Vol. 81 Wednesday, 

No. 164 August 24, 2016 

Part II 

Environmental Protection Agency 

40 CFR Parts 50, 51, and 93 

Fine Particulate Matter National Ambient Air Quality Standards: State 

Implementation Plan Requirements; Final Rule 

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58010 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

ENVIRONMENTAL PROTECTION 

AGENCY 

40 CFR Parts 50, 51, and 93 

[EPA–HQ–OAR–2013–0691; FRL–9946–36– 

OAR] 

RIN 2060–AQ48 

Fine Particulate Matter National 

Ambient Air Quality Standards: State 

Implementation Plan Requirements 

AGENCY: Environmental Protection 

Agency (EPA). 

ACTION: Final rule. 

SUMMARY: The Environmental Protection 

Agency (EPA) is finalizing 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 document provides details on 

meeting 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 rule clarifies the 

specific attainment planning 

requirements that 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 document the EPA 

is revoking the 1997 primary annual 

standard for areas designated as 

attainment for that standard because the 

EPA revised the primary annual 

standard in 2012. The EPA first 

established the PM2.5 NAAQS in 1997, 

completed a review and revision of 

those standards in 2006, and most 

recently completed a review and 

revision of the PM2.5 NAAQS on 

December 14, 2012. 

DATES: This final rule is effective on 

October 24, 2016. 

ADDRESSES: The EPA has established a 

docket for this action, identified by 

Docket ID No. EPA–HQ–OAR–2013– 

0691. All documents in the docket are 

listed in the http://www.regulations.gov 

Web site. Although listed in the index, 

some information is not publicly 

available, e.g., Confidential Business 

Information or other information whose 

disclosure is restricted by statute. 

Certain other material, such as 

copyrighted material, is not placed on 

the Internet and will be publicly 

available only in hard copy. Publicly 

available docket materials are available 

either electronically in http://

www.regulations.gov. 

FOR FURTHER INFORMATION CONTACT: For 

general information on this rule, contact 

Mr. Rich Damberg, Office of Air Quality 

Planning and Standards, U.S. EPA, by 

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

damberg.rich@epa.gov; or Mr. Patrick 

Lessard, Office of Air Quality Planning 

and Standards, U.S. EPA, by phone at 

(919) 541–5383 or by email at 

lessard.patrick@epa.gov. For 

information on the Information 

Collection Request (ICR), contact Mr. 

Butch Stackhouse, Office of Air Quality 

Planning and Standards, U.S. EPA, by 

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

stackhouse.butch@epa.gov. 

SUPPLEMENTARY INFORMATION: 

I. General Information 

A. Preamble Glossary of Terms and 

Acronyms 

The following are abbreviations of 

terms used in the preamble. 

AERR Air Emissions Reporting 

Requirements 

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. Entities Affected by This Rule 

Entities potentially affected directly 

by this final 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 final 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). Parties affected by the 

conformity-related elements include 

state and local transportation and air 

quality agencies, metropolitan planning 

organizations (MPOs), and all federal 

agencies including the U.S. Department 

of Transportation, the U.S. Department 

of Defense, the U.S. Department of 

Interior and the U.S. Department of 

Agriculture. Others potentially affected 

indirectly by this final 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. 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58011 

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://www3.epa.gov/ttn/naaqs/ 

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

C. Obtaining 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://www3.epa.gov/

airquality/particlepollution/

actions.html. 

D. Organization of This Federal Register 

Document 

The information presented in this 

document is organized as follows: 

I. General Information 

A. Preamble Glossary of Terms and 

Acronyms 

B. Entities Affected by This Rule 

C. Obtaining a Copy of This Document and 

Other Related Information 

D. Organization of This Federal Register 

Document 

II. Background 

A. Introduction 

B. Overview of PM2.5 NAAQS and 

Implementation 

C. Atmospheric Chemistry of PM2.5 and Its 

Precursors 

III. Requirements With Respect to the 

Treatment of PM2.5 Precursors in 

Attainment Plans and the NNSR Program 

A. Background 

B. Summary of Proposal 

C. Final Rule 

IV. Requirements for PM2.5 Moderate 

Nonattainment Area 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. Reclassification of a PM2.5 Moderate 

Nonattainment Area to Serious 

A. Discretionary Authority 

B. Mandatory Duty 

VI. Requirements for PM2.5 Serious 

Nonattainment Area 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. Requirements Under CAA Section 189(d) 

for PM2.5 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. NNSR Requirements for PM2.5

Nonattainment Areas 

A. Background 

B. What are the final NNSR requirements 

for PM2.5? 

C. Transition Provisions for Major Source 

Permitting in PM2.5 Nonattainment Areas 

IX. Other Requirements and Considerations 

for 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. Multi-Pollutant Considerations 

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. Revocation of the 1997 Primary Annual 

PM2.5 NAAQS 

A. Background 

B. History of Revocation of Other NAAQS 

C. Requirements for Revocation and 

Related Anti-Backsliding Requirements 

for the 1997 Primary Annual PM2.5

NAAQS 

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 (PRA) 

C. Regulatory Flexibility Act (RFA) 

D. Unfunded Mandates Reform Act 

(UMRA) 

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. Congressional Review Act (CRA) 

L. Determination Under Section 307(d) 

M. Judicial Review 

XIII. Statutory Authority 

II. Background 

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 the 

following: 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 PM 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 ammonium nitrate and ammonium 

sulfate). 

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 the 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/ 

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2 78 FR 3086 (January 15, 2013). 

3This final rulemaking applies to implementation 

of 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 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://www3.epa.gov/ttn/

naaqs/standards/pm/s_pm_2007_ria.html. 

5 Ibid. 

6 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. 

7When 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. 

8See 76 FR 48208 (August 8, 2011). 9 62 FR 38652 (July 18, 1997). 

10For a complete summary of legal challenges 

and related court decisions on the PM NAAQS, see 

generally 78 FR 3086 (January 15, 2013). 

11 70 FR 944 (January 5, 2005). 

12 72 FR 20583 (April 25, 2007). 

13 73 FR 28231 (May 16, 2008). 

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 implementation of the PM2.5 NAAQS, 

it should be noted that in December 

2012, the EPA also did not revise the 

level or form of the primary and 

secondary 24-hour PM10 NAAQS, 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. Overview of PM2.5 NAAQS and 

Implementation 

1. General Background 

Sections 108 and 109 of the Clean Air 

Act (CAA or Act) govern the 

establishment, review and revision, as 

appropriate, of the 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 CAA also 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 pollution control agencies (‘‘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 a timely manner in each 

nonattainment area, consistent with the 

requirements of the CAA. The EPA often 

assists states by promulgating 

regulations or providing guidance for 

meeting implementation requirements 

and by providing technical tools, 

including information on control 

measures.6 7

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 

states by achieving emissions reductions 

from certain categories of sources 

nationwide, which can help with local 

attainment needs in a given 

nonattainment area. The EPA also has 

authority to provide funding, technical 

assistance, and guidance to states to 

support implementation of the NAAQS. 

In addition, the EPA has authority to 

address 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.8 In addition, the EPA has the 

authority and responsibility to review 

and take action to approve or 

disapprove attainment plans submitted 

by states based upon whether they meet 

applicable statutory and regulatory 

requirements and to initiate the process 

for imposition of sanctions and/or issue 

federal implementation plans (FIPs) 

when states fail to fulfill their CAA 

obligations. 

2. History of PM2.5 NAAQS 

Implementation 

The EPA first promulgated annual 

and 24-hour NAAQS for PM2.5 in July 

1997.9 Prior to that time, the EPA had 

addressed ambient PM 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 2002.10 The EPA 

subsequently promulgated designations 

for the 1997 PM2.5 NAAQS nationwide, 

designating a number of areas as 

nonattainment for the 1997 PM2.5

NAAQS, effective April 2005.11 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’’).12 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’’).13 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 

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14 71 FR 61144 (October 17, 2006). 

15 74 FR 58688 (November 13, 2009). 

16Memorandum of March 2, 2012 (withdrawn 

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

Office of Air Quality Planning and Standards, to the 

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://

www3.epa.gov/ttn/naaqs/aqmguide/collection/cp2/

20120302_page_implement_guidance_2006-24-hr_

pm2.5_naaqs.pdf. 

17 77 FR 38890 (June 29, 2012). 

18 78 FR 3086 (January 15, 2013). 

19Spatial averaging of monitored ambient air 

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

monitoring regulations which had the potential for 

masking particularly high PM2.5 concentrations at 

certain monitored locations within nonattainment 

areas. 

20 71 FR 61144 (October 17, 2006). 

21 General information regarding the health 

effects associated with PM2.5 exposures is available 

at: http://www3.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. 

22NRDC v. EPA, 706 F.3d 428 (D.C. Cir. 2013). 

nonattainment areas for the PM2.5

NAAQS were subject solely to the 

general attainment 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 the 

NAAQS for PM, and in particular the 

EPA revised the 24-hour PM2.5

standards.14 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 2009.15 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.16 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, 2012.17 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.18 The EPA 

also eliminated spatial averaging as part 

of the form of the annual standard to 

avoid potential disproportionate 

impacts on at-risk populations.19 The 

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.20 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.21 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 D.C. 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’’).22 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 thus 

implementation of the PM2.5 NAAQS is 

subject to the same statutory 

requirements as the PM10 NAAQS. 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 in nonattainment areas. 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’s 2012 guidance for attainment 

plans for the 2006 PM2.5 NAAQS 

premised solely upon subpart 1 

requirements was no longer appropriate. 

The EPA issued a notice of proposed 

rulemaking (NPRM) on March 23, 2015 

(80 FR 15340) titled, ‘‘Fine Particulate 

Matter National Ambient Air Quality 

Standards: State Implementation Plan 

Requirements’’ (PM2.5 SIP Requirements 

Rule) to meet a number of objectives. 

This final rule accomplishes those 

objectives. It clarifies how states should 

meet the statutory SIP requirements that 

apply to areas designated nonattainment 

for any PM2.5 NAAQS under subparts 1 

and 4. It does so by establishing 

regulatory requirements and providing 

guidance 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. In addition, this 

action responds to the D.C. Circuit’s 

remand of the 2007 PM2.5

Implementation Rule and the 2008 

PM2.5 NSR Rule. As a result, the 

requirements of the rule will also govern 

future actions associated with states’ 

ongoing implementation efforts for the 

1997 and 2006 PM2.5 NAAQS. 

The public comment period for the 

proposed PM2.5 SIP Requirements Rule 

closed on May 29, 2015, and the EPA 

received 56 comments during that 

period. The preamble to this final rule 

includes discussion of the most 

significant comments received on the 

proposal and how the EPA considered 

them in developing the agency’s final 

action concerning the specific 

nonattainment planning requirements. 

The Response to Comments document 

that accompanies this final rule 

provides more detailed responses to the 

significant comments received. The 

public comments received on the NPRM 

and the EPA’s Response to Comment 

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58014 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

23The 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. 

24Certain commercial or industrial activities 

involving high temperature processes (e.g., fuel 

combustion, metal processing, cooking operations) 

emit gaseous pollutants into the ambient air that 

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. 

25Seinfeld J.H. and Pandis S.N., 2006. 

Atmospheric Chemistry and Physics: From Air 

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

New York. 

26U.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. 

document are posted in the docket at 

http://www.regulations.gov (Docket ID 

No. EPA–HQ–OAR–2013–0691). 

C. 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. 

As noted earlier, the term PM2.5 refers 

to particles of solid and liquid material 

less than 2.5 microns in aerodynamic 

diameter.23 ‘‘Primary’’ PM2.5 is emitted 

directly from emissions sources or 

activities, such as from diesel fuel 

combustion, wood burning, 

construction activities, and unpaved 

roads, and it includes both filterable and 

condensable particles.24 ‘‘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. To illustrate the types of 

sources that emit relevant pollutants, 

Table 1 provides National Emissions 

Inventory (NEI) data for 2011 that 

represent nonattainment area 

anthropogenic and wildfire 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 PM2.5 NONATTAINMENT AREAS a

[In tons/year] 

Source: 2011 National Emissions Inventory (Version 2) b

Category Direct PM2.5 SO2 NOX VOC NH3

Fuel combustion, electric generating utilities (EGUs) ......... 11,339 324,658 82,509 3,001 3,572 

Fuel combustion, industrial .................................................. 10,286 23,762 57,690 6,251 892 

Fuel combustion, other ........................................................ 29,582 8,224 60,636 32,320 8,819 

Chemical and allied products .............................................. 1,504 1,329 1,056 2,828 685 

Metals processing ................................................................ 4,037 19,490 4,543 4,586 130 

Petroleum and related industries ......................................... 1,534 7,273 3,775 18,830 215 

Other industrial processes ................................................... 24,168 8,466 22,599 24,928 1,094 

Solvent utilization ................................................................. 1,089 39 56 242,022 68 

Storage and transport .......................................................... 3,420 628 7,067 55,410 3,684 

Waste disposal and recycling .............................................. 4,143 830 4,130 16,492 19,389 

Onroad mobile ..................................................................... 21,073 2,598 540,800 234,136 17,525 

Offroad mobile ..................................................................... 13,660 5,874 239,169 152,504 150 

Miscellaneous (includes emissions from fire,c dust and 

some agricultural operations) ........................................... 158,565 7,368 13,734 248,835 236,577 

Total .............................................................................. 284,401 410,540 1,037,764 1,042,144 292,800 

aThere were 33 areas designated as nonattainment for the 1997, 2006, or 2012 PM2.5 NAAQS as of June 6, 2016. These areas were comprised of 67 whole or partial counties. The emissions data in this table represents whole county emissions for the 67 counties because such data 

is readily available in EPA databases. Actual emissions totals for the 33 nonattainment areas in aggregate would be somewhat lower because 

some nonattainment areas include partial counties. bFor 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. cEmissions from fire include wildfire, prescribed fire, and agricultural burning. 

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).25 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.26

Section II.C.3.d of this preamble 

provides more details on 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.C.4 of this preamble 

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 

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27Appel, 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. 

28U.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: 

https://www.epa.gov/sites/production/files/2015- 

07/documents/2008report.pdf. 

29Carlton, 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. 

30Pandis S.N., Harley R.A., Cass G.R., and 

Seinfeld J.H., 1992. Secondary Organic Aerosol 

Formation and Transport, Atmospheric 

Environment, 26, 2266–82. 

31Carlton, 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. 

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.C 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 include 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.27

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 currently coming from other 

industrial sources, such as oil refining 

and pulp and paper production.28 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 

electric generating units (EGUs), 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 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.29

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 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 

percentage of PM2.5 in the summer than 

in the winter.30

Anthropogenic sources of VOC 

include mobile sources, petrochemical 

manufacturing, oil and gas emissions, 

fire emissions, and solvents.31 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 

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32Seinfeld, J.H. and Pandis, S.N. (1998), 

Atmospheric Chemistry and Physics: From Air 

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

New York. 

33NARSTO, 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. 34Carlton, 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. 

35The 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. 

36Reff and Rao, Memo to the docket, 2013. 

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. 

Catalytic converters installed on lightduty gasoline vehicles are designed to 

convert NOX to nitrogen (N2); however, 

some ammonia is formed as a secondary 

product and emitted 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.32 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.33

f. Role of NOX in 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 to enhance the secondary 

formation of organic compounds that 

make up SOA. NOX is thus involved in 

all secondary PM chemistry, not just in 

particulate nitrate formation.34

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).35

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 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 action.36

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

[Source: EPA Speciation Trends Network] 

Region Statistic 

Concentration 

(μg/m3) 

Sulfate Nitrate OM EC Crustal 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 

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 

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37Note that in this document the term 

‘‘attainment plan’’ refers to a state’s required SIP 

submittal elements other than those elements 

related to the NNSR program. 

38See the General Preamble, 57 FR 13498, (April 

16, 1992). 

39See 2007 PM2.5 Implementation Rule, 72 FR 

20586 (April 25, 2007). The rule discussed the fact 

that emissions of SO2, NOX, VOC and ammonia are 

factual and scientific precursors to PM2.5. 

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

[Source: EPA Speciation Trends Network] 

Region Statistic 

Concentration 

(μg/m3) 

Sulfate Nitrate OM EC Crustal PM2.5

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 

III. Requirements With Respect to the 

Treatment of PM2.5 Precursors in 

Attainment Plans and the NNSR 

Program 

A. Background 

The EPA recognizes that the treatment 

of PM2.5 precursors is an important issue 

in developing a PM2.5 attainment plan 37

or implementing the NNSR program in 

a nonattainment area. The EPA has long 

recognized the scientific basis for 

concluding that there are multiple 

scientific precursors to PM1038and 

PM2.5.39 Appropriate control of 

precursors is especially important for 

attaining the PM2.5 NAAQS because 

secondarily formed particles (such as 

ammonium nitrate, ammonium sulfate, 

and some portion of organic carbon) 

comprise a large fraction of ambient 

PM2.5 concentrations in many 

nonattainment areas. However, in some 

PM2.5 nonattainment areas, a particular 

precursor or precursors may not 

contribute significantly to PM2.5 levels 

that exceed the relevant NAAQS. This 

section of the preamble describes 

optional precursor demonstrations that 

a state may choose to submit to the EPA 

in order to establish that sources of 

particular precursors need not be 

regulated for purposes of attainment 

planning or in the NNSR permitting 

program for a specific nonattainment 

area. 

Section III.A of this preamble 

provides background on the January 

2013 NRDC v. EPA court decision, in 

which the court found that subpart 4 of 

part D of the CAA presumptively 

requires regulation of all PM2.5

precursors, except under certain 

circumstances. Section III.A of this 

preamble also provides information on 

the requirements of the subpart 4 

provisions applicable to attainment 

plans for PM NAAQS. Section III.B of 

this preamble provides a summary of 

the precursor demonstration options in 

the proposed rule and comments 

received. Section III.C of this preamble 

provides a discussion of the optional 

precursor demonstrations provided in 

the final rule. 

The final rule describes how in some 

cases a state may demonstrate that the 

adoption of additional emission 

reduction measures for a particular 

precursor is not needed for purposes of 

achieving expeditious attainment nor 

for advancing the attainment date by at 

least a year in a nonattainment area. 

(This is referred in the preamble as an 

‘‘expeditious attainment 

demonstration.’’) The rule also describes 

three optional approaches for 

demonstrating that a particular 

precursor is not a significant contributor 

to ambient PM2.5 levels that exceed the 

standard in a particular nonattainment 

area. These three precursor 

demonstrations are: (a) Comprehensive 

precursor demonstration; (b) major 

stationary source precursor 

demonstration; and (c) NNSR precursor 

demonstration. If a state chooses to 

submit a precursor demonstration, it 

must do so in accordance with 

provisions in the final rule. A state may 

use this type of demonstration to justify 

that sources of the given precursor may 

be excluded from certain PM2.5

attainment plan requirements and/or 

NNSR requirements, although the 

particular sources and requirements 

eligible for exclusion will depend on the 

type of demonstration submitted. 

Section III.C of this preamble also 

outlines certain technical issues, such as 

the appropriate geographic scope of a 

precursor demonstration, recommended 

significance thresholds, and 

recommended analytical approaches for 

evaluating precursor contributions to 

ambient PM2.5 levels and the sensitivity 

of PM2.5 levels in an area to decreases 

or increases of emissions. 

January 2013 court decision in NRDC 

v. EPA. As explained in the proposed 

rule, the EPA’s approach to the 

evaluation and regulation of PM2.5

precursors pursuant to subpart 1 in both 

the 2007 PM2.5 Implementation Rule 

and the 2008 PM2.5 NSR Rule was 

invalidated 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 of part D of the CAA, 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 

opinion specifically discussed the 

approach to precursors in both the 2007 

PM2.5 Implementation Rule and the 

2008 PM2.5 NSR Rule and compared that 

approach 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

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40NRDC v. EPA, 706 F.3d 428, 437, n.7 (D.C. Cir. 

2013). 

41NRDC v. EPA, 706 F.3d 428, 437, n.10 (D.C. Cir. 

2013). 

42The EPA notes that it previously had addressed 

the requirements of subpart 4 for precursors, 

specifically within the context of the requirements 

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

the Federal Register published on April 16, 1992 

(57 FR 13498, 13539, 13541 and 13542). 

43See CAA requirements for states to demonstrate 

attainment ‘‘as expeditiously as practicable’’ (CAA 

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

44 57 FR 13498 (April 16, 1992). 

45 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). 

46See Section IV of this preamble for a thorough 

discussion of past policy and guidance on 

reasonably available control measures (RACM) and 

reasonably available control technology (RACT). 

Section IV of this preamble discusses the EPA’s 

final 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 

and PM10. For a PM10 nonattainment area 

governed by subpart 4, a precursor is 

presumptively regulated. See 42 U.S.C. 

7513a(e) [CAA section 189(e)]. 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.40

The court continued to hold that ‘‘[i]n 

light of our disposition, we need not 

address the petitioners’ challenge to the 

presumptions in 40 CFR 51.1002(c)(3)– 

(4) that volatile organic compounds and 

ammonia are not PM2.5 precursors, as 

subpart 4 expressly governs precursor 

presumptions.’’ 41

Section 189(e) of the CAA establishes 

requirements for precursors to PM10

(which the court concluded expressly 

includes PM2.5) and 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. 

Subpart 4 of part D of the CAA. The 

provisions of subpart 4 (CAA sections 

188–190) do not define the term 

‘‘precursor’’ for purposes of PM10, nor 

do they explicitly require the control of 

any specifically identified PM 

precursor. However, 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.’’ See 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 apply equally 

to emissions of direct PM2.5 and these 

precursors in PM2.5 nonattainment 

areas, except as otherwise provided in 

the statute. Section 189(e) of the CAA 

explicitly requires the control of 

precursors from all major stationary 

sources in PM2.5 nonattainment areas 

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 

nonattainment area.42 Section 189(e) of 

the CAA contains the only express 

exception to control requirements for 

PM precursors under subpart 4. 

When Congress adopted the 1990 

CAA Amendments, the 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 PM10 precursors in the 

atmosphere led to the formation of PM10

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, CAA section 189(e) 

provided a possible exception to the 

requirement to control all PM10

precursors from major sources in a 

particular nonattainment area. 

Consistent with past practice for 

implementation of the PM10 NAAQS, 

the EPA proposed to interpret the 

control requirements addressed by CAA 

section 189(e) to include RACM/RACT 

(and additional reasonable measures) for 

Moderate nonattainment areas, BACM/

BACT (and additional feasible 

measures) for Serious nonattainment 

areas, most stringent measures (MSM) 

(for Serious areas 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 CAA section 189(e) to 

both existing and new major stationary 

sources, including new and modified 

sources subject to NNSR permitting 

requirements. Even though CAA section 

189(e) only explicitly contemplates 

exceptions to control requirements for 

PM2.5 precursors from major stationary 

sources in nonattainment areas, 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 sources in nonattainment 

areas as well, under appropriate 

circumstances. 

While CAA section 189(e) expressly 

requires control of precursors from 

major stationary sources, it is clear that 

subpart 4 and other CAA provisions 

collectively require the control of direct 

PM2.5 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 

nonattainment area.43 Longstanding 

EPA guidance for RACM has indicated 

that the state should inventory all 

emissions of the relevant pollutants and 

precursors in the nonattainment area, 

evaluate the available control measures 

for the relevant pollutant and precursors 

to determine if such controls are 

economically and technologically 

feasible, and then adopt those measures 

that are deemed reasonably available 

and necessary in order to attain the 

NAAQS as expeditiously as 

practicable.44 The EPA guidance has 

also long indicated that the state must 

ensure that there is no other collection 

of available control measures that if 

adopted would advance the attainment 

date by at least 1 year.45 Section IV.D of 

this preamble provides additional 

discussion on the development of 

emissions inventories and the 

identification, adoption and 

implementation of reasonably available 

control measures for PM2.5

nonattainment areas, including a 

discussion particular to wildfire and 

wildland prescribed fire found in 

Section IV.D.3.b.46

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demonstrate attainment as expeditiously as 

practicable. 47See the Federal Register published on April 16, 

1992 (57 FR 13498, 13540 and 13541). 48See, e.g., Assoc. of Irritated Residents v. EPA, 

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

49The three proposed options were: (1) Option 

1—two independent analyses consisting of an 

attainment planning analysis showing that control 

measures for a particular precursor are not needed 

for expeditious attainment and an optional NNSR 

analysis showing that major stationary sources of a 

particular precursor do not contribute significantly 

to levels that exceed the PM2.5 standard, (2) Option 

2—a single analysis (for purposes of attainment 

planning and NNSR) showing that all emissions of 

a particular precursor do not contribute 

significantly to levels that exceed the PM2.5

standard, and (3) Option 3—a single analysis (for 

purposes of attainment planning and NNSR) 

showing that control measures for all sources for a 

particular precursor are not needed for expeditious 

attainment. 

In light of the court’s decision in 

NRDC v. EPA, the EPA considers it 

necessary to describe how states must 

address regulation of PM2.5 precursors 

in attainment plans and NNSR programs 

for the PM2.5 NAAQS. The court’s 

decision made clear that appropriate 

regulation of all precursors in 

designated nonattainment areas is 

presumptively required under the CAA, 

and the regulation of precursors in 

general is a critical issue for attainment 

of the PM2.5 NAAQS because 

secondarily formed particles are a 

substantial component of PM2.5

concentrations in most nonattainment 

areas of the United States. 

For the purposes of this rule, the EPA 

considers that for all PM2.5

nonattainment areas, the PM2.5

precursors for regulatory purposes are 

the four scientific precursors that the 

EPA has previously identified: SO2, 

NOX, VOC and ammonia. This rule does 

not include any national presumption 

that would allow a state to exclude, 

without a demonstration, sources of 

emissions of a particular precursor from 

further analysis for attainment plan or 

NNSR control requirements in a PM2.5

nonattainment area. However, the EPA’s 

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 nonattainment 

area, i.e., states may determine that only 

certain precursors need to be regulated 

in a particular PM2.5 nonattainment area 

for attainment purposes.47 Courts have 

upheld this approach to the 

requirements of subpart 4 for PM10.48

The EPA believes that application of a 

similar approach to PM2.5 precursors 

under subpart 4 is appropriate and 

reasonable. 

The EPA interprets the CAA to 

require states to inventory emissions 

and adopt control measures as 

appropriate for direct PM2.5 and all 

PM2.5 precursors. This interpretation is 

based on CAA section 302(g), which 

defines an air pollutant as including 

precursors contributing to the formation 

of that pollutant; the EPA’s 

identification of the four main scientific 

PM2.5 precursors; and the CAA 

provisions requiring adoption of all 

control measures (i.e., RACM and 

RACT) needed in order to attain the 

standard as expeditiously as practicable. 

CAA section 189(e) explicitly requires 

that the control requirements applicable 

for major stationary sources of direct 

PM2.5 emissions 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 

that exceed the standard in the 

nonattainment area of concern. Thus, 

the statute generally requires control of 

all PM2.5 precursors in a nonattainment 

area, but it provides an express 

exception applicable to major stationary 

sources in such areas if an appropriate 

demonstration is made. 

The EPA also notes that CAA section 

189(e) contains certain ambiguities that 

require interpretation. For example, 

CAA section 189(e) does not specify the 

precise method by which a state or the 

EPA should determine whether 

precursor emissions from major 

stationary sources do not ‘‘contribute 

significantly’’ to levels which exceed 

the standard in a given nonattainment 

area. Subpart 4 also does not explicitly 

address whether it would be appropriate 

to include a potential exemption from 

precursor controls for all source 

categories under certain circumstances, 

because a specific exemption from 

precursor controls is expressly made 

available in the statute only for major 

stationary sources. These issues are 

addressed in this final rule. 

B. Summary of Proposal 

In the proposal, the EPA sought 

comment on how states could focus 

regulatory efforts on the appropriate 

PM2.5 precursors in each area. Rather 

than simply requiring each state to 

regulate direct PM2.5 and all PM2.5

precursors without regard to whether 

that would be appropriate and necessary 

for expeditious attainment of the 

NAAQS, EPA took comment on 

different approaches for states to focus 

regulatory efforts on the appropriate 

pollutants. Thus, in the proposal, the 

EPA sought comment on three options 

by which a state could demonstrate that 

emission control requirements for a 

particular PM2.5 precursor or precursors 

would not be required for sources in a 

particular nonattainment area.49 The 

proposed ‘‘precursor demonstration’’ 

options outlined procedures and 

technical analyses a state could elect to 

perform to demonstrate that control 

requirements for sources of a particular 

precursor are not needed for expeditious 

attainment, or that a particular PM2.5

precursor does not significantly 

contribute to PM2.5 concentrations in the 

area. The proposal indicated that if the 

EPA were to approve such a precursor 

demonstration, then it would not be 

necessary for the state to adopt control 

requirements for sources of the 

precursor or precursors in the PM2.5

attainment planning process generally 

and/or in the NNSR permitting process 

for that particular area. The EPA 

requested comment on whether the final 

rule should include one or more 

precursor demonstration approaches, 

and whether it would be appropriate to 

combine specific elements from 

different options. 

The EPA also described three 

technical issues associated with any 

such precursor demonstration and 

sought comment on the following: (1) 

The appropriate geographic scope of the 

analysis; (2) whether specific types of 

technical analyses (such as evaluating 

the contribution of the precursor to total 

PM2.5 concentrations, or evaluating the 

sensitivity of the area to decreases or 

increases of the precursor) should be 

required for a precursor demonstration; 

and (3) whether the EPA should 

establish a bright-line ambient air 

quality threshold (e.g., 3 percent of the 

level of the relevant NAAQS in the area) 

to define an air quality change below 

which a precursor contribution should 

not be considered to be significant, 

thereby establishing that control of 

sources of the precursor is unnecessary 

in the area. 

Lastly, the EPA indicated in the 

proposal that if a state had an approved 

precursor demonstration for a particular 

precursor in a Moderate area and the 

EPA later reclassifies the area to 

Serious, then the state would be 

required to develop an updated 

precursor demonstration if the state 

were again interested in having the 

precursor treated as insignificant for 

purposes of the Serious area plan. An 

updated precursor demonstration is 

necessary because many factors (e.g., 

emissions, air quality and fine particle 

concentrations) could have changed 

substantially since the original 

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50For more information on the proposed 

precursor demonstration options, see 80 FR 15340, 

at 15350–15362. 51See, e.g., Assoc. of Irritated Residents v. EPA, 

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

52See Section IV.D.1 of this preamble, 

Background for Attainment Plan Control Strategy, 

for further discussion of ‘‘additional reasonable 

measures.’’ 

demonstration for the Moderate area 

attainment plan.50

C. Final Rule 

The EPA received many comments on 

the three proposed precursor 

demonstration approaches. Most 

commenters supported the inclusion of 

some kind of optional precursor 

demonstration in the final rule. Some 

commenters suggested that states should 

have the flexibility to develop any of the 

types of demonstrations that the EPA 

described in the three proposed options. 

One group of commenters opposed any 

option that would exempt a particular 

precursor from control measures even if 

the state could demonstrate it could 

expeditiously attain the standard by the 

attainment date without controls on 

sources of the precursor. Another group 

of commenters suggested that if only 

one option is finalized, it should allow 

a state to rely on a sensitivity analysis 

to show that changes in emissions of a 

particular precursor would not have a 

substantial contribution to PM2.5

concentrations in the area. 

The EPA agrees with commenters 

who suggested that states should have 

the flexibility to conduct different types 

of precursor demonstrations appropriate 

to the area in question. Regardless of the 

type of precursor demonstration, the 

state will still need to provide adequate 

technical support and that 

demonstration will be subject to EPA 

approval. Thus, the EPA concludes that 

the specific form of the demonstration is 

not as crucial as its content and 

adequacy, in light of the facts and 

circumstances in the area. The EPA 

disagrees with commenters who argued 

that a state should not be able to 

determine insignificance for a precursor 

based on an attainment planning 

analysis showing expeditious 

attainment in the area without adopting 

new emissions reduction measures for 

the precursor in question. This 

approach has been upheld under 

subpart 4 with respect to 

implementation of the PM10 NAAQS, 

and the EPA finds that it is reasonable 

to allow for a similar policy when 

implementing the PM2.5 NAAQS.51

After consideration of the numerous 

comments received on this issue, the 

EPA has decided to adopt a final 

approach that allows exclusion of 

certain precursor sources from certain 

SIP requirements, provided that states 

make the appropriate demonstrations. 

However, the EPA has revised the 

details of the specific types of 

demonstrations based on further 

evaluation of the comments received. 

Section III.C.1 of this preamble 

describes the expeditious attainment 

demonstration, in which a state shows 

that control requirements for a 

particular precursor are not needed for 

expeditious attainment by the Moderate 

area attainment date. Section III.C.2 of 

this preamble describes the three types 

of optional precursor demonstrations a 

state may submit to the EPA to establish 

that emissions of a precursor do not 

contribute significantly to PM2.5 levels 

in a particular nonattainment area: (a) 

Comprehensive precursor 

demonstration; (b) major stationary 

source precursor demonstration; and (c) 

NNSR precursor demonstration. Each 

option is described in detail in the 

following subsections. 

Section III.C.3 of this preamble 

highlights various technical issues 

associated with precursor 

demonstrations, including the 

appropriate geographic scope of the 

analyses, thresholds for characterizing 

an insignificant air quality change, and 

different analytical methods for 

assessing precursor contributions. 

Section III.C.4 of this preamble 

discusses certain procedural issues 

associated with precursor 

demonstrations. Section III.C.5 of this 

preamble addresses other relevant 

comments and responses. 

1. Expeditious Attainment 

Demonstration 

As noted earlier, the EPA’s 

interpretation of subpart 1 and 4 

requirements with respect to precursors 

in attainment plans for PM10 has been 

that a state may develop an attainment 

plan that regulates only those precursors 

that are necessary to control for 

purposes of timely attainment in the 

area. The EPA believes that a similar 

policy approach for PM2.5 precursors is 

also appropriate. 

Under the expeditious attainment 

demonstration, a state may be able to 

determine through its identification of 

RACM/RACT for existing sources in an 

area whether expeditious attainment 

could be achieved without new control 

measures for a particular PM2.5

precursor. It is important to note that 

this approach is available to a state only 

if the demonstration for the area (1) 

ensures attainment by the Moderate area 

attainment date (i.e., the end of the sixth 

calendar year after designation), and (2) 

ensures that the area could not advance 

the attainment date by at least 1 year if 

it were to adopt reasonable control 

measures for the precursor in question. 

If the state determines that the area 

cannot practicably attain by the relevant 

Moderate area attainment date, then the 

state still would have the option of 

developing one of the precursor 

demonstrations described in Sections 

III.C.2.a–c of this preamble for showing 

that the precursor contribution is not 

significant. The expeditious attainment 

option is not available for Serious 

nonattainment areas because BACM/

BACT measures for Serious areas are not 

solely limited to those measures needed 

for expeditious attainment under this 

final rule. (See further discussion of this 

issue in Section VI.D of this preamble, 

Serious Area Attainment Plan Control 

Strategies.) 

For the expeditious attainment 

demonstration, the required analysis is 

what is already needed for a Moderate 

area attainment demonstration: The 

identification of reasonably available 

control measures that provide for 

expeditious attainment by the 

attainment date, and a determination 

that attainment cannot be advanced 

through the imposition of other 

reasonable measures (i.e. RACM/RACT 

and other reasonable measures that are 

identified for the area but not necessary 

for the area to attain within 6 years). See 

40 CFR 51.1006(a). After a 

comprehensive emissions inventory has 

been developed, the state should then 

identify potential control measures and 

assess factors related to technological 

feasibility, economic feasibility, and 

time needed for implementation for all 

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

stationary, area, mobile) and all 

precursors emitted by such sources as 

included in the emissions inventory. 

After identifying the set of control 

measures that are economically and 

technologically feasible for all 

precursors, the state may be able to 

show (using best available information 

on emissions, control options, 

technologies, and costs, along with 

appropriate air quality modeling) that 

those measures that could be identified 

as RACM/RACT and additional 

reasonable measures would not need to 

include new control measures for 

sources of a given precursor.52 The state 

could show this by demonstrating that 

one set of control measures to be 

adopted into the plan would provide for 

attainment by the statutory attainment 

date; and that an additional set of 

potential control measures (including 

measures for the precursor in question, 

and remaining measures for all other 

contributing pollutants) collectively 

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would not advance the attainment date 

by at least 1 year (i.e., enable the area 

to attain 1 year earlier). Under these 

circumstances, the state would not need 

to adopt the second set of measures 

(including measures for the particular 

precursor) because they would not 

expedite attainment of the NAAQS in 

the area. 

If the attainment planning 

demonstration shows that the area can 

attain the NAAQS expeditiously 

without new emission reduction 

measures for a particular precursor, the 

state would be required to adopt control 

measures for only a subset of the four 

PM2.5 precursors as part of the 

attainment plan for the area, and 

existing sources in the nonattainment 

area would not be required to adopt new 

control measures for the particular 

precursor. Accordingly, the state would 

not need to address the precursor in the 

reasonable further progress plan, in 

quantitative milestones and associated 

reports, or be required to adopt 

contingency measures to reduce the 

precursor. See 40 CFR 51.1009(a)(4)(i). 

(Note that for purposes of meeting the 

contingency measure requirement, 

however, the state would still have the 

discretion to adopt control measures as 

contingency measures for a precursor 

that would otherwise not be subject to 

RACM/RACT requirements.) 

It also should be noted that 

development of an approvable 

attainment plan that does not include 

new control measures for a particular 

precursor would not exempt the state 

from the requirements to address the 

same precursor with respect to the 

NNSR program, nor would it excuse the 

state from reconsidering the significance 

of the precursor to the PM 

nonattainment problem in any 

subsequent Serious area SIPs that could 

be required for the nonattainment area. 

2. Optional Precursor Demonstrations 

a. Comprehensive Precursor 

Demonstration. In line with the EPA’s 

proposal for precursor insignificance 

demonstrations, the EPA is finalizing an 

option whereby a state may submit a 

comprehensive precursor demonstration 

as part of any Moderate or Serious area 

attainment plan. The use of the term 

‘‘comprehensive’’ here refers to the fact 

that the demonstration covers all 

existing stationary, area, and mobile 

sources, rather than major sources 

alone. Note, however, that the 

comprehensive precursor demonstration 

does not affect precursor requirements 

for future new sources. Under this 

comprehensive precursor 

demonstration, the state would need to 

show that emissions of a particular 

precursor from all existing stationary, 

area, and mobile sources located in the 

nonattainment area do not contribute 

significantly to PM2.5 levels that exceed 

the standard in the area. The state 

would first need to evaluate the 

contribution of all existing source 

emissions of the particular precursor to 

PM2.5 concentrations that exceed the 

PM2.5 standard (described in Section 

III.C.2 of this preamble). If the state 

cannot demonstrate via the 

concentration-based precursor 

demonstration that sources of a 

particular precursor have an 

insignificant contribution to PM2.5 levels 

in an area,, then the state could still 

demonstrate that the precursor’s 

contribution is insignificant by 

conducting a sensitivity analysis to 

evaluate the sensitivity of ambient PM2.5

concentrations in the nonattainment 

area to decreases in the precursor 

emissions in the area (e.g., whether a 

given decrease is insignificant) as 

discussed further in Section III.C.2.c of 

this preamble. 

If a comprehensive precursor 

demonstration for a precursor is 

approved, the state would not establish 

a motor vehicle emissions budget for the 

relevant precursor, and regional 

emissions analyses for the precursor 

would not be required to be included in 

transportation conformity 

determinations. This is consistent with 

the transportation conformity rule’s 

provisions concerning PM2.5 precursors. 

(See 40 CFR 93.102(b)(2)(iv) and (v)). 

Separately, states may continue to 

determine that on-road emissions of 

PM2.5 precursors are insignificant even 

if emissions of a given precursor from 

other sources are significant. (See 40 

CFR 93.102(b)(2)(iv) and (v) and 

93.109(f)). With regard to general 

conformity, if a state precursor 

demonstration is approved for one or 

more precursors, federal agencies would 

not be required to address the affected 

precursor(s) in general conformity 

determinations. 

If a comprehensive precursor 

demonstration is approved by the EPA, 

then in developing the attainment plan 

for the area, the state would not be 

required to adopt control measures (e.g., 

RACM/RACT) for the precursor for any 

existing stationary, area, or mobile 

sources in the nonattainment area. The 

attainment plan also would not be 

required to address the relevant 

precursor in meeting the RFP or 

quantitative milestone requirements, or 

in adopting contingency measures 

because these requirements commonly 

apply to pollutants that are the subject 

of emission reduction measures in the 

attainment plan. (Note that for purposes 

of meeting the contingency measure 

requirement, however, the state would 

still have the discretion to adopt 

emission reduction requirements on the 

precursor in question, in conjunction 

with emission reduction requirements 

on other pollutants.) The state would 

still need to include the precursor in all 

nonattainment area emission inventory 

submissions. 

It also should be noted that 

development of an approvable 

attainment plan that does not include 

new control measures for a particular 

precursor would not exempt the state 

from the requirements to address that 

precursor with respect to the NNSR 

program, nor would it excuse the state 

from reevaluating the significance of the 

precursor to the PM nonattainment 

problem in any subsequent Serious area 

SIPs that could be required for the 

nonattainment area. 

b. Major Stationary Source Precursor 

Demonstration. The state has the option 

of submitting a major stationary source 

precursor demonstration as part of any 

Moderate or Serious area plan, 

consistent with CAA section 189(e). 

This demonstration differs from the 

comprehensive demonstration in that it 

only evaluates existing major sources, 

and therefore may only be used to 

justify the exclusion of existing major 

sources from the control requirements 

for the applicable precursor. Although 

the EPA expects that most states making 

precursor demonstrations will opt for 

comprehensive demonstrations, this 

option is provided to offer additional 

flexibility. The requirements for a 

stationary source precursor 

demonstration are nearly identical to 

those of the comprehensive precursor 

demonstration, except the state would 

only need to show that a particular 

precursor from all existing major 

stationary sources located in the 

nonattainment area do not contribute 

significantly to PM2.5 levels that exceed 

the standard in the area. Similar to the 

comprehensive demonstration, the state 

must first evaluate the contribution of 

major stationary source emissions of the 

particular precursor to PM2.5 levels that 

exceed the PM2.5 standard (pursuant to 

section III.C.3.c of this preamble). If the 

state cannot demonstrate via the 

concentration-based precursor 

demonstration that sources of a 

particular precursor have an 

insignificant contribution to PM2.5 levels 

in an area, then the state could still try 

to demonstrate that the precursor is 

insignificant by conducting a sensitivity 

analysis to evaluate the sensitivity of 

PM2.5 levels in the nonattainment area 

to a reduction in major stationary source 

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emissions in the area (pursuant to 

Section III.C.3.d of this preamble). 

If such a demonstration is approved 

by the EPA, then in developing the 

attainment plan for the area, the state 

would not be required to adopt control 

measures for the precursor for existing 

major stationary sources in the 

nonattainment area. The attainment 

plan also would not be required to 

address the emissions of the relevant 

precursor from major stationary sources 

in meeting the RFP or quantitative 

milestone requirements, or in adopting 

contingency measures. (Note that for 

purposes of meeting the contingency 

measure requirement, however, the state 

would still have the discretion to adopt 

emission reduction requirements on the 

precursor in question, in conjunction 

with emission reduction requirements 

on other pollutants.) The state would 

still need to include stationary source 

emissions of the precursor in all 

nonattainment area emission inventory 

submissions. 

Note that a state might consider 

developing a major stationary source 

demonstration to avoid the requirement 

to adopt nonattainment planning 

control measures for a particular 

precursor emitted from existing major 

stationary sources in the area if the state 

does not believe that it could 

comprehensively demonstrate that the 

precursor does not have a significant 

contribution, and if major stationary 

source emissions of the precursor do not 

make up a very large percentage of the 

emissions inventory in the area. For 

example, it might be possible that in a 

particular area the overwhelming 

amount of emissions of a certain 

precursor could originate from mobile 

or area sources, or both, but not from 

existing major stationary sources. If the 

EPA approves a major stationary source 

precursor demonstration, the attainment 

plan would still need to evaluate and 

potentially impose control requirements 

for the relevant precursor for existing 

non-major stationary sources, area 

sources and mobile sources in order to 

demonstrate expeditious attainment. 

It also should be noted that 

development of an approvable 

attainment plan that does not include 

new control measures for a particular 

precursor would not exempt the state 

from the requirements to address that 

precursor with respect to the NNSR 

program, nor would it excuse the state 

from the requirement to evaluate and 

adopt control measures for the precursor 

in any subsequent Serious area SIPs that 

could be required for the nonattainment 

area. 

c. NNSR Precursor Demonstration. 

The state also has the option of 

submitting a NNSR precursor 

demonstration as part of any Moderate 

or Serious area plan. This specific type 

of precursor demonstration is the only 

one of the three demonstrations 

described in this section that if 

approved would exempt new and 

modified major stationary sources of a 

precursor from regulation under the 

NNSR permitting program. 

Under the NNSR precursor 

demonstration, the state would need to 

conduct an analysis to evaluate the 

sensitivity of PM2.5 levels in the 

nonattainment area to an increase in 

emissions of a particular precursor in 

the area, simulating the response of the 

atmosphere (and associated PM2.5

concentrations) to the addition of one or 

more new or modified stationary 

sources in the nonattainment area (see 

Section III.C.3.d of this preamble). 

Section III.C.3 of this preamble 

addresses additional issues related to 

technical analyses for precursor 

demonstrations. 

The EPA believes that this approach 

to interpreting CAA section 189(e) of the 

statute as it applies to control 

requirements for the NNSR program is 

appropriate because (1) an analysis that 

evaluates the sensitivity of the 

atmosphere in an area to increases in 

emissions would most closely replicate 

the scenario of concern, where 

precursor emissions from new major 

stationary sources or major 

modifications are added to the existing 

inventory for the area; and (2) this 

approach would take into consideration 

the specific atmospheric chemistry and 

emissions profile that varies from area 

to area. For example, one nonattainment 

area may have low emissions of a 

particular precursor from all existing 

sources (and corresponding low current 

ambient contributions from the 

precursor), but the introduction of a 

new major stationary source of 

emissions of that particular precursor 

could in some cases significantly 

contribute to the ambient PM2.5 levels in 

the area because other pollutants with 

which the precursor reacts in the 

atmosphere could be relatively 

abundant. 

For purposes of the NNSR precursor 

demonstration, the state is not required 

to first evaluate the contribution of 

existing major sources to PM2.5 levels 

that exceed the standard in the area, as 

would be required by the 

comprehensive and major stationary 

source demonstrations. Since NNSR 

permitting requirements do not apply to 

existing sources (unless such sources 

engage in a major modification), the 

EPA does not believe it is necessary or 

reasonable to require evaluation of 

current emissions from existing major 

stationary sources as it would not 

inform the question of whether 

increases in emissions would 

significantly contribute to PM2.5 levels 

in the area. Note, however, that the 

NNSR precursor demonstration is used 

only to justify an exclusion of sources 

of the precursor from the NNSR control 

requirements in the area. A state would 

need to pair the NNSR precursor 

demonstration with another type of 

precursor demonstration to address 

control requirements beyond NNSR, as 

described previously for each type of 

demonstration. 

3. Technical Issues Associated With 

Precursor Demonstrations 

a. Geographic Area. The proposal 

indicated that the emissions inventory 

to be used as the starting point for the 

comprehensive, major stationary source, 

and NNSR precursor demonstrations 

should represent emissions from 

sources located in the nonattainment 

area, and the final rule remains 

unchanged. The EPA believes that 

limiting the emissions inventory for 

these analyses to sources in the 

nonattainment area is appropriate based 

on the statutory construction of CAA 

section 189(e), in which the relevant test 

is whether ‘‘such sources contribute 

significantly to [PM2.5] levels which 

exceed the standard in the area.’’ The 

EPA believes that a reasonable 

interpretation is that this provision 

applies to sources in the nonattainment 

area. 

b. Significance Threshold. The 

proposal described the concept of 

including a bright-line threshold of 3 

percent of the relevant NAAQS in the 

rule for precursor demonstrations other 

than the expeditious attainment 

approach, such that if an air quality 

contribution was found not to exceed 

the threshold amount, then it would not 

be considered significant. The proposal 

also included an option for no brightline threshold in the final rule, based on 

the recognition that all nonattainment 

area situations are different. 

Some commenters supported the 

bright-line threshold concept, but they 

suggested thresholds across a broad 

range, from less than 1 percent of the 

relevant NAAQS, to up to 5 percent. 

Some commenters stated that inclusion 

of a bright-line threshold of 3 percent of 

the relevant NAAQS was preferred 

because without such a threshold, states 

would be unsure about whether their 

proposed precursor assessment would 

be acceptable. Other commenters 

supported having no bright line 

threshold because the circumstances of 

each area are unique, and for that reason 

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53For more information on CMAQ, see http://

www.epa.gov/air-research/community-multi-scaleair-quality-cmaq-modeling-system-air-qualitymanagement. For more information on CAMx, see 

http://www.camx.com/. 

each area should be considered on a 

case-by-case basis. 

The EPA found merit in comments 

supporting both proposed options. The 

EPA agrees that an insignificance 

threshold can help avoid situations 

where lack of clarity may lead to delays 

in the EPA assessment of precursor 

demonstrations. At the same time, the 

EPA understands that PM2.5

nonattainment problems are complex 

and vary greatly based on the facts and 

circumstances of each area. 

After considering the range of 

comments on this issue and the 

complexity of the types of analyses that 

may be conducted for precursor 

demonstrations, the EPA has decided 

that the best approach is for the final 

rule to codify the availability and basic 

requirements for precursor 

demonstrations, but to provide technical 

details (such as a recommended 

approach for assessing whether a 

particular air quality concentration 

threshold can be considered to be 

insignificant in a given area) in 

guidance supporting this final rule. 

c. Concentration-based Contribution 

Analysis. The first type of analysis 

required for the comprehensive 

precursor demonstration (or, less 

commonly, the major stationary source 

precursor demonstration) is an existing 

source contribution analysis that would 

demonstrate whether emissions of a 

particular precursor from all existing 

sources (or, for a major source precursor 

demonstration, emissions from existing 

major sources) in the nonattainment 

area do not significantly contribute to 

PM2.5 concentrations that exceed the 

standard in the area. The state should 

use technically credible approaches for 

estimating the ambient contribution of 

emissions of a particular precursor to 

total PM2.5 concentration in the 

nonattainment area. The EPA 

anticipates that the forthcoming 

technical guidance will discuss the 

possible use of advanced air quality 

modeling tools to estimate precursor 

contributions to total PM2.5

concentrations in an area. For example, 

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.53

Other techniques such as the analysis 

of chemical speciation data and 

emissions inventories also may be 

appropriate for determining the 

contribution of a particular precursor to 

PM2.5 concentrations. For example, SO2

emissions and measured sulfate 

concentrations (in the form of 

ammonium sulfate or other forms) may 

be small in a particular nonattainment 

area. A simple analysis of measured 

species concentrations (attributable to a 

particular precursor) combined with 

nonattainment area emissions and other 

relevant data analyses may be sufficient 

to show that a precursor does not 

contribute significantly to PM2.5

concentrations in the area. 

d. Sensitivity-based Contribution 

Analysis. A second type of analysis may 

also be used in developing 

comprehensive precursor 

demonstrations (or, less commonly, 

major source precursor demonstrations). 

This type of analysis is a sensitivitybased contribution analysis that would 

demonstrate the degree to which 

concentrations in the nonattainment 

area are sensitive to decreases of a 

precursor. Changes in PM2.5

concentrations at a particular location 

often will not be linear with respect to 

changes in PM2.5 precursor emissions; 

therefore, sensitivity analyses are useful 

for better understanding the complexity 

and variability of the atmospheric 

chemistry affecting PM2.5 concentrations 

in different areas across the country. A 

sensitivity-based contribution analysis 

evaluating the effect of precursor 

emissions reductions could be used in 

the event the state cannot demonstrate 

via the concentration-based analysis 

that sources of a particular precursor 

have an insignificant contribution to 

PM2.5 levels in an area. 

The EPA also requires a sensitivitybased analysis as the means for 

conducting the NNSR precursor 

demonstration. In this case, in contrast 

to the assessment of decreases described 

for the comprehensive (or major source) 

precursor demonstration for existing 

sources, the appropriate sensitivity 

analysis is one that evaluates the impact 

of precursor emissions increases— 

without the need for a separate 

evaluation of existing source 

contribution to PM2.5 concentrations. 

This analysis is clearly most appropriate 

for NNSR, which is a program that 

governs emissions increases. Thus, the 

final rule requires that such an analysis 

must be used if a state chooses to submit 

a NNSR precursor demonstration. 

The EPA states in the final rule that 

a sensitivity-based analysis is an 

appropriate approach for understanding 

whether emissions of a precursor make 

an insignificant contribution to PM2.5

levels in an area. Several main 

components of PM2.5 are secondarily 

formed in the atmosphere and are the 

result of chemical reactions between 

various PM2.5 precursors. In some areas, 

one precursor may be abundant while a 

second precursor, with which it 

primarily reacts, may be less abundant. 

In such cases, a sensitivity analysis may 

find that reducing emissions of the 

second, less abundant precursor (the 

‘‘limiting’’ precursor) may be generally 

more effective for reducing PM2.5

concentrations. It may also find that 

increasing emissions of the less 

abundant precursor may be more 

effective at increasing PM2.5

concentrations than a comparable 

tonnage increase of a more abundant 

precursor. 

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. In such an 

area, a sensitivity analysis may be able 

to demonstrate that sources of a 

particular precursor in the 

nonattainment area do not contribute 

significantly to PM2.5 levels that exceed 

the standard, and that the potential air 

quality improvement from reducing 

emissions of the precursor in the area 

may be limited. 

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. The EPA therefore 

believes that it is a reasonable 

interpretation of the statute to allow a 

precursor to be excluded from control 

requirements if the PM2.5 concentration 

in the area is insensitive to decreases of 

that precursor. 

For states that choose to develop an 

optional precursor demonstration, the 

final rule provides that in addition to 

the basic requirement to do a 

concentration-based contribution 

analysis, the state may choose to 

develop a sensitivity-based contribution 

analysis evaluating potential emissions 

reductions for either a comprehensive 

precursor demonstration or a major 

stationary source demonstration 

intended to show that emissions 

reductions of the particular precursor 

are not effective in reducing PM2.5 levels 

that exceed the standard in the area. As 

noted previously, the EPA expects to 

recommend approaches for assessing 

whether a particular air quality 

concentration threshold can be 

considered to be insignificant in a given 

area. If a concentration-based 

contribution analysis conducted for 

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either a comprehensive precursor 

demonstration or a major stationary 

source precursor demonstration shows 

that the contribution from a precursor is 

less than a particular threshold which 

may be considered insignificant at each 

PM2.5 monitor in the area, then the EPA 

could approve the concentration-based 

contribution analysis. However, if a 

concentration-based contribution 

analysis cannot be approved (e.g., shows 

that the contribution of a precursor to 

PM2.5 levels in the area is not less than 

such a threshold at one or more 

monitors), then the overall precursor 

demonstration still could be approved, 

but only if the state also provides an 

appropriate sensitivity-based 

contribution analysis. If the sensitivitybased contribution analysis shows that 

the reduction in PM2.5 concentration at 

each PM2.5 monitor resulting from an 

emission reduction level that would not 

exceed such a threshold, then the EPA 

could approve the overall precursor 

demonstration, and the state would not 

be required to adopt control 

requirements for the precursor or 

address the precursor for attainment 

planning purposes. 

In evaluating whether it would be 

appropriate to exclude sources of any 

precursors from NNSR regulation in a 

nonattainment area, it is important to 

understand the sensitivity of the 

atmosphere to potential increases in 

precursor emissions that could result 

from major source growth (from both 

new sources and major modifications at 

existing major sources) in the 

nonattainment area. For example, in 

some circumstances, adding a few 

hundred tons of a ‘‘less abundant’’ 

precursor to an area could result in a 

significant increase in PM2.5

concentrations even if there are 

currently very few existing major 

sources of the precursor in the area. In 

contrast to the emissions reduction 

analyses described for attainment 

planning purposes, sensitivity analyses 

that consider the effect of potential 

emissions increases of a particular 

precursor in the nonattainment area will 

help the state and the EPA to 

understand the potential response of 

PM2.5 concentrations to increased 

emissions in the area in order to assess 

whether the contribution from such 

increases is not significant under CAA 

section 189(e). In assessing whether a 

state precursor demonstration (i.e., for 

attainment planning or for NNSR) can 

be approved, the EPA will consider the 

air quality changes estimated in the 

state’s technical sensitivity analyses, 

their relationship to thresholds 

developed under any EPArecommended approaches (including 

any thresholds that EPA may 

recommend), and any other information 

presented by the state. 

4. Procedural Considerations 

a. Consultation and Public Review. 

The EPA anticipates that a state’s 

development of an approvable PM2.5

precursor demonstration will require a 

substantial level of effort and 

consultation with the EPA. Such a 

demonstration by the state would likely 

involve technically rigorous and 

complex analyses, such as air quality 

modeling and ambient data analyses. 

Accordingly, the EPA strongly 

recommends that any state that is 

considering limiting the applicability 

and associated control strategy 

decisions only to specific precursors, 

either for the attainment plan, for the 

NNSR permitting program, or for both, 

should develop a precursor 

demonstration early in the attainment 

plan development process. The EPA is 

committed to consulting with states on 

designing technically appropriate 

precursor demonstrations consistent 

with EPA technical guidance. If a state 

chooses to develop a precursor 

demonstration, it must be submitted to 

the appropriate EPA regional office no 

later than the date of submission of the 

relevant attainment plan or NNSR 

program revision; an earlier submission 

is preferable. For example, if a state 

submits the Moderate area plan 

elements no later than 18 months from 

the date of designation (as discussed in 

Section IV.A of the preamble), it should 

submit any precursor demonstration no 

later than this same date. In its review 

of any precursor demonstration 

provided by a state, the EPA will 

consider all relevant information. 

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 not be 

able to reasonably determine whether 

reductions of a given PM2.5 precursor 

are needed for expeditious attainment, 

or whether sources of such precursor are 

insignificant contributors to PM2.5 levels 

above the standard in an area, unless the 

state has adequately accounted for all 

nonattainment area emissions in its 

emissions inventory. (See section IV.B 

of this preamble for more details on 

emission inventory requirements.) 

In the preamble to proposed rule, we 

indicated that if a state developed a 

precursor demonstration as part of its 

draft attainment plan or NNSR program 

submission, then in accordance with the 

state rulemaking process, the 

demonstration would be subject to 

public review at the state level. We 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 ensuring that this important 

issue was explicitly addressed and 

supported in any attainment plan or 

NNSR program revision 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 final rule 

includes similar language requiring 

public review of any proposed precursor 

demonstration. 

If a state chooses to develop a 

comprehensive precursor demonstration 

or major stationary source precursor 

demonstration for a nonattainment area, 

it must submit a concentration-based 

contribution analysis and, if applicable, 

a sensitivity-based contribution analysis 

conducted for the area. In cases where 

a sensitivity-based analysis was 

developed the concentration-based 

analysis must also still be submitted. 

Although the rule clearly provides that 

the precursor demonstration 

requirement may still be satisfied in 

such cases, the information in the 

concentration-based analysis will help 

inform review of the overall 

demonstration by the EPA. Similarly, 

the data from the concentration-based 

analysis should be available in the 

public record because it will help 

inform the review of the overall 

precursor demonstration by the public. 

See 40 CFR 51.1006(b). 

b. Precursor Demonstration to be 

Reevaluated for Each New State 

Implementation Plan. There may be 

situations where the EPA approved a 

Moderate area plan that excluded a 

precursor from regulation from one or 

more requirements based on an 

approvable precursor demonstration, 

and then the area is reclassified as a 

Serious area, triggering an additional 

plan submission requirement. (Section 

V of this preamble provides additional 

detail on reclassification of areas from 

Moderate to Serious under subpart 4.) In 

addition, an area that had been 

reclassified as Serious later may be 

required to submit one or more 

additional SIPs if it obtains an extension 

of the Serious area attainment date, or 

if it fails to attain the standard by the 

end of the tenth year after designation. 

For a state seeking to continue a 

precursor exclusion in a subsequent 

attainment plan or NNSR program 

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submission, the final rule requires the 

state to assess the appropriateness of 

continuing the exclusion by providing a 

new precursor demonstration updated 

to reflect the type of plan and the 

conditions in effect when the new plan 

is submitted. 

When an area is reclassified to 

Serious, existing sources of all PM2.5

precursors in the area are again 

presumptively subject to evaluation for 

BACM/BACT control measures and 

potential future control requirements, 

unless a new precursor demonstration is 

developed and approved as part of the 

Serious area plan. As noted in the 

discussion of the provisions for 

excluding sources of precursors from 

certain Moderate area requirements 

based on an expeditious attainment 

demonstration, this option is not 

available for Serious areas. Accordingly, 

if the state seeks to submit an updated 

precursor demonstration for a Serious 

area, at this stage it must submit a 

comprehensive, major stationary source, 

or NNSR precursor demonstration. 

Regardless of the type of 

demonstration(s) provided in the 

Moderate area plan, the final rule 

requires that the state must submit a 

reevaluated and updated precursor 

demonstration for the Serious area plan. 

The reason for this is that the Serious 

area plan would be due several years 

after the submission of a state’s original 

precursor demonstration, and over that 

period, substantial emissions changes 

could have occurred that might call into 

question the basis of the previous 

precursor demonstration. In addition, 

because the area failed to attain by the 

Moderate area attainment date, it is 

reasonable and appropriate to require 

the state to reconsider and update its 

prior precursor demonstration. The final 

rule also requires similar updates for 

each successive plan beyond the initial 

Serious area plan (such as a revised 

Serious area plan for an area that fails 

to attain by the end of the tenth calendar 

year after designation). The EPA 

recommends that in developing a 

revised precursor demonstration, the 

state should consider changes in a 

number of factors, including: Changes in 

emissions inventory levels due to 

implementation of control programs, 

growth in emissions, and changes in 

emission estimation methodologies; 

recent ambient air quality 

concentrations; fine particle 

composition and the sensitivity of the 

atmosphere to increases and decreases 

of different precursors; advances in 

technical tools and modeling techniques 

to assess the effectiveness of precursor 

reductions; and advances in control 

technologies and emission reduction 

programs. 

5. Comments and Responses. 

Comment: With regard to whether the 

existing source contribution analysis or 

the sensitivity-based contribution 

analyses should be required if a state 

opts to submit a precursor 

demonstration, a number of commenters 

supported only the sensitivity analysis 

because they believed the analysis 

would help identify the control 

measures that are most effective at 

reducing PM2.5 concentrations. Some 

commenters noted that conducting a 

‘‘zero-out’’ analysis (i.e., simulating the 

change in atmospheric chemistry and 

PM2.5 concentrations due to a 

hypothetical removal of 100 percent of 

the emissions of a precursor from the 

inventory) is not appropriate for a 

sensitivity analysis because the 

response of the photochemical grid 

model is highly non-linear under such 

circumstances. 

Another group of commenters 

supported requiring only the 

concentration-based existing source 

contribution analysis because only that 

analysis would address the question 

alluded to in the statute, which is 

whether sources of the precursor 

contribute significantly to levels which 

exceed the standard in the area. These 

commenters stated that sensitivity-based 

analyses reflect localized conditions and 

do not represent a consistent effect 

across an air basin. The commenters 

suggested that sensitivity analyses might 

be considered to inform what pollutants 

are most cost-effective to control, but 

believed that this is dubious because the 

fact that certain pollutants are very 

abundant is likely the result of a history 

of under-regulation. They suggested that 

it actually may be cheaper to control the 

more abundant pollutant than the less 

abundant pollutant in order to achieve 

an equal amount of air quality 

improvement. 

Response: The EPA agrees with 

commenters who suggested that the rule 

should closely align with the statutory 

language in CAA section 189(e) of 

subpart 4 and include provisions for 

evaluating the contribution of existing 

sources to PM2.5 levels which exceed the 

standard in the area. For this reason, the 

final rule states that the existing source 

contribution analysis should be required 

for any comprehensive precursor 

demonstration or major stationary 

source precursor demonstration seeking 

to exempt a precursor from attainment 

planning requirements. 

The EPA also believes that a 

sensitivity-based contribution analysis 

is consistent with the language and 

intent of CAA section 189(e). As applied 

to attainment plans, CAA section 189(e) 

allows states to evaluate whether PM2.5

precursors significantly contribute to 

levels which exceed the standard in the 

area. The intent of CAA section 189(e) 

in applying control requirements to 

PM2.5 precursors is to ensure 

expeditious attainment of the standard. 

However, if conditions in a particular 

area are such that control of sources of 

one or more precursors does not reduce 

PM2.5 concentrations in the area, then 

those controls will not help the area 

attain (expeditiously or otherwise). 

Therefore, the EPA disagrees with 

commenters who argue that sensitivitybased contribution analyses are not 

appropriate for determining if 

precursors do not significantly 

contribute to PM2.5 levels in the area. 

The EPA believes that sensitivity-based 

contribution analyses can be useful for 

determining whether adoption of 

control requirements for sources of a 

particular precursor would be effective 

in reducing PM2.5 concentrations, and 

can be useful for determining whether 

potential emissions increases under the 

NNSR program would lead to 

insignificant air quality changes. For 

this reason, the final rule allows states 

to conduct sensitivity-based 

contribution analyses for the 

comprehensive, major stationary source, 

and NNSR precursor demonstrations. 

Comment: Some commenters 

expressed support for the precursor 

option from the proposal (i.e., Option 3) 

that would have allowed for an 

expeditious attainment precursor 

demonstration to be deemed to 

demonstrate under CAA section 189(e) 

that emissions of the precursor do not 

need to be addressed for all major 

stationary source requirements, such as 

the NNSR program. 

Response: Upon further consideration 

of this potential approach, the EPA 

decided that it would not be appropriate 

to include such an approach in the final 

rule. The reason for this is that an 

expeditious attainment planning 

analysis on its own would determine 

that the area could attain the standard 

by the Moderate area attainment date 

without new control requirements for 

sources of a particular precursor, but it 

would not address the potential impact 

of increased emissions of the precursor 

in the area due to new or modified 

sources, as is reasonably needed under 

the NNSR precursor demonstration. The 

evaluation of controls required for 

expeditious attainment does not 

consider what happens if new sources 

move into an area. Thus, while a state 

might be able to show that controlling 

existing sources of a precursor does not 

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54See 57 FR 13498, 13536, 13537, 13538, 13539, 

13540, 13541, 13542, 13543, 13544 and 13545 

(April 16, 1992); and 59 FR 41988 (August 16, 

1994). 

55The EPA notes that Congress provided different 

statutory deadlines for submission of attainment 

plans under subpart 1 and subpart 4. Under section 

172(b) of the CAA, 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 

CAA 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). 

advance attainment, the analysis would 

not determine whether a new major 

source of that precursor might have a 

significant contribution to air quality. 

The EPA believes it is important for 

purposes of CAA section 189(e) and our 

overall environmental goal under the 

NNSR program to evaluate emissions 

increases. Consequently, the EPA has 

revised the details of the specific types 

of demonstrations to include a specific 

stand-alone demonstration for purposes 

of exempting new major stationary 

sources and major modifications of a 

precursor from regulation under the 

NNSR permitting program. 

IV. Requirements for PM2.5 Moderate 

Nonattainment Area 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 (CAA section 

189(a)(1)(A)); (ii) a demonstration that 

the plan provides for attainment by no 

later than the applicable Moderate area 

attainment date or a demonstration that 

attainment by that date is impracticable 

CAA (section 189(a)(1)(B)); (iii) 

provisions for the implementation of 

RACM and RACT no later than 4 years 

after designation (CAA section 

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

milestones that will be used to evaluate 

compliance with the requirement to 

demonstrate reasonable further progress 

(RFP) (CAA 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 provided for major 

stationary sources under CAA section 

189(e)). In addition, subpart 1 

requirements for attainment plans 

continue to apply to PM2.5

nonattainment areas unless they are 

superseded by subpart 4 provisions and 

include the following: (i) A description 

of the expected annual incremental 

reductions in emissions that will 

demonstrate RFP (CAA section 

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

necessary (CAA section 172(c)(3)); (iii) 

other control measures (besides RACM 

and RACT) needed for attainment (CAA 

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

measures (CAA section 172(c)(9)). The 

EPA notes that its longstanding 

guidance on interpreting these statutory 

requirements is embodied in the 

General Preamble and the Addendum.54

The preamble for the proposed rule 

presented several interpretations of 

these provisions, and further explained 

where its proposal varies from past EPA 

guidance and the reasons for the 

variance. The following sections of this 

preamble explain the EPA’s final 

approach and, where different from the 

proposal, also explain EPA’s reasons for 

finalizing an amended approach. This 

final rule reflects our careful 

consideration of the numerous 

thoughtful comments we received from 

air agencies, who are responsible under 

the CAA for these implementation 

activities, and a variety of other 

stakeholders. 

A. Plan Due Dates 

1. Summary of Proposal 

The EPA proposed to require that all 

Moderate area plan elements for a 

nonattainment area be submitted by the 

state no later than 18 months from the 

effective date of designation. The 

attainment plan submission would thus 

include all necessary plan elements 

required under CAA subparts 1 and 4. 

2. Final Rule 

The final regulations at 51.1003(a) 

require all Moderate nonattainment area 

elements to be submitted by no later 

than 18 months from the date of 

designation, as proposed. 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 

nonattainment designation.55 While 

subpart 1 of the CAA could potentially 

be interpreted to authorize the EPA to 

provide up to 3 years after designation 

for states to submit certain attainment 

plan elements, the EPA believes that 

such an interpretation would be 

inconsistent with the specific deadlines 

that Congress imposed in subpart 4. The 

EPA concludes that all subpart 1 and 

subpart 4 nonattainment area 

requirements should be considered 

together in order to facilitate state 

development, and EPA review, of a 

comprehensive plan to attain the PM2.5

NAAQS in a given nonattainment area. 

In fact, the EPA finds that meeting key 

subpart 1 requirements within the 18- 

month timeframe of subpart 4 is 

fundamentally necessary for the state to 

develop an approvable plan. For 

example, the state must develop an 

emissions inventory (or inventories) 

either before or at the same time as the 

other attainment plan elements due 

under subpart 4 because the information 

contained in the emissions inventory is 

critical for development of other 

elements of the Moderate area 

attainment plan, such as its precursor 

analysis, analysis of RACM and RACT 

and additional reasonable measures, 

and attainment demonstration 

modeling. The EPA’s ability to evaluate 

the submitted attainment plan therefore 

will be impaired if the state does not 

submit all the required plan elements at 

the same time. 

3. Comments and Responses 

Comment: Commenters suggested that 

the EPA should interpret the statute to 

allow more time for states to develop 

and submit contingency measures. 

Response: As discussed earlier in this 

section, the EPA believes that it would 

be inconsistent with the specific 

deadlines that Congress imposed in 

subpart 4 to allow contingency 

measures to be submitted later than the 

other elements of the attainment plan. 

Contingency measures need to be 

adopted and ready for rapid and timely 

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. 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 

the pollutants and sources to be 

addressed in meeting the RACM/RACT 

requirements, and the amount of 

emissions reductions that the 

contingency measures should achieve, 

based upon the facts and circumstances 

of the attainment plan for the area. The 

same types of facts and analyses that are 

necessary for the other elements of an 

attainment plan are directly relevant to 

the development of contingency 

measures. 

Although nothing in the CAA 

prohibits states from making separate 

attainment plan submissions to meet the 

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individual required elements 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 efficient, 

both for the state and for the EPA in 

reviewing the state’s submission. A 

Moderate area implementation plan 

with a single SIP submission due date 

will be less administratively 

burdensome than a program with two 

SIP submission due dates. Under an 

approach with two submissions, the 

state would likely need to issue two sets 

of proposed regulations, hold two sets of 

public hearings, and respond to two sets 

of public comments, rather than dealing 

with all of these requirements in one 

comprehensive action. Likewise, the 

EPA would have two separate 

submissions to review and two sets of 

proposed and final actions to publish in 

the Federal Register for every Moderate 

nonattainment area. Thus, for the 

reasons outlined earlier, the final rule 

includes a single Moderate area 

attainment plan submission deadline of 

18 months after designation. 

Accordingly, the areas designated as 

nonattainment for the 2012 PM2.5

NAAQS (with an effective date of April 

15, 2015) are required to submit 

Moderate area attainment plans to the 

EPA no later than October 15, 2016. See 

40 CFR 51.1003(a). 

B. Emissions Inventory Requirements 

1. Summary of Proposal 

In the proposal, the EPA proposed for 

both Moderate and Serious areas to 

require both a ‘‘base year inventory for 

the nonattainment area’’ and an 

‘‘attainment projected inventory for the 

nonattainment area.’’ The proposal 

spelled out a list of requirements for 

each of these inventories. The proposal 

also specified, based on the timing 

requirements of CAA section 172(b), 

that the emissions inventories required 

for a Moderate area must be submitted 

within 18 months after the effective date 

of the designation of the nonattainment 

area. 

The EPA proposed that the base year 

inventory for the nonattainment area: (a) 

Be required to represent one of the 3 

years used for designations or another 

technically appropriate year; (b) include 

actual emissions of all sources within 

the nonattainment area; (c) be annual 

total or average-season-day emissions in 

accordance with the NAAQS 

violation(s) (annual and/or 24-hour); (d) 

include direct PM2.5 (filterable and 

condensable) as well as all scientific 

PM2.5 precursors; (e) follow the Air 

Emissions Reporting Requirements 

(AERR), 40 CFR part 51, subpart A for 

the emissions thresholds for point 

sources; (f) use the level of detail as 

prescribed by the AERR; and (g) still 

meet the public review requirements 

even if submitted as a separate plan. 

The EPA further proposed that the 

attainment projected inventory for the 

nonattainment area (a) be required to 

represent projected emissions in the 

first year for which attainment is 

demonstrated by the modeled 

attainment demonstration; (b) include 

projected emissions of the same sources 

included in the base year inventory for 

the nonattainment area; (c) use the same 

temporal period as the base year 

inventory (annual or average-seasonday); (d) include the same pollutants as 

the base year inventory; (e) report as 

point sources the same sources treated 

as point sources in the base year 

inventory; (f) be consistent in inventory 

detail with the base year inventory; and 

(g) still meet the public review 

requirements even if submitted as a 

separate plan. 

2. Final Rule 

The final regulations at 51.1008 

provide the inventory requirements for 

Moderate areas. The EPA received a 

number of comments on the emissions 

inventory requirements for Moderate 

areas. Commenters both supported the 

provisions of the proposed rule and 

objected to some aspects of the 

inventory requirements. The EPA is 

finalizing all of the proposed Moderate 

area requirements with some 

modifications based on comments. 

Specifically, the definition of what can 

constitute a seasonal inventory has been 

made more flexible to accommodate 

certain cases, as explained in Section 

IV.B.2.c of this preamble. 

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 PM, Congress did not create 

a specific emissions inventory 

requirement in subpart 4 that would 

supersede the emissions inventory 

requirement under subpart 1. Thus, the 

CAA 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 CAA 

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 later. 

Emissions inventory data serve as the 

foundation for various types of analyses 

performed by states and by the EPA. For 

example, these data 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 

https://www.epa.gov/air-emissionsinventories/emissions-inventoryguidance-documents. 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. 

a. Inventory Requirements. As 

explained in the proposed rule, CAA 

section 172(c)(3) requires states to 

submit an emissions inventory and 

periodic revisions thereof with an 

attainment plan. 80 FR at 15363. In 

addition, pursuant to CAA section 301, 

the EPA has authority to promulgate 

regulations as necessary for the 

implementation of the PM2.5 NAAQS, 

including requirements pertaining to 

emissions inventories. In this final 

action, the EPA is establishing several 

different inventory requirements that 

the agency has determined are necessary 

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56Point sources are the same as major stationary 

sources, and the term indicates sources that must 

be reported at an individual facility with processlevel details. Nonpoint sources are all other 

stationary sources, and the term indicates sources 

that are reported as a county total. The definitions 

for this rule (see 51.1000) refer to the definitions in 

the AERR (40 CFR part 51, subpart A). Nonpoint 

sources include minor sources, synthetic minor 

sources, and area sources such as residential 

heating and other sources where it is not realistic 

to estimate emissions from each emissions point. 

for the proper implementation of the 

PM2.5 NAAQS in attainment plans. 

There are three key facets of the 

emissions inventory requirements, as 

described later: (i) The type of 

inventories required; (ii) the timing of 

submission of these inventories; and 

(iii) the content of these inventories. 

These content requirements are 

described in this section; however, the 

EPA’s rationale for these content 

requirements is in some cases further 

described in subsequent sections of this 

document. 

First, states must 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 from sources located 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 called the ‘‘base year 

inventory for the nonattainment area,’’ 

and the second type of inventory is 

called the ‘‘attainment projected 

inventory for the nonattainment area.’’ 

See 40 CFR 51.1000. The base year 

inventory for the nonattainment area is 

necessary for development and 

evaluation of various elements of the 

attainment plan, such as the 

determination of appropriate pollutants, 

sources, and emission controls 

addressed in other elements of the 

attainment plan for the nonattainment 

area. The attainment projected 

inventory is necessary to implement the 

attainment demonstration requirement 

of CAA section 189(a)(1)(B), and it also 

may be used as part of meeting the RFP 

requirement (see Section IV.F of this 

preamble). The need for the attainment 

projected inventory also stems from the 

need for both the EPA and the public to 

be able to compare, during their reviews 

of the attainment plan, the base year 

inventory against the attainment 

projected inventory for the 

nonattainment area. For these reasons, 

this rule establishes a regulatory 

requirement at 51.1008 that Moderate 

area attainment plans must include a 

base year inventory for the 

nonattainment area and an attainment 

projected inventory for the 

nonattainment area. 

Second, as noted in Section IV.A of 

this preamble, to meet the statutory 

requirements for submission of certain 

attainment plan elements required 

under subpart 4, the EPA believes that 

states must meet the same submission 

schedule for emissions inventories as 

for the other elements of an attainment 

plan, i.e., within 18 months after the 

effective date 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 CAA section 172(b), this 

rule establishes a regulatory 

requirement for Moderate areas that 

states must submit the required base 

and projected emissions inventories by 

18 months after designation. 

Third, the EPA is establishing 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, this final 

rule requires that the base year 

inventory for Moderate nonattainment 

areas must meet the following minimum 

criteria 1 through 7: 

(1) The inventory year must be one of 

the 3 years used for designations for the 

relevant PM2.5 NAAQS 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, to allow 

the base year to be consistent with the 

base year needed for the conformity 

rule, 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 that 

the inventory will adequately represent 

the emissions sources that contributed 

to the nonattainment designation for the 

area. See 40 CFR 51.1008(a)(1)(i). 

(2) The inventory must include actual 

emissions of all sources within the 

nonattainment area. This requirement 

stems directly from the language in CAA 

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 CAA 

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

all emissions that may contribute to the 

formation of PM2.5 within the 

nonattainment area. This means that the 

inventory must include point sources, 

stationary nonpoint sources,56 mobile 

sources, prescribed fires and wildfires. 

The EPA encourages states and tribes to 

work together to ensure that the 

information used in developing the base 

year inventory for the nonattainment 

area is inclusive of all emissions from 

the designated nonattainment area, 

including emissions from sources in 

tribal areas located therein. See 40 CFR 

51.1008(a)(1)(ii). 

(3) The emissions must be reported as 

annual total emissions, average-seasonday emissions, or both, as appropriate 

for the relevant PM2.5 NAAQS. The 

rationale for the type(s) of emissions 

provided must be included as part of the 

attainment plan. When seasonal 

emissions are included, the rationale for 

the seasonal period must also be 

included as part of the attainment plan. 

A discussion of the EPA’s rationale for 

including the option of seasonal or 

annual inventories is provided in 

Section IV.B.2.c of this preamble. See 40 

CFR 51.1008(a)(1)(iii). 

(4) As discussed earlier and consistent 

with past implementation rule 

requirements, the inventory must 

include emissions of direct PM2.5 (both 

filterable PM2.5 and condensable PM2.5,

provided as separate components), as 

well as all scientific PM2.5 precursors 

(SO2, NOX, VOC and ammonia). A 

discussion of the EPA’s rationale for 

including this requirement is provided 

in Section IV.B.2.d of this preamble. See 

40 CFR 51.1008(a)(1)(iv). 

(5) States must follow the Air 

Emissions Reporting Requirements 

(AERR), 40 CFR part 51, subpart A 

criteria for emissions thresholds for 

states to use to determine which 

emissions sources must be reported as 

point sources. This requirement is 

consistent with past implementation 

rules and is needed to specify whether 

emissions must be submitted as specific 

major source stationary facilities with 

detailed emissions processes or whether 

emissions can be provided as county 

totals (i.e., area sources, also called 

nonpoint sources). A discussion of the 

use of 40 CFR part 51, subpart A for the 

emissions thresholds is provided in 

Section IV.B.2.e of this preamble. See 40 

CFR 51.1008(a)(1)(v). 

(6) The level of 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 emissions 

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inventory, this information can be 

summarized for other elements of the 

attainment plan. This requirement is 

consistent with the remanded 2007 

PM2.5 Implementation Rule and is 

needed to define the data reporting 

elements (i.e., how they are reported) as 

opposed to the emissions values (i.e., 

how much emissions derive from each 

source or source category) of the 

emissions inventories submitted to the 

EPA. See 40 CFR 51.1008(a)(1)(vi). 

(7) 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 the notice and public 

hearing requirements of CAA sections 

110(a)(1) and 110(a)(2). 

For the attainment projected 

inventory for Moderate nonattainment 

areas, this final rule also establishes 

specific requirements necessary to 

implement the PM2.5 NAAQS 

effectively. Accordingly, the attainment 

projected inventory must meet the 

following minimum criteria 1 through 7: 

(1) The year of the projected inventory 

must be the most expeditious year for 

which projected emissions show 

modeled PM2.5 concentrations below the 

level of the NAAQS, consistent with the 

requirement for expeditious attainment 

by no later than the applicable 

deadlines provided in the statute. See 

40 CFR 51.1008(a)(2)(i). 

(2) The emissions must be projected 

emissions from the same sources 

included in the base year inventory for 

the nonattainment area and any new 

sources projected to locate within the 

boundaries of the nonattainment area. 

The projected emissions 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 

changes in emissions 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 modeled 

attainment demonstration. See 40 CFR 

51.1008(a)(2)(ii). For prescribed and 

wildfire emissions, Section IV.D.3.b of 

this preamble describes in more detail 

the appropriate way to handle these 

sources in the attainment projected 

inventory. 

(3) The temporal period of emissions 

must be the same temporal period 

(annual, average-season-day, or both) as 

the base year inventory for the 

nonattainment area. See 40 CFR 

51.1008(a)(2)(iii). 

(4) 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 provided as 

separate components), as well as all 

emissions of the scientific precursors 

(SO2, NOX, VOC and ammonia). See 40 

CFR 51.1008(a)(2)(iv). 

(5) 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 

delineations as the base year inventory. 

See 40 CFR 51.1008(a)(2)(v). 

(6) 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). See 40 CFR 

51.1008(a)(2)(vi). 

(7) 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), then the inventory must still 

meet all the notice and public hearing 

requirements of CAA sections 110(a)(1) 

and 110(a)(2). 

b. Comparison to Inventory 

Requirements from Earlier PM2.5

Implementation Rules. The 2007 PM2.5

Implementation Rule required states to 

submit specific emissions inventories in 

connection with the RFP requirements 

of CAA section 172(c)(2) under subpart 

1. In this rule, no specific RFP related 

inventory is required, but the attainment 

projected inventory for the 

nonattainment area also may serve a 

purpose for evaluation of RFP. Past EPA 

guidance with respect to RFP 

requirements under subpart 4 has not 

explicitly required a separate emissions 

inventory for this purpose for PM10

NAAQS. Through evaluation of the RFP 

requirement in connection with this 

rulemaking, however, EPA has 

determined that there may be 

circumstances in which such an 

approach may be appropriate. For this 

reason, the EPA describes this issue 

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 

included the statewide emissions 

inventory requirement because it was 

relevant to evaluation of emissions 

reductions from sources outside of the 

designated nonattainment area for 

purposes of RFP. The EPA no longer 

interprets the CAA to allow such 

reductions for purposes of RFP, so this 

particular form of emissions inventory 

is not needed for attainment plan for 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 

inventory requirement is sufficient for 

understanding the PM2.5 nonattainment 

contributions from areas outside of the 

nonattainment area, which is a 

necessary component of modeled 

attainment demonstrations described in 

Section IV.E of this preamble. 

c. Seasonal Inventories. The statute 

does not explicitly address whether the 

emissions inventory required under 

CAA 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 values on 

particular days with high levels of 

ambient 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. For the PM2.5 NAAQS, 

states can meet the inventory 

requirement with different 

combinations of temporal resolutions 

for the emissions. For the annual 

standard, annual emissions must be 

submitted. For the 24-hour standard, 

states must submit either an annual or 

an average-season-day inventory and 

optionally may submit both. For a 

nonattainment area for both the annual 

and 24-hour standard, states can meet 

the inventory requirement with only an 

annual inventory or with both an annual 

and average-season-day inventory. 

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

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57 72 FR 20647 (April 25, 2007). 

NAAQS, there are circumstances in 

which the EPA believes that only 

seasonal emissions inventories may be 

useful for attainment planning 

purposes. This rule at 40 CFR 

51.1008(a)(1)(iii) allows states to use 

seasonal inventories for attainment plan 

development for attaining the 24-hour 

PM2.5 standard in areas that are 

designated nonattainment for only the 

24-hour standard. Use of a seasonal 

emissions inventory will also be 

appropriate only if the monitored 

violations of the 24-hour PM2.5 NAAQS 

in the area occur during an identifiable 

season. 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. Further, this 

rule requires that seasonal inventories 

must use average-season-day emissions 

values for this purpose, defined by 40 

CFR 51.1000. 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 emissions inventory, the state 

must demonstrate why a seasonal 

emissions inventory is appropriate for 

the particular PM2.5 nonattainment area 

in question. 

Commenters recommended that the 

EPA should allow episode-specific 

inventories, in lieu of seasonal 

inventories. As a result, the EPA 

acknowledges in this final rule that, for 

some source categories, it may be 

advisable to limit the ‘‘season’’ 

considered in calculating emissions to 

an episodic period to reflect periods of 

higher emissions during periods of high 

ambient PM2.5. Such an approach could 

help to ensure the nonattainment area 

inventory reflects the emissions 

conditions that led to an initial 

nonattainment area designation. For 

example, if nonattainment conditions 

are associated only with periods of peak 

emissions from residential wood 

combustion, then an episodic average 

for residential wood combustion may be 

more appropriate than a seasonal 

average. The resulting seasonal 

emissions inventory would then have a 

mix of the seasonal averages as defined 

by 40 CFR 51.1000 for most categories, 

but using a shorter period for the 

emissions categories that can be 

justified and an improvement. In such 

cases, in addition to the requirement to 

justify the seasonal period, the state 

must additionally justify the factual 

basis for the period used to calculate 

emissions from such categories, and this 

would be subject to EPA approval. 

While the EPA encourages using the 

same averaging period for all sectors for 

purposes of simplicity, an episodic 

averaging period may only be needed 

for a select group of sources or even for 

a single category of sources. Those 

special cases must be explained in the 

emissions inventory part of the state 

implementation plan [see 40 CFR 

51.1008(a)(1)(iii)]. For the purposes of 

the definitions included in this final 

rule, all non-annual emissions (whether 

seasonal or episodic) will be referred to 

as ‘‘seasonal’’ in this rule. 

d. Pollutant Requirements. This rule 

requires that states must submit 

emissions inventories that include all 

emissions of direct PM2.5 and all 

emissions of scientific PM2.5 precursors: 

SO2, NOX, VOC and ammonia. 

Furthermore, the inventories must 

differentiate between the condensable 

and filterable portions of direct PM2.5

emissions, and states must provide this 

information in the emissions inventories 

as separate components. As described in 

Section IV.B.3 of this preamble, 

commenters disagreed with the EPA’s 

proposal to require inclusion of 

ammonia emissions and to require 

separate reporting of condensable and 

filterable emissions. The approach being 

finalized in this rule does not differ 

from the EPA’s proposal despite these 

adverse comments. 

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 2007 

PM2.5 NAAQS Implementation Rule in 

the past.57 Section 172(c)(3) of the CAA 

explicitly requires states to submit a 

‘‘comprehensive, accurate, current 

inventory of actual emissions of the 

relevant pollutants’’ and the EPA 

continues to believe that 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 states to use the 

best available methodologies for 

estimating emissions of PM2.5 and its 

precursors. 

e. The AERR Defines the Thresholds, 

Data Elements and Data Methods. 

Because the provisions of the CAA do 

not specify the form of the emissions 

information to be reported to the EPA 

for meeting the attainment plan 

inventory requirement under CAA 

section 172(c)(3), it is necessary for the 

EPA to prescribe specifically the data 

elements of that emissions inventory 

and the attainment projected inventory. 

The EPA uses the AERR to define basic 

requirements/parameters of reporting 

emissions for all pollutants. This 

approach creates consistency and eases 

the burden for the states, because states 

have one basic set of rules that apply to 

all emissions they have to report to the 

EPA. 

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. Under this final rule, states 

must use the emissions elements from 

40 CFR part 51, subpart A in preparing 

their inventories to be submitted to the 

EPA for implementing the PM2.5

NAAQS. It also requires that states use 

point source thresholds from Appendix 

A of the same subpart. This is consistent 

with past requirements for the form of 

emissions inventories. 

In addition to defining the point 

source thresholds and 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 to the 

emissions elements—the definitions, 

data codes and required data fields. 

Later, the EPA addresses the issue of 

whether the emissions values submitted 

through the AERR are relevant to the 

inventory requirements of this final rule 

(see Section IV.B.2.g of this preamble). 

As noted earlier, the EPA 

recommends that states consult the SIP 

Emissions Inventory Guidance in 

preparing the inventories required by 

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 

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other fields that are optional in the 

AERR data collection system. The EPA 

is updating the SIP Emissions Inventory 

Guidance in coordination with this final 

rule. It provides specific guidance to 

states 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 

states should prepare and document the 

data for attainment plan submissions. 

In the case of prescribed fires and 

wildfires, the AERR no longer requires 

those categories to be submitted, but 

rather the emissions data can be 

optionally provided as an ‘‘Event’’ 

source, which is a day-specific source at 

a point location. For this rule as 

described earlier, states are required to 

include prescribed fires and wildfires 

for the base year inventory for the 

nonattainment area and the attainment 

projected inventory for the 

nonattainment area. For this rule, states 

are not expected to use the ‘‘Event’’ 

detail to meet their inventory reporting 

requirements. Instead, states can report 

these fire emissions by county as 

nonpoint sources are reported. 

f. Emissions Inventories for Support of 

Modeled Attainment Demonstrations. 

This section clarifies 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 establishing 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 are required to 

submit either an attainment 

demonstration (which includes air 

quality modeling) to show how the area 

will attain the NAAQS by the applicable 

attainment date or a demonstration 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 the modeled attainment 

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 

from sources in 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. 

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, 

annual or season-day data may not be 

sufficient for modeling purposes. For 

example, greater spatial detail (gridded 

rather than county total) and temporal 

detail (hourly rather than annual) are 

needed for on-road mobile modeling 

inventories as compared to the base year 

inventory for the nonattainment area. 

Rather, for the nonattainment area base 

year inventory, one goal is to allow for 

the repeatability of the approach in 

order to create average-season-day or 

annual inventories to help meet other 

attainment plan requirements, such as 

RFP or motor vehicle emissions budgets 

established for transportation 

conformity purposes. That goal is not 

necessarily compatible with the 

modeling need for greater spatial and 

temporal detail, which requires much 

greater effort and expense than is 

practical for RFP or establishing motor 

vehicle emissions budgets. In cases 

where some differences are 

unavoidable, states should attempt to 

promote consistency where feasible. 

g. Using AERR (40 CFR part 51, 

subpart A) Inventory Submission to 

Meet the Requirement for the Base Year 

Inventory for the Nonattainment Area. 

The AERR includes both triennial and 

annual statewide reporting 

requirements, with more extensive 

reporting requirements for triennial 

inventory years. All AERR submissions 

are required to be made electronically. 

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 data 

from all other sources of emissions must 

be reported as from either 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 other 

implementation rules. To avoid 

confusion, the EPA explains here the 

limited circumstances under which the 

AERR emissions inventories will be 

considered to meet the base year 

inventory requirement for Moderate 

nonattainment areas. The following 

conditions must be met to use AERR 

inventories for attainment planning: 

(1) The AERR emissions inventory 

must have gone through the notice and 

public hearing requirements of CAA 

sections 110(a)(1) and 110(a)(2). 

(2) The AERR emissions inventory 

includes all sources of emissions and all 

pollutants required for the base year 

inventory for the nonattainment area. 

This is only possible if the 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. 

(3) The EPA’s inventory data system 

must be accepting data for the inventory 

year being submitted. 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. 

(4) The AERR submission must 

include emissions from all sources 

required for the base year inventory for 

the nonattainment area consistent with 

40 CFR 51.1008(a)(1), and must include 

mobile source emissions in 

nonattainment areas (instead of simply 

providing inputs or other data that is 

allowed under the AERR). In some 

cases, the AERR requirement can be met 

without actually ‘‘submitting’’ 

emissions; for example, states may elect 

to accept the EPA estimates for some 

nonpoint emissions sectors. Accepting 

EPA emissions does not meet the 

requirements of CAA section 172(c)(3) 

or this rule. In addition, the AERR 

revision finalized in February 2015 (80 

FR 8787) replaces the prior requirement 

of reporting onroad mobile and nonroad 

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58032 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

58Section 172(c)(3) of the CAA requires that 

emission inventories be based on the most 

comprehensive, accurate and current information 

available. To do so, air agencies should use the 

most up to date method for estimating emissions. 

59At this time, the California onroad mobile 

model is called EMFAC2014. 

60 In 2005, the EPA offered animal feeding 

operations (AFOs) an opportunity to participate in 

a voluntary consent agreement referred to as the Air 

Compliance Agreement. Under the Agreement, 

participating AFOs provided the funding for the 

National Air Emissions Monitoring Study 

(NAEMS)—a 2 year, nationwide emissions 

monitoring study of the animal confinement 

structures and manure storage and treatment units 

in the broiler, egg-layer, swine, and dairy industries 

(see 70 FR 4958). 

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. Because the ‘‘statewide’’ 

emissions are actually provided for 

individual point sources and counties, 

the EPA believes that the AERR 

submission can be sufficient for most 

PM2.5 nonattainment areas. 

h. Mobile Source Emissions Models. 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 that the attainment 

plan inventory is developed.58 In 

general, for states other than California 

that choose to fulfill various modeling 

requirements by using the latest EPA 

emissions model, the latest approved 

version of the MOVES model should be 

used 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.59

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. 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. If a state chooses to 

use MOVES to create emissions 

inventories for purposes of RFP and 

establishing motor vehicle emissions 

budgets for transportation conformity 

purposes, it must use the same MOVES 

approach in the base year inventory for 

the nonattainment area, and using a 

straightforward MOVES approach 

without gridded meteorology is more 

reasonable for that purpose. 

Likewise, if states choose to fulfill 

various inventory requirements by using 

the latest EPA emissions model, the 

most current version of the NONROAD 

model or its successor must 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://www3.epa.gov/otaq/

models.htm. 

3. Comments and Responses 

Comment: Several commenters 

pointed out the uncertainties associated 

with ammonia emissions and organic 

matter emissions from livestock and 

fertilizer application sources, including 

in data developed by the EPA such as 

the National Emissions Inventory. 

Commenters pointed to the data 

available through the National Air 

Emissions Monitoring Study (NAEMS) 

for use in developing improved 

ammonia estimation approaches from 

livestock activities, and asserted that the 

EPA cannot move forward with SIP 

implementation requirements that 

implicate livestock and poultry farmers 

without using the NAEMS data. The 

commenters stated that not only is this 

technically unsound, but that the idea of 

moving forward on regulating livestock 

operations without the most critical tool 

for establishing requirements is a 

violation of the spirit of the consent 

agreements 60 and the NAEMS. 

Response: The EPA acknowledges 

that there is some uncertainty in 

quantifying ammonia emissions and 

other PM2.5 precursors from source 

categories such as livestock and 

fertilizer application. This uncertainty 

extends to the emissions and chemical 

composition of VOC and PM2.5, which 

also have an impact on ambient PM2.5. 

These uncertainties have an impact on 

attainment demonstrations because they 

cause uncertainty in the modeling done 

to demonstrate future attainment of the 

PM2.5 standard. However, the EPA 

disagrees with the assertion that these 

uncertainties should eliminate certain 

pollutants from consideration for 

control measures or should slow 

progress on attainment planning. 

Emissions uncertainty is a fact of air 

quality planning and cannot be avoided. 

Despite uncertainties in inventories of 

all kinds throughout the NAAQS 

program, great progress in improving air 

quality has been made through the 

attainment planning process and the 

implementation of control measures 

selected in part based on modeled 

attainment demonstrations. While 

emissions uncertainties remain, enough 

information is available for PM2.5

implementation planning purposes. The 

requirements contained in this final rule 

may drive further improvements in our 

understanding of emissions, and while 

the EPA strives to provide approaches 

for estimating emissions from a variety 

of source categories, the CAA places the 

burden for developing accurate 

emissions inventories on the states. The 

CAA does not allow for implementation 

of the NAAQS to be put on hold until 

all emissions uncertainties are 

eliminated. In fact, in spite of numerous 

uncertainties, states have developed 

emissions inventories for PM2.5 and 

PM2.5 precursors and performed 

modeling for PM2.5 attainment 

demonstrations for the previous 1997 

and 2006 NAAQS over the last 10 or 

more years. 

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 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58033 

61For more information on the NAEMS study, 

see: http://www3.epa.gov/airquality/agmonitoring/. 

Monitoring Study.61 For the 2008 and 

2011 national emission inventories, the 

EPA compiled state and county-level 

ammonia emissions estimates using 

information from state and local 

governments, the USDA Census of 

Agriculture and National Agriculture 

Statistical Service, and from existing 

ammonia emissions models. A new 

approach in development for use in the 

2014 NEI uses the NAEMS data to 

improve the EPA’s approach for 

estimating county-total emissions. The 

EPA expects that this update and other 

uses of the NAEMS data 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. The EPA disagrees 

that implementation planning should 

wait until NAEMS results are fully 

available. The EPA continues to make 

progress in using these data; however, 

the full use and implementation of new 

methods based on these data is not a 

prerequisite for progress on considering 

ammonia as a PM2.5 precursor for the 

NAAQS implementation purposes. 

Moreover, in order for a state to 

demonstrate a precursor’s insignificance 

(as necessary under this rule before 

excluding it from certain control or 

planning requirements), in some cases it 

may need to move forward without 

waiting until the NAEMS results are 

fully available. The EPA and USDA are 

continuing to work collaboratively to 

better understand agricultural ammonia 

related emissions in order to more 

accurately represent the emissions and 

impacts of ammonia in relation to PM2.5. 

Comment: Commenters supported the 

EPA’s proposed approach to require 

distinct emissions for filterable and 

condensable PM2.5. Commenters 

asserted that this proposed requirement 

created an additional inventory 

requirement beyond what is already 

required in the AERR. Commenters also 

asserted that this requirement places an 

unnecessary burden on states and 

industry. 

Response: The EPA disagrees with the 

assertion that an additional inventory 

requirement has been imposed by this 

rule. Within the AERR, 40 CFR 

51.15(a)(1)(vi) states (with regard to 

what must be reported): ‘‘Primary PM2.5.

As applicable, also report filterable and 

condensable components.’’ The term 

‘‘also’’ implies ‘‘in addition to total 

primary PM2.5,’’ and the phrase ‘‘as 

applicable’’ is intended to mean when 

such emissions are emitted from the 

source. This requirement has been in 

place since 2008, providing ample time 

for states to ensure compliance with this 

reporting requirement in advance of this 

final rule. Furthermore, the EPA points 

out that it would be much more difficult 

for the EPA to assess (as part of 

evaluating an attainment plan) whether 

states have met the requirement to 

include condensable emissions, and 

thus a complete PM2.5 inventory, 

without the states providing 

condensable emissions as something 

separate and distinct from filterable and 

total PM2.5. In addition, having a 

complete emission inventory of 

filterable and condensable PM2.5

emissions will enable a state to better 

identify contributing sources and 

develop a more effective plan. 

The EPA also notes that new electric 

generating units that are subject to (40 

CFR part 60, subpart Da) without PM 

continuous emissions monitors (CEMs) 

have to conduct annual testing for 

condensable PM using Method 202 of 

appendix M of part 51. 

Comment: Some commenters 

supported the EPA’s proposed approach 

to require an attainment projected 

inventory for the nonattainment area. 

Other commenters asserted that such an 

inventory should not be required 

because it has not been required before 

and because the attainment 

demonstration is sufficient. 

Response: The EPA disagrees with the 

latter commenters, noting that the 

rationale that such inventories have not 

been required before is not in and of 

itself a reasonable basis on which to 

exclude such a requirement now. The 

purpose of these inventories is well 

justified by the need for both the EPA 

and the public to be able to compare, 

during their reviews of the attainment 

plan, the base year inventory to the 

attainment projected inventory. Without 

such information, it is extremely 

difficult for the EPA to assess the 

projected emissions changes in the 

nonattainment area that the state asserts 

contribute to attainment. The attainment 

projected inventory may also play a role 

in meeting the RFP requirements of this 

rule. Furthermore, while the EPA has 

not explicitly required submittal of an 

attainment projected inventory in 

regulation, many states have developed 

such future year inventories as part of 

attainment demonstrations and have 

submitted them as part of PM2.5

attainment plans in the past, thus 

demonstrating their viability and utility. 

Comment: Commenters supported the 

EPA’s proposed approach to allow 

seasonal inventories. Some commenters 

requested the use of clear language 

stating an allowance for episode-specific 

inventories in lieu of seasonal 

inventories. 

Response: The EPA agrees with the 

commenters that for some source 

categories, seasonally averaged winter 

conditions would not be sufficient to 

represent the conditions leading to 

violations of the 24-hour PM2.5 standard. 

As described in Section IV.B.2.c of this 

preamble, some modifications have 

been made to the explanation of 

seasonal inventories to clarify that it 

would be reasonable to use an episodic 

average from the modeled attainment 

demonstration in some cases. 

C. Pollutants To Be Addressed in the 

Plan 

Under subpart 4 of the CAA, states are 

presumptively 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. Direct PM2.5 emissions 

include both filterable and condensable 

PM2.5 emissions. See further discussion 

of filterable and condensable PM2.5

emissions in the background section 

(Section II of this preamble) and in the 

emissions inventory requirements for 

Moderate area attainment plans (Section 

IV.B of this preamble). 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. 

With regard to PM2.5 precursors, 

Section III of the preamble describes 

that the rule provides for the possibility 

that the state may demonstrate that 

nonattainment area emissions of a 

particular precursor may not make a 

significant contribution to PM2.5 levels 

that exceed the standard in the area, or 

that emissions reductions of the 

precursor may not be needed for 

expeditious attainment. Thus, the rule 

presumptively requires the state to 

evaluate potential control measures for 

all four precursors, but the state may not 

need to address one or more 

requirements for a particular precursor 

with an approvable precursor 

demonstration. 

D. Attainment Plan Control Strategy 

1. Background on Attainment Planning 

and the Evaluation of Control Measures 

a. Summary of Proposal. The proposal 

included an overview of the statutory 

requirements and general guidance 

associated with attainment planning 

and evaluation of control measures. 

b. Final Rule. The following overview 

of statutory requirements and general 

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58034 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

62Because in CAA section 172(c) the term 

‘‘reasonably available control measures,’’ or RACM, 

also includes ‘‘reasonably available control 

technology,’’ or RACT, this document uses the 

abbreviation ‘‘RACM/RACT’’ to represent these 

requirements collectively, where appropriate. 

63States 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. See 40 CFR 

51.1003(b). 

64This interpretation is consistent with guidance 

described in the General Preamble. See 57 FR 13498 

(April 16, 1992), at page 13540. 

65The appendices to the General Preamble, 57 FR 

18070 (April 28, 1992), included sections on 

available fugitive dust control measures, available 

residential wood combustion measures, and 

available prescribed burning control measures. 

66See 57 FR 13498 (April 16, 1992), at pages 

13540–41. See also the Addendum. 

67 Ibid. 

68 Ibid. 

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

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

guidance remains unchanged except as 

discussed in this final rule. 

The attainment planning 

requirements of subparts 1 and 4 were 

established to ensure that two important 

CAA goals are met: (i) That states 

implement measures that provide for 

attainment of the PM2.5 NAAQS as 

expeditiously as practicable, but not 

later than the statutory attainment date; 

and (ii) that states adopt effective 

emissions reduction strategies in 

nonattainment areas. The Moderate 

nonattainment area attainment date is as 

expeditiously as practicable, but not 

later than the end of the sixth calendar 

year after designation. 

CAA section 172(c) of subpart 1 of the 

CAA 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.62 The 

attainment planning requirements in 

subpart 4 that are specific to PM10

(including PM2.5) likewise impose upon 

states an obligation to develop 

attainment plans that require RACM and 

RACT for 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/RACT are implemented by 

no later than 4 years after designation of 

the area.63 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.64 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 1992 General Preamble 

helps inform our interpretation of 

RACM and RACT for the purpose of 

implementing the PM2.5 NAAQS. 

The EPA’s guidance on RACM for 

sources of PM10 and PM10 precursors 

under subpart 4 in the General Preamble 

and Serious area Addendum includes 

the following: (i) A recommended list of 

potential measures to reduce PM10 for 

states to consider; 65 (ii) an emphasis on 

state evaluation of the technological and 

economic feasibility of potential control 

measures to determine whether such 

measures are reasonably available for 

implementation; (iii) an expectation that 

the state will provide a reasoned 

explanation for a decision not to adopt 

a particular control measure, including 

those measures recommended to the 

state in public comments or at a public 

hearing; and (iv) a discussion that in 

some cases partial implementation of an 

emissions reduction program may be 

considered RACM when full 

implementation would be infeasible 

within the given Moderate area 

timeframe.66 Thus, the RACM 

requirement under subpart 4 applies to 

all types of sources and is not focused 

only on forms of control that are 

technology-based. 

With respect to RACT requirements, 

the EPA’s guidance in the General 

Preamble includes the following: (i) 

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) RACT 

generally applies to stationary sources, 

both stack and fugitive emissions; (iii) 

major stationary sources (i.e., sources 

with potential to emit 100 tons per year 

or more of direct PM2.5 or any PM2.5

precursor) should be the minimum 

starting point for a state’s RACT 

analysis, but states are recommended to 

evaluate RACT for smaller stationary 

sources as needed for attainment and 

considering the feasibility of controls; 67

and (iv) it is possible that a State could 

demonstrate that an existing source in 

an area should not be subject to a 

control technology especially where 

such technology is unreasonable in light 

of the area’s attainment needs, or such 

technology is infeasible. In such a case, 

it could be concluded that no control 

technology is ‘‘reasonably available,’’ 

and RACT for the source could be 

considered to be no additional 

control.68 Thus, the RACT requirement 

under subpart 4 is primarily focused on 

stationary sources and forms of 

emissions control that are technologybased. 

The appendices to the General 

Preamble noted 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. 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. 

This final rule specifies the basic 

requirements that states must meet in 

identifying and selecting the complete 

suite of measures needed for an 

attainment plan submission for a 

Moderate PM2.5 nonattainment area. 

This preamble, together with the 

General Preamble, provides further 

description of the recommended process 

for states to follow in meeting these 

requirements. Under this process, the 

specific determination of RACM and 

RACT is to 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 Moderate area 

attainment date as expeditiously as 

practicable.69

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statutory interpretation of RACM, that the CAA 

does not compel a state to consider a measure 

without regard to whether it would expedite 

attainment. 

70The proposal described situations where some 

control measures could be exempted from 

consideration at the beginning of the analytical 

process. For example, control measures for a 

particular precursor would not need to be evaluated 

if the air agency submits an acceptable precursor 

demonstration as described in Section III of the 

preamble. 

71This has been the EPA’s longstanding 

interpretation of RACM/RACT in CAA sections 

172(c)(1) and 189(a)(1)(C), which were enacted as 

part of the amendments to the Act in 1990. Even 

prior to the 1990 amendments, the EPA interpreted 

the statutory term RACM to encompass only those 

measures ‘‘necessary to assure reasonable further 

progress and attainment by the required date.’’ 44 

FR 20375 (Apr. 4, 1979); see 40 CFR 51.1(o) (1972) 

(defining RACT in similar terms); 42 U.S.C. 

7502(b)(2) (1988) (requiring RACM in the precursor 

to current CAA section 172(c)(1)). In the 1990 

amendments to the Act, Congress enacted a 

‘‘[g]eneral savings clause’’ stating that ‘‘[e]ach 

regulation, standard, rule, notice, order and 

guidance promulgated or issued by [EPA] under 

this chapter, as in effect [before the 1990 

Amendments], shall remain in effect according to 

its terms.’’ 42 U.S.C. 7415. Since the passage of the 

1990 amendments, the EPA’s interpretation of 

RACM and RACT as encompassing only those 

measures necessary to advance attainment has been 

upheld in multiple U.S. Circuit Courts of Appeals. 

See NRDC v. EPA, 571 F.3d 1245, 1251–1253 (D.C. 

Cir. 2009); Sierra Club v. EPA, 314 F.3d 735, 743– 

744 (5th Cir. 2002); Sierra Club v. EPA, 294 F.3d 

155, 162 (D.C. Cir. 2002). But cf. Sierra Club v. EPA, 

793 F.3d 656 (6th Cir. 2015) (holding that an area 

must have subpart 1 RACM/RACT approved into its 

SIP prior to redesignation, regardless of whether the 

area is attaining the NAAQS). 

72 In addition to the statutory requirements under 

CAA sections 172(c)(1) and 189(a)(1)(C) for RACM 

and RACT, CAA 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, 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. 

73The 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. 

The final rule requires that all 

moderate area plans contain RACM, 

which is defined as any technologically 

and economically feasible measure that 

can be implemented in whole or in part 

within 4 years after the effective 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). The EPA 

recommends that to meet this 

definition, the state should follow a 

process by which it first identifies all 

sources of emissions of direct PM2.5

(including filterable and condensable 

PM2.5) and all PM2.5 precursors in the 

nonattainment area, and all potential 

control measures to reduce emissions 

from those source categories.70 The state 

next determines if any of the identified 

potential control measures are not 

technologically feasible and whether 

any of the identified technologically 

feasible control measures are not 

economically feasible. Measures that are 

not necessary for attainment need not be 

considered as RACM/RACT.71

Measures that can only be 

implemented after the 4-year deadline 

for RACM and RACT, but before the end 

of the sixth calendar year following 

designation, are defined in the final rule 

as ‘‘additional reasonable measures.’’ 72

The EPA has created this new definition 

based on the recognition that in some 

areas there could be emission reduction 

strategies that still could be 

implemented beginning 4 years after 

designation through the attainment date 

that could help to improve air quality 

and attain the standard expeditiously in 

the area. Note also that the 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, and it 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. 

Lastly, the final rule requires the state 

to perform an analysis (typically an air 

quality modeling analysis) to determine 

the earliest practicable attainment date 

for the area. This analysis should take 

into account projected emissions 

reductions associated with existing 

federal and state regulations, plus any 

additional reductions that would be 

achieved due to new control measures 

that would be needed for expeditious 

attainment. 

In the case of a Moderate area that can 

demonstrate it can attain by the 

statutory attainment date without 

implementing all reasonably available 

control measures (i.e. RACM/RACT and 

additional reasonable measures), the 

state would not be required to adopt 

certain otherwise reasonable measures if 

the state demonstrates that collectively 

such measures would not enable the 

area to attain the standard at least 1 year 

earlier (i.e., ‘‘advance the attainment 

date’’ by 1 year). The EPA has long 

applied this particular test to satisfy the 

statutory provision related to an area 

demonstrating attainment ‘‘as 

expeditiously as practicable.’’ 73 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 actual attainment needs of a 

particular PM2.5 nonattainment area. In 

the case of a Moderate area that cannot 

demonstrate that it will practicably 

attain by the statutory attainment date, 

the state would be required to evaluate 

potential control measures for sources 

in the nonattainment area and adopt all 

reasonable measures (i.e., RACM and 

RACT, and any ‘‘additional reasonable 

measures’’). 

The following sections of the 

preamble describe the steps of the 

control measure evaluation process in 

more detail, and include discussion of 

the consideration of public comments as 

appropriate. 

2. Step 1: Identify Sources of Emissions 

a. Summary of Proposal 

The proposal stated that the 

identification of all sources of emissions 

of direct PM2.5 (including filterable and 

condensable PM2.5) and all four PM2.5

precursors in the nonattainment area is 

the starting point for the state’s analysis 

of potential control measures. It was 

noted that an exception to this 

comprehensive review requirement 

might be possible if the final rule 

includes a policy that would allow a 

state to demonstrate that one or more 

precursors in a nonattainment area do 

not significantly contribute to PM2.5

levels that exceed the standard. If such 

a demonstration were approved by EPA, 

then the state would not be required to 

adopt control measures for the 

precursor. 

The proposal also included 

discussion of a possible de minimis 

source category exemption concept for 

Moderate areas. Under the approach, the 

analysis and identification of ‘‘de 

minimis source categories’’ for Moderate 

areas would occur early in the planning 

process, before potential control 

measures are identified or attainment 

modeling is conducted. The proposal 

recognized the challenges associated 

with defining ‘‘source categories.’’ The 

proposal also included potential options 

on how source categories could be 

defined, and requested comment on 

using the North American Industry 

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58036 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

Classification System (NAICS) (which 

provides a detailed hierarchy of 

numeric codes for different industries 

and process types) at the two, four, or 

six digit levels. 

The proposal also presented the 

concept of a possible bright line ambient 

impact threshold for determining 

whether a source category should be 

considered de minimis (in the event a 

de minimis concept is adopted). 

Comments were requested on two 

options: (1) No bright line threshold; 

and (2) a threshold in the range of 1–3 

percent of the relevant PM2.5 NAAQS. 

This range was selected because it was 

similar to the de minimis source 

category threshold range (2.0–3.3 

percent of the PM10 NAAQS) included 

in the 1994 Serious Area Addendum. 

b. Final Rule 

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.’’ Consistent with the 

proposal, the final rule maintains the 

policy that the state must begin the 

control consideration process by 

identifying potential control measures 

for all the sources included in the most 

recently available emissions inventory 

for the nonattainment area. The 

inventory must include emissions 

information for all existing major 

stationary sources as point sources, 

nonpoint sources (as defined by 40 CFR 

51.50) including non-major point 

sources, and mobile sources of direct 

PM2.5 (including filterable and 

condensable PM2.5) and PM2.5

precursors in the nonattainment area. 

Section IV.B of this preamble provides 

a detailed discussion of emission 

inventory requirements. 

The rule requires that a state must 

identify all of the sources reflected in 

the nonattainment area’s base year 

inventory as the initial step in 

developing reasonable control measures 

for the area, as each of these sources 

may play a role in the area’s PM2.5

problem. A state would need to consider 

all inventoried sources of direct PM2.5

emissions (including filterable and 

condensable PM2.5) and sources of all 

four scientific PM2.5 precursors as it 

conducts its determination of reasonable 

control measures for an area. 

Some commenters suggested that 

subpart 4 only provides authority to 

regulate precursors from major 

stationary sources and not from other 

types of sources, such as area or mobile 

sources. However, EPA disagrees with 

these commenters, given that the CAA 

provides an overarching requirement to 

attain the standard as expeditiously as 

practicable, PM2.5 precursor emissions 

play a very significant role in fine 

particle concentrations nationally, nonmajor sources are important sources of 

precursor emissions, and nothing in the 

statutory requirements for RACM and 

BACM limits these requirements only to 

major stationary sources. 

As discussed in the previous section, 

the final rule provides that states may 

develop a precursor demonstration 

showing that a particular PM2.5

precursor does not contribute 

significantly to PM2.5 levels that exceed 

the standard. If such a demonstration is 

approved by the EPA, then the state 

would not be required to adopt control 

measures for the precursor. Note that 

the state would still be obligated to 

evaluate and adopt control measures 

from a source if the source has 

emissions of direct PM2.5 and/or the 

remaining PM2.5 precursors that must be 

controlled in the plan. 

The EPA received a diverse set of 

comments on whether to include a de 

minimis source category exemption 

policy. Some commenters questioned 

why an up-front (i.e., before analysis of 

potential control measures) source 

category by source category exemption 

should be included in the final rule in 

the first place, when the traditional 

RACT/RACM policy approach for the 

NAAQS implementation has enabled 

states not to adopt otherwise reasonable 

control measures if after analyzing 

potential control measures it is 

determined that such measures are not 

needed for expeditious attainment. 

These commenters also suggested that a 

de minimis source category approach 

would undermine any RACM/RACT 

analysis to evaluate whether a collection 

of measures could advance the 

attainment date by a year, because a de 

minimis exemption policy would 

potentially allow for an area to exempt 

many categories which together could 

have a substantial ambient impact. 

Other commenters noted that providing 

a source category exemption in one 

nonattainment area would give those 

companies a competitive advantage over 

the same types of sources in other areas. 

A number of commenters supported 

the de minimis source category concept 

because they believed it could result in 

a reduced burden in the control measure 

evaluation stage and help avoid 

regulating sources with limited impact 

on PM2.5 levels. However, a number of 

commenters also expressed concern 

about the analytical resources that might 

be needed to conduct air quality 

modeling for a de minimis source 

category analysis. To address this 

analytical concern, some commenters 

suggested that the EPA include an 

emissions-based threshold (e.g., tons per 

day) rather than an air quality based 

threshold, and allow for its use only if 

controls on the source are not needed 

for expeditious attainment. However, 

the commenters did not address the fact 

that the air quality impact of a specific 

tons per day rate could vary widely 

from one pollutant to another within a 

particular nonattainment area. Other 

commenters noted that the NAICS 

system does not provide categories for 

nonpoint sources, and that this issue 

would need to be addressed if the 

NAICS approach were to be included in 

the final rule. Other commenters 

suggested that the rule not have a de 

minimis threshold at all but include the 

ability for the state to propose de 

minimis source categories to the EPA on 

a case-by-case basis. 

After taking the range of comments on 

the de minimis source category concept 

into consideration, the EPA has decided 

to not finalize a de minimis source 

category approach for Moderate areas. 

The EPA is persuaded by commenters 

who argued it is not necessary, and 

believes that without this concept, the 

final rule will nevertheless provide 

sufficient flexibility in the Moderate 

area control measure analysis and 

attainment demonstration process due 

to the availability of precursor 

demonstrations, considerations of casespecific factors in determining technical 

and economic feasibility, and the 

longstanding ability for the state not to 

adopt certain otherwise reasonable 

measures if they are not needed for 

expeditious attainment. The EPA also 

finds that from a technical perspective, 

it would be very challenging to 

implement a de minimis source category 

process in a consistent manner 

nationally without clear guidelines 

describing how narrowly or how 

broadly a de minimis exemption could 

apply, or how the technical analysis 

would need to be performed. The EPA 

agrees with commenters that NAICS 

codes do not provide an appropriately 

comprehensive approach for defining 

source categories for this purpose. We 

note that a de minimis source category 

exemption process has been available in 

PM10 NAAQS implementation guidance 

(the Addendum) since 1994, and 

remains available. In many PM10 areas, 

it is relatively straightforward to 

identify the predominant source 

categories contributing to the NAAQS 

violations (such as direct PM emissions 

from dust or wood smoke), and 

therefore to be able to identify what 

categories might be considered de 

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74Note that the term ‘‘control measures’’ as used 

in this preamble broadly represents a range of 

enforceable approaches for reducing emissions. 

These enforceable approaches include, but are not 

limited to, installation of control technology, 

process changes, a change in fuel use, limitations 

on use or operation of a particular pollutantemitting device, equipment replacement, dust 

minimization practices, and road paving. 

75Additional guidance on evaluating potential 

control measures is provided in the previous 

Section III.D.1 of this preamble, Background. 

76See 75 FR 80118 (December 21, 2010), 

revisions to test methods for measuring 

condensable PM emissions from stationary sources 

(Method 202). 

minimis. However, implementation of 

the PM2.5 NAAQS presents more 

complex challenges. Precursors and 

their contribution to secondarily formed 

PM play a much greater role in PM2.5

nonattainment areas than in PM10

nonattainment areas. In addition, the 

relative impact of each precursor to 

local PM2.5 concentrations varies from 

area to area. For these reasons, a de 

minimis source category concept for 

PM2.5 is not included in this final rule. 

c. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

3. Step 2: Identify Existing and Potential 

Control Measures 

a. General Guidance 

i. Summary of Proposal 

The proposal preamble described 

general guidance for identifying existing 

and potential control measures. 

ii. Final Rule 

The guidance remains largely 

unchanged from the proposal. The 

state’s compilation of existing and 

potential control measures 74 should 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 (including filterable and 

condensable 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, states should identify and 

consider control measures for all types 

of sources.75

It is important to note that the 

emission inventory provisions of this 

rule require states with sources of direct 

PM2.5 to include emissions data for both 

filterable PM2.5 and condensable PM2.5

in the base year inventory for the 

nonattainment area. For some types of 

sources, condensable emissions can be 

much larger than filterable emissions, in 

some cases by ten times or more. 

Because the availability of condensable 

PM2.5 emissions data has been limited to 

date but more data will become 

available through nonattainment 

planning efforts, the EPA recommends 

that states pay particular attention to 

identifying potential control measures 

for source categories with substantial 

condensable emissions. If measures are 

found to be technically and 

economically feasible for reducing 

condensable PM2.5 emissions as well as 

filterable PM2.5 emissions from a source, 

the state will need to adopt a new 

emissions limit for the source that 

accounts for both the filterable and 

condensable portions, and includes 

requirements for ensuring compliance 

using source test methods updated in 

2011.76

The control measure evaluation 

process described in this section 

generally 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. In 

section 51.1009(a)(3)(iii) of the final 

rule, the state is required to include a 

complete and reasoned explanation to 

support its selection and rejection of 

control measures as part of the 

attainment plan submission for any 

Moderate nonattainment area. 

Existing control measures. As a 

starting point when identifying 

candidate control measures, a state 

should include an initial list of control 

measures 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 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 the existence of 

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 control 

technology analyses to address 

emissions for previous RACM/RACT 

analyses or for other statutory purposes. 

Some of these determinations may have 

been done relatively recently, while 

other determinations may be several 

years old. A state may not simply rely 

on a previous RACM or RACT 

determination or other control 

technology analysis for a particular 

source or source category, regardless of 

how recently it was performed, when 

developing the attainment plan for a 

PM2.5 NAAQS. Past experience has 

shown that due to ongoing innovation, 

cost-effective control technologies and 

process alternatives for many sectors 

continue to be developed, and new 

reasonable opportunities to reduce 

emissions in the future are expected to 

be available for existing sources, 

particularly those with technology 

determinations made several years ago. 

For this reason, the state must 

determine whether the existing controls 

or emissions reduction approach at the 

source can be updated or improved with 

reasonably available controls or 

strategies to achieve increased levels of 

emission reduction. In cases where a 

stationary source has installed new 

state-of-the-art emissions controls fairly 

recently (e.g., within the last 3 years), 

the state technically would still need to 

provide a RACT analysis for the source, 

but in such cases it may be appropriate 

to find that existing controls satisfy the 

RACT requirement. Based on this 

policy, the state’s updated RACM and 

RACT analyses will represent the most 

thorough, up-to-date review of control 

measures for its PM2.5 nonattainment 

area. The collection of existing control 

measures, any updated RACT/RACM 

determinations, and potential new 

control measures can then be 

considered together by the state as part 

of a comprehensive analysis to ensure 

the area will attain expeditiously. The 

EPA notes, however, that the more 

recently this analysis has been done, the 

less effort is expected to be needed to 

verify that it is up to date. 

Potential control measures. In 

addition to identifying and reviewing 

existing control measures for sources in 

a Moderate PM2.5 nonattainment area, a 

state must develop a comprehensive list 

of potential new control measures. This 

process should involve close 

coordination between the state, source 

owners, municipalities, and other 

interested stakeholders. The potential 

measures should also have a strong 

technical basis. Analysis of emission 

inventory data summaries, fine particle 

speciation monitoring data and source 

apportionment air quality modeling data 

can help identify key sectors 

contributing to the PM2.5 problem in an 

area. Other analyses to characterize the 

seasonal variation of PM2.5

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77Links are provided to a number of national, 

state and local air quality agency sites from the 

EPA’s PM2.5 Web site: http://www3.epa.gov/pm/

measures.html. 

78The EPA notes that some wildland logging 

operations are conducted for the same purposes as 

prescribed fire (e.g., reducing fuel load, ecosystem 

benefits, etc.). The fact that some of the removed 

trees may be sold as timber does not make 

commercial timber sale the primary purpose of such 

operations. 

concentrations and associated 

meteorology may help inform the state 

in identifying contributing sources and 

potential control measures. 

Information about potential control 

measures and control technologies is 

available from a number of sources. One 

important source of information is the 

combined regulatory experience of other 

states. A compilation of existing control 

regulations that are on the books in 

other states can be a useful starting 

point for identifying potential control 

measures. Another source of 

information is the EPA’s Office of Air 

Quality Planning and Standards 

(OAQPS) ‘‘Menu of Control Measures’’ 

document, available online at http://

www3.epa.gov/ttn/naaqs/pdfs/

MenuOfControlMeasures.pdf. This 

document was developed to provide 

information useful in the development 

of local emissions reduction and the 

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, and can be searched for 

control approaches that address specific 

pollutants. 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.77 Again, 

the EPA recognizes that 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. 

iii. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

b. Managing Emissions From Wildfire 

and Wildland Prescribed Fire. 

i. Proposed Rule 

The EPA proposed to recommend as 

guidance but not as a requirement of the 

final rule that, if wildfire impacts are 

significant, contributing to exceedances 

of the standard, then states should 

consider RACM for wildfires (which 

RACM could include a required 

program of prescribed fires). The EPA 

also proposed to recommend that states 

should consider RACM for managing 

emissions from prescribed fires 

(including those prescribed fires 

conducted to reduce future wildfire 

emissions). The proposal noted that 

information is available from the DOI 

and the USDA Forest Service on smoke 

management programs and basic smoke 

management practices (BSMP). The EPA 

requested comment on the concept of, 

and practical considerations associated 

with RACM for wildfire and RACM for 

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. 

ii. Final Rule 

Wildfire can make a large 

contribution to air pollution (including 

PM2.5), and wildfire events can threaten 

public safety. These effects can be 

mitigated through management of 

wildland vegetation, including through 

prescribed fire. Such mitigation can 

help manage the contribution of fires to 

PM2.5 levels in nonattainment areas. 

Prescribed fire (and some wildfires) can 

mimic the natural processes necessary 

to maintain fire dependent ecosystems, 

minimizing catastrophic wildfires and 

the risks they pose to safety, property 

and air quality. 

Upon consideration of public 

comments and further consultation with 

other federal agencies, the EPA 

recommends, as guidance for states as 

they implement the final rule, that states 

follow a different approach to 

addressing RACM for wildland fire than 

the approach that the EPA proposed to 

recommend. Before explaining this 

recommendation further, the EPA 

wishes to clarify that the 

recommendation is focused on wildland 

fire management. There are other uses of 

prescribed fire and other types of 

burning that occur in nonattainment 

areas, or that affect downwind 

nonattainment areas, such as burning of 

land clearing debris, agricultural 

burning, and burning of logging slash on 

land where the primary purpose of the 

logging is for commercial timber sale.78

The challenges with applying the 

traditional nonattainment planning 

framework that are raised in this 

discussion are particular to wildland 

fire, and the EPA believes that 

addressing these other uses of 

prescribed fire does not present nearly 

the same level of challenge, and thereby 

can still be accommodated within the 

nonattainment planning framework. For 

example, where these other types of 

burning currently contribute to PM2.5

levels in a nonattainment area, states 

may, with an adequate technical 

demonstration, be able to take credit for 

reductions resulting from improvement 

in smoke management techniques for 

these types of prescribed fire where the 

improvement results in a demonstrated 

reduction in impacts in the 

nonattainment area. The remainder of 

this discussion is not meant to address 

these categories, and is instead focused 

on prescribed fire on wildlands. 

The EPA also wants to clarify that it 

is not the intention to in any way 

discourage federal, state, local or tribal 

agencies or private land owners from 

taking situation-appropriate steps to 

minimize impacts from prescribed fire 

emissions on wildland. The EPA 

encourages all land owners and 

managers to apply appropriate basic 

smoke management practices to reduce 

emissions from prescribed fires, 

especially where a state has determined 

that prescribed fires are a significant 

source affecting air quality. The EPA 

understands that the federal land 

managers (FLMs) apply these measures 

routinely and will be available to 

consult with other agencies and private 

parties interested in doing the same. 

However, for several reasons, the EPA 

does not believe it would be effective 

policy or technically appropriate to 

recommend that control measures for 

wildland fire be adopted into the SIP as 

enforceable measures and credited for 

emissions reductions (of PM2.5 and 

precursors) that would help the area 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58039 

79These reasons include concerns raised by 

commenters about the difficulties associated with 

requiring or even encouraging states to incorporate 

wildland fire emissions into existing nonattainment 

planning procedures and practices under the CAA; 

high year-to-year variability and unpredictability 

with emissions from wildland fires; uncertainty in 

the amount of credit to give for reduced wildfire 

within the planning period and in the amount of 

benefit that exists after accounting for increases in 

prescribed fires within the planning period; and 

finally, the fact that air quality data actually 

influenced by fire events may ultimately be 

excluded under the provisions of the Exceptional 

Events Rule. 

attain the standard.79 Instead, EPA 

recommends that PM2.5 nonattainment 

plans (and in particular the attainment 

demonstrations) not expressly account 

for expected air quality changes over the 

planning period resulting from changes 

in the use of wildland prescribed fire to 

reduce future wildfires, or air quality 

changes over the planning period 

resulting from changes in wildland fire 

emissions due to a program of 

prescribed fire or due to any other cause 

including climate change. In most cases, 

state attainment demonstration 

modeling should assume that wildland 

prescribed fire and wildfire emissions in 

the attainment year will be equal to, and 

have the same temporal and geographic 

pattern as, those assumed in the 

baseline inventory year. 

The EPA acknowledges that some 

temporal and spatial patterns of fire 

emissions must still be assumed in the 

attainment demonstration in order to 

ensure that the required air quality 

modeling results in a realistic physical 

and chemical environment and a 

correspondingly realistic model 

response against which to analyze the 

changes from categories where express 

accounting of changes is still being 

done. This rule is not intended to 

constrain the options for states 

regarding the appropriate assumptions 

to make for fire emissions. Rather, it 

simply recommends that once this base 

level is established, PM2.5 plans should 

not attempt to expressly project changes 

over the planning period in emissions 

from wildfires or prescribed fires on 

wildland within the nonattainment area, 

or in upwind areas included in the 

modeling domain, that are due to 

variability in wildfire occurrence or 

changes in the use of prescribed fire or 

other wildland fire management 

practices. Moreover, the EPA anticipates 

that changes in spatial and temporal 

patterns of wildfire will likewise be too 

uncertain for them to be allowed to have 

the effect of reducing or increasing the 

control requirement on conventional 

anthropogenic sources. The EPA 

therefore recommends that baseline 

wildland fire emissions should 

generally be held constant over the 

planning period, regardless of whether 

wildland fire management practices by 

land managers are expected, and 

possibly encouraged, to change. 

States still have flexibility in 

determining how best to represent 

baseline wildland fire emissions. As 

noted earlier, base year emission 

inventories for the nonattainment areas 

should represent the conditions leading 

to nonattainment and be consistent with 

inventories used for modeling. For fires, 

the EPA additionally encourages states 

to use a representative mix of prescribed 

fire and wildfire in their inventories. In 

the past, some plans under previous 

PM2.5 NAAQS have estimated the actual 

fire emissions and temporal and spatial 

patterns from a given year and used this 

estimate as the assumed future baseline 

for planning, while others have used 

average emissions over multiple years. 

Other approaches may be appropriate as 

well. Moreover, regardless of the 

approach used, the EPA still encourages 

states to submit actual wildfire and 

prescribed fire activity data that are 

critical to developing emissions 

estimates to the NEI as suggested in the 

AERR. 

A consequence of the 

recommendation of not expressly 

accounting for changes in wildland fires 

in attainment demonstrations is that 

measures to reduce emissions from 

wildland fires, such as prescribed fire 

for wildland wildfire prevention and 

mitigation purposes or smoke 

management programs and BSMP for 

prescribed fires in wildland, need not be 

included as RACM for the respective 

fire types. This is because the changes 

in emissions due to such measures 

would not be accounted for in 

determining what is necessary for 

attainment and/or what would advance 

the attainment date, which is how the 

EPA is recommending that RACM be 

determined. So, for example, in an area 

that can attain in 6 years with measures 

that do not address wildland fire, the 

EPA does not recommend that states 

attempt to quantify whether increased 

prescribed fire could advance the 

attainment date by 1 year, due to 

aforementioned difficulties associated 

with such quantification. 

To be clear, nothing about this policy 

regarding RACM is intended to suggest 

that fires should be ignited in wildland 

(or elsewhere) without regard to the air 

quality or public health consequences. 

As noted earlier, the EPA believes these 

consequences are important to address, 

and intends to engage in dialogue with 

the FLMs, air agencies, tribes, state and 

private land owners and other 

stakeholders at appropriate times, such 

as during the process for the 

development of land management plans, 

about how land managers determine 

when and where prescribed fire is 

appropriate for particular wildlands and 

how to identify and implement 

appropriate mitigation measures. The 

policy simply makes clear the EPA’s 

view regarding its recommendation for 

RACM for wildland fires. 

The EPA notes that this 

recommendation regarding RACM 

differs somewhat from the 

recommendation that was offered in the 

preamble as guidance to states as they 

implement the EPA’s recent SIP 

Requirements Rule for the 1997 and 

2008 ozone NAAQS. The reasons for the 

strategy outlined earlier apply equally 

well to attainment demonstrations for 

the ozone NAAQS, and so EPA hereby 

makes the same recommendation for 

implementation of these ozone NAAQS 

as well. This recommendation, offered 

here in the same manner as the prior 

recommendation, supersedes the prior 

recommendation on RACM for wildfire 

in the preamble to the final SIP 

Requirements Rule for the 1997 and 

2008 ozone NAAQS. The EPA will 

convey this revised recommendation to 

the air agencies that are working to 

prepare these ozone SIPs. The EPA also 

anticipates making this 

recommendation as part of our planned 

rulemaking on implementation of the 

2015 ozone NAAQS. Note that this 

discussion pertains only to the RACM 

policy, and that other aspects of the fire 

discussions in the ozone SIP 

Requirements Rule remain applicable. 

Finally, the EPA notes that, because a 

significant element of the rationale for 

this policy is the uncertainty in the 

timing of wildfires, we may reconsider 

this recommendation in the future, if 

adequate tools emerge that allow for 

predicting fire emissions with sufficient 

specificity. However, even if such tools 

emerge, due to inherent uncertainties it 

may be impossible to satisfactorily 

incorporate the use of such information 

into an attainment demonstration 

framework. 

iii. Comments and Responses 

The EPA received many comments 

expressing agreement with EPA’s 

recognition of the importance of 

wildland prescribed fire, and 

welcoming continued dialogue among 

states, the EPA, and other federal 

agencies on how best to ensure that land 

managers have adequate management 

tools available, including prescribed fire 

and some wildfire, but also to ensure 

that use of these tools does not result in 

unhealthy air. The EPA intends to 

engage in such dialogue. 

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58040 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

80See the Federal Register published on April 25, 

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

81See ‘‘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 CAA 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). 

82Letter 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. 

83 79 FR 32892 (June 9, 2013). 

84See the proposed PM2.5 SIP requirements rule 

(80 FR 15340, 15373) 

Some commenters also took positions 

on how specifically to define RACM for 

wildfires, ranging from required smoke 

management plans to simply stating that 

fires themselves are RACM with no 

further measures required. In light of the 

fact that EPA did not propose specific 

guidance on defining RACM for 

wildfires and typically does not define 

RACM for specific categories, and the 

fact that EPA is not recommending that 

states include RACM as proposed, we 

are not providing further guidance in 

response to those comments. Similarly, 

regarding baseline fire emissions, some 

commenters provided detailed 

suggestions regarding approaches to 

calculating baselines based not on 

actual fires (which may include periods 

when fires were suppressed) but on 

science-based fire regimes, fire return 

intervals and ecosystem types, 

including characteristics of wildland 

vegetation. The EPA notes that this 

guidance is not establishing or 

recommending any particular approach 

to calculating baseline fire emissions. 

c. RACT for EGUs 

i. Summary of Proposal 

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 cap-and-trade 

program for such emissions.80 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.81 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.82 83 In that proposal, the EPA 

explained that given the explicit 

wording of CAA 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, in the proposal the EPA 

stated that it did not intend to include 

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 stated that it 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. 

ii. Final Rule 

The final rule maintains the proposed 

policy approach as described earlier. As 

required by the CAA, states are required 

to analyze what constitutes RACM and 

RACT for EGUs in each nonattainment 

area, just as they are required to do for 

all other types of sources. 

iii. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

4. Step 3: Determine Whether an 

Available Control Measure or 

Technology Is Technologically Feasible 

a. Summary of Proposal 

The proposal cited longstanding 

guidance from the General Preamble 

regarding factors to consider when 

determining the technological feasibility 

of a potential control measure or control 

technology, and it requested comment 

on the factors. These factors included 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. One 

sentence in the proposal stated: ‘‘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 

. . .’’ 84

b. Final Rule 

Several comments addressed the 

EPA’s inclusion of the social 

acceptability factor in the proposal. In 

reviewing this issue, the EPA 

determined that this factor actually has 

not been identified as a factor in the 

EPA’s longstanding guidance, and thus 

was mischaracterized in the proposal. 

Nevertheless, some commenters 

supported inclusion of the factor 

because no other factor is presented to 

help limit or eliminate a potential 

measure with strong public opposition. 

Other commenters that opposed use of 

such a factor suggested that including it 

in the final rule could allow a state to 

reject almost any control measures that 

is otherwise found to be technically and 

economically feasible. 

When the EPA issued a proposed 

PM2.5 NAAQS implementation rule in 

2005, it requested comment on the same 

social acceptability factor, and 

ultimately did not include social 

acceptability as a factor for determining 

RACM in the final 2007 PM2.5

implementation rule. In the 2007 final 

rule, however, the EPA stated: 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58041 

85See the Federal Register published on April 16, 

1992 (57 FR 13498, 13540 and 13541). 

86Addendum 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 applying it here for 

Moderate area RACM determinations. 

87See the EPA Web site at https://www3.epa.gov/ 

airquality/agriculture/. 

88See the USDA NRCS Air Quality Technical 

Resources at http://www.nrcs.usda.gov/wps/portal/

nrcs/main/national/air/quality/. 

89 ‘‘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. 

90Letter 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. 

‘‘Therefore, given the concerns raised by 

commenters that establishment of 

‘social acceptability’ as a factor in the 

RACM analysis is without basis in the 

CAA and might result in inappropriate 

skewing of control strategies, we have 

removed this term from the final rule. 

We reiterate, however, that capability of 

effective implementation and 

enforcement are relevant considerations 

in the RACM analysis, even though 

public ‘unpopularity’ is not. Moreover, 

in assessing the efficacy of measures 

and the credit they should be given in 

the context of attainment 

demonstrations or RFP calculations, 

EPA believes that such considerations 

are important.’’ For the same reason it 

was not included in the previous 

implementation rule, the EPA has 

decided to not include the social 

acceptability factor in this final rule as 

well. See 40 CFR 51.1009(a)(3)(i). 

The following guidance is similar to 

what was presented in the proposal but 

has been updated to exclude the social 

acceptability factor: 

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. 

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 4.85 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. A state may 

consider such factors in determining 

whether a control measure is or is not 

technologically feasible to implement.86

In addition, with respect to 

determining whether a given control 

measure might not be technologically 

feasible for an area or mobile source, the 

EPA also retains its longstanding 

practice that a state may consider 

relevant factors in conducting its 

analysis, 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. 

c. Comments and Responses 

Comment: Some commenters stated 

that the EPA should make clearer in its 

rule and guidance that some categories 

of sources, particularly those such as 

animal and crop production, do not 

lend themselves to national 

determinations of best control practices; 

instead, these types of sources should be 

evaluated on nonattainment area 

specific conditions in determining the 

appropriate level of control measures. 

Response: The EPA agrees that 

nonattainment area-specific conditions 

are important factors when considering 

emission reduction options. States need 

to consider the feasibility of all 

identified options that have been 

demonstrated to reduce PM2.5 and PM2.5

precursors to determine whether such 

measures are appropriate for use in a 

particular PM2.5 nonattainment area. 

The EPA believes the determination 

of best control practices for any 

operation, particularly for animal 

production or crop production 

operations, should be a case-specific 

process. The process should start with 

the identification of PM2.5 and PM2.5

precursor emissions from the operation. 

Then it should consider which of the 

measures for reducing PM2.5 and PM2.5

precursors in a particular PM2.5

nonattainment area are technically and 

economically feasible for a particular 

operation. The EPA recognizes that 

there are a number of factors specific to 

each operation that could determine 

whether a potential emission reduction 

measure is technically and 

economically feasible for 

implementation. 

Although the EPA is not making any 

national determinations of best control 

practices for animal production and 

crop production operations, we do note 

that there are many relevant references 

on potential emissions reduction 

options, including the Agricultural Air 

Quality Conservation Measures 

Reference Guide for Cropping Systems 

and Land Management.87 The EPA and 

USDA jointly developed this document 

to identify measures that have been 

demonstrated to reduce emissions and 

describe factors related to the 

applicability of each measure. A 

companion document is under 

development by the EPA and USDA that 

will identify potential emission 

reduction approaches for livestock 

operations. Additionally, USDA’s 

Natural Resources Conservation Service 

(NRCS) provides a list of approved 

practices in managing air emissions of 

concern for particulate matter, ozone, 

greenhouse gas, and odor-related 

issues.88 A number of regulatory and 

non-regulatory programs are already 

being implemented (in nonattainment 

and attainment areas alike) to reduce 

emissions of PM2.5 and PM2.5 precursors 

from agricultural operations. Finally, a 

large body of information is available on 

topics such as feed management, 

livestock housing, conservation tillage, 

road use and other topics from federal 

agencies, states, industry groups, 

academic institutions, and international 

organizations. 

5. Step 4: Determine Whether an 

Available Control Measure or 

Technology Is Economically Feasible 

a. Summary of Proposal 

The proposal described that in the 

1992 General Preamble, EPA’s 

longstanding interpretation of the term 

‘‘economic feasibility’’ in the context of 

evaluating potential RACM and RACT 

has included a presumption that it is 

reasonable for similar sources to bear 

similar costs of emissions reductions, 

even if they are in different 

nonattainment areas or different states. 

The proposal indicated that this 

presumption was not included in the 

2007 implementation rule for the PM2.5

NAAQS that the EPA had received a 

petition for reconsideration with respect 

to this issue, and that EPA had granted 

this petition in 2011.89 90 The March 

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58042 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

91See the Federal Register published on April 16, 

1992 (57 FR 13498, 13540 and 13541). 

92These longstanding factors were established in 

the EPA guidance in 1992 and are applicable to 

implementation programs for all the NAAQS 

pollutants. See the appendices to the General 

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

2015 proposed PM2.5 SIP requirements 

rule indicated the EPA’s intention to not 

adopt the economic feasibility factors as 

described in the 2007 rule, but to return 

to the original interpretation from the 

1992 General Preamble, including the 

presumption that it is reasonable for 

similar sources to bear similar costs of 

emissions reductions. 

The proposal also characterized past 

guidance from the 1992 General 

Preamble as stating that if a state 

contends that a source-specific control 

level should not be established because 

the source(s) cannot afford the control 

measure that is demonstrated to be 

economically feasible for other sources 

in its source category, then the state 

must support the claim with 

information regarding the impact of 

imposing the identified control measure 

or technology on the several financial 

indicators. The proposal also 

recommended that cost effectiveness 

should generally be evaluated by 

assessing the cost per ton of emissions 

reduced associated with a control 

measure, but the proposal also 

requested comment on an alternative 

metric to assess cost effectiveness in 

terms of the cost per unit of air quality 

improvement (i.e., ‘‘cost per 

microgram’’). 

b. Final Rule 

Based on a consideration of the 

comments received, the EPA has 

determined that economic feasibility 

considerations should generally align 

with the interpretation in the 1992 

General Preamble. Note that the 

proposal indicated that if it is claimed 

that a control approach is not 

economically feasible for a specific 

source, the state needs to provide 

information related to several financial 

indicators to support the claim. We note 

that the original policy in the 1992 

General Preamble suggests that if a 

source desires to make such a claim, it 

should provide such information to the 

state for its consideration. This final 

rule characterizes the policy in a similar 

manner, where the source would have 

the option of providing this financial 

information to the state for its review. 

This approach should address the 

concerns of some commenters that such 

financial information may not be readily 

available to the state. Thus, the final 

policy for considering economic 

feasibility of control measures is 

described in the following paragraphs. 

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 

and the cost of emissions reduction 

measures that have been implemented 

at other similar sources in the same or 

other areas.91 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 

similar sources have implemented the 

control technology, process change or 

measure in question. 

For each technologically feasible 

control measure, a state should evaluate 

the economic feasibility of the measure 

or control, through consideration of 

factors such as 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. A state should 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 for sources in the 

nonattainment area. See 40 CFR 

51.1009(a)(3). 

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. In considering what level of 

control is reasonable, the EPA does not 

recommend a specific fixed dollar per 

ton cost threshold for economic 

feasibility of controls identified as 

potential RACM and RACT. 

If a source contends that a sourcespecific control-level should not be 

established because the source cannot 

afford the control measure or technology 

that is demonstrated to be economically 

feasible for other sources in its source 

category, the source should make its 

claim known to the state and 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).92

c. Comments and Responses 

Comment: With regard to the 

presumption that it is reasonable for 

similar sources to bear similar costs of 

emissions reductions, some commenters 

supported returning to the approach 

described in the General Preamble as 

EPA proposed, while other commenters 

suggested that based on its experience 

with industry the EPA knows that just 

because a technology will work at one 

source does not mean that it will 

necessarily work at a similar source due 

to source configuration and non-RACT 

reasons (e.g., enforcement proceedings) 

for the installation of different 

technology at ‘‘similar’’ sources. 

Response: The latter commenters 

appear concerned that the rule would 

require the imposition of all controls on 

similar sources without allowing for 

consideration of whether such controls 

are technologically and economically 

feasible. This is not what EPA proposed. 

Instead, the EPA proposed, and is now 

finalizing, a requirement that the state 

first identify potential control measures 

for sources in a nonattainment area. The 

state should then identify which control 

measures are economically and 

technologically feasible based on its 

review of various factors. If the state 

determines that certain controls are not 

reasonably available based on its review 

of these factors, it must provide a 

written justification to the EPA 

explaining its rationale. This review 

should at least evaluate the feasibility of 

all the identified controls on similar 

sources to determine whether 

implementation of such controls in the 

nonattainment area at issue is 

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93 57 FR 13498 (April 16, 1992), at page 13541. 

94With 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 

Continued 

reasonable. The EPA recognizes that 

there are a number of source-specific 

factors that the state can take into 

account in making these determinations. 

Factors such as the physical onsite 

configuration of a facility may 

determine whether a particular control 

device or operation can be feasibly 

implemented. Likewise, a state should 

take into account information provided 

by the source on particular economic 

factors such as those described earlier in 

making a case-by-case determination of 

the economic feasibility of a control 

measure. 

Comment: Two commenters 

supported the EPA’s proposal that costeffectiveness should consider capital 

costs, operating costs and maintenance 

costs at the particular source in 

question. 

Some commenters supported using an 

alternative cost effectiveness metric 

such as cost per microgram of air quality 

improvement where appropriate air 

quality modeling has been developed 

for the area and can reasonably 

characterize the relative importance of 

various precursors. Some commenters 

opposed the proposal’s alternative costeffectiveness metric because the 

approach is overly complex and the 

impacts are rarely uniform across an 

area. 

Response: The EPA has decided to 

maintain its traditional recommendation 

to use a cost per ton approach for 

evaluating the cost effectiveness of 

particular control options. The EPA 

does not recommend the cost per 

microgram alternative approach because 

there are a number of technical and 

resource challenges associated with 

implementing it in a technically 

rigorous manner based on detailed air 

quality modeling information. The EPA 

believes that this policy approach 

would unnecessarily add complication 

and extra burden to the state’s process 

for determining economic feasibility for 

subject sources in a nonattainment area. 

Moreover, the EPA believes that the 

flexibility described here to consider 

cost-effectiveness in assessing economic 

feasibility, when coupled with the 

upcoming discussion of Step 6, and 

with the major stationary source and 

comprehensive precursor 

demonstrations previously described 

will ensure that unreasonable 

application of measures (e.g., those that 

are not effective in reducing PM2.5

concentrations) will not occur. 

6. Step 5: Determine the Earliest Date by 

Which a Control Measure or Technology 

Can be Implemented in Whole or in Part 

a. Summary of Proposal 

In this section, the proposal discussed 

two main issues related to the date by 

which control measures can be 

implemented. First, it proposed that 

when a state is determining RACM/

RACT, it must consider whether a 

control measure can be implemented in 

part when full implementation of the 

measure within 4 years of designation is 

not feasible. The proposal also 

introduced the concept of ‘‘additional 

reasonable measures,’’ meaning those 

measures that can only be implemented 

after the fourth year but prior to the 

Moderate area 6-year attainment date. It 

was proposed that a state must identify 

additional reasonable measures and 

adopt those measures as needed for 

expeditious attainment. 

b. Final Rule 

This section remains relatively 

unchanged from the proposal. 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 

‘‘implemented’’ 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 retains this definition in this rule. 

See 40 CFR 51.1000. 

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.’’ 93 The EPA continues to 

interpret the RACM/RACT definition to 

mean 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, a state must 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. See 40 CFR 

51.1009(a)(4)(i)(A). 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 candidate 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 

such a measure is needed for timely 

attainment of the PM2.5 NAAQS in the 

area. 

Therefore, for the purposes of meeting 

the RACM/RACT requirement, 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 

candidate measures may constitute 

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, 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, but before the 

attainment date. The statutory 4-year 

timing requirement for implementing 

RACM and RACT under CAA 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 

interprets this provision to include 

‘‘additional reasonable measures,’’ 

which are those measures and 

technologies that can be applied at 

sources in the nonattainment area that 

are otherwise technologically and 

economically feasible but can only be 

implemented in whole or in part later 

than 4 years after designation.94

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through the sixth calendar year following 

designation. 95 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). 

96Note 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. 

7. Step 6: Evaluate the Collective Impact 

of Potential Control Measures To 

Determine Whether the Area Can Attain 

Expeditiously or Whether it is 

Impracticable to Attain by the 

Attainment Date, and Adopt the 

Appropriate Set of Control Measures 

a. Summary of Proposal 

The proposal described the control 

measure requirements for two 

situations: The case where the state can 

demonstrate attainment by the 

attainment date; and the case where the 

state demonstrates the area cannot 

practicably attain by the attainment 

date. 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. Those technologically 

and economically feasible measures 

needed for attainment that can be 

implemented within 4 years of the date 

of designation would be considered to 

be RACM/RACT. Those measures 

needed for attainment that cannot be 

implemented within 4 years but can be 

implemented no later than the 

attainment date would be considered to 

be ‘‘additional reasonable measures.’’ 

The proposal stated that, consistent 

with longstanding policy, this means 

that the state may choose to not adopt 

certain measures if collectively they 

would not advance the attainment date 

by 1 year.95

For the situation where a state 

determines that it is impracticable to 

attain by the Moderate area attainment 

date, the proposal included two policy 

options for describing what control 

measures must be adopted and 

implemented. One option would have 

required the state to adopt all 

technologically and economically 

feasible control measures, as stated in 

past guidance in the General Preamble. 

The other option would have required 

adoption of technologically and 

economically feasible control measures 

with an explicit exception for those 

measures that collectively are 

determined to be ‘‘ineffective in 

reducing ambient PM2.5 levels.’’ The 

proposal also reviewed the proposed 

options for demonstrating that a 

precursor does not make a significant 

contribution to PM2.5 levels that exceed 

the standard, and discussed how the 

final precursor policy may be an 

important consideration in deciding 

upon a control measure policy approach 

for Moderate areas that demonstrate 

they cannot practicably attain. 

b. Final Rule (General) 

For an area that can demonstrate that 

it will attain by the attainment date, the 

final rule maintains the same approach 

as described in the proposal regarding 

the collective evaluation of potential 

control measures to determine whether 

the area can advance the attainment 

date by 1 year. For an area that 

demonstrates that it would be 

impracticable to attain by the attainment 

date, the final rule does not include an 

explicit exception for those measures 

that collectively are determined to be 

‘‘ineffective in reducing ambient PM2.5

levels.’’ More details are provided in 

sections (c) and (d) that follow. 

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 requirements for 

attainment demonstration modeling is 

presented in Section IV.E of this 

preamble. However, one of the key 

features of attainment demonstration 

modeling and related analysis is that 

they provide 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 use the 

results of their analyses 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 CAA 

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

explained later.96

Section 188 establishes the attainment 

dates for Moderate and Serious PM10

nonattainment areas, and this rule also 

applies such dates to Moderate and 

Serious PM2.5 nonattainment 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 twostep 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 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 of 

this preamble. 

c. Final Rule—Step 6 (Attainment Case): 

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 

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97The concept of an ‘‘impracticability 

demonstration’’ is established in CAA section 

188(b), which addresses reclassifying Moderate 

PM2.5 areas to Serious. Section 188(b)(1) of the CAA 

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, CAA 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. 

98 57 FR 13498 (April 16, 1992), at page 13544. 

99 Ibid. at 13544. 

100 Ibid. 

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 CAA section 

172(c)(6) as ‘‘additional reasonable 

measures’’ for the area and necessary to 

demonstrate timely attainment under 

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

For this type of situation, 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 defines 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. The EPA maintains that 

identifying a complete set of measures 

that qualify as RACM/RACT and 

additional reasonable measures but that 

are not necessary for attainment within 

6 years is imperative to adequately 

demonstrate that such measures will not 

collectively advance the attainment date 

for a Moderate area by at least 1 year. 

The EPA will require a robust analysis 

and explanation by the state when such 

determinations are made. See 40 CFR 

51.1009(a)(4)(i). 

d. Final Rule—Step 6 (Impracticability 

Case): If the State Cannot Demonstrate 

Attainment by the Statutory Attainment 

Date for a Moderate Area, Then the State 

Must Adopt All Reasonably Available 

Control Measures 

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

anticipates that not all Moderate 

nonattainment areas will be able to 

demonstrate attainment by the 

attainment date, and it incorporates the 

concept of an ‘‘impracticability 

demonstration’’ for such areas.97

Commenters on this issue stated that 

nowhere in the statute is there an 

explicit exception for those measures 

that collectively are determined to be 

‘‘ineffective in reducing ambient PM2.5

levels.’’ Further, they suggested that 

such an approach would enable the 

most polluted areas to exempt sources 

that individually are small by some 

arbitrary test when in other cleaner 

areas such sources would be required to 

reduce emissions because they 

collectively would advance attainment. 

Other commenters emphasized that 

sources located in such Moderate areas 

should still be subject to the regular 

review process for determining whether 

potential control measures are not 

technologically or economically 

feasible. 

After considering comments on the 

two options described in the proposal, 

the EPA has decided to keep the policy 

in this final rule consistent with past 

guidance in the General Preamble. This 

guidance stated 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].’’ 98 The EPA believes that this 

interpretation is compelled by the 

language of CAA 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 showing that with those 

measures it cannot attain the NAAQS by 

the applicable attainment date. 

Under this approach, if the state had 

an approved precursor demonstration 

(as described in Section III of this 

preamble) showing that a particular 

precursor does not have a significant 

contribution on PM2.5 levels that exceed 

the standard, then it would not need to 

adopt control measures for that 

particular precursor. The state then 

would be required to identify potential 

control measures for sources in the area 

that emit direct PM2.5 and any 

remaining significant precursors. Of 

these potential measures, the state 

would determine which would be 

technologically feasible to implement. 

Then the state would identify which of 

the technologically feasible measures 

are economically feasible to implement. 

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.’’ 99

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.’’ 100 Thus, the 

state should assess the remaining set of 

technologically and economically 

feasible measures with regard to the 

compatibility of implementing RACM/

RACT in the near term in a way that 

supports addressing BACM/BACT for 

such sources when the area is 

reclassified to Serious. 

The General Preamble also provided 

guidance for stationary source controls 

in this situation: ‘‘In many instances, 

the installation of pollution controls 

representing RACT may involve 

substantial capital expenditures. In the 

event that BACT is later required for 

those sources, this may require controls 

significantly incompatible with those 

recently installed as RACT, largely 

wasting those recent expenditures. 

Under such circumstances, the 

installation of controls in the first round 

of SIP planning would be 

unreasonable.’’ Accordingly, SIPs for 

the Moderate areas that cannot 

practicably attain need not require 

major changes to the control systems for 

specific stack and process sources 

where a State reasonably demonstrates 

that such changes will be significantly 

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58046 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

incompatible with the application of 

BACT-level control systems. A State’s 

demonstration should include, for 

example, showing what the State 

believes are RACT and BACT for the 

source, and why they are significantly 

incompatible. 

The EPA believes that in such cases, 

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. 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. 

e. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

8. RACM and RACT and Additional 

Reasonable Measures Submission 

Requirements 

a. Summary of Proposal 

The proposal described a set of 

submission requirements for RACM/

RACT and additional reasonable 

measures. 

b. Final Rule 

The requirements in the final rule 

remain very similar to those that were 

included in the proposal. 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 requires under the authority of 

section 301(a) of the CAA that a state 

must submit the following information 

as part of its submission: 

(1) A list of all sources and activities 

in the nonattainment area that emit 

direct PM2.5 or any PM2.5 precursor (for 

multi-state nonattainment areas, this 

would include source categories, 

sources and activities from all states 

which make up the area). See 40 CFR 

51.1008(a)(1). 

(2) For each source or activity in the 

nonattainment area, an inventory of 

direct PM2.5 emissions and emissions of 

all PM2.5 precursors, and a 

comprehensive list of potential control 

measures considered by the state for the 

nonattainment area. See 40 CFR 

51.1009(a)(2). If the state submitted a 

precursor demonstration that was 

approved by the EPA, the state would 

not be required to submit a list of 

sources and potential measures to 

control emissions of the relevant 

precursor from the stationary sources 

addressed by the demonstration (i.e., all 

sources for a comprehensive precursor 

demonstration, or major sources for a 

major source precursor demonstration). 

See 40 CFR 51.1006(a)(1) and (2). Note 

that the emissions inventory would still 

need to include all sources of the 

relevant precursor. See 40 CFR 

51.1008(a)(1). 

(3) 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. See 40 

CFR 51.1009(a)(3). 

(4) For each technologically feasible 

emission control measure or technology, 

a determination of whether the measure 

is economically feasible must be 

included, with narrative explanation 

and quantitative supporting 

documentation to justify the state’s 

conclusion. See 40 CFR 51.1009(a)(3). 

The following additional information 

relevant to economic feasibility should 

be included as necessary to justify the 

determination: (a) The control efficiency 

by pollutant; (b) the possible emissions 

reductions by pollutant; and, (c) the 

estimated cost per ton of pollutant 

reduced. 

(5) For each technologically and 

economically feasible emission control 

measure or technology, the date by 

which the technology or measure could 

reasonably be implemented, in whole or 

in part. See 40 CFR 51.1009(a)(4)(i)–(ii). 

Each of these elements will provide 

information needed by the EPA to 

evaluate 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 

is finalizing a requirement for emissions 

inventory information specifically 

relevant to the RACM and RACT 

element of the state’s attainment plan in 

order to ensure that the EPA or any 

other party can appropriately evaluate 

the state’s RACM and RACT analysis. 

c. Comments and Responses 

Comment: Some commenters 

supported the general submission 

requirements because in some cases 

RACM/RACT demonstrations fail to 

provide the information necessary for 

the EPA to reasonably conclude that 

these requirements have been met and 

are supported by a systematic analysis. 

Response: The EPA agrees with the 

commenters and the final rule generally 

tracks the proposal. 

9. Criteria for Effective Regulations to 

Implement RACM and RACT and 

Additional Reasonable Measures 

a. Summary of Proposal 

The preamble to the proposed rule 

described the four main criteria for 

effective control measure regulations: 

Such regulations must be quantifiable, 

enforceable, replicable and accountable. 

b. Final Rule 

The guidance in this preamble to the 

final rule remains very similar to what 

was proposed. After a state has 

identified a particular control measure 

as RACM or RACT or additional 

reasonable measure for a particular 

nonattainment area, it must 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 

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101See 75 FR 80118 (December 21, 2010), 

revisions to test methods for measuring 

condensable PM emissions from stationary sources 

(Method 202). 

102The 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 https://www.epa.gov/

environmentaljustice. 

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. Note that if 

measures are found to be technically 

and economically feasible for reducing 

condensable PM2.5 emissions as well as 

filterable PM2.5 emissions from a source, 

the state will need to adopt a new 

emission limit for the source that 

accounts for both the filterable and 

condensable portions, and includes 

requirements for ensuring compliance 

using condensable PM2.5 source test 

methods updated in 2011.101

In response to a comment on this 

criterion, the EPA clarifies that an 

enforceable regulation for a CAA 

program must be enforceable by the 

EPA, the state, and citizens. By taking 

action to approve emissions limitations 

and related provisions into the SIP, the 

EPA thereby makes those emission 

limitations a federally enforceable 

component of the SIP that the state, the 

EPA, and citizens can enforce thereafter 

in the event of a violation. SIP 

provisions that effectively preclude 

enforcement of violations by the EPA or 

citizens, whether through impermissible 

exemptions or other SIP provisions that 

function to bar effective enforcement, 

are not acceptable. 

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. 

c. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

10. Determination of RACM and RACT 

and Additional Reasonable Measures in 

Multi-State Nonattainment Areas 

a. Summary of Proposal 

The proposal included several 

proposed recommendations about the 

development of control measures by 

states with multi-state nonattainment 

areas. 

b. Final Rule 

The guidance in the final preamble 

remains very similar to what was 

proposed. 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. 

c. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

11. Environmental Justice 

Considerations in Developing the 

Attainment Plan Control Strategy for a 

Moderate PM2.5 Nonattainment Area 

a. Summary of Proposal 

The proposal provided guidance 

about environmental justice 

considerations in developing the 

attainment plan control strategy for a 

Moderate area. 

b. Final Rule 

The guidance remains very similar to 

what was proposed. Current air quality 

data indicate that the more severe PM2.5

nonattainment areas contain a high 

population of people with low socioeconomic status, who are among the 

most at-risk for adverse health effects 

from exposure to PM2.5. As part of its 

EJ2020 Action Agenda, the EPA is 

committed to making progress on 

improving air quality in communities 

with high particulate pollution. The 

EPA, therefore, 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.102 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 XI of this 

preamble discusses possible approaches 

for states to address environmental 

justice concerns associated with 

implementation of the PM2.5 NAAQS in 

their SIP development process and 

attainment plans. 

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103An 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. 

104Pursuant to CAA section 188(b)(1)(B), upon 

the 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 SIP due date. 

c. Comments and Responses 

Any comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

E. Modeling for Attainment 

Demonstrations 

1. Demonstrations for Moderate Areas 

a. Summary of Proposal 

Section 189(a) of the CAA generally 

requires a state with a designated 

Moderate nonattainment area to submit 

an attainment plan for such area. 

Section 189(a)(1)(B) of the CAA 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. The EPA therefore 

proposed to require all Moderate 

nonattainment areas to submit either an 

attainment demonstration which 

includes air quality modeling which 

establishes that the area will attain the 

PM2.5 NAAQS by the applicable 

attainment date, or an impracticability 

demonstration which documents that 

the area will not attain the NAAQS by 

the applicable attainment date. The EPA 

proposed that the impracticability 

demonstration must also include air 

quality modeling, but also asked for 

comments on an alternative option that 

would not require air quality modeling 

as part of an impracticability 

demonstration. The EPA also proposed 

to allow states to fulfill the statutory 

modeling requirement through either 

locally generated photochemical and/or 

dispersion modeling or, with proper 

justification, appropriate regional or 

national modeling. 

An attainment demonstration is a 

plan that provides an explanation of 

how a state will attain the PM2.5 NAAQS 

by the applicable attainment date in a 

particular nonattainment area.103 The 

EPA proposed that the demonstration 

must contain: (i) Technical analyses 

such as base year and future year 

modeling of emissions which identifies 

sources and quantifies their 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. 

The EPA further proposed that 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 area will attain the 

NAAQS as expeditiously as practicable, 

but not later than the sixth 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, 

in particular, must explain why any 

cumulative group of reasonable and 

available control measures that the state 

elected not to adopt will not collectively 

advance the attainment date by at least 

1 year. 

b. Final Rule. As required by CAA 

section 189(a)(1)(B), the EPA is 

finalizing a requirement for states with 

Moderate nonattainment areas to submit 

a demonstration 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. 

As proposed, attainment 

demonstrations must include analyses 

(including air quality modeling) 

supporting the state’s determination of 

its proposed attainment date. In all 

cases, the state must show that the area 

will attain the NAAQS as expeditiously 

as practicable, but not later than the 

sixth calendar year after designation. 

The demonstration must include 

implementation of all measures 

identified as RACT/RACM plus 

additional reasonable measures, as 

necessary, for expeditious attainment. 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, in particular, must 

explain why the cumulative group of 

reasonable and available control 

measures that the state elected not to 

adopt will not collectively advance the 

attainment date by at least 1 year. See 

40 CFR 51.1009(a)(4). 

The EPA is not finalizing a regulatory 

requirement for air quality modeling to 

be included as part of an 

impracticability demonstration. See 40 

CFR 51.1009(a)(4). Since all 

nonattainment areas will have modeling 

requirements associated with their 

attainment demonstration, the EPA 

believes it is likely that modeling will 

be submitted in support of 

impracticability demonstrations. 

However, it may be possible in some 

cases to support an impracticability 

demonstration with ambient PM2.5 data 

and other relevant non-modeling 

information. For example, the ambient 

data in a nonattainment area may be so 

far above the NAAQS, and the 

reasonable and available controls (i.e. 

RACM/RACT and additional reasonable 

measures) so limited, that it is clearly 

impossible (and thus also impracticable) 

for the area to attain by the Moderate 

area attainment date.104 In order to 

support this type of demonstration, the 

state must show that, even if all 

reasonable controls (i.e. RACM or RACT 

and additional reasonable measures) 

were implemented, the state could not 

attain the NAAQS within the statutory 

timeframe for a Moderate area. 

The EPA continues to assume that in 

most cases photochemical grid 

modeling will be required to 

demonstrate attainment with the PM2.5

NAAQS. However, the EPA recognizes 

that more simplistic modeling 

techniques (such as dispersion, 

receptor, and/or box models) may 

suffice to demonstrate that an area will 

attain the NAAQS, especially in areas 

that are dominated by primary PM2.5

emissions (e.g. residential wood smoke). 

c. Comments and Responses. 

Comment: Some commenters supported 

the EPA’s proposal to require modeling 

to demonstrate that attainment is not 

practicable. The commenters stated that 

such an interpretation flows logically 

from the Act’s requirement in section 

189(a)(1)(B) that attainment 

demonstrations be supported by 

modeling. One commenter supported 

the alternative approach described in 

the proposal in which air quality 

modeling would not be required for a 

Moderate area impracticability 

demonstration. 

Response: After further consideration 

of this issue, the EPA has determined 

that modeling need not be a regulatory 

requirement to support an 

impracticability demonstration. We note 

that CAA section 189(a)(1)(B)(i) 

includes the parenthetical ‘‘including 

air quality modeling’’ which clearly 

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105The PM2.5 attainment demonstration modeling 

guidance can be found at the following Web site: 

http://www3.epa.gov/ttn/scram/guidance_sip.htm. 

106See updated guidance at https://

www3.epa.gov/ttn/scram/guidance/guide/Draft_

O3–PM–RH_Modeling_Guidance-2014.pdf: ‘‘Draft 

Modeling Guidance for Demonstrating Attainment 

of Air Quality Goals for Ozone, PM2.5, and Regional 

Haze,’’ December 2014. 

makes modeling a statutory requirement 

for moderate area attainment 

demonstrations. However, the same 

parenthetical statement is absent from 

CAA section 189(a)(1)(B)(ii), which 

addresses an impracticability 

demonstration. While we believe that 

most impracticability demonstrations 

will indeed be supported by air quality 

modeling, there are cases where a 

modeling demonstration may not be 

needed. In addition, the EPA believes 

the burden of proof for an 

impracticability demonstration is 

logically lower than for an attainment 

demonstration because submission of an 

impracticability demonstration also 

requires reclassification to a serious 

nonattainment area and the 

accompanying more stringent regulatory 

requirements (e.g. BACT/BACM). The 

area is still required to meet RACT/

RACM requirements and will also be 

required to submit a serious area 

attainment demonstration, which will 

necessarily need to include air quality 

modeling. 

Comment: Some commenters agreed 

with the EPA that states should be 

afforded flexibility to fulfill the 

statutory modeling requirement through 

appropriate regional or national 

modeling. 

Response: The EPA agrees that, where 

appropriate, regional and/or national 

scale air quality modeling could be 

sufficient to fulfill the statutory 

modeling requirement for attainment 

demonstration modeling. However, as 

with any attainment demonstration, the 

modeling must be shown to be 

appropriate for the nonattainment area, 

including good model performance, 

appropriate emissions and 

meteorological inputs, and 

consideration of emissions control 

strategies. It should be noted, however, 

that it may be difficult to fulfill other 

CAA requirements (such as emissions 

inventory, RACM, RFP, establishing 

motor vehicle emissions budgets for 

transportation conformity purposes, 

etc.) using regional or national modeling 

data. In order to fulfill those 

requirements, states may need more 

detailed data for sources in their 

nonattainment area compared to what is 

available through regional or national 

modeling. 

Comment: Some commenters stated 

that, as the proposal stands, if states 

wish to preclude RACT/RACM for any 

sources in the nonattainment area, they 

must do modeling for the year preceding 

the attainment year to demonstrate early 

attainment; this would require modeling 

for 3 years, rather than 2 years. 

Response: Although a RACM analysis 

is required, and eliminating potential 

control measures requires an assessment 

of whether the measures collectively 

could advance the attainment date by 1 

year, EPA did not propose any specific 

modeling requirements for the RACM 

analysis. There are several components 

to the analysis. First, potential 

emissions reductions need to be 

assessed. Then, an assessment of 

whether those emissions reductions can 

advance attainment by at least a year 

needs to be completed. One way to 

minimize the number of future modeled 

years is to establish (through sensitivity 

modeling) a relationship between PM2.5

and PM2.5 precursor emissions 

reductions and PM2.5 concentrations in 

the nonattainment area. The established 

relationship can be used to estimate 

whether a particular set of emissions 

reductions will be able to advance the 

attainment date by at least a year. Also, 

in some cases, the emissions reductions 

identified through the RACM analysis 

may be relatively small (as a percentage 

of area-wide emissions) that a modeling 

analysis is not needed to show that the 

attainment date cannot be advanced. 

2. Available Modeling Guidance for 

Demonstrating Attainment 

a. Summary of Proposal. The EPA 

proposed that attainment 

demonstrations should be consistent 

with the procedures for modeling PM2.5

as 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’’ 105 as well as the 

Guideline on Air Quality Models (40 

CFR part 51, Appendix W). 

The PM2.5 attainment demonstration 

modeling guidance (hereafter referenced 

as the ‘‘modeling guidance’’) describes 

how states can apply air quality models 

to generate results needed to 

demonstrate attainment. Models are 

used to test whether control measures in 

an attainment plan to be adopted into a 

SIP are likely to result in attainment of 

the relevant standards. 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. 

b. Final Rule. In the final rule, EPA is 

continuing to recommend that 

attainment demonstrations should be 

consistent with the procedures for 

modeling PM2.5 as described in the 

PM2.5 attainment demonstration 

modeling guidance and Appendix W. 

The 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 has updated the 2007 PM2.5

modeling guidance to include 

additional information related to the 

2012 PM2.5 NAAQS and associated 

monitoring requirements.106 The main 

components of the modeling guidance 

and the modeled attainment test have 

not changed. Additional information 

has been added to address near-road 

monitoring sites and other information 

that was not available when the 

guidance was first released in 2007. 

The modeling guidance continues to 

recommend a relative attainment test for 

both the annual and 24-hour PM2.5

NAAQS. The EPA is not recommending 

a specific model for use in the 

attainment demonstration for the PM2.5

NAAQS. At present, there is no single 

model that has been extensively tested 

and shown to be clearly superior to 

other available models. The current 

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107SMAT–CE replaced the Modeled Attainment 

Test Software (MATS) in January 2016. SMAT–CE 

performs the same functionality as MATS, but is 

open source, runs faster, and is more stable than its 

predecessor. 108 78 FR 3283. 

modeling guideline, 40 CFR part 51, 

appendix W, does not identify a 

preferred model for use in attainment 

demonstrations of the NAAQS for PM2.5. 

Thus, states may choose from several 

alternatives. 

The EPA has developed software to 

perform both the annual and 24-hour 

PM2.5 attainment test (including 

interpolating PM species data where 

necessary). The current software is 

called the Software for the Modeled 

Attainment Test—Community Edition 

(SMAT–CE).107 The software is 

provided as a way to make it relatively 

easy for states to apply the 

recommended modeled attainment 

test(s). However, states are not required 

to use SMAT–CE and can develop their 

own post-processing software as 

necessary. 

The modeling guidance continues to 

describe 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 nonmodeled emissions control strategies, 

including voluntary programs. 

The application of air quality models 

requires a substantial effort by state and 

local agencies. Therefore, states should 

work closely with their EPA regional 

office in executing each step of the 

modeling process. By doing so, it will 

increase the likelihood of the EPA’s 

approval of the state demonstration 

submitted at the end of the modeling 

and overall attainment plan 

development process. 

c. Comments and Responses. 

Comment: Several commenters 

questioned the ability of the current 

most common photochemical models to 

accurately model how the PM2.5

precursors impact overall PM2.5

concentrations. They raise particular 

concerns about ammonia emissions and 

the ability of models to predict PM2.5

formation from ammonia precursor 

emissions. The commenters stated that 

emissions inventories necessary for 

such modeling, as well as the tools used 

to measure those emissions, remain 

uncertain and are sometimes inaccurate; 

e.g., emission rates are too often based 

on unreliable data, due to either lack of 

representative information or technical 

issues associated with test methods. 

Some commenters stated that these 

concerns are particularly salient here 

because the PM2.5 SIP Requirements 

Proposal requires that states account for 

new precursors, including VOCs and 

ammonia. 

Response: The EPA disagrees with the 

commenters’ assertion that emissions 

inventory and modeling tools are 

insufficient to estimate PM2.5

concentrations and the predicted change 

in PM2.5 due to changes in PM2.5

emissions and PM2.5 precursors. While 

there will always be uncertainty in 

emissions inventories and modeling, 

photochemical models of PM2.5

concentrations, including secondary 

formation through chemistry, have been 

used in the scientific and regulatory 

community for over 30 years. State 

attainment demonstration modeling has 

been performed by numerous states over 

the last 10+ years to support the 1st 

round of PM2.5 SIPs that were due in 

2007. In addition, the EPA has used 

photochemical modeling of PM2.5 to 

support numerous regulatory 

rulemakings over the last decade. 

The technical tools to perform 

photochemical modeling are well 

established and have been improved 

almost continuously over many years. 

New versions of the CMAQ and CAMx 

models with numerous science updates 

are released every 1 to 2 years. National 

emissions inventories that include 

primary PM2.5 and all scientific 

precursors (SO2, NOX, VOC and 

ammonia) have existed since the NEI for 

2002. The NEI is released every 3 years 

with methodological improvements 

with every release. 

In addition, the commenters refer to 

VOC and ammonia as ‘‘new precursors,’’ 

which is not accurate. VOC and 

ammonia have always been ‘‘scientific’’ 

PM2.5 precursors, and as such have 

always been inventoried and modeled 

with chemistry in PM2.5 photochemical 

models. The only thing ‘‘new’’ is that 

VOC and ammonia are now assumed to 

be presumptive PM2.5 precursors. 

However, even though the previous 

implementation rule did not assume 

that VOC and ammonia were default 

precursors, all photochemical modeling 

of PM2.5 has always included VOC and 

ammonia emissions and the resultant 

chemical formation of ammonium 

sulfate, ammonium nitrate, and 

secondary organic carbon. 

The commenters were concerned that 

model errors in the formation of PM2.5

from ammonia sources would impose an 

unreasonable regulatory burden on 

sources of ammonia such as animal 

agriculture. Even though there may be 

general uncertainty in ammonia 

inventories, it is not clear how those 

uncertainties would lead to an 

unreasonable regulatory burden on any 

emissions sources in particular. Every 

modeling application in support of an 

attainment demonstration must be 

shown to adequately represent the 

emissions, chemistry, and PM2.5

concentrations in the nonattainment 

area. Ambient measurements of PM2.5

and precursors are used in a model 

performance evaluation to demonstrate 

that the modeling system is appropriate 

to use to determine the sensitivity of 

PM2.5 mass to emissions changes. In 

addition, all SIPs are required to 

undergo a public comment process 

where specific emissions and/or 

modeling concerns can be raised to the 

state. And then, after review of the SIP 

submission by EPA, all approvals or 

disapprovals of attainment SIPs go 

through a notice and comment 

rulemaking process. There are therefore 

numerous opportunities for both 

industry and the general public to 

participate in the SIP development 

process. States are expected to use the 

appropriate tools and the best 

information available to demonstrate 

how they will attain the PM2.5 NAAQS 

by the attainment date. The EPA 

believes that the appropriate tools are 

available to perform the modeling 

needed for an attainment 

demonstration. 

3. Demonstrating Attainment at NearRoad Monitors 

a. Summary of Proposal. The 2012 

PM2.5 NAAQS final rule contains new 

requirements for operating near-road 

monitors in the largest metropolitan 

areas.108 The first set of monitors was 

required to be in place by January 1, 

2015. Some of the near-road monitors 

began operation prior to 2015. However, 

none of the monitors will have the 

requisite 3 years of monitoring data that 

can be used to calculate a PM2.5 design 

value until 2017 at the earliest. 

Therefore, these data were not used for 

the initial designations for the 2012 

PM2.5 NAAQS (finalized in December 

2014) and in most nonattainment areas, 

there will be less than 3 years’ worth of 

data available when the initial 

attainment demonstrations for Moderate 

nonattainment areas are due in 2016. As 

a result of this timing, the EPA proposed 

that the initial set of Moderate area 

attainment demonstrations will not 

need to include projected design values 

for near-road monitors. But when 3 or 

more years’ worth of complete ambient 

data are available at near-road monitors, 

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states will need to address those 

monitors in their attainment 

demonstrations and will need to include 

a demonstration that those monitors 

will attain the NAAQS by the applicable 

statutory attainment date. 

b. Final Rule. For the final rule, the 

EPA maintains the policy of not 

requiring the use of ambient air quality 

data in a modeled PM2.5 attainment 

demonstration unless there is at least 

one complete design value of data 

available (generally 3 complete years of 

data). This applies to both near-road and 

other PM2.5 ambient monitoring data. 

Some states may have installed their 

monitors well before the January 1, 2015 

deadline and may therefore have 

complete data before the SIP deadline. 

In addition, some attainment 

demonstrations may be submitted after 

the statutory deadline. Because of the 

varying monitor installation dates, the 

use of near-road monitoring data in 

attainment demonstrations depends on 

the timing of the attainment 

demonstration submission relative to 

the installation date of the monitor(s). 

Ambient data with sufficient 

completeness to calculate a design value 

may not be ignored in an attainment 

demonstration. Such data can be 

addressed either in the attainment 

demonstration analysis of ambient 

monitors or as part of an unmonitored 

area analysis (see the next section), as 

appropriate. 

The revised PM2.5 modeling guidance 

document includes procedures for 

applying a dispersion model or a 

combination of photochemical grid 

models and dispersion modeling to 

demonstrate attainment at monitors 

with large primary PM2.5 concentration 

gradients. Depending on the nature of 

the ambient data in a particular area, it 

may be appropriate to treat near-road 

monitors as high concentration gradient 

locations. However, in other cases, nearroad monitors may have little or no 

gradient compared to other nearby 

monitors. Therefore, the appropriate 

treatment of near-road monitors in 

attainment demonstrations should be 

evaluated on a case-by-case, depending 

on the facts and circumstances in each 

nonattainment area. 

c. Comments and Responses. 

Comment: Some commenters stated the 

EPA’s proposal to excuse areas from 

having to include projected design 

values for near-road monitoring 

locations promises to undermine the 

likelihood of success for attainment 

demonstrations. The commenters stated 

the EPA’s blanket waiver for near-road 

data has no rational basis and that just 

because such monitors were not 

required before January 1, 2015, does 

not mean that areas did not have them 

in place before then. The commenters 

stated the EPA should at least clarify 

that if an area has 3 years of near-road 

monitoring data, it should use such data 

in its attainment modeling. The 

commenters stated this would be 

particularly important, for example, if 

an area is late in preparing its 

demonstration. 

Response: The EPA agrees there 

should not be a ‘‘blanket waiver’’ for the 

use of near-road monitoring data in 

attainment demonstrations that are due 

in 2016 or thereafter. The statements in 

the proposal referenced the fact that the 

near-road monitors were not required to 

be in place before January 1, 2015. This 

makes it unlikely that sufficient data 

from these monitors will be available to 

be considered in attainment 

demonstrations that are due in 2016. 

However, if complete data are available 

at near-road monitors during the 

development of the attainment 

demonstration, the data should be 

considered as appropriate (similar to 

any other PM2.5 monitoring data). Since 

the near-road PM2.5 monitoring network 

is relatively new, there may not be 3 

years of complete data in time to be 

considered in the upcoming attainment 

demonstrations. In addition, the base 

modeling year of the attainment 

demonstration may predate the startup 

date of the near-road monitor(s). In this 

case, it may be possible to consider the 

near-road data in the attainment 

demonstration, but the recommended 

default projection methodology may not 

be applicable (since the time period of 

the near-road data may not correspond 

to the 5 year time period centered about 

the base modeling year, as 

recommended in the modeling 

guidance). Additionally, near-road 

PM2.5 monitors are only required in the 

27 largest metropolitan areas of the 

country. Some PM2.5 nonattainment 

areas may not have any near-road 

monitoring sites. States should consult 

with the appropriate EPA regional office 

to determine the best way to treat nearroad data in their attainment 

demonstration. 

4. Demonstrating Attainment in 

Unmonitored Areas 

a. Summary of Proposal. The 2007 

PM2.5 modeling guidance describes a 

recommended ‘‘relative’’ attainment test 

that is based on showing attainment at 

ambient monitoring locations. The 

guidance also recommends that states 

conduct further analyses based on 

modeling results to determine whether 

there are unmonitored areas that merit 

additional analysis or investigation. In 

order to clarify the statutory and rule 

requirements of a modeled attainment 

demonstration, the EPA proposed four 

options for demonstrating attainment in 

unmonitored areas in an attainment 

demonstration. 

Option 1 would require the 

attainment demonstration modeling to 

demonstrate attainment at ambient 

monitoring locations. There would be 

no requirement to specifically examine 

attainment in unmonitored areas. 

Option 2 would require modeling to 

demonstrate attainment at ambient 

monitoring locations and in 

unmonitored areas within the 

nonattainment area. Enforceable 

emissions reductions would be required 

to eliminate any potential future year 

NAAQS violations in all locations 

within the nonattainment area 

(including unmonitored areas). Option 3 

would require modeling to demonstrate 

attainment at ambient monitoring 

locations and in unmonitored areas 

within the nonattainment area. 

However, rather than requiring states to 

impose additional enforceable 

emissions reductions in the SIP to 

address potential violations in 

unmonitored areas, states would be 

required to use the unmonitored area 

analysis results to develop an 

assessment of the likelihood of 

violations in unmonitored areas. The 

assessment would be used to evaluate 

the need for additional controls and/or 

could be used to inform the ambient 

monitoring plan (the need to add 

additional monitors or move existing 

monitors). Option 4 would require 

modeling to demonstrate attainment at 

ambient monitoring locations and 

recommend the analysis of unmonitored 

areas within the nonattainment area. 

This differs from Option 3 in that there 

would be no rule requirement to 

perform an unmonitored area analysis. 

But the submission of an unmonitored 

area analysis would still be 

recommended, especially 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. 

b. Final Rule. The EPA is finalizing 

proposed Option 4. This option requires 

states to show attainment at all current 

and recent monitoring locations. States 

will not be required to provide an 

unmonitored area analysis as a 

mandatory element of each attainment 

demonstration. However, an 

unmonitored area analysis can provide 

useful information about PM2.5

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109A monitor must have 3 years of quality 

assured ambient data available to be used to 

calculate a PM2.5 design value and determine 

compliance with the NAAQS. 

concentrations and gradients in the 

nonattainment area and therefore the 

EPA recommends that all attainment 

demonstrations should contain an 

unmonitored area analysis. The EPA 

encourages states to use information 

available to them to consider what, if 

any, impacts may be occurring in 

unmonitored areas. States can evaluate 

the need to perform an unmonitored 

area analysis by using available 

information such as modeling data, 

emissions inventories, or non-FEM 

monitoring data (such as from special 

purpose monitors or saturation 

monitoring studies) to indicate the 

potential high PM2.5 concentrations in 

areas that are currently unmonitored. 

An unmonitored area analysis is 

strongly 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. The EPA 

will consider whether the state has 

adequately addressed all available 

information about potential exceedances 

of the NAAQS in unmonitored areas 

when determining whether the plan can 

be approved. 

The EPA is requiring an attainment 

demonstration approach that relies 

primarily on existing monitoring sites 

and modeling to project attainment in 

future years. This approach to 

evaluating monitored and unmonitored 

areas is consistent with how EPA 

determines whether an area meets the 

PM2.5 NAAQS for purposes of 

designations and redesignations. 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.109

Although the EPA considers other 

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. 

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. 

In addition, the ‘‘relative’’ attainment 

test for PM2.5 attainment demonstrations 

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. 

While the unmonitored area analysis 

is not a regulatory requirement, and 

states are not required to identify 

enforceable emissions reductions to 

eliminate potential violations in 

unmonitored areas, an unmonitored 

area analysis has the potential to 

provide additional important 

information about PM2.5 levels and 

gradients in the nonattainment area. The 

results of the analysis can be used to 

provide information to inform future 

monitoring plans, to examine the need 

for potential emissions controls, to 

evaluate potential environmental justice 

concerns, and to provide additional 

information to the public. The EPA 

believes that Option 4 provides the best 

balance between the regulatory 

requirements of the attainment 

demonstration and additional analyses 

which could provide helpful 

information to inform future regulatory 

activities. 

Where information is available, states 

and the EPA have obligations to address 

potential violations in unmonitored 

areas, and, although we expect this to be 

relatively rare, attainment plans need to 

address air quality in unmonitored areas 

where information exists suggesting the 

potential for such violations. Where an 

unmonitored area analysis is performed, 

states should use model results and 

available ambient data to develop an 

assessment of the likelihood of 

violations in unmonitored areas. The 

nature of the assessment depends on the 

available information and the nature of 

the local PM2.5 problem, 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 evaluate the accuracy of the 

modeled violations in unmonitored 

areas. If potential violations are 

determined to be likely, additional steps 

could include imposition of 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 should 

document the assessment, including 

analyses of emissions, meteorological 

inputs and ambient data. 

The PM2.5 modeling guidance 

recommends a default procedure for 

applying an unmonitored area analysis, 

which combines gridded model data 

with interpolated ambient data. States 

can apply the default recommended 

approach or develop their own analysis 

which may be more appropriate for the 

specific area or situation. States are 

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 and how the analysis 

should be performed. 

c. Comments and Responses. 

Comment: Some commenters stated 

that, of the options for addressing 

unmonitored areas, only Option 2 is 

technically and legally defensible (80 

FR 15382). The commenters stated the 

Act requires that ambient 

concentrations in all areas meet the 

applicable NAAQS and cited 42 U.S.C. 

7407(a) as requiring states to assure ‘‘air 

quality within the entire geographic area 

comprising such State’’ will achieve the 

national standards and requiring ‘‘an 

implementation plan [to] . . . specify 

the manner in which national primary 

and secondary ambient air quality 

standards will be achieved and 

maintained’’). The commenters also 

cited 42 U.S.C. 7410(a)(1) as requiring 

implementation plans to provide for 

implementation of the NAAQS ‘‘in each 

air quality control region (or portion 

thereof) within such State’’). The 

commenters stated it is insufficient to 

suggest that an area need only show 

attainment at monitored locations and 

need only adopt controls that will 

address those locations. 

Response: The EPA does not agree 

that Option 2 is the only technically and 

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110See fine particulate (PM2.5) design criteria at 

40 CFR part 58–Appendix D to part 58. 

legally defensible option. The CAA 

requires states with nonattainment areas 

to submit an attainment demonstration 

as part of their PM2.5 SIP. States must 

show that they will attain the NAAQS 

by their attainment date. The CAA also 

requires states to use air quality 

modeling in their attainment 

demonstration. But other than those 

general requirements, the EPA believes 

states have discretion to interpret how 

and where to show attainment of the 

NAAQS through modeling in support of 

an attainment demonstration. 

In addition, the EPA believes that a 

monitor based attainment 

demonstration satisfies the CAA 

requirement to show that ‘‘the entire 

geographic area’’ will attain the 

NAAQS. The EPA’s monitoring 

requirements for PM2.5 are designed to 

ensure a robust nationwide monitoring 

network in both nonattainment and 

attainment areas. States 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).110 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. The 

EPA has identified recommended 

procedures for PM2.5 modeled 

attainment demonstrations. These 

recommendations are contained in 

modeling guidance. The recommended 

attainment test relies on the ambient 

monitors to provide the ‘‘anchor point’’ 

for future year air quality projections. 

This ensures that future year 

concentration predictions are grounded 

by ‘‘real world’’ measurements. Since 

the attainment test relies on ambient 

monitoring data, 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. 

Therefore, the EPA continues to believe 

that for PM2.5 attainment 

demonstrations, modeling results in 

unmonitored areas are too uncertain to 

use in this manner. For the reasons 

stated earlier, in the final rule, the EPA 

does not believe that it is necessary to 

require states to submit an unmonitored 

area analysis and to show that any 

potential violations of the NAAQS in 

unmonitored areas have been 

eliminated through enforceable controls. 

Comment: Several commenters 

supported Option 1 where only 

monitored grid cells are included in the 

attainment plan. Commenters stated 

that, due to their concerns related to the 

accuracy of air dispersion modeling 

tools and protocols, it is not appropriate 

to use air dispersion modeling to predict 

receptor impacts in unmonitored areas. 

Some commenters stated that Option 1 

is the approach that most closely 

describes the current EPA rule. 

Response: The EPA agrees that the 

modeling results are too uncertain in 

unmonitored areas to require an 

unmonitored area analysis as part of the 

attainment demonstration (for the 

reasons enumerated earlier). However, 

the EPA disagrees that Option 1 is the 

approach that most closely describes the 

attainment demonstration requirements 

in the 2007 PM2.5 implementation rule. 

An unmonitored area analysis has never 

been an implementation rule 

requirement, but was a recommended 

analysis in the PM2.5 modeling 

guidance. Therefore, the EPA believes 

that Option 4 is closer to the current 

status quo. This final rule clearly states 

the continued recommendation to 

perform an unmonitored area analysis 

and the benefits of doing so. 

Comment: Some commenters stated 

that an ‘‘unmonitored area analysis’’ is 

essential since speciation monitoring is 

conducted at a limited number of sites. 

The commenters stated that, however, 

given the inherent uncertainty from 

modeling analysis in unmonitored 

areas, results from such analysis should 

only be used to inform additional 

actions. The commenters stated that, 

while modeling analysis in 

unmonitored areas can be used as a 

reference for additional studies, it 

should not be used for the attainment 

demonstration in the SIP. The 

commenters stated that, under any of 

the options, the EPA should specify the 

recommended level of detail for an 

unmonitored area analysis, especially if 

it is required. The commenters 

recommended that the analysis need not 

require modeled results at finer spatial 

scales than those specified in the 

modeling protocol. 

Response: The EPA agrees that an 

unmonitored area analysis is important 

and continues to recommend 

development of unmonitored area 

analyses to support attainment 

demonstrations. The EPA also agrees 

that due to uncertainty, the results from 

such analysis should only be used to 

inform additional actions. As stated 

earlier, the PM2.5 modeling guidance 

contains a default recommended 

unmonitored area analysis technique 

which combines gridded modeling data 

and interpolated ambient data 

(including PM2.5 speciation data). But 

the exact nature of the unmonitored area 

analysis can be considered based on the 

information relevant to each 

nonattainment area. The EPA also 

agrees that where an unmonitored area 

analysis is conducted, it should be at 

the same spatial scale (model 

resolution) as the modeled attainment 

demonstration at monitoring locations. 

For example, if the gridded modeling 

analysis is performed at 4km resolution 

(model grids that are 4km on a side), 

then the unmonitored areas should be 

examined at the same resolution. 

Similarly, if near road monitors are 

examined with a dispersion model at a 

finer resolution (compared to the other 

monitors) as part of the attainment 

demonstration, the unmonitored area 

analysis could also examine 

unmonitored near-road areas at a finer 

resolution. 

Comment: Several commenters 

disagreed with the proposal to require 

states to perform the attainment test at 

‘‘recent’’ monitoring locations. 

Commenters stated that, within the 

EPA’s description of Option 1, the 

proposal indicates that the attainment 

test required under Option 1 would also 

apply to locations that have ‘‘recent’’ 

FRM and/or FEM monitoring data. 

Commenters stated the current FRM/

FEM monitoring data should be 

sufficient to demonstrate attainment. 

Response: States must demonstrate 

that they will attain the PM2.5 NAAQS 

in the nonattainment area as 

expeditiously as practicable, and no 

later than the moderate area attainment 

date. The recommended attainment test 

in the modeling guidance uses recent 

ambient data that encompass a 5-year 

period that is dependent on the base 

modeling year. For example, for a base 

modeling year of 2014, the guidance 

recommends using ambient PM2.5 data 

from the 2012–2016 period. The 

guidance also recommends only using 

ambient data from a particular 

monitoring site if it has at least one 

complete design value period during the 

relevant 5-year period. With these 

recommendations in mind, there are 

numerous cases where a monitoring site 

may have only partial data from the 

relevant 5-year period or may be a new 

monitor that started collecting data after 

the 5-year period or may have been shut 

down before the 5-year period. The EPA 

agrees that it is generally not necessary 

to examine the modeling results where 

monitors were shut down before the 

base modeling period. These monitors 

will not be used to make future 

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58054 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

111Note 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. 

112A demonstration that the area cannot attain by 

the moderate area attainment date would not be the 

only trigger for a reclassification to serious 

nonattainment. The Administrator maintains wide 

discretion in making a determination that an area 

cannot practicably attain the NAAQS by their 

attainment date. 

decisions relating to attainment status of 

the area. However, monitors that are 

new or were operating during the base 

modeling period are still relevant and 

can be used to provide additional 

information in the attainment 

demonstration. The data from these 

monitors may serve as the basis for 

examining potential violations in the 

area as part of an unmonitored area 

analysis. This is especially the case for 

new monitors, which may not have 

enough data to provide a robust future 

year concentration estimate in the 

attainment demonstration. But the 

monitoring data, combined with 

modeled information, can provide 

information about the likelihood of 

future violations in the area surrounding 

the monitor location. 

5. Future Year(s) To Be Modeled in 

Attainment Demonstrations 

a. Summary of Proposal. 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 emissions control measures 

relied on for attainment will have been 

fully implemented by the beginning of 

that year. The EPA proposed that 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 

result in PM2.5 concentrations that meet 

the level of the standard.111 While states 

should choose the future modeling year 

based on a number of factors, the EPA 

proposed the last possible year 

permitted under the statute as a starting 

point for modeling. 

b. Final Rule. The EPA is finalizing 

the recommendation that the last 

possible year permitted under the 

statute is an appropriate starting point 

for modeling. See 40 CFR 51.1011(a)(6). 

For a state that is submitting an 

attainment demonstration, modeling the 

sixth calendar year is a logical starting 

point to determine if attainment by that 

year is likely. Even though attainment is 

determined by averaging 3 years’ worth 

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 3 years’ 

worth 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 3 year average is less than the 

NAAQS). Therefore, it can be 

appropriate to model any of the 3 years 

used to determine attainment. In 

addition, 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. Therefore, modeling 

attainment-level concentrations for the 

last year permitted by statute is 

acceptable. 

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 also the sixth 

calendar year after designation. 

For the reasons stated earlier, 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. For 

example, since designations for the 2012 

PM2.5 NAAQS were effective in March 

2015, it is appropriate for states to 

model air quality for 2021 in the 

attainment demonstrations for 

designated nonattainment areas. 

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 expected growth and known 

controls that are already in effect or that 

are adopted and will be in effect by 

January 1 of the future year. For 

example, for a Moderate nonattainment 

area for the 2012 PM2.5 NAAQS, a future 

base case scenario for the year 2021 

would project future air quality given 

implementation of existing federal, state 

and local measures. If this future base 

case scenario demonstrates attainment, 

then the state must determine if 

attainment can be achieved in an earlier 

year through the application of 

additional measures. Therefore, the state 

must conduct an analysis of RACM and 

RACT and additional reasonable 

measures to determine if, collectively, 

all technologically and economically 

feasible measures identified by the state 

that can be implemented by the 

beginning of the sixth calendar year 

following designations can advance the 

attainment date by at least 1 year (note 

that RACM and RACT controls must be 

implemented within 4 years of an area 

being designated nonattainment, but 

additional reasonable measures for an 

area for which a state can demonstrate 

attainment by the end of the sixth 

calendar year following designation of 

the area are those technologically and 

economically feasible measures that can 

be implemented by the beginning of the 

last year prior to the projected 

attainment date). 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, on the other hand, the future base 

case scenario does not demonstrate 

attainment, then a control case scenario 

is needed to examine whether the 

reasonable, technically and 

economically feasible measures 

identified by the state would result in 

attainment in the analysis year (i.e., in 

2021 for purposes of this example based 

on the 2012 PM2.5 NAAQS). The control 

case scenario would add potential 

control measures—e.g. RACM and 

RACT (which must be implemented in 

4 years) and additional reasonable 

measures, plus any 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 for the 2012 

PM2.5 NAAQS, 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 outermost statutory attainment 

date for Moderate areas is impracticable. 

This in turn could serve as a technical 

basis for the Administrator to reclassify 

the area to Serious.112 If the analysis 

does demonstrate attainment, then the 

remaining step is to assess whether the 

attainment date can be advanced by 1 

year. 

In conducting this assessment, the 

EPA believes that it is not reasonable to 

require states to model each and every 

calendar year to determine the 

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113 If several future modeling years are available, 

it may in some cases be appropriate for states to 

interpolate PM2.5 concentrations between years. 

114For more information on PM2.5 precursor 

requirements, see CAA 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). 

115 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. 

appropriate attainment date. 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.113

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 sensitivity factors (i.e., 

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 or using advanced 

modeling techniques such as DDM) 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 RACT and RACM 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 EPA Regional Office as 

part of the modeling protocol 

development process and before 

embarking on the modeling. 

c. Comments and Responses. 

Comment: Some commenters disagreed 

with the proposal that the future year 

should reflect when all control 

measures relied on have been fully 

implemented by the beginning of that 

year and it should be no later than the 

beginning of the last calendar year 

preceding the attainment date. The 

commenters stated the CAA provides 

attainment must be achieved as 

expeditiously as practicable but no later 

than the end of the sixth calendar year 

(except RACT/RACM are required 

within 4 years) and states should be 

given the full period to demonstrate 

attainment and to require control of 

emissions. 

Response: The proposal to require the 

modeling to reflect control measures 

that have been fully implemented no 

later than the beginning of the last 

calendar year preceding the attainment 

date does give nonattainment areas ‘‘the 

full period’’ to demonstrate attainment 

and to require control of emissions. 

Since the design value is an average of 

3 years’ worth of data, it could be 

argued that modeling and related 

emissions controls should be in place 3 

years before the attainment date. 

However, 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. Therefore, modeling 

attainment level concentrations for the 

last year permitted by statute is 

acceptable. But in order to measure 

attainment level concentrations in the 

final year, controls must be in place for 

the full year (at the beginning of the 

year). Implementation of emissions 

controls at the end of the year would not 

be consistent with modeling attainment 

level or measuring attainment level 

concentrations during the year. 

6. 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.114 It 

should be noted that states that submit 

impracticability demonstrations for 

Moderate areas under CAA section 

189(a)(1)(B)(ii) are not required to 

submit motor vehicle emissions budgets 

for attainment purposes because the 

submitted SIP does not demonstrate 

attainment. 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. 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, 

unless EPA approves the state’s use of 

an alternative model.115

F. RFP Requirements 

1. Background on 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 

attainment plan provisions in general. 

Section 172(c)(2) of the CAA requires 

attainment plans to provide for RFP, 

which is defined in CAA 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 189(c) of 

the CAA requires that ‘‘[P]lan 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 CAA section 171(1), 

toward attainment by the applicable 

date.’’ Quantitative milestones are 

discussed later in Section IV.G of the 

preamble. 

Section 172(c)(3) of the CAA 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) of the CAA 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) . . .’’ 

Section 172(c)(9) requires the state plan 

to ‘‘provide for the implementation of 

specific measures to be undertaken if 

the area fails to make reasonable further 

progress . . . Such measures shall be 

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116 80 FR 15385. 

included in the plan revision as 

contingency measures to take effect in 

any such case without further action by 

the State or the Administrator.’’ For 

additional background on statutory 

requirements and existing guidance, 

refer to preamble Section IV.F of the 

proposal for this rule.116

2. General Approach to RFP 

a. Summary of Proposal. To satisfy 

the statutory requirements for RFP at 

CAA section 172(c)(2), the EPA 

proposed that a state must submit an 

RFP plan as part of its Moderate area 

attainment plan submission. The EPA 

proposed the following two options for 

developing an RFP plan. 

Under the first option, the EPA 

proposed 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; or (ii) 

stepwise progress toward attainment. 

Stepwise emissions reductions would 

be slower than ‘‘generally linear’’ 

reductions for certain periods, and then 

would decline sharply (due to 

implementation of a new emission 

reduction program, or new operation of 

control technology on one or more 

stationary sources). The EPA proposed 

that a state must follow one primary 

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 show that 

nonattainment area emissions of each 

pollutant decline from the base year to 

the attainment year, either in a generally 

linear manner or in a stepwise manner. 

In the optional secondary analysis, the 

state could show that emissions of the 

various pollutants would change in a 

manner that would provide a change in 

air quality during the attainment period 

that is equivalent or more expeditious 

than the air quality change that would 

be estimated to occur under the primary 

approach. This optional analysis was 

referred to as an equivalency 

determination. 

Under the second proposed option, 

the state would provide the control 

strategy implementation schedule and 

estimate the emissions reductions 

anticipated from the control measures 

(i.e., RACM/RACT and additional 

reasonable measures) for sources in the 

nonattainment area. The state then 

would employ modeling or another 

quantitative method to predict the 

overall PM2.5 concentrations in the 

nonattainment area for each milestone 

year. The milestone years would 

correspond to the years for which the 

state would be required to provide 

quantitative milestones pursuant to the 

requirement in section 189(c) of the Act. 

b. Final Rule. The EPA is finalizing 

RFP requirements that allow the state 

flexibility to demonstrate RFP under 

CAA section 172(c)(2) using any of the 

general approaches included in the 

proposed rule. As part of its Moderate 

area attainment plan submission, the 

state must submit an RFP plan that 

includes three components: (1) An 

implementation schedule for control 

measures on sources in the 

nonattainment area, (2) RFP projected 

emissions for each applicable 

quantitative milestone year determined 

in Section IV.G of this preamble, based 

on the anticipated control measure 

implementation schedule; and (3) an 

analysis that demonstrates that this 

schedule of aggregate emissions 

reductions achieves sufficient progress 

toward attainment between the 

applicable baseline year to the 

attainment year. See 40 CFR 51.1012(a). 

The first component of the RFP plan 

is the implementation schedule for all 

required control measures contained in 

the control strategy. The schedule 

should describe which measures will be 

implemented within the first 4 years 

following designation (and therefore 

would meet the statutory requirement 

for RACM and RACT). It should also 

describe the implementation schedule 

of additional reasonable measures (to be 

implemented more than 4 years 

following designation but before the 

attainment date) that have been adopted 

to help provide for expeditious 

attainment of the standard. Any 

Moderate area that cannot demonstrate 

attainment by the statutory Moderate 

area attainment date is required to 

provide an implementation schedule for 

all of the control measures identified as 

RACM/RACT and additional reasonable 

measures, in the same manner as an area 

that can demonstrate attainment. 

The second component of the RFP 

plan is an analysis by the state 

identifying the RFP projected emissions 

by pollutant that are expected to be 

achieved by the control measures 

implemented within the nonattainment 

area according to the implementation 

schedule. The EPA requires the state to 

estimate these RFP projected emissions 

for each quantitative milestone year 

(i.e., for a Moderate area, at 4.5 years 

and 7.5 years after designation of the 

area) by sector on a pollutant-bypollutant basis. These milestone year 

projected emissions are discussed 

further in Section IV.F.3 of the 

preamble. This information will be used 

by the state to show that the area is 

complying with quantitative milestone 

and RFP requirements for the area 

(discussed in Section IV.G of this 

preamble). 

The final component of the RFP plan 

is an analysis demonstrating that the 

schedule of emissions changes achieves 

reasonable progress toward attainment 

between the applicable baseline year 

and the attainment year. This 

demonstration can be expressed in the 

form of emissions reductions only, or 

emissions reductions converted to air 

quality concentrations. This optional air 

quality RFP analysis is discussed later 

in this section. 

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 

finalizing a requirement that states use 

the same year as the base year inventory 

used for developing the control strategy 

and associated air quality modeling 

demonstrating that the area will attain 

expeditiously. 

A demonstration based on only 

emissions reductions must show that 

the implementation schedule achieves 

either: (i) Generally linear progress 

toward the projected attainment date; or 

(ii) stepwise progress toward the 

projected attainment date. For example, 

in one area 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. In 

another area, regulations to reduce 

emissions from certain stationary source 

sectors could have a single compliance 

date by which controls must be in place, 

which could result in a significant drop 

in emissions in a ‘‘stepwise’’ manner 

over a relatively short period. 

In the first case, the EPA expects that, 

so long as the attainment date is as 

expeditious as practicable, then 

generally linear progress toward 

attainment by that date would satisfy 

the RFP requirement. In the second 

case, where progress is slower than 

generally linear, the state is required to 

submit a clear rationale and supporting 

information to explain why generally 

linear progress is not appropriate (e.g., 

due to the nature of the nonattainment 

problem, the types of sources 

contributing to PM2.5 levels in the area 

and the implementation schedule for 

control requirements at such sources). 

Similarly, for areas that cannot 

demonstrate attainment within the 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58057 

Moderate area statutory deadline in 

CAA section 188(c)(1), the state must 

demonstrate either generally linear or 

stepwise emissions reductions toward 

the full amount of reductions that will 

be achieved by that deadline, i.e., the 

amount that reflects implementation of 

all of the control measures identified as 

RACM and RACT and additional 

reasonable measures for the entire 

period of the applicable attainment 

plan. Generally linear progress toward 

this full amount would meet the RFP 

requirement, but progress that is slower 

than that would require further 

justification. 

In some circumstances, the EPA 

expects that a state could develop an 

approvable RFP plan even if emissions 

of one or more PM2.5 plan precursors are 

not decreasing. In this scenario, the state 

must demonstrate that the emissions 

reductions of direct PM2.5 combined 

with the aggregate emissions reductions 

of PM2.5 plan precursors support 

expeditious attainment of the applicable 

PM2.5 NAAQS. To accomplish this, the 

EPA expects that a state could use the 

relative air quality impacts of the 

different PM2.5 plan precursors 

identified in the attainment modeling to 

demonstrate that the emissions 

reductions of direct PM2.5 and aggregate 

PM2.5 plan precursors constitute an 

acceptable RFP plan. For example, the 

state could demonstrate that even if one 

or more PM2.5 plan precursor is not 

decreasing, the emissions reductions of 

direct PM2.5 and the remaining PM2.5

plan precursors are the dominant factors 

in reducing ambient PM2.5 levels and are 

therefore adequate to support 

expeditious attainment. In providing 

this flexibility, the EPA recognizes that 

control measures for certain pollutants 

may be more effective at reducing PM2.5

concentrations than others, and that 

states may be able to implement some 

measures more quickly than others 

while still achieving reasonable overall 

progress toward attainment. 

The EPA is also providing an 

additional optional RFP analysis that 

evaluates the collective changes in 

emissions of multiple pollutants during 

the attainment period in terms of 

changes in air quality concentration. 

Under this optional approach, a state 

would have to show that the air quality 

improvement that is anticipated by 

milestone dates due to the identified 

control measures in the implementation 

schedule supports expeditious 

attainment of the PM2.5 NAAQS. For an 

area that can demonstrate attainment 

within the Moderate area statutory 

deadline, a state using this option could 

rely upon attainment demonstration 

modeling results that link emissions 

reductions with air quality 

improvements. For areas that cannot 

demonstrate attainment within the 

Moderate area statutory deadline, the 

state may have to conduct modeling or 

employ another quantitative method to 

predict the overall PM2.5 concentrations 

in the nonattainment area in each 

milestone year. The state would 

compare these air quality target values 

to certified ambient air quality 

monitoring data as part of the 

quantitative milestone report due after 

the area reaches each quantitative 

milestone date. The EPA recommends 

that states estimate air quality targets by 

establishing the relationship between 

modeled emissions reductions and air 

quality changes in the attainment plan 

(for the attainment year) and 

interpolating to the intermediate year(s) 

based on the same relationship. 

The EPA recognizes that because 

atmospheric processes are 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 when 

determining air quality targets based 

upon predicted emissions reductions. 

Nevertheless, the EPA recognizes the 

importance of providing 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 analysis. 

As previously noted, submission of 

the air quality-based RFP plan is 

optional. However, in certain 

circumstances, the applicable Regional 

Administrator may strongly recommend 

that a state or local agency submit an 

RFP plan with air quality targets for 

milestone years in order to satisfy the 

statutory RFP requirement. This 

approach could be appropriate when 

one or more pollutants is not decreasing 

over the attainment planning period or 

for areas that have experienced 

longstanding and persistent PM2.5

pollution problems despite the prior 

implementation of required control 

measures. The EPA will review each 

RFP plan on a case-by-case basis to 

determine whether it provides for such 

annual incremental reductions in 

emissions of the relevant air pollutant(s) 

as are necessary for the purpose of 

ensuring attainment by the applicable 

attainment date. See 40 CFR 51.1012. 

An additional RFP analysis will be 

required as part of a Serious area 

attainment plan if EPA reclassifies the 

area to Serious. 

c. Comments and Responses. 

Comment: Some commenters generally 

supported the equivalency 

determination concept because they 

noted that different precursors are more 

or less effective in reducing atmospheric 

concentrations of PM2.5. Some 

commenters stated that, because the 

goal is timely attainment regardless of 

when controls are implemented for each 

precursor that is to be controlled, the 

EPA should allow both options, 

including the option for states to 

determine whether to approach the 

demonstration on a pollutant-bypollutant basis, or overall. 

Response: The final rule allows for 

emissions from one or more PM2.5 plan 

precursors to increase over the 

attainment planning period, as long as 

the emissions of direct PM2.5 and 

aggregate PM2.5 plan precursors decrease 

consistent with RFP and the state can 

demonstrate that the emissions increase 

does not delay expeditious attainment. 

This approach recognizes the fact that 

different precursors have different 

impacts on PM2.5 concentrations 

depending upon the specific 

atmospheric chemistry of each area. As 

previously noted, submission of the air 

quality-based RFP plan is optional but 

may be strongly recommend by the 

applicable Regional Administrator 

depending upon the unique 

circumstances of the nonattainment 

area. 

Comment: One commenter suggested 

that the equivalency determination must 

be based on modeling of ambient 

concentrations, not simply on interpollutant equivalency ratios. 

Response: The EPA recognizes the 

importance of modeling and notes that 

there are potential benefits of using 

modeling when providing the optional 

air quality analysis. Additionally, in the 

preamble, the EPA described when 

these types of tools could be useful in 

the development the air quality targets. 

Because the development of air quality 

targets is optional and complements the 

emissions reductions analysis, the EPA 

does not require modeling of ambient 

conditions for this purpose. 

Comment: A few commenters 

supported the proposed Option 1 and 

the allowance for either generally linear 

or stepwise progress toward attainment. 

These commenters stated that allowing 

both methods is consistent with the 

pattern of many federal emissions 

reduction measures and it provides the 

most flexibility to states. Other 

commenters stated that existing 

guidance in the Addendum failed to 

recognize that, in many cases, more can 

be accomplished during one given year 

than in another. The commenters 

suggested the EPA provide states with 

the flexibility to manage their resources 

for rulemaking such that emissions 

reductions are obtained to attain 

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58058 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

117According to CAA section 189(a)(2)(B), 

Moderate area attainment plans are due to the EPA 

18 months after designation. 

118For more information on PM2.5 precursor 

requirements, see CAA section 93.102(b)(1) and 

(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). 

119A 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. 

120 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. 

121 40 CFR 93.101. 

generally linear progress averaged over 

the 3-year period rather than in each 

individual year. 

Response: As stated earlier, this rule 

requires that the RFP analysis must 

demonstrate either generally linear or 

stepwise emissions reduction progress 

toward attainment. If there are 

significant differences between 

emissions reductions in different years, 

which make the emissions reductions 

no longer generally linear, then the state 

would have to provide a justification for 

the stepwise progress as discussed 

earlier. Therefore, the suggestion of 

averaging the emissions reductions to 

obtain generally linear progress over a 3- 

year period is not an acceptable way to 

demonstrate RFP. In this example, the 

state would have to submit a 

justification of why stepwise emissions 

reductions are more appropriate for 

their area. However, the EPA notes that 

if stepwise emissions reductions are 

achieved more rapidly than expected 

and consistent with the amount 

necessary to demonstrate RFP toward 

timely attainment, this would be in line 

with the overall principles of the CAA 

and would not require the 

aforementioned justification. 

3. RFP Projected Emissions for RFP 

Analyses 

a. Summary of Proposal. The EPA 

proposed that a state with a Moderate 

PM2.5 nonattainment area must submit 

RFP projected emissions for sources 

within the nonattainment area as part of 

the RFP plan. The EPA also proposed 

that these RFP projected emissions 

would, at a minimum, include projected 

emissions of each pollutant by different 

source types corresponding to the 

quantitative milestone dates for the area. 

b. Final Rule. The EPA is finalizing 

that a state with a Moderate PM2.5

nonattainment area must submit RFP 

projected emissions for sources within 

the nonattainment area as part of the 

RFP plan. These RFP projected 

emissions shall, at a minimum, include 

projected emissions of each pollutant 

(i.e., direct PM2.5 and PM2.5 plan 

precursors) by different source types 

corresponding to the quantitative 

milestone dates for the area 

(quantitative milestone dates are 

described in greater detail in Section 

IV.G of this preamble). Specifically, the 

EPA requires that the RFP plan for any 

Moderate area must contain RFP 

projected emissions for each calendar 

year in which quantitative milestones 

for a Moderate nonattainment area must 

be met. As explained in Section IV.G 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.117 For example, the first round 

of designations for the 2012 PM2.5

NAAQS became 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 will 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 

this approach, the state will be required 

to submit such RFP projected emissions 

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 will be due (i.e., 

2019 and 2022 inventories in this 

example). 

The transportation conformity rule 

requires that RFP plans establish motor 

vehicle emissions budgets. RFP plans 

would therefore be required to establish 

motor vehicle emissions budgets for 

direct PM2.5 and any relevant PM2.5

precursor as determined under the 

transportation conformity rule.118

Precursors that are relevant for 

transportation conformity purposes 

would be limited to the PM2.5 plan 

precursors but may not include all of 

the PM2.5 plan precursors. For example, 

it is likely that many PM2.5 plans will 

include SO2 as a plan precursor. 

However, emissions of SO2 from onroad sources are usually low compared 

to stationary sources. The transportation 

conformity rule allows for the state to 

determine through its SIP development 

process if it is necessary to establish 

motor vehicle emissions budgets for 

SO2. See 40 CFR 93.102(b)(2)(v). On the 

other hand, if a state provides a 

precursor demonstration approved by 

the EPA which shows that VOCs do not 

have a significant contribution to PM2.5

levels in a particular nonattainment 

area, then a motor vehicle emissions 

budget for VOCs would not need to be 

established for the area for 

transportation conformity purposes. 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 earlier.119

Such motor vehicle emissions budgets 

will 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, unless the 

EPA approves the state’s use of an 

alternative model.120

c. Comments and Responses. 

Comment: Some commenters stated that 

since RFP is one of the general 

attainment plan provisions listed in 

CAA section 172(c), the EPA’s proposal 

to require motor vehicle emissions 

budgets as part of RFP plans extends 

beyond just the implementation of the 

PM2.5 NAAQS and, as a result, this 

proposal should be presented within the 

context of a revision to the conformity 

rule itself and not just this PM2.5

implementation rule. 

Response: The EPA disagrees with the 

commenters. The transportation 

conformity rule already states that 

motor vehicle emissions budgets come 

from control strategy SIPs.121

Additionally, the transportation 

conformity rule defines control strategy 

SIPs as RFP plans and attainment 

demonstrations. It goes further to say 

that control strategy SIPs include the 

SIPs required by CAA sections 172(c), 

189(a)(1)(B) and 189(b)(1)(A). The 

requirement in this PM2.5 SIP 

Requirements Rule does not amend the 

transportation conformity rule; it merely 

explains what is already required. 

4. Geographic Coverage of Emission 

Sources for RFP 

a. Summary of Proposal. The EPA 

proposed 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 proposed policy approach differed 

from the remanded 2007 PM2.5

implementation rule. As explained in 

the proposal, the difference was due to 

the evolution of policy on a similar RFP 

issue in the ozone NAAQS 

implementation program that stemmed 

in part from a petition for 

reconsideration and a DC Circuit 

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122This 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. 123Letter 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. 

124See NRDC v. EPA, 571 F.3d 1245 (D.C. Cir. 

2009). 

125See Phase 2 Ozone Implementation rule, 70 FR 

71612 (November 29, 2005). 

decision on the November 2005 Phase 2 

Ozone Implementation Rule. The EPA 

received a similar petition for 

reconsideration of the 2007 PM2.5

Implementation Rule, which 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.122 The EPA granted the petition 

for reconsideration on this issue in 

2010, after the DC Circuit issued its 

decision on litigation on the Phase 2 

Ozone Implementation Rule.123 124 In 

light of these developments, the 

proposal indicated that the EPA now 

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. 

b. Final Rule. The EPA is finalizing 

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. 

Commenters disagreed with limiting the 

RFP demonstration to include emissions 

only for sources located in the 

nonattainment area stating that some 

areas are so dominated by upwind 

emissions and local sources over which 

they have no control, such as motor 

vehicles, that they cannot demonstrate 

RFP. One of these commenters noted 

they have provided extensive comments 

on this issue in connection with the 

EPA’s proposal for the recent ozone 

implementation rule and incorporated 

by reference their prior comments. 

Other commenters agreed with the 

proposal and stated the EPA’s 

conclusion is compelled by CAA 

sections 172(c)(1), 172(c)(3) and 189(d), 

which all focus on emissions and 

reductions in the area. 

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.125 Under this 

policy, 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 accounting work associated 

with developing: (i) An expanded 

baseline emissions inventory for the 

entire geographic area and, (ii) a 

projected attainment year inventory for 

this expanded area outside the 

boundaries of the designated 

nonattainment area. 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 provide 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. 

Both the 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 that 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 RACT-level 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 is that the term ‘‘sources in 

the area’’ should be interpreted in the 

same manner as 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 CAA section 

182(b)(2) requires that a SIP must 

provide for implementation of RACT 

(under CAA section 172(c)) for 

emissions sources ‘‘in the area,’’ 

meaning in the nonattainment area. 

Similarly, the EPA position is that when 

CAA 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. 

Turning to PM2.5, the EPA has 

determined that the DC Circuit’s 

interpretation of the phrase ‘‘sources in 

the area’’ should apply to RACT and 

RFP requirements for both the ozone 

NAAQS and the PM2.5 NAAQS. In 

particular, for PM2.5, the statutory 

language at CAA 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 CAA 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 

consider only sources located within the 

nonattainment area when conducting its 

analysis to determine the annual 

emissions reductions necessary for 

demonstrating RFP. 

Beyond the Court’s interpretation, 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 

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126See 80 FR 12264. 

reasons. First, the EPA believes that it 

makes policy sense for the PM2.5

implementation rule approach to be 

consistent with the approach finalized 

in the 2008 NAAQS for Ozone: SIP 

Requirements rule.126 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 that 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 CAA section 189(d). 

Section 189(d) of the CAA 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). Therefore, the 

EPA is finalizing an RFP policy 

approach that is consistent with CAA 

section 189(d). 

c. Comments and Responses. 

Comment: Some commenters supported 

the EPA’s general guidance for 

developing the RFP demonstration. In 

particular, these commenters agreed 

with the EPA’s interpretation of the 

CAA to require that emissions 

reductions for purposes of meeting the 

RFP requirement must come from 

sources within the designated 

nonattainment area. Thus, the 

commenters supported the EPA’s 

proposal that the RFP demonstration 

submitted by states as a part of the 

attainment plan cannot take credit for 

emissions reductions occurring outside 

the nonattainment area to meet the RFP 

requirement. These commenters 

asserted that the EPA’s conclusion is 

compelled by sections 172(c)(1), 

172(c)(3) and 189(d), which all focus on 

emissions and reductions in the 

designated nonattainment area. The 

commenters further stated the EPA has 

not identified any rational way for states 

to pick and choose what sources and 

related emissions outside the designated 

nonattainment area would need to be 

included in inventories and attainment 

planning in order to rationally measure 

RFP. 

Other commenters disagreed with the 

EPA’s interpretation of the CAA on this 

issue and advocated that the EPA 

should provide an option for states to 

meet the RFP requirement with 

emissions reductions from sources 

outside the designated nonattainment 

area in addition to reductions from 

sources inside the area. One commenter 

suggested the EPA should provide this 

option to states and also consider 

alternatives to simplify the ‘‘overly 

complicated analysis’’ needed to 

support this option in the now 

superseded 2007 PM2.5 implementation 

rule. The comment did not address the 

consistency of such an interpretation of 

the RFP requirements with the statute. 

Another commenter asserted that the 

EPA should interpret the statute to 

permit states to meet the RFP 

requirement through emissions 

reductions from sources outside the 

designated area based upon several 

practical arguments. The commenter 

stated that, as the PM2.5 standards 

become lower and reductions from 

sources within a designated 

nonattainment area become more 

challenging to find, it may be necessary 

to obtain emissions reductions from 

sources beyond the designated area in 

order to attain the NAAQS. According 

to the commenters, some nonattainment 

areas are so dominated by emissions 

from outside the area and from local 

sources over which they have no control 

that they cannot demonstrate RFP, even 

though they could demonstrate timely 

attainment due to reductions from 

sources outside the nonattainment area. 

The commenters thus argued that the 

EPA should provide states with the 

option to meet the RFP requirement 

with emissions reductions from sources 

outside the nonattainment area in cases 

where they believe it would be 

unreasonable or impossible to do so 

only with emissions reductions from 

within the nonattainment area. 

In response to the EPA’s request for 

comment on any potential legal basis for 

authorizing states to meet the RFP 

requirement with emissions reductions 

from outside the nonattainment area, 

the commenter suggested potential 

theories. The primary legal theory was 

that EPA should by regulation redefine 

the term ‘‘area’’ for purposes of the RFP 

requirement so that it would encompass 

geographic areas that are not part of the 

designated nonattainment area. Through 

this theory, the commenters suggested 

that the EPA could authorize states to 

meet the RFP requirement based on 

reductions from the ‘‘total area’’ 

affecting that nonattainment area, rather 

than from the actual designated 

nonattainment area. As an alternative 

theory, the commenter argued that the 

EPA could regulatorily redefine the 

emissions inventory requirement of 

section 172(c)(3). To support this 

theory, the commenter disagreed with 

the EPA’s position that because the base 

year inventory required by section 

172(c)(3) includes the emissions from 

sources within the designated 

nonattainment area, it supports the 

EPA’s reading of the statute with respect 

to the RFP requirement. The commenter 

instead argued that because the 

emissions information used for 

modeling purpose includes emissions 

from a much broader region (not just 

within the nonattainment area or even 

just within the state), the EPA was 

wrong to say in the proposal that the 

base year inventory for sources in the 

area is the ‘‘foundation for the 

attainment plan.’’ Finally, the 

commenter argued more broadly for the 

EPA to alter its interpretation of the 

statutory language to allow for the 

commenter’s preferred approach to RFP. 

In support of their preferred approach to 

the RFP requirement, the commenters 

noted that the EPA acknowledged in the 

proposal that ‘‘a literal interpretation is 

illogical’’ for other statutory 

requirements. To support this 

contention, the commenters point to the 

criteria in section 188(d) that provide 

the criteria for an extension of the 

Moderate area attainment date that 

require significant interpretation in 

order to make them appropriate for the 

statistical form of the current PM2.5

NAAQS rather than for the exceedancebased form of the PM10 NAAQS that 

existed when the CAA was amended in 

1990. 

Response: The final rule requires that 

states demonstrate that they meet the 

RFP requirement through emissions 

reductions from sources in the 

nonattainment area. The EPA has 

decided to adopt this approach for two 

reasons. First, it is the most consistent 

with the statute. It aligns with RFP as 

defined in CAA section 171(1) and as 

required in CAA section 172(c)(2) and 

189(c), and is also most consistent with 

other related requirements for 

attainment plans, such as the 

requirements for imposition of emission 

controls, e.g., RACM and RACT, and 

with the process for designations of 

nonattainment areas pursuant to section 

107(d). Second, this approach is more 

straightforward to administer because it 

retains a nonattainment area focus to the 

RFP requirement and, while the 

alternative approaches would require 

complex and potentially burdensome 

requirements to define the scope of the 

out-of-area sources that must be 

inventoried and accounted for in the 

determination of what constitutes RFP. 

The EPA has concluded that such 

emissions reductions from sources 

outside the nonattainment area are more 

properly accounted for and reflected in 

other elements of the attainment plan, 

such as the attainment demonstration 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58061 

modeling which will take into account 

the emissions reductions that occur 

outside the nonattainment area in a less 

burdensome fashion. 

The EPA does not agree with the 

statutory interpretation of the RFP 

requirement preferred by the 

commenters who suggested that the EPA 

allow credit for emissions reductions 

from outside the area. Pursuant to 

section 171(1), the statute defines the 

term ‘‘reasonable further progress’’ to 

mean ‘‘such annual incremental 

reductions in emissions . . . as are 

required by this part or may reasonably 

be required by the Administrator for the 

purposes of ensuring attainment of the 

applicable [NAAQS] by the applicable 

date.’’ This provision plainly provides 

EPA with discretion to interpret this 

term within certain statutory 

parameters, i.e., ‘‘as are required by this 

part,’’ and consistent with the EPA’s 

determination of what will be the 

appropriate approach for timely 

attainment, i.e., ‘‘for the purpose of 

ensuring attainment . . . by the 

applicable date.’’ Thus, for example, the 

EPA has authority to interpret the RFP 

requirement to allow states to 

demonstrate generally linear reductions 

or stepwise reductions, rather than as a 

specific percentage of emissions 

reductions each year, as appropriate 

methods for meeting the RFP 

requirement for purposes of the subpart 

1 and subpart 4 provisions applicable to 

the PM2.5 NAAQS. It does not follow, 

however, that EPA is obligated to 

interpret the term ‘‘reasonable further 

progress’’ in other ways that the EPA 

considers inconsistent with other 

relevant statutory requirements for 

attainment plans or more broadly. 

To the contrary, the EPA believes that 

interpretation of the RFP requirement to 

reflect reductions in emissions ‘‘as are 

required by this part,’’ properly includes 

consideration of the context and 

structure of the statute with respect to 

the other attainment plan requirements. 

As explained in the proposal for this 

action, the EPA has concluded that 

several other related requirements for 

attainment plans support an 

interpretation of the RFP requirement 

for purposes of PM2.5 to be limited to 

emissions reductions from sources 

located within the nonattainment area. 

These requirements include the 

emissions inventory requirement of 

section 172(c)(3), the RACM/RACT 

requirement of section 172(c)(1) and 

section 189(a)(1)(C), and the not less 

than 5 percent emission reduction 

requirement of section 189(d). 

With respect to the inventory 

requirement of section 172(c)(3), the 

EPA explained in the proposal its view 

that because the emissions inventory 

requirement explicitly refers to a 

comprehensive, accurate, and current 

emissions inventory of emissions ‘‘from 

all sources of the relevant pollutant or 

pollutants in such area,’’ this statutory 

language supports the view that the 

primary focus of the attainment plan is 

reductions of emissions from the 

nonattainment area, not emissions 

reductions from sources elsewhere. 

Similarly, EPA explained in the 

proposal its views that the court’s 

decision in NRDC v. EPA, 571 F.3d 1245 

(D.C. Cir. 2009) supports an 

interpretation of the RFP requirement to 

apply to emissions reductions from 

sources within the area. Although that 

decision focused on the RACT 

requirement for ozone in particular, the 

reasoning of the court’s decision based 

upon the phrase ‘‘in the area’’ is 

consistent with the EPA’s longstanding 

approach to both RACM and RACT (or 

BACM and BACT for serious areas) 

being required for emissions sources 

within the nonattainment area. Given 

that states typically elect to demonstrate 

that they meet the RFP requirement 

through emissions reductions that result 

from expeditious imposition of RACM/ 

RACT or BACM/BACT emission 

controls applied to sources within the 

area, it is logical that the separate RFP 

requirement should likewise be based 

upon the expeditious progress towards 

attainment achieved through those 

emission controls. The EPA emphasizes 

that the RFP requirement and the 

requirements of section 172(c)(6) are 

separate components of an attainment 

plan. In those unusual circumstances 

where a state needs to impose specific 

additional controls on sources outside 

the nonattainment area in accordance 

with section 172(c)(6) to reach 

attainment, the state is not required to 

alter the base year emissions inventory 

for sources within the area or to alter its 

RFP analysis. As with other emissions 

reductions from sources outside the area 

that the state may rely upon, emissions 

reductions from measures states may 

impose to meet section 172(c)(6) will be 

reflected in the modeled attainment 

demonstration and thus included and 

taken into account in that fashion. [See 

sections IV.D.1 and VI.D.2 of the 

preamble for additional discussion of 

section 172(c)(6).] 

The EPA also considers this 

interpretation of the RFP requirement to 

be consistent with the comparable 

requirements of CAA section 189(d). 

Specifically, section 189(d) requires that 

states with nonattainment areas that fail 

to attain by the applicable attainment 

date must make a new attainment plan 

submission in order to achieve 

emissions reductions of not less than 5 

percent of the most recent emissions 

inventory ‘‘for such area.’’ As discussed 

in Section VII.F of this rule, the EPA 

interprets the statute to require an area 

subject to section 189(d) to achieve not 

less than a 5 percent reduction of the 

most recent emissions inventory of 

direct PM2.5 or any PM2.5 plan precursor 

‘‘for such area’’ (meaning from sources 

located within the nonattainment area). 

As a result, the EPA’s interpretation of 

‘‘in such area’’ and ‘‘for such area’’ are 

consistently applied for these related 

provisions of the CAA. 

As explained in the proposal, the EPA 

also sees no appropriate legal or policy 

basis for addressing the geographic area 

from which emissions reductions for 

RFP must be achieved for PM2.5

differently than is required by CAA 

section 182 for ozone. Both pollutants 

typically result from emissions from 

numerous sources that mix in the 

atmosphere and can transport great 

distances. For both pollutants, the CAA 

provides different tools for states and 

the EPA to address both the regional 

and the local contributions to violations 

of the NAAQS in a given area. With 

respect to the local contribution, the 

CAA provides a specific set of 

requirements (including RFP) designed 

to assure that states are properly 

addressing the emissions from sources 

located within the nonattainment area, 

whereas other requirements of the CAA 

are designed to address contributions 

from greater distances, whether from 

within the state, from other states, or 

even internationally. Were EPA to 

interpret the RFP requirements to 

authorize states to meet the emissions 

reductions requirement from sources 

outside the area, this would be 

inconsistent with the requirements 

specifically designed to assure that 

states get necessary reductions from the 

local sources that contribute to the 

violations through the attainment plan. 

One commenter recommended a 

potential statutory interpretation in 

support of an outside-the-area approach. 

The EPA appreciates the suggestion, but 

has determined that it would be too 

inconsistent with the structure and 

purpose of the attainment plan 

requirements of the statute. The 

commenter specifically suggested that 

EPA should redefine the term ‘‘area’’ to 

encompass not just the designated 

nonattainment area, but also some larger 

geographic area with sources of 

emissions that cause or contribute to the 

ambient air quality; and that reductions 

from such sources should be allowed to 

count towards meeting the RFP 

requirement in addition to reductions 

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58062 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

127See the discussion of this prior approach to 

RFP in the proposal for this action. 80 FR 15388– 

89. By its terms, the 2007 PM2.5 Implementation 

Rule applied only to the 1997 PM2.5 NAAQS. The 

EPA’s guidance for the 2006 PM2.5 NAAQS did not 

follow this approach with respect to the RFP 

requirement for purposes of the 2006 PM2.5

NAAQS. The EPA later withdrew the guidance for 

the 2006 PM2.5 NAAQS as a result of the court 

decision in NRDC v. EPA, 706 F.3d 428 (D.C. Cir. 

2013). 

128See, Letter to David S. Baron, EarthJustice, 

from Gina McCarthy, Assistant Administrator, 

dated May 13, 2010. A copy of this letter is in the 

docket for this action. 

129See, e.g., ‘‘Approval and Promulgation of 

Implementation Plans; California; 2007 South Coast 

PM2.5 Plan and 2007 State Strategy; Proposed Rule,’’ 

76 FR 41567, 41577–78 (July 14, 2011); Final 

Approval of Air Quality Implementation Plans; 

California; South Coast Attainment Plan for the 

1997 PM2.5 NAAQS Standards; Final Rule,’’ 76 FR 

69928 (November 9, 2011). 

130 Ibid. at 42016. 

from sources in the designated 

nonattainment area. The EPA considers 

such an approach inappropriate for 

several reasons. First, such a reading 

would be inconsistent with the EPA’s 

longstanding reading of this same term 

in many important places throughout 

the statute, including but not limited to 

explicit statutory references to the 

‘‘area’’ in section 107(d)(1) (relevant to 

designations), section 107(d)(3) 

(relevant to redesignations), section 

110(a)(2)(I) (relevant to the scope of all 

of the attainment plan requirements 

imposed by Part D), section 189(B)(2) 

(relevant to the schedule for submission 

of attainment plans under subpart 4), 

and section 189(e) (relevant to the 

statutory test for regulating precursors 

in a given ‘‘area’’). Creating a different 

and conflicting definition of the word 

‘‘area’’ for RFP purposes is not 

appropriate for common sense reasons, 

and it would require that the same word 

to be interpreted in multiple ways. 

Second, the EPA considers the 

redefinition of the term ‘‘area’’ 

inappropriate because it could be 

perceived as an attempt to alter the 

meaning of the term as the D.C. Circuit 

has already interpreted it in the NRDC 

v. EPA decision concerning the plain 

meaning of the term ‘‘in the area.’’ 

Third, to the extent that there are 

situations in which the boundaries of 

the nonattainment area are incorrect 

because they fail to include the sources 

that contribute violations in an adjacent 

area to the extreme degree posited by 

the commenters, the statute already 

provides a straightforward solution to 

such a situation through the initial 

designation and redesignation 

provisions of section 107(d). 

Finally, the EPA acknowledges that in 

the prior 2007 PM2.5 implementation 

rule, the EPA did adopt a different 

interpretation of the RFP requirement 

for the first time that would have 

authorized states to meet the RFP 

requirement with emissions reductions 

from sources outside the nonattainment 

area within certain narrow parameters 

for purposes of the 1997 PM2.5

NAAQS.127 The EPA received a petition 

for reconsideration on this specific issue 

and granted the petition to reexamine 

that aspect of the 2007 PM2.5

implementation rule.128 Before the EPA 

proceeded with that reconsideration, 

however, the litigation over the 2007 

PM2.5 implementation rule and the 2008 

NSR revisions (addressing the PM2.5

NAAQS) proceeded with challenges on 

other statutory authority issues while 

the petition for reconsideration was still 

under evaluation. This litigation 

resulted in the court’s decision in NRDC 

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

In that decision, the court remanded the 

entire 2007 PM2.5 implementation rule, 

including the portions relevant to the 

RFP requirement, to the EPA for failure 

to comply with the statutory 

requirements of subpart 4. This 

rulemaking constitutes the EPA’s 

response to that judicial remand and 

through this process the EPA is 

replacing the 2007 PM2.5

implementation rule, including the 

prior regulatory provisions and 

guidance related to states meeting the 

RFP requirements with emissions 

reductions from outside the designated 

nonattainment area. Accordingly, upon 

completion of this rulemaking the EPA 

will be interpreting the RFP requirement 

consistent with past practice. The EPA 

also notes, as a factual matter, that states 

have not been using this feature of the 

2007 PM2.5 implementation rule.129

Aside from the lack of a legal basis for 

the commenter’s preferred approach to 

RFP, thus far the EPA’s interpretation of 

the requirements has not posed the 

practical difficulties that the commenter 

raised. 

5. Other RFP Considerations 

a. Summary of Proposal. The proposal 

outlined the statutory requirements and 

existing guidance for RFP. During this 

discussion, the following guidance from 

the Addendum was referenced, 

‘‘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.’’ 130 The proposal also 

discussed other RFP considerations, 

including PM2.5 nonattainment areas 

that are shared by more than one state 

or tribe. 

b. Final Rule. The EPA is finalizing 

that, although early implementation of 

the most cost-effective control measures 

is often appropriate, states should 

consider both cost-effectiveness and 

pollution reduction effectiveness when 

developing implementation schedules 

for their control measures and may 

implement measures that are more 

effective at reducing PM2.5 earlier to 

provide greater public health benefits. 

This increased flexibility enables states 

to develop a more effective 

implementation schedules for their 

control measures while efficiently using 

their resources. 

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 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 states within the 

nonattainment area will provide for 

attainment as expeditiously as 

practicable and demonstrate RFP 

consistent with these regulations. 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 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. 

c. Comments and Responses. 

Comment: Some commenters asserted 

that the EPA should not ‘‘require’’ 

implementing the most cost-effective 

measures first since states should have 

the flexibility to implement the more 

effective but less cost-effective measure 

earlier, thus providing earlier and 

greater public health benefits. 

Response: In this final rule, the EPA 

is providing states with the flexibility to 

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131 General Preamble, 57 FR 13498 (April 16, 

1992), at page 13539. 132 57 FR 13539. 133 80 FR 2206, January 15, 2015. 134The EPA promulgated nonattainment area 

designations for the 1997 PM2.5 NAAQS effective 

April 2005 (70 FR 944, January 5, 2005 and 70 FR 

19844, April 14, 2005). The EPA promulgated 

nonattainment area designations for the 2006 PM2.5

NAAQS effective December 2009 (74 FR 58688, 

November 13, 2009), March 2011 (76 FR 6056, 

February 3, 2011), and November 2012 (77 FR 

65310, October 26, 2012). 135 79 FR 31566 (June 2, 2014) (final rule 

establishing subpart 4 moderate area classifications 

and deadline for related SIP submissions) 

(‘‘Classification and Deadline Rule’’). Although the 

Classification and Deadline Rule did not affect any 

action that the EPA had previously taken under 

CAA section 110(k) on a SIP for a PM2.5

nonattainment area, the EPA noted that states may 

need to submit additional SIP elements to fully 

satisfy the applicable requirements of subpart 4, 

even for areas with previously approved PM2.5

attainment plans, and that the deadline for any such 

additional plan submissions was December 31, 

2014. Id. at 31569. 

136See, e.g., Addendum at 42016, n. 43 (noting 

that the plain terms of CAA section 189(c) require 

that milestones be achieved every 3 years until the 

area is redesignated attainment and, therefore, do 

not contemplate any breaks in the milestones due 

to an area’s reclassification). 

implement measures that are more 

effective at reducing PM2.5 earlier to 

provide greater public health benefits, 

but is not requiring it. This increased 

flexibility is in keeping with the overall 

requirement of expeditious attainment 

of the NAAQS. 

G. Quantitative Milestones 

1. General Approach to Quantitative 

Milestones 

a. Summary of the Proposal. The 

proposal built from the statutory 

language of 189(c)(1), which requires 

quantitative milestones that (1) 

demonstrate RFP, and (2) must be 

achieved every 3 years until the area is 

redesignated attainment. The proposal 

first addressed the issue of the starting 

date for counting the 3-year periods. For 

a Moderate area that cannot practicably 

attain the relevant PM2.5 NAAQS within 

the statutory timeframe for a Moderate 

area, the EPA proposed that a state must 

submit two sets of quantitative 

milestones—the first 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 also 

proposed 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. The EPA therefore 

proposed 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. In addition to 

this general proposed approach for 

selecting quantitative milestones for a 

Moderate nonattainment area, the EPA 

proposed 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. 

b. Final Rule. Section 189(c) of the 

Act explicitly requires that quantitative 

milestones must be achieved every 3 

years, but does not specify the starting 

date for counting the 3 year periods. In 

the General Preamble and Addendum, 

the agency stated that quantitative 

milestones must be achieved every 3 

years starting from the due date for the 

plan submission (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 

area is redesignated attainment.131 The 

EPA is finalizing this approach for the 

PM2.5 NAAQS. The EPA interprets this 

requirement to be the most appropriate 

reading of CAA section 189(c)(1) which 

requires ‘‘quantitative milestones which 

are to be achieved every 3 years until 

the area is redesignated attainment.’’ 

This approach is also consistent with 

the longstanding approach outlined in 

the General Preamble.132 These 

timeframes for the quantitative 

milestones apply to all areas designated 

nonattainment for a PM2.5 NAAQS on or 

after January 15, 2015, including all 

areas designated nonattainment 

effective April 15, 2015 for the 2012 

PM2.5 NAAQS.133 See 40 CFR 51.1013(a). 

For all areas designated 

nonattainment for the 1997 and/or 2006 

PM2.5 NAAQS before January 15, 

2015,134 the EPA is establishing 

December 31, 2014 as the starting point 

for the first 3 year period for 

quantitative milestones under CAA 

section 189(c). This is because 

December 31, 2014, was the due date for 

states to submit additional SIP elements 

necessary to satisfy the subpart 4 

Moderate area requirements for the 1997 

and 2006 PM2.5 standards.135

Establishing December 31, 2014 as the 

starting point for the first 3 year period 

under CAA section 189(c) for the 1997 

and 2006 PM2.5 standards is in keeping 

with the EPA’s historical approach to 

quantitative milestone dates (i.e., using 

the due date for the Moderate area plan 

submission as the starting point for the 

first 3 year milestone period). Thus, for 

any area designated nonattainment for 

the 1997 and/or 2006 PM2.5 NAAQS that 

has not yet attained these NAAQS and 

therefore continues to have attainment 

planning obligations for these NAAQS, 

the state must submit quantitative 

milestones to be achieved by December 

31, 2017 (the first milestone date), at 

minimum. Additional milestone dates 

may also apply to such an area 

depending on the relevant attainment 

planning period. See 40 CFR 

51.1013(a)(4). 

Regardless of whether or not an 

attainment plan demonstrates 

attainment by the statutory attainment 

date, the EPA requires that all Moderate 

area PM2.5 attainment plans must define 

appropriate quantitative milestones to 

be achieved by 4.5 years and 7.5 years 

following designation of the area. 

Although it occurs after the Moderate 

area attainment date, the EPA is 

requiring Moderate area plans to contain 

this 7.5 year milestone, even where 

those plans demonstrate attainment 

before the milestone would arrive. 

Where the EPA uses its discretionary 

authority in CAA section 188(b)(1) to 

reclassify an area before the Moderate 

area attainment date applicable to the 

area, CAA section 189(b)(2) allows the 

state up to 4 years to submit the 

required Serious area attainment 

demonstration and related plan 

elements, such as quantitative 

milestones. For example, if the 

reclassification occurs 4 years after 

designation, the state may be allowed to 

submit the Serious area quantitative 

milestones up to 8 years after 

designation, well after the second 

milestone date (7.5 years after 

designation) has passed. Without the 7.5 

year milestone requirement, this 

circumstance would undermine the 

purpose of the quantitative milestone 

requirement, which is to ensure that 

states will report to EPA on each 

nonattainment area’s progress toward 

attainment at regular intervals, even 

following reclassification.136

A similar issue would result in the 

event that a Moderate area that did 

demonstrate attainment in the original 

attainment plan fails to attain by the 

statutory attainment date. In this case, 

the area would have failed to meet the 

attainment date which is as 

expeditiously as practicable but no later 

than the end of the sixth calendar year 

after designation as required by CAA 

section 188(c)(1). Section 188(b)(2) of 

the Act allows the Administrator up to 

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137Addendum to the General Preamble, 59 FR 

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

6 months to determine that a Moderate 

failed to attain and reclassify that area 

to Serious, which would be at least 6.5 

years after designation. As described in 

Section VI.A.1 of this preamble, the 

Serious area would have 18 months 

from reclassification due to a failure to 

attain (8 years after designation) in order 

to submit an attainment plan. The EPA 

has therefore determined that, in order 

to avoid gaps of greater than 3 years in 

the implementation of quantitative 

milestones, all Moderate area attainment 

plans must contain quantitative 

milestones to be achieved 4.5 years and 

7.5 years after designation and which 

demonstrate continued progress toward 

timely attainment of the relevant PM2.5

NAAQS. In the event that the area fails 

to attain, this will provide the EPA with 

appropriate tools necessary to continue 

to monitor the area’s continued progress 

toward attainment while the state 

develops the Serious area attainment 

plan. 

The quantitative milestones contained 

in the attainment plan for a Moderate 

nonattainment area should 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 determine whether the area is 

making the necessary progress towards 

attainment by the applicable attainment 

date.137 The EPA interprets Section 

189(c) of the Act to allow states to 

identify 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. 

This rule requires that each 

attainment plan for a Moderate PM2.5

nonattainment area contain quantitative 

milestones that provide for objective 

evaluation of RFP toward attainment in 

the PM2.5 nonattainment area, whether 

the plan provides for attainment of the 

PM2.5 NAAQS by the statutory 

attainment date or demonstrates that 

attainment by such date is 

impracticable. For this approach, the 

EPA does not require that such 

quantitative milestones take any 

particular form, merely that they 

provide a means to evaluate progress 

(i.e., demonstrate RFP) meaningfully. 

The EPA will review each attainment 

plan submission on a case-by-case basis 

to determine whether the quantitative 

milestones contained in the plan are 

specific enough to provide an objective 

means for evaluating the area’s progress 

toward attainment, consistent with the 

statutory requirements of CAA section 

189(c). The EPA recommends that states 

confer with their respective EPA 

regional office to develop appropriate 

quantitative milestones. See 40 CFR 

51.1013(a). 

The Addendum stated that the 

Moderate area quantitative milestones 

‘‘will be met by showing that emissions 

reductions scheduled to be made 

between the SIP due date and the 

attainment date for these moderate areas 

were actually achieved. Most of these 

emissions reductions will result from 

implementation of RACM (including 

RACT) as part of the moderate area 

SIP.’’ However, this rule does not 

specify that quantitative milestones 

must be expressed in terms of emissions 

reductions. The EPA recognizes 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 CAA section 189(c)(2). Therefore, 

the final rule requires that, at a 

minimum, states must include in all 

attainment plans for Moderate PM2.5

nonattainment areas a milestone that all 

control measures identified and adopted 

as RACM and RACT for the area have 

been fully implemented within 4 years 

of designation. This milestone 

specifically derives from section 

189(a)(1)(C) of the Act, 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. 

See 40 CFR 51.1013(a)(1)(iii). 

For an area that submitted air quality 

targets with the RFP plan under the 

optional provision that was described in 

Section IV.F of this preamble, an air 

quality based milestone (i.e., one that is 

expressed in terms of an ambient PM2.5

level) is strongly recommended to be 

included in order to confirm that the air 

quality target has been met for the 

quantitative milestone year. If used, this 

milestone will be compared to the most 

recently certified monitored ambient air 

data as part of the milestone report due 

after the area reaches each quantitative 

milestone date. The EPA recognizes that 

certified monitored ambient air data are 

not available for some period after a 

calendar year ends. As a result, the EPA 

expects that this quantitative milestone 

may sometimes be satisfied with data 

that are over a year old. For example, for 

Moderate areas having an effective date 

of designations in April 2015, the first 

quantitative milestone date will be in 

October 2019 (3 years after the 18 month 

SIP due date), and the associated report 

will be due 90 days later, in January 

2020. In this example, the state would 

likely have to rely upon certified air 

quality data for 2018 because data for 

the 2019 calendar year would not yet be 

fully certified. Additionally, this 

milestone should normally be reported 

in the same form as the applicable PM2.5

NAAQS. However, the EPA expects that 

in some circumstances, it may be 

appropriate to use annual averages 

instead of the 3 year average to help 

justify variations due to meteorological 

occurrences. 

c. Comments and Responses. 

Comment: Some commenters stated the 

Act may be read to conclude that the 

requirement to include any quantitative 

milestones in a Moderate area plan does 

not apply to a plan demonstrating the 

impracticability of attaining the NAAQS 

by the attainment date. 

Response: The EPA’s longstanding 

interpretation of CAA section 189(c) as 

a requirement that applies to all PM10

nonattainment area plans, including 

those demonstrating that attainment by 

the applicable attainment date is 

impracticable, is consistent with the 

purpose and structure of subpart 4. The 

design of the CAA for PM 

nonattainment areas combines the 

requirements of subpart 1 and subpart 4 

to support expeditious attainment of the 

applicable NAAQS. RFP is the 

prescribed tool available to a state to 

plan their emission reduction progress 

toward expeditious attainment. 

Quantitative milestones are a critical 

aspect of the CAA and the attainment 

plan in order for the EPA to monitor the 

area’s RFP toward expeditious 

attainment and trigger the appropriate 

response if RFP is not maintained. The 

EPA thus determined that allowing an 

area to simply not submit any 

quantitative milestones would not 

afford the EPA the necessary tools to 

monitor RFP toward expeditious 

attainment. 

2. Milestone Report Submission 

a. Summary of the Proposal. Because 

the statute does not define the 

parameters of quantitative milestone 

demonstrations, the EPA has discretion 

to determine the components of the 

required demonstration and the form 

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138 Ibid. at 42017. 

and manner for submission. The 

proposal took comment on options for 

doing this. The EPA proposed to require 

that the milestone report submission 

must include the following four 

components: (i) A certification by the 

Governor or Governor’s designee that 

the state’s attainment plan control 

strategy is being implemented as 

described in the applicable attainment 

plan, (ii) technical support 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, (iii) as 

applicable, 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, and (iv) an evaluation of 

whether the PM2.5 NAAQS will be 

attained by the projected attainment 

date for the area. In addition, the EPA 

proposed 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. 

The EPA also sought comment on 

how electronic reporting could facilitate 

a state’s submission of the required 

milestone report, how it could 

accommodate the various narrative and 

data-dependent components that the 

EPA proposed be part of such a 

submission, and what particular system 

features might be desirable to 

accommodate milestone report 

submissions through the eSIP system. 

b. Final Rule. The final rule, mirroring 

section 189(c)(2) of the Act, requires 

that each state containing a PM2.5

nonattainment area submit to EPA, 

within 90 days after each milestone date 

applicable to the area, a demonstration 

that all measures in the approved plan 

(including the RFP plan) for the area 

have been implemented and that the 

milestone has been met. This rule 

outlines the content required by the 

EPA for the quantitative milestone 

report. The EPA must then determine 

whether or not a state’s demonstration 

is adequate within 90 days after 

receiving a demonstration which 

contains the required information and 

analysis. The EPA intends to promptly 

inform the relevant state of any 

determination that the state has failed to 

submit a timely quantitative milestone 

report and any determination that a 

submitted milestone report is not 

adequate. 

The EPA will work with a state to 

assist them in meeting the reporting 

deadline, and expects that, because the 

report is to be fairly low burden and 

may be submitted electronically through 

eSIP, in most cases the state will submit 

it on time, especially if they have 

implemented the programs required to 

meet their milestones. If, however, a 

state fails to submit a milestone 

demonstration report by the due date or 

the EPA determines that a milestone 

was not met, the final rule requires the 

state to 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 CAA 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 CAA 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 CAA section 

188(b)(1). 

As previously noted, the EPA has 

offered guidance about what the 

milestone report should contain. The 

Addendum says, ‘‘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 

emissions 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 

emissions 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.’’ 138 This 

guidance is still appropriate for states 

demonstrating compliance with RFP 

and quantitative milestones for PM2.5

NAAQS. The EPA requires that the 

milestone report submission must 

include the following components. See 

40 CFR 51.1013(b). 

First, the report must include a 

certification by the Governor or 

Governor’s designee that the SIP control 

strategy is being implemented 

consistent with the RFP plan, as 

described in the applicable attainment 

plan. Second, the report must contain 

technical support, including 

calculations, sufficient to document 

completion statistics for each 

quantitative milestone 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. Additionally, 

the report must include a discussion of 

whether the PM2.5 NAAQS will be 

attained by the projected attainment 

date for the area. See 40 CFR 51.1013(b). 

The EPA decided not to finalize the 

proposed requirements to include an air 

quality screening analysis or the 

description and schedule for remedial 

actions taken by the state to address a 

failure to meet a quantitative milestone. 

This decision was made because the 

remaining components of the 

quantitative milestone report are 

sufficient to enable the EPA to assess 

whether the nonattainment area is 

meeting RFP. 

As stated in the Addendum, 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. 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 encourages 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. 

c. Comments and Responses. 

Comment: Some commenters did not 

support the proposal and stated that 

requiring this level of documentation is 

unnecessary and puts an excessive 

workload burden on states and local 

agencies. 

Response: The EPA recognizes that 

there is some level of resources required 

to address the requirements prescribed 

by every rule. However, the EPA 

concluded that the benefit offered to the 

public by reviewing quantitative 

milestone reports while assessing 

whether nonattainment areas are 

making reasonable further progress 

toward attaining the PM2.5 NAAQS and 

the associated public health benefits 

outweigh the anticipated workload 

burden for states. 

Comment: Some commenters stated 

that the first two components of the 

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139 Ibid. at 42015. 

quantitative milestone report described 

in the proposal are sufficient to comply 

with the requirements of CAA section 

189(c)(2). The commenters stated that 

the proposed air quality screening 

analysis is not supported by the statute 

and is unnecessary if the second 

component is fulfilled. The commenters 

stated that the proposed description and 

schedule for remedial actions the state 

has taken or will take to address any 

failure to meet a quantitative milestone 

is more than what is necessary to 

demonstrate compliance with RFP 

milestones and could require revisions 

to the SIP. 

Response: After considering these 

comments and in an effort to simplify 

the rule, the EPA decided to eliminate 

the two proposed requirements for the 

quantitative milestone report as 

suggested by these commenters. As 

stated earlier, this decision was made 

because the EPA determined that the 

remaining components of the 

quantitative milestone report are 

sufficient to enable the EPA to assess 

whether the nonattainment area is 

meeting RFP. 

Comment: One commenter stated that, 

while they would not object to filing 

periodic reports, as part of their 

milestone report, the EPA should not 

insist on the state actually inspecting all 

covered facilities and indicating that 

RACT or RACM has not been 

implemented if a small subset of 

facilities is found in violation. 

Response: It is not the intent of the 

EPA to require states to physically 

inspect all covered sources to verify the 

implementation of required control 

measures. The intent is that, at the time 

of the milestone due date, all covered 

sources would be legally required to 

have implemented required control 

measures and the state has reasonably 

been assured that this occurred. 

H. Contingency Measures 

1. Summary of the Proposal 

The Act requires Moderate PM2.5

nonattainment area plans to contain 

contingency measures consistent with 

CAA section 172(c)(9). Contingency 

measures are additional control 

measures to be implemented in the 

event that the EPA determines that an 

area failed to meet RFP requirements 

(including associated quantitative 

milestones) or failed to attain the PM2.5

primary 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 proposed and sought 

comment on general requirements for 

contingency measures for Moderate 

PM2.5 nonattainment areas. 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. These 

documents provide guidance and 

recommendations for states to follow in 

submitting contingency measures, and 

the proposal did not contain any 

significant changes to the existing 

guidance and recommendations. 

However, the EPA sought comment on 

whether the guidance needed to be 

revised or expanded. Additionally, as 

discussed in the proposal, the EPA 

believes that the DC Circuit’s decision 

in NRDC v. EPA does not affect the 

overall contingency measure 

requirements that were finalized in the 

remanded 2007 PM2.5 Implementation 

Rule. The EPA determined this because 

CAA 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. As a 

result, the proposal for this rule 

remained very similar to the final 2007 

PM2.5 Implementation Rule. 

2. Final Rule 

Consistent with the proposal, the final 

rule codifies existing policies on 

contingency measures, but does not 

make significant changes to these 

policies. Although CAA section 

172(c)(9) requires contingency 

measures, the provision does not specify 

exactly what parameters such measures 

must meet. The EPA is finalizing an 

approach to contingency measures for 

the PM2.5 NAAQS that is similar to the 

approach recommended in earlier EPA 

guidance. Specifically, in order for 

contingency measures to be approvable 

as part of a state’s Moderate area 

attainment plan submission for the 

PM2.5 NAAQS, the state plan must meet 

the following general requirements (See 

40 CFR 51.1014): 

(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, failure to 

meet any quantitative milestone, failure 

to submit a quantitative milestone 

report or failure to attain the standard 

by the applicable 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) The contingency measures shall 

consist of control measures that are not 

otherwise included in the control 

strategy or that achieve emissions 

reductions not otherwise relied upon in 

the control strategy for the area. 

(4) Contingency measures should 

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. 

Regarding the first two points, 

consistent with prior guidance, 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 PM2.5 nonattainment area has 

failed to meet an RFP requirement or to 

attain the PM2.5 NAAQS, the EPA 

generally expects all actions needed to 

effect full implementation of the 

contingency measures to occur within 

60 days after the EPA notifies the state 

of the area’s failure. The EPA intends to 

notify the state of a failure to meet RFP 

or to attain the NAAQS by publication 

of its determination in the Federal 

Register. The state should ensure that 

the contingency measures are fully 

implemented as expeditiously as 

practicable after such notice.139

Regarding the third point, the EPA 

interprets the contingency measure 

requirement of CAA section 172(c)(9) to 

require control measures that are not 

otherwise included in the control 

strategy or that achieve emissions 

reductions not otherwise relied upon in 

the control strategy for the area. 

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 

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140See LEAN v. EPA, 382 F.3d 575 (5th Cir., 

2004). 141See, 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); 

78 FR 64402 (October 29, 2013). 

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. 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. 

As discussed in Section IV.D of this 

preamble, the RACM/RACT provisions 

in this rule require that, for Moderate 

areas that cannot practicably attain the 

NAAQS by the statutory attainment 

date, states must implement all control 

measures that they determine to be 

reasonable (i.e., all technologically and 

economically feasible measures) for 

sources in the area. In such cases, the 

contingency measures for such 

nonattainment areas would necessarily 

exceed the criteria for determining 

whether a measure is reasonable for 

purposes of RACM/RACT and 

additional reasonable measures. For 

example, contingency measures could 

consist of reasonable controls on 

sources outside the nonattainment area, 

early implementation of BACM/BACT 

on select sources inside the area, other 

measures identified by the state, or a 

combination thereof, that collectively 

provide approximately equivalent to 1 

year’s worth of emissions reductions/air 

quality improvement. 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 these 

measures in a timely way as part of the 

Serious area attainment plan that it will 

develop once the EPA reclassifies such 

an area. However, if a Moderate area 

that cannot practicably attain the 

NAAQS fails to meet RFP when 

reviewed as part of the quantitative 

milestone either 4.5 or 7.5 years after 

designation, the requirement to 

implement contingency measures would 

be triggered as required by CAA section 

172(c)(9). 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 offer reasonable assurance that 

the appropriate air quality impact will 

result within the nonattainment area. 

The final rule continues to allow 

states 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 that provide emissions 

reductions in excess of those needed to 

provide for RFP or expeditious 

attainment. The key is that the statute 

requires that contingency measures 

provide for additional emissions 

reductions that are not relied on for RFP 

or attainment and that are not included 

in the RFP or attainment demonstrations 

as meeting part or all of the contingency 

measure requirements. The purpose is 

‘‘to provide a cushion while the plan is 

being revised to meet the missed 

milestone.’’ Nothing in the statute 

precludes a State from implementing 

such measures before they are triggered. 

Additionally, the EPA determined that 

the court ruling upholding contingency 

measures that were previously required 

and implemented where they were in 

excess of the attainment demonstration 

and RFP for ozone attainment plans 

necessitates similar treatment for PM2.5

NAAQS.140 The EPA has approved 

numerous SIPs under this 

interpretation, i.e., SIPs that use as 

contingency measures one or more 

federal or local measures that are in 

place and provide reductions that are in 

excess of the reductions required by the 

attainment demonstration or RFP 

plan.141

For these reasons, the EPA concluded 

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 is not allowable for 

Moderate areas that cannot practicably 

attain by the statutory attainment date. 

Under the EPA’s approach for 

calculating RFP for such areas, 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 

should be no difference between 

emissions reductions estimated from 

control measures and those estimated 

for demonstrating RFP. 

Finally, consistent with the EPA’s 

past approach for contingency measures 

for PM2.5 nonattainment areas, the EPA 

expects that the emissions reductions 

from contingency measures should be 

approximately equivalent to 1 year’s 

worth of emissions reductions while the 

state is revising its attainment plan for 

the area. States should explain the 

amount of anticipated emissions 

reductions to be accomplished by the 

contingency measures outlined in the 

plan. In the rare event that an area is 

unable to identify contingency measures 

to account for approximately 1 year’s 

worth of emissions reductions, the state 

should provide a reasoned justification 

why the smaller amount of emissions 

reductions is appropriate. As described 

in Section IV.F of this preamble, the 

EPA requires 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 

finalizing a similar approach for 

calculating 1 year’s worth of emissions 

reductions for purposes of adopting 

appropriate contingency measures. That 

is, the EPA’s 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 plan 

precursors needed from sources located 

inside the nonattainment area. As 

explained earlier, however, some or all 

of the contingency measures reductions 

can come from outside the area if they 

are demonstrated to produce the 

appropriate air quality impact within 

the nonattainment area. 

This rule requires that states must 

implement contingency measures after 

the EPA determines that the area has 

either failed to meet RFP requirements, 

failed to meet any quantitative 

milestone, failed to submit a 

quantitative milestone report, 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 

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determine within 90 days after receiving 

a state’s quantitative milestone 

demonstration, and within 6 months 

after the attainment date for an area, 

whether these requirements have been 

met. The additional 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. 

See Section IV.A of this preamble for 

a discussion of the due dates for 

submission of contingency measures 

and other attainment plan elements. 

3. Comments and Responses 

Comment: Commenters stated that 

requiring contingency measures in areas 

with mature air pollution control 

programs is very challenging because 

they already have developed aggressive 

control measures to meet CAA 

requirements and support expeditious 

attainment. Commenters asserted that it 

would be extremely difficult to develop 

further control measures to meet any 

contingency measure requirements. 

Commenters objected to the proposed 

requirement that contingency measures 

must be approximately equivalent to 1 

year’s worth of emissions reductions 

because it is a departure from existing 

guidance which states the contingency 

emissions reductions ‘‘should be’’ 

approximately equal and because 

sometimes identifying control measures 

for this level of reductions is just not 

possible. Commenters advocated that 

EPA should provide a more reasonable 

approach to the contingency measure 

requirement, but did not provide 

specific recommendations. Other 

commenters stated that contingency 

measures should provide 1 year’s worth 

of emissions reductions needed for RFP. 

Response: The EPA acknowledges 

that states containing areas with more 

longstanding and pervasive 

nonattainment problems may already 

have implemented many control 

measures for purposes of attaining the 

NAAQS, and there may be fewer 

sources and measures available to meet 

the contingency measure requirements 

of the statute. However, the EPA notes 

that section 172(c)(9) of the CAA 

explicitly requires states to adopt 

contingency measures to apply in the 

event of failure to meet RFP or failure 

to attain the NAAQS as a required 

component of all attainment plans. 

Typically, contingency measures will be 

comprised of measures that a state and 

the EPA have determined are not 

required to meet RACM/RACT or other 

requirements, e.g., on the grounds that 

they are more technologically or 

economically challenging. As a result, 

such measures may not be required as 

RACM/RACT, but are nevertheless 

available for use as contingency 

measures. Another approach to 

contingency measures, if appropriate, 

would be to rely on control measures 

imposed on sources outside the 

boundaries of the designated 

nonattainment area. Such contingency 

measures require adequate support to 

establish that the reductions would have 

the intended impacts within the 

nonattainment area, but can be a source 

of additional measures for this purpose. 

Finally, the EPA notes that its 

longstanding guidance is that 

contingency measures should provide 

approximately 1 year’s worth of RFP, 

but this amount may vary based upon 

appropriate facts and circumstances of 

each unique nonattainment area. As 

discussed, states should explain the 

amount of anticipated emissions 

reductions to be accomplished by the 

contingency measures outlined in the 

plan. In the rare event that an area is 

unable to identify contingency measures 

to account for approximately 1 year’s 

worth of emissions reductions, the state 

should provide a reasoned justification 

why the smaller amount of emissions 

reductions is appropriate. 

Comment: Commenters stated that 

‘‘excess’’ emissions reductions (i.e., 

emission reduction measures that are 

included in a modeled attainment 

demonstration indicating that the area 

will improve air quality to well below 

the standard) should not be used as 

contingency measures in the event an 

area actually fails to attain. Commenters 

asserted that the failure to attain should 

be considered a demonstration that 

excess emissions reductions do not 

exist. Further, the commenters stated 

that excess reductions do not provide 

the public health benefit intended by 

Congress. Other commenters stated that 

Moderate areas that cannot attain by the 

statutory attainment date could also 

have excess emissions reductions 

creditable as contingency measures. 

Response: In keeping with 

longstanding practice, the final rule 

allows excess emissions reductions to 

be credited as contingency measures in 

plans that demonstrate attainment but 

not for plans that demonstrate an 

impracticability to attain. This allows 

nonattainment areas to credit emissions 

reductions beyond those planned to 

satisfy attainment plan requirements as 

meeting part or all of the contingency 

measure requirements. This allowance 

is further supported by the court’s 

ruling in LEAN v. EPA, which found 

that emissions reductions in excess of 

what were needed for the attainment 

demonstration and RFP in ozone 

attainment plans are creditable for 

contingency measures. Because the 

contingency measures requirement for 

both ozone and PM2.5 originates in CAA 

section 172(c)(9), it is applicable for all 

areas designated nonattainment for any 

NAAQS. Therefore, the EPA concluded 

that the same approach is appropriate 

for Moderate PM2.5 nonattainment areas 

that can demonstrate attainment by the 

statutory attainment date. Allowing 

‘‘excess’’ emissions reductions affords 

proper credit for these areas as they 

continue to make progress toward 

attainment while the new SIP is 

developed for the area. Additionally, in 

support of the overarching goal of the 

CAA, public health will benefit from the 

excess emissions reductions. However, 

such an allowance for a Moderate area 

that cannot practicably attain is not 

acceptable because all emissions 

reductions anticipated from control 

measures while developing the 

attainment plan should be accounted for 

in the RFP plan. With all of these 

reductions accounted for in the RFP 

plan, there are no excess reductions 

beyond the attainment planning period 

to be credited as contingency measures. 

I. Attainment Dates 

1. Summary of Proposal 

The proposal described the CAA 

section 188(c)(1) requirement for 

Moderate areas to attain the standard 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 proposed to interpret the term 

‘‘area’s designation’’ as meaning ‘‘the 

area’s effective date of designation,’’ 

consistent with the agency’s past 

approach for implementing the 1997 

and 2006 PM2.5 NAAQS, and with its 

approach for implementing the NAAQS 

for other criteria pollutants under part 

D, title I of the CAA. The EPA requested 

comment on this interpretation. The 

preamble to the proposal also described 

the process for determining whether an 

area has attained the NAAQS. 

2. Final Rule 

The final rule maintains the 

requirement interpreting of CAA section 

188(c)(1) to mean that the attainment 

date must be as expeditiously as 

practicable, but no later than the end of 

the sixth calendar after the effective date 

of an area’s designation. See 

51.1004(a)(1). Thus, as an example, for 

areas designated nonattainment in the 

first round of designations for the 2012 

PM2.5 NAAQS, the effective date of 

designation is April 15, 2015, and the 

Moderate area attainment date would be 

as expeditious as practicable, but no 

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142See ‘‘Procedures for Processing Requests to 

Redesignate Areas to Attainment,’’ Memorandum 

from John Calcagni, USEPA Office of Air Quality 

Planning and Standards, Director, Air Quality 

Management Division, September 4, 1992. 

later than December 31, 2021 (i.e., the 

end of the sixth calendar year after 

designation). Serious area attainment 

dates are discussed fully in Section VI.I 

of this preamble. 

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 40 CFR 51.1000 and 

51.1004(a)(1)(ii). As discussed more 

fully in Section VI.I of this preamble, 

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. 

Once an area has an approved 

attainment date and has implemented 

its plan, the EPA has the responsibility 

for determining whether the 

nonattainment area has attained the 

standard by its applicable attainment 

date. Section 179(c)(1) of the CAA 

requires the EPA to make 

determinations of attainment no later 

than 6 months following the attainment 

date for the area. Under CAA section 

179(c)(2), the EPA must publish a notice 

in the Federal Register identifying those 

areas that 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) of the CAA 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 that have been entered 

into the EPA’s Air Quality System 

(AQS) database. The state is not 

required to make any special or 

additional submission in order for EPA 

to make a determination of attainment. 

A Moderate PM2.5 nonattainment 

area’s air quality status is determined in 

accordance with Appendix N of 40 CFR 

part 50. To show attainment of the 

current 24-hour and annual standards 

for PM2.5, data from the most recent 3 

consecutive years 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 indicate 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 unless 

the area also has been granted a clean 

data determination. If the EPA 

determines that an area has attained the 

standard as of its attainment date, the 

area will remain designated as 

nonattainment until the state has 

submitted an acceptable redesignation 

request and maintenance plan, and EPA 

has approved them. 

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: 

(1) The EPA has determined that the 

area has attained the PM2.5 NAAQS; 

(2) The EPA has fully approved the 

applicable state implementation plan; 

(3) The improvement in air quality is 

due to permanent and enforceable 

reductions in emissions; 

(4) The EPA has fully approved a 

maintenance plan for the area; and 

(5) The state(s) containing the area or 

portions of the area have met all 

applicable requirements under CAA 

section 110 and part D.142

J. Attainment Date Extensions 

1. Attainment Date Extension Criteria 

a. Summary of Proposal. Subpart 4 of 

title I of the CAA provides the EPA with 

authority to grant up to two 1-year 

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 

monitored air quality in the area and the 

implementation of measures in the 

attainment plan. Under CAA section 

188(d), a state may apply to the EPA for 

an extension of a Moderate area’s 

attainment date of 1 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) of the CAA also provides for the 

possibility that the EPA may grant a 

second 1-year extension if the Moderate 

area meets specific criteria. The 

proposal took comment on two 

ambiguous aspects of this language that 

warrant further interpretation through 

this rule. 

First, the proposal addressed the 

statutory language explicitly setting 

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. The requirement in CAA 

section 188(d)(2) states that an 

extension may be granted if ‘‘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.’’ The proposal noted that 

the form of the 2006 24-hour PM2.5

NAAQS is a percentile-based form and 

not a ‘‘one expected exceedance’’ form 

as is the PM10 NAAQS, and therefore 

the statutory language requires some 

interpretation with regard to how it 

applies to the PM2.5 NAAQS. 

The EPA included a proposed option 

and requested comment on two other 

alternatives. 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 

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143For 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). 

144Nonattainment areas designated for both the 

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

central and southern CA. 

145This interpretation as applied to CAA 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). 

state is seeking the extension of the 

attainment date. The second approach 

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 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. 

Second, the proposal addressed how 

the language of CAA section 188(d)(2) 

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.143 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.144 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 CAA 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. 

Regarding the ‘‘requirements and 

commitments’’ criterion, the EPA 

proposed to interpret this provision to 

mean that the state has adopted and is 

implementing the control measures in 

the SIP submission it made to address 

the attainment plan requirements for the 

applicable PM2.5 NAAQS. The proposal 

also described a second potential 

interpretation, in which the state would 

not be eligible for an attainment date 

extension unless it has adopted and 

submitted its Moderate area SIP and has 

received full approval from the EPA. 

b. Final Rule. The EPA received a 

number of comments on the attainment 

date extension criteria. With respect to 

the criterion requiring compliance with 

all requirements and commitments in 

the applicable implementation plan, 

several commenters agreed with the 

EPA’s proposed approach that the state 

must have adopted and submitted its 

Moderate area SIP but does not need to 

have full approval of the plan by the 

EPA in order to receive an extension. 

These commenters indicated that a state 

should not be penalized for a failure by 

the EPA to take timely action on the 

implementation plan. Some commenters 

opposed the proposed approach, stating 

that an area’s attainment date is not 

predetermined as the end of the sixth 

calendar year after designation, but 

instead is to be ‘‘as expeditiously as 

practicable,’’ and no later than the end 

of the sixth calendar year. For this 

reason, the commenters stated that the 

actual attainment date to be extended 

would not be known until after approval 

of the SIP by the EPA. 

After considering the comments 

received on this issue, the EPA is 

finalizing an approach similar to the 

preferred option in the proposal. This 

interpretation is based on the plain 

language of CAA 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.145 In 

other words, the EPA believes that CAA 

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 

CAA section 188(d)(1). See section 

51.1005(a)(1) of the CAA. 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 FIP. In the 

case that the ‘‘applicable 

implementation plan’’ is a FIP (or 

combination of SIP and FIP), then the 

EPA requires the state to have 

implemented the control measures 

contained therein in order to meet the 

statutory criteria at CAA section 

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

date extension. 

With respect to the air quality 

criterion, several commenters supported 

the EPA’s preferred option because it 

would require an area to show clean 

data only for the specific standard for 

which it is seeking an extension year. 

Some commenters acknowledged that a 

literal reading of the statute may seem 

to require a showing of clean data for 

both the annual and 24-hour PM2.5

standards in order to receive an 

extension, but suggested that this 

interpretation would not make sense 

under the circumstance where the two 

standards have different attainment 

dates. The commenter believed it would 

lead to absurd results if, in order to 

receive an extension for one standard, 

an area were required to show clean 

data for the other standard for which the 

attainment date had not yet passed. On 

the other hand, other commenters 

favored the option that would require 

clean data for both standards in order to 

obtain an extension for one standard 

because they believed that only 

requiring clean data for one standard 

would allow the area to avoid or delay 

achieving additional emissions 

reductions. 

After considering the comments on 

the air quality criterion, the EPA has 

decided to finalize the approach that 

would require an area to show clean 

data during the attainment year only for 

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the specific standard for which it is 

seeking an extension. See 40 CFR 

51.1005(a)(1). Under this approach, the 

EPA interprets the requirement to 

demonstrate that the area had ‘‘no more 

than one exceedance’’ of the 24-hour 

PM2.5 NAAQS to mean that the state 

must simply demonstrate that the area 

had ‘‘clean data’’ in the attainment year. 

Thus, 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 with respect to the 

statistical form of that particular 

standard (i.e., for the 2006 PM2.5

NAAQS, the 98th percentile value did 

not exceed 35 mg/m3) in the calendar 

year prior to the applicable attainment 

date for the area. 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, a state seeking 

an attainment date extension for an 

annual PM2.5 NAAQS would be required 

to demonstrate that the area had clean 

data for that particular standard (i.e., for 

the 2012 annual PM2.5 NAAQS, the 

annual mean value did not exceed 12.0 

mg/m3) in the calendar year prior to the 

applicable attainment date for the area, 

but would not have to demonstrate that 

the area had clean data for any other 

PM2.5 NAAQS. 

The EPA believes this interpretation 

of CAA section 188(d)(2) is appropriate 

for two main reasons. First, 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, in contrast, 

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 both 24-hour and annual 

PM2.5 NAAQS, the EPA believes it also 

is 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, if an area is 

designated as nonattainment for both 

the 24-hour and annual PM2.5 standards 

and receives an extension for one 

standard while still working toward a 

later attainment date for the other 

standard, public health protection 

would not be delayed because the state 

would still be subject to the ongoing 

mandate to adopt and implement 

measures to ensure expeditious 

attainment of the other standard. 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

2. Process for Attainment Date 

Extension Request Submissions 

a. Summary of Proposal. The proposal 

recognized that CAA section 188(d) 

does not specify the process by which 

the state should submit a Moderate area 

attainment date extension request, nor 

how the EPA should evaluate and act 

upon such a request. The proposal 

described the elements that the state 

would be required to submit for the 

various options proposed regarding the 

CAA section 188(d) extension criteria 

for 1) compliance with requirements 

and commitments in the applicable SIP, 

and 2) air quality data. The proposal 

suggested that any Moderate area 

extension request should be submitted 

to the EPA by the attainment date for 

the area (i.e., by December 31 of the 

attainment year), and it proposed 

requiring the state to submit certified air 

quality data for the attainment year to 

the EPA by February 28 of the following 

year in order for the EPA to issue a 

determination within 6 months of the 

attainment date regarding whether the 

area attained or failed to attain. The 

proposal stated that an attainment date 

extension should be granted only after 

the agency provides notice in the 

Federal Register and an opportunity for 

the public to comment. Lastly, the 

proposal clarified that any 1-year 

extension would extend from January 1 

to December 31 for the year following 

the year including the December 31 

attainment date. 

b. Final Rule. As discussed in the 

previous section, in order for the EPA to 

make a decision on whether to grant a 

1-year attainment date extension, the 

state needs to submit sufficient 

information to demonstrate that it has 

both complied with applicable 

requirements and commitments in the 

applicable implementation plan, and 

that it has clean data for the attainment 

year. Under the final rule, 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. The SIP revision 

would need to have been adopted and 

submitted by the state, but it would not 

need to have been approved by the EPA 

in order for the state to qualify for an 

extension. See 40 CFR 51.1005(a)(1)(i). 

The state also would need to have 

‘‘clean’’ air quality data in the 

attainment year, as explained in the 

previous section. See 40 CFR 

51.1005(a)(1)(ii)–(iii). 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. 

Some commenters suggested that in 

some cases a state will not know if it 

should seek an extension request until 

after the attainment date has passed, 

particularly for areas that commonly 

have higher air quality levels in the 

cooler months at the end of the calendar 

year. The commenter recommended that 

states should have until February 28 of 

the following year to submit an 

extension request along with certified 

air quality data. Other commenters 

stated that there is no legal basis for 

requiring the certification of monitoring 

data by February 28th of the following 

year, and therefore it should not be a 

requirement that could potentially 

disqualify a state from having an 

extension request be approved. 

The EPA considered these comments 

in light of the EPA’s obligation under 

the CAA to issue a determination of 

attainment or failure to attain within 6 

months of the original attainment date. 

After considering these comments, the 

EPA strongly recommends that a state 

should submit a Moderate area 1-year 

extension request to the appropriate 

EPA Regional Office by February 28 of 

the following year. In addition, the EPA 

strongly recommends that the state 

provide certified air quality data for the 

previous calendar year by this date or as 

close to this date as possible. The EPA 

understands that there may be certain 

situations that prevent the full 

certification of filter-based PM2.5

monitoring data by this date. If air 

quality data for the previous full 

calendar year has not been fully 

certified by February 28, the extension 

request should include any available 

preliminary data the state can provide. 

Submission of the necessary air quality 

data must occur as soon as possible after 

the attainment date to enable the EPA to 

review the state’s request expeditiously 

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). 

As indicated in the proposal, the EPA 

believes that an attainment date 

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146Note that a reclassification for a multi-state 

nonattainment area will be done in a single action 

by the EPA; separate actions are not needed to 

reclassify the portion of each state comprising the 

multi-state nonattainment area. 

147See the Federal Register published on April 

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

extension should only be granted after 

the agency provides notice in the 

Federal Register and an opportunity for 

the public to comment. A notice-andcomment rulemaking allows for the EPA 

to adequately evaluate whether the area 

meets the air quality and program 

implementation criteria, and to consider 

other relevant facts and information 

presented by the state and the public in 

determining whether the extension 

request should be granted or denied. 

This process also is consistent with past 

practice by the EPA in granting 

attainment date extensions, most 

recently for ozone nonattainment areas. 

Regarding the extension period, the 

EPA interprets CAA 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 is 

finalizing this interpretation at 40 CFR 

51.1005(a)(4). The EPA believes this is 

a reasonable approach, as the original 

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 demonstrated that it could advance 

attainment by at least 1 year. 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. 

As noted earlier in this discussion of 

Moderate area attainment date 

extensions, CAA 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 CAA 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, for 

a second 1-year attainment date 

extension request, the EPA intends to 

apply the same interpretations of the 

statutory criteria as described earlier in 

this section, including the 

recommended deadlines for the state to 

submit the extension request and the 

certified air quality data. 

c. Comments and Responses. 

Comment: Some commenters described 

the situation where the EPA has 

approved a Moderate area attainment 

date that is earlier than the latest date 

allowed by the statute (for example, 

assume the approved attainment date is 

the end of the 5th calendar year after 

designation). The commenter suggested 

that if the area was unable to attain by 

its ‘‘earlier’’ approved attainment date, 

CAA section 188(d) should be 

interpreted in a way that would not 

require the state to submit a request for 

an attainment date extension. The 

commenter suggested that the state 

should only be required to meet the 

CAA section 188(d) requirements if the 

area is seeking an extension beyond the 

latest Moderate area attainment date 

allowed by statute (i.e. the end of the 

sixth calendar year after designations). 

Response: The EPA does not agree 

with the commenter because the statute 

appears to address this situation clearly. 

Section 188(c)(1) of the CAA states that 

the Moderate area attainment date is ‘‘as 

expeditiously as practicable but no later 

than the end of the sixth calendar year 

after the area’s designation as 

nonattainment.’’ If the area had 

provided an attainment demonstration 

supporting the approval of an earlier 

attainment date by the EPA, then that 

approved attainment date is then 

regarded as the ‘‘applicable attainment 

date’’ for that area. Section 188(d)(1) of 

the CAA of the statute then enables the 

EPA to grant a 1-year extension for the 

‘‘date specified in paragraph (c)(1),’’ 

which in this case would be the earlier 

attainment date. 

V. Reclassification of a PM2.5 Moderate 

Nonattainment Area 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, CAA section 188(b) describes 

two pathways by which the EPA has the 

authority and/or the duty to reclassify a 

Moderate nonattainment area to a 

Serious nonattainment area. Pursuant to 

CAA 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 CAA 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 in the following 

sections.146

A. Discretionary Authority 

1. Summary of Proposal 

The proposal provided background on 

the EPA’s discretionary authority to 

reclassify a Moderate area to Serious. It 

proposed to interpret the statute to give 

EPA broad authority to reclassify based 

on available information, noting that the 

EPA could base this determination upon 

whatever factors are pertinent. The 

proposal sought comment on whether 

EPA should discretionarily reclassify an 

area without a request or submission 

from the affected state. The proposal 

also addressed the mandatory statutory 

timing for discretionary reclassification 

(i.e., within 18 months of the moderate 

area SIP due date), and took comment 

on the appropriateness of EPA acting to 

reclassify an area beyond 18 months 

after the Moderate area SIP due date, 

including right up to the Moderate area 

attainment date. 

2. Final Rule 

The final rule remains largely 

unchanged with regard to this issue. 

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 cannot practicably attain by its 

statutory attainment date. 

The CAA does not specify the basis 

on which the EPA may make a 

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 facts are pertinent, and 

could 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 CAA section 

189(a)(1)(B).147 The EPA may make such 

a determination based on evaluation of 

the attainment plan for the Moderate 

area in question, or based on 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 

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148 Ibid. at 13537. 

149See, Vigil v. Leavitt, 366 F.3d 1025, amended 

at 381 F.3d 826 (9th Cir. 2004). 150 57 FR 13498 (April 16, 1992), at page 13537. 

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. The 

EPA believes that while a Moderate area 

impracticability demonstration as 

contemplated in CAA 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. 

Regarding the timing of discretionary 

reclassifications, CAA section 

188(b)(1)(B) establishes timeframes by 

which EPA is to 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 

CAA 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. 

However, as noted earlier, there may 

be situations in which it may be 

appropriate to reclassify an area at a 

point in time more than 18 months after 

the SIP due date. On this issue, the 

General Preamble stated 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.’’ 148

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. See Section VI.A.2 

of this preamble for a discussion of the 

due dates for submission of attainment 

plan elements for areas that receive a 

discretionary reclassification. 

The EPA emphasizes that a state with 

an area designated as nonattainment for 

the PM2.5 NAAQS is required to meet all 

Moderate area attainment plan 

requirements, even after the EPA 

reclassifies the area to Serious. Section 

189(b)(1) of the CAA 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 

attainment plan requirements.149 Thus, 

the EPA believes that reclassifying 

Moderate areas to Serious at any time 

under its discretionary authority does 

not provide incentives to 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.150

The EPA considers this longstanding 

interpretation of CAA section 188(b)(1) 

to be the correct interpretation of the 

statutory requirements governing the 

discretionary reclassification of 

Moderate areas. The EPA will reclassify 

any area it determines cannot 

practicably attain by the Moderate area 

attainment date through notice-andcomment rulemaking. See 40 CFR 

51.1002(b)(1). 

3. Comments and Responses 

Comment: Some commenters stated 

that while it may be desirable for a state 

or local agency to provide an 

impracticability demonstration to the 

EPA, the EPA is not prohibited from 

using the weight of available evidence 

to reclassify an area to Serious even 

before the Moderate area plan is due if 

it has a particularly challenging air 

quality situation. Other commenters did 

not agree with the EPA’s interpretation 

of the statute, and believed that the 

EPA’s authority should be limited to 

reclassification of areas that submit an 

impracticability demonstration. 

Response: For the reasons described 

earlier, the EPA agrees with the first 

commenter and does not believe its 

authority is limited in the manner 

suggested by the second commenter. 

B. Mandatory Duty 

1. Summary of Proposal 

The proposal provided background on 

the EPA’s mandatory duty pursuant to 

CAA section 188(b)(2) to reclassify a 

Moderate area to Serious when the area 

fails to attain the standard by the 

attainment date. The CAA directs the 

EPA to reclassify an area from Moderate 

to Serious if the area fails to attain the 

relevant NAAQS by the applicable 

Moderate area attainment date 

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58074 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

(including any attainment date that had 

been extended by one or 2 years 

pursuant to CAA section 188(d)). 

Reclassification occurs by operation of 

law when the EPA determines that the 

area failed to attain the NAAQS by the 

applicable attainment date, in 

accordance with CAA section 

188(b)(2)(A). Section 188(b)(2) of the 

CAA 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 proposed that the date of 

reclassification would be the effective 

date of the Federal Register notice 

issued by the EPA that determines the 

area failed to attain by the attainment 

date. 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 actual date of 

reclassification for the area would be the 

effective date of the Federal Register 

document (e.g. in July or August 2022). 

To meet the requirements of CAA 

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

attainment plan for the area would be 

due within 18 months of the actual 

reclassification date (i.e., in early 2024). 

The proposal also discussed a 

possible alternative option, which 

would be to consider the date of 

reclassification to Serious to be the same 

as the Moderate area attainment date. 

Applying this approach in the example 

earlier would yield an earlier date of 

reclassification of December 31, 2021, 

and an earlier Serious area attainment 

plan due date of June 30, 2023. 

2. Final Rule 

Several commenters supported the 

EPA’s proposed approach to interpret 

the date of reclassification as the 

effective date of the Federal Register 

notice announcing the area had failed to 

attain the standard by the Moderate area 

attainment date because this approach 

would allow adequate time for the EPA 

to evaluate air quality data and any 

exceptional events claims before making 

the determination that the area failed to 

attain. Some commenters opposed the 

proposed approach and supported 

interpreting the date of reclassification 

as being the same as the missed 

attainment date for the Moderate area. 

This commenter suggested that the 

proposed approach could introduce 

additional delay because the EPA does 

not always issue determinations of 

failure to attain promptly. They also 

claimed that the term ‘‘reclassified by 

operation of law’’ in CAA section 

188(b)(2)(A) would have no meaning 

(i.e., surplusage) if the proposed 

approach was adopted. 

After taking the comments received 

under consideration, the EPA has 

decided to retain the proposed 

approach. The date of reclassification is 

the effective date of the Federal Register 

notice issued by the EPA that 

determines the area failed to attain by 

the attainment date. For practical 

reasons, the EPA does not believe that 

as a general matter it can be expected to 

make a determination on December 31 

that an area failed to attain. Because the 

PM2.5 ambient monitoring method 

requires laboratory analysis of filters 

prior to determining the ambient mass 

for each day, adequate time is needed 

after December 31 to ensure that the 

filter-based measurements have been 

evaluated and quality-assured in an 

accurate manner. 

Although CAA section 188(b)(2) does 

not explicitly address this issue, the 

EPA believes that this approach is a 

reasonable interpretation of statutory 

ambiguity in CAA section 188(b)(2) and 

preferable over the alternative approach 

for two additional reasons. First, the 

statute at CAA 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 

workload associated with developing a 

Serious area plan can be substantial, 

and the EPA believes that it is 

reasonable to resolve the statutory 

ambiguity in favor of providing the state 

with the full 18 months from the 

effective date of reclassification to 

develop and submit a thorough, 

complete and accurate Serious area 

attainment plan that will provide for 

expeditious 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. 

Thus, the EPA interprets the CAA 

such that the date of reclassification for 

an area reclassified under the EPA’s 

mandatory duty is to be considered 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. The EPA intends to 

make determinations of whether an area 

attained the relevant NAAQS pursuant 

to CAA section 188(b)(2) by notice-andcomment rulemaking. See 40 CFR 

51.1002(b)(2). Accordingly, the final 

rule establishes a definition of ‘‘date of 

reclassification’’ to mean the effective 

date of a PM2.5 area reclassification from 

Moderate to Serious as promulgated by 

the Administrator. This definition is 

then used, for example, to establish the 

due date for the Serious area SIP. (See 

Section VI.A.1 of this preamble for more 

information on mandatory 

reclassification area SIP due dates.) 

3. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

VI. Requirements for PM2.5 Serious 

Nonattainment Area Plans 

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

include the following requirements for 

Serious area attainment plan 

submissions: (i) An attainment 

demonstration (CAA 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 (CAA section 189(b)(1)(B)); (iii) 

quantitative milestones that will be used 

to evaluate compliance with the 

requirement to demonstrate RFP (CAA 

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 

CAA 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 (CAA section 

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

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

control measures (besides BACM and 

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151See Vigil v. Leavitt, 366 F.3d 1025, amended 

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

152Section V of this preamble provides a more 

detailed discussion of the process for reclassifying 

areas with severe nonattainment problems to 

Serious. 

153Addendum to the General Preamble, 59 FR 

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

BACT) needed for attainment (CAA 

section 172(c)(6)); and (iv) contingency 

measures (CAA section 172(c)(9)). 

Additionally, CAA 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 CAA section 

189(b)(1) to require states with areas 

that are reclassified to Serious to meet 

Moderate area attainment plan 

requirements, including all 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.151 The following section 

describes the EPA’s final actions in this 

rule regarding Serious area attainment 

plan requirements in greater detail. 

A. Plan Due Dates 

The proposal discussed the statutory 

provisions that informed the options for 

the submission due dates for the various 

components of Serious area attainment 

plans. The timing of Serious area 

attainment plan elements is dictated by 

two provisions of the CAA: CAA section 

189(b)(2) for certain subpart 4 elements 

and CAA section 172(b) for subpart 1 

elements not superseded by subpart 4 

requirements. Section 189(b)(2) of the 

CAA addresses the due dates for Serious 

area attainment demonstrations due 

under CAA section 189(b)(1)(A) and 

provisions for BACM and BACT 

implementation under CAA 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 

governing the reclassification action. 

For an area reclassified to Serious by 

operation of law under CAA 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 CAA section 188(b)(1), 

a state must submit a new attainment 

demonstration no later than 4 years after 

reclassification of the area.152 For all 

Serious nonattainment areas, CAA 

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.’’ 

When considering attainment plan 

due dates for areas that have been 

discretionarily reclassified, it is also 

important to keep in mind the 

requirements of CAA section 188(b)(1). 

Section 188(b)(1) of the CAA generally 

states 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.’’ In addition, CAA section 

188(b)(1)(B) provides 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.’’ Since all Moderate area SIPs are 

due 18 months after designation, then 

this provision contemplates that EPA 

will typically exercise its discretionary 

reclassification authority within 3 years 

of the area’s designation as 

nonattainment. Taken together with 

CAA section 189(b)(2), which for 

discretionary reclassifications requires 

the state to submit the attainment 

demonstration within 4 years of 

reclassification to Serious, subpart 4 

contemplates that attainment plans for 

discretionary reclassifications will be 

submitted no later than 7 years after 

designation. However, as noted in the 

previous section, the EPA believes it can 

discretionarily reclassify an area more 

than 18 months after the Moderate area 

SIP due date under certain 

circumstances, meaning that the Serious 

area attainment demonstration for such 

a plan could be submitted to EPA more 

than 7 years after designation. (See more 

discussion in Section V.A of this 

preamble on the timing of discretionary 

reclassifications.) 

Lastly, because some of the Serious 

area plan requirements noted earlier are 

established in subpart 1 of the Act (CAA 

section 172), the proposal also noted 

that CAA section 172(b) provides the 

EPA discretion to set a due date for 

submission of these 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 

a Moderate area to Serious to be 

analogous to the date of designation of 

the area to nonattainment. Accordingly, 

some of the options presented in the 

proposal included 3 year SIP due dates 

for certain plan requirements that stem 

from subpart 1.153

1. Area Reclassified to Serious After 

Failing To Attain the PM2.5 NAAQS 

a. Summary of Proposal. The proposal 

noted that for an area reclassified to 

Serious after failing to attain the PM2.5

NAAQS by the Moderate area 

attainment date, CAA section 189(b)(2) 

requires the state to submit both the 

attainment demonstration for an area 

and provisions to ensure timely BACM 

and BACT implementation to the EPA 

within 18 months after reclassification. 

The EPA proposed a straightforward 

codification of this 18 month deadline. 

Assuming the effective date of the 

Federal Register reclassification notice 

is typically about 6 months after the end 

of the calendar year, this means that the 

attainment demonstration and BACM/

BACT provisions would be required at 

about 8 years after designations. The 

notice also proposed that (1) in addition 

to BACM/BACT and the attainment 

demonstration, the emission inventory 

would also be required to be submitted 

within 18 months of the effective date 

of reclassification because it is essential 

for the development of BACM/BACT 

determinations; and (2) additional 

feasible measures (i.e., control measures 

that may be able to help the area attain 

by the attainment date or advance the 

attainment date by a year, and that may 

be implemented later than BACM/BACT 

but before the attainment date) would 

also be required to be submitted within 

18 months of the effective date of 

reclassification because such measures 

would be identified as part of the 

overall control measures analysis. 

Regarding the SIP submission date for 

the remaining required plan elements 

(i.e., RFP, quantitative milestones and 

contingency measures), the proposal 

included two options: (1) no later than 

18 months after reclassification (i.e., at 

about 8 years after designation, or 2 

years prior to the Serious area 

attainment date; or (2) within 3 years 

after reclassification (i.e., at about 9.5 

years after designation, or 6 months 

prior to the Serious area attainment 

date). 

b. Final Rule. Some commenters 

opposed the proposed requirements for 

SIP elements other than BACM/BACT 

and the attainment demonstration to be 

due within 18 months of the effective 

date of reclassification because they 

favored providing states with as much 

time and flexibility as possible to 

provide their submissions. Other 

commenters suggested that having all 

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58076 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

154Under the EPA’s prior interpretation as 

described in the Addendum at 42015, 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 

CAA section 172(b). 

elements—including RFP, quantitative 

milestones, and contingency measures— 

be due at the same time would be more 

administratively efficient for states and 

would allow for EPA to conduct a single 

coordinated review of these plans, and 

should therefore all be due within 18 

months of the effective date of 

reclassification. They also indicated that 

the alternative would not make sense 

because RFP, quantitative milestones, 

and contingency measures are all linked 

to the attainment demonstration. 

After taking these comments into 

consideration, the EPA has decided to 

require all Serious area plan elements to 

be due within 18 months of the effective 

date of reclassification for any area 

reclassified due to a failure to attain by 

the Moderate area attainment date. The 

EPA believes that the proposed 

alternative 3 year deadline, which 

would have allowed some elements to 

be submitted as late as 6 months prior 

to the attainment date, would mean that 

the state would be required to submit 

two different SIPs and would require 

greater state government resources to 

conduct the administrative and public 

procedures required to submit the 

separate plans to the EPA. This 

approach also would not provide the 

EPA with sufficient time to 

appropriately review and take action on 

the state’s submission prior to the 

attainment date. It also is appropriate to 

have the RFP, quantitative milestones, 

and contingency measures elements be 

developed and submitted at the same 

time as the attainment demonstration 

because they build from the information 

in the attainment demonstration. The 

EPA also 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 should prove to be 

most efficient for states and the EPA. 

The EPA further agrees with 

commenters that a program requiring 

two submissions rather than one can 

generally be expected to be less 

administratively efficient because it will 

involve separate public hearings and 

comment periods at the state level, and 

separate proposed and final approval 

actions in the Federal Register by the 

EPA. Thus, the final rule requires any 

area that has been reclassified to Serious 

as a result of a failure to attain the 

standard by the Moderate area 

attainment date to submit all the plan 

elements to the EPA within 18 months 

of reclassification: updated base year 

emission inventory (described in more 

detail in the next section); BACM/BACT 

determinations and adopted regulations; 

analysis of additional feasible measures 

(i.e., control measures that may be able 

to help the area attain by the attainment 

date or advance the attainment date by 

a year, and that may be implemented 

later than BACM/BACT but before the 

attainment date) and adopted 

regulations, as appropriate; attainment 

demonstration; RFP; quantitative 

milestones; and contingency measures. 

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

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

2. Area Reclassified to Serious Because 

the EPA Finds in Its Discretion That the 

Area Cannot Practicably Attain the 

NAAQS by the Statutory Moderate Area 

Attainment Date 

a. Summary of Proposal. The proposal 

noted that for an area reclassified to 

Serious because the area cannot 

practicably attain the standard by the 

Moderate area attainment date, CAA 

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

submit its BACM/BACT analyses and 

any adopted regulations to the EPA 

within 18 months; and to submit the 

attainment demonstration within 4 

years of reclassification. Similar to the 

proposal for mandatory reclassification 

areas, the notice also proposed that an 

updated emission inventory (required 

under section 172(b) of the CAA) be 

required to be submitted within 18 

months of reclassification because it is 

essential for the development of BACM/ 

BACT determinations. 

The notice also discussed a potential 

control measure option (described in 

Section VI.D. of the proposal, 

Attainment Plan Control Strategy, at 

page 15410) that would closely link the 

BACM/BACT determinations to the 

attainment demonstrations (rather than 

consider BACM/BACT as an 

independent requirement). Therefore, to 

facilitate this linked approach to BACM/ 

BACT, an alternative option was 

proposed for submission of the 

attainment demonstration within 18 

months of reclassification, instead of 

within 4 years. 

The proposal also addressed the 

remaining plan elements: additional 

feasible measures (i.e., control measures 

that may be able to help the area attain 

by the attainment date or advance the 

attainment date by a year, and that may 

be implemented later than BACM/BACT 

but before the attainment date); RFP; 

quantitative milestones; and 

contingency measures. Two SIP 

submission due date options were 

proposed for the remaining plan 

elements: (1) No later than 3 years after 

reclassification 154; or (2) no later than 4 

years after reclassification. The proposal 

requested comments on all of the 

proposed options for the various 

elements of a Serious area attainment 

plan. 

b. Final Rule. Most commenters 

opposed the option requiring the 

attainment demonstration to be due 

within 18 months, at the same time as 

the BACM/BACT submission. Some of 

these commenters suggested that a 4- 

year due date for the attainment 

demonstration and other elements 

would provide maximum flexibility to 

the states. While some commenters 

acknowledged the reasoning behind 

requiring submittal of the attainment 

demonstration and BACM/BACT at the 

same time if BACM/BACT is linked to 

the attainment demonstration, most 

commenters favored an approach that 

provided additional time for submittal 

of the attainment demonstration. 

Some commenters stated that for an 

area that is reclassified to Serious 

because it cannot practicably attain the 

NAAQS by the Moderate area 

attainment date, CAA section 

188(b)(1)(B) requires the EPA to 

reclassify the area within 3 years of 

designation (i.e. within 18 months of the 

Moderate area SIP due date), and then 

per CAA section 189(b)(2) the 

attainment demonstration for such area 

would be due 4 years later (i.e., 7 years 

from designation). The commenter 

stated that, if the EPA finalizes any 

discretionary reclassifications beyond 3 

years after designation, then it cannot 

allow the area to have the full 4 years 

for development of the attainment 

demonstration because it would 

undermine the deadlines and schedules 

that Congress was plainly trying to 

impose. 

For discretionary reclassification 

areas, just as for mandatory 

reclassification areas, the EPA is 

finalizing the statutory due date of 18 

months for the BACT/BACM 

submission. However, after considering 

comments received on the timing 

options for submission of the attainment 

demonstration, the EPA has determined 

that the attainment demonstration 

should generally be due later than 18 

months for areas subject to discretionary 

reclassifications. Because the statutory 

provision in CAA section 189(b)(2) 

provides up to 4 years, the EPA believes 

that an appropriate default due date for 

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the attainment demonstration should be 

4 years after reclassification for areas 

reclassified within 3 years of initial 

designation. However, after further 

consideration of this issue, the EPA also 

believes that a due date of less than 4 

years should be required for areas that 

are reclassified closer to the Moderate 

area attainment date (i.e., reclassified 

between 4 and 6 years after initial 

designation). In considering what would 

be a reasonable submission deadline for 

the attainment demonstration in this 

situation, the EPA considered the 

provisions applicable to areas that fail to 

attain by the attainment date. 

Specifically, CAA section 189(b)(2) 

requires the attainment demonstration 

(and the rest of the plan) to be submitted 

no later than 8 years after designation. 

As explained further, the EPA believes 

this requirement provides a reasonable 

outer bound for submission of Serious 

area plans for any area that is 

discretionarily reclassified to Serious. 

The circumstance that one of the 

commenters identifies, where the EPA 

reclassifies an area to Serious at a point 

in time more than 3 years after 

designation, raises an important timing 

issue that was not explicitly addressed 

in the proposal. The EPA was aware that 

it might need to reclassify an area to 

Serious beyond 3 years after designation 

(e.g., for an area that fails to submit a 

Moderate area attainment plan at all; or 

for an area that is discretionarily 

reclassified by the EPA because it has 

very high air quality values). However, 

the proposal did not address the issue 

of when the attainment demonstration 

and other elements should be required 

for submission when this circumstance 

occurs. The comment raises the 

question regarding whether, in the most 

extreme example, it would be 

reasonable for an area to be reclassified 

just before the Moderate area attainment 

date (end of the sixth calendar year after 

designation) and then to have until just 

before the Serious area attainment date 

(end of the tenth calendar year after 

designation) to submit the attainment 

demonstration. This situation would 

provide little meaningful time for the 

state and relevant emissions sources to 

implement measures to reach 

attainment by the attainment date, nor 

would it provide sufficient time for the 

EPA to review and take action on the 

plan. 

The EPA maintains that the statutory 

authority to ‘‘reclassify as a Serious PM– 

10 nonattainment area . . . any area that 

the Administrator determines cannot 

practicably attain [the NAAQS] by the 

attainment date . . . for Moderate 

Areas’’ includes the authority to make 

that determination and issue a 

discretionary reclassification any time 

before the Moderate area attainment 

date, as long as doing so does not 

otherwise unreasonably frustrate the 

primary goals of the statute. For 

example, the EPA must consider the 

timing for submission of Serious area 

SIP requirements to ensure the state has 

sufficient time to implement an effective 

plan and the agency has sufficient time 

to review and act on the plan in advance 

of the outermost Serious area attainment 

date (i.e., the end of the tenth calendar 

year after initial designation as 

nonattainment). See CAA section 

188(c)(2). 

The EPA interprets the statute to 

provide authority to require submission 

of attainment plan requirements, 

including the attainment demonstration, 

by a date less than 4 years from 

reclassification to Serious when 

exercising its discretionary authority to 

reclassify an area to serious 

nonattainment pursuant to CAA section 

188(b)(1). While the EPA generally 

prefers to give states as much time as 

possible to develop and submit plans, 

the agency concluded that allowing 4 

years for submission of the attainment 

demonstration in all discretionary 

reclassification actions would 

potentially frustrate the goals of the 

statute. 

To resolve this issue, EPA is finalizing 

a specific schedule for submission of the 

attainment demonstration following 

discretionary reclassification. As 

discussed earlier, the terms of the 

statute provide some guidance as to the 

appropriate schedule because, as 

explained earlier, a state would have 

until the end of the 7th calendar year to 

submit the attainment demonstration 

after a discretionary reclassification that 

follows the timing in CAA section 

188(b)(1)(B), and a state would have 

until the end of the 8th calendar year 

after a mandatory reclassification to 

submit the attainment demonstration. 

See generally CAA sections 188(b) and 

189(b). 

While not dispositive, these 

provisions indicate that Congress 

believes that Serious area attainment 

plans should be submitted at least 2 

years in advance of the outermost 

statutory attainment date for Serious 

areas to ensure expeditious attainment 

of the NAAQS. The EPA finds that a 

minimum of 2 years is appropriate 

because (1) it provides time for emission 

reduction measures adopted by the state 

to take effect and improve air quality; 

(2) it will allow the agency sufficient 

time to evaluate and act on the Serious 

area attainment demonstration; and (3) 

for every other NAAQS, the CAA SIP 

submission dates are generally 2 years 

or more prior to the attainment date. If 

for example the plan is not submitted 

until just before year 10, and the agency 

determines the plan will not lead to 

attainment, there will be no time to take 

corrective action before the attainment 

date to ensure attainment of the 

NAAQS. Such a result would not be 

reasonable. 

Therefore, the EPA believes that a 

reasonable attainment demonstration 

due date for any discretionary 

reclassification to Serious would be the 

earlier of (1) 4 years from the date of 

reclassification, or (2) the end of the 

eighth calendar year after designation. 

As an example, an area that is 

reclassified at the end of year 5 would 

have 3 years rather than four years to 

submit the attainment demonstration 

and other plan elements by the end of 

year 8. An area that is reclassified no 

later than the end of year 4 would have 

the full four years, and any area 

reclassified after this point would have 

less than 4 years. At the outer extreme, 

in the unlikely event that the EPA 

chooses to exercise its discretion to 

reclassify an area in the sixth calendar 

year after designation (i.e., within a year 

of the attainment date), the area would 

still have 2 years to submit the 

attainment demonstration, which is still 

no less than the timeframe Congress 

provided for a Moderate area that is 

reclassified because it fails to attain. See 

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

Lastly, this section addresses 

appropriate SIP submission dates for the 

other required plan elements. Regarding 

the base year emission inventory, the 

EPA believes it is appropriate to require 

the updated base year emissions 

inventory at the same time that the 

BACM/BACT submission is due (18 

months) because the updated inventory 

will be a critical element relied on for 

making control measure determinations. 

Regarding the remaining planning 

elements (i.e., additional feasible 

measures, RFP, quantitative milestones, 

contingency measures, and attainment 

projected inventory), the proposed 

options allowed for the possibility of up 

to three separate submissions under 

certain policy combinations, and we 

believe having such an outcome would 

be very inefficient. Thus, the EPA has 

determined that the remaining elements 

must be submitted at the same time as 

the attainment demonstration (i.e., the 

earlier of 4 years from the date of 

reclassification, or the end of the eighth 

calendar year after designation). This 

approach will provide for the most 

efficient process and at the same time 

provide the states with the maximum 

reasonable time when they are 

reclassified pursuant to the EPA’s 

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58078 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

155Section 189(e) of the CAA requires that the 

control requirements applicable to major stationary 

sources of PM2.5 also apply to major stationary 

sources of PM2.5 precursors, except where the state 

demonstrates to the EPA’s satisfaction that such 

sources do not contribute significantly to PM2.5

levels that exceed the standard in the area. 

156All definitions described in Section III.B of 

this preamble for areas classified as Moderate apply 

in this section. 

discretionary authority in CAA section 

188(b)(2). 

With regard to the due date for 

submission of NNSR program revisions 

that may be required when an area is 

reclassified to Serious, such as revisions 

to meet nonattainment NSR program 

requirements to lower the ‘‘major 

stationary source’’ threshold from 100 

tons per year (tpy) to 70 tpy (CAA 

section 189(b)(3)) and to address the 

control requirements for major 

stationary sources of PM2.5 precursors 

[CAA section 189(e)], 155 the Act does 

not specify a deadline for the State’s 

submission following reclassification of 

a Moderate PM2.5 nonattainment area as 

Serious nonattainment under subpart 4. 

Pursuant to EPA’s gap-filling authority 

in CAA section 301(a) and to effectuate 

the statutory control requirements in 

section 189 of the Act, the final rule 

requires the state to submit these 

nonattainment NSR SIP revisions no 

later than 18 months after the effective 

date of final reclassification. This due 

date is also consistent with the due date 

for submission of BACM and BACT 

provisions and the emission inventory; 

thus, at most, a state will have two 

required SIP submissions after being 

reclassified. See 40 CFR 51.1003(b)(2)(i) 

and (ii). 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

B. Emissions Inventory Requirements 

1. Summary of Proposal 

The EPA proposed that the inventory 

requirements for Serious areas were the 

same as those for Moderate areas with 

some additions. In addition to the 

Moderate area requirements, the EPA 

proposed that Serious area inventory 

requirements would include using a 

major source threshold of 70 tons/year 

for reporting sources as point sources 

for both the base year inventory for the 

nonattainment area and the attainment 

projected inventory for the 

nonattainment area. 

With regard to the due date for the 

attainment projected inventory for the 

nonattainment area, the EPA proposed 

two cases. In the case where the area is 

reclassified after failing to attain the 

NAAQS by the Moderate area 

attainment date, the attainment 

projected inventory for the 

nonattainment area was proposed to be 

submitted no later than 18 months after 

reclassification. In the case where the 

area is reclassified by the EPA because 

the area cannot practicably attain the 

NAAQS by the statutory attainment 

date, the EPA proposed that the 

attainment projected inventory for the 

nonattainment area would be due no 

later than 4 years after reclassification. 

2. Final Rule 

a. What Emissions Inventory 

Requirements Apply to Serious Area 

Attainment Plans? As with Moderate 

PM2.5 nonattainment areas, 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 

inventory requirements that apply for 

Serious area attainment plans continue 

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

explicitly requires ‘‘a comprehensive, 

accurate, 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.156

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 https://www.epa.gov/airemissions-inventories/emissionsinventory-guidance-documents. The 

EPA recommends that states consult 

this guidance while developing 

emissions inventories to meet 

requirements for Serious area 

attainment plans. 

b. 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, this 

rule includes specific emissions 

inventory requirements that the EPA 

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 emissions inventory 

requirements: (i) The types of 

inventories required; (ii) the content of 

these inventories; and, (iii) the timing of 

submission of these inventories. The 

three facets are addressed in the 

following paragraphs. 

First, 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 is called the ‘‘base year 

inventory for the nonattainment area,’’ 

and the second type of inventory is 

called the ‘‘attainment projected 

inventory for the nonattainment area.’’ 

See 40 CFR 51.1000. The attainment 

projected inventory is necessary to 

implement the attainment 

demonstration requirement of section 

189(a)(1)(B), and it also may be used as 

part of the RFP requirement (see Section 

VI.F). For these reasons, this rule 

establishes a regulatory requirement that 

Serious area attainment plans must 

include a base year inventory for the 

nonattainment area and an attainment 

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projected inventory for the 

nonattainment area. 

Second, the content of the inventories 

will follow the content requirements for 

Moderate area inventories, with two 

exceptions needed to meet the 

requirements of section 189(b)(3). The 

first exception for Serious areas stems 

from the Section 189(b)(3) definition of 

a separate emissions threshold for major 

sources in Serious nonattainment areas 

(70 tpy potential to emit of 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 major 

stationary sources (rather than the 

nonmajor stationary source category that 

would apply for these in Moderate area 

plans) using the lower threshold 

specified in the CAA. Also as described 

earlier and in 40 CFR part 51, subpart 

A, this means that all other smaller 

stationary sources within the 

nonattainment area must be included in 

the base year inventory and projected 

attainment year inventory as nonpoint 

sources. 

As described previously for Moderate 

areas, Appendix A of Table 1 of 40 CFR 

part 51, subpart A (the AERR) is 

required by this rule to define which 

sources must be reported as point 

sources for inventories associated with 

this rule (base year and projected 

attainment year inventories). To be 

consistent with the 70 tpy threshold 

finalized in this rule, this rule is also 

amending Table 1 of Appendix A of the 

AERR to include the 70 tpy threshold 

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

for point sources within nonattainment 

areas. 

The second difference between the 

Serious area and Moderate area 

inventory requirements is a minor 

wording difference for the year that 

should be chosen for the base year 

inventory. The year should be one of the 

3 years used for reclassification (rather 

than designation for Moderate areas) 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 

that the inventory will represent the 

emissions sources whose contributions 

resulted in a nonattainment designation 

for the area. 

The third facet of the Serious area 

inventory requirements is the timing, 

which is somewhat different than for 

Moderate areas. Section VI.A of this 

preamble describes the requirement that 

states 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)). This is 

because the base year inventory serves 

as the starting point for conducting a 

BACM and BACT determination. In 

contrast to the base year inventory, the 

attainment projected inventory is more 

closely related to the Serious area 

attainment demonstration. Thus, the 

attainment projected inventory is most 

appropriately submitted with the 

attainment demonstration for a given 

Serious area to allow effective 

evaluation of the attainment plan as a 

whole. 

Consequently, this rule requires that 

attainment projected emissions 

inventories be submitted at the same 

time as the Serious area attainment 

demonstration. This requirement gives 

rise to two possible deadlines for 

Serious areas to submit the attainment 

projected emissions inventory for the 

nonattainment area. For areas that are 

reclassified after failing to attain the 

NAAQS by the applicable Moderate area 

attainment date, the deadline is no later 

than 18 months after reclassification 

(same time period as for Moderate 

areas). For areas reclassified by the EPA 

because the area cannot practicably 

attain the NAAQS by the statutory 

Moderate area attainment date, the 

deadline is the earlier of 4 years from 

the date of reclassification, or the end of 

the eighth calendar year after 

designation. 

3. Comments and Responses 

Comment: Some commenters noted 

that the proposal was unclear with 

regard to the inventory year for areas 

that are reclassified from Moderate to 

Serious, and whether the terms 

‘‘reclassification’’ and ‘‘designation’’ are 

interchangeable in this regard. 

Response: In the final rule, the EPA 

clarifies that for areas that are 

redesignated to Serious, the inventory 

year must be one of the 3 years used for 

reclassification. Any additional 

comments received on this section are 

addressed in the Response to Comments 

document found in the docket for this 

action. 

C. Pollutants To Be Addressed in the 

Plan 

All PM2.5 precursors are 

presumptively required to be addressed 

in any Serious area attainment plan. 

Section III of this preamble includes a 

detailed discussion about optional 

analyses that a state may provide to 

demonstrate that sources of a precursor 

do not significantly contribute to PM2.5

concentrations in a particular 

nonattainment area. These 

demonstrations may be conducted for 

all sources of a precursor in an area (i.e., 

comprehensive precursor 

demonstration), or just for major sources 

of the precursor (i.e., major source 

precursor demonstration). It also 

discussed a similar demonstration that 

may be conducted for NNSR (i.e., NNSR 

precursor demonstration). These 

demonstrations may be used to justify 

the exclusion of certain types of 

precursor sources from certain SIP 

requirements in Serious area plans, just 

as in Moderate area plans. However, the 

expeditious attainment demonstration is 

not available for Serious area plans. 

As noted in Section III of this 

preamble, if the EPA approves a state’s 

precursor demonstration for the 

Moderate area plan, the state would 

need to re-evaluate whether the 

precursor contributes significantly to 

PM2.5 levels that exceed the standard for 

the Serious area plan. The reason for 

this is that precursor emissions and air 

quality concentrations will have 

changed since the submission of the 

demonstration for the Moderate area, 

and precursor emissions technical 

information and scientific 

understanding of precursor emissions 

and interactions in the area should be 

better understood several years later, 

and the Serious area plan needs to be 

based on the best available information 

to date. If the state reevaluates a 

precursor for potential exclusion from 

one or more of the Serious area plan 

requirements, it should take into 

account factors such as increases or 

decreases in emissions since the last 

precursor demonstration; new ambient 

monitoring data for fine particle 

composition and concentrations of 

important gases (such as ammonia); and 

improved air quality modeling programs 

that reflect improved understanding of 

the role of precursors in atmospheric 

transformation processes. To the extent 

appropriate, this precursor 

demonstration can build off the analyses 

conducted for the Moderate area 

precursor demonstration. 

If the EPA approves a comprehensive 

precursor demonstration for the Serious 

area plan, then the state would not be 

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157 Ibid. at 42008–09. 

obligated to evaluate BACM/BACT 

measures for reducing that precursor in 

the nonattainment area, nor would it 

need to account for that precursor in the 

RFP plan, quantitative milestones, and 

contingency measures. If a major 

stationary source precursor 

demonstration is approved, then the 

state would not be obligated to evaluate 

BACM/BACT measures for reducing 

that precursor from major sources in the 

nonattainment area, nor would it need 

to account for emissions of that 

precursor from major sources in the RFP 

plan, quantitative milestones, and 

contingency measures. If a NNSR 

precursor demonstration is approved, 

then the state would not be obligated to 

address LAER and emission offset 

requirements for that precursor in the 

NNSR program for that nonattainment 

area. 

D. Attainment Plan Control Strategy 

1. General Approach to Designing a 

Control Strategy for a Serious 

Nonattainment Area 

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 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 

recommended 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/BACT and Additional Feasible 

Measures 

a. Summary of Proposal. The proposal 

provided background information on 

statutory requirements and existing 

guidance regarding Serious area control 

strategies, and then presented two broad 

approaches describing the steps for 

determining BACM/BACT and 

additional feasible measures (i.e. control 

measures that may be able to help the 

area attain by the attainment date or 

advance the attainment date by a year, 

and that may be implemented later than 

BACM/BACT but before the attainment 

date). The first approach is consistent 

with current guidance for PM10 NAAQS 

implementation in the Serious Area 

Addendum. Under the first approach, 

the emphasis of the analysis would be 

on the identification of feasible control 

measures. The analysis would be 

considered to be ‘‘generally 

independent’’ of whether such measures 

are needed for expeditious attainment of 

the relevant NAAQS. However, this 

approach also would allow the state to 

identify de minimis source categories 

before conducting any further analysis 

of technologically feasible or 

economically feasible control measures. 

The proposal requested comment on 

inclusion of an ambient impact 

threshold of 3 percent for determining 

whether a source category impact would 

be de minimis. This proposed threshold 

level was similar to the de minimis 

ambient levels included in the Serious 

Area Addendum for implementation of 

the PM10 NAAQS, and the state would 

likely need to conduct air quality 

modeling to demonstrate de minimis 

impacts below a particular threshold. 

The proposal noted the challenges 

associated with providing a nationally 

consistent definition of what would be 

a ‘‘source category.’’ For source 

categories found to be de minimis, the 

state would not be obligated to evaluate 

potential control measures. The basic 

analytical steps for proposed option 1 

were presented as follows: (1) Update 

base year emissions inventory for the 

area; (2) evaluate source category 

impacts; (3) identify existing and 

potential control measures; (4) 

determine whether an available control 

measure or technology is 

technologically feasible; (5) determine 

whether an available control measure or 

technology is economically feasible; (6) 

determine the earliest date by which a 

control measure or technology can be 

implemented in whole or in part. 

Under the second proposed option, 

there would be a greater emphasis on 

linking the control strategy evaluation 

process with the attainment needs for 

the area. Accordingly, this option would 

not include a ‘‘de minimis’’ step 2 early 

in the process. However, at the end of 

the process, the state would be able to 

choose to not adopt certain measures 

that would otherwise meet the criteria 

for BACM/BACT if those measures 

collectively would not be necessary to 

bring the area into attainment or to 

advance the attainment date by 1 year 

(similar to the approach that EPA uses, 

and has historically used, for RACM/

RACT). The EPA requested comment on 

all aspects of these options, and 

indicated the agency may finalize either 

approach or various elements of each 

approach after evaluating the comments 

that had been received. 

b. Final Rule. The EPA has considered 

the comments that were submitted on 

the two proposed options for 

determining BACM/BACT (and 

additional feasible measures), and has 

determined that the final rule should 

include aspects of each option. The 

following sections provide background 

information and guidance on the steps 

of the process for determining Serious 

area control measures for PM2.5

nonattainment areas. 

i. BACM and BACT 

A Serious area attainment 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. For 

implementation of the PM2.5 NAAQS, 

the EPA finds it reasonable to maintain 

the same interpretation. The legislative 

history for the 1990 Amendments to the 

CAA supports this interpretation, as the 

EPA has explained in past guidance.157

Additionally, the requirement for BACT 

for existing sources in the context of 

PM2.5 NAAQS implementation in 

nonattainment areas is separate and 

distinct from the requirement for BACT 

for new and modified sources 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, however, the process and 

criteria that states have historically used 

to determine BACT for new and 

modified sources under the PSD 

program have also been referenced and 

applied to the process for determining 

BACT for PM10 NAAQS 

implementation, but these requirements 

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158 Ibid. at 42009. 

159 Ibid. at 42009. 

160 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 BACM 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 

case-by-case basis as particular circumstances 

warrant.’’ 

161 Ibid. 

162 Ibid. at 42011. 163 Ibid at 42011. 

are otherwise unrelated. Consistent with 

past policy, BACT determinations for 

PM2.5 NAAQS implementation are to 

follow the same process and criteria that 

are applied to the BACT determination 

process for the PSD program. 

Longstanding guidance in the General 

Preamble and Addendum, together with 

past practice associated with 

implementing the PM10 NAAQS under 

subpart 4, has 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 

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.158 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.159 The EPA discussed in 

the Addendum that when Congress 

amended the CAA, Congress selected 

the same ‘‘best’’ terminology for PM10

nonattainment areas as it 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.160 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.161

ii. BACM/BACT ‘‘Generally 

Independent’’ of Attainment 

As noted earlier, the issue of whether 

BACM/BACT should be considered 

generally independent of attainment or 

more closely tied to attainment for 

purposes of implementing the PM2.5

NAAQS was a central issue 

distinguishing the two proposed options 

for determining BACM/BACT. Some 

commenters suggested that the 

overarching requirement of the CAA is 

to attain the standard expeditiously, and 

therefore the benefits of a ‘‘generally 

independent’’ BACM/BACT 

requirement are not clear. On the other 

hand, some other commenters 

supported maintaining the longstanding 

policy from the Serious Area 

Addendum that the BACM/BACT 

requirement is generally independent of 

attainment, citing the emphasis on 

‘‘best’’ control measures and the 

statutory provision requiring BACM/

BACT well before the attainment 

demonstration for certain reclassified 

areas. For the reasons discussed later in 

this section, the EPA has decided to 

maintain the policy that BACM/BACT 

determinations are to be ‘‘generally 

independent’’ of attainment for 

purposes of implementing the PM2.5

NAAQS. 

In the Serious Area Addendum, the 

EPA described BACM as a generally 

independent requirement, to be 

determined without regard to the 

specific attainment analysis (i.e., 

attainment demonstration) for the 

area.162 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 to interpret the statute as 

requiring a different analysis for 

determining BACM, i.e., that while 

RACM emphasizes the attainment needs 

of the area, BACM has a greater 

emphasis on identifying measures that 

are feasible to implement. 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, the General Preamble noted 

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.163

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, contrasted against 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 (for 

areas where it is impracticable to attain 

by the attainment date) to submit the 

attainment demonstration for such 

areas. 

Additionally, the EPA believes that 

interpreting the Serious PM2.5

nonattainment area BACM/BACT 

requirements to be ‘‘generally 

independent’’ of attainment is 

consistent with the structure and 

substance of the CAA control measure 

requirements for ground-level ozone 

nonattainment areas with more serious 

air quality problems. In the CAA ozone 

implementation requirements, an area 

that is reclassified to a more serious 

category because it failed to attain the 

standard or because it is impracticable 

to attain by the attainment date is then 

subject to additional specific control 

measure requirements that are 

considered to be generally independent 

of attainment (for example, see CAA 

section 182(b) through (e)). The statute 

includes these specific requirements in 

order to ensure continued progress 

toward attainment for these areas with 

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more difficult air quality problems. The 

EPA believes it is appropriate to have a 

similar interpretation of the PM2.5

Serious area control measure 

requirements. In a similar manner, 

interpreting BACM/BACT to be 

generally independent of the attainment 

needs of a Serious PM2.5 area will 

ensure continued progress toward 

attainment for those areas with more 

difficult air quality problems. The EPA 

also believes this more rigorous 

‘‘independent control measure’’ 

approach for implementing the PM2.5

standards in a manner similar to ozone 

is appropriate because the health effects 

of both standards are very significant 

(including premature mortality), and 

robust emission reduction programs are 

needed to bring about expeditious 

attainment and public health protection 

for citizens in these nonattainment 

areas. 

iii. No de Minimis Source Category 

Analysis for PM2.5 NAAQS 

Implementation 

Another central issue distinguishing 

the two proposed options for how to 

determine BACM/BACT was the issue 

of whether, before analyzing any 

potential BACM/BACT, the state should 

conduct technical analyses to identify 

whether there are any source categories 

having a de minimis contribution to 

PM2.5 levels in the PM2.5 nonattainment 

area. This de minimis analysis is part of 

the process described in the Serious 

Area Addendum for implementation of 

the PM10 standards. Under the proposal, 

for source categories found to be de 

minimis, the state would not be 

obligated to evaluate potential control 

measures. 

As noted previously, the proposal 

requested comment on inclusion of an 

ambient impact threshold of 3 percent 

for determining whether a source 

category impact would be de minimis. 

This proposed threshold level was 

similar to the de minimis ambient levels 

included in the Serious Area 

Addendum for implementation of the 

PM10 NAAQS, and the state would 

likely need to conduct air quality 

modeling to demonstrate de minimis 

impacts below a particular threshold. 

The proposal noted the challenges 

associated with providing a nationally 

consistent definition of what would be 

a ‘‘source category.’’ 

The EPA also proposed a similar de 

minimis source category concept for the 

RACM/RACT process for Moderate area 

plans, and many of the comments 

received on the proposed Moderate area 

‘‘upfront’’ de minimis source category 

analysis are also applicable when 

considering whether to include a de 

minimis source category analysis 

concept for Serious areas in the final 

rule. A number of commenters 

expressed concern about the analytical 

resources that might be needed to 

conduct air quality modeling to identify 

whether all the sources in a particular 

source category have an ambient air 

quality contribution exceeding an air 

quality threshold. Some commenters 

suggested that a de minimis source 

category approach for either Moderate 

or Serious areas would allow the state 

to ignore a set of control measures that 

later in the control measure evaluation 

process could be determined to provide 

for a more expeditious attainment date. 

They believe that allowing the 

exemption of de minimis source 

categories would undermine any 

analysis to evaluate whether a collection 

of measures could advance the 

attainment date by a year. For example, 

it would be possible for a state to 

identify multiple de minimis source 

categories at the beginning of the 

process, and then after all potential 

control measures are identified, the state 

and the EPA would be unable to 

determine whether the collective 

reductions and air quality impact of the 

exempted categories could actually be 

sufficient to advance the attainment 

date. Other commenters noted that 

providing a source category exemption 

in one nonattainment area would lead to 

inconsistent treatment within a state or 

across states because it would give the 

exempted companies a competitive 

advantage over the same types of 

sources in other areas. 

A number of commenters supported 

the de minimis source category concept 

because they believed it could result in 

a reduced burden in the control measure 

evaluation stage and help avoid 

regulating sources with limited impact 

on PM2.5 levels. Some commenters 

supported the de minimis concept only 

if controls on the source are not needed 

for expeditious attainment. Some 

commenters suggested that the EPA 

include an emissions-based threshold 

(e.g. tons per day) rather than an air 

quality based threshold to reduce 

potential analytical burden associated 

with de minimis source category 

analyses. However, in their comments 

they did not address the fact that the air 

quality impact of a specific tons per day 

rate could vary greatly from one 

pollutant to another within a particular 

nonattainment area, or across different 

nonattainment areas. One state 

commenter noted that the NAICS 

system does not provide categories for 

nonpoint sources, and that this issue 

would need to be addressed if the 

NAICS approach were to be included in 

the final rule. Other commenters 

suggested that the rule not have a de 

minimis threshold at all but include the 

ability for the state to propose de 

minimis source categories to the EPA on 

a case-by-case basis. 

After taking the range of comments on 

the de minimis source category concept 

into consideration, the EPA has decided 

to not finalize a de minimis source 

category approach for the purposes of 

implementing the PM2.5 NAAQS. The 

EPA is persuaded by commenters who 

argued it is not necessary, and believes 

that without this concept the final rule 

will nevertheless provide sufficient 

flexibility in the Serious area control 

measure analysis and attainment 

demonstration process, due to the 

availability of provisions enabling states 

to identify sources that should not be 

subject to control measures, including 

the ability to develop precursor 

demonstrations to exclude certain 

precursors from control requirements, 

and to consider case-specific factors in 

determining technical and economic 

feasibility of potential control measures. 

If the final rule were to include an 

explicit step to conduct a de minimis 

source category analysis on the entire 

inventory early in the control measure 

identification process, the EPA believes 

that there is a risk that such an analysis 

may bring about investment of scarce 

time and analytical resources on 

analysis of categories to exclude rather 

than on the identification of the most 

beneficial control measures for reducing 

PM2.5 and its precursors to achieve 

expeditious attainment of the standard. 

In addition, the EPA finds merit in 

comments suggesting that an upfront 

exemption of multiple de minimis 

source categories in an area would 

undermine the ability of the state (or 

other interested parties) to evaluate, 

after the identification of potential 

control measures, whether the area 

could advance the attainment date in 

order to attain ‘‘as expeditiously as 

practicable.’’ 

Moreover, as noted in Section IV.D of 

this preamble on Moderate areas, the 

EPA also finds that from a technical 

perspective, it would be very 

challenging to implement a de minimis 

source category process in a consistent 

manner nationally without clear 

guidelines describing how narrowly or 

how broadly a de minimis exemption 

could apply to a ‘‘source category,’’ or 

how the technical analysis would need 

to be performed. For example, should a 

source category consist of all industrial 

boilers? Or all industrial boilers that 

burn a particular fuel? Or all industrial 

boilers that burn a particular fuel and 

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are within a specific size range? The 

NAICS codes do not provide an 

appropriately comprehensive approach 

for defining source categories for all 

stationary, mobile, and area sources for 

this purpose. It has been noted that a de 

minimis source category exemption 

process is described in the 1994 PM10

NAAQS implementation guidance (the 

Serious Area Addendum). In PM10

areas, however, it may have been 

relatively straightforward to identify 

what were the predominant source 

categories contributing to the NAAQS 

violations (such as direct PM2.5

emissions from dust or wood smoke), 

and therefore to be able to identify what 

categories might be considered as not 

predominant contributors (or de 

minimis). However, implementation of 

the PM2.5 NAAQS presents much more 

complex challenges. Precursors and 

their contribution to secondarily formed 

PM play a much greater role in PM2.5

nonattainment areas than in PM10

nonattainment areas. In addition, the 

relative impact of each precursor to 

local PM2.5 concentrations varies from 

area to area, and even within sections of 

the same area. To appropriately 

implement an approach allowing for de 

minimis source category impacts, the 

EPA believes that a nationally 

consistent source category definition 

would be needed, along with 

sophisticated air quality modeling to 

evaluate the relative impacts of 

precursors emitted from different 

‘‘source categories.’’ The resources 

needed to conduct such analyses could 

be substantial, and would ultimately not 

help identify what control measures 

would be needed to solve the air quality 

problem. For all of these reasons, a de 

minimis source category concept is not 

included in the final rule for Serious 

areas. 

iv. Additional Feasible Measures 

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 CAA 

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, CAA 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 proposed that the 

other measures required under CAA 

section 172(c)(6) must include 

‘‘additional feasible measures,’’ which 

would be those measures and 

technologies that otherwise meet the 

criteria for BACM/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. 

Some commenters agreed that an area 

must also consider adopting control 

measures that cannot be implemented 

within the 4-year deadline for 

implementation of BACM and BACT. 

Some commenters suggested that 

additional feasible measures should 

only be tied to expeditious attainment. 

In the final rule, additional feasible 

measures would necessarily be 

implemented by sources in the 

nonattainment area, and a state is 

required to implement them if they are 

needed in addition to BACM and BACT 

to bring the area into expeditious 

attainment. The state must also adopt 

other emission reduction measures for 

sources within the state but outside the 

nonattainment area if such measures in 

conjunction with other control measures 

would enable the area to attain the 

standard by the attainment date, or 

enable the area to advance the 

attainment date by at least 1 year. 

These ‘‘additional feasible measures’’ 

would be analogous to the ‘‘additional 

reasonable measures’’ in the 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 the approach 

for determining BACM and BACT for 

sources in a Serious nonattainment area 

described 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 with regard 

to Serious areas, only a nonattainment 

area that is reclassified under the 

agency’s discretionary authority might 

have sufficient time between the 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 

feasible 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 

requirement for 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 provide for attainment by the 

attainment date or advance the 

attainment date for the area by at least 

1 year. Accordingly the EPA has 

codified a definition of ‘‘additional 

feasible measures’’ and specified the 

conditions under which such measures 

would need to be included in a serious 

area plan submission. See 40 CFR 

51.1000 and 40 CFR 51.1010(a)(4)(ii). 

v. Steps of the BACM/BACT Selection 

Process 

In addition to the regulatory decisions 

earlier, the EPA summarized and sought 

comment on further guidance for states 

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164For additional information, see ibid. at 42012– 

13. 

165Addendum to the General Preamble, 59 FR 

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

166Add cite to 2006 STAPPA ALAPCO document 

and other control measure summaries. Add cite to 

menu of measures. 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.’’ 

167Links are provided to a number of national, 

state and local air quality agency sites from the 

EPA’s PM2.5 Web site: http://www3.epa.gov/pm/

measures.html. 

168 Ibid. at 42012. 

169 Ibid. at 42013. 

to follow in selecting BACM/BACT. The 

guidance was primarily derived from 

the Addendum. This section reviews 

that guidance, clarifies and updates it 

for purposes of PM2.5, and responds to 

significant comments on the guidance 

discussion included in the proposal. 

The BACM/BACT selection process 

for implementation of the PM2.5 NAAQS 

is designed to take into account the 

local facts and circumstances and the 

nature of the air pollution problem in a 

given nonattainment area. The following 

sections describe the steps of the 

process, including: (i) Develop a 

comprehensive inventory of sources and 

source categories of directly emitted 

PM2.5 and PM2.5 precursors; (ii) identify 

existing and potential control measures 

for the sources in the inventory; (iii) 

evaluate the technological feasibility of 

potential control measures; (iv) evaluate 

the economic feasibility of potential 

control measures; and (v) determine the 

earliest date by which a control measure 

or technology can be implemented in 

whole or in part.164 These steps are 

described more fully in the following 

subsections. 

Step 1: Develop a comprehensive 

inventory of sources and source 

categories of directly emitted PM2.5 and 

PM2.5 precursors. As with any control 

strategy analysis for a nonattainment 

area, the EPA recommends that the state 

begin with a current detailed emissions 

inventory of the various sources that 

emit direct PM2.5 and PM2.5 precursors 

in the Serious area. The inventory 

should identify major stationary sources 

(i.e., sources with the potential to emit 

70 tpy of direct PM2.5 or any precursor), 

nonmajor stationary sources, mobile 

sources, and area sources. The inventory 

also should identify both anthropogenic 

and nonanthropogenic emissions 

sources.165 The EPA expects the state to 

start with the base year emissions 

inventory submitted with the Moderate 

area attainment plan as required under 

CAA 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. This inventory 

should be the most comprehensive and 

accurate inventory available, and it 

should be consistent with the emissions 

inventory requirements for Serious area 

plans as described in Section VI.B of 

this preamble. 

Step 2: Identify potential control 

measures. The state should identify 

potential control measures for all 

sources and source categories in the 

latest base year emission inventory for 

the nonattainment area. The list of 

existing and potential control measures 

should include options not previously 

considered as RACM/RACT for the area, 

as well as additional measures not 

previously evaluated in the RACM/

RACT analysis. For purposes of 

identifying new measures to consider in 

its BACM/BACT analysis, the EPA 

recommends that the state obtain and 

evaluate a wide range of sources of 

information on existing and potential 

control measures. Other nonattainment 

areas in the same state, and other states 

across the country are important sources 

of information about control measures 

that are currently being implemented. 

Regional planning organizations, and 

state and local air quality consortiums 

have in the past developed summaries 

of control measures that should provide 

useful information for this process.166

The EPA’s RBLC 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 

control measures for states to 

consider.167

The state must incorporate 

appropriate 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 the list 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. 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 that would 

control emissions even more stringently 

than the measures included in the 

RACM/RACT analysis. In this way, the 

state will begin its BACM/BACT 

determination with a list of potential 

control options that is as complete and 

up-to-date as possible. 

Step 3: 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.168

(1) Stationary sources. As described 

under the technological feasibility 

criteria for the control measures analysis 

for Moderate area attainment plans in 

Section IV.D of this preamble, 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.169

(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, 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 local circumstances, 

the condition and extent of needed 

infrastructure, or population size or 

workforce type and habits, which may 

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170 Ibid. 

171 Ibid. 

172These longstanding factors were established in 

the EPA guidance in 1992 and are applicable to 

implementation programs for all of the NAAQS 

pollutants. See the appendices to the General 

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

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 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, 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. 

Step 4: Determine whether an 

available control technology or measure 

is economically feasible. The fourth step 

of this process 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. 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 for purposes of the 

RACM/RACT analysis. States need 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/BACT, 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.’’ 170

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.’’ 171 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, 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 cost 

prohibitive. 

As with the EPA’s approach for 

evaluating economic feasibility of 

potential reasonable measures for 

Moderate area attainment plans, for 

each technologically feasible control 

measure or technology, a state must 

evaluate the economic feasibility of the 

measure 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 

not establishing a fixed dollar per ton 

cost threshold for economic feasibility 

of controls identified as potential BACM 

and BACT, the cost per ton of an 

acceptable measure for the BACM and 

BACT analysis generally would be 

higher than it was for the RACM and 

RACT analysis for the same 

nonattainment area. In addition, if a 

source contends that a source-specific 

control level should not be established 

because the source 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 

source should make its claim known to 

the state and support the claim with 

information regarding the impact of 

imposing the identified control measure 

or technology on the following financial 

indicators,172 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). 

Step 5: Determine the earliest date by 

which a control measure or technology 

can be implemented in whole or in part. 

Section 189(b)(1)(B) of the CAA 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. The EPA thus expects a state 

with a Serious nonattainment area to 

take timely action to implement BACM 

and BACT in the area. 

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. 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. 

Where the earliest date that a measure 

can be implemented is beyond the 4 

year mark following reclassification to 

Serious, the measure may still be 

needed as an ‘‘additional feasible 

measure’’ if the 4 year mark occurs 

before the Serious area attainment date. 

‘‘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. 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

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58086 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

173The 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. 

174The Menu of Control Measures document is 

available at: http://www3.epa.gov/ttn/naaqs/pdfs/

MenuOfControlMeasures.pdf. 

Comments document found in the 

docket for this action. 

3. BACM and BACT Submission 

Requirements 

a. Summary of Proposal. The proposal 

further specified the submission 

requirements once a state has 

determined the BACT/BACM 

requirements in its plan. The proposal 

required the state to submit a list of 

emissions sources, an emissions 

inventory for such sources, and several 

pieces of information regarding 

potential control measures for these 

sources. 

b. Final Rule. The final rule remains 

relatively unchanged from the proposal. 

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, 40 CFR 

51.1010(a)(1)–(5) require the state to 

submit the following information as part 

of its Serious area attainment plan 

submission: 

(1) 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); 

(2) For each source category, source or 

activity in the nonattainment area, an 

inventory of direct PM2.5 and all PM2.5

precursor emissions; 

(3) 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; 173 174

(4) 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; 

(5) 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 emissions 

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; 

(6) For each technologically and 

economically feasible emission control 

measure or technology, the date by 

which the technology or measure can be 

implemented. 

As with a Moderate area attainment 

plan submission, the EPA recognizes 

that the base year emissions inventory 

that the state submits for the area in 

conjunction with its Serious area 

attainment plan will likely contain the 

information 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 requiring the 

state to include the base year emissions 

inventory information with the BACM 

and BACT submission and as one 

element of the state’s attainment plan 

due 18 months after reclassification of 

the area to Serious. 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

4. Criteria for Effective Regulations to 

Implement BACM and BACT and 

Additional Feasible Measures 

a. Summary of Proposal. The proposal 

described the four main criteria for 

effective control measure regulations: 

such regulations must be quantifiable, 

enforceable, replicable, and 

accountable. 

b. Final Rule. Guidance on effective 

control measure regulations is provided 

in the control strategy discussion for 

Moderate areas. See section IV.D.9 of 

this preamble, criteria for effective 

regulations to implement RACM and 

RACT and additional reasonable 

measures. 

5. Relevance of Prior BACT, LAER and 

BART Determinations 

a. Summary of Proposal. The 

preamble of the proposed rule stated 

that it should not be assumed that past 

control technology determinations 

would automatically be deemed to meet 

the Serious area control measure 

requirements (BACM, BACT, or 

additional feasible measures) for an 

area. 

b. Final Rule. The guidance on this 

issue in the preamble to the final rule 

remains largely unchanged. 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 potentially 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 sometime in the past, that 

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 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. 

At the same time, the EPA notes that the 

presence of previously installed control 

technology, and the technical and 

economic considerations that would be 

associated with upgrading to a measure 

that achieves greater reductions, is 

something that should be considered in 

the assessments of technological and 

economic feasibility of the newer 

measure. 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

6. Multi-state Nonattainment Areas 

a. Summary of Proposal. The 

preamble to the proposed rule provided 

general guidance on coordination 

between states in multi-state 

nonattainment areas to ensure they 

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adopt sufficient BACM/BACT and 

additional feasible measures to ensure 

expeditious attainment of the standard. 

b. Final Rule. The guidance in the 

final rule remains largely unchanged. 

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. 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

7. Environmental Justice Considerations 

for Developing the Attainment Plan 

Control Strategy for a Serious PM2.5

Nonattainment Area 

a. Summary of Proposal. The proposal 

provided general guidance for ensuring 

that overburdened populations are 

appropriately protected. 

b. Final Rule. The guidance in the 

final rule remains largely unchanged. 

The EPA strongly urges states to 

consider the environmental justice 

aspects of any control measures they 

have identified as BACM and BACT or 

additional feasible measures in order to 

provide health protection for 

overburdened populations. Please see 

Section XI of this preamble, which 

discusses possible approaches for states 

to address environmental justice 

concerns associated with 

implementation of the PM2.5 NAAQS in 

their SIP development process and 

attainment plans. 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

E. Modeling for Attainment 

Demonstrations 

1. Due Dates for Submission of Serious 

Area Attainment Demonstrations 

a. Summary of Proposal. Section IV.E 

of this preamble describes the EPA’s 

attainment demonstration and modeling 

requirements for Moderate area plans. 

The EPA proposed that the same general 

attainment demonstration and modeling 

requirements for Moderate area plans 

should apply to Serious area attainment 

demonstrations. However, Serious area 

plans have additional statutory 

requirements. 

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, CAA 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. The EPA proposed an 

approach for determining an 

appropriate attainment plan control 

strategy for a Serious PM2.5

nonattainment area that requires 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. 

b. Final Rule. The statutory 

attainment demonstration provisions for 

Serious areas are as follows: Section 

189(b) of the CAA requires a state with 

a designated Serious nonattainment area 

to submit an attainment plan for such 

area. As discussed earlier, CAA 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. A 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 CAA 

section 188(e)). 

The EPA is not finalizing the 

proposed approach of requiring all 

Serious area attainment demonstrations 

to be 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, the attainment 

demonstration will be due in 18 

months. States with Serious 

nonattainment areas that were 

reclassified before the Moderate area 

attainment deadline must submit 

attainment demonstrations the earlier of 

4 years after reclassification of the area 

to Serious or the end of the eighth 

calendar year after initial designation. 

However, these areas are still required 

to submit BACT/BACM measures 

within 18 months of being reclassified 

as Serious. Sections VI.A and VI.D of 

this preamble describe more fully the 

EPA’s approach for plan due dates and 

control strategy analyses for all elements 

of a Serious area attainment plan. 

Section VI.J of this preamble provides a 

complete discussion of the EPA’s 

criteria for granting a Serious area 

attainment date extension. 

c. Comments and Responses. Any 

comments received on this section are 

addressed in the Response to Comments 

document found in the docket for this 

action. 

2. Attainment Demonstration 

Requirements for Serious Areas 

a. Summary of Proposal. The proposal 

described the attainment demonstration 

and impracticability demonstration 

requirements for Serious nonattainment 

areas. The EPA proposed that a serious 

area plan must include an attainment 

demonstration that demonstrates how a 

state will attain the PM2.5 NAAQS by 

the applicable attainment date, must 

include analyses supporting the state’s 

determination of its proposed 

attainment date, and must show that the 

area will attain the NAAQS as 

expeditiously as practicable, but not 

later than the tenth calendar year after 

designation. The proposal indicated that 

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 include all BACM 

and BACT controls in the analysis. 

b. Final Rule. The final rule 

requirements for Serious area 

attainment demonstrations are generally 

unchanged from the proposal. As 

described in Section IV.E of this 

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58088 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

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 

finalizing a requirement 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 

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 include all BACM 

and BACT controls in the analysis. 

A state with a Serious nonattainment 

area can also submit an impracticability 

demonstration (under CAA section 

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

extension of the attainment date under 

CAA section 188(e). The 

impracticability demonstration for a 

Serious area would be similar to an 

impracticability demonstration for 

Moderate areas because it must show 

that the area will not be able to attain 

the PM2.5 NAAQS by the latest possible 

statutory attainment date, which in this 

case is by the end of the tenth calendar 

year following designation. 

In order to support a Serious area 

impracticability demonstration, the state 

must show (through modeling) that 

attainment cannot be reached by the 

latest 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 

(as may be necessary to meet the 

requirements of 172(c)(6)), 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 CAA section 

188(e). (MSM are discussed in more 

detail in Section VI.J of this preamble). 

As a result, the required plan in the case 

of a Serious area that cannot attain by 

the statutory attainment date is both an 

impracticability demonstration (to 

justify an extension beyond the 

statutory attainment date) and an 

attainment demonstration that serves as 

the basis for proposing an appropriate 

alternative attainment date. Note that 

this is different from a Moderate area 

impracticability demonstration, which 

is not required to serve as the basis for 

proposing a new area attainment date. 

c. Comments and Responses. Any 

comments received on this section are 

addressed in the Response to Comments 

document found in the docket for this 

action. 

3. Air Quality Modeling Required for 

Serious Area Attainment 

Demonstrations and Impracticability 

Demonstrations 

a. Summary of Proposal. The EPA 

proposed to require air quality modeling 

in support of both a Serious area 

attainment demonstration and a Serious 

area impracticability demonstration. 

b. Final Rule. The EPA is finalizing a 

requirement for states to submit air 

quality modeling in support of both 

attainment demonstrations and 

impracticability demonstrations for 

Serious PM2.5 nonattainment areas. 

Unlike the impracticability 

demonstration for Moderate areas 

described in CAA section 

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

demonstration for Serious areas in CAA 

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. 

Some commenters believed that both 

Moderate and Serious area 

impracticability demonstrations must 

include air quality modeling. The EPA 

does not agree and believes the statute 

only requires air quality modeling for 

Serious area impracticability 

demonstrations. This stems from the 

slightly different statutory construction 

in CAA section 189(b)(1)(A) compared 

to CAA section 189(a)(1)(B). Section 

189(b)(1)(A) of the CAA specifies an air 

quality modeling requirement as a 

parenthetical, which the EPA interprets 

to apply to both the requirements in 

CAA section 189(b)(1)(A)(i) [attainment 

demonstrations] and CAA section 

189(b)(1)(A)(ii) [impracticability 

demonstrations]. Additionally, the fact 

that a Serious area impracticability 

demonstration must also include an 

attainment demonstration with an 

alternative attainment date logically 

supports the final rule conclusion that 

a Serious area impracticability 

demonstration must include air quality 

modeling. Modeling is needed to 

demonstrate attainment and to propose 

an alternative attainment date for the 

Serious area. This differs from a 

Moderate area impracticability 

demonstration, which only serves to 

demonstrate that attainment cannot be 

reached by the Moderate area 

attainment date. A Moderate area 

impracticability demonstration does not 

require a demonstration of attainment or 

setting of an alternative future 

attainment date. It merely starts the 

process of reclassifying an area to 

Serious and the eventual required 

submission of a Serious area 

implementation plan. 

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 the 

modeling requirements and guidance for 

all PM2.5 nonattainment areas. 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

4. Attainment Demonstrations Required 

To Be Submitted by an Area 

Reclassified to Serious 

a. Summary of Proposal. The proposal 

discussed the attainment demonstration 

requirements for Moderate 

nonattainment areas that subsequently 

are reclassified to Serious 

nonattainment. The EPA proposed that 

states with Moderate nonattainment 

areas that get reclassified to Serious 

nonattainment areas must first submit a 

Moderate area plan and then a separate 

Serious area plan. 

b. Final Rule. The EPA is finalizing 

requirements for states to submit a 

Moderate area attainment demonstration 

(or impracticability demonstration) and 

then if reclassified to Serious 

nonattainment, a separate Serious area 

attainment demonstration. Under CAA 

section 189(a)(1)(B), a state with a 

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175Note 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. 

Moderate nonattainment area is 

required to submit a demonstration that 

the area either will attain or cannot 

practicably attain the NAAQS by the 

statutory attainment date. Regardless of 

whether the state submits an attainment 

demonstration or an impracticability 

demonstration for a Moderate area, if 

such an area is reclassified to Serious 

prior to or after failing to attain the 

applicable NAAQS, the state is required 

under CAA 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 is 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, an 

area dominated by wood smoke 

emissions may 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. 

c. Comments and Responses 

Comment: Some commenters agreed 

with the EPA that areas seeking to be 

reclassified from moderate to serious 

must submit two separate attainment 

plan submissions. The commenter 

stated the Act promises that all areas, 

even the most polluted, will implement 

reasonably available controls and 

provide at least some interim health 

protections while preparing a serious 

area plan containing more protective 

requirements. 

Response: The EPA agrees with the 

comment. In the final rule, an area that 

is reclassified to Serious must submit 

both Moderate and Serious area plans, 

and all statutory requirements for a 

Moderate area (including RACT and 

RACM) must be met by the statutory 

deadline. 

5. Future Year(s) To Be Modeled in 

Attainment Demonstrations 

a. Summary of proposal. A state 

performing a modeling analysis for an 

attainment demonstration or a Serious 

area impracticability analysis must 

select a future year for the analysis. The 

EPA proposed that 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. The EPA 

recommended the last year of the 

statutory attainment date as a starting 

point for Serious nonattainment area 

modeling demonstrations. 

b. Final Rule. The EPA is finalizing a 

requirement that all emissions control 

measures relied on for attainment must 

have been implemented by the 

beginning of the attainment year. See 40 

CFR 51.1011(b)(6). 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.175

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 CAA 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 is 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 ten 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 by 

averaging 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 three annual values is less 

than the NAAQS). Therefore, it is 

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. 

Criteria for establishment of the Serious 

area attainment date are discussed in 

Section VI.I of this preamble. In 

evaluating such considerations, the 

question arises as to whether additional 

future modeling is required beyond the 

recommended final year modeling just 

discussed. For purposes of determining 

the attainment date that is as 

expeditious as practicable, the state 

must conduct future year modeling that 

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 in 2015 and subsequently 

reclassified to Serious in 2021, a future 

case scenario for the year 2025 (10 years 

after the initial nonattainment 

designation) would be needed to 

examine whether existing federal, state, 

and local measures (including 

previously identified and implemented 

RACT/RACM controls for the area) plus 

the BACM and BACT identified by the 

state would result in attainment. Since 

the EPA is finalizing the requirement 

that 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. 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 

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176States 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. 

177For more information on PM2.5 precursor 

requirements, see CAA 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). 

178A 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. 

179 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. 180 Ibid. 

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 CAA 

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.176 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 sensitivity 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 or using advanced 

modeling techniques such as DDM) 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 

multiple additional future years. 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. 

c. Comments and Responses. Any 

comments received on this section are 

addressed in the Response to Comments 

document found in the docket for this 

action. 

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.177 If a state’s SIP 

submission demonstrates that a Serious 

area cannot attain by the end of the 

tenth calendar year after the area’s 

designation, motor vehicle emissions 

budgets are not required for that tenth 

calendar year, but are required for the 

year that the state demonstrates to be 

the area’s attainment year. 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.178 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, 

unless EPA approves the state’s use of 

an alternative model.179

F. RFP Requirements 

1. General Approach to RFP 

a. Summary of the Proposal. The EPA 

generally proposed 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, similar to a Moderate area 

attainment plan. The EPA proposed that 

the applicable baseline year must be the 

same year as that represented by the 

latest base year inventory for the Serious 

area. The EPA proposed that the state 

must include in its RFP analysis the 

anticipated emissions reductions 

expected to be achieved through the 

implementation of control measures 

required by the control strategy 

explained in Section VI.D of this 

preamble (BACM and BACT, additional 

feasible measures and MSM if 

applicable). As with RFP plans for 

Moderate areas, the EPA proposed that 

a state must submit RFP projected 

emissions 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). The EPA also 

proposed that motor vehicle emissions 

budgets must also be established for 

direct PM2.5 and any PM2.5 plan 

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.180 It 

was not necessary to propose that RFP 

plans for Serious areas include motor 

vehicle emissions budgets for direct 

PM2.5 and any PM2.5 plan precursor 

because, as stated in the section of this 

rule that addresses RFP requirements for 

Moderate PM2.5 areas, the transportation 

conformity rule already requires that 

RFP plans establish motor vehicle 

emissions budgets. RFP plans would 

therefore be required to establish motor 

vehicle emissions budgets for direct 

PM2.5 and any relevant PM2.5 plan 

precursor. The EPA also proposed that 

guidance found in the Moderate 

nonattainment areas RFP section of the 

proposal should also apply to Serious 

nonattainment areas. 

b. Final Rule. The EPA is finalizing 

rule provisions for Serious areas that 

essentially mirror the approach to 

Moderate areas found in Section IV.F of 

this preamble. The EPA is further 

clarifying application of those 

provisions by providing guidance that 

closely follows the Moderate area 

guidance regarding how to prepare an 

RFP plan, RFP projected emissions, 

geographic coverage of emission sources 

for RFP, and RFP requirements for 

multi-state nonattainment areas. 

As with a Moderate area attainment 

plan, the EPA is finalizing that a state 

must submit an RFP plan as part of any 

Serious area attainment plan in order to 

satisfy the statutory requirements for 

RFP. The 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 

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181As noted in Section V.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. 

182 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. 

statutory definition of RFP. The plan 

must include three components: (1) An 

implementation schedule for control 

measures on sources in the 

nonattainment area, (2) RFP projected 

emissions for each applicable 

quantitative milestone year determined 

in Section VI.G of this preamble, based 

on the anticipated control measure 

implementation schedule; and (3) an 

analysis that demonstrates that this 

schedule of aggregate emissions 

reductions achieves sufficient progress 

toward attainment between the 

applicable baseline year to the 

attainment year. For additional 

discussion of each of the components of 

the RFP plan, refer to Section IV.F of 

this preamble. See 40 CFR 51.1012(a). 

The EPA requires 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 for a Serious area that can 

demonstrate attainment pursuant to 

CAA section 189(b)(1)(A), or up to the 

end of the fifteenth year following 

designation for a Serious area that 

sought an extension of the statutory 

attainment date pursuant to CAA 

section 188(e).181 As with Moderate 

areas, the RFP analysis must clearly 

convey how the schedule for 

implementing the control strategy will 

provide for generally linear or stepwise 

progress towards attainment. If stepwise 

progress is more appropriate for the 

specific nonattainment area, the state is 

required to submit a clear rationale and 

supporting information to explain why 

generally linear progress towards 

attainment in the area is not appropriate 

(e.g., due to the nature of the 

nonattainment problem, the types of 

sources contributing to PM2.5 levels in 

the area, and the ability to perform 

timely implementation of control 

measures). For a Serious area, the EPA 

requires that the state must include in 

its RFP analysis the anticipated 

emissions reductions expected to be 

achieved through the implementation of 

control measures required by the control 

strategy described in Section VI.D of 

this preamble (BACM and BACT, 

additional feasible measures and MSM, 

if applicable). Similar to Moderate areas, 

the optional air quality analysis 

discussed in Section IV.F of this 

preamble is also available for use by a 

state preparing a Serious area RFP plan. 

Additionally, the EPA requires that 

motor vehicle emissions budgets must 

also be established for direct PM2.5 and 

PM2.5 plan precursors 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.182 See 40 CFR 51.1012(a). 

Finally, similar to Moderate areas, 

Serious areas that are multi-state or 

multi-jurisdictional shall provide RFP 

plans for each state represented in the 

nonattainment area that 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. For 

further information, see Section IV.F.5 

of this preamble. See 40 CFR 51.1012(b). 

c. Comments and Responses. Any 

additional comments received related to 

RFP are addressed Section IV.F of this 

preamble or in the Response to 

Comments document found in the 

docket for this action. 

G. Quantitative Milestones 

1. Summary of the Proposal 

The EPA proposed 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 

7.5 and 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 proposed that the state must 

include in the Serious area attainment 

plan quantitative milestones to be 

achieved at 7.5, 10.5 and 13.5 years 

from the area’s date of designation. 

The EPA proposed that the general 

approach to selecting quantitative 

milestones outlined in the Moderate 

nonattainment area section of the 

proposal should apply to any attainment 

plan for a PM2.5 nonattainment area, 

independent of its classification. 

Specifically, the EPA proposed 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 CAA section 

189(c). Additionally, the EPA proposed 

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 CAA section 

189(b)(1)(B). 

2. Final Rule 

The final rule provisions for Serious 

area quantitative milestones are similar 

to such provisions for Moderate areas 

discussed in Section IV.G of this 

preamble. As required for Moderate 

areas, Serious area attainment plans 

must include quantitative milestones 

that demonstrate RFP towards 

attainment to be achieved every 3 years 

until the area is redesignated to 

attainment. To account for variations in 

the timing of possible additional plans 

that may be required beyond the Serious 

area attainment plan (such as a plan 

revision under CAA section 189(d) for a 

Serious area that fails to attain) the EPA 

is also clarifying, consistent with the 

requirements discussed in Section IV.G 

of this preamble for Moderate areas, that 

all Serious area attainment plans must 

contain one additional quantitative 

milestone to be met in the 3-year period 

beyond the applicable Serious area 

attainment date. This will provide the 

EPA with appropriate tools necessary to 

continue to monitor the area’s 

continued progress toward attainment 

in the event that the area fails to attain 

and develops a new attainment plan. 

For an area that is discretionarily 

reclassified to Serious under the 

provisions of CAA section 188(b)(1), the 

Serious area plan must contain 

quantitative milestones to be achieved 

by 7.5 years from the area’s date of 

designation as nonattainment. In this 

case, the 7.5 year quantitative milestone 

that was submitted with the Moderate 

area plan may still be sufficient to 

demonstrate RFP or may have to be 

adjusted to reflect the difference in 

actual progress from the projections of 

the Moderate area plan. For an area that 

is reclassified to Serious under CAA 

section 188(b)(2) due to failure to attain, 

the 7.5 year quantitative milestones that 

were submitted with the Moderate area 

plan are still required and would be 

sufficient for the EPA to evaluate the 

area’s progress toward attaining the 

NAAQS while the Serious area plan is 

being developed. All Serious area plans 

must also include quantitative 

milestones to be achieved 10.5 years 

from designation, to help assess the 

state’s progress toward attaining the 

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183Addendum to the General Preamble, 59 FR 

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

PM2.5 NAAQS in the event the area fails 

to attain by the applicable attainment 

date. Finally, for a Serious area that 

cannot demonstrate attainment by the 

statutory Serious area attainment date, 

the state must include quantitative 

milestones to be achieved every 3 years, 

such that the final milestone falls within 

the 3 years after the applicable Serious 

area attainment date. For example, if a 

state requests an attainment date 

extension to 14 years after designation 

pursuant to CAA section 188(e), the 

attainment plan should contain not only 

the 7.5 and 10.5 year milestones, but 

also milestones to be achieved 13.5 and 

16.5 years from designation. 

The Addendum included guidance 

that recommended milestones ‘‘should 

be addressed by quantifying and 

comparing the annual incremental 

emissions 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.’’ 183 The final rule does 

not specify that the milestones must be 

expressed in terms of emissions 

reductions. While the EPA notes that 

the Addendum contains this 

fundamental concept, 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 CAA section 189(c)(2). Therefore, 

the final rule requires that states 

selecting quantitative milestones for a 

Serious area plan should use the 

approach outlined for Moderate areas, 

as described in Section IV.G of this 

preamble. This approach applies to any 

attainment plan for a PM2.5

nonattainment area, independent of its 

classification. Specifically, the final rule 

requires 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 CAA section 

189(c). See 40 CFR 51.1013(a)(2). 

In addition to this general approach 

for selecting quantitative milestones and 

similar to what the final rule requires 

for Moderate area attainment plans, the 

final rule requires that, at a minimum, 

states must ensure that the quantitative 

milestones for Serious PM2.5

nonattainment areas assure RFP is being 

met by demonstrating that BACM and 

BACT have been implemented, as 

appropriate considering the timing of 

the milestone report, in order to comply 

with the statutory requirement at CAA 

section 189(b)(1)(B). The agency is 

further finalizing a corresponding 

requirement for Serious PM2.5

nonattainment areas that receive an 

attainment date extension. For these 

areas, the quantitative milestone should 

assure that RFP is being met by 

demonstrating that MSM for the area 

has been implemented as required 

pursuant to CAA section 188(e). This 

requirement was not specifically 

outlined in the proposal. However, 

while considering the requirements that 

were proposed for Serious areas, the 

EPA determined that including this 

additional provision within quantitative 

milestones would enable the agency to 

better evaluate progress toward 

attainment in areas that receive a 

Serious area extension. The EPA 

acknowledges that the precise 

quantifiable metric for a quantitative 

milestone (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, which 

quantitative milestone (i.e., 7.5 or 10.5 

years from designation), and the 

anticipated implementation timing and 

nature of the BACM and BACT controls 

themselves. Nonetheless, the EPA 

believes it is appropriate to include 

confirmation that such control measures 

and technologies are implemented 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. 

Additional provisions discussed in 

the Moderate area quantitative 

milestones requirements in Section IV.G 

of the preamble also apply to Serious 

areas. Specifically, if a Serious area 

submitted the optional air quality 

targets with the RFP plan then an air 

quality based milestone (i.e., one that is 

expressed in terms of an ambient PM2.5

level) is strongly recommended to be 

included in order to confirm that the air 

quality target has been met for the 

quantitative milestone year. If used, this 

milestone will be compared to the most 

recently certified monitored ambient air 

data as part of the milestone report due 

after the area reaches each quantitative 

milestone date. For additional details on 

this optional provision, refer to Section 

IV.G of this preamble. 

Finally, the quantitative milestone 

report requirements outlined in Section 

IV.G of this preamble apply to Serious 

areas as well. Specifically, the 

requirements associated with the timing 

and contents of the quantitative 

milestone report submission for a 

Moderate area also requirements in a 

Serious area. For additional details on 

these requirements, refer to Section IV.G 

of this preamble. See 40 CFR 51.1013(b). 

3. Comments and Responses 

Any additional comments received on 

this section are addressed in Section 

IV.G of this preamble or in the Response 

to Comments document found in the 

docket for this action. 

H. Contingency Measures 

1. Summary of the Proposal 

In the proposal, the EPA proposed 

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. The EPA also proposed that, as 

with Moderate areas, a state may elect 

to rely on contingency measures that 

achieve emissions reductions not only 

from sources within the nonattainment 

area, but also from sources located 

outside the nonattainment area but 

within the state, 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 area 

attainment plans, the EPA proposed 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 

agency also proposed options for 

submission deadlines for Serious area 

contingency measures. 

2. Final Rule 

As noted in Section IV.G of this 

preamble, all PM2.5 nonattainment areas 

must include in their attainment plans 

contingency measures consistent with 

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184See LEAN v. EPA, 382 F.3d 575 (5th Cir. 

2004). 

185Addendum to General Preamble, 59 FR 41988 

(August 16, 1994), at 42015. 

CAA section 172(c)(9). Contingency 

measures are additional control 

measures to be implemented in the 

event that an area fails to meet RFP 

requirements, fails to meet any 

quantitative milestone, fails to submit a 

quantitative milestone report 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 a failure 

occurred, and such measures are 

required to take effect without 

significant further action by the state or 

the EPA. 

The statutory contingency measure 

requirement at CAA 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. Accordingly, the final rule 

requires the criteria for identifying and 

selecting contingency measures for a 

Serious area attainment plan that are the 

same as those for Moderate area plans. 

Specifically, the EPA is finalizing 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, failure to 

meet any quantitative milestone, failure 

to submit a quantitative milestone 

report or failure to meet the standard by 

the applicable 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 should 

consist of control measures that are not 

otherwise included in the control 

strategy for the SIP, or that achieve 

emissions reductions not otherwise 

relied upon in the control strategy for 

the area. 

(4) Contingency measures should 

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 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. 

The EPA is also finalizing its proposal 

to allow a state to rely on contingency 

measures that achieve emissions 

reductions on sources located outside 

the nonattainment area, but within the 

state 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 

allows a state under these circumstances 

to rely on additional reductions from 

federal or local measures already 

scheduled for implementation as part or 

all of their contingency measures. The 

EPA could 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 

nonattainment provisions (such as to 

meet BACM/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.184 As with 

contingency measures for Moderate area 

attainment plans, the EPA requires that 

the emissions reductions associated 

with contingency measures for Serious 

area plans should be approximately 

equivalent to 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. See 40 

CFR 51.1014(b)(2). 

The Addendum provided guidance 

related specifically to the selection and 

implementation of contingency 

measures for Serious nonattainment 

areas. First, the 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.’’ 185 The 

EPA continues to believe that this 

approach to the statutory contingency 

measure requirement is appropriate and 

is finalizing it for purposes of 

implementing the PM2.5 NAAQS in 

Serious nonattainment areas. See 40 

CFR 51.1014. 

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, failed to meet any 

quantitative milestone, failed to submit 

a quantitative milestone report 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 expects 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. 

3. Comments and Responses 

Comment: One commenter supported 

the proposal that contingency measures 

may be approved if they will result in 

the equivalent air quality improvement 

as would be obtained by implementing 

measures obtaining 1 year’s worth of 

emissions reductions needed to 

demonstrate attainment. 

Response: In the case where a state 

selected the optional RFP analysis that 

includes air quality targets, the EPA 

expects that an area contingency 

measures may be approved if they will 

result in approximately 1 year’s worth 

of air quality improvement. 

I. Attainment Dates 

1. Summary of Proposal 

Section 188(c) of the CAA states that 

the attainment date for a Serious area is 

to be the end of the tenth calendar year 

after designation. The EPA proposed to 

interpret the reference to ‘‘designation’’ 

in section 188(c) as meaning the 

‘‘effective date of designation.’’ 

2. Final Rule 

As explained earlier, section 188 

establishes the attainment dates for both 

Moderate and Serious areas. For a 

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186The EPA believes that there is no real effect 

on attainment date determinations due to the small 

difference in statutory language in CAA 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). 

187Notably, 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 CAA section 

188(d). 

188This 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). 

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

381 F.3d 826 (9th Cir. 2004), the court indicated 

that an area that had previously failed to meet a 

requirement of the CAA could still be eligible to 

receive an attainment date extension: ‘‘Nowhere 

does the provision limit extensions to those states 

that never made a misstep in their efforts to comply 

with the Act.’’ 

Serious area, CAA 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.’’ 186 For 

example, for an area initially designated 

as a Moderate nonattainment area 

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 of this preamble, the EPA interprets 

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. 

3. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

J. Attainment Date Extensions 

Background. Section 188(e) of the 

CAA provides that the EPA may grant 

a Serious area 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.’’ 

The statute also includes factors that 

the EPA may consider in determining 

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.’’ 187

The proposal described the four main 

elements the state must submit when 

requesting a Serious area attainment 

date extension: (1) A demonstration that 

attainment by the statutory Serious area 

attainment date is impracticable; (2) a 

demonstration that the area is 

complying with all requirements and 

commitments in the applicable 

attainment plan; (3) a demonstration 

that the plan includes the MSM that are 

included in the implementation plan of 

any state, or are achieved in practice in 

any state; and (4) a demonstration of 

attainment by the most expeditious 

alternative date practicable. The 

proposal also included a discussion 

about the timing of extension request 

submissions, and how to interpret the 

second element in cases where the 

extension request is submitted after the 

state has already submitted an initial 

Serious area attainment plan. These 

topics are addressed in the following 

sections. 

1. Demonstration That Attainment by 

the Statutory Serious Area Attainment 

Date is Impracticable 

a. Summary of Proposal. The 

proposed rule discussed the 

requirements for a demonstration to 

show that it is impracticable for a 

Serious area to attain by the attainment 

date. This demonstration involves 

evaluating through air quality modeling 

whether all best available control 

measures will enable the area to attain 

the standard by the attainment date. 

b. Final Rule. This section remains 

relatively unchanged from the proposal. 

In order to demonstrate that it is 

impracticable for an area to attain by the 

attainment date, the state would have to 

show that the implementation of all 

BACM/BACT (and additional feasible 

measures) 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).188 The statutory provision 

for demonstrating that it is 

impracticable to attain by the Serious 

area attainment date requires that the 

demonstration be based on air quality 

modeling (see CAA section 

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

this demonstration is provided in 

Section VI.E of this preamble. 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

2. Demonstration That the Area is 

Complying With all Requirements and 

Commitments in the Applicable 

Implementation Plan 

a. Extension Request Submitted at the 

Same Time as the Serious Area 

Attainment Plan 

i. Summary of Proposal 

The EPA proposed to interpret the 

criterion under CAA 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 CAA 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 proposed to read CAA 

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 EPA also proposed 

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.189

ii. Final Rule 

Some commenters stated that an area 

should only be able to receive an 

extension if the Moderate area plan had 

been fully approved by the EPA. Other 

commenters agreed with the EPA’s 

proposed approach. They suggested that 

if a part of the Moderate plan had been 

disapproved, but it was clear that the 

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190Addendum to the General Preamble, 59 FR 

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

area could not practicably attain by the 

Serious area attainment date, then the 

area should be able to receive an 

extension. Other commenters suggested 

that an area should not be deprived an 

extension if the approval of all or part 

of the Moderate area attainment plan is 

delayed due to logistical reasons or the 

EPA’s inability to take final action in a 

timely manner. 

The final rule does not require the 

area to have a fully approved Moderate 

area plan when the attainment date 

extension request is submitted at the 

same time as the Serious area plan. An 

extension is allowed if the area is 

complying with all Moderate area 

requirements and commitments 

pertaining to that area in the state’s 

submitted Moderate area 

implementation plan, but the plan does 

not need to be fully approved by EPA. 

The EPA considers this to be a 

reasonable interpretation of the statute 

because, as noted by commenters, there 

may be various reasons why an area 

may not have a fully approved Moderate 

area SIP by the time an extension 

request may be granted. 

iii. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

b. Extension Request Submitted After 

Submission of an ‘‘Original’’ Serious 

Area Attainment Plan 

i. Summary of Proposal 

For a Serious area extension request 

that was submitted after submission of 

an ‘‘original’’ Serious area attainment 

plan that contained an attainment 

demonstration meeting the requirements 

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

proposed to read CAA 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 EPA stated 

that this proposed interpretation of this 

criterion would apply whether the area 

was reclassified to Serious under the 

EPA’s discretionary authority (CAA 

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

upon failing to attain by the Moderate 

area attainment date (CAA section 

188(b)(2)). 

The proposal also requested comment 

on an ‘‘alternative interpretation’’ that, 

as pointed out by some commenters, 

appears to also have mistakenly 

required the same thing as the first 

option: That the state would need to 

have a fully approved Moderate area 

attainment plan in order to receive an 

extension. 

The EPA notes that Section VI.C of 

this preamble, Timing of Extension 

Request Submission, also discusses this 

issue. It requested comment on whether, 

for areas that had already submitted 

Serious area attainment plans, it would 

be appropriate that the state must have 

complied with all requirements and 

commitments in the area’s initial 

Serious area plan (the EPA’s preferred 

option), or in the Moderate area plan. 

ii. Final Rule 

After considering the comments 

received on this issue, the EPA is 

finalizing an approach that requires 

that, where a Serious area attainment 

date extension is being submitted after 

the initial Serious area attainment plan 

has been submitted, the state would 

need to demonstrate that it was 

complying with all Serious area 

requirements and commitments 

pertaining to the area in the plan it had 

initially submitted. However, it would 

not need a fully approved Serious area 

attainment plan. The EPA believes the 

state should not be prevented from 

obtaining an attainment date extension 

in the event the EPA is unable to take 

final action on a submitted plan in a 

timely manner. The original proposal 

did not specify Serious area provisions 

implementing this approach, but 

commenters noted the proposed 

analogous provisions for Moderate areas 

seeking 1-year extensions, and 

suggested that EPA should adopt a 

similar approach for Serious areas. 

Under this approach, the state would 

not need a fully approved Serious area 

plan; it would be able to receive an 

extension if it had already submitted the 

Serious area plan but had not received 

EPA approval yet, and if it was 

complying with all Serious area 

requirements and commitments 

pertaining to the area in the state’s 

implementation plan. The EPA also 

considered an alternative option 

wherein the state would be able to 

receive an extension only if it had a 

fully approved Serious area attainment 

plan. The commenters did not favor this 

option, nor does the EPA. 

iii. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

3. Demonstration That the Plan Includes 

the MSM That Are Included in the 

Implementation Plan of Any State, or 

Are Achieved in Practice in Any State 

To qualify for any extension of a 

Serious area attainment date, CAA 

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 

measures’’ (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.190

a. Summary of Proposal. The proposal 

suggested 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/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 also 

proposed 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/BACT. 

For each approach, the proposal 

described a five step process for 

determining MSM: (1) Update the 

emissions inventories for the 

nonattainment area; (2) identify de 

minimis source categories through 

modeling; (3) identify potential MSM; 

(4) compare MSM to control measures 

already adopted in the SIP for the 

nonattainment area; and (5) adopt and 

implement any MSM that are more 

stringent than any measures that are 

already approved into the SIP. The 

proposal requested comment on 

whether the two proposed approaches 

are sufficiently consistent with the 

agency’s respective proposed 

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approaches to BACM/BACT 

determinations. 

b. Final Rule. Almost all comments 

received on this section involved the 

issue of whether the rule should allow 

for de minimis source categories to be 

exempted in the process of determining 

MSM. A few commenters supported the 

identification of de minimis source 

categories and their exemption from the 

MSM requirement. These commenters 

were split in terms of their preference 

for the two de minimis approaches that 

were presented. Some commenters 

suggested that under any approach, an 

area could still exclude a measure from 

MSM based on the inability to feasibly 

implement the measure in the area. 

Some commenters stated that it would 

be too burdensome to require a state to 

evaluate whether a particular source 

category had a ‘‘significant’’ or de 

minimis impact on air quality, while 

others supported the approach. One 

group of commenters disagreed with the 

notion that a Serious area could exempt 

de minimis sources from the MSM 

requirement in the first place. They 

stated that de minimis exemptions 

would not be appropriate for MSM, for 

which the CAA has expansive language 

requiring the most stringent measures 

required in any SIP or achieved in 

practice in any state. 

After considering the comments 

received on the de minimis source 

category issue, the EPA is adopting a 

final rule that does not include an 

explicit de minimis source category 

exemption in determining MSM. The 

agency’s reasons for not allowing a de 

minimis source category or de minimis 

impact concept, articulated in prior 

sections on determining RACM/RACT 

(Section IV.D) and BACM/BACT 

(Section VI.D), apply equally here. 

Moreover, the EPA believes it would be 

particularly inappropriate to allow for a 

de minimis source category approach for 

MSM. The statute requires MSM to be 

implemented because the area is unable 

to attain the standard within 10 years of 

designation and has a more severe air 

quality problem. Congress clearly 

intended for such areas to more widely 

explore potential control measure 

possibilities, and a de minimis source 

category exclusion would be contrary to 

that intent. 

The EPA believes the rule provides 

sufficient flexibility in the MSM area 

control measure analysis and attainment 

demonstration process enabling states to 

identify sources that should not be 

subject to control measures, including 

the ability to develop precursor 

demonstrations to exclude precursors 

from control requirements, and to 

consider case-specific factors in 

determining technological and 

economic feasibility of potential control 

measures. If the final rule were to 

include an explicit step to conduct a de 

minimis source category analysis on the 

entire inventory early in MSM process, 

the EPA also believes that there is a risk 

that such an analysis may bring about 

investment of scarce time and analytical 

resources on analysis of categories to 

exclude rather than on the identification 

of the most stringent control measures 

necessary to attain the standard. As 

noted in Section IV.D of this preamble 

on Moderate areas, and again in [serious 

area section] the EPA also finds that 

from a technical perspective, it would 

be very challenging to implement a de 

minimis source category process in a 

consistent manner nationally without 

clear guidelines describing how 

narrowly or how broadly a de minimis 

exemption could apply to a ‘‘source 

category,’’ or how the technical analysis 

would need to be performed. For all of 

these reasons, a de minimis source 

category concept is not included in the 

final rule for MSM. 

Process for determining MSM. The 

following sections describe the process 

for determining MSM that is finalized in 

this rule: (a) Update emissions 

inventories; (b) identify potential MSM; 

(c) compare MSM to control measures 

already adopted in the SIP for the 

nonattainment area; and (d) adopt and 

implement any MSM that are more 

stringent than any measures that are 

already approved into the SIP. (See 40 

CFR 51.1010(b)(1)–(4).) 

i. Update Emissions Inventories 

The first step 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 CAA 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 submission 

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 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 

CAA 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. 

ii. Identify Potential MSM 

The second step in determining MSM 

involves identifying the potentially 

MSM in other state implementation 

plans for PM2.5 or other NAAQS, or that 

are used in practice in other states for 

controlling emissions from sources 

similar to those listed in the emissions 

inventory. This information can be 

obtained from a number of sources, 

including state regulations on the books, 

state summaries of control measures, 

state permitting databases, the RACT/

BACT/LAER Clearinghouse, and control 

measure compilations developed by 

regional or state/local organizations. 

Elsewhere in this preamble, the EPA 

recommends that a state identify 

potential measures for consideration as 

RACM/RACT or BACM/BACT by 

evaluating control 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 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. 

For each measure, the state is required 

to determine its technological and 

economic feasibility for sources in the 

area. States should apply more stringent 

criteria for determining the feasibility of 

potential MSM than that described for 

BACM and BACT in Section VI.D of this 

preamble. 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, if 

such sources 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, in some cases it may 

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 

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interprets the MSM provision so as to 

increase the potential that it will result 

in additional controls beyond the set of 

measures adopted as BACM and BACT. 

In the MSM analysis, in addition to 

identifying additional candidate MSM, 

the state is required 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. 

iii. Compare MSM to Control Measures 

Already Adopted in the SIP for the 

Nonattainment Area 

The third step requires the state to 

compare the potential MSM that have 

been identified for each source type or 

source category against the measures, if 

any, already adopted into the Serious 

area SIP for that source category to 

determine if such MSM would provide 

any additional reductions. This 

comparison will be used in determining 

what measures to adopt in the next step. 

iv. Adopt and Implement Any MSM 

That are More Stringent Than Any 

Measures That Are Already Approved 

Into the SIP 

The fourth step requires the adoption 

of any MSM that are more stringent than 

existing measures as a regulation, and 

requires submission of the regulation as 

part of the SIP, as well as expeditious 

implementation of the regulation. For 

any measures that the state determines 

cannot be feasibly implemented in the 

area, it should provide a reasoned 

justification for rejecting the potential 

MSM. 

The EPA notes that CAA section 

188(e) does not identify a deadline for 

a state to implement MSM, whereas 

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 CAA section 188(e) is to 

minimize the length of a Serious area 

attainment date extension, the EPA 

requires that the implementation of 

MSM must be as expeditious as 

practicable but no later than 1 year prior 

to the alternate Serious area attainment 

date identified by the state in its 

extension request. 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

4. Demonstration of Attainment by the 

Most Expeditious Alternative Date 

Practicable 

Section 189(b)(1)(A) of the CAA 

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 

demonstration modeling for Serious 

area attainment plans. 

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 of this preamble. 

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. 

6. Timing of Extension Request 

Submission 

The EPA has identified two potential 

Serious area attainment date extension 

scenarios: (1) The more straightforward 

scenario where the attainment date 

extension is included with the initial 

Serious area plan, and (2) the scenario 

where a state may prepare and fully 

implement a timely Serious area plan 

that includes a modeling analysis that 

demonstrates the area would attain no 

later than the statutory Serious area 

attainment date (the end of the tenth 

calendar year following designation), 

and yet the state 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 CAA 

section 189(d)), the EPA also believes 

that the criteria of CAA 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 CAA section 188(e)). 

In the first scenario, there is no need 

to specify any further timing 

requirements beyond those previously 

described for Serious area plan 

submission. However, for the second 

scenario the final rule needs to specify 

a due date for the request. The EPA 

believes that it would be acceptable for 

a state to submit a Serious area 

attainment date extension request (as 

described earlier) together with a new 

Serious area attainment plan meeting all 

of the statutory requirements that apply 

to such plans. The state should submit 

the extension request and new 

implementation plan to EPA as early as 

possible, but the final rule requires that 

it must be submitted no later than 60 

days prior to the approved attainment 

date for the area or, in the absence of an 

approved attainment date, no later than 

60 days prior to the applicable statutory 

attainment date for Serious areas (i.e., 

the end of the tenth year after 

designation). See 40 CFR 51.1005(b)(6). 

The EPA believes that this deadline is 

necessary due to its statutory obligation 

to determine whether the area attained 

by the attainment date. In order to 

preserve the possibility that EPA could 

review and take action on the new 

attainment plan for the area and the 

accompanying attainment date 

extension request prior to its deadline 

for making the attainment determination 

the EPA estimates that the 60-day 

deadline provides the minimum amount 

of necessary time. The EPA notes that 

during this time, it would have to 

ascertain the status of compliance with 

all requirements and commitments in 

the Moderate and initial Serious area 

attainment plans for the area, evaluate 

the state’s justification for the selection 

of the alternate attainment date 

(including modeling), and review 

provisions for the implementation of 

MSM). 

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58098 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

VII. Requirements Under CAA Section 

189(d) for PM2.5 Serious Areas That Fail 

To Attain the NAAQS by the Applicable 

Attainment Date 

Background. In the event that a 

Serious area fails to attain the PM2.5

NAAQS by the applicable attainment 

date, CAA 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.’’ 

In addition to the requirement for the 

submission of control measures 

providing for a 5 percent reduction in 

emissions of certain pollutants on an 

annual basis, the EPA interprets CAA 

section 189(d) as requiring the State to 

submit an attainment plan that includes 

the same basic statutory plan elements 

that are required for other attainment 

plans. Because section 189(d) does not 

include a specific provision specifying a 

new attainment date, the EPA relies on 

sections 179(d)(3) and 172(a)(2) of the 

CAA to establish the attainment date for 

such plans to be as expeditiously as 

practicable, and no later than five years 

from the effective date of the EPA’s 

determination that the area failed to 

attain. Pursuant to those provisions, the 

Administrator may also extend the 

attainment date to the extent the 

Administrator deems appropriate, for a 

period no greater than 10 years from the 

effective date of the EPA’s 

determination that the area failed to 

attain, considering the severity of 

nonattainment and the availability and 

feasibility of pollution control measures. 

The state must submit as part of the new 

attainment plan a justification 

explaining that it represents an 

attainment date that is as expeditious as 

practicable. 

A state must submit to the EPA its 

plan to meet the requirements of CAA 

section 189(d) in the form of a complete 

attainment plan submission that 

includes the following elements: (i) Base 

year and attainment projection year 

emissions inventory requirements; (ii) 

additional attainment plan control 

strategy requirements, including control 

measures and a demonstration that each 

year the area will achieve at least a 5 

percent reduction in emissions of direct 

PM2.5 or a 5 percent reduction in 

emissions of a PM2.5 plan precursor 

based on the most recent emissions 

inventory for the area; (iii) attainment 

demonstration and modeling; (iv) RFP 

plan and quantitative milestones; and 

(v) contingency measures. 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 CAA 

sections 172 and 189 of the CAA that 

have not already been satisfied. These 

elements are discussed in more detail in 

the following sections. 

A. Plan Due Dates 

1. Summary of Proposal 

The proposed rule indicated that 

under CAA section 189(d), the state 

would be required to submit the 

attainment plan for a Serious area that 

failed to attain the NAAQS by the 

Serious area attainment date within 12 

months after the applicable attainment 

date. 

2. Final Rule 

The final rule remains unchanged 

from the proposal. Section 189(d) of the 

CAA 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 ‘‘applicable attainment date.’’ 

The EPA finds that the most 

straightforward interpretation of the 

statutory language is that the state must 

submit a new attainment plan for the 

area—with all required elements— 

within 12 months after the missed 

applicable attainment date. Although 

the EPA may take up to 6 months to 

make a determination that the area 

failed to attain, the text of the statute 

ties the 12-month SIP due date to the 

missed attainment date, not to the date 

that the EPA determines that the area 

failed to attain. Because all attainment 

dates for implementation of the PM2.5

NAAQS under subpart 4 are expressed 

in terms of the end of a calendar year, 

the new due date for a SIP required 

under CAA section 189(d) also would be 

due on December 31—of the year 

following the area’s Serious area 

attainment date. This requirement is 

consistent with the manner in which the 

CAA section 189(d) SIP submission date 

has been interpreted for implementation 

of the PM10 NAAQS in the past. The 

EPA recognizes that this statutory 

timeline is shorter than for Moderate or 

Serious area attainment plans, but 

expects that, given the prior planning 

history for such areas, much of the 

analyses to support these new 

attainment plan submissions will be 

based on updates to previous analyses, 

which would require less time than 

generating new analyses. In any event, 

it is clear from the face of the statute 

that Congress intended that states with 

areas that fail to attain the NAAQS by 

the outermost statutory attainment date 

for Serious areas must proceed more 

quickly to revise their SIPs to provide 

for attainment of the NAAQS. 

3. Comments and Responses 

Any comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

B. Emissions Inventory Requirements 

1. Summary of Proposal 

The EPA also proposed that the 

inventory requirements under section 

189(d) for Serious areas that fail to 

attain by the attainment date should be 

the same as those for Moderate and 

Serious areas, but with a change to the 

appropriate year for the inventory. The 

EPA proposed that for these areas, 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. 

In addition, the EPA proposed an 

alternative approach that would allow 

the state to use an earlier year than one 

of the 3 years used to determine that the 

area failed to attain. As proposed, this 

alternative approach would require 

written justification that included an 

explanation of how the inventory 

modifications adequately incorporate 

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, and 

through implementation of MSM if 

appropriate. 

2. Final Rule 

The statute requires states to use an 

emissions inventory that meets the 

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

final rule recommends using an 

inventory for one of the 3 years for 

which air quality data were used to 

determine that the area failed to attain 

in order to meet this requirement. 

However it also allows the state to use 

an earlier inventory year under certain 

circumstances. 

As with all other attainment plan 

submissions required for Moderate and 

Serious PM2.5 nonattainment areas, a 

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state must develop its submission to 

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

most recent 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 CAA section 172(c)(3), 

which requires ‘‘a comprehensive, 

accurate, current inventory of actual 

emissions of the relevant pollutants’’ in 

the nonattainment area. Therefore this 

rule requires that the inventory 

submitted with an attainment plan to 

meet CAA section 189(d) requirements 

must also meet the EPA’s regulatory 

requirements for such emissions 

inventories as described earlier in this 

preamble under Section IV.B of this 

preamble (for Moderate area attainment 

plans) and Section VI.B of this preamble 

(for Serious area attainment plans). 

One important aspect of the emissions 

inventory required to be submitted with 

an attainment plan under CAA section 

189(d) is its role as the basis for 

calculating the emissions reductions of 

direct PM2.5 or any PM2.5 plan precursor 

necessary to satisfy the 5 percent annual 

reduction criterion of CAA section 

189(d). For this reason, the ‘‘most recent 

inventory’’ for the area must not only 

meet the criteria described for a base 

year inventory submitted pursuant to 

CAA section 172(c)(3) and in Section 

VI.B of this preamble, but it also must 

fully account for emissions reductions 

achieved to date through the 

implementation of all RACM and RACT, 

BACM and BACT, additional reasonable 

and feasible measures, and MSM (as 

applicable) 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 CAA section 189(d) 

and bring the area into attainment as 

expeditiously as practicable. 

To ensure that the inventory is 

representative of the nonattainment 

problem in the area current at the time 

of the CAA section 189(d) submission, 

the EPA strongly recommends that the 

inventory year be one of the 3 years 

from which monitored air quality data 

were 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 

control measures (e.g., BACM and BACT 

controls and additional feasible 

measures) for sources in the area may 

not be implemented until the beginning 

of the attainment year. Thus, using 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 control 

measures for Moderate and Serious 

areas. 

The EPA recognizes that the timing 

and resource requirements for inventory 

preparation may make it challenging in 

some cases for a state to use an 

inventory for a year that is 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. To address such cases, 

the final rule allows states to use an 

earlier inventory year in the plan, 

provided that (1) the year is selected in 

consultation with the appropriate EPA 

Regional Office, and (2) the state 

provides a written justification for 

selecting the earlier year in its SIP 

submission. See 51.1008(c)(1). At a 

minimum, the inventory must 

adequately incorporate 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, and MSM if appropriate. 

Because these emissions reductions may 

have occurred after the inventory year 

the state intends to use, adjustments to 

the original inventory for that year 

would need to be made to reflect those 

reductions. The written justification 

must also include an explanation of 

how those reductions have been 

incorporated into the inventory. In 

considering use of an ‘‘older’’ inventory, 

the EPA recommends that states weigh 

the possible impact of using an older 

inventory that could have higher 

emissions than a more current 

inventory. The state may be obligated to 

achieve a larger annual emissions 

reduction to satisfy the 5 percent annual 

reduction criteria of CAA section 189(d) 

than would otherwise be required if a 

newer inventory were used with lower 

emissions. 

3. Comments and Responses 

Any additional comments received on 

this section are addressed in the 

Response to Comments document found 

in the docket for this action. 

C. Pollutants To Be Addressed in the 

Plan 

1. Summary of Proposal 

The proposed rule indicated that to 

determine what pollutants need to be 

addressed in the attainment plan and 5 

percent requirement in CAA section 

189(d), the state could provide a 

demonstration to the EPA showing that 

a particular precursor does not 

significantly contribute to PM2.5 levels 

that exceed the standard. The proposal 

suggested that if the precursor 

demonstration is approved by the EPA, 

then the state would not be required to 

evaluate or adopt control measures for 

that precursor, nor would the state need 

to address the precursor in meeting the 

5 percent annual emissions reduction 

requirement in section 189(d). The 

proposal indicated that Section III of the 

preamble further discussed options 

describing optional precursor 

demonstrations. 

2. Final Rule 

The final rule remains relatively 

unchanged with respect to this issue. 

Section 189(d) of the CAA 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 

describes optional approaches by which 

a state could demonstrate that a PM2.5

precursor does not contribute 

significantly to PM2.5 levels that exceed 

the standard in the area, and thereby 

would not need to adopt control 

measures for that precursor in the area. 

The EPA also interprets the CAA 

generally to allow a state to provide 

such a ‘‘precursor demonstration’’ for 

the attainment plan required under 

section 189(d), even if the area has 

previously failed to attain the relevant 

NAAQS by the applicable Serious area 

attainment date. If the state has 

provided a demonstration with the 

previous Serious area attainment plan to 

establish that a precursor does not 

significantly contribute to PM2.5 levels 

for purposes of the attainment plan for 

the area, and it seeks to maintain the 

status of that precursor as not 

significantly contributing to PM2.5 levels 

in the area, the state would still need to 

provide an updated precursor 

demonstration for the new section 

189(d) SIP because emissions and 

atmospheric conditions will have 

changed since the previous 

demonstration was submitted, and the 

conclusions from any previous 

precursor demonstration may no longer 

be appropriate. See Section III of this 

preamble for more information about 

potential precursor demonstrations that 

could be conducted to show that a 

particular precursor does not contribute 

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191For example, see 69 FR 30006 (May 26, 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. 

significantly to PM2.5 levels that exceed 

the standard. 

3. Comments and Responses 

Any comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

D. Attainment Plan Control Strategy 

1. Background 

As for other PM2.5 NAAQS attainment 

demonstrations, the overarching 

requirement for the CAA section 189(d) 

control strategy is that it needs to 

provide for attainment of the standard 

as expeditiously as practicable. The 

strategy must include any additional 

measures (beyond those already adopted 

in previous SIPs for the area as RACM/ 

RACT, BACM/BACT, MSM (if 

applicable), for example) that are 

needed for the area to attain 

expeditiously. The plan must also 

demonstrate that the new attainment 

plan will at a minimum achieve an 

annual 5 percent reduction in emissions 

of direct PM2.5 or any PM2.5 plan 

precursor from sources in the area, 

based on the most recent emissions 

inventory for the area. However, it is 

important to emphasize that a CAA 

section 189(d) plan must require other 

control measures (even if beyond those 

sufficient to meet the annual 5 percent 

reduction requirement) that are needed 

in order to meet the overarching goal of 

attaining the standard as expeditiously 

as practicable. 

2. 5 Percent Annual Reduction in Direct 

PM2.5 or Any PM2.5 Plan Precursor 

a. Summary of Proposal. Section 

189(d) of the CAA requires 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.’’ 

Because the statute is ambiguous with 

regard to how this language should 

apply for the PM2.5 NAAQS, the EPA 

proposed two options for interpreting 

this provision. One option interpreted 

this language to require a 5 percent 

annual reduction in all pollutants that 

contribute to PM2.5, meaning direct 

PM2.5 and the four precursors (SO2,

NOX, VOC, and ammonia), or those 

precursors that are necessary to control 

in the area. A second option interpreted 

the language more literally, meaning 

that it required a 5 percent annual 

reduction of either direct PM2.5 or PM2.5

precursor emissions on an annual basis, 

and that a state could elect to control 

either direct PM2.5 or PM2.5 precursor 

emissions in a given year. (Note that 

under either proposed option, a 

precursor still could be excluded from 

control requirements if the state 

submitted a new precursor 

demonstration as part of the revised 

CAA section 189(d) implementation 

plan showing that the precursor does 

not contribute significantly to levels that 

exceed the relevant PM2.5 NAAQS, and 

such demonstration is approved by the 

EPA). 

b. Final Rule. One group of 

commenters supported the inclusion of 

direct PM2.5 and all precursors in the 

calculation of the annual emission 

reduction requirement because 

precursors typically play a significant 

role in PM2.5 formation, and they 

believed that allowing states to be able 

to pick and choose which pollutants to 

reduce would undermine efforts to 

attain most expeditiously. Other 

commenters supported the second 

option because they believe it follows a 

plain reading of the statute (i.e., it uses 

the word ‘‘or’’), and because it would 

allow a state to devote resources toward 

achieving emissions reductions in those 

pollutants that are most effective in 

reducing PM2.5 concentrations and thus 

in attaining the NAAQS most 

expeditiously. 

After considering comments on this 

issue, the EPA agrees that the second 

option is the more appropriate reading 

of the statute. When paired with the 

overarching requirement for the area to 

reach attainment of the NAAQS as 

expeditiously as practicable, and with 

provisions in the rule allowing a state to 

demonstrate that a precursor does not 

provide a significant contribution to 

PM2.5 levels, the EPA believes that such 

an interpretation is reasonable and 

would authorize states to focus emission 

reduction efforts on those pollutants 

that will be most effective for purposes 

of attainment in a given area. For 

example, interpreting the statutory 

provision to require emissions 

reductions in a specific precursor 

merely for purposes of meeting a 5 

percent requirement, without regard to 

whether the reductions would be 

effective for purposes of attainment, 

could be counterproductive to reducing 

the emissions of other pollutants that 

could result in earlier attainment. This 

interpretation of CAA section 189(d) is 

also consistent with past EPA actions 

for an area that failed to attain the PM10

Serious area attainment date.191

Thus, in applying the statutory 

language to implementation of the PM2.5

NAAQS in the final rule, the EPA 

interprets an ‘‘annual reduction in PM10

or PM10 precursor emissions within the 

area of not less than 5 percent of the 

amount of such emissions’’ to mean that 

an attainment demonstration for a 

Serious area that failed to attain by the 

attainment date must include control 

measures providing for a 5 percent 

annual reduction in direct PM2.5

emissions or in the emissions of any 

PM2.5 plan precursor. The EPA 

considered whether the statutory phrase 

‘‘precursor emissions’’ requires a 5 

percent reduction of each individual 

plan precursor in each year, but 

determined that such an interpretation 

was unnecessarily restrictive in light of 

the overarching requirement for states to 

adopt the control measures that will 

result in attainment as expeditiously as 

practicable, and is not compelled by the 

wording of the 5 percent requirement in 

the statute. Accordingly, the final rule 

requires an annual reduction of either 

direct PM2.5 or any single PM2.5

precursor. 

Because this requirement is an annual 

one, the final rule also authorizes the 

state to meet the 5 percent requirement 

to vary between direct PM2.5 and PM2.5

precursors, or among precursors, from 

year to year throughout the duration of 

the section 189(d) attainment plan, so 

long as the attainment plan provides for 

expeditious attainment and meets the 

other applicable attainment plan 

requirements. For example, in year 1 a 

state could provide for a 5 percent 

reduction of direct PM2.5, and in year 2 

could provide for a 5 percent reduction 

in a precursor, and so on. 

c. Comments and Responses. 

Comment: Some commenters suggested 

that a more appropriate approach would 

be to require a 5 percent annual 

reduction in PM2.5 ambient 

concentrations (rather than in pollutant 

emissions), and allow the state to meet 

this air quality target with any 

combination of emissions reductions. 

Response: The EPA does not find that 

this approach would be consistent with 

the statutory language in CAA section 

189(d), which clearly expresses the 

requirement in terms of emissions 

reductions (i.e., ‘‘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.’’) Moreover, the 

EPA is concerned that this approach 

would necessitate, on an annual basis, 

a complex modeling analysis or at the 

very least some other analytical 

approach to translate emissions to 

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192See Section IV.D.3 of this preamble for a 

discussion on sources of information for control 

measures. 

193 69 FR 30006 (May 26, 2004). 

ambient concentrations. The burdens of 

such analysis could be significant, and 

it is unclear what benefit would be 

realized from such an approach. States 

are already obligated to provide a 

modeled attainment demonstration as 

part of the new SIP submission to meet 

the requirements of section 189(d), and 

the 5 percent requirement is a separate 

requirement that the statute explicitly 

imposes in addition to that modeled 

attainment demonstration. For these 

reasons, the EPA is not adopting the 

commenter’s suggested air quality 

approach in the final rule. 

3. Calculating the 5 Percent Annual 

Reductions 

a. Summary of Proposal. The 

proposed rule provided an example of 

how annual reductions would be 

tracked under this provision, and it also 

provided another example describing 

how reductions in excess of the 5 

percent requirement in 1 year could be 

‘‘carried forward’’ to help meet the 

requirement in a future year. 

b. Final Rule. The previous section 2 

explains that the EPA interprets the 

statute to require a 5 percent annual 

reduction in direct PM2.5 emissions or in 

the emissions of any one PM2.5 plan 

precursor in each year, until attainment. 

The requisite minimum 5 percent 

emissions reduction level for any 

pollutant must be calculated from the 

total emissions of the pollutant 

contained in the most recent inventory 

for the area, as described earlier in this 

section. The requirement for a 5 percent 

annual reduction in any one pollutant, 

calculated based on the emissions levels 

in the most recent inventory, must then 

be achieved every year between the 

CAA section 189(d) plan submission 

date and the new projected attainment 

date for the area. 

For example, assume it is 2026, and 

based on monitoring data from years 

2023–2025, 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 CAA section 189(d) is 

for the year 2023. This inventory would 

serve as the base inventory for 

determining the 5 percent emissions 

reduction requirement under CAA 

section 189(d). If the state elects to 

reduce direct PM2.5 emissions each year 

of the plan (i.e., instead of choosing to 

reduce a precursor), and the most recent 

inventory (‘‘base inventory’’) indicates 

that emissions of direct PM2.5 from all 

sources in the area are 10,000 tons/year, 

then the area at a minimum would need 

to reduce emissions of direct PM2.5 by 

5 percent of the 2023 base inventory, or 

500 tons, each year until the area attains 

the NAAQS. Thus, in the first year 

following submission of the CAA 

section 189(d) plan for the area, 

emissions of direct PM2.5 could not 

exceed 9500 tons/year; in the second 

year, emissions could not exceed 9000 

tons/year; and so forth. Note that if the 

area needs emissions reductions beyond 

this amount (i.e., in direct PM2.5 or in 

PM2.5 plan precursors) in order to meet 

the overarching requirement of attaining 

the standard as expeditiously as 

practicable, then it must adopt and 

implement such control measures.192

Although CAA 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 maximize 

emissions reductions in earlier years 

and still meet the 5 percent per year 

requirement for subsequent years. 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 earlier, the 

annual reduction requirement for the 

area would be 500 tons/year from a base 

year emissions level of 10,000 tons/year. 

The required level after year 1 would be 

9500 tons/year, after year 2 the level 

would be 9000 tons/year, and so on. If 

the area reached a level of 8100 tons/

year by the end of year 3, then by the 

end of year 4 it would only need to 

reduce emissions by 100 tons/year to 

yield an emissions level of 8000 tons/

year. Thus, this approach will 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, as long as those 

emissions reductions are realized after 

the Serious area attainment date.193

The previous example addresses a 

situation where the state chooses to 

reduce only direct PM2.5. In that 

example, the 5 percent annual reduction 

amount for any year would be 5 percent 

of the 2023 PM2.5 emission inventory 

amount of 10,000 tons. The final rule 

allows the state to meet its 5 percent 

reduction each year in terms of reducing 

direct PM2.5 or any PM2.5 plan 

precursor. Thus, if the area had a 2023 

emission inventory that included 5000 

tons of each of the four PM2.5

precursors, and if the state chose to 

meet its ‘‘5% reduction’’ obligation in a 

particular year by reducing SO2, it 

would need to achieve emissions 

reductions of 250 tons of SO2 in that 

year. 

The EPA is also clarifying its 

interpretation of the statutory language 

under CAA 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 

clarification is intended to make clear 

that even if a state is late in submitting 

its CAA section 189(d) plan, the area 

must still achieve its annual 5 percent 

emissions reductions beginning from 

the date by which the state is required 

to make its CAA section 189(d) plan 

submission, not by some later date. 

Because attainment dates for PM2.5

nonattainment areas established under 

subpart 4 occur at the end of the 

calendar year, any CAA 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. 

c. Comments and Responses. Any 

additional comments received on this 

section are addressed in the Response to 

Comments document found in the 

docket for this action. 

4. Additional Guidance on CAA Section 

189(d) Control Measures 

The EPA believes that an appropriate 

starting point for a state to identify 

measures to provide for attainment and 

to meet 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 to be identified as part 

of the RACM and RACT determination 

process, the BACM and BACT 

determination process, or the MSM 

determination process (if appropriate) 

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. Control measures that the state 

identified but did not previously adopt 

may be likely measures for inclusion in 

an attainment plan to meet the 

requirements of section 189(d). 

However, for purposes of meeting the 

requirements of CAA section 189(d), the 

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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. 

In addition, a state may include in the 

CAA section 189(d) plan control 

strategy for the area any control 

measures triggered as contingency 

measures after the 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

emissions or in emissions of any one 

PM2.5 plan precursor, 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 

triggered contingency measures may be 

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 CAA 

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. As 

explained previously, however, the EPA 

interprets the statute to require that any 

new 189(d) submission must meet all 

the statutory requirements applicable to 

all submissions, including the 

requirement to identify contingency 

measures. Thus, if contingency 

measures from the Serious area 

attainment plan are relied on in the new 

attainment demonstration as part of the 

control strategy, then the state must 

submit additional contingency measures 

for the CAA section 189(d) attainment 

plan. See 40 CFR 51.1003(c)(1)(vii). 

5. 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 annual reductions in emissions 

of direct PM2.5 or any PM2.5 plan 

precursor, the final rule requires that a 

state must submit information about the 

new control strategy for an area subject 

to section 189(d) in a manner consistent 

with the requirements described in 

section VI.D.3. 

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—which in the case of 

189(d) plans is also 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 

CAA section 189(d) plan base year 

emissions inventory information as a 

necessary part of the control strategy 

submission and as one element of the 

state’s CAA section 189(d) plan due 12 

months after the missed attainment date 

for the area. In addition, the state must 

provide information as part of any 

attainment plan submitted to meet the 

requirements of CAA 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. 

E. Modeling for Attainment 

Demonstrations 

Section 189(d) of the CAA 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 same general requirements for 

attainment demonstrations and 

modeling that apply to Moderate area 

plans and Serious area plans due under 

CAA sections 189(a) and 189(b) should 

also apply to CAA section 189(d) 

attainment plans. However, the EPA is 

including additional requirements in 

the final rule specific to plans submitted 

pursuant to CAA section 189(d), as 

described in the following sections. 

1. Attainment Demonstrations for 

Serious Areas That Fail To Attain the 

NAAQS by the Applicable Attainment 

Date 

a. Summary of Proposal. The EPA 

proposed attainment demonstration 

modeling requirements for Serious areas 

that fail to attain the NAAQS by the 

applicable attainment date. See Section 

VI.E of this preamble, for more details 

on Serious area attainment 

demonstrations. 

b. Final Rule. The final rule 

requirements are unchanged from the 

proposal with respect to this 

requirement. Attainment 

demonstrations for Serious areas subject 

to CAA section 189(d) requirements 

must consist of: (i) Technical analyses 

such as base year and future year 

modeling of emissions that identify 

sources and quantify their emissions 

that are contributing to violations of the 

PM2.5 NAAQS; (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 (iii) 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 CAA 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. 

c. Comments and Responses. Any 

comments received on this section are 

addressed in the Response to Comments 

document found in the docket for this 

action. 

2. Air Quality Modeling Required for 

Serious Areas Subject to the 

Requirements of CAA Section 189(d) 

a. Summary of Proposal. The EPA 

proposed that states are required to 

submit air quality modeling in support 

of an attainment demonstration for a 

nonattainment area subject to the 

requirements of CAA section 189(d). 

b. Final Rule. The final rule 

requirements are unchanged from the 

proposal with respect to this issue. 

States are required to submit air quality 

modeling in support of an attainment 

demonstration for a Serious 

nonattainment area subject to the 

requirements of CAA 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 or any PM2.5 plan precursor, 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. 

c. Comments and Responses. Any 

comments received on this section are 

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194Note 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. 

195For more information on PM2.5 precursor 

requirements, see CAA 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). 

196A 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. 

197 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. 198 Ibid. 

addressed in the Response to Comments 

document found in the docket for this 

action. 

3. Future Year(s) To Be Modeled in 

Attainment Demonstrations 

a. Summary of Proposal. The EPA 

proposed that a state performing a 

modeling analysis for a plan submitted 

under CAA 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 calendar 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. 

b. Final Rule. 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 CAA section 189(d) and must 

do so according to the provisions of 

CAA 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. In addition, 

the EPA may extend the attainment date 

by up to 5 additional years (thus up 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 EPA 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 that takes into 

account emissions growth, known 

controls (including any controls that 

were previously determined to be 

RACM and RACT, BACM and BACT, 

and MSM if appropriate, for the area), 

the 5 percent per year emissions 

reductions required by CAA 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 CAA 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.194

For a PM2.5 nonattainment area 

subject to CAA section 189(d), the state 

must 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. 

c. Comments and Responses. Any 

comments received on this section are 

addressed in the Response to Comments 

document found in the docket for this 

action. 

4. Attainment Year Motor Vehicle 

Emissions Budgets 

As with all other PM2.5 NAAQS 

attainment plans, the transportation 

conformity rule requires that attainment 

plans for areas subject to CAA 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.195 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.196 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, unless the 

EPA approves the state’s use of an 

alternative model.197

F. RFP Requirements 

1. Specific Requirements 

a. Summary of the Proposal. The EPA 

proposed to determine that a state has 

satisfied the RFP requirement if the state 

submits an approvable control strategy 

under CAA section 189(d) that 

demonstrates that the state will achieve 

at least 5 percent reductions in direct 

PM2.5 or PM2.5 precursor emissions from 

sources in the area annually until 

attainment. Additionally, the EPA 

proposed 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 plan 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).198

b. Final Rule. The EPA is finalizing 

RFP requirements for attainment plans 

required pursuant to CAA section 

189(d) that are similar to other Serious 

area RFP requirements discussed in 

section VI.F of this preamble. The EPA 

is providing similar guidance regarding 

how to prepare an RFP analysis, RFP 

projected emissions, geographic 

coverage of emission sources for RFP, 

and RFP requirements for multi-state 

nonattainment areas. 

The RFP analysis must contain 

appropriate information to demonstrate 

that the state will achieve the emissions 

reductions from the control strategy 

necessary to result in generally linear 

reductions in emissions and provide for 

expeditious attainment as discussed in 

Section VII.D of this preamble. As with 

other Serious area RFP analyses, the 

state may consider PM2.5 plan precursor 

emissions reductions in the aggregate 

for RFP purposes in a 189(d) area. 

The state’s RFP analysis must include 

three components: (1) An 

implementation schedule for control 

measures on sources in the 

nonattainment area, (2) RFP projected 

emissions for each applicable 

quantitative milestone year (discussed 

in Section VII.G of this preamble), based 

on the anticipated control measure 

implementation schedule; and (3) an 

analysis that demonstrates that this 

schedule of aggregate emissions 

reductions achieves sufficient progress 

toward attainment between the 

applicable baseline year to the 

attainment year. For additional 

discussion of each of the components of 

the RFP analysis, refer to Section IV.F 

of this preamble. See 40 CFR 51.1012(a). 

In the proposal, the EPA proposed an 

option to require at least 5 percent 

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58104 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

199 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. 

emissions reductions in direct PM2.5 and 

all PM2.5 plan precursor from sources in 

the area annually until attainment to 

meet the separate RFP requirement for 

attainment plans. However, some 

commenters did not agree that EPA 

should consider an area meeting the 5 

percent requirement under CAA section 

189(d) to automatically have satisfied 

the RFP requirement. The EPA agrees 

with this comment and is therefore not 

finalizing an approach to the RFP 

requirement that is tied to the 5 percent 

requirement. Instead, the final RFP 

requirement will be tied to progress 

toward expeditious attainment (which 

the EPA recommends should be 

generally linear but may also be 

stepwise with appropriate justification), 

just as it is for all other types of 

Moderate and Serious area plans for 

PM2.5 as summarized in the previous 

paragraph. The emissions reductions 

that a state achieves for purposes of 

meeting the 5 percent requirement may 

also be counted towards meeting the 

separate RFP requirement, but the EPA 

does not believe that meeting the 5 

percent requirement would 

automatically equate to meeting the RFP 

requirement. That determination 

requires the separate evaluations 

required for the RFP analysis. 

The EPA requires that the applicable 

baseline year for the RFP analysis must 

be the same year as that represented by 

the latest base year inventory for the 

Serious area. The projected attainment 

date should be as expeditiously as 

practicable and is discussed further in 

Section VII.I of this preamble. The RFP 

analysis must clearly convey how the 

schedule for implementing the control 

strategy will provide for generally linear 

or stepwise progress towards 

attainment. If stepwise progress is more 

appropriate for the specific 

nonattainment area, the state is required 

to submit a clear rationale and 

supporting information to explain why 

generally linear progress towards 

attainment in the area is not appropriate 

(e.g., due to the nature of the 

nonattainment problem, the types of 

sources contributing to PM2.5 levels in 

the area, and the ability to perform 

timely implementation of control 

measures). Further, if a stepwise 

approach is needed, this does not 

relieve the state of the requirements of 

CAA section 189(d). As stated earlier, 

the EPA requires that a section 189(d) 

plan must include in its RFP analysis 

the anticipated emissions reductions 

expected to be achieved through the 

implementation of control measures 

required by the control strategy 

described in Section VII.D of this 

preamble. Further, the optional air 

quality analysis discussed in Section 

IV.F of this preamble is also available 

for use by a state preparing a section 

189(d) plan. 

Additionally, the EPA requires states 

to establish motor vehicle emissions 

budgets for direct PM2.5 and PM2.5 plan 

precursors using the latest planning 

assumptions and the latest approved 

motor vehicle emissions model 

available at the time that the 189(d) plan 

is developed.199 See 40 CFR 51.1012(a).It 

is also important to note that if a section 

189(d) area is multi-state or multijurisdictional, the states or jurisdictions 

comprising the area must provide a 

coordinated approach to meeting the 

RFP requirement for the shared area. For 

further information, see Section IV.F.5 

of this preamble. See 40 CFR 51.1012(b). 

c. Comments and Responses. Any 

additional comments received on RFP 

are addressed in the Response to 

Comments document found in the 

docket for this action. 

G. Quantitative Milestones 

1. Specific Requirements 

a. Summary of the Proposal. The 

proposal indicated that quantitative 

milestones would need to be achieved 

every 3 years until the area attains the 

relevant NAAQS, similar to proposed 

requirements for Moderate area plans 

and other types of Serious area plans. In 

the proposal, the EPA stated that, at a 

minimum, quantitative milestones 

selected for an attainment plan 

submitted under CAA section 189(d) 

would need to demonstrate a reduction 

of at least 15 percent (i.e., 5 percent for 

each year in the 3-year period) in 

emissions of direct PM2.5 and PM2.5 plan 

precursors below those emissions 

reported in the most recent inventory 

for the area. The proposal identified 

requirements for direct PM2.5 and 

precursors, to be consistent with the 

RFP proposal. The EPA proposed that 

attainment plans developed pursuant to 

CAA section 189(d) would have to 

contain quantitative milestones 

beginning at 13.5 years or 16.5 years 

from designation (depending on 

whether the section 189(d) plan would 

be due before or after the 13.5 year 

mark), and every 3 years thereafter until 

the attainment date for the area. 

The EPA also proposed that the 

requirements for quantitative 

milestones, described in Section VI.G of 

this preamble, should also apply to 

quantitative milestones submitted with 

any revised Serious area attainment 

plan pursuant to CAA section 189(d). 

b. Final Rule. 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 CAA section 

189(c). These quantitative milestones 

should track the progress being made in 

the nonattainment area in the 

implementation of specific control 

measures in the SIP, and may 

potentially be in the form of metrics for 

tracking air quality improvement or 

emissions reductions over time. The 

EPA wishes to clarify that the 

quantitative milestones for a section 

189(d) plan are designed to track RFP, 

not solely to track progress in achieving 

the minimum 5 percent annual emission 

reduction requirement in this section of 

the CAA. The RFP discussion in the 

previous section noted that in some 

cases, the state may need to adopt 

additional emission reduction measures 

(beyond those existing or new measures 

that will meet the 5 percent emission 

reduction requirement) in order for the 

plan to meet the overarching 

requirement to attain the standard as 

expeditiously as practicable. Thus, the 

RFP plan and quantitative milestones 

must be designed to track progress 

based on the overall set of control 

measures needed for expeditious 

attainment. 

The quantitative milestones need to 

be achieved every 3 years until the area 

attains the relevant NAAQS. Therefore, 

at a minimum, the final rule requires 

that quantitative milestones selected for 

an attainment plan submitted under 

CAA section 189(d) need to track 

progress in the implementation of 

control measures required to achieve 

RFP in emissions reductions of direct 

PM2.5 and/or all PM2.5 plan precursors 

described in the previous section. The 

CAA section 189(d) plan must contain 

quantitative milestones to be achieved 

every 3 years, beginning with a 

milestone at either 13.5 years or 16.5 

years from the area’s date of 

designation. If the attainment plan is 

due prior to a date 13.5 years from 

designation of the area, then the plan 

shall contain milestones to be achieved 

by no later than a milestone date of 13.5 

years from the date of designation of the 

area, and every 3 years thereafter, with 

the final milestone being the first 3-year 

milestone date falling after the 

applicable attainment date. If the 

attainment plan is due later than a date 

13.5 years from designation of the area, 

then the plan shall contain milestones 

to be achieved by no later than a 

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200See LEAN v. EPA, 382 F.3d 575 (5th Cir. 

2004). 

milestone date of 16.5 years from the 

date of designation of the area, and 

every 3 years thereafter, with the final 

milestone being the first 3-year 

milestone date falling after the 

applicable attainment date. See 40 CFR 

51.1013(a)(3). 

The EPA is also finalizing that the 

requirements for quantitative milestones 

described in Section VI.G of this 

preamble shall also apply to 

quantitative milestones submitted with 

any revised attainment plan pursuant to 

CAA section 189(d), including but not 

limited to, the construction, content, 

reporting requirements and a 

quantitative milestone that specifically 

tracks implementation of control 

measures identified in the plan to attach 

the standard as expeditiously as 

practicable. See 40 CFR 51.1013(a)(3). 

c. Comments and Responses. Any 

additional comments received on 

quantitative milestones are addressed in 

the Response to Comments document 

found in the docket for this action. 

H. Contingency Measures 

1. Summary of the Proposal 

The EPA proposed that contingency 

measures for attainment plans under 

CAA section 189(d) for Serious areas 

that fail to attain the NAAQS by the 

applicable attainment date must meet 

the same criteria as contingency 

measures for a Serious area attainment 

plan outlined in Section VI.H of this 

preamble. The EPA also proposed that 

the contingency measures should 

achieve approximately 1 year’s worth of 

emissions reductions. 

2. Final Rule 

All PM2.5 attainment plans, including 

plans for areas subject to CAA section 

189(d), must contain contingency 

measures that are consistent with CAA 

section 172(c)(9). Section VI.H of this 

preamble describes the EPA’s criteria for 

contingency measures for a Serious area 

attainment plan, and contingency 

measures for a section 189(d) plan must 

meet the same criteria. The final rule 

reiterates the EPA’s longstanding policy 

that contingency measures should 

provide for emissions reductions 

approximately equivalent to 1 year’s 

worth of reductions needed for RFP. 

The statutory contingency measure 

requirement at CAA section 172(c)(9) is 

not superseded or subsumed by any 

requirement under subpart 4. Thus, 

contingency measures are required as 

part of a state’s attainment plan 

submission under section 189(d). 

Accordingly, the final rule requires the 

criteria for identifying and selecting 

contingency measures for a section 

189(d) submission that are the same as 

for Moderate or Serious area attainment 

plans. 

Specifically, the EPA is finalizing that 

the following requirements must be met 

in order for contingency measures to be 

approvable as part of a state’s 

attainment plan submission for 

purposes of section 189(d): 

(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, failure to 

meet any quantitative milestone, failure 

to submit a quantitative milestone 

report or failure to meet the standard by 

the applicable 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 should 

consist of control measures that are not 

otherwise included in the control 

strategy for the SIP, or that achieve 

emissions reductions not otherwise 

relied upon in the control strategy for 

the area. 

(4) Contingency measures should 

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 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. 

The EPA is also finalizing its proposal 

to allow a state to rely on contingency 

measures that achieve emissions 

reductions on sources located outside 

the nonattainment area, but within the 

state 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 or Serious areas, the EPA 

allows a state under these circumstances 

to rely on additional reductions from 

federal or local measures already 

scheduled for implementation as part or 

all of their contingency measures. The 

EPA could 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 

nonattainment provisions (e.g., such as 

to meet BACM/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.200 As with 

contingency measures for Moderate area 

or Serious area attainment plans, the 

EPA requires that the emissions 

reductions associated with contingency 

measures for attainment plans under 

section 189(d) should be approximately 

equivalent to 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. See 40 

CFR 51.1014(b)(2). 

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 any new control measures to achieve 

the requisite minimum 5 percent 

reductions in direct PM2.5 or PM2.5 plan 

precursor emissions necessary for 

expeditious attainment. However, for an 

area that has not implemented MSM, 

states could identify potential 

contingency measures by reviewing 

attainment plans for other 

nonattainment areas. The state should 

also reevaluate control measures that 

were identified previously as 

technologically or economically 

infeasible for the area, or otherwise 

removed from consideration as part of 

the RACM/RACT or BACM/BACT 

process. Additionally, states can review 

other sources of control measure 

information, such as the RBLC (a central 

database of air pollution control 

technology information) and the EPA’s 

Menu of Control Measures document 

available at http://www3.epa.gov/ttn/

naaqs/pdfs/

MenuOfControlMeasures.pdf. See 40 

CFR 51.1014. 

3. Comments and Responses 

Comment: Commenters stated that 

because 189(d) requires annual 

emissions reductions of not less than 5 

percent, then the EPA cannot assume 

that 1 year’s worth of emissions 

reductions will be no greater than 5 

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201For 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. 

percent. The commenter stated that only 

if an area shows that the 5 percent 

reduction requirement of CAA section 

189(d) is greater than what would be 

necessary to demonstrate RFP annually 

may an area assume that contingency 

measures must achieve only the 5 

percent target. 

Response: The EPA agrees with the 

commenters. As discussed earlier and in 

Sections IV.H and VI.H of this preamble, 

contingency measures should equal 

approximately 1 year’s worth of 

emissions reductions necessary to 

achieve RFP for the area. The EPA notes 

that RFP might require more than the 5 

percent emissions reductions required 

by CAA section 189(d). Therefore, if 

contingency measures should equal 

approximately 1 year’s worth of 

emissions reductions necessary to 

achieve RFP, then those contingency 

measures should provide more than 5 

percent of emissions reductions in 

direct PM2.5 or aggregate PM2.5 plan 

precursors. 

Comment: Commenters suggested 

that, similar to the ozone program, the 

EPA should consider whether the 

contingency measures for an area that 

failed to attain by the deadline for 

Serious areas could anticipate the 

development of proven new technology, 

with a requirement to add further 

contingency measures if such 

technology does not develop as 

anticipated. 

Response: The EPA disagrees with the 

commenters, noting that CAA section 

182(e)(5) provides this flexibility for 

Extreme areas that are nonattainment for 

the ozone NAAQS. That section of the 

Act falls within subpart 2 of part D, 

which identifies additional contingency 

measure provisions applicable only in 

ozone nonattainment areas. Subpart 4 

does not contain a provision similar to 

that in subpart 2. Therefore, CAA 

section 172(c)(9) applies and, as 

explained earlier, that provision 

requires contingency measures be 

included in the attainment plan. 

Comment: Commenters requested the 

EPA to allow a state to demonstrate, in 

the alternative, that its contingency 

measures will achieve a 5 percent 

reduction in PM2.5 ambient 

concentrations, and that such 

reductions can be obtained by reducing 

direct PM2.5 emissions, emissions of one 

or more precursors, or both. 

Response: The EPA is finalizing the 

optional air quality analysis as an 

additional component of the RFP plan, 

as previously discussed in Section IV.F 

of the preamble. Therefore, although the 

state could demonstrate that its 

contingency measures will achieve a 5 

percent reduction in PM2.5 ambient 

concentrations, the EPA notes that this 

optional analysis does not relieve the 

requirements of 189(d). Specifically, the 

area remains required to achieve an 

emissions reduction of not less than 5 

percent of direct PM2.5 or any PM2.5 plan 

precursor. 

I. Attainment Dates 

1. Summary of the Proposal 

The proposed rule indicated that the 

new attainment date for an area that 

failed to attain by the Serious area 

attainment date would be governed by 

sections 172(a)(2) and 179(d)(3) of the 

CAA. Under the proposal, the 

attainment date would be as 

expeditiously 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 based on certain 

criteria. 

2. Final Rule 

As described in the proposal, the final 

rule includes the overarching 

requirement for a Serious area that 

failed to attain by the previous 

attainment date to establish a new date 

for attaining the standard as 

expeditiously as practicable. However, 

neither CAA section 189(d) nor other 

sections in subpart 4 explicitly establish 

or provide the authority to establish a 

new attainment date for the area. 

Therefore, once an area is beyond the 

attainment dates that Congress specified 

in subpart 4 for the PM10 NAAQS, the 

EPA must look to other provisions of 

part D of the CAA to provide authority 

for a new attainment date. Sections 

179(d)(3) and 172(a)(2) of the CAA 

provide generally applicable attainment 

dates that fill the gap in the statute left 

for areas subject to the requirements of 

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

nonattainment area subject to CAA 

section 189(d) requirements, the EPA 

must establish a new attainment date 

according to the provisions of CAA 

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.201

Applying these provisions, the final 

rule therefore provides that the new 

attainment date in a CAA section 189(d) 

plan 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 CAA 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. The EPA 

will consider the state’s proposed 

attainment date for the area based on its 

revised attainment demonstration and 

modeling of its updated control strategy, 

and other relevant facts and 

circumstances for the area, in order to 

identify the most expeditious 

attainment date practicable for the area. 

3. Comments and Responses 

Comment: Some commenters stated 

that the EPA should set a date that is as 

expeditious as practicable, but if it takes 

longer than 10 more years to attain, the 

EPA may approve such a plan, as long 

as the minimum 5 percent reduction 

requirement is met. The commenter 

stated that this is the plain meaning of 

CAA section 189(d)’s reference that the 

plan shall provide for at least 5 percent 

reductions ‘‘from the date of such 

submission until attainment.’’ 

Response: The EPA does not agree 

with the commenter. As indicated 

earlier, the EPA’s longstanding 

interpretation is that the statutory 

provisions of CAA sections 172(c)(2) 

and 179(d)(3) govern the attainment 

date for new plans required under CAA 

section 189(d) for Serious areas that 

previously fail to attain by the Serious 

area attainment date. Under certain 

circumstances, these provisions would 

allow for an attainment date up to 10 

years from the effective date of a finding 

of failure to attain, but would not allow 

for an attainment date longer than that. 

VIII. NNSR Requirements for PM2.5

Nonattainment Areas 

A. Background 

1. 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 

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202The federal PSD program enables the EPA or 

a state that has been delegated authority by the EPA 

to issue PSD permits. 

203More information on the PSD requirements for 

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

responses to those comments is contained in the 

January 15, 2013 Federal Register document (78 FR 

3086, beginning at page 3251). 

204See the EPA’s final rule to implement certain 

aspects of the 1990 CAA Amendments relating to 

NSR and PSD, published in the Federal Register on 

November 29, 2005 (70 FR 71612, 71677 and 

71678). 

205States with designated PM2.5 nonattainment 

areas for the 1997 and 2006 PM2.5 standards were 

required to submit SIPs, including a NNSR program 

satisfying the requirements of the 2008 PM2.5 NSR 

Rule, by May 16, 2011, 3 years from the date of 

publication of that 2008 rule. See 73 FR 28321 (May 

16, 2008), at page 28342. States must continue to 

implement those approved state programs 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. 

206Appendix 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 applications for 

construction permits for new or modified sources 

be disapproved where the source would interfere 

with attainment of the NAAQS, see 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 CAA section 110(n)(3)), 

it left in place the use of the interim NNSR program 

under Appendix S. 

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.a and 

b of this preamble, the preconstruction 

review of each proposed new major 

stationary source and major 

modification generally is carried out on 

a pollutant-specific basis and the 

permitting 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. 

a. Prevention of Significant 

Deterioration. 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 locating in areas 

designated attainment or unclassifiable 

for any NAAQS. These requirements 

constitute the Prevention of Significant 

Deterioration (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).202 The EPA last amended the 

PSD regulations for PM2.5 on January 15, 

2013, in the final rule revising the PM2.5

NAAQS.203 This final rule does not 

relate to the PSD program, nor does it 

amend the PSD regulations. 

b. Nonattainment New Source Review. 

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 locating in designated 

nonattainment areas, referred to as the 

Nonattainment New Source Review 

(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 CAA section 172(c)(5), which 

requires preconstruction and operating 

permits for new major stationary 

sources and major modifications 

locating in nonattainment areas. Section 

173 of the CAA 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 published at 73 FR 28321, 

May 16, 2008. 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, 

CAA 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 

CAA section 173 of subpart 1. Subpart 

4 also includes some additional 

preconstruction review requirements, 

which, until the court’s decision in 

NRDC v. EPA, the EPA has only applied 

to major sources of PM10 located in 

PM10 nonattainment areas. The specific 

NNSR requirements contained in both 

subparts 1 and 4 are described later, 

including the changes that we are 

making in this final rule to the NNSR 

regulations to address these 

requirements with respect to PM2.5. 

2. Federal NNSR Regulations 

The EPA has adopted numerous 

NNSR regulations in 40 CFR parts 51 

and 52, including § 51.165; part 51 

Appendix S; and § 52.24. An approvable 

NNSR program in a state’s 

implementation plan must, at a 

minimum, meet the applicable program 

requirements set forth in the federal 

NNSR provisions at 40 CFR 51.165, 

which for PM2.5 have been based on 

changes to that section made by the 

2008 PM2.5 NSR Rule. States with 

designated nonattainment areas for a 

particular pollutant are required to 

adopt regulations consistent with those 

applicable plan requirements, including 

any subsequent rule changes that the 

EPA may make, 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 or 

the EPA, as appropriate. 

The EPA interprets the requirement 

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

the CAA that states regulate the 

construction and modification of 

sources to apply as of the effective date 

of an area’s designation to 

nonattainment for a given pollutant.204

Although CAA 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 the EPA approves a 

state’s NNSR program to address a given 

pollutant, the EPA regulations at 40 CFR 

52.24(k) authorize states to apply 40 

CFR part 51, Appendix S, known as the 

Emission Offset Interpretative Ruling or 

simply the Offset Ruling, during the 

interim period.205 206

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. First, any state 

that already has a SIP-approved NNSR 

program for PM2.5 (e.g., where the state 

has had other PM2.5 nonattainment areas 

for which the EPA has approved an 

NNSR program) should continue to 

apply those permitting requirements in 

the interim. Second, any state that lacks 

an approved NNSR program for PM2.5

may rely upon the NNSR provisions in 

Appendix S until the EPA approves that 

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207See 40 CFR 51.165(a)(1)(v)(A), (a)(2)(ii)(A). As 

will be explained in ensuing discussions, the 

nonattainment pollutant and any applicable 

precursors for that pollutant are considered 

separately for NNSR applicability purposes. 

208The basic NNSR requirements are set forth in 

CAA section 173 of subpart 1. Subpart 4 adds a 

more stringent definition of ‘‘major source’’ for 

PM10 sources locating in PM10 nonattainment areas 

classified as Serious and sets forth provisions for 

the regulation and potential exemption from 

regulation 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 to 

PM2.5. 

209See 62 FR 38652 (July 18, 1997). 

210See 71 FR 61144 (October 17, 2006). 

211See 73 FR 28321 (May 16, 2008). 

212See 72 FR 20589. 

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

concluded that SO2 should be regulated as a 

precursor for PM2.5 in all areas. In addition, the EPA 

or the states could rebut the initial presumptions 

regarding NOX, VOC or ammonia on an area-by-area 

basis with a demonstration approved by the 

Administrator and thus reverse any of those 

presumptions in the state’s implementation plan for 

that area. See 73 FR 28327. 

state’s SIP submission 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. 

a. General Applicability. Stationary 

sources are considered to be ‘‘major’’ 

sources based on the amount of a given 

pollutant (or a precursor for that 

pollutant) the source emits or has the 

potential to emit, as defined by the 

statute. New major stationary sources 

are subject to the NNSR requirements 

when they are major for the pollutant 

(or a precursor for that 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 same nonattainment 

pollutant (or same precursor for that 

pollutant).207

For each proposed new major 

stationary source and major 

modification, the general NNSR 

requirements to be included in a state’s 

SIP include the following: (i) The 

installation and continuous operation of 

pollution control technology that 

complies with the Lowest Achievable 

Emission Rate (LAER); (ii) the 

acquisition of creditable emissions 

reductions to adequately offset the 

proposed emissions increase of the 

nonattainment pollutant; and (iii) a 

certification that all other sources 

owned by the applicant are complying 

with all applicable requirements of the 

CAA.208 These NNSR requirements 

apply as of the effective date of the 

designation of an area as nonattainment 

for the pollutant and must be satisfied 

by a proposed major new source or 

major modification locating in such area 

as a prerequisite for obtaining a NNSR 

permit. 

b. Historical Overview of NNSR for 

PM10 and PM2.5 National Ambient Air 

Quality Standards (NAAQS). 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 PM10.209 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.210 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.211 The 

EPA included specific provisions in the 

2008 PM2.5 NSR Rule that 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 

limited to 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 that, under 

the appropriate conditions, NOX, SO2, 

VOC and ammonia could each 

contribute to the formation of PM2.5 in 

the ambient air. However, the EPA 

issued regulations that did not require 

states to subject all of these precursors 

to regulation as part of the attainment 

plan or NSR permitting requirements 

applicable in a given nonattainment 

area.212 Instead, 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.213

As described in Section II.B of this 

preamble, in January 2013 the court’s 

decision in NRDC v. EPA held that the 

EPA erred in implementing the PM2.5

NAAQS under the general 

implementation requirements in subpart 

1, rather than relying on the 

implementation requirements specific to 

PM10 in subpart 4 of the CAA. 

Accordingly, the court directed the EPA 

to comply with the requirements of 

subpart 4 when developing 

implementing regulations for PM2.5

nonattainment areas. 

The NRDC decision has specific 

implications for implementing the 

NNSR program for PM2.5. Two 

provisions of subpart 4 impose 

additional requirements on NNSR plans 

developed to address sources locating in 

areas designated nonattainment for 

PM2.5. The first relates to the definition 

of ‘‘major stationary source’’ that applies 

to areas initially designated as Moderate 

nonattainment areas and subsequently 

reclassified as Serious. In such areas, 

section 189(b)(3) of the CAA defines the 

major source threshold as 70 tpy of 

PM10. The second relevant subpart 4 

provision governs the treatment of major 

sources of PM10 precursors. As 

previously described in Section III of 

this preamble, section 189(e) of the CAA 

requires that the control requirements 

applicable to major stationary sources of 

PM10 also apply to major stationary 

sources of PM10 precursors, unless the 

Administrator determines that such 

sources of PM10 precursors do not 

contribute significantly to PM10 levels 

that exceed the standard in that area. 

The EPA’s proposed amendments to 

address the subpart 4 requirements with 

respect to PM2.5 and the EPA’s 

responses to comments received on its 

proposal are summarized in the relevant 

subsections later. 

It is worth noting that the 2008 PM2.5

NSR Rule promulgated new NSR 

requirements for implementation of 

PM2.5 in both nonattainment areas 

(NNSR) and attainment/unclassifiable 

areas (PSD). As subpart 4 includes 

requirements only pertinent to 

nonattainment areas, the EPA does not 

consider the portions of the 2008 PM2.5

NSR Rule that address requirements for 

PM2.5 attainment and unclassifiable 

areas to be affected by the court’s 

opinion in NRDC v. EPA. Therefore, the 

EPA did not propose to revise any PSD 

requirements promulgated in the 2008 

PM2.5 NSR Rule in order to comply with 

the court’s decision. 

B. Final NNSR Requirements for PM2.5

Nonattainment Areas 

This section provides a description of 

the changes that the EPA is making to 

the NNSR requirements for PM2.5 that 

are contained in 40 CFR 51.165, which 

provides the minimum requirements for 

a NNSR program under an approved 

implementation plan, and in Appendix 

S, which serves as an interim NNSR 

permitting program pending approval of 

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214The EPA explained earlier in this preamble 

that the court’s 2013 decision in NRDC v. EPA 

reasoned that the EPA’s approach to precursors in 

the 2007 and 2008 PM2.5 regulations had the effect 

of reversing the presumption embodied with 

subpart 4 at CAA section 189(e) that a state should 

regulate major sources of all PM precursors unless 

the state has made a specific showing why 

regulation of sources of a particular precursor is not 

necessary. 

a state’s SIP to address NNSR 

requirements for a particular pollutant. 

For both sets of regulations, we will 

describe the changes that were 

proposed, the final requirements, the 

comments received, and the EPA’s 

responses to them. 

1. 40 CFR 51.165 

In this final rule, as explained in more 

detail later, the EPA is making the 

following revisions that affect the NNSR 

regulations for PM2.5 at 40 CFR 51.165: 

(a) Amending the definition of 

‘‘regulated NSR pollutant’’ with regard 

to PM2.5 precursors; (b) amending the 

definition of ‘‘major stationary source’’ 

with regard to major sources of direct 

PM2.5 emissions and PM2.5 precursors 

locating in PM2.5 nonattainment areas 

classified as Moderate and Serious; (c) 

amending the definition of ‘‘significant’’ 

with regard to emissions of PM2.5

precursors; and (d) codifying the EPA’s 

policy for determining whether a source 

is ‘‘major’’ for PM2.5 with regard to 

emissions of direct PM2.5 and its 

precursors. 

Also, the EPA explains in this section 

that it is codifying the schedule for 

states to submit NNSR SIP revisions for 

PM2.5 that meet the requirements of 40 

CFR 51.165. The schedules for 

submitting revised NNSR programs for 

PM2.5 for Moderate and Serious areas are 

not contained in 40 CFR 51.165 NNSR 

regulations but in new 40 CFR 

51.1003(a) and (b), respectively. 

a. Definition of ‘‘regulated NSR 

pollutant’’—PM2.5 Precursors 

i. Summary of Proposal 

CAA section 189(e) requires that the 

control requirements applicable to 

major stationary sources of PM10 also 

apply to major stationary sources of 

PM10 precursors, unless the 

Administrator determines that such 

sources of PM10 precursors do not 

contribute significantly to PM10 levels 

that exceed the standard in that area. In 

order to align the NNSR regulations for 

PM2.5 with the requirements of CAA 

section 189(e), the EPA proposed 

several amendments to certain 

definitions within 40 CFR 51.165, as 

explained in the subsections that follow, 

in order to regulate all four identified 

PM2.5 precursors consistent with the 

statute.214 The EPA proposed to revise 

the NNSR definition of ‘‘regulated NSR 

pollutant’’ to include SO2, NOX, VOC 

and ammonia as regulated PM2.5

precursors. 

The EPA also proposed to add 

language to the definition of ‘‘regulated 

NSR pollutant’’ to address the provision 

of CAA section 189(e) that allows an 

exemption from the NNSR permit 

requirements for major stationary 

sources or major modifications of a 

particular precursor if the state 

demonstrates to the satisfaction of the 

EPA that major stationary sources of 

such precursor do not contribute 

significantly to PM2.5 levels that exceed 

the PM2.5 ambient standards in a 

particular nonattainment area. In 

Section III of the preamble of the 

proposal, the EPA proposed and sought 

comment on several policy approaches 

that a state could use to make the 

necessary demonstration that would 

enable the state to exempt sources of a 

particular precursor from being 

regulated under the attainment plan for 

a particular PM2.5 nonattainment area 

altogether or from individual 

components of that plan, including the 

NNSR permitting requirements. See 80 

FR 15350–62. 

ii. Final Rule 

The EPA is amending the definition of 

‘‘regulated NSR pollutant’’ at 40 CFR 

51.165 to include a new provision 

stating that SO2, NOX, VOC and 

ammonia are PM2.5 precursors in any 

PM2.5 nonattainment area. See 40 CFR 

51.165(a)(1)(xxxvii)(C)(2). The EPA is 

also providing in this final rule that 

sources of a particular precursor may be 

exempted from the NNSR control 

requirements via a demonstration 

approved by the Administrator showing 

that new major stationary sources and 

major modifications of a particular 

precursor would not contribute 

significantly to levels of PM2.5 that 

exceed the standard in a particular 

nonattainment area. It is noted, 

however, that the exemption provision 

is not being codified within the 

definition of ‘‘regulated NSR pollutant’’ 

as originally proposed. Instead, this 

exemption provision is contained in a 

new paragraph 51.165(a)(13), which is 

based on CAA section 189(e) and 

provides generally that the control 

requirements applicable to new major 

stationary sources and major 

modifications of PM2.5 are also 

applicable to new major stationary 

sources and major modifications of 

PM2.5 precursors. 

In addition, the provision has also 

been revised to focus on the exemption 

of control requirements for sources of a 

particular precursor rather than the 

exemption of the precursor itself. The 

EPA believes that this shift in focus is 

more consistent with the statutory 

language at CAA section 189(e), which 

also focuses on the exemption of 

sources from the control requirements 

for that precursor. As explained in 

Section III of this preamble, the EPA has 

defined a precursor demonstration 

specifically for exempting major sources 

of a particular precursor from regulation 

under the NNSR program. This 

demonstration involves a sensitivitybased analysis that evaluates the 

sensitivity of ambient PM2.5

concentrations in a nonattainment area 

to increases of precursor emissions 

resulting from potential major source 

growth in the area. The EPA intends to 

issue a technical assistance document 

that provides additional information on 

conducting appropriate sensitivitybased analyses for this purpose. A more 

complete description of this and the 

other types of precursor demonstrations 

is contained in Section III of this 

preamble. 

The EPA recommends that the state 

consult with the appropriate EPA 

Regional Office as early as possible to 

discuss appropriate analyses for the 

NNSR precursor demonstration. If the 

appropriate precursor demonstration is 

submitted to and approved by the 

Administrator, the state would not be 

required to regulate new major 

stationary sources and major 

modifications of the insignificant 

precursor under the state’s approved 

NNSR program in a particular 

nonattainment area. Such exemption 

from the NNSR control requirements 

would include an exemption from all of 

the prerequisite conditions set forth in 

40 CFR 51.165 for PM2.5, including the 

requirements to implement LAER and to 

obtain emissions offsets for the 

precursor. 

iii. Comments and Responses 

Comments: Some commenters 

supported revising the definition of 

‘‘regulated NSR pollutant’’ consistent 

with the NRDC decision and subpart 4 

to establish SO2, NOX, VOC and 

ammonia as regulated PM2.5 precursors, 

unless a state demonstrates that major 

stationary sources of a particular 

precursor do not contribute significantly 

to PM2.5 levels that exceed the standard 

in the nonattainment area. 

On the other hand, several 

commenters urged the EPA not to begin 

regulating VOC and ammonia as PM2.5

precursors under the NNSR program at 

this time. Some of the commenters cited 

ongoing technical challenges related to 

evaluating the contribution of PM2.5

precursor gases to ambient PM2.5

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215See NRDC v. EPA, 706 F.3d at 437, n.7 & n.10. 

216States should use Appendix S to issue NNSR 

permits to new major stationary sources and major 

modifications with respect to a particular 

nonattainment pollutant if the state’s 

implementation plan lacks a NNSR program for that 

pollutant. Where a state’s existing NNSR program 

for a particular pollutant lacks certain provisions 

for which revision in required, the existing 

program—not Appendix S—is the applicable permit 

program for issuing NNSR permits until the 

necessary revisions are approved by the EPA. 

concentrations, while some commenters 

stated that the EPA should provide an 

up-front rebuttable presumption that a 

state is not required to regulate VOC and 

ammonia as PM2.5 precursors under 

NNSR. A commenter stated that 

requiring NNSR to apply to sources of 

these precursors that would have an 

insignificant impact on the 

nonattainment issue is a waste of 

resources and will unnecessarily lead to 

burdensome over-regulation for affected 

sources. 

Response: We do not agree with the 

commenters who oppose the EPA’s 

proposal to require regulation of all four 

technical and scientific precursors in 

PM2.5 nonattainment areas. Specifically, 

we do not agree that a delay in 

regulating VOC and ammonia under a 

state’s NNSR permitting program is 

reasonable or permissible. Similarly, the 

EPA does not agree that it has the 

authority to provide a rebuttable 

presumption to exempt VOC and 

ammonia from NNSR permitting 

requirements. CAA section 189(e) 

explicitly requires the regulation of 

major sources of PM2.5 precursors unless 

the state demonstrates to the EPA’s 

satisfaction that such regulation is 

unnecessary. Thus, CAA section 189(e) 

does not allow the EPA to unilaterally 

exempt an identified scientific and 

technical PM2.5 precursor from 

regulation, nor does it permit the EPA 

to establish a rebuttable presumption 

exempting any PM2.5 precursor from 

regulation. The EPA’s use of a rebuttable 

presumption exempting certain 

precursors from regulation in its prior 

PM2.5 implementation rules was directly 

at issue in NRDC v. EPA, wherein the 

court made it clear that it would be 

inappropriate for the EPA to establish 

such presumptions pursuant to the 

requirements of subpart 4.215

In some PM2.5 nonattainment areas, 

the minimization (and offsetting) of new 

precursor emissions from major source 

growth in the area could be an 

important component of a state’s 

attainment plan for the PM2.5 NAAQS. 

Where it is not, CAA section 189(e) 

provides states with the opportunity to 

make an area-by-area demonstration that 

would enable the state to exempt 

sources of any PM2.5 precursor from 

regulation if it is shown that sources of 

the precursor does not contribute 

significantly to the PM levels that 

exceed the standard in a particular 

nonattainment area. Accordingly, 

consistent with CAA section 189(e), this 

final rule provides guidance to assist 

states in preparing a NNSR precursor 

demonstration, as described in Section 

III of this preamble, by which sources of 

VOC, ammonia or any other PM2.5

precursor may be exempted from the 

NNSR requirements for PM2.5 if the state 

shows that increased source emissions 

of the relevant precursor would not 

contribute significantly to PM2.5

concentrations in a PM2.5 nonattainment 

area. 

Moreover, as described in Section 

VIII.B.2 of this preamble, the EPA is not 

commencing with the regulation of VOC 

and ammonia (hence not requiring 

NNSR review of any new major 

stationary sources and major 

modifications of such precursors) for 

those states relying on Appendix S to 

issue NNSR permits during the interim 

SIP development period.216 This 

provides states with an opportunity to 

evaluate the contribution of VOC and 

ammonia emissions from potential 

major source growth to ambient PM2.5

concentrations and determine whether 

an exemption of new and modified 

sources of either of these precursors 

from the NNSR permitting requirements 

is justified before such sources will be 

subject to regulation. 

b. Definition of ‘‘major stationary 

source’’ in Moderate and Serious PM2.5

Nonattainment Areas—Direct PM2.5

Emissions and PM2.5 Precursors 

i. Summary of Proposal 

Subpart 4, as described earlier in this 

document, contains provisions for the 

classifications of PM10 nonattainment 

areas as either Moderate or Serious 

areas. However, 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 as Moderate and 

Serious areas. Accordingly, in the 

proposal for this final rule, the EPA 

proposed to amend its definition of 

‘‘major stationary source’’ in the 40 CFR 

51.165 NNSR regulations for PM2.5 to 

address subpart 4 requirements 

concerning the regulation of direct PM2.5

and PM2.5 precursors in both Moderate 

and Serious nonattainment areas for 

PM2.5. First, the EPA proposed to revise 

the definition of ‘‘major stationary 

source’’ by qualifying the term 

‘‘regulated NSR pollutant’’ with the new 

phrase ‘‘(as defined in paragraph 

(a)(1)(xxxvii) of this section).’’ The new 

phrase explicitly cross-references the 

definition of ‘‘regulated NSR pollutant,’’ 

which also defines each of the PM2.5

precursors. Hence, sources of both 

direct PM2.5 emissions and emissions of 

each PM2.5 precursor would clearly be 

included in the definition of a ‘‘major 

stationary source.’’ 

Second, the EPA proposed to amend 

the definition of ‘‘major stationary 

source’’ consistent with section 

189(b)(3) of the CAA to establish a lower 

major source threshold for new major 

stationary sources and major 

modifications locating in PM2.5

nonattainment areas classified as 

Serious. CAA section 302(j) generally 

defines a ‘‘major stationary source’’ as a 

source that emits or has the potential to 

emit 100 tpy or more of any air 

pollutant. The provision explicitly 

states that this definition applies for 

purposes of the CAA except as 

otherwise expressly provided in the 

statute. Thus, for sources locating in 

PM2.5 nonattainment areas classified as 

Moderate, where no CAA provision 

provides otherwise, the applicable 

major source threshold for direct PM2.5

emissions and for each PM2.5 precursor 

is 100 tpy. Subpart 4, meanwhile, 

establishes a major source threshold for 

PM10 nonattainment areas classified as 

Serious at 70 tpy in CAA section 

189(b)(3). Therefore, the EPA proposed 

to set the major source threshold for 

direct PM2.5 emissions and for each 

PM2.5 precursor at 70 tpy of direct PM2.5

emissions and each individual 

precursor. The alternative proposed for 

consideration was to promulgate a PM2.5

major source threshold lower than 70 

tpy of direct PM2.5 emissions, 

recognizing that PM2.5 is a subset of 

PM10. The EPA sought comment on 

possible ways in which a PM2.5

emissions rate different from the 

statutory 70 tpy rate for PM10 emissions 

could be established, taking into 

account variations in the PM10/PM2.5

ratio for different source categories and 

activities. Nevertheless, the agency 

indicated that the proposed option (i.e., 

a major source threshold of 70 tpy of 

direct PM2.5 emissions for stationary 

sources proposing to construct or 

modify in PM2.5 nonattainment areas 

classified as Serious) represented the 

preferred approach. 

In its effort to ensure that major 

sources of PM2.5 precursors locating in 

Serious areas are regulated in the same 

manner as major sources of direct PM2.5

emissions locating in Serious areas, the 

EPA proposed major source thresholds 

for PM2.5 precursors would be consistent 

with the threshold already defined for 

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217See 80 FR 15433. The 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 PM2.5 NSR Rule. See also 

73 FR 28321 (May 16, 2008), at page 28339. 

direct PM2.5 emissions in PM2.5

nonattainment areas reclassified as 

Serious. Consistent with the EPA’s 

preferred approach for direct PM2.5

emissions, the EPA proposed to define 

‘‘major’’ for each PM2.5 precursor as 70 

tpy. However, the EPA also solicited 

comments on the appropriateness of 

setting the precursor major source 

thresholds at a different rate, 

particularly if, as alternatively 

proposed, the agency defined ‘‘major 

stationary source’’ for sources of direct 

PM2.5 emissions in Serious PM2.5

nonattainment areas at a rate lower than 

70 tpy of PM2.5 emissions. For example, 

if the agency had set the major source 

threshold at 60 tpy of direct PM2.5

emissions in Serious PM2.5

nonattainment areas, the agency would 

have also considered setting the major 

source threshold for each PM2.5

precursor at 60 tpy of that particular 

precursor. 

Regardless of whether the major 

source threshold for direct PM2.5

emissions was set at 70 tpy or some 

lower rate, the EPA indicated in the 

proposal that it believed a reasonable 

technical argument could be made that 

the threshold set for direct PM2.5

emissions would be too low to be 

regarded as ‘‘major’’ for each precursor 

when considering the effects that any 

precursor sources could have on 

ambient PM2.5 concentrations. In 

support of higher emissions rates for 

defining ‘‘major’’ for PM2.5 precursors, 

the EPA cited a previous analysis that 

it had undertaken to examine the 

relationship between emissions of SO2

and NOX and the formation of 

secondary PM2.5 in the ambient air.217

However, the agency also identified 

potential legal impediments to setting a 

major source threshold for precursors at 

a rate higher than those statutorily 

prescribed for direct emissions of a 

pollutant. Accordingly, the agency 

solicited comments on the general 

appropriateness of setting higher major 

source thresholds for one or more PM2.5

precursors in PM2.5 nonattainment 

areas, and asked commenters to include 

legal and technical considerations that 

should be made part of the EPA’s future 

analysis of NNSR requirements with 

respect to PM2.5 precursors. 

ii. Final Rule 

In this final rule, the EPA has 

followed its preferred approach and has 

made the changes necessary to ensure 

that ‘‘major’’ is defined for direct PM2.5

emissions as well as all PM2.5 precursors 

in Moderate and Serious PM2.5

nonattainment areas. For Moderate 

areas, the major source threshold of 100 

tpy applies individually to direct PM2.5

emissions and to each PM2.5 precursor; 

in Serious areas, the major source 

thresholds for direct PM2.5 emissions 

and emissions of each PM2.5 precursor 

are individually defined as 70 tpy. As 

explained in Section VIII.B.1.d of this 

preamble, the determination of whether 

sources of direct PM2.5 emissions or 

each PM2.5 precursor are ‘‘major’’ is to 

be made separately for each pollutant. 

That is, emissions rates for individual 

precursors should not be added together 

to determine a source’s major source 

status with regard to PM2.5. See 40 CFR 

51.165(a)(2)(i). 

iii. Comments and Responses 

Comment: Most commenters generally 

supported the preferred approach of 

setting a major source threshold at 70 

tpy of direct PM2.5 emissions in Serious 

areas, agreeing with the EPA that 

establishing a PM2.5 equivalency to PM10

emissions would be problematic. Some 

commenters specifically opposed any 

effort to set a threshold for PM2.5 that is 

lower than the threshold for PM10. A 

commenter stated that, if PM2.5 is legally 

subject to subpart 4 because it is a 

subset of PM10, and Congress meant to 

subject all sources of PM10 emissions to 

subpart 4, then Congress meant to have 

the major source threshold for PM10

apply to PM2.5 as well. No commenter 

advocated that the EPA set a major 

source threshold lower than 70 tpy for 

direct PM2.5 emissions. 

Response: The EPA agrees with the 

commenters that it is reasonable to set 

the major source threshold at 70 tpy of 

direct PM2.5 emissions for sources 

locating in PM2.5 nonattainment areas 

classified as Serious. While CAA section 

189(b)(3) does not explicitly define a 

‘‘major source’’ and ‘‘major stationary 

source’’ as 70 tpy of PM2.5 for PM2.5

nonattainment areas reclassified as 

Serious (because it refers to PM10), the 

most straightforward and consistent 

application of the statutory provision is 

to establish the same numerical 

threshold for sources of PM2.5 in Serious 

PM2.5 nonattainment areas as the 

threshold for sources of PM10 emissions 

in Serious PM10 nonattainment areas. 

Sources locating in Moderate 

nonattainment areas are already subject 

to the same numerical major source 

threshold (100 tpy) under CAA section 

302(j) for direct emissions of both PM10

and PM2.5, so the EPA believes that it is 

also reasonable to establish the 

threshold for PM2.5 in Serious areas at 

the same numerical rate as the threshold 

that applies to PM10 in Serious areas. 

We also agree that it would be 

difficult to establish a lower uniform 

major source threshold for PM2.5 that 

would represent a rate that is equivalent 

to 70 tpy of PM10 emissions at all 

sources subject to NNSR permitting 

requirements. With regard to the 

commenter who stated that ‘‘Congress 

meant to have the major source 

threshold for PM10 apply to PM2.5 as 

well,’’ it is not clear whether the 

commenter advocates that proposed 

sources of PM2.5 be subjected to NNSR 

permitting using a major source 

threshold of 70 tpy of PM10 emissions or 

a major source threshold of 70 tpy of 

PM2.5 emissions for sources of PM2.5

locating in PM2.5 nonattainment areas. 

The former is not the EPA’s 

interpretation of the CAA. While PM2.5

is a subset of PM10, to assume that a 

source emitting major amounts of PM10

will also emit a substantial amount of 

PM2.5 is not always reasonable. The 

relative amounts of PM10 and PM2.5

emitted by various source categories is 

known to vary significantly and we do 

not believe that it would be reasonable 

to subject sources to major source 

review for PM2.5 on the basis of the level 

of PM10 emissions as this could mean 

that sources are subject to NNSR based 

on different levels of PM2.5 emissions on 

an area-by-area basis. We do not believe 

that Congress intended such a lack of 

uniformity in the application of the 

major source threshold to sources of 

direct PM2.5. Moreover, even if it were 

permissible to interpret CAA section 

189(b)(3) in this manner, we have 

determined that the most reasonable 

and straightforward approach is to 

establish a separate major source 

threshold for direct emissions of PM2.5

at 70 tpy for sources locating in PM2.5

nonattainment areas classified as 

Serious. 

Comment: With regard to the 

definition of ‘‘major stationary source’’ 

for PM2.5 precursors in Moderate and 

Serious areas, several commenters 

supported using the same major source 

threshold value for direct PM2.5

emissions and PM2.5 precursors. One of 

these commenters expressly opposed 

any alternative approach that would set 

a different threshold for PM2.5

precursors than for direct PM2.5

emissions because the commenter 

asserted that it would be impossible to 

set a uniform national ratio reflecting 

the effect of the various precursors on 

ambient PM2.5 concentrations relative to 

direct PM2.5 emissions. 

On the other hand, some commenters 

wanted the EPA to include a provision 

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218 Ibid. 

219See 57 FR 13498 (April 16, 1992), at page 

13538. 

220 Ibid. (emphasis added). 

221 42 U.S.C. 7602(j). 

222H.R. Rep. 101–490. 

223South Coast Air Quality Mgmt. Dist. v. EPA, 

472 F.3d 882, 900–902 (D.C. Cir. 2006) (South Coast 

decision). 

224See South Coast decision (holding that 

‘‘controls’’ in CAA section 172(e) anti-backsliding 

provision include NSR requirements such as LAER, 

offset ratios, and major source thresholds). 

in the NNSR regulations allowing states 

to make a case-by-case demonstration to 

use higher major source thresholds for 

PM2.5 precursors for permit reviews. 

These commenters expressed concern 

that the 100 tpy major source threshold 

for Moderate areas, and the 70 tpy 

threshold for Serious, are both too low 

for the PM2.5 precursors and do not 

realistically reflect the effect that each 

precursor has on ambient PM2.5

concentrations. These commenters 

suggested the EPA should conduct 

further analyses to determine what 

higher quantity of emissions of each 

regulated precursor would be equivalent 

to 100 tpy (for Moderate areas) and 70 

tpy (for Serious areas) of direct PM2.5

emissions in terms of contribution to 

PM2.5 concentrations in ambient air. 

These commenters recommended that 

the EPA use the information gained 

from the recommended analyses to 

determine appropriate thresholds and 

make its proposed thresholds available 

for public comment. 

Response: In setting 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 direct PM2.5

emissions and each of the regulated 

precursors (at that time SO2 and 

NOX).218 Setting the same 100 tpy major 

source thresholds for sources of PM2.5

emissions and regulated PM2.5 precursor 

emissions is also consistent with the 

way in which we have historically 

interpreted the requirements of CAA 

section 189(e) as they applied to 

emissions of PM10 and PM10

precursors.219

Moreover, section 302(j) of the CAA 

contains a definition of ‘‘major emitting 

facility’’ and ‘‘major stationary source’’ 

that applies to, among other things, 

programs implemented under subpart 1 

such as the general NNSR program 

requirements in CAA section 173.220

This definition also applies to programs 

implemented under subpart 4 to the 

extent that they regulate PM2.5

nonattainment areas classified as 

Moderate, as subpart 4 does not 

establish a different definition of major 

sources for such areas. That definition 

defines a source as ‘‘major’’ whenever a 

facility or source ‘‘emits, or has the 

potential to emit, one hundred tons per 

year or more of any air pollutant.’’ 221

This provision does not clearly provide 

the EPA with the authority to set a 

major source threshold higher than 100 

tpy for a pollutant merely because it is 

a precursor for another pollutant. 

Rather, CAA section 302(g) clearly 

defines the term ‘‘air pollutant’’ to 

‘‘include any precursors to the 

formation of any air pollutant.’’ 

With regard to the setting of the major 

source thresholds for PM10 precursors in 

Serious areas, a House of 

Representatives Report accompanying 

the 1990 amendments to the CAA 

described the effects of adding CAA 

section 189(b)(3), defining ‘‘major’’ 

sources locating in PM nonattainment 

areas classified as Serious as those 

sources that emit or have the potential 

to emit 70 tpy of PM10. The report 

specifically notes that ‘‘new or modified 

sources emitting 70 tons or more per 

year of VOC [a PM2.5 precursor] will be 

subject to new source review 

requirements.’’ 222 Thus, Congress 

contemplated that the same major 

source threshold would apply to sources 

of direct PM10 emissions and PM10

precursors in Serious PM10

nonattainment areas. The same 

approach logically applies when 

applying the provision to sources 

locating in areas designated as Serious 

PM2.5 nonattainment areas. 

Since the EPA may not have the legal 

authority to establish major source 

thresholds for PM2.5 precursors at levels 

higher than the statutory threshold 

applied to sources of direct PM2.5

emissions, it would be inappropriate to 

allow states discretion for setting major 

source thresholds for PM2.5 precursors 

that exceed the statutory thresholds. 

Moreover, while we acknowledge that 

PM2.5 precursors will not likely form 

ambient PM2.5 in the nonattainment area 

on a ton-per-ton basis, there is not 

currently sufficient technical basis that 

would enable the agency to propose 

uniform higher major source thresholds 

for any of the four PM2.5 precursors. As 

stated in the proposal, the EPA intends 

to continue its analysis of the 

relationship between each precursor 

and ambient PM2.5 concentrations. 

Comment: Some commenters 

questioned the EPA’s interpretation of 

the 2006 court decision in South Coast 

Air Quality Mgmt. Dist. v. EPA 223 as 

precluding higher major source 

thresholds because the court determined 

that NSR provisions, including major 

source thresholds, were control 

requirements subject to anti-backsliding 

provisions of the statute. The 

commenter argued that the South Coast 

decision did not address setting a major 

source threshold for a precursor 

pollutant that is as stringent as, or more 

stringent than, the major source 

threshold for the pollutant when the 

pollutant is directly emitted. The 

commenter stated the statutory 

provision on which the court in South 

Coast relied [CAA section 172(e)] is 

applicable on its face only when the 

EPA relaxes the NAAQS, which the 

commenter claimed is not relevant to 

the current situation here, where the 

EPA has promulgated progressively 

more stringent NAAQS for PM. 

Response: CAA section 189(e) 

requires the control requirements that 

are applicable to major stationary 

sources of PM2.5 to also apply to major 

stationary sources of PM2.5 precursors. 

The court in South Coast held that the 

term ‘‘controls’’ under section 172(e) of 

the CAA includes NSR requirements, 

and in particular includes major source 

thresholds specified by the statute.224

The commenter did not explain why the 

term ‘‘control’’ in CAA section 189(e) of 

the statute should be interpreted 

differently than the term ‘‘control’’ in 

other parts of the statute. Section 172(e) 

of the CAA is a provision in subpart 1 

of part D of the statute concerning antibacksliding requirements in designated 

nonattainment areas. It is reasonable for 

the EPA to conclude that the term 

‘‘control’’ in one part of the statute 

pertaining to nonattainment area 

requirements should be interpreted 

consistent with the use of that term in 

other provisions of part D pertaining to 

nonattainment area requirements, 

particularly where both provisions 

apply to designated PM2.5

nonattainment areas. Thus, consistent 

with the holding of South Coast 

regarding the definition of ‘‘controls,’’ 

the EPA interprets the use of the term 

‘‘control requirements’’ in CAA section 

189(e) to require the same major source 

threshold be applied to PM2.5 precursors 

as applies to direct PM2.5 emissions. 

The commenter also did not explain, 

and it is not clear, how a relaxation 

versus a strengthening of the NAAQS 

would bear on whether the EPA has 

authority to set different control 

requirements (e.g., major source 

thresholds) for sources of direct 

emissions of a pollutant and sources of 

precursors of that pollutant. The EPA 

notes that Congress, in adding 

additional particulate matter 

requirements in subpart 4 of the CAA, 

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225See the Federal Register published on May 16, 

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

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

226See the Federal Register published on May 16, 

2008 (73 FR 28321 and 28333). 227The EPA notes that the 2015 NPRM included 

some potentially conflicting statements concerning 

the development of a SER for VOC. First, the 

preamble indicated that the EPA intended to 

consider a separate rulemaking to consider 

proposing new SERs for SO2 and NOX, while also 

proposing individual significant emissions rates for 

VOC and ammonia. Later in the same preamble, the 

EPA indicated that it was proposing to add VOC as 

a precursor with a 40 tpy significant emissions rate, 

and included regulatory text to show that aspect of 

the proposal, i.e., proposed 40 CFR 

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

decided that more stringent 

requirements were required to address 

air quality in particulate matter 

nonattainment areas. Hence, it would be 

inconsistent with that intention for 

Congress to allow higher major source 

thresholds to apply to sources of 

precursors than apply to direct PM2.5

emissions. 

The EPA therefore believes that at this 

time the most reasonable approach for 

defining the major source threshold for 

PM2.5 precursors in both Moderate and 

Serious areas is to use the same 

threshold that is being defined for direct 

PM2.5 emissions. As explained earlier, 

the EPA currently has studies underway 

to better understand the effects of 

emissions of each precursor on the 

secondary formation of ambient PM2.5

concentrations. However, even if such 

studies support the commenters’ 

recommendation for higher precursor 

thresholds, the EPA must consider the 

potential legal restrictions on setting 

thresholds for precursors above the 

statutory requirements for direct 

emissions of an air pollutant. 

c. Significant Emissions Rates (SERs) for 

PM2.5 Precursors 

i. Summary of Proposal 

As noted earlier, stationary sources 

locating in nonattainment areas are 

subject to the NNSR permitting 

requirements to the extent construction 

at the source qualifies as a major 

modification with respect to a pollutant 

for which the area is designated 

nonattainment. A major modification of 

a stationary source is defined in the 

NNSR regulations at 40 CFR 

51.165(a)(1)(v)(A) as ‘‘any physical 

change in or change in the method of 

operation of a major stationary source’’ 

that would result in (1) a significant 

emissions increase of a regulated NSR 

pollutant, and (2) a significant net 

emissions increase of that pollutant. The 

term ‘‘significant’’ is separately defined 

at 40 CFR 51.165(a)(1)(x)(A) to mean a 

rate of emissions specified for each 

pollutant or precursor for that pollutant. 

This is known as a significant emissions 

rate (SER). In the 2008 PM2.5 NSR Rule, 

the EPA defined ‘‘significant’’ for SO2

and NOX as PM2.5 precursors with an 

emissions rate of 40 tpy for each 

precursor.225 Also, in the preamble to 

the 2008 PM2.5 NSR Rule, the EPA 

indicated that it would consider 40 tpy 

of VOC emissions to be ‘‘significant’’ in 

any state regulating VOC as a PM2.5

precursor; however, that significant 

emissions rate was not codified in any 

of the NSR regulations because the 

regulations governing both NNSR and 

PSD permitting programs 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 SER 

unless it demonstrated that a more 

stringent SER (lower rate) is more 

appropriate.’’226

The EPA did not include any changes 

to the existing SERs for SO2 and NOX as 

PM2.5 precursors in the proposal. Nor 

did we propose a SER for ammonia, 

citing a lack of adequate technical 

support. However, the EPA proposed to 

codify a SER of 40 tpy for VOC in the 

NNSR permitting regulations. See 55 FR 

15434.227 The EPA further stated that, as 

a result, only the ammonia SER would 

remain to be defined by each state that 

needs to control major stationary 

sources of ammonia as part of its NNSR 

program for PM2.5. While not proposing 

to revise the existing 40 tpy SER values 

for SO2 and NOX, the EPA indicated it 

believed that, when more data are 

available, such data might provide a 

reasonable basis for considering 

subsequent changes to the SER for each 

PM2.5 precursor for purposes of 

implementing the PM2.5 NAAQS. 

Moreover, the EPA indicated that a 

separate rulemaking might be used to 

propose a new SER for each PM2.5

precursor. See 80 FR 15434. 

ii. Final Rule 

The EPA is finalizing its proposed 

approach with some changes to the final 

regulatory language. The final rule 

amends the definition of ‘‘significant’’ 

in the NNSR regulations at 40 CFR 

51.165(a)(1)(x)(A) to add a SER for VOC. 

Thus, the revised definition contains 

individual SERs for direct PM2.5

emissions (10 tpy), SO2 emissions (40 

tpy), NOX emissions (40 tpy), and VOC 

emissions (40 tpy). The revised 

definition does not contain a SER for 

ammonia emissions. Instead, a new 

subparagraph has been added to the 

definition of ‘‘significant’’ to require 

that an implementation plan defines the 

term for ammonia in cases where 

sources of ammonia are not otherwise 

exempted from NNSR control 

requirements. See 40 CFR 

51.165(a)(1)(x)(F). Such definition of 

‘‘significant’’ for ammonia would need 

to be established by the state for a 

particular nonattainment area as part of 

its SIP submission for NNSR. The EPA’s 

rationale for not establishing an 

ammonia SER in this action is provided 

in greater detail in the following section. 

iii. Comments and Responses 

Comment: Several commenters 

generally recommended that the EPA 

establish higher SERs for the PM2.5

precursors. These commenters 

expressed the need for values that more 

accurately represented each precursor’s 

relative effect on ambient PM2.5

concentrations. One of these 

commenters stated that in the absence of 

such higher SERs in the NNSR 

regulations, the EPA should allow states 

to demonstrate the appropriateness of a 

higher SER for a particular precursor on 

either a statewide or area-by-area basis 

in a SIP submission, or through the 

NNSR program on a case-by-case basis. 

Another of the commenters 

supporting higher significance 

thresholds for each precursor stated that 

the CAA’s definitions of ‘‘major source’’ 

and ‘‘major emitting facility’’ trigger the 

statutory control requirements and its 

permit requirements for affected 

sources, but they do not define how 

much of a pollutant is regulated after 

the control or permit requirement is 

triggered by the CAA. The commenter 

stated that the EPA would appear to 

have ample authority to require that 

precursors be regulated based on 

different thresholds once a major source 

triggers a particular control or permit 

requirement, provided there is adequate 

technical basis for doing so. 

Response: The EPA did not propose to 

reconsider or revise the SERs for SO2

and NOX; therefore, revisions to these 

rates are outside the scope of this action. 

Even if the EPA were to consider such 

a revision, it would provide little relief 

to new or modified sources subject to 

NSR. Because SO2 and NO2 are 

pollutants for which the EPA has 

established NAAQS and because NOX

and VOC are precursors for ozone, 

modifications with emissions increases 

above the current SERs for SO2, NOX or 

VOC would still be subject to some form 

of new source review (PSD if the area is 

attainment for the NAAQS pollutant or 

nonattainment NSR if the area is 

nonattainment) even if the SERs for 

these pollutants as PM2.5 precursors 

were revised to a higher value. 

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228Compare the definitions of ‘‘significant’’ under 

the PSD regulations at 40 CFR 51.166(b)(23) and 

52.21(b)(23), especially subparagraph (ii), with the 

NNSR definition at 40 CFR 51.165(a)(x). 

229The NNSR definition of ‘‘major stationary 

source’’ includes a provision at 40 CFR 

51.165(a)(iv)(A)(3) that requires any physical 

change at an existing source that would not 

otherwise qualify as a major stationary source if the 

change would constitute a major stationary source 

by itself. 

Moreover, we do not believe that the 

statute would permit the EPA or states 

to adopt a definition of ‘‘significant’’ for 

purposes of identifying modifications 

subject to NSR permitting with rates 

greater than the statutory and regulatory 

definitions of a major source in a 

nonattainment area, as defined in CAA 

section 302(j) for sources locating in 

PM2.5 nonattainment areas classified as 

Moderate (100 tpy) and as defined in 

CAA section 189(b)(3) for sources 

locating in PM2.5 nonattainment areas 

classified as Serious (70 tpy). 

Consequently, we do not believe that 

there would be substantial cost savings 

to many sources if we were to revise the 

SERs for these pollutants specifically as 

PM2.5 precursors. 

Comment: Some commenters directed 

specific attention to the definition of a 

SER for ammonia. These commenters 

urged the EPA to set a significance 

threshold for ammonia as soon as 

possible. These commenters stated that, 

without a SER, any significant 

emissions increase greater than zero 

tons per year would result in a major 

source review for NNSR. 

Some commenters stated that, while 

the EPA indicates that a SER for 

ammonia may be developed in a 

subsequent rulemaking, if that 

rulemaking is not timely, the state 

would need to develop a SER for 

ammonia to reduce the burden on 

permit applicants and avoid permit 

issuance delays related to major source 

applicability determinations and permit 

development for ammonia and PM2.5. 

Two of the commenters noted that 

ammonia is used in many industry and 

source types to control NOX emissions 

through the implementation of selective 

catalytic reduction (SCR) and selective 

non-catalytic reduction (SNCR) control 

devices. These commenters stated that, 

without a SER for ammonia, it’s very 

possible that many NNSR reviews will 

be initiated simply because of any 

ammonia increase at a major source. To 

address this problem, some commenters 

stated that, until the EPA completes its 

analysis for ammonia, states need the 

ability to conduct case-by-case reviews 

for NNSR permits by requiring 

applicants to submit a technical 

demonstration showing that emissions 

of a particular precursor do not 

significantly contribute to PM2.5 levels 

that exceed the standard in an area, thus 

exempting the precursor from being 

controlled by that source. 

Some commenters recommended that 

the EPA propose a SER for ammonia 

before finalizing the March 23, 2015, 

proposal and suggested the EPA should 

also provide definitive guidance for 

state and local agencies on how to 

conduct permitting of major sources of 

ammonia until a SER is established. 

Other commenters stated that, at the 

time the EPA proposes new significant 

emission rates for precursors, the EPA 

should also establish the significant 

emission rate for ammonia. Yet another 

commenter stated that any precursor 

analyses conducted by the EPA should 

be done in close coordination with 

designated nonattainment areas to 

reduce duplication of efforts and 

conflicting outcomes that could in turn 

lead to more costly impacts on sources 

and on agencies’ limited resources. 

Finally, some commenters stated that 

the EPA should at least provide 

guidance for states to develop a SER for 

ammonia as a PM2.5 precursor. 

Response: The EPA did not propose a 

SER for ammonia and, therefore, this 

rule does not finalize a SER for 

ammonia. The EPA’s initial plan, as 

explained in the proposal, was to 

establish a SER for ammonia in a 

separate rulemaking, which was also 

intended to establish significant impact 

levels (SILs) for Ozone and PM2.5 in 

order to streamline the air quality 

impact analysis under the PSD 

permitting program. However, based on 

the imminent need for the SILs 

(especially for ozone) for PSD 

permitting, the agency has decided to 

issue guidance in lieu of a rulemaking 

for the PSD-based SILs. After due 

consideration, the EPA has also 

concluded that a separate rulemaking 

solely for the purpose of developing a 

SER for ammonia is not warranted. We 

anticipate that very few states will 

actually need to control source 

modifications of ammonia under their 

NNSR programs for PM2.5 since (1) 

stationary sources of ammonia generally 

are not one of the primary causes of 

ambient PM2.5 concentrations in most 

PM2.5 nonattainment areas, and (2) 

according to information in the EPA’s 

NEI database, most existing PM2.5

nonattainment areas do not have an 

existing major stationary source of 

ammonia to which the ammonia SER 

would be applied to determine whether 

a proposed modification of such major 

source would be ‘‘major’’ for ammonia. 

Unlike the EPA’s PSD regulations, the 

definition of ‘‘significant’’ in the NNSR 

regulations at 40 CFR 51.165 does not 

include a provision stipulating that, for 

any pollutant that does not have a listed 

emissions rate, ‘‘any increase’’ must be 

considered significant.228 Therefore, 

contrary to the concerns of some 

commenters, the absence of an ammonia 

SER in the EPA’s NNSR regulations at 

40 CFR 51.165 does not result in a 

default ‘‘any increase’’ interpretation of 

‘‘significant’’ that must be contained in 

state NNSR programs. Accordingly, for 

the above reasons and due to the time, 

resources and process investment 

associated with a national rulemaking, 

the EPA believes that a national 

rulemaking to develop a SER for 

ammonia is neither warranted nor 

effective. As explained above, the EPA 

is finalizing a provision that requires 

states that must regulate modified major 

stationary sources of ammonia to 

develop and submit a definition of 

‘‘significant,’’ such as an appropriate 

SER, for ammonia to be included, 

subject to the EPA’s approval in the 

state’s SIP. See 40 CFR 

51.165(a)(1)(x)(F). The EPA 

recommends that states consult with the 

appropriate EPA Regional Office to 

develop an ammonia SER as a means of 

defining ‘‘significant’’ for a particular 

nonattainment area. As a general rule, 

the EPA believes that the ammonia SER 

in a Moderate nonattainment area 

should be an emissions rate no greater 

than 100 tpy of ammonia. Any SER that 

exceeds 100 tpy could not be approved 

by the EPA because any higher 

emissions rate would exceed the major 

source threshold established in the 

CAA.229 In the event that a 

nonattainment area is classified Serious 

for PM2.5, the maximum acceptable 

ammonia SER would be a rate no greater 

than 70 tpy in accordance with the 

major source thresholds being finalized 

in this rule for major stationary sources 

of direct PM2.5 emissions and PM2.5

precursors locating in Serious PM2.5

nonattainment areas. States that regulate 

ammonia as a PM2.5 precursor should 

also include a technical justification for 

the ammonia SER for a nonattainment 

area that the state includes as a part of 

its NNSR SIP rules submission for EPA 

approval. 

d. NNSR Applicability Determinations 

i. Summary of Proposal 

In setting SERs and major source 

thresholds for emissions of direct PM2.5

and PM2.5 precursors, the EPA 

explained in the preamble to the 

proposal that it intended for direct PM2.5

emissions and each individual PM2.5

precursor to be treated separately for 

determining the applicability of the 

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NNSR requirements to a proposed new 

source or modification. The EPA stated 

that such individual treatment of direct 

emissions and precursors was consistent 

with its policy as explained in previous 

rulemakings. In particular, the preamble 

to the 2008 PM2.5 NSR Rule explained 

that this applicability interpretation 

applied to both PSD and NNSR. 

However, at that time, we did not codify 

this interpretation in any of the NSR 

regulations. See 73 FR 28231, May 16, 

2008, at page 28331. In the proposal, the 

EPA proposed language in the NNSR 

regulations at 40 CFR 51.165(a)(2)(i) to 

explicitly codify the policy. 

ii. Final Action 

The EPA is revising the NNSR 

regulations at 40 CFR 51.165(a)(2)(i) to 

codify the EPA’s policy that direct 

emissions of a pollutant and emissions 

of any applicable precursor are to be 

considered independently for purposes 

of determining the applicability of the 

NNSR requirements for PM2.5 sources. 

For example, in order for a source to be 

subject to the NNSR requirements for 

PM2.5 with respect to NOX as a PM2.5

precursor, the source must be either (1) 

a new stationary source that emits or 

has the potential to emit major amounts 

of NOX (new major source of NOX); or 

(2) an existing major source of NOX that 

proposes to increase its emissions of 

NOX by a significant amount and also 

results in a significant net emissions 

increase. 

iii. Comments and Responses 

Comment: A commenter requested 

that the EPA clarify in its NSR rules 

how to evaluate major source 

applicability for NNSR and PSD with 

respect to PM2.5 precursors. The 

commenter agreed that major source 

applicability determinations should be 

based on individual precursor pollutant 

emissions, and that different pollutants, 

including individual precursors, should 

not be summed to determine 

applicability for NNSR major stationary 

source or major modification. The 

commenter also raised various questions 

pertaining to how the precursors would 

trigger major source applicability for 

other pollutants. 

Response: This final rule contains the 

following statement within the NNSR 

regulations at 40 CFR 51.165(a)(2)(i), 

‘‘Different pollutants, including 

individual precursors, are not summed 

to determine applicability of a major 

stationary source or major 

modification.’’ The commenter’s 

specific precursor-related applicability 

questions and the EPA’s responses are 

included in the Response to Comment 

document contained in the Docket for 

this rulemaking. 

e. NNSR Plan Due Dates 

i. Summary of Proposal 

In the proposal, the EPA explained 

that CAA section 189(a)(2)(B) requires 

states to submit to the EPA an 

attainment plan satisfying the 

applicable requirements within 18 

months of an area being designated 

nonattainment pursuant to a new or 

revised PM2.5 NAAQS. See 80 FR 15437. 

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

specifically requires that such plans 

include the NNSR permitting 

requirements under CAA section 173. 

Thus, the EPA indicated that states 

would be required to submit the 

applicable NNSR program requirements 

for PM2.5 within 18 months from the 

effective date of area designations for 

the 2012 PM2.5 NAAQS. See 80 FR 

15437. 

The EPA also noted that the CAA 

does not specify a deadline for the 

states’ submittal of NNSR program 

revisions in the event that a Moderate 

PM2.5 nonattainment area is 

subsequently reclassified as Serious like 

the CAA establishes a deadline for other 

plan provisions. Accordingly, the EPA 

used its gap-filling authority under CAA 

section 301(a) to propose a similar 18- 

month deadline, from the effective date 

of a final reclassification of the area as 

Serious, for states to submit a plan 

prescribing the more stringent NNSR 

requirements required by the statute for 

Serious areas. However, in light of the 

fact that such revisions would generally 

be straightforward to make, and to 

assure that new major sources and major 

modifications in the area would be 

subject to the more stringent NNSR 

requirements contained in subpart 4 for 

Serious areas, the EPA sought comments 

on an alternative 12-month timeframe 

for submittal of the NNSR plan revisions 

for Serious areas. 

ii. Final Rule 

The EPA is finalizing an 18-month 

deadline for states to submit plan 

revisions for NNSR requirements for 

PM2.5 after an area is initially designated 

to nonattainment (Moderate area) or 

reclassified to Serious. See 40 CFR 

51.1003(a) and (b), respectively. As 

explained elsewhere in this Section VIII 

of the preamble, plan revisions 

applicable to areas reclassified as 

Serious must address the more stringent 

major source thresholds for direct PM2.5

emissions and each applicable PM2.5

precursor for Serious areas. With regard 

to the provisions for precursors, the EPA 

emphasizes that if the state seeks to 

continue to exempt a precursor from 

NNSR control requirements, the state 

will need to reevaluate any previous 

finding that resulted in the exclusion of 

a precursor from the NNSR control 

requirements on the grounds that the 

precursor did not significantly 

contribute to PM2.5 levels that exceed 

the NAAQS. The requirement at 40 CFR 

51.1006(b) calling for a new NNSR 

precursor demonstration means that, 

even if the existing NNSR program 

already includes the necessary 

provisions for a Serious area 

classification under a prior approval, a 

plan revision pertaining to NNSR may 

still be required to add requirements for 

a precursor that had previously been 

exempted, if a new NNSR precursor 

demonstration does not support 

continued exemption of that precursor. 

The requirements for submitting plan 

revisions at 40 CFR 51.1003 also 

provide for situations where an area 

classified as Serious is subject to CAA 

section 189(d) for failing to attain the 

PM2.5 NAAQS by the applicable Serious 

area attainment date. See 40 CFR 

51.1003(c). The list at § 51.1003(c), 

which contains attainment plan 

requirements that must be submitted as 

plan revisions, does not include the 

NNSR plan requirements contained at 

§ 51.165. This omission results from the 

fact that Serious area requirements 

should have already been included in 

the NNSR program when the area was 

originally reclassified as Serious. Hence, 

there is no explicit requirement to revise 

the NNSR plan requirements in such 

cases. However, in light of the fact that 

states have the opportunity to submit a 

new NNSR precursor demonstration for 

each required plan revision (40 CFR 

51.1006(b)), there may indeed be a need 

to revise the NNSR requirements in the 

event that a previous exemption can no 

longer be supported by the new NNSR 

precursor demonstration. Therefore, to 

the extent that a state’s plan previously 

exempted sources of a precursor from 

NNSR regulation, a plan revision for a 

Serious area that fails to attain the PM2.5

NAAQS by the applicable Serious area 

attainment date will need to include a 

re-evaluated NNSR precursor 

demonstration if the state wishes to 

continue to exempt sources of that 

precursor. Such a plan revision is 

required to be submitted no later than 

12 months from the applicable Serious 

area attainment date that was previously 

missed, in accordance with 40 CFR 

51.1003(c)(2). The NNSR regulations 

have also been amended at 40 CFR 

51.165(a)(13) to address the need to reevaluate such a demonstration to 

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230The EPA notes that in the preamble to the 

proposal, it was stated that the EPA proposed to 

add NOX as a PM2.5 precursor at section 

II.A.31.(iii)(b) of Appendix S. This was an incorrect 

reference, which should have read ‘‘section 

II.A.31.(ii)(b).’’ This final rule cites the correct 

section for the affected portion of the definition of 

‘‘regulated NSR pollutant,’’ where NOX is being 

added as a PM2.5 precursor. 

exempt a particular precursor from the 

NNSR requirements for PM2.5.

iii. Comments and Responses 

Comment: Some commenters 

supported allowing states at least 18 

months to make the required SIP 

submission for NNSR. A commenter 

who supported the longer submission 

period stated that, although it is easy to 

write the rule language to make this 

change, it is likely to be quite difficult 

to perform the environmental and socioeconomic analyses required by state law 

if the lowering of the threshold for a 

Serious area does indeed have a 

significant effect on the building of new 

or the repowering of existing power 

plants. 

Response: Although the types of 

revisions needed to an existing NNSR 

program to address the new subpart 4 

requirements for PM2.5 are relatively 

straightforward, the EPA acknowledges 

that such changes nevertheless often 

involve related analyses as well as state 

legislative review and approval. In 

addition, some states will be submitting 

NNSR regulations for PM2.5 for the first 

time and, as such, could need more than 

12 months to obtain the necessary 

legislative review and approval. 

Accordingly, the EPA believes that the 

most reasonable approach for 

establishing the plan due date for 

revised plans for PM2.5 is to establish an 

18-month deadline for submission of 

plans both upon initial designation to 

nonattainment for a particular PM2.5

standard and upon any subsequent 

reclassification to Serious. 

2. Offset Ruling at 40 CFR Part 51 

Appendix S 

In this final rule, as explained later, 

the EPA is making the following 

revisions for PM2.5 in the Emission 

Offset Interpretive Ruling (40 CFR part 

51, Appendix S): (a) Amending the 

definition of ‘‘regulated NSR pollutant’’ 

with regard to PM2.5 precursors; (b) 

amending the definition of ‘‘major 

stationary source’’ with regard to major 

sources of direct PM2.5 emissions and 

PM2.5 precursors in Serious areas; and 

(c) amending the definition of 

‘‘significant’’ with regard to identifying 

major modifications of sources of PM2.5

precursors. 

a. Appendix S Definition of ‘‘Regulated 

NSR Pollutant’’—PM2.5 Precursors 

i. Summary of Proposal 

The definition of ‘‘regulated NSR 

pollutant’’ contained in Appendix S at 

section II.A.31(ii)(b)(2) has, to date, only 

required regulation of SO2 as a PM2.5

precursor for states relying on Appendix 

S to issue permits to sources locating in 

PM2.5 nonattainment areas. The EPA 

proposed to revise the definition in 

Appendix S of ‘‘regulated NSR 

pollutant’’ to also require regulation of 

NOX as a PM2.5 precursor.230 The EPA 

noted that this proposed approach 

would ensure that states using the 

permitting requirements contained in 

Appendix S to issue permits to major 

new and modified sources in PM2.5

nonattainment areas will regulate the 

same precursors that have been subject 

to regulation in states that have already 

adopted NNSR requirements for PM2.5

based on the 2008 PM2.5 NSR Rule. 

The EPA also proposed an alternative 

approach based on similar logic that 

would initially require only SO2 and 

NOX to be regulated as PM2.5 precursors, 

while later phasing in VOC and 

ammonia after states have prepared and 

the EPA has had sufficient time to 

evaluate any pending precursor 

demonstrations. See 80 FR 15436–37. 

Finally, the EPA also sought comments 

on an alternative to require the 

immediate regulation of all four 

scientific PM2.5 precursors (SO2, NOX, 

VOC and ammonia) in Appendix S. 

ii. Final Rule 

The EPA is amending Appendix S in 

this final rule to provide for the 

immediate regulation of SO2 and NOX as 

regulated NSR pollutants (specifically as 

PM2.5 precursors) and for the subsequent 

conditional phasing in of VOC and 

ammonia as regulated NSR pollutants 

(PM2.5 precursors) on the date 24 

months from the effective date of the 

nonattainment designation in each area. 

The EPA was persuaded by the 

comments received expressing concerns 

that states may delay NNSR SIP 

development to instead rely on a lessinclusive Appendix S for NNSR 

permitting if only SO2 and NOX were 

regulated. 

The alternative proposal featuring the 

phase-in approach balances the 

opportunity for states to demonstrate in 

the short-term that certain precursors 

need not be regulated with the need to 

ensure that the appropriate precursors 

are controlled in a manner consistent 

with the CAA. NNSR is unique among 

the nonattainment area requirements in 

that sources seeking a construction 

permit must comply with NNSR 

requirements for a particular pollutant 

as soon as an area is designated 

nonattainment for that pollutant and not 

some months or years later, when the 

EPA formally approves a state plan and 

the sources comply with the remaining 

plan provisions. With respect to 

precursors in particular, this means that 

new and modified major sources of 

direct PM2.5 or a regulated PM2.5

precursor would be subject to NNSR 

regulation upon the effective date of the 

area designation to nonattainment. If the 

EPA required the immediate regulation 

of all four scientific PM2.5 precursors in 

Appendix S, states issuing permits 

pursuant to those provisions during the 

interim SIP development period would 

need to require regulation of certain 

precursors that the state may later be 

able to demonstrate through a SIP 

submission do not significantly 

contribute to PM2.5 levels that exceed 

the standard in a particular area. As 

state plans making such a NNSR 

precursor demonstration are not due 

until 18 months after the effective date 

of the area designation, and as the 

statute allows the EPA up to 18 months 

to act on such submissions, sources 

seeking permits to locate in such areas 

during this interim period might for 

several years be subject to more 

stringent controls than necessary to 

address PM2.5 nonattainment in that 

area. 

The EPA is also cognizant, however, 

that some states have relied on 

Appendix S to conduct NNSR 

permitting well beyond the statutory SIP 

development period. In such cases, it 

would be inequitable if states could 

indefinitely rely on Appendix S that 

requires little to no regulation of some 

of the scientific PM2.5 precursors when 

other states are fulfilling their statutory 

duty to submit a SIP revision addressing 

all PM2.5 precursors. In particular, states 

that have submitted NNSR SIPs 

addressing PM2.5 requirements for the 

1997 and 2006 standards have to date 

regulated SO2 and NOX as PM2.5

precursors. These SIP provisions will 

continue to apply with respect to any 

areas designated nonattainment as to the 

2012 standard in those states until the 

states submit SIP revisions to address 

the 2012 NAAQS, including provisions 

necessary to comply with the precursor 

requirements in CAA section 189(e). 

States either continuing to rely on 

Appendix S by virtue of a 

nonattainment area designation under a 

prior PM2.5 standard or states newly 

relying on Appendix S by virtue of a 

nonattainment area designation under 

the 2012 standard have to date only 

been required to regulate SO2 as a 

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231The minimum requirements for evaluating the 

completeness of such submissions can be found in 

40 CFR part 51, Appendix V, Criteria for 

Determining the Completeness of Plan Submissions. 

232 If the EPA disapproves a state’s NNSR 

precursor demonstration but the state’s NNSR 

program is otherwise approvable, the EPA may 

partially disapprove the NNSR SIP provisions for 

failure to properly regulate sources of the relevant 

precursor and otherwise partially approve the 

program. Upon the partial approval of a state’s 

NNSR program, Appendix S will no longer be the 

applicable set of requirements by which NNSR 

permits are to be issued by the state. Thus, the 

phase-in of the relevant precursor will only occur 

in the event that the EPA both disapproves the 

NNSR program for PM2.5 and the state’s NNSR 

precursor demonstration. The partial disapproval of 

a state’s NNSR program with respect to the 

regulation of a precursor will obligate the EPA to 

promulgate a federal implementation plan (FIP) 

pursuant to CAA section 110(c)(1) to address the 

regulation of that precursor within 2 years of the 

disapproval unless the Administrator approves a 

state plan or plan revision correcting the deficiency. 

The disapproval will also trigger the application of 

sanctions pursuant to CAA section 179(a) unless the 

state corrects the deficiency within 18 months. 

233CAA section 110(k)(1)(B) specifically requires 

the Administrator to evaluate the completeness of 

a SIP submission within 60 days of receipt, but no 

later than 6 months after the date by which the SIPs 

were due. If the Administrator does not 

affirmatively evaluate the completeness of the SIP 

within that time period, the statute provides that 

the SIP shall be deemed complete by operation of 

law 6 months after receipt. 

regulated NSR pollutant (specifically as 

a PM2.5 precursor). 

In order to balance these competing 

interests and concerns, the EPA has 

determined in this final rule to revise 

Appendix S in order to require that any 

state relying on Appendix S initially 

regulate both SO2 and NOX as regulated 

NSR pollutants (PM2.5 precursors) for 

NNSR permits, thereby aligning the 

requirements of Appendix S with the 

prevailing requirements of SIP-approved 

NNSR permitting provisions for PM2.5 in 

other states. See Appendix S, section 

II.A.31.(ii)(b)(2). Further, the final rule 

provides that VOC and ammonia will be 

phased in as regulated NSR pollutants 

(PM2.5 precursors) according to a 

prescribed schedule based on existing 

and future nonattainment area 

designations for PM2.5, unless the EPA 

has determined, prior to the scheduled 

phase-in, that the state submitted a 

complete proposed NNSR program for 

PM2.5 that includes a NNSR precursor 

demonstration. The EPA believes it is 

reasonable not to require regulation of 

sources of VOC and ammonia in 

Appendix S during the interim SIP 

development period because we expect 

that, in many cases, states will submit 

SIPs that include as part of their 

proposed NNSR rules for PM2.5 a NNSR 

precursor demonstration indicating that 

they do not need to regulate new major 

stationary sources and major 

modifications of ammonia (and in some 

cases of VOC) under their NNSR 

programs in order to provide for 

attainment of the PM2.5 NAAQS. 

Under the phase-in schedules being 

finalized in Appendix S, permits issued 

by states under the requirements in 

Appendix S will not be required to 

address VOC and ammonia as regulated 

NSR pollutants (PM2.5 precursors) until 

the state has had an opportunity to 

show that, as part of a proposed NNSR 

program for PM2.5, sources of a 

particular precursor does not 

significantly contribute to PM2.5

concentrations that exceed the standard 

in a given nonattainment area. If a state 

submits such a NNSR precursor 

demonstration as to either VOC or 

ammonia as part of a complete SIP 

submission that includes the state’s 

proposed NNSR program for PM2.5, the 

state would not be required to regulate 

the applicable precursor pursuant to the 

provisions of Appendix S, unless the 

EPA reviews that proposed NNSR 

program for PM2.5 and the NNSR 

precursor demonstration and either 

determines that the SIP submission is 

incomplete or disapproves both the 

NNSR program and the NNSR precursor 

demonstration. Thus, the regulation of 

VOC and ammonia as regulated NSR 

pollutants (PM2.5 precursors) pursuant 

to Appendix S will occur in three 

circumstances. First, in the absence of a 

plan submission that includes the 

appropriate NNSR precursor 

demonstration, VOC and ammonia will 

be phased in as regulated precursors 

pursuant to Appendix S 24 months after 

the effective date of area designations 

for PM2.5. This will prevent states that 

fail to make a complete plan submission 

from continuing to rely on Appendix S 

to regulate only SO2 and NOX as PM2.5

precursors indefinitely. Second, if the 

EPA determines that the portion of the 

SIP containing the NNSR precursor 

demonstration submitted by the state is 

incomplete within the time allowed 

under CAA section 110(k)(1)(B), all 

precursors must be regulated upon 

EPA’s determination of incompleteness 

or by the prescribed phase-in date, 

whichever date is later. The EPA 

believes it is important to condition the 

phase-in of VOC and ammonia 

regulation on the completeness of the 

SIP submission in order to deter the 

submission of plans that do not meet 

certain minimum criteria simply to 

avoid the regulation of these additional 

precursors.231 Finally, if the EPA 

disapproves both the proposed NNSR 

program for PM2.5 and the 

accompanying NNSR precursor 

demonstration, the relevant precursors 

will be phased in to be regulated under 

Appendix S as of the effective date of 

the disapproval or by the prescribed 

phase-in date, whichever date is 

later.232

The EPA chose this 24-month period 

for phase-in of VOC and ammonia as 

PM2.5 precursors in accordance with (1) 

the requirement under CAA section 

189(a)(2)(B) of subpart 4 that plan 

revisions for PM2.5 attainment plans be 

submitted to the EPA within 18 months 

of area designations, and (2) the 

requirement under CAA section 

110(k)(1)(B) that the EPA determine no 

later than six months after the date by 

which a state is required to submit a SIP 

whether a state has made a submission 

that meets the minimum completeness 

criteria established per CAA section 

110(k)(1)(A).233 In order to provide an 

appropriate balance between the EPA’s 

interests in providing states with the 

opportunity to develop precursor 

demonstrations prior to regulation of 

those precursors and in encouraging 

states to submit SIPs in a timely 

manner, the EPA believes it is 

reasonable to align the conditional 

phase-in of VOC and ammonia as 

regulated NSR pollutants (PM2.5

precursors)with the statutory timeframe 

for states to make SIP submissions 

addressing precursor regulation for 

NNSR and for the EPA to evaluate 

whether a state has made a complete 

submission. Thus, if by this 24-month 

deadline, a state has not submitted a 

precursor demonstration that VOC and/ 

or ammonia need not be regulated, 

which has been determined to be 

complete by the EPA or deemed 

complete by the operation of law by this 

24-month deadline, Appendix S will 

require regulation of these precursors 

going forward. 

The EPA has specifically included the 

6-month period for EPA’s completeness 

review because we believe it is 

important to discourage states from 

submitting SIPs that do not meet the 

minimum completeness criteria found 

in 40 CFR part 51, Appendix V. 

Conditioning the phase-in on a 

completeness review will not only 

encourage states to make timely SIP 

submissions addressing the NNSR 

requirements, but also ensure that those 

submissions contain the minimum 

information necessary to enable the 

Administrator to determine whether the 

SIP complies with the statute. If a state 

with a designated PM2.5 nonattainment 

area that is currently relying on 

Appendix S makes a submission 

addressing NNSR program 

requirements, including a NNSR 

precursor demonstration, within 18 

months of the designation (as required 

by CAA section 189(a)(2)(B)), either EPA 

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must evaluate the submission for 

completeness within 6 months or the 

SIP will become complete by operation 

of law, pursuant to CAA section 

110(k)(1)(B). The latest date that a 

timely-submitted implementation plan 

would be determined to be complete by 

the EPA or deemed complete by 

operation of law is 24 months from the 

effective date of the PM2.5

nonattainment area designation. In other 

words, in the absence of EPA action to 

evaluate completeness, a state that 

submits a timely SIP addressing NNSR 

and including a NNSR precursor 

demonstration can be confident the 

submission will become complete by 

operation of law by the 24-month 

conditional phase-in date, and such 

states will not be required to regulate 

the precursor addressed by its 

demonstration (VOC or ammonia) in the 

PM2.5 nonattainment area pursuant to 

Appendix S during the period of EPA’s 

review of the SIP. States that submit 

untimely SIPs, after the 18-month SIP 

submission deadline, cannot rely on the 

SIP becoming complete by operation of 

law before the 24-month conditional 

phase-in date. If the EPA has not acted 

to evaluate the completeness of the 

state’s untimely SIP by the 24-month 

conditional phase-in, control of VOC 

and ammonia are automatically phased 

in for the PM2.5 nonattainment area 

under Appendix S, regardless of 

whether such SIP submission might 

later be determined complete, whether 

by EPA or by operation of law. Thus, if 

a state submits an untimely SIP 

addressing NNSR for a particular PM2.5

nonattainment area, including an NNSR 

precursor demonstration, such state can 

only avoid the conditional phase-in of 

VOC and ammonia control pursuant to 

Appendix S if the EPA affirmatively 

determines the submission to be 

complete by 24 months from the date of 

the area designation. In such 

circumstances, states are encouraged to 

coordinate with the appropriate EPA 

Regional Office. 

The timing of the phase-in for a 

particular area will depend upon the 

effective date of the designation to 

nonattainment for PM2.5. Because this 

rule establishes requirements that apply 

in both present and future 

nonattainment areas, the regulations 

address the timing of the precursor 

phase-in both for areas already 

designated nonattainment for PM2.5 and 

for areas that may be so designated in 

the future. 

For any existing nonattainment area 

that was first designated nonattainment 

for PM2.5 effective on or before April 15, 

2015 (which includes areas designated 

for the 1997, 2006 and 2012 PM2.5

NAAQS), VOC and ammonia will be 

required to be controlled as PM2.5

precursors for any NNSR permit issued 

on or after April 15, 2017 (24 months 

from the date of area designations for 

the 2012 PM2.5 NAAQS), unless the state 

has submitted before the phase-in date 

a complete SIP revision that includes 

the state’s proposed NNSR program for 

PM2.5 and a NNSR precursor 

demonstration showing that VOC, 

ammonia, or both do not contribute 

significantly to PM2.5 concentrations 

that exceed the standard in a given 

PM2.5 nonattainment area, consistent 

with the requirements of 51.1003, in 

which case the control of the precursors 

addressed by the submitted 

demonstration will not be required to be 

controlled at the 24-month mark. See 

Appendix S, section II.A.31.(ii)(b)(3). In 

order to satisfy this condition, such 

demonstration must be submitted in the 

form of a SIP revision and must either 

be determined to be complete by the 

EPA or deemed to be complete by 

operation of law pursuant to the 

provisions in CAA section 110(k)(1)(B). 

Although areas were designated 

nonattainment for the 1997, 2006, and 

2012 standards at different times, the 

EPA believes it is reasonable to apply 

the same phase-in date for all areas 

designated nonattainment as of the date 

of the designations for the 2012 

standard. Area designations for the 2012 

PM2.5 standards were finalized on April 

15, 2015, and plans addressing the 

nonattainment area requirements as to 

that standard are due October 15, 2016. 

Therefore, states evaluating their NNSR 

programs in light of the subpart 4 

requirements with respect to the 2012 

standard will have some, if limited, 

opportunity to consider the 

requirements of this rule and EPA’s 

technical guidance before submitting a 

plan revision addressing the statutory 

and regulatory requirements. By 

contrast, area designations for the 1997 

standards were finalized many years 

ago. As to those areas, after the court’s 

decision in NRDC v. EPA, the EPA 

promulgated a rule setting a deadline of 

December 31, 2014, for states to submit 

any attainment plan provisions that may 

be necessary to satisfy the subpart 4 

requirements. 79 FR 31566 (June 2, 

2014) at 31570. This included any 

submissions necessary to address NNSR 

permitting such as the CAA section 

189(e) requirement that states regulate 

all PM2.5 precursors absent a 

demonstration that such regulation is 

unnecessary. This deadline superseded 

previous SIP submission deadlines 

initially established by application of 

the subpart 1 requirements. As that 

deadline has passed, if the EPA were to 

apply the 24-month phase-in policy 

strictly, states relying upon Appendix S 

to issue NNSR permits in these areas 

would have had to commence regulating 

VOC and ammonia as PM2.5 precursors 

in June 2015—6 months after the SIP 

submission deadline. The EPA believes 

it is reasonable to provide states that 

have areas designated nonattainment 

with respect to the 1997 and 2006 PM2.5

standards with at least some limited 

opportunity to consider the 

requirements of this rule and EPA’s 

technical guidance and submit a plan 

revision addressing the statutory and 

regulatory requirements before the state 

will be required to regulate sources of 

VOC and ammonia in such areas. 

Accordingly, the EPA finds that it is 

reasonable to subject all areas 

designated nonattainment for any PM2.5

standard as of April 15, 2015, to the 

same Appendix S requirements in this 

final rule. 

For any area that is first designated 

nonattainment for any PM2.5 NAAQS 

after April 15, 2015 (that is, the area was 

not already designated nonattainment 

with respect to another PM2.5 NAAQS 

immediately prior to such date), any 

state relying on Appendix S to issue a 

NNSR permit on or after the effective 

date of such area designation must 

require control of SO2 and NOX as 

regulated NSR pollutants (PM2.5

precursors). Beginning on the date 24 

months from the effective date of such 

area designation, a state relying on 

Appendix S to issue a NNSR permit 

must also require control of VOC and 

ammonia as regulated NSR pollutants 

(PM2.5 precursors) in that area, unless by 

that date the state has submitted a 

complete SIP revision that includes the 

state’s proposed NNSR program for 

PM2.5 and an accompanying NNSR 

precursor demonstration that sources of 

VOC, ammonia, or both ammonia do not 

contribute significantly to the PM2.5

concentrations that exceed the standard 

in the PM2.5 nonattainment area. See 

Appendix S, section II.A.31.(ii)(b)(4). As 

explained earlier, such demonstration 

must be submitted as part of a SIP 

revision that is determined to be 

complete by the EPA or deemed to be 

complete by operation of law by the 

conditional phase-in date. 

As noted earlier, the second phase-in 

provision applies to PM2.5

nonattainment areas that were not 

already designated as nonattainment for 

PM2.5 immediately prior to that date. If 

at the time of a new designation, an area 

was already designated nonattainment 

as to any prior PM2.5 NAAQS, and 

Appendix S applied and continues to 

apply for NNSR permitting with respect 

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to that existing nonattainment area, all 

PM2.5 precursors would likely already 

be required to be regulated in 

accordance with a prior phase-in 

schedule prescribed under Appendix S 

for that existing nonattainment 

designation. In such cases, all 

precursors would continue to be subject 

to regulation for NNSR permitting under 

Appendix S, even as to the new 

nonattainment designation. That is, 

once Appendix S definition of regulated 

NSR pollutant applies to all PM2.5

precursors in a given nonattainment 

area, it is not possible to later defer 

regulation of any precursors so long as 

the state continues to rely on Appendix 

S for NNSR permitting in that area. 

Once the state submits a SIP including 

an NNSR program and any appropriate 

NNSR precursor demonstration, and the 

EPA approves the SIP, Appendix S will 

no longer apply for the issuance of 

NNSR permits for PM2.5. 

iii. Comments and Responses 

Comment: Several commenters 

generally supported the EPA’s preferred 

approach in the proposal that would 

require only SO2 and NOX as PM2.5

precursors for NNSR permits issued 

pursuant to Appendix S. One 

commenter supported the alternative 

approach to phase in VOC and ammonia 

as PM2.5 precursors, while another 

commenter expressly opposed the EPA’s 

preferred approach and the phase-in 

alternative, claiming that any approach 

that does not regulate all four scientific 

precursors of PM2.5 is contrary to CAA 

subpart 4 and unlawful. 

Commenters supporting the preferred 

approach did not believe that it was 

appropriate to require NSR permitting 

during an interim period for sources 

that may be exempted from control 

requirements if a state can demonstrate 

that these sources do not contribute 

significantly to nonattainment in a 

particular area. These commenters 

stated that, since most, if not all, areas 

will not be able to demonstrate that SO2

and NOX do not contribute significantly 

to nonattainment levels of PM2.5, the 

EPA’s approach to include these two 

precursors in the interim is reasonable. 

One commenter who supported the 

EPA’s alternative approach to phase in 

VOC and ammonia as PM2.5 precursors 

stated that there are many unanswered 

questions and the science is not 

adequate to justify regulation of 

secondary formation precursors at this 

time. The commenter further stated that 

Appendix S should initially require 

sources issued a NNSR permit to control 

only SO2 and NOX as PM2.5 precursors, 

and only later, after a prescribed date 

(e.g., the date on which SIP revisions 

based on subpart 4 requirements are 

due), require sources to control 

emissions of VOC and ammonia, if 

applicable. 

A commenter who opposed any 

approach that did not immediately 

require the control of all four scientific 

precursors of PM2.5 stated that such 

approaches are unlawful and must be 

rejected. The commenter stated that the 

EPA must require immediate regulation 

of all four precursors, as only that 

alternative follows the plain language of 

the CAA and the NRDC decision. The 

commenter objected to the presumptive 

exemption of VOC and ammonia 

emissions as being identical to the 

‘‘gamesmanship’’ that both Congress 

intended to curtail with subpart 4, and 

that the DC circuit found illegal in the 

NRDC decision. The commenter stated 

that the scope of the statutory 

definition, and consequently the 

application of subpart 4, did not change 

when the EPA subdivided PM10 by 

regulation. The commenter stated that 

only this option would conform 

Appendix S to the requirements of 

subpart 4, and in so doing, align 

Appendix S with forthcoming state 

obligations to harmonize the PM2.5

portions of their SIPs with the 

obligations of subpart 4. The commenter 

stated that this approach would 

encourage states to submit SIPs in a 

timely fashion, rather than to rely on 

Appendix S for an extended period of 

time. The commenter stated that, in 

contrast, were the EPA to adopt illegally 

lax provisions into Appendix S, states 

might delay submitting replacement 

SIPs, particularly in those parts of the 

country with high VOC or ammonia 

precursor emissions. 

Response: The EPA took each of these 

comments into consideration in 

concluding that the proposed phase-in 

alternative is a reasonable approach that 

balances competing factors regarding 

the regulation of PM2.5 precursors for 

NNSR permits issued pursuant to 

Appendix S. While CAA section 189(e) 

generally requires state plans to control 

all PM2.5 precursors, it also affords states 

an opportunity to demonstrate that a 

particular precursor does not contribute 

significantly to levels of PM2.5 that 

exceed the standard in a PM2.5

nonattainment area. Section 189(e) of 

the CAA clearly addresses how PM2.5

precursors must be regulated in the 

state’s plan, but the statute does not 

address exactly when precursors are to 

be regulated pursuant to the NNSR 

requirements of Appendix S prior to the 

submission of the state’s plan. As noted 

earlier, the NNSR provisions are unique 

among the nonattainment area 

requirements in that sources are 

required to address NNSR immediately 

upon the effective date of an area’s 

designation to nonattainment, rather 

than upon the EPA’s approval of the 

state’s SIP, which could be as much as 

3 years after the nonattainment area 

designation (e.g., states have 18 months 

to submit attainment plans and the EPA 

may have up to 18 months from the date 

of the SIP submission to finalize action 

on such plans). Given this ambiguity in 

the statute and the unique application of 

the NNSR requirements, we believe a 

reasonable and balanced approach to 

the Appendix S requirements would 

allow states a time-limited period to 

submit a NNSR program for PM2.5 that 

includes a NNSR precursor 

demonstration that sources of a 

precursor do not contribute significantly 

to PM2.5 levels in a PM2.5 nonattainment 

area. The time limit will discourage 

states from unreasonably delaying 

regulation of such precursors where 

otherwise required to do so. 

Moreover, the EPA believes it is 

reasonable to construct the Appendix S 

provisions regulating PM2.5 precursors 

in a manner that closely follows the way 

in which the precursors are being 

regulated in most state NSR programs 

based on EPA’s 2008 NSR regulation. 

For areas that were designated 

attainment or unclassifiable prior to a 

new nonattainment designation, the 

PSD permit program was in effect and 

required that, at minimum, SO2 and 

NOX be regulated as PM2.5 precursors. It 

is therefore reasonable to ensure that 

those precursors continue to be 

regulated as part of the interim NNSR 

permit program via Appendix S. 

Moreover, in areas that were already 

designated nonattainment for a preexisting PM2.5 NAAQS, and an approved 

plan containing NNSR permit 

requirements for PM2.5 is in effect, 

sources are required to control SO2 and 

NOX as PM2.5 precursors, as required 

under the 2008 PM2.5 NSR rule, until the 

EPA approves a SIP revision conforming 

those NNSR programs to the 

requirements of CAA subpart 4. 

Similarly, the EPA believes it is 

reasonable to not require the regulation 

of VOC and ammonia immediately upon 

designation of an area to nonattainment 

because it result in more regulation in 

newly designated nonattainment areas 

relying on Appendix S than is required 

in most states with approved programs. 

All states will ultimately be required to 

address the regulation of ammonia and 

VOC at the time their state plans are due 

or, failing submission of such plan by 

states relying on Appendix S to issue 

NNSR permits, Appendix S will require 

such regulation. 

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58120 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

234The preamble language did not explicitly state 

that it was our intent to revise the definition in 

Appendix S to add separate major source thresholds 

for direct PM2.5 emissions and PM2.5 precursors, in 

the same way that earlier we had proposed to revise 

the definition of ‘‘major stationary source’’ in the 

NNSR regulations at 40 CFR 51.165. Instead, the 

preamble referred only to a change to the definition 

of ‘‘major stationary source’’ at proposed section 

II.A.4(i)(a)(7) of Appendix S, where a 70 tpy 

threshold for direct PM2.5 emissions is addressed. 

The proposed regulatory text did, however, also 

include new section II.A.4(i)(a)(8) of Appendix S, 

which adds a 70 tpy major source threshold for 

emissions of individual PM2.5 precursors. Despite 

this omission in the preamble discussion of the 

proposed changes to Appendix S, we believe that 

commenters had ample opportunity to comment on 

the actual changes being made to the definition of 

‘‘major stationary source’’ in Appendix S because 

the intended change concerning emissions of PM2.5

and PM2.5 precursors was accurately provided in 

the regulatory text. 

235The EPA also notes that the definition of 

‘‘major stationary source’’ in Appendix S is being 

revised in this rule at section II.A.4(i)(a) of 

Appendix S, which currently ends with the phrase 

‘‘according to paragraphs II.A.4(i)(a)(1) through (6) 

of this ruling.’’ By proposing to add new paragraphs 

(7) and (8), this phrase will be revised to read 

‘‘according to paragraphs II.A.4(i)(a)(1) through (8) 

of this ruling.’’ The phrase is being modified 

accordingly in this final rule. 

The phase-in schedule contained in 

this final rule requires that VOC and 

ammonia be phased in as PM2.5

precursors 24 months from the effective 

date of area designations for PM2.5; 

however, states will not be required to 

control VOC and ammonia as PM2.5

precursors as part of a NNSR permit 

issued under Appendix S so long as the 

state submits a plan revision that 

includes the state’s NNSR program for 

PM2.5 and a NNSR precursor 

demonstration to show that sources of a 

precursor does not contribute 

significantly to PM2.5 levels that exceed 

the standard in a PM2.5 nonattainment 

area. See Appendix S, sections 

II.A.31.(ii)(b)(3) and (4). 

In initially requiring sources to 

control SO2 and NOX as regulated NSR 

pollutants (PM2.5 precursors), states that 

rely on Appendix S to issue NNSR 

permits generally will implement NNSR 

consistent with those states that issue 

NNSR permits for PM2.5 under the 

NNSR program in their approved SIP. 

The EPA believes that it is reasonable 

and appropriate to assure this 

consistency in the issuance of NNSR 

permits during the interim period when 

all states must revise their plans to 

address the 2012 PM2.5 NAAQS. 

Moreover, this final rule allows states to 

submit a SIP revision that contains a 

NNSR precursor demonstration showing 

that new major stationary sources and 

major modifications of either SO2 or 

NOX should be exempted where an 

analysis of increases in emissions of the 

particular precursor shows that sources 

of the precursor do not contribute 

significantly to PM2.5 levels that exceed 

the standard in the PM2.5 nonattainment 

area. In this case, the opportunity to 

exempt sources of either SO2 or NOX as 

PM2.5 precursors is addressed in the 

NNSR rules at 51.165. See 40 CFR 

51.165(a)(13). Hence, when the EPA 

approves a state’s plan revision 

containing the NNSR program for PM2.5

and a NNSR precursor demonstration 

showing an insignificant contribution, a 

new major stationary source or major 

modification of either SO2 or NOX as 

PM2.5 precursors will not be required to 

be controlled going forward in a NNSR 

permit issued to address PM2.5, which 

permit would then be issued in 

accordance with the NNSR 

requirements in the approved plan, 

rather than the NNSR requirements in 

Appendix S. 

With regard to the commenter’s 

concern that states might delay 

submitting NNSR programs as part of 

their PM2.5 SIPs if Appendix S regulates 

only SO2 and NOX, the phase-in 

approach in this final rule will negate 

any incentive that a state may have to 

delay submitting an NNSR program for 

PM2.5 addressing the CAA section 189(e) 

requirement to regulate all four 

precursors, absent a showing that such 

regulation is unnecessary. In fact, the 

phase-in requirement should actually 

encourage states to timely submit their 

NNSR programs for PM2.5. Given CAA 

section 189(e) does not directly speak to 

its application to the Appendix S 

requirements, the EPA believes this 

approach represents a reasonable and 

equitable application of the CAA section 

189(e) requirements regarding 

regulation of PM2.5 precursors to states 

applying Appendix S. 

b. Appendix S Definition of ‘‘major 

stationary source’’ in Serious PM2.5

Nonattainment Areas 

i. Summary of Proposal 

The EPA proposed 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 of 

direct PM2.5 and PM2.5 emissions in 

PM2.5 nonattainment areas reclassified 

as Serious. This proposed amendment 

to Appendix S was similar to one that 

was proposed to the definition of ‘‘major 

stationary source’’ in 40 CFR 51.165.234

ii. Final Rule 

In this final rule, the EPA is amending 

the definition of ‘‘major stationary 

source’’ in Appendix S to include 70 tpy 

major source thresholds for direct PM2.5

emissions and individual PM2.5

precursors, applicable in Serious PM2.5

nonattainment areas.235 See Appendix S 

sections II.A.4(i)(a)(7) and (8), 

respectively. As described earlier, 

applicability of the NNSR requirements 

to a source will be determined 

individually for direct PM2.5 emissions 

and for emissions of individual PM2.5

precursors. For example, if a new source 

locating in a Serious PM2.5

nonattainment area would emit 70 tpy 

of the PM2.5 precursor SO2, it will be 

considered a major source of PM2.5 (with 

respect to the SO2 precursor) and will be 

subject to the NNSR requirements for 

PM2.5 with regard to the SO2 emissions. 

However, if the same proposed source 

does not emit 70 tpy of direct PM2.5

emissions or another PM2.5 precursor, 

the emissions increase of direct PM2.5 or 

the other precursor will not be subject 

to control based on the NNSR 

requirements for PM2.5. It should also be 

noted that VOC and ammonia are 

subject to the phase-in schedule 

described in the definition of ‘‘regulated 

NSR pollutant’’ in the NNSR regulations 

at Appendix S, section II.A.31.(ii)(b)(2). 

iii. Comments and Responses 

As explained in Section VIII.B.1.b of 

this preamble, commenters addressing 

the proposed major source threshold of 

70 tpy for sources of PM2.5 and its 

precursors locating in Serious areas had 

mixed responses, particularly with 

regard to the appropriate thresholds for 

precursors. Most of the comments 

applied generally to the proposed 

thresholds in 40 CFR 51.165 and 

Appendix S. The EPA’s responses to 

these comments are provided in that 

earlier section of the preamble. 

Comment: One commenter, however, 

recommended that during the SIP 

transition period (and while the EPA 

continues its analysis of the precursor 

relationships to PM2.5), the EPA should 

allow states to make a case-by-case 

permitting demonstration to use higher 

major source thresholds for precursors 

for NNSR permit reviews. 

Response: As explained previously, in 

light of the ongoing precursor impact 

studies as well as concerns about the 

legality of setting higher major source 

thresholds than those specified in the 

CAA, the EPA believes it is most 

reasonable to establish a 70 tpy major 

source threshold under Appendix S for 

sources of direct PM2.5 emissions and 

each PM2.5 precursor locating in Serious 

nonattainment areas. 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58121 

c. Significant Emissions Rates (SERs) in 

Appendix S—PM2.5 Precursors 

i. Summary of Proposal 

As explained earlier, the EPA 

proposed as its preferred approach to 

add NOX as a PM2.5 precursor in the 

Appendix S definition of ‘‘regulated 

NSR pollutant.’’ Accordingly, the EPA 

also proposed to amend the definition of 

‘‘significant’’ at section II.A.10(i) of 

Appendix S to establish a SER of 40 tpy 

for NOX as a PM2.5 precursor. The 

Appendix S definition already contains 

a SER for SO2 as a PM2.5 precursor at 40 

tpy of SO2. The EPA did not explicitly 

propose to include SERs for VOC and 

ammonia in Appendix S as part of the 

preferred approach; however, the EPA’s 

proposed alternative approach to phase 

in VOC and ammonia as PM2.5

precursors at a later date would 

inherently necessitate adding SERs for 

those two additional precursors in the 

event that an alternative approach was 

ultimately selected for the final rule. 

ii. Final Action 

The EPA is revising the definition of 

‘‘significant’’ in Appendix S at section 

II.A.31(ii)(b)(2) to provide SERs for NOX

and VOC as PM2.5 precursors, consistent 

with its decision to conditionally phase 

in regulation of all four PM2.5 precursors 

24 months from the date of 

redesignation. The individual SERs for 

NOX and VOC as PM2.5 precursors, 

being added to the existing SER for SO2

as a PM2.5 precursor, are each defined as 

40 tpy of the respective precursor, 

consistent with the SERs provided in 

the revised definition of significant in 

40 CFR 51.165. 

The EPA is not adding a SER for 

ammonia (as a PM2.5 precursor) in the 

Appendix S definition of ‘‘significant’’ 

in this action. Consistent with the EPA’s 

approach for allowing states to define 

‘‘significant’’ for ammonia in their 

NNSR rules, and for the reasons 

explained in Section VIII.B.1.c of this 

preamble, the EPA will allow states that 

issue NNSR permits pursuant to the 

requirements in Appendix S to define 

‘‘significant’’ with respect to ammonia 

in a particular area in each NNSR 

permit issued pursuant to Appendix S. 

The state should provide a technical 

justification to support the definition of 

‘‘significant’’ for ammonia, including 

any SER developed by the state for a 

particular nonattainment area, and such 

justification should be included in the 

administrative record for each proposed 

permit. The state also has the discretion 

to define ‘‘significant’’ with respect to 

ammonia as a PM2.5 precursor in those 

cases where it is determined that the 

proposed modification will result in 

insignificant increases of ammonia and 

the source will therefore not be required 

to obtain a major NNSR permit. In such 

cases, the state and the source should 

also document the technical 

justification for determining the source 

impacts will be insignificant, including 

any SER developed by the state for a 

particular nonattainment area, whether 

such documentation occurs in the 

administrative record for a minor source 

permit, a nonapplicability 

determination, or some other form in 

the state or source’s records. The state 

should consult with the appropriate 

EPA Regional Office for assistance in 

developing an appropriate definition of 

‘‘significant’’ for ammonia as a PM2.5

precursor in each permit or for each 

nonattainment area. 

iii. Comments and Responses 

The comments regarding the proposed 

addition of SERs for NOX and VOC 

emissions as PM2.5 precursors in the 

NNSR definition of ‘‘significant’’ were 

summarized in Section VIII.B.1.c of this 

preamble. Those comments applied 

generally to the NNSR regulations at 40 

CFR 51.165 and Appendix S. The reader 

is referred to that earlier section of the 

preamble to review the comments and 

the EPA’s responses to them. 

Comment: Some commenters 

seemingly addressing NNSR under 

Appendix S recommended that the EPA 

include a provision allowing states to 

make case-by-case determinations to use 

higher SERs for precursors for NNSR 

permits issued before the SIP is 

effective. The commenter stated that the 

precursor SERs are too low and do not 

realistically reflect the effect that each 

precursor has on ambient PM2.5

concentrations. 

Response: The EPA believes that the 

commenter’s concern is partially 

addressed by the fact that, in using 

Appendix S to review NNSR permit 

applications, neither VOC nor ammonia 

will need to be controlled as PM2.5

precursors if the state has submitted to 

the EPA a complete SIP submission that 

includes the state’s NNSR program for 

PM2.5 and a NNSR precursor 

demonstration showing that a particular 

precursor does not contribute 

significantly to ambient concentrations 

of PM2.5 in the nonattainment area, even 

though the plan revision containing 

such demonstration has not yet been 

formally approved. Until the SIP 

development period has passed and 

unless the state has failed to submit 

such a demonstration, the state issuing 

permits pursuant to Appendix S will 

not be required to regulate VOC or 

ammonia as PM2.5 precursors. If a state 

has not submitted a SIP including the 

state’s NNSR program for PM2.5 and a 

NNSR precursor demonstration for 

either VOC or ammonia, sources of 

these precursor emissions must be 

controlled as PM2.5 precursors in any 

NNSR permit issued pursuant to 

Appendix S beginning on the prescribed 

phase-in date. 

C. Transition Provisions for Major 

Source Permitting in PM2.5

Nonattainment Areas 

The EPA did not propose any 

transition provisions for NNSR permit 

applications in either 40 CFR 51.165 or 

Appendix S that would expressly 

grandfather pending PSD or NNSR 

permit applications for proposed new 

and modified major stationary sources 

from newly established NNSR permit 

requirements applicable to PM2.5

nonattainment areas. In the final 2012 

PM NAAQS Rule, the EPA provided a 

grandfathering provision only for 

certain PSD permit applications with 

respect to the revised PM2.5 standard. 

Historically, the EPA has not provided 

for the grandfathering of any permit 

applications from new NNSR 

requirements or from application of 

existing NNSR requirements to new or 

revised standards. Nevertheless, in 

promulgating the 2012 PM NAAQS 

Rule, the EPA received unsolicited 

comments advocating for grandfathering 

of NNSR requirements for the revised 

standard. Thus, while explaining the 

reasons why it did not believe that 

NNSR grandfathering was appropriate, 

the EPA sought comments in the 

proposal on possible circumstances 

where grandfathering similar to the PSD 

grandfathering provision established for 

the 2012 PM2.5 standard might be 

appropriate with respect to changes 

made regarding NNSR requirements for 

PM2.5 in this rulemaking. 

Several comments received during the 

2012 p.m. NAAQS rulemaking 

recommended that the EPA establish a 

grandfathering provision for NNSR as 

was proposed for the PSD program. A 

subset of these commenters 

recommended that PSD permit 

applications be grandfathered from the 

NNSR requirements for the revised 2012 

PM2.5 standard by establishing an 

effective date for designations 1 year 

after initial publication in the Federal 

Register. The commenters presumably 

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 and permits issued 

under the PSD requirements rather than 

the NNSR requirements for PM2.5. 

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58122 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

236The applicable NNSR requirements would be 

either the NNSR requirements for PM2.5 in the 

state’s existing approved SIP or the requirements 

found at 40 CFR part 51 Appendix S, when a state’s 

approved 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, but those additional 

requirements will not apply in states with approved 

SIPs that include NNSR requirements for PM2.5

until the EPA approves the SIP revision. See 78 FR 

3086 (January 15, 2013), at page 3263. 

237See 78 FR 3249 at page 3250. 

238Compare CAA section 165(a) (permitting 

requirements for sources locating in attainment and 

unclassifiable areas) with CAA sections 172(c)(5) 

and 173 (permitting requirements for sources 

locating in nonattainment areas). 239See 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. 

The EPA explained at the time 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 PM2.5.236 Also, the EPA 

does not agree with the commenters’ 

recommendation that the effective date 

of the area designation be delayed by 1 

year because this approach, similar to 

delaying the effective date of the 

NAAQS, would also delay the 

implementation of the attainment plan 

and defer the important health benefits 

associated with the revised NAAQS. In 

the same preamble, the EPA proposed a 

schedule for promulgating area 

designations for PM2.5 that involved the 

maximum allowable 2-year period from 

the signature date of the 2012 PM2.5

NAAQS, as provided in CAA section 

107(d)(1)(B). The CAA allows for a 1- 

year extension for such designations, 

but only if there is insufficient 

information to enable such designations 

to be made.237

In response to the EPA’s request for 

comments in the proposal, commenters 

recommended that the EPA clarify the 

PM2.5 NSR grandfather policy to explain 

that both PSD and NNSR permit 

applications are exempt from the 

precursor and planning requirements 

being finalized in this rulemaking. In 

particular, the commenters 

recommended that the EPA establish a 

PM2.5 NSR transition policy that delays 

regulation of the scientific precursors of 

PM2.5 under any NSR program until the 

EPA has a better understanding of how 

these precursors contribute to 

nonattainment and could deteriorate air 

quality. One of the commenters 

indicated that a transitional policy is 

especially important until the EPA 

completes a rulemaking on a SER for 

ammonia. One of the commenters 

recommended that the EPA should 

allow for the grandfathering of pending 

PSD permit applications, similar to the 

PSD grandfathering provision for the 

2012 PM2.5 NAAQS, for sources that 

will not be issued a permit until after 

the effective date of the nonattainment 

designation under certain conditions. 

This commenter stated that CAA section 

165(c), which forms part of the EPA’s 

basis for grandfathering in the PSD 

context, should also apply to NNSR 

permit decisions. 

The EPA does not find a compelling 

reason to grandfather pending NNSR 

permit applications for which a permit 

has not yet issued once the new NNSR 

requirements—primarily affecting the 

control of PM2.5 precursors—become 

effective. The EPA believes that it is 

reasonable to require that a new or 

modified major stationary source 

control emissions of PM2.5 precursors 

where such emissions contribute 

significantly to PM2.5 levels in the 

nonattainment area. If such precursor 

emissions are not effectively controlled, 

and offset by reductions in existing 

emissions, an increased burden could be 

placed on the overall attainment plan to 

address those emissions in order to 

attain the NAAQS in a timely manner. 

While the final rule contains no 

general grandfathering provision, this 

final rule does provide a phase-in 

process for states relying on Appendix 

S for purposes of issuing NNSR permits 

for PM2.5. Appendix S will require the 

immediate regulation of SO2 and NOX as 

PM2.5 precursors, the regulation of VOC 

and ammonia as PM2.5 precursors will 

only be required under certain 

conditions and on a delayed timetable. 

See Appendix S, revised section 

II.A.31.(ii)(b)(2)–(5). The precursor 

provisions in Appendix S should 

alleviate some of the commenter’s 

concerns that the regulation of 

additional precursors will be required 

immediately upon the effective date of 

this final rule. Instead, the phase-in 

schedule for the regulation of VOC and 

ammonia will permit states the 

opportunity allowed by CAA section 

189(e) to demonstrate that a particular 

precursor need not be subjected to 

control in a particular nonattainment 

area. Accordingly under the interim 

NNSR requirements in Appendix S, a 

state will not be required to begin 

immediate regulation of precursors for 

which sources will likely be exempted 

from the regulations upon review of a 

state’s NNSR SIP submission. Similarly, 

where the state has a previously 

approved NNSR program for PM2.5, the 

existing requirements for controlling 

precursors would continue to apply 

until the new SIP revisions required by 

this rule, including new precursor 

control requirements, are approved. 

Thus, such states would not be required 

to immediately regulate any PM2.5

precursors not already required by the 

approved plan during the interim plan 

development period. 

With regard to grandfathering PSD 

permit applications, we do not interpret 

the CAA to allow for the issuance of a 

PSD permit in an area that is designated 

nonattainment. 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 designation.238

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 in a given 

area 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.239

IX. Other Requirements and 

Considerations for PM2.5

Nonattainment Areas 

A. Waivers Under CAA Section 188(f) 

1. Statutory Requirements and Existing 

Guidance 

a. Summary of Proposal. The proposal 

summarized the statutory requirements 

and existing guidance for CAA section 

188(f), which 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 it provides that, ‘‘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.’’ The agency requested 

comment on whether the existing 

guidance in the Addendum is 

appropriate when implementing the 

current and any future PM2.5 NAAQS. 

b. Final Rule. The EPA is hereby 

affirming its reliance on the 

interpretation of CAA section 188(f) 

described in the Addendum for 

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240See 59 FR 42003–42008, August 16, 1994. 

241Section 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. 

242References to ‘‘air agencies’’ are meant to 

include state, local and tribal air agencies 

responsible for implementing the Exceptional 

Events Rule. 

243The 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. 

purposes of implementing the PM2.5

NAAQS.240 For example, the 

Addendum lays out a series of questions 

that should be answered before the 

waiver provisions can be applied, 

including questions related to the types 

of sources that may be considered 

anthropogenic and nonanthropogenic, 

the specific conditions under which the 

attainment date for a Moderate area may 

be waived, and the time period that 

would apply to an attainment date 

waiver. The EPA believes that these 

questions, and the general guidance 

provided in the Addendum on how to 

evaluate the answers, provide adequate 

direction to the EPA and to states 

potentially interested in seeking waivers 

for certain PM2.5 NAAQS nonattainment 

areas. The EPA therefore refers 

interested states to the waiver guidance 

contained in the Addendum for more 

detail on how the agency interprets 

CAA section 188(f) for purposes of 

implementing the PM2.5 NAAQS. 

c. Comments and Responses. The 

comments received on this section are 

addressed in the Response to Comments 

document found in the docket for this 

action. 

2. Relationship Between the CAA 

Section 188(f) Waiver Provisions and 

the EPA’s Exceptional Events Rule 

a. Summary of Proposal. The proposal 

summarized the relationship between 

the 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 319.241 The 

Exceptional Events Rule provides a 

mechanism by which the EPA can 

concur with a state’s request to exclude 

from regulatory decisions air quality 

monitoring data determined by the EPA 

to have been affected by exceptional 

events.242 The Exceptional Events Rule 

applies to all the NAAQS pollutants, 

including PM2.5. CAA section 188(f) and 

the Exceptional Events Rule provide 

separate mechanisms by which states 

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. 

b. Final Rule. The EPA did not make 

any revisions to its interpretation of the 

relationship between the CAA section 

188(f) waiver provisions and EPA’s 

Exceptional Events Rule. 

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.243

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 a state’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, states 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. 

The EPA notes that there could be 

some potential overlap between the 

application of the Exceptional Events 

Rule and CAA section 188(f) because 

the conditions necessary for the 

Administrator to make a determination 

under CAA section 188(f)—i.e., the lack 

of a significant anthropogenic 

contribution to a violation—may 

overlap with conditions that may be 

considered an exceptional event, 

particularly a natural event, which by 

definition represents a nonanthropogenic contribution. The EPA 

believes that this potential for overlap 

can best be addressed by considering 

the applicability of the Exceptional 

Events Rule and CAA section 188(f) in 

sequence. Thus, the EPA recommends 

that states first consider whether the 

monitored air quality data on specific 

days were influenced by an exceptional 

event. If the state 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, and there would be no need 

for a CAA section 188(f) waiver. If the 

state determines that, even with the 

exclusion of the event-influenced data, 

the waiver provisions of CAA 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. 

Given that section 188(f) has rarely been 

invoked, a state wishing to pursue this 

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244This final rule was not challenged, nor was it 

affected 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. 

provision should work closely with its 

EPA Regional Office. 

c. Comments and Responses. 

Comments: Some commenters urged the 

EPA to clarify the two-step approach. 

Some commenters recommended that 

the EPA refrain from directing the 

sequence and allow states to decide 

which of these provisions should apply 

in the specific circumstances that they 

are addressing, consistent with the 

commenter’s overall recommendation 

that the EPA give states the maximum 

flexibility in developing PM2.5 SIPs. 

Some commenters urged the EPA to 

provide guidance to the states on when 

this two-step approach would be 

appropriate, and when it would be 

inappropriate. Commenters did not 

want implementation planning to follow 

the EPA’s exceptional events 

justification model in which there is 

great variability among the EPA regions. 

Commenter encouraged the EPA to work 

to ensure that PM2.5 implementation 

plan reviews are subject to similar 

requirements in all EPA regions with 

clarifying language in the final guidance 

to ensure some level of national 

consistency. 

Response: The EPA agrees with the 

first comment that, rather than the EPA 

‘‘directing the sequence,’’ the affected 

state and the appropriate EPA regional 

office should discuss the scenario and 

the affected data to determine whether 

the Exceptional Events Rule or CAA 

section 188(f) is the most appropriate 

mechanism. This decision would be 

made on a case-by-case basis 

considering the specific, relevant facts. 

In most cases, if the monitored air 

quality data satisfy the requirements of 

the Exceptional Events Rule, then 

applying these provisions would likely 

provide additional regulatory 

flexibilities beyond those that CAA 

section 188(f) would provide. However, 

regardless of whether the data in 

question meet or do not meet the 

requirements of the Exceptional Events 

Rule (e.g., because the exceptional 

events definition is not met in that the 

data do not constitute an exceedance or 

violation of the NAAQS or because 

other Exceptional Events rule criteria 

are not met), the waiver provisions in 

CAA section 188(f) could apply. 

The EPA recognizes the 

implementation challenges associated 

with the 2007 Exceptional Events Rule 

and recently proposed revisions to this 

rule to address certain substantive 

issues raised by state, local and tribal 

co-regulators and other stakeholders 

since promulgation of the rule and to 

increase the administrative efficiency of 

the Exceptional Events Rule criteria and 

process (80 FR 72840, November 20, 

2015). The public comment period on 

this rule closed on February 3, 2016. 

The EPA will consider timely comments 

provided to the Exceptional Events Rule 

docket as we finalize the revisions to 

this rule. 

B. Conformity Requirements 

1. Requirements That Apply to Both 

Transportation Conformity and General 

Conformity 

a. Background on 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.244 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 the 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 transportation 

conformity rulemakings, policy 

guidance and outreach materials, see the 

EPA’s Web site at http://www3.epa.gov/ 

otaq/stateresources/transconf/

index.htm. The EPA issued 

transportation conformity guidance 

related to the implementation of the 

2012 primary annual PM2.5 NAAQS in 

November 2015. The guidance is 

available at http://www3.epa.gov/otaq/

stateresources/transconf/documents/

420b15091.pdf. 

With regard to general conformity, the 

EPA first promulgated general 

conformity regulations in November 

1993 (40 CFR part 51, subpart W and 40 

CFR part 93, subpart B). Subsequently, 

the EPA finalized revisions to the 

general conformity regulations on April 

5, 2010. (75 FR 17254–17279) The 

general conformity program ensures that 

federal actions not covered by the 

transportation conformity rule will not 

interfere with the SIP. General 

conformity 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 www.epa.gov/

airquality/genconform/. 

b. Conformity in the Proposed Rule. 

The EPA did not propose any changes 

to the transportation conformity 

program as part of the current action. 

Nevertheless, to provide clarity in 

applying those regulations, the EPA is 

providing 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. Finally, we 

proposed a change to the general 

conformity rule that addresses de 

minimis levels that apply to federal 

actions in PM2.5 areas. 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 

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245For 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). 

and air quality agencies, metropolitan 

planning organizations (MPOs), and all 

federal agencies including the U.S. 

Department of Transportation, the U.S. 

Department of Defense, the U.S. 

Department of Interior and the U.S. 

Department of Agriculture. 

c. Applicability of Transportation and 

General Conformity 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, April 15, 2016. 

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 the 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 the 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 

includes any part of an MPO area 

designated under 23 U.S.C. 134 or is an 

isolated rural area. Within 1 year after 

the effective date of the initial 

nonattainment designation for a given 

pollutant and the NAAQS, the MPOs 

and DOT must make a transportation 

conformity determination with regard to 

that pollutant and standard for all of the 

metropolitan 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.245 For the 

purposes of the implementation of the 

2012 PM2.5 NAAQS, MPOs and any 

adjacent donut areas in a 2012 PM2.5

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 

conformity determination for that 

NAAQS, the area would be in a 

conformity ‘‘lapse.’’ During a conformity 

lapse, only certain projects can receive 

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). Transportation conformity 

requirements for isolated rural 

nonattainment and maintenance areas 

can be found at 40 CFR 93.109(g). The 

CAA section 176(c)(6) 1-year grace 

period for newly designated 

nonattainment areas applies to isolated 

rural areas. Therefore, 1 year after the 

effective date of the initial 

nonattainment designation for a given 

pollutant and the 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 an 

applicable 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 

transportation conformity guidance 

related to the implementation of the 

2012 primary annual PM2.5 NAAQS for 

further information on how the EPA has 

implemented this conformity grace 

period in metropolitan, donut and 

isolated rural areas. The guidance is 

available at http://www3.epa.gov/otaq/

stateresources/transconf/documents/

420b15091.pdf. 

d. Applicability of Transportation and 

General Conformity With Regard to the 

1997 Annual PM2.5 NAAQS, Which was 

Retained as a Secondary NAAQS. In the 

December 2012 PM NAAQS final 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), 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 2206) and 

were effective on April 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. 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) requires 

compliance with transportation and 

general conformity only in: (1) 

Nonattainment areas and (2) areas that 

have been redesignated to attainment 

and are required to develop a 

maintenance plan under CAA section 

175A. 

CAA section 175A(a), in turn, 

establishes the requirements that must 

be fulfilled by nonattainment areas in 

order to be redesignated to attainment. 

That section only requires that 

nonattainment areas for the primary 

standard submit a plan addressing 

maintenance of the primary NAAQS in 

order to be redesignated to attainment; 

it does not require nonattainment areas 

for secondary NAAQS to submit 

maintenance plans in order to be 

redesignated to attainment. See 42 

U.S.C. 7505a(a) Therefore, since 

conformity does not apply in areas that 

have been redesignated without CAA 

section 175A maintenance plans, the 

EPA concludes that transportation and 

general conformity do not apply in areas 

that have been redesignated to 

attainment for any secondary NAAQS, 

such as the 1997 secondary annual 

PM2.5 NAAQS. 

Elsewhere in this final rule, the EPA 

is finalizing one of the proposed 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. As 

discussed in detail in Section X of this 

preamble, the EPA is finalizing the 

option that calls for revoking the 1997 

primary annual PM2.5 NAAQS in areas 

that have always been designated 

attainment for that NAAQS and in areas 

that have been redesignated to 

attainment for that NAAQS. As a result, 

after the effective date of the revocation, 

areas that have been redesignated to 

attainment for the 1997 annual PM2.5

NAAQS (i.e., maintenance areas for the 

1997 annual PM2.5 NAAQS) will not be 

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246This is not currently the case for the areas 

designated for the 2012 PM2.5 NAAQS, but the EPA 

is noting this in the event that future designations 

result in this situation. 

required to make transportation or 

general conformity determinations for 

the 1997 annual PM2.5 NAAQS. The 

revocation would leave nonattainment 

designations in place for the 1997 

annual NAAQS for areas that have not 

yet been redesignated to attainment for 

that NAAQS. The EPA will continue to 

redesignate areas to attainment as states 

submit redesignation requests for the 

remaining nonattainment areas. Any 

area that is designated as nonattainment 

for the 1997 annual NAAQS at the time 

of the initial revocation would have to 

continue to make transportation and 

general conformity determinations for 

that NAAQS until such time that they 

are redesignated to attainment for that 

NAAQS. 

For any area that has been 

redesignated to attainment for the 1997 

annual PM2.5 NAAQS (i.e., a 

maintenance area for the 1997 annual 

PM2.5 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 earlier, the CAA does not 

require maintenance areas for secondary 

NAAQS to make conformity 

determinations and the 1997 primary 

annual NAAQS will have been revoked. 

This means that, after the effective date 

of the revocation, areas redesignated to 

attainment for the 1997 annual PM2.5

NAAQS will no longer be required to 

make metropolitan transportation plan, 

TIP, or project-level transportation 

conformity determinations for that 

NAAQS. In addition, federal agencies 

will no longer be required to make 

conformity determinations for that 

NAAQS. Areas that remain designated 

nonattainment for the 1997 annual 

PM2.5 NAAQS will continue to make 

metropolitan 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 these areas 

attain that NAAQS and are redesignated 

to attainment (i.e., until the effective of 

the redesignation to attainment). Table 3 

shows which types of areas are required 

to make conformity determinations for 

either the 1997 or 2012 annual PM2.5

NAAQS after the revocation of the 1997 

primary annual NAAQS is effective. 

TABLE 3—WHERE IS CONFORMITY REQUIRED FOR THE VARIOUS PM2.5 NAAQS AFTER THE REVOCATION OF THE 1997 

PRIMARY ANNUAL PM2.5 NAAQS? 

Attainment status 

1997 Primary and 

secondary annual 

NAAQS 

1997 24-Hour 

NAAQS 

2006 24-Hour 

NAAQS 

2012 Primary 

annual NAAQS 

Nonattainment .......................................................................... X X X X 

Redesignated to Attainment (i.e., Maintenance) ..................... .............................. X X X 

e. Impact of Implementation of a New 

or Revised PM2.5 NAAQS (such as the 

2012 PM2.5 NAAQS) 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 

making any changes to its transportation 

conformity regulations and no 

transportation conformity SIP revisions 

are necessary. The only change that the 

EPA is making to its general conformity 

regulations is to change the de minimis 

levels in its general conformity 

regulations as discussed in Section 

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

general conformity SIP should evaluate 

the need to revise those SIPs in light of 

this change. States with new 

nonattainment areas may also need to 

revise conformity SIPs in order to 

ensure the state regulations apply in any 

newly designated areas. 

In the event that a nonattainment 

designation causes transportation 

conformity to apply for the first time in 

a state,246 such a state is required by the 

statute and the 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://

www3.epa.gov/otaq/stateresources/

transconf/policy/420b09001.pdf). 

2. Additional General Conformity 

Requirements for PM2.5 Nonattainment 

Areas 

a. De minimis Emission Levels 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 

emission 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. 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 93.153(b)(1) does not reflect the 

rebuttable presumptions for certain 

PM2.5 precursors, the EPA is finalizing 

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 does not 

reflect the rebuttable presumptions for 

VOC and ammonia. To address the lack 

of rebuttable presumptions for VOC and 

ammonia the EPA is revising the tables 

in 40 CFR 93.153(b)(1) and (2) remove 

‘‘(if determined to be a significant 

precursor)’’ from the entries in the 

tables that apply to VOC and ammonia 

emissions as PM2.5 precursors. 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, 

the EPA is finalizing changes to the 

PM2.5 precursor de minimis levels 

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

make those levels consistent with the 

statutory requirements for major 

stationary source thresholds under 

subpart 4 and any relevant changes 

finalized in Section III of this preamble. 

Comments received on this proposed 

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247USDA 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. 

248 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 designed 

to bring an area into attainment for the 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 the 

given NAAQS. 

249See 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, titled ‘‘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. 

change were supportive. The EPA is 

setting 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 4. 

TABLE 4—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. Implementation Considerations for 

the General Conformity Program. The 

EPA did not propose any other revisions 

to the general conformity regulations 

and is not taking any additional final 

actions in this rule. However, as areas 

develop SIPs 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. 

In a few cases, tracts of land under 

federal management may also be 

included in nonattainment and 

maintenance 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.247

C. Clean Data Policy 

1. Summary of the Proposal 

In the proposed rule, the EPA 

described its longstanding clean data 

policy and proposed to codify the policy 

in regulatory text. A clean data 

determination (CDD) is a notice-andcomment rulemaking wherein the EPA 

determines that a specific 

nonattainment area has attained the 

relevant NAAQS based on 3 years of 

quality-assured certified air quality 

monitoring data. The CDD suspends the 

state’s obligation to submit to the EPA 

the planning elements related to 

attaining the standard required of 

nonattainment areas under the Clean 

Air Act for as long as the area continues 

to attain the standard.248 The CDD does 

not suspend certain CAA requirements, 

such as an emissions inventory, 

nonattainment new source review 

requirements, and certain emission 

reduction requirements, that are 

considered independent of attainment 

needs. 

The proposal provided additional 

discussion about attainment 

demonstrations, control requirements 

for Moderate areas, RFP and 

quantitative milestones, and 

contingency measures. With regard to 

control requirements for Serious areas, 

the proposal included two options: one 

option would suspend BACT/BACM 

requirements under a CDD if elsewhere 

in the rule such requirements were 

considered necessary for expeditious 

attainment, and the other option would 

not suspend BACT/BACM requirements 

if elsewhere in the rule such 

requirements were considered to be 

generally independent of attainment. 

2. Final Rule 

The final rule codifies the clean data 

policy in rules governing the 

implementation of current and future 

PM2.5 NAAQS, and much of the 

guidance discussed in the proposal 

regarding which requirements are 

suspended remains the same. The EPA 

has already codified the clean data 

policy in a regulation implementing the 

1997 8-hour ozone NAAQS that was 

specifically challenged and upheld by 

the D.C. Circuit in NRDC v. EPA, 571 

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

numerous United States Circuit Courts 

of Appeal have upheld the Clean Data 

Policy, including the EPA’s application 

of this interpretation of the CAA with 

regard to implementation of the PM10

NAAQS under subpart 4. See Latino 

Issues Forum v. EPA, Nos. 06–75831 

and 08–71238 (9th Cir. March 2, 2009) 

(memorandum opinion). The EPA had 

also codified the clean data policy for 

PM2.5 in the now remanded 2007 PM2.5

implementation rule. For a complete 

discussion of the Clean Data Policy’s 

history and EPA’s longstanding 

interpretation under the Clean Air Act, 

please refer to the proposal. 

The planning elements under subpart 

1 and subpart 4 generally include 

reasonable further progress (RFP) 

requirements, attainment 

demonstrations, RACM and RACT, 

nonattainment area contingency 

measures, and other state planning 

requirements related to attaining the 

NAAQS.249 The suspension of the 

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250 Ibid. 

obligation to submit such requirements 

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 determination of 

attainment is not equivalent to a 

redesignation, and the state must still 

meet the statutory requirements for 

redesignation in order to be 

redesignated to attainment. A 

determination of attainment for 

purposes of the Clean Data Policy/

regulations 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 CAA 

section 188(b). Note also that if the EPA 

determines that an area with a clean 

data determination subsequently is 

violating the standard prior to being 

redesignated to attainment, the area will 

be required to address the pertinent 

requirements when it submits the SIP to 

EPA. As has long been the EPA’s policy, 

areas subject to a determination that a 

CDD is rescinded due to subsequent 

violation of the NAAQS would receive 

a reasonable amount of time to address 

the previously suspended requirements 

and submit revisions to their SIPs. The 

EPA would establish this SIP submittal 

date on a case-by-case basis, taking into 

account individual circumstances 

surrounding the particular SIP 

provisions at issue.250

This rule specifies that a 

determination that a nonattainment area 

is attaining the current and future PM2.5

NAAQS would suspend the following 

attainment planning related 

requirements under subpart 1 and 

subpart 4: (i) The part D, subpart 4 and 

subpart 1 obligation to provide an 

attainment demonstration pursuant to 

CAA section 189(a)(1)(B); (ii) the RACM 

and RACT provisions of CAA section 

189(a)(1)(C); (iii) the RFP and 

quantitative milestones provisions of 

CAA section 189(c); and, (iv) related 

attainment demonstration, RACM and 

RACT, RFP and contingency measure 

provisions requirements of subpart 1, 

section 172. The following sections a–d 

provide additional detail on the PM2.5

NAAQS planning requirements that 

would be suspended by a CDD. 

a. Attainment Demonstrations. With 

respect to the attainment demonstration 

requirements of section 172(c) and 

section 189(a)(1)(B) of the CAA, the EPA 

finds that if an area already has air 

quality monitoring data demonstrating 

attainment of the standard, there is no 

need for an area to make a further 

submission containing additional 

measures to achieve attainment, nor is 

there a need for the area to perform 

future modeling to show how the area 

will achieve attainment. The plain 

language of CAA 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. 

b. Control Measure Requirements for 

Moderate Areas. Both CAA 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 EPA has long 

interpreted ‘‘reasonably available 

control measures’’ under CAA sections 

172(c)(1) and 189(a)(1)(C) to mean only 

those measures that are necessary to 

help an area achieve attainment. 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. The EPA is interpreting CAA 

section 189(a)(1)(C) consistent with its 

interpretation of CAA section 172(c)(1). 

c. 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.’’ 

d. 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 CAA sections 

172(c)(9). The EPA has interpreted the 

obligation to submit contingency 

measure requirements of CAA 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. 

e. Control Measure Requirements for 

Serious Areas. Section VII.D of the 

preamble explains the rationale of the 

EPA’s decision to maintain its 

longstanding policy of considering the 

BACT/BACM requirement of CAA 

section 189(b)(1)(B) to be generally 

independent of attainment. 

Accordingly, this rule states that a clean 

data determination would not suspend 

the obligation for the state to submit any 

applicable outstanding BACM and 

BACT requirements. 

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 

CAA 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 CAA section 

189(d). Once such an area is attaining 

the relevant NAAQS, a clean data 

determination would suspend the CAA 

section 189(d) submission requirement. 

3. Comments and Responses 

Comment: Several commenters 

supported the EPA’s proposal to codify 

the clean data policy in the final rule 

because they believe the policy is lawful 

and relieves states from unnecessary 

planning burdens in areas where the 

NAAQS is met. Some commenters 

stated the policy has specifically been 

upheld by the D.C. Circuit in the context 

of review of nationally applicable 

implementation rules for the EPA’s 

ozone NAAQS [Natural Res. Def. 

Council v. EPA, 571 F.3d 1245, 1260–61 

(D.C. Cir. 2009)]. Other commenters, 

however, asserted that they ‘‘reiterate 

their previous comments regarding the 

illegality of the Clean Data Policy.’’ To 

the extent that the Agency planned to 

continue to follow the policy, these 

commenters agreed with the EPA’s 

interpretation that only those 

requirements tied to an area’s 

demonstration of attainment should be 

suspended. To that end, the commenters 

requested clarification that measures 

that have been responsible for the area’s 

attainment must be submitted and 

approved into the SIP even following a 

Clean Data Determination. Similarly, 

other commenters requested 

clarification as to EPA’s statement that 

‘‘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.’’ The commenter 

wondered if ‘‘all measures adopted into 

the SIP’’ includes measures that were 

included and identified as RACT or 

RACM in the original SIP, even if those 

measures have not yet been submitted to 

EPA in regulatory form. 

Finally, some commenters noted that 

the Act requires that RACM/RACT be 

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251See, e.g., NRDC v. EPA, 571 F.3d 1245 (D.C. 

Cir. 2009); Sierra Club v. EPA, 99 F.3d 1551 (10th 

Cir. 1996); Latino Issues Forum v. EPA, Nos. 06– 

75831 and 08–71238 (9th Cir. March 2, 2009) 

(memorandum opinion). 

implemented within 4 years of a 

nonattainment designation and stated 

that, as sources reduce emissions of 

PM2.5 and regional PM precursors due to 

national rules yet to be fully 

implemented (e.g., Boiler NESHAPS, 

CSAPR) it is entirely possible that an 

area may attain the standard prior to 

complete implementation of RACM/

RACT. The commenters stated that, if an 

area attains the NAAQS prior to 

implementation of the planning 

requirements, it is meaningless and 

overly burdensome to require the area to 

continue implementing RACM/RACT. 

Response: The EPA disagrees with 

commenters who allege, without 

explanation, that the Clean Data Policy 

is ‘‘illegal.’’ Rather, as noted by 

supportive commenters, the EPA has 

long interpreted certain CAA 

requirements that are designed to bring 

an area into attainment to serve no 

purpose once an area is attaining, and 

thus has interpreted the Act as 

permitting the Agency to suspend the 

requirements to submit revisions to the 

SIP addressing those requirements. This 

position has been upheld by multiple 

Circuit Courts of Appeals.251

In response to the requests for 

clarification of which RACM 

requirements are suspended by a CDD, 

we note that, for over 30 years, the EPA 

has consistently interpreted the RACM 

requirement in CAA section 172(c)(1) to 

apply only to those measures that, 

individually or collectively, contribute 

to expeditious attainment of the 

NAAQS. The suspension of the 

statutory requirement to submit RACM 

is premised on the idea that, ‘‘[t]o the 

extent an area is already achieving 

attainment as expeditiously as possible, 

imposition of additional control 

[measures] would not hasten 

achievement of the NAAQS. In such a 

situation, the EPA may reasonably 

conclude that no control [measures] are 

reasonably available and the area need 

not implement further [measures] to 

satisfy the [RACM] requirement.’’ See 

NRDC v. EPA, 571 F.3d 1245, 1253 (D.C. 

Cir. 2009). Thus, upon the EPA’s 

finalization of a CDD for a particular 

NAAQS, the EPA formally suspends the 

obligation to submit attainment-related 

plan elements for that particular 

NAAQS, including RACM. A CDD does 

not, however, affect the criteria in CAA 

section 107(d)(3)(E) for redesignation to 

attainment, including the requirement 

for the state to demonstrate to the EPA’s 

satisfaction that the improvement in air 

quality is due to ‘‘permanent and 

enforceable reductions in emissions 

resulting from implementation of the 

applicable implementation plan’’ and 

other permanent and enforceable 

reductions. Thus, to the extent certain 

state/local control measures were 

necessary to an area’s attainment of the 

NAAQS, the state may need to submit 

those measures to the EPA for SIP 

approval in order to meet the statutory 

criteria for redesignation in CAA section 

107(d)(3)I, notwithstanding the 

suspension of planning obligations 

under a CDD. 

In this case, it is not clear to the EPA 

what the commenter means by the 

phrase ‘‘original SIP,’’ since the SIP is 

only those measures that have been 

submitted and approved by the EPA. To 

the extent that a measure was adopted 

into the SIP prior to an area’s attainment 

of the NAAQS, and therefore 

contributed to an area’s attainment, that 

measure is therefore required to remain 

as part of the SIP. We infer that the 

comment might be referring to 

commitments that were approved into a 

SIP to adopt future measures, or that 

commenters might be asking for 

clarification regarding measures that 

have been adopted locally or at a state 

level prior to the area’s coming into 

attainment but have not yet been 

submitted to the EPA for approval into 

the federally-approved SIP. As 

explained above, a CDD has no effect on 

the state’s obligation to demonstrate that 

an area’s improvement in air quality is 

due to ‘‘permanent and enforceable’’ 

emissions reductions in order to meet 

the statutory requirements for 

redesignation to attainment in CAA 

section 107(d)(3)(E). Additionally, a 

CDD does not alter the effect of any 

measure (including any state 

commitment) that has already been 

approved into a SIP, even if that 

measure is a commitment to adopt or 

submit a future measure. Once approved 

into a SIP, such a measure becomes an 

enforceable emission standard or 

limitation subject to EPA or citizen 

enforcement under CAA section 304, 

which cannot be altered except through 

a SIP revision approved by the EPA. 

Along those same lines, even if an area 

has adopted into its SIP RACM/RACT 

but has yet to fully implement those 

measures when the area first starts 

attaining the NAAQS, a CDD does not 

excuse the area from continuing to 

implement its SIP requirements, i.e., the 

RACM/RACT measures that have been 

approved into the SIP. The CDD merely 

suspends the requirement to submit 

RACM/RACT, that is, additional 

measures on top of what brought the 

area into attainment; a state may only 

stop implementing those measures 

already in its SIP through a SIP revision 

approved by the EPA. 

Comment: Some commenters 

supported the EPA’s proposal to retain 

the BACM/BACT submission 

requirement even with a CDD (80 FR 

15444). Other commenters, however, 

stated that, once the EPA makes an 

attainment determination, the EPA 

should suspend the requirements to 

submit BACM/BACT and that to do 

otherwise is illogical. 

Response: The EPA is finalizing the 

option that requires BACM/BACT to be 

submitted even if the EPA has issued a 

CDD for an area. As discussed in our 

proposal and earlier in this section, the 

legal underpinning of the Clean Data 

Policy is that the EPA interprets the 

CAA not to require the submission of 

requirements that are designed to get an 

area to attainment once that area is 

already attaining the NAAQS. Thus, 

only those ‘‘attainment planning’’ 

requirements are suspended by a CDD. 

It is therefore illogical for the EPA to 

extend the Clean Data Policy to the 

submission of the BACM/BACT 

requirement for Serious Areas. Because 

the EPA interprets BACM/BACT as 

independent of attainment, as discussed 

above in Section VII.D of the preamble, 

the requirement to submit BACM/BACT 

continues to apply regardless of whether 

the EPA has determined that the area is 

attaining. 

D. CAA Section 179B/International 

Border Areas 

1. Specific Requirements 

a. Summary of Proposal. Section 179B 

of the CAA, titled ‘‘International Border 

Areas,’’ applies to areas that would 

attain the relevant NAAQS by the 

statutory attainment date ‘‘but for’’ 

emissions emanating from outside the 

U.S. Under CAA section 179B, if 

applicable, the provision modifies 

subpart 4 attainment plan obligations 

applicable to areas designated 

nonattainment for any PM NAAQS. The 

EPA proposed and sought comment on 

two approaches that would give greater 

clarity to the agency’s existing 

interpretation of the RACM/RACT and 

additional reasonable measure 

requirements for Moderate area 

attainment plans to be approved under 

CAA section 179B. The first proposed 

interpretation would have clarified 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 

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252Addendum to the General Preamble, 59 FR 

41998 (August 16, 1994), at page 42001. 

253 Ibid. 

254 Ibid. 

255 Ibid. 

technologically and economically 

feasible and implementable on sources 

in the area by the end of the sixth 

calendar year following designation of 

the area. Under this approach, inclusion 

of such measures would satisfy 

requirements for RACM and RACT (for 

measures that can be implemented 

within four years) and additional 

reasonable measures (for measures than 

can be implemented within six years 

but not within four). The proposal also 

sought comment on a possible exception 

for any such measures that collectively 

would not be effective in reducing 

ambient PM2.5 levels in the area. The 

second proposed approach would have 

required a state 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. Inclusion of these 

proportional measures would thus 

satisfy RACM/RACT and additional 

reasonable measures under the second 

approach. The EPA sought comment on 

these two approaches to clarify what 

constitutes a reasonable control strategy 

in the context of a SIP submitted 

pursuant to CAA section 179B. 

The EPA also proposed that any 

Moderate area attainment plan 

submitted under CAA section 179B 

must include an RFP plan with required 

air quality targets consistent with the 

RFP Option 2. In addition, the EPA 

proposed requirements for establishing 

and reporting on quantitative milestones 

for areas with approved ‘‘but for’’ 

demonstrations. 

b. Final Rule 

Section 179B(a) of the CAA provides 

that the EPA shall approve an 

attainment plan for a nonattainment 

area that is an international border area 

if: (i) the attainment plan meets all other 

applicable requirements of the CAA, 

and (ii) the submitting state can 

demonstrate satisfactorily that ‘‘but for 

emissions emanating from outside of the 

United States,’’ the area would attain 

and maintain the relevant NAAQS. In 

addition, CAA section 179B(d) provides 

that if a state demonstrates that an area 

would have attained the NAAQS but for 

emissions emanating from outside the 

U.S., then the area is not subject to the 

mandatory reclassification element of 

CAA section 188(b)(2) for Moderate 

areas that fail to attain by the applicable 

attainment date. 

Under CAA 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. Such an area 

that is violating the relevant NAAQS 

will be designated nonattainment even 

if emissions from outside the U.S. 

contribute to that violation. Second, as 

a result of that designation, the state is 

required to meet the applicable 

attainment plan requirements for the 

relevant NAAQS. Section 179B of the 

CAA does not negate the attainment 

plan requirements. Rather, it allows the 

EPA to approve an attainment plan that 

demonstrates attainment and 

maintenance of the NAAQS ‘‘but for’’ 

international emissions. 

The EPA has determined that under 

the best reading of CAA section 179B, 

states remain obligated to meet the 

attainment plan requirements other than 

the requirement to demonstrate 

attainment and maintenance of the 

relevant NAAQS. This determination is 

based upon the fact that 179B(a)(1) 

explicitly states that such an attainment 

plan must meet all the requirements of 

the CAA with that exception. The 

applicable requirements for an 

attainment plan for PM2.5 include those 

requirements that apply to a Moderate 

area attainment plan. Those 

requirements include an emissions 

inventory, RACM and RACT, additional 

reasonable measures, RFP, quantitative 

milestones, contingency measures, 

NNSR and motor vehicle emissions 

budgets for transportation conformity 

purposes. The Addendum includes a 

discussion of the applicable attainment 

plan requirements in the context of 

developing a SIP subject to CAA 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.’’ 252 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.’’ 253

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 CAA section 179B. Indeed, 

to the extent an affected State can 

satisfactorily demonstrate that 

implementation of such measures 

clearly would not have advanced the 

attainment date, the EPA could 

conclude they are unreasonable and 

hence do not constitute RACM.’’ 254

In the proposal, the EPA specifically 

took comment on the most appropriate 

way to address the RACM and RACT 

requirements. The past interpretation of 

RACM and RACT requirements in the 

context of CAA section 179B was 

considered when the agency proposed 

an option to allow a state not to adopt 

such measures if the state could 

demonstrate that collectively the 

measures will not be effective in 

reducing PM2.5 levels in the area. Some 

commenters supported this exception, 

stating that it would prevent wasting 

resources on ineffective measures. Some 

commenters stated that requiring 

implementation of all RACM/RACT and 

additional reasonable measures 

circumvents Congressional intent and 

the CAA. Other commenters disagreed, 

stating that these areas should 

implement all measures due to the 

importance to public health. 

Regarding RACM/RACT and 

additional reasonable measures, the 

EPA reviewed the comments received 

and its past interpretation of RACM and 

RACT requirements in the context of 

CAA section 179B attainment plans for 

PM2.5 NAAQS. The EPA is persuaded 

that this approach is most appropriate 

and most consistent with the Act and 

with the control requirements for other 

Moderate areas that demonstrate they 

cannot practicably attain by the 

Moderate area attainment date. See 

section 51.1009(a)(4)(ii). In longstanding 

guidance the EPA has encouraged 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.’’ 255 Given that 

the primary purpose of an attainment 

plan is to ensure expeditious attainment 

of the NAAQS and protection of public 

health and welfare through 

implementation of control measures that 

achieve emissions reductions, adopting 

an interpretation that would allow for 

continued emissions of pollutants that 

the state could reasonably reduce would 

be antithetical to the objectives of the 

CAA. Just as it is appropriate and 

consistent with the Act to adopt 

reasonable measures (i.e., RACT/RACM 

or additional reasonable measures) in 

areas that cannot practicably attain by 

the attainment date, as previously 

discussed, it is also appropriate and 

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consistent with the Act to adopt 

reasonable measures in areas that 

cannot attain due to international 

emissions. 

Therefore, the EPA requires that 

Moderate area attainment plans 

approved under CAA section 179B must 

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 (i.e., 

RACM and RACT and additional 

reasonable measures). This requirement 

is intended 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. This approach 

parallels the requirements described in 

Section IV.D in this preamble, pursuant 

to CAA section 189(a)(1), for Moderate 

PM2.5 nonattainment areas that cannot 

practicably attain the NAAQS by the 

latest statutory attainment date for the 

area. Requiring the implementation of 

all reasonable measures is even more 

important in the context of a Moderate 

area for which CAA section 179B 

applies because sources in such areas 

will not be subject to the more stringent 

BACM/BACT, MSM, or 5 percent 

requirement because such areas are not 

subject to mandatory reclassification as 

Serious areas pursuant to CAA section 

179B(d). Thus, the only level of PM2.5

control requirements that will likely 

ever apply to these sources is the lessstringent RACM/RACT and additional 

reasonable measures level of control; 

therefore, all the sources in the area 

should reduce emissions if such 

reduction is reasonable since the public 

in those areas will continue to be 

subject to ambient levels of emissions 

that the agency has determined are 

unsafe notwithstanding implementation 

of those reasonable measures. 

Additionally, the EPA notes that the 

process to determine RACM already 

allows states to identify the subset of all 

control measures that are 

technologically and economically 

feasible, which should be adequate to 

prevent significant wasting of resources 

on ineffective measures. 

The EPA has determined that it will 

not finalize the proposed option of 

achieving reductions in PM2.5 levels in 

proportion to the area’s contribution to 

overall PM2.5 levels. The EPA received 

several comments on the proposed 

option to allow states to implement 

control measures for a Moderate 

nonattainment area with a plan 

approved under CAA section 179B that 

would achieve reductions in PM2.5

levels in proportion to the area’s 

contribution to overall PM2.5 levels. 

Although some commenters supported 

the possibility of proportionally 

implementing control measures, other 

commenters raised possible negative 

consequences of this option. 

Commenters highlighted the difficulty 

that states would face in apportioning 

responsibility for emissions between 

foreign and non-foreign sources, which 

would be necessary under the 

proportional approach. These 

commenters also disagreed as to 

whether the EPA or states should be 

responsible to determine the 

proportional allocation of international 

emissions. The EPA is also concerned 

that a proportional approach would 

introduce too much complexity into an 

already complex analytical process. 

Additionally, the EPA notes that no 

other NAAQS pollutant offers a 

proportional approach to 

implementation of control measures and 

is not convinced that there are sufficient 

reasons to finalize this approach for 

PM2.5 nonattainment areas. 

Section 179B(d) of the CAA states that 

any area for which the state establishes 

to the EPA’s satisfaction that the area 

‘‘would have attained the NAAQS by 

the applicable attainment date, but for 

emissions emanating from outside the 

United States, shall not be subject to the 

provisions of section [188(b)(2)].’’ CAA 

section 188(b)(2) requires the EPA to 

determine, within 6 months following 

the applicable attainment date for a 

Moderate PM2.5 nonattainment area, 

whether the area attained the NAAQS 

by that date and to reclassify the area as 

Serious if it is not in attainment after the 

applicable attainment date. For any 

Serious area subject to an EPA 

determination of failure to attain by the 

Serious area attainment date, CAA 

section 189(d) requires the state to 

submit plan revisions which provide for 

attainment of the PM2.5 NAAQS and for 

annual emissions reductions of not less 

than 5 percent until the area attains. 

These planning requirements in section 

189(d) apply only upon the EPA’s 

determination that a Serious area has 

failed to attain the applicable NAAQS 

by the Serious area attainment date. 

Because section 179B(d) explicitly 

provides that any area that satisfies the 

‘‘but for’’ attainment test in CAA section 

179B shall not be subject to the 

provisions for reclassification to Serious 

upon failure to attain in CAA section 

188(b)(2), the consequences for failure 

to attain by the Serious area attainment 

date in section 189(d) generally do not 

apply to such areas. 

In the event that the EPA has already 

reclassified an international border area 

as Serious, when the state submits a 

‘‘but for’’ demonstration under section 

179B, all of the Serious area 

requirements that apply to the area (e.g., 

the requirements to implement BACM/ 

BACT and additional feasible measures) 

would remain in effect. This is because 

at the time the state submits the ‘‘but 

for’’ demonstration, these statutory 

requirements already apply. Upon the 

EPA’s approval of a Serious area plan 

and section 179B demonstration for 

such an area, however, the EPA would 

no longer be obligated to make a 

determination of failure to attain by the 

Serious area attainment date triggering 

the additional planning requirements of 

section 189(d). Consistent with 

Congress’s clear intent in section 

179B(d) to relieve Moderate PM2.5

nonattainment areas that satisfy the ‘‘but 

for’’ attainment test of the additional 

planning obligations that result from a 

mandatory determination of failure to 

attain by the Moderate area attainment 

date, the EPA interprets section 179B as 

also relieving Serious PM2.5

nonattainment areas of the additional 

planning obligations in section 189(d) 

that result from a mandatory 

determination of failure to attain by the 

Serious area attainment date, once the 

EPA approves the state’s Serious area 

plan and section 179B demonstration. 

Where a Serious area fails to attain by 

the Serious area attainment date and is 

therefore subject to the requirements of 

section 189(d), the EPA’s approval of a 

section 189(d) plan and 179B 

demonstration would mean that the 

EPA is no longer obligated to make 

further determinations of failure to 

attain or to trigger additional planning 

requirements. The EPA intends to 

review each SIP submission containing 

a ‘‘but for’’ attainment demonstration for 

an international border area for 

compliance with the requirements of 

section 179B. 

The EPA notes that, with one 

exception for contingency measures, the 

final rule provisions governing for the 

RFP, quantitative milestone, and 

contingency measure requirements for 

PM2.5 nonattainment areas are the same 

for areas seeking plan approval under 

CAA section 179B as they are for any 

other area. For example, the EPA 

requires that as part of any Moderate 

area attainment plan submitted under 

CAA section 179B, a state must include 

an RFP plan developed consistent with 

the process described in Section IV.F of 

this preamble as a Moderate 

nonattainment area that cannot 

practicably attain the relevant NAAQS 

by the statutory attainment date. In 

addition, the EPA requires that the state 

must identify quantitative milestones 

for the area to be achieved 4.5 years and 

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58132 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

256 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. 257See 40 CFR 40 CFR 50.1, 50.14 and 51.930. 

7.5 years from the date of designation of 

the area. The EPA will apply the same 

requirements for establishing and 

reporting on quantitative milestones for 

Moderate nonattainment areas with an 

approved ‘‘but for’’ demonstration 

under CAA section 179B as for all other 

Moderate nonattainment areas, as 

described in Section IV.G of this 

preamble. Furthermore, the state must 

include as part of any attainment plan 

submission made for such an area 

contingency measures that are ready to 

be implemented quickly and with 

minimal further action by the state or by 

the EPA in the event the EPA 

determines that such area failed to meet 

RFP or quantitative milestone 

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. The exception to 

the contingency measure requirement 

for areas with approved CAA section 

179B demonstrations is that 

contingency measures for failure to 

attain are not required in such plans, 

because under CAA section 179B(d) the 

EPA is not required to make 

determinations concerning attainment 

for such areas. Further explanation of 

contingency measures can be found in 

Section IV.H of this preamble. 

Regarding the ‘‘but for’’ 

demonstrations under CAA section 

179B, the EPA has historically evaluated 

these demonstrations on a case-by-case 

basis, based on the 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.256 The Moderate area 

attainment demonstration modeling and 

other elements of the attainment 

demonstration must show attainment 

and maintenance of the NAAQS but for 

the emissions from outside of the U.S. 

However, CAA section 179B does not 

provide authority to exclude monitoring 

data influenced by international 

transport from regulatory 

determinations related to attainment 

and nonattainment. 

Where international transport of 

emissions contributes to an exceedance 

or violation, such data may be excluded 

from consideration only if they were 

significantly influenced by exceptional 

events under section 319(b) of the CAA. 

If the data meet the criteria contained in 

the EPA’s Exceptional Events Rule, the 

exceedance can be addressed by that 

rule.257 Specifically, if the EPA concurs 

with a state’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, which may be used as part of a 

regulatory determination. 

The EPA expects 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 exceptional events 

demonstrations and attainment plans for 

which CAA 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. 

c. Comments and Responses 

Comment: Commenters stated the 

EPA should not require the state to 

implement a section 189(d) 5 percent 

reduction plan, since attaining such 

reductions may well be impossible if 

there are significant international 

emissions. 

Response: The EPA agrees that as long 

as the affected nonattainment area 

satisfactorily meets the provisions of 

CAA section 179B, that area should not 

be subjected to the additional 

requirements of CAA section 189(d) 

even if the area fails to attain. 

Comment: Commenters stated that 

requiring implementation of all RACM 

and RACT for CAA section l79B 

nonattainment areas would penalize 

rural communities and would run 

counter to the intent of CAA section 

179B of providing regulatory relief to 

areas affected by foreign emissions. 

Response: For the reasons stated 

earlier, the EPA has determined that 

section 179B nonattainment areas 

should be required to implement control 

measures to the same extent as a 

Moderate nonattainment area that 

demonstrates it will not be able to attain 

the PM2.5 NAAQS by the statutory 

attainment date. 

Comment: Some commenters stated 

that the EPA’s current interpretation of 

section 179B and the agency’s guidance 

which encourages states ‘‘to reduce 

emissions beyond the minimum 

necessary to satisfy the ‘but for’ test,’’ 

circumvents Congressional intent and 

the CAA and establishes a second 

ambient air quality threshold not related 

to the NAAQS. 

Response: The EPA disagrees that 

encouraging states to minimize 

emissions as much as possible to protect 

public health circumvents 

Congressional intent. The EPA has 

determined that the reasonable control 

measure requirements outlined in 

section 51.1009(a)(4)(ii) represent the 

most appropriate interpretation of the 

CAA in line with the overriding 

Congressional intent to protect and 

improve air quality thereby enabling the 

associated public health benefit. 

Comment: Some commenters stated 

that if an area’s demonstration is 

approved under CAA section 179B, any 

contingency measures should only be 

required to obtain emissions reductions 

in proportion to the contribution of 

emissions excluding the international 

pollution, or at least to the contribution 

of emissions reductions that the state 

can feasibly attain. 

Response: The EPA agrees that 

contingency measures relate to the 

domestic portion of emissions affecting 

the nonattainment area. The state will 

not be required to develop contingency 

measures to make up for those 

emissions coming from international 

sources. The EPA emphasizes that 

contingency measures for a section 179B 

area will be for failure to meet RFP 

requirements, not for failure to attain. 

However, the EPA expects states with 

a section 179B area to follow the 

guidance and requirements outlined in 

Section IV.H of this preamble to identify 

contingency measures that can provide 

emissions reductions from sources 

within the state’s jurisdiction. As 

discussed in Section IV.H of the 

preamble, this should include an 

explanation of the amount of 

anticipated emissions reductions to be 

accomplished by the contingency 

measures. If such an area is unable to 

identify approximately 1 year’s worth of 

emissions reductions to constitute 

contingency measures, the explanation 

should describe the factors considered 

by the state when reaching this 

conclusion. 

E. Enforcement and Compliance 

a. Summary of Proposal. The agency 

proposed 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. The EPA proposed that an 

enforceable regulation would also 

specify the timeframes within which 

these requirements must be met, and 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58133 

258See the CAM rule, available at 40 CFR part 64. 

definitively state the recordkeeping and 

monitoring requirements appropriate to 

the type of sources being regulated. 

Additionally, the EPA proposed that an 

enforceable regulation would also 

contain test procedures in order to 

determine whether sources are in 

compliance. 

b. Final Rule. 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 finalizes 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 must include 

requirements for both performance 

testing of emissions and ongoing 

monitoring of the compliance 

performance of control measures, and 

the agency requires that SIP regulations 

that establish emission limits include 

the following for performance testing: 

(1) 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); 

(2) 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); 

(3) Sample collection characteristics— 

conditions related to the sample 

collection portion of the performance 

test. Such conditions would include 

duration of sampling period, either on a 

time or volume collected basis; the 

number of runs comprising a test (e.g., 

three runs per test); and the averaging 

period, i.e., the time over which the 

emissions limit is averaged (e.g., 8 

hours); and, 

(4) Frequency—the 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 requires that regulations adopted 

into the SIP must include the following 

critical elements: 

(1) 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 

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; 

(2) 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; 

(3) 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; 

(4) 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, 

(5) 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 acknowledges that one way 

for regulatory authorities to have owners 

or operators of regulated sources 

demonstrate compliance via ongoing 

monitoring is to use a Compliance 

Assurance Monitoring (CAM) rule-type 

approach.258 Under such an approach, 

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58134 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

259Under 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 the NAAQS has been 

promulgated, including PM2.5. 

an owner or operator would be able to 

establish operating ranges of 

continuously monitored parameters 

determined through concurrent 

performance testing as indicators of 

performance. A CAM rule-type 

approach would require owners or 

operators who chose parameter 

monitoring as indicative of compliance 

to immediately take corrective action 

should a measured parameter value 

occur outside the demonstrated range 

associated with compliance. Moreover, 

concurrent performance testing and 

parameter measurement would be 

necessary on a periodic basis, generally 

annually, and may be necessary on a 

more frequent basis to reverify or reset 

parameter value range, particularly 

when the operating range is exceeded. 

Failure of the owner or operator to take 

immediate corrective action would 

constitute a violation of the applicable 

rule. Moreover, failure of a parameter 

range to demonstrate compliance when 

reverification or resetting performance 

testing occurred would also constitute a 

violation of the emission limit. This 

implementation rule does not prohibit 

states from taking a CAM rule type 

approach and making parameters 

directly enforceable limits. 

The EPA continues to believe that 

approval of regulations adopted into 

SIPs should 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, should be representative 

of and accountable to the assumptions 

used in a state’s attainment 

demonstration. This accountability 

should include the ability to transfer the 

applicable regulatory requirements to a 

title V operating permit subject to the 

EPA and public review.259

c. Comments and Responses 

Comment: Commenters suggested that 

the proposal’s use of the term 

‘‘indicators of compliance’’ is confusing 

and suggested the EPA should simply 

express that emission limitations must 

identify the pollutant of interest and the 

units of measurement. The commenters 

suggested the EPA use the term 

‘‘measurement method’’ and the EPA 

acknowledge that sources may use 

procedures that are not published by the 

EPA, especially for pollutants for which 

there is no federally promulgated test 

method, performance specification, or 

voluntary consensus standard. The 

commenters disagreed that ‘‘averaging 

time’’ is always the appropriate term, 

since it has no applicability for 

standards that use test methods that 

specify minimum run times or sample 

volumes, and numbers of runs, and 

suggested the EPA use the term ‘‘sample 

time or volume’’ and make clear that it 

can be a minimum or an absolute value. 

Response: The EPA does not agree 

with the commenters’ suggestion. The 

proposal identified four components 

associated with demonstrating 

compliance via performance testing— 

the indicator of compliance (for which 

the commenters expressed concern), the 

test method, the averaging time 

associated with the test method, and the 

frequency of conducting the test—as 

well as five components associated with 

demonstrating compliance via ongoing 

monitoring. However, the commenters 

appear to suggest to expand compliance 

demonstration techniques beyond 

testing and monitoring. To the extent 

that SIP regulations are developed that 

do not rely on performance testing or 

ongoing monitoring as means for 

demonstrating compliance, the EPA 

agrees that other components, including 

emission limitations that identify the 

pollutant of interest and units of 

measurement, as suggested by the 

commenter, would be appropriate. 

The EPA believes neither a change in 

term from ‘‘test method’’ to 

‘‘measurement method’’ nor an 

additional acknowledgement regarding 

its current wording ‘‘specific EPA or 

other published set of [criteria]’’ is 

needed. The component to which the 

commenter refers is based on 

performance testing; ongoing 

measurement components are covered 

as ‘measurement technique’ in one of 

the five critical elements for ongoing 

measurement. 

The EPA agrees with the commenters 

that in some circumstances, test 

methods rely on sample volumes as 

opposed to specific durations. The 

‘averaging time’ component of 

performance tests will be changed to 

‘sample collection characteristics’, 

where such characteristics will include 

averaging time, duration, or sample 

volume and number of runs, as 

applicable. While the EPA does not 

believe it to be necessary to identify that 

the sample collection characteristics 

could be minima, maxima, or ranges, 

the preamble discussion associated with 

this change indicates that specific test 

methods, or regulatory agencies, may 

impose restrictions or specific 

conditions on sample collection 

characteristics. 

Comment: Some commenters stated 

the EPA should make clear that states 

can rely on CAM-type parameters as 

indicators of compliance. The 

commenters stated the EPA should 

make clear that states that follow the 

CAM rule model are not required to 

establish those ‘‘indicators’’ as directly 

enforceable limitations, as long as the 

SIP imposes directly enforceable review 

and corrective action requirements that 

will ensure that the source takes 

corrective action prior to the point when 

the indicator would predict 

noncompliance with an emission 

limitation. 

Response: The EPA agrees with the 

commenters that one way regulatory 

authorities have owners or operators of 

regulated sources demonstrate 

compliance via ongoing monitoring is to 

use a CAM rule-type approach. Under 

such an approach, an owner or operator 

would be able to establish operating 

ranges of continuously monitored 

parameters determined through 

concurrent performance testing as 

indicators of performance (indicators of 

compliance are components of 

performance testing). Nothing in the 

CAM rule precludes an owner or 

operator from establishing parameters as 

directly enforceable limitations, and 

neither does this rule. The CAM ruletype approach would require owners or 

operators who chose parameter 

monitoring as indicative of compliance 

to immediately take corrective action 

should a measured parameter value 

occur outside the demonstrated range 

associated with compliance. Moreover, 

concurrent performance testing and 

parameter measurement would be 

necessary on a periodic basis and may 

be necessary on a more frequent basis to 

reverify or reset a parameter value 

range. Failure to take immediate 

corrective action would constitute a 

violation. Moreover, failure of a 

parameter range to demonstrate 

compliance when reverification or 

resetting performance testing occurred 

would also constitute a violation. 

Comment: Commenters agreed that a 

compliance monitoring provision must 

specify a ‘‘measurement technique’’ and 

stated the EPA should defer to states 

regarding the most appropriate 

measurement techniques. The 

commenter disagreed that use of CEMS 

for ‘‘directly enforceable measurements’’ 

is always preferable. 

Response: The EPA appreciates the 

commenters’ support and notes that the 

measurement technique component 

used in this rule corresponds to a 

similarly-named component contained 

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260See 80 FR 15099, March 20, 2015. 

261See http://www2.epa.gov/sites/production/

files/2014-09/documents/next-gen-compliancestrategic-plan-2014-2017.pdf. 

262Recommendations to the Clean Air Act 

Advisory Committee: Phase II, June 2007, http://

www2.epa.gov/caaac/caaac-reports. 

in the definition of monitoring in the 

general provisions of 40 CFR part 63. To 

the extent that regulatory authorities 

choose appropriate measurement 

techniques, the EPA agrees with the 

commenter. The EPA believes the 

commenters take the language regarding 

use of directly enforceable emissions 

measurements out of context; the EPA 

said it is preferred wherever feasible, 

not that it is always required. 

Comment: Commenters stated the 

EPA should make clear that ‘‘averaging 

time’’ is only required for measurement 

techniques that collect continuous data 

that will be averaged over some period 

in order to assess source operations; i.e., 

the element is only essential to certain 

types of compliance monitoring 

requirements. The commenters 

suggested the EPA should not attempt to 

impose or require minimum frequencies 

in terms of calendar days, months, or 

year and urged the EPA to allow states 

flexibility to determine how best to 

address operational variability. 

Response: The EPA disagrees with the 

commenters, noting that averaging time 

remains an important aspect of 

demonstrating compliance via ongoing 

monitoring for all types of monitoring. 

It remains important to know how the 

period over which collected data are 

used to determine compliance, whether 

that period is daily, hourly, or annually. 

The EPA has not assigned minimum 

averaging times that regulatory 

authorities must use; however, the EPA 

expects those regulatory authorities to 

select averaging times appropriate to 

demonstrate compliance for specific 

types of sources. 

Comment: Commenters supported the 

EPA’s recommendation that information 

demonstrating compliance be made 

available online for general public 

access (80 FR 15448) so that the public 

can provide the oversight that the Act 

contemplates (42 U.S.C. 7604). Other 

commenters opposed an absolute 

requirement that all monitoring, testing, 

and reporting be done electronically 

since many permits are for small 

businesses who may not have the 

capital and technical expertise for 

electronic recordkeeping and reporting; 

commenters recommended that the EPA 

change this criterion into a 

recommendation that electronic means 

be used where feasible. 

Response: The EPA agrees that 

electronic reporting and public access to 

information is important. The EPA notes 

that it is and has been moving towards 

electronic emissions reporting from all 

regulated sources for some time now. 

New NSPS and NESHAP require 

electronic emissions reporting, and 

efforts are underway to require existing 

NSPS and NESHAP to use electronic 

emissions reporting.260 Consistent with 

this approach, and with the approach 

taken by the next generation of 

compliance program,261 this rule will 

assist the shift toward electronic 

reporting to make environmental 

reporting more accurate, complete, and 

efficient. Moreover, electronic reporting 

of emissions will help us and regulatory 

authorities better manage information, 

improve effectiveness, and improve 

transparency. 

F. Multi-Pollutant Considerations 

1. Summary of Proposal 

The EPA described many benefits of 

coordinating air quality planning efforts 

across a range of air quality programs 

addressing the NAAQS, air toxics, and 

climate change and encouraged states to 

pursue multipollutant planning 

approaches where possible. 

2. Final Rule 

The final rule reiterates many of the 

points made in support of 

multipollutant planning efforts in the 

proposal. Efforts to reduce fine particle 

concentrations fit well as part of multi 

pollutant planning efforts because of the 

involvement of PM2.5 precursor gases 

(i.e., NOX, SO2, VOC, and ammonia) and 

direct PM2.5 emissions in a number of 

other air quality and climate issues. 

NOX and VOC play important roles in 

atmospheric chemistry and in the 

formation of ground-level ozone. Certain 

VOCs and constituents of direct PM2.5

are also hazardous air pollutants. SO2

and NOX emissions, and their reactions 

with ammonia to form ammonium 

sulfate and ammonium nitrate, have 

played important roles in acidic 

deposition, haze in national parks, and 

in fine particle formation. Black carbon 

from direct PM2.5 emissions is an 

important short-lived climate pollutant. 

Increasing average temperatures due to 

climate change are expected to lead to 

higher ozone concentrations. Many 

efforts to address traditional air 

pollutants have important co-benefits in 

terms of reducing emissions of CO2 and 

other GHGs, and vice versa. For these 

reasons, efforts to reduce air pollution to 

address multiple objectives can provide 

important benefits to states, the 

regulated community, and the general 

public. 

Multipollutant planning issues have 

been an area of strong interest by 

scientists and policymakers for many 

years. In 1995–1997, the EPA sought 

recommendations from a federal 

advisory committee with broad 

stakeholder representation on ways to 

coordinate and make more efficient the 

implementation programs for upcoming 

ozone and PM2.5 standards and the 

regional haze program. The National 

Academy of Sciences issued ‘‘Air 

Quality Management in the United 

States,’’ a report on multipollutant 

planning issues and recommendations, 

in 2004. 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.262 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 believes that in many cases 

it can be more efficient for states to 

develop integrated control strategies 

that address multiple pollutants rather 

than separate strategies for individual 

air quality programs. 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. The EPA has encouraged states 

to take a multi-pollutant approach to 

managing air quality to the extent 

possible. 

While the agency encourages states to 

develop multi-pollutant plans, it 

recognizes that certain factors can make 

such efforts challenging. For example, 

the NAAQS are to be reviewed every 5 

years, and any revisions to the standards 

will lead to a series of implementation 

steps required by specific statutory 

schedules. In some cases program 

requirements and deliverables may not 

be coordinated easily, but in other 

situations there are good opportunities 

for conducting technical analyses and 

developing policy approaches that can 

have important health and 

environmental benefits while 

addressing multiple key air pollution 

issues at the same time. 

One such opportunity is the increased 

use of multi-pollutant assessments. A 

multi-pollutant assessment, or oneatmosphere modeling, is conducted 

with a single air quality model (such as 

CMAQ or CAMx) that is capable of 

simulating transport and formation of 

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263 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. 

264See EPA 2011. Policy Assessment for the 

Review of the Particulate Matter National Ambient 

Air Quality Standards, Office of Air Quality 

Planning and Standards, Research Triangle Park, 

NC, EPA 452/R–11–003, April 2011. 

265 78 FR 3086 (January 15, 2013). 

266 In the final 2012 PM 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). 

multiple pollutants simultaneously.263

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. It can also 

account for estimated changes in 

traditional air pollutant emissions 

resulting from programs (such as energy 

efficiency and renewable energy 

programs) to reduce emissions of CO2

and other greenhouse gases. 

Models and data analysis intended to 

address PM2.5 could be beneficial for use 

in addressing ozone, visibility 

impairment, and climate change. States 

that undertake multi-pollutant 

assessments as part of their attainment 

demonstration have the opportunity to 

assess the impact of their PM2.5

strategies on ozone, visibility, and 

climate programs to ensure that optimal 

emission reduction strategies are 

developed 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. 

3. Comments and Response 

Comments: Some commenters urged 

the EPA to provide assistance to those 

states that might be precluded from 

developing Multi-Pollutant SIPs due to 

lack of resources. Other commenters 

stated the EPA should support the 

states’ use of various approaches and 

tools suggested the EPA make the 

Control Strategy (CoST) tool fully 

available, as well as provide any 

necessary training to facilitate states’ 

ability to effectively use the tool. The 

commenter also suggested that the EPA 

entertain the possibility for states to 

demonstrate that the controls put in 

place to comply with multi-pollutant 

CAIR and CSAPR are valid and should 

be accepted as part of attainment 

demonstrations; allowing states to credit 

emissions reductions that have 

occurred. 

Response: The Control Strategy Tool 

(CoST) is a component of the EPA’s 

Emissions Modeling Framework that is 

a client-server system developed to 

support emissions modeling. CoST was 

developed by the EPA to model the 

emissions reductions and engineering 

costs associated with control strategies 

applied to point, area, and mobile 

sources of air pollutant emissions to 

support the analyses of the EPA air 

pollution policies and regulations. Links 

to the software and documentation are 

available at the EPA’s CoST Web site at 

http://www3.epa.gov/ttnecas1/cost.htm. 

Note that because of resource 

limitations, the EPA is not able to 

provide any support for the installation 

or operation of CoST outside of the 

agency. 

G. Measures to Ensure Appropriate 

Protections for Overburdened 

Populations 

1. Summary of Proposal 

The EPA requested comments on 

ways that states can provide public 

health protection specifically for 

overburdened populations when 

preparing attainment plans for the PM2.5

NAAQS. 

2. Final Rule 

Environmentally overburdened, 

underserved, and economically 

distressed communities may be subject 

to a higher risk of pollutant-related 

health effects than the general 

population because they may be 

exposed to higher pollutant 

concentrations than the general 

population; they may experience a 

larger health impact at a given pollutant 

concentration; or they may be adversely 

affected by lower pollutant 

concentrations than the general 

population.264 Thus, the NAAQS review 

process inherently takes into 

consideration appropriate 

environmental justice factors as part of 

the standard-setting process for each 

pollutant. 

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. The policy assessment for 

the 2012 PM NAAQS review (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. 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) to 

provide increased protection against 

health effects associated with long- and 

short-term PM2.5 exposures.265 The 

agency also (1) 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; and (2) directed states to 

relocate a limited number of existing 

monitors to near-roadway sites in large 

urban areas. Both of these actions 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. 

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.266

Relationship between direct PM2.5

emissions and PM2.5 precursor 

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267See 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. 

268Wesson, 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. 

269For more information on SEPs, go to https:// 

www.epa.gov/enforcement/supplementalenvironmental-projects-seps. 

270See 78 FR 27220 (May 9, 2013) notice of 

availability, ‘‘EPA Activities To Promote 

Environmental Justice in the Permit Application 

Process.’’ 

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.267

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. 

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 at-risk populations, states can 

maximize health benefits, thereby 

creating greater net benefits for the state 

in a cost-effective manner.268 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. 

Such information can be used to 

support updates to the state’s annual 

monitoring plan. 

Screening is a useful first step in 

understanding or highlighting locations 

that may be candidates for further 

review. The EPA has developed 

EJSCREEN, a public screening tool that 

allows users to access high-resolution 

environmental and demographic 

information for locations in the United 

States, and compare their selected 

locations to the rest of the state, the EPA 

region, or the nation. The tool may help 

users identify areas with minority and/ 

or low-income populations, potential 

environmental quality issues, a 

combination of environmental and 

demographic indicators that is greater 

than usual, and other factors that may 

be of interest. Other 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 that 

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 III.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 III.D 

and V.D of this preamble, 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 lower 

thresholds for minor source permitting; 

• Prioritize targeted enforcement 

strategies; and 

• Develop a list of potential supplemental 

environmental projects (SEPs) 269 that could 

be applied in the target area. 

In addition to the previous steps, 

states could increase opportunities for 

meaningful involvement of community 

groups in attainment plan development, 

annual monitoring network plan 

reviews, and permitting processes 270 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 such as permit actions; 

• Maintain multi-lingual Web sites and 

offer translators for public meetings and 

hearings; and, 

• Coordinate with the state’s EJ 

coordinator, if applicable, to assist with 

outreach efforts. 

3. Comment and Response 

Comment: Some commenters 

supported the EPA’s recommendations 

for measures to ensure protections for 

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271On January 17, 2014, the United States Court 

of Appeals for the District of Columbia Circuit 

overburdened communities, but stated 

that the EPA’s proposal to allow areas 

to ignore near-roadway monitors is 

inconsistent with these objectives. The 

commenter stated that communities 

near heavily trafficked areas tend to be 

disproportionately low-income minority 

communities that suffer from 

disproportionately higher PM2.5

exposure risks; and that the EPA and 

states should address the information 

gaps that disempower these 

communities in their ability to protect 

themselves from pollution sources. The 

commenter also stated that making 

sources disclose and report compliance 

information and providing that 

information in easy to access formats 

would go a long way to improve the 

ability of these communities to be 

informed of their risks and to assure 

compliance in their communities. 

Response: The EPA agrees that nearroad monitoring data should not be 

ignored in future attainment planning. 

However, the EPA wishes to clarify that 

the statements in the proposal 

referenced the fact that the near-road 

monitors were not required to be in 

place before January 1, 2015. 

Compliance with the PM2.5 standards is 

based on 3 years of complete, qualityassured data at a monitor. Thus, the 

earliest that these monitors would have 

valid design values would be in early 

2018 (based on data from 2015–2017). 

This timing makes it unlikely that 

sufficient data from these monitors will 

be available to be considered in 

attainment demonstrations that are due 

in 2016. In addition, the base modeling 

year of the attainment demonstration 

may pre-date the startup date of the 

near-road monitor(s). In this case, it may 

be possible to consider the near-road 

data in the attainment demonstration, 

but the recommended default projection 

methodology may not be applicable 

(since the time period of the near-road 

data may not correspond to the 5 year 

time period centered about the base 

modeling year, as recommended in the 

modeling guidance). Additionally, nearroad PM2.5 monitors are only required in 

the 27 largest metropolitan areas of the 

country, and some PM2.5 nonattainment 

areas may not have any near-road 

monitoring sites. Thus, when complete 

data from near-road PM2.5 ambient 

monitors become available, the data 

should be used by states and the EPA 

for all aspects of the NAAQS 

implementation process, from 

attainment planning to the 

determination of attainment, in a 

manner similar to any other qualityassured PM2.5 monitoring data. States 

should consult with the appropriate the 

EPA regional office to determine how 

and when near-road data should be used 

in the PM2.5 NAAQS implementation 

process for specific nonattainment 

areas. 

With regard to the comment about 

having easy access to facility 

compliance information, the EPA 

directs the commenter to the 

Enforcement and Compliance History 

Online Web site to search for facilities 

to assess compliance with 

environmental regulations. The site 

provides the ability to investigate 

pollution sources, examine and create 

enforcement-related maps, or explore an 

individual state’s performance. As noted 

earlier in this section, the EJSCREEN 

tool can also provide important 

information about estimated pollution 

impacts in specific communities. 

H. Tribal Issues 

The 1998 Tribal Authority Rule (TAR) 

(40 CFR part 49), which implements 

section 301(d) of the CAA, gives tribes 

the option of developing Tribal 

Implementation Plans (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 submission and 

implementation deadlines for the 

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 that meets the 

needs of the tribe and 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 

opportunity and flexibility, but not the 

obligation to develop 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), that 

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 these 

elements of the TIP are reasonably 

severable from other CAA requirements. 

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 matter at issue and to 

receive authorization from the EPA to 

run a CAA program. 

The EPA would review and approve, 

where appropriate, these 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.271 Tribes and 

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issued a decision vacating the EPA’s 2011 rule 

titled ‘‘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. 

272On 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. 

273For 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:// 

www3.epa.gov/ttn/caaa/t1/memoranda/evm_ievm_

g.pdf. 

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 2014 

Office of Air and Radiation’s 

‘‘Handbook for Interacting with 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. For additional information and a 

list of areas that are currently 

participating in the program, see https:// 

www.epa.gov/advance. 

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, indoor wood furnaces, 

hydronic heaters and fireplaces emit 

more than 382,000 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’’ 

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.272 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.273 To 

access the document, go to https://

epa.gov/burnwise/burn-wise-strategiesreducing-residential-wood-smoke. For 

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274 72 FR 20586 (April 25, 2007). 

275 75 FR 80118 (December 21, 2010). 

more information on the EPA’s wood 

smoke reduction program, see https://

www.epa.gov/burnwise. 

J. Improved Stationary Source 

Emissions Monitoring 

1. Summary of Proposal 

For purposes of demonstrating 

compliance with the EPA’s air quality 

regulatory requirements, the EPA, states, 

and sources rely on two basic types of 

monitoring: ambient air quality 

monitoring and stationary source 

emissions monitoring. Ambient air 

quality monitoring 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. 

Accurate stationary source emissions 

monitoring is also critical for the 

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 indicated that emission levels 

may 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 SIP. 

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 states. As a result of this interest, 

the EPA sought to gather information 

about ways to make the source 

emissions monitoring data collection 

process easier and more transparent. In 

the proposal, the EPA therefore asked 

for information regarding appropriate 

examples and supporting data from 

individual sources and states with 

experience in this area to inform such 

future guidance. The EPA sought 

comment on specific topics and 

questions regarding source monitoring 

techniques and asked commenters to 

submit any examples of improved 

stationary source emissions monitoring 

and any other methodologies—complete 

with equations and explanations—for 

estimating emissions reductions due to 

improved monitoring. 

2. Final Rule 

The EPA did not propose any specific 

changes to source monitoring 

requirements for PM2.5 and is therefore 

not finalizing any specific requirements, 

beyond what is required elsewhere in 

the final rule. 

3. Comments and Responses 

Comment. Several commenters 

focused on critiquing PM CEMS, PM 

CPMS and BLDS technology and claim 

that improved monitoring changes the 

stringency of existing rules and requires 

rulemaking. The commenters provided 

no examples or specific information in 

response to the request for information. 

Response. We appreciate the 

information submitted by the 

commenters, but we are not responding 

to the comments here because they are 

not directly pertinent to the rule being 

finalized. The EPA will continue to 

explore and implement innovative, costeffective 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. See the response to 

comments document for more detailed 

information. 

K. Stationary Source Test Methods for 

Emissions of Condensable PM2.5

1. Summary of Proposal 

As discussed in the proposal, direct 

PM2.5 is comprised of two components: 

Filterable PM2.5 and condensable PM2.5

emissions. Accurate test methods for 

condensable PM2.5 emissions have only 

been recently developed and approved 

by the EPA, and in the proposal the EPA 

explained that use of these test methods, 

including methods to quantify 

condensable PM2.5 emissions, were 

essential for identifying sources of 

direct PM2.5 emissions which, if better 

controlled, can help to bring a PM2.5

nonattainment area into attainment. 

However, the EPA did not propose any 

changes to those test methods. 

The EPA did propose to require that, 

where a state needs to adopt new or 

revised 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). The EPA proposed that 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. 

The 2007 PM2.5 Implementation Rule 

required, beginning on January 1, 2011, 

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.274 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).275 The revisions to those 

test methods added procedures to 

measure PM2.5 filterable and 

condensable particulate material and 

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. 

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2. Final Rule 

The EPA is finalizing the PM2.5

emissions limit and testing requirement 

as proposed. For sources that are 

required to adopt a new or revised 

direct PM2.5 emissions limit as part of 

the attainment demonstration 

(including, but not limited to, for RACT, 

BACT, or MSM), the state must specify 

PM2.5 emission limits in its SIP that 

include both filterable and condensable 

emissions. In addition, compliance 

testing requirements for those sources 

must include both measurement of 

filterable and condensable emissions. 

Existing filterable PM emission 

limitations that are not being revised as 

part of a Moderate area or Serious area 

attainment plan can remain expressed 

in terms of filterable PM and can rely on 

the existing test method used by the 

state for compliance determination. 

The EPA continues to believe that 

using these improved test methods, 

including methods to quantify 

condensable PM2.5 emissions, 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. Comments and Responses 

Comment: Some commenters stated 

that the EPA should make clear that as 

long as testing and monitoring is 

required for any new filterable and/or 

condensable PM emission limitation 

imposed, testing for ‘‘total PM2.5’’ is not 

required and the EPA should allow 

states flexibility in determining the best 

way to demonstrate compliance with 

any new emission limitations. The new 

emission limitation could take the form 

either of a limitation on condensable 

PM2.5 or a limitation on total direct 

PM2.5 emissions. The commenter further 

stated the EPA should make clear that 

states that specify condensable PM or 

total PM2.5 emission limitations are not 

required to adopt Method 202 as the 

compliance test method. 

Response: In the final rule, the EPA is 

requiring new or revised PM2.5

emissions limits and associated source 

testing to account for condensable 

emissions, but the EPA is not imposing 

any specific source testing requirements 

that would require total PM2.5 testing or 

the use of a specific test method. The 

EPA acknowledges that states have 

flexibility to determine the necessary 

emissions limitations of PM2.5 to meet 

SIP requirements for the NAAQS 

attainment. When states assess the 

contribution of the filterable and 

condensable PM component to PM2.5

they may require stationary source tests 

that include both filterable PM2.5 and 

condensable particulate matter to ensure 

emission limits are attained by subject 

facilities. Since we recognize that 

primary PM2.5 emissions can be 

measured with the combination of 

several promulgated test methods 

depending on the stationary source 

emission temperature and moisture 

content, states have the flexibility to 

require the appropriate filterable and 

condensable particulate measurement 

methods based on source conditions. 

Comment: Some commenters agreed 

with the EPA’s proposal not to require 

consideration of condensable PM in any 

existing emission limitations that are 

not otherwise being revised. The 

commenters stated that no purpose 

would be served by requiring states to 

include condensable PM in such 

standards if no revision is necessary to 

demonstrate attainment. Other 

commenters objected to the EPA’s 

proposal to not require states to update 

all existing PM emission limitations to 

include limitations on condensable PM. 

The commenters stated the EPA’s 

proposal is nonsensical and undermines 

any ability to demonstrate compliance 

with the Act. The commenters stated 

that, by the EPA’s own admission, 

inventories that do not reflect measured 

condensables from direct PM2.5 sources 

are not an ‘‘accurate’’ inventory of 

‘‘actual emissions.’’ The commenters 

further stated that, similarly, areas could 

not satisfy the criteria for RACM or 

BACM, or demonstrate expeditious 

attainment if the existing state emission 

limitations are not required to be 

updated to account for condensable 

emissions from these sources. 

Response. The EPA agrees with the 

commenters who maintain that existing 

PM2.5 emissions limits do not need to be 

revised to include emissions limits for 

condensable PM for sources from which 

additional emissions reductions are not 

needed in order to demonstrate 

attainment. The EPA does not agree that 

all existing direct PM2.5 emissions limits 

in the SIP have to include emissions 

limits that account for or specifically 

address condensable PM. However 

sources with new or revised PM2.5

emissions limits and associated source 

testing must account for condensable 

emissions. 

If the state has submitted an 

attainment demonstration that includes 

an adequate RACT, BACT, and/or MSM 

analysis, and has taken into account all 

known emissions of filterable and 

condensable PM2.5 in the area, then 

there is no need to require new 

condensable PM2.5 emissions limits and 

testing for sources that were not needed 

to be additionally controlled for 

attainment purposes. The state may 

want to require additional condensable 

PM2.5 emissions limits and testing to 

gain a better understanding of the 

sources in the nonattainment area 

(especially for sources which may be 

most likely to emit condensables). This 

could provide additional information 

for future SIPs and control programs if 

nonattainment persists. However, unless 

specific direct PM2.5 emissions 

reductions are shown to be needed in 

order for the area to attain the NAAQS, 

there does not need to be a SIP 

requirement to include new 

condensable emissions limits and 

testing for all existing sources with 

PM2.5 emissions limits. 

Additionally, the commenters stated 

that emissions inventories would not be 

‘‘accurate’’ and states could not satisfy 

their RACM/BACM requirements if 

condensable emissions were not 

included in the SIP. Regardless of 

emissions limits and source testing 

requirements, quantification and 

reporting of filterable and condensable 

PM2.5 emissions is required as part of 

the emissions inventory and RACT/

BACT rule requirements. In some cases, 

condensable PM2.5 information is 

available from previous source testing. 

In other cases, condensable PM2.5

emissions must be estimated through 

the use of emissions factors that have 

been developed from source testing of 

similar sources. States are therefore 

already required to take into account 

both filterable and condensable 

emissions as part of their inventory and 

control strategy (RACT/BACT) 

development. See section IV.B of this 

preamble for more information on 

emissions inventory requirements, 

section IV.D of this preamble for more 

information on RACT requirements, and 

section VI.D of this preamble for more 

information on BACT requirements. 

X. Revocation of the 1997 Primary 

Annual PM2.5 NAAQS 

A. Summary of the Proposal 

The EPA proposed two options for 

revoking the 1997 primary annual PM2.5

NAAQS and sought comment on 

whether to revoke the NAAQS at the 

current time. 

The two proposed options were: 

• 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; and 

• Option 2: Revoke the 1997 primary 

annual PM2.5 NAAQS for all purposes in all 

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58142 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

276Areas 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). 

277The guidance is available at: http://

www3.epa.gov/otaq/stateresources/transconf/

documents/420b15091.pdf. 278 78 FR 3086 (January 15, 2013). 

nonattainment and attainment areas for that 

NAAQS 1 year after the effective date of the 

designations for the 2012 primary annual 

PM2.5 NAAQS. 

Under the first proposed option, the 

EPA 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 the future as additional areas 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 annual 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 as long as it is 

designated nonattainment for that 

NAAQS. This option is consistent with 

the approach established for the 

transition to the current lead and SO2

NAAQS. 

Areas designated nonattainment for 

the 2012 primary annual PM2.5 NAAQS 

would be required under Option 1 to 

comply with applicable CAA 

requirements as set forth in the CAA. 

For transportation conformity purposes, 

these requirements began to apply 1- 

year after the effective date of 

designations and include using 

adequate or approved SIP motor vehicle 

emissions budgets for the 1997 annual 

PM2.5 NAAQS or the 2006 24-hour PM2.5

NAAQS where they exist until the area 

has approved or adequate budgets for 

the 2012 primary annual PM2.5

NAAQS.276 Areas that have adequate or 

approved motor vehicle emissions 

budgets for both the 1997 annual PM2.5

NAAQS or the 2006 24-hour PM2.5

NAAQS should refer to Question 3.3 in 

EPA’s ‘‘Implementing Transportation 

Conformity Guidance for 2012 PM2.5

Nonattainment Areas’’ for additional 

information on which budgets to use in 

conformity determinations prior to 

having adequate or approved budgets 

for the 2012 primary annual PM2.5

NAAQS.277 The use of such budgets 

serves as the appropriate antibacksliding measure for transportation 

conformity purposes. 

Under the second proposed option, 

the EPA would revoke the 1997 primary 

annual PM2.5 NAAQS for all CAA 

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 associated with 

revoking the 1997 primary annual PM2.5

NAAQS in attainment areas for that 

NAAQS would be the same as those that 

would apply under Option 1. However, 

revoking the 1997 primary annual PM2.5

NAAQS in nonattainment areas for that 

NAAQS would require anti-backsliding 

measures for areas designated 

nonattainment for the 1997 annual 

PM2.5 NAAQS at the time of the 

revocation. For details on the proposed 

anti-backsliding measures, refer to the 

discussion in the proposal for this final 

rule. (80 FR 15340) 

The EPA also requested comment on 

not revoking the 1997 primary annual 

PM2.5 NAAQS at this time. For 

additional details on all of the proposed 

options refer to the proposal. (80 FR 

15340) 

The EPA did not propose 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 PM2.5.278

For details on past revocations of the 

NAAQS including the 1-hour and 1997 

ozone NAAQS and prior SO2 and lead 

NAAQS, refer to the proposal for this 

final rule. (80 FR 15340) 

B. Final Rule 

The EPA is finalizing the revocation 

of the 1997 primary annual PM2.5

NAAQS for all purposes in attainment 

areas for that NAAQS as described in 

Option 1. See 40 CFR 50.13(d). The EPA 

had proposed that the revocation would 

be effective 1 year after the effective 

date of designations for the 2012 

primary annual PM2.5 NAAQS. Those 

designations were effective on April 15, 

2015. (80 FR 2206) Therefore, the 

proposed effective date of the revocation 

was effectively April 15, 2016. However, 

this final rule will not be effective 

before April 15, 2016. Therefore, the 

EPA is establishing the effective date of 

this final rule as the effective date of the 

revocation of the 1997 primary annual 

PM2.5 NAAQS. 

On the effective date of this final rule, 

the 1997 primary annual PM2.5 NAAQS 

will be revoked for all purposes in all 

attainment areas for that NAAQS, 

including the areas that were initially 

designated attainment for the 1997 

annual PM2.5 NAAQS. The final rule 

will have no practical impact on these 

areas that have always attained the 1997 

primary annual PM2.5 NAAQS. These 

areas have never been required to 

conduct air quality planning for this 

NAAQS for any CAA nonattainment 

purpose, although these areas would 

continue to implement applicable PSD 

requirements. 

This final rule also revokes the 1997 

primary annual PM2.5 NAAQS in areas 

that have been redesignated to 

attainment for this NAAQS (i.e., 

maintenance areas for this NAAQS). 

These areas will be required to 

implement their approved maintenance 

plan for the 1997 primary annual PM2.5

NAAQS and their PSD program. The 

approved maintenance plan can only be 

revised if the revision meets the 

requirements of CAA section 110(l) and, 

if applicable, CAA section 193, 

Similarly, all states will be required to 

continue to implement applicable 

control requirements in a FIP or 

approved SIP designed to address the 

interstate transport requirements of 

CAA section 110(a)(2)(D)(i) and (ii) with 

respect to the 1997 primary annual 

PM2.5 NAAQS, such as CAIR or CSAPR. 

These requirements continue to be 

necessary for downwind nonattainment 

areas to make progress towards 

attainment and to assure that the air 

quality protection achieved in all areas 

is maintained into the future. These 

provisions may only be modified if the 

revision meets the requirements of 

section 110(l). A similar provision was 

finalized to preserve interstate transport 

requirements with respect to the 

revocation of the 1997 ozone NAAQS. 

See 40 CFR 51.1105. 

For areas that remain nonattainment 

for the 1997 annual PM2.5 NAAQS, the 

EPA will continue to redesignate areas 

to attainment as appropriate. For an area 

that is redesignated to attainment after 

the effective date of this final rule, the 

1997 primary annual PM2.5 NAAQS will 

be revoked in such an area on the 

effective date of its redesignation to 

attainment for that NAAQS. The EPA 

will not revoke the 1997 primary annual 

PM2.5 NAAQS in any area as long as it 

is designated nonattainment for that 

NAAQS. 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. 

After revocation of the 1997 primary 

annual PM2.5 NAAQS in a given area, 

the designation for that standard is no 

longer in effect. The only PM2.5

designations that remain in effect in 

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279Nonattainment areas that were redesignated to 

attainment with an approved CAA section 175A 

maintenance plan are referred to throughout this 

document as ‘‘maintenance areas.’’ 

280Unimplemented 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. 

281Areas 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 or the 2006 24-hour 

PM2.5 NAAQS. In that case, such an area would be 

required to implement an NNSR program for that 

NAAQS. 

areas where the 1997 primary annual 

PM2.5 NAAQS has been revoked are 

those for the 1997 24-hour PM2.5

NAAQS, the 1997 secondary annual 

PM2.5 NAAQS, the 2006 24-hour PM2.5

NAAQS and the 2012 primary annual 

PM2.5 NAAQS. However, the EPA is 

retaining the listing of the designated 

areas for the 1997 annual PM2.5 NAAQS 

in 40 CFR part 81, for the purposes of 

identifying which areas remain 

designated as nonattainment for the 

1997 annual PM2.5 NAAQS and 

therefore subject to the requirements of 

subpart 4 and the areas that have been 

redesignated to attainment for the 1997 

secondary annual PM2.5 NAAQS. 

Accordingly, such references to 

historical designations of areas where 

the 1997 primary annual PM2.5 NAAQS 

has been revoked should not be viewed 

as current designations under CAA 

section 107(d) for the 1997 primary 

annual PM2.5. As additional areas are 

redesignated to attainment for the 1997 

annual PM2.5 NAAQS, the EPA will 

indicate in the redesignation rulemaking 

that the 1997 primary annual NAAQS is 

revoked on the effective date of the 

redesignation. 

The EPA notes that areas designated 

nonattainment for the 1997 annual 

PM2.5 NAAQS at the time of the final 

rule’s revocation would be required to 

continue to comply with applicable 

conformity requirements for that 

NAAQS. This obligation would 

continue until the effective date of the 

redesignation of such an area to 

attainment for the 1997 annual PM2.5

NAAQS. Transportation and general 

conformity would apply in all areas that 

are designated nonattainment for the 

more health protective 2012 primary 

annual PM2.5 NAAQS on April 15, 2016, 

the end of the conformity grace period 

(CAA section 176 (c)(c)(6) and 40 CFR 

93.102(d)). Any areas that are also 

designated nonattainment or 

redesignated to attainment for the 1997 

24-hour PM2.5 NAAQS or the 2006 24- 

hour PM2.5 NAAQS are required to 

continue to make conformity 

determinations for those NAAQS. See 

Section IX.B of this preamble for more 

information about conformity 

implementation including information 

pertaining to conformity requirements 

for the 1997 secondary annual NAAQS. 

As with other NAAQS revocations, 

this revocation is framed in the context 

of the CAA requirements that apply to 

the 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 or maintenance plan if the 

revision would reduce air quality 

protection. CAA section 193 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. CAA 

section 172(e), which addresses 

relaxations of the NAAQS, requires 

protections for areas that have not 

attained the 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. CAA Section 

110(l) provides that a SIP revision 

cannot be approved if it will interfere 

with attainment or other CAA 

requirements. Under CAA 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.279 280

The EPA has concluded that revoking 

the 1997 primary annual PM2.5 NAAQS 

in attainment areas for that NAAQS is 

consistent with the CAA and precedent 

in transitioning from a previous NAAQS 

to a new, more stringent NAAQS. The 

approach taken in this final rule is 

consistent with the approach taken in 

the transition from the past SO2 and 

lead NAAQS to the current NAAQS for 

those pollutants. Revoking the 1997 

primary annual PM2.5 NAAQS only in 

attainment areas ensures that any areas 

that remain designated nonattainment 

for the 1997 annual PM2.5 NAAQS make 

progress toward attaining that NAAQS 

as expeditiously as practicable by 

implementing the CAA requirements 

that apply to PM2.5 nonattainment areas 

as described elsewhere in this final rule. 

Continued attainment of the 1997 

primary annual PM2.5 NAAQS in areas 

that have been redesignated to 

attainment for that NAAQS will be 

ensured through the ongoing 

implementation of the approved 

maintenance plan that applies in these 

areas. These areas are required to 

implement their approved CAA section 

175A maintenance plan for the 1997 

primary annual PM2.5 NAAQS. They are 

also required to implement a PSD 

program for the annual PM2.5 NAAQS, 

unless they are designated 

nonattainment for the 2012 primary 

annual PM2.5 NAAQS where an NNSR 

program would apply.281 Revisions to 

the approved maintenance plan can 

only be made if the revisions meet the 

requirements of CAA section 110(l) and, 

if applicable, CAA section 193. 

Under the selected option for 

revocation, it is unnecessary to finalize 

anti-backsliding requirements that 

would apply to nonattainment areas for 

the 1997 primary annual PM2.5 NAAQS, 

because the NAAQS is only being 

revoked in attainment areas. 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. For areas that were initially 

designated as attainment for both the 

1997 annual PM2.5 NAAQS and the 2012 

primary annual PM2.5 NAAQS, the 

approved PSD SIPs satisfy the obligation 

to submit an approvable maintenance 

plan for the 2012 primary annual PM2.5

NAAQS under CAA section 110(a)(1). 

The NAAQS is not being revoked in 

nonattainment areas. Therefore, 

nonattainment areas will continue to 

comply with the requirements 

applicable to their classification for the 

1997 annual PM2.5 NAAQS as described 

in this final rule. For example, areas 

classified as Serious will be required to 

implement BACT and BACM level 

controls and implement an NNSR 

program that meets the Serious area 

requirements. Any areas that do not 

attain by the Serious area deadline 

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282Areas designated nonattainment for the 2012 

primary annual PM2.5 NAAQS would implement a 

NNSR program for that NAAQS, instead of a PSD 

program for the 1997 primary annual PM. 

283See South Coast Air Quality Management 

District v. EPA, 472 F.3d at 882. 

284Such areas without adequate or approved SIP 

budgets for either the 1997 annual PM2.5 NAAQS 

or the 2006 24-hour PM2.5 NAAQS are required to 

demonstrate transportation conformity using one of 

the interim emissions tests depending on their 

classification as required by 40 CFR 93.119. 

would be required to comply with other 

requirements including most stringent 

measures and a 5 percent plan. This 

would ensure that these areas continue 

to make progress toward attaining the 

1997 annual PM2.5 NAAQS and attain 

that NAAQS as expeditiously as 

practicable. It would also serve to 

provide early emissions reductions 

toward attaining the 2012 primary 

annual PM2.5 NAAQS. When these areas 

are eligible for redesignation to 

attainment, they may submit a 

redesignation request including a 

maintenance plan for the 1997 primary 

annual PM2.5 NAAQS as required by 

CAA sections 107(d)(3) and 175A. On 

the effective date of the approval of the 

redesignation request and maintenance 

plan, the 1997 primary annual PM2.5

NAAQS would be revoked and the 

approved maintenance plan along with 

the implementation of a PSD program 

for this NAAQS, if they are designated 

attainment for the 2012 primary annual 

PM2.5 NAAQS, would ensure continued 

attainment of the 1997 primary annual 

PM2.5 NAAQS.282 Revisions to the 

approved maintenance plan can only be 

made if the revisions meet the 

requirements of CAA section 110(l) and, 

if applicable, CAA section 193. 

As the EPA proposed, the areas where 

the NAAQS is being revoked are not 

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 helps to minimize 

the burden associated with preparing 

SIPs for a succession of the NAAQS of 

increasing stringency. These areas are 

required to continue to implement their 

approved maintenance plans for the 

1997 primary annual PM2.5 NAAQS. 

The maintenance plan remains in effect 

beyond the end of the maintenance 

period. It may only be revised if the 

revision complies with the requirements 

of CAA section 110(l) and, if applicable, 

CAA section 193. Any areas that are 

designated nonattainment for the 2012 

primary annual PM2.5 NAAQS are 

required to comply with the applicable 

CAA requirements as described in this 

final rule. 

The EPA notes that most of the 39 

areas that were initially designated as 

nonattainment for the 1997 annual 

PM2.5 NAAQS have already been 

redesignated to attainment (i.e., they are 

maintenance areas) and their approved 

maintenance plans and PSD programs 

along with the CAA’s anti-backsliding 

provisions in CAA sections 110(l) and 

193 ensure continued attainment of the 

1997 primary annual PM2.5 NAAQS. If 

additional areas are redesignated to 

attainment for the 1997 primary annual 

PM2.5 NAAQS, their approved 

maintenance plan and PSD program for 

the 1997 primary annual PM2.5 NAAQS 

would prevent backsliding for that 

NAAQS. As stated previously, 

applicable conformity requirements 

would continue to apply for the 1997 

annual PM2.5 NAAQS until the effective 

date of the redesignation of such an area 

to attainment for the 1997 annual PM2.5

NAAQS. 

In addition, transportation and 

general conformity will apply in all 

areas that are designated nonattainment 

for the more health protective 2012 

primary annual PM2.5 NAAQS on April 

15, 2016, the end of the conformity 

grace period (CAA section 176(c)(6) and 

40 CFR 93.102(d)). In the D.C. Circuit 

Court’s December 2006 decision in 

South Coast v. EPA, as modified 

following rehearing, the Court held with 

respect to the anti-backsliding approach 

for transportation 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 8-hour 

ozone NAAQS are available.283 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 

2012 primary annual PM2.5 NAAQS are 

found adequate or are approved.284

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. However, general conformity 

determinations will be required in 

nonattainment areas for the 2012 

primary annual NAAQS as required by 

CAA section 176(c)(5) to ensure that the 

actions 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. 

The EPA believes that revoking the 

1997 primary annual PM2.5 NAAQS is 

logical because it results 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, 

on the effective date of this rulemaking, 

which is after the end of the 1-year 

conformity grace period that applies to 

newly designated nonattainment areas. 

(CAA section 176(c)(6)). 

An area that is attaining the more 

health-protective 2012 primary annual 

PM2.5 NAAQS would no longer have to 

expend resources to make conformity 

determinations or complete other 

applicable CAA air quality planning 

requirements for any of the current 

annual PM2.5 NAAQS after the 1997 

primary annual PM2.5 NAAQS is 

revoked in the area. 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. See 

further information for how conformity 

will be implemented for the 2012 PM2.5

NAAQS in Section IX.B of this 

preamble. 

C. Comments and Responses 

1. Comments on Revocation Options 1 

and 2 and Not Revoking the 1997 

Primary Annual PM2.5 NAAQS 

Comment: Two commenters 

supported Option 1 and stated that any 

areas that are attaining the more 

protective 2012 PM2.5 NAAQS are also 

necessarily attaining the less stringent 

1997 PM2.5 NAAQS. Some commenters 

agreed that it is confusing to continue to 

maintain two NAAQS for the same 

pollutant. Two commenters stated that 

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revocation of the 1997 NAAQS would 

relieve the states of the administrative 

burden of developing and submitting an 

additional maintenance plan, as well as 

demonstrating transportation 

conformity, for areas that are in 

compliance with the more stringent 

2012 PM2.5 NAAQS. 

Response: The EPA is finalizing 

Option 1, and we agree with the 

commenter that: 

• Any area that is attaining the more 

health protective 2012 primary annual PM2.5

NAAQS of 12.0 mg/m3 is also attaining the 

1997 annual PM2.5 NAAQS of 15.0 mg/m3; 

• revoking the 1997 primary annual 

NAAQS in areas that have either always been 

in attainment for that NAAQS or have been 

redesignated to attainment reduces confusion 

concerning implementation of the various 

PM2.5 NAAQS; and 

• burden on states is reduced because a 

second 10-year maintenance plan is not being 

required for the 1997 primary annual PM2.5

NAAQS. 

If the 1997 primary annual PM2.5

NAAQS were to remain in place after 

CAA requirements begin to apply for the 

2012 primary annual PM2.5 NAAQS, 

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 are now designated 

nonattainment for the 2012 primary 

annual NAAQS would be required to 

implement CAA requirements for both 

annual PM2.5 NAAQS concurrently. 

Additionally, some areas would also be 

implementing requirements for the 2006 

24-hour PM2.5 NAAQS, and two areas 

remain subject to 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, as 

boundaries for several areas do, and the 

same test of conformity cannot be used 

for all the PM2.5 NAAQS. Even where an 

area’s boundaries are unchanged, 

different analysis years under the 

transportation conformity rule 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. 

Comment: Some commenters opposed 

revocation of the 1997 primary annual 

PM2.5 NAAQS but stated that if the EPA 

decides to revoke the standard, then 

Option 1 is preferable since it more fully 

complies with the health protection 

functions of the Act. This commenter 

stated that Option 2 would violate the 

Act by creating flexibility for regions 

that have failed to meet the standard. 

The commenter provides a number of 

reasons for why Option 2 should not be 

finalized. The commenter is primarily 

concerned that revoking the 1997 

primary annual NAAQS in areas that are 

designated nonattainment for that 

NAAQS at the time of revocation would 

delay improvements in air quality and 

allow areas to postpone implementation 

of controls that apply in PM2.5 areas that 

are classified as Serious. The 

commenter also stated that the EPA 

must identify specific problems to be 

addressed by revocation and a beneficial 

purpose for the revocation, and not 

solely on a claim of the need for 

flexibility. While the D.C. Circuit held 

that the EPA can revoke a NAAQS, the 

EPA cannot do so to maximize its own 

discretion. 

Response: The EPA concluded that it 

is important to have all of the CAA’s 

tools in subpart 4 and, as applicable, 

subpart 1 available in order to bring 

areas that are still violating the 1997 

annual PM2.5 NAAQS into attainment as 

expeditiously as practicable. Finalizing 

Option 1, which revokes the 1997 

primary annual PM2.5 NAAQS in 

attainment areas, including areas 

redesignated to attainment with an 

approved CAA section 175A 

maintenance plan, leaves the CAA’s 

compliance plan for PM areas in place 

as Congress envisioned it. As described 

earlier, the EPA is finalizing Option 1 

for revoking the 1997 primary annual 

PM2.5 NAAQS. Under Option 1, the 

primary annual NAAQS is being 

revoked in areas that have always been 

attainment for the 1997 annual PM2.5

NAAQS and in areas that have been 

redesignated to attainment for that 

NAAQS. Any area that remains 

designated nonattainment for the 1997 

annual PM2.5 NAAQS on the date of the 

revocation will have the 1997 primary 

annual PM2.5 NAAQS revoked after the 

area attains the 1997 annual PM2.5

NAAQS and is redesignated to 

attainment consistent with CAA section 

107(d)(3)(E) (including the requirement 

to have an approved CAA section 175A 

maintenance plan for the primary 

NAAQS). This means that any area that 

remains designated nonattainment on 

the date of the revocation will remain 

subject to all subpart 4 requirements, 

including Serious area requirements 

such as BACT and BACM and more 

stringent NNSR requirements. If the area 

does not attain by the Serious area 

deadline and is not eligible for a 1-year 

attainment date extension, the area 

would become subject to the 

requirement to develop a 5 percent plan. 

If the area has still not attained, it would 

be subject to the requirements in CAA 

section 179(d) for areas that fail to 

attain. 

The EPA agrees with the commenter’s 

assessment that attaining the 1997 

annual PM2.5 NAAQS as expeditiously 

as practicable has both health and 

welfare benefits. The final rule ensures 

that attainment of the 1997 PM2.5

NAAQS is achieved in all areas. 

Furthermore, the final rule also requires 

that progress is made toward attainment 

of the 2012 primary annual PM2.5

NAAQS in nonattainment areas for that 

NAAQS. In addition, the 1997 annual 

secondary NAAQS was retained to 

protect against certain welfare effects. 

The EPA agrees that if we had revoked 

the 1997 primary annual PM2.5 NAAQS 

in areas that are still violating that 

NAAQS those areas would have started 

over as Moderate areas for the 2012 

NAAQS, rather than being required to 

move forward with more stringent 

measures that would have applied to a 

Serious area for the 1997 annual PM2.5

NAAQS. The revocation of the 1997 

primary annual PM2.5 NAAQS as 

proposed under Option 1 and being 

finalized is fully consistent with 

principles of CAA section 172(e). The 

1997 primary annual PM2.5 NAAQS is 

only revoked after an area has attained 

that NAAQS and been redesignated to 

attainment with an approved CAA 

section 175A maintenance plan for that 

NAAQS. The NAAQS is not being 

revoked in any area that remains 

designated nonattainment for the 

NAAQS and areas that continue to 

violate the NAAQS continue to be 

required to implement all of the 

measures required by subpart 4 (e.g., 

BACT, BACM and Serious area NNSR) 

and would be subject to additional 

subpart 4 requirements (e.g., most 

stringent measures and a 5 percent plan) 

if the area cannot or does not attain by 

the Serious area deadline. 

The EPA is finalizing the revocation 

of the 1997 primary annual PM2.5

NAAQS only in former nonattainment 

areas that have been redesignated to 

attainment. Areas that continue to 

violate the 1997 annual NAAQS must 

attain that NAAQS and be redesignated 

to attainment with an approved CAA 

section 175A maintenance plan for the 

1997 primary annual PM2.5 NAAQS. 

The nonattainment areas where the 

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NAAQS is not being revoked will be 

required to comply with all subpart 4 

requirements in order to bring them into 

attainment with the 1997 annual PM2.5

NAAQS as expeditiously as practicable. 

In sum, the final rule requires CAA 

subpart 4 to be implemented in all 

nonattainment areas for the 1997 

primary annual PM2.5 NAAQS. 

The EPA also disagrees with the 

commenter’s assertion that the final rule 

changes CAA subpart 4’s requirements. 

Revocation under Option 1 requires that 

nonattainment areas attain the 1997 

annual PM2.5 NAAQS and be 

redesignated to attainment before that 

NAAQS is revoked. Any area that 

remains nonattainment and continues to 

violate the 1997 annual NAAQS must 

first attain that NAAQS by complying 

with the requirements for subpart 4 and 

then be redesignated to attainment with 

an approved maintenance plan for the 

1997 primary annual PM2.5 NAAQS as 

described earlier. 

The EPA has concluded that the final 

rule fully complies with CAA 

requirements and is consistent with 

both past precedents for revoking the 

original SO2 and lead NAAQS and the 

tenets of the South Coast decision 

concerning revocation of the 1-hour 

ozone NAAQS. (South Coast Air Quality 

Management Dist. v. EPA, 472 F.3d 882) 

Areas that continue to violate the 1997 

annual NAAQS at the time of the initial 

revocation are required to attain that 

NAAQS as expeditiously as practicable 

through implementation of 

requirements in subpart 4. This will 

ensure that these areas continue to make 

progress toward and eventually attain 

the 1997 annual NAAQS and make 

progress toward expeditious attainment 

of the more health protective 2012 

primary annual PM2.5 NAAQS. 

With regard to the comment that the 

EPA needs a better rationale for the 

revocation, the EPA is revoking the 1997 

primary annual PM2.5 NAAQS in areas 

that have always been attainment for 

that NAAQS and in areas that were 

initially designated nonattainment but 

have been redesignated to attainment for 

that NAAQS because this action ensures 

that only one primary annual PM2.5

NAAQS—the more protective 2012 

primary annual PM2.5 NAAQS—applies 

in areas that are designated as 

attainment for the 1997 annual PM2.5

NAAQS. These areas have successfully 

attained the less stringent 1997 annual 

PM2.5 NAAQS and have a maintenance 

plan in place to ensure that they do not 

slip back into nonattainment for that 

NAAQS. These areas can only revise 

their approved maintenance plans if the 

revision complies with CAA section 

110(l) and, if applicable, CAA section 

193. Any of these areas that are 

designated nonattainment for the more 

health protective 2012 primary annual 

PM2.5 NAAQS can now focus their 

efforts on expeditiously attaining the 

more protective NAAQS as required 

under subpart 4. Any of these areas that 

are designated attainment for the more 

health protective 2012 primary annual 

PM2.5 NAAQS can focus their resources 

on other pressing air quality issues. 

The EPA believes that appropriately 

integrating prior requirements with new 

goals facilitates coherent, effective and 

timely planning and controls, and 

minimizes the separate potentially 

duplicative submission of requirements 

left over from previous standards. 

Expeditious attainment of the 1997 

annual PM2.5 NAAQS in nonattainment 

areas provides both health and welfare 

benefits that should not be delayed by 

allowing nonattainment areas to restart 

the PM2.5 planning process under the 

Moderate area classification in subpart 4 

for areas that are designated 

nonattainment for the more health 

protective 2012 primary annual PM2.5

NAAQS. For these reasons and the 

reasons stated earlier in Section X.a of 

this preamble, the EPA believes that the 

revocation of the 1997 primary annual 

PM2.5 NAAQS in areas that have always 

been attainment for that NAAQS and in 

areas that have been redesignated to 

attainment for that NAAQS provides the 

appropriate way to move toward 

attaining the more protective standard 

in a timely and effective manner. This 

approach ensures that progress made 

under previous PM2.5 NAAQS continues 

in attainment areas and continues in 

nonattainment areas. 

Comment: Other commenters stated 

that it causes unnecessary complexity, 

confusion, and burden to have multiple 

national standards for the same criteria 

pollutant. The commenter stated that 

any concerns about states and 

nonattainment areas not continuing to 

make progress or reversing progress can 

be mitigated through anti-backsliding 

requirements. On the other hand, two 

commenters supported the option of not 

revoking the standard at all. One of 

these commenters believed that past 

experience has led to confusion and 

litigation and has diminished the 

urgency to attain a new NAAQS. 

Response: As described earlier, the 

EPA is finalizing revocation Option 1, 

which leaves the nonattainment 

designation in place until the area is 

redesignated to attainment and for those 

areas to fulfill the requirements of CAA 

subpart 4 that apply to them. Revoking 

the 1997 primary annual PM2.5 NAAQS 

in areas that were designated 

nonattainment at the time of the 

revocation could delay attainment of 

that NAAQS and slow progress on 

attaining the 2012 primary annual PM2.5

NAAQS because such areas would not 

be subject to all of the planning 

requirements in CAA subpart 4 after the 

date of the revocation. The EPA believes 

that the final rule simplifies the 

revocation because the approved 

maintenance plan and an area’s PSD 

program serve to prevent backsliding. 

Anti-backsliding measures are not 

required for nonattainment areas 

because the NAAQS is not being 

revoked in nonattainment areas. 

Comment: Several commenters 

supported Option 2 and stated that it is 

consistent with implementation rules 

for the other NAAQS, the 2012 primary 

annual PM2.5 NAAQS is more stringent 

and more protective of health than the 

1997 primary annual PM2.5 standard, 

and revocation of the 1997 PM2.5

NAAQS would reduce the burden on 

states. One of these commenters also 

stated that, in 1997 PM2.5 NAAQS 

maintenance areas that have good PM2.5

air quality, revoking the 1997 PM2.5

NAAQS in its entirety will alleviate 

transportation conformity requirements 

as well as requirements for the 

submission of additional maintenance 

plans. 

Response: As discussed in the 

proposal, the revocations of the prior 

lead and SO2 NAAQS were 

accomplished in a manner consistent 

with Option 1. (80 FR 15340) The EPA 

notes that both Options 1 and 2 would 

reduce burden on the states. Under 

Option 1, areas that are redesignated to 

attainment would not be required to 

submit a second 10-year maintenance 

plan. However, under Option 1, areas 

that are designated nonattainment at the 

time of the revocation would remain 

subject to the CAA subpart 4 

requirements applicable to the area until 

it attains the NAAQS and is 

redesignated to attainment through 

approval of a redesignation request and 

a CAA section 175A maintenance plan 

for the primary NAAQS. Under Option 

2, areas that remain designated 

nonattainment at the time of the 

revocation would be required to 

implement their approved SIPs for the 

1997 annual PM2.5 NAAQS but would 

not be susceptible to a reclassification 

from Moderate to Serious, and thus 

would not be required to adopt 

additional subpart 4 requirements 

including requirements for Serious areas 

that would apply if such an area were 

reclassified. Not requiring Serious area 

measures in such an area would delay 

emissions reductions and improvements 

in air quality. 

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285Note 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. 

286On December 18, 2014, the EPA issued final 

area designations for the 2012 annual national air 

quality standard for fine particulate matter (PM2.5). 

The EPA designated 14 areas in six states as 

‘‘nonattainment.’’ The effective date was April 15, 

2015. 

The EPA also notes it retained the 

1997 secondary annual NAAQS when 

the PM2.5 NAAQS was revised in 

December 2012, thus, full revocation of 

the 1997 standard would not be 

appropriate. 

Comment: Two commenters opposed 

the possible approach of not revoking 

the 1997 primary annual PM2.5 NAAQS 

at this time because it would be 

inconsistent with past actions when a 

NAAQS has been replaced by the more 

stringent NAAQS and because it 

presents an unnecessary burden. 

Response: The EPA is finalizing the 

proposed revocation of the 1997 

primary annual PM2.5 NAAQS for the 

reasons set forth earlier. 

2. Comments on Anti-Backsliding 

Requirements Under Option 1 

Comment: Some commenters 

expressed concern that the proposal that 

an approved CAA section 175A 

maintenance plan would serve as the 

anti-backsliding measures may not be 

consistent with the language of CAA 

section 172(e). 

Response: The EPA disagrees with the 

commenter. CAA section 172(e) applies 

in areas that have not attained the prior 

NAAQS. In this final rule, the EPA is 

only revoking the 1997 primary annual 

PM2.5 NAAQS in areas that have 

attained that NAAQS and been 

redesignated to attainment with an 

approved CAA section 175A 

maintenance plan. The EPA has 

determined that implementing the 

approved maintenance plan along with 

a PSD program will serve to prevent 

backsliding in the areas where the 

NAAQS is being revoked. The approved 

maintenance plan can only be revised if 

the revision meets the requirements of 

CAA section 110(l) and, if applicable, 

CAA section 193. In order for the 1997 

primary annual PM2.5 NAAQS to be 

revoked in the future in an area that 

remains designated nonattainment at 

the time of the initial revocation, such 

an area would have to attain the 

NAAQS, submit a redesignation request 

including a maintenance plan for the 

primary NAAQS, and the EPA would 

have to approve that submission. The 

1997 primary annual PM2.5 NAAQS 

would then be revoked in such an area 

on the effective date of the approval of 

the redesignation and maintenance 

plan. That approved maintenance plan 

would serve to prevent backsliding. 

Comment: Some commenters 

questioned whether the EPA’s 

conclusion is correct that under Option 

1 there is no need for anti-backsliding 

measures, because the area would have 

already attained. Commenter stated 

there may be no need for implementing 

additional measures, but it seems the 

state should continue to keep in effect 

those measures that have brought it to 

attainment (except NNSR which by 

statute is replaced by PSD permitting). 

Response: The final rule addresses 

this comment. Former nonattainment 

areas where the 1997 primary annual 

PM2.5 NAAQS is being revoked are 

required to implement the approved 

maintenance plan for that NAAQS and 

to implement a PSD program. The 

approved maintenance plan remains in 

effect beyond the end of the 

maintenance period. The approved 

maintenance plan can only be revised if 

the revision complies with CAA section 

110(l) and, if applicable, CAA section 

193. 

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 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 of this preamble on Moderate 

area attainment plan control strategies; 

Section VI.D.7 on Serious area 

attainment plan control strategies; and 

Section IX.G of this preamble, 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.285

B. Paperwork Reduction Act (PRA) 

The information collection activities 

in this rule have been submitted 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 2258.04, 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 finalizing 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 14 existing 

nonattainment areas for the 1997and 

2006 PM2.5 NAAQS, and 14 designated 

nonattainment areas.286 The attainment 

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 

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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 are 

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 14 

designated 2012 PM2.5 nonattainment 

areas, averaged over the first 3 years of 

this ICR, is estimated to be a total of 

42,000 labor hours per year at an annual 

a labor cost of $2.5 million (present 

value) over the 3 year period, or 

approximately $420,000 per state for the 

6 state respondents. The average annual 

reporting burden is approximately 2,625 

hours per response, with approximately 

3 responses per state for 16 state 

responses. There are no capital or 

operating and maintenance costs 

associated with the proposal 

requirements. Burden is defined at 5 

CFR 1320.3(b). 

The annual state burden for this 

information collection for the 14 

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 48,600 labor 

hours per year at an annual labor cost 

of $2.9 million (present value) over the 

3 year period, or approximately 

$417,000 per state for the 7 state 

respondents. The average annual 

reporting burden is approximately 3,240 

hours per response, with approximately 

two responses per state for 15 state 

responses. There are no capital or 

operating and maintenance costs 

associated with the proposal 

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. 

C. Regulatory Flexibility Act (RFA) 

I certify that this action will not have 

a significant economic impact on a 

substantial number of small entities 

under the RFA. In making this 

determination, the impact of concern is 

any significant adverse economic 

impact on small entities. An agency may 

certify that a rule will not have a 

significant economic impact on a 

substantial number of small entities if 

the rule relieves regulatory burden, has 

no net burden or otherwise has a 

positive economic effect on the small 

entities subject to the rule. This rule 

will not impose any requirements 

directly on small entities. Entities 

potentially affected directly by this final 

rule 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. 

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. 

F. Executive Order 13175: Consultation 

and Coordination With Indian Tribal 

Governments 

This final rule does not have tribal 

implications. It would not have a 

substantial direct effect on one or more 

Indian tribes. Furthermore, these 

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 relationship. 

Thus, Executive Order 13175 does not 

apply to this action. 

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. 

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 

This rulemaking does not involve 

technical 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. However, 

because of the benefits of improved air 

quality on low SES populations, the 

EPA conducted outreach to 

communities on the proposal to 

encourage comment including a March 

2014 environmental justice conference 

in Research Triangle Park, NC, 

conference calls and a meeting with the 

National Environmental Justice 

Advisory Committee. 

K. Congressional Review Act (CRA) 

This action is subject to the CRA, and 

the EPA will submit a rule report to 

each House of the Congress and to the 

Comptroller General of the United 

States. This action is not a ‘‘major rule’’ 

as defined by 5 U.S.C. 804(2). 

L. 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 

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287See, e.g., State of Texas, et al. v. EPA, 2011 

U.S. App. LEXIS 5654 (5th Cir. 2011) (finding SIP 

call to 13 states to be of nationwide scope and effect 

and thus transferring the case to the U.S. Court of 

Appeals for the D.C. Circuit in accordance with 

CAA section 307(b)(1)). 

actions as the Administrator may 

determine.’’ 

M. Judicial Review 

Section 307(b)(1) of the CAA indicates 

which Federal Courts of Appeal have 

venue for petitions of review of final 

agency actions by the EPA under the 

CAA. This section provides, in part, that 

petitions for review must be filed in the 

U.S. Court of Appeals for the District of 

Columbia Circuit (i) when the agency 

action consists of ‘‘nationally applicable 

regulations promulgated, or final actions 

taken, by the Administrator’’ or (ii) 

when such action is locally or regionally 

applicable, if ‘‘such action is based on 

a determination of nationwide scope or 

effect and if in taking such action the 

Administrator finds and publishes that 

such action is based on such a 

determination.’’ 

This rule implementing the PM2.5 SIP 

Requirements is ‘‘nationally applicable’’ 

within the meaning of CAA section 

307(b)(1). First, the rulemaking 

addresses the NAAQS that applies to all 

states and territories in the U.S. Second, 

the rulemaking addresses issues 

relevant to specific existing SIP 

provisions in states across the U.S. that 

are located in each of the ten EPA 

regions, numerous federal circuits and 

multiple time zones. Third, the 

rulemaking addresses a common core of 

knowledge and analysis involved in 

formulating the decision and a common 

interpretation of the requirements of the 

CAA being applied to SIPs in states 

across the country. Fourth, the 

rulemaking, by addressing issues 

relevant to appropriate SIP provisions in 

one state, may have precedential 

impacts upon the SIPs of other states 

nationwide. Courts have found similar 

rulemaking actions to be of nationwide 

scope and effect.287

Under section 307(b)(1) of the Act, 

petitions for judicial review of this 

action must be filed in the United States 

Court of Appeals for the District of 

Columbia Circuit by October 24, 2016. 

Any such judicial review is limited to 

only those objections that are raised 

with reasonable specificity in timely 

comments. Filing a petition for 

reconsideration by the Administrator of 

this final rule does not affect the finality 

of this rule for the purposes of judicial 

review nor does it extend the time 

within which a petition for judicial 

review may be filed and shall not 

postpone the effectiveness of such rule 

or action. Under section 307(b)(2) of the 

Act, the requirements of this final action 

may not be challenged later in civil or 

criminal proceedings brought by us to 

enforce these requirements. 

XIII. 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, Sulfur 

dioxide, Nitrogen oxides, Volatile 

organic compounds, Ammonia. 

40 CFR Part 51 

Environmental protection, Air 

pollution control, Intergovernmental 

relations, Particulate matter, Sulfur 

dioxide, Nitrogen oxides, Volatile 

organic compounds, Ammonia. 

40 CFR Part 93 

Environmental protection, Air 

pollution control, Intergovernmental 

relations, Particulate matter, Sulfur 

dioxide, Nitrogen oxides, Volatile 

organic compounds, Ammonia. 

Dated: July 29, 2016. 

Gina McCarthy, 

Administrator. 

For the reasons stated in the 

preamble, Title 40, Chapter I of the Code 

of Federal Regulations is amended as 

follows: 

PART 50—NATIONAL PRIMARY AND 

SECONDARY AMBIENT AIR QUALITY 

STANDARDS 

■ 1. The authority citation for part 50 

continues to read as follows: 

Authority: 42 U.S.C. 7401, et seq. 

■ 2. In § 50.13, add paragraph (d) to read 

as follows: 

§ 50.13 National primary and secondary 

ambient air quality standards for PM2.5. 

* * * * * 

(d) Until the effective date of the final 

Fine Particulate Matter National 

Ambient Air Quality Standards: State 

Implementation Plan Requirements rule 

to be codified at 40 CFR 51.1000 

through 51.1016, the 1997 annual PM2.5

NAAQS set forth in this section will 

continue in effect, notwithstanding the 

promulgation of the 2012 primary 

annual PM2.5 NAAQS under § 50.18. 

The 1997 primary annual PM2.5 NAAQS 

set forth in this section will no longer 

apply upon the effective date of the final 

Fine Particulate Matter National 

Ambient Air Quality Standards: State 

Implementation Plan Requirements rule; 

except that for areas designated 

nonattainment for the 1997 annual 

PM2.5 NAAQS set forth in this section as 

of the effective date of the final Fine 

Particulate Matter National Ambient Air 

Quality Standards: State 

Implementation Plan Requirements rule, 

the requirements applicable to the 1997 

primary 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 PM2.5

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. The area 

designations and classifications with 

respect to the 1997 annual and 24-hour 

PM2.5 NAAQS remain codified in 40 

CFR part 81 in order to provide 

information on where the 1997 primary 

annual PM2.5 NAAQS has been revoked 

and to facilitate the implementation of 

the 1997 secondary annual PM2.5

NAAQS and the 1997 24-hour PM2.5

NAAQS. 

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. 

■ 4. In Appendix A to subpart A of part 

51, revise table 1 to read as follows: 

Appendix A to Subpart A of Part 51— 

Tables 

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58150 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

TABLE 1 TO APPENDIX A OF SUBPART A—EMISSION THRESHOLDS 1 BY POLLUTANT FOR TREATMENT AS POINT SOURCE

UNDER 40 CFR 51.30 

Pollutant 

Every-year Triennial 

Type A 

sources 2 Type B sources NAA sources 3

(1) SO2 ................................................................................................................. ≥2500 ≥100 ........................... ≥100. 

PM2.5 (serious) ≥70. 

(2) VOC ................................................................................................................ ≥250 ≥100 ........................... ≥100. 

O3 (serious) ≥50. 

O3 (severe) ≥25. 

O3 (extreme) ≥10. 

PM2.5 (serious) ≥70. 

(3) NOX ................................................................................................................ ≥2500 ≥100 ........................... ≥100. 

PM2.5 (serious) ≥70. 

(4) CO .................................................................................................................. ≥2500 ≥1000 ......................... O3 (all areas) ≥100. 

CO (all areas) ≥100. 

(5) Lead ............................................................................................................... ........................ ≥0.5 (actual) .............. ≥0.5 (actual). 

(6) Primary PM10 ................................................................................................. ≥250 ≥100 ........................... ≥100. 

PM10 (serious) ≥70. 

(7) Primary PM2.5 ................................................................................................. ≥250 ≥100 ........................... ≥100. 

PM2.5 (serious) ≥70. 

(8) NH3 ................................................................................................................. ≥250 ≥100 ........................... ≥100. 

PM2.5 (serious) ≥70. 

1Thresholds for point source determination shown in tons per year of potential to emit as defined in 40 CFR part 70, with the exception of 

lead. Reported emissions should be in actual tons emitted for the required time period. 2Type A sources are a subset of the Type B sources and are the larger emitting sources by pollutant. 

3 NAA = Nonattainment Area. The point source reporting thresholds vary by attainment status for SO2, VOC, NOX, CO, PM10, PM2.5, and NH3. 

* * * * * 

Subpart I—Review of New Sources and 

Modifications 

■ 5. In § 51.165: 

■ a. Revise paragraphs (a)(1)(iv)(A)(1) 

and (a)(1)(x)(A); 

■ b. Add paragraph (a)(1)(x)(F); 

■ c. Revise paragraph 

(a)(1)(xxxvii)(C)(2); 

■ d. Remove paragraphs 

(a)(1)(xxxvii)(C)(3), and (4); 

■ e. Revise paragraphs (a)(2)(i) and 

(a)(2)(ii)(A); and 

■ f. Add paragraph (a)(13). 

The revisions and additions 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. 

(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 

individual precursor for PM2.5 (as 

defined in paragraph (a)(1)(xxxvii) of 

this section), 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, or 40 

tpy of VOC emissions, to the extent 

that any such pollutant is defined as 

a precursor for PM2.5 in paragraph 

(a)(1)(xxxvii) of this section. 

* * * * * 

(F) For the purposes of applying the 

requirements of paragraph (a)(13) of this 

section to modifications at existing 

major stationary sources of Ammonia 

located in a PM2.5 nonattainment area, if 

the plan requires that the control 

requirements of this section apply to 

major stationary sources and major 

modifications of Ammonia as a 

regulated NSR pollutant (as a PM2.5

precursor), the plan shall also define 

‘‘significant’’ for Ammonia for that area, 

subject to the approval of the 

Administrator. 

* * * * * 

(xxxvii) * * * 

(C) * * * 

(2) Sulfur dioxide, Nitrogen oxides, 

Volatile organic compounds and 

Ammonia are precursors to PM2.5 in any 

PM2.5 nonattainment 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 

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40 CFR part 81. Such a program shall 

apply to any new major stationary 

source or major modification that is 

major for the pollutant 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. 

* * * * * 

(13) The plan shall require that the 

control requirements of this section 

applicable to major stationary sources 

and major modifications of PM2.5 shall 

also apply to major stationary sources 

and major modifications of PM2.5

precursors in a PM2.5 nonattainment 

area, except that a reviewing authority 

may exempt new major stationary 

sources and major modifications of a 

particular precursor from the 

requirements of this section for PM2.5 if 

the NNSR precursor demonstration 

submitted to and approved by the 

Administrator shows that such sources 

do not contribute significantly to PM2.5

levels that exceed the standard in the 

area. Any demonstration submitted for 

the Administrator’s review must meet 

the conditions for a NNSR precursor 

demonstration as set forth in 

§ 51.1006(a)(3). 

* * * * * 

■ 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 and 

reclassifications. 

51.1003 Attainment plan due dates and 

submission requirements. 

51.1004 Attainment dates. 

51.1005 Attainment date extensions. 

51.1006 Optional PM2.5 precursor 

demonstrations. 

51.1007 [Reserved] 

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. 

51.1016 Continued applicability of the FIP 

and SIP requirements pertaining to 

interstate transport under CAA section 

110(a)(2)(D)(i) and (ii) after revocation of 

the 1997 primary annual PM2.5 NAAQS. 

Subpart Z—Provisions for 

Implementation of PM2.5 National 

Ambient Air Quality Standards 

§ 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). 

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 effective date of designation of 

a nonattainment area and no later than 

the end of the sixth calendar year 

following the effective 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 the 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 

the 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 for 

the nonattainment area means the 

projected emissions of direct PM2.5 and 

all PM2.5 precursors on the projected 

attainment date for the area. This 

projected inventory includes sources 

included in the base year inventory for 

the nonattainment area revised to 

account for changes in direct PM2.5 and 

all PM2.5 precursors through 

implementation of the plan and any 

additional sources of such emissions 

expected within the boundaries of the 

nonattainment area by the projected 

attainment date for the area. 

Average-season-day emissions means 

the sum of all emissions during the 

applicable season divided by the 

number of days in that season. 

Base year inventory for the 

nonattainment area 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. 

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 Moderate PM2.5

nonattainment area to Serious and that 

generally can achieve greater permanent 

and enforceable emissions reductions in 

direct PM2.5 emissions and/or emissions 

of PM2.5 plan 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 or 

liquid particles emitted directly from an 

air emissions source or activity, or 

reaction products of gases emitted 

directly from an air emissions source or 

activity which form particulate matter 

as they reach ambient temperatures. 

Direct PM2.5 emissions include filterable 

and condensable PM2.5 emissions 

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composed of elemental carbon, directly 

emitted organic carbon, directly emitted 

sulfate, directly emitted nitrate, and 

other organic or inorganic particles that 

exist or form through reactions as 

emissions reach ambient temperatures 

(including but not limited to crustal 

material, metals, and sea salt). 

Implemented means adopted by the 

state, fully approved into the SIP by the 

EPA, and requiring expeditious 

compliance by affected sources with 

installation and/or operation of any 

equipment, control device, process 

change, or other emission reduction 

activity. 

Major stationary source means any 

stationary source of air pollutant(s) that 

emits, or has the potential to emit 100 

tons per year or more of direct PM2.5 or 

any PM2.5 precursor in any Moderate 

nonattainment area for the PM2.5

NAAQS, or 70 tons per year or more of 

direct PM2.5 or any PM2.5 precursor in 

any Serious nonattainment area for the 

PM2.5 NAAQS. 

Mobile source means mobile sources 

as defined by 40 CFR 51.50. 

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

plan precursors from among those 

control measures which are either 

included in the SIP for any other 

NAAQS, or have been achieved in 

practice in any state, and that can 

feasibly be implemented in the relevant 

PM2.5 NAAQS nonattainment area. 

Nonpoint source means nonpoint 

sources as defined by 40 CFR 51.50. 

PM2.5 design value (DV) for a PM2.5

nonattainment area is the highest of the 

3-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 plan precursors are those PM2.5

precursors required to be regulated in 

the applicable attainment plan and/or 

NNSR program. 

PM2.5 precursors are Sulfur dioxide 

(SO2), Oxides of nitrogen (NOX), 

Volatile organic compounds (VOC), and 

Ammonia (NH3). 

Point source means point sources as 

defined by 40 CFR 51.50. 

Precursor demonstration means an 

optional set of analyses provided by a 

state that are designed to show that 

emissions of a particular PM2.5

precursor do not contribute significantly 

to PM2.5 levels that exceed the relevant 

PM2.5 standard in a particular 

nonattainment area. The three types of 

precursor demonstrations provided in 

this rule are the comprehensive 

precursor demonstration, the major 

stationary source precursor 

demonstration, and the NNSR precursor 

demonstration. 

Reasonable further progress (RFP) 

means such annual incremental 

reductions in emissions of direct PM2.5

and PM2.5 plan precursors as are 

required for the purpose of ensuring 

attainment of the applicable PM2.5

NAAQS in a nonattainment area by the 

applicable attainment date. 

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 effective 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 plan precursor 

emissions from sources in the area. 

RACM includes reasonably available 

control technology (RACT). 

RFP projected emissions means the 

estimated emissions for direct PM2.5 and 

PM2.5 plan precursors by source 

category or subcategory for the years in 

which quantitative milestones are due 

for a nonattainment area. 

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 and 

reclassifications. 

(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 due dates and 

submission requirements. 

(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 state(s) shall submit 

a Moderate area attainment plan that 

meets all of the following requirements: 

(i) Base year emissions inventory 

requirements set forth at § 51.1008(a)(1); 

(ii) Attainment projected 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 

§ 51.165. 

(2) The state(s) shall submit its 

Moderate area attainment plan to the 

EPA no later than 18 months from the 

effective 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 submission 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) Base year emissions inventory 

requirements set forth at § 51.1008(b)(1); 

(ii) Attainment projected 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 

§ 51.165. 

(2) The state(s) shall submit its 

Serious area attainment plan to the EPA 

according to the following schedule: 

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(i) Discretionary reclassification. (A) 

For any nonattainment area reclassified 

to Serious for a particular PM2.5 NAAQS 

under § 51.1002(b)(1) because the EPA 

determined it cannot practicably attain 

the NAAQS by the applicable Moderate 

area attainment date, the state(s) shall 

submit to the EPA no later than 18 

months from the effective date of 

reclassification the portion of the 

Serious area attainment plan that meets 

the following requirements: 

(1) Base year emissions inventory 

requirements set forth at § 51.1008(b)(1); 

(2) Serious area attainment plan 

control strategy requirements set forth at 

§ 51.1010(a)(1) through (4); and, 

(3) Nonattainment new source review 

plan requirements pursuant to § 51.165. 

(B) The state(s) shall submit to the 

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 the EPA by a date that is 

no later than 4 years after the effective 

date of reclassification, or 2 years prior 

to the attainment date, whichever is 

earlier. 

(ii) Mandatory reclassification. For 

any nonattainment area reclassified to 

Serious for a particular PM2.5 NAAQS 

under § 51.1002(b)(2) because the EPA 

determined it failed to attain the 

NAAQS by the applicable Moderate area 

attainment date, the state(s) shall submit 

to the EPA a Serious area attainment 

plan meeting the requirements set forth 

at paragraphs (b)(1)(i) through (viii) of 

this section within 18 months from the 

effective date of reclassification, or 2 

years before the attainment date, 

whichever is earlier. 

(iii) If the state(s) submits to the 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 the PM2.5 NAAQS by 

the applicable Serious area attainment 

date, the state(s) shall submit a revised 

Serious area attainment plan that 

demonstrates that each year the area 

will achieve at least a 5 percent 

reduction in emissions of direct PM2.5 or 

a 5 percent reduction in emissions of a 

PM2.5 plan precursor based on the most 

recent emissions inventory for the area. 

The revised attainment plan shall meet 

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) 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 

§ 51.165. 

(2) The state(s) shall submit to the 

EPA the revised attainment plan 

meeting the requirements set forth at 

paragraphs (c)(1)(i) through (vii) of this 

section no later than 12 months from the 

applicable Serious area attainment date 

that was previously missed. 

(d) Any attainment plan submitted to 

the 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 through the 

implementation of all control measures 

required under § 51.1009. The 

attainment date may be as late as the 

end of the sixth calendar year after the 

effective date of designation if the state 

demonstrates that the implementation of 

the control measures that qualify as 

RACM, RACT, and additional 

reasonable measures, but that are not 

necessary for demonstrating attainment 

by the end of the sixth calendar year 

after the effective 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 effective date of 

designation of the area with the 

implementation of all control measures 

required under § 51.1009 shall be the 

end of the sixth calendar year after the 

effective date of designation 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 effective date of designation. 

(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 effective 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 following the effective 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, but no later 

than 5 years following the effective date 

of the EPA’s finding that the area failed 

to attain by the original Serious area 

attainment date, except that the 

Administrator may extend the 

attainment date to the extent the 

Administrator deems appropriate, for a 

period no greater than 10 years from the 

effective date of the EPA’s 

determination that the area failed to 

attain, considering the severity of 

nonattainment and the availability and 

feasibility of pollution control measures. 

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(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 

effective date of designation of the area, 

the EPA shall proceed under the 

provisions of § 51.1002(b)(1) to 

reclassify the area to Serious through 

notice-and-comment rulemaking. 

(2) [Reserved] 

§ 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 calendar year 

that includes 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 24-hour concentration at each 

monitor in the area for the calendar year 

that includes 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 

that includes 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 the EPA to meet 

the requirements of § 51.1003(a). 

(3) A Moderate area 1-year attainment 

date extension runs from January 1 to 

December 31 of the year following the 

year that includes the applicable 

attainment date. 

(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 for the first 1-year extension 

year. 

(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 the EPA a Serious area 

attainment plan that meets the following 

requirements: 

(i) Base year and attainment projected 

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), and best available control 

measures not previously submitted; 

(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, and that demonstrate 

attainment as expeditiously as 

practicable; 

(iv) Reasonable Further Progress (RFP) 

requirements set forth at § 51.1012; 

(v) Quantitative milestone 

requirements set forth at § 51.1013; 

(vi) Contingency measure 

requirements set forth at § 51.1014; and, 

(vii) Nonattainment new source 

review plan requirements pursuant to 

§ 51.165. 

(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 the 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 the 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 the 

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 

attainment of the NAAQS by the 

applicable attainment date consistent 

with § 51.1004(a)(2)(i) at the time of 

submission 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: 

(1) Evidence that all control measures 

submitted in the applicable attainment 

plan have been implemented, and 

(2) 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. 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58155 

§ 51.1006 Optional PM2.5 precursor 

demonstrations 

(a) A state may elect to submit to the 

EPA one or more precursor 

demonstrations for a specific 

nonattainment area. The analyses 

conducted in support of any precursor 

demonstration must be based on 

precursor emissions attributed to 

sources and activities in the 

nonattainment area. 

(1) A comprehensive precursor 

demonstration must show that 

emissions of a particular precursor from 

all existing stationary, area, and mobile 

sources located in the nonattainment 

area do not contribute significantly to 

PM2.5 levels that exceed the standard in 

the area. If the state chooses to conduct 

a comprehensive precursor 

demonstration, the state must conduct 

the analysis in paragraph (a)(1)(i) of this 

section and it may conduct the analysis 

in paragraph (a)(1)(ii) of this section. 

(i) Concentration-based contribution 

analysis. The comprehensive precursor 

demonstration must evaluate the 

contribution of a particular precursor to 

PM2.5 levels in the area. If the 

contribution of the precursor to PM2.5

levels in the area is not significant, 

based on the facts and circumstances of 

the area, then the EPA may approve the 

demonstration. 

(ii) Sensitivity-based contribution 

analysis. If the concentration-based 

contribution analysis does not support a 

finding of insignificant contribution, 

based on the facts and circumstances of 

the area, then the state may choose to 

submit an analysis evaluating the 

sensitivity of PM2.5 levels in the area to 

a decrease in emissions of the precursor 

in order to determine whether the 

resulting air quality changes are 

significant. If the estimated air quality 

changes determined in the sensitivity 

analysis are not significant, based on the 

facts and circumstances of the area, then 

the EPA may approve the 

demonstration. 

(iii) If a comprehensive precursor 

demonstration is approved by the EPA, 

the state will not be required to control 

emissions of the relevant precursor from 

existing sources in the current 

attainment plan. 

(2) A major stationary source 

precursor demonstration must show that 

emissions of a particular precursor from 

all existing major stationary sources 

located in the nonattainment area do not 

contribute significantly to PM2.5 levels 

that exceed the standard in the area. If 

the state chooses to conduct a major 

stationary source precursor 

demonstration, the state must conduct 

the analysis in paragraph (a)(2)(i) of this 

section and it may conduct the analysis 

in paragraph (a)(2)(ii) of this section. 

(i) Concentration-based contribution 

analysis. The major stationary source 

precursor demonstration must evaluate 

the contribution of major source 

emissions of a particular precursor to 

PM2.5 levels in the area. If the 

contribution of the precursor to PM2.5

levels in the area is not significant, 

based on the facts and circumstances of 

the area, then the EPA may approve the 

demonstration. 

(ii) Sensitivity-based contribution 

analysis. If the concentration-based 

contribution analysis does not support a 

finding of insignificant contribution, 

based on the facts and circumstances of 

the area, then the state may choose to 

submit an analysis evaluating the 

sensitivity of PM2.5 levels in the area to 

a decrease in emissions of the precursor 

in order to determine whether the 

resulting air quality changes are 

significant. If the estimated air quality 

changes determined in the sensitivity 

analysis are not significant, based on the 

facts and circumstances of the area, then 

the EPA may approve the 

demonstration. 

(iii) If a major stationary source 

precursor demonstration is approved by 

the EPA, the state will not be required 

to control emissions of the relevant 

precursor from existing major stationary 

sources in the current attainment plan. 

(3)(i) A NNSR precursor 

demonstration must evaluate the 

sensitivity of PM2.5 levels in the 

nonattainment area to an increase in 

emissions of a particular precursor in 

order to determine whether the resulting 

air quality changes are significant. If the 

estimated air quality changes 

determined in the sensitivity analysis 

are not significant, based on the facts 

and circumstances of the area, the state 

may use that information to identify 

new major stationary sources and major 

modifications of a precursor that will 

not be considered to contribute 

significantly to PM2.5 levels that exceed 

the standard in the nonattainment area. 

(ii) If a NNSR precursor 

demonstration for a particular PM2.5

nonattainment area is approved, the 

state may exempt such new major 

stationary sources or major 

modifications of the particular precursor 

from the requirements for PM2.5 in 

§ 51.165. 

(b) If an area with one or more 

precursor demonstrations approved by 

the EPA is required to submit another 

PM2.5 attainment plan in accordance 

with § 51.1003 of this part, the current 

precursor demonstration(s) will not 

apply to the new plan. The state must 

submit the appropriate updated 

precursor demonstration(s) if it seeks to 

exempt sources of a particular precursor 

from control requirements in the new 

Serious area attainment demonstration 

or in the NNSR program for the Serious 

area. 

§ 51.1007 [Reserved] 

§ 51.1008 Emissions inventory 

requirements. 

(a) For any nonattainment area 

initially classified as Moderate, the state 

shall submit to the 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 for which monitored data 

were 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, averageseason-day emissions, or both, as 

appropriate for the relevant PM2.5

NAAQS. The state shall include as part 

of the plan a rationale for providing 

annual or seasonal emissions, and the 

justification for the period used for any 

seasonal emissions calculations. 

(iv) The inventory shall include direct 

PM2.5 emissions, separately reported 

PM2.5 filterable and condensable 

emissions, and emissions of the 

scientific PM2.5 precursors, including 

precursors that are not PM2.5 plan 

precursors pursuant to a precursor 

demonstration under § 51.1006. 

(v) The state shall report emissions as 

point sources according to the point 

source emissions thresholds of the Air 

Emissions Reporting Requirements 

(AERR), 40 CFR part 51, subpart A. 

(vi) The detail of the emissions 

inventory shall be consistent with the 

detail and 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 projected emissions show 

modeled PM2.5 concentrations below the 

level of the NAAQS. 

(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) and any 

new sources. The state shall include in 

this inventory projected emissions 

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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, average-season-day, or both) 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, separately reported PM2.5

filterable and condensable emissions, 

and emissions of the scientific PM2.5

precursors, including precursors that are 

not PM2.5 plan precursors pursuant to a 

precursor demonstration under 

§ 51.1006 of this part. 

(v) The same sources reported as 

point sources in the base year inventory 

for the nonattainment area shall be 

included as point sources in the 

attainment projected inventory for the 

nonattainment area. Stationary 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 for the 

nonattainment area. 

(vi) The same detail of the emissions 

included shall be consistent with the 

level of detail and data elements as in 

the base year inventory for the 

nonattainment area (i.e., as required by 

40 CFR part 41, subpart A). 

(b) For any nonattainment area 

reclassified as Serious, the state shall 

submit to the 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 paragraphs 

(a)(1) (ii) through (a)(1)(vi) of this 

section. In addition, the inventory shall 

use the Serious area definition of a 

major source listed under 

§ 51.165(a)(1)(iv)(A), and(a)(1)(vii) and 

(viii), and consistent with Table 1 of 

Appendix A to subpart A of this part in 

determining sources to include as point 

sources. Finally, the inventory year 

shall be one of the 3 years for which 

monitored data were used for 

reclassification to Serious, or another 

technically appropriate inventory year if 

justified by the state in the plan 

submission. 

(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 the 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 the 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 paragraphs 

(a)(1) (ii) through (a)(1)(vi) of this 

section. In addition, the inventory shall 

use the Serious area definition of a 

major source listed under 

§ 51.165(a)(1)(iv)(A)(vii) and (viii) and 

consistent with Table 1 of Appendix A 

to subpart A of this part in determining 

sources to include as point sources. The 

inventory year shall be one of the 3 

years for which monitored data were 

used to determine that the area failed to 

attain the PM2.5 NAAQS by the 

applicable Serious area attainment date, 

or another technically appropriate 

inventory year if justified by the state in 

the plan submission. 

(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 plan 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 plan precursors in 

the nonattainment area identified under 

paragraph (a)(1) of this section. 

(i) The state is not required to identify 

and evaluate potential control measures 

to reduce emissions of a particular PM2.5

precursor from any existing sources if 

the state has submitted a comprehensive 

precursor demonstration approved by 

the EPA pursuant to § 51.1006, except 

where the EPA requires such 

information as necessary to evaluate the 

comprehensive precursor demonstration 

pursuant to § 51.1006(a)(1)(ii). 

(ii) The state is not required to 

identify and evaluate potential control 

measures to reduce emissions of a 

particular PM2.5 precursor from any 

existing major stationary sources if the 

state has submitted a major stationary 

source precursor demonstration 

approved by the EPA pursuant to 

§ 51.1006, except where the EPA 

requires such information as necessary 

to evaluate the major stationary source 

precursor demonstration pursuant to 

§ 51.1006(a)(1)(ii). 

(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 effective 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 the 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 plan 

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 effective date of 

designation of the area. The state may 

use air quality modeling to demonstrate 

that the Moderate PM2.5 nonattainment 

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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 effective 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. If the state demonstrates through 

this analysis that control measures for 

reducing emissions of a PM2.5 precursor 

would not be necessary for attainment 

as expeditiously as practicable or to 

advance the attainment date, then the 

state would not be required to include 

control measures for the precursor in 

the Moderate area attainment plan, nor 

be required to address the precursor in 

the RFP plan, quantitative milestones 

and associated reports, and contingency 

measures. 

(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 

effective 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 

effective date of designation of the 

Moderate PM2.5 nonattainment area and 

the applicable attainment date for the 

area shall be considered an additional 

reasonable measure for the area. 

(ii) If the state demonstrates that the 

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, 

the state shall adopt all technologically 

and economically feasible control 

measures identified under paragraph 

(a)(3) of this section. This requirement 

also applies to areas that demonstrate 

pursuant to section 179B that the plan 

would be adequate to attain or maintain 

the standard but for emissions 

emanating from outside the United 

States. 

(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 

effective 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 

effective date of designation of the 

Moderate PM2.5 nonattainment area 

through the end of the sixth calendar 

year following the effective date of 

designation of the area shall be 

considered an additional reasonable 

measure for the area. 

(b) The state shall adopt control 

measures, including control 

technologies, on sources of direct PM2.5

emissions and sources of emissions of 

PM2.5 plan precursors located within the 

state but outside the Moderate PM2.5

nonattainment area if adopting such 

control measures is necessary to provide 

for attainment of the applicable PM2.5

NAAQS in such area. 

(c) For new or revised source 

emissions limitations on sources of 

direct PM2.5 emissions, the state shall 

establish such emission limitations to 

apply either to the total of the filterable 

plus condensable fractions of direct 

PM2.5, or to filterable PM2.5 and 

condensable PM2.5 separately. 

§ 51.1010 Serious area attainment plan 

control strategy requirements. 

(a) The state shall identify, adopt, and 

implement best available control 

measures, including control 

technologies, on sources of direct PM2.5

emissions and sources of emissions of 

PM2.5 plan precursors located in any 

Serious PM2.5 nonattainment area or 

portion thereof located within the state 

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 plan 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 for direct 

PM2.5 and PM2.5 plan precursors not 

previously identified by the state during 

the development of the Moderate area 

attainment plan for the area. 

(ii) The state is not required to 

identify and evaluate potential control 

measures to reduce emissions of a 

particular PM2.5 precursor from any 

existing sources if the state has 

submitted a comprehensive precursor 

demonstration approved by the EPA, 

except where the EPA requires such 

information as necessary to evaluate the 

comprehensive precursor demonstration 

pursuant to § 51.1006(a)(1)(ii). 

(iii) The state is not required to 

identify and evaluate potential control 

measures to reduce emissions of a 

particular PM2.5 precursor from any 

existing major stationary sources if the 

state has submitted a major stationary 

source precursor demonstration 

approved by the EPA, except where the 

EPA requires such information as 

necessary to evaluate the major 

stationary source demonstration 

pursuant to § 51.1006(a)(1)(ii). 

(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 effective 

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 the 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 

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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 plan 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 effective 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. 

(b) For a Serious PM2.5 nonattainment 

area for which air quality modeling 

demonstrates the area 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 

requirements. 

(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 plan precursors in 

the nonattainment area identified under 

paragraph (b)(1) of this section. 

(i) For the sources and source 

categories represented in the emission 

inventory for the nonattainment area, 

the state shall identify the most 

stringent measures for reducing direct 

PM2.5 and PM2.5 plan precursors 

adopted into any SIP or used in practice 

to control emissions in any state. 

(ii) The state shall reconsider and 

reassess any measures previously 

rejected by the state during the 

development of any previous Moderate 

area or Serious area attainment plan 

control strategy for the area. 

(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 the 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. 

(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 collectively 

shall achieve attainment as 

expeditiously as practicable but no later 

than 5 years after the applicable 

attainment date for the area. 

(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 most stringent measures; 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 plan 

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 fifteenth 

calendar year following the effective 

date of designation of the area. 

(c) For a Serious PM2.5 nonattainment 

area that the EPA has determined has 

failed to attain by the applicable 

attainment date, the state shall submit a 

revised attainment plan with a control 

strategy that demonstrates that each year 

the area will achieve at least a 5 percent 

reduction in emissions of direct PM2.5 or 

a 5 percent reduction in emissions of a 

PM2.5 plan precursor based on the most 

recent emissions inventory for the area; 

and that the area will attain the standard 

as expeditiously as practicable 

consistent with § 51.1004(a)(3). The 

plan shall meet the requirements of 

§ 51.1003(c)–(d), and the following 

requirements: 

(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 plan precursors in 

the nonattainment area identified under 

paragraph (c)(1) of this section. 

(i) For the sources and source 

categories represented in the emission 

inventory for the nonattainment area, 

the state shall identify the most 

stringent measures for reducing direct 

PM2.5 and PM2.5 plan precursors 

adopted into any SIP or used in practice 

to control emissions in any state, as 

applicable. 

(ii) The state shall reconsider and 

reassess any measures previously 

rejected by the state during the 

development of any Moderate area or 

Serious area attainment plan control 

strategy for the area. 

(3) The state may make a 

demonstration that a measure identified 

under paragraph (c)(2) of this section is 

not technologically or economically 

feasible to implement in whole or in 

part within 5 years or such longer 

period as the EPA may determine is 

appropriate after the EPA’s 

determination that the area failed to 

attain by the Serious area attainment 

date, 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 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58159 

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 the 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 

(c)(2) of this section on the basis of 

technological or economic infeasibility. 

(4) Except as provided under 

paragraph (c)(3) of this section, the state 

shall adopt and implement all control 

measures identified under paragraph 

(c)(2) of this section that collectively 

achieve attainment of the standard as 

expeditiously as practicable pursuant to 

§ 51.1004(a)(3). 

(5) The state shall conduct air quality 

modeling that meets the requirements of 

§ 51.1011(b) and that accounts for 

emissions reductions due to control 

measures needed to meet the annual 

reduction requirement of 5 percent of 

direct PM2.5 or a PM2.5 plan precursor; 

most stringent measures; 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 plan 

precursors in the area in order to 

demonstrate that the area can attain the 

PM2.5 NAAQS as expeditiously as 

practicable. 

(d) The state shall adopt control 

measures, including control 

technologies, on sources of direct PM2.5

emissions and sources of emissions of 

PM2.5 plan precursors located within the 

state but outside the Serious PM2.5

nonattainment area if adopting such 

control measures is necessary to provide 

for attainment of the applicable PM2.5

NAAQS in such area by the attainment 

date. 

(e) For new or revised source 

emissions limitations on sources of 

direct PM2.5 emissions, the state shall 

establish such emission limitations to 

apply either to the total of the filterable 

plus condensable fractions of direct 

PM2.5, or to filterable PM2.5 and 

condensable PM2.5 separately. 

§ 51.1011 Attainment demonstration and 

modeling requirements. 

(a) Nonattainment areas initially 

classified as Moderate. The attainment 

demonstration due to the EPA as part of 

any 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) 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 containing the 

applicable attainment date, 

notwithstanding RACM implementation 

deadline requirements in § 51.1009. 

(b) Nonattainment areas reclassified 

as Serious. The attainment 

demonstration due to the EPA as part of 

a Serious area attainment plan required 

under § 51.1003(b) or (c) 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. 

(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 a Serious area attainment 

demonstration shall be consistent with 

the control strategies required pursuant 

to § 51.1003 and § 51.1010. 

(5) 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 

containing the applicable attainment 

date, notwithstanding BACM 

implementation deadline requirements 

in § 51.1010. 

§ 51.1012 Reasonable further progress 

(RFP) requirements. 

(a) Each attainment plan for a PM2.5

nonattainment area shall include an 

RFP plan that demonstrates that sources 

in the area will achieve such annual 

incremental reductions in emissions of 

direct PM2.5 and PM2.5 plan precursors 

as are necessary to ensure attainment of 

the applicable PM2.5 NAAQS as 

expeditiously as practicable. The RFP 

plan shall include all of the following: 

(1) A schedule describing the 

implementation of control measures 

during each year of the applicable 

attainment plan. Control measures for 

Moderate area attainment plans are 

required in § 51.1009, and control 

measures for Serious area attainment 

plans are required in § 51.1010. 

(2) RFP projected emissions for direct 

PM2.5 and all PM2.5 plan precursors for 

each applicable milestone year, based 

on the anticipated implementation 

schedule for control measures required 

in paragraph (a)(1) of this section. For 

purposes of establishing motor vehicle 

emissions budgets for transportation 

conformity purposes (as required in 40 

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58160 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

CFR part 93) for a PM2.5 nonattainment 

area, the state shall include in its RFP 

submission an inventory of on-road 

mobile source emissions in the 

nonattainment area for each milestone 

year. 

(3) An analysis that presents the 

schedule of control measures and 

estimated emissions changes to be 

achieved by each milestone year, and 

that demonstrates that the control 

strategy will achieve reasonable 

progress toward attainment between the 

applicable base year and the attainment 

year. The analysis shall rely on 

information from the base year 

inventory for the nonattainment area 

required in § 51.1008(a)(1) and the 

attainment projected inventory for the 

nonattainment area required in 

§ 51.1008(a)(2), in addition to the RFP 

projected emissions required in 

paragraph (a)(2) of this section. 

(4) 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), 

pollutant emissions will be at levels that 

reflect either generally linear progress or 

stepwise progress in reducing emissions 

on an annual basis between the base 

year and the attainment year. A 

demonstration of stepwise progress 

must be accompanied by appropriate 

justification for the selected 

implementation schedule. 

(5) At the state’s election, an analysis 

that identifies air quality targets 

associated with the RFP projected 

emissions identified for the milestone 

years at the design value monitor 

locations. 

(b) 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) Except as 

provided in paragraph (a)(4) of this 

section, each attainment plan submittal 

for a Moderate PM2.5 nonattainment area 

shall contain quantitative milestones to 

be achieved no later than a milestone 

date of 4.5 years and 7.5 years from the 

date of designation of the area. 

(ii) The plan shall contain 

quantitative milestones to be achieved 

by the milestone dates specified in 

paragraph (a)(1)(i) of this section, as 

applicable, and that provide for 

objective evaluation of reasonable 

further progress toward timely 

attainment of the applicable PM2.5

NAAQS in the area. At a minimum, 

each quantitative milestone plan must 

include a milestone for tracking 

progress achieved in implementing the 

SIP control measures, including RACM 

and RACT, by each milestone date. 

(2) Nonattainment areas reclassified 

as Serious. (i) Except as provided in 

paragraph (a)(4) of this section, each 

attainment plan submission 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) 

shall contain 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) Except as provided in paragraph 

(a)(4) of this section, each attainment 

plan submission 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) shall 

contain quantitative milestones to be 

achieved no later than milestone dates 

of 7.5 years, 10.5 years, and 13.5 years 

from the date of designation of the area. 

If the attainment date is beyond 13.5 

years from the date of designation of the 

area, such attainment plan shall also 

contain a quantitative milestones to be 

achieved no later than milestone dates 

of 16.5 years, respectively, from the date 

of designation of the area. 

(iii) The plan shall contain 

quantitative milestones to be achieved 

by the milestone dates specified in 

paragraphs (a)(2)(i) and (ii) of this 

section, as applicable, and that provide 

for objective evaluation of reasonable 

further progress toward timely 

attainment of the applicable PM2.5

NAAQS in the area. At a minimum, 

each quantitative milestone plan must 

include a milestone for tracking 

progress achieved in implementing SIP 

control measures, including BACM and 

BACT, by each milestone date. 

(3) Serious areas that fail to attain by 

the applicable Serious area attainment 

date. (i) Except as provided in 

paragraph (a)(4) of this section, each 

attainment plan submission 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) shall contain quantitative 

milestones. 

(A) If the attainment plan is due prior 

to a date 13.5 years from designation of 

the area, then the plan shall contain 

milestones to be achieved by 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 

milestone date that falls within 3 years 

after the applicable attainment date. 

(B) If the attainment plan is due later 

than a date 13.5 years from designation 

of the area, then the plan shall contain 

milestones to be achieved by no later 

than a milestone date of 16.5 years from 

the date of designation of the area, and 

every 3 years thereafter, until the 

milestone date that falls within 3 years 

after the applicable attainment date. 

(ii) The plan shall contain 

quantitative milestones to be achieved 

by the milestone dates for the area, and 

that provide for objective evaluation of 

reasonable further progress toward 

timely attainment of the applicable 

PM2.5 NAAQS in the area. At a 

minimum, each quantitative milestone 

plan must include a milestone for 

tracking progress achieved in 

implementing the SIP control measures 

by each milestone date. 

(4) Each attainment plan submission 

for an area designated nonattainment for 

the 1997 and/or 2006 PM2.5 NAAQS 

before January 15, 2015, shall contain 

quantitative milestones to be achieved 

no later than 3 years after December 31, 

2014, and every 3 years thereafter until 

the milestone date that falls within 3 

years after the applicable attainment 

date. 

(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: 

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Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 58161 

(1) A certification by the Governor or 

Governor’s designee that the SIP control 

strategy is being implemented 

consistent with the RFP plan, as 

described in the applicable attainment 

plan; 

(2) 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; and, 

(3) A discussion of whether the area 

will attain the applicable PM2.5 NAAQS 

by the projected attainment date for the 

area. 

(c) If a state fails to submit a milestone 

report by the date specified in paragraph 

(b) of this section, the Administrator 

shall require the state to submit, within 

9 months after such failure, a plan 

revision that assures that the area will 

achieve the next milestone or attain the 

applicable NAAQS by the applicable 

date, whichever is earlier. If the 

Administrator determines that an area 

has not met any applicable milestone by 

the milestone date, the state shall 

submit, within 9 months after such 

determination, a plan revision that 

assures that the area 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 the EPA following 

a determination by the Administrator 

that the area has failed: 

(1) To meet any RFP requirement in 

an attainment plan approved in 

accordance with § 51.1012; 

(2) To meet any quantitative 

milestone in an attainment plan 

approved in accordance with § 51.1013; 

(3) To submit a quantitative milestone 

report required under § 51.1013(b); or, 

(4) 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 or that achieve emissions 

reductions not otherwise relied upon in 

the control strategy for the area; and, 

(2) Each contingency measure shall 

specify the timeframe within which its 

requirements become effective following 

a determination by the Administrator 

under paragraph (a) of this section. 

(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 the 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, 

quantitative milestones and quantitative 

milestone reports, 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) The 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 the 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 the 

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, quantitative 

milestones and quantitative milestone 

reports, 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) The 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 the EPA and 

announced through publication in the 

Federal Register at the time the EPA 

determines the area is violating the 

PM2.5 NAAQS. 

§ 51.1016 Continued applicability of the 

FIP and SIP requirements pertaining to 

interstate transport under CAA section 

110(a)(2)(D)(i) and (ii) after revocation of the 

1997 primary annual PM2.5 NAAQS. 

All control requirements associated 

with a FIP or approved SIP in effect for 

an area pursuant to obligations arising 

from CAA section 110(a)(2)(D)(i) and (ii) 

as of October 24, 2016, such as the CAIR 

or the CSAPR, shall continue to apply 

after revocation of the 1997 primary 

annual PM2.5 NAAQS. Control 

requirements associated with a FIP or 

approved into the SIP pursuant to 

obligations arising from CAA section 

110(a)(2)(D)(i) and (ii), including 40 CFR 

51.123, 51.124, 52.35, 52.36, 52.38 and 

52.39, may be modified by the state only 

if the requirements of § 51.123, 51.124, 

52.35, 52.36, 52.38 and 52.39, including 

statewide annual SO2 and annual NOX

emission budgets, continue to be in 

effect. Any such modification must meet 

the requirements of CAA section 110(l). 

■ 7. In Appendix S to Part 51: 

■ a. Revise paragraph II.A.4.(i)(a) 

introductory text; 

■ b. Add paragraphs II.A.4.(i)(a)(7)–(8); 

■ c. Revise paragraph II.A.10.(i); 

■ d. Add paragraph II.A.10.(vi); 

■ e. Revise paragraph II.A.31.(ii)(b)(2); 

and 

■ f. Add paragraphs II.A.31.(ii)(b)(3) and 

(4). 

The revisions and additions 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), 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 (8) 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 individual 

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: 

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58162 Federal Register / Vol. 81, No. 164 / Wednesday, August 24, 2016 / Rules and Regulations 

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, or 

40 tpy of Volatile organic compound 

emissions, to the extent that any such 

pollutant is defined as a precursor for 

PM2.5 in paragraph II.A.31 of this 

Ruling. 

* * * * * 

(vi) In any nonattainment area for 

PM2.5 in which a state must regulate 

Ammonia as a regulated NSR pollutant 

(as a PM2.5 precursor) as defined in 

paragraph II.A.31 of this Ruling, the 

reviewing authority shall define 

‘‘significant’’ for Ammonia for that area 

and establish a record to document its 

supporting basis. All sources with 

modification projects with increases in 

Ammonia emissions that are not subject 

to Section IV of this Ruling must 

maintain records of the nonapplicability of Section IV that reference 

the definition of ‘‘significant’’ for 

Ammonia that is established by the 

reviewing authority in the 

nonattainment area where the source is 

located. 

31. * * * 

(ii) * * * 

(b) * * * 

(2) Sulfur dioxide and Nitrogen 

oxides are regulated as precursors to 

PM2.5 in all PM2.5 nonattainment areas. 

(3) For any area that was designated 

nonattainment for PM2.5 on or before 

April 15, 2015, Volatile organic 

compounds and Ammonia shall be 

regulated as precursors to PM2.5

beginning on April 15, 2017, with 

respect to any permit issued for PM2.5,

unless the following conditions are met: 

The state submits a SIP for the 

Administrator’s review containing the 

state’s preconstruction review 

provisions for PM2.5 consistent with 

§ 51.165 and a complete NNSR 

precursor demonstration consistent with 

§ 51.1006(a)(3); and such SIP is 

determined to be complete by the 

Administrator or deemed to be complete 

by operation of law in accordance with 

section 110(k)(1)(B) of the Act by April 

15, 2017. If these conditions are met, the 

precursor(s) addressed by the NNSR 

precursor demonstration (Volatile 

organic compounds, Ammonia, or both) 

shall not be regulated as a precursor to 

PM2.5 in such area. If the Administrator 

subsequently disapproves the state’s 

preconstruction review provisions for 

PM2.5 and the NNSR precursor 

demonstration, the precursor(s) 

addressed by the NNSR precursor 

demonstration shall be regulated as a 

precursor to PM2.5 under this Ruling in 

such area as of April 15, 2017, or the 

effective date of the disapproval, 

whichever date is later. 

(4) For any area that is designated 

nonattainment for PM2.5 after April 15, 

2015, and was not already designated 

nonattainment for PM2.5 on or 

immediately prior to such date, Volatile 

organic compounds and Ammonia shall 

be regulated as precursors to PM2.5

under this Ruling beginning 24 months 

from the date of designation as 

nonattainment for PM2.5 with respect to 

any permit issued for PM2.5, unless the 

following conditions are met: the state 

submits a SIP for the Administrator’s 

review which contains the state’s 

preconstruction review provisions for 

PM2.5 consistent with § 51.165 and a 

complete NNSR precursor 

demonstration consistent with 

§ 51.1006(a)(3); and such SIP is 

determined to be complete by the 

Administrator or deemed to be complete 

by operation of law in accordance with 

section 110(k)(1)(B) of the Act by the 

date 24 months from the date of 

designation. If these conditions are met, 

the precursor(s) addressed by the NNSR 

precursor demonstration (Volatile 

organic compounds, Ammonia, or both) 

shall not be regulated as a precursor to 

PM2.5 in such area. If the Administrator 

subsequently disapproves the state’s 

preconstruction review provisions for 

PM2.5 and the NNSR precursor 

demonstration, the precursor(s) 

addressed by the NNSR precursor 

demonstration shall be regulated as a 

precursor to PM2.5 under this Ruling in 

such area as of the date 24 months from 

the date of designation, or the effective 

date of the disapproval, whichever date 

is later. 

* * * * * 

PART 93—DETERMINING 

CONFORMITY OF FEDERAL ACTIONS 

TO STATE OR FEDERAL 

IMPLEMENTATION PLANS 

■ 8. 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 

■ 9. 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. 2016–18768 Filed 8–23–16; 8:45 am] 

BILLING CODE 6560–50–P 

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