Air Quality: EPA’s 2023 Proposed Changes to the Particulate Matter (PM) Standard

Air Quality: EPA’s 2023 Proposed Changes to

the Particulate Matter (PM) Standard

August 16, 2023

Congressional Research Service

https://crsreports.congress.gov

R47652

SUMMARY

Air Quality: EPA’s 2023 Proposed Changes to

the Particulate Matter (PM) Standard

The Clean Air Act (CAA) requires the U.S. Environmental Protection Agency (EPA) to issue

national ambient (outdoor) air quality criteria (standards) for certain listed pollutants and then

review those standards every five years. Among the air pollutants for which EPA issued a

national ambient air quality standard (NAAQS) was particulate matter (PM), especially PM 2.5

micrometers or less in diameter (PM2.5). Exposure to PM has been associated with adverse health

effects, with haze formation, and with other ecological effects.

R47652

August 16, 2023

Omar M. Hammad

Analyst in Environmental

Policy

On January 27, 2023, EPA proposed to review and modify the NAAQS for PM. EPA has established short-term (24-hour)

and long-term (annual) standards for two categories of PM based on size: PM 2.5 for particles smaller than 2.5 micrometers,

and slightly larger, inhalable particles less than or equal to 10 micrometers (referred to as PM10). The CAA provides for two

types of NAAQS: (1) primary standards, “the attainment and maintenance of which in the judgment of the [EPA]

Administrator ... are requisite to protect the public health” with “an adequate margin of safety”; and (2) secondary standards,

which are necessary to protect public welfare.

EPA’s 2023 proposal would lower the primary PM2.5 annual NAAQS limit from 12.0 micrograms per cubic meter (μg/m 3) to

a value between 9.0 to 10.0 μg/m3. The proposal also sought comments on alternative annual standard levels down to 8.0

μg/m3 and up to 11.0 μg/m3. The proposal would maintain the current primary and secondary 24-hour PM2.5 standards,

primary and secondary 24-hour standards for PM10, and the secondary annual PM2.5 standard. In addition, EPA proposed

revisions to other aspects related to the PM NAAQS, including to the Air Quality Index (AQI) and monitoring requirements

for the PM standards.

Revising a NAAQS established under the CAA sets in motion a process under which the states and EPA identify areas that

exceed the standard (nonattainment areas) using multiyear air quality monitoring data and other criteria. The CAA directs

states and tribes, within 12 months from the effective date of the issuance of a final new or revised NAAQS, to submit

designation recommendations to EPA as to whether an area is attaining the standard. Using the recommendations and

information from air quality monitors and/or models, EPA designates areas as either attainment/unclassifiable or

nonattainment. If designated nonattainment, states are required to submit to EPA a State Implementation Plan (SIP) detailing

efforts to reduce pollutant concentrations in order to meet the standard. The area is designated attainment/unclassifiable if it

is attaining the standard and unclassifiable if EPA is not able to determine the status after evaluating the available

information for an area.

Congress and numerous stakeholders often raise concern over EPA and state application of an updated standard. These

concerns can involve the designation process, timelines, implementation, cross-boundary impacts, and exceptional events.

For EPA’s proposed reconsideration of the PM NAAQS, some in Congress have raised concern over items such as the

additional resources needed to document wildfire- and prescribed-fire-related exceptional events. The EPA defines

exceptional events as “unusual or naturally occurring events that can affect air quality but are not reasonably controllable

using techniques that air agencies may implement in order to attain and maintain the [NAAQS].” Exceptional events may

include wildfires, prescribed fires, high wind dust events, stratospheric ozone intrusions, and volcanic and seismic activities.

Some in Congress, some states, and certain stakeholders have expressed concern that EPA’s proposed PM NAAQS will

require considerable resources to document the effect on air quality of wildland fire-related exceptional events, in order to

have those events and their data excluded from regulatory consideration and the designation process.

Congressional Research Service

Air Quality: EPA’s 2023 Proposed Changes to the Particulate Matter (PM) Standard

Contents

Introduction ..................................................................................................................................... 1

NAAQS Requirements and Designation Process ............................................................................ 2

PM2.5 NAAQS Designations and Implementation Timelines ................................................... 3

New Source Review (NSR) ...................................................................................................... 4

PM2.5 Proposed Reconsideration ..................................................................................................... 5

Prior PM NAAQS Regulations ................................................................................................. 7

Regulatory Impact Analysis for a Lower PM2.5 NAAQS .......................................................... 8

Possible Impacts of a Lower Annual PM2.5 NAAQS ................................................................ 9

EPA SIP Requirements and Implementation Rules ........................................................................ 11

Framework Used to Address the “Good Neighbor” Provisions .............................................. 12

Current PM NAAQS Requirements and Implementation Rule .............................................. 13

Exceptional Events and the NAAQS ............................................................................................. 14

Prescribed Fires and Wildfire Exceptional Events .................................................................. 15

Issues for Consideration ................................................................................................................ 17

Issues Regarding the PM NAAQS .......................................................................................... 17

Issues Regarding Exceptional Events ..................................................................................... 19

Figures

Figure 1. Areas Currently (2023) Designated Nonattainment for a PM2.5 Standard ...................... 10

Figure 2. Areas That Would Likely Not Meet the Proposed PM2.5 NAAQS Based on Their

2019-2021 Design Values............................................................................................................ 11

Figure 3. Prescribed Fire Exceptional Events Process .................................................................. 16

Tables

Table A-1. Timeline of Particulate Matter (PM) National Ambient Air Quality Standards

(NAAQS) ................................................................................................................................... 21

Table B-1. Fine Particle Annual Design Values for Counties with Monitoring Data .................... 24

Appendixes

Appendix A. PM NAAQS Chronology ......................................................................................... 21

Appendix B. PM Design Values .................................................................................................... 24

Appendix C. PM Implementation Rule Requirements .................................................................. 29

Contacts

Author Information........................................................................................................................ 30

Congressional Research Service

Air Quality: EPA’s 2023 Proposed Changes to the Particulate Matter (PM) Standard

Congressional Research Service

Air Quality: EPA’s 2023 Proposed Changes to the Particulate Matter (PM) Standard

Introduction

Under Sections 108-109 of the Clean Air Act (CAA),1 the U.S. Environmental Protection Agency

(EPA) is to issue national ambient (outdoor) air quality standards (NAAQS) for certain listed

pollutants (1) whose emissions “may reasonably be anticipated to endanger public health or

welfare” and (2) whose presence in ambient air “results from numerous or diverse mobile or

stationary sources.”2 EPA has identified and promulgated NAAQS for six principal pollutants,

commonly referred to as criteria pollutants:

1.

2.

3.

4.

5.

6.

particulate matter (PM),

ozone (O3),

nitrogen dioxide (NO2),3

sulfur dioxide (SO2),

carbon monoxide (CO), and

lead (Pb).

PM refers to a mixture of solid particles and liquid droplets in the atmosphere. PM components

may include acids, organic chemicals, metals, and soil or dust particles. The size of PM varies,

ranging from tiny particles that can be seen only through a high-power microscope to larger

particles (e.g., soot). Exposure to PM has been associated with adverse health effects (e.g.,

aggravated asthma, chronic bronchitis, and premature death).4 PM has also been linked with haze

formation and other ecological effects.5

For PM, EPA established short-term (24-hour) and long-term (annual) standards. Additionally,

EPA established separate standards for two categories of PM based on size: “fine” PM 2.5

micrometers or less in diameter (referred to as PM2.5) and slightly larger, but still inhalable,

particles less than or equal to 10 micrometers in diameter (referred to as PM10).

The statute requires that EPA review the latest scientific studies and either reaffirm or modify

previously established NAAQS every five years. EPA last revised the PM NAAQS in 2012. On

December 18, 2020, EPA reviewed and decided to retain the 2012 PM2.5 and PM10 standards,

without revision. While EPA is meant to review the NAAQS every five years, it has rarely met its

statutory obligation.6 On January 27, 2023, EPA proposed a reconsideration of the 2020 decision

to retain the PM NAAQS and would lower the annual PM2.5 allowable limit. (See PM NAAQS

chronology presented in Table A-1.)

This report focuses on the NAAQS implementation process and timelines, primarily as they relate

to PM2.5 and the proposed reconsideration of the PM2.5 NAAQS. Also included in this report is an

1 These sections can be found at 42 U.S.C. §7408 and §7409.

2 For more information regarding the Clean Air Act (CAA) and its major requirements, see CRS Report RL30853,

Clean Air Act: A Summary of the Act and Its Major Requirements, by Richard K. Lattanzio.

3 The national ambient air quality standard (NAAQS) is for nitrogen dioxide (NO ); nitrogen gases that are ozone

2

precursors are referred to as nitrogen oxides, or NOx.

4 See Section 3.3, “Health Effects Evidence,” of the U.S. Environmental Protection Agency’s (EPA’s) final “Policy

Assessment for the Reconsideration of the National Ambient Air Quality Standards for Particulate Matter,” at

https://www.epa.gov/system/files/documents/2022-05/Final%20Policy%20Assessment%20for%20the%20

Reconsideration%20of%20the%20PM%20NAAQS_May2022_0.pdf.

5 Ibid., Section 5.3.1, “Visibility Effects.”

6 The EPA has met the statutory obligation to review the NAAQS within five years twice. See EPA, “EPA Finalizes

Ozone NAAQS, Retaining Current Standards,” press release, December 23, 2020, at https://www.epa.gov/

newsreleases/epa-finalizes-ozone-naaqs-retaining-current-standards.

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Air Quality: EPA’s 2023 Proposed Changes to the Particulate Matter (PM) Standard

overview of the exceptional events process by which EPA excludes air monitoring data influenced

by situations such as wildfires and prescribed burns, known as wildland fires, when taking

regulatory actions with regard to the air quality standards.7 The report concludes with a discussion

of issues for potential consideration by Congress.

NAAQS Requirements and Designation Process

The CAA directs EPA to establish two types of NAAQS:

1. primary standards, “the attainment and maintenance of which in the judgment of

the [EPA] Administrator ... are requisite to protect the public health” with “an

adequate margin of safety”;8 and

2. secondary standards,9 which are necessary to protect public welfare,10 a broad

term that includes visibility impairment as well as damage to crops and

vegetation, and effects on soil and nutrient cycling, water, wildlife, property, and

building materials, among other things.

Establishing NAAQS does not directly limit emissions or compel specific emissions controls;

rather, it represents the EPA Administrator’s formal judgment regarding the level of ambient

pollution that will protect public health with an adequate margin of safety. In setting the NAAQS,

the EPA may not consider the costs of implementing the standards.11 Promulgation of NAAQS

sets in motion a process under which the states and tribes first identify geographic nonattainment

areas (i.e., those areas failing to meet the NAAQS) based on monitoring and analysis of relevant

air quality data.12 Ambient air monitoring is “the systematic, long-term assessment of pollutant

levels by measuring the quantity and types of certain pollutants in the surrounding, outdoor air.”13

EPA then establishes nonattainment areas based on the data and recommendations. States with

nonattainment areas then submit State Implementation Plans (SIPs) to EPA, which identify

7 The terms wildland fire and wildfire often are used interchangeably, although each term has a distinct definition. The

National Wildfire Coordinating Group (NWCG) defines wildland fire as any nonstructure fire that occurs in vegetation

or natural fuels, including prescribed fire and wildfire. NWCG defines wildfire as a wildland fire originating from an

unplanned ignition, including unauthorized human-caused fires, escaped prescribed fire projects, and all other wildland

fires where the objective is to put out the fire. See NWCG, “Glossary of Wildland Fire Terminology,” September 2020,

at https://www.nwcg.gov/glossary/a-z. Prescribed burning is the deliberate use of fire in specific areas within specified

fuel and weather conditions. For further information, see CRS Report R46583, Federal Wildfire Management: TenYear Funding Trends and Issues (FY2011-FY2020), by Katie Hoover.

8 42 U.S.C. §7409(b)(1).

9 42 U.S.C. §7409(b)(2).

10 42 U.S.C. 7602(h). The use of public welfare in the CAA “includes, but is not limited to, effects on soils, water,

crops, vegetation, manmade materials, animals, wildlife, weather, visibility, and climate, damage to and deterioration of

property, and hazards to transportation, as well as effects on economic values and on personal comfort and well-being,

whether caused by transformation, conversion, or combination with other air pollutants.”

11 The D.C. Circuit’s holding on the cost and constitutional issues were appealed to the U.S. Supreme Court. In

February 2001, the Supreme Court issued a unanimous decision upholding the EPA’s position on both the cost and

constitutional issues. Am. Trucking Ass’ns v. EPA, 531 U.S. 457, 465–472, 475–76 (2001); Am. Trucking Ass’ns, Inc.

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

12 While 42 U.S.C. §7407(d) specifically addresses states, EPA generally follows the same process and schedule for

tribes pursuant to 42 U.S.C. §7601(d), “Tribal Authority and the Tribal Authority Rule.”

13 For information on EPA’s air monitoring methods, see EPA, “Air Monitoring Methods—Criteria Pollutants,” at

https://www.epa.gov/amtic/air-monitoring-methods-criteria-pollutants.

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Air Quality: EPA’s 2023 Proposed Changes to the Particulate Matter (PM) Standard

specific state and federal regulations and emissions control requirements that are to bring areas

into compliance, as well as actions for maintaining compliance.14

The CAA requires EPA to review the scientific data upon which the NAAQS are based every five

years, and revise the standards, if necessary. More often than not, EPA has taken more than five

years in reviewing the standards, but the establishment of a deadline has allowed interested

parties to force review of the standards by filing suit.15 The CAA also requires EPA to appoint an

independent scientific review committee composed of seven members, known as the Clean Air

Scientific Advisory Committee (CASAC), that assist in the review process.16 The CAA directs

CASAC to review the NAAQS every five years and recommend to the EPA Administrator “any

new national ambient air quality standards and revisions of existing criteria and standards as may

be appropriate.”17

PM2.5 NAAQS Designations and Implementation Timelines

The CAA directs EPA and states to take the following actions following promulgation of a new or

revised PM2.5 NAAQS:

•

•

•

Within a year after a final NAAQS is promulgated, state and tribal area

designation recommendations must be submitted to EPA. Areas are designated as

meeting (attainment/unclassifiable areas) or not meeting (nonattainment areas)

the final NAAQS.18

No later than 120 days before promulgating final designations, EPA notifies

states and tribes regarding any modifications to their recommendations.19

Within two years after a final NAAQS is promulgated, EPA must designate areas

with available information as attainment/unclassifiable areas or nonattainment

areas, considering the most recent air quality monitoring data and input from

states and tribes. All PM2.5 nonattainment areas are initially designated as

Moderate (i.e., the lesser of the two NAAQS PM nonattainment

classifications).20

14 Under certain circumstances EPA may disapprove a State Implementation Plan (SIP) and promulgate a Federal

Implementation Plan (FIP). For information regarding SIPs and FIPs, see 42 U.S.C. §7410.

15 For example, in response to a case filed by the Missouri Coalition for the Environment, the U.S. District Court,

Eastern District of Missouri, Eastern Division, issued a decision in September 2005 that a review of the lead NAAQS

should be completed by September 1, 2008 (Missouri Coalition for the Environment vs EPA, Civil Action No. 4:04CV-0066 (ERW) (E.D. Mo. Sept. 14, 2005)).

16 For information regarding the Clean Air Scientific Advisory Committee (CASAC) PM review panel and its activities

and reports, see EPA, Clean Air Scientific Advisory Committee (CASAC), at https://casac.epa.gov/ords/sab/f?p=113:1:

4378852111566:::::.

17 42 U.S.C. §7409(d) regulates the independent scientific review committee regarding the review and revision of

criteria air pollutants and the national ambient air quality standards. If the EPA Administrator decides to revise the

NAAQS, the regulation is proposed in the Federal Register, public comments are considered, and EPA issues a final

rule in the Federal Register and codifies the regulation in the Code of Federal Regulations. For more information see

EPA, “The Basics of the Regulatory Process,” at https://www.epa.gov/laws-regulations/basics-regulatory-process.

18 In accordance with 42 U.S.C. §7407(d), the EPA Administrator may not require a governor to submit the initial

designation requests sooner than 120 days, but not later than one year. For information on the designation process, see

EPA, “NAAQS Designations Process,” at https://www.epa.gov/criteria-air-pollutants/naaqs-designations-process.

19 42 U.S.C. §7407(d)(B)(ii). Known as the “120-day letter.”

20 EPA is required to designate areas within two years of promulgation of a NAAQS; however, EPA can take an

additional year if the Administrator determines it is warranted. PM nonattainment areas are typically initially

(continued...)

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•

•

•

•

•

•

•

Final area designations are typically effective 90 days after Federal Register

publication.21

Within three years after a final NAAQS is promulgated, CAA Section 110

requires all states to submit SIP revisions to show they have the basic air quality

management program components in place to implement the final NAAQS.22

States with new transportation projects must submit a conformity determination

within one year of the effective date of nonattainment designation.23

Within 18 months after the effective date of designations, nonattainment area

PM2.5 SIPs are due.

The end of the sixth calendar year after the effective date of designations is the

attainment date for areas classified as Moderate for PM2.5 nonattainment

designations.24

The end of the 10th calendar year after the effective date of designations is the

attainment date for areas classified as Serious for PM2.5 nonattainment

designations.25

Designated nonattainment areas, as well as those designated unclassifiable or

attainment/unclassifiable for the NAAQS, are also subject to New Source

Review (NSR) requirements. As such, states must update stationary source

permitting requirements.26

New Source Review (NSR)

The fundamental framework of the Clean Air Act provides for different treatment of new versus

existing sources of air pollution, and “modification” of existing sources. The distinction was

based in part on the expectation that older sources would be replaced by newer ones over time.

Accordingly, these newer sources would be subject to more stringent control requirements, and

requiring existing sources to adopt stringent controls would be needlessly expensive and

unwarranted given the expected replacement with controls applicable to new sources. New

Source Review (NSR) aims to ensure that newly constructed facilities or major modifications to

designated as Moderate, but can be reclassified to the more stringent Serious classification. For more information

regarding PM classifications, see EPA, “Particulate Matter (PM) Nonattainment Area SIP Requirements,” at

https://www.epa.gov/pm-pollution/particulate-matter-pm-nonattainment-area-sip-requirements.

21 See National Archives, Federal Register, “Table of Effective Dates & Time Periods,” at

https://www.federalregister.gov/reader-aids/using-federalregister-gov/table-of-effective-dates-time-periods.

22 These are known as infrastructure SIPs, or iSIPs. The list of requirements is codified at 42 U.S.C. §7410(a)(2). 42

U.S.C. §7410(a)(2)(D)(i)(I) Prongs 1 and 2 are known as the “good neighbor” provisions.

23 EPA, “Fine Particulate Matter National Ambient Air Quality Standards: State Implementation Plan Requirements,”

81 Federal Register 58124, August 24, 2016.

24 The attainment date is the latest statutory date by which a nonattainment area is required to attain a particular PM

2.5

NAAQS; see 40 C.F.R. 51.1000. For the Moderate 2012 PM2.5 NAAQS attainment date, see EPA, “Fine Particulate

Matter National Ambient Air Quality Standards: State Implementation Plan Requirements,” 81 Federal Register

58068, August 24, 2016.

25 For the Serious 2012 PM

2.5 NAAQS attainment date, see EPA, “Fine Particulate Matter National Ambient Air

Quality Standards: State Implementation Plan Requirements,” 81 Federal Register 58093, August 24, 2016.

26 See 42 U.S.C. §§7470-7479 for the Prevention of Significant Deterioration (PSD) of air quality requirements. See 42

U.S.C. §§7491-7492 for the PSD requirements for visibility protection. See 42 U.S.C. §§7501-7508 for the

nonattainment New Source Review (NSR) requirements.

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existing facilities do not result in violation of applicable air quality standards.27 NSR provisions

outline permitting requirements both for construction of new major pollution sources and for

modifications to existing major pollution sources. The specific NSR requirements for affected

sources depend on whether the sources are subject to Prevention of Significant Deterioration

(PSD) or nonattainment provisions.28

PSD (attainment area permitting) applies with respect to a new standard in all areas of the United

States designated attainment or unclassifiable for the pollutant upon the effective date of the new

standard. Any new or modified major emitting facility must undergo preconstruction review and

permitting, including the installation of Best Available Control Technology (BACT).29 State

permitting agencies determine BACT on a case-by-case basis, taking into account energy,

environmental, and economic impacts. BACT cannot be less stringent than the federal New

Source Performance Standards (NSPS), but it can be more so.30 More stringent controls can be

required if modeling indicates that BACT is insufficient to avoid violating PSD emission

limitations, or the NAAQS itself.31

Nonattainment New Source Review (nonattainment NSR, or NNSR) applies in areas designated

nonattainment for the pollutant, which includes any areas newly designated nonattainment at or

after the effective date of designations.32

PM2.5 Proposed Reconsideration

On January 27, 2023, EPA proposed reconsideration of the PM2.5 annual NAAQS, with a

comment period that closed on March 28, 2023.33 The proposal would lower the PM2.5 annual

NAAQS limit from 12.0 micrograms per cubic meter (μg/m3) to a range between 9.0 to 10.0

27 An existing major stationary source proposing a physical change or a change in its method of operation must

determine whether that project is a major modification subject to the NSR preconstruction permitting requirements by

following a two-step test. The first step is to determine if there is a “significant emission increase” of a regulated NSR

pollutant from the proposed modification. If there is, the second step is to determine if there is a “significant net

emission increase” of that pollutant. EPA, “Prevention of Significant Deterioration (PSD) and Nonattainment New

Source Review (NNSR): Project Emissions Accounting,” 85 Federal Register 74890, November 24, 2020.

28 42 U.S.C. §7476 authorizes EPA to establish regulations for PSD of any pollutant for which EPA has issued a

national standard.

29 According to 40 C.F.R. §52.21(b)(1), the term major emitting facility is defined as a stationary source that emits, or

has a potential to emit, at least 100 tons per year, if the source is in 1 of 28 listed source categories, or, if the source is

not, then at least 250 tons per year, of “any air pollutant.”

30 Section 111 of the CAA requires EPA to establish nationally uniform, technology-based standards (called New

Source Performance Standards, or NSPS) for categories of new industrial facilities. These standards accomplish two

goals: (1) they establish a consistent baseline for pollution control that competing firms must meet, and thereby remove

any incentive for states or communities to weaken air pollution standards in order to attract polluting industry; and (2)

they preserve clean air to accommodate future growth, as well as for its own benefits. For more information on NSPS,

see CRS Report RL30853, Clean Air Act: A Summary of the Act and Its Major Requirements, by Richard K. Lattanzio.

31 The 1977 CAA broadened the air quality control regimen with the addition of the PSD and visibility impairment

provisions. The PSD program (Part C of Title I of the CAA) focuses on ambient concentrations of SO2, NOx, and PM

in areas where air quality is better than the NAAQS. The provision allows some increase in clean areas’ pollution

concentrations depending on their classification. In general, historic or recreation areas (e.g., national parks) are

classified Class I areas with very little degradation allowed, while most other areas are classified Class II areas with

moderate degradation allowed. States are allowed to reclassify Class II areas to Class III areas, which would be

permitted to degrade up to the NAAQS, but none have ever been reclassified to Class III.

32 42 U.S.C. §7503. Nonattainment New Source Review (NNSR) applies to new major sources or major modifications

at existing sources for pollutants where the area the source is located is nonattainment with a NAAQS.

33 EPA, “Reconsideration of the National Ambient Air Quality Standards for Particulate Matter,” 88 Federal Register

5558, January 27, 2023.

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μg/m3. The proposal also took comment on alternative annual standard levels from 8.0 μg/m3 to

11.0 μg/m3. See Table A-1 for a review of previous PM NAAQS and the current proposal. If EPA

adopts the proposed revision of the PM2.5 NAAQS, the agency would then be required to go

through the designation process upon promulgations of the revised NAAQS.34

Designations are based on the most recently available design values, a statistic that describes the

air quality status of a given location relative to the level of the NAAQS.35 Design values are

computed using Federal Reference Method or equivalent data reported by state, tribal, and local

air monitoring agencies to EPA’s Air Quality System (AQS).36 Federal Reference Methods are

methods developed and evaluated by EPA for accurately and reliably measuring pollutants in

outdoor air. If concentrations are flagged by state, tribal, or local monitoring agencies as having

been affected by an exceptional event (e.g., wildfire, volcanic eruption) and the associated EPA

Regional Office concurs, then the associated data are not included in the design value

calculations.37 States and tribes can consider exceptional events data in their designation

recommendations.38 EPA is not proposing to revise the PM2.5 Implementation Rule (i.e., 40 C.F.R.

§51, Subpart Z).39 (For more on the Implementation Rule, see section “EPA SIP Requirements

and Implementation Rules” of this report.)

The notice also proposed to maintain the current primary and secondary 24-hour PM2.5 standards,

primary and secondary 24-hour standards for PM10, and the secondary annual PM2.5 standard.

In addition, the EPA notice proposed revisions to other key aspects related to the PM NAAQS,

including to the Air Quality Index (AQI) and monitoring requirements for the PM NAAQS.40

These revisions include

•

•

•

•

•

•

addressing updates in data calculations,

approval of reference and equivalent methods,

updates in quality assurance statistical calculations to account for lower

concentration measurements,

updates to support improvements in PM monitoring methods,

changes to the PM2.5 network design to account for at-risk populations,

updates to the probe and monitoring path siting criteria for NAAQS pollutants,

34 42 U.S.C. § 7407(d).

35 The particulate matter (PM) 2.5 design value is the “annual mean, averaged over 3 years.” See EPA, “Criteria Air

Pollutants NAAQS Table,” at https://www.epa.gov/criteria-air-pollutants/naaqs-table.

36 The Air Quality System (AQS) contains ambient air pollution data collected by EPA, state, local, and tribal air

pollution control agencies from over thousands of monitors. AQS also contains meteorological data, descriptive

information about each monitoring station, and data quality assurance/quality control information. See EPA, “Air

Quality System (AQS),” at https://www.epa.gov/aqs.

37 Exceptional events are unusual or naturally occurring events that can affect air quality but are not reasonably

controllable using techniques that tribal, state, or local air agencies may implement in order to attain and maintain the

NAAQS. See 42 U.S.C. §7619(b).

38 For more information on the NAAQS and attainment requirements, see CRS Report RL30853, Clean Air Act: A

Summary of the Act and Its Major Requirements, by Richard K. Lattanzio.

39 The PM Implementation Rule establishes planning requirements for states with areas that do not meet the PM

NAAQS. See EPA, “Fine Particulate Matter National Ambient Air Quality Standards: State Implementation Plan

Requirements,” 81 Federal Register 58010, August 24, 2016.

40 The Air Quality Index (AQI) is EPA’s color-coded tool used by state and local governments to help inform the public

about current and daily air quality; it also recommends steps that individuals can take to reduce their exposure to air

pollution. See EPA, “Air Quality Index (AQI) Basics,” at https://www.airnow.gov/aqi/aqi-basics/.

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•

•

•

changes to the PM2.5 AQI value of 50 to correspond to a concentration range

between 9.0 and 10.0 μg/m3,41

updates to the PM2.5 AQI values of 200, 300, and 500 to correspond to a

concentration of 125.4 μg/m3, 225.4 μg/m3, and 325.4 μg/m3, respectively,42 and

changes to the AQI daily reporting requirement from five days per week to seven

days per week.

The proposal also included language to modify the PM2.5 monitoring network design criteria to

include an environmental justice factor. This factor aims to account for proximity of populations

at increased risk of adverse health effects from PM2.5 exposures to sources of concern.

Prior PM NAAQS Regulations

Prior to the 2023 proposal, EPA took several actions with respect to the PM NAAQS, some of

which were controversial and subject to legal challenge. Table A-1 of Appendix A is a

chronology of the PM NAAQS and its revisions. The agency promulgated separate standards for

both coarse and fine particulate matter in 1997.43 EPA’s review and establishment of the 1997 PM

NAAQS was the subject of litigation and challenges. Industry groups argued that EPA’s

regulations were overly stringent. Environmental groups charged that EPA had not regulated

stringently enough. Others made claims regarding the constitutionality of the CAA and the scope

of EPA’s regulatory authority. The agency’s action was the subject of a Supreme Court decision,

and the standards themselves were ultimately upheld by the U.S. Court of Appeals for the District

of Columbia Circuit (D.C. Circuit).44

In 2005, EPA completed a statutorily required review of the PM NAAQS. Based on that review,

in 2006, EPA revised the standards.45 Several states and industry, agriculture, business, and

environmental and public health advocacy groups petitioned the U.S. Court of Appeals for the

District of Columbia Circuit, challenging certain aspects of EPA’s revisions of the PM NAAQS as

promulgated in December 2006. A February 24, 2009, decision by the D.C. Circuit granted the

petitions in part, denying other challenges, and remanded the standards to EPA for further

consideration, but did not vacate the 2006 standards.46

In 2012, EPA completed a statutorily required review of the PM NAAQS, concluded the 2006

standards were inadequately protective of public health, and revised the standards. In December

2012, EPA announced its final decisions to revise the primary NAAQS for PM.47 Petitioners

41 The current AQI levels align with the 2012 PM NAAQS; a revised PM

2.5 NAAQS would require a shift in the PM2.5

AQI to reflect the new standard. See EPA, “AQI Breakpoints,” at https://aqs.epa.gov/aqsweb/documents/codetables/

aqi_breakpoints.html.

42 The proposal would revise the upper AQI levels (200 and above) and replace the existing linear-relationship

approach used in 1999 (64 Federal Register 42530, August 4, 1999) to set these levels, with an approach that more

fully considers the PM2.5 health effects evidence from controlled human exposure and epidemiologic studies that has

become available in the last 20 years. See 88 Federal Register 5563, January 27, 2023.

43 EPA, “National Ambient Air Quality Standards for Particulate Matter,” 62 Federal Register 38652, July 18, 1997.

44 Am. Trucking Ass’ns v. EPA, 531 U.S. 457 (2001); Am. Trucking Ass’ns, Inc. v. EPA, 283 F.3d 355 (D.C. Cir.

2002). For questions regarding this case or other legal challenges to EPA’s PM NAAQS, congressional offices may

contact CRS Legislative Attorney Kate R. Bowers.

45 EPA, “National Ambient Air Quality Standards for Particulate Matter,” 71 Federal Register 61143, December 18,

2006.

46 Am. Farm Bureau Fed’n v. EPA, 559 F.3d 512 (D.C. Cir. 2009).

47 EPA, “National Ambient Air Quality Standards for Particulate Matter; Final Rule,” 78 Federal Register 3086,

January 15, 2013.

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challenged EPA’s final rule and argued that EPA acted unreasonably in revising the level and form

of the annual standard and in amending the monitoring network provisions. On judicial review,

the D.C. Circuit upheld the revised standards and monitoring requirements in all respects.48

In May 2018, the EPA Administrator issued a memorandum describing a “back-to-basics” process

for reviewing the NAAQS.49 The memorandum announced EPA would ensure any needed

revisions to the PM NAAQS would be finalized by December 2020. In October 2018, the EPA

Administrator announced that the role of reviewing the key science assessments developed as part

of the ongoing review of the PM NAAQS would be performed by the seven-member chartered

CASAC—an independent expert committee tasked with assisting EPA in reviewing the

NAAQS.50 On December 18, 2020, EPA finalized the retention of the primary and secondary PM

NAAQS, without revision.51

On January 20, 2021, the Biden Administration issued an Executive Order titled “Protecting

Public Health and the Environment and Restoring Science to Tackle the Climate Crisis,” which

identified several environmental and climate policy goals of the incoming Administration.52 An

accompanying fact sheet provided a “non-exclusive list of agency actions that heads of the

relevant agencies will review in accordance with the Executive Order,” including the 2020 PM

NAAQS action.53

Regulatory Impact Analysis for a Lower PM2.5 NAAQS

EPA has prepared cost estimates for all economically significant rules since the Carter

Administration as the result of executive orders.54 Under Executive Order (E.O.) 12866, each

economically significant regulatory action taken by executive branch agencies (under any

statutory authority) must include estimates of the cost and benefits of the action in a Regulatory

Impact Analysis (RIA) before it is proposed, and again before it is promulgated.55 RIAs are part

of the interagency review process overseen by the Office of Management and Budget, which

precedes the publication of significant rules in the Federal Register.56

48 Nat’l Ass’n of Manufacturers v. EPA, 750 F.3d 921 (D.C. Cir. 2014).

49 See Memorandum from EPA Administrator E. Scott Pruitt to Assistant Administrators, “Back-to-Basics Process for

Reviewing National Ambient Air Quality Standards,” May 9, 2018, at https://www.epa.gov/sites/default/files/2018-05/

documents/image2018-05-09-173219.pdf.

50 EPA, “Acting Administrator Wheeler Announces Science Advisors for Key Clean Air Act Committee, Tasks

Chartered Panel to Lead Review of Ozone and Particulate Matter Standards Under Reformed Process,” press release,

October 10, 2018, at https://www.regulations.gov/document/EPA-HQ-OAR-2015-0072-0223.

51 Proposed in 85 Federal Register 24094, April 30, 2020, and finalized in 85 Federal Register 82684, December 18,

2020.

52 Executive Order 13990; 86 Federal Register 7037, January 25, 2021.

53 See item 14 in White House, “Fact Sheet: List of Agency Actions for Review,” January 20, 2021, at

https://www.whitehouse.gov/briefing-room/statements-releases/2021/01/20/fact-sheet-list-of-agency-actions-forreview/.

54 The Carter Administration order, Executive Order 12044, “Improving Government Regulations,” March 23, 1978, is

at http://www.thecre.com/pdf/12044.PDF.

55 Executive Order 12866, “Regulatory Planning and Review,” September 30, 1993, at http://www.plainlanguage.gov/

populartopics/regulations/eo12866.pdf. For a discussion of Executive Order 12866 and the regulatory review process,

see CRS Report RL32397, Federal Rulemaking: The Role of the Office of Information and Regulatory Affairs,

coordinated by Maeve P. Carey.

56 For more information on cost and benefit considerations in CAA regulations, see CRS Report R44840, Cost and

Benefit Considerations in Clean Air Act Regulations, by James E. McCarthy and Richard K. Lattanzio.

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EPA conducted an RIA for the proposed reconsideration of the PM NAAQS.57 In the RIA, EPA

evaluated the proposed PM2.5 annual standards of 9.0 and 10.0 μg/m3, represented as 9/35 and

10/35, respectively, to illustrate the proposed annual and 24-hour standards. The RIA also

reviewed an alternative PM2.5 annual standard of 8.0 μg/m3 (8/35), and an alternative annual

standard of 10.0 μg/m3 in combination with a 24-hour PM2.5 standard of 30 μg/m3 (10/30).58

In the RIA, EPA quantified the number and economic value of the estimated avoided premature

deaths and illnesses attributable to applying hypothetical national control strategies for more

stringent annual PM2.5 standards with a sensitivity analysis for a more stringent 24-hour standard

that reduces PM2.5 concentrations in 2032.59 The RIA estimates that the 2032 avoided premature

mortalities for adults (ages 18-99) for the proposed annual standard of 9/35 would be 4,200

adults, with an annual monetized benefit ranging from $19 billion to $43 billion, and for the

proposed annual standard of 10/35, the 2032 avoided premature mortalities for adults would be

1,700 adults, with an annual monetized benefit ranging from $7.6 billion to $17 billion. For the

alternative annual standard of 8/35, the avoided premature mortality would be 9,200 adults, with

an annual monetized benefit ranging from $41 billion to $95 billion, and for the alternative

standard of 10/30, the avoided premature mortality would be 1,900 adults, with an annual

monetized benefit ranging from $8.6 billion to $20 billion.60

In the RIA, EPA also estimated the annualized control costs attributable to applying hypothetical

national control strategies for more stringent annual PM2.5 standards. The RIA estimates that the

2032 annualized control costs for the proposed annual standard of 9/35 would be $393.3 million,

and for the proposed annual standard of 10/35 it would be $94.5 million. For the alternative

annual standard of 8/35, the 2032 annualized control costs would be $1.8 billion, and for the

alternative standard of 10/30, it would be $257.2 million.61

Possible Impacts of a Lower Annual PM2.5 NAAQS

Air agencies input monitoring data into the AQS and certify the data on an annual basis.

Certification of air monitoring data and accompanying reports are due to EPA May 1 of each

year.62 If the proposed revision is finalized, the designation process will not be based on past or

57 EPA develops Regulatory Impact Analyses (RIAs) to support the development of national air pollution regulations.

RIAs contain descriptions of the potential social benefits and social costs of a regulation, including those that cannot be

quantified in monetary terms and a determination of the potential net benefits of the rule, including an evaluation of the

effects that are not monetarily quantified. For more information on EPA RIAs, see EPA, “Regulatory Impact Analyses

for Air Pollution Regulations,” at https://www.epa.gov/economic-and-cost-analysis-air-pollution-regulations/

regulatory-impact-analyses-air-pollution.

58 EPA, “Regulatory Impact Analysis for the Proposed Reconsideration of the National Ambient Air Quality Standards

for Particulate Matter,” at https://www.epa.gov/system/files/documents/2023-01/naaqs-pm_ria_proposed_2022-12.pdf.

59

The NAAQS RIAs hypothesize the control strategies that states may choose to enact when implementing a revised

NAAQS; individual states will formulate air quality management plans whose mix of emissions controls may differ

substantially from those simulated in an RIA. Hence, NAAQS RIAs are illustrative.

60 Table 5-5 of the RIA for the Proposed Reconsideration of the National Ambient Air Quality Standards for Particulate

Matter includes the avoided mortality and avoided morbidity for the proposed and alternative PM NAAQS. The

estimated monetized benefits are summarized in Tables 5-8 and 5-9; see https://www.epa.gov/system/files/documents/

2023-01/naaqs-pm_ria_proposed_2022-12.pdf.

61 Chapter 4 of the RIA for the Proposed Reconsideration of the National Ambient Air Quality Standards for Particulate

Matter includes the engineering cost analyses with the annual control costs summarized in Tables 4-1 through 4-5; see

https://www.epa.gov/system/files/documents/2023-01/naaqs-pm_ria_proposed_2022-12.pdf.

62 For more information on air monitoring data and the certification process see EPA, “Questions and Answers on

Ambient Air Monitoring Data Certification for CY2022 Data,” at https://www.epa.gov/system/files/documents/202212/Ambient%20Air%20Monitoring%20Data%20Certification%20QA%20for%20CY2022%20FINAL.pdf.

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current monitoring data; rather, the process will partly use monitoring data that either have not yet

been certified or have not yet been collected. EPA estimates that the data likely to be used for the

designation process will be 2021-2024 monitoring data.

For the current existing PM2.5 NAAQS (1997, 2006, and 2012 standards), several areas remain

nonattainment. Figure 1 illustrates the areas that are nonattainment for one or more of the current

PM2.5 standards.

Figure 1. Areas Currently (2023) Designated Nonattainment for a PM2.5 Standard

(existing PM2.5 include the 1997, 2006, and 2012 standards)

Source: U.S. Environmental Protection Agency (EPA), Green Book Area Maps for Counties Designated

Nonattainment for PM-2.5 (1997), PM-2.5 (2006), and/or PM-2.5 (2012), at https://www3.epa.gov/airquality/

greenbook/mappm25both.html.

Notes: Nonattainment areas are indicated by color and current as of July 31, 2023. When only a portion of a

county is shown in color, it indicates that only part of the county is within a nonattainment area boundary.

Hawaii is not included, because there are no areas designated nonattainment in Hawaii.

Available complete county-level PM2.5 three-year design values (collected over 2019-2021) can

be used to identify the counties that could possibly be affected by a reconsidered PM2.5 annual

NAAQS.63 For example, Figure 2 illustrates the location of counties listed in Table B-1, which

63 A design value is a statistic that describes the air quality status of a given location relative to the level of the NAAQS

(as described in 40 C.F.R. Part 50). The PM2.5 design value is described in Appendix N of 40 C.F.R. Part 50.

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lists the counties that exceed the proposed PM2.5 standard of 9.0 μg/m3 based on their 2019-2021

design values.

These counties are highlighted for illustrative purposes only, and the figure is not intended to

project or predict the outcome of any forthcoming designation process. Future area designations

(attainment/nonattainment) will not be based on these data, but likely on monitoring data

collected between 2021 and 2024.

Figure 2. Areas That Would Likely Not Meet the Proposed PM2.5 NAAQS

Based on Their 2019-2021 Design Values

Source: U.S. Environmental Protection Agency (EPA), Proposed Decision for the Reconsideration of the

National Ambient Air Quality Standards for Particulate Matter (PM), at https://www.epa.gov/system/files/

documents/2023-01/PM%20Maps%20-%202022%20proposal%20%282%29.pdf.

Notes: Map reflects monitored counties with complete monitoring data. Future area designations will not be

based on these data, but on future monitoring data. Of the 112 counties with 2019-2021 design values above 9.0

μg/m3, 24 counties are totally or partially contained in nonattainment areas for the current 2012 PM2.5 standards.

These counties are highlighted for illustrative purposes only, and the figure is not intended to project or predict

the outcome of any forthcoming designation process. Future area designations will not be based on these data,

but likely on monitoring data collected between 2021 and 2024.

Counties meeting the current standard likely would not meet a lowered standard, based on current

measurements. The number of counties not meeting a lowered standard would depend on the new

standard, with more stringent standards having a higher number of nonattainment counties. For

example, 88 counties meeting the current standard would not meet the proposed 9.0 μg/m3 level

based on their 2019-2021 PM2.5 design values.

EPA SIP Requirements and Implementation Rules

After EPA finalizes a new or revised NAAQS, Section 110(a)(1) of the CAA requires states to

submit new or revised SIPs that provide for implementation, maintenance, and enforcement of

that NAAQS. All states are required to submit SIPs that include the basic program requirements

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for managing air quality required in Section 110(a)(2) of the CAA showing that they have the

capacity to attain, maintain, and enforce the revisions associated with a new or revised NAAQS.64

These infrastructure SIP (iSIP) submissions must address several basic elements, including

•

•

•

•

ambient air quality monitoring and data systems,

programs for enforcement of control measures,

adequate authority and resources to implement the plan, and

prohibition of interstate pollution transport.

In the event EPA promulgates a new PM2.5 annual standard, revised iSIPs must also demonstrate

provisions adequate to ensure the states will not adversely affect other states’ ability to attain the

new NAAQS (known as the “good neighbor” provisions). EPA’s implementation rule describes

the requirements that states and tribes must meet in their implementation plans to achieve and

maintain attainment. EPA typically issues a revised implementation rule after promulgating a new

NAAQS.

Framework Used to Address the “Good Neighbor” Provisions

Section 110(a)(2)(D)(i) of the CAA contains elements that revised iSIPs must address. The first

two elements require each state in its iSIP to demonstrate adequate provisions for the ability to

prohibit air emissions within the state that (1) contribute significantly to another state’s

nonattainment of the NAAQS, or (2) interfere with another state’s maintenance of the NAAQS.65

These are often referred to as the good neighbor provisions.66

For the 2012 PM NAAQS, in March 2016, EPA issued a memorandum to provide guidance for

states and tribes as they developed their PM iSIPs and addressed the required good neighbor

provisions.67 The memorandum was based on EPA’s established framework previously used to

address the good neighbor provisions and provided modeled potential future year PM2.5 design

values for PM2.5 ambient monitors throughout the United States.68 The memorandum also

described how these projected potential design values could be used to help determine which air

quality monitors should be further evaluated to potentially address situations where emissions

from other states significantly contribute to nonattainment or interfere with maintenance of the

2012 PM2.5 NAAQS at those monitoring sites.

EPA has developed a four-step framework to address states’ good neighbor obligations. The four

steps include

1. identifying downwind areas with monitors that are expected to have problems

attaining or maintaining the NAAQS;

64 42 U.S.C. §7410.

65 40 C.F.R. §93.152. Maintenance area means any geographic region of the United States previously designated

nonattainment pursuant to the CAA Amendments of 1990 and subsequently redesignated to attainment subject to the

requirement to develop a maintenance plan under Section 175A of the CAA, as amended.

66 42 U.S.C. §7410(a)(2)(D)(i) also includes the provisions for the prevention of significant deterioration and protection

of visibility that must be included in the iSIP.

67 See EPA, “Information on the Interstate Transport ‘Good Neighbor’ Provision for the 2012 Fine Particulate Matter

National Ambient Air Quality Standards Under Clean Air Act Section 110(a)(2)(D)(i)(I),” memorandum, March 17,

2016, at https://www.epa.gov/sites/default/files/2016-08/documents/good-neighbor-memo_implementation.pdf.

68 Previous rulemakings applying this framework include the “Clean Air Interstate Rule Final Rule,” 70 Federal

Register 25162, May 12, 2005; and the “CSAPR Final Rule,” 76 Federal Register 48208, August 8, 2011. The

Supreme Court upheld CSAPR in EPA v. EME Homer City Generation, L.P., 572 U.S. 489 (2014).

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2. identifying which upwind states contribute to these identified problems in

amounts sufficient to warrant further review and analysis;

3. for states identified as contributing to downwind air quality problems, identifying

upwind emissions reductions necessary to prevent an upwind state from

significantly contributing to nonattainment or interfering with maintenance of the

NAAQS downwind; and

4. for states that are found to have emissions that significantly contribute to

nonattainment or interfere with maintenance of the NAAQS downwind, reducing

the identified upwind emissions through adoption of permanent and enforceable

measures.

For the 2012 PM2.5 NAAQS, EPA noted that “with support from the modeling…, most states will

be able to develop good neighbor SIPs that demonstrate that they do not contribute significantly

to nonattainment or interfere with maintenance of the 2012 PM2.5 NAAQS in any downwind

state.”69

Current PM NAAQS Requirements and Implementation Rule

EPA typically publishes an implementation rule that describes the requirements that states and

tribes must meet in their implementation plans to achieve and maintain attainment. The rule also

provides guidance and procedures for establishing controls to achieve and maintain attainment. In

addition, the implementation rule generally includes guidance for submitting a SIP when reaching

attainment within the required time frame is impractical. The implementation rule considers

existing (and often pending) federal regulations that contribute to controlling criteria pollutants

and their precursors.

The current PM implementation rule establishes planning requirements for states with areas that

do not meet the NAAQS for the PM2.5 standards. These states must develop plans that

demonstrate how they will meet the standards.70 Nonattainment areas are initially classified as

Moderate. See Appendix C for a list of the Moderate plan requirements. EPA is not proposing to

revise the PM2.5 Implementation Rule (i.e., 40 C.F.R. §51, Subpart Z) at this time.

If a Moderate nonattainment area fails to attain by the applicable date or the extension date, or if

EPA determines the area cannot practicably attain by that date, it is then likely reclassified as a

Serious nonattainment area. See Appendix C for a list of the Serious plan requirements.

If an area is reclassified from Moderate nonattainment to Serious nonattainment, its major

stationary source threshold, for sources subject to permitting and controls, is reduced from 100

tons per year (tpy) to 70 tpy.71 In addition, Moderate nonattainment areas require Reasonably

Available Control Measures and Technology (RACM/RACT) to be implemented as expeditiously

as possible. When an area is reclassified to Serious, in addition to the threshold being lowered,

the area implements Best Available Control Measures and Technology (BACM/BACT). BACM

is more stringent than RACM, and it may achieve greater reductions in PM2.5 and its precursor

pollutants than do the RACM control measures. Finally, if the state requests an extension for an

69 See Conclusion section on page 7 of EPA, “Information on the Interstate Transport ‘Good Neighbor’ Provision for

the 2012 Fine Particulate Matter National Ambient Air Quality Standards under Clean Air Act Section

110(a)(2)(D)(i)(I),” memorandum, March 17, 2016, at https://www.epa.gov/sites/default/files/2016-08/documents/

good-neighbor-memo_implementation.pdf.

70 The provisions for implementation of the PM

2.5 NAAQS are codified at 40 C.F.R. §51, Subpart Z.

71 A major stationary source is any stationary source of air pollutants that emits, or has the potential to emit, 100 tons

per year or more of any regulated NSR pollutant, unless a lower threshold applies. 40 U.S.C. §51.165(a)(1)(iv)(A).

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area’s Serious nonattainment date, it must demonstrate that the SIP for the area includes the Most

Stringent Measures (MSM). See Appendix C for further information on RACM, BACM, and

MSM.

The implementation rule identifies sulfur dioxide (SO2), oxides of nitrogen (NOx), volatile

organic compounds (VOC), and ammonia as PM2.5 precursors that may be addressed in

attainment planning and NNSR permitting. It also authorizes a state not to adopt control

requirements to reduce emissions of a particular PM2.5 precursor if the state adequately

demonstrates that the precursor does not contribute significantly to PM2.5 levels that exceed the

NAAQS in a PM2.5 nonattainment area.

Exceptional Events and the NAAQS

EPA’s NAAQS regulations rely on ambient air quality data. Section 319(a) authorizes the

establishment of a national ambient air quality network to provide data that EPA then uses in

developing NAAQS. Congress has recognized that some data collected through that network may

not be appropriate for consideration in developing the NAAQS. In 2005, Congress amended CAA

Section 319 to include the exceptional events provision.72 Section 319(b) defines an exceptional

event, directs the EPA Administrator to establish exceptional events regulations, and lists the

principles and requirements for establishing the exceptional events guidance. Section 319(b) also

authorizes EPA to exclude air monitoring data influenced by exceptional events when making

certain regulatory determinations, such as establishing area designations under a NAAQS.73

Exceptional events may include wildfires, prescribed fires, high-wind dust events, stratospheric

ozone intrusions, and volcanic and seismic activities. If a state wishes to have EPA exclude air

monitoring data, it must submit to EPA an “exceptional events demonstration,” which documents

how the exceptional event caused an exceedance of the NAAQS for any of the criteria

pollutants.74

The 2016 Exceptional Events Rule (40 C.F.R. §50.14(c)(3)) states that an exceptional event

demonstration must include the following elements:

•

•

•

•

a narrative conceptual model that describes the event(s) causing the exceedance

or violation and a discussion of how emissions from the event(s) led to the

exceedance or violation at the affected monitor(s);

a demonstration that the event affected air quality in such a way that there exists

a clear causal relationship between the specific event and the monitored

exceedance or violation;

analyses comparing the claimed event-influenced concentration(s) to

concentrations at the same monitoring site at other times (the EPA Administrator

shall not require a state to prove a specific percentile point in the distribution of

data);

a demonstration that the event was both not reasonably controllable and not

reasonably preventable;

72 EPA finalized a rule to govern the review and handling of air quality monitoring data influenced by exceptional

events in 2007; see 55 Federal Register 13560, March 22, 2007.

73 42 U.S.C. §7619(b)(3)(B) states regulations shall provide criteria and procedures for the governor of a state to

petition the EPA Administrator to exclude air quality monitoring data that is directly affected by an exceptional event

from use in determinations with respect to exceedances or violations of the NAAQS.

74 For more information, see CRS Insight IN12194, Wildfire Smoke and Air Quality, by James D. Werner.

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•

•

a demonstration that the event was caused by human activity that is unlikely to

recur at a particular location or was a natural event; and

documentation that the submitting air agency followed the public comment

process.

If the current annual PM2.5 NAAQS is revised, certain exceptional events, which would otherwise

not have regulatory significance, would require an exceptional events demonstration and

concurrence by EPA.75 In establishing area designations, EPA concurrence on an exceptional

events demonstration means the air quality data affected by the event will be excluded from the

NAAQS designation process.

Prescribed Fires and Wildfire Exceptional Events

In addition to the 2016 Exceptional Events Rule, EPA published 2019 exceptional events

guidance for prescribed fires on wildlands that may influence PM concentrations.76 In that

guidance, EPA explained when it is appropriate to develop an exceptional events demonstration

for prescribed fires. The air quality impacts of prescribed fires are often less severe than

uncontrolled wildfires, because prescribed fires are conducted under specific conditions on

specific days.77

75 The 2016 Exceptional Events Rule applies to several types of regulatory determinations made by the EPA

Administrator, as specified in 40 C.F.R. §50.14(a)(1). Among the determinations that would have regulatory

significance is an action to designate an area, pursuant to Clean Air Act Section 107(d)(1), or redesignate an area,

pursuant to Clean Air Act Section 107(d)(3), for a particular NAAQS.

76 EPA, “Exceptional Events Guidance for Prescribed Fires,” August 2019, at https://www.epa.gov/sites/default/files/

2019-08/documents/ee_prescribed_fire_final_guidance_-_august_2019.pdf.

77 For more information on prescribed fires, see CRS Report R40811, Wildfire Fuels and Fuel Reduction, by Katie

Hoover.

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Figure 3. Prescribed Fire Exceptional Events Process

Source: Congressional Research Service, based on data adapted from the U.S. Environmental Protection Agency

(EPA), “Exceptional Events Guidance for Prescribed Fires,” August 2019, at https://www.epa.gov/sites/default/files/

2019-08/documents/ee_prescribed_fire_final_guidance_-_august_2019.pdf.

Notes: FLM = Federal Land Manager. AQS = Air Quality System.

Figure 3 illustrates that the process begins if there is an exceedance or violation of the PM

NAAQS and a nearby prescribed fire. Because the PM2.5 NAAQS annual standard is an annual

average, air agencies and/or Federal Land Managers (FLMs) must track these prescribed burns

and determine if they had any regulatory significance.78 If the prescribed fire did not occur on

wildlands, the air agency consults with its EPA regional office to complete the exceptional events

78 16 U.S.C. §470bb. A Federal Land Manager (FLM) means, with respect to any public lands, the Secretary of the

department, or the head of any other agency or instrumentality of the United States, having primary management

authority over such lands.

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process.79 If prescribed burn is on wildlands, the air agency and/or FLM provide initial

notification to the EPA regional office and work collaboratively to determine the scope of the

exceptional event. This includes the relevant dates, monitors that have regulatory significance,

and EPA approvability considerations. Next, the air agency flags the data in AQS and completes

the demonstration in accordance with the exceptional events guidance. The demonstration is

submitted to EPA, and EPA responds either with an “on-hold letter” within 60 days or an initial

review within 120 days for demonstrations that are deemed to have regulatory significance. If

there is regulatory significance, EPA issues its decision on the demonstration within 12 months,

either concurring with the AQS flagged data or not concurring.

The need for an exceptional events demonstration is dependent on the time, duration, location,

and impact of the prescribed fire, in addition to the regulatory significance and the status of the

affected monitor(s). EPA has issued updates to its “Exceptional Events Rule: Frequently Asked

Questions” document,80 “Exceptional Events Guidance: Prescribed Fire on Wildland,”81 and its

“Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events.”82

Issues for Consideration

Because the health and economic consequences of PM standards are potentially significant, the

PM NAAQS are likely to remain an issue of interest during the 118th Congress.

Issues Regarding the PM NAAQS

EPA actions to establish or modify NAAQS have no direct impact on air pollution control or

costs. EPA is mandated to issue primary NAAQS based solely on scientific considerations

“allowing an adequate margin of safety…requisite to protect the public health.” Nonetheless, the

values established for NAAQS have a cascading series of indirect impacts, including

requirements and associated costs for pollution control equipment, State Implementation Plans,

individual facility and emissions unit permits, and morbidity and mortality impacts resulting from

decreased ambient concentrations of certain air pollutants.

Analyses indicate a revised PM NAAQS could result in fewer adverse health effects among the

general population—particularly within sensitive populations such as children, asthmatics, and

the elderly—as well as improved welfare effects.83 However, concerns remain regarding the

associated compliance costs of a more stringent standard.

79 EPA has 10 regional offices, each of which is responsible for the execution of their programs within several states

and territories in their jurisdiction. See EPA, “Regional and Geographic Offices,” at https://www.epa.gov/aboutepa/

regional-and-geographic-offices.

80

See EPA, “2016 Revisions to the Exceptional Events Rule: Update to Frequently Asked Questions”, at

https://www.epa.gov/sites/default/files/2019

07/documents/updated_faqs_for_exceptional_events_final_2019_july_23.pdf.

81 See EPA, “Exceptional Events Guidance: Prescribed Fire on Wildland that May Influence Ozone and Particulate

Matter Concentrations,” at https://www.epa.gov/sites/default/files/2019-08/documents/ee_prescribed_fire_final_

guidance_ _august_2019.pdf.

82 See EPA, “Guidance on the Preparation of Exceptional Events Demonstrations for Wildfire Events that May

Influence Ozone Concentrations,” at https://www.epa.gov/sites/default/files/2018-10/documents/exceptional_events_

guidance_9-16-16_final.pdf.

83 See Section 3.3, “Health Effects Evidence,” in EPA’s final “Policy Assessment for the Reconsideration of the

National Ambient Air Quality Standards for Particulate Matter,” at https://www.epa.gov/system/files/documents/202205/Final%20Policy%20Assessment%20for%20the%20Reconsideration%20of%20the%20PM%20NAAQS_

May2022_0.pdf.

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The evolution and development of the PM NAAQS have been the subject of extensive

congressional oversight.84 EPA not performing timely review and revision of the NAAQS as

required under the CAA has also been an area of concern to some in Congress and others.

Commenters had a wide range of feedback on the proposed reconsideration of the PM2.5 NAAQS.

Some commenters called for the annual standard to remain unchanged, citing “harm to businesses

and workers up and down the supply chain.”85 Some commenters called for the annual standard to

be set at 11.0 μg/m3, arguing that “uncertainties remain in the current epidemiological

evidence.”86

Some commenters agreed with the proposal, stating that “a move to reduce the burden of fine

particulate matter pollution is a move towards justice.”87 Others called for the annual standard to

be set at the higher end of the proposed range of 9.0 to 10.0 μg/m3, stating that “our preference

for the 10 μg/m3 standard reflects the concerns expressed by CASAC members about the

scientific and technical bases for a more substantial reduction of the current 12 μg/m3 standard.

Our views also are influenced by the potential adverse job impacts of creating new or expanded

nonattainment areas under a standard of 8 or 9 μg/m3.”88

Some commenters noted that the proposed reconsideration is “neither stringent enough

to promote ... health and safety ... nor establish clean air,” arguing that the annual standard should

be set at 8.0 μg/m3 and the 24-hour standards should be no higher than 25.0 μg/m3.89 Similarly, a

coalition of 18 state attorneys general called for the annual standard to be set at 8.0 μg/m3 and the

24-hour standards to be in a range of 25.0 to 30.0 μg/m3.90 Some noted that if the EPA does not

lower the annual standard to 8.0 μg/m3 and the 24-hour standards to 25.0 μg/m3, then “the Agency

should at least lower the standard for communities of color and communities with low income,

84 U.S. Congress, Senate Committee on Environment and Public Works, The Science and Risk Assessment Behind the

EPA’s Proposed Revisions to the Particulate Matter Air Quality Standards, July 19, 2006; U.S. Congress, Senate

Committee on Environment and Public Works, Subcommittee on Clean Air, Climate Change, and Nuclear Safety,

EPA’s Proposed Revisions to the Particulate Matter Air Quality Standards, July 13, 2006; U.S. Congress, Senate

Committee on Environment and Public Works, Subcommittee on Clean Air, Climate Change, and Nuclear Safety,

Implementation of the Existing Particulate Matter and Ozone Air Quality Standards, November 10, 2005; and U.S.

Congress, House Energy and Commerce, Subcommittee on Energy and Power, The American Energy Initiative, Part

21: A Focus on the New Proposal by the Environmental Protection Agency To Tighten National Standards for Fine

Particulate Matter in the Ambient Air, June 28, 2012. See also Letter from 47 Members of the House of

Representatives to the U.S. EPA Administrator, November 21, 2012, at http://latta.house.gov/uploadedfiles/

2012_11_29_final_pm2_5_letter_signed_w_attchmt.pdf.

85 See Comment from Georgia State Representative Doug Stoner to Members of the Environmental Protection Agency

(EPA), March 29, 2023, at https://www.regulations.gov/comment/EPA-HQ-OAR-2015-0072-1958.

86 See Letter from the Alamo Area Council of Governments (AACOG) to the EPA Administrator Michael S. Regan,

February 22, 2023, at https://www.regulations.gov/comment/EPA-HQ-OAR-2015-0072-1891.

87

See Letter from Mass Comment Campaign sponsored by National Religious Partnership for the Environment to Mr.

Michael S. Regan, Administrator, March 23, 2023, at https://www.regulations.gov/comment/EPA-HQ-OAR-20150072-1921.

88 See Letter from Unions for Jobs & Environmental Progress (UJEP) to U.S. Environmental Protection Agency,

February 10, 2023, at https://www.regulations.gov/comment/EPA-HQ-OAR-2015-0072-1748.

89 See Letter from District of Columbia Department of Energy and Environment to U.S. Environmental Protection

Agency, March 29, 2023, at https://www.regulations.gov/comment/EPA-HQ-OAR-2015-0072-1995.

90 See Letter from the Attorneys General for the States of California, Connecticut, Delaware, Illinois, Maryland,

Massachusetts, Michigan, Minnesota, New Jersey, New York, Oregon, Pennsylvania, Rhode Island, Vermont,

Washington, and Wisconsin, the District of Columbia, and the City of New York on the EPA Administrator’s

Reconsideration of the National Ambient Air Quality Standards for Particulate Matter, March 28, 2023, at

https://oag.ca.gov/system/files/attachments/press-docs/2023-03-28%20AGO%20Coalition%20-%20PM%20

NAAQS%20Comment%20Letter.pdf.

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i.e., EJ communities.”91 Other commenters noted that the proposed standard “is too high to

protect health,” and, according to World Health Organization (WHO) guidelines, the annual PM2.5

NAAQS should be no more than 5.0 μg/m3.92

Changes to the NAAQS have historically triggered litigation alleging that the standards are too

stringent or not stringent enough, often resulting in delays in implementation. The agency’s final

designations of nonattainment areas and the proposed PM2.5 NAAQS are expected to generate

further interest and oversight.

Issues Regarding Exceptional Events

Persistent drought in some areas and changes to the timing, duration, and intensity of wildfire

seasons have occurred.93 The number of acres affected annually by wildfires, while variable,

generally has increased.94 This has raised concerns about the emissions from these fires affecting

air quality, and whether EPA air quality protection programs address these emissions effectively.

EPA’s implementation of the exceptional events provision has received criticism and attention

from some stakeholders. For example, states raised several concerns about implementation of the

rule, such as administrative burden on state agencies, consistency across EPA regions,

complexities of documenting evidence, and the clarity of requirements and definitions.95

Some in Congress and some state and local air agencies have expressed concern regarding the

resources expected to be needed for documenting exceptional events should EPA promulgate a

lower annual standard for PM2.5. If the PM2.5 NAAQS is lowered, more wildfires would qualify as

regulatorily significant and require exceptional event demonstrations. Some commenters noted

the following:

If the annual standard for PM2.5 is lowered to 10 μg/m3or lower, Maricopa County will

spend considerable resources documenting the effect of exceptional events on air quality,

to have those events excluded from regulatory consideration. In the past, it has cost tens of

thousands of dollars in staff time to complete a single demonstration that an exceedance

was caused by wildfire smoke, rather than inadequate local controls. Lowering the annual

standard will require more exceptional event demonstrations, resulting in a significant

increase in workload for the State of Arizona and Maricopa County, with no benefit to air

quality or public health. These resources would be better spent on local programs to reduce

PM2.5 concentrations and to protect human health when the area is impacted by wildfire

smoke and dust storms.96

91 See Draft Letter from the White House Environmental Justice Advisory Council to The Honorable Ms. Brenda

Mallory, Chair, The Council on Environmental Quality, June 15, 2023, at https://insideepa.com/sites/insideepa.com/

files/documents/2023/jun/epa2023_1106.pdf.

92 See Letter from District of Physicians for Social Responsibility (PSR) to U.S. Environmental Protection Agency,

March 15, 2023, at https://www.regulations.gov/comment/EPA-HQ-OAR-2015-0072-1935.

93 See CRS Report R43429, Federal Lands and Related Resources: Overview and Selected Issues for the 118th

Congress, coordinated by Katie Hoover.

94 See CRS In Focus IF10244, Wildfire Statistics, by Katie Hoover and Laura A. Hanson.

95 See comments from Arizona Department of Environmental Quality (ADEQ), Alabama Prescribed Fire Council

(ALPFC), Washington State Department of Ecology, Texas Commission on Environmental Quality (TCEQ), Nevada

Division of Environmental Protection (NDEP), Georgia Environmental Protection Division (EPD), and Virginia

Department of Environmental Quality (DEQ) to the Environmental Protection Agency, at https://www.regulations.gov/

document/EPA-HQ-OAR-2015-0229-0001/comment.

96 See Letter from the Maricopa County Air Quality Department (MCAQD) to U.S. Environmental Protection Agency,

“Re: Docket EPA-HQ-OAR-2015-0072, Proposed Rule, Reconsideration of the 2020 National Ambient Air Quality

Standards for Particulate Matter (88 Federal Register 5558, January 27, 2023),” March 8, 2023, at

https://www.regulations.gov/comment/EPA-HQ-OAR-2015-0072-1898.

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Some have also called for “expanding the EPA Exceptional Events Rule for prescribed fire” to

include a wider range of prescribed fires that are currently regulatorily significant under the

rule.97 Not all prescribed fire exceptional event demonstrations are deemed to have regulatory

significance. Some commenters noted the following:

Prescribed fire, which is being used more frequently with the aim of preventing or curbing

more dangerous fires, also poses PM2.5 problems in some areas. It is important that EPA’s

exceptional events rule and guidance be viewed through the lens of state and local air

agencies’ struggles and that a concerted collaborative initiative be undertaken right away

by EPA and state and local air agencies to identify and discuss issues of concern and

approaches for addressing them in a way that facilitates reasonable exceptional events

demonstrations and EPA approval of them and, at the same time, ensures protection of

public health.98

Some commenters noted that the proposed PM2.5 NAAQS would “impede the use of beneficial

fire in fire-dependent ecosystems, countering EPA’s own support, by limiting the number of

weather-appropriate days available to public, private, and tribal fire practitioners to implement

beneficial fire across the United States.”99 They note that a revised PM2.5 NAAQS could affect

and jeopardize the use of prescribed fires used to maintain tallgrass prairies in the Flint Hills of

Kansas and Oklahoma and prescribed fires in Idaho, Iowa, and Georgia where officials rely on

the PM2.5 NAAQS to decide prescribed burn days. They also note that the proposed PM2.5

NAAQS could “place undue burden upon fire practitioners and state air quality regulatory

agencies to submit technically demanding and expensive Exceptional Event Demonstrations.”100

Congress may wish to ask EPA to revisit the 2016 Exceptional Events Rule and subsequent

guidance documents to address process-based concerns regarding wildfire- and prescribed-firerelated exceptional events.

97 See Letter from the Georgia Prescribed Fire Council (GPFC) to the Honorable Michael S. Regan, Administrator,

March 27, 2023, at https://www.regulations.gov/comment/EPA-HQ-OAR-2015-0072-2086.

98 See Letter from the National Association of Clean Air Agencies (NACAA) to the U.S. Environmental Protection

Agency, March 28, 2023, at https://www.4cleanair.org/wp-content/uploads/NACAA_Comments-EPA_Proposed_PM_

NAAQS_Recon-032823-lh.pdf.

99 Beneficial fire is defined as prescribed fire, cultural burning practiced by Indigenous peoples and tribes, and managed

wildfire; see Letter from The Nature Conservancy (TNC) to the Honorable Michael Regan, Administrator, March 28,

2023, at https://www.regulations.gov/comment/EPA-HQ-OAR-2015-0072-2219.

100 See Letter from The Nature Conservancy (TNC) to the Honorable Michael Regan, Administrator, March 28, 2023,

at https://www.regulations.gov/comment/EPA-HQ-OAR-2015-0072-2219.

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Appendix A. PM NAAQS Chronology

Table A-1. Timeline of Particulate Matter (PM) National Ambient Air Quality

Standards (NAAQS)

History of the NAAQS for Particulate Matter, from 1971 to 2023

Year

1971b

Final

Rule/Decision

Primary/

Secondary

Indicator

Averaging

Time

Levela

36 Federal

Register 8186

April 30, 1971

Primaryc

TSPd

24-hour

260

Not to be exceeded

more than once per year

Annual

75

Annual geometric mean

24-hour

150

Not to be exceeded

more than once per year

Annual

60

Annual geometric mean

24-hour

150

Not to be exceeded

more than once per year

on average over a threeyear period

Annual

50

Annual arithmetic mean,

averaged over three

years

24-hour

65

98th percentile, averaged

over three years

Annual

15.0

Annual arithmetic mean,

averaged over three

yearsef

24-hour

150

Not to be exceeded

more than once per year

on average over a threeyear periodg

Annual

50

Annual arithmetic mean,

averaged over three

years

24-hour

35

98th percentile, averaged

over three yearsh

Annual

15.0

Annual arithmetic mean,

averaged over three

years

24-hour

150

Not to be exceeded

more than once per year

on average over a threeyear period

Annual

—

EPA revoked the annual

PM10 NAAQS

Annual

12.0

Annual arithmetic mean,

averaged over three

years

Secondary

1987

1997

52 Federal

Register 24634

July 1, 1987

62 Federal

Register 38652

July 18, 1997

Primary and

Secondary

Primary and

Secondary

TSP

PM10

PM2.5

PM10

2006

71 Federal

Register 61143

December 18,

2006

Primary and

Secondary

PM2.5

PM10

2012

78 Federal

Register 3085

Primary

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Year

Final

Rule/Decision

Primary/

Secondary

Averaging

Time

Levela

January 15, 2013

Secondary

Annual

15.0

Annual arithmetic mean,

averaged over three

years

Primary and

Secondary

24-hour

35

98th percentile, averaged

over three years

24-hour

150

Not to be exceeded

more than once per year

on average over a threeyear period

Primary and

Secondary

2020

2023i

Indicator

PM10

Form

Primary and secondary standards retained without revision

85 Federal Register 82684

December 18, 2020

88 Federal

Register 5558j

January 27, 2023

Primary

Annual

8.0 to

k

11.0

Annual arithmetic mean,

averaged over three

years

Secondary

Annual

15.0

Annual arithmetic mean,

averaged over three

years (proposed

unchanged)

Primary and

Secondary

24-hour

35

98th percentile, averaged

over three years

(proposed unchanged)

24-hour

150

Not to be exceeded

more than once per year

on average over a threeyear period (proposed

unchanged)

Primary and

Secondary

PM2.5

PM10

Source: CRS, based on data adapted from the U.S. Environmental Protection Agency, (EPA), “Timeline of Particulate

Matter (PM) National Ambient Air Quality Standards (NAAQS),” at https://www.epa.gov/pm-pollution/timelineparticulate-matter-pm-national-ambient-air-quality-standards-naaqs.

a.

Units of measure are micrograms per cubic meter of air, μg/m3.

b.

EPA set its first particulate matter standards in 1971. The first standards were based on total suspended

particulate matter (TSP). Monitors for TSP detected particles up to 45 micrometers (μm) in diameter.

State-specific smoke and soot regulations date as far back as the 1930s and helped inform EPA’s first

standard. For example, see Missouri Department of Natural Resources, “Missouri Skies Now and Then,” at

https://dnr.mo.gov/air/hows-air/missouri-skies-now-then.

Primary standards are those whose attainment and maintenance, “in the judgment of the [EPA] Administrator

... are requisite to protect the public health” with “an adequate margin of safety.” Secondary standards are

those necessary to protect public welfare, a broad term that includes visibility impairment as well as damage

to crops and vegetation, and effects on soil and nutrient cycling, water, wildlife, property, and building

materials, among other things (42 U.S.C. §7409).

TSP = total suspended particles.

c.

d.

e.

The level of the annual standard is defined to one decimal place (i.e., 15.0 μg/m3) as determined by

rounding. For example, a three-year average annual mean of 15.04 μg/m3 would round to 15.0 μg/m3 and

thus meet the annual standard, and a three-year average of 15.05 μg/m3 would round to 15.1 μg/m3 and

hence violate the annual standard (40 C.F.R. Part 50, Appendix N).

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f.

g.

h.

i.

j.

k.

The level of the standard was to be compared to measurements made at sites that represent “communitywide air quality” recording the highest level, or, if specific requirements were satisfied, to average

measurements from multiple community-wide air quality monitoring sites (“spatial averaging”).

Initially promulgated as 99th percentile, averaged over three years; when 1997 standards for PM10 were

vacated, the form of 1987 standards remained in place. See 69 Federal Register 45592, July 30, 2004.

The level of the 24-hour standard is defined as an integer (zero decimal places) as determined by rounding.

For example, a three-year average 98th percentile concentration of 35.49 μg/m3 would round to 35 μg/m3

and thus meet the 24-hour standard, and a three-year average of 35.50 μg/m3 would round to 36 μg/m3 and

hence violate the 24-hour standard (40 C.F.R. Part 50, Appendix N).

This is a proposed reconsideration of the 2020 PM NAAQS Final Action.

Proposed rule.

The proposed rule would lower the standard to a range between 9.0 and 10.0 μg/m3 while taking comment

on alternative annual standard levels from 8.0 μg/m3 to 11.0 μg/m3.

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Appendix B. PM Design Values

Table B-1 illustrates the counties that exceed the proposed PM2.5 standard of 9.0 μg/m3

based on their 2019-2021 design values.

Table B-1. Fine Particle Annual Design Values for Counties with Monitoring Data

(based on air quality data from 2019 to 2021)

State

County

2019-2021 Annual

Design Value

(μg/m3)a

Alabama

Jefferson

11.0

No

Alabama

Russell

9.3

No

Alaska

Fairbanks North Star

13.2

Yes

Arizona

Maricopa

9.8

No

Arizona

Santa Cruz

10.0

No

Arizona

Pinal

13.0

Yes

California

Butte

11.4

No

California

Colusa

10.4

No

California

Mendocino

9.2

No

California

Nevada

9.7

No

California

San Diego

9.6

No

California

Shasta

9.5

No

California

Siskiyou

10.5

No

California

Sutter

13.1c

No

California

Tehama

9.8

No

California

Contra Costa

9.3

Yes

California

Fresno

15.3

Yes

California

Imperial

11.0

Yes

California

Kern

17.8

Yes

California

Kings

15.9

Yes

California

Los Angeles

13.0

Yes

California

Madera

13.0

Yes

California

Merced

11.9

Yes

California

Orange

11.1

Yes

California

Placer

10.4

Yes

California

Plumas

16.5

Yes

California

Riverside

13.9

Yes

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State

County

2019-2021 Annual

Design Value

(μg/m3)a

California

Sacramento

11.1

Yes

California

San Bernardino

14.2

Yes

California

San Joaquin

11.8

Yes

California

Santa Clara

10.3

Yes

California

Solano

9.7

Yes

California

Stanislaus

13.0

Yes

California

Tulare

17.8

Yes

Colorado

Denver

10.2

No

Colorado

Weld

9.5

No

Florida

Broward

9.2

No

Florida

Escambia

9.2

No

Georgia

Chatham

9.3

No

Georgia

Clarke

9.4

No

Georgia

Dougherty

9.5

No

Georgia

Fulton

9.6

No

Georgia

Houston

9.4

No

Georgia

Richmond

11.1

No

Georgia

Washington

9.2

No

Idaho

Benewah

10.2

No

Idaho

Lemhi

9.8

No

Idaho

Shoshone

10.6

No

Illinois

Cook

10.4

No

Illinois

Macon

9.4

No

Illinois

Madison

10.2

No

Illinois

Saint Clair

9.7

No

Illinois

Will

9.9

No

Indiana

Hamilton

9.8

No

Indiana

Lake

9.7

No

Indiana

Marion

12.0

No

Indiana

St. Joseph

9.2

No

Indiana

Vanderburgh

9.1

No

Indiana

Vigo

9.1

No

Kansas

Neosho

9.3

No

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Air Quality: EPA’s 2023 Proposed Changes to the Particulate Matter (PM) Standard

State

County

2019-2021 Annual

Design Value

(μg/m3)a

Kansas

Sumner

9.2

No

Kentucky

Jefferson

10.5

No

Kentucky

McCracken

9.2

No

Louisiana

Caddo

9.9

No

Michigan

Wayne

11.5

No

Mississippi

Forrest

9.4

No

Mississippi

Harrison

9.2

No

Mississippi

Hinds

10.1

No

Missouri

St. Louis City

9.2

No

Montana

Lincoln

13.3

No

Montana

Missoula

9.3

No

Nevada

Clark

10.0

No

Nevada

Washoe

9.7

No

New Jersey

Camden

9.4

No

New Mexico

Bernalillo

9.1

No

North Carolina

Mecklenburg

9.1

No

Ohio

Cuyahoga

9.5

No

Ohio

Franklin

9.1

No

Ohio

Hamilton

11.0

No

Ohio

Montgomery

9.6

No

Ohio

Stark

9.5

No

Oklahoma

Cleveland

10.3

No

Oklahoma

Kay

9.7

No

Oklahoma

Oklahoma

10.1

No

Oklahoma

Tulsa

9.1

No

Oregon

Crook

10.4

No

Oregon

Harney

11.1

No

Oregon

Jackson

13.0

No

Oregon

Josephine

11.3

No

Oregon

Lane

11.1

No

Oregon

Klamath

16.2

Yes

Pennsylvania

Cambria

9.2

No

Pennsylvania

Dauphin

9.5

No

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State

County

2019-2021 Annual

Design Value

(μg/m3)a

Pennsylvania

Lancaster

9.5

No

Pennsylvania

York

9.6

No

Pennsylvania

Allegheny

11.2

Yes

Tennessee

Davidson

9.1

No

Tennessee

Knox

9.1

No

Texas

Bowie

9.6

No

Texas

Cameron

9.7

No

Texas

Dallas

9.1

No

Texas

Harris

11.1

No

Texas

Hidalgo

10.6

No

Texas

Tarrant

9.2

No

Texas

Travis

9.5

No

Texas

Webb

10.4

No

Utah

Salt Lake

9.9

Yes

Washington

Okanogan

12.4

No

Washington

Yakima

11.8

No

West Virginia

Brooke

9.1

No

West Virginia

Marshall

9.3

No

Wisconsin

Waukesha

9.4

No

Currently in a PM2.5

Nonattainment

Areab

Source: CRS, based on data adapted from the U.S. Environmental Protection Agency (EPA), “Fine Particle

Concentrations for Counties with Monitors Based on Air Quality Data from 2019 – 2021,” at

https://www.epa.gov/system/files/documents/2023-01/

Fine%20Particle%20Concentrations%20for%20Counties%20with%20Monitors.pdf.

Notes: Bold typeface represents areas that would not meet a proposed annual primary fine particle (PM2.5)

standard of 10.0 μg/m3; nonbold typeface represents areas that would not meet a proposed annual primary fine

particle (PM2.5) standard of 9.0 μg/m3. This information is provided for illustrative purposes only and is not

intended to project or predict the outcome of any forthcoming designation process. Future area designations will

not be based on these data, but likely on monitoring data collected between 2021 and 2024.

a. Design values included for counties with monitors and with complete design value data. The design values

shown here are computed using Federal Reference Method or equivalent data reported by state, tribal, and

local monitoring agencies to EPA’s Air Quality System (AQS) as of May 24, 2022. Federal Reference Methods

are methods developed and evaluated by EPA for accurately and reliably measuring these pollutants in

outdoor air. Concentrations flagged by state, tribal, or local monitoring agencies as having been affected by

an exceptional event (e.g., wildfire, volcanic eruption) and concurred by the associated EPA Regional Office

are not included in these calculations.

b. The design value is the annual mean concentration, averaged over three consecutive years. The design value

listed for each area is the highest annual mean concentration among monitors with valid design values that

meet the completeness requirements in accordance with 40 C.F.R. Part 50 Appendix N. Current PM2.5

nonattainment areas are those that were designated as violating a promulgated PM2.5 NAAQS.

c. Counties that have areas that exceed the PM2.5 NAAQS are not automatically assumed to be

nonattainment. In the event an area violates the NAAQS after initial designation as attainment or

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redesignation, the area is not immediately subject to redesignation back to nonattainment. For more

information, see EPA, “Regional Consistency for the Administrative Requirements of State Implementation

Plan Submittals,” at https://www3.epa.gov/ttn/naaqs/aqmguide/collection/cp2/

20110406_mccabe_regional_consistancy_admin_requirements.pdf.

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Appendix C. PM Implementation Rule

Requirements

For any area designated as nonattainment and initially classified as Moderate for a PM2.5

NAAQS, the state(s) shall submit a Moderate area attainment plan that meets all the following

requirements:

•

•

•

•

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base year emissions inventory requirements;101

attainment projected emissions inventory requirements;102

Moderate area attainment plan control strategy requirements;103

attainment demonstration and modeling requirements;104

reasonable further progress (RFP) requirements;105

quantitative milestone reporting;106

contingency measure requirements;107 and

nonattainment new source review plan requirements.108

When designated, each PM 2.5 nonattainment area is initially classified as Moderate. The area

submits its Moderate area attainment plan to EPA no later than 18 months from the effective date

of designation of the area. The Moderate area attainment plan control strategy includes the

implementation schedule of reasonably available control measures/reasonably available control

technology (RACM/RACT). RACM is any technologically and economically feasible measure

that can be implemented in whole or in part within four years after the effective date of

designation of a PM2.5 nonattainment area and that achieves permanent and enforceable

reductions in direct PM2.5 emissions and/or PM2.5 plan precursor emissions from sources in the

area. RACM includes RACT.

Each state in which all or part of a Serious nonattainment area is located shall submit an

implementation plan for that area that includes each of the following:

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base year emissions inventory requirements;109

attainment projected emissions inventory requirements;110

Serious area attainment plan control strategy requirements;111

attainment demonstration and modeling requirements;112

101 Set forth at 40 C.F.R. §51.1008(a)(1).

102

Set forth at 40 C.F.R. §51.1008(a)(2).

103 Set forth at 40 C.F.R. §51.1009, “Moderate area attainment plan control strategy requirements.”

104 Set forth at 40 C.F.R. §51.1011, “Attainment demonstration and modeling requirements.”

105 Set forth at 40 C.F.R. §51.1012, “Reasonable further progress (RFP) requirements.”

106 Set forth at 40 C.F.R. §51.1013, “Quantitative milestone requirements.”

107 Set forth at 40 C.F.R. §51.1014, “Contingency measure requirements.”

108 Pursuant to 40 C.F.R. §51.165, “Permit requirements.”

109 Set forth at 40 C.F.R. §51.1008(b)(1).

110 Set forth at 40 C.F.R. §51.1008(b)(2).

111 Set forth at 40 C.F.R. §51.1010, “Serious area attainment plan control strategy requirements.”

112 Set forth at 40 C.F.R. §51.1011, “Attainment demonstration and modeling requirements.”

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Air Quality: EPA’s 2023 Proposed Changes to the Particulate Matter (PM) Standard

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RFP requirements;113

quantitative milestone reporting;114

contingency measure requirements;115 and

nonattainment new source review plan requirements.116

Serious area attainment plan control strategies include provisions to assure that best available

control measures/best available control technology (BACM/BACT) shall be implemented no later

than four years after the date the area is reclassified as a Serious nonattainment area. BACM is

any technologically and economically feasible control measure that can be implemented in whole

or in part within four years after the date of reclassification of a Moderate PM2.5 nonattainment

area to Serious and that generally can achieve greater permanent and enforceable emissions

reductions in direct PM2.5 emissions and/or emissions of PM2.5 plan precursors from sources in

the area than can be achieved through the implementation of RACM on the same source(s).

BACM includes BACT.

If the state requests an extension of an area’s Serious nonattainment date, it must demonstrate that

the SIP for the area includes the most stringent measures (MSM). MSM is any permanent and

enforceable control measure that achieves the most stringent emissions reductions in direct PM2.5

emissions and/or emissions of PM2.5 plan precursors from among those control measures that are

either included in the SIP for any other NAAQS, or have been achieved in practice in any state,

and that can feasibly be implemented in the relevant PM2.5 NAAQS nonattainment area.

Author Information

Omar M. Hammad

Analyst in Environmental Policy

Disclaimer

This document was prepared by the Congressional Research Service (CRS). CRS serves as nonpartisan

shared staff to congressional committees and Members of Congress. It operates solely at the behest of and

under the direction of Congress. Information in a CRS Report should not be relied upon for purposes other

than public understanding of information that has been provided by CRS to Members of Congress in

connection with CRS’s institutional role. CRS Reports, as a work of the United States Government, are not

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its entirety without permission from CRS. However, as a CRS Report may include copyrighted images or

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113 Set forth at 40 C.F.R. §51.1012, “Reasonable further progress (RFP) requirements.”

114 Set forth at 40 C.F.R. §51.1013, “Quantitative milestone requirements.”

115 Set forth at 40 C.F.R. §51.1014, “Contingency measure requirements.”

116 Pursuant to 40 C.F.R. §51.165, “Permit requirements.”

Congressional Research Service

R47652 · VERSION 1 · NEW

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