on the HREA, stating that ‘‘The 

CASAC finds that the current primary NAAQS for 

ozone is not protective of human health and needs 

to be revised’’ (Frey, 2014a, p. 15). 

proposed rulemaking as part of the 

reconsideration, CASAC again stated 

that the current standard should be 

revised to provide additional protection 

to the public health (Samet, 2010): 

CASAC fully supports EPA’s proposed 

range of 0.060–0.070 parts per million (ppm) 

for the 8-hour primary ozone standard. 

CASAC considers this range to be justified by 

the scientific evidence as presented in the 

Air Quality Criteria for Ozone and Related 

Photochemical Oxidants (March 2006) and 

Review of the National Ambient Air Quality 

Standards for Ozone: Policy Assessment of 

Scientific and Technical Information, 

OAQPS Staff Paper (July 2007). As stated in 

our letters of October 24, 2006, March 26, 

2007 and April 7, 2008 to former 

Administrator Stephen L. Johnson, CASAC 

unanimously recommended selection of an 8- 

hour average ozone NAAQS within the range 

proposed by EPA (0.060 to 0.070 ppm). In 

proposing this range, EPA has recognized the 

large body of data and risk analyses 

demonstrating that retention of the current 

standard would leave large numbers of 

individuals at risk for respiratory effects and/ 

or other significant health impacts including 

asthma exacerbations, emergency room visits, 

hospital admissions and mortality. 

In response to the EPA’s request for 

additional advice on the reconsideration 

in 2011, CASAC reaffirmed their 

conclusion that ‘‘the evidence from 

controlled human and epidemiological 

studies strongly supports the selection 

of a new primary ozone standard within 

the 60–70 ppb range for an 8-hour 

averaging time’’ (Samet, 2011, p ii). As 

requested by the EPA, CASAC’s advice 

and recommendations were based on 

the scientific and technical record from 

the 2008 rulemaking. In considering the 

record for the 2008 rulemaking, CASAC 

stated the following to summarize the 

basis for their conclusions (Samet, 2011, 

pp. ii to iii): 

(1) The evidence available on doseresponse for effects of O3 shows 

associations extending to levels within 

the range of concentrations currently 

experienced in the United States. 

(2) There is scientific certainty that 

6.6-hour exposures with exercise of 

young, healthy, non-smoking adult 

volunteers to concentrations ≥80 ppb 

cause clinically relevant decrements of 

lung function. 

(3) Some healthy individuals have 

been shown to have clinically relevant 

responses, even at 60 ppb. 

(4) Since the majority of clinical 

studies involve young, healthy adult 

populations, less is known about health 

effects in such potentially ozone 

sensitive populations as the elderly, 

children and those with 

cardiopulmonary disease. For these 

susceptible groups, decrements in lung 

function may be greater than in healthy 

volunteers and are likely to have a 

greater clinical significance. 

(5) Children and adults with asthma 

are at increased risk of acute 

exacerbations on or shortly after days 

when elevated O3 concentrations occur, 

even when exposures do not exceed the 

NAAQS concentration of 75 ppb. 

(6) Large segments of the population 

fall into what the EPA terms a ‘‘sensitive 

population group,’’ i.e., those at 

increased risk because they are more 

intrinsically susceptible (children, the 

elderly, and individuals with chronic 

lung disease) and those who are more 

vulnerable due to increased exposure 

because they work outside or live in 

areas that are more polluted than the 

mean levels in their communities. 

With respect to evidence from 

epidemiologic studies, CASAC stated 

‘‘while epidemiological studies are 

inherently more uncertain as exposures 

and risk estimates decrease (due to the 

greater potential for biases to dominate 

small effect estimates), specific evidence 

in the literature does not suggest that 

our confidence on the specific 

attribution of the estimated effects of 

ozone on health outcomes differs over 

the proposed range of 60–70 ppb’’ 

(Samet, 2011, p. 10). 

Following its review of the second 

draft PA in the current review, which 

considers an updated scientific and 

technical record since the 2008 

rulemaking, CASAC concluded that 

‘‘there is clear scientific support for the 

need to revise the standard’’ (Frey, 

2014c, p. ii). In particular, CASAC noted 

the following (Frey, 2014c, p. 5): 

[T]he scientific evidence provides strong 

support for the occurrence of a range of 

adverse respiratory effects and mortality 

under air quality conditions that would meet 

the current standard. Therefore, CASAC 

unanimously recommends that the 

Administrator revise the current primary 

ozone standard to protect public health.73

In supporting these conclusions, 

CASAC judged that the strongest 

evidence comes from controlled human 

exposure studies of respiratory effects. 

The Committee specifically noted that 

‘‘the combination of decrements in FEV1

together with the statistically significant 

alterations in symptoms in human 

subjects exposed to 72 ppb ozone meets 

the American Thoracic Society’s 

definition of an adverse health effect’’ 

(Frey, 2014c, p. 5). CASAC further 

judged that ‘‘if subjects had been 

exposed to ozone using the 8-hour 

averaging period used in the standard, 

adverse effects could have occurred at 

lower concentration’’ and that ‘‘the level 

at which adverse effects might be 

observed would likely be lower for more 

sensitive subgroups, such as those with 

asthma’’ (Frey, 2014c, p. 5). With regard 

to 60 ppb exposures, CASAC noted that 

‘‘a level of 60 ppb corresponds to the 

lowest exposure concentration 

demonstrated to result in lung function 

decrements large enough to be judged 

an abnormal response by ATS and that 

could be adverse in individuals with 

lung disease’’ (Frey, 2014c, p. 7). The 

CASAC further noted that ‘‘a level of 60 

ppb also corresponds to the lowest 

exposure concentration at which 

pulmonary inflammation has been 

reported’’ (Frey, 2014c, p. 7). 

In their advice, CASAC also took note 

of estimates of O3 exposures of concern 

and the risk of O3-induced lung function 

decrements. With regard to the 

benchmark concentrations used in 

estimating exposures of concern, 

CASAC stated the following (Frey, 

2014c, p. 6): 

The 80 ppb-8hr benchmark level represents 

an exposure level for which there is 

substantial clinical evidence demonstrating a 

range of ozone-related effects including lung 

inflammation and airway responsiveness in 

healthy individuals. The 70 ppb-8hr 

benchmark level reflects the fact that in 

healthy subjects, decreases in lung function 

and respiratory symptoms occur at 

concentrations as low as 72 ppb and that 

these effects almost certainly occur in some 

people, including asthmatics and others with 

low lung function who are less tolerant of 

such effects, at levels of 70 ppb and below. 

The 60 ppb-8hr benchmark level represents 

the lowest exposure level at which ozonerelated effects have been observed in clinical 

studies of healthy individuals. Based on its 

scientific judgment, the CASAC finds that the 

60 ppb-8hr exposure benchmark is relevant 

for consideration with respect to adverse 

effects on asthmatics. 

With regard to lung function risk 

estimates, CASAC concluded that 

‘‘estimation of FEV1 decrements of 

≥15% is appropriate as a scientifically 

relevant surrogate for adverse health 

outcomes in active healthy adults, 

whereas an FEV1 decrement of ≥10% is 

a scientifically relevant surrogate for 

adverse health outcomes for people with 

asthma and lung disease’’ (Frey, 2014c, 

p. 3). The Committee further concluded 

that ‘‘[a]sthmatic subjects appear to be at 

least as sensitive, if not more sensitive, 

than non-asthmatic subjects in 

manifesting O3-induced pulmonary 

function decrements’’ (Frey, 2014c, p. 

4). 

Although CASAC judged that 

controlled human exposure studies of 

respiratory effects provide the strongest 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65323 

74Although the Administrator noted that 

reductions in O3 precursor emissions (e.g., NOX; 

VOC) to achieve O3 concentrations that meet the 

current standard could also increase public health 

protection by reducing the ambient concentrations 

of pollutants other than O3 (e.g., PM2.5, NO2), we 

did not quantitatively analyze these effects, 

consistent with CASAC advice (Frey, 2014a, p.10). 

However, the Administrator is not setting the 

standard to address risks from pollutants other than 

O3. 

75Based on the exposure surrogates used in 

recent epidemiologic studies of long-term O3

exposure, it is not possible to distinguish between 

the impacts of long-term O3 exposure and exposure 

to repeated short-term peaks over an O3 season. 

evidence supporting their conclusion on 

the current standard, the Committee 

judged that there is also ‘‘sufficient 

scientific evidence based on 

epidemiologic studies for mortality and 

morbidity associated with short-term 

exposure to ozone at the level of the 

current standard’’ (Frey, 2014c, p. 5) 

and noted that ‘‘[r]ecent animal 

toxicological studies support 

identification of modes of action and, 

therefore, the biological plausibility 

associated with the epidemiological 

findings’’ (Frey, 2014c, p. 5). 

e. Administrator’s Proposed Decision 

Section II.D.5 in the proposal (79 FR 

75287–75291) discusses the 

Administrator’s proposed conclusions 

related to the adequacy of the public 

health protection provided by the 

current primary O3 standard, resulting 

in her proposed decision to revise that 

standard. These proposed conclusions 

and her proposed decision, summarized 

below, were based on the 

Administrator’s consideration of the 

available scientific evidence, exposure/ 

risk information, the comments and 

advice of CASAC, and public input that 

had been received by the time of 

proposal. 

As an initial matter, the Administrator 

concluded that reducing precursor 

emissions to achieve O3 concentrations 

that meet the current primary O3

standard will provide important 

improvements in public health 

protection, compared to recent air 

quality. In reaching this initial 

conclusion, she noted the discussion in 

section 3.4 of the PA (U.S. EPA, 2014c). 

In particular, the Administrator noted 

that this initial conclusion is supported 

by (1) the strong body of scientific 

evidence indicating a wide range of 

adverse health outcomes attributable to 

exposures to O3 concentrations 

commonly measured in the ambient air 

and (2) estimates indicating decreased 

occurrences of O3 exposures of concern 

and decreased O3-associated health risks 

upon meeting the current standard, 

compared to recent air quality. Thus, 

she concluded that it would not be 

appropriate in this review to consider a 

standard that is less protective than the 

current standard.74

After reaching the initial conclusion 

that meeting the current primary O3

standard will provide important 

improvements in public health 

protection, and that it is not appropriate 

to consider a standard that is less 

protective than the current standard, the 

Administrator next considered the 

adequacy of the public health protection 

that is provided by the current standard. 

In doing so, the Administrator first 

noted that studies evaluated since the 

completion of the 2006 AQCD support 

and expand upon the strong body of 

evidence that, in the last review, 

indicated a causal relationship between 

short-term O3 exposures and respiratory 

health effects, the strongest 

determination under the ISA’s 

hierarchical system for classifying 

weight of evidence for causation. 

Together, experimental and 

epidemiologic studies support 

conclusions regarding a continuum of 

O3 respiratory effects ranging from small 

reversible changes in pulmonary 

function, and pulmonary inflammation, 

to more serious effects that can result in 

respiratory-related emergency 

department visits, hospital admissions, 

and premature mortality. The 

Administrator further noted that recent 

animal toxicology studies support 

descriptions of modes of action for these 

respiratory effects and provide support 

for biological plausibility for the role of 

O3 in reported effects. With regard to 

mode of action, evidence indicates that 

antioxidant capacity may modify the 

risk of respiratory morbidity associated 

with O3 exposure, and that the inherent 

capacity to quench (based on individual 

antioxidant capacity) can be 

overwhelmed, especially with exposure 

to elevated concentrations of O3. In 

addition, based on the consistency of 

findings across studies and evidence for 

the coherence of results from different 

scientific disciplines, evidence indicates 

that certain populations are at increased 

risk of experiencing O3-related effects, 

including the most severe effects. These 

include populations and lifestages 

identified in previous reviews (i.e., 

people with asthma, children, older 

adults, outdoor workers) and 

populations identified since the last 

review (i.e., people with certain 

genotypes related to antioxidant and/or 

anti-inflammatory status; people with 

reduced intake of certain antioxidant 

nutrients, such as Vitamins C and E). 

The Administrator further noted that 

evidence for adverse respiratory health 

effects attributable to long-term 75 O3

exposures is much stronger than in 

previous reviews, and noted the ISA’s 

conclusion that there is ‘‘likely to be’’ a 

causal relationship between such O3

exposures and adverse respiratory 

health effects (the second strongest 

causality determination). She noted that 

the evidence available in this review 

includes new epidemiologic studies 

using a variety of designs and analysis 

methods, conducted by different 

research groups in different locations, 

evaluating the relationships between 

long-term O3 exposures and measures of 

respiratory morbidity and mortality. 

New evidence supports associations 

between long-term O3 exposures and the 

development of asthma in children, 

with several studies reporting 

interactions between genetic variants 

and such O3 exposures. Studies also 

report associations between long-term 

O3 exposures and asthma prevalence, 

asthma severity and control, respiratory 

symptoms among asthmatics, and 

respiratory mortality. 

In considering the O3 exposure 

concentrations reported to elicit 

respiratory effects, the Administrator 

agreed with the conclusions of the PA 

and with the advice of CASAC (Frey, 

2014c) that controlled human exposure 

studies provide the most certain 

evidence indicating the occurrence of 

health effects in humans following 

exposures to specific O3 concentrations. 

In particular, she noted that the effects 

reported in controlled human exposure 

studies are due solely to O3 exposures, 

and interpretation of study results is not 

complicated by the presence of cooccurring pollutants or pollutant 

mixtures. 

In considering the evidence from 

controlled human exposure studies, the 

Administrator first noted that these 

studies have reported a variety of 

respiratory effects in healthy adults 

following exposures to O3

concentrations of 60, 72, or 80 ppb, and 

higher. The largest respiratory effects, 

and the broadest range of effects, have 

been studied and reported following 

exposures of healthy adults to 80 ppb O3

or higher, with most exposure studies 

conducted at these higher 

concentrations. She further noted that 

recent evidence includes controlled 

human exposure studies reporting the 

combination of lung function 

decrements and respiratory symptoms 

in healthy adults engaged in quasicontinuous, moderate exertion 

following 6.6 hour exposures to 

concentrations as low as 72 ppb, and 

lung function decrements and 

mstockstill on DSK4VPTVN1PROD with RULES2

65324 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

76This CASAC advice and ATS recommendations 

are discussed in more detail in section II.C.4 below 

(see also II.A.1.c, above). 

77As noted above, HREA analyses indicate that 

activity data for asthmatics is generally similar to 

non-asthmatics (U.S. EPA, 2014a, Appendix 5G, 

Tables 5G2-to 5G–5). 

pulmonary inflammation following 

exposures to O3 concentrations as low 

as 60 ppb. As discussed below, 

compared to the evidence available in 

the last review, the Administrator 

viewed these studies as having 

strengthened support for the occurrence 

of abnormal and adverse respiratory 

effects attributable to short-term 

exposures to O3 concentrations below 

the level of the current standard. The 

Administrator stated that such 

exposures to O3 concentrations below 

the level of the current standard are 

potentially important from a public 

health perspective, given the following: 

(1) The combination of lung function 

decrements and respiratory symptoms 

reported to occur in healthy adults 

following exposures to 72 ppb O3 or 

higher, while at moderate exertion, meet 

ATS criteria for an adverse response. In 

specifically considering the 72 ppb 

exposure concentration, CASAC noted 

that ‘‘the combination of decrements in 

FEV1 together with the statistically 

significant alterations in symptoms in 

human subjects exposed to 72 ppb 

ozone meets the American Thoracic 

Society’s definition of an adverse health 

effect’’ (Frey, 2014c, p. 5). 

(2) With regard to 60 ppb O3, CASAC 

agreed that ‘‘a level of 60 ppb 

corresponds to the lowest exposure 

concentration demonstrated to result in 

lung function decrements large enough 

to be judged an abnormal response by 

ATS and that could be adverse in 

individuals with lung disease’’ (Frey, 

2014c, p. 7). CASAC further noted that 

‘‘a level of 60 ppb also corresponds to 

the lowest exposure concentration at 

which pulmonary inflammation has 

been reported’’ (Frey, 2014c, p. 7). 

(3) The controlled human exposure 

studies reporting these respiratory 

effects were conducted in healthy 

adults, while at-risk groups (e.g., 

children, people with asthma) could 

experience larger and/or more serious 

effects. In their advice to the 

Administrator, CASAC concurred with 

this reasoning (Frey, 2014a, p. 14; Frey, 

2014c, p. 5). 

(4) These respiratory effects are 

coherent with the serious health 

outcomes that have been reported in 

epidemiologic studies evaluating 

exposure to O3 (e.g., respiratory-related 

hospital admissions, emergency 

department visits, and mortality). 

As noted above, the Administrator’s 

proposed conclusions regarding the 

adequacy of the current primary O3

standard placed a large amount of 

weight on the results of controlled 

human exposure studies. In particular, 

given the combination of lung function 

decrements and respiratory symptoms 

following 6.6-hour exposures to O3

concentrations as low as 72 ppb, and 

given CASAC advice regarding effects at 

72 ppb, along with ATS adversity 

criteria, she concluded that the evidence 

in this review supports the occurrence 

of adverse respiratory effects following 

exposures to O3 concentrations lower 

than the level of the current standard.76

As discussed below, the Administrator 

further considered information from the 

broader body of controlled human 

exposure studies within the context of 

quantitative estimates of exposures of 

concern and O3-induced FEV1

decrements. 

While putting less weight on 

information from epidemiologic studies 

than on information from controlled 

human exposure studies, the 

Administrator also considered what the 

available epidemiologic evidence 

indicates with regard to the adequacy of 

the public health protection provided by 

the current primary O3 standard. She 

noted that recent epidemiologic studies 

provide support, beyond that available 

in the last review, for associations 

between short-term O3 exposures and a 

wide range of adverse respiratory 

outcomes (including respiratory-related 

hospital admissions, emergency 

department visits, and mortality) and 

with total mortality. Associations with 

morbidity and mortality are stronger 

during the warm or summer months, 

and remain robust after adjustment for 

copollutants. 

In considering information from 

epidemiologic studies within the 

context of her conclusions on the 

adequacy of the current standard, the 

Administrator considered the extent to 

which available studies support the 

occurrence of O3 health effect 

associations with air quality likely to be 

allowed by the current standard. Most of 

the epidemiologic studies considered by 

the Administrator were conducted in 

locations likely to have violated the 

current standard over at least part of the 

study period. However, she noted three 

U.S. single-city studies that support the 

occurrence of O3-associated hospital 

admissions or emergency department 

visits at ambient O3 concentrations 

below the level of the current standard, 

or when virtually all monitored 

concentrations were below the level of 

the current standard (Mar and Koenig, 

2009; Silverman and Ito, 2010; 

Strickland et al., 2010) (section II.D.1 of 

the proposal). While the Administrator 

acknowledged greater uncertainty in 

interpreting air quality for multicity 

studies, she noted that O3 associations 

with respiratory morbidity or mortality 

have been reported when the majority of 

study locations (though not all study 

locations) would likely have met the 

current O3 standard. When taken 

together, the Administrator reached the 

initial conclusion at proposal that 

single-city epidemiologic studies and 

associated air quality information 

support the occurrence of O3-associated 

hospital admissions and emergency 

department visits for ambient O3

concentrations likely to have met the 

current standard, and that air quality 

analyses in locations of multicity 

studies provide some support for this 

conclusion for a broader range of effects, 

including mortality. 

Beyond her consideration of the 

scientific evidence, the Administrator 

also considered the results of the HREA 

exposure and risk analyses in reaching 

initial conclusions regarding the 

adequacy of the current primary O3

standard. In doing so, as noted above, 

she focused primarily on exposure and 

risk estimates based on information 

from controlled human exposure studies 

(i.e., exposures of concern and O3- 

induced lung function decrements) and 

placed relatively less weight on 

epidemiologic-based risk estimates. 

With regard to estimates of exposures 

of concern, the Administrator 

considered the extent to which the 

current standard provides protection 

against exposures to O3 concentrations 

at or above 60, 70, and 80 ppb. 

Consistent with CASAC advice (Frey, 

2014c), the Administrator focused on 

children in these analyses of O3

exposures, noting that estimates for all 

children and asthmatic children are 

virtually indistinguishable, in terms of 

the percent estimated to experience 

exposures of concern.77 Though she 

focused on children, she also recognized 

that exposures to O3 concentrations at or 

above 60 or 70 ppb could be of concern 

for adults. As discussed in the HREA 

and PA (and II.C.2.a of the proposal), 

the patterns of exposure estimates 

across urban study areas, across years, 

and across air quality scenarios are 

similar in adults with asthma, older 

adults, all children, and children with 

asthma, though smaller percentages of 

adult populations are estimated to 

experience exposures of concern than 

children and children with asthma. 

Thus, the Administrator recognized that 

the exposure patterns for children 

across years, urban study areas, and air 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65325 

78The Administrator noted that not all people 

who experience an exposure of concern will 

experience an adverse effect (even members of atrisk populations). For most of the endpoints 

evaluated in controlled human exposure studies 

(with the exception of O3-induced FEV1

decrements, as discussed below), the number of 

those experiencing exposures of concern who will 

experience adverse effects cannot be reliably 

quantified. 

79The Administrator’s considerations related to 

estimated O3 exposures of concern, including her 

views on estimates of two or more and one or more 

such exposures, are discussed in more detail within 

the context of her consideration of public comments 

on the level of the revised standard and her final 

decision on level (II.C.4.b and II.C.4.c, below). 

80Almost no children in those areas would be 

estimated to experience two or more exposures of 

concern at or above 80 ppb. 

81As discussed below (II.C.4), in her 

consideration of potential alternative standard 

levels, the Administrator placed less weight on 

estimates of the risk of O3-induced FEV1

decrements. In doing so, she particularly noted that, 

unlike exposures of concern, the variability in lung 

Continued 

quality scenarios are indicative of the 

exposure patterns in a broader group of 

at-risk populations that also includes 

asthmatic adults and older adults. 

She further noted that while single 

exposures of concern could be adverse 

for some people, particularly for the 

higher benchmark concentrations (70, 

80 ppb) where there is stronger evidence 

for the occurrence of adverse effects, she 

became increasingly concerned about 

the potential for adverse responses as 

the number of occurrences increases (61 

FR 75122).78 In particular, she noted 

that repeated occurrences of the types of 

effects shown to occur following 

exposures of concern can have 

potentially adverse outcomes. For 

example, repeated occurrences of 

airway inflammation could potentially 

result in the induction of a chronic 

inflammatory state; altered pulmonary 

structure and function, leading to 

diseases such as asthma; altered lung 

host defense response to inhaled 

microorganisms; and altered lung 

response to other agents such as 

allergens or toxins (U.S. EPA, 2013, 

section 6.2.3). Thus, the Administrator 

noted that the types of respiratory 

effects shown to occur in some 

individuals following exposures to O3

concentrations from 60 to 80 ppb, 

particularly if experienced repeatedly, 

provide a mode of action by which O3

may cause other more serious effects 

(e.g., asthma exacerbations). Therefore, 

the Administrator placed the most 

weight on estimates of two or more 

exposures of concern (i.e., as a surrogate 

for the occurrence of repeated 

exposures), though she also considered 

estimates of one or more, particularly 

for the 70 and 80 ppb benchmarks.79

As illustrated in Table 1 (above), the 

Administrator noted that if the 15 urban 

study areas evaluated in the HREA were 

to just meet the current O3 standard, 

fewer than 1% of children in those areas 

would be estimated to experience two or 

more exposures of concern at or above 

70 ppb, though approximately 3 to 8% 

of children, including approximately 3 

to 8% of asthmatic children, would be 

estimated to experience two or more 

exposures of concern to O3

concentrations at or above 60 ppb 80

(based on estimates averaged over the 

years of analysis). To provide some 

perspective on these percentages, the 

Administrator noted that they 

correspond to almost 900,000 children 

in urban study areas, including about 

90,000 asthmatic children, estimated to 

experience two or more exposures of 

concern at or above 60 ppb. Nationally, 

if the current standard were to be just 

met, the number of children 

experiencing such exposures would be 

larger. In the worst-case year and 

location (i.e., year and location with the 

largest exposure estimates), the 

Administrator noted that over 2% of 

children are estimated to experience 

two or more exposures of concern at or 

above 70 ppb and over 14% are 

estimated to experience two or more 

exposures of concern at or above 60 

ppb. 

Although, as discussed above and in 

section II.E.4.d of the proposal, the 

Administrator was less concerned about 

single occurrences of exposures of 

concern, she noted that even single 

occurrences can cause adverse effects in 

some people, particularly for the 70 and 

80 ppb benchmarks. Therefore, she also 

considered estimates of one or more 

exposures of concern. As illustrated in 

Table 1 (above), if the 15 urban study 

areas evaluated in the HREA were to 

just meet the current O3 standard, fewer 

than 1% of children in those areas 

would be estimated to experience one or 

more exposures of concern at or above 

80 ppb (based on estimates averaged 

over the years of analysis). However, 

approximately 1 to 3% of children, 

including 1 to 3% of asthmatic children, 

would be estimated to experience one or 

more exposures of concern to O3

concentrations at or above 70 ppb and 

approximately 10 to 17% would be 

estimated to experience one or more 

exposures of concern to O3

concentrations at or above 60 ppb. In 

the worst-case year and location, the 

Administrator noted that over 1% of 

children are estimated to experience one 

or more exposures of concern at or 

above 80 ppb, over 8% are estimated to 

experience one or more exposures of 

concern at or above 70 ppb, and about 

26% are estimated to experience one or 

more exposures of concern at or above 

60 ppb. 

In addition to estimated exposures of 

concern, the Administrator also 

considered HREA estimates of the 

occurrence of O3-induced lung function 

decrements. In doing so, she 

particularly noted CASAC advice that 

‘‘estimation of FEV1 decrements of 

≥15% is appropriate as a scientifically 

relevant surrogate for adverse health 

outcomes in active healthy adults, 

whereas an FEV1 decrement of ≥10% is 

a scientifically relevant surrogate for 

adverse health outcomes for people with 

asthma and lung disease’’ (Frey, 2014c, 

p. 3). While these surrogates provide 

perspective on the potential for the 

occurrence of adverse respiratory effects 

following O3 exposures, the 

Administrator agreed with the 

conclusion in past reviews that a more 

general consensus view of the adversity 

of moderate responses emerges as the 

frequency of occurrence increases 

(citing to 61 FR 65722–3) (Dec, 13, 

1996). Therefore, in the proposal the 

Administrator expressed increasing 

concern about the potential for adversity 

as the frequency of occurrences 

increased and, as a result, she focused 

primarily on estimates of two or more 

O3-induced FEV1 decrements (i.e., as a 

surrogate for repeated exposures). 

When averaged over the years 

evaluated in the HREA, the 

Administrator noted that the current 

standard is estimated to allow about 1 

to 3% of children in the 15 urban study 

areas (corresponding to almost 400,000 

children) to experience two or more O3- 

induced lung function decrements 

≥15%, and to allow about 8 to 12% of 

children (corresponding to about 

180,000 asthmatic children) to 

experience two or more O3-induced 

lung function decrements ≥10%. 

Nationally, larger numbers of children 

would be expected to experience such 

O3-induced decrements if the current 

standard were to be just met. The 

current standard is also estimated to 

allow about 3 to 5% of children in the 

urban study areas to experience one or 

more decrements ≥15% and about 14 to 

19% of children to experience one or 

more decrements ≥10%. In the worstcase year and location, the current 

standard is estimated to allow 4% of 

children in the urban study areas to 

experience two or more decrements 

≥15% (and 7% to experience one or 

more such decrements) and 14% of 

children to experience two or more 

decrements ≥10% (and 22% to 

experience one or more such 

decrements).81

mstockstill on DSK4VPTVN1PROD with RULES2

65326 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

function risk estimates across urban study areas is 

often greater than the differences in risk estimates 

between various standard levels (Table 2, above). 

Given this, and the resulting considerable overlap 

between the ranges of lung function risk estimates 

for different standard levels, although the 

Administrator noted her confidence in the lung 

function risk estimates themselves, she viewed 

them as providing a more limited basis than 

exposures of concern for distinguishing between the 

degree of public health protection provided by 

alternative standard levels. 

82 In doing so, she concluded that lower 

confidence should be placed in the results of the 

assessment of respiratory mortality risks associated 

with long-term O3 exposures, primarily because that 

analysis is based on only one study (even though 

that study is well-designed) and because of the 

uncertainty in that study about the existence and 

identification of a potential threshold in the 

concentration-response function (U.S. EPA, 2014a, 

section 9.6) (section II.D.2 of the proposal). CASAC 

also called into question the extent to which it is 

appropriate to place confidence in risk estimates for 

respiratory mortality (Frey, 2014a, p. 11). 

In further considering the HREA 

results, the Administrator considered 

the epidemiology-based risk estimates. 

Compared to the weight given to HREA 

estimates of exposures of concern and 

lung function risks, she placed 

relatively less weight on epidemiologybased risk estimates. Consistent with the 

conclusions in the PA, her 

determination to attach less weight to 

the epidemiologic-based risk estimates 

reflected her consideration of key 

uncertainties, including the 

heterogeneity in effect estimates 

between locations, the potential for 

exposure measurement errors, and 

uncertainty in the interpretation of the 

shape of concentration-response 

functions for O3 concentrations in the 

lower portions of ambient distributions 

(U.S. EPA, 2014a, section 9.6) (section 

II.D.2 of the proposal). 

The Administrator focused on 

estimates of total mortality risk 

associated with short-term O3

exposures.82 Given the decreasing 

certainty in the shape of concentrationresponse functions for area-wide O3

concentrations at the lower ends of 

warm season distributions (U.S. EPA, 

2013, section 2.5.4.4), the Administrator 

focused on estimates of risk associated 

with O3 concentrations in the upper 

portions of ambient distributions. Even 

when considering only area-wide O3

concentrations from these upper 

portions of seasonal distributions, the 

Administrator noted that the current 

standard is estimated to allow hundreds 

to thousands of O3-associated deaths per 

year in urban study areas (79 FR 75291 

citing to section II.C.3 of the proposal). 

In addition to the evidence and 

exposure/risk information discussed 

above, the Administrator took note of 

the CASAC advice in the current review 

and in the 2010 proposed 

reconsideration of the 2008 decision 

establishing the current standard. As 

discussed in more detail above, the 

current CASAC ‘‘finds that the current 

NAAQS for ozone is not protective of 

human health’’ and ‘‘unanimously 

recommends that the Administrator 

revise the current primary ozone 

standard to protect public health’’ (Frey, 

2014c, p. 5). 

In consideration of all of the above, 

the Administrator proposed that the 

current primary O3 standard is not 

adequate to protect public health, and 

that it should be revised to provide 

increased public health protection. This 

proposed decision was based on the 

Administrator’s initial conclusions that 

the available evidence and exposure and 

risk information clearly call into 

question the adequacy of public health 

protection provided by the current 

primary standard and, therefore, that the 

current standard is not requisite to 

protect public health with an adequate 

margin of safety. With regard to the 

evidence, she specifically noted that (1) 

controlled human exposure studies 

provide support for the occurrence of 

adverse respiratory effects following 

exposures to O3 concentrations below 

the level of the current standard (i.e., as 

low as 72 ppb), and that (2) single-city 

epidemiologic studies provide support 

for the occurrence of adverse respiratory 

effects under air quality conditions that 

would likely meet the current standard, 

with multicity studies providing limited 

support for this conclusion for a broader 

range of effects (i.e., including 

mortality). In addition, based on the 

analyses in the HREA, the 

Administrator concluded that the 

exposures and risks projected to remain 

upon meeting the current standard can 

reasonably be judged to be important 

from a public health perspective. Thus, 

she reached the proposed conclusion 

that the evidence and information, 

together with CASAC advice based on 

their consideration of that evidence and 

information, provide strong support for 

revising the current primary standard in 

order to increase public health 

protection against an array of adverse 

effects that range from decreased lung 

function and respiratory symptoms to 

more serious indicators of morbidity 

(e.g., including emergency department 

visits and hospital admissions), and 

mortality. 

2. Comments on the Need for Revision 

The EPA received a large number of 

comments, more than 430,000 

comments, on the proposed decision to 

revise the current primary O3 standard. 

These comments generally fell into one 

of two broad groups that expressed 

sharply divergent views. 

Many commenters asserted that the 

current primary O3 standard is not 

sufficient to protect public health, 

especially the health of sensitive groups, 

with an adequate margin of safety. 

These commenters agreed with the 

EPA’s proposed decision to revise the 

current standard to increase public 

health protection. Among those calling 

for revisions to the current primary 

standard were medical groups (e.g., 

American Academy of Pediatrics (AAP), 

American Medical Association, 

American Lung Association (ALA), 

American Thoracic Society, American 

Heart Association, and the American 

College of Occupational and 

Environmental Medicine); national, 

state, and local public health and 

environmental organizations (e.g., the 

National Association of County and City 

Health Officials, American Public 

Health Association, Physicians for 

Social Responsibility, Sierra Club, 

Natural Resources Defense Council, 

Environmental Defense Fund, Center for 

Biological Diversity, and Earthjustice); 

the majority of state and local air 

pollution control authorities that 

submitted comments (e.g., agencies from 

California Air Resources Board and 

Office of Environmental Health Hazard 

Assessment, Connecticut, Delaware, 

Iowa, Illinois, Maryland, Minnesota, 

New Hampshire, New York, North 

Dakota, Oregon, Pennsylvania, 

Tennessee, and Wisconsin); the 

National Tribal Air Association; State 

organizations (e.g., National Association 

of Clean Air Agencies (NACAA), 

Northeast States for Coordinated Air 

Use Management, Ozone Transport 

Commission). While all of these 

commenters agreed with the EPA that 

the current O3 standard needs to be 

revised, many supported a more 

protective standard than proposed by 

EPA, as discussed in more detail below 

(II.C.4). Many individual commenters 

also expressed similar views. 

A second group of commenters, 

representing industry associations, 

businesses and some state agencies, 

opposed the proposed decision to revise 

the current primary O3 standard, 

expressing the view that the current 

standard is adequate to protect public 

health, including the health of sensitive 

groups, and to do so with an adequate 

margin of safety. Industry and business 

groups expressing this view included 

the American Petroleum Institute (API), 

the Alliance of Automobile 

Manufacturers (AAM), the American 

Forest and Paper Association, the Dow 

Chemical Company, the National 

Association of Manufacturers, the 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65327 

83See 79 FR 75287–91 (noting, among other 

things, that exposure to ambient O3 concentrations 

below the level of the current standard has been 

associated with diminished lung function capacity, 

respiratory symptoms, and respiratory health effects 

resulting in emergency room visits or hospital 

admissions, and that a single-city epidemiologic 

study showed associations with asthma emergency 

department visits in an area that would have met 

the current standard over the entire study period). 

See also Frey 2014c, p. 5 (CASAC reiterated its 

conclusion, after multiple public comment 

opportunities, that as a matter of science the current 

standard ‘‘is not protective of public health’’ and 

provided the bases for that conclusion). 

84Background O3 can be generically defined as 

the portion of O3 in ambient air that comes from 

sources outside the jurisdiction of an area and can 

include natural sources as well as transported O3 of 

anthropogenic origin. EPA has identified two 

specific definitions of background O3 relevant to 

this discussion: natural background (NB) and 

United States background (USB). NB is defined as 

the O3 that would exist in the absence of any 

manmade precursor emissions. USB is defined as 

that O3 that would exist in the absence of any 

manmade emissions inside the U.S. This includes 

anthropogenic emissions outside the U.S. as well as 

naturally occurring ozone. In many cases, the 

comments reference background O3 only in the 

generic sense. Unless explicitly noted otherwise, we 

have assumed all references to background in the 

comments are intended to refer to USB. 

National Mining Association, the U.S. 

Chamber of Commerce (in a joint 

comment with other industry groups), 

and the Utility Air Regulatory Group 

(UARG). State environmental agencies 

opposed to revising the current primary 

O3 standard included agencies from 

Arkansas, Georgia, Louisiana, Kansas, 

Michigan, Mississippi, Nebraska, North 

Carolina, Ohio, Texas, Virginia, and 

West Virginia. 

The following sections discuss 

comments submitted by these and other 

groups, and the EPA’s responses to 

those comments. Comments dealing 

with overarching issues that are 

fundamental to EPA’s decision-making 

methodology are addressed in section 

II.B.2.a. Comments on the health effects 

evidence, including evidence from 

controlled human exposure and 

epidemiologic studies, are addressed in 

section II.B.2.b. Comments on human 

exposure and health risk assessments 

are addressed in section II.B.2.c. 

Comments on the appropriate indicator, 

averaging time, form, or level of a 

revised primary O3 standard are 

addressed below in section II.C. In 

addition to the comments addressed in 

this preamble, the EPA has prepared a 

Response to Comments document that 

addresses other specific comments 

related to standard setting, as well as 

comments on implementation- and/or 

cost-related factors that the EPA may 

not consider as part of the basis for 

decisions on the NAAQS. This 

document is available for review in the 

docket for this rulemaking and through 

the EPA’s OAQPS TTN Web site (http:// 

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

ozone/s_o3_index.html). 

a. Overarching Comments 

Some commenters maintained that 

the proposed rule (and by extension the 

final rule) is fundamentally flawed 

because it does not quantify, or 

otherwise define, what level of 

protection is ‘‘requisite’’ to protect the 

public health. These commenters 

asserted that ‘‘EPA has not explained 

how far above zero-risk it believes is 

appropriate or how close to background 

is acceptable. EPA has failed to explain 

how the current standard is inadequate 

on this specific basis’’ (e.g., UARG, p. 

10). These commenters further 

maintained that the failure to quantify a 

requisite level of protection ‘‘drastically 

reduces the value of public 

participation’’ since ‘‘the public does 

not understand what is driving EPA’s 

decision’’ (e.g., UARG, p. 11). 

The EPA disagrees with these 

comments and notes that industry 

petitioners made virtually the same 

argument before the D.C. Circuit in ATA 

III, on remand from the Supreme Court, 

arguing that unless EPA identifies and 

quantifies a degree of acceptable risk, it 

is impossible to determine if a NAAQS 

is requisite (i.e., neither too stringent or 

insufficiently stringent to protect the 

public health). The D.C. Circuit rejected 

petitioners’ argument, holding that 

‘‘[a]lthough we recognize that the Clean 

Air Act and circuit precedent require 

EPA qualitatively to describe the 

standard governing its selection of 

particular NAAQS, we have expressly 

rejected the notion that the Agency must 

‘establish a measure of the risk to safety 

it considers adequate to protect public 

health every time it establish a 

[NAAQS]’’’ ATA III, 283 F. 3d at 369 

(quoting NRDC v. EPA, 902 F.2d 962, 

973 (D.C. Cir. 1990)). The court went on 

to explain that the requirement is only 

for EPA to engage in reasoned decisionmaking, ‘‘not that it definitively identify 

pollutant levels below which risks to 

public health are negligible.’’ ATA III, 

283 F. 3d at 370. 

Thus, the Administrator is required to 

exercise her judgment in the face of 

scientific uncertainty to establish the 

NAAQS to provide appropriate 

protection against risks to public health, 

both known and unknown. As 

discussed below, in the current review, 

the Administrator judges that the 

existing primary O3 standard is not 

requisite to protect public health with 

an adequate margin of safety, a 

judgment that is consistent with 

CASAC’s conclusion that ‘‘there is clear 

scientific support for the need to revise 

the standard’’ (Frey, 2014c, p. ii). 

Further, in section II.C.4 below, the 

Administrator has provided a thorough 

explanation of her rationale for 

concluding that a standard with a level 

of 70 ppb is requisite to protect public 

health with an adequate margin of 

safety, explaining the various scientific 

uncertainties which circumscribe the 

range of potential alternative standards, 

and how she exercised her ‘‘judgment’’ 

(per section 109 (b)(1) of the CAA) in 

selecting a standard from within that 

range of scientifically reasonable 

choices. This ‘‘reasoned decision 

making’’ is what the Act requires, 283 

F. 3d at 370, not the quantification 

advocated by these commenters. 

The EPA further disagrees with the 

comment that a failure to quantify a 

requisite level of protection impaired or 

impeded public notice and comment 

opportunities. In fact, the EPA clearly 

gave adequate notice of the bases both 

for determining that the current 

standard does not afford requisite 

protection,83 and for determining how 

the standard should be revised. In 

particular, the EPA explained in detail 

which evidence it considered critical, 

and the scientific uncertainties that 

could cause the Administrator to weight 

that evidence in various ways (79 FR 

75308–75310). There were robust 

comments submitted by commenters 

from a range of viewpoints on all of 

these issues, an indication of the 

adequacy of notice. The public was also 

afforded multiple opportunities to 

comment to the EPA and to CASAC 

during the development of the ISA, 

REA, and PA. Thus, the EPA does not 

agree that lack of quantification of a risk 

level that is ‘‘requisite’’ has deprived 

commenters of adequate notice and 

opportunity to comment in this 

proceeding. 

Various commenters maintained that 

it was inappropriate to revise the 

current NAAQS based on their view that 

natural background concentrations in 

several states are at or above O3

concentrations associated with meeting 

a NAAQS set at a level less than 75 ppb 

(presumably retaining the same 

indicator, form, and averaging time), 

making the NAAQS impossible for those 

states to attain and maintain, a result 

they claim is legally impermissible. In 

support for their argument, the 

commenters cite monitoring and 

modelling results from various areas in 

the intermountain west, state that EPA 

analyses provide underestimates of 

background O3 and conclude that high 

concentrations of background O3 84 exist 

mstockstill on DSK4VPTVN1PROD with RULES2

65328 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

85The analysis of observations in Utah notes the 

influence of domestic emissions—either from Salt 

Lake City (for two of the areas) or from Los Angeles 

and California (for the third of the areas)—on O3

concentrations at each of the locations included 

(NMA comments, Appendix E). Additionally, the 

analysis of monitoring data for Nevada also 

describes the influence of the monitoring sites by 

domestic emissions from other western states 

(NMA, Appendix H). 

86Specific aspects of the comments on the EPA 

analyses are addressed in more detail in the RTC. 

in many parts of the United States that 

will ‘‘prevent attainment’’ of a revised 

standard (NMA, p. 5). 

The courts have clearly established 

that ‘‘[a]ttainability and technological 

feasibility are not relevant 

considerations in the promulgation of 

[NAAQS].’’ API v. EPA, 665 F. 2d 1176, 

1185 (D.C. Cir. 1981). Further, the courts 

have clarified that the EPA may 

consider proximity to background 

concentrations as a factor in the 

decision whether and how to revise the 

NAAQS only in the context of 

considering standard levels within the 

range of reasonable values supported by 

the air quality criteria and judgments of 

the Administrator. 79 FR 75242–43 

(citing ATA III, 283 F. 3d at 379). In this 

review, the overall body of scientific 

evidence and exposure/risk information, 

as discussed in Section II.B of this 

notice, is clear and convincing: The 

existing standard is not adequate to 

protect public health with an adequate 

margin of safety and that the standard 

needs to be revised to reflect a lower 

level to provide that protection. The 

EPA analyses indicate that there may be 

infrequent instances in a limited 

number of rural areas where background 

O3 would be appreciable but not the 

sole contributor to an exceedance of the 

revised NAAQS, but do not indicate 

U.S. background (USB) O3

concentrations will prevent attainment 

of a revised O3 standard with a level of 

70 ppb. USB is defined as that O3 that 

would exist even in the absence of any 

manmade emissions within the United 

States. 

The EPA’s estimates of U.S. 

background ozone concentrations are 

based on frequently-utilized, state-ofthe-science air quality models and are 

considered reasonable and reliable, not 

underestimates. In support of their 

view, the commenters state that 

monitored (not modelled) ozone 

concentrations in remote rural locations 

include instances of 8-hour average 

concentrations very occasionally higher 

than 70 ppb. Monitoring data from 

places like the Grand Canyon and 

Yellowstone National Parks, are 

examples cited in comments. It is 

inappropriate to assume that monitored 

O3 concentrations at remote sites can be 

used as a proxy for background O3. Even 

at the most remote locations, local O3

concentrations are impacted by 

anthropogenic emissions from within 

the U.S. The EPA modeling analyses 

(U.S. EPA, 2014c, Figure 2–18) estimate 

that, on a seasonal basis, 10–20% of the 

O3 at even the most remote locations in 

the intermountain western U.S. 

originates from manmade emissions 

from the U.S., and thus is not part of 

USB. This conclusion is supported by 

commenter-submitted recent data 

analyses of rural O3 observations in 

Nevada and Utah (NMA, Appendices D 

and H). These analyses conclude that 

natural sources, international O3

transport, O3 transported from upwind 

states, and O3 transported from urban 

areas within a state all contributed to O3

concentrations at rural sites.85 Thus, 

while O3 in high-altitude, rural portions 

of the intermountain western U.S. can, 

at times, be substantially influenced by 

background sources such as wildfires, 

international transport or the 

stratosphere, measured O3 in rural 

locations are also influenced by 

domestic emissions and so cannot, by 

themselves, be used to estimate USB 

concentrations. Accordingly, the fact 

that 2011–2013 design values in 

locations like Yellowstone National 

Park (66 ppb) or Grand Canyon National 

Park (72 ppb) approach or exceed 70 

ppb, does not support the conclusion 

that a standard with a level of 70 ppb 

is impossible to attain. 

To accurately estimate USB 

concentrations, it is necessary to use air 

quality models which can estimate how 

much of the O3 at any given location 

originates from sources other than 

manmade emissions within the U.S. As 

part of the rulemaking, the EPA has 

summarized a variety of modeling-based 

analyses of background O3 (U.S. EPA, 

2013, Chapter 3) and conducted our 

own multi-model assessment of USB 

concentrations across the U.S. (U.S. 

EPA, 2014c, Chapter 2). The EPA 

analyses, which are consistent with the 

previously-summarized studies 

highlighted by commenters, concluded 

that seasonal mean daily maximum 

8-hour average concentrations of USB 

O3 range from 25–50 ppb, with the 

highest estimates located across the 

intermountain western U.S. 

Importantly, the modeling analyses 

also indicate that the highest O3 days 

(i.e., the days most relevant to the form 

of the NAAQS) generally have similar 

daily maximum 8-hour average USB 

concentrations as the seasonal means of 

this metric, but have larger 

contributions from U.S. anthropogenic 

sources. As summarized in the PA, ‘‘the 

highest modeled O3 site-days tend to 

have background O3 levels similar to 

mid-range O3 days . . . [T]he days with 

highest O3 levels have similar 

distributions (i.e. means, inter-quartile 

ranges) of background levels as days 

with lower values, down to 

approximately 40 ppb. As a result, the 

proportion of total O3 that has 

background origins is smaller on high 

O3 days (e.g. greater than 60 ppb) than 

on the more common lower O3 days that 

tend to drive seasonal means’’ (U.S. 

EPA, 2014c, p. 2–21, emphasis added). 

When averaged over the entire U.S., the 

models estimate that the mean USB 

fractional contribution to daily 

maximum 8-hour average O3

concentrations above 70 ppb is less than 

35 percent. U.S. anthropogenic emission 

sources are thus the dominant 

contributor to the majority of modeled 

O3 exceedances across the U.S. (U.S. 

EPA, 2014c, Figures 2–14 and 2–15). 

As noted in the PA, and as 

highlighted by the commenters based on 

existing modeling, there can be 

infrequent events where daily maximum 

8-hour O3 concentrations approach or 

exceed 70 ppb largely due to the 

influence of USB sources like a wildfire 

or stratospheric intrusion. As discussed 

below in Section V, the statute and EPA 

implementing regulations allow for the 

exclusion of air quality monitoring data 

from design value calculations when 

there are exceedances caused by certain 

event-related U.S. background 

influences (e.g., wildfires or 

stratospheric intrusions). As a result, 

these ‘‘exceptional events’’ will not 

factor into attainability concerns. 

In sum, the EPA believes that the 

commenters have failed to establish the 

predicate for their argument. 

Uncontrollable background 

concentrations of O3 are not expected to 

preclude attainment of a revised O3

standard with a level of 70 ppb. The 

EPA also disagrees with aspects of the 

specific statements made by the 

commenters as support for their view 

that the EPA analyses have 

underestimated background O3.86 Thus, 

even assuming the commenters are 

correct that the EPA may use proximity 

to background as a justification for not 

revising a standard that, in the judgment 

of the Administrator, is inadequate to 

protect public health, the commenters’ 

arguments for the justification and need 

to do so for this review are based on a 

flawed premise. 

b. Comments on the Health Effects 

Evidence 

As noted above, comments on the 

adequacy of the current standard fell 

into two broad categories reflecting very 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65329 

87As discussed in section I.C above, the EPA has 

provisionally considered studies that were 

highlighted by commenters and that were published 

after the ISA. These studies are generally consistent 

with the evidence assessed in the ISA, and they do 

not materially alter our understanding of the 

scientific evidence or the Agency’s conclusions 

based on that evidence. 

different views of the available scientific 

evidence. Commenters who expressed 

support for the EPA’s proposed decision 

to revise the current primary O3

standard generally concluded that the 

body of scientific evidence assessed in 

the ISA is much stronger and more 

compelling than in the last review. 

These commenters also generally 

emphasized CASAC’s interpretation of 

the body of available evidence, which 

formed an important part of the basis for 

CASAC’s reiterated recommendations to 

revise the O3 standard to provide 

increased public health protection. In 

some cases, these commenters 

supported their positions by citing 

studies published since the completion 

of the ISA. 

The EPA generally agrees with these 

commenters regarding the need to revise 

the current primary O3 standard in order 

to increase public health protection 

though, in many cases, not with their 

conclusions about the degree of 

protection that is appropriate (II.C.4.b 

and II.C.4.c, below). The scientific 

evidence noted by these commenters 

was generally the same as that assessed 

in the ISA (U.S. EPA, 2013) and the 

proposal,87 and their interpretation of 

the evidence was often, though not 

always, consistent with the conclusions 

of the ISA and CASAC. The EPA agrees 

that the evidence available in this 

review provides a strong basis for the 

conclusion that the current O3 standard 

is not adequately protective of public 

health. In reaching this conclusion, the 

EPA places a large amount of weight on 

the scientific advice of CASAC, and on 

CASAC’s endorsement of the 

assessment of the evidence in the ISA 

(Frey and Samet, 2012). 

In contrast, while commenters who 

opposed the proposed decision to revise 

the primary O3 standard generally 

focused on many of the same studies 

assessed in the ISA, these commenters 

highlighted different aspects of these 

studies and reached 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. These commenters generally 

concluded that information about the 

health effects of concern has not 

changed significantly since 2008 and 

that the uncertainties in the underlying 

health science have not been reduced 

since the 2008 review. In some cases, 

these commenters specifically 

questioned the EPA’s approach to 

assessing the scientific evidence and to 

reaching conclusions on the strength of 

that evidence in the ISA. For example, 

several commenters asserted that the 

EPA’s causal framework, discussed in 

detail in the ISA, is flawed and that it 

has not been applied consistently across 

health endpoints. Commenters also 

noted departures from other published 

causality frameworks (Samet and 

Bodurow, 2008) and from the criteria for 

judging causality put forward by Sir 

Austin Bradford Hill (Hill, 1965). 

The EPA disagrees with comments 

questioning the ISA’s approach to 

assessing the evidence, the causal 

framework established in the ISA, or the 

consistent application of that framework 

across health endpoints. While the EPA 

acknowledges the ISA’s approach 

departs from assessment and causality 

frameworks that have been developed 

for other purposes, such departures 

reflect appropriate adaptations for the 

NAAQS. As with other ISAs, the O3 ISA 

uses a five-level hierarchy that classifies 

the weight of evidence for causation. In 

developing this hierarchy, the EPA has 

drawn on the work of previous 

evaluations, most prominently the 

IOM’s Improving the Presumptive 

Disability Decision-Making Process for 

Veterans (Samet and Bodurow, 2008), 

EPA’s Guidelines for Carcinogen Risk 

Assessment (U.S. EPA, 2005), and the 

U.S. Surgeon General’s smoking report 

(CDC, 2004). The ISA’s weight of 

evidence evaluation is based on the 

integration of findings from various 

lines of evidence from across the health 

and environmental effects disciplines. 

These separate judgments are integrated 

into a qualitative statement about the 

overall weight of the evidence and 

causality. The ISA’s causal framework 

has been developed over multiple 

NAAQS reviews, based on extensive 

interactions with CASAC and based on 

the public input received as part of the 

CASAC review process. In the current 

review, the causality framework, and 

the application of that framework to 

causality determinations in the O3 ISA, 

have been reviewed and endorsed by 

CASAC (Frey and Samet, 2012). 

Given these views on the assessment 

of the evidence in the ISA, it is relevant 

to note that many of the issues and 

concerns raised by commenters on the 

EPA’s interpretation of the evidence, 

and on the EPA’s conclusions regarding 

the extent to which uncertainties have 

been reduced since the 2008 review, are 

essentially restatements of issues raised 

during the development of the ISA, 

HREA, and/or PA. The CASAC O3 Panel 

reviewed the interpretation of the 

evidence, and the EPA’s use of 

information from specific studies, in 

drafts of these documents. In CASAC’s 

advice to the Administrator, which 

incorporates its consideration of many 

of the issues raised by commenters, 

CASAC approved of the scientific 

content, assessments, and accuracy of 

the ISA, REA, and PA, and indicated 

that these documents provide an 

appropriate basis for use in regulatory 

decision making for the O3 NAAQS 

(Frey and Samet, 2012, Frey, 2014a, 

Frey, 2014c). Therefore, the EPA’s 

responses to many of the comments on 

the evidence rely heavily on the process 

established in the ISA for assessing the 

evidence, which is the product of 

extensive interactions with CASAC over 

a number of different reviews, and on 

CASAC advice received as part of this 

review of the O3 NAAQS. 

The remainder of this section 

discusses public comments and the 

EPA’s responses, on controlled human 

exposure studies (II.B.2.b.i); 

epidemiologic studies (II.B.2.b.ii); and 

at-risk populations (II.B.2.b.iii). 

i. Evidence From Controlled Human 

Exposure Studies 

This section discusses major 

comments on the evidence from 

controlled human exposure studies and 

provides the Agency’s responses to 

those comments. To support their views 

on the adequacy of the current standard, 

commenters often highlighted specific 

aspects of the scientific evidence from 

controlled human exposure studies. Key 

themes discussed by these commenters 

included the following: (1) The 

adversity of effects demonstrated in 

controlled human exposure studies, 

especially studies conducted at 

exposure concentrations below 80 ppb; 

(2) representativeness of different 

aspects of the controlled human 

exposure studies for making inferences 

to the general population and at-risk 

populations; (3) results of additional 

analyses of the data from controlled 

human exposure studies; (4) evaluation 

of a threshold for effects; and (5) 

importance of demonstration of 

inflammation at 60 ppb. This section 

discusses these key comment themes, 

and provides the EPA’s responses. More 

detailed discussion of individual 

comments, and the EPA’s responses, is 

provided in the Response to Comments 

document. 

Adversity 

Some commenters who disagreed 

with the EPA’s proposed decision to 

revise the current primary O3 standard 

disputed the Agency’s characterization 

mstockstill on DSK4VPTVN1PROD with RULES2

65330 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

88Commenters who supported revising the 

primary O3 standard often concluded that there is 

clear evidence for adverse effects following 

exposures to O3 concentrations at least as low as 60 

ppb, and that such adverse effects support setting 

the level of a revised primary O3 standard at 60 ppb. 

These comments, and the EPA’s responses, are 

discussed below within the context of the 

Administrator’s decision on a revised level 

(II.C.4.b). 

89The figure provided in comments by Gradient 

only clearly illustrated the responses of 30 out of 

31 subjects. 

of the adversity of the O3-induced 

health effects shown to occur in 

controlled human exposure studies. 

Some of these commenters contended 

that the proposal does not provide a 

clear definition of adversity or that there 

is confusion concerning what responses 

the Administrator considers adverse. 

The EPA disagrees with these 

comments, and notes that section 

II.E.4.d of the proposal describes the 

Administrator’s proposed approach to 

considering the adversity of effects 

observed in controlled human exposure 

studies. Her final approach to 

considering the adversity of these 

effects, and her conclusions on 

adversity, are described in detail below 

(II.C.4.b, II.C.4.c). 

Other commenters disagreed with the 

EPA’s judgments regarding adversity 

and expressed the view that the effects 

observed in controlled human exposure 

studies following 6.6-hour exposures to 

O3 concentrations below the level of the 

current standard (i.e., 75 ppb) are not 

adverse.88 This group of commenters 

cited several reasons to support their 

views, including that: (1) The lung 

function decrements and respiratory 

symptoms observed at 72 ppb in the 

study by Schelegle et al. (2009) were not 

correlated with each other, and 

therefore were not adverse; and (2) 

group mean FEV1 decrements observed 

following exposures below 75 ppb are 

small (e.g., <10%, as highlighted by 

some commenters), transient and 

reversible, do not interfere with daily 

activities, and do not result in 

permanent respiratory injury or 

progressive respiratory dysfunction. 

While the EPA agrees that not all 

effects reported in controlled human 

exposure studies following exposures 

below 75 ppb can reasonably be 

considered to be adverse, the Agency 

strongly disagrees with comments 

asserting that none of these effects can 

be adverse. As an initial matter, the 

Administrator notes that, when 

considering the extent to which the 

current or a revised standard could 

allow adverse respiratory effects, based 

on information from controlled human 

exposure studies, she considers not only 

the effects themselves, but also 

quantitative estimates of the extent to 

which the current or a revised standard 

could allow such effects. Quantitative 

exposure and risk estimates provide 

perspective on the extent to which 

various standards could allow 

populations, including at-risk 

populations such as children and 

children with asthma, to experience the 

types of O3 exposures that have been 

shown in controlled human exposure 

studies to cause respiratory effects. As 

discussed further below (II.B.3, II.C.4.b, 

II.C.4.c), to the extent at-risk 

populations are estimated to experience 

such exposures repeatedly, the 

Administrator becomes increasingly 

concerned about the potential for 

adverse responses in the exposed 

population. Repeated exposures provide 

a plausible mode of action by which O3

may cause other more serious effects. 

Thus, even though the Administrator 

concludes there is important 

uncertainty in the adversity of some of 

the effects observed in controlled 

human exposure studies based on the 

single exposure periods evaluated in 

these studies (e.g., FEV1 decrements 

observed following exposures to 60 ppb 

O3, as discussed in sections II.C.4.b and 

II.C.4.c below), she judges that the 

potential for adverse effects increases as 

the number of exposures increases. 

Contrary to the commenters’ views 

noted above, the Administrator 

considers the broader body of available 

information (i.e., including quantitative 

exposure and risk estimates) when 

considering the extent to which the 

current or a revised standard could 

allow adverse respiratory effects (II.B.3, 

II.C.4.b, II.C.4.c, below). 

In further considering commenters’ 

views on the potential adversity of the 

respiratory effects themselves (i.e., 

without considering quantitative 

estimates), the EPA notes that although 

the results of controlled human 

exposure studies provide a high degree 

of confidence regarding the occurrence 

of health effects following exposures to 

O3 concentrations from 60 to 80 ppb, 

there are no universally accepted 

criteria by which to judge the adversity 

of the observed effects. Therefore, as in 

the proposal, the Administrator relies 

upon recommendations from the ATS 

and advice from CASAC to inform her 

judgments on adversity. 

In particular, the Administrator 

focuses on the ATS recommendation 

that ‘‘reversible loss of lung function in 

combination with the presence of 

symptoms should be considered 

adverse’’ (ATS, 2000a). The study by 

Schelegle et al. (2009) reported a 

statistically significant decrease in 

group mean FEV1 and a statistically 

significant increase in respiratory 

symptoms in healthy adults following 

6.6-hour exposures to average O3

concentrations of 72 ppb. In considering 

these effects, CASAC noted that ‘‘the 

combination of decrements in FEV1

together with the statistically significant 

alterations in symptoms in human 

subjects exposed to 72 ppb ozone meets 

the American Thoracic Society’s 

definition of an adverse health effect’’ 

(Frey, 2014c, p. 5). 

As mentioned above, some 

commenters nonetheless maintained 

that the effects observed in Schelegle et 

al. (2009) following exposure to 72 ppb 

O3 (average concentration) were not 

adverse because the magnitudes of the 

FEV1 decrements and the increases in 

respiratory symptoms (as measured by 

the total subjective symptoms score, 

TSS) were not correlated across 

individual study subjects. A commenter 

submitted an analysis of the individuallevel data from the study by Schelegle 

et al. (2009) to support their position. 

This analysis indicated that, while the 

majority of study volunteers (66%) did 

experience both lung function 

decrements and increased respiratory 

symptoms following 6.6-hour exposures 

to 72 ppb O3, some (33%) did not (e.g., 

Figure 3 in comments from Gradient).89

In addition, the study subjects who 

experienced relatively large lung 

function decrements did not always also 

experience relatively large increases in 

respiratory symptoms. These 

commenters interpreted the lack of a 

statistically significant correlation 

between the magnitudes of decrements 

and symptoms as meaning that the 

effects reported by Schelegle et al. 

(2009) at 72 ppb did not meet the ATS 

criteria for an adverse response. 

However, the ATS recommendation 

that the combination of lung function 

decrements and symptomatic responses 

be considered adverse is not restricted 

to effects of a particular magnitude nor 

a requirement that individual responses 

be correlated. Similarly, CASAC made 

no such qualifications in its advice on 

the combination of respiratory 

symptoms and lung function 

decrements (See e.g., Frey, 2014c, p. 5). 

Therefore, as in the proposal and 

consistent with both CASAC advice and 

ATS recommendations, the EPA 

continues to conclude that the finding 

of both statistically significant 

decrements in lung function and 

significant increases in respiratory 

symptoms following 6.6-hour exposures 

to an average O3 concentration of 72 ppb 

provides a strong indication of the 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65331 

90 Indeed, the finding of statistically significant 

decreases in lung function and increases in 

respiratory symptoms in the same study population 

indicates that, on average, study volunteers did 

experience both effects. 

91For example, as discussed in the proposal (79 

FR 75252) and the ISA (p. 6–76), inflammation 

induced by a single exposure (or several exposures 

over the course of a summer) can resolve entirely. 

However, repeated occurrences of airway 

inflammation could potentially result in the 

induction of a chronic inflammatory state; altered 

pulmonary structure and function, leading to 

diseases such as asthma; altered lung host defense 

response to inhaled microorganisms; and altered 

lung response to other agents such as allergens or 

toxins (ISA, section 6.2.3). 

92See also National Environmental Development 

Associations Clean Action Project v. EPA, 686 F. 3d 

803, 811 (D.C. Cir. 2012) (EPA drew legitimate 

inference that serious asthmatics would experience 

more serious health effects than clinical test 

subjects who did not have this degree of lung 

function impairment). 

potential for exposed individuals to 

experience this combination of effects.90

In particular, the Administrator notes 

that lung function provides an objective 

measure of the respiratory response to 

O3 exposure while respiratory 

symptoms are subjective, and as 

evaluated by Schelegle et al. (2009) were 

based on a TSS score. If an O3 exposure 

causes increases in both objectively 

measured lung function decrements and 

subjective respiratory symptoms, which 

indicate that people may modify their 

behavior in response to the exposure, 

then the effect is properly viewed as 

adverse. As noted above, the 

commenter’s analysis shows that the 

majority of study volunteers exposed to 

72 ppb O3 in the study by Schelegle et 

al. (2009) did, in fact, experience both 

a decrease in lung function and an 

increase in respiratory symptoms. 

In further considering this comment, 

the EPA recognizes that, consistent with 

commenter’s analysis, some individuals 

may experience large decrements in 

lung function with minimal to no 

respiratory symptoms (McDonnell et al., 

1999), and vice versa. As indicated 

above and discussed in the proposal (79 

FR 75289), the Administrator 

acknowledges such interindividual 

variability in responsiveness in her 

interpretation of estimated exposures of 

concern. Specifically, she notes that not 

everyone who experiences an exposure 

of concern, including for the 70 ppb 

benchmark, is expected to experience an 

adverse response. However, she further 

judges that the likelihood of adverse 

effects increases as the number of 

occurrences of O3 exposures of concern 

increases. In making this judgment, she 

notes that the types of respiratory effects 

that can occur following exposures of 

concern, particularly if experienced 

repeatedly, provide a plausible mode of 

action by which O3 may cause other 

more serious effects.91 Therefore, her 

decisions on the primary standard 

emphasize the public health importance 

of limiting the occurrence of repeated 

exposures to O3 concentrations at or 

above those shown to cause adverse 

effects in controlled human exposure 

studies (II.B.3, II.C.4.b, II.C.4.c). The 

Administrator views this approach to 

considering the evidence from 

controlled human exposure studies as 

being consistent with commenter’s 

analysis indicating that, while the 

majority did, not all study volunteers 

exposed to 72 ppb O3 experienced the 

adverse combination of lung function 

decrements and respiratory symptoms 

following the single exposure period 

evaluated by Schelegle et al. (2009). 

Representativeness 

A number of commenters raised 

issues concerning the representativeness 

of controlled human exposure studies 

considered by the Administrator in this 

review, based on different aspects of 

these studies. These commenters 

asserted that since the controlled human 

exposure studies were not 

representative of real-world exposures, 

they should not be relied upon as a 

basis for finding that the current 

standard is not adequate to protect 

public health. Some issues highlighted 

by commenters include: Small size of 

the study populations; unrealistic 

activity levels used in the studies; 

unrealistic exposure scenarios (i.e., 

triangular exposure protocol) used in 

some studies, including Schelegle et al. 

(2009); and differences in study design 

that limit comparability across studies. 

Some commenters noted that the 

controlled human exposure studies 

were not designed to have individuals 

represent portions of any larger group 

and that the impacts on a small number 

of people do not implicate the health of 

an entire subpopulation, particularly 

when the FEV1 decrements are small, 

temporary, and reversible. These 

commenters also noted that the 

Administrator failed to provide an 

explanation or justification for why the 

individuals in these studies can be 

viewed as representatives of a 

subpopulation. Further, they asserted 

that EPA’s use of results from 

individuals, rather than the group mean 

responses, contradicts the intent of CAA 

section 109 to protect groups of people, 

not just the most sensitive individuals 

in any group (79 FR 75237). 

Consistent with CASAC advice (Frey, 

2014c, p. 5), the EPA concludes that the 

body of controlled human exposure 

studies are sufficiently representative to 

be relied upon as a basis for finding that 

the current standard is not adequate to 

protect public health. These studies 

generally recruit healthy young adult 

volunteers, and often expose them to O3

concentrations found in the ambient air 

under real-world exposure conditions. 

As described in more detail above in 

section II.A.1.b, the evidence from 

controlled human exposure studies to 

date makes it clear that there is 

considerable variability in responses 

across individuals, even in young 

healthy adult volunteers, and that group 

mean responses are not representative of 

more responsive individuals. It is 

important to look beyond group mean 

responses to the responses of these 

individuals to evaluate the potential 

impact on more responsive members of 

the population. Moreover, relying on 

group mean changes to evaluate lung 

function responses to O3 exposures 

would mask the responses of the most 

sensitive groups, particularly where, as 

here, the group mean reflects responses 

solely among the healthy young adults 

who were the study participants. Thus, 

the studies of exposures below 80 ppb 

O3 show that 10% of young healthy 

adults experienced FEV1 decrements 

>10% following exposures to 60 ppb O3, 

and 19% experienced such decrements 

following exposures to 72 ppb (under 

the controlled test conditions involving 

moderate exertion for 6.6 hours). These 

percentages would likely have been 

higher had people with asthma or other 

at-risk populations been exposed (U.S. 

EPA, 2013, pp. 6–17 and 6–18; Frey 

2014c, p. 7; Frey, 2014a, p. 14).92

Moreover, the EPA may legitimately 

view the individuals in these studies as 

representatives of the larger 

subpopulation of at-risk or sensitive 

groups. As stated in the Senate Report 

to the 1970 legislation establishing the 

NAAQS statutory provisions, ‘‘the 

Committee emphasizes that included 

among these persons whose health 

should be protected by the ambient 

standard are particularly sensitive 

citizens such as bronchial asthmatics 

and emphysematics who in the normal 

course of daily activity are exposed to 

the ambient environment. In 

establishing an ambient standard 

necessary to protect the health of these 

persons, reference should be made to a 

representative sample of persons 

comprising the sensitive group rather 

than to a single person in such a 

group. . . . For purposes of this 

description, a statistically related 

sample is the number of persons 

necessary to test in order to detect a 

deviation in the health of any person 

within such sensitive group which is 

attributable to the condition of the 

ambient air.’’ S. Rep. No. 11–1196, 91st 

mstockstill on DSK4VPTVN1PROD with RULES2

65332 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

93Exercise consisted of alternating periods 

walking on a treadmill at a pace of 17–18 minutes 

per mile inclined to a grade of 4–5% or cycling at 

a load of about 72 watts. Typical heart rates during 

the exercise periods were between 115–130 beats 

per minute. This activity level is considered 

moderate (Table 6–1, U.S. EPA, 2013, p. 6–18). 

Cong. 2d sess. at 10. As just noted 

above, 10% of healthy young adults in 

these studies experienced >10% FEV1

decrements following exposure to 60 

ppb O3, and the proportion of 

individuals experiencing such 

decrements increases with increasing O3

exposure concentrations. This 

substantial percentage certainly can be 

viewed as ‘‘a representative sample of 

persons’’ and as a sufficient number to 

‘‘detect a deviation in the health of any 

person within such sensitive group,’’ 

especially given that it reflects the 

percentage of healthy adults who 

experienced decrements >10%. 

These results are consistent with 

estimates from the MSS model, which 

makes reliable quantitative predictions 

of the lung function response to O3

exposures, and reasonably predicts the 

magnitude of individual lung function 

responses following such exposures. As 

described in section II.A.2.c above, and 

documented in the HREA, when the 

MSS model was used to quantify the 

risk of O3-induced FEV1 decrements in 

15 urban study areas, the current 

standard was estimated to allow about 

8 to 12% of children to experience two 

or more O3-induced FEV1 decrements 

≥10%, and about 2 to 3% to experience 

two or more decrements ≥15% (Table 2, 

above). These percentages correspond to 

hundreds of thousands of children in 

urban study areas, and tens of 

thousands of asthmatic children. While 

the Administrator judges that there is 

uncertainty with regard to the adversity 

of these O3-induced lung function 

decrements (see II.C.4.b, II.C.4.c, below), 

such risk estimates clearly indicate that 

they are a matter of public health 

importance on a broad scale, not 

isolated effects on idiosyncratically 

responding individuals. 

Other commenters considered the 

ventilation rates used in controlled 

human exposure studies to be 

unreasonably high and at the extreme of 

prolonged daily activity. Some of these 

commenters noted that these scenarios 

are unrealistic for sensitive populations, 

such as asthmatics and people with 

COPD, whose conditions would likely 

prevent them from performing the 

intensity of exercise, and therefore 

experiencing the ventilation rates, 

required to produce decrements in lung 

function observed in experimental 

settings. 

The EPA disagrees with these 

commenters. The activity levels used in 

controlled human exposure studies 

were summarized in Table 6–1 of the 

ISA (U.S. EPA, 2013). The exercise level 

in the 6.6-hour exposure studies by 

Adams (2006), Schelegle et al. (2009), 

and Kim et al. (2011) of young healthy 

adults was moderate and ventilation 

rates are typically targeted for 20 L/minm2 BSA.93 Following the exposures to 

60 ppb at this activity level, 10% of the 

individuals had greater than a 10% 

decrement in FEV1 (U.S. EPA, 2013, p. 

6–18). Similar 6.6-hour exposure studies 

of individuals with asthma are not 

available to assess either the effects of 

O3 on their lung function or their ability 

to perform the required level of 

moderate exercise. 

However, referring to Tables 6–9 and 

6–10 of the HREA (U.S. EPA, 2014a), 

between 42% and 45% of FEV1

decrements ≥ 10% were estimated to 

occur at exercise levels of <13 L/min-m2

BSA. This corresponds to light exercise, 

and this level of exercise has been used 

in a 7.6-hour study of healthy people 

and people with asthma exposed to 160 

ppb O3 (Horstman et al., 1995). In that 

study, people with asthma exercised 

with an average minute ventilation of 

14.2 L/min-m2 BSA. Adjusted for 

filtered air responses, an average 19% 

FEV1 decrement was seen in the people 

with asthma versus an average 10% 

FEV1 decrement in the healthy people. 

In addition, the EPA noted in the HREA 

that the data underlying the exposure 

assessment indicate that ‘‘activity data 

for asthmatics [is] generally similar to 

[that for] non-asthmatics’’ (U.S. EPA, 

2014a, p. 5–75, Tables 5G–2 and 5G–3). 

Thus, contrary to the commenters’ 

assertion, based on both the HREA and 

the Horstman et al. (1995) study, people 

with respiratory disease such as asthma 

can exercise for a prolonged period 

under conditions where they would 

experience >10% FEV1 decrements in 

response to O3 exposure. 

Additionally, a number of 

commenters asserted that the exposure 

scenarios in Schelegle et al. (2009), 

which are based on a so-called 

triangular study protocol, where O3

concentrations ramp up and down as 

the study is conducted, are not directly 

generalizable to most healthy or 

sensitive populations because of large 

changes in the O3 concentrations from 

one hour to the next. Commenters stated 

that although large fluctuations in O3

are possible in certain locations due to 

meteorological conditions (e.g., in 

valleys on very hot, summer days), they 

believe that, in general, concentrations 

of O3 do not fluctuate by more than 20– 

30 ppb from one hour to the next. Thus, 

commenters suggested the Schelegle et 

al. (2009) study design could happen in 

a ‘‘worst-case’’ exposure scenario, but 

that the exposure protocol was not 

reflective of conditions in most cities 

and thus not informative with regard to 

the adequacy of the current standard. 

The EPA disagrees with the comment 

that these triangular exposure scenarios 

are not generalizable because of hour-tohour fluctuations. Adams (2002, 2006) 

showed that FEV1 responses following 

6.6 hours of exposure to 60 and 80 ppb 

average O3 exposures do not differ 

between triangular (i.e. ramping 

concentration up and down) and squarewave (i.e. constant concentration). 

Schelegle et al. (2009) used the 80 ppb 

triangular protocol and a slightly 

modified 60 ppb triangular protocol 

(concentrations during the third and 

fourth hours were reversed) from Adams 

(2006). Therefore, in considering pre- to 

post-exposure changes in lung function, 

concerns about the hour-by-hour 

changes in O3 concentrations at 60 and 

80 ppb in the Schelegle et al. (2009) 

study are unfounded. 

Finally, some commenters also stated 

that the Kim et al. (2011) study is 

missing critical information and its 

study design makes comparison to the 

other studies difficult. That is, the 

commenter suggests that data at times 

other than pre- and post-exposure 

should have been provided. 

The EPA disagrees with this 

comment. With regard to providing data 

at other time points besides pre- and 

post-exposure, there is no standard that 

suggests an appropriate frequency at 

which lung function should be 

measured in prolonged 6.6-hour 

exposure studies. The Adams (2006) 

study showed that lung function 

decrements during O3 exposures with 

moderate exercise become most 

apparent following the third hour of 

exposure. As such, it makes little sense 

to measure lung function during the first 

couple hours of exposure. However, 

having data at multiple time points 

toward the end of an exposure can 

provide evidence that the mean postexposure FEV1 response is not a single 

anomalous data point. The FEV1

response data for the 3-, 4.6-, 5.6-, and 

6.6-hour time points of the Kim et al. 

(2011) study are available in Figure 6 of 

the McDonnell et al. (2012) paper where 

they are plotted with the Adams (2006) 

data for 60 ppb. Similar to the Adams 

(2006) study, the responses at 5.6 hours 

are only marginally smaller than the 

response at 6.6 hours in the Kim et al. 

(2011) study. This indicates that the 

post-exposure FEV1 responses in both 

studies are consistent with responses at 

an earlier time point and thus not likely 

to be anomalous data. 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65333 

Additional Studies 

Several commenters analyzed the data 

from controlled human exposure 

studies, or they commented on the 

EPA’s analysis of the data from some of 

these studies (Brown et al., 2008), to 

come to a different conclusion than the 

EPA’s interpretation of these studies 

thereby questioning the proposed 

decision that the current standard is not 

adequate to protect public health. One 

commenter submitted an independent 

assessment of the scientific evidence 

and risk, and used this analysis to assert 

that there are multiple flaws in the 

underlying studies and their 

interpretation by the EPA. This 

commenter stated that the EPA’s 

discussion of the spirometric responses 

of children and adolescents and older 

adults to O3 was misleading. They 

claimed that the EPA did not mention 

that ‘‘the responses of children and 

adolescents are equivalent to those of 

young adults (18–35 years old; 

McDonnell et al., 1985) and that this 

response diminishes in middle-aged and 

older adults (Hazucha 1985).’’ The EPA 

notes that the commenter 

misrepresented our characterization of 

the effect of age on FEV1 responses to 

O3 and asserted mistakenly that EPA did 

not mention diminished responses on 

older adults. In fact, the proposal clearly 

states that, ‘‘Respiratory symptom 

responses to O3 exposure appears to 

increase with age until early adulthood 

and then gradually decrease with 

increasing age (U.S. EPA, 1996b); lung 

function responses to O3 exposure also 

decline from early adulthood (U.S. EPA, 

1996b)’’ (79 FR 75267) (see also U.S. 

EPA, 2014c p. 3–82). With regard to 

differences between children and 

adults, it was clearly stated in the ISA 

(U.S. EPA, 2013, p. 6–21) that healthy 

children exposed to filtered air and 120 

ppb O3 experienced similar spirometric 

responses, but lesser symptoms than 

similarly exposed young healthy adults 

(McDonnell et al., 1985). In addition, 

the EPA’s approach to modeling the 

effect of age on responses to O3 is 

clearly provided in the HREA (U.S. 

EPA, 2014a, Table 6–2). 

The commenter also stated that the 

EPA’s treatment of filtered air responses 

in the dose-response curve was 

incorrect. They claimed that when 

creating a dose-response curve, it is 

most appropriate to include a zero-dose 

point and not to subtract the filtered air 

response from responses to O3. Contrary 

to this assertion, EPA correctly adjusted 

FEV1 responses to O3 by responses 

following filtered air, as was also done 

in the McDonnell et al. (2012) model. As 

indicated in the ISA (U.S. EPA, 2013, p. 

6–4), the majority of controlled human 

exposure studies investigating the 

effects O3 are of a randomized, 

controlled, crossover design in which 

subjects were exposed, without 

knowledge of the exposure condition 

and in random order, to clean filtered 

air and, depending on the study, to one 

or more O3 concentrations. The filtered 

air control exposure provides an 

unbiased estimate of the effects of the 

experimental procedures on the 

outcome(s) of interest. Comparison of 

responses following this filtered air 

exposure to those following an O3

exposure allows for estimation of the 

effects of O3 itself on an outcome 

measurement while controlling for 

independent effects of the experimental 

procedures, such as ventilation rate. 

Thus, the commenter’s approach does 

not provide an estimate of the effects of 

O3 alone. Furthermore, as illustrated in 

these comments, following ‘‘long’’ 

filtered air exposures, there is about a 

1% improvement in FEV1. By not 

accounting for this increase in FEV1, the 

commenter underestimated the FEV1

decrement due to O3 exposure. The 

commenter’s approach thus is 

fundamentally flawed. 

The commenter also asserted that the 

McDonnell et al. (2012) model and 

exposure-response (E–R) models 

incorrectly used only the most 

responsive people and that EPA’s 

reliance on data from clinical trials that 

use only the most responsive people 

irrationally ignores large portions of 

relevant data. The EPA rejects this 

assertion that the McDonnell et al. 

(2012) model and the E–R analysis 

ignored large portions of relevant data. 

The McDonnell et al. (2012) model was 

fit to the FEV1 responses of 741 

individuals to O3 and filtered air (i.e., 

reflecting all available data for O3- 

induced changes in FEV1). The filtered 

air responses were subtracted from 

responses measured during O3

exposures. Subsequently, as illustrated 

by the figures in the McDonnell et al. 

(2012) paper and described in the text 

of paper, the model was fit to all 

available FEV1 data measured during 

the course of O3 exposures, including 

exposures shorter than 6.6 hours. Thus, 

the model predicts temporal dynamics 

of FEV1 response to any set of O3

exposure conditions that might 

reasonably be experienced in the 

ambient environment, predicting the 

mean responses and the distribution of 

responses around the mean. For the 

HREA (EPA, 2014a), the proportion of 

individuals, under variable exposure 

conditions, predicted to have FEV1

decrements ≥10, 15 and 20% was 

estimated. 

Finally, the commenter referenced the 

exposure-response model on p. 6–18 of 

the HREA. However, they neglected to 

note that this was in a section 

describing the exposure-response 

function approach used in prior reviews 

(U.S. EPA, 2014a, starting on p. 6–17). 

Thus, the commenter confused the 

exposure-response model used in the 

last review with the updated approach 

used in this review. 

The commenter also stated that EPA 

did not properly consider O3 dose when 

interpreting the human clinical data. 

Ozone total dose includes three factors: 

duration of exposure, concentration, 

and ventilation rate. The commenter 

claimed the EPA emphasized only 

concentration without properly 

considering and communicating 

duration of exposure and ventilation 

rate. Further, they asserted that because 

people are not exposed to the same 

dose, they cannot be judged to have the 

same exposure and would therefore not 

be expected to respond consistently. 

The EPA rejects the claim that we 

emphasized only concentration without 

properly incorporating the other two 

factors. As noted in the ISA, total O3

dose does not describe the temporal 

dynamics of FEV1 responses as a 

function of concentration, ventilation 

rate, time and age of the exposed 

individuals (U.S. EPA, 2013, p. 6–5). 

Thus, the use of total O3 dose is 

antiquated and the EPA therefore 

conducted a more sophisticated analysis 

of FEV1 response to O3 in the HREA. In 

this review, the HREA estimates risks of 

lung function decrements in schoolaged children (ages 5 to 18), asthmatic 

school-aged children, and the general 

adult population for 15 urban study 

areas. A probabilistic model designed to 

account for the numerous sources of 

variability that affect people’s exposures 

was used to simulate the movement of 

individuals through time and space and 

to estimate their exposure to O3 while 

occupying indoor, outdoor, and invehicle locations. That information was 

linked with the McDonnell et al. (2012) 

model to estimate FEV1 responses over 

time as O3 exposure concentrations and 

ventilation rates changed. As noted 

earlier, CASAC agreed that this 

approach is both scientifically valid and 

a significant improvement over 

approaches used in past O3 reviews 

(Frey, 2014a, p. 2). 

Several commenters criticized the 

EPA analysis published by Brown et al. 

(2008). One commenter suggested that 

the EPA needed to state why the Brown 

et al. (2008) analysis was relied on 

rather than Nicolich (2007) or Lefohn et 

mstockstill on DSK4VPTVN1PROD with RULES2

65334 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

94The DC Circuit has held that EPA reasonably 

used and interpreted the Brown (2007) study in the 

last review. Mississippi, 744 F. 3d at 1347. In this 

review, there is now additional corroborative 

evidence supporting the Brown (2007) analysis, in 

the form of further controlled human clinical 

studies finding health effects in young, healthy 

adults at moderate exercise at O3 concentrations of 

60 ppb over a 6.6 hour exposure period. 

95Conversely, another group of commenters who 

supported revising the standard to a level of 60 ppb 

noted that the results of these models are consistent 

with the results of controlled human exposure 

studies finding adverse health effects at 60 ppb. 

These comments are discussed below (II.C.4.b), 

within the context of the Administrator’s decision 

on a revised standard level. 

96 Inflammation induced by exposure of humans 

to O3 can have several potential outcomes, ranging 

from resolving entirely following a single exposure 

to becoming a chronic inflammatory state (U.S. 

EPA, 2013, section 6.2.3). Lung injury and the 

resulting inflammation provide a mechanism by 

which O3 may cause other more serious morbidity 

effects (e.g., asthma exacerbations) (U.S. EPA, 2013, 

section 6.2.3). See generally section II.A.1.a above. 

al. (2010). Further, commenters stated 

that the analysis of the Adams (2006) 

data in Brown et al. (2008) was flawed. 

Among other reasons, one commenter 

expressed the opinion that it was not 

appropriate for Brown et al. (2008) to 

only examine a portion of the Adams 

(2006) data, citing comments submitted 

by Gradient. 

The EPA disagrees with these 

commenters.94 As an initial matter, 

Nicolich (2007) was a public comment 

and is not a peer-reviewed publication 

that would be used to assess the 

scientific evidence for effects of O3 on 

lung function in the ISA (U.S. EPA, 

2013). The Nicolich (2007) comments 

were specifically addressed by the EPA 

on pp. 24–25 in the Response to 

Comments Document for the 2007 

proposed rule (U.S. EPA, 2008). On page 

A–3 of his comments, Dr. Nicolich 

stated ‘‘that the residuals are not 

normally distributed and the 

observations do not meet the 

assumptions required for the model’’ 

and that ‘‘the subject-based errors are 

not independently, identically and 

normally distributed and the subjects do 

not meet the assumptions required for 

the model.’’ The EPA reasonably chose 

not to rely on this analysis: ‘‘Therefore, 

given that the underlying statistical 

assumptions required for his analyses 

were not met and that significance 

levels are questionable, in EPA’s 

judgment the analyses presented by Dr. 

Nicolich are ambiguous’’ (U.S. EPA, 

2008). It is likely that the Lefohn et al. 

(2010) analysis of the Adams (2006) data 

would similarly not meet the statistical 

assumptions of the model (e.g., 

homoscedasticity). In contrast, 

recognizing the concerns related to the 

distribution of responses, Brown et al. 

(2008) conservatively used a 

nonparametric sign test to obtain a pvalue of 0.002 for the comparison 

responses following 60 ppb O3 versus 

filter air. Other common statistical tests 

also showed significant effects on lung 

function. In addition, the effects of 60 

ppb O3 on FEV1 responses in Brown et 

al. (2008) remained statistically 

significant even following the exclusion 

of three potential outliers. 

EPA disagrees with the comment 

stating that it was not appropriate for 

Brown et al. (2008) to only examine a 

portion of the Adams (2006) data. In 

fact, there is no established single 

manner or protocol decreeing that data 

throughout the protocol must be 

analyzed and included. Furthermore, 

Brown et al. (2008) was a peer-reviewed 

journal publication. CASAC also 

expressed favorable comments in their 

March 30, 2011, letter to Administrator 

Jackson. With reference to a 

memorandum (Brown, 2007) that 

preceded the Brown et al. (2008) 

publication, on p. 6 of the CASAC 

Consensus Responses to Charge 

Questions CASAC stated, ‘‘The results 

of the Adams et al. study also have been 

carefully reanalyzed by EPA 

investigators (Brown et. al., [2008]), and 

this reanalysis showed a statistically 

significant group effect on FEV1 after 60 

ppb ozone exposure.’’ On p. A–13, a 

CASAC panelist and biostatistician 

stated, ‘‘Thus, from my understanding 

of the statistical analyses that have been 

conducted, I would argue that the 

analysis by EPA should be preferred to 

that of Adams for the specific 

comparison of the FEV1 effects of 0.06 

ppm exposure relative to filtered air 

exposure.’’ (Samet 2011, p. a-13) 

Threshold 

Several commenters used the new 

McDonnell et al. (2012) and Schelegle et 

al. (2012) models to support their views 

about the O3 concentrations associated 

with a threshold for adverse lung 

function decrements. For example, one 

commenter who supported retaining the 

current standard noted that McDonnell 

et al. (2012) found that the threshold 

model fit the observed data better than 

the original (no-threshold) model, 

especially at earlier time points and at 

the lowest exposure concentrations. The 

commenter expressed the view that the 

threshold model showed that the 

population mean FEV1 decrement did 

not reach 10% until exposures were at 

least 80 ppb, indicating that O3

exposures of 80 ppb or higher may 

cause lung function decrements and 

other respiratory effects.95

As described above in section II.A.1.b, 

the McDonnell et al. (2012) and 

Schelegle et al. (2012) models represent 

a significant technological advance in 

the exposure-response modeling 

approach since the last review, and 

these models indicate that a dosethreshold model fits the data better than 

a non-threshold model. However, the 

EPA disagrees that using the predicted 

group mean response from the 

McDonnell model provides support for 

retaining the current standard. As 

discussed above, the group mean 

responses do not convey information 

about interindividual variability, or the 

proportion of the population estimated 

to experience the larger lung function 

decrements (e.g., 10 or 15% FEV1

decrements) that could be adverse. In 

fact, it masks this variability. These 

variable effects in individuals have been 

found to be reproducible. In other 

words, a person who has a large lung 

function response after exposure to O3

will likely have about the same response 

if exposed again in a similar manner 

(raising health concerns, as noted 

above). Group mean responses are not 

representative of this segment of the 

population that has much larger than 

average responses to O3. 

Inflammation 

Some commenters asserted that the 

pulmonary inflammation observed 

following exposure to 60 ppb in the 

controlled human exposure study by 

Kim et al. (2011) was small and unlikely 

to result in airway damage. It was also 

suggested that this inflammation is a 

normal physiological response in all 

living organisms to stimuli to which 

people are normally exposed. 

The EPA recognized in the proposal 

(79 FR 75252) and the ISA (U.S. EPA, 

2013, p. 6–76) that inflammation 

induced by a single exposure (or several 

exposures over the course of a summer) 

can resolve entirely. Thus, the 

inflammatory response observed 

following the single exposure to 60 ppb 

in the study by Kim et al. (2011) is not 

necessarily a concern. However, the 

EPA notes that it is also important to 

consider the potential for continued 

acute inflammatory responses to evolve 

into a chronic inflammatory state and to 

affect the structure and function of the 

lung.96 The Administrator considers 

this possibility through her 

consideration of estimated exposures of 

concern for the 60 ppb benchmark 

(II.B.3, II.C.4). As discussed in detail 

below (II.C.4.b), while she judges that 

there is uncertainty in the adversity of 

the effects shown to occur following 

exposures to 60 ppb O3, including the 

inflammation reported by Kim et al. 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65335 

97As discussed in section II.E.4.d of the proposal, 

is the Administrator noted the greater uncertainty 

in using analyses of short-term O3 air quality in 

locations of the multicity studies in this review to 

inform decisions on the primary O3 standard. This 

is because the health information in these studies 

cannot be disaggregated by individual city. Thus, 

the multicity effect estimates reported in these 

studies do not provide clear indication of the extent 

to which health effects are associated with the 

ambient O3 concentrations in the study locations 

that met the current O3 standard, versus the 

ambient O3 concentrations in the study locations 

that violated the standard. 

(2011), she gives some consideration to 

estimates of two or more exposures of 

concern for the 60 ppb benchmark (i.e., 

as a health-protective surrogate for 

repeated exposures of concern at or 

above 60 ppb), particularly when 

considering the extent to which the 

current and revised standards 

incorporate a margin of safety. 

ii. Evidence Fom epidemiologic studies 

This section discusses key comments 

on the EPA’s assessment of the 

epidemiologic evidence and provides 

the Agency’s responses to those 

comments. The focus in this section is 

on overarching comments related to the 

EPA’s approach to assessing and 

interpreting the epidemiologic evidence 

as a whole. Detailed comments on 

specific studies, or specific 

methodological or technical issues, are 

addressed in the Response to Comments 

document. As discussed above, many of 

the issues and concerns raised by 

commenters on the interpretation of the 

epidemiologic evidence are essentially 

restatements of issues raised during the 

development of the ISA, HREA, and/or 

PA, and in many instances were 

considered by CASAC in the 

development of its advice on the current 

standard. The EPA’s responses to these 

comments rely heavily on the process 

established in the ISA for assessing the 

evidence, and on CASAC advice 

received as part of this review of the O3

NAAQS. 

As with evidence from controlled 

human exposure studies, commenters 

expressed sharply divergent views on 

the evidence from epidemiologic 

studies, and on the EPA’s interpretation 

of that evidence. One group of 

commenters, representing medical, 

public health and environmental 

organizations, and some states, 

generally supported the EPA’s 

interpretation of the epidemiologic 

evidence with regard to the consistency 

of associations, the coherence with 

other lines of evidence, and the support 

provided by epidemiologic studies for 

the causality determinations in the ISA. 

These commenters asserted that the 

epidemiologic studies evaluated in the 

ISA provide valuable information 

supporting the need to revise the level 

of the current primary O3 standard in 

order to increase public health 

protection. In reaching this conclusion, 

commenters often cited studies 

(including a number from the past 

review) which they interpreted as 

showing health effect associations in 

locations with O3 air quality 

concentrations below the level of the 

current standard. A second group of 

commenters, mostly representing 

industry associations, businesses, and 

states opposed to revising the primary 

O3 standard, expressed the general view 

that while many new epidemiologic 

studies have been published since the 

last review of the O3 NAAQS, 

inconsistencies and uncertainties 

inherent in these studies as a whole, 

and in the EPA’s assessment of study 

results, should preclude any reliance on 

them as justification for a more stringent 

primary O3 standard. To support their 

views, these commenters often focused 

on specific technical or methodological 

issues that contribute to uncertainty in 

epidemiologic studies, including the 

potential for exposure error, 

confounding by copollutants and by 

other factors (e.g., weather, season, 

disease, day of week, etc.), and 

heterogeneity in results across locations. 

The EPA agrees with certain aspects 

of each of these views. Specifically, 

while the EPA agrees that epidemiologic 

studies are an important part of the 

broader body of evidence that supports 

the ISA’s causality determinations, and 

that these studies provide support for 

the decision to revise the current 

primary O3 standard, the Agency also 

acknowledges that there are important 

uncertainties and limitations associated 

with these epidemiologic studies that 

should be considered when reaching 

decisions on the current standard. Thus, 

although these studies show consistent 

associations between O3 exposures and 

serious health effects, including 

morbidity and mortality, and some of 

these studies reported such associations 

with ambient O3 concentrations below 

the level of the current standard, there 

are also uncertainties regarding the 

ambient O3 concentrations in critical 

studies, such that they lend only limited 

support to establishing a specific level 

for a revised standard. (See generally, 

Mississippi, 744 F. 3d at 1351 (noting 

that in prior review, EPA reasonably 

relied on epidemiologic information in 

determining to revise the standard but 

appropriately gave the information 

limited weight in determining a level of 

a revised standard); see also ATA III, 

283 F. 3d at 370 (EPA justified in 

revising NAAQS when health effect 

associations are observed in 

epidemiologic studies at levels allowed 

by the current NAAQS); Mississippi, 

744 F. 3d at 1345 (same)). 

Uncertainties in the evidence were 

considered by the Administrator in the 

proposal, and contributed to her 

decision to place less weight on 

information from epidemiologic studies 

than on information from controlled 

human exposure studies when 

considering the adequacy of the current 

primary O3 standard (see 79 FR 75281– 

83). Despite receiving less weight in the 

proposal, the EPA does not agree with 

commenters who asserted that 

uncertainties in the epidemiologic 

evidence provide a basis for concluding 

that the current primary standard does 

not need revision. The Administrator 

specifically considered the extent to 

which available studies support the 

occurrence of O3 health effect 

associations with air quality likely to be 

allowed by the current standard, while 

also considering the implications of 

important uncertainties, as assessed in 

the ISA and discussed in the PA. This 

consideration is consistent with CASAC 

comments on consideration of these 

studies in the draft PA (Frey, 2014c, p. 

5). 

Based on analyses of study area air 

quality in the PA, the EPA notes that 

most of the U.S. and Canadian 

epidemiologic studies evaluated were 

conducted in locations likely to have 

violated the current standard over at 

least part of the study period. Although 

these studies support the ISA’s causality 

determinations, they provide limited 

insight into the adequacy of the public 

health protection provided by the 

current primary O3 standard. However, 

as discussed in the proposal, air quality 

analyses in the locations of three U.S. 

single-city studies provide support for 

the occurrence of O3-associated hospital 

admissions or emergency department 

visits at ambient O3 concentrations 

below the level of the current 

standard.97 Specifically, a U.S. singlecity study reported associations with 

respiratory emergency department visits 

in children and adults in a location that 

would have met the current O3 standard 

over the entire study period (Mar and 

Koenig, 2009). In addition, for two 

studies conducted in locations where 

the current standard was likely not met 

(i.e., Silverman and Ito, 2010; Strickland 

et al., 2010), PA analyses indicate that 

reported concentration-response 

functions and available air quality data 

support the occurrence of O3-health 

effect associations on subsets of days 

with virtually all monitored ambient O3

concentrations below the level of the 

current standard (U.S. EPA, 2014c, 

mstockstill on DSK4VPTVN1PROD with RULES2

65336 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

98Air quality analyses in locations of the studies 

by Silverman and Ito (2010) and Strickland et al. 

(2010) were used in the PA to inform staff 

conclusions on the adequacy of the current primary 

O3 standard. However, the appropriate 

interpretation of these analyses became less clear 

for standard levels below 75 ppb, as the number of 

days increased with monitored concentrations 

exceeding the level being evaluated (U.S. EPA, 

2014c, Appendix 3B, Tables 3B–6 and 3B–7). 

Therefore, these analyses were not used in the PA 

to inform conclusions on potential alternative 

standard levels lower than 75 ppb (U.S. EPA, 2014c, 

Chapters 3 and 4). 

section 3.1.4.2, pp. 3–66 to 67).98 Thus, 

the EPA notes that a small number of O3

epidemiologic studies provide support 

for the conclusion that the current 

primary standard is not requisite, and 

that it should be revised to increase 

public health protection. 

As part of a larger set of comments 

criticizing the EPA’s interpretation of 

the evidence from time series 

epidemiologic studies, some 

commenters objected to the EPA’s 

reliance on the studies by Strickland et 

al. (2010), Silverman and Ito (2010), and 

Mar and Koenig (2009). These 

commenters highlighted what they 

considered to be key uncertainties in 

interpreting these studies, including 

uncertainties due to the potential for 

confounding by co-pollutants, 

aeroallergens, or the presence of upper 

respiratory infections; and uncertainties 

in the interpretation of zero-day lag 

models (i.e., specifically for Mar and 

Koenig, 2009). 

While the EPA agrees that there are 

uncertainties associated with 

interpreting the O3 epidemiologic 

evidence, as discussed above and 

elsewhere in this preamble, we disagree 

with commenters’ assertion that these 

uncertainties should preclude the use of 

the O3 epidemiologic evidence in 

general, or the studies by Silverman and 

Ito, Strickland, or Mar and Koenig in 

particular, as part of the basis for the 

Administrator’s decision to revise the 

current primary standard. As a general 

point, when considering the potential 

importance of uncertainties in 

epidemiologic studies, we rely on the 

broader body of evidence, not restricted 

to these three studies, and the ISA 

conclusions based on this evidence. The 

evidence, the ISA’s interpretation of 

specific studies, and the use of 

information from these studies in the 

HREA and PA, was considered by 

CASAC in its review of drafts of the 

ISA, HREA, and PA. Based on the 

assessment of the evidence in the ISA, 

and CASAC’s endorsement of the ISA 

conclusions, as well as CASAC’s 

endorsement of the approaches to using 

and considering information from 

epidemiologic studies in the HREA and 

PA (Frey, 2014c, p. 5), we do not agree 

with these commenters’ conclusions 

regarding the usefulness of the 

epidemiologic studies by Strickland et 

al. (2010), Silverman and Ito (2010), and 

Mar and Koenig (2009). 

More specifically, with regard to 

confounding by co-pollutants, we note 

the ISA conclusion that, in studies of 

O3-associated hospital admissions and 

emergency department visits ‘‘O3 effect 

estimates remained relatively robust 

upon the inclusion of PM . . . and 

gaseous pollutants in two-pollutant 

models’’ (U.S. EPA, 2013, pp. 6–152 and 

6–153). This conclusion was supported 

by several studies that evaluated copollutant models including, but not 

limited to, two of the studies 

specifically highlighted by commenters 

(i.e., Silverman and Ito, 2010; Strickland 

et al., 2010) (U.S. EPA, 2013, section 

6.2.7.5; Figure 6–20 and Table 6–29). 

Other potential uncertainties 

highlighted by commenters have been 

evaluated less frequently (e.g., 

confounding by allergen exposure, 

respiratory infections). However, we 

note that Strickland et al. (2010) did 

consider the potential for pollen (a 

common airborne allergen) to confound 

the association between ambient O3 and 

emergency department visits. While 

quantitative results were not presented, 

the authors reported that ‘‘estimates for 

associations between ambient air 

pollutant concentrations and pediatric 

asthma emergency department visits 

were similar regardless of whether 

pollen concentrations were included in 

the model as covariates’’ (Strickland et 

al., 2010, p. 309). This suggests a limited 

impact of aeroallergens on O3

associations with asthma-related 

emergency department visits and 

hospital admissions. 

With respect to the comment about 

epidemiologic studies not controlling 

for respiratory infections in the model, 

the EPA disagrees with the commenter’s 

assertion. We recognize that asthma is a 

multi-etiologic disease and that air 

pollutants, including O3, represent only 

one potential avenue to trigger an 

asthma exacerbation. Strickland et al. 

attempted to further clarify the 

relationship between short-term O3

exposures and asthma emergency 

department visits by controlling for the 

possibility that respiratory infections 

may lead to an asthma exacerbation. By 

including the daily count of upper 

respiratory visits as a covariate in the 

model, Strickland et al. were able to 

account for the possibility that 

respiratory infections contribute to the 

daily counts of asthma emergency 

department visits, and to identify the O3

effect on asthma emergency department 

visits. In models that controlled for 

upper respiratory infection visits, 

associations between O3 and emergency 

department visits remained statistically 

significant (Strickland et al., Table 4 in 

published study), demonstrating a 

relatively limited influence of 

respiratory infections on the association 

observed between short-term O3

exposures and asthma emergency 

department visits, contrary to the 

commenter’s claim. 

In addition, with regard to the 

criticism of the results reported by Mar 

and Koenig, the EPA disagrees with 

commenters who questioned the 

appropriateness of a zero-day lag. These 

commenters specifically noted 

uncertainty in the relative timing of the 

O3 exposure and the emergency 

department visit when they occurred on 

the same day. However, based on the 

broader body of evidence the ISA 

concludes that the strongest support is 

for a relatively immediate respiratory 

response following O3 exposures. 

Specifically, the ISA states that ‘‘[t]he 

collective evidence indicates a rather 

immediate response within the first few 

days of O3 exposure (i.e., for lags days 

averaged at 0–1, 0–2, and 0–3 days) for 

hospital admissions and [emergency 

department] visits for all respiratory 

outcomes, asthma, and chronic 

obstructive pulmonary disease in allyear and seasonal analyses’’ (U.S. EPA, 

2013, p. 2–32). Thus, the use of a zeroday lag is consistent with the broader 

body of evidence supporting the 

occurrence of O3-associated health 

effects. In addition, while Mar and 

Koenig reported the strongest 

associations for zero-day lags, they also 

reported positive associations for lags 

ranging from zero to five days (Mar and 

Koenig, 2009, Table 5 in the published 

study). In considering this study, the 

ISA stated that Mar and Koenig (2009) 

‘‘found consistent positive associations 

across individual lag days’’ and that 

‘‘[f]or children, consistent positive 

associations were observed across all 

lags . . . with the strongest associations 

observed at lag 0 (33.1% [95% CI: 3.0, 

68.5]) and lag 3 (36.8% [95% CI: 6.1, 

77.2])’’ (U.S. EPA, 2013, p. 6–150). 

Given support for a relatively immediate 

response to O3 and given the generally 

consistent results in analyses using 

various lags, we disagree with 

commenters who asserted that the use of 

a zero-day lag represents an important 

uncertainty in the interpretation of the 

study by Mar and Koenig (2009). 

Given all of the above, we do not 

agree with commenters who asserted 

that uncertainties in the epidemiologic 

evidence in general, or in specific key 

studies, should preclude the 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65337 

99Cf. Coalition for Responsible Regulation v. 

EPA, 684 F. 3d 102, 119 (D.C. Cir. 2012) (aff’d in 

part and rev’d in part on other grounds sub. nom 

UARG v. EPA, S Ct. (2014)) (‘‘EPA simply did here 

what it and other decision-makers often must do to 

make a science-based judgment: it sought out and 

reviewed existing scientific evidence to determine 

whether a particular finding was warranted. It 

makes no difference that much of the scientific 

evidence in large part consisted of ‘syntheses’ of 

individual studies and research. Even individual 

studies and research papers often synthesize past 

work in an area and then build upon it. That is how 

science works’’). 

100See also section II.C.4.b below responding to 

comments from environmental interests that EPA 

inappropriately omitted many studies which (in 

their view) support establishing a revised standard 

at a level of 60 ppb or lower. Although, as 

explained there, the EPA disagrees with these 

comments, the comments illustrate that the EPA 

was even-handed in its consideration of the 

epidemiologic evidence, and most certainly did not 

select merely studies favorable to the point of view 

of revising the current standard. 

Administrator from relying on those 

studies to inform her decisions on the 

primary O3 standard. 

Some commenters also objected to the 

characterization in the ISA and the 

proposal that the results of 

epidemiologic studies are consistent. 

These commenters contended that the 

purported consistency of results across 

epidemiologic studies is the result of 

inappropriate selectivity on the part of 

the EPA in focusing on specific studies 

and specific results within those 

studies. In particular, commenters 

contend that EPA favors studies that 

show positive associations and 

selectively ignores certain studies that 

report null results. They also cite a 

study published after the completion of 

the ISA (Goodman et al., 2013) 

suggesting that, in papers where the 

results of more than one statistical 

model are reported, the EPA tends to 

report the results with the strongest 

associations. 

The EPA disagrees that it has 

inappropriately focused on specific 

positive studies or specific positive 

results within individual studies. The 

ISA appropriately builds upon the 

assessment of the scientific evidence 

presented in previous AQCDs and 

ISAs.99 When evaluating new literature, 

‘‘[s]election of studies for inclusion in 

the ISA is based on the general scientific 

quality of the study, and consideration 

of the extent to which the study is 

informative and policy-relevant’’ (U.S. 

EPA, 2013, p. liii). In addition, ‘‘the 

intent of the ISA is to provide a concise 

review, synthesis, and evaluation of the 

most policy-relevant science to serve as 

a scientific foundation for the review of 

the NAAQS, not extensive summaries of 

all health, ecological and welfare effects 

studies for a pollutant’’ (U.S. EPA, 2013, 

p. lv). Therefore, not all studies 

published since the previous review 

would be appropriate for inclusion in 

the ISA.100 With regard to the specific 

studies that are included in the ISA, and 

the analyses focused upon within given 

studies, the EPA notes that the ISA 

undergoes extensive peer review in a 

public setting by the CASAC. This 

process provides ample opportunity for 

CASAC and the public to comment on 

studies not included in the ISA, and on 

the specific analyses focused upon 

within individual studies. In endorsing 

the final O3 ISA as adequate for rulemaking purposes, CASAC agreed with 

the selection and presentation of 

analyses on which to base the ISA’s key 

conclusions. 

iii. Evidence Pertaining to At-Risk 

Populations and Lifestages 

A number of groups submitted 

comments on the EPA’s identification of 

at-risk populations and lifestages. Some 

industry commenters who opposed 

revising the current standard disagreed 

with the EPA’s identification of people 

with asthma or other respiratory 

diseases as an at-risk population for O3- 

attributable effects, citing controlled 

human exposure studies that did not 

report larger O3-induced FEV1

decrements in people with asthma than 

in people without asthma. In contrast, 

comments from medical, environmental, 

and public health groups generally 

agreed with the at-risk populations 

identified by EPA, and also identified 

other populations that they stated 

should be considered at risk, including 

people of lower socio-economic status, 

people with diabetes or who are obese, 

pregnant women (due to reproductive 

and developmental effects, and African 

American, Asian, Hispanic/Latino or 

tribal communities. As support for the 

additional populations, these 

commenters cited various studies, 

including some that were not included 

in the ISA (which we have provisionally 

considered, as described in section I.C 

above). 

With regard to the former group of 

comments stating that the evidence does 

not support the identification of 

asthmatics as an at-risk population, we 

disagree. As summarized in the 

proposal, the EPA’s identification of 

populations at risk of O3 effects is based 

on a systematic approach that assesses 

the current scientific evidence across 

the relevant scientific disciplines (i.e., 

exposure sciences, dosimetry, 

controlled human exposure, toxicology, 

and epidemiology), with a focus on 

studies that conducted stratified 

analyses allowing for an evaluation of 

different populations exposed to similar 

O3 concentrations within the same 

study design (U.S. EPA, 2013, pp. 8–1 

to 8–3). Based on this established 

process and framework, the ISA 

identifies individuals with asthma 

among the populations and lifestages for 

which there is ‘‘adequate’’ evidence to 

support the conclusion of increased risk 

of O3-related health effects. Other 

populations for which the evidence is 

adequate are individuals with certain 

genotypes, younger and older age 

groups, individuals with reduced intake 

of certain nutrients, and outdoor 

workers. These conclusions are based 

on consistency in findings across 

studies and evidence of coherence in 

results from different scientific 

disciplines. 

For example, with regard to people 

with asthma, the ISA notes a number of 

epidemiologic and controlled human 

exposure studies reporting larger and/or 

more serious effects in people with 

asthma than in people without asthma 

or other respiratory diseases. These 

include epidemiologic studies of lung 

function, respiratory symptoms, and 

medication use, as well as controlled 

human exposure studies showing larger 

inflammatory responses and markers 

indicating altered immune functioning 

in people with asthma, and also 

includes evidence from animal models 

of asthma that informs the EPA’s 

interpretation of the other studies. We 

disagree with the industry commenters’ 

focus solely on the results of certain 

studies without an integrated 

consideration of the broader body of 

evidence, and wider range of respiratory 

endpoints. It is such an integrated 

approach that supports EPA’s 

conclusion that ‘‘there is adequate 

evidence for asthmatics to be an at-risk 

population’’ (U.S. EPA, 2013, section 

8.2.2). 

We also disagree with commenters’ 

misleading reference to various studies 

cited to support the claim that 

asthmatics are not at increased risk of 

O3-related health effects. One of the 

controlled human studies cited in those 

comments (Mudway et al. 2001) 

involved asthmatic adults who were 

older than the healthy controls, and it 

is well-recognized that responses to O3

decrease with age (U.S. EPA, 2014c, p. 

3–80). Another study (Alexis et al. 2000) 

used subjects with mild asthma who are 

unlikely to be as responsive as people 

with more severe disease (Horstman et 

al., 1995) (EPA 2014c, p. 3–80). 

Controlled human exposure studies and 

epidemiologic studies of adults and 

children amply confirm that ‘‘there is 

adequate evidence for asthmatics to be 

an at-risk population’’ (U.S. EPA, 2014c, 

p. 3–81). 

mstockstill on DSK4VPTVN1PROD with RULES2

65338 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

We also do not agree with the latter 

group of commenters that there is 

sufficient evidence to support the 

identification of additional populations 

as at risk of O3-attributable health 

effects. Specifically with regard to 

pregnant women, the ISA concluded 

that the ‘‘evidence is suggestive of a 

causal relationship between exposures 

to O3 and reproductive and 

developmental effects’’ including birth 

outcomes, noting that ‘‘the collective 

evidence for many of the birth outcomes 

examined is generally inconsistent’’ 

(U.S. EPA, 2013, pp. 7–74 and 7–75). At 

the time of the completion of the ISA, 

no studies had been identified that 

examined the relationship between 

exposure to O3 and the health of 

pregnant women (e.g., studies on preeclampsia, gestational hypertension). 

Due to the generally inconsistent 

epidemiologic evidence for effects on 

birth outcomes, the lack of studies on 

the health of pregnant women, and the 

lack of studies from other disciplines to 

provide biological plausibility for the 

effects examined in epidemiologic 

studies, pregnant women were not 

considered an at-risk population. Based 

on the EPA’s provisional consideration 

of studies published since the 

completion of the ISA (I.C, above), 

recent studies that examine exposure to 

O3 and pre-eclampsia and other health 

effects experienced by pregnant women 

are not sufficient to materially change 

the ISA’s conclusions on at-risk 

populations (I.C, above). In addition, as 

summarized in the proposal, the ISA 

concluded that the evidence for other 

populations was either suggestive of 

increased risk, with further 

investigation needed (e.g., other genetic 

variants, obesity, sex, and 

socioeconomic status), or was 

inadequate to determine if they were of 

increased risk of O3-related health 

effects (influenza/infection, COPD, CVD, 

diabetes, hyperthyroidism, smoking, 

race/ethnicity, and air conditioning use) 

(U.S. EPA, 2013, section 2.5.4.1). The 

CASAC has concurred with the ISA 

conclusions (Frey, 2014c). 

c. Comments on Exposure and Risk 

Assessments 

This section discusses major 

comments on the EPA’s quantitative 

assessments of O3 exposures and health 

risks, presented in the HREA and 

considered in the PA, and the EPA’s 

responses to those comments. The focus 

in this section is on overarching 

comments related to the EPA’s approach 

to assessing exposures and risks, and to 

interpreting the exposure/risk results 

within the context of the adequacy of 

the current primary O3 standard. More 

detailed discussion of comments and 

Agency responses is provided in the 

Response to Comments document. 

Section II.B.2.c.i discusses comments on 

estimates of O3 exposures of concern, 

section II.B.2.c.ii discusses comments 

on estimates of the risk of O3-induced 

lung function decrements, and section 

II.B.2.b.iii discusses comments on 

estimates of the risk of O3-associated 

mortality and morbidity. 

i. O3 Exposures of Concern 

The EPA received a number of 

comments expressing divergent views 

on the estimation of, and interpretation 

of, O3 exposures of concern. In general, 

comments from industry, business, and 

some state groups opposed to revising 

the current primary O3 standard 

asserted that the approaches and 

assumptions that went into the HREA 

assessment result in overestimates of O3

exposures. These commenters 

highlighted several aspects of the 

assessment, asserting that the HREA 

overestimates the proportion of the 

population expected to achieve 

ventilation rates high enough to 

experience an exposure of concern; that 

the use of out-of-date information on 

activity patterns results in overestimates 

of the amount of time people spend 

being active outdoors; and that exposure 

estimates do not account for the fact that 

people spend more time indoors on 

days with bad air quality (i.e., they 

engage in averting behavior). In contrast, 

comments from medical, public health, 

and environmental groups that 

supported revision of the current 

standard asserted that the HREA 

assessment of exposures of concern, and 

the EPA’s interpretation of exposure 

estimates, understates the potential for 

O3 exposures that could cause adverse 

health effects. These commenters 

claimed that the EPA’s focus on 8-hour 

exposures understates the O3 impacts on 

public health since effects in controlled 

human exposure studies were shown 

following 6.6-hour exposures; that the 

HREA exposure estimates do not 

capture the most highly exposed 

populations, such as highly active 

children and outdoor workers; and that 

the EPA’s interpretation of estimated 

exposures of concern impermissibly 

relies on the assumption that people 

stay indoors to avoid dangerous air 

pollution (i.e., that they engage in 

averting behavior). 

In considering these comments, the 

EPA first notes that as discussed in the 

HREA, PA, and the proposal, there are 

aspects of the exposure assessment that, 

considered by themselves, can result in 

either overestimates or underestimates 

of the occurrence of O3 exposures of 

concern. Commenters tended to 

highlight the aspects of the assessment 

that supported their positions, including 

aspects that were discussed in the 

HREA and/or the PA and that were 

considered by CASAC. In contrast, 

commenters tended to ignore the 

aspects of the assessment that did not 

support their positions. The EPA has 

carefully described and assessed the 

significance of the various uncertainties 

in the exposure analysis (U.S. EPA, 

2014a, Table 5–10), noting that, in most 

instances, the uncertainties could result 

in either overestimates or 

underestimates of exposures and that 

the magnitudes of the impacts on 

exposure results were either ‘‘low,’’ 

‘‘low to moderate,’’ or ‘‘moderate’’ (U.S. 

EPA, 2014a, Table 5–10). 

Consistent with the characterization 

of uncertainties in the HREA, PA, and 

the proposal, the EPA agrees with some, 

though not all, aspects of these 

commenters’ views. For example, the 

EPA agrees with the comment by groups 

opposed to revision that the equivalent 

ventilation rate (EVR) used to 

characterize individuals as at moderate 

or greater exertion in the HREA likely 

leads to overestimates of the number of 

individuals experiencing exposures of 

concern (U.S. EPA, 2014a, Table 5–10, 

p. 5–79). In addition, we note that other 

physiological processes that are 

incorporated into exposure estimates are 

also identified in the HREA as likely 

leading to overestimates of O3

exposures, based on comparisons with 

the available scientific literature (U.S. 

EPA, 2014a, Table 5–10, p. 5–79). These 

aspects of the exposure assessment are 

estimated to have either a ‘‘moderate’’ 

(i.e., EVR) or a ‘‘low to moderate’’ (i.e., 

physiological processes) impact on 

exposure estimates (U.S. EPA, 2014a, 

Table 5–10, p. 5–79). Focusing on these 

aspects of the assessment, by 

themselves, could lead to the 

conclusion that the HREA overstates the 

occurrence of O3 exposures of concern. 

However, the EPA notes that there are 

also aspects of the HREA exposure 

assessment that, taken by themselves, 

could lead to the conclusion that the 

HREA understates the occurrence of O3

exposures of concern. For example, as 

noted above, some medical, public 

health, and environmental groups 

asserted that the exposure assessment 

could underestimate O3 exposures for 

highly active populations, including 

outdoor workers and children who 

spend a large portion of time outdoors 

during summer. In support of these 

assertions, commenters highlighted 

sensitivity analyses conducted in the 

HREA. However, as noted in the HREA 

(U.S. EPA, 2014a, Table 5–10), this 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65339 

aspect of the assessment is likely to 

have a ‘‘low to moderate’’ impact on 

exposure estimates (i.e., a smaller 

impact than uncertainty associated with 

the EVR, and similar in magnitude to 

uncertainties related to physiological 

processes, as noted above). Therefore, 

when considered in the context of all of 

the uncertainties in exposure estimates, 

it is unlikely that the HREA’s approach 

to using data on activity patterns leads 

to overall underestimates of O3

exposures. The implications of this 

uncertainty are discussed in more detail 

below (II.C.4.b), within the context of 

the Administrator’s decision on a 

revised standard level. 

In addition, medical, public health, 

and environmental groups also pointed 

out that the controlled human exposures 

studies that provided the basis for 

health effect benchmarks were 

conducted in healthy adults, rather than 

at-risk populations, and these studies 

evaluated 6.6 hour exposures, rather 

than the 8-hour exposures evaluated in 

the HREA exposure analyses. They 

concluded that adverse effects would 

occur at lower exposure concentrations 

in at-risk populations, such as people 

with asthma, and if people were 

exposed for 8 hours, rather than 6.6 

hours. In its review of the PA, CASAC 

clearly recognized these uncertainties, 

which provided part of the basis for 

CASAC’s advice to consider exposures 

of concern for the 60 ppb benchmark. 

For example, when considering the 

results of the study by Schelegle et al. 

(2009) for 6.6-hour exposures to an 

average O3 concentration of 72 ppb, 

CASAC judged that if subjects had been 

exposed for eight hours, the adverse 

combination of lung function 

decrements and respiratory symptoms 

‘‘could have occurred’’ at lower O3

exposure concentrations (Frey, 2014c, p. 

5). With regard to at-risk populations, 

CASAC concluded that ‘‘based on 

results for clinical studies of healthy 

adults, and scientific considerations of 

differences in responsiveness of 

asthmatic children compared to healthy 

adults, there is scientific support that 60 

ppb is an appropriate exposure of 

concern for asthmatic children’’ (Frey, 

2014c, p. 8). As discussed below (II.B.3, 

II.C.4.b, II.C.4.c), based in large part on 

CASAC advice, the Administrator does 

consider exposure results for the 60 ppb 

benchmark. 

Thus, rather than viewing the 

potential implications of various aspects 

of the HREA exposure assessment in 

isolation, as was done by many 

commenters, the EPA considers them 

together, along with other issues and 

uncertainties related to the 

interpretation of exposure estimates. As 

discussed above, CASAC recognized the 

key uncertainties in exposure estimates, 

as well as in the interpretation of those 

estimates in the HREA and PA (Frey, 

2014a, c). In its review of the 2nd draft 

REA, CASAC concluded that ‘‘[t]he 

discussion of uncertainty and variability 

is comprehensive, appropriately listing 

the major sources of uncertainty and 

their potential impacts on the APEX 

exposure estimates’’ (Frey, 2014a, p. 6). 

Even considering these and other 

uncertainties, CASAC emphasized 

estimates of O3 exposures of concern as 

part of the basis for their 

recommendations on the primary O3

NAAQS. In weighing these 

uncertainties, which can bias exposure 

results in different directions but tend to 

have impacts that are similar in 

magnitude (U.S. EPA, 2014a, Table 5– 

10), and in light of CASAC’s advice 

based on its review of the HREA and the 

PA, the EPA continues to conclude that 

the approach to considering estimated 

exposures of concern in the HREA, PA, 

and the proposal reflects an appropriate 

balance, and provides an appropriate 

basis for considering the public health 

protectiveness of the primary O3

standard. 

The EPA disagrees with other aspects 

of commenters’ views on HREA 

estimates of exposures of concern. For 

example, commenters on both sides of 

the issue objected to the EPA’s handling 

of averting behavior in exposure 

estimates. Some commenters who 

supported retaining the current standard 

claimed that the HREA overstates 

exposures of concern because available 

time-location-activity data do not 

account for averting behavior. These 

commenters noted sensitivity analyses 

in the HREA that estimated fewer 

exposures of concern when averting 

behavior was considered. In contrast, 

commenters supporting revision of the 

standard criticized the EPA’s estimates 

of exposures of concern, claiming that 

the EPA ‘‘emphasizes the role of 

averting behavior, noting that it may 

result in an overestimation of exposures 

of concern, and cites this behavior 

(essentially staying indoors or not 

exercising) in order to reach what it 

deems an acceptable level of risk’’ (e.g., 

ALA et al., p. 120). 

The EPA disagrees with both of these 

comments. In brief, the NAAQS must 

‘‘be established at a level necessary to 

protect the health of persons,’’ not the 

health of persons refraining from normal 

activity or resorting to medical 

interventions to ward off adverse effects 

of poor air quality (S. Rep. No. 11–1196, 

91st Cong. 2d Sess. at 10). On the other 

hand, ignoring normal activity patterns 

for a pollutant like O3, where adverse 

responses are critically dependent on 

ventilation rates, will result in a 

standard which provides more 

protection than is requisite. This issue 

is discussed in more detail below 

(II.C.4.b), within the context of the 

Administrator’s decision on a revised 

standard level. 

These commenters also misconstrue 

the EPA’s limited sensitivity analyses 

on impacts of averting behavior in the 

HREA. The purpose of the HREA 

sensitivity analyses was to provide 

perspective on the potential role of 

averting behavior in modifying O3

exposures. These sensitivity analyses 

were limited to a single urban study 

area, a 2-day period, and a single air 

quality adjustment scenario (U.S. EPA, 

2014a, section 5.4.3.3). In addition, the 

approach used in the HREA to simulate 

averting behavior was itself uncertain, 

given the lack of actual activity pattern 

data that explicitly incorporated this 

type of behavioral response. In light of 

these important limitations, sensitivity 

analyses focused on averting behavior 

were discussed in the proposal within 

the context of the discussion of 

uncertainties in the HREA assessment of 

exposures of concern (II.C.2.b in the 

proposal) and, contrary to the claims of 

some commenters, they were not used 

to support the proposed decision. 

Some industry groups also claimed 

that the time-location-activity diaries 

used by APEX to estimate exposures are 

out-of-date, and do not represent 

activity patterns in the current 

population. These commenters asserted 

that the use of out-of-date diary 

information leads to overestimates in 

exposures of concern. This issue was 

explicitly addressed in the HREA and 

the EPA disagrees with commenters’ 

conclusions. In particular, diary data 

was updated in this review to include 

data from studies published as late as 

2010, directly in response to CASAC 

concerns. In their review of this data, 

CASAC stated that ‘‘[t]he addition of 

more recent time activity pattern data 

addresses a concern raised previously 

by the CASAC concerning how activity 

pattern information should be brought 

up to date’’ (Frey, 2014a, p. 8). As 

indicated in the HREA (U.S. EPA, 

2014a, Appendix 5G, Figures 5G–7 and 

Figure 5G–8), the majority of diary days 

used in exposure simulations of 

children originate from the most 

recently conducted activity pattern 

studies (U.S. EPA, 2014a, Table 5–3). In 

addition, evaluations included in the 

HREA indicated that there were not 

major systematic differences in timelocation-activity patterns based on 

information from older diaries versus 

those collected more recently (U.S. EPA, 

mstockstill on DSK4VPTVN1PROD with RULES2

65340 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

2014a, Appendix 5G, Figures 5G–1 and 

5G–2). Given all of the above, the EPA 

does not agree with commenters who 

claimed that the time-location-activity 

diaries used by APEX are out-of-date, 

and result in overestimates of exposures 

of concern. 

ii. Risk of O3-Induced FEV1 Decrements 

The EPA also received a large number 

of comments on the FEV1 risk 

assessment presented in chapter 6 of the 

HREA (U.S. EPA, 2014a) and 

summarized in the proposal (II.C.3.a in 

the proposal). Commenters representing 

medical, public health, and 

environmental groups generally 

expressed the view that these risk 

estimates support the need to revise the 

current primary O3 standard in order to 

increase public health protection, 

though these groups also questioned 

some of the assumptions inherent in the 

EPA’s interpretation of those risk 

estimates. For example, ALA et al. (p. 

127) stated that ‘‘[t]he HREA uses a risk 

function derived from a controlled 

human exposure study of healthy young 

adults to estimate lung function 

decrements in children, including 

children with asthma. This assumption 

could result in an underestimate of 

risk.’’ On this same issue, commenters 

representing industry groups opposed to 

revising the standard also asserted that 

assumptions about children’s responses 

to O3 exposures are highly uncertain. In 

contrast to medical and public health 

groups, these commenters concluded 

that this uncertainty, along with others 

discussed below, call into question the 

use of FEV1 risk estimates to support a 

decision to revise the current primary 

O3 standard. 

The EPA agrees that an important 

source of uncertainty is the approach to 

estimating the risk of FEV1 decrements 

in children and in children with asthma 

based on data from healthy adults. 

However, this issue is discussed at 

length in the HREA and the PA, and was 

considered carefully by CASAC in its 

review of draft versions of these 

documents. The conclusions of the 

HREA and PA, and the advice of 

CASAC, were reflected in the 

Administrator’s interpretation of FEV1

risk estimates in the proposal, as 

described below. Commenters have not 

provided additional information that 

changes the EPA’s views on this issue. 

As discussed in the proposal 

(II.C.3.a.ii in the proposal), in the near 

absence of controlled human exposure 

data for children, risk estimates are 

based on the assumption that children 

exhibit the same lung function response 

following O3 exposures as healthy 18- 

year olds (i.e., the youngest age for 

which sufficient controlled human 

exposure data is available) (U.S. EPA, 

2014a, section 6.5.3). As noted by 

CASAC (Frey, 2014a, p. 8), this 

assumption is justified in part by the 

findings of McDonnell et al. (1985), who 

reported that children (8–11 years old) 

experienced FEV1 responses similar to 

those observed in adults (18–35 years 

old). The HREA concludes that this 

approach could result in either over- or 

underestimates of O3-induced lung 

function decrements in children, 

depending on how children compare to 

the adults used in controlled human 

exposure studies (U.S. EPA, 2014a, 

section 6.5.3). With regard to people 

with asthma, although the evidence has 

been mixed (U.S. EPA, 2013, section 

6.2.1.1), several studies have reported 

statistically larger, or a tendency for 

larger, O3-induced lung function 

decrements in asthmatics than in nonasthmatics (Kreit et al., 1989; Horstman 

et al., 1995; Jorres et al., 1996; Alexis et 

al., 2000). On this issue, CASAC noted 

that ‘‘[a]sthmatic subjects appear to be at 

least as sensitive, if not more sensitive, 

than non-asthmatic subjects in 

manifesting O3-induced pulmonary 

function decrements’’ (Frey, 2014c, p. 

4). To the extent asthmatics experience 

larger O3-induced lung function 

decrements than the healthy adults used 

to develop exposure-response 

relationships, the HREA could 

underestimate the impacts of O3

exposures on lung function in 

asthmatics, including asthmatic 

children (U.S. EPA, 2014a, section 

6.5.4). As noted above, these 

uncertainties have been considered 

carefully by the EPA and by CASAC 

during the development of the HREA 

and PA. In addition, the Administrator 

has appropriately considered these and 

other uncertainties in her interpretation 

of risk estimates, as discussed further 

below (II.B.3, II.C.4.b, II.C.4.c). 

Some commenters additionally 

asserted that the HREA does not 

appropriately characterize the 

uncertainty in risk estimates for O3- 

induced lung function decrements. 

Commenters pointed out that there is 

statistical uncertainty in model 

coefficients that is not accounted for in 

risk estimates. One commenter 

presented an analysis of this 

uncertainty, and concluded that there is 

considerable overlap between risk 

estimates for standard levels of 75, 70, 

and 65 ppb, undercutting the 

confidence in estimated risk reductions 

for standard levels below 75 ppb. 

The Agency recognizes that there are 

important sources of uncertainty in the 

FEV1 risk assessment. In some cases, 

these sources of uncertainty can 

contribute to substantial variability in 

risk estimates, complicating the 

interpretation of those estimates. For 

example, as discussed in the proposal, 

the variability in FEV1 risk estimates 

across urban study areas is often greater 

than the differences in risk estimates 

between various standard levels (Table 

2, above and 79 FR 75306 n. 164). Given 

this, and the resulting considerable 

overlap between the ranges of FEV1 risk 

estimates for different standard levels, 

in the proposal the Administrator 

viewed these risk estimates as providing 

a more limited basis than exposures of 

concern for distinguishing between the 

degree of public health protection 

provided by alternative standard levels. 

Thus, although the EPA does not agree 

with the overall conclusions of industry 

commenters, their analysis of statistical 

uncertainty in risk estimates, and the 

resulting overlap between risk estimates 

for standard levels of 75, 70, and 65 

ppb, tends to reinforce the 

Administrator’s approach, which places 

greater weight on estimates of O3

exposures of concern than on risk 

estimates for O3-induced FEV1

decrements. 

iii. Risk of O3-Associated Mortality and 

Morbidity 

In the proposal, the Administrator 

placed the greatest emphasis on the 

results of controlled human exposure 

studies and on quantitative analyses 

based on information from these 

studies, and less weight on mortality 

and morbidity risk assessments based 

on information from epidemiology 

studies. The EPA received a number of 

comments on its consideration of 

epidemiology-based risks, with some 

commenters expressing support for the 

Agency’s approach and others 

expressing opposition. 

In general, commenters representing 

industry organizations or states opposed 

to revising the current primary O3

standard agreed with the 

Administrator’s approach in the 

proposal to viewing epidemiology-based 

risk estimates, though these commenters 

reached a different conclusion than the 

EPA regarding the adequacy of the 

current standard. In supporting their 

views, these commenters highlighted a 

number of uncertainties in the 

underlying epidemiologic studies, and 

concluded that risk estimates based on 

information from such studies do not 

provide an appropriate basis for revising 

the current standard. For example, 

commenters noted considerable spatial 

heterogeneity in health effect 

associations; the potential for cooccurring pollutants (e.g., PM2.5) to 

confound O3 health effect associations; 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65341 

101The ISA concludes that there is less certainty 

in the shape of concentration-response functions for 

area-wide O3 concentrations at the lower ends of 

warm season distributions (i.e., below about 20 to 

40 ppb) (U.S. EPA, 2013, section 2.5.4.4). 

102Available experimental studies provide the 

strongest evidence for O3-induced effects following 

exposures to O3 concentrations corresponding to 

the upper portions of typical ambient distributions. 

In particular, as discussed above, controlled human 

exposure studies showing respiratory effects 

following exposures to O3 concentrations at or 

above 60 ppb. 

and the lack of statistically significant 

O3 health effect associations in many of 

the individual cities evaluated as part of 

multicity analyses. In contrast, some 

commenters representing medical, 

public health, or environmental 

organizations placed greater emphasis 

than the EPA on epidemiology-based 

risk estimates. These commenters 

asserted that risk estimates provide 

strong support for a lower standard 

level, and pointed to CASAC advice to 

support their position. 

As in the proposal, the EPA continues 

to place the greatest weight on the 

results of controlled human exposure 

studies and on quantitative analyses 

based on information from these studies 

(particularly exposures of concern, as 

discussed below in II.B.3 and II.C.4), 

and less weight on risk analyses based 

on information from epidemiologic 

studies. In doing so, the Agency 

continues to note that controlled human 

exposure studies provide the most 

certain evidence indicating the 

occurrence of health effects in humans 

following specific O3 exposures. In 

addition, the effects reported in these 

studies are due solely to O3 exposures, 

and interpretation of study results is not 

complicated by the presence of cooccurring pollutants or pollutant 

mixtures (as is the case in epidemiologic 

studies). The Agency further notes the 

CASAC judgment that ‘‘the scientific 

evidence supporting the finding that the 

current standard is inadequate to protect 

public health is strongest based on the 

controlled human exposure studies of 

respiratory effects’’ (Frey, 2014c, p. 5). 

Consistent with this emphasis, the 

HREA conclusions reflect relatively 

greater confidence in the results of the 

exposure and risk analyses based on 

information from controlled human 

exposure studies than the results of 

epidemiology-based risk analyses. As 

discussed in the HREA (U.S. EPA, 

2014a, section 9.6), several key 

uncertainties complicate the 

interpretation of these epidemiologybased risk estimates, including the 

heterogeneity in O3 effect estimates 

between locations, the potential for 

exposure measurement errors in these 

epidemiologic studies, and uncertainty 

in the interpretation of the shape of 

concentration-response functions at 

lower O3 concentrations. Commenters 

who opposed the EPA’s approach in the 

proposal to viewing the results of 

quantitative analyses tended to 

highlight aspects of the evidence and 

CASAC advice that were considered by 

the EPA at the time of proposal and 

nothing in these commenters’ views has 

changed those considerations. 

Therefore, the EPA continues to place 

the most emphasis on using the 

information from controlled human 

exposure studies to inform 

consideration of the adequacy of the 

primary O3 standard. 

However, while the EPA agrees that 

there are important uncertainties in the 

O3 epidemiology-based risk estimates, 

the Agency disagrees with industry 

commenters that these uncertainties 

support a conclusion to retain the 

current standard. As discussed below, 

the decision to revise the current 

primary O3 standard is based on the 

EPA’s consideration of the broad body 

of scientific evidence, quantitative 

analyses of O3 exposures and risks, 

CASAC advice, and public comments. 

While recognizing uncertainties in the 

epidemiology-based risk estimates here, 

and giving these uncertainties 

appropriate consideration, the Agency 

continues to conclude that these risk 

estimates contribute to the broader body 

of evidence and information supporting 

the need to revise the primary O3

standard. 

Some commenters opposed to 

revising the current O3 standard 

highlighted the fact that, in a few urban 

study locations, larger risks are 

estimated for standard levels below 75 

ppb than for the current standard with 

its level of 75 ppb. For example, TCEQ 

(p. 3) states that ‘‘differential effects on 

ozone in urban areas also lead to the 

EPA’s modeled increases in mortality in 

Houston and Los Angeles with 

decreasing ozone standards.’’ These 

commenters cited such increases in 

estimated risk as part of the basis for 

their conclusion that the current 

standard should be retained. 

For communities across the U.S. 

(including in the Houston and Los 

Angeles areas), exposure and risk 

analyses indicate that reducing 

emissions of O3 precursors (NOX, VOCs) 

to meet a revised standard with a level 

of 70 ppb will substantially reduce the 

occurrence of adverse respiratory effects 

and mortality risk attributable to high 

O3 concentrations (U.S. EPA, 2014a, 

Appendix 9A; U.S. EPA, 2014c, sections 

4.4.2.1 to 4.4.2.3). However, because of 

the complex chemistry governing the 

formation and destruction of O3, some 

NOX control strategies designed to 

reduce the highest ambient O3

concentrations can also result in 

increases in relatively low ambient O3

concentrations. As a result of the way 

the EPA’s epidemiology-based risk 

assessments were conducted (U.S. EPA, 

2014a, Chapter 7), increases estimated 

in low O3 concentrations impacted 

mortality and morbidity risks, leading to 

the estimated risk increases highlighted 

by some commenters. However, while 

the EPA is confident that reducing the 

highest ambient O3 concentrations will 

result in substantial improvements in 

public health, including reducing the 

risk of O3-associated mortality, the 

Agency is far less certain about the 

public health implications of the 

changes in relatively low ambient O3

concentrations (79 FR at 75278/3, 

75291/1, and 75308/2). Therefore, 

reducing precursor emissions to meet a 

lower O3 standard is expected to result 

in important reductions in O3

concentrations from the part of the air 

quality distribution where the evidence 

provides the strongest support for 

adverse health effects. 

Specifically, for area-wide O3

concentrations at or above 40 ppb,101 a 

revised standard with a level of 70 ppb 

is estimated to reduce the number of 

premature deaths associated with shortterm O3 concentrations by about 10%, 

compared to the current standard. In 

addition, for area-wide concentrations at 

or above 60 ppb, a revised standard with 

a level of 70 ppb is estimated to reduce 

O3-associated premature deaths by 

about 50% to 70%.102 The EPA views 

these results, which focus on the 

portion of the air quality distribution 

where the evidence indicates the most 

certainty regarding the occurrence of 

adverse O3-attributable health effects, 

not only as supportive of the need to 

revise the current standard (II.B.3, 

below), but also as showing the benefits 

of reducing the peak O3 concentrations 

associated with air quality distributions 

meeting the current standard (II.C.4, 

below). 

In addition, even considering risk 

estimates based on the full distribution 

of ambient O3 concentrations (i.e., 

estimates influenced by decreases in 

higher concentrations and increases in 

lower concentrations), the EPA notes 

that, compared to the current standard, 

standards with lower levels are 

estimated to result in overall reductions 

in mortality risk across the urban study 

areas evaluated (U.S. EPA, 2014c, Figure 

4–10). As discussed above (II.A.2.a, 

II.A.2.c), analyses in the HREA indicate 

that these overall risk reductions could 

understate the actual reductions that 

mstockstill on DSK4VPTVN1PROD with RULES2

65342 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

103Specifically, the HREA urban study areas tend 

to underrepresent populations living in suburban, 

smaller urban, and rural areas, where reducing NOX

emissions would be expected to result in decreases 

in warm season averages of daily maximum 8-hour 

ambient O3 concentrations (U.S. EPA, 2014a, 

section 8.2.3.2). 

would be experienced by the U.S. 

population as a whole. 

For example, the HREA’s national air 

quality modeling analyses indicate that 

the HREA urban study areas tend to 

underrepresent the populations living in 

areas where reducing NOX emissions 

would be expected to result in decreases 

in warm season averages of daily 

maximum 8-hour ambient O3

concentrations.103 Given the strong 

connection between these warm season 

average O3 concentrations and risk, risk 

estimates for the urban study areas are 

likely to understate the average 

reductions in O3-associated mortality 

and morbidity risks that would be 

experienced across the U.S. population 

as a whole upon reducing NOX

emissions (U.S. EPA, 2014a, section 

8.2.3.2). 

In addition, in recognizing that the 

reductions in modeled NOX emissions 

used in the HREA’s core analyses are 

meant to be illustrative, rather than to 

imply a particular control strategy for 

meeting a revised O3 NAAQS, the HREA 

also conducted sensitivity analyses in 

which both NOX and VOC emissions 

reductions were evaluated. In all of the 

urban study areas evaluated in these 

analyses, the increases in low O3

concentrations were smaller for the 

NOX/VOC emission reduction scenarios 

than the NOX only emission reduction 

scenario (U.S. EPA, 2014a, Appendix 

4D, section 4.7). This was most apparent 

for Denver, Houston, Los Angeles, New 

York, and Philadelphia. These results 

suggest that in some locations, 

optimized emissions reduction 

strategies could result in larger 

reductions in O3-associated mortality 

and morbidity than indicated by 

HREA’s core estimates. 

Thus, the patterns of estimated 

mortality and morbidity risks across 

various air quality scenarios and 

locations have been evaluated and 

considered extensively in the HREA and 

the PA, as well as in the proposal. 

Epidemiology-based risk estimates have 

also been considered by CASAC, and 

those considerations are reflected in 

CASAC’s advice. Specifically, in 

considering epidemiology-based risk 

estimates in its review of the REA, 

CASAC stated that ‘‘[a]lthough these 

estimates for short-term exposure 

impacts are subject to uncertainty, the 

CASAC is confident that that the 

evidence of health effects of O3

presented in the ISA and Second Draft 

HREA in its totality, indicates that there 

are meaningful reductions in mean, 

absolute, and relative premature 

mortality associated with short-term 

exposures to O3 levels lower than the 

current standard’’ (Frey, 2014a, p. 3). 

Commenters’ views on this issue are not 

based on new information, but on an 

interpretation of the analyses presented 

in the HREA that is different from the 

EPA’s, and CASAC’s, interpretation. 

Given this, the EPA’s considerations 

and conclusions related to this issue, as 

described in the proposal and as 

summarized briefly above, remain valid. 

Therefore, the EPA does not agree with 

commenters who cited increases in 

estimated risk in some locations as 

supporting a conclusion that the current 

standard should be retained. 

For risk estimates of respiratory 

mortality associated with long-term O3, 

several industry commenters supported 

placing more emphasis on threshold 

models, and including these models as 

part of the core analyses rather than as 

sensitivity analyses. The EPA agrees 

with these commenters that an 

important uncertainty in risk estimates 

of respiratory mortality associated with 

long-term O3 stems from the potential 

for the existence of a threshold. Based 

on sensitivity analyses included in the 

HREA in response to CASAC advice, the 

existence of a threshold could 

substantially reduce estimated risks. 

CASAC discussed this issue at length 

during its review of the REA and 

supported the EPA’s approach to 

including a range of threshold models as 

sensitivity analyses (Frey, 2014a p. 3). 

Based in part on uncertainty in the 

existence and identification of a 

threshold, the HREA concluded that 

lower confidence should be placed in 

risk estimates for respiratory mortality 

associated with long-term O3 exposures 

(U.S. EPA, 2014a, section 9.6). This 

uncertainty was also a key part of the 

Administrator’s rationale for placing 

only limited emphasis on risk estimates 

for long-term O3 exposures. In her final 

decisions, discussed below (II.B.3, 

II.C.4.b, II.C.4.c), the Administrator 

continues to place only limited 

emphasis on these estimates. The EPA 

views this approach to considering risk 

estimates for respiratory mortality as 

generally consistent with the approach 

supported by the commenters noted 

above. 

3. Administrator’s Conclusions on the 

Need for Revision 

This section discusses the 

Administrator’s conclusions related to 

the adequacy of the public health 

protection provided by the current 

primary O3 standard, and her final 

decision that the current standard is not 

requisite to protect public health with 

an adequate margin of safety. These 

conclusions, and her final decision, are 

based on the Administrator’s 

consideration of the available scientific 

evidence assessed in the ISA (U.S. EPA, 

2013), the exposure/risk information 

presented and assessed in the HREA 

(U.S. EPA, 2014a), the consideration of 

that evidence and information in the PA 

(U.S. EPA, 2014c), the advice of CASAC, 

and public comments received on the 

proposal. 

As an initial matter, the Administrator 

concludes that reducing precursor 

emissions to achieve O3 concentrations 

that meet the current primary O3

standard will provide important 

improvements in public health 

protection, compared to recent air 

quality. In reaching this conclusion, she 

notes the discussion in section 3.4 of the 

PA (U.S. EPA, 2014c). In particular, the 

Administrator notes that this conclusion 

is supported by (1) the strong body of 

scientific evidence indicating a wide 

range of adverse health outcomes 

attributable to exposures to O3 at 

concentrations commonly found in the 

ambient air and (2) estimates indicating 

decreased occurrences of O3 exposures 

of concern and decreased O3-associated 

health risks upon meeting the current 

standard, compared to recent air quality. 

Thus, she concludes that it would not 

be appropriate in this review to consider 

a standard that is less protective than 

the current standard. 

After reaching the conclusion that 

meeting the current primary O3 standard 

will provide important improvements in 

public health protection, and that it is 

not appropriate to consider a standard 

that is less protective than the current 

standard, the Administrator next 

considers the adequacy of the public 

health protection that is provided by the 

current standard. In doing so, the 

Administrator first notes that studies 

evaluated since the completion of the 

2006 AQCD support and expand upon 

the strong body of evidence that, in the 

last review, indicated a causal 

relationship between short-term O3

exposures and respiratory morbidity 

outcomes (U.S. EPA, 2013, section 2.5). 

This is the strongest causality finding 

possible under the ISA’s hierarchical 

system for classifying weight of 

evidence for causation. In addition, the 

Administrator notes that the evidence 

for respiratory health effects attributable 

to long-term O3 exposures, including the 

development of asthma in children, is 

much stronger than in previous reviews, 

and the ISA concludes that there is 

‘‘likely to be’’ a causal relationship 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65343 

104For a 60 ppb target exposure concentration, 

Schelegle et al. (2009) reported that the actual 6.6- 

hour mean exposure concentration was 63 ppb. 105For a 70 ppb target exposure concentration, 

Schelegle et al. (2009) reported that the actual 6.6- 

hour mean exposure concentration was 72 ppb. 

between such O3 exposures and adverse 

respiratory health effects (the second 

strongest causality finding). 

Together, experimental and 

epidemiologic studies support 

conclusions regarding a continuum of 

O3 respiratory effects ranging from 

small, reversible changes in pulmonary 

function, and pulmonary inflammation, 

to more serious effects that can result in 

respiratory-related emergency 

department visits, hospital admissions, 

and premature mortality. Recent animal 

toxicology studies support descriptions 

of modes of action for these respiratory 

effects and augment support for 

biological plausibility for the role of O3

in reported effects. With regard to mode 

of action, evidence indicates that the 

initial key event is the formation of 

secondary oxidation products in the 

respiratory tract, that antioxidant 

capacity may modify the risk of 

respiratory morbidity associated with O3

exposure, and that the inherent capacity 

to quench (based on individual 

antioxidant capacity) can be 

overwhelmed, especially with exposure 

to elevated concentrations of O3. 

In addition, based on the consistency 

of findings across studies and the 

coherence of results from different 

scientific disciplines, the available 

evidence indicates that certain 

populations are at increased risk of 

experiencing O3-related effects, 

including the most severe effects. These 

include populations and lifestages 

identified in previous reviews (i.e., 

people with asthma, children, older 

adults, outdoor workers) and 

populations identified since the last 

review (i.e., people with certain 

genotypes related to antioxidant and/or 

anti-inflammatory status; people with 

reduced intake of certain antioxidant 

nutrients, such as Vitamins C and E). 

In considering the O3 exposure 

concentrations reported to elicit 

respiratory effects, as in the proposal, 

the Administrator agrees with the 

conclusions of the PA that controlled 

human exposure studies provide the 

most certain evidence indicating the 

occurrence of health effects in humans 

following specific O3 exposures. In 

particular, she notes that the effects 

reported in controlled human exposure 

studies are due solely to O3 exposures, 

and interpretation of study results is not 

complicated by the presence of cooccurring pollutants or pollutant 

mixtures (as is the case in epidemiologic 

studies). Therefore, consistent with 

CASAC advice (Frey, 2014c), she places 

the most weight on information from 

controlled human exposure studies in 

reaching conclusions on the adequacy of 

the current primary O3 standard. 

In considering the evidence from 

controlled human exposure studies, the 

Administrator first notes that these 

studies have reported a variety of 

respiratory effects in healthy adults 

following exposures to O3

concentrations of 60, 63,104 72,105 or 80 

ppb, and higher. The largest respiratory 

effects, and the broadest range of effects, 

have been studied and reported 

following exposures of healthy adults to 

80 ppb O3 or higher, with most exposure 

studies conducted at these higher 

concentrations. As discussed above 

(II.A.1), the Administrator further notes 

that recent evidence includes controlled 

human exposure studies reporting the 

combination of lung function 

decrements and respiratory symptoms 

in healthy adults engaged in moderate 

exertion following 6.6-hour exposures to 

concentrations as low as 72 ppb, and 

lung function decrements and 

pulmonary inflammation following 

exposures to O3 concentrations as low 

as 60 ppb. 

As discussed in her response to 

public comments above (II.B.2.b.i), and 

in detail below (II.C.4.b, II.C.4.c), the 

Administrator concludes that these 

controlled human exposure studies 

indicate that adverse effects are likely to 

occur following exposures to O3

concentrations below the level of the 

current standard. The effects observed 

following such exposures are coherent 

with the serious health outcomes that 

have been reported in O3 epidemiologic 

studies (e.g., respiratory-related hospital 

admissions, emergency department 

visits), and the Administrator judges 

that such effects have the potential to be 

important from a public health 

perspective. 

In reaching these conclusions, she 

particularly notes that the combination 

of lung function decrements and 

respiratory symptoms reported to occur 

in healthy adults following exposures to 

72 ppb O3 meets ATS criteria for an 

adverse response (II.B.2.b.i, above). In 

specifically considering the 72 ppb 

exposure concentration, CASAC noted 

that ‘‘the combination of decrements in 

FEV1 together with the statistically 

significant alterations in symptoms in 

human subjects exposed to 72 ppb 

ozone meets the American Thoracic 

Society’s definition of an adverse health 

effect’’ (Frey, 2014c, p. 5). In addition, 

given that the controlled human 

exposure study reporting these results 

was conducted in healthy adults, 

CASAC judged that the adverse 

combination of lung function 

decrements and respiratory symptoms 

‘‘almost certainly occur in some people’’ 

(e.g., people with asthma) following 

exposures to lower O3 concentrations 

(Frey, 2014c, p. 6). 

While the Administrator is less 

certain regarding the adversity of the 

lung function decrements and airway 

inflammation that have been observed 

following exposures as low as 60 ppb, 

as discussed in more detail elsewhere in 

this preamble (II.B.2.b.i, II.C.4.b, 

II.C.4.c), she judges that these effects 

also have the potential to be adverse, 

and to be of public health importance, 

particularly if they are experienced 

repeatedly. With regard to this 

judgment, she specifically notes the ISA 

conclusion that, while the airway 

inflammation induced by a single 

exposure (or several exposures over the 

course of a summer) can resolve 

entirely, continued inflammation could 

potentially result in adverse effects, 

including the induction of a chronic 

inflammatory state; altered pulmonary 

structure and function, leading to 

diseases such as asthma; altered lung 

host defense response to inhaled 

microorganisms; and altered lung 

response to other agents such as 

allergens or toxins (U.S. EPA, 2013, 

section 6.2.3). Thus, the Administrator 

becomes increasingly concerned about 

the potential for adverse effects at 60 

ppb O3 as the number of exposures 

increases, though she notes that the 

available evidence does not indicate a 

particular number of occurrences of 

such exposures that would be required 

to achieve an adverse respiratory effect, 

and that this number is likely to vary 

across the population. 

In addition to controlled human 

exposure studies, the Administrator also 

considers what the available 

epidemiologic evidence indicates with 

regard to the adequacy of the public 

health protection provided by the 

current primary O3 standard. She notes 

that recent epidemiologic studies 

provide support, beyond that available 

in the last review, for associations 

between short-term O3 exposures and a 

wide range of adverse respiratory 

outcomes (including respiratory-related 

hospital admissions, emergency 

department visits, and mortality) and 

with total mortality. As discussed above 

in the EPA responses to public 

comments (II.B.2.b.ii), associations with 

morbidity and mortality are stronger 

during the warm or summer months, 

and remain robust after adjustment for 

copollutants (U.S. EPA, 2013, Chapter 

6). 

mstockstill on DSK4VPTVN1PROD with RULES2

65344 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

106The large majority of locations evaluated in 

U.S. epidemiologic studies of long-term O3 would 

have violated the current standard during study 

periods, thus providing limited insight into the 

adequacy of the current standard (U.S. EPA, 2014c, 

section 3.1.4.3). 

107As noted in the proposal (II.E.4.d), this 

uncertainty applies specifically to interpreting air 

quality analyses within the context of multicity 

effect estimates for short-term O3 concentrations, 

where effect estimates for individual study cities 

are not presented (as is the case for the key O3

studies analyzed in the PA, with the exception of 

the study by Stieb et al. (2009) where none of the 

city-specific effect estimates for asthma emergency 

department visits were statistically significant). 

This specific uncertainty does not apply to 

multicity epidemiologic studies of long-term O3

concentrations, where multicity effect estimates are 

based on comparisons across cities. For example, 

see discussion of study by Jerrett et al. (2009) in the 

PA (U.S. EPA, 2014c, section 3.1.4.3). 

In considering information from 

epidemiologic studies within the 

context of her conclusions on the 

adequacy of the current standard, the 

Administrator specifically considers 

analyses in the PA that evaluate the 

extent to which O3 health effect 

associations have been reported for air 

quality concentrations likely to be 

allowed by the current standard. She 

notes that such analyses can provide 

insight into the extent to which the 

current standard would allow the 

distributions of ambient O3

concentrations that provided the basis 

for these health effect associations. 

While the majority of O3 epidemiologic 

studies evaluated in the PA were 

conducted in areas that would have 

violated the current standard during 

study periods, as discussed above 

(II.B.2.b.ii), the Administrator observes 

that the study by Mar and Koenig (2009) 

reported associations between shortterm O3 concentrations and asthma 

emergency department visits in children 

and adults in a U.S. location that would 

have met the current O3 standard over 

the entire study period.106 Based on 

this, she notes the conclusion from the 

PA that the current primary O3 standard 

would have allowed the distribution of 

ambient O3 concentrations that 

provided the basis for the associations 

with asthma emergency department 

visits reported by Mar and Koenig 

(2009) (U.S. EPA, 2014c, section 

3.1.4.2). 

In addition, even in some single-city 

study locations where the current 

standard was violated (i.e., those 

evaluated in Silverman and Ito, 2010; 

Strickland et al., 2010), the 

Administrator notes that PA analyses of 

reported concentration-response 

functions and available air quality data 

support the occurrence of O3- 

attributable hospital admissions and 

emergency department visits on subsets 

of days with virtually all ambient O3

concentrations below the level of the 

current standard. PA analyses of study 

area air quality further support the 

conclusion that exposures to the 

ambient O3 concentrations present in 

the locations evaluated by Strickland et 

al. (2010) and Silverman and Ito (2010) 

could have plausibly resulted in the 

respiratory-related emergency 

department visits and hospital 

admissions reported in these studies 

(U.S. EPA, 2014c, section 3.1.4.2). The 

Administrator agrees with the PA 

conclusion that these analyses indicate 

a relatively high degree of confidence in 

reported statistical associations with 

respiratory health outcomes on days 

when virtually all monitored 8-hour O3

concentrations were 75 ppb or below. 

She further agrees with the PA 

conclusion that although these analyses 

do not identify true design values, the 

presence of O3-associated respiratory 

effects on such days provides insight 

into the types of health effects that 

could occur in locations with maximum 

ambient O3 concentrations below the 

level of the current standard. 

Compared to the single-city 

epidemiologic studies discussed above, 

the Administrator notes additional 

uncertainty in interpreting the 

relationships between short-term O3 air 

quality in individual study cities and 

reported O3 multicity effect estimates. In 

particular, she judges that the available 

multicity effect estimates in studies of 

short-term O3 do not provide a basis for 

considering the extent to which 

reported O3 health effect associations 

are influenced by individual locations 

with ambient O3 concentrations low 

enough to meet the current O3 standard, 

versus locations with O3 concentrations 

that violate this standard.107 While such 

uncertainties limit the extent to which 

the Administrator bases her conclusions 

on air quality in locations of multicity 

epidemiologic studies, she does note 

that O3 associations with respiratory 

morbidity or premature mortality have 

been reported in several multicity 

studies when the majority of study 

locations (though not all study 

locations) would have met the current 

O3 standard (U.S. EPA, 2014c, section 

3.1.4.2). 

Looking across the body of 

epidemiologic evidence, the 

Administrator thus reaches the 

conclusion that analyses of air quality in 

study locations support the occurrence 

of adverse O3-associated effects at 

ambient O3 concentrations that met, or 

are likely to have met, the current 

standard. She further concludes that the 

strongest support for this conclusion 

comes from single-city studies of 

respiratory-related hospital admissions 

and emergency department visits 

associated with short-term O3

concentrations, with some support also 

from multicity studies of morbidity or 

mortality. 

Taken together, the Administrator 

concludes that the scientific evidence 

from controlled human exposure and 

epidemiologic studies calls into 

question the adequacy of the public 

health protection provided by the 

current standard. In reaching this 

conclusion, she particularly notes that 

the current standard level is higher than 

the lowest O3 exposure concentration 

shown to result in the adverse 

combination of lung function 

decrements and respiratory symptoms 

(i.e., 72 ppb), and that CASAC 

concluded that such effects ‘‘almost 

certainly occur in some people’’ 

following exposures to O3

concentrations below 72 ppb (Frey, 

2014c, p. 6). While she also notes that 

the current standard level is well-above 

the lowest O3 exposure concentration 

shown to cause respiratory effects (i.e., 

60 ppb), she has less confidence that the 

effects observed at 60 ppb are adverse 

(discussed in II.B.2.b.i, II.C.4.b, II.C.4.c). 

She further considers these effects, and 

the extent to which the current primary 

O3 standard could protect against them, 

within the context of quantitative 

analyses of O3 exposures (discussed 

below). With regard to the available 

epidemiologic evidence, the 

Administrator notes PA analyses of O3

air quality indicating that, while most 

O3 epidemiologic studies reported 

health effect associations with ambient 

O3 concentrations that violated the 

current standard, a small number of 

single-city U.S. studies support the 

occurrence of asthma-related hospital 

admissions and emergency department 

visits at ambient O3 concentrations 

below the level of the current standard, 

including one study with air quality that 

would have met the current standard 

during the study period. Some support 

for such O3 associations is also provided 

by multicity studies of morbidity or 

mortality. The Administrator further 

judges that the biological plausibility of 

associations with clearly adverse 

morbidity effects is supported by the 

evidence noted above from controlled 

human exposure studies conducted at, 

or in some cases below, typical warmseason ambient O3 concentrations. 

Beyond her consideration of the 

scientific evidence, the Administrator 

also considers the results of the HREA 

exposure and risk analyses in reaching 

final conclusions regarding the 

adequacy of the current primary O3

standard. In doing so, consistent with 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65345 

108She focuses on estimates for all children and 

estimates for children with asthma, noting that 

exposure and risk estimates for these groups are 

virtually indistinguishable in terms of the percent 

estimated to experience exposures of concern or O3- 

induced FEV1 decrements (U.S. EPA, 2014c, 

sections 3.2 and 4.4.2). 

109As noted below (II.C.4.2), this includes 

populations of highly active adults, such as outdoor 

workers. Limited sensitivity analyses in the HREA 

indicate that when diaries were selected to mimic 

exposures that could be experienced by outdoor 

workers, the percentages of modeled individuals 

estimated to experience exposures of concern were 

generally similar to the percentages estimated for 

children (i.e., using the full database of diary 

profiles) in the urban study areas and years with the 

largest exposure estimates (U.S. EPA, 2014, section 

5.4.3.2, Figure 5–14). 

110Not all people who experience an exposure of 

concern will experience an adverse effect (even 

members of at-risk populations). For the endpoints 

evaluated in controlled human exposure studies, 

the number of those experiencing exposures of 

concern who will experience adverse effects cannot 

be reliably quantified. 

111 Virtually no children in those areas would be 

estimated to experience two or more exposures of 

concern at or above 80 ppb. 

112That is, adverse effects are a possible outcome 

of single exposures of concern at/above 70 or 80 

ppb, though the available information is not 

sufficient to estimate the likelihood of such effects. 

her consideration of the evidence, she 

focuses primarily on quantitative 

analyses based on information from 

controlled human exposure studies (i.e., 

exposures of concern and risk of O3- 

induced FEV1 decrements). Consistent 

with the considerations in the PA, and 

with CASAC advice (Frey, 2014c), she 

particularly focuses on exposure and 

risk estimates in children.108 As 

discussed in the HREA and PA (and 

II.B, above), the patterns of exposure 

and risk estimates across urban study 

areas, across years, and across air 

quality scenarios are similar in children 

and adults though, because children 

spend more time being physically active 

outdoors and are more likely to 

experience the types of O3 exposures 

shown to cause respiratory effects, 

larger percentages of children are 

estimated to experience exposures of 

concern and O3-induced FEV1

decrements. Children also have intrinsic 

risk factors that make them particularly 

susceptible to O3-related effects (e.g., 

higher ventilation rates relative to lung 

volume) (U.S. EPA, 2013, section 

8.3.1.1; see section II.A.1.d above). In 

focusing on exposure and risk estimates 

in children, the Administrator 

recognizes that the exposure patterns for 

children across years, urban study areas, 

and air quality scenarios are indicative 

of the exposure patterns in a broader 

group of at-risk populations that also 

includes asthmatic adults and older 

adults. She judges that, to the extent the 

primary O3 standard provides 

appropriate protection for children, it 

will also do so for adult populations,109

given the larger exposures and intrinsic 

risk factors in children. 

In first considering estimates of 

exposures of concern, the Administrator 

considers the extent to which estimates 

indicate that the current standard limits 

population exposures to the broader 

range of O3 concentrations shown in 

controlled human exposure studies to 

cause respiratory effects. In doing so, 

she focuses on estimates of O3

exposures of concern at or above the 

benchmark concentrations of 60, 70, and 

80 ppb. She notes that the current O3

standard can provide some protection 

against exposures of concern to a range 

of O3 concentrations, including 

concentrations below the standard level, 

given that (1) with the current fourthhigh form, most days will have 

concentrations below the standard level 

and that (2) exposures of concern 

depend on both the presence of 

relatively high ambient O3

concentrations and on activity patterns 

in the population that result in 

exposures to such high concentrations 

while at an elevated ventilation rate 

(discussed in detail below, II.C.4.b and 

II.C.4.c). 

In considering estimates of O3

exposures of concern allowed by the 

current standard, she notes that while 

single exposures of concern could be 

adverse for some people, particularly for 

the higher benchmark concentrations 

(70, 80 ppb) where there is stronger 

evidence for the occurrence of adverse 

effects (II.B.2.b.i, II.C.4.b, II.C.4.c, 

below), she becomes increasingly 

concerned about the potential for 

adverse responses as the number of 

occurrences increases.110 In particular, 

as discussed above with regard to 

inflammation, she notes that the types 

of lung injury shown to occur following 

exposures to O3 concentrations from 60 

to 80 ppb, particularly if experienced 

repeatedly, provide a mode of action by 

which O3 may cause other more serious 

effects (e.g., asthma exacerbations). 

Therefore, the Administrator places the 

most weight on estimates of two or more 

exposures of concern (i.e., as a surrogate 

for the occurrence of repeated 

exposures), though she also considers 

estimates of one or more exposures for 

the 70 and 80 ppb benchmarks. 

In considering estimates of exposures 

of concern, the Administrator first notes 

that if the 15 urban study areas 

evaluated in the HREA were to just meet 

the current O3 standard, fewer than 1% 

of children in those areas would be 

estimated to experience two or more 

exposures of concern at or above 70 

ppb, based on exposure estimates 

averaged over the years of analysis, 

though up to about 2% would be 

estimated to experience such exposures 

in the worst-case year and location (i.e., 

year and location with the largest 

exposure estimates).111 Although the 

Administrator is less concerned about 

single occurrences of exposures of 

concern, she notes that even single 

occurrences could cause adverse effects 

in some people, particularly for the 70 

and 80 ppb benchmarks.112 As 

illustrated in Table 1 (above), the 

current standard could allow up to 

about 3% of children to experience one 

or more exposures of concern at or 

above 70 ppb, averaged over the years 

of analysis, and up to about 8% in the 

worst-case year and location. In 

addition, in the worst-case year and 

location, the current standard could 

allow about 1% of children to 

experience at least one exposure of 

concern at or above 80 ppb, the highest 

benchmark evaluated. 

While the Administrator has less 

confidence in the adversity of the effects 

observed following exposures to 60 ppb 

O3 (II.B.2.b.i, II.C.4.b, II.C.4.c), 

particularly for single exposures, she 

judges that the potential for adverse 

effects increases as the number of 

exposures of concern increases. With 

regard to the 60 ppb benchmark, she 

particularly notes that the current 

standard is estimated to allow 

approximately 3 to 8% of children in 

urban study areas, including 

approximately 3 to 8% of asthmatic 

children, to experience two or more 

exposures of concern to O3

concentrations at or above 60 ppb, based 

on estimates averaged over the years of 

analysis. To provide some perspective 

on the average percentages estimated, 

the Administrator notes that they 

correspond to almost 900,000 children 

in urban study areas, including about 

90,000 asthmatic children. Nationally, if 

the current standard were to be just met, 

the number of children experiencing 

such exposures would be larger. 

Based on her consideration of these 

estimates within the context of her 

judgments on adversity, as discussed in 

her responses to public comments 

(II.B.2.b.i, II.C.4.b), the Administrator 

concludes that the exposures projected 

to remain upon meeting the current 

standard can reasonably be judged to be 

important from a public health 

perspective. In particular, given that the 

average percent of children estimated to 

experience two or more exposures of 

concern for the 60 ppb benchmark 

approaches 10% in some areas, even 

based on estimates averaged over the 

mstockstill on DSK4VPTVN1PROD with RULES2

65346 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

113Though this advice is less clear regarding the 

adversity of effects at 60 ppb than CASAC’s advice 

regarding the adversity of effects at 72 ppb (II.C.4.b, 

II.C.4.c). 

114Courts have repeatedly held that this type of 

evidence justifies an Administrator’s conclusion 

that it is ‘‘appropriate’’ (within the meaning of 

section 109 (d)(1) of the CAA) to revise a primary 

NAAQS to provide further protection of public 

health. See e.g. Mississippi, 744 F. 3d at 1345; 

American Farm Bureau, 559 F. 3d at 525–26. 

years of the analysis, she concludes that 

the current standard does not 

incorporate an adequate margin of safety 

against the potentially adverse effects 

that can occur following repeated 

exposures at or above 60 ppb. Although 

she has less confidence that the effects 

observed at 60 ppb are adverse, 

compared to the effects at and above 72 

ppb, she judges that this approach to 

considering the results for the 60 ppb 

benchmark is appropriate given CASAC 

advice, which clearly focuses the EPA 

on considering the effects observed at 60 

ppb (Frey, 2014c) (II.C.4.b, II.C.4.c 

below).113 This approach to considering 

estimated exposures of concern is 

consistent with setting standards that 

provide some safeguard against dangers 

to human health that are not fully 

certain (i.e., standards that incorporate 

an adequate margin of safety) (See, e.g., 

State of Mississippi, 744 F. 3d at 1353). 

In addition to estimated exposures of 

concern, the Administrator also 

considers HREA estimates of the risk of 

O3-induced FEV1 decrements ≥10 and 

15%. In doing so, she particularly notes 

CASAC advice that ‘‘estimation of FEV1

decrements of ≥15% is appropriate as a 

scientifically relevant surrogate for 

adverse health outcomes in active 

healthy adults, whereas an FEV1

decrement of ≥10% is a scientifically 

relevant surrogate for adverse health 

outcomes for people with asthma and 

lung disease’’ (Frey, 2014c, p. 3). The 

Administrator notes that while single 

occurrences of O3-induced lung 

function decrements could be adverse 

for some people, as discussed above 

(II.B.1), she agrees with the judgment in 

past reviews that a more general 

consensus view of the potential 

adversity of such decrements emerges as 

the frequency of occurrences increases. 

Therefore, as in the proposal, the 

Administrator focuses primarily on the 

estimates of two or more O3-induced 

lung function decrements. When 

averaged over the years evaluated in the 

HREA, the Administrator notes that the 

current standard is estimated to allow 

about 1 to 3% of children in the 15 

urban study areas (corresponding to 

almost 400,000 children) to experience 

two or more O3-induced lung function 

decrements ≥15%, and to allow about 8 

to 12% of children (corresponding to 

about 180,000 asthmatic children) to 

experience two or more O3-induced 

lung function decrements ≥10%. 

In further considering the HREA 

results, the Administrator considers the 

epidemiology-based risk estimates. As 

discussed in the proposal, compared to 

the weight given to HREA estimates of 

exposures of concern and lung function 

risks, she places relatively less weight 

on epidemiology-based risk estimates. 

In giving some consideration to these 

risk estimates, as discussed in the 

proposal and above in the EPA’s 

responses to public comments 

(II.B.2.b.iii), the Administrator focuses 

on the risks associated with O3

concentrations in the upper portions of 

ambient distributions. In doing so, she 

notes the increasing uncertainty 

associated with the shapes of 

concentration-response curves for O3

concentrations in the lower portions of 

ambient distributions and the evidence 

from controlled human exposure 

studies, which provide the strongest 

support for O3-induced effects following 

exposures to O3 concentrations 

corresponding to the upper portions of 

typical ambient distributions (i.e., 60 

ppb and above). Even when considering 

only area-wide O3 concentrations from 

the upper portions of seasonal 

distributions (i.e., ≥40, 60 ppb, Table 3 

in the proposal), the Administrator 

notes that the general magnitude of 

mortality risk estimates suggests the 

potential for a substantial number of O3- 

associated deaths and adverse 

respiratory events to occur nationally, 

even when the current standard is met 

(79 FR 75277 and II.B.2.c.iii above). 

In addition to the evidence and 

exposure/risk information discussed 

above, the Administrator also takes note 

of the CASAC advice in the current 

review, in the 2008 review and decision 

establishing the current standard, and in 

the 2010 reconsideration of the 2008 

decision. As discussed in more detail 

above, the current CASAC ‘‘finds that 

the current NAAQS for ozone is not 

protective of human health’’ and 

‘‘unanimously recommends that the 

Administrator revise the current 

primary ozone standard to protect 

public health’’ (Frey, 2014c, p. 5). The 

prior CASAC O3 Panel likewise 

recommended revision of the current 

standard to one with a lower level due 

to the lack of protectiveness of the 

current standard. This earlier 

recommendation was based entirely on 

the evidence and information in the 

record for the 2008 standard decision, 

which, as discussed above, has been 

substantially strengthened in the current 

review (Samet, 2011; Frey and Samet, 

2012). 

In consideration of all of the above, 

the Administrator concludes that the 

current primary O3 standard is not 

requisite to protect public health with 

an adequate margin of safety, and that 

it should be revised to provide 

increased public health protection. This 

decision is based on the Administrator’s 

conclusions that the available evidence 

and exposure and risk information 

clearly call into question the adequacy 

of public health protection provided by 

the current primary standard such that 

it is not appropriate, within the meaning 

of section 109(d)(1) of the CAA, to retain 

the current standard. With regard to the 

evidence, she particularly notes that the 

current standard level is higher than the 

lowest O3 exposure concentration 

shown to result in the adverse 

combination of lung function 

decrements and respiratory symptoms 

(i.e., 72 ppb), and also notes CASAC’s 

advice that at-risk groups (e.g., people 

with asthma) could experience adverse 

effects following exposure to lower 

concentrations. In addition, while the 

Administrator is less certain about the 

adversity of the effects that occur 

following lower exposure 

concentrations, she judges that recent 

controlled human exposure studies at 

60 ppb provide support for a level 

below 75 ppb in order to provide an 

increased margin of safety, compared to 

the current standard, against effects 

with the potential to be adverse, 

particularly if they are experienced 

repeatedly. With regard to O3

epidemiologic studies, she notes that 

while most available studies reported 

health effect associations with ambient 

O3 concentrations that violated the 

current standard, a small number 

provide support for the occurrence of 

adverse respiratory effects at ambient O3

concentrations below the level of the 

current standard.114

Based on the analyses in the HREA, 

the Administrator concludes that the 

exposures and risks projected to remain 

upon meeting the current standard can 

reasonably be judged to be important 

from a public health perspective. In 

particular, this conclusion is based on 

her judgment that it is appropriate to set 

a standard that would be expected to 

eliminate, or almost eliminate, 

exposures of concern at or above 70 and 

80 ppb. In addition, given that the 

average percent of children estimated to 

experience two or more exposures of 

concern for the 60 ppb benchmark 

approaches 10% in some urban study 

areas, the Administrator concludes that 

the current standard does not 

incorporate an adequate margin of safety 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65347 

115The DC Circuit upheld the use of O3 as the 

indicator for photochemical oxidants based on 

these same considerations. American Petroleum 

Inst. v. Costle, 665 F. 2d 1176, 1186 (D.C. Cir. 1981). 

116This 8-hour averaging time reflects daily 

maximum 8-hour average O3 concentrations. 

against the potentially adverse effects 

that could occur following repeated 

exposures at or above 60 ppb. Beyond 

estimated exposures of concern, the 

Administrator concludes that the HREA 

risk estimates (FEV1 risk estimates, 

mortality risk estimates) further support 

a conclusion that the O3-associated 

health effects estimated to remain upon 

just meeting the current standard are an 

issue of public health importance on a 

broad national scale. Thus, she 

concludes that O3 exposure and risk 

estimates, when taken together, support 

a conclusion that the exposures and 

health risks associated with just meeting 

the current standard can reasonably be 

judged important from a public health 

perspective, such that the current 

standard is not sufficiently protective 

and does not incorporate an adequate 

margin of safety. 

In the next section, the Administrator 

considers what revisions are appropriate 

in order to set a standard that is 

requisite to protect public health with 

an adequate margin of safety. 

C. Conclusions on the Elements of a 

Revised Primary Standard 

Having reached the conclusion that 

the current O3 standard is not requisite 

to protect public health with an 

adequate margin of safety, based on the 

currently available scientific evidence 

and exposure/risk information, the 

Administrator next considers the range 

of alternative standards supported by 

that evidence and information. 

Consistent with her consideration of the 

adequacy of the current standard, the 

Administrator’s conclusions on the 

elements of the primary standard are 

informed by the available scientific 

evidence assessed in the ISA, exposure/ 

risk information presented and assessed 

in the HREA, the evidence-based and 

exposure-/risk-based considerations and 

conclusions in the PA, CASAC advice, 

and public comments. The sections 

below discuss the evidence and 

exposure/risk information, CASAC 

advice and public input, and the 

Administrator’s proposed conclusions, 

for the major elements of the NAAQS: 

Indicator (II.C.1), averaging time (II.C.2), 

form (II.C.3), and level (II.C.4). 

1. Indicator 

In the 2008 review, the EPA focused 

on O3 as the most appropriate indicator 

for a standard meant to provide 

protection against ambient 

photochemical oxidants. In this review, 

while the complex atmospheric 

chemistry in which O3 plays a key role 

has been highlighted, no alternatives to 

O3 have been advanced as being a more 

appropriate indicator for ambient 

photochemical oxidants. More 

specifically, the ISA noted that O3 is the 

only photochemical oxidant (other than 

NO2) that is routinely monitored and for 

which a comprehensive database exists 

(U.S. EPA, 2013, section 3.6). Data for 

other photochemical oxidants (e.g., 

peroxyacetyl nitrate, hydrogen peroxide, 

etc.) typically have been obtained only 

as part of special field studies. 

Consequently, no data on nationwide 

patterns of occurrence are available for 

these other oxidants; nor are extensive 

data available on the relationships of 

concentrations and patterns of these 

oxidants to those of O3 (U.S. EPA, 2013, 

section 3.6). In its review of the second 

draft PA, CASAC stated ‘‘The indicator 

of ozone is appropriate based on its 

causal or likely causal associations with 

multiple adverse health outcomes and 

its representation of a class of pollutants 

known as photochemical oxidants’’ 

(Frey, 2014c, p. ii). 

In addition, the PA notes that meeting 

an O3 standard can be expected to 

provide some degree of protection 

against potential health effects that may 

be independently associated with other 

photochemical oxidants, even though 

such effects are not discernible from 

currently available studies indexed by 

O3 alone (U.S. EPA, 2014c, section 4.1). 

That is, since the precursor emissions 

that lead to the formation of O3

generally also lead to the formation of 

other photochemical oxidants, measures 

leading to reductions in population 

exposures to O3 can generally be 

expected to lead to reductions in 

population exposures to other 

photochemical oxidants. In considering 

this information, and CASAC’s advice, 

the Administrator reached the proposed 

conclusion that O3 remains the most 

appropriate indicator for a standard 

meant to provide protection against 

photochemical oxidants.115

The EPA received very few comments 

on the indicator of the primary 

standard. Those who did comment 

supported the proposed decision to 

retain O3 as the indicator, noting the 

rationale put forward in the preamble to 

the proposed rule. These commenters 

generally expressed support for 

retaining the current indicator in 

conjunction with retaining other 

elements of the current standard, such 

as the averaging time and form. After 

considering the available evidence, 

CASAC advice, and public comments, 

the Administrator concludes that O3

remains the most appropriate indicator 

for a standard meant to provide 

protection against photochemical 

oxidants. Therefore, she is retaining O3

as the indicator for the primary standard 

in this final rule. 

2. Averaging Time 

The EPA established the current 8- 

hour averaging time 116 for the primary 

O3 NAAQS in 1997 (62 FR 38856). The 

decision on averaging time in that 

review was based on numerous 

controlled human exposure and 

epidemiologic studies reporting 

associations between adverse 

respiratory effects and 6- to 8-hour O3

concentrations (62 FR 38861). The EPA 

also noted that a standard with a 

maximum 8-hour averaging time is 

likely to provide substantial protection 

against respiratory effects associated 

with 1-hour peak O3 concentrations. 

The EPA reached similar conclusions in 

the last O3 NAAQS review and thus, the 

EPA retained the 8-hour averaging time 

in 2008. 

In reaching a proposed conclusion on 

averaging time in the current review, the 

Administrator considered the extent to 

which the available evidence continues 

to support the appropriateness of a 

standard with an 8-hour averaging time 

(79 FR 75292). Specifically, the 

Administrator considered the extent to 

which the available information 

indicates that a standard with the 

current 8-hour averaging time provides 

appropriate protection against shortand long-term O3 exposures. These 

considerations from the proposal are 

summarized below in sections II.C.2.a 

(short-term) and II.C.2.b (long-term). 

Section II.C.2.c summarizes the 

Administrator’s proposed decision on 

averaging time. Section II.C.2.d 

discusses comments received on 

averaging time. Section II.C.2.e presents 

the Administrator’s final decision 

regarding averaging time. 

a. Short-Term 

As an initial consideration with 

respect to the most appropriate 

averaging time for the O3 NAAQS, in the 

proposal the Administrator noted that 

the strongest evidence for O3-associated 

health effects is for respiratory effects 

following short-term exposures. More 

specifically, the Administrator noted the 

ISA conclusion that the evidence is 

‘‘sufficient to infer a causal 

relationship’’ between short-term O3

exposures and respiratory effects. The 

ISA also judges that for short-term O3

exposures, the evidence indicates 

‘‘likely to be causal’’ relationships with 

mstockstill on DSK4VPTVN1PROD with RULES2

65348 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

117Though the Administrator also notes 

important uncertainties associated with these risk 

estimates, as discussed in section II.C.3.b of the 

proposal. 

both cardiovascular effects and 

mortality (U.S. EPA, 2013, section 

2.5.2). Therefore, as in past reviews, the 

Administrator noted that the strength of 

the available scientific evidence 

provides strong support for a standard 

that protects the public health against 

short-term exposures to O3. 

In first considering the level of 

support available for specific short-term 

averaging times, the Administrator 

noted in the proposal the evidence 

available from controlled human 

exposure studies. As discussed in more 

detail in Chapter 3 of the PA, substantial 

health effects evidence from controlled 

human exposure studies demonstrates 

that a wide range of respiratory effects 

(e.g., pulmonary function decrements, 

increases in respiratory symptoms, lung 

inflammation, lung permeability, 

decreased lung host defense, and airway 

hyperresponsiveness) occur in healthy 

adults following 6.6-hour exposures to 

O3 (U.S. EPA, 2013, section 6.2.1.1). 

Compared to studies evaluating shorter 

exposure durations (e.g., 1-hour), 

studies evaluating 6.6-hour exposures in 

healthy adults have reported respiratory 

effects at lower O3 exposure 

concentrations and at more moderate 

levels of exertion. 

The Administrator also noted in the 

proposal the strength of evidence from 

epidemiologic studies that evaluated a 

wide variety of populations (e.g., 

including at-risk lifestages and 

populations, such as children and 

people with asthma, respectively). A 

number of different averaging times 

have been used in O3 epidemiologic 

studies, with the most common being 

the max 1-hour concentration within a 

24-hour period (1-hour max), the max 8- 

hour average concentration within a 24- 

hour period (8-hour max), and the 24- 

hour average. These studies are assessed 

in detail in Chapter 6 of the ISA (U.S. 

EPA, 2013). Limited evidence from 

time-series and panel epidemiologic 

studies comparing risk estimates across 

averaging times does not indicate that 

one exposure metric is more 

consistently or strongly associated with 

respiratory health effects or mortality, 

though the ISA notes some evidence for 

‘‘smaller O3 risk estimates when using a 

24-hour average exposure metric’’ (U.S. 

EPA, 2013, section 2.5.4.2; p. 2–31). For 

single- and multi-day average O3

concentrations, lung function 

decrements were associated with 1-hour 

max, 8-hour max, and 24-hour average 

ambient O3 concentrations, with no 

strong difference in the consistency or 

magnitude of association among the 

averaging times (U.S. EPA, 2013, p. 6– 

71). Similarly, in studies of short-term 

exposure to O3 and mortality, Smith et 

al. (2009) and Darrow et al. (2011) have 

reported high correlations between risk 

estimates calculated using 24-hour 

average, 8-hour max, and 1-hour max 

averaging times (U.S. EPA, 2013, p. 6– 

253). Thus, the Administrator noted that 

the epidemiologic evidence alone does 

not provide a strong basis for 

distinguishing between the 

appropriateness of 1-hour, 8-hour, and 

24-hour averaging times. 

Considering the health information 

discussed above, in the proposal the 

Administrator concluded that an 8-hour 

averaging time remains appropriate for 

addressing health effects associated 

with short-term exposures to ambient 

O3. An 8-hour averaging time is similar 

to the exposure periods evaluated in 

controlled human exposure studies, 

including recent studies that provide 

evidence for respiratory effects 

following exposures to O3

concentrations below the level of the 

current standard. In addition, 

epidemiologic studies provide evidence 

for health effect associations with 8- 

hour O3 concentrations, as well as with 

1-hour and 24-hour concentrations. As 

in previous reviews, the Administrator 

noted that a standard with an 8-hour 

averaging time (combined with an 

appropriate standard form and level) 

would also be expected to provide 

substantial protection against health 

effects attributable to 1-hour and 24- 

hour exposures (e.g., 62 FR 38861, July 

18, 1997). This conclusion is consistent 

with the advice received from CASAC 

that ‘‘the current 8-hour averaging time 

is justified by the combined evidence 

from epidemiologic and clinical 

studies’’ (Frey, 2014c, p. 6). 

b. Long-Term 

The ISA concludes that the evidence 

for long-term O3 exposures indicates 

that there is ‘‘likely to be a causal 

relationship’’ with respiratory effects 

(U.S. EPA, 2013, chapter 7). Thus, in 

this review the Administrator also 

considers the extent to which currently 

available evidence and exposure/risk 

information suggests that a standard 

with an 8-hour averaging time can 

provide protection against respiratory 

effects associated with longer term 

exposures to ambient O3. 

In considering this issue in the 2008 

review of the O3 NAAQS, the Staff 

Paper noted that ‘‘because long-term air 

quality patterns would be improved in 

areas coming into attainment with an 8- 

hr standard, the potential risk of health 

effects associated with long-term 

exposures would be reduced in any area 

meeting an 8-hr standard’’ (U.S. EPA, 

2007, p. 6–57). In the current review, 

the PA further evaluates this issue, with 

a focus on the long-term O3 metrics 

reported to be associated with mortality 

or morbidity in recent epidemiologic 

studies. As discussed in section 3.1.3 of 

the PA (U.S. EPA, 2014c, section 4.2), 

much of the recent evidence for such 

associations is based on studies that 

defined long-term O3 in terms of 

seasonal averages of daily maximum 1- 

hour or 8-hour concentrations. 

As an initial consideration, in the 

proposal the Administrator noted the 

risk results from the HREA for 

respiratory mortality associated with 

long-term O3 concentrations. These 

HREA analyses indicate that as air 

quality is adjusted to just meet the 

current 8-hour standard, most urban 

study areas are estimated to experience 

reductions in respiratory mortality 

associated with long-term O3

concentrations based on the seasonal 

averages of 1-hour daily maximum O3

concentrations evaluated in the study by 

Jerrett et al. (2009) (U.S. EPA, 2014a, 

chapter 7).117 As air quality is adjusted 

to meet lower alternative standard 

levels, for standards based on 3-year 

averages of the annual fourth-highest 

daily maximum 8-hour O3

concentrations, respiratory mortality 

risks are estimated to be reduced further 

in urban study areas. This analysis 

indicates that an O3 standard with an 8- 

hour averaging time, when coupled with 

an appropriate form and level, can 

reduce respiratory mortality reported to 

be associated with long-term O3

concentrations. 

In further considering the study by 

Jerrett et al. (2009), in the proposal the 

Administrator noted the PA comparison 

of long-term O3 concentrations 

following model adjustment in urban 

study areas (i.e., adjusted to meet the 

current and alternative 8-hour 

standards) to the concentrations present 

in study cities that provided the basis 

for the positive and statistically 

significant association with respiratory 

mortality. As indicated in Table 4–3 of 

the PA (U.S. EPA, 2014c, section 4.2), 

this comparison suggests that a standard 

with an 8-hour averaging time can 

decrease seasonal averages of 1-hour 

daily maximum O3 concentrations, and 

can maintain those O3 concentrations 

below the seasonal average 

concentration where the study indicates 

the most confidence in the reported 

concentration-response relationship 

with respiratory mortality (U.S. EPA, 

2014c, sections 4.2 and 4.4.1). 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65349 

The Administrator also noted in the 

proposal that the HREA conducted 

analyses evaluating the impacts of 

reducing regional NOX emissions on the 

seasonal averages of daily maximum 8- 

hour O3 concentrations. Seasonal 

averages of 8-hour daily max O3

concentrations reflect long-term metrics 

that have been reported to be associated 

with respiratory morbidity effects in 

several recent O3 epidemiologic studies 

(e.g., Islam et al., 2008; Lin et al., 2008a, 

2008b; Salam et al., 2009). The HREA 

analyses indicate that the large majority 

of the U.S. population lives in locations 

where reducing NOX emissions would 

be expected to result in decreases in 

seasonal averages of daily max 8-hour 

ambient O3 concentrations (U.S. EPA, 

2014a, chapter 8). Thus, consistent with 

the respiratory mortality risk estimates 

noted above, these analyses suggest that 

reductions in O3 precursor emissions in 

order to meet a standard with an 8-hour 

averaging time would also be expected 

to reduce the long-term O3

concentrations that have been reported 

in recent epidemiologic studies to be 

associated with respiratory morbidity. 

c. Administrator’s Proposed Conclusion 

on Averaging Time 

In the proposal the Administrator 

noted that, when taken together, the 

analyses summarized above indicate 

that a standard with an 8-hour averaging 

time, coupled with the current fourthhigh form and an appropriate level, 

would be expected to provide 

appropriate protection against the shortand long-term O3 concentrations that 

have been reported to be associated with 

respiratory morbidity and mortality. The 

CASAC agreed with this conclusion, 

stating that ‘‘[t]he current 8-hour 

averaging time is justified by the 

combined evidence from epidemiologic 

and clinical studies’’ and that ‘‘[t]he 8- 

hour averaging window also provides 

protection against the adverse impacts 

of long-term ozone exposures, which 

were found to be ‘‘likely causal’’ for 

respiratory effects and premature 

mortality’’ (Frey, 2014c, p. 6). Therefore, 

considering the available evidence and 

exposure risk information, and CASAC’s 

advice, the Administrator proposed to 

retain the current 8-hour averaging time, 

and not to set an additional standard 

with a different averaging time. 

d. Comments on Averaging Time 

Most public commenters did not 

address the issue of whether the EPA 

should consider additional or 

alternative averaging times. Of those 

who did address this issue, some 

commenters representing state agencies 

or industry groups agreed with the 

proposed decision to retain the current 

8-hour averaging time, generally noting 

the supportive evidence discussed in 

the preamble to the proposed rule. In 

contrast, several medical organizations 

and environmental groups questioned 

the degree of health protection provided 

by a standard based on an 8-hour 

averaging time. For example, one group 

asserted that ‘‘[a]veraging over any time 

period, such as 8 hours, is capable of 

hiding peaks that may be very 

substantial if they are brief enough.’’ 

The EPA agrees with these 

commenters that an important issue in 

the current review is the 

appropriateness of using a standard 

with an 8-hour averaging time to protect 

against adverse health effects that are 

attributable to a wide range of O3

exposure durations, including those 

shorter and longer than 8 hours. This is 

an issue that has been thoroughly 

evaluated by the EPA in past reviews, as 

well as in the current review. 

The 8-hour O3 NAAQS was originally 

set in 1997, as part of revising the thenexisting standard with its 1-hour 

averaging time, and was retained in the 

review completed in 2008 (73 FR 

16472). In both of these reviews, several 

lines of evidence and information 

provided support for an 8-hour 

averaging time rather than a shorter 

averaging time. For example, substantial 

health evidence demonstrated 

associations between a wide range of 

respiratory effects and 6- to 8-hour 

exposures to relatively low O3

concentrations (i.e., below the level of 

the 1-hour O3 NAAQS in place prior to 

the review completed in 1997). A 

standard with an 8-hour averaging time 

was determined to be more directly 

associated with health effects of concern 

at lower O3 concentrations than a 

standard with a 1-hour averaging time. 

In addition, results of quantitative 

analyses showed that a standard with an 

8-hour averaging time can effectively 

limit both 1- and 8-hour exposures of 

concern, and that an 8-hour averaging 

time results in a more uniformly 

protective national standard than a 1- 

hour averaging time. In past reviews, 

CASAC has agreed that an 8-hour 

averaging time is appropriate. 

In reaching her proposed decision to 

retain the 8-hour averaging time in the 

current review, the Administrator again 

considered the body of evidence for 

adverse effects attributable to a wide 

range of O3 exposure durations, 

including studies specifically referenced 

by public commenters who questioned 

the protectiveness of a standard with an 

8-hour averaging time. For example, as 

noted above a substantial body of health 

effects evidence from controlled human 

exposure studies demonstrates that a 

wide range of respiratory effects occur 

in healthy adults following 6.6-hour 

exposures to O3 (U.S. EPA, 2013, section 

6.2.1.1). Compared to studies evaluating 

shorter exposure durations (e.g., 1- 

hour), studies evaluating 6.6-hour 

exposures in healthy adults have 

reported respiratory effects at lower O3

exposure concentrations and at more 

moderate levels of exertion. The 

Administrator also noted the strength of 

evidence from epidemiologic studies 

that evaluated a number of different 

averaging times, with the most common 

being the maximum 1-hour 

concentration within a 24-hour period 

(1-hour max), the maximum 8-hour 

average concentration within a 24-hour 

period (8-hour max), and the 24-hour 

average. Evidence from time-series and 

panel epidemiologic studies comparing 

risk estimates across averaging times 

does not indicate that one exposure 

metric is more consistently or strongly 

associated with respiratory health 

effects or mortality (U.S. EPA, 2013, 

section 2.5.4.2; p. 2–31). For single- and 

multi-day average O3 concentrations, 

lung function decrements were 

associated with 1-hour max, 8-hour 

max, and 24-hour average ambient O3

concentrations, with no strong 

difference in the consistency or 

magnitude of association among the 

averaging times (U.S. EPA, 2013, p. 6– 

71). Similarly, in studies of short-term 

exposure to O3 and mortality, Smith et 

al. (2009) and Darrow et al. (2011) have 

reported high correlations between risk 

estimates calculated using 24-hour 

average, 8-hour max, and 1-hour max 

averaging times (U.S. EPA, 2013, p. 6– 

253). Thus, the epidemiologic evidence 

does not provide a strong basis for 

distinguishing between the 

appropriateness of 1-hour, 8-hour, and 

24-hour averaging times. 

In addition, quantitative exposure and 

risk analyses in the HREA are based on 

an air quality adjustment approach that 

estimates hourly O3 concentrations, and 

on scientific studies that evaluated 

health effects attributable to a wide 

range of O3 exposure durations. For 

example, the risk of lung function 

decrements is estimated using a model 

based on controlled human exposure 

studies with exposure durations ranging 

from 2 to 7.6 hours (U.S. EPA, 2013, 

section 6.2.1.1). Epidemiology-based 

risk estimates are based on studies that 

reported health effect associations with 

short-term ambient O3 concentrations 

ranging from 1-hour to 24-hours and 

with long-term seasonal average 

concentrations (U.S. EPA, 2014a, Table 

7–2). Thus, the HREA estimated health 

mstockstill on DSK4VPTVN1PROD with RULES2

65350 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

118For a standard with a 1-expected-exceedance 

form to be met at an air quality monitoring site, the 

fourth-highest air quality value in 3 years, given 

adjustments for missing data, must be less than or 

equal to the level of the standard. 

119As discussed (61 FR 65731), this is because 

with an exceedance-based form, days on which the 

ambient O3 concentration is well above the level of 

the standard are given equal weight to those days 

on which the O3 concentration is just above the 

standard (i.e., each day is counted as one 

exceedance), even though the public health impact 

of such days would be very different. With a 

concentration-based form, days on which higher O3

concentrations occur would weigh proportionally 

more than days with lower O3 concentrations since 

the actual concentrations are used directly to 

calculate whether the standard is met or violated. 

120See American Trucking Assn’s v. EPA, 283 F. 

3d at 374–75 (less stable implementation programs 

may be less effective and would thereby provide 

less public health protection; EPA may therefore 

legitimately consider programmatic stability in 

determining the form of a NAAQS). 

risks associated with a wide range of O3

exposure durations and the 

Administrator’s conclusions on 

averaging time in the current review are 

based, in part, on consideration of these 

estimates. 

When taken together, the evidence 

and analyses indicate that a standard 

with an 8-hour averaging time, coupled 

with the current fourth-high form and 

an appropriate level, would be expected 

to provide appropriate protection 

against the short- and long-term O3

concentrations that have been reported 

to be associated with respiratory 

morbidity and mortality. The CASAC 

agreed with this, stating the following 

(Frey, 2014c, p. 6): 

The current 8-hour averaging time is 

justified by the combined evidence from 

epidemiologic and clinical studies referenced 

in Chapter 4. Results from clinical studies, 

for example, show a wide range of respiratory 

effects in healthy adults following 6.6 hours 

of exposure to ozone, including pulmonary 

function decrements, increases in respiratory 

symptoms, lung inflammation, lung 

permeability, decreased lung host defense, 

and airway hyperresponsiveness. These 

findings are supported by evidence from 

epidemiological studies that show causal 

associations between short-term exposures of 

1, 8 and 24-hours and respiratory effects and 

‘‘likely to be causal’’ associations for 

cardiovascular effects and premature 

mortality. The 8-hour averaging window also 

provides protection against the adverse 

impacts of long-term ozone exposures, which 

were found to be ‘‘likely causal’’ for 

respiratory effects and premature mortality. 

Given all of the above, the EPA 

disagrees with commenters who 

question the protectiveness of an O3

standard with an 8-hour averaging time, 

particularly for an 8-hour standard with 

the revised level of 70 ppb that is being 

established in this review, as discussed 

below (II.C.4). 

e. Administrator’s Final Decision 

Regarding Averaging Time 

In considering the evidence and 

information summarized in the proposal 

and discussed in detail in the ISA, 

HREA, and PA; CASAC’s views; and 

public comments, the Administrator 

concludes that a standard with an 8- 

hour averaging time can effectively limit 

health effects attributable to both shortand long-term O3 exposures. As was the 

case in the proposal, this final 

conclusion is based on (1) the strong 

evidence that continues to support the 

importance of protecting public health 

against short-term O3 exposures (e.g., ≤ 

1-hour to 24-hour) and (2) analyses in 

the HREA and PA supporting the 

conclusion that the current 8-hour 

averaging time can effectively limit 

long-term O3 exposures. Furthermore, 

the Administrator observes that the 

CASAC Panel agreed with the choice of 

averaging time (Frey, 2014c). Therefore, 

in the current review, the Administrator 

concludes that it is appropriate to retain 

the 8-hour averaging time and to not set 

a separate standard with a different 

averaging time in this final rule. 

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 that 

standard. The foremost consideration in 

selecting a form is the adequacy of the 

public health protection provided by the 

combination of the form and the other 

elements of the standard. In this review, 

the Administrator considers the extent 

to which the available evidence and/or 

information continue to support the 

appropriateness of a standard with the 

current form, defined by the 3-year 

average of annual fourth-highest 8-hour 

daily maximum O3 concentrations. 

Section II.C.3.a below summarizes the 

basis for the current form. Section 

II.C.3.b discusses the Administrator’s 

proposed decision to retain the current 

form. Section II.C.3.c discusses public 

comments received on the form of the 

primary standard. Section II.C.3.d 

discusses the Administrator’s final 

decision on form. 

a. Basis for the Current Form 

The EPA established the current form 

of the primary O3 NAAQS in 1997 (62 

FR 38856). Prior to that time, the 

standard had a ‘‘1-expectedexceedance’’ form.118 An advantage of 

the current concentration-based form 

recognized in the 1997 review is that 

such a form better reflects the 

continuum of health effects associated 

with increasing ambient O3

concentrations. Unlike an expected 

exceedance form, a concentration-based 

form gives proportionally more weight 

to years when 8-hour O3 concentrations 

are well above the level of the standard 

than years when 8-hour O3

concentrations are just above the level 

of the standard.119 The EPA judged it 

appropriate to give more weight to 

higher O3 concentrations, given that 

available health evidence indicated a 

continuum of effects associated with 

exposures to varying concentrations of 

O3, and given that the extent to which 

public health is affected by exposure to 

ambient O3 is related to the actual 

magnitude of the O3 concentration, not 

just whether the concentration is above 

a specified level. 

During the 1997 review, the EPA 

considered a range of alternative 

‘‘concentration-based’’ forms, including 

the second-, third-, fourth- and fifthhighest daily maximum 8-hour 

concentrations in an O3 season. The 

fourth-highest daily maximum was 

selected, recognizing that a less 

restrictive form (e.g., fifth-highest) 

would allow a larger percentage of sites 

to experience O3 peaks above the level 

of the standard, and would allow more 

days on which the level of the standard 

may be exceeded when the site attains 

the standard (62 FR 38856). The EPA 

also considered setting a standard with 

a form that would provide a margin of 

safety against possible but uncertain 

chronic effects, and would provide 

greater stability to ongoing control 

programs.120 A more restrictive form 

was not selected, recognizing that the 

differences in the degree of protection 

afforded by the alternatives were not 

well enough understood to use any such 

differences as a basis for choosing the 

most restrictive forms (62 FR 38856). 

In the 2008 review, the EPA 

additionally considered the potential 

value of a percentile-based form. In 

doing so, the EPA recognized that such 

a statistic is useful for comparing 

datasets of varying length because it 

samples approximately the same place 

in the distribution of air quality values, 

whether the dataset is several months or 

several years long. However, the EPA 

concluded that a percentile-based 

statistic would not be effective in 

ensuring the same degree of public 

health protection across the country. 

Specifically, a percentile-based form 

would allow more days with higher air 

quality values in locations with longer 

O3 seasons relative to locations with 

shorter O3 seasons. Thus, in the 2008 

review, the EPA concluded that a form 

based on the nth-highest maximum O3

concentration would more effectively 

ensure that people who live in areas 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65351 

with different length O3 seasons receive 

the same degree of public health 

protection. 

Based on analyses of forms specified 

in terms of an nth-highest concentration 

(n ranged from 3 to 5), advice from 

CASAC, and public comment, the 

Administrator concluded that a fourthhighest daily maximum should be 

retained (73 FR 16465, March 27, 2008). 

In reaching this decision, the 

Administrator recognized that ‘‘there is 

not a clear health-based threshold for 

selecting a particular nth-highest daily 

maximum form of the standard’’ and 

that ‘‘the adequacy of the public health 

protection provided by the combination 

of the level and form is a foremost 

consideration’’ (73 FR 16475, March 27, 

2008). Based on this, the Administrator 

judged that the existing form (fourthhighest daily maximum 8-hour average 

concentration) should be retained, 

recognizing the increase in public 

health protection provided by 

combining this form with a lower 

standard level (i.e., 75 ppb). 

The Administrator also recognized 

that it is important to have a form that 

provides stability with regard to 

implementation of the standard. In the 

case of O3, for example, he noted the 

importance of a form insulated from the 

impacts of extreme meteorological 

events that are conducive to O3

formation. Such events could have the 

effect of reducing public health 

protection, to the extent they result in 

frequent shifts in and out of attainment 

due to meteorological conditions. The 

Administrator noted that such frequent 

shifting could disrupt an area’s ongoing 

implementation plans and associated 

control programs (73 FR 16474, March 

27, 2008). In his final decision, the 

Administrator judged that a fourth-high 

form ‘‘provides a stable target for 

implementing programs to improve air 

quality’’ (id. at 16475). 

b. Proposed Decision on Form 

In the proposal for the current review, 

the Administrator considered the extent 

to which newly available information 

provides support for the current form 

(79 FR 75293). In so doing, she took 

note of the conclusions of prior reviews 

summarized above. She recognized the 

value of an nth-high statistic over that 

of an expected exceedance or percentilebased form in the case of the O3

standard, for the reasons summarized 

above. The Administrator additionally 

took note of the importance of stability 

in implementation to achieving the level 

of protection specified by the NAAQS. 

Specifically, she noted that to the extent 

areas engaged in implementing the O3

NAAQS frequently shift from meeting 

the standard to violating the standard, it 

is possible that ongoing implementation 

plans and associated control programs 

could be disrupted, thereby reducing 

public health protection. 

In light of this, while giving foremost 

consideration to the adequacy of public 

health protection provided by the 

combination of all elements of the 

standard, including the form, the 

Administrator considered particularly 

the findings from prior reviews with 

regard to the use of the nth-high metric. 

As noted above, the EPA selected the 

fourth-highest daily maximum, 

recognizing the public health protection 

provided by this form, when coupled 

with an appropriate averaging time and 

level, and recognizing that such a form 

can provide stability for implementation 

programs. In the proposal the 

Administrator concluded that the 

currently available evidence and 

information do not call into question 

these conclusions from previous 

reviews. In reaching this initial 

conclusion, the Administrator noted 

that CASAC concurred that the O3

standard should be based on the fourthhighest, daily maximum 8-hour average 

value (averaged over 3 years), stating 

that this form ‘‘provides health 

protection while allowing for atypical 

meteorological conditions that can lead 

to abnormally high ambient ozone 

concentrations which, in turn, provides 

programmatic stability’’ (Frey, 2014c, p. 

6). Thus, a standard with the current 

fourth-high form, coupled with a level 

lower than 75 ppb as discussed below, 

would be expected to increase public 

health protection relative to the current 

standard while continuing to provide 

stability for implementation programs. 

Therefore, the Administrator proposed 

to retain the current fourth-highest daily 

maximum form for an O3 standard with 

an 8-hour averaging time and a revised 

level. 

c. Public Comments on Form 

Several commenters focused on the 

stability of the standard to support their 

positions regarding form. Some industry 

associations and state agencies support 

changing to a form that would allow a 

larger number of exceedances of the 

standard level than are allowed by the 

current fourth-high form. In some cases, 

these commenters argued that a 

standard allowing a greater number of 

exceedances would provide the same 

degree of public health protection as the 

current standard. Some commenters 

advocated a percentile-based form, such 

as the 98th percentile. These 

commenters cited a desire for 

consistency with short-term standards 

for other criteria pollutants (e.g., PM2.5, 

NO2), as well as a desire to allow a 

greater number of exceedances of the 

standard level, thus making the 

standard less sensitive to fluctuations in 

background O3 concentrations and to 

extreme meteorological events. 

Other commenters submitted analyses 

purporting to indicate that a fourth-high 

form provides only a small increase in 

stability, relative to forms that allow 

fewer exceedances of the standard level 

(i.e., first-high, second-high). These 

commenters also called into question 

the degree of health protection achieved 

by a standard with a fourth-high form 

and a level in the proposed range (i.e., 

65 to 70 ppb). They pointed out that a 

fourth-high form will, by definition, 

allow 3 days per year, on average, with 

8-hour O3 concentrations above the 

level of the standard. Commenters 

further stated that ‘‘[i]f ozone levels on 

these peak days are appreciably higher 

than on the fourth-highest day, given 

EPA’s acknowledged concerns regarding 

single or multiple (defined by EPA as 2 

or more) exposures to elevated ozone 

concentrations, EPA must account for 

the degree of under-protection in setting 

the level of the NAAQS’’ (e.g., ALA et 

al., p. 138). 

For the reasons discussed in the 

proposal, and summarized above, the 

EPA disagrees with commenters who 

supported a percentile-based form, such 

as the 98th percentile, for the O3

NAAQS. As noted above, a percentilebased statistic would not be effective in 

ensuring the same degree of public 

health protection across the country. 

Rather, a percentile-based form would 

allow more days with higher air quality 

values in locations with longer O3

seasons relative to locations with 

shorter O3 seasons. Thus, as in the 2008 

review, in the current review the EPA 

concludes that a form based on the nthhighest maximum O3 concentration 

would more effectively ensure that 

people who live in areas with different 

length O3 seasons receive the same 

degree of public health protection. 

In considering various nth-high 

values, as in past reviews (e.g., 73 FR 

16475, March 27, 2008), the EPA 

recognizes that there is not a clear 

health-based threshold for selecting a 

particular nth-highest daily maximum 

form. Rather, the primary consideration 

is the adequacy of the public health 

protection provided by the combination 

of all of the elements of the standard, 

including the form. Environmental and 

public health commenters are correct 

that a standard with the current fourthhigh form will allow 3 days per year, on 

average, with 8-hour O3 concentrations 

higher than the standard level. 

However, the EPA disagrees with these 

mstockstill on DSK4VPTVN1PROD with RULES2

65352 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

commenters’ assertion that using a 

fourth-high form results in a standard 

that is under-protective. The O3

exposure and risk estimates that 

informed the Administrator’s 

consideration of the degree of public 

health protection provided by various 

standard levels were based on air 

quality that ‘‘just meets’’ various 

standards with the current 8-hour 

averaging time and fourth-high, 3-year 

average form (U.S. EPA, 2014a, section 

4.3.3). Therefore, air quality adjusted to 

meet various levels of the standard with 

the current form and averaging time will 

include days with concentrations above 

the level of the standard, and these days 

contribute to exposure and risk 

estimates. In this way, the 

Administrator has reasonably 

considered the public health protection 

provided by the combination of all of 

the elements of the standard, including 

the fourth-high form. 

In past reviews, EPA selected the 

fourth-highest daily maximum form in 

recognition of the public health 

protection provided by this form, when 

coupled with an appropriate averaging 

time and level, and recognizing that 

such a form can provide stability for 

ongoing implementation programs. As 

noted above, some commenters 

submitted analyses suggesting that a 

fourth-high form provides only a small 

increase in stability, relative to a firstor second-high form. The EPA has 

conducted analyses of ambient O3

monitoring data to further consider 

these commenters’ assertions regarding 

stability. The EPA’s analyses of nth-high 

concentrations ranging from first-high to 

fifth-high have been summarized in a 

memo to the docket (Wells, 2015a). 

Consistent with commenters’ analyses, 

Wells (2015a) indicates a progressive 

decrease in the variability of O3

concentrations, and an increase in the 

stability of those concentrations, as ‘‘n’’ 

increases. Based on these analyses, there 

is no clear threshold for selecting a 

particular nth-high form based on 

stability alone. Rather, as in past 

reviews, the decision on form in this 

review focuses first and foremost on the 

Administrator’s judgments on public 

health protection, with judgments 

regarding stability of the standard being 

a legitimate, but secondary 

consideration. The Administrator’s final 

decision on form is discussed below. 

d. Administrator’s Final Decision 

Regarding Form 

In reaching a final decision on the 

form of the primary O3 standard, as 

described in the proposal and above, the 

Administrator recognizes that there is 

not a clear health-based rationale for 

selecting a particular nth-highest daily 

maximum form. Her foremost 

consideration is the adequacy of the 

public health protection provided by the 

combination of all of the elements of the 

standard, including the form. In this 

regard, the Administrator recognizes the 

support from analyses in previous 

reviews, and from the CASAC in the 

current review, for the conclusion that 

the current fourth-high form of the 

standard, when combined with a 

revised level as discussed below, 

provides an appropriate balance 

between public health protection and a 

stable target for implementing programs 

to improve air quality. In particular, she 

notes that the CASAC concurred that 

the O3 standard should be based on the 

fourth-highest, daily maximum 8-hour 

average value (averaged over 3 years), 

stating that this form ‘‘provides health 

protection while allowing for atypical 

meteorological conditions that can lead 

to abnormally high ambient ozone 

concentrations which, in turn, provides 

programmatic stability’’ (Frey, 2014c, p. 

6). Based on these considerations, and 

on consideration of public comments on 

form as discussed above, the 

Administrator judges it appropriate to 

retain the current fourth-high form 

(fourth-highest daily maximum 8-hour 

O3 concentration, averaged over 3 years) 

in this final rule. 

4. Level 

This section summarizes the basis for 

the Administrator’s proposed decision 

to revise the current standard level 

(II.C.4.a); discusses public comments, 

and the EPA’s responses, on that 

proposed decision (II.C.4.b); and 

presents the Administrator’s final 

decision regarding the level of the 

primary O3 standard (II.C.4.c). 

a. Basis for the Administrator’s 

Proposed Decision on Level 

In conjunction with her proposed 

decisions to retain the current indicator, 

averaging time, and form (II.C.1 to II.C.3, 

above), the Administrator proposed to 

revise the level of the primary O3

standard to within the range of 65 to 70 

ppb. In proposing this range of standard 

levels, as discussed in section II.E.4 of 

the proposal, the Administrator 

carefully considered the scientific 

evidence assessed in the ISA (U.S. EPA, 

2013); the results of the exposure and 

risk assessments in the HREA (U.S. 

EPA, 2014a); the evidence-based and 

exposure-/risk-based considerations and 

conclusions in the PA (U.S. EPA, 

2014c); CASAC advice and 

recommendations, as reflected in 

CASAC’s letters to the Administrator 

and in public discussions of drafts of 

the ISA, HREA, and PA (Frey and 

Samet, 2012; Frey, 2014 a, c); and public 

input received during the development 

of these documents. 

The Administrator’s proposal to 

revise the standard level built upon her 

proposed conclusion that the overall 

body of scientific evidence and 

exposure/risk information calls into 

question the adequacy of public health 

protection afforded by the current 

primary O3 standard, particularly for atrisk populations and lifestages. In 

reaching proposed conclusions on 

alternative levels for the primary O3

standard, the Administrator considered 

the extent to which various alternatives 

would be expected to protect the public, 

including at-risk populations, against 

the wide range of adverse health effects 

that have been linked with short- or 

long-term O3 exposures. 

As was the case for her consideration 

of the adequacy of the current primary 

O3 standard (II.B.3, above), the 

Administrator placed the greatest 

weight on the results of controlled 

human exposure studies and on 

exposure and risk analyses based on 

information from these studies. In doing 

so, she noted that controlled human 

exposure studies provide the most 

certain evidence indicating the 

occurrence of health effects in humans 

following exposures to specific O3

concentrations. The effects reported in 

these studies are due solely to O3

exposures, and interpretation of study 

results is not complicated by the 

presence of co-occurring pollutants or 

pollutant mixtures (as is the case in 

epidemiologic studies). She further 

noted the CASAC judgment that ‘‘the 

scientific evidence supporting the 

finding that the current standard is 

inadequate to protect public health is 

strongest based on the controlled human 

exposure studies of respiratory effects’’ 

(Frey, 2014c, p. 5). 

In considering the evidence from 

controlled human exposure studies, the 

Administrator first noted that the largest 

respiratory effects, and the broadest 

range of effects, have been studied and 

reported following exposures to 80 ppb 

O3 or higher, with most exposure 

studies conducted at these higher 

concentrations. Exposures of healthy 

adults to O3 concentrations of 80 ppb or 

higher have been reported to decrease 

lung function, increase airway 

inflammation, increase respiratory 

symptoms, result in airway 

hyperresponsiveness, and decrease lung 

host defenses. The Administrator 

further noted that O3 exposure 

concentrations as low as 72 ppb have 

been shown to both decrease lung 

function and increase respiratory 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65353 

121As noted above, for the 70 ppb target exposure 

concentration, Schelegle et al. (2009) reported that 

the actual mean exposure concentration was 72 

ppb. 

122 In the study by Schelegle, for the 60 ppb target 

exposure concentration, study authors reported that 

the actual mean exposure concentration was 63 

ppb. 

123The Administrator judged that the evidence is 

less compelling, and indicates greater uncertainty, 

with regard to the potential for adverse effects 

following single occurrences of O3 exposures of 

concern. While acknowledging this greater 

uncertainty, she noted that a standard with a level 

of 70 ppb would also be expected to virtually 

eliminate all occurrences (including single 

occurrences) of exposures of concern at or above 80 

ppb, even in the worst-case year and location. She 

also judged that such a standard will achieve 

important reductions, compared to the current 

standard, in the occurrence of one or more 

exposures of concern at or above 70 and 60 ppb. 

symptoms (Schelegle et al., 2009),121 a 

combination that meets the ATS criteria 

for an adverse response, and that 

exposures as low as 60 ppb have been 

reported to decrease lung function and 

increase airway inflammation. 

Based on this evidence, the 

Administrator reached the initial 

conclusion that the results of controlled 

human exposure studies strongly 

support setting the level of a revised O3

standard no higher than 70 ppb. In 

reaching this conclusion, she placed a 

large amount of weight on the 

importance of setting the level of the 

standard well below 80 ppb, the 

exposure concentration at which the 

broadest range of effects have been 

studied and reported, and below 72 ppb, 

the lowest exposure concentration 

shown to result in the adverse 

combination of lung function 

decrements and respiratory symptoms. 

She placed significant weight on this 

combination of effects, as did CASAC, 

in making judgments regarding the 

potential for adverse responses. 

In further considering the potential 

public health implications of a standard 

with a level of 70 ppb, the 

Administrator also considered 

quantitative estimates of the extent to 

which such a standard would be 

expected to limit population exposures 

to the broader range of O3

concentrations shown in controlled 

human exposure studies to cause 

respiratory effects. In doing so, she 

focused on estimates of O3 exposures of 

concern at or above the benchmark 

concentrations of 60, 70, and 80 ppb. 

The Administrator judged that the 

evidence supporting the occurrence of 

adverse respiratory effects is strongest 

for exposures at or above the 70 and 80 

ppb benchmarks. Therefore, she placed 

a large amount of emphasis on the 

importance of setting a standard that 

limits exposures of concern at or above 

these benchmarks. 

The Administrator expressed less 

confidence that adverse effects will 

occur following exposures to O3

concentrations as low as 60 ppb. In 

reaching this conclusion, she 

highlighted the fact that statistically 

significant increases in respiratory 

symptoms, combined with lung 

function decrements, have not been 

reported following exposures to 60 or 63 

ppb O3, though several studies have 

evaluated the potential for such effects 

(Kim et al., 2011; Schelegle et al., 2009; 

Adams, 2006).122 The proposal 

specifically stated that ‘‘[t]he 

Administrator has decreasing 

confidence that adverse effects will 

occur following exposures to O3

concentrations below 72 ppb. In 

particular, compared to O3 exposure 

concentrations at or above 72 ppb, she 

has less confidence that adverse effects 

will occur following exposures to O3

concentrations as low as 60 ppb’’ (79 FR 

73304–05). 

However, she noted the possibility for 

adverse effects following such 

exposures given that: (1) CASAC judged 

the adverse combination of lung 

function decrements and respiratory 

symptoms ‘‘almost certainly occur in 

some people’’ following exposures to O3

concentrations below 72 ppb (though 

CASAC did not specify or otherwise 

indicate how far below) (Frey, 2014c, p. 

6); (2) CASAC indicated the moderate 

lung function decrements (i.e., FEV1

decrements ≥ 10%) that occur in some 

healthy adults following exposures to 60 

ppb O3 could be adverse to people with 

lung disease; and (3) airway 

inflammation has been reported 

following exposures as low as 60 ppb 

O3. She also took note of CASAC advice 

that the occurrence of exposures of 

concern at or above 60 ppb is an 

appropriate consideration for people 

with asthma (Frey, 2014c, p. 6). 

Therefore, while the Administrator 

expressed less confidence that adverse 

effects will occur following exposures to 

O3 concentrations as low as 60 ppb, 

compared to 70 ppb and above, based 

on the evidence and CASAC advice she 

also gave some consideration to 

exposures of concern for the 60 ppb 

benchmark. 

Due to interindividual variability in 

responsiveness, the Administrator 

further noted that not every occurrence 

of an exposure of concern will result in 

an adverse effect, and that repeated 

occurrences of some of the effects 

demonstrated following exposures of 

concern could increase the likelihood of 

adversity (U.S. EPA, 2013, section 

6.2.3). Therefore, the Administrator was 

most concerned about protecting at-risk 

populations against repeated 

occurrences of exposures of concern. 

Based on the above considerations, the 

Administrator focused on the extent to 

which a revised standard with a level of 

70 ppb would be expected to protect 

populations from experiencing two or 

more O3 exposures of concern (i.e., as a 

surrogate for repeated exposures). 

As illustrated in Table 1 in the 

proposal (and Table 1 above), the 

Administrator noted that, in urban 

study areas, a revised standard with a 

level of 70 ppb is estimated to eliminate 

the occurrence of two or more exposures 

of concern to O3 concentrations at and 

above 80 ppb and to virtually eliminate 

the occurrence of two or more exposures 

of concern to O3 concentrations at and 

above 70 ppb, even in the worst-case 

urban study area and year evaluated. 

Though the Administrator 

acknowledged greater uncertainty with 

regard to the occurrence of adverse 

effects following exposures to 60 ppb, 

she noted that a revised standard with 

a level of 70 ppb would also be expected 

to protect the large majority of children 

in the urban study areas (i.e., about 96% 

to more than 99% of children in 

individual urban study areas) from 

experiencing two or more exposures of 

concern at or above the 60 ppb 

benchmark. Compared to the current 

standard, this represents a reduction of 

more than 60%.123

In further evaluating the potential 

public health impacts of a standard with 

a level of 70 ppb, the Administrator also 

considered the HREA estimates of O3- 

induced lung function decrements. To 

inform her consideration of these 

decrements, the Administrator took note 

of CASAC advice that ‘‘estimation of 

FEV1 decrements of ≥ 15% is 

appropriate as a scientifically relevant 

surrogate for adverse health outcomes in 

active healthy adults, whereas an FEV1

decrement of ≥ 10% is a scientifically 

relevant surrogate for adverse health 

outcomes for people with asthma and 

lung disease’’ (Frey, 2014c, p. 3). 

Although these FEV1 decrements 

provide perspective on the potential for 

the occurrence of adverse respiratory 

effects following O3 exposures, the 

Administrator agreed with the 

conclusion in past reviews that a more 

general consensus view of the adversity 

of moderate responses emerges as the 

frequency of occurrence increases (61 

FR 65722–3, Dec, 13, 1996). 

Specifically, she judged that not every 

estimated occurrence of an O3-induced 

FEV1 decrement will be adverse and 

mstockstill on DSK4VPTVN1PROD with RULES2

65354 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

124 In the proposal, the Administrator further 

judged that it would not be appropriate to set a 

standard that is intended to eliminate all O3- 

induced FEV1 decrements. She noted that this is 

consistent with CASAC advice, which did not 

include a recommendation to set the standard level 

low enough to eliminate all O3-induced FEV1

decrements ≥ 10 or 15% (Frey, 2014c). 

125Although the Administrator was less 

concerned about the public health implications of 

single O3-induced lung function decrements, she 

also noted that a revised standard with a level of 

65 ppb is estimated to reduce the risk of one or 

more O3-induced decrements per season, compared 

to the current standard. 

126Although the widest range of effects have been 

evaluated following exposures to 80 ppb O3, there 

is no evidence that 80 ppb is a threshold for these 

effects. 

127The Administrator also concluded that 

analyses in the HREA and PA indicate that a 

standard with an 8-hour averaging time, coupled 

with the current fourth-high form and a level from 

65 to 70 ppb, would be expected to provide 

increased protection, compared to the current 

standard, against the long-term O3 concentrations 

that have been reported to be associated with 

respiratory morbidity or mortality (79 FR 75293; 

75308). 

that repeated occurrences of moderate 

responses could lead to more serious 

illness. Therefore, the Administrator 

noted increasing concern about the 

potential for adversity as the number of 

occurrences increases and, as a result, 

she focused primarily on estimates of 

two or more O3-induced FEV1

decrements (i.e., as a surrogate for 

repeated exposures).124

The Administrator noted that a 

revised O3 standard with a level of 70 

ppb is estimated to protect about 98 to 

99% of children in urban study areas 

from experiencing two or more O3- 

induced FEV1 decrements ≥15%, and 

about 89 to 94% from experiencing two 

or more decrements ≥10%. She judged 

that these estimates reflect important 

risk reductions, compared to the current 

standard. Given these estimates, as well 

as estimates of one or more decrements 

per season (about which she was less 

concerned (79 FR 75290, December 17, 

2014)), the Administrator concluded 

that a revised standard with a level of 

70 ppb would be expected to provide 

substantial protection against the risk of 

O3-induced lung function decrements, 

and would be expected to result in 

important reductions in such risks, 

compared to the current standard. The 

Administrator further noted, however, 

that the variability in lung function risk 

estimates across urban study areas is 

often greater than the differences in risk 

estimates between various standard 

levels (Table 2, above). Given this, and 

the resulting considerable overlap 

between the ranges of lung function risk 

estimates for different standard levels, 

in the proposal the Administrator 

viewed lung function risk estimates as 

providing a more limited basis than 

exposures of concern for distinguishing 

between the degrees of public health 

protection provided by alternative 

standard levels (79 FR 75306 n. 164). 

In next considering the additional 

protection that would be expected from 

standard levels below 70 ppb, the 

Administrator evaluated the extent to 

which a standard with a level of 65 ppb 

would be expected to further limit O3

exposures of concern and O3-induced 

lung function decrements. In addition to 

eliminating almost all exposures of 

concern to O3 concentrations at or above 

80 and 70 ppb, even in the worst-case 

years and locations, the Administrator 

noted that a revised standard with a 

level of 65 ppb would be expected to 

protect more than 99% of children in 

urban study areas from experiencing 

two or more exposures of concern at or 

above 60 ppb and to substantially 

reduce the occurrence of one or more 

such exposures, compared to the current 

standard. With regard to O3-induced 

lung function decrements, an O3

standard with a level of 65 ppb is 

estimated to protect about 98% to more 

than 99% of children from experiencing 

two or more O3-induced FEV1

decrements ≥15% and about 91 to 99% 

from experiencing two or more 

decrements ≥10%.125

Taken together, the Administrator 

concluded that the evidence from 

controlled human exposure studies, and 

the information from quantitative 

analyses that draw upon these studies, 

provide strong support for standard 

levels from 65 to 70 ppb. In particular, 

she based this conclusion on the fact 

that such standard levels would be well 

below the O3 exposure concentration 

shown to result in the widest range of 

respiratory effects (i.e., 80 ppb),126 and 

below the lowest O3 exposure 

concentration shown to result in the 

adverse combination of lung function 

decrements and respiratory symptoms 

(i.e., 72 ppb). A standard with a level 

from 65 to 70 ppb would also be 

expected to result in important 

reductions, compared to the current 

standard, in the occurrence of O3

exposures of concern for all of the 

benchmarks evaluated (i.e., 60, 70, and 

80 ppb) and in the risk of O3-induced 

lung function decrements ≥10 and 15%. 

In further considering the evidence 

and exposure/risk information, the 

Administrator considered the extent to 

which the epidemiologic evidence also 

provides support for standard levels 

from 65 to 70 ppb. In particular, the 

Administrator noted analyses in the PA 

(U.S. EPA, 2014c, section 4.4.1) 

indicating that a revised standard with 

a level of 65 or 70 ppb would be 

expected to maintain distributions of 

short-term ambient O3 concentrations 

below those present in the locations of 

all the single-city epidemiologic studies 

of hospital admissions or emergency 

department visits analyzed. She 

concluded that a revised standard with 

a level at least as low as 70 ppb would 

result in improvements in public health, 

beyond the protection provided by the 

current standard, in the locations of the 

single-city epidemiologic studies that 

reported significant health effect 

associations.127

The Administrator noted additional 

uncertainty in interpreting air quality in 

locations of multicity epidemiologic 

studies of short-term O3 for the purpose 

of evaluating alternative standard levels 

(II.D.1 and U.S. EPA, 2014c, section 

4.4.1). While acknowledging this 

uncertainty, and therefore placing less 

emphasis on these analyses of study 

location air quality, she noted that PA 

analyses suggest that standard levels of 

65 or 70 ppb would require reductions, 

beyond those required by the current 

standard, in ambient O3 concentrations 

present in several of the locations that 

provided the basis for statistically 

significant O3 health effect associations 

in multicity studies. 

In further evaluating information from 

epidemiologic studies, the 

Administrator considered the HREA’s 

epidemiology-based risk estimates for 

O3-associated morbidity or mortality 

(U.S. EPA, 2014a, Chapter 7). Compared 

to the weight given to the evidence from 

controlled human exposure studies, and 

to HREA estimates of exposures of 

concern and lung function risks, she 

placed relatively less weight on 

epidemiology-based risk estimates. In 

doing so, she noted that the overall 

conclusions from the HREA likewise 

reflect relatively less confidence in 

estimates of epidemiology-based risks 

than in estimates of exposures of 

concern and lung function risks. 

In considering epidemiology-based 

risk estimates, the Administrator 

focused on risks associated with O3

concentrations in the upper portions of 

ambient distributions, given the greater 

uncertainty associated with the shapes 

of concentration-response curves for O3

concentrations in the lower portions of 

ambient distributions (i.e., below about 

20 to 40 ppb depending on the O3

metric, health endpoint, and study 

population) (U.S. EPA, 2013, section 

2.5.4.4). The Administrator further 

noted that experimental studies provide 

the strongest evidence for O3-induced 

effects following exposures to O3

concentrations corresponding to the 

upper portions of typical ambient 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65355 

128 In general, commenters who expressed the 

view that the EPA should retain the current O3

NAAQS (i.e., commenters representing industry 

and business groups, and some states) did not 

provide comments on alternative standard levels. 

As a result, this section focuses primarily on 

comments from commenters who expressed support 

for the proposed decision to revise the current 

primary O3 standard. 

129Similarly, Senator Muskie remarked during 

the floor debates on the 1977 Amendments that 

‘‘there is no such thing as a threshold for health 

effects. Even at the national primary standard level, 

which is the health standard, there are health 

effects that are not protected against’’. 123 Cong. 

Rec. S9423 (daily ed. June 10, 1977). 

distributions. In particular, as discussed 

above, she noted controlled human 

exposure studies showing respiratory 

effects following exposures to O3

concentrations at or above 60 ppb (79 

FR 75308, December 17, 2014). 

Therefore, in considering risks 

associated with O3 concentrations in the 

upper portions of ambient distributions, 

the Administrator focused on the extent 

to which revised standards with levels 

of 70 or 65 ppb are estimated to reduce 

the risk of premature deaths associated 

with area-wide O3 concentrations at or 

above 40 ppb and 60 ppb. 

Given all of the above evidence, 

exposure/risk information, and advice 

from CASAC, the Administrator 

proposed to revise the level of the 

current primary O3 standard to within 

the range of 65 to 70 ppb. In considering 

CASAC advice on the range of standard 

levels, the Administrator placed a large 

amount of weight on CASAC’s 

conclusion that there is adequate 

scientific evidence to consider a range 

of levels for a primary standard that 

includes an upper end at 70 ppb. She 

also noted that although CASAC 

expressed concern about the margin of 

safety at a level of 70 ppb, it further 

acknowledged that the choice of a level 

within the range recommended based 

on scientific evidence is a policy 

judgment (Frey, 2014c, p. ii). While she 

agreed with CASAC that it is 

appropriate to consider levels below 70 

ppb, as reflected in her range of 

proposed levels from 65 to 70 ppb, for 

the reasons discussed above she also 

concluded that a standard level as high 

as 70 ppb, which CASAC concluded 

could be supported by the scientific 

evidence, could reasonably be judged to 

be requisite to protect public health 

with an adequate margin of safety. 

In considering the appropriateness of 

standard levels below 65 ppb, the 

Administrator noted the conclusions of 

the PA and the advice of CASAC that it 

would be appropriate for her to consider 

standard levels as low as 60 ppb. In 

making the decision to not propose 

levels below 65 ppb, she focused on 

CASAC’s rationale for a level of 60 ppb, 

which focused on the importance of 

limiting exposures to O3 concentrations 

as low as 60 ppb (Frey, 2014c, p. 7). As 

discussed above, the Administrator 

agreed that it is appropriate to consider 

the implications of a revised standard 

level for estimated exposures of concern 

at or above 60 ppb. She noted that 

standards within the proposed range of 

65 to 70 ppb would be expected to 

substantially limit the occurrence of 

exposures of concern to O3

concentrations at or above 60 ppb, 

particularly the occurrence of two or 

more exposures. When she further 

considered that not all exposures of 

concern lead to adverse effects, and that 

the NAAQS are not meant to be zerorisk or background standards, the 

Administrator judged that alternative 

standard levels below 65 ppb are not 

needed to further reduce such 

exposures. 

b. Comments on Level 

A number of groups representing 

medical, public health, or 

environmental organizations; some state 

agencies; and many individuals 

submitted comments on the appropriate 

level of a revised primary O3

standard.128 Virtually all of these 

commenters supported setting the 

standard level within the range 

recommended by CASAC (i.e., 60 to 70). 

Some expressed support for the overall 

CASAC range, without specifying a 

particular level within that range, while 

others expressed a preference for the 

lower part of the CASAC range, often 

emphasizing support for a level of 60 

ppb. Some of these commenters stated 

that if the EPA does not set the level at 

60 ppb, then the level should be set no 

higher than 65 ppb (i.e., the lower 

bound of the proposed range of standard 

levels). 

To support their views on the level of 

a revised standard, some commenters 

focused on overarching issues related to 

the statutory requirements for the 

NAAQS. For example, some 

commenters maintained that the 

primary NAAQS must be set at a level 

at which there is an absence of adverse 

effects in sensitive populations. While 

this argument has some support in the 

case law and in the legislative history to 

the 1970 CAA (see Lead Industries Ass’n 

v. EPA, 647 F. 2d 1147, 1153 (D.C. Cir. 

1980)), it is well established that the 

NAAQS are not meant to be zero risk 

standards. See Lead Industries v. EPA, 

647 F.2d at 1156 n.51; Mississippi v. 

EPA, 744 F. 3d at 1351. From the 

inception of the NAAQS standardsetting process, the EPA and the courts 

have acknowledged that scientific 

uncertainties in general, and the lack of 

clear thresholds in pollutant effects in 

particular, preclude any such definitive 

determinations. Lead Industries, 647 F. 

2d at 1156 (setting standard at a level 

which would remove most but not all 

sub-clinical effects). Likewise, the 

House report to the 1977 amendments 

addresses this question (H. Rep. 95–294, 

95th Cong. 1st sess. 127): 129

Some have suggested that since the 

standards are to protect against all known or 

anticipated effects and since no safe 

threshold can be established, the ambient 

standards should be set at zero or background 

levels. Obviously, this no-risk philosophy 

ignores all economic and social 

consequences and is impractical. This is 

particularly true in light of the legal 

requirement for mandatory attainment of the 

national primary standards within 3 years. 

Thus, post-1970 jurisprudence makes 

clear the impossibility, and lack of legal 

necessity, for NAAQS removing all 

health risk. See ATA III, 283 F. 3d at 360 

(‘‘[t]he lack of a threshold concentration 

below which these pollutants are known 

to be harmless makes the task of setting 

primary NAAQS difficult, as EPA must 

select standard levels that reduce risks 

sufficiently to protect public health 

even while recognizing that a zero-risk 

standard is not possible’’); Mississippi, 

744 F. 3d at 1351 (same); see also id. at 

1343 (‘‘[d]etermining what is ‘requisite’ 

to protect the ‘public health’ with an 

‘adequate’ margin of safety may indeed 

require a contextual assessment of 

acceptable risk. See Whitman, 531 U.S. 

at 494–95 (Breyer J. concurring)’’). 

In this review, EPA is setting a 

standard based on a careful weighing of 

available evidence, including a 

weighing of the strengths and 

limitations of the evidence and 

underlying scientific uncertainties 

therein. The Administrator’s choice of 

standard level is rooted in her 

evaluation of the evidence, which 

reflects her legitimate uncertainty as to 

the O3 concentrations at which the 

public would experience adverse health 

effects. This is a legitimate, and well 

recognized, exercise of ‘‘reasoned 

decision-making.’’ ATA III. 283 F. 3d at 

370; see also id. at 370 (‘‘EPA’s inability 

to guarantee the accuracy or increase the 

precision of the . . . NAAQS in no way 

undermines the standards’ validity. 

Rather, these limitations indicate only 

that significant scientific uncertainty 

remains about the health effects of fine 

particulate matter at low atmospheric 

concentration. . . .’’); Mississippi, 744 

F. 3d at 1352–53 (appropriate for EPA 

to balance scientific uncertainties in 

determining level of revised O3

NAAQS). 

mstockstill on DSK4VPTVN1PROD with RULES2

65356 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

130The CHAD database used in the HREA’s 

exposure assessment contains over 53,000 

individual daily diaries including time-locationactivity patterns for individuals of both sexes across 

a wide range of ages (U.S. EPA, 2014a, Chapter 5). 

131CASAC generally agreed with the EPA’s 

methodology for characterizing exposures of 

concern (Frey, 2014a, pp. 5–6). 

132See 79 FR 75269 (‘‘The activity pattern of 

individuals is an important determinant of their 

exposure. Variation in O3 concentrations among 

various microenvironments means that the amount 

of time spent in each location, as well as the level 

of activity, will influence an individual’s exposure 

to ambient O3. Activity patterns vary both among 

and within individuals, resulting in corresponding 

variations in exposure across a population and over 

time’’ (internal citations omitted). 

133For healthy young adults exposed at rest for 

2 hours, 500 ppb is the lowest O3 concentration 

reported to produce a statistically significant O3- 

induced group mean FEV1 decrement (U.S. EPA, 

2013, section 6.2.1.1). 134The EPA was aware of the possibility of 

averting behavior during the development of the 

HREA, and that document includes sensitivity 

analyses to provide perspective on the potential 

role of averting behavior in modifying O3

exposures. As discussed further above (II.B.2.c), 

these sensitivity analyses were limited and the 

results were discussed in the proposal within the 

context of uncertainties in the HREA assessment of 

exposures of concern. 

135See Mississippi, 744 F. 3d at 1343 

(‘‘[d]etermining what is ‘requisite’ to protect the 

‘public health’ with an ‘adequate’ margin of safety 

may indeed require a contextual assessment of 

acceptable risk. See Whitman, 531 U.S. at 494–95 

(Breyer, J. concurring . . .))’’ 

In an additional overarching 

comment, some commenters also 

fundamentally objected to the EPA’s 

consideration of exposure estimates in 

reaching conclusions on the primary O3

standard. These commenters’ general 

assertion was that NAAQS must be 

established so as to be protective, with 

an adequate margin of safety, regardless 

of the activity patterns that feed into 

exposure estimates. They contended 

that ‘‘[a]ir quality standards cannot rely 

on avoidance behavior in order to 

protect the public health and sensitive 

groups’’ and that ‘‘[i]t would be 

unlawful for EPA to set the standard at 

a level that is contingent upon people 

spending most of their time indoors’’ 

(e.g., ALA et al., p. 124). To support 

these comments, for example, ALA et al. 

analyzed ambient monitoring data from 

Core-Based Statistical Areas (CBSAs) 

with design values between 66–70 ppb 

(Table 17, pp. 145–151 in ALA et al.) 

and 62–65 ppb (Table 18, pp. 153–154 

in ALA et al.) and pointed out that there 

are many more days with ambient 

concentrations above the benchmark 

levels than were estimated in the EPA’s 

exposure analysis (i.e., at and above the 

benchmark level of 60, 70 and 80 ppb). 

The EPA disagrees with these 

commenters’ conclusions regarding the 

appropriateness of considering exposure 

estimates, and notes that NAAQS must 

be ‘‘requisite’’ (i.e., ‘‘sufficient, but not 

more than necessary’’ (Whitman, 531 

U.S. at 473)) to protect the ‘‘public 

health’’ (‘‘the health of the public’’ 

(Whitman, 531 U.S. at 465)). Estimating 

exposure patterns based on extensive 

available data 130 is a reasonable means 

of ascertaining that standards are 

neither under- nor over-protective, and 

that standards address issues of public 

health rather than health issues 

pertaining only to isolated 

individuals.131 Behavior patterns are 

critical in assessing whether ambient 

concentrations of O3 may pose a public 

health risk.132 Exposures to ambient or 

near-ambient O3 concentrations have 

only been shown to result in potentially 

adverse effects if the ventilation rates of 

people in the exposed populations are 

raised to a sufficient degree (e.g., 

through physical exertion) (U.S. EPA, 

2013, section 6.2.1.1).133 Ignoring 

whether such elevated ventilation rates 

are actually occurring, as advocated by 

these commenters, would not provide 

an accurate assessment of whether the 

public health is at risk. Indeed, a 

standard established without regard to 

behavior of the public would likely lead 

to a standard which is more stringent 

than necessary to protect the public 

health. 

While setting the primary O3 standard 

based only on ambient concentrations, 

without consideration of activity 

patterns and ventilation rates, would 

likely result in a standard that is overprotective, the EPA also concludes that 

setting a standard based on the 

assumption that people will adjust their 

activities to avoid exposures on highpollution days would likely result in a 

standard that is under-protective. The 

HREA’s exposure assessment does not 

make this latter assumption.134 The 

time-location-activity diaries that 

provided the basis for exposure 

estimates reflect actual variability in 

human activities. While some diary 

days may reflect individuals spending 

less time outdoors than would be 

typical for them, it is similarly likely 

that some days reflect individuals 

spending more time outdoors than 

would be typical. Considering the actual 

variability in time-location-activity 

patterns is at the least a permissible way 

of identifying standards that are neither 

over- nor under-protective.135

Further, the EPA sees nothing in the 

CAA that prohibits consideration of the 

O3 exposures that could result in effects 

of public health concern. While a 

number of judicial opinions have 

upheld the EPA’s decisions in other 

NAAQS reviews to place little weight 

on particular risk or exposure analyses 

(i.e., because of scientific uncertainties 

in those analyses), none of these 

opinions have suggested that such 

analyses are irrelevant because actual 

exposure patterns do not matter. See, 

e.g. Mississippi, 744 F. 3d at 1352–53; 

ATA III, 283 F. 3d at 373–74. Therefore, 

because behavior patterns are critical in 

assessing whether ambient 

concentrations of O3 may pose a public 

health risk, the EPA disagrees with the 

views expressed by these commenters 

objecting to the consideration of O3

exposures in reaching decisions on the 

primary O3 standard. 

In addition to these overarching 

comments, a number of commenters 

supported their views on standard level 

by highlighting specific aspects of the 

scientific evidence, exposure/risk 

information, and/or CASAC advice. Key 

themes expressed by these commenters 

included the following: (1) Controlled 

human exposure studies provide strong 

evidence of adverse lung function 

decrements and airway inflammation in 

healthy adults following exposures to 

O3 concentrations as low as 60 ppb, and 

at-risk populations would be likely to 

experience more serious effects or 

effects at even lower concentrations; (2) 

epidemiologic studies provide strong 

evidence for associations with mortality 

and morbidity in locations with ambient 

O3 concentrations below 70 ppb, and in 

many cases in locations with 

concentrations near and below 60 ppb; 

(3) quantitative analyses in the HREA 

are biased such that they understate O3

exposures and risks, and the EPA’s 

interpretation of lung function risk 

estimates is not appropriate and not 

consistent with other NAAQS; and (4) 

the EPA must give deference to CASAC 

advice, particularly CASAC’s policy 

advice to set the standard level below 70 

ppb. The next sections discuss 

comments related to each of these 

points, and provide the EPA’s responses 

to those comments. More detailed 

discussion of individual comments, and 

the EPA’s responses, is provided in the 

Response to Comments document. 

i. Effects in Controlled Human Exposure 

Studies 

Some commenters who advocated for 

a level of 60 ppb (or absent that, for 65 

ppb) asserted that controlled human 

exposure studies have reported adverse 

respiratory effects in healthy adults 

following exposures to O3

concentrations as low as 60 ppb. These 

commenters generally based their 

conclusions on the demonstration of 

FEV1 decrements ≥ 10% and increased 

airway inflammation following 

exposures of healthy adults to 60 ppb 

O3. They concluded that even more 

serious effects would occur in at-risk 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65357 

136With regard to this latter recommendation, as 

discussed above (II.A.1.c), the ATS concluded that 

elevations of biomarkers such as cell numbers and 

types, cytokines, and reactive oxygen species may 

signal risk for ongoing injury and more serious 

effects or may simply represent transient responses, 

illustrating the lack of clear boundaries that 

separate adverse from nonadverse events. 

populations exposed to 60 ppb O3, and 

that such populations would experience 

adverse effects following exposures to 

O3 concentrations below 60 ppb. 

While the EPA agrees that information 

from controlled human exposure studies 

conducted at 60 ppb can help to inform 

the Administrator’s decision on the 

standard level, the Agency does not 

agree that this information necessitates 

a level below 70 ppb. In fact, as 

discussed in the proposal, a revised O3

standard with a level of 70 ppb can be 

expected to provide substantial 

protection against the effects shown to 

occur following various O3 exposure 

concentrations, including those 

observed following exposures to 60 ppb. 

This is because the degree of protection 

provided by any NAAQS is due to the 

combination of all of the elements of the 

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

form, level). In the case of the fourthhigh form of the O3 NAAQS, which the 

Administrator is retaining in the current 

review (II.C.3), the large majority of days 

in areas that meet the standard will have 

8-hour O3 concentrations below the 

level of the standard, with most days 

well below the level. Therefore, as 

discussed in the proposal, in 

considering the degree of protection 

provided by an O3 standard with a 

particular level, it is important to 

consider the extent to which that 

standard would be expected to limit 

population exposures of concern to the 

broader range of O3 exposure 

concentrations shown in controlled 

human exposure studies to result in 

health effects. The Administrator’s 

consideration of such exposures of 

concern is discussed below (II.C.4.c). 

Another important part of the 

Administrator’s consideration of 

exposure estimates is the extent to 

which she judges that adverse effects 

could occur following specific O3

exposures. While controlled human 

exposure studies provide a high degree 

of confidence regarding the extent to 

which specific health effects occur 

following exposures to O3

concentrations from 60 to 80 ppb, the 

Administrator notes that there are no 

universally accepted criteria by which 

to judge the adversity of the observed 

effects. Therefore, in making judgments 

about the extent to which the effects 

observed in controlled human exposure 

studies have the potential to be adverse, 

the Administrator considers the 

recommendations of ATS and advice 

from CASAC (II.A.1.c, above). 

As an initial matter, with regard to the 

effects shown in controlled human 

exposure studies following O3

exposures, the Administrator notes the 

following: 

1. The largest respiratory effects, and 

the broadest range of effects, have been 

studied and reported following 

exposures to 80 ppb O3 or higher, with 

most exposure studies conducted at 

these higher concentrations. 

Specifically, 6.6-hour exposures of 

healthy young adults to 80 ppb O3, 

while engaged in quasi-continuous, 

moderate exertion, can decrease lung 

function, increase airway inflammation, 

increase respiratory symptoms, result in 

airway hyperresponsiveness, and 

decrease lung host defenses. 

2. Exposures of healthy young adults 

for 6.6 hours to O3 concentrations as 

low as 72 ppb, while engaged in quasicontinuous, moderate exertion, have 

been shown to both decrease lung 

function and result in respiratory 

symptoms. 

3. Exposures of healthy young adults 

for 6.6 hours to O3 concentrations as 

low as 60 ppb, while engaged in quasicontinuous, moderate exertion, have 

been shown to decrease lung function 

and to increase airway inflammation. 

To inform her judgments on the 

potential adversity to public health of 

these effects reported in controlled 

human exposure studies, as in the 

proposal, the Administrator considers 

the ATS recommendation that 

‘‘reversible loss of lung function in 

combination with the presence of 

symptoms should be considered 

adverse’’ (ATS, 2000a). She notes that 

this combination of effects has been 

shown to occur following 6.6-hour 

exposures to O3 concentrations at or 

above 72 ppb. In considering these 

effects, CASAC observed that ‘‘the 

combination of decrements in FEV1

together with the statistically significant 

alterations in symptoms in human 

subjects exposed to 72 ppb ozone meets 

the American Thoracic Society’s 

definition of an adverse health effect’’ 

(Frey, 2014c, p. 5). 

Regarding the potential for adverse 

effects following exposures to lower 

concentrations, the Administrator notes 

the CASAC judgment that the adverse 

combination of lung function 

decrements and respiratory symptoms 

‘‘almost certainly occur in some people’’ 

following exposures to O3

concentrations below 72 ppb (Frey, 

2014c, p. 6). In particular, when 

commenting on the extent to which the 

study by Schelegle et al. (2009) suggests 

the potential for adverse effects 

following O3 exposures below 72 ppb, 

CASAC judged that: 

[I]f subjects had been exposed to ozone 

using the 8-hour averaging period used in the 

standard [rather than the 6.6-hour exposures 

evaluated in the study], adverse effects could 

have occurred at lower concentration. 

Further, in our judgment, the level at which 

adverse effects might be observed would 

likely be lower for more sensitive subgroups, 

such as those with asthma (Frey, 2014c, p. 5). 

Though CASAC did not provide 

advice as to how far below 72 ppb 

adverse effects would likely occur, the 

Administrator agrees that such effects 

could occur following exposures at least 

somewhat below 72 ppb. 

The Administrator notes that while 

adverse effects could occur following 

exposures at least somewhat below 72 

ppb, the combination of statistically 

significant increases in respiratory 

symptoms and decrements in lung 

function has not been reported 

following 6.6-hour exposures to average 

O3 concentrations of 60 ppb or 63 ppb, 

though studies have evaluated the 

potential for such effects (Adams, 2006; 

Schelegle et al., 2009; Kim et al., 2011). 

In the absence of this combination, the 

Administrator looks to additional ATS 

recommendations and CASAC advice in 

order to inform her judgments regarding 

the potential adversity of the effects that 

have been observed following O3

exposures as low as 60 ppb. 

With regard to ATS, she first notes the 

recommendations that ‘‘a small, 

transient loss of lung function, by itself, 

should not automatically be designated 

as adverse’’ and that ‘‘[f]ew . . . 

biomarkers have been validated 

sufficiently that their responses can be 

used with confidence to define the point 

at which a response should be equated 

to an adverse effect warranting 

preventive measures’’ (ATS, 2000a).136

Based on these recommendations, 

compared to effects following exposures 

at or above 72 ppb, the Administrator 

has less confidence in the adversity of 

the respiratory effects that have been 

observed following exposures to 60 or 

63 ppb. 

She further notes that some 

commenters who advocated for a level 

of 60 ppb also focused on ATS 

recommendations regarding populationlevel risks. These commenters 

specifically stated that lung function 

decrements ‘‘may be adverse in terms of 

‘population risk,’ where exposure to air 

pollution increases the risk to the 

population even though it might not 

harm lung function to a degree that is, 

on its own, ‘clinically important’ to an 

individual’’ (e.g., ALA et al., p. 118). 

These commenters asserted that the EPA 

mstockstill on DSK4VPTVN1PROD with RULES2

65358 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

137ATS provided additional recommendations to 

help inform judgments regarding the adversity of air 

pollution-related effects (e.g., related to ‘‘quality of 

life’’), though it is not clear whether, or how, such 

recommendations should be applied to the 

respiratory effects observed in controlled human 

exposure studies following 6.6-hour O3 exposures 

(ATS, 200a, p. 672). 

has not appropriately considered the 

potential for such population-level risk. 

Contrary to the views expressed by 

these commenters, the Administrator 

carefully considers the potential for 

population risk, particularly within the 

context of the ATS recommendation 

that ‘‘a shift in the risk factor 

distribution, and hence the risk profile 

of the exposed population, should be 

considered adverse, even in the absence 

of the immediate occurrence of frank 

illness’’ (ATS, 2000a). Given that 

exposures to 60 ppb O3 have been 

shown in controlled human exposure 

studies to cause transient and reversible 

decreases in group mean lung function, 

the Administrator notes the potential for 

such exposures to result in similarly 

transient and reversible shifts in the risk 

profile of an exposed population. 

However, in contrast to commenters 

who advocated for a level of 60 ppb, the 

Administrator also notes that the 

available evidence does not provide 

information on the extent to which a 

short-term, transient decrease in lung 

function in a population, as opposed to 

a longer-term or permanent decrease, 

could affect the risk of other, more 

serious respiratory effects (i.e., change 

the risk profile of the population). This 

uncertainty, together with the additional 

ATS recommendations noted above, 

indicates to the Administrator that her 

judgment that there is uncertainty in the 

adversity of the effects shown to occur 

at 60 ppb is consistent with ATS 

recommendations.137

With regard to CASAC advice, the 

Administrator notes that, while CASAC 

clearly advised the EPA to consider the 

health effects shown to occur following 

exposures to 60 ppb O3, its advice 

regarding the adversity of those effects 

is less clear. In particular, she notes that 

CASAC was conditional about whether 

the lung function decrements observed 

in some people at 60 ppb (i.e., FEV1

decrements ≥ 10%) are adverse. 

Specifically, CASAC stated that these 

decrements ‘‘could be adverse in 

individuals with lung disease’’ (Frey, 

2014c, p. 7, emphasis added) and that 

they provide a ‘‘surrogate for adverse 

health outcomes for people with asthma 

and lung disease’’ (Frey, 2014c, p. 3, 

emphasis added). Further, CASAC did 

not recommend considering standard 

levels low enough to eliminate O3- 

induced FEV1 decrements ≥ 10% (Frey, 

2014c). With regard to the full range of 

effects shown to occur at 60 ppb (i.e., 

FEV1 decrements, airway inflammation), 

CASAC stated that exposures of concern 

for the 60 ppb benchmark are ‘‘relevant 

for consideration’’ with respect to 

people with asthma (Frey, 2014c, p. 6, 

italics added). In addition, ‘‘[t]he 

CASAC concurs with EPA staff 

regarding the finding based on scientific 

evidence that a level of 60 ppb 

corresponds to the lowest exposure 

concentration demonstrated to result in 

lung function decrements large enough 

to be judged an abnormal response by 

ATS and that could be adverse in 

individuals with lung disease’’ (Frey, 

2014c, p. 7, italics added). The 

Administrator contrasts these 

statements with CASAC’s clear advice 

that ‘‘the combination of decrements in 

FEV1 together with the statistically 

significant alterations in symptoms in 

human subjects exposed to 72 ppb 

ozone meets the American Thoracic 

Society’s definition of an adverse health 

effect’’ (Frey, 2014c, p. 5). 

Based on her consideration of all of 

the above recommendations and advice 

noted above, the Administrator judges 

that, compared to exposure 

concentrations at and above 72 ppb, 

there is greater uncertainty with regard 

to the adversity of effects shown to 

occur following O3 exposures as low as 

60 ppb. However, based on the effects 

that have been shown to occur at 60 ppb 

(i.e., lung function decrements, airway 

inflammation), and CASAC advice 

indicating the importance of 

considering these effects (though its 

advice regarding the adversity of effects 

at 60 ppb is less clear), she concludes 

that it is appropriate to give some 

consideration to the extent to which a 

revised standard could allow such 

effects. 

In considering estimates of exposures 

of concern for the 60, 70, and 80 ppb 

benchmarks within the context of her 

judgments on adversity, the 

Administrator notes that, due to 

interindividual variability in 

responsiveness, not every occurrence of 

an exposure of concern will result in an 

adverse effect. As discussed above 

(II.B.2.b.i), this point was highlighted by 

some commenters who opposed 

revision of the current standard, based 

on their analysis of effects shown to 

occur following exposures to 72 ppb O3. 

This point was also highlighted by some 

commenters who advocated for a level 

of 60 ppb, based on the discussion of 

O3-induced inflammation in the 

proposal. In particular, this latter group 

of commenters highlighted discussion 

from the proposal indicating that 

‘‘[i]nflammation induced by a single O3

exposure can resolve entirely but, as 

noted in the ISA (U.S. EPA, 2013, p. 6– 

76), ‘continued acute inflammation can 

evolve into a chronic inflammatory 

state’’’ (e.g., ALA et al., p. 48). 

Consistent with these comments, and 

with her consideration of estimated 

exposurs of concern in the proposal, the 

Administrator judges that the types of 

respiratory effects that can occur 

following exposures of concern, 

particularly if experienced repeatedly, 

provide a plausible mode of action by 

which O3 may cause other more serious 

effects. Because of this, as in the 

proposal, the Administrator is most 

concerned about protecting against 

repeated occurrences of exposures of 

concern. 

The Administrator’s consideration of 

estimated exposures of concern is 

discussed in more detail below 

(II.C.4.b.iv, II.C.4.c). In summary, 

contrary to the conclusions of 

commenters who advocated for a level 

of 60 ppb, the Administrator judges that 

a revised standard with a level of 70 ppb 

will effectively limit the occurrence of 

the O3 exposures for which she is most 

confident in the adversity of the 

resulting effects (i.e., based on estimates 

for the 70 and 80 ppb benchmarks). She 

further concludes that such a standard 

will provide substantial protection 

against the occurrence of O3 exposures 

for which there is greater uncertainty in 

the adversity of effects (i.e., based on 

estimates for the 60 ppb benchmark). 

As noted above, commenters also 

pointed out that benchmark 

concentrations are based on studies 

conducted in healthy adults, whereas atrisk populations are likely to experience 

more serious effects and effects at lower 

O3 exposure concentrations. In 

considering this issue, the EPA notes 

CASAC’s endorsement of 60 ppb as the 

lower end of the range of benchmarks 

for evaluation, and its advice that ‘‘the 

60 ppb-8hr exposure benchmark is 

relevant for consideration with respect 

to adverse effects on asthmatics’’ (Frey, 

2014c, p. 6). As discussed in detail 

below (II.C.4.c), the Administrator has 

carefully considered estimated 

exposures of concern for the 60 ppb 

benchmark. In addition, though the 

available information does not support 

the identification of specific 

benchmarks below 60 ppb that could be 

appropriate for consideration for at-risk 

populations, and though CASAC did not 

recommend consideration of any such 

benchmarks, the EPA expects that a 

revised standard with a level of 70 ppb 

will also reduce the occurrence of 

exposures to O3 concentrations at least 

somewhat below 60 ppb (U.S. EPA, 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65359 

138Air quality analyses in the HREA indicate that 

reducing the level of the primary standard from 75 

ppb to 70 ppb will result in reductions in the O3

concentrations in the upper portions of ambient 

distributions. This includes 8-hour ambient O3

concentrations at, and somewhat below, 60 ppb 

(U.S. EPA, 2014a, Figures 4–9 and 4–10). 

139The uncertainty associated with the potential 

adversity of any such effects would be even greater 

than that discussed above for the 60 ppb 

benchmark. 

140As noted above (II.B.2.b.ii and II.B.3), the 

studies by Silverman and Ito (2010) and Strickland 

et al. (2010) provided support for the 

Administrator’s decision to revise the current 

primary O3 standard, but do not provide insight 

into the appropriateness of specific standard levels 

below 75 ppb. 

141For one study conducted in Vancouver, where 

data from individual monitors did indicate ambient 

concentrations below the level of the current 

standard (Vedal et al., 2003), the Staff Paper noted 

that the study authors questioned whether O3, other 

gaseous pollutants, and PM in this study may be 

Continued 

2014a, Figures 4–9 and 4–10).138 Thus, 

even if some members of at-risk 

populations may experience effects 

following exposures to O3

concentrations somewhat below 60 ppb, 

a revised level of 70 ppb would be 

expected to reduce the occurrence of 

such exposures.139 Therefore, the EPA 

has considered O3 exposures that could 

be relevant for at-risk populations such 

as children and people with asthma, 

and does not agree that controlled 

human exposure studies reporting 

respiratory effects in healthy adults 

following exposures to 60 ppb O3

necessitate a standard level below 70 

ppb. 

ii. Epidemiologic Studies 

Commenters representing 

environmental and public health 

organizations also highlighted 

epidemiologic studies that, in their 

view, provide strong evidence for 

associations with mortality and 

morbidity in locations with ambient O3

concentrations near and below 60 ppb. 

These commenters focused both on the 

epidemiologic studies evaluated in the 

PA’s analyses of study location air 

quality (U.S. EPA, 2014c, Chapter 4) and 

on studies that were not explicitly 

analyzed in the PA, and in some cases 

on studies that were not included in the 

ISA. 

The EPA agrees that epidemiologic 

studies can provide perspective on the 

degree to which O3-associated health 

effects have been identified in areas 

with air quality likely to have met 

various standards. However, as 

discussed below, we do not agree with 

the specific conclusions drawn by these 

commenters regarding the implications 

of epidemiologic studies for the 

standard level. As an initial matter in 

considering epidemiologic studies, the 

EPA notes its decision, consistent with 

CASAC advice, to place the most 

emphasis on information from 

controlled human exposure studies 

(II.B.2 and II.B.3, above). This decision 

reflects the greater certainty in using 

information from controlled human 

exposure studies to link specific O3

exposures with health effects, compared 

to using air quality information from 

epidemiologic studies of O3 for this 

purpose. 

While being aware of the 

uncertainties discussed above 

(II.B.2.b.ii), in considering what 

epidemiologic studies can tell us, the 

EPA notes analyses in the PA (U.S. EPA, 

2014c, section 4.4.1) indicating that a 

revised standard with a level at or below 

70 ppb would be expected to maintain 

distributions of short-term ambient O3

concentrations below those present in 

the locations of all of the single-city 

epidemiologic studies analyzed. As 

discussed in the PA (U.S. EPA, 2014c, 

section 4.4.1), this includes several 

single-city studies conducted in 

locations that would have violated the 

current standard, and the study by Mar 

and Koenig (2009) that reported positive 

and statistically significant associations 

with respiratory emergency department 

visits with children and adults in a 

location that would have met the 

current standard over the entire study 

period, but would have violated a 

standard with a level of 70 ppb.140

While these analyses provide support 

for a level at least as low as 70 ppb, the 

Administrator judges that they do not 

provide a compelling basis for 

distinguishing between the 

appropriateness of 70 ppb and lower 

standard levels. 

As in the proposal, the EPA 

acknowledges additional uncertainty in 

interpreting air quality in locations of 

multicity epidemiologic studies of 

short-term O3 for the purpose of 

evaluating alternative standard levels 

(U.S. EPA, 2014c, sections 3.1.4.2, 

4.4.1). In particular, the PA concludes 

that interpretation of such air quality 

information is complicated by 

uncertainties in the extent to which 

multicity effect estimates (i.e., which are 

based on combining estimates from 

multiple study locations) can be 

attributed to ambient O3 in the subset of 

study locations that would have met a 

particular standard, versus O3 in the 

study locations that would have 

violated the standard. While giving only 

limited weight to air quality analyses in 

these study areas because of this 

uncertainty, the EPA also notes PA 

analyses indicating that a standard level 

at or below 70 ppb would require 

additional reductions, beyond those 

required by the current standard, in the 

ambient O3 concentrations that 

provided the basis for statistically 

significant O3 health effect associations 

in multicity epidemiologic studies. As 

was the case for the single-city studies, 

and contrary to the views expressed by 

the commenters noted above, the 

Administrator judges that these studies 

do not provide a compelling basis for 

distinguishing between the 

appropriateness of alternative standard 

levels at or below 70 ppb. 

In some cases, commenters 

highlighted studies that were assessed 

in the 2008 review of the O3 NAAQS, 

but were not included in the ISA in the 

current review. These commenters 

asserted that such studies support the 

occurrence of O3 health effect 

associations in locations with air quality 

near or, in some cases, below 60 ppb. 

Specifically, commenters highlighted a 

number of studies included in the 2007 

Staff Paper that were not included in the 

ISA, claiming that these studies support 

a standard level below 70 ppb, and as 

low as 60 ppb. 

As an initial matter with regard to 

these studies, the EPA notes that the 

focus of the ISA is on assessing the most 

policy-relevant scientific evidence. In 

the current review, the ISA considered 

over 1,000 new studies that have been 

published since the last review. Thus, it 

is not surprising that, as the body of 

evidence has been strengthened since 

the last review, some of the studies 

considered in the last review are no 

longer among the most policy relevant. 

However, based on the information 

included in the 2007 Staff Paper, the 

EPA does not agree that the studies 

highlighted by commenters provide 

compelling support for a level below 70 

ppb. In fact, as discussed in the Staff 

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

2007, p. 6–9; Appendix 3B), the O3

concentrations reported for these 

studies, and the concentrations 

highlighted by commenters, were based 

on averaging across multiple monitors 

in study areas. Given that the highest 

monitor in an area is used to determine 

whether that area meets or violates the 

NAAQS, the averaged concentrations 

reported in the Staff Paper are thus not 

appropriate for direct comparison to the 

level of the O3 standard. When the Staff 

Paper considered the O3 concentrations 

measured at individual monitors for the 

subset of these study areas with 

particularly low concentrations, they 

were almost universally found to be 

above, and in many cases well above, 

even the current standard level of 75 

ppb.141 Based on the above 

mstockstill on DSK4VPTVN1PROD with RULES2

65360 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

acting as surrogate markers of pollutant mixes that 

contain more toxic compounds, ‘‘since the low 

measured concentrations were unlikely, in their 

opinion, to cause the observed effects’’ (U.S. EPA, 

2007, p. 6–16). The Staff Paper further noted that 

another study conducted in Vancouver failed to 

find statistically significant associations with O3

(Villeneuve et al., 2003). 

142More specifically, based on all children’s 

diaries, just under 0.1% of children are estimated 

to experience two or more exposures of concern at 

or above 70 ppb. Based on simulated profiles of 

highly exposed children, this estimate increased to 

just over 0.1% (U.S. EPA, 2014a, Chapter 5 

Appendices, Figure 5G–9). 

143 In addition, when diaries were selected to 

mimic exposures that could be experienced by 

outdoor workers, the percentages of modeled 

individuals estimated to experience exposures of 

concern were generally similar to the percentages 

estimated for children (i.e., using the full database 

of diary profiles) in the worst-case cities and years 

(i.e., cities and years with the highest exposure 

estimates) (U.S. EPA, 2014, section 5.4.3.2, Figure 

5–14). 

144As discussed in II.B.2.b above, in weighing the 

various uncertainties, which can bias exposure 

results in different directions but tend to have 

impacts that are similar in magnitude (U.S. EPA, 

2014a, Table 5–10), and in light of CASAC’s advice 

based on its review of the HREA and the PA, the 

EPA continues to conclude that the approach to 

considering estimated exposures of concern in the 

HREA, PA, and the proposal reflects an appropriate 

balance, and provides an appropriate basis for 

considering the public health protectiveness of the 

primary O3 standard. 

considerations, and consistent with the 

Administrator’s overall decision to 

place less emphasis on air quality in 

locations of epidemiologic studies to 

select a standard level, the EPA 

disagrees with commenters who 

asserted that epidemiologic studies 

included in the last review, but not 

cited in the ISA or PA in this review, 

necessitate a level below 70 ppb. In fact, 

the EPA notes that these studies are 

consistent with the majority of the U.S. 

studies evaluated in the PA in the 

current review, in that most were 

conducted in locations that would have 

violated the current O3 NAAQS over at 

least part of the study periods. 

iii. Exposure and Risk Assessments 

Some commenters supporting levels 

below 70 ppb also asserted that 

quantitative analyses in the HREA are 

biased such that they understate O3

exposures of concern and risks of O3- 

induced FEV1 decrements. Many of 

these comments are discussed above 

within the context of the adequacy of 

the current standard (II.B.2.b.i), 

including comments pointing out that 

exposure and risk estimates are based 

on information from healthy adults 

rather than at-risk populations; 

comments noting that the exposure 

assessment evaluates 8-hour O3

exposures rather than the 6.6-hour 

exposures used in controlled human 

exposure studies; and comments 

asserting that the EPA’s exposure and 

risk analyses rely on people staying 

indoors on high pollution days (i.e., 

averting behavior). 

As discussed in section II.B.2.b.i 

above, while the EPA agrees with 

certain aspects of these commenters’ 

assertions, we do not agree with their 

overall conclusions. In particular, there 

are aspects of the HREA’s quantitative 

analyses that, if viewed in isolation, 

would tend to either overstate or 

understate O3 exposures and/or health 

risks. While commenters tended to 

focus on those aspects of the 

assessments that support their position, 

they tended to ignore aspects of the 

assessments that do not support their 

position (points that were often raised 

by commenters on the other side of the 

issue). Rather than viewing the potential 

implications of these aspects of the 

HREA assessments in isolation, the EPA 

considers them together, along with 

other issues and uncertainties related to 

the interpretation of exposure and risk 

estimates. 

For example, some commenters who 

advocated for a level below 70 ppb 

asserted that the exposure assessment 

could underestimate O3 exposures for 

highly active populations, including 

outdoor workers and children who 

spend a large portion of time outdoors 

during summer. In support of these 

assertions, commenters highlighted 

sensitivity analyses conducted in the 

HREA. However, as noted in the HREA 

(U.S. EPA, 2014a, Table 5–10), this 

aspect of the assessment is likely to 

have only a ‘‘low to moderate’’ impact 

on the magnitude of exposure estimates. 

To put this magnitude in perspective, 

HREA sensitivity analyses conducted in 

a single urban study area indicate that, 

regardless of whether exposure 

estimates for children are based on all 

available diaries or on a subset of diaries 

restricted to simulate highly exposed 

children, a revised standard with a level 

of 70 ppb is estimated to protect more 

than 99% of children from experiencing 

two or more exposures of concern at or 

above 70 ppb (U.S. EPA, 2014a, Chapter 

5 Appendices, Figure 5G–9).142 143 In 

contrast to the focus of commenters who 

supported a level below 70 ppb, other 

aspects of quantitative assessments, 

some of which were highlighted by 

commenters who opposed revising the 

current standard (II.B.2), tend to result 

in overestimates of O3 exposures. These 

aspects are characterized in the HREA 

as having either a ‘‘low,’’ a ‘‘low-tomoderate,’’ or a ‘‘moderate’’ impact on 

the magnitudes of exposure estimates. 

In its reviews of the HREA and PA, 

CASAC recognized many of the 

uncertainties and issues highlighted by 

commenters. Even considering these 

uncertainties, CASAC endorsed the 

approaches adopted by the EPA to 

assess O3 exposures and health risks, 

and CASAC used exposure and risk 

estimates as part of the basis for their 

recommendations on the primary O3

NAAQS (Frey, 2014c). Thus, as 

discussed in section II.B.2.b.i above, the 

EPA disagrees with commenters who 

claim that the aspects of the quantitative 

assessments that they highlight lead to 

overall underestimates of exposures or 

health risks.144

Some commenters further contended 

that the level of the primary O3 standard 

should be set below 70 ppb in order to 

compensate for the use of a form that 

allows multiple days with 

concentrations higher than the standard 

level. These groups submitted air 

quality analyses to support their point 

that the current fourth-high form allows 

multiple days per year with ambient O3

concentrations above the level of the 

standard. While the EPA does not 

dispute the air quality analyses 

submitted by these commenters, and 

agrees that fourth-high form allows 

multiple days per year with ambient O3

concentrations above the level of the 

standard (3 days per year, on average 

over a 3-year period), the Agency 

disagrees with commenters’ assertion 

that, because of this, the level of the 

primary O3 standard should be set 

below 70 ppb. As discussed above 

(II.A.2), the quantitative assessments 

that informed the Administrator’s 

proposed decision, presented in the 

HREA and considered in the PA and by 

CASAC, estimated O3 exposures and 

health risks associated with air quality 

that ‘‘just meets’’ various standards with 

the current 8-hour averaging time and 

fourth-high, 3-year average form. Thus, 

in considering the degree of public 

health protection appropriate for the 

primary O3 standard, the Administrator 

has considered quantitative exposure 

and risk estimates that are based a 

fourth-high form, and therefore on a 

standard that, as these commenters 

point out, allows multiple days per year 

with ambient O3 concentrations above 

the level of the standard. 

iv. CASAC Advice 

Many commenters, including those 

representing major medical, public 

health, or environmental groups; some 

state agencies; and a large number of 

individual commenters, focused on 

CASAC advice in their rationale 

supporting levels below 70 ppb, and as 

low as 60 ppb. These commenters 

generally asserted that the EPA must 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65361 

145The EPA notes, of course, that the CAA places 

the responsibility for judging what standard is 

requisite with the Administrator and only requires 

that, if her decision differs in important ways from 

CASAC’s advice, she explain her reasoning for 

differing. 

146Percent reductions in this section refer to 

reductions in the number of children in HREA 

urban study areas (averaged over the years 

evaluated in the HREA) estimated to experience 

exposures of concern, based on the information in 

Table 1 above. 

give deference to CASAC. In some cases, 

these commenters expressed strong 

objections to a level of 70 ppb, noting 

CASAC policy advice that such a level 

would provide little margin of safety. 

The EPA agrees that CASAC advice is 

an important consideration in reaching 

a decision on the standard level (see e.g. 

CAA section 307 (d)(3)),145 though not 

with commenters’ conclusion that 

CASAC advice necessitates a standard 

level below 70 ppb. As discussed above 

(II.C.4.a), the Administrator carefully 

considered CASAC advice in the 

proposal, and she judged that her 

proposed decision to revise the level to 

within the range of 65 to 70 ppb was 

consistent with CASAC advice, based 

on the available science. 

As in the proposal, in her final 

decision on level the Administrator 

notes CASAC’s overall conclusion that 

‘‘based on the scientific evidence from 

clinical studies, epidemiologic studies, 

animal toxicology studies, as 

summarized in the ISA, the findings 

from the exposure and risk assessments 

as summarized in the HREA, and the 

interpretation of the implications of all 

of these sources of information as given 

in the Second Draft PA . . . there is 

adequate scientific evidence to 

recommend a range of levels for a 

revised primary ozone standard from 70 

ppb to 60 ppb’’ (Frey, 2014c, p. 8). Thus, 

CASAC used the health evidence and 

exposure/risk information to inform its 

range of recommended standard levels, 

a range that included an upper bound of 

70 ppb based on the scientific evidence, 

and it did not use the evidence and 

information to recommend setting the 

primary O3 standard at any specific 

level within the range of 70 to 60 ppb. 

In addition, CASAC further stated that 

‘‘the choice of a level within the range 

recommended based on scientific 

evidence [i.e., 70 to 60 ppb] is a policy 

judgment under the statutory mandate 

of the Clean Air Act’’ (Frey, 2014c, p. ii). 

In addition to its advice based on the 

scientific evidence, CASAC offered the 

‘‘policy advice’’ to set the level below 70 

ppb, stating that a standard level of 70 

ppb ‘‘may not meet the statutory 

requirement to protect public health 

with an adequate margin of safety’’ 

(Frey, 2014c, p. ii). In supporting its 

policy advice to set the level below 70 

ppb, CASAC noted the respiratory 

effects that have been shown to occur in 

controlled human exposure studies 

following exposures from 60 to 80 ppb 

O3, and the extent to which various 

standard levels are estimated to allow 

the occurrence of population exposures 

that can result in such effects (Frey, 

2014c, pp. 7–8). 

The EPA agrees that an important 

consideration when reaching a decision 

on level is the extent to which a revised 

standard is estimated to allow the types 

of exposures shown in controlled 

human exposure studies to cause 

respiratory effects. In reaching her final 

decision that a level of 70 ppb is 

requisite to protect public health with 

an adequate margin of safety (II.C.4.c, 

below), the Administrator carefully 

considers the potential for such 

exposures and effects. In doing so, she 

emphasizes the importance of setting a 

standard that limits the occurrence of 

the exposures about which she is most 

concerned (i.e., those for which she has 

the most confidence in the adversity of 

the resulting effects, which are repeated 

exposures of concern at or above 70 or 

80 ppb, as discussed above in II.C.4.b.i). 

Based on her consideration of 

information from controlled human 

exposure studies in light of CASAC 

advice and ATS recommendations, the 

Administrator additionally judges that 

there is important uncertainty in the 

extent to which the effects shown to 

occur following exposures to 60 ppb O3

are adverse to public health (discussed 

above, II.C.4.b.i and II.C.4.b.iii). 

However, based on the effects that have 

been shown to occur, CASAC advice 

indicating the importance of 

considering these effects, and ATS 

recommendations indicating the 

potential for adverse population-level 

effects (II.C.4.b.i, II.C.4.b.iii), she 

concludes that it is appropriate to give 

some consideration to the extent to 

which a revised standard could allow 

the respiratory effects that have been 

observed following exposures to 60 ppb 

O3. 

When considering the extent to which 

a revised standard could allow O3

exposures that have been shown in 

controlled human exposures studies to 

result in respiratory effects, the 

Administrator is most concerned about 

protecting the public, including at-risk 

populations, against repeated 

occurrences of such exposures of 

concern (II.C.4.b.i, above). In 

considering the appropriate metric for 

evaluating repeated occurrences of 

exposures of concern, the Administrator 

acknowledges that it is not clear from 

the evidence, or from the ATS 

recommendations, CASAC advice, or 

public comments, how particular 

numbers of exposures of concern could 

impact the seriousness of the resulting 

effects, especially at lower exposure 

concentrations. Therefore, the 

Administrator judges that focusing on 

HREA estimates of two or more 

exposures of concern provides a healthprotective approach to considering the 

potential for repeated occurrences of 

exposures of concern that could result 

in adverse effects. She notes that other 

possible metrics for considering 

repeated occurrences of exposures of 

concern (e.g., 3 or more, 4 or more, etc.) 

would result in smaller exposure 

estimates. 

As discussed further below (II.C.4.c), 

the Administrator notes that a revised 

standard with a level of 70 ppb is 

estimated to eliminate the occurrence of 

two or more exposures of concern to O3

concentrations at or above 80 ppb and 

to virtually eliminate the occurrence of 

two or more exposures of concern to O3

concentrations at or above 70 ppb (Table 

1, above). For the 70 ppb benchmark, 

this reflects about a 90% reduction in 

the number of children estimated to 

experience two or more exposures of 

concern, compared to the current 

standard.146 Even considering the worstcase urban study area and worst-case 

year evaluated in the HREA, a standard 

with a level of 70 ppb is estimated to 

protect more than 99% of children from 

experiencing two or more exposures of 

concern to O3 concentrations at or above 

70 ppb (Table 1). 

Though the Administrator judges that 

there is greater uncertainty with regard 

to the occurrence of adverse effects 

following exposures as low as 60 ppb, 

she notes that a revised standard with 

a level of 70 ppb is estimated to protect 

the vast majority of children in urban 

study areas (i.e., about 96% to more 

than 99% in individual areas) from 

experiencing two or more exposures of 

concern at or above 60 ppb. Compared 

to the current standard, this represents 

a reduction of more than 60% in 

exposures of concern for the 60 ppb 

benchmark (Table 1). Given the 

Administrator’s uncertainty regarding 

the adversity of the effects following 

exposures to 60 ppb O3, and her healthprotective approach to considering 

repeated occurrences of exposures of 

concern, the Administrator judges that 

this degree of protection is appropriate 

and that it reflects substantial protection 

against the occurrence of O3-induced 

effects, including effects for which she 

judges the adversity to public health is 

uncertain. 

mstockstill on DSK4VPTVN1PROD with RULES2

65362 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

147As discussed above (II.C.4.b.i), when 

commenting on the extent to which the study by 

Schelegle et al. (2009) suggests the potential for 

adverse effects following O3 exposures below 72 

ppb, CASAC stated the following: ‘‘[I]f subjects had 

been exposed to ozone using the 8-hour averaging 

period used in the standard [rather than the 6.6- 

hour exposures evaluated in the study], adverse 

effects could have occurred at lower concentration. 

Further, in our judgment, the level at which adverse 

effects might be observed would likely be lower for 

more sensitive subgroups, such as those with 

asthma’’ (Frey, 2014c, p. 5). 

148At-risk populations include people with 

asthma; children and older adults; people who are 

active outdoors, including outdoor workers; people 

with certain genetic variants; and people with 

reduced intake of certain nutrients. 

149See, e.g. NRDC v. EPA, 902 F. 2d 962, 973– 

74 (D.C. Cir. 1990). 

While being less concerned about 

single occurrences of exposures of 

concern, especially at lower exposure 

concentrations, the Administrator also 

notes that a standard with a level of 70 

ppb is estimated to (1) virtually 

eliminate all occurrences of exposures 

of concern at or above 80 ppb; (2) 

protect ≥ about 99% of children in 

urban study areas from experiencing 

any exposures of concern at or above 70 

ppb; and (3) to achieve substantial 

reductions (i.e., about 50%), compared 

to the current standard, in the 

occurrence of one or more exposures of 

concern at or above 60 ppb (Table 1). 

Given the information and advice 

noted above (and in II.C.4.b.i, 

II.C.4.b.iii), the Administrator judges 

that a revised standard with a level of 

70 ppb will effectively limit the 

occurrence of the O3 exposures for 

which she has the most confidence in 

the adversity of the resulting effects (i.e., 

based on estimates for the 70 and 80 

ppb benchmarks). She further judges 

that such a standard will provide a large 

degree of protection against O3

exposures for which there is greater 

uncertainty in the adversity of effects 

(i.e., those observed following exposures 

to 60 ppb O3), contributing to the 

margin of safety of the standard. See 

Mississippi, 744 F. 3d at 1353 (‘‘By 

requiring an ‘adequate margin of safety’, 

Congress was directing EPA to build a 

buffer to protect against uncertain and 

unknown dangers to human health’’). 

Given the considerable protection 

provided against repeated exposures of 

concern for all of the benchmarks 

evaluated, including the 60 ppb 

benchmark, the Administrator judges 

that a standard with a level of 70 ppb 

will provide an adequate margin of 

safety against the adverse O3-induced 

effects shown to occur following 

exposures at or above 72 ppb, and 

judged by CASAC likely to occur 

following exposures somewhat below 72 

ppb.147

Contrary to the conclusions of 

commenters who advocated for a level 

below 70 ppb, the Administrator notes 

that her final decision is consistent with 

CASAC’s advice, based on the scientific 

evidence, and with CASAC’s focus on 

setting a revised standard to further 

limit the occurrence of the respiratory 

effects observed in controlled human 

exposure studies, including effects 

observed following exposures to 60 ppb 

O3. Given her judgments and 

conclusions discussed above, and given 

that the CAA reserves the choice of the 

standard that is requisite to protect 

public health with an adequate margin 

of safety for the judgment of the EPA 

Administrator, she disagrees with 

commenters who asserted that CASAC 

advice necessitates a level below 70 

ppb, and as low as 60 ppb. The 

Administrator’s final conclusions on 

level are discussed in more detail below 

(II.C.4.c). 

c. Administrator’s Final Decision 

Regarding Level 

Having carefully considered the 

public comments on the appropriate 

level of the primary O3 standard, as 

discussed above and in the Response to 

Comments document, the Administrator 

believes her scientific and policy 

judgments in the proposal remain valid. 

In conjunction with her decisions to 

retain the current indicator, averaging 

time, and form (II.C.1 to II.C.3, above), 

the Administrator is revising the level of 

the primary O3 standard to 70 ppb. In 

doing so, she is selecting a primary O3

standard that is requisite to protect 

public health with an adequate margin 

of safety, in light of her judgments based 

on an interpretation of the scientific 

evidence and exposure/risk information 

that neither overstates nor understates 

the strengths and limitations of that 

evidence and information and the 

appropriate inferences to be drawn 

therefrom. 

The Administrator’s decision to revise 

the level of the primary O3 standard to 

70 ppb builds upon her conclusion that 

the overall body of scientific evidence 

and exposure/risk information calls into 

question the adequacy of public health 

protection afforded by the current 

standard, particularly for at-risk 

populations and lifestages (II.B.3).148

Consistent with the proposal, her 

decision on level places the greatest 

emphasis on the results of controlled 

human exposure studies and on 

quantitative analyses based on 

information from these studies, 

particularly analyses of O3 exposures of 

concern. As in the proposal, and as 

discussed further below, she views the 

results of the lung function risk 

assessment, analyses of O3 air quality in 

locations of epidemiologic studies, and 

epidemiology-based quantitative health 

risk assessments as providing 

information in support of her decision 

to revise the current standard, but a 

more limited basis for selecting a 

particular standard level among a range 

of options. See Mississippi, 744 F. 3d at 

1351–52 (studies can legitimately 

support a decision to revise the 

standard, but not provide sufficient 

information to justify their use in setting 

the level of a revised standard). 

Given her consideration of the 

evidence, exposure/risk information, 

advice from CASAC, and public 

comments, the Administrator judges 

that a standard with a level of 70 ppb 

is requisite to protect public health with 

an adequate margin of safety. She notes 

that the determination of what 

constitutes an adequate margin of safety 

is expressly left to the judgment of the 

EPA Administrator. See Lead Industries 

Association v. EPA, 647 F.2d at 1161– 

62; Mississippi, 744 F. 3d at 1353. She 

further notes that in evaluating how 

particular standards address the 

requirement to provide an adequate 

margin of safety, it is appropriate to 

consider such factors as the nature and 

severity of the health effects, the size of 

sensitive population(s) at risk, and the 

kind and degree of the uncertainties 

present (I.B, above). Consistent with 

past practice and long-standing judicial 

precedent, the Administrator takes the 

need for an adequate margin of safety 

into account as an integral part of her 

decision-making on the appropriate 

level, averaging time, form, and 

indicator of the standard.149

In considering the need for an 

adequate margin of safety, the 

Administrator notes that a standard 

with a level of 70 ppb O3 would be 

expected to provide substantial 

improvements in public health, 

including for at-risk groups such as 

children and people with asthma. The 

following paragraphs summarize the 

basis for the Administrator’s conclusion 

that a revised primary O3 standard with 

a level of 70 ppb is requisite to protect 

the public health with an adequate 

margin of safety. 

As an initial matter, consistent with 

her conclusions on the need for revision 

of the current standard (II.B.3), in 

reaching a decision on level the 

Administrator places the most weight 

on information from controlled human 

exposure studies. In doing so, she notes 

that controlled human exposure studies 

provide the most certain evidence 

indicating the occurrence of health 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65363 

effects in humans following specific O3

exposures. In particular, she notes that 

the effects reported in controlled human 

exposure studies are due solely to O3

exposures, and interpretation of study 

results is not complicated by the 

presence of co-occurring pollutants or 

pollutant mixtures (as is the case in 

epidemiologic studies). The 

Administrator also observes that her 

emphasis on information from 

controlled human exposure studies is 

consistent with CASAC’s advice and 

interpretation of the scientific evidence 

(Frey, 2014c). 

With regard to the effects shown in 

controlled human exposure studies 

following specific O3 exposures, as 

discussed in more detail above (II.B, 

II.C.4.b.i), the Administrator notes that 

(1) the largest respiratory effects, and 

the broadest range of effects, have been 

studied and reported following 

exposures to 80 ppb O3 or higher (i.e., 

decreased lung function, increased 

airway inflammation, increased 

respiratory symptoms, AHR, and 

decreased lung host defense); (2) 

exposures to O3 concentrations as low 

as 72 ppb have been shown to both 

decrease lung function and result in 

respiratory symptoms; and (3) exposures 

to O3 concentrations as low as 60 ppb 

have been shown to decrease lung 

function and to increase airway 

inflammation. 

While such controlled human 

exposure studies provide a high degree 

of confidence regarding the occurrence 

of health effects following exposures to 

O3 concentrations from 60 to 80 ppb, 

there are no universally accepted 

criteria by which to judge the adversity 

of the observed effects. To inform her 

judgments on the potential adversity to 

public health of effects reported in 

controlled human exposure studies, the 

Administrator considers ATS 

recommendations and CASAC advice, 

as described in detail above (II.B.2, 

II.C.4.b.i, II.C.4.b.iii, II.C.4.b.iv). Based 

on her consideration of such 

recommendations and advice, the 

Administrator is confident that the 

respiratory effects that have been 

observed following exposures to 72 ppb 

O3 or above can be adverse. In addition, 

she judges that adverse effects are likely 

to occur following exposures somewhat 

below 72 ppb (II.C.4.b.i). However, as 

described above (II.C.4.b.i, II.C.4.b.iii, 

II.C.4.b.iv), the Administrator is notably 

less confident in the adversity to public 

health of the respiratory effects that 

have been observed following exposures 

to O3 concentrations as low as 60 ppb, 

given her consideration of the following: 

(1) ATS recommendations indicating 

uncertainty in judging adversity based 

on lung function decrements alone; (2) 

uncertainty in the extent to which a 

short-term, transient population-level 

decrease in FEV1 would increase the 

risk of other, more serious respiratory 

effects in that population (i.e., per ATS 

recommendations on population-level 

risk); and (3) compared to 72 ppb, 

CASAC advice is less clear regarding the 

potential adversity of effects at 60 ppb. 

Taken together, the Administrator 

concludes that the evidence from 

controlled human exposure studies 

provides strong support for her 

conclusion that a revised standard with 

a level of 70 ppb is requisite to protect 

the public health with an adequate 

margin of safety. She bases this 

conclusion, in part, on the fact that such 

a standard level would be well below 

the O3 exposure concentration shown to 

result in the widest range of respiratory 

effects (i.e., 80 ppb), and below the 

lowest O3 exposure concentration 

shown to result in the adverse 

combination of lung function 

decrements and respiratory symptoms 

(i.e., 72 ppb). See Lead Industries, 647 

F. 2d at 1160 (setting NAAQS at level 

well below the level where the clearest 

adverse effects occur, and at a level 

eliminating most ‘‘sub-clinical effects’’ 

provides an adequate margin of safety). 

As discussed above (II.C.4.b.i), the 

Administrator also notes that a revised 

O3 standard with a level of 70 ppb can 

provide substantial protection against 

the broader range of O3 exposure 

concentrations that have been shown in 

controlled human exposure studies to 

result in respiratory effects, including 

exposure concentrations below 70 ppb. 

The degree of protection provided by 

any NAAQS is due to the combination 

of all of the elements of the standard 

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

level) and, in the case of the fourth-high 

form of the revised primary O3 standard 

(II.C.3), the large majority of days in 

areas that meet the revised standard will 

have 8-hour O3 concentrations below 70 

ppb, with most days having 8-hour O3

concentrations well below this level. In 

addition, the degree of protection 

provided by the O3 NAAQS is also 

dependent on the extent to which 

people experience health-relevant O3

exposures in locations meeting the 

NAAQS. As discussed above, for a 

pollutant like O3 where adverse 

responses are critically dependent on 

ventilation rates, the Administrator 

notes that it is important to consider 

activity patterns in the exposed 

population. Not considering activity 

patterns, and corresponding ventilation 

rates, can result in a standard that 

provides more protection than is 

requisite. Therefore, as discussed in the 

proposal, in considering the degree of 

protection provided by a revised 

primary O3 standard, the Administrator 

considers the extent to which that 

standard would be expected to limit 

population exposures of concern (i.e., 

which take into account activity 

patterns and estimated ventilation rates) 

to the broader range of O3 exposure 

concentrations shown to result in health 

effects. 

Due to interindividual variability in 

responsiveness, the Administrator notes 

that not every occurrence of an exposure 

of concern will result in an adverse 

effect (II.C.4.b.i). Moreover, repeated 

occurrences of some of the effects 

demonstrated following exposures of 

concern could increase the likelihood of 

adversity (U.S. EPA, 2013, Section 6.2.3, 

p. 6–76). In particular, she notes that the 

types of respiratory effects that can 

occur following exposures of concern, 

particularly if experienced repeatedly, 

provide a plausible mode of action by 

which O3 may cause other more serious 

effects. Therefore, as in the proposal, the 

Administrator is most concerned about 

protecting at-risk populations against 

repeated occurrences of exposures of 

concern. In considering the appropriate 

metric for evaluating repeated 

occurrences of exposures of concern, the 

Administrator acknowledges that it is 

not clear from the evidence, or from the 

ATS recommendations, CASAC advice, 

or public comments, how particular 

numbers of exposures of concern could 

impact the seriousness of the resulting 

effects, especially at lower exposure 

concentrations. Therefore, the 

Administrator judges that focusing on 

HREA estimates of two or more 

exposures of concern provides a healthprotective approach to considering the 

potential for repeated occurrences of 

exposures of concern that could result 

in adverse effects. 

Based on her consideration of 

adversity discussed above, the 

Administrator places the most emphasis 

on setting a standard that appropriately 

limits repeated occurrences of 

exposures of concern at or above the 70 

and 80 ppb benchmarks. She notes that 

a revised standard with a level of 70 ppb 

is estimated to eliminate the occurrence 

of two or more exposures of concern to 

O3 concentrations at or above 80 ppb 

and to virtually eliminate the 

occurrence of two or more exposures of 

concern to O3 concentrations at or above 

70 ppb for all children and children 

with asthma, even in the worst-case year 

and location evaluated. 

While she is less confident that 

adverse effects will occur following 

exposures to O3 concentrations as low 

as 60 ppb, as discussed above, the 

mstockstill on DSK4VPTVN1PROD with RULES2

65364 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

150For example, the average percentage of 

children estimated to experience two or more 

decrements ≥10% ranges from approximately 6 to 

11% for a standard level of 70 ppb, up to about 9% 

for a level of 65 ppb, and up to about 6% for a level 

of 60 ppb (Table 2, above). 

151As discussed above (II.B.2.c.ii and II.B.3), the 

study by Mar and Koenig (2009) reported positive 

and statistically significant associations with 

respiratory emergency department visits in a 

location that would have met the current standard 

over the entire study period, but violated a standard 

with a level of 70 ppb. In addition, air quality 

analyses in the locations of two additional studies 

highlighted in sections II.B.2 and II.B.3 (Silverman 

and Ito, 2010; Strickland et al., 2010) were used in 

the PA to inform staff conclusions on the adequacy 

of the current primary O3 standard. However, they 

did not provide insight into the appropriateness of 

standard levels below 75 ppb and, therefore, these 

analyses were not used to inform conclusions on 

potential alternative standard levels lower than 75 

ppb (U.S. EPA, 2014c, Chapters 3 and 4). See 

Mississippi, 744 F. 3d at 1352–53 (study 

appropriate for determining causation may not be 

probative for determining level of a revised 

standard). 

Administrator judges that it is also 

appropriate to consider estimates of 

exposures of concern for the 60 ppb 

benchmark. Consistent with this 

judgment, although CASAC advice 

regarding the potential adversity of 

effects at 60 ppb was less definitive than 

for effects at 72 ppb, CASAC did clearly 

advise the EPA to consider the extent to 

which a revised standard is estimated to 

limit the effects observed following 60 

ppb exposures (Frey, 2014c). Therefore, 

the Administrator considers estimated 

exposures of concern for the 60 ppb 

benchmark, particularly considering the 

extent to which the health protection 

provided by a revised standard includes 

a margin of safety against the occurrence 

of adverse O3-induced effects. The 

Administrator notes that a revised 

standard with a level of 70 ppb is 

estimated to protect the vast majority of 

children in urban study areas (i.e., about 

96% to more than 99% of children in 

individual areas) from experiencing two 

or more exposures of concern at or 

above 60 ppb. Compared to the current 

standard, this represents a reduction of 

more than 60%. 

Given the considerable protection 

provided against repeated exposures of 

concern for all of the benchmarks 

evaluated, including the 60 ppb 

benchmark, the Administrator judges 

that a standard with a level of 70 ppb 

will incorporate a margin of safety 

against the adverse O3-induced effects 

shown to occur following exposures at 

or above 72 ppb, and judged likely to 

occur following exposures somewhat 

below 72 ppb. 

While the Administrator is less 

concerned about single occurrences of 

O3 exposures of concern, especially for 

the 60 ppb benchmark, she judges that 

estimates of one or more exposures of 

concern can provide further insight into 

the margin of safety provided by a 

revised standard. In this regard, she 

notes that a standard with a level of 70 

ppb is estimated to (1) virtually 

eliminate all occurrences of exposures 

of concern at or above 80 ppb; (2) 

protect the vast majority of children in 

urban study areas from experiencing 

any exposures of concern at or above 70 

ppb (i.e., ≥ about 99%, based on mean 

estimates; Table 1); and (3) to achieve 

substantial reductions, compared to the 

current standard, in the occurrence of 

one or more exposures of concern at or 

above 60 ppb (i.e., about a 50% 

reduction; Table 1). The Administrator 

judges that these results provide further 

support for her conclusion that a 

standard with a level of 70 ppb will 

incorporate an adequate margin of safety 

against the occurrence of O3 exposures 

that can result in effects that are adverse 

to public health. 

The Administrator additionally judges 

that a standard with a level of 70 ppb 

would be expected to result in 

important reductions, compared to the 

current standard, in the populationlevel risk of O3-induced lung function 

decrements (≥10%, ≥15%) in children, 

including children with asthma. 

Specifically, a revised standard with a 

level of 70 ppb is estimated to reduce 

the risk of two or more O3-induced 

decrements by about 30% and 20% for 

decrements ≥15 and 10%, respectively 

(Table 2, above). However, as discussed 

above (II.C.4.b.i), the Administrator 

judges that there are important 

uncertainties in using lung function risk 

estimates as a basis for considering the 

occurrence of adverse effects in the 

population given (1) the ATS 

recommendation that ‘‘a small, transient 

loss of lung function, by itself, should 

not automatically be designated as 

adverse’’ (ATS, 2000a); (2) uncertainty 

in the extent to which a transient 

population-level decrease in FEV1

would increase the risk of other, more 

serious respiratory effects in that 

population (i.e., per ATS 

recommendations on population-level 

risk); and (3) that CASAC did not advise 

considering a standard that would be 

estimated to eliminate O3-induced lung 

function decrements ≥10 or 15% (Frey, 

2014c). Moreover, as at proposal, the 

Administrator notes that the variability 

in lung function risk estimates across 

urban study areas is often greater than 

the differences in risk estimates between 

various standard levels (Table 2, 

above).150 Given this, and the resulting 

considerable overlap between the ranges 

of lung function risk estimates for 

different standard levels, the 

Administrator puts limited weight on 

the lung function risk estimates for 

distinguishing between the degrees of 

public health protection provided by 

alternative standard levels. Therefore, 

the Administrator judges that while a 

standard with a level of 70 ppb would 

be expected to result in important 

reductions, compared to the current 

standard, in the population-level risk of 

O3-induced lung function decrements 

(>10%, 15%) in children, including 

children with asthma, she also judges 

that estimated risks of O3-induced lung 

function decrements provide a more 

limited basis than exposures of concern 

for distinguishing between the 

appropriateness of the health protection 

afforded by a standard level of 70 ppb 

versus lower levels. 

The Administrator also considers the 

epidemiologic evidence and the 

quantitative risk estimates based on 

information from epidemiologic studies. 

As discussed in the proposal, and above 

in the EPA’s responses to significant 

comments, although the Administrator 

acknowledges the important 

uncertainties in using the O3

epidemiologic studies as a basis for 

selecting a standard level, she notes that 

these studies can provide perspective on 

the degree to which O3-associated 

health effects have been identified in 

areas with air quality likely to have met 

various standards. Specifically, the 

Administrator notes analyses in the PA 

(U.S. EPA, 2014c, section 4.4.1) 

indicating that a revised standard with 

a level of 70 ppb would be expected to 

require additional reductions, beyond 

those required by the current standard, 

in the short- and long-term ambient O3

concentrations that provided the basis 

for statistically significant O3 health 

effect associations in both the single-city 

and multicity epidemiologic studies 

evaluated. As discussed above in the 

response to comments, while the 

Administrator concludes that these 

analyses support a level at least as low 

as 70 ppb, based on a study reporting 

health effect associations in a location 

that met the current standard over the 

entire study period but that would have 

violated a revised standard with a level 

of 70 ppb,151 she further judges that 

they are of more limited utility for 

distinguishing between the 

appropriateness of the health protection 

estimated for a standard level of 70 ppb 

and the protection estimated for lower 

levels. Thus, the Administrator notes 

that a revised standard with a level of 

70 ppb will provide additional public 

health protection, beyond that provided 

by the current standard, against the 

clearly adverse effects reported in 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65365 

epidemiologic studies. She judges that a 

standard with a level of 70 ppb strikes 

an appropriate balance between setting 

the level to require reductions in the 

ambient O3 concentrations associated 

with statistically significant health 

effects in epidemiologic studies, while 

not being more protective than 

necessary in light of her considerable 

uncertainty in the extent to which 

studies clearly show O3-attributable 

effects at lower ambient O3

concentrations. This judgment is 

consistent with the Administrator’s 

conclusions based on information from 

controlled human exposure studies, as 

discussed above. 

With regard to epidemiology-based 

risk estimates, the Administrator takes 

note of the CASAC conclusion that 

‘‘[a]lthough the estimates for short-term 

exposure impacts are subject to 

uncertainty, the data supports a 

conclusion that there are meaningful 

reductions in mean premature mortality 

associated with ozone levels lower than 

the current standard’’ (Frey, 2014a, p. 

10). While she concludes that 

epidemiology-based risk analyses 

provide only limited support for any 

specific standard level, consistent with 

CASAC advice the Administrator judges 

that, compared to the current standard, 

a revised standard with a level of 70 ppb 

will result in meaningful reductions in 

the mortality and respiratory morbidity 

risk that is associated with short-or 

long-term ambient O3 concentrations. 

Given all of the evidence and 

information discussed above, the 

Administrator judges that a standard 

with a level of 70 ppb is requisite to 

protect public health with an adequate 

margin of safety, and that a level below 

70 ppb would be more than ‘‘requisite’’ 

to protect the public health. In reaching 

this conclusion, she notes that a 

decision to set a lower level would 

place a large amount of emphasis on the 

potential public health importance of (1) 

further reducing the occurrence of O3

exposures of concern, though the 

exposures about which she is most 

concerned are estimated to be almost 

eliminated with a level of 70 ppb, and 

lower levels would be expected to 

achieve virtually no additional 

reductions in these exposures (see Table 

1, above); (2) further reducing the risk 

of O3-induced lung function decrements 

>10 and 15%, despite having less 

confidence in judging the potential 

adversity of lung function decrements 

alone and the considerable overlap 

between risk estimates for various 

standard levels that make it difficult to 

distinguish between the risk reductions 

achieved; (3) further reducing ambient 

O3 concentrations, relative to those in 

locations of epidemiologic studies, 

though associations have not been 

reported for air quality that would have 

met a standard with a level of 70 ppb 

across all study locations and over 

entire study periods, and despite her 

consequent judgment that air quality 

analyses in epidemiologic study 

locations are not informative regarding 

the additional degree of public health 

protection that would be afforded by a 

standard set at a level below 70 ppb; 

and (4) further reducing epidemiologybased risk estimates, despite the 

important uncertainties in those 

estimates. As discussed in this section 

and in the responses to significant 

comments above, the Administrator 

does not agree that it is appropriate to 

place significant weight on these factors 

or to use them to support the 

appropriateness of standard levels 

below 70 ppb O3. Compared to an O3

standard level of 70 ppb, the 

Administrator concludes that the extent 

to which lower standard levels could 

result in further public health 

improvements becomes notably less 

certain. 

Thus, having carefully considered the 

evidence, information, CASAC advice, 

and public comments relevant to her 

decision on the level of the primary O3

standard, as discussed above and in the 

Response to Comments document, the 

Administrator is revising the level of the 

primary O3 standard to 70 ppb. She is 

mindful that the selection of a primary 

O3 standard that is requisite to protect 

public health with an adequate margin 

of safety requires judgments based on an 

interpretation of the scientific evidence 

and exposure/risk information that 

neither overstate nor understate the 

strengths and limitations of that 

evidence and information and the 

appropriate inferences to be drawn 

therefrom. Her decision places the 

greatest emphasis on the results of 

controlled human exposure studies and 

on quantitative analyses based on 

information from these studies, 

particularly analyses of O3 exposures of 

concern. As in the proposal, and as 

discussed above, she views the results 

of the lung function risk assessment, 

analyses of O3 air quality in locations of 

epidemiologic studies, and 

epidemiology-based quantitative health 

risk assessments as providing 

information in support of her decision 

to revise the current standard, but a 

more limited basis for selecting a 

particular standard level among a range 

of options. 

In making her decision to revise the 

level of the primary O3 standard to 70 

ppb, the Administrator judges that a 

revised standard with a level of 70 ppb 

strikes the appropriate balance between 

limiting the O3 exposures about which 

she is most concerned and not going 

beyond what would be required to 

effectively limit such exposures. 

Specifically, the Administrator judges it 

appropriate to set a standard estimated 

to eliminate, or almost eliminate, 

repeated occurrences of exposures of 

concern for the 70 and 80 ppb 

benchmarks. She further judges that a 

lower standard level would not be 

appropriate given that lower levels 

would be expected to achieve virtually 

no additional reductions in repeated 

occurrences of exposures of concern for 

these benchmarks. For the 60 ppb 

benchmark, a level of 70 ppb is 

estimated to protect the vast majority of 

children (including children with 

asthma) in urban study areas from 

experiencing two or more exposures of 

concern, reflecting important reductions 

in such exposures compared to the 

current standard and indicating that the 

revised primary O3 standard provides an 

adequate margin of safety. Given these 

results, including the considerable 

protection provided against repeated 

exposures of concern for the 60 ppb 

benchmark, the Administrator judges 

that a standard with a level of 70 ppb 

incorporates an adequate margin of 

safety against the occurrence of adverse 

O3-induced effects. 

For all of the above reasons, the 

Administrator concludes that a primary 

O3 standard with an 8-hour averaging 

time; a 3-year average, fourth-high form; 

and a level of 70 ppb is requisite to 

protect public health, including the 

health of at-risk populations, with an 

adequate margin of safety. Therefore, in 

this final rule she is setting the level of 

the primary O3 standard at 70 ppb. 

D. Decision on the Primary Standard 

For the reasons discussed above, and 

taking into account information and 

assessments presented in the ISA, 

HREA, and PA, the advice and 

recommendations of the CASAC Panel, 

and the public comments, the 

Administrator has decided to revise the 

existing 8-hour primary O3 standard. 

Specifically, the Administrator is 

revising the level of the primary O3

standard to 70 ppb. The revised 8-hour 

primary standard, with a level of 70 

ppb, would be met at an ambient air 

monitoring site when the 3-year average 

of the annual fourth-highest daily 

maximum 8-hour average O3

concentration is less than or equal to 70 

ppb. Data handling conventions are 

specified in the new Appendix U that is 

adopted, as discussed in section V 

below. 

mstockstill on DSK4VPTVN1PROD with RULES2

65366 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

152EPA issued the AQI in 1999, updating the 

previous Pollutant Standards Index (PSI) to send ‘‘a 

clear and consistent message to the public by 

providing nationally uniform information on air 

quality.’’ The rule requires metropolitan areas of 

350,000 and larger to report the AQI [and associated 

health effects] daily; all other AQI-related 

activities—including real-time ozone and particle 

pollution reporting, next-day air quality forecasting 

and action days—are voluntary and are carried out 

at the discretion of state, local and tribal air 

agencies. In the 1999 rule, we acknowledged these 

other programs, noting, for example, that while 

states primarily use the AQI ‘‘to provide general 

information to the public about air quality and its 

relationship to public health,’’ some state, local or 

tribal agencies use the index to call ‘‘action days.’’ 

Action days encourage additional steps, usually 

voluntary, that the public, business or industry 

could take to reduce emissions when higher levels 

of pollution are forecast to occur. As the 1999 rule 

notes, agencies may have several motivations for 

calling action days, including: providing health 

information to the public; attaining or maintaining 

NAAQS attainment status; meeting specific 

emission reduction targets; and managing or 

reducing traffic congestion. State, local and tribal 

agencies should consider whether non-voluntary 

emissions or activity curtailments are necessary (as 

opposed to a suite of voluntary measures) for days 

when the AQI is forecasted to be on the lower end 

of the moderate category. 

153Exposures to 50 ppb have not been evaluated 

experimentally, but are estimated to potentially 

affect only a small proportion of healthy adults and 

with only a half to a third of the moderate to large 

lung function decrements observed at 60 ppb 

(McDonnell et al., 2012; Figure 7). 

At this time, EPA is also promulgating 

revisions to the Air Quality Index (AQI) 

for O3 to be consistent with the 

revisions to the primary O3 standard 

and the health information evaluated in 

this review of the standards. These 

revisions are discussed below in section 

III. 

III. Communication of Public Health 

Information 

Information on the public health 

implications of ambient concentrations 

of criteria pollutants is currently made 

available primarily through EPA’s AQI 

program. The AQI has been in use since 

its inception in 1999 (64 FR 42530). It 

provides accurate, timely, and easily 

understandable information about daily 

levels of pollution. It is designed to tell 

individual members of the public how 

clean or unhealthy their air is, whether 

health effects might be a concern, and, 

if so, measures individuals can take to 

reduce their exposure to air 

pollution.152 See CAA section 127. The 

AQI focuses on health effects 

individuals may experience within a 

few hours or days after breathing 

unhealthy air. The AQI establishes a 

nationally uniform system of indexing 

pollution concentrations for O3, CO, 

NO2, PM and SO2. 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 concentrations 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 NAAQS for 

each pollutant. For the 2008 O3 NAAQS, 

an 8-hour average concentration of 75 

ppb corresponds to an AQI value of 100. 

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). An additional 

consideration in selecting breakpoints is 

for each category to span at least a 15 

ppb range to allow for more accurate air 

pollution forecasting. Decisions about 

the pollutant concentrations at which to 

set the various AQI breakpoints, that 

delineate the various AQI categories, 

draw directly from the underlying 

health information that supports the 

NAAQS review. 

A. Proposed Revisions to the AQI 

Recognizing the importance of 

revising the AQI in a timely manner to 

be consistent with any revisions to the 

NAAQS, EPA proposed conforming 

changes to the AQI, in connection with 

the Agency’s proposed decision on 

revisions to the O3 NAAQS. These 

conforming changes included setting the 

100 level of the AQI at the same level 

as the revised primary O3 NAAQS and 

also making adjustments based on 

health information from this NAAQS 

review to AQI breakpoints at the lower 

end of each range (i.e., AQI values of 50, 

150, 200 and 300). The EPA did not 

propose to change the level at the top of 

the index (i.e., AQI value of 500) that 

typically is set equal to the Significant 

Harm Level (40 CFR 51.16), which 

would apply to state contingency plans. 

The EPA proposed to revise the AQI 

for O3 by setting an AQI value of 100 

equal to the level of the revised O3

standard (65–70 ppb). The EPA also 

proposed to revise the following 

breakpoints: an AQI value of 50 to 

within a range from 49–54 ppb; an AQI 

value of 150 to 85 ppb; an AQI value of 

200 to 105 ppb, and an AQI value of 300 

to 200 ppb. All these levels are averaged 

over 8 hours. The EPA proposed to set 

an AQI value of 50, the breakpoint 

between the good and moderate 

categories, at 15 ppb below the value of 

the proposed standard, i.e. to within a 

range from 49 to 54 ppb. The EPA took 

comment on what level within this 

range to select, recognizing that there is 

no health message for either at-risk or 

healthy populations in the good 

category. Thus, the level selected should 

be below the lowest concentration (i.e., 

60 ppb) that has been shown in 

controlled human exposure studies of 

young, healthy adults exposed to O3

while engaged in quasi-continuous 

moderate exercise for 6.6 hours to cause 

moderate lung function decrements (i.e., 

FEV1 decrements ≥ 10%, which could 

be adverse to people with lung disease) 

and airway inflammation.153 The EPA 

proposed to set an AQI value of 150, the 

breakpoint between the unhealthy for 

sensitive groups and unhealthy 

categories, at 85 ppb. At this level, 

controlled human exposure studies of 

young, healthy adults indicate that up to 

25% of exposed people are likely to 

have moderate lung function 

decrements (i.e., 25% have FEV1

decrements ≥ 10%; 12% have FEV1

decrements ≥ 15%) and up to 7% are 

likely to have large lung function 

decrements (i.e., FEV1 decrements ≥ 

20%) (McDonnell et al., 2012; Figure 7). 

Large lung function decrements would 

likely interfere with normal activity for 

many healthy people. For most people 

with lung disease, large lung function 

decrements would not only interfere 

with normal activity but would increase 

the likelihood that they would seek 

medical treatment (72 FR 37850, July 

11, 2007). The EPA proposed to set an 

AQI value of 200, the breakpoint 

between the unhealthy and very 

unhealthy categories, at 105 ppb. At this 

level, controlled human exposure 

studies of young, healthy adults indicate 

that up to 38% of exposed people are 

likely to have moderate lung function 

decrements (i.e., 38% have FEV1

decrements ≥ 10%; 22% have FEV1

decrements ≥ 15%) and up to 13% are 

likely to have large lung function 

decrements (i.e., FEV1 decrements ≥ 

20%). The EPA proposed to set an AQI 

value of 300, the breakpoint between the 

very unhealthy and hazardous 

categories, at 200 ppb. At this level, 

controlled human exposure studies of 

healthy adults indicate that up to 25% 

of exposed individuals are likely to have 

large lung function decrements (i.e., 

FEV1 decrements ≥ 20%), which would 

interfere with daily activities for many 

of them and likely cause people with 

lung disease to seek medical attention. 

EPA stated that the proposed 

breakpoints reflect an appropriate 

balance between reflecting the health 

evidence that is the basis for the 

proposed primary O3 standard and 

providing category ranges that are large 

enough to be forecasted accurately, so 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65367 

154Under 40 CFR 58.50, any MSA with a 

population exceeding 350,000 is required to report 

AQI data. 

155Although we do not contest the assertion that 

the new AQI breakpoints will lead to fewer green 

days in the near future, we do not agree that 

commenters’ analysis sufficiently demonstrates that 

there would be fewer green days in 2025 than in 

2013. In their analysis, they compared observed 

2013 data with modeled 2025 data without doing 

any model performance evaluation for AQI 

categories or comparison of current year modeled 

and observed data. The current year observations 

are not directly comparable to the future-year 

modeling data without some such evaluation and, 

as such, we cannot support their quantitative 

conclusions. 

that the new AQI for O3 can be 

implemented more easily in the public 

forum for which the AQI ultimately 

exists. However, the EPA recognized 

alternative approaches to viewing the 

evidence and information and solicited 

comment on the proposed revisions to 

the AQI. 

With respect to reporting 

requirements (40 CFR part 58, section 

58.50), EPA proposed to revise 40 CFR 

part 58, section 58.50 (c) to determine 

the areas subject to AQI reporting 

requirements based on the latest 

available census figures, rather than the 

most recent decennial U.S. census.154

This change is consistent with our 

current practice of using the latest 

population figures to make monitoring 

requirements more responsive to 

changes in population. 

B. Comments on Proposed Revisions to 

the AQI 

EPA received many comments on the 

proposed changes to the AQI. Three 

issues came up in the comments, 

including: (1) Whether the AQI should 

be revised at all, even if the primary 

standard is revised; (2) whether an AQI 

value of 100 should be set equal to the 

level of the primary standard and the 

other breakpoints adjusted accordingly; 

and, (3) whether the AQI reporting 

requirements should be based on the 

latest available census figures rather 

than the most recent decennial census. 

With respect to the first issue, some 

industry commenters stated that the 

AQI should not be revised at all, even 

if the level of the primary O3 standard 

is revised. In support of this position, 

these commenters stated that the 

proposed conforming changes to the 

AQI would lower O3 levels in each 

category, and would mean that air 

quality that is actually improving would 

be reported as less healthy. According to 

commenters, the revised AQI would fail 

to capture these improvements and 

potentially mislead the public into 

thinking that air quality has degraded 

and that EPA and state regulators are 

not doing their jobs. These commenters 

noted that there is no requirement to 

revise the AQI, and that the CAA does 

not tie the AQI to the standards, stating 

that the purpose of section 319(a) of the 

CAA is to provide a consistent, uniform 

means of gauging air quality. These 

commenters further asserted that EPA’s 

proposed changes run counter to that 

uniformity by changing the air quality 

significance of a given index value and 

category and that retention of the 

current AQI breakpoints would allow 

continued uniform information on air 

quality. Commenters stated that it is 

important that the EPA clearly 

communicates that the immediate 

increases in moderate rated days are due 

to AQI breakpoint adjustment and not 

due to a sudden decline in air quality. 

One commenter estimated the increased 

proportion of days in the moderate 

category and above in 10 metropolitan 

areas for 2013 and also for 2025 for 4 

cities from the original 10 that were 

estimated to attain a standard below 70 

ppb, to compare with 2013. This 

commenter noted that the change in the 

proposed AQI breakpoint between 

‘‘good’’ and ‘‘moderate’’ would result in 

a larger number of days that did not 

meet the ‘‘good’’ criteria. They went 

further to claim that the change in 

breakpoints would result in fewer 

‘‘good’’ days in the year 2025 (using the 

new breakpoint) than occurred in 2013 

(using the old breakpoints) despite 

substantial improvement in air quality 

over that time period. 

On the other hand, state and local 

agencies and their organizations, 

environmental and medical groups, and 

members of the public overwhelmingly 

supported revising the AQI when the 

level of the standard is revised. Even 

state agencies that did not support 

revising the standard, expressed support 

for revising the AQI at the same time as 

the standard, if the standard is revised. 

Recognizing the importance of the 

AQI as a communication tool that 

allows members of the public to take 

exposure reduction measures when air 

quality poses health risks, the EPA 

agrees with these comments about 

revising the AQI at the same time as the 

primary standard. The EPA agrees with 

state and local agency commenters that 

its historical approach of setting an AQI 

value of 100 equal to the level of the 

revised 8-hour primary O3 standard is 

appropriate, both from a public health 

and a communication perspective. 

EPA disagrees with commenters who 

stated that the AQI should not be linked 

to the primary standards. As noted in 

the August 4, 1999, rulemaking (64 FR 

149, 42531) that established the current 

AQI, the EPA established the nationally 

uniform air quality index, called the 

Pollutant Standards Index (PSI), in 1976 

to meet the needs of state and local 

agencies with the following advantages: 

It sends a clear and consistent message 

to the public by providing nationally 

uniform information on air quality; it is 

keyed as appropriate to the NAAQS and 

the Significant Harm Level which have 

a scientific basis relating air quality and 

public health; it is simple and easily 

understood by the public; it provides a 

framework for reflecting changes to the 

NAAQS; and it can be forecasted to 

provide advance information on air 

quality. Both the PSI and AQI have 

historically been normalized across 

pollutants by defining an index value of 

100 as the numerical level of the shortterm (i.e., averaging time of 24-hours or 

less) primary NAAQS for each 

pollutant. Moreover, this approach does 

not mislead the public. Since the 

establishment of the AQI, the EPA and 

state and local air agencies and 

organizations have developed 

experience in educating the public 

about changes in the standards and, 

concurrently, related changes to AQI 

breakpoints and advisories. When the 

standards change, EPA and state and 

local agencies have tried to help the 

public understand that air quality is not 

getting worse, it’s that the health 

evidence underlying the standards and 

the AQI has changed. EPA’s Air Quality 

System (AQS), the primary repository 

for air quality monitoring data, is also 

adjusted to reflect the revised 

breakpoints. Specifically, all historical 

AQI values in AQS are recomputed with 

the revised breakpoints, so that all data 

queries and reports downstream of AQS 

will show appropriate trends in AQI 

values over time.155

In general, commenters who 

supported revising the AQI when the 

standard is revised, also supported 

setting an AQI value of 100 equal to the 

level of the 8-hour primary O3 standard. 

The EPA agrees with these commenters. 

With respect to an AQI value of 100, the 

EPA is taking final action to set an AQI 

value of 100 equal to the level of the 8- 

hour primary standard at 70 ppb O3. 

With respect to proposed changes to 

other AQI breakpoints, some state and 

local agency commenters expressed 

general support for all the changes in O3

breakpoints (in Table 2 of Appendix G). 

In addition, we received a few 

comments specifically about the 

breakpoint between the good and 

moderate categories. One state 

expressed the view that forecasting the 

AQI for O3 is not an exact science, so 

it is important to provide a range large 

enough to reasonably predict O3

mstockstill on DSK4VPTVN1PROD with RULES2

65368 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

156http://www.census.gov/popest/data/metro/

totals/2014/CBSA-EST2014-alldata.html. 

concentrations for the following day (≥ 

20 ppb). Although not supporting 

revision of the standard, this state 

recommended that if the primary 

standard was revised to 70 ppb, the 

lower end of moderate category should 

be set at 50 ppb to allow for a 20 ppb 

spread in that category. Several 

commenters recommending a 

breakpoint between the good and 

moderate categories of no higher than 50 

ppb stated that this breakpoint should 

be set on health information, pointing to 

epidemiologic data and the World 

Health organization guidelines. The 

Agency agrees that AQI breakpoints 

should take into consideration health 

information when possible, and also 

that it is important for AQI categories to 

span ranges large enough to support 

accurate forecasting. The EPA is setting 

the breakpoint at the lower end of the 

moderate category at 55 ppb, which is 

15 ppb below the level of the standard 

of 70 ppb. This is consistent with past 

practice of making a proportional 

adjustment to this AQI breakpoint, 

relative to an AQI value of 100 (i.e., 70 

ppb), and also retains the current 

practice of providing a 15 ppb range in 

the moderate category to allow for 

accurate forecasting. This level is below 

the lowest concentration (i.e., 60 ppb) 

that has been shown in controlled 

human exposure studies of healthy 

adults to cause moderate lung function 

decrements (i.e., FEV1 decrements ≥ 

10%, which could be adverse to people 

with lung disease), large lung function 

decrements (i.e., FEV1 decrements ≥ 

20%) in a small proportion of people, 

and airway inflammation, 

notwithstanding the Administrator’s 

judgment that there is uncertainty in the 

adversity of the effects shown to occur 

at 60 ppb. 

We received fewer comments on 

proposed changes to the AQI values of 

150, 200 and 300. Again, some state and 

local agency commenters expressed 

general support for proposed changes to 

the AQI. Some states specifically 

supported these breakpoints. However, 

a commenter suggested setting an AQI 

value at the lower end of the unhealthy 

category, at a level much lower than 85 

ppb, since they state that it is a key 

threshold that is often used in air 

quality action day programs as a trigger 

to encourage specific behavior 

modifications or reduce emissions of O3

precursors (e.g., by taking public 

transportation to work). This commenter 

stated that setting the breakpoint at 85 

ppb would, in the Agency’s own 

rationale, not require the triggering of 

these pollution reduction measures 

until air quality threatened to impact 

25% of people exposed. We disagree 

with this commenter because EPA does 

not have any requirements for voluntary 

programs. State and local air agencies 

have discretion to set the trigger for 

voluntary action programs at whatever 

level they choose, and they are currently 

set at different levels, not just at the 

unhealthy breakpoint specified in the 

comment. For example, Houston, 

Galveston and Brazoria TX metropolitan 

area calls ozone action days when air 

quality reaches the unhealthy for 

sensitive groups category. For more 

information about action days programs 

across the U.S. see the AirNow Web site 

(www.airnow.gov) and click on the link 

to AirNow Action Days. The unhealthy 

category represents air quality where 

there are general population-level 

effects. We believe that setting the 

breakpoint between the unhealthy for 

sensitive groups and unhealthy 

categories, at 85 ppb where, as 

discussed in section IIIA above, 

controlled human exposure studies of 

young, healthy adults exposed to O3

while engaged in quasi-continuous 

moderate exercise for 6.6 hours indicate 

that up to 25% of exposed people are 

likely to have moderate lung function 

decrements and up to 7% are likely to 

have large lung function decrements 

(McDonnell et al., 2012; Figure 7) is 

appropriate. A smaller proportion of 

inactive or less active individuals would 

be expected to experience lung function 

decrements at 85 ppb. Moreover, a 

breakpoint at 85 ppb allows for category 

ranges large enough for accurate 

forecasting. Accordingly, the EPA is 

adopting the proposed revisions to the 

AQI values of 150, 200 and 300. 

As noted earlier, the EPA proposed to 

revise 40 CFR part 58, section 58.50(c) 

to determine the areas subject to AQI 

reporting requirements based on the 

latest available census figures, rather 

than the most recent decennial U.S. 

census. 

A total of five state air monitoring 

agencies provided comments on this 

proposed change. Four agencies 

supported the proposal. One state 

commenter did not support the 

proposal, noting that the change would 

unnecessarily complicate AQI reporting 

and possibly increase reporting burdens 

in an unpredictable manner. 

The EPA notes that the majority of 

monitoring network minimum 

requirements listed in Appendix D to 

Part 58 include a reference to ‘‘latest 

available census figures.’’ Minimum 

network requirements for O3, PM2.5, 

SO2, and NO2 all include this language 

in the regulatory text and monitoring 

agencies have successfully adopted 

these processes into their planning 

activities and the subsequent revision of 

their annual monitoring network plans 

which are posted for public review. 

Annual population estimates are easily 

obtainable from the U.S. Census Bureau 

and the EPA does not believe the 

burden in tracking these annual 

estimates is excessive or complicated.156

Although the changes in year to year 

estimates are typically modest, there are 

MSAs that are approaching (or have 

recently exceeded) the 350,000 

population AQI reporting limit and 

there is great value in having the AQI 

reported for these areas when the 

population threshold is exceeded versus 

waiting potentially up to 10 years for a 

revision to the decennial census. 

Accordingly, the EPA is finalizing the 

proposed revision to 40 CFR part 58, 

section 58.50(c) to require the AQI 

reporting requirements to be based on 

the latest available census figures. 

One state requested additional 

guidance on the frequency of updating 

the AQI reporting threshold, and 

recommended linking the AQI reporting 

requirement evaluation with the annual 

air monitoring network plan 

requirements, and recommended 

requiring AQI reporting to begin no later 

than January 1 of the following year. 

The EPA notes that the census bureau 

estimates appear to be released around 

July 1 of each year which would not 

provide sufficient time for monitoring 

agencies to incorporate AQI reporting in 

their annual plans for that year, which 

are also due by July 1 each year. EPA 

believes that it should be unnecessary 

for monitoring agencies to wait until the 

implementation of the following year’s 

annual plan (i.e., approximately 18 

months later) to begin AQI reporting. 

Accordingly, EPA is not at this time 

including a specific deadline for 

commencement of AQI reporting for 

newly-subject areas in 40 CFR part 58, 

but will work with agencies to 

implement additional AQI reporting as 

needed to ensure that information is 

being disseminated in a timely fashion. 

C. Final Revisions to the AQI 

For the reasons discussed above, the 

EPA is revising the AQI for O3 by setting 

an AQI value of 100 equal to 70 ppb, 8- 

hour average, the level of the revised 

primary O3 standard. The EPA is also 

revising the following breakpoints: An 

AQI value of 50 is set at 54 ppb; an AQI 

value of 150 is set at 85 ppb; an AQI 

value of 200 is set at 105 ppb; and an 

AQI value of 300 is set at 200 ppb. All 

of these levels are averaged over 8 

hours. The revisions to all of the 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65369 

breakpoints are based on estimated 

health outcomes at relevant ambient 

concentrations and to allow for each 

category to span at least a 15–20 ppb 

category range to allow for more 

accurate air pollution forecasting. The 

EPA believes that the revised 

breakpoints provide a balance between 

adjustments to reflect the health 

information supporting the revised O3

standard and providing category ranges 

that are large enough to be forecasted 

accurately, so that the AQI can be 

implemented more easily in the public 

forum for which the AQI ultimately 

exists. With respect to AQI reporting 

requirements (40 CFR part 58, section 

58.50), the EPA is revising 40 CFR part 

58, section 58.50(c) to make the AQI 

reporting requirements based on the 

latest available census figures, rather 

than the most recent decennial U.S. 

census. This change is consistent with 

our current practice of using the latest 

population figures to make monitoring 

requirements more responsive to 

changes in population. 

IV. Rationale for Decision on the 

Secondary Standard 

A. Introduction 

This section (IV) presents the 

rationale for the Administrator’s 

decisions regarding the need to revise 

the current secondary standard for O3, 

and the appropriate revision. Based on 

her consideration of the full body of 

welfare effects evidence and related 

analyses, including the evidence of 

effects associated with cumulative 

seasonal exposures of the magnitudes 

allowed by the current standard, the 

Administrator has concluded that the 

current secondary standard for O3 does 

not provide the requisite protection of 

public welfare from known or 

anticipated adverse effects. She has 

decided to revise the level of the current 

secondary standard to 0.070 ppm, in 

conjunction with retaining the current 

indicator, averaging time and form. 

The Administrator has made this 

decision based on judgments regarding 

the currently available welfare effects 

evidence, the appropriate degree of 

public welfare protection for the revised 

standard, and currently available air 

quality information on seasonal 

cumulative exposures that may be 

allowed by such a standard. In so doing, 

she has focused on O3 effects on tree 

seedling growth as a proxy for the full 

array of vegetation-related effects of O3, 

ranging from effects on sensitive species 

to broader ecosystem-level effects. Using 

this proxy in judging effects to public 

welfare, the Administrator has 

concluded that the requisite protection 

from adverse effects to public welfare 

will be provided by a standard that 

limits cumulative seasonal exposures to 

17 ppm-hrs or lower, in terms of a 3- 

year W126 index, in nearly all 

instances, and she has also concluded 

that such control of cumulative seasonal 

exposures may be achieved by revising 

the level of the current standard to 70 

ppb. Based on all of these 

considerations, the Administrator has 

decided that a secondary standard with 

a level of 0.070 ppm, and the current 

form and averaging time, will provide 

the requisite protection of public 

welfare from known or anticipated 

adverse effects. 

As discussed more fully below, this 

decision is based on a thorough review, 

in the ISA, of the latest scientific 

information on O3-induced 

environmental effects. This decision 

also takes into account (1) staff 

assessments in the PA of the most 

policy-relevant information in the ISA 

regarding evidence of adverse effects of 

O3 to vegetation and ecosystems, 

information on biologically-relevant 

exposure metrics, WREA analyses of air 

quality, exposure, and ecological risks 

and associated ecosystem services, and 

staff analyses of relationships between 

levels of a W126-based metric and a 

metric based on the form and averaging 

time of the current standard 

summarized in the PA and in the 

proposal notice; (2) CASAC advice and 

recommendations; and (3) public 

comments received during the 

development of these documents, either 

in connection with CASAC meetings or 

separately, and on the proposal notice. 

This decision draws on the ISA’s 

integrative synthesis of the entire body 

of evidence, generally published 

through July 2011, on environmental 

effects associated with the presence of 

O3 and related photochemical oxidants 

in the ambient air (U.S. EPA, 2013, ISA 

chapters 9–10), and includes more than 

four hundred new studies that build on 

the extensive evidence base from the 

last review. In addition to reviewing the 

most recent scientific information as 

required by the CAA, this rulemaking 

incorporates the EPA’s response to the 

judicial remand of the 2008 secondary 

O3 standard in State of Mississippi v. 

EPA, 744 F. 3d 1334 (D.C. Cir. 2013) 

and, in accordance with the court’s 

decision in that case, fully explains the 

Administrator’s conclusions as to the 

level of air quality that provides the 

requisite protection of public welfare 

from known or anticipated adverse 

effects. In drawing conclusions on the 

secondary standard, the decision 

described in this rulemaking is a public 

welfare policy judgment made by the 

Administrator. The Administrator’s 

decision draws upon the available 

scientific evidence for O3-attributable 

welfare effects and on analyses of 

exposures and public welfare risks 

based on impacts to vegetation, 

ecosystems and their associated 

services, as well as judgments about the 

appropriate weight to place on the range 

of uncertainties inherent in the evidence 

and analyses. As described in sections 

IV.B.3 and IV.C.3 below, such 

judgments in the context of this review 

include judgments on the weight to 

place on the evidence of specific 

vegetation-related effects estimated to 

result across a range of cumulative 

seasonal concentration-weighted O3

exposures; on the weight to give 

associated uncertainties, including 

those related to the variability in 

occurrence of such effects in areas of the 

U.S., especially areas of particular 

public welfare significance; and on the 

extent to which such effects in such 

areas may be considered adverse to 

public welfare. 

Information related to vegetation and 

ecosystem effects, biologically relevant 

exposure indices, and vegetation 

exposure and risk assessments were 

summarized in sections IV.A through 

IV.C of the proposal (79 FR at 75314– 

75329), respectively, and key 

observations from the proposal are 

briefly outlined in sections IV.A.1 to 

IV.A.3 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 

the current standard is not requisite to 

protect public welfare from known or 

anticipated adverse effects (section 

IV.B), and that it is appropriate to revise 

the current secondary standard to 

provide additional public welfare 

protection by revising the level while 

retaining the current indicator, form and 

averaging time (section IV.C). A 

summary of the final decisions on 

revisions to the secondary standard is 

presented in section IV.D. 

1. Overview of Welfare Effects Evidence 

a. Nature of Effects 

In the more than fifty years that have 

followed identification of O3’s 

phytotoxic effects, extensive research 

has been conducted both in and outside 

of the U.S. to examine the impacts of O3

on plants and their associated 

ecosystems (U.S. EPA, 1978, 1986, 

1996a, 2006a, 2013). As was established 

in prior reviews, O3 can interfere with 

carbon gain (photosynthesis) and 

allocation of carbon within the plant, 

making fewer carbohydrates available 

mstockstill on DSK4VPTVN1PROD with RULES2

65370 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

157As described in the ISA, ‘‘[r]adiative forcing 

by a greenhouse gas or aerosol is a metric used to 

quantify the change in balance between radiation 

coming into and going out of the atmosphere caused 

by the presence of that substance’’ (U.S. EPA, 2013, 

p. 1–13). 

158Climate responses, including increased surface 

temperature, have downstream climate-related 

ecosystem effects (U.S. EPA, 2013, p. 10–7). As 

noted in section I.D above, such effects may include 

an increase in the area burned by wildfires, which, 

in turn, are sources of O3 precursor emissions. 

for plant growth, reproduction, and/or 

yield. For seed-bearing plants, these 

reproductive effects will culminate in 

reduced seed production or yield (U.S. 

EPA, 1996a, pp. 5–28 and 5–29). Recent 

studies, assessed in the ISA, together 

with this longstanding and wellestablished literature on O3-related 

vegetation effects, further contribute to 

the coherence and consistency of the 

vegetation effects evidence (U.S. EPA, 

2013, chapter 9). 

The strongest evidence for effects 

from O3 exposure on vegetation is from 

controlled exposure studies, which 

‘‘have clearly shown that exposure to O3

is causally linked to visible foliar injury, 

decreased photosynthesis, changes in 

reproduction, and decreased growth’’ in 

many species of vegetation (U.S. EPA, 

2013, p. 1–15). Such effects at the plant 

scale can also be linked to an array of 

effects at larger spatial scales, with the 

currently available evidence indicating 

that ‘‘ambient O3 exposures can affect 

ecosystem productivity, crop yield, 

water cycling, and ecosystem 

community composition’’ (U.S. EPA, 

2013, p. 1–15; Chapter 9, section 9.4). 

The current body of O3 welfare effects 

evidence confirms and strengthens 

support for the conclusions reached in 

the last review on the nature of O3- 

induced welfare effects and is 

summarized in the ISA as follows (U.S. 

EPA, 2013, p. 1–8). 

The welfare effects of O3 can be observed 

across spatial scales, starting at the 

subcellular and cellular level, then the whole 

plant and finally, ecosystem-level processes. 

Ozone effects at small spatial scales, such as 

the leaf of an individual plant, can result in 

effects along a continuum of larger spatial 

scales. These effects include altered rates of 

leaf gas exchange, growth, and reproduction 

at the individual plant level, and can result 

in broad changes in ecosystems, such as 

productivity, carbon storage, water cycling, 

nutrient cycling, and community 

composition. 

Based on assessment of this extensive 

body of science, the EPA has 

determined that, with respect to 

vegetation and ecosystems, a causal 

relationship exists between exposure to 

O3 in ambient air and visible foliar 

injury effects on vegetation, reduced 

vegetation growth, reduced productivity 

in terrestrial ecosystems, reduced yield 

and quality of agricultural crops and 

alteration of below-ground 

biogeochemical cycles (U.S. EPA, 2013, 

Table 1–2). In consideration of the 

evidence of O3 exposure and alterations 

in stomatal performance, ‘‘which may 

affect plant and stand transpiration and 

therefore possibly affecting hydrological 

cycling,’’ the ISA concludes that 

‘‘[a]lthough the direction of the response 

differed among studies,’’ the evidence is 

sufficient to conclude a likely causal 

relationship between O3 exposure and 

the alteration of ecosystem water 

cycling (U.S. EPA, 2013, section 2.6.3). 

The evidence is also sufficient to 

conclude a likely causal relationship 

between O3 exposure and the alteration 

of community composition of some 

terrestrial ecosystems (U.S. EPA, 2013, 

section 2.6.5). Related to the effects on 

vegetation growth, productivity and, to 

some extent, below-ground 

biogeochemical cycles, the EPA has 

additionally determined that a likely 

causal relationship exists between 

exposures to O3 in ambient air and 

reduced carbon sequestration (also 

termed carbon storage) in terrestrial 

ecosystems (U.S. EPA, 2013, p. 1–10 

and section 2.6.2). Modeling studies 

available in this review consistently 

found negative impacts of O3 on carbon 

sequestration, although the severity of 

impact was influenced by ‘‘multiple 

interactions of biological and 

environmental factors’’ (U.S. EPA, 2013, 

p. 2–39). 

Ozone in the troposphere is also a 

major greenhouse gas and radiative 

forcing agent,157 with the ISA formally 

concluding that ‘‘the evidence supports 

a causal relationship between changes 

in tropospheric O3 concentrations and 

radiative forcing’’ (U.S. EPA, 2013, p. 1– 

13 and section 2.7.1). While 

tropospheric O3 has been ranked third 

in importance after carbon dioxide and 

methane, there are ‘‘large uncertainties 

in the magnitude of the radiative forcing 

estimate attributed to tropospheric O3, 

making the impact of tropospheric O3

on climate more uncertain than the 

effect of the longer-lived greenhouse 

gases’’ (U.S. EPA, 2013, p. 2–47). The 

ISA notes that ‘‘[e]ven with these 

uncertainties, global climate models 

indicate that tropospheric O3 has 

contributed to observed changes in 

global mean and regional surface 

temperatures’’ and concludes that ‘‘[a]s 

a result of such evidence presented in 

climate modeling studies, there is likely 

to be a causal relationship between 

changes in tropospheric O3

concentrations and effects on climate’’ 

(U.S. EPA, 2013, p. 2–47).158 The ISA 

additionally states that ‘‘[i]mportant 

uncertainties remain regarding the effect 

of tropospheric O3 on future climate 

change’’ (U.S. EPA, 2013, p. 10–31). 

b. Vegetation Effects 

Given the strong evidence base and 

the findings of causal or likely causal 

relationships with O3 in ambient air, 

including the quantitative assessments 

of relationships between O3 exposure 

and occurrence and magnitude of 

effects, this review has given primary 

consideration to three main kinds of 

vegetation effects, some of which 

contribute to effects at scales beyond the 

plant level, such as at the ecosystem 

level and on ecosystem services. The 

three kinds of effects are addressed 

below in the following order: 1) Visible 

foliar injury, 2) impacts on tree growth, 

productivity and carbon storage, and 3) 

crop yield loss. 

Visible foliar injury resulting from 

exposure to O3 has been well 

characterized and documented over 

several decades of research on many 

tree, shrub, herbaceous, and crop 

species (U.S. EPA, 2013, p. 1–10; U.S. 

EPA, 2006a, 1996a, 1986, 1978). Ozoneinduced visible foliar injury symptoms 

on certain plant species, such as black 

cherry, yellow-poplar and common 

milkweed, are considered diagnostic of 

exposure to O3 based on the consistent 

association established with 

experimental evidence (U.S. EPA, 2013, 

p. 1–10). The evidence has found that 

visible foliar injury occurs only when 

sensitive plants are exposed to elevated 

O3 concentrations in a predisposing 

environment; a major modifying factor 

is the amount of available soil moisture 

during the year (U.S. EPA, 2013, section 

9.4.2). 

The significance of O3 injury at the 

leaf and whole plant levels depends on 

an array of factors, and therefore, it is 

difficult to quantitatively relate visible 

foliar injury symptoms to vegetation 

effects such as individual tree growth, 

or effects at population or ecosystem 

levels (U.S. EPA, 2013, p. 9–39). The 

ISA notes that visible foliar injury ‘‘is 

not always a reliable indicator of other 

negative effects on vegetation’’ (U.S. 

EPA, 2013, p. 9–39). Factors that 

influence the significance to the leaf and 

whole plant include the amount of total 

leaf area affected, age of plant, size, 

developmental stage, and degree of 

functional redundancy among the 

existing leaf area (U.S. EPA, 2013, 

section 9.4.2). Although there remains a 

lack of robust exposure-response 

functions that would allow prediction of 

visible foliar injury severity and 

incidence under varying air quality and 

environmental conditions, 

‘‘[e]xperimental evidence has clearly 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65371 

159These functions for RBL estimate reduction in 

a year’s growth as a percentage of that expected in 

the absence of O3 (U.S. EPA, 2013, section 9.6.2; 

U.S. EPA, 2014b, section 6.2). 

established a consistent association of 

visible injury with O3 exposure, with 

greater exposure often resulting in 

greater and more prevalent injury’’ (U.S. 

EPA, 2013, section 9.4.2, p. 9–41). 

By far the most extensive field-based 

dataset of visible foliar injury incidence 

is that obtained by the U.S. Forest 

Service Forest Health Monitoring/Forest 

Inventory and Analysis (USFS FHM/

FIA) biomonitoring network program 

(U.S. EPA, 2013, section 9.4.2.1; Smith, 

2012; Coulston et al., 2007). A recently 

published trend analysis of data from 

the sites located in 24 states of the 

northeast and north central U.S. for the 

16-year period from 1994 through 2009 

(Smith, 2012) describes evidence of 

visible foliar injury occurrence in the 

field as well as some insight into the 

influence of changes in air quality and 

soil moisture on visible foliar injury and 

the difficulty inherent in predicting 

foliar injury response under different air 

quality and soil moisture scenarios 

(Smith, 2012; U.S. EPA, 2013, section 

9.4.2.1). Study results showed that 

incidence and severity of foliar injury 

were dependent on local site conditions 

for soil moisture availability and O3

exposure (U.S. EPA, 2013, p. 9–41). 

Although the study indicated that 

moderate O3 exposures continued to 

cause visible foliar injury at sites 

throughout the study area, there was an 

overall declining trend in the incidence 

of visible foliar injury as peak O3

concentrations declined (U.S. EPA, 

2013, p. 9–40). 

Ozone has been shown to affect a 

number of important U.S. tree species 

with respect to growth, productivity, 

and carbon storage. Ambient O3

concentrations have long been known to 

cause decreases in photosynthetic rates 

and plant growth. As discussed in the 

ISA, research published since the 2006 

AQCD substantiates prior conclusions 

regarding O3-related effects on forest 

tree growth, productivity and carbon 

storage, and further strengthens the 

support for those conclusions. A variety 

of factors in natural environments can 

either mitigate or exacerbate predicted 

O3-plant interactions and are recognized 

sources of uncertainty and variability. 

Such factors include multiple 

genetically influenced determinants of 

O3 sensitivity, changing sensitivity to O3

across vegetative growth stages, cooccurring stressors and/or modifying 

environmental factors (U.S. EPA, 2013, 

section 9.4.8). In considering of the 

available evidence, the ISA states, 

‘‘previous O3 AQCDs concluded that 

there is strong evidence that exposure to 

O3 decreases photosynthesis and growth 

in numerous plant species’’ and that 

‘‘[s]tudies published since the 2008 

review support those conclusions’’ (U.S. 

EPA, 2013, p. 9–42). The available 

studies come from a variety of different 

study types that cover an array of 

different species, effects endpoints, 

levels of biological organization and 

exposure methods and durations. The 

O3-induced effects at the scale of the 

whole plant may translate to the 

ecosystem scale, with changes in 

productivity and carbon storage. As 

stated in the ISA, ‘‘[s]tudies conducted 

during the past four decades have 

demonstrated unequivocally that O3

alters biomass allocation and plant 

reproduction’’ (U.S. EPA, 2013, p. 1– 

10). 

The strong evidence of O3 impacts on 

trees includes robust exposure-response 

(E–R) functions for reduced growth, 

termed relative biomass loss (RBL),159 in 

seedlings of 11 species. These functions 

were developed under the National 

Health and Environmental Effects 

Research Laboratory-Western Ecology 

Division program, a series of 

experiments that used open top 

chambers (OTCs) to investigate seedling 

growth response for a single growing 

season under a variety of O3 exposures 

(ranging from near background to well 

above current ambient concentrations) 

and growing conditions (U.S. EPA, 

2013, section 9.6.2; Lee and Hogsett, 

1996). The evidence from these studies 

shows that there is a wide range in 

sensitivity across the studied species in 

the seedling growth stage over the 

course of a single growing season, with 

some species being extremely sensitive 

and others being very insensitive over 

the range of cumulative O3 exposures 

studied (U.S. EPA, 2014c, Figure 5–1). 

At the other end of the organizational 

spectrum, field-based studies of species 

growing in natural stands have 

compared observed plant responses 

across a number of different sites and/ 

or years when exposed to varying 

ambient O3 exposure conditions. For 

example, a study conducted in forest 

stands in the southern Appalachian 

Mountains during a period when O3

concentrations exceeded the current 

standard found that the cumulative 

effects of O3 decreased seasonal stem 

growth (measured as a change in 

circumference) by 30–50 percent for 

most of the examined tree species (i.e., 

tulip poplar, black cherry, red maple, 

sugar maple) in a high-O3 year in 

comparison to a low-O3 year (U.S. EPA, 

2013, section 9.4.3.1; McLaughlin et al., 

2007a). The study also reported that 

high ambient O3 concentrations can 

increase whole-tree water use and in 

turn reduce late-season streamflow 

(McLaughlin et al., 2007b; U.S. EPA, 

2013, p. 9–43). 

The magnitude of O3 impact on 

ecosystem productivity and on forest 

composition can vary among plant 

communities based on several factors, 

including the type of stand or 

community in which the sensitive 

species occurs (e.g., single species 

versus mixed canopy), the role or 

position of the species in the stand (e.g., 

dominant, sub-dominant, canopy, 

understory), and the sensitivity of cooccurring species and environmental 

factors (e.g., drought and other factors). 

For example, recent studies found O3 to 

have little impact on white fir, but to 

greatly reduce growth of ponderosa pine 

in southern California locations, with 

associated reductions in ponderosa pine 

abundance in the community, and to 

cause decreased net primary production 

of most forest types in the mid-Atlantic 

region, with only small impacts on 

spruce-fir forest (U.S. EPA, 2013, 

section 9.4.3.4). 

There is previously and newly 

available evidence of the potential for 

O3 to alter biomass allocation and plant 

reproduction in seasons subsequent to 

exposure (U.S. EPA, 2013, section 

9.4.3). For example, several studies 

published since the 2006 AQCD further 

demonstrate that O3 can alter the timing 

of flowering and the number of flowers, 

fruits and seeds in herbaceous and 

woody plant species (U.S. EPA, 2013, 

section 9.4.3.3). Further, limited 

evidence in previous reviews reported 

that vegetation effects from a single year 

of exposure to elevated O3 could be 

observed in the following year. For 

example, growth affected by a reduction 

in carbohydrate storage in one year may 

result in the limitation of growth in the 

following year. Such ‘‘carry-over’’ 

effects have been documented in the 

growth of some tree seedlings and in 

roots (U.S. EPA, 2013, section 9.4.8; 

Andersen et al., 1997). In the current 

review, additional field-based evidence 

expands the EPA’s understanding of the 

consequences of single and multi-year 

O3 exposures in subsequent years. 

A number of studies were conducted 

at a planted forest at the Aspen free-air 

carbon-dioxide and ozone enrichment 

(FACE) experiment site in Wisconsin. 

These studies, which occurred in a field 

setting (more similar to natural forest 

stands than OTC studies), observed tree 

growth responses when grown in single 

or two species stands within 30-m 

diameter rings and exposed over a 

period of ten years to existing ambient 

conditions and elevated O3

mstockstill on DSK4VPTVN1PROD with RULES2

65372 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

160The CASAC cautioned the EPA against placing 

too much emphasis on the eastern cottonwood data. 

In comments on the draft PA, the CASAC stated 

that the eastern cottonwood response data from a 

single study ‘‘receive too much emphasis,’’ 

explaining that these ‘‘results are from a gradient 

study that did not control for ozone and climatic 

conditions and show extreme sensitivity to ozone 

compared to other studies’’ and that ‘‘[a]lthough 

they are important results, they are not as strong as 

those from other experiments that developed E–R 

functions based on controlled ozone exposure’’ 

(Frey, 2014c, p. 10). 

161These functions for RYL estimate reduction in 

a year’s growth as a percentage of that expected in 

the absence of O3 (U.S. EPA, 2013, section 9.6.2; 

U.S. EPA, 2014b, section 6.2). 

162The NCLAN program, which was undertaken 

in the early to mid-1980s, assessed multiple U.S. 

crops, locations, and O3 exposure levels, using 

consistent methods, to provide the largest, most 

uniform database on the effects of O3 on agricultural 

crop yields (U.S. EPA 1996a; U.S. EPA, 2006a; U.S. 

EPA, 2013, sections 9.2, 9.4, and 9.6, Frey, 2014c, 

p. 9). The SoyFACE experiment was a chamberless 

(or free-air) field-based exposure study conducted 

in Illinois from 2001—2009 (U.S. EPA, 2013, 

section 9.2.4). 

concentrations. Some studies indicate 

the potential for carry-over effects, such 

as those showing that the effects of O3

on birch seeds (reduced weight, 

germination, and starch levels) could 

lead to a negative impact on species 

regeneration in subsequent years, and 

that the O3-attributable effect of reduced 

aspen bud size might have been related 

to the observed delay in spring leaf 

development. These effects suggest that 

elevated O3 exposures have the 

potential to alter carbon metabolism of 

overwintering buds, which may have 

subsequent effects in the following year 

(Darbah, et al., 2008, 2007; Riikonen et 

al., 2008; U.S. EPA, 2013, section 9.4.3). 

Other studies found that, in addition to 

affecting tree heights, diameters, and 

main stem volumes in the aspen 

community, elevated O3 over a 7-year 

study period was reported to increase 

the rate of conversion from a mixed 

aspen-birch community to a community 

dominated by the more tolerant birch, 

leading the authors to conclude that 

elevated O3 may alter intra- and interspecies competition within a forest 

stand (U.S. EPA, 2013, section 9.4.3; 

Kubiske et al., 2006; Kubiske et al., 

2007). These studies confirm earlier 

FACE results of aspen growth 

reductions from exposure to elevated O3

during the first seven years of stand 

growth and of cumulative biomass 

impacts associated with changes in 

annual production in studied tree 

communities (U.S. EPA, 2013, section 

9.4.3; King et al., 2005). 

Robust and well-established E–R 

functions for RBL are available for 11 

tree species: black cherry, Douglas fir, 

loblolly pine, ponderosa pine, quaking 

aspen, red alder, red maple, sugar 

maple, tulip poplar, Virginia pine, and 

white pine (U.S. EPA, 2013; U.S. EPA, 

2014c). While these 11 species represent 

only a small fraction (0.8 percent) of the 

total number of native tree species in 

the contiguous U.S. (1,497), this small 

subset includes eastern and western 

species, deciduous and coniferous 

species, and species that grow in a 

variety of ecosystems and represent a 

range of tolerance to O3 (U.S. EPA, 2013, 

section 9.6.2; U.S. EPA, 2014b, section 

6.2, Figure 6–2, Table 6–1). Supporting 

the E–R functions for each of these 

species are studies in OTCs, with most 

species studied multiple times under a 

wide range of exposure and/or growing 

conditions, with separate E–R functions 

developed for each combination of 

species, exposure condition and 

growing condition scenario (U.S. EPA, 

2013, section 9.6.1). Based on these 

separate E–R functions, species-specific 

composite E–R functions have been 

developed and successfully used to 

predict the biomass loss response from 

tree seedling species over a range of 

cumulative exposure conditions (U.S. 

EPA, 2013, section 9.6.2). These 11 

composite functions, as well as the E– 

R function for eastern cottonwood 

(derived from a field study in which O3

and climate conditions were not 

controlled),160 are described in the ISA 

and graphed in the WREA to illustrate 

the predicted responses of these species 

over a wide range of cumulative 

exposures (U.S. EPA, 2014b, section 6.2, 

Table 6–1 and Figure 6–2; U.S. EPA, 

2013, section 9.6.2). For some of these 

species, the E–R function is based on a 

single study (e.g., red maple), while for 

other species there were as many as 11 

studies available (e.g., ponderosa pine). 

In total, the E–R functions developed for 

these 12 species (the 11 with robust 

composite E–R functions plus eastern 

cottonwood) reflect 52 tree seedling 

studies. A stochastic analysis in the 

WREA, summarized in section IV.C of 

the proposal, indicates the potential for 

within-species variability in these 

relationships for each species. 

Consideration of biomass loss estimates 

in the PA and in discussions below, 

however, is based on conventional 

methods and focuses on estimates for 

the 11 species for which the robust 

datasets from OTC experiments are 

available, in consideration of CASAC 

advice. 

The ‘‘detrimental effect of O3 on crop 

production has been recognized since 

the 1960s’’ (U.S. EPA, 2013, p. 1–10, 

section 9.4.4). On the whole, the newly 

available evidence supports and 

strengthens previous conclusions that 

exposure to O3 reduces growth and 

yield of crops. The ISA describes 

average crop yield loss reported across 

a number of recently published metaanalyses and identifies several new 

exposure studies that support prior 

findings for a variety of crops of 

decreased yield and biomass with 

increased O3 exposure (U.S. EPA, 2013, 

section 9.4.4.1, Table 9–17). Studies 

have also ‘‘linked increasing O3

concentration to decreased 

photosynthetic rates and accelerated 

aging in leaves, which are related to 

yield’’ and described effects of O3 on 

crop quality, such as nutritive quality of 

grasses, macro- and micronutrient 

concentrations in fruits and vegetable 

crops and cotton fiber quality (U.S. EPA, 

2013, p. 1–10, section 9.4.4). The 

findings of the newly available studies 

do not change the basic understanding 

of O3-related crop yield loss since the 

last review and little additional 

information is available in this review 

on factors that influence associations 

between O3 levels and crop yield loss 

(U.S. EPA, 2013, section 9.4.4.). 

However, the evidence available in this 

review continues to support the 

conclusion that O3 in ambient air can 

reduce the yield of major commodity 

crops in the U.S. Further, the recent 

evidence increases our confidence in 

the use of crop E–R functions based on 

OTC experiments to characterize the 

quantitative relationship between 

ambient O3 concentrations and yield 

loss (U.S. EPA, 2013, section 9.4.4). 

The new evidence has strengthened 

support for previously established E–R 

functions for 10 crops (barley, field 

corn, cotton, kidney bean, lettuce, 

peanut, potato, grain sorghum, soybean 

and winter wheat), reducing two 

important areas of uncertainty, 

especially for soybean, as summarized 

in more detail in section IV.A of the 

proposal. The established E–R functions 

for relative yield loss (RYL)161 were 

developed from OTC-type experiments 

from the National Crop Loss Assessment 

Network (NCLAN) (U.S. EPA, 2013, 

section 9.6.3; U.S. EPA, 2014b, section 

6.2; U.S. EPA, 2014c, Figure 5–4 and 

section 6.3). With regard to the first area 

of uncertainty reduced, evaluations in 

the ISA found that yield loss in soybean 

from O3 exposure at the SoyFACE 

(Soybean Free Air Concentration 

Enrichment) field experiment was 

reliably predicted by soybean E–R 

functions developed from NCLAN data 

(U.S. EPA, 2013, section 9.6.3.1),162

demonstrating a robustness of the 

NCLAN-based E–R functions for 

predicting relative yield loss from O3

exposure. A second area of uncertainty 

that was reduced is that regarding the 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65373 

163 In describing the form as ‘‘seasonal,’’ the EPA 

is referring generally to the growing season of O3- 

sensitive vegetation, not to the seasons of the year 

(i.e., spring, summer, fall, winter). 

164The SUM06 index is a threshold-based 

approach described as the sum of all hourly O3

concentrations greater or equal to 0.06 ppm 

observed during a specified daily and seasonal time 

window (U.S. EPA, 2013, section 9.5.2). The W126 

index is a non-threshold approach, described more 

fully below. 

application of the NCLAN E–R 

functions to more recent cultivars 

currently growing in the field. Recent 

studies, especially those focused on 

soybean, provide little evidence that 

crops are becoming more tolerant of O3

(U.S. EPA, 2006a; U.S. EPA, 2013, 

sections 9.6.3.1 and 9.6.3.4 and p. 9–59). 

The ISA comparisons of NCLAN and 

SoyFACE data referenced above also 

‘‘confirm that the response of soybean 

yield to O3 exposure has not changed in 

current cultivars’’ (U.S. EPA, 2013, p. 9– 

59; section 9.6.3.1). Additionally, a 

recent assessment of the relationship 

between soybean yield loss and O3 in 

ambient air over the contiguous area of 

Illinois, Iowa, and Indiana found a 

relationship that correlates well with 

previous results from FACE- and OTCtype experiments (U.S. EPA, 2013, 

section 9.4.4.1). 

c. Biologically Relevant Exposure Metric 

In assessing biologically based indices 

of exposure pertinent to O3 effects on 

vegetation, the ISA states the following 

(U.S. EPA, 2013, p. 2–44). 

The main conclusions from the 1996 and 

2006 O3 AQCDs [Air Quality Criteria 

Documents] regarding indices based on 

ambient exposure remain valid. These key 

conclusions can be restated as follows: ozone 

effects in plants are cumulative; higher O3

concentrations appear to be more important 

than lower concentrations in eliciting a 

response; plant sensitivity to O3 varies with 

time of day and plant development stage; 

[and] quantifying exposure with indices that 

cumulate hourly O3 concentrations and 

preferentially weight the higher 

concentrations improves the explanatory 

power of exposure/response models for 

growth and yield, over using indices based 

on mean and peak exposure values. 

The long-standing body of available 

evidence upon which these conclusions 

are based includes a wealth of 

information on aspects of O3 exposure 

that are important in influencing plant 

response (U.S. EPA, 1996a; U.S. EPA, 

2006a; U.S. EPA, 2013). Specifically, a 

variety of ‘‘factors with known or 

suspected bearing on the exposureresponse relationship, including 

concentration, time of day, respite time, 

frequency of peak occurrence, plant 

phenology, predisposition, etc.,’’ have 

been identified (U.S. EPA, 2013, section 

9.5.2). In addition, the importance of the 

duration of the exposure and the 

relatively greater importance of higher 

concentrations over lower 

concentrations in determining plant 

response to O3 have been consistently 

well documented (U.S. EPA, 2013, 

section 9.5.3). Based on improved 

understanding of the biological basis for 

plant response to O3 exposure, a large 

number of ‘‘mathematical approaches 

for summarizing ambient air quality 

information in biologically meaningful 

forms for O3 vegetation effects 

assessment purposes’’ have been 

developed (U.S. EPA, 2013, section 

9.5.3), including those that cumulate 

exposures over some specified period 

while weighting higher concentrations 

more than lower (U.S. EPA, 2013, 

section 9.5.2). As with any summary 

statistic, these exposure indices retain 

information on some, but not all, 

characteristics of the original 

observations. 

Based on extensive review of the 

published literature on different types of 

exposure-response metrics, including 

comparisons between metrics, the EPA 

has focused on cumulative, 

concentration-weighted indices, 

recognizing them as the most 

appropriate biologically based metrics 

to consider in this context (U.S. EPA, 

1996a; U.S. EPA, 1996b; U.S. EPA, 

2006a; U.S. EPA, 2013). In the last two 

reviews of the O3 NAAQS, the EPA 

concluded that the risk to vegetation 

comes primarily from cumulative 

exposures to O3 over a season or 

seasons 163 and focused on metrics 

intended to characterize such 

exposures: SUM06 164 in the 1997 

review (61 FR 65716, December 13, 

1996) and W126 in the 2008 review (72 

FR 37818, July 11, 2007). Although in 

both reviews the policy decision was 

made not to revise the form and 

averaging time of the secondary 

standard, the Administrator, in both 

cases, also concluded, consistent with 

CASAC advice, that a cumulative, 

seasonal index was the most 

biologically relevant way to relate 

exposure to plant growth response (62 

FR 38856, July 18, 1997; 73 FR 16436, 

March 27, 2008). This approach for 

characterizing O3 exposure 

concentrations that are biologically 

relevant with regard to potential 

vegetation effects received strong 

support from CASAC in the last review 

and again in this review, including 

strong support for use of such a metric 

as the form for the secondary standard 

(Henderson, 2006, 2008; Samet, 2010; 

Frey, 2014c). 

Alternative methods for 

characterizing O3 exposure to predict 

plant response have, in recent years, 

included flux models, which some 

researchers have claimed may ‘‘better 

predict vegetation responses to O3 than 

exposure-based approaches’’ because 

they estimate the ambient O3

concentration that actually enters the 

leaf (i.e., flux or deposition). However, 

the ISA notes that ‘‘[f]lux calculations 

are data intensive and must be carefully 

implemented’’ (U.S. EPA, 2013, p. 9– 

114). Further, the ISA states, ‘‘[t]his 

uptake-based approach to quantify the 

vegetation impact of O3 requires 

inclusion of those factors that control 

the diurnal and seasonal O3 flux to 

vegetation (e.g., climate patterns, 

species and/or vegetation-type factors 

and site-specific factors)’’ (U.S. EPA, 

2013, p. 9–114). In addition to these 

data requirements, each species has 

different amounts of internal 

detoxification potential that may protect 

species to differing degrees. The lack of 

detailed species- and site-specific data 

required for flux modeling in the U.S. 

and the lack of understanding of 

detoxification processes have continued 

to make this technique less viable for 

use in vulnerability and risk 

assessments at the national scale in the 

U.S. (U.S. EPA, 2013, section 9.5.4). 

Therefore, consistent with the ISA 

conclusions regarding the 

appropriateness of considering 

cumulative exposure indices that 

preferentially weight higher 

concentrations over lower for predicting 

O3 effects of concern based on the wellestablished conclusions and supporting 

evidence described above, and in light 

of continued CASAC support, we 

continue to focus on cumulative 

concentration-weighted indices as the 

most biologically relevant metrics for 

consideration of O3 exposures eliciting 

vegetation-related effects. Quantifying 

exposure in this way ‘‘improves the 

explanatory power of exposure/response 

models for growth and yield over using 

indices based on mean and peak 

exposure values’’ (U.S. EPA, 2013, 

section 2.6.6.1, p. 2–44). In this review, 

as in the last review, we use the W126- 

based cumulative, seasonal metric (U.S. 

EPA, 2013, sections 2.6.6.1 and 9.5.2) 

for consideration of the effects evidence 

and in the exposure and risk analyses in 

the WREA. 

This metric, commonly called the 

W126 index, is a non-threshold 

approach described as the sigmoidally 

weighted sum of all hourly O3

concentrations observed during a 

specified daily and seasonal time 

window, where each hourly O3

concentration is given a weight that 

increases from zero to one with 

increasing concentration (U.S. EPA, 

2014c, p. 5–6; U.S. EPA 2013, p. 9–101). 

mstockstill on DSK4VPTVN1PROD with RULES2

65374 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

165Sampling sites in the FIA/FHM O3

biomonitoring program, called ‘‘biosites’’, are plots 

of land on which data are collected regarding the 

incidence and severity of visible foliar injury on a 

variety of O3-sensitive plant species. Biosite index 

scores are derived from these data (U.S. EPA, 

2014b, section 7.2.1). 

166All of the analyses are described in detail in 

the WREA and summarized in the PA and in 

section IV.C of the proposal (U.S. EPA, 2014a; U.S. 

EPA, 2014b; 79 FR 75324–75329, December 17, 

2014). 

167Although the scenarios and the grid cell O3

concentrations on which they are based were 

limited to the contiguous U.S., we have generally 

used the phrase ‘‘national-scale’’ in reference to the 

WREA scenarios and surfaces. 

168The U.S. regions referenced here and in 

section IV.C below are NOAA climate regions, as 

shown in Figure 2B–1 of the PA. 

169The adjustment results in broad regional 

reductions in O3 and includes reductions in O3 at 

some monitors that were already at or below the 

target level. These reductions do not represent an 

optimized control scenario, but rather characterize 

one potential distribution of air quality across a 

region that meets the scenario target (U.S. EPA, 

2014b, sections 4.3.4.2 and 4.4). 

170 In regions where the air quality adjustment 

was applied, it was based on emissions reductions 

determined necessary for the highest monitor in 

that region to just equal the existing standard or the 

W126 target for the scenario. Concentrations at all 

other monitor locations in the region were also 

adjusted based on the same emissions reductions 

assumptions. 

171The VNA technique is described in the WREA 

(U.S. EPA, 2014b, Appendix 4A). 

172Thus, it can be seen that application of the 

VNA interpolation method to estimate W126 index 

values at the centroid of every 12 km x 12 km grid 

cell rather than only at each monitor location 

results in a lowering of the highest values in each 

region. 

The first step in calculating the seasonal 

W126 index, as described and 

considered in this review, is to sum the 

weighted ambient O3 concentrations 

during daylight hours (defined as 8:00 

a.m. to 8:00 p.m.) within each calendar 

month, resulting in monthly index 

values (U.S. EPA, 2014b, pp. 4–5 to 

4–6). As more completely described in 

the WREA, the monthly W126 index 

values are calculated from hourly O3

concentrations as follows: 

where N is the number of days in the 

month, d is the day of the month (d = 

1, 2, . . ., N), h is the hour of the day 

(h = 0, 1, . . ., 23), and Cdh is the hourly 

O3 concentration observed on day d, 

hour h, in parts per million. The 

seasonal W126 index value for a specific 

year is the maximum sum of the 

monthly index values for three 

consecutive months. Three-year W126 

index values are calculated by taking 

the average of seasonal W126 index 

values for three consecutive years (U.S. 

EPA, 2014b, pp. 4–5 to 4–6; Wells, 

2014a). 

2. Overview of Welfare Exposure and 

Risk Assessment 

This section outlines the information 

presented in section IV.C of the 

proposal regarding the WREA 

conducted for this review, which built 

upon similar analyses performed in the 

last review. The WREA focuses 

primarily on analyses related to two 

types of effects on vegetation: Reduced 

growth (biomass loss) in both trees and 

agricultural crops, and foliar injury. The 

assessments of O3-associated reduced 

growth in native trees and crops 

(specifically, RBL and RYL, 

respectively) include analysis of 

associated changes in related ecosystem 

services, including pollution removal, 

carbon sequestration or storage, and 

hydrology, as well as economic impacts 

on the forestry and agriculture sectors of 

the economy. The foliar injury 

assessments include cumulative 

analyses of the proportion of USFS 

biosite index scores 165 above zero (or 

five, in a separate set of analyses) with 

increasing W126 exposure index 

estimates, with and without 

consideration of soil moisture 

conditions. The implications of visible 

foliar injury in national parks were 

considered in a screening level 

assessment and three case studies.166

Growth-related effects were assessed 

for W126-based exposure estimates in 

five scenarios of national-scale 167 air 

quality: Recent conditions (2006 to 

2008), the existing secondary standard, 

and W126 index values of 15 ppm-hrs, 

11 ppm-hrs, and 7 ppm-hrs, using 3- 

year averages (U.S. EPA, 2014b, chapter 

4). For each of these scenarios, 3-year 

average W126 exposure index values 

were estimated for 12 kilometer (km) by 

12 km grid cells in a national-scale 

spatial surface. The method for creating 

these grid cell estimates generally 

involved two steps (summarized in 

Table 5–4 of the PA). 

The first step in creating the grid cell 

estimates for each scenario was 

calculation of the average W126 index 

value (across the three years) at each 

monitor location. For the recent 

conditions scenario, this value was 

based on unadjusted O3 concentrations 

from monitoring data. For the other four 

scenarios, the W126 index value for 

each monitor location was calculated 

from model-adjusted hourly O3

concentrations. The adjusted 

concentrations were based on modelpredicted relationships between O3 at 

each monitor location and reductions in 

NOX. Adjustments were applied 

independently for each of the nine U.S. 

regions (see U.S. EPA, 2014b, section 

4.3.4.1).168 The existing standard 

scenario was created first, with the 

result being a national dataset for which 

the highest monitor location in each 

U.S. region had a design value equal to 

the level of the current standard.169 The 

W126 scenarios were created from the 

hourly concentrations used to create the 

existing standard scenario, with modelbased adjustments made at all monitor 

sites in those regions with a site not 

already at or below the target W126 

value for that scenario (U.S. EPA, 2014b, 

section 4.3.4.1).170

After completing step one for all the 

scenarios, the second step involved 

creating the national-scale spatial 

surfaces (composed of 3-year W126 

index values at grid cell centroids). 

These were created by applying the 

Voronoi Neighbor Averaging (VNA) 

spatial interpolation technique to the 

monitor-location, 3-year W126 index 

values (described in step 1).171 This step 

of creating the gridded spatial surfaces 

resulted in further reduction of the 

highest values in each modeling region, 

as demonstrated by comparing the 

W126 index values from steps one and 

two for the existing standard scenario. 

After the step-one adjustment of the 

monitor location concentrations such 

that the highest location in each NOAA 

region just met the existing standard 

(using relationships mentioned above), 

the maximum 3-year average W126 

values in the nine regions ranged from 

18.9 ppm-hrs in the West region to 2.6 

ppm-hrs in the Northeast region (U.S. 

EPA, 2014b, Table 4–3). After 

application of the VNA technique in the 

second step, however, the highest 3-year 

average W126 values across the national 

surface grid cells, which were in the 

Southwest region, were below 15 ppmhrs (U.S. EPA, 2014b, Figure 4–7).172

All of the assessments based on 

growth impacts relied on the W126 

index estimates from the national-scale 

spatial surfaces (created from the 3-year 

average monitor location values as 

described above). Among the analyses 

related to visible foliar injury, a small 

component of the screening-level 


mstockstill on DSK4VPTVN1PROD with RULES2ER26OC15.000</GPH>
Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65375 

173The adjustment is applied to all monitor 

locations in each region. In this way, the adjustment 

results in broad regional reductions in O3 and 

includes reductions in O3 at some monitors that 

were already meeting or below the target level. 

Thus, the adjustments performed to develop a 

scenario meeting a target level at the highest 

monitor in each region did result in substantial 

reduction below the target level in some areas of the 

region. This result at the monitors already well 

below the target indicates an uncertainty with 

regard to air quality expected from specific control 

strategies that might be implemented to meet a 

particular target level. 

174Some uncertainty is inherent in any approach 

to characterizing O3 air quality over broad 

geographic areas based on concentrations at 

monitor locations. 

175 In the visible foliar injury dataset used for the 

cumulative analysis, underestimation of W126 

index values at sites with injury would contribute 

to overestimates of the cumulative proportion of 

sites with injury plotted for the lower W126 values. 

national park assessment and also the 

three national park case studies 

involved summarizing 3-year W126 

index estimates from the four air quality 

scenarios. However, the visible foliar 

injury cumulative proportion analyses 

and a component of the national park 

screening-level assessment relied on 

national-scale spatial surfaces of singleyear, unadjusted W126 index values 

created for each year from 2006 through 

2010 using the VNA interpolation 

technique applied to the monitor 

location index values for these years 

(U.S. EPA, 2014b, section 4.3.2, 

Appendix 4A). 

Because the W126 estimates generated 

for the different air quality scenarios 

assessed are inputs to the vegetation risk 

analyses for tree biomass and crop yield 

loss, and also used in some components 

of the visible foliar injury assessments, 

limitations and uncertainties in the air 

quality analyses, which are discussed in 

detail in the WREA and some of which 

are mentioned here, are propagated into 

those analyses (U.S. EPA, 2014b, 

chapters 4 and 8 and section 8.5, Table 

4–5). An important uncertainty in the 

analyses is the application of regionally 

determined emissions reductions to 

meet the existing standard (U.S. EPA, 

2014b, section 8.5.1). The model 

adjustments are based on emissions 

reductions in NOx and characterize only 

one potential distribution of air quality 

across a region when all monitor 

locations meet the standard, as well as 

for the W126 scenarios (U.S. EPA, 

2014b, section 4.3.4.2).173

An additional uncertainty related to 

the W126 index estimates in the 

national surfaces for each air quality 

scenario, and to the estimates for the 

single-year surfaces used in the visible 

foliar injury cumulative analysis, comes 

with the creation of the national-scale 

spatial surfaces of grid cells from the 

monitor-location O3 data.174 In general, 

spatial interpolation techniques perform 

better in areas where the O3 monitoring 

network is denser. Therefore, the W126 

index values estimated using this 

technique in rural areas in the West, 

Northwest, Southwest, and West North 

Central regions where there are few or 

no monitors (U.S. EPA, 2014b, Figure 2– 

1) are more uncertain than those 

estimated for areas with denser 

monitoring. Further, as described above, 

this interpolation method generally 

underpredicts the highest W126 

exposure index values. Due to the 

important influence of higher exposures 

in determining risks to plants, the 

potential for the VNA interpolation 

approach to dampen peak W126 index 

values could result in an 

underestimation of risks to vegetation in 

some areas.175

The vegetation analyses performed in 

the WREA, along with key observations, 

insights, uncertainties and limitations 

were summarized in sections IV.C.2 

through IV.C.3 of the proposal. 

Highlights for the three categories of 

biomass loss and foliar injury 

assessments are summarized here. 

a. Tree Growth, Productivity and Carbon 

Storage 

These assessments rely on the 

species-specific E–R functions described 

in section IV.A.1.b above. For the air 

quality scenarios described above, the 

WREA applied the species-specific E–R 

functions to develop estimates of O3- 

associated RBL and associated effects on 

productivity, carbon storage and 

associated ecosystem services (U.S. 

EPA, 2014b, Chapter 6). More 

specifically, the WREA derived speciesspecific and weighted RBL estimates for 

grid cells across the continental U.S. 

and summarized the estimates by 

counties and national parks. Additional 

WREA case study analyses focused on 

selected urban areas. The WREA 

estimates indicate substantial 

heterogeneity in plant responses to O3, 

both within species (e.g., study-specific 

variation), between species, and across 

regions of the U.S. National variability 

in the estimates (e.g., eastern vs western 

U.S.) is influenced by there being 

different sets of resident species (with 

different E–R functions) in different 

areas of the U.S., as well as differences 

in number of national parks and O3

monitors. For example, the eastern U.S. 

has different resident species compared 

to the western U.S., and the eastern U.S. 

has far more such species. Additionally, 

there are more national parks in the 

western than the eastern U.S., yet fewer 

O3 monitors (U.S. EPA, 2014b, chapter 

8). 

Relative biomass loss nationally 

(across all of the air quality surface grid 

cells) was estimated for each of the 12 

studied species from the composite E– 

R functions for each species described 

above and information on the 

distribution of those species across the 

U.S. (U.S. EPA, 2014b, section 6.2.1.3 

and Appendix 6A). In consideration of 

CASAC advice (summarized in section 

IV.A.1.b above), the WREA derived RBL 

and weighted RBL (wRBL) estimates 

separately, both with and without the 

eastern cottonwood, and the PA and 

proposal gave primary focus to analyses 

that exclude cottonwood. These 

analyses provided estimates of perspecies and cross-species RBL in the 

different air quality scenarios. Air 

quality scenario estimates were also 

developed in terms of proportion of 

basal area affected at different 

magnitudes of RBL. The wRBL analysis 

integrated the species-specific estimates, 

providing an indication of potential 

magnitude of ecological effect possible 

in some ecosystems. The county 

analyses also included analyses focused 

on the median species response. The 

WREA also used the E–R functions to 

estimate RBL across tree lifespans and 

the resulting changes in consumer and 

producer/farmer economic surplus in 

the forestry and agriculture sectors of 

the economy. Case studies in five urban 

areas provided comparisons across air 

quality scenarios of estimates for urban 

tree pollutant removal and carbon 

storage or sequestration. 

The array of uncertainties associated 

with estimates from these tree RBL 

analyses are summarized in the 

proposal and described in detail in the 

WREA, including the potential for the 

air quality scenarios to underestimate 

the higher W126 index values and 

associated implications for the RBLrelated estimates, as referenced above. 

b. Crop Yield Loss 

These assessments rely on the 

species-specific E–R functions described 

in section IV.A.1.b above. For the 

different air quality scenarios, the 

WREA applied the species-specific E–R 

functions to develop estimates of O3

impacts related to crop yield, including 

annual yield losses estimated for 10 

commodity crops grown in the U.S. and 

how these losses affect producer and 

consumer economic surpluses (U.S. 

EPA, 2014b, sections 6.2, 6.5). The 

WREA derived estimates of crop RYL 

nationally and in a county-specific 

analysis, relying on information 

regarding crop distribution (U.S. EPA, 

2014b, section 6.5). As with the tree 

analyses described above, the county 

analysis included estimates based on 

mstockstill on DSK4VPTVN1PROD with RULES2

65376 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

176 Data were not available for several western 

states (Montana, Idaho, Wyoming, Nevada, Utah, 

Colorado, Arizona, New Mexico, Oklahoma, and 

portions of Texas). 

177As discussed in section IV.C.2 below, as the 

cumulative set increases, with increasing W126 

values, the overall prevalence of visible foliar injury 

in the cumulative set is more and more influenced 

by data for the lower W126 values. Accordingly, the 

‘‘leveling off’’ observed above ∼10 ppm-hrs in the 

‘all sites’ analysis likely reflects the 

counterbalancing of visible foliar injury occurrence 

at the relatively fewer higher O3 sites by the larger 

representation within the subset of the lower W126 

conditions associated with which there is lower 

occurrence or extent of foliar injury. 

the median O3 response across the 

studied crop species (U.S. EPA, 2014b, 

section 6.5.1, Appendix 6B). 

Overall effects on agricultural yields 

and producer and consumer surplus 

depend on the ability of producers/

farmers to substitute other crops that are 

less O3 sensitive, and the 

responsiveness, or elasticity, of demand 

and supply (U.S. EPA, 2014b, section 

6.5). The WREA discusses multiple 

areas of uncertainty associated with the 

crop yield loss estimates, including 

those associated with the model-based 

adjustment methodology as well as 

those associated with the projection of 

yield loss using the Forest and 

Agriculture Sector Optimization Model 

(with greenhouse gases) at the estimated 

O3 concentrations (U.S. EPA, 2014b, 

Table 6–27, section 8.5). Because the 

W126 index estimates generated in the 

air quality scenarios are inputs to the 

vegetation risk analyses for crop yield 

loss, any uncertainties in the air quality 

scenario estimation of W126 index 

values are propagated into those 

analyses (U.S. EPA, 2014b, Table 6–27, 

section 8.5). Therefore, the air quality 

scenarios in the crop yield analyses 

have the same uncertainties and 

limitations as in the biomass loss 

analyses (summarized above), including 

those associated with the model-based 

adjustment methodology (U.S. EPA, 

2014b, section 8.5). 

c. Visible Foliar Injury 

The WREA presents a number of 

analyses of O3-related visible foliar 

injury and associated ecosystem 

services impacts (U.S. EPA, 2014b, 

Chapter 7). In the initial analysis, the 

WREA used the biomonitoring site data 

from the USFS FHM/FIA Network 

(USFS, 2011),176 associated soil 

moisture data during the sample years, 

and national surfaces of ambient air O3

concentrations based on spatial 

interpolation of monitoring data from 

2006 to 2010 in a cumulative analysis of 

the proportion of biosite records with 

any visible foliar injury, as indicated by 

a nonzero biosite index score (U.S. EPA, 

2014b, section 7.2). This analysis was 

done for all records together, and also 

for subsets based on soil moisture 

conditions (normal, wet or dry). 

In each cumulative analysis, the 

biosite records were ordered by W126 

index and then, moving from low to 

high W126 index, the records were 

cumulated into a progressively larger 

dataset. With the addition of each new 

data point (composed of biosite index 

score and W126 index value for a biosite 

and year combination) to the cumulative 

dataset, the percentage of sites with a 

nonzero biosite index score was derived 

and plotted versus the W126 index 

estimate for the just added data point. 

The cumulative analysis for all sites 

indicates that (1) as the cumulative set 

of sites grows with addition of sites with 

progressively higher W126 index values, 

the proportion of the dataset for which 

no foliar injury was recorded changes 

(increases) noticeably prior to about 10 

ppm-hrs (10.46 ppm-hrs), and (2) as the 

cumulative dataset grows still larger 

with the addition of records for higher 

W126 index estimates, the proportion of 

the cumulative dataset with no foliar 

injury remains relatively constant (U.S. 

EPA, 2014b, Figure 7–10). The data for 

normal moisture years are very similar 

to the dataset as a whole, with an 

overall proportion of about 18 percent 

for presence of any foliar injury. The 

data for relatively wet years have a 

much higher proportion of biosites 

showing injury, approximately 25% 

when all data are included, and a 

proportion of approximately 20% when 

data for W126 index estimates up to 

about 5–8 ppm-hrs are included (U.S. 

EPA, 2014b, Figure 7–10).177 The 

overall proportion showing injury for 

the subset for relatively dry conditions 

is much lower, less than 15% for the 

subset (U.S. EPA, 2014b, section 7.2.3, 

Figures 7–10). While these analyses 

indicate the potential for foliar injury to 

occur under conditions that meet the 

current standard, the extent of foliar 

injury that might be expected under 

different exposure conditions is unclear 

from these analyses. 

Criteria derived from the cumulative 

analyses were then used in two 

additional analyses. The national-scale 

screening-level assessment compared 

W126 index values estimated within 

214 national parks using the VNA 

technique described above for the 

individual years from 2006 to 2010 with 

benchmark criteria developed from the 

biosite data analysis (U.S. EPA, 2014b, 

Appendix 7A and section 7.3). Separate 

case study analyses described visits, as 

well as visitor uses and expenditures for 

three national parks, and the 3-year 

W126 index estimates in those parks for 

the four air quality scenarios (U.S. EPA, 

2014b, section 7.4). Uncertainties 

associated with these analyses, included 

those associated with the W126 index 

estimates, are discussed in the WREA, 

sections 7.5 and 8.5.3, and in WREA 

Table 7–24, and also summarized in the 

PA (e.g., U.S. EPA, 2014c, section 6.3). 

3. Potential Impacts on Public Welfare 

As provided in the CAA, section 

109(b)(2), the secondary standard is to 

‘‘specify a level of air quality the 

attainment and maintenance of which in 

the judgment of the Administrator . . . 

is requisite to protect the public welfare 

from any known or anticipated adverse 

effects associated with the presence of 

such air pollutant in the ambient air.’’ 

Effects on welfare include, but are not 

limited to, ‘‘effects on soils, water, 

crops, vegetation, man-made 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’’ (CAA section 

302(h)). The secondary standard is not 

meant to protect against all known or 

anticipated O3-related effects, but rather 

those that are judged to be adverse to 

the public welfare, and a bright-line 

determination of adversity is not 

required in judging what is requisite (78 

FR 8312, January 15, 2013; see also 73 

FR 16496, March 27, 2008). Thus, the 

level of protection from known or 

anticipated adverse effects to public 

welfare that is requisite for the 

secondary standard is a public welfare 

policy judgment to be made by the 

Administrator. In the current review, 

the Administrator’s judgment is 

informed by conclusions drawn with 

regard to adversity of effects to public 

welfare in decisions on secondary O3

standards in past reviews. 

As indicated by the Administrator in 

the 2008 decision, the degree to which 

O3 effects on vegetation should be 

considered to be adverse to the public 

welfare depends on the intended use of 

the vegetation and the significance of 

the vegetation to the public welfare (73 

FR 16496, March 27, 2008). Such 

judgments regarding public welfare 

significance in the last O3 NAAQS 

decision gave particular consideration 

to O3 effects in areas with special 

federal protections, and lands set aside 

by states, tribes and public interest 

groups to provide similar benefits to the 

public welfare (73 FR 16496, March 27, 

2008). For example, in reaching his 

conclusion regarding the need for 

revision of the secondary standard in 

the 2008 review, the Administrator took 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65377 

178For example, the National Park Service 

Organic Act of 1916 established the National Park 

Service (NPS) and, in describing the role of the NPS 

with regard to ‘‘Federal areas known as national 

parks, monuments, and reservations’’, stated that 

the ‘‘fundamental purpose’’ for these federal areas 

‘‘is to conserve the scenery and the natural and 

historic objects and the wild life therein and to 

provide for the enjoyment of the same in such 

manner and by such means as will leave them 

unimpaired for the enjoyment of future 

generations.’’ 16 U.S.C. 1. 

179As a second example, the Wilderness Act of 

1964 defines designated ‘‘wilderness areas’’ in part 

as areas ‘‘protected and managed so as to preserve 

[their] natural conditions’’ and requires that these 

areas ‘‘shall be administered for the use and 

enjoyment of the American people in such manner 

as will leave them unimpaired for future use and 

enjoyment as wilderness, and so as to provide for 

the protection of these areas, [and] the preservation 

of their wilderness character . . .’’ 16 U.S.C. 1131 

(a). 

180Areas designated as Class I include all 

international parks, national wilderness areas 

which exceed 5,000 acres in size, national memorial 

parks which exceed 5,000 acres in size, and 

national parks which exceed six thousand acres in 

size, provided the park or wilderness area was in 

existence on August 7, 1977. Other areas may also 

be Class I if designated as Class I consistent with 

the CAA. 

181Ecosystem services have been defined as ‘‘the 

benefits that people obtain from ecosystems’’ (U.S. 

EPA, 2013, Preamble, p. 1xxii; UNEP, 2003) and 

thus are an aspect of the use of a type of vegetation 

or ecosystem. Similarly, a definition used for the 

purposes of the EPA benefits assessments states that 

ecological goods and services are the ‘‘outputs of 

ecological functions or processes that directly or 

indirectly contribute to social welfare or have the 

potential to do so in the future’’ and that ‘‘[s]ome 

outputs may be bought and sold, but most are not 

marketed’’ (U.S. EPA, 2006b). Ecosystem services 

analyses were one of the tools used in the last 

review of the secondary standards for oxides of 

nitrogen and sulfur to inform the decisions made 

with regard to adequacy and as such, were used in 

conjunction with other considerations in the 

discussion of adversity to public welfare (77 FR 

20241, April 3, 2012). 

182Public surveys have indicated that Americans 

rank as very important the existence of resources, 

the option or availability of the resource and the 

ability to bequest or pass it on to future generations 

(Cordell et al., 2008). 

note of ‘‘a number of actions taken by 

Congress to establish public lands that 

are set aside for specific uses that are 

intended to provide benefits to the 

public welfare, including lands that are 

to be protected so as to conserve the 

scenic value and the natural vegetation 

and wildlife within such areas, and to 

leave them unimpaired for the 

enjoyment of future generations’’ (73 FR 

16496, March 27, 2008). As further 

recognized in the 2008 notice, ‘‘[s]uch 

public lands that are protected areas of 

national interest include national parks 

and forests, wildlife refuges, and 

wilderness areas’’ (73 FR 16496, March 

27, 2008).178 179 Such areas include 

Class I areas180 which are federally 

mandated to preserve certain air quality 

related values. Additionally, as the 

Administrator recognized, ‘‘States, 

Tribes and public interest groups also 

set aside areas that are intended to 

provide similar benefits to the public 

welfare, for residents on State and 

Tribal lands, as well as for visitors to 

those areas’’ (73 FR 16496, March 27, 

2008). The Administrator took note of 

the ‘‘clear public interest in and value 

of maintaining these areas in a 

condition that does not impair their 

intended use and the fact that many of 

these lands contain O3-sensitive 

species’’ (73 FR 16496, March 27, 2008). 

The concept described in the 2008 

notice regarding the degree to which 

effects on vegetation in specially 

protected areas, such as those identified 

above, may be judged adverse also 

applies beyond the species level to the 

ecosystem level, such that judgments 

can depend on the intended use181 for, 

or service (and value) of, the affected 

vegetation, ecological receptors, 

ecosystems and resources and the 

significance of that use to the public 

welfare (73 FR 16496, March 27, 2008). 

Uses or services provided by areas that 

have been afforded special protection 

can flow in part or entirely from the 

vegetation that grows there. Aesthetic 

value and outdoor recreation depend, at 

least in part, on the perceived scenic 

beauty of the environment (U.S. EPA, 

2014b, chapters 5 and 7). Further, 

analyses have reported that the 

American public values—in monetary 

as well as nonmonetary ways—the 

protection of forests from air pollution 

damage. In fact, studies that have 

assessed willingness-to-pay for sprucefir forest protection in the southeastern 

U.S. from air pollution and insect 

damage have found that values held by 

the survey respondents for the more 

abstract services (existence, option and 

bequest)182 were greater than those for 

recreation or other services (U.S. EPA, 

2014b, Table 5–6; Haefele et al., 1991; 

Holmes and Kramer, 1995). 

The spatial, temporal and social 

dimensions of public welfare impacts 

are also influenced by the type of 

service affected. For example, a national 

park can provide direct recreational 

services to the thousands of visitors that 

come each year, but also provide an 

indirect value to the millions who may 

not visit but receive satisfaction from 

knowing it exists and is preserved for 

the future (U.S. EPA, 2014b, chapter 5, 

section 5.5.1). Similarly, ecosystem 

services can be realized over a range of 

temporal scales. An evaluation of 

adversity to the public welfare might 

also consider the likelihood, type, and 

magnitude of the effect, as well as the 

potential for recovery and any 

uncertainties relating to these 

conditions, as stated in the preamble of 

the 2012 final notice of rulemaking on 

the secondary standards for oxides of 

nitrogen and sulfur (77 FR 20232, April 

3, 2012). 

The three main categories of effects on 

vegetation discussed in section IV.A.1.b 

above differ with regard to aspects 

important to judging their public 

welfare significance. Judgments 

regarding crop yield loss, for example, 

depend on considerations related to the 

heavy management of agriculture in the 

U.S., while judgments regarding the 

other categories of effects generally 

relate to considerations regarding 

forested areas. For example, while both 

tree growth-related effects and visible 

foliar injury have the potential to be 

significant to the public welfare through 

impacts in Class I and other protected 

areas, they differ in how they might be 

significant and with regard to the clarity 

of the data that describe the relationship 

between the effect and the services 

potentially affected. 

With regard to effects on tree growth, 

reduced growth is associated with 

effects on an array of ecosystem services 

including reduced productivity, altered 

forest and forest community (plant, 

insect and microbe) composition, 

reduced carbon storage and altered 

water cycling (U.S. EPA, 2013, Figure 9– 

1, sections 9.4.1.1 and 9.4.1.2; U.S. EPA, 

2014b, section 6.1). For example, forest 

or forest community composition can be 

affected through O3 effects on growth 

and reproductive success of sensitive 

species in the community, with the 

extent of compositional changes 

dependent on factors such as 

competitive interactions (U.S. EPA, 

2013, sections 9.4.3 and 9.4.3.1). 

Depending on the type and location of 

the affected ecosystem, services 

benefitting the public in other ways can 

be affected as well. For example, other 

services valued by people that can be 

affected by reduced tree growth, 

productivity and carbon storage include 

aesthetic value, food, fiber, timber, other 

forest products, habitat, recreational 

opportunities, climate and water 

regulation, erosion control, air pollution 

removal, and desired fire regimes (U.S. 

EPA 2013, sections 9.4.1.1 and 9.4.1.2; 

U.S. EPA, 2014b, section 6.1, Figure 6– 

1, section 6.4, Table 6–13). Further, 

impacts on some of these services (e.g., 

forest or forest community composition) 

may be considered of greater public 

welfare significance when occurring in 

Class I or other protected areas. 

Consideration of the magnitude of tree 

growth effects that might cause or 

contribute to adverse effects for trees, 

forests, forested ecosystems or the 

public welfare is complicated by aspects 

mstockstill on DSK4VPTVN1PROD with RULES2

65378 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

183The identification, monitoring and assessment 

of AQRVs with regard to an adverse effect is an 

approach used for assessing the potential for air 

pollution impacts in Class I areas from pending 

permit actions (USFS, NPS, USFWS, 2010). An 

adverse impact is recognized by the National Park 

Service as one that results in diminishment of the 

Class I area’s national significance or the 

impairment of the ecosystem structure or 

functioning, as well as impairment of the quality of 

the visitor experience (USFS, NPS, USFWS, 2010). 

Federal land managers make such adverse impact 

determinations on a case-by-case basis, using 

technical and other information that they provide 

for consideration by permitting authorities. The 

National Park Service has developed a document 

describing an overview of approaches related to 

assessing projects under the National 

Environmental Policy Act and other planning 

initiatives affecting the National Park System 

(http://www.nature.nps.gov/air/Pubs/pdf/

AQGuidance_2011-01-14.pdf). 

184The National Park Service identifies various 

ranges of W126 index values in providing 

approaches for assessing air quality-related impacts 

of various development projects which appear to be 

based on the 1996 workshop report (Heck and 

Cowling, 1997), and may, at the low end, relate to 

a benchmark derived for the highly sensitive 

species, black cherry, for growth effects (10% RBL), 

rather than visible foliar injury (Kohut, 2007; 

Lefohn et al., 1997). As noted in section IV.A.1.b 

above, visible foliar injury is not always a reliable 

indicator of other negative effects on vegetation 

(U.S. EPA, 2013, p. 9–39). We also note that the 

USFS biomonitoring analyses of visible foliar injury 

biomonitoring data commonly make use of a set of 

biosite index categories for which risk assumptions 

have been assigned, providing a relative scale of 

possible impacts (Campbell et al, 2007); however, 

little information is available on the studies, effects 

and judgments on which these categories are based. 

of, or limitations in, the available 

information. For example, the evidence 

on tree seedling growth effects, deriving 

from the E–R functions for 11 species 

(described in section IV.A.1 above), 

provides no clear threshold or 

breakpoint in the response to O3

exposure. Additionally, there are no 

established relationships between 

magnitude of tree seedling growth 

reduction and forest ecosystem impacts 

and, as noted in section IV.A.1.b above, 

other factors can influence the degree to 

which O3-induced growth effects in a 

sensitive species affect forest and forest 

community composition and other 

ecosystem service flows from forested 

ecosystems. These include (1) the type 

of stand or community in which the 

sensitive species is found (i.e., single 

species versus mixed canopy); (2) the 

role or position the species has in the 

stand (i.e., dominant, sub-dominant, 

canopy, understory); (3) the O3

sensitivity of the other co-occurring 

species (O3 sensitive or tolerant); and (4) 

environmental factors, such as soil 

moisture and others. The lack of such 

established relationships complicates 

judgments as to the extent to which 

different estimates of impacts on tree 

seedling growth would indicate 

significance to the public welfare and 

thus be an important consideration in 

the level of protection for the secondary 

standard. 

During the 1997 review of the 

secondary standard, views related to 

this issue were provided by a 1996 

workshop of 16 leading scientists in the 

context of discussing their views for a 

secondary O3 standard (Heck and 

Cowling, 1997). In their consideration of 

tree growth effects as an indicator for 

forest ecosystems and crop yield 

reduction as an indicator of agricultural 

systems, the workshop participants 

identified annual percentages, of RBL 

for forest tree seedlings and RYL for 

agricultural crops, considered important 

to their judgments on the standard. With 

regard to forest ecosystems and seedling 

growth effects as an indicator, the 

participants selected a range of 1–2% 

RBL per year ‘‘to avoid cumulative 

effects of yearly reductions of 2%.’’ 

With regard to crops, they indicated an 

interest in protecting against crop yield 

reductions of 5% RYL yet noted 

uncertainties surrounding such a 

percentage which led them to 

identifying 10% RYL for the crop yield 

endpoint (Heck and Cowling, 1997). The 

workshop report provides no explicit 

rationale for the percentages identified 

(1–2% RBL and 5% or 10% RYL); nor 

does it describe their connection to 

ecosystem impacts of a specific 

magnitude or type, nor to judgments on 

significance of the identified effects for 

public welfare, e.g., taking into 

consideration the intended use and 

significance of the affected vegetation 

(Heck and Cowling, 1997). In 

recognition of the complexity of 

assessing the adversity of tree growth 

effects and effects on crop yield in the 

broader context of public welfare, the 

EPA’s consideration of those effects in 

both the 1997 and 2008 reviews 

extended beyond the consideration of 

various benchmark responses for the 

studied species, and, with regard to 

crops, additionally took note of their 

extensive management (62 FR 38856, 

July 18, 1997; 73 FR 16436, March 27, 

2008). 

While, as noted above, public welfare 

benefits of forested lands can be 

particular to the type of area in which 

the forest occurs, some of the potential 

public welfare benefits associated with 

forest ecosystems are not location 

dependent. A potentially extremely 

valuable ecosystem service provided by 

forested lands is carbon storage, a 

regulating service that is ‘‘of paramount 

importance for human society’’ (U.S. 

EPA, 2013, section 2.6.2.1 and p. 9–37). 

As noted above, the EPA has concluded 

that this ecosystem service has a likely 

causal relationship with O3 in ambient 

air. The service of carbon storage is 

potentially important to the public 

welfare no matter in what location the 

sensitive trees are growing or what their 

intended current or future use. In other 

words, the benefit exists as long as the 

tree is growing, regardless of what 

additional functions and services it 

provides. Another example of locations 

potentially vulnerable to O3-related 

impacts but not necessarily identified 

for such protection might be forested 

lands, both public and private, where 

trees are grown for timber production. 

Forests in urbanized areas also provide 

a number of services that are important 

to the public in those areas, such as air 

pollution removal, cooling, and 

beautification. There are also many 

other tree species, such as species 

identified by the USFS and various 

ornamental and agricultural species 

(e.g., Christmas trees, fruit and nut 

trees), that provide ecosystem services 

that may be judged important to the 

public welfare but whose vulnerability 

to O3 impacts has not been 

quantitatively characterized (U.S. EPA, 

2014b, Chapter 6). 

As noted above, in addition to tree 

growth-related effects, O3-induced 

visible foliar injury also has the 

potential to be significant to the public 

welfare through impacts in Class I and 

other similarly protected areas. Visible 

foliar injury is a visible bioindicator of 

O3 exposure in species sensitive to this 

effect, with the injury affecting the 

physical appearance of the plant. 

Accordingly visible foliar injury surveys 

are used by federal land managers as 

tools in assessing potential air quality 

impacts in Class I areas. These surveys 

may focus on plant species that have 

been identified as potentially sensitive 

air quality related values (AQRVs) due 

to their sensitivity to O3-induced foliar 

injury (USFS, NPS, FWS, 2010). An 

AQRV is defined by the National Park 

Service as a ‘‘resource, as identified by 

the [federal land manager] for one or 

more Federal areas that may be 

adversely affected by a change in air 

quality,’’ and the resource ‘‘may include 

visibility or a specific scenic, cultural, 

physical, biological, ecological, or 

recreational resource identified by the 

[federal land manager] for a particular 

area’’ (USFS, NPS, USFWS, 2010).183 No 

criteria have been established, however, 

regarding a level or prevalence of visible 

foliar injury considered to be adverse to 

the affected vegetation, and, as noted in 

section IV.A.1.b above, there is not a 

clear relationship between visible foliar 

injury and other effects, such as reduced 

growth and productivity.184 Thus, key 

considerations with regard to public 

welfare significance of this endpoint 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65379 

185See http://www2.nature.nps.gov/air/Pubs/pdf/ 

flag/NPSozonesensppFLAG06.pdf. 

186Basal area for resident species in national 

forests and parks are available in files accessible at: 

http://www.fs.fed.us/foresthealth/technology/

nidrm2012.shtml. Basal area is generally described 

as the area of ground covered by trees. 

have related to qualitative consideration 

of the plant’s aesthetic value in 

protected forested areas. Depending on 

the extent and severity, O3-induced 

visible foliar injury might be expected to 

have the potential to impact the public 

welfare in scenic and/or recreational 

areas during the growing season, 

particularly in areas with special 

protection, such as Class I areas. 

The ecosystem services most likely to 

be affected by O3-induced visible foliar 

injury (some of which are also 

recognized above for tree growth-related 

effects) are cultural services, including 

aesthetic value and outdoor recreation. 

In addition, several tribes have 

indicated that many of the species 

identified as O3 sensitive (including 

bioindicator species) are culturally 

significant (U.S. EPA, 2014c, Table 5–1). 

The geographic extent of protected areas 

that may be vulnerable to such public 

welfare effects of O3 is potentially 

appreciable. Sixty-six plant species that 

occur on U.S. National Park Service 

(NPS) and U.S. Fish and Wildlife 

Service lands 185 have been identified as 

sensitive to O3-induced visible foliar 

injury, and some also have particular 

cultural importance to some tribes (U.S. 

EPA, 2014c, Table 5–1 and Appendix 5– 

A; U.S. EPA, 2014b, section 6.4.2). Not 

all species are equally sensitive to O3, 

however, and quantitative E–R 

relationships for O3 exposure and other 

important effects, such as seedling 

growth reduction, are only available for 

a subset of 12 of the 66, as summarized 

in section IV.A.1.b above. A diverse 

array of ecosystem services has been 

identified for these twelve species (U.S. 

EPA, 2014c, Table 5–1). Two species in 

this group that are slightly more 

sensitive than the median for the group 

with regard to effects on growth are the 

ponderosa pine and quaking aspen (U.S. 

EPA, 2014b, section 6.2), the ranges for 

which overlap with many lands that are 

protected or preserved for enjoyment of 

current and future generations 

(consistent with the discussion above on 

Class I and other protected areas), 

including such lands located in the west 

and southwest regions of the U.S. where 

ambient O3 concentrations and 

associated cumulative seasonal 

exposures can be highest (U.S. EPA, 

2014c, Appendix 2B).186

With regard to agriculture-related 

effects, the EPA has recognized other 

complexities, stating that the degree to 

which O3 impacts on vegetation that 

could occur in areas and on species that 

are already heavily managed to obtain a 

particular output (such as commodity 

crops or commercial timber production) 

would impair the intended use at a level 

that might be judged adverse to the 

public welfare has been less clear (73 FR 

16497, March 27, 2008). As noted in 

section IV.B.2 of the proposal, while 

having sufficient crop yields is of high 

public welfare value, important 

commodity crops are typically heavily 

managed to produce optimum yields. 

Moreover, based on the economic theory 

of supply and demand, increases in crop 

yields would be expected to result in 

lower prices for affected crops and their 

associated goods, which would 

primarily benefit consumers. These 

competing impacts on producers and 

consumers complicate consideration of 

these effects in terms of potential 

adversity to the public welfare (U.S. 

EPA, 2014c, sections 5.3.2 and 5.7). 

When agricultural impacts or vegetation 

effects in other areas are contrasted with 

the emphasis on forest ecosystem effects 

in Class I and similarly protected areas, 

it can be seen that the Administrator has 

in past reviews judged the significance 

to the public welfare of O3-induced 

effects on sensitive vegetation growing 

within the U.S. to differ depending on 

the nature of the effect, the intended use 

of the sensitive plants or ecosystems, 

and the types of environments in which 

the sensitive vegetation and ecosystems 

are located, with greater significance 

ascribed to areas identified for specific 

uses and benefits to the public welfare, 

such as Class I areas, than to areas for 

which such uses have not been 

established (FR 73 16496–16497, March 

27, 2008). 

In summary, several considerations 

are recognized as important to 

judgments on the public welfare 

significance of the array of effects of 

different O3 exposure conditions on 

vegetation. While there are complexities 

associated with the consideration of the 

magnitude of key vegetation effects that 

might be concluded to be adverse to 

ecosystems and associated services, 

there are numerous locations where O3- 

sensitive tree species are present that 

may be vulnerable to impacts from O3

on tree growth, productivity and carbon 

storage and their associated ecosystems 

and services. Cumulative exposures that 

may elicit effects and the significance of 

the effects in specific situations can vary 

due to differences in exposed species 

sensitivity, the importance of the 

observed or predicted O3-induced effect, 

the role that the species plays in the 

ecosystem, the intended use of the 

affected species and its associated 

ecosystem and services, the presence of 

other co-occurring predisposing or 

mitigating factors, and associated 

uncertainties and limitations. These 

factors contribute to the complexity of 

the Administrator’s judgments regarding 

the adversity of known and anticipated 

effects to the public welfare. 

B. Need for Revision of the Secondary 

Standard 

The initial issue to be addressed in 

this review of the secondary standard 

for O3 is whether, in view of the 

currently available scientific evidence, 

exposure and risk information and air 

quality analyses, as reflected in the 

record, the standard should be retained 

or revised. In drawing conclusions on 

adequacy of the current O3 secondary 

standard, the Administrator has taken 

into account both evidence-based and 

quantitative exposure- and risk-based 

considerations, as well as advice from 

CASAC and public comment. Evidencebased considerations draw upon the 

EPA’s assessment and integrated 

synthesis of the scientific evidence from 

experimental and field studies 

evaluating welfare effects related to O3

exposure, with a focus on policyrelevant considerations, as discussed in 

the PA. Air quality analyses inform 

these considerations with regard to 

cumulative, seasonal exposures 

occurring in areas of the U.S. that meet 

the current standard. Exposure- and 

risk-based considerations draw upon the 

EPA assessments of risk of key welfare 

effects, including O3 effects on forest 

growth, productivity, carbon storage, 

crop yield and visible foliar injury, 

expected to occur in model-based 

scenarios for the current standard, with 

appropriate consideration of associated 

uncertainties. 

In evaluating whether it is appropriate 

to revise the current standard, the 

Administrator’s considerations build on 

the general approach used in the last 

review, as summarized in section IV.A 

of the proposal, and reflect the body of 

evidence and information available 

during this review. The approach used 

is based on an integration of the 

information on vegetation effects 

associated with exposure to O3 in 

ambient air, as well as policy judgments 

on the adversity of such effects to public 

welfare and on when the standard is 

requisite to protect public welfare from 

known or anticipated adverse effects. 

Such judgments are informed by air 

quality and related analyses, 

quantitative assessments, when 

available, and qualitative assessment of 

impacts that could not be quantified. 

The Administrator has taken into 

mstockstill on DSK4VPTVN1PROD with RULES2

65380 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

account both evidence of effects on 

vegetation and ecosystems and public 

uses of these entities that may be 

important to the public welfare. The 

decision on adequacy of the protection 

provided by the current standard has 

also considered the 2013 remand of the 

secondary standard by the D.C. Circuit 

such that this decision incorporates the 

EPA’s response to this remand. 

Section IV.B.1 below summarizes the 

basis for the proposed decision by the 

Administrator that the current 

secondary standard should be revised. 

Significant comments received from the 

public on the proposal are discussed in 

section IV.B.2 and the Administrator’s 

final decision is described in section 

IV.B.3. 

1. Basis for Proposed Decision 

In evaluating whether it was 

appropriate to propose to retain or 

revise the current standard, as discussed 

in section IV.D of the proposal, the 

Administrator carefully considered the 

assessment of the current evidence in 

the ISA, findings of the WREA, 

including associated limitations and 

uncertainties, considerations and staff 

conclusions and associated rationales 

presented in the PA, views expressed by 

CASAC, and public comments that had 

been offered up to that point. In the 

paragraphs below, we summarize the 

proposal presentation of the PA 

considerations with regard to adequacy 

of the current secondary standard, 

advice from the CASAC, and the 

Administrator’s proposed conclusions, 

drawing from section IV.D of the 

proposal, where a fuller discussion is 

presented. 

a. Considerations and Conclusions in 

the PA 

The PA evaluation is based on the 

longstanding evidence for O3 effects and 

the associated conclusions in the 

current review of causal and likely 

causal relationships between O3 in 

ambient air and an array of welfare 

effects at a range of biological and 

ecological scales of organization, as 

summarized in section IV.A.1 above 

(and described in detail in the ISA). 

Drawing from the ISA and CASAC 

advice, the PA emphasizes the strong 

support in the evidence for the 

conclusion that effects on vegetation are 

attributable to cumulative seasonal O3

exposures, taking note of the improved 

‘‘explanatory power’’ (for effects on 

vegetation) of the W126 index over 

other exposure metrics, as summarized 

in section IV.A.1.c above. The PA 

further recognizes the strong basis in the 

evidence for the conclusion that it is 

appropriate to use a cumulative 

seasonal exposure metric, such as the 

W126 index, to judge impacts of O3 on 

vegetation; related effects on ecosystems 

and services, such as carbon storage; 

and the level of public welfare 

protection achieved for such effects 

(U.S. EPA, 2014c, p. 5–78). As a result, 

based on the strong support in the 

evidence and advice from CASAC in the 

current and past reviews, the PA 

concludes that the most appropriate and 

biologically relevant way to relate O3

exposure to plant growth, and to 

determine what would be adequate 

protection for public welfare effects 

attributable to the presence of O3 in 

ambient air, is to characterize exposures 

in terms of a cumulative seasonal form, 

and in particular the W126 metric (U.S. 

EPA, 2014c, pp. 5–7 and 5–78). 

Accordingly, in considering the 

evidence with regard to level of 

protection provided by the current 

secondary standard, the PA considers 

air quality data and exposure-response 

relationships for vegetation effects, 

particularly those related to forest tree 

growth, productivity and carbon storage, 

in terms of the W126 index (U.S. EPA, 

2014c, section 5.2; 79 FR 75330–75333, 

December 17, 2014). 

In considering the extent to which 

such growth-related effects might be 

expected to occur under conditions that 

meet the current secondary standard, 

the PA focused particularly on tree 

seedling RBL estimates for the 11 

species for which robust E–R functions 

have been developed, noting the CASAC 

concurrence with use of O3-related tree 

biomass loss as a surrogate for related 

effects extending to the ecosystem scale 

(U.S. EPA, 2014c, p. 5–80, Frey, 2014c, 

p. 10). The PA evaluation relied on RBL 

estimates for these 11 species derived 

using the robust OTC-based E–R 

functions, noting that analyses newly 

performed in this review have reduced 

the uncertainty associated with using 

OTC E–R functions to predict tree 

growth effects in the field (U.S. EPA, 

2014c, section 5.2.1; U.S. EPA, 2013, 

section 9.6.3.2). 

In considering the RBL estimates for 

different O3 conditions associated with 

the current standard, the PA focused 

primarily on the median of the speciesspecific (composite) E–R functions. In 

so doing, in the context of considering 

the adequacy of protection afforded by 

the current standard, the PA takes note 

of CASAC’s view regarding a 6% 

median RBL (Frey, 2014c, p. 12). Based 

on the summary of RBL estimates in the 

PA, the PA notes that the median 

species RBL estimate, across the 11 

estimates derived from the robust 

species-specific E–R functions, is at or 

above 6% for W126 index values of 19 

ppm-hrs and higher (U.S. EPA, 2014c, 

Tables 6–1 and 5C–3). 

In recognition of the potential 

significance to public welfare of 

vegetation effects in Class I areas, the 

proposal described in detail findings of 

the PA analysis of the occurrence of O3

concentrations associated with the 

potential for RBL estimates above 

benchmarks of interest in Class I areas 

that meet the current standard, focusing 

on 22 Class I areas for which air quality 

data indicated the current standard was 

met and cumulative seasonal exposures, 

in terms of a 3-year average W126 index, 

were at or above 15 ppm-hrs (79 FR 

75331–75332, Table 7, December 17, 

2014; U.S. EPA, 2014c, Table 5–2). The 

PA noted that W126 index values (both 

annual and 3-year average values) in 

many such areas, distributed across 

multiple states and NOAA climatic 

regions, were above 19 ppm-hrs. The 

highest 3-year average value was over 22 

ppm-hrs and the highest annual value 

was over 27 ppm-hrs, exposure values 

for which the corresponding median 

species RBL estimates markedly exceed 

6%, which CASAC has termed 

‘‘unacceptably high’’ (U.S. EPA, 2014c, 

section 5.2). The PA additionally 

considered the species-specific RBL 

estimates for two tree species (quaking 

aspen and ponderosa pine) that are 

found in many of these Class I areas and 

that have a sensitivity to O3 exposure 

that places them slightly more sensitive 

than the median of the group for which 

robust E–R functions have been 

established (U.S. EPA, 2014c, sections 

5.2 and 5.7). As further summarized in 

the proposal, the PA describes the 

results of this analysis, particularly in 

light of advice from CASAC regarding 

the significance of the 6% RBL 

benchmark, as evidence of the 

occurrence in Class I areas, during 

periods when the current standard is 

met, of cumulative seasonal O3

exposures of a magnitude for which the 

tree growth impacts indicated by the 

associated RBL estimates might 

reasonably be concluded to be 

important to public welfare (79 FR 

75332; U.S. EPA, 2014c, sections 5.2.1 

and 5.7). 

The proposal also noted that the PA 

additionally considered findings of the 

WREA analyses of O3 effects on tree 

growth and an array of ecosystem 

services provided by forests, including 

timber production, carbon storage and 

air pollution removal (79 FR 75332– 

75333; U.S. EPA, 2014b, sections 6.2– 

6.8; U.S. EPA, 2014c, section 5.2). While 

recognizing that these analyses provide 

quantitative estimates of impacts on tree 

growth and associated services for 

several different air quality scenarios, 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65381 

the PA takes note of the large 

uncertainties associated with these 

analyses (see U.S. EPA, 2014b, Table 6– 

27) and the potential for these findings 

to underestimate the response at the 

national scale. While noting the 

potential usefulness of considering 

predicted and anticipated impacts to 

these services in assessing the extent to 

which the current information supports 

or calls into question the adequacy of 

the protection afforded by the current 

standard, the PA also recognizes 

significant uncertainties associated with 

the absolute magnitude of the estimates 

for these ecosystem service endpoints 

which limited the weight staff placed on 

these results (U.S. EPA, 2014c, sections 

5.2 and 5.7). 

As described in the proposal, the PA 

also considered O3 effects on crops, 

taking note of the extensive and longstanding evidence of the detrimental 

effect of O3 on crop production, which 

continues to be confirmed by evidence 

newly available in this review (79 FR 

75333; U.S. 2014c, sections 5.3 and 5.7). 

With regard to consideration of the 

quantitative impacts of O3 exposures 

under exposure conditions associated 

with the current standard, the PA 

focused on RYL estimates that had 

strong support in the current evidence 

(as characterized in the ISA, section 9.6) 

in light of CASAC comments regarding 

RYL benchmarks (Frey, 2014c, pp. iii 

and 14). In considering such evidencebased analyses, as well as the exposure/ 

risk-based information for crops, the PA 

notes the CASAC comments regarding 

the use of crop yields as a surrogate for 

consideration of public welfare impacts, 

which noted that ‘‘[c]rops provide food 

and fiber services to humans’’ and that 

‘‘[e]valuation of market-based welfare 

effects of O3 exposure in forestry and 

agricultural sectors is an appropriate 

approach to take into account damage 

that is adverse to public welfare’’ (Frey, 

2014c, p. 10; U.S. EPA, 2014c, section 

5.7). The PA additionally notes, 

however, as recognized in section 

IV.A.3 above that the determination of 

the point at which O3-induced crop 

yield loss becomes adverse to the public 

welfare is still unclear, given that crops 

are heavily managed (e.g., with 

fertilizer, irrigation) for optimum yields, 

have their own associated markets and 

that benefits can be unevenly 

distributed between producers and 

consumers (79 FR 75322; U.S. EPA, 

2014c, sections 5.3 and 5.7). 

With regard to visible foliar injury, as 

summarized in the proposal, the PA 

recognizes the long-standing evidence 

that has established that O3 causes 

diagnostic visible foliar injury 

symptoms on studied bioindicator 

species and also recognizes that such 

O3-induced impacts have the potential 

to impact the public welfare in scenic 

and/or recreational areas, with visible 

foliar injury associated with important 

cultural and recreational ecosystem 

services to the public, such as scenic 

viewing, wildlife watching, hiking, and 

camping, that are of significance to the 

public welfare and enjoyed by millions 

of Americans every year, generating 

millions of dollars in economic value 

(U.S. EPA, 2014b, section 7.1). In 

addition, several tribes have indicated 

that many of the O3-sensitive species 

(including bioindicator species) are 

culturally significant (U.S. EPA, 2014c, 

Table 5–1). Similarly, the PA notes 

CASAC comments that ‘‘visible foliar 

injury can impact public welfare by 

damaging or impairing the intended use 

or service of a resource,’’ including 

through ‘‘visible damage to ornamental 

or leafy crops that affects their economic 

value, yield, or usability; visible damage 

to plants with special cultural 

significance; and visible damage to 

species occurring in natural settings 

valued for scenic beauty or recreational 

appeal’’ (Frey, 2014c, p. 10). Given the 

above, and taking note of CASAC views, 

the PA recognizes visible foliar injury as 

an important O3 effect which, 

depending on severity and spatial 

extent, may reasonably be concluded to 

be of public welfare significance, 

especially when occurring in nationally 

protected areas, such as national parks 

and other Class I areas. 

As summarized in the proposal, the 

PA additionally takes note of the 

evidence described in the ISA regarding 

the role of soil moisture conditions that 

can decrease the incidence and severity 

of visible foliar injury under dry 

conditions (U.S. EPA, 2014c, sections 

5.4 and 5.7). As recognized in the PA, 

this area of uncertainty complicates 

characterization of the potential for 

visible foliar injury and its severity or 

extent of occurrence for given air quality 

conditions and thus complicates 

identification of air quality conditions 

that might be expected to provide a 

specific level of protection from this 

effect (U.S. EPA, 2014c, sections 5.4 and 

5.7). While noting the uncertainties 

associated with describing the potential 

for visible foliar injury and its severity 

or extent of occurrence for any given air 

quality conditions, the PA notes the 

occurrence of O3-induced visible foliar 

injury in areas, including federally 

protected Class I areas that meet the 

current standard, and suggests it may be 

appropriate to consider revising the 

standard for greater protection. In so 

doing, however, the PA recognizes that 

the degree to which O3-induced visible 

foliar injury would be judged important 

and potentially adverse to public 

welfare is uncertain (U.S. EPA, 2014c, 

section 5.7). 

As noted in the proposal, with regard 

to other welfare effects, for which the 

ISA determined a causal or likely causal 

relationships with O3 in ambient air, 

such as alteration of ecosystem water 

cycling and changes in climate, the PA 

concludes there are limitations in the 

available information that affect our 

ability to consider potential impacts of 

air quality conditions associated with 

the current standard. 

Based on the considerations described 

in the PA, summarized in the proposal 

and outlined here, the PA concludes 

that the currently available evidence 

and exposure/risk information call into 

question the adequacy of the public 

welfare protection provided by the 

current standard and provide support 

for considering potential alternative 

standards to provide increased public 

welfare protection, especially for 

sensitive vegetation and ecosystems in 

federally protected Class I and similarly 

protected areas. In this conclusion, staff 

gives particular weight to the evidence 

indicating the occurrence in Class I 

areas that meet the current standard of 

cumulative seasonal O3 exposures 

associated with estimates of tree growth 

impacts of a magnitude that may 

reasonably be considered important to 

public welfare. 

b. CASAC Advice 

The proposal also summarized advice 

offered by the CASAC in the current 

review, based on the updated scientific 

and technical record since the 2008 

rulemaking. The CASAC stated that it 

‘‘[supports] the conclusion in the 

Second Draft PA that the current 

secondary standard is not adequate to 

protect against current and anticipated 

welfare effects of ozone on vegetation’’ 

(Frey, 2014c, p. iii) and that the PA 

‘‘clearly demonstrates that ozoneinduced injury may occur in areas that 

meet the current standard’’ (Frey, 2014c, 

p. 12). The CASAC further stated ‘‘[w]e 

support the EPA’s continued emphasis 

on Class I and other protected areas’’ 

(Frey, 2014c, p. 9). Additionally, the 

CASAC indicated support for the 

concept of ecosystem services ‘‘as part 

of the scope of characterizing damage 

that is adverse to public welfare’’ and 

‘‘concur[red] that trees are important 

from a public welfare perspective 

because they provide valued services to 

humans, including aesthetic value, food, 

fiber, timber, other forest products, 

habitat, recreational opportunities, 

climate regulation, erosion control, air 

mstockstill on DSK4VPTVN1PROD with RULES2

65382 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

pollution removal, and hydrologic and 

fire regime stabilization’’ (Frey, 2014c, 

p. 9). Similar to comments from CASAC 

in the last review, and comments on the 

proposed reconsideration, the current 

CASAC also endorsed the PA 

discussions and conclusions on 

biologically relevant exposure metrics 

and the focus on the W126 index 

accumulated over a 12-hour period (8 

a.m.–8 p.m.) over the 3-month 

summation period of a year resulting in 

the maximum value (Frey, 2014c, p. iii). 

In addition, CASAC stated that 

‘‘relative biomass loss for tree species, 

crop yield loss, and visible foliar injury 

are appropriate surrogates for a wide 

range of damage that is adverse to 

public welfare,’’ listing an array of 

related ecosystem services (Frey, 2014c, 

p. 10). With respect to RBL for tree 

species, CASAC states that it is 

appropriate to identify in the PA ‘‘a 

range of levels of alternative W126- 

based standards that include levels that 

aim for not greater than 2% RBL for the 

median tree species’’ and that a median 

tree species RBL of 6% is ‘‘unacceptably 

high’’ (Frey, 2014c, pp. 13 and 14). With 

respect to crop yield loss, CASAC points 

to a benchmark of 5%, stating that a 

crop RYL for median species over 5% is 

‘‘unacceptably high’’ and described crop 

yield as a surrogate for related services 

(Frey, 2014c, p. 13). 

c. Administrator’s Proposed 

Conclusions 

At the time of proposal, the 

Administrator took into account the 

information available in the current 

review with regard to the nature of O3- 

related effects on vegetation and the 

adequacy of protection provided by the 

current secondary standard. The 

Administrator recognized the 

appropriateness and usefulness of the 

W126 metric in evaluating O3 exposures 

of potential concern for vegetation 

effects, additionally noting support 

conveyed by CASAC for such a use for 

this metric. Further, the Administrator 

took particular note of (1) the PA 

analysis of the magnitude of tree 

seedling growth effects (biomass loss) 

estimated for different cumulative, 

seasonal, concentration-weighted 

exposures in terms of the W126 metric; 

(2) the monitoring analysis in the PA of 

cumulative exposures (in terms of W126 

index) occurring in locations where the 

current standard is met, including those 

locations in or near Class I areas, and 

associated estimates of tree seedling 

growth effects; and (3) the analyses in 

the WREA illustrating the geographic 

distribution of tree species for which E– 

R functions are available and estimates 

of O3-related growth impacts for 

different air quality scenarios, taking 

into account the identified potential for 

the WREA’s existing standard scenario 

to underestimate the highest W126- 

based O3 values that would be expected 

to occur. 

With regard to considering the 

adequacy of public welfare protection 

provided by the current secondary 

standard at the time of proposal, the 

Administrator focused first on welfare 

effects related to reduced native plant 

growth and productivity in terrestrial 

systems, taking note of the following: (a) 

The ISA conclusion of a causal 

relationship between O3 in the ambient 

air and these welfare effects, and 

supporting evidence related to O3 effects 

on vegetation growth and productivity, 

including the evidence from OTC 

studies of tree seedling growth that 

support robust E–R functions for 11 

species; (b) the evidence, described in 

section IV.D.1 of the proposal and 

summarized above, of the occurrence of 

cumulative seasonal O3 exposures for 

which median species RBL estimates are 

of a magnitude that CASAC has termed 

‘‘unacceptably high’’ in Class I areas 

during periods where the current 

standard is met; (c) actions taken by 

Congress to establish public lands that 

are set aside for specific uses intended 

to provide benefits to the public welfare, 

including lands that are to be protected 

so as to conserve the scenic value and 

the natural vegetation and wildlife 

within such areas for the enjoyment of 

future generations, such as national 

parks and forests, wildlife refuges, and 

wilderness areas (many of which have 

been designated Class I areas); and (d) 

PA conclusions that the current 

information calls into question the 

adequacy of the current standard, based 

particularly on impacts on tree growth 

(and the potential for associated 

ecosystem effects), estimated for Class I 

area conditions meeting the current 

standard, that are reasonably concluded 

to be important from a public welfare 

standpoint in terms of both the 

magnitude of the vegetation effects and 

the significance to public welfare of 

such effects in such areas. 

At the time of proposal, the 

Administrator also recognized the 

causal relationships between O3 in the 

ambient air and visible foliar injury, 

reduced yield and quality of agricultural 

crops, and alteration of below-ground 

biogeochemical cycles associated with 

effects on growth and productivity. As 

to visible foliar injury, she took note of 

the complexities and limitations in the 

evidence base regarding characterizing 

air quality conditions with respect to 

the magnitude and extent of risk for 

visible foliar injury, and she 

additionally recognized the challenges 

of associated judgments with regard to 

adversity of such effects to public 

welfare. In taking note of the 

conclusions with regard to crops, she 

recognized the complexity of 

considering adverse O3 impacts to 

public welfare due to the heavy 

management common for achieving 

optimum yields and market factors that 

influence associated services and 

additionally took note of the PA 

conclusions that placing emphasis on 

the protection afforded to trees 

inherently also recognizes a level of 

protection afforded for crops. 

Based on her consideration of the 

conclusions in the PA, and with 

particular weight given to PA findings 

pertaining to tree growth-related effects, 

as well as with consideration of 

CASAC’s conclusion that the current 

standard is not adequate, the 

Administrator proposed to conclude 

that the current standard is not requisite 

to protect public welfare from known or 

anticipated adverse effects and that 

revision is needed to provide the 

requisite public welfare protection, 

especially for sensitive vegetation and 

ecosystems in federally protected Class 

I areas and in other areas providing 

similar public welfare benefits. The 

Administrator further concluded that 

the scientific evidence and quantitative 

analyses on tree growth-related effects 

provide strong support for consideration 

of alternative standards that would 

provide increased public welfare 

protection beyond that afforded by the 

current O3 secondary standard. She 

further noted that a revised standard 

would provide increased protection for 

other growth-related effects, including 

for carbon storage and for areas for 

which it is more difficult to determine 

public welfare significance, as 

recognized in section IV.B.2 of the 

proposal, as well as other welfare effects 

of O3, including visible foliar injury and 

crop yield loss. 

2. Comments on the Need for Revision 

In considering comments on the need 

for revision, we first note the advice and 

recommendations from CASAC with 

regard to the adequacy of the current 

standard. In its review of the second 

draft PA, CASAC stated that it 

‘‘supports the scientific conclusion in 

the Second Draft PA that the current 

secondary standard is not adequate to 

protect against current and anticipated 

welfare effects of ozone on vegetation’’ 

(Frey, 2014c). 

General comments received from the 

public on the proposal that are based on 

relevant factors and either supported or 

opposed the proposed decision to revise 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65383 

the current O3 secondary standard are 

addressed in this section. Comments on 

specific issues or information that relate 

to consideration of the appropriate 

elements of a revised secondary 

standard are addressed below in section 

IV.C. Other specific comments related to 

standard setting, as well as general 

comments based on implementationrelated factors that are not a permissible 

basis for considering the need to revise 

the current standard, are addressed in 

the Response to Comments document. 

Public comments on the proposal 

were divided with regard to support for 

the Administrator’s proposed decision 

to revise the current secondary 

standard. Many state and local 

environmental agencies or government 

bodies, tribal agencies and 

organizations, and environmental 

organizations agreed with the EPA’s 

proposed conclusion on the need to 

revise the current standard, stating that 

the available scientific information 

shows that O3-induced vegetation and 

ecosystem effects are occurring under 

air quality conditions allowed by the 

current standard and, therefore, 

provides a strong basis and support for 

the conclusion that the current 

secondary standard is not adequate. In 

support of their view, these commenters 

relied on the entire body of evidence 

available for consideration in this 

review, including evidence assessed 

previously in the 2008 review. These 

commenters variously pointed to the 

information and analyses in the PA and 

the conclusions and recommendations 

of CASAC as providing a clear basis for 

concluding that the current standard 

does not provide adequate protection of 

public welfare from O3-related effects. 

Many of these commenters generally 

noted their agreement with the rationale 

provided in the proposal with regard to 

the Administrator’s proposed 

conclusion on adequacy of the current 

standard, and some gave additional 

emphasis to several aspects of that 

rationale, including the appropriateness 

of the EPA’s attention to sensitive 

vegetation and ecosystems in Class I 

areas and other public lands that 

provide similar public welfare benefits 

and of the EPA’s reliance on the strong 

evidence of impacts to tree growth and 

growth-related effects. 

Comments from tribal organizations 

additionally noted that many Class I 

areas are of sacred value to tribes or 

provide treaty-protected benefits to 

tribes, including the exercise of 

gathering rights. Tribal organizations 

also noted the presence in Class I areas 

of large numbers of culturally important 

plant species, which they indicate to be 

impacted by air quality conditions 

allowed by the current standard. The 

impacts described include visible foliar 

injury, loss in forest growth and crop 

yield loss, which these groups describe 

as especially concerning when 

occurring on lands set aside for the 

benefit of the public or that are of sacred 

value to tribes or provide treatyprotected benefits to tribes. 

As described in section IV.B.3 below, 

the EPA generally agrees with the view 

of these commenters regarding the need 

for revision of the current secondary 

standard and with CASAC that the 

evidence provides support for the 

conclusions that the current secondary 

standard is not adequate to protect 

public welfare from known or 

anticipated adverse effects, particularly 

with respect to effects on vegetation. 

A number of industries, industry 

associations, or industry consultants, as 

well as some state governors, attorneys 

general and environmental agencies, 

disagreed with the EPA’s proposed 

conclusion on the adequacy of the 

current standard and recommended 

against revision. In support of their 

position, these commenters variously 

stated that the available evidence is 

little changed from that available at the 

time of the 2008 decision, and that the 

evidence is too uncertain, including 

with regard to growth-related effects and 

visible foliar injury, to support revision, 

and does not demonstrate adverse 

effects to public welfare for conditions 

associated with the current standard, 

with some commenters stating 

particularly that the EPA analysis of 

Class I areas did not document adverse 

effects to public welfare. They also cited 

the WREA modeling analyses as 

indicating that any welfare 

improvements associated with a revised 

standard would be marginal; in 

particular, compared to the benefits of 

achieving the current standard. Further, 

they state that, because of long-range 

transport of O3 and precursors, it is not 

appropriate for the EPA to draw 

conclusions about the level of 

protection offered by the current 

standard based on current air quality 

conditions; in support of this view, 

these commenters point to different 

modeling analyses as demonstrating that 

under conditions where the current 

standard is met throughout the U.S., the 

associated W126 values would all be 

below the upper end of the range 

proposed as providing requisite public 

welfare protection and nearly all below 

the lower end of 13 ppm-hrs. 

As an initial matter, we note that, as 

noted in sections I.C and IV.A above, 

the EPA’s 2008 decision on the 

secondary standard was remanded back 

to the Agency because in setting the 

2008 secondary standard, the EPA failed 

to specify what level of air quality was 

requisite to protect public welfare from 

known or anticipated adverse effects or 

explain why any such level would be 

requisite. So, in addressing the court 

remand, the EPA has more explicitly 

considered the extent to which 

protection is provided from known or 

anticipated effects that the 

Administrator may judge to be adverse 

to public welfare, and has described 

how the air quality associated with the 

revised standard would provide 

requisite public welfare protection, 

consistent with CAA section 109(b)(2) 

and the court’s decision remanding the 

2008 secondary standard. In 

undertaking this review, consistent with 

the direction of the CAA, the EPA has 

considered the current air quality 

criteria. 

While we recognize, as stated in the 

proposal, that the evidence newly 

available in this review is largely 

consistent with the evidence available at 

the time of the last review (completed 

in 2008) with regard to the welfare 

effects of O3, we disagree with the 

commenters’ interpretations of the 

evidence and analyses available in this 

review and with their views on the 

associated uncertainties. As 

summarized in section IV.A above, the 

ISA has determined causal relationships 

to exist between several vegetation and 

ecosystem endpoints and O3 in ambient 

air (U.S. 2013, section 9.7). The ISA 

characterized the newly available 

evidence as largely consistent with and 

supportive of prior conclusions, as 

summarized in section IV.A above. This 

is not to say, however, that there is no 

newly available evidence and 

information in this review or that it is 

identical to that available in the last 

review. In some respects, the newly 

available evidence has strengthened the 

evidence available in the last review 

and reduced important uncertainties. As 

summarized in section IV.A.1.b above, 

newly available field studies confirm 

the cumulative effects and effects on 

forest community composition over 

multiple seasons. Additionally, among 

the newly available evidence for this 

review are analyses documented in the 

ISA that evaluate the RBL and RYL E– 

R functions for aspen and soybean, 

respectively, with experimental datasets 

that were not used in the derivation of 

the functions (U.S. 2013, section 9.6.3). 

These evaluations confirm the 

pertinence of the tree seedling RBL 

estimates for aspen, a species with 

sensitivity roughly midway in the range 

of sensitivities for the studied species, 

across multiple years in older trees. 

mstockstill on DSK4VPTVN1PROD with RULES2

65384 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

187Use of RBL estimates in the proposal, and in 

this final decision, focuses on the RBL for the 

studied species as a surrogate for a broad array of 

growth-related effects of potential public welfare 

significance, consistent with the CASAC advice. 

188These four species, aspen, Douglas fir, 

ponderosa pine and red alder, range broadly in 

sensitivities that fall above, below and at the 

median for the 11 species (Lee and Hogsett, 1996; 

U.S. EPA, 2014c, Table 5C–1). 

189The WREA notes a few additional, limited 

analyses using modeling tools and data from 

previous publications that indicate there may be 

species-specific differences in the extent of 

similarities between seedling and adult growth 

response to O3, with some species showing greater 

and some lesser response for seedlings as compared 

to mature tree, but a general comparability (U.S. 

EPA 2014b, section 6.2.1.1 and p. 6–67). 

With regard to crops, the ISA 

evaluations demonstrate a robustness of 

the E–R functions to predict O3- 

attributable RYL and confirm the 

relevance of the crop RYL estimates for 

more recent cultivars currently growing 

in the field. Together, the information 

newly available in this review confirms 

the basis for the E–R functions and 

strengthens our confidence in 

interpretations drawn from their use in 

other analyses newly available in this 

review that have been described in the 

WREA and PA. 

With regard to comments on 

uncertainties associated with estimates 

of RBL, we first note that these 

established, robust E–R functions, 

which the EPA gave particular emphasis 

in this review, are available for seedling 

growth for 11 tree species native to the 

U.S., as summarized in section IV.A.1.b 

above and described in the proposal. 

These E–R functions are based on 

studies of multiple genotypes of 11 tree 

species grown for up to three years in 

multiple locations across the U.S. (U.S. 

EPA, 2013, section 9.6.1). We have 

recognized the uncertainty regarding the 

extent to which the studied species 

encompass the O3 sensitive species in 

the U.S. and also the extent to which 

they represent U.S. vegetation as a 

whole (U.S. EPA, 2014b, section 6.9). 

However, the studied species include 

both deciduous and coniferous trees 

with a wide range of sensitivities and 

species native to every region across the 

U.S. and in most cases are resident 

across multiple states and NOAA 

climatic regions (U.S. EPA, 2014b, 

Appendix 6A). While the CASAC stated 

that there is ‘‘considerable uncertainty 

in extrapolating from the [studied] forest 

tree species to all forest tree species in 

the U.S.,’’ it additionally expressed the 

view that it should be anticipated that 

there are highly sensitive vegetation 

species for which we do not have E–R 

functions and others that are 

insensitive.187 In so doing, the CASAC 

stated that it ‘‘should not be assumed 

that species of unknown sensitivity are 

tolerant to ozone’’ and ‘‘[i]t is more 

appropriate to assume that the 

sensitivity of species without E–R 

functions might be similar to the range 

of sensitivity for those species with E– 

R functions’’ (Frey, 2014c, p. 11). 

Accordingly, we disagree with 

commenters’ view that effects on these 

species are not appropriate 

considerations for evaluation of the 

adequacy of the current standard. 

In support of their view that RBL 

estimates are too uncertain to inform a 

conclusion that the current standard is 

not adequately protective of public 

welfare, some commenters state that 

some of the 11 E–R functions are based 

on as few as one study. The EPA agrees 

that there are two species for which 

there is only one study supporting the 

E–R function (Virginia pine and red 

maple). We also note, however, that 

those two species are appreciably less 

sensitive than the median (Lee and 

Hogsett, 1996; U.S. EPA, 2014c, Table 

5C–1). Thus, in the relevant analyses, 

they tend to influence the median 

toward a relatively less (rather than 

more) sensitive response. Further, there 

are four species for which the E–R 

functions are based on more than five 

studies,188 contrary to the commenters’ 

claims of there being no functions 

supported by that many studies. That 

said, the EPA has noted the relatively 

greater uncertainty in the species for 

which fewer studies are available, and 

it is in consideration of such 

uncertainties that the EPA focused in 

the proposal on the median E–R 

function across the 11 species, rather 

than a function for a species much more 

(or less) sensitive than the median. The 

EPA additionally notes that it gave less 

emphasis to the E–R function available 

for one species, eastern cottonwood, 

based on CASAC advice that the study 

results supporting that E–R function 

were not as strong as the results of the 

other experiments that support the 

other, robust E–R functions and that the 

eastern cottonwood study results 

showed extreme sensitivity to O3

compared to other studies (Frey, 2014c, 

p. 10). Accordingly, the EPA has 

appropriately considered the strength of 

the scientific evidence and the 

associated uncertainties in considering 

revision of the secondary standard. 

Other commenters stated that the 

scientific evidence does not support 

revising the NAAQS, pointing to 

uncertainty related to interpretation of 

the RBL estimates (based on tree 

seedling studies) with regard to effects 

on older tree lifestages. Some of these 

commenters’ claim that mature canopy 

trees experience reduced O3 effects. The 

EPA agrees that the quantitative 

information for O3 growth effects on 

older tree lifestages is available for a 

more limited set of species than that 

available for tree seedlings. We note, 

however, that this is an area for which 

there is information newly available in 

this review. A detailed analysis of study 

data for seedlings and older lifestages of 

aspen shows close agreement between 

the O3-attributable reduced growth 

observed in the older trees and 

reductions predicted from the seedling 

E–R function (U.S. EPA, 2013, section 

9.6.3.2; discussed in the PA, section 

5.2.1 as noted in the proposal, p. 75330). 

This finding, newly available in this 

review and documenting impacts on 

mature trees, improves our confidence 

in conclusions drawn with regard to the 

significance of RBL estimates for this 

species, which is prevalent across 

multiple regions of the U.S.189 It is also 

noteworthy that this species is generally 

more sensitive to O3 effects on growth 

than the median of the 11 species with 

robust E–R functions (as shown in U.S. 

EPA 2014c, Table 5C–1). Other newly 

available studies, summarized in section 

IV.A.1.b above and section IV.B.1.b of 

the proposal, provide additional 

evidence of O3 impacts on mature trees, 

including a meta-analysis reporting 

older trees to be more affected by O3

than younger trees (U.S. EPA, 2013, p. 

9–42; Wittig et al., 2007). We 

additionally note that CASAC 

‘‘concur[red] that biomass loss in trees 

is a relevant surrogate for damage to tree 

growth that affects ecosystem services 

such as habitat provision for wildlife, 

carbon storage, provision of food and 

fiber, and pollution removal’’ 

additionally stating that ‘‘[b]iomass loss 

may also have indirect process-related 

effects such as on nutrient and 

hydrologic cycles’’ leading them to 

conclude that ‘‘[t]herefore, biomass loss 

is a scientifically valid surrogate of a 

variety of adverse effects to public 

welfare’’ (Frey, 2014c, p. 10). 

As noted in section IV.A above and 

discussed below, the Administrator’s 

final decision on the adequacy of the 

current standard draws upon, among 

other things, the available evidence and 

quantitative analyses as well as 

judgments about the appropriate weight 

to place on the range of uncertainties 

inherent in the evidence and analyses. 

The strengthening in this review, as 

compared with the last review, of the 

basis for the robust E–R functions for 

tree seedling RBL, as well as other 

newly available quantitative analyses, 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65385 

190The 15 km distance was selected as a natural 

breakpoint in distance of O3 monitoring sites from 

Class I areas and as still providing similar 

surroundings to those occurring in the Class I area. 

We note that given the strict restrictions on 

structures and access within some of these areas, it 

is common for monitors intended to collect data 

pertaining to air quality in these types of areas to 

be sited outside their boundaries. 

191There is an O3 monitor within fewer than 15% 

of all Class I areas, and fewer than half of all Class 

I areas have a monitor within 15 km. 

192This compares to 20 areas in eight states and 

four regions in the earlier analysis. 

will, accordingly, contribute to 

judgments made by the Administrator 

with regard to these effects in reaching 

her final decisions in this review. 

Amongst the newly available 

information in this review is a new 

analysis describing W126-based 

exposures occurring in counties 

containing Class I areas for which 

monitoring data indicated compliance 

with the current standard. The PA gave 

particular attention to this analysis in 

consideration of the adequacy of the 

current standard, and this analysis was 

also described in the proposal (U.S. 

EPA, 2014c, Appendix 5B and pp. 5–27 

to 5–29; 79 FR 75331–75332, December 

17, 2014). Some of the commenters who 

disagreed with the EPA’s conclusion on 

adequacy of the current standard 

variously stated that this analysis does 

not demonstrate growth effects are 

occurring in Class I areas and that the 

analysis is too uncertain for reliance on 

by the Administrator in her judgment on 

adequacy of the current standard. While 

the EPA agrees with commenters that 

data on the occurrence of growth effects 

in the areas and time periods identified 

are not part of this analysis, we note that 

this is because such data have not been 

collected and consequently cannot be 

included. As a result, the EPA has 

utilized measurements of O3 in or near 

these areas in combination with the 

established E–R functions to estimate 

the potential for growth impacts in these 

areas under conditions where the 

current standard is met. The EPA 

additionally notes that species for 

which E–R functions have been 

developed have been documented to 

occur within these areas (see Table 3). 

The EPA disagrees with commenters 

regarding the appropriateness of this 

analysis for the Administrator’s 

consideration. This analysis documents 

the occurrence of cumulative growing 

season exposures in these ecosystems 

which the EPA and CASAC have 

interpreted, through the use of the 

established E–R functions for tree 

seedling growth effects summarized in 

section IV.A.1.b above (and described in 

the ISA, PA and proposal), as indicating 

the potential for growth effects of 

significance in these protected areas. To 

the extent that these comments imply 

that the Administrator may only 

consider welfare effects that are certain 

in judging the adequacy of the current 

standard, we note that section 109(b)(2) 

of the CAA plainly provides for 

consideration of both known and 

anticipated adverse effects in 

establishing or revising secondary 

NAAQS. 

In support of some commenters’ view 

that this analysis is too uncertain to 

provide a basis for the Administrator’s 

proposed conclusion that the current 

standard is not adequate, one 

commenter observed that the O3

monitors used for six of the 22 Class I 

areas in the analysis, although in the 

same county, were sited outside of the 

Class I areas. This was the case due to 

the analysis being focused on the 

highest monitor in the county that met 

the current standard. To clarify the 

presentation, however, we have 

refocused the presentation, restricting it 

to data for monitors sited in or within 

15 kilometers of a Class I area,190 and 

note that the results are little changed, 

continuing to call into question the 

adequacy of the current standard. As 

shown in Table 3, the dataset in the 

refocused presentation, which now 

spans 1998 up through 2013, includes 

17 Class I areas for which monitors were 

identified in this manner. For context, 

we note that this represents nearly a 

quarter of the Class I areas for which 

there are O3 monitors within 15 km.191

In recognition of the influence that 

other environmental factors can exert in 

the natural environment on the 

relationship between ambient O3

exposures and RBL, potentially 

modifying the impact predicted by the 

E–R functions, the PA and proposal took 

particular note of the occurrence of 3- 

year average W126 index values at or 

above 19 ppm-hrs. In the re-focused 

analysis in Table 3, there are 11 areas, 

distributed across four states in two 

NOAA climatic regions, for which the 3- 

year W126 exposure index values 

ranged at or above 19 ppm-hrs, a value 

for which the corresponding median 

species RBL estimate for a growing 

season’s exposure is 6%, a magnitude 

termed ‘‘unacceptably high’’ by CASAC 

(Frey, 2014c, p. 13). The highest 3-year 

W126 index values in these 11 areas 

ranged from 19.0 up to 22.2 ppm-hrs, a 

cumulative seasonal exposure for which 

the median species RBL estimate is 9% 

for a single growing season. The annual 

W126 index values range above 19 ppmhrs in 15 of the areas in the re-focused 

table provided here; these areas are 

distributed across six states (AZ, CA, 

CO, KY, SD, UT) and four regions (West, 

Southwest, West North Central and 

Central).192 The highest index values in 

the areas with annual index values 

above 19 ppm-hrs range from 19.1 to 

26.9 ppm-hrs. As is to be expected from 

the focus on a smaller dataset, the 

number of states with 1-year W126 

index values above 19 ppm-hrs is 

smaller in the refocused analysis (15 as 

compared to 20), although the number 

of regions affected is the same. More 

importantly, however, the number of 

areas with 3-year W126 index values at 

or above 19 ppm-hrs is the same, 11 

Class I areas across two regions, 

supporting the prior conclusions. 

TABLE 3—O3 CONCENTRATIONS FOR CLASS I AREAS DURING PERIOD FROM 1998 TO 2013 THAT MET THE CURRENT

STANDARD AND WHERE 3-YEAR AVERAGE W126 INDEX VALUE WAS AT OR ABOVE 15 ppm-hrs 

Class I area 

(distance away, if monitor is not at/

within boundaries) 

State/ 

County 

Design 

value 

(ppb)* 

3-Year average W126 

(ppm-hrs)* 

(# ≥ 19 ppm-hrs, range) 

Annual W126 

(ppm-hrs)* 

(# ≥ 19 ppm-hrs, range) 

Number of 

3-year 

periods 

Bridger Wilderness Area QA, DF (8.9 

km).

WY/Sublette .............. 70–72 16.2–17.0 13.9–18.8 4 

Canyonlands National Park 

QA, DF, PP.

UT/San Juan ............. 70–73 15.4–19.5 (2, 19.1–19.5 ) 9.6–23.6 (4, 19.2–23.6 ) 8 

Chiricahua National Monument DF, PP (12 km).AZ/Cochise ................ 69–73 15.2–19.8 (1, 19.8 ) 11.7–21.9 (2, 19.8–21.9 ) 10 

Grand Canyon National Park 

QA, DF, PP.

AZ/Coconino .............. 68–74 15.3–22.2 (7, 19.1–22.2 ) 10.1–26.9 (6, 19.8–26.9 ) 12 

Desolation Wilderness PP (3.9 km) .. CA/El Dorado ............ 75 19.8 (1, 19.8 ) 15.6–22.9 (2, 21.0–22.9 ) 1 

mstockstill on DSK4VPTVN1PROD with RULES2

65386 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

193Basic information on forest processes, 

including the role of seedlings is available at: 

http://www.na.fs.fed.us/stewardship/pubs/NE_

forest_regeneration_handbook_revision_130829_

desktop.pdf. 

TABLE 3—O3 CONCENTRATIONS FOR CLASS I AREAS DURING PERIOD FROM 1998 TO 2013 THAT MET THE CURRENT

STANDARD AND WHERE 3-YEAR AVERAGE W126 INDEX VALUE WAS AT OR ABOVE 15 ppm-hrs—Continued 

Class I area 

(distance away, if monitor is not at/

within boundaries) 

State/ 

County 

Design 

value 

(ppb)* 

3-Year average W126 

(ppm-hrs)* 

(# ≥ 19 ppm-hrs, range) 

Annual W126 

(ppm-hrs)* 

(# ≥ 19 ppm-hrs, range) 

Number of 

3-year 

periods 

Lassen Volcanic National Park DF, PP.CA/Shasta ................. 72–74 15.3–15.6 11.5–19.1 (1, 19.1 ) 2 

Mammoth Cave National Park 

BC, C, LP, RM, SM, VP, YP (0.1 km).

KY/Edmonson ........... 74 15.7 12.3–22.0 (1, 22.0 ) 1 

Maroon Bells-Snowmass Wilderness Area QA, DF (0.8 km).CO/Gunnison ............. 68–73 15.6–20.2 (1, 20.2 ) 13.0–23.8 (3, 21.3–23.8 ) 8 

Mazatzal Wilderness DF, PP (10.9 

km).

AZ/Maricopa .............. 74–75 17.8–19.9 (1, 19.9 ) 10.3–26.2 (3, 19.7–26.2 ) 2 

Mesa Verde National Park DF .......... CO/Montezuma ......... 67–73 15.4–20.7 (1, 20.7 ) 10.7–23.4 (4, 19.5–23.4 ) 11 

Petrified Forest National Park C ...... AZ/Navajo .................. 70 15.4–16.9 12.7–18.6 2 

Rocky Mountain National Park 

QA, DF, PP (0.9 km).

CO/Larimer ................ 73–74 15.3–18.4 8.3–26.2 (4, 19.4–26.2 ) 5 

Saguaro National Park DF, PP (0.1 

km)**.

AZ/Pima ..................... 69–74 15.4–19.0 (1, 19.0 ) 7.3–22.9 (3, 19.6–22.9 ) 6 

AZ/Gila ...................... 72–75 16.6–20.9 (2, 19.0–20.9 ) 13.8–25.5 (4, 19.0–25.5 ) 5 

Superstition Wilderness Area PP

(6.3, 14.9 km and 7.2 km)**.

AZ/Maricopa .............. 70–75 15–20.2 (1, 20.2 ) 6.3–23.9 (4, 19.6–23.9 ) 4 

AZ/Pinal ..................... 72–75 15.3–21.1 (1, 21.1 ) 10.2–24.7 (4, 21.4–24.7 ) 7 

Weminuche Wilderness Area 

QA, DF, PP (14.9 km).

CO/La Plata ............... 70–74 15.1–19.1 (1, 19.1 ) 10.8–21.0 (2, 20.8–21.0 ) 6 

Wind Cave National Park QA, PP ...... SD/Custer .................. 70 15.4 12.3–20.5 (1, 20.5 ) 1 

Zion National Park QA, DF, PP (3.6 

km).

UT/Washington .......... 70–73 17.0–20.1 (2, 19.4–20.1 ) 14.2–23.2 (3, 19.8–23.2 ) 6 

* Based on hourly O3 concentration data retrieved from AQS on June 25, 2014, and additional CASTNET data downloaded from http://java.

epa.gov/castnet/epa_jsp/prepackageddata.jsp on June 25, 2014. Design values shown above are derived in accordance with Appendix P to 40 

CFR Part 50. Annual W126 index values are derived as described in section IV.A.1 above; three consecutive year annual values are averaged 

for 3-year averages. Prior to presentation, both types of W126 index values are rounded to one decimal place. The full list of monitoring site 

identifiers and individual statistics is available in the docket for this rulemaking. 

** No monitor was sited within these Areas and multiple monitors were sited within 15 km. Data for the closest monitor per county are presented. 

Superscript letters refer to species present for which E–R functions have been developed. QA=Quaking Aspen, BC=Black Cherry, 

C=Cottonwood, DF=Douglas Fir, LP=Loblolly Pine, PP=Ponderosa Pine, RM=Red Maple, SM=Sugar Maple, VP=Virginia Pine, YP=Yellow (Tulip) 

Poplar. Sources include USDA–NRCS (2014, http://plants.usda.gov), USDA–FS (2014, http://www.fs.fed.us/foresthealth/technology/

nidrm2012.shtml) UM–CFCWI (2014, http://www.wilderness.net/printFactSheet.cfm?WID=583), NPS (http://www.nps.gov/pefo/planyourvisit/

upload/Common-Plants-Site-Bulletin-sb-2013.pdf) and Phillips and Comus (2000). 

As support for their view that the 

Class I area analysis is too uncertain to 

provide a basis for the Administrator’s 

proposed conclusion that the current 

standard is not adequate, some 

commenters stated that forests in Class 

I areas were composed of mature trees 

and that the tree seedling E–R functions 

do not predict growth impacts in mature 

forests. The EPA disagrees with the 

commenters’ statement that Class I areas 

are only made up of mature trees. 

Seedlings exist throughout forests as 

part of the natural process of replacing 

aging trees and overstory trees affected 

by periodic disturbances.193 Seedlings 

also tend to occur in areas affected by 

natural disturbances, such as fires, 

insect infestations and flooding, and 

such disturbances are common in many 

natural forests. As noted above, 

information newly available in this 

review strengthens our understanding 

regarding O3 effects on mature trees for 

aspen, an important and O3-sensitive 

species (U.S. EPA, 2013, section 

9.6.3.2). 

One commenter additionally stated 

that the EPA has not shown reduced 

biomass to be adverse to public welfare, 

variously citing individual studies, most 

of which are not considering O3, as 

support for their view that such an 

effect of O3 may not occur in the 

environment and may be of no 

significance if it does. With regard to the 

occurrence of O3-related reduced growth 

in the field, we note the strength of the 

evidence from field OTC studies on 

which the E–R functions are based, and 

evidence from comparative studies with 

open-air chamberless control treatments 

suggests that characteristics particular to 

the OTC did not significantly affect 

plant response (U.S. EPA, 2013, p. 9–5). 

Thus, we view the OTC systems as 

combining aspects of controlled 

exposure systems with field conditions 

to facilitate a study providing data that 

represent the role of the studied 

pollutant in a natural system. 

Further, we disagree with the 

commenters on the significance of O3- 

attributable reduced growth in natural 

ecosystems. Even in the circumstances 

cited by the commenter (e.g., 

subsequent to large-scale disturbances, 

nutrient limited system, multigeneration 

exposure), O3 can affect growth of 

seedlings and older trees, with the 

potential for effects on ecosystem 

productivity, handicapping the sensitive 

species and affecting community 

dynamics and associated community 

composition, as well as ecosystem 

hydrologic cycles (U.S. EPA, 2013, p. 1– 

8). For example, two recent studies 

report on the role of O3 exposure in 

affecting water use in a mixed 

deciduous forest and indicated that O3

increased water use in the forest and 

also reduced growth rate (U.S. EPA, 

2013, p. 9–43, McLaughlin, 2007a, 

2007b). Contrary to the lesser effects 

implied by the commenters, the authors 

of these two studies noted implications 

of their findings with regard to the 

potential for effects to be amplified 

under conditions of increased 

temperature and associated reduced 

water availability (McLaughlin, 2007a). 

We additionally note comments from 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65387 

194Although commenters cite to both analyses as 

if providing the same information, there are many 

differences in specific aspects of the RIA approach 

from that of the WREA, which derive, at least in 

part, from their very different purposes. The RIA is 

not developed for consideration in the NAAQS 

review. Rather, it is intended to provide insights 

and analysis of an illustrative control strategy that 

states might adopt to meet the revised standard. The 

EPA does not consider this analysis informative to 

consideration of the protection provided by the 

current standard, and the results of the RIA have 

not been considered in the EPA’s decisions on the 

O3 standards. 

the CASAC, summarized above, in 

which it concurs with a focus on 

biomass loss and the use of RBL 

estimates, calling biomass loss in trees 

a ‘‘relevant surrogate for damage to tree 

growth’’ that affects an array of 

ecosystem services (Frey, 2014c, p. 10), 

and identifies 6% RBL as ‘‘unacceptably 

high’’ (Frey, 2014c, p. 13). The evidence 

we presented includes evidence related 

to RBL estimates above that benchmark. 

Thus, while we agree that some 

reductions in tree growth may not be 

concluded to be adverse to public 

welfare, we disagree with commenters 

that we have not presented the 

evidence, which includes RBL estimates 

well above the 6% magnitude identified 

by CASAC, that supports the 

Administrator’s judgments on adversity 

that may be indicated by such estimates 

and her conclusion that adequate 

protection is not provided by the 

current standard, as described in section 

IV.B.3 below. 

Some commenters disagree with the 

EPA’s consideration of the Class I areas 

analysis, stating that it is not 

appropriate for the EPA to evaluate the 

level of protection offered by the current 

primary O3 standard under current 

conditions due to the long-range 

transport of O3 and O3 precursors to 

Class I areas from upwind nonattainment areas. It is the view of these 

commenters that once the upwind areas 

make emissions reductions to attain the 

current standard, downwind areas will 

see improvements in air quality and 

decreasing W126 levels. In support of 

this view, commenters point to several 

modeling analyses. Some commenters 

point to air quality modeling conducted 

by an environmental consultant that 

projects all sites to have W126 index 

values below 13 ppm-hrs when 

emissions are adjusted such that all 

upwind monitors are modeled to meet 

the current standard. Detailed 

methodology, results and references for 

the commenter’s modeling analysis 

were not provided, precluding a 

thorough evaluation and comparison to 

the EPA’s modeling. While the EPA 

agrees that transport of O3 and O3

precursors can affect downwind 

monitors, we disagree with commenters 

regarding the conclusions that are 

appropriate to draw from modeling 

simulations for the reasons noted below. 

As support for their view that the 

current standard provides adequate 

protection, some commenters pointed to 

estimates drawn from the EPA’s air 

quality modeling performed for the RIA, 

stating that this modeling for an 

alternative standard level of 70 ppb 

indicates ‘‘only a handful’’ of 

monitoring sites approaching as high as 

13 ppm-hrs as a 3-year average (e.g., 

UARG, p. 76). These commenters 

further point to the WREA modeling, 

noting that those estimates project that 

attainment of the current standard 

would result in only 5 sites above 15 

ppm-hrs. Based on these statements, 

these commenters state that the current 

standard is likely to provide conditions 

with no site having a monitor over 17 

ppm-hrs and a ‘‘minimal number’’ likely 

exceeding 13 ppm-hrs (e.g., UARG, p. 

77). We disagree with commenters’ 

interpretation of the modeling 

information from the two different 

assessments. As we summarized in 

section IV.C.1 of the proposal with 

regard to the WREA modeling, the 

modeling estimates are each based on a 

single set of precursor emissions 

reductions that are estimated to achieve 

the desired target conditions, which is 

also the case for the RIA modeling194

(U.S. EPA, 2014c, pp. 5–40 to 5–41; see 

also section 1.2.2 of the 2014 RIA). 

As noted in section IV.A.2 above, and 

in the proposal, the model-adjusted air 

quality in the WREA scenario for the 

current standard does not represent an 

optimized control scenario that just 

meets the current standard, but rather 

characterizes one potential distribution 

of air quality across a region when all 

monitor locations meet the standard (79 

FR 75322; U.S. EPA, 2014b, section 

4.3.4.2). Alternate precursor emissions 

reductions would be expected to 

produce different patterns of O3

concentrations and associated 

differences in W126 index values. 

Specifically, the precursor emissions 

reductions scenarios examined in the 

WREA focuses on regional reductions 

over broad areas rather than localized 

cuts that may focus more narrowly on 

areas violating the current standard 

(U.S. EPA, 2014b, p. 4–35). The 

assumption of regionally determined 

across-the-board emissions reductions is 

a source of potential uncertainty with 

the potential to overestimate W126 

scenario benefits (U.S. EPA, 2014b, 

Table 4–5 [row G]). The application of 

emissions reductions to all locations in 

each region to bring down the highest 

monitor in the region to meet the 

current standard could potentially lead 

to W126 index underestimates at some 

locations, as noted in the WREA: 

‘‘[w]hile the scenarios implemented in 

this analysis show that [] bringing down 

the highest monitor in a region would 

lead to reductions below the targeted 

level through the rest of the region, to 

the extent that the regional reductions 

from on-the-books controls are 

supplemented with more local controls 

the additional benefit may be 

overestimated’’ (U.S. EPA, 2014b, p. 4– 

36; U.S. EPA, 2014c, pp. 5–40 to 5–41). 

This point was emphasized by CASAC 

in their comments on the 2nd draft 

WREA. CASAC noted that, ‘‘[m]eeting a 

target level at the highest monitor 

requires substantial reductions below 

the targeted level through the rest of the 

region’’ and stated that ‘‘[t]his artificial 

simulation does not represent an actual 

control strategy and may conflate 

differences in control strategies required 

to meet different standards’’ (Frey, 

2014b, p. 2). 

Due to the uncertainty about what 

actual future emissions control 

strategies might be and their associated 

emissions reductions, and the impact 

such uncertainty might have on 

modeling estimates involving 

reductions from recent conditions, we 

believe it is important to place weight 

on ambient air monitoring data for 

recent conditions in drawing 

conclusions regarding W126 index 

values that would be expected in areas 

that meet the current standard. The 

analysis of air quality data for Class I 

areas described in the proposal, and 

updated in Table 3 above (1998–2013), 

indicates the occurrence of 3-year W126 

exposure index values well above 19 

ppm-hrs, a cumulative exposure value 

for which CASAC termed the associated 

median RBL estimate ‘‘unacceptably 

high,’’ in multiple Class I areas that 

meet the current standard (79 FR 75312, 

December 17, 2014, Table 7; updated in 

Table 3 above). Additionally, analysis of 

recent air quality data (2011–2013) for 

all locations across the U.S. indicates 10 

monitor locations distributed across two 

NOAA climatic regions that meet the 

current standard and at which 3-year 

W126 index values are above 19 ppmhrs, with the highest values extending 

up to 23 ppm-hrs (Wells, 2015b). 

In support of their view that the EPA’s 

modeling supports the conclusion that 

W126 index values of interest are 

achieved under the current secondary 

standard, some commenters 

additionally state that the W126 values 

in the WREA are overestimated in 

unmonitored rural areas due to the 

much greater prevalence of urban 

monitors across the U.S. The EPA 

mstockstill on DSK4VPTVN1PROD with RULES2

65388 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

195The current evidence indicates that‘‘[t]he 

significance of O3 injury at the leaf and whole plant 

levels depends on how much of the total leaf area 

of the plant has been affected, as well as the plant’s 

age, size, developmental stage, and degree of 

functional redundancy among the existing leaf 

area’’ and ‘‘in some cases, visible foliar symptoms 

have been correlated with decreased vegetative 

growth . . . and with impaired reproductive 

function’’ (U.S. EPA, 2013, p. 9–39). The ISA 

concludes, however, ‘‘it is not presently possible to 

determine, with consistency across species and 

environments, what degree of injury at the leaf level 

has significance to the vigor of the whole plant’’ 

(U.S. EPA, 2013, p. 9–39). 

disagrees with this conclusion. In order 

to estimate O3 concentrations in grid 

cells across a national-scale spatial 

surface, the WREA applied the VNA 

spatial interpolation technique after 

applying the HDDM technique to adjust 

O3 concentrations at monitoring sites 

based on the emissions reductions 

necessary to just meet the current 

standard. In estimating concentrations 

in unmonitored areas, the VNA method 

considers only the ‘‘neighboring’’ 

monitors, using an inverse distance 

squared weighting formula, which 

assigns the greatest influence to the 

nearest neighboring monitor (U.S. EPA, 

2014b, p. 4A–6). By this approach, 

monitors in less-densely monitored 

areas contribute to the concentration 

estimates over much larger areas than 

do monitors in more-densely monitored 

areas. In an urban area, neighboring 

monitors may be quite close to one 

another, such that any one monitor may 

only be influencing concentration 

estimates for a handful of spatial grid 

cells in the immediate vicinity. By 

contrast, monitors in rural areas may 

influence hundreds of grid cells. A 

specific example of this is the monitor 

in Great Basin National Park in eastern 

Nevada. The VNA algorithm assigns 

very high weights to this monitor for all 

of the grid cells covering a 100 km 

radius around it, simply because there 

are no other monitors in that area and 

it is the closest. On the other hand, a 

monitor near downtown Las Vegas may 

only get a high weight for, and thus 

exert influence on the concentration 

estimate in, the one grid cell containing 

it. We agree with the commenter that 

urban monitors may influence the 

spatial surface for some distance away 

from the urban areas, although the 

influence wanes with increasing 

distance from that area and decreasing 

distance to the next closest monitor. As 

we lack data for the intervening 

locations, however, we have no reason 

to conclude that the VNA surface is 

overestimating the W126 index values. 

Further, as was summarized in section 

IV.A.2 above, and in the WREA, the PA 

and the proposal (U.S. EPA, 2014b, 

Table 6–27, section 8.5; U.S. EPA, 

2014c, p. 5–49; 79 FR 75323, December 

17, 2014), the VNA approach results in 

a lowering of the highest W126 index 

values at monitoring sites, which 

contributes to underestimates of the 

highest W126 index values in each 

region. 

In support of their view that the 

current standard is adequate, some 

industry commenters additionally cite 

WREA analyses for the current standard 

scenario, including the W126 index 

estimates in national parks, as showing 

that the current standard provides more 

than adequate protection, with 

alternative scenarios providing only 

marginal and increasingly uncertain 

benefits. As we noted in the proposal 

and section IV.A.2 above, there are an 

array of uncertainties associated with 

the W126 index estimates, in the current 

standard scenario and in the other 

scenarios, which, as they are inputs to 

the vegetation risk analyses, are 

propagated into those analyses (79 FR 

75323; December 17, 2014). As a result, 

consistent with the approach in the 

proposal, the Administrator has not 

based her decision with regard to 

adequacy of the current standard in this 

review on these air quality scenario 

analyses. 

In support of their view that the 

current standard provides adequate 

protection and should not be revised, 

some commenters described their 

concerns with any consideration of 

visible foliar injury in the decision 

regarding the secondary standard. These 

commenters variously stated that visible 

foliar injury cannot be reliably 

evaluated for adversity given lack of 

available information, is not an adverse 

effect on public welfare that must be 

addressed through a secondary 

standard, and is not directly relatable to 

growth suppression (and the EPA’s use 

of RBL captures that effect anyway). 

Additionally, some state that any 

associated ecosystem services effects are 

not quantifiable. In sum, the view of 

these commenters is that it is not 

appropriate for the Administrator to 

place any weight on this O3 effect in 

determining the adequacy of the current 

standard. As an initial matter, the EPA 

agrees with the comment that the 

current evidence does not include an 

approach for relating visible foliar 

injury to growth suppression,195 as 

recognized in section IV.A.1.b above. 

Further, we note that, similar to 

decisions in past O3 reviews, the 

Administrator’s proposed decision in 

this review recognized the 

‘‘complexities and limitations in the 

evidence base regarding characterizing 

air quality conditions with respect to 

the magnitude and extent of risk for 

visible foliar injury’’ and the 

‘‘challenges of associated judgments 

with regard to adversity of such effects 

to public welfare’’ (79 FR 75336; 

December 17, 2014). Contrary to the 

implications of the commenters, 

although the Administrator took into 

consideration the potential for adverse 

effects on public welfare from visible 

foliar injury, she placed weight 

primarily on growth-related effects of 

O3, both in her proposed decision on 

adequacy and with regard to proposed 

judgments on what revisions would be 

appropriate. Although visible foliar 

injury may impact the public welfare 

and accordingly has the potential to be 

adverse to the public welfare (as noted 

in section IV.B.2 of the proposal), the 

Administrator placed less weight on 

visible foliar injury considerations in 

identifying what revisions to the 

standard would be appropriate to 

propose. In considering these effects for 

this purpose, she recognized 

‘‘significant challenges’’ in light of ‘‘the 

variability and the lack of clear 

quantitative relationship with other 

effects on vegetation, as well as the lack 

of established criteria or objectives that 

might inform consideration of potential 

public welfare impacts related to this 

vegetation effect’’ (79 FR 75349; 

December 17, 2014). As summarized in 

section IV.A.1.a above, the evidence 

demonstrates a causal relationship of O3

with visible foliar injury. Accordingly, 

we note that the uncertainty associated 

with visible foliar injury is not with 

regard to whether O3 causes visible 

foliar injury. Rather, the uncertainty is, 

as discussed in sections IV.A.1.b and 

IV.A.3 above, with the lack of 

established, quantitative exposureresponse functions that document 

visible foliar injury severity and 

incidence under varying air quality and 

environmental conditions and 

information to support associated 

judgments on the significance of such 

responses with regard to associated 

public welfare impacts. As with the 

Administrator’s proposed decisions on 

the standard, such considerations also 

informed her final decisions, described 

in sections IV.B.3 and IV.C.3 below. 

In support of their view that the 

current standard should be retained, 

some commenters note the WREA 

finding for the current standard scenario 

of no U.S. counties with RYL estimates 

at or above 5%, the RYL value 

emphasized by CASAC and state that 

policy reasons provide support for not 

focusing on crops in the decision; other 

commenters state that additional studies 

on crops and air quality are needed. As 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65389 

described previously in this section, and 

in section IV.A.2 above, an aspect of 

uncertainties associated with the WREA 

air quality scenarios, including the 

current standard scenario, is 

underestimation of the highest W126 

index values, contributing to 

underestimates in the effects associated 

with the current standard scenario. The 

EPA agrees with commenters that 

additional studies on crops and air 

quality will be useful to future reviews. 

Additionally, however, as noted above, 

the Administrator’s proposed 

conclusion on adequacy of the current 

standard, as well as her final decision 

described in section IV.B.3 below, gives 

less weight to consideration of effects on 

agricultural crops in recognition of the 

complicating role of heavy management 

in that area. 

Lastly, we note that many 

commenters cited the costs of 

compliance as supporting their view 

that the standard should not be revised, 

although as we have described in 

section I.B above, the EPA may not 

consider the costs of compliance in 

determining what standard is requisite 

to protect public welfare from known or 

anticipated adverse effects. 

3. Administrator’s Conclusions on the 

Need for Revision 

Having carefully considered the 

advice from CASAC and public 

comments, as discussed above, the 

Administrator believes that the 

fundamental scientific conclusions on 

the welfare effects of O3 in ambient air 

reached in the ISA and summarized in 

the PA and in section IV.B of the 

proposal remain valid. Additionally, the 

Administrator believes the judgments 

she reached in the proposal (section 

IV.D.3) with regard to consideration of 

the evidence and quantitative 

assessments and advice from CASAC 

remain appropriate. Thus, as described 

below, the Administrator concludes that 

the current secondary standard is not 

requisite to protect public welfare from 

known and anticipated adverse effects 

associated with the presence of O3 in 

the ambient air and that revision is 

needed to provide additional protection. 

In considering the adequacy of the 

current secondary O3 standard, the 

Administrator has carefully considered 

the available evidence, analyses and 

conclusions contained in the ISA, 

including information newly available 

in this review; the information, 

quantitative assessments, considerations 

and conclusions presented in the PA; 

the advice and recommendations from 

CASAC; and public comments. The 

Administrator gives primary 

consideration to the evidence of growth 

effects in well-studied tree species and 

information, presented in the PA and 

represented with a narrower focus in 

section IV.B.2 above, on cumulative 

exposures occurring in Class I areas 

when the current standard is met. This 

information indicates the occurrence of 

exposures associated with Class I areas 

during periods when the current 

standard is met for which associated 

estimates of growth effects, in terms of 

the tree seedling RBL in the median 

species for which E–R functions have 

been established, extend above a 

magnitude considered to be 

‘‘unacceptably high’’ by CASAC. This 

analysis estimated such cumulative 

exposures occurring under the current 

standard for nearly a dozen areas, 

distributed across two NOAA climatic 

regions of the U.S. The Administrator 

gives particular weight to this analysis, 

given its focus in Class I areas. Such an 

emphasis on lands afforded special 

government protections, such as 

national parks and forests, wildlife 

refuges, and wilderness areas, some of 

which are designated Class I areas under 

the CAA, is consistent with such 

emphasis in the 2008 revision of the 

secondary standard (73 FR 16485, 

March 27, 2008). As noted in section 

IV.A above, Congress has set such lands 

aside for specific uses that are intended 

to provide benefits to the public welfare, 

including lands that are to be protected 

so as to conserve the scenic value and 

the natural vegetation and wildlife 

within such areas, and to leave them 

unimpaired for the enjoyment of future 

generations. The Administrator 

additionally recognizes that states, 

tribes and public interest groups also set 

aside areas that are intended to provide 

similar benefits to the public welfare for 

residents on those lands, as well as for 

visitors to those areas. 

As noted in prior reviews, judgments 

regarding effects that are adverse to 

public welfare consider the intended 

use of the ecological receptors, 

resources and ecosystems affected. 

Thus, the Administrator recognizes that 

the median RBL estimate for the studied 

species is a quantitative tool within a 

larger framework of considerations 

pertaining to the public welfare 

significance of O3 effects on the public 

welfare. Such considerations include 

effects that are associated with effects 

on growth and that the ISA has 

determined to be causally or likely 

causally related to O3 in ambient air, yet 

for which there are greater uncertainties 

affecting our estimates of impacts on 

public welfare. These other effects 

include reduced productivity in 

terrestrial ecosystems, reduced carbon 

sequestration in terrestrial ecosystems, 

alteration of terrestrial community 

composition, alteration of below-grown 

biogeochemical cycles, and alteration of 

terrestrial ecosystem water cycles, as 

summarized in section IV.A.1. Thus, in 

her attention to CASAC’s 

characterization of a 6% estimate for 

tree seedling RBL in the median studied 

species as ‘‘unacceptably high’’, the 

Administrator, while mindful of 

uncertainties with regard to the 

magnitude of growth impact that might 

be expected in mature trees, is also 

mindful of related, broader, ecosystemlevel effects for which our tools for 

quantitative estimates are more 

uncertain and those for which the 

policy foundation for consideration of 

public welfare impacts is less well 

established. She finds her consideration 

of tree growth effects consistent with 

CASAC advice regarding consideration 

of O3-related biomass loss as a surrogate 

for the broader array of O3 effects at the 

plant and ecosystem levels. 

The Administrator also recognizes 

that O3-related effects on sensitive 

vegetation can occur in other areas that 

have not been afforded special federal 

protections, including effects on 

vegetation growing in managed city 

parks and residential or commercial 

settings, such as ornamentals used in 

urban/suburban landscaping or 

vegetation grown in land use categories 

that are heavily managed for 

commercial production of commodities 

such as timber. In her consideration of 

the evidence and quantitative 

information of O3 effects on crops, the 

Administrator recognizes the 

complexity of considering adverse O3

impacts to public welfare due to the 

heavy management common for 

achieving optimum yields and market 

factors that influence associated 

services. In so doing, she notes that her 

judgments that place emphasis on the 

protection of forested ecosystems 

inherently also recognize a level of 

protection for crops. Additionally, for 

vegetation used for residential or 

commercial ornamental purposes, the 

Administrator believes that there is not 

adequate information specific to 

vegetation used for those purposes, but 

notes that a secondary standard revised 

to provide protection for sensitive 

natural vegetation and ecosystems 

would likely also provide some degree 

of protection for such vegetation. 

The Administrator also takes note of 

the long-established evidence of 

consistent association of the presence of 

visible foliar injury with O3 exposure 

and the currently available information 

that indicates the occurrence of visible 

foliar injury in sensitive species of 

mstockstill on DSK4VPTVN1PROD with RULES2

65390 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

vegetation during recent air quality in 

public forests across the U.S. She 

additionally notes the PA conclusions 

regarding difficulties in quantitatively 

relating visible foliar injury symptoms 

to vegetation effects such as growth or 

related ecosystem effects. As at the time 

of the last review, the Administrator 

believes that the degree to which such 

effects should be considered to be 

adverse depends on the intended use of 

the vegetation and its significance. The 

Administrator also believes that the 

significance of O3-induced visible foliar 

injury depends on the extent and 

severity of the injury and takes note of 

studies in the evidence base 

documenting increased severity and/or 

prevalence with higher O3 exposures. 

However, the Administrator takes note 

of limitations in the available 

information with regard to judging the 

extent to which the extent and severity 

of visible foliar injury occurrence 

associated with conditions allowed by 

the current standard may be considered 

adverse to public welfare. 

Based on these considerations, and 

taking into consideration the advice and 

recommendations of CASAC, the 

Administrator concludes that the 

protection afforded by the current 

secondary O3 standard is not sufficient 

and that the standard needs to be 

revised to provide additional protection 

from known and anticipated adverse 

effects to public welfare, related to 

effects on sensitive vegetation and 

ecosystems, most particularly those 

occurring in Class I areas. The 

Administrator additionally recognizes 

that states, tribes and public interest 

groups also set aside areas that are 

intended to provide similar benefits to 

the public welfare for residents on those 

lands, as well as for visitors to those 

areas. Given the clear public interest in 

and value of maintaining these areas in 

a condition that does not impair their 

intended use, and the fact that many of 

these areas contain O3-sensitive 

vegetation, the Administrator further 

concludes that it is appropriate to revise 

the secondary standard in part to 

provide increased protection against O3- 

caused impairment to vegetation and 

ecosystems in such areas, which have 

been specially protected to provide 

public welfare benefits. She further 

notes that a revised standard would 

provide increased protection for other 

growth-related effects, including for 

crop yield loss, reduced carbon storage 

and for areas for which it is more 

difficult to determine public welfare 

significance, as recognized in section 

IV.A.3 above, as well other welfare 

effects of O3, such as visible foliar 

injury. 

C. Conclusions on Revision of the 

Secondary Standard 

The elements of the standard— 

indicator, averaging time, form, and 

level—serve to define the standard and 

are considered collectively in evaluating 

the welfare protection afforded by the 

secondary standard. Section IV.C.1 

below summarizes the basis for the 

proposed revision. Significant 

comments received from the public on 

the proposal are discussed in section 

IV.C.2 and the Administrator’s final 

decision on revisions to the secondary 

standard is described in section IV.C.3. 

1. Basis for Proposed Revision 

At the time of proposal, in 

considering what revisions to the 

secondary standard would be 

appropriate, the Administrator 

considered the ISA conclusions 

regarding the weight of the evidence for 

a range of welfare effects associated 

with O3 in ambient air and associated 

areas of uncertainty; quantitative risk 

and exposure analyses in the WREA for 

different adjusted air quality scenarios 

and associated limitations and 

uncertainties; staff evaluations of the 

evidence, exposure/risk information and 

air quality information in the PA; 

additional air quality analyses of 

relationships between air quality 

metrics based on form and averaging 

time of the current standards and a 

cumulative seasonal exposure index; 

CASAC advice; and public comments 

received as of that date in the review. In 

the paragraphs below, we summarize 

the proposal presentation with regard to 

key aspects of the PA considerations, 

advice from the CASAC, air quality 

analyses of different air quality metrics 

and the Administrator’s proposed 

conclusions, drawing from section IV.E 

of the proposal. 

a. Considerations and Conclusions in 

the PA 

As summarized in the proposal, in 

identifying alternative secondary 

standards appropriate to consider in this 

review, the PA focused on standards 

based on a cumulative, seasonal, 

concentration-weighted form consistent 

with the CASAC advice in the current 

and last review. Based on conclusions of 

the ISA, as also summarized in section 

IV.A above, the PA considered a 

cumulative, seasonal, concentrationweighted exposure index to provide the 

most scientifically defensible approach 

for characterizing vegetation response to 

ambient O3 and comparing study 

findings, as well as for defining indices 

for vegetation protection, as 

summarized in the proposal section 

IV.E.2.a. With regard to the appropriate 

index, the PA considered the evidence 

for a number of different such indices, 

as described in the proposal, and noted 

the ISA conclusion that the W126 index 

has some important advantages over 

other similarly weighted indices. The 

PA additionally considered the 

appropriate diurnal and seasonal 

exposure periods in a given year by 

which to define the seasonal W126 

index and based on the evidence in the 

ISA and CASAC advice, as summarized 

in the proposal, decided on the 12-hour 

daylight window (8:00 a.m. to 8:00 p.m.) 

and the 3-consecutive-month period 

providing the maximum W126 index 

value. 

Based on these considerations, the PA 

concluded it to be appropriate to retain 

the current indicator of O3 and to 

consider a secondary standard form that 

is an average of the seasonal W126 

index values (derived as described in 

section IV.A.1.c above) across three 

consecutive years (U.S. EPA, 2014c, 

section 6.6). In so doing, the PA 

recognized that there is limited 

information to discern differences in the 

level of protection afforded for 

cumulative growth-related effects by 

potential alternative W126-based 

standards of a single-year form as 

compared to a 3-year form (U.S. EPA, 

2014c, pp. 6–30). The PA concluded a 

3-year form to be appropriate for a 

standard intended to provide the 

desired level of protection from longerterm effects, including those associated 

with potential compounding, and that 

such a form might be concluded to 

contribute to greater stability in air 

quality management programs, and 

thus, greater effectiveness in achieving 

the desired level of public welfare 

protection than might result from a 

single-year form. (U.S. EPA, 2014c, 

section 6.6). 

As summarized in the proposal, the 

PA noted that, due to the variability in 

the importance of the associated 

ecosystem services provided by 

different species at different exposures 

and in different locations, as well as 

differences in associated uncertainties 

and limitations, it is essential to 

consider the species present and their 

public welfare significance, together 

with the magnitude of the ambient 

concentrations in drawing conclusions 

regarding the significance or magnitude 

of public welfare impacts. Therefore, in 

development of the PA conclusions, 

staff took note of the complexity of 

judgments to be made by the 

Administrator regarding the adversity of 

known and anticipated effects to the 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65391 

196The CASAC provided several comments 

related to 2% RBL for tree seedlings both with 

regard to its use in summarizing WREA results and 

with regard to consideration of the potential 

significance of vegetation effects, as summarized in 

sections IV.D.2 and IV.E.3 of the proposal. 

public welfare and recognized that the 

Administrator’s ultimate judgments on 

the secondary standard will most 

appropriately reflect an interpretation of 

the available scientific evidence and 

exposure/risk information that neither 

overstates nor understates the strengths 

and limitations of that evidence and 

information. In considering an 

appropriate range of levels to consider 

for an alternative standard, the PA 

primarily considered tree growth, crop 

yield loss, and visible foliar injury, as 

well as impacts on the associated 

ecosystem services, while noting key 

uncertainties and limitations. 

In specifically evaluating exposure 

levels, in terms of the W126 index, as 

to their appropriateness for 

consideration in this review with regard 

to providing the desired level of 

vegetation protection for a revised 

secondary standard, the PA focused 

particularly on RBL estimates for the 

median across the 11 tree species for 

which robust E–R functions are 

available. Table 4 below presents these 

estimates (U.S. EPA, 2014c, Appendix 

5C, Table 5C–3; also summarized in 

Table 8 of the proposal). In so doing and 

recognizing the longstanding, strong 

evidence base supporting these 

relationships, the PA also noted 

uncertainties regarding inter-study 

variability for some species, as well as 

with regard to the extent to which tree 

seedling E–R functions can be used to 

represent mature trees. As summarized 

in the proposal, the PA conclusions on 

a range of W126 levels appropriate to 

consider are based on specific advice 

from CASAC with regard to median tree 

seedling RBL estimates that might be 

considered unacceptably high (6%), as 

well as its judgment on a RBL 

benchmark (2%) for identification of the 

lower end of a W126 index value range 

for consideration that might give more 

emphasis to the more sensitive tree 

seedlings (Frey, 2014c, p. 14).196

TABLE 4—TREE SEEDLING BIOMASS LOSS AND CROP YIELD LOSS ESTIMATED FOR O3 EXPOSURE OVER A SEASON

W126 index 

value for exposure period 

Tree seedling biomass loss A Crop yield loss B

Median value Individual species Median value Individual species 

23 ppm-hrs ........ Median species w. 7.6% loss ≤ 2% loss: 3/11 species ....

≤ 5% loss: 4/11 species ....

≤10% loss: 8/11 species ...

≤15% loss: 10/11 species

>40% loss: 1/11 species ...

Median species w. 8.8% loss ≤ 5% loss: 4/10 species 

>5,<10% loss: 1/10 species 

>10,<20% loss: 4/10 species 

>20: 1/10 species 

22 ppm-hrs ........ Median species w. 7.2% loss ≤ 2% loss: 3/11 species ....

≤ 5% loss: 4/11 species ....

≤10% loss: 7/11 species ...

≤15% loss: 10/11 species

>40% loss: 1/11 species ...

Median species w. 8.2% loss ≤ 5% loss: 4/10 species 

>5,<10% loss: 1/10 species 

>10,<20% loss: 4/10 species 

>20: 1/10 species 

21 ppm-hrs ........ Median species w. 6.8% loss ≤ 2% loss: 3/11 species ....

≤ 5% loss: 4/11 species ....

≤10% loss: 7/11 species ...

≤15% loss: 10/11 species

>40% loss: 1/11 species ...

Median species w. 7.7% loss ≤ 5% loss: 4/10 species 

>5,<10% loss: 3/10 species 

>10,<20% loss: 3/10 species 

20 ppm-hrs ........ Median species w. 6.4% loss ≤ 2% loss: 3/11 species ....

≤ 5% loss: 5/11 species ....

≤10% loss: 7/11 species ...

≤15% loss: 10/11 species

>40% loss: 1/11 species ...

Median species w. 7.1% loss ≤ 5% loss: 5/10 species 

>5,<10% loss: 3/10 species 

>10,<20% loss: 2/10 species 

19 ppm-hrs ........ Median species w. 6.0% loss ≤ 2% loss: 3/11 species ....

≤5% loss: 5/11 species .....

≤10% loss: 7/11 species ...

≤15% loss: 10/11 species

>30% loss: 1/11 species ...

Median species w. 6.4% loss ≤ 5% loss: 5/10 species 

>5, <10% loss: 3/10 species 

>10,<20% loss: 2/10 species 

18 ppm-hrs ........ Median species w. 5.7% loss ≤ 2% loss: 5/11 species ....

≤ 5% loss: 5/11 species ....

≤10% loss: 7/11 species ...

≤15% loss: 10/11 species

>30% loss: 1/11 species ...

Median species w. 5.7% loss ≤ 5% loss: 5/10 species 

>5,<10% loss: 3/10 species 

>10,<20% loss: 2/10 species 

17 ppm-hrs ........ Median species w. 5.3% loss ≤ 2% loss: 5/11 species ....

≤5% loss: 5/11 species .....

≤10% loss: 9/11 species ...

≤15% loss: 10/11 species

>30% loss: 1/11 species ...

Median species w. 5.1% loss ≤ 5% loss: 5/10 species 

>5, <10% loss: 3/10 species 

>10,<20% loss: 2/10 species 

16 ppm-hrs ........ Median species w. 4.9% loss ≤ 2% loss: 5/11 species ....

≤ 5% loss: 6/11 species ....

≤10% loss: 10/11 species

>30% loss: 1/11 species ...

Median species w. ≤5.0% loss ≤ 5% loss: 5/10 species 

>5,<10% loss: 4/10 species 

>10,<20% loss: 1/10 species 

15 ppm-hrs ........ Median species w. 4.5% loss ≤ 2% loss: 5/11 species ....

≤5% loss: 6/11 species .....

≤10% loss: 10/11 species

>30% loss: 1/11 species ...

Median species w. ≤5.0% loss ≤ 5% loss: 6/10 species 

>5, <10% loss: 4/10 species 

14 ppm-hrs ........ Median species w. 4.2% loss ≤ 2% loss: 5/11 species ....

≤ 5% loss: 6/11 species ....

≤10% loss: 10/11 species

>30% loss: 1/11 species ...

Median species w. ≤5.0% loss ≤ 5% loss: 6/10 species 

>5,<10% loss: 4/10 species 

13 ppm-hrs ........ Median species w. 3.8% loss ≤ 2% loss: 5/11 species ....

<5% loss: 7/11 species .....

<10% loss: 10/11 species

>20% loss: 1/11 species ...

Median species w. ≤5.0% loss ≤ 5% loss: 6/10 species 

>5, <10% loss: 4/10 species 

mstockstill on DSK4VPTVN1PROD with RULES2

65392 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

TABLE 4—TREE SEEDLING BIOMASS LOSS AND CROP YIELD LOSS ESTIMATED FOR O3 EXPOSURE OVER A SEASON— 

Continued 

W126 index 

value for exposure period 

Tree seedling biomass loss A Crop yield loss B

Median value Individual species Median value Individual species 

12 ppm-hrs ........ Median species w. 3.5% loss ≤ 2% loss: 5/11 species ....

≤ 5% loss: 8/11 species ....

≤10% loss: 10/11 species

>20% loss: 1/11 species ...

Median species w. ≤5.0% loss ≤ 5% loss: 8/10 species 

>5,<10% loss: 2/10 species 

11 ppm-hrs ........ Median species w. 3.1% loss ≤ 2% loss: 5/11 species ....

≤5% loss: 8/11 species .....

≤10% loss: 10/11 species

>20% loss: 1/11 species ...

Median species w. ≤5.0% loss ≤ 5% loss: 9/10 species 

>5, <10% loss: 1/10 species 

10 ppm-hrs ........ Median species w. 2.8% loss ≤ 2% loss: 5/11 species ....

≤ 5% loss: 9/11 species ....

<10% loss: 10/11 species

>20% loss: 1/11 species ...

Median species w. ≤5.0% loss ≤ 5% loss: 9/10 species 

>5,<10% loss: 1/10 species 

9 ppm-hrs .......... Median species w. 2.4% loss ≤ 2% loss: 5/11 species ....

≤ 5% loss: 10/11 species ..

>20% loss: 1/11 species ...

Median species w. ≤5.0% loss ≤ 5% loss: all species 

8 ppm-hrs .......... Median species w. 2.0% loss ≤ 2% loss: 5/11 species ....

≤ 5% loss: 10/11 species ..

>15% loss: 1/11 species ...

Median species w. ≤5.0% loss ≤ 5% loss: all species 

7 ppm-hrs .......... Median species w. <2.0% loss ≤ 2% loss: 7/11 species ....

≤5% loss: 10/11 species ...

>15% loss: 1/11 species ...

Median species w. ≤5.0% loss ≤ 5% loss: all species 

A Estimates here are based on the E–R functions for 11 species described in the WREA, section 6.2 and discussed in the PA, section 5.2.1. 

The cottonwood was excluded to address CASAC comments (Frey, 2014c; U.S. EPA, 2014b, U.S. EPA, 2014c, Appendix 6F). The median is the 

median of the 11 composite E–R functions (U.S. EPA, 2014c, Appendix 5C). B Estimates here are based on the 10 E–R functions for crops described in the WREA, section 6.2 and discussed in the PA, section 5.3.1. The 

median is the median of the 10 composite E–R functions (U.S. EPA, 2014b; U.S. EPA, 2014c, Appendix 5C). 

With regard to secondary standard 

revisions appropriate to consider in this 

review, as summarized in the proposal, 

the PA concluded it to be appropriate to 

consider a W126-based secondary 

standard with index values within the 

range of 7 to 17 ppm-hrs and a form 

averaged over 3 years (U.S. EPA, 2014c, 

section 6.7). The PA additionally 

recognized the role of policy judgments 

required of the Administrator with 

regard to the public welfare significance 

of identified effects, the appropriate 

weight to assign the range of 

uncertainties inherent in the evidence 

and analyses, and ultimately, in 

identifying the requisite protection for 

the secondary O3 standard. 

The PA additionally recognized that 

to the extent the Administrator finds it 

useful to consider the public welfare 

protection that might be afforded by 

revising the level of the current 

standard, this is appropriately judged by 

evaluating the impact of associated O3

exposures in terms of the cumulative 

seasonal W126-based index, an 

exposure metric considered appropriate 

for evaluating impacts on vegetation 

(U.S. EPA, 2014c, section 6.7). 

Accordingly, the PA included several 

air quality data analyses that might 

inform such consideration (U.S. EPA, 

2014c, section 6.4). Additional air 

quality analyses were performed 

subsequent to the PA, described in the 

proposal and are summarized below. 

b. CASAC Advice 

Advice received from the CASAC 

during the current review, similar to 

that in the last review, recommended 

retaining O3 as the indicator, while also 

recommending consideration of a 

secondary standard with a revised form 

and averaging time based on the W126 

index (Frey, 2014c, p. iii). The CASAC 

concurred with the 12-hour period (8 

a.m. to 8 p.m.) and 3-month summation 

period resulting in the maximum W126 

index value, as described in the PA, 

while recommending a somewhat 

narrower range of levels from 7 ppm-hrs 

to 15 ppm-hrs. While the CASAC 

recommended a W126 index limited to 

a single year, in contrast with the PA’s 

conclusion that it was appropriate to 

consider the W126 index averaged 

across three years, it also noted that the 

Administrator may prefer, as a policy 

matter, to base the secondary standard 

on a 3-year averaging period. In such a 

case, the CASAC recommended revising 

downward the level for such a metric to 

avoid a seasonal W126 index value 

above a level in their recommended 

range in any given year of the 3-year 

period, indicating an upper end of 13 

ppm-hrs as an example for such a 3-year 

average W126 index range (Frey, 2014c, 

p. iii and iv). 

c. Air Quality Analyses 

The proposal additionally 

summarized several analyses of air 

quality that considered relationships 

between metrics based on a 3-year W126 

index and based on the form and 

averaging time of the current standard, 

the ‘‘fourth-high’’ metric (U.S. EPA, 

2014c, Chapter 2, Appendix 2B and 

section 6.4; Wells, 2014a), as well as 

describing the uncertainties and 

limitations associated with these 

analyses. The proposal concluded that 

these analyses suggest that, depending 

on the level, a standard of the current 

averaging time and form can be 

expected to control cumulative seasonal 

O3 exposures to such that they may 

meet specific 3-year average W126 

index values. The fourth-high and W126 

metrics, and changes in the two metrics 

over the past decade, were found to be 

highly correlated (U.S. EPA, 2014c, 

section 6.4 and Appendix 2B; Wells, 

2014a). From these analyses, it was 

concluded that future control programs 

designed to help meet a standard based 

on the fourth-high metric are also 

expected to result in reductions in 

values of the W126 metric (Wells, 

2014a). Further, the second analysis also 

found that the Southwest and West 

NOAA climatic regions, which showed 

the greatest potential for sites to 

measure elevated cumulative, seasonal 

O3 exposures without the occurrence of 

elevated daily maximum 8-hour average 

O3 concentrations, exhibited the greatest 

reduction in W126 metric value per unit 

reduction in fourth-high metric (Wells, 

2014a, Figures 5b and 12 and Table 6). 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65393 

197The CASAC made this comment while 

focusing on Table 6–1 in the second draft PA and 

the entry for 17 ppm-hrs (Frey, 2014c, p. 14). That 

table was revised for inclusion in the final PA in 

consideration of CASAC comments on the E–R 

function for eastern cottonwood, and after that 

revision, the median RBL estimate for 17 ppm-hrs 

in the final table (see Table 4 above) is below the 

value of 6% that CASAC described in this way. 

Analyses of the most recent periods 

studied in the two analyses (2009–2011 

and 2011–2013) had similar findings 

regarding the highest W126 metric 

values occurring at monitoring sites that 

meet alternative levels of the fourthhigh metric (U.S. EPA, 2014c, section 

6.4; Wells, 2014a). In both analyses, the 

highest W126 metric values were in the 

Southwest and West NOAA climatic 

regions. In both analyses, no monitoring 

sites for which the fourth-high metric 

was at or below 70 ppb had a W126 

metric value above 17 ppm-hrs (U.S. 

EPA, 2014c, Figure 2B–3b; Wells, 2014a, 

Table 4). All U.S. regions were 

represented in these subsets. In the 

2011–2013 subset of sites for which the 

fourth-high metric was at or below a 

potential alternative primary standard 

level of 65 ppb, no monitoring sites had 

W126 metric values above 11 ppm-hrs 

(Wells, 2014a, Table 4). 

d. Administrator’s Proposed 

Conclusions 

At the time of proposal, the 

Administrator concluded it to be 

appropriate to continue to use O3 as the 

indicator for a secondary standard that 

is intended to address effects associated 

with exposure to O3 alone and in 

combination with related 

photochemical oxidants. While the 

complex atmospheric chemistry in 

which O3 plays a key role has been 

highlighted in this review, no 

alternatives to O3 have been advanced 

as being a more appropriate surrogate 

for ambient photochemical oxidants and 

their effects on vegetation. The CASAC 

agreed that O3 should be retained as the 

indicator for the standard (Frey, 2014c, 

p. iii). In proposing to retain O3 as the 

indicator, the Administrator recognized 

that measures leading to reductions in 

ecosystem exposures to O3 would also 

be expected to reduce exposures to 

other photochemical oxidants. 

The Administrator proposed to retain 

the current averaging time and form and 

to revise the level of the current 

secondary standard to a level within the 

range of 0.065 to 0.070 ppm. She based 

this proposal on her provisional 

conclusions regarding the level of 

cumulative seasonal O3 exposures that 

would provide the requisite protection 

against known or anticipated adverse 

effects to the public welfare and on a 

policy option that would provide this 

level of protection. With regard to the 

former, the Administrator concluded 

that in judging the extent of public 

welfare protection that might be 

afforded by a revised standard and 

whether it meets the appropriate level of 

protection, it is appropriate to use a 

cumulative, seasonal concentrationweighted exposure metric. For this 

purpose, the Administrator concluded it 

to be appropriate to use the W126 index 

value, averaged across three years, with 

each year’s value identified as that for 

the 3-month period yielding the highest 

seasonal value and with daily O3

exposures within a 3-month period 

cumulated for the 12-hour period from 

8:00 a.m. to 8:00 p.m. 

To identify the range of cumulative 

seasonal exposures, in terms of the 

W126 index, expected to be associated 

with the appropriate degree of public 

welfare protection, the Administrator 

gave primary consideration to growthrelated impacts, using tree seedling RBL 

estimates for a range of W126 exposure 

index values and CASAC advice 

regarding such estimates. Additionally 

taking into account judgments on 

important uncertainties and limitations 

inherent in the current available 

scientific evidence and quantitative 

assessments, and judgments regarding 

the extent to which different RBL 

estimates might be considered 

indicative of effects adverse to public 

welfare, the Administrator proposed 

that ambient O3 concentrations resulting 

in cumulative seasonal O3 exposures of 

a level within the range from 13 ppmhrs to 17 ppm-hrs, in terms of a W126 

index averaged across three consecutive 

years, would provide the requisite 

protection against known or anticipated 

adverse effects to the public welfare. In 

identifying policy options for a revised 

secondary standard that would control 

exposures to such an extent, the 

Administrator considered the results of 

air quality analyses that examined the 

responsiveness of cumulative exposures 

(in terms of the W126 index) to O3

reductions in response to the current 

and prior standard for which the form 

and averaging time are summarized as a 

fourth-high metric, and also examined 

the extent to which cumulative 

exposures (in terms of the W126 index) 

may be limited by alternative levels of 

a metric based on the current standard 

averaging time and form. Based on the 

results of these analyses, she proposed 

that revision of the level of the current 

secondary standard to within the range 

of 0.065 to 0.070 ppm would be 

expected to provide the requisite public 

welfare protection, depending on final 

judgments concerning such requisite 

protection. 

2. Comments on Proposed Revision 

Significant comments from the public 

regarding revisions to the secondary 

standard are addressed in the 

subsections below. We first discuss 

comments related to our consideration 

of growth-related effects and visible 

foliar injury in identifying appropriate 

revisions to the standard (sections 

IV.C.2.a and IV.C.2.b). Next, we address 

comments related to the use of the 

W126 metric in evaluating vegetation 

effects and public welfare protection 

and comments related to the form and 

averaging time for the revised standard 

(sections IV.C.2.c and IV.C.2.d). 

Comments on revisions to the level of 

the standard are described in section 

IV.C.2.e, and those related to the way in 

which today’s rulemaking addresses the 

2013 court remand are addressed in 

section IV.C.2.f. Other significant 

comments related to consideration of a 

revised secondary standard, and that are 

based on relevant factors, are addressed 

in the Response to Comments 

document. 

a. Consideration of Growth-Related 

Effects 

In considering public comments 

received on the consideration of growthrelated effects of O3 in the context of the 

proposed decision on a revised 

secondary standard, we first note related 

advice and comments from the CASAC 

provided during development of the PA, 

stating, as summarized in section 

IV.B.1.b above, that ‘‘relative biomass 

loss for tree species, crop yield loss, and 

visible foliar injury are appropriate 

surrogates for a wide range of damage 

that is adverse to public welfare’’ (Frey, 

2014c, p. 10). Additionally, in the 

context of different standard levels they 

considered appropriate for the EPA to 

consider, CASAC stated that it is 

appropriate to ‘‘include[] levels that aim 

for not greater than 2% RBL for the 

median tree species’’ and that a median 

tree species RBL of 6% is ‘‘unacceptably 

high’’ (Frey, 2014c, p. 14).197 With 

respect to crop yield loss, CASAC points 

to a benchmark of 5%, stating that a 

crop RYL for median species over 5% is 

‘‘unacceptably high’’ (Frey, 2014c, p. 

13). 

In addition, regarding consideration 

of RBL benchmarks for tree seedlings, 

the CASAC stated that ‘‘[a] 2% biomass 

loss is an appropriate scientifically 

based value to consider as a benchmark 

of adverse impact for long-lived 

perennial species such as trees, because 

effects are cumulative over multiple 

mstockstill on DSK4VPTVN1PROD with RULES2

65394 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

198The CASAC provided several comments 

related to 2% RBL for tree seedlings both with 

regard to its use in summarizing WREA results and 

with regard to consideration of the potential 

significance of vegetation effects, as summarized in 

sections IV.D.2 and IV.E.3 of the proposal. 

199The CASAC made this comment while 

focusing on Table 6–1 in the second draft PA, 

which included odd-numbered W126 index values 

and in which the median RBL values were based 

on 12 species. That table was revised for inclusion 

in the final PA in consideration of CASAC 

comments on the E-R function for eastern 

cottonwood, such that the median RBL species 

estimate for both 7 ppm-hrs and 8 ppm-hrs are less 

than or equal to 2.0% in the final table (see Table 

4 above and Table 5C–3 of the final PA). 

years’’ (Frey, 2014c, p. 14).198 With 

regard to this benchmark, the CASAC 

also commented that ‘‘it is appropriate 

to identify a range of levels of 

alternative W126-based standards that 

includes levels that aim for not greater 

than 2% RBL for the median tree 

species’’ in the PA (Frey, 2014c, p. 14). 

The CASAC noted that the ‘‘level of 7 

ppm-hrs is the only level analyzed for 

which the relative biomass loss for the 

median tree species is less than or equal 

to 2 percent,’’ indicating that 7 ppm was 

appropriate as a lower bound for the 

recommended range (Frey, 2014c, p. 

14).199

With regard to consideration of effects 

on crops, in addition to their comments 

regarding a median species RYL over 

5% yield loss, noted above (Frey, 2014c, 

p. 13), the CASAC further noted that 

‘‘[c]rop loss appears to be less sensitive 

than these other indicators, largely 

because of the CASAC judgment that a 

5% yield loss represents an adverse 

impact, and in part due to more 

opportunities to alter management of 

annual crops’’ (Frey, 2014c, p. 14). 

Comments from the public with 

regard to how the EPA considered 

growth-related effects in the proposed 

decision on a revised secondary 

standard varied. Generally, those 

commenters who recommended against 

revision of the standard expressed the 

view that RBL estimates based on the 

established E–R functions for the 11 

studied species, and their pertinence to 

mature trees, were too uncertain to serve 

as a basis for judgments regarding 

public welfare protection afforded by 

the secondary standard. The EPA 

generally disagrees with this view, as 

discussed in section IV.B.2 above, and 

addressed in more detail in the 

Response to Comments document. 

Some commenters also took note of 

the unclear basis for CASAC’s 2% 

benchmark, stating that the CASAC 

advice on this point is ‘‘not wholly 

scientific,’’ given that it referenced the 

1996 workshop, which provided little 

specificity as to scientific basis for such 

a benchmark; based on this, the 

commenters described this CASAC 

advice as a policy judgment and 

described the important role of the 

EPA’s judgment in such instances. As 

noted in section IV.E.3 of the proposal, 

we generally agree with these 

commenters regarding the unclear 

scientific basis for the 2% value. 

Consistent with this advice from 

CASAC, however, the range of levels for 

a revised secondary standard that the 

PA concluded was appropriate for the 

Administrator to consider did include a 

level for which the estimated median 

RBL across the 11 studied tree species 

would be 2%, as well as a level for 

which the median RBL would be below 

2% (U.S. EPA, 2014c, section 6.7 and 

Tables 6–1 and 5C–3), and, as described 

in the proposal, the Administrator 

considered the conclusions of the PA in 

reaching her proposed decision that it 

was appropriate to consider a range for 

the revised secondary standard that did 

not focus on this benchmark. The 

Administrator has further considered 

and explained any differences from 

CASAC’s recommendations on this 

point in her final decision, as described 

in section IV.C.3 below. 

Some of the state and local 

environmental agencies and 

organizations and environmental groups 

that supported the EPA’s proposed 

decision to revise the secondary 

standard additionally indicated their 

view that the EPA should give more 

weight to growth-related effects by 

setting the standard at a level for which 

the estimated RBL would be at or below 

2% in the median studied species. In 

support of this recommendation, the 

commenters cited the CASAC advice 

and stated that the EPA’s rationale 

deviates from that advice with regard to 

consideration of RBL. In so doing, the 

commenters implied incorrectly that the 

EPA’s proposal did not put the most 

weight on the median RBL. In fact, in 

considering RBL as a metric for growth 

effects, the Administrator’s proposed 

conclusions focused solely on the 

median RBL estimates, indicating that 

appreciable weight was given to growthrelated effects and on the median RBL. 

Additionally, the commenters implied 

that the EPA misconstrued the CASAC 

comment on 6% RBL to indicate that it 

was acceptable. Yet, the proposal notes 

CASAC’s view that a 6% RBL is 

‘‘unacceptably high’’ nine times, and, in 

section IV.B.3 above, the Administrator 

takes note of this view in reaching the 

decision that the current standard 

should be revised. The EPA considers 

this statement from CASAC, provided in 

the context of considering effects related 

to different W126 index values, to be of 

a different nature than CASAC advice 

discussed above that options for the 

EPA consideration ‘‘include’’ a level 

that aims for median RBL at or below 

2%. 

The comments that state that the 

standard should control cumulative 

exposures to levels for which the 

estimated median species RBL is at or 

below 2% provided little rationale 

beyond citing to CASAC advice. We 

note, however, that the CASAC did not 

specify that the revised secondary 

standard be set to limit cumulative 

exposures to that extent. Nor, in 

identifying a range of alternatives for the 

EPA to consider, did CASAC 

recommend that the EPA consider only 

W126 index levels associated with 

median RBL estimates at or below 2%. 

Rather, the CASAC stated that ‘‘it is 

appropriate to identify a range of levels 

of alternative W126-based standards 

that includes {emphasis added} levels 

that aim for not greater than 2% RBL for 

the median tree species’’ (Frey, 2014c, 

p. 14) and seven of the nine levels in the 

CASAC-recommended range of W126 

index levels were associated with higher 

RBL estimates (as shown in Table 4 

above). 

In citing to CASAC advice, 

commenters quoted the CASAC 

characterization of a 2% RBL as ‘‘an 

appropriate scientifically based value to 

consider as a benchmark of adverse 

impact for long-lived perennial species 

such as trees, because effects are 

cumulative over multiple years’’ (Frey, 

2014, p. 14). Presumably to indicate 

reasoning for this statement, the 

subsequent sentence in the same 

CASAC letter referenced findings for 

biomass loss in aspen exposed to 

elevated O3 over seven years, citing 

Wittig et al., 2009. As noted in the 

proposal, however, the way in which 

these findings would provide a basis for 

CASAC’s view with regard to 2% is 

unclear, as the original publication that 

is the source for the 7-year biomass loss 

value (King, et al., 2005) and which is 

cited in Wittig et al. (2009) indicates 

yearly RBL values during this 7-year 

exposure that are each well above 2%, 

and, in fact, are all above 20% (King, et 

al., 2005). In the same paragraph, the 

CASAC letter additionally referenced 

the report of the 1996 workshop 

sponsored by the Southern Oxidants 

Study group (Heck and Cowling, 1997, 

noted in section IV.A.3 above). The 

workshop report identified 1–2% per 

year growth reduction (based on a stated 

interest in avoiding 2% cumulative 

effects) as an appropriate endpoint for 

consideration of growth effects in trees, 

although an explicit rationale for the 

identified percentages is not provided 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65395 

200The report of the 1996 workshop provides no 

more explicit rationale for the percentages 

identified or specification with regard to number or 

proportion of species for which such percentages 

should be met (Heck and Cowling, 1997). 

(Frey, 2014c, p. 14).200 Like the 1996 

workshop, the CASAC describes 2% 

RBL as providing the basis for 

consideration of 7 ppm-hrs, the lower 

end of their recommended W126 range 

(Frey, 2014c, p. 14). As a result, the 

specific scientific basis for judging a 

value of 2% RBL in the median studied 

species as an appropriate benchmark of 

adverse impact for trees and other longlived perennials is not clear, which, as 

described in the proposal, contributed 

to the Administrator noting the greater 

uncertainty regarding the extent to 

which estimates of benefits in terms of 

ecosystem services and reduced effects 

on vegetation at O3 exposures below her 

identified range of 13 to 17 ppm-hrs 

might be judged significant to the public 

welfare. 

Some commenters recommended 

revision of the standard to 7 ppm-hrs as 

a W126 form stating that such a change 

is needed to protect against climate 

change. In so doing, one commenter 

expressed the view that the relatively 

lesser weight the EPA placed on the 

WREA estimates of carbon storage (in 

terms of CO2) in consideration of a 

proposed revision to the secondary 

standard is inconsistent with the 

emphasis that the EPA placed on CO2

emissions reductions estimated for the 

proposed Clean Power Plan (79 FR 

34830, 34931–33). As support for this 

view of inconsistency, the commenter 

compared the WREA 30-year estimate of 

the amount of CO2 removed from the air 

and stored in vegetation with estimated 

reductions in CO2 emissions from power 

plants over a 4-year period. We note, 

however, some key distinctions between 

the two types of estimates which 

appropriately lead to different levels of 

emphasis by the EPA in the two actions. 

First, we note that the lengths of time 

pertaining to the two estimates that the 

commenter states to be ‘‘roughly equal’’ 

(e.g., ALA et al., p. 211) differ by more 

than a factor of seven (4 years compared 

to 30). Second, the CPP estimates are for 

reductions in CO2 produced and emitted 

from power plants, while the WREA 

estimates are for amounts of CO2

removed from the air and stored in 

vegetation as a result of plant 

photosynthesis occurring across the U.S. 

This leads to two important differences. 

The first is whether a ton of additional 

carbon uptake by plants is equal to a ton 

of reduced emissions from fossil fuels. 

This is still an active area of discussion 

due in part to the potentially transient 

nature of the carbon storage in 

vegetation. The second is that there are 

much larger uncertainties involved in 

attempting to quantify the additional 

carbon uptake by plants which requires 

complex modeling of biological and 

ecological processes and their 

associated sources of uncertainty. 

Therefore, as summarized in section 

IV.C.3 below, the Administrator is 

judging, as at the time of proposal, that 

the quantitative uncertainties are too 

great to support identification of a 

revised standard based specifically on 

the WREA quantitative estimates of 

carbon storage benefits to climate. In so 

doing, she notes that a revised standard, 

established primarily based on other 

effects for which our quantitative 

estimates are less uncertain, can be 

expected to also provide increased 

protection in terms of carbon storage. 

b. Consideration of Visible Foliar Injury 

In considering public comments 

received on the EPA’s consideration of 

visible foliar injury in its decision on a 

revised secondary standard, the EPA 

first notes related advice and comments 

from the CASAC received during 

development of the PA. The CASAC 

stated that ‘‘[w]ith respect to the 

secondary standard, the CASAC concurs 

with the EPA’s identification of adverse 

welfare effects related to . . . damage to 

resource use from foliar injury’’ (Frey, 

2014, p. iii). In its comments on levels 

of a W126-based standard, the CASAC, 

seemingly in reference to the WREA 

visible foliar injury analyses, 

additionally stated that ‘‘[a] level below 

10 ppm-hrs is required to reduce foliar 

injury’’ (Frey, 2014, pp. iii and 15), with 

‘‘W126 values below 10 ppm-hr 

required to reduce the number of sites 

showing visible foliar injury’’ (Frey, 

2014, p. 14). 

Public comments were generally split 

between two views, either that visible 

foliar injury was not appropriate to 

consider in decisions regarding the 

standard, based on variously identified 

reasons, or that it should be considered 

and it would lead the EPA to focus on 

a W126 value below approximately 10 

ppm-hrs. Comments of the former type 

are discussed in section IV.B.2 above, 

with, in some cases, additional detail in 

the Response to Comments document. 

Commenters expressing the latter view 

variously cite CASAC advice and figures 

from the WREA cumulative analysis of 

USFS biosite data with WREA W126 

index value estimates. The EPA 

disagrees that only a reduction in 

cumulative exposures to W126 index 

values below 10 ppm-hrs will affect the 

occurrence or extent of visible foliar 

injury. In so doing, we note that the 

extensive evidence, which is 

summarized in the ISA (including 

studies of the USFS biomonitoring 

program), analyses in the 2007 Staff 

Paper and also observations based on 

the WREA dataset do not support this 

conclusion. 

The evidence regarding visible foliar 

injury as an indicator of O3 exposure is 

well established and generally 

documents a greater extent and severity 

of visible foliar injury with higher O3

exposures and a modifying role of soil 

moisture conditions (U.S. EPA, 2013, 

section 9.4.2). As stated in the ISA, 

‘‘[v]isible foliar injury resulting from 

exposure to O3 has been well 

characterized and documented over 

several decades of research on many 

tree, shrub, herbaceous and crop 

species’’ and ‘‘[o]zone-induced visible 

foliar injury symptoms on certain 

bioindicator plant species are 

considered diagnostic as they have been 

verified experimentally’’ (U.S. EPA, 

2013, p. 9–41). Further, a recent study 

highlighted in the ISA, which analyzed 

trends in the incidence and severity of 

foliar injury, reported a declining trend 

in the incidence of foliar injury as peak 

O3 concentrations declined (U.S. EPA, 

2013, p. 9–40; Smith, 2012). Another 

study available in this review that 

focused on O3-induced visible foliar 

injury in forests of west coast states 

observed that both percentage of biosites 

with injury and average biosite index 

were higher for sites with average 

cumulative O3 concentrations above 25 

ppm-hrs in terms of SUM06 (may 

correspond to W126 of approximately 

21 ppm-hrs [U.S. EPA, 2007, p. 8–26, 

Appendix 7B]) as compared to groups of 

sites with lower average cumulative 

exposure concentrations, with much 

less clear differences between the two 

lower exposure groups (Campbell et al., 

2007, Figures 27 and 28 and p. 30). A 

similar finding was reported in the 2007 

Staff Paper which reported on an 

analysis that showed a smaller 

percentage of injured sites among the 

group of sites with O3 exposures below 

a SUM06 metric of 15 ppm-hrs or a 

fourth-high metric of 74 ppb as 

compared to larger groups that also 

included sites with SUM06 values up to 

25 ppm-hrs or fourth-high metric up to 

84 ppb, respectively (U.S. EPA 2007, pp. 

7–63 to 7–64). 

With regard to the comments 

referencing the WREA cumulative 

analysis of USFS FHM/FIA biosite data 

or related CASAC comments, we note 

some clarification of this analysis. This 

analysis does not show, as implied by 

the comments, that at W126 index 

values above 10 ppm-hrs, there is little 

change with increasing W126 index in 

mstockstill on DSK4VPTVN1PROD with RULES2

65396 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

201We additionally note that the median species 

RBL estimate for 17 ppm-hrs in the final PA is 

nearly identical to the estimate for 15 ppm-hrs (the 

value corresponding to the upper end of the 

CASAC-identified range) that was in the second 

draft PA (5.2%) which was the subject of the 

CASAC review (U.S. EPA, 2014c, Table 6–1; U.S. 

EPA, 2014d, Table 6–1). 

the proportion of records with any 

visible foliar injury (biosite index above 

0). As the analysis is a cumulative 

analysis, each point graphed in the 

analysis includes the records for the 

same and lower W126 index values, so 

the analysis does not compare results 

for groups of records with differing, 

non-overlapping W126 index values. 

Rather, the points represent groups with 

records (and W126 index values) in 

common and the number of records in 

the groups is greater for higher W126 

index values (U.S. EPA, 2014b, section 

7.2). Additionally, we note that the 

pattern observed in the cumulative 

analysis is substantially influenced by 

the large number of records for which 

the W126 index estimates are at or 

below 11 ppm-hrs, more than two thirds 

of the dataset (Smith and Murphy, 2015, 

Table 1). 

To more fully address the comments 

related to this WREA analysis, we have 

drawn several additional observations 

from the WREA dataset, re-presenting 

the same data in a different format in a 

technical memorandum to the docket 

(Smith and Murphy, 2015). Contrary to 

the implication of the statements from 

the commenters and CASAC that no 

reduction in the occurrence of visible 

foliar injury can be achieved with 

exposures above 10 ppm-hrs, both the 

proportion of records with injury and 

the average biosite index are lower for 

groups of records with W126 index 

estimates at or below 17 ppm-hrs 

compared to the group for the highest 

W126 index range. This is true when 

considered regardless of soil moisture 

conditions (all records), as well as for 

dry, normal and wet records, separately 

(Smith and Murphy, 2015, Table 2). The 

pattern of the two measures across 

record groups with lower W126 index 

values differs with moisture level, with 

the wetter than normal records generally 

showing decreasing proportions of 

injured sites and decreasing average 

biosite index with lower W126 index 

values, while little difference in these 

measures is seen among the middle 

W126 values although they are lower 

than the highest W126 index group and 

higher than the lowest W126 index 

group (Smith and Murphy, 2015, Table 

2). In summary, the EPA disagrees with 

commenters, noting that the available 

information, including additional 

observations from the WREA dataset, 

indicate declines in the occurrence of 

visible foliar injury across decreasing 

W126 index values that are higher than 

10 ppm-hrs. 

c. Use of W126 Metric in Evaluating 

Vegetation Effects and Public Welfare 

Protection 

In considering public comments 

received on the EPA’s use of the W126 

exposure index in its decision on a 

revised secondary standard, the EPA 

first notes related advice and comments 

from the CASAC received during 

development of the PA. Although we 

recognize that CASAC’s comments on 

the W126 index were provided in the 

context of its recommendation for a 

secondary standard of that form, we find 

them to also relate to our use of the 

W126 metric in evaluating the 

magnitude and extent of vegetation 

effects that might be expected and 

conversely the level of protection that 

might be provided under different air 

quality conditions. In comments on the 

first draft PA, the CASAC stated that 

‘‘discussions and conclusions on 

biologically relevant exposure metrics 

are clear and compelling and the focus 

on the W126 form is appropriate’’ (Frey 

and Samet, 2012a). With regard to 

specific aspects of the W126 index, the 

CASAC concurred with the second draft 

PA focus on ‘‘the biologically-relevant 

W126 index accumulated over a 12-hour 

period (8 a.m.–8 p.m.) over the 3-month 

summation period of a single year 

resulting in the maximum value of 

W126’’ (Frey, 2014c, p. iii). 

The CASAC advice on levels of the 

W126 index on which to focus for 

public welfare protection recommended 

a level within the range of 7 ppm-hrs to 

15 ppm-hrs (Frey, 2014c, p. iii). We 

note, however, as summarized in 

section IV.E.3 of the proposal, that this 

advice was provided in the context of 

the CASAC review of the second draft 

PA, which concluded that a range from 

7 to 17 ppm-hrs was appropriate to 

consider. In considering the upper end 

of this range, the CASAC consulted 

Table 6–1 of the second draft PA which 

indicated for a W126 index value of 17 

ppm-hrs an RBL estimate of 6%, a 

magnitude that CASAC described as 

‘‘unacceptably high’’ and that 

contributed to a lack CASAC support for 

W126 exposures values higher than 15 

ppm-hrs (Frey, 2014c, p. 14; U.S. EPA 

2014d, Table 6–1). As noted in section 

IV.E.3 of the proposal, revisions to the 

RBL estimate table in the final PA, 

which were made in consideration of 

other CASAC comments, have resulted 

in changes to the median species RBL 

estimate associated with each W126 

index value, such that the median 

species RBL estimate for a W126 index 

value of 17 ppm-hrs in this table in the 

final PA was 5.3%, rather than the 

‘‘unacceptably high’’ value of 6% (U.S. 

EPA, 2014c, Table 6–1; U.S. EPA, 

2014d, Table 6–1; Frey, 2014c, p. 14).201

Additionally, the CASAC recognized 

that the Administrator may, as a policy 

matter, prefer to use a 3-year average, 

and stated that in that case, the range of 

levels should be revised downward 

(Frey, 2014c, p. iii–iv). 

The majority of comments on the 

W126 index concurred with its use for 

assessing O3 exposures, while some 

commenters additionally expressed the 

view that this index should be used as 

the form of the secondary standard (as 

discussed in section IV.C.2.d below). 

Most submissions from state and local 

environmental agencies or governments, 

as well as organizations of state 

agencies, that provided comments on 

the magnitude of cumulative exposure, 

in terms of the W126 index, appropriate 

to consider for a revised secondary 

standard, recommended that the EPA 

focus on an index value within the 

EPA’s proposed range of 13 to 17 ppmhrs, as did the industry commenters. 

These commenters variously noted their 

agreement with the rationale provided 

by the EPA in the proposal or cited to 

CASAC comments, including for a 

downward adjustment of its 

recommended values if a 3-year average 

W126 was used rather than a single year 

index. Some other commenters, 

including two groups of environmental 

organizations, submitted comments 

recommending a focus on a W126 index 

level as low as 7 ppm-hrs based on 

reasons generally focused on 

consideration of visible foliar injury. 

Some aspects of these comments have 

been addressed in sections IV.C.2.a and 

IV.C.2.b above. In the Response to 

Comments document, we have 

additionally addressed other comments 

that recommend a focus on W126 index 

values for specific reasons other than 

generally citing the CASAC 

recommended range. Further, in her 

consideration of a target level of 

protection for the revised secondary 

standard in section IV.C.3 below, the 

Administrator has considered comments 

from the CASAC regarding the basis for 

their recommended range. 

An additional comment from an 

organization of western state air quality 

managers indicated a concern with the 

use of W126 for vegetation in arid and 

high altitude regions, such as those in 

the western states, which the 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65397 

202For example, we note that among the 11 

species for which robust E–R functions have been 

established for O3 effects on tree seedling growth, 

the sensitivity of ponderosa pine, a species 

occurring in arid and high altitude regions of the 

western U.S., is similar to the median (U.S. EPA, 

2014c, Table 5C–1). 

203No O3 exposure studies on cacti or other 

species that utilize CAM photosynthesis are 

reported in the ISA (U.S. EPA, 2013). 

commenter hypothesized may have 

reduced sensitivity. The commenters 

did not provide evidence of this 

hypothesis, calling for further research 

in order to characterize the sensitivity of 

vegetation in such areas. The EPA 

agrees that additional research would be 

useful in more completely 

characterizing the response of species in 

such areas, as well as other less well 

studied areas, but does not find support 

in the currently available evidence for 

the commenter’s suggestion that species 

in arid and high altitude regions may be 

less sensitive than those in other 

areas.202

Among the small number of 

commenters recommending against 

using the W126 metric to assess O3

exposure, a few expressed the view that 

some other, not-yet-identified 

cumulative exposure metric should be 

used. These commenters cited a variety 

of concerns that they state are not 

addressed by the W126 index: that plant 

exposure to and uptake of O3 are not 

always equivalent because of variations 

in stomatal conductance and plant 

defenses and their respective diel 

patterns, which will also influence plant 

response; that the duration between 

harmful O3 exposures affects the plant’s 

ability to repair damage; and, that nighttime exposures may be important. These 

commenters do not identify an 

alternative to the W126 index that they 

conclude to better represent exposures 

relevant to considering O3 effects on 

vegetation and particularly for growth 

effects. The EPA has considered the 

items raised by these commenters, 

recognizing some as areas of uncertainty 

(U.S. EPA, 2013, pp. 9–109 to 9–113), 

yet has concluded that based on the 

information available at this time, 

exposure indices that cumulate and 

differentially weight the higher hourly 

average concentrations while also 

including the ‘‘mid-level’’ values offer 

the most appropriate approach for use 

in developing response functions and 

comparing studies of O3 effects on 

vegetation (U.S. EPA, 2013, p. 9–117). 

When considering the response of 

vegetation to O3 exposures represented 

by the threshold (e.g., SUM06) and nonthreshold (e.g., W126) indices, the ISA 

notes that ‘‘the W126 metric does not 

have a cut-off in the weighting scheme 

as does SUM06 and thus it includes 

consideration of potentially damaging 

exposures below 60 ppb’’ and that ‘‘[t]he 

W126 metric also adds increasing 

weight to hourly concentrations from 

about 40 ppb to about 100 ppb’’ (U.S. 

EPA, 2013, p. 9–104). This aspect of 

W126 is one way it differs from cut-off 

metrics such as the SUM06 where all 

concentrations above 60 ppb are treated 

equally and is identified by the ISA as 

‘‘an important feature of the W126 since 

as hourly concentrations become higher, 

they become increasingly likely to 

overwhelm plant defenses and are 

known to be more detrimental to 

vegetation’’ (U.S. EPA, 2013, p. 9–104). 

Further, we note the concurrence by 

CASAC with the EPA’s focus on the 

W126 exposure index, as noted above. 

Some commenters also raised 

concerns regarding the sensitivity of 

vegetation in desert areas where plants 

take in ambient air during nighttime 

rather than daylight hours, such that 

little exposure occurs from 8 a.m. to 8 

p.m., stating that the W126 index as 

defined by the EPA to cumulate hourly 

O3 from 8 a.m. to 8 p.m. may result in 

an overly stringent exposure level in 

areas with such vegetation. The EPA 

recognizes that plants, such as cacti, 

that commonly occur in desert systems 

exhibit a particular type of metabolism 

(referred to as CAM photosynthesis) 

such that they only open their stomata 

at night (U.S. EPA, 2013, p. 9–109). We 

note, however, that few if any O3

exposure studies of these species are 

available 203 to further inform our 

characterization of these species’ 

responses to O3, and we have no basis 

on which to conclude that an exposure 

level based on the studied species and 

a daylight exposure metric would be 

overly or underly stringent in areas 

where only species utilizing CAM 

photosynthesis occur. As summarized 

above, the CASAC advice concurred 

with the use of an 8am to 8pm diurnal 

period for the W126 exposure index. 

Thus, we conclude that for our purposes 

in this review the focus on daylight 

hours is appropriate. Our use of the 

W126 index in this review has been for 

purposes of characterizing the potential 

harm and conversely the potential 

protection that might be afforded from 

the well-characterized effects of O3 on 

vegetation, while recognizing associated 

uncertainties and limitations. We note 

that different ecosystems across the U.S. 

will be expected to be of varying 

sensitivities with regard to the effects of 

O3. For example, large water bodies 

without vegetation extending above the 

water’s surface would be expected to be 

less sensitive than forests of sensitive 

species. The EPA notes, however, that 

the NAAQS are set with applicability to 

all ambient air in the U.S., such that the 

secondary O3 standard provides 

protection in areas across the U.S. 

regardless of site-specific aspects of 

vegetation sensitivity to O3. In 

considering the evidence on O3 and 

associated welfare effects, we recognize 

variability in sensitivity that may relate 

to a number of factors, as discussed in 

the ISA (U.S. EPA, 2013, section 9.4.8). 

This variability is among the 

Administrator’s considerations in 

setting the secondary standard for O3

that is requisite to protect public welfare 

against anticipated or known adverse 

effects. 

Further, some commenters who 

agreed with a focus on the W126 

exposure index also stated that the 

EPA’s definition of the index for the 

daylight hours of 8 a.m. to 8 p.m. and 

a 3-month period was not appropriate, 

stating that derivation of the W126 

metric should involve summing 

concentrations for all 24 hours in each 

day and all months in each year to avoid 

underestimating O3 exposure that the 

commenters viewed as pertinent. 

Support for the EPA’s definition of the 

W126 index, with which CASAC 

concurred (Frey, 2014c, p. iii), is based 

on the assessment of the evidence in the 

ISA (U.S. 2013, section 9.5.3.2) and the 

context for use of the W126 index in 

relating O3 exposure to magnitude and/ 

or extent of O3 response. This context 

has a particular focus on growth effects 

for the purposes of judging the potential 

for public welfare impacts, as well as 

the level of protection, associated with 

different exposure circumstances. We 

note that the ISA stated there is a lack 

of information that would allow 

consideration of the extent to which 

nocturnal exposures that may be of 

interest occur (U.S. EPA, 2013, p. 9– 

109). Additionally, in our use of the 

W126 index, we are relying on E–R 

functions based on studies that were 

generally of 3-month duration and 

involved controlled exposures during 

the daylight period. Accordingly we 

have relied on the E–R function derived 

for 12-hour and 3-month W126 indices, 

as described in section IV.A.1 above. To 

apply these E–R functions to the W126 

estimates derived using 24 hours-perday index values would inaccurately 

represent the response observed in the 

study (producing an overestimate). 

Similarly, with regard to the 3-month 

duration, ‘‘[d]espite the possibility that 

plants may be exposed to ambient O3

longer than 3 months in some locations, 

there is generally a lack of exposure 

experiments conducted for longer than 

mstockstill on DSK4VPTVN1PROD with RULES2

65398 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

204Section 5.7 of the PA states that ‘‘the evidence 

continues to provide a strong basis for concluding 

that it is appropriate to judge impacts of O3 on 

vegetation, related effects and services, and the 

level of public welfare protection achieved, using 

a cumulative, seasonal exposure metric, such as the 

W126-based metric,’’ references the support of 

CASAC for a W126-based secondary standard, and 

then concludes that ‘‘based on the consistent and 

well-established evidence described above, . . . the 

most appropriate and biologically relevant way to 

relate O3 exposure to plant growth, and to 

determine what would be adequate protection for 

public welfare effects attributable to the presence of 

O3 in the ambient air, is to characterize exposures 

in terms of a cumulative seasonal form, and in 

particular the W126 metric’’ (U.S. EPA, 2014c, p. 

5–78). 

205The CASAC also mentioned its support for 

revising the secondary standard to a W126 indexbased form in its review of Chapter 6 of the second 

draft PA (Frey, 2014c, p. 13). Similar to section 5.7, 

in that chapter of the PA staff concluded that 

‘‘specific features associated with the W126 index 

still make it the most appropriate and biologically 

relevant cumulative concentration-weighted form 

for use in the context of the secondary O3 NAAQS 

review’’ (U.S. EPA, 2014c, p. 6–5) and also 

concluded that ‘‘it is appropriate to consider a 

revised secondary standard in terms of the 

cumulative, seasonal, concentration-weighted form, 

the W126 index’’ (U.S. EPA, 2014c, p. 6–57). 

206The term design value is commonly used to 

refer to the metric for the standard. Consistent with 

the summary in section I.D above, a design value 

is the statistic that describes the air quality of a 

given location in terms of the indicator, form and 

averaging time of the standard such that it can then 

be compared to the level of the standard. 

3 months’’ (U.S. EPA, 2014c, p. 9–112). 

Thus, in consideration of the lack of 

support in the current evidence for 

characterizing exposure for purposes of 

estimating RBL based on cumulative 

exposures derived from a combination 

of daytime and nighttime exposures and 

consideration of year-round O3

concentrations across the U.S., we 

disagree with the commenters’ view of 

the appropriateness of using an 

exposure index based on 24-hour, yearround O3 concentrations. 

The commenters supporting the use of 

the W126 exposure index were divided 

with regard to whether the EPA should 

focus on an annual index or one 

averaged over three years. Some of the 

commenters indicating support for the 

EPA’s proposed focus on a 3-year 

average W126 index stated that this was 

appropriate in light of the wide 

variations in W126 index values that 

can occur on a year-to-year basis as a 

result of the natural variation of climatic 

conditions that have a direct impact on 

O3 formation; in their view, these factors 

are mitigated by use of a 3-yr average, 

which thus provides ‘‘stability’’ in the 

assessment dampening out the natural 

variation of climatic conditions that 

have a direct impact on O3 formation. 

Others noted that use of a 3-year average 

may be supported as matter of policy. 

We generally concur with the relevance 

of these points, among others, to a focus 

on the 3-year average W126. Other 

commenters expressed the view that the 

EPA should focus on an annual W126 

index, generally making these 

comments in the context of expressing 

their support for a secondary standard 

with a W126 form. These commenters 

variously cited CASAC advice and its 

rationale for preferring a single year 

W126 form, stated that vegetation 

damage occurs on an annual basis, and/ 

or questioned the EPA’s statements of 

greater confidence in conclusions as to 

O3 impacts based on a 3-year average 

exposure metric. 

The EPA agrees with commenters 

that, as discussed in the PA and the 

proposal, depending on the exposure 

conditions, O3 can contribute to 

measurable effects on vegetation in a 

single year. We additionally recognize 

that, as described in the PA and 

proposal, there is generally a greater 

significance for effects associated with 

multiple-year exposures. The proposal 

described a number of considerations 

raised in the PA as influencing the 

Administrator’s decision to focus on a 3- 

year average W126 index (79 FR 75347, 

December 17, 2014). These included, 

among others, the observation of a 

greater significance for effects associated 

with multiple-year exposures, and the 

uncertainties associated with 

consideration of annual effects relative 

to multiple-year effects. 

Further, we note that among the 

judgments contributing to the 

Administrator’s decision on the level of 

protection appropriate for the secondary 

standard are judgments regarding the 

weight to place on the evidence of 

specific vegetation-related effects 

estimated to result across a range of 

cumulative seasonal concentrationweighted O3 exposures and judgments 

on the extent to which such effects in 

such areas may be considered adverse to 

public welfare (79 FR 75312, December 

17, 2014). Thus, conclusions regarding 

the extent to which the size and/or 

prevalence of effects on vegetation in a 

single year and any ramifications for 

future years represent an adverse effect 

to the public welfare, conclusions that 

are also inherently linked to overall 

magnitudes of exposures, are dependent 

on the Administrator’s judgment. 

Accordingly, the decision regarding the 

need to focus on a 1-year or 3-year 

W126 index value is also a judgment of 

the Administrator, informed by the 

evidence, staff evaluations and advice 

from CASAC, as described in section 

IV.C.3 below. 

d. Form and Averaging Time 

In considering comments received on 

the proposed form for the revised 

standard, the EPA first notes the advice 

and comments from the CASAC, 

received in its review of the second 

draft PA. Similar to its advice in the last 

review, the CASAC recommended 

‘‘establishing a revised form of the 

secondary standard to be the 

biologically relevant W126 index’’ 

(Frey, 2014c, p. iii). With regard to its 

reasons for this view, the CASAC cites 

the PA in stating that it ‘‘concurs with 

the justification in [section 5.7] that the 

form of the standard should be changed 

from the current 8-hr form to the 

cumulative W126 index’’ (Frey, 2014c, 

p. 12). In addressing specific aspects of 

this index, the CASAC concurred with 

the EPA’s focus on the 3-month period 

with the highest index value and further 

states that ‘‘[a]ccumulation over the 

08:00 a.m.–08:00 p.m. daytime 12-hour 

period is a scientifically acceptable and 

recommended means of generalizing 

across latitudes and seasons’’ (Frey, 

2014c, p. 13). As section 5.7 of the PA 

discusses the W126 index in the context 

of the support in the evidence for use of 

the W126 exposure index for assessing 

impacts of O3 on vegetation and the 

extent of protection from such impacts, 

we interpret CASAC’s statement on this 

point to indicate that the basis for 

CASAC’s view with regard to the form 

for the secondary standard relates to the 

appropriateness of the W126 exposure 

index for those assessment 

purposes.204 205

The public comments on the form for 

a revised secondary standard were 

divided. Most of the state and local 

environmental agencies or governments, 

and all of the tribal agencies and 

organizations that provided comments 

on the form for the secondary standard 

concurred with the EPA’s proposed 

decision, as did the industry 

commenters. These commenters 

generally indicated agreement with the 

rationale provided in the proposal that 

drew from the EPA analyses of recent 

air quality data examining relationships 

at sites across the U.S. between values 

of the fourth-high metric (the current 

design value) and values of a 3-year 

average W126-based metric, stating that 

this analysis showed that a standard in 

the form of the fourth-high metric, as 

proposed, can provide air quality 

consistent with or below the range of 3- 

year W126 exposure index values 

identified in the proposal. Some 

commenters additionally stated that the 

choice of form was a policy decision for 

the EPA and that little or no additional 

protection of public welfare would be 

gained by adopting a W126-based form. 

Some of these commenters provided 

analyses of data for their state or region 

that further supported this view. As 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65399 

206The term design value is commonly used to 

refer to the metric for the standard. Consistent with 

the summary in section I.D above, a design value 

is the statistic that describes the air quality of a 

given location in terms of the indicator, form and 

averaging time of the standard such that it can then 

be compared to the level of the standard. 

described in section IV.C.3 below, the 

EPA generally agrees with these 

commenters. 

Some commenters, including a 

regional organization of state agencies 

and two groups of environmental 

organizations, submitted comments 

recommending revision of the standard 

to a cumulative, seasonal form based on 

the W126 index. In support of their 

position, these commenters generally 

cited CASAC advice, variously 

additionally indicating their view that 

the standard form should be a metric 

described as biologically relevant, and 

that the existing form, with a level in 

the proposed range, would not provide 

adequate ecosystem protection. Some 

commenters additionally suggested that 

the EPA cannot lawfully retain the form 

and averaging time that were initially 

established for purposes of the primary 

standard when the EPA has identified 

the W126 index as a metric appropriate 

for judging vegetation-related effects on 

public welfare. With regard to the EPA 

air quality analyses, summarized in the 

proposal, of the W126 index values at 

sites where O3 concentrations met 

different levels of fourth-high metric, 

some of these commenters stated that 

the analyses showed widespread 

variation in W126 values for each 

fourth-high metric examined. Further, 

some commenters disagreed with the 

EPA that the analyses indicated that a 

revised standard level within the 

proposed range would be expected to 

limit W126 exposures in the future to 

the extent suggested by the analyses of 

data from the past. 

We agree with public commenters and 

CASAC regarding the appropriateness of 

the W126 index (the sum of hourly 

concentrations over a specified period) 

as a biologically relevant metric for 

assessing exposures of concern for 

vegetation-related public welfare effects, 

as discussed in the proposal, PA and 

ISA. Accordingly, we agree that this 

metric is appropriate for use in 

considering the protection that might be 

expected to be afforded by potential 

alternative secondary standards, as 

discussed in section IV.C.2.c above. We 

disagree with commenters, however, 

that use of the W126 metric for this 

purpose dictates that we must establish 

a secondary standard with a W126 

index form. 

In support of this position, we note 

the common use, in assessments 

conducted for NAAQS reviews, of 

exposure metrics that differ in a variety 

of ways from the ambient air 

concentration metrics of those 

standards.206 Across reviews for the 

various NAAQS pollutants, we have 

used a variety of exposure metrics to 

evaluate the protection afforded by the 

standards. These exposure metrics are 

based on the health or welfare effects 

evidence for the specific pollutant and 

commonly, in assessments for primary 

standards, on established exposureresponse relationships or health-based 

benchmarks (doses or exposures of 

concern) for effects associated with 

specific exposure circumstances. Some 

examples of exposure metrics used to 

evaluate health impacts in primary 

standard reviews include the 

concentration of lead in blood of young 

children and a 5-minute exposure 

concentration for sulfur dioxide. In 

contrast, the health-based standards for 

these two pollutants are the 3-month 

concentration of lead in total suspended 

particles and the average across three 

years of the 99th percentile of 1-hour 

daily maximum concentration of sulfur 

dioxide in ambient air, respectively (73 

FR 66964, November 12, 2008; 75 FR 

35520, June 22, 2010). In somewhat 

similar manner, in the 2012 PM review, 

the EPA assessed the extent to which 

the existing 24-hour secondary standard 

for PM2.5, expressed as a 24-hour 

concentration (of PM2.5 mass per cubic 

meter of air) not to be exceeded more 

than once per year on average over three 

years, could provide the desired 

protection from effects on visibility in 

terms of the 90th percentile, 24-hour 

average PM2.5 light extinction, averaged 

over three years, based on speciated 

PM2.5 mass concentrations and relative 

humidity data (79 FR 3086, January 15, 

2013). Additionally, in the case of the 

screening-level risk analyses in the 2008 

review of the secondary standard for 

lead, concentrations of lead in soil, 

surface water and sediment were 

evaluated to assess the potential for 

welfare effects related to lead deposition 

from air, while the standard is 

expressed in terms of the concentration 

of lead in particles suspended in air (73 

FR 67009, November 12, 2008). 

Further, depending on the evidence 

base, some NAAQS reviews may 

consider multiple exposure metrics in 

assessing risks associated with a 

particular pollutant in ambient air in 

order to judge the adequacy of an 

existing standard in providing the 

required level of protection. And a 

standard with an averaging time of one 

duration may provide protection against 

effects elicited by exposures of 

appreciably shorter or longer durations. 

For example, in the current review of 

the primary O3 standard, as described in 

section II above, we have considered the 

potential for effects associated with both 

short- and long-term exposures and 

concluded, based on a combination of 

air quality and risk analyses and the 

health effects evidence, that the existing 

standard with its short (8-hour) 

averaging time provides control of both 

the long and short term exposures (e.g., 

from one hour to months or years) that 

may be of concern to public health. 

Similarly, during the 1996 review of the 

NO2 primary standard, while health 

effects were recognized to result from 

both long-term and short-term 

exposures to NO2, the primary standard, 

which was a long-term (annual) 

standard, was concluded to provide the 

requisite protection against both longand short-term exposures (61 FR 52852, 

Oct 8 1996). In the subsequent review of 

the NO2 primary standard in which the 

available air quality information 

indicated that the annual standard was 

not providing the needed control of the 

shorter term exposures, an additional 

short-term standard was established (75 

FR 6474, February 9, 2010). 

Thus, we note that different metrics 

may logically, reasonably, and for 

technically sound reasons, be used in 

assessing exposures of concern or 

characterizing risk as compared to the 

metric of the standard which is used to 

control air quality to provide the desired 

degree of protection. That is, exposure 

metrics are used to assess the likely 

occurrence and/or frequency and extent 

of effects under different air quality 

conditions, while the air quality 

standards are intended to control air 

quality to the extent requisite to protect 

from the occurrence of public health or 

welfare effects judged to be adverse. In 

this review of the secondary standard 

for O3, the EPA agrees that, for the 

reasons summarized in section IV.A.1 

above and described in the ISA, the 

W126 index—and not an 8-hour daily 

maximum concentration that has 

relevance in human health risk 

characterization, as described in section 

II above—is the appropriate metric for 

assessing exposures of concern for 

vegetation, characterizing risk to public 

welfare, and evaluating what air quality 

conditions might provide the desired 

degree of public welfare protection. We 

disagree, however, that the secondary 

standard must be established using that 

same metric. 

Moreover, we note that the CAA does 

not require that the secondary O3

standard be established in a specific 

mstockstill on DSK4VPTVN1PROD with RULES2

65400 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

207 In fact, the D.C. Circuit has upheld secondary 

NAAQS that were identical to the corresponding 

primary standard for the pollutant (e.g., ATA III, 

283 F.3d at 375, 380 [D.C. Cir. 2002, upholding 

secondary standards for PM2.5 and O3 that were 

identical to primary standards]). 

208See CAA sections 307(d)(3) and 307(d)(6)(A); 

see also Mississippi v. EPA, 744 F.3d 1334, 1354 

(D.C. Cir. 2013) (‘‘Although EPA is not bound by 

CASAC’s recommendations, it must fully explain 

its reasons for any departure from them’’). 

209The EPA additionally notes that commenters 

contradict their own assertion when, after stating 

their view that no relationship exists between the 

4th high and W126 metrics, the commenter then 

states that there is a nonlinear relationship and yet 

then relies on a predicted linear relationship to 

estimate W126 values occurring when air quality 

meets different values for the 4th high metric at 11 

national parks. 

form. Section 109(b)(2) provides only 

that any secondary NAAQS ‘‘shall 

specify a level of air quality the 

attainment and maintenance of which in 

the judgment of the Administrator, 

based on [the air quality] criteria, is 

requisite to protect the public welfare 

from any known or anticipated adverse 

effects associated with the presence of 

such air pollutant in the ambient air. 

. . . [S]econdary standards may be 

revised in the same manner as 

promulgated.’’ The EPA interprets this 

provision to leave it considerable 

discretion to determine whether a 

particular form is appropriate, in 

combination with the other aspects of 

the standard (averaging time, level and 

indicator), for specifying the air quality 

that provides the requisite protection, 

and to determine whether, once a 

standard has been established in a 

particular form, that form must be 

revised. Moreover, nothing in the Act or 

the relevant case law precludes the EPA 

from establishing a secondary standard 

equivalent to the primary standard in 

some or all respects, as long as the 

Agency has engaged in reasoned 

decision-making.207

With regard to the commenter’s 

emphasis on advice from CASAC on the 

form of the secondary standard, the EPA 

agrees with the importance of giving 

such advice careful consideration. The 

EPA further notes, however, that the 

Administrator is not legally precluded 

from departing from CASAC’s 

recommendations, when she has 

provided an explanation of the reasons 

for such differences.208 Accordingly, in 

reaching conclusions on the revised 

secondary standard in this review, the 

Administrator has given careful 

consideration to the CASAC advice in 

this review and, when she has differed 

from CASAC recommendations, she has 

fully explained the reasons and 

judgments that led her to a different 

conclusion, as described in section 

IV.C.3 below. 

In disagreeing with the EPA’s 

conclusions drawn from analyses of 

recent air quality data on the extent to 

which cumulative seasonal exposures 

might be limited to within or below the 

identified 3-year average W126 index 

values by controlling air quality using 

different values for the fourth-high 

metric, one group of environmental 

organizations emphasized the range of 

W126 index values that occur at 

monitors with concentrations at or 

below specific values for the fourth-high 

metric. For monitor observations for 

which the fourth-high metric was at or 

below 70 ppb, this commenter group 

stated that some sites have 3-year 

average W126 index values above 17 

ppm-hrs and noted a maximum 3-year 

W126 index value of 19.1 ppm-hrs, 

while additionally noting occurrences of 

other W126 values above the CASAC 

range of 7 to 15 ppm-hrs. This 

commenter additionally stated that the 

air quality data ‘‘do not support a claim 

of congruence’’ between the fourth-high 

and W126 metrics (e.g., ALA et al., p. 

196), that there is no basis for 

concluding that there is some 

fundamental underlying relationship 

that assures meeting the fourth-high 

metric will mean meeting any of the 

W126 options, and that the relationship 

between the metrics is non-linear with 

significant spread in the data (citing 

visual inspection of a graph). 

The EPA does not agree with the 

commenter’s statements regarding the 

relationship between the two metrics.209

We have not, as stated by the 

commenter, claimed there to be 

‘‘congruence’’ between the two metrics 

(e.g., ALA et al., p. 196), or that the two 

metrics coincide exactly. Rather, at any 

location, values of both metrics are a 

reflection of the temporal distribution of 

hourly O3 concentrations across the year 

and both vary in response to changes in 

that distribution. While the EPA’s air 

quality analysis shows that the specific 

relationship differs among individual 

sites, it documents an overall strong, 

positive, non-linear relationship 

between the two metrics (Wells, 2014a, 

p. 6, Figures 5a and 5b; Wells, 2015b). 

Further, this analysis finds the amount 

of year-to-year variability in the two 

metrics tended to decrease over time 

with decreasing O3 concentrations, 

especially for the W126 metric, as 

described in section IV.E.4 of the 

proposal (Wells, 2014a; Wells, 2015b). 

With regard to the highest 3-year 

average W126 exposure index values 

that might reasonably be expected in the 

future in areas where a revised standard 

with a fourth-high form is met, we 

disagree with the commenters as to the 

significance of the W126 index value of 

19.1 ppm-hrs in the 13-year dataset. 

This value, for a site during the period 

2006–2008, is the only occurrence at or 

above 19 ppm-hrs in the nearly 4000 3- 

year W126 index values—across the 11 

3-year periods extending back in time 

from 2013—for which the fourth-high 

metric for the same monitor location is 

at or below 70 ppb. This is clearly an 

isolated occurrence. 

In considering this comment, we have 

expanded the technical memorandum 

that was available at the time of 

proposal (Wells, 2014a). The expanded 

memorandum describes the same air 

quality analyses for 3-year periods from 

2001 through 2013 as the 2014 

memorandum, and includes additional 

summary tables for all 3-year periods 

from 2001 through 2013 as well as 

tables for the most recent period, 2011– 

2013 (Wells, 2015b). After the 3-year 

W126 index value of 19 ppm-hrs, the 

next three highest 3-year average W126 

index values, which are the only other 

such values above 17 ppm-hrs in the 13- 

year dataset, and which also occur 

during periods in the past, round to 18 

ppm-hrs (Wells, 2015b). Additionally, 

we note that reductions in the fourthhigh metric over the 13-year period 

analyzed are strongly associated with 

reductions in the cumulative W126 

index (Wells, 2014a, Figure 11, Table 6; 

Wells, 2015b). Specifically, the 

regression analysis of changes in W126 

index between the 2001–2003 period 

and the 2011–2013 period with changes 

in the fourth-high metric across the 

same periods indicates a fairly linear 

and positive relationship between 

reductions of the two types of metrics, 

with, on average, a change of 

approximately 0.7 ppm-hr in the W126 

index per ppb change in the fourth-high 

metric value. From this information we 

conclude that W126 exposures above 17 

ppm-hrs at sites for which the fourthhigh metric is at or below 70 ppb would 

be expected to continue to be rare in the 

future, particularly as steps are taken to 

meet a 70 ppb standard. 

With regard to the comment that the 

relationship between the two metrics 

varies across locations, the EPA agrees 

that there is variation in cumulative 

seasonal O3 exposure (in terms of a 3- 

year average W126 index) among 

locations that are at or below the same 

fourth-high metric. As noted in the 

proposal, the analysis illustrates this 

variation, with the locations in the West 

and Southwest NOAA climatic regions 

tending to have the highest cumulative 

seasonal exposures for the same fourthhigh metric value. In considering 

expectations for the future in light of 

this observation, however, we note that 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65401 

210Additionally, O3 levels at any location are 

influenced by upwind precursor emissions, and 

many rural areas, including the site referenced by 

the commenter, are impacted by precursor 

emissions from upwind urban areas, such that as 

emissions are reduced to meet a revised standard 

in the upwind locations, reductions in those 

upwind emissions will contribute to reductions at 

the downwind sites (Wells, 2014a; ISA, pp. 3–129 

to 3–133). 

211As described earlier in this section, the EPA 

has also considered the air quality specified by one 

secondary standard in a decision on the need for 

a second secondary standard. In the decision not to 

adopt a second PM2.5 secondary standard specific 

to visibility-related welfare effects, the 

Administrator, after describing the public welfare 

protection objective related to visibility effects, 

considered analyses that related air quality 

associated with the existing secondary standard to 

that expected for the proposed visibility-focused 

secondary standard. From these analyses, she 

concluded sufficient protection against visibility 

effects would be provided by the existing standard, 

and to the extent that the existing standard would 

provide more protection than had been her 

objective for such effects, adoption of a second 

secondary standard focused on visibility would not 

change that result (78 FR 3227–3228, January 15, 

2013). This decision responded to a court remand 

of the prior EPA decision that visibility protection 

would be afforded by a secondary standard set 

equal to the primary standard based on the court’s 

conclusion that the EPA had not adequately 

described the Administrator’s objectives for 

visibility-related public welfare protection under 

the standard (American Farm Bureau, 559 F.3d at 

530–531). 

the regional regressions of reductions in 

W126 metric with reductions in the 

fourth-high metric indicate that the 

Southwest and West regions, which had 

the greatest potential for sites having 3- 

year W126 index values greater than the 

various W126 values of interest when 

fourth-high values are less than or equal 

to the various fourth-high metric values 

of interest, also exhibited the greatest 

reduction in the W126 index values per 

unit reduction in the fourth-high values 

(Wells, 2015b). Thus, in considering the 

potential for occurrences of values 

above 17 ppm-hrs in the future in areas 

that meet a fourth-high of 70 ppb, the 

EPA notes that the analysis indicates 

that those areas that exhibited the 

greatest likelihood of occurrence of a 3- 

year W126 index above a level of 

interest (e.g., the commenters’ example 

in the Southwest region of a value of 

19.1 ppm-hrs [2006–2008] in 

comparison to the W126 level of 17 

ppm-hrs) also exhibit the greatest 

improvement in W126 per unit decrease 

in fourth-high metric.210 It is expected 

that future control programs designed to 

meet a standard with a fourth-high form 

would provide similar improvements in 

terms of the W126 metric. 

As part of their rationale in support of 

revising the current form and averaging 

time, one commenter pointed to the 

regional variation in the highest W126 

index values expected at sites that just 

meet a fourth-high metric of 70 ppb, 

based on the EPA’s analysis of recent air 

quality data available at the time of the 

proposal (Wells, 2014a). This 

commenter observed that, while in some 

U.S. regions, locations that meet a 

potential alternative standard with the 

current form and a level of 70 ppb also 

have 3-year average W126 index values 

no higher than 17 ppm-hrs, the highest 

W126 index values in other parts of the 

country are lower. As a result, the 

commenter concluded that such a 

standard would result in regionally 

differing levels of welfare protection. 

The commenter additionally states that, 

for extreme values, a W126 form for the 

secondary standard would also offer 

different levels of protection, although 

with the primary standard setting the 

upper boundary for such values. 

The EPA recognizes that a standard 

with the current form might be expected 

to result in regionally differing 

distributions of W126 exposure index 

values (including different maximum 

values) depending on precursor sources, 

local meteorology, and patterns of O3

formation. Variation in exposures is to 

be expected with any standard 

(secondary or primary) of any form. In 

fact, variation in exposures and any 

associated variation in welfare or health 

risk is generally an inherent aspect of 

the Administrator’s judgment on a 

specific standard, and any associated 

variation in welfare or health protection 

may play a role in the Administrator’s 

judgment with regard to public welfare 

or public health protection objectives 

for a national standard. In considering 

the comment, however, we have focused 

only on the extent to which the 

commenter’s conclusion that a 

secondary standard of the current form 

and averaging time would provide 

regionally varying welfare protection 

might indicate that the specified air 

quality is more (or less) than necessary 

to achieve the purposes of the standard. 

In so doing, we additionally respond to 

a separate comment that the EPA needs 

to address how the revised secondary 

standard is neither more or less than 

necessary to protect the public welfare. 

The CAA requirement in establishing 

a standard is that it be set at a level of 

air quality that is requisite, meaning 

‘‘sufficient, but not more than 

necessary’’ (Whitman v. American 

Trucking Ass’ns, 531 U.S. 457, 473 

[2001]). We note that the air quality that 

is specified by the revised primary 

standard has been concluded to be 

‘‘necessary’’ and it may be reasonable 

and appropriate to consider the 

stringency of the secondary standard in 

light of what is identified as 

‘‘necessary’’ for the primary standard. 

The EPA considered the stringency of 

the O3 secondary standard in this way 

in the 1979 decision (44 FR 8211, 

February 8, 1979), which was upheld in 

subsequent litigation (API v Costle, 665 

F.2d 1176 [D.C. Cir. 1991]). We note 

that, in similar manner, the commenter 

considered public welfare protection 

that might be afforded by the primary 

standard in noting that the primary 

standard would be expected to provide 

welfare protection from extreme 

values.211

In addressing the remand of the 2008 

secondary standard in this rulemaking, 

as discussed in section IV.C.2.e below, 

the EPA recognizes that it must explain 

the basis for concluding that the 

standard selected by the Administrator 

specifies air quality that will provide 

the degree of public welfare protection 

needed from the secondary standard 

(Mississippi v. EPA, 744 F.3d 1334, 

1360–61 [D.C. Cir. 2013]). In this 

review, the Administrator describes the 

degree or level of public welfare 

protection needed from the secondary 

standard and fully explains the basis for 

concluding that the standard selected 

specifies air quality that will provide 

that degree of protection. If the 

Administrator concludes that the level 

of air quality specified by the primary 

standard would provide sufficient 

protection against known or anticipated 

adverse public welfare effects, the EPA 

believes that a secondary standard with 

that indicator, level, form and averaging 

time could be considered to be requisite. 

If the level of air quality that areas will 

need to achieve or maintain for 

purposes of the primary standard also 

provides a level of air quality that is 

adequate to provide the level of 

protection identified for the secondary 

standard, there would be little purpose 

in requiring the EPA to establish a less 

stringent secondary standard. For these 

reasons, the expectation of regionally 

differing cumulative exposures under a 

secondary standard of the current form 

and averaging time does not lead us to 

conclude that the air quality specified 

by such a standard would be more (or 

less) than necessary (and thus not 

requisite) for the desired level of public 

welfare protection. 

e. Revisions to the Standard Level 

Some comments specifically 

addressed the level for a revised 

secondary standard of the current form 

and averaging time. Of the comments 

that addressed this, some from states or 

industry groups generally supported a 

level within the proposed range, 

frequently specifying the upper end of 

the range (70 ppb), while comments 

mstockstill on DSK4VPTVN1PROD with RULES2

65402 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

from tribes and tribal organizations, and 

a few others, recommended a level no 

higher than 65 ppb. The Administrator 

has considered such comments in 

reaching her decision on the appropriate 

revisions to the standard, described in 

section IV.C.3. Detailed aspects of these 

comments are discussed in the 

Response to Comments document. 

f. 2013 Court Remand and Levels of 

Protection 

Both industry groups and a group of 

environmental advocacy organizations 

submitted comments on the extent to 

which the proposal addressed the July 

2013 remand of the secondary standard 

by the U.S. Court of Appeals for the D.C. 

Circuit. The former generally concluded 

that the proposal had adequately 

addressed the remand, while the latter 

expressed the view that the EPA had 

failed to comply with the court’s 

remand because it had failed to identify 

the target levels of vegetation protection 

for which the proposed range of 

standards would provide the requisite 

protection, claiming that the identified 

W126 index range of 13–17 ppm-hrs 

was not based on a proposed level of 

protection against biomass loss, carbon 

storage loss, or foliar injury that the EPA 

had identified as requisite for public 

welfare. 

We agree with the comments that 

state that we have addressed the court’s 

remand. More specifically, with this 

rulemaking, including today’s decision 

and the Administrator’s conclusions 

described in section IV.C.3 below, the 

EPA has fully addressed the remand of 

the 2008 secondary O3 standard. In 

Mississippi v. EPA, the D.C. Circuit 

remanded the 2008 secondary O3

standard to the EPA for reconsideration 

because it had not adequately explained 

why that standard provided the 

requisite public welfare protection. 744 

F.3d 1334, 1360–61 (D.C. Cir. 2013). In 

doing so, the court relied on the 

language of CAA section 109(b)(2), and 

the court’s prior decision, American 

Farm Bureau Federation v. EPA, 559 

F.3d 512, 528–32 (D.C. Cir. 2009), which 

came to the same conclusion for the 

2006 secondary PM2.5 standard. Both 

decisions recognize that the plain 

language of section 109(b)(2) requires 

the EPA to ‘‘specify a level of air quality 

the maintenance of which . . . is 

requisite to protect the public welfare 

from any known or anticipated adverse 

effects’’ (Mississippi, 744 F.3d at 1360 

[citing American Farm Bureau, 559 F.3d 

at 530]). Further, explaining that it was 

insufficient for the EPA ‘‘merely to 

compare the level of protection afforded 

by the primary standard to possible 

secondary standards and to find the two 

roughly equivalent’’ (Mississippi, 744 

F.3d at 1360), the court rejected the 

EPA’s justification for setting the 

secondary standard equivalent to the 

primary standard because that 

justification was based on comparing 

the protection from the primary 

standard to that expected from one 

possible standard with a cumulative, 

seasonal form (21 ppm-hrs) without 

stating that such a cumulative seasonal 

standard would be requisite to protect 

welfare or explaining why that would be 

so. Because the EPA had ‘‘failed to 

determine what level of protection was 

‘requisite to protect the public welfare’’ 

(Mississippi, 744 F.3d at 1362), the court 

found that the EPA’s rationale failed to 

satisfy the requirements of the Act. 

Today’s rulemaking both satisfies the 

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

Act and addresses the issues raised in 

the court’s remand. In this rulemaking, 

the Administrator has established a 

revised secondary standard that replaces 

the remanded 2008 secondary standard. 

In so doing, based on her consideration 

of the currently available evidence and 

quantitative exposure and air quality 

information, as well as advice from 

CASAC and input from public 

comments, the Administrator has 

described the requisite public welfare 

protection for the secondary standard 

and explained how the standard 

selected specifies air quality that will 

provide that protection. As explained in 

detail in IV.C.3 below, in this review the 

Administrator is describing the public 

welfare protection she finds requisite in 

terms of seedling RBL in the median 

species, which serves as a surrogate for 

a broader array of O3 effects at the plant 

and ecosystem levels. This description 

of the desired protection sufficiently 

articulates the standard that the 

Administrator is using to evaluate 

welfare protection. Further, the 

Administrator has considered air quality 

analyses in determining how to achieve 

the air quality conditions associated 

with the desired protection. Based on 

these analyses, the Administrator is 

determining that revising the level of 

the secondary standard to 70 ppb, while 

retaining the current form, averaging 

time, and indicator, specifies a level of 

air quality that will provide the 

requisite public welfare protection. 

To the extent the comments suggest 

that the EPA is required in establishing 

a standard to identify a precise and 

quantified level of public welfare 

protection that is requisite with respect 

to every potentially adverse public 

welfare impact (e.g., visible foliar injury, 

crop yield loss) that is considered in 

establishing the standard, we disagree. 

While the D.C. Circuit has required the 

EPA to ‘‘qualitatively describe the 

standard governing its selection of 

particular NAAQS,’’ it has expressly 

‘‘rejected the notion that the Agency 

must establish a measure of the risk to 

safety it considers adequate to protect 

public health every time it establishes a 

NAAQS’’ (ATA III, 283 F.3d at 369 

[internal marks and citations omitted]). 

That is, the EPA must ‘‘engage in 

reasoned decision-making,’’ but is not 

required to ‘‘definitively identify 

pollutant levels below which risks to 

public health are negligible’’ (ATA III, 

283 F.3d at 370). This principle 

recognizes that the Act requires the EPA 

to establish NAAQS even when the risks 

or effects of a pollutant cannot be 

quantified or precisely identified 

because of scientific uncertainty 

concerning such effects at atmospheric 

concentrations (ATA III, 283 F.3d at 

370). Though these decisions 

specifically address setting a primary 

standard under CAA section 109(b)(1), 

we believe the same principles apply to 

the parallel provision in section 

109(b)(2) governing secondary 

standards. Accordingly, while the EPA 

recognizes that it must explain the basis 

for concluding that the standard 

selected by the Administrator specifies 

air quality that will provide the 

protection against adverse effects on 

public welfare needed from the 

secondary standard (Mississippi v. EPA, 

744 F.3d 1334, 1360–61 [D.C. Cir. 

2013]), the CAA does not require the 

EPA to precisely quantify the measure 

of protection that is necessary to protect 

the public welfare in establishing a 

secondary standard. In light of the 

Administrator’s description of the 

desired public welfare protection in 

IV.C.3 below, which has both qualitative 

and quantitative components, the EPA 

is not required to further reduce this 

description to a precise, quantitative 

target level of vegetation protection. 

Moreover, nothing in the CAA or in case 

law requires the EPA to identify a target 

level of protection for any particular 

public welfare effect, such as vegetation 

effects, but rather leaves the 

Administrator discretion in judging how 

to describe the public welfare protection 

that she concludes is requisite. In IV.C.3 

below, the Administrator explains her 

reasoning for giving primary focus to 

growth-related effects in describing the 

requisite welfare protection, rather than 

to other welfare effects such as foliar 

injury, for which there are more 

uncertainties and less predictability 

with respect to the severity of the effects 

that would be expected from varying O3

exposures in the natural environment 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65403 

and the significance of the associated 

impacts to public welfare. 

3. Administrator’s Conclusions on 

Revision 

In reaching her decision on the 

appropriate revisions to the secondary 

standard, the Administrator has drawn 

on (1) the ISA conclusions regarding the 

weight of the evidence for a range of 

welfare effects associated with O3 in 

ambient air, quantitative findings 

regarding air quality and ecosystem 

exposures associated with such effects, 

and associated limitations and 

uncertainties; (2) staff evaluations in the 

PA of the evidence summarized in the 

ISA, the exposure/risk information 

developed in the WREA and analyses of 

air quality monitoring information; (3) 

additional air quality analyses of 

relationships between air quality 

metrics based on form and averaging 

time of the current standard and the 

W126 cumulative seasonal exposure 

index; (4) CASAC advice; and (5) 

consideration of public comments. After 

giving careful consideration to all of this 

information, the Administrator believes 

that the conclusions and policy 

judgments supporting her proposed 

decision remain valid. 

The Administrator concludes it is 

appropriate to continue to use O3 as the 

indicator for a secondary standard 

intended to address adverse effects to 

public welfare associated with exposure 

to O3 alone and in combination with 

related photochemical oxidants. In this 

review, no alternatives to O3 have been 

advanced as being a more appropriate 

surrogate for ambient photochemical 

oxidants. Advice from CASAC concurs 

with the appropriateness of retaining 

the current indicator. Thus, as is the 

case for the primary standard (discussed 

above in section II.C.1), the 

Administrator has decided to retain O3

as the indicator for the secondary 

standard. In so doing, she recognizes 

that measures leading to reductions in 

ecosystem exposures to O3 would also 

be expected to reduce exposures to 

other photochemical oxidants. 

In her decision on the other elements 

of the standard, the Administrator has 

considered the body of evidence and 

information in a systematic fashion, 

giving appropriate consideration to the 

important findings of the ISA as to the 

effects of O3 in ambient air that may 

present risks to the public welfare, 

measures of exposure best formulated 

for assessment of these effects, 

associated evidence regarding 

ecosystem exposures and air quality 

associated with such effects; judgments 

regarding the weight to place on 

strengths, limitations and uncertainties 

of this full body of information; and 

public welfare policy judgments on the 

appropriate degree of protection and the 

form and level of a revised standard that 

will provide such protection. In 

reaching her decision, the Administrator 

recognizes that the Act does not require 

that NAAQS be set at zero-risk or 

background levels, but rather at levels 

that reduce risk sufficiently to protect 

public welfare from known or 

anticipated adverse effects. In addition, 

we note that the elements of the 

standard (indicator, level, form, and 

averaging time) are considered together 

in assessing the protection provided by 

a new or revised standard, and the 

EPA’s approach for considering the 

elements of a new or revised standard 

is part of the exercise of the judgment 

of the Administrator. 

As an initial matter, the Administrator 

recognizes the robustness of the 

longstanding evidence, described in the 

ISA, of O3 effects on vegetation and 

associated terrestrial ecosystems. The 

newly available studies and analyses 

have strengthened the evidence for the 

current review that provides the 

foundation for the Administrator’s 

consideration of O3 effects, associated 

public welfare protection objectives, 

and the revisions to the current standard 

needed to achieve those objectives. In 

light of the extensive evidence base in 

this regard, the Administrator focuses 

on protection against adverse public 

welfare effects of O3 related effects on 

vegetation. In so doing, she takes note 

of effects that compromise plant 

function and productivity, with 

associated effects on ecosystems. She is 

particularly concerned about such 

effects in natural ecosystems, such as 

those in areas with protection 

designated by Congress for current and 

future generations, as well as areas 

similarly set aside by states, tribes and 

public interest groups with the intention 

of providing similar benefits to the 

public welfare. She additionally 

recognizes that providing protection for 

this purpose will also provide a level of 

protection for other vegetation that is 

used by the public and potentially 

affected by O3 including timber, 

produce grown for consumption and 

horticultural plants used for 

landscaping. 

A central issue in this review of the 

secondary standard, as in the last review 

(completed in 2008), has been 

consideration of the role for a 

cumulative seasonal exposure index. In 

the last review, the Administrator 

proposed such an index as one of two 

options for the form of a revised 

standard. The Administrator’s decision 

in that review was to retain the existing 

form and averaging time, while revising 

the standard level to provide the desired 

level of protection. As described in 

section IV.A above, this decision was 

remanded to the EPA in 2013 by the DC 

Circuit. In the current review, the ISA 

evaluates the evidence and concludes 

that, among the approaches 

investigated, quantifying exposure with 

a cumulative seasonal index best 

captures the aspects of exposure that 

relate to effects on vegetation, 

particularly those related to growth and 

yield. The PA considered this finding 

both in the context of assessing 

potential impacts, and, conversely, the 

protection from such impacts that might 

be realized, as well as in the context of 

using a cumulative seasonal exposure 

index as a form for the secondary 

standard. In the proposal, the 

Administrator focused on the former 

context, as an exposure index, while 

additionally soliciting comment on use 

of the index as the form for the revised 

standard. Advice from CASAC, all of 

which was received prior to the 

proposal, has largely emphasized the 

latter context, and that was also the 

focus of some comments. 

In considering revisions to the 

secondary standard that will specify a 

level of air quality to provide the 

necessary public welfare protection, the 

Administrator focuses on use of a 

cumulative seasonal exposure index, 

including specifically the W126 index 

as defined in the proposal, for assessing 

exposure, both for making judgments 

with regard to the potential harm to 

public welfare posed by conditions 

allowed by various levels of air quality 

and for making the associated 

judgments regarding the appropriate 

degree of protection against such 

potential harm. In so doing, the 

Administrator takes note of the 

conclusions in the ISA and PA, with 

which the CASAC concurred, that, 

based on the currently available 

evidence, a cumulative seasonal 

concentration-weighted index best 

captures the aspects of ecosystem 

exposure to O3 in ambient air that 

impact vegetation. In considering the 

public comments in this area, she notes 

the broad support for use of such a 

metric as an exposure index, with many 

additionally supporting its use as the 

form for a revised standard, in light of 

CASAC advice on that point. Thus, 

based on the substantial support in the 

evidence and CASAC advice, and in 

consideration of public comments, the 

Administrator concludes that it is 

appropriate to use such a cumulative 

seasonal concentration-weighted index 

for purposes of assessing the potential 

mstockstill on DSK4VPTVN1PROD with RULES2

65404 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

public welfare risks, and similarly, for 

assessing the potential protection 

achieved against such risks on a 

national scale. 

The Administrator has considered 

conclusions of the ISA and PA, as well 

as advice from CASAC and public 

comments, regarding different 

cumulative, concentration-weighted 

metrics, and different temporal 

definitions of aspects of these metrics. 

The Administrator takes note of the PA 

conclusions in support of the W126 

exposure index, recognized by the ISA 

for its strength in weighting potentially 

damaging O3 concentrations that 

contributes to the advantages it offers 

over other weighted cumulative indices. 

With regard to the relevant definitions 

for the temporal aspects of this index, 

conclusions in the ISA and PA, and 

such considerations in the last review, 

have led to a focus on a maximum 3- 

month, 12-hour index, defined by the 3- 

consecutive-month period within the O3

season with the maximum sum of 

W126-weighted hourly O3

concentrations during the period from 

8:00 a.m. to 8:00 p.m. each day (as 

explained in section IV.A.1.c above). 

The Administrator takes note of the 

support in the ISA and PA, as well as 

CASAC recommendations for 

consideration of the W126 index 

defined in this way. While recognizing 

that no one definition of an exposure 

metric used for the assessment of 

protection for multiple effects at a 

national scale will be exactly tailored to 

every species or each vegetation type, 

ecosystem and region of the country, as 

discussed in section IV.C.2 above, the 

Administrator judges that on balance, a 

W126 index derived in this way, and 

averaged over three years, as discussed 

below, will be appropriate for such 

purposes. 

In considering the appropriate 

exposure index to facilitate assessment 

of the level of protection afforded to the 

public welfare by alternative secondary 

standards in the proposal, the 

Administrator concluded that a 3-year 

average W126 index was appropriate for 

these purposes. A number of 

considerations raised in the PA 

influenced the Administrator’s 

conclusion at the time of proposal, in 

combination with public welfare 

judgments regarding the weight to place 

on the evidence of specific vegetationrelated effects estimated to result across 

a range of cumulative seasonal 

concentration-weighted O3 exposures 

and judgments on the extent to which 

such effects in such areas may be 

considered adverse to public welfare (79 

FR 76347, 75312, December 17, 2014,). 

Some comments were received from the 

public on this aspect of the proposed 

decision, as discussed in section IV.C.2 

above, and have been considered in the 

conclusions reached here. 

The Administrator continues to place 

weight on key aspects raised in the PA 

and summarized in the proposal on the 

appropriateness of considering a 3-year 

average index. The Administrator notes 

the PA consideration of the potential for 

multiple consecutive years of critical O3

exposures to result in larger impacts on 

forested areas than intermittent 

occurrences of such exposures due to 

the potential for compounding effects 

on tree growth. The Administrator 

additionally notes the evidence, as 

considered in the PA and summarized 

in the proposal, for some perennial 

species of some effects associated with 

a single year’s exposure of a critical 

magnitude that may have the potential 

for some ‘‘carry over’’ of effects on plant 

growth or reproduction in the 

subsequent season. Further, the 

Administrator notes the occurrence of 

visible foliar injury and growth or yield 

loss in annual plants or crops associated 

with exposures of a critical magnitude. 

While the Administrator appreciates 

that the scientific evidence documents 

the effects on vegetation resulting from 

individual growing season exposures of 

specific magnitude, including those that 

can affect the vegetation in subsequent 

years, she is also mindful, both of the 

strengths and limitations of the 

evidence, and of the information on 

which to base her judgments with 

regard to adversity of effects on the 

public welfare. The Administrator also 

recognizes uncertainties associated with 

interpretation of the public welfare 

significance of effects resulting from a 

single-year exposure, and that the 

public welfare significance of effects 

associated with multiple years of critical 

exposures are potentially greater than 

those associated with a single year of 

such exposure. 

As she did for the proposal, the 

Administrator has considered advice 

from CASAC in this area, including the 

CASAC comments that it favors a W126- 

based secondary standard with a single 

year form, that its recommended range 

of levels relates to such a form, and that 

a lower range (e.g., with 13 ppm-hrs at 

the upper end) would pertain to a 3-year 

form. The Administrator also notes 

CASAC’s recognition that her decision 

on use of a 3-year average over a singleyear W126 index may be a matter of 

policy. While recognizing the potential 

for effects on vegetation associated with 

a single-year exposure, the 

Administrator concludes that use of a 3- 

year average metric can address the 

potential for adverse effects to public 

welfare that may relate to shorter 

exposure periods, including a single 

year. 

While the Administrator recognizes 

the scientific information and 

interpretations, as well as CASAC 

advice, with regard to a single-year 

exposure index, she also takes note of 

uncertainties associated with judging 

the degree of vegetation impacts for 

annual effects that would be adverse to 

public welfare. Even in the case of 

annual crops, the assessment of public 

welfare significance is unclear for the 

reasons discussed below related to 

agricultural practices. The 

Administrator is also mindful of the 

variability in ambient air O3

concentrations from year to year, as well 

as year-to-year variability in 

environmental factors, including rainfall 

and other meteorological factors, that 

influence the occurrence and magnitude 

of O3-related effects in any year, and 

contribute uncertainties to 

interpretation of the potential for harm 

to public welfare over the longer term. 

As noted above, the Administrator also 

recognizes that the public welfare 

significance of effects associated with 

multiple years of critical exposures are 

potentially greater than those associated 

with a single year of such exposure. 

Based on all of these considerations, the 

Administrator recognizes greater 

confidence in judgments related to 

public welfare impacts based on a 3- 

year average metric. Accordingly, the 

considerations identified here lead the 

Administrator to conclude it is 

appropriate to use an index averaged 

across three years for judging public 

welfare protection afforded by a revised 

secondary standard. 

In reaching a conclusion on the 

amount of public welfare protection 

from the presence of O3 in ambient air 

that is appropriate to be afforded by a 

revised secondary standard, the 

Administrator has given particular 

consideration to the following: (1) The 

nature and degree of effects of O3 on 

vegetation, including her judgments as 

to what constitutes an adverse effect to 

the public welfare; (2) the strengths and 

limitations of the available and relevant 

information; (3) comments from the 

public on the Administrator’s proposed 

decision, including comments related to 

identification of a target level of 

protection; and (4) CASAC’s views 

regarding the strength of the evidence 

and its adequacy to inform judgments 

on public welfare protection. The 

Administrator recognizes that such 

judgments include judgments about the 

interpretation of the evidence and other 

information, such as the quantitative 

analyses of air quality monitoring, 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65405 

exposure and risk. She also recognizes 

that such judgments should neither 

overstate nor understate the strengths 

and limitations of the evidence and 

information nor the appropriate 

inferences to be drawn as to risks to 

public welfare. The CAA does not 

require that a secondary standard be 

protective of all effects associated with 

a pollutant in the ambient air but rather 

those known or anticipated effects 

judged adverse to the public welfare (as 

described in section IV.A.3 above). The 

Administrator additionally recognizes 

that the choice of the appropriate level 

of protection is a public welfare policy 

judgment entrusted to the Administrator 

under the CAA taking into account both 

the available evidence and the 

uncertainties. 

The Administrator finds the 

coherence and strength of the weight of 

evidence concerning effects on 

vegetation from the large body of 

available literature compelling. The 

currently available evidence addresses a 

broad array of O3-induced effects on a 

variety of tree species across a range of 

growth stages (i.e., seedlings, saplings 

and mature trees) using diverse fieldbased (e.g., free air, gradient and 

ambient) and OTC exposure methods. 

The Administrator gives particular 

attention to the effects related to native 

tree growth and productivity, 

recognizing their relationship to a range 

of ecosystem services, including forest 

and forest community composition. She 

is also mindful of the significance of 

community composition changes, 

particularly in protected areas, such as 

Class I areas. At the same time, she 

recognizes, while the evidence strongly 

supports conclusions regarding O3

impacts on growth and the evidence 

showing effects on tree seedlings, as 

well as on older trees, there are 

limitations in our ability to predict 

impacts in the environment or to 

estimate air quality or exposures that 

will avoid such impacts. Such 

limitations relate to the variability of 

environmental factors or characteristics 

that can influence the extent of O3

effects. 

In recognition of the CASAC advice 

and the potential for adverse public 

welfare effects, the Administrator has 

considered the nature and degree of 

effects of O3 on the public welfare. In so 

doing, the Administrator recognizes that 

the significance to the public welfare of 

O3-induced effects on sensitive 

vegetation growing within the U.S. can 

vary, depending on the nature of the 

effect, the intended use of the sensitive 

plants or ecosystems, and the types of 

environments in which the sensitive 

vegetation and ecosystems are located. 

Any given O3-related effect on 

vegetation and ecosystems (e.g., biomass 

loss, visible foliar injury), therefore, may 

be judged to have a different degree of 

impact on the public depending, for 

example, on whether that effect occurs 

in a Class I area, a residential or 

commercial setting, or elsewhere. The 

Administrator notes that such a 

distinction is supported by CASAC 

advice in this review. In her judgment, 

like those of the Administrator in the 

last review, it is appropriate that this 

variation in the significance of O3- 

related vegetation effects should be 

taken into consideration in making 

judgments with regard to the level of 

ambient O3 concentrations that is 

requisite to protect the public welfare 

from any known or anticipated adverse 

effects. As a result, the Administrator 

concludes that of those known and 

anticipated O3-related vegetation and 

ecosystem effects identified and 

discussed in this notice, particular 

significance should be ascribed to those 

that may occur on sensitive species that 

are known to or are likely to occur in 

federally protected areas such as Class 

I areas or on lands set aside by states, 

tribes and public interest groups to 

provide similar benefits to the public 

welfare, for residents on those lands, as 

well as visitors to those areas. 

Likewise, the Administrator also 

notes that less protection related to 

growth effects may be called for in the 

case of other types of vegetation or 

vegetation associated with other uses or 

services. For example, the maintenance 

of adequate agricultural crop yields is 

extremely important to the public 

welfare and currently involves the 

application of intensive management 

practices. With respect to commercial 

production of commodities, the 

Administrator notes that judgments 

about the extent to which O3-related 

effects on commercially managed 

vegetation are adverse from a public 

welfare perspective are particularly 

difficult to reach, given that the 

extensive management of such 

vegetation (which, as CASAC noted, 

may reduce yield variability) may also 

to some degree mitigate potential O3- 

related effects. The management 

practices used on these lands are highly 

variable and are designed to achieve 

optimal yields, taking into consideration 

various environmental conditions. In 

addition, changes in yield of 

commercial crops and commercial 

commodities, such as timber, may affect 

producers and consumers differently, 

further complicating the question of 

assessing overall public welfare 

impacts. Thus, the Administrator 

concludes, while research on 

agricultural crop species remains useful 

in illuminating mechanisms of action 

and physiological processes, 

information from this sector on O3- 

induced effects is considered less useful 

in informing judgments on what specific 

standard would provide the appropriate 

public welfare protection. In so doing, 

the Administrator notes that a standard 

revised to increase protection for 

forested ecosystems would also be 

expected to provide some increased 

protection for agricultural crops and 

other commercial commodities, such as 

timber. 

The Administrator also recognizes 

that O3-related effects on sensitive 

vegetation can occur in other areas that 

have not been afforded special federal or 

other protections, including effects on 

vegetation growing in managed city 

parks and residential or commercial 

settings, such as ornamentals used in 

urban/suburban landscaping or 

vegetation grown in land use categories 

involving commercial production of 

commodities, such as timber. For 

vegetation used for residential or 

commercial ornamental purposes, the 

Administrator believes that there is not 

adequate information at this time to 

establish a secondary standard based 

specifically on impairment of these 

categories of vegetation, but notes that a 

secondary standard revised to provide 

protection for sensitive natural 

vegetation and ecosystems would likely 

also provide some degree of protection 

for such vegetation. 

Based on the above considerations, in 

identifying the appropriate level of 

protection for the secondary standard, 

the Administrator finds it appropriate to 

focus on sensitive trees and other native 

species known or anticipated to occur in 

protected areas such as Class I areas or 

on other lands set aside by the Congress, 

states, tribes and public interest groups 

to provide similar benefits to the public 

welfare, for residents on those lands, as 

well as visitors to those areas. In light 

of their public welfare significance, the 

Administrator gives particular weight to 

protecting such vegetation and 

ecosystems. Given the reasons for the 

special protection afforded such areas 

(identified in section I.A.3 above), she 

recognizes the importance of protecting 

these natural forests from O3-induced 

impacts, including those related to O3

effects on growth, and including those 

extending in scale from individual 

plants to the ecosystem. The 

Administrator also recognizes that the 

impacts identified for O3 range from 

those for which the public welfare 

significance may be more easily judged, 

but for which quantitative relationships 

mstockstill on DSK4VPTVN1PROD with RULES2

65406 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

212As summarized in IV.C.2 above (and noted in 

section IV.E.3 of the proposal), revisions to this 

table in the final PA, made in consideration of other 

CASAC comments, have resulted in changes to the 

median species RBL estimates such that the median 

species RBL estimate for a W126 index value of 17 

ppm-hrs in this table in the final PA (5.3%) is 

nearly identical to the median species estimate for 

15 ppm-hrs (the value corresponding to the upper 

end of the CASAC-identified range) in the second 

draft PA (5.2%), the review of which was the 

context for CASAC’s advice on this point (Frey, 

2014c). The median RBL estimate ranges from 5.3% 

to 3.8% across the range of W126 exposures (17 

ppm-hrs to 13 ppm-hrs) that the Administrator 

proposed to conclude would provide the 

appropriate public welfare protection for a revised 

secondary standard. 

with O3 in ambient air are less well 

established, such as impacts on forest 

community composition in protected 

wilderness areas, carbon storage and 

other important ecosystem services, to 

specific plant-level effects, such as 

growth impacts (in terms of RBL) in tree 

seedlings, for which our quantitative 

estimates are more robust. 

For considering the appropriate 

public welfare protection objective for a 

revised standard, the Administrator 

finds appropriate and useful the 

estimates of tree seedling growth 

impacts (in terms of RBL) associated 

with a range of W126-based index 

values developed from the robust E–R 

functions for 11 tree species, that were 

described in the PA and proposal and 

are summarized in Table 4 above. In 

making judgments based on those 

observations, however, the 

Administrator has considered the 

broader evidence base and public 

welfare implications, including 

associated strengths, limitations and 

uncertainties. Thus, in drawing on 

estimates from this table, she is not 

making judgments simply about a 

specific magnitude of growth effect in 

seedlings that would be acceptable or 

unacceptable in the natural 

environment. Rather, the Administrator 

is using the estimates in the table, as 

suggested by CASAC and emphasized 

by some commenters, as a surrogate or 

proxy for consideration of the broader 

array of vegetation-related effects of 

potential public welfare significance, 

that include effects on growth of 

individual sensitive species and extend 

to ecosystem-level effects, such as 

community composition in natural 

forests, particularly in protected public 

lands, as well as forest productivity. In 

so doing, she notes that CASAC 

similarly viewed biomass loss as ‘‘a 

scientifically valid surrogate of a variety 

of adverse effects to public welfare’’ 

(Frey, 2014c, p. 10). Thus, in 

considering the appropriate level of 

public welfare protection for the revised 

standard, the Administrator gives 

primary attention to the relationship 

between W126 exposures and estimates 

of RBL in tree seedlings in Table 4, 

finding this to be a useful quantitative 

tool to inform her judgments in this 

matter. 

In considering the RBL estimates in 

Table 4 above (drawn from the final 

PA), the Administrator takes note of 

comments from CASAC that also give 

weight to these relationships in 

formulating its advice and notes the 

CASAC comments on specific RBL 

values (Frey, 2014c). In so doing, she 

considers and contrasts comments and 

their context on RBL estimates of 2% 

and 6% for the median studied species. 

With regard to the CASAC advice 

regarding 2% RBL for the median 

studied tree species, the Administrator 

notes, as an initial matter, the unclear 

basis for such a focus, as described in 

section IV.C.2 above and in the 

proposal. Further, she notes that the 

CASAC advice related to this RBL value 

was that it would be appropriate for the 

range of levels identified in the PA for 

the Administrator’s consideration to 

‘‘include[] levels that aim for not greater 

than 2% RBL for the median tree 

species’’ (Frey, 2014c, p. 14). As 

described in the proposal, the range 

identified in the PA, which the 

Administrator considered, extended 

down to W126 index levels for which 

the estimated RBL in the median tree 

species is less than or equal to 2%, 

consistent with the CASAC advice. In 

addition, the Administrator notes that 

only the lowest portion of this range (7– 

8 ppm-hrs) corresponds to an estimated 

RBL for the median tree species of less 

than or equal to 2%, with the remainder 

of CASAC’s range (up to 15 ppm-hrs) 

associated with higher median RBL 

estimates. Thus, the Administrator 

understands CASAC to have identified 

2% RBL for the median tree species as 

a benchmark falling within, and at one 

end of, the range of levels of protection 

that the CASAC considers appropriate 

for the revised standard to provide. 

However, the fact that the CASAC range 

included levels for which the RBL 

estimates were appreciably greater than 

2% indicates that CASAC did not judge 

it necessary that the revised standard be 

based on the 2% RBL benchmark. 

Accordingly, the Administrator 

proposed revisions to the secondary 

standard based on options related to 

higher RBL estimates and associated 

exposures. After also considering public 

comments, the Administrator continues 

to consider the uncertainty regarding 

the extent to which associated effects on 

vegetation at lower O3 exposures would 

be adverse to public welfare to be too 

great to provide a foundation for public 

welfare protection objectives for a 

revised secondary standard. 

With regard to the CASAC comments 

on a 6% RBL estimate, the 

Administrator takes particular note of 

their characterization of this level of 

effect in the median studied species as 

‘‘unacceptably high’’ (Frey, 2014c, pp. 

iii, 13, 14). These comments were 

provided in the context of CASAC’s 

considering the significance of effects 

associated with a range of alternatives 

for the secondary standard. Moreover, 

the range recommended by CASAC 

excluded W126 index values for which 

the median species was estimated to 

have a 6% RBL,212 based on the 

information before CASAC at the time 

(Frey, 2014c, p. 12–13). Accordingly, 

the EPA interprets these comments 

regarding 6% RBL to be of a different 

nature than the CASAC advice regarding 

a 2% median RBL, both because these 

two comments are framed to address 

different questions and because CASAC 

treated them differently in its 

recommended range. 

In the Administrator’s consideration 

of the RBL estimates to inform 

judgments on O3 exposures of concern 

to public welfare and the appropriate 

protection that the secondary standard 

should provide from such exposures, 

she has given particular consideration to 

the current evidence for the relationship 

of reduced growth of sensitive tree 

species with ecosystem effects (as 

described in the ISA), CASAC’s view of 

6% RBL for the median studied species 

as unacceptably high, and the role of the 

Administrator’s judgments regarding 

public welfare impacts of effects in 

specially protected natural systems, 

such as Class I areas. With regard to a 

point of focus among the median RBL 

estimates extending below 6% for 

purposes of judging the appropriate 

public welfare protection objectives for 

a revised secondary standard, the 

Administrator is mindful of the CASAC 

advice to consider lower levels if using 

a 3-year average, rather than annual, 

W126 index value. 

In considering the CASAC advice, the 

Administrator notes that her judgments 

on a 3-year average index focus on the 

level of confidence in conclusions that 

might be drawn with regard to single as 

compared to multiple year impacts, as 

described above. For example, the 

Administrator, while recognizing the 

strength of the evidence with regard to 

quantitative characterization of O3

effects on growth of tree seedlings and 

crops, and in addition to noting the 

additional difficulties for assessing the 

welfare impacts of O3 on crops, takes 

note of the uncertainty associated with 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65407 

drawing conclusions with regard to the 

extent to which small percent 

reductions in annual growth contribute 

to adverse effects on public welfare and 

the role of annual variability in 

environmental factors that affect plant 

responses to O3. Moreover, as explained 

above, the Administrator concludes that 

concerns related to the possibility of a 

single unusually damaging year, 

inclusive of those described by the 

CASAC, can be addressed through use 

of a 3-year average metric. Thus, similar 

to the CASAC’s view that a lower level 

would be appropriate with a 3-year 

form, the Administrator considers it 

appropriate to focus on a standard that 

would generally limit cumulative 

exposures to those for which the median 

RBL estimate would be somewhat lower 

than 6%. 

In focusing on cumulative exposures 

associated with a median RBL estimate 

somewhat below 6%, the Administrator 

considers the relationships in Table 4, 

noting that the median RBL estimate is 

6% for a cumulative seasonal W126 

exposure index of 19 ppm-hrs. 

Considering somewhat lower values, the 

median RBL estimate is 5.7% (which 

rounds to 6%) for a cumulative seasonal 

W126 exposure index of 18 ppm-hrs 

and the median RBL estimate is 5.3% 

(which rounds to 5%) for 17 ppm-hrs. 

In light of her decision that it is 

appropriate to use a 3-year cumulative 

exposure index for assessing vegetation 

effects (described above), the potential 

for single-season effects of concern, and 

CASAC comments on the 

appropriateness of a lower value for a 3- 

year average W126 index, the 

Administrator concludes it is 

appropriate to identify a standard that 

would restrict cumulative seasonal 

exposures to 17 ppm-hrs or lower, in 

terms of a 3-year W126 index, in nearly 

all instances. In reaching this 

conclusion, based on the current 

information to inform consideration of 

vegetation effects and their potential 

adversity to public welfare, she 

additionally judges that the RBL 

estimates associated with marginally 

higher exposures in isolated, rare 

instances are not indicative of effects 

that would be adverse to the public 

welfare, particularly in light of 

variability in the array of environmental 

factors that can influence O3 effects in 

different systems and uncertainties 

associated with estimates of effects 

associated with this magnitude of 

cumulative exposure in the natural 

environment. 

While giving primary consideration to 

growth effects using the surrogate of 

RBL estimates based on tree seedling 

effects, the Administrator also 

recognizes the longstanding and robust 

evidence of O3 effects on crop yield. She 

takes note of CASAC concurrence with 

the PA description of such effects as of 

public welfare significance and agrees. 

As recognized in the proposal, the 

maintenance of adequate agricultural 

crop yields is extremely important to 

the public welfare. Accordingly, 

research on agricultural crop species 

remains important for further 

illumination of mechanisms of action 

and physiological processes. Given that 

the extensive management of such 

vegetation, which as CASAC noted may 

reduce yield variability, may also to 

some degree mitigate potential O3- 

related effects, however, judgments 

about the extent to which O3-related 

effects on crop yields are adverse from 

a public welfare perspective are 

particularly difficult to reach. Further, 

management practices for agricultural 

crops are highly variable and generally 

designed to achieve optimal yields, 

taking into consideration various 

environmental conditions. As a result of 

this extensive role of management in 

optimizing crop yield, the 

Administrator notes the potential for 

greater uncertainty with regard to 

estimating the impacts of O3 exposure 

on agricultural crop production than 

that associated with O3 impacts on 

vegetation in natural forests. For all of 

these reasons, the Administrator is not 

giving the same weight to CASAC’s 

statement regarding crop yield loss as a 

surrogate for adverse effects on public 

welfare, or the magnitude that would 

represent an adverse impact to public 

welfare, as to the CASAC’s comments 

on RBL as a surrogate for an array of 

growth-related effects. Similarly, given 

the considerations summarized above 

and in the proposal, the Administrator 

concludes that agricultural crops do not 

have the same need for additional 

protection from the NAAQS as forested 

ecosystems and finds protection of 

public welfare from crop yield impacts 

to be a less important consideration in 

this review for the reasons identified, 

including the extensive management of 

crop yields and the dynamics of 

agricultural markets. Thus, the 

Administrator is not giving a primary 

focus to crop yield loss in selecting a 

revised secondary standard. She notes, 

however, that a standard revised to 

increase protection for forested 

ecosystems would also be expected to 

provide some increased protection for 

agricultural crops. 

The Administrator has additionally 

considered the evidence and analyses of 

visible foliar injury. In so doing, the 

Administrator notes the ISA conclusion 

that ‘‘[e]xperimental evidence has 

clearly established a consistent 

association of visible injury with O3

exposure, with greater exposure often 

resulting in greater and more prevalent 

injury’’ (U.S. EPA, 2013, section 9.4.2, 

p. 9–41). The Administrator also 

recognizes the potential for this effect to 

affect the public welfare in the context 

of affecting values pertaining to natural 

forests, particularly those afforded 

special government protection, as 

discussed in section IV.A.3 above. 

However, she recognizes significant 

challenges in judging the specific extent 

and severity at which such effects 

should be considered adverse to public 

welfare, in light of the variability in the 

occurrence of visible foliar injury and 

the lack of clear quantitative 

relationships with other effects on 

vegetation, as well as the lack of 

established criteria or objectives that 

might inform consideration of potential 

public welfare impacts related to this 

vegetation effect. 

Further, the Administrator takes note 

of the range of evidence on visible foliar 

injury and the various related analyses, 

including additional observations 

drawn from the WREA biosite dataset in 

response to comments, as summarized 

in section IV.C.2 above. In so doing, she 

does not agree with CASAC’s comment 

that a level of W126 exposure below 10 

ppm-hrs is required to reduce foliar 

injury, noting some lack of clarity in the 

WREA and PA presentations of the 

WREA cumulative proportion analysis 

findings and their meaning (described 

in section IV.C.2.b above). She notes 

that the additional observations 

summarized in section IV.C.2 above 

indicate declines in proportions of sites 

with any visible foliar injury and biosite 

index scores with reductions in 

cumulative W126 exposure across a 

range of values extending at the high 

end well above 20 ppm-hrs, down past 

and including 17 ppm-hrs. In 

considering this information, however, 

the Administrator takes note of the 

current lack of robust exposure-response 

functions that would allow prediction of 

visible foliar injury severity and 

incidence under varying air quality and 

environmental conditions, as recognized 

in section IV.A.1.b above. Thus, while 

the Administrator notes that the 

evidence is not conducive to use for 

identification of a specific quantitative 

public welfare protection objective, due 

to uncertainties and complexities 

described in sections IV.A.1.b and 

IV.A.3 above, she concludes that her 

judgments above, reached with a focus 

on RBL estimates, would also be 

expected to provide an additional 

mstockstill on DSK4VPTVN1PROD with RULES2

65408 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

desirable degree of protection against 

visible foliar injury in sensitive 

vegetation. Accordingly, she considers a 

conclusion on the appropriateness of 

selecting a standard that will generally 

limit cumulative exposures above 17 

ppm-hrs to be additionally supported by 

evidence for visible foliar injury, while 

not based on specific consideration of 

this effect. 

With the public welfare protection 

objectives identified above in mind, the 

Administrator turns to her consideration 

of form and level for the revised 

secondary standard. In considering 

whether the current form should be 

retained or revised in order to provide 

the appropriate degree of public welfare 

protection, the Administrator has 

considered the analyses of air quality 

data from the last 13 years that describe 

the cumulative exposures, in terms of a 

3-year W126 index, occurring at 

monitoring sites across the U.S. when 

the air quality metric at that location, in 

terms of the current standard’s form and 

averaging time, is at or below different 

alternative levels. The Administrator 

notes both the conclusions drawn from 

analyses of the strong, positive 

relationship between these metrics and 

the findings that indicate the amount of 

control provided by the fourth-high 

metric. 

The Administrator has also 

considered advice from CASAC and 

public commenters that support 

revision of the form to the W126 

exposure index. The Administrator 

concurs with the underlying premise 

that O3 effects on vegetation are most 

directly assessed using a cumulative 

seasonal exposure index, specifically 

the W126 exposure index. The 

Administrator additionally recognizes, 

based on analyses of the last 13 years of 

monitoring data, and consideration of 

modeling analyses with associated 

limitations and uncertainties, that 

cumulative seasonal exposures appear 

to have a strong relationship with 

design values based on the current form 

and averaging time. She additionally 

notes the correlation of reductions in 

W126 index values with reductions in 

precursor emissions over the past 

decade that were targeted at meeting the 

current O3 standards (with fourth-high 

form), which indicate the control of 

cumulative seasonal exposures that can 

be achieved with a standard of the 

current form and averaging time. 

With regard to recommendations from 

the CASAC that the form for the revised 

secondary standard should be the 

biologically relevant exposure metric, 

and related comments from the public 

indicating that the secondary standard 

must have such a form, the 

Administrator disagrees. In so doing, 

she notes that CAA section 109 does not 

impose such a requirement on the form 

or averaging time for the NAAQS, as 

explained in IV.C.2 above. She further 

notes that the averaging time and form 

of primary standards are often not the 

same as the exposure metrics used in 

reviews of primary standards, in which 

specific information on quantitative 

relationships between different 

exposure metrics and health risk is more 

often available than it is in reviews of 

secondary NAAQS. As discussed in 

section IV.C.2 above, with examples, a 

primary standard with a particular 

averaging time and form may provide 

the requisite public health protection 

from health effects that are most 

appropriately assessed using an 

exposure metric of a different averaging 

time and form and indicator, and the 

same principle can apply when 

establishing or revising secondary 

standards. The Administrator recognizes 

that the exposure metric and the 

standard metric can be quite similar, as 

in the case of consideration of shortterm health effects with the primary O3

standard. She also notes, however, as 

illustrated by the examples described in 

section IV.C.2 above, that it is not 

uncommon for the EPA to retain or 

adopt elements of an existing standard 

that the Administrator judges in 

combination across all elements, 

including in some cases a revised level, 

to provide the requisite protection 

under the Act, even if those elements do 

not neatly correspond to the exposure 

metric. Accordingly, she concludes that 

the Act does not require that the 

secondary O3 standard be revised to 

match the exposure metric identified as 

biologically relevant in this review, as 

long as the revised standard provides 

the degree of protection required under 

CAA section 109(b)(2). 

Based on the considerations described 

here, including the use of an exposure 

metric that CASAC has agreed to be 

biologically relevant and appropriate, 

related considerations summarized in 

the proposal with regard to air quality 

analyses and common uses of exposure 

metrics in other NAAQS reviews, the 

Administrator finds that, in 

combination with a revised level, the 

current form and averaging time for a 

revised secondary standard can be 

expected to provide the desired level of 

public welfare protection. Accordingly, 

she next turns to the important 

consideration of a level that, in 

combination with the form and 

averaging time, will yield a standard 

that specifies the requisite air quality for 

protection of public welfare. In so 

doing, she has recognized the 

recommendation by CASAC for revision 

of the form and averaging time and 

provided the basis for her alternative 

view, as described above. Further, in the 

context of the Administrator’s decision 

on objectives for public welfare 

protection of a revised secondary 

standard, and with consideration of the 

advice from CASAC on levels for a 

W126-based standard, the Administrator 

has also reached the conclusion, as 

described above, that in order to provide 

the appropriate degree of public welfare 

protection, the revised secondary 

standard should restrict cumulative 

seasonal exposures to 17 ppm-hrs or 

lower, in terms of a 3-year average W126 

index, in nearly all instances. Thus, the 

Administrator finds it appropriate to 

revise the standard level to one that, in 

combination with the form and 

averaging time, will exert this desired 

degree of control for cumulative 

seasonal exposures. 

In considering a revised standard 

level, the Administrator has, in light of 

public comments, revisited the 

information she considered in reaching 

her proposed decision on a level within 

the range of 65 to 70 ppb, and additional 

information or insights conveyed with 

public comments. The primary focus of 

the Administrator’s considerations in 

reaching her proposed decision was the 

multi-faceted analysis of air quality data 

from 2001 through 2013 documented in 

the technical memo in the docket 

(Wells, 2014a), as well as the earlier 

analyses and related information 

described in the PA (as summarized in 

section IV.E.4 of the proposal). This 

analysis describes the occurrences of 3- 

year W126 index values of a magnitude 

from 17 ppm-hrs through 7 ppm-hrs at 

monitor locations where O3

concentrations met different alternative 

standards with the current form and 

averaging time, and has been expanded 

in consideration of public comments to 

present in summary form the more 

extensive historical dataset 

accompanying this analysis (Wells, 

2015b). Focusing first on the air quality 

analyses for the most recent period for 

which data are available (2011–2013) 

and with the protection objectives 

identified above in mind, the 

Administrator observes that across the 

sites meeting the current standard of 75 

ppb, the analysis finds 25 sites 

distributed across different NOAA 

climatic regions with 3-year average 

W126 index values above 17 ppm-hrs, 

with the values at nearly half of the sites 

extending above 19 ppm-hrs, with some 

well above. In comparison, she observes 

that across sites meeting an alternative 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65409 

standard of 70 ppb, the analysis for the 

period from 2011–2013 finds no 

occurrences of W126 metric values 

above 17 ppm-hrs and less than a 

handful of occurrences that equal 17 

ppm-hrs. The more than 500 monitors 

that would meet an alternative standard 

of 70 ppb during the 2011–2013 period 

are distributed across all nine NOAA 

climatic regions and 46 of the 50 states 

(Wells, 2015b and associated dataset in 

the docket). 

The Administrator notes that some 

public commenters, who disagreed with 

her proposed decision on form and 

averaging time, emphasized past 

occurrences of cumulative W126 

exposure values above the range 

identified in the proposal (of 13 to 17 

ppm-hrs). For example, these 

commenters emphasize data from 

farther back across the full time period 

of the dataset analyzed in the technical 

memorandum (2001–2013), identifying 

a value of 19.1 ppm-hrs at a monitor for 

which the fourth-high metric is 70 ppb 

for the 3-year period of 2006–2008. The 

Administrator notes, as discussed in 

section IV.C.2 above, that this was one 

of fewer than a handful of isolated 

occurrences of sites for which the 

fourth-high was at or below 70 ppb and 

the W126 index value was above 17 

ppm-hrs, all but one of which were 

below 19 ppm-hrs. The Administrator 

additionally recognizes her underlying 

objective of a revised secondary 

standard that would limit cumulative 

exposures in nearly all instances to 

those for which the median RBL 

estimate would be somewhat lower than 

6%. She observes that the single 

occurrence of 19 ppm-hrs identified by 

the commenter among the nearly 4000 

3-year W126 index values from across 

the most recently available 11 3-year 

periods of data at monitors for which 

the fourth-high metric is at or below 70 

ppb is reasonably regarded as an 

extremely rare and isolated occurrence 

(Wells, 2015b). As such, it is unclear 

whether it would recur, particularly as 

areas take further steps to reduce O3 to 

meet revised primary and secondary 

standards. Further, based on the 

currently available information, the 

Administrator does not judge RBL 

estimates associated with marginally 

higher exposures in isolated, rare 

instances to be indicative of adverse 

effects to the public welfare. Thus, the 

Administrator concludes that a standard 

with a level of 70 ppb and the current 

form and averaging time may be 

expected to limit cumulative exposures, 

in terms of a 3-year average W126 

exposure index, to values at or below 17 

ppm-hrs, in nearly all instances, and 

accordingly, to eliminate or virtually 

eliminate cumulative exposures 

associated with a median RBL of 6% or 

greater. 

The Administrator recognizes that any 

standard intended to exert a very high 

degree of control on cumulative 

seasonal exposures, with the objective 

of limiting exposures above 17 ppm-hrs 

across the U.S., in nearly all instances, 

will, due to regional variation in 

meteorology and sources of O3

precursors, result in cumulative 

seasonal exposures well below 17 ppmhrs in many areas. Even implementation 

of a standard set in terms of the 

cumulative seasonal exposure metric, 

while limiting the highest exposures, 

would, due to regional variation in 

meteorology and sources of O3

precursors, result in many areas with 

much lower exposures. Such variation 

in exposures occurring under a specific 

standard is not unexpected and the 

overall distribution of exposures 

estimated to occur with air quality 

conditions associated with different 

alternative standards is a routine part of 

the consideration of public health 

protection in reviews of primary 

standards, and can also play a role in 

the review of secondary standards. For 

these reasons, and in light of the 

discussion in section IV.C.2.d above on 

consideration of ‘‘necessary’’ protection, 

the Administrator notes that an 

expectation of differing exposures is 

not, in itself, a basis for concluding that 

the air quality would be more (or less) 

than necessary (and thus not requisite) 

for the desired level of public welfare 

protection. 

The Administrator has also 

considered the protection afforded by a 

revised standard against other effects 

studied in this review, such as visible 

foliar injury and reduced yield for 

agricultural crops, and also including 

those associated with climate change. 

While noting the evidence supporting a 

relationship of O3 in ambient air with 

climate forcing effects, as concluded in 

the ISA, the Administrator judges the 

quantitative uncertainties to be too great 

to support identification of a standard 

specific to such effects such that she 

concludes it is more important to focus, 

as she has done above, on setting a 

standard based on providing protection 

against vegetation-related effects which 

would be expected to also have positive 

implications for climate change 

protection through the protection of 

ecosystem carbon storage. 

The Administrator additionally 

considers the extent of control for 

cumulative seasonal exposures exerted 

by a revised standard level of 65 ppb, 

the lower end of the proposed range. In 

focusing on the air quality analyses for 

the most recent 3-year period for which 

data are available, the Administrator 

observes that across the sites meeting a 

fourth-high metric of 65 ppb, the 

analysis finds no occurrences of W126 

metric values above 11 ppm-hrs and 35 

occurrences of a value between 7 ppmhrs and 11 ppm-hrs, scattered across 

NOAA climatic regions. The 

Administrator finds these magnitudes of 

cumulative seasonal exposures to 

extend appreciably below the objectives 

she identified above for affording public 

welfare protection. In considering this 

alternative level, she additionally notes 

that data for only 276 monitors (less 

than 25 percent of the total with valid 

fourth-high and W126 metric values) 

were at or below a fourth-high value of 

65 ppb during the period from 2011– 

2013. In so noting, she recognizes the 

appreciably smaller and less 

geographically extensive dataset 

available and the associated uncertainty 

for conclusions based on such an 

analysis. 

Thus, based on the support provided 

by currently available information on air 

quality, the evidence base of O3 effects 

on vegetation and her public welfare 

policy judgments, and after carefully 

taking the above comments and 

considerations into account, fully 

considering the scientific views of the 

CASAC, and also taking note of 

CASAC’s policy views, the 

Administrator has decided to retain the 

current indicator, form and averaging 

time and to revise the secondary 

standard level to 70 ppb. In the 

Administrator’s judgment, based on the 

currently available evidence and 

quantitative exposure and air quality 

information, a standard set at this level, 

in combination with the currently 

specified form, averaging time and 

indicator would be requisite to protect 

the public welfare from known or 

anticipated adverse effects. A standard 

set at this level provides an appreciable 

increase in protection compared to the 

current standard. The Administrator 

judges that such a standard would 

protect natural forests in Class I and 

other similarly protected areas against 

an array of adverse vegetation effects, 

most notably including those related to 

effects on growth and productivity in 

sensitive tree species. The 

Administrator believes that a standard 

set at 70 ppb would be sufficient to 

protect public welfare from known or 

anticipated adverse effects and believes 

that a lower standard would be more 

than what is necessary to provide such 

protection. This judgment by the 

Administrator appropriately recognizes 

mstockstill on DSK4VPTVN1PROD with RULES2

65410 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

that the CAA does not require that 

standards be set at a zero-risk level, but 

rather at a level that reduces risk 

sufficiently so as to protect the public 

welfare from known or anticipated 

adverse effects. Accordingly, the 

Administrator concludes that it is 

appropriate to revise the level for the 

secondary standard to 70 ppb (0.070 

ppm), in combination with retaining the 

current form, indicator, and averaging 

time, in order to specify the level of air 

quality that provides the requisite 

protection to the public welfare from 

any known or anticipated adverse 

effects associated with the presence of 

O3 in the ambient air. 

D. Decision on the Secondary Standard 

For the reasons discussed above, and 

taking into account information and 

assessments presented in the ISA and 

PA, the advice and recommendations of 

CASAC, and the public comments, as 

well as public welfare judgments, the 

Administrator is revising the level of the 

current secondary standard. 

Specifically, the Administrator has 

decided to revise the level of the 

secondary standard to a level of 0.070 

ppm, in conjunction with retaining the 

current indicator, averaging time and 

form. Accordingly the revised secondary 

standard is 0.070 ppm O3, as the annual 

fourth-highest daily maximum 8-hour 

average concentration, averaged over 

three years. 

V. Appendix U: Interpretation of the 

Primary and Secondary NAAQS for O3

A. Background 

The EPA is finalizing the proposed 

Appendix U to 40 CFR part 50: 

Interpretation of the Primary and 

Secondary National Ambient Air 

Quality Standards for Ozone. The 

proposed Appendix U addressed the 

selection of ambient O3 monitoring data 

to be used in making comparisons with 

the NAAQS, data reporting and data 

handling conventions for comparing 

ambient O3 monitoring data with the 

level of the NAAQS, and data 

completeness requirements. The EPA 

solicited public comment on four 

elements where the proposed Appendix 

U differed from Appendix P to 40 CFR 

part 50, which addressed data handling 

conventions for the previous O3

NAAQS. These included the following: 

(1) the addition of a procedure to 

combine data collected from two or 

more O3 monitors operating 

simultaneously at the same physical 

location, (2) the addition of a provision 

allowing the Regional Administrator to 

approve ‘‘site combinations’’, or the 

combination of data from two nearby 

monitoring sites for the purpose of 

calculating a valid design value, (3) a 

change from the use of one-half of the 

method detection limit (1⁄2MDL) to zero 

(0.000 ppm) as the substitution value in 

8-hour average data substitution tests, 

and 4) a new procedure for calculating 

daily maximum 8-hour average O3

concentrations for the revised NAAQS. 

The EPA is also finalizing, as 

proposed, exceptional events 

scheduling provisions in 40 CFR 50.14 

that will apply to the submission of 

information supporting claimed 

exceptional events affecting pollutant 

data that are intended to be used in the 

initial area designations for any new or 

revised NAAQS. The new scheduling 

provisions will apply to initial area 

designations for the 2015 O3 NAAQS. 

B. Data Selection Requirements 

The EPA proposed this section in 

Appendix U to clarify which data are to 

be used in comparisons with the revised 

O3 NAAQS. The EPA is finalizing this 

section in Appendix U as proposed. 

First, the EPA proposed to combine 

data at monitoring sites with two or 

more O3 monitoring instruments 

operating simultaneously into a single 

site-level data record for determining 

compliance with the NAAQS, and 

proposed an analytical approach to 

perform this combination (79 FR 75351– 

75352, December 17, 2014). Several 

commenters supported the EPA’s 

proposed approach, including the State 

of Iowa, where 15 of the 20 monitoring 

sites currently operating two O3

monitors simultaneously are located. 

Commenters supporting the proposal 

noted that a similar approach is already 

being used for lead and particulate 

monitoring, and that the proposed 

approach will help states meet data 

completeness requirements. 

A few commenters supported the 

EPA’s proposed approach with the 

additional restrictions that the 

monitoring instruments must use 

identical methods and be operated by 

the same monitoring agency. The EPA 

notes that at the time of this rulemaking, 

all monitors reporting O3 concentration 

data to the EPA for regulatory use were 

FEMs. All current O3 FEMs use an 

ultraviolet photometry sampling 

methodology and have been found to 

meet the performance criteria in 40 CFR 

part 53. Therefore, the EPA has no 

reason to believe that O3 concentration 

data should not be combined across 

monitoring methods at the site level. 

Regarding the commenters’ suggestion 

that data should not be combined when 

two or more monitors at the same site 

are operated by different monitoring 

agencies, the EPA is aware of only one 

instance where this presently occurs. In 

this instance, the monitors have been 

assigned distinct site ID numbers in the 

AQS database, so that data will not be 

combined across these monitors. Should 

future instances arise where two or 

more monitoring agencies decide to 

operate O3 monitors at the same site, the 

EPA encourages these agencies to work 

together to establish a plan for how the 

data collected from these monitors 

should be used in regulatory decision 

making. 

One state objected to combining data 

across monitors because the secondary 

monitors at their sites were used only 

for quality assurance purposes and data 

from these monitors should not be 

combined with data reported from the 

primary monitors. The EPA notes that 

concentration data collected to meet 

quality assurance requirements (i.e. 

precision and bias data) are reported 

and stored in a separate location within 

the AQS database and are not used for 

determining compliance with the 

NAAQS. The required quality assurance 

data are derived from O3 standards and 

not from a separate O3 monitor. 

However, if a separate O3 monitor is 

used strictly for quality assurance 

purposes and does not meet the 

applicable monitoring requirements, it 

can be distinguished in AQS in such a 

manner that data from the secondary 

monitor would not be combined with 

data from the primary monitor. 

Another commenter objected to the 

proposal because it would reduce the 

total number of comparisons made with 

the NAAQS. While this is true, the 

number of physical locations being 

compared with the NAAQS will not 

decrease under the proposed approach, 

and in fact may increase due to 

additional sites meeting the data 

completeness requirements. 

Finally, two commenters submitted 

similar comments citing the EPA’s 

evaluation of collocated O3 monitoring 

data and precision data in the ISA (U.S. 

EPA, 2013, section 3.5.2), and stated 

that although the median differences in 

concentrations reported by the pairs of 

monitoring instruments were near zero, 

the extreme values were close to +/¥ 

3.5%. The commenter argued that since 

the O3 NAAQS are based on the fourthhighest annual value, data should not be 

combined across monitors because of 

the imprecision in the extreme values. 

The EPA disagrees, noting that the data 

presented in the ISA are based on 

hourly concentrations, while design 

values for the O3 NAAQS are based on 

a 3-year average of 8-hour average 

concentrations. Thus, the random 

variability in the hourly O3

concentration data due to monitoring 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65411 

213This procedure will be adopted only for the 

revised O3 NAAQS. Design values for the 1997 8- 

hour O3 NAAQS and the 2008 8-hour O3 NAAQS 

will continue to be calculated according to 

Appendix I and Appendix P of 40 CFR part 50, 

respectively. 

imprecision will be reduced when 

concentrations are averaged for 

comparison with the NAAQS. 

Additionally, the precision data are 

typically collected at concentrations at 

or above the level of the NAAQS, thus 

the EPA expects that the level of 

precision documented in the ISA 

analysis is consistent with the level of 

precision in the fourth-highest daily 

maximum concentrations used for 

determining compliance with the 

NAAQS. 

The EPA is finalizing this addition in 

Appendix U as proposed. In addition, 

the AQS database will be updated to 

require state agencies to designate a 

primary monitor at O3 monitoring sites 

that report data under more than one 

Pollutant Occurrence Code (POC), a 

numeric indicator in AQS used to 

identify individual monitoring 

instruments. O3 design value 

calculations in AQS will be updated so 

that the data will automatically be 

combined across POCs at a site, and a 

single design value will be reported for 

each site. The EPA notes that the 

substitution approach described above 

will only be applied to design value 

calculations for the revised O3

standards, and that design values for 

previous O3 standards will continue to 

be calculated at the monitor level, in 

accordance with the applicable 

appendices of 40 CFR part 50. 

Second, the EPA proposed to add a 

provision in Appendix U that would 

allow the Regional Administrator to 

approve ‘‘site combinations’’, or to 

combine data across two nearby 

monitors for the purpose of calculating 

a valid design value. Although data 

handling appendices for previous O3

standards do not explicitly mention site 

combinations, the EPA has approved 

over 100 site combinations since the 

promulgation of the first 8-hour O3

NAAQS in 1997. Thus, the EPA’s 

intention in proposing this addition was 

merely to codify an existing convention, 

and to improve transparency by 

implementing site combinations in AQS 

design value calculations. 

Public commenters unanimously 

supported this proposed addition. Two 

commenters suggested that the EPA 

should require monitoring agencies to 

provide technical documentation 

supporting the similarities between sites 

approved for combining data, including 

a requirement for simultaneous 

monitoring whenever possible. One 

state requested that the EPA provide 

more detailed acceptability criteria for 

approving site combinations, while 

another state urged the EPA not to 

create a regulatory burden by 

prescribing detailed requirements 

codified in regulations. 

The EPA is finalizing this addition as 

proposed in Appendix U. The EPA 

believes that approval of site 

combinations should be handled on a 

case-by-case basis, and that any requests 

for supporting documentation should be 

left to the discretion of the Regional 

Administrator. The EPA may issue 

future guidance providing general 

criteria for determining an acceptable 

level of similarity in air quality 

concentrations between monitored 

locations, but is not prescribing detailed 

criteria for approval of site 

combinations in this rulemaking. 

Additionally, the AQS database will 

be updated with new fields for 

monitoring agencies to request site 

combinations, and an additional field 

indicating Regional Administrator 

approval. All pre-existing site 

combinations will be initially entered 

into the database as having already been 

approved by the Regional 

Administrator. Since this provision has 

already been used in practice under 

previous O3 standards, site 

combinations will be applied to AQS 

design value calculations for both the 

revised O3 standards and previous O3

standards. 

C. Data Reporting and Data Handling 

Requirements 

First, the EPA proposed a change in 

Appendix U to the pre-existing 8-hour 

average data substitution test (40 CFR 

part 50, Appendix P, section 2.1) which 

is used to determine if a site would have 

had a valid 8-hour average greater than 

the NAAQS when fewer than 6 hourly 

O3 concentration values are available for 

a given 8-hour period. The EPA 

proposed to change the value 

substituted for the missing hourly 

concentrations from one-half of the 

method detection limit of the O3

monitoring instrument (1⁄2MDL) to zero 

(0.000 ppm). 

Several commenters supported the 

proposed change, stating that the use of 

a constant substitution value instead of 

1⁄2 MDL, which can vary across O3

monitoring methods, would simplify 

design value calculations. One 

commenter noted that with a 

substitution value of zero, the data 

substitution test for an 8-hour average 

value greater than the NAAQS is 

equivalent to a sum of hourly O3

concentrations greater than 0.567 ppm 

(i.e., if the sum is 0.568 ppm or higher, 

the resulting 8-hour average must be at 

least 0.071 ppm, which is greater than 

the revised O3 NAAQS of 0.070 ppm). 

Finally, one commenter opposed the 

proposed change in favor of some type 

of mathematical or statistical 

interpolation approach, but did not 

provide a specific recommendation. 

The EPA is finalizing the proposed 

change in Appendix U, with the 

addition of a short clause making note 

of the equivalent summation approach 

described above. The purpose of the 

data substitution test is to identify 8- 

hour periods that do not meet the 

requirements for a valid 8-hour average, 

yet the reported hourly concentration 

values are so high that the NAAQS 

would have been exceeded regardless of 

the magnitude of the missing 

concentration values. The EPA believes 

that zero, being the lowest measured O3

concentration physically possible, is the 

most appropriate value to substitute in 

this situation. Additionally, the EPA 

does not support the use of 

interpolation or other means of filling in 

missing monitoring data for O3 NAAQS 

comparisons. Such an approach would 

be contrary to the EPA’s long-standing 

policy of using only quality-assured and 

certified ambient air quality 

measurement data to determine 

compliance with the O3 NAAQS. 

Second, the EPA proposed a new 

procedure in Appendix U for 

determining daily maximum 8-hour O3

concentrations for the revised 

NAAQS.213 The EPA proposed to 

determine the daily maximum 8-hour 

O3 concentration based on 17 

consecutive moving 8-hour periods in 

each day, beginning with the 8-hour 

period from 7:00 a.m. to 3:00 p.m., and 

ending with the 8-hour period from 

11:00 p.m. to 7:00 a.m. In addition, the 

EPA proposed that a daily maximum 

value would be considered valid if 8- 

hour averages were available for at least 

13 of the 17 consecutive moving 8-hour 

periods, or if the daily maximum value 

was greater than the level of the 

NAAQS. This procedure is designed to 

eliminate ‘‘double counting’’ 

exceedances of the NAAQS based on 

overlapping 8-hour periods from two 

consecutive days with up to 7 hours in 

common, which was allowed under 

previous 8-hour O3 NAAQS. A dozen 

public commenters expressed support 

for the proposed procedure, including 

several states. 

One regional air quality management 

organization and three of its member 

states submitted similar comments 

stating that they agreed with the 

principle of eliminating ‘‘double 

counting’’ exceedances of the NAAQS 

mstockstill on DSK4VPTVN1PROD with RULES2

65412 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

214The EPA intends to consider changes to these 

retained scheduling requirements as part of the 

planned notice and comment rulemaking revisions 

to the 2007 Exceptional Events Rule. 215 Governors may also use 2013 data to formulate 

their recommendations regarding designations. 

based on overlapping 8-hour periods, 

but suggested an alternative calculation 

procedure that would accomplish the 

same objective. The alternative 

procedure iteratively finds the highest 

8-hour period in a given year, then 

removes this 8-hour period and all other 

8-hour periods associated with that day, 

including any overlapping 8-hour 

periods on adjacent days, from the data 

until a daily maximum value is 

determined for each day of the year with 

sufficient monitoring data. The EPA 

examined a similar iterative procedure 

in a previous data analysis supporting 

the proposal (Wells, 2014b, Method 1). 

The EPA compared this procedure to 

the procedure proposed by the 

commenters using the data from the 

original analysis and found the resulting 

daily maximum 8-hour values to be 

nearly identical (Wells, 2015a). 

Additionally, the commenters’ 

procedure suffers from the same 

limitations the EPA identified 

previously in the original analysis: 

added complexity in design value 

calculations, longer computational time, 

and challenges to real-time O3 data 

reporting systems, which would have to 

re-calculate daily maximum 8-hour 

values for the entire year each time the 

system was updated with new data. 

Three states submitted comments 

stating that they agreed with the 

proposed calculation procedure, but 

disagreed with the proposed 

requirements for determining a valid 

daily maximum 8-hour O3

concentration. These states were 

primarily concerned that the proposed 

requirements would only allow a 

monitoring site to have four missing 8- 

hour averages during a day before the 

entire day would be invalidated, 

compared with six missing 8-hour 

averages allowed previously. Two of 

these states also stated concerns that the 

proposed requirements would be more 

difficult to meet while maintaining 

compliance with existing monitoring 

requirements such as biweekly quality 

assurance checks. The EPA compared 

annual data completeness rates 

calculated using the Appendix U 

requirements to annual data 

completeness rates calculated using the 

requirements under the previous O3

standards across all U.S. monitoring 

sites based on data from 2004–2013 

(Wells, 2015a). The national mean 

annual data completeness rate was 0.1% 

higher under the proposed Appendix U 

requirements than under the previous 

O3 standards, and the national median 

annual data completeness rates were 

identical. In addition, the EPA notes 

that the Appendix U requirements allow 

for biweekly quality assurance checks 

and other routine maintenance to be 

performed between 5:00 a.m. and 9:00 

a.m. local time without affecting data 

completeness. Thus, the EPA does not 

believe that the proposed daily data 

completeness requirements in Appendix 

U will be more difficult for monitoring 

agencies to meet. 

Finally, two public commenters 

opposed the proposed procedures for 

determining daily maximum 8-hour 

concentrations. These commenters 

expressed similar concerns, primarily 

that not considering 8-hour periods 

starting midnight to 6:00 a.m. is less 

protective of public health than the 

procedure used to determine daily 

maximum 8-hour concentrations for the 

previous O3 standards. The EPA 

believes that this approach provides the 

appropriate degree of protection for 

public health, noting that the hourly 

concentrations from midnight to 7:00 

a.m. are covered under the 8-hour 

period from 11:00 p.m. to 7:00 a.m., 

which is included in the design value 

calculations proposed in Appendix U. 

At the same time, the proposed 

approach ensures that individual hourly 

concentrations may not contribute to 

multiple exceedances of the NAAQS, 

which the EPA believes is inappropriate 

given that people are only exposed 

once. 

The EPA is finalizing as proposed in 

Appendix U the procedure for 

determining daily maximum 8-hour 

concentrations. The EPA does not 

believe that daily maximum 8-hour 

concentrations for two consecutive days 

should be based on overlapping 8-hour 

periods, since the exposures 

experienced by individuals only occur 

once. The EPA believes that the new 

procedure will avoid this outcome 

while continuing to make use of all 

hourly concentrations in determining 

attainment of the standards, without 

introducing unnecessary complexity 

into design value calculations, and 

without creating additional difficulties 

for monitoring agencies to meet the data 

completeness requirements. 

D. Exceptional Events Information 

Submission Schedule 

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 this section and in more 

detail in the O3 NAAQS proposal, 

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 a new or revised NAAQS is 

promulgated or because the generic 

deadlines require submission of 

documentation at least 12 months prior 

to the date by which the EPA must make 

a regulatory decision, which may be 

before air agencies have collected some 

of the potentially affected data. Specific 

to the revised O3 NAAQS, revisions to 

40 CFR 50.14 are needed because it is 

not possible for air agencies to flag and 

submit documentation for any 

exceptional events that occur in October 

through December of 2016 by 1 year 

before the designations are made in 

October 2017, as is required by the 

existing generic schedule. 

The EPA is finalizing exceptional 

events scheduling provisions in 40 CFR 

50.14, as proposed and as supported by 

multiple commenters, that will apply to 

the submission of information 

supporting claimed exceptional events 

affecting pollutant data that are 

intended to be used in the initial area 

designations for any new or revised 

NAAQS. The new scheduling 

provisions will apply to initial area 

designations for the revised O3 NAAQS. 

The provisions that we are promulgating 

use a ‘‘delta schedule’’ that calculates 

the timelines associated with flagging 

data potentially influenced by 

exceptional events, submitting initial 

event descriptions and submitting 

exceptional events demonstrations 

based on the promulgation date of a new 

or revised NAAQS. The general data 

flagging deadlines in the Exceptional 

Events Rule at 40 CFR 50.14(c)(2)(iii) 

and the general schedule for submission 

of demonstrations at 40 CFR 

50.14(c)(3)(i) continue to apply to data 

used in regulatory decisions other than 

those related to the initial area 

designations process under a new or 

revised NAAQS.214

The EPA acknowledges the concern 

raised by several commenters that a 

strengthened O3 NAAQS may result in 

numerous demonstrations for 

exceptional events occurring between 

2014 and 2016, the data years that the 

EPA will presumably use for initial area 

designation decisions made in October 

2017.215 Commenters noted that the 

proposed schedule is particularly 

burdensome for agencies needing to 

submit exceptional events packages for 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65413 

216See Section VIII.B for additional detail on the 

initial area designations process for the revised O3

NAAQS. 

the third year to be used in a 3-year 

design value (i.e., 2016 data). Several 

commenters recommended that the EPA 

either establish no defined schedule for 

data flagging and exceptional events 

demonstration submittal or allow a 

minimum of 2 years from the setting of 

any new or revised NAAQS for air 

agencies to provide a complete 

exceptional events demonstration. 

Given the CAA requirement that the 

EPA follow a 2-year designations 

schedule, the EPA cannot remove 

submittal schedules entirely for data 

influenced by exceptional events or 

provide a minimum 2-year period from 

the setting of a new or revised NAAQS 

for documentation submittal. Neither of 

these options would ensure that the 

EPA has time to consider eventinfluenced data in initial area 

designation decisions. Rather, the EPA 

is promulgating in this action an 

exceptional events schedule that 

provides air agencies with the 

maximum amount of time available to 

prepare exceptional events 

demonstrations and will still allow the 

EPA sufficient time to consider such 

exceptional events demonstrations in 

the designations process in advance of 

the date by which the EPA must send 

120-day notification letters to states.216

The EPA recognizes that the schedule 

promulgated in this action is 

compressed, particularly for the third 

year of data to be used in a 3-year design 

value, and we will work cooperatively 

with air agencies to accommodate this 

scenario. 

Under the schedule promulgated in 

this action and assuming initial area 

designation decisions in October 2017 

for the revised O3 NAAQS, affected air 

agencies would need to flag data, submit 

initial event descriptions and submit 

demonstrations for exceptional events 

occurring in 2016 by May 31, 2017. This 

schedule provides approximately 5 

months between the EPA’s receipt of the 

demonstration package and the 

expected date of designation decisions 

and approximately 1 month between the 

EPA’s receipt of a package and the date 

by which the EPA must notify states and 

tribes of intended modifications to the 

Governors’ recommendations for 

designations (i.e., 120-day letters). 

While, for the third year of data 

anticipated to be used in a 3-year design 

value for the revised O3 NAAQS, the 

promulgated schedule provides for 

demonstration submission 5 months 

after the end of the calendar year, the 

EPA expects that most submitting 

agencies will have additional time to 

prepare documentation as we expect the 

majority of potential O3-related 

exceptional events to occur during the 

warmer months (e.g., March through 

October). Additionally, the EPA will 

soon propose rule revisions to the 2007 

Exceptional Events Rule and will 

release through a Federal Register 

Notice of Availability a draft guidance 

document to address Exceptional Events 

Rule criteria for wildfires that could 

affect O3 concentrations. We expect to 

promulgate Exceptional Events Rule 

revisions and finalize the new guidance 

document before the October 2016 date 

by which states, and any tribes that 

wish to do so, are required to submit 

their initial designation 

recommendations for the revised O3

NAAQS. Considered together, the EPA 

believes the exceptional events 

scheduling dates promulgated in this 

action, the upcoming Exceptional 

Events Rule revisions, the forthcoming 

guidance, and the existing guidance and 

examples of submitted demonstrations 

currently on the EPA’s exceptional 

events Web site at http://www2.epa.gov/ 

air-quality-analysis/treatment-datainfluenced-exceptional-events, will help 

air agencies submit information in a 

timely manner. 

Applying the ‘‘delta schedule’’ 

promulgated in this action for air 

quality data collected in 2013 through 

2014 that could be influenced by 

exceptional events and be considered 

during the initial area designations 

process for the revised O3 NAAQS, 

results in extending to July 1, 2016, the 

otherwise applicable generic deadlines 

of July 1, 2014, and July 1, 2015, 

respectively, for flagging data and 

providing an initial description of an 

event (40 CFR 50.14(c)(2)(iii)). The 

schedule promulgated in this action also 

results in a July 1, 2016, date for 

flagging data and providing an initial 

description of an event for air quality 

data collected in 2015. The July 1, 2016, 

date for data collected in 2015 is the 

same as that which would apply under 

the existing generic deadline in the 2007 

Exceptional Events Rule. Under the 

schedule promulgated in this action, 

October 1, 2016 is the deadline for 

submitting exceptional events 

demonstrations for data years 2013 

through 2015. As noted previously, 

under the schedule promulgated in this 

action, affected air agencies would need 

to flag, submit initial event descriptions 

and submit demonstrations for 

exceptional events occurring in 2016 by 

May 31, 2017. The EPA believes these 

revisions will provide adequate time for 

air agencies to review potential O3

exceptional events influencing 

compliance with the revised O3

NAAQS, to notify the EPA by flagging 

the relevant data and providing an 

initial event description in AQS, and to 

submit documentation to support 

exceptional events demonstrations. The 

schedule revisions promulgated in this 

action will also allow the EPA to 

consider and act on the submitted 

information during the initial area 

designation process. 

While the EPA will make every effort 

to designate areas for any new or revised 

NAAQS on a 2-year schedule, the EPA 

recognizes that under some 

circumstances we may need up to an 

additional year for the designations 

process to ensure that air agencies and 

the EPA base designations decisions on 

complete and sufficient information. 

The promulgated schedule accounts for 

the possibility that the EPA might 

announce after promulgating a new or 

revised NAAQS that we are extending 

the designations schedule beyond 2 

years using authority provided in CAA 

section 107(d)(B)(i). If the EPA 

determines that we will follow a 3-year 

designation schedule, the deadline is 2 

years and 7 months after promulgation 

of a new or revised NAAQS for states to 

flag data influenced by exceptional 

events, submit initial event descriptions 

and submit exceptional events 

demonstrations for the last year of data 

that will be used in the designations 

(e.g., if the EPA were to designate areas 

in October 2018, the exceptional events 

submittal deadline for 2017 data would 

be May 31, 2018). If the EPA notifies 

states and tribes of a designations 

schedule between 2 and 3 years, the 

deadline for states to flag data affected 

by exceptional events, submit initial 

event descriptions, and submit 

exceptional events demonstrations 

associated with data from the last year 

to be considered would be 5 months 

prior to the date specified for 

designation decisions. 

Therefore, using the authority 

provided in CAA section 319(b)(2) and 

in the 2007 Exceptional Events Rule at 

40 CFR 50.14(c)(2)(vi), the EPA is 

modifying the schedule for flagging data 

and submitting exceptional events 

demonstrations considered for initial 

area designations by replacing the 

deadlines and information in Table 1 in 

40 CFR 50.14 with the deadlines and 

information presented in Table 5. As we 

did in the O3 NAAQS proposal, we are 

also providing Table 6 to illustrate how 

the promulgated schedule might apply 

to the designations process for the 

revised O3 NAAQS and to designations 

mstockstill on DSK4VPTVN1PROD with RULES2

65414 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

217The range of dates identified in Table 6 is 

illustrative of the dates for the revised O3 NAAQS. 

Users could increment these dates by any constant 

number (for example by 6 years for a hypothetical 

NAAQS promulgated in 2021) to develop a table 

with dates relevant to NAAQS promulgated in the 

future. 

processes for other future new or 

revised NAAQS.217

Additionally, in conjunction with 

promulgating exceptional events 

schedules for initial area designations 

for new or revised NAAQS, the EPA, as 

proposed, is removing obsolete 

regulatory language in 40 CFR 

50.14(c)(2)(iv) and (v) and 40 CFR 

50.14(c)(3)(ii) and (iii) associated with 

exceptional events schedules for all 

historical standards. 

TABLE 5—SCHEDULE FOR FLAGGING AND DOCUMENTATION SUBMISSION FOR DATA INFLUENCED BY EXCEPTIONAL EVENTS

FOR USE IN INITIAL AREA DESIGNATIONS

Exceptional events/Regulatory action Exceptional events deadline schedule d

Flagging and initial event description deadline for data years 

1, 2 and 3 a.

If state and tribal initial designation recommendations for a new/revised NAAQS 

are due August through January, then the flagging and initial event description 

deadline will be the July 1 prior to the recommendation deadline. If state and 

tribal recommendations for a new/revised NAAQS are due February through 

July, then the flagging and initial event description deadline will be the January 

1 prior to the recommendation deadline. 

Exceptional events demonstration submittal deadline for data 

years 1, 2 and 3 a.

No later than the date that state and tribal recommendations are due to the EPA. 

Flagging, initial event description and exceptional events 

demonstration submittal deadline for data year 4 b and, 

where applicable, data year 5 c.

By the last day of the month that is 1 year and 7 months after promulgation of a 

new/revised NAAQS, unless either option a or b applies. 

a. If the EPA follows a 3-year designation schedule, the deadline is 2 years and 

7 months after promulgation of a new/revised NAAQS. 

b. If the EPA notifies the state/tribe that it intends to complete the initial area 

designations process according to a schedule between 2 and 3 years, the 

deadline is 5 months prior to the date specified for final designations decisions 

in such EPA notification. 

a Where data years 1, 2, and 3 are those years expected to be considered in state and tribal recommendations. 

b Where data year 4 is the additional year of data that the EPA may consider when it makes final area designations for a new/revised NAAQS 

under the standard designations schedule. c Where data year 5 is the additional year of data that the EPA may consider when it makes final area designations for a new/revised NAAQS 

under an extended designations schedule. d The date by which air agencies must certify their ambient air quality monitoring data in AQS is annually on May 1 of the year following the 

year of data collection as specified in 40 CFR 58.15(a)(2). In some cases, however, air agencies may choose to certify a prior year’s data in advance of May 1 of the following year, particularly if the EPA has indicated its intent to promulgate final designations in the first 8 months of the 

calendar year. Data flagging, initial event description and exceptional events demonstration deadlines for ‘‘early certified’’ data will follow the 

deadlines for ‘‘year 4’’ and ‘‘year 5’’ data. 

mstockstill on DSK4VPTVN1PROD with RULES2


ER26OC15.001</GPH>mstockstill on DSK4VPTVN1PROD with RULES2

Table 6. Examples by Month of Applying the Promulgated Revised Schedule for Flagging and Documentation Sub

Influenced by Exceptional Events for Use in Initial Area Designations 

Month ofNAAQS Promulgation, State and Tribal Recommendation, and Fina

Exceptional Oct Nov Dec Jan Feb Mar Apr Mayd Jund Ju

Events I 

Regulatory Exceptional Events Deadline Oct Nov Dec Jan Feb Mar Apr May Jun J

Action Schedule' 2015 2015 2015 2016 2016 2016 2016 2016 2016 20

If state and tribal initial designation 

recommendations for a new/revised 

NAAQS are due August through 

January, then the flagging and initial 

event description deadline will be the 

July I prior to the recommendation July 1, July 1, July 1, July 1, Jan 1, Jan 1, Jan 1, Jan I, Jan 1, Ja

deadline. If state and tribal 2016 2016 2016 2016 2017 2017 2017 2017 2017 2

recommendations for a new/revised (data (data (data (data (data (data (data (data (data (

Flagging and initial NAAQS are due February through July, years years years years years years years years years y

event description then the flagging and initial event 2013, 2013, 2013, 2013, 2013, 2013, 2013, 2013, 2014, 2

deadline for data description deadline will be the January 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2015, 2

vears 1, 2, and 3.' 1 prior to the recommendation deadline. 2015) 2015) 2015) 2015) 2015) 2015) 2015) 2015) 2016) 2

by Oct by Nov by Dec by Jan by Feb by Mar by Apr by May by June by 

2016 2016 2016 2017 2017 2017 2017 2017 2017 2

Exceptional events (data (data (data (data (data (data (data (data (data (

demonstration years years years years years years years years years y

submittal deadline 2013, 2013, 2013, 2013, 2013, 2013, 2013, 2013, 2014, 2

for data years 1, 2, No later than the date that state and 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2014, 2015, 2

and 3.' tribal recommendations are due to EPA. 2015) 2015) 2015) 2015) 2015) 2015) 2015) 2015) 2016) 2

AQS quality 

assurance and data Annually on May 1 of the year 

certification following the year of data collection May 1 May 1 May 1 May 1 May 1 May 1 May 1 May 1 May 1 M

By the last day of the month that is 1 

year and 7 months after promulgation 

of a new/revised NAAQS, unless either 

option a or b applies. 

a. If the EPA follows a 3 year 

designation schedule, the deadline is 

Flagging, initial 2 years and 7 months after by Aug by Sep by Oct by Nov by Dec 

event description promulgation of a new/revised 31, 30, 31, 30, 31, 

and exceptional NAAQS. 2017 2017 2017 2017 2017 

events b. If the EPA notifies the state/tribe that (data (data (data (data (data 

demonstration it intends to complete the initial area by May by June by July year year year year year by Jan by 

submittal deadline designations process according to a 31, 30, 31, 2016 2016 2016 2016 2016 31, 28

for data year 4 b schedule between 2 and 3 years, the 2017 2017 2017 and and and and and 2018 2

and, where deadline is 5 months prior to the date (data (data (data potentia potentia potentia potentia potentia (data (applicable, data specified for fmal designations year year year lly lly lly lly lly year 

year 5.' decisions in such EPA notification. 2016) 2016) 2016) 2017) 2017) 2017) 2017) 2017) 2017) 2

Oct Nov Dec Jan Feb Mar Apr May June Ju

State & Tribal Recommendations to EPA 2016 2016 2016 2017 2017 2017 2017 2017 2017 20

EPA notifies States/Tribes of intended modifications to June July Aug Sep Oct Nov Dec Jan Feb M

recommendations (EPA sends 120-day letters) 2017 2017 2017 2017 2017 2017 2017 2018 2018 20

Oct Nov Dec Jan Feb Mar Apr May June Ju

Administrator Promul2ates Final Desi2nations 2017 2017 2017 2018 2018 2018 2018 2018 2018 20

'Where data years 1, 2, and 3 are those years expected to be considered in state and tribal recommendatiOns. 

b Where data year 4 is the additional year of data that the EPA may consider when it makes final area designations for a new/revised NAAQS under the standard designations 

'Where data year 5 is the additional year of data that the EPA may consider when it makes final area designations for a new/revised NAAQS under an extended designations 

d The date by which air agencies must certify their ambient air quality monitoring data in AQS is armually on May 1 of the year following the year of data collection as specif

cases, however, air agencies may choose to certify a prior year's data in advance of May 1 of the following year, particularly if the EPA has indicated its intent to promulgate 

months of the calendar year. Data flagging, initial event description and exceptional events demonstration deadlines for "early certified" data will follow the deadlines for "ye
65416 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

218Public reporting requirements are detailed in 

40 CFR part 58 Appendix G, Uniform Air Quality 

Index (AQI) and Daily Reporting. 

219See http://airnow.gov/. 

VI. Ambient Monitoring Related to O3

Standards 

A. Background 

The EPA proposed to revise the stateby-state O3 monitoring seasons; the 

PAMS monitoring requirements; the 

FRM for measuring O3; and the FEM 

performance requirement specifications 

for automated O3 analyzers. The EPA 

also proposed to make additional minor 

changes to the FEM analyzer 

performance testing requirements for 

NO2 and particulate matter in part 53. 

The EPA is finalizing changes to the 

length of the required O3 monitoring 

season for 32 states and the District of 

Columbia. Section VI.B of this preamble 

provides an overview of the proposed 

changes to the length of the required O3

monitoring seasons, a summary of 

significant public comments and our 

responses, and a summary of the final 

decisions made to the O3 monitoring 

seasons for each state. 

The EPA is finalizing changes to the 

PAMS monitoring requirements in 40 

CFR part 58, Appendix D Section 5. 

Section VI.C of this preamble provides 

background on the PAMS program and 

current monitoring requirements, a 

summary of the proposed changes to the 

PAMS requirements, a summary of 

significant public comments and our 

responses, and a summary of the 

changes to the PAMS requirements in 

this final rule. 

The EPA is finalizing changes to the 

FRM for O3 in Section VI.D of this 

preamble and to the associated FEM 

performance requirement specifications 

for automated O3 analyzers in Section 

VI.E. A summary of significant public 

comments and our responses are 

provided and a summary of the final 

changes to the FRM and FEM 

requirements in this final rule. The EPA 

is also finalizing minor additional 

changes to Part 53 including conforming 

changes to the FEM performance testing 

requirements in Table B–1 and Figure 

B–5 for NO2; extending the period of 

time for the Administrator to take action 

on a request for modification of a FRM 

or FEM from 30 days to 90 days in part 

53.14; and removing an obsolete 

provision for manufacturers to submit 

Product Manufacturing Checklists for 

fine and coarse particulate matter 

monitors in part 53.9. 

B. Revisions to the Length of the 

Required O3 Monitoring Seasons 

Unlike the ambient monitoring 

requirements in 40 CFR part 58 for other 

criteria pollutants that mandate yearround monitoring at State and Local Air 

Monitoring Stations (SLAMS), O3

monitoring is only required during the 

seasons of the year that are conducive 

to O3 formation. These seasons vary in 

length from place-to-place as the 

conditions conducive to the formation 

of O3 (i.e., seasonally-dependent factors 

such as ambient temperature, strength of 

solar insolation, and length of day) 

differ by location. In some locations, 

conditions conducive to O3 formation 

are limited to the summer months of the 

year. In other states with warmer 

climates (e.g., California, Nevada, and 

Arizona), the currently required O3

season is year-round. Elevated levels of 

winter-time O3 have also been measured 

in some western states where precursor 

emissions can interact with sunlight off 

the snow cover under very shallow, 

stable boundary layer conditions (U.S. 

EPA 2013). 

The EPA has determined that the 

proposed lengthening of the O3

monitoring seasons in 32 states and the 

District of Columbia is appropriate. 

Ambient O3 concentrations in these 

areas could approach or exceed the level 

of the NAAQS, more frequently and 

during more months of the year 

compared with the current season 

lengths. It is important to monitor for O3

during the periods when ambient 

concentrations could approach the level 

of the NAAQS to ensure that the public 

is informed when exposure to O3 could 

reach or has reached a level of concern. 

The EPA completed an analysis to 

address whether extensions of currently 

required monitoring seasons are 

appropriate (Rice, 2014). In this 

analysis, we used all available data in 

AQS, including data from monitors that 

collected O3 data year-round during 

2010–2013. More than half of O3

monitors are voluntarily operated on a 

year-round basis by monitoring 

agencies. We determined the number of 

days where one or more monitors had 

a daily maximum 8-hour O3 average 

equal to or above 0.060 ppm in the 

months outside each state’s current O3

monitoring season and the pattern of 

those days in the out-of-season months. 

We believe that a threshold of 0.060 

ppm, taking into consideration 

reasonable uncertainty, serves as an 

appropriate indicator of ambient 

conditions that may be conducive to the 

formation of O3 concentrations that 

approach or exceed the NAAQS. We 

also considered regional consistency, 

particularly for those states with little 

available data. We note that seasonal O3

patterns vary year-to-year due primarily 

to highly variable meteorological 

conditions conducive to the formation 

of elevated O3 concentrations early or 

late in the season in some years and not 

others. The EPA believes it is important 

that O3 monitors operate during all 

periods when there is a reasonable 

possibility of ambient levels 

approaching the level of the NAAQS. 

Basing O3 monitoring season 

requirements on the goal of ensuring 

monitoring when ambient O3 levels 

approach or exceed the level of the 

NAAQS supports established 

monitoring network objectives 

described in Appendix D of Part 58, 

including the requirement to provide air 

pollution data to the general public in 

a timely manner 218 and to support 

comparisons of an area’s air pollution 

levels to the NAAQS. The operation of 

O3 monitors during periods of time 

when ambient levels approach or 

exceed the level of the NAAQS ensures 

that unusually sensitive people and 

sensitive groups are alerted to O3 levels 

of potential health concern allowing 

them to take precautionary measures. 

The majority of O3 monitors in the U.S. 

report to AIRNOW,219 as well as to 

state-operated Web sites and automated 

phone reporting systems. These 

programs support many objectives 

including real-time air quality reporting 

to the public, O3 forecasting, and the 

verification of real-time air quality 

forecast models. 

1. Proposed Changes to the Length of 

the Required O3 Monitoring Seasons 

The EPA proposed to extend the 

length of the required O3 monitoring 

season in 32 states and the District of 

Columbia. The proposed changes were 

an increase of one month for 22 states 

(Connecticut, Delaware, Idaho, Illinois, 

Iowa, Kansas, Maryland, Massachusetts, 

Minnesota, Missouri, Nebraska, New 

Hampshire, New Jersey, New York, 

North Carolina, Ohio, Pennsylvania, 

Rhode Island, South Carolina, Texas 

(northern portion only), Virginia, and 

West Virginia) and the District of 

Columbia, an increase of one and one 

half months for Wisconsin, an increase 

of two months for four states (Indiana, 

Michigan, Montana, and North Dakota), 

an increase of four months for Florida 

and South Dakota, an increase of five 

months for Colorado, and an increase of 

seven months for Utah. For Wyoming, 

we proposed to add three months at the 

beginning of the season and remove one 

month at the end of the season, resulting 

in a net increase of two months. Ozone 

season requirements are currently split 

by Air Quality Control Region (AQCR) 

in Louisiana and Texas. We proposed 

lengthening the required season in the 

northern part of Texas (AQCR 022, 210, 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65417 

220See 40 CFR part 58, appendix D, Table D–2. 

211, 212, 215, 217, and 218) by one 

month and leaving the year-round O3

season in the southern part of Texas 

(AQCRs 106, 153, 213, 214, and 216) 

unchanged. No changes were proposed 

for the AQCRs in Louisiana. As noted 

earlier, in a few states with limited 

available data and few exceedance days 

outside the currently-required season 

(Iowa, Missouri, and West Virginia), the 

proposed changes were made by 

considering supporting information 

from the surrounding states. These 

changes involved the proposed addition 

of one month (March) to the currentlyrequired O3 seasons for these states. 

The EPA also proposed that O3

monitors at all National Core 

Multipollutant Monitoring Stations 

(NCore) be operated year-round, January 

through December, regardless of the 

length of the required O3 season for the 

remainder of the SLAMS within each 

state. 

We noted that the EPA Regional 

Administrators have previously 

approved deviations from the required 

O3 monitoring seasons as allowed by 

paragraph 4.1(i) of 40 CFR part 58, 

Appendix D. We proposed to retain the 

rule language permitting such 

deviations from the required O3

monitoring seasons, but note that 

finalized changes to O3 monitoring 

season requirements would revoke all 

existing Regional Administrator-granted 

waiver approvals. As appropriate, 

monitoring agencies could seek new 

approvals for seasonal deviations. Any 

seasonal deviations based on the 

Regional Administrator’s waiver of 

requirements must be described in the 

state’s annual monitoring network plan 

and updated in the AQS. 

Given the timing of the final 

rulemaking and any associated burden 

on state/local monitoring agencies to 

implement the extended O3 seasons, we 

proposed that implementation of the 

revised O3 seasons would become 

effective at SLAMS (including NCore 

sites) on January 1, 2017. We solicited 

comment on whether the revised 

seasons could be implemented 

beginning January 1, 2016, for all 

monitors or for a subset of monitors, 

such as those currently operating yearround or on a schedule that corresponds 

to the proposed O3 season. 

2. Comments on the Length of the 

Required O3 Monitoring Seasons 

We received several comments on the 

proposed revisions to O3 monitoring 

seasons. Several commenters supported 

the proposed O3 season length changes 

and agreed that O3 monitoring seasons 

should reflect the times of year when O3

may approach or exceed the level of the 

NAAQS. A few commenters noted the 

complexities that would arise in the 

implementation of multi-state planning 

agreements if states that shared an MSA 

had different required O3 monitoring 

seasons. Two state agencies that 

supported season length changes also 

recommended changes to neighboring 

states’ O3 seasons. New York 

recommended that Connecticut’s 

proposed O3 season be further extended 

(adding the month of October) to match 

the proposed season in New York 

(March–October) because they share a 

major MSA and nonattainment area, and 

the highest design value monitor in the 

nonattainment area is often in 

Connecticut. The results from the EPA’s 

analysis did not support the addition of 

October for Connecticut. The EPA 

recognizes that there may be value in 

having a consistent O3 season across 

multi-state planning areas. We 

recommend that monitoring agency 

representatives from New York and 

Connecticut contact their respective 

EPA Regional Office to jointly develop 

a monitoring plan to provide coverage of 

the MSA for a longer period of time. 

Consistent with the results from the 

EPA’s analysis and consistent with our 

proposal, the EPA is finalizing the 

March–October season in New York and 

the March–September season in 

Connecticut. 

Although no changes were proposed 

for Arkansas, the Arkansas Department 

of Environmental Quality recommended 

that the O3 season in the nonattainment 

area that includes Crittenden County, 

Arkansas (March–November) be 

consistent with the O3 seasons in 

Tennessee (March–October) and 

Mississippi (March–October) by either 

shortening the O3 season in Arkansas or 

lengthening the O3 season by one month 

in Tennessee and Mississippi. Based on 

the results from the EPA’s analysis and 

consistent with our proposal, the EPA is 

not finalizing any changes to the current 

O3 seasons in Arkansas, Tennessee, or 

Mississippi. There is currently one 

monitor operating in Crittenden County. 

We recommend that Arkansas work 

with their EPA Regional Administrator 

to consider a waiver for the monitor(s) 

in Crittenden County to allow a 

deviation (shortened season) from the 

required O3 season if the agency 

demonstrates that such a deviation is 

appropriate for consistency in the 

nonattainment area. 

Two commenters noted the need to 

extend seasons to capture wintertime O3

events. One commenter urged the EPA 

to extend monitoring to year-round in 

the intermountain west (specifically 

Wyoming) to adequately capture 

summer and winter O3 problem days 

and noted especially two monitors in 

the Pinedale area of Wyoming that 

should be operated year-round. The 

EPA’s analysis showed that there were 

no days that were ≥ 0.060 ppm in 

Wyoming for the months of October– 

December and that the Wyoming 

Department of Environmental Quality is 

currently operating about 70% of their 

O3 monitors year-round including all O3

monitors in Sublette County, which 

includes the Pinedale area. Another 

commenter supported lengthening the 

seasons for states in the western U.S. 

where wintertime O3 could be an issue 

in light of the unique and growing O3

pollution problems caused by oil and 

gas development activities. They also 

recommended that the EPA expand the 

O3 monitoring season to year-round for 

North Dakota, South Dakota, and 

Montana beyond what was proposed. 

The number of observed days that were 

≥ 0.060 ppm in the months outside the 

season proposed for these states (one 

day for North Dakota and no days 

observed for South Dakota and 

Montana) do not support a further 

extension to the length of the O3

monitoring season beyond what was 

proposed. These states are already 

operating a large percentage of their 

monitors year-round (89% in North 

Dakota, 100% in South Dakota, and 

78% in Montana). The EPA is finalizing 

the seasons as proposed in Wyoming 

(January–September), North Dakota 

(March–September), South Dakota 

(March–October), and Montana (April– 

September). The EPA encourages these 

states to continue year-round operation 

of their monitors to determine what 

areas are affected by elevated levels of 

winter-time O3. 

The commenters who opposed 

lengthening the O3 monitoring seasons 

noted concerns with the threshold 

(0.060 ppm) used as the basis for the 

changes and the length of time (2010– 

2013) for which ambient data were 

retrieved and analyzed. Many of those 

with concerns recommended that levels 

in the proposed range (e.g., 0.065 ppm 

or 0.070 ppm) or the current NAAQS 

level of 0.075 ppm be used as the 

appropriate threshold for determining 

the O3 season. With regard to the 0.060 

ppm threshold used, this value is 

consistent with the 85 percent threshold 

used to require additional O3

monitoring based on Appendix D 

requirements, which include the MSA 

population and design value.220 As 

noted previously, year-to-year 

variability occurs in seasonal O3

patterns based on highly variable and 

unpredictable meteorological 

mstockstill on DSK4VPTVN1PROD with RULES2

65418 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

conditions, which can support the 

formation of early or late season 

elevated O3 concentrations in some 

years and not in other years. This 

threshold serves as an appropriate 

indicator of ambient conditions that 

may be conducive to the formation of O3

concentrations that approach or exceed 

the level of the NAAQS. 

Certain logistical complexities were 

noted if longer seasons were required, 

including site access during winter and 

the challenge of getting the monitoring 

equipment ready in time. Four states 

noted concerns with operator safety and 

anticipated their inability to access sites 

due to early spring snowfall. The EPA 

agrees that site access could be an issue 

depending on weather conditions and 

notes that specific site monitoring 

season deviations may be appropriate. 

We suggest that this be addressed 

through the monitoring season waiver 

process with the EPA Regional 

Administrator. Any deviations based on 

the Regional Administrator’s waiver of 

requirements must be described in the 

state’s annual monitoring network plan 

and updated in AQS. 

Several commenters had concerns 

about the additional cost and resources 

needed to expand the O3 monitoring 

seasons. There was some disagreement 

with the EPA’s total annual average cost 

estimate of $230,000 which took into 

account the number of O3 monitors 

already operating year-round across the 

country. Commenters noted specifically 

that the proposed extension of required 

monitoring seasons would increase 

operational costs and potentially impact 

the resources available for other 

monitoring efforts. The added cost of 

operating O3 monitors over a longer 

period was noted by some commenters, 

referencing both the cost of staff to 

operate the monitors, as well as the 

additional wear and tear those O3

monitors would experience over a 

longer operational period. They noted 

that extending their required monitoring 

season by adding the month of March 

would increase staffing requirements for 

monitor operation and quality 

assurance. They also noted that the life 

expectancy of equipment would be 

reduced due to increased wear and tear. 

The EPA acknowledges that operational 

costs for O3 monitoring networks will 

incrementally increase in states where 

required seasons have been lengthened. 

We encourage monitoring agencies to 

review available technology and 

operational procedures to institute 

practices that could potentially reduce 

such costs, such as the automation of 

quality control and calibration checks 

and remote access to evaluate monitor 

operations. As noted earlier, all states 

operated at least a portion of their O3

monitoring network outside of the 

required O3 season during the 2010– 

2013 data period and reported the data 

to AQS. In addition, many states are 

operating more than the minimum 

number of monitors required to support 

the basic monitoring objectives 

described in 40 CFR part 58, Appendix 

D. Some states have a large percentage 

of their total O3 monitors operating 

outside the currently-required O3 season 

and some states have a small 

percentage. In situations where states 

are already operating a large number of 

their O3 monitors outside their current 

O3 season, the actual cost increase will 

be less. In cases where states have a 

small number of monitors operating 

outside their current O3 season, in 

addition to automation and remote 

access, those states could investigate 

with their Regional Administrator the 

process in 40 CFR part 58.14 for 

reducing the total number of operating 

monitors that are above the number 

required by 40 CFR, part 58, appendix 

D to offset the cost of extending the O3

monitoring season in their state. 

Two commenters had concerns about 

the 4-year period of time evaluated in 

the EPA’s analysis and noted that the 4- 

year period of time evaluated does not 

take into account meteorological 

anomalies and other weather induced 

situations and is not consistent with the 

3 years used to calculate design values. 

One state agency’s comments referenced 

their own analysis showing 

concentrations going back 20 years. 

They noted that 2010 was an unusual 

year and inclusion of such an unusual 

year in the 4-year period (2010–2013) of 

the EPA’s analysis provides too much 

weight on those data. As noted earlier, 

year-to-year variability occurs in 

seasonal O3 patterns based on variable 

meteorological conditions and given the 

impracticality of forecasting such 

conditions that affect O3

photochemistry, the EPA believes it is 

important that O3 monitors operate 

when there is a reasonable possibility of 

ambient levels approaching the level of 

the NAAQS. Another state agency 

commented that 4 years appeared to be 

an unusual number of years given that 

design values are based on 3 years. To 

support the proposed rule in 2014, the 

EPA’s analysis of O3 seasons began in 

2013. At that time the EPA’s analysis 

considered the most recent 3 years of 

certified data (2010–2012) and updated 

the analysis to add a fourth year (2013) 

when the data were quality-assured, 

certified, and available in AQS. We used 

4 years of data, including the most 

recent year (2013) to include an 

additional year of potentially-variable 

meteorological conditions to propose 

changes to the seasons. The EPA treated 

all years equally and did not put any 

more weight on the 2010 data than any 

of the other years used in the analysis. 

The EPA believes that using recentlyavailable data across multiple years to 

capture varying meteorological 

conditions was appropriate to support 

the decisions on extending the O3

seasons. One commenter disagreed with 

the EPA’s definition of year-round (at 

least 20 daily observations in all 12 

months of at least 1 year of the 4-year 

period). The definition of year-round 

was used to estimate the number of 

monitors being operated outside a 

state’s required O3 season and also used 

for the EPA’s Information Collection 

Request (ICR). All available data in AQS 

were used for the O3 season analysis, 

including data from year-round 

monitors. 

Two commenters noted that ‘‘regional 

consistency’’ is not a scientific reason 

and is not needed for making changes to 

the O3 seasons. One commenter noted 

that significant geographical, 

meteorological and demographic 

differences exist between neighboring 

states that may not warrant identical 

monitoring seasons. The EPA notes that 

regional consistency was considered, 

but only important for a few states 

where little data were available and the 

neighboring states had more available 

data and a sufficient number of days 

that were ≥ 0.060 ppm to support the 

proposed O3 season changes. Regional 

consistency was not important for other 

states. 

Some commenters expressed support 

for the proposed requirement that NCore 

O3 sites operate year-round. They 

questioned whether data from NCore 

stations outside the O3 season will be 

used for designations and requested that 

the EPA exclude those data from the 

designations process. Consistent with 

the designations process for all criteria 

pollutants, the states, tribes, and the 

EPA use all data available in AQS that 

meet the quality assurance requirements 

in 40 CFR part 58, Appendix A for the 

designations process. Given that O3 data 

from NCore stations will meet these 

requirements, there is no rational basis 

for excluding these data from 

comparison to the NAAQS. 

Accordingly, such data from NCore 

stations cannot be excluded and will be 

treated in a manner equivalent to all 

other O3 data in AQS. The EPA expects 

that the highest O3 values will occur 

during the required O3 season; therefore, 

we don’t anticipate that NCore data 

from the out-of-season months will 

contribute to the design value used in 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65419 

221Air Quality Control Region. 

the designations process. The EPA is 

finalizing the requirement for yearround O3 monitoring at NCore stations. 

The EPA Regional Administrators 

have previously approved deviations 

from the required O3 monitoring seasons 

through rulemakings (64 FR 3028, 

January 20, 1999; 67 FR 57332, 

September 10, 2002; and 69 FR 52836, 

August 30, 2004). The current ambient 

monitoring rule, in paragraph 4.1(i) of 

40 CFR part 58, Appendix D (71 FR 

61319, October 17, 2006), allows the 

EPA Regional Administrators to approve 

changes to the O3 monitoring season 

without rulemaking. The EPA is 

retaining the rule language allowing 

such deviations from the required O3

monitoring seasons without rulemaking. 

In the finalized revision to paragraph 

4.1(i) of 40 CFR part 58, Appendix D, 

the EPA is clarifying the minimum 

considerations that should be taken into 

account when reviewing requests, and 

clarifying that changes to the O3 seasons 

finalized in this rule revoke all 

previously approved seasonal 

deviations. The EPA clarifies that all O3

season waivers will be revoked when 

this final rule becomes effective. We 

encourage monitoring agencies with 

existing waivers to engage their EPA 

Regions as soon as possible to evaluate 

whether new or continued waivers are 

appropriate given the level of the 

revised O3 NAAQS. 

We received three comments for and 

three comments against early 

implementation of the revised O3

seasons by the start of the applicable O3

season in each state by January 1, 2016. 

Those commenters in favor of early 

implementation of the revised O3

seasons are already operating a large 

percentage of O3 monitors year-round or 

outside the current O3 monitoring 

season in their state. Those commenters 

against early implementation cited 

concerns with the need for additional 

time to implement the revised O3

seasons, especially in areas where 

access in order to service and support 

the monitoring equipment may be 

problematic during winter weather 

conditions, and the undue burden on 

already constrained state resources. One 

commenter noted that given the date for 

the final rule (October 1, 2015) that 

there is insufficient time for public 

review of their annual monitoring 

network plan due July 1, 2015, for early 

implementation in 2016. The EPA 

encourages those agencies who are able 

to implement the O3 season changes 

early to do so by the start of the 

applicable O3 season in their state in 

2016. However, taking into 

consideration the timing and potential 

burden on monitoring agencies, the EPA 

is finalizing the requirement for 

implementing the revised O3 seasons no 

later than the start of the applicable O3

monitoring season in 2017, as proposed. 

3. Final Decisions on the Length of the 

Required O3 Monitoring Seasons 

Final changes to the required O3

monitoring seasons are summarized in 

this section as well as in revised Table 

D–3 in 40 CFR part 58, Appendix D. 

Detailed state-by-state technical 

information has been placed in the 

docket to document the basis for the 

EPA’s decision on each state. This 

information includes state-by-state maps 

and number of days that were ≥ 0.060 

ppm; distribution charts of the number 

of days that were ≥ 0.060 ppm by month 

and state; and detailed information 

regarding AQS site IDs, dates and 

concentrations of all occurrences of the 

8-hour daily maximum of at least 0.060 

ppm between 2010 and 2013. 

Summaries have also been prepared for 

each state including the former and 

proposed O3 monitoring seasons. 

No changes to the required O3

monitoring season were proposed or 

finalized for these states: Alabama, 

Alaska, Arizona, Arkansas, California, 

Georgia, Hawaii, Kentucky, Northern 

Louisiana (AQCR 221 019, 022), 

Southern Louisiana (AQCR 106), Maine, 

Mississippi, Nevada, New Mexico, 

Oklahoma, Oregon, Tennessee, 

Southern Texas (AQCR 106, 153, 213, 

214, 216), Vermont, Washington, Puerto 

Rico, Virgin Islands, Guam, and 

American Samoa. All existing O3 season 

deviations or waivers are revoked. 

Changes to the required O3

monitoring seasons are finalized as 

follows for these states and the District 

of Columbia and all existing O3 season 

deviations or waivers are revoked. 

Colorado: Proposed addition of 

January, February, October, November, 

and December is finalized. The required 

season is revised to January–December. 

Connecticut: Proposed addition of 

March is finalized, revising season to 

March–September. 

Delaware: Proposed addition of March 

is finalized, revising season to March– 

October. 

District of Columbia: Proposed 

addition of March is finalized, revising 

season to March–October. 

Florida: Proposed addition of January, 

February, November, and December is 

finalized. The required season is revised 

to January–December. 

Idaho: Proposed addition of April is 

finalized, revising season to April– 

September. 

Illinois: Proposed addition of March 

is finalized, revising season to March– 

October. 

Indiana: Proposed addition of March 

and October, revising season to March– 

October. 

Iowa: Proposed addition of March is 

finalized, revising season to March– 

October. 

Kansas: Proposed addition of March is 

finalized, revising season to March– 

October. 

Maryland: Proposed addition of 

March is finalized, revising season to 

March–October. 

Massachusetts: Proposed addition of 

March is finalized, revising season to 

March–September. 

Michigan: Proposed addition of 

March and October is finalized, revising 

season to March–October. 

Minnesota: Proposed addition of 

March is finalized, revising season to 

March–October. 

Missouri: Proposed addition of March 

is finalized, revising season to March– 

October. 

Montana: Proposed addition of April 

and May is finalized, revising season to 

April–September. 

Nebraska: Proposed addition of March 

is finalized, revising season to March– 

October. 

New Hampshire: Proposed addition of 

March is finalized, revising season to 

March–September. 

New Jersey: Proposed addition of 

March is finalized, revising season to 

March–October. 

New York: Proposed addition of 

March is finalized, revising season to 

March–October. 

North Carolina: Proposed addition of 

March is finalized, revising season to 

March–October. 

North Dakota: Proposed addition of 

March and April is finalized, revising 

season to March–September. 

Ohio: Proposed addition of March is 

finalized, revising season to March– 

October. 

Pennsylvania: Proposed addition of 

March is finalized, revising season to 

March–October. 

Rhode Island: Proposed addition of 

March is finalized, revising season to 

March–September. 

South Carolina: Proposed addition of 

March is finalized, revising season to 

March–October. 

South Dakota: Proposed addition of 

March, April, May, and October is 

finalized, revising season to March– 

October. 

Texas (Northern AQCR 022, 210, 211, 

212, 215, 217, 218): Proposed addition 

of November is finalized, revising 

season to March–November. 

Utah: Proposed addition of January, 

February, March, April, October, 

mstockstill on DSK4VPTVN1PROD with RULES2

65420 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

November, and December is finalized. 

The required season is revised to 

January–December. 

Virginia: Proposed addition of March 

is finalized, revising season to March– 

October. 

West Virginia: Proposed addition of 

March is finalized, revising season to 

March—October. 

Wisconsin: Proposed addition of 

March and April 1—15 is finalized, 

revising season to March—October 15. 

Wyoming: Proposed addition of 

January, February, March, and removal 

of October is finalized, revising season 

to January—September. 

Finally, we are finalizing the required 

O3 monitoring season for all NCore 

stations to be year-round (January— 

December) regardless of the required 

monitoring season for the individual 

state in which the NCore station is 

located. 

C. Revisions to the PAMS Network 

Requirements 

Section 182 (c)(1) of the CAA required 

the EPA to promulgate rules for 

enhanced monitoring of O3, NOX, and 

VOCs for nonattainment areas classified 

as serious (or above) to obtain more 

comprehensive and representative data 

on O3 air pollution. In addition, Section 

185B of the CAA required the EPA to 

work with the National Academy of 

Sciences (NAS) to conduct a study on 

the role of O3 precursors in tropospheric 

O3 formation and control. As a result of 

this study, the NAS issued the report 

entitled, ‘‘Rethinking the Ozone 

Problem in Urban and Regional Air 

Pollution’’, (NAS, 1991). 

In response to the CAA requirements 

and the recommendations of the NAS 

report, on February 12, 1993 (58 FR 

8452), the EPA revised the ambient air 

quality surveillance regulations to 

require PAMS in each O3 nonattainment 

area classified as serious, severe, or 

extreme (‘‘PAMS areas’’). As noted in 

the EPA’s Technical Assistance 

Document (TAD) for Sampling and 

Analysis of Ozone Precursors (U.S. EPA, 

1998), the current objectives of the 

PAMS program are to: (1) Provide a 

speciated ambient air database that is 

both representative and useful in 

evaluating control strategies and 

understanding the mechanisms of 

pollutant transport by ascertaining 

ambient profiles and distinguishing 

among various individual volatile 

organic compounds (VOCs); (2) provide 

local, current meteorological and 

ambient data to serve as initial and 

boundary condition information for 

photochemical grid models; (3) provide 

a representative, speciated ambient air 

database that is characteristic of source 

emission impacts to be used in 

analyzing emissions inventory issues 

and corroborating progress toward 

attainment; (4) provide ambient data 

measurements that would allow later 

preparation of unadjusted and adjusted 

pollutant trends reports; (5) provide 

additional measurements of selected 

criteria pollutants for attainment/

nonattainment decisions and to 

construct NAAQS maintenance plans; 

and (6) provide additional 

measurements of selected criteria and 

non-criteria pollutants to be used for 

evaluating population exposure to air 

toxics as well as criteria pollutants. 

The original requirements called for 

two to five fixed sites per PAMS area 

depending on the area’s population. 

Four types of PAMS sites were 

identified including upwind (Type 1), 

maximum precursor emission rate (Type 

2), maximum O3 concentration (Type 3), 

and extreme downwind (Type 4) sites. 

Each PAMS site was required to 

measure O3, nitrogen oxide (NO), NO2, 

speciated VOCs, selected carbonyl 

compounds, and selected 

meteorological parameters. In addition, 

upper air meteorological monitoring 

was required at one site in each PAMS 

area. 

In the October 17, 2006 monitoring 

rule (71 FR 61236), the EPA revised the 

PAMS requirements to only require two 

sites per PAMS area. The intent of the 

revision was to ‘‘allow PAMS 

monitoring to be more customized to 

local data needs rather than meeting so 

many specific requirements common to 

all subject O3 nonattainment areas; the 

changes also gave states the flexibility to 

reduce the overall size of their PAMS 

programs—within limits—and to use 

the associated resources for other types 

of monitoring they consider more 

useful.’’ In addition to reducing the 

number of required sites per PAMS area, 

the 2006 revisions also limited the 

requirement for carbonyl measurements 

(specifically formaldehyde, 

acetaldehyde, and acetone) to areas 

classified as serious or above for the 8- 

hour O3 standards. This change was 

made in recognition of carbonyl 

sampling issues which were believed to 

cause significant uncertainty in the 

measured concentrations. 

Twenty-two areas were classified as 

serious or above O3 nonattainment at 

the time the PAMS requirements were 

promulgated in 1993. On July 18, 1997 

(62 FR 38856), the EPA revised the 

averaging time of the O3 NAAQS from 

a 1-hour averaging period to an 8-hour 

averaging period. On June 15, 2005 (70 

FR 44470), the EPA revoked the 1-hour; 

however, PAMS requirements were 

identified as requirements that had to be 

retained in the anti-backsliding 

provisions included in that action. 

Therefore, PAMS requirements continue 

to be applicable to areas that were 

classified as serious or above 

nonattainment for the 1-hour O3

standards as of June 15, 2004. Currently, 

25 areas are subject to the PAMS 

requirements with a total of 75 sites. As 

will be discussed in detail later, the 

current PAMS sites are concentrated in 

the Northeast U.S. and California with 

relatively limited coverage in the rest of 

the country (Cavender, 2014). 

The first PAMS sites began operation 

in 1994, and have been in operation for 

over 20 years. Since the start of the 

program, there have been many changes 

to the nature and scope of the O3

problem in the U.S. as well as to our 

understanding of it. The O3 standards 

has been revised multiple times since 

the PAMS program was first 

implemented. On July 18, 1997, the EPA 

revised the O3 NAAQS to a level of 0.08 

parts per million (ppm), with a form 

based on the 3-year average of the 

annual fourth-highest daily maximum 8- 

hour average O3 concentration. On 

March 28, 2008 (73 FR 16436), the EPA 

revised the O3 standards to a level of 

0.075 ppm, with a form based on the 3- 

year average of the annual fourthhighest daily maximum 8-hour average 

O3 concentration. These changes in the 

level and form of the O3 NAAQS, along 

with notable decreases in O3 levels in 

most parts of the U.S., have changed the 

landscape of O3 NAAQS violations in 

the U.S. At the time of the first round 

of designations for the 8-hour standards 

(June 15, 2005), only 5 areas were 

classified as serious or above for the 8- 

hour standards as compared to 22 areas 

that were classified as serious or above 

for the 1-hour standards. While the 

number of serious and above areas 

decreased, the number of nonattainment 

areas remained nearly the same. In 

addition to the change in the landscape 

of O3 nonattainment issues, much of the 

equipment used at PAMS sites is 

outdated and in need of replacement. 

New technologies have been developed 

since the inception of the PAMS 

program that should be considered for 

use in the network to simplify 

procedures and improve data quality. 

For these reasons, the EPA determined 

that it would be appropriate to reevaluate the PAMS program as 

explained below. 

In 2011, the EPA initiated an effort to 

re-evaluate the PAMS requirements in 

light of changes in the needs of PAMS 

data users and the improvements in 

monitoring technology. The EPA 

consulted with the Clean Air Science 

Advisory Committee (CASAC), Air 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65421 

222The EPA noted that the proposed change 

would expand the PAMS applicability beyond that 

required in 182(c)(1) of the CAA. Thus, in this final 

rule, the EPA is relying on the authority provided 

in Sections 103(c), 110(a)(2)(B), 114(a) and 301(a)(1) 

of the CAA to expand the PAMS applicability to 

areas other than those that are serious or above O3

nonattainment. 

Monitoring and Methods Subcommittee 

(AMMS) to seek advice on potential 

revisions to the technical and regulatory 

aspects of the PAMS program; including 

changes to required measurements and 

associated network design requirements. 

The EPA also requested advice on 

appropriate technology, sampling 

frequency, and overall program 

objectives in the context of the most 

recently revised O3 NAAQS and 

changes to atmospheric chemistry that 

have occurred over the past 10–15 years 

in the significantly impacted areas. The 

CASAC AMMS met on May 16 and May 

17, 2011, and provided a report with 

their advice on the PAMS program on 

September 28, 2011 (U.S. EPA, 2011f). 

In addition, the EPA met multiple times 

with the National Association of Clean 

Air Agencies (NACAA) Monitoring 

Steering Committee (MSC) to seek 

advice on the PAMS program. The MSC 

includes monitoring experts from 

various State and local agencies actively 

engaged in ambient air monitoring and 

many members of the MSC have direct 

experience with running PAMS sites. 

Specific advice obtained from the 

CASAC AMMS and the MSC that was 

considered in making the proposed 

changes to the PAMS requirements is 

discussed in the appropriate sections 

below. 

Based on the findings of the PAMS 

evaluation and the consultations with 

the CASAC AMMS and NACAA MSC, 

the EPA proposed to revise several 

aspects of the PAMS monitoring 

requirements including changes in (1) 

network design, (2) VOC sampling, (3) 

carbonyl sampling, (4) nitrogen oxides 

sampling, and (5) meteorology 

measurements. The following 

paragraphs summarize the proposed 

changes, the comments received, and 

the final changes and supporting 

rationale. 

1. Network Design 

As discussed above, the current 

PAMS network design calls for two sites 

(a Type 2, and a Type 1 or Type 3) per 

PAMS area. In their report (U.S EPA, 

2011f), the CASAC AMMS found ‘‘that 

the existing uniform national network 

design model for PAMS is outdated and 

too resource intensive,’’ and 

recommended ‘‘that greater flexibility 

for network design and implementation 

of the PAMS program be transferred to 

state and local monitoring agencies to 

allow monitoring, research, and data 

analysis to be better tailored to the 

specific needs of each O3 problem area.’’ 

While stating that the current PAMS 

objectives were appropriate, the AMMS 

report also stated that ‘‘objectives may 

need to be revised to include both a 

national and regional focus because 

national objectives may be different 

from regional objectives.’’ The NACAA 

MSC also advised the EPA that the 

existing PAMS requirements were too 

prescriptive and may hinder state efforts 

to collect other types of data that were 

more useful in understanding their local 

O3 problems. 

The EPA agrees with CASAC that the 

PAMS objectives include both local and 

national objectives, and believes that the 

current PAMS network design is no 

longer suited for meeting either sets of 

objectives. As part of the PAMS 

evaluation, it was determined that at the 

national level the primary use of the 

PAMS data has been to evaluate 

photochemical model performance. Due 

to the locations of the current PAMS 

areas and the current network design, 

existing PAMS sites are clustered along 

the northeast and west coasts leading to 

significant redundancy in these areas 

and very limited coverage throughout 

the remainder of the country (Cavender, 

2014). The resulting uneven spatial 

coverage greatly limits the value of the 

PAMS data for evaluation of model 

performance. CASAC (U.S. EPA, 2011f) 

noted the spatial coverage issue and 

advised that the EPA should consider 

requiring PAMS measurements in areas 

in addition to ‘‘areas classified as 

serious and above for the O3 NAAQS to 

improve spatial coverage.’’ The EPA 

also agrees with CASAC and NACAA 

that the PAMS requirements should be 

revised to provide monitoring agencies 

greater flexibility in meeting local 

objectives. 

The EPA proposed changes to the 

network design requirements to better 

serve both national and local objectives. 

The EPA proposed a two part network 

design. The first part of the design 

included a network of fixed sites 

(‘‘required PAMS sites’’) intended to 

support O3 model development and the 

tracking of trends of important O3

precursor concentrations. The second 

part of the network design required 

states with O3 non-attainment areas to 

develop and implement Enhanced 

Monitoring Plans (EMPs) which were 

intended to allow monitoring agencies 

the needed flexibility to implement 

additional monitoring capabilities to 

suit the needs of their area. 

To implement the fixed site portion of 

the network design, the EPA proposed 

to require PAMS measurements at any 

existing NCore site in an O3

nonattainment area in lieu of the current 

PAMS network design requirements.222

The NCore network is a multi-pollutant 

monitoring network consisting of 80 

sites (63 urban, 17 rural) sited in typical 

neighborhood scale locations and 

supports multiple air quality objectives 

including some of the objectives of the 

PAMS program including the 

development and evaluation of 

photochemical models (including both 

PM2.5 and O3 models), development and 

evaluation of control strategies, and the 

tracking of regional precursor trends. 

The EPA recognized that in limited 

situations existing NCore sites may not 

be the most appropriate locations for 

making PAMS measurements. For 

example, an existing PAMS site in an O3

nonattainment area may be sited at a 

different location than the existing 

NCore site. In this case, it may be 

appropriate to continue monitoring at 

the existing PAMS site to support 

ongoing research and to maintain trends 

information. To account for these 

situations, the EPA also proposed to 

provide the EPA Regional Administrator 

the authority to approve an alternative 

location for a required PAMS site where 

appropriate. The EPA also solicited 

comments on alternative frameworks 

using other benchmarks such as 

attainment status or population to 

ensure an appropriately sized fixed 

PAMS monitoring network. The EPA 

received several comments on the 

proposed changes to the network 

design, primarily from state and local 

monitoring agencies. The following 

paragraphs summarize the major 

comments made on the proposed 

network design, our response, and final 

network design requirements. 

Most commenters agreed with the 

need to revise the existing network 

design. One commenter agreed that 

‘‘requiring PAMS monitoring at already 

existing NCore locations will benefit 

national and local objectives to 

understand ozone formation and would 

also provide significant cost 

efficiencies.’’ Another commenter stated 

that they supported the proposed 

changes, ‘‘especially the flexibility 

provided by EMPs designed to meet 

local objectives and achieve a better 

understanding of photochemical 

precursors.’’ Another commenter 

supporting the changes stated that the 

‘‘proposed network revision will 

provide states the flexibility to use their 

resources effectively.’’ One commenter 

stated that the proposed changes 

‘‘reflect a more efficient use of state and 

local monitoring resources by availing 

mstockstill on DSK4VPTVN1PROD with RULES2

65422 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

223Section 184(c) of the CAA establishes the OTR 

as comprised of the states of Connecticut, Delaware, 

Maine, Maryland, Massachusetts, New Hampshire, 

New Jersey, New York, Pennsylvania, Rhode Island, 

Vermont, and Consolidated Metropolitan Statistical 

Area that includes the District of Columbia. 

monitoring agencies of existing NCore 

infrastructure to fulfill PAMS 

requirements.’’ 

A number of concerns were also 

raised with the proposed network 

design. Several commenters stated that 

the proposal ‘‘would drastically reduce 

the PAMS network in the Northeast.’’ 

One commenter stated that ‘‘this is not 

acceptable for the Northeast and Midatlantic Corridor, which requires 

monitoring of the complex transport 

from multiple large metropolitan areas 

in the region.’’ One commenter 

recognized that the EPA had intended to 

allow states to use EMPs to address 

upwind and downwind data needs, but 

raised concerns that states with 

historically important upwind and 

downwind sites in the Ozone Transport 

Region 223 (OTR) may not be required to 

develop an EMP since those sites would 

be in states that are attaining the O3

NAAQS. One commenter suggested that 

‘‘the EPA consider the entire OTR when 

designing a PAMS network rather than 

pockets of nonattainment areas in the 

region.’’ The EPA agrees that the 

reduction of sites in the OTR is a 

potential issue and that many important 

existing PAMS sites would not be part 

of the required PAMS sites based on the 

proposed network design. As noted by 

several commenters, the EPA intended 

the state directed EMPs to give states 

flexibility in determining data needed to 

understand local O3 formation, 

including transport in the Northeast. 

However, the EPA also agrees that as 

proposed many states in the OTR would 

not be required to develop EMPs and, 

therefore, may not be provided PAMS 

resources. To address these concerns 

and ensure adequate network coverage 

in the OTR, the EPA is adding a 

requirement that all states in the OTR 

develop and implement an EMP 

regardless of O3 attainment status. This 

change will help ensure that an EMP 

appropriate for the entire OTR can be 

implemented. 

Concerns were raised by some states 

that existing NCore sites may not be the 

most appropriate location for making 

PAMS measurements. One commenter 

noted that their NCore site was inland 

but that their ‘‘most significant ozone 

problems occur along the shoreline due 

to transport along the lake’’, and that 

‘‘the NCore site cannot provide insight 

into these important lakeshore ozone 

processes.’’ Another commenter stated 

that ‘‘while it was laudable to leverage 

sites where data is already being 

collected, it is unclear whether NCore 

sites adequately meet the objectives of 

the PAMS program’’, and that ‘‘the 

current NCore network may not be 

adequate to depict boundary conditions 

or areas of maximum emissions.’’ One 

commenter stated that ‘‘in some 

nonattainment areas an NCore site may 

be an appropriate location for a PAMS 

monitor, but in other areas it would be 

preferable to install the PAMS 

monitoring in a location downwind of a 

source region where higher ozone 

exposures occur’’ and that ‘‘State and 

local boundaries should not be part of 

the network design criteria.’’ One 

commenter noted that while the EPA 

had proposed to allow waivers, it was 

unclear if waivers would be allowed 

where the alternative site was in a 

different CBSA or state than the 

required PAMS site. As stated in our 

proposal, the EPA recognizes that in 

some cases existing PAMS sites (or 

other sites) may be better suited to meet 

local and national data needs. For this 

reason, we had proposed to allow 

waivers in these situations. We do agree 

that it is appropriate in some cases to 

allow these waivers to cross CBSA and 

state boundaries. Therefore, we have 

added specific language to the final 

waiver provisions to clarify that waivers 

can be allowed to cross CBSA and state 

boundaries. Where a monitoring agency 

receives a waiver from siting a monitor 

in reliance on a monitor operated by a 

different monitoring agency (e.g., across 

state lines), the waiver will be 

conditioned on the monitor being 

properly included in the other agency’s 

network plan, and operated in 

accordance with the requirements of 

Part 58, including the relevant 

appendices. 

In addition to the concerns raised 

about closing important existing PAMS 

sites discussed above, some commenters 

raised concerns that many of the newly 

required PAMS sites would be in 

locations that were expected to attain 

the revised O3 NAAQS soon after the 

new sites would be installed. One 

commenter noted that ‘‘requiring 

marginal nonattainment areas to install 

PAMS sites would result in a large 

undertaking at an area that would most 

likely be back in attainment at or around 

the time the PAMS site started 

collecting data.’’ One commenter stated 

that by tying the network requirement to 

NAAQS attainment ‘‘threatens to 

underserve areas that are very close to 

exceeding the revised ozone NAAQS 

and results in significant gaps in the 

spatial coverage of the PAMS network’’ 

and ‘‘has the potential to introduce 

undesirable uncertainty on the size and 

spatial extent of the PAMS network over 

the long term.’’ Another commenter was 

concerned that the proposed network 

would be unstable, and would 

experience frequent changes as areas 

came into attainment or went out of 

attainment thus reducing the value of 

the data collected, and resulting in 

inefficient use of resources. One 

commenter noted that ‘‘a more stable 

monitoring network design will allow 

for the examination of trends from 

spatially robust, long running sites and 

will allow states to firmly establish the 

infrastructure costs.’’ 

The EPA noted in the proposal that 

the size and locations of the proposed 

required PAMS network is sensitive to 

the level of the revised O3 NAAQS and 

future O3 concentrations. We recognize 

and agree that if current downward 

trends in O3 concentrations continue, 

many initially required sites may no 

longer be required to make PAMS 

measurements soon after the sites were 

installed. Non-required sites could be 

closed, soon after being installed, at the 

state’s discretion. We agree this would 

result in an inefficient use of resources. 

We also note that if these sites were 

closed following a potential 

reclassification to attainment, the loss of 

those sites could lead to a network with 

poor spatial coverage. Therefore, the 

EPA is making changes to the proposed 

revisions to the network design to 

improve the stability of the fixed site 

network. As explained below, the final 

requirements are based on options for 

which we requested comments in the 

proposal and the comments we have 

received. 

We requested comments on additional 

options to define the fixed PAMS 

network component of the new network 

design. These options were further 

discussed in a memorandum to the 

docket (Cavender, 2014). One option 

discussed was to require PAMS 

measurements at all NCore sites 

irrespective of the O3 attainment status 

of the area. One commenter noted that 

‘‘requiring PAMS monitoring at all 

NCore sites, regardless of ozone 

attainment status, provides the most 

spatially robust and stable monitoring 

network.’’ We noted that this 

requirement would result in a network 

of approximately 80 sites, which would 

be larger than the current network. In 

the supporting memorandum, we noted 

that a fixed network of 80 sites would 

strain existing resources and would not 

allow adequate resources to implement 

the state directed EMPs. 

Another option discussed in the 

proposal included requiring PAMS 

measurements at NCore sites in O3

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65423 

224NOy includes NO, NO2, and other oxidized 

nitrogen compounds (NOz). 

nonattainment areas with a population 

greater than 1,000,000. We noted that 

this option would result in a network of 

between 31 and 37 sites depending on 

the level of the revised O3 NAAQS. We 

also noted that focusing the 

applicability of PAMS to those NCore 

sites in larger CBSAs would still 

provide the desired improvement in 

geographic distribution while reducing 

the number of required sites down to a 

level that would provide sufficient 

resources to implement the statedirected EMP portion of the network. 

One commenter stated that they 

‘‘supported a 1,000,000 population 

threshold because it would help 

prioritize resources to areas based on 

the greatest human health impacts.’’ In 

addition, a number of commenters, 

while not commenting on the need for 

a population limit, did raise concerns 

about their ability to acquire and retain 

staff with the necessary expertise to 

collect PAMS measurements in less 

urbanized areas. As with the proposed 

network design, we recognize that the 

total number of sites and the ultimate 

spatial coverage under this option is 

also sensitive to changes in O3

concentrations. If current downward 

trends in O3 concentrations continue, 

many initially required sites would not 

be required soon after they were 

installed. As with the proposed option, 

this option could result in an unstable 

network resulting in an inefficient use 

of resources and inadequate spatial 

coverage to meet the network goals 

discussed above. 

Upon further consideration and in 

response to the comments received, we 

are finalizing a network design that 

includes a requirement for states to 

make PAMS measurements at all NCore 

sites in CBSAs with a population of 

1,000,000 people or more, irrespective 

of O3 attainment status. We believe this 

requirement will result in an 

appropriately sized network (roughly 40 

sites) that will provide adequate spatial 

coverage to meet national model 

evaluation needs (Cavender, 2015). 

Redundancy is greatly reduced while 

important network coverage is added in 

the midwest, southeast, and mountain 

west. The improved spatial coverage 

will also strengthen the EPA’s ability to 

track trends in precursor concentrations 

regionally. 

Because the network requirement is 

not tied to attainment status, this final 

requirement will ensure network 

stability and allows for more efficient 

use of available resources. This final 

requirement also removes uncertainty as 

to applicability and aids planning and 

logistics involved with implementing 

the new requirements. Monitoring 

agencies can determine the applicability 

of the fixed site requirements to their 

areas today, and begin to make plans for 

investments in equipment, shelter 

improvements, and staffing and training 

needs necessary to implement the fixed 

site requirements without having to wait 

for the designations process to be 

completed. In addition, this final 

requirement should alleviate concerns 

raised by monitoring agencies in more 

rural locations over the ability to attract 

and retain staff with the skills necessary 

to make PAMS measurements. 

By adding the PAMS measurements to 

existing NCore sites, significant 

efficiencies can be obtained which 

should further reduce the costs of the 

fixed site network as NCore sites 

currently make many of the PAMS 

measurements. Furthermore, adding the 

additional PAMS measurements (e.g., 

speciated VOCs, carbonyls, and mixing 

height) to existing NCore sites will 

improve our ability to assess other 

pollutants (e.g., air toxics and PM2.5). 

Although, as discussed in comment 

and summarized above, we believe there 

are good reasons for not tying the 

requirement for fixed PAMS sites to O3

attainment status, we continue to 

believe that requiring PAMS 

measurements in areas that historically 

have had low O3 concentrations is 

unlikely to provide data of significant 

value to warrant the expense and effort 

of making such measurements. 

Therefore, we have included a provision 

that would allow a monitoring agency to 

obtain a waiver, based on Regional 

Administrator approval, in instances 

where CBSA-wide O3 design values are 

equal to or less than 85% of the 8-hour 

O3 NAAQS and where the site is not 

considered an important upwind or 

downwind site for other nonattainment 

areas. The EPA selected 85% as the 

threshold for this waiver provision as it 

has been used historically to identify 

locations needing additional monitoring 

for both the O3 and PM2.5 NAAQS. The 

EPA will work with the monitoring 

agencies and the Regions to help ensure 

consistent implementation of this 

waiver provision. 

The second part of the proposed 

PAMS network design included 

monitoring agency directed enhanced 

O3 monitoring activities intended to 

provide data needed to understand an 

area’s specific O3 issues. To implement 

this part of the PAMS network design, 

the EPA proposed to add a requirement 

for states with O3 nonattainment areas 

to develop an EMP. The purpose of the 

EMP was to improve monitoring for 

ambient concentrations of O3, NOX, total 

reactive nitrogen (NOy) 224, VOC, and 

meteorology. The EPA suggested that 

types of activities that might be 

included in the state’s EMP could 

include additional PAMS sites (e.g., 

upwind or downwind sites), additional 

O3 and NOX monitoring, ozonesondes or 

other aloft measurements, rural 

measurements, mobile PAMS sites, 

additional meteorological 

measurements, and episodic or 

intensive studies. The intent of the 

EMPs is to allow monitoring agencies 

flexibility in determining and collecting 

the information they need to understand 

their specific O3 problems. 

We received comments on the 

proposed requirement for an EMP in 

states with O3 nonattainment areas. 

Most comments supported the 

requirement, but other comments raised 

a number of concerns. A number of 

commenters questioned the need for 

EMPs in Marginal and Moderate O3

nonattainment areas. They noted that in 

most cases, Marginal O3 nonattainment 

areas were expected to come into 

compliance without state-specific 

controls. One commenter stated that 

‘‘nonattainment areas projected to attain 

the standard without additional statelevel actions may not need the PAMS 

resources and additional monitoring to 

develop a better understanding of their 

ozone issues.’’ One commenter noted 

that ‘‘marginal ozone nonattainment 

areas are given only a few requirements 

because it is assumed that the areas will 

reach attainment within three years.’’ 

Another commenter stated ‘‘requiring 

enhanced monitoring for any marginal 

or moderate area should only be 

implemented where such analyses show 

the need for this data.’’ The EPA agrees 

that based on current trends in O3

concentrations and the EPA’s own 

projections, states in Marginal 

nonattainment areas likely will comply 

with the revised NAAQS without 

additional state-directed controls, and 

as such, an EMP is not necessary in 

Marginal O3 attainment areas. 

Accordingly, the EPA is finalizing a 

requirement for EMPs in areas classified 

as Moderate or above O3 nonattainment 

and, thereby, removing the applicability 

of the requirement for Marginal areas. 

We believe this final requirement will 

provide the desired flexibility to allow 

states to identify enhanced monitoring 

needs while focusing resources for 

EMPs in areas of greater need of 

enhanced monitoring data. 

Commenters expressed concerns over 

the lack of detail on what an approvable 

EMP would entail. As proposed, the 

mstockstill on DSK4VPTVN1PROD with RULES2

65424 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

225The EPA notes that isoprene (the dominant 

biogenic compound in the Southeast) is well 

measured using autoGCs. The EPA is also 

evaluating the potential of modern autoGC’s to 

measure alpha and beta pinene; however that work 

is not complete. 

EMPs would be reviewed and approved 

by the EPA Regional Administrator as 

part of the annual monitoring plan 

review process. One commenter 

recommended that the ‘‘EPA detail the 

requirements of the EMPs for ozone 

nonattainment areas in future 

implementation guidance.’’ One 

commenter stated that the ‘‘EPA should 

provide some coordination between 

regional offices and technical guidance 

to state agencies that would be of 

assistance in developing and executing 

the EMPs.’’ The requirements for the 

EMPs were intentionally left quite 

general in order to maximize the 

flexibility for states in identifying their 

specific data needs. Regional approval 

of the plans is required to ensure the 

enhanced monitoring planned will be 

commensurate with grant funds 

provided for EMPs. Nonetheless, the 

EPA understands the need for guidance 

on developing EMPs and commits to 

working with monitoring agencies and 

the regions to develop appropriate 

guidance on developing and reviewing 

EMPs. 

2. Speciated VOC Measurements 

Measurement of speciated VOCs 

important to O3 formation is a key 

aspect of the PAMS program. The 

existing PAMS requirements allow for a 

number of options in measuring 

speciated VOCs at PAMS sites which 

include (1) hourly measurements using 

an automatic gas chromatograph 

(‘‘autoGC’’), (2) eight 3-hour samples 

daily using canisters, or (3) one morning 

and one afternoon sample with a 3-hour 

or less averaging time daily using 

canisters plus continuous Total Nonmethane Hydrocarbon (TNMHC) 

measurements. 

The EPA believes that the current 

options provided for VOC measurement 

limit the comparative value of the data 

being collected, and proposed that 

required PAMS sites must measure and 

report hourly speciated VOCs, which 

effectively would require them to use an 

autoGC to measure VOCs in lieu of 

canisters. More complete and consistent 

speciated VOC data nationally would 

better help meet certain objectives of the 

PAMS program described above (e.g., a 

speciated ambient air database useful in 

evaluating control strategies, analyzing 

emissions inventory issues, 

corroborating progress toward 

attainment, and evaluating population 

exposure to air toxics). Furthermore, as 

noted by the CASAC AMMS, hourly 

VOC data are ‘‘particularly useful in 

evaluating air quality models and 

performing diagnostic emission 

attribution studies. These data can be 

provided on a near real-time basis and 

presented along with other precursor 

species (e.g., oxides of nitrogen and 

carbon monoxide) collected over similar 

averaging times.’’ Longer time-averaged 

data are of significantly lower value for 

model evaluation. In addition, creating 

consistent monitoring requirements 

across the network would provide better 

data for analyzing regional trends and 

spatial patterns. 

At the time the original PAMS 

requirements were promulgated, the 

canister options were included because 

the EPA recognized that the 

technologies necessary to measure 

hourly average speciated VOCs 

concentrations were relatively new and 

may not have been suitable for broad 

network use. At that time, GCs designed 

for laboratory use were equipped with 

auto-samplers designed to ‘‘trap’’ the 

VOC compounds from a gas sample, and 

then ‘‘purge’’ the compounds onto the 

GC column. The EPA did not believe 

that autoGCs were universally 

appropriate due to the technical skill 

and effort necessary at that time to 

properly operate an autoGC. 

While the basic principles of autoGC 

technology have not changed, the 

hardware and software of modern 

autoGCs are greatly improved over that 

available at the time of the original 

PAMS requirements. Based on advice 

from the CASAC AMMS, the EPA 

initiated an evaluation of current 

autoGCs potentially suitable for use in 

the PAMS network. Based on the 

preliminary results, the EPA believes 

that typical site operators, with 

appropriate training, will have the skill 

necessary to operate a modern autoGC 

successfully. Considering the advances 

in autoGC technology, the added value 

obtained from hourly data, and the 

proposed move of PAMS measurements 

to NCore sites in O3 nonattainment 

areas, the EPA proposed to require 

hourly speciated VOC sampling at all 

PAMS sites. The EPA noted that this 

proposed requirement would effectively 

prevent the use of canisters to collect 

speciated VOCs at the required PAMS 

sites but that canister sampling may 

continue to be an appropriate method 

for collecting speciated VOCs at other 

locations as part of discretionary 

monitoring designed within the EMPs. 

While the EPA believes that the 

proposed transition to hourly speciated 

VOC sampling is the appropriate 

strategy to take advantage of improved 

technology and to broaden the utility of 

collected data, we are also mindful of 

the additional rigidity that the proposed 

mandatory use of autoGCs may have for 

monitoring agencies, especially those 

that have experience with and have 

established effective and reliable 

canister sampling programs. Therefore, 

the EPA requested comment on the 

proposed requirement for hourly VOC 

sampling as well as the range of 

alternatives that might be appropriate in 

lieu of a strict requirement. 

The EPA received a number of 

comments on the requirement to 

measure hourly VOCs at required PAMS 

sites. Many commenters agreed with 

requiring hourly VOC data. One 

commenter agreed that ‘‘hourly VOC 

data collection is the most appropriate 

and useful for PAMS monitors’’ and that 

‘‘it is only appropriate to approve an 

alternative data collection interval if it 

is believed that the high ozone in an 

area is due to other pollutants, such as 

NOX or methane.’’ One commenter 

stated they ‘‘supported the movement 

towards hourly PAMS VOC speciated 

measurements with flexibility to use 

canisters if programmatic or logistical 

needs indicate.’’ 

However, some commenters raised 

concerns with the hourly VOC 

requirement. Some commenters 

questioned if autoGCs would be capable 

of measuring important VOC species in 

their environment. One commenter 

noted that in their location (high desert) 

‘‘the largest VOC present in our 

inventory is creosote, a compound not 

commonly measured with this 

instrumentation.’’ One commenter 

stated that the ‘‘Southeastern United 

States is dominated by biogenic VOC 

emissions’’ and questioned ‘‘the benefits 

of an autoGC in understanding ozone 

formation in any potential 

nonattainment area in our State.’’ 225

Some questioned the detection 

capabilities of autoGCs as compared to 

canister sampling. One commenter 

found that the method detection limit 

(MDL) for their canister sampling was 

‘‘consistently equal to or less than the 

autoGC instrumentation’’ based on the 

EPA’s autoGC evaluation laboratory 

report (RTI, 2014). Another commenter 

noted that the MDLs for many of the 

compounds and systems reported in the 

laboratory report were too high to be 

useful at PAMS sites. Another 

commenter stated that they found that 

‘‘retention-time shifts made it difficult 

for instant identification of chemical 

peaks’’ and that ‘‘states should be 

allowed the flexibility to continue using 

canisters instead of autoGC.’’ 

As noted in the preamble, and the 

comments received, the EPA is 

currently completing an evaluation of 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65425 

226Several factors combined to result in the high 

relative MDL estimates reported in laboratory 

report. The MDL testing in the laboratory was 

conducted during concurrent tests for interferences 

from humidity and temperature. In addition, the 

MDL testing was conducted at relatively high 

concentrations compared to the concentrations 

testing would be conducted at for conventional 

MDL testing. Finally, as noted in the laboratory 

report, a number of instruments were having 

technical difficulties during the testing which 

greatly impacted their MDL results. The EPA is 

continuing the autoGC evaluation and has 

conducted a field study during the summer of 2015. 

A final report is expected in early 2016. 

commercially available autoGCs. A copy 

of the report for the laboratory phase of 

the study is available in the docket (RTI, 

2014). As noted in the laboratory report, 

the MDL estimates made for the 

laboratory study were not conducted 

according to normal MDL testing 

procedures and as such the results 

should only be used to compare the 

various instruments being tested against 

each other.226 As part of the evaluation, 

the EPA identified the manufacturer’s 

specifications for MDL. Most of the 

systems that are being evaluated have a 

manufacturer’s estimated MDL in the 

range of 0.1 ppb to 0.5 ppb. Based on 

the evaluation of MDL capabilities and 

typical ambient concentrations of O3

precursors, the EPA believes that 

autoGCs are an appropriate method for 

gathering VOC data at most urban 

locations. However, canister sampling 

may be more appropriate in locations 

with low VOC concentrations. 

For the reasons discussed above and 

in the proposed rule, the EPA is 

finalizing a requirement for hourly 

speciated VOC measurements at 

required PAMS sites. The EPA believes 

that hourly VOC measurements will 

provide a more complete and consistent 

speciated VOC database to help meet 

the PAMS program objectives described 

above. Hourly VOC data are particularly 

useful in evaluating air quality models 

and performing diagnostic emission 

attribution studies. Longer timeaveraged data are of lower value for 

model evaluation. Consistent 

monitoring requirements across the 

network will provide better data for 

analyzing regional trends and spatial 

patterns. 

However, the EPA agrees that there 

may be locations where an autoGC may 

not be the most appropriate method for 

VOC measurement and that it is 

appropriate to allow for canister 

sampling in limited situations. 

Accordingly, the EPA is adding a waiver 

option (to be approved by the EPA 

Regional Administrator) to allow three 

8-hour average samples every 3rd day as 

an alternative in cases where VOCs are 

not well measured by autoGC due to 

low concentrations of target compounds 

or where the predominant VOC 

compounds cannot be measured using 

autoGC technology (e.g., creosote in 

high desert environments). This 

alternative sampling frequency was 

selected to be consistent with the 

sampling frequency selected for 

carbonyls, which is discussed later in 

this preamble. 

3. Carbonyl Measurements 

Carbonyls include a number of 

compounds important to O3 formation 

that cannot currently be measured using 

the autoGCs or canisters used at PAMS 

sites to measure speciated VOCs. The 

current method for measuring carbonyls 

in the PAMS program is Compendium 

Method TO–11A (U.S. EPA, 1999). In 

this method, carbonyl compounds are 

adsorbed and converted into stable 

hydrazones using 

dinitrophenylhydrazine (DNPH) 

cartridges. These cartridges are then 

analyzed for the individual carbonyl 

compounds using liquid 

chromatography (LC) techniques. Three 

carbonyls are currently required to be 

measured in the PAMS program— 

formaldehyde, acetaldehyde, and 

acetone. 

In 2006, the EPA revised the PAMS 

requirements such that carbonyl 

sampling was only required in areas 

classified as serious or above 

nonattainment for O3 under the 8-hour 

O3 standard which effectively reduced 

the applicability of carbonyl sampling to 

a few areas in California. This change 

was made in recognition that there were 

a number of issues with Method TO– 

11A that raised concerns with the 

uncertainty in the carbonyl data being 

collected. These issues include 

interferences (humidity and O3) and 

breakthrough (i.e., overloading of the 

DNPH cartridge) at high concentrations. 

While solutions for these issues have 

been investigated, these improvements 

have not been incorporated into Method 

TO–11A. 

A recent evaluation of the importance 

of VOCs and carbonyls to O3 formation 

determined that carbonyls, especially 

formaldehyde, are very important to O3

formation (Cavender, 2013). CASAC 

AMMS (U.S. EPA, 2011f) also noted the 

importance of carbonyls stating that 

‘‘There are many compelling scientific 

reasons to measure carbonyls. They are 

a very important part of O3 chemistry 

almost everywhere.’’ Although the EPA 

recognizes the issues that have been 

raised about the current method of 

measuring carbonyls, due to the 

importance of carbonyls to 

understanding O3 chemistry, the EPA 

proposed to require all required PAMS 

sites to measure carbonyls. 

Several commenters agreed with the 

need for carbonyl data at PAMS sites. 

However, a number of commenters 

questioned the proposed frequency of 

eight 3-hour samples every day during 

the PAMS sampling season (June 

through August). Several commenters 

indicated that the frequency was too 

high. One commenter noted that the 

requirement would require 800 samples 

per season at each PAMS site and 

pointed out that this requirement, 

which was required at the inception of 

the PAMS program in the 1990s was 

‘‘found to be prohibitively expensive, 

technically unsustainable, and 

qualitatively compromised.’’ Another 

commenter stated that ‘‘this level of 

sampling would require a substantial 

amount of agency resources and seems 

unduly burdensome.’’ A number of 

commenters also questioned the 

commercial availability of an 8-channel 

carbonyl sampler that would be needed 

to take eight 3-hour samples daily. In 

light of the comments and upon further 

review, the EPA agrees that the 

proposed frequency is unduly 

burdensome and is finalizing a 

requirement with a lower frequency. 

A number of alternative frequencies 

were suggested in the comments. 

Several commenters suggested a 

frequency of three 8-hour samples on 

either a 1-in-6 day or 1-in-3 day basis. 

Another commenter suggested a 

frequency of eight 3-hour samples on a 

1 in 6 day basis. The EPA notes that 

sampling on a 1-in-6 day frequency 

would lead to as little as 15 sampling 

days per PAMS sampling season. The 

EPA believes that 15 sampling days is 

too few to provide a meaningful 

representation of carbonyl 

concentrations over the PAMS sampling 

period. A sampling frequency of 1-in-3 

days would lead to 30 sampling days 

per season with each day of the week 

being represented at least 4 times per 

sampling season. With regards to 

samples per day, a 3-hour sampling 

duration provides a better diurnal 

representation of carbonyl sampling 

compared with an 8-hour sampling 

duration; however 8-hour sampling can 

provide information useful for 

evaluating diurnal differences in 

carbonyl concentrations. Upon further 

consideration and in light of the 

comments received, the EPA is 

finalizing a carbonyl sampling 

requirement with a frequency of three 8- 

hour samples on a 1-in-3 day basis. This 

final requirement will result in 

approximately 90 samples per PAMS 

sampling season which the EPA 

believes is not unduly burdensome and 

mstockstill on DSK4VPTVN1PROD with RULES2

65426 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

will provide a reasonable representation 

of carbonyl concentrations. 

A number of commenters noted the 

ongoing development of continuous 

formaldehyde instruments, and 

recommended that EPA allow for 

continuous formaldehyde 

measurements as an alternative to the 

manual cartridge based TO–11A 

method. The EPA agrees that 

continuous formaldehyde, with the 

ability to obtain hourly averaged 

measurements, would be a significantly 

more valuable that the longer averaged 

measurements. As a result, the EPA has 

added an option to allow for continuous 

formaldehyde as an alternative to the 

carbonyl measurements using TO–11A. 

4. Nitrogen Oxides Measurements 

It is well known that NO and NO2

play important roles in O3 formation 

(U.S. EPA, 2013, Section 3.2.2). Under 

the current network design, Type 2 

PAMS sites are required to measure 

NOX (which by definition is the sum of 

NO and NO2), and Types 1, 3, and 4 

sites are required to measure NOy. 

NCore sites are currently required to 

measure NOy but are not required to 

measure NO2 separately. 

In conventional NOX analyzers, NO2

is determined as the difference between 

the measured NO and NOX

concentrations. However, due to the 

non-selective reduction of oxidized 

nitrogen compounds by the 

molybedenum converter used in 

conventional NOX monitors, the NO2

measurement made by conventional 

NOX monitors can be biased high due to 

the varying presence of NOz compounds 

that may be reported as NO2. The 

unknown bias from the NOz compounds 

is undesirable when attempting to 

understand O3 chemistry. 

Improvements in reactive nitrogen 

measurements have been made since the 

original PAMS requirements were 

promulgated that allow for improved 

NO2 measurements. Selective photolytic 

converters have been developed that are 

not significantly biased by NOz 

compounds (Ryerson et al., 2000). 

Monitors using photolytic converters are 

commercially available and have been 

approved as FEMs for the measurement 

of NO2. In addition, methods that 

directly read NO2 have been developed 

that allow for very accurate readings of 

NO2 without some of the issues inherent 

to the ‘‘difference method’’ used in 

converter-based NOX analyzers. 

However, these direct reading NO2

analyzers generally do not provide an 

NO estimate, and would need to be 

paired with a converter-based NOX

monitor or NOy monitor in order to also 

measure NO. 

As discussed above, the EPA is 

finalizing a PAMS network design such 

that PAMS measurements will be 

required at existing NCore sites in 

CBSAs with a population of 1,000,000 

people or more. NCore sites currently 

are required to measure NO and NOy. 

NCore sites are not currently required to 

measure NO2. Due to the importance of 

accurate NO2 data to the understanding 

of O3 formation, the EPA proposed to 

require NO2 measurements at required 

PAMS sites. Since existing NCore sites 

currently measure NOy, either a direct 

reading NO2 analyzer or a photolyticconverter NOX analyzer could be used 

to meet the proposed requirement. The 

EPA believes conventional NOX

analyzers would not be appropriate for 

making PAMS measurements due to the 

uncertainty caused by interferences 

from NOz compounds. 

A number of commenters questioned 

the need for both NOy and NO2

measurements at PAMS sites. One 

commenter stated that ‘‘in dense urban 

areas an NO/NO2/NOX instrument may 

be adequate but in a more rural area an 

NO/NOy instrument may be preferable.’’ 

Another commenter stated that due to 

the size of the grid cells used in grid 

models that ‘‘the impact of NOz 

interferences would be very small 

compared to other modeling 

uncertainties such as emission 

inventories and mixing heights.’’ 

Another commenter suggested that 

‘‘EPA should provide clear and specific 

guidance on how agencies can request 

that the NOy monitoring be eliminated 

from the NCore suite based on 

comparative data between the NO2 and 

NOy monitors.’’ 

The comments suggest that the 

model’s ability to simulate the 

partitioning of reactive nitrogen is 

unimportant because there may be other 

errors in the model. The EPA believes 

that measurements should be routinely 

collected so that it can be demonstrated 

that the chemistry, meteorology, and 

emissions in the model are all of 

sufficient reliability for use in informing 

air quality management decisions. 

Monitoring sites rarely fall into simple 

categories of urban or rural, and the 

speciation of NOy varies considerably as 

a function of meteorology and time of 

day at a given site. The state-of-thescience in regulatory air quality 

modeling is such that accurate 

measurements of key O3 precursors 

must be available to demonstrate the 

credibility of the model predictions. The 

increased availability of special field 

study observations is leading to 

increased scrutiny of the chemical 

mechanisms used in regulatory 

modeling. Comprehensive and accurate 

measurement sites are needed to 

demonstrate the adequacy of the models 

and to respond to these challenges. 

Measurements of NO, NO2, and NOy

concentrations are critical to 

understanding atmospheric aging and 

photochemistry. These measurements 

will provide essential information about 

whether NOy compounds are fresh or 

aged which is important for 

understanding both local 

photochemistry (i.e. through indicator 

ratios to distinguish NOX vs VOC 

limited conditions) as well as for 

characterizing transport from upwind 

regions. These evaluations may be 

conducted using observations, box 

modeling or through complex 

photochemical grid based modeling. 

Accurate speciated and total NOy

measurements are necessary for all three 

types of analysis. For these reasons, the 

EPA is finalizing the requirement for 

required PAMS sites to measure true 

NO2 in addition to NO and NOy.

5. Meteorology Measurements 

The current PAMS requirements 

require monitoring agencies to collect 

surface meteorology at all required 

PAMS sites. As noted in the EPA’s 

Technical Assistance Document (U.S. 

EPA, 1998) for the PAMS program, the 

PAMS requirements do not provide 

specific surface meteorological 

parameters to be monitored. As part of 

the implementation efforts for the 

original PAMS program, a list of 

recommended parameters was 

developed and incorporated into the 

TAD which includes wind direction, 

wind speed, temperature, humidity, 

atmospheric pressure, precipitation, 

solar radiation, and ultraviolet (UV) 

radiation. Currently, NCore sites are 

required to measure the above 

parameters with the exceptions of 

atmospheric pressure, precipitation, 

solar radiation, and UV radiation. In 

recognition of the importance of these 

additional measurements for 

understanding O3 formation, the EPA 

proposed to specify that required PAMS 

sites are required to collect wind 

direction, wind speed, temperature, 

humidity, atmospheric pressure, 

precipitation, solar radiation, and UV 

radiation. Since NCore sites are 

currently required to measure several of 

these surface meteorological parameters, 

the net impact of the proposal was to 

add the requirement for the monitoring 

of atmospheric pressure, precipitation, 

solar radiation, and UV radiation at 

affected NCore sites. The EPA received 

no significant comments on this portion 

of the proposal, and therefore is 

finalizing the requirement as proposed. 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65427 

The existing PAMS requirements also 

require the collection of upper air 

meteorological measurements at one site 

in each PAMS area. The term upper air 

meteorological is not well defined in the 

existing PAMS requirements. As part of 

the implementation efforts for the 

original PAMS program, mixing height 

was added to the PAMS TAD as a 

recommended meteorological parameter 

to be monitored. Most monitoring 

agencies installed radar profilers to meet 

the requirement to collect upper air 

meteorology. Radar profilers provide 

data on wind direction and speed at 

multiple heights in the atmosphere. 

Radio acoustic sounding system (RASS) 

profilers are often included with radar 

profilers to obtain atmospheric 

temperature at multiple heights in the 

atmosphere and to estimate mixing 

height. The EPA recognizes that the 

upper air data on wind speed and wind 

direction from radar profilers can be 

very useful in O3 modeling. However, 

many of the current PAMS radar 

profilers are old and in need of 

replacement or expensive maintenance. 

In addition, the cost to install and 

operate radar profilers at all required 

PAMS sites would be prohibitive. 

Therefore, the EPA did not propose to 

add upper air wind speed and direction 

as required meteorological parameters to 

be monitored at required PAMS sites. 

Where monitoring agencies find the 

radar profiler data valuable, continued 

operation of existing radar profilers or 

the installation of new radar profilers 

would be appropriate to consider as part 

of the state’s EMP. 

As discussed above, mixing height is 

one upper air meteorological 

measurement that has historically been 

measured at PAMS sites. A number of 

methods can be used to measure mixing 

height in addition to radar profiler 

technology discussed above. Recent 

developments in ceilometer technology 

allow for the measurement of mixing 

height by changes in particulate 

concentrations at the top of the 

boundary layer (Eresmaa et al., 2006). 

Ceilometers provide the potential for 

continuous mixing height data at a 

fraction of the cost of radar profilers. 

Due to the importance of mixing height 

measurements for O3 modeling, the EPA 

proposed to add the requirement for 

monitoring agencies to measure mixing 

height at required PAMS sites. 

A number of commenters questioned 

the need for mixing height 

measurements at PAMS sites. One 

commenter stated, ‘‘the photochemical 

modeling community has a long history 

of relying upon National Weather 

Service measurements for mixing 

height.’’ Another commenter stated that 

‘‘in some areas of the country the 

models used to predict mixing height 

are adequate, but in other mountainous 

or marine areas model-predicted mixing 

height data is inadequate.’’ Accurate 

estimates of mixing height are important 

for appropriately characterizing 

concentrations of O3 and O3 precursors. 

Mixing height is also important for 

characterizing how modeled O3 may 

change as a result of changing NOX and 

VOC concentrations. For instance, if the 

modeled mixing height is too low 

causing unrealistically high 

concentration of NOX, then O3

destruction could be predicted when O3

production may be happening in the 

atmosphere. When this or the opposite 

situation exists in modeling it may lead 

O3 response to emissions changes that 

are less reliable for air quality planning 

purposes. While models are believed to 

do a reasonable job of predicting mixing 

height during the day, there is 

considerably more uncertainty in 

predicting this parameter during 

morning and evening transition periods 

and at night. Model O3 predictions are 

particularly sensitive to mixing height 

during the time periods for which 

uncertainty in this parameter is greatest. 

Several commenters noted that nearby 

National Oceanic and Atmospheric 

Administration (NOAA) Automated 

Surface Observing System (ASOS) sites 

may be a better alternative for collection 

of mixing height data. As indicated in 

the proposal, the EPA is aware of the 

network of ceilometers operated by 

NOAA as part of ASOS. The EPA has 

been in discussions with NOAA 

regarding the potential for these systems 

to provide the needed mixing height 

data. However, the ASOS ceilometers 

are not currently equipped to provide 

mixing height data and NOAA has no 

current plans to measure continuous 

mixing height in the future. 

Nonetheless, the EPA will continue to 

work with NOAA to determine if the 

ASOS ceilometers can be upgraded to 

meet the need for mixing height data, 

and included proposed regulatory 

language that will allow states a waiver 

to use nearby mixing height data from 

ASOS (or other sources) to meet the 

requirement to collect mixing height 

data at required PAMS sites when such 

data are suitable and available. 

The EPA is finalizing the requirement 

for the measurement of mixing height at 

required PAMS sites due to the 

importance of mixing height in O3

modeling. A waiver option, to be 

approved by the Regional 

Administrator, is also being included to 

allow mixing height measurements to be 

obtained from other nearby sites (e.g., 

NOAA ASOS sites). 

6. PAMS Season 

Currently, PAMS measurements are 

required to be taken during the months 

of June, July, and August. This 3-month 

period is referred to as the ‘‘PAMS 

Season.’’ As part of the PAMS reevaluation, the EPA considered changes 

to the PAMS season. The 3-month 

PAMS season was originally selected to 

represent the most active period for O3

formation. However, the EPA notes that 

in many areas the highest O3

concentrations are observed outside of 

the PAMS season. As an example, the 

highest O3 concentrations in the 

mountain-west often occur during the 

winter months. Data collected during 

the current PAMS season would have 

limited value in understanding winter 

O3 episodes. 

The CASAC AMMS (U.S. EPA, 2011f) 

noted in their report to the EPA that ‘‘it 

would be desirable to extend the PAMS 

monitoring season beyond the current 

June, July, August sampling period.’’ 

But that ‘‘the monitoring season should 

not be mandated and rigid; it should be 

flexible and adopted and coordinated on 

a regional airshed basis.’’ The EPA 

agrees with CASAC on the need for 

flexibility in determining when PAMS 

measurements should be taken to meet 

local monitoring needs but also agrees 

with CASAC that the flexibility ‘‘should 

not conflict with national goals for the 

PAMS program.’’ A significant benefit of 

the standard PAMS season is that it 

ensures data availability from all PAMS 

sites for national- or regional-scale 

modeling efforts. 

While the EPA agrees with the 

potential benefit of extending the 

availability of PAMS measurements 

outside of the current season, we also 

considered the burden of requiring 

monitoring agencies to operate 

additional PAMS measurements (e.g., 

hourly speciated VOC) for periods that 

in some cases, might be much longer 

than the current 3-month season, for 

example, if the PAMS season was 

extended to match each state’s required 

O3 monitoring season. Being mindful of 

the potential burden associated with a 

lengthening of the PAMS season as well 

as the potential benefits of the 

additional data, the EPA proposed to 

maintain the current 3-month PAMS 

monitoring season for required PAMS 

sites rather than extending the PAMS 

season to other periods where elevated 

O3 may be expected. No significant 

comments were received on the 

proposed PAMS season, and as such, for 

the reasons stated here and in the 

proposal, the EPA is not changing the 3- 

month PAMS season of June, July, and 

August. 

mstockstill on DSK4VPTVN1PROD with RULES2

65428 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

The EPA believes that the 3-month 

PAMS season will provide a consistent 

data set of O3 and O3 precursor 

measurements for addressing the 

national PAMS objectives. Monitoring 

agencies are strongly encouraged to 

consider collecting PAMS 

measurements in additional periods 

beyond the required PAMS season as 

part of their EMP. The monitoring 

agencies should consider factors such as 

the periods of expected peak O3

concentrations and regional consistency 

when determining potential expansion 

of their specific monitoring periods 

beyond the required PAMS season. 

7. Timing and Other Implementation 

Issues 

The EPA recognizes that the changes 

to the PAMS requirements will require 

resources and a reasonable timeline in 

order to be successfully implemented. 

The PAMS program is funded, in part, 

as part of the EPA’s section 105 grants. 

The EPA believes that the current 

national funding level of the PAMS 

program is sufficient to support these 

final changes, but changes in the 

distribution of PAMS funds will need to 

be made. The network design changes 

will require some monitoring agencies 

to start collection of new PAMS 

measurements, while other monitoring 

agencies will see reductions in PAMS 

measurement requirements. The EPA 

will work with the NAACA, AAPCA, 

and other monitoring agencies to 

develop an appropriate PAMS grant 

distribution strategy. 

In addition to resources, the affected 

monitoring agencies will need time to 

implement the revised PAMS 

requirements. For the required PAMS 

sites, monitoring agencies can 

determine now which NCore sites will 

be required to make PAMS 

measurements based on readily 

available census data. However, 

monitoring agencies will still need time 

to evaluate and seek approval for 

alternative sites or alternative VOC 

methods. In addition, monitoring 

agencies will need time to make capital 

investments (primarily for the 

installation of autoGCs, NO2 monitors, 

and ceilometers), prepare appropriate 

QA documents, and develop the 

expertise needed to successfully collect 

PAMS measurements via training or 

otherwise. In order to ensure monitoring 

agencies have adequate time to plan and 

successfully implement the revised 

PAMS requirements, the EPA is 

requiring that monitoring agencies 

identify their plans to implement the 

PAMS measurements at NCore sites in 

their Annual Network Plan due July 1, 

2018, and to begin making PAMS 

measurements at NCore sites by June 1, 

2019. The EPA believes some 

monitoring agencies may be able to 

begin making PAMS measurements 

sooner than June 2019 and encourages 

early deployment where possible. 

Monitoring agencies will need to wait 

until O3 designations are made to 

officially determine the applicability of 

the EMP requirement. The EPA 

proposed to allow two years after 

designations to develop EMPs, and that 

the EMPs would be submitted as part of 

their Annual Network Plan. Several 

commenters stated that due to the level 

of planning and coordination required 

for the EMPs, that the plans should 

instead be included as part of the 5-year 

network assessment. While the EPA 

agrees that the EMPs will require a 

substantial amount of planning and 

coordination, the next 5 year network 

assessment will not be due until July 1, 

2020—nearly 5 years from the date of 

this final rulemaking. The EPA believes 

that it would be inappropriate to wait 5- 

years from the date of this rulemaking 

to develop plans for enhanced O3

monitoring. In addition, the EPA 

believes that the first round of EMP 

development should receive additional 

focus and review that may not be 

afforded as part of the larger network 

assessment. Finally, most monitoring 

agencies will be aware of their likely O3

attainment status well in advance of the 

official designations. In order to ensure 

timely development of the initial EMPs, 

the EPA is requiring affected monitoring 

agencies to submit their initial EMPs no 

later than two years following 

designations. States in the OTR do not 

need to wait until designations to 

determine EMP applicability and may 

not be classified as Moderate or above. 

As such, the final rule includes a 

requirement for states in the OTR to 

submit their initial EMPs by October 1, 

2019 (which is consistent with the 

expected timeline for the remaining 

EMPs). However, subsequent review 

and revisions to the EMPs are to be 

made as part of the 5-year network 

assessments beginning with the 

assessments due in 2025. 

D. Addition of a New FRM for O3

The use of FRM analyzers for the 

collection of air monitoring data 

provides uniform, reproducible 

measurements of concentrations of 

criteria pollutants in ambient air. FRMs 

for various pollutants are described in 

several appendixes to 40 CFR part 50. 

For most gaseous criteria pollutants 

(including O3 in Appendix D of part 50), 

the FRM is described as a particular 

measurement principle and calibration 

procedure to be implemented, with 

further reference to specific analyzer 

performance requirements specified in 

40 CFR part 53. 

The EPA allows new or alternative 

monitoring technologies—identified as 

FEMs—to be used in lieu of FRMs, 

provided that such alternative methods 

produce measurements closely 

comparable to corresponding FRM 

measurements. Part 53 sets forth the 

specific performance requirements as 

well as the performance test procedures 

required by the EPA for determining 

and designating both FRM and FEM 

analyzers by brand and model. 

To be used in a determination of 

compliance with the O3 NAAQS, 

ambient O3 monitoring data must be 

obtained using either a FRM or a FEM, 

as defined in parts 50 and 53. For O3, 

nearly all the monitoring methods 

currently used by state and local 

monitoring agencies are FEM (not FRM) 

continuous analyzers that utilize an 

alternative measurement principle 

based on quantitative measurement of 

the absorption of UV light by O3. This 

type of O3 analyzer was introduced into 

monitoring networks in the 1980s and 

has since become the predominant type 

of method used because of its alloptoelectronic design and its ease of 

installation and operation. 

The existing O3 FRM specifies a 

measurement principle based on 

quantitative measurement of 

chemiluminescence from the reaction of 

ambient O3 with ethylene (ET–CL). 

Ozone analyzers based on this FRM 

principle were once widely deployed in 

monitoring networks, but now they are 

no longer used for routine O3 field 

monitoring because readily available 

UV-type FEMs are substantially less 

difficult to install and operate. In fact, 

the extent of the utilization of UV-type 

FEMs over FRMs for O3 monitoring is 

such that FRM analyzers have now 

become commercially unavailable. The 

last new commercial FRM analyzer was 

designated by the EPA in 1979. The 

current list of all approved FRMs and 

FEMs capable of providing ambient O3

data for use in NAAQS attainment 

decisions may be found on the EPA’s 

Web site and in the docket for this 

action (U.S. EPA, 2014e). However, that 

list does not indicate whether or not 

each listed method is still commercially 

available. 

1. Proposed Changes to the FRM for O3

Although the existing O3 FRM is still 

a technically sound methodology, the 

lack of commercially available FRM O3

analyzers severely impedes the use of 

FRM analyzers, which are needed for 

quality control purposes and as the 

standard to which candidate FEMs are 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65429 

required to be compared. Therefore, the 

EPA proposed to establish a new FRM 

measurement technique for O3 based on 

NO-chemiluminescence (NO–CL) 

methodology. This new 

chemiluminescence technique is very 

similar to the existing ET–CL 

methodology with respect to operating 

principle, so the EPA proposed to 

incorporate it into the existing O3 FRM 

as a variation of the existing ET–CL 

methodology, coupled with the same 

existing FRM calibration procedure. 

A revised Appendix D to 40 CFR part 

50 was proposed to include both the 

original ET–CL methodology as well as 

the new NO–CL methodology, such that 

use of either measurement technique 

would be acceptable for implementation 

in commercial FRM analyzers. 

Currently, two O3 analyzer models (from 

the same manufacturer) employing the 

NO–CL methodology have been 

designated by the EPA as FEMs and 

would qualify for re-designation as 

FRMs under the revised O3 FRM. The 

rationale for selecting the new NO–CL 

FRM methodology, including what 

other methodologies were also 

considered, and additional information 

to support its selection are discussed in 

the preamble to the proposal for this 

action (79 FR 75366–75368). No 

substantive change was proposed to the 

existing O3 FRM calibration procedure, 

which would be applicable to both 

chemiluminescence FRM 

methodologies. 

The proposed FRM in part 50, 

Appendix D also included numerous 

editorial changes to provide clarification 

of some provisions, some revised 

wording, additional details, and a more 

refined numbering system and format 

consistent with that of two other 

recently revised FRMs (for SO2 and CO). 

As noted in the proposal, there is 

substantial similarity between the new 

and previously existing FRM 

measurement techniques, and 

comparative field data show excellent 

agreement between ambient O3

measurements made with the two 

techniques (U.S. EPA 2014f). Therefore, 

the EPA believes that there will be no 

significant impact on the comparability 

between existing ambient O3 monitoring 

data based on the original ET–CL 

methodology and new monitoring data 

that may be based on the NO–CL 

methodology. 

The proposed FRM retains the 

original ET–CL methodology, so all 

existing FEMs, which were designated 

under part 53 based on demonstrated 

comparability to that ET–CL 

methodology, will retain their FEM 

designations. Thus, there will be no 

negative consequences or disruption to 

monitoring agencies, which will not be 

required to make any changes to their 

O3 monitors due to the revised O3 FRM. 

New FEMs would be designated under 

part 53, based on demonstrated 

acceptable comparability to either FRM 

methodology. 

2. Comments on the FRM for O3

Comments that were received from 

the public on the proposed new O3 FRM 

technique are addressed in this section. 

Most commenters expressed general 

support for the proposed changes, 

although a few commenters expressed 

some concerns. The most significant 

issue discussed in comments was the 

relatively small but nevertheless 

potentially significant interference of 

water vapor observed in the ET–CL 

technique. As some comments pointed 

out, this interference is positive and 

could possibly affect NAAQS 

attainment decisions. The available NO– 

CL FEM analyzers include a sample 

dryer, which minimizes this 

interference. As noted previously, very 

few, if any, ET–CL FRM analyzers are 

still in operation. The ET–CL (with and 

without a sample dryer), the proposed 

NO–CL FRM, and all designated FEM 

analyzers have demonstrated 

compliance with the substantially 

reduced water vapor interference 

equivalent limit specified in 40 CFR 

part 53. 

The proposed FRM mentioned the 

need for a sample air dryer for both ET– 

CL and NO–CL FRM analyzers. In 

response to these comments, the 

wording of the ET–CL FRM has been 

augmented to clarify the requirement for 

a dryer in all newly designated FRMs 

(the only change being made by the EPA 

to the existing ET–CL FRM as 

proposed). Also, the interference 

equivalent limit for water vapor in part 

53 was proposed to be substantially 

reduced from the current 0.02 ppm to 

0.002 ppm. The interference equivalent 

test for water vapor applicable to the 

new NO–CL candidate FRM analyzers 

(specified in Table B–3 of part 53) was 

proposed to be more stringent than the 

corresponding existing test for ET–CL 

FRM analyzers by requiring that water 

vapor be mixed with O3. This mixing 

requirement was not part of the existing 

test for ET–CL candidate analyzers 

(denoted by footnote 3 in Table B–3). 

However, in further response to these 

commenters’ concerns, the EPA has 

modified Table B–3 to extend this water 

vapor mixing requirement to newly 

designated ET–CL analyzers, as well. 

These measures should insure that 

potential water vapor interference is 

minimized in all newly designated FRM 

analyzers. 

Several comments indicated concern 

that currently-designated FEM analyzers 

retain their designation without 

retesting if the new FRM were 

promulgated. The current ET–CL FRM 

is being retained; therefore, it is not 

necessary to make these new 

requirements retroactive to existing 

designated FEM analyzers. The existing 

FEM analyzers will not be required to be 

retested, and their FEM designation will 

be retained so that there will be no 

disruption to current monitoring 

networks. 

Although beyond the scope of this 

rulemaking, other comments concerned 

potential hazards of the NO compressed 

gas supply required for NO–CL analyzer 

operation, and the current nonavailability of a photolytic converter to 

provide an alternative source of NO 

from a less hazardous nitrous oxide gas 

supply. With regard to the photolytic 

converter, the EPA would approve such 

a converter as a source of NO if 

requested by an FRM analyzer 

manufacturer, upon demonstration of 

adequate functionality. 

A few commenters liked the 

‘‘scrubberless UV absorption’’ (SL–UV) 

measurement technique. The EPA has 

identified the SL–UV method as a 

potentially advantageous candidate for 

the O3 FRM, but could not propose 

adopting it until additional test and 

performance information becomes 

available. A related comment requested 

clarification that promulgation of the 

proposed revised FRM would not 

preclude future consideration of other 

O3 measurement techniques such as SL– 

UV. In response, the EPA can always 

consider new technologies for FRMs 

under 40 CFR 53.16 (Supersession of 

reference methods). However, a revised 

or amended FRM that included the SL– 

UV technique, as set forth in Appendix 

D of 40 CFR part 50, would have to be 

promulgated as part of a future 

rulemaking, before a SL–UV analyzer 

could be approved as an FRM under 40 

CFR part 53. 

One comment suggested that the 

value for the absorption cross section of 

O3 at 254 nm used by the FRM’s 

calibration procedure should be 

changed. The comment indicated that 

the nearly 2% difference effectively 

lowers the O3 NAAQS by that amount. 

Using the corrected value would resolve 

much of the difference observed 

between O3 measurements calibrated 

against the UV standard reference 

photometer versus those calibrated 

using NO gas phase titration and it 

would allow the EPA to adopt the less 

complex and more economical Gas 

Phase Titration (GPT) technique as the 

primary calibration standard for the 

mstockstill on DSK4VPTVN1PROD with RULES2

65430 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

FRM. The EPA will await the results of 

further studies determining the value of 

the O3 cross section at 254 nm before 

making a change to the calibration 

procedures and will not finalize changes 

to the calibration procedures in this 

final rule. 

E. Revisions to the Analyzer 

Performance Requirements 

1. Proposed Changes to the Analyzer 

Performance Requirements 

In close association with the proposed 

O3 FRM, the EPA also proposed changes 

to the associated analyzer performance 

requirements for designation of FRMs 

and FEMs for O3, as set forth in 40 CFR 

part 53. These changes were largely 

confined to Table B–1, which specifies 

performance requirements for FRM and 

FEM analyzers for SO2, CO, O3, and 

NO2, and to Table B–3, which specifies 

test concentrations for the various 

interfering agent (interferent) tests. 

Minor changes were also proposed for 

Figure B–5 and the general provisions in 

subpart A of part 53. All of these 

proposed changes are described and 

discussed more fully in the preamble to 

the proposal for this action (79 FR 

75368–75369). 

Modest changes proposed for Table 

B–3 would add new interferent test 

concentrations specifically for NO–CL 

O3 analyzers, which include a test for 

NO2 interference. 

Several changes to Table B–1 were 

proposed. Updated performance 

requirements for ‘‘standard range’’ 

analyzers were proposed to be more 

consistent with current O3 analyzer 

performance capabilities, including 

reduced limits for noise allowance, 

lower detectable limit (LDL), 

interference equivalent, zero drift, span 

drift, and lag, rise, and fall times. The 

previous limit on the total of all 

interferents was proposed to be 

withdrawn as unnecessary and to be 

consistent with that same change made 

previously for SO2 and CO analyzers. 

Also, the span drift limit at 20% of the 

upper range limit (URL) was proposed 

to be withdrawn because it has similarly 

been shown to be unnecessary and to 

maintain consistency with that same 

change made previously for SO2 and CO 

analyzers. 

The form of the precision limits at 

both 20% and 80% of the URL was 

proposed to be changed from ppm to 

percent. The proposed new limits (in 

percent) were set to be equivalent to the 

previously existing limits (in ppm) and 

thus remain effectively unchanged. This 

change in form of the precision limits in 

Table B–1 has been previously made for 

SO2 and CO analyzers, and was 

proposed to extend also to analyzers for 

NO2, (again with equivalent limits) for 

consistency and to simplify Table B–1 

across all types of analyzers to which 

the table applies. A new footnote 

proposed for Table B–1 clarifies the new 

form for precision limits as ‘‘standard 

deviation expressed as percent of the 

URL.’’ Also proposed was a revision to 

Figure B–5 (Calculation of Zero Drift, 

Span Drift, and Precision) to reflect the 

changes proposed in the form of the 

precision limits and the withdrawal of 

the limits for total interference 

equivalent. 

Concurrent with the proposed 

changes to the performance 

requirements for candidate O3

analyzers, the EPA conducted a review 

of all designated FRM and FEM O3

analyzers currently in production or 

being used, and verified that all meet 

the proposed new performance 

requirements. Therefore, none would 

require withdrawal or cancellation of 

their current FRM or FEM respective 

designations. 

Finally, the EPA proposed new, 

optional, ‘‘lower range’’ performance 

limits for O3 analyzers operating on 

measurement ranges lower (i.e., more 

sensitive) than the standard range 

specified in Table B–1. The new 

performance requirements are listed in 

a new ‘‘lower range’’ column in Table 

B–1 and will provide for more stringent 

performance in applications where more 

sensitive O3 measurements are needed. 

Two minor changes were proposed to 

the general, administrative provisions in 

Subpart A of part 53. These include an 

increase in the time allowed for the EPA 

to process requests for approval of 

modifications to previously designated 

FRMs and FEMs in 53.14 and the 

withdrawal of a requirement for annual 

submission of Product Manufacturing 

Checklists associated with FRMs and 

FEMs for PM2.5 and PM10–2.5 in 53.9. No 

comments were received on these 

proposed changes and the EPA will be 

finalizing these revisions in this 

rulemaking. 

2. Comments on the Analyzer 

Performance Requirements 

Several comments were received 

related to the proposed changes to the 

analyzer performance requirements of 

part 53, and most were supportive. 

Comments from a few monitoring 

agencies suggested that the more 

stringent performance requirements 

proposed might be difficult to achieve 

or would increase monitor maintenance 

and cost. The EPA is also clarifying that 

these requirements apply only to the 

performance qualification requirements 

for designations of new FRM and FEM 

analyzers and will have no impact on a 

monitoring agency’s operation of 

existing O3 analyzers. 

More specific comments from an 

analyzer manufacturer pointed out that 

the proposed lower limits for noise and 

LDL may be too stringent, the former 

because low-cost portable analyzers may 

have shorter absorption cells, and the 

latter because of limitations of current 

calibration technology. After further 

consideration of available analyzer 

performance data in light of these 

comments, the EPA agrees and is 

changing the noise limits from the 

proposed values of 1 ppb and 0.5 ppb 

(for the standard and lower ranges, 

respectively) to 2.5 ppb and 1 ppb 

(respectively). The EPA is also changing 

the LDL limit from the proposed values 

of 3 ppb and 1 ppb (respectively) to 5 

ppb and 2 ppb (respectively). These new 

limits are still considerably more 

stringent than the previous limits (for 

the standard range) and are also 

consistent with those recommended by 

the commenter and the current 

performance capabilities of existing 

analyzer/calibration technology. 

This commenter also pointed out that 

the proposed lower limit for 12-hour 

zero drift, together with the way the 

prescribed test is carried out, resulted in 

the test being dominated by analyzer 

noise rather than drift. The EPA agrees 

with this comment in general but 

believes that further study is needed 

before any specific changes can be 

proposed for the 12-hour zero drift test, 

particularly since any such changes 

would affect analyzers for other gaseous 

pollutants, as well. 

Other comments suggested that there 

was no need for the proposed new, lowrange performance requirements, 

because of cost and that available 

calibrators would be inadequate for 

calibration of such low ranges. The EPA 

disagrees with these comments and 

believes, as noted in the proposal 

preamble, that there is a definite need 

for low-level O3 measurements in some 

applications and that suitable 

calibration for such low-level 

measurement ranges can be adequately 

carried out. As stated previously, the 

new ‘‘low range’’ specifications for O3

analyzers are optional. 

Several comments pointed out some 

typographical errors related to footnotes 

in Table B–3, as proposed; these errors 

have been corrected in the version of 

Table B–3 being finalized today. 

EPA is finalizing the proposed 

amendments to both the O3 FRM in 

Appendix D of part 50 and provisions 

in part 53, modified as described above, 

in response to the comments received. 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65431 

VII. Grandfathering Provision for 

Certain PSD Permits 

This section addresses the 

grandfathering provision for certain 

Prevention of Significant Deterioration 

(PSD) permit applications that is being 

finalized in this rule. Section VIII.C of 

this preamble contains a description of 

the PSD and Nonattainment New Source 

Review (NNSR) permitting programs 

and additional discussion of the 

implementation of those programs for 

the O3 NAAQS. 

A. Summary of the Proposed 

Grandfathering Provision 

The EPA proposed to amend the PSD 

regulations to add a transition plan that 

would address the extent to which the 

revised O3 NAAQS will apply to 

pending PSD permit applications. This 

transition plan is reflected in a 

grandfathering provision that applies to 

permit applications that meet certain 

milestones in the review process prior 

to either the signature date or effective 

date of the revised O3 NAAQS. Absent 

such a grandfathering provision in the 

EPA’s regulations, the EPA interprets 

section 165(a)(3)(B) of the CAA and the 

implementing PSD regulations at 40 

CFR 52.21(k)(1) and 51.166(k)(1) to 

require that PSD permit applications 

include a demonstration that emissions 

from the proposed facility will not cause 

or contribute to a violation of any 

NAAQS that is in effect as of the date 

the PSD permit is issued. The proposal 

included a grandfathering provision that 

would enable eligible PSD applications 

to make the demonstration that the 

proposed project would not cause or 

contribute to a violation of any NAAQS 

with respect to the O3 NAAQS in effect 

at the time the relevant permitting 

benchmark for grandfathering was 

reached, rather than the revised O3

NAAQS. We proposed that the 

grandfathering provision would apply 

specifically to either of two categories of 

pending PSD permit applications: (1) 

Applications for which the reviewing 

authority has formally determined that 

the application is complete on or before 

the signature date of the final rule 

revising the O3 NAAQS; and (2) 

applications for which the reviewing 

authority has first published a public 

notice of the draft permit or preliminary 

determination before the effective date 

of the revised NAAQS. 

In the proposal, we also noted that for 

sources subject to the federal PSD 

program under 40 CFR 52.21, the EPA 

and air agencies that have been 

delegated authority to implement the 

federal PSD program for the EPA would 

apply the grandfathering provision to 

any PSD application that satisfies either 

of the two criteria that make an 

application eligible for grandfathering. 

Accordingly, if a particular application 

does not qualify under the first criterion 

based on a complete application 

determination, it may qualify under the 

second criterion based on a public 

notice announcing the draft permit or 

preliminary determination. Conversely, 

a source may qualify for grandfathering 

under the first criterion, even if it does 

not satisfy the second. 

The EPA also proposed revisions to 

the PSD regulations at 40 CFR 51.166 

that would afford air agencies that issue 

PSD permits under a SIP-approved PSD 

permit program the discretion to adopt 

provisions into the SIP that allow for 

grandfathering of pending PSD permits 

under the same circumstances as set 

forth in the federal PSD regulations. 

With regard to implementing the 

grandfathering provision, we also 

explained that air agencies with EPAapproved PSD programs in their SIPs 

would have additional flexibility for 

implementing the proposed 

grandfathering provision to the extent 

that any alternative approach is at least 

as stringent as the federal provision. In 

addition, the proposal recognized that 

some air agencies do not make formal 

completeness determinations; thus, only 

the latter criterion based on the issuance 

of a public notice would be relevant in 

such cases and the state could elect to 

adopt only that criterion into its SIP. 

Accordingly, the EPA proposed to add 

a grandfathering provision to 40 CFR 

51.166 containing the same two criteria 

as proposed for 40 CFR 52.21. 

B. Comments and Responses 

Many of the comments supported the 

concept of grandfathering. Some of 

these comments, mostly by state and 

local air agencies, supported the 

grandfathering provision as proposed. 

Many others recommended alternative 

approaches to grandfathering based on 

several different dates. Several 

comments recommended that air 

agencies be allowed to grandfather 

certain PSD permit applications and 

issue a PSD permit based on the 2008 

O3 NAAQS after the area is designated 

nonattainment for the revised O3

NAAQS. An opposing set of comments, 

representing a coalition of eight 

environmental groups and one health 

advocacy group, strongly objected to the 

proposal for grandfathering, claiming 

that the EPA did not have any authority 

under the CAA to exempt or grandfather 

permit applicants from the statutory 

PSD permitting requirements. We are 

addressing some of these comments 

below and others in the Response to 

Comment Document that is included in 

the docket for this rule. 

Comments that recommended 

broadening the scope of the proposed 

grandfathering provision suggested a 

variety of approaches. Some air agency 

and industry comments recommended 

that the EPA adopt a grandfathering 

provision applicable only to those PSD 

applications for which the reviewing 

authority has determined the 

application to be complete on or before 

the signature date of the revised 

NAAQS. Other air agency and industry 

comments recommended that 

grandfathered status be determined only 

on the basis of whether the relevant 

permitting milestone has been achieved 

by the effective date of the revised 

NAAQS. 

The EPA disagrees with these 

comments; the final rule uses separate 

dates for the two grandfathering 

milestones, as proposed. If the effective 

date of the revised NAAQS were used 

as the date for the complete application 

milestone, this could lead to pressure on 

state permitting authorities to 

prematurely issue completeness 

determinations in order to qualify for 

the grandfathering provision in the time 

period between signature of this final 

rule and the effective date. Using the 

signature date of the revised O3 NAAQS 

as the date for the grandfathering 

milestone based on the completeness 

determination is thus intended to help 

preserve the integrity of the 

completeness determination process. 

Permit applications that have not yet 

been determined complete can be 

supplemented or revised to address the 

revised O3 standards before the 

completeness determination is issued. 

Conversely, the amount and type of 

work required for a preliminary 

determination or a draft permit reduces 

the risk that such a document would be 

released prematurely merely to qualify 

for grandfathering. Similarly, because 

these documents are released for the 

purpose of providing an adequate 

opportunity for public participation in 

the permitting process, it would not 

behoove a reviewing authority to 

precipitately release such documents 

merely to satisfy the grandfathering 

milestone. Accordingly, the EPA does 

not have the same concerns about using 

the effective date of this final rule for 

the preliminary determination or draft 

permit milestone and further finds it 

reasonable to provide additional time 

for satisfying this milestone. Moreover, 

using the proposed milestones and 

corresponding dates is consistent with 

the milestones and corresponding dates 

that were used in the grandfathering 

provisions for the 2012 PM2.5 NAAQS. 

mstockstill on DSK4VPTVN1PROD with RULES2

65432 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

Several other comments 

recommended that the grandfathering 

provision apply to all PSD applications 

for which a final PSD permit will be 

issued prior to the effective date of the 

area designations for the revised 

NAAQS. Some of these comments 

explained that without some transition 

provisions in the final rule, it may be 

impossible for a source to demonstrate 

attainment if the current ambient air 

monitoring data indicates a revised, 

lowered standard is not being met. The 

comments also suggested that the 

extended period for grandfathering a 

source from the revised NAAQS would 

provide states with additional time to 

establish offset banks or similar systems 

for new nonattainment areas. 

Other comments recommended that 

air agencies be allowed to grandfather 

either all or certain PSD permit 

applications received before the 

effective date of the final nonattainment 

designations for the revised O3 NAAQS. 

These comments supported allowing air 

agencies to issue PSD permits to 

grandfathered sources even after the 

area in which the source proposes to 

locate is designated nonattainment for 

the revised O3 NAAQS. One comment 

saw this as being necessary because the 

development of the regulatory 

framework that will support the revised 

NAAQS, such as development of a 

credit market or even a transition into 

NNSR permitting, does not 

instantaneously accompany the revised 

standard. Hence, the comment added 

that ‘‘[d]uring the Interim Period (the 

time between the revision of the 

NAAQS rule and development of the 

regulatory framework) the project may 

be unable to secure offsets and no 

offsets would be available for 

purchase.’’ Another comment explained 

that the extended period for 

grandfathering sources from the revised 

O3 NAAQS was needed to ‘‘minimize 

disruption to complex projects that may 

have been under development since 

before the EPA published the proposed 

NAAQS revision.’’ This comment noted 

the ‘‘PSD projects commonly undergo 

years of engineering and other 

development resources before an air 

permit application can be prepared.’’ 

The EPA does not agree with the 

comments recommending that the EPA 

use a date after the effective date of the 

revised O3 NAAQS as the date by which 

the permit application must reach the 

relevant milestone to qualify for 

grandfathering. The EPA does not 

believe it is appropriate to unreasonably 

or unnecessarily delay implementation 

of these revised standards under the 

PSD program. As explained in more 

detail below, the purpose of the 

grandfathering provision is to provide a 

reasonable transition mechanism for 

certain PSD applications and the EPA 

believes that the milestones proposed 

and finalized here strike the appropriate 

balance in providing for such a 

reasonable transition. Moreover, in 

some cases, some of these recommended 

approaches could enable a situation 

where a PSD permit would be issued to 

a source during a future period when 

the area is designated nonattainment for 

the revised O3 NAAQS. As explained 

below, the EPA does not believe that 

this specific outcome is permissible 

under the CAA. 

The EPA does not agree with the 

comments suggesting that the 

grandfathering provision should be 

expanded to apply to any PSD 

application received before the effective 

date of the final nonattainment 

designations for the revised O3 NAAQS. 

Because the process for reviewing PSD 

permit applications and issuing a final 

PSD permit is time consuming, such an 

approach could allow issuance of PSD 

permits to grandfathered sources even 

after the area in which the source 

proposes to locate is designated 

nonattainment for the revised O3

NAAQS. The EPA does not agree that 

grandfathering should be extended in a 

way that would allow a source located 

in an area designated as nonattainment 

for a pollutant at the time of permit 

issuance to obtain a PSD permit for that 

pollutant rather than a NNSR permit. 

The EPA does not interpret the CAA or 

its implementing regulations to allow 

such an outcome. The PSD requirements 

under CAA section 165 only apply in 

areas designated attainment or 

unclassifiable for the pollutant. 

Alabama Power v. Costle, 636 F.2d 323, 

365–66, 368 (D.C. Cir. 1980). 

Accordingly, the PSD implementing 

regulations at 40 CFR 52.21(i)(2) contain 

an exemption that provides that the 

substantive PSD requirements shall not 

apply to a pollutant if the owner or 

operator demonstrates that the facility is 

located in an area designated 

nonattainment for that pollutant under 

CAA section 107 of the Act. See also 40 

CFR 51.166(i)(2) (allowing for the same 

exemption in SIP-approved PSD 

permitting programs). In addition, under 

CAA section 172(c)(5) implementation 

plans must require that permits issued 

to new or modified stationary sources 

‘‘anywhere in the nonattainment area’’ 

meet the requirements of CAA section 

173, which contains the NNSR permit 

requirements. See 40 CFR part 51, 

Appendix S, IV.A (providing that, if a 

major new source or major modification 

that would locate in an area designated 

as nonattainment for a pollutant for 

which the source or modification would 

be major, approval to construct may be 

granted only if the specific conditions 

for NNSR are met, including obtaining 

emission offsets and an emission 

limitation that specifies the lowest 

achievable emissions rate). Moreover, 

given the adverse air quality conditions 

that already exist in a nonattainment 

area and the congressional directive to 

reach attainment as expeditiously as 

practicable, construction of a major 

stationary source that significantly 

increases emissions in such an area 

should be expected to address all of the 

NNSR requirements, which are designed 

to ensure that a new or modified major 

stationary source will not interfere with 

reasonable progress toward attainment, 

even if this could cause delay to the 

permit applicant. 

With respect to the comments that 

suggested the effective date of the 

NAAQS should be used as the date for 

both milestones, the EPA does not agree 

that such a change is necessary. The 

purpose of the grandfathering provision 

is to provide a reasonable transition 

mechanism in the following 

circumstances: first, the PSD application 

is one for which both the applicant and 

the reviewing authority have committed 

substantial resources; and, second, this 

situation is one where the need to 

satisfy the demonstration requirement 

under CAA section 165(a)(3) could 

impact the reviewing authority’s ability 

to meet the statutory deadline for 

issuing a permit within one year of the 

completeness determination. In 

situations where the reviewing authority 

has not yet issued a completeness 

determination as of the signature date of 

the revised O3 NAAQS, both the permit 

applicant and the reviewing authority 

have sufficient notice of the revised 

standard so that it can be addressed 

before the completeness determination 

is issued and the one-year clock begins 

to run. The grandfathering provision 

issued in this rulemaking is crafted to 

draw a reasonable balance that 

accommodates the requirements under 

both CAA sections 165(a)(3) and 165(c). 

Any modification of the dates further 

than is necessary to accommodate these 

concerns could upset this balance. 

With respect to the comments that 

suggested adopting a grandfathering 

provision applicable only to those PSD 

applications for which the reviewing 

authority has determined the 

application to be complete on or before 

the signature date of the revised 

NAAQS, the EPA is not making this 

change because we understand that not 

all reviewing authorities issue formal 

completeness determinations. Including 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65433 

a grandfathering provision based on the 

publication of a public notice of the 

draft permit or preliminary 

determination provides a reasonable 

transition mechanism for PSD 

applications in situations where the 

reviewing authority does not issue 

formal completeness determinations, 

but the applicant and the reviewing 

authority have both committed 

substantial resources to the pending 

permit application at the time the 

revisions to the O3 NAAQS are 

finalized. 

An opposing set of comments— 

submitted by a consortium of eight 

environmental groups and one health 

advocacy group—challenged the 

proposed grandfathering provision on 

the basis that the EPA did not have the 

legal authority to grandfather sources 

from PSD requirements. These 

commenters argued that the plain 

language of CAA section 165 forecloses 

the EPA’s proposed approach and raised 

several other legal considerations. The 

EPA disagrees with these comments, 

including the interpretations of the CAA 

that they offer. As summarized in the 

rationale for the final action below in 

section VII.C of this preamble, the EPA 

believes that the CAA provides it 

authority and discretion to establish a 

PSD grandfathering provision such as 

the one being adopted today through a 

rulemaking process. The EPA is 

providing a further, detailed analysis 

fully responding to this set of 

comments, as well as other comments 

related to the grandfathering provision, 

in the Response to Comment Document 

in the docket for this rule. 

C. Final Action and Rationale 

After consideration and evaluation of 

all the public comments received on the 

grandfathering provision, the EPA is 

finalizing this provision as proposed, 

with minor revisions that enhance the 

clarity of the grandfathering provision, 

without changing its substantive effect. 

While these revisions lead to slight 

differences in wording for the 

grandfathering provision for the 2012 

PM2.5 NAAQS and the grandfathering 

provision finalized in this rulemaking, 

those differences are not intended to 

create a different meaning; rather, the 

grandfathering provision finalized in 

this rulemaking is intended to have the 

same substantive effect and meaning for 

the revised O3 standards as the 

grandfathering provision for the 2012 

PM2.5 NAAQS had for the revised PM 

standards. Other than those clarifying 

revisions, this final rule includes the 

same rule language for the 

grandfathering provision as previously 

proposed for the PSD regulations at 40 

CFR 52.21(i)(12) and 51.166(i)(11), 

respectively. The provision in the final 

rule reflects the same two milestones 

and corresponding dates as the 

proposed grandfathering provision. 

Thus, under the grandfathering 

provision as finalized, either of the 

following two categories of pending PSD 

permit applications would be eligible 

for grandfathering: (1) Applications for 

which the reviewing authority has 

formally determined that the 

application is complete on or before the 

signature date of the revised O3 NAAQS, 

or (2) applications for which the 

reviewing authority has first published 

a notice of a draft permit or preliminary 

determination before the effective date 

of the revised O3 NAAQS. The EPA 

believes that it continues to be 

appropriate to include the two proposed 

milestones for pending permit 

applications to be eligible for 

grandfathering. While a completeness 

determination is often the first event, 

some air agencies do not determine 

applications complete as part of their 

permit process. 

Under 40 CFR 52.21, a permit 

application may qualify for 

grandfathering under either of the two 

sets of milestones and dates contained 

in the provision. Where the EPA is the 

reviewing authority, the EPA intends to 

apply the grandfathering provision to 

PSD applicants pursuant to PSD 

regulations at 40 CFR 52.21 primarily 

through the use of the completeness 

determination milestone because the 

EPA Regional Offices make a formal 

completeness determination for any 

PSD application that they receive and 

review. The EPA is including the 

second criterion in 40 CFR 52.21 so that 

pending applications can still qualify 

for grandfathering under the second 

criterion if any air agency that 

incorporates 40 CFR 52.21 into a SIPapproved program does not make formal 

completeness determinations as part of 

its permit review process. 

The EPA is also amending the PSD 

regulations at 40 CFR 51.166 to enable 

states and other air agencies that issue 

PSD permits under SIP-approved PSD 

programs to adopt a comparable 

grandfathering provision. Nevertheless, 

such air agencies have discretion to not 

grandfather PSD applications or to 

apply grandfathering under their 

approved PSD programs in another 

manner as long as that program is at 

least as stringent as the provision being 

added to 40 CFR 51.166. Accordingly, 

an air agency may elect to rely on both 

sets of milestones and dates or it may 

grandfather on the sole basis of only one 

set. However, the EPA anticipates that 

once a decision is made concerning the 

use of either set of milestones and dates, 

the air agency will apply grandfathering 

consistently to all pending PSD permit 

applications. 

As explained in more detail in the 

proposal, absent a regulatory 

grandfathering provision, the EPA 

interprets section 165(a)(3)(B) of the 

CAA and the implementing PSD 

regulations at 40 CFR 52.21(k)(1) and 

51.166(k)(1) to require that PSD permit 

applications include a demonstration 

that emissions from the proposed 

facility will not cause or contribute to a 

violation of any NAAQS that is in effect 

as of the date the PSD permit is issued. 

However, reading CAA section 

165(a)(3)(B) in context with other 

provisions of the Act and the legislative 

history, the EPA interprets the Act to 

provide the EPA with authority to 

establish grandfathering provisions 

through regulation. The EPA has 

explained its interpretation of its 

authority to promulgate grandfathering 

provisions in previous rulemaking 

actions, most recently in the rule 

establishing the grandfathering 

provision for the 2012 PM2.5 NAAQS (78 

FR 3086, 3254–56, January 15, 2013), as 

well as in the proposal for this final 

action. The EPA is providing additional 

discussion of this authority in the 

Response to Comment Document 

contained in the docket for this final 

action. 

To summarize briefly, the addition of 

this grandfathering provision is 

permissible under the discretion 

provided by the CAA for the EPA to 

craft a reasonable implementation 

regulation that balances competing 

objectives of the statutory PSD program 

found in CAA section 165. Specifically, 

section 165(a)(3) requires a permit 

applicant to demonstrate that its 

proposed project will not cause or 

contribute to a violation of any NAAQS, 

while section 165(c) requires that a PSD 

permit be granted or denied within one 

year after the permitting authority 

determines the application for such 

permit to be complete. Section 109(d)(1) 

of the CAA requires the EPA to review 

existing NAAQS and make appropriate 

revisions every five years. When these 

provisions are considered together, a 

statutory ambiguity arises concerning 

how the requirements under CAA 

section 165(a)(3)(B) should be applied to 

a limited set of pending PSD permit 

applications when the O3 NAAQS is 

revised. The Act does not clearly 

address how the requirements of CAA 

section 165(a)(3)(B) should be met for 

PSD permit applications that are 

pending when the NAAQS are revised, 

particularly when the EPA also 

determines that complying with the 

mstockstill on DSK4VPTVN1PROD with RULES2

65434 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

227This case specifically involved an action by 

the EPA to issue an individual PSD permit, which 

grandfathered a specific permit applicant from 

certain requirements without any revision to the 

regulations that were in effect. The court’s 

reasoning in this case distinguishes that type of 

permit-specific grandfathering from establishing 

grandfathering provisions through a rulemaking 

process. While the court was not persuaded that 

there was a conflict between the requirements of 

sections 165(a)(3) and 165(c) of the CAA that 

supported the permit-specific grandfathering at 

issue in that case, it did not extend that uncertainty 

to its discussion of the EPA’s rulemaking authority. 

In fact, in its favorable discussion of the EPA’s 

authority to grandfather pending permit 

applications through regulation, the court noted 

that the power of an administrative agency ‘‘to 

administer a congressionally created and funded 

program necessarily requires the formulation of 

policy and the making of rules to fill any gap left, 

implicitly or explicitly, by Congress’’ though ‘‘such 

decision cannot be made on an ad hoc basis.’’ Sierra 

Club v. EPA, 762 F.3d 971, 983 (9th Cir. 2014) 

(internal quotations and marks omitted). This 

indicates that the court believed there is a gap in 

the CAA that supports including grandfathering 

provisions in regulations. 

demonstration requirement for the 

revised NAAQS could hinder 

compliance with the requirement under 

section 165(c) to issue a permit within 

one year of the completeness 

determination for a certain subset of 

pending permits. The CAA also does not 

address how the requirements of CAA 

sections 165(a)(3) and 165(c) should be 

balanced in light of the statutory 

requirement to review the NAAQS every 

five years. As Congress has not spoken 

precisely to this issue, the EPA has the 

discretion to apply a permissible 

interpretation of the Act that balances 

the statutory requirements to make a 

decision on a permit application within 

one year and to ensure the new and 

modified sources will only be 

authorized to construct after showing 

they can meet the substantive 

permitting criteria. See Chevron, U.S.A., 

Inc. v. Natural Res. Def. Council, Inc., 

467 U.S. 837, 843–44 (1984). 

In addressing these gaps in the CAA 

and the tension that may arise in section 

165 in these circumstances, the EPA 

also applies CAA section 301, where the 

Administrator is authorized ‘‘to 

prescribe such regulations as are 

necessary to carry out his functions 

under this chapter.’’ Sections 165(a)(3) 

and 165(c) of the CAA make clear that 

the interests behind CAA section 165 

include both protection of air quality 

and timely decision-making on pending 

permit applications. The 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’’). 

Thus, when read in combination, these 

provisions of the CAA provide the EPA 

with the discretion to issue regulations 

to grandfather pending permit 

applications from having to address a 

revised NAAQS where necessary to 

achieve both CAA objectives—to protect 

the NAAQS and to avoid delays in 

processing PSD permit applications. 

Accordingly, the EPA is seeking in this 

action to balance the requirements in 

the CAA 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 that 

apply to them. The EPA is achieving 

this balance by determining through 

rulemaking which O3 NAAQS apply to 

certain permit applications that are 

pending when the EPA finalizes the 

revisions to the O3 NAAQS in this final 

rule. We are clarifying, for the limited 

purpose of satisfying the requirements 

under section 165(a)(3)(B) for those 

permits, which O3 NAAQS are 

applicable to those permit applications 

and must be addressed in the source’s 

demonstration that its emissions do not 

cause or contribute to a violation of the 

NAAQS. 

This approach is consistent with a 

recent opinion by the U.S. Court of 

Appeals for the Ninth Circuit, which 

recognized the EPA’s traditional 

exercise of grandfathering authority 

through rulemaking. The court observed 

that this approach was consistent with 

the statutory requirement to ‘‘enforce 

whatever regulations are in effect at the 

time the agency makes a final decision’’ 

because it involved identifying ‘‘an 

operative date, incident to setting the 

new substantive standard, and the 

grandfathering of pending permit 

applications was explicitly built into the 

new regulations.’’ Sierra Club v. EPA, 

762 F.3d 971, 983 (9th Cir. 2014). As 

discussed in more detail in the EPA’s 

Response to Comment Document 

contained in the docket for this rule, 

this case supports the EPA’s action in 

this rulemaking. The court favorably 

discussed prior adoption of regulatory 

grandfathering provisions that are 

similar to the action in this rulemaking, 

such as the grandfathering provision 

that the EPA promulgated when revising 

the PM2.5 NAAQS that became effective 

in 2013. See id. at 982–83.227

This adoption of a grandfathering 

provision in this action is also 

consistent with previous actions in 

which the EPA has recognized that the 

CAA provides discretion for the EPA to 

establish grandfathering provisions for 

PSD permit applications through 

regulations. Some examples of previous 

references to the EPA’s authority to 

grandfather certain applications through 

rulemaking include 45 FR 52683, 

August 7, 1980; 52 FR 24672, July 1, 

1987; and most recently 78 FR 3086, 

January 15, 2013. 

This grandfathering provision does 

not apply to any applicable PSD 

requirements related to O3 other than 

the requirement to demonstrate that the 

proposed source does not cause or 

contribute to a violation of the revised 

O3 NAAQS. Sources with projects 

qualifying under the grandfathering 

provision will be required to meet all 

the other applicable PSD requirements, 

including applying BACT to all 

applicable pollutants, demonstrating 

that emissions from the proposed 

facility will not cause or contribute to a 

violation of the O3 NAAQS in effect at 

the time of the relevant grandfathering 

milestone, and addressing any Class I 

area and additional O3-related impacts 

in accordance with the applicable PSD 

requirements. In addition, this 

grandfathering provision would not 

apply to any permit application for a 

new or modified major stationary source 

of O3 located in an area designated 

nonattainment for O3 on the date the 

permit is issued. 

VIII. Implementation of the Revised O3

Standards 

This section provides background 

information for understanding the 

implications of the revised O3 NAAQS 

and describes the EPA’s plans for 

providing revised rules or additional 

guidance on some subjects in a timely 

manner to assist states with their 

implementation efforts under the 

requirements of the CAA. This section 

also describes existing EPA rules, 

interpretations of CAA requirements, 

and other EPA guidance relevant to 

implementation of the revised O3

NAAQS. Relevant CAA provisions that 

provide potential flexibility with regard 

to meeting implementation timelines are 

highlighted and discussed. This section 

also contains a discussion of how 

existing requirements to reduce the 

impact on O3 concentrations from the 

stationary source construction in permit 

programs under the CAA are affected by 

the revisions to the O3 NAAQS. These 

are the PSD and Nonattainment New 

Source Review (NNSR) programs. As 

discussed in section VII of this 

preamble, to facilitate a smooth 

transition to the PSD requirements for 

the revised O3 NAAQS, the EPA is 

finalizing as part of this rulemaking a 

grandfathering provision that applies to 

certain PSD permit applications that are 

pending and have met certain 

milestones in the permitting process 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65435 

228This and all subsequent references to ‘‘state’’ 

are meant to include state, local, and tribal agencies 

responsible for the implementation of an O3 control 

program. 

when the revised O3 NAAQS is signed 

or before the effective date of the revised 

O3 NAAQS, depending on the 

milestone. 

In the preamble for the O3 NAAQS 

proposal, the EPA solicited comments 

on several issues related to 

implementing the revised O3 NAAQS 

that the agency anticipated addressing 

in future guidance or regulatory actions, 

but for which the EPA was not at that 

time proposing any action. The EPA 

received numerous comments on those 

and other implementation issues. 

Consistent with what the EPA indicated 

in the O3 NAAQS proposal (79 FR 

75370), the agency is not responding to 

the implementation comments that are 

not related to a specific proposal. 

However, the EPA intends to take these 

comments under advisement as the 

agency develops rules and guidance to 

assist with implementation of the 

revised NAAQS. Because the EPA did 

specifically propose and is finalizing 

provisions in the regulations addressing 

grandfathering for certain PSD permit 

applications and requirements, as 

discussed in section VII of this 

preamble, the EPA is responding to 

comments on the proposed PSD 

grandfathering provisions. 

A. NAAQS Implementation Plans 

1. Cooperative Federalism 

As directed by the CAA, reducing 

pollution to meet national air quality 

standards always has been a shared task, 

one involving the federal government, 

states, tribes and local air quality 

management agencies. The EPA 

develops regulations and strategies to 

reduce pollution on a broad scale, while 

states and tribes are responsible for 

implementation planning and any 

additional emission reduction measures 

necessary to bring specific areas into 

attainment. The agency supports 

implementation planning with technical 

resources, guidance, and program rules 

where necessary, while air quality 

management agencies use their 

knowledge of local needs and 

opportunities in designing emission 

reduction strategies that will work best 

for their industries and communities. 

This partnership has proved effective 

since the EPA first issued O3 standards 

more than three decades ago. For 

example, 101 areas were designated as 

nonattainment for the 1-hour O3

standards issued in 1979. As of the end 

of 2014, air quality in all but one of 

those areas meets the 1-hour standards. 

The EPA strengthened the O3 standards 

in 1997, shifting to an 8-hour standard 

to improve public health protection, 

particularly for children, the elderly, 

and other sensitive individuals. The 

1997 standards drew significant public 

attention when they were proposed, 

with numerous parties voicing concerns 

about states’ ability to comply. 

However, after close collaboration 

between the EPA, states, tribes and local 

governments to reduce O3-forming 

pollutants, significant progress has been 

made. Air quality in 108 of the original 

115 areas designated as nonattainment 

for the 1997 O3 NAAQS now meets 

those standards. Air quality in 18 of the 

original 46 areas designated as 

nonattainment for the 2008 O3 NAAQS 

now meets those standards. 

The revisions to the primary and 

secondary O3 NAAQS discussed in 

sections II.D and IV.D of this preamble 

trigger a process under which states 228

make recommendations to the 

Administrator regarding area 

designations. Then, the EPA 

promulgates the final area designations. 

States also are required to review 

capacity and authorities in their existing 

SIPs to ensure the CAA requirements 

associated with the new standards can 

be carried out, and modify or 

supplement their existing SIPs as 

needed. The O3 NAAQS revisions also 

apply to the transportation conformity 

and general conformity determinations, 

and affect which preconstruction 

permitting requirements apply to 

sources of O3 precursor emissions, and 

the nature of those requirements. 

The EPA has regulations in place 

addressing the general requirements for 

SIPs, and there are also provisions in 

these existing rules that cover O3 SIPs 

(40 CFR part 51). States likewise have 

provisions in their existing SIPs to 

address air quality for O3 and to 

implement the existing O3 NAAQS. In 

the course of the past 45 years of 

regulating criteria pollutants, including 

O3, the EPA has also provided general 

guidance on the development of SIPs 

and administration of construction 

permitting programs, as well as specific 

guidance on implementing the O3

NAAQS in some contexts under the 

CAA and the EPA regulations. 

The EPA has considered the extent to 

which existing EPA regulations and 

guidance are sufficient to implement the 

revised standards. The CAA does not 

require that the EPA promulgate new 

implementing regulations or issue new 

guidance for states every time that a 

NAAQS is revised. Likewise, the CAA 

does not require the issuance of 

additional implementing regulations or 

guidance by the EPA before a revised 

NAAQS becomes effective. It is 

important to note that the existing EPA 

regulations in 40 CFR part 51 applicable 

to SIPs generally and to particular 

pollutants, including O3 and O3

precursors, continue to apply unless 

and until they are updated. 

Accordingly, the discussion below 

provides the EPA’s current thoughts 

about the extent to which revisions to 

existing regulations and additional 

guidance are appropriate to aid in the 

implementation of the revised O3

NAAQS. 

2. Additional New Rules and Guidance 

The EPA has received comments from 

a variety of states and organizations 

asking for rules and guidance associated 

with a revised NAAQS to be issued in 

a timely manner. As explained above, 

and consistent with the proposal, the 

EPA is not responding to these 

comments at this time because they are 

not related to any changes to existing 

regulations that EPA proposed in this 

rule. Moreover, although issuance of 

such rules and guidance is not a part of 

the NAAQS review process, National 

Ass’n of Manufacturers v. EPA, 750 F. 

3d 921, 926–27 (D.C. Cir. 2014), toward 

that end, the EPA intends to develop 

appropriate revisions to necessary 

implementation rules and provide 

additional guidance in time frames that 

are useful to states when developing 

implementation plans that meet CAA 

requirements. 

Certain requirements under the PSD 

preconstruction permit review program 

apply immediately to a revised NAAQS 

upon the effective date of that NAAQS, 

unless the EPA has established a 

grandfathering provision through 

rulemaking. To ensure a smooth 

transition to a revised O3 NAAQS, the 

EPA is finalizing a grandfathering 

provision similar to the provision 

finalized in the 2012 PM2.5 NAAQS 

Rule. See section VII.C of this preamble 

for more details on the PSD program 

and the final grandfathering provision. 

Promulgation or revision of the 

NAAQS starts a clock for the EPA to 

designate areas as either attainment or 

nonattainment. State recommendations 

for area designations are due to the EPA 

within 12 months of promulgating or 

revising the NAAQS. In an effort to 

allow states to make more informed 

recommendations for these particular 

standards, the EPA intends to issue 

additional guidance concerning the 

designations process for these standards 

within four months of promulgation of 

the NAAQS, or approximately eight 

months before state recommendations 

are due. The EPA generally completes 

mstockstill on DSK4VPTVN1PROD with RULES2

65436 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

229See memorandum from Stephen D. Page to 

Regional Air Directors, ‘‘Guidance on Infrastructure 

State Implementation Plan (SIP) Elements under 

Clean Air Act Sections 110(a)(1) and 110(a)(2)’’ 

September 13, 2013, which is available at http://

www3.epa.gov/airquality/urbanair/sipstatus/docs/

Guidance_on_Infrastructure_SIP_Elements_

Multipollutant_FINAL_Sept_2013.pdf. 

230Note that the relief mechanisms discussed 

here do not include the CAA’s interstate transport 

provisions found in sections 110(a)(2)(D) and 126. 

The interstate transport provisions are intended to 

address the cross-state transport of O3 and O3

precursor emissions from man-made sources within 

the continental U.S. rather than background O3 as 

it is defined in this section. As noted in section 

II.A.2.a above, many of the instances where 

commenters pointed to remote monitored locations 

having O3 exceedances due to background O3 in fact 

reflected sizeable contributions from domestic 

sources, including interstate contributions 

(including from the Los Angeles Basin and other 

California locations). 

area designations two years after 

promulgation of a NAAQS. See section 

VIII.B of this preamble for additional 

information on the initial area 

designation process. 

Under CAA section 110, a NAAQS 

revision triggers the review and, as 

necessary, revision of SIPs to be 

submitted within three years of 

promulgation of a revised NAAQS. 

These SIPs are referred to as 

‘‘infrastructure SIPs.’’ The EPA issued 

general guidance on submitting 

infrastructure SIPs on September 13, 

2013.229 It should be noted that this 

guidance did not address certain state 

planning and emissions control 

requirements related to interstate 

pollution transport. This guidance 

remains relevant for the revised O3

NAAQS. See section VIII.A.4 of this 

preamble for additional information on 

infrastructure SIPs. 

While much of the existing rules and 

guidance for prior ozone standards 

remains applicable to the new 

standards, the EPA intends to propose 

to adopt revised rules on some subjects 

to facilitate air agencies’ efforts to 

implement the revised O3 NAAQS 

within one year after the revised 

NAAQS is established. The rules would 

address nonattainment area 

classification methodologies and 

attainment dates, attainment plan and 

NNSR SIP submission due dates, and 

any other necessary revisions to existing 

regulations for other required 

implementation programs. The EPA 

anticipates finalizing these rules by the 

time areas are designated 

nonattainment. Finalizing rules and 

guidance on these subjects by this time 

would assist air quality management 

agencies with development of any CAArequired SIPs associated with 

nonattainment areas. See section 

VIII.A.5 of this preamble for additional 

information on nonattainment SIPs and 

section VIII.C.3 for additional 

information on nonattainment New 

Source Review requirements applicable 

to new major sources and major 

modifications of existing sources. 

3. Background O3

The EPA and state, local and tribal air 

agencies, strive to determine how to 

most effectively and efficiently use the 

CAA’s various provisions to provide 

required public health and welfare 

protection from the harmful effects of 

O3. In most cases, reducing man-made 

emissions of NOX and VOCs within the 

U.S. will reduce O3 formation and 

provide additional health and welfare 

protection. The EPA recognizes, 

however, that there can be infrequent 

events where daily maximum 8-hour O3

concentrations approach or exceed 70 

ppb largely due to the influence of 

wildfires or stratospheric intrusions, 

which contribute to U.S. background 

(USB) levels but may also qualify for 

consideration under the Exceptional 

Events Rule. See section I.D; but see 

section II.A.2.a above (percentage of 

anthropogenic O3 tends to increase on 

high O3 days relative to percentage of 

background, including in intermountain 

west). 

The term ‘‘background’’ O3 is often 

used to refer to O3 that originates from 

natural sources of O3 (e.g., wildfires and 

stratospheric O3 intrusions) and O3

precursors, as well as from man-made 

international emissions of O3

precursors. Using the term generically, 

however, can lead to confusion as to 

what sources of O3 are being considered. 

Relevant to the O3 implementation 

provisions of the CAA, we define 

background O3 the same way the EPA 

defines USB: O3 that would exist in the 

absence of any man-made emissions 

inside the U.S. 

While the great majority of modeled 

O3 exceedances have local and regional 

emissions as their primary cause, there 

can be events where O3 levels approach 

or exceed the concentration level of the 

revised O3 standards in large part due to 

background sources. These cases of high 

USB levels on high O3 days typically 

result from stratospheric intrusions of 

O3 or wildfire O3 plumes. These events 

are infrequent and the CAA contains 

provisions that can be used to help deal, 

in particular, with stratospheric 

intrusion and wildfire events with O3

contributions of this magnitude, 

including providing varying degrees of 

regulatory relief for air agencies and 

potential regulated entities. The EPA 

intends to work closely with states to 

identify affected locations and ensure 

that the appropriate regulatory 

mechanisms are employed. 

Statutory and regulatory relief 

associated with U.S. background O3 may 

include: 230

• Relief from designation as a 

nonattainment area through exclusion of 

data affected by exceptional events; 

• Relief from the more stringent 

requirements of higher nonattainment 

area classifications through treatment as 

a rural transport area, through exclusion 

of data affected by exceptional events, 

or through international transport 

provisions; 

• Relief from having to demonstrate 

attainment and having to adopt more 

than reasonable controls on local 

sources through international transport 

provisions. 

Further discussion of these 

mechanisms is provided in sections 

VIII.B.2 (exceptional events), VIII.B.1 

(rural transport areas), and VIII.E.2 

(international transport). 

Although these relief mechanisms 

require some level of assessment or 

demonstration by a state and/or the EPA 

to invoke, they have been used 

successfully in the past under 

appropriate circumstances. For 

example, the EPA has historically acted 

on every exceptional events 

demonstration that has affected a 

regulatory decision regarding initial area 

designations. See e.g., Idaho: West 

Silver Valley Nonattainment Area— 

Area Designations for the 2012 primary 

annual PM2.5 NAAQS Technical 

Support Document, pp. 10–14, 

December 2014. For the revised O3

standards, the areas that would most 

likely need to use the mechanisms 

discussed in this section as part of 

attaining the revised O3 standards are 

locations in the western U.S. where we 

have estimated the largest seasonal 

average values of background O3 occur. 

We expect some of these areas to use the 

provisions in the Exceptional Events 

Rule during the designations process for 

the revised O3 standards. The EPA will 

then give priority to exceptional events 

demonstrations submitted by air 

agencies with areas whose designation 

decision could be influenced by the 

exclusion of data under the Exceptional 

Events Rule. In addition, as discussed in 

more detail in sections V.D and VIII.B.2 

of this action, to streamline the 

exceptional events process, the EPA will 

soon propose revisions to the 2007 

Exceptional Events Rule and will 

release through a Federal Register 

Notice of Availability a draft guidance 

document to address Exceptional Events 

Rule criteria for wildfires that could 

affect O3 concentrations. We expect to 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65437 

231While the CAA allows the EPA to set a shorter 

time for submission of these SIPs, the EPA does not 

currently intend to do so for this revision to the O3

NAAQS. 

232Section 181(a)(1) of the CAA establishes 

classification categories for areas designated 

nonattainment for the primary O3 NAAQS. These 

categories range from ‘‘Marginal,’’ the lowest O3

classification with the fewest requirements 

associated with it, to ‘‘Extreme,’’ the highest 

classification with the most required programs. 

Areas with worse O3 problems are given more time 

to attain the NAAQS and more associated emission 

control requirements. 

233 Implementation of the 2008 National Ambient 

Air Quality Standards for Ozone: State 

Implementation Plan Requirements; Final Rule (80 

FR 12264; March 6, 2015) and Implementation of 

the 2008 National Ambient Air Quality Standards 

for Ozone: Nonattainment Area Classifications 

Approach, Attainment Deadlines and Revocation of 

the 1997 Ozone Standards for Transportation 

Conformity Purposes (77 FR 30160; May 21, 2012). 

promulgate Exceptional Events Rule 

revisions and finalize the new guidance 

document before the October 2016 date 

by which states, and any tribes that 

wish to do so, are required to submit 

their initial designation 

recommendations for the revised O3

NAAQS. 

4. Section 110 State Implementation 

Plans 

The CAA section 110 specifies the 

general requirements for SIPs. Within 

three years after the promulgation of 

revised NAAQS (or such shorter period 

as the Administrator may prescribe 231) 

each state must adopt and submit 

‘‘infrastructure’’ SIPs to the EPA to 

address the requirements of section 

110(a)(1) and (2), as applicable. These 

‘‘infrastructure SIP’’ submissions 

establish the basic state programs to 

implement, maintain, and enforce 

revised NAAQS and provide assurances 

of state resources and authorities. States 

are required to develop and maintain an 

air quality management infrastructure 

that includes enforceable emission 

limitations, a permitting program, an 

ambient monitoring program, an 

enforcement program, air quality 

modeling capabilities, and adequate 

personnel, resources, and legal 

authority. Because the revised primary 

NAAQS and secondary NAAQS are 

identical, the EPA does not at present 

discern any need for there to be any 

significant substantive difference in the 

infrastructure SIP elements for the two 

standards and thus believes it would be 

more efficient for states and the EPA if 

each affected state submits a single 

section 110 infrastructure SIP that 

addresses both standards at the same 

time (i.e., within three years of 

promulgation of the O3 NAAQS). 

Accordingly the EPA is not extending 

the SIP deadline for purposes of a 

revised secondary standard. 

It is the responsibility of each state to 

review its air quality management 

program’s compliance with the 

infrastructure SIP provisions in light of 

each new or revised NAAQS. Most 

states have revised and updated their 

infrastructure SIPs in recent years to 

address requirements associated with 

the 2008 O3 NAAQS. We expect that the 

result of these prior updates is that, in 

most cases, states will already have 

adequate state regulations previously 

adopted and approved into the SIP to 

address a particular requirement with 

respect to the revised O3 NAAQS. For 

such portions of the state’s 

infrastructure SIP submission, the state 

may provide a ‘‘certification’’ specifying 

that certain existing provisions in the 

SIP are adequate to meet applicable 

requirements. Although the term 

‘‘certification’’ does not appear in the 

CAA as a type of infrastructure SIP 

submittal, the EPA sometimes uses the 

term in the context of infrastructure 

SIPs, by policy and convention, to refer 

to a state’s SIP submission. If a state 

determines that its existing EPAapproved SIP provisions are adequate in 

light of the revised O3 NAAQS with 

respect to a given infrastructure SIP 

element (or sub-element), then the state 

may make a ’’certification’’ that the 

existing SIP contains provisions that 

address those requirements of the 

specific CAA section 110(a)(2) 

infrastructure elements. In the case of a 

certification, the submittal does not 

have to include another copy of the 

relevant provision (e.g., rule or statute) 

itself. Rather, the submission may 

provide citations to the already SIPapproved state statutes, regulations, or 

non-regulatory measures, as 

appropriate, which meet the relevant 

CAA requirement. Like any other SIP 

submission, such certification can be 

made only after the state has provided 

reasonable notice and opportunity for 

public hearing. This ‘‘reasonable notice 

and opportunity for public hearing’’ 

requirement for infrastructure SIP 

submittals appears at section 110(a), and 

it comports with the more general SIP 

requirement at section 110(l) of the 

CAA. Under the EPA’s regulations at 40 

CFR part 51, if a public hearing is held, 

an infrastructure SIP submission must 

include documentation by the state that 

the public hearing was held in 

accordance with the EPA’s procedural 

requirements for public hearings. See 40 

CFR part 51, Appendix V, paragraph 

2.1(g), and 40 CFR 51.102. In the event 

that a state’s existing SIP does not 

already meet applicable requirements, 

then the infrastructure SIP submission 

must include the modifications or 

additions to the state’s SIP in order to 

update it to meet the relevant elements 

of section 110(a)(2). 

5. Nonattainment Area Requirements 

Part D of the CAA describes the 

various program requirements that 

apply to states with nonattainment areas 

for different NAAQS. Clean Air Act 

Section 182 (found in subpart 2 of part 

D) includes the specific SIP 

requirements that govern the O3

program, and supplements the more 

general nonattainment area 

requirements in CAA sections 172 and 

173. Under CAA section 182, states 

generally are required to submit 

attainment demonstration SIPs within 

three or four years after the effective 

date of area designations promulgated 

by the EPA, depending on the 

classification of the area.232 These SIP 

submissions need to show how the 

nonattainment area will attain the 

primary O3 standard ‘‘as expeditiously 

as practicable,’’ but no later than within 

the relevant time frame from the 

effective date of designations associated 

with the classification of the area. 

The EPA believes that the overall 

framework and policy approach of the 

implementation rules associated with 

the 2008 O3 NAAQS provide an 

effective and appropriate template for 

the general approach states would 

follow in planning for attainment of the 

revised O3 standard.233 However, to 

assist with the implementation of the 

revised O3 standards, the EPA intends to 

develop and propose an additional O3

NAAQS Implementation Rule that will 

address certain subjects specific to the 

new O3 NAAQS finalized here. This 

will include establishing air quality 

thresholds associated with each 

nonattainment area classification (i.e., 

Marginal, Moderate, etc.), associated 

attainment deadlines, and deadlines for 

submitting attainment planning SIP 

elements (e.g., RACT for major sources, 

RACT VOC control techniques 

guidelines, etc.). The rulemaking will 

also address whether to revoke the 2008 

O3 NAAQS, and to impose appropriate 

anti-backsliding requirements to ensure 

that the protections afforded by that 

standard are preserved. The EPA 

intends to propose this implementation 

rule within one year after the revised O3

NAAQS is promulgated, and finalize 

this implementation rule by no later 

than the time the area designations 

process is finalized (approximately two 

years after promulgation of the revised 

O3 NAAQS). 

We know that developing the 

implementation plans that outline the 

steps a nonattainment area will take to 

mstockstill on DSK4VPTVN1PROD with RULES2

65438 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

234Page, 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 Office of Air Quality Planning and 

Standards to Regional Air Directors, Regions I–X, 

December 20, 2011. Available: http://www.epa.gov/ 

ttn/oarpg/t1/memoranda/20120117naaqs

guidance.pdf. 

235For the 1979 1-hour O3 standard, Door County 

Area, Wisconsin; Edmonson County Area, 

Kentucky; Essex County Area (Whiteface 

Mountain), New York; and Smyth County Area 

(White Top Mountain), Virginia were recognized by 

the EPA as rural transport areas. No rural transport 

areas were recognized for the 1997 or 2008 8-hour 

O3 standards. 

236U.S. Environmental Protection Agency (2005). 

Criteria For Assessing Whether an Ozone 

Nonattainment Area is Affected by Overwhelming 

Transport [Draft EPA Guidance]. U.S. 

Environmental Protection Agency, Research 

Triangle Park, NC. June 2005. Available at http:// 

meet an air quality standard requires a 

significant amount of work on the part 

of state, tribal or local air agencies. The 

EPA routinely looks for ways to reduce 

this workload, including assisting with 

air quality modeling by providing 

inputs such as emissions, 

meteorological and boundary 

conditions; and sharing national-scale 

model results that states can leverage in 

their development of attainment 

demonstrations. 

B. O3 Air Quality Designations 

1. Area Designation Process 

After the EPA establishes or revises a 

NAAQS, the CAA directs the EPA and 

the states to take steps to ensure that the 

new or revised NAAQS is met. One of 

the first steps, 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 any nearby areas that contribute to 

areas that do not meet the new or 

revised NAAQS. 

Section 107(d)(1) of the CAA provides 

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. The EPA must then 

promulgate the area designations 

according to a specified process, 

including procedures to be followed if 

the EPA intends to modify a state’s 

initial recommendation. 

Clean Air Act Section 107(d)(1)(B)(i) 

further provides, ‘‘Upon promulgation 

or revision of a national ambient air 

quality standard, 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 of the new or revised 

national ambient air quality standard. 

Such period may be extended for up to 

one year in the event the Administrator 

has insufficient information to 

promulgate the designations.’’ By no 

later than 120 days prior to 

promulgating area designations, the EPA 

is required to notify states of any 

intended modifications to their 

recommendations that the EPA may 

deem necessary. States then have an 

opportunity to demonstrate why any 

proposed modification is inappropriate. 

Whether or not a state provides a 

recommendation, the EPA must timely 

promulgate the designation that the 

agency deems appropriate. 

While section 107 of the CAA 

specifically addresses states, the EPA 

intends to follow the same process for 

tribes to the extent practicable, pursuant 

to CAA section 301(d) 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 designation process.234

As discussed in sections II and IV of 

this preamble, the EPA is revising both 

the primary and secondary O3 NAAQS. 

Accordingly, the EPA intends to 

complete designations for both NAAQS 

following the standard 2-year process 

discussed above. In accordance with 

section 107(d)(1) of the CAA, state 

Governors (and tribes, if they choose) 

should submit their initial designation 

recommendations for a revised primary 

and secondary NAAQS by 1 year after 

October 1, 2015. If the EPA intends to 

modify any state recommendation, the 

EPA would notify the appropriate state 

Governor (or tribal leader) no later than 

120 days prior to making final 

designation decisions. A state or tribe 

that believes the modification is 

inappropriate would then have the 

opportunity to demonstrate to the EPA 

why it believes its original 

recommendation (or a revised 

recommendation) is more appropriate. 

The EPA would take any additional 

input into account in making the final 

designation decisions. 

The CAA defines an area as 

nonattainment if it is violating the 

NAAQS or if it is contributing to a 

violation in a nearby area. Consistent 

with previous area designations 

processes, the EPA intends to use areaspecific analysis of multiple factors to 

support area boundary decisions. The 

EPA intends to evaluate information 

related to the following factors for 

designations: air quality data, emissions 

and emissions-related data, 

meteorology, geography/topography, 

and jurisdictional boundaries. 

Additional guidance on the designation 

process and how these factors may be 

evaluated and inform the process will 

be issued by the EPA early in 2016 to 

assist states in developing their 

recommendations. 

Areas that are designated as 

nonattainment are also classified at the 

time of designation by operation of law 

according to the severity of their O3

problem. The classification categories 

are Marginal, Moderate, Serious, Severe, 

and Extreme. Ozone nonattainment 

areas are subject to specific mandatory 

measures depending on their 

classification. As indicated previously, 

the thresholds for the classification 

categories will be established in a future 

O3 implementation rule. 

Clean Air Act section 182(h) 

authorizes the EPA Administrator to 

determine that an area designated 

nonattainment can be treated as a rural 

transport area. Regardless of its 

classification, a rural transport area is 

deemed to have fulfilled all O3-related 

planning and control requirements if it 

meets the CAA’s requirements for areas 

classified Marginal, which is the lowest 

classification specified in the CAA. In 

accordance with the statute, a 

nonattainment area may qualify for this 

determination if it meets the following 

criteria: 

• The area does not contain emissions 

sources that make a significant 

contribution to monitored O3

concentrations in the area, or in other 

areas; and 

• The area does not include and is 

not adjacent to a Metropolitan Statistical 

Area. 

Historically, the EPA has listed four 

nonattainment areas as rural transport 

areas under this statutory provision.235

The EPA has not issued separate written 

guidance to further elaborate on the 

interpretation of these CAA 

qualification criteria. However, the EPA 

developed draft guidance in 2005 that 

explains the kinds of technical analyses 

that states could use to establish that 

transport of O3 and/or O3 precursors 

into the area is so overwhelming that 

the contribution of local emissions to an 

observed 8-hour O3 concentration above 

the level of the NAAQS is relatively 

minor and determine that emissions 

within the area do not make a 

significant contribution to the O3

concentrations measured in the area or 

in other areas.236 While this guidance 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65439 

www.epa.gov/scram001/guidance/guide/owt_

guidance_07-13-05.pdf. 

237A natural event is further described in 40 CFR 

50.1(k) as ‘‘an event in which human activity plays 

little or no direct causal role.’’ 

238 72 FR 13,560 (March 22, 2007), ‘‘Treatment of 

Data Influenced by Exceptional Events,’’ Final Rule; 

see also 40 CFR parts 50 and 51. 

239The preamble to the Exceptional Events Rule 

(72 FR 13560) identifies both stratospheric O3

intrusions and wildfires as natural events that could 

also qualify as exceptional events under the CAA 

and Exceptional Event Rule criteria. Note that O3

resulting from routine natural emissions from 

vegetation, microbes, animals and lightning are not 

exceptional events authorized for exclusion under 

the section 319 of the CAA. 

240U.S. EPA (2014) Treatment of Data Influenced 

by Exceptional Events: Examples of Reviewed 

Exceptional Event Submissions. U.S. 

Environmental Protection Agency, Research 

Triangle Park, NC, available at http://www.epa.gov/ 

ttn/analysis/exevents.htm. 

241U.S. EPA (2014) Treatment of Data Influenced 

by Exceptional Events: Examples of Reviewed 

Exceptional Event Submissions. U.S. 

Environmental Protection Agency, Research 

Triangle Park, NC. Examples of O3-related 

exceptional event submissions, available at http:// 

www.epa.gov/ttn/analysis/exevents.htm. 

was not prepared specifically for rural 

transport areas, it could be useful to 

states for developing technical 

information to support a request that the 

EPA treat a specific O3 nonattainment 

area as a rural transport area. The EPA 

will work with states to ensure 

nonattainment areas eligible for 

treatment as rural transport areas are 

identified. 

2. Exceptional Events 

During the initial area designations 

process, the EPA intends to evaluate 

multiple factors, including air quality 

data, when identifying and determining 

boundaries for areas of the country that 

meet or do not meet the revised O3

NAAQS. In some cases, these data may 

be influenced by exceptional events. 

Under the Exceptional Events Rule, an 

air agency can request and the EPA can 

agree to exclude data associated with 

event-influenced exceedances or 

violations of a NAAQS, including the 

revised O3 NAAQS, provided the event 

meets the statutory requirements in 

section 319(b) of the CAA, which 

requires that: 

• the event ‘‘affects air quality;’’ 

• the event ‘‘is not reasonably 

controllable or preventable;’’ 

• the event is ‘‘caused by human 

activity that is unlikely to recur at a 

particular location or [is] a natural 

event,’’ 237 and 

• that ‘‘a clear causal relationship 

must exist between the measured 

exceedances of a [NAAQS] and the 

exceptional event. . . .’’ 

The EPA’s implementing regulations, 

the Exceptional Events Rule, further 

specify certain requirements for air 

agencies making exceptional events 

demonstrations.238

The ISA contains discussions of 

natural events that may contribute to O3

or O3 precursors. These include 

stratospheric O3 intrusion and wildfire 

events.239 As indicated above, to satisfy 

the exceptional events requirements and 

to qualify for data exclusion under the 

Exceptional Events Rule, an air agency 

must develop and submit a 

demonstration, including evidence, 

addressing each of the identified 

criteria. The extent to which a 

stratospheric O3 intrusion event or a 

wildfire event contributes to O3 levels 

can be uncertain, and in most cases 

requires detailed analyses to determine. 

Strong stratospheric O3 intrusion 

events, most prevalent at high elevation 

sites during winter or spring, can be 

identified based on measurements of 

low relative humidity, evidence of deep 

atmospheric mixing, and a low ratio of 

CO to O3 based on ambient 

measurements. Accurately determining 

the extent of weaker intrusion events 

remains challenging (U.S. EPA 2013, p. 

3–34). Although states have submitted 

only a few exceptional events 

demonstrations for stratospheric O3

intrusion, the EPA recently approved a 

demonstration from Wyoming for a June 

2012 stratospheric O3 event.240

While stratospheric O3 intrusions can 

increase monitored ground-level 

ambient O3 concentrations, wildfire 

plumes can either suppress or enhance 

O3 depending upon a variety of factors 

including fuel type, combustion stage, 

plume chemistry, aerosol effects, 

meteorological conditions and distance 

from the fire (Jaffe and Wigder, 2012). 

As a result, determining the impact of 

wildfire emissions on specific O3

observations is challenging. The EPA 

recently approved an exceptional events 

demonstration for wildfires affecting 1- 

hour O3 levels in Sacramento, California 

in 2008 that successfully used a variety 

of analytical tools (e.g., regression 

modeling, back trajectories, satellite 

imagery, etc.) to support the exclusion 

of O3 data affected by large fires.241

In response to previously expressed 

stakeholder feedback regarding 

implementation of the Exceptional 

Events Rule and specific stakeholder 

concerns regarding the burden of 

exceptional events demonstrations, the 

EPA is currently engaged in a 

rulemaking process to amend the 

Exceptional Events Rule. As part of an 

upcoming notice and comment 

rulemaking effort (and related activities, 

including the issuance of relevant 

guidance documents), the EPA sees 

opportunities to standardize best 

practices for collaboration between the 

EPA and air agencies, clarify and 

simplify demonstrations, and improve 

tools and consistency. 

Additionally, the EPA intends to 

develop guidance to address 

implementing the Exceptional Events 

Rule criteria for wildfires that could 

affect ambient O3 concentrations. 

Wildfire emissions are a component of 

background O3 (Jaffe and Wigder, 2012) 

and in some locations can significantly 

contribute to periodic high O3 levels 

(Emery, 2012). The threat from wildfires 

can be mitigated through management 

of wildland vegetation. Planned and 

managed fires are one tool that land 

managers can use to reduce fuel load, 

unnatural understory and tree density, 

thus helping to reduce the risk of 

catastrophic wildfires. Allowing some 

wildfires to continue and the thoughtful 

use of prescribed fire can influence the 

occurrence of catastrophic wildfires, 

which may reduce the probability of 

fire-induced smoke impacts and 

subsequent health effects. Thus, 

appropriate use of prescribed fire may 

help manage the contribution of 

wildfires to both background and 

periodic peak O3 air pollution. Several 

commenters expressed concern that the 

revised O3 NAAQS could limit the 

future use of prescribed fire. Under the 

current Exceptional Events Rule, 

prescribed fires meeting the rule criteria 

may also qualify as exceptional events. 

The EPA intends to further clarify the 

Exceptional Events Rule criteria for 

prescribed fire on wildland in its 

upcoming rulemaking. 

The EPA is committed to working 

with federal land managers, other 

federal agencies, tribes and states to 

effectively manage prescribed fire use to 

reduce the impact of wildfire-related 

emissions on O3 through policies and 

regulations implementing these 

standards. 

C. How do the New Source Review 

(NSR) requirements apply to the revised 

O3 NAAQS? 

1. NSR Requirements for Major 

Stationary Sources for the Revised O3

NAAQS 

The CAA, at parts C and D of title I, 

contains preconstruction review and 

permitting programs applicable to new 

major stationary sources and major 

modifications of existing major sources. 

The preconstruction review of each new 

major stationary source and major 

modification applies on a pollutantspecific basis, and the requirements that 

apply for each pollutant depend on 

whether the area in which the source is 

situated is designated as attainment (or 

mstockstill on DSK4VPTVN1PROD with RULES2

65440 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

242This description of paragraph (i)(2) of the PSD 

regulations at 40 CFR 51.166 and 52.21 reflects 

revisions made in the final 2008 O3 NAAQS SIP 

Requirements Rule. See 80 FR 12264 at 12287 

(March 6, 2015). 

243The definition of ‘‘regulated NSR pollutant’’ is 

found in the PSD regulations at 40 CFR 

51.166(b)(49) and 52.21(b)(50), and in the NNSR 

regulations at 40 CFR 51.165(a)(1)(xxxvii). 244 VOC and NOX are defined as precursors of 

ozone in the PSD regulations at 40 CFR 

51.166(b)(49)(i)(b)(1) and 52.21(b)(50)(i)(b)(1), and 

in the NNSR regulations at 40 CFR 

51.165(a)(1)(xxxvii)(B) and (C)(1) and part 51, 

Appendix S, II.A.31(ii)(b)(1). 

245Congress established certain Class I areas in 

section 162(a) of the CAA, including international 

parks, national wilderness areas, and national parks 

that meet certain criteria. Such Class I areas, known 

as mandatory federal Class I areas, are afforded 

special protection under the CAA. In addition, 

states and tribal governments may establish Class I 

areas within their own political jurisdictions to 

provide similar special air quality protection. 

246An exception occurs in cases where the EPA 

has included a grandfathering provision in its PSD 

regulations for a particular pollutant. The EPA 

historically has exercised its discretion to transition 

the implementation of certain new requirements 

through grandfathering, under appropriate 

circumstances, either by rulemaking or through a 

case-by-case determination for a specific permit 

application. In 2014, the United States Court of 

Appeals for the Ninth Circuit vacated a decision by 

the EPA to issue an individual PSD permit 

grandfathering a permit applicant from certain 

requirements. See Sierra Club v. EPA, 762 F.3d 971 

(9th Cir. 2014). In light of that decision, the EPA 

is no longer asserting authority to grandfather 

permit applications on a case-by-case basis. This 

decision is addressed in more detail in the 

discussion of the grandfathering provisions that the 

EPA is issuing through this rulemaking in section 

VII of this preamble. 

unclassifiable) or nonattainment for that 

pollutant. In areas designated 

attainment or unclassifiable for a 

pollutant, the PSD requirements under 

part C apply to construction at major 

sources. In areas designated 

nonattainment for a pollutant, the NNSR 

requirements under part D apply to 

major source construction. Collectively, 

those two sets of permit requirements 

are commonly referred to as the ‘‘major 

New Source Review’’ or ‘‘major NSR’’ 

programs. 

Until an area is formally designated 

with respect to the revised O3 NAAQS, 

the NSR provisions applicable under 

that area’s current designation for the 

2008 O3 NAAQS (including any 

applicable anti-backsliding 

requirements) will continue to apply. 

That is, for areas designated as 

attainment/unclassifiable for the 2008 

O3 NAAQS, PSD will apply for new 

major stationary sources and major 

modifications that trigger major source 

permitting requirements for O3; areas 

designated nonattainment for the 2008 

O3 NAAQS must comply with the NNSR 

requirements for new major stationary 

sources and major modifications that 

trigger major source permitting 

requirements for O3. When the new 

designations for the revised O3 NAAQS 

become effective, under the current 

rules, those designations will generally 

serve to determine whether PSD or 

NNSR applies to O3 and its precursors. 

The PSD regulations at 40 CFR 

51.166(i)(2) and 52.21(i)(2) provide that 

the substantive PSD requirements do 

not apply for a particular pollutant if the 

owner or operator of the new major 

stationary source or major modification 

demonstrates that the area in which the 

source is located is designated 

nonattainment for that pollutant under 

CAA section 107. Thus, new major 

sources and modifications will generally 

be subject to the PSD program 

requirements for O3 if they are locating 

in an area that does not have a current 

nonattainment designation under CAA 

section 107 for O3. These rules further 

provide that nonattainment designations 

for a revoked NAAQS, as contained in 

40 CFR part 81, are not viewed as 

current designations under CAA section 

107 for purposes of determining the 

applicability of such PSD 

requirements.242

The EPA’s major NSR regulations 

define the term ‘‘regulated NSR 

pollutant’’ to include any pollutant for 

which a NAAQS has been promulgated 

and any pollutant identified in EPA 

regulations as a constituent or precursor 

to such pollutant.243 Both the PSD and 

NNSR regulations identify VOC and 

NOX as precursors to O3. Accordingly, 

the major NSR programs for O3 are 

applied to emissions of VOC and NOX

as precursors of O3.244

2. Prevention of Significant 

Deterioration (PSD) Program 

The statutory requirements for a PSD 

permit program set forth under part C of 

title I of the CAA (sections 160 through 

169) are addressed by the EPA’s PSD 

regulations found at 40 CFR 51.166 

(minimum requirements for an 

approvable PSD SIP) and 40 CFR 52.21 

(PSD permitting program for permits 

issued under the EPA’s federal 

permitting authority). Both sets of 

regulations already apply for O3 when 

the area is designated attainment or 

unclassifiable for O3 and when the new 

source or modification triggers PSD 

requirements for O3. 

For PSD, a ‘‘major stationary source’’ 

is one that emits or has the potential to 

emit 250 tons per year (tpy) or more of 

any regulated NSR pollutant, unless the 

new or modified source 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 source 

categories, a ‘‘major stationary source’’ 

is one that emits or has the potential to 

emit 100 tpy or more of any regulated 

NSR pollutant. A ‘‘major modification’’ 

is a physical change or a change in the 

method of operation of an existing major 

stationary source that results first, in a 

significant emissions increase of a 

regulated NSR pollutant for the project, 

and second, in a significant net 

emissions increase of that pollutant at 

the source. See 40 CFR 51.166(b)(2)(i), 

40 CFR 52.21(b)(2)(i). 

Among other things, for each 

regulated NSR pollutant emitted or 

increased in significant amounts, the 

PSD program requires a new major 

stationary source or a major 

modification to apply Best Available 

Control Technology and to conduct an 

air quality impact analysis to 

demonstrate that the proposed source or 

project will not cause or contribute to a 

violation of any NAAQS or PSD 

increment (see CAA section 165(a)(3)– 

(4), 40 CFR 51.166(j)–(k), 40 CFR 

52.21(j)–(k)). The PSD requirements may 

also include, in appropriate cases, an 

analysis of potential adverse impacts on 

Class I areas (see CAA sections 162 and 

165).245 The EPA has generally 

interpreted the requirement for an air 

quality impact analysis under CAA 

section 165(a)(3) and the implementing 

regulations to include a requirement to 

demonstrate that emissions from the 

proposed facility will not cause or 

contribute to a violation of any NAAQS 

that is in effect as of the date a PSD 

permit is issued.246 See, e.g., 73 FR 

28321, 28324, 28340 (May 16, 2008); 78 

FR 3253 (Jan. 15, 2013); Memorandum 

from Stephen D. Page, Director, Office of 

Air Quality Planning & Standards, 

‘‘Applicability of the Federal Prevention 

of Significant Deterioration Permit 

Requirements to New and Revised 

National Ambient Air Quality 

Standards’’ (April 1, 2010). Consistent 

with this interpretation, the 

demonstration required under CAA 

section 165(a)(3) and 40 CFR 51.166(k) 

and 52.21(k) will apply to any revised 

O3 NAAQS when such NAAQS become 

effective, except to the extent that a 

pending permit application is subject to 

a grandfathering provision that the EPA 

establishes through rulemaking. In 

addition, the other existing 

requirements of the PSD program will 

remain applicable to O3 after the revised 

O3 NAAQS takes effect. 

Because the complex chemistry of O3

formation in the atmosphere poses 

significant challenges for the assessing 

the impacts of individual stationary 

sources on O3 formation, the EPA’s 

judgment historically has been that it is 

not technically sound to designate a 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65441 

247See In re Footprint Power Salem Harbor 

Development, LP, 16 E.A.D ___, PSD Appeal No. 

14–02, at 20–25 (EAB, Sept. 2, 2014) (including 

description of EPA’s position on application of 

BACT to ozone precursors) available at http://

yosemite.epa.gov/oa/EAB_Web_Docket.nsf/

PSD+Permit+Appeals+(CAA)?OpenView. 

248Any proposed major stationary source or 

major modification subject to PSD for O3 that does 

not receive its PSD permit by the effective date of 

a new O3 nonattainment designation for the area 

where the source would locate would then be 

required to satisfy all of the applicable NNSR 

preconstruction permit requirements for O3, even if 

such source had been grandfathered under the PSD 

regulations from the demonstration requirement 

under CAA section 165(a)(3) for O3. 

249The EPA has historically recognized in 

regulations and through other actions that sources 

applying for PSD permits may have the option of 

utilizing offsets as part of the required PSD 

demonstration under CAA section 165(a)(3)(B). See, 

e.g., 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). 52 FR 

24698 (July 1, 1987); 78 FR 3261–62 (Jan. 15, 2013). 

specific air quality model that must be 

used in the PSD permitting process to 

make this demonstration for O3. To 

address ambient impacts of emissions 

from proposed individual stationary 

sources on O3, the EPA proposed 

amendments to Appendix W to 40 CFR 

part 51 in July 2015 that would, among 

other things, revise the Appendix W 

provisions relating to the analytical 

techniques for demonstrating that an 

individual PSD source or modification 

does not cause or contribute to a 

violation of the O3 NAAQS (80 FR 

45340, July 29, 2015). Until any 

revisions are finalized and in effect, PSD 

permit applicants should continue to 

follow the current provisions in the 

applicable regulations and Appendix W 

in order to demonstrate that a proposed 

source or modification does not cause or 

contribute to a violation of the O3

NAAQS. 

a. What transition plan is the EPA 

providing for implementing the PSD 

requirements for the revised O3

NAAQS? 

In this rulemaking, the EPA is 

amending the PSD regulations at 40 CFR 

51.166 and 40 CFR 52.21 to include a 

grandfathering provision that will allow 

reviewing authorities to continue to 

review certain pending PSD permit 

applications in accordance with the O3

NAAQS that was in effect when a 

specific permitting milestone was 

reached, rather than the revised O3

NAAQS. The EPA is finalizing the 

grandfathering provision as proposed 

with two trigger dates—the signature 

date of the revised O3 NAAQS rule for 

complete applications and the effective 

date of the revised O3 NAAQS for a draft 

permit or preliminary determination. A 

more detailed discussion of the final 

provision, comments received and our 

responses to those comments is 

provided in section VII of this preamble, 

which addresses this change to the PSD 

regulations, as well as the Response to 

Comment Document contained in the 

docket for this rulemaking. 

b. What screening and compliance 

demonstration tools are used to 

implement the PSD program? 

The EPA has historically allowed the 

use of screening and compliance 

demonstration tools to help facilitate the 

implementation of the NSR program by 

reducing the source’s burden and 

streamlining the permitting process for 

circumstances where the emissions or 

ambient impacts of a particular 

pollutant could be considered de 

minimis. For example, the EPA has 

established significant emission rates, or 

SERs, that are used as screening tools to 

determine when a pollutant would be 

considered to be emitted in a significant 

amount and, accordingly, when the NSR 

requirements should be applied to that 

pollutant. See 40 CFR 51.166(b)(23) and 

52.21(b)(23). For O3, the EPA 

established a SER of 40 tpy for 

emissions of each O3 precursor—VOC 

and NOX. For PSD, the O3 SER applies 

independently to emissions of VOC and 

NOX (emissions of precursors are not 

added together) to determine when the 

proposed major stationary source or 

major modification must undergo PSD 

review for that precursor and whether 

individual PSD requirements, such as 

BACT, apply to that precursor.247

In the context of the PSD air quality 

impact analysis, the EPA has also used 

a value called a significant impact level 

(SIL) as a compliance demonstration 

tool. The SIL, expressed as an ambient 

concentration of a pollutant, may be 

used first to determine the geographical 

scope of the ambient impact analysis 

that must be completed for the 

applicable pollutant to satisfy the air 

quality demonstration requirement 

under CAA section 165(a)(3). A second 

use is to guide the determination of 

whether the impact of the source is 

considered to cause or contribute to a 

violation of any NAAQS. The EPA has 

not established a SIL for O3. The EPA 

is currently considering development of 

a SIL for O3 through either guidance or 

a rulemaking process. Such a SIL would 

complement proposed revisions to 

Appendix W mentioned above (80 FR 

45340, July 29, 2015) and would assist 

in the implementation of the PSD air 

quality analysis requirement for 

protection of the O3 NAAQS. However, 

the EPA is not making revisions in this 

rulemaking to address the PSD air 

quality analysis for O3. Until any 

rulemaking to amend existing PSD 

regulations for O3 is completed, 

permitting decisions should continue to 

be based on the existing provisions in 

the applicable regulations. 

Several commenters addressed 

statements that the EPA made 

concerning screening tools for O3 in the 

preamble to the O3 NAAQS proposal. 

These statements were not linked to any 

proposed amendments to EPA 

regulations. Aside from adopting the 

grandfathering provision addressed in 

section VII of this preamble, the EPA is 

not revising the PSD requirements for 

O3 in this final rule. Therefore, the EPA 

is not responding to those comments at 

this time, consistent with the EPA’s 

general approach to comments on 

implementation topics described above. 

c. Other PSD Transition Issues 

The EPA anticipates that the existing 

O3 air quality in some areas currently 

designated attainment of unclassifiable 

for O3 will not meet the revised O3

NAAQS upon its effective date and that 

some of these areas will ultimately be 

designated ‘‘nonattainment’’ for the 

revised O3 NAAQS through the formal 

area designation process set forth under 

the CAA (see section VIII.B above). 

However, until the EPA issues such 

nonattainment designations, proposed 

new major sources and major 

modifications situated in any area 

designated attainment or unclassifiable 

for the 2008 O3 NAAQS will continue 

to be required to address O3 in a PSD 

permit.248 As mentioned above, the PSD 

permitting program requires that 

proposed new major stationary sources 

and major modifications must 

demonstrate that the emissions from the 

proposed source or modification will 

not cause or contribute to a violation of 

any NAAQS. In the notice of proposed 

rulemaking, the EPA provided 

information concerning its views on the 

possibility that some PSD permit 

applications could satisfy the air quality 

analysis requirements for O3 by 

obtaining air quality offsets (called PSD 

offsets).249 Several commenters 

expressed concern that without some 

transition provisions in the final rule 

exempting PSD permit applications for 

sources located in such areas from 

meeting the air quality analysis 

requirements for the revised O3 NAAQS, 

such applications might not be able to 

satisfy the demonstration requirement, 

as the current ambient air monitoring 

data indicate the revised lower 

standards are not being met. The O3

NAAQS proposal included no proposed 

revisions to PSD regulations on this 

mstockstill on DSK4VPTVN1PROD with RULES2

65442 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

250See Appendix S, Part I; 40 CFR 52.24(k). 

251As appropriate, certain NNSR requirements 

under 40 CFR 51.165 or Appendix S can also apply 

to sources and modifications located in areas that 

are designated attainment or unclassifiable in the 

Ozone Transport Region. See, e.g., CAA 184(b)(2), 

40 CFR 52.24(k). 

252States with SIP-approved NNSR programs for 

O3 should evaluate that program to determine 

whether they can continue to issue permits under 

their approved program or whether revisions to 

their program are necessary to address the revised 

O3 NAAQS. 

253See, for example, emission reduction credit 

banking programs in Ohio (OAC Chapter 3745– 

1111) and California (H&SC Section 40709). 

topic and the EPA is not making any 

revisions to the PSD requirements for O3

in this action to address this issue. 

Therefore, the EPA is not responding to 

those comments at this time, consistent 

with its general approach to comments 

on implementation topics described 

above. However, to help address this 

concern raised by commenters, the EPA 

is considering issuing additional 

guidance on how PSD offsets can be 

implemented. 

3. Nonattainment NSR 

Part D of title I of the CAA includes 

preconstruction review and permitting 

requirements for new major stationary 

sources and major modifications when 

they locate in areas designated 

nonattainment for a particular pollutant. 

The relevant part D requirements are 

typically referred to as the 

nonattainment NSR (NNSR) program. 

The EPA regulations for the NNSR 

program are contained at 40 CFR 51.165, 

52.24 and part 51 Appendix S. The 

EPA’s minimum requirements for a 

NNSR program to be approvable into a 

SIP are contained in 40 CFR 51.165. 

Appendix S to 40 CFR part 51 contains 

an interim NNSR program. This interim 

program enables implementation of 

NNSR permitting in nonattainment 

areas that lack a SIP-approved NNSR 

permitting program for the particular 

nonattainment pollutant, and the 

interim program can be applied during 

the time between the date of the 

relevant nonattainment designation and 

the date on which the EPA approves 

into the SIP a NNSR program or 

additional components of an NNSR 

program for a particular pollutant.250

This interim program is commonly 

known as the Emissions Offset 

Interpretative Rule, and is applicable to 

all criteria pollutants, including O3.251

The EPA is not modifying any 

existing NNSR requirements in this 

rulemaking. Under the CAA, area 

designations for new or revised NAAQS 

are addressed subsequent to the 

effective date of the new or revised 

NAAQS. If the EPA determines that any 

revisions to the existing NNSR 

requirements, including those in 

Appendix S, are appropriate, the EPA 

expects, at a later date contemporaneous 

with the designation process for the 

revised O3 NAAQS, to propose those 

revisions. If any changes are proposed to 

Appendix S requirements, the EPA 

anticipates that it would intend for 

those changes to become effective no 

later than the effective date of the area 

designations. This timing would allow 

air agencies that lack an approved 

NNSR program for O3 to use the relevant 

Appendix S provisions to issue NNSR 

permits addressing O3 on and after the 

effective date of designations of new 

nonattainment areas for O3 until such 

time as a NNSR program for O3 is 

approved into the SIP.252

For NNSR, new major stationary 

sources and major modifications for O3

must comply with the Lowest 

Achievable Emission Rate (LAER) 

requirements as defined in the CAA and 

NNSR rules, and must perform other 

analyses and satisfy other requirements 

under section 173 of the CAA. For 

example, under CAA section 173(c) 

emissions reductions, known as 

emissions offsets, must be secured to 

offset the increased emissions of the air 

pollutant (including the relevant 

precursors) from the new or modified 

source by an equal or greater reduction, 

as applicable, of such pollutant. The 

appropriate emissions offset needed for 

a particular source will depend upon 

the classification for the O3

nonattainment area in which the source 

or modification will locate, such that 

areas with more severe nonattainment 

classifications have more stringent offset 

requirements. This ranges from 1.1:1 for 

areas classified as Marginal to 1.5:1 for 

areas classified as Extreme. See, e.g., 

CAA section 182, 40 CFR 51.165(a)(9) 

and 40 CFR part 51 Appendix S section 

IV.G.2. 

To facilitate continued economic 

development in nonattainment areas, 

many states have established offset 

banks or registries.253 Such banks or 

registries can help new or modified 

major stationary source owners meet 

offset requirements by streamlining 

identification and access to available 

emissions reductions. Some states have 

established offset banks to help ensure 

a consistent method for generating, 

validating and transferring NOX and 

VOC offsets. Offsets in these areas are 

generated by emissions reductions that 

meet specific creditability criteria set 

forth by the SIP consistent with the EPA 

regulations. See 40 CFR 

51.165(a)(3)(ii)(A)-(J) and part 51 

Appendix S section IV.C. The EPA 

received comments expressing concern 

about the limited availability of offsets 

in nonattainment areas. Since the EPA 

did not propose, and is not finalizing, 

any amendments related to the NNSR 

offset provisions, the EPA is not 

responding to those comments at this 

time, consistent with the EPA’s general 

approach to comment on 

implementation topics as described 

above. 

D. Transportation and General 

Conformity 

1. What are transportation and general 

conformity? 

Conformity is required under CAA 

section 176(c) to ensure that federal 

actions are consistent with (‘‘conform 

to’’) the purpose of the SIP. Conformity 

to the purpose of the SIP means that 

federal activities will not cause new air 

quality violations, worsen existing 

violations, or delay timely attainment of 

the relevant NAAQS or interim 

reductions and milestones. Conformity 

applies to areas that are designated 

nonattainment, and those 

nonattainment areas redesignated to 

attainment with a CAA section 175A 

maintenance plan after 1990 

(‘‘maintenance areas’’). 

The EPA’s Transportation Conformity 

Rule (40 CFR 51.390 and part 93, 

subpart A) establishes the criteria and 

procedures for determining whether 

transportation activities conform to the 

SIP. These activities include adopting, 

funding or approving transportation 

plans, transportation improvement 

programs (TIPs) and federally supported 

highway and transit projects. For further 

information on conformity rulemakings, 

policy guidance and outreach materials, 

see the EPA’s Web site at http://www.

epa.gov/otaq/stateresources/transconf/

index.htm. The EPA may issue future 

transportation conformity guidance as 

needed to implement a revised O3

NAAQS. 

With regard to general conformity, the 

EPA first promulgated general 

conformity regulations in November 

1993. (40 CFR part 51, subpart W, 40 

CFR part 93, subpart B) Subsequently 

the EPA finalized revisions to the 

general conformity regulations on April 

5, 2010. (75 FR 17254–17279). Besides 

ensuring that federal actions not 

covered by the transportation 

conformity rule will not interfere with 

the SIP, the general conformity program 

also fosters communications between 

federal agencies and state/local air 

quality agencies, provides for public 

notification of and access to federal 

agency conformity determinations, and 

allows for air quality review of 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65443 

254USDA Forest Service and Natural Resources 

Conservation Service, Basic Smoke Management 

Practices Tech Note, October 2011, http://www.

nrcs.usda.gov/Internet/FSE_DOCUMENTS/stelprd

b1046311.pdf. 

255The text of section 126 codified in the United 

States Code cross references section 110(a)(2)(D)(ii) 

instead of section 110(a)(2)(D)(i). The courts have 

confirmed that this is a scrivener’s error and the 

correct cross reference is to section 110(a)(2)(D)(i), 

See Appalachian Power Co. v. EPA, 249 F.3d 1032, 

1040–44 (D.C. Cir. 2001). 

individual federal actions. More 

information on the general conformity 

program is available at http://www.epa.

gov/air/genconform/. 

2. When would transportation and 

general conformity apply to areas 

designated nonattainment for the 

revised O3 NAAQS? 

Transportation and general 

conformity apply one year after the 

effective date of nonattainment 

designations for the revised O3 NAAQS. 

This is because CAA section 176(c)(6) 

provides a 1-year grace period from the 

effective date of initial designations for 

any revised NAAQS before 

transportation and general conformity 

apply in areas newly designated 

nonattainment for a specific pollutant 

and NAAQS. 

3. Impact of a Revised O3 NAAQS on a 

State’s Existing Transportation and/or 

General Conformity SIP 

In this final rule, the EPA is revising 

the O3 NAAQS, but is not making 

specific changes to its transportation or 

general conformity regulations. 

Therefore, states should not need to 

revise their transportation and/or 

general conformity SIPs. While we are 

not making any revisions to the general 

conformity regulations at this time, we 

recommend, when areas develop SIPs 

for a revised O3 NAAQS, that state and 

local air quality agencies work with 

federal agencies with large emitting 

activities that are subject to the general 

conformity regulations to establish an 

emissions budget for those facilities and 

activities in order to facilitate future 

conformity determinations under the 

conformity regulations. Finally, states 

with existing conformity SIPs and new 

nonattainment areas may also need to 

revise their conformity SIPs in order to 

ensure the state regulations apply in any 

newly designated areas. 

Because significant tracts of land 

under federal management may be 

included in nonattainment area 

boundaries, the EPA encourages state 

and local air quality agencies to work 

with federal agencies to assess and 

develop emissions budgets that consider 

emissions from projects subject to 

general conformity, including emissions 

from fire on wildland, in any baseline, 

modeling and SIP attainment inventory. 

Where appropriate, states, land 

managers, and landowners may also 

consider developing plans to ensure that 

fuel accumulations are addressed 

Information is available from DOI and 

USDA Forest Service on the ecological 

role of fire and on smoke management 

programs and basic smoke management 

practices.254

If this is the first time that 

transportation conformity will apply in 

a state, such a state is required by the 

statute and EPA regulations to submit a 

SIP revision that addresses three 

specific transportation conformity 

requirements that address consultation 

procedures and written commitments to 

control or mitigation measures 

associated with conformity 

determinations for transportation plans, 

TIPs or projects. (40 CFR 51.390) 

Additional information and guidance 

can be found in the EPA’s ‘‘Guidance for 

Developing Transportation Conformity 

State Implementation Plans’’ (http://

www.epa.gov/otaq/stateresources/

transconf/policy/420b09001.pdf). 

E. Regional and International Pollution 

Transport 

1. Interstate Transport 

The CAA contains provisions that 

specifically address and require 

regulation of the interstate transport of 

air pollution that does not otherwise 

qualify for data exclusion under the 

Act’s exceptional events provisions. As 

previously noted, emissions from 

events, such as wildfires, may qualify as 

exceptional events and may be 

transported across jurisdictional 

boundaries. The EPA intends to address 

the transport of event-related emissions 

in our upcoming proposed revisions to 

the Exceptional Events Rule and draft 

guidance document addressing the 

Exceptional Events Rule criteria for 

wildfires that could affect O3

concentrations. The EPA encourages 

affected air agencies to coordinate with 

their EPA regional office to identify 

approaches to evaluate the potential 

impacts of transported event-related 

emissions and determine the most 

appropriate information and analytical 

methods for each area’s unique 

situation. 

CAA section 110(a)(2)(D)(i)(I), 

Interstate Transport—CAA section 

110(a)(2)(D)(i)(I) requires states to 

develop and implement a SIP to address 

the interstate transport of emissions. 

Specifically, this provision requires the 

SIP to prohibit ‘‘any source or other type 

of emissions activity within the state’’ 

that would ‘‘significantly contribute to 

nonattainment’’ of any NAAQS in 

another state, or that would ‘‘interfere 

with maintenance’’ of any NAAQS in 

another state. When EPA promulgates or 

revises a NAAQS, each state is required 

to submit a SIP addressing this 

interstate transport provision within 3 

years. 

CAA section 126, Interstate 

Transport—CAA section 126(b) 

provides states and political 

subdivisions with a mechanism to 

petition the Administrator for a finding 

that ‘‘any major source or group of 

stationary sources emits or would emit 

any air pollution in violation of the 

prohibition of [CAA section 

110(a)(2)(D)(i)(I)].’’ 255 Where the EPA 

makes such finding, the source is 

allowed to operate beyond a 3-month 

period after such finding only if the EPA 

establishes emissions limitations and a 

compliance schedule designated to 

bring the source into compliance as 

expeditiously as practicable, but no later 

than three years after such finding. This 

mechanism is available to downwind 

states and political subdivisions, 

regardless of designation status, that 

would be affected by emissions from 

upwind states. 

2. International Transport 

The agency is active in work to reduce 

the international transport of O3 and 

other pollutants that can contribute to 

‘‘background’’ O3 levels in the U.S. 

Under the Convention on Long-Range 

Transboundary Air Pollution (LRTAP) 

of the United Nations Economic 

Commission for Europe, the U.S. has 

been a party to the Protocol to Abate 

Acidification, Eutrophication, and 

Ground-level Ozone (known as the 

Gothenburg Protocol) since 2005. The 

U.S. is also active in the LRTAP Task 

Force for Hemispheric Transport of Air 

Pollution. The U.S. has worked 

bilaterally with Canada under the USCanada Air Quality Agreement to adopt 

an Ozone Annex to address 

transboundary O3 impacts and 

continues to work with China on air 

quality management activities. This 

work includes supporting China’s 

efforts to rapidly deploy power plant 

pollution controls that can achieve NOX

reductions of at least 80 to 90%. The 

U.S. also continues to work bilaterally 

with Mexico on the Border 2020 

program to support efforts to improve 

environmental conditions in the border 

region. One of the main goals of the 

program is to reduce air pollution, 

including emissions that can cause 

transboundary O3 impacts. 

mstockstill on DSK4VPTVN1PROD with RULES2

65444 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

Clean Air Act section 179B recognizes 

the possibility that certain 

nonattainment areas may be impacted 

by O3 or O3 precursor emissions from 

international sources beyond the 

regulatory jurisdiction of the state. The 

EPA’s science review suggests that the 

influence of international sources on 

U.S. O3 levels will be largest in 

locations that are in the immediate 

vicinity of an international border with 

Canada or Mexico. The science review 

also cites two recent studies which 

indicate that intercontinental transport 

of pollution, along with other natural 

sources and local pollutant sources, can 

affect O3 air quality in the western U.S. 

under specific conditions. (U.S. EPA 

2013, p. 3–140). Section 179B allows 

states to consider in their attainment 

plans and demonstrations whether an 

area might meet the O3 NAAQS by the 

attainment date ‘‘but for’’ emissions 

contributing to the area originating 

outside the U.S. If a state is unable to 

demonstrate attainment of the NAAQS 

in such an area impacted by 

international transport after adopting all 

reasonably available control measures 

(e.g., RACM, including RACT, as 

required by CAA section 182(b)), the 

EPA can nonetheless approve the CAArequired state attainment plan and 

demonstration using the authority in 

section 179B. 

When the EPA approves this type of 

attainment plan and demonstration, and 

there would be no adverse consequence 

for a finding that the area failed to attain 

the NAAQS by the relevant attainment 

date. States can also avoid potential 

sanctions and FIPs that would otherwise 

apply for failure to submit a required 

SIP submission or failure to submit an 

approvable SIP submission. For 

example, section 179B explicitly 

provides that the area shall not be 

reclassified to the next highest 

classification or required to implement 

a section 185 penalty fee program if a 

state meets the applicable criteria. 

Section 179B authority does not allow 

an area to avoid a nonattainment 

designation or for the area to be 

classified with a lower classification 

than is indicated by actual ambient air 

quality. Section 179B also does not 

provide for any relaxation of mandatory 

emissions control measures (including 

contingency measures) or the prescribed 

emissions reductions necessary to 

achieve periodic emissions reduction 

progress requirements. In this way, 

section 179B insures that states will take 

actions to mitigate the public health 

impacts of exposure to ambient levels of 

pollution that violate the NAAQS by 

imposing reasonable control measures 

on the sources that are within the 

jurisdiction of the state while also 

authorizing EPA to approve such 

attainment plans and demonstrations 

even though they do not fully address 

the public health impacts of 

international transport. Also, generally, 

monitoring data influenced by 

international transport may not be 

excluded from regulatory 

determinations. However, depending on 

the nature and scope of international 

emissions events affecting air quality in 

the U.S., the event-influenced data may 

qualify for exclusion under the 

Exceptional Events Rule. The EPA 

encourages affected air agencies to 

coordinate with their EPA regional 

office to identify approaches to evaluate 

the potential impacts of international 

transport and to determine the most 

appropriate information and analytical 

methods for each area’s unique 

situation. The EPA will also work with 

states that are developing attainment 

plans for which section 179B is 

relevant, and ensure the states have the 

benefit of the EPA’s understanding of 

international transport of ozone and 

ozone precursors. 

The EPA has used section 179B 

authority previously to approve 

attainment plans for Mexican border 

areas in El Paso, TX (O3, PM10, and CO 

plans); and Nogales, AZ (PM10 plan). 

The 24-hour PM10 attainment plan for 

Nogales, AZ, was approved by EPA as 

sufficient to demonstrate attainment of 

the NAAQS by the Moderate 

classification deadline, but for 

international emissions sources in the 

Nogales Municipality, Mexico area (77 

FR 38400, June 27, 2012). 

States are encouraged to consult with 

their EPA Regional Office to establish 

appropriate technical requirements for 

these analyses. 

IX. Statutory and Executive Order 

Reviews 

Additional information about these 

statutes and Executive Orders can be 

found at http://www2.epa.gov/lawsregulations/laws-and-executive-orders. 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

This action is an economically 

significant regulatory action that was 

submitted to the Office of Management 

and Budget (OMB) for review. Any 

changes made in response to OMB 

recommendations have been 

documented in the docket. The EPA 

prepared an analysis of the potential 

costs and benefits associated with this 

action. This analysis is contained in the 

document, Regulatory Impact Analysis 

of the Final National Ambient Air 

Quality Standards for Ground-Level 

Ozone, October 2015. A copy of the 

analysis is available in the RIA docket 

(EPA–HQ–OAR–2013–0169) and the 

analysis is briefly summarized here. The 

RIA estimates the costs and monetized 

human health and welfare benefits of 

attaining three alternative O3 NAAQS 

nationwide. Specifically, the RIA 

examines the alternatives of 65 ppb and 

70 ppb. The RIA contains illustrative 

analyses that consider a limited number 

of emissions control scenarios that 

states and Regional Planning 

Organizations might implement to 

achieve these alternative O3 NAAQS. 

However, the CAA and judicial 

decisions make clear that the economic 

and technical feasibility of attaining 

ambient standards are not to be 

considered in setting or revising 

NAAQS, although such factors may be 

considered in the development of state 

plans to implement the standards. 

Accordingly, although an RIA has been 

prepared, the results of the RIA have not 

been considered in issuing this final 

rule. 

B. Paperwork Reduction Act 

The information collection 

requirements in this final rule have been 

submitted for approval to the Office of 

Management and Budget (OMB) under 

the Paperwork Reduction Act (PRA). 

The information collection requirements 

are not enforceable until OMB approves 

them. The Information Collection 

Request (ICR) document prepared by the 

EPA for these revisions has been 

assigned EPA ICR #2313.04. 

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 and ecosystems 

impacts, to develop emission control 

strategies, and to measure progress for 

the air pollution program. We are 

extending the length of the required O3

monitoring season in 32 states and the 

District of Columbia and the revised O3

monitoring seasons will become 

effective on January 1, 2017. We are also 

revising the PAMS monitoring 

requirements to reduce the number of 

required PAMS sites while improving 

spatial coverage, and requiring states in 

moderate or above O3 non-attainment 

areas and the O3 transport region to 

develop an enhanced monitoring plan 

as part of the PAMS requirements. 

Monitoring agencies will need to 

comply with the PAMS requirements by 

June 1, 2019. In addition, we are 

revising the O3 FRM to establish a new, 

additional technique for measuring O3

in the ambient air. It will be 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65445 

incorporated into the existing O3 FRM, 

using the same calibration procedure in 

Appendix D of 40 CFR part 50. We are 

also making changes to the procedures 

for testing performance characteristics 

and determining comparability between 

candidate FEMs and reference methods. 

For the purposes of ICR number 

2313.04, the burden figures represent 

the burden estimate based on the 

requirements contained in this rule. The 

burden estimates are for the 3-year 

period from 2016 through 2018. The 

implementation of the PAMS changes 

will occur beyond the time frame of this 

ICR with implementation occurring in 

2019. The cost estimates for the PAMS 

network (including revisions) will be 

captured in future routine updates to 

the Ambient Air Quality Surveillance 

ICR that are required every 3 years by 

OMB. The addition of a new FRM in 40 

CFR part 50 and revisions to the O3 FEM 

procedures for testing performance 

characteristics in 40 CFR part 53 does 

not add any additional information 

collection requirements. 

The ICR burden estimates are 

associated with the changes to the O3

seasons in this final rule. This 

information collection is estimated to 

involve 158 respondents for a total cost 

of approximately $24,597,485 (total 

capital, labor, and operation and 

maintenance) plus a total burden of 

339,930 hours for the support of all 

operational aspects of the entire O3

monitoring network. The labor costs 

associated with these hours are 

$20,209,966. Also included in the total 

are other costs of operations and 

maintenance of $2,254,334 and 

equipment and contract costs of 

$2,133,185. The actual labor cost 

increase to expand the O3 monitoring 

seasons is $2,064,707. In addition to the 

costs at the state, local, and tribal air 

quality management agencies, there is a 

burden to EPA of 41,418 hours and 

$2,670,360. 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 

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 EPA’s 

regulations in 40 CFR are listed in 40 

CFR part 9. 

C. Regulatory Flexibility Act (RFA) 

I certify that this action will not have 

a significant economic impact on a 

substantial number of small entities 

under the RFA. This action will not 

impose any requirements on small 

entities. Rather, this rule establishes 

national standards for allowable 

concentrations of O3 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). Similarly, the revisions to 40 

CFR part 58 address the requirements 

for states to collect information and 

report compliance with the NAAQS and 

will not impose any requirements on 

small entities. Similarly, the addition of 

a new FRM in 40 CFR part 50 and 

revisions to the FEM procedures for 

testing in 40 CFR part 53 will not 

impose any requirements on small 

entities. 

D. Unfunded Mandates Reform Act 

(UMRA) 

This action does not contain an 

unfunded federal mandate of $100 

million or more as described in UMRA, 

2 U.S.C. 1531–1538, and does not 

significantly or uniquely affect small 

governments. The revisions to the O3

NAAQS impose no enforceable duty on 

any state, local, or tribal governments or 

the private sector beyond those duties 

already established in the CAA. The 

expected costs associated with the 

monitoring requirements are described 

in the EPA’s ICR document, and these 

costs are not expected to exceed $100 

million in the aggregate for any year. 

Furthermore, as indicated previously, 

in setting 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 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 RIA pursuant to the 

UMRA would not furnish any 

information which the court could 

consider in reviewing the NAAQS]). 

With regard to the sections of the rule 

preamble discussing implementation of 

the revisions to the O3 NAAQS, the 

CAA imposes the obligation for states to 

submit SIPs to implement the NAAQS 

for O3. To the extent the EPA’s 

discussion of implementation topics in 

this final rule may reflect some 

interpretations of those requirements, 

those interpretations do not impose 

obligations beyond the duties already 

established in the CAA and thus do not 

constitute a federal mandate for 

purposes of UMRA. The EPA is also 

adopting a grandfathering provision for 

certain PSD permits in this action, as 

described above. However, that 

provision does not impose any mandate 

on any state, local, or tribal government 

or the private sector, but rather provides 

relief from requirements that would 

otherwise result from the new 

standards. In addition, the EPA is not 

requiring states to revise their SIPs to 

include such a provision. 

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. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

This action does not have tribal 

implications as specified in Executive 

Order 13175. It does not have a 

substantial direct effect on one or more 

Indian tribes. This rule provides 

increased protection from adverse 

effects of ozone for the entire country, 

including for sensitive populations, and 

tribes are not obligated to adopt or 

implement any NAAQS. In addition, 

tribes are not obligated to conduct 

ambient monitoring for O3 or to adopt 

the ambient monitoring requirements of 

40 CFR part 58. Even if this action were 

determined to have tribal implications 

within the meaning of Executive Order 

13175, it will neither impose substantial 

direct compliance costs on tribal 

governments, nor preempt tribal law. 

Thus, consultation under Executive 

Order 13175 was not required. 

Nonetheless, consistent with the 

‘‘EPA Policy on Consultation and 

Coordination with Indian Tribes’’, the 

EPA offered government-to-government 

consultation on the proposed rule. No 

tribe requested government-togovernment consultation with the EPA 

on this rule. In addition, the EPA 

conducted outreach to tribal 

environmental professionals, which 

included participation in the Tribal Air 

call sponsored by the National Tribal 

Air Association, and two other calls 

available to tribal environmental 

professionals. During the public 

comment period we received comments 

on the proposed rule from seven tribes 

and three tribal organizations. 

G. Executive Order 13045: Protection of 

Children From Environmental Health & 

Safety Risks 

This action is subject to Executive 

Order 13045 because it is an 

mstockstill on DSK4VPTVN1PROD with RULES2

65446 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

256As used here and similarly throughout this 

document, the term population refers to people 

having a quality or characteristic in common, 

including a specific pre-existing illness or a specific 

age or lifestage. 

257This refers to monitored areas with O3 design 

values above the revised and alternative standards. 

economically significant regulatory 

action as defined by Executive Order 

12866, and the EPA believes that the 

environmental health risk addressed by 

this action may have a disproportionate 

effect on children. The rule will 

establish uniform NAAQS for O3; these 

standards are designed to protect public 

health with an adequate margin of 

safety, as required by CAA section 109. 

However, the protection offered by these 

standards may be especially important 

for children because children, especially 

children with asthma, along with other 

at-risk populations 256 such as all people 

with lung disease and people active 

outdoors, are at increased risk for health 

effects associated with exposure to O3 in 

ambient air. Because children are 

considered an at-risk lifestage, we have 

carefully evaluated the environmental 

health effects of exposure to O3

pollution among children. Discussions 

of the results of the evaluation of the 

scientific evidence, policy 

considerations, and the exposure and 

risk assessments pertaining to children 

are contained in sections II.B and II.C of 

this preamble. 

H. Executive Order 13211: Actions That 

Significantly Affect Energy Supply, 

Distribution, or Use 

This action is not a ‘‘significant 

energy action’’ because it is not likely to 

have a significant adverse effect on the 

supply, distribution, or use of energy. 

The purpose of this rule is to establish 

revised NAAQS for O3, establish an 

additional FRM, revise FEM procedures 

for testing, and revises air quality 

surveillance requirements. The rule 

does not prescribe specific pollution 

control strategies by which these 

ambient standards and monitoring 

revisions will be met. Such strategies 

will be developed by states on a caseby-case basis, and the EPA cannot 

predict whether the control options 

selected by states will include 

regulations on energy suppliers, 

distributors, or users. Thus, the EPA 

concludes that this rule is not likely to 

have any adverse energy effects and 

does not constitute a significant energy 

action as defined in Executive Order 

13211. 

I. National Technology Transfer and 

Advancement Act 

This rulemaking involves 

environmental monitoring and 

measurement. Consistent with the 

Agency’s Performance Based 

Measurement System (PBMS), the EPA 

is not requiring the use of specific, 

prescribed analytical methods. Rather, 

the Agency is allowing the use of any 

method that meets the prescribed 

performance criteria. Ambient air 

concentrations of O3 are currently 

measured by the FRM in 40 CFR part 50, 

Appendix D (Measurement Principle 

and Calibration Procedure for the 

Measurement of Ozone in the 

Atmosphere) or by FEM that meet the 

requirements of 40 CFR part 53. 

Procedures are available in part 53 that 

allow for the approval of an FEM for O3

that is similar to the FRM. Any method 

that meets the performance criteria for 

a candidate equivalent method may be 

approved for use as an FEM. This 

approach is consistent with EPA’s 

PBMS. The PBMS approach 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. The EPA is not precluding 

the use of any 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 

The EPA believes that this action will 

not have disproportionately high and 

adverse human health or environmental 

effects on minority populations, lowincome populations or indigenous 

peoples. The action described in this 

notice is to strengthen the NAAQS for 

O3.

The primary NAAQS are established 

at a level that is requisite to protect 

public health, including the health of 

sensitive or at-risk groups, with an 

adequate margin of safety. The NAAQS 

decisions are based on an explicit and 

comprehensive assessment of the 

current scientific evidence and 

associated exposure/risk analyses. More 

specifically, EPA expressly considers 

the available information regarding 

health effects among at-risk populations, 

including that available for low-income 

populations and minority populations, 

in decisions on NAAQS. Where lowincome populations or minority 

populations are among the at-risk 

populations, the decision on the 

standard is based on providing 

protection for these and other at-risk 

populations and lifestages. Where such 

populations are not identified as at-risk 

populations, a NAAQS that is 

established to provide protection to the 

at-risk populations would also be 

expected to provide protection to all 

other populations, including lowincome populations and minority 

populations. 

The ISA, HREA, and PA for this 

review, which include identification of 

populations at risk from O3 health 

effects, are available in the docket, EPA– 

HQ–OAR–2008–0699. The information 

on at-risk populations for this NAAQS 

review is summarized and considered 

earlier in this preamble (see section 

II.A). This final rule increases the level 

of environmental protection for all 

affected populations without having any 

disproportionately high and adverse 

human health or environmental effects 

on any population, including any 

minority populations, low-income 

populations or indigenous peoples. This 

rule establishes uniform national 

standards for O3 in ambient air that, in 

the Administrator’s judgment, protect 

public health, including the health of 

sensitive groups, with an adequate 

margin of safety. 

Although it is part of a separate 

docket (EPA–HQ–OAR–2013–0169) and 

is not part of the rulemaking record for 

this action, EPA has prepared a RIA of 

this decision. As part of the RIA, a 

demographic analysis was conducted. 

While, as noted in the RIA, the 

demographic analysis is not a full 

quantitative, site-specific exposure and 

risk assessment, that analysis examined 

demographic characteristics of persons 

living in areas with poor air quality 

relative to the proposed standard. 

Specifically, Chapter 9, section 9.10 

(page 9–7) and Appendix 9A of the RIA 

describe this proximity and sociodemographic analysis. This analysis 

found that in areas with poor air quality 

relative to the revised standard,257 the 

representation of minority populations 

was slightly greater than in the U.S. as 

a whole. Because the air quality in these 

areas does not currently meet the 

revised standard, populations in these 

areas would be expected to benefit from 

implementation of the strengthened 

standard, and, thus, would be more 

affected by strategies to attain the 

revised standard. This analysis, which 

evaluates the potential implications for 

minority populations and low-income 

populations of future air pollution 

control actions that state and local 

agencies may consider in implementing 

the revised O3 NAAQS described in this 

decision notice are discussed in 

Appendix 9A of the RIA. The RIA is 

available on the Web, through the EPA’s 

Technology Transfer Network Web site 

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

standards/ozone/s_o3_index.html and 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65447 

in the RIA docket (EPA–HQ–OAR– 

2013–0169). As noted above, although 

an RIA has been prepared, the results of 

the RIA have not been considered in 

issuing this final rule. 

K. Congressional Review Act (CRA) 

This action is subject to the CRA, and 

the EPA will submit a rule report to 

each House of the Congress and to the 

Comptroller General of the United 

States. This action is a ‘‘major rule’’ as 

defined by 5 U.S.C. 804(2). 

References 

Adams, WC. (2006). Comparison of chamber 

6.6 hour exposures to 0.04–0.08 ppm 

ozone via square-wave and triangular 

profiles on pulmonary responses. 

Inhalation Toxicol. 18:127–136. http://

dx.doi.org/10.1080/08958370500306107. 

Adams, WC. (2002). Comparison of chamber 

and face-mask 6.6-hour exposures to 

ozone on pulmonary function and 

symptoms responses. Inhal Toxicol 

14:745–764. http://dx.doi.org/10.1080/

08958370290084610. 

Akinbami, LJ; Lynch, CD; Parker, JD; 

Woodruff, TJ. (2010). The association 

between childhood asthma prevalence 

and monitored air pollutants in 

metropolitan areas, United States, 2001– 

2004. Environ Res 110:294–301. http://

dx.doi.org/10.1016/j.envres.2010.01.001. 

Alexis, N; Urch, B; Tarlo, S; Corey, P; 

Pengelly, D; O’Byrne, P; Silverman, F. 

(2000). Cyclooxygenase metabolites play 

a different role in ozone-induced 

pulmonary function decline in 

asthmatics compared to normals. Inhal 

Toxicol 12:1205–1224. 

American Thoracic Society. (2000a). What 

constitutes an adverse health effect of air 

pollution? Am. J. Respir. Crit. Care Med. 

161:665–673. 

American Thoracic Society. (2000b). 

Guidelines for methacholine and 

exercise challenge testing—1999. Am. J. 

Respir. Crit. Care Med. 161:309–329. 

American Thoracic Society. (1985). 

Guidelines as to what constitutes an 

adverse respiratory health effect, with 

special reference to epidemiological 

studies of air pollution. Am. Rev. Respir. 

Dis. 131:666–668. 

Andersen, CP; Wilson, R; Plocher, M; 

Hogsett, WE. (1997). Carry-over effects of 

ozone on root growth and carbohydrate 

concentrations of ponderosa pine 

seedlings. Tree Physiol 17:805–811. 

Basha, MA; Gross, KB; Gwizdala, CJ; Haidar, 

AH; Popovich, J, Jr. (1994). 

Bronchoalveolar lavage neutrophilia in 

asthmatic and healthy volunteers after 

controlled exposure to ozone and filtered 

purified air. Chest 106:1757–1765. 

Bell, ML; Peng, RD; Dominici, F. (2006). The 

exposure-response curve for ozone and 

risk of mortality and the adequacy of 

current ozone regulations. Environ 

Health Perspect 114:532–536. 

Bloom, B; Cohen, RA; Freeman, G. (2011). 

Summary health statistics for U.S. 

children: National Health Interview 

Survey, 2010. National Center for Health 

Statistics. Vital Health Stat 10 (250). 

http://www.cdc.gov/nchs/data/series/sr_

10/sr10_250.pdf. 

Brauer, M; Blair, J; Vedal, S. (1996). Effect of 

ambient ozone exposure on lung 

function in farm workers. Am J Respir 

Crit Care Med 154:981–987. 

Brown, JS; Bateson, TF; McDonnell, WF. 

(2008). Effects of exposure to 0.06 ppm 

ozone on FEV1 in humans: A secondary 

analysis of existing data. Environ Health 

Perspect 116:1023–1026. http://dx.doi.

org/10.1289/ehp.11396. 

Brown, JS. (2007). The effects of ozone on 

lung function at 0.06 ppm in healthy 

adults. June 14, 2007. Memo to the 

Ozone NAAQS Review Docket. EPA– 

HQ–OAR–2005–0172–0175. http://www.

epa.gov/ttn/naaqs/standards/ozone/s_

o3_cr_td.html. 

Brunekreef, B; Hoek, G; Breugelmans, O; 

Leentvaar, M. (1994). Respiratory effects 

of low-level photochemical air pollution 

in amateur cyclists. Am J Respir Crit 

Care Med 150:962–966. 

Cakmak, S; Dales, RE; Judek, S. (2006). 

Respiratory health effects of air pollution 

gases: Modification by education and 

income. Arch Environ Occup Health 

61:5–10. http://dx.doi.org/10.3200/

AEOH.61.1.5–10. 

Campbell, SJ; Wanek, R; Coulston, JW. 

(2007). Ozone injury in west coast 

forests: 6 years of monitoring— 

Introduction. Portland, OR: U.S. 

Department of Agriculture. 

Cavender, K. (2015). Summary of Final 

PAMS Network Design. Memorandum to 

the Ozone NAAQS Review Docket, EPA– 

HQ–OAR–2008–0699. 

Cavender, K. (2014). Network Design 

Considerations for the PAMS Network: 

Memorandum to the Ozone NAAQS 

Review Docket, EPA–HQ–OAR–2008– 

0699. 

Cavender, K. (2013). Revisions to the PAMS 

Compound Target List: Memorandum to 

the Ozone NAAQS Review Docket, EPA– 

HQ–OAR–2008–0699. 

Centers for Disease Control and Prevention. 

(2004). The health consequences of 

smoking: A report of the Surgeon 

General. Washington, DC: U.S. 

Department of Health and Human 

Services. http://www.surgeongeneral.

gov/library/smokingconsequences/. 

Cordell, HK; Betz, CJ; Fly, M; Mou, S; Green, 

GT. (2008) How do Americans View 

Wilderness. A WILDERNESS Research 

Report in the Internet Research 

Information Series. National Survey on 

Recreation and the Environment. This 

research is a collaborative effort between 

the U.S. Department of Agriculture 

Forest Service’s Southern Research 

Station and its Forestry Sciences 

Laboratory in Athens, Georgia; the 

University of Georgia in Athens; and the 

University of Tennessee in Knoxville, 

Tennessee. http://warnell.forestry.uga.

edu/nrrt/nsre/IRISWild/IrisWild

1rptR.pdf. 

Dales, RE; Cakmak, S; Doiron, MS. (2006). 

Gaseous air pollutants and 

hospitalization for respiratory disease in 

the neonatal period. Environ Health 

Perspect 114:1751–1754. http://dx.doi.

org/10.1289/ehp.9044. 

Darbah, JNT; Kubiske, ME; Nelson, N; 

Oksanen, E; Vaapavuori, E; Karnosky, 

DF. (2008). Effects of decadal exposure to 

interacting elevated CO2 and/or O3 on 

paper birch (Betula papyrifera) 

reproduction. Environ Pollut 155:446– 

452. http://dx.doi.org/10.1016/j.envpol.

2008.01.033. 

Darbah, JNT; Kubiske, ME; Nelson, N; 

Oksanen, E; Vaapavuori, E; Karnosky, 

DF. (2007). Impacts of elevated 

atmospheric CO2 and O3 on paper birch 

(Betula papyrifera): Reproductive fitness. 

Scientific World Journal 7:240–246. 

http://dx.doi.org/10.1100/tsw.2007.42. 

Darrow, LA; Klein, M; Sarnat, JA; 

Mulholland, JA; Strickland, MJ; Sarnat, 

SE; Russell, AG; Tolbert, PE. (2011a). 

The use of alternative pollutant metrics 

in time-series studies of ambient air 

pollution and respiratory emergency 

department visits. J Expo Sci Environ 

Epidemiol 21:10–19. http://dx.doi.org/

10.1038/jes.2009.49. 

Eresmaa, N, Karppinen, SM; Joffre, SM; 

Rasanene, J; Talvitie, H. (2006). Mixing 

Height Determination by Ceilometer, 

Atmospheric Chemistry and Physics, 6. 

1485–1493. 

Franze, T; Weller, MG; Niessner, R; Po ̈ schl, 

U. (2005). Protein nitration by polluted 

air. Environ Sci Technol 39:1673–1678. 

http://dx.doi.org/10.1021/es0488737. 

Frey, HC; Samet, JM. (2012a). Letter from Dr. 

H. Christopher Frey, Chair and Dr. 

Jonathan M. Samet, Immediate Past 

Chair, Clean Air Scientific Advisory 

Committee, to Administrator Lisa P. 

Jackson. Re: CASAC Review of the EPA’s 

Policy Assessment for the Review of the 

Ozone National Ambient Air Quality 

Standards (First External Review Draft— 

August 2012). EPA–CASAC–13–003. 

November 26, 2012. 

Frey, HC; Samet, JM. (2012b). Letter from Dr. 

H. Christopher Frey, Chair and Dr. 

Jonathan M. Samet, Immediate Past 

Chair, Clean Air Scientific Advisory 

Committee, to Administrator Lisa P. 

Jackson. Re: CASAC Review of the EPA’s 

Health Risk and Exposure Assessment 

for Ozone (First External Review Draft— 

Updated August 2012) and Welfare Risk 

and Exposure Assessment for Ozone 

(First External Review Draft—Updated 

August 2012). EPA–CASAC–13–002. 

November 19, 2012. 

Frey, HC. (2014a). Letter from Dr. H. 

Christopher Frey, Chair, Clean Air 

Scientific Advisory Committee, to 

Administrator Gina McCarthy. Re: 

CASAC Review of the EPA’s Health Risk 

and Exposure Assessment for Ozone 

(Second External Review Draft— 

February, 2014). EPA–CASAC–14–005. 

July 1, 2014. 

Frey, HC. (2014b). Letter from Dr. H. 

Christopher Frey, Chair, Clean Air 

Scientific Advisory Committee, to 

Administrator Gina McCarthy. CASAC 

Review of the EPA’s Welfare Risk and 

Exposure Assessment for Ozone (Second 

External Review Draft). EPA–CASAC– 

14–003. June 18, 2104. 

mstockstill on DSK4VPTVN1PROD with RULES2

65448 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

Frey, HC. (2014c). Letter from Dr. H. 

Christopher Frey, Chair, Clean Air 

Scientific Advisory Committee, to 

Administrator Gina McCarthy. CASAC 

Review of the EPA’s Second Draft Policy 

Assessment for the Review of the Ozone 

National Ambient Air Quality Standards. 

EPA–CASAC–14–004. June, 26, 2014. 

Gielen, MH; Van Der Zee, SC; Van Wijnen, 

JH; Van Steen, CJ; Brunekreef, B. (1997). 

Acute effects of summer air pollution on 

respiratory health of asthmatic children. 

Am J Respir Crit Care Med 155:2105– 

2108. 

Goodman, JE; Prueitt, RL; Sax, SN; Bailey, LI; 

Rhomberg, LR. (2013). Evaluation of the 

causal framework used for setting the 

National Ambient Air Quality Standards, 

Crit. Rev. Toxicol. 43(10):829–849. 

Haefele, M., R.A. Kramer, and T.P. Holmes. 

(1991). Estimating the Total Value of a 

Forest Quality in High-Elevation SpruceFir Forests. The Economic Value of 

Wilderness: Proceedings of the 

Conference. Gen. Tech. Rep. SE–78 (pp. 

91–96). Southeastern For. Exper. Station. 

Asheville, NC: USDA Forest Service. 

Heck, WW; Cowling, EB. (1997). The need for 

a long term cumulative secondary ozone 

standard—An ecological perspective. EM 

January:23–33. 

Henderson, R. (2008). Letter from Dr. Rogene 

Henderson, Chair, Clean Air Scientific 

Advisory Committee, to Administrator 

Stephen Johnson. Subject: Clean Air 

Scientific Advisory Committee 

Recommendations Concerning the Final 

Rule for the National Ambient Air 

Quality Standards for Ozone. EPA– 

CASAC–08–009. April 7, 2008. 

Henderson, R. (2006). Letter from Dr. Rogene 

Henderson, Chair, Clean Air Scientific 

Advisory Committee, to Administrator 

Stephen Johnson. Subject: Clean Air 

Scientific Advisory Committee’s 

(CASAC) Peer Review of the Agency’s 

2nd Draft Ozone Staff Paper. EPA– 

CASAC–07–001. October 24, 2006. 

Hill, AB. (1965). The environment and 

disease: Association or causation? Proc R 

Soc Med 58:295–300. 

Hoek, G; Brunekreef, B; Kosterink, P; Van 

den Berg, R; Hofschreuder, P. (1993). 

Effect of ambient ozone on peak 

expiratory flow of exercising children in 

the Netherlands. Arch Environ Occup 

Health 48:27–32. http://dx.doi.org/

10.1080/00039896.1993.9938390. 

Holmes, T; Kramer, R. (1995). ‘‘An 

Independent Sample Test of Yea-Saying 

and StartingPoint Bias in DichotomousChoice Contingent Valuation.’’ Journal of 

Environmental Economics and 

Management 28:121–132. 

Hoppe, P; Peters, A; Rabe, G; Praml, G; 

Lindner, J; Jakobi, G; Fruhmann, G; 

Nowak, D. (2003). Environmental ozone 

effects in different population subgroups. 

Int J Hyg Environ Health 206:505–516. 

http://dx.doi.org/10.1078/1438-4639- 

00250. 

Horstman, DH; Ball, BA; Brown, J; Gerrity, T; 

Folinsbee, LJ. (1995). Comparison of 

pulmonary responses of asthmatic and 

nonasthmatic subjects performing light 

exercise while exposed to a low level of 

ozone. Toxicol Ind Health 11:369–385. 

Howden, LM; Meyer, JA. (2011). U.S. Census 

Bureau, 2010 Census Briefs, C2010BR– 

03, Age and Sex Composition: 2010, U.S. 

Department of Commerce, Economics 

and Statistics Administration, U.S. 

Census Bureau, Washington, DC 20233. 

http://www.census.gov/prod/cen2010/

briefs/c2010br-03.pdf. 

Hwang, BF; Lee, YL; Lin, YC; Jaakkola, JJK; 

Guo, YL. (2005). Traffic related air 

pollution as a determinant of asthma 

among Taiwanese school children. 

Thorax 60:467–473. 

Islam, T; McConnell, R; Gauderman, WJ; 

Avol, E; Peters, JM; Gilliland, FD. (2008). 

Ozone, oxidant defense genes and risk of 

asthma during adolescence. Am J Respir 

Crit Care Med 177:388–395. http://

dx.doi.org/10.1164/rccm.200706-863OC. 

Jacob DJ; Winner DA. (2009). Effect of climate 

change on air quality. Atmos Environ 

43:51–63. 

Jerrett, M; Burnett, RT; Pope, CA, III; Ito, K; 

Thurston, G; Krewski, D; Shi, Y; Calle, E; 

Thun, M. (2009). Long-term ozone 

exposure and mortality. N Engl J Med 

360:1085–1095. http://dx.doi.org/

10.1056/NEJMoa0803894. 

Jorres, R; Nowak, D; Magnussen, H; Speckin, 

P; Koschyk, S. (1996). The effect of ozone 

exposure on allergen responsiveness in 

subjects with asthma or rhinitis. Am J 

Respir Crit Care Med 153:56–64. 

Katsouyanni, K; Samet, JM; Anderson, HR; 

Atkinson, R; Le Tertre, A; Medina, S; 

Samoli, E; Touloumi, G; Burnett, RT; 

Krewski, D; Ramsay, T; Dominici, F; 

Peng, RD; Schwartz, J; Zanobetti, A. 

(2009). Air pollution and health: A 

European and North American approach 

(APHENA). (Research Report 142). 

Boston, MA: Health Effects Institute. 

http://pubs.healtheffects.org/view.php

?id=327. 

Kim, CS; Alexis, NE; Rappold, AG; Kehrl, H; 

Hazucha, MJ; Lay, JC; Schmitt, MT; Case, 

M; Devlin, RB; Peden, DB; Diaz-Sanchez, 

D. (2011). Lung function and 

inflammatory responses in healthy 

young adults exposed to 0.06 ppm ozone 

for 6.6 hours. Am J Respir Crit Care Med 

183:1215–1221. http://dx.doi.org/

10.1164/rccm.201011-1813OC. 

King, JS; Kubiske, ME; Pregitzer, KS; 

Hendrey, GR; McDonald, EP; Giardina, 

CP; Quinn, VS; Karnosky, DF. (2005). 

Tropospheric O3 compromises net 

primary production in young stands of 

trembling aspen, paper birch and sugar 

maple in response to elevated 

atmospheric CO2. New Phytol 168:623– 

635. http://dx.doi.org/10.1111/j.1469- 

8137.2005.01557.x. 

Kohut, R. (2007). Assessing the risk of foliar 

injury from ozone on vegetation in parks 

in the U.S. National Park Service’s Vital 

Signs Network. Environ Pollut 149:348– 

357. 

Kreit, JW; Gross, KB; Moore, TB; Lorenzen, 

TJ; D’Arcy, J; Eschenbacher, WL. (1989). 

Ozone-induced changes in pulmonary 

function and bronchial responsiveness in 

asthmatics. J Appl Physiol 66:217–222. 

Kubiske, ME; Quinn, VS; Heilman, WE; 

McDonald, EP; Marquardt, PE; Teclaw, 

RM; Friend, AL; Karnoskey, DF. (2006). 

Interannual climatic variation mediates 

elevated CO2 and O3 effects on forest 

growth. Global Change Biol 12:1054– 

1068. http://dx.doi.org/10.1111/j.1365– 

2486.2006.01152.x. 

Kubiske, ME; Quinn, VS; Marquardt, PE; 

Karnosky, DF. (2007). Effects of elevated 

atmospheric CO2 and/or O3 on intra- and 

interspecific competitive ability of 

aspen. Plant Biol (Stuttg) 9:342–355. 

http://dx.doi.org/10.1055/s-2006-924760. 

Lee, EH; Hogsett, WE. (1996). Methodology 

for calculating inputs for ozone 

secondary standard benefits analysis: 

Part II. Research Triangle Park, NC: U.S. 

Environmental Protection Agency. 

Lefohn, AS; Hazucha, MJ; Shadwick, D; 

Adams, WC. (2010). An alternative form 

and level of the human health ozone 

standard. Inhal Toxicol 22:999–1011. 

http://dx.doi.org/10.3109/08958378.

2010.505253. 

Lefohn, AS; Jackson, W; Shadwick, DS; 

Knudsen, HP. (1997). Effect of surface 

ozone exposures on vegetation grown in 

the southern Appalachian Mountains: 

Identification of possible areas of 

concern. Atmos Environ 31:1695–1708. 

http://dx.doi.org/10.1016/S1352- 

2310(96)00258-0. 

Lin, S; Bell, EM; Liu, W; Walker, RJ; Kim, 

NK; Hwang, SA. (2008a). Ambient ozone 

concentration and hospital admissions 

due to childhood respiratory diseases in 

New York State, 1991–2001. Environ Res 

108:42–47. http://dx.doi.org/10.1016/

j.envres.2008.06.007. 

Lin, S; Liu, X; Le, LH; Hwang, SA. (2008b). 

Chronic exposure to ambient ozone and 

asthma hospital admissions among 

children. Environ Health Perspect 

116:1725–1730. http://dx.doi.org/

10.1289/ehp.11184. 

Mar, TF; Koenig, JQ. (2009). Relationship 

between visits to emergency departments 

for asthma and ozone exposure in greater 

Seattle, Washington. Ann Allergy 

Asthma Immunol 103:474–479. 

McCarthy, G. (2012). Letter from Gina 

McCarthy, Assistant Administrator, U.S. 

Environmental Protection Agency to 

Robert Ukeiley. January 4, 2012. http:// 

www.epa.gov/scram001/10thmodconf/

review_material/Sierra_Club_Petition_

OAR-11-002-1093.pdf. 

McDonnell, WF; Stewart, PW; Smith, MV; 

Kim, CS; Schelegle, ES. (2012). 

Prediction of lung function response for 

populations exposed to a wide range of 

ozone conditions. Inhal Toxicol 24:619– 

633. 

McDonnell, WF; Chapman, RS; Horstman, 

DH; Leigh, MW; Abdul-Salaam, S. 

(1985). A comparison of the responses of 

children and adults to acute ozone 

exposure. 

McLaughlin, SB; Nosal, M; Wullschleger, SD; 

Sun, G. (2007a). Interactive effects of 

ozone and climate on tree growth and 

water use in a southern Appalachian 

forest in the USA. New Phytol 174:109– 

124. http://dx.doi.org/10.1111/j.1469- 

8137.2007.02018.x. 

McLaughlin, SB; Wullschleger, SD; Sun, G; 

Nosal, M. (2007b). Interactive effects of 

ozone and climate on water use, soil 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65449 

moisture content and streamflow in a 

southern Appalachian forest in the USA. 

New Phytol 174:125–136. http://

dx.doi.org/10.1111/j.1469- 

8137.2007.01970.x. 

Medina-Ramon, M; Zanobetti, A; Schwartz, J. 

(2006). The effect of ozone and PM10 on 

hospital admissions for pneumonia and 

chronic obstructive pulmonary disease: 

A national multicity study. Am J 

Epidemiol 163:579–588. http://

dx.doi.org/10.1093/aje/kwj078. 

Mortimer, KM; Neas, LM; Dockery, DW; 

Redline, S; Tager, IB. (2002). The effect 

of air pollution on inner-city children 

with asthma. Eur Respir J 19:699–705. 

http://dx.doi.org/10.1183/

09031936.02.00247102. 

Mudway, IS; Kelly, FJ. (2004). An 

investigation of inhaled ozone dose and 

the magnitude of airway inflammation in 

healthy adults. Am J Respir Crit Care 

Med 169:1089–1095. 

National Academy of Sciences. (1991). 

Rethinking the Ozone Problem in Urban 

and Regional Air Pollution, Committee 

on Tropospheric Ozone, National 

Resource Council, National Academy 

Press, Washington, DC 20001. ISBN: 0– 

309–56037–3. 

National Institutes of Health, National Heart 

Lung and Blood Institute. (2007). Expert 

panel report 3: Guidelines for the 

diagnosis and management of asthma. 

(07–4051). Bethesda, MD: National 

Institute of Health. 

National Research Council. (2008). 

Estimating Mortality Risk Reduction and 

Economic Benefits from Controlling 

Ozone Air Pollution. Washington, DC: 

The National Academies Press. 

Nicholich, M. (2007). Some additional 

statistical analyses of the FEV1 

pulmonary response data from the W.C. 

Adams data (2006). Appendix A. In: 

ExxonMobil comments, Docket No. 

EPA–HQ–OAR–2005–0172, October 9, 

2007. 

Page, S. (2010). Memorandum from Stephen 

D. Page, Director, Office of Air Quality 

Planning & Standards, U.S. EPA, to Air 

Division Directors and Deputies, Regions 

I–X. Re: Applicability of the Federal 

Prevention of Significant Deterioration 

Permit Requirements to New and 

Revised National Ambient Air Quality 

Standards. April 1, 2010. 

Page, S. (2011). Memorandum from Stephen 

D. Page, Director, Office of Air Quality 

Planning and Standards, U.S. EPA, to 

Regional Air Directors, Regions I–X. Re: 

Guidance to Regions for Working with 

Tribes during the National Ambient Air 

Quality Standards (NAAQS) 

Designations Process. December 20, 

2011. http://www.epa.gov/ttn/oarpg/t1/

memoranda/

20120117naaqsguidance.pdf. 

Page, S. (2013). Memorandum from Stephen 

D. Page, Director, EPA Office of Air 

Quality Planning and Standards to 

Regional Air Directors, Regions I–X. Re: 

Guidance on Infrastructure State 

Implementation Plan (SIP) Elements 

under Clean Air Act Sections 110(a)(1) 

and 110(a)(2). September 13, 2013. 

http://www.epa.gov/oar/urbanair/

sipstatus/infrastructure.html. 

Phillips, SJ; Comus, PWA. (2000). Natural 

History of the Sonoran Desert. University 

of California Press, 628 pages. 

Pope, CA, III; 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. 

Rice, J. (2014). Ozone Monitoring Season 

Analysis. Memorandum to the Ozone 

NAAQS Review Docket, EPA–HQ–OAR– 

2008–0699. 

Riikonen, J; Kets, K; Darbah, J; Oksanen, E; 

Sober, A; Vapaavuori, E; Kubiske, ME; 

Nelson, N; Karnosky, DF. (2008). Carbon 

gain and bud physiology in Populus 

tremuloides and Betula papyrifera grown 

under longterm exposure to elevated 

concentrations of CO2 and O3. Tree 

Physiol 28:243–254. http://dx.doi.org/

10.1093/treephys/28.2.243. 

RTI International. (2014). Gas Chromatograph 

(GC) Evaluation Study: Laboratory 

Evaluation Phase Report. http://

www.epa.gov/ttnamti1/files/ambient/

pams/labevalreport.pdf. 

Ryerson, TB; Williams, EJ; Fehsenfeld, FC. 

(2000). An Efficient Photolysis System 

for Fast-Response NO2 Measurements, 

Journal of Geophysical Research, Volume 

105, Issue D21. 

Salam, MT; Islam, T; Gauderman, WJ; 

Gilliland, FD. (2009). Roles of arginase 

variants, atopy, and ozone in childhood 

asthma. J Allergy Clin Immunol 123:596– 

602. http://dx.doi.org/10.1016/

j.jaci.2008.12.020. 

Samet, JM. (2011). Letter from Dr. Jonathan 

M. Samet, Chair, Clean Air Scientific 

Advisory Committee to Administrator 

Lisa P. Jackson. Re: Clean Air Scientific 

Advisory Committee (CASAC) Response 

to Charge Questions on the 

Reconsideration of the 2008 Ozone 

National Ambient Air Quality Standards. 

EPA–CASAC–11–004. March 30, 2011. 

http://yosemite.epa.gov/sab/sabproduct.

nsf/0/F08BEB48C1139E2A8525785E0

06909AC/$File/EPA-CASAC-11-004- 

unsigned+.pdf. 

Samet, JM. (2010). Letter from Dr. Jonathan 

M. Samet, Chair, Clean Air Scientific 

Advisory Committee to Administrator 

Lisa P. Jackson. Re: Review of EPA’s 

Proposed Ozone National Ambient Air 

Quality Standard (Federal Register, Vol. 

75, Nov. 11, January 19, 2010). EPA– 

CASAC–10–007. February 19, 2010. 

http://yosemite.epa.gov/sab/sabproduct.

nsf/264cb1227d55e02c852574020

07446a4/610BB57CFAC8A41C85257

6CF007076BD/$File/EPA-CASAC-10- 

007-unsigned.pdf. 

Samet, JM; Bodurow, CC. (2008). Improving 

the presumptive disability decisionmaking process for veterans. In JM 

Samet; CC Bodurow (Eds.). Washington, 

DC: National Academies Press. http://

www.nap.edu/openbook.php?record_

id=11908. 

Samoli, E; Zanobetti, A; Schwartz, J; 

Atkinson, R; Le Tertre, A; Schindler, C; 

Pe ́rez, L; Cadum, E; Pekkanen, J; Paldy, 

A; Touloumi, G; Katsouyanni, K. (2009). 

The temporal pattern of mortality 

responses to ambient ozone in the 

APHEA project. J Epidemiol Community 

Health 63:960–966. http://dx.doi.org/

10.1136/jech.2008.084012. 

Sasser, E. (2014). Memorandum from Erika 

Sasser, Acting Director, Health and 

Environmental Impacts Division, Office 

of Air Quality Planing and Standards, 

U.S. EPA, to Holly Stallworth, 

Designated Federal Office, Clean Air 

Scientific Advisory Committee. Re: 

Request for Revised Ozone HREA 

Chapter 7 Appendix Tables. May 9, 

2014. http://www.epa.gov/ttn/naaqs/

standards/ozone/s_o3_2008_rea.html. 

Scannell, C; Chen, L; Aris, RM; Tager, I; 

Christian, D; Ferrando, R; Welch, B; 

Kelly, T; Balmes, JR. (1996). Greater 

ozone-induced inflammatory responses 

in subjects with asthma. Am J Respir Crit 

Care Med 154:24–29. 

Schelegle, ES; Adams, WC; Walby, WF; 

Marion, MS. (2012). Modelling of 

individual subject ozone exposure 

response kinetics. Inhal Toxicol 24:401– 

415. http://dx.doi.org/10.3109/08958378.

2012.683891. 

Schelegle, ES; Morales, CA; Walby, WF; 

Marion, S; Allen, RP. (2009). 6.6-hour 

inhalation of ozone concentrations from 

60 to 87 parts per billion in healthy 

humans. Am J Respir Crit Care Med 

180:265–272. http://dx.doi.org/10.1164/

rccm.200809-1484OC. 

Schiller, JS; Lucas, JW; Ward, BW; Peregoy, 

JA. (2012). Summary health statistics for 

U.S. adults: National Health Interview 

Survey, 2010. National Center for Health 

Statistics. Vital Health Stat 10(252). 

http://www.cdc.gov/nchs/data/series/sr_

10/sr10_252.pdf. 

Silverman, RA; Ito, K. (2010). Age-related 

association of fine particles and ozone 

with severe acute asthma in New York 

City. J Allergy Clin Immunol 125:367– 

373. 

http://dx.doi.org/10.1016/

j.jaci.2009.10.061. 

Smith, JT.; Murphy, DL. (2015). Additional 

Observations From WREA Datasets for 

Visible Foliar Injury. Memorandum to 

the Ozone NAAQS Review Docket, EPA– 

HQ–OAR–2008–0699. 

Smith, G. (2012). Ambient ozone injury to 

forest plants in Northeast and North 

Central USA: 16 years of biomonitoring. 

Environ Monit Assess 184:4049–4065. 

http://dx.doi.org/10.1007/s10661-011- 

2243-z. 

Smith, RL; Xu, B; Switzer, P. (2009). 

Reassessing the relationship between 

ozone and short-term mortality in U.S. 

urban communities. Inhal Toxicol 21:37– 

61. http://dx.doi.org/10.1080/08958370

903161612. 

Stafoggia, M; Forastiere, F; Faustini, A; 

Biggeri, A; Bisanti, L; Cadum, E; 

Cernigliaro, A; Mallone, S; Pandolfi, P; 

Serinelli, M; Tessari, R; Vigotti, MA; 

Perucci, CA. (2010). Susceptibility 

factors to ozone-related mortality: A 

population-based case-crossover 

analysis. Am J Respir Crit Care Med 

182:376–384. http://dx.doi.org/10.1164/

rccm.200908-1269OC. 

mstockstill on DSK4VPTVN1PROD with RULES2

65450 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

Stieb, DM; Szyszkowicz, M; Rowe, BH; 

Leech, JA. (2009). Air pollution and 

emergency department visits for cardiac 

and respiratory conditions: A multi-city 

time-series analysis. Environ Health 

Global Access Sci Source 8:25. http://

dx.doi.org/10.1186/1476-069X-8-25. 

Strickland, MJ; Darrow, LA; Klein, M; 

Flanders, WD; Sarnat, JA; Waller, LA; 

Sarnat, SE; Mulholland, JA; Tolbert, PE. 

(2010). Short-term associations between 

ambient air pollutants and pediatric 

asthma emergency department visits. Am 

J Respir Crit Care Med 182:307–316. 

http://dx.doi.org/10.1164/rccm.200908- 

1201OC. 

Tolbert, PE; Klein, M; Peel, JL; Sarnat, SE; 

Sarnat, JA. (2007). Multipollutant 

modeling issues in a study of ambient air 

quality and emergency department visits 

in Atlanta. J Expo Sci Environ Epidemiol 

17:S29–S35. http://dx.doi.org/10.1038/

sj.jes.7500625. 

Ulmer, C; Kopp, M; Ihorst, G; Frischer, T; 

Forster, J; Kuehr, J. (1997). Effects of 

ambient ozone exposures during the 

spring and summer of 1994 on 

pulmonary function of schoolchildren. 

Pediatr Pulmonol 23:344–353. http://

dx.doi.org/10.1002/(SICI)1099- 

0496(199705)23:53.0.CO;2-K. 

United Nations Environment Programme. 

(2003). Millennium Ecosystem 

Assessment: Ecosystems and human 

well-being: A framework for assessment. 

Washington, DC: Island Press. 

U.S. Department of Agriculture, U.S. Forest 

Service (2014). Tree basal area data. 

http://www.fs.fed.us/foresthealth/

technology/nidrm2012.shtml. 

U.S. Department of Agriculture, National 

Resources Conservation Service (2014), 

The PLANTS Database (http://

plants.usda.gov, 2014), National Plant 

Data Center, Baton Rouge, LA. 

U.S. Department of Agriculture, Agricultural 

Research Service. (2012). Effects of 

Ozone Air Pollution on Plants. http://

www.ars.usda.gov/Main/

docs.htm?docid=12462. 

U.S. Department of Health, Education, and 

Welfare. (1970). Air Quality Criteria for 

Photochemical Oxidants. Washington, 

DC: National Air Pollution Control 

Administration; publication no. AP–63. 

Available from NTIS, Springfield, VA; 

PB–190262/BA. 

U.S. Environmental Protection Agency. 

(2015) Climate Change in the United 

States: Benefits of Global Action. U.S. 

Environmental Protection Agency. Office 

of Atmospheric Programs. EPA 430–F– 

15–001, June 2015. Available at 

www.epa.gov/cira. 

U.S. Environmental Protection Agency. 

(2014a). Health Risk and Exposure 

Assessment for Ozone. Office of Air 

Quality Planning and Standards, 

Research Triangle Park, NC. EPA–452/P– 

14–004a. http://www.epa.gov/ttn/naaqs/

standards/ozone/s_o3_index.html. 

U.S. Environmental Protection Agency. 

(2014b). Welfare Risk and Exposure 

Assessment for Ozone. Office of Air 

Quality Planning and Standards, 

Research Triangle Park, NC. EPA–452/P– 

14–005a. http://www.epa.gov/ttn/naaqs/

standards/ozone/s_o3_index.html. 

U.S. Environmental Protection Agency. 

(2014c). Policy Assessment for Ozone. 

Office of Air Quality Planning and 

Standards, Research Triangle Park, NC. 

EPA–452/R–14–006. http://www.epa.

gov/ttn/naaqs/standards/ozone/s_o3_

index.html. 

U.S. Environmental Protection Agency. 

(2014d) Policy Assessment for Ozone, 

Second External Review Draft. Office of 

Air Quality Planning and Standards, 

Research Triangle Park, NC. EPA–452/P– 

14–002. 

U.S. Environmental Protection Agency 

(2014e). List of Designated Reference and 

Equivalent Methods. U.S. Environmental 

Protection Agency, Office of Research 

and Development, Research Triangle 

Park, NC 27711. http://epa.gov/ttn/

amtic/files/ambient/criteria/referenceequivalent-methods-list.pdf. 

U.S. Environmental Protection Agency 

(2014f). Performance of the Proposed 

New Federal Reference Method for 

Measuring Ozone Concentrations in 

Ambient Air. U.S. Environmental 

Protection Agency, Office of Research 

and Development, Research Triangle 

Park, NC. EPA/600/R–14/432. 

U.S. Environmental Protection Agency 

(2013). Integrated Science Assessment of 

Ozone and Related Photochemical 

Oxidants (Final Report). U.S. 

Environmental Protection Agency, 

Washington, DC. EPA/600/R–10/076F. 

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

standards/ozone/s_o3_2008_isa.html. 

U.S. Environmental Protection Agency 

(2012). Integrated Science Assessment of 

Ozone and Related Photochemical 

Oxidants (Third External Review Draft). 

U.S. Environmental Protection Agency, 

Washington, DC, EPA/600/R–10/076C, 

2012. 

U.S. Environmental Protection Agency 

(2011a). Integrated Review Plan for the 

Ozone National Ambient Air Quality 

Standards. U.S. Environmental 

Protection Agency, National Center for 

Environmental Assessment and Office of 

Air Quality Planning and Standards, 

Research Triangle Park, NC. EPA 452/R– 

11–006. April 2011. http://www.epa.gov/ 

ttn/naaqs/standards/ozone/data/2011_

04_OzoneIRP.pdf. 

U.S. Environmental Protection Agency 

(2011b) Integrated Science Assessment 

for Ozone and Related Photochemical 

Oxidants: First External Review Draft, 

U.S. Environmental Protection Agency, 

Washington, DC. EPA/600/R–10/076A. 

U.S. Environmental Protection Agency 

(2011c). 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. 

U.S. Environmental Protection Agency 

(2011d). Ozone National Ambient Air 

Quality Standards: Scope and Methods 

Plan for Health Risk and Exposure 

Assessment. U.S. Environmental 

Protection Agency, Office of Air Quality 

Planning and Standards, Research 

Triangle Park, NC. EPA–452/P–11–001. 

April 2011. http://www.epa.gov/ttn/

naaqs/standards/ozone/s_o3_2008_

pd.html. 

U.S. Environmental Protection Agency 

(2011e). Ozone National Ambient Air 

Quality Standards: Scope and Methods 

Plan for Welfare Risk and Exposure 

Assessment. U.S. Environmental 

Protection Agency, Office of Air Quality 

Planning and Standards, Research 

Triangle Park, NC. EPA–452/P–11–002. 

April 2011. http://www.epa.gov/ttn/

naaqs/standards/ozone/s_o3_2008_

pd.html. 

U.S. Environmental Protection Agency 

(2011f). Review of EPA’s Photochemical 

Assessment Monitoring Stations (PAMS) 

Network Re-engineering Project. U.S. 

Environmental Protection Agency, Office 

of the Administrator, Science Advisory 

Board, Washington DC. EPA–CASAC– 

11–010. 

U.S. Environmental Protection Agency 

(2010). Final Assessment: Integrated 

Science Assessment for Carbon 

Monoxide. U.S. Environmental 

Proteciton Agency, Washington, DC, 

EPA/600/R–09/019F. 

U.S. Environmental Protection Agency 

(2009a). Assessment of the Impacts of 

Global Change on Regional U.S. Air 

Quality: A Synthesis of Climate Change 

Impacts on Ground Level-Ozone. An 

Interim Report of the U.S. EPA Global 

Change Research Program. U.S 

Environmental Protection Agency, 

Washington, DC. EPA/600/R–07/094. 

U.S. Environmental Protection Agency 

(2009b). Integrated Science Assessment 

for Particulate Matter (Final Report). U.S. 

Environmental Protection Agency, 

Washington, DC, EPA/600/R–08/139F, 

2009. 

U.S. Environmental Protection Agency 

(2008). Responses to Significant 

Comments on the 2007 Proposed Rule on 

the National Ambient Air Quality 

Standards for Ozone. U.S. Environmental 

Protection Agency, Washington, DC, 

March 2008. http://www.epa.gov/ttn/

naaqs/standards/ozone/data/2008_03_

rtc.pdf. 

U.S. Environmental Protection Agency 

(2007). Review of the National Ambient 

Air Quality Standards for Ozone: Policy 

Assessment of Scientific and Technical 

Information, OAQPS Staff Paper. EPA– 

452/R–07–007. 

U.S. Environmental Protection Agency 

(2006a). Air Quality Criteria for Ozone 

and Related Photochemical Oxidants 

(2006 Final). U.S. Environmental 

Protection Agency, Washington, DC. 

EPA/600/R–05/004aF–cF. March 2006. 

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

standards/ozone/s_o3_cr_cd.html. 

U.S. Environmental Protection Agency 

(2006b). Ecological Benefits Assessment 

Strategic Plan. EPA–240–R–06–001. 

Office of Administrator, Washington, DC. 

http://yosemite.epa.gov/ee/epa/eed.nsf/

Webpages/ecologbenefitsplan.html. 

U.S. Environmental Protection Agency 

(2005). Guidelines for carcinogen risk 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65451 

assessment. Risk Assessment Forum, 

U.S. EPA, Washington, DC. EPA/630/P– 

03/001F. http://www.epa.gov/

cancerguidelines/. 

U.S. Environmental Protection Agency 

(1999). Compendium Method TO–11A, 

Determination of Formaldehyde in 

Ambient Air using Adsorbent Cartridge 

Followed by High Performance Liquid 

Chromatography (HPLC). U.S. 

Environmental Protection Agency, Office 

of Research and Development, 

Cincinnati, OH. EPA/625/R–96/010b. 

U.S. Environmental Protection Agency 

(1998). Technical Assistance Document 

(TAD) for Sampling and Analysis of 

Ozone Precursors. U.S. Environmental 

Protection Agency, Office of Research 

and Development, Research Triangle 

Park. EPA/600–R–98/161. 

U.S. Environmental Protection Agency 

(1996a). Air quality criteria for ozone 

and related photochemical oxidants. U.S. 

Environmental Protection Agency, 

Research Triangle Park, NC. EPA/600/P– 

93/004aF, cF. 

U.S. Environmental Protection Agency 

(1996b). Review of national ambient air 

quality standards for ozone: Assessment 

of scientific and technical information: 

OAQPS staff paper. Office of Air Quality 

Planning and Standards, Research 

Triangle Park, NC. EPA/452/R–96/007. 

http://www.ntis.gov/search/product.aspx

?ABBR=PB96203435. 

U.S. Environmental Protection Agency 

(1992). Summary of selected new 

information on effects of ozone on health 

and vegetation: Supplement to 1986 air 

quality criteria for ozone and other 

photochemical oxidants. Research 

Triangle Park, NC: Office of Health and 

Environmental Assessment, 

Environmental Criteria and Assessment 

Office; EPA report no. EPA/600/8–88/

105F. Available from NTIS, Springfield, 

VA; PB92–235670. 

U.S. Environmental Protection Agency 

(1989). Review of the National Ambient 

Air Quality Standards for Ozone: Policy 

Assessment of Scientific and Technical 

Information. OAQPS Staff Paper. Office 

of Air Quality Planning and Standards, 

Research Triangle Park, NC. 

U.S. Environmental Protection Agency 

(1986). Air quality criteria for ozone and 

other photochemical oxidants. Research 

Triangle Park, NC. EPA–600/8–84–

020aF–EPA–600/8–84–020eF. http://

www.ntis.gov/search/product.aspx

?ABBR=PB87142949. 

U.S. Environmental Protection Agency 

(1978). Air quality criteria for ozone and 

other photochemical oxidants. 

Washington, DC. EPA/600/8–78/004. 

USFS (U.S. Forest Service). (2011). Forest 

Health Monitoring Network. 

U.S. Forest Service; National Park Service; 

U.S. Fish and Wildlife Service. (2010). 

Federal land managers’ air quality 

related values work group (FLAG): Phase 

I report—revised (2010). Natural 

Resource Report NPS/NRPC/NRR—2010/ 

232. National Park Service, Denver, CO. 

http://www.nature.nps.gov/air/Pubs/pdf/

flag/FLAG_2010.pdf. 

U.S. National Park Service. (2003). Ozone 

Sensitive Plant Species on National Park 

Service and U.S. Fish and Wildlife 

Service Lands: Results of a June 24–25, 

2003 Workshop. Baltimore, MD. http://

www.nature.nps.gov/air/pubs/pdf/balt

finalreport1.pdf. 

U.S. National Park Service. (2006). Ozone 

Sensitive Plant Species, by Park, 

November 2006. http://www.nature.nps.

gov/air/Permits/ARIS/docs/Ozone_

Sensitive_ByPark_3600.pdf. 

Ulmer, C; Kopp, M; Ihorst, G; Frischer, T; 

Forster, J; Kuehr, J. (1997). Effects of 

ambient ozone exposures during the 

spring and summer of 1994 on 

pulmonary function of schoolchildren. 

Pediatr Pulmonol 23:344–353. http://dx.

doi.org/10.1002/(SICI)1099-0496(199705)

23:5<344::AID-PPUL6>3.0.CO;2-K. 

Vagaggini, B; Cianchetti, S; Bartoli, M; Ricci, 

M; Bacci, E; Dente, FL; Di Franco, A; 

Paggiaro, P. (2007). Prednisone blunts 

airway neutrophilic inflammatory 

response due to ozone exposure in 

asthmatic subjects. Respiration 74:61–58. 

http://dx.doi.org/10.1159/000096078. 

Vagaggini, B; Taccola, M; Conti, I; Carnevali, 

S; Cianchetti, S; Bartoli, ML; Bacci, E; 

Dente, FL; Di Franco, A; Giannini, D; 

Paggiaro, PL. (2001). Budesonide reduces 

neutrophilic but not functional airway 

response to ozone in mild asthmatics. 

Am J Respir Crit Care Med 164:2172– 

2176. 

Vedal, S; Brauer, M; White, R; Petkau, J. 

(2003). Air pollution and daily mortality 

in a city with low levels of pollution. 

Environ. Health Perspect. 111:45–51. 

Villeneuve, PJ; Chen, L; Rowe, BH; Coates, F. 

(2007). Outdoor air pollution and 

emergency department visits for asthma 

among children and adults: A casecrossover study in northern Alberta, 

Canada. Environ Health Global Access 

Sci Source 6:40. http://dx.doi.org/

10.1186/1476-069X-6-40. 

Wegman, LN. (2012). 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. Re: 

Updates to Information Presented in the 

Scope and Methods Plans for the Ozone 

NAAQS Health and Welfare Risk and 

Exposure Assessments. May 2, 2012. 

Wells, B. (2015a). Data Analyses Supporting 

Responses to Public Comments for the 

O3 NAAQS. Memorandum to the Ozone 

NAAQS Review Docket, EPA–HQ–OAR– 

2008–0699. 

Wells, B. (2015b). Expanded Comparison of 

Ozone Metrics Considered in Current 

NAAQS Review. Memorandum to the 

Ozone NAAQS Review Docket, EPA– 

HQ–OAR–2008–0699. 

Wells, B. (2014a). Comparison of Ozone 

Metrics Considered in Current NAAQS 

Review. Memorandum to the Ozone 

NAAQS Review Docket, EPA–HQ–OAR– 

2008–0699. 

Wells, B. (2014b). Analysis of Overlapping 8- 

hour Daily Maximum Ozone 

Concentrations. Memorandum to the 

Ozone NAAQS Review Docket, EPA– 

HQ–OAR–2008–0699. 

Wittig, VE; Ainsworth, EA; Naidu, SL; 

Karnosky, DF; Long, SP. (2009). 

Quantifying the impact of current and 

future tropospheric ozone on tree 

biomass, growth, physiology and 

biochemistry: A quantitative metaanalysis. Global Change Biol 15:396–424. 

http://dx.doi.org/10.1111/j.1365-2486.

2008.01774.x. 

Wittig, VE; Ainsworth, EA; Long, SP. (2007). 

To what extent do current and projected 

increases in surface ozone affect 

photosynthesis and stomatal 

conductance of trees? A meta-analytic 

review of the last 3 decades of 

experiments [Review]. Plant Cell Environ 

30:1150–1162. http://dx.doi.org/10.1111/ 

j.1365-3040.2007.01717.x. 

Wolff, GT. (1995). Letter to EPA 

Administrator Carol Browner: ‘‘CASAC 

Closure on the Primary Standard Portion 

of the Staff Paper for Ozone,’’ EPA–SAB– 

CASAC–LTR–96–002, November 30, 

1995. 

Wong, CM; Vichit-Vadakan, N; Vajanapoom, 

N; Ostro, B; Thach, TQ; Chau, PY; Chan, 

EK; Chung, RY; Ou, CQ; Yang, L; Peiris, 

JS; Thomas, GN; Lam, TH; Wong, TW; 

Hedley, AJ; Kan, H; Chen, B; Zhao, N; 

London, SJ; Song, G; Chen, G; Zhang, Y; 

Jiang, L; Qian, Z; He, Q; Lin, HM; Kong, 

L; Zhou, D; Liang, S; Zhu, Z; Liao, D; 

Liu, W; Bentley, CM; Dan, J; Wang, B; 

Yang, N; Xu, S; Gong, J; Wei, H; Sun, H; 

Qin, Z. (2010). Part 5. Public health and 

air pollution in Asia (PAPA): A 

combined analysis of four studies of air 

pollution and mortality. In Public Health 

and Air Pollution in Asia (PAPA): 

Coordinated Studies of Short-Term 

Exposure to Air Pollution and Daily 

Mortality in Four Cities (pp. 377–418). 

Boston, MA: Health Effects Institute. 

http://pubs.healtheffects.org/view.php

?id=348. 

Zanobetti, A; Schwartz, J. (2011). Ozone and 

survival in four cohorts with potentially 

predisposing diseases. Am J Respir Crit 

Care Med 184:836–841. http://dx.doi.

org/10.1164/rccm.201102-0227OC. 

Zanobetti, A; Schwartz, J. (2008). Mortality 

displacement in the association of ozone 

with mortality: An analysis of 48 cities 

in the United States. Am J Respir Crit 

Care Med 177:184–189. http://dx.doi.

org/10.1164/rccm.200706-823OC. 

Zanobetti, A; Schwartz, J. (2006). Air 

pollution and emergency admissions in 

Boston, MA. J Epidemiol Community 

Health 60:890–895. http://dx.doi.org/

10.1136/jech.2005.039834. 

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 

mstockstill on DSK4VPTVN1PROD with RULES2

65452 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

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, Reporting and 

recordkeeping requirements. 

40 CFR Part 58 

Environmental protection, 

Administrative practice and procedure, 

Air pollution control, Intergovernmental 

relations, Reporting and recordkeeping 

requirements. 

Dated: October 1, 2015. 

Gina McCarthy, 

Administrator. 

For the reasons set forth in the 

preamble, chapter I of title 40 of the 

Code of Federal Regulations is amended 

as follows: 

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. Amend § 50.14 by: 

■ a. Revising paragraphs (c)(2)(iii) and 

(vi) and (c)(3)(i); and 

■ b. Removing and reserving paragraphs 

(c)(2)(iv) and (v) and (c)(3)(ii) and (iii). 

The revisions read as follows: 

§ 50.14 Treatment of air quality monitoring 

data influenced by exceptional events. 

* * * * * 

(c) * * * 

(2) * * * 

(iii) Flags placed on data as being due 

to an exceptional event together with an 

initial description of the event shall be 

submitted to EPA not later than July 1st 

of the calendar year following the year 

in which the flagged measurement 

occurred, except as allowed under 

paragraph (c)(2)(vi) of this section. 

* * * * * 

(vi) Table 1 identifies the data 

submission process for a new or revised 

NAAQS. This process shall apply to 

those data that will or may influence the 

initial designation of areas for any new 

or revised NAAQS. 

TABLE 1—SCHEDULE FOR FLAGGING AND DOCUMENTATION SUBMISSION FOR DATA INFLUENCED BY EXCEPTIONAL EVENTS

FOR USE IN INITIAL AREA DESIGNATIONS

Exceptional events/regulatory action Exceptional events deadline schedule d

Flagging and initial event description deadline for data 

years 1, 2 and 3.a.

If state and tribal initial designation recommendations for a new/revised NAAQS are 

due August through January, then the flagging and initial event description deadline will be the July 1 prior to the recommendation deadline. If state and tribal recommendations for a new/revised NAAQS are due February through July, then the 

flagging and initial event description deadline will be the January 1 prior to the recommendation deadline. 

Exceptional events demonstration submittal deadline for 

data years 1, 2 and 3.a.

No later than the date that state and tribal recommendations are due to EPA. 

Flagging, initial event description and exceptional events 

demonstration submittal deadline for data year 4 b and, 

where applicable, data year 5.c.

By the last day of the month that is 1 year and 7 months after promulgation of a 

new/revised NAAQS, unless either option a or b applies. 

a. If the EPA follows a 3-year designation schedule, the deadline is 2 years and 7 

months after promulgation of a new/revised NAAQS. 

b. If the EPA notifies the state/tribe that it intends to complete the initial area designations process according to a schedule between 2 and 3 years, the deadline is 

5 months prior to the date specified for final designations decisions in such EPA 

notification. 

aWhere data years 1, 2, and 3 are those years expected to be considered in state and tribal recommendations. 

bWhere data year 4 is the additional year of data that the EPA may consider when it makes final area designations for a new/revised NAAQS 

under the standard designations schedule. cWhere data year 5 is the additional year of data that the EPA may consider when it makes final area designations for a new/revised NAAQS 

under an extended designations schedule. dThe date by which air agencies must certify their ambient air quality monitoring data in AQS is annually on May 1 of the year following the 

year of data collection as specified in 40 CFR 58.15(a)(2). In some cases, however, air agencies may choose to certify a prior year’s data in advance of May 1 of the following year, particularly if the EPA has indicated its intent to promulgate final designations in the first 8 months of the 

calendar year. Data flagging, initial event description and exceptional events demonstration deadlines for ‘‘early certified’’ data will follow the 

deadlines for ‘‘year 4’’ and ‘‘year 5’’ data. 

(3) Submission of demonstrations. (i) 

Except as allowed under paragraph 

(c)(2)(vi) of this section, a State that has 

flagged data as being due to an 

exceptional event and is requesting 

exclusion of the affected measurement 

data shall, after notice and opportunity 

for public comment, submit a 

demonstration to justify data exclusion 

to EPA not later than the lesser of 3 

years following the end of the calendar 

quarter in which the flagged 

concentration was recorded or 12 

months prior to the date that a 

regulatory decision must be made by 

EPA. A State must submit the public 

comments it received along with its 

demonstration to EPA. 

* * * * * 

■ 3. Section 50.19 is added to read as 

follows: 

§ 50.19 National primary and secondary 

ambient air quality standards for ozone. 

(a) The level of the national 8-hour 

primary ambient air quality standard for 

ozone (O3) is 0.070 parts per million 

(ppm), daily maximum 8-hour average, 

measured by a reference method based 

on appendix D to this part and 

designated in accordance with part 53 of 

this chapter or an equivalent method 

designated in accordance with part 53 of 

this chapter. 

(b) The 8-hour primary O3 ambient air 

quality standard is met at an ambient air 

quality monitoring site when the 3-year 

average of the annual fourth-highest 

daily maximum 8-hour average O3

concentration is less than or equal to 

0.070 ppm, as determined in accordance 

with appendix U to this part. 

(c) The level of the national secondary 

ambient air quality standard for O3 is 

0.070 ppm, daily maximum 8-hour 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65453 

average, measured by a reference 

method based on appendix D to this 

part and designated in accordance with 

part 53 of this chapter or an equivalent 

method designated in accordance with 

part 53 of this chapter. 

(d) The 8-hour secondary O3 ambient 

air quality standard is met at an ambient 

air quality monitoring site when the 3- 

year average of the annual fourthhighest daily maximum 8-hour average 

O3 concentration is less than or equal to 

0.070 ppm, as determined in accordance 

with appendix U to this part. 

■ 4. Revise appendix D to part 50 to 

read as follows: 

Appendix D to Part 50—Reference 

Measurement Principle and Calibration 

Procedure for the Measurement of 

Ozone in the Atmosphere 

(Chemiluminescence Method) 

1.0 Applicability. 

1.1 This chemiluminescence method 

provides reference measurements of the 

concentration of ozone (O3) in ambient air for 

determining compliance with the national 

primary and secondary ambient air quality 

standards for O3 as specified in 40 CFR part 

50. This automated method is applicable to 

the measurement of ambient O3

concentrations using continuous (real-time) 

sampling and analysis. Additional quality 

assurance procedures and guidance are 

provided in 40 CFR part 58, appendix A, and 

in Reference 14. 

2.0 Measurement Principle. 

2.1 This reference method is based on 

continuous automated measurement of the 

intensity of the characteristic 

chemiluminescence released by the gas phase 

reaction of O3 in sampled air with either 

ethylene (C2H4) or nitric oxide (NO) gas. An 

ambient air sample stream and a specific 

flowing concentration of either C2H4 (ET–CL 

method) or NO (NO–CL method) are mixed 

in a measurement cell, where the resulting 

chemiluminescence is quantitatively 

measured by a sensitive photo-detector. 

References 8–11 describe the 

chemiluminescence measurement principle. 

2.2 The measurement system is calibrated 

by referencing the instrumental 

chemiluminescence measurements to 

certified O3 standard concentrations 

generated in a dynamic flow system and 

assayed by photometry to be traceable to a 

National Institute of Standards and 

Technology (NIST) standard reference 

photometer for O3 (see Section 4, Calibration 

Procedure, below). 

2.3 An analyzer implementing this 

measurement principle is shown 

schematically in Figure 1. Designs 

implementing this measurement principle 

must include: an appropriately designed 

mixing and measurement cell; a suitable 

quantitative photometric measurement 

system with adequate sensitivity and 

wavelength specificity for O3; a pump, flow 

control, and sample conditioning system for 

sampling the ambient air and moving it into 

and through the measurement cell; a sample 

air dryer as necessary to meet the water vapor 

interference limit requirement specified in 

subpart B of part 53 of this chapter; a means 

to supply, meter, and mix a constant, flowing 

stream of either C2H4 or NO gas of fixed 

concentration with the sample air flow in the 

measurement cell; suitable electronic control 

and measurement processing capability; and 

other associated apparatus as may be 

necessary. The analyzer must be designed 

and constructed to provide accurate, 

repeatable, and continuous measurements of 

O3 concentrations in ambient air, with 

measurement performance that meets the 

requirements specified in subpart B of part 

53 of this chapter. 

2.4 An analyzer implementing this 

measurement principle and calibration 

procedure will be considered a federal 

reference method (FRM) only if it has been 

designated as a reference method in 

accordance with part 53 of this chapter. 

2.5 Sampling considerations. The use of a 

particle filter on the sample inlet line of a 

chemiluminescence O3 FRM analyzer is 

required to prevent buildup of particulate 

matter in the measurement cell and inlet 

components. This filter must be changed 

weekly (or at least often as specified in the 

manufacturer’s operation/instruction 

manual), and the sample inlet system used 

with the analyzer must be kept clean, to 

avoid loss of O3 in the O3 sample air prior 

to the concentration measurement. 

3.0 Interferences. 

3.1 Except as described in 3.2 below, the 

chemiluminescence measurement system is 

inherently free of significant interferences 

from other pollutant substances that may be 

present in ambient air. 

3.2 A small sensitivity to variations in the 

humidity of the sample air is minimized by 

a sample air dryer. Potential loss of O3 in the 

inlet air filter and in the air sample handling 

components of the analyzer and associated 

exterior air sampling components due to 

buildup of airborne particulate matter is 

minimized by filter replacement and cleaning 

of the other inlet components. 

4.0 Calibration Procedure. 

4.1 Principle. The calibration procedure is 

based on the photometric assay of O3

concentrations in a dynamic flow system. 

The concentration of O3 in an absorption cell 

is determined from a measurement of the 

amount of 254 nm light absorbed by the 

sample. This determination requires 

knowledge of (1) the absorption coefficient 

(a) of O3 at 254 nm, (2) the optical path 

length (l) through the sample, (3) the 

transmittance of the sample at a nominal 

wavelength of 254 nm, and (4) the 

temperature (T) and pressure (P) of the 

sample. The transmittance is defined as the 

ratio I/I0, where I is the intensity of light 

which passes through the cell and is sensed 

by the detector when the cell contains an O3

sample, and I0 is the intensity of light which 

passes through the cell and is sensed by the 

detector when the cell contains zero air. It is 

assumed that all conditions of the system, 

except for the contents of the absorption cell, 

are identical during measurement of I and I0. 

The quantities defined above are related by 

the Beer-Lambert absorption law, 

Where: 

a = absorption coefficient of O3 at 254 nm = 

308 ±4 atm¥1 cm¥1 at 0 °C and 760 

torr,1, 2, 3, 4, 5, 6, 7

c = O3 concentration in atmospheres, and 

l = optical path length in cm. 

A stable O3 generator is used to produce O3

concentrations over the required calibration 

concentration range. Each O3 concentration is 

determined from the measurement of the 

transmittance (I/I0) of the sample at 254 nm 

with a photometer of path length l and 

calculated from the equation, 


mstockstill on DSK4VPTVN1PROD with RULES2ER26OC15.002</GPH> ER26OC15.003</GPH>
65454 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

The calculated O3 concentrations must be 

corrected for O3 losses, which may occur in 

the photometer, and for the temperature and 

pressure of the sample. 

4.2 Applicability. This procedure is 

applicable to the calibration of ambient air O3

analyzers, either directly or by means of a 

transfer standard certified by this procedure. 

Transfer standards must meet the 

requirements and specifications set forth in 

Reference 12. 

4.3 Apparatus. A complete UV calibration 

system consists of an O3 generator, an output 

port or manifold, a photometer, an 

appropriate source of zero air, and other 

components as necessary. The configuration 

must provide a stable O3 concentration at the 

system output and allow the photometer to 

accurately assay the output concentration to 

the precision specified for the photometer 

(4.3.1). Figure 2 shows a commonly used 

configuration and serves to illustrate the 

calibration procedure, which follows. Other 

configurations may require appropriate 

variations in the procedural steps. All 

connections between components in the 

calibration system downstream of the O3

generator must be of glass, Teflon, or other 

relatively inert materials. Additional 

information regarding the assembly of a UV 

photometric calibration apparatus is given in 

Reference 13. For certification of transfer 

standards which provide their own source of 

O3, the transfer standard may replace the O3

generator and possibly other components 

shown in Figure 2; see Reference 12 for 

guidance. 

4.3.1 UV photometer. The photometer 

consists of a low-pressure mercury discharge 

lamp, (optional) collimation optics, an 

absorption cell, a detector, and signalprocessing electronics, as illustrated in 

Figure 2. It must be capable of measuring the 

transmittance, I/I0, at a wavelength of 254 nm 

with sufficient precision such that the 

standard deviation of the concentration 

measurements does not exceed the greater of 

0.005 ppm or 3% of the concentration. 

Because the low-pressure mercury lamp 

radiates at several wavelengths, the 

photometer must incorporate suitable means 

to assure that no O3 is generated in the cell 

by the lamp, and that at least 99.5% of the 

radiation sensed by the detector is 254 nm 

radiation. (This can be readily achieved by 

prudent selection of optical filter and 

detector response characteristics.) The length 

of the light path through the absorption cell 

must be known with an accuracy of at least 

99.5%. In addition, the cell and associated 

plumbing must be designed to minimize loss 

of O3 from contact with cell walls and gas 

handling components. See Reference 13 for 

additional information. 

4.3.2 Air flow controllers. Air flow 

controllers are devices capable of regulating 

air flows as necessary to meet the output 

stability and photometer precision 

requirements. 

4.3.3 Ozone generator. The ozone generator 

used must be capable of generating stable 

levels of O3 over the required concentration 

range. 

4.3.4 Output manifold. The output 

manifold must be constructed of glass, 

Teflon, or other relatively inert material, and 

should be of sufficient diameter to insure a 

negligible pressure drop at the photometer 

connection and other output ports. The 

system must have a vent designed to insure 

atmospheric pressure in the manifold and to 

prevent ambient air from entering the 

manifold. 

4.3.5 Two-way valve. A manual or 

automatic two-way valve, or other means is 

used to switch the photometer flow between 

zero air and the O3 concentration. 

4.3.6 Temperature indicator. A device to 

indicate temperature must be used that is 

accurate to ±1 °C. 

4.3.7 Barometer or pressure indicator. A 

device to indicate barometric pressure must 

be used that is accurate to ±2 torr. 

4.4 Reagents. 

4.4.1 Zero air. The zero air must be free of 

contaminants which would cause a 

detectable response from the O3 analyzer, 

and it must be free of NO, C2H4, and other 

species which react with O3. A procedure for 

generating suitable zero air is given in 

Reference 13. As shown in Figure 2, the zero 

air supplied to the photometer cell for the I0

reference measurement must be derived from 

the same source as the zero air used for 

generation of the O3 concentration to be 

assayed (I measurement). When using the 

photometer to certify a transfer standard 

having its own source of O3, see Reference 12 

for guidance on meeting this requirement. 

4.5 Procedure. 

4.5.1 General operation. The calibration 

photometer must be dedicated exclusively to 

use as a calibration standard. It must always 

be used with clean, filtered calibration gases, 

and never used for ambient air sampling. A 

number of advantages are realized by locating 

the calibration photometer in a clean 

laboratory where it can be stationary, 

protected from the physical shock of 

transportation, operated by a responsible 

analyst, and used as a common standard for 

all field calibrations via transfer standards. 

4.5.2 Preparation. Proper operation of the 

photometer is of critical importance to the 

accuracy of this procedure. Upon initial 

operation of the photometer, the following 

steps must be carried out with all 

quantitative results or indications recorded 

in a chronological record, either in tabular 

form or plotted on a graphical chart. As the 

performance and stability record of the 

photometer is established, the frequency of 

these steps may be reduced to be consistent 

with the documented stability of the 

photometer and the guidance provided in 

Reference 12. 

4.5.2.1 Instruction manual. Carry out all set 

up and adjustment procedures or checks as 

described in the operation or instruction 

manual associated with the photometer. 

4.5.2.2 System check. Check the 

photometer system for integrity, leaks, 

cleanliness, proper flow rates, etc. Service or 

replace filters and zero air scrubbers or other 

consumable materials, as necessary. 

4.5.2.3 Linearity. Verify that the 

photometer manufacturer has adequately 

established that the linearity error of the 

photometer is less than 3%, or test the 

linearity by dilution as follows: Generate and 

assay an O3 concentration near the upper 

range limit of the system or appropriate 

calibration scale for the instrument, then 

accurately dilute that concentration with zero 

air and re-assay it. Repeat at several different 

dilution ratios. Compare the assay of the 

original concentration with the assay of the 

diluted concentration divided by the dilution 

ratio, as follows 

Where: 

E = linearity error, percent 

A1 = assay of the original concentration 

A2 = assay of the diluted concentration 

R = dilution ratio = flow of original 

concentration divided by the total flow 

The linearity error must be less than 5%. 

Since the accuracy of the measured flowrates will affect the linearity error as 

measured this way, the test is not necessarily 

conclusive. Additional information on 

verifying linearity is contained in Reference 

13. 

4.5.2.4 Inter-comparison. The photometer 

must be inter-compared annually, either 

directly or via transfer standards, with a 

NIST standard reference photometer (SRP) or 

calibration photometers used by other 

agencies or laboratories. 

4.5.2.5 Ozone losses. Some portion of the 

O3 may be lost upon contact with the 

photometer cell walls and gas handling 

components. The magnitude of this loss must 

be determined and used to correct the 

calculated O3 concentration. This loss must 

not exceed 5%. Some guidelines for 

quantitatively determining this loss are 

discussed in Reference 13. 

4.5.3 Assay of O3 concentrations. The 

operator must carry out the following steps 

to properly assay O3 concentrations. 

4.5.3.1 Allow the photometer system to 

warm up and stabilize. 

4.5.3.2 Verify that the flow rate through the 

photometer absorption cell, F, allows the cell 

to be flushed in a reasonably short period of 

time (2 liter/min is a typical flow). The 

precision of the measurements is inversely 

related to the time required for flushing, 

since the photometer drift error increases 

with time. 

4.5.3.3 Ensure that the flow rate into the 

output manifold is at least 1 liter/min greater 

than the total flow rate required by the 

photometer and any other flow demand 

connected to the manifold. 


mstockstill on DSK4VPTVN1PROD with RULES2ER26OC15.004</GPH>
Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65455 

4.5.3.4 Ensure that the flow rate of zero air, 

Fz, is at least 1 liter/min greater than the flow 

rate required by the photometer. 

4.5.3.5 With zero air flowing in the output 

manifold, actuate the two-way valve to allow 

the photometer to sample first the manifold 

zero air, then Fz. The two photometer 

readings must be equal (I = I0). 

Note: In some commercially available 

photometers, the operation of the two-way 

valve and various other operations in section 

4.5.3 may be carried out automatically by the 

photometer. 

4.5.3.6 Adjust the O3 generator to produce 

an O3 concentration as needed. 

4.5.3.7 Actuate the two-way valve to allow 

the photometer to sample zero air until the 

absorption cell is thoroughly flushed and 

record the stable measured value of Io. 

4.5.3.8 Actuate the two-way valve to allow 

the photometer to sample the O3

concentration until the absorption cell is 

thoroughly flushed and record the stable 

measured value of I. 

4.5.3.9 Record the temperature and 

pressure of the sample in the photometer 

absorption cell. (See Reference 13 for 

guidance.) 

4.5.3.10 Calculate the O3 concentration 

from equation 4. An average of several 

determinations will provide better precision. 

Where: 

[O3]OUT = O3 concentration, ppm 

a = absorption coefficient of O3 at 254 nm = 

308 atm¥1 cm¥1 at 0° C and 760 torr 

l = optical path length, cm 

T = sample temperature, K 

P = sample pressure, torr 

L = correction factor for O3 losses from 

4.5.2.5 = (1¥fraction of O3 lost). 

Note: Some commercial photometers may 

automatically evaluate all or part of equation 

4. It is the operator’s responsibility to verify 

that all of the information required for 

equation 4 is obtained, either automatically 

by the photometer or manually. For 

‘‘automatic’’ photometers which evaluate the 

first term of equation 4 based on a linear 

approximation, a manual correction may be 

required, particularly at higher O3 levels. See 

the photometer instruction manual and 

Reference 13 for guidance. 

4.5.3.11 Obtain additional O3

concentration standards as necessary by 

repeating steps 4.5.3.6 to 4.5.3.10 or by 

Option 1. 

4.5.4 Certification of transfer standards. A 

transfer standard is certified by relating the 

output of the transfer standard to one or more 

O3 calibration standards as determined 

according to section 4.5.3. The exact 

procedure varies depending on the nature 

and design of the transfer standard. Consult 

Reference 12 for guidance. 

4.5.5 Calibration of ozone analyzers. Ozone 

analyzers must be calibrated as follows, using 

O3 standards obtained directly according to 

section 4.5.3 or by means of a certified 

transfer standard. 

4.5.5.1 Allow sufficient time for the O3

analyzer and the photometer or transfer 

standard to warm-up and stabilize. 

4.5.5.2 Allow the O3 analyzer to sample 

zero air until a stable response is obtained 

and then adjust the O3 analyzer’s zero 

control. Offsetting the analyzer’s zero 

adjustment to +5% of scale is recommended 

to facilitate observing negative zero drift (if 

any). Record the stable zero air response as 

‘‘Z’’. 

4.5.5.3 Generate an O3 concentration 

standard of approximately 80% of the 

desired upper range limit (URL) of the O3

analyzer. Allow the O3 analyzer to sample 

this O3 concentration standard until a stable 

response is obtained. 

4.5.5.4 Adjust the O3 analyzer’s span 

control to obtain the desired response 

equivalent to the calculated standard 

concentration. Record the O3 concentration 

and the corresponding analyzer response. If 

substantial adjustment of the span control is 

necessary, recheck the zero and span 

adjustments by repeating steps 4.5.5.2 to 

4.5.5.4. 

4.5.5.5 Generate additional O3

concentration standards (a minimum of 5 are 

recommended) over the calibration scale of 

the O3 analyzer by adjusting the O3 source or 

by Option 1. For each O3 concentration 

standard, record the O3 concentration and the 

corresponding analyzer response. 

4.5.5.6 Plot the O3 analyzer responses 

(vertical or Y-axis) versus the corresponding 

O3 standard concentrations (horizontal or Xaxis). Compute the linear regression slope 

and intercept and plot the regression line to 

verify that no point deviates from this line by 

more than 2 percent of the maximum 

concentration tested. 

4.5.5.7 Option 1: The various O3

concentrations required in steps 4.5.3.11 and 

4.5.5.5 may be obtained by dilution of the O3

concentration generated in steps 4.5.3.6 and 

4.5.5.3. With this option, accurate flow 

measurements are required. The dynamic 

calibration system may be modified as shown 

in Figure 3 to allow for dilution air to be 

metered in downstream of the O3 generator. 

A mixing chamber between the O3 generator 

and the output manifold is also required. The 

flow rate through the O3 generator (Fo) and 

the dilution air flow rate (FD) are measured 

with a flow or volume standard that is 

traceable to a NIST flow or volume 

calibration standard. Each O3 concentration 

generated by dilution is calculated from: 

Where: 

[O3]′OUT = diluted O3 concentration, ppm 

FO = flow rate through the O3 generator, 

liter/min 

FD = diluent air flow rate, liter/min 

Note: Additional information on 

calibration and pollutant standards is 

provided in Section 12 of Reference 14. 

5.0 Frequency of Calibration. 

5.1 The frequency of calibration, as well as 

the number of points necessary to establish 

the calibration curve, and the frequency of 

other performance checking will vary by 

analyzer; however, the minimum frequency, 

acceptance criteria, and subsequent actions 

are specified in Appendix D of Reference 14: 

Measurement Quality Objectives and 

Validation Templates. The user’s quality 

control program shall provide guidelines for 

initial establishment of these variables and 

for subsequent alteration as operational 

experience is accumulated. Manufacturers of 

analyzers should include in their instruction/ 

operation manuals information and guidance 

as to these variables and on other matters of 

operation, calibration, routine maintenance, 

and quality control. 

6.0 References. 

1. E.C.Y. Inn and Y. Tanaka, ‘‘Absorption 

coefficient of Ozone in the Ultraviolet 

and Visible Regions’’, J. Opt. Soc. Am., 

43, 870 (1953). 

2. A. G. Hearn, ‘‘Absorption of Ozone in the 

Ultraviolet and Visible Regions of the 

Spectrum’’, Proc. Phys. Soc. (London), 

78, 932 (1961). 

3. W. B. DeMore and O. Raper, ‘‘Hartley Band 

Extinction Coefficients of Ozone in the 

Gas Phase and in Liquid Nitrogen, 

Carbon Monoxide, and Argon’’, J. Phys. 

Chem., 68, 412 (1964). 

4. M. Griggs, ‘‘Absorption Coefficients of 

Ozone in the Ultraviolet and Visible 

Regions’’, J. Chem. Phys., 49, 857 (1968). 

5. K. H. Becker, U. Schurath, and H. Seitz, 

‘‘Ozone Olefin Reactions in the Gas 

Phase. 1. Rate Constants and Activation 

Energies’’, Int’l Jour. of Chem. Kinetics, 

VI, 725 (1974). 

6. M. A. A. Clyne and J. A. Coxom, ‘‘Kinetic 

Studies of Oxy-halogen Radical 

Systems’’, Proc. Roy. Soc., A303, 207 

(1968). 

7. J. W. Simons, R. J. Paur, H. A. Webster, and 

E. J. Bair, ‘‘Ozone Ultraviolet Photolysis. 

VI. The Ultraviolet Spectrum’’, J. Chem. 

Phys., 59, 1203 (1973). 

8. Ollison, W.M.; Crow, W.; Spicer, C.W. 

‘‘Field testing of new-technology 


mstockstill on DSK4VPTVN1PROD with RULES2ER26OC15.005</GPH> ER26OC15.006</GPH>
65456 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

ambient air ozone monitors.’’ J. Air 

Waste Manage. Assoc., 63 (7), 855–863 

(2013). 

9. Parrish, D.D.; Fehsenfeld, F.C. ‘‘Methods 

for gas-phase measurements of ozone, 

ozone precursors and aerosol 

precursors.’’ Atmos. Environ., 34 (12– 

14), 1921–1957(2000). 

10. Ridley, B.A.; Grahek, F.E.; Walega, J.G. 

‘‘A small, high-sensitivity, mediumresponse ozone detector suitable for 

measurements from light aircraft.’’ J. 

Atmos. Oceanic Technol., 9 (2), 142– 

148(1992). 

11. Boylan, P., Helmig, D., and Park, J.H. 

‘‘Characterization and mitigation of 

water vapor effects in the measurement 

of ozone by chemiluminescence with 

nitric oxide.’’ Atmos. Meas. Tech. 7, 

1231–1244 (2014). 

12. Transfer Standards for Calibration of 

Ambient Air Monitoring Analyzers for 

Ozone, EPA publication number EPA– 

454/B–13–004, October 2013. EPA, 

Office of Air Quality Planning and 

Standards, Research Triangle Park, NC 

27711. [Available at www.epa.gov/

ttnamti1/files/ambient/qaqc/Ozone

TransferStandardGuidance.pdf.] 

13. Technical Assistance Document for the 

Calibration of Ambient Ozone Monitors, 

EPA publication number EPA–600/4– 

79–057, September, 1979. [Available at 

www.epa.gov/ttnamti1/files/ambient/

criteria/4–79–057.pdf.] 

14. QA Handbook for Air Pollution 

Measurement Systems—Volume II. 

Ambient Air Quality Monitoring 

Program. EPA–454/B–13–003, May 2013. 

[Available at http://www.epa.gov/

ttnamti1/files/ambient/pm25/qa/QAHandbook-Vol-II.pdf.] 


mstockstill on DSK4VPTVN1PROD with RULES2ER26OC15.007</GPH>
Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65457 


mstockstill on DSK4VPTVN1PROD with RULES2ER26OC15.008</GPH>

I 

FLOW 

CONTROLLER 

FlOW 

CONTROllER 

UVPHOTOMETER 

DETECTOR 

SIGNAL 

PROCESSING 

ELECTRONICS 

o. 

GENERATOR 

OUTPUT 

MANIFOLD 

- ____r--" ~ VENT 

I I LJ 

ABSORPllONCELL 

1 EXTRAOUTLETSCAPPED 

WHEN NOT IN USE 

TOINLETOFANALVZER 

UNDERCAUBRATION 

--- 1 

OPllCS 

SOURCE 

0 

FLOW 

CONTROLLER 

L ______________ _ 

Figure 2. Schematic diagram of a typical UV photometric calibration system. 
65458 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

■ 5. Add appendix U to Part 50 to read 

as follows: 

Appendix U to Part 50—Interpretation 

of the Primary and Secondary National 

Ambient Air Quality Standards for 

Ozone 

1. General 

(a) This appendix explains the data 

handling conventions and computations 

necessary for determining whether the 

primary and secondary national ambient air 

quality standards (NAAQS) for ozone (O3) 

specified in § 50.19 are met at an ambient O3

air quality monitoring site. Data reporting, 

data handling, and computation procedures 

to be used in making comparisons between 

reported O3 concentrations and the levels of 

the O3 NAAQS are specified in the following 

sections. 

(b) Whether to exclude or retain the data 

affected by exceptional events is determined 

by the requirements under §§ 50.1, 50.14 and 

51.930. 

(c) The terms used in this appendix are 

defined as follows: 

8-hour average refers to the moving average 

of eight consecutive hourly O3 concentrations 

measured at a site, as explained in section 3 

of this appendix. 

Annual fourth-highest daily maximum 

refers to the fourth highest value measured at 

a site during a year. 

Collocated monitors refers to the instance 

of two or more O3 monitors operating at the 

same physical location. 

Daily maximum 8-hour average O3

concentration refers to the maximum 

calculated 8-hour average value measured at 

a site on a particular day, as explained in 

section 3 of this appendix. 

Design value refers to the metric (i.e., 

statistic) that is used to compare ambient O3

concentration data measured at a site to the 

NAAQS in order to determine compliance, as 

explained in section 4 of this appendix. 

Minimum data completeness requirements 

refer to the amount of data that a site is 

required to collect in order to make a valid 

determination that the site is meeting the 

NAAQS. 

Monitor refers to a physical instrument 

used to measure ambient O3 concentrations. 

O3 monitoring season refers to the span of 

time within a year when individual states are 

required to measure ambient O3

concentrations, as listed in Appendix D to 

part 58 of this chapter. 

Site refers to an ambient O3 air quality 

monitoring site. 

Site data record refers to the set of hourly 

O3 concentration data collected at a site for 

use in comparisons with the NAAQS. 

Year refers to calendar year. 

2. Selection of Data for use in Comparisons 

With the Primary and Secondary Ozone 

NAAQS 

(a) All valid hourly O3 concentration data 

collected using a federal reference method 

specified in Appendix D to this part, or an 

equivalent method designated in accordance 

with part 53 of this chapter, meeting all 

applicable requirements in part 58 of this 

chapter, and submitted to EPA’s Air Quality 

System (AQS) database or otherwise 

available to EPA, shall be used in design 

value calculations. 

(b) All design value calculations shall be 

implemented on a site-level basis. If data are 

reported to EPA from collocated monitors, 

those data shall be combined into a single 

site data record as follows: 

(i) The monitoring agency shall designate 

one monitor as the primary monitor for the 

site. 

(ii) Hourly O3 concentration data from a 

secondary monitor shall be substituted into 


mstockstill on DSK4VPTVN1PROD with RULES2ER26OC15.009</GPH>
Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65459 

the site data record whenever a valid hourly 

O3 concentration is not obtained from the 

primary monitor. In the event that hourly O3

concentration data are available for more 

than one secondary monitor, the hourly 

concentration values from the secondary 

monitors shall be averaged and substituted 

into the site data record. 

(c) In certain circumstances, including but 

not limited to site closures or relocations, 

data from two nearby sites may be combined 

into a single site data record for the purpose 

of calculating a valid design value. The 

appropriate Regional Administrator may 

approve such combinations after taking into 

consideration factors such as distance 

between sites, spatial and temporal patterns 

in air quality, local emissions and 

meteorology, jurisdictional boundaries, and 

terrain features. 

3. Data Reporting and Data Handling 

Conventions 

(a) Hourly average O3 concentrations shall 

be reported in parts per million (ppm) to the 

third decimal place, with additional digits to 

the right of the third decimal place truncated. 

Each hour shall be identified using local 

standard time (LST). 

(b) Moving 8-hour averages shall be 

computed from the hourly O3 concentration 

data for each hour of the year and shall be 

stored in the first, or start, hour of the 8-hour 

period. An 8-hour average shall be 

considered valid if at least 6 of the hourly 

concentrations for the 8-hour period are 

available. In the event that only 6 or 7 hourly 

concentrations are available, the 8-hour 

average shall be computed on the basis of the 

hours available, using 6 or 7, respectively, as 

the divisor. In addition, in the event that 5 

or fewer hourly concentrations are available, 

the 8-hour average shall be considered valid 

if, after substituting zero for the missing 

hourly concentrations, the resulting 8-hour 

average is greater than the level of the 

NAAQS, or equivalently, if the sum of the 

available hourly concentrations is greater 

than 0.567 ppm. The 8-hour averages shall be 

reported to three decimal places, with 

additional digits to the right of the third 

decimal place truncated. Hourly O3

concentrations that have been approved 

under § 50.14 as having been affected by 

exceptional events shall be counted as 

missing or unavailable in the calculation of 

8-hour averages. 

(c) The daily maximum 8-hour average O3

concentration for a given day is the highest 

of the 17 consecutive 8-hour averages 

beginning with the 8-hour period from 7:00 

a.m. to 3:00 p.m. and ending with the 8-hour 

period from 11:00 p.m. to 7:00 a.m. the 

following day (i.e., the 8-hour averages for 

7:00 a.m. to 11:00 p.m.). Daily maximum 8- 

hour average O3 concentrations shall be 

determined for each day with ambient O3

monitoring data, including days outside the 

O3 monitoring season if those data are 

available. 

(d) A daily maximum 8-hour average O3

concentration shall be considered valid if 

valid 8-hour averages are available for at least 

13 of the 17 consecutive 8-hour periods 

starting from 7:00 a.m. to 11:00 p.m. In 

addition, in the event that fewer than 13 

valid 8-hour averages are available, a daily 

maximum 8-hour average O3 concentration 

shall also be considered valid if it is greater 

than the level of the NAAQS. Hourly O3

concentrations that have been approved 

under § 50.14 as having been affected by 

exceptional events shall be included when 

determining whether these criteria have been 

met. 

(e) The primary and secondary O3 design 

value statistic is the annual fourth-highest 

daily maximum 8-hour O3 concentration, 

averaged over three years, expressed in ppm. 

The fourth-highest daily maximum 8-hour O3

concentration for each year shall be 

determined based only on days meeting the 

validity criteria in 3(d). The 3-year average 

shall be computed using the three most 

recent, consecutive years of ambient O3

monitoring data. Design values shall be 

reported in ppm to three decimal places, 

with additional digits to the right of the third 

decimal place truncated. 

4. Comparisons With the Primary and 

Secondary Ozone NAAQS 

(a) The primary and secondary national 

ambient air quality standards for O3 are met 

at an ambient air quality monitoring site 

when the 3-year average of the annual fourthhighest daily maximum 8-hour average O3

concentration (i.e., the design value) is less 

than or equal to 0.070 ppm. 

(b) A design value greater than the level of 

the NAAQS is always considered to be valid. 

A design value less than or equal to the level 

of the NAAQS must meet minimum data 

completeness requirements in order to be 

considered valid. These requirements are met 

for a 3-year period at a site if valid daily 

maximum 8-hour average O3 concentrations 

are available for at least 90% of the days 

within the O3 monitoring season, on average, 

for the 3-year period, with a minimum of at 

least 75% of the days within the O3

monitoring season in any one year. 

(c) When computing whether the minimum 

data completeness requirements have been 

met, meteorological or ambient data may be 

sufficient to demonstrate that meteorological 

conditions on missing days were not 

conducive to concentrations above the level 

of the NAAQS. Missing days assumed less 

than the level of the NAAQS are counted for 

the purpose of meeting the minimum data 

completeness requirements, subject to the 

approval of the appropriate Regional 

Administrator. 

(d) Comparisons with the primary and 

secondary O3 NAAQS are demonstrated by 

examples 1 and 2 as follows: 

EXAMPLE 1—SITE MEETING THE PRIMARY AND SECONDARY O3 NAAQS 

Year 

Percent valid 

days within O3

monitoring 

season (Data 

completeness) 

1st highest 

daily max 

8-hour O3

(ppm) 

2nd highest 

daily max 

8-hour O3

(ppm) 

3rd highest 

daily max 

8-hour O3

(ppm) 

4th highest 

daily max 

8-hour O3

(ppm) 

5th highest 

daily max 

8-hour O3

(ppm) 

2014 ......................................................... 100 0.082 0.080 0.075 0.069 0.068 

2015 ......................................................... 96 0.074 0.073 0.065 0.062 0.060 

2016 ......................................................... 98 0.070 0.069 0.067 0.066 0.060 

Average .................................................... 98 ........................ ........................ ........................ 0.065 

As shown in Example 1, this site meets the 

primary and secondary O3 NAAQS because 

the 3-year average of the annual fourthhighest daily maximum 8-hour average O3

concentrations (i.e., 0.065666 ppm, truncated 

to 0.065 ppm) is less than or equal to 0.070 

ppm. The minimum data completeness 

requirements are also met (i.e., design value 

is considered valid) because the average 

percent of days within the O3 monitoring 

season with valid ambient monitoring data is 

greater than 90%, and no single year has less 

than 75% data completeness. 

EXAMPLE 2—SITE FAILING TO MEET THE PRIMARY AND SECONDARY O3 O3 NAAQS 

Year 

Percent valid 

days within O3

monitoring 

season (Data 

completeness) 

1st highest 

daily max 

8-hour O3

(ppm) 

2nd highest 

daily max 

8-hour O3

(ppm) 

3rd highest 

daily max 

8-hour O3

(ppm) 

4th highest 

daily max 

8-hour O3

(ppm) 

5th highest 

daily max 

8-hour O3

(ppm) 

2014 ......................................................... 96 0.085 0.080 0.079 0.074 0.072 

mstockstill on DSK4VPTVN1PROD with RULES2

65460 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

258NO2 precision in Table B–1 is also changed to 

percent to agree with the calculation specified in 

53.23(e)(10)(vi). 

EXAMPLE 2—SITE FAILING TO MEET THE PRIMARY AND SECONDARY O3 O3 NAAQS—Continued 

Year 

Percent valid 

days within O3

monitoring 

season (Data 

completeness) 

1st highest 

daily max 

8-hour O3

(ppm) 

2nd highest 

daily max 

8-hour O3

(ppm) 

3rd highest 

daily max 

8-hour O3

(ppm) 

4th highest 

daily max 

8-hour O3

(ppm) 

5th highest 

daily max 

8-hour O3

(ppm) 

2015 ......................................................... 74 0.084 0.083 0.072 0.071 0.068 

2016 ......................................................... 98 0.083 0.081 0.081 0.075 0.074 

Average .................................................... 89 ........................ ........................ ........................ 0.073 

As shown in Example 2, this site fails to 

meet the primary and secondary O3 NAAQS 

because the 3-year average of the annual 

fourth-highest daily maximum 8-hour 

average O3 concentrations (i.e., 0.073333 

ppm, truncated to 0.073 ppm) is greater than 

0.070 ppm, even though the annual data 

completeness is less than 75% in one year 

and the 3-year average data completeness is 

less than 90% (i.e., design value would not 

otherwise be considered valid). 

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–—Review of New Sources 

and Modifications 

■ 8. Amend § 51.166 by adding 

paragraph (i)(11) to read as follows: 

§ 51.166 Prevention of significant 

deterioration of air quality. 

* * * * * 

(i) * * * 

(11) The plan may provide that the 

requirements of paragraph (k)(1) of this 

section shall not apply to a permit 

application for a stationary source or 

modification with respect to the revised 

national ambient air quality standards 

for ozone published on October 26, 2015 

if: 

(i) The reviewing authority has 

determined the permit application 

subject to this section to be complete on 

or before October 1, 2015. Instead, the 

requirements in paragraph (k)(1) of this 

section shall apply with respect to the 

national ambient air quality standards 

for ozone in effect at the time the 

reviewing authority determined the 

permit application to be complete; or 

(ii) The reviewing authority has first 

published before December 28, 2015 a 

public notice of a preliminary 

determination or draft permit 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 ozone 

in effect at the time of first publication 

of a public notice of the preliminary 

determination or draft permit. 

* * * * * 

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. Amend § 52.21 by adding paragraph 

(i)(12) to read as follows: 

§ 52.21 Prevention of significant 

deterioration of air quality. 

* * * * * 

(i) * * * 

(12) The requirements of paragraph 

(k)(1) of this section shall not apply to 

a permit application for a stationary 

source or modification with respect to 

the revised national ambient air quality 

standards for ozone published on 

October 26, 2015 if: 

(i) The Administrator has determined 

the permit application subject to this 

section to be complete on or before 

October 1, 2015. Instead, the 

requirements in paragraph (k)(1) of this 

section shall apply with respect to the 

national ambient air quality standards 

for ozone in effect at the time the 

Administrator determined the permit 

application to be complete; or 

(ii) The Administrator has first 

published before December 28, 2015 a 

public notice of a preliminary 

determination or draft permit 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 ozone 

in effect on the date the Administrator 

first published a public notice of a 

preliminary determination or draft 

permit. 

* * * * * 

PART 53—AMBIENT AIR MONITORING 

REFERENCE AND EQUIVALENT 

METHODS 

■ 10. The authority citation for part 53 

continues to read as follows: 

Authority: Sec. 301(a) of the Clean Air Act 

(42 U.S.C. 1857g(a)), as amended by sec. 

15(c)(2) of Pub. L. 91–604, 84 Stat. 1713, 

unless otherwise noted. 

Subpart A—General Provisions 

§ 53.9 [Amended] 

■ 11. Amend § 53.9 by removing 

paragraph (i). 

■ 12. Amend § 53.14 by revising 

paragraph (c) introductory text to read 

as follows: 

§ 53.14 Modification of a reference or 

equivalent method. 

* * * * * 

(c) Within 90 calendar days after 

receiving a report under paragraph (a) of 

this section, the Administrator will take 

one or more of the following actions: 

* * * * * 

Subpart B—Procedures for Testing 

Performance Characteristics of 

Automated Methods for SO2, CO, O3, 

and NO2

■ 13. Amend § 53.23 by revising 

paragraph (e)(1)(vi) to read as follows: 

§ 53.23 Test procedures. 

* * * * * 

(e) * * * 

(1) * * * 

(vi) Precision: Variation about the 

mean of repeated measurements of the 

same pollutant concentration, denoted 

as the standard deviation expressed as 

a percentage of the upper range 

limits.258

* * * * * 

■ 14. Revise Table B–1 to Subpart B of 

Part 53 to read as follows: 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65461 

TABLE B–1 TO

SUBPART B OF

PART 53—PERFORMANCE

LIMIT

SPECIFICATIONS FOR

AUTOMATED

METHODS

Performance parameter Units 1

SO2 O3 CO NO2

(Std. range) 

Definitions and test 

procedures Std. range 3 Lower range 2 3 Std. range 3 Lower range 2 3 Std. range 3 Lower range 2 3

1. Range ......................... ppm ............ 0–0.5 <0.5 0–0.5 <0.5 0–50 <50 0–0.5 Sec. 53.23(a) 2. Noise ........................... ppm ............ 0.001 0.0005 0.0025 0.001 0.2 0.1 0.005 Sec. 53.23(b) 3. Lower detectable limit ppm ............ 0.002 0.001 0.005 0.002 0.4 0.2 0.010 Sec. 53.23(c) 4. Interference equivalent 

Each interferent ....... ppm ............ ±0.005 4 ±0.005 ±0.005 ±0.005 ±1.0 ±0.5 ±0.02 Sec. 53.23(d) Total, all interferents ppm ............ – – – – – – 0.04 Sec. 53.23(d) 

5. Zero drift, 12 and 24 

hour.

ppm ............ ±0.004 ±0.002 ±0.004 ±0.002 ±0.5 ±0.3 ±0.02 Sec. 53.23(e) 

6. Span drift, 24 hour 

20% of upper range 

limit.

Percent ...... – – – – – – ±20.0 Sec. 53.23(e) 

80% of upper range 

limit.

Percent ...... ±3.0 ±3.0 ±3.0 ±3.0 ±2.0 ±2.0 ±5.0 Sec. 53.23(e) 

7. Lag time ...................... Minutes ...... 2 2 2 2 2.0 2.0 20 Sec. 53.23(e) 8. Rise time ..................... Minutes ...... 2 2 2 2 2.0 2.0 15 Sec. 53.23(e) 9. Fall time ...................... Minutes ...... 2 2 2 2 2.0 2.0 15 Sec. 53.23(e) 10. Precision 

20% of upper range 

limit.

– – – – – – Sec. 53.23(e) 

Percent 5 .... 2 2 2 2 1.0 1.0 4 Sec. 53.23(e) 

80% of upper range 

limit.

– – – – – – Sec. 53.23(e) 

Percent 5 .... 2 2 2 2 1.0 1.0 6 Sec. 53.23(e) 

Sec. 53.23(e) 

1To convert from parts per million (ppm) to μg/m3 at 25 °C and 760 mm Hg, multiply by M/0.02447, where M is the molecular weight of the gas. Percent means percent of the upper 

measurement range limit. 2Tests for interference equivalent and lag time do not need to be repeated for any lower range provided the test for the standard range shows that the lower range specification (if applicable) is met for each of these test parameters. 3For candidate analyzers having automatic or adaptive time constants or smoothing filters, describe their functional nature, and describe and conduct suitable tests to demonstrate their 

function aspects and verify that performances for calibration, noise, lag, rise, fall times, and precision are within specifications under all applicable conditions. For candidate analyzers with operator-selectable time constants or smoothing filters, conduct calibration, noise, lag, rise, fall times, and precision tests at the highest and lowest settings that are to be included in the FRM or FEM designation. 4For nitric oxide interference for the SO2 UVF method, interference equivalent is ±0.0003 ppm for the lower range. 5Standard deviation expressed as percent of the URL. 

mstockstill on DSK4VPTVN1PROD with RULES2


ER26OC15.010</GPH>mstockstill on DSK4VPTVN1PROD with RULES2

Table B-3 to Subpart B of Part 53-lnterferent Test Concentration/ Parts per M

(!) !-< 

!-< 0 0 ro "'0 (!) §< 

§ !-< ::cl ·s (!) (!) 

(!) N C) 0/JQ) (!) (!) (!) 0 (!) (!) > 

"5 :>, 0 0 8"'0 ,B:Q 0/J"'C o"C (!) (!) !-< 

!-< 

j 0 ...... C) .D ...... 

- (!) .

- (!) "'0"'0 "Ct;:1 - :><:: !-< :><:: ·c a - :>, ...... »- .g 0 

;:::1 .9 0 ...... N I 

0 

...... 

p.. ::r: g ::r: f;l if'J"'d z f.I.1 0 s u 

SOz Ultraviolet 5 0.1 4 0.14 0.5 0.5 0.5 0.2 20,000 

fluorescence 

SOz Flame photometric 0.01 4 0.14 750 3 20,000 50 SOz Gas 0.1 4 0.14 750 3 20,000 50 

chromatography 

SOz Spectrophotometric 0.2 0.1 0.1 4 0.14 0.5 750 0.5 

-wet chemical (pararosanaline) 

SOz Electrochemical 0.2 0.1 0.1 4 0.14 0.5 0.5 0.2 0.5 3 20,000 SOz Conductivity 0.2 0.1 4 0.14 0.5 750 SOz Spectrophotometric 4 0.14 0.5 0.5 0.2 

-gas phase, 

including DOAS 

03 Ethylene 0.1 750 20,000 

chemiluminescene 4 0.08 

03 0.1 0.5 750 4 0.08 20,000 

chemiluminescene 

03 Electrochemical 30.1 0.5 0.5 4 0.08 03 Spectrophotometric 30.1 0.5 0.5 0.5 4 0.08 

-wet chemical (potassium iodide) 

ER26OC15.011</GPH>mstockstill on DSK4VPTVN1PROD with RULES2

03 Spectrophotometric 0.5 0.5 0.5 4 0.08 0.02 20,000 

-gas phase, 

including 

ultraviolet 

absorption and 

DOAS 

co IN on-dispersive 750 20,000 4 10 

Infrared 

co Gas 20,000 4 10 

chromatography 

with flame 

ionization detector 

co Electrochemical 0.5 0.2 20,000 410 co Catalytic 0.1 750 0.2 20,000 4 10 

combustion-thermal detection 

co IR fluorescence 750 20,000 4 10 co Mercury 0.2 4 10 

replacement-UV 

photometric 

NOz Chemiluminescent 3 0.1 0.5 4 0.1 0.5 20,000 NOz Spectrophotometric 0.5 4 0.1 0.5 750 0.5 

-wet chemical (azo-dye reaction) 

NOz Electrochemical 0.2 30.1 0.5 4 0.1 0.5 750 0.5 20,000 50 NOz Spectrophotometric 30.1 0.5 4 0.1 0.5 0.5 20,000 50 

-gas phase 

ER26OC15.012</GPH>mstockstill on DSK4VPTVN1PROD with RULES2

1. Concentrations of interferents listed must be prepared and controlled to ± 10 percent of the stated value. 

2

· Analyzer types not listed will be considered by the Administrator as special cases. 

3

· Do not mix with the pollutant. 

4

· Concentration of pollutant used for test. These pollutant concentrations must be prepared to ±10 percent o

5

· If candidate method utilizes an elevated-temperature scrubber for removal of aromatic hydrocarbons, perfo

6

· If naphthalene test concentration cannot be accurately quantified, remove the scrubber, use a test concentr

scale response, reattach the scrubber, and evaluate response for interference. 

ER26OC15.013</GPH>mstockstill on DSK4VPTVN1PROD with RULES2

CALCULATION OF ZERO DRIFT, SPAN DRIFT, AND PRECISION 

Date 

--------

Applicant. __________________________ _ 

Pollutant 

-----

Analyzer __________________________ _ 

TEST 

PARAMETERS CALCULATIONS 

-

12 

HOUR 12ZD = Cmax - Cmin 

ZERO 

124 

Z = (L1 + L2)/2 

DRIFT 

HOUR IZ4ZD = Zn - Zn-1 

24ZD = Z' n -Z' n-1 

1 12 

Sn =6Lpi 

SPAN 124 S Sn- Sn 1 

DRIFT HOUR Dn = - X 100% Sn 1 

S -S' 

SDn = n -· n-1 X 100% 

20% 

URL Pzo =%STANDARD 

PREC- I /n \ DEVIATION OF (P1 .•. P6) 

lSI ON I --IV 

, Pso =%STANDARD 

DEVIATION OF (P7 .•. Pn) 

Figure B-5. Form for calculating zero drift, span drift, and precision(§ 53.23(e)). 
65466 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

* * * * * 

Subpart C—Procedures for 

Determining Comparability between 

Candidate Methods and Reference 

Methods 

■ 17. Amend § 53.32 by revising 

paragraph (g)(1)(iii) to read as follows: 

§ 53.32 Test procedures for methods for 

SO2, CO, O3, and NO2. 

* * * * * 

(g) * * * 

(1) * * * 

(iii) The measurements shall be made 

in the sequence specified in table C–2 

of this subpart. 

* * * * * 

Figure E–2 to Subpart E of Part 53 

[Removed] 

■ 18. Amend subpart E by removing 

figure E–2 to subpart E of part 53. 

PART 58—AMBIENT AIR QUALITY 

SURVEILLANCE 

■ 19. The authority citation for part 58 

continues to read as follows: 

Authority: 42 U.S.C. 7403, 7405, 7410, 

7414, 7601, 7611, 7614, and 7619. 

Subpart B—Monitoring Network 

■ 20. Amend § 58.10 by adding 

paragraphs (a)(9) through (11) to read as 

follows: 

§ 58.10 Annual monitoring network plan 

and periodic network assessment. 

(a) * * * 

(9) The annual monitoring network 

plan shall provide for the required O3

sites to be operating on the first day of 

the applicable required O3 monitoring 

season in effect on January 1, 2017 as 

listed in Table D–3 of appendix D of this 

part. 

(10) A plan for making Photochemical 

Assessment Monitoring Stations 

(PAMS) measurements, if applicable, in 

accordance with the requirements of 

appendix D paragraph 5(a) of this part 

shall be submitted to the EPA Regional 

Administrator no later than July 1, 2018. 

The plan shall provide for the required 

PAMS measurements to begin by June 1, 

2019. 

(11) An Enhanced Monitoring Plan for 

O3, if applicable, in accordance with the 

requirements of appendix D paragraph 

5(h) of this part shall be submitted to 

the EPA Regional Administrator no later 

than October 1, 2019 or two years 

following the effective date of a 

designation to a classification of 

Moderate or above O3 nonattainment, 

whichever is later. 

* * * * * 

■ 21. Section § 58.11 is amended by 

revising paragraph (c) to read as follows: 

§ 58.11 Network technical requirements. 

* * * * * 

(c) State and local governments must 

follow the network design criteria 

contained in appendix D to this part in 

designing and maintaining the SLAMS 

stations. The final network design and 

all changes in design are subject to 

approval of the Regional Administrator. 

NCore and STN network design and 

changes are also subject to approval of 

the Administrator. Changes in SPM 

stations do not require approvals, but a 

change in the designation of a 

monitoring site from SLAMS to SPM 

requires approval of the Regional 

Administrator. 

* * * * * 

■ 22. Amend § 58.13 by adding 

paragraphs (g) and (h) to read as follows: 

§ 58.13 Monitoring network completion. 

* * * * * 

(g) The O3 monitors required under 

appendix D, section 4.1 of this part must 

operate on the first day of the applicable 

required O3 monitoring season in effect 

January 1, 2017. 

(h) The Photochemical Assessment 

Monitoring sites required under 40 CFR 

part 58 Appendix D, section 5(a) must 

be physically established and operating 

under all of the requirements of this 

part, including the requirements of 

appendix A, C, D, and E of this part, no 

later than June 1, 2019. 

Subpart F—Air Quality Index Reporting 

■ 23. Amend § 58.50 by revising 

paragraph (c) to read as follows: 

§ 58.50 Index reporting. 

* * * * * 

(c) The population of a metropolitan 

statistical area for purposes of index 

reporting is the latest available U.S. 

census population. 

Subpart G—Federal Monitoring 

■ 24. Amend appendix D to part 58, 

under section 4, by revising section 

4.1(i) and table D–3 to appendix D of 

part 58, and by revising section 5 to read 

as follows: 

Appendix D to part 58—Network 

Design Criteria for Ambient Air Quality 

Monitoring 

* * * * * 

4. Pollutant-Specific Design Criteria for 

SLAMS Sites 

* * * * * 

4.1 * * * 

(i) Ozone monitoring is required at SLAMS 

monitoring sites only during the seasons of 

the year that are conducive to O3 formation 

(i.e., ‘‘ozone season’’) as described below in 

Table D–3 of this appendix. These O3 seasons 

are also identified in the AQS files on a stateby-state basis. Deviations from the O3

monitoring season must be approved by the 

EPA Regional Administrator. These requests 

will be reviewed by Regional Administrators 

taking into consideration, at a minimum, the 

frequency of out-of-season O3 NAAQS 

exceedances, as well as occurrences of the 

Moderate air quality index level, regional 

consistency, and logistical issues such as site 

access. Any deviations based on the Regional 

Administrator’s waiver of requirements must 

be described in the annual monitoring 

network plan and updated in AQS. Changes 

to the O3 monitoring season requirements in 

Table D–3 revoke all previously approved 

Regional Administrator waivers. Requests for 

monitoring season deviations must be 

accompanied by relevant supporting 

information. Information on how to analyze 

O3 data to support a change to the O3 season 

in support of the 8-hour standard for the 

entire network in a specific state can be 

found in reference 8 to this appendix. Ozone 

monitors at NCore stations are required to be 

operated year-round (January to December). 

TABLE D–3 1 TO APPENDIX D OF PART 58. OZONE MONITORING SEASON BY STATE

State Begin Month End Month 

Alabama .................................................................................................. March ............................................. October. 

Alaska ...................................................................................................... April ................................................ October. 

Arizona .................................................................................................... January .......................................... December. 

Arkansas .................................................................................................. March ............................................. November. 

California ................................................................................................. January .......................................... December. 

Colorado .................................................................................................. January .......................................... December. 

Connecticut .............................................................................................. March ............................................. September. 

Delaware ................................................................................................. March ............................................. October. 

District of Columbia ................................................................................. March ............................................. October. 

mstockstill on DSK4VPTVN1PROD with RULES2

Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 65467 

TABLE D–3 1 TO APPENDIX D OF PART 58. OZONE MONITORING SEASON BY STATE—Continued 

State Begin Month End Month 

Florida ...................................................................................................... January .......................................... December. 

Georgia .................................................................................................... March ............................................. October. 

Hawaii ...................................................................................................... January .......................................... December. 

Idaho ........................................................................................................ April ................................................ September. 

Illinois ....................................................................................................... March ............................................. October. 

Indiana ..................................................................................................... March ............................................. October. 

Iowa ......................................................................................................... March ............................................. October. 

Kansas ..................................................................................................... March ............................................. October. 

Kentucky .................................................................................................. March ............................................. October. 

Louisiana (Northern) AQCR 019, 022 ..................................................... March ............................................. October. 

Louisiana (Southern) AQCR 106 ............................................................ January .......................................... December. 

Maine ....................................................................................................... April ................................................ September. 

Maryland .................................................................................................. March ............................................. October. 

Massachusetts ......................................................................................... March ............................................. September. 

Michigan .................................................................................................. March ............................................. October. 

Minnesota ................................................................................................ March ............................................. October. 

Mississippi ............................................................................................... March ............................................. October. 

Missouri ................................................................................................... March ............................................. October. 

Montana ................................................................................................... April ................................................ September. 

Nebraska ................................................................................................. March ............................................. October. 

Nevada .................................................................................................... January .......................................... December. 

New Hampshire ....................................................................................... March ............................................. September. 

New Jersey .............................................................................................. March ............................................. October. 

New Mexico ............................................................................................. January .......................................... December. 

New York ................................................................................................. March ............................................. October. 

North Carolina ......................................................................................... March ............................................. October. 

North Dakota ........................................................................................... March ............................................. September. 

Ohio ......................................................................................................... March ............................................. October. 

Oklahoma ................................................................................................ March ............................................. November. 

Oregon ..................................................................................................... May ................................................ September. 

Pennsylvania ........................................................................................... March ............................................. October. 

Puerto Rico .............................................................................................. January .......................................... December. 

Rhode Island ........................................................................................... March ............................................. September. 

South Carolina ......................................................................................... March ............................................. October. 

South Dakota ........................................................................................... March ............................................. October. 

Tennessee ............................................................................................... March ............................................. October. 

Texas (Northern) AQCR 022, 210, 211, 212, 215, 217, 218 ................. March ............................................. November. 

Texas (Southern) AQCR 106, 153, 213, 214, 216 ................................. January .......................................... December. 

Utah ......................................................................................................... January .......................................... December. 

Vermont ................................................................................................... April ................................................ September. 

Virginia ..................................................................................................... March ............................................. October. 

Washington .............................................................................................. May ................................................ September. 

West Virginia ........................................................................................... March ............................................. October. 

Wisconsin ................................................................................................ March ............................................. October 15. 

Wyoming .................................................................................................. January .......................................... September. 

American Samoa ..................................................................................... January .......................................... December. 

Guam ....................................................................................................... January .......................................... December. 

Virgin Islands ........................................................................................... January .......................................... December. 

1The required O3 monitoring season for NCore stations is January through December. 

* * * * * 

5. Network Design for Photochemical 

Assessment Monitoring Stations (PAMS) and 

Enhanced Ozone Monitoring 

(a) State and local monitoring agencies are 

required to collect and report PAMS 

measurements at each NCore site required 

under paragraph 3(a) of this appendix located 

in a CBSA with a population of 1,000,000 or 

more, based on the latest available census 

figures. 

(b) PAMS measurements include: 

(1) Hourly averaged speciated volatile 

organic compounds (VOCs); 

(2) Three 8-hour averaged carbonyl 

samples per day on a 1 in 3 day schedule, 

or hourly averaged formaldehyde; 

(3) Hourly averaged O3; 

(4) Hourly averaged nitrogen oxide (NO), 

true nitrogen dioxide (NO2), and total 

reactive nitrogen (NOy); 

(5) Hourly averaged ambient temperature; 

(6) Hourly vector-averaged wind direction; 

(7) Hourly vector-averaged wind speed; 

(8) Hourly average atmospheric pressure; 

(9) Hourly averaged relative humidity; 

(10) Hourly precipitation; 

(11) Hourly averaged mixing-height; 

(12) Hourly averaged solar radiation; and 

(13) Hourly averaged ultraviolet radiation. 

(c) The EPA Regional Administrator may 

grant a waiver to allow the collection of 

required PAMS measurements at an 

alternative location where the monitoring 

agency can demonstrate that the alternative 

location will provide representative data 

useful for regional or national scale modeling 

and the tracking of trends in O3 precursors. 

The alternative location can be outside of the 

CBSA or outside of the monitoring agencies 

jurisdiction. In cases where the alternative 

location crosses jurisdictions the waiver will 

be contingent on the monitoring agency 

responsible for the alternative location 

including the required PAMS measurements 

in their annual monitoring plan required 

under § 58.10 and continued successful 

collection of PAMS measurements at the 

alternative location. This waiver can be 

revoked in cases where the Regional 

Administrator determines the PAMS 

measurements are not being collected at the 

alternate location in compliance with 

paragraph (b) of this section. 

(d) The EPA Regional Administrator may 

grant a waiver to allow speciated VOC 

measurements to be made as three 8-hour 

averages on every third day during the PAMS 

mstockstill on DSK4VPTVN1PROD with RULES2

65468 Federal Register / Vol. 80, No. 206 / Monday, October 26, 2015 / Rules and Regulations 

season as an alternative to 1-hour average 

speciated VOC measurements in cases where 

the primary VOC compounds are not well 

measured using continuous technology due 

to low detectability of the primary VOC 

compounds or for logistical and other 

programmatic constraints. 

(e) The EPA Regional Administrator may 

grant a waiver to allow representative 

meteorological data from nearby monitoring 

stations to be used to meet the meteorological 

requirements in paragraph 5(b) where the 

monitoring agency can demonstrate the data 

is collected in a manner consistent with EPA 

quality assurance requirements for these 

measurements. 

(f) The EPA Regional Administrator may 

grant a waiver from the requirement to 

collect PAMS measurements in locations 

where CBSA-wide O3 design values are equal 

to or less than 85% of the 8-hour O3 NAAQS 

and where the location is not considered by 

the Regional Administrator to be an 

important upwind or downwind location for 

other O3 nonattainment areas. 

(g) At a minimum, the monitoring agency 

shall collect the required PAMS 

measurements during the months of June, 

July, and August. 

(h) States with Moderate and above 8-hour 

O3 nonattainment areas and states in the 

Ozone Transport Region as defined in 40 CFR 

51.900 shall develop and implement an 

Enhanced Monitoring Plan (EMP) detailing 

enhanced O3 and O3 precursor monitoring 

activities to be performed. The EMP shall be 

submitted to the EPA Regional Administrator 

no later than October 1, 2019 or two years 

following the effective date of a designation 

to a classification of Moderate or above O3

nonattainment, whichever is later. At a 

minimum, the EMP shall be reassessed and 

approved as part of the 5-year network 

assessments required under 40 CFR 58.10(d). 

The EMP will include monitoring activities 

deemed important to understanding the O3

problems in the state. Such activities may 

include, but are not limited to, the following: 

(1) Additional O3 monitors beyond the 

minimally required under paragraph 4.1 of 

this appendix, 

(2) Additional NOX or NOy monitors 

beyond those required under 4.3 of this 

appendix, 

(3) Additional speciated VOC 

measurements including data gathered 

during different periods other than required 

under paragraph 5(g) of this appendix, or 

locations other than those required under 

paragraph 5(a) of this appendix, and 

(4) Enhanced upper air measurements of 

meteorology or pollution concentrations. 

* * * * * 

■ 25. Appendix G of Part 58 is amended 

by revising table 2 to read as follows: 

Appendix G to Part 58—Uniform Air 

Quality Index (AQI) and Daily 

Reporting 

* * * * * 

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 

0.000–0.054 — 0.0—12.0 0–54 0.0–4.4 0–35 0–53 0–50 Good. 

0.055–0.070 — 12.1—35.4 55–154 4.5–9.4 36–75 54–100 51–100 Moderate. 

0.071–0.085 0.125–0.164 35.5—55.4 155–254 9.5–12.4 76–185 101–360 101–150 Unhealthy for 

Sensitive 

Groups. 

0.086–0.105 0.165–0.204 3 55.5—150.4 255–354 12.5–15.4 4 186–304 361–649 151–200 Unhealthy. 

0.106–0.200 0.205–0.404 3 150.5—250.4 355–424 15.5–30.4 4 305–604 650–1249 201–300 Very 

Unhealthy. 

0.201-(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 > 301 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 concentration. 

[FR Doc. 2015–26594 Filed 10–23–15; 8:45 am] 

BILLING CODE 6560–50–P 

mstockstill on DSK4VPTVN1PROD with RULES2