Particulate Matter Air Quality Standards: Background and Current Developments

CRS Report for Congress
Particulate Matter Air Quality Standards:
Updated January 10, 2005
Robert Esworthy
Specialist in Environmental Policy
Resources, Science, and Industry Division

Congressional Research Service ˜ The Library of Congress

Particulate Matter Air Quality Standards: Background
The Environmental Protection Agency (EPA) is nearing completion of its
review of contentious air quality standards for particulate matter (PM), with final
action expected in late 2005. The current standards are among the most far-reaching
regulations on EPA’s agenda. Promulgated in 1997, but only now being
implemented, the standards could potentially prevent the loss of thousands of lives
annually at an annual cost estimated by the agency to be $8.6 billion.
The Clean Air Act (CAA, Sections 108 and 109) requires that air quality criteria
used in determining National Ambient Air Quality Standards (NAAQS) reflect the
latest scientific information. The act includes provisions for the periodic review and
revision, as appropriate, of existing criteria and standards. It is this periodic review
process that is nearing completion. In October 2004, EPA released Air Quality
Criteria for Particulate Matter, reflecting the agency’s synthesis of relevant PM
research conducted since the agency’s last review, completed in 1996. This report,
referred to as a “criteria document,” will provide the scientific basis for assessments
and policy decisions regarding the adequacy of the current PM NAAQS. Further
decisions, including recommendations regarding the standards, are expected early in

2005, following the release of what is referred to as a “staff paper.”

Meanwhile, EPA is continuing implementation of the 1997 particulate matter
standards, which had been delayed several years by litigation and other factors. On
January 5, 2005, EPA published the final designations of geographical areas for the
fine particulate matter or “PM2.5” (particles less than 2.5 micrometers in diameter)
NAAQS. EPA designated 225 counties in 20 states, and the District of Columbia,
as “nonattainment areas”; those areas with (or contributing to) air quality levels
exceeding the annual and 24-hour PM2.5 standards.
Congress and a wide variety of stakeholders have closely followed the evolution
and development of PM NAAQS. In 1997, when the current standards were
promulgated, Congress held 28 days of hearings on the EPA rule. Subsequently,
more than 100 plaintiffs sued to overturn the standards. This litigation went to the
Supreme Court before being resolved, largely in EPA’s favor, in February 2001.
Since FY1998, in an effort to expedite research and strengthen the science
underlying EPA’s review of the standards, Congress has appropriated funding
specifically for PM research annually ($62 million for FY2005). The research,
including re-analysis of key studies underlying the 1997 standards, has largely
confirmed EPA’s earlier conclusions, although new questions have been raised
regarding the methodology used in some of the studies. The National Academy of
Sciences (NAS) has issued four reports on the state of PM research at EPA, and EPA
released a report reviewing its five-year progress of PM research.
Because of the potential impacts particulate matter standards could have on both
public health and the economy, EPA’s reassessment of the PM standards will likely
be of continued interest to Congress. This report will be updated as events warrant.

In troduction ..................................................1
Recent Developments..........................................2
Review of Particulate Matter Scientific Data....................2
Implementation of Current (1997) PM NAAQS..................2
Overview ....................................................3
Process for Setting National Ambient Air Quality Standards............4
History of Particulate Matter Standards.............................6
1997 Ozone NAAQS.......................................8
Legal Challenges to the 1997 PM NAAQS..........................9
Court of Appeals..........................................9
Supreme Court...........................................11
On Remand to the Court of Appeals..........................11
Health Effects of Particulate Matter...............................12
Science Behind the 1997 PM NAAQS........................12
Particulate Matter Scientific Knowledge Since 1997.................14
Increased Particulate Matter Research Funding..................14
National Academy of Science (NAS) Particulate Matter
Research Priorities....................................15
HEI-Sponsored National Morbidity Mortality and
Air Pollution Studies..................................17
Re-analyses of Selected Time-Series Studies...................20
Status of EPA’s Review of the 1997 PM NAAQS...................20
Schedule ................................................21
2004 Particulate Matter Criteria Document.....................21
EPA Particulate Matter Staff Paper...........................23
Opposing Views, Potential Challenges and Litigation............24
Implementation of the 1997 PM NAAQS..........................26
PM2.5 Monitoring Network..................................26
PM2.5 Attainment/Nonattainment Geographical Designation........27
Other Activities Impacting PM NAAQS Implementation..............28
Current CAA Regulation...................................28
Proposed Regulations and Legislation.........................29
California Particulate Matter Standards........................29
International Particulate Matter Standards......................30
Conclusions .................................................32
List of Tables
Table 1. Changes to Particulate Matter National Ambient
Air Quality Standards (NAAQS)..................................7
Table 2. Research Priorities for Particulate Matter Identified by
the National Academy of Sciences...............................16
Table 3. California’s State Particulate Matter Standards and
the 1997 National Primary Particulate Matter Standards...............30
Table 4. PM10 and PM2.5 Air Quality Standard Comparison of
United States and Selected Countries.............................31

Particulate Matter Air Quality Standards:
Under the Clean Air Act (CAA), EPA is responsible for protecting public health
and the environment from emissions that pollute ambient, or outdoor, air. Under
Sections 108-109 of the CAA, Congress mandated that EPA set national ambient air
quality standards (NAAQS) for pollutants whose emissions “may reasonably be
anticipated to endanger public health or welfare” and “the presence of which in the
ambient air results from numerous or diverse mobile or stationary sources” (42
U.S.C. 7408(a)(1)).
EPA has identified and promulgated NAAQS for six principal pollutants
classified by the agency as “criteria pollutants”: particulate matter (PM), ozone (O3,
a key measure of smog), nitrogen dioxide (NO2, or, inclusively, nitrogen oxides,1
NOx), sulfur oxides (SOx, or, specifically, SO2), carbon monoxide (CO), and lead
(Pb). Every five years, according to the statute (but less frequently in practice), EPA
is required to review the latest scientific studies and either reaffirm or modify the
NAAQS. The most recent changes, a strengthening of the particulate matter and
ozone standards, were promulgated jointly in 1997.
Since they were modified in 1997, the particulate matter standards (also referred
to as the PM NAAQS) issued by EPA,2 and the subsequent review to evaluate
whether to revise these standards again, have been the source of significant
controversy. The particulate matter standards have prompted a national debate
regarding how much scientific information is necessary before a regulation can be put
in place, and the appropriate levels of health protection. Congress has been especially
interested in EPA’s promulgation of these CAA standards and has held numerous
hearings on particulate matter.
As required by the CAA, EPA has been reviewing the current particulate matter
standards. The agency recently finalized its review of the scientific research
completed since 1996 and is expected to complete its determination of whether to
increase or decrease the stringency of the standard, or reaffirm the current standards,
by late 2005 or early 2006.

1 The NAAQS is for NO2; nitrogen gases that are ozone precursors are referred to as NOx.
2 The original PM NAAQS were for “Total Suspended Particulates” (TSP). In 1987, the
standards focused on particles smaller than 10 microns (PM10). In 1997 EPA added
standards for “fine” particles smaller than 2.5 microns (PM2.5), for the first time. EPA also
revised the existing NAAQS for PM10 (61 Federal Register 38652-38896, December 13,

1996). See discussion later in this report.

This report is intended to assist the reader in understanding the history of the
particulate matter standards.3 Following a brief summary of recent developments
regarding the implementation and re-evaluation of the 1997 standards, the report
provides a broad overview of the standard-setting process, followed by a description
of revisions to earlier standards, legal challenges to the 1997 standard, and particulate
matter health effects research. EPA’s ongoing progress in reviewing the 1997
standard is then summarized. Other activities that potentially impact the
implementation and review of the particulate matter standards, such as other air
quality regulations and proposed legislation, are also discussed in this report.
Recent Developments
Review of Particulate Matter Scientific Data. In October 2004, EPA
released Air Quality Criteria for Particulate Matter. Referred to as a “criteria
document,” the report has undergone extensive peer review and comment, and
presents the results of the EPA’s review of numerous studies and related research
compiled since the agency completed its previous review in 1996. The information
in the report will serve as the scientific basis for further assessment by EPA technical
staff in developing options to be considered regarding policy decisions affecting the
adequacy of the current PM NAAQS promulgated in 1997. The ultimate
determination by the EPA Administrator of whether to change the existing PM
NAAQS is not expected until late 2005 or early 2006.
Implementation of Current (1997) PM NAAQS. EPA recently completed
the process for designating geographical areas as attainment or nonattainment with
respect to the current particulate matter air quality standard. The EPA Administrator
signed a final rule on December 17, 2004, designating of all or part of 225 counties4
in 20 states, as well as the District of Columbia, for nonattainment of the NAAQS for
fine particulalte matter or “PM2.5” (particles less than 2.5 micrometers (µm) in
diameter). The final rule was published in the Federal Register on January 5, 2005
(70 Fed. Reg. 944-1019), and goes into effect April 5, 2005 (90 days from the date
of publication).
Nonattainment designation begins a process in which states (and tribes) must
develop and adopt emission control programs sufficient to bring air quality into
compliance by an EPA-defined deadline. States are required to submit
“implementation” plans for how they will meet the PM2.5 NAAQS by early 2008, and
must be in compliance by 2010 unless they are granted a five-year extension. For a
more detailed discussion of the implementation of the 1997 PM NAAQS, and the
associated designation process, see CRS Report RL32431, Particulate Matter
(PM2.5): National Ambient Air Quality Standards (NAAQS) Implementation.

3 Given the historical nature of the report, portions of the discussion are unchanged from an
August 6, 2002, report under the same title, prepared by Anne L. Hardenberg, formerly of
the Congressional Research Service, Resources, Science, and Industry Division.
4 Includes 7 cities: Baltimore, MD; St. Louis, MO; Alexandria, VA; Fairfax, VA; Falls
Church, VA; Manassas, VA; and Manassas Park, VA.

Similar to the review that led to the establishment of the existing PM NAAQS
in 1997, EPA’s current review of the national particulate matter standards is expected
to be controversial. Both the health effects of particulate matter and the economic
effects associated with particulate matter control are potentially significant.
On the one hand, large concentrations of particulate matter have been known to
cause deaths, most infamously in London’s “Killer Fog,” which killed as many as
4,000 people in December 1952. Smaller concentrations of particulate matter have
also been linked to health effects, particularly for sensitive populations, such as
children, asthmatics, and the elderly. Stricter controls on particulate matter should
mean fewer health effects.
In issuing its 1997 NAAQS for particulate matter which included a standard for
fine particles (PM2.5) for the first time, EPA projected that attaining the new standard
for PM2.5 would annually reduce deaths in Los Angeles County by approximately 280
and reduce cases of respiratory symptoms by roughly 20,000.5 For Philadelphia
County, an area with relatively cleaner air, attaining the 1997 PM2.5 standard was
estimated to reduce deaths by 40 and cases of respiratory symptoms by 1,000 each
year.6 Overall, EPA estimated that partial attainment of the 1997 PM2.5 standard
would annually result in the avoidance of 3,300 to 15,600 incidences of premature
mortality nationwide.7
The 1997 PM NAAQS and the supporting scientific data generated significant
scrutiny and controversy, and were the subject of multiple lawsuits. Various
stakeholders disagreed on whether the standards were too strong or too weak.
Although the standards were upheld in litigation, EPA, Congress, the Clean Air
Scientific Advisory Committee mandated by the 1977 CAA Amendments, and other
scientific groups recognized the need to enhance the scientific basis for the PM
NAAQS. The resulting coordinated research effort has advanced the understanding
of the potential health effects associated with particulate matter, but critical
information gaps continue.
Achieving the PM NAAQS will entail costs. In particular, some of the areas
expected to be out of compliance with the 1997 PM2.5 standards have not previously
been designated nonattainment for any other NAAQS. Many large industries, such
as utilities, refineries, and the trucking industry, are concerned that they likely will
be affected by the necessary controls on particulate matter emissions to achieve
compliance. Stricter controls on particulate matter will likely mean more costs for

5 61 Federal Register 65651, December 13, 1996.
6 61 Federal Register 65651, December 13, 1996.
7 EPA, Regulatory Impact Analysis for the Particulate Matter and Ozone National Ambient
Air Quality Standards and Proposed Regional Haze Rule, July 1997, p. ES-18. Available
at [].

affected industries. EPA estimated the costs to partially attain the 1997 PM2.5 standard
by 2010 at $8.6 billion annually,8 while industry estimates were several times higher.
Another concern of areas facing nonattainment designation, particularly of local
businesses and governments, is that it will have potential negative impacts on an
area’s economic development. Nonattainment designation requires new major
sources of pollution to offset their pollution by equivalent, or greater, emission
reductions from existing sources, and requires highway and transit planners to
demonstrate that new projects “conform” to the area’s state implementation plans.
Although EPA has not analyzed the potential economic impact of designating areas
as nonattainment for particulate matter, a recent EPA analysis found that ozone
nonattainment designations had no net negative impact on those areas.9
Due to the significance of these issues, Congress is likely to remain interested
in the outcome of EPA’s ongoing implementation and review of the existing PM
Process for Setting National Ambient Air Quality Standards10
The first step in regulating criteria pollutants is the issuance of what is known
as a “criteria document.” This document must “accurately reflect the latest scientific
knowledge useful in indicating the kind and extent of all identifiable effects on public
health or welfare which may be expected from the presence of such pollutant in the
ambient air” (42 U.S.C. 7408(a)(2)). Included in this document is information on
“variable factors” that change public health effects, other types of pollutants that may
interact with the criteria pollutants to adversely affect public health, and “known or
anticipated adverse effects on welfare” (42 U.S.C. 7408(a)(2)(A-C)).
Subsequent to the preparation of the criteria document, EPA has inserted an
administrative step into the process known as the “staff paper.” The staff paper,
compiled by EPA technical staff, provides the Administrator with a report that
describes the policy implications of the criteria document and provides
recommendations based on these implications. Emphasis is placed on “identifying
those conclusions and uncertainties in the available scientific literature that the staff
believes should be considered in selecting particulate pollutant indicators, forms,
averaging times, and levels for the primary (health) and secondary (welfare)
standards” (EPA, Particulate Matter Staff Paper (1996), p. I-1).
Both the staff paper and the criteria document are reviewed by the Clean Air
Scientific Advisory Committee (CASAC). This committee, mandated under Section
109(d)(2)of the CAA, consists of seven outside experts who recommend revisions
to the documents and comment on the desirability of new standards, as appropriate.

8 EPA, Regulatory Impact Analysis, July 1997, Table 13-1.
9 U.S. EPA, Office of Air and Radiation, The Historical Record: Nonattainment Status and
Economic Growth, February 26, 2002.
10 For more information on the standard-setting process, see CRS Report 97-722 ENR, Air
Quality Standards: The Decisionmaking Process.

The CASAC creates a panel to review each NAAQS. Each panel consists of the
members of the CASAC plus consultant members to assure full coverage of the
expertise needed to assess fully the issues involved. The panel recommends
improvements and eventually, after further meetings that are open to the public and
reviews, signs off only when they are convinced that each of the two documents
accurately reflects the status of the science. The CASAC “closure letter” represents
panel members’ agreement that the criteria document and the staff paper provide an
adequate scientific basis for regulatory decision making.
With the release of the criteria document and the staff paper, EPA is to issue
proposed standards to control the criteria pollutant. These standards are known as
primary and secondary national ambient air quality standards (NAAQS). Primary
NAAQS are set at a level “requisite to protect the public health” with an “adequate
margin of safety” (42 U.S.C. 7409(b)(1)). Secondary NAAQS are set at a level
“requisite to protect the public welfare” (42 U.S.C. 7409(b)(2)).11 Secondary
standards are implemented in the same manner as primary NAAQS, with the key
difference that there is no federally enforceable specified deadline for attainment.
After EPA promulgates a nationwide standard for a criteria pollutant, the agency
is to designate geographical areas as in “attainment” or “nonattainment” with the
standards through a federal-states/tribes cooperative process. Areas are to be
identified as “nonattainment” when they violate or contribute to the violation of
National Ambient Air Quality Standards (NAAQS), or “attainment/unclassified”
when they meet the standard or the data are insufficient for making a determination
of compliance with the NAAQS. Nonattainment designation begins a process in
which states (and tribes) must develop and adopt emission control programs
sufficient to bring air quality into compliance by an EPA-defined deadline (statutory
for the primary standards).
Following designation of an area as nonattainment, the state where the area is
located must develop a State Implementation Plan (SIP) that demonstrates how
attainment with the NAAQS will be achieved, and submit it to the EPA within three
years of designation (Section 110 of the CAA). These plans must include, among
other items, emissions limitations, monitoring provisions, and enforcement programs
designed to achieve compliance with the standard, generally within a 10-year period.
Thus, under the statute, EPA sets only the nationwide standard for criteria pollutants;
the states are responsible for placing limits on emissions that contribute to criteria
pollution and for regulating entities emitting criteria pollutants. (If states fail to
develop an adequate implementation plan, EPA can impose one).
Reviews and updates of the criteria document are to take place at least every five
years and standards may be modified on the basis of new information identified and
evaluated during the update of the criteria document.

11 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” (42 U.S.C. 7602(h)).

History of Particulate Matter Standards
EPA set the 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 (:m) in diameter. There were two forms to the
primary standards: 24-hour (daily) average and annual geometric mean. The primary
standards were set at a 24-hour average not to exceed 260 micrograms of particulate
matter per cubic meter of air (:g/m3) more than once per year, and an annual
geometric mean of 75 :g/m3. The secondary standards were set only in the 24-hour
form at 150 :g/m3, not to be exceeded more than once per year.
EPA began revising the criteria document for the PM NAAQS in 1979. Three
draft criteria documents were prepared, comments were received, and several public
meetings were held. In 1984, EPA issued its final criteria document and proposed
changes to the 1971 standards. These changes were finalized in 1987. Because
research indicated that health effects were associated with smaller particles, the
indicator for particulate matter was changed from TSP to particles with a diameter
of 10 :m or less in 1987. These particles are generally denoted PM10. The form of the
annual standard was changed from annual geometric mean to annual arithmetic
mean.12 Primary NAAQS for PM10 were set at a 24-hour average of 150 :g/m3, with
no more than one expected exceedance averaged over three years, and an annual
arithmetic mean of 50 :g/m3 averaged over three years. Secondary NAAQS were set
at levels identical to primary NAAQS.
EPA’s announcement of the next round of revisions to the particulate matter
criteria document came in 1994. After drafts of both the criteria document and staff
paper were provided for public comment, EPA issued proposed changes to the 1987
standards in November 1996. During the comment period for the proposed changes,
EPA held four public hearings at locations across the nation, in addition to two
satellite broadcasts. EPA also developed a toll-free national hotline and an e-mail
address to facilitate participation by interested persons. EPA notes that it received
more than 14,000 calls and 4,000 e-mails in response to the proposed changes, with
a total of over 50,000 comments.
Final NAAQS from this second round of revisions were issued July 18, 1997,
as per a court order.13 In these new standards EPA added the indicator PM2.5, because
of new data showing significant public health effects from fine particles. This
indicator regulates particles with a diameter less than 2.5 :m, also known as “fine
particles.” EPA retained the PM10 indicator to regulate “coarse” particles.

12 According to EPA, the annual geometric mean was replaced because it was greatly
influenced by days of relatively clean air and de-emphasized the effects of short-term peak
concentrations. EPA indicated that the annual arithmetic mean did a better job of addressing
these problems. See 52 Federal Register 24640. July 1, 1987.
13 EPA was under a court order entered in American Lung Association v. Browner, CIV-93-

643-TUC-ACM (D. Ariz., October 6, 1994) to publish the final PM standards by July 19,


The form of the 24-hour standards was also changed in 1997. The previous
form was known as the “one-expected-exceedance” form; monitoring stations could
exceed the 24-hour PM NAAQS only once, averaged over three years. With the 1997
final rule, EPA changed to a concentration-based percentile form. This percentile
form indicates the percent of the time that a monitoring station can exceed the
standard. For instance, a 99th percentile 24-hour standard indicates that a monitoring
station can exceed the standard 1% of the time, or 3.65 days a year, if monitoring
occurs every day. The form of the annual standard remained the same in the 1997
Finally, EPA revised the levels of the PM NAAQS. The new PM2.5 indicator
was set at 65 :g/m3, based on a three-year average of the 98th percentile of 24-hour
PM2.5 concentrations, and at 15 :g/m3 for the annual arithmetic mean averaged over
three years. The levels of PM10 remained the same; however, the form of the PM10

24-hour standard was changed to be based on a three-year average of the 99th

percentile of 24-hour PM10 concentrations. By changing the form to a concentration-
based percentile, EPA allowed more exceedances than were previously permitted
under the 1987 standard. Thus, although the level of the PM10 standards was not
changed, the change in form had the effect of weakening the PM10 standard by
allowing more exceedances. Nonetheless, the new PM2.5 standards would require
additional controls. Secondary standards were set equal to these new primary
NAAQS. The changes to the PM NAAQS are summarized in Table 1.
Table 1. Changes to Particulate Matter
National Ambient Air Quality Standards (NAAQS)
IndicatorTotal SuspendedPM10PM10 and PM2.5
Particulate Matter
Form24-hour average (not24-hour average (1-24-hour average
to be exceeded moreexpected-exceedance,(concentration-based
than once per year)3-year average)percentile)
Annual geometricAnnual arithmeticAnnual arithmetic

24-hour260 :g/m3150 :g/m3PM10: 150 :g/m3 (99th

P rimary percentile) 3 th
NAAQSPM2.5: 65 :g/m (98
Annual 75 :g/m350 :g/m3PM10: 50 :g/m33
PrimaryPM2.5: 15 :g/m
Level of150 :g/m3 24-hourSame as primarySame as primary
Secondary standard
Source: Prepared by the Congressional Research Service.

As proposed, the new PM NAAQS generated significant controversy.14 Once
finalized, the standards were subject to lawsuits from a number of parties, some
seeking a stronger standard, others seeking a weaker standard.
1997 Ozone NAAQS.The final PM NAAQS were signed by the EPA
Administrator at the same time as new NAAQS for ground-level ozone, on July 16,
1997. The two NAAQS were jointly published on July 18, 1997 (62 Federal Register
38652-38896). Generally referred to as the 8-hour ozone standard, the new standard
for ground-level ozone requires a more stringent concentration limit (0.08 parts per
million vs. the previous 0.12), but it averages the ozone concentrations measured
over 8 hours rather than the previous 1 hour. (See CRS Report RL32345,
Implementation of EPA’s 8-Hour Ozone Standard.)
Ozone is not a pollutant that is directly emitted; rather it forms in the
atmosphere in the presence of sunlight, primarily as the result of reactions including
volatile organic compounds (VOCs). Nitrogen oxides (NOx) are considered PM2.5,
as well as ozone precursors. Thus, the emitters of NOx, such as various industrial
processes, motor vehicles, and other fuel combustion sources, will be subject to
controls for purposes of meeting two different NAAQS. In addition, many of the
areas designated nonattainment with respect to the 8-hour ozone standards are
expected to overlap with those designated nonattainment for the PM NAAQS. In its
PM2.5 guidance for geographical area designation, EPA recommended states consider
using the same boundaries for nonattainment for both PM2.5 and 8-hour ozone.
Implementation of the 8-hour ozone standard, which currently precedes the PM
NAAQS implementation, as well as challenges or other delays, will likely impact the
implementation, and potentially the review of the PM NAAQS. Following their joint
promulgation in 1997, both the ozone and the PM NAAQS were the subject of many
of the same challenges and litigation, including a Supreme Court decision in 2001
(see discussion later in this report).
On April 15, 2004, EPA designated areas in 32 states and the District of
Columbia (474 counties in all) as “nonattainment areas” for the new ozone air quality
standard (69 Federal Register 23857-23951). The EPA designations, and the new
implementation rule (69 Federal Register 23951-24000) that accompanied the
designations, have been challenged for being too lenient by several states and various
public interest groups, and too restrictive by industry groups. Since June of 2004,
several petitions for reconsideration15 have been submitted to EPA, and 17 challenges
have been filed in the U.S. Court of Appeals for the District of Columbia Circuit (as
of December 2004). Based on an unopposed motion filed by EPA November 24,
2004, the cases have been aligned by the issues into two consolidations (South Coast
Air Quality Management District v. EPA, No. 04-1200 (D.C. Cir. filed 6/25/04), and
Alcoa Inc. v. EPA, No. 04-1189 (D.C. Cir. filed 6/18/04)). The outcome of these

14 For more information on Congressional hearings related to the proposed standards and
issues related to implementation of the standard, see CRS Report 97-8 ENR, Air Quality:
Background Analysis of EPA’s 1997 Ozone and Particulate Matter Standards, pp. 27-31.
15 For information regarding the petitions for reconsideration see EPA’s Office of Air and
Radiation website at [].

challenges, and their potential impact on the PM NAAQS implementation and
review, may not be known for some time.
Legal Challenges to the 1997 PM NAAQS
Court of Appeals. On July 18, 1997, the day of promulgation for the final
PM NAAQS (and new 8-hour ozone standard), the American Trucking Associations
(ATA), together with five other groups, filed a suit against the EPA. Several other
groups also challenged EPA’s PM NAAQS in court, including states, industries,
small businesses, environmental groups, and private persons. In all, more than 100
petitioners challenged EPA’s PM NAAQS, including three states and over 60
utilities; six states filed briefs in support of EPA. These plaintiffs filed a total of 38
cases against EPA; the cases were consolidated by the U.S. Court of Appeals for the16
District of Columbia Circuit.
The plaintiffs advanced ten arguments against EPA’s 1997 revisions to the
particulate matter standards. Various plaintiffs claimed that EPA:
!Unconstitutionally interpreted §§ 108 and 109 of the CAA;
!Arbitrarily and capriciously chose PM10 as the coarse particle
!Must consider costs in setting NAAQS;
!Must consider the financial impact of complying with the NAAQS
on the Abandoned Mine Reclamation Fund;
!Must treat PM2.5 as a “new” pollutant and develop a separate criteria
!Must identify a biological mechanism through which particulate
matter causes health effects;
!Must set secondary PM NAAQS such that all visibility impairment
is eliminated;
!Failed to comply with relevant requirements of the National
Environmental Policy Act;
!Violated the Unfunded Mandates Reform Act in revising PM
NAAQS by not preparing an official Regulatory Impact Statement;
!Violated the Regulatory Flexibility Act, as amended by the Small
Business Regulatory Enforcement Fairness Act, in revising PM
NAAQS by not performing a regulatory flexibility analysis to
determine the impact of the NAAQS on small entities.
The Court of Appeals rejected the last eight claims of the petitioners. On the
first claim, the Court noted that EPA’s construction of the NAAQS section of the
CAA allowed the agency to set NAAQS at “any point between zero and a hair below

16 American Trucking Associations v. EPA, 175 F.3d 1027 (D.C. Cir. 1999). The challenges
to the PM standards were also consolidated with challenges made to EPA’s ozone standards
released the same day.

the concentrations yielding London’s Killer Fog.”17 The court ruled that the statutory
language was an unconstitutional delegation of legislative power. However, rather
than hold these sections of the CAA unconstitutional, the Court of Appeals decided
to “give the agency an opportunity to extract a determinate standard on its own.”18
In its decision, the Court of Appeals presented some options for the “intelligible
principle” EPA might use to develop a constitutional interpretation of the act.
As to the second claim, the Court of Appeals agreed that EPA’s use of PM10 as
the coarse particle indicator was arbitrary and capricious. PM10 includes all particles
smaller than 10 :m. Because EPA had also chosen PM2.5 as an indicator of fine
particulate matter, the choice of PM10 constituted a “double regulation” of PM2.5 and
an “underregulation” of PM10-2.5, that is, particles between 2.5 and 10 :m in
diameter.19 The Court of Appeals vacated the PM10 standard and directed EPA to
select a different indicator.
The challenge to the science behind the PM NAAQS — the claim that EPA had
to identify a biological mechanism — was unsuccessful before this court. The
petitioners had argued that EPA had to prove that particulate matter caused health
effects before issuing standards, and that there was no scientific basis to regulate
coarse particulate matter. Although the Court of Appeals found that EPA’s retention
of PM10 as an indicator was arbitrary and capricious, the court found “ample support
for EPA’s decision to regulate coarse particulate pollution above the 1987 levels.”20
The Court of Appeals’ decision was 2-1, with the dissenter arguing that Sections
108 and 109 did not effect an unconstitutional delegation of legislative power and
therefore did not violate the nondelegation doctrine.21 For invoking the nondelegation
doctrine, the decision was variously seen as “[giving] a warning to overzealous
regulators,”22 “[lobbing] a constitutional time bomb that potentially could have
governmentwide impact,”23 and as “[defying] 60 years of Supreme Court rulings.”24
EPA’s then-Administrator, Carol Browner, called the ruling “extreme, illogical, and

17 175 F.3d at 1037.
18 175 F.3d at 1038.
19 175 F.3d at 1054.
20 175 F.3d at 1054.
21 175 F.3d at 1057 (Tatel, dissenting).
22 Lieberman, Ben. “Clearing the Air on Regulatory Excess.” The Washington Times 19 May

1999: A16.

23 May, Randolph J. “D.C. Circuit Decision Draws Needed Spotlight to Nondelegation
Doctrine.” Legal Times 21 Jun. 1999: 20.
24 Lieberman, Joseph I. and Henry Waxman. “A New Arena for Attacks on Clean Air: The
Courts.” The Hartford Courant 10 Sept. 1999: A23.

bizarre.”25 In contrast, the U.S. Chamber of Commerce stated “this ruling strikes
right at the heart of EPA’s abuse of regulatory authority.”26
Supreme Court. EPA sought to have the Court of Appeals rehear the case,
but was denied. EPA then appealed the ruling to the Supreme Court. EPA sought the
Court’s opinion on whether the CAA impermissibly delegates legislative power to27
the agency. ATA and other groups also appealed the decision and asked the
Supreme Court to review the question of whether EPA must take the cost of the
standards into account when setting NAAQS. The Supreme Court consolidated the
cases and issued its decision on February 27, 2001.28
On the two principal issues (whether EPA was unconstitutionally exercising
legislative power, and whether costs should be considered in setting NAAQS), the
Supreme Court ruled in EPA’s favor. Justice Scalia wrote the unanimous opinion of
the Court, and some Justices added separate concurring opinions. The Court affirmed
the judgment of the Court of Appeals regarding cost consideration in setting
NAAQS: “the text of 109(b) ... unambiguously bars cost considerations from the
NAAQS-setting process.”29 The Court overturned the judgment of the Court of
Appeals regarding the nondelegation doctrine, stating “Section 109(b)(1) ... fits
comfortably within the scope of discretion permitted by our precedent.”30 The Court
stated that the provision contains an “intelligible principle” to guide the
Administrator in setting standards, and that is all that is constitutionally required.
On Remand to the Court of Appeals. In the original case, the petitioners
had raised other challenges to the standards that the Court of Appeals stated “cannot
be resolved until such time as EPA may develop a constitutional construction of the
act.”31 Because the Supreme Court subsequently ruled that Sections 108 and 109
were constitutional in respect to delegation, the Court remanded the case to the Court
of Appeals for consideration of petitioners’ arguments raised under CAA
§307(d)(9).32 The question facing the Court of Appeals was whether EPA reasonably
exercised its discretion under the CAA in establishing PM2.5 NAAQS (the PM10
standard was vacated in the earlier decision).33 The plaintiffs in this case advanced
nine arguments against EPA’s rulemaking. Various plaintiffs claimed that EPA:

25 Kennedy, James. “Court Decision on Ozone, PM Rules Called ‘Extreme, Illogical’ by
Browner.” Daily Environment Report 21 May 1999: AA-1.
26 Kennedy, James. “EPA Eyes Appeal of PM-Ozone Ruling, Says Ruling Supportive of
Science, Process.” Daily Environment Report 17 May 1999.
27 EPA also sought the Supreme Court’s opinion on two ozone questions unrelated to the PM
discussion in this report.
28 Whitman v. American Trucking Associations, 531 U.S. 457 (2001).
29 531 U.S. at 471.
30 531 U.S. at 476.
31 ATA v. EPA, 175 F.3d at 1034.
32 American Trucking Associations v. EPA, 283 F.3d 355 (D.C. Cir 2002).
33 283 F.3d at 363-364.

!Did not identify or apply any legal standard in setting NAAQS;
!Did not show the 1987 PM standards to be inadequate to protect
public health;
!Attributed adverse health effects to PM that are accounted for by
other factors, such as the presence of other pollutants, temperature,
and humidity;
!Conceded that NAAQS rely on questionable assumptions, such as
the existence of a “continuum of health risks”;
!Failed to justify the 24-hour standard;
!Did not present enough evidence in the rulemaking record to support
the level of the annual standard;
!Must obtain and publish underlying data from studies it uses in
!Should have set a stricter daily standard; and
!Set secondary standards that were inadequate to improve visibility.
The Court of Appeals rejected all these claims with the exception of the fifth claim
(failure to justify the 24-hour standard), which it declined to consider because the
claim was not raised in the original case.34 The effect of these cases has been to
demonstrate that EPA does have authority to promulgate NAAQS, that cost cannot
be considered in setting the NAAQS, that EPA’s revision of the PM NAAQS was not
arbitrary and capricious, and that stricter regulation of particulate matter was
supported by the record, although selection of PM10 as the coarse particle indicator
was arbitrary and capricious.
Health Effects of Particulate Matter
Science Behind the 1997 PM NAAQS. EPA began its review of the
relevant scientific literature in 1994 to determine what studies to include in the
criteria document. The studies selected were peer-reviewed, mainly by non-EPA
researchers. In researching particulate matter health effects, EPA reviewed more than

2,000 studies. In the criteria document, EPA noted, “recent studies [provide]

evidence that serious health effects (mortality, exacerbation of chronic disease,
increased hospital admissions, etc.) are associated with exposures to ambient levels
of particulate matter found in contemporary U.S. urban air sheds even at35
concentrations below current U.S. PM standards.”
The reviewed studies, taken as a whole, revealed significant health effects from
particulate matter. Health effects EPA found to be associated with particulate matter

34 283 F.3d at 358, 371.
35 EPA, Air Quality Criteria for Particulate Matter, April 1996, EPA/600/P-95-001aF. p.

13-1, at [].

!Premature mortality from short-term exposure (based on 38 analyses
and re-analyses of studies published between 1988 and 1996),36 and
long-term exposure (based on studies from the 1987 revision and 2
new studies);37
!Aggravation of respiratory and cardiovascular disease from short-
term exposure (based on 12 studies);38
!Changes in lung function and increased respiratory symptoms (based
on 26 short-term and 7 long-term studies);39
!Changes to lung tissues and structure (based on studies from the
1987 revision);40 and
!Altered respiratory defense mechanisms (based on studies from the

1987 revision).41

Of the epidemiological studies EPA reviewed, more than 80 of them addressed
particulate matter’s association with morbidity and mortality based on short-term
exposures. Of these 80, 60 studies found statistically significant associations between
increases in various indicators of particulate matter and increases in morbidity or
mortality.42 Many of these studies were based on PM10 or TSP, because of the lack
of data on PM2.5 concentrations.
Two studies aroused particular interest on the part of scientists, industry,
Congress, and the public. In one, researchers tracked more than 550,000 participants
from 1982-1989 in 154 U.S. cities.43 This study is known as the American Cancer
Society (ACS) Study.44 In the other, researchers tracked just over 8,100 adults for 14-
16 years in six U.S. cities beginning in the 1970s.45 This study is known as the Six
Cities Study.46 Because EPA relied particularly (although not solely) on these studies
in supporting its view that long-term exposure to fine particulate matter is associated

36 61 Federal Register 65642, December 13, 1996.
37 61 Federal Register 65642, December 13, 1996.
38 61 Federal Register 65643, December 13, 1996,
39 EPA, Criteria Document, April 1996, Tables 13-3, 4, 5.
40 61 Federal Register 65643, December 13, 1996.
41 61 Federal Register 65644, December 13, 1996.
42 61 Federal Register 65646, December 13, 1996.
43 Health Effects Institute, “Statement: Synopsis of the Particle Epidemiology Reanalysis
Project.” Reanalysis of the Harvard Six Cities Study and the American Cancer Society Study
of Particulate Air Pollution and Mortality, July 2000 (includes Nov. 1, 2001 errata sheet),
p. i. Available at [], viewed
November 21, 2004.
44 Pope, C. Arden, III, et al. “Particulate Air Pollution as a Predictor of Mortality in a
Prospective Study of U.S. Adults.” American Journal of Respiratory and Critical Care
Medicine 151 (1995): 669-674.
45 HEI July 2000, “Statement.” p. i.
46 Dockery, Douglas W. et al. “An Association Between Air Pollution and Mortality in Six
U.S. Cities.” New England Journal of Medicine 329 (1993): 1753-1759.

with mortality, many people wished to see the underlying data. The researchers who
did the studies were concerned that releasing the data would violate the privacy of the
studies’ subjects. To solve this dilemma, the researchers agreed to release their data
to the Health Effects Institute for re-analysis. The Health Effects Institute (HEI) was
begun in 1980 and is funded jointly by industry and EPA to supply “high-quality,
impartial, and relevant science on the health effects of pollutants from motor vehicles
and from other sources in the environment.”47
HEI created a nine-member Expert Panel to provide oversight for the project
and to select researchers to complete the re-analysis. This re-analysis team consisted
of 30 epidemiologists and biostatisticians. After the re-analysis team completed its
work, the research was peer-reviewed by a separate independent team of eight
experts. HEI completed its re-analysis of the two studies in 2000.
The re-analysis was divided into two sections. First, the researchers attempted
to replicate the results of the original studies. Then, researchers used different models
and variables to determine the sensitivity of the results — that is, whether results
would change when subjected to different approaches. In the first part of the project,
researchers were able to replicate the results of the two studies using the original data
and the same methods. In the second part, a number of sensitivity analyses were
conducted. On the whole, these analyses did not materially change the results of the
studies, although they did indicate the need for further research on particulate matter.
HEI’s conclusion was:
Overall, the Reanalysis assured the quality of the original data, replicated the
original results, and tested those results against alternative risk models and
analytic approaches without substantively altering the original finding of an48
association between indicators of particulate matter air pollution and mortality.
Particulate Matter Scientific Knowledge Since 1997
Increased Particulate Matter Research Funding. Congressional
recognition of the need for more research on health effects of particulate matter, and
the need to expedite research, led to an increased amount of funding directed toward
such study. The FY1998 appropriations for EPA (P.L. 105-65) included language
directing the National Academy of Sciences (NAS) to develop a research plan for
particulate matter that EPA was to follow. Additional money for such research was
appropriated above and beyond EPA’s general budget. This action by Congress,
based on consultation with EPA, NAS, and numerous scientific and research
stakeholder groups, was one result of the controversy regarding the 1997 PM
NAAQS. In particular, the Conference Report (H.Rept. 105-297) supporting the
FY1998 appropriations noted that any research conducted with this funding would
be available to the public, thus avoiding the controversy stemming from the ACS and
Six Cities studies.

47 Health Effects Institute. “What is the Health Effects Institute?” Available at
[], viewed November 19, 2004.
48 HEI,”Statement,” July 2000, pp. i-ii.

The FY1998 appropriation more than doubled the funding provided to EPA for
particulate matter research.49 Congress increased funding in subsequent years, nearly
tripling the funding in FY2001 compared to FY1997. Congress provided $65.5
million for particulate matter research in FY2002, $64.4 million in FY2003, and
$58.6 million in FY2004. The funding has supported numerous EPA intramural and
extramural particulate matter research projects, and the establishment of five
academically based particulate matter research centers around the country. The
conference report (H.Rept. 108-892) for the FY2005 Consolidated Appropriations
Act (P.L 108-447) includes $61.0 million for particulate matter research for FY2005.
National Academy of Science (NAS) Particulate Matter Research
Priorities. NAS established the Committee on Research Priorities for Airborne
Particulate Matter to fulfill the Congressional request. The committee has released
four reports50 pursuant to the legislation. The first report identified 10 priorities for
particulate matter research. A description of how the committee is monitoring
particulate matter research and revisions to the priorities were included in the second
report. The priorities, as revised, are listed in Table 2 presented on the next page.
The third report provided a review of EPA’s progress in particulate matter research
from 1998 to mid-2000. The committee’s fourth report, published March 24, 2004,
is a final review of progress and includes recommendations for future directions in
particulate matter research.
In the third report, the committee indicated that EPA had made some progress
in targeting research for the priorities in the period 1998 to mid-2000, but found that
other areas of particulate matter research were not proceeding as well. In the report,
the committee designated research under six of the priorities (2, 3, 4, 6, 7, and 8) as
either not proceeding as planned, not targeted toward the committee’s priorities, or
not yet adequate. The committee’s report noted that research for priorities 1, 5, 9, and
10 was proceeding satisfactorily. An April 2002 HEI paper came to a similar
conclusion. HEI indicated that current research is providing important information
under research priorities 5, 9, and 10. According to HEI, particulate matter research
has begun to determine what aspects of particles cause health effects, suggest what
biological mechanisms may be responsible for particulate matter’s reported health
impacts, and identify which groups are most susceptible.51

49 National Academy of Sciences, National Research Council, Committee on Research
Priorities for Airborne Particulate Matter, Research Priorities for Airborne Particulate
Matter: III. Early Research Progress. (Washington, D.C.: National Academy Press, 2000),
p. 2 (hereafter Research Priorities III).
50 The four reports are available from the National Academy of Sciences, National Research
Council, Committee on Research Priorities for Airborne Particulate Matter, Washington,
D.C., National Academy Press: Research Priorities for Airborne Particulate Matter: I.
Immediate Priorities and a Long-Range Research Portfolio (Report 1, 1998); Research
Priorities for Airborne Particulate Matter: II. Evaluating Research Progress and Updating
the Portfolio (Report 2, 1999); Research Priorities for Airborne Particulate Matter: III.
Early Research Progress (Report 3, 2000); Research Priorities for Airborne Particulate
Matter: IV. Continuing Research Progress (Report 4, 2004). See [].
51 Health Effects Institute, “Understanding the Health Effects of Components of the

Table 2. Research Priorities for Particulate Matter Identified by
the National Academy of Sciences
PriorityExample Research Question

1Outdoor Measures VersusActual Human ExposureHow is the concentration of PM measuredoutdoors related to personal PM exposure?

2Exposures of SusceptibleSubpopulationsWhat components of PM most affect the healthof particularly vulnerable people?

3Characterization ofEmissions SourcesWhat are the characteristics of PM emitted byprimary sources?

4Air-Quality ModelDevelopment and TestingHow are source emissions and ambient PMconcentrations related?

5Assessment of HazardousPM ComponentsWhat aspects of PM negatively affect health?

DosimetryIn vulnerable populations, where does PM
6deposit in the respiratory tract and where does it
ultimately end up?

7Combined Effects of PMand Other PollutantsHow can the effects of PM and the effects ofother pollutants be separated?

8Susceptible SubpopulationsWho is particularly vulnerable to PM?

9Mechanisms of InjuryHow does PM cause harm?

10Analysis and MeasurementHow do models and measurement errors affectrisk estimates?

Source: Table prepared by Congressional Research Service, based on pages 39-93 of NAS report.
National Academy of Sciences, National Research Council, Committee on Research Priorities for
Airborne Particulate Matter, Research Priorities for Airborne Particulate Matter: II. Evaluating
Research Progress and Updating the Portfolio (Washington, D.C.: National Academy Press, 1999).
In its fourth and final report released in March 2004, the NAS Committee on
Research Priorities for Airborne Particulate Matter described the overall progress on
several of the priority topics as “encouraging” and demonstrating that targeted
research can resolve some key uncertainties. However, the committee determined
that much remained to be done from the original research agenda.
The committee emphasized the characterization of emission sources (topic 3),
air quality model development and testing (topic 4), and assessment of particulate
matter hazardous components (topic 5). The need to advance the assessment of
particulate matter hazardous components was identified as a central component for
advancing several of the topic research areas, including developing targeted exposure
studies under topic 2, refining emission inventories and models under topics 3 and

51 (...continued)
Particulate Matter Mix: Progress and Next Steps,” HEI Perspectives: Insights from HEI’s
Research Programs, April 2002. Available at [

4, advancing research on biological mechanisms under topic 9, and identifying
susceptible subpopulations under topic 8. The committee identified the need for
further methodological research as evidenced by recent findings on the sensitivity of
time-series results to modeling approaches52 (see discussion in the next section of this
report). The final NAS report contained extensive discussion of progress (or lack of
progress) and recommendations for continuing under each topic area.
Research results under these topics reflect an expansion of the scope of health
concerns and the emergence of new challenges since the committee’s initial report
in 1998. The report highlighted seven challenges for the coming years that are
central to continuing the particulate matter research agenda:
!completing the particulate matter emission inventory and improving
air quality models necessary for NAAQS implementation;
!developing a systematic program for accessing toxicity of particulate
matter mixture components;
!enhancing air quality monitoring for research to serve multiple
!investigating the health effects of long-term exposure to air
!improving toxicological approaches;
!expanding beyond a particulate matter research program to a multi-
pollutant program;
!integrating research and collaboration across disciplines.
The conclusions in the committee’s fourth report parallel EPA’s own
assessment of the particulate matter research program as presented in the agency’s
report released in September 2004. Particulate Matter Research Program: Five
Years of Progress53 highlights the research funded under the program, provides an
update of what has been learned and summarizes future research challenges and
recommendations. In the report, EPA contends that the research to date reconfirms
links between exposure and serious health problems, has provided new evidence
regarding cardiovascular effects, and where and how exposure occurs indoors and
outdoors, and has resulted in the development of more sophisticated air measuring
and modeling tools. However, despite these achievements, the agency emphasized
that many uncertainties remain, and research must be expanded and redirected to
addresses these gaps.
HEI-Sponsored National Morbidity Mortality and Air Pollution
Studies. In 1994, the Health Effects Institute (HEI) initiated a research program to
investigate the complex set of issues associated with human health effects of
exposure to particulate matter. HEI has funded more than 40 studies and re-analyses

52 Subsequent to the release of the committee’s third report, problems were identified with
the application of a model and statistical package widely used in time-series analysis. The
recognition of these problems required re-analysis of several research studies that were the
basis for characterizing short-term risks associated with air pollutants.
53 U.S. Environmental Protection Agency, Office of Research and Development, EPA

600/R-04/058, July 2004, at [].

during the last 10 years, as well as several “special” reports on particulate matter
research. As presented earlier in this report, HEI was responsible for the re-analyses
of the ACS and Six Cities studies. Also, as part of their collaboration on particulate
matter, EPA and HEI maintain a website where researchers can post current
particulate matter research projects.54 These projects are submitted to HEI and are
reviewed by HEI staff before being posted on the website. The site includes more
than 500 particulate matter projects.
A major area of focus for the HEI-sponsored particulate matter research has
been uncertainties regarding the associated impacts of particulate matter on daily
mortality, including the effects of other pollutants. In 1996 HEI provided funding
initiating the National Morbidity, Mortality and Air Pollution Study (NMMAPS)
conducted by researchers at Johns Hopkins University,55 which to date has resulted
in a series of three primary reports and several re-analyses. These analyses concluded
that “PM10 concentrations were positively associated with mortality and morbidity
outcomes on average across locations.”
The initial report released in May 2000, NMMAPS I, was a compilation of
methodological approaches for three topical priorities: measurement error in air
pollution exposure, mortality displacement, and methods for combining evidence in
multiple locations.56 Results of the study, which included analyses of the 20 and 90
largest U.S. cities and hospital admissions of the elderly in 14 cities, were the basis
of the second report — NMMAPS II.57 This report was of particular interest because
of its results, as well as the subsequent discovery by the authors of errors in a
statistical software program used to analyze the data that lead to bias in the results
(more discussion follows).
A third HEI-sponsored NMMAPS report (NMMAPS III),58 published in May
2004, is a study of time-series data (1987-1994) of PM10 effects on mortality for the
20 largest U.S. cities. The study examined the question of whether there is a
threshold below which there does not appear to be an association between particulate

54 The address is [].
55 Departments of Epidemiology and Biostatistics, Johns Hopkins School of Public Health,
Baltimore MD, and Department of Environmental Health, Harvard School of Public Health.
For copies of relevant publications and information regarding ongoing research visit [http://
www.biostat.j] .
56 Jonathan M. Samet, et al. The National Morbidity, Mortality and Air Pollution Study Part
I: Methods and Methodologic Issues (NMMAPS I), Final Version, Cambridge, MA, Health
Effects Institute, no. 94, part I, October 2000. Available at [
57 Jonathan M. Samet, et al. The National Morbidity, Mortality and Air Pollution Study Part
II: Morbidity and Mortality from Air Pollution in the United States (NMMAPS II),
Cambridge, MA: Health Effects Institute, no. 94, part II, 2000. Available at [http://www. Pubs/Samet2.pdf].
58 Michael J. Daniels, et al. The National Morbidity, Mortality and Air Pollution Study Part
III: PM10 Concentrations-Response Curves and Thresholds for the 20 Largest U.S. Cities,
Cambridge, MA: Health Effects Institute, no. 94, part III, 2004. Available at [http://www. Pubs/Daniels94-3.pdf].

matter levels and mortality. A critique of the approach and results of the study by a
Special Panel of the HEI Review Committee concluded that the development and
application of complex statistical methods to describe concentration-response
relationships has advanced the understanding of air pollutant health effects, and the
results of the study have important implications for setting air quality standards.59
However, because of several limitations presented in their review, the panel was
apprehensive about the study’s conclusions, and cautions drawing conclusions from
the apparent absence of a threshold in the concentration-response relationship.
The original NMMAPS II report released in 2000 had found a 0.41% increase
in daily mortality for every additional 10 :g/m3 of PM10 for the 90 largest U.S. cities
over an eight-year period. However, in May 2002, the researchers announced they
had discovered errors in a statistical software program used to analyze the data and
determined that the errors overstated this percentage. In a re-analyses, completed in
2002, researchers found a 0.27% increase.60 Despite the error, the researchers stated
that the conclusions of their report remain unchanged, namely:
Overall, this study provides strong evidence of association between PM10 levels
and exacerbation of chronic heart and lung disease sufficiently severe to warrant
hospitalization. The association cannot be explained by confounding [the
presence of other pollutants] that is addressed in both stages of the analysis,
although there is always the possibility of some residual confounding.61
Confounding by weather was considered above and can be set aside.
The error was associated with the application of a general additive model
(GAM) in the S-Plus statistical software. GAMs, effective for conducting nonlinear
regression analysis of one or more variables (e.g., air pollution, weather, time), had
been widely used in contemporary time-series research of health effects on air
pollution and other similar applications since about 1990. The researchers found that
their application of GAM in conjunction with the default conversion criteria in the
software could result in upward or downward bias of estimated relative risk,62
potentially skewing the final results. The researchers conducted a re-analysis of the
NMMAPS substituting alternative approaches in place of the model that created the
error. In the re-analysis the researchers concluded that:
While the quantitative estimates changed with the tighter convergence criteria in
the gam function or switching to GLM (approaches used in the re-analysis), the
major scientific findings of the NMMAPS did not. Strong evidence remains of

59 NMMAPS III, May 2004, p. 23-29.
60 Francesca Dominici, et al., A Special Report to the Health Effects Institute on the Revised
Analyses of the NMMAPS II Data, 2003, Health Effects Institute, Cambridge , MA. See also
Joel Schwartz, et al, A Special Report to the Health Effects Institute on the Revised Analyses
of the NMMAPS II Data: Morbidity and Mortality Among Elderly Residents of Cities with
Daily Measurements, 2003, Health Effects Institute, Cambridge, MA.
61 NMMAPS II, 2000, p. 44.
62 Fancesca Dominici, et al., On the Use of Generalized Additive Models in Time Series
Studies of Air Pollution and Health: Commentary, American Journal of Epidemiology 2002,

156, pp. 193-203. Available at [].

an association between acute exposure to particulate air pollution (PM10) and
daily mortality one day later (lag 1). This association was strongest for
respiratory and cardiovascular causes of death, as anticipated based on concepts63
of susceptibility.
The re-analyses of the NMMAPS were part of a larger effort for re-analyses of
more than 40 selected time-series studies at the request of the EPA and the CASAC.
HEI compiled its review of these re-analyses in a special report entitled Revised64
Analyses of Time-Series Studies of Air Pollution and Health, released in May 2003.
Re-analyses of Selected Time-Series Studies. The discovery of the
problems65 associated with certain applications of GAMs occurred as EPA was
proceeding with its review of the inventory of scientific information for reassessment
of the PM NAAQS. This model had been the basis for numerous particulate matter
times-series studies conducted since 1990, many of which were the basis of EPA’s
review, and their results were potentially affected. The reported errors associated
with the GAM had no effect on the results of the Harvard Six Cities Study and the
American Cancer Society study, both of which were re-analyzed in depth and
confirmed in 2000.
During the summer of 2002, EPA and the CASAC conducted an extensive
evaluation of the studies included in the review. Roughly 40 studies were identified
for re-analysis, including the NMMAPS. EPA requested that the researchers of the
potentially affected studies conduct re-analyses to ensure the validity of their results,
providing necessary guidance. The agency relied on the HEI to review the re-
analyses and compile its evaluation of changes in the original results. HEI was not
specifically tasked with evaluating the original designs and methods of the studies.
The HEI reported that overall, although the effects varied substantially across
studies, the re-analyses resulted in estimates of effect lower than the original
analyses. However, there continues to be an association of particulate matter with
mortality/morbidity, particularly with respect to cardiovascular and respiratory
diseases. The HEI review also commented that the revisions “renewed the interest
in important questions and uncertainties that should inform future time-series
analysis of air pollution and health.”66
Status of EPA’s Review of the 1997 PM NAAQS
EPA’s review of the 1997 PM NAAQS, which began not long after the current67
standards were promulgated, is ongoing. As discussed previously in this report, the

63 Francesca Dominici et al. 2003, p. 19.
64 Health Effects Institute website, at [].
65 In addition to the concerns raised by the NMMAPS researchers, Health Canada found that
the use of GAMs under certain conditions caused underestimates of standard errors.
66 HEI, Special Report, May 2003, p. v.
67 For details of EPA’s original plans for reviewing the PM NAAQS, see 62 Federal

CAA requires the criteria document for each criteria pollutant to be reviewed and, if
appropriate, the NAAQS revised, every five years. As the implementation of the

1997 PM NAAQS has been delayed, so too has the review.

Schedule. The American Lung Association and several public interest groups
filed an action in March 2003, in response to EPA’s failure to meet the 2002 statutory68
deadline for review of the PM and ozone NAAQS. Through a consent decree
approved by the District Court of the District of Columbia on July 31, 2003, EPA and
the parties to the lawsuit reached an agreement that included the establishment of
deadlines for issuance of the particulate matter criteria document by July 30, 2004,
a preliminary decision regarding revisions to the PM NAAQS by March 31, 2005,
and final revised PM NAAQS (if deemed appropriate) by December 20, 2005.
On July 12, 2004, EPA filed an opposed motion for a further extension of the
particulate matter criteria document until October 29, 2004, which was granted by
the court. At the time of the motion, EPA expressed concern with its ability to meet
the remaining deadlines, and the court, in its July 23, 2004 order, further directed the
parties to consult to address the remaining consent decree deadlines. EPA shared a
proposal for extending the remaining particulate matter deadlines with the plaintiffs
on August 13, 2004, and it was later submitted to the court as part of a negotiation69
with the parties of the consent agreement. Specifically, EPA proposed the following
modifications to the PM NAAQS schedule:
!Extension from March 31, 2005, to December 31, 2005, to sign
notice of proposed rulemaking setting forth its proposed decision
concerning EPA’s review of the PM NAAQS;
!Extension from December 20, 2005, to September 30, 2006, for
EPA to sign a notice of final rulemaking setting forth EPA’s final
decision concerning review of the PM NAAQS.
As of December 2004, the plaintiffs, who have offered to continue consultations with
EPA, were considering the agency’s proposal.
2004 Particulate Matter Criteria Document. Following the federal court
approval extending the deadline, EPA announced the availability of the updated
criteria document, Air Quality Criteria for Particulate Matter, in the October 29,
2004, Federal Register (69 FR 63111). The 2004 criteria document is not intended
to be a complete and detailed literature review, but rather a thorough evaluation of
information relevant to PM NAAQS criteria development from pertinent literature
that has become available between 1996 through April 2002. A few studies

67 (...continued)
Register 55201, October 23, 1997.
68 Consent agreement, July 2003, C.A. No. 03-778 (ESH), American Lung Association, et
al v. the U.S. Environmental Protection et al. (EPA), U.S. District Court for the District of
69 Joint Status Report, September 2004,C.A. No. 03-778 (ESH), American Lung Association,
et al v. the U.S. Environmental Protection et al. (EPA), U.S. District Court for the District
of Columbia.

published through 2003 were determined to be critical to the assessment and included
in the review. Although a primary focus of the review was on the latest available
dosimetric and health effects data, other scientific data were also included to provide
information on the nature, sources, size distribution, measurement, and
concentrations of PM in the environment and contributions of ambient particulate
matter to total human exposure.
The criteria document is the result of extensive public comment and rigorous
review by experts from academia, various U.S. federal and state government units,
non-governmental health and environmental organizations, and private industry. The
document also reflects the review and deliberations of interim drafts, and the final
approval and recommendations of the congressionally mandated CASAC. Drafts
were revised in response to comments, and as necessary, to include relevant studies
completed between drafts.
EPA issued its first draft of the criteria document in October 1999. A second
draft was issued in March 2001, and included relevant studies through December
2000. Each of these two drafts was reviewed by CASAC and sent back with
comments to the agency. EPA published a third draft of the criteria document in
April 2002. CASAC reviewed this criteria document at its meeting in mid-July 2002.
Although CASAC had originally indicated that closure on the criteria document was
likely, assuming EPA made the modifications requested by CASAC in the second
review,70 CASAC did not close on the criteria document at the July 2002 meeting.
EPA modified the criteria document to reflect changes to the outcomes of studies that
were affected by the software problem found in the NMMAPS study.
Following the fourth external review in June 2003, the CASAC reached closure
on Chapters 1 through 6 during its August 21-25, 2003, meeting, requiring only
minor changes. The chapters on toxicology (Chapter 7), human health (Chapter 8),
and integrative synthesis (Chapter 9) required extensive revision and restructuring.
Additional CASAC and public reviews of the three revised chapters in December
2003 and June 2004 resulted in closure on Chapters 7 and 8. Chapter 9 continued to
be reviewed and revised until CASAC completed its overall review71 after a
September 20, 2004 teleconference.
The two-volume report contains extensive discussions of the findings and their
relevance to establishing PM NAAQS in the context of the defined research
priorities. The bullets below provide brief highlights of some of the conclusions
excerpted from Chapter 9 of the 2004 criteria document, but without the associated
details and caveats. Readers interested in the specific referenced findings should

70 CASAC review, September 2001, Review of the Air Quality Criteria Document for
Particulate Matter: Second External Review Draft EPA (600/P-99/002bB): A CASAC
Review, letter to the Administrator, September 27, 2001, EPA-SAB-CASAC-LTR-01-001,
p. 2. Available at [].
71 CASAC final review, October 2004, EPA’s Fourth External Review Draft of Air Quality
Criteria for Particulate Matter: A Peer Review by the Clean Air Scientific Advisory
Committee Particulate Matter Review Panel, U.S. EPA, EPA-SAB-CASAC-05-01.
Available at [].

refer to the corresponding sections of Chapter 9 (identified in parentheses) as well as
relevant chapters in the document. The criteria document conclusions include the
!The 1996 recommendation that fine and coarse particles be
considered as separate subclasses of particulate matter pollution is
reinforced (Chap. 9, sec. 9.2.1);
!Epidemiological evidence continues to support likely causal
associations between PM2.5 and PM10 and morbidity and mortality
from cardiovascular and respiratory diseases, but suggest no clear
thresholds in particulate matter-mortality relationships (Chap. 9, sec.


!New epidemiological re-analyses and extensions of previous studies
show substantial evidence for increased lung cancer; toxicological
evidence supports plausible association between particles
(particularly fine particles) with physiological endpoints indicative
of increased risk of heart disease, and supports plausible biological
pathways for respiratory effects (Chap. 9, sec. 9.2.3);
!Recent studies support considering older adults and children as
susceptible groups, given the overlap between age categories and
pre-existence of cardiopulmonary diseases; evidence from
toxicological studies suggests there are populations who are
genetically predisposed to particulate matter-related effects (Chap.

9, sec. 9.2.4);

!Local visibility standards intended to reflect “adverse thresholds”
associated with minimum visual range, and the criteria used to set
these standards, may be relevant for consideration in assessing
national secondary standards (Chap. 9, sec. 9.3.1);
!Considerable uncertainty remains with respect to the impact of the
deposition of particulate matter on vegetation ecosystems; this issue
requires additional research (Chap. 9, sec. 9.3.2);
!No significant advances have been made since the 1996 particulate
matter review in reducing the uncertainties regarding the relationship
of particulate matter to climate change processes (Chap. 9, sec.


!Insufficient data with respect to pollutant concentration, particle
size, and chemical composition continue to prohibit quantifying
pollutant exposure levels that result in observable soiling and
damage to man-made materials (Chap. 9, sec. 9.3.4).
EPA Particulate Matter Staff Paper. A draft staff paper issued in 2001 by
EPA’s Office of Air Quality Planning and Standards for this new round of review did
not contain any policy recommendations. However, a subsequent draft staff paper
released in August 200372 indicated that “the latest scientific, health and technical

72 Office of Air Quality Planning and Standards (OAQPS), U.S. Environmental Protection
Agency, Review of the National Ambient Air Quality Standards for Particulate Matter:
Policy Assessment of Scientific and Technical Information, EPA OAQPS Staff Paper —

information does not support relaxing” EPA’s current PM NAAQS, and
recommends that the agency consider revising standards to provide additional health
protection. This is a draft paper and does not reflect the technical staff’s official final
The staff paper will not be finalized until, as in the past, EPA technical staff
interpret the most relevant information in the current criteria document and,
combined with other relevant information, recommend options to be considered
regarding policy decisions affecting the adequacy of the current 1997 PM NAAQS.
The paper will not be used as the basis for any policy decisions until it is reviewed
by the CASAC, others in the scientific community, industry, public interest groups,
and the general public. As discussed earlier in this report, following its review of the
staff paper, the CASAC panel will recommend improvements and eventually, after
further meetings that are open to the public and reviews, sign off only when the panel
are convinced that the paper accurately reflects the status of the science.
The staff assessment, in conjunction with the CASAC closure letter, will be
used by the EPA Administrator to determine whether or not changes to the PM
NAAQS are necessary. The CAA specifies that the Administrator shall use his/her
“judgment ..., based on [the] criteria [document] and allowing an adequate margin
of safety” to determine the NAAQS “requisite to protect the public health” (CAA,
§109(b)(1)). Based on the recent EPA deadline proposal submitted for consideration
by the court described earlier in this report, proposed modifications to the standards
are not expected until December 2005, followed by a final rule in December 2006.
As EPA proceeds with the review of the particulate matter criteria and standards, the
agency is continuing implementation of the PM NAAQS promulgated in 1997.
Opposing Views, Potential Challenges and Litigation. As discussed
earlier, the decisions by the Administrator of the EPA in July 1997 to revise ambient
air quality standards (NAAQS) for ozone and particulate matter refocused attention
on the criteria and the process by which these decisions are made. The new standards
were the subject of numerous oversight hearings as well as litigation, which
culminated in a Supreme Court ruling February 27, 2001.
Stakeholders continue to challenge the adequacy of the scientific data supporting
the PM NAAQS. According to the EPA Docket,73 numerous comments have been
submitted throughout the current criteria document review process. Despite the
agency’s attempts to be responsive to the concerns raised, varying interpretations of
the data and their conclusions, and disagreements regarding which studies to include
or not include, are likely to continue.

72 (...continued)
First Draft (EPA-452/D-03-001), August 2003. Obtained from EPA website at [http://www.] on November 16, 2004.
73 EPA Docket #OAR-2001-0017, available on EPA’s E-Docket website at [http://docket.], viewed November 22, 2004.

EPA’s NAAQS rulemaking is subject to several statutory procedural
requirements, compliance with which is subject to judicial review.74 Given the
history of the previous review and development of PM NAAQS, it is likely that
litigation or other challenges will occur and potentially further delay the process.
Also, the agency’s criteria document and subsequent staff paper could be
challenged under the Data Quality Act (DQA; also referred to as the Information
Quality Act), enacted in December 2000.75 Intended to ensure quality, objectivity,
utility, and integrity of information, the DQA required the Office of Management and
Budget (OMB) to issue policy and procedural guidance to federal agencies. The act
required each covered agency to issue its own information quality guidelines within
one year of the issuance of the OMB guidelines. Following review and comment on
earlier proposals, OMB published its guidelines on February 22, 2002 (67 Federal
Register 8452)76 and agency guidelines were subsequently developed and reviewed
by OMB.77
Those who have submitted public comment in response to a federal agency
action and who are dissatisfied with how their correction requests were handled
through the Administrative Procedures Act process could appeal that agency’s
decision through the DQA administrative appeal process. For additional background
regarding the DQA, see CRS Report RL32532, The Information Quality Act: OMB’s
Guidance and Initial Implementation.
EPA will likely encounter more extensive challenges following its
determinations regarding revisions to the 1997 PM NAAQS. The first suits
challenging the ozone and 1997 PM NAAQS were filed in the D.C. Circuit Court of
Appeals on July 18, 1997, the day the final rules appeared in the Federal Register.
During 1997 a total of 38 suits were filed for judicial review of various aspects of the
ozone and PM NAAQS. These suits were consolidated in the American Trucking
Associations v. U.S. E.P.A., argued December 17, 1998, and decided May 14, 1999
(175 F.3d 1027 (D.C. Cir. 1999)). Many of the stakeholders who were party to those
lawsuits are expected to continue to challenge the justification of the current
standards as well as modifications as a result of the current review.
The 1997 standards have been attacked both as overly stringent and as
inadequately protective of health; as ignoring costs and as giving costs too much
deference; as going beyond what is scientifically conclusive; and as failing to be

74 The basic framework is spelled out in the CAA, §307(d) (42 U.S.C. §7607(d)) and details
the requirements for public notice and participation in the process.
75 Enacted in December 2000 as Section 515 of the Treasury and General Government
Appropriations Act for Fiscal Year 2001 (P.L. 106-554) (44 U.S.C. 3504(d)(1) and 3516).
76 For a copy of the OMB guidelines, see [
77 Agencies’ guidelines are published on OMB’s website, although it cautioned the public
that the list is not complete and will be updated as more guidelines are posted online. See
[http://www.wh omb/inforeg/ agency_info_quality_links .html ].

sufficiently precautionary.78 EPA’s general interpretation of the criteria supporting
NAAQS has been the subject of various challenges. Some have argued, and continue
to argue, that the science does not enable the agency to establish a clear threshold,
and if there is no “threshold,” then there cannot be a “margin of safety” as required
by the CAA. As a result, the whole NAAQS process of necessity becomes a risk
management decision — that is, one in which the EPA Administrator balances risks
with costs to decide where to set the standard. Others argue that the lack of a
threshold justifies the tightest possible standards.
Another, continuing debate comes from the view that only in adding a margin
of safety does the Administrator layer a policy judgment onto an objective —
scientifically determined NAAQS. Some argue that this judgmental aspect means
that the margin of safety phrase implicitly endorses the consideration of costs in
setting NAAQS; as discussed later, the lead industry sued EPA over lead standards
on the basis that the margin of safety required EPA to take costs into account in
setting NAAQS, but the court ruled that the statute and its legislative history are
against that interpretation (Lead Industries Association v. Environmental Protection
Agency, 647 F.2d 1130 (D.C. Cir. 1980)).
These issues were the subject of numerous oversight hearings as well as
litigation, which culminated in the Supreme Court ruling of February 27, 2001
(discussed earlier in this report). The court upheld those NAAQS setting procedures
at question, in particular definitively rejecting the consideration of costs in setting
Implementation of the 1997 PM NAAQS
PM2.5 Monitoring Network. Revising the PM NAAQS in 1997, which added
standards for PM2.5, necessitated establishing a monitoring network to measure the
fine particles. At the time the new NAAQS were being finalized, EPA also developed
methods for monitoring fine particles. Using funding specifically authorized for this79
purpose in EPA appropriations FY1998-FY2000, the agency worked closely with
states and tribes to initiate the deployment of a portion of the network of 1,200
monitors in January of 1999.
PM2.5 attainment or nonattainment designations are to be made primarily on the
basis of three-year federally referenced PM2.5 monitoring data.80 The majority of the
monitors were not in place until January of 2000; therefore, the necessary three years
of data became available at the end of 2002. In response to the need for additional
time to establish effective PM2.5 monitoring, and other delays, Congress mandated

78 See CRS Report 97-8, Air Quality: EPA’s New Ozone and Particulate Matter Standards.
79 Appropriations for monitoring averaged roughly $50 million per year, P.L. 105-65, P.L.

105-226, P.L. 106-74.

80 A federally referenced monitor is one that has been accepted for use by EPA for
comparison of the NAAQS by meeting the design specifications, and certain precision and
bias (performance) specifications (40 Code of Federal Regulations Part 58).

that EPA designate nonattainment areas for the PM2.5 standard by the end of 2005
(Title VI of the 1998 Transportation Equity Act for the 21st Century, P.L.105-178).
Operation of the network of monitors was phased in from 1999 through 2000,
making three-year monitoring data available at different points depending on area
location. Rather than a staggered designation schedule that would likely result in
hampering cross-coordination of implementation plans, the EPA proposed a single
date for state/tribal recommendations and final EPA designations. In the agency
guidance, states/tribes were expected to rely on data collected during 2000-2002 for
their area designation recommendations. EPA considered the 2001-2003 data to
make the final designations.
PM2.5 Attainment/Nonattainment Geographical Designation. 81 An area
designated as nonattainment is defined as any area that does not meet, or that
contributes to ambient air quality in a nearby area that does not meet, an air quality
standard. Nonattainment designation begins a process in which states (and tribes)
must develop and adopt emission control programs sufficient to bring air quality into
compliance by an EPA defined deadline.
The CAA (Section 107(d)(1)(A); 42 U.S.C. 7407) establishes a cooperative82
federal-state/tribe process for designating nonattainment areas and setting their
boundaries. However, it provides the EPA Administrator discretion in determining
the final boundaries. Based on provisions of the CAA and non-binding EPA
guidance, 18 states and the District of Columbia recommended 145 counties as83
potential nonattainment areas for PM2.5 NAAQS at the end of February 2004.
By the end of June 2004, EPA completed its review of the state/tribe
submissions and, using its authorized discretion, recommended modifications
resulting in nonattainment designations for 244 counties in 21 states and the District
of Columbia. As required by statute, the EPA notified each of the affected states
regarding its specific modifications to allow sufficient opportunity to provide new
information and demonstrate why a proposed modification was inappropriate. Some
states responding to the EPA’s proposal continued to support their original

81 For a more detailed discussion of the implementing the 1997 PM NAAQS and the
associated designation process and associated issues, see CRS Report RL32431, Particulate
Matter (PM2.5): National Ambient Air Quality Standards (NAAQS) Implementation.
82 Tribes are not required, but were encouraged, to submit PM area designation
recommendations. The area designation requirements under the CAA (Section 107) are
specific with respect to states, but not tribes. EPA plans to follow the same designation
process for tribes per sections 110(o) and 301(d) of the CAA and pursuant to the 1988
Tribal Authority Rule, which specifies that tribes shall be treated as states in selected cases
(40 Code of Federal Regulations Part 49). Tribes have participated in the PM2.5 designation
recommendation process, recommending designations of attainment/unclassified (see [http://
www.e p a . go v/ pmde s i gn a t i ons ] ) .
83 For PM2.5 geographical designation recommendations from individual states and tribes, see
EPA’s “PM2.5 Designations” website at [].

EPA’s final nonattainment designations for all or part of 225 counties in 20
states, and the District of Columbia, published in the January 5, 2005, Federal
Register, reflect minor modifications to its June 2004 proposal. The modifications
are primarily the result of removing 19 counties from the list of nonattainment areas,
and redefining other counties by designating only specified geographical locations
(“partial”) within the county as nonattainment.
The final PM2.5 designation rule allows states to submit no later than February
22, 2005, certified, quality-assured 2004 monitoring data that suggests a change in
designation is appropriate for consideration (70 Federal Register 948). A
nonattainment designation could be withdrawn if the EPA agrees that the additional
data warrants such a change.
Other Activities Impacting PM NAAQS Implementation
Current CAA Regulation. EPA has concluded that in many cases, PM2.5
attainment will be reached as the result of implementing strategies developed under84
the 1999 visibility protection regulations (“Regional Haze Rule”); voluntary diesel
engine retrofit programs; new federal standards on cars, light trucks, and heavy duty
diesel engines that are scheduled to be implemented between 2004 and 2010; and the

1998 regional strategy to reduce nitrogen oxides from eastern states referred to as the85

“NOx SIP Call.” Although it was primarily designed to meet the ozone NAAQS,
EPA predicts the NOx SIP call will also provide some benefits in terms of reduced
levels of nitrate fine particles.
According to a December 2004, EPA report, The Particle Pollution Report:
Current Understanding of Air Quality and Emissions through 2003, monitored
concentrations of PM2.5 have decreased 10 percent, and PM10 have decreased 7 percent
since 1999, primarily in areas with the highest concentrations.86 EPA attributes a
large portion of these decreases to the Acid Rain Program.
On April 15, 2004, EPA designated areas in 32 states and the District of
Columbia (474 counties) as “nonattainment areas” for a new ozone air quality87
standard. Many of the areas designated nonattainment for the new ozone standards
are likely to be the same as those designated for PM NAAQS, and the approaches to
control ozone included in state implementation plans will likely control particulate

84 64 Federal Register 35714, July 1, 1999. EPA recently published a proposal revising the
regional haze rule, intended to provide guidelines for state and tribal air quality agencies to
use in determining how to set air pollution limits (69 Federal Register 25184, May 5, 2004).
See CRS Report RL32483, Visibility, Regional Haze, and the Clean Air Act: Status of
85 64 Federal Register 35714, October 27, 1998. For background see CRS Report RS20553,
Air Quality and Electricity: Initiatives to Increase Pollution Controls.
86 U.S. Environmental Protection Agency, EPA 454-R-04-002, December 2004. Revised
report posted on EPA’s website [],December 23,


87 See CRS Report RL32345, Implementation of EPA’s 8-Hour Ozone Standard.

matter, including PM2.5 indirectly. The agency’s non-binding guidance for PM2.5 area
designations recommended that states/tribes consider using the same boundaries for
nonattainment for both the PM2.5 and 8-hour ozone standards, to facilitate consistency
in future implementation plans.
Proposed Regulations and Legislation. Proposed legislation and EPA
regulations for controlling coal-fired electric power plants’ emissions, such as “Clear
Skies”/multi-pollutant legislation and the proposed “Clean Air Interstate Rule”
(CAIR, also referred to as the Interstate Air Quality Rule”(IAQ)) to be implemented
between 2004 and 2015,88 could also contribute national and regional measures for
attaining PM2.5 standards. The EPA predicts that, of an estimated 120 eastern
counties out of compliance with PM2.5 NAAQS in 2002, the Clean Air Interstate
Rule will bring 28 more counties into compliance in addition to the 58 counties
predicted to come into compliance under existing programs.89 The extent of
pollution reduction that is projected as a result of these proposals has been the subject
of considerable debate among stakeholders, and some Members of Congress.
California Particulate Matter Standards. States are permitted to adopt
more stringent ambient air quality standards than EPA’s NAAQS. Since 1982,
California has had more stringent particulate matter standards than the national
standards. California’s standards for PM10 are 30 :g/m3 annual geometric average and

50 :g/m3 24-hour average, as compared to EPA’s 1997 PM10 standards of 50 :g/m3

annual arithmetic mean and 150 :g/m3 24-hour average.
In 1999, the California legislature passed a bill requiring examination of the
standards for their adequacy in protecting health, particularly that of children. A
December 2000 report by the California Air Resources Board (CARB) found that the
PM standards were not adequate to protect human health. The 1999 California law
mandated revision of these standards by December 31, 2002. California’s process for
revision is somewhat similar to EPA’s NAAQS revision process in that a staff paper
is produced and an Air Quality Advisory Committee reviews the report.
In May 2002, CARB staff published a paper suggesting revising the standards
for PM10 and establishing new standards for PM2.5. The staff paper maintained the
level and form of the 24-hour PM10 standard but tightened the annual standard to 20
:g/m3 annual arithmetic average, not to be exceeded. The new standards for PM2.5
were recommended to be 12 :g/m3 annual arithmetic average, not to be exceeded,
and 25 :g/m3 24-hour average standard, not to be exceeded. The staff had not
originally recommended a 24-hour standard for PM2.5, but did so after the Air Quality
Advisory Committee concluded that adequate information existed to set a standard.
In June 2002, CARB held a public hearing on the staff paper recommendations.
Because of the software problem revealed in the NMMAPS study discussed above,
CARB decided not to include the PM2.5 24-hour standard on the agenda for the

88 For a further discussion, see CRS Report RL32755, Air Quality: Multi-Pollutant
Legislation in the 109th Congress, and CRS Report RL32273, Air Quality: EPA’s Proposed
Interstate Air Quality Rule.
89 CRS Report RL32273, Air Quality: EPA’s Proposed Interstate Air Quality Rule, p. 11.

meeting because some of the studies supporting the standard had used the faulty
software. At the meeting, CARB unanimously approved the three other particulate
matter standard recommendations. Following the required administrative law
review, the standards became effective July 5, 2003. Table 3 compares California’s

1982 standards, California’s 2002 standards, and EPA’s 1997 PM NAAQS.

Table 3. California’s State Particulate Matter Standards and the 1997
National Primary Particulate Matter Standards
California’s 1982 StateCalifornia’s 2002 State1997 National Primary
St andard St andard St andard
IndicatorPM10PM10 and PM2.5PM10 and PM2.5
Form24-hour average (not to24-hour average (not to24-hour average (concentration-
be exceeded)be exceeded)based percentile)
Annual geometric meanAnnual arithmetic meanAnnual arithmetic mean
(not to be exceeded)(not to be exceeded)

24-hour 50 :g/m3PM10: 50 :g/m3PM10: 150 :g/m3 (99th percentile)3th

NAAQSPM2.5: nonePM2.5: 65 :g/m (98 percentile)
Annual30 :g/m3PM10: 20 :g/m33PM10: 50 :g/m33
NAAQSPM2.5: 12 :g/mPM2.5: 15 :g/m
Source: Prepared by the Congressional Research Service.
California is currently considering amendments to its designation criteria, and
current area designations to account for the particulate standards adopted in June
2002. Legislation signed by the governor on October 8, 2003, required additional
specific requirements for PM10 and PM2.5 nonattainment areas. California Senate Bill
656 (SB 656)90 requires the development and adoption of a list of the “most readily
available, feasible, and cost-effective control measures to reduce PM10, PM2.5, and
their precursor emissions,” by January 1, 2005.
California’s decision on particulate matter may have national ramifications,
although no other states have set particulate matter standards different from the
federal standards. How California’s actions regarding particulate matter might impact
EPA’s decision upon conclusion of its current review is unclear.
International Particulate Matter Standards. Several countries have
established relatively comparable air quality standards for a number of the same
pollutants as the U.S., including particular matter. A recent study91 compared various
aspects of the U.S. air quality and water quality standards with those of other
countries. According to the study, the U.S. standards for PM10 are less stringent than

64% of the countries identified. Canada is the only other country that currently has

90 For more information, see the California Air Resources Board website at [http://www. pm/pmmeasures/pmmeasures.htm] .
91 Timothy Benner, “Brief Survey of EPA Standard-Setting and Health Assessments,”
Environmental Science and Technology, vol. 38, no. 13, 2004. Published on the American
Chemical Society website at [].

standards for PM2.5; their 24-hour standard is more stringent (30 µg/m3) than the U.S.
24-hour standard (65 µg/m3) . Several countries include standards for total suspended
particulates (TSP), which U.S. EPA discontinued regulating in 1987 when the agency
focused attention on PM10.
For purposes of illustration, Table 4 (below) presents comparisons of U.S. PM10
and PM2.5 standards with standards in other selected countries as reported in the
study. The comparisons of the various countries’ particulate matter standards in this
survey introduce interesting insights and raise empirical questions about why they
differ. The significance of these differences requires a more complete understanding
of the individual statutory authority, the data and interpretations of the data, and other
factors each country used in establishing their standards, as well as their intended
outcomes in terms of particulate matter emissions.
Table 4. PM10 and PM2.5 Air Quality Standard Comparison of United States
and Selected Countries
US EU Brazil China France Germany India M ex. N.Z. S.Afri ca Sp ain UK
PM10 (µg/m3)
24- hour 150 50 150 150 50 50 100 150 50 180 50 50
Annual5020a 501004040605020 6020a 40
Source: Prepared by the Congressional Research Service based onBrief Survey of EPA Standard-Setting and Health
Assessment,” by Timothy Benner, U.S. Environmental Protection Agency, Office of Research and development, Office
of Science Policy. Published by the American Chemical Society May 28, 2004. As printed in Environmental Science
and Technology, vol. 38, no. 13, 2004. a
Final 2010.
Some of the differences are likely to be the result of different interpretation of
the same data. In addition, the U.S. was among the first to establish standards for
particulate matter; several other countries are only now considering comparable PM2.5
standards. The lag in establishing particulate matter standards by other countries may
be part of the reason for the comparable stringency in the PM10 standards. Other
countries that established these standards later than the U.S. had the advantage of
expanded information. As noted in the study, an important consideration with regard
to this type of comparison is the implementation and adequacy of enforcement
regulations for actually achieving improved air quality. According to the study,
although it varies from country to country, EPA’s implementation and enforcement
appears to be more successful than most other countries.
The level at which other countries are setting their particulate matter standards
might be indicative of an emerging international agreement regarding the scientific
knowledge about particulate matter health effects. However, it is not clear if the
comparison of the U.S. particulate matter standards to those of other countries will
be a factor as EPA continues the simultaneous review and implementation of the
current PM NAAQS.

Particulate matter standards have been a source of significant controversy.
EPA’s promulgation of standards for both coarse and fine particulate matter in 1997
prompted critics to charge EPA with over-regulation and spurred environmental
groups to claim that EPA had not gone far enough. Not only was the science behind
the PM NAAQS challenged, but EPA was also accused of unconstitutional behavior.
However, EPA’s decision to issue these standards was upheld, for the most part, and
the science behind the standards was generally vindicated by an HEI review.
EPA is proceeding with its review of new information to determine whether
further revision of the PM NAAQS is necessary. Congress’s provision of
significantly more funding for particulate matter research has resulted in an increased
number of ongoing studies to determine particulate matter health effects. Recent
scientific findings in the NMMAPS and other related research have prompted further
concern about the health effects of particulate matter. However, a number of
stakeholders still contend that the scientific does not adequately support the PM
As EPA evaluates the need to revise current PM NAAQS, stakeholder interest
remains high. PM2.5 standards are expected to affect numerous areas, including some
that have not previously been designated nonattainment for a NAAQS. This has
raised concerns regarding the potential impacts, and triggered numerous questions
regarding the specifics of the implementation process. EPA projects that federal
measures, such as recent auto and truck emission standards and controls on power
plants, will be sufficient to demonstrate attainment in a large portion of monitored
nonattainment counties by 2015, and help alleviate the development and
implementation of local measures. Some Members of Congress, and others, have
questioned the agency’s predictions regarding the relative magnitude of the emission
reductions associated with existing and proposed air quality controls.
If EPA decides to tighten the PM NAAQS again based on the results of its
review, more areas could be classified as nonattainment and need to implement new
controls on particulate matter. This would require states and local governments to
develop and implement new plans for addressing emissions in those areas that do not
meet any new standards. A stricter standard may mean more costs for these
transportation and large industries, including utilities, refineries, and the trucking
industry, impacted by particulate matter controls. In terms of public health, a stricter
standard may mean fewer health effects for the general population and particularly
sensitive populations such as children, asthmatics, and the elderly. Because both the
health and economic consequences of particulate matter standards are so potentially
significant, the PM NAAQS are likely to remain a prominent issue of interest to
many, including Members of Congress.
Actions following the release of the 8-hour ozone designations will likely affect
certain decisions and the schedule regarding PM2.5. In addition, California and several
countries have established particulate matter standards that are more stringent than
the current U.S. standards. Whether these actions can be considered indicative of
what EPA will decide to do in its current review of the PM NAAQS is unclear.

The agency’s previous review and establishment of PM NAAQS was the subject
of litigation and challenges, including a Supreme Court decision in 2001. It would
not be surprising if interested parties return to the courts or initiate challenges under
the 2000 Data Quality Act in the months ahead, as the agency continues its review
and implementation of the PM NAAQS. Thus, the final form of the current efforts
to implement the PM2.5 standards, and EPA’s response to the current review of PM
NAAQS and the science information, may not be known for some time. It could be
some time before the final form of the PM NAAQS resulting from the current EPA
review is known. Likewise, the EPA’s current PM2.5 implementation efforts could
also potentially be delayed.