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Draft Integrated Review Plan for the
National Ambient Air Quality
Standards for Particulate Matter
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EPA 452/P-08-006
October 2007
Integrated Review Plan for the National
Ambient Air Quality Standards for
Particulate Matter
U.S. Environmental Protection Agency
National Center for Environmental Assessment
Office of Research and Development
and
Health and Environmental Impacts Division
Office of Air Quality Planning and Standards
Office of Air and Radiation
Research Triangle Park, North Carolina
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DISCLAIMER
This draft integrated review plan for the national ambient air quality standards (NAAQS)
for particulate matter (PM) is an informational document prepared for external review purposes
and does not constitute U.S. Environmental Protection Agency policy. This plan, once finalized,
will serve as a management tool for the U.S. Environmental Protection Agency's National Center
for Environmental Assessment and the Office of Air Quality Planning and Standards. The
approach described in the final plan may be modified to reflect information developed during the
review of the PM NAAQS and to address advice and comments received from the Clean Air
Scientific Advisory Committee and the public throughout this review. Mention of trade names
or commercial products does not constitute endorsement or recommendation for use.
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TABLE OF CONTENTS
1 INTRODUCTION 1
1.1 OVERVIEW OF THE NAAQS REVIEW PROCESS 2
1.2 LEGISLATIVE REQUIREMENTS 3
1.3 HISTORY OF REVIEWS OF THE NAAQS FOR PM 5
1.4 SCOPE OF THE CURRENT REVIEW 10
2 REVIEW SCHEDULE 13
3 KEY POLICY-RELEVANT ISSUES 15
3.1 ISSUES TO BE CONSIDERED IN THE CURRENT REVIEW OF THE PRIMARY PM NAAQS 15
3.2 ISSUES TO BE CONSIDERED IN THE CURRENT REVIEW OF THE SECONDARY PM NAAQS . 17
4 SCIENCE ASSESSMENT 20
4.1 SCOPE AND ORGANIZATION 20
4.2 ASSESSMENT APPROACH 21
4.3 SCIENTIFIC AND PUBLIC REVIEW 35
5 HUMAN HEALTH ASSESSMENT 36
5.1 OVERVIEW 36
5.2 OVERVIEW OF HEALTH RISK ASSESSMENT FROM PRIOR REVIEW 36
5.3 CURRENT AIR QUALITY CHARACTERIZATION 39
5.4 CURRENT HUMAN POPULATION EXPOSURE ASSESSMENT APPROACH 40
5.5 CURRENT HEALTH RISK ASSESSMENT APPROACH 43
5.6 BROADER RISK CHARACTERIZATION 47
5.7 SCIENTIFIC AND PUBLIC REVIEW 48
6 VISIBILITY AND OTHER WELFARE-RELATED ASSESSMENTS 49
6.1 OVERVIEW 49
6.2 OVERVIEW OF VISIBILITY-RELATED ASSESSMENT FROM PRIOR REVIEW 49
6.3 CURRENT VISIBLITY AND OTHER WELFARE-RELATED ASSESSMENT APPROACH 54
6.4 SCIENTIFIC AND PUBLIC REVIEW 56
7 AMBIENT AIR MONITORING 57
7.1 OVERVIEW 57
7.2 HISTORICAL PERSPECTIVE 57
7.3 MONITORING ISSUES TO BE CONSIDERED IN THE CURRENT REVIEW OF THE PM NAAQS 59
8 POLICY ASSESSMENT/RULEMAKING 64
9 REFERENCES 65
APPENDIX A 69
U.S. EPA SCIENCE ADVISORY BOARD CLEAN AIR SCIENTIFIC ADVISORY COMMITTEE MEMBERS
69
APPENDIX B 72
P ARTICULATE MATTER INTEGRATED SCIENCE ASSESSMENT -PROPOSED OUTLINE 72
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i 1 INTRODUCTION
2 The U.S. Environmental Protection Agency (EPA) is conducting a review of the existing
3 air quality criteria for particulate matter (PM) and the primary (health-based) and secondary
4 (welfare-based) national ambient air quality standards (NAAQS) for PM. The purpose of this
5 document is to communicate the plan for reviewing the air quality criteria for PM associated
6 with human health and welfare effects and the primary and secondary standards for PM.
7 This integrated review plan is a draft document and will be subject to consultation at a
8 public meeting with the Clean Air Scientific Advisory Committee (CAS AC) of EPA's Science
9 Advisory Board. Public comments are also being solicited on this draft document. For purposes
10 of this review, the 7-member CAS AC has been supplemented by additional scientific experts
11 collectively referred to as the CASAC PM Review Panel (see Appendix A). The final integrated
12 review plan will be informed by comments received from CASAC and the public.
13 This review will provide an integrative assessment of relevant scientific information on
14 PM and will focus on the basic elements of the primary and secondary PM air quality standards:
15 the indicator, averaging time, form,1 and level. These elements, which serve to define each
16 ambient air quality standard, must be considered collectively in evaluating the health protection
17 afforded by the standard. The current standards use PM2.5 andPMio as the indicators for fine and
18 thoracic coarse particles, respectively.
19 This draft integrated review plan is organized into eight sections. Section 1 presents
20 background information on the review process, the legislative requirements for the review of the
21 NAAQS, and past reviews of the NAAQS for PM. Section 2 presents the proposed review
22 schedule. Section 3 presents a set of policy-relevant questions that will serve to focus this
23 review on the critical scientific and policy issues. Sections 4 through 8 discuss the planned
24 scope and organization of the key assessment documents, the planned approaches for preparing
25 the documents, specific monitoring issues, and plans for scientific and public review of the
26 documents. As the assessments proceed, the plan described here may be modified to reflect
27 information received during the review process.
1 The "form" of a standard defines the air quality statistic that is to be compared to the level of the standard in
determining whether an area attains the standard.
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1 1.1 OVERVIEW OF THE NAAQS REVIEW PROCESS
2 The Agency has recently decided to make a number of changes to the process for
3 reviewing the NAAQS (described at http://www.epa.gov/ttn/naaqs/). In making these changes,
4 the Agency consulted with CASAC, which provides advice to the Administrator on key elements
5 of NAAQS reviews, and the public. This new process, which is being applied to the current
6 review of the NAAQS for PM, contains four major components. Each of these components is
7 described in this section.
8 The first component of the review process is the development of an integrated review
9 plan. This plan will specify the schedule for the review, the process for conducting the review,
10 and the key policy-relevant science issues that will guide the review.
11 The second component of the review process is a science assessment. Under the new
12 process, a concise synthesis of the most policy-relevant science will be compiled into an
13 Integrated Science Assessment (ISA), which will be informed by input from CASAC, outside
14 scientists, and the public. The ISA for this review of the air quality criteria for PM will critically
15 evaluate and integrate scientific information on the health and welfare effects associated with
16 exposure to PM in the ambient air. It will focus on scientific information that has become
17 available since the last review and will reflect the current state of knowledge on the most
18 relevant issues pertinent to the review of the primary and secondary PM NAAQS. The ISA will
19 be supported by more detailed information about the scientific literature, which will be compiled
20 into a series of annexes. The ISA and its annexes will replace the Air Quality Criteria Document
21 (AQCD) from previous PM NAAQS reviews.
22 The third component of the review process is a risk/exposure assessment, which will be
23 informed by input from CASAC, outside scientists, and the public. This assessment will
24 develop, as appropriate, quantitative estimates of human exposures and/or risks associated with
25 current ambient levels of PM, with levels that just meet the current standards, and with levels
26 that just meet possible alternative standards. EPA will prepare a concise risk/exposure
27 assessment report that focuses on key results, observations, and uncertainties.
28 The fourth component of the revised process is a policy assessment/rulemaking. Under
29 the new process, a staff paper, such as that prepared in previous NAAQS reviews, will not be
30 prepared. Rather, the Agency's views on policy options will be published in the Federal Register
31 as an advance notice of proposed rulemaking (ANPR). The ANPR will present a policy
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1 assessment and will be accompanied by supporting documents, such as air quality analyses and
2 technical support documents, as appropriate. Taking into account CASAC advice and
3 recommendations as well as public comment on the ANPR, the Agency will publish a proposed
4 rule, to be followed by a public comment period. Taking into account comments received on the
5 proposed rule, the Agency will issue a final rule to complete the rulemaking process.
6 1.2 LEGISLATIVE REQUIREMENTS
7 Two sections of the Clean Air Act (CAA) govern the establishment and revision of the
8 NAAQS. Section 108 (42 U.S.C. 7408) directs the Administrator to identify and list "air
9 pollutants" that "in his judgment, may reasonably be anticipated to endanger public health and
10 welfare" and whose "presence ... in the ambient air results from numerous or diverse mobile or
11 stationary sources" and to issue air quality criteria for those that are listed. 42 U.S.C. § 7408(a)
12 & (b). Air quality criteria are intended to "accurately reflect the latest scientific knowledge
13 useful in indicating the kind and extent of identifiable effects on public health or welfare which
14 may be expected from the presence of [a] pollutant in ambient air ... ." 42 U.S.C. § 7408(b).
15 Section 109 (42 U.S.C. 7409) directs the Administrator to propose and promulgate
16 "primary" and "secondary" NAAQS for pollutants listed under section 108. 42 U.S.C. § 7409
17 (a). Section 109(b) (1) defines a primary standard as one "the attainment and maintenance of
18 which in the judgment of the Administrator, based on such criteria and allowing an adequate
19 margin of safety, are requisite to protect the public health."2 42 U.S.C. § 7409(b)(l). A
20 secondary standard, as defined in section 109(b)(2), must "specify a level of air quality the
21 attainment and maintenance of which, in the judgment of the Administrator, based on such
22 criteria, is required to protect the public welfare from any known or anticipated adverse effects
23 associated with the presence of [the] pollutant in the ambient air."3 42 U.S.C. § 7409(b)(2).
24
2
The legislative history of section 109 indicates that a primary standard is to be set at "the maximum permissible
ambient air level.. . which will protect the health of any [sensitive] group of the population," and that for this
purpose "reference should be made to a representative sample of persons comprising the sensitive group rather than
to a single person in such a group" [S. Rep. No. 91-1196, 91st Cong., 2d Sess. 10 (1970)].
Welfare effects as defined in section 302(h) [42 U.S.C. 7602(h)] include, but are not limited to, "effects on soils,
water, crops, vegetation, man-made 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."
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1 The requirement that primary standards include an adequate margin of safety was
2 intended to address uncertainties associated with inconclusive scientific and technical
3 information available at the time of standard setting. It was also intended to provide a reasonable
4 degree of protection against hazards that research has not yet identified. See Lead Industries
5 Association v. EPA, 647 F.2d 1130, 1154 (D.C. Cir 1980), cert, denied, 449 U.S. 1042 (1980);
6 American Petroleum Institute v. Costle, 665 F.2d 1176, 1186 (D.C. Cir. 1981), cert, denied, 455
7 U.S. 1034(1982). Both kinds of uncertainties are components of the risk associated with
8 pollution at levels below those at which human health effects can be said to occur with
9 reasonable scientific certainty. Thus, in selecting primary standards that include an adequate
10 margin of safety, the Administrator is seeking not only to prevent pollution levels that have been
11 demonstrated to be harmful but also to prevent lower pollutant levels that may pose an
12 unacceptable risk of harm, even if the risk is not precisely identified as to nature or degree.
13 In selecting a margin of safety, the EPA considers such factors as the nature and severity
14 of the health effects involved, the size of sensitive population(s) at risk, and the kind and degree
15 of the uncertainties that must be addressed. The selection of any particular approach to
16 providing an adequate margin of safety is a policy choice left specifically to the Administrator's
17 judgment. See Lead Industries Association v. EPA, supra, 647 F.2d at 1161-62.
18 In setting standards that are "requisite" to protect public health and welfare, as provided in
19 section 109(b), EPA's task is to establish standards that are neither more nor less stringent than
20 necessary for these purposes. In so doing, EPA may not consider the costs of implementing the
21 standards. See generally Whitman v. American Trucking Associations, 531 U.S. 457, 465-472,
22 475-76 (2001).
23 Section 109(d)(l) requires that "not later than December 31, 1980, and at 5-year
24 intervals thereafter, the Administrator shall complete a thorough review of the criteria
25 published under section 108 and the national ambient air quality standards . . . and shall make
26 such revisions in such criteria and standards and promulgate such new standards as may be
27 appropriate . . . ." 42 U.S.C. § 7409(d)(l). Section 109(d)(2) requires that an independent
28 scientific review committee "shall complete a review of the criteria . . . and the national primary
29 and secondary ambient air quality standards . . . and shall recommend to the Administrator any
30 new . . . standards and revisions of existing criteria and standards as may be appropriate . . . ."
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1 42 U.S.C. § 7409(d)(2). Since the early 1980's, this independent review function has been
2 performed by CAS AC of EPA's Science Advisory Board.
3 1.3 HISTORY OF REVIEWS OF THE NAAQS FOR PM
4 Particulate matter is the generic term for a broad class of chemically and physically
5 diverse substances that exist as discrete particles (liquid droplets or solids) over a wide range of
6 sizes. Particles originate from a variety of anthropogenic stationary and mobile sources as well
7 as from natural sources. Particles may be emitted directly or formed in the atmosphere by
8 transformations of gaseous emissions such as sulfur oxides (SOX), nitrogen oxides (NOX), and
9 volatile organic compounds (VOC). The chemical and physical properties of PM vary greatly
10 with time, region, meteorology, and source category, thus complicating the assessment of health
11 and welfare effects.
12 EPA first established NAAQS for PM in 1971 (36 FR 8186, April 30, 1971), based on
13 the original criteria document (DHEW, 1969). The reference method specified for determining
14 attainment of the original standards was the high-volume sampler, which collects PM up to a
15 nominal size of 25 to 45 micrometers (|im) (referred to as total suspended particulates or TSP).
16 The primary standards (measured by the indicator TSP) were 260 |ig/m3, 24-hour average, not to
17 be exceeded more than once per year, and 75 |ig/m3, annual geometric mean. The secondary
18 standard was 150 |ig/m3, 24-hour average, not to be exceeded more than once per year.
19 In October 1979 (44 FR 56731), EPA announced the first periodic review of the air
20 quality criteria and NAAQS for PM, and significant revisions to the original standards were
21 promulgated in 1987 (52 FR 24634, July 1, 1987). In that decision, EPA changed the indicator
22 for particles from TSP to PMio, the latter including particles with a mean aerodynamic diameter4
23 less than or equal to 10 jim, which delineated that subset of inhalable particles small enough to
24 penetrate to the thoracic region (including the tracheobronchial and alveolar regions) of the
25 respiratory tract (referred to as thoracic particles). EPA also revised the level and form of the
26 primary standards by (1) replacing the 24-hour TSP standard with a 24-hour PMio standard of
27 150 |ig/m3 with no more than one expected exceedence per year; and (2) replacing the annual
4 The more precise term is 50 percent cut point or 50 percent diameter (D50). This is the aerodynamic particle
diameter for which the efficiency of particle collection is 50 percent. Larger particles are not excluded altogether,
but are collected with substantially decreasing efficiency and smaller particles are collected with increasing (up to
100 percent) efficiency.
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1 TSP standard with a PMio standard of 50 |ig/m3, annual arithmetic mean. The secondary
2 standard was revised by replacing it with 24-hour and annual standards identical in all respects to
3 the primary standards. The revisions also included a new reference method for the measurement
4 of PMio in the ambient air and rules for determining attainment of the new standards. On
5 judicial review, the revised standards were upheld in all respects. Natural Resources Defense
6 Council v. Administrator, 902 F. 2d 962 (D.C. Cir. 1990, cert, denied. 498 U.S. 1082 (1991).
7 In April 1994, EPA announced its plans for the second periodic review of the air quality
8 criteria and NAAQS for PM, and promulgated significant revisions to the NAAQS in 1997 (62
9 FR 38652, July 18, 1997). In that decision, EPA revised the PM NAAQS in several respects.
10 While EPA determined that the PM NAAQS should continue to focus on particles less than or
11 equal to 10 jim in diameter (PMio), EPA also determined that the fine and coarse fractions of
12 PMio should be considered separately. The EPA added new standards, using PM2.5 as the
13 indicator for fine particles (with PM2.5 referring to particles with a nominal mean aerodynamic
14 diameter less than or equal to 2.5 jim), and using PMio as the indicator for purposes of regulating
15 the coarse fraction of PMio (referred to as thoracic coarse particles or coarse-fraction particles;
16 generally including particles with a nominal mean aerodynamic diameter greater than 2.5 jim
17 and less than or equal to 10 jim, or PMio-2.s). The EPA established two new PM2.5 standards: an
3
18 annual standard of 15 |ig/m , based on the 3-year average of annual arithmetic mean PM2.
5
19 concentrations from single or multiple community-oriented monitors; and a 24-hour standard of
20 65 |ig/m3, based on the 3-year average of the 98th percentile of 24-hour PM2 5 concentrations at
21 each population-oriented monitor within an area. Also, EPA established a new reference method
22 for the measurement of PM2 5 in the ambient air and adopted rules for determining attainment of
23 the new standards. To continue to address thoracic coarse particles, EPA retained the annual
24 PMio standard, while revising the form, but not the level, of the 24-hour PMio standard to be
25 based on the 99th percentile of 24-hour PMio concentrations at each monitor in an area. The EPA
26 revised the secondary standards by making them identical in all respects to the primary
27 standards.
28 Following promulgation of the 1997 PM NAAQS, petitions for review were filed by a
29 large number of parties, addressing a broad range of issues. In May 1999, a three-judge panel of
30 the U.S. Court of Appeals for the District of Columbia Circuit issued an initial decision that
31 upheld EPA's decision to establish fine particle standards, holding that "the growing empirical
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1 evidence demonstrating a relationship between fine particle pollution and adverse health effects
2 amply justifies establishment of new fine particle standards." American Trucking Associations v.
3 EPA , 175 F. 3d 1027, 1055-56 (D.C. Cir. 1999) (rehearing granted in part and denied in part,
4 195 F. 3d 4 (D.C. Cir. 1999)), affirmed in part and reversed in part, Whitman v. American
5 Trucking Associations, 531 U.S. 457 (2001). The Panel also found "ample support" for EPA's
6 decision to regulate coarse particle pollution, but vacated the 1997 PMio standards, concluding
7 that EPA had not provided a reasonable explanation justifying use of PMio as an indicator for
8 coarse particles. 175 F. 3d at 1054-55. Pursuant to the court's decision, EPA removed the
9 vacated 1997 PMio standards from the Code of Federal Regulations (CFR) (69 FR 45592, July
10 30, 2004) and deleted the regulatory provision (at 40 CFR 50.6(d)) that controlled the transition
11 from the pre-existing 1987 PMio standards to the 1997 PMio standards (65 FR 80776, December
12 22, 2000). The pre-existing 1987 PMio standards remained in place. Id at 80777.
13 More generally, the panel held (over one judge's dissent) that EPA's approach to
14 establishing the level of the standards in 1997, both for PM and for ozone NAAQS promulgated
15 on the same day, effected "an unconstitutional delegation of legislative authority." Id. at 1034-
16 40. Although the panel stated that "the factors EPA uses in determining the degree of public
17 health concern associated with different levels of ozone and PM are reasonable," it remanded the
18 rule to EPA, stating that when EPA considers these factors for potential non-threshold pollutants
19 "what EPA lacks is any determinate criterion for drawing lines" to determine where the
20 standards should be set. Consistent with EPA's long-standing interpretation and D.C. Circuit
21 precedent, the panel also reaffirmed prior rulings holding that in setting NAAQS EPA is "not
22 permitted to consider the cost of implementing those standards." Id. at 1040-41.
23 Both sides filed cross appeals on these issues to the United States Supreme Court, and
24 the Court granted certiorari. In February 2001, the Supreme Court issued a unanimous decision
25 upholding EPA's position on both the constitutional and cost issues. Whitman v. American
26 Trucking Associations, 531 U.S. 457, 464, 475-76. On the constitutional issue, the Court held
27 that the statutory requirement that NAAQS be "requisite" to protect public health with an
28 adequate margin of safety sufficiently guided EPA's discretion, affirming EPA's approach of
29 setting standards that are neither more nor less stringent than necessary. The Supreme Court
30 remanded the case to the Court of Appeals for resolution of any remaining issues that had not
31 been addressed in that court's earlier rulings. Id. at 475-76. In March 2002, the Court of
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1 Appeals rejected all remaining challenges to the standards, holding under the traditional standard
2 of judicial review that EPA's PM2.5 standards were reasonably supported by the administrative
3 record and were not "arbitrary and capricious" American Trucking Associations v. EPA, 283 F.
4 3d 355, 369-72 (D.C. Cir. 2002).
5 In October 1997, EPA published its plans for the third periodic review of the air quality
6 criteria and NAAQS for PM (62 FR 55201, October 23, 1997), including the 1997 PM2.5
7 standards and the 1987 PMi0 standards. After CAS AC and public review of several drafts, EPA's
8 National Center for Environmental Assessment finalized the Air Quality Criteria Document for
9 Paniculate Matter (henceforth, the "Criteria Document") in October 2004 (U. S. EPA, 2004).
10 A second draft Staff Paper, based on the final Criteria Document, was released at the end of
11 January 2005, and was reviewed by CAS AC and the public at a meeting held in April 2005. The
12 CASAC's advice and recommendations to the Administrator, based on its review of the second
13 draft Staff Paper, were further discussed during a public teleconference held in May 2005 and
14 were provided in a June 6, 2005 letter to the Administrator (Henderson, 2005a). The final Staff
15 Paper, issued in June, 2005, took into account the advice and recommendations of CASAC and
16 public comments received on the earlier drafts of this document. The Administrator
17 subsequently received additional advice and recommendations from the CASAC, specifically on
18 potential standards for thoracic coarse particles in a teleconference on August 11, 2005, and in a
19 letter to the Administrator dated September 15, 2005 (Henderson, 2005b). The final Staff Paper
20 was reissued in December 2005 to add CASAC's final letter as an attachment (U.S. EPA, 2005).
21 On December 20, 2005, EPA announced its proposed decision to revise the NAAQS for
22 PM (71 FR 2620, January 17, 2006) (hereafter "proposal"). In the proposal, EPA identified
23 proposed revisions, based on the air quality criteria for PM, and solicited public comments on
24 alternative primary and secondary standards. EPA proposed to revise the level of the 24-hour
25 PM2.5 standard to 35 |ig/m3 to provide increased protection against health effects associated with
26 short-term PM2.5 exposures, including premature mortality and increased hospital admission and
27 emergency room visits and to retain the level of the annual PM2.5 standard at 15 |ig/m3,
28 continuing protection against health effects associated with long-term exposure including
29 premature mortality and development of chronic respiratory disease. With regard to the primary
30 standards for PMio, EPA proposed to revise the 24-hour PMio standard in part by establishing a
31 new indicator for thoracic coarse particles (particles generally between 2.5 and 10 jim in
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1 diameter, PMio-2.s), qualified so as to include any ambient mix of PMio-2.5 that was dominated by
2 resuspended dust from high density traffic on paved roads and PM generated by industrial
3 sources and construction sources, and proposed to exclude any ambient mix of PMi0-2.5 that was
4 dominated by rural windblown dust and soils and PM generated by agricultural and mining
5 sources. The EPA proposed to set a PMio-2.5 standard at a level of 70 |ig/m3 to continue to
6 provide a level of protection against health effects associated with short-term exposure
7 (including hospital admissions for cardiopulmonary diseases, increased respiratory symptoms
8 and possibly premature mortality) generally equivalent to the level of protection provided by the
9 existing 24-hour PMio standard. Also, EPA proposed to revoke, upon finalization of a primary
10 24-hour standard for PMio-2.5, the 24-hour PMio standard as well as the annual PMio standard.
11 EPA proposed to revise the secondary standards by making them identical to the suite of
12 proposed primary standards for fine and coarse particles, providing protection against PM-related
13 public welfare effects including visibility impairment, effects on vegetation and ecosystems, and
14 materials damage and soiling. EPA also solicited comment on adding a new sub-daily PM2.5
15 secondary standard to address visibility impairment in urban areas. CASAC provided additional
16 advice to EPA in a letter to the Administrator requesting reconsideration of CASAC's
17 recommendations for both the primary and secondary PM2.5 standards as well as standards for
18 thoracic coarse particles (Henderson, 2006a).
19 On September 21, 2006, EPA announced its final decisions to revise the primary and
20 secondary NAAQS for PM to provide increased protection of public health and welfare,
21 respectively (71 FR 61144, October 17, 2006). With regard to the primary and secondary
22 standards for fine particles, EPA revised the level of the 24-hour PM2.5 standard to 35 |ig/m3,
23 retained the level of the annual PM2.5 annual standard at 15 |ig/m3, and revised the form5 of the
24 annual PM2.s standard by narrowing the constraints on the optional use of spatial averaging.
25 With regard to the primary and secondary standards for PMio, EPA retained the 24-hour
When EPA sets NAAQS, it also must specify the air quality statistics that the Agency will use to determine
whether an area is meeting the standards. These statistics are known as the "form of the standard" and are derived
separately for each standard. The current forms for the PM2 5 and PM10 NAAQS are as follows:
24-hour PM2.5 standard - 98th percentile of 24-hour PM2 5 concentrations in a year, averaged over three
years
Annual PM2.5 standard - three-year average of the annual average PM25 concentrations; revisions in 2006
limited the conditions under which some areas may average measurements from multiple community-
oriented monitors to determine compliance (see 71 FR 61165-61167, October 17, 2006)
24-hour PM10 standard - not to be exceeded more than once per year on average over a three year period
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1 standard at 150 |ig/m3 and revoked the annual standard because available evidence generally did
2 not suggest a link between long-term exposure to current ambient levels of coarse particles and
3 health or welfare effects. Following the final decision, CASAC, in a letter to the Administrator,
4 provided recommendations concerning the final PM NAAQS (Henderson, 2006b).
5 The revisions to the PM NAAQS also included a new reference method (Federal
6 reference method or FRM) for the measurement of PMio-2.5 in the ambient air. Although the
7 standards for thoracic coarse particles do not use a PMi0-2.5 indicator, the new FRM for PMi0-2.5
8 will provide a basis for approving Federal Equivalent Methods (FEMs) and promote the
9 gathering of scientific data to support future reviews of the PM NAAQS. One of the reasons for
10 not finalizing a PMio-2.5 standard in 2006 was the limited body of evidence on health effects
11 associated with thoracic coarse particles from studies that use PMio-2.5 measurements of ambient
12 thoracic coarse particle concentrations. With an FRM, researchers will likely include PMio-2.5
13 measurements of thoracic coarse particles in health studies either by directly using the FRM or
14 by utilizing approved FEMs.
15 1.4 SCOPE OF THE CURRENT REVIEW
16 In the last PM NAAQS review, EPA focused on particle mass and primarily
17 distinguished between two categories of particle pollution based on size (i.e., fine- and thoracic
18 coarse-fraction particles), and conducted parallel evaluations of the available scientific evidence
19 relating to each category. The importance of specific PM components and sources was evaluated
20 within the context of this basic size differentiation. In that review, it was determined that size-
21 fractionated particle mass, rather than particle composition, remained the most appropriate
22 approach for addressing ambient PM. Building upon the last review, EPA plans to continue to
23 review the scientific evidence available based on particle size, considering fine and coarse-
24 fraction particles separately. Within this basic structure, EPA will evaluate relevant scientific
25 evidence on specific PM components and sources.
26 In considering what components of PM are relevant to the review of the primary PM
27 NAAQS, EPA notes that the health effects associated with particulate species of nitrogen and
28 sulfur oxides were considered within the context of the last PM NAAQS review. Building upon
29 the last review, EPA plans to continue to include these particles in this review of the health
30 effects of ambient particles. In addition, EPA has separate efforts under way to review the
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1 current NO2 and SO2 primary NAAQS focusing on the gaseous species of nitrogen and sulfur
2 oxides.6
3 In the last review of the suite of primary PM standards, EPA focused on evidence of
4 health effects associated with daily and long-term (months to years) exposures to particles,
5 specifically premature mortality, aggravation of respiratory and cardiovascular disease (as
6 indicated by increased hospital admission and emergency department visits), changes in lung
7 function and increased respiratory symptoms, as well as new evidence for more subtle indicators
8 of cardiovascular health. In this review, EPA will integrate these previous findings with the
9 results of new studies on these health endpoints and, to the extent data are available, on
10 additional endpoints of concern (e.g., developmental, reproductive, systemic effects). Evidence
11 of health effects associated with peak PM exposures (less than 24-hours) will also be considered.
12 Susceptible or vulnerable subpopulations that were considered to be at greater risk to
13 effects associated with PM exposures in the last review included individuals with pre-existing
14 heart and lung diseases, older adults, and children. In this review, EPA will integrate the
15 previous understanding of sensitive subpopulations with new evidence on these and possibly
16 additional sensitive subpopulations (e.g., fetuses, neonates).
17 In the last review of the suite of secondary standards, EPA focused on evaluating
18 visibility impairment associated with aerosol compounds present in ambient air, selecting PM2.5
19 as the appropriate indicator for the standard. Other welfare effects including effects on climate
20 change processes, vegetation, and ecosystems as well as materials damage and soiling related to
21 both fine and coarse particles were considered to a lesser extent. In this review, EPA will
22 continue to focus the assessment of welfare effects on visibility-related impacts associated with
23 fine particles. This review will include consideration of the impacts on visibility impairment
24 related to the mixture of aerosol compounds in ambient air including nitrates and sulfates. In
25 addition, drawing on the information in the ISA, EPA will again consider other welfare effects in
26 this review, for example, climate-related effects and/or welfare effects associated with deposition
27 of specific particles (e.g., ecotoxicity of heavy metals). In a separate effort, EPA has recently
28 initiated a joint review of the nitrogen dioxide (NO2) and sulfur dioxide (SO2) secondary
6Please see http://www.cpa.gOv/itii/naaqs/standards/nox/s nox index.html for more information on the review of
the primary NO2 NAAQS and hitp://www.cpa.gov/itn/naaqs/standards/so2/s so2 indcx.html for more information
on the review of the primary SC>2 NAAQS.
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1 NAAQS.7 That review will consider gaseous and particulate species of NOx and SOx with
2 respect to acidification effects on ecosystems and will focus on the ecosystem-related welfare
3 effects that result from the deposition of these pollutants and transformation products in the gas-
4 phase, rather than on the effects of particulate NOx and SOx that remain in the atmosphere.
7 Please see htip://www.cpa.gov/itn/naaqs/standards/no2so2scc/indcx.html for more information on the NOx/SOx
Secondary NAAQS review.
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i 2 REVIEW SCHEDULE
2 Table 2-1 outlines the schedule under which the Agency will conduct this review.
3 Consistent with this schedule, in June 2007, EPA's National Center for Environmental
4 Assessment in Research Triangle Park, NC (NCEA-RTP) announced the initiation of the current
5 periodic review of the air quality criteria for PM and the PM2.5 and PMio NAAQS and issued a
6 call for information in the Federal Register (72 FR 35462, June 28, 2007). Also, as an initial step
7 in the new NAAQS review process described in Section 1.1 above, EPA invited a wide range of
8 external experts as well as EPA staff, representing a variety of areas of expertise (e.g.,
9 epidemiology, human and animal toxicology, statistics, risk/exposure analysis, atmospheric
10 science) to participate in two workshops: (1) Workshop to Discuss Policy-Relevant Science to
11 Inform EPA's Integrated Plan for the Review of the Primary PM NAAQS (conducted July 11-
12 13, 2007 in Research Triangle Park, NC) and (2) Workshop to Discuss Policy-Relevant Science
13 to Inform EPA's Integrated Plan for the Review of the Secondary PM NAAQS (conducted July
14 16, 2007 in Chapel Hill, NC) (72 FR 34003 and 34005, June 20, 2007). These workshops
15 provided an opportunity for the participants to broadly discuss the key policy issues around
16 which EPA would structure the PM NAAQS review and to discuss the most meaningful new
17 science that would be available to inform our understanding of these issues. Based in part on
18 the workshop discussions, EPA has developed this draft integrated review plan outlining the
19 schedule, the process, and the key policy-relevant science issues that will guide the evaluation of
20 the air quality criteria for PM and the review of the primary and secondary PM NAAQS.
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Table 2-1. Proposed Schedule for Development of Revised PM Integrated Science Assessment
(ISA) and Review of PM25 and PM10 NAAQS
Stage of Review
Major Milestone
Draft Target Dates
Integrated Plan Literature Search
Federal Register Call for Information
Workshops on Science/Policy Issues
Prepare Draft Integrated Review Plan
CASAC Consultation
Prepare Final Integrated Review Plan
Ongoing
June 2007
July 2007
October 2007
November 2007
December 2007
Science
Assessment
Prepare First Draft ISA
CASAC/Public Review of First Draft ISA
Prepare Second Draft ISA
CASAC/Public Review of Second Draft ISA
Prepare Final ISA
August 2008
October 2008
March 2009
May 2009
September 2009
Risk/Exposure
Assessments
Prepare Draft Scope and Methods Plan
CASAC Consultation on Scope and Methods Plan
Prepare First Draft Risk/Exposure Assessments
CASAC/Public Review of First Draft Risk/Exposure
Assessments
Prepare Second Draft Risk/Exposure Assessments
CASAC/Public Review of Second Draft Risk/Exposure
Assessments
Prepare Final Risk/Exposure Assessments
September 2008
October 2008
April 2009
May 2009
November 2009
January 2010
March 2010
Policy
Assessment/
Rulemaking
Advance Notice of Proposed Rulemaking (ANPR)
CASAC Review/Public Comment on ANPR
Proposed Rulemaking
Final Rulemaking
June 2010
August 2010
January 2011
October 2011
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i 3 KEY POLICY-RELEVANT ISSUES
2 The key policy-relevant issues to be addressed in this review are presented below as a
3 series of policy-relevant questions that will frame our approach to determining whether the
4 current primary and secondary NAAQS for PM should be retained or revised. The ISA,
5 risk/exposure assessment, and visibility and other welfare-related assessment to be conducted in
6 this review will provide the basis for addressing these questions. The answers to these questions,
7 and the resulting conclusions regarding the corresponding policy-relevant issues, will inform the
8 policy assessment/rulemaking that will lead to the decision of whether to retain or revise the
9 current 24-hour and annual primary and secondary standards for PM2.5 and the 24-hour primary
10 and secondary standards for PMi0.
11 In the last PM NAAQS review, EPA focused on particle mass and primarily
12 distinguished between two categories of particle pollution based on size (i.e., fine- and coarse-
13 fraction particles), and conducted parallel evaluations of the available scientific evidence relating
14 to each category. The importance of specific PM components and sources was evaluated within
15 the context of this basic size differentiation. In this review, EPA will consider the extent to which
16 new information has become available to assess and determine how particle pollution is defined.
17 Specific characteristics to consider will include particle size/mass, composition, and
18 sources/environments (e.g., urban and rural areas).
19 3.1 ISSUES TO BE CONSIDERED IN THE CURRENT REVIEW OF THE
20 PRIMARY PM NAAQS
21 The first step in reviewing the adequacy of the current primary PM standards is to
22 consider whether the available body of scientific evidence, assessed in the ISA and addressed in
23 the air quality and risk/exposure assessments, supports or calls into question the scientific
24 conclusions reached in the last review regarding health effects related to exposure to fine and
25 thoracic coarse particles in the ambient air. This evaluation of the available scientific evidence
26 will focus on policy-relevant issues by addressing a series of questions including the following:
27 • Has new information altered the scientific support for the occurrence of health effects
28 following short- and/or long-term exposure to levels of fine and thoracic coarse particles
29 found in the ambient air?
30 • Has new information altered conclusions from previous reviews regarding the plausibility
31 of adverse health effects associated with PM exposures?
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1 • What evidence is available from recent studies focused on specific components or
2 sources of PM to inform our understanding of the nature of PM exposures that are linked
3 to various health outcomes?
4 "To what extent is key scientific evidence becoming available to improve our
5 understanding of the health effects associated with various time periods of PM exposures,
6 including not only daily and chronic (months to years) exposures, but also peak PM
7 exposures (less than 24-hour)? To what extent is critical research becoming available
8 that could improve our understanding of the relationship between various health
9 endpoints and different lag periods (e.g., single day, multi-day distributed lags)?
10 • What data are available to improve our understanding of spatial and/or temporal
11 heterogeneity of exposures to PM and its components?
12 "At what levels of PM exposure do health effects of concern occur? Is there evidence for
13 the occurrence of adverse health effects at levels of PM lower than those observed
14 previously? If so, at what levels and what are the important uncertainties associated with
15 that evidence?
16 "Do risk/exposure estimates suggest that exposures of concern for PM-induced health
17 effects will occur with current ambient levels of PM or with levels that just meet the
18 current standards? If so, are these risks/exposures of sufficient magnitude such that the
19 health effects might reasonably be judged to be important from a public health
20 perspective? What are the important uncertainties associated with these risk/exposure
21 estimates?
22 • To what extent is key evidence becoming available that could inform our understanding
23 of subpopulations that are particularly sensitive to PM exposures? Specifically, is there
24 new or emerging evidence on health effects beyond cardiovascular and respiratory
25 endpoints (e.g., systemic effects, developmental effects) that suggest additional sensitive
26 subpopulations should be given increased focus in this review (e.g., fetuses, neonates)?
27 • To what extent have important uncertainties identified in the last review been reduced
28 and/or have new uncertainties emerged?
29
30 Drawing upon the evidence and analyses presented in the ISA and risk/exposure
31 assessment, EPA will evaluate whether revisions to the current suite of primary PM standards
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1 might be appropriate and, if so, how these standards might be revised. Specifically, EPA will
2 evaluate how the scientific evidence informs decisions regarding the basic elements of the
3 NAAQS: indicator, averaging time, level, and form. These elements will be considered
4 collectively in evaluating the health protection afforded by the current or any alternative
5 standards considered. Specific policy-relevant questions that will be addressed include:
6 • Do the evidence, the air quality assessment, and the risk/exposure assessment provide
7 support for considering different pollutant indicators for fine and thoracic coarse
8 particles? Specifically, is there evidence to support continuing to maintain the basic mass
9 size-fraction approach used in the last review or does the evidence support an alternative
10 approach for defining particle pollution, including other size fractions, specific
11 components, specific source-related mixtures, and/or indicators other than mass?
12 • Do the evidence, the air quality assessment, and the risk/exposure assessment provide
13 support for considering different averaging times?
14 • What range of levels is supported by the evidence, the air quality assessment, and the
15 risk/exposure assessments? What are the uncertainties and limitations in the evidence
16 and the assessments?
17 • What is the range of forms supported by the evidence, the air quality assessment, and the
18 risk/exposure assessments? What are the uncertainties and limitations in the evidence
19 and the assessments?
20 3.2 ISSUES TO BE CONSIDERED IN THE CURRENT REVIEW OF THE
21 SECONDARY PM NAAQS
22 The first step in reviewing the adequacy of the current secondary PM standards is to
23 consider whether the available body of scientific evidence, assessed in the ISA and addressed in
24 the air quality and visibility and other welfare-related effects assessment, supports or calls into
25 question the scientific conclusions reached in the last review regarding visibility impairment and
26 climate-related effects associated with ambient PM and other welfare-related effects associated
27 with exposures to deposited fine and/or coarse particles. This evaluation of the available
28 scientific evidence will focus on policy-relevant issues by addressing a series of questions
29 including the following:
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1 • What new evidence is available on the relationship between PM mass/size fraction and/or
2 specific PM components and visibility impairment and climate-related and other welfare
3 effects?
4 "To what extent has key scientific evidence now become available to improve our
5 understanding of the nature and magnitude of visibility, climate, and ecosystem responses
6 to PM and the variability associated with those responses (including ecosystem type,
7 climatic conditions, environmental effects and interactions with other environmental
8 factors and pollutants)?
9 "At what levels of ambient PM do visibility impairment and/or environmental effects of
10 concern occur? Is there evidence for the occurrence of adverse visibility and other
11 welfare-related effects at levels of PM lower than those observed previously? If so, at
12 what levels and what are the important uncertainties associated with the evidence?
13 • Do the analyses suggest that PM-induced visibility impairment and/or other welfare-
14 effects will occur with current ambient levels of PM or with levels that just meet the
15 current standards? If so, are these effects of sufficient magnitude such that these effects
16 might reasonably be judged to be important from a public welfare perspective? What are
17 the uncertainties associated with these estimates?
18 "To what extent have important uncertainties identified in the last review been reduced
19 and/or have new uncertainties emerged?
20 Drawing upon the evidence and analyses presented in the ISA and visibility and other
21 welfare-related assessments, EPA will evaluate whether revisions to the current suite of
22 secondary PM standards might be appropriate and, if so, how these standards might be revised.
23 Specifically, EPA will evaluate how the scientific evidence informs decisions regarding the
24 basic elements of the NAAQS: indicator, averaging time, level, and form. These elements will
25 be considered collectively in evaluating the welfare protection afforded by the current or any
26 alternative standards considered. Specific policy-relevant questions that will be addressed
27 include:
28 • Do the evidence, the air quality assessment and the visibility and other welfare-related
29 assessments provide support for considering different pollutant indicators or averaging
30 times? What are the uncertainties and limitations in the evidence and the assessments?
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1 • What range of levels is supported by the evidence, the air quality assessments, and the
2 visibility and other welfare-related assessments? What are the important uncertainties
3 associated with that evidence?
4 • What is the range of forms supported by the evidence, the air quality assessment, and the
5 visibility and other welfare-related assessments? What are the uncertainties and
6 limitations in the evidence and the assessments?
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i 4 SCIENCE ASSESSMENT
2 4.1 SCOPE AND ORGANIZATION
3 The science assessment for PM will consist of the ISA and its supporting annexes. The
4 ISA will critically evaluate and integrate the scientific information on exposure, health, and
5 welfare effects associated with PM in ambient air. The annexes, which will summarize relevant
6 studies, will provide a detailed basis for developing the ISA. The annexes will include scientific
7 evidence in the discipline areas of epidemiology, toxicology, and dosimetry as well as human
8 exposure and atmospheric science relevant to the review of the primary PM NAAQS. The
9 annexes will also include scientific evidence related to welfare effects categories, including
10 visibility impairment, effects on soils, animals, and vegetation related to or associated with
11 deposition of particulate metals, and the relationship of PM to climate that are relevant to the
12 review of the secondary PM NAAQS. The ISA will draw from this evidence and synthesize the
13 current state of knowledge on the most relevant issues pertinent to the review of the NAAQS for
14 PM. Information from other scientific fields will be integrated into the health and welfare effects
15 evidence if it contributes to a better understanding of population exposure and/or risk or to a
16 better understanding of the nature, sources, distribution, measurement, and/or concentrations of
17 PM in ambient air. The ISA discussions will be designed to focus on the key policy-relevant
18 questions described in Section 3 of this document.
19 The focus of the ISA will be on literature not included in the previous review of the
20 air quality criteria for PM. Key findings and conclusions from the 2004 Air Quality Criteria
21 Document (AQCD, U.S. EPA, 2004) for PM will be briefly summarized at the beginning of
22 the ISA. Also included in the ISA will be information on studies included in the 2006
23 Provisional Assessment of Recent Studies on Particulate Matter (U.S. EPA, 2006a). This
24 document presented findings of EPA's survey and provisional assessment of studies relevant
25 to assessing the health effects of PM that were published too recently to be included in the
26 2004 PM AQCD.
27 The results of new studies will be integrated with previous findings. Important older
28 studies will be more specifically discussed if they are open to reinterpretation in light of newer
29 data. Generally, only information that has undergone scientific peer review and that has been
30 published (or accepted for publication) in the open literature will be considered. Emphasis will
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1 be placed on studies conducted at or near PM concentrations found in ambient air. However, in
2 recognition of the fact that toxicologic studies do not necessarily reflect effects in the most
3 sensitive populations, studies at higher exposure levels will be included when they provide
4 information relevant to previously unreported effects, evidence of the potential mechanism for an
5 observed effect, or information on exposure-response relationships.
6 4.2 ASSESSMENT APPROACH
7 Introduction
8 The EPA's National Center for Environmental Assessment in Research Triangle Park
9 (NCEA-RTP) is responsible for preparing the ISA and its annexes for PM. Expert authors
10 include EPA staff with an extensive base of knowledge in their respective fields and extramural
11 scientists contracted to the EPA.
12 Literature Search
13 The NCEA-RTP will use a systematic approach to identify relevant studies for
14 consideration. A Federal Register notice (72 FR 35462, June 28, 2007) was published to
15 announce the initiation of this review and request information from the public. An initial
16 publication base will be established by searching MEDLINE, Toxfile, Pascal, Biosis, and
17 Embase using as key words the terms particulate, particle, PM, PM2.5, PMio, coarse, fine,
18 ultrafme, carbon black, ROFA, oil fly ash, CAPS, diesel, metals associated with PM, elemental
19 carbon, organic carbon, nitrate, sulfate, traffic, visibility, light extinction, and soot. As
20 appropriate, the search strategy will be reexamined and modified to enhance identification of
21 pertinent published papers. Additional papers will be identified for inclusion in the publication
22 base in several ways. First, EPA staff will review pre-publication tables of contents for journals
23 in which relevant papers may be published. Second, expert Section authors will be charged with
24 independently identifying relevant literature. Finally, additional publications that may be
25 pertinent will be identified by both CASAC and the public during the external review process.
26 The studies identified will include research published or accepted for publication by a date
27 determined to be as inclusive as possible given the relevant target dates in the PM NAAQS
28 review schedule. Some additional studies, published after that date, may also be included if they
29 provide new information that impacts one or more key scientific issues. The combination of
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1 these approaches should produce the comprehensive collection of pertinent studies needed to
2 form the basis of the ISA.
3 Criteria for Study Selection
4 In selecting epidemiologic studies for the present assessment, EPA will consider whether
5 a given study contains information on (1) short- or long-term exposures at or near ambient levels
6 of PM; (2) health effects of specific PM components or mixtures related to PM sources (e.g.,
7 motor vehicle emissions, combustion-related particles); (3) health endpoints that repeat or extend
8 findings from earlier assessments as well as those not previously extensively researched; (4)
9 populations that are susceptible and/or vulnerable to PM exposures8; (5) multiple pollutant
10 analyses and other approaches to address issues related to potential interactions (e.g., are there
11 synergistic effects of PM with other pollutants), confounding (e.g., is PM associated with health
12 endpoints independent of copollutants, and effect modification (e.g., is the effect of PM on health
13 endpoints modified by the presence of copollutants); and/or (6) important methodological issues
14 (e.g., lag of effects, model specifications, thresholds, mortality displacement) related to PM
15 exposure effects. Among the epidemiologic studies, particular emphasis will be focused on
16 those relevant to standard setting in the United States. Specifically, studies conducted in the U.S.
17 or Canada will be generally accorded more emphasis than those from other geographic regions,
18 as the potential impacts of different health care systems and the underlying health status of
19 populations need to be accounted for in the assessment. In addition, emphasis will be placed on
20 discussion of (1) new, multi-city studies that employ standardized methodological analyses for
21 evaluating PM effects, provide overall estimates for effects based on combined analyses of
22 information pooled across cities, and examine results for consistency across cities; (2) new
23 studies that provide quantitative effect estimates for populations of interest; and (3) studies that
24 regard PM as a component of a complex mixture of air pollutants and thus give consideration to
25 the levels of other copollutants, correlate PM levels with these copollutants, and include
26 multipollutant analyses in the study design.
Susceptibility refers to innate (e.g., genetic or developmental) or acquired (e.g., age, disease, or smoking) factors
that make individuals more likely to experience effects with exposure to PM. Vulnerability refers to PM-related
effects due to factors including socioeconomic status (e.g., reduced access to health care) or particularly elevated
exposure levels.
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1 A set of explicit criteria will also be used to select toxicologic studies for the present
2 assessment. The selection of research evaluating controlled exposures to laboratory animals will
3 focus primarily on those studies conducted at or near ambient PM concentrations and those
4 studies that approximate expected human dose conditions in terms of concentration, size
5 distributions, and duration, which will depend on the toxicokinetics and biological sensitivity of
6 the particular laboratory animals examined. For example, rodents typically require PM
7 concentrations greater than ambient to mimic retention of particles in the lung in terms of mass
8 or surface area per lung area equivalent to humans. Additionally, animal researchers must limit
9 the number of animals used in experimental protocols, and thus must use higher concentrations
10 to observe effects. Thus, animal toxicology experiments, by necessity, are carried out at greater-
11 than-ambient concentrations. In discussing the mechanisms of PM toxicity, studies conducted
12 under atmospherically-relevant conditions will be emphasized, but studies at higher
13 concentrations also will be considered when these studies provide useful information to inform
14 our understanding of species-to-species differences and potential differences in sensitivity
15 between healthy individuals and especially susceptible human populations. Another
16 consideration in evaluating PM studies using animals is the use of inhalation vs. instillation
17 exposures. All else being equal, those studies using inhalation exposures will be given greater
18 emphasis than those using instillation exposures because inhalation studies better simulate
19 human exposure to PM. However, instillation studies must be used when assessing the effects of
20 thoracic coarse particles in rodents.
21 For research evaluating controlled human exposures to PM, emphasis will be placed on
22 studies that: (1) investigate effects both on healthy populations and on potentially susceptible
23 populations such as asthmatics or diabetics, particularly studies where subjects serve as their own
24 control to compare responses following PM exposure and sham exposure and where responses in
25 susceptible individuals are compared with those in age-matched healthy controls; (2) address
26 issues such as dose-response or time-course of responses; (3) investigate exposure to PM
27 separately and in combination with other pollutants such as 63 and NO2; (4) include control
28 exposures to filtered air; and (5) have sufficient sample size to assess findings adequately.
29 For evaluation of welfare effects research, emphasis shall be placed on (1) recent U.S.
30 studies; (2) studies that evaluate effects at realistic ambient levels; and (3) studies that consider
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1 PM as a component of a complex mixture of air pollutants. Studies conducted in other countries
2 that contribute significantly to the knowledge base will be included in the assessment.
3 These criteria provide benchmarks for evaluating various studies and for focusing on the
4 highest quality studies in assessing the body of health and welfare effects evidence. Detailed
5 critical analysis of all PM health and welfare effects studies, especially in relation to the above
6 considerations, is beyond the scope of this document. Of most relevance for evaluation of
7 studies is whether they provide useful qualitative or quantitative information on exposure-effect
8 or exposure-response relationships for effects associated with current ambient air concentrations
9 of PM likely to be encountered in the United States.
10 Quality Assurance
11 Important quality assurance measures will be incorporated from the start of the current
12 PM review. EPA uses an NCEA-RTP Plan for Information Search which details an approach to
13 gathering the scientific information, usually found in peer-reviewed journal articles, books, and
14 reports. Additionally, NCEA has Data Quality Objectives which identify inputs to the science
15 assessment and provide quality assurance (QA) instruction for researchers citing secondary
16 information.
17 Content and Organization of the ISA
18 The organization of the ISA for PM will be consistent with that used in the recent draft
19 ISAs for Nitrogen Oxides and Sulfur Oxides (U.S. EPA 2007 a, b). The ISA will contain
20 information relevant to considering whether it is appropriate to retain or revise the current
21 standards. Taking into consideration the broad policy-relevant questions outlined in Section 3,
22 the policy-relevant questions that will guide development of the ISA are related to two
23 overarching issues. The first issue is whether new evidence reinforces or calls into question the
24 scientific evidence presented and evaluated in the last PM NAAQS review. The second issue is
25 whether uncertainties from the last review have been addressed and/or whether new uncertainties
26 have emerged. Specific questions related to the review of the scientific literature for PM that
27 stem from these issues will guide the content of the ISA. These questions were derived from the
28 previous review of the PM NAAQS, as well as from discussions of new scientific evidence that
29 occurred at two recent EPA workshops as outlined in Section 2 above. These questions are listed
30 below by topic area.
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1 Source to Dose
2 Air Quality and Atmospheric Chemistry: The ISA will present and evaluate data related to
3 ambient concentrations of PM and its components; sources leading to the presence of PM in the
4 atmosphere; and chemical reactions that determine the formation, transformation, and lifetime of
5 PM in the atmosphere.
6 • The ISA will evaluate studies of commercial samplers to determine whether they
7 meet size selection performance standards. Specifically, what are the strengths and
8 weaknesses of various methods for measuring PM? To what extent are these methods
9 subject to interference from gas-phase pollutants or other gas- or aerosol-phase
10 substances? Are new research methods available to understand the spatial and
11 temporal distribution of different sizes and/or components of PM?
12 • Based on recent air quality and emissions data, what are the current emissions and
13 ambient concentrations of PM? What spatial and temporal patterns can be seen in the
14 air quality data for PM? What new information is available on PM components (both
15 primary and secondary particles) and mixtures of particles found in various regions of
16 the country? How do particles in urban areas differ from those emitted or formed in
17 rural areas?
18 • Using air quality and emissions data on PM and precursor gases, together with
19 atmospheric chemical-transport models, what are the likely policy-relevant
20 background9 concentrations of PM?
21 • Because the regulatory ambient monitoring networks typically provide PM
22 concentrations only once in every three or six days, are there other techniques that
23 can augment ambient monitoring data to define better the range of concentrations and
24 the spatial and temporal variability of PM over the U.S.? How useful are satellite
25 retrievals and three-dimensional chemical transport models for understanding
26 processes and spatial and temporal variations? Can satellite data be used on a regular
27 basis to improve the characterization of PM emissions?
9 "Policy-relevant background" has been defined as the PM concentrations that would be observed in the U.S. in the
absence of anthropogenic emissions of directly emitted PM particles and PM precursors (e.g., VOC, NOx, and SOx)
in the U.S., Canada, and Mexico.
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1 • The ISA will also evaluate new information on specific PM components that merit
2 attention including information on the spatial and temporal heterogeneity of PM
3 components. Participants from the July 2007 Primary PM NAAQS workshop
4 identified elemental carbon, organics, nickel, vanadium, sulfates, and products of
5 photochemically oxidized organics as PM components that should be given greater
6 attention in this review.
7 • The ISA will assess new evidence on the characterization of particles from various
8 sources, including primary and secondary particles, and the methods used to
9 characterize particle sources. The ISA will discuss the utility of source
10 apportionment modeling techniques in determining exposure surrogates for
11 epidemiology.
12 Human Exposure: The ISA will evaluate the factors that influence exposure to PM and the
13 uncertainties associated with extrapolation from ambient concentrations to personal exposures to
14 PM of ambient origin, particularly in the context of interpreting results from epidemiologic
15 studies. The issues of uncertainty differ by the exposure period of interest. Short-term exposure
16 studies (e.g., population-level studies using time-series analyses, field/panel studies) rely on
17 temporal variation in exposure while long-term exposure studies (e.g., longitudinal cohort
18 studies) rely on spatial variability of exposure. The ISA will consider the available information
19 on differential exposures to fine and coarse particles and particle characteristics such as chemical
20 composition, size, surface area, and source.
21 • Are new data available that classify PM exposure according to PM characteristics
22 such as chemical constituents, size fraction, surface area, and source?
23 • What new data are available on the relationship between exposures to PM
24 components, size fractions, and sources? What data exist on relationships between
25 PM exposure and exposure to gaseous co-pollutants?
26 • What are the uncertainties when extrapolating between stationary PM monitoring
27 instruments and personal exposure to PM of ambient origin, especially for susceptible
28 subpopulations? Issues include measurement error in outdoor ambient monitors, the
29 use of centralized monitors for estimating community concentrations, and the use of
30 centralized monitors as a surrogate for personal exposure to PM of ambient origin.
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1 • What do measurements of ambient concentrations of PM represent? To what extent
2 do they provide an estimate of ambient exposures for health studies, an indicator of
3 personal exposure to PM, and/or an indicator of exposure to other pollutants or
4 pollutant mixtures?
5 • What data are available to interpret peak, short-term, and long-term PM exposures?
6 This includes such information as air exchange rates, indoor sources, distance to
7 highways, and methods for measuring personal exposures to ambient PM. Is this
8 information available classified by PM characteristic (e.g., size, chemical
9 composition)?
10 • How do modeled predictions of PM concentrations compare with monitoring results?
11 Do quality assurance (QA) checks suggest that modeling is accurate? How do the
12 models perform at the tails of the distribution, in high concentrations areas and near
13 roadways?
14 Health Effects
15 The ISA will evaluate the literature related to cardiovascular, respiratory, and other health
16 effects associated with short and/or long term exposures to PM. This will include evaluation of
17 mortality and morbidity effects. Other health effects that may be evaluated include reproductive,
18 developmental, and neurological outcomes. Health effects that occur following short- and/or
19 long-term exposures to PM will be evaluated in epidemiologic, human clinical, and toxicologic
20 studies.
21 For a given type of health outcome, the ISA will evaluate the strength, robustness and
22 consistency of the findings from the different disciplines. The health findings will be further
23 integrated, using the toxicologic and human clinical studies to assess biologic plausibility and
24 mechanistic evidence for the epidemiology findings. A key focus of the integration of health
25 evidence will be on the attribution of health effects to exposure to different size classes,
26 components or characteristics of PM. Thus, the integrative synthesis of coherence and
27 plausibility in the health evidence for effects (e.g., respiratory morbidity with short-term
28 exposure) will focus on findings for various PM indices, to the extent that information is
29 available. Efforts will be directed at identifying the lower levels at which effects are observed
30 and at determining concentration-response relationships for various PM sizes and components.
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1 The ISA will evaluate the scientific evidence on the occurrence of health effects from long-term
2 or short-term exposure to PM at ambient levels that are lower than previously observed. The
3 ISA will also assess the evidence for uncertainties related to these associations and information
4 on the public health impacts related to ambient PM exposure. The evaluation will also focus on
5 which exposure time windows are most strongly associated with effects, for both short-term and
6 long-term exposures.
7 Short-Term Exposure:
8 • What new evidence is available on associations between PM and mortality (total,
9 respiratory or cardiovascular)?
10 • How do results of recent studies expand current understanding of the relationship
11 between acute exposure to PM and respiratory effects, such as lung function changes,
12 lung inflammation, and host defense against infectious disease? What new evidence is
13 available on the potential clinical relevance of these effects?
14 • To what extent does new evidence from studies of hospital admissions or emergency
15 department visits support previous findings regarding respiratory effects of PM? Is
16 there evidence of coherence and plausibility for effects of different PM sizes or
17 characteristics on the respiratory system?
18 • What new evidence is available on PM-related effects on the cardiovascular system?
19 Which electrocardiogram changes may be indicative of an adverse response to PM
20 and which populations may be particularly susceptible to these effects? What do
21 studies of heart rate variability tell us? Do these effects appear to be reversible and to
22 what extent? How does PM affect vascular and endothelial function and through
23 which pathways? The ISA will evaluate evidence from studies of hospitalization or
24 emergency department visits for cardiovascular diseases, and the extent to which
25 there is evidence of coherence or plausibility for effects of different PM sizes or
26 characteristics on the cardiovascular system.
27 • To what extent does exposure to PM contribute to health effects in the renal, hepatic,
28 nervous, or other systems?
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1 • What is the nature of health effects in persons exposed to multipollutant mixtures that
2 contain PM in comparison to exposure to PM alone?
3 • What biomarkers of early effect may be used in the assessments?
4 Long-Term Exposure:
5 • How do results of recent studies expand current understanding of the relationships
6 between acute, repeated exposure to PM and lung function or lung function
7 development?
8 • Can long-term exposures to PM result in chronic effects manifested as permanent
9 lung tissue damage, reduction in baseline lung function, or impaired lung function
10 development? To what extent does long-term PM exposure promote development of
11 asthma or chronic lung or cardiovascular disease? What is the relationship between
12 long-term PM exposure and shortening of human life span via promotion of such
13 diseases?
14 "To what extent does the evidence indicate that long-term exposure to PM can increase
15 the incidence of cancer, or have mutagenic or genotoxic effects? How does PM
16 affect the developing fetus or infant?
17 • What new studies are investigating measures of cardiovascular disease development
18 with chronic PM exposure? What evidence exists that demonstrates a link between
19 long-term PM exposure and atherosclerosis development or progression? Can long-
20 term exposure to PM result in chronic effects manifested as permanent cardiovascular
21 tissue damage or reductions in baseline cardiac function? What is the role of
22 systemic inflammation in initiating these effects?
23 • The ISA will also assess the evidence from studies linking long-term exposure to PM
24 with mortality from cardiovascular and respiratory diseases or cancer.
25 Causality: The ISA will evaluate the evidence for and against a causal relationship between
26 observed health outcomes and PM exposures, focusing on different size classes, components
27 and/ or characteristics of PM, to the extent possible. Biologic plausibility and coherence of the
28 evidence will be key considerations in drawing conclusions about causality. The ISA will place
29 emphasis on epidemiologic studies conducted at or near typical ambient levels, except regarding
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1 evidence of biological plausibility and mechanisms, as these may only be observable in animal
2 or human exposure study populations at higher levels than they might be observed in susceptible
3 human populations. The ISA will also assess information available from "intervention" studies
4 regarding the health impacts of decreases in ambient levels of PM that is relevant to the
5 evaluation of causality in PM-health outcome relationships.
6 Uncertainties: The ISA will evaluate uncertainty in the scientific data, particularly in relation to
7 observed epidemiologic findings.
8 • How does confounding by coexposure to other pollutants (e.g., 63, NC>2, 862, and
9 CO) and meteorological factors influence the uncertainty of the evidence base for
10 both short- and long-term PM exposures?
11 BTo what extent are the observed health effects associations attributable to PM versus
12 the pollutant mixtures that PM may be representing? For example, what is the
13 possibility that PM ambient concentrations may serve as a surrogate for personal
14 exposure to mixtures or sources, such as motor vehicle exhaust?
15 • What are the uncertainties due to other confounding or effect modification factors in
16 epidemiologic studies (e.g., demographic and lifestyle attributes, socioeconomic
17 status, genetic susceptibility factors, occupational exposure, and medical care)?
18 • What are the shapes of the concentration-response models (e.g., linear vs. threshold
19 models) and how do they influence public health impacts?
20 • What uncertainties surround the evidence for long-term effects such as life shortening
21 and development/progression of disease?
22 • How do the findings of the available studies improve our understanding of exposure
23 error? What evidence is newly available on the uncertainties related to statistical
24 model specification and how can it be used to assess the influence of these
25 uncertainties on the outcome of epidemiologic studies?
26 Biological Mechanisms of Action: The ISA will evaluate the data examining mechanisms for
27 the health outcomes associated with exposure to PM.
28 • Is there new information related to the pathways and biological mechanism(s) of
29 action for PM of different size classes or characteristics?
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1 • What are the potential mechanisms of response to PM, with a focus on
2 physical-chemical particle characteristics, response pathway(s), oxidative stress, and
3 exposure-dose-response relationships?
4 • What are the inherent interspecies differences in sensitivity to PM and in PM
5 dosimetry in different regions of the respiratory tract? How does dosimetry differ
6 based upon particle size?
7 • What are the interspecies differences in basic mechanisms of lung injury and repair
8 and cardiovascular responses?
9 • What PM reaction products can be found in the respiratory tract cells, tissues, or
10 fluids as biomarkers of PM exposure?
11 • Are there interactions between PM components that increase bioavailability, such as
12 sulfate increasing the bioavailability or activity of iron or other transition metals?
13 • What are the mechanisms and time-courses of PM-induced cellular and tissue injury,
14 repair, and remodeling?
15 • Which PM-induced health effects are sufficiently characterized to be quantitatively
16 compared across species?
17 Susceptible and Vulnerable Populations—; The ISA will examine health outcome data to identify
18 specific groups that are more susceptible and/or vulnerable to the adverse effects of PM exposure
19 than normal healthy adults (e.g., patients with COPD, children, and asthmatics). The host and
20 environmental factors that are responsible for differential susceptibility to PM will be
21 investigated.
22 • What do controlled human exposure, animal toxicologic, and epidemiologic studies
23 indicate regarding the relationship between acute exposures to PM and health effects
24 of concern in healthy individuals and in those individuals with preexisting diseases
25 (e.g., asthma, COPD, cardiovascular diseases)? What other medical conditions (e.g.,
Susceptibility refers to innate (e.g., genetic or developmental) or acquired (e.g., age, disease, or smoking) factors
that make individuals more likely to experience effects with exposure to PM. Vulnerability refers to PM-related
effects due to factors including socioeconomic status (e.g., reduced access to health care) or particularly elevated
exposure levels.
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1 diabetes, metabolic syndrome) are identified as increasing susceptibility to PM
2 effects? What are the pathways and mechanisms through which PM may be acting
3 for these groups? What is the nature and time-course of the development of effects in
4 healthy persons and in persons with pre-existing disease (e.g., asthma, heart disease)?
5 • The ISA will assess new evidence on the extent to which children and older adults are
6 more sensitive than the general population to effects from PM exposure?
7 • The ISA will evaluate the extent to which susceptibility to the effects of short-term
8 PM exposure is associated with long-term PM susceptibility.
9 • What evidence is available regarding susceptibility of other subgroups, such as those
10 based on gender or on genetic makeup, on PM-induced responses?
11 • What host and environmental factors (e.g., demographic, socioeconomic, and genetic)
12 are associated with susceptibility and/or vulnerability to short- and long-term
13 exposure to PM?
14 • New evidence will be evaluated regarding population groups with potentially greater
15 vulnerability to effects of PM, such as those populations living near roads or in other
16 areas with increased exposures.
17 • What information is available on exposure of sensitive and vulnerable populations to
18 PM and its components?
19 Public Health Impact: The ISA will present concepts related to the potential for defining adverse
20 health effects. To accomplish this, the implications for public health of different health effects
21 will be discussed. This will include, as available, estimates of the numbers of people in specific
22 at-risk populations groups (e.g., asthmatics, diabetics, older adults, children).
23 Ecological and Welfare Effects
24 Visibility: The ISA will summarize long-known information needed for placing current
25 information in context. Previous evaluations have indicated that anthropogenic sulfate and
26 nitrate particles are responsible for most of the regional haze in the eastern U.S. while the largest
27 haze contributors in the West are anthropogenic nitrates and organics, either directly emitted or
28 formed secondarily from other emissions. Additional sources of regional haze (e.g., dust, smoke,
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1 sea salt) have anthropogenic, biogenic, and geogenic sources that vary in strength and
2 significance by region. The ISA will evaluate newly available evidence, summarizing the recent
3 important policy-relevant findings and will include sections for aerosol/optical characteristics,
4 spatial/temporal trends, and causes of haze.
5 • The ISA will present the relationship between visibility impacts and PM and will
6 include definitions and metrics and algorithms to estimate haze from PM species
7 levels.
8 • The ISA will include a section on aerosol/optical characteristics that presents details
9 of the size-resolved chemistry, transformation relationships and effects, and the
10 algorithms used to estimate haze from paniculate data taken in the regulatory
11 measurement networks.
12 • Other findings to be included in the ISA will be spatial patterns (e.g., the Midwest
13 nitrate bulge in the U.S. and enhancement of sulfate concentrations in the eastern
14 U.S.), urban excess above remote-area background, seasonal patterns, and multiyear
15 trends, including descriptions of the roles of emissions changes and annual
16 meteorology in helping determine those trends.
17 • The ISA will discuss results of valuation studies that evaluate the extent to which air
18 pollution-related visibility impairment may be considered to be adverse.
19
20 Non-nutrient Ecosystem and Environmental Effects. Discussions will include issues of non-
21 nutrient (N and S) particle chemistry/composition (e.g., cations, trace metals, semi-volatile
22 organics); associated size fraction, and magnitude and rates of wet and dry deposition across the
23 landscape. Both direct and indirect secondary welfare effects will be discussed in the ISA,
24 including effects on vegetation, soils, waters and wildlife (e.g., bioaccumulation) as described in
25 the phytotoxicology and ecotoxicology literature (focusing on copper, mercury, other trace
26 metals). Soiling and materials damage will also be discussed. Nutrient N and S ecosystem
27 effects will be addressed in the concurrent review of NC>2 and SC>2 secondary NAAQS.n
28
1: Please see hltp://www.cpa.gov/itn/naaqs/standards/no2so2scc/indcx.html for more information on the NO2/SO2
Secondary NAAQS review.
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1 Effects of PM on Climate: The ISA will present information on temperature effects related to
2 the various components of PM. Also addressed will be aerosol size/effect dependencies (e.g.,
3 cloud formation and precipitation) and aerosol constituent/effect dependencies (e.g., black
4 carbon vs. 804).
5
6 Effects of Climate on PM: The ISA will review information on the role of future predicted
7 climate change in altering the emissions, transport and transformation, and fate of PM in the U.S.
8 Additionally, information on the feedbacks to climate from primary and secondary PM in the
9 U.S. will be collected and assessed.
10 Outline and Annexes
11 In addition to these major research areas and specific questions pertaining to each area, a
12 broader question is how to organize this complex information. A draft outline is attached in
13 Appendix B which details a high-level organizational strategy for the ISA.
14 The ISA will be supplemented by a series of annexes, which will be focused on
15 accomplishing two goals. The first goal will be to identify scientific research that is relevant to
16 informing key policy-relevant issues. The second goal will be to produce a base of evidence
17 containing all of the publications relevant to the PM review. The annexes will provide
18 information on (1) the chemistry, physics, sources, emissions, and measurement of PM; (2)
19 environmental concentrations and human exposure to PM; (3) dosimetry; (4) toxicologic studies
20 of PM health effects in laboratory animals and in vitro systems; (5) human clinical studies
21 examining health effects following controlled exposure to PM; (6) epidemiologic studies of
22 health effects from short- and long-term exposure to PM; (7) environmental studies on visibility,
23 material damage, and ecosystem stress; and (8) climate change related to PM. More detailed
24 information on various methods and results for the health and environmental studies will be
25 summarized in tabular form in the annexes. These tables will generally be organized to include
26 information about (1) concentrations, size fractions and components of PM and related averaging
27 times; (2) description of study methods used; (3) results and comments; and (4) quantitative
28 outcomes for PM measures. Additionally, annexes will contain background material on
29 legislative requirements, the NAAQS review process, and the history of earlier PM reviews.
30
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1 4.3 SCIENTIFIC AND PUBLIC REVIEW
2 Drafts of the ISA will be reviewed by the CAS AC PM Review Panel and made available
3 for public comment. The annexes to the ISA will also be made available to CASAC in order to
4 assist with their review; however, the panel will not be specifically charged with reviewing the
5 annexes. The CASAC PM Review Panel will review the first draft ISA and discuss their
6 comments in a public meeting announced in the Federal Register. Based on CASAC's past
7 practice, EPA anticipates that key CASAC advice and recommendations for revision of the first
8 draft ISA will be summarized by the CASAC Chair in a letter to the EPA Administrator. In
9 revising the first draft ISA, EPA will take into account any such recommendations. EPA will
10 also consider comments received from CASAC or from the public at the meeting itself and any
11 written public comments. EPA will prepare a second draft ISA for CASAC review and public
12 comment. The CASAC PM Review Panel will review the second draft ISA and discuss their
13 comments in a public meeting announced in the Federal Register. Again, based on CASAC's
14 past practice, EPA anticipates that key CASAC advice and recommendations for revision of the
15 second draft ISA will be summarized by the CASAC Chair in a letter to the EPA Administrator.
16 In finalizing the ISA, EPA will take into account any such recommendations. EPA will also
17 consider comments received from CASAC or from the public at the meeting itself and any
18 written public comments. After appropriate revision, the final document will be made publicly
19 available on an EPA website and in hard copy. A notice announcing the availability of the final
20 ISA will be published in the Federal Register. In addition, the final ISA will be placed in the
21 rulemaking docket.
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i 5 HUMAN HEALTH ASSESSMENT
2 5.1 OVERVIEW
3 Characterizing health risks for the current review of the primary NAAQS for PM will
4 include conducting air quality analyses to support quantitative risk and/or exposure assessments
5 in specific locations as well as putting the results into a broader public health perspective. These
6 assessments will be designed to estimate human exposures and to characterize the potential
7 health risks that are associated with current ambient levels, with ambient levels simulated to just
8 meet the current standards, and with ambient levels simulated to just meet alternative standards
9 that may be considered. As part of such analyses, explicit and, where possible, quantitative
10 characterizations of the uncertainties associated with the air quality analyses, as well as risk and
11 exposure estimates will be developed. In addition, information on baseline incidence rates for
12 specific health effects endpoints will be considered in the analyses.
13 The major components of the risk characterization (e.g., air quality analyses, quantitative
14 exposure assessment, quantitative health risk assessment, broad health risk characterization) are
15 outlined below and will be described in greater detail in a Scope and Methods Plan. Preparation
16 of this detailed plan is underway and coincides with the development of the first draft ISA to
17 facilitate the integration of policy-relevant science into both documents. In particular, the
18 availability of air quality and concentration-response data will impact the type of risk and
19 exposure assessments that will be developed.
20 An important issue associated with conducting human health assessments is the
21 characterization of uncertainty and variability. Uncertainty refers to the lack of knowledge
22 regarding both the actual values of model input variables (parameter uncertainty) and the
23 physical systems or relationships (model uncertainty - e.g., the shapes of concentration-response
24 relationships). Variability refers to the heterogeneity in a population of variable of interest that is
25 inherent and cannot be reduced through further research.
26 5.2 OVERVIEW OF HEALTH RISK ASSESSMENT FROM PRIOR
27 REVIEW
28 In the last PM NAAQS review, EPA conducted a quantitative health risk assessment for
29 selected health endpoints to provide additional information and insights that could help inform
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1 decisions on the standards. The limitations of such an assessment were clearly articulated.12
2 EPA did not conduct an exposure assessment for that review. The approach used to develop
3 quantitative risk estimates associated with exposures to PM2.5 was built upon the more limited
4 risk assessment conducted during the review completed in 1997. The expanded and updated
5 assessment conducted in the review completed in 2006 included estimates of risks of mortality
6 (total non-accidental, cardiovascular, and respiratory), morbidity (hospital admissions for
7 cardiovascular and respiratory causes), and respiratory symptoms (not requiring hospitalization)
8 associated with recent short-term (daily) ambient PM2.5 levels and risks of total,
9 cardiopulmonary, and lung cancer mortality associated with long-term exposure to PM2.5 in a
10 numb er of exampl e urb an areas.13
11 The EPA recognized that there were many sources of uncertainty and variability inherent
12 in the inputs to this assessment and that there was a high degree of uncertainty in the resulting
13 PM2 5 risk estimates. Such uncertainties generally related to a lack of clear understanding of a
14 number of important factors, including, for example, the shape of concentration-response
15 functions, particularly when effect thresholds could neither be discerned nor determined not to
16 exist; issues related to selection of appropriate statistical models for the analysis of the
17 epidemiologic data; the role of potentially confounding and modifying factors in the
18 concentration-response relationships; issues related to simulating how PM2.5 air quality
19 distributions would likely change in any given area upon meeting a particular standard, since
20 strategies to reduce emissions had not yet been defined; and whether there would be differential
21 reductions in the many components within PM2 5 and, if so, whether this would result in
22 differential reductions in risk. While some of these uncertainties were addressed quantitatively
23 in the form of estimated confidence ranges around central risk estimates, other uncertainties and
24 the variability in key inputs were not reflected in these confidence ranges, but rather were
25 addressed through separate sensitivity analyses or characterized qualitatively (U.S. EPA, 2005,
26 Section 4; Abt Associates, 2005)
12 The EPA continues to support the development and application of risk assessment methods with the goal of
improving the characterization of risks and the communication of uncertainties in such risk estimates.
13 The risk assessment was discussed in the Staff Paper (EPA, 2005, Section 4) and presented more fully in a
technical support document, Particulate Matter Health Risk Assessment for Selected Urban Areas (Abt Associates,
2005). The assessment scope and methodology were developed with considerable input from the CASAC Panel and
the public, with CASAC concluding that the general assessment methodology and framework were appropriate
(Hopke, 2002).
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1 The concentration-response relationships used in the assessment were based on findings
2 from human epidemiologic studies that relied on fixed-site, population-oriented, ambient
3 monitors as a surrogate for actual ambient PM2.s exposures. The risk assessment included a
4 series of base case estimates that, for example, included various cutpoints intended as surrogates
5 for alternative assumed population thresholds. In its review of the Staff Paper and quantitative
6 risk assessment, the CASAC Panel commented that, for the purpose of estimating public health
7 impacts, it "favored the primary use of an assumed threshold of 10 |ig/m3," 24-hour average, and
8 that "a major research need is for more work to determine the existence and level of any
9 thresholds that may exist or the shape of nonlinear concentration-response curves at low levels of
10 exposure that may exist" (Henderson, 2005a). Other uncertainties were addressed in various
11 sensitivity analyses (e.g., the use of single- versus multi-pollutant models, use of single- versus
12 multi-city models, use of a distributed lag model) and had a more moderate and often variable
13 impact on the risk estimates in some or all of the cities.
14 Key observations and insights from the PM2.5 risk assessment, together with important
15 caveats and limitations, were discussed in Section II.B of the 2006 proposal notice (71 FR 2637
16 to 2641, January 17, 2006). In general, estimated risk reductions associated with going from just
17 meeting the current suite of PM2.5 standards to just meeting alternative suites of annual and 24-
18 hour standards for all the various assumed cutpoints showed patterns of increasing estimated risk
19 reductions as either the annual or 24-hour standard, or both, were reduced over the range
20 considered in the assessment, and the estimated percentage reductions in risk were strongly
21 influenced by the assumed cutpoint level (see U.S. EPA, 2005, Figures 5-1, 5-2, 5A-1, and 5A-
22 2).
23 The general overview and discussion of key components of the risk assessment used to
24 develop risk estimates for PM2 5 presented above is also applicable to the risk assessment done
25 for PMio-2.5 as part of the last review. However, the scope of the risk assessment for PMi0-2.5 was
26 much more limited than that for PM2.5, reflecting the much more limited body of epidemiologic
27 evidence and air quality information available for PMio-2.5- As discussed in Section 4 of the
28 Staff Paper (U.S. EPA, 2005), the PMio-2.5 risk assessment included risk estimates for just three
29 urban areas for two categories of health endpoints related to short-term exposure to PMio-2.s:
30 hospital admissions for cardiovascular and respiratory causes, and respiratory symptoms.
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1 Estimates of hospital admissions attributable to short-term exposure to PMio-2.5 were
2 developed for Detroit (cardiovascular and respiratory admissions) and Seattle (respiratory
3 admissions), and estimates of respiratory symptoms were developed for St. Louis. While one of
4 the goals of the PMio-2.5 risk assessment was to provide estimates of the risk reductions
5 associated with just meeting alternative PMio-2.5 standards, EPA concluded that the nature and
6 magnitude of the uncertainties and concerns associated with this portion of the risk assessment
7 weighed against use of these risk estimates as a basis for recommending specific standard levels
8 (U.S. EPA, 2005, p. 5-69). These uncertainties and concerns were summarized in the proposal
9 notice (see FR 71 2662, January 17, 2006) and discussed more fully in the Staff Paper (U.S.
10 EPA, 2005, Section 4) and associated technical support document (Abt Associates, 2005).
11 5.3 CURRENT AIR QUALITY CHARACTERIZATION
12 Air quality analyses are required to conduct both exposure and health risk assessments for
13 NAAQS reviews. These analyses will build upon the analyses included in the ISA and include
14 consideration of: (1) summaries of recent air quality data, (2) estimates of policy-relevant
15 background (PRB) concentrations, and 3) air quality simulation procedures that modify recent air
16 quality data to reflect changes in the distribution of air quality estimated to occur at some
17 unspecified time in the future when an area just meets a given set of NAAQS. In this review, air
18 quality analyses will be conducted to support quantitative risk and/or exposure assessments for
19 specific locations. Air quality analyses also will be conducted to place the results of the
20 quantitative risk/exposure assessments into a broader public health perspective.
21 As part of these analyses, it will be necessary to adjust recent PM air quality data to
22 simulate just meeting the current suite and any alternative suites of PM standards. In the last
23 review, EPA used a proportional rollback approach (U.S. EPA, 2005, section 4.3.1.2). EPA will
24 consider alternative air quality simulation procedures for use in this current review, and will
25 evaluate candidate procedures for simulating changes in PM air quality likely to result from just
26 meeting the current or alternative suites of standards based on analyzing changes in PM levels
27 that have been observed historically and/or analyzing changes in PM levels predicted by air
28 quality models. EPA will consider factors which may influence the concentration distributions
29 such as potential source concentrations, as well as the influence of local and regional pollution.
30 In this review, EPA also will examine current techniques that may be used to assess the
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1 variability and uncertainty of the simulated change in concentrations likely to result from just
2 meeting the current or alternative standards.
3 5.4 CURRENT HUMAN POPULATION EXPOSURE ASSESSMENT
4 APPROACH
5 As part of the last PMNAAQS review, EPA did not conduct an exposure assessment. For
6 this review, EPA is considering conducting a quantitative exposure assessment. This assessment
7 would build upon the information presented in the ISA and include discussions of factors that
8 affect exposure to ambient PM and the use of fixed site measurements of ambient PM
9 concentrations as a surrogate for population exposure in epidemiologic studies. There are two
10 specific purposes that such an assessment would serve: (1) providing insight on population
11 exposures with respect to informing the interpretation of available epidemiologic studies; and (2)
12 assessing population exposures above benchmark levels of concern, and possibly providing input
13 to quantitative risk assessments based on evidence from clinical studies.14
14 Performing an exposure analysis will be helpful for identifying the various personal and
15 building-related factors which may be responsible for some of the differences observed in
16 epidemiologic studies of ambient PM. Exposure-related factors may contribute to city-to-city
17 differences (mostly seen in time-series studies) in the reported PM concentration-response
18 functions or in the results from intra-urban studies (e.g., cohort studies of long-term exposures to
19 PM). Thus, an important reason for conducting an exposure assessment for PM would be to shed
20 some light on these issues and attempt to examine and quantify uncertainties in the existing PM
21 epidemiology literature. EPA will consider modeling specific locations and time periods which
22 coincide with epidemiologic studies, if evidence indicates that such an analysis would prove to
23 be useful.
24 An exposure assessment addressing the second purpose would be designed to estimate
25 population exposures to ambient PM2.5 and PMio-2.s in a number of generally representative
26 urban areas across the U.S. These areas would be selected to represent a variety of populations,
27 geographic areas, climates, and patterns of PM air quality levels. In addition, selection criteria
28 might include consideration of locations of critical PM field and epidemiologic studies used to
29 support the planned quantitative risk assessment. The exposure periods to be modeled would, at
14 At this time, based on discussions at the July 2007 Workshop, EPA staff are unaware of any results from human
clinical studies that would provide the basis for exposure-response functions that could inform a quantitative risk
assessment.
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1 a minimum, encompass the most recent 3-year period for which air quality data are available.
2 EPA is considering developing exposure estimates for the general population as well as for
3 selected sensitive subpopulations (e.g., children, children with asthma or diabetes, adults over 70
4 years of age, individuals with pre-existing heart or respiratory conditions). The areas, time
5 periods, and populations modeled will depend on the availability of data and time and resource
6 constraints.
7 A quantitative exposure assessment would take into account factors including the
8 magnitude and duration of PM exposures and the frequency of repeated peak exposures.
9 Estimates could be developed for several measures of exposure to various levels of PM2.5 and/or
10 PMio-2.5 air quality, including estimates of the number of people exposed one or more times at or
11 above a given PM concentration, and estimates of person-occurrences which accumulate
12 occurrences of specific exposure conditions over all people in the population of interest.
13 EPA is considering developing estimates for population exposures associated with
14 current PM2.5 and PMio-2.5 levels and with meeting the current PM2.5 standards and potential
15 alternative PM2.5 standards. These exposure estimates could provide information on population
16 exposures exceeding levels of concern that may be identified for various health endpoints.
17 Exposure estimates may be used as an input to the quantitative risk assessment if health
18 endpoints are identified in the ISA for which there are exposure-response functions.
19 Planning for conducting an exposure assessment will include building upon the
20 information presented in the ISA and its annexes. This includes information on atmospheric
21 chemistry and components of PM, air quality data, factors that influence exposures, human
22 exposures, and information on sensitive subpopulations. EPA currently is considering
23 conducting an exposure assessment that will focus primarily on ambient PM2.5, but will consider,
24 to the extent relevant information is available, exposures associated with ambient PMio-2.5 as
25 well. EPA currently believes that exposure modeling for PMio-2.5 would likely be significantly
26 more uncertain than for PM2.s, primarily due to the limitations of the spatial coverage of
27 available ambient PMio-2.5 data.
28 The Population Exposure Model
29 If an exposure assessment is conducted, EPA is considering using the Air Pollutants
30 Exposure (APEX) model (Richmond et al., 2002; U.S. EPA, 2006 b, c). APEX has its origins in
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1 the NAAQS Exposure Model (NEM) which was developed in the early 1980's (McCurdy,
2 1994), has been continually improved since then, and was recently used during EPA's ozone
3 NAAQS review. APEX, also referred to as the Total Risk Integrated Methodology/Exposure
4 (TREVI.Expo) model, is a Monte Carlo simulation model that simulates a large number of
5 randomly sampled individuals within a metropolitan area to represent area-wide population
6 exposures. APEX simulates the movements of individuals through time and space and their
7 exposure to a given pollutant in indoor, outdoor, and in-vehicle microenvironments. The model
8 stochastically generates simulated individuals using census-derived probability distributions for
9 demographic characteristics. A large number of simulated individuals are modeled, and
10 collectively they represent a random sample of the study area population.
11 Drawing on information from the ISA, EPA will consider specific microenvironments
12 that could be evaluated in a quantitative exposure assessment for PM. The development of
13 appropriate distributions representing variability and uncertainty in various model inputs (e.g.,
14 air exchange rates, decay rates, indoor source emissions, and physiological parameters) will be a
15 key aspect of this modeling effort. APEX employs a flexible approach for simulating
16 microenvironmental concentrations, where the user can define the microenvironments to be
17 modeled and their characteristics. Using input from the ISA, EPA will consider specific
18 microenvironments that could be evaluated in a quantitative exposure assessment.
19 In considering conducting an exposure assessment, EPA plans to review the
20 methodologies, inputs and results of other inhalation exposure modeling assessments to help
21 inform the development of inputs for APEX and to understand the most significant uncertainties
22 involved in estimating PM2.5 exposures. PM exposure modeling studies to be reviewed would
23 include exposure modeling of Philadelphia using the Stochastic Human Exposure and Dose
24 Simulation model (SHEDS) (Burke et al., 2001) and the recent studies by McBride et al., 2007;
25 Cressie et al., 2007; Issarayangyun and Greaves, 2007; Hertel et al., 2006; Klepeis and Nazaroff,
26 2006; Fryer et al., 2006; Wilson and Zawar-Reza, 2006; Georgopoulos et al., 2005; Wu et al.,
27 2005; Gulliver and Briggs, 2005; Marshall et al., 2005, as well as additional studies identified in
28 the ISA.
29
30
31
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1 Uncertainty and Variability
2 The primary difficulty in performing an exposure modeling uncertainty analysis is the
3 quantitative characterization of the uncertainties of the model inputs and model formulation.
4 Information about the variability of model inputs or the variability and uncertainty combined is
5 often available, but it is usually difficult to estimate the uncertainty separately from the
6 variability. In considering the use of APEX for a PM exposure assessment, EPA will consider
7 the availability of information to provide reasonable distributions or ranges for the uncertainties
8 of all of the model inputs. EPA will build upon the APEX exposure modeling uncertainty
9 analysis conducted in support of the review of the ozone NAAQS (Langstaff, 2007), as well as
10 an uncertainty analysis using SHEDS (Burke et al., 2001), improving on their distributions of
11 variability and uncertainty where data are available to do so and extending the analysis of model
12 formulation uncertainty.
13 Once estimates of the uncertainty of the model inputs have been developed, one can
14 propagate these uncertainties through the model to quantify the resultant uncertainty of the
15 model predictions. The APEX uncertainty methodology incorporates a 2-stage Monte Carlo
16 modeling approach that explicitly characterizes and models the variability and uncertainty in
17 inputs and outputs. Essentially, this approach entails performing thousands of model runs with
18 model inputs randomly sampled from specified distributions reflecting variability and
19 uncertainty of the model inputs. This 2-dimensional Monte Carlo method allows for the separate
20 characterization of the variability and uncertainty in the model results (Morgan and Henri on,
21 1990).
22 5.5 CURRENT HEALTH RISK ASSESSMENT APPROACH
23 The goals of a PM health risk assessment are: (1) to provide estimates of the potential
24 magnitude of mortality and/or selected morbidity health effects in the population associated with
25 recent ambient PM2.5 and PMio-2.5 levels and with meeting the current suite of PM standards and
26 any alternative standards that might be considered in specific urban areas, (2) to develop a better
27 understanding of the influence of various inputs and assumptions on the risk estimates; and (3) to
28 gain insights into the distribution of risks and patterns of risk reduction and uncertainties in those
29 risk estimates. The approach to the current health risk assessment will build upon the methods
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1 developed and insights gained from the risk assessment completed for the last review. Several
2 key considerations in planning for the health risk assessment are discussed below.
3 EPA is proposing to focus the quantitative risk assessments primarily on fine particles
4 (PM2.s), but will consider, to the extent relevant information is available, risks associated with
5 PMio-2.5 in the ambient air, as well as risks associated with specific PM components. For PM2.5,
6 EPA is proposing to focus the risk assessment on the most important health effect endpoints
7 from the standpoint of public health significance and for which the weight of the evidence
8 supports the judgment that the effect category is likely caused by exposure to PM2.5 either alone
9 and/or in combination with other pollutants.
10 The risk and exposure assessments will draw upon the information presented in the ISA
11 and its annexes. This includes information on atmospheric chemistry and components of PM, air
12 quality, human exposure, the impact of local source emissions, and health effects of concern. In
13 particular, the availability of air quality, concentration-response, and baseline incidence rate data
14 will impact the type of risk assessments that will be performed.
15 Air Quality Considerations
16 As described in Section 5.3 above, air quality inputs are required to conduct the health
17 risk assessment including: (1) recent air quality data for PM2.5 and PMio-2.5 from suitable
18 monitors for each selected location, (2) estimates of PRB concentrations for each location, and 3)
19 simulated air quality that reflects changes in the distribution of PM air quality estimated to occur
20 when an area just meets a given set of PM standards. While incremental risk reductions do not
21 require estimates of PRB, estimates of the risks remaining upon meeting the current or potential
22 alternative standards, do require EPA to estimate PRB. Both kinds of risk estimates are
23 considered relevant to inform the EPA Administrator's decision on the adequacy of a given
24 standard. The approach to estimating PRB for PM2.5 and PMio-2.5 for use in conducting the
25 health risk assessment will be informed by the discussion and evaluation contained in the draft
26 ISA and will build on the approach used in the previous review (Langstaff, 2004, 2005). The
27 proposed approach for the current review will be discussed further in the Scope and Methods
28 plan. EPA considerations with respect to exploring alternative air quality simulation procedures
29 are discussed above in Section 5.3 and will be discussed in more detail in the Scope and Methods
30 plan.
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1 Concentration-Response Functions
2 As noted above, the health risk assessment conducted in this review will build on the
3 approach developed and applied in the last review. EPA will rely on a weight-of-evidence
4 approach, as provided in the ISA, based on evaluation of new and prior epidemiologic studies
5 including identification of relevant concentration-response functions that characterize the
6 relationships between short- and long-term PM exposures and health outcomes, particularly
7 those conducted at or near current ambient concentrations. Quantitative relationships provided
8 in the specific studies or derived from the data presented in the epidemiologic studies describe
9 the change in concentration (generally based on ambient fixed-site monitors) associated with a
10 change in health response. These concentration-response relationships will be combined with air
11 quality data, baseline incidence data, and population data to develop population health risk
12 estimates.
13 Epidemiologic studies typically provide estimated concentration-response relationships
14 based on data collected in real-world settings. Ambient PM2.5 and PMi0-2.5 concentrations are
15 typically measured as the area-wide average of monitor-specific measurements, although
16 personal exposures are occasionally measured. Common health responses for PM2.5 have
17 included associations with respiratory symptoms in asthmatic children, asthma emergency
18 department visits, respiratory related hospital admissions and premature mortality. EPA will
19 consider the type of health response function(s) available and the availability of ambient PM2.5
20 and PMio-2.5 concentration data to characterize public health risks. EPA considers that these
21 analyses are most appropriately applied in areas where the specific epidemiologic studies were
22 performed. It should be noted that a risk characterization based on epidemiologic studies also
23 requires baseline incidence rates and population data for the specific locations evaluated in the
24 risk assessment.
25 EPA plans to develop concentration-response relationships for health effects associated
26 with short- and long-term exposures to PM2 5 and to a lesser extent, associated with short-term
27 exposures to PMio-2.5 exposures based on recently conducted and previous epidemiologic studies
28 presented in the ISA. EPA will also consider the scientific evidence presented in the ISA to
29 determine if sufficient exposure-response data from controlled clinical studies are available to
30 characterize health risks based on these studies.
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1 Uncertainty and Variability
2 In the health risk assessment developed for the review completed in 2006, staff
3 recognized that there were many sources of uncertainty and variability in the inputs to the
4 assessment and that there was a high degree of uncertainty in the resulting risk estimates. The
5 principle uncertainty, statistical uncertainty surrounding the estimated PM2.5 and PMio-2.5
6 coefficients in concentration-response functions, was addressed quantitatively in the last review.
7 Additional uncertainties were addressed through sensitivity analyses and/or qualitatively.
8 A persistent issue raised in CASAC and public review of the quantitative risk assessment
9 was the desire to provide a more comprehensive characterization of the most significant
10 uncertainties impacting the health risk estimates. For the current health risk assessment, EPA is
11 considering the use of, at a minimum, a similar approach to that used in the prior assessment to
12 characterize uncertainties in the risk estimates. In addition, EPA is considering the feasibility of
13 conducting an expert elicitation to characterize and quantify the most important sources of
14 uncertainty. As part of EPA's final regulatory impact analysis for the PM NAAQS review
15 completed in 2006, EPA conducted a study of the concentration-response relationship between
16 changes in PM2.5 exposures and mortality using formally elicited expert judgments (IEC, 2006).
17 The goal of the study was to elicit, from a sample of health experts, probabilistic distributions
18 describing uncertainty in estimates of the reduction in mortality among the adult U.S. population
19 resulting from reductions in ambient annual average PM2.5 levels. These distributions were
20 obtained through a formal interview protocol using methods designed to elicit subjective expert
21 judgments.
22 The full-scale expert elicitation study involved personal interviews with twelve health
23 experts who have conducted research on the relationship between PM2.5 exposures and mortality
24 (IEC, 2006; Roman et al., submitted). These experts were selected through a peer-nomination
25 process and included experts in epidemiology, toxicology, and medicine. The elicitation
26 interview consisted of a protocol of carefully structured questions, both qualitative and
27 quantitative, about the nature of the PlVh.s-mortality relationship. The questions requiring
28 qualitative responses probed experts' beliefs concerning key evidence and critical sources of
29 uncertainty and enabled them to establish a conceptual basis supporting their quantitative
30 judgments. Questions covered topics such as potential biological mechanisms linking PM2.5
31 exposures with mortality; the role of study design in capturing PM/mortality effects; key
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1 scientific evidence on the magnitude of the PM/mortality relationship; sources of potential error
2 or bias in epidemiological results; the likelihood of a causal relationship between PM2.5 and
3 mortality, and the shape of the concentration-response function.
4 As noted above, EPA is considering the feasibility and value of conducting an expert
5 elicitation as part of the current PM health risk assessment to improve the quantitative
6 characterization of the most significant uncertainties associated with the risk assessment. Factors
7 that will be weighed in making a decision on whether or not to proceed with such an assessment
8 include the perceived value of the project in informing the Administrator's decision in view of
9 the considerable resources and effort required to carry out such an assessment and the time
10 constraints for developing the risk assessment.
11 The prior risk assessment incorporated some of the variability in key inputs to the
12 assessment by using location-specific inputs (e.g., location-specific concentration-response
13 functions, baseline incidence rates, population data, and air quality data). In the last review, nine
14 urban areas were included in the health risk assessment to provide some sense of the variability
15 in the risk estimates across the U.S. For the current review, EPA is considering extending the
16 risk assessment to a broader range of urban areas to provide greater coverage of additional
17 regions of the country where significant PM exposures occur. EPA will consider the feasibility
18 of developing concentration-response relationships that can be applied on a regional basis. It is
19 very likely that the geographic (and population) coverage will vary for different health endpoint
20 categories due to data limitations (e.g., the availability of hospital admission baseline incidence
21 data is more limited than mortality baseline incidence data).
22 5.6 BROADER RISK CHARACTERIZATION
23 Beyond the quantitative risk/exposure assessments conducted for this review, EPA will
24 consider ways to put the results of those assessments into a broader context. Specifically, EPA
25 will explore analyses that would complement quantitative risk/exposure assessments conducted
26 for a limited number of locations and selected health endpoints to better characterize the nature,
27 magnitude, extent, variability, and uncertainty of the public health impacts associated with PM
28 exposures on a broader scale. EPA will consider how additional analyses could be used to
29 inform our understanding of:
30 • Additional health endpoints not considered in the quantitative risk assessment;
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1 • Additional locations not evaluated in the quantitative risk/exposure assessment to inform
2 a broader understanding of public health impacts;
3 • Regional differences in PM risks taking into consideration the following factors:
4 - variations in individual and/or population susceptibility including consideration of
5 population demographics;
6 - variations in exposures;
7 - variations in particle size, composition, and/or levels; and
8 - impacts of potential effect modifiers (e.g., weather).
9 5.7 SCIENTIFIC AND PUBLIC REVIEW
10 A draft of the Scope and Methods Plan for the risk/exposure assessment will be submitted
11 to CASAC for consultation and will be provided to the public for comment. The CASAC PM
12 Review Panel will discuss their comments on the draft Scope and Methods Plan in a public
13 meeting that will be announced in the Federal Register. In conducting the risk/exposure
14 assessment, EPA will take into account comments received from CASAC or from the public at
15 the meeting itself and in any written comments. EPA will prepare two drafts of the risk/exposure
16 assessment for CASAC review and public comment. The CASAC PM Review Panel will review
17 each draft risk/exposure assessment and discuss their comments in two public meetings to be
18 announced in the Federal Register. Based on CASAC's past practice, EPA anticipates that key
19 CASAC advice and recommendations for revision of the draft risk/exposure assessment will be
20 presented in letters to the EPA Administrator. EPA will also consider comments received from
21 CASAC or from the public at the meetings themselves and any written public comments. In
22 finalizing the risk/exposure assessment, EPA will take into account any such comments and
23 recommendations. After appropriate revision, the final risk/exposure assessment document will
24 be made publicly available on an EPA website and in hard copy. A notice announcing the
25 availability of the final document will be published in the Federal Register. In addition, the final
26 risk/exposure assessment document will be placed in the rulemaking docket.
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i 6 VISIBILITY AND OTHER WELFARE-RELATED
2 ASSESSMENTS
3 6.1 OVERVIEW
4 The assessments conducted in this review of the secondary PM NAAQS will focus
5 primarily on visibility-related issues, with special emphasis on addressing those issues remaining
6 at the conclusion of the last review associated with urban visibility impairment (see Section 6.2
7 below). In addition, depending on the nature of the information described in the ISA, there may
8 also be opportunity to conduct limited assessment(s) on the potential for phyto- or eco-toxic
9 related welfare impacts from the deposition of particulate or aerosol heavy metal compounds, or
10 on the magnitude and associated benefits of materials damage from soiling. Though
11 understanding and characterizing the potential climate/PM-related feedbacks and interactions
12 that might occur under various alternative PM air quality scenarios is an important policy issue,
13 we do not anticipate there will be sufficient information available to support quantitative
14 analyses related to this public welfare effect in this review.
15 The major components of the visibility-related and other welfare-related assessments are
16 outlined below and will be described in greater detail in a Scope and Methods Plan. Preparation
17 of this detailed plan is underway and coincides with the development of the first draft ISA to
18 facilitate the integration of policy-relevant science into both documents.
19 6.2 OVERVIEW OF VISIBILITY-RELATED ASSESSMENT FROM
20 PRIOR REVIEW
21 EPA has long recognized that impairment of visibility is an important effect of PM on
22 public welfare, and that it is experienced throughout the U.S. in urban areas as well as in remote
23 Class I areas15 (62 FR 38680, July 18, 1997). Visibility is an important welfare effect because it
24 has direct significance to people's enjoyment of daily activities in all parts of the country.
25 Individuals value good visibility for the sense of well-being it provides them directly, both in
26 places where they live and work, and in places where they enjoy recreational opportunities.
27 Visibility can be defined as the degree to which the atmosphere is transparent to visible
28 light. Visibility conditions are determined by the scattering and absorption of light by particles
Class I areas: as defined by the Clean Air Act, include national parks greater than 6,000 acres, wilderness areas
and national memorial parks greater than 5,000 acres, and international parks that existed as of August 1977.
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1 and gases, from both natural and anthropogenic sources. Visibility is often described in terms of
2 visual range, light extinction, or deciviews.16 The classes of fine particles principally responsible
3 for visibility impairment are sulfates, nitrates, organic matter, elemental carbon, and soil dust.
4 Fine particles are more efficient per unit mass at scattering light than coarse particles. The
5 scattering efficiency of certain classes of fine particles, such as sulfates, nitrates, and some
6 organics, increases as relative humidity rises because these particles can absorb water and grow
7 to sizes comparable to the wavelength of visible light. In addition to limiting the distance that
8 one can see, the scattering and absorption of light caused by air pollution can also degrade the
9 color, clarity, and contrast of scenes.
10 Air Quality Analyses
11 In the last review, EPA summarized information on the general types of visibility
12 impairment: local visibility impairment manifested as an urban haze, sometimes referred to as a
13 "brown cloud" and regional haze generally resulting from pollutant emissions from a multitude
14 of sources located across a broad geographic region. In addition, EPA conducted analyses
15 evaluating trends and conditions in Class I and non-urban areas, visibility conditions in urban
16 areas, and approaches for evaluating public perceptions of visibility impairment and judgments
17 about the acceptability of varying degrees of impairment. Key insights and observations from
18 the visibility assessment were discussed in Section IV. A of the 2006 proposal notice (see 71 FR
19 2675 to 2681, January 17, 2006). In the last review, EPA concluded that fine particle mass
20 concentrations could be used as a general surrogate for visibility impairment (U.S. EPA, 2005,
21 Section 2.8.1). EPA also concluded that the available data on visibility conditions indicated that
22 urban areas generally have higher loadings of PM2 5 and, thus, higher visibility impairment than
23 monitored Class I areas. EPA recognized that the Regional Haze Program (64 FR 35713; July 1,
24 1999), implemented under sections 169 A and 169B of the CAA, addressed all human-caused
25 visibility in Class I areas and that the Clean Air Interstate Rule (CAIR) (70 FR 25162; May 12,
26 2005) would result in improvements to visual air quality, particularly in eastern Class I and non-
16 Visual range can be defined as the maximum distance at which one can identify a black object against the horizon
sky. It is typically described in kilometers or miles. Light extinction is the sum of light scattering and absorption by
particles and gases in the atmosphere. It is typically expressed in terms of inverse megameters (Mm"1), with larger
values representing poorer visibility. The deciview metric describes perceived visual changes in a linear fashion
over its entire range, analogous to the decibel scale for sound.
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1 urban areas. Therefore, the visibility-related assessments conducted in the last review focused
2 primarily on evaluating visibility impairment in urban areas.
3 In evaluating correlations between urban visibility and PM2.5 mass, EPA considered that
4 direct relationships existed between measured ambient pollutant concentrations and their
5 contributions to light extinction and thus to visibility impairment. The contribution of each PM
6 constituent to total light extinction was derived by multiplying the constituent concentration by
7 its extinction efficiency to calculate a "reconstructed" light extinction.17 For certain fine particle
8 constituents, extinction efficiencies increased significantly with increases in relative humidity.
9 As a consequence, while higher PM2.5 mass concentrations generally indicated higher levels of
10 visibility impairment, it was not as precise a metric as the light extinction coefficient.
11 Nonetheless, by using historic averages, regional estimates, and actual day-specific, component-
12 specific ambient measurements of PM2.5 total mass, reasonable estimates of light extinction from
13 PM mass concentrations were developed.
14 In an effort to characterize urban visibility, EPA analyzed the available data on PM2.5
15 ambient air concentrations primarily in urban areas. The national data base of PM2 5 ambient air
16 concentrations had expanded greatly since the 1997 PM2.5 NAAQS had been promulgated and
17 included 24-hour measurements of total PM2.5 mass, continuous measurements of hourly (total)
18 PM2.5 mass, and 24-hour duration PM2.5 chemical speciation (component) measurements. These
19 data allowed for analyses that explored factors that have historically complicated efforts to
20 address visibility impairment nationally, including regional differences related to levels of
21 primarily fine particles and to relative humidity. The analyses showed a consistently high
22 correlation between visibility, in terms of reconstructed light extinction, and PM2 5
23 concentrations (daily, hourly, and block hourly) for urban areas in a number of regions across the
24 U.S. and, more generally, in the eastern and western U.S. The correlations in urban areas were
25 generally similar in the East and West, in sharp contrast to the East/West differences observed in
26 rural areas.
17 Extinction efficiencies vary by type of constituent and have been obtained for typical atmospheric aerosols by a
combination of empirical approaches and theoretical calculations. As discussed in the Staff Paper, EPA's guidance
for tracking progress under the Regional Haze Program specified an algorithm for calculating total light extinction
as a function of the major fine particle components (U.S. EPA, 2005, Section 2.8.1). "Reconstructed" light
extinction simply refers to the calculation of PM-related light extinction by the use of that formula.
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1 While the average daily relative humidity levels were generally higher in the East than in
2 the West, in both regions relative humidity levels were appreciably lower during daylight as
3 compared to nighttime hours. The reconstructed light extinction coefficient, for a given mass
4 and concentration, increased sharply as relative humidity rose. Thus, with lower relative
5 humidity levels, visibility impacts related to East/West differences in average relative humidity
6 were minimized during daylight hours, when relative humidity is generally lower.
7 Both 24-hour and shorter-term daylight hour averaging periods were considered in
8 evaluations of correlations between PM2.5 concentrations in urban areas and visibility in eastern
9 and western areas, as well as nationwide. Clear and similarly strong correlations were found
10 between visibility and 24-hour average PM2.5 in eastern, western, and all urban areas (U.S. EPA,
11 2005, Figure 6-3). Somewhat stronger correlations were observed between visibility and PM2 5
12 concentrations averaged over certain sub-daily (e.g., a 4-hour) time periods (U.S. EPA, 2005,
13 Figure 6-5). The correlations between visibility and PM2 5 concentrations during daylight hours
14 in urban areas were relatively more reflective of PM2 5 mass rather than relative humidity effects,
15 in comparison to correlations based on a 24-hour averaging time.
16 Surveys of Public Perception
17 In the last review, EPA considered survey research on public awareness of visual air
18 quality. The importance of visual air quality to public welfare across the country had been
19 demonstrated by a number of studies designed to quantify the benefits (or willingness to pay)
20 associated with potential improvements in visibility (Chestnut and Dennis, 1997; Chestnut and
21 Rowe, 1991). These economic benefits may include the value of improved aesthetics during
22 daily activities (e.g., driving or walking, daily recreations), for special activities (e.g., visiting
23 parks and scenic vistas, hiking, hunting), and for viewing scenic photography. They may also
24 include the value of improved road and air safety, and/or preservation of the resource for its own
25 sake.
26 EPA considered new methods and tools that had been developed to communicate and
27 evaluate public perceptions of varying visual effects associated with alternative levels of
28 visibility impairment relative to varying pollution levels and environmental conditions. New
29 survey methods have been applied and evaluated in various studies, such as those done in
30 Denver, Phoenix, and the Lower Fraser Valley in British Columbia. These methods were
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1 intended to assess public perceptions in focus group sessions as to the acceptability of varying
2 levels of visual air quality, considered in these studies to be an appropriate basis for developing
3 goals and standards for visibility protection. In the last review, EPA conducted a pilot study in
4 Washington D.C. in order to test both the session design and survey questions that would
5 potentially be used in the broader focus group effort (Abt Associates, 2001). Even with
6 variations in each study's approaches, the public perception survey methods used for the Denver,
7 Phoenix, and British Columbia studies produced reasonably consistent results from location to
8 location, with each study indicating that a majority of participants found visual ranges within
9 about 40 to 60 km to be acceptable.
10 These public perception studies used images of urban and distant scenic views under
11 different visibility conditions together with survey techniques designed to elicit judgments from
12 members of the public about the acceptability of differing levels of visual air quality. Images
13 used were either photographs or computer simulations using the WinHaze program. The
14 WinHaze program is a sophisticated visual air quality image modeling program for personal
15 computers that used simplified algorithms based on a sophisticated modeling technique (Air
16 Resource Specialists, 2003). A base photographic image captured the cleanest air quality
17 conditions possible for a given site and then digitized the photograph to assign an optical density
18 to each pixel. Using the digital imaging information, combined with the physical and optical
19 properties of assumed alternative aerosol mixes, WinHaze generated a series of images that
20 showed the impact of various levels of ambient aerosol on the visual quality of the scene. The
21 WinHaze simulation technique had the advantage that it could be done for any location as long
22 as a very clear base photo was available. By using the same base picture in all images, in effect,
23 this approach standardized the perception of the images and enabled researchers to avoid
24 potentially biased responses that might occur if different pictures of the same scene were used.
25 An alternative approach could use actual photographs of the site of interest at different ambient
26 pollution levels. However, EPA did not consider this alternative approach because long-term
27 photo archives of this type existed for only a few cities.
28 Information on the pilot project was presented in the preliminary draft Staff Paper (US
29 EPA, 2001) to elicit CASAC and public comment on the use of this type of approach to help
30 inform EPA's review of the secondary PM NAAQS, and, more specifically, to elicit comments
31 on various aspects of the survey methodology used in the pilot project. The project was
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1 premised on the view that public perceptions of and judgments about the acceptability of
2 visibility impairment in urban areas are relevant factors in assessing what constitutes an adverse
3 level of visibility impairment in the context of this NAAQS review. EPA received general
4 support for the use of this type of approach, and also received advice from members of CASAC
5 as to how the survey methodology could be improved. At that time, EPA staff expressed the
6 intention of refining the approach based on that advice, and preparing a revised methodology
7 document for additional review by CASAC and the public prior to conducting a more extensive
8 survey that could appropriately inform this review. Resource constraints prevented this work
9 from being conducted in the last review.
10 6.3 CURRENT VISIBLITY AND OTHER WELFARE-RELATED
11 ASSESSMENT APPROACH
12 To help inform the overarching policy-relevant question regarding the adequacy of the
13 current suite of secondary standards in protecting the public welfare from any known or
14 anticipated adverse effects associated with the presence of PM in the ambient air, EPA will look
15 to the following types of assessments.
16 Urban Visibility
17 As indicated in Section 6.2 above, the last review expanded consideration of the public
18 welfare effect of visibility impairment beyond areas traditionally identified for protection (e.g.,
19 federally designated Class I areas) to include urban areas. In this review, EPA has identified
20 several issues specific to visibility impairment in urban or suburban areas. In order to progress
21 the assessment of urban visibility impairment, EPA plans to address the following issues:
22 • Refining the algorithms relating light extinction to PM species concentrations originally
23 developed for rural/remote sites using IMPROVE data to be more applicable to urban
24 areas using data being collected by the new PM speciation network.
25 • Exploring different ways to characterize the relationship between light extinction and PM
26 concentrations, which is a function of PM component concentrations and relative
27 humidity.
28
29 In addition to the above issues, both the Administrator and the CASAC panel observed in
30 the last review that one of the key limitations to selecting an appropriate level of PM2.5 that
31 would afford the requisite protection against visibility impairment in urban areas was the limited
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1 number of cities for which information of this nature (e.g., public perceptions of adverse impacts
2 on visibility in urban settings) was available. In this review, EPA will consider the
3 appropriateness of building on and expanding the pilot study evaluating public perceptions of
4 and judgments about the acceptability of visibility impairment in urban areas conducted for the
5 last review (see Section 6.2 above) so the results of a more extensive survey can be used to help
6 inform this or future reviews of the PM secondary standards. For this to be realized, a number of
7 different issues and challenges must be addressed. These include:
8 • Identifying new literature that addresses methods for characterizing the value of visibility
9 and assessing which approach(es) are potentially appropriate for use in the NAAQS
10 review process. This effort could potentially be expanded to incorporate literature that
11 includes information on how the psychological value of visual air quality, stress and
12 human behavior are related and how those qualitative aspects are or could be included.
13 • Expanding the characterization of perceptions of visibility impairment to include urban
14 areas having sight paths to fixed scenic elements that are too short to be sensitive to
15 changes in haze by exploring alternative ways to communicate change (e.g., based on
16 changes in sky color and the appearance of clouds in the sky). Several methods are
17 available to represent different levels of visual air quality (see discussion of the EPA pilot
18 study above, Abt Associates, 2001).
19 • Expanding the characterization of perceptions of adversity for urban areas with non-
20 traditional views18 as described above by developing new or modifying existing survey
21 techniques to elicit information about what constitutes an acceptable versus unacceptable
22 degradation of the scene (e.g., clouds against a blue sky).
23 Other Welfare Effects
24 There are several new or expanded sources of speciated PM data that might lend
25 themselves to further analysis with respect to the welfare effects associated with deposition of
26 heavy metals to vegetation and ecosystems, deposition of fine and coarse particles onto man-
27 made structures, and the potential localized impacts of aerosol pollution on downwind
28 precipitation patterns and trends. These new data sources include the urban PM speciation
18 Photographic views for urban areas traditionally are taken from an elevated vantage point near the edge of the city
with the city skyline shown against distant mountains in the background. In areas where such distant views are not
readily available, it is not clear at this time what could substitute for distant scenic elements.
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1 network and data from assessments being conducted by state-run regional planning organizations
2 (RPOs) in conjunction with fulfilling the requirements of the Regional Haze Rule. EPA will
3 therefore investigate these and any other additional sources of information identified in the ISA
4 and associated annexes and consider whether additional welfare effects assessments are
5 appropriate.
6 6.4 SCIENTIFIC AND PUBLIC REVIEW
7 A draft of the Scope and Methods Plan for the visibility and other welfare-related
8 assessments will be submitted to CASAC for consultation and will be provided to the public for
9 comment. The CASAC PM Review Panel will discuss their comments on the draft Scope and
10 Methods Plan in a public meeting that will be announced in the Federal Register. In conducting
11 the visibility and other welfare-related assessments, EPA will take into account comments
12 received from CASAC or from the public at the meeting itself and in any written comments.
13 EPA will prepare two drafts of the visibility and other welfare-related assessments for CASAC
14 review and public comment. The CASAC PM Review Panel will review each draft visibility and
15 other welfare-related assessment and discuss their comments in two public meetings to be
16 announced in the Federal Register. Based on CASAC's past practice, EPA anticipates that key
17 CASAC advice and recommendations for revision of the draft risk/exposure assessment will be
18 presented in letters to the EPA Administrator. EPA will also consider comments received from
19 CASAC or from the public at the meetings themselves and any written public comments. In
20 finalizing the visibility and other welfare-related assessments, EPA will take into account any
21 such comments and recommendations. After appropriate revision, the final visibility and other
22 welfare-related assessment document will be made publicly available on an EPA website and in
23 hard copy. A notice announcing the availability of the final document will be published in the
24 Federal Register. In addition, the final visibility and welfare-related assessment document will
25 be placed in the rulemaking docket.
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i 7 AMBIENT AIR MONITORING
2 7.1 OVERVIEW
3 The PM monitoring networks provide data for a wide variety of purposes as part of an
4 iterative process in managing air quality. These include: (1) determining compliance with the
5 NAAQS; (2) characterizing air quality status; (3) supporting air quality analyses used to conduct
6 assessments of exposure, health risks, and welfare effects; (4) developing and evaluating
7 emissions control strategies; and (5) measuring overall progress for the air pollution control
8 program.
9 Federal rules that regulate ambient monitoring programs are found in 40 CFR parts 50,
10 53 and 58. As noted below in Section 7.2, EPA amended these regulations in 2006, in part, to
11 support changes necessary for implementation of the revised PM NAAQS. EPA expects to
12 follow a similar process during this review, with the development of a complementary
13 rulemaking effort, if appropriate, to support monitoring rule changes associated with any
14 revisions to the PM NAAQS. Potential monitoring rule changes include the Federal Reference
15 Methods (FRMs) that exist as appendices to part 50, the procedures for approval of Federal
16 Reference and Federal Equivalent Methods (FEMs) contained in part 53, and the rules applicable
17 to ambient monitoring network planning and operations that are the basis for part 58 and
18 appendices A through E.
19 7.2 HISTORICAL PERSPECTIVE
20 As a result of the 1987 standard for PMio, EPA and its state/local partners implemented
21 the first size-selective PM monitoring network in 1990 with the establishment of a PMio network
22 consisting of mainly high-volume samplers. Approximately 1,000 PMio samplers remain in
23 operation to assess mass concentrations across the U.S., although some divestment in the
24 network is expected as thoracic coarse particle monitoring methods transition to PMio-2.5
25 sampling. After setting the first PM2.5 NAAQS in 1997, EPA implemented a PM2.5 network
26 consisting of ambient air monitoring sites with mass and/or chemical speciation measurements.
27 Within the PM2.5 network, there are approximately 900 FRM filter-based samplers that provide
28 24-hour PM2.5 mass concentration data and about 600 continuous PM2.5 mass monitors that
29 provide hourly data on a near real-time basis. Due to the complex nature of fine particles, EPA
30 implemented the Chemical Speciation Network (CSN) to better understand the components of
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1 fine particle mass at selected locations. Chemical speciation measurements are made at 54
2 '' Speciation Trends Network (STN)'' sites that are intended to remain in operation indefinitely
3 and about 150 other, potentially less permanent sites used to support State Implementation Plan
4 (SIP) development and other monitoring objectives.19 In addition, specific components of fine
5 particles are measured through the Interagency Monitoring of Protected Visual Environments
6 (IMPROVE) monitoring program20 which supports regional haze characterization and tracks
7 changes in visibility in Class I areas as well as many other rural and some urban areas. Together,
8 the IMPROVE and CSN data provide chemical species information for fine particles that are
9 critical for use in health and epidemiologic studies to help inform reviews of the PM NAAQS.
10 EPA recently made changes to the NAAQS-related monitoring regulations. Specifically,
11 the general monitoring network design requirements for the minimum number of ambient air
12 monitors were modified to focus more on populated areas with air quality problems and to
13 significantly reduce the requirements for criteria pollutant monitors that have measured ambient
14 air concentrations well below the applicable NAAQS. A number of the changes related
15 specifically to monitoring PM2 5, including revisions to the requirements for reference and
16 equivalent method determinations (including specifications and test procedures) for fine particle
17 monitors. These regulations also added a requirement for a new multi-pollutant monitoring
18 network called National Core (NCore) and revised certain provisions regarding monitoring
19 network descriptions and periodic assessments, quality assurance, and data certifications (71 FR
20 61236, October 17, 2006).
21 In the last review, EPA promulgated a new FRM for the measurement of PMio-2.5 in
22 ambient air. Although the standard for thoracic coarse particles does not use a PMio-2.5 indicator,
23 a new FRM for PMio-2.5 was developed to provide a basis for approving FEMs and promote the
24 gathering of scientific data to support future reviews of the PM NAAQS. The new PMio-2.5 FRM
25 - or an approved FEM, if available - is to be implemented at required NCore stations by January
26 1, 2011. Despite this long period of implementation, there are already a number of collocated
19 See http://www.epa.gov/ttn/amtic/speciepg.htnil for more information on the PM2.5 speciation monitoring
program.
20Recognizing the importance of visual air quality, Congress included legislation in the 1977 Clean Air Act to
prevent future and remedy existing visibility impairment in Class I areas. To aid the implementation of this
legislation, the IMPROVE program was initiated in 1985 and substantially expanded in 2000-2003. This program
implemented an extensive long term monitoring program to establish the current visibility conditions, track changes
in visibility and determine causal mechanism for the visibility impairment in the National Parks and Wilderness
Areas. For more information see hltp://www.cpa.gov/ttn/amlic/visdata. html.
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and PM2.5 low-volume FRMs operating across the country that are essentially providing
2 the PMio-2.5 FRM measurement now. There is currently no chemical speciation network for
3 characterizing the specific components of thoracic coarse particles. EPA is developing an
4 implementation plan for a thoracic coarse particle speciation network as PMio-2.5 at about 75
5 locations that will be part of the NCore monitoring stations.
6 7.3 MONITORING ISSUES TO BE CONSIDERED IN THE CURRENT
7 REVIEW OF THE PM NAAQS
8 This review of the PM NAAQS will explore a number of policy-relevant issues
9 associated with measuring and characterizing fine and thoracic coarse particles in ambient air.
10 EPA will draw upon the information presented in the ISA to inform the evaluation of appropriate
11 ambient monitoring methods and network design for PM, including considering the available
12 information on probe and siting criteria that could best support the current or alternative PM
13 standards.
15
16
14 Network Design
Monitoring sites must represent ambient air (e.g., that portion of the atmosphere, external
to buildings, to which the general public has access). The minimum number of required monitors
17 for PM is stated in 40 CFR part 58, Appendix D, Network Design Criteria for Ambient Air
18 Quality Monitoring. EPA negotiates with States to determine the total number of monitors
19 needed to represent an area's air quality. The total number is typically greater than the basic rule
20 requirements. It should be noted that although monitors are often sited with the intention to
21 represent an area of a certain geographic scale, in general, a monitor need not be representative
22 of the ambient air quality across an area of any specific size to be eligible for comparison to most
NAAQS. The current monitoring requirements for the PM2.5 NAAQS are an exception. Data
from a PM2.5 monitor can be compared to the NAAQS only if its location is "population-
oriented."21 Consequently, the existing PM monitoring network is primarily designed to be
LL 1 , * * , 1 •)•)
23
24
25
26 "population-oriented.'
21 As defined in 40 CFR part 58.1, "Population-oriented monitoring sites" apply to residential areas, commercial
areas, recreational areas, industrial areas, and other areas where a substantial number of people may spend a
significant fraction of their day. Also, note Subpart D of 40 CFR part 58, Special considerations for data
comparisons to the NAAQS.
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1 Network design issues related to population exposure that will be considered in this
2 review are reflected in the following questions:
3 "Is there a need to define more quantitative criteria for population-oriented exposure (e.g.,
4 minimum population density requirements, proximity to closest residences or work areas)
5 than is currently provided in the 40 CFR part 58?
6 "Is there evidence to support expanding the network from being mainly based on monitors
7 representing community-wide air quality to also consider "hot-spot" monitoring where
8 ambient concentrations are potentially higher? As an example, sites that represent
9 populations that reside near roadways (e.g., an environmental justice community with a
10 middle-scale22 or micro-scale23 location for protection against acute exposures to fine
11 particles).
12 "Is there new evidence to support a network expansion to improve the characterization of
13 ambient PM concentrations in additional areas such as remote areas that are not
14 considered "population-oriented?" In what ways could this information be used to assess
15 potential health and/or welfare effects in these areas?
16
17 Additional PMio-2.5 network design issues that will be considered in this review are
18 reflected in the following questions:
19 • What factors should be considered in identifying the size (number of monitors,
20 geographic distribution) of a PMi0-2.5 mass and speciation monitoring network (including
21 consideration of the NCore network requirements) that would be sufficient to
22 characterize levels across urban and rural areas?
23 • What additional sampling and statistical techniques (e.g., saturation sampling) are
24 available to help determine the minimum number of PMi0-2.5 monitors needed across an
25 urban area to adequately assess issues of spatial and temporal variability?
26 • What are the appropriate monitor placement criteria for thoracic coarse particle
27 characterization of PMio-2.5, including the distance relative to sources, measurement
22 A middle scale-sized area is one in which there are significant differences in concentrations between locations that
are 100 meters to 500 meters apart, and generally are areas that are impacted by nearly adjacent (but not
immediately adjacent) sources, such as industrial sites, roadways, or construction sites.
23 A micro-scale environment is one in which there are significant differences in concentrations between locations
that are 10 meters to 100 meters apart, and generally are areas that are impacted by immediately adjacent sources
such as industrial sites, roadways, or construction sites.
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1 scale, and inlet height? Should data from PMio-2.5 monitors located nearly adjacent to
2 sources (micro-scale) be excluded from comparison with a potential NAAQS?
3 Sampling Methods
4 Federal Reference Methods (FRMs) provide the methodological basis for comparison to
5 the NAAQS and also serve as the "gold-standard" for the comparison of other methods being
6 reviewed for potential approval as equivalent methods. FEMs for PM are largely continuous
7 monitors that can provide data for multiple monitoring objectives (e.g., an approved continuous
8 PM method would provide hourly data that would be more cost effective for daily sampling and
9 also provide data for reporting the Air Quality Index). For PM methods, only PMio currently has
10 approved continuous FEM monitors.
11 Policy-relevant issues that will be considered in this review to inform the selection of
12 monitoring methods are reflected in the following questions:
13 "To what extent do the variations in PMio sampling architecture used in FRM and FEM
14 sampling heads lead to significant changes in measured PMio in areas affected by high
15 concentrations of particles greater than 10 microns in size relative to each other and to the
16 required performance specifications in 40 CFR part 53?
17 "In 2006, EPA considered, but did not adopt, a sub-daily PM2.5 secondary NAAQS to
18 protect against visibility-related impairment in urban areas. Have new data altered
19 previous conclusions about using continuous PM2.5 monitoring methods capable of
20 providing hourly time resolution to support a potential sub-daily standard and/or other
21 metrics (e.g., light scattering) that may be considered? What method(s) should be
22 considered as the reference method?
23 • What new information is available to inform options and technologies for sampling and
24 analysis of components of thoracic coarse particles? Speciation monitoring of PMio-2.5 is
25 required in some areas as part of the NCore monitoring network that must be
26 implemented by 2011. What operational experiences learned in the PM2.s speciation
27 network can be useful in the evaluation of sampler design and laboratory analysis
28 methods being considered for PMio-2.5 filters?
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1 "In addition to PMio-2.5 monitoring being implemented as part of NCore, what other PM
2 and PM precursor-related measurements (e.g., ammonia, true NO2, nitric acid) should be
3 considered for incorporation into these multi-pollutant monitoring stations?
4 "Is new technology available to advance ambient monitoring methods for ultra-fine
5 particles (particles less than 100 nanometers in diameter) from being research-only
6 instruments to being field-ready techniques that can be operated within conventional
7 monitoring networks?
8 "To what extent should sample volume measurement24 be consistent across the various
9 PM methods? Is there evidence to support modifying the PMio FRM to operate at local
10 rather than standard conditions?
11 Data Reporting and Assessments
12 In the 2006 revisions to the PM2.5 FRM reporting requirements, EPA reduced the data
13 reporting requirements associated with the PM2.5 FRM to decrease the data management burden
14 for monitoring agencies. EPA also added a requirement for submission of data on PM2.s field
15 blank mass in addition to PM2.s filter-based measurements. Reporting requirements will be the
16 same for PMio-2.5 monitoring data. Quality assurance (QA) and network assessments are also an
17 important part of evaluating and confirming that the data from the monitoring networks continue
18 to meet the data needs. States conduct in-depth network assessments intended to ensure that
19 future gaps between data needs and monitoring operations are identified and filled in a timely
20 manner. Network assessments are required every 5 years, with the next one due by July 1, 2010.
21 As part of the QA framework, EPA establishes data quality objectives (DQOs) so that data can
22 be used effectively in making decisions regarding attainment of the NAAQS. DQOs for PM2.s
23 and PMio-2.5 monitoring data have been developed. Regular data quality assessments are
24 performed to determine if the data are continually meeting the specified DQOs.
25 Data reporting and assessment issues that will be considered in this review are reflected
26 in the following questions:
24 The current PM10 FRM requires operation and data reporting on a standard temperature and pressure basis,
(measurements adjusted to 25 degrees C and 1 atmosphere). The current PM2 5 and PM10_2.5 FRMs are required to
operate on a local (actual) temperature and pressure basis to better represent conditions of actual measurement and
population exposure. Significant differences can occur between PM measurements calculated on standard
conditions versus local conditions in some circumstances (e.g., high elevation monitoring sites).
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1 • What has been learned from the analysis of PM2.5 filter blank mass data that was newly
2 required to be reported to the Air Quality System (AQS) in the 2006 revisions to
3 monitoring regulations? To what extent should the blank data be considered in this
4 review of the PM2.5 NAAQS?
5 • An increase in the number of low volume PMio samplers is expected with the transition
6 to PMio-2.5 measurement and the desire of monitoring agencies to deploy more automated
7 (sequential) filter-based samplers into the networks. Does an analysis of precision and
8 bias data sets from high-volume and low-volume PMio samplers demonstrate a
9 significant advantage for low-volume samplers to the extent that the phase-out of high-
10 volume samplers PMio should be considered?
11 • What new assessments of PM2.5 data should be considered to evaluate the performance of
12 newer, continuous FEMs and Approved Regional Methods (ARMs) in comparison to the
13 FRM? What should be the consequences of identifying a poor comparison between an
14 approved FEM or ARM versus a collocated FRM?
15 • In anticipation of the use of hourly continuous PM2.5 data to help inform consideration of
16 a potential sub-daily secondary NAAQS, should FEM approval regulations (40 CFR part
17 53) and/or ambient monitoring quality assurance regulations (40 CFR part 58, Appendix
18 A) be modified to specifically require quantitative assessment of sub-daily data (e.g.,
19 precision assessment of hourly data)?
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i 8 POLICY ASSESSMENT/ RULEMAKING
2 Based on the information in the ISA, the risk/exposure assessment, and the
3 visibility/welfare-related assessment, the Agency will develop an ANPR that reflects EPA's
4 initial views regarding the need to retain or revise the NAAQS for PM2.5 and PMio. In doing so,
5 the Agency will consider the policy-relevant questions outlined in Section 3 including the
6 fundamental questions associated with the adequacy of the current standards and consideration of
7 alternative standards in terms of the specific elements of the standards: indicator, averaging
8 time, level, and form.
9 The ANPR will identify conceptual evidence-based and risk/exposure-based approaches
10 for reaching public health policy judgments. It will discuss the implications of the science and
11 risk/exposure assessments for the adequacy of the current standards, and it will present
12 risk/exposure information associated with alternative standards under consideration. The ANPR
13 will also describe a range of policy options for standard setting including a description of the
14 underlying interpretations of the scientific evidence and risk/exposure information that might
15 support such alternative standards and that could be considered by the Administrator in making
16 decisions for the suite of PM standards.
17 The use of an ANPR will provide an opportunity for CAS AC and the public to evaluate
18 the policy options under consideration and to offer comments and recommendations to inform
19 the development of a proposed rule. Taking into account CAS AC advice and recommendations
20 and public comment on the ANPR, the Agency will publish a proposed rule. This proposal will
21 be followed by a public comment period. Taking into account comments received on the
22 proposed rule, the Agency will then issue a final rule to complete the rulemaking process.
23 Monitoring rule changes associated with any revisions to the PM standards as outlined in Section
24 7 will be developed, if necessary, in conjunction with this NAAQS rulemaking.
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i 9 REFERENCES
2 Abt Associates (2001). Assessing Public Opinions on Visibility Impairment Due to Air
3 Pollution: Summary Report. Prepared for EPA Office of Air Quality Planning and
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16 Cressie, Noel, Bruce E. Buxton, Catherine A. Calder, Peter F. Craigmile, Crystal Dong, Nancy J.
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21 DEHW (1969). Air Quality Criteria for Particulate Matter. U. S. Department of Health,
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25 (2006). Human exposure modelling for chemical risk assessment: a review of current
26 approaches and research and policy implications. Environmental Science & Policy,
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28 Georgopoulos, P.O., Wang, S., Vyas, V.M., Sun, Q., Burke, J.M., Vedantham, R., McCurdy, T.,
29 and Ozkaynak, H (2005). A source-to-dose assessment of population exposures to fine PM
30 and ozone in Philadelphia, PA, during a summer 1999 episode. J Expos Anal Environ
31 Epidemiol 15: 439-457
32 Gulliver, John and David J. Briggs (2005). Time-space modeling of journey-time exposure to
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36 Henderson, R. (2005a). EPA's Review of the National Ambient Air Quality Standards for
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38 Particulate Matter Review Panel of the EPA Clean Air Scientific Advisory Committee.
39 June 6, 2005. Available: httg://w^w^e2aigow^abi/^^
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1 Henderson, R. (2005b). Clean Air Scientific Advisory Committee (CAS AC) Review of the EPA
2 Staff Recommendations Concerning a Potential Thoracic Coarse PM Standard in the
3 Review of the National Ambient Air Quality Standards for Parti culate Matter: Policy
4 Assessment of Scientific and Technical Information (Final PM OAQPS Staff Paper,
5 EPA-452/R-05-005). September 15, 2005. Available:
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1
8 Henderson, R. (2006a). Letter from Dr. Rogene Henderson, Chair, Clean Air Scientific
9 Advisory Committee to the Honorable Stephen L. Johnson, Administrator, US EPA.
10 Clean Air Scientific Advisory Committee Recommendations Concerning the Proposed
1 1 National Ambient Air Quality Standards for Parti culate Matter. March 21, 2006.
12 Available: http://www.epa.gov/sab/pdf/casac4tr-06-002.pdf
13
14 Henderson, R. (2006b). Letter from Dr. Rogene Henderson, Chair, Clean Air Scientific
15 Advisory Committee to the Honorable Stephen L. Johnson, Administrator, US EPA.
16 Clean Air Scientific Advisory Committee Recommendations Concerning the Final
17 National Ambient Air Quality Standards for Parti culate Matter. September 29, 2006.
18 Available: http://www.epa.gov/sab/pdf/casac-ltr-06-003.pdf
19
20 Hopke, P. (2002). Letter from Dr. Philip Hopke, Chair Clean Air Scientific Advisory Committee
21 to Honorable Christine Todd Whitman, Administrator, U.S. EPA. Final advisory review
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23 assessment. May 23, 2002. Available: htt|i^/wgwLeBa4im^
24 IEC (2006). Expanded Expert Judgment Assessment of the Concentration-Response
25 Relationship Between PM2.5 Exposure and Mortality. Final Report. Prepared for the
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28 Issarayangyun, Tharit and Stephen Greaves (2007). Analysis of minute-by-minute exposure to
29 fine particulates inside a car - A time-series modelling approach. Transportation Research
30 Part D: Transport and Environment, Volume 12, Issue 5, July 2007, Pages 347-357.
3 1 Klepeis, Neil E. and William W. Nazaroff (2006). Modeling residential exposure to secondhand
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33 Langstaff, J. (2004). OAQPS Staff Memorandum to PM NAAQS Review Docket (OAR-2001-
34 0017). Subject: A Methodology for Incorporating Short-term Variable Background
35 Concentrations in Risk Assessment. December 17, 2004. Available:
36 http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_cr_td.html.
37 Langstaff, J. (2005). OAQPS Staff Memorandum to PM NAAQS Review Docket (OAR-2001-
38 0017). Subject: Estimation of Policy -Relevant Background Concentrations of Particulate
39 Matter. January 27, 2005. Available:
40 http://www.epa.gov/ttn/naaq s/standards/pm/s_pm_cr_td.html
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42 Langstaff, J. (2007). Analysis of Uncertainty in Ozone Population Exposure Modeling.
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1 January 31, 2007. Memo to the Ozone NAAQS Review Docket. EPA-HQ-OAR-2005-
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3 Marshall, J.D., I.E. McKone, and W.W. Nazaroff (2005). Inhalation of Primary Motor Vehicle
4 Emissions: Effects of Urban Population and Land Area, Atmospheric Environment, 39(2):
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6 McBride, Sandra J., Ron W. Williams and John Creason (2007). Bayesian hierarchical modeling
7 of personal exposure to paniculate matter. Atmospheric Environment, Volume 41, Issue
8 29, Pages 6143-6155.
9 McCurdy, T. (1994). Human Exposure to Ambient Ozone, Chapter 4 in Tropospheric Ozone:
10 Human Health and Agricultural Impacts. Ed. David J. MacKee. CRC Press.
11 Morgan and Henrion (1990). Uncertainty: A Guide to Dealing with Uncertainty in Qualitative
12 Risk and Policy Analysis. Cambridge University Press.
13 Richmond H., Palma, T, Langstaff, J., McCurdy, T., Glenn, G., Smith, L. (2002). Further
14 Refinements and Testing of APEX (3.0): EPA's population exposure model for criteria and
15 air toxic inhalation exposures. Joint meeting of the International Society of Exposure
16 Analysis and International Society of Environmental Epidemiology, Vancouver, CAN.
17 August 11-15, 2002.
18 Roman, H.A., Walker, K.D., Gettleman, T, Conner, L., Richmond, H.M., Hubbell, B.J., Kinney,
19 P.L. (in press). An Expert Judgment Assessment of the Mortality Impact of Changes in
20 Ambient Fine Particulate Matter in the U.S. Industrial Economics, Inc., Cambridge, MA;
21 U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards;
22 Columbia University Mailman School of Public Health.
23 U.S. EPA (2001). Review of the National Ambient Air Quality Standards for Particulate Matter:
24 Policy Assessment of Scientific and Technical Information, Preliminary Draft OAQPS
25 Staff Paper. Research Triangle Park, NC 27711: Office of Air Quality Planning and
26 Standards. June 2001.
27 U.S. EPA (2002). Consolidated Human Activities Database (CHAD) Users Guide. Database
28 and documentation available at: htt^7/www.eEa.goy/chadnetl/
29
30 U.S. EPA (2004). Air Quality Criteria for Particulate Matter. National Center for Environmental
31 Assessment, Office of Research and Development, U.S. Environmental Protection
32 Agency, Research Triangle Park, NC 27711; report no. EPA/600/P-99/002aF and
33 EPA/600/P-99/002bF. October 2004. Available:
34 httBl//wwwji|3
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1 U.S. EPA (2006a). Provisional Assessment of Recent Studies on Health Effects of Parti culate
2 Matter Exposure. National Center for Environmental Assessment, Office of Research
3 and Development, U.S. Environmental Protection Agency, Research Triangle Park, NC
4 2771 1; report no. EPA/600/R-06/063. July 2006. Available:
5 tffiBl/Mwwjiga^
6 U. S. EPA (2006b). Total Risk Integrated Methodology (TRIM) - Air Pollutants Exposure Model
7 Documentation (TRIM.Expo / APEX, Version 4) Volume I: User's Guide. OAQPS, U.S.
8 Environmental Protection Agency, Research Triangle Park, NC. June 2006. Available at:
9 http ://www. epa. gov/ttn/fera/human_apex.html
10 U.S. EPA (2006c). Total Risk Integrated Methodology (TRIM) - Air Pollutants Exposure Model
1 1 Documentation (TRIM.Expo / APEX, Version 4) Volume II: Technical Support Document.
12 OAQPS, U.S. Environmental Protection Agency, Research Triangle Park, NC. June 2006.
13 Available at: htt|r//ww\^
14 U.S. EPA (2007a). Integrated Science Assessment for Oxides of Nitrogen - Health Criteria (First
15 External Review Draft). U.S. Environmental Protection Agency, Research Triangle Park,
16 NC, EPA/600/R-07/093. Available at:
17 http://cfpub. epa.gov/ncea/cfm/recordisplay. cfm?deid=l 81 71 2
18 U. S. EPA (2007b). Integrated Science Assessment (ISA) for Sulfur Oxides - Health Criteria
19 (First External Review Draft). U.S. Environmental Protection Agency, Research Triangle
20 Park,NC, EPA/600/R-07/108. Available at:
21 http://cfpub. epa.gov/ncea/cfm/recordisplay. cfm?deid= 182057
22 Wilson, J. Gaines and Peyman Zawar-Reza (2006). Intraurban-scale dispersion modelling of
23 particulate matter concentrations: Applications for exposure estimates in cohort studies,
24 Atmospheric Environment, Volume 40, Issue 6, Pages 1053-1063.
25 Wu, Chang-Fu, Ralph J. Delfino, Joshua N. Floro, Penelope J.E. Quintana, Behzad S. Samimi,
26 Michael T. Kleinman, Ryan W. Allen and L.-J. Sally Liu (2005). Exposure assessment
27 and modeling of particulate matter for asthmatic children using personal nephelometers.
28 Atmospheric Environment, Volume 39, Issue 19, Pages 3457-3469.
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i APPENDIX A
2 U.S. EPA SCIENCE ADVISORY BOARD
3 CLEAN AIR SCIENTIFIC ADVISORY
4 COMMITTEE MEMBERS
5 FISCAL YEAR 2007
6
7 The Clean Air Scientific Advisory Committee (CASAC) has a statutorily mandated
8 responsibility to review and offer scientific and technical advice to the Administrator on the air
9 quality criteria and regulatory documents that form the basis for the national ambient air quality
10 standards (NAAQS), which currently include standards for lead (Pb), particulate matter (PM),
11 ozone (Os), carbon monoxide (CO), nitrogen dioxide (NO2) and sulfur dioxide (802).
12 To perform such reviews, in each case the Committee forms a review panel consisting of
13 CASAC members augmented by selected consultants with expertise in scientific or technical
14 areas pertinent to the given pollutant or pollutant class under review.
15 CHAIR
16 Dr. Rogene Henderson
17 Lovelace Respiratory Symposium
18 Lovelace Respiratory Research Institute
19 Albuquerque, NM 87185
20 PAST CHAIR
21 Dr. Philip Hopke
22 Robert A. Plane Professor
23 Department of Chemical Engineering
24 Clarkson University
25 Potsdam, NY 13699
26 MEMBERS
27 Dr. Ellis B. Cowling
28 University Distinguished Professor At-Large
29 Colleges of Natural Resources and Agriculture and Life Sciences
30 North Carolina State University
31 Raleigh, NC 27695
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1 Dr. James Crapo
2 Professor, Department of Medicine
3 National Jewish Medical and Research Center
4 Denver, CO 80206
5
6 Dr. Douglas J. Crawford-Brown
7 Director, Carolina Environmental Program
8 Professor, Environmental Sciences and Engineering
9 Professor, Public Policy, Department of Environmental Sciences and Engineering,
10 University of North Carolina at Chapel Hill
11 Chapel Hill, NC 27599
12
13 Dr. Donna Kenski
14 Director of Data Analysis
15 Lake Michigan Air Directors Consortium (LADCO)
16 Rosemont, IL 60018
17
18 Dr. Armistead Russell
19 Georgia Power Distinguished Professor of Environmental Engineering
20 Environmental Engineering Group, School of Civil and Environmental Engineering
21 Georgia Institute of Technology
22 Atlanta, GA 30332
23
24 Dr. Jonathan Samet
25 Professor and Chairman, Department of Epidemiology
26 Bloomberg School of Public Health
27 Johns Hopkins University
28 Baltimore, MD 21205
29
30 PM PANEL CONSULTANTS
31 TO BE DETERMINED
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1 SCIENCE ADVISORY BOARD STAFF
2
3 Mr. Fred A. Butterfield, III
4 Designated Federal Officer
5 Clean Air Scientific Advisory Committee
6 Science Advisory Board (1400A)
7 US Environmental Protection Agency
8 Washington, DC 20460
9
10 Ms. Zisa Lubarov-Walton
11 Management Assistant
12 Science Advisory Board (1400A)
13 US Environmental Protection Agency
14 Washington, DC 20460
15
16
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APPENDIX B
PARTICIPATE MATTER INTEGRATED SCIENCE ASSESSMENT -
PROPOSED OUTLINE
1. INTRODUCTION
DOCUMENT DEVELOPMENT
ORGANIZATION OF THE DOCUMENT
2. SOURCE TO DOSE
INTRODUCTION
ATMOSPHERIC CHEMISTRY, PHYSICS, SOURCES, EMISSIONS
MEASUREMENT TECHNIQUES AND CONCENTRATIONS
ISSUES ASSOCIATED WITH EVALUATING EXPOSURE TO PM
GENERAL CONSIDERATIONS FOR PERSONAL EXPOSURES
indoor sources, penetration of ambient PM indoors
PERSONAL EXPOSURE AND AMBIENT CONCENTRATION
EXPOSURE MEASUREMENT ERROR
DOSIMETRY OF INHALED PM -deposition, clearance, overload, modeling
3. INTEGRATED HEALTH EFFECTS OF PM EXPOSURE
POTENTIAL MECHANISMS OF INJURY/MODES OF ACTION
MORBIDITY ASSOCIATED WITH SHORT-TERM EXPOSURE
Cardiovascular effects - by endpoint, then type of PM, then by discipline
Respiratory effects - by endpoint, then type of PM, then by discipline
Other system effects - by endpoint, then type of PM, then by discipline
MORTALITY ASSOCIATED WITH SHORT-TERM EXPOSURE
Multi-city studies and meta-analyses, risk estimates, confounding,
cause-specific mortality
MORBIDITY ASSOCIATED WITH LONG-TERM EXPOSURE
Cardiovascular effects - by endpoint, then type of PM, then by discipline
Respiratory effects - by endpoint, then type of PM, then by discipline
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Adverse birth outcomes
Cancer incidence, mutagenicity, genotoxicity
Other effects - by endpoint, then type of PM, then by discipline
MORTALITY ASSOCIATED WITH LONG-TERM EXPOSURE
US and European studies, estimations of exposure, summary of risk
4. PUBLIC HEALTH IMPLICATIONS OF PM
ENVIRONMENTAL CONCENTRATIONS -
Ambient air quality data
Spatial and temporal variability
Policy-relevant background
HUMAN EXPOSURES
SUSCEPTIBLE AND VULNERABLE POPULATIONS- pre-existing disease,
age, high-exposure groups, genetic factors, SES, potential numbers of people
C-R FUNCTION AND THRESHOLD
HETEROGENEITY IN EFFECTS FROM EXPOSURE TO PM
POTENTIAL PUBLIC HEALTH IMPACTS - adversity of effects, numbers of
persons in susceptible populations
5. WELFARE EFFECTS OF PM
VISIBILITY
organics, metrics, Regional Haze Rule, aerosol/optical characteristics,
spatial patterns, seasonal patterns, multiyear trends
ECOLOGICAL AND ENVIRONMENTAL EFFECTS
ecosystem effects, deposition, direct and indirect ecosystem stress,
ecotoxicology, nutrient cycling
EFFECTS OF PM ON CLIMATE
EFFECTS OF CLIMATE ON PM
6. PUBLIC WELFARE IMPLICATIONS OF PM
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7. FINDINGS, CONCLUSIONS, AND RECOMMENDATIONS
SUMMARY OF KEY FINDINGS - SOURCE TO DOSE
Atmospheric science, exposure assessment
SUMMARY OF KEY FINDINGS - HEALTH EFFECTS
2004 Findings, new findings
SUMMARY OF KEY FINDINGS - ENVIRONMENTAL EFFECTS
CONCLUSIONS
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United States Office of Air Quality Planning and Standards Publication No. EPA 452/P-08-006
Environmental Protection Health and Environmental Impacts Division October 2007
Agency Research Triangle Park, NC
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