Fine Particulate Matter National Ambient Air Quality Standards: State Implementation Plan Requirements

Federal RegisterMar 23, 2015

Ask Donna

What actually matters in this document.

Text

ENVIRONMENTAL PROTECTION AGENCY

40 CFR Parts 50, 51, and 93

[EPA-HQ-OAR-2013-0691; FRL-9916-08-OAR]

RIN 2060-AQ48

Fine Particulate Matter National Ambient Air Quality Standards: State Implementation Plan Requirements

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

The Environmental Protection Agency (EPA) is proposing requirements that state, local and tribal air agencies would have to meet as they implement the current and future national ambient air quality standards (NAAQS) for fine particulate matter (PM

2.5

). Specifically, this notice provides details on how the EPA proposes that air agencies meet the statutory state implementation plan (SIP) requirements that apply to areas designated nonattainment for any PM

2.5

NAAQS, such as: general requirements for attainment plan due dates and attainment dates; emissions inventories; attainment demonstrations; provisions for demonstrating reasonable further progress; quantitative milestones; contingency measures; and nonattainment New Source Review (NNSR) permitting programs, among other things. This proposed rule clarifies the specific attainment planning requirements that would apply to PM

2.5

NAAQS nonattainment areas based on their classification (either Moderate or Serious), and the process for reclassifying Moderate areas to Serious. Additionally in this notice, the EPA is proposing to revoke the 1997 primary annual standard because the EPA revised the primary annual standard in 2012. The EPA first established the PM

2.5

NAAQS in 1997, completed a review of those standards in 2006, and most recently completed a review of the PM

2.5

NAAQS on December 14, 2012.

DATES:

Comments.

Comments must be received on or before May 22, 2015.

Public Hearing.

The EPA plans to hold one public hearing concerning the proposed rule in Washington, DC. The date, time and location will be announced separately. Please refer to

SUPPLEMENTARY INFORMATION

for additional information on the comment period and the public hearing.

Information Collection Request.

Under the Paperwork Reduction Act (PRA), comments on the information collection provisions are best assured of having full effect if the Office of Management and Budget (OMB) receives a copy of your comments on or before April 22, 2015.

ADDRESSES:

Submit your comments, identified by Docket ID No. EPA-HQ-OAR-2013-0691, by one of the following methods:

•

http://www.regulations.gov

. Follow the on-line instructions for submitting comments.

•

Email: a-and-r-docket@epa.gov

•

Mail:

Air and Radiation Docket and Information Center, Attention Docket ID No. EPA-HQ-OAR-2013-0691, Environmental Protection Agency, Mailcode: 28221T, 1200 Pennsylvania Avenue NW., Washington, DC 20460. In addition, please mail a copy of your comments on the information collection (ICR) provisions to the Office of Information and Regulatory Affairs, Office of Management and Budget (OMB), Attn: Desk Officer for EPA, 725 17th Street NW., Washington, DC 20503.

•

Hand Delivery:

Air and Radiation Docket and Information Center, Attention Docket ID No. EPA-HQ-OAR-2013-0691, Environmental Protection Agency in the EPA Headquarters Library, Room No. 3334 in the EPA Docket Center, located at William Jefferson Clinton Building West, 1301 Constitution Avenue NW., Washington, DC 20004. Such deliveries are only accepted during the Docket's normal hours of operation, and special arrangements should be made for delivery of boxed information.

Instructions:

Direct your comments to Docket ID No. EPA-HQ-OAR-2013-0691. The EPA's policy is that all comments received will be included in the public docket without change and may be made available online at

http://www.regulations.gov

, including any personal information provided, unless the comment includes information claimed to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through

http://www.regulations.gov

or email. The

http://www.regulations.gov

Web site is an “anonymous access” system, which means the EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an email comment directly to the EPA without going through

http://www.regulations.gov

, your email address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the Internet. If you submit an electronic comment, the EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD-ROM you submit. If the EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, the EPA may not be able to consider your comment. Electronic files should avoid the use of special characters, any form of encryption and be free of any defects or viruses. For additional information about the EPA's public docket visit the EPA Docket Center homepage at

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

. For additional instructions on submitting comments, go to the

SUPPLEMENTARY INFORMATION

section of this document.

Docket:

All documents in the docket are listed in the

http://www.regulations.gov

index. Although listed in the index, some information is not publicly available,

e.g.,

CBI or other information whose disclosure is restricted by statute. Certain other material, such as copyrighted material, will be publicly available only in hard copy. Publicly available docket materials are available either electronically in

http://www.regulations.gov

or in hard copy at the Air and Radiation Docket and Information Center in the EPA Headquarters Library, Room No. 3334 in the William Jefferson Clinton Building West, located at 1301 Constitution Avenue NW., Washington, DC 20460. The Public Reading Room is open from 8:30 a.m. to 4:30 p.m., Monday through Friday, excluding legal holidays. The phone number for the Public Reading Room is (202) 566-1744.

FOR FURTHER INFORMATION CONTACT:

For general information on this proposed rule, contact Mr. Rich Damberg, Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, by phone at (919) 541-5592 or by email at

damberg.rich@epa.gov

; or Ms. Megan Brachtl, Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, by phone at (919) 541-2648 or by email at

brachtl.megan@epa.gov

. For information on the public hearing, contact Ms. Pamela Long, Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, by phone at (919) 541-0641 or by email at

long.pam@epa.gov

. For information on the ICR, contact Mr. Butch Stackhouse, Office of Air Quality Planning and Standards, U.S. Environmental Protection Agency, by phone at (919) 541-5208 or by email at

stackhouse.butch@epa.gov

SUPPLEMENTARY INFORMATION:

I. General Information

A. Preamble Glossary of Terms and Acronyms

The following are abbreviations of terms used in the preamble.

AERR Air Emissions Reporting Rule

BACM Best Available Control Measures

BACT Best Available Control Technology

BART Best Available Retrofit Technology

BC Black Carbon

CAA Clean Air Act

CAIR Clean Air Interstate Rule

CAMx Comprehensive Air Quality Model with Extensions

CBI Confidential Business Information

CBSA Core-based Statistical Area

CDD Clean Data Determination

CFR Code of Federal Regulations

CMAQ Community Multi-Scale Air Quality Model

CSAPR Cross-State Air Pollution Rule

CSN Chemical Speciation Network

DOD Department of Defense

DOT Department of Transportation

EC Elemental Carbon

EGU Electric Generating Unit

EPA Environmental Protection Agency

Fe Iron

FEM Federal Equivalent Method

FIP Federal Implementation Plan

FRM Federal Reference Method

HCl Hydrogen Chloride

ICR Information Collection Request

LAER Lowest Achievable Emission Rate

MACT Maximum Achievable Control Technology

MATS Mercury and Air Toxics Standards

MSM Most Stringent Measures

MPO Metropolitan Planning Organization

NAAQS National Ambient Air Quality Standards

NAICS North American Industry Classification System

NAPAP National Acid Precipitation Assessment Program

NEI National Emissions Inventory

NESHAP National Emissions Standard for Hazardous Air Pollutants

Ammonia

Ammonium

Ammonium Nitrate

HSO

Ammonium Bi-Sulfate

(NH

)

Ammonium Sulfate

NNSR Nonattainment New Source Review

Nitrogen Oxides

Nitrate

NSPS New Source Performance Standards

Ozone

OM Organic Mass

OMB Office of Management and Budget

PM Particulate Matter

2.5

Particulate Matter Equal to or Less than 2.5 Microns in Diameter (Fine Particulate Matter)

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

Sulfur Dioxide

Sulfate

TAR Tribal Authority Rule

TIP Tribal Implementation Plan

TIP Transportation Improvement Program

TSP Total Suspended Particles

µm Micrometer (Micron)

VMT Vehicle Miles Traveled

VOC Volatile Organic Compounds

B. Does this action apply to me?

Entities potentially affected directly by this proposed rule include state, local and tribal governments and air pollution control agencies responsible for attainment and maintenance of the NAAQS. Entities potentially affected indirectly by this proposed rule as regulated sources include owners and operators of sources that emit PM

2.5

, sulfur dioxide (SO

), oxides of nitrogen (NO

), volatile organic compounds (VOC) and/or ammonia (NH

). Others potentially affected indirectly by this proposed rule include members of the general public who live, work, or recreate in areas affected by elevated ambient PM

2.5

levels in areas designated nonattainment for a PM

2.5

NAAQS.

C. What should I consider as I prepare my comments for the EPA?

1. Submitting CBI.

Do not submit this information to the EPA through

http://www.regulations.gov

or email. Clearly mark the specific information that you claim to be CBI. For CBI in a disk or CD-ROM that you mail to the EPA, mark the outside of the disk or CD-ROM as CBI and then identify electronically within the disk or CD-ROM the specific information that is claimed as CBI. In addition to one complete version of the comment that includes information claimed as CBI, a copy of the comment that does not contain the information claimed as CBI must be submitted for inclusion in the public docket. Information so marked will not be disclosed except in accordance with procedures set forth in 40 CFR part 2.

Tips for preparing comments.

When submitting comments, remember to:

• Identify the rulemaking by docket number and other identifying information (subject heading,

Federal Register

date and page number).

• Follow directions. The proposed rule may ask you to respond to specific questions or organize comments by referencing a Code of Federal Regulations (CFR) part or section number.

• Explain why you agree or disagree, suggest alternatives and substitute language for your requested changes.

• Describe any assumptions and provide any technical information and/or data that you used to support your comment.

• If you estimate potential costs or burdens, explain how you arrived at your estimate in sufficient detail to allow for it to be reproduced.

• Provide specific examples to illustrate your concerns wherever possible, and suggest alternatives.

• Explain your views as clearly as possible, avoiding the use of profanity or personal threats.

• Make sure to submit your comments by the comment period deadline identified.

D. What information should I know about possible public hearings?

For information pertaining to the one public hearing on this document, contact Ms. Pamela Long, Air Quality Policy Division, Office of Air Quality Planning and Standards (C504-03), Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone number (919) 541-0641; fax number (919) 541-5509; email address:

long.pam@epa.gov

E. Where can I obtain a copy of this document and other related information?

In addition to being available in the docket, an electronic copy of this

Federal Register

document will be posted at

http://www.epa.gov/airquality/particlepollution/actions.html

F. How is this Federal Register document organized?

The information presented in this document is organized as follows:

I. General Information

A. Preamble Glossary of Terms and Acronyms

B. Does this action apply to me?

C. What should I consider as I prepare my comments for the EPA?

D. What information should I know about possible public hearings?

E. Where can I obtain a copy of this document and other related information?

F. How is this

Federal Register

document organized?

II. Background for Proposal

A. Introduction

B. Atmospheric Chemistry of PM

2.5

and Its Precursors

C. Historical Overview of PM

2.5

NAAQS Setting and Implementation

D. State Implementation Planning Process for PM

2.5

NAAQS

III. What is the EPA proposing with respect to the treatment of PM

2.5

precursors in nonattainment area planning and permitting?

A. Background

B. Proposed Precursor Policy Options

C. Technical Approaches for Demonstrating That a Precursor Does Not Need To Be Subject to Control Requirements

IV. What are the EPA's proposed requirements for Moderate area attainment plans?

A. Plan Due Dates

B. Emissions Inventory Requirements

C. Pollutants To Be Addressed in the Plan

D. Attainment Plan Control Strategy

E. Modeling for Attainment Demonstrations

F. RFP Requirements

G. Quantitative Milestones

H. Contingency Measures

I. Attainment Dates

J. Attainment Date Extensions

V. How would a PM

2.5

Moderate nonattainment area be reclassified to Serious?

A. Discretionary Authority

B. Mandatory Duty

VI. What are the EPA's proposed requirements for Serious area attainment plans?

A. Plan Due Dates

B. Emissions Inventory Requirements

C. Pollutants To Be Addressed in the Plan

D. Attainment Plan Control Strategy

E. Modeling for Attainment Demonstrations

F. RFP Requirements

G. Quantitative Milestones

H. Contingency Measures

I. Attainment Dates

J. Attainment Date Extensions

VII. What are the EPA's proposed requirements for attainment plans under CAA section 189(d) for Serious areas that fail to attain the NAAQS by the applicable attainment date?

A. Plan Due Dates

B. Emissions Inventory Requirements

C. Pollutants To Be Addressed in the Plan

D. Attainment Plan Control Strategy

E. Modeling for Attainment Demonstrations

F. RFP Requirements

G. Quantitative Milestones

H. Contingency Measures

I. Attainment Dates

VIII. What are the EPA's proposed NNSR permitting requirements?

A. Statutory Requirements for NSR

B. Federal NNSR Regulations

C. What changes is the EPA proposing for NNSR for PM

2.5

nonattainment areas?

D. Plan Due Dates

E. Avoidance of Dual Review for PSD and NNSR for PM

2.5

IX. What other proposed requirements would apply in PM

2.5

nonattainment areas?

A. Waivers Under Section 188(f)

B. Conformity Requirements

C. Clean Data Policy

D. Section 179B/International Border Areas

E. Enforcement and Compliance

F. Efforts To Encourage a Multi-Pollutant Approach When Developing PM

2.5

Attainment Plans

G. Measures to Ensure Appropriate Protections for Overburdened Populations

H. Tribal Issues

I. Voluntary Programs for Reducing Ambient PM

2.5

J. Improved Stationary Source Emissions Monitoring

K. Stationary Source Test Methods for Emissions of Condensable PM

2.5

X. What is the EPA proposing with respect to revoking the 1997 primary annual PM

2.5

NAAQS?

A. Background

B. History of Revocation of Other NAAQS

C. Proposed Options for Revocation and Related Anti-Backsliding Requirements for the 1997 Primary Annual PM

2.5

NAAQS

D. Discussion of Options

XI. Environmental Justice Considerations

XII. Statutory and Executive Order Reviews

A. Executive Order 12866: Regulatory Planning and Review and Executive Order 13563: Improving Regulation and Regulatory Review

B. Paperwork Reduction Act

C. Regulatory Flexibility Act

D. Unfunded Mandates Reform Act

E. Executive Order 13132: Federalism

F. Executive Order 13175: Consultation and Coordination with Indian Tribal Governments

G. Executive Order 13045: Protection of Children from Environmental Health and Safety Risks

H. Executive Order 13211: Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use

I. National Technology Transfer and Advancement Act

J. Executive Order 12898: Federal Actions to Address Environmental Justice in Minority Populations and Low-Income Populations

K. Determination Under Section 307(d)

Statutory Authority

List of Subjects

II. Background for Proposal

A. Introduction

Ambient, or outdoor, air can contain a variety of pollutants, including particulate matter (PM). Airborne PM can be comprised of either solid or liquid particles, and can be a complex mixture of particles in both solid and liquid form. The most common constituents of airborne PM include: sulfate (SO

); nitrate (NO

); ammonium (NH

); elemental carbon (EC); organic mass (OM); and inorganic material, generally referred to as “crustal” material, which can include metals, dust, sea salt and other trace elements. Airborne PM can be of different sizes, commonly referred to as “coarse” and “fine” particles. Fine particles, in general terms, are particulate matter with an aerodynamic diameter less than or equal to a nominal 2.5 micrometers (μm). For this reason, particles of this size are referred to as PM

2.5

. PM

2.5

particles commonly include “primary” particles and “secondary” particles. Primary particles, or direct PM

2.5

, 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 PM

2.5

precursors (

e.g.,

reactions between NO

and SO

emissions from mobile and stationary sources combined with ammonia to form NO

and SO

The human health effects associated with long- or short-term exposure to PM

2.5

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 PM

2.5

levels include visibility impairment as well as effects on sensitive ecosystems, materials damage and soiling and climatic and radiative processes.

For a complete discussion of the human health and welfare effects associated with exposure to elevated concentrations of particulate matter,

see generally

“Integrated Science Assessment for Particulate Matter.” U.S. Environmental Protection Agency, Office of Research and Development, National Center for Environmental Assessment-RTP Division, February 10, 2010. EPA/600/R-08/139F. Available at:

http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_isa.html

See

Chapter 2.

On December 14, 2012, the EPA made revisions to the suite of NAAQS for PM to provide requisite protection of public health and welfare with an adequate margin of safety. The EPA also made corresponding revisions to the data handling conventions for PM and the ambient air monitoring, reporting and network design requirements for PM. Specifically, the agency revised the primary annual PM

2.5

standard by lowering the level from 15.0 to 12.0 μg/m

to provide increased protection against health effects associated with long- and short-term PM

2.5

exposures. The EPA did not revise the secondary annual PM

2.5

standard which remains at 15.0 μg/m

The EPA eliminated spatial averaging as part of the form of the PM

2.5

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 PM

2.5

standards to continue to provide supplemental protection against health effects associated with short-term PM

2.5

exposures. Although not directly relevant to this rulemaking with respect to the PM

2.5

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 PM

standards, which remain at 150 μg/m

78 FR 3086 (January 15, 2013).

This proposed rulemaking is to develop implementation regulations with respect to the PM

2.5

NAAQS. For the PM

NAAQS, states and the EPA will continue to implement those NAAQS in accordance with the applicable statutory requirements of the Clean Air Act (CAA) and the EPA's existing guidance in the “The General Preamble for Implementation of Title I of the Clean Air Act (CAA) Amendments,” 57 FR 13498 (April 16, 1992); and “State Implementation Plans for Serious PM-10 Nonattainment Areas: Addendum to the General Preamble for the Implementation of Title I of the Clean Air Act (CAA) Amendments,” 59 FR 41998 (August 16, 1994). Throughout this preamble, these documents will be referred to as the “General Preamble” and the “Addendum,” respectively.

Estimates show that attainment of the primary PM

2.5

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.

Attainment of the primary PM

2.5

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.

“Regulatory Impact Analysis for the Final Revisions to the National Ambient Air Quality Standards for Particulate Matter.” U.S. Environmental Protection Agency, Office of Air Quality and Planning Standards, Health and Environmental Impacts Division, February 28, 2013. EPA-452/R-12-005.

See: http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_ria.html

Ibid.

B. Atmospheric Chemistry of PM

2.5

and Its Precursors

1. Overview

In order to determine how to regulate sources of direct PM

2.5

and PM

2.5

precursors to attain the PM

2.5

NAAQS in a given nonattainment area, it is necessary to understand the basic chemical processes that cause or contribute to the formation of ambient PM

2.5

. Accordingly, an understanding of these processes is necessary to design appropriate regulations for implementation of the PM

2.5

NAAQS. Properly designed regulatory requirements will help to assure that the PM

2.5

NAAQS are attained effectively and expeditiously in all areas.

As noted earlier, the term PM

2.5

refers to particles of solid and liquid material less than 2.5 microns in aerodynamic diameter.

“Primary” PM

2.5

is emitted directly from emissions sources or activities, such as from diesel fuel combustion, wood burning, construction activities or unpaved roads, and it includes both filterable and condensable particles.

“Secondary” PM

2.5

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 PM

2.5

formation are SO

, from the combustion of coal or other high sulfur fuels; NO

, from many types of fossil fuel combustion; VOC, from certain fuels, solvents and industrial processes; and ammonia, from sources such as animal feeding operations, wastewater treatment and fertilizer. Table 1 provides National Emissions Inventory (NEI) data for 2011 that represent nationwide anthropogenic emissions estimates for direct PM

2.5

and the four main PM

2.5

precursor gases from major source sectors.

The regulatory definition of PM

2.5

includes particles with an upper 50 percent cut-point of 2.5μm aerodynamic diameter (the 50 percent cut-point diameter is the diameter at which the sample collects 50 percent of the particles and rejects 50 percent of the particles). PM

2.5

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.

Certain commercial or industrial activities involving high temperature processes (

e.g.,

fuel combustion, metal processing, cooking operations) emit gaseous pollutants into the ambient air which rapidly condense into particle form. These “condensable” PM emissions exist almost entirely in the 2.5 or less micron range and can consist of organic material, sulfuric acid and metals.

Table 1—Total Emissions of PM

2.5

and Precursors for Major Sectors (in tons/year)

[Source: 2011 National Emissions Inventory (Version 1)

]

Category

Direct PM

2.5

VOC

Chemical and allied products

16,464

125,768

49,867

79,236

23,044

Fuel combustion—electric generating utilities (EGUs)

196,685

4,612,641

2,031,855

40,597

24,968

Fuel combustion —other

628,199

987,552

1,856,716

588,346

79,679

Other industrial

273,857

185,859

348,561

328,222

53,039

Onroad mobile

208,629

28,969

5,785,570

2,413,026

119,654

Metals processing

48,451

144,630

70,655

34,277

1,140

Miscellaneous (mainly fire emissions, dust and some agricultural operations)

4,489,694

219,318

434,547

5,810,566

3,934,405

Offroad mobile

207,543

92,036

3,133,798

2,159,368

3,270

Petroleum & related industries

31,738

116,317

684,808

2,488,123

1,643

Solvent utilization

3,810

107

893

2,814,551

577

Storage and transport

20,098

9,109

19,079

1,221,185

5,734

Waste disposal and recycling

172,144

16,842

83,469

131,777

68,281

For more details on the definitions of the emission categories listed in Table 1,

see

Sector/Tier crosswalk table for the 2011 NEI, available at:

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

2. Composition and Sources of PM

2.5

Constituents

2.5

is a complex and highly variable mixture of particles, but the majority of PM

2.5

by mass is often comprised of five constituents: (i) OM; (ii) EC; (iii) crustal material; (iv) ammonium sulfate ((NH

)

); and (v) ammonium nitrate (NH

The discussion that follows provides an overview of each of the five major components of PM

2.5

, all of which are known to contribute to ambient PM

2.5

levels in areas throughout the U.S.

Section II.B.3 provides more details on

the atmospheric chemistry involved in the formation of sulfate, nitrate and OM, to illustrate the importance of controlling emissions of PM

2.5

precursors as part of any comprehensive strategy to reduce ambient PM

2.5

levels in excess of the NAAQS. Section II.B.4 presents a brief overview of PM

2.5

composition by region of the U.S.

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

Atmospheric Chemistry and Physics: From Air Pollution to Climate Change

. 2nd edition, J. Wiley, New York.

U.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

OM is the fraction of ambient PM

2.5

with the most diverse chemical composition, containing potentially thousands of different organic compounds (

i.e.,

those compounds containing carbon) composed primarily of carbon, hydrogen, oxygen and nitrogen. Both primary particles and secondary particles contribute to ambient OM concentrations, with combustion sources being the dominant type of emissions sources. Another portion of primary OM particles results from direct emissions of organic compounds from sources of incomplete combustion, such as gas and diesel engines. Secondary OM particle formation involves oxidation of both anthropogenic and biogenic (plant-derived) VOC, and can involve other, more complex chemical reactions. Further details of the chemistry behind the formation of secondary OM, known more commonly as secondary organic aerosols (SOA), are described in Section II.B.3 of this preamble.

EC refers to particulate carbon that has a graphitic molecular structure, and is sometimes referred to as “black carbon” (BC). It is emitted directly from emission sources and does not undergo any significant reactions with other gases in the atmosphere. EC particles result from primary emissions involving combustion, especially from diesel-fueled vehicles, but also from other processes involving the burning of fossil fuels. The latter includes anthropogenic sources such as boilers and waste disposal. In addition, some EC particles originate from biomass combustion such as from prescribed fires, wildfires and residential wood combustion.

Crustal PM is comprised of particles of soil and oxides of metals from some industrial processes. Compounds comprised of elements such as silicon, aluminum, iron, calcium, titanium, magnesium and potassium, as well as oxygen, are major components.

Sources of crustal PM

2.5

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 PM

2.5

comprised of elements, like iron (Fe), and their oxides can also be emitted from industrial sources.

Appel, 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.

The remaining portion of ambient PM

2.5

is mostly composed of SO

, NO

and NH

, which react in the ambient air to form ammonium sulfate ((NH

)

) and ammonium nitrate (NH

). Another common PM

2.5

particle is ammonium bi-sulfate (NH

HSO

). In some areas, less common ions such as chloride are also found in PM

2.5

samples in the form of particles that include sodium chloride and ammonium chloride. Particle-bound water is often also associated with this fraction of PM

2.5

. Sulfate, nitrate and ammonium particles originate through both primary and secondary mechanisms, although the vast majority of these PM

2.5

particles are formed through secondary formation, as described in the following section.

3. Secondary Formation of PM

2.5

From Gaseous Precursors

Overview.

The composition of PM

2.5

is complex and highly variable due in part to the large contribution of secondary PM

2.5

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 non-linear in nature, can convert the gases SO

, NO

, VOC and ammonia to PM

2.5

. Thus, these gases are precursors to PM

2.5

. A brief discussion of SO

, NO

and SOA formation, as well as the role of ammonia in their formation, follows.

formation

. SO

is emitted mostly from the combustion of fossil fuels in boilers operated by electric utilities and other industries, with less than 10 percent of SO

emissions nationwide coming from other industrial sources, such as oil refining and pulp and paper production.

When SO

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 (NH

)

, a less acidic compound and one of the five major components of PM

2.5

. If there is not enough ammonia present to fully neutralize the sulfuric acid, part of it may convert to NH

HSO

, which is more acidic than (NH

)

, but less so than sulfuric acid. There is a large amount of emerging scientific evidence that SO

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 SO

emissions, generally from electricity generating units, and from meteorological conditions that are conducive to sulfate formation.

U.S. Environmental Protection Agency, 2013. “2008 National Emissions Inventory: Review Analysis and Highlights.” Office of Air Quality Planning and Standards, Air Quality Assessment Division, May 2013. EPA-454/R-005. Available at:

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

formation

. The main sources of NO

emissions are combustion of fossil fuel in boilers and mobile sources, accounting for more than 80 percent of national anthropogenic NO

emissions (based on the 2011 NEI), with boilers and electric generating units (EGUs) contributing about 27 percent and mobile sources contributing 56 percent. Oxides of nitrogen react in the atmosphere to form nitric acid, another prime contributor to acid deposition in the environment. Nitric acid converts to ammonium nitrate, one of the five main components of PM

2.5

, 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.

Carlton, 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.

SOA formation.

As discussed earlier, the OM component of ambient PM

2.5

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” PM

2.5

) or can be formed by reactions in the ambient air to make SOA (

i.e.,

as “secondary” PM

2.5

VOC (both anthropogenic and biogenic) are key precursors to the SOA component of PM

2.5

. 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 PM

2.5

in the summer than in the winter.

Pandis S.N., Harley R.A., Cass G.R., and Seinfeld J.H., 1992. Secondary Organic Aerosol Formation and Transport, Atmospheric Environment, 26, 2266-82.

Anthropogenic sources of VOC include mobile sources, petrochemical manufacturing, oil and gas emissions and solvents.

In addition, some biogenic VOC, emitted by vegetation such as trees, can also contribute significantly to SOA formation, especially in heavily forested areas, such as the southeastern U.S. It should be noted, however, that anthropogenic contributions to SOA are likely highest in the wintertime when biogenic SOA levels are lower; conversely, in the summertime, biogenic contributions to SOA are likely higher. Despite significant progress that has been made in understanding the origins and properties of SOA, it remains the least understood component of PM

2.5

and continues to be a significant topic of research and investigation.

Carlton, 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.

Role of ammonia in sulfate, nitrate and SOA formation.

Ammonia is a gaseous pollutant emitted by natural and anthropogenic sources. The EPA's 2011 NEI shows that the two main sources of ammonia emissions are fertilizer application (27 percent) and livestock raising (54 percent). It should be noted that the 2011 NEI indicates that mobile sources in the aggregate contribute about 3 percent of nationwide ammonia emissions. Much of those emissions comes from catalytic converters installed on light-duty gasoline vehicles, which are designed to convert NO

to nitrogen (N

); however, some ammonia is formed as a secondary product during this process.

As indicated earlier, ammonia plays an important role in neutralizing acids, such as sulfuric acid and nitric acid, in clouds, precipitation and particles. On the other hand, deposited ammonia can contribute to problems of eutrophication in water bodies due to its nutritive properties.

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 PM

2.5

mass in a given area. The ammonium portion by itself roughly accounts for between 5 percent and 20 percent of the total PM

2.5

mass in the East.

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

Atmospheric Chemistry and Physics: From Air Pollution to Climate Change,

1st edition, J. Wiley, New York.

NARSTO, 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

Role of NO

in sulfate, nitrate and SOA formation

. In addition to the contribution of NO

emissions to secondary particulate nitrate formation, NO

also reacts with anthropogenic and biogenic VOC that have an impact on secondary formation of organic compounds that make up SOA. NO

is thus involved in all secondary PM chemistry, not just in particulate nitrate formation.

Carlton, 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.

4. Fine Particulate Composition By Location

Table 2 shows regional 3-year mean concentrations (2009-2011) of PM

2.5

and its main components at sites in the Chemical Speciation Network (CSN).

In addition to the mean values for all sites in each region, the table includes the minimum and maximum observed PM

2.5

and species concentrations for sites within each region. These data illustrate broad observed spatial patterns across the U.S. in PM

2.5

concentrations and its composition. For example, PM

2.5

concentrations are highest on average in the Central and West regions. Sulfate mass comprises a larger fraction of PM

2.5

than nitrate mass in the northeastern U.S., whereas nitrate has a greater contribution than that of sulfate in the West. OM is the dominant component in all regions, with the highest concentrations of OM on average found in the West, Northwest and Southeast. On a percentage basis, the concentrations of EC and crustal material are relatively low throughout all regions of the U.S. compared to the other major PM

2.5

components.

The 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). PM

2.5

concentrations come from measurements of the Federal Reference/Equivalance Methods (FRM/FEM) rather than from the CSN PM

2.5

measurement.

The composition of PM

2.5

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 PM

2.5

components can be found in the docket for this proposal.

Reff and Rao, Memo to the docket, 2013.

Table 2—PM

2.5

Chemical Composition Data at 2009-2011 Nonattainment Sites

[Source: EPA Speciation Trends Network]

Region

Statistic

Concentration (μg/m

)

CrM

2.5

Central

Min (μg/m

)

1.46

0.3

2.73

0.31

0.01

8.92

Mean (μg/m

)

2.69

1.49

3.57

0.68

0.26

11.63

Max (μg/m

)

4.19

3.34

4.81

1.1

1.0

13.51

East North Central

Min (μg/m

)

0.83

0.38

1.97

0.19

0.01

6.03

Mean (μg/m

)

1.68

1.8

2.84

0.48

0.19

9.86

Max (μg/m

)

2.51

3.57

3.69

0.79

0.61

11.87

North East

Min (μg/m

)

0.58

0.12

1.74

0.14

4.42

Mean (μg/m

)

2.06

0.97

3.14

0.69

0.17

9.33

Max (μg/m

)

5.12

2.26

5.05

1.69

0.52

15.05

North West

Min (μg/m

)

0.24

0.05

2.91

0.42

0.01

6.06

Mean (μg/m

)

0.54

0.4

5.02

0.81

0.15

8.33

Max (μg/m

)

1.09

1.79

8.44

1.25

0.53

10.96

South

Min (μg/m

)

0.88

0.18

1.36

0.12

0.02

5.22

Mean (μg/m

)

2.06

0.8

3.32

0.57

0.5

10.05

Max (μg/m

)

3.08

1.67

5.1

1.48

2.38

14.27

South East

Min (μg/m

)

1.6

0.2

1.75

0.37

0.01

6.76

Mean (μg/m

)

2.39

0.53

4.12

0.63

0.26

10.77

Max (μg/m

)

4.33

1.51

5.71

1.2

0.85

13.38

South West

Min (μg/m

)

0.34

0.07

2.34

0.46

0.02

5.3

Mean (μg/m

)

0.63

0.49

3.01

0.7

0.5

7.93

Max (μg/m

)

1.13

2.65

4.39

1.04

1.96

9.73

West

Min (μg/m

)

0.33

0.08

1.79

0.52

0.01

6.84

Mean (μg/m

)

0.9

1.4

5.22

0.85

0.32

11.49

Max (μg/m

)

2.08

5.14

10.27

1.56

1.05

16.57

West North Central

Min (μg/m

)

0.29

0.06

1.22

0.09

3.23

Mean (μg/m

)

0.67

0.48

3.16

0.44

0.22

7.25

Max (μg/m

)

1.79

2.02

8.28

1.21

0.53

13.72

C. Historical Overview of PM

2.5

NAAQS Setting and Implementation

Sections 108 and 109 of the CAA govern the establishment, review and revision, as appropriate, of NAAQS for widespread pollutants emitted from numerous and diverse sources considered harmful to public health and the environment. The CAA requires two types of NAAQS: (i)

Primary

standards, which set limits to protect public health, including the health of at-risk populations; and (ii)

secondary

standards, which set limits to protect public welfare, including protection against visibility impairment, damage to animals, crops, vegetation and buildings.

The EPA first promulgated annual and 24-hour NAAQS for PM

2.5

in July 1997.

Prior to that time, the EPA had addressed ambient particulate matter through other means, first by regulating “total suspended particles” (TSP) and then later by regulating PM

. After protracted litigation, the 1997 NAAQS for PM

2.5

were upheld by the U.S. Court of Appeals for the District of Columbia Circuit in March 2002.

The EPA subsequently promulgated designations for the 1997 PM

2.5

NAAQS nationwide, and designated a number of areas as nonattainment for the 1997 PM

2.5

NAAQS, effective April 2005.

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 PM

2.5

Implementation Rule”).

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 PM

2.5

NSR Rule”).

The EPA premised both the 2007 PM

2.5

Implementation Rule and the 2008 PM

2.5

NSR Rule on the EPA's interpretation of the statute that nonattainment areas for the PM

2.5

NAAQS were subject solely to the general nonattainment plan requirements of subpart 1, part D of title I of the CAA (“subpart 1”).

62 FR 38652 (July 18, 1997).

For a complete summary of legal challenges and related court decisions on the PM NAAQS,

see generally

78 FR 3086 (January 15, 2013).

70 FR 944 (January 5, 2005).

72 FR 20583 (April 25, 2007).

73 FR 28231 (May 16, 2008).

Section 109(d)(1) of the CAA requires the EPA periodically to review the science upon which the standards are based and the standards themselves, and to revise the standards as may be appropriate. In October 2006, the EPA promulgated revisions to the suite of NAAQS for PM, and in particular the EPA revised the 24-hour PM

2.5

standards.

In accordance with section 107(d), the EPA subsequently designated a number of areas as nonattainment for the revised 2006 24-hour PM

2.5

standards, effective December 2009.

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 PM

2.5

NAAQS in designated nonattainment areas.

The EPA's guidance for the 2006 PM

2.5

NAAQS was based, in large part, on the requirements finalized in the 2007 PM

2.5

Implementation Rule, which the EPA based solely upon the statutory requirements of subpart 1.

71 FR 61144 (October 17, 2006).

74 FR 58688 (November 13, 2009).

Memorandum of March 2, 2012 (withdrawn June 6, 2013), from Stephen D. Page, Director, Office of Air Quality Planning and Standards, to EPA Regional Air Directors, Regions I-X, “Implementation Guidance for the 2006 24-Hour Fine Particle (PM

2.5

) National Ambient Air Quality Standards (NAAQS).” Available at:

http://epa.gov/ttn/naaqs/pm/pm25_guide.html

The EPA initiated a review of the PM

2.5

NAAQS in June 2007, proposing revisions to the primary and secondary PM

2.5

NAAQS on June 29, 2012.

The EPA issued its final rule on December 14, 2012, in which it lowered the primary annual PM

2.5

standard from 15.0 μg/m

to 12.0 μg/m

to provide increased protection against health effects associated with long- and short-term fine particle exposures.

The EPA also eliminated spatial averaging as part of the form of the annual standard to avoid potential disproportionate impacts on at-risk populations.

The

EPA retained the level (35 μg/m

) and form (98th percentile, averaged over 3 years) of the primary 24-hour PM

2.5

standard, as revised in 2006, to provide supplemental protection against health effects associated with short-term PM

2.5

exposures, especially in areas with high peak PM

2.5

concentrations.

This suite of primary PM

2.5

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 PM

2.5

-related effects that include premature mortality, increased hospital admissions and emergency department visits and development of chronic respiratory disease.

With regard to the secondary (welfare-based) standards, the EPA retained the existing annual PM

2.5

standard of 15.0 μg/m

and the existing 24-hour PM

2.5

standard of 35 μg/m

to protect against PM-related non-visibility welfare effects including ecological effects, effects on materials and climate impacts. In addition, the secondary 24-hour PM

2.5

standard provides protection for PM-related visibility impairment.

77 FR 38890 (June 29, 2012).

78 FR 3086 (January 15, 2013).

Spatial averaging of monitored ambient air quality data was a feature of the prior PM

2.5

NAAQS

monitoring regulations which had the potential for masking particularly high PM

2.5

concentrations at certain monitored locations within nonattainment areas.

71 FR 61144 (October 17, 2006).

General information regarding the health effects associated with PM

2.5

exposures is available at:

http://www.epa.gov/airquality/particlepollution/health.html

. Additional information, such as the EPA's technical documents supporting the latest review of the standards, is available at:

http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_index.html

On January 4, 2013, shortly after the EPA promulgated the 2012 revisions to the suite of PM NAAQS, the DC Circuit issued its decision in a challenge to the 2007 PM

2.5

Implementation Rule and the 2008 PM

2.5

NSR Rule. In

NRDC

EPA,

the court held that the EPA erred in implementing the 1997 PM

2.5

NAAQS pursuant only to the general implementation requirements of subpart 1, rather than also to the implementation requirements specific to particulate matter (PM

) in subpart 4, part D of title I of the CAA (“subpart 4”).

The court reasoned that the plain meaning of the CAA requires implementation of the 1997 PM

2.5

NAAQS under subpart 4 because PM

2.5

particles fall within the statutory definition of PM

and are thus subject to the same statutory requirements. In addition, although the court stated that its decision that the EPA must implement the PM

2.5

NAAQS pursuant to subpart 4 requirements meant that it did not have to reach decisions on other issues concerning the regulation of precursors to PM

2.5,

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 PM

2.5

Implementation Rule and the 2008 PM

2.5

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 PM

2.5

NAAQS. The court instructed the EPA “to repromulgate these rules pursuant to Subpart 4 consistent with this opinion.” Given the D.C. Circuit's opinion in

NRDC

EPA,

the EPA withdrew its 2012 guidance document for the 2006 24-hour PM

2.5

NAAQS in June 2013. Because the court had concluded that the EPA and states must implement the PM

2.5

NAAQS consistent with the statutory requirements of subpart 4, the EPA 2012 guidance for attainment plans for the 2006 PM

2.5

NAAQS premised solely upon subpart 1 requirements was no longer appropriate.

NRDC

EPA,

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

The EPA intends to use this current rulemaking to accomplish multiple objectives. First, the EPA is taking this action to clarify how air agencies should meet the statutory SIP requirements that apply to areas designated nonattainment for any PM

2.5

NAAQS under subparts 1 and 4. To this end, the EPA is proposing regulatory requirements that will be applicable to attainment plans for the 2012 PM

2.5

NAAQS and any future revisions of the PM

2.5

NAAQS, subject to revisions that may be necessary for implementation purposes in the future. Second, the EPA is taking this action to provide guidance, in addition to regulatory requirements, to assist air agencies in developing attainment plans for the 2012 PM

2.5

NAAQS and any future revisions of the PM

2.5

NAAQS. Finally, the EPA is taking this action in response to the DC Circuit's remand of the 2007 PM

2.5

Implementation Rule and the 2008 PM

2.5

NSR Rule. Through this rulemaking, the EPA intends to address requirements associated with states' ongoing implementation efforts for the 1997 and 2006 PM

2.5

NAAQS. In the interim, the EPA will rely on the statutory attainment planning requirements

contained in subparts 1 and 4 and on the EPA's General Preamble and Addendum for guidance on how to apply those requirements to current PM

2.5

NAAQS nonattainment areas.

General Preamble, 57 FR 13498 (April 16, 1992).

D. State Implementation Planning Process for PM

2.5

NAAQS

1. Overview

The CAA establishes important roles both for state and tribal governments and for the EPA in implementing the NAAQS. In accordance with the principle of cooperative federalism, both state and tribal governments and the EPA have respective authorities and responsibilities under the CAA. At the outset, the EPA has the authority and responsibility to promulgate the NAAQS. In turn, state, local and tribal air agencies have the authority and primary responsibility for developing and implementing attainment plans that contain emission control measures needed to achieve the air quality standards in each nonattainment area, consistent with the requirements of the CAA. The EPA often assists air agencies by promulgating regulations or providing guidance for meeting implementation requirements and technical tools, including information on control measures.

For example, the EPA intends this rulemaking to clarify the specific statutory requirements, and schedule for meeting those requirements, that state and tribal air pollution control agencies (“air agencies”) must address as they prepare SIP submissions for the PM

2.5

standards in future.

It is important to note that the EPA does not have a mandatory duty to promulgate an implementation rule for the PM

2.5

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 PM

2.5

NAAQS.

When 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.

The EPA also promulgates nationally applicable control requirements and emission limits for many sources such as new motor vehicles, certain categories of new and modified major stationary sources and existing stationary sources of toxic air pollutants. These federal actions assist state and tribal air agencies by achieving emission reductions from certain categories of sources nationwide, which can help with local attainment needs in a given nonattainment area. In addition, the EPA has authority to address

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 PM

2.5

NAAQS.

In addition, the EPA has the authority and responsibility to review and take action to approve or disapprove submitted attainment plans based upon whether they meet applicable statutory and regulatory requirements, to provide funding and technical assistance to states and to initiate the process for imposition of sanctions and/or issue federal implementation plans (FIPs) when states fail to fulfill their CAA obligations. More information on area designations, the role of ambient air monitoring, the SIP development process and the role of federal measures in bringing an area into attainment is presented below.

See

70 FR 25162 (May 12, 2005) and 76 FR 48208 (August 8, 2011).

2. Initial Area Designations and Classifications

The NAAQS implementation planning process begins with initial area designations, through which states and the EPA identify areas of the country that either meet or do not meet the new or revised NAAQS, along with identifying the nearby areas contributing to violations of the NAAQS. Section 107(d)(1) of the CAA requires that: “By such date as the Administrator may reasonably require, but not later than 1 year after promulgation of a new or revised national ambient air quality standard for any pollutant under section 109, the Governor of each state shall . . . submit to the Administrator a list of all areas (or portions thereof) in the State” that designates those areas as nonattainment, attainment, or unclassifiable.

Thus, states are required to make their initial designation recommendations to the EPA by no later than 1 year after the promulgation of new or revised NAAQS. Section 107(d)(1)(B)(i) further provides: “Upon promulgation or revision of a NAAQS, the Administrator shall promulgate the designations of all areas (or portions thereof) . . . as expeditiously as practicable, but in no case later than 2 years from the date of promulgation. Such period may be extended for up to 1 year in the event the Administrator has insufficient information to promulgate the designations.” Thus, the EPA is required to promulgate the actual designations for all areas across the U.S. by no later than 2 years after the promulgation of any new or revised NAAQS, unless the EPA elects to take up to one additional year in situations where there is insufficient information. Under section 107(d)(1)(B)(ii), the EPA is authorized to modify the designations recommendations from the states, with respect to the designation of an area and the boundaries of an area, if the EPA deems that necessary. By no later than 120 days prior to promulgating final designations, the EPA is required to notify states of any intended modifications to their recommendations. States then have an opportunity to demonstrate to the EPA why the EPA's intended modification is inappropriate. Regardless of whether a state provides an initial designation recommendation for any area, the EPA must timely promulgate the designations it deems appropriate.

While the CAA provides for “designating” with respect to the Governor's list, in the full context of the CAA section 107 it is clear that the Governor actually makes a recommendation, to which the EPA must respond using a specified process if the EPA does not accept the recommendation.

While section 107 of the CAA specifically addresses states, the EPA is following the same process for tribes that choose to make a recommendation to the extent practicable, pursuant to section 301(d) of the CAA regarding tribal authority, and the TAR. 63 FR 7254 (February 12, 1998). To provide for clarity and consistency, the EPA issued a 2011 guidance memorandum for working with tribes during the designations process. Memorandum of December 20, 2011 from Stephen D. Page, Director, Office of Air Quality Planning and Standards, to EPA Regional Administrators, Regions I-X re: “Guidance to Regions for Working with Tribes during the National Ambient Air Quality Standards (NAAQS) Designations Process.” Available at:

http://www.epa.gov/ttn/oarpg/t1/memoranda/20120117naaqsguidance.pdf

Under subpart 4, the CAA provides for classification of PM

2.5

nonattainment areas as either “Moderate” or “Serious.” As provided in section 188(a) and reiterated in the General Preamble, all PM

nonattainment areas and by extension all PM

2.5

nonattainment areas are initially classified as Moderate by operation of law at the time of designation. Initial classifications are not subject to public notice-and-comment pursuant to section 107(d)(2)(B), although the EPA may elect to take comment on designations and classifications and its recent practice has been to do so.

All areas designated as nonattainment for the 2012 PM

2.5

NAAQS and any future revised PM

2.5

NAAQS will be initially classified as Moderate nonattainment areas upon designation, regardless of the severity of the PM

2.5

problem in the area. This statutory approach to classifications for nonattainment areas under subpart 4 for the PM

2.5

NAAQS is notably different from the approach for ozone NAAQS nonattainment areas under subpart 2 (of part D, title I of the CAA), wherein the statute includes several area classifications, and initial classifications are based on monitored ozone levels. Thus, unlike for ozone nonattainment areas, all PM

2.5

nonattainment areas initially receive the same classification—Moderate—and the EPA only reclassifies such areas to Serious upon a showing by the state or a determination by the agency that the area cannot practicably attain by the statutory attainment date, or upon a finding that the area in fact failed to attain the NAAQS by the applicable Moderate area attainment date. The statute requires that Moderate nonattainment areas attain the NAAQS as expeditiously as practicable, but not later than the end of the sixth calendar year following designation. States have an incentive to avoid having a Moderate area reclassified to Serious because, as discussed later in this preamble, the specific subpart 4 requirements for areas classified as Serious include, among other things, a more stringent level of control for sources of direct PM

2.5

and PM

2.5

precursors than for Moderate areas.

As of the date of this proposal, the first round of initial designations for most areas for the 2012 primary annual PM

2.5

NAAQS has been completed, and those designations will become effective on April 15, 2015. All areas designated as nonattainment for the 2012 PM

2.5

NAAQS were classified as Moderate nonattainment areas.

See

the

Federal Register

notice for the first round of designations for the 2012 PM

2.5

NAAQS at 80 FR 2206 (January 15, 2015).

3. Ambient Air Monitoring for PM

2.5

Ambient air quality monitoring for PM

2.5

plays an integral role in implementation of a NAAQS, including identifying areas violating the NAAQS, control strategy development and tracking progress toward attainment. States are required to monitor PM

2.5

mass concentrations using approved methods to determine compliance with the NAAQS.

The locations of monitors are identified in states' Annual Monitoring Network Plans, which are required to be submitted to the EPA by July 1 of each year.

The EPA in turn reviews these annual plans for compliance with applicable regulations and consistency with relevant guidance. Currently there are more than 900

monitoring locations across the country eligible for comparison to the PM

2.5

NAAQS. States are required to maintain monitors in designated nonattainment areas in order to track progress toward attainment and ultimately determine whether the area has attained the PM

2.5

standards. In addition to the approved monitors for comparison to the NAAQS, the EPA and states also maintain a chemical speciation network (CSN) of about 200 stations around the country to support analyses of chemical composition of PM

2.5

(

e.g.

sulfate, nitrate and organic carbon). The data provided by the CSN help states identify contributing source categories and develop control strategies to reach attainment.

The ambient air monitoring requirements that apply to the PM

2.5

NAAQS are detailed in 40 CFR part 58. These monitoring requirements are applicable to state and local air agencies.

See

40 CFR 58.10.

In conjunction with the promulgation of the 2012 PM

2.5

NAAQS, the EPA finalized a schedule for deployment of PM

2.5

monitors at near-road monitoring locations. Under revised monitoring requirements, states are required to locate a minimum of one PM

2.5

monitor in each core-based statistical area (CBSA) with a population of 1 million or more, to be phased-in between January 2015 and January 2017.

Near-road monitors for CBSAs larger than 2.5 million in population are to be operational by 1/1/2015; and monitors for CBSAs with population larger than 1 million but less than 2.5 million are to be operational by 1/1/2017. CBSA is defined by OMB as a statistical geographic entity consisting of the county or counties associated with at least one urbanized area/urban cluster of at least 10,000 population, plus adjacent counties having a high degree of social and economic integration.

For initial area designations for any PM

2.5

NAAQS, the EPA relies on monitoring data to identify areas to be designated nonattainment due to violations of the standard(s). The EPA uses other information to identify areas contributing to the monitored violations in those areas.

The agency's protocol for designating areas and determining whether an area has attained the PM

2.5

NAAQS is based on monitored air quality data collected over a period of 3 calendar years. Data from the new PM

2.5

near-road monitors were not available for the EPA to consider within the timeframe for initial area designations provided by the CAA for the 2012 PM

2.5

NAAQS; the agency will not be able to consider data from a near-road monitor in the implementation process until 3 years of data are available. The initial set of near-roadway PM

2.5

monitors are to be fully deployed by January 2015, with the first 3 years of air quality data (2015-2017) available beginning in 2018; the second set of near-roadway monitors are to have the first 3 years of data available beginning in 2020.

See Catawba County

EPA,

571 F.3d 20 (D.C. Cir. 2009).

4. SIP Development Process

In general terms, a SIP is the compilation of EPA-approved state statutes, regulations and programs that a state develops and relies upon to carry out its NAAQS implementation responsibilities under the CAA, including the attainment, maintenance and enforcement of NAAQS. States use the SIP development process to identify the emissions sources that contribute to the nonattainment problem in a particular area, and to select the required emissions reduction measures most appropriate for that area, considering factors such as technological and economic feasibility. As part of developing an attainment plan, the states must meet specific requirements of the CAA to attain the NAAQS,

e.g.,

a state with a Moderate PM

2.5

nonattainment area must impose RACM (including RACT) and additional reasonable measures on sources located in the nonattainment area. Under the CAA, states must develop attainment plans that ensure that areas reach attainment as expeditiously as practicable, but no later than the applicable statutory attainment date. In these attainment plans, states may take into consideration emission reductions resulting from federally applicable national programs (such as mobile source regulations, the national acid rain program, or maximum achievable control technology (MACT) standards for air toxics), as well as from state or local programs not directly mandated, but authorized, under the CAA, if such measures are incorporated into the SIP and thus are made federally enforceable.

5. Geographic Extent of PM

2.5

Problem

The EPA recognizes the significant variability in the nature and sources of PM

2.5

in different nonattainment areas and believes it is important to keep this variability in mind when providing guidance to states as they develop control strategies to bring their PM

2.5

nonattainment areas into attainment with the relevant NAAQS. The variability of PM

2.5

concentrations across the country has a substantial regional component because the formation and transport of secondarily formed particles, such as sulfates and nitrates, can extend over hundreds of miles. As a result, monitored violations of the PM

2.5

NAAQS can often reflect the impact of the combination of “local” sources of emissions located within the designated nonattainment area and “regional” sources of emissions that may be located much farther away.

In addition, data suggest that ambient PM

2.5

concentrations tend to rise and fall in a consistent manner across very large geographic areas. The transport phenomenon associated with PM

2.5

and its precursors has been well documented for many years. For example, one significant source of information on long-range transport is the National Acid Precipitation Assessment Program (NAPAP) research from the 1980s and its associated reports published in 1991.

Additional studies and air quality modeling analyses since that time have added to the body of information documenting the regional nature of PM

2.5

National Acid Precipitation Assessment Program. Acid Deposition: State of the Science and Technology. Washington, DC 1991.

See also Sierra Club

EPA,

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

See

Section IV of this preamble for a thorough discussion of past reasonably available control measures (RACM) and reasonably available control technology (RACT) policy and guidance. Section IV discusses the EPA's proposed policy that under subpart 4, for Moderate areas that demonstrate that attainment by the statutory attainment date is impracticable, RACM and RACT would constitute all those technologically and economically feasible measures available for sources in the area that can be implemented within 4 years of designation, but they would not constitute the complete set of measures required to demonstrate attainment as expeditiously as practicable.

B. Proposed Precursor Policy Options

The EPA is proposing this rule to address the attainment plan and certain NNSR requirements for PM

2.5

under subpart 4. In light of the court's decision in

NRDC

EPA,

the EPA considers it necessary to address in this implementation rule how states must address regulation of PM

2.5

precursor gases in attainment plans and NNSR programs for the PM

2.5

NAAQS. As noted earlier, the court's decision made clear that appropriate regulation of all precursors is initially presumptively required under the CAA, and the regulation of precursors is a critical issue for attainment of the PM

2.5

NAAQS because secondarily formed particles are a substantial component of the PM

2.5

nonattainment problem in most areas of the U.S.

For the purposes of this implementation rule, the EPA considers that for all nonattainment areas, the PM

2.5

precursors for regulatory purposes are SO

, NO

, VOC and ammonia. This rule does not propose any national presumption that would simply allow a state to exclude sources of emissions of a particular precursor from further analysis for control requirements. However, the EPA's existing interpretation of subpart 4 requirements—with respect to precursors in attainment plans for PM

, as set out in the General Preamble—contemplates that the state may develop an attainment plan that regulates only those precursors that are necessary to control for purposes of timely attainment in the area,

i.e.,

states may determine that only certain precursors need to be regulated for attainment purposes.

Courts have upheld this approach to the requirements of subpart 4 for PM

See

the

Federal Register

published on April 16, 1992 (57 FR 13498, 13540 and 13541).

See, e.g., Assoc. of Irritated Residents

EPA, et al.,

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

The EPA believes that application of a similar approach to PM

2.5

precursors under subpart 4 is appropriate and reasonable. Thus, this proposal describes three proposed precursor options that provide for the possibility that, with appropriate justification provided by the state, further evaluation and implementation of control strategies for one or more PM

2.5

precursors in a given nonattainment area may not be needed or required. Under each option, a state may provide a technical demonstration and reasoned justification for the exclusion of a PM

2.5

precursor or precursors from control requirements for a particular nonattainment area.

As explained above, the EPA interprets the CAA to require states to inventory and regulate all sources of PM

2.5

precursors from all sources in the area, including area sources, mobile sources and stationary sources. This interpretation is based on CAA provisions requiring adoption of all RACM needed to attain the standard as expeditiously as practicable; section 302(g), which defines an air pollutant as including all precursors contributing to the formation of that pollutant; and, the EPA's identification of the four main PM

2.5

precursors. For major stationary sources, section 189(e) requires that the control requirements applicable for major stationary sources of PM

2.5

must also apply to major stationary sources of PM

2.5

precursors, unless the state provides a showing that emissions of a particular precursor from major stationary sources do not contribute significantly to levels which exceed the standard in the area. Thus, the statute generally requires control of all PM

2.5

precursors, but it provides an express exception applicable to major stationary sources. Because the statutory provisions of subparts 1 and 4 are not explicit with respect to how states should address PM

2.5

precursors from non-major sources, the EPA is proposing regulations to assure proper evaluation and regulation of PM

2.5

precursor emissions in PM

2.5

nonattainment areas. Moreover, even with respect to regulation of precursor emissions from major stationary sources, section 189(e) contains ambiguities that require interpretation. For example, section

189(e) does not specify the method by which the EPA should determine whether precursor emissions from major stationary sources contribute significantly to levels which exceed the standard in a given nonattainment area. Given that the provisions of subpart 4 are ambiguous with respect to these issues, the EPA believes that it is necessary to interpret those requirements in this rulemaking.

The EPA is thus seeking comment on three potential approaches to address PM

2.5

precursors pursuant to the specific statutory requirements of subpart 4 and the overarching requirements of the CAA. In these proposed options, particular emphasis is given to the situations and circumstances under which the state would or would not be required to evaluate emission controls for a particular precursor and to adopt those controls that are necessary to demonstrate attainment of the NAAQS as expeditiously as practicable. Note that these options describe analyses that the state may choose to pursue to demonstrate that control requirements should not apply to a particular precursor. However, the state also may choose to require controls for all PM

2.5

precursors in attainment plans and in its NNSR permitting program, and choose not to conduct any analyses to eliminate one or more precursors from consideration for controls.

The descriptions of the three precursor policy options being proposed in this section discuss how PM

2.5

precursors would need to be addressed by the state with regard to three specific implementation situations: (1) A Moderate area for which attainment of the relevant NAAQS by the end of the sixth calendar year after designation can be demonstrated; (2) a Moderate area for which it can be demonstrated that the relevant NAAQS cannot practicably be attained by the end of the sixth calendar year after designation; and (3) an area that is reclassified to Serious and is obligated to develop a Serious area attainment plan to attain the relevant NAAQS. Additionally, the EPA describes how each of the proposed precursor policy options would apply to the implementation of NNSR in a Moderate or Serious PM

2.5

nonattainment area. Later in this section, the EPA discusses specific issues related to the technical “precursor demonstrations” that states could choose to develop. The technical demonstration section includes a discussion of several types of analyses that a state could provide to the EPA to show that control measures for a specific PM

2.5

precursor would not be needed for attainment or to expedite attainment, or to show that major stationary sources of a given precursor collectively do not significantly contribute to PM

2.5

levels that exceed the relevant NAAQS in a given area.

Before discussing the three precursor options, it is important to introduce a new term that is used throughout this section and other sections of the notice. Under subpart 4, RACM (including RACT) are those measures that can and must be implemented within 4 years of the area's designation as nonattainment (pursuant to section 189(a)(1)(C)). The EPA recognizes, however, that other, similarly reasonable emissions reduction measures could be implemented after this 4 year period, and as late as the end of the sixth calendar year following designation, to help an area attain as expeditiously as practicable. Therefore, in this proposal the EPA is proposing to define the term “additional reasonable measures” to describe those technologically and economically feasible control measures that could not be implemented within the 4 year period after designation, but could be implemented starting any time after that 4 year period through the end of the sixth calendar year after designation (note that this period could extend almost 3 additional years, depending on when during the year area designations are finalized).

See

proposed 40 CFR 51.1000. The EPA proposes to require implementation of these “other” control measures to the extent necessary to demonstrate attainment by the applicable attainment date pursuant to section 172(c)(6) of the CAA. That provision provides that nonattainment “plan provisions shall include enforceable emissions limitations, and such other control measures . . . as may be necessary or appropriate to provide for attainment of such standard in such area by the applicable attainment date . . .” Together, RACM and RACT and “additional reasonable measures” make up the set of control strategies referred to in this proposed rule as “reasonable control measures.”

(Section IV.D of this preamble provides a detailed discussion of how a state must determine reasonable control measures for a Moderate PM

2.5

nonattainment area.) The EPA requests comment on each of the three proposed options discussed below which describe how a state may demonstrate that additional emissions reductions of a particular precursor would not be needed or appropriate for an area's attainment plan, and how it could demonstrate that emissions control requirements for a particular precursor would not be needed in NNSR permits for new or modified sources in the area. In particular, the EPA requests comment on whether only one of these approaches should be included in the final rule, or whether it would be appropriate to include multiple approaches (

e.g.,

both Options 1 and 2), or only specific elements from the different options. The three proposed options are summarized as follows:

In Section VI.D, the EPA describes a parallel approach for distinguishing control measures required under sections 172(c)(6) and 189(b)(1)(B) for Serious nonattainment areas.

• Option 1: Two independent analyses: (a) An attainment planning analysis demonstrating that control measures for a particular precursor are not needed for expeditious attainment, meaning that the precursor can be excluded from measures needed to attain as expeditiously as practicable for all types of sources; and (b) a section 189(e) technical demonstration showing that major stationary sources of a particular precursor do not contribute significantly to levels that exceed the PM

2.5

standard, meaning that the precursor can be excluded from control requirements for major sources including NNSR permitting;

• Option 2: Single analysis demonstrating that all emissions of a particular precursor from within the area do not significantly contribute to PM

2.5

levels that exceed the standard, meaning that control requirements for emissions of the precursor from major stationary and area sources, as well as mobile sources, would not be required for expeditious attainment, control requirements for major sources, or for NNSR permitting;

• Option 3: An attainment planning analysis demonstrating that control measures for all types of sources of a particular precursor are not needed for expeditious attainment also would be deemed to meet the section 189(e) technical demonstration requirement, meaning that the state would not need to regulate emissions of the particular precursor from major stationary sources under the NNSR permitting program or other control requirements for major stationary sources.

Each of these proposed options is presented in greater detail below.

Option 1:

Two independent analyses: (a) An attainment planning analysis demonstrating that control measures for a particular precursor are not needed for expeditious attainment, meaning that the precursor can be excluded from measures needed to attain as expeditiously as practicable for

all types of sources; and (b) a section 189(e) technical demonstration showing that major stationary sources of a particular precursor do not contribute significantly to levels that exceed the PM

2.5

standard, meaning that the precursor can be excluded from control requirements for major sources and from NNSR permitting.

As with the other options discussed below, the critical first step in any precursor analysis is the development of a comprehensive inventory of all precursor emissions in the nonattainment area. A state will be unable to reasonably determine whether emissions of a given PM

2.5

precursor contribute significantly to the nonattainment problem in an area if the state has failed to account adequately for all such emissions in the area in its emissions inventory.

In general terms, Option 1 would require separate analyses for purposes of attainment planning and for NNSR. Section 189(a) of the CAA describes the requirements for Moderate nonattainment areas. Within 18 months of designation as nonattainment, the state is required to submit a Moderate area plan that either demonstrates attainment as expeditiously as practicable but by no later than the end of the sixth year following designation, or demonstrates that attainment by such date would be impracticable.

Under Option 1, the state would determine the precursors for which new control measures need to be adopted for a given nonattainment area through its determination of reasonable control measures needed for attainment. The state's analysis of reasonable measures for a given PM

2.5

NAAQS nonattainment area should begin by identifying potential control measures (and factors related to technological feasibility, economic feasibility, and time needed for implementation) for all precursors from all types of sources in the area (

i.e.,

stationary, area, mobile) included in the emissions inventory. The analysis of reasonable measures and selection by the state of those emissions reduction measures that would provide for attainment as expeditiously as practicable (but no later than the end of the sixth calendar year after designation) would determine which precursors must be regulated in the nonattainment area for purposes of attainment. Except for the requirement to determine whether implementation of all remaining reasonable measures could collectively advance attainment by a year, there would be no additional demonstration needed by the state to justify that attainment planning control requirements should not apply to a particular precursor. Therefore, the analysis of reasonable measures may result in the state controlling only a subset of the four main PM

2.5

precursors as part of the attainment demonstration.

Moderate area for which the state can demonstrate attainment by the statutory attainment date.

For certain nonattainment areas, the state may be able to demonstrate that attainment of the standard “as expeditiously as practicable” is possible by the end of the sixth year after designation (the statutory Moderate area attainment date) or sooner, and could be achieved by adopting regulations to reduce emissions of only a subset of the four PM

2.5

precursors. Under this scenario, the state would be expected to provide analytical information showing that, even though new economically and technically feasible control measures may be available for one or more precursors, the reductions in emissions of the precursor(s) that could be achieved are not necessary for expeditious attainment and would not advance the attainment date by at least a year. Under Option 1, if the state determined that new emissions reductions of a particular precursor are not necessary for attainment and would not accelerate the attainment date by at least 1 year, then for the purposes of this particular PM

2.5

Moderate area attainment plan, the state would not need to adopt additional control measures for that PM

2.5

precursor. Given that additional regulation of that PM

2.5

precursor would not be necessary for attaining the standard as expeditiously as practicable, the EPA would be able to approve the attainment plan for the area as meeting the requirements of subpart 4.

Moderate area for which the state can demonstrate that attainment by the statutory attainment date is impracticable.

Section 189(a)(1)(B) provides that for certain nonattainment areas, the state may demonstrate that, even with implementation of all reasonable control measures available for reducing emissions of all direct PM and PM

2.5

precursors, it would be impracticable to attain the standard by the end of the sixth calendar year after designation. In other words, the analysis would need to demonstrate that implementing all economically and technically feasible control measures that are available in the area, and the expected air quality change from such measures, would not be able to provide for attainment by the end of the sixth year after designation.

For states that can make the showing that they cannot attain the NAAQS by the end of the sixth calendar year after designation, the question arises as to whether the state should be required to adopt all reasonable measures (

i.e.

measures that represent RACM and RACT because they are technologically and economically feasible and can be implemented in 4 years and all additional reasonable measures that can be implemented within 6 years) through regulation as part of the Moderate area plan, even if a subset of these measures collectively would have a minimal effect on reducing ambient PM

2.5

concentrations. The EPA proposes two sub-options for areas that cannot demonstrate attainment during the Moderate area timeframe even with the implementation of all reasonable measures in the area. Under the first sub-option, the state would be required to adopt all available control measures for precursors through regulation as part of the Moderate area plan. The rationale supporting this approach would be that adopting all technologically and economically feasible measures would bring the area as close to attainment as possible during the timeframe prescribed for Moderate areas. Under this approach, if a measure can be implemented by the end of the sixth calendar year after the nonattainment designation and it meets the criteria for being considered “reasonable,” then the state must adopt and implement the measure.

Under the second sub-option, the state would be able to elect not to impose those technologically and economically feasible measures that collectively have minimal effect on ambient PM

2.5

levels in the area, based on the premise that such measures would be unreasonable to implement. To support this conclusion, the state would need to submit a technical demonstration showing that implementing available emissions controls for a particular precursor and/or a specific set of sources would provide only minimal changes in PM

2.5

concentrations in the area, and therefore such control measures should not be required during the timeframe prescribed for Moderate areas. The EPA requests comment on these two sub-options, including any technical information that would help support the commenter's position. Regarding the second sub-option, the EPA requests comment on what degree of air quality change should be considered minimal for purposes of this analysis.

Note that under either sub-option, the state would be able to show that control of precursor emissions from major stationary sources would not be required if it could be demonstrated that such emissions do not contribute significantly to PM

2.5

levels that exceed the standard, consistent with section 189(e).

Area reclassified to Serious.

A Moderate area can be reclassified to a Serious area under two scenarios. Under the first scenario, if a Moderate area fails to attain the standard by the applicable attainment date, it would then be reclassified by the EPA as a Serious area and the state would be required to develop and submit a Serious area attainment plan within 18 months of reclassification. Under the second scenario, the EPA could reclassify an area to Serious prior to the Moderate area attainment date if the EPA determines that it would be impracticable for the area to attain by the Moderate area attainment date. (Section V of this preamble provides additional detail on reclassifying a Moderate area to Serious under subpart 4.)

After an area has been reclassified to Serious, subpart 4 requires a state's Serious area attainment plan to include the imposition of more stringent control measures (best available control measures (BACM) and best available control technology (BACT)) intended to bring the area into attainment as expeditiously as practicable but no later than the end of the tenth calendar year after designation. Given that the CAA requires a more stringent new attainment plan for Serious areas, under Option 1 the state would be required to identify the best available measures for all sources of direct PM

2.5

emissions and emissions of PM

2.5

precursors and adopt those measures to attain the standard as expeditiously as practicable.

The EPA's two proposed options for determining BACM and BACT are discussed in detail in Section VI.D of this preamble.

The BACM and BACT determination requires a more rigorous analysis than the RACM and RACT analysis, and such measures collectively should lead to a greater degree of emission reduction in the area than the analysis of reasonable control measures for the Moderate area plan. For this reason, under Option 1, if the state's previous Moderate area attainment plan had indicated that new emissions reduction measures from sources of one or more precursors were not needed to attain by the end of the sixth calendar year after designation, then for the Serious area plan the state would need to reevaluate the best control measures addressing all PM

2.5

precursors (

i.e.

, VOC, and ammonia) and require implementation of those “best” available control measures for all precursors in order to bring the area into attainment as expeditiously as practicable, but no later than the end of the tenth year after designation. Under Option 1, any precursor demonstration that excluded one or more precursors from regulation in the Moderate area plan would not by itself also be sufficient to exclude the precursors from regulation in the Serious area plan. Further analysis would be needed to determine if control measures for those precursors qualify as “best” control measures. The EPA has interpreted the starting point for considering “best” control measures as including those control measures to reduce emissions of direct PM

2.5

or PM

2.5

precursors that have been adopted by any state, particularly those states with the most severe PM

2.5

air quality problems. (Note that in Section VI.D of this preamble, more details are provided on BACM and BACT determination criteria. The EPA is taking comment on two options for BACM and BACT determinations—one that expresses it as a requirement independent of the attainment demonstration, and one that expresses it as only those “best” measures that are needed for expeditious attainment no later than the end of the tenth calendar year after designation. The BACM and BACT determination approach adopted in the final rule accordingly will determine whether all best available emission controls for a particular precursor must be adopted or not in a Serious area).

NNSR.

Under Option 1, the initial expectation is that the state will need to address all four PM

2.5

precursors under the NNSR program pursuant to the CAA and as reinforced by the January 2013

NRDC

EPA

court decision. Pursuant to section 189(e), however, the state may provide a demonstration showing that emissions of a particular precursor from existing major stationary sources located in the nonattainment area do not contribute significantly to PM

2.5

levels that exceed the standard in the area. Under Option 1, this analysis under section 189(e) for major sources would be completed independently from the analysis of reasonable control measures conducted for attainment planning purposes. Such an analysis would involve assessing the potential addition of precursor emissions in the area due to potential new major stationary sources, and would likely involve air quality modeling and other technical analyses by the state, developed in consultation with the EPA (

see

Section III.C. of this preamble for further discussion on such technical demonstrations). Note that under this provision of the CAA, it might be possible that a precursor would be considered important for attainment planning purposes, but would not be regulated as a PM

2.5

precursor in NNSR permitting actions which, by definition, only apply to major sources of the nonattainment pollutant. For example, it might be possible that in a particular area the principal source of emissions of a certain precursor could be from mobile and area sources but not from major stationary sources of that precursor. The EPA requests comment on all aspects of proposed Option 1 as discussed above.

Option 2:

Single analysis demonstrating that all emissions of a particular precursor from within the area do not significantly contribute to PM

2.5

levels that exceed the standard, meaning that control requirements for emissions of the precursor from stationary major and area sources, as well as mobile sources, would not be required for expeditious attainment, control requirements for major sources, or for NNSR permitting.

Option 2 would provide the state the opportunity to provide the EPA with a scientifically credible technical analysis that would demonstrate that one or more precursors do not contribute significantly to the PM

2.5

levels that exceed the standard, therefore controls on those emissions would not be effective in reducing PM

2.5

levels in the area. As noted earlier in this section of the preamble, section 302(g) of the CAA includes “precursors” in the definition of “air pollutant,” but provides the EPA with some discretion in defining how these terms should be interpreted. In subpart 4, the CAA does not explicitly address control of precursors, except with regard to major stationary sources in section 189(e). The EPA interprets subpart 4 to require states to address PM

2.5

precursors from all source categories in the evaluation of controls needed for attainment in a given area,

e.g.,

in the evaluation of RACM and RACT level controls. By analogy to section 189(e), the EPA also believes that there may be circumstances in which states may validly demonstrate that control of one or more PM

2.5

precursors is not needed to attain the relevant NAAQS expeditiously.

Section 189(e) provides that precursor control requirements apply to major stationary sources of precursors of PM

2.5

if major sources of PM are regulated under the attainment plan, unless it can be shown that such precursor emissions do not contribute significantly to exceedances of the relevant NAAQS in the area. Under Option 2, the EPA relies on the discretion provided in section 302(g) and the section 189(e) concept of precursor emissions in an area having a significant or insignificant effect on

2.5

concentrations that exceed the standard to propose two precursor technical demonstration suboptions. Option 2A would allow the state to provide a technical demonstration showing that all emissions (

i.e.,

from area, mobile and stationary sources in the area) of a particular precursor collectively do not provide a significant contribution to PM

2.5

levels that exceed the standard in the area. The kinds of analytical approaches that could be appropriate for this type of “contribution demonstration” are described later in this section.

For Option 2B, the EPA proposes to allow states to provide a technical demonstration showing that PM

2.5

concentrations in the area are not sensitive to potential reductions or increases in emissions of a particular precursor in the nonattainment area (

e.g.

because the particular precursor is not the limiting factor in secondary PM

2.5

formation). More information is provided later in this section about possible analytical approaches to assess precursor “sensitivities” in an area (the optional technical demonstration described for Options 2A and 2B hereafter will be referred to as a “precursor demonstration”). The EPA requests comment on which of the two options (Option 2A or Option 2B) would be more preferable, and why. The EPA encourages commenters to provide examples of specific situations and areas in support of their recommendations.

These proposed options are consistent with the EPA's past practice for determining which technologically and economically feasible controls are necessary for expeditious attainment of the NAAQS. Specifically, the EPA has interpreted the RACM requirement in the CAA as requiring imposition of all reasonable controls as needed for expeditious attainment or to advance the attainment date by at least 1 year. The statute does not require imposition of additional controls if collectively such measures would not advance the attainment date. The EPA maintains it is reasonable to treat regulation of PM

2.5

precursors in a manner similar to the agency's treatment of direct pollutants and therefore concludes that states should not be required to implement control measures for a particular precursor or precursors if such measures will have little or no impact on PM

2.5

concentrations in the area or if the state demonstrates that all emissions of a given precursor or precursors do not contribute significantly to the PM

2.5

NAAQS exceedances in the area.

Moderate area for which the state can demonstrate attainment by the statutory attainment date or for which the state can demonstrate that attainment by the statutory attainment date is impracticable.

An approved precursor demonstration under Option 2A would show that emissions of the particular precursor from all types of sources do not contribute significantly to PM

2.5

levels that exceed the standard. As proposed, this type of demonstration therefore by definition would also satisfy the section 189(e) provision (which allows the state to demonstrate that emissions from just major stationary sources are not significant and therefore should not be subject to control requirements, such as NNSR, that apply to major stationary sources of direct PM

2.5

). Thus, the state could possibly develop one precursor demonstration analysis that would serve the purposes of both attainment planning and the section 189(e) insignificant major source contribution demonstration.

The sensitivity analyses required under Option 2B would need to assess a series of precursor emissions reductions and increases to determine the sensitivity to air quality in the area. For example, the analysis should evaluate the effect on PM

2.5

concentrations of various precursor emissions reduction scenarios appropriate to determine the sensitivity of precursors for the area (as would be relevant for an attainment plan); the analysis should also evaluate the effect on PM

2.5

concentrations of various precursor emissions increase scenarios appropriate to determine the sensitivity of precursors for the area, simulating the potential effect of the addition of potential new major stationary sources (or major modifications) to the nonattainment area under the NNSR program.

The EPA would evaluate the relevant analyses and other supporting information provided by the state. By submitting a “precursor demonstration” of this type, the state would not need to compile additional information on precursor control measures, or to proceed with actions to adopt and implement local or state regulations for the precursor. Precursor demonstrations as described in Options 2A or 2B could be conducted for Moderate areas for which the state can show that it can attain the standard by the end of the sixth calendar year after designation and for Moderate areas where the state's plan demonstrates that attainment by such date would be impracticable.

The EPA believes that general legal authorities under the CAA support the proposal of the overall precursor demonstration concept described above, and that requesting comment on these proposed options is appropriate from both a technical and a legal standpoint. This case specific approach is technically appropriate because the mix of PM

2.5

precursor emissions and other relevant technical factors varies from area to area. For example, in some areas, one precursor may be abundant while the main precursor with which it reacts may be less abundant. In such cases, reducing emissions of the less abundant precursor (the “limiting” precursor) is generally more effective for reducing PM

2.5

concentrations. In another type of area, the PM

2.5

concentrations that exceed the standard may be commonly dominated by primary PM

2.5

emissions rather than by secondarily formed PM

2.5

. The emissions of the particular precursor from sources in the nonattainment area could be found to have an insignificant contribution to PM

2.5

levels that exceed the standard, and the potential air quality improvement from reducing emissions of the precursor in the area may be limited.

The EPA believes that proposing Options 2A and 2B is appropriate from a legal standpoint based on authority provided the Administrator in sections 302(g) and 301(a)(1) of the CAA. Section 302(g) includes in the definition of “air pollutant” all the precursors to that pollutant, and it allows the EPA Administrator to regulate precursors for “the particular purpose for which the term `air pollutant' is used.” Under section 301(a)(1), “[t]he Administrator is authorized to prescribe such regulations as are necessary to carry out his functions under this Act.” Thus, with Option 2, the EPA proposes a framework by which the regulation of PM

2.5

precursors for a specific nonattainment area can be modified if the state provides the EPA with a credible technical demonstration for exempting a particular precursor which meets certain criteria and can be approved by the EPA. In addition, as noted earlier the set of analyses described under Option 2A could also satisfy the section 189(e) provision allowing the state to demonstrate that major stationary source emissions of a particular precursor do not significantly contribute to levels that exceed the standard. While this approach is not explicitly described in the statute, the EPA believes that the proposed Option 2 approach to precursor regulation is reasonable and allowed under the statutory authority provided in sections 302(g) and 301(a)(1) noted above.

The EPA anticipates that development of an approvable PM

2.5

precursor demonstration by the state at the

beginning of the attainment plan development process will require a substantial level of effort and consultation with the EPA. Such a demonstration by the state would likely involve a combination of technically rigorous and complex analyses, such as air quality modeling and ambient data analyses. The extensive nature of this type of a technical demonstration early in the attainment plan development process is necessary because the demonstration serves as the basis for limiting the applicability and associated control strategy decisions only to specific precursors for both the attainment plan and for the NNSR permitting program.

Area reclassified to serious.

As noted earlier in this section, a Moderate area can be reclassified to Serious under two scenarios. Under the first scenario, if a Moderate area fails to attain the standard by the end of the sixth calendar year after designation, it would then be reclassified by the EPA as a Serious area, and the state would be required to develop and submit a Serious area attainment plan within 18 months of reclassification. Under the second scenario, EPA could reclassify an area to Serious prior to the Moderate area attainment date if it can be shown that it would be impracticable for the area to attain by the Moderate area attainment date.

Proposed Option 2 would allow a “precursor demonstration” approach for Serious area plans in the same manner as for Moderate area plans. However, if the state had previously submitted a precursor demonstration that the EPA approved for the Moderate area attainment plan, under either proposed Option 2A or 2B the state would be required to review and update the precursor demonstration, taking into account any changes in the emissions inventory and any other relevant information or advances in technical tools developed since the initial demonstration was approved. Examples of such information would be improved emission estimation methods or emission factors for key source categories; changes in precursor emissions inventories due to emissions control programs or new source growth; the development of more advanced technical tools to assess the effectiveness of precursor reductions; and, updated information about new or more effective control technologies or emission reduction techniques. Any precursor demonstration that is approved as part of the Serious area attainment plan would need to be revised and updated if the area cannot attain the standard by the end of the tenth calendar year after designation and seeks an extension under section 188(e) or does not attain the standard by the applicable Serious area attainment date and is subsequently subject to 5 percent annual emission reductions under section 189(d).

One other important factor to consider is the substantial amount of time that can elapse between the submission of a Moderate area attainment plan for a particular nonattainment area, and submission of a Serious area attainment plan. The plan for a Moderate area is due within 18 months of designation. Under the EPA's overall proposed approach to attainment plan development, the state would be required to evaluate control measures for all types of sources and for all PM

2.5

precursors in order to ensure attainment of the standard as expeditiously as practicable. The full assessment to identify reasonable control measures would involve a thorough compilation and analysis of information on control technologies and the technological feasibility of implementation of such measures for sources in the area; the assessment of associated control costs and economic feasibility of implementation; information on the time needed for deployment and implementation of such control measures; and, the resulting timeline for achieving emissions reductions.

If the Moderate area does not attain the standard by the end of the sixth calendar year after designation, then as required by to the CAA, the EPA would have 6 months to make a determination to that effect, and the area would be reclassified to Serious. The state would then have 18 months to submit, at a minimum, a new attainment demonstration and control strategy comprising BACM and BACT. Thus, under these circumstances, these key Serious area plan elements would be due at least 8 years after the EPA designated the area nonattainment, and more than 6 years after the state submitted the original Moderate area plan. Because of the potentially protracted timeline for developing, implementing and revising as necessary the SIP for a given PM

2.5

nonattainment area under subpart 4, the EPA believes it is reasonable for the state to be required to update any precursor demonstration it had previously developed for the area if the area is reclassified as Serious.

The EPA requests comment on the requirement for the state to review and update any previously approved “precursor demonstration” if the area fails to attain the standard by the applicable Moderate area attainment date. The EPA also requests comment on the requirement for the state to review and update any previously approved “precursor demonstration” if the area fails to attain the standard by the applicable Serious area attainment date.

NNSR.

An approvable precursor demonstration under either Option 2A or Option 2B would evaluate emissions of a particular precursor from all types of sources. Accordingly, if the state provides an approvable precursor demonstration for all types of sources of a particular precursor as described above, then under Option 2A, the state would also be able to rely on the same technical demonstration to conclude that emissions of that precursor just from major stationary sources in the area do not provide a “significant contribution” to PM

2.5

concentrations in the area pursuant to section 189(e). Thus, under Option 2A, the state would not need to apply the NNSR control requirements for PM

2.5

to that precursor in the particular PM

2.5

nonattainment area(s) for which the EPA approves the demonstration.

Under Option 2B, the state would conduct analyses to determine the sensitivity of PM

2.5

levels in the area (that exceed the standard) to potential increases in emissions (relevant for NNSR) and decreases (relevant for attainment demonstrations). If the state provided an approvable precursor demonstration showing that PM

2.5

concentrations are insensitive to potential increases in emissions of a particular precursor in the area, then under Option 2B the state would be able to rely on this technical demonstration as the basis for not regulating that precursor for major stationary sources under NNSR.

Additionally, there could be a situation where the state finds that emissions of another precursor (

i.e.,

a precursor that was not the subject of the initial precursor demonstration) from only major stationary sources located in the nonattainment area could be considered to have an insignificant contribution to PM

2.5

levels that exceed the standard in the area (under Option 2A). For example, mobile and area source emissions of a PM

2.5

precursor could be determined to provide a larger contribution to PM

2.5

levels than major stationary sources in a given nonattainment area and would be the focus of the attainment strategy, and the major stationary source emissions of that same precursor might have only a minimal contribution to PM

2.5

levels. In this situation, the state could develop a separate demonstration under section 189(e) to support the exclusion of the

additional precursor from implementation requirements applicable to all major stationary sources, including NNSR program requirements (assuming the state analysis includes appropriate consideration of potential new sources of the relevant precursor). With an approved demonstration under section 189(e), major stationary sources of that precursor could also be excluded from the NNSR control requirements for PM

2.5.

The EPA seeks comment on all aspects of proposed Option 2.

Option 3:

An attainment planning analysis demonstrating that control measures for all types of sources of a particular precursor are not needed for expeditious attainment also would be deemed to meet the section 189(e) technical demonstration requirement, meaning that the state would not need to regulate emissions of the particular precursor from major stationary sources under the NNSR permitting program or other control requirements for major stationary sources.

Under proposed Option 3, the consideration of precursors in the attainment planning process for Moderate and Serious areas would closely follow the approach described for Option 1 (

see

Sections III.B.1.a-c of this preamble). As described for Option 1, after developing a comprehensive emissions inventory, the state would conduct an analysis to identify the new reasonable control measures that need to be adopted and implemented in order for the Moderate area to attain the standard as expeditiously as practicable, but no later than by the end of the sixth calendar year after designation (this analysis is described in greater detail in Section III.B.1.a in this preamble). If the state determines that adoption of additional economically and technically feasible emission reduction measures for a particular precursor are not necessary for expeditious attainment by the end of the sixth calendar year after designation, and that such measures collectively would not accelerate the attainment date by at least a year, then for the purposes of this Moderate area attainment plan, the state would not need to adopt such additional measures because they would not be considered reasonable. (Note that the need for additional emissions reductions of the particular precursor would have to be re-evaluated if the area is reclassified to Serious, or if the area submitted a SIP revision requesting an extension of the Serious area attainment date under section 188(e)).

To clarify the intent of Option 3, unlike under Option 1, a separate analysis to show that major stationary sources of a particular precursor do not contribute significantly to PM

2.5

levels in a given PM

2.5

nonattainment area for purposes of section 189(e) would not be needed. If the state's single analysis shows that emission reduction measures are not needed from sources of a particular precursor in order to demonstrate expeditious attainment, then under proposed Option 3 the same analysis would also be considered adequate to meet the requirements of section 189(e). In effect, the attainment planning analysis would define the set of precursors that would be subject to control under both the attainment plan and the NNSR permitting program for the area.

Note that while the NNSR program needs to be implemented from the effective date of an area's nonattainment designation, in some situations the state would implement either its existing NNSR program for PM

2.5

or, in the absence of such program, 40 CFR part 51 Appendix S, the default NNSR program, until the EPA approves the state's PM

2.5

attainment plan and revised NNSR regulations for PM

2.5

The rationale supporting the Option 3 approach focuses on the section 189(e) emphasis on precursor control requirements. If control measures are not needed in a Moderate nonattainment area to reduce emissions of a particular precursor from all types of sources in order to demonstrate attainment or to advance the attainment date, then under the rationale of proposed Option 3, it would follow that the state would not need to include any other control requirements that apply to major stationary sources of that precursor, including control requirements for PM

2.5

under the NNSR program. The theory for this option would be that if the state determines that new control requirements for emissions of the particular precursor are not needed for purposes of attainment planning because they would not contribute to reducing PM

2.5

levels that exceed the standard, then other control requirements to address emissions of that precursor also would not be needed. Note that under this option, the state also would not be required to analyze the potential effect of increases in emissions of the particular precursor (

e.g.,

from the possible permitting of new sources) on PM

2.5

concentrations in the area. The EPA requests comment on the rationale supporting Option 3.

Additionally, under Option 3, as was the case with Option 2, there could be a situation where the state determines that control measures for a particular precursor are generally needed in order to demonstrate attainment as expeditiously as practicable, but that the major stationary sources of that precursor that are located in the nonattainment area have an insignificant contribution to PM

2.5

levels that exceed the standard in the area. Under this Option 3, the EPA believes that section 189(e) provides the state with the authority to develop a separate demonstration to show that, even though control measures for a specific precursor emitted by sources other than major stationary sources are necessary to demonstrate expeditious attainment in an area, major stationary sources of that precursor have an insignificant contribution to PM

2.5

concentrations that exceed the standard in the area. Thus, controls from major stationary sources of that precursor would not be required for either the attainment plan or the NNSR program. More discussion on the potential options for precursor technical demonstrations is included in Section III.C of this preamble. The EPA seeks comment on all aspects of proposed Option 3.

The EPA also seeks comment on whether only one of these approaches should be included in the final rule, or whether it would be appropriate to include multiple approaches (

e.g.,

both Options 1 and 2) or a hybrid of two approaches by which a state could demonstrate that a particular precursor would not need to be addressed in the attainment plan or NNSR permitting program for a specific area.

C. Technical Approaches for Demonstrating That a Precursor Does Not Need To Be Subject to Control Requirements

As noted earlier, in the preamble to the 2007 PM

2.5

Implementation Rule, the EPA included a discussion allowing for the state to submit a technical demonstration to show to the satisfaction of the EPA that emissions of a particular precursor do not significantly contribute to PM

2.5

concentrations in the area. In that preamble discussion, the EPA indicated that such a demonstration should be based on the weight of evidence of available information, and that any such demonstration by the state must be approved by the EPA. The 2007 PM

2.5

Implementation Rule also discussed a number of types of analyses that could inform this precursor demonstration, such as speciation data analyses, air quality modeling studies, chemical tracer studies, emissions inventories, or special intensive measurement studies to evaluate specific atmospheric chemistry in an area. In the 2007 PM

2.5

Implementation Rule, the EPA intended to provide states with the flexibility to provide a range of different supporting analyses that would be appropriate for

the area, recognizing that nonattainment areas differed in terms of such factors as: (i) The mix of emissions sources located in the nonattainment area and outside the area that are contributing to PM

2.5

concentrations in the area; (ii) the levels of PM

2.5

species measured in the area; (iii) the times of year when highest PM

2.5

concentrations are observed; (iv) the topography of the area; (v) the severity of the nonattainment problem; and, (vi) the patterns of emissions and population growth in and around the nonattainment area. Under the 2007 PM

2.5

Implementation Rule, an important criterion for any technical precursor demonstration provided by a state, however, was that it had to fairly represent the information available to the state and the information made available to it by the public.

For this proposed implementation rule, the EPA similarly proposes that the state should have the flexibility to present multiple types of analyses to support any demonstration for exempting a precursor from control requirements as long as they fairly represent the available information, and accordingly proposes that the EPA should review any such demonstration based on the weight of evidence. Unlike in the prior implementation rule, however, later in this section the EPA raises the question of whether certain specific types of analyses should be included as minimum required components of any precursor demonstration that a state chooses to submit to the EPA for approval.

The preamble to the 2007 PM

2.5

Implementation Rule indicated that if a state developed a precursor demonstration as part of its draft SIP, then in accordance with the state rulemaking process, the demonstration would be subject to public review at the state level. It also stated that, as required under any rulemaking process, the state had to consider and provide a response in the rulemaking record to any information or evidence brought forward by commenters during the state's SIP planning, development and review process. By insuring that this important issue was explicitly addressed and supported in the attainment plan submitted to the EPA, the EPA could better evaluate the precursor demonstration in accordance with its obligations under the CAA. The EPA believes these are sound procedural steps for a state rulemaking process, and the regulations being proposed as part of this rule include similar language providing for public review of any proposed precursor demonstration.

The 2007 PM

2.5

Implementation Rule did not provide a specific due date for submittal of any precursor demonstration, although it was assumed that if a state were to pursue such a demonstration, it would need to be done early in the attainment plan development process and submitted to the EPA no later than the date of the attainment plan submission itself. It was recommended that the state develop any such demonstration in consultation with the appropriate EPA Regional Office. In this proposal, the EPA is proposing that if a state is interested in developing a PM

2.5

precursor demonstration to support not regulating one or more PM

2.5

precursors in the attainment plan for an area, it should consult with the EPA Regional Office as early as possible to discuss appropriate analyses to be included. In its review of any precursor demonstration provided by a state, the EPA will consider all currently available information.

Under all three proposed precursor policy options described above, the state would have the opportunity to provide a precursor demonstration to meet the requirements of section 189(e) of the CAA. Precursor demonstrations pursuant to section 189(e) should evaluate the significance of the contribution of emissions of a particular precursor from existing major stationary sources to fine particle concentrations that exceed the standard. However, Options 2A and 2B differ from the others in that they would provide the state with the ability to conduct a precursor demonstration that comprehensively assesses the contribution of a particular precursor from all types of sources in the nonattainment area (not just from major stationary sources as specifically addressed by section 189(e)) for the purposes of informing which precursors must be addressed in both the attainment plan and in the NNSR program for a particular PM

2.5

nonattainment area. (Note that Option 2 would not prevent the state from also conducting an additional analysis under section 189(e), if warranted, to further demonstrate that while all emissions of a particular precursor make a significant contribution to PM

2.5

levels that exceed the standard, the emissions from just the major stationary sources of that precursor collectively do not contribute significantly to PM

2.5

levels that exceed the NAAQS in the area.) The EPA has considered three important questions regarding the scope and the potential requirements associated with precursor demonstrations, and requests comment on the questions and technical analysis options presented below.

1. What is the geographic area from which precursor emissions should be assessed?

In the 2007 PM

2.5

Implementation Rule, the preamble indicated that a precursor demonstration analysis addressing all source types covered by the attainment plan should evaluate the impact of emissions from sources located throughout the entire state. In contrast, the 2008 PM

2.5

NSR Rule suggested that a precursor demonstration for NNSR purposes should evaluate emissions from major stationary sources of a particular precursor located within the nonattainment area only.

In determining which approach to include in the present proposal, the EPA believes that it continues to be reasonable that any precursor demonstration conducted to assess precursor significance for NNSR purposes should evaluate emissions from major stationary sources of the precursor from within the nonattainment area only. Section 189(e) is included in a part of the CAA that specifically sets forth nonattainment area requirements. For attainment planning purposes it is less clear that the evaluation of emissions should be limited only to sources from within the nonattainment area, because the state has jurisdiction over emissions sources located throughout the state, and can impose emission reduction requirements on contributing sources outside of nonattainment areas if necessary to help bring areas with violating monitors into attainment. At the same time, that argument would suggest that section 189(e) should be interpreted as requiring two different analyses of the impacts of precursors emitted from two different geographic scales (from within the nonattainment area, as well as from a broader area that influences air quality within the nonattainment area, which could include the entire state). The EPA does not believe such an interpretation is required, nor does it believe that such multiple analyses are warranted. The statute simply refers in general terms to precursor emissions from major stationary sources and does not differentiate between control requirements for attainment planning and control requirements for other purposes, such as NNSR permitting. The statute also does not indicate that multiple analyses must be done to assess major stationary source impacts from multiple geographic scales. For these reasons, the EPA is proposing that

any precursor demonstration must include an evaluation of emissions from sources located in the nonattainment area only. The EPA requests comment on this proposed approach.

2. Should the EPA's guidance provide a specific list of analyses as “minimum requirements” that must be included in any proposed precursor demonstration?

As noted above, the EPA encourages states to provide a range of analyses to thoroughly understand the effect of precursor emissions on PM

2.5

concentrations in an area. In past discussions with state representatives regarding potential approaches to regulating PM

2.5

precursors, some representatives have suggested that this PM

2.5

implementation rulemaking should include more specificity about the minimum requirements for technical demonstrations to support exclusion of PM

2.5

precursors from regulatory requirements in attainment plans, while others have recommended a less prescriptive approach. One overarching issue is how detailed the EPA's guidance should be with regard to the analytical requirements for any proposed precursor demonstration. As noted earlier, technical demonstrations can include data such as ambient speciation data analyses, air quality modeling studies, chemical tracer studies, emissions inventories, and/or special intensive measurement studies. Air quality modeling analyses are discussed in more detail below.

Contribution analysis.

Based on the statutory language of section 189(e), it appears that, at a minimum, any precursor demonstration conducted specifically pursuant to section 189(e) must evaluate the contribution of current emissions of the relevant precursor from existing major stationary sources to current (or most recent) PM

2.5

concentrations observed in the nonattainment area (note that this type of analysis is possible under Option 1 and Option 3). In addition, as described above, any precursor demonstration under Option 2A must evaluate the contribution of emissions of the relevant precursor from all sources (not just major stationary sources) to current (or recent) PM

2.5

concentrations observed in the nonattainment area.

In light of the statutory language and the capabilities of existing technical tools, the EPA proposes to require that the state conduct such a contribution analysis at a minimum as part of any proposed precursor demonstration, and that the state conduct an analysis using an air quality modeling system that adequately accounts for the PM

2.5

pollution problem within the nonattainment area. Several photochemical air quality models (

e.g.,

Community Multi-Scale Air Quality Model (CMAQ) and the Comprehensive Air Quality Model with Extensions (CAMx)) can be used to quantify the contributions of precursor emissions to PM

2.5

concentrations in the area.

For example, states could compare base case conditions (at current precursor emissions levels) with a separate model simulation in which the relevant precursor emissions are reduced by a large percentage. The difference in the estimated PM

2.5

concentrations provides one indication of the relative significance of the precursor emissions to PM

2.5

concentrations in the area. This type of contribution analysis can also be accomplished by using existing advanced tools within photochemical air quality models, such as “source apportionment” capabilities which allow one to track precursor emissions as they “form” PM

2.5 (

in the model) and then report their contributions separately. The EPA requests comment on including a contribution analysis as a minimum requirement in any proposed precursor demonstration under Option 2A.

For more information on CMAQ,

see http://www.epa.gov/AMD/Research/RIA/cmaq.html

. For more information on CAMx,

seehttp://www.camx.com/

Sensitivity analysis.

The EPA notes that changes in PM

2.5

concentrations from current conditions in any area will not necessarily be linear with respect to changes in PM

2.5

precursor emissions. Therefore, another important question is whether any precursor demonstration should be required to include an assessment of how “sensitive” the area will be to potential reductions or increases in emissions of the relevant precursor. Sensitivity analyses of potential reductions in emissions would be most appropriate for attainment planning (and relevant to Option 2B), whereas sensitivity analyses of potential increases in emissions (

e.g.,

relevant to NNSR permitting) would be appropriate for all section 189(e) technical evaluations (possible under Options 1, 2B and 3). Sensitivity analyses are important because of the complexity and variability of the atmospheric chemistry affecting PM

2.5

concentrations in different areas across the country.

The principal PM

2.5

components that are secondarily formed in the atmosphere are the result of chemical reactions between various PM

2.5

precursors (

see

Section II of this preamble for more information on specific precursor reactions). Thus, the most effective precursor strategies for reducing PM

2.5

concentrations as part of attainment planning will vary from area to area, depending upon which specific precursors play a role in forming or limiting PM

2.5

formation in the particular area. Likewise, in evaluating which precursors would be appropriate to exclude from regulation for NNSR in an area, it is important to understand the current sensitivity of the atmosphere to potential increases in precursor emissions that could result from the addition of new sources to the nonattainment area.

One approach to assessing precursor sensitivities would be to conduct a model simulation that evaluates the effect on PM

2.5

concentrations in the area resulting from a given set of precursor emission reductions and emission increases. Simulations could be conducted to assess a set of emission reduction and emission increase scenarios deemed appropriate to determine the sensitivity of a particular precursor in a specific area. Another approach that could be used is a scientific technique called the “decoupled direct method” (DDM), which efficiently estimates the impacts on PM

2.5

concentrations as a result of reducing or increasing precursor emissions in the model.

See

Simon et al., Memorandum to ozone NAAQS docket EPA-HQ-OAR-2008-0699, “Model-based Rollback Using the Higher Order Direct Decoupled Method (HDDM),” August 14, 2012.

For the reasons discussed above, the EPA also proposes that any precursor demonstration conducted under proposed Option 2B must provide a set of sensitivity analyses that evaluate the effect of a range of emissions changes associated with measures considered economically and technically feasible in a particular nonattainment area. Analyses that reduce emissions of a particular precursor will help the state and the EPA to understand how “responsive” the atmosphere would be to control measures and how effective such reductions would be relative to other precursor reductions. Although not specifically required for other options under this proposed rule, precursor sensitivity analyses evaluating the effect of varying degrees of potential precursor reductions would provide meaningful information for any precursor demonstration intended to show that a particular precursor does not need to be addressed for attainment planning. Conversely, sensitivity analyses that consider the effect of a range of potential emissions increases in the nonattainment area will help the state and the EPA to understand the potential response of PM

2.5

concentrations to projected growth in the area, including potential increases in emissions associated with potential newly permitted sources that emit the precursor in question. Any precursor demonstration intended to show that a particular precursor does not need to be addressed for NNSR should include sensitivity analyses evaluating the effect of varying degrees of precursor emission increases in the area. The EPA recommends that the state conduct these analyses using air quality modeling tools, but the state could provide additional relevant analyses as well. The EPA requests comment on the proposed requirement for inclusion of sensitivity analyses in any precursor demonstration.

3. Should there be a “bright line” value to indicate that any estimated contribution to annual average or 98th percentile PM

2.5

concentrations in the nonattainment area that exceeds this value would be considered “significant”?

In considering this question, it is helpful to first look to how the concept of a significant, or insignificant, contribution has been interpreted with regard to particulate matter in past PM

guidance (Addendum to the General Preamble) and in other PM

2.5

-related regulations, such as the CAIR. In the Addendum, the EPA introduced the concept of a “

de minimis”

impact from a source category for the purposes of the identification and evaluation of BACM.

While a later discussion in this proposal addresses whether or not to maintain a similar

de minimis

source category-based policy approach for future BACM and BACT source category analyses, what is relevant for this precursor discussion is the EPA's guidance in the Addendum on what could be considered a “

de minimis,”

or “insignificant,” ambient impact for purposes of PM

. In the Addendum, the EPA indicated that a 1 μg/m

cont

This text is long and has been trimmed here. Open the source document for the complete record.

This is a copy of a public record, reproduced as it was published. It is not legal advice, and it may not be the version a court would rely on. Check the official source before you cite it.