Vol. 80 Monday, 

No. 55 March 23, 2015 

Part III 

Environmental Protection Agency 

40 CFR Parts 50, 51, and 93 

Fine Particulate Matter National Ambient Air Quality Standards: State 

Implementation Plan Requirements; Proposed Rule 

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15340 Federal Register / Vol. 80, No. 55 / Monday, March 23, 2015 / Proposed Rules 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Parts 50, 51, and 93 

[EPA–HQ–OAR–2013–0691; FRL–9916–08– 

OAR] 

RIN 2060–AQ48 

Fine Particulate Matter National 

Ambient Air Quality Standards: State 

Implementation Plan Requirements 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Proposed rule. 

SUMMARY: The Environmental Protection 

Agency (EPA) is proposing requirements 

that state, local and tribal air agencies 

would have to meet as they implement 

the current and future national ambient 

air quality standards (NAAQS) for fine 

particulate matter (PM2.5). Specifically, 

this notice provides details on how the 

EPA proposes that air agencies meet the 

statutory state implementation plan 

(SIP) requirements that apply to areas 

designated nonattainment for any PM2.5

NAAQS, such as: general requirements 

for attainment plan due dates and 

attainment dates; emissions inventories; 

attainment demonstrations; provisions 

for demonstrating reasonable further 

progress; quantitative milestones; 

contingency measures; and 

nonattainment New Source Review 

(NNSR) permitting programs, among 

other things. This proposed rule 

clarifies the specific attainment 

planning requirements that would apply 

to PM2.5 NAAQS nonattainment areas 

based on their classification (either 

Moderate or Serious), and the process 

for reclassifying Moderate areas to 

Serious. Additionally in this notice, the 

EPA is proposing to revoke the 1997 

primary annual standard because the 

EPA revised the primary annual 

standard in 2012. The EPA first 

established the PM2.5 NAAQS in 1997, 

completed a review of those standards 

in 2006, and most recently completed a 

review of the PM2.5 NAAQS on 

December 14, 2012. 

DATES: Comments. Comments must be 

received on or before May 22, 2015. 

Public Hearing. The EPA plans to hold 

one public hearing concerning the 

proposed rule in Washington, DC. The 

date, time and location will be 

announced separately. Please refer to 

SUPPLEMENTARY INFORMATION for 

additional information on the comment 

period and the public hearing. 

Information Collection Request. Under 

the Paperwork Reduction Act (PRA), 

comments on the information collection 

provisions are best assured of having 

full effect if the Office of Management 

and Budget (OMB) receives a copy of 

your comments on or before April 22, 

2015. 

ADDRESSES: Submit your comments, 

identified by Docket ID No. EPA–HQ– 

OAR–2013–0691, by one of the 

following methods: 

• http://www.regulations.gov. Follow 

the on-line instructions for submitting 

comments. 

• Email: a-and-r-docket@epa.gov. 

• Mail: Air and Radiation Docket and 

Information Center, Attention Docket ID 

No. EPA–HQ–OAR–2013–0691, 

Environmental Protection Agency, 

Mailcode: 28221T, 1200 Pennsylvania 

Avenue NW., Washington, DC 20460. In 

addition, please mail a copy of your 

comments on the information collection 

(ICR) provisions to the Office of 

Information and Regulatory Affairs, 

Office of Management and Budget 

(OMB), Attn: Desk Officer for EPA, 725 

17th Street NW., Washington, DC 20503. 

• Hand Delivery: Air and Radiation 

Docket and Information Center, 

Attention Docket ID No. EPA–HQ– 

OAR–2013–0691, Environmental 

Protection Agency in the EPA 

Headquarters Library, Room No. 3334 in 

the EPA Docket Center, located at 

William Jefferson Clinton Building 

West, 1301 Constitution Avenue NW., 

Washington, DC 20004. Such deliveries 

are only accepted during the Docket’s 

normal hours of operation, and special 

arrangements should be made for 

delivery of boxed information. 

Instructions: Direct your comments to 

Docket ID No. EPA–HQ–OAR–2013– 

0691. The EPA’s policy is that all 

comments received will be included in 

the public docket without change and 

may be made available online at http:// 

www.regulations.gov, including any 

personal information provided, unless 

the comment includes information 

claimed to be Confidential Business 

Information (CBI) or other information 

whose disclosure is restricted by statute. 

Do not submit information that you 

consider to be CBI or otherwise 

protected through http://

www.regulations.gov or email. The 

http://www.regulations.gov Web site is 

an ‘‘anonymous access’’ system, which 

means the EPA will not know your 

identity or contact information unless 

you provide it in the body of your 

comment. If you send an email 

comment directly to the EPA without 

going through http://

www.regulations.gov, your email 

address will be automatically captured 

and included as part of the comment 

that is placed in the public docket and 

made available on the Internet. If you 

submit an electronic comment, the EPA 

recommends that you include your 

name and other contact information in 

the body of your comment and with any 

disk or CD–ROM you submit. If the EPA 

cannot read your comment due to 

technical difficulties and cannot contact 

you for clarification, the EPA may not 

be able to consider your comment. 

Electronic files should avoid the use of 

special characters, any form of 

encryption and be free of any defects or 

viruses. For additional information 

about the EPA’s public docket visit the 

EPA Docket Center homepage at http:// 

www.epa.gov/epahome/dockets.htm. 

For additional instructions on 

submitting comments, go to the 

SUPPLEMENTARY INFORMATION section of 

this document. 

Docket: All documents in the docket 

are listed in the http://

www.regulations.gov index. Although 

listed in the index, some information is 

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

information whose disclosure is 

restricted by statute. Certain other 

material, such as copyrighted material, 

will be publicly available only in hard 

copy. Publicly available docket 

materials are available either 

electronically in http://

www.regulations.gov or in hard copy at 

the Air and Radiation Docket and 

Information Center in the EPA 

Headquarters Library, Room No. 3334 in 

the William Jefferson Clinton Building 

West, located at 1301 Constitution 

Avenue NW., Washington, DC 20460. 

The Public Reading Room is open from 

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

Friday, excluding legal holidays. The 

phone number for the Public Reading 

Room is (202) 566–1744. 

FOR FURTHER INFORMATION CONTACT: For 

general information on this proposed 

rule, contact Mr. Rich Damberg, Office 

of Air Quality Planning and Standards, 

U.S. Environmental Protection Agency, 

by phone at (919) 541–5592 or by email 

at damberg.rich@epa.gov; or Ms. Megan 

Brachtl, Office of Air Quality Planning 

and Standards, U.S. Environmental 

Protection Agency, by phone at (919) 

541–2648 or by email at brachtl.megan@

epa.gov. For information on the public 

hearing, contact Ms. Pamela Long, 

Office of Air Quality Planning and 

Standards, U.S. Environmental 

Protection Agency, by phone at (919) 

541–0641 or by email at long.pam@

epa.gov. For information on the ICR, 

contact Mr. Butch Stackhouse, Office of 

Air Quality Planning and Standards, 

U.S. Environmental Protection Agency, 

by phone at (919) 541–5208 or by email 

at stackhouse.butch@epa.gov. 

SUPPLEMENTARY INFORMATION: 

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Federal Register / Vol. 80, No. 55 / Monday, March 23, 2015 / Proposed Rules 15341 

I. General Information 

A. Preamble Glossary of Terms and 

Acronyms 

The following are abbreviations of 

terms used in the preamble. 

AERR Air Emissions Reporting Rule 

BACM Best Available Control Measures 

BACT Best Available Control Technology 

BART Best Available Retrofit Technology 

BC Black Carbon 

CAA Clean Air Act 

CAIR Clean Air Interstate Rule 

CAMx Comprehensive Air Quality Model 

with Extensions 

CBI Confidential Business Information 

CBSA Core-based Statistical Area 

CDD Clean Data Determination 

CFR Code of Federal Regulations 

CMAQ Community Multi-Scale Air Quality 

Model 

CSAPR Cross-State Air Pollution Rule 

CSN Chemical Speciation Network 

DOD Department of Defense 

DOT Department of Transportation 

EC Elemental Carbon 

EGU Electric Generating Unit 

EPA Environmental Protection Agency 

Fe Iron 

FEM Federal Equivalent Method 

FIP Federal Implementation Plan 

FRM Federal Reference Method 

HCl Hydrogen Chloride 

ICR Information Collection Request 

LAER Lowest Achievable Emission Rate 

MACT Maximum Achievable Control 

Technology 

MATS Mercury and Air Toxics Standards 

MSM Most Stringent Measures 

MPO Metropolitan Planning Organization 

NAAQS National Ambient Air Quality 

Standards 

NAICS North American Industry 

Classification System 

NAPAP National Acid Precipitation 

Assessment Program 

NEI National Emissions Inventory 

NESHAP National Emissions Standard for 

Hazardous Air Pollutants 

NH3 Ammonia 

NH4 Ammonium 

NH4NO3 Ammonium Nitrate 

NH4HSO4 Ammonium Bi-Sulfate 

(NH4)2SO4 Ammonium Sulfate 

NNSR Nonattainment New Source Review 

NOX Nitrogen Oxides 

NO3 Nitrate 

NSPS New Source Performance Standards 

O3 Ozone 

OM Organic Mass 

OMB Office of Management and Budget 

PM Particulate Matter 

PM2.5 Particulate Matter Equal to or Less 

than 2.5 Microns in Diameter (Fine 

Particulate Matter) 

PM10 Particulate Matter Equal to or Less 

than 10 Microns in Diameter 

PRA Paperwork Reduction Act 

PSD Prevention of Significant Deterioration 

RACM Reasonably Available Control 

Measures 

RACT Reasonably Available Control 

Technology 

RFP Reasonable Further Progress 

RICE Reciprocating Internal Combustion 

Engines 

SIP State Implementation Plan 

SOA Secondary Organic Aerosols 

SO2 Sulfur Dioxide 

SO4 Sulfate 

TAR Tribal Authority Rule 

TIP Tribal Implementation Plan 

TIP Transportation Improvement Program 

TSP Total Suspended Particles 

mm Micrometer (Micron) 

VMT Vehicle Miles Traveled 

VOC Volatile Organic Compounds 

B. Does this action apply to me? 

Entities potentially affected directly 

by this proposed rule include state, 

local and tribal governments and air 

pollution control agencies responsible 

for attainment and maintenance of the 

NAAQS. Entities potentially affected 

indirectly by this proposed rule as 

regulated sources include owners and 

operators of sources that emit PM2.5, 

sulfur dioxide (SO2), oxides of nitrogen 

(NOX), volatile organic compounds 

(VOC) and/or ammonia (NH3). Others 

potentially affected indirectly by this 

proposed rule include members of the 

general public who live, work, or 

recreate in areas affected by elevated 

ambient PM2.5 levels in areas designated 

nonattainment for a PM2.5 NAAQS. 

C. What should I consider as I prepare 

my comments for the EPA? 

1. Submitting CBI. Do not submit this 

information to the EPA through http:// 

www.regulations.gov or email. Clearly 

mark the specific information that you 

claim to be CBI. For CBI in a disk or 

CD–ROM that you mail to the EPA, 

mark the outside of the disk or CD–ROM 

as CBI and then identify electronically 

within the disk or CD–ROM the specific 

information that is claimed as CBI. In 

addition to one complete version of the 

comment that includes information 

claimed as CBI, a copy of the comment 

that does not contain the information 

claimed as CBI must be submitted for 

inclusion in the public docket. 

Information so marked will not be 

disclosed except in accordance with 

procedures set forth in 40 CFR part 2. 

2. Tips for preparing comments. 

When submitting comments, remember 

to: 

• Identify the rulemaking by docket 

number and other identifying 

information (subject heading, Federal 

Register date and page number). 

• Follow directions. The proposed 

rule may ask you to respond to specific 

questions or organize comments by 

referencing a Code of Federal 

Regulations (CFR) part or section 

number. 

• Explain why you agree or disagree, 

suggest alternatives and substitute 

language for your requested changes. 

• Describe any assumptions and 

provide any technical information and/ 

or data that you used to support your 

comment. 

• If you estimate potential costs or 

burdens, explain how you arrived at 

your estimate in sufficient detail to 

allow for it to be reproduced. 

• Provide specific examples to 

illustrate your concerns wherever 

possible, and suggest alternatives. 

• Explain your views as clearly as 

possible, avoiding the use of profanity 

or personal threats. 

• Make sure to submit your 

comments by the comment period 

deadline identified. 

D. What information should I know 

about possible public hearings? 

For information pertaining to the one 

public hearing on this document, 

contact Ms. Pamela Long, Air Quality 

Policy Division, Office of Air Quality 

Planning and Standards (C504–03), 

Environmental Protection Agency, 

Research Triangle Park, North Carolina 

27711; telephone number (919) 541– 

0641; fax number (919) 541–5509; email 

address: long.pam@epa.gov. 

E. Where can I obtain a copy of this 

document and other related 

information? 

In addition to being available in the 

docket, an electronic copy of this 

Federal Register document will be 

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

airquality/particlepollution/

actions.html. 

F. How is this Federal Register 

document organized? 

The information presented in this 

document is organized as follows: 

I. General Information 

A. Preamble Glossary of Terms and 

Acronyms 

B. Does this action apply to me? 

C. What should I consider as I prepare my 

comments for the EPA? 

D. What information should I know about 

possible public hearings? 

E. Where can I obtain a copy of this 

document and other related information? 

F. How is this Federal Register document 

organized? 

II. Background for Proposal 

A. Introduction 

B. Atmospheric Chemistry of PM2.5 and Its 

Precursors 

C. Historical Overview of PM2.5 NAAQS 

Setting and Implementation 

D. State Implementation Planning Process 

for PM2.5 NAAQS 

III. What is the EPA proposing with respect 

to the treatment of PM2.5 precursors in 

nonattainment area planning and 

permitting? 

A. Background 

B. Proposed Precursor Policy Options 

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15342 Federal Register / Vol. 80, No. 55 / Monday, March 23, 2015 / Proposed Rules 

1For a complete discussion of the human health 

and welfare effects associated with exposure to 

elevated concentrations of particulate matter, see 

generally ‘‘Integrated Science Assessment for 

Particulate Matter.’’ U.S. Environmental Protection 

Agency, Office of Research and Development, 

National Center for Environmental Assessment-RTP 

Division, February 10, 2010. EPA/600/R–08/139F. 

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

standards/pm/s_pm_2007_isa.html. See Chapter 2. 

2 78 FR 3086 (January 15, 2013). 

C. Technical Approaches for 

Demonstrating That a Precursor Does Not 

Need To Be Subject to Control 

Requirements 

IV. What are the EPA’s proposed 

requirements for Moderate area 

attainment plans? 

A. Plan Due Dates 

B. Emissions Inventory Requirements 

C. Pollutants To Be Addressed in the Plan 

D. Attainment Plan Control Strategy 

E. Modeling for Attainment 

Demonstrations 

F. RFP Requirements 

G. Quantitative Milestones 

H. Contingency Measures 

I. Attainment Dates 

J. Attainment Date Extensions 

V. How would a PM2.5 Moderate 

nonattainment area be reclassified to 

Serious? 

A. Discretionary Authority 

B. Mandatory Duty 

VI. What are the EPA’s proposed 

requirements for Serious area attainment 

plans? 

A. Plan Due Dates 

B. Emissions Inventory Requirements 

C. Pollutants To Be Addressed in the Plan 

D. Attainment Plan Control Strategy 

E. Modeling for Attainment 

Demonstrations 

F. RFP Requirements 

G. Quantitative Milestones 

H. Contingency Measures 

I. Attainment Dates 

J. Attainment Date Extensions 

VII. What are the EPA’s proposed 

requirements for attainment plans under 

CAA section 189(d) for Serious areas that 

fail to attain the NAAQS by the 

applicable attainment date? 

A. Plan Due Dates 

B. Emissions Inventory Requirements 

C. Pollutants To Be Addressed in the Plan 

D. Attainment Plan Control Strategy 

E. Modeling for Attainment 

Demonstrations 

F. RFP Requirements 

G. Quantitative Milestones 

H. Contingency Measures 

I. Attainment Dates 

VIII. What are the EPA’s proposed NNSR 

permitting requirements? 

A. Statutory Requirements for NSR 

B. Federal NNSR Regulations 

C. What changes is the EPA proposing for 

NNSR for PM2.5 nonattainment areas? 

D. Plan Due Dates 

E. Avoidance of Dual Review for PSD and 

NNSR for PM2.5

IX. What other proposed requirements would 

apply in PM2.5 nonattainment areas? 

A. Waivers Under Section 188(f) 

B. Conformity Requirements 

C. Clean Data Policy 

D. Section 179B/International Border Areas 

E. Enforcement and Compliance 

F. Efforts To Encourage a Multi-Pollutant 

Approach When Developing PM2.5

Attainment Plans 

G. Measures to Ensure Appropriate 

Protections for Overburdened 

Populations 

H. Tribal Issues 

I. Voluntary Programs for Reducing 

Ambient PM2.5

J. Improved Stationary Source Emissions 

Monitoring 

K. Stationary Source Test Methods for 

Emissions of Condensable PM2.5

X. What is the EPA proposing with respect 

to revoking the 1997 primary annual 

PM2.5 NAAQS? 

A. Background 

B. History of Revocation of Other NAAQS 

C. Proposed Options for Revocation and 

Related Anti-Backsliding Requirements 

for the 1997 Primary Annual PM2.5

NAAQS 

D. Discussion of Options 

XI. Environmental Justice Considerations 

XII. Statutory and Executive Order Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

B. Paperwork Reduction Act 

C. Regulatory Flexibility Act 

D. Unfunded Mandates Reform Act 

E. Executive Order 13132: Federalism 

F. Executive Order 13175: Consultation 

and Coordination with Indian Tribal 

Governments 

G. Executive Order 13045: Protection of 

Children from Environmental Health and 

Safety Risks 

H. Executive Order 13211: Actions 

Concerning Regulations 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. Determination Under Section 307(d) 

Statutory Authority 

List of Subjects 

II. Background for Proposal 

A. Introduction 

Ambient, or outdoor, air can contain 

a variety of pollutants, including 

particulate matter (PM). Airborne PM 

can be comprised of either solid or 

liquid particles, and can be a complex 

mixture of particles in both solid and 

liquid form. The most common 

constituents of airborne PM include: 

sulfate (SO4); nitrate (NO3); ammonium 

(NH4); elemental carbon (EC); organic 

mass (OM); and inorganic material, 

generally referred to as ‘‘crustal’’ 

material, which can include metals, 

dust, sea salt and other trace elements. 

Airborne PM can be of different sizes, 

commonly referred to as ‘‘coarse’’ and 

‘‘fine’’ particles. Fine particles, in 

general terms, are particulate matter 

with an aerodynamic diameter less than 

or equal to a nominal 2.5 micrometers 

(mm). For this reason, particles of this 

size are referred to as PM2.5. PM2.5

particles commonly include ‘‘primary’’ 

particles and ‘‘secondary’’ particles. 

Primary particles, or direct PM2.5, are 

emitted by sources directly into the air 

as solid or liquid particles (e.g., 

elemental carbon from diesel engines or 

wildfires, or condensable organic 

particles from gasoline engines). 

Secondary particles are formed in the 

atmosphere as a result of chemical 

reactions between specific pollutants 

known as PM2.5 precursors (e.g., 

reactions between NOX and SO2

emissions from mobile and stationary 

sources combined with ammonia to 

form NO3 and SO4). 

The human health effects associated 

with long- or short-term exposure to 

PM2.5 are significant and include 

premature mortality, aggravation of 

respiratory and cardiovascular disease 

(as indicated by increased hospital 

admissions and emergency room visits) 

and development of chronic respiratory 

disease. In addition, welfare effects 

associated with elevated PM2.5 levels 

include visibility impairment as well as 

effects on sensitive ecosystems, 

materials damage and soiling and 

climatic and radiative processes.1

On December 14, 2012, the EPA made 

revisions to the suite of NAAQS for PM 

to provide requisite protection of public 

health and welfare with an adequate 

margin of safety. The EPA also made 

corresponding revisions to the data 

handling conventions for PM and the 

ambient air monitoring, reporting and 

network design requirements for PM. 

Specifically, the agency revised the 

primary annual PM2.5 standard by 

lowering the level from 15.0 to 12.0 mg/ 

m3 to provide increased protection 

against health effects associated with 

long- and short-term PM2.5 exposures. 

The EPA did not revise the secondary 

annual PM2.5 standard which remains at 

15.0 mg/m3.2 The EPA eliminated spatial 

averaging as part of the form of the 

PM2.5 annual standards to avoid 

potential disproportionate impacts on 

at-risk populations. In addition, the EPA 

retained the level and form of the 

primary and secondary 24-hour PM2.5

standards to continue to provide 

supplemental protection against health 

effects associated with short-term PM2.5

exposures. Although not directly 

relevant to this rulemaking with respect 

to the PM2.5 NAAQS, it should be noted 

that in December 2012, the EPA also did 

not revise the level or form of the 

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Federal Register / Vol. 80, No. 55 / Monday, March 23, 2015 / Proposed Rules 15343 

3This proposed rulemaking is to develop 

implementation regulations with respect to the 

PM2.5 NAAQS. For the PM10 NAAQS, states and the 

EPA will continue to implement those NAAQS in 

accordance with the applicable statutory 

requirements of the Clean Air Act (CAA) and the 

EPA’s existing guidance in the ‘‘The General 

Preamble for Implementation of Title I of the Clean 

Air Act (CAA) Amendments,’’ 57 FR 13498 (April 

16, 1992); and ‘‘State Implementation Plans for 

Serious PM–10 Nonattainment Areas: Addendum to 

the General Preamble for the Implementation of 

Title I of the Clean Air Act (CAA) Amendments,’’ 

59 FR 41998 (August 16, 1994). Throughout this 

preamble, these documents will be referred to as the 

‘‘General Preamble’’ and the ‘‘Addendum,’’ 

respectively. 

4 ‘‘Regulatory Impact Analysis for the Final 

Revisions to the National Ambient Air Quality 

Standards for Particulate Matter.’’ U.S. 

Environmental Protection Agency, Office of Air 

Quality and Planning Standards, Health and 

Environmental Impacts Division, February 28, 2013. 

EPA–452/R–12–005. See: http://www.epa.gov/ttn/

naaqs/standards/pm/s_pm_2007_ria.html. 

5 Ibid. 

6The regulatory definition of PM2.5 includes 

particles with an upper 50 percent cut-point of 

2.5mm aerodynamic diameter (the 50 percent cutpoint diameter is the diameter at which the sample 

collects 50 percent of the particles and rejects 50 

percent of the particles). PM2.5 particles have a 

penetration curve as measured by a reference 

method based on Appendix L of 40 CFR part 50 and 

designated in accordance with 40 CFR part 53, by 

an equivalent method designed in accordance with 

40 CFR part 53, or by an approved regional method 

designated in accordance with Appendix C of 40 

CFR part 58. 

7Certain commercial or industrial activities 

involving high temperature processes (e.g., fuel 

combustion, metal processing, cooking operations) 

emit gaseous pollutants into the ambient air which 

rapidly condense into particle form. These 

‘‘condensable’’ PM emissions exist almost entirely 

in the 2.5 or less micron range and can consist of 

organic material, sulfuric acid and metals. 

8Seinfeld J.H. and Pandis S.N., 2006. 

Atmospheric Chemistry and Physics: From Air 

Pollution to Climate Change. 2nd edition, J. Wiley, 

New York. 

9U.S. Environmental Protection Agency, 2004. 

‘‘The Particle Pollution Report: Current 

Understanding of Air Quality and Emissions 

through 2003.’’ Office of Air Quality Planning and 

Standards, Emissions, Monitoring, and Analysis 

Division, December 2004. Available at: http://

www.epa.gov/airtrends/reports.html. 

primary and secondary 24-hour PM10

standards, which remain at 150 mg/m3.3

Estimates show that attainment of the 

primary PM2.5 standards will result in 

hundreds fewer premature deaths each 

year, prevent tens of thousands of 

hospital admissions each year and 

prevent hundreds of thousands of 

doctor visits, absences from work and 

school and respiratory illnesses in 

children annually.4 Attainment of the 

primary PM2.5 standards will have 

welfare co-benefits in addition to direct 

human health benefits. The term welfare 

co-benefits covers both environmental 

and societal benefits of reducing 

pollution, such as reductions in 

visibility impairment, materials damage 

and ecosystem damage.5

B. Atmospheric Chemistry of PM2.5 and 

Its Precursors 

1. Overview 

In order to determine how to regulate 

sources of direct PM2.5 and PM2.5

precursors to attain the PM2.5 NAAQS in 

a given nonattainment area, it is 

necessary to understand the basic 

chemical processes that cause or 

contribute to the formation of ambient 

PM2.5. Accordingly, an understanding of 

these processes is necessary to design 

appropriate regulations for 

implementation of the PM2.5 NAAQS. 

Properly designed regulatory 

requirements will help to assure that the 

PM2.5 NAAQS are attained effectively 

and expeditiously in all areas. 

As noted earlier, the term PM2.5 refers 

to particles of solid and liquid material 

less than 2.5 microns in aerodynamic 

diameter.6 ‘‘Primary’’ PM2.5 is emitted 

directly from emissions sources or 

activities, such as from diesel fuel 

combustion, wood burning, 

construction activities or unpaved 

roads, and it includes both filterable and 

condensable particles.7 ‘‘Secondary’’ 

PM2.5 is formed as a result of emissions 

of certain precursor gases that undergo 

chemical reactions in the atmosphere. 

The principal precursor gases that 

contribute to secondary PM2.5 formation 

are SO2, from the combustion of coal or 

other high sulfur fuels; NOX, from many 

types of fossil fuel combustion; VOC, 

from certain fuels, solvents and 

industrial processes; and ammonia, 

from sources such as animal feeding 

operations, wastewater treatment and 

fertilizer. Table 1 provides National 

Emissions Inventory (NEI) data for 2011 

that represent nationwide 

anthropogenic emissions estimates for 

direct PM2.5 and the four main PM2.5

precursor gases from major source 

sectors. 

TABLE 1—TOTAL EMISSIONS OF PM2.5 AND PRECURSORS FOR MAJOR SECTORS (IN TONS/YEAR) 

[Source: 2011 National Emissions Inventory (Version 1) a] 

Category Direct PM2.5 SO2 NOX VOC NH3

Chemical and allied products .............................................. 16,464 125,768 49,867 79,236 23,044 

Fuel combustion—electric generating utilities (EGUs) ........ 196,685 4,612,641 2,031,855 40,597 24,968 

Fuel combustion —other ...................................................... 628,199 987,552 1,856,716 588,346 79,679 

Other industrial ..................................................................... 273,857 185,859 348,561 328,222 53,039 

Onroad mobile ..................................................................... 208,629 28,969 5,785,570 2,413,026 119,654 

Metals processing ................................................................ 48,451 144,630 70,655 34,277 1,140 

Miscellaneous (mainly fire emissions, dust and some agricultural operations) ........................................................... 4,489,694 219,318 434,547 5,810,566 3,934,405 

Offroad mobile ..................................................................... 207,543 92,036 3,133,798 2,159,368 3,270 

Petroleum & related industries ............................................ 31,738 116,317 684,808 2,488,123 1,643 

Solvent utilization ................................................................. 3,810 107 893 2,814,551 577 

Storage and transport .......................................................... 20,098 9,109 19,079 1,221,185 5,734 

Waste disposal and recycling .............................................. 172,144 16,842 83,469 131,777 68,281 

aFor more details on the definitions of the emission categories listed in Table 1, see Sector/Tier crosswalk table for the 2011 NEI, available at: 

ftp://ftp.epa.gov/EmisInventory/2011/doc/scc_eis_crosswalk_2011neiv1.xlsx. 

2. Composition and Sources of PM2.5

Constituents 

PM2.5 is a complex and highly 

variable mixture of particles, but the 

majority of PM2.5 by mass is often 

comprised of five constituents: (i) OM; 

(ii) EC; (iii) crustal material; (iv) 

ammonium sulfate ((NH4)2SO4); and (v) 

ammonium nitrate (NH4NO3).8 The 

discussion that follows provides an 

overview of each of the five major 

components of PM2.5, all of which are 

known to contribute to ambient PM2.5

levels in areas throughout the U.S.9

Section II.B.3 provides more details on 

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10Appel, K.W., Pouliot, G.A., Simon, H., Sarwar, 

G., Pye, H.O.T., Napelenok, S.L., Akhtar, F., and 

Roselle, S.J., 2013. Evaluation of dust and trace 

metal estimates from the Community Multiscale Air 

Quality (CMAQ) model version 5.0, Geoscientific 

Model Development Discussions 61859–1899; 

Sorooshian, A., Shingler, T., Harpold, A., Feagles, 

C.W., Meixner, T., and Brooks, P.D., 2013. Aerosol 

and precipitation chemistry in the southwestern 

United States: spatiotemporal trends and 

interrelationships, Atmospheric Chemistry and 

Physics 13, 7361–7379. 

11U.S. Environmental Protection Agency, 2013. 

‘‘2008 National Emissions Inventory: Review 

Analysis and Highlights.’’ Office of Air Quality 

Planning and Standards, Air Quality Assessment 

Division, May 2013. EPA–454/R–005. Available at: 

http://www.epa.gov/ttn/chief/net/2008report.pdf. 

12Carlton, A.G., Pinder, R.W., Bhave, P.B., 

Pouliout, G.A., 2010. To What Extent Can Biogenic 

SOA Be Controlled, Environmental Science and 

Technology 44(9), 3376–80. 

the atmospheric chemistry involved in 

the formation of sulfate, nitrate and OM, 

to illustrate the importance of 

controlling emissions of PM2.5

precursors as part of any comprehensive 

strategy to reduce ambient PM2.5 levels 

in excess of the NAAQS. Section II.B.4 

presents a brief overview of PM2.5

composition by region of the U.S. 

OM is the fraction of ambient PM2.5

with the most diverse chemical 

composition, containing potentially 

thousands of different organic 

compounds (i.e., those compounds 

containing carbon) composed primarily 

of carbon, hydrogen, oxygen and 

nitrogen. Both primary particles and 

secondary particles contribute to 

ambient OM concentrations, with 

combustion sources being the dominant 

type of emissions sources. Another 

portion of primary OM particles results 

from direct emissions of organic 

compounds from sources of incomplete 

combustion, such as gas and diesel 

engines. Secondary OM particle 

formation involves oxidation of both 

anthropogenic and biogenic (plantderived) VOC, and can involve other, 

more complex chemical reactions. 

Further details of the chemistry behind 

the formation of secondary OM, known 

more commonly as secondary organic 

aerosols (SOA), are described in Section 

II.B.3 of this preamble. 

EC refers to particulate carbon that 

has a graphitic molecular structure, and 

is sometimes referred to as ‘‘black 

carbon’’ (BC). It is emitted directly from 

emission sources and does not undergo 

any significant reactions with other 

gases in the atmosphere. EC particles 

result from primary emissions involving 

combustion, especially from dieselfueled vehicles, but also from other 

processes involving the burning of fossil 

fuels. The latter includes anthropogenic 

sources such as boilers and waste 

disposal. In addition, some EC particles 

originate from biomass combustion such 

as from prescribed fires, wildfires and 

residential wood combustion. 

Crustal PM is comprised of particles 

of soil and oxides of metals from some 

industrial processes. Compounds 

comprised of elements such as silicon, 

aluminum, iron, calcium, titanium, 

magnesium and potassium, as well as 

oxygen, are major components.10

Sources of crustal PM2.5 include 

windblown dust, dust from mechanical 

resuspension (e.g. dust from 

construction activities or vehicles 

driving on unpaved roads) and some 

forms of combustion, especially of coal. 

Crustal PM2.5 comprised of elements, 

like iron (Fe), and their oxides can also 

be emitted from industrial sources. 

The remaining portion of ambient 

PM2.5 is mostly composed of SO4, NO3

and NH4, which react in the ambient air 

to form ammonium sulfate ((NH4)2SO4) 

and ammonium nitrate (NH4NO3). 

Another common PM2.5 particle is 

ammonium bi-sulfate (NH4HSO4). In 

some areas, less common ions such as 

chloride are also found in PM2.5 samples 

in the form of particles that include 

sodium chloride and ammonium 

chloride. Particle-bound water is often 

also associated with this fraction of 

PM2.5. Sulfate, nitrate and ammonium 

particles originate through both primary 

and secondary mechanisms, although 

the vast majority of these PM2.5 particles 

are formed through secondary 

formation, as described in the following 

section. 

3. Secondary Formation of PM2.5 From 

Gaseous Precursors 

a. Overview. The composition of PM2.5

is complex and highly variable due in 

part to the large contribution of 

secondary PM2.5 to total fine particle 

mass in most locations, and to the 

complexity of secondary particle 

formation processes. A large number of 

possible chemical reactions, often nonlinear in nature, can convert the gases 

SO2, NOX, VOC and ammonia to PM2.5. 

Thus, these gases are precursors to 

PM2.5. A brief discussion of SO4, NO3

and SOA formation, as well as the role 

of ammonia in their formation, follows. 

b. SO4 formation. SO2 is emitted 

mostly from the combustion of fossil 

fuels in boilers operated by electric 

utilities and other industries, with less 

than 10 percent of SO2 emissions 

nationwide coming from other 

industrial sources, such as oil refining 

and pulp and paper production.11 When 

SO2 oxidizes it forms sulfuric acid, a 

highly corrosive compound toxic to 

humans and to ecosystems that 

contributes to acid deposition (acid 

rain). In the presence of ammonia, 

however, sulfuric acid will react to form 

(NH4)2SO4, a less acidic compound and 

one of the five major components of 

PM2.5. If there is not enough ammonia 

present to fully neutralize the sulfuric 

acid, part of it may convert to NH4HSO4, 

which is more acidic than (NH4)2SO4, 

but less so than sulfuric acid. There is 

a large amount of emerging scientific 

evidence that SO2 may also contribute 

to the formation of SOA from biogenic 

VOC emissions (see section later on 

SOA). Sulfate levels in the ambient air 

peak in summer months due to 

increased SO2 emissions, generally from 

electricity generating units, and from 

meteorological conditions that are 

conducive to sulfate formation. 

c. NO3 formation. The main sources of 

NOX emissions are combustion of fossil 

fuel in boilers and mobile sources, 

accounting for more than 80 percent of 

national anthropogenic NOX emissions 

(based on the 2011 NEI), with boilers 

and electric generating units (EGUs) 

contributing about 27 percent and 

mobile sources contributing 56 percent. 

Oxides of nitrogen react in the 

atmosphere to form nitric acid, another 

prime contributor to acid deposition in 

the environment. Nitric acid converts to 

ammonium nitrate, one of the five main 

components of PM2.5, in the presence of 

ammonia. Low temperatures and high 

relative humidity create ideal 

conditions for the formation of 

ammonium nitrate, typically leading to 

higher atmospheric levels in winter 

months and lower levels in summer 

months.12

d. SOA formation. As discussed 

earlier, the OM component of ambient 

PM2.5 is a complex mixture of hundreds 

or even thousands of anthropogenic and 

biogenic organic compounds. These 

compounds are either emitted directly 

from sources (i.e., as ‘‘primary’’ PM2.5) 

or can be formed by reactions in the 

ambient air to make SOA (i.e., as 

‘‘secondary’’ PM2.5). 

VOC (both anthropogenic and 

biogenic) are key precursors to the SOA 

component of PM2.5. The relative 

importance of these compounds in the 

formation of organic particles varies 

between geographic areas, depending 

upon local emission sources, 

atmospheric chemistry and season of 

the year. It should be further noted that 

not all inventoried VOC may be 

contributing to the formation of organic 

particles. For example, chemical 

reactions involving VOC are generally 

accelerated in warmer temperatures, 

and for this reason studies show that 

SOA typically comprises a higher 

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13Pandis S.N., Harley R.A., Cass G.R., and 

Seinfeld J.H., 1992. Secondary Organic Aerosol 

Formation and Transport, Atmospheric 

Environment, 26, 2266–82. 

14Carlton, A.G., Bhave, P.B., Napelenok, S.L., 

Edney, E.O., Sarwar, G., Pinder, R.W., Pouliout, 

G.A., and Houyoux, M. (2010), Model 

Representation of Secondary Organic Aerosol in 

CMAQ4.7, Environmental Science and Technology 

44(22), 8553–60. 

15Seinfeld, J.H. and Pandis, S.N. (1998), 

Atmospheric Chemistry and Physics: From Air 

Pollution to Climate Change, 1st edition, J. Wiley, 

New York. 

16NARSTO, 2003. Particulate Matter Science for 

Policy Makers. A NARSTO Assessment. Parts 1 and 

2. NARSTO. Management Office (Envair), Pasco, 

Washington. Available at: http://narsto.org/pm_

science_assessment. 

17Carlton, A.G., Pinder, R.W., Bhave, P.B., and 

Pouliout, G.A., 2010. To what extent can Biogenic 

SOA be Controlled, Environmental Science and 

Technology 44(9), 3376–3380. 

18The organic matter (OM) values in Table 2 were 

calculated by multiplying the measured organic 

carbon (OC) concentrations by 1.6 (Turpin and Lim 

(2001), Aerosol Science and Technology, 35, 602– 

610). PM2.5 concentrations come from 

measurements of the Federal Reference/Equivalance 

Methods (FRM/FEM) rather than from the CSN 

PM2.5 measurement. 

19Reff and Rao, Memo to the docket, 2013. 

percentage of PM2.5 in the summer than 

in the winter.13

Anthropogenic sources of VOC 

include mobile sources, petrochemical 

manufacturing, oil and gas emissions 

and solvents.14 In addition, some 

biogenic VOC, emitted by vegetation 

such as trees, can also contribute 

significantly to SOA formation, 

especially in heavily forested areas, 

such as the southeastern U.S. It should 

be noted, however, that anthropogenic 

contributions to SOA are likely highest 

in the wintertime when biogenic SOA 

levels are lower; conversely, in the 

summertime, biogenic contributions to 

SOA are likely higher. Despite 

significant progress that has been made 

in understanding the origins and 

properties of SOA, it remains the least 

understood component of PM2.5 and 

continues to be a significant topic of 

research and investigation. 

e. Role of ammonia in sulfate, nitrate 

and SOA formation. Ammonia is a 

gaseous pollutant emitted by natural 

and anthropogenic sources. The EPA’s 

2011 NEI shows that the two main 

sources of ammonia emissions are 

fertilizer application (27 percent) and 

livestock raising (54 percent). It should 

be noted that the 2011 NEI indicates 

that mobile sources in the aggregate 

contribute about 3 percent of 

nationwide ammonia emissions. Much 

of those emissions comes from catalytic 

converters installed on light-duty 

gasoline vehicles, which are designed to 

convert NOX to nitrogen (N2); however, 

some ammonia is formed as a secondary 

product during this process. 

As indicated earlier, ammonia plays 

an important role in neutralizing acids, 

such as sulfuric acid and nitric acid, in 

clouds, precipitation and particles. On 

the other hand, deposited ammonia can 

contribute to problems of eutrophication 

in water bodies due to its nutritive 

properties.15 Ammonia would not exist 

in particles if not for the presence of 

acidic species with which it can 

combine to form a particle. In the 

eastern U.S., sulfate, nitrate and the 

ammonium associated with them can 

together account for between roughly 30 

percent and 75 percent of the total PM2.5

mass in a given area. The ammonium 

portion by itself roughly accounts for 

between 5 percent and 20 percent of the 

total PM2.5 mass in the East.16

f. Role of NOX in sulfate, nitrate and 

SOA formation. In addition to the 

contribution of NOX emissions to 

secondary particulate nitrate formation, 

NOX also reacts with anthropogenic and 

biogenic VOC that have an impact on 

secondary formation of organic 

compounds that make up SOA. NOX is 

thus involved in all secondary PM 

chemistry, not just in particulate nitrate 

formation.17

4. Fine Particulate Composition By 

Location 

Table 2 shows regional 3-year mean 

concentrations (2009–2011) of PM2.5

and its main components at sites in the 

Chemical Speciation Network (CSN).18

In addition to the mean values for all 

sites in each region, the table includes 

the minimum and maximum observed 

PM2.5 and species concentrations for 

sites within each region. These data 

illustrate broad observed spatial 

patterns across the U.S. in PM2.5

concentrations and its composition. For 

example, PM2.5 concentrations are 

highest on average in the Central and 

West regions. Sulfate mass comprises a 

larger fraction of PM2.5 than nitrate mass 

in the northeastern U.S., whereas nitrate 

has a greater contribution than that of 

sulfate in the West. OM is the dominant 

component in all regions, with the 

highest concentrations of OM on 

average found in the West, Northwest 

and Southeast. On a percentage basis, 

the concentrations of EC and crustal 

material are relatively low throughout 

all regions of the U.S. compared to the 

other major PM2.5 components. 

The composition of PM2.5 also varies 

between urban and rural areas. This is 

reflective of the distribution of urban 

and regional emission sources, 

atmospheric reactions and transport of 

fine particles. More details about the 

spatial distribution and origins of PM2.5

components can be found in the docket 

for this proposal.19

TABLE 2—PM2.5 CHEMICAL COMPOSITION DATA AT 2009–2011 NONATTAINMENT SITES

[Source: EPA Speciation Trends Network] 

Region Statistic 

Concentration (μg/m3) 

SOe NO3 OM EC CrM PM2.5

Central ..................................... Min (μg/m3) ............................. 1 .46 0 .3 2 .73 0 .31 0 .01 8 .92 

Mean (μg/m3) ......................... 2 .69 1 .49 3 .57 0 .68 0 .26 11 .63 

Max (μg/m3) ............................ 4 .19 3 .34 4 .81 1 .1 1 .0 13 .51 

N ............................................. 61 61 50 50 61 42 

East North Central .................. Min (μg/m3) ............................. 0 .83 0 .38 1 .97 0 .19 0 .01 6 .03 

Mean (μg/m3) ......................... 1 .68 1 .8 2 .84 0 .48 0 .19 9 .86 

Max (μg/m3) ............................ 2 .51 3 .57 3 .69 0 .79 0 .61 11 .87 

N ............................................. 29 28 20 20 28 23 

North East ............................... Min (μg/m3) ............................. 0 .58 0 .12 1 .74 0 .14 0 4 .42 

Mean (μg/m3) ......................... 2 .06 0 .97 3 .14 0 .69 0 .17 9 .33 

Max (μg/m3) ............................ 5 .12 2 .26 5 .05 1 .69 0 .52 15 .05 

N ............................................. 59 59 39 39 59 46 

North West .............................. Min (μg/m3) ............................. 0 .24 0 .05 2 .91 0 .42 0 .01 6 .06 

Mean (μg/m3) ......................... 0 .54 0 .4 5 .02 0 .81 0 .15 8 .33 

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20 62 FR 38652 (July 18, 1997). 

21For a complete summary of legal challenges 

and related court decisions on the PM NAAQS, see 

generally 78 FR 3086 (January 15, 2013). 

22 70 FR 944 (January 5, 2005). 

23 72 FR 20583 (April 25, 2007). 

24 73 FR 28231 (May 16, 2008). 

25 71 FR 61144 (October 17, 2006). 

26 74 FR 58688 (November 13, 2009). 27Memorandum of March 2, 2012 (withdrawn 

June 6, 2013), from Stephen D. Page, Director, 

Office of Air Quality Planning and Standards, to 

EPA Regional Air Directors, Regions I–X, 

‘‘Implementation Guidance for the 2006 24-Hour 

Fine Particle (PM2.5) National Ambient Air Quality 

Standards (NAAQS).’’ Available at: http://epa.gov/ 

ttn/naaqs/pm/pm25_guide.html. 

28 77 FR 38890 (June 29, 2012). 

29 78 FR 3086 (January 15, 2013). 

30Spatial averaging of monitored ambient air 

quality data was a feature of the prior PM2.5 NAAQS 

TABLE 2—PM2.5 CHEMICAL COMPOSITION DATA AT 2009–2011 NONATTAINMENT SITES—Continued 

[Source: EPA Speciation Trends Network] 

Region Statistic 

Concentration (μg/m3) 

SOe NO3 OM EC CrM PM2.5

Max (μg/m3) ............................ 1 .09 1 .79 8 .44 1 .25 0 .53 10 .96 

N ............................................. 33 33 13 13 33 14 

South ....................................... Min (μg/m3) ............................. 0 .88 0 .18 1 .36 0 .12 0 .02 5 .22 

Mean (μg/m3) ......................... 2 .06 0 .8 3 .32 0 .57 0 .5 10 .05 

Max (μg/m3) ............................ 3 .08 1 .67 5 .1 1 .48 2 .38 14 .27 

N ............................................. 36 27 23 23 36 23 

South East .............................. Min (μg/m3) ............................. 1 .6 0 .2 1 .75 0 .37 0 .01 6 .76 

Mean (μg/m3) ......................... 2 .39 0 .53 4 .12 0 .63 0 .26 10 .77 

Max (μg/m3) ............................ 4 .33 1 .51 5 .71 1 .2 0 .85 13 .38 

N ............................................. 44 43 30 30 43 29 

South West ............................. Min (μg/m3) ............................. 0 .34 0 .07 2 .34 0 .46 0 .02 5 .3 

Mean (μg/m3) ......................... 0 .63 0 .49 3 .01 0 .7 0 .5 7 .93 

Max (μg/m3) ............................ 1 .13 2 .65 4 .39 1 .04 1 .96 9 .73 

N ............................................. 46 46 11 11 46 12 

West ........................................ Min (μg/m3) ............................. 0 .33 0 .08 1 .79 0 .52 0 .01 6 .84 

Mean (μg/m3) ......................... 0 .9 1 .4 5 .22 0 .85 0 .32 11 .49 

Max (μg/m3) ............................ 2 .08 5 .14 10 .27 1 .56 1 .05 16 .57 

N ............................................. 44 44 20 20 44 21 

West North Central ................. Min (μg/m3) ............................. 0 .29 0 .06 1 .22 0 .09 0 3 .23 

Mean (μg/m3) ......................... 0 .67 0 .48 3 .16 0 .44 0 .22 7 .25 

Max (μg/m3) ............................ 1 .79 2 .02 8 .28 1 .21 0 .53 13 .72 

N ............................................. 30 30 7 7 30 10 

C. Historical Overview of PM2.5 NAAQS 

Setting and Implementation 

Sections 108 and 109 of the CAA 

govern the establishment, review and 

revision, as appropriate, of NAAQS for 

widespread pollutants emitted from 

numerous and diverse sources 

considered harmful to public health and 

the environment. The CAA requires two 

types of NAAQS: (i) Primary standards, 

which set limits to protect public 

health, including the health of at-risk 

populations; and (ii) secondary 

standards, which set limits to protect 

public welfare, including protection 

against visibility impairment, damage to 

animals, crops, vegetation and 

buildings. 

The EPA first promulgated annual 

and 24-hour NAAQS for PM2.5 in July 

1997.20 Prior to that time, the EPA had 

addressed ambient particulate matter 

through other means, first by regulating 

‘‘total suspended particles’’ (TSP) and 

then later by regulating PM10. After 

protracted litigation, the 1997 NAAQS 

for PM2.5 were upheld by the U.S. Court 

of Appeals for the District of Columbia 

Circuit in March 2002.21 The EPA 

subsequently promulgated designations 

for the 1997 PM2.5 NAAQS nationwide, 

and designated a number of areas as 

nonattainment for the 1997 PM2.5

NAAQS, effective April 2005.22 In April 

2007, the EPA issued a detailed 

implementation rule to assist states with 

the development of SIP submissions to 

meet attainment plan requirements for 

the 1997 NAAQS (the ‘‘2007 PM2.5

Implementation Rule’’).23 In May 2008, 

the EPA issued another rule to assist 

states with SIP submissions to meet the 

specific requirements for permitting 

programs for NNSR purposes in 

designated nonattainment areas (the 

‘‘2008 PM2.5 NSR Rule’’).24 The EPA 

premised both the 2007 PM2.5

Implementation Rule and the 2008 

PM2.5 NSR Rule on the EPA’s 

interpretation of the statute that 

nonattainment areas for the PM2.5

NAAQS were subject solely to the 

general nonattainment plan 

requirements of subpart 1, part D of title 

I of the CAA (‘‘subpart 1’’). 

Section 109(d)(1) of the CAA requires 

the EPA periodically to review the 

science upon which the standards are 

based and the standards themselves, 

and to revise the standards as may be 

appropriate. In October 2006, the EPA 

promulgated revisions to the suite of 

NAAQS for PM, and in particular the 

EPA revised the 24-hour PM2.5

standards.25 In accordance with section 

107(d), the EPA subsequently 

designated a number of areas as 

nonattainment for the revised 2006 24- 

hour PM2.5 standards, effective 

December 2009.26 In March 2012, the 

EPA issued a guidance document 

specifically to aid states in preparing 

their SIP submissions to meet 

attainment plan requirements for the 

2006 24-hour PM2.5 NAAQS in 

designated nonattainment areas.27 The 

EPA’s guidance for the 2006 PM2.5

NAAQS was based, in large part, on the 

requirements finalized in the 2007 PM2.5

Implementation Rule, which the EPA 

based solely upon the statutory 

requirements of subpart 1. 

The EPA initiated a review of the 

PM2.5 NAAQS in June 2007, proposing 

revisions to the primary and secondary 

PM2.5 NAAQS on June 29, 2012.28 The 

EPA issued its final rule on December 

14, 2012, in which it lowered the 

primary annual PM2.5 standard from 

15.0 mg/m3 to 12.0 mg/m3 to provide 

increased protection against health 

effects associated with long- and shortterm fine particle exposures.29 The EPA 

also eliminated spatial averaging as part 

of the form of the annual standard to 

avoid potential disproportionate 

impacts on at-risk populations.30 The 

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monitoring regulations which had the potential for 

masking particularly high PM2.5 concentrations at 

certain monitored locations within nonattainment 

areas. 

31 71 FR 61144 (October 17, 2006). 

32 General information regarding the health 

effects associated with PM2.5 exposures is available 

at: http://www.epa.gov/airquality/particlepollution/

health.html. Additional information, such as the 

EPA’s technical documents supporting the latest 

review of the standards, is available at: http://

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

index.html. 

33NRDC v. EPA, 706 F.3d 428 (D.C. Cir. 2013). 

34 General Preamble, 57 FR 13498 (April 16, 

1992). 

35 It is important to note that the EPA does not 

have a mandatory duty to promulgate an 

implementation rule for the PM2.5 NAAQS, and the 

obligations of state and tribal air agencies to 

develop and submit an attainment plan are 

independent obligations and not conditioned upon 

the EPA promulgating an implementation rule for 

the PM2.5 NAAQS. 

36When the term ‘‘state’’ is used hereafter, it will 

refer generically to states, local air agencies, and 

tribal governments electing to be treated as states 

for the purposes of implementing the CAA. Of 

additional note is that the 1998 Tribal Authority 

Rule (TAR), which is found in 40 CFR part 49, 

which implements section 301(d) of the CAA, 

provides that tribes be treated in the same manner 

as a state when implementing certain sections of the 

CAA. It gives tribes the option of developing tribal 

implementation plans (TIPs), but unlike states, 

tribes are not required to develop implementation 

plans. Section IX.I of this preamble provides further 

discussion of tribal issues. 

EPA retained the level (35 mg/m3) and 

form (98th percentile, averaged over 3 

years) of the primary 24-hour PM2.5

standard, as revised in 2006, to provide 

supplemental protection against health 

effects associated with short-term PM2.5

exposures, especially in areas with high 

peak PM2.5 concentrations.31 This suite 

of primary PM2.5 standards provides 

increased public health protection, 

including the health of at-risk 

populations which include children, 

older adults, persons with pre-existing 

health and lung disease and persons of 

lower socioeconomic status, against a 

broad range of PM2.5-related effects that 

include premature mortality, increased 

hospital admissions and emergency 

department visits and development of 

chronic respiratory disease.32 With 

regard to the secondary (welfare-based) 

standards, the EPA retained the existing 

annual PM2.5 standard of 15.0 mg/m3

and the existing 24-hour PM2.5 standard 

of 35 mg/m3 to protect against PMrelated non-visibility welfare effects 

including ecological effects, effects on 

materials and climate impacts. In 

addition, the secondary 24-hour PM2.5

standard provides protection for PMrelated visibility impairment. 

On January 4, 2013, shortly after the 

EPA promulgated the 2012 revisions to 

the suite of PM NAAQS, the DC Circuit 

issued its decision in a challenge to the 

2007 PM2.5 Implementation Rule and 

the 2008 PM2.5 NSR Rule. In NRDC v. 

EPA, the court held that the EPA erred 

in implementing the 1997 PM2.5 NAAQS 

pursuant only to the general 

implementation requirements of subpart 

1, rather than also to the 

implementation requirements specific to 

particulate matter (PM10) in subpart 4, 

part D of title I of the CAA (‘‘subpart 

4’’).33 The court reasoned that the plain 

meaning of the CAA requires 

implementation of the 1997 PM2.5

NAAQS under subpart 4 because PM2.5

particles fall within the statutory 

definition of PM10 and are thus subject 

to the same statutory requirements. In 

addition, although the court stated that 

its decision that the EPA must 

implement the PM2.5 NAAQS pursuant 

to subpart 4 requirements meant that it 

did not have to reach decisions on other 

issues concerning the regulation of 

precursors to PM2.5, the court 

nonetheless noted that subpart 4 has 

specific requirements with respect to 

regulation of such precursors. As a 

result, the court remanded to the EPA 

both the 2007 PM2.5 Implementation 

Rule and the 2008 PM2.5 NSR Rule, both 

of which were premised on the EPA’s 

interpretation of the statute that subpart 

1 was the only applicable subpart for 

the implementation of the 1997 PM2.5

NAAQS. The court instructed the EPA 

‘‘to repromulgate these rules pursuant to 

Subpart 4 consistent with this opinion.’’ 

Given the D.C. Circuit’s opinion in 

NRDC v. EPA, the EPA withdrew its 

2012 guidance document for the 2006 

24-hour PM2.5 NAAQS in June 2013. 

Because the court had concluded that 

the EPA and states must implement the 

PM2.5 NAAQS consistent with the 

statutory requirements of subpart 4, the 

EPA 2012 guidance for attainment plans 

for the 2006 PM2.5 NAAQS premised 

solely upon subpart 1 requirements was 

no longer appropriate. 

The EPA intends to use this current 

rulemaking to accomplish multiple 

objectives. First, the EPA is taking this 

action to clarify how air agencies should 

meet the statutory SIP requirements that 

apply to areas designated nonattainment 

for any PM2.5 NAAQS under subparts 1 

and 4. To this end, the EPA is proposing 

regulatory requirements that will be 

applicable to attainment plans for the 

2012 PM2.5 NAAQS and any future 

revisions of the PM2.5 NAAQS, subject 

to revisions that may be necessary for 

implementation purposes in the future. 

Second, the EPA is taking this action to 

provide guidance, in addition to 

regulatory requirements, to assist air 

agencies in developing attainment plans 

for the 2012 PM2.5 NAAQS and any 

future revisions of the PM2.5 NAAQS. 

Finally, the EPA is taking this action in 

response to the DC Circuit’s remand of 

the 2007 PM2.5 Implementation Rule 

and the 2008 PM2.5 NSR Rule. Through 

this rulemaking, the EPA intends to 

address requirements associated with 

states’ ongoing implementation efforts 

for the 1997 and 2006 PM2.5 NAAQS. In 

the interim, the EPA will rely on the 

statutory attainment planning 

requirements 34 contained in subparts 1 

and 4 and on the EPA’s General 

Preamble and Addendum for guidance 

on how to apply those requirements to 

current PM2.5 NAAQS nonattainment 

areas. 

D. State Implementation Planning 

Process for PM2.5 NAAQS 

1. Overview 

The CAA establishes important roles 

both for state and tribal governments 

and for the EPA in implementing the 

NAAQS. In accordance with the 

principle of cooperative federalism, 

both state and tribal governments and 

the EPA have respective authorities and 

responsibilities under the CAA. At the 

outset, the EPA has the authority and 

responsibility to promulgate the 

NAAQS. In turn, state, local and tribal 

air agencies have the authority and 

primary responsibility for developing 

and implementing attainment plans that 

contain emission control measures 

needed to achieve the air quality 

standards in each nonattainment area, 

consistent with the requirements of the 

CAA. The EPA often assists air agencies 

by promulgating regulations or 

providing guidance for meeting 

implementation requirements and 

technical tools, including information 

on control measures.35 For example, the 

EPA intends this rulemaking to clarify 

the specific statutory requirements, and 

schedule for meeting those 

requirements, that state and tribal air 

pollution control agencies (‘‘air 

agencies’’) must address as they prepare 

SIP submissions for the PM2.5 standards 

in future.36

The EPA also promulgates nationally 

applicable control requirements and 

emission limits for many sources such 

as new motor vehicles, certain 

categories of new and modified major 

stationary sources and existing 

stationary sources of toxic air 

pollutants. These federal actions assist 

state and tribal air agencies by achieving 

emission reductions from certain 

categories of sources nationwide, which 

can help with local attainment needs in 

a given nonattainment area. In addition, 

the EPA has authority to address 

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37See 70 FR 25162 (May 12, 2005) and 76 FR 

48208 (August 8, 2011). 

38While the CAA provides for ‘‘designating’’ with 

respect to the Governor’s list, in the full context of 

the CAA section 107 it is clear that the Governor 

actually makes a recommendation, to which the 

EPA must respond using a specified process if the 

EPA does not accept the recommendation. 

39While section 107 of the CAA specifically 

addresses states, the EPA is following the same 

process for tribes that choose to make a 

recommendation to the extent practicable, pursuant 

to section 301(d) of the CAA regarding tribal 

authority, and the TAR. 63 FR 7254 (February 12, 

1998). To provide for clarity and consistency, the 

EPA issued a 2011 guidance memorandum for 

working with tribes during the designations 

process. Memorandum of December 20, 2011 from 

Stephen D. Page, Director, Office of Air Quality 

Planning and Standards, to EPA Regional 

Administrators, Regions I–X re: ‘‘Guidance to 

Regions for Working with Tribes during the 

National Ambient Air Quality Standards (NAAQS) 

Designations Process.’’ Available at: http://

www.epa.gov/ttn/oarpg/t1/memoranda/20120117

naaqsguidance.pdf. 

40See the Federal Register notice for the first 

round of designations for the 2012 PM2.5 NAAQS 

at 80 FR 2206 (January 15, 2015). 

41The ambient air monitoring requirements that 

apply to the PM2.5 NAAQS are detailed in 40 CFR 

part 58. These monitoring requirements are 

applicable to state and local air agencies. 

42See 40 CFR 58.10. 

interstate transport of pollutants, in the 

event that states fail to do so. Through 

this authority, the EPA has addressed 

regional transport of pollutants from 

upwind states to downwind states, and 

has previously done so for purposes of 

the PM2.5 NAAQS.37 In addition, the 

EPA has the authority and responsibility 

to review and take action to approve or 

disapprove submitted attainment plans 

based upon whether they meet 

applicable statutory and regulatory 

requirements, to provide funding and 

technical assistance to states and to 

initiate the process for imposition of 

sanctions and/or issue federal 

implementation plans (FIPs) when 

states fail to fulfill their CAA 

obligations. More information on area 

designations, the role of ambient air 

monitoring, the SIP development 

process and the role of federal measures 

in bringing an area into attainment is 

presented below. 

2. Initial Area Designations and 

Classifications 

The NAAQS implementation 

planning process begins with initial area 

designations, through which states and 

the EPA identify areas of the country 

that either meet or do not meet the new 

or revised NAAQS, along with 

identifying the nearby areas 

contributing to violations of the 

NAAQS. Section 107(d)(1) of the CAA 

requires 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.38 Thus, 

states are required to make their initial 

designation recommendations to the 

EPA by no later than 1 year after the 

promulgation of new or revised 

NAAQS. Section 107(d)(1)(B)(i) further 

provides: ‘‘Upon promulgation or 

revision of a NAAQS, the Administrator 

shall promulgate the designations of all 

areas (or portions thereof) . . . as 

expeditiously as practicable, but in no 

case later than 2 years from the date of 

promulgation. Such period may be 

extended for up to 1 year in the event 

the Administrator has insufficient 

information to promulgate the 

designations.’’ Thus, the EPA is 

required to promulgate the actual 

designations for all areas across the U.S. 

by no later than 2 years after the 

promulgation of any new or revised 

NAAQS, unless the EPA elects to take 

up to one additional year in situations 

where there is insufficient information. 

Under section 107(d)(1)(B)(ii), the EPA 

is authorized to modify the designations 

recommendations from the states, with 

respect to the designation of an area and 

the boundaries of an area, if the EPA 

deems that necessary. By no later than 

120 days prior to promulgating final 

designations, the EPA is required to 

notify states of any intended 

modifications to their 

recommendations. States then have an 

opportunity to demonstrate to the EPA 

why the EPA’s intended modification is 

inappropriate. Regardless of whether a 

state provides an initial designation 

recommendation for any area, the EPA 

must timely promulgate the 

designations it deems appropriate.39

Under subpart 4, the CAA provides 

for classification of PM2.5 nonattainment 

areas as either ‘‘Moderate’’ or ‘‘Serious.’’ 

As provided in section 188(a) and 

reiterated in the General Preamble, all 

PM10 nonattainment areas and by 

extension all PM2.5 nonattainment areas 

are initially classified as Moderate by 

operation of law at the time of 

designation. Initial classifications are 

not subject to public notice-andcomment pursuant to section 

107(d)(2)(B), although the EPA may 

elect to take comment on designations 

and classifications and its recent 

practice has been to do so. 

All areas designated as nonattainment 

for the 2012 PM2.5 NAAQS and any 

future revised PM2.5 NAAQS will be 

initially classified as Moderate 

nonattainment areas upon designation, 

regardless of the severity of the PM2.5

problem in the area. This statutory 

approach to classifications for 

nonattainment areas under subpart 4 for 

the PM2.5 NAAQS is notably different 

from the approach for ozone NAAQS 

nonattainment areas under subpart 2 (of 

part D, title I of the CAA), wherein the 

statute includes several area 

classifications, and initial classifications 

are based on monitored ozone levels. 

Thus, unlike for ozone nonattainment 

areas, all PM2.5 nonattainment areas 

initially receive the same 

classification—Moderate—and the EPA 

only reclassifies such areas to Serious 

upon a showing by the state or a 

determination by the agency that the 

area cannot practicably attain by the 

statutory attainment date, or upon a 

finding that the area in fact failed to 

attain the NAAQS by the applicable 

Moderate area attainment date. The 

statute requires that Moderate 

nonattainment areas attain the NAAQS 

as expeditiously as practicable, but not 

later than the end of the sixth calendar 

year following designation. States have 

an incentive to avoid having a Moderate 

area reclassified to Serious because, as 

discussed later in this preamble, the 

specific subpart 4 requirements for areas 

classified as Serious include, among 

other things, a more stringent level of 

control for sources of direct PM2.5 and 

PM2.5 precursors than for Moderate 

areas. 

As of the date of this proposal, the 

first round of initial designations for 

most areas for the 2012 primary annual 

PM2.5 NAAQS has been completed, and 

those designations will become effective 

on April 15, 2015. All areas designated 

as nonattainment for the 2012 PM2.5

NAAQS were classified as Moderate 

nonattainment areas.40

3. Ambient Air Monitoring for PM2.5

Ambient air quality monitoring for 

PM2.5 plays an integral role in 

implementation of a NAAQS, including 

identifying areas violating the NAAQS, 

control strategy development and 

tracking progress toward attainment. 

States are required to monitor PM2.5

mass concentrations using approved 

methods to determine compliance with 

the NAAQS.41 The locations of monitors 

are identified in states’ Annual 

Monitoring Network Plans, which are 

required to be submitted to the EPA by 

July 1 of each year.42 The EPA in turn 

reviews these annual plans for 

compliance with applicable regulations 

and consistency with relevant guidance. 

Currently there are more than 900 

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43Near-road monitors for CBSAs larger than 2.5 

million in population are to be operational by 1/1/ 

2015; and monitors for CBSAs with population 

larger than 1 million but less than 2.5 million are 

to be operational by 1/1/2017. CBSA is defined by 

OMB as a statistical geographic entity consisting of 

the county or counties associated with at least one 

urbanized area/urban cluster of at least 10,000 

population, plus adjacent counties having a high 

degree of social and economic integration. 

44See Catawba County v. EPA, 571 F.3d 20 (D.C. 

Cir. 2009). 

45National Acid Precipitation Assessment 

Program. Acid Deposition: State of the Science and 

Technology. Washington, DC 1991. See also 

Environmental Protection Agency. (2004) Air 

Quality Criteria for Particulate Matter. Research 

Triangle Park, NC: Office of Research and 

Development; report no. EPA/600/P–99/002a,bF. 

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

standards/pm/s_pm_cr_cd.html. 

46For example, see technical information for the 

Cross-State Air Pollution Rule (CSAPR) at: http:// 

www.epa.gov/airmarkt/programs/cair/index.html; 

and the Clean Air Interstate Rule (CAIR) at: 

http://www.epa.gov/airmarkt/programs/cair/

index.html. See also: NARSTO (2004) Particulate 

Matter Assessment for Policy Makers: A NARSTO 

Assessment. P. McMurry, M. Shepherd, and J. 

Vickery, eds. Cambridge University Press, 

Cambridge, England. ISBN 0 52 184287 5. 

monitoring locations across the country 

eligible for comparison to the PM2.5

NAAQS. States are required to maintain 

monitors in designated nonattainment 

areas in order to track progress toward 

attainment and ultimately determine 

whether the area has attained the PM2.5

standards. In addition to the approved 

monitors for comparison to the NAAQS, 

the EPA and states also maintain a 

chemical speciation network (CSN) of 

about 200 stations around the country to 

support analyses of chemical 

composition of PM2.5 (e.g. sulfate, 

nitrate and organic carbon). The data 

provided by the CSN help states identify 

contributing source categories and 

develop control strategies to reach 

attainment. 

In conjunction with the promulgation 

of the 2012 PM2.5 NAAQS, the EPA 

finalized a schedule for deployment of 

PM2.5 monitors at near-road monitoring 

locations. Under revised monitoring 

requirements, states are required to 

locate a minimum of one PM2.5 monitor 

in each core-based statistical area 

(CBSA) with a population of 1 million 

or more, to be phased-in between 

January 2015 and January 2017.43

For initial area designations for any 

PM2.5 NAAQS, the EPA relies on 

monitoring data to identify areas to be 

designated nonattainment due to 

violations of the standard(s). The EPA 

uses other information to identify areas 

contributing to the monitored violations 

in those areas.44 The agency’s protocol 

for designating areas and determining 

whether an area has attained the PM2.5

NAAQS is based on monitored air 

quality data collected over a period of 

3 calendar years. Data from the new 

PM2.5 near-road monitors were not 

available for the EPA to consider within 

the timeframe for initial area 

designations provided by the CAA for 

the 2012 PM2.5 NAAQS; the agency will 

not be able to consider data from a nearroad monitor in the implementation 

process until 3 years of data are 

available. The initial set of nearroadway PM2.5 monitors are to be fully 

deployed by January 2015, with the first 

3 years of air quality data (2015–2017) 

available beginning in 2018; the second 

set of near-roadway monitors are to have 

the first 3 years of data available 

beginning in 2020. 

4. SIP Development Process 

In general terms, a SIP is the 

compilation of EPA-approved state 

statutes, regulations and programs that a 

state develops and relies upon to carry 

out its NAAQS implementation 

responsibilities under the CAA, 

including the attainment, maintenance 

and enforcement of NAAQS. States use 

the SIP development process to identify 

the emissions sources that contribute to 

the nonattainment problem in a 

particular area, and to select the 

required emissions reduction measures 

most appropriate for that area, 

considering factors such as 

technological and economic feasibility. 

As part of developing an attainment 

plan, the states must meet specific 

requirements of the CAA to attain the 

NAAQS, e.g., a state with a Moderate 

PM2.5 nonattainment area must impose 

RACM (including RACT) and additional 

reasonable measures on sources located 

in the nonattainment area. Under the 

CAA, states must develop attainment 

plans that ensure that areas reach 

attainment as expeditiously as 

practicable, but no later than the 

applicable statutory attainment date. In 

these attainment plans, states may take 

into consideration emission reductions 

resulting from federally applicable 

national programs (such as mobile 

source regulations, the national acid 

rain program, or maximum achievable 

control technology (MACT) standards 

for air toxics), as well as from state or 

local programs not directly mandated, 

but authorized, under the CAA, if such 

measures are incorporated into the SIP 

and thus are made federally enforceable. 

5. Geographic Extent of PM2.5 Problem 

The EPA recognizes the significant 

variability in the nature and sources of 

PM2.5 in different nonattainment areas 

and believes it is important to keep this 

variability in mind when providing 

guidance to states as they develop 

control strategies to bring their PM2.5

nonattainment areas into attainment 

with the relevant NAAQS. The 

variability of PM2.5 concentrations 

across the country has a substantial 

regional component because the 

formation and transport of secondarily 

formed particles, such as sulfates and 

nitrates, can extend over hundreds of 

miles. As a result, monitored violations 

of the PM2.5 NAAQS can often reflect 

the impact of the combination of ‘‘local’’ 

sources of emissions located within the 

designated nonattainment area and 

‘‘regional’’ sources of emissions that 

may be located much farther away. 

In addition, data suggest that ambient 

PM2.5 concentrations tend to rise and 

fall in a consistent manner across very 

large geographic areas. The transport 

phenomenon associated with PM2.5 and 

its precursors has been well 

documented for many years. For 

example, one significant source of 

information on long-range transport is 

the National Acid Precipitation 

Assessment Program (NAPAP) research 

from the 1980s and its associated 

reports published in 1991.45 Additional 

studies and air quality modeling 

analyses since that time have added to 

the body of information documenting 

the regional nature of PM2.5.46

6. Strategies for Reducing Ambient 

PM2.5

The control measures identified and 

adopted by a state through the SIP 

development process for bringing 

nonattainment areas into attainment 

constitute an important component of 

the CAA’s overall strategy for meeting 

the PM2.5 standards, but they are not the 

only component. The CAA also includes 

requirements for national rules or 

programs that will reduce emissions and 

help achieve cleaner air. Specifically, 

the EPA has adopted a number of 

national rules over the past few years 

that require or will require emission 

reductions from sources of both direct 

PM2.5 and PM2.5 precursors, especially 

of SO2 and NOX. The national rules that 

will help states meet their attainment 

dates include, but are not limited to: 

The Tier 2 Light-Duty Vehicle Rule; the 

Tier 3 Tailpipe and Evaporative 

Emission and Vehicle Fuel Standards; 

the Heavy-Duty Engine and Vehicle 

Standards and Highway Diesel Fuel 

Sulfur Control Requirements; the Clean 

Air Nonroad Diesel Rule; the Regional 

Haze Regulations and Guidelines for 

Best Available Retrofit Technology 

Determinations; the NOX Emission 

Standard for New Commercial Aircraft 

Engines; the CSAPR; the Emissions 

Standards for Locomotives and Marine 

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47Compliance with the MATS emission standard 

for acid gas hazardous air pollutants (HAP) is 

demonstrated by direct measurement of either 

hydrogen chloride (HCl) or SO2 as surrogates for all 

acid gas HAP. Thus, compliance with MATS is 

expected to result in a substantial amount of new 

pollution controls (scrubbers and dry sorbent 

injection) and upgrading of existing acid gas 

controls that will significantly reduce acid gas 

emissions, including SO2 emissions, from power 

plants. MATS implementation is projected to 

reduce nationwide SO2 emissions from power 

plants to a level more than 40 percent lower than 

the SO2 emissions projected under CSAPR without 

MATS in place. For more information, see: 

http://www.epa.gov/mats. 

48See 2007 PM2.5 Implementation Rule, 72 FR 

20586, 20589, 20590, 20591, 20592, 20593, 20594, 

20595, 20596 and 20597 (April 25, 2007). 

49 Ibid. For example, the EPA’s 2007 PM2.5

Implementation Rule discussed the fact that 

emissions of SO2, NOX, VOC and ammonia are 

factual and scientific precursors to PM2.5. 

Compression-Ignition Engines; the 

Control of Emissions for Nonroad Spark 

Ignition Engines and Equipment; the C3 

Oceangoing Vessels rule; area and major 

source Boilers NESHAPs, New Source 

Performance Standards and Emission 

Guidelines for Hospital/Medical/

Infectious Waste Incinerators; the 

Reciprocating Internal Combustion 

Engines (RICE) NESHAPs; and the 

Mercury and Air Toxics Standards 

(MATS).47

Additionally, there are PM2.5

reductions that will be achieved as a 

result of previously adopted state and 

local agency regulations and voluntary 

programs to the extent they can be 

relied on under the EPA’s voluntary 

measures policies, such as the use of 

low sulfur fuel for home heating and 

industrial purposes, curtailment of 

residential wood burning and burn 

bans. Furthermore, under the voluntary 

PM Advance program, the EPA works 

with states, tribes and local 

governments to ensure they are aware of 

the advantages of early action and to 

provide assistance in taking steps to 

achieve emission reductions in areas 

currently attaining the PM2.5 NAAQS 

but approaching levels that could lead 

to nonattainment in the future. Early 

reductions may help these areas 

maintain the annual and 24-hour PM2.5

NAAQS over the long-term. 

Furthermore, there may be emissions 

controls that can be implemented to 

meet NAAQS for ozone (O3) or SO2 that 

may have co-benefits for meeting and 

continuing to meet the current PM2.5

NAAQS and any future revised PM2.5

NAAQS. 

The EPA will continue to work 

closely with air agencies as they 

develop and use an appropriate 

combination of national, regional and 

local pollution reduction measures to 

meet the standards as expeditiously as 

practicable, as required by the CAA. 

III. What is the EPA proposing with 

respect to the treatment of PM2.5

precursors in nonattainment area 

planning and permitting? 

A. Background 

The EPA recognizes that a threshold 

question in developing PM2.5 attainment 

plans and implementing NNSR 

programs is the question of which 

precursors must be regulated in a given 

nonattainment area in order to attain the 

relevant NAAQS and to meet the 

statutory requirements of part D, 

including subpart 4, of the CAA. Before 

discussing the specific CAA attainment 

plan and NNSR requirements in detail 

in Sections IV through IX of this 

preamble, the EPA discusses in this 

section how a state should evaluate 

PM2.5 precursors in order to identify the 

specific precursors to which the PM2.5

attainment plan and NNSR 

requirements will apply in a given 

nonattainment area. This section first 

provides a brief overview of the 

precursor policies that the agency 

included in the 2007 PM2.5

Implementation Rule and in the 2008 

PM2.5 NSR Rule for the 1997 PM2.5

NAAQS that were remanded by the 

court. It then describes the EPA’s three 

proposed options for addressing PM2.5

precursors under the attainment 

planning and NNSR programs to meet 

the statutory requirements of subpart 4. 

Lastly, this section discusses possible 

approaches for states to develop an 

adequate technical demonstration 

showing whether emissions of a given 

PM2.5 precursor significantly contribute 

to ambient concentrations that exceed 

the standard. The EPA requests public 

comment on the options and 

information presented below. 

The EPA’s 2007 PM2.5

Implementation Rule included 

regulatory presumptions concerning the 

need to address certain PM2.5 precursors 

in attainment plans and through control 

measures related to those plans.48 The 

EPA has long recognized the scientific 

basis for concluding that there are 

multiple scientific precursors to PM10, 

and in particular to PM2.5.49 As 

described in Section II of this preamble 

(on technical background issues 

associated with PM2.5 and PM2.5

precursors), appropriate control of 

precursors is especially important 

because secondarily formed particles 

comprise a large fraction of ambient 

PM2.5 concentrations in many 

nonattainment areas. 

Section 302(g) of the CAA indicates 

that the term ‘‘air pollutant’’ includes 

‘‘any precursors to the formation of any 

air pollutant, to the extent the 

Administrator has identified such 

precursor or precursors for the 

particular purpose for which the term 

‘air pollutant’ is used.’’ In the 2007 

PM2.5 Implementation Rule and the 

2008 PM2.5 NSR Rule, the EPA 

recognized that the main scientific 

precursors of fine particle formation are 

SO2, NOX, VOC, and ammonia. Pursuant 

to the discretionary authority provided 

under section 302(g) to identify PM2.5

precursors for a particular program, the 

EPA also included requirements 

describing which precursor gases states 

were to evaluate for potential emission 

reductions as part of the state’s analysis 

of control measures to bring the area 

into attainment as expeditiously as 

practicable. 

To facilitate the evaluation and 

identification of reasonable control 

measures, the 2007 PM2.5

Implementation Rule included 

nationally applicable presumptions 

regarding the need to evaluate and 

potentially control emissions of certain 

precursors. Specifically, in 40 CFR 

51.1002, the EPA provided that a state 

must evaluate sources of direct PM2.5

and SO2 for potential control measures; 

a state presumptively was required to 

evaluate sources of NOX for potential 

control measures; and, a state was 

presumptively not required to evaluate 

sources of VOC and ammonia emissions 

for potential control measures. The EPA 

established these presumptions 

concerning VOC and ammonia in the 

2007 PM2.5 Implementation Rule 

because of factors such as uncertainties 

regarding the emissions inventories for 

ammonia, uncertainties concerning the 

role of some VOC in the formation of 

particles, and uncertainties regarding 

the effectiveness of specific precursor 

control measures in various regions of 

the country in reducing PM2.5

concentrations. For example, in some 

areas of the U.S., emission reductions of 

a particular precursor may lead to large 

changes in PM2.5 concentrations because 

there are relatively few tons of such 

precursor emissions in the area in the 

first place. In other areas, the opposite 

may be true, where emission reductions 

of a particular precursor may lead to 

small changes in PM2.5 concentrations 

because the area has an abundance of 

emissions of that particular precursor. 

The rule also included provisions for 

potentially reversing the EPA’s initial 

presumptions for certain precursors in a 

nonattainment area where the state or 

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50 Ibid. 

51See the Federal Register published on May 16, 

2008 (73 FR 28321, 28326 and 28327). 

52 Ibid. 

53NRDC v. EPA, 706 F.3d 428, 437, n.7 (D.C. Cir. 

2013). 

54NRDC v. EPA, 706 F.3d 428, 437, n.10 (D.C. Cir. 

2013). 

55 Ibid. 

56The EPA notes that it has already addressed the 

requirements of subpart 4 for precursors, 

specifically within the context of the requirements 

of section 189(e), in the General Preamble. See the 

Federal Register published on April 16, 1992 (57 

FR 13498, 13539, 13541 and 13542). 

the EPA had information demonstrating 

that the presumption was not valid for 

that area. The EPA left open the 

possibility in the 2007 PM2.5

Implementation Rule for regulation of 

VOC and ammonia emissions as PM2.5

precursors in any nonattainment area 

where regulation was necessary for 

purposes of attaining the 1997 PM2.5

NAAQS. Similarly, the EPA left open 

the possibility for not regulating NOX

where NOX sources from within the 

state did not have a significant 

contribution to PM2.5 concentrations in 

the nonattainment area. The preamble to 

the 2007 PM2.5 Implementation Rule 

discussed that to ‘‘reverse’’ the 

presumptions in the rule for NOX, VOC 

or ammonia, the state would need to 

provide an appropriate technical 

demonstration, and it provided 

examples of the types of analyses that 

could be included in such a 

demonstration. The EPA intended these 

to be rebuttable presumptions that 

either the state or the EPA might reverse 

through notice-and-comment 

rulemaking. These presumptions were 

not limited to precursor emissions only 

from major stationary sources, but rather 

were presumptions applicable to 

precursor emissions from all sources of 

such emissions within the area.50

The 2008 PM2.5 NSR Rule included 

similar policies for precursor 

presumptions in connection with the 

NSR requirements for nonattainment 

areas (the NNSR program).51 That rule 

provided a discussion of the possibility 

for the state or the EPA to provide a 

technical demonstration to reverse the 

presumptions for NOX, VOC or 

ammonia.52 The one significant 

difference between the two rules was 

the geographic scope of the 

requirements. The 2008 PM2.5 NSR Rule 

indicated that a precursor presumption 

could be rebutted if the emissions of 

that precursor from sources within the 

nonattainment area (emphasis added) 

did not significantly contribute to PM2.5

concentrations in the nonattainment 

area. This distinction is logical because 

the requirements of the NNSR program 

apply only to sources located within a 

designated nonattainment area. 

Conversely, the 2007 PM2.5

Implementation Rule indicated that the 

evaluation of whether a given precursor 

should be regulated should be based on 

emissions from sources throughout the 

entire state (emphasis added), because 

the state air agency has jurisdiction over 

sources throughout the entire state in 

developing strategies to improve air 

quality specifically in nonattainment 

areas. A more complete discussion of 

the 2008 NNSR program requirements 

for the PM2.5 NAAQS and the proposed 

changes concerning the regulation of 

PM2.5 precursors from new or modified 

major stationary sources of PM2.5

precursors in PM2.5 nonattainment areas 

is provided in Section VIII of this 

preamble. 

The EPA’s approach to the evaluation 

and regulation of PM2.5 precursors in 

both the 2007 and 2008 rules for 

implementing the 1997 PM2.5 NAAQS 

was called into question in the court’s 

2013 decision in NRDC v. EPA. As an 

example of the distinction between the 

divergent substantive requirements of 

subpart 1 and subpart 4, the court noted 

that subpart 4 has specific provisions 

related to regulation of precursors not 

present in subpart 1. Although the court 

stated that it was not reaching a 

decision on the issue of regulation of 

precursors, the court’s decision 

specifically discussed both the approach 

to precursors in the 2007 PM2.5

Implementation Rule and the 2008 

PM2.5 NSR Rule and compared those to 

section 189(e) of the CAA, which 

contains the sole explicit reference to 

the regulation of precursors in subpart 

4. The court decision included the 

following statements with regard to 

precursors: 

Ammonia is a precursor to fine particulate 

matter, making it a precursor to both PM2.5

and PM10. For a PM10 nonattainment area 

governed by subpart 4, a precursor is 

presumptively regulated. See 42 U.S.C. 

7513a(e) [section 189(e)]. But under the PM 

rules challenged here, the EPA established a 

rebuttable presumption against regulating 

ammonia unless a state or the EPA ‘‘provides 

an appropriate technical demonstration’’ that 

shows emissions from ammonia 

‘‘significantly contribute to PM concentration 

in the nonattainment area.’’ 40 CFR 

51.1002(c)(4)(i). When Congress enacted 

subpart 4, it sought to end this administrative 

gamesmanship.53

* * * * * 

In light of our disposition, we need not 

address the petitioners’ challenge to the 

presumptions in [40 CFR 51.1002] that 

volatile organic compounds and ammonia are 

not PM2.5 precursors, as subpart 4 expressly 

governs precursor presumptions.54

Section 189(e) for PM10 precursors 

(which the court concluded expressly 

includes PM2.5) provides that: ‘‘The 

control requirements applicable under 

plans in effect under this part for major 

stationary sources of PM10 shall also 

apply to major stationary sources of 

PM10 precursors, except where the 

Administrator determines that such 

sources do not contribute significantly 

to PM10 levels which exceed the 

standard in the area.’’ The court 

reasoned that the EPA’s approach to 

precursors in the 2007 PM2.5

Implementation Rule and 2008 PM2.5

NSR Rule had the effect of reversing the 

presumption embodied within subpart 4 

that a state should address all PM10

precursors unless the state has made a 

specific showing why regulation of a 

particular precursor is not necessary.55

The provisions of subpart 4 do not 

define the term ‘‘precursor’’ for 

purposes of PM10, nor do they explicitly 

require the control of any specifically 

identified particulate matter precursor. 

However, as stated above, the statutory 

definition of ‘‘air pollutant’’ provides 

that the term ‘‘includes any precursors 

to the formation of any air pollutant, to 

the extent the Administrator has 

identified such precursor or precursors 

for the particular purpose for which the 

term ‘air pollutant’ is used.’’ CAA 

section 302(g). The EPA has determined 

that SO2, NOX, VOC and ammonia are 

factual and scientific precursors to PM, 

and thus the attainment plan 

requirements of subpart 4 initially apply 

equally to emissions of direct PM2.5 and 

all of its identified precursors, except as 

otherwise provided in the statute (e.g. 

CAA section 189(e)). Section 189(e) 

explicitly requires the control of 

precursors from all major stationary 

sources, unless there is a demonstration 

to the satisfaction of the Administrator 

that such major stationary sources do 

not contribute significantly to PM levels 

that exceed the standards in the area.56

Section 189(e) contains the only express 

exception to control requirements under 

subpart 4. The control requirements for 

major sources referred to in this 

exception include requirements for 

RACM and RACT, additional reasonable 

measures, BACM and BACT, most 

stringent measures (as applicable) and 

NNSR on all major sources of precursors 

in the nonattainment areas. The General 

Preamble indicates that consideration of 

precursors is necessary for attainment 

plans, and it recognizes the specific 

applicability of section 189(e) to both 

existing and new major stationary 

sources, including new and modified 

sources subject to NNSR permitting 

requirements. Even though section 

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57See CAA requirements for states to demonstrate 

attainment ‘‘as expeditiously as practicable’’ 

(section 188(c)(1); section 172(a)(2)). 

58 57 FR 13498 (April 16, 1992). 

59 In the context of the PM10 NAAQS, the EPA has 

concluded that ‘‘advancement of the attainment 

date’’ should mean an advancement of at least 1 

calendar year. See State Implementation Plans; 

General Preamble for the Implementation of Title I 

of the CAA Amendments of 1990, 57 FR 13498 

(April 16, 1992). See also Sierra Club v. EPA, 294 

F.3d 155 (D.C. Cir. 2002). 

60See Section IV of this preamble for a thorough 

discussion of past reasonably available control 

measures (RACM) and reasonably available control 

technology (RACT) policy and guidance. Section IV 

discusses the EPA’s proposed policy that under 

subpart 4, for Moderate areas that demonstrate that 

attainment by the statutory attainment date is 

impracticable, RACM and RACT would constitute 

all those technologically and economically feasible 

measures available for sources in the area that can 

be implemented within 4 years of designation, but 

they would not constitute the complete set of 

measures required to demonstrate attainment as 

expeditiously as practicable. 

61See the Federal Register published on April 16, 

1992 (57 FR 13498, 13540 and 13541). 

62See, e.g., Assoc. of Irritated Residents v. EPA, 

et al., 423 F.3d 989 (9th Cir. 2005). 

189(e) only explicitly contemplates 

exceptions to control requirements for 

PM2.5 precursors from major stationary 

sources, the EPA believes that by 

analogy it has authority to promulgate 

regulations that allow states to 

determine that it is not necessary to 

regulate PM2.5 precursors from other 

source categories as well, under 

appropriate circumstances. 

When Congress adopted the 1990 

CAA Amendments, a NAAQS for PM10

was in effect, but no standard for PM2.5

had yet been established. At that time, 

it was understood that the interaction of 

PM precursors in the atmosphere led to 

the formation of particulate matter in 

many areas. However, in some of the 

PM10 nonattainment areas, air quality 

problems were caused primarily by area 

sources emitting direct PM emissions 

(e.g., a nonattainment area with 

numerous wood burning devices or with 

substantial sources of windblown coarse 

particles from construction sites), and 

precursor emissions from major 

stationary sources were not considered 

to make a significant contribution to the 

local nonattainment problem. For cases 

such as these, section 189(e) provided a 

possible exception to the requirement to 

control all PM2.5 precursors from major 

sources in all nonattainment areas. 

While section 189(e) expressly 

requires control of precursors from 

major stationary sources where direct 

PM from major sources is to be 

controlled unless certain conditions are 

met, as stated above, it is clear that 

subpart 4 and other CAA provisions 

collectively require the control of direct 

PM and all PM2.5 precursors from all 

types of sources (i.e., stationary sources, 

area sources, and mobile sources) as 

may be needed for the purposes of 

demonstrating attainment as 

expeditiously as practicable in a given 

area.57 Long-standing EPA guidance for 

RACM has stated that the state should 

inventory all emissions of the relevant 

pollutants and precursors in the 

nonattainment area and evaluate all 

economically and technologically 

feasible control measures for the 

relevant pollutant and precursors, and 

that the state should adopt those 

measures that are deemed reasonably 

available and necessary in order to 

attain the NAAQS as expeditiously as 

practicable.58 The state also must ensure 

that there is no other collection of 

available control measures that if 

adopted would advance the attainment 

date by at least one year.59 Section IV.D 

of this preamble provides additional 

discussion on the development of 

emissions inventories and the 

identification, adoption and 

implementation of reasonable control 

measures for Moderate PM2.5

nonattainment areas. 60

B. Proposed Precursor Policy Options 

The EPA is proposing this rule to 

address the attainment plan and certain 

NNSR requirements for PM2.5 under 

subpart 4. In light of the court’s decision 

in NRDC v. EPA, the EPA considers it 

necessary to address in this 

implementation rule how states must 

address regulation of PM2.5 precursor 

gases in attainment plans and NNSR 

programs for the PM2.5 NAAQS. As 

noted earlier, the court’s decision made 

clear that appropriate regulation of all 

precursors is initially presumptively 

required under the CAA, and the 

regulation of precursors is a critical 

issue for attainment of the PM2.5

NAAQS because secondarily formed 

particles are a substantial component of 

the PM2.5 nonattainment problem in 

most areas of the U.S. 

For the purposes of this 

implementation rule, the EPA considers 

that for all nonattainment areas, the 

PM2.5 precursors for regulatory purposes 

are SO2, NOX, VOC and ammonia. This 

rule does not propose any national 

presumption that would simply allow a 

state to exclude sources of emissions of 

a particular precursor from further 

analysis for control requirements. 

However, the EPA’s existing 

interpretation of subpart 4 

requirements—with respect to 

precursors in attainment plans for PM10, 

as set out in the General Preamble— 

contemplates that the state may develop 

an attainment plan that regulates only 

those precursors that are necessary to 

control for purposes of timely 

attainment in the area, i.e., states may 

determine that only certain precursors 

need to be regulated for attainment 

purposes.61 Courts have upheld this 

approach to the requirements of subpart 

4 for PM10.62

The EPA believes that application of 

a similar approach to PM2.5 precursors 

under subpart 4 is appropriate and 

reasonable. Thus, this proposal 

describes three proposed precursor 

options that provide for the possibility 

that, with appropriate justification 

provided by the state, further evaluation 

and implementation of control strategies 

for one or more PM2.5 precursors in a 

given nonattainment area may not be 

needed or required. Under each option, 

a state may provide a technical 

demonstration and reasoned 

justification for the exclusion of a PM2.5

precursor or precursors from control 

requirements for a particular 

nonattainment area. 

As explained above, the EPA 

interprets the CAA to require states to 

inventory and regulate all sources of 

PM2.5 precursors from all sources in the 

area, including area sources, mobile 

sources and stationary sources. This 

interpretation is based on CAA 

provisions requiring adoption of all 

RACM needed to attain the standard as 

expeditiously as practicable; section 

302(g), which defines an air pollutant as 

including all precursors contributing to 

the formation of that pollutant; and, the 

EPA’s identification of the four main 

PM2.5 precursors. For major stationary 

sources, section 189(e) requires that the 

control requirements applicable for 

major stationary sources of PM2.5 must 

also apply to major stationary sources of 

PM2.5 precursors, unless the state 

provides a showing that emissions of a 

particular precursor from major 

stationary sources do not contribute 

significantly to levels which exceed the 

standard in the area. Thus, the statute 

generally requires control of all PM2.5

precursors, but it provides an express 

exception applicable to major stationary 

sources. Because the statutory 

provisions of subparts 1 and 4 are not 

explicit with respect to how states 

should address PM2.5 precursors from 

non-major sources, the EPA is proposing 

regulations to assure proper evaluation 

and regulation of PM2.5 precursor 

emissions in PM2.5 nonattainment areas. 

Moreover, even with respect to 

regulation of precursor emissions from 

major stationary sources, section 189(e) 

contains ambiguities that require 

interpretation. For example, section 

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63 In Section VI.D, the EPA describes a parallel 

approach for distinguishing control measures 

required under sections 172(c)(6) and 189(b)(1)(B) 

for Serious nonattainment areas. 

189(e) does not specify the method by 

which the EPA should determine 

whether precursor emissions from major 

stationary sources contribute 

significantly to levels which exceed the 

standard in a given nonattainment area. 

Given that the provisions of subpart 4 

are ambiguous with respect to these 

issues, the EPA believes that it is 

necessary to interpret those 

requirements in this rulemaking. 

The EPA is thus seeking comment on 

three potential approaches to address 

PM2.5 precursors pursuant to the 

specific statutory requirements of 

subpart 4 and the overarching 

requirements of the CAA. In these 

proposed options, particular emphasis 

is given to the situations and 

circumstances under which the state 

would or would not be required to 

evaluate emission controls for a 

particular precursor and to adopt those 

controls that are necessary to 

demonstrate attainment of the NAAQS 

as expeditiously as practicable. Note 

that these options describe analyses that 

the state may choose to pursue to 

demonstrate that control requirements 

should not apply to a particular 

precursor. However, the state also may 

choose to require controls for all PM2.5

precursors in attainment plans and in its 

NNSR permitting program, and choose 

not to conduct any analyses to eliminate 

one or more precursors from 

consideration for controls. 

The descriptions of the three 

precursor policy options being proposed 

in this section discuss how PM2.5

precursors would need to be addressed 

by the state with regard to three specific 

implementation situations: (1) A 

Moderate area for which attainment of 

the relevant NAAQS by the end of the 

sixth calendar year after designation can 

be demonstrated; (2) a Moderate area for 

which it can be demonstrated that the 

relevant NAAQS cannot practicably be 

attained by the end of the sixth calendar 

year after designation; and (3) an area 

that is reclassified to Serious and is 

obligated to develop a Serious area 

attainment plan to attain the relevant 

NAAQS. Additionally, the EPA 

describes how each of the proposed 

precursor policy options would apply to 

the implementation of NNSR in a 

Moderate or Serious PM2.5

nonattainment area. Later in this 

section, the EPA discusses specific 

issues related to the technical 

‘‘precursor demonstrations’’ that states 

could choose to develop. The technical 

demonstration section includes a 

discussion of several types of analyses 

that a state could provide to the EPA to 

show that control measures for a 

specific PM2.5 precursor would not be 

needed for attainment or to expedite 

attainment, or to show that major 

stationary sources of a given precursor 

collectively do not significantly 

contribute to PM2.5 levels that exceed 

the relevant NAAQS in a given area. 

Before discussing the three precursor 

options, it is important to introduce a 

new term that is used throughout this 

section and other sections of the notice. 

Under subpart 4, RACM (including 

RACT) are those measures that can and 

must be implemented within 4 years of 

the area’s designation as nonattainment 

(pursuant to section 189(a)(1)(C)). The 

EPA recognizes, however, that other, 

similarly reasonable emissions 

reduction measures could be 

implemented after this 4 year period, 

and as late as the end of the sixth 

calendar year following designation, to 

help an area attain as expeditiously as 

practicable. Therefore, in this proposal 

the EPA is proposing to define the term 

‘‘additional reasonable measures’’ to 

describe those technologically and 

economically feasible control measures 

that could not be implemented within 

the 4 year period after designation, but 

could be implemented starting any time 

after that 4 year period through the end 

of the sixth calendar year after 

designation (note that this period could 

extend almost 3 additional years, 

depending on when during the year area 

designations are finalized). See 

proposed 40 CFR 51.1000. The EPA 

proposes to require implementation of 

these ‘‘other’’ control measures to the 

extent necessary to demonstrate 

attainment by the applicable attainment 

date pursuant to section 172(c)(6) of the 

CAA. That provision provides that 

nonattainment ‘‘plan provisions shall 

include enforceable emissions 

limitations, and such other control 

measures . . . as may be necessary or 

appropriate to provide for attainment of 

such standard in such area by the 

applicable attainment date . . .’’ 

Together, RACM and RACT and 

‘‘additional reasonable measures’’ make 

up the set of control strategies referred 

to in this proposed rule as ‘‘reasonable 

control measures.’’ 63 (Section IV.D of 

this preamble provides a detailed 

discussion of how a state must 

determine reasonable control measures 

for a Moderate PM2.5 nonattainment 

area.) The EPA requests comment on 

each of the three proposed options 

discussed below which describe how a 

state may demonstrate that additional 

emissions reductions of a particular 

precursor would not be needed or 

appropriate for an area’s attainment 

plan, and how it could demonstrate that 

emissions control requirements for a 

particular precursor would not be 

needed in NNSR permits for new or 

modified sources in the area. In 

particular, the EPA requests comment 

on whether only one of these 

approaches should be included in the 

final rule, or whether it would be 

appropriate to include multiple 

approaches (e.g., both Options 1 and 2), 

or only specific elements from the 

different options. The three proposed 

options are summarized as follows: 

• Option 1: Two independent 

analyses: (a) An attainment planning 

analysis demonstrating that control 

measures for a particular precursor are 

not needed for expeditious attainment, 

meaning that the precursor can be 

excluded from measures needed to 

attain as expeditiously as practicable for 

all types of sources; and (b) a section 

189(e) technical demonstration showing 

that major stationary sources of a 

particular precursor do not contribute 

significantly to levels that exceed the 

PM2.5 standard, meaning that the 

precursor can be excluded from control 

requirements for major sources 

including NNSR permitting; 

• Option 2: Single analysis 

demonstrating that all emissions of a 

particular precursor from within the 

area do not significantly contribute to 

PM2.5 levels that exceed the standard, 

meaning that control requirements for 

emissions of the precursor from major 

stationary and area sources, as well as 

mobile sources, would not be required 

for expeditious attainment, control 

requirements for major sources, or for 

NNSR permitting; 

• Option 3: An attainment planning 

analysis demonstrating that control 

measures for all types of sources of a 

particular precursor are not needed for 

expeditious attainment also would be 

deemed to meet the section 189(e) 

technical demonstration requirement, 

meaning that the state would not need 

to regulate emissions of the particular 

precursor from major stationary sources 

under the NNSR permitting program or 

other control requirements for major 

stationary sources. 

Each of these proposed options is 

presented in greater detail below. 

1. Option 1: Two independent 

analyses: (a) An attainment planning 

analysis demonstrating that control 

measures for a particular precursor are 

not needed for expeditious attainment, 

meaning that the precursor can be 

excluded from measures needed to 

attain as expeditiously as practicable for 

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64Note that under either sub-option, the state 

would be able to show that control of precursor 

emissions from major stationary sources would not 

be required if it could be demonstrated that such 

emissions do not contribute significantly to PM2.5

all types of sources; and (b) a section 

189(e) technical demonstration showing 

that major stationary sources of a 

particular precursor do not contribute 

significantly to levels that exceed the 

PM2.5 standard, meaning that the 

precursor can be excluded from control 

requirements for major sources and from 

NNSR permitting. 

As with the other options discussed 

below, the critical first step in any 

precursor analysis is the development of 

a comprehensive inventory of all 

precursor emissions in the 

nonattainment area. A state will be 

unable to reasonably determine whether 

emissions of a given PM2.5 precursor 

contribute significantly to the 

nonattainment problem in an area if the 

state has failed to account adequately 

for all such emissions in the area in its 

emissions inventory. 

In general terms, Option 1 would 

require separate analyses for purposes of 

attainment planning and for NNSR. 

Section 189(a) of the CAA describes the 

requirements for Moderate 

nonattainment areas. Within 18 months 

of designation as nonattainment, the 

state is required to submit a Moderate 

area plan that either demonstrates 

attainment as expeditiously as 

practicable but by no later than the end 

of the sixth year following designation, 

or demonstrates that attainment by such 

date would be impracticable. 

Under Option 1, the state would 

determine the precursors for which new 

control measures need to be adopted for 

a given nonattainment area through its 

determination of reasonable control 

measures needed for attainment. The 

state’s analysis of reasonable measures 

for a given PM2.5 NAAQS nonattainment 

area should begin by identifying 

potential control measures (and factors 

related to technological feasibility, 

economic feasibility, and time needed 

for implementation) for all precursors 

from all types of sources in the area (i.e., 

stationary, area, mobile) included in the 

emissions inventory. The analysis of 

reasonable measures and selection by 

the state of those emissions reduction 

measures that would provide for 

attainment as expeditiously as 

practicable (but no later than the end of 

the sixth calendar year after 

designation) would determine which 

precursors must be regulated in the 

nonattainment area for purposes of 

attainment. Except for the requirement 

to determine whether implementation of 

all remaining reasonable measures 

could collectively advance attainment 

by a year, there would be no additional 

demonstration needed by the state to 

justify that attainment planning control 

requirements should not apply to a 

particular precursor. Therefore, the 

analysis of reasonable measures may 

result in the state controlling only a 

subset of the four main PM2.5 precursors 

as part of the attainment demonstration. 

a. Moderate area for which the state 

can demonstrate attainment by the 

statutory attainment date. For certain 

nonattainment areas, the state may be 

able to demonstrate that attainment of 

the standard ‘‘as expeditiously as 

practicable’’ is possible by the end of 

the sixth year after designation (the 

statutory Moderate area attainment date) 

or sooner, and could be achieved by 

adopting regulations to reduce 

emissions of only a subset of the four 

PM2.5 precursors. Under this scenario, 

the state would be expected to provide 

analytical information showing that, 

even though new economically and 

technically feasible control measures 

may be available for one or more 

precursors, the reductions in emissions 

of the precursor(s) that could be 

achieved are not necessary for 

expeditious attainment and would not 

advance the attainment date by at least 

a year. Under Option 1, if the state 

determined that new emissions 

reductions of a particular precursor are 

not necessary for attainment and would 

not accelerate the attainment date by at 

least 1 year, then for the purposes of this 

particular PM2.5 Moderate area 

attainment plan, the state would not 

need to adopt additional control 

measures for that PM2.5 precursor. Given 

that additional regulation of that PM2.5

precursor would not be necessary for 

attaining the standard as expeditiously 

as practicable, the EPA would be able to 

approve the attainment plan for the area 

as meeting the requirements of subpart 

4. 

b. Moderate area for which the state 

can demonstrate that attainment by the 

statutory attainment date is 

impracticable. Section 189(a)(1)(B) 

provides that for certain nonattainment 

areas, the state may demonstrate that, 

even with implementation of all 

reasonable control measures available 

for reducing emissions of all direct PM 

and PM2.5 precursors, it would be 

impracticable to attain the standard by 

the end of the sixth calendar year after 

designation. In other words, the analysis 

would need to demonstrate that 

implementing all economically and 

technically feasible control measures 

that are available in the area, and the 

expected air quality change from such 

measures, would not be able to provide 

for attainment by the end of the sixth 

year after designation. 

For states that can make the showing 

that they cannot attain the NAAQS by 

the end of the sixth calendar year after 

designation, the question arises as to 

whether the state should be required to 

adopt all reasonable measures (i.e. 

measures that represent RACM and 

RACT because they are technologically 

and economically feasible and can be 

implemented in 4 years and all 

additional reasonable measures that can 

be implemented within 6 years) through 

regulation as part of the Moderate area 

plan, even if a subset of these measures 

collectively would have a minimal 

effect on reducing ambient PM2.5

concentrations. The EPA proposes two 

sub-options for areas that cannot 

demonstrate attainment during the 

Moderate area timeframe even with the 

implementation of all reasonable 

measures in the area. Under the first 

sub-option, the state would be required 

to adopt all available control measures 

for precursors through regulation as part 

of the Moderate area plan. The rationale 

supporting this approach would be that 

adopting all technologically and 

economically feasible measures would 

bring the area as close to attainment as 

possible during the timeframe 

prescribed for Moderate areas. Under 

this approach, if a measure can be 

implemented by the end of the sixth 

calendar year after the nonattainment 

designation and it meets the criteria for 

being considered ‘‘reasonable,’’ then the 

state must adopt and implement the 

measure. 

Under the second sub-option, the 

state would be able to elect not to 

impose those technologically and 

economically feasible measures that 

collectively have minimal effect on 

ambient PM2.5 levels in the area, based 

on the premise that such measures 

would be unreasonable to implement. 

To support this conclusion, the state 

would need to submit a technical 

demonstration showing that 

implementing available emissions 

controls for a particular precursor and/ 

or a specific set of sources would 

provide only minimal changes in PM2.5

concentrations in the area, and therefore 

such control measures should not be 

required during the timeframe 

prescribed for Moderate areas. The EPA 

requests comment on these two suboptions, including any technical 

information that would help support the 

commenter’s position. Regarding the 

second sub-option, the EPA requests 

comment on what degree of air quality 

change should be considered minimal 

for purposes of this analysis.64

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levels that exceed the standard, consistent with 

section 189(e). 

65The EPA’s two proposed options for 

determining BACM and BACT are discussed in 

detail in Section VI.D of this preamble. 

c. Area reclassified to Serious. A 

Moderate area can be reclassified to a 

Serious area under two scenarios. Under 

the first scenario, if a Moderate area fails 

to attain the standard by the applicable 

attainment date, it would then be 

reclassified by the EPA as a Serious area 

and the state would be required to 

develop and submit a Serious area 

attainment plan within 18 months of 

reclassification. Under the second 

scenario, the EPA could reclassify an 

area to Serious prior to the Moderate 

area attainment date if the EPA 

determines that it would be 

impracticable for the area to attain by 

the Moderate area attainment date. 

(Section V of this preamble provides 

additional detail on reclassifying a 

Moderate area to Serious under subpart 

4.) 

After an area has been reclassified to 

Serious, subpart 4 requires a state’s 

Serious area attainment plan to include 

the imposition of more stringent control 

measures (best available control 

measures (BACM) and best available 

control technology (BACT)) intended to 

bring the area into attainment as 

expeditiously as practicable but no later 

than the end of the tenth calendar year 

after designation. Given that the CAA 

requires a more stringent new 

attainment plan for Serious areas, under 

Option 1 the state would be required to 

identify the best available measures for 

all sources of direct PM2.5 emissions and 

emissions of PM2.5 precursors and adopt 

those measures to attain the standard as 

expeditiously as practicable.65

The BACM and BACT determination 

requires a more rigorous analysis than 

the RACM and RACT analysis, and such 

measures collectively should lead to a 

greater degree of emission reduction in 

the area than the analysis of reasonable 

control measures for the Moderate area 

plan. For this reason, under Option 1, if 

the state’s previous Moderate area 

attainment plan had indicated that new 

emissions reduction measures from 

sources of one or more precursors were 

not needed to attain by the end of the 

sixth calendar year after designation, 

then for the Serious area plan the state 

would need to reevaluate the best 

control measures addressing all PM2.5

precursors (i.e. SO2, NOX, VOC, and 

ammonia) and require implementation 

of those ‘‘best’’ available control 

measures for all precursors in order to 

bring the area into attainment as 

expeditiously as practicable, but no later 

than the end of the tenth year after 

designation. Under Option 1, any 

precursor demonstration that excluded 

one or more precursors from regulation 

in the Moderate area plan would not by 

itself also be sufficient to exclude the 

precursors from regulation in the 

Serious area plan. Further analysis 

would be needed to determine if control 

measures for those precursors qualify as 

‘‘best’’ control measures. The EPA has 

interpreted the starting point for 

considering ‘‘best’’ control measures as 

including those control measures to 

reduce emissions of direct PM2.5 or 

PM2.5 precursors that have been adopted 

by any state, particularly those states 

with the most severe PM2.5 air quality 

problems. (Note that in Section VI.D of 

this preamble, more details are provided 

on BACM and BACT determination 

criteria. The EPA is taking comment on 

two options for BACM and BACT 

determinations—one that expresses it as 

a requirement independent of the 

attainment demonstration, and one that 

expresses it as only those ‘‘best’’ 

measures that are needed for 

expeditious attainment no later than the 

end of the tenth calendar year after 

designation. The BACM and BACT 

determination approach adopted in the 

final rule accordingly will determine 

whether all best available emission 

controls for a particular precursor must 

be adopted or not in a Serious area). 

d. NNSR. Under Option 1, the initial 

expectation is that the state will need to 

address all four PM2.5 precursors under 

the NNSR program pursuant to the CAA 

and as reinforced by the January 2013 

NRDC v. EPA court decision. Pursuant 

to section 189(e), however, the state may 

provide a demonstration showing that 

emissions of a particular precursor from 

existing major stationary sources located 

in the nonattainment area do not 

contribute significantly to PM2.5 levels 

that exceed the standard in the area. 

Under Option 1, this analysis under 

section 189(e) for major sources would 

be completed independently from the 

analysis of reasonable control measures 

conducted for attainment planning 

purposes. Such an analysis would 

involve assessing the potential addition 

of precursor emissions in the area due 

to potential new major stationary 

sources, and would likely involve air 

quality modeling and other technical 

analyses by the state, developed in 

consultation with the EPA (see Section 

III.C. of this preamble for further 

discussion on such technical 

demonstrations). Note that under this 

provision of the CAA, it might be 

possible that a precursor would be 

considered important for attainment 

planning purposes, but would not be 

regulated as a PM2.5 precursor in NNSR 

permitting actions which, by definition, 

only apply to major sources of the 

nonattainment pollutant. For example, 

it might be possible that in a particular 

area the principal source of emissions of 

a certain precursor could be from 

mobile and area sources but not from 

major stationary sources of that 

precursor. The EPA requests comment 

on all aspects of proposed Option 1 as 

discussed above. 

2. Option 2: Single analysis 

demonstrating that all emissions of a 

particular precursor from within the 

area do not significantly contribute to 

PM2.5 levels that exceed the standard, 

meaning that control requirements for 

emissions of the precursor from 

stationary major and area sources, as 

well as mobile sources, would not be 

required for expeditious attainment, 

control requirements for major sources, 

or for NNSR permitting. 

Option 2 would provide the state the 

opportunity to provide the EPA with a 

scientifically credible technical analysis 

that would demonstrate that one or 

more precursors do not contribute 

significantly to the PM2.5 levels that 

exceed the standard, therefore controls 

on those emissions would not be 

effective in reducing PM2.5 levels in the 

area. As noted earlier in this section of 

the preamble, section 302(g) of the CAA 

includes ‘‘precursors’’ in the definition 

of ‘‘air pollutant,’’ but provides the EPA 

with some discretion in defining how 

these terms should be interpreted. In 

subpart 4, the CAA does not explicitly 

address control of precursors, except 

with regard to major stationary sources 

in section 189(e). The EPA interprets 

subpart 4 to require states to address 

PM2.5 precursors from all source 

categories in the evaluation of controls 

needed for attainment in a given area, 

e.g., in the evaluation of RACM and 

RACT level controls. By analogy to 

section 189(e), the EPA also believes 

that there may be circumstances in 

which states may validly demonstrate 

that control of one or more PM2.5

precursors is not needed to attain the 

relevant NAAQS expeditiously. 

Section 189(e) provides that precursor 

control requirements apply to major 

stationary sources of precursors of PM2.5

if major sources of PM are regulated 

under the attainment plan, unless it can 

be shown that such precursor emissions 

do not contribute significantly to 

exceedances of the relevant NAAQS in 

the area. Under Option 2, the EPA relies 

on the discretion provided in section 

302(g) and the section 189(e) concept of 

precursor emissions in an area having a 

significant or insignificant effect on 

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PM2.5 concentrations that exceed the 

standard to propose two precursor 

technical demonstration suboptions. 

Option 2A would allow the state to 

provide a technical demonstration 

showing that all emissions (i.e., from 

area, mobile and stationary sources in 

the area) of a particular precursor 

collectively do not provide a significant 

contribution to PM2.5 levels that exceed 

the standard in the area. The kinds of 

analytical approaches that could be 

appropriate for this type of 

‘‘contribution demonstration’’ are 

described later in this section. 

For Option 2B, the EPA proposes to 

allow states to provide a technical 

demonstration showing that PM2.5

concentrations in the area are not 

sensitive to potential reductions or 

increases in emissions of a particular 

precursor in the nonattainment area (e.g. 

because the particular precursor is not 

the limiting factor in secondary PM2.5

formation). More information is 

provided later in this section about 

possible analytical approaches to assess 

precursor ‘‘sensitivities’’ in an area (the 

optional technical demonstration 

described for Options 2A and 2B 

hereafter will be referred to as a 

‘‘precursor demonstration’’). The EPA 

requests comment on which of the two 

options (Option 2A or Option 2B) would 

be more preferable, and why. The EPA 

encourages commenters to provide 

examples of specific situations and 

areas in support of their 

recommendations. 

These proposed options are consistent 

with the EPA’s past practice for 

determining which technologically and 

economically feasible controls are 

necessary for expeditious attainment of 

the NAAQS. Specifically, the EPA has 

interpreted the RACM requirement in 

the CAA as requiring imposition of all 

reasonable controls as needed for 

expeditious attainment or to advance 

the attainment date by at least 1 year. 

The statute does not require imposition 

of additional controls if collectively 

such measures would not advance the 

attainment date. The EPA maintains it is 

reasonable to treat regulation of PM2.5

precursors in a manner similar to the 

agency’s treatment of direct pollutants 

and therefore concludes that states 

should not be required to implement 

control measures for a particular 

precursor or precursors if such measures 

will have little or no impact on PM2.5

concentrations in the area or if the state 

demonstrates that all emissions of a 

given precursor or precursors do not 

contribute significantly to the PM2.5

NAAQS exceedances in the area. 

a. Moderate area for which the state 

can demonstrate attainment by the 

statutory attainment date or for which 

the state can demonstrate that 

attainment by the statutory attainment 

date is impracticable. An approved 

precursor demonstration under Option 

2A would show that emissions of the 

particular precursor from all types of 

sources do not contribute significantly 

to PM2.5 levels that exceed the standard. 

As proposed, this type of demonstration 

therefore by definition would also 

satisfy the section 189(e) provision 

(which allows the state to demonstrate 

that emissions from just major 

stationary sources are not significant 

and therefore should not be subject to 

control requirements, such as NNSR, 

that apply to major stationary sources of 

direct PM2.5). Thus, the state could 

possibly develop one precursor 

demonstration analysis that would serve 

the purposes of both attainment 

planning and the section 189(e) 

insignificant major source contribution 

demonstration. 

The sensitivity analyses required 

under Option 2B would need to assess 

a series of precursor emissions 

reductions and increases to determine 

the sensitivity to air quality in the area. 

For example, the analysis should 

evaluate the effect on PM2.5

concentrations of various precursor 

emissions reduction scenarios 

appropriate to determine the sensitivity 

of precursors for the area (as would be 

relevant for an attainment plan); the 

analysis should also evaluate the effect 

on PM2.5 concentrations of various 

precursor emissions increase scenarios 

appropriate to determine the sensitivity 

of precursors for the area, simulating the 

potential effect of the addition of 

potential new major stationary sources 

(or major modifications) to the 

nonattainment area under the NNSR 

program. 

The EPA would evaluate the relevant 

analyses and other supporting 

information provided by the state. By 

submitting a ‘‘precursor demonstration’’ 

of this type, the state would not need to 

compile additional information on 

precursor control measures, or to 

proceed with actions to adopt and 

implement local or state regulations for 

the precursor. Precursor demonstrations 

as described in Options 2A or 2B could 

be conducted for Moderate areas for 

which the state can show that it can 

attain the standard by the end of the 

sixth calendar year after designation and 

for Moderate areas where the state’s 

plan demonstrates that attainment by 

such date would be impracticable. 

The EPA believes that general legal 

authorities under the CAA support the 

proposal of the overall precursor 

demonstration concept described above, 

and that requesting comment on these 

proposed options is appropriate from 

both a technical and a legal standpoint. 

This case specific approach is 

technically appropriate because the mix 

of PM2.5 precursor emissions and other 

relevant technical factors varies from 

area to area. For example, in some areas, 

one precursor may be abundant while 

the main precursor with which it reacts 

may be less abundant. In such cases, 

reducing emissions of the less abundant 

precursor (the ‘‘limiting’’ precursor) is 

generally more effective for reducing 

PM2.5 concentrations. In another type of 

area, the PM2.5 concentrations that 

exceed the standard may be commonly 

dominated by primary PM2.5 emissions 

rather than by secondarily formed PM2.5. 

The emissions of the particular 

precursor from sources in the 

nonattainment area could be found to 

have an insignificant contribution to 

PM2.5 levels that exceed the standard, 

and the potential air quality 

improvement from reducing emissions 

of the precursor in the area may be 

limited. 

The EPA believes that proposing 

Options 2A and 2B is appropriate from 

a legal standpoint based on authority 

provided the Administrator in sections 

302(g) and 301(a)(1) of the CAA. Section 

302(g) includes in the definition of ‘‘air 

pollutant’’ all the precursors to that 

pollutant, and it allows the EPA 

Administrator to regulate precursors for 

‘‘the particular purpose for which the 

term ‘air pollutant’ is used.’’ Under 

section 301(a)(1), ‘‘[t]he Administrator is 

authorized to prescribe such regulations 

as are necessary to carry out his 

functions under this Act.’’ Thus, with 

Option 2, the EPA proposes a 

framework by which the regulation of 

PM2.5 precursors for a specific 

nonattainment area can be modified if 

the state provides the EPA with a 

credible technical demonstration for 

exempting a particular precursor which 

meets certain criteria and can be 

approved by the EPA. In addition, as 

noted earlier the set of analyses 

described under Option 2A could also 

satisfy the section 189(e) provision 

allowing the state to demonstrate that 

major stationary source emissions of a 

particular precursor do not significantly 

contribute to levels that exceed the 

standard. While this approach is not 

explicitly described in the statute, the 

EPA believes that the proposed Option 

2 approach to precursor regulation is 

reasonable and allowed under the 

statutory authority provided in sections 

302(g) and 301(a)(1) noted above. 

The EPA anticipates that development 

of an approvable PM2.5 precursor 

demonstration by the state at the 

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beginning of the attainment plan 

development process will require a 

substantial level of effort and 

consultation with the EPA. Such a 

demonstration by the state would likely 

involve a combination of technically 

rigorous and complex analyses, such as 

air quality modeling and ambient data 

analyses. The extensive nature of this 

type of a technical demonstration early 

in the attainment plan development 

process is necessary because the 

demonstration serves as the basis for 

limiting the applicability and associated 

control strategy decisions only to 

specific precursors for both the 

attainment plan and for the NNSR 

permitting program. 

b. Area reclassified to serious. As 

noted earlier in this section, a Moderate 

area can be reclassified to Serious under 

two scenarios. Under the first scenario, 

if a Moderate area fails to attain the 

standard by the end of the sixth 

calendar year after designation, it would 

then be reclassified by the EPA as a 

Serious area, and the state would be 

required to develop and submit a 

Serious area attainment plan within 18 

months of reclassification. Under the 

second scenario, EPA could reclassify 

an area to Serious prior to the Moderate 

area attainment date if it can be shown 

that it would be impracticable for the 

area to attain by the Moderate area 

attainment date. 

Proposed Option 2 would allow a 

‘‘precursor demonstration’’ approach for 

Serious area plans in the same manner 

as for Moderate area plans. However, if 

the state had previously submitted a 

precursor demonstration that the EPA 

approved for the Moderate area 

attainment plan, under either proposed 

Option 2A or 2B the state would be 

required to review and update the 

precursor demonstration, taking into 

account any changes in the emissions 

inventory and any other relevant 

information or advances in technical 

tools developed since the initial 

demonstration was approved. Examples 

of such information would be improved 

emission estimation methods or 

emission factors for key source 

categories; changes in precursor 

emissions inventories due to emissions 

control programs or new source growth; 

the development of more advanced 

technical tools to assess the 

effectiveness of precursor reductions; 

and, updated information about new or 

more effective control technologies or 

emission reduction techniques. Any 

precursor demonstration that is 

approved as part of the Serious area 

attainment plan would need to be 

revised and updated if the area cannot 

attain the standard by the end of the 

tenth calendar year after designation 

and seeks an extension under section 

188(e) or does not attain the standard by 

the applicable Serious area attainment 

date and is subsequently subject to 5 

percent annual emission reductions 

under section 189(d). 

One other important factor to consider 

is the substantial amount of time that 

can elapse between the submission of a 

Moderate area attainment plan for a 

particular nonattainment area, and 

submission of a Serious area attainment 

plan. The plan for a Moderate area is 

due within 18 months of designation. 

Under the EPA’s overall proposed 

approach to attainment plan 

development, the state would be 

required to evaluate control measures 

for all types of sources and for all PM2.5

precursors in order to ensure attainment 

of the standard as expeditiously as 

practicable. The full assessment to 

identify reasonable control measures 

would involve a thorough compilation 

and analysis of information on control 

technologies and the technological 

feasibility of implementation of such 

measures for sources in the area; the 

assessment of associated control costs 

and economic feasibility of 

implementation; information on the 

time needed for deployment and 

implementation of such control 

measures; and, the resulting timeline for 

achieving emissions reductions. 

If the Moderate area does not attain 

the standard by the end of the sixth 

calendar year after designation, then as 

required by to the CAA, the EPA would 

have 6 months to make a determination 

to that effect, and the area would be 

reclassified to Serious. The state would 

then have 18 months to submit, at a 

minimum, a new attainment 

demonstration and control strategy 

comprising BACM and BACT. Thus, 

under these circumstances, these key 

Serious area plan elements would be 

due at least 8 years after the EPA 

designated the area nonattainment, and 

more than 6 years after the state 

submitted the original Moderate area 

plan. Because of the potentially 

protracted timeline for developing, 

implementing and revising as necessary 

the SIP for a given PM2.5 nonattainment 

area under subpart 4, the EPA believes 

it is reasonable for the state to be 

required to update any precursor 

demonstration it had previously 

developed for the area if the area is 

reclassified as Serious. 

The EPA requests comment on the 

requirement for the state to review and 

update any previously approved 

‘‘precursor demonstration’’ if the area 

fails to attain the standard by the 

applicable Moderate area attainment 

date. The EPA also requests comment 

on the requirement for the state to 

review and update any previously 

approved ‘‘precursor demonstration’’ if 

the area fails to attain the standard by 

the applicable Serious area attainment 

date. 

c. NNSR. An approvable precursor 

demonstration under either Option 2A 

or Option 2B would evaluate emissions 

of a particular precursor from all types 

of sources. Accordingly, if the state 

provides an approvable precursor 

demonstration for all types of sources of 

a particular precursor as described 

above, then under Option 2A, the state 

would also be able to rely on the same 

technical demonstration to conclude 

that emissions of that precursor just 

from major stationary sources in the 

area do not provide a ‘‘significant 

contribution’’ to PM2.5 concentrations in 

the area pursuant to section 189(e). 

Thus, under Option 2A, the state would 

not need to apply the NNSR control 

requirements for PM2.5 to that precursor 

in the particular PM2.5 nonattainment 

area(s) for which the EPA approves the 

demonstration. 

Under Option 2B, the state would 

conduct analyses to determine the 

sensitivity of PM2.5 levels in the area 

(that exceed the standard) to potential 

increases in emissions (relevant for 

NNSR) and decreases (relevant for 

attainment demonstrations). If the state 

provided an approvable precursor 

demonstration showing that PM2.5

concentrations are insensitive to 

potential increases in emissions of a 

particular precursor in the area, then 

under Option 2B the state would be able 

to rely on this technical demonstration 

as the basis for not regulating that 

precursor for major stationary sources 

under NNSR. 

Additionally, there could be a 

situation where the state finds that 

emissions of another precursor (i.e., a 

precursor that was not the subject of the 

initial precursor demonstration) from 

only major stationary sources located in 

the nonattainment area could be 

considered to have an insignificant 

contribution to PM2.5 levels that exceed 

the standard in the area (under Option 

2A). For example, mobile and area 

source emissions of a PM2.5 precursor 

could be determined to provide a larger 

contribution to PM2.5 levels than major 

stationary sources in a given 

nonattainment area and would be the 

focus of the attainment strategy, and the 

major stationary source emissions of 

that same precursor might have only a 

minimal contribution to PM2.5 levels. In 

this situation, the state could develop a 

separate demonstration under section 

189(e) to support the exclusion of the 

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66Note that while the NNSR program needs to be 

implemented from the effective date of an area’s 

nonattainment designation, in some situations the 

state would implement either its existing NNSR 

program for PM2.5 or, in the absence of such 

program, 40 CFR part 51 Appendix S, the default 

NNSR program, until the EPA approves the state’s 

PM2.5 attainment plan and revised NNSR 

regulations for PM2.5. 

additional precursor from 

implementation requirements 

applicable to all major stationary 

sources, including NNSR program 

requirements (assuming the state 

analysis includes appropriate 

consideration of potential new sources 

of the relevant precursor). With an 

approved demonstration under section 

189(e), major stationary sources of that 

precursor could also be excluded from 

the NNSR control requirements for 

PM2.5. The EPA seeks comment on all 

aspects of proposed Option 2. 

3. Option 3: An attainment planning 

analysis demonstrating that control 

measures for all types of sources of a 

particular precursor are not needed for 

expeditious attainment also would be 

deemed to meet the section 189(e) 

technical demonstration requirement, 

meaning that the state would not need 

to regulate emissions of the particular 

precursor from major stationary sources 

under the NNSR permitting program or 

other control requirements for major 

stationary sources. 

Under proposed Option 3, the 

consideration of precursors in the 

attainment planning process for 

Moderate and Serious areas would 

closely follow the approach described 

for Option 1 (see Sections III.B.1.a–c of 

this preamble). As described for Option 

1, after developing a comprehensive 

emissions inventory, the state would 

conduct an analysis to identify the new 

reasonable control measures that need 

to be adopted and implemented in order 

for the Moderate area to attain the 

standard as expeditiously as practicable, 

but no later than by the end of the sixth 

calendar year after designation (this 

analysis is described in greater detail in 

Section III.B.1.a in this preamble). If the 

state determines that adoption of 

additional economically and technically 

feasible emission reduction measures 

for a particular precursor are not 

necessary for expeditious attainment by 

the end of the sixth calendar year after 

designation, and that such measures 

collectively would not accelerate the 

attainment date by at least a year, then 

for the purposes of this Moderate area 

attainment plan, the state would not 

need to adopt such additional measures 

because they would not be considered 

reasonable. (Note that the need for 

additional emissions reductions of the 

particular precursor would have to be 

re-evaluated if the area is reclassified to 

Serious, or if the area submitted a SIP 

revision requesting an extension of the 

Serious area attainment date under 

section 188(e)). 

To clarify the intent of Option 3, 

unlike under Option 1, a separate 

analysis to show that major stationary 

sources of a particular precursor do not 

contribute significantly to PM2.5 levels 

in a given PM2.5 nonattainment area for 

purposes of section 189(e) would not be 

needed. If the state’s single analysis 

shows that emission reduction measures 

are not needed from sources of a 

particular precursor in order to 

demonstrate expeditious attainment, 

then under proposed Option 3 the same 

analysis would also be considered 

adequate to meet the requirements of 

section 189(e). In effect, the attainment 

planning analysis would define the set 

of precursors that would be subject to 

control under both the attainment plan 

and the NNSR permitting program for 

the area.66

The rationale supporting the Option 3 

approach focuses on the section 189(e) 

emphasis on precursor control 

requirements. If control measures are 

not needed in a Moderate 

nonattainment area to reduce emissions 

of a particular precursor from all types 

of sources in order to demonstrate 

attainment or to advance the attainment 

date, then under the rationale of 

proposed Option 3, it would follow that 

the state would not need to include any 

other control requirements that apply to 

major stationary sources of that 

precursor, including control 

requirements for PM2.5 under the NNSR 

program. The theory for this option 

would be that if the state determines 

that new control requirements for 

emissions of the particular precursor are 

not needed for purposes of attainment 

planning because they would not 

contribute to reducing PM2.5 levels that 

exceed the standard, then other control 

requirements to address emissions of 

that precursor also would not be 

needed. Note that under this option, the 

state also would not be required to 

analyze the potential effect of increases 

in emissions of the particular precursor 

(e.g., from the possible permitting of 

new sources) on PM2.5 concentrations in 

the area. The EPA requests comment on 

the rationale supporting Option 3. 

Additionally, under Option 3, as was 

the case with Option 2, there could be 

a situation where the state determines 

that control measures for a particular 

precursor are generally needed in order 

to demonstrate attainment as 

expeditiously as practicable, but that the 

major stationary sources of that 

precursor that are located in the 

nonattainment area have an 

insignificant contribution to PM2.5 levels 

that exceed the standard in the area. 

Under this Option 3, the EPA believes 

that section 189(e) provides the state 

with the authority to develop a separate 

demonstration to show that, even 

though control measures for a specific 

precursor emitted by sources other than 

major stationary sources are necessary 

to demonstrate expeditious attainment 

in an area, major stationary sources of 

that precursor have an insignificant 

contribution to PM2.5 concentrations 

that exceed the standard in the area. 

Thus, controls from major stationary 

sources of that precursor would not be 

required for either the attainment plan 

or the NNSR program. More discussion 

on the potential options for precursor 

technical demonstrations is included in 

Section III.C of this preamble. The EPA 

seeks comment on all aspects of 

proposed Option 3. 

The EPA also seeks comment on 

whether only one of these approaches 

should be included in the final rule, or 

whether it would be appropriate to 

include multiple approaches (e.g., both 

Options 1 and 2) or a hybrid of two 

approaches by which a state could 

demonstrate that a particular precursor 

would not need to be addressed in the 

attainment plan or NNSR permitting 

program for a specific area. 

C. Technical Approaches for 

Demonstrating That a Precursor Does 

Not Need To Be Subject to Control 

Requirements 

As noted earlier, in the preamble to 

the 2007 PM2.5 Implementation Rule, 

the EPA included a discussion allowing 

for the state to submit a technical 

demonstration to show to the 

satisfaction of the EPA that emissions of 

a particular precursor do not 

significantly contribute to PM2.5

concentrations in the area. In that 

preamble discussion, the EPA indicated 

that such a demonstration should be 

based on the weight of evidence of 

available information, and that any such 

demonstration by the state must be 

approved by the EPA. The 2007 PM2.5

Implementation Rule also discussed a 

number of types of analyses that could 

inform this precursor demonstration, 

such as speciation data analyses, air 

quality modeling studies, chemical 

tracer studies, emissions inventories, or 

special intensive measurement studies 

to evaluate specific atmospheric 

chemistry in an area. In the 2007 PM2.5

Implementation Rule, the EPA intended 

to provide states with the flexibility to 

provide a range of different supporting 

analyses that would be appropriate for 

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the area, recognizing that nonattainment 

areas differed in terms of such factors 

as: (i) The mix of emissions sources 

located in the nonattainment area and 

outside the area that are contributing to 

PM2.5 concentrations in the area; (ii) the 

levels of PM2.5 species measured in the 

area; (iii) the times of year when highest 

PM2.5 concentrations are observed; (iv) 

the topography of the area; (v) the 

severity of the nonattainment problem; 

and, (vi) the patterns of emissions and 

population growth in and around the 

nonattainment area. Under the 2007 

PM2.5 Implementation Rule, an 

important criterion for any technical 

precursor demonstration provided by a 

state, however, was that it had to fairly 

represent the information available to 

the state and the information made 

available to it by the public. 

For this proposed implementation 

rule, the EPA similarly proposes that the 

state should have the flexibility to 

present multiple types of analyses to 

support any demonstration for 

exempting a precursor from control 

requirements as long as they fairly 

represent the available information, and 

accordingly proposes that the EPA 

should review any such demonstration 

based on the weight of evidence. Unlike 

in the prior implementation rule, 

however, later in this section the EPA 

raises the question of whether certain 

specific types of analyses should be 

included as minimum required 

components of any precursor 

demonstration that a state chooses to 

submit to the EPA for approval. 

The preamble to the 2007 PM2.5

Implementation Rule indicated that if a 

state developed a precursor 

demonstration as part of its draft SIP, 

then in accordance with the state 

rulemaking process, the demonstration 

would be subject to public review at the 

state level. It also stated that, as required 

under any rulemaking process, the state 

had to consider and provide a response 

in the rulemaking record to any 

information or evidence brought 

forward by commenters during the 

state’s SIP planning, development and 

review process. By insuring that this 

important issue was explicitly 

addressed and supported in the 

attainment plan submitted to the EPA, 

the EPA could better evaluate the 

precursor demonstration in accordance 

with its obligations under the CAA. The 

EPA believes these are sound 

procedural steps for a state rulemaking 

process, and the regulations being 

proposed as part of this rule include 

similar language providing for public 

review of any proposed precursor 

demonstration. 

The 2007 PM2.5 Implementation Rule 

did not provide a specific due date for 

submittal of any precursor 

demonstration, although it was assumed 

that if a state were to pursue such a 

demonstration, it would need to be done 

early in the attainment plan 

development process and submitted to 

the EPA no later than the date of the 

attainment plan submission itself. It was 

recommended that the state develop any 

such demonstration in consultation 

with the appropriate EPA Regional 

Office. In this proposal, the EPA is 

proposing that if a state is interested in 

developing a PM2.5 precursor 

demonstration to support not regulating 

one or more PM2.5 precursors in the 

attainment plan for an area, it should 

consult with the EPA Regional Office as 

early as possible to discuss appropriate 

analyses to be included. In its review of 

any precursor demonstration provided 

by a state, the EPA will consider all 

currently available information. 

Under all three proposed precursor 

policy options described above, the state 

would have the opportunity to provide 

a precursor demonstration to meet the 

requirements of section 189(e) of the 

CAA. Precursor demonstrations 

pursuant to section 189(e) should 

evaluate the significance of the 

contribution of emissions of a particular 

precursor from existing major stationary 

sources to fine particle concentrations 

that exceed the standard. However, 

Options 2A and 2B differ from the 

others in that they would provide the 

state with the ability to conduct a 

precursor demonstration that 

comprehensively assesses the 

contribution of a particular precursor 

from all types of sources in the 

nonattainment area (not just from major 

stationary sources as specifically 

addressed by section 189(e)) for the 

purposes of informing which precursors 

must be addressed in both the 

attainment plan and in the NNSR 

program for a particular PM2.5

nonattainment area. (Note that Option 2 

would not prevent the state from also 

conducting an additional analysis under 

section 189(e), if warranted, to further 

demonstrate that while all emissions of 

a particular precursor make a significant 

contribution to PM2.5 levels that exceed 

the standard, the emissions from just the 

major stationary sources of that 

precursor collectively do not contribute 

significantly to PM2.5 levels that exceed 

the NAAQS in the area.) The EPA has 

considered three important questions 

regarding the scope and the potential 

requirements associated with precursor 

demonstrations, and requests comment 

on the questions and technical analysis 

options presented below. 

1. What is the geographic area from 

which precursor emissions should be 

assessed? 

In the 2007 PM2.5 Implementation 

Rule, the preamble indicated that a 

precursor demonstration analysis 

addressing all source types covered by 

the attainment plan should evaluate the 

impact of emissions from sources 

located throughout the entire state. In 

contrast, the 2008 PM2.5 NSR Rule 

suggested that a precursor 

demonstration for NNSR purposes 

should evaluate emissions from major 

stationary sources of a particular 

precursor located within the 

nonattainment area only. 

In determining which approach to 

include in the present proposal, the EPA 

believes that it continues to be 

reasonable that any precursor 

demonstration conducted to assess 

precursor significance for NNSR 

purposes should evaluate emissions 

from major stationary sources of the 

precursor from within the 

nonattainment area only. Section 189(e) 

is included in a part of the CAA that 

specifically sets forth nonattainment 

area requirements. For attainment 

planning purposes it is less clear that 

the evaluation of emissions should be 

limited only to sources from within the 

nonattainment area, because the state 

has jurisdiction over emissions sources 

located throughout the state, and can 

impose emission reduction 

requirements on contributing sources 

outside of nonattainment areas if 

necessary to help bring areas with 

violating monitors into attainment. At 

the same time, that argument would 

suggest that section 189(e) should be 

interpreted as requiring two different 

analyses of the impacts of precursors 

emitted from two different geographic 

scales (from within the nonattainment 

area, as well as from a broader area that 

influences air quality within the 

nonattainment area, which could 

include the entire state). The EPA does 

not believe such an interpretation is 

required, nor does it believe that such 

multiple analyses are warranted. The 

statute simply refers in general terms to 

precursor emissions from major 

stationary sources and does not 

differentiate between control 

requirements for attainment planning 

and control requirements for other 

purposes, such as NNSR permitting. The 

statute also does not indicate that 

multiple analyses must be done to 

assess major stationary source impacts 

from multiple geographic scales. For 

these reasons, the EPA is proposing that 

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15360 Federal Register / Vol. 80, No. 55 / Monday, March 23, 2015 / Proposed Rules 

67For more information on CMAQ, see http://

www.epa.gov/AMD/Research/RIA/cmaq.html. For 

more information on CAMx, seehttp://

www.camx.com/. 

68See Simon et al., Memorandum to ozone 

NAAQS docket EPA–HQ–OAR–2008–0699, 

‘‘Model-based Rollback Using the Higher Order 

Direct Decoupled Method (HDDM),’’ August 14, 

2012. 

any precursor demonstration must 

include an evaluation of emissions from 

sources located in the nonattainment 

area only. The EPA requests comment 

on this proposed approach. 

2. Should the EPA’s guidance provide a 

specific list of analyses as ‘‘minimum 

requirements’’ that must be included in 

any proposed precursor demonstration? 

As noted above, the EPA encourages 

states to provide a range of analyses to 

thoroughly understand the effect of 

precursor emissions on PM2.5

concentrations in an area. In past 

discussions with state representatives 

regarding potential approaches to 

regulating PM2.5 precursors, some 

representatives have suggested that this 

PM2.5 implementation rulemaking 

should include more specificity about 

the minimum requirements for technical 

demonstrations to support exclusion of 

PM2.5 precursors from regulatory 

requirements in attainment plans, while 

others have recommended a less 

prescriptive approach. One overarching 

issue is how detailed the EPA’s 

guidance should be with regard to the 

analytical requirements for any 

proposed precursor demonstration. As 

noted earlier, technical demonstrations 

can include data such as ambient 

speciation data analyses, air quality 

modeling studies, chemical tracer 

studies, emissions inventories, and/or 

special intensive measurement studies. 

Air quality modeling analyses are 

discussed in more detail below. 

a. Contribution analysis. Based on the 

statutory language of section 189(e), it 

appears that, at a minimum, any 

precursor demonstration conducted 

specifically pursuant to section 189(e) 

must evaluate the contribution of 

current emissions of the relevant 

precursor from existing major stationary 

sources to current (or most recent) PM2.5

concentrations observed in the 

nonattainment area (note that this type 

of analysis is possible under Option 1 

and Option 3). In addition, as described 

above, any precursor demonstration 

under Option 2A must evaluate the 

contribution of emissions of the relevant 

precursor from all sources (not just 

major stationary sources) to current (or 

recent) PM2.5 concentrations observed in 

the nonattainment area. 

In light of the statutory language and 

the capabilities of existing technical 

tools, the EPA proposes to require that 

the state conduct such a contribution 

analysis at a minimum as part of any 

proposed precursor demonstration, and 

that the state conduct an analysis using 

an air quality modeling system that 

adequately accounts for the PM2.5

pollution problem within the 

nonattainment area. Several 

photochemical air quality models (e.g., 

Community Multi-Scale Air Quality 

Model (CMAQ) and the Comprehensive 

Air Quality Model with Extensions 

(CAMx)) can be used to quantify the 

contributions of precursor emissions to 

PM2.5 concentrations in the area.67 For 

example, states could compare base case 

conditions (at current precursor 

emissions levels) with a separate model 

simulation in which the relevant 

precursor emissions are reduced by a 

large percentage. The difference in the 

estimated PM2.5 concentrations provides 

one indication of the relative 

significance of the precursor emissions 

to PM2.5 concentrations in the area. This 

type of contribution analysis can also be 

accomplished by using existing 

advanced tools within photochemical 

air quality models, such as ‘‘source 

apportionment’’ capabilities which 

allow one to track precursor emissions 

as they ‘‘form’’ PM2.5 (in the model) and 

then report their contributions 

separately. The EPA requests comment 

on including a contribution analysis as 

a minimum requirement in any 

proposed precursor demonstration 

under Option 2A. 

b. Sensitivity analysis. The EPA notes 

that changes in PM2.5 concentrations 

from current conditions in any area will 

not necessarily be linear with respect to 

changes in PM2.5 precursor emissions. 

Therefore, another important question is 

whether any precursor demonstration 

should be required to include an 

assessment of how ‘‘sensitive’’ the area 

will be to potential reductions or 

increases in emissions of the relevant 

precursor. Sensitivity analyses of 

potential reductions in emissions would 

be most appropriate for attainment 

planning (and relevant to Option 2B), 

whereas sensitivity analyses of potential 

increases in emissions (e.g., relevant to 

NNSR permitting) would be appropriate 

for all section 189(e) technical 

evaluations (possible under Options 1, 

2B and 3). Sensitivity analyses are 

important because of the complexity 

and variability of the atmospheric 

chemistry affecting PM2.5 concentrations 

in different areas across the country. 

The principal PM2.5 components that 

are secondarily formed in the 

atmosphere are the result of chemical 

reactions between various PM2.5

precursors (see Section II of this 

preamble for more information on 

specific precursor reactions). Thus, the 

most effective precursor strategies for 

reducing PM2.5 concentrations as part of 

attainment planning will vary from area 

to area, depending upon which specific 

precursors play a role in forming or 

limiting PM2.5 formation in the 

particular area. Likewise, in evaluating 

which precursors would be appropriate 

to exclude from regulation for NNSR in 

an area, it is important to understand 

the current sensitivity of the atmosphere 

to potential increases in precursor 

emissions that could result from the 

addition of new sources to the 

nonattainment area. 

One approach to assessing precursor 

sensitivities would be to conduct a 

model simulation that evaluates the 

effect on PM2.5 concentrations in the 

area resulting from a given set of 

precursor emission reductions and 

emission increases. Simulations could 

be conducted to assess a set of emission 

reduction and emission increase 

scenarios deemed appropriate to 

determine the sensitivity of a particular 

precursor in a specific area. Another 

approach that could be used is a 

scientific technique called the 

‘‘decoupled direct method’’ (DDM), 

which efficiently estimates the impacts 

on PM2.5 concentrations as a result of 

reducing or increasing precursor 

emissions in the model.68

For the reasons discussed above, the 

EPA also proposes that any precursor 

demonstration conducted under 

proposed Option 2B must provide a set 

of sensitivity analyses that evaluate the 

effect of a range of emissions changes 

associated with measures considered 

economically and technically feasible in 

a particular nonattainment area. 

Analyses that reduce emissions of a 

particular precursor will help the state 

and the EPA to understand how 

‘‘responsive’’ the atmosphere would be 

to control measures and how effective 

such reductions would be relative to 

other precursor reductions. Although 

not specifically required for other 

options under this proposed rule, 

precursor sensitivity analyses evaluating 

the effect of varying degrees of potential 

precursor reductions would provide 

meaningful information for any 

precursor demonstration intended to 

show that a particular precursor does 

not need to be addressed for attainment 

planning. Conversely, sensitivity 

analyses that consider the effect of a 

range of potential emissions increases in 

the nonattainment area will help the 

state and the EPA to understand the 

potential response of PM2.5

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69Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42011. 

70See Rule To Reduce Interstate Transport of Fine 

Particulate Matter and Ozone (Clean Air Interstate 

Rule); Revisions to Acid Rain Program; Revisions to 

the NOX SIP Call, 70 FR 25162 (May 12, 2005). 

concentrations to projected growth in 

the area, including potential increases 

in emissions associated with potential 

newly permitted sources that emit the 

precursor in question. Any precursor 

demonstration intended to show that a 

particular precursor does not need to be 

addressed for NNSR should include 

sensitivity analyses evaluating the effect 

of varying degrees of precursor emission 

increases in the area. The EPA 

recommends that the state conduct 

these analyses using air quality 

modeling tools, but the state could 

provide additional relevant analyses as 

well. The EPA requests comment on the 

proposed requirement for inclusion of 

sensitivity analyses in any precursor 

demonstration. 

3. Should there be a ‘‘bright line’’ value 

to indicate that any estimated 

contribution to annual average or 98th 

percentile PM2.5 concentrations in the 

nonattainment area that exceeds this 

value would be considered 

‘‘significant’’? 

In considering this question, it is 

helpful to first look to how the concept 

of a significant, or insignificant, 

contribution has been interpreted with 

regard to particulate matter in past PM10

guidance (Addendum to the General 

Preamble) and in other PM2.5-related 

regulations, such as the CAIR. In the 

Addendum, the EPA introduced the 

concept of a ‘‘de minimis’’ impact from 

a source category for the purposes of the 

identification and evaluation of 

BACM.69 While a later discussion in 

this proposal addresses whether or not 

to maintain a similar de minimis source 

category-based policy approach for 

future BACM and BACT source category 

analyses, what is relevant for this 

precursor discussion is the EPA’s 

guidance in the Addendum on what 

could be considered a ‘‘de minimis,’’ or 

‘‘insignificant,’’ ambient impact for 

purposes of PM10. In the Addendum, the 

EPA indicated that a 1 mg/m3

contribution to the annual PM10

standard of 50 mg/m3 (equal to 2 percent 

of the applicable NAAQS at the time), 

or a 5 mg/m3 contribution to the 24-hour 

PM10 standard of 150 mg/m3 (equal to 

3.3 percent of the applicable NAAQS at 

the time) presumptively would be 

considered ‘‘de minimis.’’ The EPA set 

forth these levels in a Federal Register 

document, citing the discretionary 

authority of an administrative agency to 

exempt from regulation emissions (from 

source categories) ‘‘which contribute 

only negligibly to ambient 

concentrations which exceed the 

NAAQS.’’ 

Developed pursuant to subpart 4, this 

past guidance on what could be 

considered to be a de minimis or 

insignificant level of PM10 contribution 

from a source category can potentially 

inform this proposed rule for 

implementing the PM2.5 NAAQS. 

Accordingly, this proposal includes two 

options: (i) A ‘‘no-threshold’’ option, 

and (ii) a proposed threshold option 

derived from the ambient levels relied 

on for the PM10 source category de 

minimis thresholds, but adjusted to 

account for the 2012 PM2.5 NAAQS. 

The concept of ‘‘significant 

contribution’’ also has been a central 

one with regard to interstate transport 

and the interpretation of section 

110(a)(2)(D) of the CAA. In past 

programs to address interstate transport, 

such as the CAIR, an ‘‘upwind’’ state 

was identified as potentially subject to 

additional emission control 

requirements if the impact of SO2 and 

NOX emissions from the upwind state to 

any nonattainment area in a downwind 

state exceeded 1 percent of the relevant 

PM2.5 standard at a violating monitor in 

another state. This was merely the first 

step of the analysis, but it provided an 

initial threshold for determining 

whether further analysis was warranted. 

In this proposal, the concept of a 

significant contribution refers to the 

effect of emissions of a particular 

precursor from sources within the state 

or nonattainment area to local PM2.5

concentrations in the nonattainment 

area. The specific purpose and context 

for which the phrase ‘‘contribute 

significantly’’ is used in section 189(e) 

is very different from the purpose and 

context for which it is used in section 

110(a)(2)(D). Thus, while a previous 

interstate transport rule under section 

110(a)(2)(D) considered the combined 

impact of SO2 and NOX emissions from 

an upwind state on ambient PM2.5 at a 

violating monitor to be insignificant if it 

was less than 1 percent (i.e., 0.15 mg/m3

on an annual average basis), it would 

not necessarily be appropriate to also 

consider the contribution from 

emissions of a specific precursor within 

a nonattainment area to be 

‘‘insignificant’’ if it does not exceed a 

similar 1 percent ambient concentration 

level.70

There are a number of important 

distinctions between the section 

110(a)(2)(D) interstate transport 

provision and the section 189(e) 

provision addressing contributions of 

major stationary sources in a 

nonattainment area which would 

indicate that the 1 percent of the 

NAAQS significant contribution 

thresholds that have been included in 

section 110(a)(2)(D) rulemakings may 

not be relevant for purposes of section 

189(e) precursor demonstrations. 

Section 110(a)(2)(D) was designed to 

address the collective contribution of 

interstate transport of pollution from 

multiple upwind states, while section 

189(e) addresses contributions from 

major stationary sources in a single 

nonattainment area. In addition, section 

110(a)(2)(D) requires that SIPs contain 

provisions to eliminate the 

contributions that are deemed 

significant, whereas section 189(e) 

merely requires that the emissions be 

controlled. Given the differences in 

purpose, scale, and scope, the EPA does 

not believe it is necessary for a 

threshold for ‘‘significant contribution’’ 

to be the same for the two programs. 

Based on the considerations discussed 

above regarding inclusion of a potential 

significance ‘‘threshold’’ for purposes of 

this PM2.5 implementation rulemaking, 

the EPA proposes and seeks comment 

on two options. The first option would 

not specify a threshold for what is a 

significant contribution to levels that 

exceed the relevant NAAQS in a given 

area. Rather, the state would be required 

to conduct a contribution analysis and 

sensitivity analyses as described above 

to determine the estimated level of 

ambient impact from the relevant 

precursor, and to provide the analyses 

to the EPA as part of its precursor 

demonstration. The EPA would then 

consider these analyses in addition to 

the other analyses provided by the state 

in determining whether to approve the 

precursor demonstration. This option 

would provide greatest flexibility for the 

state and the EPA to consider the 

contribution analysis in combination 

with other information relevant to the 

unique PM2.5 composition, source mix, 

and attainment needs of each individual 

nonattainment area. See proposed 40 

CFR 51.1006. 

The second option would specify a 

‘‘significance’’ threshold of 3 percent, 

such that if contribution modeling 

indicated that base year emissions of the 

precursor from the relevant sources in 

the nonattainment area (i.e. from major 

stationary sources for all analyses 

pursuant to section 189(e); from all 

types of sources for the upfront analysis 

in Option 2) leads to an ambient impact 

that exceeds 3 percent of the PM2.5

NAAQS (e.g.,, 0.36 mg/m3 on an annual 

average basis for the 2012 primary 

annual PM2.5 NAAQS) at monitors in 

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71See the Federal Register published on April 16, 

1992 (57 FR 13498, 13536, 13537, 13538, 13539, 

13540, 13541, 13542, 13543, 13544 and 13545); and 

see the Federal Register published on August 16, 

1994 (59 FR 41988). 

72The EPA notes that Congress provided different 

statutory deadlines for submission of attainment 

plans under subpart 1 and subpart 4. Under section 

172(b), the EPA is directed to establish the date for 

the attainment plan submission, but it can extend 

no later than 3 years from the date of a 

nonattainment designation. By contrast, under 

section 189(a)(2)(B), the statute provides that states 

must make the attainment plan submissions within 

18 months after designation. Due to the December 

2013 court decision in NRDC v. EPA, however, the 

EPA promulgated an alternative submission date of 

December 31, 2014 for attainment plans for the 

1997 PM2.5 and 2006 PM2.5 NAAQS in order to 

provide a reasonable, prospective due date for 

attainment plans that must comply with subpart 4 

requirements and to clarify the requirements that a 

state must meet prior to redesignation of a PM2.5

nonattainment area. See 79 FR 31566 (June 2, 2014). 

the nonattainment area, then the 

precursor demonstration would not be 

approvable. The threshold equivalent to 

3 percent of the relevant PM2.5 NAAQS 

is proposed as reasonable because it is 

between the two de minimis ambient 

contribution levels included in previous 

PM10 guidance issued under subpart 4 

to identify a de minimis level of ambient 

contribution from a group of emissions 

sources. The EPA acknowledges that the 

context in which the proposed 

threshold is used here is different from 

the context in which it was used in 

previous guidance. Absent any explicit 

language provided in the statute to 

define significant contribution in the 

context of section 189(e), however, the 

only other existing guidance that in 

some way addresses the concept of 

significant contribution for PM10 is the 

de minimis source category threshold 

values from the Addendum. One benefit 

of having a specific threshold in the rule 

is that states will have more concrete 

guidance on what could potentially be 

approvable in a precursor 

demonstration. 

The EPA therefore seeks comment on: 

(1) Whether a specific significant 

contribution threshold should be 

included in the final rule or not; (2) if 

the commenter considers inclusion of a 

specific threshold to be appropriate, 

whether the proposed 3 percent of the 

relevant NAAQS threshold and its basis 

would be appropriate, and why; and (3) 

whether a threshold with an alternative 

level and supporting rationale would be 

more appropriate. 

IV. What are the EPA’s proposed 

requirements for Moderate area 

attainment plans? 

Sections 189(a), (c), and (e) of the 

CAA require that Moderate area 

attainment plans contain the following: 

(i) An approved permit program for 

construction of new and modified major 

stationary sources (section 189(a)(1)(A)); 

(ii) a demonstration that the plan 

provides for attainment by no later than 

the applicable Moderate area deadline 

or a demonstration that attainment by 

that deadline is impracticable (section 

189(a)(1)(B)); (iii) provisions for the 

implementation of RACM and RACT no 

later than 4 years after designation 

(section 189(a)(1)(C)); (iv) quantitative 

milestones that will be used to evaluate 

compliance with the requirement to 

demonstrate reasonable further progress 

(RFP) (section 189(c)); and, (v) 

evaluation and regulation of PM2.5

precursors (in general to meet RACM 

and RACT and other attainment 

planning requirements, and as 

specifically required for major 

stationary sources by section 189(e)). 

Other subpart 1 requirements for 

attainment plans continue to apply to 

PM2.5 nonattainment areas subject to 

subpart 4 and include the following: (i) 

a description of the expected annual 

incremental reductions in emissions 

that will demonstrate RFP (section 

172(c)(2)); (ii) emissions inventories 

(section 172(c)(3)); (iii) other control 

measures (besides RACM and RACT) 

needed for attainment (section 172(c)(6); 

and, (iv) contingency measures (section 

172(c)(9)). 

Each of these statutory requirements 

is described more fully below. In certain 

cases, the EPA is proposing options for 

implementing a statutory requirement 

for purposes of the PM2.5 NAAQS. Based 

on comments the agency receives, the 

EPA will then promulgate regulations to 

implement the statutory requirements in 

the final action on this proposal, as 

appropriate. The EPA notes that its 

longstanding guidance on these 

statutory requirements is embodied in 

the General Preamble and the 

Addendum.71 Where appropriate, this 

proposal notes options that may vary 

from past EPA guidance and explains 

the EPA’s reasons for considering an 

amended approach. 

A. Plan Due Dates 

Section 189 of the CAA specifies the 

schedule by which states must submit 

attainment plans for the PM2.5 NAAQS. 

Specifically, CAA section 189(a)(2)(B) 

requires states to submit an attainment 

plan that meets Moderate area 

attainment plan requirements no later 

than 18 months from the date of a 

nonattainment designation.72 To be 

consistent with this subpart 4 deadline 

for the attainment plan submission, the 

EPA is proposing that states must also 

submit those elements of the attainment 

plan required under subpart 1 (i.e., 

emissions inventories and contingency 

measures) no later than 18 months from 

the date of designation of the area. The 

provisions of subpart 4 do not explicitly 

specify when states must submit these 

attainment plan elements that carry over 

from subpart 1, so the EPA needs to 

interpret the requirements of the CAA to 

meet the objectives of the attainment 

plan requirements. The EPA believes 

that requiring states to submit the 

necessary emissions inventory (or 

inventories) either before or at the same 

time as the other attainment plan 

elements due under subpart 4 is 

necessary, given that a state will need 

information contained in the emissions 

inventory for other elements of its 

Moderate area attainment plan, such as 

its precursor analysis, analysis of RACM 

and RACT and additional reasonable 

measures, and attainment 

demonstration modeling. The EPA also 

believes it is reasonable to require the 

state to submit contingency measures, 

which need to be adopted and ready for 

immediate implementation in the event 

a nonattainment area fails to meet RFP 

requirements or fails to attain the PM2.5

NAAQS by the applicable attainment 

date, simultaneous with the other 

elements of the attainment plan. The 

state’s evaluation of what emissions 

controls are appropriate to meet the 

contingency measure requirement is 

closely related to other aspects of the 

attainment plan, such as addressing the 

proper pollutants for control in a given 

area, the appropriate sources for 

controls beyond those already required 

for RACM and RACT for the area, and 

the amount of emission reductions that 

the contingency measures should 

achieve, based upon the facts and 

circumstances of the attainment plan for 

the area. 

The EPA believes that the statutory 

deadline for submission of a Moderate 

area attainment plan for the PM2.5

NAAQS is straightforward and, absent 

unusual circumstances, the statute 

requires states to make such attainment 

plan submissions within 18 months 

after the effective date of a 

nonattainment designation for an area. 

See proposed 40 CFR 51.1003(a). 

Although nothing in the CAA prohibits 

states from making separate attainment 

plan submissions to meet the individual 

statutory requirements for attainment 

plans in advance of the required date, 

the EPA presumes that development 

and submission of all of the attainment 

plan elements simultaneously will be 

most effective, both for the state in the 

first instance and for the EPA in 

reviewing the state’s submission. For 

example, the EPA designated areas as 

nonattainment for the 2012 PM2.5

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NAAQS with an effective date of April 

15, 2015; states will thus be required by 

statute to submit Moderate area 

attainment plans for any nonattainment 

areas to the EPA no later than October 

15, 2016. 

B. Emissions Inventory Requirements 

Pursuant to its authority under 

section 110 of title I of the CAA, the 

EPA has long required states to submit 

inventories of the emissions of criteria 

pollutants and their precursors. The 

EPA codified these requirements in 40 

CFR part 51, subpart Q in 1979 and 

amended them in 1987. Additionally, 

the 1990 CAA Amendments revised 

many of the provisions of the CAA 

related to attainment of the NAAQS and 

the protection of visibility in mandatory 

Class I federal areas (certain national 

parks and wilderness areas). These 

revisions established new emissions 

inventory requirements applicable to 

areas that were designated 

nonattainment for certain pollutants. In 

the case of particulate matter, Congress 

did not create a specific emissions 

inventory requirement in subpart 4 that 

would supersede the emissions 

inventory requirement under subpart 1. 

Thus, the section 172(c)(3) emissions 

inventory requirements continue to 

apply, and that provision explicitly 

requires ‘‘a comprehensive, accurate, 

and current inventory of actual 

emissions of the relevant pollutants’’ in 

the nonattainment area. In addition, the 

specific attainment plan requirements 

for the PM2.5 NAAQS set forth in section 

189(a) and associated modeling 

requirements make an accurate and upto-date emissions inventory a critical 

element of any viable attainment plan. 

Because of the nature of PM2.5, the EPA 

concludes that the statutory 

requirements for emissions inventories 

need further elaboration through 

additional regulatory requirements as 

described below. 

Emissions inventory data serve as the 

foundation for various types of analyses 

that enable states to evaluate the degree 

to which different emissions sources 

contribute to the nonattainment 

problem in a given nonattainment area 

and enable states to estimate the air 

quality improvement that can be 

achieved through different control 

measures. States should use the best 

available, current emissions inventory 

information for attainment plan 

development, because high quality 

emissions inventory data are essential 

for the development of an effective 

control strategy. To assist states in 

preparing complete, high quality 

inventories, the EPA provides guidance 

for developing emissions inventories 

called ‘‘Emissions Inventory Guidance 

for Implementation of Ozone and 

Particulate Matter National Ambient Air 

Quality Standards (NAAQS) and 

Regional Haze,’’ which is available from 

http://www.epa.gov/ttn/chief/eidocs/

eiguid/index.html. This guidance is 

commonly called the ‘‘SIP Emissions 

Inventory Guidance.’’ The EPA 

recommends that states consult this 

guidance while developing the 

emissions inventories to meet statutory 

and regulatory requirements. 

1. How do states meet the inventory 

requirements for the PM2.5 NAAQS? 

Neither section 172(c)(3), nor the 

provisions specifically applicable to 

attainment plans for the PM2.5 NAAQS 

in subpart 4, specify how states should 

meet statutory emissions inventory 

requirements. Although section 

172(c)(3) explicitly requires that states 

submit only ‘‘an’’ emissions inventory 

in conjunction with other elements of 

an attainment plan, that term is 

ambiguous in the context of the PM2.5

NAAQS, and the EPA is authorized to 

interpret that term and to impose 

additional requirements as necessary 

and appropriate. In addition, pursuant 

to section 301, the EPA has additional 

authority to promulgate regulations as 

necessary for the implementation of the 

PM2.5 NAAQS, including requirements 

pertaining to emissions inventories. 

Accordingly, the EPA is proposing 

specific emissions inventory 

requirements it considers necessary to 

effectuate the attainment plan 

requirements of the CAA for the PM2.5

NAAQS. 

There are three key facets of the EPA’s 

proposed emissions inventory 

requirements, as laid out below: (i) The 

type of inventories required; (ii) the 

timing of submittal of these inventories; 

and, (iii) the content of these 

inventories. These inventory 

requirements are being proposed to 

provide all of the requirements in a 

concise and direct way. In some cases, 

the EPA’s rationale for the content 

requirements needs additional 

supporting description, which is 

provided in the subsequent text related 

to the use of seasonal inventories, 

required pollutants, etc. 

First, the EPA believes that in order 

to implement the PM2.5 NAAQS 

effectively, states will be required to 

submit at least two separate and distinct 

nonattainment area emissions 

inventories as elements of an attainment 

plan. The first emissions inventory is 

relevant for assessing the current or base 

year emissions in the nonattainment 

area; the second emissions inventory is 

a projected inventory relevant for 

assessing emissions in the target 

attainment year in the nonattainment 

area. The first type of inventory is 

expressly required by section 172(c)(3), 

and is called the ‘‘base year inventory 

for the nonattainment area.’’ The second 

type of inventory the EPA is proposing 

to require under section 301(a)(1) as 

necessary to implement the attainment 

demonstration requirement of section 

189(a)(1)(B), and is called the 

‘‘attainment projected inventory for the 

nonattainment area.’’ See proposed 40 

CFR 51.1000. The need for this latter 

inventory stems from the need for both 

the EPA and the public to be able to 

compare, during their reviews of the 

plan, the base year inventory against the 

attainment projected inventory for the 

nonattainment area. For these reasons, 

the EPA is proposing to establish the 

regulatory requirement that attainment 

plans must include a base year 

inventory for the nonattainment area 

and an attainment projected inventory 

for the nonattainment area. 

Second, as noted above, to meet the 

statutory requirements for submission of 

attainment plans under subpart 4, the 

EPA believes that states must meet the 

same submission schedule for these 

emissions inventories as for the other 

elements of an attainment plan, i.e., 

within 18 months after the effective 

dates of the designation of the 

nonattainment area. This schedule must 

apply to both of these emissions 

inventories because they are necessary 

for effective evaluation of the attainment 

plan as a whole. Consequently, under 

the authority of section 172(b), the EPA 

is proposing to establish the regulatory 

requirement that emissions inventories 

be submitted by 18 months after 

designation. 

Third, the EPA proposes to establish 

specific requirements for both the base 

year inventory for the nonattainment 

area and for the attainment projected 

inventory for the nonattainment area in 

order to implement the PM2.5 NAAQS 

most effectively. Accordingly, the EPA 

proposes that the base year inventory for 

the nonattainment area must meet the 

following minimum criteria (a) through 

(g): 

(a) The inventory year must be one of 

the 3 years used for designations or 

another technically appropriate 

inventory year. Another inventory year 

may be chosen under specific 

circumstances (e.g., to account for a 

change in sources in the nonattainment 

area, changes in nonattainment area 

boundaries, or significant time lag 

between designations and preparation of 

the inventory) with consultation from 

the appropriate EPA Regional Office. 

This requirement is intended to ensure 

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that the inventory will represent the 

emissions sources whose contributions 

resulted in a nonattainment designation 

for the area. 

(b) The inventory must include actual 

emissions of all sources within the 

nonattainment area. This requirement 

stems directly from the wording of 

section 172(c)(3). Sources outside of the 

nonattainment area are explicitly not 

included in the section 172(c)(3) 

requirement with the words ‘‘in such 

area.’’ Furthermore, the EPA interprets 

the Act requirement for ‘‘actual 

emissions from all sources’’ in section 

172(c)(3) as intending to include all 

emissions that may contribute to the 

formation of PM2.5 within the 

nonattainment area. 

(c) The emissions values must either 

be annual total emissions or averageseason-day emissions, as appropriate for 

the nonattainment problem. The 

rationale for providing annual or 

seasonal emissions must be included as 

part of the plan. A discussion of the 

EPA’s rationale for proposing the option 

of seasonal or annual inventories is 

provided in Section IV.B.4 of this 

preamble. 

(d) As discussed above and consistent 

with past implementation rule 

requirements, the inventory must 

include emissions of direct PM2.5 (both 

filterable PM2.5 and condensable PM2.5), 

as well as all scientific PM2.5 precursors 

(SO2, NOX, VOC and ammonia). A 

discussion of the EPA’s rationale for 

proposing this requirement is provided 

in Section IV.B.5 of this preamble. 

(e) The emissions thresholds for 

which emissions sources must be 

reported as point sources must be 

followed from the Air Emissions 

Reporting Rule (AERR), 40 CFR part 51, 

subpart A. This requirement is 

consistent with past implementation 

rules and is needed to define the data 

structure (as opposed to the emissions 

values themselves) of the emissions 

submitted to the EPA. A discussion of 

the use of 40 CFR part 51, subpart A, for 

the emissions thresholds and data 

reporting elements is provided in 

Section IV.B.6 of this preamble. 

(f) The detail of the emissions 

included in the inventory must be 

consistent with the detail required by 40 

CFR part 51, subpart A. For example, all 

emissions must be subdivided to 

individual emissions processes within a 

facility or county. While these details 

should underlie the inventory, the 

emissions included in the attainment 

plan can be summarized. This 

requirement is consistent with the 2007 

PM2.5 Implementation Rule and is 

needed to define the data structure (as 

opposed to the emissions values 

themselves) of the emissions submitted 

to the EPA. 

(g) If the base year inventory for the 

nonattainment area is submitted to the 

EPA as a separate plan submission (i.e., 

severed from the overall attainment plan 

and provided separately), the inventory 

must still meet all public review 

requirements associated with that plan. 

See proposed 40 CFR 51.1008(a)(1). 

For the attainment projected 

inventory for the nonattainment area, 

the EPA also proposes to promulgate 

more specific requirements in order to 

implement the PM2.5 NAAQS most 

effectively. Accordingly, the EPA 

proposes that the attainment projected 

inventory must meet the following 

minimum criteria (a) through (g): 

(a) The year of the projected inventory 

must be the first year for which 

attainment is demonstrated by the 

modeled attainment plan. 

(b) The emissions values must be 

projected emissions of the same sources 

included in the base year inventory for 

the nonattainment area (i.e., only those 

located within the nonattainment area) 

and any new sources. The projected 

emissions values should be the best 

available representation of expected 

emissions, and thus should take into 

account emissions growth and 

contraction, facility closures, new 

facilities, new controls and other factors 

forecast to occur between the base year 

and the attainment year. In deciding 

what factors are relevant, states should 

consider factors affecting projected 

emissions that could significantly alter 

the conclusions of the attainment 

demonstration. 

(c) The temporal period of emissions 

must be the same temporal period 

(annual or average-season-day) as the 

base year inventory for the 

nonattainment area. 

(d) Consistent with the base year 

inventory for the nonattainment area, 

the inventory must include all 

emissions of direct PM2.5 (both filterable 

and condensable PM2.5), as well as all 

emissions of all scientific precursors 

(SO2, NOX, VOC and ammonia). 

(e) The same sources reported as point 

sources in the base year inventory for 

the nonattainment area must also be 

provided as point sources in the 

attainment projected inventory for the 

nonattainment area. Likewise, nonpoint 

and mobile source projected emissions 

must also be provided using the same 

detail (e.g., state, county and process 

codes) as the base year inventory. 

(f) The detail of the emissions 

included must be consistent with the 

level of detail in the base year inventory 

(i.e., as required by 40 CFR part 41, 

subpart A). 

(g) If the attainment projected 

inventory for the nonattainment area is 

submitted to the EPA as a separate plan 

submission (e.g., severed from the 

overall attainment plan and provided 

separately), the inventory must still 

meet all public review requirements 

associated with that SIP submission. See 

proposed 40 CFR 51.1008(a)(2). 

2. Are there new inventory requirements 

in this proposed rule that have not been 

included in previous rules? 

This proposed rule includes more 

specific requirements for emissions 

inventories than past implementation 

rules. First, the EPA proposes to require 

the attainment projected inventory for 

the nonattainment area. In practice, 

some states were providing this 

information at the request of their 

respective EPA Regional Offices, but it 

was not a specific requirement. The EPA 

believes that a specific requirement is 

necessary to ensure that the EPA and 

the public can reasonably assess the 

changes in emissions in the 

nonattainment area that the state 

maintains demonstrate that the area will 

attain the standard or that it is 

impracticable to attain the standard by 

the attainment date. Without such 

information, there is no way for the EPA 

to assess the projected emissions 

changes in the nonattainment area that 

the state asserts contribute to 

attainment. In addition, this proposed 

requirement would support the EPA’s 

first proposed approach for conducting 

an RFP analysis as described in Section 

IV.F of this preamble. 

This proposed rule also is more 

specific about the requirements for the 

emissions inventories submitted. While 

the various criteria (a) through (g) listed 

above have been implicit in prior rules 

and associated guidance, the EPA 

believes that not having these specific 

requirements has caused confusion and 

inconsistencies across attainment plan 

inventories in the past. Thus, the EPA 

is proposing to require these minimum 

criteria in this proposed rule. 

Furthermore, the option for using only 

seasonal inventories in some attainment 

plans is a new facet of this rule, further 

described in Section IV.B.5 of this 

preamble. 

3. Are there other inventory 

requirements from earlier PM2.5

implementation rules that the EPA is 

proposing to retain or change? 

The 2007 PM2.5 Implementation Rule 

required states to submit specific 

emissions inventories in connection 

with the RFP requirements of section 

172(c)(2) under subpart 1. The EPA 

believes that a separate emissions 

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73For more information on the NAEMS study, 

see: http://www.epa.gov/agriculture/

airmonitoringstudy.html. 

inventory will be important to illustrate 

how a nonattainment area may achieve 

incremental emissions reductions 

toward attainment, and would be 

appropriate in light of the agency’s 

proposed approaches for states to meet 

the statutory RFP requirements. Past 

EPA guidance with respect to RFP 

requirements under subpart 4 has not 

required any explicit, separate 

emissions inventory for this purpose for 

PM10 NAAQS. For this reason, the EPA 

describes this issue and proposed 

approaches more fully in Section IV.F of 

this preamble. 

The 2007 PM2.5 Implementation Rule 

also required states to submit a 

statewide base year emissions inventory 

as part of the attainment plan. The EPA 

proposes not to include this statewide 

emissions inventory requirement in this 

rule. Subpart 4 does not expressly 

require such an inventory, and the EPA 

does not believe that it is needed for 

successful attainment of the PM2.5

NAAQS. Furthermore, statewide 

inventories are already required as part 

of the AERR (40 CFR part 51, subpart A) 

on a triennial basis. While these 

inventories do not receive the same 

level of scrutiny as inventories 

associated with attainment plans, the 

EPA believes that this existing statewide 

requirement is sufficient for 

understanding the PM2.5 nonattainment 

problems nationally and assessing the 

quality of inventories proposed to be 

required by this rule. 

4. Why is the EPA proposing to permit 

seasonal inventories to meet the 

inventory reporting requirements? 

The statute does not explicitly 

address whether the emissions 

inventory required under section 

172(c)(3) should include emissions 

throughout an entire calendar year or 

emissions during some shorter portion 

of the year that may be appropriate for 

implementation of a particular NAAQS. 

In the case of the PM2.5 NAAQS, the 

standards currently include both annual 

NAAQS and 24-hour NAAQS. With 

respect to the annual NAAQS, the form 

of the NAAQS includes monitored 

ambient PM2.5 values at all times 

throughout the course of the year and 

thus an annual emissions inventory is 

necessarily required for development of 

an appropriate attainment plan for a 

given area. In the case of the 24-hour 

NAAQS, however, the form of the 

NAAQS is based upon monitored 

ambient PM2.5 values on particular days 

with high levels of PM2.5, and in some 

nonattainment areas those days may 

occur only during a distinct and 

definable season of the year. The EPA 

considers it appropriate to interpret the 

emissions inventory requirements of the 

CAA in light of the specific inventory 

needs that are relevant for the NAAQS 

in question, and in the case of the PM2.5

NAAQS, the inventory requirement may 

thus include both an annual emissions 

inventory for the attainment area, and a 

seasonal emissions inventory for the 

area as appropriate for the attainment 

plan at issue. 

In contrast with the annual PM2.5

NAAQS, the 24-hour PM2.5 NAAQS are 

designed to protect against peak 

exposures. Thus, for the 24-hour PM2.5

NAAQS, there are circumstances in 

which the EPA believes that only 

seasonal emissions inventories may be 

required for attainment planning 

purposes. The EPA proposes to allow 

states to use only seasonal inventories 

for attainment plan development for 

attaining the 24-hour PM2.5 standard in 

areas that are nonattainment for only the 

24-hour standard. In the event that it is 

appropriate to rely on a seasonal 

emissions inventory, the state should 

confer with the EPA concerning the 

exact length of the season and the start 

and stop dates of the season. The 

duration and start and stop dates of the 

season will be an important component 

of the attainment plan and must be 

approved by the EPA along with other 

elements of the attainment plan for a 

given nonattainment area. The EPA 

further proposes to require that seasonal 

inventories must use average-season-day 

emissions values for this purpose. The 

average-season-day is defined as the 

sum of all emissions during the 

applicable season divided by the 

number of days in that season. The 

nature of some seasonal PM2.5 emissions 

sources (e.g., residential wood 

combustion) does not allow for only 

weekday emissions to be included in 

the inventory, therefore all days must be 

included. The state would need to 

explain the rationale for the duration of 

the season used for the inventory as part 

of the attainment plan submission. To 

justify the use of a seasonal inventory, 

the state must demonstrate why a 

seasonal attainment plan is appropriate 

for the particular PM2.5 nonattainment 

area in question. 

5. Why is the EPA requiring certain 

pollutants be included in the 

inventories? 

The EPA is proposing that states must 

submit emissions inventories that 

include all emissions of direct PM2.5 and 

all emissions of all PM2.5 precursors: 

SO2, NOX, VOC and ammonia. 

Furthermore, the inventory must 

differentiate between the condensable 

and filterable portions of direct PM2.5

emissions. Section II.B of this preamble 

describes the background needed to 

understand the importance of including 

these precursors in emissions 

inventories for attainment plan 

purposes for the PM2.5 NAAQS. 

Emissions information about PM2.5 and 

its precursors is a necessary 

precondition to meeting other core 

attainment plan requirements, such as 

effective evaluation of control measures 

and adequate demonstration of 

projected future attainment of the 

NAAQS through modeling. The EPA 

notes that with respect to requiring 

states to include emissions of direct 

PM2.5 and PM2.5 precursors in emissions 

inventories, the agency is following the 

requirements it established for the PM2.5

NAAQS in the past. Section 172(c)(3) 

explicitly requires states to submit a 

‘‘comprehensive, accurate, and current 

inventory of actual emissions of the 

relevant pollutants’’ and the EPA 

concludes that in order to meet these 

basic statutory requirements for the 

PM2.5 NAAQS, states must address 

PM2.5 and all PM2.5 precursors in their 

emissions inventories. 

The EPA requires air agencies to use 

the best available methodologies for 

estimating emissions of PM2.5 and its 

precursors. It should be noted that for 

ammonia, in particular, updated 

emissions estimating methodologies for 

animal feeding operations are under 

development using data collected 

during the period 2007–2009 from 

representative operations pursuant to 

the National Air Emissions Monitoring 

Study.73 The EPA is hopeful that such 

updated methodologies will help to 

reduce uncertainties in current 

ammonia inventories and will improve 

the quality of future emissions 

inventories needed for implementing 

the PM2.5 NAAQS. 

6. Why is the AERR used to define data 

elements and data methods that are 

required for the emissions inventories 

required by this rule? 

Because the provisions of the CAA do 

not specifically state the form of the 

emissions information to be reported to 

the EPA for meeting their attainment 

plan inventory requirement, it is 

necessary for the EPA to prescribe 

specifically the data elements of those 

emissions inventories. Distinct from the 

emissions values (i.e., how much 

emissions derive from each source or 

source category), the emissions elements 

(i.e., how they are reported) refer to the 

reporting definitions, data codes and 

required data fields. The EPA proposes 

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74The EPA encourages states to consider in any 

baseline, modeling, and SIP attainment inventory 

used and/or submitted to include emissions 

expected from projects subject to general 

conformity and emissions from wildland fire that 

reasonably may be expected in the area. 

that states must use the emissions 

elements from 40 CFR part 51, subpart 

A, in preparing their inventories 

submitted to the EPA for implementing 

the PM2.5 NAAQS. This is consistent 

with past requirements for the form of 

emissions inventories. 

In addition to defining the data 

elements, 40 CFR part 51, subpart A also 

requires states to submit emissions 

information to the EPA. The EPA is not 

referring to those emissions submission 

requirements here, but rather the 

emissions elements—the definitions, 

data codes and required data fields. 

Below, the EPA addresses the issue of 

whether the emissions values submitted 

through the AERR are relevant to the 

inventory requirements of this proposed 

rule (see Section IV.B.8 of this 

preamble). 

As noted earlier, the EPA 

recommends that states consult the SIP 

Emissions Inventory Guidance in 

preparing the inventories needed for 

this rule. In addition to the AERR, this 

guidance includes definitions for data 

fields that are not required by the AERR, 

such as seasonal emissions values and 

other fields that are optional in the data 

system that collects data submitted for 

the AERR. The EPA is updating the SIP 

Emissions Inventory Guidance in 

coordination with this proposal. It 

provides specific guidance to air 

agencies on how to develop base year 

inventories for the nonattainment area 

and attainment projected inventories for 

8-hour ozone, PM2.5, and regional haze 

SIPs. While the AERR sets forth 

requirements for data elements and 

definitions, the guidance complements 

these requirements, defines all data 

elements (even those that are voluntary 

AERR elements), and indicates how the 

data should be prepared, documented 

and publicly reviewed for attainment 

plan submissions. 

7. How do emissions inventories 

support modeling for attainment 

demonstrations? 

This section attempts to clarify the 

difference between the inventories 

required to be a part of a state’s 

Moderate area attainment plan 

submission (as described earlier) and 

other modeling inventories that are also 

relevant for attainment planning. While 

the EPA is not proposing additional 

modeling inventory requirements in this 

rule (i.e., for which a state must submit 

an emissions inventory to the EPA), to 

meet the attainment demonstration 

requirements of CAA sections 189(a)(1) 

and 189(b)(1), states will need to submit 

an attainment demonstration (which 

includes air quality modeling) to show 

how the area will either attain the 

NAAQS by the applicable attainment 

date or that the area cannot attain by the 

attainment date. The modeled 

attainment demonstration requirements 

for Moderate areas are described fully in 

Section IV.E of this preamble. 

As part of this demonstration, the 

EPA presumes that states will need to 

prepare attainment demonstration 

modeling inventories for both a 

modeled base year and projected 

attainment year. Respectively, these are 

called the ‘‘base year (baseline) 

inventory for modeling’’ and the 

‘‘attainment projected inventory for 

modeling.’’ These inventories contain 

emissions for all regions (i.e., not just 

the nonattainment area) within the 

modeling domain being used for the 

attainment plan modeling 

demonstration, which typically includes 

counties and even states outside of the 

nonattainment area. They include 

detailed spatial and temporal elements 

needed to support air quality modeling. 

States should follow the requirements 

laid out in Section IV.E of this preamble 

and the procedures described in the SIP 

Emissions Inventory Guidance and the 

Air Quality Modeling Guidance to meet 

the minimum requirements for 

documentation and emissions 

summaries supporting modeling 

demonstrations.74

The base year inventory and projected 

attainment year inventory include 

emissions from only within the 

nonattainment area. The EPA expects 

that modeling inventories will be 

consistent with those nonattainment 

area inventories; however, some 

exceptions may exist. Where possible, 

the nonattainment area base year and 

projected attainment year inventories 

can be a sum (for annual data) or 

average (for PM2.5 season-day data) of 

day-specific or hour-specific data used 

for modeling. In some cases, however, 

this approach may not be sufficient for 

modeling purposes. For example, 

greater spatial and temporal detail are 

needed for on-road mobile modeling 

inventories as compared to the base year 

inventory for the nonattainment area. 

For the nonattainment area base year 

inventory, one goal is to allow for the 

repeatability of the approach in order to 

create average, seasonal or annual 

inventories for use in rule requirements, 

such as reasonable further progress or 

conformity demonstrations. That goal is 

not necessarily compatible with the 

modeling need for greater spatial and 

temporal detail. In cases where some 

differences are unavoidable, air agencies 

should attempt to promote consistency 

where feasible. 

The AERR includes both triennial and 

annual statewide reporting 

requirements, with more extensive 

reporting requirements for triennial 

inventory years. For the interim annual 

inventories, reporting is limited to 

emissions data from only the larger 

point sources (Type ‘‘A’’ sources), as 

defined by Appendix A of 40 CFR part 

51, subpart A. For the triennial 

inventories, lower point source 

thresholds are given in Appendix A, 

consistent with the definition of major 

sources in 40 CFR part 70, and all other 

sources of emissions must be reported 

as nonpoint or mobile sources on a 

county basis. 

In the past, some states have 

incorrectly asserted that their AERR 

submission meets the requirements for 

base year inventories required by past 

implementation rules. To avoid 

confusion, the EPA provides here the 

limited circumstances in which the 

AERR emissions inventories can meet 

the base year inventory for the 

nonattainment area requirement for 

Moderate areas. The following 

conditions must be met to use AERR 

inventories for attainment planning: 

(a) The AERR emissions inventory 

must have gone through the public 

review process required for attainment 

plans. 

(b) The AERR emissions inventory 

needs to include all sources of 

emissions and all pollutants required for 

the base year inventory for the 

nonattainment area. This is only 

possible if the inventory year for the 

base year inventory for the 

nonattainment area aligns with a 

triennial AERR year, because the data 

system implementing the AERR only 

accepts emissions from point sources 

and not other source categories in nontriennial years. 

(c) The EPA must be accepting data 

for the inventory year. Inventories are 

allowed to be submitted to the AERR for 

a given year for only a limited time 

during the development cycle of the 

National Emissions Inventory. 

(d) The AERR submission must 

include emissions from all relevant 

sources as described for the base year 

inventory for the nonattainment area 

requirements. In some cases, the AERR 

requirement can be met without 

electronically ‘‘submitting’’ emissions, 

which would not meet the requirements 

for the base year inventory for the 

nonattainment area. For example, states 

may elect to accept the EPA estimates 

for some nonpoint emissions sectors, 

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75Section 172(c)(3) requires that SIP inventories 

and control measures be based on the most current 

information and applicable models that are 

available when a SIP is developed. 

76At this time, the California onroad mobile 

model is called EMFAC. 

but this would not meet the 

requirements of section 172(c)(3). In 

addition, the AERR revision finalized in 

February 2015 replaces the prior 

requirement of reporting onroad mobile 

and nonroad mobile source emissions 

with a requirement for reporting the 

input parameters that can be used to run 

the EPA models to generate the 

emissions. If choosing to use an AERR 

submission to meet the base year 

inventory for the nonattainment area 

requirement, the state should submit the 

nonattainment area emissions, 

irrespective of the options provided to 

meet the AERR requirements. Since the 

‘‘statewide’’ emissions are actually 

provided for individual point sources 

and counties, the EPA believes that 

these resolutions can be sufficient for 

most PM2.5 nonattainment areas. 

8. What models should be used for 

mobile source emissions? 

A key part of emissions inventory 

development includes estimating 

mobile source emissions. For all of the 

mobile source inventories used for PM2.5

NAAQS implementation, states should 

use the latest emissions models 

available at the time the attainment plan 

inventory is developed.75 In general, the 

latest approved version of the MOVES 

model should be used by states other 

than California to estimate emissions 

from onroad transportation sources. 

States should use the latest available 

planning emission inputs including, but 

not limited to, vehicle miles traveled 

(VMT), speeds, fleet mix, SIP control 

measures and fuels. The current version 

of MOVES is available at http://

www.epa.gov/otaq/models/moves/

index.htm. The appropriate EPAapproved model(s) should similarly be 

used for California onroad source 

emissions.76 When using MOVES, states 

should follow the most current version 

of the MOVES Technical Guidance, 

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

models/moves/index.htm#sip. MOVES 

includes multiple options for estimating 

and processing emissions that could 

result in different emissions inventories. 

The EPA recommends that states use the 

same approach in any analysis that 

compares two or more emissions cases 

(e.g., different control scenarios, 

different years). If different approaches 

are taken for inventories that serve 

different purposes (for example between 

inventories developed for air quality 

modeling, which may require greater 

temporal and spatial detail, and 

inventories used as the motor vehicle 

emissions budget), states should seek to 

understand and minimize any 

differences in results. For example, an 

approach may be used for the modeled 

attainment demonstration that uses 

gridded temperatures and other 

meteorological data, but this approach 

could be too burdensome for use in the 

base year inventory for the 

nonattainment area. This is because 

emissions inventories created for 

purposes of RFP and transportation 

conformity analysis must use the same 

MOVES approach used in the base year 

inventory for the nonattainment area, 

and using a straightforward MOVES 

approach without gridded meteorology 

is more reasonable for that purpose. 

The most current version of the 

NONROAD model should be used for 

estimates of nonroad mobile source 

emissions, preferably with statesupplied model input data. States can 

alternatively develop technologically 

equivalent or superior state-specific 

nonroad emissions estimates, but 

should explain why their approach 

gives a better estimate than the EPA 

model. For nonroad sources not 

estimated by the NONROAD model, the 

best available methods should be used, 

and the EPA recommends that states 

refer to the SIP Emissions Inventory 

Guidance for more information on 

emissions from these sources. Links to 

Federal Register documents and policy 

guidance memos on the latest approved 

versions of MOVES and NONROAD can 

be found at http://www.epa.gov/otaq/

models.htm. 

9. What special considerations exist for 

tribal areas? 

In the past, there have been instances 

where portions of tribal areas have been 

included in designated nonattainment 

areas, but when the base year inventory 

for the nonattainment area was 

prepared, emissions from the tribal 

lands were not included. This has had 

the effect of preventing tribes from 

generating emissions reductions from 

existing sources to develop emissions 

offsets, as well as impairing the ability 

of the state to prepare as accurate a 

modeling demonstration as possible. It 

could also cause sources in tribal areas 

to remain uncontrolled even though 

they are contributing to violations in a 

given nonattainment area. The EPA 

encourages states and tribes to work 

together to ensure that the information 

used in developing the baseline 

emissions inventory is inclusive of all 

emissions from a designated 

nonattainment area, including 

emissions from sources in tribal areas 

located therein. 

C. Pollutants To Be Addressed in the 

Plan 

Under subpart 4 of the CAA, air 

agencies are initially required to analyze 

and evaluate emissions reduction 

measures for all sources of direct PM2.5

and PM2.5 precursors (i.e., SO2, NOX, 

VOC and ammonia) in developing PM2.5

attainment plans. As described in 

Section II of this preamble, and 

reiterated in the proposed emissions 

inventory requirements for Moderate 

area attainment plans under Section 

IV.B of this preamble, direct PM2.5

includes both filterable and condensable 

PM2.5 emissions. Thus, a state must 

evaluate control measures for sources of 

filterable and condensable PM2.5

emissions as part of an approvable 

control strategy for a Moderate PM2.5

nonattainment area. 

In addition, while evaluating sources 

of direct PM2.5 for reasonably available 

controls is an implicit requirement in 

the context of implementing the PM2.5

NAAQS under any scenario, the EPA is 

proposing and seeking comment on 

several options for evaluating PM2.5

precursors under the PM2.5 NAAQS 

implementation program. The EPA 

interprets the requirements of the CAA 

to allow the air agency to provide a 

‘‘precursor demonstration’’ to the EPA 

that supports a state’s finding that one 

or more PM2.5 precursors need not be 

subject to control requirements in a 

given nonattainment area. Section III of 

this preamble presents a complete 

discussion of the EPA’s proposed 

options for states to address PM2.5

precursors in attainment plans and in 

the NNSR permitting program. 

Specifically, the EPA is proposing and 

seeking comment on three options 

describing different approaches to such 

precursor demonstrations, and requests 

comment on each. In general terms, the 

three options can be summarized as 

follows: 

• Option 1: Two independent 

analyses: (a) an attainment planning 

analysis demonstrating that control 

measures for a particular precursor are 

not needed for expeditious attainment, 

meaning that the precursor can be 

excluded from measures needed to 

attain as expeditiously as practicable for 

all types of sources; and, (b) a section 

189(e) technical demonstration showing 

that major stationary sources of a 

particular precursor do not contribute 

significantly to levels that exceed the 

PM2.5 standard, meaning that the 

precursor can be excluded from control 

requirements for major sources and from 

NNSR permitting; 

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77Such exemptions could be due to a 

demonstrated lack of significant contribution of a 

certain PM2.5 precursor to the area’s elevated PM2.5

concentrations or due to a presumptive 

determination that a certain source category 

contributes only a de minimis amount toward PM2.5

levels in a nonattainment area. 

78States with areas later reclassified as ‘‘Serious’’ 

nonattainment areas under subpart 4 must also 

develop and submit later plans to meet additional 

requirements for Serious areas. 

79This interpretation is consistent with guidance 

described in the General Preamble. See 57 FR 13498 

(April 16, 1992), at page 13540. 

• Option 2: Single analysis 

demonstrating that all emissions of a 

particular precursor from within the 

area do not significantly contribute to 

PM2.5 levels that exceed the standard, 

meaning that control requirements for 

emissions of the precursor from major 

stationary and area sources, as well as 

mobile sources, would not be required 

for expeditious attainment, control 

requirements for major sources, or for 

NNSR permitting; 

• Option 3: An attainment planning 

analysis demonstrating that control 

measures for all types of sources of a 

particular precursor are not needed for 

expeditious attainment also would be 

deemed to meet the section 189(e) 

technical demonstration requirement, 

meaning that the state would not need 

to regulate emissions of the particular 

precursor from major stationary sources 

under the NNSR permitting program or 

other control requirements for major 

stationary sources. 

The EPA will finalize its approach to 

PM2.5 precursors and clarify the 

implications for states conducting 

analyses to identify required control 

measures after considering public 

comment received on this proposal. 

D. Attainment Plan Control Strategy 

1. General Approach to Designing a 

Control Strategy for a Moderate 

Nonattainment Area 

The statutory attainment planning 

requirements of subparts 1 and 4 were 

established to ensure that the following 

goals of the CAA are met: (i) That states 

implement measures that provide for 

attainment of the PM2.5 NAAQS as 

expeditiously as practicable; and, (ii) 

that states adopt emissions reduction 

strategies that will be the most effective, 

and the most cost effective, at reducing 

PM2.5 levels in nonattainment areas. In 

addition to having an obligation to meet 

the statutory requirements for specific 

control measures on sources located 

within a nonattainment area (e.g., 

RACM and RACT), a state has discretion 

to require reductions from any source 

inside or outside of a PM2.5

nonattainment area (but within the 

state’s boundaries) in order to fulfill its 

obligation to demonstrate attainment in 

a PM2.5 nonattainment area as 

expeditiously as practicable. A state 

may need to require emissions 

reductions on sources located outside of 

a PM2.5 nonattainment area if such 

reductions are needed in order to 

provide for expeditious attainment of 

the PM2.5 NAAQS. 

With this in mind, the following 

sections describe the EPA’s proposed 

approach for a state to follow in order 

to identify and select the complete suite 

of measures needed for an attainment 

plan submission for a Moderate PM2.5

nonattainment area. The proposed 

process consists of identifying all 

technologically and economically 

feasible control measures, including 

control technologies, for all sources of 

direct PM2.5 and PM2.5 precursors in the 

emissions inventory for the 

nonattainment area which are not 

otherwise exempted from consideration 

for controls.77 From that list of 

measures, the state must identify those 

that it can implement within 4 years of 

designation of the area (and which 

would thus meet the statutory 

requirements for RACM and RACT) and 

any ‘‘additional reasonable measures,’’ 

which the EPA proposes to define as 

those technologically and economically 

feasible measures that the state can only 

implement on sources in the 

nonattainment area after the 4 year 

deadline for RACM and RACT has 

passed. See proposed 40 CFR 51.1000. 

The state must also assess whether there 

are other measures that it can 

implement to control sources within the 

state but outside the nonattainment area 

that contribute to the PM2.5

nonattainment status of the area in order 

to bring the area into attainment as 

expeditiously as practicable. 

As discussed in Section II.D.6 of this 

preamble, one important component of 

a state’s control strategy for a PM2.5

nonattainment area is the suite of 

control measures that a state is already 

implementing or will be implementing 

to comply with national, regional, or 

state and local regulations already 

adopted or promulgated, as long as such 

measures will lead to permanent and 

enforceable reductions in emissions 

after the area is designated 

nonattainment. Such ‘‘existing’’ 

measures could apply to sources inside 

the nonattainment area, in which case 

the state must include them in the 

RACM and RACT and additional 

reasonable measures analysis for the 

area. The measures may also apply to 

sources located outside the 

nonattainment area but would achieve 

reductions in direct PM2.5 emissions or 

emissions of PM2.5 precursors to help 

bring the area into attainment. A state 

must evaluate the potential effects of all 

of these measures as part of its modeled 

attainment demonstration for the area, 

and must clearly indicate which of these 

measures will contribute toward timely 

attainment for the area in the attainment 

plan submission. 

2. Identification and Selection of RACM 

and RACT and Additional Reasonable 

Measures 

a. Statutory requirements and existing 

guidance. CAA section 172(c) under 

subpart 1 describes the general 

attainment plan requirement for RACM 

and RACT, requiring that attainment 

plan submissions ‘‘provide for the 

implementation of all reasonably 

available control measures as 

expeditiously as practicable (including 

such reductions in emissions from 

existing sources in the area as may be 

obtained through the adoption, at a 

minimum, of reasonably available 

control technology) and shall provide 

for attainment’’ of the NAAQS. The 

attainment planning requirements 

specific to PM10, including PM2.5, under 

subpart 4 likewise impose upon states 

an obligation to develop attainment 

plans that impose RACM on sources of 

direct PM2.5 and PM2.5 precursors 

within a Moderate nonattainment area. 

CAA section 189(a)(1)(C) requires that 

states with areas classified as Moderate 

have attainment plan provisions to 

assure that RACM are implemented by 

no later than 4 years after designation of 

the area.78 The EPA reads CAA sections 

172(c)(1) and 189(a)(1)(C) together to 

require that attainment plans for 

Moderate nonattainment areas must 

provide for the implementation of 

RACM and RACT for existing sources of 

PM2.5 and PM2.5 precursors in the 

nonattainment area as expeditiously as 

practicable but no later than 4 years 

after designation.79

The terms RACM and RACT are not 

defined within subpart 4, nor do the 

provisions of subpart 4 specify how 

states are to meet the RACM and RACT 

requirements. However, the EPA’s 

longstanding guidance in the General 

Preamble described in detail 

considerations for determining what 

control measures constitute RACM and 

RACT for purposes of subpart 4. The 

EPA’s guidance for RACM for sources of 

PM10 and PM10 precursors under 

subpart 4 in the General Preamble 

included: (i) A list of some potential 

measures for states to consider; (ii) a 

statement of the EPA’s expectation that 

the state will provide a reasoned 

explanation for a decision not to adopt 

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80See 57 FR 13498 (April 16, 1992), at pages 

13540–41. 

81 Ibid. 

82 In Sierra Club v. EPA, 294 F.3d 155 (D.C. Cir. 

2002), the court stated, in upholding the EPA’s 

statutory interpretation of RACM, that the CAA 

does not compel a state to consider a measure 

without regard to whether it would expedite 

attainment. 

83The term ‘‘expeditious attainment’’ is used 

throughout this proposal to describe the ability of 

a nonattainment area to attain ‘‘as expeditiously as 

practicable’’ based on the test described here. 

a particular control measure; (iii) 

recognition that some control measures 

might be unreasonable because the 

emissions from the sources that would 

be affected by the measure in the area 

are de minimis (i.e., aggregate emissions 

from all sources in a particular source 

category do not contribute significantly 

to PM2.5 concentrations in the area); (iv) 

an emphasis on state evaluation of 

potential control measures for 

reasonableness, considering factors such 

as technological and economic 

feasibility; and, (v) encouragement to 

states evaluating potential control 

measures imposed upon municipal or 

other governmental entities to include 

consideration of the impacts on such 

entities, and the possibility of partial 

implementation when full 

implementation would be infeasible 

(e.g., phased implementation of 

measures such as road paving).80 Thus, 

the RACM requirement under subpart 4 

applies to all types of sources and is not 

necessarily focused upon forms of 

control that are strictly technologybased. 

With respect to RACT requirements, 

the EPA’s guidance in the General 

Preamble: (i) noted that RACT has 

historically been defined as ‘‘the lowest 

emission limit that a source is capable 

of meeting by the application of control 

technology that is reasonably available 

considering technological and economic 

feasibility’’; (ii) Noted that RACT 

generally applies to stationary sources, 

both stack and fugitive emissions; (iii) 

suggested that major stationary sources 

be the minimum starting point for a 

state’s RACT analysis; and, (iv) 

recommended that states evaluate RACT 

not only for major stationary sources, 

but for other source categories as needed 

for attainment and considering the 

feasibility of controls.81 Thus, the RACT 

requirement under subpart 4 is 

primarily focused on stationary sources 

and forms of emissions control that are 

technology-based. 

In addition to the statutory 

requirements under sections 172(c)(1) 

and 189(a)(1)(C) for RACM and RACT, 

section 172(c)(6) requires that a state’s 

attainment plan for a nonattainment 

area ‘‘include enforceable emission 

limitations, and such other control 

measures, means or techniques 

(including economic incentives such as 

fees, marketable permits, and auctions 

of emission rights), as well as schedules 

and timetables for compliance, as may 

be necessary or appropriate to provide 

for attainment of such standard in such 

area by the applicable attainment date 

specified in this part.’’ The EPA 

interprets this statutory provision to 

require a state to identify, select and 

implement additional measures to those 

identified as RACM and RACT for the 

area if needed to provide for timely 

attainment of the area. In the EPA’s 

proposed approach detailed in this 

section, the EPA describes criteria for 

identifying and selecting ‘‘additional 

reasonable measures’’ for sources of 

direct PM2.5 and PM2.5 precursors in a 

Moderate nonattainment area which 

may be necessary in order to bring the 

area into expeditious attainment. 

b. Proposed approach. This section 

describes the EPA’s proposed approach 

for determining what measures qualify 

as RACM and RACT or as additional 

reasonable measures for controlling 

sources contributing to nonattainment 

in a Moderate PM2.5 nonattainment area. 

Under the proposed approach, the 

specific determination of RACM and 

RACT would be made within the 

broader context of assessing control 

measures for all stationary, area and 

mobile sources of direct PM2.5 and PM2.5

precursors that would collectively 

contribute to meeting the statutory 

Moderate area attainment date as 

expeditiously as practicable.82 The 

proposed approach is designed to 

ensure that states consider and adopt 

control measures for sources in a way 

that is consistent with the statute’s 

overarching requirement to attain the 

standards as expeditiously as 

practicable, yet to provide flexibility for 

states to focus regulatory resources on 

those sources of emissions whose 

control will most effectively and 

expeditiously contribute to attainment 

in a given area. 

Specifically, the EPA proposes that a 

state must follow a process by which it 

would: (i) Identify all sources of 

emissions of direct PM2.5 and all PM2.5

precursors in the nonattainment area 

and all potential control measures to 

reduce emissions from those source 

categories not otherwise deemed de 

minimis; (ii) determine if any of the 

identified potential control measures are 

technologically infeasible; (iii) 

determine if any of the identified 

technologically feasible control 

measures are economically infeasible; 

(iv) determine which technologically 

and economically feasible measures can 

be implemented, in whole or in part, 

within 4 years from the date of 

designation of the area and which can 

be implemented, in whole or in part, by 

the end of the sixth calendar year 

following designation; and, (v) perform 

an analysis to determine the earliest 

practicable attainment date for the area 

and identify the control measures and 

control technologies that will be needed 

to achieve attainment by the 

demonstrated attainment date and to 

meet statutory control requirements. 

The statutory attainment date for 

Moderate nonattainment areas is as 

expeditiously as practicable, but not 

later than the end of the sixth calendar 

year after designation of the area as 

nonattainment. In the case of Moderate 

areas that can reach attainment by the 

statutory attainment date, and 

consistent with existing policies, states 

would be required to evaluate the 

combined effect of reasonably available 

control measures that are not necessary 

to demonstrate attainment within the 

maximum statutory timeframe to 

determine whether implementation of 

the remaining measures could advance 

the attainment date by at least 1 year. 

The EPA has long applied this 

particular test—whether reasonably 

available control measures that were not 

necessary to demonstrate attainment 

within the maximum statutory 

timeframe, collectively can advance an 

area’s applicable attainment date by at 

least 1 year—to satisfy the statutory 

provision related to an area 

demonstrating attainment ‘‘as 

expeditiously as practicable.’’ 83 The 

EPA continues to believe that this 

approach provides an appropriate 

degree of flexibility to a state to tailor 

its attainment plan control strategy to 

the needs of a particular PM2.5

nonattainment area. In the case of 

Moderate areas that cannot practicably 

attain by the statutory attainment date, 

states would be required to implement 

all RACM and RACT, together with any 

additional reasonable measures on 

sources in the nonattainment area. In 

either case, the statute requires that a 

state’s attainment plan provide for 

implementation of RACM and RACT 

within 4 years of designation. 

The following discussion provides 

further detail on the specific steps and 

criteria that the EPA proposes states 

must apply when making their 

determinations for RACM and RACT 

and additional reasonable measures. 

The EPA seeks comment on the 

proposed steps, criteria and 

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84See Section III of this preamble for further 

details on the agency’s proposed options for how 

to handle precursors in attainment planning. 

85 57 FR 13498 (April 16, 1992), at page 13540. 

86Where the sources at issue contribute only 

negligibly to ambient concentrations that exceed the 

NAAQS, the EPA’s policy is that it would be 

unreasonable to regulate those sources, and, 

therefore, the sources would not be subject to 

RACM or other control requirements, unless it is 

determined that even sources identified as de 

minimis must be controlled in order for the area to 

attain the NAAQS. In this regard, it is worth noting 

that the inherent authority of administrative 

agencies to exempt de minimis situations from 

regulation has been recognized by courts as ‘‘a tool 

to be used in implementing the legislative design’’ 

(see Alabama Power Co. v. Costle, 636 F.2d 323, 360 

(D.C. Cir. 1979)). 

87 Ibid. See Alabama Power v. Costle, 636 F.2d 

323, 360–61 (D.C. Cir. 1979). 

88More information on the NAICS is available at: 

http://www.census.gov/eos/www/naics (last 

accessed August 12, 2013). 

considerations described below. See 

proposed 40 CFR 51.1009(a). 

Step 1: Identify sources to be 

controlled and existing and potential 

control measures 

i. Identify sources to be controlled. As 

described more fully in Section IV.B of 

this preamble, section 172(c)(3) of the 

CAA requires that attainment plans for 

PM2.5 nonattainment areas include a 

‘‘comprehensive, accurate, current 

inventory of actual emissions from all 

sources of the relevant pollutant or 

pollutants.’’ As proposed, the inventory 

must include emissions information for 

all major stationary sources, nonpoint or 

area sources, and mobile sources of 

direct PM2.5 and PM2.5 precursors in the 

nonattainment area. 

The EPA proposes to require that a 

state must look at all of the sources 

reflected in the nonattainment area’s 

base year inventory as part of the first 

step in identifying reasonable control 

measures for the area, as each of these 

sources may play a role in the area’s 

PM2.5 problem and thus may be 

controlled currently or may need to be 

controlled to bring the area into 

attainment as expeditiously as 

practicable. Under this proposed 

approach, a state would need to 

consider all inventoried sources of 

direct PM2.5 emissions and sources of all 

four scientific PM2.5 precursors as it 

conducts its determination of reasonable 

control measures for an area. A possible 

exception to this comprehensive review 

requirement for all inventoried sources 

could arise if the EPA finalizes a 

precursor approach that would allow a 

state to demonstrate that one or more 

precursors in a nonattainment area do 

not significantly contribute to the PM2.5

problem in the area and/or that reducing 

emissions of one or more precursors in 

an area would not be effective in 

reducing PM2.5 concentrations in the 

area.84 In such a case, a state could 

exempt sources of any precursor for 

which the state has made such a 

demonstration from further 

consideration for measures to control 

emissions of that precursor. 

Independent of whether or not the EPA 

finalizes such an approach to 

precursors, however, a state could still 

determine that it is not necessary to 

control emissions of direct PM2.5 or any 

of the PM2.5 precursors in order to attain 

the PM2.5 NAAQS in a given area, or to 

advance the attainment date for that 

area, at a later point in this proposed 

process for determining RACM and 

RACT and additional reasonable 

measures. 

ii. De minimis source category 

exemptions. The concept of exempting 

certain source categories from 

consideration for control measures due 

to their minimal (i.e., de minimis) 

contribution is discussed at length in 

the Addendum for sources located in 

Serious PM10 nonattainment areas that 

would otherwise be subject to BACM 

and BACT requirements. The EPA’s 

guidance in the General Preamble on 

Moderate PM10 nonattainment area 

requirements also provided support for 

exempting de minimis source categories 

from RACM and RACT requirements: ‘‘If 

it can be shown that one or more 

measures are unreasonable because 

emissions from the sources affected are 

insignificant (i.e., de minimis), those 

measures may be excluded from further 

consideration as they would not 

represent RACM for that area.’’ 85 86

As with RACM for PM10, the EPA 

proposes to allow states to exempt de 

minimis source categories from further 

consideration as they determine 

reasonable control measures for bringing 

a Moderate PM2.5 nonattainment area 

into attainment with the relevant 

NAAQS. The EPA proposes that if a 

state can demonstrate that a particular 

source category does not contribute 

significantly to nonattainment of the 

PM2.5 NAAQS in a Moderate 

nonattainment area, then the state may 

eliminate the source category from 

further consideration for control 

measures.87 A state would be required 

to evaluate all other sources in the 

nonattainment area in source categories 

that do not qualify as de minimis for 

reasonable control measures. 

The EPA notes that there are some 

challenges in establishing de minimis 

source categories for PM2.5 sources in 

the same manner as was performed for 

PM10 sources and seeks comment on the 

following proposed options. 

(1) Defining source categories. Source 

categories, in particular for stationary 

sources, can be defined very broadly or 

narrowly, and the definition could 

determine which sources are able to 

meet the thresholds for de minimis 

exemptions. The North American 

Industry Classification System (NAICS) 

is the standard industrial classification 

system used by federal agencies. NAICS 

codes are between 2 and 6 digits, with 

greater industrial source specificity with 

increased digits.88 Each digit in the code 

is part of a series of progressively 

narrower categories, and the more digits 

in the code signify greater classification 

detail. The first two digits designate the 

economic sector, the third digit 

designates the subsector, the fourth digit 

designates the industry group, the fifth 

digit designates the NAICS industry, 

and the sixth digit designates the 

national industry. The 5-digit NAICS 

code is the level at which there is 

comparability in code and definitions 

for most of the NAICS sectors across the 

three countries participating in NAICS 

(the United States, Canada and Mexico). 

The 6-digit level allows for the United 

States, Canada, and Mexico each to have 

country-specific detail. A complete and 

valid NAICS code contains six digits. 

Defining source categories by NAICS 

codes would still require a 

determination of how broadly to set the 

source category boundaries as NAICS 

codes with fewer digits represent larger 

source categories (e.g., sector ‘21’ is for 

mining processes, while a further 

specification of ‘2122’ is for metal 

mining processes, and ‘212210’ is for 

iron ore mining). If source categories are 

defined in a very narrow or specific 

way, it is possible that many source 

categories will be below a set de 

minimis threshold, and therefore 

potentially inappropriately exempted 

from consideration for reasonable 

control measures. For this reason, the 

EPA proposes and seeks comment on a 

requirement that a state would need to 

define any source category for which a 

NAICS code exists at the four-digit 

industry group level. The EPA believes 

that relying on the four-digit industry 

group level to define ‘‘source category’’ 

for this purpose would provide an 

appropriate degree of distinction 

between industrial processes, while not 

making the source category definition 

overly broad. The EPA also seeks 

comment on two other alternative 

approaches for defining source category 

for this purpose, at the six-digit level, 

and the two-digit level. The EPA notes 

that not all source categories have 

NAICS codes, and for these other 

categories, states would need to use the 

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89 55 FR 38327 and 57 FR 13560. 

appropriate recognized categories, e.g., 

on-road mobile sources. The EPA also 

seeks comment on alternative source 

categorization approaches that would 

ensure that sources that could be 

controlled with reasonable control 

measures to achieve meaningful 

reductions are not inappropriately 

excluded from consideration for such 

control measures as de minimis. 

(2) Determining the appropriate 

threshold for de minimis emissions. For 

the PM10 NAAQS, the EPA’s guidance 

in the Addendum recommended that a 

source category is presumed not to be de 

minimis if the aggregate emissions from 

such source category have an impact 

that exceeds 5 mg/m3 with respect to the 

then-applicable 24-hour PM10 NAAQS 

or an impact that exceeds 1 mg/m3 with 

respect to the then-applicable annual 

PM10 NAAQS. The EPA designed these 

presumptive thresholds for de minimis 

source categories to apply to PM10

NAAQS nonattainment areas and to the 

level and form of the PM10 NAAQS at 

the time the Addendum was written. 

However, because of the differences in 

level and form of the PM10 and PM2.5

NAAQS, the agency finds that those 

levels are not appropriate for current or 

future PM2.5 NAAQS implementation. 

The EPA therefore proposes two 

options regarding the threshold for de 

minimis emissions. Under the first 

proposed option, the EPA would not 

establish a nationally applicable ‘‘bright 

line’’ threshold for defining a de 

minimis source category for purposes of 

implementing the PM2.5 NAAQS in a 

Moderate nonattainment area. Rather, 

under this option, the EPA proposes to 

allow a state to determine whether a 

particular source category should be 

considered de minimis given the 

particular facts and circumstances of a 

specific PM2.5 nonattainment area and 

subject to approval by the EPA. See 

proposed 40 CFR 51.1007. 

Under the second option, the EPA 

proposes to establish a nationally 

applicable de minimis source category 

threshold that would be a specific 

percentage of the level of the relevant 

PM2.5 NAAQS. The EPA seeks comment 

on what value within the range of 1 and 

3 percent of the relevant NAAQS would 

represent an appropriate threshold 

level. The 3 percent upper end of the 

proposed range is generally derived 

from the de minimis source category 

contribution levels for PM10 as 

described in the General Preamble. The 

EPA defined these PM10 de minimis 

levels as follows: (i) For the annual 

standard of 50 mg/m3, a source category 

contribution of 1 mg/m3 or less to the 

annual average design value (e.g., a 

contribution of about 2 percent or less); 

and, (ii) for the 24-hour standard of 150 

mg/m3, a source category contribution of 

5 mg/m3 or less to the 24-hour design 

value (e.g., a contribution of about 3 

percent or less). The 1 percent lower 

end of the proposed range is consistent 

with the value that the EPA established 

in the CAIR as a preliminary threshold 

for further evaluation of a state’s 

contribution to interstate transport. That 

is, under the CAIR, a state was 

identified as potentially subject to 

additional emission control 

requirements if the impact of SO2 and 

NOX emissions from sources in that 

state to any nonattainment or 

maintenance area in another state 

exceeded 1 percent of the relevant PM2.5

standard at a receptor monitor in the 

other state. This value was merely the 

first step of the analysis, but it provided 

an initial threshold for determining 

whether further analysis was warranted. 

The EPA is requesting comment on 

the appropriateness of including de 

minimis threshold options for 

exempting certain source categories 

from consideration for reasonable 

control measure determinations, and 

seeks input on several key questions: 

First, if a de minimis threshold is 

included, what is the appropriate 

definition for source categories? In 

addition, what are the appropriate 

thresholds for impacts on ambient PM2.5

concentrations that would adequately 

reflect presumptive de minimis 

concentrations from a given source 

category comparable to those 

recommended for purpose of the PM10

NAAQS? Also, should the de minimis 

source category thresholds be a 

percentage of the relevant NAAQS (i.e., 

similar to what was recommended for 

PM10, but set at a level that is more 

appropriate for the level and form of the 

relevant NAAQS)? The EPA requests 

that commenters submit any relevant 

data or analyses to support their 

comments with respect to these issues. 

Furthermore, the EPA notes that even in 

the event the agency finalizes this 

rulemaking with a de minimis source 

category policy of any kind, states are 

obligated under the CAA to demonstrate 

how their PM2.5 nonattainment area(s) 

will attain the standard as expeditiously 

as practicable. Accordingly, a state 

could not elect to treat source categories 

as de minimis if doing so would prevent 

the state from being able to demonstrate 

attainment for an area by the statutory 

attainment date. 

iii. Identify existing and potential 

control measures and technologies. The 

state’s compilation of existing and 

potential control measures must be 

sufficiently broad to provide a basis for 

identifying all technologically and 

economically feasible controls that may 

be RACM or RACT for sources of direct 

PM2.5 and PM2.5 precursor emissions in 

the nonattainment area at issue. Because 

RACM applies to area and mobile 

sources as well as stationary sources, 

the EPA proposes to require that states 

consider a variety of types of measures 

in conducting their control strategy 

analysis. As stated earlier, inherent to 

the concept of RACM and RACT is the 

basic premise that the measure be 

‘‘reasonable,’’ thus the EPA believes that 

a state may decline to evaluate control 

measures that are plainly ‘‘absurd, 

unenforceable, or impractical,’’ for 

example, measures that would cause 

‘‘severely disruptive socioeconomic 

impacts, (e.g. gas rationing and 

mandatory source shutdowns).’’ It is the 

agency’s interpretation that evaluation 

of such measures is not required by the 

CAA.89

Furthermore, the EPA believes that 

reducing air emissions may not justify 

adversely affecting other resources, for 

example, by increasing pollution in 

bodies of water, creating additional 

solid waste disposal problems or 

creating excessive energy demands. An 

otherwise available control technology 

may not be reasonable if these other 

environmental impacts are sufficiently 

adverse and cannot reasonably be 

mitigated. The EPA proposes that a state 

may consider a control measure for 

direct PM2.5 or a PM2.5 precursor not 

reasonable if, considering the 

availability of mitigating adverse 

impacts of that control on pollution of 

other media, the control would not, in 

the state’s reasoned judgment, provide a 

net benefit to public health and the 

environment. It should be noted that, in 

many past situations, states and owners 

of existing sources have adopted control 

technologies for direct PM2.5 and/or 

PM2.5 precursors with known energy 

penalties and some adverse effects on 

other media, based on the reasoned 

judgment that installation of such 

technology would result in a net benefit 

to public health and the environment. 

States should consider this before 

determining that a control technology is 

not reasonable because it may have 

other, negative environmental impacts 

that are, on balance, marginal. 

Generally, this proposed approach 

allows states to apply reasoned 

judgment as they identify potential 

control measures for sources of direct 

PM2.5 and PM2.5 precursors in their 

respective nonattainment areas, and the 

EPA expects that a state will provide a 

complete and reasoned explanation to 

support its selection of potential control 

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90Links are provided to a number of national, 

state and local air quality agency sites from the 

EPA’s PM2.5 Web site: http://www.epa.gov/pm/

measures.html. 

91For example, see ‘‘miscellaneous’’ category of 

direct PM2.5 emissions in Table 1. 

92 Indeed, ‘‘fire policy that focuses on [wildfire] 

suppression only, delays the inevitable, promising 

more dangerous and destructive future . . . fires.’’ 

Stephens, SL; Agee, JK; Fule, PZ; North, MP; 

Romme, WH; Swetnam, TW. (2013). Managing 

Forests and Fire in Changing Climates. Science 342: 

41–42. 

measures and control technologies as 

part of the attainment plan submission 

for any Moderate nonattainment area. 

The proposed regulations include 

language to require the inclusion of this 

explanation in a state’s attainment plan 

submission. 

(1) Existing control measures. The 

EPA proposes that, as a starting point, 

a state must include in its initial list of 

control measures those measures and 

technologies that are being implemented 

or will be implemented due to 

promulgated and/or adopted (i.e., ‘‘on 

the books’’) regulations for sources of 

direct PM2.5 and PM2.5 precursors in its 

Moderate PM2.5 nonattainment area. The 

EPA expects that the state will 

incorporate current or anticipated 

emissions reductions from these 

‘‘existing’’ control measures (such as 

expected SO2 reductions from the 

MATS; reductions of NOX and direct 

PM2.5 from engine and fuel standards to 

reduce emissions from on-road and 

nonroad mobile sources) into its 

attainment demonstration modeling for 

the nonattainment area, and therefore 

the EPA believes it is appropriate for the 

state to clearly indicate such measures 

in the attainment plan for the area. 

The EPA recognizes that for some 

sources located in a Moderate PM2.5

nonattainment area, a state may have 

previously conducted RACM and RACT 

analyses to address emissions for other 

statutory purposes. Some of the RACM 

and RACT determinations could be 

relatively recent, while other 

determinations may be 15 years old or 

older. The EPA proposes that a state 

may not simply rely on a previous 

RACM or RACT determination for a 

particular source or source category 

when developing the attainment plan 

for a PM2.5 NAAQS, but rather that the 

state must consider all existing and 

potential new measures together as part 

of a comprehensive RACM and RACT 

analysis. In this way, the state’s new 

RACM and RACT analysis will 

represent the most thorough, up-to-date 

review of control measures for its PM2.5

nonattainment area. For example, the 

state would still need to provide a 

RACT analysis for a stationary source 

that has installed new emissions 

controls recently (e.g., within the last 3 

years), but the state’s determination may 

consider that recent installation when 

determining whether additional control 

is technologically and economically 

feasible. 

(2) Potential control measures. In 

addition to identifying existing control 

measures for sources in a Moderate 

PM2.5 nonattainment area, a state must 

develop a comprehensive list of 

potential control measures for sources 

in the area. There are a number of 

resources available to assist states in 

identifying additional, potential control 

measures and control technologies for 

their RACM and RACT and additional 

reasonable measures determinations for 

their Moderate PM2.5 nonattainment 

areas. First, the EPA’s Office of Air 

Quality Planning and Standards 

maintains a Menu of Control Measures 

document, available online at http://

www.epa.gov/air/criteria.html. This 

document was developed to provide 

information useful in the development 

of local emissions reduction and 

NAAQS SIP scenarios, and identifying 

and evaluating potential control 

measures. It provides a broad, though 

not comprehensive, listing of potential 

emissions reduction measures for direct 

PM2.5 and precursors of ozone and PM2.5

from stationary, area and mobile 

sources. More complete information on 

mobile source control measures can be 

found on the EPA’s Office of 

Transportation and Air Quality Web site 

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

The RACT/BACT/LAER 

Clearinghouse (RBLC) provides a central 

database of air pollution technology 

information (including past RACT, 

BACT and LAER decisions contained in 

NSR permits) to promote the sharing of 

information among permitting agencies 

and to aid in future case-by-case control 

measure determinations. The RBLC 

permit database contains over 5,000 

determinations that can help a state 

identify appropriate technologies to 

mitigate most air pollutant emission 

streams. The RBLC includes data 

submitted by several U.S. territories and 

all 50 states on over 200 different air 

pollutants and 1,000 industrial 

processes. The RBLC can be found at: 

http://cfpub.epa.gov/rblc/. 

Additionally, the EPA maintains a 

Web site with links to other online 

sources of information on control 

measures for states to consider.90 Again, 

the EPA recognizes that some control 

technology guidance for certain source 

categories has not been updated for 

many years, and, for this reason, the 

agency expects states to identify and 

consider new and updated information 

in their RACM and RACT 

determinations as it becomes available. 

(3) RACM for managing emissions 

from wildfire and prescribed fire. 

Wildfire emissions account for a large 

portion of direct PM2.5 emissions 

nationally and can significantly 

contribute to periodic high PM2.5

levels.91 Besides their effect on air 

quality, wildfires pose a direct threat to 

public safety—a threat that can be 

mitigated through management of 

wildland vegetation. Attempts to 

suppress wildfires have resulted in 

unintended consequences, including 

increased risks to both humans and 

ecosystems.92 The use of wildland 

prescribed fire can influence the 

occurrence, behavior, and effects of 

catastrophic wildfires which may help 

manage the contribution of wildfires to 

background PM2.5 levels and periodic 

peak PM2.5 events. Additionally 

prescribed fires can have benefits to 

those plant and animal species that 

depend upon natural fires for 

propagation, habitat restoration, and 

reproduction, as well as myriad 

ecosystem functions (e.g., carbon 

sequestration). The EPA understands 

the importance of prescribed fire which 

mimics a natural process necessary to 

manage and maintain fire-adapted 

ecosystems and climate change 

adaptation, while reducing risk of 

uncontrolled emissions from 

catastrophic wildfires, and is committed 

to working with federal land managers, 

tribes, and states to effectively manage 

prescribed fire use to reduce the impact 

of wildfire related emissions on PM2.5. 

If wildfire impacts are significant, 

contributing to exceedances of the 

standard, the EPA proposes that air 

agencies should consider RACM for this 

source. Fires play an important 

ecological role across the globe, 

benefiting those plant and animal 

species that depend upon natural fires 

for propagation, habitat restoration, and 

reproduction. Fires are one tool that can 

be used to reduce fuel load, unnatural 

understory, and tree density, helping to 

reduce the risk of catastrophic wildfires. 

Some wildfires and the 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. RACM must 

be determined for each area on a caseby-case basis. Possible RACM for 

wildfire may include measures that 

reduce wildland fuels through fuels 

management, including the use of 

prescribed fire and possibly allowing 

some wildfire to occur naturally in 

systems that are ecologically fire 

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93See the Federal Register published on April 25, 

2007 (72 FR 20586, 20623, 20624 and 20625). 

94See ‘‘Petition for Reconsideration,’’ filed by 

Paul Cort, Earthjustice, on behalf of the American 

Lung Association, Medical Advocates for Healthy 

Air, Natural Resources Defense Council, and the 

Sierra Club (June 25, 2007). A copy of the petition 

is in the docket for this action. The EPA’s decision 

to grant the petition for reconsideration on the issue 

of the CAIR being presumptively equal to RACT for 

EGUs was in part based on a D,C. Circuit decision 

related to a similar issue. Specifically, the Court 

decided that the provisions in the Phase 2 Ozone 

Implementation Rule indicating that a state need 

not perform (or submit) a NOX RACM/RACT 

analysis for EGU sources subject to a cap-and-trade 

program that meets the requirements of the NOX SIP 

Call are inconsistent with the statutory 

requirements of section 172(c)(1). The Court 

concluded that the phrase ‘‘in the area’’ means that 

reductions must occur from sources within the area 

and ‘‘reductions from outside the nonattainment 

area do not satisfy the requirement.’’ See NRDC v. 

EPA, 571 F.3d 1245 (D.C. Cir. 2009). 

95Letter dated April 25, 2011, from former 

Administrator Lisa Jackson to Paul Cort, 

Earthjustice. A copy of this letter is located in the 

docket for this action. 

96 79 FR 32892 (June 9, 2013). 

97See the Federal Register published on April 16, 

1992 (57 FR 13498, 13540 and 13541). 

98Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42013. Guidance 

is provided in the context of Serious area BACM 

determination, but the EPA is proposing to apply 

it here for Moderate area RACM determinations. 

dependent. Where appropriate, states, 

land managers, and landowners may 

consider developing plans to ensure that 

fuel accumulations are addressed and 

fuels management efforts, including 

prescribed fire, are not delayed. The 

EPA also proposes that air agencies 

should consider RACM for managing 

emissions from prescribed fires 

(including those prescribed fires 

conducted to reduce future wildfire 

emissions). Information is available 

from the DOI and the USDA Forest 

Service on smoke management 

programs and basic smoke management 

practices. The EPA requests comment 

on the concept of, and practical 

considerations associated with, RACM 

for wildfire and prescribed fire, 

including such issues as how such 

measures can be characterized in the 

emissions inventory and attainment 

demonstration and made federally 

enforceable for adoption in a SIP. 

(4) RACT for EGUs. Through guidance 

in the preamble to the 2007 PM2.5

Implementation Rule, the EPA 

established a rebuttable presumption 

that compliance with the CAIR would 

satisfy RACM and RACT requirements 

for SO2 and NOX emissions from EGUs 

in states participating in the CAIR capand-trade program for such emissions.93

The EPA indicated that states could 

presume that EGUs located within a 

given nonattainment area were meeting 

the RACM and RACT requirements, 

based solely upon a regional program 

that imposed controls for SO2 and NOX

emissions from sources both within and 

outside designated nonattainment areas. 

In June 2007, the EPA received a 

petition for reconsideration questioning 

the legality of this presumption, which 

the D.C. Circuit later found to be 

unlawful in the context of a similar 

presumption in the Phase 2 Ozone 

(NAAQS) Implementation Rule.94 The 

agency granted the petition for 

reconsideration in 2011 and proposed to 

withdraw from the 2007 PM2.5

Implementation Rule any presumption 

that compliance with the CAIR 

automatically satisfies RACM and RACT 

requirements for SO2 and NOX

emissions from EGUs located in 

nonattainment areas for the 1997 PM2.5

NAAQS.95 96 In that proposal, the EPA 

explained that given the explicit 

wording of section 172(c)(1) that sources 

‘‘in the area’’ (i.e., in the nonattainment 

area) must at a minimum adopt RACT 

controls for that area, the agency 

believes that it is no longer appropriate 

to presume that this requirement is 

satisfied merely based upon the 

participation of a source in a regional 

cap-and-trade program. Indeed, implicit 

in a regional cap-and-trade program is 

that some sources, including those 

located within nonattainment areas, 

may elect to buy allowances in lieu of 

controlling emissions in order to meet 

the regional emissions reductions 

requirements. 

Accordingly, the EPA is not proposing 

any rebuttable presumption that the 

CAIR or any other regional control 

strategy constitutes RACM or RACT for 

EGUs or any other source category. 

Instead, the EPA is clarifying that in 

order to meet the RACM and RACT 

requirements for the PM2.5 NAAQS, 

states should evaluate EGU sources for 

RACM and RACT level controls just like 

any other source category, and not 

merely presume for EGUs located in a 

nonattainment area that compliance 

with a cap-and-trade program, including 

the CAIR or any other program, would 

satisfy their obligation to implement 

RACM and RACT. As required by the 

CAA, states are required to analyze what 

constitutes RACM and RACT for EGUs 

in each nonattainment area. 

Step 2: Determine whether an 

available control measure or technology 

is technologically feasible. Once a state 

has identified existing and potential 

control measures and technologies for 

sources of direct PM2.5 and PM2.5

precursors in the nonattainment area(s), 

it must evaluate these controls to 

determine if any of those controls would 

be technologically infeasible in the 

particular nonattainment area. 

i. Stationary sources. With respect to 

the technological feasibility of control 

technologies for stationary sources, the 

EPA has a longstanding approach to 

evaluating facts relevant to this criterion 

under subpart 4.97 The EPA interprets 

the term technological feasibility to 

include consideration of factors such as 

a source’s processes and operating 

procedures, raw materials, physical 

plant layout, and potential 

environmental impacts such as 

increased water pollution, waste 

disposal and energy requirements. For 

example, the EPA recognizes that the 

process, operating procedures and raw 

materials used by a source can affect the 

feasibility of implementing process 

changes that reduce emissions and can 

also affect the selection of add-on 

emissions control equipment. The 

feasibility of modifying processes or 

applying control equipment also can be 

influenced by the physical layout of the 

particular plant, if the physical space 

available in which to implement such 

changes limits the choices. The EPA 

proposes to retain its longstanding 

practice that a state should be allowed 

to consider such factors in order to 

eliminate from consideration control 

measures that are not technologically 

feasible to implement.98

ii. Area and mobile sources. With 

respect to determining whether a given 

control measure might not be 

technologically feasible for an area or 

mobile source, the EPA also proposes to 

retain its longstanding practice that a 

state may consider relevant factors in 

conducting its analysis, such as the 

social acceptability of the measure (e.g., 

residential woodstove change-out 

programs rely in large part on the 

willingness of individual citizens to 

participate in such a program) and local 

circumstances, such as the condition 

and extent of needed infrastructure, 

population size, or workforce type and 

habits, which may prohibit certain 

potential control measures from being 

implementable. 

The EPA seeks comment on the 

factors described above for states to 

consider when determining whether a 

control technology or measure is 

technologically feasible. 

Step 3: Determine whether an 

available control measure or technology 

is economically feasible. The EPA has a 

longstanding interpretation of the term 

‘‘economic feasibility’’ in the context of 

evaluating potential RACM and RACT 

which involves considering the cost of 

reducing emissions and the difference 

between the cost of an emissions 

reduction measure at a particular source 

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15374 Federal Register / Vol. 80, No. 55 / Monday, March 23, 2015 / Proposed Rules 

99See the Federal Register published on April 16, 

1992 (57 FR 13498, 13540 and 13541). 

100 ‘‘Petition for Reconsideration,’’ filed by Paul 

Cort, Earthjustice, on behalf of the American Lung 

Association, Medical Advocates for Healthy Air, 

Natural Resources Defense Council, and the Sierra 

Club (June 25, 2007). A copy of the petition is in 

the docket for this action. 

101Letter dated April 25, 2011, from former 

Administrator Lisa Jackson to Paul Cort, 

Earthjustice. A copy of this letter is located in the 

docket for this action. 

102These long-standing factors were established 

in EPA guidance in 1992 and are applicable to 

implementation programs for all NAAQS 

pollutants. See the appendices to the General 

Preamble, 57 FR 18070 (April 28, 1992). 

103 57 FR 13498 (April 16, 1992), at page 13541. 

and the cost of emissions reduction 

measures that have been implemented 

at other similar sources in the same or 

other areas.99 Absent other indications, 

the EPA presumes that it is reasonable 

for similar sources to bear similar costs 

of emissions reductions. Economic 

feasibility of RACM and RACT is thus 

largely informed by evidence that other 

sources in a source category have in fact 

applied the control technology, process 

change or measure in question in 

similar circumstances. 

In the preamble to the 2007 PM2.5

Implementation Rule, the EPA provided 

guidance on how to interpret the term 

‘‘economic feasibility’’ which deviated 

from the agency’s longstanding 

interpretation of the term. After 

promulgating the final rule, the EPA 

received and granted a petition for 

reconsideration on issues related to the 

agency’s revised approach to 

interpreting the term ‘‘economically 

feasible.’’ 100 101 Consistent with the 

EPA’s granting of that petition for 

reconsideration, the EPA is proposing in 

this action an interpretation of 

economic feasibility that is consistent 

with the EPA’s longstanding 

interpretation of what factors are 

appropriate for consideration of 

economic feasibility in a RACM and 

RACT analysis, instead of that adopted 

in the 2007 PM2.5 Implementation Rule. 

Specifically, the EPA proposes that 

for each technologically feasible control 

measure or technology, a state must 

evaluate the economic feasibility of the 

measure or control, through 

consideration of the capital costs, 

operating and maintenance costs, and 

cost effectiveness (i.e., cost per ton of 

pollutant reduced by that measure or 

technology) associated with such 

measure or control. Furthermore, the 

EPA proposes that a state may not reject 

a technologically feasible control 

measure or technology as being 

economically infeasible if such a 

measure or technology has been 

implemented at other similar sources 

(i.e., at sources that would be included 

in the same source category in the 

emissions inventory data collection 

process), unless the state provides an 

adequate justification that clearly 

explains the specific circumstances of 

the source or sources in the 

nonattainment area that make such a 

measure or technology economically 

infeasible in that particular area. 

The EPA believes that it is 

appropriate for states to give substantial 

weight to cost effectiveness in 

evaluating the economic feasibility of an 

emission reduction measure or 

technology. The cost effectiveness of a 

measure is its annualized cost ($/year) 

divided by the emissions reduced (tons/ 

year) which yields a cost per amount of 

emission reduction ($/ton). Cost 

effectiveness provides a relative value 

for each emissions reduction option that 

is comparable with other options and, in 

the case of control technologies, other 

facilities. 

The EPA also seeks comment on an 

alternative cost effectiveness metric that 

would allow a state to take into account 

the effect of controlling a particular 

precursor on reducing PM2.5

concentrations in the area. Such a cost 

effectiveness metric would be the 

annualized cost ($/year) of a control 

measure divided by the emissions 

reduced (tons/year) multiplied by the 

amount of reductions needed in the 

precursor emissions to yield 1 mg/m3

reduction in PM2.5 ($/(mg/m3)). Such a 

metric would allow a state to compare 

the relative cost effectiveness associated 

with each measure toward the 

attainment goal for the nonattainment 

area. The EPA notes the difficulty in 

determining the appropriate value to 

relate precursor reductions to 

reductions in ambient PM2.5

concentrations, and therefore seeks 

comment on the appropriateness of this 

approach and how a state might 

demonstrate the validity of the input 

values it chooses to use. 

In considering what level of control is 

reasonable, the EPA is not proposing a 

fixed dollar per ton cost threshold for 

economic feasibility of controls 

identified as potential RACM and 

RACT. In addition, if a state contends 

that a source-specific control-level 

should not be established because the 

source(s) cannot afford the control 

measure or technology that is 

demonstrated to be economically 

feasible for other sources in its source 

category, the EPA proposes that the state 

must support the claim with 

information regarding the impact of 

imposing the identified control measure 

or technology on the following financial 

indicators, to the extent applicable: 

1. Fixed and variable production costs 

($/unit) 

2. Product supply and demand 

elasticity 

3. Product prices (cost absorption vs. 

cost pass-through) 

4. Expected costs incurred by 

competitors 

5. Company profits 

6. Employment costs 

7. Other costs (e.g., for RACM 

implemented by public sector 

entities).102

The EPA seeks comment on the 

factors described above for states to 

consider when determining whether a 

control technology or measure is 

economically feasible. 

Step 4: Determine the earliest date by 

which a control measure or technology 

can be implemented in whole or in part. 

CAA section 189(a)(1)(C) requires that 

the attainment plan for a Moderate 

PM2.5 nonattainment area provide for 

the implementation of RACM and RACT 

no later than 4 years after designation. 

The agency has long interpreted the 

term ‘‘implement’’ to mean that a 

control measure or technology has not 

only been submitted to the EPA for 

approval as part of a SIP but has also 

been built, installed and/or otherwise 

physically manifested, and is achieving 

the intended emissions reductions, and 

the EPA proposes to retain such a 

definition in this rule. See proposed 40 

CFR 51.1000. However, the EPA 

recognizes that a state may be able to 

implement a given control measure only 

partially within 4 years after 

designation. The EPA addressed this 

situation in the General Preamble, 

stating: ‘‘It is important to note that a 

State should consider the feasibility of 

implementing measures in part when 

full implementation would be 

infeasible.’’ 103 This guidance endorses 

the notion that a state should not reject 

an otherwise technologically and 

economically feasible control measure 

or technology as RACM or RACT even 

if it can be only partially implemented 

within the statutory 4-year timeframe 

following designation of the area. 

Instead, the EPA interprets the statute to 

require states to adopt as RACM and 

RACT that portion of a control measure 

or technology that can feasibly be 

implemented within 4 years of the 

effective date of designation. For 

instance, if paving unpaved roads is a 

control measure that is technologically 

and economically feasible in a 

nonattainment area but a state cannot 

pave all roads within 4 years of 

designation, the state must adopt as 

RACM a measure that requires paving of 

that portion of roads that the state could 

feasibly accomplish within 4 years if 

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104With respect to ‘‘partial measures’’ under this 

proposed approach, the EPA would require that a 

state implement as RACM that portion of any 

control measure determined to be technologically 

and economically feasible and implementable 

within 4 years after designation of a nonattainment 

area. The state would then be required to 

implement as an additional reasonable measure that 

portion of the same control measure that can be 

implemented starting 4 years from designation 

through the sixth calendar year following 

designation. 

105Note that under section 110(l) of the CAA, 

after a state has adopted a control measure into the 

SIP for an attainment demonstration, it may remove 

or modify a measure if the state demonstrates to the 

satisfaction of the EPA that such removal or 

modification will not interfere with any applicable 

requirement of the CAA, such as attainment of the 

PM2.5 NAAQS or meeting RFP requirements. 

such a measure is needed for timely 

attainment of the PM2.5 NAAQS in the 

area. 

The EPA thus proposes that a state 

must identify those technologically and 

economically feasible control measures 

and technologies that it can implement 

fully or partially within 4 years of 

designation of its Moderate PM2.5

nonattainment area. Depending on the 

severity of the PM2.5 nonattainment 

problem in the area, some or all of these 

measures identified as implementable 

within 4 years may be needed in order 

to bring the area into attainment as 

expeditiously as practicable. These 

measures will satisfy the EPA’s criteria 

for RACM and RACT if the state 

determines, through its attainment 

demonstration that it needs to 

implement them to achieve timely 

attainment for the area. 

In addition, the EPA proposes that a 

state must separately identify those 

technologically and economically 

feasible control measures that can only 

be implemented after the statutory 

window for implementing RACM and 

RACT. The statutory 4-year timing 

requirement for implementing RACM 

and RACT under section 189(a)(1)(C) 

limits the control measures and 

technologies that can qualify as RACM 

and RACT for a Moderate PM2.5

nonattainment area. However, the 

statutory requirement of CAA 172(c)(6) 

also requires states to implement ‘‘other 

measures’’ necessary to provide for 

timely attainment in an area. The EPA 

proposes that among such other 

measures should be ‘‘additional 

reasonable measures,’’ which would be 

those measures and technologies that 

are otherwise technologically and 

economically feasible but can only be 

implemented in whole or in part later 

than 4 years after designation and 

initiated no later than the beginning of 

the sixth calendar year following 

designation of the area.104 Such 

additional reasonable measures would 

necessarily be implemented on sources 

in the nonattainment area. However, the 

EPA interprets the ‘‘other measures’’ 

required under section 172(c)(6) to 

apply to stationary, area and mobile 

sources located outside of the 

nonattainment area but within the state 

if the application of reasonable control 

measures on such sources would 

facilitate attainment of the PM2.5

NAAQS in the nonattainment area. See 

proposed 40 CFR 51.1009(b). 

Step 5: Model to determine the 

attainment date that is as expeditious as 

practicable and select the control 

measures necessary to achieve 

attainment and meet statutory 

requirements for control measures. 

Section 189(a)(1) of the CAA establishes 

a requirement that the attainment plan 

for a Moderate PM2.5 nonattainment area 

must demonstrate either that an area can 

attain the relevant NAAQS by the 

applicable attainment date or that it is 

impracticable for the area to do so. As 

noted previously, for Moderate PM2.5

nonattainment areas, the ‘‘applicable 

attainment date’’ is as expeditious as 

practicable, but no later than the end of 

the sixth calendar year after designation 

as nonattainment. A complete 

discussion of the EPA’s proposed 

requirements for attainment 

demonstration modeling is presented in 

Section IV.E of this preamble. However, 

one of the key features of attainment 

demonstration modeling is that it 

provides a means of synthesizing the 

effects of emissions reductions from all 

existing and potential new control 

measures identified for sources in a 

given nonattainment area on overall air 

quality in that area. States will be 

required to use the results of their 

attainment demonstration modeling to 

identify the appropriate combination of 

reasonable control measures for sources 

in their Moderate PM2.5 nonattainment 

area and any other control measures 

needed on sources outside the 

nonattainment area to ensure 

expeditious attainment of the relevant 

NAAQS in the area and to meet the 

statutory requirements of sections 

189(a)(1)(B) and 172(c)(6) as explained 

below.105

Step 5a: If the state can demonstrate 

attainment in the area by the statutory 

attainment date for a Moderate area, 

then the state must implement those 

control measures needed for expeditious 

attainment of the NAAQS in the area. If 

a state determines that a Moderate 

nonattainment area can attain the PM2.5

NAAQS by the statutory attainment 

date, the state must adopt and 

implement any technologically and 

economically feasible control measures 

that are necessary to ensure that the area 

will attain the NAAQS as expeditiously 

as practicable. The EPA will consider 

any such measures that can be 

implemented within 4 years of 

designation of the area to fulfill the 

RACM and RACT requirements for the 

area. In addition, the EPA will consider 

any such measures that can only be 

implemented between 4 years and the 

sixth calendar year after designation to 

meet the requirements of section 

172(c)(6) as ‘‘additional reasonable 

measures’’ for the area and necessary to 

demonstrate timely attainment under 

section 189(a)(1)(B). 

Under this approach, the state may 

reject any otherwise technologically or 

economically feasible measures that are 

not needed to demonstrate attainment or 

that will not advance the attainment 

date by at least 1 year. That is, for a 

Moderate area that can demonstrate 

attainment by the statutory Moderate 

area attainment date, the EPA proposes 

to define as ‘‘reasonable’’ only those 

technologically and economically 

feasible measures that are necessary for 

expeditious attainment of the NAAQS, 

as the CAA does not require a state to 

adopt measures that are not needed for 

expeditious attainment in a Moderate 

PM2.5 nonattainment area. Thus, a state 

may exclude those otherwise reasonably 

available measures that, if adopted and 

considered collectively, would not 

advance the attainment date for the area 

by at least 1 year, so long as the state 

can demonstrate attainment as 

expeditiously as practicable and no later 

than the statutory Moderate area 

attainment date. See proposed 40 CFR 

51.1009(a)(4)(i). 

The EPA recognizes that identifying 

which measures could not collectively 

advance the attainment date for a 

Moderate area by at least 1 year may be 

an iterative process that requires 

additional analysis and/or modeling. 

The agency believes that such effort is 

reasonable for a state seeking to 

demonstrate the lack of need for certain 

controls that are determined to be 

technologically and economically 

feasible in light of the requirement for 

expeditious attainment in a given 

Moderate nonattainment area. The basis 

for deciding that it would be reasonable 

not to require imposition of otherwise 

available and appropriate controls 

because they would not be needed for 

attainment, or would not advance 

attainment, requires a suitably robust 

analysis and explanation. 

Step 5b: If the state cannot 

demonstrate attainment by the statutory 

attainment date for a Moderate area, 

then the state must adopt all reasonable 

control measures. As noted elsewhere in 

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106The concept of an ‘‘impracticability 

demonstration’’ is established in section 188(b), 

which addresses reclassifying Moderate PM2.5 areas 

to Serious. Section 188(b)(1) describes the EPA’s 

discretionary authority to reclassify an area upon a 

determination that an area cannot practicably attain 

by the Moderate area attainment date. More relevant 

to this determination, however, section 189(a)(1)(B) 

specifically provides for submission of a 

demonstration addressing this concept in the case 

of Moderate areas that cannot attain the NAAQS by 

the applicable attainment date. 

107 57 FR 13498 (April 16, 1992), at page 13544. 

this section, section 189(a)(1)(B) of the 

CAA requires a state to submit as part 

of the attainment plan either a 

demonstration that the plan will 

provide for attainment of the relevant 

NAAQS by the applicable attainment 

date, or a demonstration that attainment 

by such date is ‘‘impracticable.’’ This 

subpart 4 requirement anticipates that 

not all nonattainment areas initially 

classified as Moderate will necessarily 

be able to attain by the latest statutory 

attainment date for Moderate areas, and 

it incorporates the concept of an 

‘‘impracticability demonstration’’ for 

such areas.106 The CAA is thus 

structured to provide that Moderate 

areas that cannot timely attain the 

NAAQS through the required elements 

of a Moderate area attainment plan will 

be reclassified to Serious and will have 

to meet additional control requirements 

beyond those that are ‘‘reasonable’’ to 

assure attainment of the NAAQS by a 

later date that is as expeditious as 

practicable. 

Existing guidance in the General 

Preamble on implementing this section 

of the CAA states that ‘‘the EPA believes 

it is reasonable for all available control 

measures that are technologically and 

economically feasible to be adopted for 

areas that do not demonstrate 

attainment [by the applicable attainment 

date].’’ 107 The EPA maintains that it is 

reasonable to require a state to model 

the effects of emissions reductions from 

all technologically and economically 

feasible controls identified by the state 

for sources in a nonattainment area 

before asserting a claim that the area 

cannot practicably attain the relevant 

NAAQS by the Moderate area 

attainment date. However, the 

magnitude of certain PM2.5 precursor 

emissions and/or local atmospheric 

conditions of some PM2.5 nonattainment 

areas may render certain technologically 

and economically feasible control 

measures ineffective in reducing 

ambient PM2.5 levels. Therefore, even in 

a Moderate PM2.5 nonattainment area 

that cannot practicably attain the 

relevant NAAQS by the statutory 

attainment date, the EPA believes that it 

may not be reasonable in all cases to 

require that a state implement all 

technologically and economically 

feasible control measures identified for 

sources in the area. 

Consistent with the EPA’s longstanding interpretation that subpart 4 

Moderate area control requirements 

must be reasonable, the EPA proposes 

that, for a Moderate PM2.5

nonattainment area that cannot 

practicably attain the NAAQS by the 

statutory attainment date, a state must 

adopt and implement all technologically 

and economically feasible measures 

identified for sources in the area, except 

for any such measures that collectively 

will not effectively reduce ambient 

PM2.5 concentrations. See proposed 40 

CFR 51.1009(a)(4)(ii). The EPA views 

this approach as similar to the agency’s 

approach of allowing states to reject any 

otherwise technologically or 

economically feasible measures that are 

not needed to demonstrate attainment 

and that will not advance the attainment 

date by at least 1 year for nonattainment 

areas for which states can demonstrate 

attainment by the statutory attainment 

date. Once again, the EPA recognizes 

that identifying which measures 

collectively will not effectively reduce 

ambient PM2.5 concentrations will likely 

be an iterative process that requires 

specific analysis, potentially including 

modeling. However, the agency believes 

that such effort is appropriate for a state 

seeking to demonstrate the lack of need 

for certain controls that are determined 

to be technologically and economically 

feasible in a Moderate nonattainment 

area that cannot practicably attain the 

relevant PM2.5 NAAQS by the latest 

statutory Moderate area attainment date. 

The basis for establishing that it would 

not be reasonable to require imposition 

of otherwise available and appropriate 

controls because they would not be 

effective in reducing ambient PM2.5

concentrations requires an adequately 

robust analysis and explanation. 

The EPA also proposes an alternative 

approach to identifying all reasonable 

control measures for a Moderate 

nonattainment area that cannot 

practicably attain the PM2.5 NAAQS by 

the end of the sixth calendar year 

following designation. Under this 

alternative, states would be required to 

implement all technologically and 

economically feasible control measures 

that they have identified for sources of 

direct PM2.5 emissions and sources of 

emissions of significant PM2.5

precursors in the area. The EPA believes 

that this interpretation would be 

consistent with the agency’s previous 

guidance in the General Preamble and is 

compelled by the language of section 

189(a)(1)(C), which separately requires a 

state to submit a Moderate area 

attainment plan and meet the RACM 

and RACT requirement, even if the state 

submits a demonstration that it cannot 

attain the NAAQS through those 

measures by the applicable attainment 

date. In addition, as with a Moderate 

PM2.5 nonattainment area which a state 

demonstrates can attain the NAAQS by 

the end of the sixth calendar year 

following designation, the EPA 

interprets the provisions of section 

172(c)(6) to require that such an area 

must implement all additional 

reasonable measures that it can 

implement through the sixth calendar 

year following designation of the area, 

in addition to those measures meeting 

the definition of RACM and RACT, in 

order to make progress toward 

attainment after the end of the fourth 

year following designation. 

As described in Section III of this 

preamble, the EPA is proposing three 

options for implementing CAA 

requirements applicable to PM2.5

precursors in the context of attainment 

planning and NNSR permitting. 

Proposed precursor Options 2A and 2B 

would provide an opportunity for a state 

to demonstrate that emissions of a 

particular precursor from all sources 

located in a Moderate PM2.5

nonattainment area do not contribute 

significantly to ambient PM2.5 levels that 

exceed the standard in the area, or 

reductions of which will not be effective 

in reducing ambient PM2.5

concentrations, in which case the state 

would not be required to identify or 

otherwise evaluate control measures for 

the particular precursor. Under 

proposed precursor Options 1 and 3, on 

the other hand, states would rely on 

their control strategy analyses (e.g., for 

Moderate nonattainment areas, analyses 

to determine RACM and RACT and 

additional reasonable measures) to 

identify whether and/or which controls 

on sources of PM2.5 precursors are 

‘‘reasonable.’’ The EPA believes that if 

proposed precursor Option 1 or 3 is 

finalized, it would be most appropriate 

to finalize the first approach to 

identifying reasonable control measures 

for Moderate areas that cannot 

practicably attain the NAAQS by the 

statutory attainment date, since states 

would not have an opportunity prior to 

evaluating the specific control measures 

for sources of PM2.5 precursors in the 

nonattainment area to demonstrate that 

controlling all sources of a particular 

precursor would not be effective in 

reducing ambient PM2.5 levels in the 

area. Likewise, if the agency finalizes 

proposed precursor Options 2A or 2B, 

the EPA believes that it would be most 

appropriate to finalize the alternative 

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108 Ibid. at 13544. 

109 Ibid. 

110 If the EPA finalizes proposed precursor Option 

2A or 2B, which would effectively allow a state to 

demonstrate that a given precursor does not 

contribute significantly to PM2.5 concentrations in 

a nonattainment area, then this step would require 

potential control measures only for sources of direct 

PM2.5 and precursors not exempted from further 

analysis. 

111Menu of Control Measures document available 

at http://www.epa.gov/air/criteria.html. 

proposed approach of requiring a state 

to implement all technologically and 

economically feasible measures 

identified by the state for sources in the 

area that can be implemented by the end 

of the sixth calendar year following 

designation if the state demonstrates 

that the area cannot practicably attain 

the NAAQS by the statutory attainment 

date, since the ‘‘measures identified by 

the state’’ would already implicitly 

exclude control measures on sources of 

any ‘‘insignificant’’ precursor. The EPA 

seeks comment on the two proposed 

approaches to selecting RACM and 

RACT and additional reasonable 

measures for Moderate nonattainment 

areas that cannot practicably attain the 

NAAQS by the statutory attainment 

date, and on the EPA’s evaluation of the 

compatibility of these proposed 

approaches with the agency’s proposed 

precursor options. 

The EPA’s proposed analytical 

process for determining RACM and 

RACT is intended to result in a 

comprehensive list of such 

technologically and economically 

feasible controls that would include 

local and state measures that could 

achieve emissions reductions from 

sources within the area, beyond those 

that could or would be achieved 

through regional or national measures. 

Furthermore, the EPA is proposing to 

require that the Moderate area 

attainment plan must include modeling 

of all RACM and RACT and additional 

reasonable measures, and other state, 

regional and federal measures, to 

demonstrate that a state will not be able 

to attain the NAAQS by the end of the 

sixth calendar year after designation due 

to the severity of nonattainment in the 

area and/or due to the lack of 

availability or feasibility of 

implementing controls in the area by 

such date. 

Subpart 4 requires that Moderate 

areas that cannot or do not meet the 

Moderate area attainment date be 

reclassified as Serious nonattainment 

areas, in which case sources in the areas 

are then subject to BACM and BACT 

requirements. In the General Preamble, 

the EPA indicated that ‘‘it may be 

reasonable, in some limited 

circumstances, for States to consider the 

compatibility of RACM and RACT with 

the BACM and BACT that will 

ultimately be implemented under the 

Serious area plans for those areas.’’ 108

Furthermore, for such areas that do not 

meet the Moderate area attainment date, 

the EPA indicated that ‘‘in the case of 

RACM for area sources, EPA anticipates 

that any future implementation of 

BACM for these sources will be additive 

to, and hence compatible with, RACM. 

This is because BACM will generally 

consist of a more extensive 

implementation of the RACM measures 

. . . Since EPA anticipates that RACM 

and BACM for these sources will be 

compatible, the SIP’s (sic) for these areas 

should reflect the application of 

available control measures to existing 

sources in moderate nonattainment 

areas as determined by the analysis 

described . . . for RACM.’’ 109 The EPA 

believes that a state should consider 

selecting and implementing controls 

that may qualify as BACM or BACT in 

a Moderate nonattainment area as part 

of their RACM and RACT analysis if 

they have reason to suspect that the area 

may not be able to attain the NAAQS by 

the applicable Moderate area attainment 

date as long as the control can be 

implemented by the statutory Moderate 

area attainment date. Early adoption of 

controls that would constitute BACM or 

BACT could be more efficient and could 

further the objectives of attaining the 

NAAQS expeditiously to protect public 

health and the environment. 

3. RACM and RACT and Additional 

Reasonable Measures Submission 

Requirements 

To ensure that attainment plan 

submissions contain the necessary 

supporting information to enable the 

EPA to review and approve a state’s 

evaluation and selection of measures 

that constitute RACM and RACT in a 

given nonattainment area, the EPA 

proposes to require under the authority 

of section 301(a) that a state must 

submit the following information as part 

of its submission: 

• A list of all source categories, 

sources and activities in the 

nonattainment area that emit direct 

PM2.5 or any PM2.5 precursor (for multistate nonattainment areas, this would 

include source categories, sources and 

activities from all states which make up 

the area); 

• For each source category, source or 

activity in the nonattainment area, an 

inventory of direct PM2.5 emissions and 

emissions of all PM2.5 precursors; 

• For each non-de minimis source 

category, source or activity in the 

nonattainment area, a comprehensive 

list of potential control measures 

considered by the state for the 

nonattainment area; 110 111

• For each potential control measure 

considered by the state but eliminated 

from further consideration due to a 

determination by the state that the 

control measure or technology was not 

technologically feasible, a narrative 

explanation and quantitative or 

qualitative supporting documentation to 

justify the state’s conclusion; 

• For each technologically feasible 

emission control measure or technology, 

the state must provide the following 

information relevant to economic 

feasibility: (1) The control efficiency by 

pollutant; (2) the possible emissions 

reductions by pollutant; (3) the 

estimated cost per ton of pollutant 

reduced; and, (4) a determination of 

whether the measure is economically 

feasible, with narrative explanation and 

quantitative supporting documentation 

to justify the state’s conclusion. 

• For each technologically and 

economically feasible emission control 

measure or technology, the date by 

which the technology or measure could 

reasonably be implemented. 

Each of these elements will provide 

information needed by the EPA to 

evaluate correctly and efficiently 

whether the state is meeting the 

statutory requirements for an attainment 

plan, and in particular meeting the 

statutory requirement for states to 

implement RACM and RACT on sources 

within the nonattainment area. The EPA 

recognizes that the base year emissions 

inventory for the area that the state 

submits in conjunction with its 

attainment plan will likely contain some 

of the information proposed to be 

required under the first two items in 

this list. However, the EPA believes that 

it is incumbent on the state to ensure 

that the information needed for the EPA 

to evaluate the state’s RACM and RACT 

analysis is presented more specifically 

as part of the RACM and RACT analysis 

and in a format that provides 

transparency, consistency and the 

ability for another party to evaluate the 

state’s analysis effectively. For this 

reason, the EPA is including emissions 

inventory information specifically 

relevant to the RACM and RACT 

element of the state’s attainment plan. 

4. Criteria for Effective Regulations To 

Implement RACM and RACT and 

Additional Reasonable Measures 

After a state has identified a particular 

control measure as RACM or RACT or 

additional reasonable measure for a 

particular nonattainment area, it must 

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112The term ‘‘overburdened populations’’ is 

defined in the EPA’s ‘‘Plan EJ 2014’’ to describe the 

minority, low-income, tribal, and indigenous 

populations or communities in the U.S. that 

potentially experience disproportionate 

environmental harms and risks as a result of greater 

vulnerability to environmental hazards. This 

increased vulnerability may be attributable to an 

accumulation of both negative and lack of positive 

environmental, health, economic or social 

conditions within these populations or 

communities. For more information on Plan EJ 

2014, see: http://www.epa.gov/

environmentaljustice/plan-ej/. 

then implement that measure through a 

legally enforceable mechanism that will 

be included in the SIP (e.g., a state rule 

that the EPA will approve as a part of 

the federally enforceable SIP for the 

state). The EPA is proposing that in 

order for the EPA to be able to approve 

any such measure as part of the SIP, the 

state would have to provide information 

to meet the following four criteria. 

These criteria are similar to the criteria 

finalized as part of the remanded 2007 

PM2.5 Implementation Rule. 

First, the base year emissions from the 

source or group of sources to which the 

control measure applies and the future 

year projected emissions from those 

sources once controlled must be 

quantifiable so that the projected 

emissions reductions from the sources 

can be attributed to the specific 

measures being implemented. It is 

important that the emissions from the 

source category in question are 

accurately represented in the base year 

inventory so that emissions reductions 

are properly calculated. In particular, it 

is especially important to ensure that 

both the filterable and condensable 

components of direct PM2.5 emissions 

are accurately represented in the base 

year. 

Second, the control measures must be 

enforceable. This means that they must 

specify clear, unambiguous and 

measurable requirements. The 

measurable requirements for larger 

emitting facilities must include periodic 

source testing, monitoring or other 

viable means to establish whether the 

affected source meets the applicable 

emission limit. Additionally, to verify 

the continued performance of the 

control measure, specific emissions 

monitoring programs appropriate for the 

type of control measure employed and 

the level of emissions must be included 

to verify the continued performance of 

the control measure. The control 

measures and monitoring program must 

also have been adopted according to 

proper legal procedures. 

Third, the results of application of the 

control measures must be replicable. 

This means that where a rule contains 

procedures for interpreting, changing or 

determining compliance with the rule, 

the procedures are sufficiently specific 

and objective so that two independent 

entities applying the procedures would 

obtain the same result. 

Fourth, the control measures must be 

accountable. This means, for example, 

that source-specific emission limits 

must be permanent and must reflect the 

assumptions used in the attainment 

plan for the area, including the 

modeling conducted in conjunction 

with the attainment demonstration. It 

also means that the attainment plan 

must establish requirements to track 

emissions changes at sources and 

provide for corrective action if 

emissions reductions are not achieved 

according to the plan. 

The EPA seeks comment on these 

criteria for approval of any control 

measures adopted by a state for a 

Moderate area to assure that such 

measures are legally enforceable. 

5. Determination of RACM and RACT 

and Additional Reasonable Measures in 

Multi-State Nonattainment Areas 

States in multi-state nonattainment 

areas will need to consult with each 

other on appropriate control measures 

for the shared nonattainment area. The 

agency anticipates that states could 

decide upon RACM and RACT and 

additional reasonable measures that 

differ from state to state in a shared 

nonattainment area, based upon each 

state’s determination of the most 

effective strategies given the relevant 

mixture of sources and potential 

controls in the respective states’ 

portions of a shared nonattainment area. 

As long as each state can adequately 

demonstrate that its chosen attainment 

strategy, including its selection and 

adoption of RACM and RACT and 

additional reasonable measures, will 

provide for meeting RFP requirements 

and for attainment of the NAAQS as 

expeditiously as practicable for the 

nonattainment area at issue, the EPA 

anticipates being able to approve 

individual state plans that may elect to 

control a different mix of sources or to 

implement different controls, under the 

proper circumstances. Nevertheless, in 

evaluating RACM and RACT and 

additional reasonable measures for a 

particular nonattainment area, states 

must consider potential reasonable 

control measures developed for other 

areas or other states, and particularly for 

other portions of an interstate 

nonattainment area. In addition, states 

in multi-state nonattainment areas must 

evaluate whether the reasonable 

measures each state may have identified 

as not being necessary for attainment 

could collectively advance the 

attainment date for the area by at least 

1 year. The EPA may consider such 

measures in assessing the approvability 

of each state’s individual attainment 

plan for a multistate nonattainment 

area. 

6. Environmental Justice Considerations 

in Developing the Attainment Plan 

Control Strategy for a Moderate PM2.5

Nonattainment Area 

The EPA strongly urges states to 

consider environmental justice concerns 

with respect to any control measures 

they have identified as potential RACM 

or RACT or additional reasonable 

measures in an area, particularly to the 

extent that control measures that a state 

may be considering are otherwise 

approximately equal (in terms of 

technological and economic feasibility) 

but unequal with respect to their direct 

or indirect impacts on overburdened 

populations.112 In such cases, the EPA 

encourages the state to prioritize 

imposition of the control measures that 

will result in the least possible burden 

and greatest degree of health protection 

for overburdened populations in the 

nonattainment area. Section IX of this 

preamble discusses this and other 

possible approaches for states to 

incorporate ways to address 

environmental justice concerns 

associated with implementation of the 

PM2.5 NAAQS in their attainment plans 

and SIP development process, and the 

EPA seeks comment on ways to more 

fully address such concerns. 

E. Modeling for Attainment 

Demonstrations 

1. Statutory Requirements 

Section 189(a) generally requires a 

state with a designated Moderate 

nonattainment area to submit an 

attainment plan for such area. As 

discussed earlier, section 189(a)(1)(B) 

more specifically requires the state to 

submit an attainment demonstration 

including air quality modeling to 

establish either: (i) That the area will 

attain the relevant NAAQS by the 

applicable attainment date; or, (ii) that 

it is impracticable for the area to attain 

the relevant NAAQS by the applicable 

attainment date. For Moderate 

nonattainment areas, the attainment 

date is as expeditiously as practicable, 

but no later than the end of the sixth 

calendar year after designation as 

nonattainment. Section 189(a)(2)(B) of 

the CAA requires states with designated 

nonattainment areas to submit 

attainment plans no later than 18 

months after designation. 

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113An area is designated nonattainment for either 

the annual PM2.5 NAAQS or the 24-hr PM2.5

NAAQS or both. The attainment demonstration 

should show that the area is attaining the form of 

the NAAQS for which they have been designated 

nonattainment. 

114Pursuant to section 188(b)(1)(B), upon an EPA 

determination that attainment by the Moderate date 

is impracticable, the EPA shall reclassify the area 

as Serious within 18 months after the Moderate area 

attainment plan due date. 

2. What is an attainment demonstration? 

Section 189(a)(2)(B) does not define 

the term ‘‘demonstration’’ and does not 

specify precisely how a state should 

make the required demonstration. Thus, 

the EPA believes it is necessary to 

provide more specific parameters for 

such demonstrations in order to assure 

that they contain the requisite 

information to allow for meaningful 

evaluation of the issues that the 

demonstrations are intended to address. 

An attainment demonstration is a set of 

analyses that provide an explanation of 

how a state will attain the PM2.5 NAAQS 

by the applicable attainment date in a 

particular nonattainment area.113 The 

EPA is proposing that the demonstration 

must contain: (i) Technical analyses 

such as base year and future year 

modeling of emissions which identify 

sources and quantify emissions that are 

contributing to violations of the PM2.5

NAAQS; and, (ii) analyses of future year 

emissions reductions and air quality 

improvement resulting from existing 

(i.e., already-adopted or ‘‘on the books’’) 

national, regional and local programs, 

and potential new local measures 

needed for attainment, including RACM 

and RACT controls for the area. Each 

state with a Moderate nonattainment 

area must submit an attainment plan 

with an attainment demonstration that 

includes analyses supporting the state’s 

determination of its proposed 

attainment date. In all cases, the state 

must show that the Moderate area will 

attain the NAAQS as expeditiously as 

practicable, but not later than the end of 

the sixth calendar year after designation. 

In order to establish that the attainment 

date is as expeditious as practicable, the 

state must explain why any control 

measures adopted in the attainment 

plan provide for the most expeditious 

attainment and, specifically, must 

demonstrate that collectively the 

reasonable measures that were not 

adopted as RACM or RACT or 

additional reasonable measures will not 

advance the attainment date by at least 

1 year if implemented. See proposed 40 

CFR 51.1011(a). 

A state may alternatively submit a 

demonstration that shows that 

attainment by the statutory attainment 

date for a Moderate area is 

impracticable.114 The statute does not 

define the term ‘‘impracticable’’ in this 

context, so it is necessary for the EPA 

to interpret this term in the context of 

a submission from the state for this 

purpose. In order to support this type of 

demonstration, the EPA proposes to 

require that the state must show that, 

even if all technologically and 

economically feasible controls that can 

be implemented within 6 years were 

implemented, the state could not attain 

the NAAQS within the statutory 

timeframe for a Moderate area. A state 

could do this by performing a modeling 

analysis which projects emissions to the 

sixth year after designations in order to 

predict future year PM2.5 design values 

in the area. The projected emissions 

would account for all existing federal 

and state SIP-adopted regulations on 

sources outside the nonattainment area 

that were in place at the time, plus all 

measures that were identified as 

technologically and economically 

feasible controls that can be 

implemented in the nonattainment area 

within 6 years of designation (i.e. all 

measures that would qualify as RACM 

or RACT or as additional reasonable 

measures), as well as any other 

reasonable measures available in the 

state that could aid in achieving timely 

attainment. If the modeling shows that 

attainment cannot be reached by the end 

of the sixth calendar year following 

designation, then the analysis could be 

used to demonstrate that it is 

impracticable for the area to attain the 

relevant NAAQS by the statutory 

attainment date. Other information can 

also be used to support the 

demonstration, including ambient data 

and emissions trends data. States are 

encouraged to work with their 

respective EPA Regional Office to 

identify appropriate information that 

could be used to support an 

impracticability demonstration. The 

EPA emphasizes that states that can 

make the required showing that a 

Moderate nonattainment area cannot 

attain the NAAQS by the statutory 

attainment date are nonetheless 

required to meet the substantive 

requirements for a Moderate area 

attainment plan, including the 

implementation of control measures that 

are RACM and RACT and additional 

reasonable measures in that area. 

3. What modeling is required? 

States are required to submit air 

quality modeling in support of an 

attainment demonstration for a 

Moderate PM2.5 nonattainment area. 

Although air quality modeling is not 

expressly required for a Moderate area 

demonstration showing that attainment 

by the attainment date is impracticable 

(per section 189(a)(1)(B)(ii)), the EPA 

proposes to interpret the CAA to require 

air quality modeling similar to that 

required for an attainment 

demonstration in order to demonstrate 

that attainment of the relevant PM2.5

NAAQS by the statutory attainment date 

is impracticable. Because air quality 

modeling is a required element of the 

attainment demonstration in section 

189(a)(1)(B), the EPA believes that it 

logically follows that similar modeling 

should also be required to show that an 

area will not be able to attain by the 

attainment date contemplated by the 

statute. 

There may be limited cases in which 

a state may be able to demonstrate 

through a rigorous technical analysis 

with supporting documentation that 

attainment by the statutory Moderate 

area attainment date is impracticable. 

Given that the statute may be 

interpreted as not requiring air quality 

modeling for an impracticability 

demonstration, the EPA proposes and 

seeks comment on an alternative option 

under which air quality modeling 

would not be a requirement for a 

Moderate area impracticability 

demonstration. The EPA would 

recommend that a state submit 

modeling as part of any Moderate area 

impracticability demonstration, but 

under this alternative option such 

modeling would not be a regulatory 

requirement. 

Given that secondarily formed PM2.5

(e.g. ammonium sulfate, ammonium 

nitrate and SOA) is a large fraction of 

the total measured PM2.5 in most PM2.5

nonattainment areas, the EPA assumes 

that photochemical grid modeling 

(which considers secondary PM2.5

formation) will be needed for a state to 

demonstrate attainment with the 

NAAQS. Most previous PM2.5

attainment demonstrations for both the 

1997 and 2006 PM2.5 NAAQS have 

utilized photochemical grid models. 

However, in some nonattainment areas 

that are dominated by primary PM2.5

emissions (e.g. residential wood smoke), 

more simplistic dispersion models, such 

as a combination of dispersion, receptor 

and box airshed models, may suffice to 

demonstrate that the area will attain the 

NAAQS. Regardless of the modeling 

approach selected to support the 

attainment demonstration, the analyses 

must be based on technically credible 

methods and provide for the timely 

submittal of the attainment 

demonstration and implementation of 

control measures. States should consult 

with their respective EPA Regional 

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115Even though the ozone NAAQS modeling will 

be focused on ozone, PM2.5 modeling results will 

likely be generated from the analysis in order to 

inform health benefits calculations. 

116The 2007 modeling guidance can be found at 

the following Web site: http://www.epa.gov/

scram001/guidance/guide/final-03-pm-rhguidance.pdf. As noted, the EPA recently released 

revised draft modeling guidance. 

Office to determine the appropriate type 

of modeling demonstration for the 

particular nonattainment area. 

4. Do states need to develop new 

modeling for their attainment 

demonstrations? 

The EPA believes that the statutory 

provision requiring attainment 

demonstrations for Moderate PM2.5

nonattainment areas to include air 

quality modeling can be fulfilled in a 

variety of ways. Thus the EPA proposes 

to allow states to fulfill the statutory 

modeling requirement through either 

locally generated photochemical and/or 

dispersion modeling or, with proper 

justification, through appropriate 

regional or national modeling. The EPA 

seeks comment on what types of 

modeling demonstrations should be 

required to fulfill the CAA requirement 

to ‘‘include air quality modeling’’ as 

part of the attainment demonstrations 

for Moderate nonattainment areas. 

New modeling analyses that follow 

the EPA modeling guidance, conducted 

by the state for implementing the PM2.5

NAAQS, will presumably satisfy the 

attainment demonstration modeling 

requirement. However, many areas that 

were designated as nonattainment for 

the 1997 and/or 2006 PM2.5 NAAQS 

have already invested considerable 

resources in local and/or regional PM2.5

modeling analyses. Most states with 

potential PM2.5 nonattainment areas are 

already participating in regional 

modeling analyses through multijurisdictional organizations (MJOs). 

These MJOs (e.g. SESARM, LADCO and 

WRAP) represent most states with PM2.5

nonattainment areas in the country. 

There is ongoing PM2.5 modeling that 

may provide useful information for state 

PM2.5 NAAQS attainment 

demonstrations. 

In addition to local and regional 

modeling, the EPA conducts nationwide 

modeling (generally limited to the 

contiguous 48 states) in support of 

various national rulemakings. The base 

and future modeling year for national 

rule modeling varies depending on 

compliance dates for the rule being 

analyzed and on when the modeling 

was conducted. For example, there are 

several analyses of recent and ongoing 

rules which may provide useful PM2.5

modeling information for state 

attainment demonstrations. Among 

them are modeling to support the 2012 

PM2.5 NAAQS review, the final Tier 3 

mobile source emissions standards, and 

the current ozone NAAQS review.115

While the analyses in these rulemaking 

actions may not be precisely relevant for 

the purposes of a PM2.5 attainment plan, 

they may nevertheless provide useful 

information or input relevant to states 

developing attainment plans for the 

PM2.5 NAAQS. Similar nationwide 

modeling efforts may be helpful for 

purposes of future PM2.5 NAAQS. 

States may be able to use regional 

and/or EPA modeling to demonstrate 

that specific nonattainment areas will 

attain the relevant PM2.5 NAAQS by the 

applicable attainment date, but states 

must evaluate the relevant modeling 

information to show that it is suitable 

for that purpose. For example, the 

modeling should be evaluated to show 

that it is performing adequately for the 

area; that the future modeling year is 

appropriate for the particular attainment 

demonstration; and that the base year 

emissions and projected emissions and 

controls adequately represent the base 

year conditions and emissions expected 

to occur in the area in the future. States 

should work closely with the 

appropriate EPA Regional Office to 

determine what (if any) existing 

modeling may be suitable for use in an 

attainment demonstration (or an 

impracticability demonstration) for a 

Moderate PM2.5 nonattainment area. 

The EPA requests comment on how 

states can use existing regional and/or 

national modeling to meet their 

attainment demonstration requirements. 

The agency also notes that even when 

regional or EPA modeling is available to 

show that an area is expected to attain 

the PM2.5 NAAQS by the applicable 

attainment date, other CAA 

requirements may be difficult to satisfy 

through the use of regional or EPA 

modeling. For example, states may or 

may not be able to satisfy their CAA 

requirements for emissions inventory 

submittals or RFP demonstrations by 

using data derived from MJO or EPA 

modeling. The available regional/

national modeling may not include an 

appropriate base year or future year, and 

the level of detail or how the emissions 

were derived may not be appropriate or 

compatible with inventories needed to 

satisfy specific CAA requirements. 

States may have to derive more local 

specific inventory data, for the 

appropriate years, to adequately satisfy 

these CAA requirements. 

Because it will be challenging for 

states to prepare new modeling analyses 

to meet the submission deadline for the 

Moderate area attainment plans, the 

EPA encourages states to start work on 

modeling analyses as soon as possible, 

in order to ensure that adequate time is 

devoted to developing a technically 

credible attainment demonstration. 

States that have the most challenging 

PM2.5 problems will likely need to 

develop new and/or updated 

photochemical modeling analyses for 

their nonattainment areas, with 

emissions (including potential new 

controls) projected to the appropriate 

future attainment year. 

5. What guidance is available for using 

models to demonstrate attainment? 

The procedures for modeling PM2.5 as 

part of an attainment demonstration are 

described in the EPA’s ‘‘Guidance on 

the Use of Models and Other Analyses 

for Demonstrating Attainment of Air 

Quality Goals for Ozone, PM2.5, and 

Regional Haze.’’ 116 All modeling in 

support of an attainment demonstration 

should be consistent with the EPA’s 

PM2.5 photochemical modeling 

guidance (referenced above) as well as 

the Guideline on Air Quality Models (40 

CFR part 51, Appendix W). 

The PM2.5 attainment demonstration 

modeling guidance describes how states 

can apply air quality models to generate 

results needed to demonstrate 

attainment. These recommendations 

include developing a conceptual 

description of the problem to be 

addressed; developing a modeling/

analysis protocol; selecting an 

appropriate model to support the 

demonstration; selecting appropriate 

meteorological episodes or time periods 

to model; choosing an appropriate area 

to model with appropriate horizontal/

vertical resolution; generating 

meteorological and air quality inputs to 

the air quality model; generating 

emissions inputs to the air quality 

model; and, evaluating performance of 

the air quality model. After these steps 

are completed, the state can apply a 

model to simulate effects of future year 

emissions and candidate control 

strategies. 

The EPA is not requiring a specific 

model for use in the attainment 

demonstration for the PM2.5 NAAQS. At 

present, there is no single model which 

has been extensively tested and shown 

to be clearly superior to other available 

models. The current modeling 

guideline, 40 CFR part 51, Appendix W, 

does not identify a preferred model for 

use in attainment demonstrations of the 

PM2.5 NAAQS. Thus, states may choose 

from several alternatives so long as the 

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117The exact years of the ‘‘recent’’ ambient data 

are defined by the base year selected for the 

modeling. The guidance recommends using 5 years 

of ambient data, centered about the base modeling 

year. 

118See ‘‘Draft Modeling Guidance for 

Demonstrating Attainment of Air Quality Goals for 

Ozone, PM2s, and Regional Haze,’’ issued by 

Richard Wayland, Director of Air Quality 

Assessment Division, EPA Office of Air Quality 

Planning and Standards, to EPA Regional Air 

Division Directors, Regions I–X, December 3, 2014. 

Available at: http://www.epa.gov/ttn/scram/

guidance/guide/Draft_O3-PM-RH_Modeling_

Guidance-2014.pdf. 

119 78 FR 3085 (January 15, 2013), at page 3283. 

alternative is appropriate for the 

nonattainment area under evaluation. 

In some cases, a state may need to 

apply multiple models in the attainment 

demonstration. In most cases, a 

photochemical grid model is needed to 

predict base and future year 

concentrations of secondary PM2.5. 

Photochemical grid models can also be 

used to predict concentrations of 

primary particulate and are useful in 

assessing steep concentration gradients 

arising from area sources. However, in 

areas with high concentrations of 

primary PM2.5, or strongly stratified air 

at the surface, a Gaussian plume model 

or puff model may also be needed to 

more accurately represent steep 

concentration gradients (or lack of 

mixing to the surface) in locations with 

a large contribution from a single or 

multiple primary PM2.5 point sources or 

locations in near-road areas. The EPA’s 

attainment demonstration modeling 

guidance provides details and 

recommendations on using multiple 

models. 

Models are used to test whether 

control measures in an attainment plan 

are likely to result in attainment of the 

relevant standard(s). The attainment 

demonstration modeling guidance 

recommends a modeled attainment test 

for the annual and 24-hour PM2.5

NAAQS that uses a combination of 

ambient PM2.5 and PM2.5 species data 

and modeled PM2.5 concentrations to 

estimate future year air quality. In the 

recommended attainment test, the state 

applies the test at each PM2.5 ambient 

monitor location within or near a 

designated nonattainment area. Models 

are used in a relative sense to estimate 

the response of measured air quality to 

future changes in emissions. Future air 

quality is estimated by multiplying 

recent monitored PM2.5 values by the 

modeled relative response (percent 

change) to projected future changes in 

emissions. If the future design value at 

all monitoring locations in the 

nonattainment area does not exceed the 

concentration of PM2.5 specified in the 

NAAQS, the area is projected to attain 

the NAAQS. 

Because PM2.5 is a mixture of 

chemical components, states should use 

recent observations and modeled 

responses of major components of PM2.5

(i.e. sulfate, nitrate, organic carbon, etc.) 

to estimate future concentrations of each 

component.117 The predicted future 

concentration of PM2.5 is the sum of the 

future year predicted component 

concentrations. 

The attainment demonstration 

modeling guidance contains additional 

details regarding the treatment of PM2.5

and speciation monitoring data. Because 

PM species data are not available at 

each PM2.5 FRM site, the EPA 

recommends a methodology which 

interpolates species data to each FRM 

site in order to estimate the species 

concentrations in the area. This 

information, combined with modeling 

results, may be used to calculate future 

air quality at each FRM monitoring site. 

The EPA has developed software to 

perform both the annual and 24-hour 

PM2.5 attainment test (including 

interpolating PM species data). The 

software is called the Modeled 

Attainment Test Software (MATS) and 

is available for no cost at: http://

www.epa.gov/scram001/modelingapps_

mats.htm. The software is provided to 

make it relatively easy for states to 

apply the recommended modeled 

attainment test. However, states are not 

required to use MATS and can develop 

their own post-processing software. 

The modeling guidance also describes 

the opportunity for states to supplement 

their modeling with a ‘‘weight of 

evidence’’ demonstration. States may 

use other information and analyses, in 

addition to the modeled attainment test, 

to estimate whether future attainment of 

the NAAQS in an area is likely. Other 

analyses may include, but are not 

limited to, emissions trends, ambient 

data trends and analyses, other 

modeling analyses, and documentation 

of other non-modeled emissions control 

strategies, including voluntary 

programs. 

The reliability of tests for estimating 

future attainment depends upon having 

reliable databases for inputs to those 

tests. The modeling guidance identifies 

and prioritizes key data-gathering 

activities and analytical capabilities that 

will increase credibility of analyses 

used to estimate if the NAAQS will be 

attained in the area by the statutory 

attainment date. 

The EPA is considering updates to the 

modeling guidance to address PM2.5

modeling for the 2012 PM2.5 NAAQS. 

The agency released a revised draft 

modeling guidance for developing 

demonstrations to meet PM2.5, ozone, 

and regional haze air quality goals in 

December 2014, and intends to revise 

the guidance after considering public 

comments received.118

The application of air quality models 

requires a substantial effort by state and 

local agencies. Therefore, states should 

work closely with their respective EPA 

Regional Office in executing each step 

of the modeling process. Doing so will 

ensure that states know what EPA 

analyses they can rely on, if they wish, 

to simplify this task, and it will increase 

the likelihood of the EPA’s approval of 

a state’s demonstration submitted at the 

end of the modeling and overall 

attainment plan development process. 

6. Demonstrating Attainment at NearRoad Monitors 

The 2012 PM2.5 NAAQS final rule 

contains new requirements for operating 

near-road monitors in the largest 

metropolitan areas.119 The first monitors 

were required to be in place as of 

January 1, 2015 (see Section II of this 

preamble for more details). These 

monitors will not have the requisite 3 

years of monitoring data necessary to 

calculate a PM2.5 design value until 

2018 at the earliest. Therefore, these 

data were not available to inform the 

first round of initial designations for the 

2012 PM2.5 NAAQS and there will be 

less than 3 years of data available when 

the initial attainment demonstrations for 

Moderate areas are due in October 2016. 

As a result of this timing, the agency is 

proposing that the initial set of 

Moderate area attainment 

demonstrations will not need to include 

projected design values for near-road 

monitor locations. However, subsequent 

attainment demonstrations for the PM2.5

NAAQS (after 2018, when 3 or more 

years of complete ambient data are 

available at near-road monitors) will 

need to address those monitor locations 

in attainment plans and will need to 

include a demonstration that those 

monitor locations will show attainment 

of the NAAQS by the applicable 

statutory attainment date. The revised 

modeling guidance document for the 

PM2.5 NAAQS includes procedures for 

applying a dispersion model or a 

combination of photochemical grid 

models and dispersion modeling to 

demonstrate attainment at near-road 

monitor locations. 

7. Demonstrating Attainment in 

Unmonitored Areas 

As explained in the 2012 PM2.5

NAAQS final rule and summarized in 

Section II of this preamble, the EPA’s 

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120As explained in the final 2012 PM NAAQS 

rule, the EPA expects that each CBSA will maintain 

its existing highest concentration area-wide 

monitoring site (referred to as the design value site), 

See 78 FR 3085 (January 15, 2013), at page 3240. 

These sites were set up during the period of time 

when the network design criteria required having 

at least one site in an area-wide location of expected 

maximum concentration. The EPA intends to 

maintain the highest priority sites in the existing 

network, which are often at the neighborhood scale, 

as the largest part of the PM2.5 monitoring network 

to continue to support a number of monitoring 

objectives, while also allowing lower value sites to 

move to near-road locations as that part of the 

network is phased in. 

121Annual monitoring network plans and 5 year 

assessments are required by regulation in 40 CFR 

58.10. The 5 year monitoring network assessment 

is a comprehensive evaluation of a monitoring 

agency’s ambient air monitoring network, while the 

annual plan describes the existing network and 

changes being proposed to support implementing 

recommendations from the most recent 5 year 

assessment as well as any applicable changes 

finalized in association with NAAQS revisions. 

122A monitor must have 3 years of qualityassured ambient data available to be used to 

calculate a PM2.5 design value and determine 

compliance with the NAAQS. 

monitoring requirements for PM2.5 are 

designed to ensure a robust nationwide 

monitoring network in both 

nonattainment and attainment areas. Air 

agencies have achieved this by 

maintaining their PM2.5 networks in 

accordance with EPA’s network design 

criteria. Historically, these criteria 

provided that CBSAs have at least one 

PM2.5 monitoring site located in an 

‘‘area-wide’’ location of expected 

maximum concentration (within the 

CBSA).120 Thus, by assuring compliance 

with the NAAQS at the location of the 

expected highest area-wide 

concentration in the CBSA, air quality is 

protected throughout each CBSA. 

However, due to limited resources, there 

are limits to the number of air quality 

monitors that can be deployed and it 

therefore may be useful to consider 

what, if any, additional analysis needs 

there may be as agencies prepare their 

attainment plans.121

Under the 2007 PM2.5 Implementation 

Rule, the EPA required states to follow 

existing modeling guidance, which 

suggested that a state’s PM2.5 attainment 

plan could be approved if it 

demonstrated attainment, through the 

modeled attainment test, at monitored 

locations only. But the guidance also 

recommended that states conduct 

further analyses based on the modeling 

results to determine whether there were 

unmonitored areas that merited 

additional analysis or investigation. The 

guidance further recommended that 

states either reduce emissions that, 

based on these recommended additional 

analyses, could cause violations in 

unmonitored areas, or that they place a 

new monitor in such an area. The EPA 

found that the minimum requirements 

for the unmonitored area analysis in the 

2007 modeling guidance (and the 2007 

PM2.5 Implementation Rule) were not 

sufficiently clear. The EPA is therefore 

proposing several alternative options in 

order to clarify the appropriate 

treatment of model results in 

unmonitored areas for purposes of 

implementing current and future PM2.5

NAAQS. 

The EPA is proposing four possible 

approaches to demonstrating attainment 

in unmonitored areas. Option 1 would 

only require states to perform the 

attainment test at locations that have 

current or recent FRM and/or FEM 

monitoring data. The EPA would not 

require states to analyze areas that have 

no monitoring data with which to 

anchor the attainment demonstration 

modeling results. The EPA is proposing 

this approach to evaluating monitored 

and unmonitored areas in order to be 

consistent with how attainment of the 

PM2.5 NAAQS is determined for 

purposes of designations and 

redesignations, and due to uncertainty 

in modeled projections in locations 

where there are no monitoring data to 

anchor the future year model results. As 

discussed in Section II of this preamble, 

the EPA promulgates designations for 

PM2.5 NAAQS nonattainment areas 

based primarily on ambient data 

measured at FRM and FEM monitors.122

Although the EPA considers other forms 

of information for purposes of 

evaluating areas with sources that 

contribute to those monitored violations 

for inclusion within the nonattainment 

area boundaries, the fundamental basis 

for designating an area as nonattainment 

for a PM2.5 NAAQS is the presence of 

one or more FRM or FEM monitors with 

data showing violations of the NAAQS 

in question. Similarly, determinations of 

attainment of the PM2.5 NAAQS for 

purposes of redesignation actions are 

based primarily on monitored data. 

When all FRM and FEM monitors in a 

nonattainment area measure attainment 

of the PM2.5 NAAQS, the state is eligible 

to submit a redesignation request for the 

area, assuming that it has complied with 

all other applicable requirements for 

purposes of redesignation. Specifically, 

the EPA’s approval of a redesignation 

request is subject to meeting the 

requirements of CAA section 

107(d)(3)(E). Among those requirements 

is that the area has attained the NAAQS. 

For the PM2.5 NAAQS, this 

determination is based on ambient data 

measured at the FRM and FEM monitors 

in the area in question. Thus, neither 

PM2.5 designations nor redesignations 

currently take into account information 

regarding potential violations of the 

NAAQS at unmonitored locations 

throughout a given area. Therefore, 

consistent with how PM2.5 areas are 

designated and redesignated, the EPA is 

first proposing to require that states only 

show attainment at PM2.5 FRM and FEM 

monitoring locations as an element of 

their attainment demonstrations for the 

PM2.5 NAAQS. 

In addition, the ‘‘relative’’ attainment 

test for PM2.5 uses FRM or FEM ambient 

monitoring data, combined with future 

year modeled percentage changes in 

PM2.5 concentrations, to project future 

year design values. Since the attainment 

test relies on ambient monitoring data, 

an analysis of future year concentrations 

in unmonitored areas can only be 

accomplished by interpolating ambient 

data to a particular location where there 

is no existing monitor or recent 

monitoring data. Therefore, in the 

context of an attainment demonstration, 

the projection of future year PM2.5

concentrations in unmonitored 

locations is inherently more uncertain 

than projections in monitored locations 

due to the fact that the ambient 

concentrations from which these 

projections are developed are unknown 

in the unmonitored locations. 

Proposed Option 2 for unmonitored 

area analyses would require the state to 

conduct an unmonitored area analysis 

as part of all attainment demonstrations 

(for Moderate and Serious areas) and 

require the state to eliminate potential 

violations in unmonitored areas through 

enforceable emissions reductions in the 

SIP. The requirement would be based on 

a premise that states must demonstrate 

attainment of the NAAQS in all 

locations of a nonattainment area, and 

models can and should be used for that 

purpose. Modeled attainment 

demonstrations using photochemical 

grid models provide modeling results 

for all grid cells in the nonattainment 

area. Therefore, notwithstanding the 

uncertainty that is inherent to this 

approach as discussed above, model 

outputs (optionally combined with 

interpolated ambient data) could be 

used to derive estimates of PM2.5

concentrations in unmonitored areas. 

Proposed Option 3 would require 

states to show attainment at all current 

and recent monitoring locations. In 

addition, states would be required to 

provide an unmonitored area analysis as 

part of all attainment demonstrations 

(for Moderate and Serious areas). 

However, rather than requiring states to 

impose additional enforceable 

emissions reductions in the SIP to 

address potential violations in these 

locations, states would be required to 

use the unmonitored area analysis 

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123All states are required to have an annual 

monitoring plan (see Section II of this preamble) 

which meets the siting criteria for PM2.5 monitors 

(40 CFR 58.10). 

results to develop an assessment of the 

likelihood of violations in unmonitored 

areas. This assessment may be 

especially important in areas with a 

relatively sparse PM2.5 monitoring 

network or in locations where 

information such as modeling data, 

emissions inventories or non-FEM 

monitoring data (such as from special 

purpose monitors or saturation 

monitoring studies) may indicate 

potential high PM2.5 concentrations in 

areas that are currently unmonitored. 

The nature of the assessment of 

likelihood of violation that is required 

under proposed Option 3 would depend 

on local area modeling, but could 

include, as appropriate, elements such 

as an evaluation of the emissions 

inventory (particularly for local direct 

PM2.5 sources), the existing ambient data 

for the area, and meteorological model 

inputs to determine if the modeled 

violations in unmonitored areas appear 

to be credible. If potential violations are 

found to be credible, additional steps 

may include imposition of enforceable 

emissions reductions at nearby emission 

sources or a commitment to deploy 

special purpose monitors and/or 

saturation monitors in the area (in order 

to further evaluate the problem). The 

state would be required to document the 

assessment, including analyses of 

emissions, meteorological inputs and 

ambient data and/or make a 

commitment to establish special 

purpose monitors as part of the 

attainment demonstration. Special 

purpose ambient air monitoring data 

that is collected after the attainment 

demonstration is submitted should be 

summarized for use in the area’s 5-year 

monitoring assessment and, where 

appropriate, annual monitoring network 

plans.123 Additionally, monitoring data 

that is collected as a result of the 

unmonitored area analysis assessment 

(after the attainment demonstration is 

submitted) must be reported as a 

quantitative milestone required under 

section 189(c)(1) (see Section IV.G of 

this preamble). 

In summary, Option 3 would clarify 

that an unmonitored area analysis 

would be required in all attainment 

demonstrations, and an assessment of 

the unmonitored area analysis results 

would be required as part of the 

attainment demonstration 

documentation. In contrast to Option 2, 

however, the unmonitored area analysis 

results would not be used as part of the 

specific analytical approach for 

determining whether a particular 

control strategy will result in the area 

attaining the NAAQS. 

Finally, proposed Option 4 would 

require states to show attainment at all 

current and recent monitoring locations. 

States would not be required to provide 

an unmonitored area analysis as part of 

the attainment demonstration. However, 

the EPA would encourage states to use 

information available to them to 

consider what, if any, impacts may be 

occurring in unmonitored areas. States 

could consider information such as 

modeling data, emissions inventories or 

non-FEM monitoring data (such as from 

special purpose monitors or saturation 

monitoring studies) which may indicate 

potential high PM2.5 concentrations in 

areas that are currently unmonitored. 

Under this approach, states could 

consider model results to develop an 

assessment of the likelihood of 

violations in unmonitored areas. This 

proposed option differs from Option 3 

in that it would not require an 

unmonitored area analysis. Rather, 

under proposed Option 4, an 

unmonitored area analysis would be 

recommended where the state and/or 

the EPA has reason to believe that 

potential violations may be occurring in 

unmonitored areas, or other available 

information indicates that further 

analysis is warranted. States would be 

expected to consult with the appropriate 

EPA Regional Office to evaluate 

available information to determine if an 

unmonitored area analysis is needed for 

a particular area. 

The four options presented above 

would lead to a range of potential 

analysis costs by requiring attainment 

demonstrations at more locations and 

with varying degrees of specificity. To 

the extent that these analyses reveal 

additional locations with potential 

violations, the effort needed to address 

these violations could also be higher, 

and may ultimately lead to additional 

reductions, with their associated costs 

and benefits. In terms of analysis costs, 

Option 1 would be expected to be the 

least costly option, whereas Option 2 

would be expected to be the most 

resource intensive. Option 3 is similar 

to Option 2, except that if a potential 

violation is indicated in an unmonitored 

area, there would not be a regulatory 

requirement for the air agency to 

identify enforceable controls to 

eliminate the potential violation. For 

example, the air agency could instead 

elect to site a new monitor to further 

characterize air quality in the area. The 

analysis costs associated with Option 3 

would thus be similar to Option 2. 

Option 4 most closely describes the 

current policy for the PM2.5 NAAQS 

implementation program. Currently, the 

EPA recommends that air agencies 

conduct an unmonitored area analysis, 

but there is no regulatory requirement 

for the air agency to either perform an 

unmonitored area analysis or to impose 

control requirements if the analysis 

indicates potential violations. Thus, 

under Option 4, if an unmonitored area 

analysis is performed, the analysis costs 

associated with this option would be the 

same as for Options 2 and 3. Under 

Option 4, if it is determined by the EPA 

and the air agency to be unnecessary to 

perform an unmonitored area analysis, 

there would be no additional analysis 

costs beyond the monitor-only approach 

of Option 1. Regarding the costs and 

benefits of reductions resulting from 

additional efforts to address 

unmonitored locations (i.e., to the 

extent that efforts necessary to address 

monitored locations do not also address 

unmonitored locations), the EPA does 

not have enough information to 

determine the extent of such areas or the 

measures that would be needed to 

address them, nor can the agency 

predict the extent to which such 

measures would be adopted under one 

option but not another. 

The EPA’s four proposed options 

reflect various combinations with 

respect to whether such an analysis is 

required and the purposes for which the 

state and the EPA might use the results 

of the analysis. The EPA requests 

comment on whether an unmonitored 

area analysis should be a required 

component of an attainment 

demonstration for a PM2.5

nonattainment area and, if required, 

how the results of an unmonitored area 

analysis should be used. The EPA also 

requests comment on the potential costs 

and benefits of each of the four specific 

options, and on which of the options the 

commenter believes should be included 

in the final rule and why. 

8. What future year(s) should states 

model in attainment demonstrations? 

A state performing a modeling 

analysis for an attainment 

demonstration or impracticability 

analysis must select a future year for the 

analysis. For an attainment 

demonstration, a state should select the 

future modeling year such that all 

control measures relied on for 

attainment will have been fully 

implemented by the beginning of that 

year. To demonstrate attainment, the 

modeling results for the nonattainment 

area must predict that emissions 

controls implemented no later than the 

beginning of the last calendar year 

preceding the attainment date will 

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124Note that for purposes of the PM2.5 NAAQS, 

a determination of attainment (or failure to attain), 

which the EPA is required to make after the 

attainment date has passed, is based on an average 

of the most recent 3 years of ambient data prior to 

the area’s attainment date. 

125A demonstration that the area cannot 

practicably attain by the Moderate area attainment 

date would not be the only trigger for a 

discretionary reclassification to Serious. The 

Administrator maintains wide discretion in making 

such a determination, with an impracticability 

demonstration serving as one potential source of 

analysis to inform such a determination. 

126 If several future modeling years are available, 

in some cases it may be appropriate for states to 

interpolate PM2.5 concentrations between years. 

result in PM2.5 concentrations that meet 

the level of the standard.124

While states should choose the future 

modeling year based on a number of 

factors, the EPA recommends the last 

possible year permitted under the 

statute as a starting point for modeling. 

There are several reasons for this. First, 

states with Moderate areas that submit 

an impracticability demonstration must 

show that the area cannot attain the 

NAAQS by the end of the sixth calendar 

year following designation of the area. 

Therefore, the appropriate future 

modeling year for such a demonstration 

is the sixth calendar year after 

designation. Even if a state does not 

submit (or does not intend to submit) an 

impracticability demonstration, 

modeling the sixth calendar year is a 

logical starting point to determine if 

attainment by that year is likely. 

Second, even though attainment is 

determined based on 3 years of ambient 

data, states do not have to model 2 years 

before the attainment date to show 

modeled attainment. Since the design 

value is an average of the annual or 98th 

percentile value for 3 consecutive years 

of data, attainment can still be shown 

even if concentrations exceed the 

NAAQS in one or more of the 3 years 

used to determine attainment (as long as 

the average of the three annual values is 

below the level of the NAAQS). 

Therefore, it can be appropriate to 

model any of the 3 years used to 

determine attainment. Third, if ambient 

data show attainment level 

concentrations in the final statutory 

attainment year, a state may be eligible 

for up to two 1-year extensions of the 

attainment date, if the area meets the 

criteria for such extensions under CAA 

section 188(d). Therefore, modeling 

attainment level concentrations for the 

last year permitted by statute is 

acceptable. 

For all of the reasons stated above, it 

is both acceptable, and will in fact be 

most efficient, for a state to begin the 

attainment demonstration process by 

modeling the last year permitted under 

the statute to determine future year 

modeled PM2.5 concentrations in the 

sixth year after designations. Thus, in 

the attainment demonstrations for areas 

designated nonattainment in the first 

round of designations for the 2012 PM2.5

NAAQS, it would be appropriate for 

states to model air quality for 2021. 

Because an area must attain ‘‘as 

expeditiously as practicable’’ according 

to the CAA, additional considerations 

are necessary before an attainment date 

can be established for a Moderate PM2.5

nonattainment area. For purposes of 

determining the attainment date that is 

as expeditious as practicable, the state 

must conduct future year modeling 

which takes into account expected 

growth and known controls. For 

example, for a Moderate nonattainment 

area for the 2012 PM2.5 NAAQS, a future 

base case scenario for the year 2021 (6 

years after designations) would project 

future air quality given implementation 

of existing federal, state and local 

measures. If this base case scenario 

demonstrates attainment, then the state 

must demonstrate whether attainment 

could be achieved in an earlier year. 

Therefore, the state needs to conduct an 

analysis to determine if, collectively, all 

technologically and economically 

feasible measures identified by the state 

for which the state can initiate 

implementation by the beginning of the 

sixth calendar year following 

designations, can advance the 

attainment date by at least 1 year. 

Results of this analysis may indicate 

attainment can be achieved earlier, 

through implementation of all 

reasonable control measures (i.e., RACM 

and RACT and additional reasonable 

measures). 

If the future base case scenario does 

not demonstrate attainment, then a 

control case scenario is needed to 

examine whether the implementation of 

all technnologically and economically 

feasible measures identified by the state 

would result in attainment in 2021 (for 

purposes of this example based on the 

2012 PM2.5 NAAQS). The control case 

scenario would add to the model 

potential control measures (i.e., RACM 

and RACT and additional reasonable 

measures, plus any additional intrastate 

transport measures or other measures on 

sources outside of the nonattainment 

area that the state has identified as 

feasible to implement by the attainment 

date). This modeling, along with other 

relevant information, would inform a 

judgment as to whether attainment of 

the relevant NAAQS is practicable by 

the end of the sixth year after 

designation or earlier. In the case of 

areas designated nonattainment for the 

2012 PM2.5 NAAQS in the first round of 

designations, if the analysis does not 

demonstrate attainment by December 

31, 2021, then the analysis could serve 

as the technical basis for the state to 

submit a demonstration that attainment 

by the latest statutory attainment date 

for Moderate areas is impracticable. 

This demonstration in turn could serve 

as the technical basis for the 

Administrator to reclassify the area to 

Serious.125

The EPA believes that it is not 

reasonable to require states to model 

each and every calendar year to 

determine the appropriate attainment 

date for a nonattainment area. 

Developing and modeling future year 

inventories is a time-consuming and 

resource intensive process. Multiple 

emissions models are needed in order to 

generate year-specific emissions for the 

various emissions sectors (e.g. mobile, 

non-road, non-EGU point and EGU 

point). In some cases it may be 

reasonable to model one additional 

interim year before the maximum 

statutory attainment date.126 However, 

in most cases, the air quality benefits of 

an identified set of RACM and RACT 

and additional reasonable measures can 

be estimated through model sensitivity 

analyses and the development of 

transfer factors (factors to relate tons of 

emissions reductions in the area to 

PM2.5 concentration changes in the 

area). For example, states can model 

across-the-board percentage reductions 

in direct PM2.5 and/or precursor 

emissions (in separate model runs) to 

determine the impact of emissions 

reductions on PM2.5 concentrations in 

the area. This modeling can be 

performed with a single attainment year 

modeling platform, which is much less 

resource intensive than modeling 

additional future years. The identified 

potential emissions reductions available 

from RACM and RACT and additional 

reasonable measures can be compared to 

the magnitude of the modeled PM2.5

reductions from the sensitivity analyses 

to determine if all such controls will 

advance attainment by a year. The EPA 

strongly recommends that states discuss 

the selection of the future year(s) to 

model with their respective EPA 

Regional Office as part of the modeling 

protocol development process and 

before embarking on running the 

model(s). 

9. Modeling Analysis of Controls That 

Have a De Minimis Impact on Ambient 

PM2.5 Concentrations 

In Section IV.D of this preamble, the 

EPA is proposing that if a state 

determines that a Moderate 

nonattainment area can attain the PM2.5

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127For more information on PM2.5 precursor 

requirements, see section 93.102(b)(2)(iv) and (v) of 

the transportation conformity rule. See also the May 

6, 2005, final transportation conformity rule that 

addressed requirements for PM2.5 precursors. (70 FR 

24280). 

128A state would also establish motor vehicle 

emissions budgets for an area’s attainment year. 

Those budgets would be the motor vehicle 

emissions that the SIP establishes as being 

necessary to attain the NAAQS. 

129 If an area includes re-entrained road dust in 

the motor vehicle emissions budget, the latest 

approved version of AP–42 should be used unless 

the EPA has approved an alternative model for the 

area. 

130Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42015. 

131 Ibid. 

132USEPA, Office of Air Quality Planning and 

Standards, ‘‘Guidance Document for Correction of 

Continued 

NAAQS by the statutory attainment 

date, the state must adopt and 

implement as reasonable control 

measures (i.e., as RACM and RACT and 

additional reasonable measures) only 

those technologically and economically 

feasible control measures that are 

necessary to ensure that the area will 

attain the NAAQS as expeditiously as 

practicable. In a Moderate PM2.5

nonattainment area that cannot 

practicably attain the relevant NAAQS 

by the statutory attainment date, the 

EPA similarly believes that it may not 

be reasonable in all cases to require that 

a state implement all technologically 

and economically feasible control 

measures. The EPA is thus proposing an 

option under which the state may 

evaluate the air quality impact of 

technologically and economically 

feasible control measures to determine if 

there is a subset of such measures that 

collectively will only achieve negligible 

reductions in ambient PM2.5

concentrations in the area. Similar to 

the EPA’s proposed approach, described 

earlier in this section, to determine if a 

set of technologically and economically 

feasible control measures can 

collectively advance the attainment date 

by a year for a Moderate nonattainment 

area for which a state can demonstrate 

attainment by the statutory attainment 

date, the state would be required under 

this proposed option (for a Moderate 

area that cannot practicably attain the 

NAAQS by the statutory attainment 

date) to use an air quality model to 

determine the impact on ambient PM2.5

levels of the set of otherwise 

‘‘reasonable’’ controls that it believes 

will not collectively reduce ambient 

PM2.5 concentrations in the area. For 

this analysis, the state would have to 

show that the collective set of controls 

will have little to no effect on reducing 

PM2.5 concentrations in the area. 

10. Attainment Year Motor Vehicle 

Emissions Budgets 

The transportation conformity rule 

requires that attainment plans establish 

motor vehicle emissions budgets for the 

area’s attainment year. Therefore, once 

an area’s attainment date has been 

established, the state would establish 

motor vehicle emissions budgets for 

direct PM2.5 and any relevant PM2.5

precursor for the attainment year.127 A 

motor vehicle emissions budget for the 

purposes of a PM2.5 attainment plan is 

that portion of the total allowable 

emissions within the nonattainment 

area allocated to on-road sources as 

defined in the submitted attainment 

plan.128 Such motor vehicle emissions 

budgets would be calculated using the 

latest planning assumptions and the 

latest approved motor vehicle emissions 

model available at the time that the 

attainment plan is developed.129

F. RFP Requirements 

1. Statutory Requirements and Existing 

Guidance 

‘‘Reasonable further progress’’ (RFP) 

is a concept included in the CAA under 

part D, title I to assure that states make 

steady, incremental progress toward 

attaining air quality standards in the 

years prior to the attainment date for a 

nonattainment area, rather than merely 

deferring implementation of control 

measures and therefore emissions 

reductions until the date by which the 

standards are to be attained. As 

discussed elsewhere in this preamble, 

section 172 of the CAA addresses 

nonattainment plan provisions in 

general. Section 172(c)(2) requires 

attainment plans to provide for RFP, 

which is defined in section 171(l) as 

‘‘such annual incremental reductions in 

emissions of the relevant air pollutant as 

are required by [part D of title I] or may 

reasonably be required by the 

Administrator for the purpose of 

ensuring attainment of the applicable 

national ambient air quality standard by 

the applicable date.’’ Section 172(c)(3) 

requires the state plan to include ‘‘a 

comprehensive, accurate, current 

inventory of actual emissions from all 

sources of the relevant pollutant or 

pollutants in such area . . .’’ Section 

172(c)(1) requires the state plan to 

include ‘‘all reasonably available control 

measures as expeditiously as practicable 

(including such reductions in emissions 

from existing sources in the area as may 

be obtained through the adoption, at a 

minimum, of reasonably available 

control technology) . . .’’ 

In general terms, the EPA interprets 

that the purpose of requiring RFP is to 

ensure that states with nonattainment 

areas develop attainment plans that 

achieve generally linear progress toward 

attainment, rather than deferring 

emissions reductions until the 

applicable attainment date for the area. 

In the context of implementing the 

PM2.5 NAAQS, ‘‘generally linear 

progress’’ means that emissions of direct 

PM2.5 and PM2.5 precursors from 

controlled sources generally decrease 

year by year such that the area 

ultimately attains the relevant NAAQS 

by the applicable attainment date. In the 

Addendum, the EPA provided guidance 

and identified four specific situations in 

which ‘‘linear progress’’ in emissions 

reductions to meet RFP may be 

appropriate: 

1. When pollutants are emitted by 

numerous and diverse sources. 

2. Where the relationship between 

any individual source and the overall 

air quality is not explicitly quantified. 

3. Where a chemical transformation is 

involved. 

4. Where the emission reductions 

necessary to attain the standard are 

inventory-wide.130

For example, a state with an area 

whose nonattainment problem is caused 

primarily by area sources, such as 

residential wood combustion, should be 

able to demonstrate generally linear 

progress toward attainment in that area. 

In such an area, the state might be able 

to require the replacement of a specified 

percentage of the residential woodstoves 

on an annual basis for each year to 

assure RFP on an annual basis. 

The EPA’s guidance in the Addendum 

also provided examples of situations in 

nonattainment areas in which it might 

be less appropriate to expect RFP to be 

linear, including: 

1. Where there are a limited number 

of sources. 

2. Where the relationships between 

individual sources and air quality are 

relatively well defined. 

3. Where the emission control systems 

utilized (e.g., at major point sources) 

will result in swift and dramatic 

emission reductions.131

In nonattainment areas characterized 

by any of these circumstances, the EPA 

understands that RFP may be better 

represented as step-wise progress as 

controls are implemented and achieve 

significant reductions soon thereafter. 

For example, if an area’s nonattainment 

problem can be attributed to a few major 

stationary sources, the EPA’s guidance 

indicates that ‘‘RFP should be met by 

‘adherence to an ambitious compliance 

schedule’ which is likely to periodically 

yield significant emission 

reductions.’’ 132 133 While the EPA noted 

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Part D SIP’s for Nonattainment Areas,’’ Research 

Triangle Park, NC, January 24, 1984, page 25. 

133Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42015. 

134 Ibid. at 42016. 

in the Addendum that adherence to 

such a schedule does not necessarily 

mean it would be unreasonable to 

achieve generally linear progress, the 

agency has long interpreted the 

language of section 171(1) not to require 

some specific level of emissions 

reductions in any given year. Unlike 

certain provisions under subpart 2 

governing ozone NAAQS 

implementation, subpart 4 does not 

specify a set percentage of emissions 

reductions to be achieved over a certain 

period of time. Accordingly, the EPA 

believes that the facts and 

circumstances of each specific area will 

be relevant to whether the emissions 

reductions meet the agency’s 

expectations for ‘‘generally linear 

progress.’’ 

With respect to implementation 

schedules, the EPA recommended in the 

Addendum that to meet the statutory 

RFP requirements, attainment plans 

must include ‘‘detailed schedules for 

compliance with emission regulations 

in the [nonattainment] areas and 

accurately indicate the corresponding 

annual emission reductions to be 

realized from each milestone in the 

schedule. In reviewing the SIP, the EPA 

will determine whether the annual 

incremental emission reductions to be 

achieved are reasonable in light of the 

statutory objective to ensure timely 

attainment of the PM10 NAAQS. 

Additionally, the EPA believes that it is 

appropriate to require early 

implementation of the most costeffective control measures . . . while 

phasing in the more expensive control 

measures.’’ 134

The EPA believes that these prior 

interpretations of the Act’s provisions 

for RFP continue to be appropriate for 

the PM2.5 NAAQS. Accordingly, the 

following section describes the EPA’s 

proposal for requirements to ensure that 

states meet the statutory provisions for 

RFP for Moderate PM2.5 nonattainment 

areas. 

2. General Proposed Approach to RFP 

To satisfy the statutory requirements 

for RFP at section 172(c)(2), the EPA 

proposes that a state must submit an 

RFP plan as part of its Moderate area 

attainment plan submission. The RFP 

plan must contain appropriate 

information to demonstrate that 

adequate emissions reductions will be 

achieved through control measures in 

the attainment plan in order to meet the 

statutory definition of RFP. The plan 

must include an implementation 

schedule for control measures on 

sources in the nonattainment area and 

an analysis that demonstrates when— 

and through what control measures— 

emissions will decline from the 

applicable baseline year to the 

attainment year. As part of the analysis, 

the RFP plan must include a projected 

inventory for sources in the area for one 

(or more) interim year(s). The EPA is 

proposing and seeking comment on two 

options for developing an RFP plan, as 

well as on related requirements, as 

described below. See proposed 40 CFR 

51.1012. The EPA also notes that 

quantitative milestones required under 

section 189(c) are directly linked to the 

RFP plan, as interim quantifiable 

indicators intended to demonstrate that 

an area is making progress toward 

attaining the PM2.5 NAAQS, and are 

therefore related to the implementation 

schedule of control measures for a PM2.5

nonattainment area. Quantitative 

milestones are more fully discussed in 

Section IV.G of this preamble. 

a. Proposed Option 1. Under the first 

option, the EPA proposes that the RFP 

analysis for any Moderate PM2.5

nonattainment area that can 

demonstrate attainment by the statutory 

attainment date must demonstrate 

either: (i) Generally linear progress 

toward attainment by the applicable 

attainment date through emissions 

reductions to be achieved annually 

between a baseline year and the 

projected attainment date for the area; 

or, (ii) step-wise progress toward 

attainment by the applicable attainment 

date that will be achieved through 

adherence to an ambitious compliance 

schedule that would not necessarily 

achieve reductions on an annual basis. 

In the second case, the state would be 

required to submit a clear rationale and 

supporting information to explain why 

generally linear progress during the 

attainment period is not reasonable on 

an annual basis (e.g., due to the nature 

of the nonattainment problem and the 

types of sources contributing to PM2.5

levels in the area as discussed in 

Section IV.F.1 of this preamble). The 

EPA also proposes to require that RFP 

analyses need to show progress in 

achieving emissions reductions only for 

direct PM2.5 and any precursors that are 

controlled in the attainment plan for the 

nonattainment area. 

Note that the two approaches 

presented in Option 1 for demonstrating 

RFP within the nonattainment area are 

consistent with the pattern of emissions 

reductions of many nationallyapplicable federal emissions reduction 

measures. For example, new emission 

standards for mobile sources may 

achieve reductions in a generally linear 

manner over time, as a portion of the 

existing vehicle fleet is replaced each 

year with new vehicles meeting the 

more stringent standards. On the other 

hand, regulations to reduce emissions 

from certain stationary source sectors 

often have a single compliance date by 

which controls must be in place, which 

typically result in a significant drop in 

emissions over a relatively short period 

(i.e., yield step-wise reductions). 

Because the statute does not clearly 

establish the applicable baseline year 

from which to begin calculating annual 

emissions reductions for purposes of 

demonstrating RFP, the EPA is 

proposing to require and seeks comment 

on a requirement that states use the 

same year as the base year inventory 

chosen for the area, as this inventory 

will serve as the basis for developing the 

control strategy necessary to bring the 

area into expeditious attainment. 

Furthermore, in developing their RFP 

analyses for specific nonattainment 

areas, the EPA expects that states will 

use the emissions inventories developed 

for those areas and air quality modeling 

they have completed for attainment 

planning purposes. This approach is 

consistent with the EPA’s proposed 

approach, described later in this section, 

not to interpret the CAA as allowing 

states to take credit for emissions 

reductions from sources outside a 

nonattainment area when developing 

their plan to meet the statutory RFP 

requirements for PM2.5 nonattainment 

areas. 

For states with Moderate areas that 

cannot demonstrate attainment by the 

statutory Moderate area attainment date, 

the statutory RFP requirements still 

apply. However, the EPA proposes to 

require that, for such areas, the state 

must provide an analysis of the 

anticipated emissions reductions 

associated with implementing the 

control measures identified as RACM 

and RACT and additional reasonable 

measures for the area. The EPA notes 

that even if a state adequately 

demonstrates that it cannot attain the 

NAAQS in a given area by the statutory 

attainment date, the CAA still requires 

the state to submit a Moderate area 

attainment plan meeting the 

requirements for such attainment plans, 

including for RFP. An additional RFP 

analysis will be required as part of the 

Serious attainment plan for the area 

once the EPA reclassifies it to Serious. 

Similar to the approach taken for RFP 

in the remanded 2007 PM2.5

Implementation Rule, the EPA is 

proposing under this option that all 

states must follow one primary 

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approach for conducting the RFP 

analysis, but that they also have an 

option to conduct a secondary analysis 

that will provide greater flexibility in 

setting RFP goals with alternative 

emissions reductions and air quality 

improvement scenarios. The primary 

approach would be to benchmark 

emissions reductions on a pollutant-bypollutant basis starting from the 

pollutant’s baseline emissions level. The 

state would then be required to 

calculate reductions in emissions of 

each pollutant on an annual basis that 

would be needed to bring the area into 

attainment by the projected attainment 

date. 

The EPA recognizes that different 

control measures address different 

pollutants, and that states may be able 

to implement some measures more 

quickly than others. Thus, in the 

optional secondary analysis, the state 

could present a different combination of 

emissions reductions at similar time 

intervals that would provide an 

equivalent or better result in terms of 

net air quality improvement. This 

‘‘equivalency determination’’ would 

allow states flexibility to address 

different pollutants (i.e., direct PM2.5

and PM2.5 precursors regulated under 

the control strategy for the area) 

according to different schedules so long 

as the EPA finds the projected net air 

quality improvements to be achieved 

through this alternative combination of 

emissions reductions to be equivalent to 

or better than those that would be 

achieved through generally linear 

emissions reductions across all 

pollutants in the area. This proposed 

approach recognizes that an important 

element of establishing appropriate 

emissions reductions targets for meeting 

RFP requirements for PM2.5 is 

quantifying the relative degrees of 

control of various pollutants. 

As discussed above, the primary 

approach for ensuring that RFP is met 

in a PM2.5 nonattainment area is to 

require that the state reduce each 

pollutant—that is, direct PM2.5 and all 

precursors not otherwise eliminated 

from control requirements—by some 

amount on an annual basis. The EPA’s 

primary proposed RFP analysis, an 

emissions benchmark analysis, would 

reflect generally linear progress (or stepwise progress if more appropriate and 

adequately justified) to reduce those 

pollutants that the state intends to 

control to attain the PM2.5 NAAQS by 

the applicable attainment date. See 

proposed 40 CFR 51.1012(b). For 

example, a state that can demonstrate 

that their Moderate nonattainment area 

can attain the 2012 PM2.5 NAAQS by an 

attainment date of December 31, 2021 

would also need to achieve emissions 

levels that represent attainment in 2021. 

If the attainment plan requires a 10 

percent reduction in NOX emissions and 

a 14 percent reduction in PM2.5 direct 

emissions from 2011 levels in order for 

the area to demonstrate attainment in 

2021, then the RFP benchmark for NOX

would reflect roughly a 1 percent 

reduction in NOX emissions per year, 

and the benchmark level for PM2.5

would be roughly a 1.4 percent 

reduction per year. 

The EPA proposes that states must 

provide an implementation schedule for 

control measures that would achieve 

emissions reductions consistent with 

those calculated as part of the RFP 

benchmark analysis. However, a state 

could choose to submit an 

‘‘equivalency’’ analysis in addition to 

the RFP benchmark analysis and 

associated implementation schedule 

that presents an alternative combination 

of pollutant emission reductions (i.e., 

alternative implementation schedule for 

control measures) that achieves air 

quality improvements that are 

equivalent to or better than the RFP 

benchmark analysis. In such a case, the 

state would need to make an adequate 

showing that the alternative schedule 

for implementing control measures will 

provide estimated air quality 

improvements that are roughly the same 

as, if not better than, those that the 

emissions reductions determined 

through the RFP benchmark analysis 

would provide. If a state elects to follow 

this approach, it must provide in its RFP 

plan the information necessary to assess 

whether an alternative schedule of 

emissions reductions is generally 

equivalent, in air quality terms, to the 

RFP benchmark analysis reduction 

levels, such as attainment 

demonstration modeling results that 

link emissions reductions of various 

precursor emissions with air quality 

improvements. Under this proposed 

approach, the EPA would require states 

to use this information to evaluate the 

equivalence of alternative combinations 

of pollutant emissions reductions. The 

EPA would recommend that states 

estimate air quality improvements 

associated with intermediate emissions 

control levels (i.e., air quality 

improvement targets) by assuming that 

the same relationship between 

emissions and air quality applies at 

intermediate levels as would apply at 

attainment levels. 

The EPA continues to recognize that 

because atmospheric processes are quite 

complex, a specific percent change in 

emissions of PM2.5 precursors does not 

lead to an equivalent percent change in 

air quality, potentially creating 

uncertainty as to whether alternate 

emissions control scenarios will achieve 

equivalent benefits. Nevertheless, the 

EPA believes that it is important to 

provide the flexibility to address 

different pollutants on different 

timetables so long as the plan can 

reasonably be expected to achieve the 

intended air quality benefits represented 

by the RFP benchmark analysis. In 

general, the EPA would not expect a 

state to conduct dispersion modeling 

specifically to assess whether an 

alternative approach to meeting RFP 

will provide equivalent air quality 

benefits as the benchmark approach. 

Instead, the attainment plan modeling 

addresses the nonlinearities at 

attainment levels, and the EPA believes 

for RFP analysis purposes that the 

relationship between emissions and air 

quality at attainment levels provides an 

adequate approximation of the 

relationship at interim RFP levels. 

b. Proposed Option 2. Under the 

second option, the EPA proposes a 

simplified approach to developing an 

RFP plan that focuses on the emissions 

reductions anticipated from each of the 

particular control measures identified 

by the state as part of the analysis to 

identify RACM and RACT and 

additional reasonable measures for 

sources in the nonattainment area. 

Under this option, the first step in 

developing the RFP plan would be for 

the state to establish the implementation 

schedule on a year-by-year basis for all 

control measures contained in the 

control strategy for sources in the area 

beginning with the date of designation 

of the area and ending with the 

projected attainment date of the area. 

The schedule would need to comply 

with the statutory requirement that all 

RACM and RACT must be implemented 

within the first 4 years following 

designation, but the state would have 

discretion beyond that requirement to 

schedule the implementation of any 

other measures necessary for 

expeditious attainment. Overall, the 

implementation schedule would need to 

demonstrate that control measures to 

bring the area into attainment will be 

implemented as expeditiously as 

practicable. 

The second step in developing an RFP 

plan under this second proposed option 

would be for the state to calculate the 

emissions reductions that would be 

achieved by all measures implemented 

on sources in the area corresponding 

with quantitative milestone dates (i.e., 

by 4.5 years and 7.5 years after 

designation of the area). These are the 

dates by which milestones for the area 

must be met, after which a report is due 

to the EPA from the state to verify that 

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135According to section 189(a)(2)(B), Moderate 

area attainment plans are due to the EPA 18 months 

after designation. 

136For more information on PM2.5 precursor 

requirements, see section 93.102(b)(2)(iv) and (v) of 

the transportation conformity rule. See also the May 

6, 2005, final transportation conformity rule that 

addressed requirements for PM2.5 precursors. (70 FR 

24280). 

137A state would also establish motor vehicle 

emissions budgets for an area’s attainment year. 

Those budgets would be the motor vehicle 

emissions that the SIP establishes as being 

necessary to attain the NAAQS. 

138 If an area includes re-entrained road dust in 

the motor vehicle emissions budget, the latest 

approved version of AP–42 should be used unless 

the EPA has approved an alternative model for the 

area. 

139See Phase 2 Ozone Implementation rule, 70 FR 

71612 (November 29, 2005). 

the area has met the milestones 

identified for the area and thereby has 

also met the RFP requirements for the 

area. The EPA proposes that the state 

must calculate the emissions reductions 

to be achieved at each milestone year on 

a pollutant-by-pollutant basis. 

The third step under this proposed 

option would be for the state to conduct 

modeling or employ another 

quantitative method to predict the 

overall PM2.5 concentrations in the 

nonattainment area in each milestone 

year. This air quality target could 

simply be interpolated between the 

design value at the time of the area’s 

designation and the design value in the 

projected attainment year. These air 

quality target values would serve as a 

points of comparison for the monitored 

ambient air data that the EPA is 

proposing that the state must submit as 

part of the milestone report due after the 

area reaches each milestone date. 

This simplified approach to 

determining RFP for a Moderate 

nonattainment area could apply equally 

well to areas that can demonstrate 

attainment with the relevant NAAQS by 

the statutory attainment date and those 

that cannot. See proposed 40 CFR 

51.1012(c). In addition, the EPA 

believes it offers a reasonable approach 

to ensure that RFP is generally being 

met in the area without requiring 

extensive quantitative analysis so long 

as it is generally linear for purposes of 

achieving annual emissions reductions. 

The EPA seeks comment on these two 

options proposed for states to meet the 

statutory RFP requirements. 

3. RFP Inventories for RFP Analyses 

The EPA proposes that a state with a 

Moderate PM2.5 nonattainment area 

must submit one or more emissions 

projections as part of the RFP plan (the 

‘‘RFP inventory’’) for the area that, at a 

minimum, includes projected emissions 

by different source types corresponding 

to the quantitative milestone date(s) for 

the area, described in greater detail in 

Section IV.H of this preamble. 

Specifically, the EPA proposes that the 

RFP plan for any Moderate area must 

contain a projected RFP inventory for 

each calendar year in which 

quantitative milestones for a Moderate 

nonattainment area must be met. For 

example, as explained in Section IV.H 

of this preamble, a state must identify as 

part of the attainment plan submission 

for a Moderate nonattainment area 

quantitative milestones to be achieved 

every 3 years from the Moderate area 

attainment plan due date, or 4.5 years 

from the effective date of designation of 

the area.135 For example, the first round 

of designations for the 2012 PM2.5

NAAQS become effective in April 2015; 

Moderate area attainment plans for 

these areas will thus be due 18 months 

later, or in October 2016. The first 

quantitative milestones for each of these 

areas would then have to be met in 

October 2019; the second quantitative 

milestones, in October 2022; and so on, 

until the area attains the NAAQS. Under 

the EPA’s proposed approach for 

projected emissions inventories for RFP 

analyses, the state would be required to 

submit such inventories as part of the 

Moderate area attainment plan due in 

October 2016 that project emissions 

from sources in the nonattainment area 

for the same calendar years as those for 

which quantitative milestones would be 

due. 

The transportation conformity rule 

requires that attainment plans establish 

motor vehicle emissions budgets. RFP 

plans submitted as part of an attainment 

plan submission would therefore be 

required to establish motor vehicle 

emissions budgets for direct PM2.5 and 

any relevant PM2.5 precursor.136 A 

motor vehicle emissions budget for the 

purposes of a PM2.5 RFP plan is that 

portion of the total allowable emissions 

allocated to on-road sources as defined 

in the submitted RFP plan for the 

relevant years as described above.137

Such motor vehicle emissions budgets 

would be calculated using the latest 

planning assumptions and the latest 

approved motor vehicle emissions 

model available at the time that the 

attainment plan is developed.138

4. Geographic Coverage of Emission 

Sources for RFP 

The EPA is proposing that the RFP 

demonstration to be included with a 

state’s PM2.5 nonattainment area plan 

must include emissions only for sources 

located in the nonattainment area, and 

not from an area larger than the 

nonattainment area. This policy 

approach differs from the remanded 

2007 PM2.5 implementation rule. This 

section describes the evolution of policy 

on a similar RFP issue in the ozone 

NAAQS implementation program, and it 

discusses the reasoning behind this 

revised approach for PM2.5. 

In the preamble to the remanded 2007 

PM2.5 Implementation Rule, the EPA 

allowed states to incorporate reductions 

of NOX and SO2 emissions up to 200 km 

from outside the nonattainment area 

(and potentially for reductions of VOC 

or ammonia) into their RFP plan when 

certain conditions were met. This policy 

was included in the 2007 PM2.5

Implementation Rule in part to be 

consistent with a similar RFP policy for 

NOX and VOC that was included in the 

November 2005 Phase 2 ozone NAAQS 

implementation rule which provided 

guidance for states on implementing the 

1997 ozone NAAQS.139

Under the policy in the 2007 PM2.5

NAAQS implementation rule, if a state 

intended to include emissions 

reductions from outside the 

nonattainment area in the RFP plan, the 

state would need to take on the 

additional work associated with 

developing: (i) An expanded baseline 

emissions inventory for the entire 

geographic area (i.e., the nonattainment 

area plus the additional area outside the 

nonattainment area) that characterizes 

emissions for all stationary, area and 

mobile sources (rather than for just a 

select few stationary sources) in the 

overall area; and, (ii) a projected 

attainment year inventory for this 

expanded area outside the boundaries of 

the designated nonattainment area. By 

requiring inclusion of all types of 

sources in these ‘‘expanded area’’ 

emissions inventories, the EPA intended 

for this approach to reflect the projected 

net emissions reductions in this area 

(the difference between the ‘‘expanded 

area’’ base year inventory and the 

projected attainment year inventory). 

However, it should be noted that 

development of these more extensive 

inventories would likely have involved 

a substantial amount of additional time 

and resources. In addition, the state 

would have needed to have provided 

information supporting its decision 

regarding how far outside the 

nonattainment area the RFP inventory 

should extend. While this ‘‘outside the 

nonattainment area’’ RFP approach was 

theoretically available to states in 

developing their PM2.5 attainment plans 

due in 2008, there were no states to the 

agency’s knowledge that elected to 

follow this approach. 

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140This same petition raised concerns regarding 

the criteria used to determine the economic 

feasibility of controls being considered for RACT for 

the 1997 PM2.5 NAAQS. See ‘‘Petition for 

Reconsideration,’’ filed by Paul Cort, Earthjustice, 

on behalf of the American Lung Association, 

Medical Advocates for Healthy Air, Natural 

Resources Defense Council, and the Sierra Club 

(June 25, 2007). A copy of the petition is in the 

docket for this action. 

141Letter dated May 13, 2010, from Gina 

McCarthy to David S. Baron and Paul Cort, 

Earthjustice. A copy of the letter is located in the 

docket for this action. 

142See NRDC v. EPA, 571 F.3d 1245 (D.C. Cir. 

2009). 

Both the 2005 Phase 2 ozone 

implementation rule and the 2007 PM2.5

Implementation Rule were challenged 

on several issues. With regard to the 

Phase 2 ozone implementation rule, the 

EPA granted a petition for 

reconsideration and ultimately issued a 

final notice of reconsideration in June 

2007. In November 2008, the U.S. Court 

of Appeals for the DC Circuit heard oral 

argument concerning multiple petitions 

for judicial review of the Phase 2 ozone 

rule and the notice of reconsideration. 

One of the issues in this case involved 

whether compliance by EGUs with a 

regional emissions trading program 

could be considered to meet the RACT 

requirement for those sources located in 

a nonattainment area. In its July 2009 

decision, the court emphasized that: 

‘‘the RACT requirement calls for 

reductions in emissions from sources in 

the area; reductions from sources 

outside the nonattainment area do not 

satisfy the requirement . . . 

Accordingly, participation in the NOX

SIP call would constitute RACT only if 

participation entailed at least RACTlevel reductions in emissions from 

sources within the nonattainment area.’’ 

In light of this court decision, the EPA 

has determined that the best reading of 

the statute would be to interpret the 

term ‘‘sources in the area’’ in the same 

manner where it appears in different 

nonattainment provisions for ozone. 

The term appears in CAA section 182 

(requirements for ozone nonattainment 

areas) with regard to RFP as well as 

RACT. The decision on the Phase 2 

ozone rule found that section 182(b)(2) 

requires that a SIP must provide for 

implementation of RACT (under section 

172(c)) for emissions sources ‘‘in the 

area,’’ meaning in the nonattainment 

area. Similarly, the EPA believes that 

when section 182(b)(1)(A)–(B) defines 

baseline emissions for RFP as ‘‘the total 

amount of actual VOC or NOX emissions 

from all anthropogenic sources in the 

area,’’ this also means sources in the 

nonattainment area. 

With regard to the 2007 PM2.5

Implementation Rule, the EPA received 

a petition for reconsideration in June 

2007 that raised objections on several 

issues. One such issue dealt with the 

EPA’s interpretation of the statutory 

RFP requirements to allow a state to 

take ‘‘credit’’ for emissions reductions 

from outside the nonattainment area 

when addressing RFP in its attainment 

plan.140 The EPA granted the petition 

for reconsideration on this issue in 

2010, after the D.C. Circuit issued its 

decision on the Phase 2 Ozone 

Implementation Rule.141 142

Specifically, the EPA believes that the 

DC Circuit’s interpretation of the phrase 

‘‘sources in the area’’ applies to RACT 

and RFP requirements for both the 

ozone NAAQS and the PM2.5 NAAQS. 

In particular, for PM2.5, the statutory 

language at section 171(1) defines RFP 

in terms of ‘‘reductions in emissions’’ 

required in an attainment plan, which 

the EPA interprets as being directly 

linked to the baseline emissions 

inventory for sources located in a PM2.5

nonattainment area. The baseline 

emissions inventory is the foundation 

for the attainment plan. The emissions 

inventory requirement of section 

172(c)(3) explicitly requires that the 

attainment plan inventory include all 

sources of the relevant pollutants ‘‘in 

such area,’’ which is a clear reference to 

the designated nonattainment area. 

Given that the baseline inventory must 

reflect the emissions ‘‘in such area,’’ and 

that this inventory provides the starting 

point for a state’s RFP analysis, in 

which the state must calculate generally 

linear progress in emissions reductions 

that will lead to attainment of the 

NAAQS in the area, the EPA believes it 

is appropriate that a state should focus 

on sources located within the 

nonattainment area when conducting its 

analysis to determine the annual 

emissions reductions necessary for 

demonstrating RFP. 

The EPA believes that the most 

appropriate approach with regard to the 

geographic area required to be covered 

for demonstrating RFP in a PM2.5

attainment plan also should be limited 

to the nonattainment area for two other 

reasons. First, EPA believes that it 

makes policy sense for the PM2.5

implementation rule approach to be 

consistent with the approach in the 

ozone implementation rule. In the past, 

a number of areas have been designated 

as nonattainment for both standards, 

and the nonattainment area boundaries 

often are the same. For such areas, a 

common policy approach for the 

geographic area covered by the RFP plan 

will be more efficient to implement and 

would be expected to be less 

burdensome for the air agency than if 

the geographic areas covered by RFP 

plans for the two pollutants differed. 

Second, a policy allowing the 

geographic area of the RFP plan to be 

larger than the nonattainment area 

would conflict with a key provision of 

subpart 4 which requires annual 

incremental reductions in emissions 

from sources within the nonattainment 

area. Under subpart 4, an area that fails 

to attain the standard by the Serious 

area attainment date is then subject to 

the provisions of section 189(d). Section 

189(d) specifies that the state must 

submit a plan revision within 12 

months which provides for ‘‘an annual 

reduction in PM10 or PM10 precursor 

emissions within the area of not less 

than 5 percent of the amount of such 

emissions as reported in the most recent 

inventory prepared for such area’’ 

(emphasis added). The EPA does not 

believe the rule should include an RFP 

policy approach which would not be 

consistent with section 189(d). 

After reconsideration of the approach 

to RFP that was opposed in the petition 

for reconsideration of the 2007 PM2.5

Implementation Rule, and in light of the 

DC Circuit decision on the Ozone Phase 

2 Implementation Rule, the EPA 

believes the best reading of the statute 

is that the CAA does not allow for a 

state to include emissions reductions 

from sources outside a nonattainment 

area when developing the plan to meet 

the CAA section 172(c)(2) RFP 

requirements for a PM2.5 nonattainment 

area. The EPA seeks comment on this 

proposed approach. 

5. Other RFP Considerations 

In general, the EPA seeks to ensure 

that PM2.5 nonattainment areas that are 

shared by more than one state or tribe 

meet RFP requirements as a whole. 

States and tribes that share a 

nonattainment area should therefore 

consult with one another to develop the 

RFP analysis and control strategy 

implementation schedule for the area as 

a whole. Such states and tribes should 

work with the EPA region or regions 

that oversee them to confirm that their 

collective approach is appropriate for 

RFP. 

The EPA’s proposed approach for 

states to meet the RFP requirement is 

designed to ensure emissions reductions 

will yield incremental improvements in 

air quality on the path to attainment, 

while being sufficiently flexible to 

accommodate the range of control 

strategies necessary to address the 

complex mixtures of pollutants 

comprising PM2.5 in different areas. The 

EPA seeks comment on all of its 

proposed requirements and options for 

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143See the Federal Register published on April 

16, 1992, General Preamble (57 FR 13498 and 

13539). 

144See the Federal Register published on August 

16, 1994, Addendum to General Preamble (59 FR 

41998, 42015, 42016 and 42017). 

145 Ibid. 

146 General Preamble, 57 FR 13498 (April 16, 

1992), at page 13539. 

147Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42016. 

RFP plans and analyses for Moderate 

PM2.5 attainment plans. 

G. Quantitative Milestones 

1. Statutory Requirements and Existing 

Guidance 

Section 189(c)(1) requires that a PM10

NAAQS attainment plan submission has 

‘‘quantitative milestones which are to be 

achieved every 3 years until the area is 

redesignated to attainment and which 

demonstrate reasonable further progress 

. . . toward attainment by the 

applicable date.’’ Section 189(c)(2) 

further requires that, within 90 days of 

each milestone, each affected state must 

submit a demonstration that all 

measures to assure RFP have been 

implemented and that the quantitative 

milestone has been met. Thus, the CAA 

imposes requirements upon states not 

only to make ‘‘reasonable further 

progress’’ toward attainment, but also to 

identify objective means (i.e., 

quantitative milestones) by which to 

measure this reasonable further progress 

every 3 years, and to submit them as 

part of the attainment plan for the 

nonattainment area. In addition, 

according to section 189(c)(2), states 

must, within 90 days of the passage of 

each such milestone, submit to the EPA 

a demonstration that control measures 

have been implemented according to the 

approved RFP plan schedule and the 

milestone has been met. 

The EPA has previously described its 

interpretation of the requirements under 

section 189(c) for the PM10 NAAQS in 

the General Preamble and the 

Addendum and believes that these 

interpretations should also apply both 

in developing plans that demonstrate 

RFP and include appropriate 

quantitative milestones, and in 

demonstrating that those milestones 

have been met for the PM2.5

NAAQS.143 144 The EPA’s guidance in 

the Addendum also noted that: ‘‘Section 

189(c) provides that the quantitative 

milestones submitted by a State for an 

area also must be consistent with RFP 

for the area. Thus, EPA will determine 

an area’s compliance with RFP in 

conjunction with determining its 

compliance with the quantitative 

milestone requirement. Because RFP is 

an annual emission reduction 

requirement and the quantitative 

milestones are to be achieved every 3 

years, when a state demonstrates an 

area’s compliance with the quantitative 

milestone requirement, it should also 

demonstrate that RFP has been achieved 

during each of the relevant 3 years.’’ 145

The EPA’s existing guidance in the 

Addendum with respect to the 

quantitative milestone requirements of 

CAA section 189(c) thus includes 

several important features: (i) That the 

control measures comprising the RFP 

plan should be implemented and in 

place to meet the statutory quantitative 

emissions reductions milestone 

requirement; (ii) that it is reasonable for 

the 3-year periods for quantitative 

milestones to run from the statutory due 

date for the Moderate area attainment 

plan submission; and, (iii) that the 

precise form that the quantitative 

milestones should take is not specified, 

but the state must choose milestones 

that will allow it to quantify or measure, 

track and report progress adequately 

and objectively. 

The EPA’s proposed approach to 

identifying quantitative milestones for 

any Moderate PM2.5 nonattainment area 

and demonstrating compliance with the 

milestones is generally consistent with 

the existing guidance, as described in 

the following sections. 

2. Proposed Approach 

The statute at section 189(c) is clear 

that quantitative milestones must be 

achieved every 3 years, however it does 

not make clear the starting date for 

counting the 3 year periods. In the 

General Preamble, the agency proposed 

that quantitative milestones must be 

achieved every 3 years starting from the 

attainment plan submission due date 

(i.e., because the Moderate area 

attainment plan is due no later than 18 

months after designation of the area, the 

first set of milestones would need to be 

achieved 4.5 years after the area’s 

designation) until the attainment 

date.146 The EPA proposes to maintain 

this approach for the PM2.5 NAAQS. 

Specifically, the EPA proposes that the 

attainment plan for a Moderate area that 

can demonstrate attainment by the 

statutory Moderate area attainment date 

must identify appropriate quantitative 

milestones to be achieved by 4.5 years 

following designation of the area. For a 

Moderate area that cannot practicably 

attain the relevant PM2.5 NAAQS within 

the statutory timeframe for a Moderate 

area, the EPA proposes that a state must 

submit two sets of quantitative 

milestones—one set to be achieved at 

year 4.5 from designation and the 

second set to be achieved at year 7.5 

from designation. The EPA believes that 

this proposed requirement will help to 

ensure that the state maintains progress 

toward bringing the area into attainment 

during the period in which such area is 

reclassified to Serious, the state works 

to develop a Serious area attainment 

plan for the area, and the EPA approves 

it. Pursuant to the statute, the EPA must 

reclassify a Moderate area for which a 

state submits an attainment 

impracticability demonstration within 

18 months after the Moderate area 

attainment plan due date, or no later 

than 3 years after the date of designation 

of the area. Even under a scenario in 

which the state develops and submits a 

Serious area attainment plan 18 months 

after being reclassified to Serious, the 

milestone date of 4.5 years after 

designation would likely come and go 

before the area had a new set of 

approved quantitative milestones with 

which to demonstrate compliance. 

Similarly, the milestone date of 7.5 

years after designation could also come 

and go before the EPA is able to fully 

approve the Serious area plan and any 

quantitative milestones contained 

therein. Because of the timing of the 

various steps involved in reclassifying a 

Moderate area to Serious and a state 

developing a new Serious area plan, the 

EPA believes that requiring a state to 

identify quantitative milestones that the 

area must achieve 4.5 years and 7.5 

years after designation as elements of its 

Moderate area attainment plan is 

reasonable and seeks comment on this 

proposed requirement. 

The EPA is also proposing that the 

quantitative milestones contained in the 

attainment plan for a Moderate 

nonattainment area must be constructed 

such that they can be tracked, quantified 

and/or measured adequately in order for 

the state to meet its milestone reporting 

obligations, which come due 90 days 

after a given milestone date. In the 

Addendum, the EPA suggested some 

possible metrics that ‘‘support and 

demonstrate how the overall 

quantitative milestones identified for an 

area may be met,’’ such as percent 

implementation of control strategies, 

percent compliance with implemented 

control measures, and adherence to a 

compliance schedule. This list was not 

exclusive or exhaustive but reflected the 

EPA’s view that the purpose of the 

quantitative milestone requirement is to 

provide an objective way to assess that 

the state is making the necessary 

progress towards attainment in the area 

by the applicable attainment date.147

The EPA continues to believe that the 

quantitative milestone requirement 

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should be interpreted to allow states to 

devise milestones that are suitable for 

the specific facts and circumstances of 

the attainment plan for a particular area, 

so long as they provide an objective 

means to measure RFP. 

The EPA therefore proposes to require 

that states select the quantitative 

milestones that are appropriate and 

quantifiable and that will provide for 

objective evaluation of progress toward 

attainment in their Moderate PM2.5

nonattainment area, whether the area 

can practicably attain the PM2.5 NAAQS 

by the statutory attainment date or not. 

For this approach, the EPA is not 

proposing to require that such 

quantitative milestones must take any 

particular form, merely that they 

provide a means to evaluate progress 

(i.e., demonstrate RFP) meaningfully. 

The EPA, in its attainment plan 

approval process, will determine if the 

specific quantitative milestones 

developed by the state for a specific 

nonattainment area satisfy the statutory 

requirements. The EPA recommends 

that states confer with their respective 

EPA regional office to develop 

appropriate quantitative milestones. See 

proposed 40 CFR 51.1013(a)(1). 

In addition to this general proposed 

approach for selecting quantitative 

milestones for a Moderate 

nonattainment area, the EPA is 

proposing and seeks comment on a 

requirement that, at a minimum, states 

must include in all attainment plans for 

Moderate PM2.5 nonattainment areas a 

metric to confirm that all control 

measures identified and adopted as 

RACM and RACT for the area have been 

fully implemented within 4 years of 

designation. This metric specifically 

derives from the statutory provision that 

applies to all Moderate areas and thus 

represents a milestone that all Moderate 

areas must meet regardless of whether it 

is listed explicitly as an individual 

milestone. The EPA believes it would be 

appropriate to include it as a metric that 

any state with a Moderate 

nonattainment area would need to 

demonstrate compliance with when 

they submit their milestone report as 

described below, and thus seeks 

comment on this proposal. 

3. Milestone Report Submittal 

Under the quantitative milestone 

requirement of section 189(c)(2), a state 

must demonstrate to the EPA that the 

RFP plan for the area and its approved 

milestones are being met within 90 days 

after the milestone due date. The EPA 

then has 90 days to determine whether 

or not a state’s demonstration is 

adequate. Specifically, section 189(c)(2) 

requires that: ‘‘Not later than 90 days 

after the date on which a milestone 

applicable to the area occurs, each State 

in which all or part of such 

[nonattainment] area is located shall 

submit to the Administrator a 

demonstration that all measures in the 

plan approved under this section have 

been implemented and that the 

milestone has been met. A 

demonstration under this subsection 

shall be submitted in such form and 

manner, and shall contain such 

information and analysis, as the 

Administrator shall require.’’ 

In the event a state fails to submit a 

milestone demonstration report by the 

due date or the EPA determines that a 

milestone was not met, the state must 

submit a SIP revision within 9 months 

of either the missed reporting deadline 

or the EPA’s determination of the state’s 

failure to meet a milestone. According 

to the statutory requirements of section 

189(c)(3), the new SIP revision must 

assure ‘‘that the State will achieve the 

next milestone (or attain the national 

ambient air quality standard . . ., if 

there is no next milestone) by the 

applicable date.’’ If a state fails to make 

a SIP submission to correct a failure to 

meet RFP expeditiously, sanctions 

under sections 110(m) and 179(b) may 

apply. If a state is unable to correct a 

failure to meet RFP, this may be 

evidence that the state cannot 

practicably attain the NAAQS by the 

applicable attainment date and may 

serve as a basis for reclassification of the 

area to Serious under the agency’s 

discretionary authority. See proposed 40 

CFR 51.1013(c). 

Because the statute does not define 

the parameters of these demonstrations, 

the statute grants the EPA discretion to 

determine the components of the 

required demonstration and the form 

and manner for submission. In the 

Addendum, the EPA offered guidance 

about what the milestone report should 

contain: ‘‘This report must contain 

technical support sufficient to 

document completion statistics for 

appropriate milestones. For example, 

the demonstration should graphically 

display RFP over the course of the 

relevant 3 years and indicate how the 

emission reductions achieved to date 

compare to those required or scheduled 

to meet RFP and the required 

[quantitative] milestones. The 

calculations (and any assumptions 

made) necessary to determine the 

emission reductions to date should also 

be submitted. The demonstration should 

also contain an evaluation of whether 

the PM10 NAAQS will be attained by the 

projected attainment date.’’ 148 The EPA 

believes this guidance is still 

appropriate for states demonstrating 

compliance with RFP and quantitative 

milestones for PM2.5 NAAQS and hereby 

proposes under the authority of section 

301(a) to require that the milestone 

report submission must include the 

following four components: 

First, the report must include a 

certification by the Governor or 

Governor’s designee that the state’s 

attainment plan control strategy, 

including the RFP plan, is being 

implemented as described in the 

applicable attainment plan. Second, as 

described in the Addendum, the report 

must contain technical support, 

including calculations, sufficient to 

document completion statistics for 

appropriate milestones and to 

demonstrate that the quantitative 

milestones have been satisfied and how 

the emissions reductions achieved to 

date compare to those required or 

scheduled to meet RFP. Third, the state 

must submit an air quality screening 

analysis to determine if measured air 

quality progress is consistent with the 

expected air quality improvement target 

correlated with the RFP emissions 

reductions for the previous 3-year 

period. Fourth, the report must contain 

an evaluation of whether the PM2.5

NAAQS will be attained by the 

projected attainment date for the area. In 

addition, the EPA proposes that the 

milestone report must include a 

description and schedule for any 

remedial actions the state has taken or 

will take to address any failure to meet 

a quantitative milestone, including the 

implementation status of contingency 

measures for failing to meet RFP in the 

area. See proposed 40 CFR 51.1013(b). 

The EPA seeks comment on these 

proposed components to a milestone 

report. 

The EPA stated in the Addendum that 

the milestone report must be submitted 

from the Governor or Governor’s 

designee to the Regional Administrator 

of the respective EPA Regional Office 

serving the submitting state, and that 

the EPA will notify the state of its 

determination (regarding whether or not 

the state’s report is adequate) by sending 

a letter to the appropriate Governor or 

Governor’s designee. The EPA believes 

that it would be appropriate for states to 

submit milestone reports, including 

supporting documents, through the 

agency’s electronic SIP (eSIP) 

submission system in order to simplify 

the process and reduce resource burden 

on all sides. The EPA seeks comment on 

how electronic reporting could facilitate 

a state’s submittal of the required 

milestone report, how it could 

accommodate the various narrative and 

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149 Ibid. at 42015. 

data-dependent components that the 

EPA is proposing be part of such a 

submittal, and what particular system 

features might be desirable to 

accommodate milestone report 

submissions through the eSIP system. 

H. Contingency Measures 

States with PM2.5 nonattainment areas 

must include contingency measures in 

their attainment plans consistent with 

section 172(c)(9). Contingency measures 

are additional control measures to be 

implemented in the event that an area 

fails to meet RFP requirements or fails 

to attain the PM2.5 standard by the 

applicable attainment date. These 

measures must be fully adopted rules or 

control measures that are ready to be 

implemented quickly upon failure to 

meet RFP or failure of the area to meet 

the standard by its attainment date, and 

such measures are required to take effect 

without further action by the state or the 

EPA. The EPA provided extensive 

guidance on contingency measures in 

the General Preamble and Addendum, 

including the following: ‘‘States must 

show that their contingency measures 

can be implemented with minimal 

further action on their part and with no 

additional rulemaking actions such as 

public hearings or legislative review. 

After the EPA determines that a 

moderate PM10 nonattainment area has 

failed to attain the PM10 NAAQS, the 

EPA generally expects all actions 

needed to effect full implementation of 

the measures to occur within 60 days 

after the EPA notifies the state of the 

area’s failure. The state should ensure 

that the measures are fully implemented 

as expeditiously as practicable after they 

take effect.’’ 149

The EPA does not believe that the 

D.C. Circuit’s decision in NRDC v. EPA 

affects the overall contingency measure 

requirements that were finalized in the 

remanded 2007 PM2.5 Implementation 

Rule, because section 172(c)(9) imposes 

the contingency measure requirement 

for attainment plans for the PM2.5

NAAQS and it is not superseded or 

subsumed by any specific contingency 

measure requirements under subpart 4. 

Although section 172(c)(9) requires 

contingency measures, the provision 

does not specify exactly what 

parameters such measures must meet. 

The EPA has longstanding 

interpretations of the statute with 

respect to the contingency measure 

requirement, both for PM and for other 

pollutants, in the General Preamble and 

Addendum. The EPA proposes to adopt 

an approach to contingency measures 

for the PM2.5 NAAQS similar to that 

recommended in earlier EPA guidance, 

but seeks comment on particular 

proposed approaches that differ in 

important ways from earlier guidance 

on contingency measures for the PM2.5

NAAQS. The EPA believes that it may 

be necessary to adopt a different 

approach to contingency measures for 

PM2.5 attainment plans due to proposed 

changes in determining RFP for a PM2.5

nonattainment area and in order to 

accommodate Moderate PM2.5

nonattainment areas that cannot 

practicably attain the standard by the 

statutory Moderate area attainment date. 

The EPA is proposing and seeking 

comment on the following general 

requirements for contingency measures 

to be approvable as part of a state’s 

Moderate area attainment plan 

submission for the PM2.5 NAAQS: 

1. Contingency measures must be 

fully adopted rules or control measures 

that are ready to be implemented 

quickly upon a determination by the 

Administrator of the nonattainment 

area’s failure to meet RFP or failure to 

meet the standard by its attainment 

date. 

2. The state’s attainment plan 

submission must contain trigger 

mechanisms for the contingency 

measures, specify a schedule for 

implementation, and indicate that the 

measures will be implemented with 

minimal further action by the state or by 

the EPA. 

3. Contingency measures must consist 

of control measures that are not 

otherwise included in the control 

strategy for the attainment plan. 

4. Contingency measures must 

provide for emissions reductions 

approximately equivalent to 1 year’s 

worth of reductions needed for RFP, 

based on the overall level of reductions 

needed to demonstrate attainment 

divided by the number of years from the 

base year to the attainment year, or 

approximately equivalent to 1 year’s 

worth of air quality improvement or 

emissions reductions proportional to the 

overall amount of air quality 

improvement or emissions reductions to 

be achieved by the area’s attainment 

plan. See proposed 40 CFR 51.1014. 

The EPA interprets the contingency 

measure requirement of section 

172(c)(9) to require control measures 

that are not already included in the 

attainment plan for other purposes, such 

as to meet RACM and RACT 

requirements. However, suitable 

contingency measures may be measures 

that were technologically and 

economically feasible for the area, but 

did not qualify as RACM or RACT or 

additional reasonable measures for one 

or more reasons. For example, a 

candidate contingency measure may 

have been deemed technologically and 

economically feasible, but it was not 

needed to achieve expeditious 

attainment in a Moderate area for which 

the state could demonstrate attainment 

by the statutory attainment date and 

therefore was not included as part of the 

attainment demonstration for the area. 

The agency believes it is important that 

states make decisions concerning 

contingency measures in conjunction 

with their determination of the overall 

control strategy for bringing the area 

into expeditious attainment, and that 

states first must identify those control 

measures needed in order to 

demonstrate expeditious attainment of 

the standards; any remaining measures 

should then be considered as candidates 

for contingency measures. 

For Moderate areas that cannot 

practicably attain the NAAQS by the 

statutory attainment date, the EPA is 

proposing that states must implement 

all control measures that they determine 

to be reasonable for sources in the area. 

In such cases, the EPA expects that 

contingency measures for such 

nonattainment areas would necessarily 

exceed the criteria for determining 

whether a measure is reasonable (i.e., 

technologically and economically 

feasible) as described in Section IV.D of 

this preamble. Such contingency 

measures would only be triggered in the 

event the area fails to meet RFP; the 

EPA does not interpret the requirement 

for contingency measures for failing to 

attain the NAAQS by the applicable 

attainment date to apply to a Moderate 

area that a state demonstrates cannot 

practicably attain the NAAQS by the 

statutory attainment date. Rather, the 

EPA believes it is appropriate for the 

state to identify and adopt contingency 

measures for failing to attain the 

NAAQS in a timely way as part of the 

Serious area attainment plan that it will 

develop once the EPA reclassifies such 

an area. 

The EPA proposes that for any 

Moderate PM2.5 nonattainment area, 

contingency measures can include 

measures that achieve emissions 

reductions on sources located outside 

the nonattainment area as well as from 

sources within the nonattainment area, 

provided that the measures are factually 

demonstrated to produce the 

appropriate air quality impact within 

the nonattainment area. The EPA 

continues to believe it appropriate that 

a state might choose to rely on federal 

measures (e.g. federal mobile source 

measures based on the incremental 

turnover of the motor vehicle fleet each 

year) and local measures already 

scheduled for implementation for 

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150See, e.g., 62 FR 15844 (April 3, 1997); 62 FR 

66279 (December 18, 1997); 66 FR 30811 (June 8, 

2001); 66 FR 586 and 66 FR 634 (January 3, 2001). 

151A court ruling upheld contingency measures 

for ozone attainment plans that were previously 

required and implemented where they were in 

excess of the attainment demonstration and RFP 

SIP. See LEAN v. EPA, 382 F.3d 575 (5th Cir., 2004). 

purposes other than meeting attainment 

plan requirements, such as RACM and 

RACT, as meeting part or all of the 

contingency measure requirements, as 

the purpose of the contingency 

measures is to provide a cushion while 

the attainment plan for the area is being 

revised to meet the missed attainment 

milestone. The EPA has approved 

numerous attainment plans under an 

interpretation that one or more federal 

or local measures that are in place and 

provide reductions in the year following 

a failure to attain the relevant NAAQS 

or meet RFP in excess of the reductions 

required by the attainment 

demonstration or RFP plan can meet the 

contingency measure 

requirements.150 151

The EPA recognizes that some states 

have historically relied on emissions 

reductions achieved through the 

implementation of control measures in 

excess of what was determined to be 

necessary to meet RFP in certain PM2.5

nonattainment areas in order to satisfy 

the contingency measure requirement in 

such areas. The EPA believes that this 

approach is reasonable for Moderate 

PM2.5 nonattainment areas that can 

demonstrate attainment by the statutory 

attainment date, as the state would 

calculate the emissions reductions 

needed for RFP separately from the 

control strategy determination for such 

an area. However, crediting an area for 

‘‘excess’’ emissions reductions to satisfy 

the contingency measure requirement 

would not be possible for a Moderate 

area that cannot practicably attain by 

the statutory attainment date under the 

EPA’s proposed approach for 

calculating RFP for such areas, as RFP 

would be calculated directly from the 

projected emissions reductions from all 

control measures identified for the area 

(as RACM and RACT or additional 

reasonable measures), such that there 

would be no difference between 

emissions reductions estimated from 

control measures and those estimated 

for demonstrating RFP. 

As mentioned earlier, contingency 

measures should represent a portion of 

the actual emissions reductions 

necessary to bring about attainment in 

the area. Consistent with the EPA’s past 

approach for contingency measures for 

PM2.5 nonattainment areas, the EPA 

proposes to require that the emissions 

reductions anticipated by imposition of 

the contingency measures must be equal 

to approximately 1 year’s worth of 

emissions reductions while the state is 

revising its attainment plan for the area. 

The EPA has historically applied a 

policy of equating 1 year’s worth of 

emissions reductions for contingency 

measures with those annual reductions 

determined to be necessary to achieve 

RFP for the area, unless the state 

demonstrates that some smaller 

reduction is appropriate. As described 

in Section IV.F of this preamble, the 

EPA is proposing an approach for 

interpreting the statutory RFP 

requirement that would require 

demonstrating RFP based on reductions 

from sources located inside the 

nonattainment area. Keeping with the 

historic linkage between RFP and 

contingency measures, the EPA is also 

proposing and seeking comment on a 

similar approach for calculating 1 year’s 

worth of emissions reductions for 

purposes of adopting appropriate 

contingency measures. That is, the 

EPA’s proposed approach for 

determining the level of emissions 

reductions for contingency measure 

purposes is to calculate the annual 

reductions in emissions of direct PM2.5

and PM2.5 precursors needed from 

sources located inside the 

nonattainment area. The EPA seeks 

comment on this proposed approach. 

The CAA requires that states must 

implement contingency measures after 

the EPA determines that the area has 

either failed to meet RFP requirements, 

or failed to attain the standards by the 

applicable attainment date. The purpose 

of the contingency measure provision is 

to ensure that corrective measures are 

put in place automatically at the time 

that the EPA makes its determination 

that an area has either failed to meet 

RFP or failed to meet the standard by its 

attainment date. The EPA is required to 

determine within 90 days after receiving 

a state’s milestone demonstration, and 

within 6 months after the attainment 

date for an area, whether these 

requirements have been met. The 

consequences for states with areas that 

fail to attain the NAAQS or to meet RFP 

are described in section 179(d) of the 

CAA and discussed in Section V of this 

preamble. 

As noted earlier in this section, the 

EPA proposes to require that states must 

submit contingency measures at the 

same time as the rest of the Moderate 

area attainment plan elements, i.e., 

within 18 months after designation. 

Section 172(b) requires the 

Administrator to ‘‘establish a schedule 

according to which the State containing 

such [nonattainment] area shall submit 

a plan or plan revision (including the 

plan items) meeting the applicable 

[subpart 1 nonattainment plan] 

requirements. . . Such schedule shall, 

at a minimum, include a date or dates, 

extending no later than 3 years from the 

date of the nonattainment designation 

. . .’’ The EPA believes it is reasonable 

to require the submittal of contingency 

measures for Moderate PM2.5

nonattainment areas on the same 

schedule as the other Moderate area 

attainment plan requirements because of 

the close relationship between an area’s 

control strategy, RFP analysis and 

selection of quantitative milestones, and 

contingency measures. The EPA seeks 

comment on this proposed due date for 

submission of contingency measures. 

I. Attainment Dates 

1. Statutory Requirements 

Section 188 establishes the attainment 

dates for Moderate and Serious PM10

nonattainment areas, which also apply 

to Moderate and Serious PM2.5

nonattainment areas. Section 188(c)(1) 

provides that for a Moderate area, ‘‘the 

attainment date shall be as 

expeditiously as practicable but no later 

than the end of the sixth calendar year 

after the area’s designation as 

nonattainment.’’ The EPA has the 

responsibility for determining whether a 

nonattainment area has attained the 

standard by its applicable attainment 

date. Section 179(c)(1) requires the EPA 

to make determinations of attainment no 

later than 6 months following the 

attainment date for the area. Under 

section 179(c)(2), the EPA must publish 

a notice in the Federal Register 

identifying those areas which failed to 

attain by the applicable attainment date. 

The statute further provides that the 

EPA may revise or supplement its 

determination of attainment for the 

affected areas based upon more 

complete information or analysis 

concerning the air quality for the area as 

of the area’s attainment date. 

Section 179(c)(1) provides that the 

EPA is to base the attainment 

determination for an area upon an area’s 

‘‘air quality data as of the attainment 

date.’’ The EPA will make the 

determination of whether an area’s air 

quality is meeting the PM2.5 NAAQS by 

the applicable attainment date based 

upon data gathered from the air quality 

monitoring sites which have been 

entered into the EPA’s Air Quality 

System (AQS) database. No special or 

additional attainment plan submission 

will be required from the state for this 

determination. 

A Moderate PM2.5 nonattainment 

area’s air quality status is determined in 

accordance with Appendix N of 40 CFR 

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part 50. To show attainment of the 

current 24-hour and annual standards 

for PM2.5, the most recent 3 consecutive 

years’ data prior to the area’s attainment 

date must show that PM2.5

concentrations over the prior 3-year 

period are at or below the levels of the 

standards. A complete year of air quality 

data, as described in part 50, Appendix 

N, is comprised of all 4 calendar 

quarters with each quarter containing 

data from at least 75 percent of the 

scheduled sampling days. 

The EPA will begin processing and 

analyzing data related to the attainment 

of Moderate PM2.5 nonattainment areas 

after the applicable attainment date for 

the affected areas. Current EPA 

regulations, under 40 CFR part 58, set 

the deadline for the state to submit air 

quality data into the AQS database as no 

later than 90 days after the end of the 

calendar year. 

While the EPA may determine that an 

area’s air quality data indicates that an 

area may be meeting the PM2.5 NAAQS 

for a specified period of time, this does 

not eliminate the state’s responsibility 

under the Act to adopt and implement 

an approvable attainment plan. If the 

area’s monitored data indicates that the 

area is factually attaining the NAAQS, 

however, the EPA may issue a ‘‘clean 

data determination’’ which will suspend 

the obligation of the state to submit the 

elements of the attainment plan for the 

area that are related to planning 

requirements, as discussed in Section 

IX.C of this preamble. If the EPA 

determines that an area has attained the 

standard as of its attainment date, the 

area will remain classified as 

nonattainment until the state has 

requested, and the EPA has approved, 

redesignation to attainment for the area. 

In order for an area to be redesignated 

as attainment, the state must comply 

with the five requirements listed under 

section 107(d)(3)(E) of the CAA. Briefly, 

this section requires that: 

• The EPA has determined that the 

area has met the PM2.5 NAAQS; 

• The EPA has fully approved the 

applicable state implementation plan; 

• The improvement in air quality is 

due to permanent and enforceable 

reductions in emissions; 

• The EPA has fully approved a 

maintenance plan for the area; and, 

• The state(s) containing the area or 

portions of the area have met all 

applicable requirements under section 

110 and part D. 

2. Proposed Approach 

As noted earlier, section 188(c)(1) 

states that for a Moderate area, ‘‘the 

attainment date shall be as 

expeditiously as practicable but no later 

than the end of the sixth calendar year 

after the area’s designation as 

nonattainment.’’ For purposes of clarity, 

the EPA proposes to interpret the 

reference to ‘‘the area’s designation’’ in 

this provision as meaning ‘‘the area’s 

effective date of designation,’’ consistent 

with the agency’s approach for 

implementing the 1997 and 2006 PM2.5

NAAQS and with its approach for 

implementing NAAQS for other criteria 

pollutants under part D, title I of the 

CAA. See proposed 40 CFR 51.1000. As 

discussed elsewhere in this preamble, 

the effective date of designation is April 

15, 2015, for areas designated 

nonattainment in the first round of 

designations for the 2012 PM2.5 NAAQS. 

For these areas, the Moderate area 

attainment date would be as expeditious 

as practicable, but no later than 

December 31, 2021 (i.e., the end of the 

sixth calendar year after designation). 

The EPA seeks comment on this 

proposed interpretation of the date of 

designation of a PM2.5 NAAQS 

nonattainment area and the resulting 

attainment date for such areas. 

As described in Sections IV.D and 

IV.E of this preamble, in the case of a 

Moderate PM2.5 nonattainment area for 

which a state can demonstrate 

attainment by the end of the sixth 

calendar year following designation, the 

state must follow a two-step process for 

determining the appropriate attainment 

date for the area. First, the state must 

demonstrate through air quality 

modeling that the area can attain the 

relevant NAAQS by the latest statutory 

attainment date and determine which 

control measures and technologies are 

needed for the area to attain by that 

date. Second, the state must determine 

whether implementing other reasonable 

controls (i.e., those not needed for 

attainment by the latest possible date 

but that are technologically and 

economically feasible) can cumulatively 

advance the attainment date for the area 

by at least 1 year. In the event that a 

state determines that the area can attain 

the relevant NAAQS earlier through the 

application of other measures, the state 

must propose the earlier date as part of 

the attainment plan submission for the 

area. When the EPA takes action to 

approve the different elements of the 

attainment plan for the area, one of the 

elements that the agency will take 

action on will be the state’s proposed 

attainment date for the area. If the EPA 

approves an attainment date for the area 

that is earlier than the latest date 

allowed by statute, then the applicable 

attainment date for the area will be the 

approved date. See proposed 40 CFR 

51.1004(a)(1)(i). If the area ultimately 

needs additional time to attain the 

relevant NAAQS, the state may request 

an attainment date extension for the 

Moderate nonattainment area under 

section 188 as long as certain conditions 

are met, as described in Section IV.J. 

The EPA’s approach to approving an 

attainment date for a PM2.5

nonattainment area will be different for 

a Moderate area that cannot practicably 

attain the relevant PM2.5 NAAQS by the 

end of the sixth calendar year after 

designation. Given that the agency will 

reclassify any such area to Serious and 

thereby trigger additional Serious area 

requirements for the area, the EPA will 

approve an attainment date for the area 

when it takes action on the Serious area 

attainment plan submitted for the area. 

In the interim, before the EPA takes 

action to reclassify the area, the 

statutory Moderate area attainment date 

will continue to apply to such an area. 

See proposed 40 CFR 51.1000 and 

51.1004(a)(1)(ii). When the EPA 

reclassifies the area, then the 

presumptive attainment date for the area 

will be as expeditious as practicable, but 

no later than the end of the tenth 

calendar year following designation. A 

complete discussion of Serious area 

attainment dates is provided in Section 

VI.H of this preamble. 

J. Attainment Date Extensions 

1. Statutory Requirements 

The CAA under subpart 4 provides 

the EPA with authority to grant 

extensions of the attainment date for a 

Moderate area that otherwise could be 

found to have failed to attain the 

relevant PM2.5 NAAQS, if the area can 

meet specific statutory criteria related to 

the implementation of measures 

contained in the attainment plan for the 

area, and to monitored air quality in the 

area. Specifically, under section 188(d), 

a state may apply to the EPA for an 

extension of a Moderate area’s 

attainment date of one additional year 

(the ‘‘Extension Year’’) if ‘‘(1) the state 

has complied with all requirements and 

commitments pertaining to the area in 

the applicable implementation plan; 

and (2) no more than one exceedance of 

the 24-hour [NAAQS] level for PM10 has 

occurred in the area in the year 

preceding the Extension Year, and the 

annual mean concentration of PM10 in 

the area for such year is less than or 

equal to the standard level.’’ Section 

188(d) limits the number of 1-year 

extensions that the EPA may grant for a 

Moderate nonattainment area to two. 

The provisions of section 188(d) thus 

allow a state an opportunity to 

demonstrate that a Moderate area 

should continue to be classified as 

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152This interpretation as applied to section 188(e) 

for Serious area attainment date extensions was 

upheld by the Ninth Circuit Court of Appeals in 

Vigil v. Leavitt, 366 F.3d 1025, amended at 381 F.3d 

826 (9th Cir. 2004). 

153The 24-hour PM10 NAAQS, set at 150 mg/m3, 

cannot be exceeded more than once per year on 

average, over 3 years. 

Moderate and not be reclassified to 

Serious even if the area exceeded the 

level of the applicable PM2.5 NAAQS in 

one or both of the 2 calendar years 

preceding the year in which the area is 

otherwise required to attain the 

NAAQS. Although section 188(d) 

provides the criteria for such an 

extension, the EPA believes that there 

are some ambiguities in the statutory 

language that warrant interpretation and 

clarification through regulations for the 

PM2.5 NAAQS. The EPA is thus 

proposing a preferred interpretation of 

section 188(d) to provide clarity to 

states about how and when they may 

qualify for a Moderate area attainment 

date extension for purposes of the PM2.5

NAAQS. 

2. Proposed Interpretations of 

Attainment Date Extension Criteria 

With respect to the criterion in 

section 188(d)(1) that requires that ‘‘the 

state has complied with all 

requirements and commitments 

pertaining to the area in the applicable 

implementation plan,’’ the EPA 

proposes to interpret this provision to 

mean that the state has implemented the 

control measures in the SIP submission 

it made to address the attainment plan 

requirements for the applicable PM2.5

NAAQS, and not to require the area to 

have a fully approved attainment plan 

that meets all of the CAA’s requirements 

for Moderate areas. This proposed 

interpretation is based on the plain 

language of section 188(d) that does not 

explicitly require that the state comply 

with all requirements pertaining to the 

area in the CAA, but merely requires 

that the state comply with all 

requirements in the applicable SIP.152 In 

other words, the EPA believes that 

section 188(d)(1) should be interpreted 

to mean that so long as the state has 

submitted the necessary attainment plan 

for the area for the applicable PM2.5

NAAQs and is implementing the control 

measures in the submission, the fact 

that the EPA has not yet acted on such 

submission to make it an approved part 

of the applicable SIP should not be a 

barrier to the state obtaining an 

extension of the attainment date under 

section 188(d)(1). For the same reason, 

the EPA also proposes to read this 

provision not to bar an extension if all 

or part of an area’s Moderate area plan 

is disapproved or has been promulgated 

by the EPA as a federal implementation 

plan (FIP). In the case that the 

‘‘applicable implementation plan’’ is a 

FIP (or combination of SIP and FIP), 

then the EPA proposes that the state 

must have implemented the control 

measures contained therein in order to 

meet the statutory criteria at section 

188(d)(1) for a Moderate area attainment 

date extension. The EPA seeks comment 

on this proposed interpretation of 

section 188(d)(1). See proposed 40 CFR 

51.1005(a)(2). 

The EPA also proposes and seeks 

comment on an alternative 

interpretation of section 188(d)(1) that 

would require a state to have a Moderate 

area attainment plan fully approved by 

the EPA as meeting the applicable 

attainment plan requirements under 

sections 172 and 189 for a Moderate 

PM2.5 nonattainment area before the 

state obtains an extension. Given that 

Moderate area attainment plans are due 

18 months from the date of designation, 

and that RACM and RACT must be 

implemented within 4 years after 

designation, states should have 

sufficient time under the statutory 

schedule to satisfy all applicable 

requirements in advance of seeking a 

Moderate area attainment date 

extension. Under this alternative 

approach, the EPA proposes that a state 

subject to a FIP (or SIP and FIP) for a 

Moderate PM2.5 nonattainment area 

could qualify for an attainment date 

extension for the area if it had 

implemented all requirements and 

commitments of the FIP (or SIP and 

FIP), as the FIP (or SIP and FIP) would 

be the ‘‘applicable implementation 

plan’’ for the area. Although this 

alternative interpretation could also be 

a reasonable reading of this criterion of 

section 188(d)(1), the EPA considers it 

less appropriate than the preferred 

interpretation because this approach 

could foreclose states from obtaining an 

otherwise appropriate extension merely 

because of logistical and timing 

considerations that might have 

prevented the EPA from acting on the 

state’s attainment plan by the requisite 

point in time. Nevertheless, the EPA 

seeks comment on this alternative 

interpretation of section 188(d)(1). 

The second criterion that states must 

meet to qualify for an extension relates 

to the monitored ambient air in a 

nonattainment area in the year prior to 

the attainment date for the area. If a 

state has met the requirements of 

section 188(d)(1), the EPA may grant an 

extension of a Moderate area’s 

attainment date if the state also satisfies 

the requirements of section 188(d)(2) 

that ‘‘no more than one exceedance of 

the 24-hour national ambient air quality 

standard level for PM10 has occurred in 

the area in the year preceding the 

Extension Year, and the annual mean 

concentration of PM10 in the area for 

such year is less than or equal to the 

standard level.’’ Again, the EPA may 

grant up to two such 1-year extensions 

and thus this criterion would apply to 

the calendar year prior to the applicable 

attainment date and to the Extension 

Year, in the case of a second extension. 

The EPA believes that the references 

to the ambient air quality standards in 

section 188(d)(2) are ambiguous in two 

significant ways in the context of the 

PM2.5 NAAQS implementation. First, 

the statutory language explicitly sets 

ambient air quality conditions for an 

attainment date extension in terms that 

relate factually to the 24-hour PM10

NAAQS that was in effect at the time of 

the 1990 Amendments of the CAA, 

which has a statistical form that is 

substantially different from the 24-hour 

PM2.5 NAAQS. Specifically, the form of 

the 24-hour PM10 NAAQS allows for no 

more than one ‘‘exceedance’’ of the 

standard per year on average over 3 

years, and if there is more than one such 

exceedance on average over 3 years the 

area is violating the NAAQS. Thus, as 

a means of limiting extensions to areas 

that are close to attaining the NAAQS in 

the calendar year prior to the applicable 

attainment date, section 188(d)(2) 

imposes the criterion of having ‘‘no 

more than one exceedance of the 24- 

hour . . . standard level’’ as a way of 

demonstrating that a nonattainment area 

has ‘‘clean data’’ for the year prior to the 

attainment date.153 This statutory 

language does not translate readily to 

the PM2.5 NAAQS, which postdate the 

creation of section 188(d) and are not 

structured with the same mathematical 

form. For example, the 2006 24-hour 

PM2.5 NAAQS incorporates a 3-year 

average of the 98th percentile form, 

which means that an area with valid 

monitored ambient readings every day 

(or almost every day) could have seven 

readings above the numerical level of 

the standard (i.e., ‘‘exceedances’’) in any 

given year and still have ‘‘clean data’’ 

for that year. A literal interpretation of 

section 188(d)(2) to permit only one 

exceedance of the 24-hour PM2.5

NAAQS, rather than the number of 

exceedances that is relevant for 

purposes of determining attainment of 

such NAAQS, is illogical. In light of the 

different form of the PM2.5 NAAQS, the 

statutory language of section 188(d)(2) is 

thus ambiguous in how it should apply 

to implementation of the 24-hour PM2.5

NAAQS. 

Additionally, the language of section 

188(d)(2) may be considered ambiguous 

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154For examples of the EPA actions to extend 

attainment dates for Moderate PM10 areas, see 61 FR 

20730 (May 8, 1996), 61 FR 66602 (December 18, 

1996), and 66 FR 32752 (June 18, 2001). 

155Nonattainment areas designated for both the 

24-hour and annual PM2.5 NAAQS are located in 

central and southern CA. 

as to how it should apply to the PM2.5

NAAQS to the extent that it does not 

specify whether the air quality criteria 

for an attainment date extension apply 

equally for a Moderate area designated 

nonattainment for both the 24-hour and 

annual standards, or for just one of the 

standards. In practice, most areas 

designated nonattainment for the PM10

NAAQS following passage of the 1990 

CAA Amendments were designated 

nonattainment only for the 24-hour 

PM10 NAAQS, with a few designated for 

only the annual PM10 NAAQS or for 

both the 24-hour and the annual PM10

NAAQS. The 24-hour NAAQS has 

served as the ‘‘controlling’’ (i.e., 

functionally more stringent) PM10

standard, such that the agency’s 

experience to date in granting PM10

Moderate area attainment date extension 

requests has been limited to extending 

the attainment date for the 24-hour PM10

NAAQS.154

The situation is distinctly different for 

PM2.5 nonattainment areas, as the 

specific facts and circumstances of a 

particular area may warrant a 

nonattainment designation for either the 

24-hour standard or the annual 

standard, but often not both. In most 

cases, for instance, the current 

nonattainment areas for PM2.5 are 

designated either for the 1997 annual 

NAAQS or for the 2006 24-hour 

NAAQS, but not both.155 For example, 

the EPA recently promulgated 

designations for areas violating only the 

annual PM2.5 NAAQS revised in 2012, 

not the 24-hour NAAQS which was 

retained at the level established during 

the 2006 p.m. NAAQS review. If a PM2.5

nonattainment area is designated only 

for the 24-hour or only for the annual 

PM2.5 NAAQS, this situation raises the 

question of how section 188(d)(2) air 

quality criteria for both standards 

should apply to such a PM2.5 NAAQS 

nonattainment area if the state seeks an 

extension of the applicable attainment 

date for such area. 

Due to the ambiguities associated 

with applying this subpart 4 

requirement to current and future PM2.5

NAAQS, the agency believes it is 

important to propose a reasonable 

interpretation of the statutory 

requirement and seek public comment 

on this preferred interpretation as well 

as two alternative interpretations 

specifying the PM2.5 standard or 

standards for which a state would need 

to demonstrate a Moderate 

nonattainment area met the air quality 

criteria of section 188(d)(2) in order to 

qualify for an attainment date extension. 

The agency also believes it is important 

to clarify how the air quality criteria of 

section 188(d)(2) apply specifically for 

the 24-hour PM2.5 NAAQS. For this 

reason, the EPA is proposing a preferred 

interpretation of section 188(d)(2) for 

application to current and future PM2.5

NAAQS, and is seeking comment on 

two alternative interpretations that the 

agency considers less appropriate. 

The preferred proposed approach 

would only require a state to 

demonstrate that in the year prior to the 

applicable attainment date for the area, 

a Moderate area did not exceed the level 

of (i.e., had clean data for) the specific 

PM2.5 NAAQS for which the area is 

designated nonattainment (the 

‘‘applicable NAAQS’’) and for which the 

state is seeking the extension of the 

attainment date. The second approach, 

on which the EPA seeks comment, 

would require that a state demonstrate 

that in the year prior to the applicable 

attainment date for an area, the 

Moderate area did not exceed the level 

of the specific PM2.5 NAAQS for which 

the area is designated nonattainment 

(the applicable NAAQS), and did not 

exceed the most stringent level of any 

other PM2.5 NAAQS in effect nationally 

at the time the area was designated for 

the applicable NAAQS. The third 

approach, on which the EPA also seeks 

comment, would require that a state 

demonstrate that in the year prior to the 

applicable attainment date for an area, 

the Moderate area did not have more 

than one exceedance of the level of the 

24-hour PM2.5 standard, and that the 

annual mean concentration of PM2.5 in 

the area for the attainment year was less 

than or equal to the annual standard, 

regardless of the NAAQS for which the 

state is seeking an attainment date 

extension. 

The EPA prefers the proposed 

interpretation (described in more detail 

later in this section) for implementing 

the Moderate area attainment date 

extension criteria of section 188(d)(2) 

considering the fact that, due to the 

specific atmospheric conditions and 

source-dependent nature of PM2.5

problems in different areas around the 

country, the EPA has historically 

designated, and may continue to 

designate, PM2.5 nonattainment areas for 

either the annual or the 24-hour 

NAAQS. As discussed earlier, the 

agency’s designations processes for the 

2006 revised 24-hour PM2.5 NAAQS and 

the 2012 revised annual PM2.5 NAAQS 

have each been conducted to address 

only one standard individually. In 

addition, the current 24-hour PM2.5

NAAQS does not have a ‘‘one 

exceedance’’ form of the standard, as 

cited in section 188(d)(2). Nevertheless, 

the EPA requests comment on the 

second and third interpretations of 

section 188(d)(2) described later in this 

section because they more closely 

reflect the specific statutory wording. 

a. Proposed approach: the EPA 

preferred option. The EPA’s proposed 

interpretation of section 188(d)(2) 

would simply require that a state 

demonstrate that in the year prior to the 

applicable attainment date for the area, 

a Moderate nonattainment area had 

clean data for the specific PM2.5 NAAQS 

for which the state was seeking an 

attainment date extension (the 

applicable NAAQS). Under this 

proposed approach, a state seeking an 

attainment date extension for a 

Moderate nonattainment area for a 24- 

hour PM2.5 NAAQS would be required 

to demonstrate that the area had clean 

data for that particular standard in the 

calendar year prior to the applicable 

attainment date for the area, rather than 

demonstrating that the area necessarily 

had no more than one exceedance of the 

24-hour PM2.5 NAAQS. 

For example, under this proposed 

interpretation of section 188(d)(2), in 

the case of a state seeking an extension 

of the attainment date for a Moderate 

area designated nonattainment for the 

2006 24-hour PM2.5 NAAQS, the state 

would need to demonstrate that the area 

had no more than the allowable number 

of valid monitored readings exceeding 

35mg/m3 to meet the 98th percentile 

statistical form of the standard in the 

year prior to the area’s attainment date. 

The state would not have to 

demonstrate that the area also had clean 

data for any other PM2.5 NAAQS, 

including any annual PM2.5 NAAQS or 

later revision of the 24-hour PM2.5

NAAQS. 

Likewise under the EPA’s preferred 

approach, a state seeking an attainment 

date extension for a Moderate 

nonattainment area for an annual PM2.5

NAAQS would be required to 

demonstrate that the area had clean data 

for that particular standard in the 

calendar year prior to the applicable 

attainment date for the area. For 

example, in the case of a state seeking 

an extension of the attainment date for 

a Moderate area designated 

nonattainment for the 2012 annual 

PM2.5 NAAQS, the state would need to 

demonstrate that the annual mean 

concentration of PM2.5 at each monitor 

in the area as analyzed in accordance 

with Appendix N to 40 CFR part 50 for 

the year prior to the area’s attainment 

date was less than or equal to 12.0 mg/ 

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156 Given the rounding provisions specified in 40 

CFR part 50, Appendix N, these criteria would be 

satisfied if the concentrations before final rounding 

are less than an annual average of 12.05 mg/m3 and 

a 24-hour value of 35.5 mg/m3. 

m3. Again, under this proposed 

approach, the state would not have to 

demonstrate that the area had clean data 

for any other PM2.5 NAAQS. 

Under the EPA’s preferred approach, 

if a state were to have an area that is 

designated nonattainment for both the 

24-hour and the annual PM2.5 NAAQS, 

with the same applicable attainment 

date, then a state seeking attainment 

date extensions for both NAAQS would 

need to meet the ambient air quality 

criterion for both NAAQS. The EPA 

notes that this would not be a common 

occurrence, but under this 

interpretation, these would be the only 

circumstances under which a state 

should be required to have clean data 

for both NAAQS in order to qualify for 

an extension of the applicable 

attainment date under section 188(d)(2). 

If a state has a nonattainment area that 

is only designated for either the 24-hour 

or the annual PM2.5 NAAQS, the EPA 

believes that the state need only meet 

the air quality criterion of section 

188(d)(2) for the NAAQS relevant to the 

attainment date at issue. See proposed 

40 CFR 51.1005(a)(1)(ii) and (iii). 

The EPA believes this preferred 

interpretation of section 188(d)(2) is 

appropriate for two reasons. First, as 

discussed above, while most PM10

nonattainment areas were designated 

nonattainment for either just the 24- 

hour PM10 NAAQS or for both the 24- 

hour and annual PM10 NAAQS, the 

majority of current PM2.5 nonattainment 

areas are designated for either the 24- 

hour or the annual PM2.5 NAAQS, and 

should arguably only need to 

demonstrate clean data for the NAAQS 

for which the area is designated 

nonattainment. For those few PM2.5

nonattainment areas designated for 24- 

hour and annual PM2.5 NAAQS, the EPA 

believes it may also be appropriate that 

a state must only demonstrate clean data 

for the specific NAAQS for which the 

state is seeking an attainment date 

extension because such an approach is 

consistent with the statute’s overall 

approach to designating nonattainment 

areas and implementing control 

strategies for each separate PM2.5

NAAQS. 

Second, as discussed earlier, the 

statutory language that requires that a 

nonattainment area have ‘‘no more than 

one exceedance of the 24-hour’’ NAAQS 

level reflects a statistical form for the 

24-hour PM10 standard that is different 

from the current form of the 24-hour 

PM2.5 NAAQS. This difference, and the 

fact that the form could be subject to 

further revision in the future, leads the 

EPA to conclude that it is appropriate to 

describe this particular criterion more 

broadly so that it can apply to any 24- 

hour PM2.5 NAAQS, now or in the 

future regardless of the specific 

statistical form any such NAAQS may 

take. The EPA seeks comment on this 

preferred proposed approach. 

b. Alternative approach 1. The EPA 

also seeks comment on two alternative 

interpretations of section 188(d)(2). The 

EPA’s first alternative interpretation of 

section 188(d)(2) would require that a 

state seeking an attainment date 

extension for a Moderate PM2.5

nonattainment area would have to 

demonstrate that the area met the level 

of the PM2.5 NAAQS for which it is 

seeking the attainment date extension, 

as well as met the numerical level of the 

most stringent PM2.5 NAAQS in effect at 

the time the area was designated 

nonattainment. That is, under this 

approach, the area would need to have 

clean data for the year preceding the 

attainment date for the PM2.5 NAAQS 

for which the state is seeking an 

attainment date extension and for the 

other PM2.5 NAAQS that were part of 

the same suite of PM2.5 standards (i.e., 

both the 24-hour and the annual PM2.5

NAAQS) in effect at the time the EPA 

designated the area nonattainment. 

For example, if a state seeks an 

extension of the attainment date for an 

area designated nonattainment only for 

the 2012 annual PM2.5 NAAQS, it would 

have to demonstrate that the annual 

mean concentration of PM2.5 at each 

monitor in the Moderate area as 

analyzed in accordance with Appendix 

N to 40 CFR part 50 in the attainment 

year was less than or equal to 12.0 mg/ 

m3. Additionally, the state would have 

to demonstrate that the 98th percentile 

of valid 24-hour monitored readings in 

the area for the year preceding the 

attainment date did not exceed 35 mg/

m3, the level of the 24-hour PM2.5

NAAQS set in 2006 and retained with 

the 2012 p.m. NAAQS review as part of 

the suite of PM NAAQS, even if the area 

was not designated nonattainment for 

the 2006 24-hour PM2.5 NAAQS.156 As 

with the agency’s preferred approach, a 

state seeking an attainment date 

extension for a Moderate nonattainment 

area for a 24-hour PM2.5 NAAQS would 

be required to demonstrate that the area 

had clean data for that particular 

standard in the calendar year prior to 

the applicable attainment date for the 

area in accordance with the statistical 

form of the 24-hour PM2.5 NAAQS, 

rather than demonstrating that the area 

had no more than one exceedance of the 

24-hour PM2.5 NAAQS. 

The EPA presents this first alternative 

interpretation of the statute for two 

reasons. First, as noted earlier, the 

statute at section 188(b)(2) does not 

specify whether the air quality criteria 

for an attainment date extension apply 

for Moderate areas designated 

nonattainment for both the 24-hour and 

annual PM10 standards, or for just one 

of the standards. Read literally, 

however, the statute seems to require 

that an area seeking an extension of a 

Moderate area attainment date for any 

PM10 NAAQS must be meeting the level 

of both the 24-hour standard and the 

annual standard, even if it was only 

designated for just one of the standards. 

Under this interpretation of the statute 

for purposes of implementing the PM2.5

NAAQS, even though an area may be 

designated nonattainment for only one 

PM2.5 NAAQS and therefore seeking an 

attainment date extension only for that 

particular NAAQS, it would also have to 

meet the level of the other PM2.5

standards. As explained above, the EPA 

does not consider this the most 

appropriate interpretation of section 

188(d). However, under this alternative 

interpretation the agency would take the 

position that the other PM2.5 standards 

whose level the state must show the 

Moderate nonattainment area met in the 

year preceding its attainment date 

would be the most stringent PM2.5

NAAQS in effect nationally at the time 

the area was designated nonattainment. 

For example, if the EPA were to 

strengthen the 24-hour PM2.5 standard 

below the current 35 mg/m3 prior to 

December 31, 2021 (the anticipated 

statutory Moderate area attainment date 

for the 2012 PM2.5 NAAQS), then an 

area seeking an extension of the 

Moderate area attainment date for the 

2012 PM2.5 NAAQS would have to 

demonstrate that the area met the most 

stringent 24-hour PM2.5 NAAQS that 

applied at the time it was designated (35 

mg/m3), and not the less stringent 24- 

hour NAAQS set in 1997 (65 mg/m3) or 

any more stringent standard set after 

designation but before the attainment 

date. 

Second, as with the proposed 

approach to interpreting section 

188(d)(2), the EPA believes it is 

appropriate to interpret the statutory 

language regarding ‘‘no more than one 

exceedance of the 24-hour’’ NAAQS 

level broadly to mean that the area had 

clean data for the 24-hour PM2.5

NAAQS, consistent with the form of the 

NAAQS at issue, so that the requirement 

can apply to any 24-hour PM2.5 NAAQS, 

now or in the future. Even if it were 

appropriate to interpret section 

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188(d)(2) to require that a state meet the 

air quality criterion for both the 24-hour 

and the annual PM2.5 NAAQS, the EPA 

believes that the statutory provision 

concerning the number of exceedances 

must still be read in light of the different 

form of the 24-hour PM2.5 NAAQS. The 

EPA seeks comment on this first 

alternative interpretation of section 

188(d)(2). 

c. Alternative approach 2. The EPA’s 

second alternative interpretation of 

section 188(d)(2) would require that a 

state demonstrate that a Moderate area 

did not have more than one exceedance 

of the applicable 24-hour PM2.5 standard 

level, and the annual mean 

concentration of PM2.5 in the area was 

less than or equal to the applicable 

annual PM2.5 standard level, in the year 

preceding the applicable attainment 

date for the area. In other words, the 

EPA would not interpret the air quality 

criterion with respect to the 24-hour 

PM2.5 NAAQS in light of the 

significantly different form of the PM2.5

NAAQS. Furthermore, as with the first 

alternative interpretation, the 

‘‘applicable’’ PM2.5 standards would be 

those that applied at the time the 

Moderate area was designated for a 

given PM2.5 NAAQS, even if the area 

was not designated nonattainment for 

all of them. This interpretation would 

mean that regardless of the form of the 

applicable 24-hour PM2.5 standard, the 

Moderate area seeking an attainment 

date extension could not have more 

than one exceedance of the numerical 

level of the applicable 24-hour standard 

in order to qualify for a Moderate area 

attainment date extension. This 

requirement would be more stringent— 

and in some cases considerably so— 

than under the preferred proposed and 

first alternative interpretations, given 

the current statistical form of the 24- 

hour PM2.5 NAAQS. Additionally, 

under this reading of section 188(d)(2), 

any future changes to the PM2.5 NAAQS 

in terms of form or averaging time 

would also not be addressed, potentially 

creating confusion with respect to how 

a PM2.5 Moderate area could qualify for 

an attainment date extension in the 

future. 

The EPA believes that, while this 

interpretation of section 188(d)(2) may 

appear to be a straightforward reading of 

the statutory language, it does not 

reasonably account for the important 

differences between the statistical form 

of the PM10 and PM2.5 NAAQS or 

between the EPA’s longstanding 

convention for designating PM10 and 

PM2.5 nonattainment areas generally. 

The EPA therefore seeks comment on its 

preferred proposed approach and two 

alternative approaches for interpreting 

the air quality criteria of section 

188(d)(2) that a state would need to 

demonstrate compliance with in order 

for the EPA to consider granting an 

extension of a Moderate PM2.5 area 

attainment date. 

3. Proposed Process for Attainment Date 

Extension Request Submittals 

Regardless of which interpretation of 

section 188(d)(1) the EPA finalizes as 

part of this rulemaking, the EPA 

proposes to require states to submit 

sufficient information to demonstrate 

that they have complied with applicable 

requirements and commitments in the 

applicable implementation plan. This 

information would be needed in order 

for the EPA to make a decision on 

whether to grant a 1-year attainment 

date extension. The EPA would not be 

authorized to grant an attainment date 

extension to an area unless the state can 

demonstrate that it has met all of the 

requirements and commitments 

contained in the state’s applicable 

implementation plan for the area. Under 

the EPA’s first proposed approach for 

interpreting section 188(d)(1), a state 

would have to demonstrate that control 

measures have been submitted in the 

form of a SIP revision and that RACM 

and RACT and additional reasonable 

measures for sources in the area have 

been implemented. Under the agency’s 

alternative proposal for interpreting 

section 188(b)(1), the attainment plan 

submitted by the state would have to 

have been fully approved by the EPA 

and the state would have to be in 

compliance with any elements required 

under any applicable FIP for the area. In 

addition, under the EPA’s second 

proposed approach, the state would 

have to demonstrate that: (i) RACM and 

RACT and additional reasonable 

measures for sources in the area have 

been implemented, and (ii) the area has 

made emissions reductions progress that 

represents RFP toward attainment of the 

NAAQS and has met its quantitative 

milestones, and the state has submitted 

a milestone compliance demonstration 

(milestone report) to that effect if due. 

Any decision made by the EPA to 

extend the attainment date for an area 

would be based on facts specific to the 

nonattainment area at issue. 

Section 188(d) does not specify the 

process by which the EPA should 

evaluate and act upon requests from 

states for an extension of the Moderate 

area attainment date. However, the EPA 

proposes that an attainment date 

extension would only be granted after 

the agency provides notice in the 

Federal Register and an opportunity for 

the public to comment. This notice-andcomment process would allow for 

appropriate evaluation of the relevant 

criteria and facts in order to assure that 

the extension is granted or denied after 

full evaluation. This process also is 

consistent with past practice by the EPA 

in granting attainment date extensions, 

most recently for ozone nonattainment 

areas. In addition, for ease of 

implementation, the EPA proposes to 

interpret section 188(d) to authorize the 

EPA to stipulate that any extension 

would begin on January 1 and end on 

December 31 of the extension year and 

these dates would not depend on when 

the state submitted its request for an 

extension or was granted the extension 

by the EPA. The EPA believes this is a 

reasonable approach as the applicable 

attainment date for the area will either 

be the end of the sixth calendar year 

following designation of the area, or the 

end of an earlier calendar year if the 

state could advance attainment of the 

area by at least 1 year through the 

implementation of extra control 

measures. In addition, compliance with 

the relevant NAAQS will be evaluated 

based on monitored data collected over 

a full calendar year (i.e., over the period 

beginning January 1 and ending 

December 31), so starting the extension 

year on January 1 is logical. 

Because air quality criteria are part of 

the conditions that must be met in order 

for the EPA to grant a Moderate area 

attainment date extension, the EPA 

proposes to require that a state seeking 

such an extension must submit its 

complete attainment date extension 

request, including any available 

preliminary data for the year preceding 

the area’s applicable Moderate 

attainment date, on or before the area’s 

attainment date. The EPA also proposes 

to require that the state requesting such 

an extension must submit to the 

respective EPA Regional Office certified 

ambient PM2.5 monitoring data for the 

year preceding the attainment date for 

the area in question by no later than 

February 28 of the year following the 

area’s attainment date. Submission of 

the necessary data by this date will 

allow the EPA to review the state’s 

request and take appropriate action on 

the request prior to the date by which 

the EPA is required to make a 

determination that the area failed to 

attain by its Moderate area attainment 

date, i.e., within 6 months of the 

applicable attainment date (see the 

discussion of reclassification in Section 

V of this preamble). The EPA seeks 

comment on these proposed deadlines 

for a state to request an extension of a 

Moderate area’s attainment date and 

submit certified air quality data as 

required under CAA section 188(d)(2). 

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157See the Federal Register published on April 

16, 1994 (57 FR 13498, 13537 and 13538). 158 Ibid. at 13537. 

As noted earlier in this discussion of 

Moderate area attainment date 

extensions, the statute at section 188(d) 

provides that a state may seek up to two 

1-year extensions of the Moderate area 

attainment date if it meets the 

applicable criteria of sections 188(d)(1) 

and 188(d)(2). The statute makes no 

distinction between the criteria that 

must be met for the first 1-year 

extension and the criteria for the second 

1-year extension, therefore the EPA 

plans to apply the same interpretations 

of the statutory criteria proposed 

throughout this section, including the 

proposed deadlines for the state to 

submit the extension request and the 

certified air quality data, for purposes of 

a state seeking a second 1-year 

attainment date extension for a 

Moderate nonattainment area. 

The EPA seeks comment on the 

proposed approaches described above 

for interpreting the criteria of section 

188(d)(1) and 188(d)(2) and establishing 

a process for states to request attainment 

date extensions for Moderate areas. 

V. How would a PM2.5 Moderate 

nonattainment area be reclassified to 

Serious? 

As discussed elsewhere in this 

preamble, subpart 4, part D of title I of 

the CAA establishes a two-tier 

classification system for areas 

designated nonattainment for the PM2.5

NAAQS. While all areas designated 

nonattainment are initially classified as 

Moderate, section 188(b) describes two 

pathways by which the EPA has the 

authority or the duty to reclassify a 

Moderate nonattainment area to a 

Serious nonattainment area. Pursuant to 

section 188 (b)(1), the EPA has general 

discretionary authority to reclassify 

from Moderate to Serious any area that 

the Administrator determines cannot 

practicably attain the NAAQS by the 

applicable Moderate area attainment 

date. Pursuant to section 188(b)(2), the 

EPA has a mandatory duty to reclassify 

from Moderate to Serious any area that 

fails to attain the NAAQS by the 

applicable Moderate area attainment 

date. Both of these pathways are more 

fully described below. 

A. Discretionary Authority 

The EPA’s discretionary authority to 

reclassify a Moderate area to Serious 

derives from language in section 

188(b)(1) of the CAA which provides 

that: ‘‘The Administrator may reclassify 

as a Serious PM10 nonattainment area 

. . . any area that the Administrator 

determines cannot practicably attain the 

[NAAQS] . . . by the attainment date 

. . . for Moderate Areas.’’ The use of 

this discretionary authority thus would 

be triggered by the EPA making a 

determination that the Moderate area in 

question could not practicably attain by 

its statutory attainment date. 

The CAA does not specify the basis 

on which the EPA may make the 

determination that the area cannot 

practicably attain by the applicable 

attainment date. In the General 

Preamble, the EPA explained that the 

agency could base this determination 

upon whatever factors are pertinent and 

do so whether or not the state in 

question has submitted a Moderate area 

attainment plan, and whether or not the 

state has made the demonstration 

contemplated in section 189(a)(1)(B).157

The EPA may make such a 

determination based on evaluation of 

the attainment plan for the Moderate 

area in question or other facts known to 

the agency. As discussed earlier in this 

preamble, the attainment plan that a 

state would submit for a Moderate 

nonattainment area must include either 

a demonstration that the area will attain 

the NAAQS by the statutory Moderate 

area attainment date or a demonstration 

that attaining by the statutory Moderate 

area attainment date is impracticable. If 

the state makes and the EPA concurs 

with an impracticability demonstration 

submitted as part of the attainment plan, 

then the demonstration could serve as 

the basis for the EPA initiating a noticeand-comment rulemaking to reclassify 

the area to Serious. However, the CAA 

does not specify the basis for the EPA’s 

exercise of its discretionary authority 

and does not require the EPA to make 

its determination based on a submission 

from the state. Indeed, such a 

prerequisite would be illogical in the 

case of a state that fails to make any 

attainment plan submission or fails to 

address the issue of the need for 

reclassification in such submission. 

Section 188(b)(1)(B) does establish 

mandatory timeframes by which EPA 

must act if it intends to exercise its 

discretionary authority to reclassify 

areas as appropriate following the 

Moderate area attainment plan due date, 

stating that ‘‘the Administrator shall 

reclassify appropriate areas within 18 

months after the required date for the 

state’s submission of a SIP for the 

Moderate Area.’’ In the case of areas 

designated nonattainment for the 2012 

PM2.5 NAAQS in the first round of 

designations, states will be required by 

statute to submit a Moderate area 

attainment plan within 18 months of the 

date of designation (April 2015), or no 

later than October 2016. Pursuant to 

section 188(b)(1)(B), the EPA would 

then have until April 2018 (18 months 

following the Moderate area attainment 

plan submission deadline) to use its 

discretionary authority to reclassify any 

area that the EPA determines at that 

time cannot practicably attain by the 

Moderate area attainment date of 

December 2021. 

As noted above, the EPA believes that 

while a Moderate area impracticability 

demonstration as contemplated in 

section 189(a)(1)(B) is desirable in order 

to help the agency make a determination 

that the area cannot practicably attain 

by its attainment date, such a 

demonstration is not necessary to trigger 

action by the EPA to reclassify a 

Moderate area to Serious. The statute 

does not prohibit the EPA from using 

the weight of available evidence, 

including information available in the 

public record of a state, to make such a 

determination, even in the absence of a 

complete attainment plan submission. 

Thus, the EPA expressed in the General 

Preamble that: 

. . . under the plain meaning of the terms of 

section 188(b)(1) EPA has general discretion 

to reclassify at any time before the applicable 

attainment date any area EPA determines 

cannot practically attain the standards by 

such date. Accordingly, CAA section 

188(b)(1) is a general expression of delegated 

rulemaking authority. In addition, 

subparagraphs (A) and (B) of CAA section 

188(b)(1) mandate that the EPA reclassify at 

specified timeframes any areas it determines 

appropriate for reclassification at those dates. 

These subparagraphs do not restrict the 

general authority but simply specify that, at 

a minimum, it must be exercised at certain 

times.158

The EPA continues to consider this the 

correct interpretation of the statutory 

requirements concerning its authority to 

reclassify a Moderate nonattainment 

area to Serious at any time prior to the 

area’s Moderate area attainment date, if 

the agency determines that the area 

cannot practicably attain the relevant 

PM2.5 NAAQS by that date. 

The EPA emphasizes that states with 

an area designated as nonattainment for 

the PM2.5 NAAQS are required to meet 

all Moderate area attainment plan 

requirements, even after the EPA 

reclassifies the area to Serious. Section 

189(b)(1) states clearly that ‘‘in addition 

to’’ the Moderate area attainment plan 

requirements, states with areas 

reclassified to Serious must also meet 

Serious area attainment plan 

requirements, i.e., the reclassification 

does not eliminate the statutory 

obligation to meet Moderate area 

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159See, Vigil v. Leavitt, 366 F.3d 1025, amended 

at 381 F.3d 826 (9th Cir. 2004). 

160 57 FR 13498 (April 16, 1992), at page 13537. 

attainment plan requirements.159 Thus, 

the EPA believes that reclassifying 

Moderate areas to Serious at any time 

under its discretionary authority does 

not reward areas who delay 

development and implementation of 

control measures by excusing states 

from meeting substantive Moderate area 

attainment plan requirements or by 

extending the applicable attainment 

date. The EPA articulated this position 

in the General Preamble, explaining that 

this interpretation: 

. . . creates an incentive for the timely 

submittal and effective implementation 

of moderate area SIP requirements and 

facilitates the PM10 attainment objective. 

For example, if an area that fails to 

submit a timely moderate area SIP is 

reclassified, this does not obviate the 

requirement that the area submit and 

implement RACM consistent with the 

moderate area schedule. Accordingly, 

the area could be subject to sanctions for 

its delay in submitting the RACM SIP 

requirement . . . Further, 

reclassification before the applicable 

attainment date will ensure that 

additional control measures (i.e., in 

addition to RACM, serious areas must 

implement best available control 

measures (BACM)), are implemented 

sooner and will expedite the application 

of more stringent new source review 

requirements to the area . . . Similarly, 

where an area submits a timely 

moderate area SIP, EPA may not 

discover that the area cannot practicably 

attain until sometime after it begins 

implementing its moderate area control 

measures. The EPA then may want to 

reclassify the area in order to facilitate 

the development and implementation of 

BACM.160

The EPA considers this the correct 

interpretation of the statutory 

requirements and proposes to apply this 

longstanding interpretation of section 

188(b)(1) to nonattainment areas for the 

PM2.5 NAAQS. 

B. Mandatory Duty 

In addition to the EPA’s discretionary 

authority to reclassify a Moderate area 

to Serious under certain circumstances, 

the CAA also directs the EPA to do so 

under other circumstances. The 

alternative circumstances under which 

the EPA will reclassify an area from 

Moderate to Serious are if that area fails 

to attain the relevant NAAQS by the 

applicable Moderate area attainment 

date, including any extension of that 

date under section 188(d) for which the 

area qualifies. Under such 

circumstances, the EPA has a mandatory 

duty to identify any area that fails to 

attain the PM2.5 NAAQS by the 

applicable Moderate area attainment 

date. Reclassification under such 

circumstances would happen by 

operation of law when the EPA 

determines that the area failed to attain 

the NAAQS by the applicable 

attainment date, in accordance with 

section 188(b)(2)(A). Section 188(b)(2) 

requires that ‘‘within six months 

following the applicable attainment date 

for a PM10 nonattainment area, the 

Administrator shall determine whether 

the area attained the standard by that 

date’’ and publish its determination in 

the Federal Register. The EPA proposes 

that the date of reclassification for an 

area reclassified under the EPA’s 

mandatory duty to reclassify an area 

would be the effective date of the 

Federal Register document announcing 

that the area had not attained the 

relevant PM2.5 NAAQS and is therefore 

reclassified by operation of law. Thus, 

for example in the case of the 2012 

PM2.5 NAAQS, assuming a Moderate 

PM2.5 nonattainment area fails to attain 

the standard by its approved attainment 

date of December 31, 2021, the EPA 

would be required to publish in the 

Federal Register no later than June 30, 

2022 its determination that the area 

failed to attain the NAAQS and is 

therefore reclassified as Serious by 

operation of law. The date of 

reclassification for the area would be the 

effective date of the Federal Register 

document, or sometime after June 30, 

2022. To meet the requirements of 

section 189(b)(2), the Serious area 

attainment plan for the area would be 

due within 18 months thereafter, or no 

later than December 2023. 

An alternative approach for setting 

the date of reclassification for an area 

reclassified to Serious under the EPA’s 

mandatory authority could be to make it 

the same date as the missed attainment 

date for the area. Applying this 

approach in the example above would 

yield an earlier date of reclassification 

of December 31, 2021, and an earlier 

Serious area attainment plan due date of 

June 30, 2023. 

Although section 188(b)(2) does not 

explicitly address this issue, the EPA 

believes that its proposed approach is a 

reasonable interpretation of statutory 

ambiguity in section 188(b)(2) and 

preferable over the alternative approach 

for two reasons. First, the statute at 

section 189(b)(2) gives a state 18 months 

from the date of reclassification of an 

area to submit for the EPA’s approval an 

attainment demonstration with air 

quality modeling and provisions to 

assure timely implementation of BACM 

and BACT on sources in the 

nonattainment area. The EPA believes 

that it is reasonable for a state with a 

Serious PM2.5 nonattainment area to 

have 18 months plus the additional time 

needed by the EPA to issue a Federal 

Register document announcing the 

area’s failure to attain by the applicable 

Moderate area attainment date and 

subsequent reclassification (up to 6 

additional months) to ensure that the 

state has time to develop and submit a 

thorough, complete and accurate 

Serious area attainment plan that will 

provide for timely attainment of the 

NAAQS. Second, the statutory 

attainment date for a Serious area 

reclassified under any circumstances is 

as expeditious as practicable but no 

later than the end of the tenth year 

following designation of the area, and is 

thus independent of the date of 

reclassification of the area. Allowing a 

state some additional amount of time 

beyond 18 months from the missed 

attainment date to develop and submit 

a complete Serious area attainment 

plan, including adopting BACM and 

BACT, will not change the statutory 

obligation on the state for the area to 

attain the relevant NAAQS by the 

applicable attainment date. On the 

contrary, the EPA believes that the extra 

time may in fact help the area timely 

attain the relevant NAAQS by allowing 

the state to develop a more effective 

attainment plan for the area. 

The EPA seeks comment on its 

proposed approach of basing the date of 

reclassification for an area reclassified 

under the agency’s mandatory duty in 

section 188(b)(2) on the effective date 

for the Federal Register document in 

which the EPA announces that the area 

failed to attain the PM2.5 NAAQS by the 

applicable Moderate area attainment 

date and is reclassified by operation of 

law. The EPA intends to make 

determinations of whether or not an 

area attained the relevant NAAQS 

pursuant to section 188(b)(2) via noticeand-comment rulemaking. 

VI. What are the EPA’s proposed 

requirements for Serious area 

attainment plans? 

Sections 189(b) and (c) of the CAA 

include the following requirements for 

Serious area attainment plan 

submissions: (i) An attainment 

demonstration (section 189(b)(1)(A)); (ii) 

provisions for the implementation of 

best available control measures (BACM) 

no later than 4 years after 

reclassification of the area to Serious 

(section 189(b)(1)(B)); (iii) quantitative 

milestones that will be used to evaluate 

compliance with the requirement to 

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161See Vigil v. Leavitt, 366 F.3d 1025, amended 

at 381 F.3d 826 (9th Cir. 2004). 

162Section V of this preamble provides a more 

detailed discussion of the process for reclassifying 

areas with severe nonattainment problems to 

Serious. 163Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42015. 

demonstrate RFP (section 189(c)); and, 

(iv) regulation of PM2.5 precursors (in 

general to meet attainment and control 

strategy requirements and as specifically 

required for major stationary sources by 

section 189(e)). Other subpart 1 

requirements for attainment plans not 

otherwise superseded under subpart 4 

also apply to Serious areas for the PM2.5

NAAQS, including: (i) A description of 

the expected annual incremental 

reductions in emissions that will 

demonstrate RFP (section 172(c)(2)); (ii) 

emissions inventories (section 

172(c)(3)); (iii) other control measures 

(besides BACM and BACT) needed for 

attainment (section 172(c)(6)); and, (iv) 

contingency measures (section 

172(c)(9)). 

Additionally, section 189(b)(1) 

requires that ‘‘in addition’’ to the 

attainment plan requirements specific to 

Serious areas, states must also meet all 

Moderate area attainment plan 

requirements. The EPA interprets the 

statutory language of section 189(b)(1) to 

require states with areas that are 

reclassified to Serious to meet Moderate 

area attainment plan requirements, 

including any areas that the EPA 

reclassifies through rulemaking under 

its discretionary authority, even if that 

occurs before the area has met all of its 

Moderate area attainment plan 

requirements.161

The remainder of this section presents 

the EPA’s proposed regulatory 

approaches to implement the 

requirements for attainment plan 

submissions for Serious areas. 

A. Plan Due Dates 

The timing of Serious area attainment 

plan elements is dictated by two 

provisions of the CAA: Section 189(b)(2) 

for certain subpart 4 elements and 

section 172(b) for subpart 1 elements 

not superseded by subpart 4 

requirements. Section 189(b)(2) 

addresses the due dates for Serious area 

attainment demonstrations due under 

section 189(b)(1)(A) and provisions for 

BACM and BACT implementation 

under section 189(b)(1)(B). Specifically, 

section 189(b)(2) stipulates two 

alternative schedules for states to 

submit Serious area attainment 

demonstrations, depending upon the 

statutory authority invoked by the EPA 

to reclassify the area from Moderate to 

Serious. For an area reclassified to 

Serious by operation of law under 

section 188(b)(2) upon a determination 

by the EPA that the area failed to attain 

the relevant NAAQS by the applicable 

Moderate area attainment date, a state 

must submit a new attainment 

demonstration for the area no later than 

18 months after reclassification. For an 

area reclassified to Serious pursuant to 

the agency’s discretionary authority 

provided under section 188(b)(1), a state 

must submit a new attainment 

demonstration no later than 4 years after 

reclassification of the area.162 For all 

Serious nonattainment areas, section 

189(b)(2) requires a state to submit 

within 18 months of an area’s 

reclassification ‘‘provisions to assure 

that the best available control measures 

[BACM] for the control of PM10 shall be 

implemented no later than 4 years after 

the date the area is classified (or 

reclassified) as a Serious Area.’’ 

In contrast, section 172(b) provides 

the EPA discretion to set a due date for 

subpart 1 attainment plan elements that 

is no later than 3 years after designation 

of the area. In the Addendum, the EPA 

interpreted the date of reclassification of 

an area to Serious to be analogous to the 

date of designation of the area to 

nonattainment generally.163 If the EPA 

selects the proposed option, discussed 

later in this section, to adopt this 

convention, the subpart 1 attainment 

plan elements of provisions to 

demonstrate RFP, emissions inventories, 

additional control measures beyond 

BACM and BACT needed for 

expeditious attainment of the PM2.5

NAAQS, and contingency measures 

could in theory be due as late as 3 years 

after reclassification of an area to 

Serious. For the reasons discussed 

below, the EPA believes that it is 

necessary to harmonize the submission 

dates of the various elements of a 

Serious are attainment plan for the 

PM2.5 NAAQS to provide for more 

effective evaluation of such attainment 

plan submissions by states, the EPA and 

members of the general public. 

As with Moderate area attainment 

plans consisting of both subpart 1 and 

4 elements, the EPA presumes that 

simultaneous development and 

submission of most, if not all, of the 

Serious area attainment plan elements 

will be most effective, both for the state 

in developing the plan and for the EPA 

in reviewing the state’s submission, 

given the interplay between all plan 

elements in the formation of a 

successful control strategy for the area. 

Just as importantly, a complete 

attainment plan submission facilitates 

the general public’s review of the entire 

control strategy adopted by the state. 

Therefore where there is ambiguity in 

the statutory provisions, the EPA is 

proposing one or more approaches to 

schedule submission of the various 

elements of Serious area attainment 

plans in a way that will facilitate better 

development and evaluation of such 

attainment plan submissions. The EPA’s 

proposed options for due dates for 

specific elements of a Serious area 

attainment plan are described below. 

1. Area Reclassified to Serious After 

Failing To Attain the PM2.5 NAAQS 

If the EPA reclassifies a Moderate area 

to Serious because of a failure to attain 

the relevant NAAQS by the applicable 

attainment date, section 189(b)(2) 

requires that the state must submit both 

the attainment demonstration for the 

area and provisions to ensure timely 

BACM and BACT implementation to the 

EPA within 18 months after 

reclassification. Because an up-to-date 

base year emissions inventory, required 

under section 172(c)(3), will serve as the 

foundation of a state’s BACM and BACT 

determination, and additional control 

measures (beyond BACM and BACT) 

that are necessary for expeditious 

attainment of the PM2.5 NAAQS as 

required under section 172(c)(6) will 

need to be identified in order to 

complete the control strategy for the 

area, the EPA proposes that both the 

base year inventory and additional 

control measures (beyond BACM and 

BACT) needed for expeditious 

attainment must also be submitted 

within 18 months after reclassification 

of the area to Serious by operation of 

law. 

The EPA also proposes and seeks 

comment on two possible due dates for 

the remaining Serious area attainment 

plan elements for areas that failed to 

attain the NAAQS by the applicable 

Moderate area attainment date. Those 

plan elements are provisions for RFP, 

quantitative milestones and contingency 

measures. The first proposed due date 

for these remaining Serious area 

attainment plan elements would be no 

later than 18 months after 

reclassification of the area, consistent 

with the due date for the plan elements 

already described above. As noted 

above, the EPA maintains that requiring 

states to submit all elements of an 

attainment plan by the same date is 

reasonable because it allows for a 

complete review of the state submission 

by the EPA, regulated entities, and the 

general public, and it also may prove 

most efficient for states. See proposed 

40 CFR 51.1003(b)(2)(ii). 

The alternate proposed due date for 

the remaining elements would be 3 

years following reclassification to 

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164 Ibid. at 42015. 165 Ibid. at 42015. 

Serious, which would be consistent 

with guidance the EPA provided in the 

Addendum specific to the due date for 

contingency measures for Serious 

areas.164 This guidance references the 

EPA’s discretion under section 172(b) to 

establish due dates up to 3 years after 

designation for attainment plan 

elements required under section 172(c), 

which also include RFP provisions. 

Subpart 4 meanwhile requires 

quantitative milestones to demonstrate 

RFP but does not specify a due date for 

submitting such milestones as part of 

the attainment plan for the area (as 

separate and distinct from the clear 

statutory requirements related to 

demonstrating compliance with those 

milestones established in the attainment 

plan). When taken together, the EPA 

believes that these statutory provisions 

may be read to permit a state to submit 

these three elements of the plan as late 

as 3 years after reclassification of the 

area. While the EPA does not believe 

that such a reading is as logical as the 

agency’s first proposed approach, the 

EPA seeks comment on this alternative 

proposed approach to setting due dates 

for a state to submit an RFP plan, 

quantitative milestones and contingency 

measures for a Serious area reclassified 

under the EPA’s mandatory authority. 

2. Area Reclassified to Serious Due to an 

Inability To Practicably Attain the 

NAAQS by the Statutory Moderate Area 

Attainment Date 

If the EPA determines that a Moderate 

area cannot practicably attain the 

relevant NAAQS by the applicable 

attainment date and reclassifies the area 

to Serious pursuant to its discretionary 

authority under section 188(b)(1), 

section 189(b)(2) requires the state to 

submit provisions to ensure timely 

implementation of BACM and BACT to 

the EPA within 18 months after 

reclassification. As stated earlier, 

because an up-to-date emissions 

inventory serves as the foundation for a 

state’s BACM and BACT determination 

and pursuant to the authority granted to 

the EPA under section 172(b), the EPA 

proposes that the state must meet the 

emissions inventory requirement under 

section 172(c)(3) also within 18 months 

after reclassification of the area by 

submission of an up-to-date emissions 

inventory. 

With respect to the attainment 

demonstration requirement for Serious 

areas reclassified pursuant to section 

188(b)(1), section 189(b)(2) allows the 

state up to 4 years after reclassification 

to submit a new attainment 

demonstration for an area reclassified to 

Serious because it cannot practicably 

attain the PM2.5 NAAQS by the 

applicable Moderate area attainment 

date. This due date could generally be 

appropriate, notwithstanding the related 

issues discussed in the following 

paragraphs, if the EPA finalizes an 

approach for determining the overall 

control strategy for the area in which 

BACM and BACT are identified 

independent of the attainment 

demonstration for the area (see 

proposed Option 1 for BACM and BACT 

determinations described in Section 

VI.D of this preamble). 

However, the EPA is also proposing 

an alternative approach for determining 

the control strategy for a Serious area, 

under which BACM and BACT and 

additional feasible measures would be 

identified in conjunction with the 

attainment demonstration for the area 

(see proposed Option 2 for BACM and 

BACT determinations described in 

Section VI.D of this preamble). Under 

such an approach, the EPA proposes 

that the due date for the Serious area 

attainment demonstration would be no 

later than 18 months after 

reclassification if the EPA finalizes its 

proposed Option 2 for determining 

BACM and BACT for the area, as the 

attainment demonstration would be 

necessary in order for the EPA and the 

public to determine whether the control 

strategy identified for the area is 

adequate, and the statute requires that a 

state submit its BACM provisions 

within 18 months after reclassification 

of an area. 

With respect to other elements of a 

Serious area attainment plan, under the 

EPA’s prior interpretation as described 

in the Addendum, the EPA had 

suggested that states could submit 

contingency measures no later than 3 

years after reclassification of an area to 

Serious because of the language of 

section 172(b).165 The EPA believes it 

may be appropriate to extend a similar 

approach to establishing due dates for 

some other attainment plan elements 

required under subpart 1. Therefore, the 

EPA proposes to provide a state with the 

maximum time permitted under section 

172(b)—3 years from the date of 

reclassification of the area—to submit 

the following plan elements: Provisions 

to demonstrate RFP, other control 

measures (beyond BACM and BACT) 

needed to bring the area into 

expeditious attainment, and 

contingency measures. The EPA 

proposes that quantitative milestones, 

required under subpart 4 but linked to 

RFP which is required under subpart 1, 

would also be included with the plan 

elements due 3 years following 

reclassification. 

The EPA believes that this proposed 

due date for certain attainment plan 

elements required under subparts 1 and 

4 would be most appropriate if finalized 

in conjunction with proposed Option 2 

for BACM and BACT, which would 

require the state to submit the 

attainment demonstration for the area 

within 18 months after reclassification 

of the area to Serious. However, in the 

event the EPA finalizes proposed 

Option 1 for determining BACM and 

BACT for a Serious nonattainment area 

independent of the attainment 

demonstration for the area, the 

attainment demonstration for the area 

would be due no later than 4 years after 

the date of reclassification of the area to 

Serious. Given the integral role that the 

attainment demonstration plays in 

helping to identify additional feasible 

measures (beyond BACM and BACT) 

that an area may need to attain the 

relevant standard expeditiously (and 

which are required under section 

172(c)(6)), to calculate emissions 

reductions needed on an annual basis to 

demonstrate RFP, and to calculate the 

emissions reductions that contingency 

measures need to achieve and identify 

what controls could constitute such 

measures, the EPA is proposing and 

seeking comment on an alternative 

submittal deadline for provisions for 

RFP and quantitative milestones, 

additional control measures needed for 

expeditious attainment, and 

contingency measures that would align 

their due date with the statutory Serious 

area attainment demonstration due date, 

no later than 4 years from the date of 

reclassification. See proposed 40 CFR 

51.1003(b)(2)(i). The EPA believes that 

coordinating submission of attainment 

plan elements so that they may be 

developed and reviewed together can 

prove most efficient for the submitting 

state, the EPA, and the general public, 

and therefore this proposed alternative 

is the agency’s preferred approach. 

However, the EPA seeks comment on all 

of its proposed due date options for the 

various elements of a Serious area 

attainment plan. 

B. Emissions Inventory Requirements 

1. What emissions inventory 

requirements apply to Serious area 

attainment plans? 

As with PM2.5 nonattainment areas 

classified as Moderate, Congress did not 

create a specific emissions inventory 

requirement in subpart 4 that would 

supersede the emissions inventory 

requirement under subpart 1 for Serious 

areas. Thus, the statutory emissions 

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166All definitions described in Section IV.B of 

this preamble for areas classified as Moderate apply 

in this section. 

inventory requirements that apply for 

Serious area attainment plans continue 

to be those of section 172(c)(3), which 

explicitly requires ‘‘a comprehensive, 

accurate, and current inventory of actual 

emissions of the relevant pollutants’’ in 

the nonattainment area. In addition, the 

specific attainment plan requirements 

for the PM2.5 NAAQS set forth in section 

189(a) and associated modeling 

requirements make an accurate and upto-date emissions inventory a critical 

element of any viable attainment plan. 

Finally, the additional attainment plan 

requirements for the PM2.5 NAAQS for 

Serious areas contained in subpart 4 at 

section 189(b) have additional 

requirements that affect the emissions 

inventory requirements for Serious 

areas.166

As noted earlier in this preamble, 

states must use the best available, 

current emissions inventory information 

for attainment plan development, 

because complete, high quality 

emissions inventory data are essential 

for the development of an effective 

control strategy. To assist states in 

preparing complete, high quality 

inventories, the EPA provides guidance 

for developing emissions inventories in 

its SIP Emissions Inventory Guidance, 

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

chief/eidocs/eiguid/index.html. The 

EPA recommends that states consult 

this guidance while developing 

emissions inventories to meet 

requirements for Serious area 

attainment plans. 

2. How do states meet the inventory 

requirements for the PM2.5 NAAQS for 

areas classified as Serious? 

As with Moderate PM2.5

nonattainment areas, neither section 

172(c)(3) nor the provisions specifically 

applicable to attainment plans for the 

PM2.5 NAAQS in subpart 4 specify how 

states should meet statutory emissions 

inventory requirements for Serious 

PM2.5 nonattainment areas. Section 

172(c)(3) requires that states submit ‘‘a 

comprehensive, accurate, current 

inventory of actual emissions from all 

sources of the relevant pollutant or 

pollutants in such area, including such 

periodic revisions as the Administrator 

may determine necessary to assure that 

the requirements of this part are met’’ 

(emphasis added). The EPA interprets 

this provision to authorize the agency to 

require states to revise their base year 

emissions inventories whenever the 

state is required to submit a new 

attainment plan because of a change in 

the nonattainment area’s status (e.g. 

failure to attain by the applicable 

attainment date resulting in 

reclassification). In addition, pursuant 

to CAA section 301, the EPA has 

additional authority to promulgate 

regulations as necessary for the 

implementation of the PM2.5 NAAQS, 

including requirements pertaining to 

emissions inventories. Accordingly, the 

EPA is proposing specific emissions 

inventory requirements it considers 

necessary to effectuate the attainment 

plan requirements of the CAA for the 

PM2.5 NAAQS. 

Like Moderate areas, there are three 

key facets of the EPA’s proposed 

emissions inventory requirements, as 

laid out below: (i) The types of 

inventories required; (ii) the content of 

these inventories; and, (iii) the timing of 

submittal of these inventories. The three 

facets are addressed in the following 

paragraphs. 

First, the EPA proposes that the same 

two types of inventories required for 

Moderate areas are also required for 

Serious areas. While these inventories 

are the same types and names of 

inventories as for Moderate areas, they 

must be created specifically for Serious 

area attainment plans in accordance 

with the applicable Serious area 

requirements. The first type of 

inventory, the ‘‘base year inventory for 

the nonattainment area,’’ is expressly 

required by section 172(c)(3). The 

second type of inventory the EPA is 

proposing to require under section 

301(a)(1) is necessary to implement the 

attainment demonstration requirement 

of section 189(a)(1)(B). This second 

inventory is called the ‘‘attainment 

projected inventory for the 

nonattainment area.’’ See proposed 40 

CFR 51.1008(b)(1) and (2). 

Second, the EPA proposes that the 

content of the inventories will follow 

the content requirements for Moderate 

area inventories, with one exception 

needed to meet the requirements of 

section 189(b)(3). For Serious areas, 

section 189(b)(3) defines a separate 

emissions threshold for major sources in 

Serious nonattainment areas (70 tpy 

potential to emit of PM10), and this 

major source threshold is used in 40 

CFR part 51, subpart A (the AERR) to 

define which sources must be reported 

as point sources for PM10. This 

threshold is lower than the 100 tpy 

potential to emit general requirement for 

major sources of PM10, PM2.5 or one of 

its precursors that is used for Moderate 

area emissions inventories. Inventories 

for Serious area attainment plans must 

include these smaller sources as point 

sources (rather than the nonpoint source 

category that would apply for these in 

Moderate area plans) using the lower 

threshold specified in the CAA and 

codified in 40 CFR part 51, subpart A. 

Also as described above and in 40 CFR 

part 51, subpart A, this means that all 

other smaller stationary sources must be 

included in the inventory as nonpoint 

sources. 

Third, Section VI.A of this preamble 

describes the EPA’s proposal to require 

that a state submit the base year 

inventory for a Serious nonattainment 

area at the same time that it submits 

provisions to implement BACM and 

BACT on sources in the area (due no 

later than 18 months from 

reclassification of the area pursuant to 

section 189(b)(2)) as the base year 

inventory serves as the starting point for 

conducting a BACM and BACT 

determination. On the other hand, 

because the attainment projected 

inventory is more closely related to the 

Serious area attainment demonstration, 

the EPA believes that a state should be 

required to submit its attainment 

projected inventory with the attainment 

demonstration for a given Serious area 

in order to allow effective evaluation of 

the attainment plan as a whole. 

Consequently, the EPA is proposing to 

establish the regulatory requirement that 

attainment projected emissions 

inventories be submitted at the same 

time as the Serious area attainment 

demonstration, which would mean no 

later than 18 months after 

reclassification for areas reclassified 

after failing to attain the NAAQS by the 

applicable Moderate area attainment 

date, or no later than 4 years after 

reclassification for areas reclassified by 

the EPA because the area cannot 

practicably attain the NAAQS by the 

statutory attainment date if the EPA 

finalizes proposed Option 1 for 

determining BACM and BACT for area. 

See proposed 40 CFR 51.1008(b)(3) and 

(4). If the EPA finalizes an approach for 

determining BACM and BACT that links 

the control strategy analysis to the 

attainment demonstration, then the 

attainment demonstration including the 

attainment projected emissions 

inventory would be due no later than 18 

months after reclassification (i.e., at the 

same time BACM provisions are due 

under the statute). 

The EPA seeks comment on these 

proposed requirements and due dates 

for emissions inventories for Serious 

area attainment plans. 

C. Pollutants To Be Addressed in the 

Plan 

Section III of this preamble includes 

a detailed discussion about how states 

should address PM2.5 precursors in 

attainment plans and in the NNSR 

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167 Ibid. at 42008–09. 

program for purposes of implementing 

current and future PM2.5 NAAQS. While 

evaluating sources of direct PM2.5 for 

BACM and BACT is an implicit 

requirement in the context of 

implementing the PM2.5 NAAQS under 

any scenario, the EPA is proposing and 

seeking comment on several options for 

addressing PM2.5 precursors under the 

PM2.5 NAAQS implementation program. 

The EPA interprets the requirements of 

the CAA to allow an air agency to 

provide a ‘‘precursor demonstration’’ 

that can seek to make a technical case 

to the EPA that one or more PM2.5

precursors need not be subject to control 

requirements in a given nonattainment 

area, whether from sources in general or 

from major stationary sources. Section 

III presented three options describing 

different proposed approaches to such 

precursor demonstrations, and 

requested comment on each. The 

discussion for each option described 

how precursors would be addressed for 

Moderate areas and for Serious areas. 

In general terms, the three options can 

be summarized as follows: 

• Option 1: Two independent 

analyses: (a) An attainment planning 

analysis demonstrating that control 

measures for a particular precursor are 

not needed for expeditious attainment, 

meaning that the precursor can be 

excluded from measures needed to 

attain as expeditiously as practicable for 

all types of sources; and, (b) a section 

189(e) technical demonstration showing 

that major stationary sources of a 

particular precursor do not contribute 

significantly to levels that exceed the 

PM2.5 standard, meaning that the 

precursor can be excluded from control 

requirements for major sources and from 

NNSR permitting. For an area 

reclassified to Serious, the state would 

once again need to evaluate potential 

control measures for all sources of direct 

PM2.5 and all PM2.5 precursor emissions 

as part of the control strategy 

determination process (described more 

fully in Section VI.D of this preamble). 

• Option 2: Single analysis 

demonstrating that all emissions of a 

particular precursor from within the 

area do not significantly contribute to 

PM2.5 levels that exceed the standard, 

meaning that control requirements for 

emissions of the precursor from major 

stationary and area sources, as well as 

mobile sources, would not be required 

for expeditious attainment, control 

requirements for major sources, or for 

NNSR permitting. For an area 

reclassified to Serious for which a 

precursor had previously been 

demonstrated to not significantly 

contribute to PM2.5 levels that exceed 

the standard, the air agency would be 

required to update the precursor 

demonstration taking into account any 

relevant information or technical tools 

that had been developed since the 

initial demonstration was approved, but 

could still conclude that control 

requirements are not required for 

Serious area attainment planning if the 

updated demonstration still shows that 

all source emissions of a precursor do 

not significantly contribute to PM2.5

levels that exceed the standard. 

• Option 3: An attainment planning 

analysis demonstrating that control 

measures for all types of sources of a 

particular precursor are not needed for 

expeditious attainment also would be 

deemed to meet the section 189(e) 

technical demonstration requirement, 

meaning that the state would not need 

to regulate emissions of the particular 

precursor from major stationary sources 

under the NNSR permitting program or 

other control requirements for major 

stationary sources. As under proposed 

precursor Option 1, for an area 

reclassified to Serious, the state would 

once again need to evaluate potential 

control measures for all sources of direct 

PM2.5 and all PM2.5 precursor emissions 

as part of the control strategy 

determination process (see Section VI.D 

of this preamble). 

The EPA will finalize its approach to 

PM2.5 precursors and clarify the 

implications for states conducting 

analyses to determine the appropriate 

control strategy for a Serious area after 

considering public comment received 

on this proposal. 

D. Attainment Plan Control Strategy 

1. General Approach To Designing a 

Control Strategy for a Serious 

Nonattainment Area 

As noted in Section IV.D of this 

preamble, the statutory attainment 

planning requirements of subparts 1 and 

4 were established to ensure that states 

meet the following goals of the CAA: (i) 

Implement measures that provide for 

attainment of the PM2.5 NAAQS as 

expeditiously as practicable, and (ii) 

adopt emission reduction strategies that 

will be the most effective, and the most 

cost effective, at reducing PM2.5 levels in 

nonattainment areas. A state has 

discretion to require reductions from 

any source inside or outside of a PM2.5

nonattainment area (but within the 

state’s boundaries) in order to fulfill its 

obligation to demonstrate attainment in 

a PM2.5 nonattainment area as 

expeditiously as practicable, in addition 

to having an obligation to meet the 

statutory requirements for specific 

control measures on sources located 

within a nonattainment area (e.g., 

BACM and BACT). A state may need to 

require emissions reductions on sources 

located outside of a PM2.5

nonattainment area if such reductions 

are needed in order to provide for 

expeditious attainment of the PM2.5

NAAQS. 

The following sections describe the 

EPA’s proposed approach for a state to 

follow in order to identify and select the 

complete suite of measures needed for 

an approvable attainment plan 

submission for a Serious PM2.5

nonattainment area. 

2. Identification and Selection of BACM 

and BACT and Additional Feasible 

Measures 

a. Statutory requirements and existing 

guidance. As discussed earlier, a state 

must prepare a new attainment plan for 

any Moderate area reclassified to 

Serious. Such a plan must include 

provisions to implement BACM on 

sources in a Serious nonattainment area, 

as provided by section 189(b)(1)(B), no 

later than 4 years after reclassification. 

Under section 189(b)(2), a state has 18 

months following reclassification to 

submit these BACM provisions. 

Section 189(b)(1)(B) refers only to 

BACM, but the EPA has long interpreted 

this term to include BACT, just as the 

analogous term for RACM includes 

RACT for Moderate areas. The 

legislative history for the 1990 

Amendments to the CAA supports this 

interpretation, as the EPA has explained 

in past guidance.167 Additionally, the 

requirement for BACT in the context of 

PM2.5 NAAQS implementation in 

nonattainment areas is separate and 

distinct from the requirement for BACT 

under the Prevention of Significant 

Deterioration (PSD) permitting program 

for new stationary sources in areas 

designated as attainment or 

unclassifiable for the PM2.5 NAAQS. As 

described later in this section, the 

process and criteria that states have 

historically used to determine BACT for 

PSD have been applied to determine 

BACT for PM10 NAAQS 

implementation, but these requirements 

are otherwise unrelated. 

Longstanding guidance in the General 

Preamble and Addendum, together with 

past practice associated with 

implementing the PM10 NAAQS under 

subpart 4, have helped to establish a 

general approach for states and the EPA 

to determine BACM and BACT for 

Serious PM10 nonattainment areas. This 

approach has served as the basis for 

developing a more stringent control 

strategy for a Serious PM10

nonattainment area than that developed 

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168 Ibid. at 42009. 169 Ibid. at 42009. 170 Ibid. at 42010. ‘‘EPA will interpret PSD BACT 

and PM–10 BACM as generally similar because, 

despite the similarity in terminology, certain key 

differences exist between control measures 

applicable in the PSD and PM–10 serious 

nonattainment area programs. The BACT under the 

PSD program applies only in areas already meeting 

the NAAQS, while PM–10 applies in areas which 

are seriously violating the NAAQS. The difference 

in policy goals, arguably, suggests that the PM–10 

BACM control standard should be more stringent 

than that for PSD BACT. . . . EPA considers it 

reasonable to use the approach adopted in the PSD 

BACT program as defined in section 169(3) of the 

Act as an analogue for determining appropriate 

PM–10 nonattainment control measures in serious 

areas, while at the same time retaining the 

discretion to depart from that approach on a caseby-case basis as particular circumstances warrant.’’ 

171 Ibid. 

172 Ibid. at 42011. 

173 Ibid. at 42011. 

174See Alabama Power Co. v. Costle, 636 F.2d 

323, 360–61 (D.C. Cir. 1979). 

for such area when it was classified as 

Moderate. Indeed, as BACM and BACT 

are required to be implemented when a 

Moderate nonattainment area is 

reclassified as Serious due to its actual 

or projected inability to attain the 

relevant NAAQS by the Moderate area 

attainment date through the 

implementation of ‘‘reasonable’’ 

measures, it is logical that ‘‘best’’ 

control measures should represent a 

more stringent and potentially more 

costly level of control.168 The level of 

stringency generally refers to the overall 

level of emissions reductions of a 

control measure or technology, or of 

such measures and technologies 

combined. 

Congress first defined BACT in CAA 

section 169(3) for the PSD permitting 

program as: ‘‘an emission limitation 

based on the maximum degree of 

reduction of each pollutant . . . which 

the permitting authority, on a case-bycase basis, taking into account energy, 

environmental, and economic impacts 

and other costs, determines is 

achievable for such facility through 

application of production processes and 

available methods, systems, and 

techniques . . .’’ 

In the Addendum, the EPA provided 

guidance concerning the requirements 

for BACM and BACT for Serious area 

attainment plan requirements for the 

PM10 NAAQS.169 The EPA discussed in 

the Addendum that when Congress 

amended the CAA, Congress selected 

the same ‘‘best’’ terminology for PM10

nonattainment areas as they did for the 

language selected for the PSD program 

in 1977. The EPA interpreted this word 

choice at the time to mean that PSD 

BACT and PM10 nonattainment area 

BACM should be generally analogous in 

definition and implementation, but with 

some differences due to different end 

policy goals between the PSD and 

nonattainment area programs.170 The 

EPA thus defined BACM for PM10

Serious nonattainment area planning to 

be the maximum degree of emission 

reduction achievable from a source or 

source category which is determined on 

a case-by-case basis, considering energy, 

economic and environmental impacts 

and other costs.171

The EPA has described BACM as a 

generally independent requirement, to 

be determined without regard to the 

specific attainment analysis (i.e., 

attainment demonstration) for the 

area.172 The EPA established that such 

an interpretation is in accordance with 

the structural scheme of the CAA, 

which by its definition requires that 

when an area is classified as Serious, 

BACM are implemented in addition to 

RACM. Because of the two types of 

measures employed, the EPA found it 

reasonable in the past to interpret the 

statute as requiring a different analysis 

for determining BACM, i.e., that while 

RACM has been interpreted as those 

reasonable measures necessary to bring 

a nonattainment area into expeditious 

attainment, BACM has been interpreted 

as those measures that best control 

sources’ emissions without regard to 

whether such measures are needed for 

purposes of attainment of the relevant 

NAAQS in the area. The view that 

BACM and BACT measures are 

generally independent of the attainment 

needs of the area is also consistent with 

the statutorily specified submission date 

for BACM and BACT control measures, 

versus the statutorily specified 

submission date for the attainment 

demonstration for Serious areas. 

Specifically, states with Serious 

nonattainment areas must submit BACM 

and BACT measures within 18 months 

of reclassification of areas to Serious, 

whereas they are given up to 4 years 

from reclassification to submit the 

attainment demonstration for such 

areas. 

In addition, the EPA has historically 

provided an exemption from BACM and 

BACT for source categories that 

contribute only de minimis levels to 

ambient PM10 concentrations in a 

Serious nonattainment area. In the 

Addendum, the EPA proposed that all 

sources in a Serious area are subject to 

BACM unless ‘‘the state adequately 

demonstrates that a particular source 

category does not contribute 

significantly to nonattainment of the 

NAAQS.’’173 Because the language 

regarding BACM implementation in 

section 189(b)(1)(B) of the CAA requires 

‘‘provisions to assure that best available 

control measures (BACM) for the control 

of PM10 shall be implemented . . .’’ 

without stating that ‘‘all’’ BACM must 

be implemented, the EPA has 

interpreted this language as providing 

the EPA discretion to exclude from 

BACM requirements source categories 

that do not contribute significantly to an 

area’s nonattainment status. 

Additionally, in the Addendum, the 

EPA argued that based on the decision 

in Alabama Power Co. v. Costle, the 

courts have supported the interpretation 

that sources that contribute negligibly to 

an area’s nonattainment status can be 

excluded from regulation.174 The EPA 

further indicated that the same criteria 

used in the NSR permitting program at 

the time to determine if a source 

category contributes significantly to an 

area’s nonattainment status should 

apply, such that a source category 

would be considered a significant 

contributor to an area’s nonattainment 

status if its emission contribution was 

expected to exceed 5 mg/m3 for the 24- 

hour PM10 NAAQS (150 mg/m3 at the 

time), or 1 mg/m3 for the annual PM10

NAAQS (50 mg/m3 at the time). 

A discussion of the EPA’s existing 

process and criteria for determining 

BACM and BACT for Serious PM10

nonattainment areas and the agency’s 

proposed options for defining the 

criteria by which a state must determine 

BACM and BACT and additional 

feasible measures for a Serious PM2.5

nonattainment area are presented in the 

sections that follow. 

In accordance with the PM10 guidance 

in the Addendum, the EPA has applied 

a four-step process for states to use to 

identify measures that constitute BACM 

or BACT for sources located in PM10

Serious areas. The four-step BACM 

selection process was designed to take 

into account the local facts and 

circumstances and the nature of the air 

pollution problem in a given 

nonattainment area. The BACM 

determination process for PM10 Serious 

nonattainment areas has historically 

entailed: (i) Developing a 

comprehensive inventory of sources and 

source categories of directly emitted 

PM10 and PM10 precursors; (ii) 

evaluating source category impact and 

determining if any source categories are 

de minimis and thus do not need further 

evaluation for emission controls; (iii) 

evaluating alternative control measures 

available for significant source 

categories for technological feasibility; 

and, (iv) evaluating costs (i.e., economic 

feasibility) of the technologically 

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175For additional information, see ibid. at 42012– 

13. 

176For examples of how states have applied these 

steps and criteria for Serious PM10 nonattainment 

areas and how the EPA has evaluated them, see 

generally Approval and Promulgation of 

Implementation Plans for California—San Joaquin 

Valley PM–10 Nonattainment Area; Serious Area 

Plan for Attainment of the 24-Hour and Annual 

PM–10 Standards, 69 FR 5412 (February 4, 2004); 

Approval and Promulgation of Implementation 

Plans for California—San Joaquin Valley PM–10 

Nonattainment Area; Serious Area Plan for 

Attainment of the 24-Hour and Annual PM–10 

Standards, 69 FR 30006 (May 26, 2004); Approval 

and Promulgation of Implementation Plans for 

Arizona; Maricopa County PM—10 Nonattainment 

Area; Serious Area Plan for Attainment of the 24- 

Hour and Annual PM–10 Standards, 73 FR 45542 

(August 14, 2008); Approval and Promulgation of 

Implementation Plans; Arizona—Maricopa County 

PM–10 Nonattainment Area; Serious Area Plan for 

Attainment of the Annual PM–10 Standard, 65 FR 

19964 (April 13, 2000), at page 19972. 

177Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42012. 

178 Ibid. 

179 Ibid. at 42012. At the time of publication of 

the Addendum, the EPA had already issued BACM 

guidance documents pursuant to section 190 for 

residential wood combustion, prescribed burning, 

and fugitive dust. The agency referred to these 

documents as establishing the control measures that 

a state should consider, at a minimum, as BACM 

for those PM10 sources in Serious PM10

nonattainment areas. 

180 Ibid. at 42013 (discussing in detail factors 

which affect the selection of mobile, area, and point 

source alternative control techniques for particulate 

matter). 

181 Ibid. at 42013. 

182EPA Air Pollution Control Cost Manual, Sixth 

Edition, (EPA/452/B–02–001), July 2002 (explaining 

how to determine costs under a BACT analysis). 

183Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42014. The 

Addendum provides one example of RACM to 

reduce PM10, to ‘‘[p]ave 4 miles of unpaved city 

streets.’’ Ibid. BACM for PM10 for the same 

nonattainment area could later mean to ‘‘[p]ave 10 

miles of the most heavily-traveled, unpaved county 

roads.’’ Ibid. Therefore, the measure itself was not 

necessarily changed, but the extent to which the 

measure was implemented was significantly 

expanded. Such a measure would also contribute to 

more expeditious attainment of the NAAQS. 

feasible control measures.175 176 These 

steps are described more fully below. 

Step 1: Inventory sources and 

precursors. As with any control strategy 

analysis for a nonattainment area, the 

EPA recommended that a state begin 

with a current emissions inventory as 

the first step toward determining what 

constitutes BACM or BACT for a 

particular Serious PM10 nonattainment 

area. The EPA expected that a state 

would start with the base year emissions 

inventory submitted with the Moderate 

area attainment plan for the area as 

required under section 172(c)(3), and 

update it as necessary to reflect new 

source construction, facility shutdowns, 

growth in certain source categories, and 

any other relevant changes. The EPA 

reiterated in the Addendum that the 

emissions inventory for the area must 

identify both nonanthropogenic and 

anthropogenic emissions sources.177

Step 2: Evaluate source category 

impact. The next step in the BACM 

analysis for PM10 Serious areas was for 

the state to identify source categories 

having significant (i.e., non-de minimis) 

impacts on air quality in the Serious 

area. The EPA suggested in the 

Addendum that receptor modeling, 

screening modeling, or refined 

dispersion modeling would likely be 

necessary to identify key source 

categories, which the state may have 

performed during the development of 

the Moderate area attainment plan.178

Step 3: Evaluate alternative control 

techniques. Once the significant source 

categories were identified for a PM10

Serious nonattainment area, the state 

was expected to evaluate the 

technological and economic feasibility 

of control measures ‘‘discussed in the 

BACM guidance documents and other 

relevant materials for all source 

categories impacting the nonattainment 

area except those with a de minimis 

impact considering emission reductions 

achieved with RACM.’’ 179 Control 

measures were supposed to be 

expanded to include options not 

previously considered RACM as well as 

consider additional measures not 

previously evaluated in the RACM 

analysis. 

Under the Addendum, the test for 

determining technological feasibility 

could differ depending on the type of 

source category evaluated. For area 

sources, the EPA’s guidance suggested 

that technological feasibility depended 

on the ability to alter the characteristics 

that affect emissions from the sources, 

such as the size or extent of the area 

sources and operation procedures. The 

EPA’s guidance suggested that for 

specific point sources, technological 

feasibility should consider factors such 

as layout of the plant, space available to 

make changes in the plant, energy 

requirements, operating procedures, and 

materials used, among others.180

Step 4: Evaluate costs of control. The 

EPA’s previous guidance recommended 

that a control should be considered 

economically feasible by the state when 

‘‘the control technology in question has 

previously been implemented at other 

sources in a similar source category 

without unreasonable economic 

impacts.’’ 181 Feasibility of public 

funding for BACM could have been a 

consideration that states evaluated for 

all of the technologically feasible 

control measures determined in Step 3. 

Other costs that could be considered 

included capital costs, operating and 

maintenance costs, and the cost 

effectiveness of a particular control 

measure or technology.182

The EPA believes that the difference 

between RACM and BACM primarily 

lies in the extent of the actual emissions 

reductions achieved through the 

application of a given suite of candidate 

measures. For example, a state may have 

deemed a candidate RACM or RACT 

measure economically infeasible 

because its cost effectiveness (dollar per 

ton of pollutant reduced) was high 

relative to other measures, but the same 

measure could qualify as BACM if, for 

the increased cost, it would ultimately 

provide substantial PM2.5 attainment 

benefits. An example of RACM might be 

to implement a particular control in a 

limited way, while BACM could mean 

a more widespread implementation of 

that same measure, even though wider 

implementation would incur greater 

cost. In the PM10 context, states and the 

EPA have determined that BACM have 

sometimes been measures that were first 

implemented as RACM, but were then 

later implemented on a broader scale as 

BACM in the nonattainment area after it 

was reclassified as Serious.183

While the proposed approaches and 

criteria for identifying appropriate 

control measures for a Serious area are 

necessarily different than for a Moderate 

area, it is important to note two 

similarities: first, that the EPA interprets 

the requirement under section 172(c)(6) 

for a state to adopt ‘‘other measures’’ 

needed for attainment to apply to 

sources located inside and outside of 

any PM2.5 nonattainment area (but 

within the state’s boundaries), whether 

the area is classified as Moderate or 

Serious; and, second, similar to the 

RACM requirement for Moderate 

nonattainment areas under subpart 4, 

section 189(b)(1)(B) requires that BACM 

must be implemented no later than 4 

years after a Moderate area is 

reclassified to Serious. 

Taking these two statutory provisions 

together, the EPA proposes that the 

other measures required under section 

172(c)(6) must include ‘‘additional 

feasible measures,’’ which would be 

those measures and technologies that 

otherwise meet the criteria for BACM 

and BACT but that can only be 

implemented in whole or in part 

beginning 4 years after reclassification 

of an area, but no later than the statutory 

attainment date for the area. See 

proposed 40 CFR 51.1000. Such 

measures would necessarily be 

implemented on sources in the 

nonattainment area, and a state would 

only be required to implement them if 

they were needed in addition to BACM 

and BACT to bring the area into 

expeditious attainment. The state must 

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184 Ibid. 

also assess whether there are other 

control measures that it can implement 

to control sources within the state but 

outside the nonattainment area that 

contribute to the PM2.5 nonattainment 

status of the area in order to bring the 

area into attainment as expeditiously as 

practicable, and may consider existing 

measures that, applied more 

extensively, could meet the more 

stringent criteria for control measures 

that must be adopted to bring a Serious 

nonattainment area into expeditious 

attainment. 

These ‘‘additional feasible measures’’ 

would be analogous to the ‘‘additional 

reasonable measures’’ in the proposed 

RACM and RACT analysis process, 

which are technologically and 

economically feasible measures that 

cannot qualify as RACM or RACT 

because they cannot be implemented 

within 4 years of designation of a 

Moderate nonattainment area. Under 

either of the two proposed approaches 

for determining BACM and BACT for 

sources in a Serious nonattainment area 

descrfibed later in this section, a state 

would identify additional feasible 

measures as part of the BACM and 

BACT determination process, just as 

additional reasonable measures would 

be identified as part of the state’s RACM 

and RACT determination process. 

The EPA recognizes that only a 

nonattainment area that is reclassified 

under the agency’s discretionary 

authority might have sufficient time 

between the required date for 

implementing BACM and BACT and the 

statutory Serious area attainment date to 

implement additional measures beyond 

BACM and BACT. BACM and BACT 

must be implemented no later than 4 

years after reclassification of the area; 

areas reclassified to Serious because 

they cannot practicably attain the 

relevant NAAQS by the applicable 

attainment date could potentially have 

significantly more than 4 years between 

the date of reclassification and the 

statutory Serious area attainment date, 

during which time the area could 

continue to implement additional 

measures to bring the area into 

attainment. By way of illustration, for 

areas designated in the first round of 

designations for the 2012 PM2.5 NAAQS, 

the statutory Moderate area attainment 

date will be no later than December 31, 

2021. If a state submits a Moderate area 

attainment plan by the statutory 

attainment plan due date (18 months 

after designation, or in this example, 

October 2016) and the plan 

demonstrates that the area cannot 

practicably attain the NAAQS by 

December 31, 2021, then the EPA has a 

statutory duty to reclassify such an area 

within 18 months of the attainment plan 

due date (i.e., by April 2018). The 

statutory Serious area attainment date 

would be the end of the tenth year 

following designation, or December 31, 

2025. In such a case, the state would 

need to implement BACM for the area 

within 4 years of reclassification, or by 

April 2022, leaving over 3.5 years 

between the statutory deadline for 

implementing BACM and the statutory 

attainment date for the area. The EPA’s 

proposal to require the state to identify 

and adopt additional feasible measures 

for the area would mean that the state 

would need to identify those control 

measures and technologies that are 

feasible (according to the proposed 

BACM and BACT criteria described 

later in this section) and that can be 

implemented between April 2022 and 

December 2025. The EPA expects that 

while such a long span of time may be 

available only to a very few Serious 

nonattainment areas, it would be 

appropriate to require such areas to 

implement measures in addition to 

BACM and BACT if, taken together, they 

can advance the attainment date for the 

area by at least 1 year. The EPA seeks 

comment on its proposal to require 

additional feasible measures for Serious 

nonattainment areas as described here. 

b. Proposed approaches for 

determining BACM and BACT and 

additional feasible measures for Serious 

PM2.5 nonattainment areas. The EPA 

proposes and seeks comment on two 

approaches for a state to meet the 

statutory control requirements that 

apply for Serious nonattainment areas. 

The EPA is first proposing an approach 

consistent with prior guidance 

summarized in the preceding section of 

this preamble which would center on 

determining BACM and BACT and 

additional feasible measures ‘‘generally 

independent’’ of whether such measures 

are needed for expeditious attainment of 

the relevant NAAQS in a Serious PM2.5

nonattainment area. Under this first 

proposed approach, states would have 

the option, with the proper evidence 

and justification, to eliminate de 

minimis source categories from 

consideration for controls. 

The EPA’s second proposed approach 

would require states to identify BACM 

and BACT and additional feasible 

measures simply within the context of 

what is necessary to bring an area into 

attainment as expeditiously as 

practicable. In other words, the second 

proposed option would take a different 

approach to determining Serious area 

control measures from the approach 

included in prior EPA guidance, in that 

it would allow states not to impose 

specific measures that would otherwise 

be BACM or BACT (or additional 

feasible measures) in the area, if those 

measures would not be necessary to 

bring the area into attainment with the 

relevant NAAQS by the statutory 

attainment date, and the collective 

emissions reductions from such 

measures would not be sufficient to 

advance the attainment date by at least 

1 year in the area. A discussion of the 

proposed options follows. 

i. Proposed Option 1. The EPA seeks 

comment on a proposed approach to 

maintain, with some modifications, the 

existing approach to determining BACM 

and BACT for Serious PM10

nonattainment areas to BACM and 

BACT determinations for Serious PM2.5

nonattainment areas. Under this 

approach, a state would be required to 

determine BACM and BACT and 

additional feasible measures for a 

Serious PM2.5 nonattainment area 

independent of an analysis of the 

specific attainment needs of the Serious 

area; in other words, the BACM and 

BACT analysis would need to be 

conducted without regard to whether all 

such controls are needed to bring the 

area into expeditious attainment. 

Keeping in mind that the overall 

objective of the implementation of 

BACM and BACT and additional 

feasible measures is to bring a Serious 

PM2.5 nonattainment area into 

attainment as expeditiously as 

practicable, this option would continue 

to provide that the test for BACM puts 

a ‘‘greater emphasis on the merits of the 

measure or technology alone,’’ rather 

than on ‘‘flexibility in considering other 

factors,’’ in contrast to the approach for 

determining RACM and RACT 

described in both the EPA’s past 

guidance and in this proposal in Section 

IV.D.184 This Option 1 is consistent with 

the statutory provisions governing the 

timing for submission of BACM and 

BACT measures versus the timing for 

attainment demonstrations for Serious 

areas. By interpreting the statutory 

requirement for BACM and BACT for 

Serious PM2.5 nonattainment areas as a 

requirement that a state must meet 

independent of the attainment planning 

needs of the area, the EPA would not 

consider such requirement to be a 

‘‘planning’’ requirement tied to the 

actual attainment status of the area, and 

thus would not suspend such a 

requirement in the event the agency 

determines that a Serious area is 

attaining the relevant PM2.5 NAAQS and 

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185For a complete discussion of the EPA’s Clean 

Data Policy and the EPA’s proposal for applying 

this policy for purposes of implementing the PM2.5

NAAQS, see Section IX.C of this preamble. 

186Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42011. 

187 Ibid. See also Alabama Power v. Costle, 636 

F.2d 323, 360–61 (D.C. Cir. 1979). 

in turn grants a clean data 

determination for the area.185

Under the EPA’s first proposed 

approach, a state would be required to 

follow a multi-step process similar to 

the existing BACM process for PM10

(outlined earlier in this section) to 

identify and select control measures and 

technologies more stringent than RACM 

and RACT and additional reasonable 

measures for non-de minimis source 

categories in the nonattainment area. 

This process would involve analyzing 

the impact of the different source 

categories identified in the up-to-date 

base year emissions inventory for the 

area to identify those with a significant 

contribution to the area’s PM2.5

concentrations. Any source categories 

found not to have such an impact would 

be considered de minimis and therefore 

exempt from further consideration. The 

specific steps the EPA is proposing for 

this approach are explained below. See 

proposed 40 CFR 51.1010(a) for 

proposed Option 1. 

Step 1: Update base year emissions 

inventory for the area. The first step 

under this proposed approach would be 

for the state to develop a detailed 

emissions inventory of the various 

sources and source categories that emit 

direct PM2.5 and PM2.5 precursors in the 

Serious area. This inventory should be 

the most comprehensive and accurate 

inventory available. The EPA expects 

that the work for this step would be 

completed in order to meet the 

emissions inventory requirements for 

Serious area plans as described in 

Section VI.B, and would start with 

reviewing and updating the emissions 

inventory submitted as part of the 

Moderate area attainment plan for the 

area. 

Step 2: Evaluate source category 

impacts. As with BACM for PM10, the 

EPA proposes to allow states to exempt 

from further consideration de minimis 

source categories in Step 2 of the 

agency’s first proposed approach for 

determining BACM and BACT for a 

Serious PM2.5 nonattainment area. The 

EPA proposes to apply the same 

overarching test for identifying de 

minimis source categories as that 

described in the Addendum.186 That is, 

if a state can demonstrate that a 

particular source category does not 

contribute significantly to 

nonattainment of the PM2.5 NAAQS 

after the application of any RACM or 

RACT controls on the sources in the 

source category, then the state may 

eliminate the source category from 

further consideration for BACM or 

BACT.187 A state would be required to 

evaluate for BACM and BACT controls 

all other sources in the nonattainment 

area in source categories that do not 

qualify as de minimis. 

This option could be beneficial for 

some states that may already exclude de 

minimis PM10 source categories from 

BACM in Serious PM10 nonattainment 

areas or that may exclude de minimis 

PM2.5 source categories from RACM and 

RACT and additional reasonable 

measures in Moderate PM2.5

nonattainment areas. As discussed 

earlier, a state may rely on receptor or 

dispersion modeling conducted for the 

area as part of its Moderate area 

attainment plan. Alternative or 

additional modeling, including 

screening modeling, or filter analysis 

may also be necessary to identify 

significant contributors to PM2.5 levels 

in the area. More discussion on the 

EPA’s proposal regarding how to 

evaluate source category impacts and 

identify those that are de minimis can 

be found in Section IV.D of this 

preamble. The EPA notes that a state 

may face the same challenges in 

establishing de minimis source 

categories for PM2.5 sources in a Serious 

nonattainment area as it did in 

establishing de minimis source 

categories for PM2.5 sources when the 

area was classified as Moderate. 

Therefore, the EPA seeks comment on 

its proposed options, described in 

Section IV.D, for defining source 

categories and determining the 

appropriate threshold for de minimis 

emissions. The EPA requests that 

commenters submit any relevant data or 

analyses to support their comments. In 

the absence of compelling evidence to 

support establishing a nationallyapplicable ‘‘bright line’’ threshold for 

defining a de minimis source category 

for purposes of implementing the PM2.5

NAAQS in a Serious nonattainment 

area, the EPA would apply a 

presumptive approach allowing a state 

to apply its own reasoned judgment to 

determine whether a particular source 

category should be considered de 

minimis in the event the EPA finalizes 

proposed Option 1 for BACM and BACT 

determinations. 

Step 3: Identify existing and potential 

control measures. After evaluating 

source category impacts to eliminate de 

minimis source categories from further 

consideration, the state would identify 

all existing and potential measures 

(including those measures that were 

rejected in the RACM and RACT 

determination and additional new 

potential measures) for reducing 

emissions from the remaining (i.e., nonde minimis) source categories listed in 

the latest base year emissions inventory 

for the area. For purposes of identifying 

new measures to consider in its BACM 

and BACT analysis, the EPA proposes to 

require that the state conduct a survey 

of other nonattainment areas for the 

PM2.5 NAAQS and other NAAQS (i.e., 

PM10, ozone, SO2 and NOX) both in the 

same state and in other states to identify 

potential control measures that other air 

agencies are implementing, and the state 

must incorporate such measures into the 

list of potential control measures for the 

source categories in the Serious 

nonattainment area. The EPA would 

expect the state to identify an array of 

existing and potential new measures at 

least as broad as that identified for the 

same area as part of the RACM and 

RACT analysis, in order to ensure that 

the state has a sufficiently expansive 

and comprehensive set of potential 

measures to evaluate. Therefore, at a 

minimum, the EPA proposes that the 

list of potential measures must include 

all measures identified as potential 

control measures for the nonattainment 

area when it was classified as Moderate 

or, for a given source category, one or 

more alternative control measures or 

technologies that would control 

emissions even more stringently than 

the measures and technologies included 

in the RACM and RACT analysis. In this 

way, the state will begin its BACM and 

BACT determination with a list of 

potential control options that is as 

complete and up-to-date as possible. 

In addition to identifying existing 

control measures for sources in a 

Serious PM2.5 nonattainment area, a 

state must develop a comprehensive list 

of potential control measures for sources 

in the area. The EPA’s RACT/BACT/

LAER Clearinghouse provides a central 

data base of air pollution technology 

information that may be highly relevant 

to states seeking information on 

stationary source control technology 

that may qualify as BACT for PM2.5

NAAQS implementation, and is 

available online at http://cfpub.epa.gov/ 

RBLC/. There are also other resources 

available to assist states in identifying 

other potential control measures and 

control technologies for their BACM and 

BACT determinations. The EPA 

encourages states with Serious PM2.5

nonattainment areas to visit the agency’s 

Web site to find links to other online 

sources of information on potential 

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188Links are provided to a number of national, 

state and local air quality agency sites from the 

EPA’s PM2.5 Web site: http://www.epa.gov/pm/

measures.html. 

189Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42013. 

190 Ibid. at 42012. 

191 Ibid. at 42013. 

192 Ibid. 

193 Ibid. 

control measures for states to 

consider.188

Specific to potential control measures 

for mobile source emissions, the EPA’s 

past guidance has indicated that where 

mobile sources contribute significantly 

to PM2.5 violations, ‘‘the state must, at 

a minimum, address the transportation 

control measures listed in CAA section 

108(f) to determine whether such 

measures are achievable in the area 

considering energy, environmental and 

economic impacts and other costs.’’ 189

The EPA proposes to retain this 

guidance and require that a state 

include for evaluation as BACM for 

mobile sources those measures listed in 

section 108(f), and the agency seeks 

comment on this specific requirement. 

Step 4: Determine whether an 

available control measure or technology 

is technologically feasible. After 

developing a list of existing and 

potential new measures to evaluate for 

BACM and BACT, the state would then 

need to determine the technological 

feasibility of each identified control 

measure in light of a number of 

considerations, including each 

measure’s individual energy and 

environmental impacts.190

(1) Stationary sources. As described 

under the technological feasibility 

criteria for the control measures analysis 

for Moderate area attainment plans in 

Section IV.D, the EPA’s prior guidance 

on factors to consider for judging 

whether a particular control technology 

is technologically feasible should 

include a source’s processes and 

operating procedures, raw materials, 

physical plant layout and potential 

environmental impacts such as 

increased water pollution, waste 

disposal and energy requirements. For 

example, the EPA recognizes that the 

process, operating procedures and raw 

materials used by a source can affect the 

feasibility of implementing process 

changes that reduce emissions and can 

also affect the selection of add-on 

emission control equipment. The 

feasibility of modifying processes or 

applying control equipment also can be 

influenced by the physical layout of the 

particular plant, if the physical space 

available in which to implement such 

changes limits the choices.191

(2) Area and mobile sources. With 

respect to determining whether a given 

control measure might not be 

technologically feasible as BACM for an 

area or mobile source, the EPA proposes 

that a state may consider factors in 

conducting its analysis that are similar 

to factors the state may have considered 

during the RACM and RACT 

determination process, such as the 

social acceptability of the measure, and 

local circumstances, such as the 

condition and extent of needed 

infrastructure, population size or 

workforce type and habits, which may 

prohibit certain potential control 

measures from being implementable. 

However, in the instance where a given 

control measure has been applied in 

another NAAQS nonattainment area (for 

PM2.5 or other pollutant), the EPA 

proposes that the state will need to 

provide a detailed justification for 

rejecting any potential BACM measure 

as technologically infeasible. 

Furthermore, if the state identifies a 

certain control measure for area or 

mobile sources that has been 

implemented in another nonattainment 

area and may qualify as BACM or BACT 

for the state’s Serious nonattainment 

area, the state must provide a reasoned 

justification if it deems it 

technologically infeasible to implement 

the same control measure to the same 

extent or magnitude as it was applied in 

the other nonattainment area. 

The EPA seeks comment on the 

factors described above for states to 

consider when evaluating the 

technological feasibility of a control 

measure or technology for BACM and 

BACT. 

Step 5: Determine whether an 

available control technology or measure 

is economically feasible. The fifth step 

under this proposed approach is to 

evaluate the costs of implementing each 

of the technologically feasible control 

measures and technologies in order to 

eliminate from further consideration 

any measures determined to be 

economically infeasible. As discussed 

elsewhere in this proposal, in assessing 

‘‘best’’ control measures and 

technologies, states with Serious PM2.5

nonattainment areas must identify a 

control strategy for the area that overall 

is more stringent than that identified for 

the area when the state considered only 

the ‘‘reasonableness’’ of potential 

control measures. Thus the EPA is 

proposing to require states to consider 

emission reduction measures with 

higher costs per ton when assessing the 

economic feasibility of BACM and 

BACT controls (and, where applicable, 

additional feasible measures) as 

compared to the economic feasibility 

criteria applied in their RACM and 

RACT analysis (and analysis for 

additional reasonable measures) for the 

same nonattainment area. 

Indeed, consistent with prior 

guidance on evaluating costs of a 

potential BACM or BACT control, the 

EPA maintains that while the economic 

feasibility of a control measure is as 

important as its technological feasibility 

under the RACM and RACT 

determination process, economic 

feasibility is a less significant factor in 

the BACM and BACT determination 

process. In other words, a state must 

apply a higher standard for eliminating 

a technologically feasible control 

measure from further consideration as 

BACM due to cost alone. 

In the Addendum, the EPA stated that 

‘‘for PM10 BACM purposes, it is 

reasonable for similar sources to bear 

similar costs of emission reduction.’’ 192

Additionally, the EPA indicated that 

‘‘economic feasibility for PM10 BACM 

purposes should focus upon evidence 

that the control technology in question 

has previously been implemented at 

other sources in a similar source 

category without unreasonable 

economic impacts.’’ 193 Thus, a state 

may not eliminate a particular control 

measure from further consideration as 

potential BACM if similar sources have 

successfully implemented such a 

measure. That is, a state must at a 

minimum continue to consider as 

potential BACM any technologically 

feasible control measures or 

technologies implemented by similar 

sources. 

In addition, the EPA seeks to clarify 

that a state may not automatically 

eliminate a particular control measure 

merely because other sources have not 

implemented the measure. In other 

words, a state must continue to consider 

technologically feasible measures that 

have not been implemented by similar 

sources but that can nonetheless 

effectively reduce emissions from the 

source category in question at a cost that 

is not wholly cost prohibitive. 

As with the EPA’s proposed approach 

for evaluating economic feasibility of 

potential reasonable measures for 

Moderate area attainment plans, the 

EPA proposes that for each 

technologically feasible control measure 

or technology, a state must evaluate the 

economic feasibility of the measure or 

control through consideration of the 

capital costs, operating and 

maintenance costs, and cost 

effectiveness (i.e., cost per ton of 

pollutant reduced by that measure or 

technology) associated with such 

measure or control. While the EPA is 

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194These long-standing factors were established 

in EPA guidance in 1992 and are applicable to 

implementation programs for all NAAQS 

pollutants. See the appendices to the General 

Preamble, 57 FR 18070 (April 28, 1992). 

not proposing a fixed dollar per ton cost 

threshold for economic feasibility of 

controls identified as potential BACM 

and BACT, the EPA proposes that the 

threshold should be higher for the 

BACM and BACT analysis than it was 

for the RACM and RACT analysis for the 

same nonattainment area. In addition, if 

a state contends that a source-specific 

control-level should not be established 

because the source(s) cannot afford the 

control measure or technology that is 

demonstrated to be economically 

feasible for purposes of BACM for other 

sources in its source category, the state 

must support the claim with 

information regarding the impact of 

imposing the identified control measure 

or technology on the following financial 

indicators, to the extent applicable: 

1. Fixed and variable production costs 

($/unit); 

2. Product supply and demand 

elasticity; 

3. Product prices (cost absorption vs. 

cost pass-through); 

4. Expected costs incurred by 

competitors; 

5. Company profits 

6. Employment costs; 

7. Other costs (e.g., for BACM 

implemented by public sector entities). 

The EPA seeks comment on the 

factors described above for states to 

consider when determining whether a 

control measure or technology is 

economically feasible as BACM or 

BACT.194

Step 6: Determine the earliest date by 

which a control measure or technology 

can be implemented in whole or in part. 

Section 189(b)(1)(B) requires that 

Serious area attainment plans provide 

for the implementation of BACM no 

later than 4 years after reclassification of 

the area to Serious. As with the EPA’s 

proposed approach to RACM and RACT, 

the EPA proposes the term ‘‘implement’’ 

to mean that the control measure or 

technology has not only been adopted 

into the SIP for the area but has also 

been built, installed and/or otherwise 

physically manifested and the affected 

sources are required to comply. See 

proposed 40 CFR 51.1000. The EPA thus 

expects a state with a Serious 

nonattainment area to take deliberate 

and timely action to implement BACM 

and BACT in the area. The EPA 

proposes that if a state evaluates a 

potential BACM or BACT measure and 

determines that it can be implemented 

only partially within 4 years after 

reclassification, the state must adopt the 

partial measure as BACM. 

The EPA proposes that a state must 

identify those technologically and 

economically feasible control measures 

and technologies that it can implement 

fully or partially within 4 years of 

reclassification of its Serious PM2.5

nonattainment area. These measures 

will be considered BACM and BACT for 

the area. ‘‘Additional feasible measures’’ 

would be ‘‘best’’-level, feasible measures 

that a state could implement in whole 

or in part on sources in the area 

sometime after the fourth year following 

reclassification and prior to the 

statutory attainment date for the area. 

ii. Proposed Option 2. The second 

proposed approach for evaluating 

control measures and technologies and 

determining which qualify as BACM or 

BACT or additional feasible measures 

for a Serious PM2.5 nonattainment area 

would directly link the control strategy 

determination process with the 

attainment demonstration for the area, 

allowing a state to eliminate potential 

measures that are not necessary to 

demonstrate attainment of the relevant 

NAAQS in the area and would not 

collectively advance the attainment date 

for the area by at least 1 year. For this 

second proposed approach, the EPA 

proposes a process similar to the one 

proposed for Moderate area control 

strategy determinations. However, the 

specific potential control measures to be 

evaluated as BACM and BACT and 

additional feasible measures would 

continue to be distinguished by stricter 

criteria to yield a set of control measures 

that reflects an overall higher level of 

stringency in the control strategy for the 

nonattainment area than that provided 

by the implementation of reasonable 

control measures (i.e., RACM and RACT 

and additional reasonable measures). 

Under the EPA’s second proposed 

approach for determining which 

measures must be part of the control 

strategy for a Serious PM2.5

nonattainment area, a state would 

follow many of the same steps as 

described under the EPA’s first 

proposed approach for the such 

determinations, with two important 

differences. First, Step 2 as described 

above would be eliminated from the 

process. That is, after a state updates the 

baseline emissions inventory for sources 

located in the area, the state would be 

required to identify existing and 

potential new measures for all sources 

in the inventory for evaluation as 

potential BACM and BACT and 

additional feasible measures without 

exempting any source categories as de 

minimis. Second, Step 6 as described 

above would not be the last step in the 

control strategy determination process, 

but rather would serve as another 

interim step in the process prior to 

making a final determination of what 

constitutes BACM and BACT and 

additional feasible measures for the area 

through modeling for the attainment 

demonstration. The EPA’s proposed 

requirements for what the state would 

need to evaluate during this step under 

this second proposed approach are 

described in greater detail in the 

following section. 

The EPA emphasizes that proposed 

Option 2 for determining BACM and 

BACT and additional feasible measures 

depends on the state submitting its 

attainment demonstration earlier than 

may otherwise be required under the 

statute so that it can be 

contemporaneous with the submission 

of BACM and BACT measures, due 18 

months after the date of reclassification 

of a PM2.5 nonattainment area to 

Serious. 

Given all of the above, the EPA is 

proposing and seeking comment on a 

second approach for determining BACM 

and BACT and additional feasible 

measures for a Serious PM2.5

nonattainment area comprised of the 

following steps. See proposed 40 CFR 

51.1010(a) for proposed Option 2. Note 

that Steps 1 through 5 would 

incorporate the same considerations and 

requirements as those in the equivalent 

steps described in the EPA’s first 

proposed approach with the two 

important exceptions discussed in the 

preceding section: 

Step 1: Update base year emissions 

inventory for the area. 

Step 2: Identify existing and potential 

control measures for all emissions 

sources in the emissions inventory for 

the area. 

Step 3: Determine whether an 

available control measure or technology 

is technologically feasible. 

Step 4: Determine whether an 

available control measure or technology 

is economically feasible. 

Step 5: Determine the earliest date by 

which a control measure or technology 

can be implemented in whole or in part. 

During this step in the process, the 

state would be required to identify two 

groups of measures. The first group of 

measures would be potential BACM and 

BACT; that is, ‘‘best’’-level, feasible 

measures that the state could implement 

in whole or in part within 4 years of 

reclassification. The second group of 

measures would be additional feasible 

measures, defined as ‘‘best’’-level, 

feasible measures that a state could 

implement in whole or in part on 

sources in the area sometime after the 

fourth year following reclassification 

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195 Ibid. 

and prior to the statutory attainment 

date for the area. 

Step 6: Model to determine the 

attainment date that is as expeditious as 

practicable. As with the proposed 

Moderate area attainment plan control 

strategy analysis, the EPA proposes that 

states would need to model air quality 

impacts to determine the Serious area 

attainment date that is as expeditious as 

practicable for the area. After 

developing an inventory, identifying 

potential measures, determining 

economic and technological feasibility, 

and determining whether a measure 

would be able to be implemented in 4 

years or between 4 years from 

reclassification and the statutory 

attainment date for the area, the state 

would conduct modeling that shows the 

combined air quality impact of all 

BACM and BACT measures and 

additional feasible measures as 

applicable. The purpose of this 

modeling would be to determine the 

attainment date that is as expeditious as 

practicable and to identify whether 

there are certain control measures that 

a state could eliminate from the Serious 

area attainment plan because they 

cannot collectively expedite attainment 

of the area by 1 year or more. A 

complete discussion of the EPA’s 

proposed modeling requirements for 

Serious area attainment demonstration 

is presented in Section VI.E below. 

Step 6a: If area can demonstrate 

attainment by the statutory attainment 

date, then select only those control 

measures needed for expeditious 

attainment as BACM or BACT or 

additional feasible measures. Under this 

second proposed approach to BACM 

and BACT determinations, the EPA 

proposes that if a Serious area will be 

able to demonstrate attainment by the 

statutory Serious area attainment date, 

then the state must adopt all measures 

identified as potential BACM and 

BACT, and additional feasible measures 

if applicable, that will ensure that the 

attainment date is as expeditious as 

practicable. The state may, however, 

reject those potential BACM and BACT 

and additional feasible measures that 

would not collectively contribute to 

emissions reductions that could 

advance the attainment date for the area 

by at least 1 year. 

The EPA recognizes that identifying 

the measures that would not collectively 

advance the attainment date for a 

Serious area by at least 1 year will likely 

be an iterative process that requires 

additional modeling. As with modeling 

for Moderate area attainment 

demonstrations, the EPA believes that 

such extra effort is reasonable for a state 

seeking to reject certain potential BACM 

or BACT or additional feasible measures 

from implementation in a given Serious 

nonattainment area. 

One notable point of discussion in the 

Addendum indicates that short-term 

BACM measures are not preferred by the 

EPA unless such a measure is the only 

way to implement BACM within 4 

years.195 This is because the ultimate 

goal of selection of BACM controls is 

that those measures will prevent future 

emissions, rather than a temporary 

reduction of emissions. Therefore, 

consistent with this previous guidance, 

the EPA proposes that those measures 

that a state must reject first under this 

proposed approach would be those that 

offer only short-term emissions 

reductions. 

Step 6b: If an area cannot 

demonstrate attainment by the statutory 

attainment date, then submit request for 

Serious area attainment date extension 

including adopting MSM. Section 

189(b)(1)(A) of the CAA requires a state 

to submit as part of its Serious area 

attainment plan either a demonstration 

that the plan will provide for attainment 

by the statutory Serious area attainment 

date, or a demonstration that attainment 

by such date is ‘‘impracticable.’’ If the 

state cannot demonstrate attainment 

based on the implementation of all 

BACM and BACT and additional 

feasible measures by the end of the 

tenth calendar year following 

designation of the area, then under 

sections 189(b)(1)(A)(ii) and 188(e), the 

state must submit as part of its Serious 

area attainment plan a complete request 

to extend the attainment date for the 

area that meets the statutory provisions 

of section 188(e) and meets all of the 

regulatory criteria proposed under 

Section VII in this preamble, including 

the evaluation and adoption of MSM. 

The EPA acknowledges that this 

second proposed approach for 

determining BACM and BACT and 

additional feasible measures for a 

Serious area, which would authorize 

states to link the attainment control 

strategy to the attainment needs for an 

area, is different from the approach the 

agency has historically applied to 

BACM determinations for PM10. The 

EPA believes that effectively eliminating 

the step of exempting de minimis source 

categories the beginning of the control 

strategy determination process and 

linking the determination of BACM and 

BACT and additional feasible measures 

with the attainment analysis for a 

Serious area would not be a relaxation 

of the statutory requirement for 

implementation of ‘‘best’’ measures in 

Serious PM2.5 nonattainment areas as 

Congress required in section 

189(b)(1)(B), however. Rather, the 

agency believes that in order to ensure 

that a state develops an appropriately 

stringent control strategy for a Serious 

PM2.5 nonattainment area, it is 

appropriate to require that state to 

identify and evaluate potential control 

measures for all sources of direct PM2.5

emissions and emissions of any PM2.5

precursors not otherwise found to 

contribute insignificantly to PM2.5 levels 

in the area. Eliminating the possibility 

for de minimis source category 

exemptions means that a state’s 

evaluation of potential control measures 

and technologies will be more thorough 

and comprehensive and potentially lead 

to the implementation of controls on a 

wider variety of source categories. 

Additionally, the test of whether the 

potential BACM and BACT and 

additional feasible measures not needed 

for an area to attain the NAAQS by the 

outside statutory attainment date could 

collectively advance the attainment date 

for the area by at least 1 year could 

result in a state implementing such 

measures on source categories which, if 

they had each been evaluated separately 

for purposes of a de minimis source 

category analysis, might have been 

exempted from control. Furthermore, as 

noted earlier in this section, in order for 

the state, the EPA, and the general 

public to be able to fully evaluate 

whether the selected control strategy 

(i.e., BACM and BACT and additional 

feasible measures) will provide for 

expeditious attainment of the NAAQS 

in a Serious PM2.5 nonattainment area, 

the state would be required to submit 

the attainment demonstration for the 

area at the same time as it submits 

provisions to meet the BACM and BACT 

requirement under section 189(b)(1)(B), 

18 months after reclassification of the 

area to Serious. This date would be 

stricter than the statutory due date for 

a Serious area attainment demonstration 

for areas reclassified to Serious under 

the EPA’s discretionary authority of 

section 188(b)(1), which is no later than 

4 years from the date of reclassification 

of the area. 

By defining a process for determining 

BACM and BACT and additional 

feasible measures in a way that is 

similar to the process for determining 

RACM and RACT and additional 

reasonable measures for the same area, 

the EPA believes that a state with a 

Serious PM2.5 nonattainment area may 

be able to conserve resources by relying 

in part on the analytical work performed 

for the RACM and RACT analysis for the 

area when it was classified as Moderate. 

Furthermore, the challenges associated 

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196The EPA believes that it is not necessary to 

identify every possible variation of every type of 

control measure, or all possible combinations of 

technologies and measures that would apply to a 

given source or activity, as long as the state has 

properly characterized the potentially available 

emissions reductions and their costs. For example, 

the EPA believes that the state can conduct a 

thorough analysis of VMT reduction measures 

without including every possible level or stringency 

of implementation of certain possible measures or 

combinations of measures for reducing VMT, so 

long as those measures would not affect the overall 

assessment of VMT reduction capabilities and the 

associated costs. 

197The Menu of Control Measures document is 

available at: http://www.epa.gov/air/criteria.html. 

with properly identifying de minimis 

source categories as described earlier in 

this section may be avoided. Finally, the 

EPA believes that tying the final 

selection of BACM and BACT and 

additional feasible measures to the 

specific attainment needs of a 

nonattainment area could help to focus 

limited air agency resources on control 

measures that are most needed to bring 

a Serious area into expeditious 

attainment for the PM2.5 NAAQS. 

The EPA seeks comment on all 

aspects of both proposed approaches 

and criteria for determining BACM and 

BACT and additional feasible measures 

for a Serious nonattainment area. The 

agency may finalize either of the 

proposed approaches or various 

elements of each after analyzing 

submitted comments. 

3. BACM and BACT Submittal 

Requirements 

To ensure that attainment plan 

submissions contain the necessary 

supporting information for EPA review 

and approval of the state’s selected 

BACM and BACT and additional 

feasible measures as applicable, the EPA 

proposes to require under the authority 

of section 301(a) that a state must 

submit the following information as part 

of its Serious area attainment plan 

submission: 

• A list of all emissions source 

categories, sources and activities in the 

nonattainment area that emit direct 

PM2.5 or any PM2.5 precursor (for multistate nonattainment areas, this would 

include source categories, sources and 

activities from all states which make up 

the area); 

• For each source category, source or 

activity in the nonattainment area, an 

inventory of direct PM2.5 and all PM2.5

precursor emissions; 

• For each source category, source or 

activity in the nonattainment area, a 

comprehensive list of potential control 

measures considered by the state for the 

nonattainment area; 196 197

• For each potential control measure 

considered by the state but eliminated 

from further consideration due to a 

determination by the state that the 

control measure or technology was not 

technologically feasible, a narrative 

explanation and quantitative or 

qualitative supporting documentation to 

justify the state’s conclusion; 

• For each technologically feasible 

emission control measure or technology, 

the state must provide the following 

information relevant to economic 

feasibility: (i) The control efficiency by 

pollutant; (ii) the possible emission 

reductions by pollutant; (iii) the 

estimated cost per ton of pollutant 

reduced; and, (iv) a determination of 

whether the measure is economically 

feasible, with narrative explanation and 

quantitative supporting documentation 

to justify the state’s conclusion; 

• For each technologically and 

economically feasible emission control 

measure or technology, the date by 

which the technology or measure could 

be implemented. 

As with a Moderate area attainment 

plan submission, the EPA recognizes 

that the base year emissions inventory 

for the area that the state submits in 

conjunction with its Serious area 

attainment plan will likely contain the 

information proposed to be required 

under the first two items in this list. 

However, the EPA believes that it is 

incumbent on the state to ensure that 

the information needed for the EPA to 

evaluate the state’s BACM and BACT 

and additional feasible measures 

analysis is presented as part of that 

analysis and in a format that provides 

transparency, consistency and the 

ability for another party to evaluate the 

state’s analysis effectively and to 

duplicate the state’s results. For this 

reason, the EPA is proposing to require 

the state to include the base year 

emissions inventory information with 

the BACM and BACT submittal and as 

one element of the state’s attainment 

plan due 18 months after 

reclassification of the area to Serious. 

4. Criteria for Effective Regulations To 

Implement BACM and BACT and 

Additional Feasible Measures 

As with control measures identified 

as part of a Moderate area’s attainment 

control strategy, after a state has 

identified its BACM and BACT and 

additional feasible measures for a 

particular nonattainment area, it must 

implement those measures through a 

legally enforceable mechanism to be 

included in the SIP. As with Moderate 

area control measures, the EPA is 

proposing that in order for the agency to 

be able to approve any Serious area 

control measure and approve it as part 

of the SIP, the state will have to provide 

information to meet the following four 

criteria. 

First, the base year emissions from the 

source or group of sources to which the 

control measure applies and the future 

year projected emissions from those 

sources once controlled must be 

quantifiable so that the projected 

emissions reductions from the sources 

can be attributed to the specific 

measures being implemented. Once 

again, it is important that the emissions 

from the source category in question are 

accurately represented in the base year 

inventory so that emissions reductions 

are properly calculated. In particular, it 

is especially important to ensure that 

both the filterable and condensable 

components of PM2.5 are accurately 

represented in the base year. 

Second, the control measures must be 

enforceable, meaning that they must 

specify clear, unambiguous and 

measurable requirements. The 

measurable requirements for larger 

emitting facilities must include periodic 

source testing to establish the capability 

of such facilities to achieve the required 

emission level. Additionally, to verify 

the continued performance of the 

control measure, specific emissions 

monitoring programs appropriate for the 

type of control measure employed and 

the level of emissions must be included 

to verify the continued performance of 

the control measure. The control 

measures and monitoring program must 

also have been adopted according to 

proper legal procedures. 

Third, the results of application of the 

control measures must be replicable. 

This means that where a rule contains 

procedures for interpreting, changing or 

determining compliance with the rule, 

the procedures are sufficiently specific 

and objective so that two independent 

entities applying the procedures would 

obtain the same result. 

Fourth, the control measures must be 

accountable. For example, sourcespecific emission limits must be 

permanent and must reflect the 

assumptions used in the attainment 

plan for the area, including the 

modeling conducted in conjunction 

with the attainment demonstration. The 

attainment plan must establish 

requirements to track emissions changes 

at sources and provide for corrective 

action if emissions reductions are not 

achieved according to the plan. 

The EPA seeks comment on these 

criteria for approval of any control 

measures adopted by a state for a 

Serious area to assure that such 

measures are legally enforceable. 

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5. Relevance of Prior BACT, LAER and 

BART Determinations 

The EPA believes that BACT or lowest 

achievable emission rate (LAER) 

provisions for new sources (as distinct 

from BACT for existing sources), or best 

available retrofit technology (BART) for 

existing sources, could qualify as BACM 

or BACT for purposes of meeting the 

Serious area attainment plan 

requirements. However, the EPA does 

not believe it is appropriate for a state 

to assume that just because a certain 

control technology was determined to 

meet BACT, LAER, or BART criteria for 

a new source, such a control will also 

automatically meet the criteria for 

BACM or BACT or additional feasible 

measures for attainment planning 

purposes because the regulated 

pollutant or source applicability may 

differ and the analyses may be 

conducted many years apart. Thus, a 

state may not simply rely on prior 

BACT, LAER or BART analyses for the 

purposes of showing that a source has 

also met BACT for the relevant PM2.5

NAAQS. Rather, the EPA expects that in 

Step 2 of either of the agency’s proposed 

approaches to the BACM and BACT 

determination process, the state would 

identify such measures as ‘‘existing 

measures’’ that should be further 

evaluated as potential BACM or BACT 

or additional feasible measures. 

6. Multi-State Nonattainment Areas 

States that share a multi-state Serious 

PM2.5 nonattainment area must consult 

with one another on BACM and BACT 

and additional feasible measures that 

will be required for the nonattainment 

area in the different states. This 

requirement would be consistent with 

the overall requirements for BACM and 

BACT and additional feasible measures 

determinations, as all states with 

Serious areas need to consider 

implementing BACM and BACT-level 

measures that have been implemented 

in other states, even if those measures 

incur higher costs. The EPA anticipates 

that states may potentially adopt 

controls that differ from state to state, 

based upon each state’s determination 

of what qualifies as ‘‘best’’ given the 

mixture of sources and potential 

controls in the state portions of relevant 

nonattainment areas, subject to EPA 

approval. If the state can adequately 

demonstrate that its chosen BACM and 

BACT and additional feasible measures 

fully meet the EPA’s proposed criteria 

for such measures, then the agency may 

consider approving individual state 

plans that differ in implementation of 

control measures. 

7. Environmental Justice Considerations 

for Developing the Attainment Plan 

Control Strategy for a Serious PM2.5

Nonattainment Area 

The EPA strongly urges states to 

consider the environmental justice 

aspect of any control measures they 

have identified as BACM and BACT or 

additional feasible measures. Because 

the criteria for determining BACM and 

BACT will lead in most cases to the 

selection of an overall more stringent 

control strategy in a Serious area than 

what RACM and RACT could provide, 

an appropriate control strategy for a 

Serious nonattainment area will likely 

implicitly include the best measures for 

ensuring that overburdened populations 

are appropriately protected. 

Nonetheless, the EPA encourages states 

when possible to select BACM and 

BACT measures that will result in the 

least possible burden and greatest 

degree of health protection for 

overburdened populations in the 

nonattainment area. 

E. Modeling for Attainment 

Demonstrations 

Section IV.E. describes the EPA’s 

proposed attainment demonstration and 

modeling requirements for Moderate 

area plans, and the EPA is proposing 

that the same general requirements 

should apply to Serious area attainment 

demonstrations. However, Serious area 

plans have additional statutory 

requirements, which the EPA proposes 

to address as described below. 

1. Statutory Requirements 

Section 189(b) generally requires a 

state with a designated Serious 

nonattainment area to submit an 

attainment plan for such area. As 

discussed earlier, section 189(b)(1)(A) 

more specifically requires the state to 

submit an attainment demonstration 

including air quality modeling to 

establish either: (i) That the area will 

attain the relevant NAAQS by the 

applicable attainment date, or (ii) if the 

state is seeking an extension of the 

attainment date, that it is impracticable 

for the area to attain the relevant 

NAAQS by the statutory Serious area 

attainment date. For Serious 

nonattainment areas, the attainment 

date is as expeditiously as practicable, 

but no later than the end of the tenth 

calendar year after designation as 

nonattainment. An attainment 

demonstration that shows that it is 

impracticable for the area to attain 

within this timeframe must also provide 

for attainment of the NAAQS by the 

most expeditious alternative date 

practicable, but no later than 5 years 

after the maximum statutory Serious 

area attainment date (based on the 

criteria specified in section 188(e)). 

Attainment demonstrations are due 18 

months after reclassification if the EPA 

reclassifies the area to Serious after 

failure of the area to attain the 

applicable Moderate area deadline. 

Alternatively, section 189(b)(2) requires 

states with designated Serious 

nonattainment areas to submit 

attainment demonstrations no later than 

4 years after reclassification of the area 

to Serious if the reclassification occurs 

before the Moderate area attainment 

deadline. However, the EPA is 

proposing an approach for determining 

an appropriate attainment plan control 

strategy for a Serious PM2.5

nonattainment area that would require 

the state to submit the attainment 

demonstration for the area within 18 

months after reclassification regardless 

of when or the authority under which 

an area was reclassified to Serious. 

Sections VI.A and VI.D of this preamble 

describe more fully the EPA’s proposed 

approach for control strategy analyses 

and due dates for all elements of a 

Serious area attainment plan. Section 

VI.J of this preamble provides a 

complete discussion of the EPA’s 

proposed criteria for granting a Serious 

area attainment date extension. 

2. Attainment Demonstrations for 

Serious Areas 

As described in Section IV.E of this 

preamble, an attainment demonstration 

is a plan that demonstrates how a state 

will attain the PM2.5 NAAQS by the 

applicable attainment date. The EPA is 

proposing that the demonstration for 

Serious areas must consist of: (i) 

Technical analyses such as base year 

and future year modeling of emissions 

which identify sources and quantify 

emissions that are contributing to 

violations of the PM2.5 NAAQS; and, (ii) 

analyses of future year projected 

emissions reductions and air quality 

improvement resulting from existing 

(i.e. already-adopted or ‘‘on the books’’) 

national, regional and local programs, 

and potential new local measures 

needed for attainment, including RACM 

and RACT and BACM and BACT 

controls for the area, as well as other 

measures either inside the 

nonattainment area or outside the 

nonattainment area but within the state 

that could potentially accelerate 

attainment. Each state with a Serious 

nonattainment area must submit an 

attainment plan with an attainment 

demonstration that includes analyses 

supporting the state’s determination of 

its proposed attainment date. In all 

cases, the state must show that the area 

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198Note that for purposes of the PM2.5 NAAQS, 

a determination of attainment (or failure to attain), 

which the EPA is required to make after the 

attainment date has passed, is based on ambient 

data from the most recent 3 years prior to the 

attainment date for the area. 

will attain the NAAQS as expeditiously 

as practicable, but not later than the 

tenth calendar year after designation. In 

order to establish that the attainment 

date is as expeditious as practicable, the 

state must explain why the control 

measures adopted in the attainment 

plan provide for the most expeditious 

attainment and must either: (i) Under 

proposed Option 1 for the BACM and 

BACT determination include all BACM 

and BACT controls in the analysis, or 

(ii) under proposed Option 2 for BACM 

and BACT, provide the requisite 

analysis to show that implementation of 

additional emissions controls, including 

any potential BACM and BACT, would 

not advance the attainment date for the 

area by at least 1 year if considered 

collectively. 

A state with a Serious nonattainment 

area can also submit an impracticability 

demonstration (under section 

189(b)(1)(A)(ii)) as part of seeking an 

extension of the attainment date under 

section 188(e). The impracticability 

demonstration for a Serious area would 

be similar to an impracticability 

demonstration for Moderate areas 

because it must include air quality 

modeling which shows that the area 

will not be able to attain the PM2.5

NAAQS by the outside statutory 

attainment date, which in this case is by 

the end of the tenth calendar year 

following designation. However, in 

order to support a Serious area 

impracticability demonstration, the state 

must also show (through modeling) that 

attainment cannot be reached by the 

statutory Serious area attainment date, 

even if all RACM and RACT and BACM 

and BACT controls, as well as other 

measures either inside the 

nonattainment area or outside the 

nonattainment area but within the state, 

were implemented before the attainment 

date. Moreover, in addition to the 

Serious area impracticability 

demonstration, to support an extension 

of the attainment date, the Serious area 

plan must demonstrate (again, using air 

quality modeling) that it provides for 

attainment by the most expeditious 

alternative date practicable employing 

MSM, as specified in section 188(e). As 

a result, the required plan is both an 

impracticability demonstration (to 

justify an extension beyond the 

statutory attainment date) and an 

attainment demonstration which serves 

as the basis for proposing an appropriate 

alternative attainment date. 

3. What modeling is required? 

States are required to submit air 

quality modeling in support of an 

attainment demonstration for a Serious 

PM2.5 nonattainment area. Unlike the 

impracticability demonstration for 

Moderate areas described in section 

189(a)(1)(B)(ii), the impracticability 

demonstration for Serious areas in 

section 189(b)(1)(A)(ii) also requires air 

quality modeling establishing the most 

expeditious alternative attainment date 

practicable. Therefore, air quality 

modeling is a required element in all 

attainment demonstrations for Serious 

areas. 

Other than the timing of plan 

submissions and additional required 

elements of a Serious area plan (such as 

BACM and BACT), the relevant air 

quality modeling procedures and 

guidance for Moderate and Serious area 

plans are the same. See Section IV.E. of 

this preamble for more details on 

proposed modeling requirements and 

guidance for all PM2.5 nonattainment 

areas. 

4. Will areas reclassified to Serious need 

to submit two separate attainment 

demonstrations? 

Under section 189(a)(1)(B), a state is 

required to submit as part of an area’s 

Moderate area attainment plan a 

demonstration that the area either will 

attain or cannot practicably attain the 

NAAQS by the statutory Moderate area 

attainment date. Regardless of whether 

the state submits an attainment 

demonstration or an impracticability 

demonstration for a Moderate area, if 

such area is reclassified to Serious prior 

to or after failing to attain the applicable 

NAAQS, the state is required under 

section 189(b)(1)(A) to submit a new 

attainment demonstration as part of an 

area’s Serious area attainment plan. The 

separate statutory requirements for 

Moderate and Serious nonattainment 

areas anticipate two separate attainment 

plan submissions, and the EPA’s 

existing guidance in the General 

Preamble and Addendum further 

support this expectation. While the state 

would be required to submit a separate 

Serious area attainment plan, the EPA 

anticipates that certain control strategies 

may build upon those previously 

adopted and implemented as part of the 

Moderate area plan. For example, it 

could be the case that an area 

dominated by woodsmoke emissions 

could not attain the standard by the 

statutory Moderate area attainment date 

because all necessary woodstove 

change-outs could not occur in that 

timeframe, but additional woodstove 

change-outs could occur by the statutory 

Serious area attainment date. 

5. What future year(s) should be 

modeled in attainment demonstrations? 

A state performing a modeling 

analysis for an attainment 

demonstration or a Serious area 

impracticability analysis must select a 

future year for the analysis. For an 

attainment demonstration, a state 

should select the future modeling year 

such that all emissions control measures 

relied on for attainment will have been 

implemented by the beginning of that 

year. To demonstrate attainment, the 

modeling results for the nonattainment 

area must predict that emissions 

reductions implemented by the 

beginning of the last calendar year 

preceding the attainment date will 

result in PM2.5 concentrations that meet 

the level of the standard.198

While states should choose the future 

modeling year based on a number of 

factors, the EPA recommends the last 

year of the statutory attainment date as 

a starting point for modeling for two 

reasons. First, a state with a Serious area 

for which it submits an attainment date 

extension request under section 188(e) 

must show that the area cannot 

practicably attain the NAAQS by the 

end of the tenth calendar year following 

designation of the area. Therefore, the 

appropriate future modeling year for 

making such a demonstration would be 

the tenth year after designations. Even if 

a state does not submit (or does not 

intend to submit) a Serious area 

attainment date extension request, 

modeling the tenth year is a logical 

starting point to determine if attainment 

by year 10 is likely. If attainment-level 

concentrations of PM2.5 are not expected 

in the tenth calendar year after 

designations, then the area must also, as 

a requirement to receive an extension of 

the Serious area attainment date, submit 

a demonstration (using air quality 

modeling) that provides for attainment 

by the most expeditious alternative date 

practicable, but no later than the end of 

the fifteenth year after designation, with 

the implementation of MSM (see 

Section VI.J of this preamble for details 

about MSM determinations). 

Second, even though attainment of 

any PM2.5 NAAQS is determined based 

on 3 years of ambient data, states do not 

have to model 2 years before the 

attainment date to show modeled 

attainment. Since the design value is an 

average of the annual or 98th percentile 

value for 3 consecutive years, 

attainment can still be shown even if 

concentrations exceed the NAAQS in 

one or more of the 3 years used to 

determine attainment (as long as the 

average of the 3 annual values is less 

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199States with Serious areas that request an 

attainment date extension beyond 10 years must 

model the tenth year after designation of the area 

as part of an impracticability demonstration, plus 

an additional year beyond that which represents the 

attainment date. 

200For more information on PM2.5 precursor 

requirements, see section 93.102(b)(2)(iv) and (v) of 

the transportation conformity rule. See also the May 

6, 2005, final transportation conformity rule that 

addressed requirements for PM2.5 precursors. (70 FR 

24280). 

201A state would also establish motor vehicle 

emissions budgets for an area’s attainment year. 

Those budgets would be the motor vehicle 

emissions that the SIP establishes as being 

necessary to attain the NAAQS. 

202 If an area includes re-entrained road dust in 

the motor vehicle emissions budget, the latest 

approved version of AP–42 should be used unless 

the EPA has approved an alternative model for the 

area. 

than the NAAQS). Therefore, it can be 

appropriate to model any of the 3 years 

used to determine attainment. For these 

reasons, it is acceptable, and may in fact 

be most efficient, for a state to begin the 

Serious area attainment demonstration 

process by modeling the final year of the 

statutory attainment date to determine 

future year modeled PM2.5

concentrations in the tenth year after 

designations. 

Because an area must attain ‘‘as 

expeditiously as practicable,’’ additional 

considerations are necessary before an 

attainment date can be established. For 

purposes of determining the attainment 

date that is as expeditious as 

practicable, the state must conduct 

future year modeling which takes into 

account growth and known controls 

(including any controls that were 

previously determined to be RACM and 

RACT for the area). For example, for an 

area designated nonattainment for the 

2012 PM2.5 NAAQS during the first 

round of designations and subsequently 

reclassified to Serious, a future case 

scenario for the year 2025 (10 years after 

the initial nonattainment designation) 

would be needed to examine whether 

the the BACM and BACT identified by 

the state would result in attainment. 

Under the proposed BACM and BACT 

determination Option 1 (where BACM 

and BACT must be determined 

independent of the attainment 

demonstration for the area), the future 

case scenario must include BACM and 

BACT controls in the analysis plus any 

additional measures on sources inside 

and outside of the nonattainment area 

(but within the state) that the state has 

identified as feasible to implement by 

the attainment date. Under proposed 

Option 2 for determining BACM and 

BACT (where BACM and BACT is 

determined according to what is needed 

to expeditiously attain the NAAQS), the 

future case scenario must show whether 

implementation of emissions controls, 

including all BACM and BACT and 

additional feasible measures on sources 

inside and outside of the nonattainment 

area (but within the state), collectively 

would advance the attainment date by at 

least 1 year. Note that similar to RACM 

and RACT, BACM and BACT controls 

must be implemented within 4 years 

after reclassification to Serious 

nonattainment. In order to justify an 

extension of the attainment date beyond 

the end of the tenth year after 

designation, the state must show that 

attainment by that date (including the 

anticipated emissions reductions from 

RACM and RACT and additional 

reasonable measures, and BACM and 

BACT and additional feasible measures) 

would be impracticable. Any proposed 

attainment date after the 10 year period 

must include modeling of BACM and 

BACT controls plus the most stringent 

measures that are included in the 

implementation plan of any state and 

can be feasibly implemented in the area. 

The attainment date extension beyond 

10 years can be for up to 5 additional 

years, but the proposed attainment date 

must also be shown to be as expeditious 

as practicable. Section VI.J of this 

preamble provides a complete 

discussion of the EPA’s proposed 

interpretation of the statutory 

requirements for a Serious area 

attainment date extension under section 

188(e). 

As with Moderate area attainment 

demonstrations, the EPA believes that it 

is not necessary or reasonable to require 

states to model each and every year to 

determine the appropriate attainment 

date for a Serious PM2.5 nonattainment 

area given the resource demands 

associated with modeling.199 In some 

cases it may be reasonable to model one 

additional interim year before the 

maximum statutory attainment date. 

However, in most cases, the air quality 

benefits of an identified set of 

reasonable control measures, BACM and 

BACT and additional feasible control 

measures can be estimated through 

model sensitivity analyses and the 

development of transfer factors (factors 

to relate tons of emissions reductions in 

the area to PM2.5 concentration changes 

in the area). The EPA strongly 

recommends that states discuss the 

selection of the future year(s) to model 

with their respective EPA Regional 

Office as part of the modeling protocol 

development process prior to embarking 

on the modeling. 

6. Attainment Year Motor Vehicle 

Emissions Budgets 

As with Moderate areas, the 

transportation conformity rule requires 

that Serious area attainment plans 

establish motor vehicle emissions 

budgets for the area’s attainment year. 

Therefore, once a Serious area’s 

attainment date has been established, 

the state is required to establish motor 

vehicle emissions budgets for direct 

PM2.5 and any relevant PM2.5 precursor 

for the attainment year.200 A motor 

vehicle emissions budget for the 

purposes of a Serious area PM2.5

attainment plan is that portion of the 

total allowable emissions within the 

nonattainment area allocated to on-road 

sources as defined in the submitted 

attainment plan.201 Such motor vehicle 

emissions budgets would be calculated 

using the latest planning assumptions 

and the latest approved motor vehicle 

emissions model available at the time 

that the attainment plan is 

developed.202

F. RFP Requirements 

1. Statutory Requirements 

As with Moderate area attainment 

plans, Serious PM2.5 nonattainment area 

plans must provide for RFP as required 

under CAA section 172(c)(2). Section 

IV.F of this preamble fully describes the 

statutory requirements and overall 

proposed approaches for states to fulfill 

the RFP requirement in the context of 

Moderate area attainment plans. The 

EPA believes that the proposed 

approaches described for RFP for 

Moderate area plans can apply to 

Serious area attainment plans as well. 

The following section offers additional 

detail about how the EPA proposes that 

the approach to RFP should apply 

specifically to Serious area attainment 

plans. 

2. Proposed Approach 

As with a Moderate area attainment 

plan, the EPA is generally proposing 

that a state must submit an RFP plan as 

part of any attainment plan submission 

for a Serious nonattainment area in 

order to satisfy the statutory 

requirements for RFP. The plan must 

include a schedule and an analysis that 

collectively demonstrate when and 

through what control measures 

emissions from sources in the 

nonattainment area will decline from 

the applicable baseline year to the 

projected attainment year. The EPA is 

proposing that the applicable baseline 

year must be the same year as that 

represented by the latest base year 

inventory for the Serious area. The 

projected attainment year may be up to 

the end of the tenth year following 

designation of the area for a Serious area 

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203As noted in Section VI.B of this preamble, 

depending upon when the area is reclassified from 

Moderate to Serious, this base year inventory may 

need to be more recent than the inventory 

submitted with the Moderate area attainment plan. 

204 If an area includes re-entrained road dust in 

the motor vehicle emissions budget, the latest 

approved version of AP–42 should be used unless 

the EPA has approved an alternative model for the 

area. 

205Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42016. 

that can demonstrate attainment 

pursuant to section 189(b)(1)(A), or up 

to the end of the fifteenth year following 

designation for a Serious area that is 

seeking an extension to the statutory 

attainment date pursuant to section 

188(e).203 The RFP analysis must clearly 

convey how the schedule for 

implementing BACM and BACT and 

any additional control measures will 

provide for generally linear progress 

towards attainment or, if step-wise 

progress is more appropriate for the 

specific nonattainment area in question, 

the analysis must convey an appropriate 

implementation schedule and must 

explain why generally linear progress 

towards emissions reductions in the 

area is not appropriate (e.g., due to the 

nature of the nonattainment problem 

and the types of sources contributing to 

PM2.5 levels in the area). For a Serious 

area that cannot demonstrate attainment 

by the statutory Serious area attainment 

date, the EPA proposes that the state 

must include in its RFP analysis the 

anticipated emissions reductions 

expected to be achieved through the 

implementation of BACM and BACT 

and MSM on sources in the 

nonattainment area. As with RFP plans 

for Moderate areas, the EPA proposes 

that a state must submit one or more 

projected emissions inventories as part 

of the RFP plan for any Serious PM2.5

nonattainment area following the same 

guidance that applies to emissions 

inventories for attainment plans (see 

Section VI.B of this preamble for a 

complete discussion of emissions 

inventories for Serious area attainment 

plans). These projected inventories must 

correspond with the quantitative 

milestone date(s) for the area as 

described in Section VI.H of this 

preamble. The EPA proposes that motor 

vehicle emissions budgets must also be 

established for direct PM2.5 and any 

relevant PM2.5 precursor using the latest 

planning assumptions and the latest 

approved motor vehicle emissions 

model available at the time that the 

Serious area attainment plan is 

developed.204

The EPA seeks comment on all 

aspects of the agency’s proposal for 

meeting the statutory RFP requirements 

as they apply to Serious nonattainment 

areas. Furthermore, the EPA seeks 

comment on the proposed options 

described in Section IV.F of this 

preamble regarding how to prepare an 

RFP plan, geographic coverage of 

emission sources for RFP, and RFP 

requirements for multi-state 

nonattainment areas, which would also 

apply to Serious area attainment plans. 

G. Quantitative Milestones 

The attainment plan for any Serious 

nonattainment area must include 

quantitative milestones pursuant to 

section 189(c). These quantitative 

milestones would be in addition to 

those identified in the area’s Moderate 

area attainment plan, and would need to 

continue to be achieved every 3 years 

until the area attains the NAAQS. 

Specifically, the Serious area plan for an 

area that can demonstrate attainment by 

the statutory Serious area attainment 

date would have to contain quantitative 

milestones to be achieved by 7.5 years 

from the area’s date of designation as 

nonattainment. This date would be 3 

years after the first quantitative 

milestones for the area, to be met 4.5 

years from designation of the area and 

3 years after the Moderate area 

attainment plan was due to the EPA. 

The EPA also proposes and seeks 

comment on a requirement that a 

Serious area plan for an area that can 

demonstrate attainment by the statutory 

Serious area attainment date must also 

include quantitative milestones to be 

reached 10.5 years from designation, to 

help assess the state’s progress toward 

attaining the PM2.5 NAAQS in the event 

the area fails to attain by the applicable 

attainment date. For a Serious area that 

cannot demonstrate attainment by the 

statutory Serious area attainment date, 

the EPA proposes that the state must 

include in the Serious area attainment 

plan quantitative milestones to be 

achieved at years 7.5, 10.5 and 13.5 

from the area’s date of designation. 

The Addendum included guidance 

that recommended milestones ‘‘should 

be addressed by quantifying and 

comparing the annual incremental 

emission reductions which result from 

implementation of BACM and BACT 

(required within 4 years after the area is 

reclassified as serious) and from 

additional measures included in the 

final serious area SIP to those 

reductions which were identified in the 

SIP as quantitative milestones necessary 

to achieve the NAAQS by the applicable 

attainment date.’’ 205

The EPA continues to agree with the 

fundamental concept conveyed in the 

existing guidance, but believes that it is 

impractical to expect that a state will 

always be able to quantify and compare 

real and projected emissions reductions, 

and submit a report to the EPA within 

90 days of a given milestone, as required 

under section 189(c)(2). Therefore, the 

EPA proposes that the general proposed 

approach to selecting quantitative 

milestones, described in Section IV.G, 

should apply to any attainment plan for 

a PM2.5 nonattainment area, 

independent of its classification. 

Specifically, the EPA proposes that 

states be allowed to select the 

quantitative milestones that they 

identify as appropriate and quantifiable 

and that will provide for objective 

evaluation of progress toward 

attainment in their Serious PM2.5

nonattainment area, and that the EPA, 

in its attainment plan approval process, 

will determine if they satisfy the 

statutory requirements of section 189(c). 

In addition to this general proposed 

approach for selecting quantitative 

milestones and similar to an option 

proposed for Moderate area attainment 

plans, the EPA proposes to require that, 

at a minimum, states must include in all 

attainment plans for Serious PM2.5

nonattainment areas a measure to 

confirm that some specific portion of 

BACM and BACT for the area has been 

implemented as appropriate in order to 

comply with the statutory requirement 

at section 189(b)(1)(B). The EPA 

acknowledges that the precise 

quantifiable metric (e.g., 50 percent of 

BACM and BACT measures 

implemented by milestone date 7.5 

years from designation) would need to 

be determined on a case-by-case basis, 

as it would depend upon the date of 

reclassification of the area, whether the 

metric is to be achieved at year 7.5 or 

year 10.5 from designation, and the 

anticipated implementation timing and 

nature of the BACM and BACT controls 

themselves. Nonetheless, the EPA 

believes it would be appropriate to 

include it as a metric that any state with 

a Serious nonattainment area must 

adopt as a quantitative milestone to 

demonstrate RFP (and thus must 

demonstrate compliance with when 

they submit their milestone report), as it 

derives from a statutory provision that 

applies to all Serious areas and thus 

represents a milestone that all Serious 

nonattainment areas must meet. 

The EPA seeks comment on these 

proposed options for interpreting the 

statutory quantitative milestone 

requirements for Serious areas. 

H. Contingency Measures 

As noted in Section IV.G of this 

preamble, all PM2.5 nonattainment areas 

must include in their attainment plans 

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206See LEAN v. EPA, 382 F.3d 575 (5th Cir. 

2004). 

207Addendum to General Preamble, 59 FR 41988 

(August 16, 1994), at 42015. 

208 Id. 

contingency measures consistent with 

section 172(c)(9). Contingency measures 

are additional control measures to be 

implemented in the event that an area 

fails to meet RFP requirements or fails 

to attain the PM2.5 standard by the 

applicable attainment date. These 

measures must be fully adopted rules or 

control measures that are ready to be 

implemented quickly upon a 

determination by the EPA that the area 

failed to meet RFP or failed to meet the 

standard by the applicable attainment 

date, and such measures are required to 

take effect without significant further 

action by the state or the EPA. 

The statutory contingency measure 

requirement at section 172(c)(9) is not 

superseded or subsumed by any 

requirement under subpart 4, nor does 

it apply only to Moderate area 

attainment plans. Thus, contingency 

measures are required for Serious PM2.5

nonattainment areas as part of a state’s 

Serious area attainment plan 

submission. The EPA proposes that the 

criteria for identifying and selecting 

contingency measures for a Serious area 

attainment plan should be the same as 

those for Moderate area plans. 

Specifically, the EPA proposes that the 

following requirements must be met in 

order for contingency measures to be 

approvable as part of a state’s Serious 

area attainment plan submission: 

1. Contingency measures must be 

fully adopted rules or control measures 

that are ready to be implemented 

quickly upon a determination by the 

Administrator of the nonattainment 

area’s failure to meet RFP or failure to 

meet the standard by its attainment 

date. 

2. The SIP must contain trigger 

mechanisms for the contingency 

measures, specify a schedule for 

implementation, and indicate that the 

measures will be implemented without 

significant further action by the state or 

by the EPA. 

3. Contingency measures must consist 

of control measures that are not 

otherwise included in the control 

strategy for the SIP, or must require 

further implementation of partial 

measures already included in the SIP as 

BACM or BACT, additional feasible 

measures, or MSM. 

4. Contingency measures must 

provide for emissions reductions 

equivalent to 1 year’s share of 

reductions needed to demonstrate 

attainment (i.e., the overall needed 

reductions divided by the number of 

years from the base year to the 

attainment year), or equivalent to 1 

year’s worth of air quality improvement 

or emissions reductions proportional to 

the overall amount of air quality 

improvement or emissions reductions to 

be achieved by the area’s attainment 

plan. 

The EPA further proposes that a state 

may elect to rely on contingency 

measures that achieve emissions 

reductions on sources located outside 

the nonattainment area, but within the 

state, as well as from within the 

nonattainment area, provided that the 

measures on sources outside the 

designated nonattainment area are 

demonstrated to produce the 

appropriate air quality impact within 

the nonattainment area. 

As with contingency measures for 

Moderate nonattainment areas, the EPA 

believes it appropriate that a state might 

rely on additional reductions in the 

years following a failure to meet RFP 

requirements or a failure to attain the 

NAAQS by the applicable attainment 

date from federal or local measures 

already scheduled for implementation 

as part or all of their contingency 

measures. The EPA could potentially 

consider such measures as meeting the 

contingency measure requirement as 

long as they produce emissions 

reductions in excess of those required to 

meet other statutory provisions, such as 

to meet BACM and BACT requirements, 

and they can be relied on to achieve a 

sufficient portion of the actual 

emissions reductions necessary to 

reduce emissions in the area while the 

state develops a new plan to bring the 

area into attainment.206 As with 

contingency measures for Moderate area 

attainment plans, the EPA proposes that 

the emissions reductions associated 

with contingency measures for Serious 

area plans must be equal to 

approximately 1 year’s worth of 

emissions reductions necessary to 

achieve RFP for the area, unless the 

state adequately demonstrates that some 

smaller amount of reductions is 

appropriate while the state is revising 

its attainment plan for the area. The 

EPA seeks comment on this 

requirement. 

The Addendum provided guidance 

related specifically to the selection and 

implementation of contingency 

measures for Serious nonattainment 

areas. First, the EPA guidance indicated 

that ‘‘for those moderate areas 

reclassified as serious, if all or part of 

the moderate area plan contingency 

measures become part of the required 

serious area control measures (i.e., 

BACM), then additional contingency 

measures must be submitted whether or 

not the previously submitted 

contingency measures had already been 

implemented. Further, the affected 

states must ensure that serious areas 

have adequate contingency measures 

considering, among other things, new 

information about the potential 

attainment shortfall for the newly 

reclassified serious area.’’ 207 The EPA 

continues to believe that this approach 

to the statutory contingency measure 

requirement is appropriate and proposes 

to adopt it for purposes of implementing 

the PM2.5 NAAQS in Serious 

nonattainment areas. 

With regard to the timing for 

implementing contingency measures, 

the EPA reiterates that the purpose of 

contingency measures is to ensure that 

corrective measures are put in place 

automatically at the time that the EPA 

makes a determination that an area has 

failed to meet RFP or failed to meet the 

NAAQS by the applicable attainment 

date. For any nonattainment area, the 

EPA is required to determine within 90 

days after receiving a state’s RFP 

demonstration, and within 6 months 

after the attainment date for an area, 

whether the state has met their statutory 

obligations for demonstrating RFP or 

attaining the standard, as appropriate. 

As with Moderate areas, the EPA 

believes that contingency measures 

should become effective for Serious 

areas within 60 days of the EPA making 

its determination that the area failed to 

meet RFP or attain the NAAQS and 

proposes to require this for purposes of 

PM2.5 NAAQS implementation in 

Serious nonattainment areas. 

Finally, while section 172(b) gives 

discretion to the Administrator to 

establish a deadline for submitting 

contingency measures up to 3 years 

from designation of the area, it does not 

explicitly address the appropriate 

submittal date for contingency measures 

for areas reclassified to Serious. In the 

Addendum, the EPA indicated that 

‘‘states must submit contingency 

measures for serious areas or otherwise 

demonstrate that adequate measures are 

in place within 3 years of 

reclassification.’’ 208 The EPA proposes 

and seeks comment on applying this 

guidance to Serious nonattainment areas 

for current and future PM2.5 NAAQS. 

In addition, as described in Section 

VI.A, the EPA proposes an alternative 

submission deadline for Serious area 

contingency measures that would align 

the contingency measure due date with 

the Serious area attainment 

demonstration due date. If an area is 

reclassified under the EPA’s 

discretionary authority, the Serious area 

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15418 Federal Register / Vol. 80, No. 55 / Monday, March 23, 2015 / Proposed Rules 

209The EPA believes that there is no real effect 

on attainment date determinations due to the small 

difference in statutory language in section 188(c) 

basing the Moderate area attainment date on the 

‘‘sixth calendar year after the area’s designation’’ 

and the Serious area attainment date on the ‘‘tenth 

calendar year beginning after the area’s 

designation,’’ (emphasis added). 

210Notably, these statutory criteria do not include 

specific ambient air quality criteria like the criteria 

that need to be met in the year prior to a Moderate 

area attainment date in order for the area to qualify 

for an attainment date extension under section 

188(d). 

attainment demonstration is due 4 years 

from the date of reclassification; under 

this alternative proposed approach, 

contingency measures would also be 

due 4 years from the date of 

reclassification for such areas. If an area 

is reclassified under the EPA’s 

mandatory duty upon failure of the area 

to attain the NAAQS by the Moderate 

area attainment date, then the Serious 

area attainment demonstration is due 18 

months from the date of reclassification; 

accordingly, under this alternative 

proposed approach, contingency 

measures would also be due 18 months 

from the date of reclassification for such 

an area. In either case, the BACM and 

BACT provisions for the Serious area 

would be due at or before the time 

contingency measures would be due, 

which is appropriate given that the EPA 

expects a state to consider its BACM 

and BACT measures as it develops its 

contingency measures. The state may 

ascertain that measures not otherwise 

required or necessary for BACM or 

BACT may nevertheless be suitable for 

purposes of contingency measures. The 

EPA seeks comment on this alternative 

approach to setting Serious area 

contingency measure due dates. 

I. Attainment Dates 

As explained earlier, section 188 

establishes the attainment dates for both 

Moderate and Serious areas. For a 

Serious area, section 188(c)(2) provides 

that ‘‘the attainment date shall be as 

expeditiously as practicable but no later 

than the end of the tenth calendar year 

beginning after the area’s designation as 

nonattainment.’’ 209 For example, for an 

area initially designated as 

nonattainment effective in April 2015 

that is reclassified to Serious at some 

future date, the Serious area attainment 

date, absent any approved Serious area 

attainment date extension, would be no 

later than December 31, 2025 (the end 

of the tenth calendar year after 

designation). As discussed in Section 

IV.I, the EPA proposes to interpret the 

references to ‘‘designation’’ in CAA 

section 188(c) as meaning ‘‘effective 

date of designation,’’ consistent with the 

agency’s prior approach for 

implementing the previous PM2.5

NAAQS under subpart 1 and other 

NAAQS. 

The process for a state to determine 

the most expeditious attainment date 

practicable for a Serious area will 

depend upon the final approach 

selected for determining BACM and 

BACT for the area. Therefore the EPA is 

proposing two approaches for 

determining the appropriate attainment 

date for a Serious area. Under the first 

approach, which would correspond to 

the agency’s proposed Option 1 for 

determining BACM and BACT— 

independent of the attainment 

demonstration for the area—the state 

would simply include the control 

measures determined to be BACM and 

BACT for the area in its air quality 

modeling, and would report the results 

of the modeling, including the earliest 

projected attainment date. 

Under the second proposed approach, 

which would correspond to the EPA’s 

proposed Option 2 for determining 

BACM and BACT—tied to the 

attainment needs of the particular 

nonattainment area—the state would be 

required to follow a two-step process for 

determining the appropriate attainment 

date for the area. First, the state would 

be required to demonstrate through air 

quality modeling that the area can attain 

the relevant NAAQS by the latest 

statutory attainment date and determine 

which control measures and 

technologies are needed for the area to 

attain by that date. Second, the state 

would be required to determine whether 

implementing any remaining BACM or 

BACT controls (i.e., those not needed 

for attainment by the latest date) or any 

other additional controls can 

cumulatively advance the attainment 

date for the area by at least 1 year. In 

the event that a state determines that the 

area can attain the relevant NAAQS 

earlier through the application of these 

other measures, the state must propose 

the earlier date as part of the attainment 

plan submission for the area. This 

second approach is similar to the 

proposed approach for determining the 

most expeditious attainment date for a 

Moderate area. 

As with Moderate area attainment 

dates, when the EPA takes action to 

approve the different elements of the 

attainment plan for the Serious area, one 

of the elements that the agency will take 

action on will be the state’s proposed 

attainment date for the area. If the EPA 

approves an attainment date for the area 

that is earlier than the latest date 

allowed by statute, then the applicable 

attainment date for the area will be the 

approved date. If the state demonstrates 

that the Serious area cannot practicably 

attain the NAAQS by the end of the 

tenth calendar year following 

designation, the state may request a 

Serious area attainment date extension 

as long as certain conditions are met, as 

described next in Section VI.J. 

J. Attainment Date Extensions 

1. Statutory Requirements 

As with Moderate areas, the EPA may 

grant an extension of the attainment 

date for a Serious PM2.5 nonattainment 

area if certain statutory criteria are met. 

Specifically, section 188(e) provides 

that the EPA may allow one attainment 

date extension of no more than 5 years 

‘‘upon application by any state . . . if 

attainment by the [original Serious area 

attainment date] would be 

impracticable, the state has complied 

with all requirements and commitments 

pertaining to that area in the 

implementation plan, and the state 

demonstrates to the satisfaction of the 

Administrator that the plan for that area 

includes the most stringent measures 

that are included in the implementation 

plan of any state or are achieved in 

practice in any state, and can feasibly be 

implemented in the area.’’ In addition to 

the required preconditions for such an 

extension, the statute also includes 

factors which the Administrator may 

use as she considers whether to grant 

the extension and the length of the 

extension, including ‘‘the nature and 

extent of nonattainment, the types and 

numbers of sources or other emitting 

activities in the area (including the 

influence of uncontrollable natural 

sources and transboundary emissions 

from foreign countries), the population 

exposed to concentrations in excess of 

the standard, the presence and 

concentrations of potentially toxic 

substances in the mix of particulate 

emissions in the area, and the 

technological and economic feasibility 

of various control measures.’’ 210

2. Proposed Approach 

In the Addendum, the EPA generally 

described the statutory requirements 

listed above and expressed an intent to 

issue guidance on applying for an 

extension of the Serious area attainment 

date, if appropriate. While ultimately 

the EPA did not deem it necessary to 

issue such guidance, the EPA has 

interpreted these statutory requirements 

through actual exercise of its authority 

under section 188(e) in past 

rulemakings for specific PM10

nonattainment areas. For example, the 

EPA interpreted section 188(e) in 

approving an extension of a Serious area 

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211Maricopa County PM10 Serious area 

attainment date extension, proposal: 65 FR 19964 

(April 13, 2000); and final: 67 FR 48718 (July 25, 

2002). 

212This proposed approach parallels the EPA’s 

proposed approach, described earlier in this 

preamble, for the impracticability option for 

Moderate areas under CAA section 189(a)(1)(B) in 

which all measures that qualify as RACM and 

RACT and all additional reasonable measures are 

required before a Moderate area plan could show 

impracticability of attainment by the statutory 

Moderate area attainment date (the end of the sixth 

calendar year after designation). 

213This interpretation as applied to section 188(e) 

for Serious area attainment date extensions was 

upheld by the Ninth Circuit Court of Appeals in 

Vigil v. Leavitt, 366 F.3d 1025, amended at 381 F.3d 

826 (9th Cir. 2004). 

214Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42010. 

attainment date for purposes of the PM10

NAAQS for the Maricopa area (AZ).211

The EPA believes that the steps 

finalized in the Maricopa County PM10

Serious area SIP approval notice 

provide an appropriate starting point for 

a proposed regulatory approach, with 

some potential modification, for states 

to meet the statutory requirements that 

could apply nationally. The EPA is thus 

proposing to require that states adhere 

to the following steps when preparing 

and submitting a request for a Serious 

area attainment date extension: 

Step 1: Demonstrate that attainment 

by the statutory Serious area attainment 

date is impracticable. In order to 

demonstrate impracticability, the state 

would have to show that the 

implementation of all BACM and BACT 

and all additional feasible measures 

required under section 172(c)(6) will not 

bring the area into attainment by the 

statutory Serious area attainment date 

(i.e., by no later than the end of the 

tenth calendar year after designation).212

The statutory provision for 

demonstrating impracticability requires 

that the demonstration be based on air 

quality modeling (see section 

189(b)(1)(A)). Additional guidance on 

this demonstration is provided in 

Section VI.E of this preamble. 

Step 2: Comply with all requirements 

and commitments in the applicable 

implementation plan. Similar to the 

proposed approach described in Section 

IV.J of this preamble for Moderate area 

attainment date extensions, the EPA 

proposes to interpret the criterion under 

section 188(e) that requires a state to 

have ‘‘complied with all requirements 

and commitments pertaining to that area 

in the implementation plan’’ simply to 

mean that the state has implemented the 

control measures in the SIP revisions it 

has submitted to address the applicable 

requirements in sections 172 and 189. 

For a Serious area attainment date 

extension request being submitted 

contemporaneously with the ‘‘original’’ 

Serious area attainment plan for the 

area, the EPA proposes to read section 

188(e) not to require the area to have a 

fully approved attainment plan that 

meets the CAA’s requirements for 

Moderate areas. The agency proposes to 

base this reading on the plain language 

of section 188(e) which requires the 

state to comply with all requirements 

and commitments pertaining to that area 

in the implementation plan but does not 

require that the state comply with all 

requirements pertaining to the area in 

the CAA.213 For the same reason, the 

EPA also proposes to read this provision 

not to bar an extension if all or part of 

an area’s Moderate area plan is 

disapproved or has been promulgated as 

a FIP, provided the area has complied 

with all of the requirements in the 

applicable FIP, or in the applicable SIP 

and FIP. 

However, for a Serious area 

attainment date extension request being 

submitted sometime after submission of 

an ‘‘original’’ Serious area attainment 

plan that contained an attainment 

demonstration meeting the requirements 

of section 189(b)(1)(A)(i), the EPA 

proposes to read section 188(e) not to 

require the area to have a fully approved 

attainment plan that meets the CAA’s 

requirements for Serious areas, but to 

have a fully approved Moderate area 

attainment plan. The rationale for this 

distinction is due to the timing of the 

Serious area attainment date extension 

request under these circumstances, 

which is discussed in greater detail later 

in this section. The EPA believes that 

this proposed interpretation of this 

criterion would apply whether the area 

was reclassified to Serious under the 

EPA’s discretionary authority (section 

188(b)(1)) or by operation of law upon 

failing to attain by the Moderate area 

attainment date (section 188(b)(2)). 

The EPA also seeks comment on an 

alternative interpretation of the 

implementation plan compliance 

criterion that would require a state to 

have a Moderate area attainment plan 

fully approved by the EPA, not just fully 

implemented by the state, at the time of 

the Serious area attainment date 

extension request, regardless of when 

such a request is submitted to the EPA. 

The EPA believes that one may 

reasonably argue that a state seeking an 

extension of the Serious area attainment 

date should have fully implemented all 

elements of an approved Moderate area 

attainment plan. The EPA believes that 

while such a condition may be 

reasonable, generally speaking, there 

may be circumstances in which a state 

submits a Moderate area attainment 

plan that the EPA is unable to approve 

in a timely way, potentially creating a 

situation in which the state cannot 

qualify for a Serious area attainment 

date extension (due to its unapproved 

Moderate area plan) even if the area is 

reclassified to Serious and cannot 

practicably attain by the statutory 

attainment date for a Serious area. The 

EPA seeks comment on this alternate 

proposed interpretation of the 

applicable implementation plan 

compliance criterion under section 

188(e). Recognizing that a situation such 

as that described above may be rare, the 

agency also seeks comment on what 

remedy might be available under the 

statute if such a situation comes to pass 

if the EPA were to finalize this 

alternative proposed interpretation of 

the applicable implementation plan 

criterion. 

Step 3: Demonstrate the inclusion of 

MSM. To qualify for any extension of a 

Serious area attainment date, section 

188(e) requires a state to ‘‘demonstrate 

to the satisfaction of the Administrator 

that the plan for the area includes the 

most stringent measures that are 

included in the implementation plan of 

any state, or are achieved in practice in 

any state, and can feasibly be 

implemented in the area.’’ In its prior 

guidance in the Addendum, the EPA 

interpreted the term ‘‘most stringent 

measure’’ (MSM) to mean the maximum 

degree of emission reduction that has 

been required or achieved from a source 

or source category in any other 

attainment plans or in practice in any 

other states and that can feasibly be 

implemented in the area seeking the 

extension, such as what LAER 

represents for new or modified sources 

under the NNSR permit program.214

The agency proposes that a state 

would need to follow a process for 

determining MSM for a Serious 

nonattainment area that is generally 

similar to proposed Option 2 for BACM 

and BACT described in Section VI.D of 

this preamble, which would include 

exemptions from MSM for sources in de 

minimis source categories if such 

measures did not collectively advance 

the attainment date for the area by at 

least 1 year. The EPA is also proposing 

an alternative approach for determining 

MSM for a Serious nonattainment area 

that would provide for de minimis 

source category exemptions for MSM 

only for those source categories that do 

not contribute significantly to ambient 

PM2.5 concentrations in the Serious 

nonattainment area, an approach more 

closely aligned with proposed Option 1 

for determining BACM and BACT. 

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215Maricopa County PM10 Serious area 

attainment date extension, 67 FR 48718 (July 25, 

2002). 

216Maricopa County PM10 Serious area 

attainment date extension proposal, 65 FR 19964 

(April 13, 2000), at page 19969. 

Under proposed approach #1 for 

MSM, the EPA would prescribe a fivestep process for states to follow when 

selecting and implementing MSM. This 

proposed approach is similar to that 

used in practice for approving the PM10

Serious area attainment plan and 

Serious area attainment date extension 

request submitted for Maricopa County 

(AZ) in 2000.215

The first step of this proposed 

approach would be for the state to 

update as needed the emissions 

inventory of direct PM2.5 and PM2.5

precursor sources and source categories 

in the Serious nonattainment area 

required under section 172(c)(3) for any 

attainment plan submission. The EPA 

expects that the state would meet this 

inventory requirement as part of its 

Serious area attainment plan submittal 

without any additional work if the state 

submits the Serious area attainment date 

extension request simultaneously with 

the plan itself. However, in the event 

the attainment date extension request is 

submitted after the ‘‘original’’ Serious 

area attainment plan for the area (i.e., 

toward the end of the Serious area 

attainment period), then the EPA 

proposes to require that the state must 

submit a more recent, complete and 

accurate emissions inventory that meets 

the same emissions inventory 

requirements for Moderate and Serious 

PM2.5 nonattainment areas pursuant to 

section 172(c)(3), as well as an 

attainment projected inventory as part 

of the new Serious area attainment plan 

for the area. The inventories submitted 

to support a Serious area attainment 

plan must also include point sources 

meeting the lower major stationary 

source threshold in 40 CFR part 51, 

subpart A. 

The second step in this proposed 

MSM determination process would 

require the state to perform air quality 

modeling in order to evaluate, for each 

of the various source categories 

included in the emissions inventory for 

the area, the impact on PM2.5

concentrations in excess of the 

applicable NAAQS in order to 

determine which categories are 

significant for the purposes of adopting 

MSM. Those source categories for which 

such modeling indicates potential 

control measures collectively would 

have only a de minimis effect on 

advancing the attainment date for the 

area could be eliminated from further 

consideration. In the context of the 

EPA’s action to approve the Maricopa 

County PM10 Serious area attainment 

plan and attainment date extension 

request, the agency finalized an 

approach for judging what constitutes a 

de minimis source category for MSM by 

applying a test of whether MSM 

controls on the allegedly de minimis 

sources would result in more 

expeditious attainment, rather than 

applying a test of whether or not 

requiring the application of controls for 

such sources would make the difference 

between attainment and nonattainment 

by the statutory Serious area deadline, 

as the latter test implicitly would be met 

through the controls chosen for 

demonstrating attainment by the 

alternate attainment date for the area. In 

the agency’s explanation of the 

proposed approach, the EPA explained 

that ‘‘Our responsibility under section 

188(e) . . . is to grant the shortest 

practicable extension of the attainment 

date by assuring the plan provides for 

attainment as expeditiously as 

practicable. Thus, one means of 

determining an appropriate de minimis 

level is to determine if applying MSM 

to the proposed de minimis source 

categories would meaningfully expedite 

attainment. If it did, then the de 

minimis level is too high, and if it did 

not, then the de minimis level is 

appropriate.’’ 216 The EPA thus proposes 

to determine whether any source 

categories should be eliminated from 

MSM controls through a de minimis 

exemption based on a demonstration 

that collectively applying MSM controls 

to such source categories would not 

advance attainment of the NAAQS in 

the area by at least 1 year. This test 

would presumably result in a more 

stringent threshold for what is 

considered a de minimis source category 

for MSM as compared to the threshold 

for de minimis source categories for 

BACM and BACT as described in the 

EPA’s proposed Option 1 for BACM and 

BACT determination criteria (see 

Section VI.D of this preamble). The EPA 

proposes and seeks comment on this 

test for determining whether any source 

categories could be found to be de 

minimis and thus not subject to MSM 

controls. 

The third step in the EPA’s first 

proposed approach to determining MSM 

for a Serious nonattainment area would 

involve identifying the potentially most 

stringent measures in other 

implementation plans for PM2.5 or other 

NAAQS, or used in practice in other 

states for controlling emissions from 

each of the remaining source categories 

listed in the emissions inventory that 

were not determined to be de minimis. 

For each measure, the state would be 

required to determine its technological 

and economic feasibility for sources in 

the area. The EPA proposes generally to 

apply more stringent criteria for 

determining the feasibility of potential 

MSM than that described for BACM and 

BACT in Section VI.D. In some 

situations, MSM could involve 

increasing the coverage of measures that 

were already adopted and implemented 

as BACM and BACT (for example, 

changing out an even greater percentage 

of woodstoves in an area, or paving even 

more roads, if such source categories 

were major contributors to the air 

quality problem in the nonattainment 

area). 

However, because BACM and BACT 

represent the ‘‘best’’ level of control 

feasible for an area, it would be possible 

for the MSM requirement to result in no 

more controls and no more emissions 

reductions in an area than result from 

the implementation of BACM and 

BACT. Stated another way, there may be 

sources or categories for which no other 

feasible controls exist beyond what a 

state has already adopted as BACM or 

BACT. Given the strategy in the 

nonattainment provisions of the CAA to 

offset longer attainment timeframes with 

more stringent control requirements, the 

EPA therefore proposes to interpret the 

MSM provision in order to increase the 

potential that it will result in additional 

controls beyond the set of measures 

adopted as BACM and BACT by 

requiring a state to reanalyze any 

measures that were rejected during the 

state’s BACM and BACT analysis for the 

area to see if they are now feasible for 

the area given the potentially longer 

attainment date (up to 5 years after the 

statutory Serious area attainment date) 

or given the changes that have occurred 

in the interim that improve the 

feasibility of previously rejected 

measures. 

The fourth step of this first proposed 

approach would require the state to 

compare the potential MSM for each 

non-de minimis source category against 

the measures, if any, already adopted for 

that source category in the Serious 

nonattainment area to determine if such 

MSM would provide any additional 

reductions. 

The fifth step would then require that 

the plan provide for the adoption and 

expeditious implementation of any 

MSM that is more stringent than 

existing measures or, in lieu of 

adoption, provide a reasoned 

justification for rejecting the potential 

MSM, i.e., provide an explanation as to 

why such measures cannot be feasibly 

implemented in the area. 

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217See the discussion of de minimis source 

categories in Section VI.D in this preamble. 

As noted earlier, the EPA expects that 

this first proposed approach to 

determining MSM would be most 

compatible with the agency’s proposed 

Option 2 for determining BACM and 

BACT, described in Section VI.D. Under 

proposed Option 2 for BACM and BACT 

determinations, a state would be 

required to implement only those ‘‘best’’ 

control measures necessary to bring a 

Serious nonattainment area into 

attainment expeditiously. Such an 

approach to BACM and BACT 

determinations would not incorporate 

an explicit step in the process for a state 

to exempt de minimis source categories 

from consideration for potential control 

measures. However, it would allow a 

state to eliminate any potential BACM 

or BACT or additional feasible measures 

that are not needed to bring a Serious 

area into attainment by the statutory 

attainment date and that cannot, 

collectively, advance the attainment 

date for the area by at least 1 year. 

Proposed Option 2 for determining 

BACM and BACT for an area is thus 

similar to the proposed approach to 

MSM described above, in which a state 

could eliminate from further 

consideration those source categories for 

which potential control measures 

collectively would have only a de 

minimis effect on advancing the 

attainment date for the area (see 

proposed step 2). 

The EPA’s proposed Option 1 for 

BACM and BACT determinations would 

include an explicit step in the process 

for exempting de minimis source 

categories from further consideration for 

potential control measures. However, 

under such approach, a state would 

need to assess whether emissions of a 

particular pollutant from a given source 

category contributed significantly to 

PM2.5 concentrations in the 

nonattainment area. If the state 

determined that the source category 

contributed only a de minimis amount 

of emissions, then the state could 

exempt the source category from further 

consideration for potential control 

measures. Thus, while it incorporates a 

step to identify de minimis source 

categories, the EPA’s proposed Option 1 

for BACM and BACT determinations is 

not wholly consistent with the agency’s 

proposed approach #1 for determining 

MSM. 

Therefore, the EPA is also proposing 

an alternative approach for determining 

MSM for a Serious nonattainment area 

that would be more compatible with the 

EPA’s proposed approach #1 for 

determining BACM and BACT. Under 

this alternative proposed approach for 

determining MSM, a state could exempt 

de minimis source categories from 

further consideration, but de minimis 

source categories would be identified by 

virtue of their lack of significant 

contribution to PM2.5 levels in the area, 

not by virtue of whether controlling 

such sources categories collectively 

could expedite attainment of the 

relevant NAAQS. In this way, de 

minimis source categories for MSM 

would be defined in a similar way, or 

subject to a similar ‘‘significant 

contribution’’ test, as de minimis source 

categories for BACM and BACT 

determinations under proposed Option 

1. Thus under proposed approach #2 for 

MSM, the steps described for 

determining MSM would generally be 

the same as under proposed approach 

#1, with the exception of step 2. Rather, 

the EPA proposes an alternative step 2 

in the MSM determination process in 

which a state could identify de minimis 

source categories to exempt from further 

control based on an analysis of the 

particular contribution made by a given 

source category to ambient PM2.5 levels 

in the nonattainment area. The EPA 

believes that defining de minimis source 

categories and ‘‘significant 

contribution’’ for determining de 

minimis source categories would be 

equally challenging in the context of 

MSM determinations as in the context 

of BACM and BACT determinations.217

However, in the event the agency 

finalizes proposed Option 1 for BACM 

and BACT determinations, the EPA 

believes it would be appropriate to 

finalize proposed approach #2 for MSM, 

and would require that a state seeking 

to exempt from MSM sources in a given 

source category apply more stringent 

criteria for evaluating whether a certain 

source category’s contributions to the 

area’s PM2.5 concentrations are indeed 

de minimis. 

The EPA believes that either of these 

proposed approaches for determining 

MSM for a Serious nonattainment area 

would be consistent with the EPA’s 

guidance in the Addendum to define 

MSM as those measures that can 

‘‘feasibly be implemented in the 

relevant area from among those which 

are either included in any other SIP or 

have been achieved in practice by any 

other state.’’ One of the key features of 

this guidance relates to identifying 

control measures implemented 

elsewhere, which is also a key feature of 

the EPA’s proposed process for 

identifying RACM and RACT and 

additional reasonable measures (and 

BACM and BACT and additional 

feasible measures, if necessary) for a 

PM2.5 nonattainment area. For these 

processes, the EPA is proposing that a 

state identify potential measures for 

consideration as RACM or RACT or 

additional reasonable measures (or 

BACM or BACT or additional feasible 

measures) by looking at measures 

implemented by other states to meet 

PM2.5 NAAQS or other NAAQS. Thus, a 

state seeking to identify MSM should be 

able to start its process using with the 

work already undertaken for the 

nonattainment area’s RACM and BACM 

determinations and to make updates to 

the list of potential control measures 

accordingly. 

The EPA notes that section 188(e) 

does not identify a deadline for a state 

to implement MSM, while elsewhere 

the statute establishes a deadline for 

implementing RACM and RACT and 

BACM and BACT (see CAA sections 

189(a)(1)(C) and 189(b)(1)(A), 

respectively). However, because the 

clear intent of section 188(e) is to 

minimize the length of a Serious area 

attainment date extension, the EPA 

proposes that the implementation of 

MSM must be as expeditious as 

practicable but no later than 1 year prior 

to the alternative Serious area 

attainment date identified by the state in 

its extension request. 

The EPA seeks comment on whether 

the two proposed approaches to 

determine MSM are sufficiently 

consistent with the agency’s respective 

proposed approaches to BACM and 

BACT determination. The agency also 

seeks comment on whether 

considerations regarding its MSM 

approach should influence the final 

selection of a BACM and BACT 

approach. 

Step 4: Demonstrate attainment by the 

most expeditious alternative date 

practicable. Section 189(b)(1)(A) 

requires that a Serious area plan 

demonstrate attainment, using air 

quality modeling, by the most 

expeditious date practicable after the 

statutory Serious area attainment date. 

This demonstration is the final criterion 

that must be met before the EPA may 

consider granting an extension. The 

agency’s determination of whether the 

plan provides for attainment by the 

most expeditious date practicable would 

depend on whether the plan provides 

for implementation of BACM and BACT 

by the statutory implementation 

deadline and MSM as expeditiously as 

practicable. In no case would a state be 

able to seek an extension of a Serious 

area attainment date to a date more than 

5 years past the statutory attainment 

date for Serious areas. Section VI.E of 

this preamble describes the EPA’s 

proposed requirements for attainment 

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demonstration modeling for Serious 

area attainment plans. 

Step 5: Apply for an attainment date 

extension. The state would have to 

apply to the EPA for any extension of 

a Serious area attainment date. The 

request would have to accompany an 

attainment plan submission containing 

an attainment demonstration showing 

attainment by the most expeditious 

alternative date practicable, and the 

state would need to submit modeling as 

part of the attainment demonstration in 

accordance with Section VI.E. 

Furthermore, the state would have to 

provide the public reasonable notice 

and a public hearing on the attainment 

date extension request before submitting 

it to the EPA, as the EPA would 

consider it an integral part of the 

attainment demonstration and part of 

the revised SIP submission which is 

subject to the requirements of the CAA 

and federal regulations for public notice 

and hearing on SIP revisions. 

3. Timing of Extension Request 

Submittal 

The EPA believes that a state may 

submit a request for an extension of the 

Serious area attainment date either at 

the time the original Serious area 

attainment plan is submitted following 

reclassification of the area or at a point 

in time closer to the Serious area 

attainment date. In the first case, when 

taken together with language under 

section 189(b)(1)(A)(ii) which describes 

the possibility of including an 

impracticability demonstration in a 

Serious area attainment plan that 

parallels the impracticability 

demonstration for a Moderate area 

attainment plan, section 188(e) appears 

to set an expectation that a state may 

request an extension of the attainment 

date for a Serious area when the state 

initially submits its Serious area plan. 

Therefore, the EPA would deem such a 

request as timely and appropriate. 

On the other hand, the EPA also 

recognizes that a state may prepare and 

fully implement a timely Serious area 

plan that includes modeling 

demonstrating attainment no later than 

the statutory Serious area attainment 

date (the end of the tenth calendar year 

following designation), and yet may see 

as the attainment date nears that the 

Serious area will in fact fail to attain by 

its projected attainment date. While the 

statute provides a remedy to be 

instituted immediately upon failure of a 

Serious area to attain the standard 

(through contingency measures and 

other measures stipulated in section 

189(d)), the EPA also believes that the 

criteria of section 188(e) could be 

applied after a state submits a Serious 

area attainment plan but prior to the 

area failing to attain, as long as the area 

had not already been granted a prior 

Serious area attainment date extension 

under section 188(e). In such a case, the 

EPA believes that it would be acceptable 

for a state to submit a Serious area 

attainment date extension request 

similar to that described above (for 

submissions made simultaneous with 

initial Serious area attainment plans) 

together with a new Serious area 

attainment plan meeting all of the 

statutory requirements that apply to 

such plans. In this case, the complete 

submission would have to be made in 

a timely way such that the EPA could 

fully review the new attainment plan for 

the area and the accompanying 

attainment date extension request, 

including the status of compliance with 

all requirements and commitments in 

the Moderate area attainment plan for 

the area, the justification for the 

selection of the alternate attainment 

date, and provisions for the 

implementation of MSM, prior to 

making its determination of failure of 

the area to timely attain the relevant 

NAAQS. 

The EPA seeks comment on this 

option, particularly with respect to 

whether the criteria proposed above are 

appropriate in a situation in which a 

state seeks a Serious area attainment 

date extension after submitting a 

Serious area attainment plan that 

initially demonstrated attainment by the 

statutory Serious area attainment date. 

For example, the EPA seeks comment in 

particular on whether it would be 

appropriate to interpret the section 

188(e) requirement for a state to have 

‘‘complied with all requirements and 

commitments pertaining to that area in 

the implementation plan’’ as referencing 

those requirements and commitments 

contained in the area’s Moderate area 

plan (as proposed above for areas 

seeking a Serious area attainment date 

extension simultaneous with submittal 

of their Serious area plan) or whether, 

for areas that already submitted Serious 

area plans demonstrating attainment, it 

is more appropriate that the state must 

have complied with all requirements 

and commitments pertaining to the area 

in the area’s original Serious area 

attainment plan. The EPA believes this 

second interpretation is the more 

appropriate interpretation as it pertains 

to Serious areas seeking an extension of 

their attainment date as they approach 

their statutory Serious area attainment 

date, and therefore the agency is 

proposing and seeking comment on this 

approach. The EPA believes that this 

second interpretation is especially 

preferable if the EPA finalizes its 

proposal that interprets the SIP 

compliance requirement for areas 

seeking an attainment date extension 

simultaneous with their Serious area 

attainment plan submittal to mean that 

the state need only have implemented 

the control measures in the SIP 

revisions it has submitted to the EPA to 

address the CAA requirements in 

section 189 (i.e., to mean that the area 

need not have a fully approved 

attainment plan that meets the CAA’s 

requirements for Serious areas). 

The EPA seeks comment on these 

proposed options for interpreting and 

implementing the statutory language at 

section 188(e) for Serious area 

attainment date extensions. 

VII. What are the EPA’s proposed 

requirements for attainment plans 

under CAA section 189(d) for Serious 

areas that fail to attain the NAAQS by 

the applicable attainment date? 

In the event that a Serious area fails 

to attain the PM2.5 NAAQS by the 

applicable attainment date, section 

189(d) requires that ‘‘the state in which 

such area is located shall, after notice 

and opportunity for public comment, 

submit within 12 months after the 

applicable attainment date, plan 

revisions which provide for attainment 

of the . . . standard and, from the date 

of such submission until attainment, for 

an annual reduction in PM10 or PM10

precursor emissions within the area of 

not less than 5 percent of the amount of 

such emissions as reported in the most 

recent inventory prepared for such 

area.’’ 

A state with a Serious nonattainment 

area subject to section 189(d) must 

submit to the EPA its plan to meet the 

requirements of section 189(d) in the 

form of a complete attainment plan 

submission that contains the following 

elements: (i) An attainment 

demonstration and provisions for the 

implementation of measures that will 

achieve annual emissions reductions of 

not less than 5 percent from the most 

recent emissions inventory for the area 

for each year until attainment (section 

189(d)); (ii) quantitative milestones that 

will be used to measure compliance 

with the RFP requirement (section 

189(c)); and, (iii) regulation of PM2.5

precursors (in general to meet 

attainment and control strategy 

requirements and as specifically 

required for major stationary sources by 

section 189(e)). Subpart 1 requirements 

that apply to Serious PM2.5

nonattainment areas also subject to the 

requirements of section 189(d) include 

the following: (i) A description of the 

expected annual incremental reductions 

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in emissions that will demonstrate RFP 

(section 172(c)(2)); (ii) emissions 

inventories (section 172(c)(3)); and, (iii) 

contingency measures (section 

172(c)(9)). A state with a Serious PM2.5

nonattainment area that fails to attain 

the NAAQS by the applicable Serious 

area attainment date must also address 

any statutory requirements relevant to 

Moderate nonattainment areas and 

Serious nonattainment areas under 

sections 172 and 189 of the CAA that 

have not already been satisfied. In 

addition, the EPA must approve a new 

attainment date for the area under 

sections 172(a)(2) and 179(d)(3). 

The remainder of this section presents 

the EPA’s proposed requirements for 

attainment plan submissions under 

section 189(d). 

A. Plan Due Dates 

Section 189(d) requires a state with a 

Serious PM10 nonattainment area that 

failed to attain the NAAQS by the 

applicable Serious area attainment date 

to submit a new attainment plan 

submission for the area within 12 

months after the missed attainment 

date. Therefore a state with a 

nonattainment area subject to section 

189(d) must submit a new attainment 

plan for the area—with all required 

elements of the attainment plan—within 

12 months after the missed attainment 

date. 

B. Emissions Inventory Requirements 

As with all other attainment plan 

submissions required for Moderate and 

Serious PM2.5 nonattainment areas, a 

state must develop its submission to 

meet section 189(d) based on ‘‘the most 

recent emissions inventory prepared for 

such [nonattainment] area.’’ This 

inventory must meet the same 

requirements that would apply to any 

other emissions inventory submitted for 

a PM2.5 nonattainment area to meet the 

requirements of section 172(c)(3), which 

requires ‘‘a comprehensive, accurate, 

and current inventory of actual 

emissions of the relevant pollutants’’ in 

the nonattainment area. Therefore the 

EPA proposes that the inventory 

submitted with an attainment plan to 

meet section 189(d) requirements must 

also meet the EPA’s proposed regulatory 

requirements for such emissions 

inventories as described earlier in this 

preamble under Section IV.B (for 

Moderate area attainment plans) and 

Section VI.B (for Serious area 

attainment plans). 

One important aspect of the emissions 

inventory required to be submitted with 

an attainment plan under section 189(d) 

is its role as the basis for calculating the 

emissions reductions of direct PM2.5 and 

PM2.5 precursors necessary to satisfy the 

5 percent annual reduction criteria of 

section 189(d). For this reason, the EPA 

proposes that the ‘‘most recent 

inventory’’ for the area must not only 

meet the criteria as that described for a 

base year inventory submitted pursuant 

to section 172(c)(3) and in Section VI.B 

of this preamble, but also must fully 

account for emissions reductions 

achieved to date through the 

implementation of all RACM and RACT, 

BACM and BACT and additional 

reasonable and feasible measures 

submitted with the Moderate and 

original Serious area attainment plans 

for the area. In this way, the state will 

calculate the additional reductions that 

the nonattainment area will need 

beyond those already required in order 

to fulfill the requirements of section 

189(d) and bring the area into 

attainment as expeditiously as 

practicable. 

In order to ensure that the ‘‘most 

recent inventory’’ is representative of 

the nonattainment problem in the area 

current at the time of the section 189(d) 

submission, the EPA proposes that the 

inventory year must be one of the 3 

years from which monitored data was 

used to determine that the area failed to 

attain the PM2.5 NAAQS by the 

applicable Serious area attainment date. 

The EPA believes that associating the 

inventory with one of these 3 years is 

reasonable in light of the fact that some 

BACM and BACT controls and 

additional feasible controls (required 

under section 172(c)(6)) for sources in 

the area may not be implemented until 

the beginning of the attainment year. 

Thus, requiring that a state use an 

emissions inventory for one of those 3 

years will help ensure that the inventory 

adequately captures the emissions 

reductions already achieved through the 

prior implementation of BACM and 

BACT and additional feasible measures. 

The EPA recognizes the additional 

level of effort that may be needed to 

produce an up-to-date emissions 

inventory for a nonattainment area, and 

therefore is proposing and seeking 

comment on an alternative approach 

that would allow a state to select an 

inventory year earlier than one of the 3 

years from which monitored data were 

used to determine that the area failed to 

attain the NAAQS by the applicable 

attainment date. Under this alternative 

proposed approach, another inventory 

year may be included in the plan under 

specific circumstances with the 

submission of a written justification for 

selecting the earlier year and in 

consultation with the appropriate EPA 

Regional Office. At a minimum, the 

state would need to demonstrate that 

the inventory for the alternative year 

adequately incorporates emissions 

reductions projected to be achieved 

through the implementation of BACM 

and BACT and additional feasible 

control measures submitted with the 

original Serious area attainment plan for 

the area. The EPA proposes that 

modification of an older inventory to 

incorporate those emissions reductions 

would be an acceptable way to meet this 

requirement. In considering use of this 

option, states could be obligated to 

achieve a larger annual reduction than 

5 percent if the older inventory has 

higher emissions levels than the ‘‘most 

recent inventory’’ for the area. 

The EPA seeks comment on these 

proposed criteria and options for 

emissions inventories to be submitted as 

part of the attainment plan due for a 

Serious area under section 189(d). 

C. Pollutants To Be Addressed in the 

Plan 

Section 189(d) requires states to 

develop a new attainment plan for an 

area that failed to attain by the 

applicable Serious area attainment date 

that provides for ‘‘an annual reduction 

in PM10 or PM10 precursor emissions 

within the area of not less than 5 

percent of the amount of such 

emissions’’ reported in the latest 

emissions inventory for the area. In 

Section III of this preamble, the EPA is 

proposing several options on how a 

state may evaluate which PM2.5

precursors to control for purposes of 

attaining the NAAQS in a particular 

nonattainment area. The EPA interprets 

the requirements of the CAA generally 

to allow an air agency to provide a 

‘‘precursor demonstration’’ that can 

support a determination that one or 

more precursors need not be subject to 

control requirements in a given 

nonattainment area, even if the area has 

failed to attain the relevant NAAQS by 

the applicable Serious area attainment 

date. 

Section III presents three options 

describing different proposed 

approaches to such precursor 

demonstrations, and requests comment 

on each. The discussion for each option 

describes how states and the EPA 

should address precursors for Moderate 

areas and for Serious areas, including 

Serious areas that fail to attain the PM2.5

NAAQS by the applicable attainment 

date. This section describes, for each of 

the three options, how the given 

precursor approach would apply to 

plans required to be submitted where 

the area has failed to attain by the 

Serious area attainment date. 

• Option 1: Two independent 

analyses: (a) An attainment planning 

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analysis demonstrating that control 

measures for a particular precursor are 

not needed for expeditious attainment, 

meaning that the precursor can be 

excluded from measures needed to 

attain as expeditiously as practicable for 

all types of sources; and (b) a section 

189(e) technical demonstration showing 

that major stationary sources of a 

particular precursor do not contribute 

significantly to levels that exceed the 

PM2.5 standard, meaning that the 

precursor can be excluded from control 

requirements for major sources and from 

NNSR permitting. Consistent with this 

approach, for an area subject to the 

requirements of section 189(d), the state 

would need to evaluate control 

measures to identify those needed to 

achieve a minimum 5 percent reduction 

in emissions of direct PM2.5 or 

precursors on an annual basis, and 

identify those control measures for 

direct PM2.5 and all precursors that 

would bring the area into attainment as 

expeditiously as practicable. 

• Option 2: Single analysis 

demonstrating that all emissions of a 

particular precursor from within the 

area do not significantly contribute to 

PM2.5 levels that exceed the standard, 

meaning that control requirements for 

emissions of the precursor from major 

stationary and area sources, as well as 

mobile sources, would not be required 

for expeditious attainment, control 

requirements for major sources, or for 

NNSR permitting. For an area subject to 

section 189(d) requirements for which a 

precursor had previously been 

demonstrated not to significantly 

contribute to PM2.5 levels that exceed 

the standard, the air agency would be 

required to update the precursor 

demonstration taking into account any 

relevant information or technical tools 

that had been developed since the 

demonstration was approved. 

Consistent with this approach, if, upon 

failure to attain, the state continued to 

demonstrate that the precursor did not 

contribute significantly to PM2.5

concentrations in the area, then the state 

would not need to identify or 

implement any measures to control that 

precursor’s emissions. 

• Option 3: An attainment planning 

analysis demonstrating that control 

measures for all types of sources of a 

particular precursor are not needed for 

expeditious attainment also would be 

deemed to meet the section 189(e) 

technical demonstration requirement, 

meaning that the state would not need 

to regulate emissions of the particular 

precursor from major stationary sources 

under the NNSR permitting program or 

other control requirements for major 

stationary sources. Consistent with this 

approach, for an area subject to the 

requirements of section 189(d), the state 

would need to evaluate control 

measures to identify those needed to 

achieve a minimum 5 percent reduction 

in emissions of direct PM2.5 or 

precursors on an annual basis, and 

identify those control measures for 

direct PM2.5 and all precursors that 

would bring the area into attainment as 

expeditiously as practicable. 

The EPA will finalize its approach to 

PM2.5 precursors and clarify the 

implications for states conducting 

analyses to identify measures to satisfy 

the requirements of section 189(d) after 

considering public comment received 

on this proposal. 

D. Attainment Plan Control Strategy 

The control strategy to be developed 

for the attainment plan submission for 

a Serious area subject to section 189(d) 

should place particular emphasis on 

control measures that can be 

implemented quickly, in order to ensure 

that the area attains the PM2.5 NAAQS 

as expeditiously as practicable. The 

control strategy would need to include 

any additional measures that are beyond 

those already adopted for the area as 

RACM and RACT and additional 

reasonable measures, or BACM and 

BACT and additional feasible measures, 

and that are necessary to achieve annual 

reductions in emissions of direct PM2.5

and PM2.5 precursors from sources in 

the area of at least 5 percent of the 

amount of such emissions reported in 

the most recent emissions inventory for 

the area. The EPA is proposing to 

interpret section 189(d) in this way to 

address the ambiguity of how the 

statutory language should apply to the 

PM2.5 NAAQS, as section 189(d) 

requires ‘‘an annual reduction in PM10

or PM10 precursor emissions . . . as 

reported in the most recent inventory 

prepared for such area.’’ 

1. Proposed Approach 

The EPA believes that in light of the 

important role that PM2.5 precursors 

play in the formation of PM2.5, it is 

appropriate to require a state to 

implement control measures for all 

types of sources in a Serious 

nonattainment area subject to section 

189(d) to achieve the requisite 5 percent 

annual reduction in emissions of both 

direct PM2.5 and PM2.5 precursors from 

sources in that area. Accordingly, the 

EPA is proposing that, for direct PM2.5

and for PM2.5 precursors that the state 

and the EPA have determined are 

necessary to be controlled for purposes 

of attainment in the area, the attainment 

plan required by section 189(d) would 

have to include control measures that 

will achieve at least 5 percent 

reductions from the latest emissions 

inventory of each such pollutant on an 

annual basis until the area attains the 

relevant PM2.5 NAAQS. The EPA 

believes this is an appropriate 

interpretation of the 5 percent 

requirement of section 189(d) and seeks 

comment on this proposed approach. 

The EPA also proposes and seeks 

comment on an alternative reading of 

the statute that would require a state to 

achieve 5 percent reductions of 

inventoried emissions of either direct 

PM2.5 or of any relevant PM2.5

precursors. This approach, while 

consistent with past guidance on how to 

interpret section 189(d) requirements for 

PM10 NAAQS implementation, could 

potentially allow a state to delay the 

implementation of measures to control 

the relevant pollutants. However, paired 

with the requirement for the area to 

reach attainment of the NAAQS as 

expeditiously as practicable, the EPA 

believes that such an interpretation may 

be reasonable and seeks comment on 

this approach. 

It is important to note that under 

implementation of either of the options 

presented above, and as described more 

fully in Section III of this preamble, the 

EPA is proposing that in the event that 

a state has demonstrated and can 

continue to demonstrate that emissions 

of a given precursor from all sources in 

a nonattainment area do not contribute 

significantly to PM2.5 concentrations in 

the area, then the state would not need 

to achieve 5 percent reductions in 

emissions of that precursor even if the 

nonattainment area becomes subject to 

the requirements of section 189(d). 

The statute requires that the requisite 

minimum 5 percent emissions 

reductions must be calculated from the 

total emissions for each precursor and 

for direct PM2.5 contained in the most 

recent inventory for the area, as 

described earlier in this section. In 

addition, the EPA proposes that these 

required reductions must then be 

achieved every year between the section 

189(d) plan submission date and the 

new projected attainment date for the 

area. For example, assume it is 2025, 

and a Serious area has failed to attain 

the 2012 PM2.5 NAAQS within 10 years 

of designation. Assume also that the 

most recent inventory available for an 

area subject to section 189(d) is for the 

year 2023. This inventory would serve 

as the base inventory for determining 

the emissions reduction requirement 

under section 189(d). If the most recent 

inventory indicates that emissions of 

direct PM2.5 from all sources in the area 

are 100 tons/day, then the area would 

need to reduce emissions of direct PM2.5

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218 69 FR 30006 (May 26, 2004). 

219Menu of Control Measures document available 

at http://www.epa.gov/air/criteria.html. 

by 5 percent of the base inventory (in 

this example, 5 percent of the 2023 base 

inventory, or 5 tons/day) each year until 

the area attains the NAAQS. Thus, in 

the first year following submission of 

the section 189(d) plan for the area, 

emissions of direct PM2.5 could not 

exceed 95 tons/day; in the second year, 

emissions could not exceed 90 tons/day; 

and so forth. 

Although section 189(d) requires that 

a state develop measures that will 

obtain annual emissions reductions of 

‘‘not less than 5 percent’’ from the most 

recent inventory, the EPA interprets this 

language to authorize states to elect to 

front-load emissions reductions in 

earlier years and still meet the 5 percent 

per year requirement. The EPA notes 

that interpreting the statute in this way 

will encourage states to implement 

measures earlier, where possible, rather 

than delay implementation of measures 

merely to assure that the 5 percent 

requirement can be met in later years. 

Thus, using the example described 

above, the annual reduction 

requirement for the area would be 5 

tons/day from a base year emissions 

level of 100 tons/day. The required level 

after year 1 would be 95 tons/day, after 

year 2 the level would be 90 tons/day, 

and so on. If the area reached a level of 

81 tons/day by the end of year 3, then 

by the end of year 4 it would only need 

to reduce emissions by 1 ton/day to 

yield an emissions level of 80 tons/day. 

Consistent with its past action to 

approve a Serious area attainment plan 

for the San Joaquin Valley (CA) PM10

nonattainment area under section 

189(d), the EPA therefore proposes and 

seeks comment on an approach to allow 

states to carry forward any emissions 

reductions beyond the required 

minimum 5 percent in a given year to 

the next year as a means to encourage 

states to achieve emissions reductions 

as quickly as possible.218

The EPA also proposes to clarify its 

interpretation of the statutory language 

under section 189(d) that requires a 

state to submit a new attainment plan to 

achieve annual reductions ‘‘from the 

date of such submission until 

attainment,’’ to mean annual reductions 

beginning from the due date of such 

submission until the new projected 

attainment date for the area based on the 

new or additional control measures 

identified to achieve at least 5 percent 

emissions reductions annually. This 

proposed clarification is intended to 

make clear that even if a state is late in 

submitting its section 189(d) plan, the 

area must still achieve its annual 5 

percent emissions reductions beginning 

from the past due date for the section 

189(d) plan submission. Because 

attainment dates for PM2.5

nonattainment areas established under 

subpart 4 occur at the end of the 

calendar year, any section 189(d) plan, 

which is required within 12 months of 

the missed attainment date for the area, 

would also be due by the end of the 

calendar year. 

2. Additional Guidance on Section 

189(d) Control Measures 

The EPA believes that an appropriate 

starting point for a state to identify 

measures to achieve the requisite 

minimum 5 percent annual emissions 

reductions of direct PM2.5 and PM2.5

precursors is the list of potential control 

measures initially required as part of the 

RACM and RACT determination for the 

area, then updated as part of the 

required BACM and BACT 

determination for the area. The EPA 

anticipates that a state should be able to 

rely on much of the work it previously 

undertook to develop this list of 

potential control measures and analyze 

their technological and economic 

feasibility, and the time required to 

implement them. However, for purposes 

of meeting the requirements of section 

189(d), the EPA recommends that the 

state first identify any additional 

potential measures not previously 

identified for the area, and then analyze 

any new or additional measures that the 

state has not already adopted in a 

previous attainment plan for the area. 

The EPA expects that such an analysis 

to identify new control measures would 

necessarily take into account recent 

technological advances in control 

technologies, the possibility of a greater 

availability of funding to expand 

implementation of control measures for 

area sources, and the additional time the 

area will have to attain the PM2.5

NAAQS under sections 189(d) and 

179(d)(3). 

In addition, a state may include in the 

section 189(d) plan control strategy for 

the area any control measures triggered 

as contingency measures upon the 

EPA’s determination that area failed to 

attain the PM2.5 NAAQS by the 

applicable attainment date. In order to 

be included as control measures that 

will help the area meet its requisite 

minimum 5 percent reductions in direct 

PM2.5 and PM2.5 precursor emissions, 

such measures would have to meet the 

same requirements as all other 

approvable control measures for being 

quantifiable, enforceable, replicable and 

accountable. The EPA believes that 

reliance on such measures is 

appropriate given the short timeline 

provided for in the statute for states to 

revise and submit their SIP revisions (12 

months from the missed attainment 

date) and the fact that the contingency 

measures included in the prior 

attainment plan for the area under 

section 172(c)(9) must be activated once 

the EPA publishes its finding of the 

area’s failure to attain the NAAQS by 

the applicable attainment date. If 

contingency measures from the Serious 

area attainment plan are relied on in the 

new attainment demonstration as part of 

the control strategy, the state will need 

to submit additional contingency 

measures for the section 189(d) 

attainment plan submission. 

3. Control Strategy Submission 

Requirements 

To ensure that attainment plan 

submissions contain the necessary 

supporting information for the EPA to 

review and approve the state’s new 

control strategy to achieve at least 5 

percent reductions in emissions of 

direct PM2.5 and significant PM2.5

precursors, the EPA proposes to require 

under the authority of section 301(a) 

that a state must submit the following 

information as part of its section 189(d) 

plan submission: 

• A list of all emissions source 

categories, sources and activities in the 

nonattainment area (for multi-state 

nonattainment areas, this would include 

source categories, sources and activities 

from all states which make up the area); 

• For each source category, source or 

activity in the nonattainment area, an 

inventory of direct PM2.5 and all PM2.5

precursor emissions; 

• For each source category, source or 

activity in the nonattainment area, a 

comprehensive list of potential control 

measures considered by the state for 

those sources in the nonattainment 

area; 219

• For each potential control measure 

considered by the state but eliminated 

from further consideration due to a 

determination by the state that the 

control measure or technology was not 

technologically feasible, a narrative 

explanation and quantitative or 

qualitative supporting documentation to 

justify the state’s conclusion; 

• For each technologically feasible 

emission control measure or technology, 

the state must provide the following 

information relevant to economic 

feasibility: (i) the control efficiency by 

pollutant; (ii) the possible emission 

reductions by pollutant; (iii) the 

estimated cost per ton of pollutant 

reduced; and, (iv) a determination of 

whether the measure is economically 

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220Note that for purposes of the PM2.5 NAAQS, 

a determination of attainment (or failure to attain), 

which the EPA is required to make after the 

attainment date has passed, is based on an average 

of the most recent 3 years of ambient data prior to 

the area’s attainment date. 

feasible, with narrative explanation and 

quantitative supporting documentation 

to justify the state’s conclusion; 

• For each technologically and 

economically feasible emission control 

measure or technology, the date by 

which the technology or measure could 

be implemented. 

As with other PM2.5 attainment plan 

submissions, the EPA believes that it is 

incumbent on the state to ensure that 

the information needed for the EPA to 

evaluate the state’s analysis of new 

control measures needed to achieve 

annual 5 percent reductions is 

presented separately as part of the 

control strategy analysis and in a format 

that provides transparency, consistency 

and the ability for another party to 

evaluate the state’s analysis effectively 

and to duplicate the state’s results. For 

this reason, the EPA is including the 

section 189(d) plan base year emissions 

inventory information as a necessary 

part of the control strategy submittal 

and as one element of the state’s section 

189(d) plan due 12 months after the 

missed attainment date for the area. In 

addition, the EPA proposes that the 

state must provide information as part 

of any attainment plan submitted to 

meet the requirements of section 189(d) 

consistent with the criteria described in 

Section VI.D.5 of this preamble to 

ensure that a state adopts effective 

regulations to implement the control 

measures identified as being needed to 

meet those requirements. Specifically, 

all control measures must be 

quantifiable, enforceable, replicable and 

accountable. 

The section 189(d) requirement to 

reduce emissions by 5 percent per year 

is in effect a fixed level of RFP to be 

achieved annually. Accordingly, just as 

quantitative milestones are used to track 

progress with RFP requirements, the 

EPA proposes that the state would be 

required to submit quantitative 

milestone reports to describe the area’s 

progress in meeting the 5 percent 

annual emissions reduction requirement 

under section 189(d). See Section VII.G 

of this preamble for more details. 

E. Modeling for Attainment 

Demonstrations 

Section 189(d) requires a state with a 

Serious nonattainment area that failed 

to attain the relevant NAAQS by the 

applicable Serious area attainment date 

to submit a new attainment plan for 

such area within 12 months after the 

missed attainment date. The EPA is 

proposing that the same general 

requirements for attainment 

demonstrations and modeling that apply 

to Moderate area plans and Serious area 

plans due under sections 189(a) and 

189(b) should also apply to section 

189(d) attainment plans. However, the 

EPA is proposing additional 

requirements specific to plans states 

submitted pursuant to section 189(d) as 

described below. 

1. Attainment Demonstrations for 

Serious Areas That Fail To Attain the 

NAAQS by the Applicable Attainment 

Date 

The EPA is proposing that the 

attainment demonstration for Serious 

areas subject to section 189(d) 

requirements must consist of: (i) 

technical analyses such as base year and 

future year modeling of emissions 

which identify sources and quantify 

their emissions that are contributing to 

violations of the PM2.5 NAAQS; and, (ii) 

analyses of future year projected 

emissions reductions and air quality 

improvement resulting from national, 

regional and local programs already 

implemented as part of previous 

Moderate and/or Serious area 

attainment plans for the area (including 

reasonable control measures, BACM and 

BACT and additional feasible 

measures), and additional measures 

needed for expeditious attainment, 

including measures needed to achieve 5 

percent emissions reductions on an 

annual basis. Each state with a 

nonattainment area subject to the 

requirements of section 189(d) must 

submit an attainment plan with an 

attainment demonstration that includes 

analyses supporting the state’s 

determination of its proposed new 

attainment date. In all cases, the state 

must show that the area will attain the 

NAAQS as expeditiously as practicable. 

2. What modeling is required? 

The EPA proposes that states are 

required to submit air quality modeling 

in support of an attainment 

demonstration for a nonattainment area 

subject to the requirements of section 

189(d). The modeling demonstration 

must show how and when the area will 

attain the NAAQS. Other than the 

timing of plan submissions and 

requirement to achieve 5 percent 

emissions reductions in direct PM2.5 and 

PM2.5 precursors, the relevant air quality 

modeling procedures and guidance for 

all PM2.5 nonattainment area plans are 

the same. See Sections IV.E. and VI.E of 

this preamble for more details on 

proposed modeling requirements and 

guidance for Moderate and Serious 

PM2.5 nonattainment areas, respectively. 

3. What future year(s) should be 

modeled in attainment demonstrations? 

As discussed more fully in Section 

VII.I of this preamble, the EPA must 

establish a new attainment date for a 

PM2.5 nonattainment area subject to 

section 189(d) and must do so according 

to the provisions of sections 179(d)(3) 

and 172(a)(2), which require that the 

new attainment date must be as 

expeditious as practicable, but no later 

than 5 years from the date of publication 

in the Federal Register of the EPA’s 

determination that the area failed to 

attain the relevant NAAQS. The EPA 

may extend the attainment date by up 

to 5 additional years (thus to 10 years 

from the date of publication of the 

notice of finding of failure to attain by 

the applicable attainment date for the 

area) if the agency deems it appropriate 

‘‘considering the severity of 

nonattainment and the availability and 

feasibility of pollution control 

measures.’’ 

For purposes of determining the 

attainment date that is as expeditious as 

practicable, the state must conduct 

future year modeling which takes into 

account emissions growth, known 

controls (including any controls that 

were previously determined to be 

RACM or RACT or additional 

reasonable measures, or BACM or BACT 

or additional feasible measures for the 

area), the 5 percent per year emissions 

reductions required by section 189(d), 

plus any other emissions controls that 

are needed for expeditious attainment of 

the NAAQS. A state performing a 

modeling analysis for a plan submitted 

under section 189(d) must select a 

future modeling year such that all 

emissions control measures relied on for 

attainment will have been implemented 

by the beginning of that year. To 

demonstrate attainment, the modeling 

results for the nonattainment area must 

predict that emissions reductions 

implemented by the beginning of the 

last calendar year preceding the 

attainment date will result in PM2.5

concentrations that meet the level of the 

standard.220

For a PM2.5 nonattainment area 

subject to section 189(d), the EPA 

expects that the state will adopt any 

control measures necessary to 

demonstrate expeditious attainment 

within 5 years of the area failing to 

attain the NAAQS by the applicable 

Serious area attainment date. 

4. Attainment Year Motor Vehicle 

Emissions Budgets 

As with all other PM2.5 NAAQS 

attainment plans, the transportation 

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221For more information on PM2.5 precursor 

requirements, see section 93.102(b)(2)(iv) and (v) of 

the transportation conformity rule. See also the May 

6, 2005, final transportation conformity rule that 

addressed requirements for PM2.5 precursors. (70 FR 

24280). 

222A state would also establish motor vehicle 

emissions budgets for an area’s attainment year. 

Those budgets would be the motor vehicle 

emissions that the SIP establishes as being 

necessary to attain the NAAQS. 

223 If an area includes re-entrained road dust in 

the motor vehicle emissions budget, the latest 

approved version of AP–42 should be used unless 

the EPA has approved an alternative model for the 

area. 

224 If an area includes re-entrained road dust in 

the motor vehicle emissions budget, the latest 

approved version of AP–42 should be used unless 

the EPA has approved an alternative model for the 

area. 

conformity rule requires that attainment 

plans for areas subject to section 189(d) 

establish motor vehicle emissions 

budgets for the area’s attainment year. 

Therefore, for such an area, the state 

would first determine the new 

attainment date as described in Section 

VII.I of this preamble. Once an area’s 

attainment date has been established, 

the state would establish motor vehicle 

emissions budgets for direct PM2.5 and 

any relevant PM2.5 precursor for the 

attainment year.221 A motor vehicle 

emissions budget for the purposes of a 

PM2.5 attainment plan is that portion of 

the total allowable emissions within the 

nonattainment area allocated to on-road 

sources as defined in the submitted 

attainment plan.222 Such motor vehicle 

emissions budgets would be calculated 

using the latest planning assumptions 

and the latest approved motor vehicle 

emissions model available at the time 

that the attainment plan is 

developed.223

The EPA seeks comment on these 

proposed attainment demonstration and 

modeling requirements for new 

attainment plans due for Serious areas 

subject to section 189(d). 

F. RFP Requirements 

As with other PM2.5 attainment plans, 

a plan submitted to meet the 

requirements of section 189(d) must 

provide for RFP as required under 

sections 172(c)(2) and 189(c)(1). Section 

171(1) defines RFP as ‘‘such annual 

incremental reductions in emissions of 

the relevant air pollution as are required 

by this part or may reasonably be 

required by the Administrator for the 

purpose of ensuring attainment of the 

applicable [NAAQS] by the applicable 

attainment date.’’ The purpose of RFP 

requirements is to assure that a state is 

making progress towards attainment on 

an annual basis through the attainment 

plan, rather than deferring emissions 

reductions until just before the 

attainment date for the area. This 

requirement is similar to, though less 

prescriptive than, the requirement 

under section 189(d) for 5 percent 

emissions reductions of direct PM2.5 or 

PM2.5 precursors from the most recent 

emissions inventory on an annual basis 

until the area attains. Therefore, the 

EPA proposes to determine that a state 

has satisfied the RFP requirement if the 

state submits an approvable control 

strategy under section 189(d) that 

demonstrates that the state will achieve 

at least 5 percent reductions in direct 

PM2.5 and PM2.5 precursor emissions 

from sources in the area annually until 

attainment. 

The EPA proposes that motor vehicle 

emissions budgets must also be 

established as part of any RFP plan for 

direct PM2.5 and for any relevant PM2.5

precursor using the latest planning 

assumptions and the latest approved 

motor vehicle emissions model 

available at the time that the plan is 

developed for a Serious area subject to 

189(d).224

The EPA seeks comment on this 

proposed approach related to RFP 

requirements for new attainment plans 

due under section 189(d). 

G. Quantitative Milestones 

The revised attainment plan for any 

Serious nonattainment area that fails to 

attain the relevant PM2.5 NAAQS by the 

applicable attainment date must include 

quantitative milestones pursuant to 

section 189(c). These quantitative 

milestones would be additional to those 

previously identified in the Moderate 

area and original Serious area 

attainment plans, and would need to 

reflect the projected emissions 

reductions or air quality improvements 

expected through the implementation of 

specific control measures identified to 

achieve the minimum 5 percent annual 

reductions required under section 

189(d). Such milestones would need to 

be achieved every 3 years until the area 

attains the relevant NAAQS, such that 

the EPA proposes that, at a minimum, 

quantitative milestones selected for an 

attainment plan submitted under 

section 189(d) would need to 

demonstrate a reduction of at least 15 

percent in emissions of direct PM2.5 and 

significant precursors below those 

emissions reported in the most recent 

inventory for the area. 

The section 189(d) plan for an area 

that failed to attain the standard by the 

applicable Serious area attainment date 

would have to contain quantitative 

milestones to be achieved by 13.5 years 

from the area’s date of designation and 

every 3 years thereafter until the area’s 

new projected attainment date. In the 

event a state is developing a revised 

attainment plan pursuant to section 

189(d) that will be due sometime after 

13.5 years following designation of the 

area, the EPA proposes to allow the state 

to submit quantitative milestones 

beginning for the year 16.5 from 

designation and every 3 years thereafter 

until the area’s projected attainment 

date. 

The EPA believes that its proposed 

requirements for quantitative 

milestones, described in Sections IV.G 

and VI.G of this preamble, should also 

apply to quantitative milestones 

submitted with any revised attainment 

plan pursuant to section 189(d), and 

thus proposes and seeks comment on 

the agency’s proposed milestone 

requirements for application to 

attainment plans due under section 

189(d). 

H. Contingency Measures 

All PM2.5 attainment plans, including 

plans for areas subject to section 189(d), 

must contain contingency measures that 

are consistent with section 172(c)(9). 

Section VI.H of this preamble describes 

the EPA’s proposed criteria for 

contingency measures for a Serious area 

attainment plan, and the agency 

proposes that contingency measures for 

a section 189(d) plan must meet the 

same criteria. The EPA proposes that the 

emissions reductions associated with 

contingency measures for section 189(d) 

plans must be at least 5 percent of direct 

PM2.5 and significant PM2.5 precursor 

emissions as reported in the most recent 

inventory for the area. The EPA believes 

this requirement would appropriately 

align the proposed requirement for 

selecting contingency measures with the 

agency’s proposed approach to RFP for 

these areas. In other words, if RFP for 

an area is equivalent to about 1 year’s 

worth of emissions reductions, or 5 

percent emissions reductions in direct 

PM2.5 and PM2.5 precursors, then the 

adopted contingency measures should 

likewise achieve about 1 year’s worth of 

emissions reductions, or 5 percent 

emissions reductions in direct PM2.5 and 

PM2.5 precursors. 

The EPA recognizes that identifying 

contingency measures for a Serious 

PM2.5 nonattainment area that failed to 

attain the relevant NAAQS by the 

applicable attainment date may be 

challenging for a state that should 

already have fully implemented all 

control measures identified as 

‘‘reasonable’’ and ‘‘best,’’ and 

potentially ‘‘most stringent,’’ in addition 

to identifying new control measures to 

achieve the requisite minimum 5 

percent reductions in direct PM2.5 and 

significant PM2.5 precursor emissions 

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225For example, see the Federal Register notice 

from June 6, 2007 (72 FR 31183) in which the EPA 

found that the Phoenix PM10 Serious nonattainment 

area failed to attain the standard by the 2006 

attainment date. 

226More information on the PSD requirements for 

PM2.5 as well as the public comments and the EPA’s 

responses to those comments and the related issues 

for which comments were received is contained in 

the January 15, 2013 Federal Register document (78 

FR 3086, beginning at page 3251). 

necessary for expeditious attainment. 

Nonetheless, given the statutory 

language of section 172(c)(9), the EPA 

seeks comment on applying the same 

proposed requirements for contingency 

measures for section 189(d) plans, and 

on the agency’s proposed approach for 

calculating the emissions reductions 

that such measures must be able to 

achieve. 

I. Attainment Dates 

As previously discussed, section 

189(d) requires a minimum 5 percent 

annual reduction in emissions of direct 

PM2.5 and PM2.5 precursors until the 

area attains the relevant NAAQS. 

However, neither section 189(d) nor 

other sections in subpart 4 explicitly 

establish or provide the authority to 

establish a new attainment date for the 

area; other subpart 4 attainment date 

provisions for Moderate or Serious areas 

are likewise not applicable to areas in 

this situation. Therefore, once an area is 

beyond the attainment dates that 

Congress specified in subpart 4 for the 

PM10 NAAQS, the EPA must look to the 

existing provisions of the CAA to 

provide authority for a new attainment 

date. Sections 179(d)(3) and 172(a)(2) 

provide generally applicable attainment 

dates that fill the gap in the statute left 

for areas subject to the requirements of 

section 189(d). Thus, for a PM2.5

nonattainment area subject to section 

189(d) requirements, the EPA must 

establish a new attainment date, and 

must do so according to the provisions 

of section 179(d)(3) and 172(a)(2). The 

EPA has followed this same approach in 

the past for PM10 nonattainment areas 

governed by subpart 4 nonattainment 

requirements.225

The new attainment date must be as 

expeditious as practicable, but no later 

than 5 years from the date of publication 

in the Federal Register of the EPA’s 

determination that the area failed to 

attain the relevant NAAQS. The EPA 

may extend the attainment date by up 

to 5 additional years (thus to 10 years 

from the date of publication of the 

notice of finding of failure to attain by 

the applicable attainment date for the 

area) if the agency deems it appropriate 

‘‘considering the severity of 

nonattainment and the availability and 

feasibility of pollution control 

measures.’’ For a PM2.5 nonattainment 

area subject to section 189(d), the EPA 

expects that the state will adopt any 

control measures necessary to 

demonstrate expeditious attainment 

within 5 years of the area failing to 

attain the NAAQS by the applicable 

Serious area attainment date. 

As discussed earlier in this section, 

the EPA will consider the state’s 

attainment demonstration and proposed 

attainment date for the area, in addition 

to the state’s revised control strategy 

and the relevant facts and 

circumstances, in order to identify the 

most expeditious attainment date 

practicable for the area. 

The EPA seeks comment on this 

proposal for interpreting the statutory 

requirements under section 189(d) for a 

Serious area that fails to attain the PM2.5

NAAQS by the applicable attainment 

date. 

VIII. What are the EPA’s proposed 

NNSR permitting requirements? 

A. Statutory Requirements for NSR 

Section 110(a)(2)(C) of the CAA 

requires states to include in their SIPs 

a preconstruction review permitting 

program that regulates the construction 

and modification of stationary sources 

as necessary to ensure that NAAQS are 

achieved. To address the regulation of 

the larger pollutant-emitting sources 

(defined as major stationary sources), 

Congress provided specific permitting 

requirements in the CAA in parts C and 

D of title I. The requirements for 

preconstruction permits under parts C 

and D of the CAA are commonly known 

collectively as the major NSR program 

because they apply specifically to the 

preconstruction review and permitting 

of new major stationary sources, and 

major modifications at existing sources. 

As explained in Sections VIII.A.1 and 2 

of this preamble, the preconstruction 

review of each new and modified major 

stationary source generally is carried out 

on a pollutant-specific basis and the 

requirements with regard to each 

pollutant apply based on whether the 

area in which the proposed major 

source or major modification would 

locate is designated attainment (or 

unclassifiable) or nonattainment for that 

pollutant at the time the permit is 

issued. 

1. PSD 

Part C of title I of the CAA (hereafter 

referred to simply as part C) contains 

implementation plan requirements that 

apply to new major stationary sources 

and major modifications in areas 

designated attainment or unclassifiable 

for any NAAQS. These requirements 

constitute the PSD program. Pursuant to 

part C, the EPA has adopted PSD 

regulations at 40 CFR 51.166 (minimum 

requirements for an approvable state 

PSD program in the SIP) and 40 CFR 

52.21 (the federal PSD program, 

applicable in areas where the state does 

not have an EPA-approved PSD program 

in its SIP). The EPA last amended the 

PSD regulations for PM2.5 on January 15, 

2013, in the final rule revising the PM2.5

NAAQS.226 This proposal does not 

relate to the PSD program, nor does it 

propose further changes to the PSD 

regulations. Any future revisions to the 

PSD regulations for PM2.5 would be 

done through a separate notice-andcomment rulemaking. 

2. NNSR 

Part D of title I of the CAA (hereafter 

referred to as part D) contains 

implementation plan requirements for 

nonattainment areas, which include the 

requirements for permitting new major 

stationary sources and major 

modifications in designated 

nonattainment areas, referred to as the 

NNSR program. As noted earlier, part D 

contains several subparts that include 

various requirements for addressing 

nonattainment areas. Subpart 1 

addresses plan requirements for 

nonattainment areas generally, 

including section 172(c)(5) which 

requires preconstruction and operating 

permits for new major stationary 

sources and major modifications in 

nonattainment areas. Section 173 

outlines the minimum statutory 

requirements for a state’s NNSR permit 

program and serves as the basis for the 

EPA’s NNSR regulations for PM2.5 as 

promulgated in the 2008 PM2.5 NSR 

Rule. Subpart 4 was added to part D as 

part of the 1990 CAA Amendments and 

includes additional plan provisions for 

designated PM10 nonattainment areas. 

Relevant here, section 189(a)(1)(A) of 

subpart 4 requires states to include in 

their implementation plan a permit 

program addressing major stationary 

sources of PM10 that meets the 

requirements under section 173 of 

subpart 1. Subpart 4 also includes some 

additional preconstruction review 

requirements for which, to date, the 

EPA has promulgated NSR regulations 

applying only to major stationary 

sources of PM10 in PM10 nonattainment 

areas. The specific NNSR requirements 

contained in both subparts 1 and 4 are 

described below including the changes 

to the NNSR regulations needed to 

address PM2.5 specifically that the EPA 

is proposing in this notice. 

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227See the Federal Register published on 

November 29, 2005 (70 FR 71612, 71677 and 

71678). 

228States with designated PM2.5 nonattainment 

areas were required to submit SIPs satisfying the 

requirements of the 2008 PM2.5 NSR 

Implementation Rule by May 16, 2011, 3 years from 

the date of publication of that rule. See 73 FR 28321 

(May 16, 2008), at page 28342. Such approved state 

programs can continue to be implemented to issue 

permits to new major stationary sources and major 

modifications until the state’s revised program 

containing the subpart 4 NNSR provisions 

promulgated in this rulemaking is approved under 

the applicable SIP. 

229Appendix S was originally promulgated in 

1976 to address whether, and to what extent, new 

and modified sources would be allowed to 

construct in nonattainment areas whose attainment 

deadlines had already passed, in light of the 

regulatory requirement that new or modified 

sources be disapproved where the source would 

interfere with attainment of the NAAQS (41 FR 

55524 (December 21 1976)). When Congress added 

the part D provisions in the 1977 CAA 

Amendments, it also added the requirement that 

SIPs contain NNSR provisions as set forth in Part 

D. Additionally, Congress provided that Appendix 

S would govern preconstruction permitting in 

nonattainment areas lacking approved part D SIPs 

before a construction ban went into effect. When 

Congress removed the construction ban via the 1990 

CAA Amendments (except as provided for in 

section 110(n)(3)) it left in place the use of the 

interim NNSR program under Appendix S. 

230As will be explained in ensuing discussions, 

the nonattainment pollutant and any applicable 

precursors for that pollutant are considered 

separately for NNSR applicability purposes. See 40 

CFR 51.165(a)(1)(v)(A), (a)(2)(ii)A). 231The basic NNSR requirements are set forth in 

section 173 of subpart 1. Subpart 4 adds a more 

stringent definition of ‘‘major source’’ for PM10

sources in PM10 nonattainment areas classified as 

Serious and sets forth provisions for the regulation 

and potential exemption of major sources of PM10

precursors in PM10 nonattainment areas. Until the 

decision in NRDC v. EPA was issued, the additional 

subpart 4 requirements had not been directly 

applied with regard to PM2.5.

232At the time the EPA promulgated the new 

PM10 NAAQS, part D of the CAA did not include 

subpart 4. See 52 FR 24672 (July 1, 1987). 

233See section 107(d)(4)(B) of the CAA. The EPA 

subsequently published a list of the statutorily 

created PM10 areas in a Federal Register document 

at 55 FR 45799 (October 31, 1990). 

234The EPA memorandum titled ‘‘New Source 

Review (NSR) Program Transition Guidance,’’ 

signed by John S. Seitz, Director, Office of Air 

Quality Planning & Standards. 

B. Federal NNSR Regulations 

Federal regulations pertaining to the 

preconstruction permitting of new major 

stationary sources and major 

modifications in areas designated 

nonattainment are contained at 40 CFR 

51.165; part 51, appendix S; and, 

§ 52.24. An approved NNSR program in 

a state’s implementation plan must, at a 

minimum, meet the program 

requirements set forth in the federal 

NNSR requirements at 40 CFR 51.165, 

which for PM2.5 are currently based on 

changes made under the 2008 PM2.5

NSR Rule. States are required to adopt 

regulations consistent with those plan 

requirements and submit them to the 

EPA for approval as part of their SIP 

within a period of time consistent with 

the schedule prescribed by the CAA. 

The EPA interprets the requirement 

established under section 110(a)(2)(C) of 

the CAA for states to regulate the 

construction and modification of 

sources to apply in nonattainment areas 

as of the effective date of a new 

nonattainment area designation.227

Although section 110(a)(2)(C) does not 

contain specific requirements a state 

must follow for issuing major source 

permits during the interim period 

between effective date of designation 

and the date when a state has an EPAapproved NNSR program, the EPA 

regulation at 40 CFR 52.24(k) authorizes 

states to apply 40 CFR part 51, 

Appendix S, known as the Emission 

Offset Interpretative Ruling, during the 

interim period. 228 229

Accordingly, states with newly 

designated nonattainment areas for the 

revised primary PM2.5 NAAQS have two 

possible means by which they can 

implement NNSR requirements for 

PM2.5 following the effective date of 

designations and until the EPA 

approves a SIP submission meeting the 

NNSR requirements for PM2.5

promulgated in this rule under subpart 

4. First, any state that has an approved 

NNSR program for PM2.5 can continue to 

apply those permitting requirements in 

the interim. Second, states that lack any 

approved NNSR program for PM2.5 may 

rely upon the NNSR provisions in 

Appendix S until the EPA approves a 

SIP submission from the state to address 

PM2.5 in order to ensure that proposed 

new major stationary sources and major 

modifications for PM2.5 in newly 

designated PM2.5 nonattainment areas 

undergo the appropriate type of 

preconstruction review in the interim. 

1. General Applicability 

New major stationary sources are 

subject to the NNSR requirements when 

they are major for the pollutant for 

which an area is designated 

nonattainment. See 40 CFR 

51.165(a)(2)(i). With regard to major 

modifications, NNSR applies to 

proposed physical changes or changes 

in the method of operation of an 

existing stationary source that (1) is 

major for the nonattainment pollutant 

(or a precursor for that pollutant) and (2) 

results in both a significant emissions 

increase and a significant net emissions 

increase of that nonattainment pollutant 

(or a precursor for that pollutant).230

For each proposed major new source 

and major modification, the general 

NNSR requirements that are required to 

be included in a state’s SIP include: (i) 

the installation and continuous 

operation of pollution control 

technology that complies with the 

LAER; (ii) the acquisition of creditable 

emissions reductions to adequately 

offset the proposed emissions increase 

of the nonattainment pollutant; and, (iii) 

a demonstration of compliance with 

other analyses as required under section 

173 of the CAA.231 These NNSR 

requirements must be satisfied by a 

major new source or major modification 

as a prerequisite for receipt of a 

construction permit and apply as of the 

effective date of designation of an area 

as nonattainment for the pollutant. 

2. Historical Overview of NNSR for 

PM10 and PM2.5 NAAQS 

Following the adoption of new PM 

NAAQS based on the PM10 indicator in 

1987 (replacing the original Total 

Suspended Particulate indicator), the 

EPA announced that it did not intend to 

designate areas as nonattainment for 

PM10. As a result, the EPA initially 

determined that part D, which at that 

point consisted only of generally 

applicable requirements, did not apply 

to the PM10 NAAQS.232 Thus, 

nonattainment area requirements, 

including the NNSR program, did not 

initially apply with respect to PM10. 

Consequently, all new major stationary 

sources and major modifications of 

PM10 were required to undergo PSD 

review as a prerequisite for construction 

or modification. 

The approach for implementing the 

NNSR program for PM changed when in 

1990 Congress established a new 

subpart 4 specifically to address 

implementation plan requirements for 

PM10 nonattainment areas, including 

new preconstruction permit 

requirements for major stationary 

sources and major modifications with 

respect to PM10 and PM10 precursors. 

Moreover, Congress created new PM10

nonattainment areas through 

designations that became effective upon 

enactment of the 1990 Amendments on 

November 15, 1990.233 In section 

189(a)(2)(A), Congress also required 

states to submit the necessary NNSR 

permit program SIP revisions for these 

areas to the EPA by June 30, 1992. 

In a letter to its Regional Offices dated 

March 11, 1991,234 the EPA initially 

indicated that states should implement 

such new requirements by operation of 

law, without the need for formal 

rulemaking by the EPA to establish the 

necessary requirements for states to 

adopt. In the General Preamble, the EPA 

offered states additional guidance and 

described the EPA’s preliminary views 

on how the states and the EPA should 

interpret various provisions of the 1990 

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235See ‘‘Final Rule to Implement Certain Aspects 

of the 1990 Amendments Relating to New Source 

Review and Prevention of Significant Deterioration 

as They Apply in Carbon Monoxide, Particulate 

Matter and Ozone NAAQS.’’ 70 FR 71611 

(November 29, 2005). 

236See 62 FR 38652 (July 18, 1997). 

237See 71 FR 61144 (October 17, 2006). 

238See 73 FR 28321 (May 16, 2008). 

239See 72 FR 20589. 

240 In the 2008 PM2.5 NSR Rule, the EPA 

concluded that SO2 should be regulated as a 

precursor for PM2.5 in all areas. See 73 FR 28327. 

Amendments, primarily those 

provisions concerning planning and 

control measure requirements for the 

attainment of the NAAQS in 

nonattainment areas. In a 2005 final 

rule, the EPA formally amended the 

NNSR regulations to incorporate the 

requirements contained in subpart 4 of 

part D of the 1990 CAA Amendments 

concerning PM10 nonattainment 

areas. 235

The EPA revised the PM NAAQS in 

1997, establishing new annual and 24- 

hour NAAQS using PM2.5 particles as a 

new indicator, while retaining the 

NAAQS for PM10.236 In 2006, the EPA 

again revised the suite of PM NAAQS by 

tightening the 24-hour PM2.5 standards 

and retaining the level of the annual 

PM2.5 standards.237 In 2008, the EPA 

issued the PM2.5 NSR Rule that 

established various provisions ensuring 

that proposed new major stationary 

sources or major modifications of 

sources of direct PM2.5 emissions or 

emissions of applicable PM2.5

precursors would be required to 

undergo preconstruction review.238 The 

EPA included specific provisions in the 

2008 PM2.5 NSR Rule to apply when 

such sources are located in a designated 

PM2.5 nonattainment area. Unlike the 

NNSR requirements for PM10 developed 

under subpart 4, the EPA determined 

that the applicable implementation 

requirements for the PM2.5 NAAQS were 

contained in the general nonattainment 

provisions under subpart 1. 

With regard to NSR applicability for 

PM2.5 precursors in the 2008 PM2.5 NSR 

Rule, the EPA recognized NOX, SO2, 

VOC and ammonia as precursors of 

PM2.5 in the scientific sense (because 

those pollutants under the appropriate 

conditions can contribute to the 

formation of PM2.5 in the ambient air) 

but did not require that states subject all 

of these precursors to control as part of 

the attainment plan or NSR permitting 

requirements applicable to a given 

nonattainment area.239 Instead, based on 

the authority in section 302(g) of the 

CAA, the EPA established the initial 

presumptions for nonattainment areas 

that SO2 and NOX should be regulated 

precursors for PM2.5, but VOC and 

ammonia need not be regulated 

precursors. The EPA or the states could 

rebut the initial presumptions regarding 

NOX, VOC or ammonia on an area-byarea basis with a demonstration 

approved by the Administrator and thus 

reverse any of those presumptions in the 

state’s implementation plan for that 

area.240

As described above in Section II.C of 

this preamble, in January 2013 the court 

in NRDC v. EPA held that the EPA erred 

in implementing the PM2.5 NAAQS 

pursuant only to the general 

implementation requirements in subpart 

1, rather than also to the 

implementation requirements specific to 

particulate matter in subpart 4. 

Accordingly, the court directed the EPA 

to comply with the requirements of 

subpart 4 when developing 

implementing regulations for PM2.5

nonattainment areas. 

The court decision, requiring that the 

EPA implement the PM2.5 NAAQS 

consistent with the requirements of 

subpart 4, clearly has specific 

implications for implementing the 

NNSR program for PM2.5. Two 

provisions of subpart 4 impose 

additional requirements on the existing 

NNSR program requirements for PM2.5. 

The first relates to the definition of 

‘‘major stationary source.’’ Section 

188(b) provides that some areas initially 

designated as Moderate areas for PM10

subsequently may be reclassified as 

Serious areas. For any PM10

nonattainment area reclassified as a 

Serious area, section 189(b)(3) provides 

that a major stationary source of PM10 be 

defined to include any stationary source 

or group of stationary sources located 

within a contiguous area and under 

common control that emits or has the 

potential to emit at least 70 tpy of PM10. 

In accordance with the statute, the EPA 

is proposing to establish a major source 

emissions threshold for stationary 

sources of PM2.5 that satisfies the intent 

of section 189(b)(3). 

The second relevant subpart 4 

provision governs the treatment of major 

sources of PM10 precursors. As 

previously explained in Section III.A of 

this preamble, the court specifically 

criticized the EPA’s prior establishment 

of the rebuttable presumptions for 

addressing PM2.5 precursors, 

specifically citing the requirement of 

section 189(e). Section 189(e) requires 

that the control requirements in the plan 

applicable to major stationary sources of 

PM10 must also apply to major 

stationary sources of PM10 precursors. 

Section 189(e) also provides that states 

may elect not to impose control 

requirements on major stationary 

sources of PM10 precursor emissions if 

such emissions do not contribute 

significantly to ambient PM10

concentrations that exceed the standard 

in the PM10 nonattainment area. Section 

189(e) requires that the EPA must make 

this determination, and thus the EPA 

must approve the decisions of a state 

that elects to use this provision to 

exempt any major stationary sources of 

PM2.5 precursors from controls in its 

attainment plan or NNSR program. 

The court’s observation that the EPA’s 

prior presumptions regarding precursors 

were inconsistent with the explicit 

requirements of section 189(e) that 

major sources of all PM2.5 precursors are 

subject to control requirements thus 

necessitates that the agency revise the 

NNSR regulations governing precursors 

for PM2.5. As explained in greater detail 

later in this section, the EPA is 

proposing different potential options to 

make the necessary changes to the 

NNSR regulations in order to address 

the precursor requirements contained in 

subpart 4. 

C. What are the changes the EPA is 

proposing for NNSR for PM2.5

nonattainment areas? 

In this section, the EPA presents for 

comment certain proposed revisions to 

the NNSR regulations as well as 

alternative approaches for incorporating 

the subpart 4 requirements into the 

NNSR regulations for PM2.5. The 

proposed changes would affect the 

existing regulations at 40 CFR 51.165 

and part 51 Appendix S. The agency 

does not intend to propose any changes 

to the regulations at 40 CFR 52.24, 

which provide the authorization for 

states to issue NNSR permits to major 

new sources and major modifications 

‘‘during the period between the date of 

designation as nonattainment and the 

date the NSR permit program meeting 

the requirements of part D is approved.’’ 

1. What are the changes the EPA is 

proposing for the NNSR requirements 

for PM2.5 at 40 CFR 51.165? 

As explained above, the existing 

NNSR regulations applicable to PM2.5

are based solely on the permit 

requirements contained in section 173 

of subpart 1. In subpart 4, section 

189(a)(1)(A) requires states to include in 

their SIPs for PM10 nonattainment areas 

a permit program meeting the 

requirements of section 173; however, 

other provisions in subpart 4 add 

additional requirements for the NNSR 

permit program. Those additional 

provisions concern (i) the definition of 

‘‘major stationary source’’ in 

nonattainment areas classified as 

Serious areas, and (ii) control 

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241See the definition of ‘‘regulated NSR 

pollutant’’ at existing 40 CFR 

51.165(a)(1)(xxxvii)(C)(2) and (3). 

requirements for applicable major 

stationary sources of PM10 precursors. 

While those particular requirements in 

subpart 4 refer specifically to PM10, the 

EPA is proposing to add similar 

requirements for PM2.5 in accordance 

with the court’s holding in NRDC v. 

EPA that subpart 4 also governs 

implementation of the PM2.5 NAAQS. 

a. Definition of ‘‘major stationary 

source’’ in Serious PM2.5 nonattainment 

areas. In Section III.A of this preamble, 

the EPA indicated its intention to 

propose new provisions based on the 

requirements in subpart 4 for 

reclassifying certain PM2.5

nonattainment areas as Serious areas. 

Because the NNSR regulations for PM2.5

set forth in the 2008 PM2.5 NSR Rule 

were developed pursuant to subpart 1, 

which does not provide for the 

classification of designated 

nonattainment areas, the EPA has not 

yet developed regulations to address 

subpart 4 requirements concerning 

nonattainment areas classified as 

Serious. With respect to NNSR, section 

189(b)(3) provides that, for any PM10

nonattainment area classified as 

Serious, the major source threshold with 

regard to the terms ‘‘major source’’ and 

‘‘major stationary source’’ shall be 70 

tpy of PM10. Accordingly, the EPA is 

proposing to amend the NNSR 

regulations at 40 CFR 51.165 consistent 

with this provision to establish a major 

source threshold for new major 

stationary sources and major 

modifications in PM2.5 nonattainment 

areas classified as Serious consistent 

with subpart 4. The EPA is proposing to 

set the major source threshold for direct 

PM2.5 emissions at 70 tpy. See proposed 

40 CFR 51.165(a)(1)(iv)(A)(1)(vii). 

While the court decision did not 

mandate that the EPA define ‘‘major 

source’’ and ‘‘major stationary source’’ 

for PM2.5 at a threshold of 70 tpy of 

PM2.5 emissions for areas reclassified as 

Serious, the most straightforward and 

consistent application of section 

189(b)(3) to PM2.5 nonattainment areas 

is to establish the same numerical 

threshold for Serious PM2.5

nonattainment areas as that which 

applies to Serious PM10 nonattainment 

areas. Moderate nonattainment areas for 

both PM10 and PM2.5 are already subject 

to the same major source thresholds by 

statute, so the EPA believes that it is 

also reasonable to establish the 

threshold for PM2.5 in Serious areas at 

the same level as the threshold that 

applies to PM10 in Serious areas. For the 

reasons explained below, the EPA 

believes that potential alternative 

approaches to setting the major source 

threshold for Serious PM2.5

nonattainment areas could have 

significant drawbacks. Nevertheless, the 

EPA is proposing and requesting 

comments on other possible thresholds 

for Serious areas. 

A possible alternative approach 

would be to promulgate a PM2.5 major 

source threshold lower than 70 tpy of 

PM2.5 emissions, recognizing that PM2.5

is a subset of PM10. Generally, any 

source’s PM2.5 emissions will be a 

fraction of that source’s PM10 emissions. 

However, determining the appropriate 

major source emissions threshold for 

PM2.5 that would be equivalent to 70 tpy 

of PM10 on a national basis is 

problematic because, while PM2.5 is 

generally a subset of PM10, there is not 

a consistent ratio of PM2.5 to PM10

emissions for all stationary sources. 

Combustion sources, such as industrial 

and commercial boilers that burn fossil 

fuels, and selected industrial processes 

emit primarily finer particles within the 

PM2.5 size range, while other industrial 

processes—typically involving crushing 

and grinding operations—tend to emit 

more coarse particles in the PM10 size 

range. While the PM10: PM2.5 ratio for 

most sources decreases when the overall 

emissions of PM are controlled, the 

quantitative difference between PM2.5

emissions and PM10 emissions from 

specific sources can still be significant, 

thus making a national PM2.5 major 

source threshold based on a single ratio 

difficult to define. The EPA seeks 

comments on possible ways in which a 

PM2.5 emissions rate different from the 

statutory 70 tpy rate for PM10 emissions 

can be established, taking into account 

variations in the PM10: PM2.5 ratio for 

different source categories and 

activities. 

Accordingly, while the EPA seeks 

comment on this alternative approach, 

because of the associated limitations 

just described, the first option (i.e., a 

major source threshold of 70 tpy of 

PM2.5 emissions for stationary sources 

proposing to construct or modify in 

PM2.5 nonattainment areas reclassified 

as Serious) represents the agency’s 

preferred approach. 

b. Control requirements for new major 

stationary sources and major 

modifications of PM2.5 precursors. The 

second key provision contained in 

subpart 4 that is not contained in 

subpart 1 relates to the control of major 

stationary sources and major 

modifications of precursor pollutants. 

Section 189(e) provides that, with 

respect to NNSR, the control 

requirements applicable to major 

stationary sources of PM10 also apply to 

major stationary sources of PM10

precursors, except that major stationary 

sources of a particular precursor may be 

exempt from the control requirements 

that apply to major stationary sources of 

PM10 if the state can demonstrate (based 

on guidance provided by the EPA) that 

the precursor emissions from those 

sources do not contribute significantly 

to ambient PM10 concentrations that 

exceed the standard in the 

nonattainment area. 

The specific ‘‘control requirements’’ 

for new or modified major stationary 

sources of PM2.5 are contained in section 

173 of the CAA (outlining requirements 

for the state permit program required to 

be submitted in a state plan under 

section 189(a)(1)(A)) and 189(b)(3) 

(establishing a major source threshold 

for sources in Serious areas). Consistent 

with these requirements, the EPA is 

proposing a series of revisions to 

address PM2.5 precursors in the NNSR 

regulations at 40 CFR 51.165, including: 

Revision of the definition of ‘‘regulated 

NSR pollutant’’ to require regulation 

under the permitting program of all 

PM2.5 precursors; the establishment of 

major stationary source thresholds (for 

both Moderate areas and Serious areas) 

for all PM2.5 precursors; and, a provision 

for an exemption from the NNSR 

requirements, pursuant to section 189(e) 

of the CAA, for major stationary sources 

of any PM2.5 precursor where such 

sources do not contribute significantly 

to ambient concentrations of PM2.5 that 

exceed the standard in a particular 

nonattainment area. As described in 

greater detail below, the EPA is not at 

this time proposing any new significant 

emissions rates for the PM2.5 precursors. 

As described in Section VIII.A.2.b of 

this preamble, the NNSR regulations at 

40 CFR 51.165 currently require states 

to regulate new major stationary sources 

and major modifications of SO2 and 

NOX as precursors under the NNSR 

requirements for PM2.5.241 Optionally, a 

state may avoid regulating new major 

stationary sources and major 

modifications of NOX under the NNSR 

requirements for PM2.5 if that state 

demonstrates to the satisfaction of the 

EPA that NOX is not a significant 

contributor to PM2.5 concentrations in a 

particular PM2.5 nonattainment area. 

Similarly, the existing regulations 

provide that a state may opt to regulate 

new major stationary sources and major 

modifications of VOC or ammonia 

under the NNSR requirements for PM2.5

if that state demonstrates to the 

satisfaction of the EPA that VOC or 

ammonia are precursors for PM2.5 that 

need to be controlled in a particular 

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242 Ibid at (a)(1)(xxxvii)(C)(3) and (4). 

243 ‘‘Different pollutants, including precursors, 

are not summed to determine applicability.’’ See 73 

FR 28231 (May 16, 2008), at page 28331. 244 Ibid. 245 Ibid. 

246See 57 FR 13498 (April 16, 1992), at page 

13538. 

PM2.5 nonattainment area.242 In 

accordance with the court’s statement 

that section 189(e) requires all PM2.5

precursors to be addressed, the EPA is 

proposing to revise the NNSR 

regulations to require that new major 

stationary sources and major 

modifications of SO2, NOX, VOC and 

ammonia meet the NNSR requirements 

for PM2.5 in PM2.5 nonattainment areas. 

In doing so, the EPA believes that it is 

necessary to propose several revisions to 

40 CFR 51.165 to ensure that the NNSR 

requirements for PM2.5 adequately 

address the regulated precursors 

consistent with the requirements of 

subpart 4. 

First, the EPA is proposing to revise 

the regulations at 40 CFR 51.165 to 

ensure that new major stationary 

sources and major modifications of the 

four scientific precursors for PM2.5 are 

subject to the same requirements under 

the NNSR regulations that apply to new 

major stationary sources and major 

modifications of direct PM2.5 emissions. 

As explained earlier in this preamble, 

the court decision in NRDC vs. EPA 

concluded that section 189(e) 

‘‘expressly governs precursor 

presumptions’’ and thus necessitates 

that the EPA revise its existing 

provisions in the NNSR rules that 

indicate that VOC and ammonia are not 

regulated PM2.5 precursors. The EPA is 

thus proposing to revise the NNSR 

definition of ‘‘regulated NSR pollutant’’ 

to ensure that the NNSR regulations are 

consistent in establishing that SO2, NOX, 

VOC and ammonia are all regulated 

PM2.5 precursors for purposes of NNSR 

requirements, except under certain 

conditions explained below. See 

proposed 40 CFR 

51.165(a)(1)(xxxvii)(C)(2). 

While section 189(e) generally 

requires that major stationary sources of 

PM2.5 precursors must apply the control 

requirements (including those for 

NNSR) for major stationary sources of 

direct PM2.5 emissions, the section also 

provides for an exemption from such 

requirements for any precursor for 

which ‘‘the Administrator determines 

that such sources do not contribute 

significantly’’ to the levels of PM2.5 that 

exceed the standard in the 

nonattainment area. Section 189(e) 

further authorizes the EPA to issue 

guidelines concerning the application of 

the exemption process. 

In Section III of this preamble, the 

EPA described the agency’s proposed 

approaches for interpreting 

requirements for states to control PM2.5

precursors in their attainment plans for 

the PM2.5 NAAQS, which includes 

several proposed options to enable 

states to exempt a precursor from the 

attainment plan control requirements 

(including NNSR) for a particular PM2.5

nonattainment area with the appropriate 

factual and analytical basis. In 

summary, the options included: (i) 

Separate analyses to determine which 

precursors are subject to the control 

requirements for attainment plans and 

which precursors are subject to the 

control requirements for NNSR for 

PM2.5; (ii) a technical demonstration 

showing that all sources of a particular 

precursor do not significantly contribute 

to the PM2.5 levels that exceed the 

standard in an area, thus exempting the 

precursor from control under both the 

attainment plan and NNSR programs; 

and, (iii) one analysis to determine 

whether control measures for a 

precursor are not needed for expeditious 

attainment for purposes of the 

attainment plan, which would also 

define the precursors that should be 

addressed for NNSR for PM2.5. 

Accompanying the description of each 

of the above options, Section III.C of this 

preamble discusses the potential 

analytical requirements for any 

proposed demonstration that any 

particular precursor should be 

exempted from the control requirements 

for PM2.5 in a given nonattainment area. 

The EPA is requesting comments on the 

three precursor options and the 

technical approaches for requesting a 

precursor exemption. Any comments 

received will be considered in 

developing the agency’s final policy for 

addressing PM2.5 precursors under the 

NNSR program for PM2.5. 

The second proposed change with 

regard to the nonattainment area control 

requirements for PM2.5 precursors 

involves the definition of ‘‘major 

stationary source’’ as it relates 

specifically to precursors. The EPA is 

proposing to revise the definition of 

‘‘major stationary source’’ contained in 

the NNSR regulations to ensure that 

new sources that emit major amounts of 

any PM2.5 precursor that the state is 

regulating in the attainment plan for the 

area are appropriately considered major 

stationary sources subject to the NNSR 

requirements for PM2.5. See proposed 40 

CFR 51.165(a)(1)(iv)(A)(1). The 

proposed change concerning the 

regulation of precursors for PM2.5 is 

being accomplished by adding to the 

term ‘‘regulated NSR pollutant’’ the 

phrase ‘‘(as defined in paragraph 

(a)(1)(xxxvii) of this section).’’ It should 

be noted that the definition of ‘‘major 

modification’’ already contains this 

phrase. As described above, the EPA is 

also proposing to revise the definition of 

‘‘regulated NSR pollutant’’ to clarify that 

four precursors are being regulated for 

PM2.5 in nonattainment areas for PM2.5.

The EPA is proposing to set the major 

source threshold for each PM2.5

precursor (SO2, NOX, VOC and 

ammonia) at 100 tpy of each precursor 

for sources locating in Moderate areas, 

and 70 tpy of any precursor for sources 

locating in Serious areas. See proposed 

40 CFR 51.165(a)(1)(iv)(A)(1) and 

(a)(1)(viii), respectively. For example, in 

order to be a major source for purposes 

of the PM2.5 NAAQS, the source would 

need to emit at least 100 tpy of PM2.5

emissions or at least 100 tpy of any 

individual PM2.5 precursor that is a 

regulated precursor in a Moderate PM2.5

nonattainment area. The individual 

treatment of pollutants and precursors 

for applicability purposes is consistent 

with the EPA’s policy as explained in 

previous rulemakings.243

In proposing to set the major source 

threshold for each PM2.5 precursor at 

100 tpy for Moderate areas, the EPA is 

following the precedent established in 

the 2008 PM2.5 NSR Rule in which the 

agency set the same 100 tpy major 

source threshold for PM2.5 and each of 

its precursors (at that time SO2 and 

NOX).244 As the EPA stated in that 2008 

notice, sections 169 and 302(j) of the 

CAA contain definitions of ‘‘major 

emitting facility’’ and ‘‘major stationary 

source’’ that apply to programs 

implemented under subpart 1, which 

contain the PSD and NNSR program 

requirements, respectively.245 Those 

definitions also apply to programs 

implemented under subpart 4 to the 

extent that they regulate areas classified 

as Moderate PM2.5 nonattainment areas, 

as subpart 4 does not establish a 

different threshold for such areas. This 

proposal to set the same 100 tpy major 

source thresholds for sources of PM2.5

emissions and applicable PM2.5

precursor emissions is also consistent 

with the requirements of section 189(e), 

which make the control requirements 

applicable to major stationary sources of 

PM10 also applicable to major stationary 

sources of applicable PM10

precursors.246

As noted above, section 189(b)(3) sets 

a lower major source threshold of 70 tpy 

of PM10 emissions for sources locating 

in PM10 nonattainment areas reclassified 

as Serious. Because subpart 4 NNSR 

requirements must be applied to PM2.5, 

the EPA must set a lower major source 

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247See Addendum to the General Preamble, 59 

FR 41998 (August 16, 1994), at page 42012 (defining 

major point sources in Serious areas as ‘‘sources 

with the potential to emit at least 70 tons per year 

of PM10 (or PM10 precursors) as required in sections 

189(b)(3) and 189(e) of the Act’’). 

248The technical assessment, with details on data 

and modeling inputs, was fully described in a 

technical memo titled ‘‘Details on Technical 

Assessment to Develop Interpollutant Trading 

Ratios for PM2.5 Offsets,’’ which was placed in the 

docket to the 2008 final rule. See also 73 FR 28321 

(May 16, 2008), at page 28339. 

249Memorandum from Gina McCarthy, then EPA 

Assistant Administrator, dated July 21, 2011, titled 

‘‘Revised Policy to Address Reconsideration of 

Interpollutant Trading Provisions for Fine Particles 

(PM2.5)’’ and sent to Regional Air Division Directors. 

250Nevertheless, while the ratios are no longer 

considered appropriate to use presumptively to 

meet the NNSR requirements for emissions offsets, 

a state may still conduct its own analysis and 

propose area-specific ratios for EPA approval on a 

case-by-case basis for interpollutant offset trading. 

251See South Coast Air Quality Management 

District v. EPA, 472 F.3d 882, 900–902 (D.C. Cir. 

2006) (holding that ‘‘controls’’ in section 172(e) 

anti-backsliding provision include NSR 

requirements such as LAER, offset ratios, and major 

source thresholds). 

252H.R. Rep. 101–490. 

threshold for PM2.5, pursuant to section 

189(b)(3), in PM2.5 nonattainment areas 

that are reclassified as Serious areas. 

Thus, the EPA’s preferred approach 

proposed above is to set a major source 

threshold of 70 tpy of PM2.5 emissions 

for sources in PM2.5 nonattainment areas 

reclassified as Serious. 

Consistent with this proposal, the 

EPA is also proposing to set the major 

source threshold for Serious areas for 

each precursor at 70 tpy of that 

particular precursor. As noted above, 

section 189(e) makes the control 

requirements for major stationary 

sources of PM10 also applicable to major 

stationary sources of PM10 precursors; 

thus, in accordance with the provision 

of the statute, the control requirements 

applicable to major stationary sources of 

PM2.5 emissions are also applicable to 

major stationary sources of PM2.5

precursors. Accordingly, the EPA must 

develop a major source threshold for 

PM2.5 precursors that is consistent with 

the threshold for direct PM2.5 that will 

apply in PM2.5 nonattainment areas 

reclassified as Serious. See proposed 40 

CFR 51.165(a)(1)(iv)(1)(viii). 

The EPA’s proposal to set a major 

source threshold of 70 tpy for Serious 

areas for each PM2.5 precursor is also 

consistent with the approach the EPA 

has taken for establishing a major source 

threshold for each PM10 precursor under 

subpart 4. In the Addendum to the 

General Preamble offering guidance as 

to how to apply the new subpart 4 

requirements in Serious areas, the EPA 

indicated that it interpreted the statute 

as applying the 70 tpy threshold to 

sources of PM10 precursors.247

The EPA also solicits comments on 

the appropriateness of setting the 

precursor major source thresholds at a 

different rate, particularly if, as 

alternatively proposed above, the 

agency defines ‘‘major stationary 

source’’ for sources of direct PM2.5 in 

Serious PM2.5 nonattainment areas at a 

rate lower than 70 tpy of PM2.5

emissions. For example, if the agency 

sets the major source threshold at 60 tpy 

of PM2.5 emissions in Serious PM2.5

nonattainment areas, the agency would 

also consider setting the major source 

threshold for each PM2.5 precursor at 60 

tpy of that particular precursor. 

Moreover, the EPA believes that a 

reasonable argument can be made that 

whatever threshold is set for PM2.5

emissions, the same level would be too 

low to be regarded as ‘‘major’’ for each 

precursor when considering the effects 

that such precursor sources could have 

on ambient PM2.5 concentrations. The 

EPA previously analyzed the 

relationship between emissions of SO2

and NOX and the formation of 

secondary PM2.5 in the ambient air 

expressly for purposes of determining 

an appropriate ratio for allowing 

interprecursor offsets for PM2.5. Those 

studies resulted in the EPA providing in 

the 2008 PM2.5 NSR Rule ‘‘preferred’’ 

ratios for both SO2 and NOX, whereby 

a source could obtain reductions of a 

PM2.5 precursor to offset an increase of 

direct PM2.5 emissions or another PM2.5

precursor based on the ‘‘preferred’’ 

offset ratios.248 In brief, the preferred 

ratios were as follows: For NOX-toprimary PM2.5: 200 to 1 (NOX tons to 

PM2.5 tons) for areas in the eastern U.S, 

and 100 to 1 for areas in the western 

U.S.; and for SO2-to-primary PM2.5: 40 to 

1 (SO2 tons for PM2.5 tons). In each case, 

the ratio illustrates that it requires 

considerably more precursor emissions 

than direct PM2.5 emissions to result in 

a particular ambient concentration of 

PM2.5. It should be noted that at that 

time the EPA did not consider using the 

preferred ratios for the purpose of 

adjusting the major source thresholds or 

significant emissions rates for SO2 and 

NOX when regulating them as PM2.5

precursors. 

The preferred ratios as presented in 

the 2008 notice were later challenged in 

a petition for reconsideration and the 

EPA withdrew them via an EPA 

memorandum issued in 2011.249 In 

withdrawing the preferred ratios, the 

EPA cited several concerns. First, it was 

determined that the preferred ratios 

were not sufficiently conservative to be 

representative of conditions in all areas 

of the country. Second, the EPA 

determined that the preferred ratios 

were not adequate for addressing the 

precursor relationship to ambient PM2.5

concentrations for the short-term (daily) 

averaging period.250 In addition, the 

EPA believes that the overall analysis 

conducted for the 2008 notice generally 

illustrates that the threshold for defining 

‘‘major’’ for either SO2 or NOX as 

precursors for PM2.5 could reasonably be 

set at an emissions rate considerably 

higher than 70 tpy of that particular 

precursor and be equally protective of 

air quality as the 70 tpy threshold 

applied to PM2.5 emissions. 

Although the statutory definition at 

section 189(b)(3) applicable to PM10

does not explicitly apply to other 

pollutants, the EPA is considering the 

possibility that it may not have the legal 

authority to set a higher major source 

threshold for PM2.5 precursors, even if it 

were technically justified. As previously 

noted, section 189(e), as interpreted in 

light of the court decision in NRDC v. 

EPA, requires that the same control 

requirements applicable to major 

stationary sources of PM2.5 also apply to 

major stationary sources of PM2.5

precursors. Courts have determined in 

other contexts that the term ‘‘controls’’ 

under the CAA includes NSR 

requirements, and in particular includes 

major source thresholds as specified in 

the statute.251 Thus, if the holding of 

South Coast directs the EPA’s actions, 

section 189(e) must be read to require 

the same major source threshold be 

applied to PM2.5 precursors as applies to 

direct emissions of PM2.5.

This conclusion is also consistent 

with the limited legislative history on 

this issue. A House (of Representatives) 

Report accompanying the 1990 

amendments to the CAA described the 

effects of adding section 189(b)(3) to 

include the requirement that ‘‘new or 

modified sources emitting 70 tons or 

more per year of VOC will be subject to 

new source review requirements.’’ 252

Thus, Congress seems to have 

contemplated that the same major 

source threshold would apply to sources 

of PM2.5 emissions and PM2.5 precursors 

in Serious areas. 

The EPA does not believe that a 

sufficient technical basis exists at this 

time to enable the agency to propose 

specific higher major source thresholds 

for any of the four PM2.5 precursors 

presumptively regulated in PM2.5

nonattainment areas. The EPA intends 

to continue its analysis of the 

relationship between each precursor 

and ambient PM2.5 concentrations with 

the possibility that higher major source 

thresholds for specific precursors could 

be established in the future. In the 

meantime, the agency solicits comments 

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253See the Federal Register published on May 16, 

2008 (73 FR 28321, 28333 and 28334); and existing 

40 CFR 51.165(a)(1)(x)(A). 

254See the Federal Register published on May 16, 

2008 (73 FR 28321 and 28333). 

255 Ibid. 

256See 73 FR 28321 (May 16, 2008), at page 

28334. 

257Compare CAA section 165(a) (permitting 

requirements for sources locating in attainment and 

unclassifiable areas) with sections 172(c)(5) and 173 

(permitting requirements for sources locating in 

nonattainment areas). 

258See Memorandum from John S. Seitz, Director, 

EPA Office of Air Quality Planning and Standards, 

on March 11, 1991, titled ‘‘New Source Review 

(NSR) Transitional Guidance,’’ Attachment p. 6, 

sent to Regional Air Division Directors. 

on the general appropriateness of setting 

higher major source thresholds for one 

or more PM2.5 precursors in PM2.5

nonattainment areas, as well as legal 

and technical considerations that 

should be made as part the EPA’s future 

analysis of NNSR requirements with 

respect to PM2.5 precursors. 

c. Significant emissions rates for PM2.5

precursors. As explained above, a 

modification to an existing major 

stationary source of a nonattainment 

pollutant such as PM2.5 is a major 

modification and subject to the NNSR 

requirements for that pollutant when 

the source proposes to make a physical 

or operational change that results in 

both a significant emissions increase 

and a significant net emissions increase 

of that nonattainment pollutant. With 

regard to PM2.5 precursors, a 

modification to a major stationary 

source of any such precursor is likewise 

a major modification subject to the 

NNSR requirements for PM2.5 when the 

source proposes a physical or 

operational change resulting in a 

significant net emissions increase of that 

precursor. The EPA defined 

‘‘significant’’ for SO2 and NOX as PM2.5

precursors in the 2008 PM2.5 NSR Rule. 

For both precursors, the EPA set the 

significant emissions rate for each 

pollutant when it is regulated as a 

precursor to PM2.5 at 40 tpy, the same 

level as the existing significant 

emissions rate for the pollutant as 

independently regulated as a criteria 

pollutant for purposes of the SO2 and 

NO2 NAAQS.253 Also, in the preamble 

to the 2008 PM2.5 NSR Rule, the EPA 

indicated that it would consider 40 tpy 

for VOC as a PM2.5 precursor; however, 

that rate was not codified in any of the 

NSR regulations because the regulations 

provided that VOC was generally 

presumed not to be a precursor to PM2.5. 

Instead, the agency explained that any 

state making a demonstration that VOC 

should be treated as a PM2.5 precursor 

in a particular nonattainment area 

‘‘would be required to adopt the 40-tpy 

significant emissions rate unless it 

demonstrated that a more stringent 

significant emissions rate (lower rate) is 

more appropriate.’’ 254

The 2008 PM2.5 NSR Rule codified the 

presumption that ammonia, like VOC, 

need not be regulated as a PM2.5

precursor and the EPA did not set a 

significant emissions rate for ammonia. 

Instead, the agency indicated that it was 

allowing states that determine that 

ammonia significantly contributes to 

PM2.5 concentrations in a given PM2.5

nonattainment area to set the significant 

emissions rate for ammonia based on 

information developed for each 

individual attainment plan.255

As explained in the 2008 PM2.5 NSR 

Rule, the EPA set the significant 

emissions rates for the presumed PM2.5

precursors at the levels for those 

pollutants already included in NSR 

programs. The EPA explained that the 

use of the existing rates where the PM2.5

precursor is also regulated as a separate 

criteria pollutant harmonizes the NSR 

program for PM2.5 with the NSR 

programs for those other criteria 

pollutants. The agency further 

explained that this approach for setting 

the significant emissions rates for PM2.5

precursors follows the precedent for 

setting the significant emissions rate for 

NOX as a precursor to ozone, where the 

same 40 tpy threshold was used for NOX

emissions as both a criteria pollutant 

(NO2) and a precursor for ozone.256

Nevertheless, the EPA gave some 

consideration in the development of the 

2008 PM2.5 NSR Rule to setting the 

significant emissions rates for the 

individual PM2.5 precursors at different 

levels based on the effect of each 

precursor on ambient PM2.5

concentrations. The EPA concluded that 

it did not have adequate data on the 

impacts of precursor emissions from 

individual sources to override the 

administrative advantages of setting the 

significant emissions rates for SO2, NOX

and VOC for purposes of the PM2.5 NSR 

program at the same levels that are 

already used for other purposes in the 

major NSR program for other NAAQS. 

The EPA continues to believe, however, 

that when more data are available, these 

data could provide a reasonable basis 

for considering subsequent changes to 

the significant emissions rates for each 

PM2.5 precursor for purposes of 

implementing the PM2.5 NAAQS, 

whereby the significant emissions rates 

for the individual PM2.5 precursors 

could more realistically reflect the effect 

that each precursor has on ambient 

PM2.5 concentrations. 

The EPA is currently undertaking a 

separate rulemaking for both NNSR and 

PSD in which it intends to include a 

technical analysis of each PM2.5

precursor to better understand the 

relationship of emissions of each 

precursor to ambient PM2.5

concentrations. The agency intends to 

consider the results of that analysis and 

other factors and may propose new 

significant emissions rates accordingly 

for SO2 and NOX as PM2.5 precursors. 

The EPA also intends to propose 

individual significant emissions rates 

for VOC and ammonia as PM2.5

precursors at that time. Thus, the EPA 

is not proposing any changes to the 

existing significant emissions rates for 

SO2 and NOX as PM2.5 precursors in this 

document. 

It is the EPA’s expectation that any 

new or revised significant emissions 

rates for the individual PM2.5 precursors 

will become effective in that separate 

rulemaking not long after the date of 

that final rule, allowing states to adopt 

and use them in their own NNSR 

regulations once the EPA approves their 

individual SIPs. However, in the event 

that the timing of that rule does not 

allow ample time for states to rely on it 

to adopt any new or revised significant 

emissions rates in their rules, it was 

explained earlier that individual 

significant emissions rates already exist 

for SO2 and NOX at 40 tpy. 

Additionally, the significant emissions 

rate for VOC was identified as 40 tpy in 

the 2008 PM2.5 NSR Rule notice (though 

not in the final regulations), but the EPA 

is proposing to add that precursor and 

emissions rate to the list of PM2.5

precursors. See proposed 40 CFR 

51.165(a)(1)(x)(A). Hence, only the 

ammonia significant emissions rate 

would remain to be defined by each 

state that needs to control major 

stationary sources of ammonia as part of 

their NNSR program. 

d. Transition provisions for PM2.5. The 

CAA requires proposed major stationary 

sources and major modifications to meet 

major NSR permitting requirements that 

apply on the basis of the area’s 

attainment designation.257 Accordingly, 

the EPA’s longstanding interpretation of 

the CAA is that a proposed new major 

stationary source or major modification 

must satisfy the appropriate major NSR 

requirements (PSD vs. NNSR) for a 

particular pollutant that are in effect on 

the date that a permit is issued to the 

source, rather than the requirements 

that may have been applicable when the 

permit application was submitted.258

In the final 2012 PM NAAQS rule, the 

EPA established a grandfathering 

provision that would enable some 

proposed new and modified sources 

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259See 78 FR 3086 (January 15, 2013), at page 

3263. 

260The applicable NNSR requirements would be 

either the NNSR requirements for PM2.5 in the 

state’s existing SIP or the requirements found at 40 

CFR part 51 Appendix S, where a state’s SIP does 

not currently include NNSR requirements for PM2.5. 

States will be required to submit to the EPA for 

approval SIP revisions containing the amended 

NNSR program requirements for PM2.5 contained in 

the final PM2.5 NAAQS implementation rule being 

proposed in this notice, but those additional 

requirements will not apply in states with SIPs that 

include NNSR requirements for PM2.5 until the EPA 

approves the SIP revision. See ibid. 261 Ibid. 

that had already submitted a PSD 

application prior to the effective date of 

the revised primary annual PM2.5

NAAQS to continue being reviewed 

under the pre-existing PSD 

requirements for PM2.5. This provision 

applies where the PSD program 

continues to be the applicable set of 

major NSR requirements for the area of 

concern. In response to the EPA’s 

proposal to add this grandfathering 

provision for certain PSD permit 

applications pending upon the effective 

date of the new NAAQS, the EPA 

received comments concerning the need 

for a transition period for implementing 

the NNSR requirements in newly 

designated PM2.5 nonattainment areas as 

a result of the tightening of the primary 

annual PM2.5 NAAQS.259 The 

commenters recommended that the EPA 

establish a grandfathering provision to 

enable pending permit applications to 

continue under review for the preexisting requirements. A subset of the 

commenters recommended that 

grandfathering be accomplished by 

establishing an effective date for 

designations 1 year after initial 

publication in the Federal Register. 

Presumably, these commenters believed 

that by delaying the effective date of any 

new nonattainment designations for the 

primary annual PM2.5 NAAQS, sources 

with pending PSD permit applications 

could continue to be reviewed under the 

PSD permitting requirements rather 

than the NNSR requirements for PM2.5. 

In the final 2012 PM NAAQS rule, the 

EPA expressed its disagreement with 

those commenters, explaining that the 

obligation to adopt new provisions 

under a state’s NNSR program will not 

apply with regard to the revised NAAQS 

until such time as an area is designated 

nonattainment, and beginning on the 

effective date of the new area 

designations for PM2.5 proposed new 

and modified major sources would be 

required to meet the applicable NNSR 

requirements for PM2.5.260 However, the 

EPA further indicated that it would 

continue to consider the need to 

establish a grandfathering provision 

under the NNSR program for PM2.5, and 

would propose such provision, if 

appropriate, as part of a subsequent NSR 

implementation rulemaking with 

additional opportunity for public 

comment.261

After further considering the issue 

during the development of this 

proposal, the EPA has decided not to 

propose a grandfathering provision that 

would apply to pending PSD permit 

applications that were submitted but not 

approved prior to the effective date of 

the new nonattainment designations for 

the 2012 primary annual PM2.5 NAAQS. 

The EPA does not believe it would be 

acceptable for the EPA or a state to issue 

a PSD permit, instead of a NNSR permit, 

with regard to a particular pollutant for 

which an area is designated 

nonattainment on the date the permit is 

to be issued. Instead, if the PSD permit 

has not been issued by the effective date 

of the new nonattainment designation, 

then the applicant should be required to 

withdraw that part of the permit 

application that addresses the 

nonattainment pollutant and submit an 

application that satisfies the applicable 

NNSR or minor NSR requirements in 

effect in the implementation plan on the 

date the permit will be issued. Given 

adverse conditions that already exist in 

a nonattainment area and the 

congressional directive to reach 

attainment as expeditiously as 

practicable, construction at a major 

stationary source that significantly 

increases emissions in such an area 

should be expected to address NNSR 

requirements, even if this could cause 

delay to the permit applicant. 

As explained in Section VIII.D of this 

preamble, states will have 18 months 

from the date of the new nonattainment 

designations to revise their existing 

NNSR programs or establish new 

programs in accordance with the 

applicable requirements under subpart 

4. Where the area was already 

designated nonattainment for any prior 

PM2.5 NAAQS before the effective date 

of designations for the 2012 NAAQS, 

the state should continue to apply the 

NNSR requirements contained in the 

approved SIP to issue the final permit 

addressing all PM2.5 NAAQS until the 

new SIP revisions required by this rule 

are approved. In areas already 

designated nonattainment for any PM2.5

NAAQS but lacking an approved NNSR 

program that applies to PM2.5, the 

requirements of Appendix S may 

continue to be applied for issuing 

permits in that area. However, any 

changes to the Appendix S requirements 

that the EPA may make via this 

rulemaking must be implemented in any 

area that applies Appendix S once these 

revisions become effective. Section 

VIII.C.2 that follows discusses the 

possible changes to the NNSR 

requirements in Appendix S that the 

agency is proposing in this action. 

The EPA is not proposing to add any 

grandfathering provisions that would 

apply to changes in NNSR permitting 

requirements in areas that the EPA may 

already have designated nonattainment 

for PM2.5 at the time the source 

submitted a permit application. For 

reasons similar to those identified above 

in cases where an area designation 

changes, the EPA generally believes that 

major sources that would contribute to 

the air quality in an area that is not 

meeting the NAAQS for a particular 

pollutant should be expected to address 

the most current requirements that 

apply in the nonattainment area. The 

agency acknowledges it is possible that 

a proposed new or modified source may 

need to address additional precursor 

control requirements that did not apply 

when a permit application was 

submitted once the EPA’s final rule is 

promulgated and the appropriate 

revisions are approved into a state’s 

NNSR SIP. However, based on the terms 

of section 189(e) of the CAA, the EPA 

generally believes that those 

requirements should be addressed in 

pending permit applications unless the 

air agency has determined, and the EPA 

has approved such demonstration, that 

major stationary sources of that 

precursor do not contribute significantly 

to PM2.5 levels in the nonattainment 

area. Nevertheless, the agency 

recognizes that there may be certain 

circumstances where proposed 

construction might be delayed and an 

applicant may feel fundamental fairness 

would support exempting a particular 

pending permit from newly established 

requirements; therefore, the EPA seeks 

comment on what circumstances, if any, 

would justify a grandfathering provision 

for pending nonattainment NSR permits 

similar to the grandfathering provision 

promulgated in the final 2012 PM 

NAAQS Rule for PSD permitting 

purposes. See 40 CFR 51.166(i)(10) 

52.21(i)(11). In addition, the EPA 

requests comment on how such a 

grandfathering provision would be 

consistent with the relevant provisions 

of the CAA. The EPA does not believe 

the statutory deadline in section 165(c) 

that forms part of the EPA’s basis for 

grandfathering in the PSD context is 

applicable to NNSR permit decisions. 

2. What are the changes the EPA is 

proposing in Appendix S? 

As described above, 40 CFR 52.24(k) 

provides that the Emission Offset 

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Interpretative Ruling, 50 CFR part 51, 

Appendix S, shall govern permits to 

construct and operate for which a NNSR 

permit application is submitted between 

the effective date of designation as 

nonattainment and the date a state’s 

NSR permit program meeting the 

requirements of part D is approved and 

effective. The EPA is considering a 

range of options concerning how and 

whether to address the proposed 

subpart 4 requirements in the interim 

NNSR program requirements contained 

in Appendix S. 

Permitting requirements for new 

major stationary sources and major 

modifications in PM2.5 nonattainment 

areas were originally added to 

Appendix S in the 2008 PM2.5 NSR 

Rule. The amendments generally 

followed the NNSR requirement 

contained in subpart 1 of part D. 

However, in the 2008 PM2.5 NSR Rule, 

the EPA determined that, in light of the 

transitional function of Appendix S, it 

would be appropriate to regulate PM2.5

precursors under Appendix S in a 

manner that differed slightly from the 

regulatory approach taken in 40 CFR 

51.165. 

As explained in Section VIII.B.2 of 

this preamble, under the existing 

requirements for NNSR plans at 40 CFR 

51.165, SO2 is regulated as a PM2.5

precursor, NOX is presumed to be a 

regulated PM2.5 precursor, and VOC and 

ammonia are presumed not to be 

regulated precursors (with either states 

or the EPA having authority to rebut any 

such presumption for a particular 

nonattainment area). However, in 

developing Appendix S, the EPA 

determined that it would be premature 

to presume that NOX is a regulated 

PM2.5 precursor in all PM2.5

nonattainment areas that proposed new 

major sources and major modifications 

in those areas should be required to 

address as a prerequisite to obtaining a 

NNSR permit, while at the same time 

the states were in the process of 

determining whether in fact NOX

emissions contribute significantly to 

ambient PM2.5 concentrations in those 

areas. Accordingly, the EPA decided to 

delay implementing any control 

requirements for NOX as a PM2.5

precursor until the states completed the 

necessary analyses to determine the 

need for NOX controls as part of their 

SIP revisions addressing the revised 

PM2.5 NAAQS. Thus, the existing NNSR 

requirements for PM2.5 under Appendix 

S do not contain a requirement for 

proposed sources to consider the control 

of NOX emissions as a PM2.5 precursor. 

Moreover, as states presumptively did 

not need to regulate VOC and ammonia 

in accordance with the 2008 PM2.5 NSR 

Rule in 40 CFR 51.165, the EPA 

similarly did not require sources 

seeking permits pursuant to the 

Appendix S requirements to address 

those precursors. 

As an interim measure to facilitate 

permitting while states develop NNSR 

rules for PM2.5, the EPA believes that the 

NNSR requirements under Appendix S 

need not be identical to those governing 

states’ development of approvable 

programs pursuant to subpart 4, which 

requires regulation of all PM2.5

precursors unless a state provides, and 

the EPA approves, a demonstration that 

such control is not necessary for major 

stationary sources in the area under 

section 189(e). This is reasonable 

because the EPA anticipates that many 

states may be able to demonstrate to the 

EPA that there is not a need to regulate 

one or more PM2.5 precursors from 

major stationary sources in a given 

nonattainment area, as described in 

Section III of this preamble. 

Accordingly, the EPA is proposing to 

revise the definition of regulated NSR 

pollutant as contained in Appendix S to 

provide for the regulation of some 

precursors during the transition period, 

but not others. Specifically, for reasons 

explained below, the EPA is proposing 

to require that both SO2 and NOX be 

considered regulated PM2.5 precursors 

in Appendix S and is proposing a 

significant emissions rate of 40 tpy for 

NOX as a PM2.5 precursor. See proposed 

Sections II.A.31(iii)(b) and II.A.10(i) of 

Appendix S, respectively. However, this 

proposal would not provide states the 

option of submitting a demonstration 

that could relieve them of the obligation 

to regulate SO2 and NOX as PM2.5

precursors during the transition period. 

The EPA believes that it is not necessary 

or efficient to expend effort on such a 

demonstration for the transitional 

program, when states are developing the 

demonstration for submittal with the 

NNSR SIP submission that, when 

approved, would replace the Appendix 

S transitional program for that area. 

The EPA is proposing to include SO2

and NOX in Appendix S based on the 

principle that the national application 

of a transition program should 

correspond to the general expectation of 

what the prevailing regulation of 

precursors will ultimately be when SIPs 

are submitted. Although such 

expectations are uncertain at this time, 

it is nonetheless appropriate to base the 

transition program on them. The EPA 

believes it is likely in many cases that 

states will determine that emissions of 

VOC and/or ammonia do not contribute 

significantly to PM2.5 concentrations in 

the affected PM2.5 nonattainment area, 

although such determinations should be 

made on a case-by-case basis for 

individual PM2.5 nonattainment areas. 

On the other hand, the EPA expects 

that the cases where NOX does not 

contribute significantly to PM2.5

concentrations in the affected PM2.5

nonattainment area will be few in 

number. Accordingly, given this 

likelihood, the EPA believes that it is 

reasonable to require the regulation of 

SO2 and NOX as PM2.5 precursors during 

the interim period when states are 

developing their PM2.5 attainment plans 

for newly designated areas (including 

the necessary revisions to the NNSR 

programs based on subpart 4). An added 

benefit of this proposed approach is that 

it will also ensure that states using the 

permitting requirements contained in 

Appendix S will regulate the same 

precursors that are required to be 

regulated in states that have already 

adopted NNSR for PM2.5 based on the 

2008 PM2.5 NSR Rule. The EPA seeks 

comment on this approach as part of 

this proposal. 

As one alternative approach that the 

EPA is presenting for public comment, 

the agency is proposing to amend 

Appendix S to regulate not only SO2

and NOX, but also VOC and ammonia, 

as PM2.5 precursors that must be 

controlled during this interim period. 

This alternative would more closely 

match the basic NNSR program 

requirements of subpart 4, which 

indicate that states should regulate 

precursors from major stationary 

sources in the nonattainment area 

unless the EPA has determined that 

such emissions do not significantly 

contribute to violations of the NAAQS 

in the area. However, it would require 

states to control new major stationary 

sources and major modifications of each 

PM2.5 precursor during the interim 

period prior to submission of the 

required SIP revisions without the 

benefit of first allowing states to 

determine whether the control of each 

precursor is warranted. The EPA does 

not prefer this option for amending 

Appendix S as an interim NNSR 

program; however, the EPA is seeking 

comment on the approach to address the 

policy and legal implications associated 

with it. This alternative, while being 

proposed for comment, is not shown in 

the proposed regulatory text. 

Another alternative that the agency is 

proposing for comment is for the EPA to 

establish a phased-in process for 

regulating PM2.5 precursors in the NNSR 

program whereby states would initially 

require sources issued a permit to 

control only SO2 and NOX as PM2.5

precursors (as under the preferred 

option), with a second requirement to 

later require sources issued a permit 

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262 Ibid. 

263See ibid. 

264The policy for applying the PSD exemption is 

clear with regard to the federal PSD program at 40 

CFR 52.21; however, the requirements for a SIPapproved PSD program state that ‘‘[t]he plan may 

provide . . .’’ Accordingly, a state may choose to 

apply a different applicability strategy if it so 

wishes. 

265 Ibid. 

after the prescribed date (e.g., the date 

on which SIP revisions based on subpart 

4 requirements are due) to control 

emissions of VOC and ammonia as well. 

For each precursor, the requirement to 

control would apply to major stationary 

sources of that particular precursor. The 

EPA believes that by phasing in the 

requirement to address all precursors, 

states that are ultimately able to 

demonstrate to the EPA’s satisfaction 

that VOC and/or ammonia do not need 

to be subject to control under the NNSR 

requirements for PM2.5, but that have 

not yet submitted such demonstration, 

will have ample time to make the 

necessary demonstration and will not 

have to control such precursors even 

temporarily. At the same time, the 

phase-in provision could address 

concerns about delays in SIP submittal 

or approval in states with PM2.5

nonattainment areas in which VOC and 

ammonia need to be regulated. Such 

delays could result in prolonged 

exclusion of these precursors from 

control requirements beyond the time 

when an EPA-approved state NNSR 

program is expected to be in place. This 

alternative, while being proposed for 

comment, is not shown in the proposed 

regulatory text. 

Separately, the EPA is proposing to 

amend Appendix S by revising the 

definition of ‘‘major stationary source’’ 

to include a separate PM2.5 major source 

threshold applicable to new major 

stationary sources and major 

modifications in PM2.5 nonattainment 

areas reclassified as Serious areas. See 

proposed section II.A.4(i)(a)(7). 

Inclusion of the new definition is not an 

immediate concern for the revised 2012 

primary annual PM2.5 NAAQS or any 

future revision to the PM2.5 NAAQS 

because the possible reclassification of 

any Moderate area to a Serious area will 

not occur for several years and states are 

required to submit their SIP revisions 

addressing NNSR requirements prior to 

such time. There is a possibility, 

however, that existing PM2.5

nonattainment areas (for the 1997 and/ 

or 2006 PM2.5 NAAQS) could be 

reclassified as Serious areas sooner. 

States that still do not have approved 

NNSR programs addressing PM2.5 would 

be without the appropriate NNSR 

provisions to address new major 

stationary sources and major 

modifications in those Serious areas 

until they submit revisions to their 

existing programs and the EPA approves 

those revisions. The EPA solicits 

comments on this proposal to 

incorporate a definition of ‘‘major 

stationary source’’ for PM2.5

nonattainment areas reclassified as 

Serious. 

The EPA is not proposing any 

Appendix S provisions for 

grandfathering proposed new and 

modified sources from newly 

established permit requirements 

applicable to PM2.5 nonattainment areas. 

The EPA generally believes that it 

would not be appropriate to grandfather 

sources from requirements that apply in 

areas that are not meeting the NAAQS. 

Nevertheless, the EPA seeks comment 

on possible circumstances where 

grandfathering, similar to the 

grandfathering provision established for 

pending PSD permits under the final 

2012 p.m. NAAQS Rule, may be 

appropriate with respect to changes 

made to Appendix S. 

D. Plan Due Dates 

For Moderate areas, section 

189(a)(2)(B) requires that states make an 

attainment plan submission satisfying 

the requirements contained therein, 

including applicable NNSR programs 

for PM10 (and PM2.5), to the EPA for 

approval within 18 months of an area 

being designated nonattainment. The 

agency recognizes that this submittal 

date represents a considerably earlier 

date than anticipated when it issued the 

final 2012 p.m. NAAQS rule.262

However as the CAA requires, the EPA 

will apply the 18 month deadline from 

the effective date of designation of a 

Moderate PM2.5 nonattainment area for 

the submission of any applicable NNSR 

program revisions for PM2.5 as included 

in any final implementation rule. 

In the event a Moderate area is 

reclassified as a Serious PM2.5

nonattainment area, it will be required 

to implement the NNSR program with a 

‘‘major stationary source’’ threshold of 

70 tons per year (per CAA section 

189(b)(3)). However, the CAA does not 

specify a deadline for the state’s 

submittal of any NNSR program 

revisions (e.g., to lower the major 

stationary source threshold from 100 tpy 

to 70 tpy) that would be needed to 

implement the program in a Serious 

area. Pursuant to the EPA’s gap-filling 

authority in CAA section 301(a), and to 

effectuate the statutory control 

requirements in section 189 of the CAA, 

the EPA proposes to require the state to 

submit these NNSR SIP revisions no 

later than 18 months from the effective 

date of final reclassification of the area 

as a Serious nonattainment area. This 

timeframe is consistent with the 18 

month timeframe required for submittal 

of certain Serious area plan elements, 

and it is consistent with the 18 month 

time for submittal of Moderate area plan 

revisions. We also request comment on 

a 12-month timeframe for submittal of 

the NNSR revisions for Serious areas. 

An approach that requires the NNSR 

revisions to be submitted on the same 

18-month schedule as other Serious area 

plan elements is expected to be more 

administratively efficient than one that 

would require the NNSR revisions on a 

different schedule. On the other hand, 

this type of revision to the NNSR 

regulations may be relatively 

straightforward and potentially could be 

completed within 12 months of the 

reclassification date, thereby assuring 

that new major sources or modified 

major sources in the area will be subject 

to the lower statutory major source 

thresholds expeditiously. The EPA 

requests comment on both the proposed 

18-month timeframe for submission of 

the NNSR SIP revisions for Serious 

areas and the alternative 12-month 

option. 

E. Avoidance of Dual Review for PSD 

and NNSR for PM2.5

Because the EPA designates 

nonattainment areas for the primary 

annual and 24-hour PM2.5 NAAQS 

independently, some areas ultimately 

may be designated nonattainment for 

one of these standards and 

unclassifiable/attainment or attainment 

for another. This may raise concerns 

that the sources locating in such an area 

may be subject to both PSD and NSSR 

for the same pollutant. In the preamble 

to the final 2012 p.m. NAAQS rule, the 

EPA explained that the existing PSD 

regulations resolved this issue.263

Specifically, the PSD regulations at 40 

CFR 51.166(i)(2) and 52.21(i)(2) provide 

that the PSD requirements do not apply 

to a major stationary source or major 

modification with respect to a pollutant 

when ‘‘as to that pollutant, the source 

or modification is located in an area 

designated as nonattainment . . . .’’ 264

[emphasis added]. This policy was 

explained in the preamble to the final 

rule promulgating the revised primary 

annual PM2.5 NAAQS.265 The EPA is 

simply reiterating in this action the 

agency’s policy for addressing NSR 

applicability for areas that may be 

designated nonattainment for one 

averaging period and attainment or 

unclassifiable for another averaging 

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266 59 FR 41998 (August 16, 1994), at page 42004. 

267Section 319 of the CAA, as amended by 

section 6013 of the Safe Accountable Flexible 

Efficient-Transportation Equity Act: A Legacy for 

Users (SAFE–TEA–LU) of 2005, required the EPA 

to propose and promulgate regulations governing 

the review and handling of air quality monitoring 

data influenced by exceptional events. 

268References to ‘‘air agencies’’ are meant to 

include state, local and tribal air agencies 

responsible for implementing the Exceptional 

Events Rule. 

269The EPA will generally consider human 

activity to have played little or no direct role in 

causing emissions of the dust generated by high 

wind for purposes of the regulatory definition of 

‘‘natural event’’ if contributing anthropogenic 

sources of the dust are reasonably controlled at the 

time of the event, regardless of the amount of dust 

coming from these reasonably controlled 

anthropogenic sources, and thus the event could be 

considered a natural event. In such cases, the EPA 

believes that it would generally be a reasonable 

interpretation of its regulations to find that the 

anthropogenic source had ‘‘little’’ direct causal role. 

If anthropogenic sources of windblown dust that are 

reasonably controllable but that did not have those 

reasonable controls applied at the time of the high 

wind event have contributed significantly to a 

measured concentration, then the event would not 

be considered a natural event. See preamble to the 

Exceptional Events Rule at 72 FR 13560 (March 22, 

2007), footnote 11 on page 13566. 

270Because of previously expressed stakeholder 

feedback regarding implementation of the 

Exceptional Events Rule and specific stakeholder 

concerns regarding the analyses that can be used to 

support wildfire-related exceptional event 

demonstrations, the EPA intends to propose 

revisions to the Exceptional Events Rule in a future 

notice-and-comment rulemaking and will solicit 

public comment at that time. Depending on the 

nature and scope of any interstate emissions events 

affecting downwind air quality, the EPA may be 

able to assist states in developing approvable 

exceptional events demonstrations. 

period. Thus, for PM2.5 only the NNSR 

requirements would apply with regard 

to major stationary sources of PM2.5

locating in that nonattainment area. 

IX. What other proposed requirements 

would apply in PM2.5 nonattainment 

areas? 

A. Waivers Under Section 188(f) 

1. Statutory Requirements and Existing 

Guidance 

Section 188(f) of the CAA provides a 

means for the EPA to waive a specific 

date for attainment and certain control 

and planning requirements for PM2.5

nonattainment areas if certain 

conditions are met in the nonattainment 

area. Specifically, the statute provides 

that: ‘‘The Administrator may, on a 

case-by-case basis, waive any 

requirement applicable to any Serious 

Area . . . where the Administrator 

determines that anthropogenic sources 

of PM10 do not contribute significantly 

to the violation of the PM10 standard in 

the area.’’ In addition, ‘‘the 

Administrator may also waive a specific 

date for attainment of the [PM10] 

standard where the Administrator 

determines that nonanthropogenic 

sources of PM10 contribute significantly 

to the violation of the PM10 standard in 

the area.’’ In the Addendum, the EPA 

provided extensive guidance on how the 

agency interpreted section 188(f) and 

how it intended to apply the statutory 

waiver provisions for purposes of 

implementing the PM10 NAAQS.266 At 

this time, the EPA is not proposing to 

revise the guidance presented in the 

Addendum with respect to section 

188(f), but the agency requests comment 

on whether the existing guidance in the 

Addendum is appropriate when 

implementing the current and any 

future PM2.5 NAAQS. 

2. Relationship Between the CAA 

Section 188(f) Waiver Provisions and 

the EPA’s Exceptional Events Rule 

On March 22, 2007, the EPA 

promulgated the ‘‘Treatment of Data 

Influenced by Exceptional Events; Final 

Rule’’ (72 FR 13560), known as the 

Exceptional Events Rule, pursuant to 

the 2005 amendment of CAA section 

319.267 The Exceptional Events Rule 

provides a mechanism by which the 

EPA can concur with an air agency’s 

request to exclude from regulatory 

decisions air quality monitoring data 

determined by the EPA to have been 

affected by exceptional events.268 The 

Exceptional Events Rule applies to all 

NAAQS pollutants, including PM2.5. 

Section 188(f) and the Exceptional 

Events Rule provide separate 

mechanisms by which states and/or 

other air agencies can seek to have 

event-influenced monitoring data 

excluded from certain regulatory 

requirements or decisions associated 

with the PM NAAQS implementation 

process, under appropriate 

circumstances. This section explains the 

EPA’s views on how these two 

mechanisms can operate. 

The Exceptional Events Rule 

addresses elevated emissions from 

specific events that influence monitored 

air quality concentrations. The EPA’s 

regulations at 40 CFR 50.1(j) define an 

‘‘exceptional event’’ as one that ‘‘affects 

air quality, is not reasonably 

controllable or preventable, is an event 

caused by human activity that is 

unlikely to recur at a particular location 

or a natural event, and is determined by 

the Administrator in accordance with 40 

CFR 50.14 to be an exceptional event.’’ 

Further, 40 CFR 50.1(j) explicitly 

provides that exceptional events do 

‘‘. . . not include stagnation of air 

masses or meteorological inversions, a 

meteorological event involving high 

temperatures or lack of precipitation, or 

air pollution relating to source 

noncompliance.’’ At 40 CFR 50.1(k), the 

EPA’s regulations define a ‘‘natural 

event’’ as an event in which human 

activity plays little or no direct causal 

role to the event in question.269 The 

Exceptional Events Rule allows the EPA 

to exclude from regulatory decisions air 

quality monitoring data that it 

determines to have been influenced by 

emissions that result from exceptional 

events. Air quality monitoring data that 

the EPA determines to have been 

influenced by an exceptional event 

under the procedural steps, substantive 

criteria, and schedule specified in the 

Exceptional Events Rule may be 

excluded from regulatory decisions such 

as initial area designations decisions 

and decisions associated with 

implementing the PM2.5 NAAQS such as 

clean data determinations, evaluation of 

attainment demonstrations, and 

discretionary or mandatory 

reclassifications of nonattainment areas 

from Moderate to Serious. While the 

EPA may agree with an air agency’s 

request to exclude event-influenced air 

quality monitoring data from regulatory 

decisions, these regulatory actions 

require the EPA to provide an 

opportunity for public comment on the 

claimed exceptional event and all 

supporting data prior to the EPA taking 

final agency action. 

If wildfire is a potential contributor to 

exceedances of the NAAQS and 

exceptional events, the EPA urges state 

and local agencies to coordinate with 

the land management agencies, as 

appropriate, in developing plans and 

appropriate public communications 

regarding public safety and reducing 

exposure. This action can directly help 

states meet their Exceptional Events 

Rule obligation whereby ‘‘states must 

provide public notice, public education, 

and must provide for implementation of 

reasonable measures to protect public 

health when an event occurs.’’ When 

wildfire impacts are significant in a 

particular area, air agencies and 

communities may be able to lessen the 

impacts of wildfires by working 

collaboratively with land managers and 

land owners to employ various 

mitigation measures including taking 

steps to minimize fuel loading in areas 

vulnerable to fire.270

The EPA notes that there could be 

some potential overlap between the 

application of the Exceptional Events 

Rule and section 188(f). The EPA 

believes that this potential for overlap 

can best be addressed by considering 

the applicability of the Exceptional 

Events Rule and section 188(f) in 

sequence. Thus, the EPA recommends 

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271This final rule was not challenged or affected 

in any way by the January 2013 D.C. Circuit Court 

decision requiring the EPA to implement the PM2.5

NAAQS pursuant to subpart 4 of the CAA. 

272For the purposes of transportation conformity, 

a ‘‘donut’’ area is the geographic area outside a 

metropolitan planning area boundary, but inside a 

designated nonattainment or maintenance area 

boundary that includes an MPO (40 CFR 93.101). 

that air agencies first consider whether 

the monitored air quality data on 

specific days were influenced by an 

exceptional event. If the air agency 

requests and the EPA agrees with this 

request and determines that the 

monitored air quality data should be 

excluded from consideration in 

regulatory decisions, then using the 

provisions in the Exceptional Events 

Rule could address the situation 

adequately. Thereafter, if the air agency 

determines that the waiver provisions of 

section 188(f) may also be applicable, 

then the EPA can evaluate that question 

based on the remaining data that are 

representative for the area in question. 

B. Conformity Requirements 

1. What requirements apply to both 

transportation and general conformity? 

a. 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. The EPA 

first promulgated the Transportation 

Conformity Rule on November 24, 1993 

(58 FR 62188), and subsequently 

published several amendments. For 

example, the EPA published a final rule 

on July 1, 2004 (69 FR 40004) that 

provided conformity procedures for 

state and local agencies under the 1997 

PM2.5 NAAQS, among other things. On 

May 6, 2005 (70 FR 24280) the EPA 

published a final rule that addressed 

transportation conformity requirements 

for PM2.5 precursors.271 The EPA 

published another final rule on March 

24, 2010 (75 FR 14260) that addressed 

additional requirements for the 2006 

PM2.5 NAAQS. Finally, the EPA 

published a final rule on March 14, 

2012 (77 FR 14979) that restructured 

portions of the transportation 

conformity rule so that they would 

clearly apply to nonattainment and 

maintenance areas for new and revised 

NAAQS, including the 2012 PM2.5

NAAQS. All of these rules apply to the 

current PM2.5 NAAQS including the 

1997 PM2.5 NAAQS, the 2006 24-hour 

PM2.5 NAAQS and the 2012 primary 

annual PM2.5 NAAQS and will apply to 

future PM2.5 NAAQS. 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 the 

2012 primary annual PM2.5 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). 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 

individual federal actions. More 

information on the general conformity 

program is available at http://

www.epa.gov/air/genconform/. 

b. Why is the EPA discussing 

transportation and general conformity 

in this proposed rulemaking? The EPA 

is discussing transportation and general 

conformity in this proposed rulemaking 

in order to provide affected parties with 

information on when conformity must 

be implemented after nonattainment 

areas are designated for a new or revised 

PM2.5 NAAQS. At this time the EPA is 

using the 2012 PM2.5 NAAQS as an 

example. The agency is also discussing 

how it plans to make the transition from 

demonstrating conformity for the 1997 

annual PM2.5 NAAQS to the 2012 

primary annual PM2.5 NAAQS because 

this transition is unique in that the 1997 

annual PM2.5 NAAQS was retained as a 

secondary NAAQS. The information 

presented here is consistent with 

existing conformity regulations and 

statutory provisions that are not 

addressed by this PM2.5 implementation 

rulemaking. Affected parties would 

include state and local transportation 

and air quality agencies, metropolitan 

planning organizations (MPOs), and 

federal agencies including the U.S. 

Department of Transportation (DOT), 

the U.S. Department of Defense, the U.S. 

Department of Interior and the U.S. 

Department of Agriculture. 

c. When would transportation and 

general conformity apply to areas 

designated nonattainment for the 2012 

primary annual PM2.5 NAAQS? 

Transportation and general conformity 

apply 1 year after the effective date of 

nonattainment designations for a new or 

revised PM2.5 NAAQS including the 

2012 primary annual PM2.5 NAAQS. 

This is because CAA section 176(c)(6) 

provides a 1-year grace period from the 

effective date of initial designations for 

any new NAAQS before transportation 

and general conformity apply in areas 

newly designated nonattainment for a 

specific pollutant and NAAQS. With 

regard to general conformity, the EPA’s 

April 2010 revisions to its general 

conformity regulations (see 75 FR 

17277; April 5, 2010) apply the same 1- 

year grace period for purposes of general 

conformity. 

With regard to transportation 

conformity, the conformity grace period 

applies to all areas designated 

nonattainment for a new or revised 

PM2.5 NAAQS including the 2012 

primary annual PM2.5 NAAQS. The 

requirements differ depending on 

whether the nonattainment area is 

within or adjacent to a MPO designated 

under 23 U.S.C. 134. Within 1 year after 

the effective date of the initial 

nonattainment designation for a given 

pollutant and NAAQS, the MPOs and 

DOT must make a conformity 

determination with regard to that 

pollutant and standard for all of the 

transportation plans and TIPs in the 

nonattainment area. The conformity 

requirements for surrounding ‘‘donut 

areas,’’ including the application of the 

1-year conformity grace period, are 

generally the same as those for 

metropolitan areas.272 For the purposes 

of the implementation of the 2012 PM2.5

NAAQS, MPOs and any adjacent donut 

areas in a 2012 PM2.5 NAAQS 

nonattainment area must continue to 

meet conformity requirements during 

the grace period for any other applicable 

NAAQS, including the 1997 annual 

PM2.5 NAAQS and the 2006 24-hour 

PM2.5 NAAQS. If, at the end of the grace 

period for the 2012 annual PM2.5

NAAQS, the MPO and DOT have not 

made a transportation plan and TIP 

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conformity determination for that 

NAAQS, the area would be in a 

conformity ‘‘lapse.’’ During a conformity 

lapse, only certain projects can receive 

additional federal funding or approvals 

to proceed. The practical impact of a 

conformity lapse will vary from area to 

area. Finally, the 1-year conformity 

grace period also applies to project level 

conformity determinations. 

Isolated rural nonattainment and 

maintenance areas are areas that do not 

contain or are not part of an MPO (40 

CFR 93.101). Conformity requirements 

for isolated rural nonattainment and 

maintenance areas can be found at 40 

CFR 93.109(g). One year after the 

effective date of the initial 

nonattainment designation for a given 

pollutant and NAAQS, conformity 

requirements with regard to that 

pollutant and standard would apply in 

any nonattainment areas that are 

isolated rural areas. Per the 

transportation conformity rule, an 

isolated rural area would be required to 

make a transportation conformity 

determination only at the point when a 

transportation project needs funding or 

approval. This project level conformity 

determination may occur significantly 

after the 1-year grace period has ended. 

See the EPA’s July 1, 2004 final rule for 

further background on how the EPA has 

implemented this conformity grace 

period in metropolitan, donut and 

isolated rural areas (69 FR 40008; July 

1, 2014; see also 69 FR 40009, 40010, 

40011, 40012, 40013 and 40014). 

d. How will transportation and 

general conformity apply with regard to 

the 1997 annual PM2.5 NAAQS, which 

was retained as a secondary NAAQS? In 

the final 2012 p.m. NAAQS rule the 

EPA established a new health-based 

primary annual PM2.5 NAAQS of 12.0 

mg/m3. In that same action the EPA 

retained the 1997 annual PM2.5 NAAQS 

of 15.0 mg/m3 as a secondary NAAQS to 

protect against certain welfare effects. In 

the 1997 PM2.5 designations rule (70 FR 

944; January 5, 2005), the EPA 

designated areas nonattainment for both 

the 1997 primary and secondary annual 

PM2.5 NAAQS (which have identical 

levels of 15.0 mg/m3). Designations for 

the 2012 primary annual PM2.5 NAAQS 

were made in January 2015 (80 FR 2205; 

January 15, 2015). This action did not 

make any changes to the designations 

that apply for the 1997 secondary 

annual PM2.5 standard. Therefore, at this 

time, all areas designated nonattainment 

in 2005 for the 1997 annual PM2.5

standard are considered as having been 

designated nonattainment for both the 

1997 primary annual PM2.5 NAAQS and 

for the 1997 secondary annual PM2.5

NAAQS where such distinctions are 

made below. Similarly, for any 1997 

PM2.5 nonattainment areas that have 

approved redesignation requests for 

attainment of the 1997 PM2.5 NAAQS, 

the redesignation applies to both the 

primary and secondary standards of the 

1997 PM2.5 NAAQS. A discussion of 

how transportation and general 

conformity apply in this situation 

follows. 

CAA section 176(c)(5) establishes that 

conformity applies to: a nonattainment 

area and each pollutant for which the 

area is designated as a nonattainment 

area; and an area that was designated as 

a nonattainment area but that was later 

redesignated by the Administrator as an 

attainment area and that is required to 

develop a maintenance plan under CAA 

section 7505a with respect to the 

specific pollutant for which the area 

was designated nonattainment. Section 

176(c)(5) is clear that transportation and 

general conformity apply in 

nonattainment areas and in areas that 

have been redesignated to attainment 

and are required to develop a 

maintenance plan under section 175A. 

Section 175A(a) establishes the 

requirements for areas that are required 

to submit a maintenance plan as one of 

the requirements that must be fulfilled 

in order for an area to be redesignated 

to attainment. 

Section 175A(a) requires 

nonattainment areas for primary 

NAAQS to submit maintenance plans in 

order to be redesignated, and such plans 

must ensure maintenance of the 

standard for at least 10 years after 

redesignation. Section 175A(a) does not 

require nonattainment areas for 

secondary NAAQS to submit 

maintenance plans in order to be 

designated to attainment. Therefore, the 

EPA concludes that transportation and 

general conformity do not apply in areas 

that have been redesignated for any 

secondary NAAQS, such as the 1997 

secondary annual PM2.5 NAAQS, since 

conformity does not apply in areas that 

have been redesignated without 

maintenance plans. 

Elsewhere in this notice, the EPA is 

proposing options for revoking the 1997 

primary annual PM2.5 NAAQS, which 

has been replaced by the more health 

protective 2012 primary annual PM2.5

NAAQS. If the EPA finalizes an option 

that results in the revocation of the 1997 

primary annual PM2.5 NAAQS, 

nonattainment and maintenance areas 

would not be required to make 

transportation or general conformity 

determinations for the 1997 primary 

annual PM2.5 NAAQS after the effective 

date of the revocation of the 1997 

primary annual NAAQS. The revocation 

would leave designations in place for 

the 1997 secondary annual NAAQS. 

Any area that is designated as 

nonattainment for the 1997 secondary 

annual NAAQS would have to continue 

to make transportation and general 

conformity determinations for that 

NAAQS as conformity applies in 

nonattainment areas for secondary 

NAAQS. 

However, for any area that has been 

redesignated to attainment for the 1997 

secondary NAAQS and is not 

designated nonattainment for the 2012 

primary annual PM2.5 NAAQS, the 

relevant planning organization will not 

have to make conformity determinations 

for any annual PM2.5 NAAQS after the 

effective date of the revocation of the 

1997 primary annual PM2.5 NAAQS 

because, as discussed above, the CAA 

does not require maintenance areas for 

secondary NAAQS to make conformity 

determinations. This means that if the 

EPA finalizes any of the options for 

revoking the 1997 primary annual PM2.5

NAAQS, after the effective date of the 

revocation, areas redesignated to 

attainment for the 1997 secondary 

annual PM2.5 NAAQS will no longer be 

required to make transportation plan, 

TIP, or project-level transportation 

conformity determinations for that 

NAAQS. In addition, federal agencies 

will no longer be required to make 

general conformity determinations for 

that NAAQS. Areas that remain 

designated nonattainment for the 1997 

secondary annual PM2.5 NAAQS will 

continue to make transportation plan, 

TIP, and project-level conformity 

determinations for that NAAQS and 

federal agencies will be required to 

continue to make general conformity 

determinations for that NAAQS in these 

areas until such time as they attain that 

NAAQS and are redesignated to 

attainment. 

e. What impact will the 

implementation of a new or revised 

PM2.5 NAAQS such as the 2012 PM2.5

NAAQS have on a state’s transportation 

and/or general conformity SIP? As long 

as the EPA does not make specific 

changes to its transportation or general 

conformity regulations states should not 

need to revise their transportation and/ 

or general conformity SIPs. The EPA is 

not proposing any changes to its 

transportation conformity regulations. 

The EPA is proposing to change the de 

minimis levels in its general conformity 

regulations as discussed in Section 

IX.B.2.b. of this preamble. States with a 

general conformity SIP should evaluate 

the need to revise those SIPs if this 

change is finalized. States with new 

nonattainment areas may also need to 

revise conformity SIPs in order to 

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273USDA Forest Service and Natural Resources 

Conservation Service, Basic Smoke Management 

Practices Tech Note, October 2011, http://

www.nrcs.usda.gov/Internet/FSE_DOCUMENTS/

stelprdb1046311.pdf. 

ensure the state regulations apply in any 

newly designated areas. 

However, 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). 

2. What additional requirements apply 

to general conformity? 

a. What de minimis emissions levels 

will apply for direct PM2.5 and its 

precursors? 

Federal actions estimated to have an 

annual net emissions increase less than 

the de minimis levels established in the 

general conformity regulations are not 

required to demonstrate conformity 

under those regulations. For direct PM2.5

and its precursors (SO2, NOX, VOC and 

ammonia), the existing de minimis 

emissions levels are set forth in the 

EPA’s general conformity regulations at 

40 CFR 93.153(b)(1). Those levels were 

based on the definition of a major 

stationary source for nonattainment 

NSR programs as established by sections 

182, 183 and 302 of the CAA. The EPA 

believes it is appropriate to continue 

this practice for implementing the 

current and any future PM2.5 NAAQS. 

However, because the definition of 

precursors currently in the general 

conformity regulations at 40 CFR 

93.152(b)(1) does not reflect the 

elimination of rebuttable presumptions 

for certain PM2.5 precursors, the EPA is 

proposing changes to these conformity 

provisions to make them consistent with 

the agency’s revised precursor 

requirements. Specifically, the current 

definition of precursors for PM2.5 in the 

general conformity regulations reflects 

the rebuttable presumptions for VOC 

and ammonia finalized in the 2007 

PM2.5 Implementation Rule (72 FR 

20583; April 25, 2007). It also does not 

reflect the subpart 4 definitions for 

‘‘major source’’ and ‘‘major stationary 

source’’ that apply for Serious PM2.5

nonattainment areas. Therefore, through 

this proposal the EPA proposes to 

change the PM2.5 precursor de minimis 

levels currently in 40 CFR 93.153(b)(1) 

to be consistent with the statutory 

requirements for major stationary source 

thresholds under subpart 4 and any 

relevant changes being proposed in 

Section III of this preamble. The EPA 

proposes to set the de minimis levels 

that apply to direct PM2.5 and PM2.5

precursors for PM2.5 nonattainment 

areas for purposes of general conformity 

as identified in Table 3 below. 

TABLE 3—GENERAL CONFORMITY De Minimis EMISSION LEVELS FOR PM2.5 PRECURSORS

Type of 

emission 

Tons/year in moderate PM2.5

nonattainment areas and all 

maintenance areas 

Tons/year in Serious PM2.5

nonattainment areas 

Direct emissions .................................................................................................. 100 70 

SO2 ...................................................................................................................... 100 70 

NOX ...................................................................................................................... 100 70 

VOC ..................................................................................................................... 100 70 

Ammonia .............................................................................................................. 100 70 

b. Are there any other impacts related 

to general conformity based on 

implementation of the 2012 PM2.5

NAAQS? The EPA is not proposing any 

other revisions to the general conformity 

regulations at this time. However, as 

states develop SIP revisions for the 2012 

and future PM2.5 NAAQS, the agency 

recommends that state and local air 

quality agencies work with federal 

agencies with large facilities (e.g., 

commercial airports, ports and large 

military bases) that are subject to the 

general conformity regulations to 

establish an emissions budget for those 

facilities in order to facilitate future 

conformity determinations under the 

conformity regulations. Such a budget 

could be used by federal agencies in 

determining conformity or identifying 

mitigation measures if the budget level 

is included and identified in the SIP. 

Significant tracts of land under 

federal management may also be 

included in nonattainment area 

boundaries. The role of fire in these 

areas should be assessed and emissions 

budgets developed in concert with those 

federal land management agencies. In 

such areas the EPA encourages states to 

consider in any baseline, modeling and 

SIP attainment inventory used and/or 

submitted to include emissions 

expected from projects subject to 

general conformity, including emissions 

from wildland fire that may be 

reasonably expected in the area. Where 

appropriate, states may consider 

developing plans for addressing 

wildland fuels in collaboration with 

land managers and owners. 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.273

C. Clean Data Policy 

This section describes the ongoing 

status of the EPA’s Clean Data Policy 

and proposes provisions applicable to 

any determinations of attainment under 

current and future PM2.5 NAAQS. This 

section also sets forth the regulatory 

consequences of an EPA determination, 

made after notice and comment 

rulemaking, that an area designated 

nonattainment for a PM2.5 standard has 

air quality attaining that standard. Upon 

such a determination by the EPA, the 

state’s requirement for the area to 

submit the separate required elements of 

an attainment plan (including an 

attainment demonstration, but not the 

emissions inventory requirement), shall 

be suspended until such time as the area 

is redesignated to attainment, at which 

time the requirements no longer apply. 

If the EPA determines that the area, after 

reaching attainment, has again violated 

that PM2.5 NAAQS, the requirements are 

again applicable. The following 

discussion of this interpretation, known 

as the EPA’s Clean Data Policy, explains 

the basis for the EPA’s interpretation 

and is relevant to all PM2.5 NAAQS 

under subpart 4. 

1. What is a clean data determination? 

The EPA’s interpretation of the CAA 

applies when the agency, after noticeand-comment rulemaking, issues a 

‘‘clean data determination’’ (CDD), in 

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274 In the context of CDDs, the EPA distinguishes 

between attainment planning requirements of the 

CAA, which relate to the attainment demonstration 

for an area and related control measures for 

bringing an area into attainment for a given NAAQS 

as expeditiously as practicable, and other types of 

requirements, such as permitting requirements 

under the NNSR program, and any specific control 

requirements independent of those strictly needed 

to ensure timely attainment of a given NAAQS. 

275See December 14, 2004 memorandum from 

Stephen D. Page, Director, EPA Office of Air Quality 

Planning and Standards, to Air Division Directors, 

EPA Regions I–X, entitled ‘‘Clean Data Policy for 

the Fine Particle National Ambient Air Quality 

Standards.’’ Available at: http://www.epa.gov/

airquality/urbanair/sipstatus/docs/pm25_clean_

data_policy_14dec2004.pdf. 

276 ‘‘The EPA’s Final Rule to implement the 8- 

hour Ozone National Ambient Air Quality 

Standard—Phase 2 (Phase 2 Final Rule).’’ See the 

Federal Register published on November 29, 2005 

(70 FR 71612, 71645 and 71646). 

which it determines that a specific 

nonattainment area has attained the 

relevant standard. For such areas, the 

EPA interprets the CAA as suspending 

the state requirements to submit to the 

EPA the planning elements of an 

attainment plan related to attaining the 

NAAQS for as long as the area continues 

to attain the standard.274 These 

planning elements generally include 

reasonable further progress (RFP) 

requirements, attainment 

demonstrations, RACM and RACT, 

nonattainment area contingency 

measures, and other state planning 

requirements related to the attainment 

of the NAAQS.275 The suspension of the 

obligation to submit applies regardless 

of when the plan submissions are due. 

The CDD does not suspend CAA 

requirements that are independent of 

helping the area achieve attainment, 

such as the requirements to submit an 

emissions inventory and nonattainment 

new source review requirements. 

The emissions inventory is a basic 

compilation of information used to 

characterize the sources of emissions of 

the nonattainment area. Section 

172(c)(3), the statutory provision 

requiring submission of an emissions 

inventory, is not tied to attainment of 

the NAAQS, unlike the attainment 

planning provisions which are 

suspended by a CDD. A base year 

inventory continues to be relevant to a 

nonattainment area that is attaining the 

NAAQS and has obtained a CDD 

because, for example, the inventory is a 

necessary component to an approvable 

redesignation request. In addition, in 

the event the air quality in the area 

exceeds the standard in a subsequent 

year, the state would be obligated to 

submit an attainment demonstration 

and other planning elements for the 

area, and a base year inventory would 

need to be available immediately in 

order for the state to submit an 

approvable attainment plan 

expeditiously. Similarly, the new source 

review requirement is not suspended 

because section 172(c)(5) is not tied to 

attainment of the NAAQS, and an area 

with a CDD is still designated 

nonattainment. NNSR permitting is 

required in each nonattainment area 

until the area is redesignated to 

attainment.’’ For the past two decades, 

and for many NAAQS, the EPA has 

consistently applied its Clean Data 

Policy interpretation to attainmentrelated provisions of subparts 1, 2 and 

4 of Part D, Title I of the CAA. The 

Clean Data Policy is the subject of 

several EPA memoranda and regulations 

and numerous individual rulemakings 

published in the Federal Register. 

These rulemakings have applied the 

interpretation to a broad spectrum of 

NAAQS, including the 1-hour and 1997 

ozone standards, PM10, 1997 and 2006 

PM2.5 standards and the carbon 

monoxide (CO) and lead standards. The 

D.C. Circuit has upheld the Clean Data 

Policy interpretation as embodied in the 

EPA’s 8-hour ozone Implementation 

Rule, 40 CFR 51.918.276 NRDC v. EPA, 

571 F. 3d 1245 (D.C. Cir. 2009). Other 

U.S. Circuit Courts of Appeals that have 

considered and reviewed the EPA’s 

Clean Data Policy interpretation have 

upheld it and the rulemakings applying 

the EPA’s interpretation. Sierra Club v. 

EPA, 99 F.3d 1551 (10th Cir. 1996); 

Sierra Club v. EPA, 375 F. 3d 537 (7th 

Cir. 2004); Our Children’s Earth 

Foundation v. EPA, N. 04–73032 (9th 

Cir. June 28, 2005) (memorandum 

opinion); Latino Issues Forum, v. EPA, 

Nos. 06–75831 and 08–71238 (9th Cir. 

March 2, 2009) (memorandum opinion). 

The EPA incorporated its Clean Data 

Policy interpretation in both its 1997 8- 

hour ozone implementation rule and in 

its remanded 2007 PM2.5

Implementation Rule in 40 CFR 

51.1004(c). See the Federal Register 

published on April 25, 2007 (72 FR 

20583, 20585 and 20665. The D.C. 

Circuit, in its January 4, 2013 decision 

remanding the PM2.5 implementation 

rule, did not address the merits of that 

regulation or the EPA’s existing 

interpretation of the statutory provisions 

as they pertained to the EPA’s Clean 

Data Policy. 

The EPA has previously articulated its 

Clean Data Policy interpretation under 

subpart 4 in implementing the PM10

standard. See, e.g., 75 FR 27944 (May 

19, 2010) (determination of attainment 

of the PM10 standard in Coso Junction, 

California); 71 FR 13021 (March 14, 

2006) (Yuma, Arizona area); 71 FR 

40023 (July 14, 2006) (Weirton, West 

Virginia area); 71 FR 44920 (August 8, 

2006) (Rillito, Arizona area); 71 FR 

63642 (October 30, 2006) (San Joaquin 

Valley, California area) 72 FR 14422 

(March 28, 2007) (Miami, Arizona area). 

In the EPA’s proposed and final 

rulemakings determining that the San 

Joaquin Valley nonattainment area 

attained the PM10 standard, the EPA set 

forth at length its rationale for applying 

the Clean Data Policy to PM10 under 

subpart 4. 71 FR at 63643–45. The Ninth 

Circuit upheld the EPA’s final 

rulemaking, and specifically the EPA’s 

Clean Data Policy, in the context of 

subpart 4. Latino Issues Forum v. EPA, 

supra. Nos. 06–75831 and 08–71238 

(9th Cir. March 2, 2009) (memorandum 

opinion). In rejecting the petitioner’s 

challenge to the Clean Data Policy under 

subpart 4 for PM10, the Ninth Circuit 

stated, ‘‘As the EPA explained, if an area 

is in compliance with PM10 standards, 

then further progress for the purpose of 

ensuring attainment is not necessary.’’ 

Thus the EPA has previously 

established its interpretation that, under 

subpart 4, a clean data determination 

suspends the obligations to submit an 

attainment demonstration, RACM/

RACT, RFP and quantitative milestones, 

contingency measures, and other 

measures related to attainment. The 

EPA is proposing to codify this 

interpretation in this implementation 

rule for the PM2.5 NAAQS. 

As with its Clean Data Policy 

interpretation for 8-hour ozone, which 

the EPA embodied in a regulation that 

was upheld by the D.C. Circuit in NRDC 

v. EPA, 571 F. 3d 1245 (D.C. Cir. 2009), 

the EPA intends to embody its 

interpretation for the Clean Data Policy 

for current and future PM2.5 NAAQS in 

a regulation as part of this proposed 

rulemaking. This interpretation 

complies with the D.C. Circuit’s ruling 

(NRDC v. EPA, 706 F.3d 428 (D.C. Cir. 

2013)) that both subparts 1 and subpart 

4 apply to implementation, and reflects 

the interpretation upheld by the Latino 

Issues Forum Court. Latino Issues 

Forum v. EPA, supra. Nos. 06–75831 

and 08–71238 (9th Cir. March 2, 2009) 

(memorandum opinion). Under this 

proposed regulation, if the EPA 

determines, after notice-and-comment 

rulemaking, that an area has attained the 

applicable PM2.5 NAAQS based on the 

most recent 3 years of complete, qualityassured data meeting the requirements 

of 40 CFR part 50, Appendix N, the 

area’s obligation to submit the following 

Moderate or Serious area attainmentrelated planning requirements is 

suspended for so long as the area 

continues to attain the PM2.5 standard: 

(i) the part D, subpart 4 and subpart 1 

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277 57 FR 13498 (April 16, 1992), at page 13560. 

278The EPA’s interpretation that the statute 

requires implementation only of RACM that would 

advance attainment was upheld by the Fifth Circuit 

Court (Sierra Club v. EPA, 314 F.3d 735, 743–745 

(5th Cir. 2002), and by the D.C. Circuit Court (Sierra 

Club v. EPA, 294 F.3d 155, 162–163 (D.C. Cir. 

2002)). 

279 57 FR 13498 (April 16, 1992), at page 13564. 

See 71 FR 40952 (July 19, 2006) and 71 FR 63642 

(October 30, 2006) (proposed and final 

determination of attainment for San Joaquin 

Valley); 75 FR 13710 (March 23, 2010) and 75 FR 

27944 (May 19, 2010) (proposed and final 

determination of attainment for Coso Junction). 

280Thus, the EPA believes that it is a distinction 

without a difference that section 189(c)(1) speaks of 

the RFP requirement as one to be achieved until an 

area is ‘‘redesignated attainment,’’ as opposed to 

section 172(c)(2), which is silent on the period to 

which the requirement pertains, or the ozone 

nonattainment area RFP requirements in sections 

182(b)(1) or 182(c)(2), which refer to the RFP 

requirements as applying until the ‘‘attainment 

date,’’ since section 189(c)(1) defines RFP by 

reference to section 171(1) of the CAA. Reference 

to section 171(1) clarifies that, as with the general 

RFP requirements in section 172(c)(2) and the 

ozone-specific requirements of section 182(b)(1) 

and 182(c)(2), the PM-specific requirements may 

only be required ‘‘for the purpose of ensuring 

attainment of the applicable national ambient air 

quality standard by the applicable date.’’ 42 U.S.C. 

7501(1). As discussed in the text of this proposed 

rulemaking, the EPA interprets the subpart 4 RFP 

requirements, in light of the definition of RFP in 

section 171(1), and its incorporation into section 

189(c)(1), to no longer apply once the EPA makes 

a determination that the standard has been attained. 

281Memorandum from John S. Seitz, titled 

‘‘Reasonable Further Progress, Attainment 

Demonstration, and Related Requirements for 

Ozone Nonattainment Areas Meeting the Ozone 

National Ambient Air Quality Standard,’’ (Seitz 

Memo). May 10, 1995. 

obligation to provide an attainment 

demonstration pursuant to section 

189(a)(1)(B); (ii) the RACM and RACT 

provisions of section 189(a)(1)(C); (iii) 

the RFP and quantitative milestones 

provisions of section 189(c); and, (iv) 

related attainment demonstration, 

RACM and RACT, RFP and contingency 

measure provisions requirements of 

subpart 1, section 172. 

A final determination of attainment, 

also known as a clean data 

determination, would not constitute a 

redesignation to attainment under CAA 

section 107(d)(3). The state would still 

have to meet the statutory requirements 

for redesignation in order to be 

redesignated to attainment. A 

determination of attainment for 

purposes of the Clean Data Policy is also 

not linked to any particular attainment 

deadline, and is not necessarily 

equivalent to a determination that an 

area has attained the standard by its 

applicable attainment deadline, e.g., 

under section 189(c). 

2. Planning Requirements Suspended 

With a CDD 

a. Control measure requirements for 

Moderate areas. Both sections 172(c)(1) 

and 189(a)(1)(C) require ‘‘provisions to 

assure that reasonably available control 

measures’’ (i.e., RACM) are 

implemented in a nonattainment area. 

Reasonably available control technology 

(i.e., RACT) is a subset of RACM. The 

General Preamble states that the EPA 

interprets section 172(c)(1) so that 

RACM requirements are a ‘‘component’’ 

of an area’s attainment 

demonstration.277 Thus, for the same 

reason the obligation to submit an 

attainment demonstration is suspended, 

the requirement for a state to submit 

RACM is suspended if the 

nonattainment area reaches attainment. 

For PM2.5, the EPA has consistently 

interpreted this provision to require 

only implementation of potential RACM 

that could contribute to RFP or to timely 

attainment (General Preamble, 57 FR 

13498). Thus, where an area is already 

attaining the standard, no additional 

RACM are required, but all measures 

adopted into the SIP prior to attainment 

would remain.278 The EPA is 

interpreting section 189(a)(1)(C) 

consistent with its interpretation of 

section 172(c)(1). 

b. RFP and quantitative milestones. 

The EPA has long interpreted the 

provisions of part D, subpart 1 of the 

CAA (sections 171 and 172) as not 

requiring the submission of RFP for an 

area already attaining the PM10 NAAQS. 

For an area that is attaining, showing 

that the state will make RFP towards 

attainment ‘‘will, therefore, have no 

meaning at that point.’’ 279 Section 

189(c)(1) states that: ‘‘Plan revisions 

demonstrating attainment submitted to 

the Administrator for approval under 

this subpart shall contain quantitative 

milestones which are to be achieved 

every 3 years until the area is 

redesignated attainment and which 

demonstrate reasonable further progress, 

as defined in section [171(1)] of this 

title, toward attainment by the 

applicable date.’’ 

With respect to RFP, section 171(1) 

states that, for purposes of part D, RFP 

‘‘means such annual incremental 

reductions in emissions of the relevant 

air pollutant as are required by this part 

or may reasonably be required by the 

Administrator for the purpose of 

ensuring attainment of the applicable 

NAAQS by the applicable date.’’ 42 

U.S.C. 7501(1). Thus, whether dealing 

with the general RFP requirement of 

section 172(c)(2), the ozone-specific RFP 

requirements of sections 182(b) and (c), 

or the specific RFP requirements for 

PM10 areas of part D, subpart 4, section 

189(c)(1), the stated purpose of RFP is 

to ensure attainment by the applicable 

attainment date. Although section 

189(c) states that revisions shall contain 

milestones which are to be achieved 

until the area is redesignated to 

attainment, such milestones are 

designed to show reasonable further 

progress ‘‘toward attainment by the 

applicable attainment date,’’ as defined 

by section 171. Thus, it is clear that 

once the area has attained the standard, 

no further milestones are necessary or 

meaningful. This interpretation is 

supported by language in section 

189(c)(3), which mandates that a state 

that fails to achieve a milestone must 

submit a plan that assures that the state 

will achieve the next milestone or attain 

the NAAQS if there is no next 

milestone. Thus, section 189(c)(3) itself 

assumes that the requirement to submit 

and achieve milestones does not 

continue after attainment of the 

NAAQS. 

In the General Preamble, the EPA 

noted with respect to section 189(c) that 

the purpose of the milestone 

requirement is ‘‘to provide for emission 

reductions adequate to achieve the 

standards by the applicable attainment 

date (H.R. Rep. No. 490 101st Cong., 2d 

Sess. 267 (1990)).’’ 57 FR 13498 (April 

16, 1992), at page 13539. If an area has 

in fact attained the standard, the stated 

purpose of the RFP requirement will 

have already been fulfilled.280 Similarly, 

the requirements of section 189(c)(2) 

with respect to milestones no longer 

apply so long as an area has attained the 

standard. Section 189(c)(2) provides in 

relevant part that: Not later than 90 days 

after the date on which a milestone 

applicable to the area occurs, each State 

in which all or part of such area is 

located shall submit to the 

Administrator a demonstration . . . that 

the milestone has been met. 

Where the area has attained the 

standard and there are no further 

milestones, there is no further 

requirement to make a submission 

showing that such milestones have been 

met. This is consistent with the position 

that the EPA took with respect to the 

general RFP requirement of section 

172(c)(2) in the General Preamble and in 

the May 10, 1995 Seitz memorandum 281

with respect to the requirements of 

sections 182(b) and (c). In the Seitz 

memorandum, the EPA also noted that 

section 182(g), the milestone 

requirement of subpart 2, which is 

analogous to provisions in section 

189(c), is suspended upon a 

determination that an area has attained. 

The memorandum, citing additional 

provisions related to attainment 

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282Memorandum from Stephen D. Page titled 

‘‘Clean Data Policy for the Fine Particle National 

Ambient Air Quality Standards’’ are equally 

pertinent to all NAAQS. December 14, 2004. 

demonstration and RFP requirements, 

stated: 

Inasmuch as each of these requirements is 

linked with the attainment demonstration or 

RFP requirements of section 182(b)(1) or 

182(c)(2), if an area is not subject to the 

requirement to submit the underlying 

attainment demonstration or RFP plan, it 

need not submit the related SIP submission 

either. (Seitz memo, page 4). 

c. Contingency measures. Other SIP 

submission requirements are linked 

with these attainment demonstration 

and RFP requirements, and similar 

reasoning applies to them. These 

requirements include the contingency 

measure requirements of sections 

172(c)(9). The EPA has interpreted the 

obligation to submit contingency 

measure requirements of sections 

172(c)(9) as suspended when an area 

has attained the standard because those 

‘‘contingency measures are directed at 

ensuring RFP and attainment by the 

applicable date.’’ 57 FR at 13564; see 

also Seitz memo at pgs. 5–6. 

Section 172(c)(9) provides that: ‘‘SIPs 

in nonattainment areas shall provide for 

the implementation of specific measures 

to be undertaken if the area fails to make 

reasonable further progress, or to attain 

the [NAAQS] by the attainment date 

applicable under this part. Such 

measures shall be included in the plan 

revision as contingency measures to 

take effect in any such case without 

further action by the state or the EPA.’’ 

The contingency measure requirement 

is inextricably tied to the RFP and 

attainment demonstration requirements. 

Contingency measures are implemented 

if RFP targets are not achieved, or if 

attainment is not realized by the 

attainment date. Where an area has 

already achieved attainment and 

continues to do so it has no need to rely 

on contingency measures to come into 

attainment or to make further progress 

to attainment. As the EPA stated in the 

General Preamble: ‘‘The section 

172(c)(9) requirements for contingency 

measures are directed at ensuring RFP 

and attainment by the applicable date.’’ 

See 57 FR 13564. 

d. Attainment demonstrations. With 

respect to the attainment demonstration 

requirements of section 172(c) and 

section 189(a)(1)(B), the EPA proposes 

to find that, as with the RFP 

requirements, if an area is already 

monitoring attainment of the standard, 

there is no need for an area to make a 

further submission containing 

additional measures to achieve 

attainment. The plain language of 

section 189(a)(1)(B) requires that the 

attainment plan provide for ‘‘a 

demonstration (including air quality 

modeling) that the [SIP] will provide for 

attainment by the applicable attainment 

date . . . .’’ Where the area has attained 

the standard, such a demonstration no 

longer serves a purpose. This 

interpretation is consistent with the 

interpretation of the section 172(c) 

requirements provided by the EPA in 

the General Preamble, the Page memo, 

and the section 182(b) and (c) 

requirements set forth in the Seitz 

memo.282 As the EPA stated in the 

General Preamble, no other measures to 

provide for attainment would be needed 

by areas seeking redesignation to 

attainment since ‘‘attainment will have 

been reached’’ (57 FR at 13564). See also 

Latino Issues Forum, v. EPA, Nos. 06– 

75831 and 08–71238 (9th Cir.), 

Memorandum Opinion, March 2, 2009. 

e. Control measure requirements for 

Serious areas. Under proposed Option 1 

for BACM and BACT determinations, 

described in Section VI.D of this 

preamble, BACM and BACT for sources 

in the nonattainment area would be 

determined independent of the 

attainment needs of the area, and thus 

the requirement for BACM and BACT 

would not be considered an attainment 

planning requirement. Therefore, under 

such an approach, a determination of 

attainment (i.e., a clean data 

determination) would not suspend the 

obligation to submit any applicable 

outstanding BACM and BACT 

requirements. Under proposed Option 2 

for BACM and BACT determinations, 

BACM and BACT would be identified 

based on the specific attainment needs 

of the area, thus tying the BACM and 

BACT requirement directly to 

attainment planning for the area. 

Consistent with this second proposed 

approach for determining BACM and 

BACT, issuance of a CDD would 

therefore also suspend BACM and 

BACT requirements. 

In addition, for a Serious area that 

failed to attain the relevant PM2.5

NAAQS by the applicable attainment 

date and that is therefore subject to the 

annual 5 percent emissions reduction 

requirement under section 189(d), but is 

nevertheless now attaining the relevant 

NAAQS, the EPA believes that the Clean 

Data Policy may apply to the obligations 

of the state to make an attainment plan 

submission to meet the requirements of 

section 189(d). Once such an area is 

attaining the relevant NAAQS, a clean 

data determination would suspend the 

section 189(d) submission requirement. 

3. Planning Requirements Not 

Suspended With a CDD 

For Moderate nonattainment areas, 

the planning elements that are not 

suspended with a clean data 

determination are: Emissions 

inventories, nonattainment new source 

review including 189(e) control 

requirements for major stationary source 

precursors, and conformity. For Serious 

nonattainment areas, the planning 

elements not suspended with a clean 

data determination are: Emissions 

inventories, nonattainment NSR 

including section 189(e) control 

requirements for major stationary 

sources of PM2.5 precursors, the Most 

Stringent Measures (MSM) requirements 

(if the area has elected to seek an 

extension of the attainment date under 

section 188(e)), and conformity. In 

addition, for a Serious PM2.5

nonattainment area, if the EPA finalizes 

proposed Option 1 for BACM and BACT 

determinations, in which BACM and 

BACT would be determined 

independent of the attainment needs for 

the area, then the requirement for 

implementation of BACM and BACT 

would not be considered an attainment 

planning requirement and would thus 

not be suspended with a clean data 

determination for the area. 

4. Violations of the NAAQS After a CDD 

The suspension of the state’s 

obligations to submit attainment plan 

elements such as provisions for RACM 

and RACT, RFP and quantitative 

milestones, contingency measures, an 

attainment demonstration and other 

related attainment planning 

requirements exists only for as long as 

the area continues to monitor 

attainment of the relevant NAAQS prior 

to redesignation. If the EPA determines, 

after notice-and-comment rulemaking 

but prior to redesignation, that the area 

has monitored a violation of the relevant 

NAAQS, the basis for the suspension of 

the requirements no longer exists. In 

that case, the area would again be 

subject to the requirement to submit the 

pertinent attainment plan elements or 

SIP revisions and would need to address 

those requirements. Thus, a final 

determination that the area need not 

currently submit one of the required 

attainment plan elements amounts to no 

more than a suspension of the obligation 

to make the submission for so long as 

the area continues to attain the 

standard. Only if and when the EPA 

redesignates the area to attainment 

under section 107(d)(3) would the area 

be permanently relieved of these 

attainment plan submission obligations. 

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283Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42001. 

284 Ibid. 

285 Ibid. 

286 Ibid. 

Upon the EPA’s determination that an 

area is currently attaining the applicable 

PM2.5 standard, the EPA proposes that 

the obligations to submit attainment 

planning provisions to meet the 

requirements for an attainment plan for 

the PM2.5 NAAQS, including RFP plans, 

RACM and RACT, quantitative 

milestones, contingency measures and 

an attainment demonstration are 

suspended for as long as the area 

continues to monitor attainment of the 

applicable PM2.5 standards. If in the 

future, prior to redesignation of the 

nonattainment area to attainment, the 

EPA determines after notice-andcomment rulemaking that the area again 

violates the applicable PM2.5 standard, 

then the basis for suspending the 

obligation of the state to make one or 

more of these submissions would no 

longer exist and these attainment plan 

elements would again be due. Since all 

attainment planning requirements had 

been suspended for this area and the 

area attained by its attainment date, the 

CAA attainment plan contingency 

measures would not apply at the time of 

the NAAQS violation. In addition, 

because the area did not have a 

maintenance plan, the CAA section 

175A maintenance plan contingency 

measures would also not apply. When 

an area violates after a CDD, and the 

statutory submission date has passed, 

CAA section 110(k)(5) applies, requiring 

that if the EPA finds that the applicable 

implementation plan is substantially 

inadequate to attain or maintain the 

NAAQS, the Administrator shall 

establish a reasonable deadline (not to 

exceed 18 months) for a state to submit 

a SIP plan revision. 

D. Section 179B/International Border 

Areas 

The EPA recognizes that some states 

are affected not only by local and 

regional sources of PM2.5 and PM2.5

precursors, but also international 

sources that can contribute to an area’s 

PM2.5 NAAQS nonattainment status. As 

discussed in Section II of this preamble, 

direct PM2.5 and more importantly PM2.5

precursors can be transported long 

distances and can be found in the air 

thousands of miles from where the 

emissions occurred and the particles 

were formed. Nitrates and sulfates 

formed from NOX and SO2 emissions are 

generally transported over wide areas 

leading to substantial background 

contributions to NAAQS violations in 

urban areas. Organic carbon, which has 

both a primary and secondary 

component, can also be transported, but 

to a far lesser degree. In general, higher 

concentrations of elemental carbon and 

crustal matter are found closer to the 

sources of these emissions. 

Section 179B of the CAA, entitled 

‘‘International Border Areas,’’ applies to 

areas that could attain the relevant 

NAAQS by the statutory attainment date 

‘‘but for’’ emissions emanating from 

outside the U.S. Specifically, section 

179B(a) provides that the EPA shall 

approve an attainment plan for such an 

area if: (i) the attainment plan meets all 

other applicable requirements of the 

CAA, and (ii) the submitting state can 

satisfactorily demonstrate that ‘‘but for 

emissions emanating from outside of the 

United States,’’ the area would attain 

and maintain the relevant NAAQS. In 

addition, section 179B(d) applies 

specifically to PM10 NAAQS (which 

would include the PM2.5 NAAQS) and 

provides that if a state demonstrates that 

an area would have timely attained the 

NAAQS but for emissions emanating 

from outside the U.S., then the area is 

not subject to the mandatory 

reclassification element of section 

188(b)(2) for Moderate areas that fails to 

attain the PM10 NAAQS by the 

applicable attainment date. 

Under section 179B, areas affected by 

emissions from outside the U.S. 

continue to have attainment plan 

obligations. First, even if the area is 

impacted by emissions from outside the 

U.S., that fact does not affect the 

designation of the area. An area that is 

violating the relevant NAAQS, even if 

emissions from outside the U.S. 

contribute to that violation, will be 

designated nonattainment. Section 179B 

does not affect designation. Second, as 

a result of that designation, the state is 

required to meet the applicable 

attainment plan requirements for the 

relevant NAAQS. Section 179B does not 

negate the attainment plan 

requirements, it only eliminates the 

obligation for an attainment 

demonstration that demonstrates 

attainment and maintenance of the 

NAAQS, and elimination of that 

obligation is conditioned upon the state 

meeting all other attainment plan 

requirements. 

Under section 179B, states remain 

obligated to meet the attainment plan 

requirements other than the requirement 

to demonstrate timely attainment. The 

applicable requirements for an 

attainment plan for PM2.5 include those 

requirements that apply to a Moderate 

area attainment plan, including an 

emissions inventory, RACM and RACT 

measures, RFP and quantitative 

milestones, and contingency measures. 

The Addendum includes a discussion of 

the applicable attainment plan 

requirements in the context of 

developing a SIP subject to section 

179B. In it, the EPA clarified that 

‘‘RACM/RACT must be implemented to 

the extent necessary to demonstrate 

attainment by the applicable attainment 

date if emissions emanating from 

outside the U.S. were not included in 

the analysis.’’ 283 The EPA further 

encouraged states ‘‘to reduce emissions 

beyond the minimum necessary to 

satisfy the ‘but for’ test in order to 

reduce the PM concentrations to which 

their populations are exposed’’.284

However, the EPA acknowledged that 

‘‘if . . . States . . . were also required, 

because of contributions to PM10

violations caused by foreign emissions, 

to shoulder more of a regulatory and 

economic burden than States not 

similarly affected . . . such a 

requirement would unfairly penalize 

States containing international border 

areas and effectively undermine the 

purpose of section 179B. Indeed, to the 

extent an affected State can 

satisfactorily demonstrate that 

implementation of such measures 

clearly would not advance the 

attainment date, EPA and the state 

could conclude they are unreasonable 

and hence do not constitute RACM.’’ 285

The EPA has considered this past 

interpretation of RACM and RACT 

requirements in the context of section 

179B attainment plans for PM2.5 NAAQS 

and no longer views it as appropriate or 

consistent with the agency’s guidance 

that encourages states ‘‘to reduce 

emissions beyond the minimum 

necessary to satisfy the ‘but for’ test in 

order to reduce the PM10 concentrations 

to which their populations are 

exposed.’’ 286 That is, given that the 

primary purpose of an attainment plan 

is to achieve emission reductions so that 

people living in a nonattainment area 

receive the public health protection 

intended by the NAAQS, adopting an 

interpretation that would allow those 

people to continue to be subjected to 

levels of PM2.5 above the NAAQS that 

the state could reasonably reduce—in 

this case not to attainment level, but to 

a level below the current level—would 

be antithetical to the objectives of the 

CAA. In addition, as with all other 

Moderate PM2.5 nonattainment areas, 

the EPA interprets the provisions of 

section 172(c)(6) to require that such 

areas must implement all additional 

reasonable measures that it can 

implement through the sixth calendar 

year following designation of the area, 

in addition to those measures meeting 

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287 Ibid. 

the definition of RACM and RACT, in 

order to make progress toward 

attainment after the end of the fourth 

year following designation. 

Therefore, the EPA is proposing and 

seeking comment on two proposed 

approaches that would give greater 

clarity to the agency’s existing 

interpretation of control strategy 

requirements for Moderate area 

attainment plans to be approved under 

section 179B. The first proposed 

interpretation would clarify that the 

control strategy for an area that could 

attain by the Moderate area attainment 

date, ‘‘but for’’ foreign emissions of 

direct PM2.5 or its precursors, must 

include all control measures identified 

by the state to be technologically and 

economically feasible and 

implementable on sources in the area by 

the end of the sixth calendar year 

following designation of the area, thus 

satisfying requirements for RACM and 

RACT and additional reasonable 

measures, with a possible exception for 

any such measures that collectively 

would not be effective in reducing 

ambient PM2.5 levels in the area. This 

interpretation would closely align the 

EPA’s interpretation of what constitutes 

a reasonable control strategy for a 

Moderate area attainment plan 

submitted pursuant to section 179B 

with the EPA’s proposed interpretation 

of what constitutes a reasonable control 

strategy for a Moderate area attainment 

plan submitted pursuant to section 

189(a)(1) for an area that cannot 

practicably attain by the statutory 

Moderate area attainment date. 

More specifically, under the first 

proposed approach for identifying 

appropriate control measures on sources 

in a Moderate PM2.5 nonattainment area 

that could attain the NAAQS ‘‘but for’’ 

foreign emissions, the EPA is proposing 

that the state would be required to 

implement all technologically and 

economically feasible measures that can 

be implemented on sources in the area 

by the end of the sixth calendar year 

following designation of the area in 

order to ensure that the area makes 

reasonable progress toward attaining the 

standard even if such measures are not 

expected to yield attainment by the 

statutory Moderate area attainment date. 

However, because the EPA recognizes 

that it may not be reasonable to require 

that a state implement those 

technologically and economically 

feasible control measures that 

collectively will not effectively reduce 

ambient PM2.5 concentrations, the 

agency is proposing to allow the state 

not to implement such measures if it 

can demonstrate that collectively they 

will not be effective in reducing PM2.5

levels in the area. The EPA seeks 

comment on this proposed approach for 

Moderate PM2.5 nonattainment areas 

potentially subject to an attainment 

demonstration waiver under section 

179B, and seeks comment on an 

alternative proposed approach that 

would not allow such an exception 

based on the collective effectiveness of 

otherwise ‘‘reasonable’’ measures. This 

alternative proposed option parallels a 

similar option described in Section IV.D 

in this preamble for Moderate PM2.5

nonattainment areas that cannot 

practicably attain the NAAQS by the 

latest statutory attainment date for the 

area. 

The EPA also seeks comment on a 

distinct, second proposed approach for 

interpreting what would constitute an 

acceptable control strategy for sources 

in an area for which a state is seeking 

an attainment plan approval under 

section 179B. Under this second option, 

a state would need to demonstrate that 

its selected control measures for a 

Moderate nonattainment area would 

achieve reductions in PM2.5 levels that 

exceeded the applicable NAAQS in 

proportion to their contribution to 

overall PM2.5 levels. For example, if 

monitors in a Moderate nonattainment 

area reveal that the area is exceeding the 

2012 PM2.5 NAAQS of 12 mg/m3 by 2 mg/ 

m3, for a total of 14 mg/m3, and the state 

concludes that foreign sources are 

contributing 3 mg/m3, then the state 

would be responsible for the remaining 

11 mg/m3 and would need to implement 

enough reasonable control measures to 

achieve reductions in monitored 

ambient PM2.5 concentrations equal to 

(11/14)*2 mg/m3 or 1.6 mg/m3. The EPA 

recognizes that this approach could 

require a high level of precision to be 

able to quantify accurately contributions 

from sources inside and outside the 

nonattainment area as well as projected 

emission reductions to be achieved with 

the implementation of each potential 

control measure for sources inside the 

area. However, the agency believes that 

such precision may be justified to 

support any ‘‘but for’’ demonstration 

submitted to the EPA and to support 

any claims that a state should only be 

required to implement a subset of 

otherwise ‘‘reasonable’’ control 

measures on sources of direct PM2.5

emissions or emissions of PM2.5

precursors located in the nonattainment 

area. 

The EPA seeks comment on these two 

approaches to clarify what constitutes a 

reasonable control strategy in the 

context of a SIP submitted pursuant to 

section 179B. The EPA is also proposing 

regulations for the PM2.5 NAAQS 

consistent with the existing guidance 

with respect to requirements for RFP 

and quantitative milestones and 

contingency measures for areas seeking 

Moderate area attainment plan approval 

under section 179B. The General 

Preamble states that: 

In international border areas, EPA will not 

require the contingency measures for PM10 to 

be implemented after the area fails to attain 

if EPA determines that the area would have 

attained the NAAQS, but for emissions 

emanating from outside the U.S. However, 

the EPA will require contingency measures to 

be implemented if it determines that the area 

failed to make RFP in achieving the required 

reductions in PM10 emissions from sources 

within the U.S., or if the area does not, in 

fact, obtain the emission reductions that were 

necessary to demonstrate timely attainment 

of the NAAQS, but for emissions emanating 

from outside the U.S.287

The EPA is proposing that this 

interpretation of section 179B(a)(1) with 

respect to contingency measures and 

RFP requirements should apply to 

Moderate nonattainment areas for the 

PM2.5 NAAQS. Specifically, the EPA 

proposes that as part of any Moderate 

area attainment plan submitted under 

section 179B, a state must include an 

RFP plan developed consistent with 

proposed Option 2 for RFP analyses for 

Moderate nonattainment areas that 

cannot practicably attain the relevant 

NAAQS by the statutory attainment 

date, described in Section IV.F of this 

preamble. Furthermore, the state must 

include as part of any attainment plan 

submission made for such an area 

contingency measures that can be 

implemented without significant effort 

in the event the EPA finds that such 

area failed to meet RFP requirements. 

The contingency measures should 

achieve approximately 1 year’s worth of 

emissions reductions as calculated by 

the state for purposes of the RFP 

analysis. In addition, the EPA proposes 

that the state must identify quantitative 

milestones for the area to be achieved 

4.5 years and 7.5 years from the date of 

designation of the area. The EPA 

proposes to apply the same proposed 

requirements for establishing and 

reporting on quantitative milestones for 

Moderate nonattainment areas seeking 

attainment date waivers under section 

179B as for all other Moderate 

nonattainment areas, described fully in 

Section IV.G of this preamble. The 

agency seeks comment on these 

proposed requirements for Moderate 

area plans submitted pursuant to section 

179B. 

The EPA has historically evaluated 

section 179B ‘‘but for’’ demonstrations 

on a case-by-case basis, based on the 

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288 Ibid. The Addendum includes further 

examples of information a state may present for the 

EPA to consider as part of the ‘‘but for’’ 

demonstration, including additional monitors in 

international border areas, more detailed emissions 

inventories, and speciation data that identifies 

PM2.5 components from foreign sources. 

289See 40 CFR 50.14. 

290The EPA’s Exceptional Events Rule Web site 

is located at: http://www.epa.gov/ttn/analysis/

exevents.htm. 

individual circumstances and data 

provided by the submitting state. These 

demonstrations have included 

information such as ambient air quality 

monitoring data, modeling scenarios, 

emissions inventory data and 

meteorological or satellite data.288 The 

Moderate area attainment demonstration 

modeling and other elements of the 

attainment demonstration must show 

timely attainment of the NAAQS but for 

the emissions from outside of the U.S. 

Section 179B does not, however, 

provide authority to exclude monitoring 

data influenced by international 

transport from regulatory 

determinations related to attainment 

and nonattainment. Thus, even if the 

EPA approves a section 179B ‘‘but for’’ 

demonstration for an area, the area 

would continue to be designated as 

nonattainment and subject to the 

applicable requirements, including 

nonattainment new source review, 

conformity and other measures 

prescribed for nonattainment areas by 

the CAA. Section 179B requires states to 

continue to meet attainment plan 

requirements, notwithstanding the 

contribution of emissions from sources 

outside the U.S., in order to provide the 

public health protection intended by the 

NAAQS. However, if the EPA approves 

a ‘‘but for’’ demonstration for a 

Moderate nonattainment area, the area 

would not be subject to reclassification 

for failure to attain by the applicable 

attainment date as explained earlier. 

Although monitor data cannot be 

excluded for a determination of whether 

an area has attained based solely on the 

fact the data are affected by emissions 

from outside the U.S., such data may be 

excluded from consideration if they 

were significantly influenced by 

exceptional events under section 

319(b)(3) of the CAA. Where 

international transport of emissions 

contributes to an exceedance or 

violation and comes from natural 

sources such as wildfires, and otherwise 

meets the criteria contained in the 

EPA’s Exceptional Events Rule, it can be 

addressed by that rule.289 Specifically, if 

the EPA concurs with an air agency’s 

request to exclude affected data, the 

event-influenced data are officially 

noted and removed from the data set 

used to calculate official design values. 

Because of previously expressed 

stakeholder feedback regarding 

implementation of the Exceptional 

Events Rule and specific stakeholder 

concerns regarding the analyses that can 

be used to support wildfire-related 

exceptional event demonstrations, the 

EPA intends to propose revisions to the 

Exceptional Events Rule in a future 

notice-and-comment rulemaking and 

will solicit public comment at that time. 

The EPA has approved PM2.5 wildfire 

influenced exceptional events 

demonstrations in the past, which are 

posted on the agency’s Exceptional 

Events Rule Web site.290

Depending on the nature and scope of 

international emissions events affecting 

air quality in the U.S., the EPA may be 

able to assist states in developing 

approvable exceptional events 

demonstrations. More generally, the 

EPA believes that the best approach for 

evaluating the potential impacts of 

international transport on 

nonattainment is for states to work with 

the EPA on a case-by-case basis to 

determine the most appropriate 

information and analytical methods for 

each area’s unique situation. The EPA 

will 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 PM2.5 and PM2.5 precursors. 

E. Enforcement and Compliance 

Section 172(c)(6) in subpart 1 of the 

CAA requires nonattainment SIPs to 

‘‘include enforceable emission 

limitations, and such other control 

measures, means or techniques . . . as 

well as schedules and timetables for 

compliance, as may be necessary or 

appropriate to provide for attainment.’’ 

In the remanded 2007 PM2.5

Implementation Rule, the EPA 

described the general elements that 

characterize an enforceable SIP 

regulation, recognizing that enforceable 

SIP regulations may address the 

elements in different ways depending 

on the type of source category being 

regulated. The agency continues to 

believe and hereby proposes that in 

general, in order for a SIP regulation to 

be enforceable, it must clearly spell out 

which sources or source types are 

subject to its requirements and what its 

requirements (e.g., emission limits or 

work practices) are. An enforceable 

regulation would also specify the 

timeframes within which these 

requirements must be met, and 

definitively state the recordkeeping and 

monitoring requirements appropriate to 

the type of sources being regulated. The 

recordkeeping and monitoring 

requirements would have to be 

sufficient to enable the state or the EPA 

to determine whether the source is 

complying with the emission limit on a 

continuous basis. An enforceable 

regulation would also contain test 

procedures in order to determine 

whether sources are in compliance. 

The EPA continues to believe that 

complete and effective regulations that 

ensure compliance with an applicable 

emissions limit would have to include 

requirements for both performance 

testing of emissions and ongoing 

monitoring of the compliance 

performance of control measures, and 

the agency proposes to require that SIP 

regulations that establish emission 

limits include the following: 

(a) Indicator(s) of compliance—the 

pollutant or pollutants of interest (e.g., 

filterable and condensable PM2.5) and 

the applicable units of measurement for 

expressing compliance (e.g., ng/J of heat 

input, lb/hr); 

(b) Test method—reference to a 

specific EPA or other published set of 

sample collection and analytical 

procedures, equipment design and 

performance criteria, and the 

calculations providing data in units of 

the indicator of compliance (Section 

IX.K of this preamble presents a 

discussion of specific test methods for 

condensable PM2.5 emissions); 

(c) Averaging time—the minimum 

length of each required test run and the 

requirement to average the results of the 

test runs (e.g., three runs) representing 

a specified period of time (e.g., 8 hours); 

and, 

(d) Frequency—the maximum time 

between emissions or performance tests 

(e.g., within 30 days of facility start-up 

and once each successive quarter, every 

6-month period, or yearly). 

In order to be complete with regard to 

compliance monitoring provisions, the 

EPA proposes that regulations adopted 

into the SIP must include the following 

critical elements: 

(a) Indicator(s) of performance—the 

parameter or parameters measured or 

observed for demonstrating proper 

operation of the pollution control 

measure or compliance with the 

applicable emissions limitation or 

standard. Indicators of performance 

could include direct or predicted 

emissions measurements, process or 

control device (and capture system) 

operational parametric values that 

correspond to compliance with 

efficiency or emissions limits, and 

recorded findings of verification of work 

practice activities, raw material or fuel 

pollutant content, or design 

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291Under the title V regulations, sources have an 

obligation to include in their title V permit 

applications, among other components, all 

emissions of pollutants for which the source is 

major, and all emissions of regulated air pollutants. 

See, e.g., 40 CFR 70.5(c)(3). The definition of 

regulated air pollutant in 40 CFR 70.2 includes any 

pollutant for which a NAAQS has been 

promulgated, including PM2.5. 

292For a list of potential control measures for 

PM2.5 and PM2.5 precursors, see http://

www.epa.gov/air/pdfs/

MenuOfControlMeasures.pdf. 

293Recommendations to the Clean Air Act 

Advisory Committee: Phase II, June 2007, http://

www2.epa.gov/caaac/caaac-reports. 

294Memorandum from Stephen D. Page to 

Regional Air Division Directors, ‘‘Consideration of 

Multiple Pollutants in Control Strategy 

Development.’’ August 10, 2005. 

characteristics. Indicators could be 

expressed as a single maximum or 

minimum value, a function of process 

variables (e.g., within a range of 

pressure drops), a particular operational 

or work practice status (e.g., a damper 

position, completion of a waste recovery 

task), raw material or fuel pollutant 

content, or an interdependency between 

two or more variables; 

(b) Measurement technique—the 

means used to gather and record 

information of or about the indicators of 

performance. The components of the 

measurement technique include the 

detector type or analytical method, 

location and installation specifications, 

inspection procedures, and quality 

assurance and quality control measures. 

Examples of measurement approaches 

include continuous emissions 

monitoring systems (CEMS), continuous 

opacity monitoring systems (COMS), 

continuous parametric monitoring 

systems (CPMS), performance testing, 

vendor or laboratory analytical data, and 

manual inspections and data collection 

that include making records of process 

conditions, raw materials or fuel 

specifications, or work practices. 

Directly enforceable emission 

measurements, such as PM CEMs, are 

preferred wherever feasible. Where 

COMS are feasible, it should be clear 

that opacity is a directly enforceable 

standard, not merely an indicator of 

compliance; 

(c) Averaging time—the period over 

which to average data to verify 

compliance with the emissions 

limitation or standard or proper 

operation of the pollution control 

measure. Examples of averaging time 

include a 3-hour average in units of the 

emissions limitation, a 30-day rolling 

average emissions value, a daily average 

of a control device operational 

parametric range, periodic (e.g., 

monthly, annual) average of raw 

materials or fuel pollutant content, and 

an instantaneous alarm; 

(d) Monitoring frequency—the 

number of monitoring data values 

recorded over a specified time interval. 

Examples of monitoring frequencies 

include at least one data value every 15 

minutes for CEMS or CPMS, at least 

every 10 seconds for COMS, upon 

receipt or application of raw materials 

or fuel to the process, or at least once 

per operating day (or week, month, etc.) 

for performance testing, work practice 

verification, or equipment design 

inspections; and, 

(e) Reporting and record retention 

requirements—criteria for retaining 

monitoring and test data in an electronic 

form and periodic electronic reporting 

of information as needed to the 

compliance office. Electronic record 

retention and submission have been 

widely adopted, and the EPA believes 

that such readily accessible 

documentation could be used by state, 

federal and other analysts to spot trends 

and non-compliance more easily than if 

these entities conducted reviews of 

paper documents. The EPA also 

recommends that compliance reports be 

made available online so that the 

general public can readily access the 

information without the need to submit 

Freedom of Information Act (FOIA) 

requests to the EPA. The EPA is in the 

process of revising federal rules to make 

similar requirements apply. 

The EPA continues to believe that 

approval of regulations adopted into 

SIPs would have to ensure that these 

critical elements are present and clearly 

defined to be approvable. In particular, 

the compliance obligations, including 

emissions limits and other applicable 

requirements, would need to be 

representative of and accountable to the 

assumptions used in a state’s attainment 

demonstration. This accountability 

would include the ability to transfer the 

applicable regulatory requirements to a 

title V operating permit subject to the 

EPA and public review.291

The EPA seeks comment on the 

elements proposed to be required to 

ensure that regulations adopted into a 

SIP are enforceable. 

F. Efforts To Encourage a MultiPollutant Approach When Developing 

PM2.5 Attainment Plans 

1. General Guidance 

From a planning and resource 

perspective, the EPA believes that it can 

be efficient for states to develop 

integrated control strategies that address 

multiple pollutants rather than separate 

strategies for each pollutant or NAAQS 

individually. An integrated air quality 

control strategy that reduces multiple 

pollutants can help ensure that 

reductions are efficiently achieved and 

produce the greatest overall air quality 

benefits. For example, it is widely 

known that certain control measures 

that reduce emissions of NOX and VOC, 

and thus reduce ambient PM2.5 levels, 

can also result in reduced ambient 

concentrations of ground-level ozone.292

Many VOC are also hazardous air 

pollutants (HAP), so a control strategy 

for a PM2.5 nonattainment area that 

reduces VOC emissions may provide the 

additional benefit of reducing air toxics. 

It is also widely known that many 

sources of PM2.5 also emit toxic metals 

as particulates, so controlling directly 

emitted PM2.5 emissions from these 

sources would also reduce the 

emissions of toxic metals. In addition, 

due to expected changes in meteorology 

resulting from climate change, the EPA 

encourages states to assess climate 

change and air pollution together and 

account for the potential effects of 

climate change in their multi-pollutant 

planning efforts. 

In June 2007, the EPA’s CAA 

Advisory Committee (CAAAC) 

recommended that the agency allow 

states to integrate SIP requirements and 

other air quality goals into a 

comprehensive plan.293 The 

recommended plan would demonstrate 

attainment/maintenance of multiple 

NAAQS, accomplish sector-based 

reductions, realize risk reductions of 

HAPs and make improvements in 

visibility. It could also be structured to 

integrate programs addressing land use, 

transportation, energy and climate. 

The EPA has encouraged states to take 

a multi-pollutant approach to managing 

air quality.294 Specifically, the agency 

has encouraged states to involve all 

stakeholders when planning to meet air 

quality standards and to provide a basic 

outline for how local jurisdiction(s) 

could address air pollutants in an 

integrated manner. 

While the agency encourages states to 

develop multi-pollutant plans, it 

recognizes that the requirement for the 

agency to review and, as necessary, 

revise NAAQS every 5 years, which can 

trigger new statutory attainment plan 

submission and attainment dates, as 

well as the ever-evolving understanding 

of pollutants and many control 

programs that may be available to 

reduce emissions, can sometimes make 

such efforts challenging. For example, 

under the current law, the 2007 

submission date for Regional Haze SIPs 

has already passed while RACT SIPs for 

nonattainment areas classified as 

Moderate or higher for the 2008 ozone 

NAAQS were due more than 2 years 

before the due date for Moderate area 

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295See http://www.epa.gov/air/aqmp/. 

296 Depending on the context, ‘‘multi-pollutant’’ 

can be defined in different ways. In this context the 

agency is defining multi-pollutant modeling as 

simultaneous modeling of PM2.5, ozone, key air 

toxics, and regional haze. Future multi-pollutant 

models may include the ability to model a broader 

array of air toxics as well as greenhouse gases. 

297The 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. Both kinds of uncertainties are 

components of the risk associated with pollution at 

concentrations 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 EPA Administrator is seeking not only to 

prevent pollution levels that have been 

demonstrated to be harmful but also to prevent 

lower pollutant levels that may pose an 

unacceptable risk of harm, even if the risk is not 

precisely identified as to nature or degree. The CAA 

does not require the Administrator to establish a 

primary NAAQS at a zero-risk level or at 

background concentration levels, but rather at a 

level that reduces risk sufficiently so as to protect 

public health with an adequate margin of safety. 

attainment plans for areas designated 

nonattainment for the 2012 annual 

PM2.5 NAAQS. Although it is not 

feasible to integrate fully these planning 

requirements, states could potentially 

use common databases and modeling 

tools for all three SIP submissions for 

these different requirements and rely on 

similar control measures as appropriate. 

Furthermore, as states develop plans to 

meet any current or future PM2.5

NAAQS, they may wish to modify 

existing plans for implementing the 

ozone NAAQS or other NAAQS, or for 

regional haze, as they consider strategies 

more comprehensively. However, it is 

important to note that states and the 

EPA must continue to meet all the CAA 

mandated planning and program 

elements for individual NAAQS. The 

EPA seeks comment on alternative 

approaches to integrate the planning 

requirements for multiple NAAQS and 

other CAA programs that are 

promulgated at different times. 

2. What is the EPA doing beyond 

encouraging states to integrate their air 

quality planning activities to the extent 

feasible? 

Ideally, an air quality management 

plan (AQMP) is a set of pollution 

reduction strategies/planning activities 

for an area demonstrating: attainment/

maintenance of one or more NAAQS; 

risk reductions from HAPs; 

improvements in visibility and 

ecosystem health; and, integration of 

land use, transportation, energy and 

climate activities in the area. Three 

areas in the country—North Carolina, 

New York and the City of St. Louis 

(involving both Missouri and Illinois)— 

participated in an EPA-led pilot effort to 

develop multi-pollutant AQMPs. The 

pilot projects provided lessons 

regarding AQMP development that 

should prove useful to other areas 

interested in better integrating their air 

quality planning. The areas’ initial 

AQMPs and other materials are 

available on the EPA’s Web site.295

Implementation of the 2012 PM2.5

NAAQS provides an opportunity for 

states to consider how to use a multipollutant approach from the beginning 

of their planning process. The EPA 

recommends that states and tribes 

wishing to take a comprehensive 

approach consider the following 

activities: 

• Develop models for the attainment 

demonstration that include previously 

implemented or planned measures to 

reduce PM2.5 precursors and secondary 

fine particles, ozone precursors, 

pollutants that contribute to regional 

haze and, where appropriate, air toxics 

and any potential negative impacts on 

ecosystems; 

• Conduct an integrated assessment 

of the impact that controls have on 

ambient levels of PM2.5, ozone, regional 

haze, and, where applicable, air toxics, 

greenhouse gases, ecosystem protection 

and environmental justice to identify 

those controls with the greatest 

potential co-benefits; and, 

• Use common data bases and 

analytical tools, where possible. 

The EPA is requesting comment on 

what incentives or assistance the agency 

might be able to provide to encourage 

states to integrate their planning 

activities. 

3. Multi-Pollutant Assessments/OneAtmosphere Modeling 

A multi-pollutant assessment, or oneatmosphere modeling, is conducted 

with a single air quality model that is 

capable of simulating transport and 

formation of multiple pollutants 

simultaneously.296 For example, this 

type of model can simulate formation 

and deposition involving pollutants 

associated with PM2.5, ozone and 

regional haze, and it can include 

algorithms simulating gas phase 

chemistry, aqueous phase chemistry, 

aerosol formation and acid deposition. 

This type of model could also include 

the formation and deposition of key air 

toxics and the chemical interactions that 

occur with these individual toxic 

species to produce PM2.5 and ozone. 

Multi-pollutant assessments are 

recommended for PM2.5 attainment 

demonstrations because the formation 

and transport of VOC and NOX are 

closely related to the formation of both 

ozone and regional haze. There is often 

a positive correlation between measured 

secondary particulate matter and ozone. 

Many of the same factors affecting PM2.5

concentrations also affect ozone 

concentrations because similarities exist 

in sources of precursors for both 

pollutants. For example, emissions of 

NOX may lead to formation of nitrates, 

which affect both ambient PM2.5 and 

ozone levels and impair visibility. Many 

VOC (such as toluene) are air toxics and 

may also be sources of precursors for 

both organic particles and ozone. In 

addition, the presence of ozone itself 

may be an important factor affecting 

secondary particle formation. 

Because of these relationships, 

models and data analysis intended to 

address PM2.5 could be beneficial for use 

in addressing ozone and visibility 

impairment. When performing a multipollutant assessment, the modeling 

should take into account previously 

implemented or planned measures to 

reduce PM2.5, ozone, and regional haze. 

States that undertake multi-pollutant 

assessments as part of their attainment 

demonstration should consider 

assessing the impact of their PM2.5

strategies on ozone and visibility 

impairment to ensure that optimal 

emission reduction strategies are 

developed for the three programs to the 

extent possible. This could facilitate 

addressing all of these pollutants in a 

more cost effective manner. 

States may also find it desirable to 

assess the impact of PM2.5, ozone, and/ 

or regional haze control strategies on 

toxic air pollutants regulated under the 

CAA or under state air toxic initiatives. 

Given the relationships that exist 

between air toxics and the formation of 

PM2.5 and ozone, states may find that 

controls can be selected to meet goals 

for PM2.5 and/or ozone attainment as 

well as those of specific air toxic 

programs. 

G. Measures To Ensure Appropriate 

Protections for Overburdened 

Populations 

1. Review of PM NAAQS and At-Risk 

Populations 

As discussed in Section II of this 

preamble, when the EPA sets a primary 

NAAQS, the CAA directs the 

Administrator to establish a standard 

that is ‘‘requisite’’ to protect public 

health with ‘‘an adequate margin of 

safety.’’ 297 In setting the NAAQS, the 

EPA considers available, relevant 

scientific information on the health 

effects that may occur in the general 

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298The legislative history of section 109 of the 

CAA 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.’’ 

299 78 FR 3086 (January 15, 2013). 

300 In the final 2012 p.m. NAAQS rule, based on 

information presented in the Integrated Science 

Assessment for Particulate Matter (U.S. EPA, 2009, 

sections 2.2.1 and 8.1.7), the EPA made a finding 

that persons with lower socioeconomic status are at 

increased risk for experiencing adverse health 

effects related to PM exposures (78 FR 3085, 

January 15, 2013, at page 3104). Persons with lower 

socioeconomic status (SES) have been generally 

found to have a higher prevalence of pre-existing 

diseases, limited access to medical treatment, and 

increased nutritional deficiencies, which can 

increase this population’s risk to PM-related effects 

(77 FR 38911, June 29, 2012). 

301See Fann, N., Fulcher, C., and B. Hubbell, 

2009. The Influence of location, source, and 

emission type in estimates of the human health 

benefits of reducing a ton of air pollution. Air 

Quality, Atmosphere & Health. Volume 2, Number 

3, 169–176, June 2009. See also Fann et. al., 2011. 

Maximizing health benefits and minimizing 

inequality: incorporating local-scale data in the 

design and evaluation of air quality policies. 

Society for Risk Analysis, vol. 31, no. 6, p. 908–922, 

June 2011. 

302Wesson, K., Fann, N., Morris, M, Fox, T., 

Hubbell, T., 2010. A multipollutant, risk-based 

approach to air quality management. Case study for 

Detroit. Atmospheric Pollution Research, 1, 296– 

304. The study compared air quality control 

strategies and concluded that the multi-pollutant, 

risk-based approach was able to produce 

approximately two times greater monetized benefits 

through avoided health impacts and was more cost 

effective than a pollutant-by-pollutant approach. 

population, as well as specific groups 

within the general population that are at 

increased risk for experiencing adverse 

pollutant-related health effects (i.e., atrisk populations).298 These groups could 

exhibit a greater risk of pollutant-related 

health effects than the general 

population for a number of reasons 

including being adversely affected at 

lower pollutant concentrations, 

experiencing a larger health impact at a 

given pollutant concentration, and/or 

being exposed to higher pollutant 

concentrations than the general 

population. Thus, the NAAQS review 

process inherently takes into 

consideration certain environmental 

justice factors as part of the standardsetting process. In setting a secondary 

standard, the CAA directs the 

Administrator to establish a standard 

that ‘‘is requisite to protect the public 

welfare from any known or anticipated 

adverse effects.’’ 

Section 109(d) of the CAA requires 

the EPA to periodically review (every 5 

years) the science upon which the 

standards are based and the standards 

themselves. As discussed elsewhere in 

this proposal, in its 2012 review of the 

PM NAAQS, the EPA revised the 

primary annual PM2.5 standard by 

lowering the level to 12.0 micrograms 

per cubic meter (mg/m3) so as to provide 

increased protection against health 

effects associated with long- and shortterm PM2.5 exposures.299 The agency 

also revised the form of the primary 

annual PM2.5 standard to eliminate the 

spatial averaging provisions to avoid 

potential disproportionate impacts on 

at-risk populations. In conjunction with 

these revisions, the EPA retained the 

primary 24-hour PM2.5 standard, as 

revised in 2006 (71 FR 61144, October 

17, 2006), to provide supplemental 

protection against health effects 

associated with short-term PM2.5

exposures, especially in areas with high 

peak PM2.5 concentrations. This suite of 

primary annual PM2.5 standards 

provides increased public health 

protection, including the health of atrisk populations which include 

children, older adults, persons with preexisting health and lung disease, and 

persons of lower socioeconomic status, 

against a broad range of PM2.5-related 

effects that include premature mortality, 

increased hospital admissions and 

emergency department visits, and 

development of chronic respiratory 

disease.300

In addition, the Policy Assessment 

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

the highest concentrations of PM2.5 in an 

area tend to be measured at monitors 

located in areas where the surrounding 

populations are more likely to live 

below the poverty line and to have 

higher percentages of minorities. The 

EPA directed states to relocate a limited 

number of existing monitors to nearroadway sites in large urban areas. Both 

of these revisions were informed by 

scientific evidence that underscored the 

potentially disproportionate exposure to 

high PM2.5 concentrations and therefore 

disproportionate risk to low-income and 

minority populations. 

2. Relationship Between Direct PM2.5

Emissions and PM2.5 Precursor 

Emissions Reductions and At-Risk 

Populations 

Sources of direct PM emissions have 

their greatest impact on PM2.5

concentrations and public health in the 

general vicinity of the source (e.g., 

within 10 miles), while sources of 

precursor emissions can contribute to 

PM2.5 concentrations more than 100 

miles away and are considered to have 

a more regional impact. To date, state 

PM2.5 attainment plans have generally 

relied to a greater extent on reductions 

of precursor pollutants rather than on 

reductions of direct PM2.5 emissions. 

Studies show, however, that on a per 

ton basis, the reduction of a ton of direct 

PM2.5 emissions leads to greater health 

benefits than the reduction of a ton of 

SO2 or NOX.301

The process for developing attainment 

plans for the current and future PM2.5

NAAQS presents a potential 

opportunity to target the health 

protections afforded by the NAAQS, as 

the EPA expects that attainment for the 

2012 PM2.5 NAAQS and future PM2.5

NAAQS in nonattainment areas with the 

most severe pollution problems may 

need to give greater emphasis to 

reducing direct PM2.5 emissions in 

combination with efforts already 

underway to further reduce precursor 

emissions. Placing greater emphasis on 

reducing emissions from sources of 

direct PM2.5 (e.g., certain industrial 

facilities located in more densely 

populated areas; areas with high motor 

vehicle and other diesel engine 

emissions, such as rail yards and near 

major roadways; and, areas with high 

wood smoke emissions) could provide 

the added benefit of reducing exposure 

to PM2.5 in low-income and minority 

communities. 

With this in mind, the EPA is seeking 

comment on additional ways that air 

agencies can provide public health 

protection specifically for overburdened 

populations when preparing attainment 

plans for the PM2.5 NAAQS. The 

discussion that follows provides some 

examples of points in the attainment 

plan development process at which a 

state could assess opportunities for 

providing such additional protections, 

and examples of what those additional 

protections might look like. 

3. Options for States To Consider To 

Ensure Appropriate Protections From 

PM2.5 Exposure for Overburdened 

Populations 

The EPA believes that states have 

sufficient flexibility and discretion 

under the CAA in implementing their 

attainment strategies to focus resources 

on controlling those sources of 

emissions that directly and adversely 

affect low-income and other at risk 

populations. By reducing impacts on atrisk populations, states can maximize 

health benefits, thereby creating greater 

net benefits for the state in a costeffective manner.302 In addition, 

reducing adverse impacts to low-income 

and minority populations advances the 

environmental justice goal of fair 

treatment for these populations. 

There are a number of actions that 

states could take to focus resources in 

this way. Some of these actions can help 

identify areas where additional ambient 

monitoring may be needed in low 

income and overburdened communities. 

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303For more information on SEPs, go to 

www2.epa.gov/enforcement/supplementalenvironmental-projects-sep. 

304See 78 FR 27220 (May 9, 2013) notice of 

availability, ‘‘EPA Activities To Promote 

Environmental Justice in the Permit Application 

Process.’’ 

Such information can be used to 

support updates to the state’s annual 

monitoring plan. Examples of actions to 

support updates to the annual 

monitoring plan include: 

• Develop databases and online 

mapping tools that enable users 

(including state staff, public, and the 

regulated community) to understand 

where sources of direct PM2.5 emissions 

are located and where new or modified 

sources of emissions could have 

potential impacts on low income and 

other overburdened communities; 

• Incorporate existing mapping tools 

which identify target areas in the 

attainment plan development process 

and related actions; and, 

• Analyze emissions data, ambient 

data, and available modeling to identify 

potential unmonitored PM2.5 hotspots in 

areas with a high percentage of low 

income, minority or indigenous persons 

(see Section IV.E of this preamble for 

further discussion of this option). 

Once target areas for addressing these 

sensitive population needs within a 

nonattainment area have been 

identified, the state could consider 

taking any of the following actions 

which help target emissions reductions 

that may be needed to attain the PM2.5

NAAQS: 

• Prioritize the selection of control 

measures that target reductions of direct 

PM2.5, particularly from sources located 

in ‘‘at-risk’’ areas as part of the state’s 

RACM and RACT analysis (for Moderate 

nonattainment areas) or BACM and 

BACT analysis (for Serious 

nonattainment areas), as well as other 

measures needed to demonstrate 

attainment (see Sections IV.D and VI.D, 

respectively, of this preamble for further 

discussion of this option); 

• Improve the understanding of the 

potential impact of minor sources by 

improving or generating an emissions 

inventory for such minor sources, 

including sources that are not currently 

required to report emissions, to generate 

options on how emissions can be 

reduced in the target area; 

• Design voluntary programs to 

reduce VMT and mobile source-related 

PM2.5 emissions (e.g., diesel retrofits); 

• Incorporate environmental justice 

criteria into the alternatives analysis to 

ensure appropriate siting and require 

cumulative impact studies for proposed 

projects; 

• Eliminate exemptions from and/or 

raise thresholds for minor source 

permitting; 

• Develop a list of potential 

supplemental environmental projects 

(SEPs) 303 that could be applied in the 

target area; and, 

• Prioritize targeted enforcement 

strategies. 

In addition to the above, states could 

increase opportunities for meaningful 

involvement of community groups in 

attainment plan development, annual 

monitoring network plan reviews, and 

permitting processes 304 for at-risk and 

minority populations by taking the 

following steps: 

• Develop advisory boards and/or 

develop enhanced notice-and-comment 

requirements for low income and 

minority communities to assure 

meaningful involvement relative to 

projects that impact their communities; 

• Provide special notice of important 

actions affecting target areas in 

appropriate languages and with 

attention to cultural barriers; 

• Provide advance notification for 

low income and minority communities 

of upcoming opportunities for public 

comment on SIPs, ambient air 

monitoring plans, and other relevant 

actions; 

• Maintain multi-lingual Web sites 

and offer translators for public meetings 

and hearings; 

• Coordinate with the state’s EJ 

coordinator to assist with outreach 

efforts; and, 

• Provide states with appropriate 

federal EJ guidance tools. 

The EPA is seeking comment on these 

examples and whether and how the EPA 

might provide recommendations to 

states preparing attainment plans for the 

2012 and any future PM2.5 NAAQS on 

additional ways to ensure equal 

protections for overburdened 

populations. 

H. Tribal Issues 

The 1998 Tribal Air Rule (TAR) (40 

CFR part 49), which implements section 

301(d) of the CAA, gives tribes the 

option of developing TIPs. Specifically, 

the TAR provides for the tribes to be 

treated in the same manner as a state in 

implementing certain sections of the 

CAA. However, tribes are not required 

to develop implementation plans. The 

EPA determined in the TAR that it was 

inappropriate to treat tribes in a manner 

similar to a state with regard to specific 

plan submittal and implementation 

deadlines for NAAQS-related 

requirements, including, but not limited 

to, such deadlines in CAA sections 

110(a)(1), 172(a)(2), 182 187, and 191. 

See 40 CFR 49.4(a). In addition, the EPA 

determined it was not appropriate to 

treat tribes similarly to states with 

respect to provisions of the CAA 

requiring as a condition of program 

approval the demonstration of criminal 

enforcement authority or providing for 

the delegation of such criminal 

enforcement authority. See 40 CFR 

49.4(g). To the extent a tribe is 

precluded from asserting criminal 

enforcement authority, the federal 

government will exercise primary 

criminal enforcement responsibility. See 

40 CFR 49.8. In such circumstances, 

tribes seeking approval for CAA 

programs provide potential investigative 

leads to an appropriate federal 

enforcement agency. 

If a tribe elects to do a TIP, the agency 

will work with the tribe to develop an 

appropriate schedule which meets the 

needs of the tribe, and which does not 

interfere with the attainment of the 

NAAQS in other jurisdictions. The tribe 

developing a TIP can work with the EPA 

Regional Office on the appropriateness 

of addressing RFP and other substantive 

SIP requirements that may or may not 

be appropriate for the tribe’s situation. 

The CAA and the TAR provide tribes 

opportunities and flexibility for the tribe 

in the preparation of a TIP to address 

the NAAQS. If a tribe elects to develop 

a TIP, the TAR offers flexibility for the 

tribe to identify and implement on a 

case-by-case basis only those CAA 

programs or reasonably severable 

program elements needed to address 

their specific air quality problems. In 

the TAR, the EPA described this flexible 

implementation approach as a modular 

approach. Each tribe may evaluate the 

particular activities, including potential 

sources of air pollution within the 

exterior boundaries of its reservation (or 

within non-reservation areas for which 

it has demonstrated jurisdiction), which 

cause or contribute to its air pollution 

problem. A tribe may adopt measures 

for controlling those sources of PM2.5- 

related emissions, as long as the 

elements of the TIP are reasonably 

severable from the package of elements 

that can be included in a whole TIP. A 

TIP must include regulations designed 

to solve specific air quality problems for 

which the tribe is seeking the EPA’s 

approval, as well as a demonstration 

that the tribal air agency has the 

authority from the tribal government to 

develop and run their program, the 

capability to enforce their rules, and the 

resources to implement the program 

they adopt. In addition, the tribe must 

receive an eligibility determination from 

the EPA to be treated in the same 

manner as a state for the particular 

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305On January 17, 2014, the United States Court 

of Appeals for the District of Columbia Circuit 

issued a decision vacating the EPA’s 2011 rule 

entitled ‘‘Review of New Sources and Modifications 

in Indian Country’’ (76 FR 38748, July 1, 2011) with 

respect to non-reservation areas of Indian country 

(See, Oklahoma Department of Environmental 

Quality v. EPA, 740 F.3d 185 (D.C. Cir. 2014)). 

Under the court’s reasoning, with respect to CAA 

state implementation plans, a state has primary 

regulatory jurisdiction in non-reservation areas of 

Indian country (i.e., Indian allotments located 

outside of reservations and dependent Indian 

communities) within its geographic boundaries 

unless the EPA or a tribe has demonstrated that a 

tribe has jurisdiction over a particular area of nonreservation Indian country within the state. 

matter at issue and to receive 

authorization from the EPA to run a 

CAA program. 

The EPA would review and approve, 

where appropriate, these partial TIPs as 

one step of an overall air quality plan to 

attain the NAAQS. A tribe may step in 

later to add other elements to the plan, 

or the EPA may step in to fill gaps in 

the air quality plan as necessary or 

appropriate. In approving a TIP, the 

agency would evaluate whether the plan 

appropriately coordinates with the 

overall air quality plan for an area when 

tribal lands are part of a multijurisdictional area. 

Because many PM2.5 nonattainment 

areas will include multiple 

jurisdictions, and in some cases both 

Indian country and state lands, it is 

particularly important for the tribes and 

the states to work together to coordinate 

their planning efforts. States need to 

incorporate Indian country emissions in 

their base emissions inventories if 

Indian country is part of an attainment 

or nonattainment area.305 Tribes and 

states should coordinate their planning 

activities as appropriate to ensure that 

neither is adversely affecting attainment 

of the NAAQS in the area as a whole. 

Coordinated planning in these areas will 

help ensure that the planning decisions 

made by the states and tribes 

complement each other and that the 

nonattainment area makes reasonable 

progress toward attainment and 

ultimately attains the applicable PM2.5

NAAQS. In reviewing and approving 

individual TIPs and SIPs, the EPA will 

determine if together they are consistent 

with the overall air quality needs of an 

area. 

To date, very few tribes have 

submitted for the EPA’s approval TIPs 

covering areas over which they have 

jurisdiction. In the absence of a TIP, the 

EPA is authorized under the TAR to 

implement CAA programs in such areas 

as necessary or appropriate. For 

example, an unhealthy air quality 

situation on an Indian reservation may 

require the EPA to develop a FIP to 

reduce emissions from sources on the 

reservation. Likewise, if the agency 

determines that sources in an area under 

tribal jurisdiction could interfere with a 

larger nonattainment area meeting the 

NAAQS by its attainment date, it would 

develop a FIP for those sources in 

consultation with the tribe, as necessary 

or appropriate. 

States have an obligation to notify 

other states in advance of any public 

hearing(s) on their state plans if such 

plans will significantly impact such 

other states. 40 CFR 51.102(d)(5). Under 

section 301(d) of the CAA and the TAR, 

tribes may become eligible to be treated 

in a manner similar to states (TAS) for 

this purpose. Affected tribes with this 

status must also be informed of the 

contents of such state plans and given 

access to the documentation supporting 

these plans. In addition to this 

mandated process, the EPA encourages 

states to extend the same notice to all 

affected tribes, regardless of their TAS 

status. 

Executive Orders and the EPA’s 

Indian policies generally call for the 

EPA to coordinate and consult with 

tribes on matters that affect tribes. 

Executive Order 13175, titled, 

‘‘Consultation and Coordination with 

Indian Tribal Governments’’ requires 

the EPA to develop a process to ensure 

‘‘meaningful and timely input by tribal 

officials in the development of 

regulatory policies that have Tribal 

implications.’’ In addition, the EPA’s 

policies include the agency’s 1984 

Indian Policy relating to Indian tribes 

and implementation of federal 

environmental programs, the April 10, 

2009, Office of Air Quality Planning and 

Standards guidance ‘‘Consulting with 

Indian Tribal Governments,’’ and the 

‘‘EPA Policy on Consultation and 

Coordination With Indian Tribes.’’ 

Consistent with these policies, the EPA 

intends to meet with tribes on activities 

potentially affecting the attainment and 

maintenance of the current and future 

PM2.5 NAAQS in Indian country, 

including agency actions on SIPs. As 

such, it would be helpful for states to 

work with tribes with land that is part 

of the same air quality area during the 

SIP development process and to 

coordinate with tribes as they develop 

their SIPs. 

I. Voluntary Programs for Reducing 

Ambient PM2.5

1. PM Advance Program 

The EPA believes there are significant 

advantages for states, tribes and local 

agencies to take steps to reduce direct 

PM2.5 emissions and emissions of PM2.5

precursors as early as possible. First and 

foremost, early reductions help to 

achieve cleaner air sooner, and help to 

ensure continued health protection. 

Second, early steps could help an area 

avoid a nonattainment designation in 

the first place, or for an area eventually 

designated as nonattainment, early 

reductions could help bring the area 

back into attainment sooner, which may 

lead to qualifying for a CDD and 

subsequent suspension of attainment 

planning requirements as described in 

Section IX.C of this preamble. In 

addition, early action to improve air 

quality can help an eventual 

nonattainment area, particularly an area 

that has never been designated 

nonattainment before, to establish 

working relationships between key 

stakeholders. The EPA’s expectation is 

that early actions to reduce emissions in 

such areas would be less resourceintensive than actions taken once a 

nonattainment designation has been 

made, since at that point the 

implementation of controls would need 

to occur in conjunction with actions to 

comply with other requirements such as 

nonattainment NSR and transportation 

conformity. 

In January 2013, the EPA began a new 

early emissions reduction program for 

attainment areas called ‘‘PM Advance,’’ 

which is much like the related ‘‘Ozone 

Advance’’ program that began in April 

2012. Additional information about the 

PM Advance program for the annual 

and 24-hour PM2.5 NAAQS is provided 

in a separate guidance document that is 

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

ozonepmadvance. 

2. Residential Wood Smoke Programs 

The EPA recognizes that residential 

wood smoke is a concern for many 

nonattainment areas. The EPA estimates 

that wood stoves, hydronic heaters and 

fireplaces emit more than 345,000 tons 

of PM2.5 into the air throughout the 

country each year—mostly during the 

winter months. Residential wood smoke 

can increase fine particle pollution to 

levels that cause significant health 

concerns (e.g., asthma attacks, heart 

attacks, premature death). Wood smoke 

causes many counties throughout the 

U.S. to either exceed the national 

health-based standards for fine particles, 

or places them on the cusp of exceeding 

the standards. Because wood stoves, 

hydronic heaters and other similar 

appliances can be used around the clock 

in residential areas, they can cause 

significant and varying health and 

quality of life issues. 

To reduce fine particle pollution, 

many PM2.5 nonattainment areas will 

need to address residential wood smoke. 

The EPA has developed the ‘‘Strategies 

for Reducing Residential Wood Smoke’’ 

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306On February 3, 2015, the EPA strengthened 

the New Source Performance Standards (NSPS) for 

new residential wood heaters and established NSPS 

for other new wood heaters, including outdoor and 

indoor wood-fired boilers (also known as hydronic 

heaters). The standards will reduce emissions of 

direct PM2.5 as well as carbon monoxide, VOC, air 

toxics (including formaldehyde, benzene and 

polycyclic organic matter), and black carbon. See 

http://www2.epa.gov/residential-wood-heaters/newsource-performance-standards-new-residentialwood-heaters-new. 

307For further guidance on incorporating 

voluntary measures into a SIP, see ‘‘Incorporating 

Emerging and Voluntary Measures in a State 

Implementation Plan (SIP).’’ U.S. EPA. Office of Air 

and Radiation. September 2004. Available at 

http://www.epa.gov/ttn/caaa/t1/memoranda/evm_

ievm_g.pdf. 

308Regulations governing the implementation of 

these programs are located at 40 CFR parts 60, 61, 

63, 64, 70, 71 and 75. 

309 Impact of Improved Monitoring on PM2.5

Emissions, memorandum from L. Barr and K. 

Schaffner, RTI International, to B. Parker, U.S. 

Environmental Protection Agency. December 2003. 

310As discussed in Section IX.E of this preamble, 

emissions monitoring has four essential 

components: (i) indicator(s) of performance; (ii) 

measurement technique(s); (iii) monitoring 

frequency; and, (iv) averaging time. 

document that provides education and 

outreach tools, information on 

regulatory approaches to reduce wood 

smoke, as well as information about 

voluntary programs that communities 

around the country have used.306 In 

addition, it includes methods for 

calculating emissions reductions, 

funding ideas and the basic components 

of a wood smoke reduction plan that 

can be adopted into a SIP as an 

enforceable control measure.307 To 

access the document, go to http://

epa.gov/burnwise/pdfs/strategies.pdf. 

For more information on the EPA’s 

wood smoke reduction program, visit 

http://www.epa.gov/burnwise. 

J. Improved Stationary Source 

Emissions Monitoring 

1. Background 

For purposes of demonstrating 

compliance with the EPA’s air quality 

regulatory requirements, the EPA, air 

agencies, and sources rely on two basic 

types of monitoring: ambient air quality 

monitoring and stationary source 

emissions monitoring. Ambient air 

quality monitoring, as discussed in 

Section II of this preamble, entails 

collecting and measuring samples of 

criteria pollutants in ambient air to 

evaluate air quality as compared to 

clean air standards and historical 

information. Stationary source 

emissions monitoring, on the other 

hand, entails collecting and using 

measurement data (or other information) 

from individual stationary sources to 

demonstrate compliance with emissions 

standards, to assess process or control 

device performance, or to verify work 

practices. While ambient air quality 

monitoring is used to assess compliance 

with the NAAQS, stationary source 

emissions monitoring is used to assess 

compliance with source-specific 

regulations under programs like the 

New Source Performance Standards 

(NSPS), the National Emissions 

Standards for Hazardous Air Pollutants 

(NESHAP), the compliance assurance 

monitoring (CAM) program, the title V 

air operating permits program, and the 

acid deposition control program, as well 

as specific SIP control measures.308

Accurate stationary source emissions 

monitoring is critical for purposes of 

developing accurate emissions 

inventories and in order to identify 

appropriate control measures to reduce 

emissions from stationary sources. In 

addition, after control measures are in 

place, stationary source emissions 

monitoring provides process and control 

device performance information to the 

facility operator so that appropriate 

corrective action can be taken if 

emission levels exceed applicable 

thresholds. Thus, appropriate stationary 

source emissions monitoring 

requirements, like the control measures 

with which they are associated, are a 

fundamental element of an approvable 

attainment plan. 

By way of example, in a limited study 

on improving stationary source 

emissions monitoring, the EPA found 

that revising the measurement 

technique at a stationary source could 

provide information to the facility 

operator to take corrective action that 

could potentially reduce emissions up 

to 15 percent, and that increasing 

monitoring frequency at the facility 

could provide information that could be 

used to inform corrective actions that 

could yield potential stationary source 

emissions reductions of up to 13 

percent.309 310 Implementation of 

stationary source emissions monitoring 

improvements could thus lead to 

actions to achieve additional emissions 

reductions not only at individual 

sources but also in the nonattainment 

areas where these sources are located. 

2. Guidance To Help Improve Stationary 

Source Emissions Monitoring 

Because of the important role that 

effective stationary source emissions 

monitoring can play in informing the 

development of attainment strategies for 

PM2.5 NAAQS nonattainment areas, the 

EPA is interested in applied best 

practices for stationary source emissions 

monitoring that could be included in 

guidance for other stationary sources 

and air agencies. The EPA seeks to 

gather information about ways to make 

the source emissions monitoring data 

collection process easier and more 

transparent. The EPA therefore seeks 

appropriate examples and supporting 

data from individual sources and air 

agencies with experience in this area to 

inform such future guidance. The EPA 

also seeks comment on the specific 

topics and questions that follow, which 

the agency may address in future 

guidance related to improved source 

monitoring. Specifically: 

(1) Based on your experience, in 

which cases do you believe improved 

monitoring techniques are more 

appropriate than visual emissions (VE) 

techniques for monitoring compliance 

with PM2.5 (or PM, in general) emissions 

limits? Please identify monitoring 

techniques that you would recommend 

in lieu of VE, and describe the instances 

in which VE remains appropriate. 

(2) Based on your experience, are bag 

leak detection systems, PM continuous 

parameter monitoring systems (CPMS), 

or PM continuous emissions monitoring 

systems (CEMS) reliable, cost-effective 

methods for monitoring compliance 

with PM emissions? Please provide 

additional information on reliability and 

cost to support your position. 

(3) Will increasing the frequency of 

VE observations resolve the issue of 

applicability of VE techniques for 

monitoring compliance with PM2.5

emissions? In other words, are there 

situations in which increased VE 

frequency (i.e., daily versus weekly) 

would be expected to have no impact on 

compliance with PM2.5 emission limits? 

If so, please provide relevant data and 

explanation of such situations. 

(4) Should the EPA consider 

mandating through rulemaking the use 

of alternatives to VE techniques for 

monitoring compliance with PM2.5 and 

PM emissions limits in certain 

situations and applications? If so, in 

what cases? 

(5) Should the EPA’s effort with 

regard to the use of improved 

monitoring techniques in lieu of VE 

monitoring be focused on applicable 

requirements established/relied upon 

for compliance with the PM2.5 NAAQS, 

or should the agency more broadly 

address other applicable requirements 

where VE techniques are commonly 

used (e.g., to estimate TSP and PM10

emissions)? 

(6) Should the EPA consider 

mandating through rulemaking the use 

of alternatives to continuous opacity 

monitoring systems (COMS) for 

monitoring compliance with PM2.5 and 

PM emissions limits in certain 

situations and applications? If so, in 

what cases? 

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311 Ibid. 

312 72 FR 20586 (April 25, 2007). 

313 75 FR 80118 (December 21, 2010). 

(7) In its study published in 2003, the 

EPA identified stationary source 

emission reduction techniques that air 

agencies should consider when 

developing their potential list of control 

measures for a PM2.5 NAAQS 

nonattainment area.311 Specifically, the 

EPA identified improved measurement 

techniques and increased monitoring 

frequency as practices that could better 

inform sources and air agencies of 

excess emissions from individual 

sources which, if responded to more 

quickly, could yield significant 

reductions and assist in bringing the 

area into attainment for the NAAQS. 

Please comment on whether these 

techniques remain appropriate, given 

that they were based on the best 

technical information available at the 

time. Are there ways to improve the 

methodologies described in the study? 

(8) Please submit any examples of 

improved stationary source emissions 

monitoring, including a description of 

the measure, monitoring data, etc. 

(9) Please submit any other 

methodologies—complete with 

equations and explanations—for 

estimating emissions reductions due to 

improved monitoring. 

The EPA will continue to explore and 

implement innovative, cost-effective 

ideas that offer tangible incentives for 

improved source monitoring to be 

adopted as part of the associated 

emissions limitations that will help 

achieve additional reductions from 

stationary sources and bring areas into 

attainment for the PM2.5 NAAQS in a 

timely way. 

K. Stationary Source Test Methods for 

Emissions of Condensable PM2.5

1. Background 

As discussed in Section II of this 

preamble, direct PM2.5 comprises of two 

components: Filterable PM2.5 and 

condensable PM2.5 emissions. Accurate 

test methods for quantifying filterable 

PM emissions have been available for 

air agencies and states to apply since the 

early 1970s. In addition, controls have 

improved over the past 40 years and 

most sources now achieve substantially 

lower emissions than required by state 

and federal emissions limits. With the 

filterable portion of PM2.5 emissions 

being relatively well controlled, the 

condensable portion of PM2.5 emissions 

now represents a larger share of overall 

PM2.5 emissions for several categories of 

stationary sources. However, accurate 

test methods for condensable PM2.5

emissions have only been recently 

developed and approved by the EPA. 

Thus, many states may have stationary 

source emission limits adopted into 

their existing SIPs based only on 

filterable PM2.5 emissions or based on 

outdated methods for measuring or 

estimating condensable PM2.5

emissions. 

The following discussion focuses on 

current test methods for quantifying 

condensable PM2.5 emissions and the 

EPA’s proposed requirements for states 

developing control strategies for PM2.5

nonattainment areas. 

2. Test Methods for Condensable PM 

From Stationary Sources 

Since January 1, 2011, the EPA has 

required that states take into 

consideration condensable PM2.5

emissions when establishing emission 

limits for stationary sources as part of 

any control strategy for PM2.5 NAAQS 

nonattainment areas.312 This date 

coincided with the effective date of the 

agency’s revisions to test methods for 

measuring filterable PM10 emissions 

from stationary sources (Method 201A) 

and for measuring condensable PM 

emissions from stationary sources 

(Method 202).313 The revisions 

increased the precision of Method 202 

and improved the consistency in the 

measurements obtained between source 

tests performed under different 

regulatory authorities. 

In the preamble to the 2007 PM2.5

Implementation Rule, the EPA 

explained that the use of the (then 

anticipated) revisions to the EPA 

Method 201A combined with Method 

202 to obtain measured source specific 

emissions of PM2.5 would improve the 

quality of emissions inventories for 

stationary sources and would aid in the 

development of a more reliable 

attainment strategy, as sources that may 

have a considerable amount of 

condensable PM2.5 emissions could be 

better characterized with the new 

methods. The EPA continues to believe 

that using these improved test methods 

can help identify sources of direct PM2.5

emissions which, if better controlled, 

can help to bring a PM2.5 nonattainment 

area into attainment. Likewise, use of 

these test methods may help a state 

identify sources whose condensable 

emissions may have been incorrectly 

estimated and therefore may not provide 

meaningful PM2.5 control opportunities. 

3. Proposed SIP Requirements for Test 

Methods For Condensable PM2.5

Emissions 

The EPA proposes to require that, 

where a state needs to adopt control 

measures for direct PM2.5 from sources 

in a nonattainment area, the state must 

specify PM2.5 emission limits in its SIP 

that include both filterable and 

condensable emissions. In addition, 

compliance testing of those sources 

must include measurement of 

condensable emissions (such as through 

the use of Method 202). Under this 

proposal, any new or revised emission 

limit used as a control measure to bring 

an area into attainment for any current 

or future PM2.5 NAAQS must use 

methods that measure PM2.5 or total PM 

including both filterable and 

condensable particulate matter. Existing 

emission limitations that are not being 

revised as part of a Moderate area or 

Serious area attainment plan can remain 

as filterable PM or whatever test method 

is used by the state for compliance 

determination. In these cases, the 

acceptability of existing stationary 

source test methods for PM2.5 attainment 

plans will depend upon what is 

required under the state’s current test 

methods for PM emissions. The EPA 

believes that this proposed requirement 

is appropriate because the addition of 

the condensable portion of PM2.5 to 

filterable PM2.5 may increase direct 

PM2.5 emissions by a factor of five or 

more, and the use of test methods that 

only measure filterable emissions 

potentially limit the control measures 

available for developing cost effective 

strategies to achieve attainment of the 

PM2.5 NAAQS. 

The EPA seeks comment on this 

proposed requirement for states to 

quantify condensable PM2.5 emissions in 

their attainment plans for PM2.5

nonattainment areas. 

X. What is the EPA proposing with 

respect to revoking the 1997 primary 

annual PM2.5 NAAQS? 

A. Background 

If the 1997 primary annual PM2.5

NAAQS were to remain in place after 

conformity requirements begin to apply 

for the 2012 primary annual PM2.5

NAAQS (1 year after the effective date 

of designations), a number of federal 

agencies, metropolitan planning 

organizations (MPOs) and other state, 

local, and federal transportation and air 

quality agencies in areas that are 

currently designated nonattainment or 

maintenance for the 1997 annual PM2.5

NAAQS and will be designated 

nonattainment for the 2012 primary 

annual NAAQS would be required to 

implement conformity requirements for 

both annual PM2.5 NAAQS 

concurrently. Additionally, some areas 

would also be implementing conformity 

requirements for the 2006 24-hour PM2.5

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314 78 FR 3086 (January 15, 2013). 

315Nonattainment areas that were redesignated to 

attainment with an approved section 175A 

maintenance plan are referred to throughout this 

document as ‘‘maintenance areas.’’ 

316Unimplemented requirements in the SIP or 

those shown to be unnecessary for maintenance can 

be shifted to the contingency measures portion of 

the SIP upon redesignation. See ‘‘Procedures for 

Processing Requests to Redesignate Areas to 

Attainment,’’ Memorandum from John Calcagni, 

Director, Air Quality Management Division, 

September 4, 1992; ‘‘State Implementation Plan 

(SIP) Requirements for Areas Submitting Requests 

for Redesignation to Attainment of the Ozone and 

Carbon Monoxide (CO) National Ambient Air 

Quality Standards (NAAQS) On or After November 

15, 1992,’’ Memorandum from Michael H. Shapiro, 

Acting Assistant Administrator for Air and 

Radiation, September 17, 1993. As discussed 

elsewhere in this document, an exception is made 

for NNSR, which can be removed from the SIP 

completely and need not be retained as a 

contingency measure after redesignation to 

attainment. 

317See the Federal Register published on January 

15, 2013 (78 FR 3085, 3124, 3125, 3126, 3137 and 

3229). 

318South Coast Air Quality Management District 

v. EPA, 472 F.3d 882 (D.C. Cir. 2006). 

319South Coast Air Quality Management District 

v. EPA, 472 F.3d 882 (D.C. Cir. 2006). 

320For a more complete discussion of the 

requirements for the transition from the 1-hour 

ozone NAAQS to the 1997 ozone NAAQS, see the 

Federal Register dated April 30, 2004 (69 FR 23951, 

23969, 23970, 23971, 23972, 23973, 23974, 23975, 

23976, 23977, 23978, 23979, 23980, 23981, 23982, 

23983, 23984, 23985, 23986, 23987, 23988 and 

23989). 

NAAQS, and two areas remain subject 

to conformity requirements for the 1997 

24-hour PM2.5 NAAQS. This could lead 

to unnecessary complexity for 

transportation conformity 

determinations, especially if an area’s 

boundaries for the various PM2.5

NAAQS differ from one another and the 

same test of conformity cannot be used 

for all of the PM2.5 NAAQS. Even where 

an area’s boundaries are unchanged, 

different analysis years under the 

conformity rules may be required for 

each PM2.5 NAAQS. It could also lead to 

general conformity determinations being 

made in areas that are attainment for the 

2012 primary annual PM2.5 NAAQS. 

Finally, state and local air quality 

agencies would be required to continue 

attainment planning activities for the 

1997 primary annual PM2.5 NAAQS 

even if they had air quality data that 

resulted in their being designated 

attainment for the 2012 primary annual 

PM2.5 NAAQS. 

The EPA believes that it is more 

important and consistent with CAA 

requirements to determine conformity 

for the new 2012 primary annual PM2.5

NAAQS, which is more stringent and 

thus more protective of health than the 

1997 PM2.5 NAAQS. This section 

therefore describes the EPA’s proposed 

approaches for transitioning from the 

1997 primary annual PM2.5 NAAQS to 

the 2012 primary annual PM2.5 NAAQS. 

This section discusses a number of 

options for revoking the 1997 primary 

annual PM2.5 NAAQS and addresses 

anti-backsliding requirements that 

would apply, as appropriate, under each 

of the revocation options. The EPA is 

not proposing to revoke the 1997 

secondary annual PM2.5 NAAQS in this 

action because that NAAQS has been 

retained in order to prevent certain 

welfare effects associated with PM2.5.314

The proposed options are framed in 

the context of the CAA requirements 

that apply to NAAQS transitions to 

ensure that states and nonattainment 

areas continue to make progress and do 

not reverse progress, or backslide, from 

improvements already made in air 

quality. The CAA contains several 

provisions indicating congressional 

intent not to allow a state to alter or 

remove provisions from an approved 

attainment plan if the revision would 

reduce air quality protection. Section 

193 of the CAA prohibits modification 

of a control requirement in effect or 

required to be adopted as of November 

15, 1990 (the date of enactment of the 

1990 CAA Amendments), unless such a 

modification would ensure equivalent 

or greater emissions reductions. Section 

172(e), which addresses relaxations of a 

NAAQS, requires protections for areas 

that have not attained a NAAQS prior to 

a relaxation by requiring controls which 

are at least as stringent as the controls 

applicable in nonattainment areas prior 

to any such relaxation. Section 110(l) 

provides that a SIP revision cannot be 

approved if it will interfere with 

attainment or other CAA requirements. 

Under section 175A(d), an area that is 

redesignated to attainment may, with an 

appropriate showing of no interference, 

cease to implement a measure that is 

contained in the SIP at the time of 

redesignation, but only if that measure 

is retained as a contingency measure in 

the area’s maintenance plan.315 316

The transition from the 1997 to the 

2012 primary annual PM2.5 NAAQS is a 

straightforward tightening of the level 

with little change in the form of the 

standard, so it is unambiguous that the 

2012 primary annual PM2.5 NAAQS is 

more stringent than the 1997 primary 

annual PM2.5 NAAQS. In the final 2012 

PM NAAQS rule the EPA eliminated the 

provisions that allowed for an area to 

use spatial averaging of monitoring data 

to determine whether or not it is 

attaining the 1997, 2012 and any future 

annual PM2.5 NAAQS.317 Eliminating 

spatial averaging provides additional 

protection for populations that may be 

at a greater risk to exposures of elevated 

levels of PM2.5. In these circumstances 

where the annual PM2.5 NAAQS has 

clearly been strengthened, section 

172(e) on its face does not apply. The 

EPA’s interpretation that antibacksliding provisions consistent with 

the purposes of section 172(e) by 

analogy should apply as upheld by the 

court in South Coast as appropriate in 

the absence of statutory provisions 

addressing tightened air quality 

standards. In proposing anti-backsliding 

requirements that would apply as 

appropriate to the options that are being 

considered, the EPA seeks to apply the 

principles of section 172(e).318

B. History of Revocation of Other 

NAAQS 

The EPA has either adopted or has 

proposed to adopt transition policies for 

other NAAQS, including the policies for 

the transitions from: 

• The 1-hour ozone NAAQS to the 

1997 ozone NAAQS; 

• The 1997 ozone NAAQS to the 2008 

ozone NAAQS; 

• The prior lead NAAQS to the 2008 

lead NAAQS; and, 

• The prior sulfur dioxide (SO2) 

NAAQS to the 2010 SO2 NAAQS. 

It is important to note that for all 

previous NAAQS transitions, the EPA 

has used revocation to reduce the 

burden associated with implementing a 

NAAQS that has been replaced with a 

more stringent NAAQS. 

In its Phase 1 Rule for the transition 

from the 1-hour ozone NAAQS to the 

1997 ozone NAAQS, the EPA stated that 

the 1-hour ozone NAAQS would be 

revoked (i.e., no longer apply) 1 year 

after the effective date of initial area 

designations for the 1997 ozone 

NAAQS. The EPA also included antibacksliding requirements in the Phase 1 

Rule to address the transition between 

the two standards. 

The Phase 1 Rule for implementation 

of the 1997 ozone NAAQS was the 

subject of legal challenges, and the 

resulting court decision in South Coast 

upheld the EPA’s authority to revoke 

the 1-hour ozone NAAQS as long as 

adequate anti-backsliding measures 

were retained to prevent backsliding.319

The decision directed the EPA to 

provide additional 1-hour ozone 

NAAQS anti-backsliding requirements 

for NNSR, section 185 fees, and section 

172(c)(9) and 182(c)(9) contingency 

measures for failure to attain the 1-hour 

ozone NAAQS by the applicable 

attainment date or to make reasonable 

further progress toward attainment of 

that standard, in addition to the antibacksliding measures contained in the 

Phase 1 rule.320

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321See the published proposal at 78 FR 34178 

(June 6, 2013) and the final SIP requirements rule 

for the 2008 ozone NAAQS at http://www.epa.gov/ 

groundlevelozone/implement.html. 

322 Ibid. 

323 77 FR 30160 (May 21, 2012). 

324See South Coast Air Quality Management 

District v. EPA, 472 F.3d 882 (D.C. Cir. 2006). 

325 40 CFR 93.101 defines ‘‘motor vehicle 

emissions budget’’ as ‘‘that portion of the total 

allowable emissions defined in the submitted or 

approved control strategy implementation plan 

revision or maintenance plan for a certain date for 

the purpose of meeting reasonable further progress 

milestones or demonstrating attainment or 

maintenance of the NAAQS, for any criteria 

pollutant or its precursors, allocated to highway 

and transit vehicle use and emissions.’’ 

326 In addition, the Court affirmed that conformity 

determinations need not be made for a revoked 

standard. 327NRDC v. EPA, No. 12–1321 (D.C. Cir.) 

(challenging EPA actions taken at 77 FR 30160 (May 

21, 2012)). 328For details on the requirements for the lead 

NAAQS and the SO2 NAAQS, respectively, see 73 

FR 66964 (November 12, 2008), at page 67043; and 

75 FR 35519 (June 22, 2010), at page 35580. 

As part of its final SIP requirements 

rule for the 2008 ozone NAAQS, the 

EPA included requirements for the 

transition from the 1997 ozone NAAQS 

to the 2008 ozone NAAQS.321 In 

developing that rulemaking, the EPA 

built upon its experience in 

implementing the Phase 1 rule for the 

transition from the 1-hour ozone 

NAAQS to the 1997 ozone NAAQS and 

the decision in the South Coast 

litigation. The EPA revoked the 1997 

ozone NAAQS on the effective date of 

the final SIP requirements rule and 

finalized anti-backsliding requirements 

consistent with the implementation of 

the court decision for the previous 

ozone transition that would apply in 

areas designated nonattainment for the 

1997 ozone NAAQS at the time of 

revocation.322

It should be noted that as part of the 

transition from the 1997 ozone NAAQS 

to the 2008 ozone NAAQS, the EPA 

revoked the 1997 ozone NAAQS for 

transportation conformity purposes only 

in a separate action related to 

classifications for the 2008 ozone 

NAAQS that was finalized prior to the 

time that the full implementation rule 

had been proposed.323 The EPA took 

this action because the D.C. Circuit 

Court in litigation on the transportation 

conformity rule and in its decision in 

the South Coast litigation affirmed that 

the use of motor vehicle emissions 

budgets that have been approved or 

found adequate for use in transportation 

conformity determinations for the prior 

NAAQS must be used in transportation 

conformity determinations for the new 

NAAQS until a state submits motor 

vehicle emissions budgets for the new 

NAAQS and those budgets are either 

found adequate or are approved.324 325

These cases seemed to indicate that the 

use of these existing budgets until new 

budgets are available is the appropriate 

anti-backsliding measure with respect to 

transportation conformity to support 

revocation for that purpose.326 It should 

be noted, however, that the revocation 

of the 1997 ozone NAAQS for 

transportation conformity purposes was 

the subject of litigation in the D.C. 

Circuit Court.327 The court issued its 

decision on December 23, 2014, and 

held that the EPA lacked authority to 

revoke the 1997 ozone NAAQS only for 

transportation conformity purposes 

because for areas that remain designated 

as nonattainment or maintenance for the 

1997 ozone NAAQS, CAA section 176(c) 

requires transportation conformity 

determinations in nonattainment and 

maintenance areas. 

Following promulgation of the 2008 

lead NAAQS and 2010 SO2 NAAQS, the 

EPA revoked the prior lead and SO2

NAAQS for all purposes in areas that 

had attained the prior NAAQS and had 

been redesignated to attainment, as well 

as in areas that had initially been 

designated as attainment for those 

NAAQS. The EPA retained the prior 

NAAQS in areas that had not yet 

attained those NAAQS until those areas 

had an approved attainment plan for the 

revised NAAQS. Because the EPA 

revoked the prior lead and SO2 NAAQS 

in areas that had been redesignated to 

attainment for those NAAQS, the EPA 

primarily relied on the CAA’s antibacksliding provisions found in sections 

110(l) and 193 in order to provide antibacksliding protection.328

In developing the options for revoking 

the 1997 primary annual PM2.5 NAAQS 

contained in this proposal, the EPA has 

drawn from these prior anti-backsliding 

approaches. 

C. Proposed Options for Revocation and 

Related Anti-Backsliding Requirements 

for the 1997 Primary Annual PM2.5

NAAQS 

The EPA is proposing and seeking 

comment on two options for revoking 

the 1997 primary annual PM2.5 NAAQS 

and is seeking comment on whether to 

revoke the NAAQS at the current time. 

Under either of the options to revoke the 

1997 NAAQS, revocation would take 

effect no sooner than 1 year after the 

effective date of designations for the 

2012 primary annual PM2.5 NAAQS. 

One of these options would provide for 

revocation at a later date for some areas. 

After revocation of the 1997 primary 

annual PM2.5 NAAQS, the designations 

(and the classifications associated with 

those designations) for that standard 

would no longer be in effect, and the 

designations that would remain in effect 

would be those for the 1997 secondary 

annual PM2.5 NAAQS, the 2006 primary 

and secondary 24-hour PM2.5 NAAQS 

and the 2012 primary annual PM2.5

NAAQS. However, the EPA would 

retain the listing of the designated 

nonattainment areas for the revoked 

1997 primary annual PM2.5 NAAQS in 

40 CFR part 81, for the sole purpose of 

identifying the anti-backsliding 

requirements that may apply to the 

areas at the time of revocation. 

Accordingly, such references to 

historical designations for the revoked 

standard should not be viewed as 

current designations under CAA section 

107(d). 

For any proposed option that allows 

for revocation in nonattainment areas 

for the 1997 primary annual PM2.5

NAAQS, the EPA is also proposing antibacksliding provisions to ensure that in 

these areas: (i) There is protection 

against degradation of air quality (e.g., 

the areas do not backslide in terms of air 

quality improvements); (ii) the areas 

continue to make progress toward 

attainment of the new, more stringent 

2012 primary annual PM2.5 NAAQS; 

and, (iii) there is consistency with the 

PM2.5 NAAQS implementation 

framework outlined in subpart 4 of part 

D, title I of the CAA. At the current time, 

there are 14 areas that continue to be 

designated as nonattainment for the 

1997 annual PM2.5 NAAQS; however all 

but 2 of these areas have 2011–2013 air 

quality data showing that they are 

attaining that NAAQS. Therefore, the 

EPA expects many of these current 

nonattainment areas will be eligible to 

seek redesignation to attainment prior to 

any revocation. The EPA is proposing 

and seeking comment on the following 

two options: 

• Option 1: Revoke the 1997 primary 

annual PM2.5 NAAQS for all purposes in 

attainment areas for that NAAQS 1 year 

after the effective date of the 

designations for the 2012 primary 

annual PM2.5 NAAQS; or, 

• Option 2: Revoke the 1997 primary 

annual PM2.5 NAAQS for all purposes in 

all nonattainment and attainment areas 

for that NAAQS 1 year after the effective 

date of the designations for the 2012 

primary annual PM2.5 NAAQS. 

More details on the proposed options 

and associated rationale are included 

below. 

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329Areas that do not have adequate or approved 

motor vehicle emissions budgets for the 1997 

annual PM2.5 NAAQS or the 2006 24-hour PM2.5

NAAQS would use one of the two interim 

emissions tests required by 40 CFR 93.109(c)(3) and 

40 CFR 93.119(b). 

330Although section 51.905(a) specified that the 

anti-backsliding requirements ‘‘attached’’ at the 

time of designation for the 1997 ozone NAAQS, 

areas were still able to redesignate to attainment for 

the 1-hour ozone NAAQS up to the date of 

revocation of that standard. 

1. Option 1: Revoke the 1997 Primary 

Annual PM2.5 NAAQS for All Purposes 

in Attainment Areas for That NAAQS 1 

Year After the Effective Date of the 

Designations for the 2012 Primary 

Annual PM2.5 NAAQS 

The EPA’s first proposed option 

would revoke the 1997 primary annual 

PM2.5 NAAQS for all purposes in areas 

that are designated as attainment for 

that NAAQS 1 year after the effective 

date of designations for the 2012 

primary annual PM2.5 NAAQS, as well 

as in future areas that are redesignated 

as attainment areas after the initial 

revocation. The areas addressed by this 

option are those that were originally 

designated as attainment areas for the 

1997 primary PM2.5 NAAQS and those 

that were originally designated as 

nonattainment but have since or will in 

the future be redesignated to attainment 

for that NAAQS. Under this option, the 

EPA would not revoke the 1997 primary 

annual PM2.5 NAAQS in any area that is 

designated nonattainment for that 

NAAQS. 

Areas that are designated 

nonattainment for the 1997 annual 

PM2.5 NAAQS at the time of the initial 

revocation would be required to 

continue to meet all applicable 

requirements for such NAAQS, and 

could continue to seek redesignation to 

attainment for the 1997 primary annual 

PM2.5 NAAQS. For example, even if the 

revocation were to become effective in 

April 2016, redesignations could 

continue to be approved after that date. 

For such areas, the effective date of the 

revocation would be the effective date of 

the area’s redesignation to attainment 

for the 1997 annual PM2.5 NAAQS. 

The EPA notes that under proposed 

Option 1 it is unnecessary to propose 

anti-backsliding requirements for the 

1997 primary annual PM2.5 NAAQS, 

since Option 1 would only revoke this 

NAAQS in attainment areas. Antibacksliding requirements are not 

applicable to attainment areas (i.e., for 

former nonattainment areas that have 

been redesignated to attainment the EPA 

has already determined through the 

redesignation process and approval of 

maintenance plans that all applicable 

requirements for the 1997 primary 

annual PM2.5 NAAQS—including antibacksliding requirements—have been 

fulfilled and areas that have always 

been designated attainment for this 

NAAQS). 

For areas that were initially 

designated as attainment for both the 

1997 and 2012 annual PM2.5 NAAQS the 

EPA is proposing that the approved PSD 

SIPs for these areas satisfy the obligation 

to submit an approvable maintenance 

plan for the 2012 primary annual PM2.5

NAAQS under section 110(a)(1). 

The EPA also notes that areas 

designated nonattainment for the 2012 

primary annual PM2.5 NAAQS would be 

required to comply with applicable 

conformity requirements beginning 1 

year after the effective date of 

designations for that NAAQS. For 

transportation conformity purposes 

these requirements would include using 

adequate or approved motor vehicle 

emissions budgets for the 1997 annual 

PM2.5 NAAQS where they exist until the 

area has approved or adequate budgets 

for the 2012 primary annual PM2.5

NAAQS.329 The use of such budgets 

serves as the appropriate antibacksliding measure for transportation 

conformity purposes. 

In general, Option 1 builds upon the 

EPA’s practice in the transition from the 

1-hour to the 1997 ozone NAAQS in 

that areas will not only be able to be 

redesignated to attainment up to the 

date of the initial revocation, but any 

remaining nonattainment areas will be 

able to be redesignated after the initial 

revocations occur 1 year after the 

effective date of designations.330 This 

approach is also consistent with the 

approach established for the transition 

from the prior lead and SO2 NAAQS to 

the current lead and SO2 NAAQS. 

2. Option 2: Revoke the 1997 Primary 

Annual PM2.5 NAAQS for All Purposes 

in All Nonattainment and Attainment 

Areas for That NAAQS 1 Year After the 

Effective Date of Designations for the 

2012 Primary Annual PM2.5 NAAQS 

Under this second proposed option, 

the EPA would revoke the 1997 primary 

annual PM2.5 NAAQS for all purposes in 

all nonattainment and attainment areas 

1 year after the effective date of 

designations for the 2012 primary 

annual PM2.5 NAAQS. The requirements 

for revoking the 1997 primary annual 

NAAQS in attainment areas for that 

NAAQS are discussed under proposed 

Option 1. However, revoking the 1997 

primary annual PM2.5 NAAQS in 

nonattainment areas for that NAAQS 

would require anti-backsliding 

measures. Therefore, the EPA is 

proposing the following anti-backsliding 

measures for any designated 

nonattainment areas that exist for the 

1997 primary annual PM2.5 NAAQS 

upon the effective date of the proposed 

revocation: 

• For areas designated attainment for 

the 2012 primary annual PM2.5 NAAQS 

and nonattainment for the 1997 primary 

annual PM2.5 NAAQS, the EPA’s 

preferred proposed option is not to 

require these areas to adopt any 

outstanding applicable requirements for 

the revoked 1997 primary annual PM2.5

standard. However, the EPA proposes 

that the approved PSD SIPs for these 

areas satisfy the obligation to submit an 

approvable maintenance plan for the 

2012 primary annual PM2.5 NAAQS 

under section 110(a)(1). 

• For these same areas (i.e., those 

designated attainment for the 2012 

primary annual PM2.5 NAAQS and 

nonattainment for the 1997 primary 

annual PM2.5 NAAQS), the EPA is also 

proposing an alternative antibacksliding option where these areas 

would be required to show maintenance 

for the 2012 primary annual PM2.5

NAAQS. This maintenance showing 

would be due 3 years after the effective 

date of designations for the 2012 

primary annual PM2.5 NAAQS. The 

maintenance showing would contain a 

demonstration of continued 

maintenance of the 2012 primary annual 

PM2.5 NAAQS in the area for 10 years 

from the effective date of the area’s 

designation as attainment for the 2012 

primary annual PM2.5 NAAQS. The EPA 

would take further action to specify the 

elements of such a maintenance 

showing should the agency require it in 

the final rule. For areas designated 

nonattainment for the 2012 primary 

annual PM2.5 NAAQS and also 

designated nonattainment for the 1997 

annual PM2.5 NAAQS, the EPA is 

proposing that these areas continue to 

implement their approved SIPs for the 

1997 annual PM2.5 NAAQS and fulfill 

any outstanding requirements, and that 

they comply with the applicable 

requirements for the current 2012 

primary annual PM2.5 NAAQS. For 

example, at some time in the future 

there may be an area that is reclassified 

as Serious for the 1997 PM2.5 NAAQS 

while also classified as Moderate for the 

2012 PM2.5 NAAQS. In such an area, the 

lower Serious area major source 

threshold of 70 tpy (PTE) would apply. 

In addition to these proposed 

requirements, if a state seeks to revise 

any measure already approved into its 

SIP for a nonattainment area for the 

1997 annual PM2.5 NAAQS, the state 

must meet the requirements of sections 

110(l) and 193, if applicable. 

The EPA notes that Option 2 for 2012 

attainment/1997 nonattainment would 

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331See the final SIP requirements rule for the 

2008 ozone NAAQS at http://www.epa.gov/

groundlevelozone/implement. 

332Areas that do not have adequate or approved 

motor vehicle emissions budgets for the 1997 

annual PM2.5 NAAQS or the 2006 24-hour PM2.5

NAAQS would use one of the two interim 

emissions tests required by 40 CFR 93.109(c)(3) and 

40 CFR 93.119(b). 

333As discussed in Section IX.B of this preamble, 

the EPA has taken action to revoke previous ozone, 

SO2 and lead NAAQS when the previous NAAQS 

has been revised. 

334Based on 2011–13 air quality data, many of the 

areas that were initially designated nonattainment 

for the 1997 annual PM2.5 NAAQS will have already 

met the 1997 annual PM2.5 NAAQS and will have 

been redesignated to attainment by the time it is 

revoked (projected to be in or around April 2016), 

and thus after revocation of the 1997 primary 

annual PM2.5 NAAQS, the number of areas with 

1997 anti-backsliding requirements will be 

correspondingly reduced. 

be similar to the approach to revocation 

of the 1-hour ozone NAAQS consistent 

with court decisions and the approach 

to revocation of the 1997 ozone NAAQS 

in the final 2008 ozone NAAQS SIP 

requirements rule.331 The EPA also 

notes that areas designated 

nonattainment for the 2012 primary 

annual PM2.5 NAAQS would be required 

to comply with applicable conformity 

requirements beginning 1 year after the 

effective date of designations for that 

NAAQS. For transportation conformity 

purposes these requirements would 

include using adequate or approved 

motor vehicle emissions budgets for the 

1997 annual PM2.5 NAAQS where they 

exist until the area has approved or 

adequate budgets for the 2012 primary 

annual PM2.5 NAAQS.332 The use of 

such budgets serves as the appropriate 

anti-backsliding measure for 

transportation conformity purposes. 

Further details regarding this option and 

associated rationale are in Section X.D 

of this preamble. 

Lastly, the EPA requests comment on 

the possible approach of not revoking 

the 1997 primary annual PM2.5 NAAQS 

at this time. Under this concept, the 

EPA would not revoke the 1997 primary 

annual PM2.5 NAAQS for any purpose at 

this time. As a result, all nonattainment 

and maintenance areas would be 

required to continue planning activities 

associated with the 1997 annual PM2.5

NAAQS such as submitting attainment 

SIPs and maintenance plans, NNSR, and 

transportation and general conformity 

requirements for the 1997 primary 

annual PM2.5 NAAQS, in addition to 

any new requirements associated with 

the more health-protective 2012 primary 

annual PM2.5 NAAQS. Under this 

approach the EPA would not have to 

establish any anti-backsliding 

requirements. 

The EPA again notes that if this 

approach were finalized it would be the 

first time that the EPA has not taken 

some action to reduce the burden 

associated with implementing a NAAQS 

that has been replaced with a more 

stringent NAAQS.333 If the EPA were to 

finalize this approach, it would result in 

state and local agencies being required 

to implement the requirements 

associated with two primary annual 

PM2.5 NAAQS. These agencies would be 

required to continue attainment 

planning activities for the 1997 primary 

annual PM2.5 NAAQS even if they had 

air quality data that resulted in their 

being designated attainment for the 

2012 primary annual PM2.5 NAAQS. 

State, local and federal agencies would 

be required to continue to make 

transportation and general conformity 

determinations for the less protective 

1997 primary annual PM2.5 NAAQS. 

D. Discussion of Options 

Until the 1997 primary annual PM2.5

NAAQS is revoked, that NAAQS 

remains in effect, in parallel with the 

2012 primary annual PM2.5 NAAQS, and 

continues to apply independently and 

by its own terms. The EPA believes that 

all of the proposed options to revoke the 

1997 primary annual PM2.5 NAAQS are 

consistent with the CAA and previous 

precedent in transitioning from a 

previous NAAQS to a new, more 

stringent NAAQS, and would ensure 

that attainment areas continue to attain 

the revoked NAAQS into the future. If 

the 1997 primary annual PM2.5 NAAQS 

is revoked, the EPA is proposing that 

the anti-backsliding requirements for 

the 1997 primary annual PM2.5 NAAQS, 

as proposed in this rulemaking, will 

become applicable. However, the EPA 

notes that most of the areas that were 

initially designated as nonattainment for 

the 1997 primary annual PM2.5 NAAQS 

where the NAAQS would be revoked 

have already been redesignated to 

attainment (i.e., they are maintenance 

areas) or could qualify for redesignation 

based on current air quality data, and in 

such cases their approved maintenance 

plan for the 1997 primary annual PM2.5

would prevent backsliding.334 Under 

Option 2 there would be a limited 

number of nonattainment areas where 

the 1997 primary annual NAAQS would 

be revoked and where anti-backsliding 

measures would be required. Under all 

of the proposed options, conformity 

would apply in areas that are designated 

nonattainment for the more health 

protective 2012 primary annual PM2.5

NAAQS. In the case of transportation 

conformity, adequate or approved motor 

vehicle emissions budgets for the 1997 

primary annual PM2.5 NAAQS would be 

used in conformity determinations until 

motor vehicle emissions budgets for the 

2012 primary annual PM2.5 NAAQS are 

found adequate or are approved. Once a 

NAAQS is revoked in a nonattainment 

area, the EPA would not designate or 

redesignate areas for that NAAQS after 

the revocation of that NAAQS except as 

described in Option 1. The extent of 

continued implementation of a revoked 

standard derives from administration of 

anti-backsliding requirements for that 

standard. 

Under Option 1, the 1997 primary 

annual PM2.5 NAAQS would be revoked 

only in areas that have attained the 1997 

annual PM2.5 NAAQS and have been 

redesignated to attainment with an 

approved section 175A maintenance 

plan for the 1997 primary annual PM2.5

NAAQS; under Option 2, many of the 

areas where the 1997 primary annual 

NAAQS would be revoked would have 

been redesignated to attainment with an 

approved maintenance plan. The EPA 

also anticipates that states will continue 

to request that areas be redesignated to 

attainment and the EPA will continue to 

act on those requests under Option 2. As 

a result the EPA anticipates that a 

number of such requests will be 

approved prior to the point in time that 

the EPA has proposed for the 

revocations to become effective (i.e., 1 

year after the effective date of 

designations for the 2012 primary 

annual PM2.5 NAAQS). Therefore, the 

number of nonattainment areas for the 

1997 primary annual PM2.5 NAAQS will 

continue to decrease and fewer areas 

will be required to comply with antibacksliding requirements, and a 

correspondingly larger number of areas 

will be required to continue to 

implement their approved section 175A 

maintenance plan for the 1997 primary 

annual PM2.5 NAAQS. 

It should also be noted that, for either 

proposed option, after the effective date 

of any revocation of the 1997 primary 

annual PM2.5 NAAQS, transportation 

and general conformity determinations 

would continue to be required in areas 

that are designated nonattainment for 

the 1997 secondary annual PM2.5

NAAQS until such areas are 

redesignated to attainment pursuant to 

the requirements of section 107(d)(3). 

Areas that are initially designated as 

nonattainment for the 2012 primary 

annual NAAQS are subject to 

transportation and general conformity 

requirements after the end of the grace 

period that ends 1 year after the 

effective date of designations for the 

2012 primary annual PM2.5 NAAQS. See 

further information for how conformity 

will be implemented for the 2012 PM2.5

NAAQS in Section IX.B of this 

preamble. Under Options 1 and 2 the 

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335Areas initially designated as attainment for the 

1997 annual PM2.5 NAAQS would also be required 

to continue to implement a PSD program unless an 

area was designated nonattainment for the 2012 

primary annual PM2.5 NAAQS. Such an area would 

be required to implement a NNSR program for that 

NAAQS. 

336Areas designated nonattainment for the 2012 

primary annual PM2.5 NAAQS would implement a 

NNSR program for that NAAQS. 

337See the the final SIP requirements rule for the 

2008 ozone NAAQS at http://www.epa.gov/

groundlevelozone/implement.html. 

338See 40 CFR 51.905(a)(3), the comparable 

provision for transitions from the 1-hour NAAQS to 

the 1997 ozone NAAQS, which allows such areas 

to request that the 1-hour NNSR provisions be 

removed from the SIP. 

339See South Coast Air Quality Management 

District v. EPA, 472 F.3d at 882 (D.C. Cir. 2006). 

timing that the EPA is proposing means 

that any area that was previously a 1997 

annual PM2.5 NAAQS nonattainment 

area, but has been redesignated to 

attainment for the 1997 annual PM2.5

NAAQS by the time of revocation of the 

1997 primary annual PM2.5 NAAQS 

(e.g., April 2016 for most areas), will not 

be subject to the anti-backsliding 

requirements for the 1997 annual PM2.5

NAAQS. This is because when an area 

has been redesignated to attainment for 

a PM2.5 NAAQS while that NAAQS is in 

effect, it has fulfilled all applicable 

requirements for that NAAQS, including 

applicable anti-backsliding 

requirements for the 1997 annual PM2.5

NAAQS. The area is, therefore, not 

subject to anti-backsliding requirements 

for the revoked 1997 primary annual 

PM2.5 NAAQS. These areas are required 

instead to implement their approved 

CAA section 175A maintenance plan for 

the 1997 primary annual PM2.5 NAAQS 

and implement a PSD program for this 

NAAQS, if they are designated 

attainment for the 2012 primary annual 

PM2.5 NAAQS.335 336 Revisions to the 

approved maintenance plan can only be 

made if the revisions meet the 

requirements of section 110(l) and, if 

applicable, section 193. The EPA 

proposes that these areas not be 

required to submit a second 10-year 

maintenance plan for the 1997 primary 

annual PM2.5 NAAQS because there is 

no justification for additional 

maintenance plan burdens to be 

imposed on these areas solely because at 

one time they were designated 

nonattainment under the revoked 1997 

primary annual PM2.5 NAAQS. Not 

requiring a second 10-year maintenance 

plan for these areas would help to 

minimize the burden associated with 

preparing SIPs for a succession of 

NAAQS of increasing stringency. 

As explained previously, for areas 

redesignated to attainment under 

Options 1 and 2, the section 175A 

maintenance plan for the 1997 primary 

annual PM2.5 NAAQS satisfies the antibacksliding requirements of these areas. 

The EPA believes that for these areas 

any further 110(a)(1) maintenance plan 

requirement under the 2012 primary 

annual PM2.5 NAAQS for areas 

designated attainment for that NAAQS 

would be unnecessarily burdensome. 

For Option 2, the EPA is applying a 

general principle to apply transition 

requirements depending on how the 

area is designated—attainment or 

nonattainment—for the 2012 primary 

annual PM2.5 NAAQS, while taking into 

account the area’s status with respect to 

the 1997 primary annual PM2.5 NAAQS. 

For those areas which have already 

incorporated measures into their 

approved SIPs that satisfy the 

nonattainment requirements for that 

standard, section 110(l) functions to 

require continued implementation of 

such measures unless revised in 

accordance with its provisions. 

Under Option 2, the EPA is proposing 

as one alternative that areas designated 

attainment for the 2012 primary annual 

PM2.5 NAAQS and nonattainment for 

the 1997 annual PM2.5 NAAQS (as of 

revocation of the 1997 primary annual 

PM2.5 NAAQS) not be required to adopt 

any outstanding applicable 

requirements for the revoked 1997 

primary annual standard. This approach 

is similar to the approach followed in 

the transition from the 1-hour ozone 

NAAQS to the 1997 ozone NAAQS. 

However, instead of submitting a 

maintenance plan the EPA is also 

proposing that the approved PSD SIPs 

for these areas satisfy the obligation to 

submit an approvable maintenance plan 

for the 2012 primary annual PM2.5

NAAQS under section 110(a)(1). This is 

similar to what the EPA finalized for the 

transition from the 1997 ozone NAAQS 

to the 2008 ozone NAAQS.337 The 

EPA’s rationale for this approach is as 

follows: Areas designated attainment for 

the 2012 primary annual PM2.5 NAAQS 

and nonattainment for the 1997 primary 

annual PM2.5 NAAQS (as of revocation 

of the 1997 primary annual PM2.5

NAAQS) have already attained the most 

stringent existing standard. These areas 

thus have developed nonattainment 

plans that in combination with federal 

measures and emissions controls in 

upwind areas have produced sufficient 

emissions reductions to achieve the 

more protective 2012 primary annual 

PM2.5 NAAQS. They remain subject to 

the 1997 nonattainment area 

requirements already approved into the 

SIP, which can be revised only upon a 

showing that such revision is consistent 

with sections 110(l) and 193, if 

applicable. At this time, and given the 

succession of NAAQS of increasing 

stringency that has occurred, the EPA 

believes that the burden of developing 

an approvable maintenance plan for the 

2012 primary annual PM2.5 NAAQS 

would outweigh any compensating 

benefit for an area that is already 

attaining that more stringent NAAQS 

and that is subject to prior 

nonattainment requirements which are 

already incorporated into the SIP. 

Under Option 2, the EPA is also 

proposing, for areas that are attainment 

for the 2012 primary annual PM2.5

NAAQS, that the NNSR anti-backsliding 

requirement(s) for the 1997 annual 

PM2.5 NAAQS cease to apply, since PSD 

will then be in effect. The state may 

request that the corresponding NSR 

requirements be removed entirely, 

rather than be retained in the SIP as a 

maintenance plan contingency 

measure.338 Areas that are designated 

nonattainment for the more stringent 

2012 primary annual PM2.5 NAAQS will 

be subject to NNSR and other 

nonattainment requirements for their 

classification under the more stringent 

2012 primary annual PM2.5 NAAQS. 

The revocation of the 1-hour ozone 

NAAQS and the associated antibacksliding provisions were the subject 

of past litigation. In its December 2006 

decision on that challenge, as modified 

following rehearing, the Court held with 

respect to the anti-backsliding approach 

for conformity that 1-hour ozone motor 

vehicle emissions budgets must be used 

in transportation conformity 

determinations for the more protective 

1997 ozone NAAQS where such SIP 

motor vehicle emissions budgets have 

been found adequate or approved, until 

SIP motor vehicle emissions budgets for 

the 1997 ozone NAAQS are available.339

In addition, the Court affirmed more 

broadly that in order for transportation 

conformity determinations to fulfill the 

requirements of CAA section 176(c)(1), 

motor vehicle emissions budgets for a 

prior NAAQS must be used in 

transportation conformity 

determinations under a revised NAAQS 

until emissions budgets for the revised 

NAAQS are either found adequate or are 

approved, but that conformity 

determinations need not be made for a 

revoked standard. Therefore, areas 

designated nonattainment for the 2012 

primary annual PM2.5 NAAQS that have 

adequate or approved SIP budgets for 

the 1997 annual PM2.5 NAAQS must 

continue to use such budgets in 

transportation conformity 

determinations until budgets for the 

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340Areas that do not have adequate or approved 

motor vehicle emissions budgets for the 1997 

annual PM2.5 NAAQS or the 2006 24-hour PM2.5

NAAQS would use one of the two interim 

emissions tests requied by 40 CFR 93.109(c)(3) and 

40 CRR 93.119(b). 

341 It should be noted that some areas will remain 

designated nonattainment for 1997 secondary 

annual PM2.5 NAAQS. Such areas will remain 

subject to transportation and general conformity for 

that NAAQS until such time that they are 

redesignated to attainment for that NAAQS 

pursuant to the requirements of section 107(d)(3). 

342Note that a regulatory impact analysis 

evaluating the costs and benefits associated with 

attaining the 2012 PM2.5 NAAQS was released at the 

time the NAAQS review was finalized. See 

‘‘Regulatory Impact Analysis for the Final Revisions 

to the National Ambient Air Quality Standards for 

Particulate Matter.’’ U.S. Environmental Protection 

Agency, Office of Air Quality and Planning 

Standards, Health and Environmental Impacts 

Division, February 28, 2013. EPA–452/R–12–005. 

343These hypothetical nonattainment areas were 

developed based on 2010–12 air quality data and 

state recommendations. Actual nonattainment 

designations and boundaries are based on the most 

recent, complete air quality data available. 

2012 primary annual PM2.5 NAAQS are 

found adequate or are approved.340

With regard to general conformity, the 

D.C. Circuit Court did not address the 

need for specific anti-backsliding 

measures in its initial decision or in the 

modified decision on the South Coast 

litigation. Therefore, if the EPA finalizes 

either Option 1 or 2 and revokes the 

1997 primary annual PM2.5 NAAQS, 

general conformity determinations will 

be required in nonattainment areas for 

the 2012 primary annual NAAQS as 

required by section 176(c)(5) to ensure 

that the action of federal agencies do not 

cause a violation of that NAAQS, make 

an existing violation worse or delay 

timely attainment of the NAAQS or an 

interim milestone.341 The EPA believes 

that revoking the 1997 primary annual 

PM2.5 NAAQS under Option 1 or 2 is 

logical because it would result in only 

one primary annual PM2.5 NAAQS—the 

2012 primary annual PM2.5 NAAQS— 

applying for purposes of transportation 

and general conformity in most areas, 

after the end of the 1-year conformity 

grace period that applies to newly 

designated nonattainment areas. (CAA 

section 176(c)(6)). 

Areas that are attaining the more 

health protective 2012 primary annual 

PM2.5 NAAQS would no longer have to 

expend resources to make conformity 

determinations for any of the current 

primary annual PM2.5 NAAQS after the 

1997 primary annual PM2.5 NAAQS is 

revoked and the area is redesignated as 

attainment for the 1997 secondary 

annual PM2.5 NAAQS. Some of these 

areas would be required to continue to 

make conformity determinations for the 

2006 24-hour PM2.5 NAAQS and based 

on 2011–13 air quality data two areas 

would be required to make conformity 

determinations for the 1997 24-hour 

PM2.5 NAAQS. It should be noted that 

any areas that are attaining the more 

health protective 2012 primary annual 

NAAQS are also necessarily attaining 

the less stringent 1997 annual PM2.5

NAAQS by a wide margin. Therefore, 

the options of this proposal would 

provide a seamless transition from 

demonstrating conformity for the 1997 

annual PM2.5 NAAQS to demonstrating 

conformity for the more stringent 2012 

primary annual PM2.5 NAAQS. 

Areas designated nonattainment for 

the 2012 primary annual PM2.5 NAAQS 

will likely need the full 1-year grace 

period provided in section 176(c)(6) to 

complete the required initial 

transportation conformity 

determination. Those areas that were 

designated as either nonattainment or 

maintenance for the 1997 annual PM2.5

NAAQS at the time of designation as 

nonattainment for the 2012 primary 

annual PM2.5 NAAQS will need 

certainty as to the specific requirements 

for that conformity determination. For 

example they need to know what 

analysis years must be addressed and, if 

the boundaries for the PM2.5 NAAQS are 

different, they need to know whether to 

address conformity for both areas and 

which test or tests would apply. 

The EPA seeks comment on the 

options proposed in the preceding 

discussion regarding revoking the 1997 

primary annual PM2.5 standard, as well 

as on whether the agency should take no 

action to revoke the standard as this 

time. 

XI. Environmental Justice 

Considerations 

The EPA believes the human health or 

environmental risk addressed by this 

action will not have disproportionately 

high and adverse human health or 

environmental effects on minority, lowincome, or indigenous populations 

because it would not negatively affect 

the level of protection provided to 

human health or the environment under 

the PM2.5 NAAQS. When promulgated, 

these proposed regulations will clarify 

the state implementation plan 

requirements and the NNSR permitting 

requirements to be met by states in 

order to attain the PM2.5 NAAQS as 

expeditiously as practicable. These 

requirements are designed to protect all 

segments of the general population. The 

EPA included specific discussion in this 

preamble about actions that could be 

considered for the protection of 

minority, low-income or indigenous 

populations in Section IV.D.6 on 

Moderate area attainment plan control 

strategies; Section VI.D.7 on Serious 

area attainment plan control strategies; 

and Section IX.G, measures to ensure 

appropriate protections for 

overburdened populations. In addition, 

as part of the consultation activities 

conducted in developing this rule, the 

EPA participated in training and 

outreach activities with representatives 

from environmental justice 

organizations in a March 2014 

conference held in Research Triangle 

Park, NC titled, ‘‘Clean Air Act 

Rulemaking and Permitting Training for 

EJ Communities.’’ These proposed 

regulations are designed to protect and 

enhance the health and safety of these 

and other populations, and they will not 

adversely affect the health or safety of 

minority, low-income or indigenous 

populations. 

XII. Statutory and Executive Order 

Reviews 

A. Executive Order 12866: Regulatory 

Planning and Review and Executive 

Order 13563: Improving Regulation and 

Regulatory Review 

This action is a significant regulatory 

action that was submitted to the Office 

of Management and Budget (OMB) for 

review because it raises novel policy 

issues. Any changes made in response 

to OMB recommendations have been 

documented in the docket.342

B. Paperwork Reduction Act (PRA) 

The information collection activities 

in this proposed rule have been 

submitted for approval to the Office of 

Management and Budget (OMB) under 

the PRA. The Information Collection 

Request (ICR) document prepared by the 

EPA has been assigned the EPA ICR 

number 2258.03, OMB Control No. 

2060–0611. You can find a copy of the 

ICR in the docket for this rule, and it is 

briefly summarized here. 

The EPA is proposing this PM2.5

NAAQS SIP Requirements Rule to 

describe the CAA requirements that 

must be met by states with 

nonattainment areas required to develop 

attainment plans for attaining and 

maintaining the NAAQS. The intended 

effect of the SIP Requirements Rule is to 

provide certainty to states regarding 

their planning obligations such that 

states may begin SIP development. Only 

states with nonattainment areas are 

required to submit SIPs under this rule. 

For purposes of analysis of the 

estimated paperwork burden, the EPA 

assumed there were 21 existing 

nonattainment areas for the 1997 and 

2006 PM2.5 NAAQS, and 15 

hypothetical, newly-designated 

nonattainment areas.343 The attainment 

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plan requirements would appear as 40 

CFR 51.1000 through 51.1015 which 

implement CAA subsections 172(c)(1) 

and (2), and 189(a)(1)(B) and (C), 

189(b)(1)(A) and (B) and 189(c). Some 

states have new nonattainment areas 

and some states should already have 

information from emission sources, as 

facilities should have provided this 

information to meet 1997 and 2006 

PM2.5 NAAQS SIP requirements, 

operating permits and/or emissions 

reporting requirements. Such 

information does not generally reveal 

the details of production processes. But, 

to the extent it may, confidential 

business information for the affected 

facilities is protected. Specifically, 

submissions of emissions and control 

efficiency information that is 

confidential, proprietary and trade 

secret and is not emission data is 

protected from disclosure under the 

requirements of subsections 503(e) and 

114(c) of the CAA. 

The annual state burden for this 

information collection for the 15 

hypothetical newly designated 2012 

PM2.5 nonattainment areas, averaged 

over the first 3 years of this ICR, is 

estimated to be a total of 54,000 labor 

hours per year at an annual labor cost 

of $3.2 million (present value) over the 

3-year period, or approximately 

$649,000 per state for the 5 state 

respondents. The average annual 

reporting burden is approximately 3,600 

hours per response, with approximately 

3 responses per state for 15 state 

responses. There are no capital or 

operating and maintenance costs 

associated with the proposed rule 

requirements. Burden is defined at 5 

CFR 1320.3(b). 

The annual state burden for this 

information collection for the 21 

existing nonattainment areas for the 

1997 and 2006 PM2.5 NAAQS, averaged 

over the first 3 years of this ICR, is 

estimated to be a total of 43,400 labor 

hours per year at an annual labor cost 

of $2.6 million (present value) over the 

3-year period, or approximately 

$370,000 per state for the 7 state 

respondents. The average annual 

reporting burden is approximately 2,000 

hours per response, with approximately 

3 responses per state for 21 state 

responses. There are no capital or 

operating and maintenance costs 

associated with the proposed rule 

requirements. Burden is defined at 5 

CFR 1320.3(b). 

An agency may not conduct or 

sponsor, and a person is not required to 

respond to, a collection of information 

unless it displays a currently valid OMB 

control number. The OMB control 

numbers for the EPA’s regulations in 40 

CFR are listed in 40 CFR part 9. 

Submit your comments on the 

agency’s need for this information, the 

accuracy of the provided burden 

estimates and any suggested methods 

for minimizing respondent burden to 

the EPA using the docket identified at 

the beginning of this rule. You may also 

send your ICR-related comments to 

OMB’s Office of Information and 

Regulatory Affairs via email to oria_

submissions@omb.eop.gov, Attention: 

Desk Officer for the EPA. Since OMB is 

required to make a decision concerning 

the ICR between 30 and 60 days after 

receipt, OMB must receive comments no 

later than April 22, 2015. The EPA will 

respond to any ICR-related comments in 

the final rule. 

C. Regulatory Flexibility Act 

The Regulatory Flexibility Act (RFA) 

generally requires an agency to prepare 

a regulatory flexibility analysis of any 

regulation subject to notice-andcomment rulemaking requirements 

under the Administrative Procedures 

Act or any other statute unless the 

agency certifies the rule will not have a 

significant economic impact on a 

substantial number of small entities. 

Small entities include small businesses, 

small organizations and small 

governmental jurisdictions. 

For purposes of assessing the impacts 

of this rule on small entities, small 

entity is defined as: (1) A small business 

as defined in the Small Business 

Administration’s (SBA) regulations at 13 

CFR 121.201; (2) a small governmental 

jurisdiction that is a government of a 

city, county, town, school district or 

special district with a population of less 

than 50,000; and (3) a small 

organization that is any not-for-profit 

enterprise which is independently 

owned and operated and is not 

dominant in its field. 

After considering the economic 

impacts of this proposed rule on small 

entities, I certify that this action will not 

have a significant economic impact on 

a substantial number of small entities. 

This proposed rule will not impose any 

requirements directly on small entities. 

Entities potentially affected directly by 

this proposal include state, local and 

tribal governments and none of these 

governments are small governments. 

Other types of small entities are not 

directly subject to the requirements of 

this rule. The EPA continues to be 

interested in the potential impacts of the 

proposed rule on small entities and 

welcomes comments on issues related to 

such impacts. 

D. Unfunded Mandates Reform Act 

(UMRA) 

This action does not contain any 

unfunded mandate as described in 

UMRA, 2 U.S.C. 1531–1538, and does 

not significantly or uniquely affect small 

governments. This action imposes no 

enforceable duty on any state, local or 

tribal governments or the private sector. 

The CAA imposes the obligation for 

states to submit attainment plans to 

implement the PM2.5 NAAQS. In this 

rule, the EPA is clarifying those 

requirements. Therefore, this action is 

not subject to the requirements of 

sections 202, 203, and 205 of the 

UMRA. 

E. Executive Order 13132: Federalism 

This action does not have federalism 

implications. It will not have substantial 

direct effects on the states, on the 

relationship between the national 

government and the states, or on the 

distribution of power and 

responsibilities among the various 

levels of government, as specified in 

Executive Order 13132. The 

requirement to submit attainment plans 

to meet a PM2.5 NAAQS is imposed by 

the CAA. This proposed rule, if made 

final, would interpret those 

requirements as they apply to current 

and future PM2.5 NAAQS. Thus, 

Executive Order 13132 does not apply 

to these proposed regulations. 

In the spirit of Executive Order 13132 

and consistent with the EPA policy to 

promote communications between the 

EPA and state and local governments, 

the EPA specifically solicits comments 

on this proposed action from state and 

local officials. In addition, the EPA 

intends to meet with organizations 

representing state and local officials 

during the comment period for this 

action. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

This proposed action does not have 

tribal implications, as specified in 

Executive Order 13175 (65 FR 67249, 

November 9, 2000). It would not have a 

substantial direct effect on one or more 

Indian tribes. Furthermore, these 

proposed regulation revisions do not 

affect the relationship or distribution of 

power and responsibilities between the 

federal government and Indian tribes. 

The CAA and the TAR establish the 

relationship of the federal government 

and tribes in characterizing air quality 

and developing plans to attain the 

NAAQS, and these revisions to the 

regulations do nothing to modify that 

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relationship. Thus, Executive Order 

13175 does not apply to this action. 

Although Executive Order 13175 does 

not apply to this action, the EPA solicits 

comment on this proposed action from 

tribal officials. The EPA also intends to 

offer to consult with any tribal 

government to discuss this proposal. 

G. Executive Order 13045: Protection of 

Children From Environmental Health 

and Safety Risks 

The EPA interprets Executive Order 

13045 as applying only to those 

regulatory actions that concern 

environmental health or safety risks that 

the EPA has reason to believe may 

disproportionately affect children, per 

the definition of ‘‘covered regulatory 

action’’ in section 2–202 of the 

Executive Order. This action is not 

subject to Executive Order 13045 

because it implements a previously 

promulgated health or safety-based 

federal standard established pursuant to 

the CAA. 

These proposed regulatory provisions 

are designed to help implement the 

current and future PM2.5 NAAQS, 

promulgated to protect the health and 

welfare of individuals, including 

children, who are susceptible to the 

adverse effects of exposure to unhealthy 

levels of ambient PM2.5. 

H. Executive Order 13211: Actions 

Concerning Regulations That 

Significantly Affect Energy Supply, 

Distribution, or Use 

This action is not a ‘‘significant 

energy action’’ as defined in Executive 

Order 13211 (66 FR 28355 (May 22, 

2001)), because it is not likely to have 

a significant adverse effect on the 

supply, distribution, or use of energy. 

I. National Technology Transfer and 

Advancement Act 

Section 12(d) of the National 

Technology Transfer and Advancement 

Act of 1995 (NTTAA), Public Law 104– 

113, section 12(d) (15 U.S.C. 272 note) 

directs the EPA to use voluntary 

consensus standards in its regulatory 

activities unless to do so would be 

inconsistent with applicable law or 

otherwise impractical. Voluntary 

consensus standards are technical 

standards (e.g., materials specifications, 

test methods, sampling procedures and 

business practices) that are developed or 

adopted by voluntary consensus 

standards bodies. NTTAA directs the 

EPA to provide Congress, through OMB, 

explanations when the agency decides 

not to use available and applicable 

voluntary consensus standards. 

This proposed rulemaking does not 

involve technical standards. Therefore, 

the EPA is not considering the use of 

any voluntary consensus standards. 

J. Executive Order 12898: Federal 

Actions To Address Environmental 

Justice in Minority Populations and 

Low-Income Populations 

The EPA believes the human health or 

environmental risk addressed by this 

action will not have disproportionately 

high and adverse human health or 

environmental effects on minority, lowincome, or indigenous populations. The 

results of this evaluation are contained 

in Section XI of this preamble. 

K. Determination Under Section 307(d) 

Pursuant to sections 307(d)(1)(E) and 

307(d)(1)(V) of the CAA, the 

Administrator proposes to determine 

that this action is subject to the 

provisions of section 307(d). Under 

section 307(d)(1)(V), the provisions of 

section 307(d) apply to ‘‘such other 

actions as the Administrator may 

determine.’’ 

Statutory Authority 

The statutory authority for this action 

is provided by 42 U.S.C. 7403, 7407, 

7410, and 7601. 

List of Subjects 

40 CFR Part 50 

Environmental protection, Air 

pollution control, Intergovernmental 

relations, Particulate matter. 

40 CFR Part 51 

Environmental protection, Air 

pollution control, Intergovernmental 

relations, Particulate matter. 

40 CFR Part 93 

Environmental protection, Air 

pollution control, Intergovernmental 

relations, Particulate matter. 

Dated: March 10, 2015. 

Gina McCarthy, 

Administrator. 

For the reasons stated in the 

preamble, Title 40, Chapter I of the Code 

of Federal Regulations is proposed to be 

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. In § 50.13, add paragraph (d) to read 

as follows: 

§ 50.13 National primary and secondary 

ambient air quality standards for PM2.5. 

* * * * * 

(d) The standards set forth in this 

section will remain applicable to all 

areas notwithstanding the promulgation 

of the 2012 primary annual PM2.5

national ambient air quality standards 

(NAAQS) in § 50.18. The 1997 primary 

annual PM2.5 NAAQS set forth in this 

section will no longer apply to an area 

1 year after the effective date of the 

designation of that area, pursuant to 

section 107 of the Clean Air Act, for the 

primary annual PM2.5 NAAQS set forth 

in § 50.18; except that for areas 

designated nonattainment for the 1997 

annual PM2.5 NAAQS set forth in this 

section as of 1 year after the effective 

date of the designations for the primary 

annual PM2.5 NAAQS established in 

§ 50.18, the requirements applicable to 

the 1997 annual PM2.5 NAAQS set forth 

in this section will apply until the 

effective date of an area’s redesignation 

to attainment for the 1997 annual 

NAAQS pursuant to the requirements of 

section 107 of the Clean Air Act. The 

1997 secondary annual PM2.5 NAAQS 

and the 1997 24-hour PM2.5 NAAQS 

shall remain in effect. 

PART 51—REQUIREMENTS FOR 

PREPARATION, ADOPTION, AND 

SUBMITTAL OF IMPLEMENTATION 

PLANS 

■ 3. 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 

■ 4. In § 51.165: 

■ a. Revise paragraphs (a)(1)(iv)(A)(1), 

(a)(1)(x)(A), and (a)(1)(xxxvii)(C)(2); 

■ b. Remove paragraphs 

(a)(1)(xxxvii)(C)(3), and (4); and 

■ d. Revise paragraphs (a)(2)(i) and 

(a)(2)(ii)(A). 

The revisions read as follows: 

§ 51.165 Permit requirements. 

(a) * * * 

(1) * * * 

(iv)(A) * * * 

(1) Any stationary source of air 

pollutants that emits, or has the 

potential to emit, 100 tons per year or 

more of any regulated NSR pollutant (as 

defined in paragraph (a)(1)(xxxvii) of 

this section), except that lower 

emissions thresholds shall apply in 

areas subject to subpart 2, subpart 3, or 

subpart 4 of part D, title I of the Act, 

according to paragraphs 

(a)(1)(iv)(A)(1)(i) through (viii) of this 

section. 

(i) 50 tons per year of volatile organic 

compounds in any serious ozone 

nonattainment area. 

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(ii) 50 tons per year of volatile organic 

compounds in an area within an ozone 

transport region, except for any severe 

or extreme ozone nonattainment area. 

(iii) 25 tons per year of volatile 

organic compounds in any severe ozone 

nonattainment area. 

(iv) 10 tons per year of volatile organic 

compounds in any extreme ozone 

nonattainment area. 

(v) 50 tons per year of carbon 

monoxide in any serious nonattainment 

area for carbon monoxide, where 

stationary sources contribute 

significantly to carbon monoxide levels 

in the area (as determined under rules 

issued by the Administrator). 

(vi) 70 tons per year of PM10 in any 

serious nonattainment area for PM10.

(vii) 70 tons per year of PM2.5 in any 

serious nonattainment area for PM2.5.

(viii) 70 tons per year of any precursor 

for PM2.5 in any serious nonattainment 

area for PM2.5.

* * * * * 

(x)(A) Significant means, in reference 

to a net emissions increase or the 

potential of a source to emit any of the 

following pollutants, a rate of emissions 

that would equal or exceed any of the 

following rates: 

Pollutant Emission Rate 

Carbon monoxide: 100 tons per year 

(tpy) 

Nitrogen oxides: 40 tpy 

Sulfur dioxide: 40 tpy 

Ozone: 40 tpy of volatile organic 

compounds or nitrogen oxides 

Lead: 0.6 tpy 

PM10: 15 tpy 

PM2.5: 10 tpy of direct PM2.5 emissions; 

40 tpy of sulfur dioxide emissions; 40 

tpy of nitrogen oxide emissions; 40 

tpy of VOC emissions; 

* * * * * 

(xxxvii) * * * 

(C) * * * 

(2) Sulfur dioxide, nitrogen oxides, 

volatile organic compounds and 

ammonia are precursors to PM2.5 in any 

PM2.5 nonattainment area, unless the 

State demonstrates to the 

Administrator’s satisfaction or the EPA 

demonstrates that major stationary 

sources of a particular precursor do not 

contribute significantly to PM2.5 levels 

that exceed the PM2.5 ambient standards 

in a particular area. 

* * * * * 

(2) Applicability procedures. (i) Each 

plan shall adopt a preconstruction 

review program to satisfy the 

requirements of sections 172(c)(5) and 

173 of the Act for any area designated 

nonattainment for any national ambient 

air quality standard under subpart C of 

40 CFR part 81. Such a program shall 

apply to any new major stationary 

source or major modification that is 

major for the pollutant (as defined in 

paragraph (a)(1)(xxxvii) of this section) 

for which the area is designated 

nonattainment under section 

107(d)(1)(A)(i) of the Act, if the 

stationary source or modification would 

locate anywhere in the designated 

nonattainment area. Different 

pollutants, including individual 

precursors, are not summed to 

determine applicability of a major 

stationary source or major modification. 

(ii) * * * 

(A) Except as otherwise provided in 

paragraphs (a)(2)(iii) and (iv) of this 

section, and consistent with the 

definition of major modification 

contained in paragraph (a)(1)(v)(A) of 

this section, a project is a major 

modification for a regulated NSR 

pollutant (as defined in paragraph 

(a)(1)(xxxvii) of this section), if it causes 

two types of emissions increases—a 

significant emissions increase (as 

defined in paragraph (a)(1)(xxvii) of this 

section), and a significant net emissions 

increase (as defined in paragraphs 

(a)(1)(vi) and (x) of this section). The 

project is not a major modification if it 

does not cause a significant emissions 

increase. If the project causes a 

significant emissions increase, then the 

project is a major modification only if it 

also results in a significant net 

emissions increase. 

* * * * * 

■ 5. In Appendix S to part 51: 

■ a. Revise paragraph II.A.4.(i)(a) 

introductory text; 

■ b. Add paragraphs II.A.4.(a)(7) and 

(8); and 

■ c. Revise paragraphs II.A.10.(i) and 

II.A.31.(ii)(b)(2). 

The revisions and addition read as 

follows: 

Appendix S to Part 51—Emission Offset 

Interpretative Ruling 

* * * * * 

II. * * * 

A. * * * 

4. (i) * * * 

(a) Any stationary source of air pollutants 

which emits, or has the potential to emit, 100 

tons per year or more of a regulated NSR 

pollutant (as defined in paragraph II.A.31 of 

this Ruling), subject to regulation under the 

Act, except that lower emissions thresholds 

shall apply in areas subject to subpart 2, 

subpart 3, or subpart 4 of part D, title I of the 

Act, according to paragraphs II.A.4(i)(a)(1) 

through (6) of this ruling. 

* * * * * 

(7) 70 tons per year of PM2.5 in any serious 

nonattainment area for PM2.5. 

(8) 70 tons per year of any PM2.5 precursor 

(as defined in paragraph II.A.31 of this 

Ruling) in any Serious nonattainment area for 

PM2.5. 

* * * * * 

10. (i) Significant means, in reference to a 

net emissions increase or the potential of a 

source to emit any of the following 

pollutants, a rate of emissions that would 

equal or exceed any of the following rates: 

Pollutant and Emissions Rate 

Carbon monoxide: 100 tons per year (tpy) 

Nitrogen oxides: 40 tpy 

Sulfur dioxide: 40 tpy 

Ozone: 40 tpy of volatile organic compounds 

or nitrogen oxides 

Lead: 0.6 tpy 

Particulate matter: 25 tpy of particulate 

matter emissions 

PM10: 15 tpy 

PM2.5: 10 tpy of direct PM2.5 emissions; 40 

tpy of sulfur dioxide emissions; 40 tpy of 

nitrogen oxides emissions 

* * * * * 

31. * * * 

(ii) * * * 

(b) * * * 

(2) Sulfur dioxide and nitrogen oxides are 

precursors to PM2.5 in all PM2.5

nonattainment areas. 

* * * * * 

■ 6. Revise subpart Z to read as follows: 

Subpart Z—Provisions for 

Implementation of PM2.5 National 

Ambient Air Quality Standards 

Sec. 

51.1000 Definitions. 

51.1001 Applicability of part 51. 

51.1002 Classifications. 

51.1003 Attainment plan submittals and 

due dates. 

51.1004 Attainment dates. 

51.1005 Attainment date extensions. 

51.1006 Requirements for demonstrating 

insignificant contribution of PM2.5

precursors. 

51.1007 Requirements for de minimis 

source category determinations for direct 

PM2.5 and PM2.5 precursors. 

51.1008 Emissions inventory requirements. 

51.1009 Moderate area attainment plan 

control strategy requirements. 

51.1010 Serious area attainment plan 

control strategy requirements. 

51.1011 Attainment demonstration and 

modeling requirements. 

51.1012 Reasonable further progress (RFP) 

requirements. 

51.1013 Quantitative milestone 

requirements. 

51.1014 Contingency measures 

requirements. 

51.1015 Clean data requirements. 

§ 51.1000 Definitions. 

The following definitions apply for 

purposes of this subpart. Any term not 

defined herein shall have the meaning 

as defined in 40 CFR 51.100 or Clean 

Air Act section 302. 

Act means the Clean Air Act as 

codified at 42 U.S.C. 7401–7671q 

(2003). 

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Additional feasible measure is any 

control measure that otherwise meets 

the definition of ‘‘best available control 

measure’’ (BACM) but can only be 

implemented in whole or in part 

beginning 4 years after the date of 

reclassification of an area as Serious and 

no later than the statutory attainment 

date for the area. 

Additional reasonable measure is any 

control measure that otherwise meets 

the definition of ‘‘reasonably available 

control measure’’ (RACM) but can only 

be implemented in whole or in part 

during the period beginning 4 years 

after the date of designation of a 

nonattainment area and no later than 

the end of the sixth calendar year 

following the date of designation of the 

area. 

Applicable annual standard is the 

annual PM2.5 NAAQS established, 

revised, or retained as a result of a 

particular PM2.5 NAAQS review. 

Applicable attainment date means the 

latest statutory date by which an area is 

required to attain a particular PM2.5

NAAQS, unless EPA has approved an 

attainment plan for the area to attain 

such NAAQS, in which case the 

applicable attainment date is the date 

approved under such attainment plan. If 

EPA grants an extension of an approved 

attainment date, then the applicable 

attainment date for the area shall be the 

extended date. 

Applicable 24-hour standard is the 

24-hour PM2.5 NAAQS established, 

revised, or retained as a result of a 

particular PM2.5 NAAQS review. 

Attainment projected inventory means 

the projected emissions of direct PM2.5

and all PM2.5 precursors from sources 

included in the base year inventory, and 

from any additional sources of such 

emissions expected within the 

boundaries of the nonattainment area by 

the projected attainment date for the 

area. 

Base year inventory means the actual 

emissions of direct PM2.5 and all PM2.5

precursors from all sources within the 

boundaries of a nonattainment area in 

one of the 3 years used for purposes of 

designations or another technically 

appropriate year. 

Benchmark RFP analysis means the 

analysis submitted as part of the RFP 

plan for a PM2.5 nonattainment area that 

requires generally linear emissions 

reductions in direct PM2.5 and in each 

PM2.5 precursor from the base year 

through the projected attainment year. 

Best available control measure 

(BACM) is any technologically and 

economically feasible control measure 

that can be implemented in whole or in 

part within 4 years after the date of 

reclassification of a PM2.5

nonattainment area and that generally 

can achieve greater permanent and 

enforceable emissions reductions in 

direct PM2.5 emissions and/or emissions 

of PM2.5 precursors from sources in the 

area than can be achieved through the 

implementation of RACM on the same 

source(s). BACM includes best available 

control technology (BACT). 

Date of designation means the 

effective date of a PM2.5 area designation 

as promulgated by the Administrator. 

Date of reclassification means the 

effective date of a PM2.5 area 

reclassification from Moderate to 

Serious as promulgated by the 

Administrator. 

Direct PM2.5 emissions means solid 

particles emitted directly from an air 

emissions source or activity, or gaseous 

emissions or liquid droplets from an air 

emissions source or activity which 

condense to form particulate matter at 

ambient temperatures. Direct PM2.5

emissions include filterable and 

condensable PM2.5 emissions composed 

of elemental carbon, directly emitted 

organic carbon, directly emitted sulfate, 

directly emitted nitrate, and other 

inorganic particles (including but not 

limited to crustal material, metals, and 

sea salt). 

Existing control measure means any 

federally enforceable national, state, or 

local control measure that results in 

reductions in direct PM2.5 emissions or 

emissions of PM2.5 precursors in a 

nonattainment area in that state. 

Implemented means adopted by the 

state and fully approved into the SIP by 

EPA for the nonattainment area; built, 

installed, and/or otherwise physically 

manifested; and, fully complied with by 

the affected sources. 

Most stringent measure (MSM) is any 

permanent and enforceable control 

measure that achieves the most stringent 

emissions reductions in direct PM2.5

emissions and/or emissions of PM2.5

precursors from among those control 

measures which are either included in 

any other SIP for any NAAQS or have 

been achieved in practice by any state 

and that can feasibly be implemented in 

the relevant PM2.5 NAAQS 

nonattainment area. 

PM2.5 design value (DV) for a PM2.5

nonattainment area is the highest of the 

three-year average concentrations 

calculated for the ambient air quality 

monitors in the area, in accordance with 

40 CFR part 50, appendix N. 

PM2.5 NAAQS are the fine particulate 

matter National Ambient Air Quality 

Standards codified at 40 CFR part 50. 

PM2.5 precursors are sulfur dioxide 

(SO2), oxides of nitrogen (NOX), volatile 

organic compounds (VOC), and 

ammonia (NH3). 

Reasonably available control measure 

(RACM) is any technologically and 

economically feasible measure that can 

be implemented in whole or in part 

within 4 years after the date of 

designation of a PM2.5 nonattainment 

area and that achieves permanent and 

enforceable reductions in direct PM2.5

emissions and/or PM2.5 precursor 

emissions from sources in the area. 

RACM includes reasonably available 

control technology (RACT). 

Reasonable further progress (RFP) 

means such annual incremental 

reductions in emissions of direct PM2.5

and PM2.5 precursors regulated in the 

attainment plan as are required for the 

purpose of ensuring attainment of the 

applicable PM2.5 NAAQS in a 

nonattainment area by the applicable 

attainment date. 

Subpart 1 means subpart 1 of part D 

of title I of the Act. 

Subpart 4 means subpart 4 of part D 

of title I of the Act. 

§ 51.1001 Applicability of part 51. 

The provisions in subparts A through 

X of this part apply to areas for purposes 

of the PM2.5 NAAQS to the extent they 

are not inconsistent with the provisions 

of this subpart. 

§ 51.1002 Classifications. 

(a) Initial classification as Moderate 

PM2.5 nonattainment area. Any area 

designated nonattainment for a PM2.5

NAAQS shall be classified at the time of 

such designation, by operation of law, 

as a Moderate PM2.5 nonattainment area. 

(b) Reclassification as Serious PM2.5

nonattainment area. A Moderate 

nonattainment area shall be reclassified 

to Serious under the following 

circumstances: 

(1) The EPA shall reclassify as Serious 

through notice-and-comment 

rulemaking any Moderate PM2.5

nonattainment area that the EPA 

determines cannot practicably attain a 

particular PM2.5 NAAQS by the 

applicable Moderate area attainment 

date. 

(2) A Moderate PM2.5 nonattainment 

area shall be reclassified by operation of 

law as a Serious nonattainment area if 

the EPA finds through notice-andcomment rulemaking that the area failed 

to attain a particular PM2.5 NAAQS by 

the applicable Moderate area attainment 

date. 

§ 51.1003 Attainment plan submittals and 

due dates. 

(a) Nonattainment areas initially 

classified as Moderate. 

(1) For any area designated as 

nonattainment and initially classified as 

Moderate for a PM2.5 NAAQS, the 

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state(s) shall submit a Moderate area 

attainment plan that meets all of the 

following requirements: 

(i) Emissions inventory requirements 

set forth at § 51.1008(a)(1); 

(ii) Emissions inventory requirements 

set forth at § 51.1008(a)(2); 

(iii) Moderate area attainment plan 

control strategy requirements set forth at 

§ 51.1009; 

(iv) Attainment demonstration and 

modeling requirements set forth at 

§ 51.1011; 

(v) Reasonable Further Progress (RFP) 

requirements set forth at § 51.1012; 

(vi) Quantitative milestone 

requirements set forth at § 51.1013; 

(vii) Contingency measure 

requirements set forth at § 51.1014; and, 

(viii) Nonattainment new source 

review plan requirements pursuant to 

section 189(a)(1)(A) and section 

172(c)(5) of the CAA. 

(2) The state(s) shall submit its 

Moderate area attainment plan to EPA 

no later than 18 months from the date 

of designation of the area. 

(b) Nonattainment areas reclassified to 

Serious. 

(1) For any nonattainment area 

reclassified to Serious for a PM2.5

NAAQS under § 51.1002(b), in addition 

to meeting the Moderate area attainment 

plan submittal requirements set forth at 

§ 51.1003(a), the state(s) shall submit a 

Serious area attainment plan that meets 

all of the following requirements: 

(i) Emissions inventory requirements 

set forth at § 51.1008(b)(1); 

(ii) Emissions inventory requirements 

set forth at § 51.1008(b)(2); 

(iii) Serious area attainment plan 

control strategy requirements set forth at 

§ 51.1010; 

(iv) Attainment demonstration and 

modeling requirements set forth at 

§ 51.1011; 

(v) Reasonable Further Progress (RFP) 

requirements set forth at § 51.1012; 

(vi) Quantitative milestone 

requirements set forth at § 51.1013; 

(vii) Contingency measure 

requirements set forth at § 51.1014; and, 

(viii) Nonattainment new source 

review plan requirements pursuant to 

section 189(b)(3) and section 172(c)(5) 

of the CAA. 

(2) The state(s) shall submit its 

Serious area attainment plan to EPA 

according to the following schedule: 

(i) For any nonattainment area 

reclassified to Serious for a particular 

PM2.5 NAAQS under § 51.1002(b)(1), the 

state(s) shall submit to EPA the portion 

of the Serious area attainment plan that 

meets the requirements set forth at 

paragraphs (b)(1)(i), (iii) and (viii) of this 

section no later than 18 months from the 

date of reclassification. The state(s) shall 

submit to EPA the portion of the Serious 

area attainment plan that meets the 

requirements set forth at paragraphs 

(b)(1)(ii) and (b)(1)(iv) through (vii) of 

this section to EPA no later than 4 years 

from the date of reclassification. 

(ii) For any nonattainment area 

reclassified to Serious for a particular 

PM2.5 NAAQS under § 51.1002(b)(2), the 

state(s) shall submit to EPA a Serious 

area attainment plan meeting the 

requirements set forth at paragraphs 

(b)(1)(i) through (viii) of this section no 

later than 18 months from the date of 

reclassification. 

(iii) If the state(s) submits to EPA a 

request for a Serious area attainment 

date extension simultaneous with the 

Serious area attainment plan due under 

paragraph (b)(1) of this section, such a 

plan shall meet the most stringent 

measure (MSM) requirements set forth 

at § 51.1010(b) in addition to the BACM 

and BACT and additional feasible 

measure requirements set forth at 

§ 51.1010(a). 

(c) Serious nonattainment areas 

subject to CAA section 189(d) for failing 

to attain the PM2.5 NAAQS by the 

applicable Serious area attainment date. 

(1) For any Serious nonattainment 

area that fails to attain a particular PM2.5

NAAQS by the applicable Serious area 

attainment date, the state(s) shall submit 

a revised Serious area attainment plan 

that demonstrates that the area annually 

will achieve at least 5 percent 

reductions in emissions of direct PM2.5

and PM2.5 precursors based on the most 

recent emissions inventory for the area 

and that meets the following 

requirements: 

(i) Emissions inventory requirements 

set forth at § 51.1008(c)(1); 

(ii) Emissions inventory requirements 

set forth at § 51.1008(c)(2); 

(iii) Demonstration of attainment and 

modeling requirements set forth at 

§ 51.1011; 

(iv) Reasonable Further Progress (RFP) 

requirements set forth at § 51.1012; 

(v) Quantitative milestone 

requirements set forth at § 51.1013; and, 

(vi) Contingency measure 

requirements set forth at § 51.1014. 

(2) The state(s) shall submit to EPA 

the revised attainment plan meeting the 

requirements set forth at paragraphs 

(c)(1)(i) through (vi) of this section no 

later than 12 months from the missed 

applicable Serious area attainment date. 

(d) Any attainment plan submitted to 

EPA under this section shall establish 

motor vehicle emissions budgets for the 

projected attainment year for the area, if 

applicable. The state shall develop such 

budgets according to the requirements 

of the transportation conformity rule as 

they apply to PM2.5 nonattainment areas 

(40 CFR part 93). 

§ 51.1004 Attainment dates. 

(a) The state shall submit a projected 

attainment date as part of its attainment 

plan submission under § 51.1003 for any 

PM2.5 NAAQS nonattainment area 

located in whole or in part within its 

boundaries. The state shall justify the 

projected attainment date for each such 

nonattainment area (or portion of a 

nonattainment area) as part of the 

demonstration of attainment developed 

and submitted according to the 

requirements set forth at § 51.1011 and 

according to the following: 

(1) Nonattainment areas initially 

classified as Moderate. 

(i) Except for nonattainment areas that 

meet the criterion under paragraph 

(a)(1)(ii) of this section, the projected 

attainment date for a Moderate PM2.5

nonattainment area shall be as 

expeditious as practicable with the 

implementation of all control measures 

required under § 51.1009 and may be as 

late as the end of the sixth calendar year 

after the date of designation if the state 

demonstrates that the implementation of 

certain control measures that qualify as 

RACM or RACT or additional 

reasonable measures, but that are not 

necessary for demonstrating attainment 

by the end of the sixth calendar year 

after the date of designation, will not 

collectively advance the attainment date 

by at least 1 year. 

(ii) The projected attainment date for 

a Moderate PM2.5 nonattainment area 

which the state demonstrates cannot 

practicably attain the applicable PM2.5

NAAQS by the end of the sixth calendar 

year after the date of designation of the 

area with the implementation of all 

control measures required under 

§ 51.1009 shall be such date unless and 

until the area is reclassified as Serious 

according to § 51.1002. 

(2) Nonattainment areas reclassified to 

Serious. 

(i) Except for nonattainment areas that 

meet the criterion under paragraph 

(a)(2)(ii) of this section, the projected 

attainment date for a Serious PM2.5

nonattainment area shall be as 

expeditious as practicable with the 

implementation of all control measures 

required under § 51.1010 but no later 

than the end of the tenth calendar year 

after the date of designation. 

[ALTERNATIVE PROPOSED 

REGULATORY TEXT] 

(i) Except for nonattainment areas that 

meet the criterion under paragraph 

(a)(2)(ii) of this section, the projected 

attainment date for a Serious PM2.5

nonattainment area shall be as 

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expeditious as practicable with the 

implementation of all control measures 

required under § 51.1010 and may be as 

late as the end of the tenth calendar year 

after the date of designation if the state 

demonstrates that the implementation of 

certain control measures that qualify as 

BACM or BACT or additional feasible 

measures, but that are not necessary for 

demonstrating attainment by the end of 

the tenth calendar year after the date of 

designation, will not collectively 

advance the attainment date by at least 

1 year.] 

(ii) A state that submits an attainment 

plan that demonstrates that a Serious 

PM2.5 nonattainment area cannot 

practicably attain the PM2.5 NAAQS by 

the end of the tenth calendar year 

following the date of designation of the 

area with the implementation of all 

control measures required under 

§ 51.1010(a) must request an extension 

of the Serious area attainment date 

consistent with § 51.1005(b). The 

request must propose a projected 

attainment date for the nonattainment 

area that is as expeditious as 

practicable, but no later than the end of 

the fifteenth calendar year from the date 

of designation of the area. 

(3) Serious nonattainment areas 

subject to CAA section 189(d) for failing 

to attain by the applicable Serious area 

attainment date. The projected 

attainment date for a Serious PM2.5

nonattainment area that failed to attain 

the PM2.5 NAAQS by the applicable 

Serious area attainment date shall be as 

expeditious as practicable based on 

annual reductions in direct PM2.5 and 

significant PM2.5 precursor emissions 

within the area of not less than 5 

percent of the amount of such emissions 

as reported in the most recent emissions 

inventory prepared for the area, but no 

later than 5 years following the missed 

Serious area attainment date. 

(b) Except for attainment plans that 

meet the conditions of paragraphs 

(a)(1)(ii) or (a)(3) of this section, the 

Administrator shall approve an 

attainment date at the same time and in 

the same manner in which the 

Administrator approves the attainment 

plan for the area. 

(1) In accordance with paragraph 

(a)(1)(ii) of this section, if a state 

demonstrates that a Moderate PM2.5

nonattainment area cannot practicably 

attain the PM2.5 NAAQS by the end of 

the sixth calendar year following the 

date of designation of the area, EPA 

shall proceed under the provisions of 

§ 51.1002(b)(1) to reclassify the area to 

Serious through notice-and-comment 

rulemaking. 

(2) In accordance with paragraph 

(a)(3) of this section, if a Serious PM2.5

nonattainment area fails to attain the 

PM2.5 NAAQS by the applicable Serious 

area attainment date, EPA will proceed 

to establish a new attainment date 

through a direct final action published 

in the Federal Register. 

§ 51.1005 Attainment date extensions. 

(a) Nonattainment areas initially 

classified as Moderate. 

(1) A state with a Moderate PM2.5

nonattainment area may apply for a 1- 

year attainment date extension for the 

area if the following conditions are met 

in the year preceding the applicable 

attainment date for the area: 

(i) The state has complied with all 

requirements and commitments 

pertaining to the area in the applicable 

implementation plan; 

(ii) For an area designated 

nonattainment for a particular 24-hour 

PM2.5 NAAQS for which the state seeks 

an attainment date extension, the 98th 

percentile concentration at each monitor 

in the area for the calendar year prior to 

the applicable attainment date is less 

than or equal to the level of the 

applicable 24-hour standard (calculated 

according to the data analysis 

requirements in 40 CFR part 50, 

appendix N); 

(iii) For an area designated 

nonattainment for a particular annual 

PM2.5 NAAQS for which the state seeks 

an attainment date extension, the 

annual average concentration at each 

monitor in the area for the calendar year 

prior to the applicable attainment date 

is less than or equal to the level of the 

applicable annual standard (calculated 

according to the data analysis 

requirements in 40 CFR part 50, 

appendix N). 

(2) The applicable implementation 

plan for a Moderate PM2.5

nonattainment area for which a state 

seeks an attainment date extension is 

the plan submitted to EPA to meet the 

requirements of § 51.1003(a). 

(3) For a Moderate PM2.5

nonattainment area, the requesting state 

(or states) shall submit a written request 

by February 28 of the year following the 

applicable attainment date for the area. 

(4) A state with a Moderate area that 

received an initial 1-year attainment 

date extension may apply for a second 

1-year attainment date extension for the 

area if the state meets the conditions 

described in paragraph (a)(1) of this 

section in the year preceding the 

approved attainment date. 

(b) Nonattainment areas reclassified 

as Serious. 

(1) A state may apply for one 

attainment date extension not to exceed 

5 years for a Serious nonattainment area 

if the following conditions are met: 

(i) The state demonstrates that 

attainment of the applicable PM2.5

NAAQS by the approved attainment 

date for the area would be impracticable 

or, in the absence of an approved 

attainment date, attainment of the 

applicable PM2.5 NAAQS by the 

applicable statutory attainment date for 

the area would be impracticable; 

(ii) The state has complied with all 

requirements and commitments 

pertaining to the area in the applicable 

implementation plan; and, 

(iii) The state demonstrates that the 

attainment plan for the area includes the 

most stringent measures (MSM) that are 

included in the attainment plan of any 

state or are achieved in practice in any 

state, and can feasibly be implemented 

in the area consistent with § 51.1010(b). 

(2) At the time of application for an 

attainment date extension, the state 

shall submit to EPA a Serious area 

attainment plan that meets the following 

requirements: 

(i) Emissions inventory requirements 

set forth at § 51.1008(b); 

(ii) Most stringent measures (MSM) 

requirement described under paragraph 

(b)(1)(iii) of this section and 

§ 51.1010(b); 

(iii) Attainment demonstration and 

modeling requirements set forth at 

§ 51.1011 that justify the state’s 

conclusion under paragraph (b)(1)(i) of 

this section; 

(iv) Reasonable Further Progress (RFP) 

requirements set forth at § 51.1012; 

(v) Quantitative milestone 

requirements set forth at § 51.1013; and, 

(vi) Contingency measure 

requirements set forth at § 51.1014. 

(3) The applicable implementation 

plan for a Serious PM2.5 nonattainment 

area for which a state seeks an 

attainment date extension under 

§ 51.1004(a)(2)(ii) is the plan submitted 

to EPA to meet the requirements set 

forth at § 51.1003(a). 

(4) The applicable implementation 

plan for a Serious PM2.5 nonattainment 

area for which a state seeks an 

attainment date extension under 

§ 51.1004(a)(2)(i) is the plan submitted 

to EPA to meet the requirements set 

forth at § 51.1003(b)(1). 

(5) A state applying for an attainment 

date extension for a Serious 

nonattainment area under 

§ 51.1004(a)(2)(ii) shall submit to EPA a 

request for an extension at the same 

time as it submits the Serious area 

attainment plan due under 

§ 51.1003(b)(1). 

(6) A state applying for an attainment 

date extension for a Serious 

nonattainment area subsequent to 

submitting an initial Serious area 

attainment plan that demonstrated 

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attainment of the NAAQS by the 

applicable attainment date consistent 

with § 51.1004(a)(2)(i) at the time of 

submittal may apply for such an 

extension no later than 60 calendar days 

prior to the approved attainment date 

for the area or, in the absence of an 

approved attainment date, no later than 

60 calendar days prior to the applicable 

statutory attainment date for the area. 

(c) Serious nonattainment areas 

subject to CAA section 189(d) for failing 

to attain by the applicable Serious area 

attainment date. If a Serious area fails to 

attain a particular PM2.5 NAAQS by the 

applicable Serious area attainment date, 

the area is then subject to the 

requirements of section 189(d) of the 

Act, and, for this reason, the state is 

prohibited from requesting an extension 

of the applicable Serious area 

attainment date for such area. 

(d) For any attainment date extension 

request submitted pursuant to this 

section, the requesting state (or states) 

shall submit a written request and 

evidence of compliance with these 

regulations which includes both of the 

following: 

(i) Evidence that all control measures 

submitted in the applicable attainment 

plan have been implemented, and 

(ii) Evidence that the area has made 

emission reduction progress that 

represents reasonable further progress 

toward timely attainment of the 

applicable PM2.5 NAAQS. 

(e) For a PM2.5 nonattainment area 

located in two or more states or 

jurisdictions, all states and/or 

jurisdictions in which such area is 

located shall submit separate attainment 

date extension requests for the area 

consistent with the requirements set 

forth at paragraph (d) of this section. 

§ 51.1006 Requirements for demonstrating 

insignificant contribution of PM2.5

precursors. 

(a) For purposes of determining that a 

particular PM2.5 precursor does not 

contribute significantly to ambient 

PM2.5 concentrations in a PM2.5

nonattainment area, the state shall 

conduct a technical analysis that 

accounts for all emissions of such PM2.5

precursor from all sources located 

within the area. 

(b) The state shall submit results and 

supporting documentation for any 

technical analyses conducted pursuant 

to paragraph (a) of this section as part 

of any attainment plan for the area. 

§ 51.1007 Requirements for de minimis 

source category determinations for direct 

PM2.5 and PM2.5 precursors. 

(a) All categories of sources of direct 

PM2.5 emissions and of emissions of 

PM2.5 precursors in a PM2.5

nonattainment area shall be considered 

non-de minimis unless and until the 

state conducts a technical analysis to 

determine whether a particular source 

category may qualify for a presumptive 

de minimis source category exemption 

from evaluation for potential control 

measures due to its minimal 

contribution to the ambient PM2.5

concentrations in the area. 

(b) The state shall define source 

categories for stationary sources 

classified under the North American 

Industry Classification System (NAICS) 

at the level represented by four (4) digits 

or fewer. 

(c) The state shall define a single 

source category for on-road mobile 

sources, including on-road vehicles and 

engines, and a single source category for 

nonroad mobile sources, including 

nonroad engines, equipment, and 

vehicles, or may define a single source 

category for all mobile sources in the 

aggregate. 

§ 51.1008 Emissions inventory 

requirements. 

(a) For any nonattainment area 

initially classified as Moderate, the state 

shall submit to EPA all of the following: 

(1) A base year inventory for the 

nonattainment area for all emissions 

sources that meets the following 

minimum criteria: 

(i) The inventory year shall be one of 

the 3 years used for designations or 

another technically appropriate 

inventory year if justified by the state in 

the plan submission. 

(ii) The inventory shall include actual 

emissions of all sources within the 

nonattainment area. 

(iii) The emissions values shall be 

either annual total emissions or averageseason-day emissions. The state shall 

include as part of the plan a rationale 

for providing annual or seasonal 

emissions. 

(iv) The inventory shall include direct 

PM2.5 emissions and emissions of all 

PM2.5 precursors. 

(v) The state shall report emissions as 

point sources according to the point 

source emissions thresholds of the Air 

Emissions Reporting Rule (AERR), 40 

CFR part 51, subpart A. 

(vi) The detail of the emissions 

inventory shall be consistent with the 

data elements required by 40 CFR part 

51, subpart A. 

(2) An attainment projected inventory 

for the nonattainment area that meets 

the following minimum criteria: 

(i) The year of the projected inventory 

shall be the most expeditious year for 

which attainment is demonstrated by 

the modeled attainment plan. 

(ii) The emissions values shall be 

projected emissions of the same sources 

included in the base year inventory for 

the nonattainment area (i.e., those only 

within the nonattainment area). The 

state shall include in this inventory 

projected emissions growth and 

contraction from both controls and other 

causes during the relevant period. 

(iii) The temporal period of emissions 

shall be the same temporal period 

(annual or average-season-day) as the 

base year inventory for the 

nonattainment area. 

(iv) Consistent with the base year 

inventory for the nonattainment area, 

the inventory shall include direct PM2.5

emissions and emissions of all PM2.5

precursors. 

(v) The same sources reported as 

point sources in the base year inventory 

for the nonattainment area shall be 

provided as point sources in the 

attainment projected inventory for the 

nonattainment area. Nonpoint and 

mobile source projected emissions shall 

be provided using the same detail (e.g., 

state, county, and process codes) as the 

base year inventory. 

(vi) The same detail of the emissions 

included shall be consistent with the 

level of detail in the base year inventory 

(i.e., as required by 40 CFR part 41, 

subpart A). 

(b) For any nonattainment area 

reclassified as Serious, the state shall 

submit to EPA all of the following: 

(1) For purposes of meeting the 

emissions inventory requirements of 

CAA section 172(c)(3), a base year 

inventory for the nonattainment area for 

all emissions sources that meets the 

requirements listed under paragraph 

(a)(1) of this section, and in addition, 

uses the Serious area definition of a 

major source listed under 

§ 51.165(a)(1)(iv)(A)(vii) and (viii) in 

determining sources to include as point 

sources. 

(2) An attainment projected inventory 

for the nonattainment area that meets 

the criteria listed under paragraph (a)(2) 

of this section. 

(c) Serious nonattainment areas 

subject to CAA section 189(d) for failing 

to attain a PM2.5 NAAQS by the 

applicable Serious area attainment date. 

No later than 12 months after EPA finds 

through notice-and-comment 

rulemaking that a Serious 

nonattainment area, or portion thereof 

contained within a state’s borders, fails 

to attain a PM2.5 NAAQS by the 

applicable attainment date and thus 

becomes subject to the requirements 

under CAA section 189(d), the state 

shall submit to EPA all of the following: 

(1) For purposes of meeting the 

emissions inventory requirements of 

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CAA section 172(c)(3), a base year 

inventory for the nonattainment area for 

all emissions sources that meets the 

requirements listed under paragraph 

(a)(1) of this section, and in addition, 

uses the Serious area definition of a 

major source listed under 

§ 51.165(a)(1)(iv)(A)(vii) and (viii) in 

determining sources to include as point 

sources. 

(2) An attainment projected inventory 

for the nonattainment area as defined by 

§ 51.1000(e) and that meets the criteria 

listed under paragraph (a)(2) of this 

section. 

§ 51.1009 Moderate area attainment plan 

control strategy requirements. 

(a) The state shall identify, adopt, and 

implement control measures, including 

control technologies, on sources of 

direct PM2.5 emissions and sources of 

emissions of PM2.5 precursors located in 

any Moderate PM2.5 nonattainment area 

or portion thereof located within the 

state consistent with the following: 

(1) The state shall identify all sources 

of direct PM2.5 emissions and all sources 

of emissions of PM2.5 precursors in the 

nonattainment area in accordance with 

the emissions inventory requirements of 

§ 51.1008(a); 

(2) The state shall identify all 

potential control measures to reduce 

emissions from all sources of direct 

PM2.5 emissions and all sources of 

emissions of PM2.5 precursors in the 

nonattainment area identified under 

paragraph (a)(1) of this section. 

(i) The state may elect not to identify 

potential control measures to reduce 

emissions from any sources of a 

particular PM2.5 precursor if the state 

demonstrates that all sources of such 

PM2.5 precursor contribute 

insignificantly to ambient PM2.5

concentrations in the area under 

§ 51.1006. 

(ii) The state may elect not to identify 

potential control measures to reduce 

emissions from sources in any source 

category of direct PM2.5 emissions or 

emissions of PM2.5 precursors 

determined to be a de minimis source 

category under § 51.1007. 

(3) For any potential control measure 

identified under paragraph (a)(2) of this 

section, the state may make a 

demonstration that such measure is not 

technologically or economically feasible 

to implement in whole or in part by the 

end of the sixth calendar year following 

the date of designation of the area, and 

the state may eliminate such whole or 

partial measure from further 

consideration under this paragraph. 

(i) For purposes of evaluating the 

technological feasibility of a potential 

control measure, the state may consider 

factors including but not limited to a 

source’s processes and operating 

procedures, raw materials, physical 

plant layout, and potential 

environmental impacts such as 

increased water pollution, waste 

disposal, and energy requirements. 

(ii) For purposes of evaluating the 

economic feasibility of a potential 

control measure, the state may consider 

factors including but not limited to 

capital costs, operating and 

maintenance costs, and cost 

effectiveness of the measure. 

(iii) The state must submit to EPA as 

part of its Moderate area attainment 

plan a detailed written justification for 

eliminating from further consideration 

any potential control measure identified 

under paragraph (a)(2) of this section on 

the basis of technological or economic 

infeasibility. 

(4) The state shall use air quality 

modeling that meets the requirements of 

§ 51.1011(a) and that accounts for 

emissions reductions estimated due to 

all technologically and economically 

feasible control measures identified for 

sources of direct PM2.5 emissions and 

sources of emissions of PM2.5 precursors 

in the Moderate PM2.5 nonattainment 

area to demonstrate that the area can 

attain the applicable PM2.5 NAAQS as 

expeditiously as practicable but no later 

than the end of the sixth year following 

the date of designation of the area, or to 

demonstrate that the Moderate PM2.5

nonattainment area cannot practicably 

attain the applicable PM2.5 NAAQS by 

such date. 

(i) If the state demonstrates through 

air quality modeling that the area can 

attain the applicable PM2.5 NAAQS by 

the end of the sixth calendar year 

following the date of designation of the 

area, the state shall adopt and 

implement all technologically and 

economically feasible control measures 

identified under paragraph (a)(3) of this 

section that are necessary to bring the 

area into attainment by such date. The 

state shall also adopt and implement all 

other technologically and economically 

feasible measures identified under 

paragraph (a)(3) of this section that, 

when considered collectively, would 

advance the attainment date for the area 

by at least 1 year. 

(A) Any control measure identified for 

adoption and implementation under 

this paragraph that can be implemented 

in whole or in part by 4 years after the 

date of designation of the Moderate 

PM2.5 nonattainment area shall be 

considered RACM for the area. Any 

such control measure that is also a 

control technology shall be considered 

RACT for the area. 

(B) Any control measure identified for 

adoption and implementation under 

this paragraph that can only be 

implemented in whole or in part during 

the period beginning 4 years after the 

date of designation of the Moderate 

PM2.5 nonattainment area and the 

beginning of the calendar year 

containing the applicable attainment 

date for the area shall be considered an 

additional reasonable measure for the 

area. 

(ii) If the state demonstrates through 

air quality modeling that the area cannot 

practicably attain the applicable PM2.5

NAAQS by the end of the sixth calendar 

year following the date of designation of 

the area, the state shall adopt all 

technologically and economically 

feasible control measures identified 

under paragraph (a)(3) of this section 

unless the state makes a demonstration 

that one or more such measures, when 

considered collectively, would have 

minimal effect on reducing ambient 

PM2.5 concentrations in the area. 

(A) Any control measure identified for 

adoption and implementation under 

this paragraph that can be implemented 

in whole or in part by 4 years after the 

date of designation of the Moderate 

PM2.5 nonattainment area shall be 

considered RACM for the area. Any 

such control measure that is also a 

control technology shall be considered 

RACT for the area. 

(B) Any control measure identified for 

adoption and implementation under 

this paragraph that can only be 

implemented in whole or in part during 

the period beginning 4 years after the 

date of designation of the Moderate 

PM2.5 nonattainment area through the 

end of the sixth calendar year following 

the date of designation of the area shall 

be considered an additional reasonable 

measure for the area. 

(b) The state shall identify, adopt, and 

implement control measures, including 

control technologies, on sources of 

direct PM2.5 emissions and sources of 

emissions of PM2.5 precursors located 

outside the Moderate PM2.5

nonattainment area, or portion thereof, 

located within the state if doing so is 

necessary to provide for attainment or 

will expedite attainment of the 

applicable PM2.5 NAAQS in such area. 

(c) For control measures on sources of 

direct PM2.5 emissions in the form of 

source emissions limitations, the state 

shall establish such limitations taking 

into account the filterable and 

condensable fractions of such 

emissions. 

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§ 51.1010 Serious area attainment plan 

control strategy requirements. 

[PROPOSED REGULATORY TEXT FOR 

OPTION 1: 

(a) The state shall identify, adopt, and 

implement control measures, including 

control technologies, on sources of 

direct PM2.5 emissions and sources of 

emissions of PM2.5 precursors located in 

any Serious PM2.5 nonattainment area or 

portion thereof located within the state 

to yield a control strategy for the area 

that is more stringent than that 

developed for the area when it was 

classified as Moderate, and consistent 

with the following: 

(1) The state shall identify all sources 

of direct PM2.5 emissions and all sources 

of emissions of PM2.5 precursors in the 

nonattainment area in accordance with 

the emissions inventory requirements of 

§ 51.1008(b); 

(2) The state shall identify all 

potential control measures to reduce 

emissions from all sources of direct 

PM2.5 emissions and sources of 

emissions of PM2.5 precursors in the 

nonattainment area identified under 

paragraph (a)(1) of this section. 

(i) The state shall survey other 

NAAQS nonattainment areas in the U.S. 

and identify any measures not 

previously identified by the state during 

the development of the Moderate area 

attainment plan for the area. 

(ii) The state may elect not to identify 

potential control measures to reduce 

emissions from any sources of a 

particular PM2.5 precursor if the state 

demonstrates that all sources of such 

PM2.5 precursor contribute 

insignificantly to ambient PM2.5

concentrations in the area under 

§ 51.1006. 

(iii) The state may elect not to identify 

potential control measures to reduce 

emissions from sources in any source 

category of direct PM2.5 emissions or 

emissions of PM2.5 precursors 

determined to be a de minimis source 

category under § 51.1007. 

(3) The state may make a 

demonstration that any measure 

identified under paragraph (a)(2) of this 

section is not technologically or 

economically feasible to implement in 

whole or in part by the end of the tenth 

calendar year following the date of 

designation of the area, and may 

eliminate such whole or partial measure 

from further consideration under this 

paragraph. 

(i) For purposes of evaluating the 

technological feasibility of a potential 

control measure, the state may consider 

factors including but not limited to a 

source’s processes and operating 

procedures, raw materials, physical 

plant layout, and potential 

environmental impacts such as 

increased water pollution, waste 

disposal, and energy requirements. 

(ii) For purposes of evaluating the 

economic feasibility of a potential 

control measure, the state may consider 

capital costs, operating and 

maintenance costs, and cost 

effectiveness of the measure. 

(iii) The state shall submit to EPA as 

part of its Serious area attainment plan 

submission a detailed written 

justification for eliminating from further 

consideration any potential control 

measure identified under paragraph 

(a)(2) of this section on the basis of 

technological or economic infeasibility. 

The state shall provide as part of its 

written justification an explanation of 

how its criteria for determining the 

technological and economic feasibility 

of potential control measures under 

paragraphs (a)(3)(i) and (ii) of this 

section are more stringent than its 

criteria for determining the 

technological and economic feasibility 

of potential control measures under 

§ 51.1009(a)(3)(i) and (ii) for the same 

sources in the PM2.5 nonattainment area. 

(4) Except as provided under 

paragraph (a)(3) of this section, the state 

shall adopt and implement all potential 

control measures identified under 

paragraph (a)(2) of this section. 

(i) Any control measure that can be 

implemented in whole or in part by the 

end of the fourth year following the date 

of reclassification of the area to Serious 

shall be considered a best available 

control measure for the area. Any such 

control measure that is also a control 

technology for a stationary source in the 

area shall be considered a best available 

control technology for the area. 

(ii) Any control measure that can be 

implemented in whole or in part 

between the end of the fourth year 

following the date of reclassification of 

the area to Serious and the applicable 

attainment date for the area shall be 

considered an additional feasible 

measure. 

(5) The state shall use air quality 

modeling that meets the requirements of 

§ 51.1011(b) and that accounts for 

emissions reductions estimated due to 

all best available control measures, 

including best available control 

technologies, and additional feasible 

measures identified for sources of direct 

PM2.5 emissions and sources of 

emissions of PM2.5 precursors in the 

area to demonstrate that the area can 

attain the PM2.5 NAAQS as 

expeditiously as practicable but no later 

than the end of the tenth calendar year 

following the date of designation of the 

area, or to demonstrate that the Serious 

PM2.5 nonattainment area cannot 

practicably attain the applicable PM2.5

NAAQS by such date.] 

[PROPOSED REGULATORY TEXT FOR 

OPTION 2: 

(a) The state shall identify, adopt, and 

implement control measures, including 

control technologies, on sources of 

direct PM2.5 emissions and sources of 

emissions of PM2.5 precursors located in 

any Serious PM2.5 nonattainment area or 

portion thereof located within the state 

to yield a control strategy for the area 

that is more stringent than that 

developed for the area when it was 

classified as Moderate, and consistent 

with the following: 

(1) The state shall identify all sources 

of direct PM2.5 emissions and sources of 

emissions of PM2.5 precursors in the 

nonattainment area in accordance with 

the emissions inventory requirements of 

§ 51.1008; 

(2) The state shall identify all 

potential control measures to reduce 

emissions from all sources of direct 

PM2.5 emissions and sources of 

emissions of PM2.5 precursors in the 

nonattainment area identified under 

paragraph (a)(1) of this section. 

(i) The state shall survey other 

NAAQS nonattainment areas in the U.S. 

and identify any measures not 

previously identified by the state during 

the development of the Moderate area 

attainment plan for the area. 

(ii) The state may elect not to identify 

potential control measures to reduce 

emissions from any sources of a 

particular PM2.5 precursor if the state 

demonstrates that all sources of such 

PM2.5 precursor contribute 

insignificantly to ambient PM2.5

concentrations in the area under 

§ 51.1006. 

(3) The state may make a 

demonstration that a measure identified 

under paragraph (a)(2) of this section is 

not technologically or economically 

feasible to implement in whole or in 

part by the end of the tenth calendar 

year following the date of designation of 

the area, and may eliminate such whole 

or partial measure from further 

consideration under this paragraph. 

(i) For purposes of evaluating the 

technological feasibility of a potential 

control measure, the state may consider 

factors including but not limited to a 

source’s processes and operating 

procedures, raw materials, physical 

plant layout, and potential 

environmental impacts such as 

increased water pollution, waste 

disposal, and energy requirements. 

(ii) For purposes of evaluating the 

economic feasibility of a potential 

control measure, the state may consider 

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capital costs, operating and 

maintenance costs, and cost 

effectiveness of the measure. 

(iii) The state shall submit to EPA as 

part of its Serious area attainment plan 

submission a detailed written 

justification for eliminating from further 

consideration any potential control 

measure identified under paragraph 

(a)(2) of this section on the basis of 

technological or economic infeasibility. 

The state shall provide as part of its 

written justification an explanation of 

how its criteria for determining the 

technological and economic feasibility 

of potential control measures under 

paragraphs (a)(3)(i) and (ii) of this 

section are more stringent than its 

criteria for determining the 

technological and economic feasibility 

of potential control measures under 

§ 51.1009(a)(3)(i) and (ii) for the same 

sources in the PM2.5 nonattainment area. 

(4) The state shall use air quality 

modeling that meets the requirements of 

§ 51.1011(b) and that accounts for 

emissions reductions estimated due to 

all technologically and economically 

feasible control measures identified for 

sources of direct PM2.5 emissions and 

sources of emissions of PM2.5 precursors 

in the area to demonstrate that the area 

can attain the applicable PM2.5 NAAQS 

as expeditiously as practicable but no 

later than the end of the tenth calendar 

year following the date of designation of 

the area, or to demonstrate that the 

Serious PM2.5 nonattainment area 

cannot practicably attain the applicable 

PM2.5 NAAQS by such date. 

(5) For a Serious PM2.5 nonattainment 

area which air quality modeling 

demonstrates that the area can attain the 

applicable PM2.5 NAAQS by the end of 

the tenth calendar year following the 

date of designation of the area, the state 

shall adopt and implement all 

technologically and economically 

feasible control measures needed to 

bring the area into attainment by such 

date and additionally any other such 

measures that, when considered 

collectively, would advance the 

attainment date for the area by at least 

1 year. 

(i) Any control measure that can be 

implemented in whole or in part by the 

end of the fourth year following the date 

of reclassification of the area to Serious 

shall be considered a best available 

control measure for the area. Any such 

control measure that is also a control 

technology for a stationary source in the 

area shall be considered a best available 

control technology for the area. 

(ii) Any control measure that can only 

be implemented in whole or in part 

between the end of the fourth year 

following the date of reclassification of 

the area to Serious and the applicable 

attainment date for the area shall be 

considered an additional feasible 

measure.] 

(b) For a Serious PM2.5 nonattainment 

area which air quality modeling 

demonstrates cannot practicably attain 

the applicable PM2.5 NAAQS by the end 

of the tenth calendar year following the 

date of designation of the area, the state 

shall identify, adopt, and implement the 

most stringent control measures that are 

included in the attainment plan for any 

state or are achieved in practice in any 

state, and can be feasibly implemented 

in the area, consistent with the 

following: 

(1) The state shall identify all sources 

of direct PM2.5 emissions and sources of 

emissions of PM2.5 precursors in the 

nonattainment area in accordance with 

the emissions inventory requirements of 

§ 51.1008(b). 

(2) The state shall identify all 

potential control measures to reduce 

emissions from all sources of direct 

PM2.5 emissions and sources of 

emissions of PM2.5 precursors in the 

nonattainment area identified under 

paragraph (a)(1) of this section and not 

otherwise determined to contribute 

insignificantly to ambient PM2.5

concentrations in the area according to 

§ 51.1006 or to be de minimis according 

to § 51.1007. 

(i) The state shall survey other 

NAAQS nonattainment areas in the U.S. 

and identify the most stringent 

measures adopted into any SIP for any 

NAAQS or used in practice to control 

emissions from any non-de minimis 

source categories. 

(ii) The state shall reanalyze any 

measures previously rejected by the 

state during the development of any 

Moderate area or Serious area 

attainment plan control strategy for the 

area, unless the extension request is 

made at the same time as the Serious 

area attainment plan required after the 

area is reclassified in accordance with 

§ 51.1005(b)(5). 

(3) The state may make a 

demonstration that a measure identified 

under paragraph (b)(2) of this section is 

not technologically or economically 

feasible to implement in whole or in 

part by 5 years after the applicable 

attainment date for the area, and may 

eliminate such whole or partial measure 

from further consideration under this 

paragraph. 

(i) For purposes of evaluating the 

technological feasibility of a potential 

control measure, the state may consider 

factors including but not limited to a 

source’s processes and operating 

procedures, raw materials, physical 

plant layout, and potential 

environmental impacts such as 

increased water pollution, waste 

disposal, and energy requirements. 

(ii) For purposes of evaluating the 

economic feasibility of a potential 

control measure, the state may consider 

capital costs, operating and 

maintenance costs, and cost 

effectiveness of the measure. 

(iii) The state shall submit to EPA as 

part of its Serious area attainment plan 

submission a detailed written 

justification for eliminating from further 

consideration any potential control 

measure identified under paragraph 

(b)(2) of this section on the basis of 

technological or economic infeasibility. 

The state shall provide as part of its 

written justification an explanation of 

how its criteria for determining the 

technological and economic feasibility 

of potential control measures under 

paragraphs (b)(3)(i) and (ii) of this 

section are more stringent than its 

criteria for determining the 

technological and economic feasibility 

of potential control measures under 

paragraphs (a)(3)(i) and (ii) of this 

section and under § 51.1009(a)(3)(i) and 

(ii) for the same sources in the PM2.5

nonattainment area. 

(4) Except as provided under 

paragraph (b)(3) of this section, the state 

shall adopt and implement all control 

measures identified under paragraph 

(b)(2) of this section that may achieve 

greater emissions reductions from any 

non-de minimis sources of direct PM2.5

emissions or sources of emissions of 

PM2.5 precursors in the area than 

previously adopted measures have 

achieved and that shall achieve 

attainment as expeditiously as 

practicable but no later than 5 years 

after the applicable attainment date for 

the area. 

(c) The state shall identify, adopt, and 

implement control measures, including 

control technologies, on sources of 

direct PM2.5 emissions and sources of 

emissions of PM2.5 precursors located 

outside the Serious PM2.5 nonattainment 

area or portion thereof, located within 

the state if doing so will expedite 

attainment of the applicable PM2.5

NAAQS within the area. 

(d) For control measures on sources of 

direct PM2.5 emissions in the form of 

source emissions limitations, the state 

shall establish such limitations taking 

into account the filterable and 

condensable fractions of such 

emissions. 

§ 51.1011 Attainment demonstration and 

modeling requirements. 

(a) Nonattainment areas initially 

classified as Moderate. The attainment 

demonstration due to EPA as part of any 

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Moderate area attainment plan required 

under § 51.1003(a) shall meet all of the 

following criteria: 

(1) The attainment demonstration 

shall show the projected attainment date 

for the Moderate nonattainment area 

that is as expeditious as practicable in 

accordance with the requirements of 

§ 51.1004(a)(1). 

(2) The attainment demonstration 

shall meet the requirements of 

Appendix W of this part and shall 

include inventory data, modeling 

results, and emission reduction analyses 

on which the state has based its 

projected attainment date. 

(3) The base year for the emissions 

inventory required for an attainment 

demonstration under this paragraph 

shall be one of the 3 years used for 

designations or another technically 

appropriate inventory year if justified by 

the state in the plan submission. 

(4) The control strategies modeled as 

part of the attainment demonstration 

shall be consistent with the following as 

applicable: 

(i) For a Moderate area that can 

demonstrate attainment of the 

applicable PM2.5 NAAQS no later than 

the end of the sixth calendar year 

following the date of designation of the 

area with the implementation of RACM 

and RACT and additional reasonable 

measures, the control strategies modeled 

as part of the attainment demonstration 

shall be consistent with control strategy 

requirements under § 51.1009(a). 

(ii) For a Moderate area that cannot 

practicably attain the applicable PM2.5

NAAQS by the end of the sixth calendar 

year following the date of designation of 

the area with the implementation of 

RACM and RACT and additional 

reasonable measures, the control 

strategies modeled as part of the 

attainment demonstration shall be 

consistent with control strategy 

requirements under § 51.1009(b). 

(5) The attainment demonstration and 

supporting air quality modeling should 

be consistent with the most current 

version of EPA’s PM2.5 attainment 

demonstration modeling guidance. 

(6) Required time frame for obtaining 

emissions reductions. For each 

Moderate nonattainment area, the 

attainment plan must provide for 

implementation of all control measures 

needed for attainment as expeditiously 

as practicable. All control measures in 

the attainment demonstration must be 

implemented no later than the 

beginning of the year prior to the 

attainment date, notwithstanding RACM 

implementation deadline requirements 

in § 51.1009. 

(b) Nonattainment areas reclassified 

as Serious. The attainment 

demonstration due to EPA as part of a 

Serious area attainment plan required 

under § 51.1003(b) shall meet all of the 

following criteria: 

(1) The attainment demonstration 

shall show the projected attainment date 

for the Serious nonattainment area that 

is as expeditious as practicable in 

accordance with the requirements of 

§ 51.1004(a)(2). 

(2) The attainment demonstration 

shall meet the requirements of 

Appendix W of this part and shall 

include inventory data, modeling 

results, and emission reduction analyses 

on which the state has based its 

projected attainment date. 

(3) The base year for the emissions 

inventories required for attainment 

demonstrations under this paragraph 

shall be one of the 3 years used for 

designations or another technically 

appropriate inventory year if justified by 

the state in the plan submission. 

(4) The control strategies modeled as 

part of the attainment demonstration 

shall be consistent with the following as 

applicable: 

(i) For a Serious area that can 

demonstrate attainment of the 

applicable PM2.5 NAAQS no later than 

the end of the tenth calendar year 

following the date of designation of the 

area with the implementation of best 

available control measures (BACM), 

including best available control 

technologies (BACT), and additional 

feasible measures, the control strategies 

modeled as part of the attainment 

demonstration shall be consistent with 

control strategy requirements under 

§ 51.1010(a). 

(ii) For a Serious area that cannot 

practicably attain the applicable PM2.5

NAAQS by the end of the tenth calendar 

year following the date of designation of 

the area with the implementation of best 

available control measures (BACM), 

including best available control 

technologies (BACT), and additional 

feasible measures, the control strategies 

modeled as part of the attainment 

demonstration shall be consistent with 

control strategy requirements under 

§ 51.1010(b). 

(5) The attainment demonstration and 

supporting air quality modeling should 

be consistent with the most current 

version of EPA’s PM2.5 attainment 

demonstration modeling guidance. 

(6) Required timeframe for obtaining 

emissions reductions. For each Serious 

nonattainment area, the attainment plan 

must provide for implementation of all 

control measures needed for attainment 

as expeditiously as practicable. All 

control measures must be implemented 

no later than the beginning of the year 

prior to the attainment date, 

notwithstanding BACM implementation 

deadline requirements in § 51.1010. 

§ 51.1012 Reasonable further progress 

(RFP) requirements. 

(a) Consistent with CAA section 

172(c)(2), the state shall submit in each 

attainment plan for a PM2.5

nonattainment area a plan that 

demonstrates that the area will achieve, 

on an annual basis, reasonable further 

progress (RFP) in reducing emissions of 

direct PM2.5 and any PM2.5 precursors 

from sources in the area that the state 

has determined are necessary to be 

controlled in order for the area to attain 

the applicable PM2.5 NAAQS as 

expeditiously as practicable. The RFP 

plan shall include all of the following: 

(1) A description of each control 

measure adopted by the state to satisfy 

the control strategy requirements of 

§ 51.1009 (for Moderate area attainment 

plans) or § 51.1010 (for Serious area 

attainment plans), as appropriate, and 

the projected reductions in direct PM2.5

emissions and emissions of PM2.5

precursors that each control measure 

will achieve by the projected attainment 

date for the area. 

(2) A schedule for implementing the 

measures described in paragraph (a)(1) 

of this section. 

(3) An analysis that demonstrates that 

by the end of the calendar year for each 

milestone date for the area determined 

in accordance with § 51.1013(a), 

emissions will be at a level that reflects 

generally linear progress in reducing 

emissions on an annual basis between 

the base year and the attainment year. 

(b) Except as provided under 

paragraph (c) of this section, the RFP 

analysis required under paragraph (a)(3) 

of this section shall include, at a 

minimum, a benchmark RFP analysis, 

and may include an alternative RFP 

analysis, consistent with the following: 

(1) The base year for the RFP 

emissions inventory shall be one of the 

3 years used for designations or another 

technically appropriate inventory year if 

justified by the state in the plan 

submission. 

(2) In the benchmark RFP analysis, 

the state must identify direct PM2.5

emissions and PM2.5 precursors 

regulated in the control strategy for the 

area and specify target emission 

reduction levels to be achieved during 

the milestone years. In developing the 

benchmark RFP analysis, the state must 

develop emissions inventory 

information for the area and calculate 

the following: 

(i) For direct PM2.5 emissions and 

each PM2.5 precursor addressed in the 

control strategy, the full implementation 

reduction is calculated by subtracting 

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the full implementation inventory from 

the base year inventory. 

(ii) The ‘‘milestone date fraction’’ is 

the ratio of the number of years from the 

base year to the milestone year divided 

by the number of years from the 

baseline year to the full implementation 

year. 

(iii) For direct PM2.5 emissions and 

each PM2.5 attainment plan precursor 

addressed in the attainment strategy, a 

benchmark emission reduction is 

calculated by multiplying the full 

implementation reduction by the 

milestone date fraction. 

(iv) The benchmark emission level in 

the milestone year is calculated for 

direct PM2.5 emissions and each PM2.5

precursor by subtracting the benchmark 

emission reduction from the base year 

emission level. 

(v) In comparing inventories between 

the base year and future years for direct 

PM2.5 emissions and emissions of PM2.5

precursors, the inventories must be 

derived for sources located within the 

nonattainment area. 

(vi) For purposes of establishing 

motor vehicle emissions budgets for 

transportation conformity purposes (as 

required in 40 CFR part 93) for a PM2.5

nonattainment area, the state shall 

include in its RFP submittal an 

inventory of on-road mobile source 

emissions in the nonattainment area for 

each milestone year. 

(3) The RFP analysis must 

demonstrate that emissions for the 

milestone year are either: 

(i) At levels that are roughly 

equivalent to the benchmark emission 

levels for direct PM2.5 emissions and 

emissions of PM2.5 precursors addressed 

in the attainment plan; or 

(ii) At levels included in an 

alternative RFP analysis that projects 

generally equivalent improvement in air 

quality by the milestone year as would 

be achieved under the benchmark RFP 

plan. 

(iii) The equivalence of an alternative 

RFP analysis to the corresponding 

benchmark analysis must be determined 

by comparing the expected air quality 

changes from the two analyses at the 

design value monitor location. This 

comparison must use the information 

developed for the attainment plan to 

assess the relationship between 

emissions reductions of the direct PM2.5

emissions and emissions of PM2.5

precursors addressed in the control 

strategy for the area and the ambient air 

quality improvement. 

(c) For an attainment plan submittal 

that demonstrates that a Moderate PM2.5

nonattainment area cannot practicably 

attain the applicable PM2.5 NAAQS by 

the end of the sixth calendar year 

following the effective date of 

designation of the area with the 

implementation of control measures as 

required under § 51.1009, the RFP 

analysis required under paragraph (a)(3) 

of this section shall demonstrate 

generally linear emissions reductions in 

direct PM2.5 emissions and emissions of 

PM2.5 precursors projected from the 

Moderate area control strategy 

determined according to § 51.1008 for 

each milestone year. 

(d) For a multi-state or multijurisdictional nonattainment area, the 

RFP plans for each state represented in 

the nonattainment area shall 

demonstrate RFP on the basis of 

common multi-state inventories. The 

states or jurisdictions within which the 

area is located must provide a 

coordinated RFP plan. Each state in a 

multi-state nonattainment area must 

ensure that the sources within its 

boundaries comply with enforceable 

emission levels and other requirements 

that in combination with the reductions 

planned in other state(s) within the 

nonattainment area will provide for 

attainment as expeditiously as 

practicable and demonstrate RFP 

consistent with these regulations. 

§ 51.1013 Quantitative milestone 

requirements. 

(a) Consistent with CAA section 

189(c)(1), the state must submit in each 

attainment plan for a PM2.5

nonattainment area specific quantitative 

milestones that demonstrate reasonable 

further progress toward attainment of 

the applicable PM2.5 NAAQS in the area 

and that meet the following 

requirements: 

(1) Nonattainment areas initially 

classified as Moderate. 

(i) For an attainment plan submittal 

that demonstrates that a Moderate PM2.5

nonattainment area can attain the 

applicable PM2.5 NAAQS by the end of 

the sixth calendar year following the 

date of designation of the area or earlier 

with the implementation of control 

measures as required under § 51.1009, 

the state shall submit quantitative 

milestones to be achieved no later than 

a milestone date of 4.5 years from the 

date of designation of the area. 

(ii) For an attainment plan submittal 

that demonstrates that a Moderate PM2.5

nonattainment area cannot practicably 

attain the applicable PM2.5 NAAQS by 

the end of the sixth calendar year 

following the effective date of 

designation of the area with the 

implementation of control measures as 

required under § 51.1009, the state shall 

submit quantitative milestones to be 

achieved no later than milestone dates 

of 4.5 years and 7.5 years, respectively, 

from the date of designation of the area. 

(iii) The state shall select quantitative 

milestones that coincide with the 

milestone due dates specified in 

paragraphs (a)(1)(i) and (ii) of this 

section, as applicable, and that provide 

for objective evaluation of emissions 

reductions and/or air quality 

improvements representing progress 

toward attainment of the applicable 

PM2.5 NAAQS in the area, including, at 

a minimum, a milestone that all control 

measures identified and adopted as 

RACM and RACT for the area will be 

fully implemented within 4 years after 

the date of designation. 

(2) Nonattainment areas reclassified to 

Serious. 

(i) For an attainment plan submittal 

that demonstrates that a Serious PM2.5

nonattainment area can attain a 

particular PM2.5 NAAQS by the end of 

the tenth calendar year following the 

effective date of designation of the area 

with the implementation of control 

measures as required under 

§ 51.1010(a), the state shall submit 

quantitative milestones to be achieved 

no later than milestone dates of 7.5 

years and 10.5 years, respectively, from 

the date of designation of the area. 

(ii) For an attainment plan submittal 

that demonstrates that a Serious PM2.5

nonattainment area cannot practicably 

attain a particular PM2.5 NAAQS by the 

end of the tenth calendar year following 

the date of designation of the area with 

the implementation of control measures 

required under § 51.1010(a), the state 

shall submit quantitative milestones to 

be achieved no later than milestone 

dates of 7.5 years, 10.5 years, and 13.5 

years, respectively, from the date of 

designation of the area. 

(iii) The state shall select quantitative 

milestones that coincide with the 

milestone due dates specified in 

paragraphs (a)(2)(i) and (ii) of this 

section, as applicable, and that provide 

for objective evaluation of emissions 

reductions and/or air quality 

improvements representing progress 

toward attainment of the applicable 

PM2.5 NAAQS in the area, including, at 

a minimum, a milestone that all control 

measures identified and adopted as 

BACM and BACT for the area will be 

fully implemented within 4 years of 

reclassification of the area to Serious. 

(3) Serious areas that fail to attain by 

the applicable Serious area attainment 

date. For an attainment plan submittal 

for a Serious area that failed to attain a 

particular PM2.5 NAAQS by the 

applicable Serious area attainment date 

and is therefore subject to the 

requirements of CAA section 189(d) and 

§ 51.1003(c), the state shall submit 

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Federal Register / Vol. 80, No. 55 / Monday, March 23, 2015 / Proposed Rules 15473 

quantitative milestones to be achieved 

no later than a milestone date of 13.5 

years from the date of designation of the 

area and every 3 years thereafter until 

the projected attainment date for the 

area. The state shall select quantitative 

milestones that coincide with the 

milestone due dates for the area, and 

that provide for objective evaluation of 

emissions reductions and/or air quality 

improvements representing progress 

toward attainment of the applicable 

PM2.5 NAAQS in the area. 

(b) Not later than 90 days after the 

date on which a milestone applicable to 

a PM2.5 nonattainment area occurs, each 

state in which all or part of such area 

is located shall submit to the 

Administrator a milestone report that 

contains all of the following: 

(1) A certification by the Governor or 

Governor’s designee that the state’s 

attainment plan control strategy, 

including the RFP plan, is being 

implemented as described in the 

applicable attainment plan; 

(2) A technical demonstration, 

including calculations, to document 

completion statistics for appropriate 

milestones and to demonstrate that the 

quantitative milestones have been 

satisfied and how the emission 

reductions achieved to date compare to 

those required or scheduled to meet 

RFP; 

(3) An air quality screening analysis 

to determine if measured air quality 

progress is consistent with the expected 

air quality improvement target 

correlated with the RFP emissions 

reductions for the previous 3-year 

period calculated in accordance with 

§ 51.1012; 

(4) An evaluation of whether the area 

will attain the applicable PM2.5 NAAQS 

by the projected attainment date for the 

area; and, 

(5) A description and schedule for any 

remedial actions the state has taken or 

will take to address any failure to meet 

a quantitative milestone, including the 

implementation status of contingency 

measures required under 

§ 51.1014(a)(1)(i) for failing to meet RFP. 

(c) In the event a state fails to submit 

a milestone report that meets the 

requirements of paragraph (b) of this 

section by the due date or the 

Administrator determines that the state 

failed to meet a milestone by the 

milestone date, the state shall submit an 

attainment plan revision within 9 

months of the missed due date or the 

Administrator’s determination of the 

state’s failure to meet a milestone that 

assures that the state will achieve the 

next milestone or attain the applicable 

NAAQS by the applicable date, 

whichever is earlier. 

§ 51.1014 Contingency measure 

requirements. 

(a) The state must include as part of 

each attainment plan submitted under 

this subpart for a PM2.5 nonattainment 

area specific contingency measures that 

shall take effect with minimal further 

action by the state or EPA within 60 

days of the Administrator making a 

determination that the area has failed to 

meet either of the following conditions: 

(1) The area failed to meet the RFP 

requirements of § 51.1012 or to submit 

a milestone report due to EPA in 

accordance with § 51.1013(b); or, 

(2) The area failed to attain the 

applicable PM2.5 NAAQS by the 

applicable attainment date. 

(b) The contingency measures 

adopted as part of a PM2.5 attainment 

plan shall meet all of the following 

requirements: 

(1) The contingency measures shall 

consist of control measures that are not 

otherwise included in the control 

strategy for the area. 

(2) The contingency measures shall 

provide for emissions reductions 

approximately equivalent to 1 year’s 

worth of reductions needed for RFP, 

based on the overall level of reductions 

needed to demonstrate attainment 

divided by the number of years from the 

base year to the attainment year, or 

approximately equivalent to 1 year’s 

worth of air quality improvement or 

emissions reductions proportional to the 

overall amount of air quality 

improvement or emissions reductions to 

be achieved by the area’s attainment 

plan. 

(c) The attainment plan submission 

shall contain a description of the 

specific trigger mechanisms for the 

contingency measures and specify a 

schedule for implementation. 

§ 51.1015 Clean data requirements. 

(a) Nonattainment areas initially 

classified as Moderate. Upon a 

determination by EPA that a Moderate 

PM2.5 nonattainment area has attained 

the PM2.5 NAAQS, the requirements for 

the state to submit an attainment 

demonstration, provisions 

demonstrating that reasonably available 

control measures, including reasonably 

available control technology for 

stationary sources, shall be 

implemented no later than 4 years 

following the date of designation of the 

area, reasonable further progress plan, 

and contingency measures for the area 

shall be suspended until such time as: 

(1) The area is redesignated to 

attainment, after which such 

requirements are permanently 

discharged; or, 

(2) EPA determines that the area has 

re-violated the PM2.5 NAAQS, at which 

time the state shall submit such 

attainment plan elements for the 

Moderate nonattainment area by a 

future date to be determined by EPA 

and announced through publication in 

the Federal Register at the time EPA 

determines the area is violating the 

PM2.5 NAAQS. 

(b) Nonattainment areas reclassified 

as Serious. Upon a determination by 

EPA that a Serious PM2.5 nonattainment 

area has attained the PM2.5 NAAQS, the 

requirements for the state to submit an 

attainment demonstration, reasonable 

further progress plan, and contingency 

measures for the area shall be 

suspended until such time as: 

(1) The area is redesignated to 

attainment, after which such 

requirements are permanently 

discharged; or, 

(2) EPA determines that the area has 

re-violated the PM2.5 NAAQS, at which 

time the state shall submit such 

attainment plan elements for the 

Moderate nonattainment area by a 

future date to be determined by EPA 

and announced through publication in 

the Federal Register at the time EPA 

determines the area is violating the 

PM2.5 NAAQS. 

[ALTERNATIVE PROPOSED 

REGULATORY TEXT: 

(b) Nonattainment areas reclassified 

as Serious. Upon a determination by 

EPA that a Serious PM2.5 nonattainment 

area has attained the PM2.5 NAAQS, the 

requirements for the state to submit an 

attainment demonstration, provisions 

demonstrating that best available 

control measures, including best 

available control technology for 

stationary sources, shall be 

implemented no later than 4 years 

following the date of reclassification of 

the area to Serious, reasonable further 

progress plan, and contingency 

measures for the area shall be 

suspended until such time as: 

(1) The area is redesignated to 

attainment, after which such 

requirements are permanently 

discharged; or, 

(2) EPA determines that the area has 

re-violated the PM2.5 NAAQS, at which 

time the state shall submit such 

attainment plan elements for the Serious 

nonattainment area by a future date to 

be determined by EPA and announced 

through publication in the Federal 

Register at the time EPA determines the 

area is violating the PM2.5 NAAQS.] 

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15474 Federal Register / Vol. 80, No. 55 / Monday, March 23, 2015 / Proposed Rules 

PART 93—DETERMINING 

CONFORMITY OF FEDERAL ACTIONS 

TO STATE OR FEDERAL 

IMPLEMENTATION PLANS 

■ 7. The authority citation for part 93 

continues to read as follows: 

Authority: 42 U.S.C. 7401–7671q. 

Subpart B—Determining Conformity of 

General Federal Actions to State or 

Federal Implementation Plans 

■ 8. In § 93.153, revise paragraphs (b)(1) 

and (2) to read as follows: 

§ 93.153 Applicability. 

* * * * * 

(b) * * * 

(1) For purposes of paragraph (b) of 

this section the following rates apply in 

nonattainment areas (NAA’s): 

Tons/year 

Ozone (VOC’s or NOX): 

Serious NAA’s .......................................................................................................................................................................... 50 

Severe NAA’s ........................................................................................................................................................................... 25 

Extreme NAA’s ......................................................................................................................................................................... 10 

Other ozone NAA’s outside an ozone transport region ........................................................................................................... 100 

Other ozone NAA’s inside an ozone transport region: 

VOC .......................................................................................................................................................................................... 50 

NOX .......................................................................................................................................................................................... 100 

Carbon Monoxide: All maintenance areas ............................................................................................................................... 100 

SO2 or NO2: All NAA’s ............................................................................................................................................................. 100 

PM10: 

Moderate NAA’s ....................................................................................................................................................................... 100 

Serious NAA’s .......................................................................................................................................................................... 70 

PM2.5 (direct emissions, SO2, NOX, VOC, and ammonia): 

Moderate NAA’s ....................................................................................................................................................................... 100 

Serious NAA’s .......................................................................................................................................................................... 70 

Pb: All NAA’s ............................................................................................................................................................................ 25 

(2) For purposes of paragraph (b) of 

this section the following rates apply in 

maintenance areas: 

Tons/year 

Ozone (NOX, SO2 or NO2): 

All maintenance areas .............................................................................................................................................................. 100 

Ozone (VOC’s): 

Maintenance areas inside an ozone transport region .............................................................................................................. 50 

Maintenance areas outside an ozone transport region ........................................................................................................... 100 

Carbon monoxide: All maintenance areas ............................................................................................................................... 100 

PM10: All maintenance areas ................................................................................................................................................... 100 

PM2.5 (direct emissions, SO2, NOX, VOC, and ammonia) ....................................................................................................... 100 

All maintenance areas .............................................................................................................................................................. 100 

Pb: All maintenance areas ....................................................................................................................................................... 25 

* * * * * 

[FR Doc. 2015–06138 Filed 3–20–15; 8:45 am] 

BILLING CODE 6560–50–P 

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