U. S. Environmental Protection Agency National Center for Environmental Assessment Office of Research and Development and Office of Air Quality Planning and Standards Office of Air and Radiation

Research Triangle Park, North Carolina 27711

April 2016 

# EP United States

Environmental



# Draft Integrated Review Plan for the National Ambient Air Quality Standards for Particulate Matter 

# EP United States

Environmental 

# EPA United States Environmental Protection AgencyApril 2016 ii Draft – Do Not Quote or Cite DISCLAIMER This draft integrated review plan has been prep ared by staff in the U.S. Environmental Protection Agency’s (EPA) Office of Air Quality Planning and Standards (OAQPS) and National Center for Environmental Assessment (NCEA). Any findings and conclusions are those of the authors and do not necessarily reflect the views of the EPA. This draft document is being circulated to facilitate discussion with the Clean Air Scien tific Advisory Committee and for public comment to inform the EPA’s review of the PM Na tional Ambient Air Quality Standards. This information is distributed for the purposes of pre-dissemination peer review under applicable information quality guidelines. It does not represen t, and should not be construed to represent, any Agency determination or policy. Questions or comments related to this draft document should be addressed to Dr. Scott Jenkins, U.S. Environmental Protection Agency, Office of Air Quality Planning and Standards, C539-06, Resear ch Triangle Park, North Carolina 27711 (email: jenkins.scott@epa.gov ) and Dr. Jason Sacks, U.S. Envir onmental Protection Agency, National Center for Environmental Assessment, MDB243- 01, Research Triangle Park, North Carolina 27711 (email: sacks.jason@epa.gov ).April 2016 iii Draft – Do Not Quote or Cite Table of Contents 1 INTRODUCTION.............................................................................................. 1-1 1.1 LEGISLATIVE REQUIREMENTS .................................................................... 1-2 1.2 OVERVIEW OF THE NAAQS REVIEW PROCESS ........................................ 1-4 1.3 HISTORY OF REVIEWS OF THE PM NAAQS ............................................... 1-8 1.4 GENERAL SCOPE OF THE CURRENT REVIEW ........................................ 1-15 1.5 ANTICIPATED SCHEDULE FO R CURRENT REVIEW .............................. 1-17 References ................................................................................................................... 1-19

2 KEY POLICY-RELEVANT ISSUES IN THE CURRENT REVIEW ......... 2-1 2.1 PRIMARY STANDARDS .................................................................................. 2-2 2.1.1 PM 2.5 Standards ........................................................................................... 2-2 2.1.2 PM 10 Standard ........................................................................................... 2-10 2.1.3 General Approach in the Current Revi ew of the Primary Standards ........ 2-13 2.2 SECONDARY STANDARDS .......................................................................... 2-17 2.2.1 Non-Visibility Welfare Effects.................................................................... 2-18 2.2.2 Visibility Effects ......................................................................................... 2-20 2.2.3 General Approach in the Current Revi ew of the Secondary Standards .... 2-25 2.3 PM AMBIENT MONITORING ........................................................................ 2-29 2.3.1 PM Monitoring Networks .......................................................................... 2-30 2.3.2 Consideration Of PM Monitoring Is sues In The Current REVIEW .......... 2-37 References ................................................................................................................... 2-38

3 SCIENCE ASSESSMENT ................................................................................ 3-1 3.1 SCOPE OF THE PM ISA .................................................................................... 3-1 3.1.1 General Description ..................................................................................... 3-1 3.1.2 Defining Policy-Relevant Literature ............................................................ 3-4 3.2 ORGANIZATION OF THE PM ISA .................................................................. 3-6 3.3 ASSESSMENT APPROACH .............................................................................. 3-7 3.3.1 Introduction.................................................................................................. 3-7 3.3.2 Literature Search and Selecti on of Relevant Studies ................................. 3-10 3.3.3 Evaluation of Individua l Study Quality...................................................... 3-11 3.4 SPECIFIC ISSUES TO BE ADDR ESSED IN THE PM ISA ........................... 3-12 3.4.1 Causal Determinations from 2009 PM ISA ............................................... 3-13 3.4.2 Uncertainties/Limitations Identified in 2009 PM ISA ............................... 3-14 3.4.3 Integration of Evidence and C ausal Determinations ................................. 3-16 3.4.4 Atmospheric Chemistry and Ambien t Concentrations of PM .................... 3-18 3.4.5 Human Exposure ........................................................................................ 3-19 3.4.6 Dosimetry ................................................................................................... 3-20 3.4.7 Modes of Action ......................................................................................... 3-21 3.4.8 Health Effects ............................................................................................. 3-22April 2016 iv Draft – Do Not Quote or Cite 3.4.9 At-Risk Lifestages and Populations and Public Health Impact ................. 3-25 3.4.10 Welfare Effects ........................................................................................... 3-26 3.5 QUALITY MANAGEMENT ............................................................................ 3-29 3.6 SCIENTIFIC AND PUBLIC REVIEW ............................................................. 3-29 References.......................................................................................3-30

4 HUMAN HEALTH RISK AND EXPO SURE ASSESSMENT ..................... 4-1 4.1 INTRODUCTION ............................................................................................... 4-1 4.2 OVERVIEW OF HEALTH RISK AND EXPOSURE ASSESSMENT FROM THE LAST REVIEW .......................................................................................... 4-2 4.2.1 Key Observations in the 2010 HREA ........................................................... 4-5 4.2.2 Key Uncertainties in the 2010 HREA .......................................................... 4-8 4.3 CONSIDERATION OF POTENTIAL QUANTITATIVE ASSESSMENTS FOR THIS REVIEW .................................................................................................. 4-10 4.3.1 Epidemiology-Based Risk Assessment ....................................................... 4-12 4.3.2 Exposure Assessment ................................................................................. 4-22 4.4 SCIENTIFIC AND PUBLIC REVIEW ............................................................. 4-26 References ................................................................................................................... 4-27

5 WELFARE-RELATED RISK AND EX POSURE ASSESSMENTS ............ 5-1 5.1 INTRODUCTION ............................................................................................... 5-1 5.2 SUMMARY OF WELFARE RISK AND EXPOSURE ASSESSMENT FROM THE LAST REVIEW .......................................................................................... 5-2 5.2.1 Quantitative Assessments of Urban Visibi lity Impairment in the Last Review

.................................................................... ....................................5-3 5.2.2 Consideration of Quantitative Assessments for Additional PM-related Welfare Effects in th e Last Review ............................................................... 5-7 5.3 CONSIDERATION OF POTENTIAL QUANTITATIVE ASSESSMENTS FOR THIS REVIEW .................................................................................................... 5-8 5.3.1 Visibility Effects ........................................................................................... 5-9 5.3.2 Ecological Effects ...................................................................................... 5-10 5.3.3 Climate Effects ........................................................................................... 5-13 5.3.4 Materials Effects ........................................................................................ 5-15 5.3.5 Characterization of Sources of Uncert ainty and Consideration of Information Newly Available in this Review .................................................................. 5-16 5.4 SCIENTIFIC AND PUBLIC REVIEW ............................................................. 5-19 References ................................................................................................................... 5-20

6 POLICY ASSESSMENT A ND RULEMAKING ........................................... 6-1 6.1 POLICY ASSESSMENT..................................................................................... 6-1 6.2 RULEMAKING ................................................................................................... 6-3 References .................................................................................................................... . 6-4April 2016 v Draft – Do Not Quote or Cite 

### List of Tables

Table 1-1. Overview of Documents Developed in NAAQS Reviews..............................1-5 Table 1-2. Summary of National Ambient Air Quality Standards Promulgated for Particulate Matter 1971-2012 ................................................................................. 1-9 Table 1-3. Anticipated Schedule for the Review of the PM NAAQS .................................. 1-18 Table 4-1. Areas of Uncertainty Associated wi th Epidemiology-Based Risk Estimates and Potential Strategies for Addressing these Sources of Uncertainty .................... 4-19

Table 4-2. Uncertainties and Limitations to Input Data used by APEX to Estimate Exposures ................................................................................................................ 4-25 Table 5-1 Areas of Uncertainty in the Welfar e Assessments and Potential Strategies to Address Them......................................................................................................... 5-17



### List of Figures
Figure 1-1. Overview of the EPA’s Process for Reviewing NAAQS............................1-4 Figure 2-1. Overview of General Approach for Review of Primary PM Standards ........ .2-14 Figure 2-2. Overview of General Approach for Review of Secondary PM Standards...... 2-26 Figure 3-1. General process for development of Integrated Science Assessments. ............. 3-9April 2016 vi Draft – Do Not Quote or Cite 

### List of acronyms/abbreviations
AER Indoor air exchange rates APEX Air Pollutants Exposure model BenMAP-CE Environmental Benefits Mappi ng and Analysis Program – Community Edition CAA Clean Air Act CASAC Clean Air Scientific Advisory Committee CHAD Consolidated Human Activity Database CMAQ Community Multi-scale Air Quality modeling system CPL Candidate Protection Levels C-R Concentration-response CSN Chemical Speciation Network DEARS Detroit Exposure Aerosol Research Study EC Elemental carbon U.S. EPA United States Environmental Protection Agency FEM Federal Equivalent Method FRM Federal Reference Method HREA Health Risk and Exposure Assessment IHD Ischemic heart disease IMPROVE Interagency Monitoring of Protected Visual Environments IPCC Intergovernmental Panel on Climate Change IRP Integrated Review Plan ISA Integrated Science Assessment LML Lowest measured level METS Metabolic equivalents of work NCEA National Center for Environmental Assessment NAAQS National Ambient Air Quality Standards NO 2 Nitrogen dioxide NO X Oxides of nitrogen OAR Office of Air and Radiation OAQPS Office of Air Qualit y Planning and Standards OC Organic carbon ORD Office of Research and Development PA Policy Assessment PM Particulate matter PM 2.5 In general terms, particulate matter with an aerodynamic diameter less than or equal to a nominal 2.5 μ m; a measurement of fine particles

In regulatory terms, particles w ith an upper 50% cut-point of 2.5 μ m aerodynamic diameter (the 50% cut point diameter is the diameter at which the sampler collects 50% of th e particles and re jects 50% of the particles) and a penetration curve as measured by a reference method based on Appendix L of 40 CFR Part 50 and designated in accordance with 40 CFR Part 53, by an equivalent method designated in accordanceApril 2016 vii Draft – Do Not Quote or Cite with 40 CFR Part 53, or by an approv ed regional method designated in accordance with Appendix C of 40 CFR Part 58

PM 10 In general terms, particulate matter with an aerodynamic diameter less than or equal to a nominal 10 μ m; a measurement of thoracic particles (i.e., that subset of inhalable part icles thought small enough to penetrate beyond the larynx into the thoracic region of the respiratory tract)

In regulatory terms, particles with an upper 50% cut-point of 10± 0.5 μ m aerodynamic diameter (the 50% cut point diameter is the diameter at which the sampler collects 50% of th e particles and re jects 50% of the particles) and a penetration curve as measured by a reference method based on Appendix J of 40 CFR Part 50 and designated in accordance with 40 CFR Part 53 or by an equivalent method designated in accordance with 40 CFR Part 53

PM 10-2.5 In general terms, particulate matter with an aerodynamic diameter less than or equal to a nominal 10 μ m and greater than a nominal 2.5 μ m; a measurement of thoracic coarse partic ulate matter or the coarse fraction of PM 10
In regulatory terms, particles w ith an upper 50% cut-point of 10 μ m aerodynamic diameter and a lower 50% cut-point of 2.5 μ m aerodynamic diameter (the 50% cut point diameter is the diameter at which the sampler collects 50% of the particles and reject s 50% of the particles) as measured by a reference method based on Appendix O of 40 CFR Part 50 and designated in accordance with 40 CFR Part 53 or by an equivalent method designated in accordance with 40 CFR Part 53

PRB Policy relevant background SES Socioeconomic status SHEDS-PM Stochastic Human Exposure and Dose Simulation for Particulate Matter SO 2 Sulfur dioxide SO X Sulfur oxides SOPM Secondary Organic Particulate Matter TRIM Total Risk Integrated Methodology TSP Total Suspended Particles UFP Ultrafine Particles UFVA Urban-Focused Visibility Assessment VAQ Visual air quality VOC Volatile organic compound WHO World Health Organization WREA Welfare Risk and Exposure AssessmentApril 2016 1-1 Draft - Do Not Quote or Cite 

## 1 INTRODUCTION 1

The U.S. Environmental Protection Agency (E PA) is conducting a revi ew of the existing 2 air quality criteria for pa rticulate matter (PM) and of the primary (health-based) and secondary 3 (welfare-based) national ambien t air quality standards (NAAQS ) for PM. This review will 4 provide an integrative assessment of relevant scientific information on PM and will focus on the 5 basic elements of the PM NAAQS: the indicator, averaging time, form, 1 and level. These 6 elements, which together serve to define each NAAQS, are considered collectively in evaluating 7 the protection to public health a nd public welfare afforded by the standards. The purpose of this 8 draft Integrated Review Plan (IRP) is to comm unicate the plan for re viewing the air quality 9 criteria and the primary and secondary NAAQS for PM. 10 The Clean Air Scientific Advisory Committ ee (CASAC), an independent scientific 11 advisory committee established und er the Clean Air Act, will revi ew this draft IRP at a public 12 meeting and will provide advice to the EPA based on that review. 2 The final IRP will reflect the 13
EPA staff’s consideration of CA SAC advice and of comments re ceived from members of the 14 public as part of the review process. As this re view progresses, the plan described in the IRP may 15
be modified to reflect information received dur ing the review process, to address additional 16 advice received from CASAC, and/or to address comments received from the public. 17 This draft IRP is organized into six chap ters. Chapter 1 presents the legislative 18 requirements for the review of the NAAQ S (section 1.1), background information on the 19 NAAQS review process (section 1.2), an overview of the decisions made in past reviews of the 20 PM NAAQS (section 1.3), the general scope of the current review (section 1.4), and the 21 anticipated schedule for the current review (s ection 1.5). Chapter 2 summarizes the supporting 22
rationales for the Administrator’s decisions in the last review of th e PM NAAQS, including the 23 important uncertainties and limitations in the scientific evidence and quantitative assessments in 24 the last review, and the key policy-relevant issues that will frame the current review. Chapters 3 25 through 6 discuss the key assessment documents for this review (i.e., Integrated Science 26 Assessment (ISA), Risk and Exposure Assessmen ts (REAs), Policy A ssessment (PA)), the 27

1 The “form” of a standard defines the ai r quality statistic that is to be compared to the level of the standard in determining whether an area attains the standard.

2 See http://yosemite.epa.gov/sab/sabpeople.nsf/WebCommi tteesSubcommittees/CASAC%20Particulate%20Matter%20R eview%20Panel%20(2015-2018) for a list of the CASAC PM Panel members.April 2016 1-2 Draft - Do Not Quote or Cite planned approaches for preparing these documen ts, and plans for their scientific and public 1 review. Chapter 6 also includes an ov erview of the rulemaking process. 2



### 1.1 LEGISLATIVE REQUIREMENTS 3

Two sections of the Clean Air Act (CAA) gove rn the establishment and revision of the 4 NAAQS. Section 108 (42 U.S.C. 74 08) directs the Administrato r to identify and list “air 5 pollutants” that, in his or her judgment, “cau se or contribute to air pollution which may 6 reasonably be anticipated to endanger public health and welfare” and whose “presence . . . in the 7
ambient air results from numerous or diverse m obile or stationary sources” and to issue air 8 quality criteria for air pollu tants that are listed. 42 U.S.C. § 7 408(a) & (b). Air quality criteria are 9 intended to “accurately reflect the latest scien tific knowledge useful in indicating the kind and 10
extent of identifiable effects on public health or welfare whic h may be expected from the 11 presence of [a] pollutant in ambient air . . . .” 42 U.S.C. § 7408(b). 12 Section 109 (42 U.S.C. 7409) directs the Administrator to propose and promulgate 13 “primary” and “secondary” NAAQS for pollutants fo r which air quality cr iteria are issued under 14 section 108. 42 U.S.C. § 7409 (a). Section 109(b)(1) defines a primary standard as one “the 15 attainment and maintenance of which in the j udgment of the Administrator, based on such 16 criteria and allowing an adequate margin of safe ty, are requisite to prot ect the public health.” 42 17 U.S.C. § 7409(b)(1). 3 A secondary standard, as defined in section 109(b)(2), “shall specify a 18 level of air quality the attainment and ma intenance of which in the judgment of the 19 Administrator, based on such crit eria, is requisite to protect the public welfare from any known 20 or anticipated adverse effects asso ciated with the presence of [the ] pollutant in the ambient air.” 4 21 42 U.S.C. § 7409(b)(2). 22 The requirement that primary standards provi de an adequate margin of safety was 23
intended to address uncertainties associated with inconclusive scientific and technical 24
information available at the time of standard set ting. It was also intended to provide a reasonable 25

3 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 an y [sensitive] group of the population,” and that for this purpose “reference should be made to a representative samp le 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)].

4 Welfare effects as defined in CAA 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.”April 2016 1-3 Draft - Do Not Quote or Cite degree of protection against hazards th at research has not yet identified. 5 Both kinds of 1 uncertainties are components of the risk associated with pollution at levels below those at which 2
human health effects can be said to occur with reasonable scientific cert ainty. Thus, in selecting 3 primary standards that provide an adequate marg in of safety, the Administrator is seeking not 4 only to prevent pollution levels that have been de monstrated to be harmfu l but also to prevent 5 lower pollutant levels that may pose an unaccepta ble risk of harm, even if the risk is not 6 precisely identified as to nature or degree. The CAA does not require the Administrator to 7 establish a primary NAAQS at a zero-risk level or at background concentra tion levels, but rather 8 at a level that reduces risk sufficiently so as to protect public health with an adequate margin of 9 safety. 6 10 In addressing the requirement for an adequate margin of safety, the EPA considers such 11 factors as the nature and severity of the health effects involved, the size of the sensitive group(s), 12 and the kind and degree of uncerta inties. The selection of any particular approach to providing an 13 adequate margin of safety is a policy choice le ft specifically to the Administrator’s judgment. 7 14 In setting standards that are “requisite” to pr otect public health and we lfare, as provided in 15 section 109(b), the EPA’s task is to establish st andards that are neither more nor less stringent 16 than necessary. In so doing, the EPA may not cons ider the costs of implementing the standards. 17 See generally Whitman v. American Trucking Associations , 531 U.S. 457, 465-472, 475-76 18 (2001). Likewise, “[a]ttainab ility and technological f easibility are not relevant considerations in 19 the promulgation of national ambient air quality standards.” American Petroleum Institute v. 20 Costle, 665 F. 2d at 1185. 21 Section 109(d)(1) requires that “not later than Decemb er 31, 1980, and at 5-year 22 intervals thereafter, the Admini strator shall complete a thor ough review of the criteria 23 published under section 108 and th e national ambient air quality st andards . . . and shall make 24
such revisions in such criteri a and standards and promulgate such new standards as may be 25 appropriate . . . .” 42 U.S.C. § 7409(d)(1). Se ctions 109(d)(2)(A) and 109(d)(2)(B) require that 26 an independent scientific review committee “shall complete a review of th e criteria . . . and the 27 national primary and secondary ambient air quality standards . . . and shall recommend to the 28

5 See Lead Industries Association v. EPA , 647 F.2d 1130, 1154 (D.C. Cir 1980); American Petroleum Institute v. Costle , 665 F.2d 1176, 1186 (D.C. Cir. 1981); American Farm Bureau Federation v. EPA , 559 F. 3d 512, 533 (D.C. Cir. 2009); and Association of Battery Recyclers v. EPA , 604 F. 3d 613, 617-18 (D.C. Cir. 2010).

6 See Lead Industries v. EPA , 647 F.2d at 1156 n.51, Mississippi v. EPA , 723 F. 3d 246, 255, 262-63 (D.C. Cir. 2013).

7 See Lead Industries Association v. EPA, 647 F.2d at 1161-62; Mississippi v. EPA, 723 F. 3d at 265.April 2016 1-4 Draft - Do Not Quote or Cite Administrator any new . . . standa rds and revisions of existing crit eria and standards as may be 1 appropriate . . . .” 42 U.S.C. § 7409(d)(2). Si nce the early 1980s, this independent review 2 function has been performed by CASAC. 3



### 1.2 OVERVIEW OF THE NAAQS REVIEW PROCESS 4

The current process for reviewing the NAAQS in cludes five major phases: (1) the planning 5 phase, (2) the science assessmen t phase, (3) the risk/exposure a ssessment phase, (4) the policy 6 assessment phase, and (5) the rulemaking phase. Figure 1-1 provides an overview of the NAAQS 7 review process and Table 1-1 provides an overvie w of each of the documents that are developed 8 as part of this process. 8 The phases of the NAAQS review process, and the documents 9 developed, are described in more detail below. 10

11 Figure 1-1. Overview of the EPA’ s Process for Reviewing NAAQS 12

8 The EPA maintains a website on which key documents developed for NAAQS reviews are made available (http://www3.epa.gov/ttn/naaqs/).April 20161-5Draft - Do Not Quote or CiteTable 1-1. Overview of Documents Developed in NAAQS Reviews1Document Purpose CASAC ReviewIntegrated ReviewPlan (IRP)Presents the anticipated scheduleand process for the review, andthe key policy-relevant science issues. Not intended to providedetailed scientific or technicalinformation, plans for quantitativeassessments, or conclusions on existing or alternative standard(s).One draft; consideration of CASACadvice and public comments on the draftIRP is reflected in the final IRP.Integrated ScienceAssessment (ISA)Comprehensive review, synthesis and evaluation of the mostpolicy-relevant science,including key sciencejudgments. Does notpresent quantitative assessmentsor conclusions on existing oralternative standard(s).Consideration of CASAC advice andpublic comments on drafts of the ISA(multiple drafts, as warranted) isreflected in the final ISA.Risk and ExposureAssessment (REA)PlanningDocument(s)Drawing upon the information in the ISA, presents the plannedapproaches and scopes of thequantitative risk and exposureanalyses that are warranted. Does not present conclusions onexisting or alternative standard(s).Consideration of CASAC advice andpublic comments on the REA Planningdocument is reflected in the REA(s).Health andWelfare REAs(HREA, WREA)Drawing upon the information in the ISA, presents quantitativeassessments of risks and exposures, as warranted, under various airquality scenarios, including just meeting the existing and potentialalternative standard(s). Does notpresent conclusions on existing oralternative standard(s).Consideration of CASAC advice andpublic comments on drafts of theREA(s) (multiple drafts, as warranted) isreflected in the final REA(s).Policy Assessment(PA)Drawing upon the information in the ISA and REA(s), provides atransparent staff analysis of the scientific basis for policy optionsfor consideration; facilitates CASAC advice to the Agency andrecommendations to the Administrator on the adequacy of theexisting standards and, as warranted, on the revisions that may beappropriate to consider.Consideration of CASAC advice andpublic comments on drafts of the PA(multiple drafts, as warranted) isreflected in the final PA.Proposed Rule Communicates the Administrator’s proposed decision(s); informedby the ISA, REA(s), PA and the advice of CASACPublic comment period, includingpublic hearings as warranted.Final Rule Communicates the Administrator’s final decision(s); informed bythe ISA, REA(s), PA, advice of CASAC and public comments onthe proposed rule.2April 2016 1-6 Draft - Do Not Quote or Cite The planning phase of the NAAQS review process begins with a public workshop 1 intended to provide the EPA an opportunity to receive input a nd advice on the key science and 2 policy issues around which the review will be st ructured. Workshop participants are asked to 3 highlight significant new and emerging research related to these key sc ience and policy issues, 4 and to make recommendations to Agency st aff regarding the design and scope of the 5 review. Drawing from workshop discussions, a draft IRP is prepared jointly by the EPA’s 6
National Center for Environmental Assessment (NCEA), within the Office of Research and 7 Development (ORD), and the EPA’s Office of Air Quality Planning and Standards (OAQPS), 8
within the Office of Air and Ra diation (OAR). The IRP presents the plan for the review, 9 including the anticipated schedule, the key policy-relevant scien ce issues that will guide the 10 review, and the approach to developing the assess ment documents that will inform the review. A 11
draft of the IRP is made available for CASAC review and for public comment, and the final IRP 12
reflects the EPA staff’s consideration of CASAC advice and public input. 13 Following the IRP, the EPA’s NCEA develops the Integrated Science Assessment (ISA). 14 The ISA provides a concise review, synthesis, and evaluation of th e most policy-relevant science 15 and includes key science judgments. The ISA pr ovides the scientific foundation for the NAAQS 16 review, and it is intended to provi de information useful in form ing judgments about air quality 17 indicator(s), averaging time(s), form(s), and level(s) for the NAAQS. The schedule typically 18 includes production of a first and, if needed, second draft IS A, both of which undergo CASAC 19 review at public meetings. 9 The final ISA reflects staff’s cons ideration of CASAC advice and of 20 the public input provided on drafts of the IS A. Chapter 3 below provides a more detailed 21 description of the planned sc ope, organization, and assessment approach for the ISA in the 22 current review of the PM NAAQS. 23 Building on the assessment of the evidence in the ISA, staff in the EPA’s OAQPS 24
considers the extent to which th ere is support for the development of Health and/or Welfare Risk 25 and Exposure Assessments (HREA, WREA). As an initial step in these considerations, staff 26 prepares Risk and Exposure Assessment planni ng document(s) (REA Planning Document(s)) 27
that consider the extent to which the availa ble scientific evidence and tools/methodologies 28 warrant the conduct of quantitative assessments. As discussed in Chapters 4 and 5 below, the 29 REA Planning Document(s) will focus on the degr ee to which important uncertainties from 30 previous reviews could be a ddressed by updated quantitative an alyses, and on the degree to 31

9 The availability of draft documents (ISA, REA, PA), and a request for public input on those documents, is also announced in the Federal Register.April 2016 1-7 Draft - Do Not Quote or Cite which updated or additional analyses could im prove the understanding of pollutant exposures 1 and/or risks. To the extent warranted, the REA Planning Document(s) will also outline a general 2 plan, including scope and methods, for conducti ng quantitative assessments. REA Planning 3 Documents are typically prepared in conjunction with the firs t or second draft ISA and are 4 reviewed by CASAC at a public meeting. 5 When developed, REAs provide concise pr esentations of exposure and/or risk 6 assessments, including presentati ons of methods, key results, a nd uncertainties. One or more 7 drafts of the REA(s) undergo CASAC review at public meetings. Sta ff considers the CASAC 8 advice and public input received in preparing fi nal REAs. Chapters 4 and 5 below provide more 9 detailed descriptions of the approaches in th is review of the PM NAAQS to considering the 10 potential support for an HREA and WREA, respectively. 11 Staff in the EPA’s OAQPS also prepares a Policy Assessment (PA), presenting staff’s 12 considerations and conclusions regarding the ade quacy of the current standards and, if warranted, 13 the range of revised standards th at could be supported by the ava ilable scientific evidence and 14 exposure/risk information. The PA integrates a nd interprets the inform ation from the ISA and 15 REA(s) to frame policy options for consideratio n by the Administrator. Such an evaluation of 16 policy options is intended to help bridge the gap between the Ag ency’s scientific assessments, 17 presented in the ISA and REA(s) (when availa ble), and the judgments required of the EPA 18 Administrator in determining whether it is approp riate to retain or revi se the NAAQS. The PA is 19
also intended to facilitate CASAC’s advice to the Agency and recommendations to the 20 Administrator on the adequacy of the existing standards and on revi sions that may be appropriate 21
to consider. Staff’s considerations and conclusions in the PA are based on the available scientific 22 evidence and quantitative expos ure and risk information, in cluding the uncertainties and 23
limitations in that evidence and information. Th e PA focuses on the evidence and information 24 that is most pertinent to evaluating the basic elements of NAAQS: i ndicator, averaging time, 25 form, and level. The schedule typically includes production of a first and, if needed, second draft 26 PA, both of which undergo CASAC review at public meetings . Staff considers the CASAC 27 advice and public input received in preparing the final PA. 28 Following issuance of the final PA, the EPA develops and publishe s a notice of proposed 29 rulemaking that communicates the Administra tor’s proposed decisions on the NAAQS. These 30 proposed decisions are based on th e Administrator’s considerati on of the scientific evidence 31 assessed in the ISA; quantitative exposure and ri sk information presented and assessed in the 32 REAs, as available; staff’s considerations and conclusions based on the evidence and 33 information, as presented in the PA; CASAC advi ce received during the development of the ISA, 34 REA(s), and PA; and public input received on draf ts of those assessment documents. Prior to 35April 2016 1-8 Draft - Do Not Quote or Cite publication in the Federal Register , a draft proposal notice unde rgoes interagency review 1 involving other federal agencies. 10 Materials upon which proposed d ecisions are based, including 2 the documents described above, are made availabl e to the public in th e regulatory docket for 3
review. 11 4 A public comment period, during which one or more public hearings are generally held, 5 follows publication of the notice of proposed rulemaking. Taking into account comments 6 received on the proposed rule, 12 the Agency develops a final rule, a draft version of which 7 undergoes interagency review prior to publication in the Federal Register . Chapter 6 of this IRP 8 discusses the development of the PA and the rulemaking steps for this review of the PM 9 NAAQS. 10



### 1.3 HISTORY OF REVIEWS OF THE PM NAAQS 11

Particulate matter is the generic term for a broad class of chemically and physically 12
diverse substances that exist as discrete liquid and/or solid partic les over a wide range of sizes. 13 Particles originate from a variety of anthropogenic stationary and mobile sources, as well as from 14 natural sources. Particles may be emitted directly, or formed in the atmosphere by 15 transformations of gaseous emissions such as sulfur oxides (SO X ), oxides of nitrogen (NO X ), and 16 volatile organic compounds (VOC). Examples of s econdary particle formation include: (1) the 17 conversion of sulfur dioxide (SO 2 ) to sulfuric acid (H 2 SO 4 ) vapor that nucleate s new particles or 18 condenses on existing particles and furt her reacts with ga seous ammonia (NH 3 ) to form various 19 inorganic salts (e.g., ammonium sulfate, (NH 4 ) 2 SO 4 , or ammonium bisulfate, NH 4 HSO 4 ); (2) the 20 conversion of nitrogen dioxide (NO 2 ) to nitric acid (HNO 3 ) vapor that condenses onto existing 21 particles and reacts further with a mmonia to form amm onium nitrate (NH 4 NO 3 ); and (3) 22 reactions involving gaseous VOC yielding organic compounds with low vapor pressures that 23 nucleate or condense on existing particles to form secondary organic particulate matter (SOPM) 24

10 Where implementation of the proposed decision would have an annual effect on the economy of $100 million of more, (e.g., by necessitating the implementation of emission s controls) the EPA also develops and releases a draft regulatory impact analysis (RIA) concurrent with the no tice of proposed rulemaking. This activity is conducted under Executive Order 12866. The RIA is conducted independently of the rulemaking process and, by law, is not considered in decisions regarding the NAAQS.

11 All documents in the docket are listed in the www.regulations.gov index. Publicly available docket materials are available either electronically at www.regulations.gov or in hard copy at the Air and Radiation Docket and Information Center. The docket ID number for this review of the PM NAAQS is EPA-HQ-OAR-2015-0072.

12 When issuing the final rulemaking, the Agency responds to all significant comments on the proposed rule.April 2016 1-9 Draft - Do Not Quote or Cite (U.S. EPA, 2004, Chapter 3). 13 The chemical and physical properties of PM vary greatly with 1 time, region, meteorology, and source categor y, complicating the asse ssment of health and 2
welfare effects. 3 This section summarizes the PM NAAQS that have been promulgated in past reviews 4 (Table 1-2). Each of these review s is discussed briefly below. 5
Table 1-2. Summary of National Ambient Air Quality Standards Promulgated for 6 Particulate Matter 1971-2012 14 7 Review Completed Indicator Avg. Time Level Form

1971 Total Suspended Particles (TSP) 24-hour 260 μg/m 3 (primary) 150 μg/m 3 (secondary) Not to be exceeded more than once
per year

Annual 75 μg/m 3 (primary) 60 μg/m 3 (secondary) Annual geometric mean

1987 PM 10 24-hour 150 μg/m 3 Not to be exceeded more than once per year on average over a 3-year period

Annual 50 μg/m 3 Annual arithmetic mean, averaged over 3 years

1997 PM 2.5 24-hour 65 μg/m 3 98 th percentile, averaged over 3 years
Annual 15.0 μg/m 3 Annual arithmetic mean, averaged over 3 years 15

PM 10 24-hour 150 μg/m 3 99 th percentile, averaged over 3
years 16
Annual 50 μg/m 3 Annual arithmetic mean, averaged over 3 years 2006 PM 2.5 24-hour 35 μg/m 3 98 th percentile, averaged over 3 years

13 As discussed below (section 1.4), the ecological effects associated with deposited particulate NO X and SO X and their transformation products are addressed in the review of the secondary NO X and SO X NAAQS.

14 When not specified, primary and secondary standards are identical.

15 The level of the 1997 annual PM 2.5 standard was to be compared to measurements made at the communityoriented monitoring site recording the highest concentrati on or, if specific constraints were met, measurements from multiple community-oriented monitoring sites could be av eraged (i.e., “spatial averaging”). Spatial averaging is discussed further in section 2.1.1, below.

16 When the 1997 standards were vacated (see below), the form of the 1987 standards remained in place (i.e., not to be exceeded more than once per year on average over a 3-year period).April 2016 1-10 Draft - Do Not Quote or Cite Annual 15.0 μg/m 3 Annual arithmetic mean, averaged over 3 years 17

PM 10 24-hour 18 150 μg/m 3 Not to be exceed more than once per year on average over a 3-year period

2012 PM 2.5 24-hour 35 μg/m 3 98 th percentile, averaged over 3 years

Annual 12.0 μg/m 3 (primary) 15.0 μg/m 3 (secondary) Annual mean, averaged over 3
years 19

PM 10 24-hour 150 μg/m 3 Not to be exceeded more than once per year on average over 3 years The EPA first established NAAQS for PM in 1971 (36 FR 8186, April 30, 1971), based 1 on the original Air Quality Criteri a Document (AQCD) (DHEW, 1969). 20 The federal reference 2 method (FRM) specified for determining attainme nt of the original standards was the high3 volume sampler, which collects PM up to a nominal size of 25 to 45 micrometers (μm) (referred 4 to as total suspended particulates or TSP) . The primary standards were set at 260 μg/m 3 , 24-hour 5 average, not to be exceeded more than once per year, and 75 μg/m 3 , annual geometric mean. The 6 secondary standards were set at 150 μg/m 3 , 24-hour average, not to be exceeded more than once 7 per year, and 60 μg/m 3 , annual geometric mean. 8 In October 1979 (44 FR 56730, October 2, 1979) , the EPA announced the first periodic 9 review of the air quality crit eria and NAAQS for PM. Revised primary and secondary standards 10 were promulgated in 1987 (52 FR 24634, July 1, 1987). In the 1987 decision, the EPA changed 11 the indicator for particles from TSP to PM 10 , in order to focus on the subset of inhalable particles 12 small enough to penetrate to the thoracic regi on of the respiratory tract (including the 13
tracheobronchial and alveol ar regions), referred to as thoracic particles. 21 The level of the 24- 14 hour standards (primary and secondary) was set at 150 μg/m 3 , and the form was one expected 15

17 The EPA tightened the constraints on the spatial averaging criteria by further limiting the conditions under which some areas may average measurements from multiple community-oriented monitors to determine compliance. Spatial averaging is discussed further in section 2.1.1, below.

18 The EPA revoked the annual PM 10 NAAQS in 2006.

19 In the 2012 decision, the EPA eliminated the option for spatial averaging.

20 Prior to the review initiated in 2007 (see below), the AQCD provided the scientific basis for the NAAQS.

21 PM 10 refers to particles with a nominal mean aerodyna mic diameter less than or equal to 10 μm. More specifically, 10 μm is the aerodynamic diam eter for which the efficien cy of particle collection is 50 percent. Larger particles are not excluded altogether , but are collected with substantially decreasing efficiency while smaller particles are collected with increasing efficiency.April 2016 1-11 Draft - Do Not Quote or Cite exceedance per year, on average over three years. The level of the annual standards (primary and 1 secondary) was set at 50 μg/m 3 , and the form was annual arithmetic mean, averaged over three 2

years. 3 In April 1994, the EPA announced its plans fo r the second periodic review of the air 4 quality criteria and NAAQS for PM, and in 1997 the EPA promulgated revisions to the NAAQS 5 (62 FR 38652, July 18, 1997). In the 1997 decision, th e EPA determined that the fine and coarse 6
fractions of PM 10 should be considered separately. This determination was based on evidence 7
that serious health effects were a ssociated with short- and long-ter m exposures to fine particles in 8 areas that met the existing PM 10 standards. The EPA added new standards, using PM 2.5 as the 9 indicator for fine particles (with PM 2.5 referring to particles with a nominal mean aerodynamic 10 diameter less than or equal to 2.5 μm). These new standards were as follows: (1) an annual 11 standard with a level of 15.0 μg/m 3 , based on the 3-year average of annual arithmetic mean 12
PM 2.5 concentrations from single or mu ltiple community-oriented monitors; 22 and (2) a 24-hour 13 standard with a level of 65 μg/m 3 , based on the 3-year average of the 98 th percentile of 24-hour 14
PM 2.5 concentrations at each monitor within an ar ea. Also, the EPA established a new reference 15
method for the measurement of PM 2.5 in the ambient air and adopted rules for determining 16
attainment of the new standards. To con tinue to address the coarse fraction of PM 10 (referred to 17 as thoracic coarse particles or PM 10-2.5 ; generally including partic les with a nominal mean 18 aerodynamic diameter greater than 2.5 μm and less th an or equal to 10 μm), the EPA retained the 19
annual PM 10 standard and revised th e form of the 24-hour PM 10 standard to be based on the 99 th 20 percentile of 24-hour PM 10 concentrations at each monitor in an area. The EPA revised the 21 secondary standards by making them identical in all respects to the primary standards. 22 Following promulgation of the 1997 PM NAAQS, petitions for review were filed by a 23 large number of parties, addressing a broad ra nge of issues. In May 1999, the U.S. Court of 24 Appeals for the District of Columbia Circuit (D.C. Circuit) upheld the EPA’s decision to 25 establish fine particle standards, holding that "the growing empirical evidence demonstrating a 26 relationship between fine particle pollution and adverse health e ffects amply justifies 27 establishment of new fine particle standards." American Trucking Associations v. EPA , 175 F. 3d 28

22 The level of the 1997 annual PM 2.5 standard was to be compared to measurements made at the communityoriented monitoring site recording the highest concentrati on or, if specific constraints were met, measurements from multiple community-oriented monitoring sites could be aver aged (i.e., “spatial averaging” as discussed in section 2.1.1, below). In the last review (completed in 2012) the EPA replaced the term “community-oriented” monitor with the term “area-wide” monitor. Area-wide monitors are those sited at the neighborhood scale or larger, as well as those monitors sited at micro-or middle scales that are representative of many such locations in the same CBSA (78 FR 3236, January 15, 2013).April 2016 1-12 Draft - Do Not Quote or Cite 1027, 1055-56 (D.C. Cir. 1999). The D.C. Circuit also found "ample support" for the EPA's 1 decision to regulate coarse partic le pollution, but vacated the 1997 PM 10 standards, concluding 2 that the EPA had not provided a reas onable explanation justifying use of PM 10 as an indicator for 3 coarse particles. 175 F. 3d at 1054-55. Pursuant to the D.C. Circuit’s decision, the EPA removed 4
the vacated 1997 PM 10 standards, and the pre-existing 1987 PM 10 standards remained in place 5 (65 FR 80776, December 22, 2000). The D.C. Circuit also upheld the EPA’s determination not to 6 establish more stringent secondary standards for fi ne particles to address effects on visibility. 175 7
F. 3d at 1027. 8 The D.C. Circuit also addressed more gene ral issues related to the NAAQS, including 9
issues related to the consideration of costs in setting NAAQS and th e EPA’s approach to 10 establishing the levels of NAAQS. Regarding the cost issue, the court reaffirmed prior rulings 11 holding that in setting NAAQS the EPA is “not permitted to consider the cost of implementing 12 those standards.” Id. at 1040-41. Regarding the le vels of NAAQS, the cour t held that the EPA’s 13 approach to establishing the leve l of the standards in 1997 (i.e., both for PM and for the ozone 14 NAAQS promulgated on the same day) effected “an unconstitutional delegation of legislative 15 authority.” Id. at 1034-40. Although the court stated that “the f actors EPA uses in determining 16 the degree of public health concern associated with different levels of ozone and PM are 17 reasonable,” it remanded the rule to the EPA, stat ing that when the EPA considers these factors 18 for potential non-threshold pollutants “what EPA l acks is any determinate criterion for drawing 19
lines” to determine where the standards should be set. 20 The D.C. Circuit’s holding on the cost and c onstitutional issues were appealed to the 21 United States Supreme Court. In February 2001, the Supreme Court issued a unanimous 22 decision upholding the EPA’s position on both the cost and constitutional issues. Whitman v. 23 American Trucking Associations , 531 U.S. 457, 464, 475-76. On the constitutional issue, the 24 Court held that the statutory requirement that NAAQS be “requi site” to protect public health 25 with an adequate margin of safety sufficiently guided the EPA’s discretion, affirming the EPA’s 26 approach of setting standards that are neith er more nor less stri ngent than necessary. 23 27

23 The Supreme Court remanded the case to the Court of Appeals for resolution of any remaining issues that had not been addressed in that court’s earlier rulings. Id. at 475-76. In a March 2002 decision, the Court of Appeals rejected all remaining challenges to the standards, holding that the EPA’s PM 2.5 standards were reasonably supported by the administrative record and were not “arbitrary and capricious” American Trucking Associations v. EPA , 283 F. 3d 355, 369-72 (D.C. Cir. 2002).April 2016 1-13 Draft - Do Not Quote or Cite In October 1997, the EPA published its plans for the third periodic review of the air 1 quality criteria and NAAQS for PM (62 FR 55201, October 23, 1997). After CASAC and public 2 review of several drafts, th e EPA’s NCEA finalized the AQC D in October 2004 (U.S. EPA, 3 2004). The EPA’s OAQPS finalized a Risk Assess ment and Staff Paper in December of 2005 4 (Abt, 2005; U.S. EPA, 2005). 24 On December 20, 2005, the EPA announced its proposed 5 decision to revise the NAAQS for PM, and solic ited comment on a broad range of options (71 6 FR 2620, January 17, 2006). 7 On September 21, 2006, the EPA announced its fina l decisions to revise the primary and 8 secondary NAAQS for PM to provide increased protection of public health and welfare, 9 respectively (71 FR 61144, October 17, 2006). With regard to the primary and secondary 10 standards for fine particles, the EP A revised the level of the 24-hour PM 2.5 standards to 35 11 μg/m 3 , retained the level of the annual PM 2.5 standards at 15.0 μg/m 3 , and revised the form of the 12
annual PM 2.5 standards by narrowing the constraints on the optional use of spatial averaging. 25 13 With regard to the primary and secondary standards for PM 10 , the EPA retained the 24-hour 14 standards, with levels at 150 μg/m 3 , and revoked the annual standard s. The Administrator judged 15 that the available evidence generally did not suggest a link between long-term exposure to 16 existing ambient levels of coarse particles and health or welf are effects. In addition, a new 17
reference method was added for the measurement of PM 10-2.5 in the ambient air, in order to 18 provide a basis for approving fe deral equivalent methods (FEMs) and to promote the gathering 19 of scientific data to support future reviews of the PM NAAQS. 20 Several parties filed petitions for review following promulgation of the revised PM 21 NAAQS in 2006. These petitions addressed the follo wing issues: (1) selecting the level of the 22 primary annual PM 2.5 standard; (2) retaining PM 10 as the indicator of a standard for thoracic 23 coarse particles, re taining the level and form of the 24-hour PM 10 standard, and revoking the 24

PM 10 annual standard; and (3) setting the secondary PM 2.5 standards identical to the primary 25 standards. On February 24, 2009, the U.S. Court of Appeals for the District of Columbia Circuit 26 issued its opinion in the case American Farm Bureau Federation v. EPA , 559 F. 3d 512 (D.C. 27 Cir. 2009). The court remanded the primary annual PM 2.5 NAAQS to EPA because EPA failed to 28 adequately explain why the standards provided the requisite protection from both short- and 29

24 Prior to the review initiated in 2007, the Staff Paper, ra ther than the PA, presented th e EPA staff’s considerations and conclusions regarding the adequacy of existing NAAQS and, when appr opriate, the potential alternative standards that could be supported by the evidence and information.

25 Spatial averaging is discussed in more detail in section 2.1.1, below.April 2016 1-14 Draft - Do Not Quote or Cite long-term exposures to fine particles, in cluding protection for at-risk populations. American 1
Farm Bureau Federation v. EPA , 559 F. 3d 512, 520-27 (D.C. Cir. 2009). With regard to the 2
standards for PM 10 , the court upheld EPA’s decisi ons to retain the 24-hour PM 10 standard to 3 provide protection from thoracic coarse pa rticle exposures and to revoke the annual PM 10 4
standard. American Farm Bureau Federation, 559 F. 2d at 533-38. With regard to the secondary 5

PM 2.5 standards, the court remanded the standards to EPA because the Agency failed to 6 adequately explain why setting the secondary PM standards identical to the primary standards 7 provided the required protection for public welfare, including protection from visibility 8 impairment. American Farm Bureau Federation , 559 F. 2d at 528-32. The EPA responded to the 9 court’s remands as part of the next review of the PM NAAQS, which was initiated in 2007 10 (discussed below). 11 In June 2007, the EPA initiated the fourth peri odic review of the ai r quality criteria and 12 the PM NAAQS by issuing a call for information in the Federal Register (72 FR 35462, June 28, 13 2007). Based on the NAAQS review process, as revised in 2008 and again in 2009, 26 the EPA 14 held science/policy issue workshops on the primary and secondary PM NAAQS (72 FR 34003, 15 June 20, 2007; 72 FR 34005, June 20, 2007), and pr epared and released the planning and 16 assessment documents that comprise the review process (i.e., IRP (U.S. EPA, 2008), ISA (U.S. 17 EPA, 2009a), REA planning documents for health and welfare (U.S. EPA, 2009b, c), a 18 quantitative health risk a ssessment (U.S. EPA, 2010a) 27 and an urban-focused visibility 19 assessment (U.S. EPA, 2010b), 28 and PA (U.S. EPA, 2011)). In June 2012, the EPA announced 20 its proposed decision to revise the NAAQS for PM (77 FR 38890, June 29, 2012). 21

26 The history of the NAAQS review process, including revisions to the process, is discussed at http://www3.epa.gov/ttn/n aaqs/review2.html.

27 The quantitative assessment of health risks condu cted in the last review was presented in the Quantitative Health Risk Assessment for Particulate Matter (U.S. EPA, 2010a). In the current review, quantitative assessments for health-related exposures and risks, if warranted, would be presented in the Health Risk and Exposure Assessment (HREA). For consistency with the documents developed under the current NAAQS process, the Quantitative Health Risk Assessment for Particulate Matter (U.S. EPA, 2010a) from the last review will be referenced in this document as the 2010 HREA.

28 The quantitative assessment of welfare effects conducted in the last review was presented, in part, in the UrbanFocused Visibility Assessment (U.S. EPA, 2010b). In th e current review, quantitativ e assessments for welfare effects, if warranted, would be presented in the Welfare Risk and Exposure Assessment (WREA). The UrbanFocused Visibility Assessment (U.S. EPA, 2010b) from the last review will be referenced in this document as the 2010 UFVA.April 2016 1-15 Draft - Do Not Quote or Cite In December 2012, the EPA announced its final decisions to revise the primary NAAQS 1 for PM to provide increased protection of public health (78 FR 3086, January 15, 2013). 29 With 2 regard to primary standards for PM 2.5 , the EPA revised the level of the annual PM 2.5 standard 30 to 3 12.0 μg/m 3 and retained the 24-hour PM 2.5 standard, with its level of 35 μg/m 3 . For the primary 4

PM 10 standard, the EPA retained th e 24-hour standard to continue to provide protection against 5 effects associated with short-term expos ure to thoracic coarse particles (i.e., PM 10-2.5 ). With 6 regard to the secondary PM standards, the EP A generally retained the 24-hour and annual PM 2.5 7
standards 31 and the 24-hour PM 10 standard to address visibility and non-visibility welfare effects. 8 On judicial review, the revised stan dards were upheld in all respects. NAM v EPA , 750 F.3d 921 9 (D.C. Cir. 2014). 10



### 1.4 GENERAL SCOPE OF THE CURRENT REVIEW 11

With regard to scope, this review is focuse d on the air quality crit eria for PM and on the 12 primary and secondary NAAQS for PM 2.5 and PM 10 . As discussed above, the current primary 13 and secondary PM 2.5 standards are meant to protect against the health and welfare effects, 14 respectively, that have been associated with exposures to fine particles. The primary and 15 secondary PM 10 standards are meant to protect against th e effects associated with exposures to 16 thoracic coarse particles (i.e., PM 10-2.5 ). Therefore, an important aspect of the current review will 17
be the EPA’s assessment of the health and welfare effects that have been associated with size 18 fractionated PM mass, with a particular focus on the PM 2.5 and PM 10-2.5 size fractions. In 19 addition, as in the last review , the EPA will also assess the av ailable scientific evidence for 20
health or welfare effects associated with additio nal size fractions (e.g., ultrafine particles) and 21 with particular PM components or groups of co mponents, sources, or environments (e.g., urban 22 and non-urban environments). 23 Based on the available scientific information, th e EPA will consider the extent to which 24
the current PM 2.5 and PM 10 standards are requisite to protect public health and welfare, within 25 the meaning of section 109(b) of the CAA (s ection 1.1, above). To the extent the available 26 information calls into question the adequacy of the protection afforded by one or more of the 27 existing PM standards, the EPA will consider po tential alternatives th at could be supported by 28

29 The bases for these decisions are discussed further in sections 2.1 and 2.2, below.

30 The EPA also eliminated the option for spatial averaging (section 2.1.1, below).

31 Consistent with the primary standard, the EPA elimin ated the option for spatial averaging with the annual standard (section 2.1.1, below).April 2016 1-16 Draft - Do Not Quote or Cite the available scientific evidence and, as available, exposure-/risk- based information, in terms of 1 the basic elements of the NAAQS (indi cator, averaging time, form, level). 2 With regard to the secondary standards in pa rticular, as in the la st review (77 FR 38991, 3 June 29, 2012), this review of the PM NAAQS will consider the PM-related welfare effects that 4 are not being addressed in the ongo ing review of the secondary NO X and SO X NAAQS. 5 Specifically, the review of the secondary NO X and SO X NAAQS is addressing the ecological 6 effects of ecosystem loading of oxides of nitrogen and oxides of sulfur, which includes 7 particulate nitrogen and sulfur compounds. 32 In this review of the PM NAAQS, welfare effects to 8 be considered include PM-related visibility impair ment, climate effects, ecological effects (other 9 than those attributable to deposition of NO X , SO X and their transfor mation products) and 10 materials damage and soiling (i.e., materials eff ects). While N and/or S may contribute to these 11 welfare effects, other components of PM play a role as well. Therefore, it is appropriate to 12
consider these welfare effects in this review of the PM NAAQS to the extent that they are not 13 being covered in the ongoing review of the secondary NO X and SO X NAAQS. In the case of 14 materials effects, the impacts of gaseous and pa rticulate N and S wet deposition cannot be clearly 15 distinguished, so both will be considered in th is review of the PM NAAQS, along with other 16
materials effects of PM-related deposition. 17 In contrast, as noted above, the ongoing re view of the secondary NAAQS for ecological 18
effects of NO X and SO X is considering the ecological effect s that result specifically from the 19 deposition of NO X and SO X and their transformation products. 33 This approach is consistent with 20 the previous review of the secondary NO 2 and SO 2 standards, 34 in which the EPA conducted a 21 joint review focused on the protection provi ded against the effects of deposition of NO X and SO X 22 to sensitive aquatic and terrestrial ecosystems. The approach in the last review recognized that 23
NO X and SO X , and their associated transformation produc ts, are linked from the perspectives of 24 both atmospheric chemistry and ecological effects, providing “a strong basis for considering 25 these pollutants together” (77 FR 20222, April 3, 2012). 26

32 See http://www3.epa.gov/ttn/naaqs/standards/no2so2sec/index.html for more information on the current review of the secondary NO X and SO X NAAQS.

33 More broadly, the review of the seco ndary NAAQS for ecological effects of NO X and SO X includes consideration of the ecological effects of ecosystem loading of particulate nitrogen and sulfur compounds.

34 When discussing specific standards, we refer to those standards by their indi cator species (i.e., in this case NO 2 and SO 2 ). As described in the draft NO X /SO X IRP (U.S. EPA, 2015, p. 1-1) the terms NO 2 and SO 2 are not interchangeable with the terms NO X and SO X . NO X and SO X include many more chemical species than just NO 2 and SO 2
.April 2016 1-17 Draft - Do Not Quote or Cite 

### 1.5 ANTICIPATED SCHEDULE FOR CURRENT REVIEW 1

In December 2014, the EPA announced the initiati on of the current peri odic review of the 2 air quality criteria for PM and of the PM 2.5 and PM 10 NAAQS and issued a call for information 3

in the Federal Register (79 FR 71764, December 3, 2014). On February 9 to 11, 2015, the EPA’s 4 NCEA and OAQPS held a public workshop to inform the planning for the current review of the 5 PM NAAQS (announced in 79 FR 71764, December 3, 2014). This workshop was meant to 6 provide the EPA an opportunity to receive input and advice on th e key science and policy issues 7 around which the PM NAAQS review will be structured. Workshop participants were asked to 8 highlight significant new and emerging PM rese arch related to these key science and policy 9 issues, and to make recommendations to the Ag ency regarding the design and scope of this 10 review. The input received at this workshop was c onsidered by the EPA staff in developing this 11 draft IRP. The EPA’s anticipated schedule for the remainder of this review is summarized in 12
Table 1-3, below. 13April 2016 1-18 Draft - Do Not Quote or Cite Table 1-3. Anticipated Schedule fo r the Review of the PM NAAQS 1
Stage of Review Major Milestone Actual or Target Date

Planning Literature Search Ongoing Federal Register Call for Information December 3, 2014 Workshop on Science/Policy Issues February 9-11, 2015 Release Draft IRP for CASAC/public review April 2016 CASAC Review Meeting for Draft IRP May 23, 2016
Release Final IRP September 2016

Science Assessment Release First Draft ISA for CASAC/public review Spring 2017 CASAC Review Meeting for First Draft ISA Summer 2017 Release Second Draft ISA for CASC/public review Winter 2018 CASAC Review Meeting for Second Draft ISA Spring 2018
Release Final ISA Spring 2019

Risk/Exposure Assessments Release REA Planning Document(s) for CASAC/public review Spring/Summer 2017

CASAC Review Meeting for REA Planning Document(s) Summer 2017 Release First Draft REA(s) for CASAC/Public Review Winter/Spring 2018 CASAC Review Meeting for First Draft REA(s) Spring 2018 Release Second Draft REA(s) for CASAC/Public Review Fall 2018 CASAC Review Meeting for Second Draft REA(s) Fall/Winter 2018 Release Final REA(s) Winter 2019

Policy Assessment/ Rulemaking Release First Draft PA for CASAC/public review Fall 2018 CASAC Review Meeting on First Draft PA Fall/Winter 2018
Release Second Draft PA Fall 2019
CASAC Review/Public Comment on Second Draft PA Fall/Winter 2019
Release Final PA Winter 2020 Proposed Rulemaking 2020 Final Rulemaking 2021

2April 2016 1-19 Draft - Do Not Quote or Cite 

### REFERENCES 1

DHEW (1969). Air Quality Criteria for Particul ate Matter. U. S. Department of Health, 2 Education, and Welfare. Public Health Servi ce, Environmental Health Service, National 3 Air Pollution Control Administra tion, Washington, D.C. January 1969. 4 U.S. EPA (2004). Air Quality Criteria for Partic ulate Matter. National Ce nter for Environmental 5 Assessment, Office of Research and Deve lopment, U.S. Environmental Protection 6 Agency, Research Triangle Park, NC 27711; report no. EPA/600/P-99/002aF and 7 EPA/600/P-99/002bF. October 2004. Available: 8 http://www3.epa.gov/ttn/naaqs/standards/pm/s_pm_cr_cd.html

. 9

U.S. EPA (2005). Review of the National Ambient Air Quality Standards for Particulate Matter: 10 Policy Assessment of Scient ific and Technical Inform ation, OAQPS Staff Paper. 11 Research Triangle Park, NC 27711: Office of Air Quality Planning and Standards. Report 12 No. EPA-452/R-05-005a. D ecember 2005. Available: 13 http://www3.epa.gov/ttn/naaqs/standards/pm/s_pm_cr_sp.html

. 14

U.S. EPA (2008). Integrated Review Plan for the National Ambient Air Quality Standards for 15 Particulate Matter. National Center for Environmental Assessment and Office of Air 16 Quality Planning and Standards, U.S. Environmental Protection Agency, Research 17 Triangle Park, NC. Report No. EPA 452/R-08-004. March 2008. Available: 18 http://www3.epa.gov/ttn/naaq s/standards/pm/s_pm_2007_pd.html

. 19

U.S. EPA (2009a). Integrated Science Assessment for Particulate Matter: Final Report. National 20 Center for Environmental Assessment- RTP Division, Office of Research and 21 Development, Research Triangle Par k, NC. EPA/600/R-08/139F. December 2009. 22 Available: http://www3.epa.gov/ttn/naaqs/ standards/pm/s_pm_2007_isa.html

. 23

U.S. EPA (2009b). Particulate Ma tter National Ambient Air Quality Standards: Scope and 24 Methods Plan for Health Risk and Exposure Assessment. Office of Air Quality Planning 25 and Standards, U.S. Environmental Protec tion Agency, Research Triangle Park, NC. 26 EPA-452/P-09-002. February 2009. Available: 27 http://www3.epa.gov/ttn/naaq s/standards/pm/s_pm_2007_pd.html

. 28

U.S. EPA (2009c). Particulate Matter National Ambient Air Quality Standards: Scope and 29 Methods Plan for Urban Visibi lity Impact Assessment. Office of Air Quality Planning 30 and Standards, U.S. Environmental Protec tion Agency, Research Triangle Park, NC. 31 EPA-452/P-09-001. February 2009. Available: 32 http://www3.epa.gov/ttn/naaq s/standards/pm/s_pm_2007_pd.html

. 33

U.S. EPA (2010a). Quantitative Health Risk A ssessment for Particulate Matter – Final Report. 34 Office of Air Quality Planning and Standard s, U.S. Environmental Protection Agency, 35 Research Triangle Park, NC. EP A-452/R-10-005. June 2010. Available: 36 http://www3.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html

. 37April 2016 1-20 Draft - Do Not Quote or Cite U.S. EPA (2010b). Particulate Ma tter Urban-Focused Visibility Assessment – Final Report. 1 Office of Air Quality Planning and Standard s, U.S. Environmental Protection Agency, 2 Research Triangle Park, NC. EP A-452/R-10-004. July 2010. Available: 3 http://www3.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html

. 4

U.S. EPA (2011). Policy Assessment for the Review of the Particulate Matter National Ambient 5 Air Quality Standards. Office of Air Quality Planning and Standards, U.S. Environmental 6 Protection Agency, Research Triangl e Park, NC. EPA 452/R-11-003. April 2011. 7 Available: http://www3.epa.gov/ttn/naaq s/standards/pm/s_pm_2007_pa.html

. 8

U.S. EPA (2015). Draft Integrated Review Plan for the Secondary National Ambient Air Quality 9 Standards for Oxides of Nitrogen and Oxides of Sulfur. Office of Air Quality Planning 10 and Standards, U.S. Environmental Protec tion Agency, Research Triangle Park, NC. 11 October 2015. 12 https://www3.epa.gov/ttn/naaqs/standards/no2s o2sec/data/IRP_NOXSOX_CompleteDraf 13 t_102915_final.pdf 14

15April 2016 2-1 Draft - Do Not Quote or Cite 

## 2 KEY POLICY-RELEVANT ISSUES IN THE CURRENT 1 

## REVIEW 2

In order to inform the Administrator’s deci sions on the adequacy of the existing primary 3 and secondary PM NAAQS, in the current review we 35 will address the following overarching 4 question: 5

 Does the currently available scientific evid ence and exposure-/risk-based information 6 support or call into question the adequacy of the protection affo rded by the current 7 primary and/or secondary PM standards? 8 If warranted, we will also addre ss a second overarching question: 9

 What alternative standards are supported by the currently available scientific evidence 10 and exposure-/risk-based information, and are appropriate for consideration? 11 To inform our evaluation of these overarching questions, we will identify a number of more 12 specific policy-relevant questions for consideration (see below). These policy-relevant questions 13 will focus on key issues reflecting aspects of the health and welfare effects evidence, air quality 14 information, and information from quantitative exposure and risk assessments that can inform 15
the Administrator’s decisions in the current review. Questions will build upon the conclusions 16
from the last review on the evidence and info rmation, including conclusions on the uncertainties 17
and limitations in that evidence and information. 18
Sections 2.1 and 2.2 below summarize the deci sions made in the last review of the PM 19 NAAQS, the interpretations of the underlying sc ientific evidence and information supporting 20 those decisions, the important uncertainties and lim itations in the evidence and information in the 21 last review, and potential key policy-rele vant questions for the current review. 36 Section 2.1 22 focuses on the primary PM standards, and sect ion 2.2 focuses on the secondary PM standards. 23 Section 2.3 provides an overview of the PM ambient monitoring networks and the key 24 monitoring-related issues to be considered as part of th e current standards review. 25

35 In this document, the terms “we” or “our” refe r to staff in the EPA’s OAQPS and/or NCEA.

36 Based on CASAC advice and public input on this dr aft IRP, we will modify these potential questions as appropriate for the final IRP. The key policy-relevant questions identified in the final PM IRP will provide an overall framework for the development of the PM ISA, REAs (if warranted), and the PA.April 2016 2-2 Draft - Do Not Quote or Cite 

### 2.1 PRIMARY STANDARDS 1

The last review of the primary PM N AAQS was completed in 2012 (78 FR 3086, January 2 15, 2013). As noted above (section 1.3), in the la st review the EPA lowered the level of the 3 primary annual PM 2.5 standard from 15.0 to 12.0  g/m 3

, 37 retained the existing 24-hour PM 2.5 4
standard with its level of 35  g/m 3 , and retained the existing 24-hour PM 10 standard with its level 5
of 150  g/m 3 . Sections 2.1.1 and 2.1.2 below discuss the primary PM 2.5 and PM 10 standards, 6 respectively. These sections summarize the rationale s for the decisions made in the last review, 7 including the Agency’s considerat ion of important uncertainties and limitations in the scientific 8 evidence and in the air quality and risk info rmation. Section 2.1.3 provides an overview of the 9 general approach and the potential key policy-relevant questions in the curr ent review of the 10 primary PM 2.5 and PM 10 standards. 11

2.1.1 PM 2.5 Standards 12
The 2012 decision to strengthe n the suite of primary PM 2.5 standards was based on the 13
Administrator’s consideration of the extensive b ody of scientific eviden ce assessed in the 2009 14 PM ISA (U.S. EPA, 2009); the quantitative risk analyses pres ented in the 2010 HREA (U.S. 15 EPA, 2010a); 38 the advice and recommendations of CASAC (e.g., Samet, 2009; 2010a, b); and 16 public comments on the proposed rule (78 FR 3086, January 15, 2013; U.S. EPA, 2012). In 17 particular, the Administrator noted the “strong and generally robust body of evidence of serious 18
health effects associated with both long- and short-term exposures to PM 2.5 ” (78 FR 3120, 19 January 15, 2013). This included epidemiologic studies reporting health eff ect associations based 20 on long-term average PM 2.5 concentrations ranging from about 15.0  g/m 3 or above (i.e., at or 21
above the level of the then-exis ting annual standard) to concentra tions “significantly below the 22 level of the annual standard” (78 FR 3120, January 15, 2013). The Administrator further 23
observed that such studies were part of an overall pattern across a broad ra nge of studies 24 reporting positive associations, which were fre quently statistically significant. Based on her 25
“confidence in the associa tion between exposure to PM 2.5 and serious public health effects, 26
combined with evidence of such an association in areas that w ould meet the current standards” 27

37 The Agency also eliminated spatial averaging provisions as part of the form of the annual standard.

38 In the last review, the EPA generated a quantitative health risk assessment for PM, and did not conduct an exposure assessment (U.S. EPA, 2010a). To be consistent with our general process for reviewing the NAAQS (section 1.2, above), and with our discussion of potentia l quantitative analyses in the current review (Chapter 4, below), we refer to the 2010 health risk assessment as the 2010 HREA.April 2016 2-3 Draft - Do Not Quote or Cite (78 FR 3120, January 15, 2013), the Administrator concluded that revision of the suite of 1 primary PM 2.5 standards was necessary in order to pr ovide increased public health protection. 2 Specifically, she concluded that the then-existing suite of primary PM 2.5 standards was not 3 sufficient, and thus not requisite, to protect public health with an adequate margin of safety. This 4
decision was consistent with advice received from CASAC (Samet, 2010b). 5
The Administrator next considered what specific revisions to the existing primary PM 2.5 6 standards were appropriate, given the available evidence and quantitative risk information. She 7
considered both the annual and 24-hour PM 2.5 standards, focusing on the basic elements of those 8 standards (i.e., indicator, aver aging time, form, and level). These considerations, and the 9
Administrator’s conclusions , are summarized below. 10
Indicator 11 In initially setting standards for fine particles in 1997, the EPA concluded it was 12 appropriate to control fine particles as a group, based on PM 2.5 mass, rather than singling out any 13 particular component or cla ss of fine particles (62 FR 38667, July 18, 1997). In the review 14 completed in 2006, based on similar consideratio ns, the EPA concluded that the available 15 information supported retaining the PM 2.5 indicator and remained too limited to support a distinct 16 standard for any specific PM 2.5 component or group of componen ts associated with particular 17 source categories of fine particle s (71 FR 61162 to 61164, October 17, 2006). 18 In the last review, the EPA again considered issues related to the appropriate indicator for 19 fine particles, with a focus on evaluating support for the existing PM 2.5 mass-based indicator and 20 for potential alternative indicators based on the ultrafine par ticle fraction or on fine particle 21 composition (78 FR 3121, January 15, 2013). 39 With regard to PM 2.5 mass, as in the 1997 and 22 2006 reviews, the health studies av ailable during the last review c ontinued to link adverse health 23 outcomes (e.g., premature mortality, hospital admissions, emergency department visits) with 24 long- and short-term exposures to fine particles indexed largely by PM 2.5 mass (78 FR 3121, 25 January 15, 2013). With regard to the ultrafine fr action of ambient PM, the PA noted the limited 26 body of health evidence assessed in the ISA (s ummarized in U.S. EPA, 2009, section 2.3.5 and 27 Table 2–6) and the limited monitoring info rmation available to characterize ambient 28
concentrations of ultrafine particles (U.S. EPA, 2011, sectio n 1.3.2 and Appendix B, section 29 B.1.3). With regard to PM composition, the ISA concluded that “the evidence is not yet 30

39 In the last review, the ISA defined ultrafine particles as generally including particles with a mobility diameter less than or equal to 0.1 μm. Mobility diameter is defined as th e diameter of a particle having the same diffusivity or electrical mobility in air as the particle of interest, and is often used to characterize particles of 0.5 μm or smaller (U.S. EPA, 2009a, pp. 3-2 to 3-3)

.April 2016 2-4 Draft - Do Not Quote or Cite sufficient to allow differentiation of those constituents or sources th at are more closely related to 1 specific health outcomes” (U.S. EPA, 2009, pp. 2-26 and 6-212; 78 FR 3123, January 15, 2013). 2 The PA further noted that “many different constituents of the fi ne particle mixture as well as 3 groups of components associated with specific so urce categories of fine particles are linked to 4 adverse health effects” (U.S. EPA, 2011, p. 2–55; 78 FR 3123, January 15, 2013). Consistent 5 with the conclusions of the PA, CASAC advised that it was appropriate to consider retaining 6

PM 2.5 as the indicator for fine particles. CASAC speci fically stated that “[t] here [is] insufficient 7 peer-reviewed literature to support any other indicator at this time” (Samet, 2010a, p. 12). The 8
Administrator concurred with the conclusions of the Policy Assessment and with CASAC 9 recommendations, and concluded that it was “appropriate to retain PM 2.5 as the indicator for fine 10 particles” (78 FR 3123, January 15, 2013). 11 Averaging time 12 In 1997, the EPA set an annual PM 2.5 standard to provide prot ection from health effects 13 associated with long- and short-term exposures to PM 2.5 , and a 24-hour standard to supplement 14 the protection afforded by the annual standa rd (62 FR 38667 to 38668, July, 18, 1997). In the 15 2006 review, the EPA retained both annual and 24-hour averaging times (71 FR 61164, October 16 17, 2006). 17 In the last review, the EPA again considered issues related to the appropriate averaging 18
times for PM 2.5 standards, with a focus on evaluating support for the exis ting annual and 24-hour 19 averaging times and for potential alternative averaging times based on sub-daily or seasonal 20
metrics. Based on the evidence assessed in th e ISA, the PA noted that the overwhelming 21 majority of studies that had been conducted si nce the 2006 review continue d to utilize annual (or 22 multi-year) or 24-hour PM averaging periods (U.S . EPA, 2011, section 2.3.2). With regard to 23 potential support for an averaging time shorter than 24-hours, the PA noted that studies of 24 cardiovascular effects associated with sub-daily PM concentrations had evaluated a variety of 25 PM metrics (e.g., PM 2.5 , PM 10 , PM 10-2.5 , ultrafine particles), averag ing periods (e.g., 1, 2, and 4 26 hours), and health outcomes (U.S. EPA, 2011, s ection 2.3.2). The PA concluded that this 27 information, when viewed as a whole, was too un certain to serve as a basis for establishing a 28 primary PM 2.5 standard with an averaging time s horter than 24-hours (U.S. EPA, 2011, p. 2- 29 57). 40 With regard to potential support for a season al averaging time, few studies were available 30

40 For respiratory effects specifically, the Administrator further noted the ISA conclusion that the strongest associations were observed with 24-hour average or longer exposures, not with exposures less than 24-hours (U.S. EPA, 2009, section 6.3).April 2016 2-5 Draft - Do Not Quote or Cite to deduce a general pattern in PM 2.5 -related risk across seasons, a nd these studies did not provide 1
information on health effects associat ed with season-long exposures to PM 2.5 (U. S. EPA, 2011, 2 p. 2-58; 78 FR 3124, January 15, 2013). 3
The PA reached the overall conclusions that the available information provided strong 4 support for considering retaining the current a nnual and 24-hour averaging times and did not 5 provide support for consideri ng alternative averaging times (U.S. EPA, 2011, p. 2-58). CASAC 6 agreed that these conclusions were reas onable (Samet, 2010a, p. 13) . The Administrator 7
concurred with the PA conclusions and with CA SAC’s advice. Specifically, she judged that it 8 was “appropriate to retain the current annual and 24-hour averaging times for the primary PM 2.5 9 standards to protect against hea lth effects associated with long- and short-term exposure periods” 10 (78 FR 3124, January 15, 2013). 11
Form 12 In 1997, the EPA established the form of the annual PM 2.5 standard as an annual 13 arithmetic mean, averaged over 3 years, from single or multiple community-oriented monitors. 41 14 That is, the level of the annual standard was to be compared to measurements made at each 15 community-oriented monitoring site or, if specific criteria we re met, measurements from 16 multiple community-oriented monitoring sites c ould be averaged together (i.e., spatial 17 averaging) 42 (62 FR 38671 to 38672, July 18, 1997). In the 1997 review, the EPA also 18
established the form of the 24-hour PM 2.5 standard as the 98 th percentile of 24-hour 19
concentrations at each monitor within an area (i.e., no spatial averaging), averaged over three 20 years (62 FR at 38671 to 38674, July 18, 1997). In the 2006 review, the EPA retained these 21 standard forms but tightened the criteria for usin g spatial averaging with the annual standard (78 22 FR 3124, January 15, 2013). 43 23

41 As noted above (section 1.3), in the last review the EPA replaced the term “community-oriented” monitor with the term “area-wide” monitor. Area-wide monitors are those sited at the neighbor hood scale or larger, as well as those monitors sited at micro-or middle scales that are repres entative of many such locations in the same CBSA (78 FR 3236, January 15, 2013). CBSAs are required to have at l east one area-wide m onitor sited in the area of expected maximum PM 2.5 concentration.

42 The original criteria for spat ial averaging included: (1) the annual mean concentration at each site shall be within 20% of the spatially averaged annual m ean, and (2) the daily valu es for each monitoring site pair shall yield a correlation coefficient of at leas t 0.6 for each calendar quarter (62 FR 38671 to 38672, July 18, 1997).

43 Specifically, the Administrator revised spatial averaging criteria such that “(1) [t]he annual mean concentration at each site shall be within 10 percent of the spatially av eraged annual mean, and (2) the daily values for each monitoring site pair shall yield a correlation coefficient of at least 0.9 for each calendar quarter (71 FR 61167, October 17, 2006).April 2016 2-6 Draft - Do Not Quote or Cite In the last review, the EPA’s consid eration of the form of the annual PM 2.5 standard again 1 included a focus on the issue of spatial averag ing. An analysis of air quality and population 2 demographic information indicated that the highest PM 2.5 concentrations in a given area tended 3
to be measured at monitors in locations wher e the surrounding populations were more likely to 4 live below the poverty line and to include larger percentages of racial an d ethnic minorities (U.S. 5 EPA, 2011, p. 2-60). Based on this an alysis, the PA concluded that spatial averaging could result 6 in disproportionate impacts in at-risk populations, including mi nority populations and 7 populations with lower socioeconomic status (SES ). Therefore, the PA concluded that it was 8 appropriate to consider revi sing the form of the annual PM 2.5 standard such that it did not allow 9 for the use of spatial averaging across monito rs (U.S. EPA, 2011, p. 2-60). The CASAC agreed 10 with staff conclusions that it was “reasonable” for the EPA to eliminate the spatial averaging 11 provisions (Samet, 2010b, p. 2), stating the followi ng: “Given mounting evidence showing that 12 persons with lower SES levels are a suscepti ble group for PM-related health risks, CASAC 13 recommends that the provisions that allow for spatial averaging across monitors be eliminated” 14 (Samet, 2010a, p. 13). 15 The Administrator concluded that public hea lth would not be protected with an adequate 16 margin of safety in all locations, as re quired by law, if disproportionately higher PM 2.5 17 concentrations in low income and minority co mmunities were averaged together with lower 18 concentrations measured at other sites in a larg e urban area. Therefore, she concluded that the 19
form of the annual PM 2.5 standard should be revised to e liminate spatial av eraging provisions. 20 Thus, the level of the annual PM 2.5 standard established in the last review is to be compared with 21 measurements from each appropriate monitor in an area, with no allowance for spatial averaging. 22 In the last review, the EPA also considered the form of the 24-hour PM 2.5 standard. The 23 Agency recognized that the existing 98 th percentile form for the 24-hour standard was originally 24 selected to provide a balance between limiting the occurrence of peak 24-hour PM 2.5 25 concentrations and identifying a stable target for risk management programs. 44 Updated air 26 quality analyses in the last review provided addi tional support for the incr eased stability of the 27
98 th percentile PM 2.5 concentration, compared to the 99 th percentile (U.S. EPA, 2011, Figure 2-2, 28 p. 2-62). Consistent with the PA conclusions base d on this analysis, the Administrator concluded 29

44 See ATA III, 283 F.3d at 374–376 which concludes that it is legitimate for the EPA to consider overall stability of the standard and its resulting promotion of overall effec tiveness of NAAQS control programs in setting a standard that is requisite to protect the public health.April 2016 2-7 Draft - Do Not Quote or Cite that it was appropriate to retain the 98 th percentile form for the 24-hour PM 2.5 standard (78 FR 1 3127, January 15, 2013). 2
Level 3 The EPA’s approach to consideri ng alternative levels of the PM 2.5 standards in the last 4 review was based on evaluating the public health protection afforded by the annual and 24-hour 5 standards, taken together, against mortality and morbidity effects associated with long-term or 6
short-term PM 2.5 exposures. This approach recognized th at there is no bright line clearly 7 directing the choice of level. Ra ther, the choice of what is appr opriate is a public health policy 8 judgment entrusted to the Administrator. In the last review, this judgment included consideration 9 of the strengths and limitations of the evidence an d the appropriate inferences to be drawn from 10 the evidence and the exposure and risk assessments. 11 In evaluating alternative standards, the Agen cy considered the extent to which specific 12
alternative PM 2.5 standard levels were likely to re duce the magnitudes of both long-term 13 exposure-related mortality risk and short-term exposure-related mortalit y and morbidity risk. 14 Results of the 2010 Health Risk and Exposure A ssessment (HREA) indicated that, compared to 15 revising the 24-hour standard, lowering the level of the annual standard would result in more 16
consistent risk reductions acr oss urban study areas, thereby potentially providing a more 17 consistent degree of public health protecti on (U.S. EPA, 2010a, pp. 5-15 to 5-17; 78 FR 3128, 18 January 15, 2013). Based on risk results, together w ith the available eviden ce, the Administrator 19 concluded that it was appropriate to lower the level of the annual standard in order to increase 20 protection against both long- and short-term PM 2.5 exposures. She further concluded that it was 21 appropriate to set the 24-hour standard in order to provide supplemental protection, particularly 22 for areas with high peak-to-mean ratios of 24-hour PM 2.5 concentrations (e.g., areas with 23 important local or season al sources) and for PM 2.5 -related effects that ma y be associated with 24 shorter-than daily exposure peri ods. The Administrator judged that this approach was the “most 25 effective and efficient way to reduce total PM 2.5 -related population risk and to protect public 26 health with an adequate margin of safety” (78 FR 3158, January 15, 2013). 27 In selecting the level of the annual PM 2.5 standard, the Administrator recognized the 28
substantial increase in the number and diversity of studies availabl e in the last review, including 29 extended analyses of seminal studies of long-term PM 2.5 exposures (i.e., American Cancer 30 Society (ACS) and Harvard Six Ci ties studies), important new long-term exposure studies, and 31 new U.S. multi-city studies that greatly expanded and reinforced our understanding of mortality 32 and morbidity effects associated with short-term PM 2.5 exposures. She placed the greatest 33 emphasis on health endpoints for which the evid ence was strongest, based on the assessment of 34
the evidence in the ISA and on the ISA’s causa lity determinations (U.S. EPA, 2009, section 35April 2016 2-8 Draft - Do Not Quote or Cite 2.3.1). 45 In particular, she noted that the evidence was sufficient to conclude a causal relationship 1
exists between PM 2.5 exposures and mortality and cardiovas cular effects (i.e., for both long- and 2 short-term exposures) and that the evidence was sufficient to conclude a causal relationship is 3 “likely” to exist between PM 2.5 exposures and respiratory effect s (i.e., for both long- and short4 term exposures). The Administrator also noted additional, but more limited, evidence for a 5 broader range of health endpoints including ev idence “suggestive of a causal relationship” 6 between long-term exposures and developmen tal and reproductive effects as well as 7 carcinogenic effects (78 FR 3158, January 15, 2013). 8 Based on information discussed and presented in the ISA, the Administrator recognized 9 that health effects may occur over the full range of ambient PM 2.5 concentrations observed in 10 epidemiologic studies, since no discernible popula tion-level threshold could be identified based 11
on the evidence available in th e last review (78 FR 3158, Ja nuary 15, 2013; U.S. EPA, 2009, 12 section 2.4.3). To inform her decisions on an appr opriate level for the annual standard in the 13 absence of a discernible populati on-level threshold, the Administra tor considered the degree to 14 which epidemiologic studies indicate confidence in the magnitude and significance of health 15
effect associations over distributions of ambient PM 2.5 concentrations. In doing so, she 16 recognized that epidemiologic studies provide greater confidence in the magnitude and 17 significance of observed associatio ns for the part of the air qu ality distribution corresponding to 18 the bulk of the health events evaluated, ge nerally at and around the long-term mean PM 2.5 19 concentrations. Accordingly, th e Administrator weighed most heavily the long-term mean 20 concentrations reported in key multi-city epid emiologic studies. She also took into account 21 additional population-level information from a subset of studies, be yond the long-term mean 22 concentrations, to identif y a broader range of PM 2.5 concentrations to consider in judging the 23 need for public health protection. 46 In doing so, the Administrator recognized that studies 24 indicate diminished confidence in the magnitude and significance of observe d associations in the 25 lower part of the air quality distribution, corre sponding to where a rela tively small proportion of 26
the health events are observed. 27 In revising the level of the annual standard to 12.0 μg/m 3 , the Administrator noted that 28 such a level was below the long-term mean PM 2.5 concentrations reported in key epidemiologic 29

45 The ISA framework for reaching causality determinations is discussed in Chapter 3, below.

46 This information characterized the di stribution of health events in the st udies, and the corresponding long-term mean PM 2.5 concentrations (78 FR 3130 to3134, January 15, 2013). The additional population-level data helped inform the Administrator’s judgment of how far below the long-term mean concentrations to set the level of the annual standard (78 FR 3160).April 2016 2-9 Draft - Do Not Quote or Cite studies that provided evidence of an array of seri ous health effects, including premature mortality 1 and increased hospitalizations for cardiovascular and respiratory effect s (78 FR 3161, January 2 15, 2013). The Administrator further noted that 12.0 μg/m 3 generally corresponded to the lower 3 portions (i.e., about the 25 th percentile) of distributions of hea lth events in the limited number of 4 epidemiologic studies for which population-level information was available. The Administrator 5 viewed this population information as helpful in guiding her determina tion as to where her 6 confidence in the magnitude and significance of the PM 2.5 associations were reduced to such a 7 degree that a standard set at a lower level was not warranted. Th e Administrator also recognized 8 that a level of 12.0 μg/m 3 reflected placing some weight on studies of reproductive and 9 developmental effects, for which the evidence was less strong (78 FR 3161-3162, January 15, 10 2013). 47 11 In conjunction with a revised annual standard with a level of 12.0 μg/m 3 , the 12
Administrator concluded that the ev idence supported retaining the 35 μg/m 3 level of the 24-hour 13

PM 2.5 standard to provide supplemental protec tion (78 FR 3163, January 15, 2013). Specifically, 14 she judged that by lowering the level of the annual standard, the di stribution of 24-hour PM 2.5 15 concentrations would be lowered as well, a ffording additional prot ection against effects 16
associated with short-term PM 2.5 exposures. 48 17 The Administrator recognized that uncertainti es remained in the scientific information. 18 She specifically noted uncertainties related to unde rstanding the relative t oxicity of the different 19 components in the fine particle mixture, the role of PM 2.5 in the complex ambient mixture, 20 exposure measurement errors in epidemiologi c studies, and the nature and magnitude of 21 estimated risks related to relatively low ambient PM 2.5 concentrations. Furthermore, the 22 Administrator noted that epidemiologic studie s had reported heterogeneity in responses both 23 within and between cities and in geographic regi ons across the U.S. She recognized that this 24 heterogeneity may be attributed, in part, to differences in fine particle composition in different 25 regions and cities. With regard to evidence fo r reproductive and developmental effects, the 26 Administrator recognized that there were a number of limitations associated with this body of 27

47 With respect to cancer, mutageni c, and genotoxic effects, the Ad ministrator observed that the PM 2.5 concentrations reported in studies evaluating these effect s generally included ambient concentrations that are equal to or greater than ambient concentrations observed in studies that reported mortality and cardiovascular and respiratory effects (U.S. EPA, 2009, section 7.5). Theref ore, the Administrator concluded that, in selecting a standard level that provides protection from mortality and cardiovascular and respiratory effects, it is reasonable to anticipate that protection will also be provided for carc inogenic effects (78 FR 3161-3162, January 15, 2013).

48 This judgment is supported by risk results presented in the 2010 HREA. For exampl e, see section 4.2.2, and Figures 4-4 and 4-6 (U.S. EPA, 2010a).April 2016 2-10 Draft - Do Not Quote or Cite evidence, including the following: the limited numb er of studies evaluating such effects; 1 uncertainties related to identifying the relevant exposure time periods of concern; and limited 2 toxicological evidence providing little information on the mode of action(s) or biological 3 plausibility for an associ ation between long-term PM 2.5 exposures and adverse birth outcomes. 4 On balance, the Administrator found that the available evidence, interpreted in light of 5 the remaining uncertainties (noted above), did no t justify an annual sta ndard level set below 12.0 6 μg/m 3 as being “requisite” (i.e., neither more nor less stringent than nece ssary) to protect public 7 health with an adequate margin of safety. Thus , the Administrator conclu ded that the available 8 evidence and information supported an a nnual standard with a level of 12.0 μg/m 3 , combined 9
with a 24-hour standard with a level of 35 μg/m 3 . She noted that this combination of standard 10
levels was consistent with CASA C’s advice to consider an annual standard level within the range 11
of 13 to 11  g/m 3 and a 24-hour standard level from 35 to 30  g/m 3 (Samet, 2010b). Taken 12 together, the Administrator conc luded that the revised annual PM 2.5 standard, with its level of 13 12.0 μg/m 3 and a form that does not allow for spatia l averaging, combined with the existing 24- 14 hour standard, would be requisite to protect the public he alth with an adequate margin of safety 15 from effects associated with long- and short-term PM 2.5 exposures. 16

2.1.2 PM 10 Standard 17

In the last review the EPA reta ined the existing 24-hour primary PM 10 standard, with its 18
level of 150  g/m 3 and its one-expected-exceedance form, in order to continue to provide public 19 health protection agai nst exposures to PM 10-2.5 . In support of this decision, the Administrator 20
considered the extent to which a standard with a PM 10 indicator can provide protection against 21 exposures to PM 10-2.5 and the degree of public health protection provided by the existing PM 10 22
standard. Her consideration of each of these issues is summarized below. 23 In reaching the conclusion that a standard with a PM 10 indicator can provide appropriate 24 protection against exposures to PM 10-2.5 , the Administrator noted that PM 10 mass includes both 25 coarse PM (PM 10-2.5 ) and fine PM (PM 2.5 ). As a result, the concentration of PM 10-2.5 allowed by a 26

PM 10 standard set at a single level de clines as the concentration of PM 2.5 increases. Because 27

PM 2.5 concentrations tend to be higher in urban areas than ru ral areas (U.S. EPA, 2005, p. 2–54, 28 and Figures 2–23 and 2–24), the Admi nistrator observed that a PM 10 standard will generally 29
allow lower PM 10-2.5 concentrations in urban areas than in rural areas. She judged it appropriate 30 to maintain such a standard given that the large majority of the evidence for PM 10-2.5 toxicity, 31 particularly at relatively low particle concentrations, came from study locations where thoracic 32 coarse particles were of urban orig in, and given the possibility that PM 10-2.5 contaminants in 33 urban areas could increase particle toxicity. Thus, in the last re view the Administrator concluded 34April 2016 2-11 Draft - Do Not Quote or Cite that it remained appropriate to maintain a standard that allows lower ambient concentrations of 1

PM 10-2.5 in urban areas, where the evidence was strongest that thoracic coarse particles are linked 2 to mortality and morbidity, and higher concentrati ons in non-urban areas, where the public health 3
concerns were less certain. 4 In specifically evaluating th e degree of public health pr otection provided by the primary 5

PM 10 standard, with its level of 150  g/m 3 and its one-expected-exceedance form, the 6 Administrator recognized that the available he alth evidence and air quality information was 7
much more limited for PM 10-2.5 than for PM 2.5 . In particular, the strongest evidence for health 8
effects attributable to PM 10-2.5 exposures was for cardiovascular effects, respiratory effects, 9 and/or premature mortality following short-te rm exposures. For each of these categories of 10 effects, the ISA determined that the evidence was “suggestive of a caus al relationship” (U.S. 11 EPA, 2009, section 2.3.3). These determin ations contrast with those for PM 2.5 , as described in 12 section 2.1.1 above, which were judged in the ISA to be either “causal” or “likely to be causal” 13 for mortality, cardiovascular eff ects, and respiratory effects (U .S. EPA, 2009, Tables 2-1 and 2- 14 2). 15 The Administrator judged that the important uncertainties and limitations associated with 16
the PM 10-2.5 evidence and information raised questions as to whether additional public health 17 improvements would be achieve d by revising the existing PM 10 standard. She specifically noted 18 the following: 19

(1) While PM 10-2.5 effect estimates reported for mortality and morbidity were generally 20 positive, most were not statistically significant, even in single-pollutant models. This 21 included effect estimates reported in some study locations with PM 10 concentrations 22 above those allowed by the current 24-hour PM 10 standard. 23

(2) The number of epidemiologic studies that have employed co-pollutant models to address 24 the potential for confounding, particularly by PM 2.5 , was limited. Therefore, the extent to 25 which PM 10-2.5 itself, rather than one or more co-po llutants, contributes to reported health 26 effects remained uncertain. 27

(3) Only a limited number of experimental stud ies provided support fo r the associations 28 reported in epidemiologic studies, resulti ng in further uncerta inty regarding the 29 plausibility of the associations between PM 10-2.5 and mortality and morbidity reported in 30 epidemiologic studies. 31

(4) Limitations in PM 10-2.5 monitoring data and the different approaches used to estimate 32 PM 10-2.5 concentrations across epidemiologic studies resulted in uncertainty in the 33 ambient PM 10-2.5 concentrations at which the reported effects occur, increasing 34April 2016 2-12 Draft - Do Not Quote or Cite uncertainty in estimates of the exte nt to which changes in ambient PM 10-2.5 concentrations 1 would likely impact public health. 49 2

(5) The composition of PM 10-2.5 , and the effects associated with the various components, 3 were uncertain. Without more informa tion on the chemical speciation of PM 10-2.5 , the 4 apparent variability in associations acro ss locations was difficult to characterize. 5

With regard to these uncertainties and limitations, the Administrator noted in particular the 6 considerable degree of uncertainty in the extent to which health effects reported in epidemiologic 7
studies are due to PM 10-2.5 itself, as opposed to one or mo re co-occurring pollutants. This 8 uncertainty reflected the relatively small number of PM 10-2.5 studies that had evaluated co9 pollutant models, particularly co-p ollutant models that included PM 2.5 , and the very limited body 10 of controlled human exposure eviden ce supporting the plausibility of PM 10-2.5 -attributable 11
adverse effects at ambient concentrations. Th e Administrator noted that these important 12 limitations in the overall body of health evidence introduce uncertainty into the interpretation of 13 individual epidemiologic studies, particularly those studies reporting associations with PM 10-2.5 14 that are not statistically significant. 15 When she viewed the evidence as a whole, the Administrator concl uded that the degree 16 of public health protection provided against short-term exposures to PM 10-2.5 should be 17
maintained but did not need to be incr eased beyond that provided by the current PM 10 standard. 18 This conclusion emphasized (1) the important uncer tainties and limitations associated with the 19 overall body of health evidence and air quality information for PM 10-2.5 , as reflected in the ISA 20 causal determinations; (2) information indicating that PM 10-2.5 effect estimates for the most 21 serious health effect, mortality, we re not statistically significant in U.S. locations that met the 22
current PM 10 standard and where coarse pa rticle concentrations were ei ther directly measured or 23 estimated based on co-located samplers; 50 and (3) that PM 10-2.5 effect estimates for morbidity 24 endpoints were both positive and negative in locations that met the current standard, with most 25 not statistically significant. Thus, the Administrator concluded that the existing 24-hour PM 10 26

49 Such limitations also contributed to the decision not to conduct a quantitative risk assessment for PM 10-2.5. The lack of a quantitative PM 10-2.5 risk assessment further contributed to unce rtainty regarding the extent to which any revisions to the current PM 10 standard would be expected to improve the protection of public health, beyond the protection provided by the current standard.

50 The Administrator noted that the study by Zanobetti and Schwartz (2009) was the only study to estimate ambient PM 10-2.5 concentrations as the difference between county-wide PM 10 mass and county-wide PM 2.5 mass (78 FR 3178, January 15, 2013). As discussed in the PA, it is not clear how such computed PM 10-2.5 measurements compare with the PM 10-2.5 concentrations obtained in other studies either by direct measurement or by calculating the difference using co-located samplers (U.S. EPA, 2009, section 6.5.2.3).April 2016 2-13 Draft - Do Not Quote or Cite standard, with its one-expected exceedance form a nd a level of 150  g/m 3 , is requisite to protect 1 public health with an adequate margin of safety against effects that have been associated with 2

PM 10-2.5 . In light of this conclusion, the EPA retained the existing PM 10 standard. 3

2.1.3 General Approach in the Current Review of the Primary Standards 4
The approach for this review will build on the substantial body of work done during the 5 course of the last review, taking into account the more recent scientific information and air 6 quality data now available to inform our unders tanding of the key policy-relevant issues. The 7 approach summarized below is most fundamenta lly based on using the EPA’s assessment of the 8
current scientific evid ence, quantitative assessm ents of exposures and/or risks, and other 9 associated analyses (e.g., air qua lity analyses) to inform the Ad ministrator’s judgments regarding 10 primary standards for PM that are requisite to protect public health with an adequate margin of 11 safety. This approach will involv e translating scientific and technical information into the basis 12 for addressing a series of key policy-relevant que stions using both eviden ce- and exposure-/risk13
based considerations. 51 14 Figure 2-1 summarizes the general approach in the current review to reaching conclusions 15 on the current primary standards and on potential a lternative standards, if appropriate. The ISA, 16 HREA (if developed), and PA developed in this review will provide the basis for addressing the 17 key policy-relevant questions and will inform th e Administrator’s decisions as to whether to 18 retain or revise the primary PM NAAQS. The four basic elements of the NAAQS (i.e., indicator, 19 averaging time, form, and level) will be considered collectiv ely in evaluating the health 20 protection afforded by the current standard s, and by any alternatives considered. 21
22

51 Evidence-based considerations include those related to the health effects evidence a ssessed and characterized in the ISA. Exposure-/risk-based considerations draw from the results of the quantitative assessments.April 2016 2-14 Draft - Do Not Quote or Cite 1 Figure 2-1. Overview of General Approach fo r Review of Primary PM Standards 2April 2016 2-15 Draft - Do Not Quote or Cite The final decisions on the ade quacy of the current standard s and, if appropr iate, potential 1 alternative standards, are largely public he alth policy judgments to be made by the 2
Administrator. The Administrator’s final deci sions will draw upon the scientific evidence for 3 PM-related health effects, quantit ative analyses of population exposur es and/or health risks, and 4 judgments about how to consider the uncertainti es and limitations that are inherent in the 5 scientific evidence and quantitative analyses. To inform the Administrato r’s public health policy 6 judgments and decisions, we will consider the su pport for, and the potential implications of, 7 placing more or less emphasis on various aspects ofthe scientific evidence, the exposure-/risk8 based information, and the associat ed uncertainties and limitations. 9 The current review of the primary PM 2.5 and PM 10 standards will build upon the 10 conclusions from the last review, taking into ac count the updated evidence and information that 11
has become available since that review. Our cons ideration of the evidence and information will 12 inform the answer to the following overarching question: 13

 Does the currently available scientific evid ence and exposure-/risk-based information 14 support or call into question the adequacy of the public health protection afforded by 15 the current primary PM 2.5 or PM 10 standards? 16 In order to answer this overarching question, we will consider a series of more specific policy17 relevant questions related to th e health effects and health risk s of short- and long-term PM 18 exposures. These questions will focus on PM exposures indexed by PM 2.5 and PM 10-2.5 mass, as 19 well as PM exposures indexed by other metrics such as other size fractions (e.g., ultrafine 20 fraction), PM characteristics other than size (e .g., chemical composition), PM from particular 21 sources, or PM present in partic ular types of environments (e .g., urban versus non-urban, various 22 geographic areas). Potentia l policy-relevant questions 52 include the following: 23

 To what extent has new eviden ce strengthened or otherwise alte red the scientific support for 24 the occurrence of advers e health effects or premature mort ality as a result of exposures to 25 particles in the ambient air? To what extent ha ve important uncertainties in the evidence from 26 the last review been addressed, a nd have new uncertainties emerged? 27

 To what extent has new evidence improved our understanding of human lifestages and 28 populations that are at increased risk of experiencing health eff ects associated with exposures 29 to ambient PM? 30

52 As noted above, based on CASAC advice and public input on this draft IRP, we will modify these potential questions as appropriate for the final IRP. The key polic y-relevant questions identified in the final PM IRP will provide an overall framework for the development of the PM ISA, REAs (if warranted), and the PA.April 2016 2-16 Draft - Do Not Quote or Cite  What does the evidence indicate with regard to confidence in the occurrence of adverse 1 health effects attributable to exposures to am bient PM concentrations that would likely have 2 met the current primary standards? 3

 What do available epidemiologic studies indicate with regard to the shapes of 4 PM concentration-response functions and confidence in PM health effect 5 associations at ambient particle concen trations that would meet the existing 6 standards? Do studies indicate depart ures from linearity at such low 7 concentrations? 8

 When taken together, what do availa ble epidemiologic and experimental 9 studies indicate with regard to confiden ce in PM-attributable adverse effects at 10 ambient PM concentrations that would meet existing standards? 11

 To what extent does the evidence indicate that he alth effects are associated with exposures to 12 PM 2.5 or PM 10-2.5 themselves (or other indicator of PM), as opposed to one or more co13 occurring pollutants, particularly at relative ly low ambient PM concentrations that would 14 meet the existing standards? 15

 To what extent are PM-attributable health e ffects larger and/or more serious with co16 exposures to other pollutant s or other stressors? 17

 Is new information available to better info rm our understanding of factors other than 18 pollutant exposures that might influence the a ssociations between ambient PM concentrations 19 and health effects (e.g., weather -related factors, behavioral f actors, heating/air conditioning 20 use, driving patterns, ti me-activity patterns)? 21

 Do studies examining the potential for effect modification, either by co-occurring pollutants 22 or by factors other than pollutant exposures, improve our understanding of the geographic 23 heterogeneity in epidemiologic associations with PM? 24

 Is new information available to improve our understanding of PM exposures, and how those 25 exposures relate to the ambient concentra tions often used as exposure surrogates in 26 epidemiologic studies? Does our understand ing of geographic variability in exposure 27 measurement error inform our understanding of geographic heterogeneity in epidemiologic 28 associations? 29

 Is new information available to improve our understanding of the PM exposure periods (e.g., 30 exposure durations and/or windows of exposure) that are most relevant for PM-associated 31 mortality and/or morbidity? 32

 To what extent do quantitative estimates indicate that PM-attributable health risks of public 33 health importance could occur at ambient PM concentrations meeting the current primary 34 standards? To what extent do uncertainties a nd limitations in the unde rlying health evidence 35 or in the assessment approaches affect our in terpretation of these quantitative estimates? 36

If the available evid ence and exposure/risk information call into question the adequacy of 37 the public health protection afforded by the current primary PM 2.5 or PM 10 standards, we will 38 also consider the following overarching question: 39April 2016 2-17 Draft - Do Not Quote or Cite  What alternative standards are supported by the currently available scientific evidence 1 and exposure-/risk-based information, and are appropriate for consideration? 2 The answer to this second overarching question will also be informed by our consideration of a 3 series of more specific questions focused on the basic elements of the NAAQS (indicator, 4 averaging time, form, level). In addressing these more specific questions, we will draw from our 5
consideration of the scientific evidence and fr om the results of any additional air quality, 6 exposure, and/or risk analyses that focus on potential alte rnative standards. 53 We will consider 7 the elements of the NAAQS collectively in evalua ting the health protection afforded by potential 8 alternative standards. Specific pol icy-relevant questions on potent ial alternative standards will 9 include the following: 10

 Do the available health effects evidence a nd air quality information provide support for 11 consideration of indicators for fine and thoracic coarse partic les in addition to, or in place of, 12 PM 2.5 and PM 10 , respectively? Does th e evidence support an a lternative approach for 13 defining particle pollution, incl uding in terms of other size fractions, specific components, 14 source-related mixtures, or specific environments? 15

 Do the available health effects evidence, air quality information, and exposure/risk 16 information provide support for considering averaging times in addition to, or in place of, the 17 current 24-hour and annual averaging times? 18

 To what extent do the available health e ffects evidence, air quality information, and 19 exposure/risk information provide support fo r consideration of a lternative standard forms ? 20

 What range of alte rnative standard levels could be supported based on the scientific evidence, 21 air quality analyses, and exposure/risk assessments? 22

 What are the important uncertainties and limita tions in the available evidence and in the 23 available quantitative analyses , and how might these uncertainties and limitations be taken 24 into consideration in identifying alternative standard indicators, averaging times, forms 25 and/or levels ? 26


### 2.2 SECONDARY STANDARDS 27

In the last review, the EPA generally reta ined the existing suite of secondary PM 28 standards (78 FR 3228, January 15, 2013). 54 As described below, the EPA retained the 29

53 Such additional quantitative analyses can inform conclusions on the magnitude of the public health improvement that would be expected upon just meeting various potential alternative standards, and on the exposures and/or risks expected to remain.

54 The previous review of the secondary PM NAAQS focused on the welfare effects associ ated with particles present in the ambient air, including the effect s of ambient particulate species of NO X and SO X . The review did not focus on the deposition related effects of particulate species of NO X and SO X . The EPA reviewed the secondary NO 2 and SO 2April 2016 2-18 Draft - Do Not Quote or Cite secondary 24-hour PM 2.5 standard, with its level of 35 μg/m 3 , and the 24-hour PM 10 standard, 1 with its level of 150 μg/m 3 . The EPA also retained the secondary annual PM 2.5 standard, with its 2 level of 15.0 μg/m 3 , except for a change to the form of th e annual standard. Consistent with the 3 change to the form of the primary annual PM 2.5 standard (section 2.1.1 above), the EPA removed 4 the option for spatial averaging from the form of the secondary annual PM 2.5 standard (78 FR 5 3228, January 15, 2013). Key aspects of the Admini strator’s decisions on the secondary PM 6 standards for non-visibility welfar e effects and visibility effects are described below in sections 7 2.2.1 and 2.2.2, respectively. Key policy -relevant issues for the curr ent review are discussed in 8
section 2.2.3. 9

2.2.1 Non-Visibility Welfare Effects 10

In the last review of the PM NAAQS, the Administrator conc luded that it was important 11 to maintain an appropriate degr ee of control of both fine and coarse particles to address non12 visibility welfare effects. Lacking information th at would support revised standards, she further 13 concluded that it was appropriate to retain the existing suite of secondary standards to protect 14 against such effects. Non-visibility welfare eff ects considered include climate effects, ecological 15 effects (e.g., effects on pl ants, soil and nutri ent cycling, wildlife and water), 55 and materials 16
effects. The Administrator’s consid eration of each of these types of effects is discussed below. 17 With regard to the role of PM in climat e, the Administrator considered whether it was 18 appropriate to establish any di stinct secondary PM standard s to address welfare effects 19 associated with climate impacts. In consideri ng the scientific evidence, she noted the ISA 20 conclusion “that a causal relationship exists between PM and effects on climate” and that 21
aerosols 56 alter climate processes dire ctly through radiative forci ng and by indirect effects on 22 cloud brightness, changes in precipitation, and po ssible changes in cloud lifetimes (U.S. EPA, 23 2009, section 9.3.10). Additionally, the ISA noted that the major aerosol components 24 contributing to climate processes (i.e., black carb on (BC), organic carbon (O C), sulfates, nitrates 25 and mineral dusts) vary in their reflectivity, forcin g efficiencies, and direction of climate forcing, 26

NAAQS separately and evaluated the ecosystem-related welfar e effects that result from the deposition of particulate species of NO X , SO X , and their transformation products.

55 As described above, the on-going NO X /SO X review includes consideration of the ecological effects of ecosystem loading of particulate nitrogen and sulfur compounds. Thus, these endpoints are not discussed in this review.

56 The term aerosol is used in this document when discussing suspended ambient particles in the context of climate impacts.April 2016 2-19 Draft - Do Not Quote or Cite though there is an overall net climate cooling asso ciated with aerosols in the global atmosphere 1 (U.S. EPA, 2009, section 9.3.10). 2 Noting the strong evidence indi cating that aerosols affect climate, the Administrator 3
further considered whether there was sufficien t information to revi se the secondary PM 4
standards. She noted that a number of uncertainties in the scientific information were identified 5 in the ISA and PA. For example, the ISA and PA noted the spatial and tem poral heterogeneity of 6 PM components that contribute to climate forcing, uncertainties in the measurement of aerosol 7 components, inadequate consider ation of aerosol impacts in cl imate modeling, insufficient data 8 on local and regional microclimate variations and heterogeneity of cloud formations. In light of 9 these uncertainties and the lack of sufficient data, the PA concluded that it was not feasible in the 10 last review “to conduct a quantit ative analysis for the purpose of informing revisions [to the 11 secondary PM NAAQS] based on climate” (U.S. EP A, 2011, pp. 5-11 to 5-12) and that there was 12
insufficient information available to base a national ambient standard on climate impacts 13
associated with ambient concentrations of PM or its constituents (U.S. EPA, 2011, section 5.2.3). 14 The Administrator agreed with this conclusion (78 FR 3225- 3226, January 15, 2013). 15
The Administrator also consid ered ecological effects in the last review, including direct 16 effects on metabolic processes of plants; contributi on to total metal loading resulting in alteration 17 of soil biogeochemistry and microbiology, plan t and animal growth and reproduction; and 18 contribution to total organics loading resulti ng in bioaccumulation and biomagnification across 19 trophic levels. The ISA determined that the evidence was sufficien t to conclude that “a causal 20 relationship is likely to exist between depositi on of PM and a variety of effects on individual 21 organisms and ecosystems” (U.S. EPA, 2009, p. 2-30; sections 2.5.3 and 9.4.7). However, the 22 ISA also noted that it is genera lly difficult to characterize the nature and magnitude of effects 23 and to quantify relationships be tween ambient concentrations of PM and ecosystem responses. 24 Such difficulty is due to signifi cant data gaps and uncertainties, as well as to the considerable 25 variability that exists in the components of PM and their various ecological effects (U.S. EPA, 26 2009, p. 9-193). Given uncertainties and limitations in the available evidence, the PA concluded 27
that the information available at the time of th e last review was insufficient for the purposes of 28 assessing the adequacy of th e protection for ecosystems afforded by the existing suite of 29 secondary PM standards or for establishing a di stinct national PM standard based on ecosystem 30 effects of particulates (U.S. EP A, 2011, p. 5-24). The Administrato r agreed with this conclusion 31 (78 FR 3225-3226, January 15, 2013). 32 With regard to materials effects, the Administ rator also considered e ffects associated with 33 the deposition of PM (i.e., dry and wet depositi on), including both physical damage (materials 34 effects) and impaired aesthetic qualities (soili ng effects). The depositi on of PM can physically 35April 2016 2-20 Draft - Do Not Quote or Cite affect materials, adding to the effects of natural weathering processes, by promoting or 1 accelerating the corrosion of meta ls; by degrading paints; and by deteriorating building materials 2 such as stone, concrete, and marble (U.S. EP A, 2009, section 9.5). Add itionally, the deposition 3 of ambient PM can reduce the aesthetic appeal of buildings and object s through soiling. The ISA 4 concluded that evidence was sufficient to suppor t a causal relationship between PM and effects 5 on materials (U.S. EPA, 2009, sections 2.5.4 and 9.5.4). However, the PA noted that quantitative 6 relationships are lacking between particle size, concentrations, and frequency of repainting and 7 repair of surfaces and that considerable uncertain ty exists in the contributions of co-occurring 8 pollutants to materials damage and soiling processes (U.S. EPA, 2011, p. 5-29). The PA 9
concluded that none of the evidence available in the last review called into question the adequacy 10 of the existing secondary PM standards to protect against material effects and that such effects 11 could play no quantitative role in determini ng whether revisions to the secondary PM NAAQS 12 were appropriate (U.S. EPA, 2011, p. 5-29). The Administrator agre ed with this conclusion (78 13 FR 3225-3226, January 15, 2013). 14 In considering non-visibility welfare effects in the last re view, as discussed above, the 15 Administrator concluded that, whil e it is important to maintain an appropriate degree of control 16 of fine and coarse particles to address non-vi sibility welfare effects, “[i]n the absence of 17 information that would support any different standa rds...it is appropriate to retain the existing 18 suite of secondary standards” (FR 78 3225 to 3226, January 15, 2013). Her decision was 19
consistent with CASAC advice related to non-visi bility effects. Specifically, CASAC agreed 20 with the PA conclusions that, while these effect s are important, “there is not currently a strong 21 technical basis to support revisions of the current standards to protect ag ainst these other welfare 22 effects” (Samet, 2010a, p. 5). Thus, the Administrator concluded that it was appropriate to retain 23 all aspects of the existing 24-hour PM 2.5 and PM 10 secondary standards. With regard to the 24 secondary annual PM 2.5 standard, the Administra tor concluded that it was appropriate to retain a 25 level of 15.0 μg/m 3 while revising only the form of the st andard to remove the option for spatial 26 averaging, consistent with this change to the primary annual PM 2.5 standard (78 FR 3225-3226, 27 January 15, 2013). 28

2.2.2 Visibility Effects 29

The Administrator also considered the level of protection that would be requisite to 30 protect public welfare with regard to visual air quality and whethe r to adopt a distinct secondary 31
standard to achieve this level of protection. In reaching her fi nal decision that the existing 24- 32
hour PM 2.5 standard provides sufficient protection agai nst PM-related visibility impairment (78 33 FR 3228, January 15, 2013), the Admini strator considered the eviden ce assessed in the ISA (U.S. 34April 2016 2-21 Draft - Do Not Quote or Cite EPA, 2009) and the analyses included in the Urban Focused Visibility Assessment (UFVA) 1 (U.S. EPA, 2010b) and the PA (U.S. EPA, 2011). Sh e also considered the degree of protection 2 for visibility that would be pr ovided by the existing secondary standard, focusing specifically on 3 the secondary 24-hour PM 2.5 standard of 35 μg/m 3 . These considerations, and the 4 Administrator’s conclusions regarding visibili ty, are discussed in more detail below. 5 In the last review, the ISA concluded that, “collectively, the evidence is sufficient to 6 conclude that a causal relationship exists betw een PM and visibility impairment” (U.S. EPA, 7 2009, p. 2-28). Visibility impairment is caused by light scattering and absorption by suspended 8 particles and gases, includi ng water content of aerosols. 57 The available evidence in the last 9 review indicated that various components of PM have been shown to contribute to visibility 10 impairment. For example, at sufficiently high rela tive humidity values, sulf ate and nitrate are the 11 particulate species that contribu te most efficiently to visibi lity impairment. Elemental carbon 12 (EC) and organic carbon (OC) also are important contributors, especially in the northwestern 13 U.S. Crustal material can be signi ficant contributors to visibil ity impairment, particularly for 14
remote areas in the arid southwestern U.S. (U.S. EPA, 2009, section 2.5.1). 15 Visibility impairment can have implications for people’s enjoyment of daily activities and 16
for their overall sense of well- being (U.S. EPA, 2009, section 9.2). In consideration of the 17 potential public welfare impli cations of various degrees of visibility impairment, the 18
Administrator considered the available visibi lity preference studies which were reviewed by 19 EPA in the 2010 UFVA (U.S. EPA, 2010b, chapter 2). 58 These preference studies provided 20 information about the potential pub lic welfare implications of visi bility impairment from survey 21 studies in which participants we re asked questions about their pr eferences or th e values they 22 placed on various visibility conditions, as displayed to them in scenic photographs or in images 23 with a range of known light extinction levels. 24

57 All particles scatter light and, although a larger particle s catters more light than a similarly shaped smaller particle of the same composition, the light scattered per unit of ma ss is greatest for particles with diameters from ~0.3-1.0
μ m (U.S. EPA, 2009, section 2.5.1). Particles with hygroscopic components (e.g., particulate sulfate and nitrate) contribute more light extinction at higher relative humidity than at lower relative humidi ty because they change size in the atmosphere in response to ambient relative humidity conditions.

58 Preference studies were available in four urban areas in the last review. Three western preference studies were available, including one in Denver, Colorado (Ely et al., 1991), one in the lower Fraser River valley near Vancouver, British Columbia, Canada (Pryor, 1996), and one in Phoeni x, Arizona (BBC Research & Consulting, 2003). A pilot focus group study was also conducted for Washington, DC (Abt Associates Inc., 2001), and a replicate study with 26 participants was also conducted for Washington, DC (Smith and Howell, 2009).April 2016 2-22 Draft - Do Not Quote or Cite In noting the relationship between ambien t PM and PM-related light extinction, the 1 Administrator focused on identifying an adequate level of protection against visibility-related 2
welfare effects. She first concl uded that a standard based on a PM 2.5 visibility index would 3 provide a measure of protection against PM-relat ed light extinction that directly takes into 4 account the factors (i.e., species composition and relative humidity) that influence the 5 relationship between PM 2.5 in ambient air and PM-relate d visibility impairment. A PM 2.5 6 visibility index standard would a fford a relatively high degree of uniformity of visual air quality 7 protection in areas across the count ry by directly incorporating th e effects of differences of PM 2.5 8 composition and relative humidity. In defining a target level of protection based on a PM 2.5 9 visibility index, as discussed below, the Administ rator considered specific elements of the index, 10 including the appropriate indicator, averaging time, level, and form. 11 With regard to the indicator of a visibility index, the Ad ministrator concluded that a 12
calculated PM 2.5 light extinction indicator that utilized an adjusted versi on of the original 13 IMPROVE algorithm, 59 in conjunction with monthly average relative humidity data based on 14 long-term climatological means, would be the most appropriate indicator for a PM 2.5 visibility 15 index standard (78 FR 3226, January 15, 2013). In reaching her final decision, the Administrator 16
further noted the CASAC conclusion that it was reasonable to rely on a calculated PM 2.5 light 17
extinction indicator based on PM 2.5 chemical composition and relative humidity. The 18
Administrator also considered the PM 2.5 mass indicator and directly measured PM 2.5 light 19
extinction. She concluded that a PM 2.5 mass-based indicator would not be appropriate because 20 the available mass monitoring met hods did not include measurement of the full water content of 21
ambient PM 2.5 , nor did they provide inform ation on the composition of PM 2.5 , both of which 22 contribute to visibility impacts (77 FR 38980, June 29, 2012). In addition, at the time of the 23 proposal, the Administrator provisionally concluded th at directly measured PM 2.5 light extinction 24 was not an appropriate option because a suitab le specification of available equipment or 25 performance-based verification procedures for di rect measurement of light extinction could not 26 be developed in the time frame of th e review (77 FR 38980-38981, June 29, 2012). 27 With regard to averaging time of the inde x, the Administrator c oncluded that a 24-hour 28 averaging time would be appropriate for a vi sibility index (78 FR 3226, January 15, 2013). She 29 concluded that hourly or sub-daily (4- to 6-hour) averaging times, within daylight hours and 30

59 The IMPROVE algorithm uses PM mass concentration measurements and relativ e humidity estimates to calculate light extinction. For more information about the derivation of and input data required for the original and revised IMPROVE algorithms, see 78 FR 3186-3177, January 15, 2013

.April 2016 2-23 Draft - Do Not Quote or Cite excluding hours with high relative hu midity, are more directly relate d to the short-term nature of 1 the perception of PM-related visibility impair ment and the relevant exposure periods for 2 segments of the viewing public th an a 24-hour averaging time. Howe ver, she also noted the data 3 quality uncertainties associat ed with the instruments us ed to provide the hourly PM 2.5 mass 4 measurements required for an averaging time shorter than 24 hours. The Administrator also 5 considered comparative analyses of 24-hour and 4-hour averaging times in conjunction with a 6
calculated PM 2.5 indicator in the PA (U .S. EPA, 2011, pp. 4-55 - 4-56, Appendix G, section G.4). 7 These analyses showed good correlation between 24-hour and 4-hour average PM 2.5 light 8 extinction, as evidenced by reasonably high city-s pecific and pooled R-squa red values, generally 9 in the range of over 0.6 to over 0.8. The Administ rator considered and agreed with the PA 10
conclusion that at a 24-hour aver aging time would be a reasonable and appropriate surrogate for 11 a sub-daily averaging time. 12 With regard to form of the index, the Ad ministrator concluded that a multi-year 13 percentile-based form offered greater stability to the air quality management process by reducing 14 the possibility that statistically unus ual indicator values would lead to transient violations in the 15 standard. She noted that a three-year average fo rm provided stability from the occasional effects 16 of inter-annual meteorological variability that ca n result in unusually high pollution levels for a 17 particular year (U.S. EPA, 2011, p. 4-58). In the UFVA, 90 th , 95 th , and 98 th percentile forms were 18 assessed for alternative PM light extincti on standards (U.S. EPA, 2010b, chapter 4). In 19 considering these altern ative percentiles, the PA noted th at the Regional Haze Program targets 20 the 20 percent most impaired days for improvements in visual air quality in Federal Class I areas. 21 A focus on improving the 20 percent most impaired days suggests that the 90 th percentile, which 22 represents the median of the di stribution of the 20 percent worst days, would be an appropriate 23 form to consider. Strategies that are implemented so that 90 percent of days would have visual 24 air quality that is at or below the level of the standard would reasonably be expected to lead to 25 improvements in visual air quality for the 20 pe rcent most impaired days. Given that the 26 preference studies did not provide information with regard to the frequency of time that visibility 27 levels should be below these values, the PA f ound no basis to conclude that it would be 28 appropriate to consider limiting the occurrence of days with peak PM-rela ted light extinction in 29 urban areas to a greater degree (U.S. EPA, 2011, p. 4-59). Based on the above considerations, the 30
Administrator concluded that a 90 th percentile form was the most appropriate form (78 FR 3226, 31 January 15, 2013). 32 With regard to level of the index, the Administrator consider ed the visibility preference 33
studies conducted in four urba n areas (U.S. EPA, 2011, p. 4-61) a nd further quantitative analyses 34 of visibility conditions for 15 urban study areas (U.S. EPA, 2 011, Appendix G, Tables G-7 and 35April 2016 2-24 Draft - Do Not Quote or Cite G-8). Based on these studies the PA identified a range of levels from 20 to 30 deciviews (dv) 60 as 1 being a reasonable range of “candi date protection levels” (CPLs). In considering this range of 2 CPLs, the Administrator noted the uncertainties and limitations in public preference studies, 3 including the small number of stated preference st udies available; the rela tively small number of 4 study participants and the extent to which the st udy participants may not be representative of the 5 broader study area population in some of the studies; and the varia tions in the specific materials 6 and methods used in each study. She concluded th at the substantial degr ees of variability and 7 uncertainty in the public preference studies should be reflected in a target protection level at the 8 upper end of the range of CPLs than if the in formation were more c onsistent and certain. 9 Therefore, the Administrator conc luded that it was appropriate to set a target level of protection 10
in terms of a 24-hour PM 2.5 visibility index at 30 dv ( 78 FR 3226-3227, January 15, 2013). 11
Based on her considerations and conclusi ons summarized above, the Administrator 12 concluded that the protection provided by a secondary standard defined in terms of a PM 2.5 13 visibility index with a 24 -hour averaging time, a 90 th percentile form averaged over 3 years, and 14 a level of 30 dv, would be requisite to protect public welfare with regard to visual air quality (78 15 FR 3227, January 15, 2013). Having reached this c onclusion, she next determined whether to 16 adopt such a visibility index as a distinct seconda ry standard, particularly in the context of the 17 full suite of existing secondary standards. 18 In determining whether a distinct seconda ry standard was needed, the Administrator 19 considered the degree of protection from visibility impairment afforded by the existing 20 secondary standards. She consideredboth whether the existing 24-hour PM 2.5 standard of 35 21 μg/m 3 is sufficient (i.e., not under-protective) and wh ether it is not more stringent than necessary 22 (i.e., not over-protec tive). In doing so, she noted that the ai r quality analyses showed that all 23 areas meeting the existing 24-hour PM 2.5 standard, with its level of 35 μg/m 3 , had visual air 24 quality at least as good as 30 dv (based on the vi sibility index defined above) (Kelly et al., 25 2012a, 2012b). Thus, the secondary 24-hour PM 2.5 standard would likely be controlling relative 26 to a 24-hour visibility index set at a level of 30 dv. Additionally, areas would be unlikely to 27 exceed the target level of protection for visibi lity of 30 dv without al so exceeding the existing 28 secondary 24-hour standard. 61 Thus, the Administrator judged that the 24-hour PM 2.5 standard 29

60 Deciview refers to a scale for characterizing visibility th at is defined directly in terms of light extinction. The deciview scale is frequently used in the scie ntific and regulatory literature on visibility.

61 The Administrator also recognized that air quality analyses indicated that “the 24-hour PM 2.5 standard of 35  g/m 3 also would likely achieve more than the target level of protection of visual air quality (30 dv) in some areas” (78 FR 3227, January 15, 2013).April 2016 2-25 Draft - Do Not Quote or Cite “provides sufficient protection in all areas against the effects of visibility impairment—i.e., that 1 the existing 24-hour PM 2.5 standard would provide at least the target level of protection for 2 visual air quality of 30 dv whic h the Administrator judges appr opriate” (78 FR 3227, January 15, 3 2013). She further judged that “[s]ince sufficient pr otection from visibility impairment would be 4 provided for all areas of the c ountry without adoption of a dis tinct secondary standard, and 5 adoption of a distinct secondary standard will not change the de gree of over-pro tection provided 6 for some areas of the country...adoption of such a distinct secondary standard is not needed to 7 provide requisite protection for both visibility an d nonvisibility related we lfare effects” (78 FR 8 3228, January 15, 2013). 9

2.2.3 General Approach in the Current Review of the Secondary Standards 10
The approach for this review builds on the substantial body of work completed during the 11 course of the last review, taking into account the more recent scientific information and air 12 quality data now available to inform our unders tanding of the key-policy relevant issues. The 13 approach described below is most fundamenta lly based on using the EPA’s assessment of the 14 current scientific evidence and associated quant itative analyses to inform the Administrator’s 15 judgments regarding secondary standards for PM th at are requisite to prot ect the public welfare 16 from any known or anticip ated adverse effects. 17 Figure 2-2 summarizes the general appro ach, including consideration of the policy18 relevant questions which will frame the current review. The ISA, WREA (if warranted), and PA 19 developed in this review will provide the basis for addressing the key policy-relevant questions 20 and will inform the Administrator’s judgments as to the adequacy of the current secondary PM 2.5 21
and PM 10 standards, as well as his/her de cisions as to whether to retain or revise these standards. 22April 2016 2-26 Draft - Do Not Quote or Cite 1April 2016 2-27 Draft - Do Not Quote or Cite Figure 2-2. Overview of General Approach for Review of Secondary PM Standards 1

The current review of the secondary PM 2.5 and PM 10 standards will build upon the 2 conclusions from the last review, taking into ac count the updated evidence and information that 3
has become available since that review. Our cons ideration of the evidence and information will 4 inform the answer to the following overarching question: 5

 Does the currently available scientific eviden ce and quantitative information support or 6 call into question the adequacy of the we lfare protection afford by the current 7 secondary PM 2.5 or PM 10 standards? 8 In order to answer this overarching question, we will consider a series of more specific policy9 relevant questions related to th e available scientific evidence a nd information from quantitative 10 assessments. Potential policy-relevant questions 62 include the following: 11

 To what extent has new scientific evidence improved our understandi ng of the nature and 12 magnitude of visibility, climate, ecosystem re sponses, and materials effects to ambient PM, 13 including the variability associated with such responses? To what extent have important 14 uncertainties in the evidence from the last revi ew been addressed, and have new uncertainties 15 emerged? 16

 To what extent is new information available that changes or enhan ces our understanding of 17 the physics of light extinction and/or its qu antification in urban and non-urban areas (e.g., 18 through light extinction or other monitori ng methods or through algorithms such as 19 IMPROVE)? 20

 To what extent are new studies available on the nature of the relationship between PM21 attributable visibility impairment and pub lic perceptions of such impairment? What 22 information is available to inform judgments about the potential adve rsity to public welfare 23 of PM-attributable visibility impairment? 24

 Is evidence available from recent stud ies in additional urban and non-urban 25 areas, beyond the studies in the previous review? 26

 To what extent is evidence available th at distinguishes visi bility preferences 27 from health preferences? 28

 To what extent is evidence available that evaluates the sensitivity of visibility 29 preferences to survey methods? 30

 To what extent is evidence available th at examines the potential relationship 31 between intensity versus fr equency of visibility impa irment in stated public 32 preferences? 33

62 As noted above (section 2.1), based on CASAC advice and public input on this draft IRP, we will modify these potential questions as appropriate for the final IRP. The ke y policy-relevant questions identified in the final PM IRP will provide an overall framework for the development of the PM ISA, REAs (if warranted), and the PA.April 2016 2-28 Draft - Do Not Quote or Cite  To what extent is new information available that changes or enhan ces our understanding of 1 the climate impacts of PM-related aerosols, pa rticularly regarding the quantification of 2 anthropogenic aerosol effects on radiative forcing? 3

 To what extent is new information available to link PM (excluding nitrates and sulfates) to 4 ecological effects? 5

 To what extent is new information available to link PM to materials effects, including 6 degradation of surfaces, and dete rioration of materials such as metal, stone, concrete and 7 marble? Are there studies linking perceptions of reduced aesthetic appeal of buildings and 8 other objects to PM or wet deposition of N and S species? 9

 Does the available evidence and/or quantitative analyses suggest that PM-induced visibility 10 impairment or other PM-related welfare effects could occur with ambien t concentrations of 11 PM that meet the current standards? If so, c ould these effects be of sufficient magnitude 12 and/or frequency such that they might reasonab ly be judged to be adverse to public welfare? 13 To what degree would updated or additional analyses improve our understanding of the 14 welfare effects that could be allowed by the current standards? 15

 To what extent have important uncertainties identified in the la st review been reduced and/or 16 have new uncertainties emerged? 17

If the available evidence and information from quantitative analyses call into question the 18 adequacy of the welfare protection afforded by the current secondary PM 2.5 or PM 10 standards, 19 we will also consider the following overarching question: 20

 What alternative standards are supported by the currently available scientific evidence 21 and quantitative information and a re appropriate for consideration? 22 To answer this second overarching question, we will also consider a series of more 23 specific questions focused on the basic elements of the NAAQS (indicator, averaging time, form, 24 level). We will consider these elements collectiv ely in evaluating the public welfare protection 25 afforded by potential alternative standards. With re gard to consideration of alternative standards, 26 the specific policy-relevant questions will include the following: 27

 Do the available welfare effects evidence a nd air quality information provide support for 28 consideration of indicators in addition to, or in place of, the current mass-based indicators? 29 Do the evidence and information from the quantitative analyses, if warranted, support 30 alternative indicators based on light extinction, chemical composition, or other factors? 31

 Do the available welfare effects evidence, air quality information, and information from 32 quantitative assessments, provi de support for considering averaging times in addition to, or 33 in place of, the current 24-hour and a nnual averaging times? Do the evidence and 34 information support a sub-daily or other alternativ e averaging time? 35

 To what extent do air quality analyses or info rmation from quantitative assessments provide 36 support for considering alternative standard forms ? To what extent do assessments support an 37 alternative form based on day light hours or other metric? 38April 2016 2-29 Draft - Do Not Quote or Cite  What range of levels should be considered, based on th e scientific evidence, air quality 1 analyses, and quantitative assessments? At what concentrations of ambient PM do adverse 2 visibility impairment and/or other environmental effects of concern for pu blic welfare occur? 3

 What are the important uncertainties and limitati ons in the available evidence, analyses, and 4 assessments and how might those uncertainties a nd limitations be taken in to consideration in 5 identifying alternative standard indicators, averaging times, forms, and/or levels ? 6



### 2.3 PM AMBIENT MONITORING 7
Achieving the degree of public health a nd welfare protection intended for the NAAQS 8 depends, in large part, on appr opriate ambient monitoring networks. In the case of PM, existing 9 monitoring networks provide data for a variety of objectives as pa rt of an iterative process in 10 managing air quality. These objectives include: (1) determining compliance with the NAAQS; 11 (2) characterizing air quality status, including providing the public with timely reports and 12 forecasts of the Air Quality Index (AQI); (3) supporting air quality analyses used to conduct 13 assessments of exposure, health risks, and welfare effects; (4) de veloping and evaluating 14 emissions control strategies; and (5) measuring trends and overal l progress for the air pollution 15 control program. 16 Federal rules that regulate ambient mon itoring programs are found in 40 CFR parts 50, 17 53 and 58. The EPA amended these regulations in the 2006 and 2012 reviews of the PM 18 NAAQS, in part to support changes necessary fo r implementation of the revised PM standards. 19 The EPA expects to follow a similar process for monitoring rule changes during this review, if 20 appropriate. Potential monitoring rule changes include the Federal Reference Methods (FRMs) 63 21 that exist as appendices to part 50, the procedures for approval of Federal Reference and Federal 22 Equivalent Methods (FEMs) contai ned in part 53, and the rules ap plicable to ambient monitoring 23 network planning and operations that are the ba sis for part 58 and Appendices A through E. 24 Section 2.3.1 below provides an overview of the PM monitoring networks and their 25 history. Section 2.3.2 summarizes th e key potential monitoring-rela ted issues in the current 26
review. 27

63 FRMs provide the methodological basis for comparison to the NAAQS and also serve as the “gold-standard” for the comparison of other methods being reviewed for potential approval as equivalent methods. The EPA keeps a complete list of designated reference and equivalent methods available on its Ambient Monitoring Technology Information Center (AMTIC) website ( http://www3.epa.gov/ttn/amtic/files/ambi ent/criteria/reference-equivalentmethods-list.pdf ).April 2016 2-30 Draft - Do Not Quote or Cite 2.3.1 PM Monitoring Networks 1
The EPA and its partners at state, local, a nd tribal monitoring agencies manage and 2 operate the nations’ ambient air monitoring ne tworks. The EPA provides minimum monitoring 3 requirements for criteria pollutants and rela ted monitoring (e.g., the Chemical Speciation 4 Network (CSN)) including iden tification of an FRM for cr iteria pollutants and guidance 5 documents to support implementation and operation of the networks. Monitoring agencies carry 6 out and perform ambient air monitoring in accordance with the EPA’s requirements and 7 guidance as well as often meeting their own state monitoring needs that may go beyond the 8 minimum federal requirements. This partnership results in a nationally consistent ambient air 9 monitoring program that supports the objectives listed above. Data from the ambient air 10 monitoring networks are availabl e from two national databases. The AirNow database provides 11 data used in public reporting and forecasting of the AQI, while the Air Quality System (AQS) 12 database is the EPA’s long-term repos itory of ambient ai r monitoring data. 13 The EPA and states currently operate robust national networks for both PM 10 and PM 2.5 , 14 as these are the two measurement pr ograms directly supporting NAAQS. PM 10 measurements 15 are based on gravimetric mass, while PM 2.5 measurements include gravimetric mass and 16 chemical speciation. A smaller network of st ations is operating and reporting data for PM 10-2.5 17 gravimetric mass and a small number of monito rs are operated to support special projects, 18 including pilot studies, for cont inuous speciation and particle c ount data. Monitoring networks 19 and additional monitoring efforts for each of the various PM size fractions and for PM 20 composition are discussed below. 64 All sampler and monitor coun ts provided below are based on 21 data submitted to the EPA for calendar year 2014, unless otherwise noted. 22
Total Suspended Particulates (TSP) Sampling 23
The EPA first established NAAQS for PM in 1971, based on the or iginal air quality 24 criteria document (DHEW, 1969). The reference me thod specified for determining attainment of 25 the original standards was the high-volume sample r, which collects PM up to a nominal size of 26 25 to 45 micrometers ( μ m) (referred to as total suspended pa rticles or TSP). TSP was replaced by 27

PM 10 as the indicator for partic les in a 1987 final notice (52 FR 24854, July 1, 1987). However, 28 TSP sampling remains in operation to provide the aerosol needed for TSP lead sampling as well 29 as for cases where a state may continue to have state standards for TSP. The size of the TSP 30 network peaked in the mid-1970s when over 4,300 TSP samplers were in operation. Today, there 31

64 More information on ambient monitoring networks can be found at http://www3.epa.gov/ttn/amtic/.April 2016 2-31 Draft - Do Not Quote or Cite are about 200 TSP samplers still in operation as part of the lead monitoring program; of these, 1 about 50 also report TSP mass. 2

PM 10 Monitoring 3

As a result of the 1987 standard for PM 10 , the EPA and its stat e and local partners 4 implemented the first size-selec tive PM monitoring network in 1990 with the establ ishment of a 5

PM 10 network consisting of mainly high-volume samplers. The PM 10 monitoring network peaked 6 in size in 1995 with 1,665 stations reporting data. 7 Approximately 750 PM 10 stations with samplers and m onitors are currently in operation 8 to support comparison of the PM 10 data to the NAAQS, trends, and reporting and forecasting of 9 the AQI. Though the current PM 10 network is relatively stab le, monitoring agencies may 10 continue divesting of some of the PM 10 monitoring stations where c oncentration levels are low 11 relative to the NAAQS. 12
While the PM 10 network is national in scope, ther e are areas of the west such as 13
California and Arizona with substantially higher PM 10 station density than the rest of the 14 country. In the PM 10 mass network, about 320 of the statio ns operate continuous mass monitors 15 approved as FEMs and 480 operate FRMs. Thus, about 50 of the PM 10 stations have collocation 16
with both continuous FEMs and FR Ms. Almost half of the PM 10 stations with FRMs operate on a 17 sample frequency of one in every sixth day, wi th about 140 operating every third day and just 18 over 100 operating every day. 19

PM 2.5 Monitoring 20
After setting the first PM 2.5 NAAQS in 1997, the EPA and states implemented a PM 2.5 21 network consisting of ambient air monitoring sites with mass and/or chemical speciation 22 measurements. Network operation began in 1999 w ith nearly 1000 monitoring stations operating 23 FRMs to provide fine particle mass. The PM 2.5 monitoring program remains one of the major 24 ambient air monitoring programs operated across the country. 25
There are three main com ponents of the current PM 2.5 monitoring program including 26 FRMs, PM 2.5 continuous mass monitors, and Chemical Speciation Network (CSN) samplers. The 27 FRMs are primarily used for comparison to the N AAQS, but also serve other important purposes 28 such as developing trends and evaluating the performance of PM 2.5 continuous mass monitors. 29

PM 2.5 continuous mass monitors are primarily used to support forecasting and reporting of the 30 AQI, but are also used for comparison to th e NAAQS, where approved as FEMs. The CSN and 31 related Interagency Monitoring of Protected Visual Environments (IMPROVE) network are used 32 to provide chemical composition of the aerosol wh ich serve a variety of objectives. This section 33 provides an overview of each of these components of the PM 2.5 monitoring program. 34April 2016 2-32 Draft - Do Not Quote or Cite As noted above, the PM 2.5 monitoring network began operation in 1999 with nearly 1,000 1 monitoring stations operating FRMs. The PM 2.5 FRM network peaked in operation in 2001 with 2 over 1,150 monitoring stati ons. In the current PM 2.5 network, there are approximately 773 FRM 3 filter-based samplers that provide 24-hour PM 2.5 mass concentration data. Of these operating 4 FRMs, 111 are providing daily PM 2.5 data, 535 every third day, and 125 every sixth day. Close to 5
800 continuous PM 2.5 mass monitors provide hourly data on a near real-time basis. About 363 of 6
the PM 2.5 continuous monitors are FEMs and theref ore used for comparison with the NAAQS 7 and AQI, and another 424 are methods not approv ed as FEMs and therefore used just for the 8 AQI. 9 Due to the complex nature of fine particles, in 2000 the EPA and states implemented the 10 CSN to better understand the components of fine particle mass at selected locations across the 11 country. The CSN was first piloted at 13 sites. Af ter the pilot phase, the program continued with 12 deployment of the Speciation Trends Network (STN) in the fall of 2000. The CSN ultimately 13 grew to 54 trends sites and peaked in operation in 2005 with 252 stations; the 54 trends stations 14 and nearly 200 supplemental stations. The original CSN program had multiple sampler 15 configurations including the Thermo Anders en RAAS, Met One SASS/SuperSASS, and URG 16 MASS. During the 2000s, the EPA and states wo rked to align the network to one common 17 sampler for elements and ions, which was the Met One SASS/SuperSASS. In 2005, CASAC 18 provided recommendations to the EPA for making changes to the CSN. These changes were 19 intended to improve data comparability with the rural IMPROVE carbon concentration data. To 20 accomplish this, the EPA replaced the existing carbon channel sampling and analysis methods 21
with a new modified IMPROVE version III mo dule C sampler, the URG 3000N. Implementation 22 of the new carbon sampler and analysis was brok en into three phases starting in May of 2007 23 through October of 2009. 24
In the current PM 2.5 CSN, long-term measurements ar e made at about 90 largely urban 25 locations comprised of either the STN or the National Core (NCore) network. 65 NCore is a 26 multipollutant network measuring pa rticles, gases, and basic meteor ology that has been in formal 27 operation since January 1, 2011. Particle m easurements made at NCore include PM 2.5 filter-based 28 mass, which is largely the FRM, except in so me rural locations which utilize the IMPROVE 29 program PM 2.5 mass filter-based measurement; PM 2.5 speciation using either the CSN program or 30 IMPROVE program; and PM 10-2.5 mass utilizing an FRM, FEM or IMPROVE for some of the 31

65 In most cases where a city has an STN station, it is located at the same site as the NCore station. In a few cases, a city may have an STN station located at a different location than the NCore station.April 2016 2-33 Draft - Do Not Quote or Cite rural locations. The NCore networ k includes a total of 78 stations of which 63 are in urban or 1 suburban stations designed to provide representative populati on exposure and another 15 rural 2 stations designed to provide background and transport information. The NCore network is 3 deployed in all 50 States, DC, and Puerto Rico with at least one station in each state and two or 4 more stations in larger population states. Since 2008, the EPA’s O ffice of Research and 5 Development has approved ten models of PM 2.5 continuous monitors as FEMs; about 75% of the 6 reporting PM 2.5 continuous FEMs in the count ry are the Met One BAM 1020. 7
Both the STN and NCore networks are intende d to remain in operation indefinitely. The 8
CSN measurements at NCore and STN stations operate every third day. Another approximately 9 70 CSN stations are known as supplemental site s are intended to be potentially less permanent 10 locations used to support State Implementation Plan (SIP) development and other monitoring 11 objectives. 66 Supplemental CSN stations typically operate every sixth day. In 2014, about 40 12 supplemental CSN stations that are largely located in the east ern half of the country stopped 13 operations to ensure a sustainable CSN networ k moving forward. Specific components of fine 14 particles are also measured thr ough the IMPROVE monitoring program 67 which supports 15 regional haze characterization and tracks changes in visibility in Class I areas as well as many 16
other rural and some urban areas. The ba se IMPROVE network includes 110 monitoring 17 locations and. another approxima tely 20 locations are operated as IMPROVE protocol sites 18 where a monitoring agency has requested pa rticipation in the program. These IMPROVE 19 protocol sites are operated the same way as the IMPROVE program, but they may serve a 20 number of monitoring objectives (i .e., the same objectives as the CS N) and are not explicitly tied 21 to the Regional Haze Program. Samplers at IM PROVE stations operate every third day. In 22 January of 2016, 8 IMPROVE protocol stations stopped operating to ensure a sustainable 23 IMPROVE program moving forward. Details on the process and outcomes of the CSN 24 supplemental and IMPROVE protocol assessments us ed to identify sites that would no longer be 25

66 See http://www.epa.gov/ttn/amtic/speciepg.html for more information on the PM 2.5 speciation monitoring
program.

67 Recognizing the importance of visual air quality, Congre ss 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 http://w ww.epa.gov/ttn/amtic/visdata.html.April 2016 2-34 Draft - Do Not Quote or Cite funded are available on an interactive website 68 . Together, the CSN and IMPROVE data provide 1 chemical species information for fine partic les that are critical fo r use in health and 2 epidemiologic studies to help in form reviews of the PM NAAQS. 69 3
Key changes made to the EPA’s monitoring requirements as a result of the 2012 PM 4 NAAQS review included the addition of PM 2.5 monitoring at near road locations in CBSAs over 5 1 million in population; the clarificat ion of terms used in siting of PM 2.5 monitors and their 6 applicability to the NAAQS; and providing flexibility on data uses to monitoring agencies where 7
their PM 2.5 continuous monitors are not providing data that meets the perfor mance criteria used 8 to approve the continuous method as an FEM. The addition of PM 2.5 monitoring at near road 9 locations is being phased in 2015 and 2017. By January 1, 2015, 22 CBSAs with a population of 10
2.5 million or more were to have a PM 2.5 FRM or FEM operating at a near-road monitoring 11 station. By January 1, 2017, 30 CBSAs with a population between 1 million and 2.5 million are 12
to have a PM 2.5 FRM or FEM operating are a near-road monitoring station. The terms clarified in 13 the 2012 rule ensure consistency with other NAAQS and long standing definitions used by the 14 EPA (78 FR 3234, January 15, 2013). The flexibility provided to monitoring agencies such that 15
data from certain PM 2.5 continuous FEM monitors are not applicable to the NAAQS, where 16 appropriate, ensures that the incentives of utilizing PM 2.5 continuous monitors (e.g., efficiencies 17 in operation and availability of hourly data in near-real time) are realized without having 18 potentially poor performing data be misuse d in a NAAQS decision (78 FR 3241, January 15, 19 2013). 70 20

PM 10-2.5 Monitoring 21
In the 2006 PM NAAQS review, the EPA prom ulgated a new FRM for the measurement 22
of PM 10-2.5 mass in ambient air. Although the standard for thoracic coarse particles uses a PM 10 23

68 See the Chemical Speciation Network Assessment Interactive Website at: https://www.sdas.battelle.org/C SNAssessment/html/Default.html 69 These data could also be used to better understand visibility through calculation of light extinction using the IMPROVE algorithm.

70 Although not explicitly required under any existing mon itoring regulations, the EPA and state and local agencies have also been working together to pilot additional PM methods at near-road monitoring stations that may be of interest to data users. These methods include such techni ques as particle counters, particle size distribution, and black carbon by aethalometer. These methods and their ra tionale for use at near-road monitoring stations are described in a Technical Assistance Document (TAD) on NO 2 near road monitoring (Near-road NO 2 Monitoring Technical Assistance Document, EP A-454/B-12-002, June 2012).April 2016 2-35 Draft - Do Not Quote or Cite indicator, a new FRM for PM 10-2.5 mass was developed to provide a basis for approving FEMs 1 and to promote the gathering of scientific data to support future reviews of the PM NAAQS. The 2

PM 10-2.5 FRM (or approved FEMs, where available) wa s implemented at required NCore stations 3 by January 1, 2011. In addition to NCore, there are other collocated PM 10 and PM 2.5 low-volume 4 FRMs operating across the country that are essentially providing the PM 10-2.5 FRM measurement 5 by the difference method. 6

PM 10-2.5 measurements are currently performed across the country at NCore stations, 7 IMPROVE monitoring stations, and at a few additio nal locations where state or local agencies 8 choose to operate the method. For urban NCor e stations and other State and Local Air 9 Monitoring Stations (SLAMS) the method employed is either a PM 10-2.5 FRM, which is 10 performed using a low-volume PM 10 FRM collocated with a low volume PM 2.5 FRM of the same 11 make and model, or FEMs for PM 10-2.5, including filter-based dichotomous methods and 12
continuous methods of which several makes and models are approved. Filter-based PM 10-2.5 13 measurements at NCore (i.e., the FRM or dich otomous filter-based FEM) operate every third 14 day, while continuous methods have data available every hour of every day. PM 10-2.5 filter-based 15 methods at other SLAMS typically operate ever y third or sixth day. For IMPROVE, which is 16 largely a rural network, PM 10-2.5 measurements are made with two sample channels; one each for 17

PM 10 and the other PM 2.5 . All IMPROVE program samplers opera te every third day. All together 18 there approximately 250 stations where PM 10-2.5 data are being reported to the EPA. 19 There is no operating chemical speciation network for characterizing the specific 20 components of thoracic coarse particles. Washingt on University at St. Louis recently reported on 21 a coarse particle speciation pilot study with se veral objectives aimed at addressing this issue, 22 such as evaluating a coarse particle species an alyte list and evaluating sampling and analytical 23
methods. 71 The coarse particle speciation pilot stud y should provide useful information for any 24 organization wishing to pursue coarse particle speciation. 25

Additional PM Metrics 26

There are additional PM measurement metrics made at a much smaller number of 27 stations. These measurements may be associated with special projects or are complementary 28
measurements to other networks where the monitoring agency has prioritized having the 29

71 Pilot Study on Coarse PM Monitoring, EPA-454/R-15-001, February 2015. http://www3.epa.gov /ttn/amtic/files/pm10pilot/PMc_R eportEPA454R-15-001.pdfApril 2016 2-36 Draft - Do Not Quote or Cite measurements. None of these measurements are required by regulation. They include PM 1 measurements such as particle counts , continuous carbon, and continuous sulfate. 2 Particle count measurements are being implemented at several near-road monitoring 3 stations as part of the recent deployment of th e near-road monitoring program, but may be used 4
at other locations. Particle c ounts are one of several measur ements identified as being a 5 secondary priority for multipollutant monitori ng at near-road monitori ng stations. Details on 6 priorities for multipollutant monitoring at near-ro ad monitoring stations can be found in Section 7
16 of the Near-road NO 2 Monitoring Technical A ssistance Document (TAD) 72

. 8 Aethalometer data has been measured and submitted to AQS for many years. Data uses 9 include characterizing black car bon and wood smoke. Ambient air m onitoring stations that may 10
have aethalometers include some of the near-ro ad monitoring stations and National Air Toxics 11 Trends Stations (NATTS). About 40 monitoring s ites across the county ar e reporting data from 12 aethalometers. While aethalometer data is available at high time resolutions, it is typically 13 reported to the AQS data ba se in one hour periods. 14 Continuous elemental and organic carbon da ta are monitored at select locations 15 participating in a pilot of the S unset EC/OC analyzer as well as a few additional sites that were 16 already operating before the EPA initiated the pilot study. The Sunset EC/OC analyzer provides 17 high time resolution carbon data, typically every hour, but in some remote locations the 18 instrument is programmed to run every 2 hours to ensure collection of enough aerosol. The data 19 from the Sunset is being compared to filter-based carbon methods from the carbon channel of the 20 CSN program. The six sites participating in th e study are Washington DC, Chicago IL, St. Louis 21 MO, Houston TX, Las Vegas NV, and Los Angeles CA . Each of the six sites participating in the 22 pilot study are operating for at least three years. 23
Continuous sulfate continues to be measured at four locations. One station each in North 24 Carolina, Tennessee, Indiana, and Maine are reporting data. The continuous sulfate analyzer 25 provides hourly data and data can be readily compared to 24-hour sulfate data collected from the 26 ion channel in the CSN program. 27 In addition, over the last few years, the EPA ha s investigated the use of a number of PM 28 sensor technologies as one of several areas of re search intended to addres s the next generation of 29 air measurements. The investigation into air sensors is envisioned to work towards near real-time 30 or continuous measurement options that are smalle r, cheaper, and more port able than traditional 31

72 Near-road NO 2 Monitoring Technical Assistance Document, Publication No. EPA-454/B-12-002, June 2012. Available on EPA’s Web site at: http://www3.e pa.gov/ttn/amtic/files/n earroad/NearRoadTAD.pdfApril 2016 2-37 Draft - Do Not Quote or Cite FRM or FEM methods. These sensor devices have the potential to be used in a number of 1 applications such as identif ying hot spots, informing netw ork design, providing personal 2 exposure monitoring, supporting risk assessments, and providing background concentration data 3 for permitting. The EPA has hosted workshops a nd published a number of documents and peer4 reviewed articles on this work (See the EPA’s web site at: http://www2.epa.gov/air5 research/next-generation-air-measuring-research ). 6

2.3.2 Consideration Of PM Monitoring Issues In The Current Review 7
This review of the PM NAAQS will include th e consideration of po licy-relevant issues 8 associated with measuring and characterizing PM in ambient air. These issues include the design 9 of the PM network, the performance of existi ng FRMs and FEMs, the perf ormance of continuous 10 monitors, PM chemical speciation, PM monitori ng near major roadways, the availability and 11 performance of low-cost PM sensors, and da ta reporting requirements. The EPA will draw upon 12 the information presented in the ISA to inform the evaluation of appropr iate ambient monitoring 13 methods and network design for PM. If there is a need for formal scientific input on important 14 changes to ambient air monitoring, the EPA may request convening the Ambient Air Monitoring 15
Subcommittee of the Clean Air Scientific Advi sory Committee. This subcommittee has worked 16 closely with the EPA during past reviews, where appropriate, to pr ovide the scientif ic review of 17 monitoring options under cons ideration as part of th e PM NAAQS review process. 73 Input and 18 development of options to improve ambient air monitoring are also based on input from 19 monitoring agencies and other interested stakeholders. 20

73 The EPA will draw upon the information presented in th e ISA to inform the evaluation of appropriate ambient monitoring methods and network design for PM. Input and development of options to improve ambient air monitoring are also based on input from monitoring agencies and other interested stakeholders.April 2016 2-38 Draft - Do Not Quote or Cite 

### REFERENCES 1

Abt Associates, Inc. (2001). Assessing Public Opinions on Visi bility Impairment due to Air 2 Pollution: Summary Report . Prepared for EPA Office of Air Quality Planning and 3 Standards; funded under EPA Contract No. 68-D-98-001. Abt Associates Inc., Bethesda, 4 MD. January 2001. Available: http://www.epa.gov /ttncaaa1/t1/reports/vis_rpt_final.pdf 5 Abt Associates, Inc. (2005). Particulate Matter Health Risk Assessment For Selected Urban 6 Areas. Prepared for EPA Office of Air Qualit y Planning and Standards; funded under 7 EPA Contract No. 68-D-03-002. Abt Associat es Inc., Bethesda, MD. December 2005. 8 Available: http://www3.epa.gov/ttn/naaq s/standards/pm/data/PMrisk20051220.pdf 9 BBC Research & Consulting (2003). Phoenix Area Visibility Surv ey. Draft Report. Available: 10 http://www.azdeq.gov/environ/air/download/vis_021903f.pdf. 11 Ely, D.W., J.T. Leary, T.R. St ewart, and D.M. Ross (1991). The Establishment of the Denver 12 Visibility Standard . Presented at the 84th Annual Meet ing & Exhibition of the Air and 13 Waste Management Association. June 16-21. 14 Pryor, S.C. (1996). Assessing public perception of visibility for standard setting exercises. 15 Atmospheric Environment 30(15):2705-2716. 16 Samet J (2009). Letter from Dr. Jonathan M. Samet, Chair, Clean Air Scientific Advisory 17 Committee to the Honorable Lisa P. Jackson, Administrator, U.S. EPA. CASAC Review 18 of EPA’s Integrated Science Assessment fo r Particulate Matter –Second External Review 19 Draft (July 2009). November 24, 2009. Do cket ID number. EPA-HQ-ORD-2007-0517- 20 0121. Available: 21 http://yosemite.epa.gov/sab/sa bproduct.nsf/264cb1227d55e02c85257402007446a4/151B 22 1F83B023145585257678006836B9/$File/EPA-CASAC-10-001-unsigned.pdf

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Samet J (2010a). Letter from Dr. Jonathan M. Samet, Chair, Clean Air Scientific Advisory 24 Committee to the Honorable Lisa P. Jackson, Administrator, U.S. EPA. CASAC Review 25 of Policy Assessment for the Review of th e PM NAAQS – First External Review Draft 26 (March 2010). May 17, 2010. Docket ID number EPA-HQ-OAR-2007-0492-0113. 27 Available: 28 http://yosemite.epa.gov/sab/sa bproduct.nsf/264cb1227d55e02c85257402007446a4/E504 29 EE3276D87A9E8525772700647AFB/$File/E PA-CASAC-10-011-unsigned.pdf

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Samet J (2010b). Letter from Dr. Jonathan M. Samet, Chair, Clean Air Scientific Advisory 31 Committee to the Honorable Lisa P. Jackson, Administrator, U.S. EPA. CASAC Review 32 of Policy Assessment for the Review of th e PM NAAQS – Second External Review Draft 33 (June 2010). September 10, 2010. Docket ID number EPA-HQ-OAR-2007-0492-0256. 34 Available: 35 http://yosemite.epa.gov/sab/sa bproduct.nsf/264cb1227d55e02c85257402007446a4/CCF9 36 F4C0500C500F8525779D0073C593/$File/E PA-CASAC-10-015-unsigned.pdf

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U.S. EPA (2005). Review of the National Ambient Air Quality Standards for Particulate Matter: 38 Policy Assessment of Scient ific and Technical Inform ation, OAQPS Staff Paper. 39 Research Triangle Park, NC 27711: Office of Air Quality Planning and Standards. Report 40April 2016 2-39 Draft - Do Not Quote or Cite No. EPA-452/R-05-005a. D ecember 2005. Available: 1 http://www3.epa.gov/ttn/naaqs/standards/pm/s_pm_cr_sp.html

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U.S. EPA (2009). Integrated Science Assessment for Particulate Matter: Final Report. National 3 Center for Environmental Assessment- RTP Division, Office of Research and 4 Development, Research Triangle Par k, NC. EPA/600/R-08/139F. December 2009. 5 Available: http://www3.epa.gov/ttn/naaqs/ standards/pm/s_pm_2007_isa.html

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U.S. EPA (2010a). Quantitative Health Risk A ssessment for Particulate Matter – Final Report. 7 Office of Air Quality Planning and Standard s, U.S. Environmental Protection Agency, 8 Research Triangle Park, NC. EP A-452/R-10-005. June 2010. Available: 9 http://www3.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html

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U.S. EPA (2010b). Particulate Ma tter Urban-Focused Visibility Assessment – Final Report. 11 Office of Air Quality Planning and Standard s, U.S. Environmental Protection Agency, 12 Research Triangle Park, NC. EP A-452/R-10-004. July 2010. Available: 13 http://www3.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html

. 14

U.S. EPA (2011). Policy Assessment for the Review of the Particulate Matter National Ambient 15 Air Quality Standards. Office of Air Quality Planning and Standards, U.S. Environmental 16 Protection Agency, Research Triangl e Park, NC. EPA 452/R-11-003. April 2011. 17 Available: http://www3.epa.gov/ttn/naaq s/standards/pm/s_pm_2007_pa.html

. 18

U.S. EPA (2012). Responses to Significant Comments on the 2012 Proposed Rule on the 19 National Ambient Air Quality Standards fo r Particulate Matter (June 29, 2012; 77 FR 20 38890). Available: http://www3.epa.gov/ttn/naaqs/standards/pm/data/20121214rtc.pdf 21

Zanobetti A; Schwartz J (2009). Th e effect of fine and coarse particulate air pollution on 22 mortality: A national analysis. Envi ron Health Perspect, 117: 898-903. 23April 2016 3-1 Draft – Do Quote or Cite 

## 3 SCIENCE ASSESSMENT 1

Integrated Science Assessments (ISAs) serve as the scientific foundation of the NAAQS 2 review process and are developed by the EPA’ s National Center for Environmental Assessment 3 in Research Triangle Park (NCEA-RTP). As outlined in sections 1.2 and 1.4 above, the 4 particulate matter (PM) ISA will inform the re view of both the primary (health-based) and 5 secondary (welfare-based) PM standards. 6



### 3.1 SCOPE OF THE PM ISA 7

3.1.1 General Description 8
The ISA provides a comprehensive synthesis an d evaluation of the mo st policy-relevant 9 science, including key science j udgments that are important to inform the development of the 10 risk and exposure assessments, as well as othe r aspects of the NAAQS review (U.S. EPA, 2016). 11 The shift to the ISA away from the Air Qualit y Criteria Documents, wh ich originally provided 12 the scientific basis of the NAAQS review process, was initiated in 2006. This change was rooted 13 in the “broad recognition that th e Criteria Document is typically ‘encyclopedic’ in nature, which 14 is seen by many as contributing to an unnece ssarily lengthy process for preparing document 15 drafts and for reviews by CASAC [(Clean Air Sc ientific Advisory Committee)] and the public, 16 and obscuring a focus on the most policy-relevant scientific information” (U.S. EPA, 2006). 17 CASAC provided positive feedback on this transiti on to the ISA, encouraging “the development 18 of a more timely and more concise integrated assessment of the policy-relevant science that 19 would replace the voluminous ai r quality criteria document”(Pe acock, 2008). The purpose of the 20 PM ISA is to provide a critical evaluation and synthesis of the current scientific literature on 21 health and welfare evidence necessary to support the PM NAAQS review process. 22 The PM ISA is not intended to provide a detailed review of all studies of the 23 aforementioned topics but rather, will draw from the available evid ence to synthesize the current 24 state of knowledge of the most policy-relevant issues for the review of the primary and 25 secondary PM NAAQS. The PM ISA will update the scie ntific assessment upon which the last 26 PM NAAQS review was based. Thus, the PM ISA will build on the conclusions of the last 27 review of the air quality criteria for PM as presented in the 2009 PM ISA and focus on peer28 reviewed literature published since that document, 74 as well as on any new interpretations of 29

74 The 2009 PM ISA included studies through May 2009.April 2016 3-2 Draft – Do Quote or Cite previously available literature. Key findings, conclusions, and uncertainties from the 2009 PM 1 ISA will be briefly summarized at the beginning of the PM ISA and at the beginning of 2 individual sections. Important ol der studies may be discussed in detail to reinforce key concepts 3 and conclusions and/or if they ar e open to reinterpretation in li ght of newer data. Older studies 4 also may be the primary focus in some subject areas or scientific disc iplines (e.g., epidemiology, 5 controlled human exposure, animal toxicology, atmos pheric science, exposure science, visibility 6 impairment, climate, materials effects, and eco logical effects) where research efforts have 7 subsided, and these older studies remain the de finitive works available in the literature. 8 In order to provide a more focused evaluation of the scientific evidence for health- and 9 welfare-related effects, the PM ISA will discuss the most important topics that address policy10 relevant questions. Therefore, the PM ISA will more fully evaluate those health and welfare 11
effects for which the evidence in the 2009 PM ISA was less certain (i.e., effects where the causal 12 determination was “likely to be causal”, “sugges tive”, or “inadequate” as detailed below in 13 section 3.4.3) and where there is now a larger body of evidence (e.g., diabetes, nervous system 14 effects, etc.). For those health and welfare e ffects where the 2009 PM ISA concluded that the 15
evidence was sufficient to infe r a causal relationship (i.e., he alth: short- and long-term PM 2.5 16 exposures and cardiovascular eff ects; short- and long-term PM 2.5 exposures and mortality; and 17 welfare: PM exposures and effects on materials, visibility, and climate), the PM ISA will focus 18 the evaluation on characterizing the extent to which new studies addre ss key uncertainties and 19 limitations identified in the previous review or provide insight on new issues. For the 20 epidemiologic studies the focus of the evaluati on will include, but not be limited to, addressing 21 the impact of exposure assessment techniques on associations observed; evaluating potential 22 copollutant confounding; assessing the impact of PM components and sources on associations 23 observed; and examining heterogeneity in PM as sociations. Those epidemiologic studies that do 24 not directly address uncertainties and limitations as identified in the 2009 PM ISA, but still meet 25
our inclusion criteria will be detailed in ta bles presenting information for consideration in 26 evaluating the adequacy of the current PM NAAQS (e.g., averaging time of exposure, 27 distribution of PM concentrations, etc.). For e xperimental studies, spec ifically toxicological 28 studies, the evaluation will focus on those stud ies that also address key uncertainties and 29 limitations in the evidence identified in the previ ous review. For example, does the new evidence 30 further our understanding of the biological mechanisms by which PM elicits a health effect or 31 provide coherence for the effects observed in epidemiologic studies? Similar to the 32 epidemiologic studies, a more detailed descri ption of key pieces of information from the 33 toxicological studies will be detailed in tables. 34April 2016 3-3 Draft – Do Quote or Cite Consistent with the goal of making the PM ISA a focused assessment of the current state 1 of the science with respect to PM, this IS A incorporates CASAC advice received during the 2
review of External Review Drafts of the 2009 PM ISA. 75 For example, CASAC provided 3 specific advice about the evaluation of PM 10 . Although the indicator for coarse particles is 4

PM 10 , 76 studies that examine the health or we lfare effects of exposures to only PM 10 are limited 5 in their ability to inform the health and welfare effects of PM 10-2.5 or PM 2.5 . As a result, CASAC 6 suggested revisions to the PM ISA to “remove the impression that PM 10 is a separate pollutant 7
from PM 2.5 and PM 10-2.5 ”, specifically the removal of causal determinations for short- and long8 term exposures to PM 10 (Samet, 2009) Additionally, CASA C suggested detailing “when 9 possible, the particle si ze distribution of the PM 10 mixture” (Samet, 2009). As such, the final 10
2009 PM ISA had minimal discussion of PM 10 health effect studies, and these studies were used 11 as supporting evidence of PM 2.5 -related health effects primarily due to the majority of PM 10 12 studies being conducted in large urban areas where, in many locations, ambient monitoring 13 typically indicates that PM 2.5 comprises a large percent of PM 10 mass. Therefore, consistent with 14 the previous CASAC panel’s recommendation, the current PM ISA will focus on the evaluation 15
of health studies of PM 2.5 and PM 10-2.5 as the most pertinent to a ddressing the key policy-relevant 16 questions of the PM NAAQS review. This is also consistent with the 2012 PM Final Rule, which 17
stated that “... the extent to which PM 10 effect estimates reflect associations with PM 10-2.5 versus 18

PM 2.5 can be highly uncertain [and, as a resu lt]... it is preferable to consider PM 10-2.5 studies 19 when such studies are available” (78 FR 3086). Therefore, the evaluation of PM 10 studies will be 20 limited to those that specifically address remaining uncertainties or limitations in the PM 2.5 or 21

PM 10-2.5 health or welfare effects evidence or evaluate a new health or welfare effect not 22 previously examined. 23 The general scope presented above will allow th e PM ISA to primarily focus on scientific 24 evaluations that are pertinent to the key polic y-relevant questions described in Chapter 2 25 (sections 2.1 and 2.2) above. Within the discussion of the health and welfare effects information, 26 other scientific information will also be presen ted and evaluated in order to provide a better 27 understanding of the following issu es: (1) the sources of PM in the ambient air; (2) fate and 28 transport of PM in the environment; (3) measur ement of PM and recent ambient concentrations 29

75 External Review Drafts of the PM ISA are available at: http://www3.epa.gov/ttn/naaqs/sta ndards/pm/s_pm_2007_isa.html

76 As discussed above (sections 1.3 and 2.1.2), the purpose of the PM 10 standard is to protect against exposures to PM 10-2.5
.April 2016 3-4 Draft – Do Quote or Cite of PM; (4) the validity of inferences that can be drawn about PM hea lth and welfare effects 1 based on exposure assessment me thodology; (5) the potential infl uence of other factors (e.g., 2 other pollutants in the ambient mi xture, ambient temperature) show n to be correlated with PM 3 and health or welfare effects; (6) the shape of the concentration-respons e (C-R) relationship at 4
PM concentrations at the low end of the dist ribution; and (7) populati ons and lifestages at 5 greatest risk of PM-related health effects. The process for evalua ting and synthesizing scientific 6 literature and addressing key po licy questions is detailed in the Preamble to the Integrated 7
Science Assessments (U.S. EPA, 2015). Collectively, the a pproach outlined for the health and 8 welfare effects will allow for the EPA to provide a focused assessment of the scientific evidence 9 that more directly informs policy-relevant consid erations detailed in the Policy Assessment (PA) 10 and Risk and Exposure Assessment(s) (R EA) as detailed in Chapter 2. 11

3.1.2 Defining Policy-Relevant Literature 12
PM is unique among the criteria pollutants in that it is composed of multiple components 13 and size fractions. PM is often examined using mass-based metrics for overall mass and the mass 14 of individual components within the following size fractions: PM 10 (thoracic PM; particulate 15 matter with a nominal mean aerodynamic diamet er less than or equal to 10 μm), PM 2.5 (fine PM; 16 particulate matter with a nominal mean aerodynamic diameter less th an or equal to 2.5 μm), and 17

PM 10-2.5 (thoracic coarse or coarse PM; particul ate matter with a nominal mean aerodynamic 18 diameter greater than 2.5 μm and less than or equal to 10 μm). Ultrafine particles (UFP, 19 generally considered as particulat es with a diameter less than or equal to 0.1 μm [typically based 20 on physical size, thermal diffusivity or electr ical mobility] (U.S. EPA, 2009)) are examined 21 using multiple indices such as mass, number c oncentration, and surface area. As discussed in 22 Chapter 1, the current indicators of the PM NAAQS are mass-based for both fine particles, 23 represented by PM 2.5 , and for thoracic coarse particles, represented by PM 10

. 24 Given the array of PM size fractions and com ponents examined in studies of atmospheric 25 chemistry, exposure, health effects, and welfare effects, it is important to clea rly define the types 26
of studies that will be evaluate d within the PM ISA to ensure its conclusions are pertinent to the 27 key questions of the PM NAAQS review, specifically: 28

 Does exposure to PM cause a direct health or welfare effect (i.e., an independent 29 effect)? 30

 Are the current indicators (i.e., PM 2.5 for fine particles and PM 10 for thoracic 31 coarse particles), averag ing times (e.g., 24-hour average, annual average), and 32 levels appropriate? 33 When evaluating the broad body of literature across scientific disciplines, the EPA 34
considers whether the studies fall within the sc ope of the PM ISA (i.e., provide information 35April 2016 3-5 Draft – Do Quote or Cite which can address the above questio ns). As a result, the focus of the PM ISA with respect to the 1
health evidence is on studies conducted at concentra tions of PM that are re levant to the range of 2 human exposures across ambient mi croenvironments (up to 2 mg/m 3 PM, which is one to two 3 orders of magnitude above ambient concentratio ns) and (1) include a composite measure of PM 77 4 or (2) apply some approach to assess the independ ent effect of PM when the exposure of interest 5 is a source-based mixture (e.g., diesel exhaust, gasoline exhaust, wood smoke). However, the 6 scope of experimental studies included in the PM ISA may be broader when examining modes of 7 action for PM, and may include in vitro studies, studies examining relative toxicity, and studies 8 conducted at concentrations > 2 mg/m 3 . In the case of (1), if a study focuses on a single 9 component, group of components, or source, the study must also examine a composite measure 10 of PM (e.g., mass of PM 2.5 , PM 10-2.5 , ultrafine particles [UFP]) to be included in this review. 11 This requirement ensures that the study is releva nt to the scope of the PM ISA and evaluated in 12 the proper context; specificall y, this approach will facilitat e a comparison of effects or 13
associations observed to the current mass-based PM indicator. Case (2) primarily applies to 14 experimental studies that attempt to disentangl e the independent effects of PM from a complex 15 air pollution mixture of part icles, gases, and semi-volatile components. This may be 16 accomplished by using filtration (e.g., a particle trap ) or other approaches to distinguish between 17 effects due to the mixture and effects due to the particles alone. 18 With respect to identifying polic y-relevant studies for welfare effects (ecological effects, 19 visibility, materials effects, and climate) PM composition and/or size fr action are important to 20 consider. For ecological effects, studies that focus on deposited components of PM (including 21 metals and organics, but not nitrogen (N) a nd sulfur (S)-containing compounds or their 22 transformation products) 78 at ambient or near-ambient concentrations of PM will be emphasized, 23 leading to the evaluation of the direct and indir ect effects of PM on vegetation, soils, and biota. 24 Generally, components of PM drive ecosystem re sponses, although size fraction may play a role 25 in the direct effects of PM such as deposition to vegetation. As a result, the emphasis will be on 26 studies of ecological effects de tailing non-nutrient (N and S) particle chemistry/composition 27 (e.g., cations, trace metals, semi-volatile organics ), associated size fraction, and magnitude and 28 rates of wet and dry depos ition across the landscape. 29

77 Composite measures of PM may include mass, vol ume, surface area, or number concentration.

78 The PM ISA will not evaluate nutrient N and S ecosyste m effects, which will be addressed in the concurrent review of the secondary NO x and SO x NAAQS for ecological effects, see: http://www3.epa.gov/ttn/naaqs/standards/no2so2sec/index.html.April 2016 3-6 Draft – Do Quote or Cite For materials effects, visibility, and climate effects, this ISA will build on information 1 available during the last review describing the role of PM on materials damage and soiling, 2 visibility impairment, and in radiative forcing resulting in global and regional climate change. 3 For effects on materials, studies wi ll be included that examine the role of PM, or related N and S 4 species as discussed in Section 1.4, on materials damage and soiling. Specifically, studies will be 5 considered that examine gaseous and particle c ontributions from nitrogen and sulfur along with 6 other PM components due to the difficulty in dete rmining whether an effect on materials is due 7 to the particle or gaseous component of NOx and SOx and because the NO x /SO x secondary ISA 8 focuses only on ecological effects, not other welf are effects. For visibi lity, studies will be 9
included which advance our unders tanding of visual impairment of airborne PM, including 10 studies of atmospheric chemistry, visibility prefer ence, or other measures of adversity to public 11 welfare, in urban and rural settings. For climate, the ISA will focus on climate as the welfare 12
effect as listed in the 1977 Amendment to th e Clean Air Act and will not focus on downstream 13 ecosystem effects, human health effects, or futu re air quality projections resulting from changes 14 in climate (Clean Air Act Amendments of 1977). The primary literature base for the evaluation 15 of the effects of airborne and deposited PM on climate will come from recent national and 16
international climate assessments such as the National Climate Assessment (Melillo et al., 2014) 17 and International Panel on Climate Change (IPCC , 2014). Focus will be on studies that inform 18 the independent role of PM in climate forcing as well as effects on U.S. national and regional 19
climate. 20



### 3.2 ORGANIZATION OF THE PM ISA 21

The broad organization of the PM ISA will be consistent with that used in the recent 22 assessments for other criteria pollutants (e .g., ISA for Ozone and Related Photochemical 23 Oxidants, U.S. EPA, 2013c). The detailed descrip tion of the procedures for the assessment of 24
scientific information within the ISA for each of the criteria air polluta nts can be found in the 25 Preamble to the Integrated Science Assessments (U.S. EPA, 2015). The PM ISA will begin with 26 a Preface discussing major legal and historical aspects of prior PM NAAQS reviews. An 27 executive summary will succinctly summarize the conclusions of the ISA. An integrative 28 synthesis chapter will provide a more detailed su mmary of the key information for each topic 29 area, including the causa l determinations for relationships between exposure to PM and health 30 and welfare effects, information describing the extent to which h ealth and welfare effects can be 31 attributable specifically to PM , evaluation of at-risk lifest ages and populations, and other 32
uncertainties related to the inte rpretation of scientific inform ation. The integrative synthesis 33 chapter also will discuss policy-relevant issues such as the exposure averaging times and the lag 34April 2016 3-7 Draft – Do Quote or Cite structure of associations for hea lth effects; the C-R relationships including the overall shape and 1 whether or not the evidence supports identificat ion of a discernible threshold below which 2 effects are not likely to occur; and the public health and welfare impact of effects associated with 3 exposure to PM. Subsequent chapters will be orga nized by subject area with the health evidence 4 presented in separate chapte rs by PM size fraction (i.e., PM 2.5 , PM 10-2.5 , and UFPs) and all of the 5 welfare (i.e., ecological, visibili ty, materials, and climate) e ffects evidence discussed in a 6 separate chapter(s). Each of the chapters will c ontain an evaluation of results from recent policy7 relevant studies integrated with previous finding s (see section 3.4 below for specific issues to be 8 addressed). Sections for each broad health effect category (e.g., respiratory effects) will conclude 9
with a causal determination about the relationshi p with relevant exposures to PM for health 10 outcomes that are specific to the size fraction being evaluated (e.g., PM 2.5 , PM 10-2.5 , UFPs). 79 11
Sections on welfare will conclude with causal dete rminations for ecological effects, visibility, 12 materials effects, and climate. The PM ISA will conclude with a chapter that examines studies 13 for evidence of differential exposure and risk fo r PM-related health effect s to draw conclusions 14 about potential at-risk lifestages and populations. 15 The PM ISA may be supplemented with other ma terials (e.g., tables, figures) if additional 16 documentation is required to support informa tion contained within the PM ISA. These 17 supplementary materials may include more deta iled and comprehensive coverage of relevant 18 publications and may accompany the PM ISA or be available in electronic form as output from 19
the Health and Environmental Research On line (HERO) database developed by the EPA 20 (http://hero.epa.gov). 80 Supplementary information that is av ailable in the HERO database will 21 be presented as electronic links in the PM ISA. 22



### 3.3 ASSESSMENT APPROACH 23

3.3.1 Introduction 24
In each NAAQS review, development of the ISA begins with a “Call for Information” 25 published in the Federal Register . This notice, which for PM was published December 3, 2014 26 (79 FR 71764), announces the EPA’s in itiation of activities in the pr eparation of an ISA for the 27 specific NAAQS review and invites the public to a ssist in this process through the submission of 28

79 Within the evaluation of the evidence for specific size fractions, the ISA will also evaluate the strength of evidence for PM components and sources.

80 For more information on the HERO database, see http://hero.epa.gov/

.April 2016 3-8 Draft – Do Quote or Cite research studies in the identified subject area s. This and subsequent key components of the 1 process currently followed for the development of an ISA are presented in Figure 3-1 and are 2 described in greater detail in the Preamble to the Integrated Science Assessments (U.S. EPA, 3 2015). Section 1.2 (above) briefly describes how th e PM ISA fits into the larger PM NAAQS 4 review. Important aspects of the development of th e PM ISA are described in the sections below, 5 including the approach for searching the litera ture, identifying releva nt publications, and 6 informing specific policy-relevant questions that are intended to guide the assessment. These 7 responsibilities are undertaken by expert authors of the PM ISA chapters, which include the EPA 8 staff in NCEA-RTP with extensive knowledge in th eir respective fields and extramural scientists 9 solicited by the EPA for their expertise in specific fields. The process for scientific and public 10
review of drafts of the PM ISA is described in section 3.5 below. 11
12April 2016 3-9 Draft – Do Quote or Cite 1 Source: Modified from Figure II of the Preamb le to the Integrated Science Assessments 2 (U.S. EPA, 2015). 3 Figure 3-1. General process for developmen t of Integrated Science Assessments. 4 

## Integrated Science Assessment Development Process

Literature Search and Study Selection

(See Figure III)

Develop Initial Sections Review and summarize conclusions from previous assessments and new study results and findings by discipline and category of outcome/effect (e.g., toxicological studies of lung function or biogeochemical studies of forests)

Development of Scientific Conclusions and Causal Determinations Characterize weight of evidence and develop judgments regarding causality for health or welfare effect categories. Develop conclusions regarding concentration- or dose-r esponse relationships, potentially at-risk populations, lifestages, or ecosystems.

Draft Integrated Science Assessment Evaluation and integration of newly published studies Clean Air Scientific Advisory Committee Independent review of draft documents for scientific quality and sound implementation of causal framework during public meetings.

Final Integrated Science Assessment Evaluation, Synthesis, and Integration of Evidence Integrate evidence from scientific disciplines. Evaluate evidence for related groups of endpoints or outcomes to draw conclusions for specific health or welfare effect categories, integrating health or welfare effects evidence with information on mode of action and exposure assessment.

Public Comments Comments on draft ISA solicited by the U.S. EPA Evaluation of Individual Study Quality After study selection, the quality of individual studies is evaluated by U.S. EPA or outside experts in the fields of atmospheric science, exposure assessment, dosimetry, animal toxicology, controlled human exposure, epidemiology, biogeochemistry, terrestrial and aquatic ecology, and other welfare effects, considering the design, methods, conduct, and documentation of each study. Strengths and limitations of individual studies that may affect the interpretation of the study are considered.

Peer Input Consultation Review of initial draft materials by scientists from both outside and within the U.S. EPA in public meeting or public teleconference.April 2016 3-10 Draft – Do Quote or Cite 3.3.2 Literature Search and Sel ection of Relevant Studies 1
The EPA uses a structured approach to iden tify relevant studies for consideration and 2 inclusion in the ISAs. To be deemed relevant, st udies must fall within the scope of the PM ISA, 3
as detailed in Section 3.1. A Federal Register notice is published that an nounces the initiation of 4 a review and requests information, including rele vant literature, from the public (79 FR 71764). 5 In addition, the EPA identifies publications by conducting a recursive mu lti-tiered literature 6 search process that includes extensive manual and computer-aided cita tion mining of computer 7 databases (e.g., PubMed, Web of Science) on specif ic topics in a variety of disciplines. The 8 search strategies are designed a priori and iteratively modified to optimize identification of 9 pertinent published papers. 10 For this PM ISA, a broad search string w ill be developed with keywords including, but 11 not limited to, particulate, PM, PM 10 , PM 2.5 , PM 10-2.5 , and ultrafine particles with the specific 12 syntax tailored for each database (e.g., PubMed, Web of Science). The broad search string will 13 then be used in combination with additional search strings to identify references relevant to 14 health and welfare topic areas. In addition to the use of the broad PM search strings, papers will 15
be identified for inclusion in several additiona l ways: specialized searches on specific topics; 16 relational searches that identify recent publications that have c ited references from previous 17 assessments; identification of relevant literature by expert scientists; recommendations from the 18 public and CASAC during the call for information a nd external review pro cess; and review of 19 citations in previous assessments. These search methods will be used to identify recent research 20 published or accepted for publication since the 20 09 PM ISA, i.e., starting in January 2009, 21 through approximately two months before the releas e of the second external review draft of the 22 PM ISA (see Table 1-3 for target dates). Stud ies published after the PM ISA cut-off date may 23 also be considered in subsequent phases of the NAAQS review, after assessing whether they 24 provide new information that impacts key scientific issues. 25 Once studies are identified through the mu ltipronged search strategy, PM ISA authors 26 (EPA staff and extramural scientists) will review the studies for relevance. Relevant to the 27 review of the primary PM NAAQS are epidemio logic, toxicological, and controlled human 28 exposure studies or reports that examine health e ffects in relation to exposure to PM as well as 29 studies or reports that examine sources, emi ssions, atmospheric chemistry, human exposure, 30 dosimetry, and modes of action. For the review of the secondary PM NAA QS relevant studies 31 are those that examine ecological effects, visibi lity, effects on materials and climate. Specific 32 information detailing the scope of the PM ISA, and subsequently those studies that will be 33
evaluated within it are deta iled above in section 3.1.2. 34April 2016 3-11 Draft – Do Quote or Cite To be included in the PM ISA, relevant stud ies and reports must have undergone scientific 1 peer review and have been published or accepte d for publication. Some pu blications retrieved 2
from the literature search will be exclude d as not being relevant (e.g., do not meet 3 aforementioned criteria) based on screening of th e title or citation (e.g., not about air pollution, 4 conference abstract, review arti cles, commentaries) a nd will not documented further. For other 5 publications, decisions about rele vance require reading beyond the title. These publications will 6
be labeled as “considered” for inclusion in the PM ISA and are listed in the HERO database 7 (http://hero.epa.gov). 8
From the group of “considered” references, studies and reports will be selected for 9
inclusion in the PM ISA based on review of the ab stract and full text. The selection process will 10 be based on the extent to which the study is potentially policy-releva nt and informative. 11 Potentially policy-relevant and informative studies will include those that provide a basis for or 12 describe the relationship between PM and effects, in particul ar, those studies that reduce 13 uncertainty or address limitations of critical issues. Also pertinent are studies that offer 14 innovation in method or design or present novel information on effects or issues previously not 15 identified. Uncertainty can be addressed, for example, by analyses of potential confounding or 16 effect modification by copollutants or other factors, analyses of C-R or dose-response 17 relationships, or analyses related to time between exposure and response. In keeping with the 18 purpose to accurately reflect the latest scientific knowledge, a majority of the discussion in the 19 PM ISA will describe studies published si nce the 2009 PM ISA. However, evidence from 20 previous studies will be include d and integrated with results fr om recent studies. In some cases, 21 evidence from previous studies may be the key polic y-relevant information in a particular subject 22 area or scientific discipline. Analyses conducted by the EPA using publicly available data, for 23 example, air quality and emissions data, will also be considered for inclusion in the PM ISA. 24 Informative studies will not be limited to specif ic study designs, model systems, or outcomes. 25 While study quality is important, it is not the sole criteria for st udy inclusion. The combination of 26 approaches described above are intended to pr oduce a comprehensive collection of pertinent 27 studies needed to address the key scientific issues that form the basis of the PM ISA. References 28 will be cited in the PM ISA by a hyperlink to th e HERO database and also are compiled into 29
reference lists. 30

3.3.3 Evaluation of Individual Study Quality 31

After selecting studies for in clusion, individual study quality is evaluated by considering 32 the design, methods, conduct, and documentation of each study, but not by considering whether 33 the study results are positive, nega tive, or null. In the PM ISA, conclusions about the strength of 34April 2016 3-12 Draft – Do Quote or Cite inference from study results will be made by weighing the author s’ conclusions and 1 independently evaluating study quality as detailed in the Preamble to the Integrated Science 2 Assessments (U.S. EPA, 2015). This uniform ap proach aims to consider the strengths, 3 limitations, and possible roles of chance, conf ounding, and other biases that may affect the 4 interpretation of the results from individual studi es for both health and welfare. In assessing the 5 scientific quality of studies, the followi ng broad parameters will be considered: 6

 How clearly were the study design, study groups , methods, data, and results presented to 7 allow for study evaluation? 8

 To what extent are the air quality data, expos ure, or dose metrics of adequate quality to 9 serve as credible exposure indicators? 10

 Were the study populations, speci es, subjects, or animal mode ls adequately selected, and 11 are they sufficiently well-defined to allow for meaningful comparisons between study or 12 exposure groups? 13

 Are the statistical analyses appropriate, prope rly performed, and properly interpreted? Do 14 the analytical methods provide adequate sensitivity and precision to support study 15 conclusions? 16

 Are likely covariates (i.e., pot ential confounding factors, modi fying factors) adequately 17 controlled for or taken into account in the study design or statistical analyses? 18

 Are the endpoint measurements meaningful, valid, and reliable? 19

Additional considerations in evaluating indivi dual study quality spec ific to particular 20 scientific disciplines (e.g. epidemiology, toxi cology, ecology) are discu ssed in detail in the 21 Preamble to the Integrated Science Assessments (U.S. EPA, 2015). 22



### 3.4 SPECIFIC ISSUES TO BE ADDRESSED IN THE PM ISA 23

The PM ISA will contain information relevant to considering whether it is appropriate to 24 retain or revise the current primary and secondary PM NAAQS. Decisions on the specific 25 content of the PM ISA will be guided by policy-relevant questions that frame the entire review of 26 the primary and secondary PM NAAQS as outlined in Chapter 2 above. These policy-relevant 27 questions are related to two overarching issues. The first ove rarching issue is whether new 28 evidence reinforces or calls into question the ev idence presented and evaluated in the last PM 29 NAAQS review: (1) with respect to factors such as the plausibili ty of health effects caused by 30 exposure to PM, specifically PM 2.5 and PM 10-2.5 , and concentrations of PM associated with health 31 effects; and (2) with respect to welfare-related effects of PM . The second overarching issue is 32
whether uncertainties from the la st review have been reduced a nd/or whether new uncertainties 33 have emerged, such as whether other measur es of PM (e.g., different size fractions or 34April 2016 3-13 Draft – Do Quote or Cite components) are better at capturing the health an d welfare effects attributed to PM exposures 1 than those used as the indicators for the current NAAQS. The PM ISA also will address a set of 2 more specific policy-releva nt questions related to the available scientific evidence that stem from 3 these issues. These questions were derived from the last PM NAAQS review, as well as from 4
discussions of the scientific evidence that occurred at the Febr uary 2015 science policy 5 workshop which initiated this PM NAAQS re view (79 FR 71764, December 3, 2014). The PM 6 ISA may include supplementary material if additional documentation is required to support 7 information contained in the PM ISA. As in recently completed ISAs, such supplementary 8
material will be available in the online HERO database and referenced in the PM ISA as 9
electronic links to HERO. 10

3.4.1 Causal Determinations from 2009 PM ISA 11

In the 2009 PM ISA, the EPA concluded that the findings of epidemiologic, controlled 12 human exposure, and animal toxi cological studies colle ctively provided evidence of a “causal 13 relationship” for shor t- and long-term PM 2.5 exposures and cardiovasc ular effects as well as 14 mortality (U.S. EPA, 2009, as summarized in Chap ter 2). In evaluating a broader range of health 15
effects for PM 2.5 , the 2009 PM ISA concluded there was evidence of a “likely to be causal 16 relationship” for shor t- and long-term PM 2.5 exposures and respirator y effects (U.S. EPA, 2009, 17 as summarized in Chapter 2). Additionall y, there was evidence “suggestive of a causal 18 relationship” for long-term PM 2.5 exposures and other health e ffects, including developmental 19 and reproductive effects (e.g., low birth weight, infant mortality) and carcinogenic, mutagenic, 20 and genotoxic effects (e.g., lung cancer mortality) (U.S. EPA, 2009, as summarized in Chapter 21 2). The 2009 PM ISA also formed causal determinations for exposures to PM 10-2.5 and ultrafine 22 particles. With respect to PM 10-2.5 , the 2009 PM ISA concluded that the evidence was 23 “suggestive of a causal relationship” for short- term exposures and cardiovascular effects, 24 respiratory effects, and mortality, with the evid ence “inadequate to infe r a causal relationship” 25 for long-term PM 10-2.5 exposures and all health effects (U.S. EPA, 2009, as summarized in 26 Chapter 2). For ultrafine partic les, the 2009 PM ISA concluded th e evidence was “suggestive of 27 a causal relationship” for short-term exposure a nd cardiovascular and resp iratory effects, but 28 “inadequate to infer a causal relationship” for sh ort-term exposures and central nervous system 29 effects and mortality, and for long-term exposur e and all health effects (U.S. EPA, 2009, as 30 summarized in Chapter 2). For welfare effects, th e evidence indicated a “ causal relationship” for 31 PM exposures and effects on visibility, climate, and materials; and a “likely to be causal 32 relationship” for PM exposures and ecological effects (U.S. EPA, 2009, as summarized in 33 Chapter 2). 34April 2016 3-14 Draft – Do Quote or Cite The causal determinations in the 2009 PM ISA, based on the causal framework and 1 integration of available evidence from previ ous and recent studies, were presented with a 2 summary of the available evidence at the end of the sections for each broad health and welfare 3 effect category and in the integrative synthesis chapter at the beginning of the PM ISA. In the 4 current review, specific policy-releva nt questions related to the causa l determinations that will be 5
addressed include: 6

 Does the evidence base from recent studies contain new information to support or re7 evaluate the causal determinations made for relationships between PM exposure and 8 various health and welfare e ffects in the 2009 PM ISA? 9

 Does new evidence confirm or extend biological plausibility of PM-related health 10 effects? 11

 What is the strength of inference from epid emiologic studies based on the extent to which 12 they have: 13

o Examined exposure metrics that capture the sp atial and/or temporal pattern of PM in 14 the study area? 15

o Assessed potential confounding by other pollutants and factors? 16

 What information is available to support a ra tionale for forming causal determinations for 17 PM size fractions other than PM 2.5 , specific PM components, or PM from specific 18 sources? 19

 What information is available regarding the health impacts of a decrease in ambient PM 20 concentrations to inform causal determinations? 21

3.4.2 Uncertainties/Limitations Identified in 2009 PM ISA 22

The causal determinations described a bove for the relationships between PM 2.5 , PM 10-2.5 , 23 and UFPs exposure and health and welfare effects were informed by uncertainties and limitations 24 in the evidence. For example, the 2009 PM ISA noted a number of uncertainties and limitations 25 in the health evidence, such as the heteroge neity often observed in multi-city epidemiologic 26
studies and whether this can be at tributed to exposure differences or regional differences in PM 27 components or sources; and uncerta inty related to the use of am bient PM concentrations from 28
central-site monitors an d their ability to represent persona l ambient PM exposure (U.S. EPA, 29 2009, Chapter 2). In each of the health and welfare effects sections, and the integrative synthesis 30 chapter, the PM ISA will evalua te uncertainties and limitations in the scientific data. These 31 uncertainties also will inform causal determinations. The PM ISA will evaluate potential 32 confounding by other ambient pollutants. To assess the independent effects of PM, the PM ISA 33 will examine whether epidemiologic associations with PM are observed in copollutant models. 34 Copollutant models are the predominant method used in air pollution epidemiology to estimate 35April 2016 3-15 Draft – Do Quote or Cite the effect of one pollutant for a given concen tration of a copollutant. The PM ISA also will 1 evaluate whether PM has interactions with copol lutants or joint effects in associations with 2 health outcomes. The assessment of potential conf ounding, interactions, or joint effects will draw 3 upon results from health effects studies, available information on copollutant interactions in the 4 atmosphere that influence the spa tial distributions of PM and copo llutants, as well as information 5 from experimental studies that examine the hea lth effects of PM exposures alone and PM in 6 combination with other pollutants. In the abse nce of these aforementi oned methods, the PM ISA 7 will examine whether single-pollutant epidemiologic associations with health effects in a given 8 study differ between PM and copollutants, and if insights regarding potential copollutant 9 confounding can be gained by examining the magn itude of correlation between pollutants. 10 Drawing from discussion about the stre ngths and limitations of various exposure 11 assessment methods, the PM ISA will evaluate the st rength of inference in epidemiologic studies 12 by considering information such as the exposure duration being examined, the extent of spatial 13 and/or temporal variability in PM in the study area, the distribu tion of monitoring sites in the 14 study area, the performance of exposure models used, and time-activity patterns of the study 15 population. Additionally, monitoring da ta will be used to characteri ze the spatial distributions in 16 ambient PM concentrations and human exposur es, and in turn, the potential exposure 17 measurement error in particular study areas based on the particular method of exposure 18 assessment used. The adequacy of exposure as sessment in epidemiologic studies will be 19 considered in weighing the quality of evidence, and in turn, forming causal determinations. 20
Epidemiologic evidence is unlikely to comp letely address the uncertainties mentioned 21 above. Any individual study is unlik ely to evaluate all potentially correlated copollutants, and the 22 limitations of epidemiologic methods in separati ng effects of highly co rrelated pollutants or 23 separating the effects of more than two pollutants in the same model are well recognized. With 24 respect to exposure measurement error, fe w studies with personal ambient exposure 25 measurements are likely to be available. Thus , coherence with other lines of evidence may 26 strengthen inferences when there are uncertainties in epidemiologic evidence due to copollutant 27 confounding or exposure measurement error. C ontrolled human exposure and toxicological 28
studies that demonstrate similar effects at relevant PM exposur es may provide coherence with 29 epidemiologic evidence. Further, experimental re sults that identify key events in the mode of 30 action may provide biological plausibility. 31

In the 2009 PM ISA, a number of uncertainties were identified with respect to quantitative 32 relationships between PM and effects on welf are. Although ecological effects due to PM 33 deposition were described in the previous ISA, there was a lack of information linking specific 34 ambient concentrations of PM to impairment of ecological receptors. For materials effects, the 35April 2016 3-16 Draft – Do Quote or Cite rate of deposition of PM onto surfaces was identified as an uncertainty as was the role of co1 pollutants in soiling effects. Th e 2009 PM ISA identified uncertainties in assessment of climate 2 effects including quantification and modeling of aerosols and relating observed effects to 3
measured concentrations of ambient PM. For visibility in the 2009 PM ISA, there were 4 uncertainties associated with the visibility pr eference studies and insu fficient urban monitoring 5
data. The PM ISA will evaluate the status of th ese uncertainties and limitations in each of the 6
welfare effects sections and this information will be used in the development of causal 7
determinations. 8

3.4.3 Integration of Evidence and Causal Determinations 9

As described in the Preamble to the Inte grated Science Assessments {U.S. EPA, 2015, 10 3037426}, the EPA uses a structured framework to pr ovide a consistent and transparent basis for 11 classifying the weight of available evidence for health and welfare effects according to a five12 level hierarchy: (1) causal relati onship; (2) likely to be a causal relationship; (3) suggestive, but 13 not sufficient, to infer a causal relationship; (4) inadequate to in fer a causal relationship; and (5) 14 not likely to be a causal relationship. In th e framework, key considerations in drawing 15 conclusions about causality include consistenc y of findings for an e ndpoint across studies, 16 coherence of the evidence across disciplines and across related endpoi nts, and biological 17 plausibility. As judged by these parameters, evidence that rules out chance, confounding, and 18
other biases with reasonable confidence is su fficient to infer a causal relationship. Increasing 19 uncertainty due to limited available informati on, inconsistency, and/or limited coherence and 20 biological plausibility leads to conclusions lowe r in the hierarchy. Causality determinations are 21 based on the confidence in the integrated body of evidence, considering study design and quality 22 and strengths and weaknesses in the overall collection of previ ous and recent studies across 23 disciplines. In discussing each determination of causality, the EPA char acterizes the evidence 24 upon which the judgment is based, including the we ight of evidence for individual endpoints 25
within the health or welfare effect category or group of related endpoints. 26 For evaluation of human health effects, dete rminations of causality are made for major 27 health effect categories (e.g., resp iratory effects) or more specifi c groups of related outcomes and 28 for the range of exposure concentrations of PM de fined to be relevant to ambient concentrations 29 (e.g., up to 2 mg/m 3 ). Findings based on higher exposure conc entrations may be considered if 30 they add to the understanding of bi ological plausibility, provided th at they do not reflect different 31 biological mechanisms operating at higher concentr ations. The main lines of evidence for use in 32 causal determinations for human health are controlled human exposure, epidemiologic, and 33 toxicological studies. Evidence is integrated from previous and recent studies. Other information 34April 2016 3-17 Draft – Do Quote or Cite including mechanistic evidence, toxicokinetics, and exposure assessment may be drawn upon if 1
relevant to the evaluation of hea lth effects and if of sufficient importance to affect the overall 2 evaluation. The relative importance of different sources of eviden ce to the conclusions varies by 3 pollutant or assessment, as does the availability of different sources of evidence when making a 4 determination regarding causality. In judgments of causality, scientists will also evaluate 5 uncertainty in the scientific evidence, consider ing issues such as generalizing results from a 6 small number of controlled human exposure subject s to the larger populati on; extrapolations of 7 observed pollutant-induced pathophy siological alterations from la boratory animals to humans; 8 confounding by co-exposure to other ambient pollutants, meteorological factors, or other factors; 9 the potential for effects to be due to exposure to air pollution mixtures; and the influence of 10 exposure measurement error on epidemiologic st udy findings. Judgments of causality also are 11 informed by the extent to which uncertainty in one line of evidence (e.g., potential copollutant 12 confounding in epidemiologic results) is addre ssed by another line of evidence (e.g., coherence 13 of effects observed in epidemiologic studies with experimental fi ndings, mode of action 14 information). Thus, evidence inte gration is not a unidi rectional process but occurs iteratively 15
within and across scientific di sciplines and related outcomes. 16 A similar process is used for the integration of evidence and determination of causality for 17 welfare-related effects. For ecological effects, several types of experimental approaches (e.g. 18 field studies, mesocosm, controlled laboratory exposures, gradie nt) may be relevant for assessing 19 PM effects to ecosystems. Field studies measur e biological changes in uncontrolled situations 20
and describe an association betw een a disturbance and an ecologica l effect. They are most useful 21 for linking stressors with effects when stressor an d effect levels are measured concurrently. The 22 presence of confounding factors can make it diffi cult to attribute observed effects to specific 23 stressors. Mesocosm studies are performed in the natural environment while controlling for 24 some, but not all, of the environmental conditions and can be considered a hybrid between a field 25 and a laboratory study. Controlled exposure studies provide the st rongest evidence for causality, 26 however the scope of inference to conditions in natural systems may be limited. Studies where 27
effects are observed at relevant ambient concen trations are weighted more heavily, however, 28 studies conducted at higher con centrations can inform the unders tanding of mode of action in 29 aquatic and terrestrial organisms. The EPA eval uates evidence relevant to understanding the 30 quantitative relationships between pollutant exposures and ecologi cal effects. Integration of 31 evidence for visibility and climate draws upon modeling and monitori ng data as well as 32 experimental approaches designed to characterize the role of PM in atmospheric processes. In the 33 case of visibility, new preference studies designe d to quantitatively assess the impact of PM on 34 visibility will also be incorpor ated if available. This includes evaluating the C-R or deposition- 35April 2016 3-18 Draft – Do Quote or Cite response relationships and, to the extent possible, drawing conclu sions on the levels at which 1 effects are observed. For materials effects, ev idence of corrosive and soiling effects on stone, 2 metals, paint and other surfaces at relevant concen trations of PM will be considered. Generally, a 3 causal determination is made based on many lines of evidence that reinforce each other and are 4 based on integrating evidence from both previous and recent studies. 5

3.4.4 Atmospheric Chemistry and Ambien t Concentrations of PM 6
The PM ISA will present and evaluate data related to ambient concentrations of PM and 7 its components; sources lead ing to the presence of PM in the atmosphere; the deposition of PM; 8 and chemical reactions that determine the formation, transformation, and lifetime of PM in the 9 atmosphere. Specific policy-releva nt questions related to atmo spheric chemistry and ambient 10
concentrations that will be a ddressed in the PM ISA include: 11

 What are the strengths and limitations of existing and new measurement methods and 12 approaches (including low cost sensors and remote sensing) for both advancing 13 science and providing routine measurements of particulate matter? What are the 14 important biases and uncertainties asso ciated with existing and new monitoring 15 methods? How do new methods and approaches compare with or complement routine 16 measurement tools (e.g., FRMs)? 17

 What changes have occurred in primary PM and PM precursor emissions rates over 18 time? Can the impacts of biomass burning (i ncluding occurrence of more fires due to 19 climate change and potentially identificati on of more fires with more sensitive 20 sensors on satellites), new transportati on and industrial technologies, improved 21 industrial and motor vehicle emission contro ls, and strategies for accounting for semi22 volatile organic emissions be observed in current atmospheric PM concentrations? 23 What are the uncertainties associated w ith source apportionment approaches, whereby 24 individual PM sources can be distinguished as a function of the chemical composition 25 of the emitted PM? 26

 What changes have occurred in the quantities of sulfate (SO 4 2- ), nitrate (NO 3 - ), and 27 secondary organic PM (SOPM) formed in the atmosphere over time? What new 28 information is available regarding mechan isms of their produc tion, including aqueous 29 phase SOPM formation, the role of sulfur and nitrogen in SOPM formation, and the 30 role of semi-volatile species? Have th e relative contributions of primary and 31 secondary PM components changed as a resu lt of decreases in precursor emissions? 32

 What are the current ambient concentrations of different size fractions of PM (i.e., 33 PM 2.5 , PM 10-2.5 , UFP), and how have they changed over time? What are the 34 uncertainties in the spatial and temporal di stributions of PM? How do those patterns 35 vary with particle size fraction? 36

 What uncertainties exist concerning the s ources and atmospheric chemistry of PM 37 components (both primary and secondar y particles)? How does PM composition 38 change over various spatial and temporal sc ales? What new information is available 39April 2016 3-19 Draft – Do Quote or Cite regarding the composition of the PM si ze fractions that could not be well 1 characterized during the last review (e.g., coarse PM, ultrafine PM)? 2

 How does intercontinental or trans-boundary transport of pollutants contribute to 3 background PM concentrations? What info rmation is available to quantify the 4 emissions from natural PM sources that c ontribute to background PM concentrations? 5 Is there enough information to estimate background concentrations of PM species? 6 The information provided in the Atmosphe ric Chemistry and Ambient Concentrations 7 chapter will provide context for understanding ambient concentration data used as surrogates for 8 human exposure and for interpretation of the heal th and welfare effects evidence in subsequent 9 chapters. 10

3.4.5 Human Exposure 11
The PM ISA will evaluate methods for estimating exposure to ambient PM, the 12 factors that influence exposure to PM, as well as the ability to make inferences about personal 13 exposure to ambient PM when extrapolating from ambient concentration data , particularly in the 14 context of interpreting results from epidemiol ogic studies, and from controlled human exposure, 15 animal toxicology, and in vitro chamber studies of near-atm ospheric conditions. The issues 16 surrounding the ability to make inferences about personal exposure differ by the exposure period 17 of interest. Short-term exposure studies (i.e., e xposures ranging from hours to days to weeks) 18 primarily rely on temporal variation in e xposure while long-term exposure studies (i.e., 19 exposures ranging from months to years) rely on spat ial variability of exposure. The PM ISA 20 will consider the available information on differential exposures to UFPs, PM 2.5 , and PM 10-2.5 21 and on particle characteristics such as chemi cal composition, size, surface area, number, and 22 source. Specific policy-relevant questions related to human exposure that will be addressed in the 23
PM ISA include: 24

 Are new models or other tec hniques available to estimat e human exposure to ambient 25 PM? What are the strengths and limitations of existing and new techniques? Do any 26 of these techniques characterize PM by size fraction or composition? 27

 What techniques are available to repli cate human exposure to ambient PM in 28 controlled human exposure, animal toxicology, and in vitro experiments? What 29 factors lead to uncertainty in the expo sure conditions established within these 30 experiments? What factors affect infe rence about human exposure from such 31 experiments? 32

 What are the limitations in our understandi ng of exposures to PM components, size 33 fractions, sources/environments , and relationships between exposure to specific PM 34 size fractions and/or components and corresponding exposure to gaseous co35 pollutants? What uncertainties exist regardi ng the spatial and temporal patterns of PM 36April 2016 3-20 Draft – Do Quote or Cite concentrations, size fractions, and component s as they relate to patterns of human 1 exposure? 2

 What are the uncertainties when extra polating from stationary PM monitoring 3 instruments to personal exposure to PM of ambient origin, especi ally in populations 4 at increased risk of PM-related health e ffects? How do these uncertainties vary for 5 particles of different size or composition? Issues include measurement error in 6 outdoor ambient monitors, the use of central ized monitors for estimating community 7 concentrations, and the use of centralized monitors as a surrogate for personal 8 exposure to PM of ambient origin. 9

 What are the uncertainties associated with using measurements of ambient 10 concentrations of PM to provide an estimat e of ambient exposures for health studies, 11 an indicator of personal exposure to PM, a nd/or an indicator of exposure to other 12 pollutants or pollutant mixtures? 13

 Higher sampler density is more likely for saturation samplers or low-costs sensors 14 than for other measurement tools with greater sensitivity and precision. How does 15 sampler density affect data quality objectives needed for individual samplers, 16 particularly for saturation samp lers or low-cost sensors? 17

 What limitations exist for interpretation of sub-daily, daily, and longer-term PM 18 concentration data used to estimate exposur es? How do factors such as air exchange 19 rates, indoor sources, ambient sources, and methods for measuring personal 20 exposures to ambient PM influence interp retation of PM concentration data over 21 different sampling periods? Does this info rmation differ by PM characteristics (e.g., 22 size, chemical composition, sources/environments)? 23

 What new developments have occurred with respect to chemical transport modeling 24 of short-term and long-term PM concentra tions for use in exposure assessment? How 25 might modeling and satellite data supp lement monitoring data for understanding 26 human exposures? What are the limitations of using modeling or satellite data in lieu 27 of monitoring data? What advancements ha ve been made with respect to techniques 28 for fusing modeling, monitoring, and/or sa tellite data for assessing long-term 29 exposures to ambient PM? What are the uncerta inties in data from chemical transport 30 models and satellites at the ex tremes of the concentration distribution, such as in low 31 concentration areas? 32

 What new developments have been made in use of source apportionment techniques 33 for assessing human exposure to ambient PM? 34

 What new developments have been made in assessing and/or correcting the influence 35 of exposure measurement error on health eff ect estimates for epidemiologic studies of 36 short-term and long-term exposure? How do these methods reduce the uncertainty 37 and/or bias in the health eff ect estimates for PM exposure? 38

3.4.6 Dosimetry 39
The PM ISA will evaluate literature focusing on dosimetry that may underlie the health 40 outcomes associated with exposure to PM. In Chapter 4 of the 2009 PM ISA, in relation to 41April 2016 3-21 Draft – Do Quote or Cite particle deposition in the body, it was concluded th at the first line of de fense for protecting the 1 lower respiratory tract from inhaled particles is the nose and mouth; that the lower respiratory 2 tract of children receive a higher surface dose of ambient PM compared to adults; and that people 3 with COPD generally have grea ter total deposition and more heterogeneous deposition patterns 4 compared to healthy individuals. In relation to pa rticle clearance, it was concluded that particles 5 depositing on the olfactory mucosa may translocate to the brain; and that a small, but statistically 6 significant fraction (<1% of deposited material) of poorly soluble partic les deposited in the 7 alveolar region may translocate in to circulation. A number of factors such as age and respiratory 8 disease were recognized as aff ecting both rates of deposition and clearance. Interspecies 9 differences in deposition and clearance were al so discussed. In the current review, specific 10 policy-relevant questions related to dosimetry th at will be addressed in the PM ISA include: 11

 Are there new data that better quantify extrathoracic and thoracic deposition of 12 particles in children, a dults, and among species? 13

 Are new data available evaluating the effect s of respiratory disease on deposition and 14 clearance? 15

 What new data or models are available that help facilitate interspecies comparisons? 16

 Is there new information related to the transl ocation of particles in to circulation or the 17 olfactory bulb? 18

3.4.7 Modes of Action 19

The PM ISA will evaluate literature focusi ng on modes of action that may underlie the 20 health outcomes associated with exposure to PM. These topic areas will be developed using both 21 human and animal data. In the current review, spec ific policy-relevant ques tions related to modes 22
of action that will be addressed include: 23

 How do physical-chemical particle characte ristics influence biological responses to 24 inhaled PM? 25

 What new evidence is available to characte rize biologic responses of various PM size 26 fractions or PM from different sources? 27

 What are the time-courses of biological responses to inhaled PM? What are the 28 implications of these time-courses for heal th effects associated with short-and long29 term exposure to PM? 30

 What are the interspecies differences in bi ological responses to inhaled PM? What are 31 the implications of interspecies differences for extrapolation of re sults to humans? 32

 Is there a common underlying biological re sponse (e.g., inflammation) that supports 33 an effect of PM exposure on an array of health outcomes (e.g., cardiovascular, 34 respiratory, or nervous system)? 35April 2016 3-22 Draft – Do Quote or Cite  What new evidence is available to el ucidate mechanisms by which pulmonary 1 deposition of PM leads to extrapulmonary effects? 2

3.4.8 Health Effects 3

In the 2009 PM ISA, the health eff ects evidence for PM largely focused on PM 2.5 ; 4
fewer studies were available for PM 10-2.5 , UFPs, and sources/components of PM. The evidence 5
indicated that a “causal rela tionship exists” for short- a nd long-term exposures to PM 2.5 and 6 cardiovascular effects and mortality, and a “likely to be causal relationship exists” for short- and 7 long-term PM 2.5 exposures and respiratory e ffects. More limited evidence with a larger degree of 8 uncertainty formed the basis for the determinatio ns for other health effects and other PM size 9 fractions (i.e., PM 10-2.5 and UFPs). Additionally, with respect to sources and PM components, the 10 EPA concluded “that many PM [components] can be linked with differing health effects and the 11 evidence is not yet sufficient to allow differentiation of those [c omponents] or sources that are 12 more closely related to specific he alth outcomes (U.S. EPA, 2009, p. 2-26)” The EPA will build 13 on the 2009 PM ISA by evaluating the newly availabl e literature related to PM exposures and 14 health effects, including, but not limited to respiratory, cardio vascular, neurologic, reproductive 15 and developmental effects, mortality, and cancer. Depending on data availability, other health 16 effects may be evaluated. 17

The PM ISA will evaluate health effects th at occur following both short- and long-term 18 exposures as examined in epidemiologic, contro lled human exposure, and animal toxicological 19
studies. Efforts will be directed towards identi fying the concentrations at which effects are 20 observed, particularly in potential at-risk lifestages and populations , and assessing the role of PM 21 within the broader mixture of ambient air pollutant s. The data will be reviewed for relevance to 22 the current elements of the PM NAAQS (i.e., indi cator, averaging time, form, and level) in order 23 to support decisions regarding the adequacy of the current primary standard. Additionally, the 24
evidence will be evaluated to determine wh ether specific chemical components and/or 25 source(s)/environment(s) (e.g., near-road) more fu lly explain PM health effects. The discussion 26 of health effects will be integr ated with relevant information on dosimetry and modes of action, 27 as well as with information from the exposure chapter. 28
In light of recent International Agency fo r Research on Cancer (IARC) conclusions on 29 the carcinogenicity of outdoor air pollution, and specifically of PM, it is important for the EPA to 30 clearly outline its approach fo r evaluating the relationship betw een long-term PM exposures and 31 cancer in the PM ISA (Loomis et al., 2013). Wh ile IARC focuses on whether a chemical is a 32 carcinogen at any concentration and through any route of exposure, the PM ISA focuses on 33 whether PM can directly cause cancer through inhalation exposures at ambient and near-ambient 34April 2016 3-23 Draft – Do Quote or Cite concentrations. When evaluating the epidemiol ogic evidence for cancer, the EPA will focus on 1 those studies with composite measures of PM a nd with exposures consis tent with the overall 2 scope of the PM ISA detailed in Section 3.1, i.e., concentrations of PM th at represent the range 3 of human exposures across ambient microenvironments (up to 2 mg/m 3 PM, which is one to two 4 orders of magnitude above ambient concentrations ). For the toxicological evidence, the EPA will 5
describe in vitro studies and other mechanistic studies related to cancer in the Mode of Action 6 chapter because these type s of studies are pertinent to the biological pathways underlying cancer. 7 Consistent with previous ISAs, in vivo studi es that examine cancer-re lated endpoints will be 8 discussed in combination with the epidemiologic evidence in the health chapters. The evaluation 9 of toxicological studies related to mutageni city, genotoxicity, epigenetic changes, and 10 carcinogenicity will focus on inhalation exposures primarily at ambient relevant concentrations 11 (i.e., up to 2 mg/m 3 ) with the potential incl usion of exposures above this concentration. Lastly, 12 the evaluation of cancer will not focus on studies that use PM filter extracts because they may 13 not mimic what is bioavailable in vivo, or on studies of individual PM components due to the 14 inability to compare effects to th e current mass-based PM indicator. 15
In the current review, specific policy-relevant questions that will be addressed in 16
consideration of health effects associated with short- and long -term exposure to PM, include the 17 following: 18
Short-Term Exposure: 19

 What new evidence is available to inform policy-relevant considerations of the PM 20 NAAQS (e.g., considerations related to indi cator, averaging time, form, level) for 21 those health categories where the 2009 PM IS A concluded that a “causal relationship” 22 exists (i.e., short-term PM 2.5 exposures and mortality and cardiovascular effects)? Do 23 new controlled human exposure and toxicologi cal studies continue to provide support 24 for biologically plausible relationships between short-term PM exposures and 25 cardiovascular health effects? Do new studi es report PM-attributable effects at lower 26 PM concentrations than indicated by studies available in the last review? 27

 How do results of recent studies expand understanding of the relationship between 28 short-term exposure to PM and respiratory e ffects, such as exacerbation of asthma or 29 chronic obstructive pulmonary disease and respiratory infection? Does recent 30 evidence improve coherence ac ross disciplines for lung function changes, pulmonary 31 inflammation, host defense mechanisms, and outcomes such as symptoms, hospital 32 admissions, or emergency department visits? 33

 To what extent is short-term exposure to PM related to or associated with the 34 progression of diabetes, other metabolic dis eases, and/or to other endocrine system 35 effects? To what extent ar e new health outcomes related to or associated with PM 36 exposures? 37April 2016 3-24 Draft – Do Quote or Cite  Across the evaluated health effects, wh at new evidence is available on effects 1 occurring from exposures at averaging times different (e.g., 1-hour) than the current 2 24-hour average PM NAAQS? 3 Long-Term Exposure: 4

 What new evidence is available to inform policy-relevant considerations of the PM 5 NAAQS (e.g., considerations related to indi cator, averaging time, form, level) for 6 those health categories where the 2009 PM IS A concluded that a “causal relationship” 7 exists (i.e., long-term PM 2.5 exposures and mortality and cardiovascular effects)? Do 8 new controlled human exposure and toxicologi cal studies continue to provide support 9 for biologically plausible relationships between long-term PM exposures and 10 cardiovascular health effects? Do new studi es report PM-attributable effects at lower 11 PM concentrations than indicated by studies available in the last review? 12

 To what extent do recent studies improve understanding of the relationships between 13 long-term PM exposure and the development of asthma or to the impairment of lung 14 development? Do recent studies improve c oherence across disciplines for respiratory 15 disease incidence, pulmonary inflammation and oxidative stress, and development of 16 allergic responses? 17

 To what extent do recent studies improve understanding of the relationship between 18 long-term PM exposure and reproductive a nd developmental health outcomes, such 19 as adverse birth outcomes, fertility and pregnancy out comes (e.g., infertility, sperm 20 quality, preeclampsia, gestational hypert ension), or developmental outcomes (e.g., 21 neurocognitive ability)? 22

 To what extent does new literature suppor t a biologically plausible relationship 23 between long-term PM exposures and a number of nervous system effects (e.g., 24 cognitive decline and autism)? 25

 How do results of recent studies expa nd our understanding of the relationship 26 between long-term PM exposure and cancer, mutagenic, genotoxic, and epigenetic 27 effects? To what extent does the eviden ce indicate that long-term exposure to PM 28 can increase the incidence of cancer? 29

 To what extent is long-term exposure to PM related to or associated with the 30 development of diabetes and other metabolic diseases, as well as to health effects in 31 the endocrine system or other organ syst ems? To what extent are new health 32 outcomes related to or asso ciated with PM exposures? 33

Additional Policy-Rele vant Considerations: 34

 Across the evaluated health effects, to what extent does new evidence inform the 35 understanding of differential e ffects from exposures to vari ous PM size fractions (i.e., 36 PM 2.5 , PM 10-2.5 , UFPs)? 37

 Do studies of mortality, hospital admissions, or emergency department visits provide 38 new information to improve our understan ding of the potential heterogeneity in 39 effects observed across the U.S. in multi-city studies? 40April 2016 3-25 Draft – Do Quote or Cite  How do recent studies support the attribution of health effects to one or more PM 1 component(s) or source(s), in addition to PM mass, for health effects for which there 2 is sufficient evidence of a strong relationship (e.g., cardiovascular effects, mortality) 3 with PM exposure? 4

 How do the results of recent studies inform the shape of the c oncentration-response 5 relationship for PM and various health outcomes (e.g., mortality, hospital admissions, 6 etc.), especially for concentrations near or below the levels of the current PM 7 NAAQS? 8

 What new evidence adds to the understandi ng of which lifestages and populations are 9 at risk of PM-relate d health effects? 10

 What new evidence supports evaluation of in ter-individual variab ility in response to 11 PM exposures? 12

 Across health effects, what new information is available to delineate the effects of 13 chronic exposure to lower concentrations versus acute, repeated exposures to higher 14 concentrations of PM? 15

 What is the nature of health effects in persons exposed to multipollutant mixtures that 16 contain PM in comparison to exposure to PM alone? 17

3.4.9 At-Risk Lifestages and Populations and Public Health Impact 18
The PM ISA will evaluate an array of factor s that may contribute to increased risk of 19 PM-related health effects for various lifestages or populations. These factors reflect the multiple 20 avenues through which a lifestage or population may be at increased risk of an air pollutant21 related health effect, specifically: intrinsic factors (e.g., biological factors such as age or genetic 22 variants), extrinsic factors (nonbiol ogical factors such as diet, lo w SES), and/or fa ctors affecting 23 dose or exposure (e.g., sex, age, out door activity or work, low SES, physical activity). It is also 24 important to recognize the in terconnectedness among th ese factors that may also confer 25 increased risk, an example being pre-existing di seases or conditions a nd socioeconomic status. 26 The 2009 PM ISA evaluated studies that provided evidence that children, older adults, people 27 with pre-existing cardiopulmonary diseases, and pe ople with lower SES are at increased risk of 28 PM-related health effects (U.S. EPA, 2009, Chap ter 8). Since completion of the 2009 PM ISA, 29 the EPA has developed a more detailed framework to provide a consistent and transparent basis 30 for communicating the overall confidence in the evidence that a particul ar factor may increase 31 the risk of an air pollutant-rela ted health effect for a lifestag e or population according to one of 32 four levels: adequate evidence, suggestive evid ence, inadequate evidence, and evidence of no 33 effect (U.S. EPA, 2013c, Table 8-1). Key consider ations in characterizi ng the evidence include 34 consistency of findings for a factor within a di scipline and, where availa ble, coherence of the 35 evidence across disciplines as we ll as biological plausibility. Se veral lines of evidence inform 36April 2016 3-26 Draft – Do Quote or Cite conclusions about at-risk lifestages and populatio ns, but primarily include observational or 1 experimental studies that compare exposure to PM or relationships with health effects among 2 groups that vary by some characteristic, such as pre-existing disease or age (i.e., exposure or 3 effect modification). Also re levant are comparisons of results among observational or 4 experimental studies that examine different lifestage or population ch aracteristics or time 5 windows of exposure and experimental studies that examine health effects of PM in a group with 6 a particular characteristic (e .g., genetic background, pre-existing disease). Where possible, the 7
discussion will also include evaluation of the advers ity of the health effects potentially associated 8 with exposure to PM. The assessment of public h ealth impact also may include, as appropriate, 9 an estimation of the sizes of pot ential at-risk lifestage s and populations. Further, to the extent 10 that evidence is available, the at-risk chapte r of the PM ISA will discuss what evidence is 11 available regarding interrelationshi ps among risk factors in a partic ular lifestage or population as 12 described in the preceding section that may add to the understanding of th e public health impact 13 of exposure to PM. Specif ic questions include: 14

 Is there new information that identifies a combination of factors (i.e., co-occurring) 15 that can lead to one lifestage or population be ing at greater risk compared to another? 16

 Have recent studies characterized whether cer tain lifestages or populations experience 17 differential exposures to PM mass, PM components or PM sources, which may 18 contribute to them bei ng at increased risk? 19

 What new evidence is available regarding additional lifestages or populations (e.g., 20 pre-existing diseases such as diabetes, pregnant women) potentially at increased risk 21 of a PM-related health effect? 22

 Have recent studies been able to delineate whether those lifestages or populations at 23 increased risk of a PM-relate d health effect differ dependi ng on exposures to different 24 PM size fractions, PM compone nts, or PM sources? 25

3.4.10 Welfare Effects 26

In the 2009 PM ISA, the welfare effects ev idence for PM focused on the effects of 27 airborne PM, including NO x and SO x , on visibility and climate, and on the effects of deposition 28
of PM constituents other than NO x and SO x , primarily metals and carbonaceous compounds on 29 materials and ecology. The evidence indicated that a “causal relati onship exists” for PM 30 exposures and effects on visibility, climate, and materials; and a “ likely to be causal relationship 31 exists” for PM exposures and ecological eff ects. The EPA will build on the 2009 PM ISA by 32 evaluating the newly available literature related to PM exposures and welfare effects, specifically 33 ecological effects, visibilit y, climate, and materials. 34
Ecological Effects 35April 2016 3-27 Draft – Do Quote or Cite The PM ISA will summarize studies of imp acts of PM deposition with the secondary 1
NO x /SO x ISA covering the depositional effects of N and S on ecological receptors. As indicated 2 in the previous ISA, chemical components of PM determine ecological response to a greater 3 degree than PM size class. However, size fraction may play a role in direct effects such as 4 deposition on vegetative surfaces near PM source s. In regards to effects of PM on ecosystem 5 components (e.g. plants, soils, wildlife, nutrient cyc ling), both direct and i ndirect effects of PM 6 deposition will be considered. PM deposited directly on vegetative surfaces may impair 7 photosynthesis and gas exchange between the plant and the atmosphere. Indirect effects of trace 8 metals and organics associated with PM depos ition on ecosystem receptors including aquatic and 9 terrestrial organisms, as well as effects on ecosystem structure and function, will be evaluated. If 10
studies are available that link PM deposition to ecosystem serv ices these findings will be 11 discussed. Specific questions include: 12

 Is there new information on PM that can be correlated to a specific physiological 13 response in aquatic a nd terrestrial biota? 14

 Do new studies show effects on ecosystem st ructure, function and biodiversity or PM 15 impacts to ecosystem services? 16

Visibility Effects 17 The PM ISA will summarize long-known in formation needed for placing current 18 information in context with respect to visibili ty. Previous evaluations have indicated that 19 anthropogenic sulfate and nitrate pa rticles are responsible for most of the regional haze in the 20 eastern U.S. In the West, sulfates may be genera lly of less importance sin ce less sulfur dioxide is 21 emitted there, but important sub-regional and seasonal differences still exist. Nitrates are a 22 leading factor in haze generati on in specific areas such as sout hern California in winter, for 23 example, while in many of the less-populous areas of the West, airborne soil particles can be the 24 largest contributor to visibili ty extinction during the spring. 25 In addition, anthropogenic nitrates and organic species, either emitted directly or formed 26 secondarily from other emissions, can be significant factors in haze formation. Other sources of 27 visibility extinction (e.g., dust, smoke, sea salt ) have anthropogenic, biogenic, and geogenic 28 sources that vary in strength and significance su b-regionally as well. Smoke from wildfires and 29 prescribed burnings contribute to visibility ex tinction both directly and indirectly, though much 30
less is known of these indirect effects thr ough SOPM generation. The PM ISA will evaluate 31 newly available evidence summarizing the recent important policy-relevant findings and will 32 include sections for aerosol opti cal characteristics, spatial and temporal trends, and causes of 33 haze. Specific questions include: 34April 2016 3-28 Draft – Do Quote or Cite  What relationships exist be tween ambient PM and visi bility impairment? How do 1 these relationships vary between urban and rural settings? 2

 What metrics and algorithms are available to estimate visibility impairment as a 3 function of PM mass, optical ch aracteristics, and composition? 4

 What role do spatial patterns (e.g., elevated particulate nitrate in the midwestern U.S. 5 and enhancement of sulfate concentrations in the eastern U.S.), seasonal patterns, 6 multi-year trends, emissions changes, a nd meteorology play with respect to PM 7 effects on visibility? 8

 What new preference studies or other metrics are available to describe the extent to 9 which PM-related visibility impairment may be considered adverse to public welfare? 10

Climate Effects 11 The PM ISA will present information on radiative forcing and climate change impacts of 12 PM and PM components. Background information on the physics of climate and radiative 13 forcing and observed trends in anthropogenic and na tural PM will be presented as well as climate 14 impacts of changes in anthropogenic PM since preindustrial times. Focus will be on information 15 necessary for interpretation of effects desc ribed in the chapter and on newly available 16
information since the last ISA. PM size/ effect dependencies (e.g., cloud formation and 17 precipitation) and PM compositi on/effect dependencies (e.g., black carbon and sulfate aerosol) 18 will be addressed as they pertain to climate effects. 19

 What are the important and relevant climate metrics used to quantify PM-related 20 climate effects and what are their strengths and limitations in assessing climate effects 21 at different temporal and spatial scales? 22

 What is the current understanding of th e magnitude and direction (warming vs. 23 cooling) of PM climate impacts and what important uncertainties remain? 24

 To what extent do we understand the indepe ndent effect of PM on climate in the 25 broader context of other climate forcers? 26

 What is the current state of knowledge of PM size and composition in relation to 27 climate forcing and what is the rela tionship between PM metrics (e.g., size, 28 composition) and important and relevant cl imate metrics used to quantify PM-related 29 climate effects? 30

 What recent advancements have been made in understanding PM effects on regional 31 climate in the U.S.? 32

Materials Effects: 33

The PM ISA will summarize soiling and deteriora tion of materials attributable to PM and 34 related N and S components because of the difficu lty associated with isolating the effects of 35 gaseous and particulate N and S wet depositi on and the NOx/SOx secondary ISA only focuses 36April 2016 3-29 Draft – Do Quote or Cite on ecological effects, not other welfare effects (See Section 1. 4). Previous PM assessments 1 indicated that stone, paint, metal and other ma terials can become disc olored and/or undergo 2 corrosion processes from particle pollution. Cultura lly important items such as buildings, statues 3 or works of art can be physically damaged and/or lose aesthetic appeal. The focus of the PM ISA 4
will be on whether there is new information on soiling and corrosion, dose-response relationships 5 between PM or related N and S species and dama ge to surfaces. Any new areas of research 6 focus on PM-related materials effects will also be emphasized in the PM ISA. 7

 Is there new information on soiling of stone, metal and paint surfaces due to PM or 8 related N and S species? Corrosive effects? 9

 Do new studies show effects on additional types of materials? 10



### 3.5 QUALITY MANAGEMENT 11

Within the EPA, Quality Management Plans (QMP) are developed to ensure that all 12 Agency materials meet a high standard for qual ity. NCEA-RTP participates in the Agency-wide 13 Quality Management System, which requires the development of a QMP. Implementation of the 14 NCEA QMP ensures that all data generated or used by NCEA scientists are “of the type and 15 quality needed and expected for their intende d use” and that all information disseminated by 16 NCEA adheres to a high standard for quality in cluding objectivity, utility, and integrity. Quality 17 assurance (QA) measures detailed in the QMP will be employed for the development of the PM 18 ISA. NCEA QA staff will be re sponsible for the review and approval of quality-related 19 documentation. NCEA scientists will be responsib le for the evaluation of all inputs to the PM 20 ISA, including primary (new) and secondary (existing) data, to ensure their quality is appropriate 21 for their intended purpose. NCEA adheres to Data Quality Objectives, which identify the most 22 appropriate inputs to the science assessment a nd provide QA instruction for researchers citing 23 secondary information. The approach es utilized to search the liter ature and criteria applied to 24
select and evaluate studies were detailed in the two preceding subsections. Generally, NCEA 25 scientists rely on scie ntific information found in peer-r eviewed journal articles, books, and 26 government reports. The PM ISA also can include information that is integrated or summarized 27 from multiple sources to create new figures, tabl es, or summation, which is subject to rigorous 28 quality assurance measures to ensure their accuracy. 29



### 3.6 SCIENTIFIC AND PUBLIC REVIEW 30

Drafts of the PM ISA will be made availabl e for review by the CASAC and the public as 31 indicated in Figure 1-1 and Tables 1-1 and 1-3 above. Availability of draft documents will be 32
announced in the Federal Register . The CASAC will review the draft PM ISA documents and 33April 2016 3-30 Draft – Do Quote or Cite discuss its comments in public meeti ngs that will be announced in the Federal Register . The 1 EPA will take into account comments, advice, and recommendations received from the CASAC 2 and from the public in revising the draft PM ISA documents. The EPA has established a public 3 docket for the development of the PM ISA. 81 After appropriate revi sion based on comments 4 received from the CASAC and the public, the fi nal document will be made available on the EPA 5 website. A notice announcing the availability of the final PM ISA will be published in the 6 Federal Register

. 7
8

81 The ISA docket can be accessed at www.regulations.gov using Docket ID number EPA-HQ-ORD-2014-0859.April 2016 3-31 Draft – Do Quote or Cite REFERENCES 1
Clean Air Act Amendments of 1977. U.S. Government Printing Office; 1977. 2 IPCC (2014). Climate Change 2014: Synthesis Repor t. Contribution of Working Groups I, II, 3 and III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change. 4 [Core Writing Team, R.K. Pachauri and L.A. Meyer (eds.)]. IPCC, Geneva, Switzerland. 5 Loomis D, Groose Y, Lauby-Secretan B, El Ghi ssassi F, et al. (2013). The carcinogenicity of 6 outdoor air pollution. Lancet Oncol 14(13):1262-3. 7 Melillo JM, Richmond TC, Yohe GW, Eds. ( 2014). Climate Change Impacts in the United 8 States: The Third National Climate Assessment. U.S. Global Change Research Program. 9 Available: 10 http://s3.amazonaws.com/nca2014/low/NCA3 _Climate_Change_Impacts_in_the_United 11 %20States_LowRes.pdf?download=1

. 12 Peacock M (2008). Letter from Marcus Peacock, Deputy Administrator, U.S. EPA to Rogene 13 Henderson, Chair, Clean Air Scientific Advisory Committee, September 8, 2008. 14 Available: http://www3.epa.gov/ttn/naaqs/pdf s/PeacocklettertoCASAC090808.pdf

. 15 Samet J (2009). Letter from Dr. Jonathan M. Samet, Chair, Clean Air Scientific Advisory 16 Committee to the Honorable Lisa P. Jackson, Administrator, U.S. EPA. CASAC Review 17 of EPA’s Integrated Science Assessment for Particulate Matter – First External Review 18 Draft, December 2008. (May 21, 2009). Available: 19 http://ofmpub.epa.gov/eims/eimsc omm.getfile?p_download_id=508493. 20 U.S. EPA (2006). Review of the Process for Se tting National Ambient Air Quality Standards. 21 NAAQS Process Review Workgroup, U.S. E nvironmental Protection Agency, March 22 2006. Available: 23 http://www3.epa.gov/ttn/naaqs/pdf s/naaqs_process_report_march2006.pdf

. 24 U.S. EPA (2009). Final Report: In tegrated Science Assessment fo r Particulate Matter. U.S. 25 Environmental Protection Agency, Washi ngton, DC, EPA/600/R-08/ 139F. Available: 26 https://cfpub.epa.gov/ncea/risk/record isplay.cfm?deid=216546&CFID=50518184&CFTO 27 KEN=64007426

. 28 U.S. EPA (2015). Preamble to the Integrated Science Assessments. U.S. Environmental 29 Protection Agency, Washington, DC, EPA/600/R-15/067. Available: 30 https://cfpub.epa.gov/ncea/isa/ recordisplay.cfm?deid=310244

. 31 U.S. EPA (2016). Process of Reviewing the Natio nal Ambient Air Quality Standards. March 4, 32 2016. Available: http://www3.epa.gov/ttn/naaqs/review.html

. 33April 2016 4-1 Draft – Do Quote or Cite 

## 4 HUMAN HEALTH RISK AND EXPOSURE 1 

## ASSESSMENT 2



### 4.1 INTRODUCTION 3

Within the context of NAAQS reviews, a quantita tive health risk and exposure assessment 4 (HREA) is designed to estimate human exposure a nd health risks associated with the existing 5 primary standards and with potential alternative primary standard(s), if any, that might be 6 appropriate to consider. This assessment can in form conclusions on the adequacy of the public 7 health protection provided by just meeting these standards. The purpose of this chapter is to 8 highlight key findings from the quantitative risk assessments conducted in the last review of the 9 PM NAAQS and to identify key issues to be addressed in planni ng for any additional 10 quantitative assessments that might be warranted for the current review. The scope of any HREA 11 would be informed by the scientific evidence in the upcoming PM ISA; existing and historical 12 air quality patterns and trends; th e availability of improved data, methods, tools, and models that 13 may better characterize important uncertainties or provide additional insights beyond those 14 provided by prior HREAs; a nd available resources. 15 In the upcoming HREA Planning Document (d iscussed in sections 1.2 and 1.5, above), the 16 EPA will evaluate newly available information within the context of the 2010 HREA from the 17 last review of the PM NAAQS to determine 1) the extent to which important uncertainties may 18 be better characterized by information newly availa ble for the current review and 2) the extent to 19 which this new information may affect the health risks estimated in the 2010 HREA in important 20 ways or suggest new quantitative analyses that can increase our understandi ng of the health risks 21 associated with ambient PM exposures. The HR EA Planning Document will also describe the 22 scope and methods for any new or updated quantit ative assessments warranted for this review. 23 CASAC advice and public comments on this draft IRP will be considered in developing the 24 HREA Planning Document, which will also be subject to CASAC review and will be made 25 available for public comment. If warranted, one or more drafts of an HREA would then be 26 prepared and released for CASAC review and public comment prior to completion of a final 27
HREA. 28 Section 4.2 describes the key analyses, fi ndings and uncertainties from the 2010 HREA. 29 Section 4.3 describes the two major components of potential new quantit ative health risk 30 assessments (i.e., epidemiology-based risk asse ssment and exposure assessment) that the EPA 31
will further evaluate in the HREA Planning Document. Section 4.4 describes the process for 32 obtaining scientific and public re view of the HREA Planning Docu ment and the HREA itself. 33April 2016 4-2 Draft – Do Quote or Cite 

### 4.2 OVERVIEW OF HEALTH RISK AND EXPOSURE ASSESSMENT 1


### FROM THE LAST REVIEW 2

In the last review of th e PM NAAQS, the EPA conducted a quantitative, epidemiology3 based risk assessment for selected health endpoin ts to provide informa tion and insights that 4 could help inform decisions on the primary standa rds, namely, the degree of protection provided 5 by the then-existing suite of primary standard s, as summarized below (in sections 4.2.1 and 6 4.2.2). The 2010 HREA (U.S. EPA, 2010a) characteri zed risk associated with ambient fine 7 particle (PM 2.5 ) concentrations because at that time it was decided that any risks estimated using 8
the limited data available fo r thoracic coarse (i.e., PM 10-2.5 ) and ultrafine particles would have 9 uncertainties too large to provi de reasonable and informative results for the review. The 2010 10 HREA quantified endpoints from health effect categories classified as having a “causal” or 11 “likely to be causal” relationship with exposure to PM 2.5 in the 2009 PM ISA (U.S. EPA, 2009a). 12 Endpoints included total, cardiopu lmonary, and lung cancer mortalit y associated with long-term 13 ( ≥ 1 year) exposure to PM 2.5 , and mortality (total non-accidental , cardiovascular, and respiratory) 14 and morbidity (hospital admissions for cardiovasc ular and respiratory causes and respiratory 15 symptoms not requiring hospitalizations) associated with short-term (24-hour) PM 2.5 exposures. 16 The 2010 HREA quantified health ri sks associated with ambient PM 2.5 concentrations (as a 17 surrogate for population exposure) in fifteen urban study areas (U.S. EPA, 2010a, section 3.1). 82 18 In addition, the 2010 HREA included a representativ eness analysis that co ntrasted these urban 19 study areas against national-level patterns and trends for key PM related attributes (e.g., PM 2.5 20 composition, demographics, and weather) and the tota l number of deaths that could be attributed 21
to PM 2.5 (U.S. EPA 2010a, sections 4.4.1 and 4.4.2). The 2010 HREA focused on estimating risk 22 remaining with PM 2.5 concentrations adjusted to just meet the then-existing primary PM 2.5 23 standards (15.0 μg/m 3 annual and 35 μg/m 3 24-hour, which are abbreviated here as 15/35 83 ), as 24 well as risk reductions from just me eting alternative suites of sta ndard levels (relative to 15/35). 25 The EPA did not conduct a quantitative popu lation-based, microenvironmental exposure 26 assessment (such as described below in section 4. 3.2) due to concerns rela ted to the utility of 27 such an assessment from both staff and CASAC (Samet, 2009a). 28

82 The 2010 HREA only estimated remaining risk and risk reductions for the urban areas where PM 2.5 improvements were needed to just meet the then-existing standards and alternative suites of standards. As described below, two of the 15 urban study areas did not exceed existing standards.

83 In discussing the then-existing standards and alternative suites of PM 2.5 standards, the notation used throughout this document is “annual standard/24-hour standard” in units of μg/m 3

.April 2016 4-3 Draft – Do Quote or Cite The health endpoints evaluated in the 2010 HREA were selected based on: 1) the overall 1 weight of evidence and subsequently causal de terminations in the 2009 PM ISA for general 2 health effect categories that is based on the collective body of evidence from epidemiologic, 3 controlled human exposure, and toxi cological studies; 2) the extent to which particular health 4 endpoints within these broader health effect cat egories are considered important from a public 5 health perspective; 3) the availability of epid emiologic studies providing effect estimates for 6 specific health endpoints; 4) the availability of air quality monitoring data in urban areas that 7 were evaluated in the epidemiologic studies; 5) the availability of baseline incidence and 8 prevalence data 84 to support population risk (incidence) modeling; and 6) the anticipated 9 usefulness of developing quantitative risk estimates 85 for the health endpo int(s) to inform 10 decision-making in the context of the PM NA AQS review. The 2010 HREA also considered 11 information in the 2009 PM ISA on at-risk popula tions, which identified the life stages of 12 children and older adults, people with pre-existi ng cardiovascular and re spiratory diseases, and 13 people with lower socioeconomic status as popula tions at increased risk for PM-related health 14
effects. 15 Criteria used in selecting the urban study area s included 1) the availa bility of air quality 16 monitoring data; 2) inclusion in an epidemio logic study providing effect estimates; 3) the 17 availability of study area-specifi c baseline incidence and prevalence data; 4) the potential for risk 18 reductions by adjusting PM 2.5 concentrations to just meet alte rnative annual and 24-hour standard 19 levels being considered, using th e lowest of the alternative suite of standards as the cutoff 20

84 The baseline incidence rate is the number of new cases of a health effect at a give n time (often per 10,000 or 100,000 of the general population in a year) in a given loca tion due to all causes, including air pollution. These data are an integral part of the C-R functions used to determine the number of new cases that can be attributed to changes in PM 2.5 concentrations. For some health endpoints (e.g., asthma exacerbation), we also use prevalence rates to define the applicable population with a given health conditi on (e.g., asthmatics). Prevalence refers to the rate of all cases in the population (both new and pre-existing).

85 The term “risk estimate” as used here refers to a quan titative, model-derived estimate of the likelihood for adverse health effects within a defined population following exposure to a specific chemical agen t or agents. In the context of NAAQS reviews, risk estimates typi cally take the form of incidence (cou nt) estimates for specific morbidity or mortality endpoints for a defined population.April 2016 4-4 Draft – Do Quote or Cite (12/25); and 5) regi onal representation. 86 After selecting the 15 urban study areas, 87 the 2010 1 HREA identified the “spatial template” to use in defining the geographical area associated with 2 each urban study area, incl uding which counties and PM 2.5 monitors were associated with a 3 particular urban study area. A national-scale asse ssment evaluated the representativeness of the 4 risk estimates for the urban study areas compared to national-level result s. First, the national5 scale assessment considered key PM 2.5 risk-related attributes to determine whether the selected 6 urban study areas are nationally re presentative or more focused on a particular portion of the 7 population distribution for a give n attribute (e.g., demographics) (U.S. EPA, 2010a, section 8 4.4.1). Second, the national-scale assessment analyzed estimates of mortality associated with 9 recent long-term PM 2.5 concentrations, 88 to assess the extent to which the 15 urban study areas 10 reflected locations within the U.S. likely to experience the highest PM 2.5 -related risk (U.S. EPA, 11 2010a, section 4.4.2). 12 The 2010 HREA quantified risks using concen tration-response (C-R) functions derived 13 from effect estimates reported in epidemiologic studies identified in the 2009 PM ISA. These 14 studies generally used ambient air quality data from fixed-site, populatio n-oriented monitors; 89 15 thus, the appropriate application of these estimates in C-R func tions for a PM risk assessment 16 similarly required the use of ambient air quality data at fixed-site, popula tion-oriented monitors. 17 The 2010 HREA adjusted ambient air quality con centrations using several different methods, 18 including a proportional “rollback” approach, 90 to simulate the distribution of PM 2.5 ambient 19

86 The goal of the 2010 HREA was to se lect at least one urban study area from each of the seven geographic regions identified in the 1996 PM Criteria Document (U.S. EPA, 1996, section 6.4) (i.e., PM regions). The selected urban study areas represented six of these seven regions, with the Upper Midwest not represented.

87 The 15 urban study areas were Tacoma, Fresno, Los Angeles, Phoenix, Salt Lake City, Dallas, Houston, St. Louis, Birmingham, Atlanta, Detroit, Pittsbu rgh, Baltimore, Philadelphia, and New York. Collectively, these 15 urban study areas comprised 31 counties.

88 These impacts were estimated down to policy relevant ba ckground (PRB) for short-term exposure and the lowest measured level (LML) observed in the epidemiologic st udy for long-term exposure. PRB concentrations have historically been defined by the EPA as those concentrations that would occur in the U.S. in the absence of anthropogenic emissions in continental North America, defined as the U.S., Canada, and Mexico. The 2010 HREA used regional PRB estimates generated using a combination of chemical transport modeling tools, as discussed in the 2009 PM ISA (section 3.2.2). LML refers to the lowest measured PM 2.5 concentration within an epidemiologic study.

89 Most studies applied the com posite monitor approach, where PM 2.5 levels were averaged across monitors within an urban study area in order to produce a single, generalizable PM 2.5 distribution for that urban area.

90 “Rollback” is a mathematical approach to lower recent concentrations at ambient monitors in order to simulate just meeting the “design value” for various standards. “D esign values” are the metrics (i.e., statistics) that are compared to the NAAQS levels to determine compliance. The proportional rollback method, which had been used in previous risk assessments, reflected a unifo rm percentage of reduction in ambient PM 2.5 concentrations across all monitors in an urban study area (U.S EPA, 2010a, section 3.2.3).April 2016 4-5 Draft – Do Quote or Cite concentrations that would “just meet” the then-e xisting and alternative su ites of standards. In 1 addition, two alternative approaches (locally focused and a hybrid of local and proportional 2 rollback approaches) were applied to improve our understanding of the un certainty associated 3 with the air quality adjustment (U.S. EPA, 2010a, section 3.2.3). 91 The general PM health risk 4
model combined PM 2.5 concentrations in specific urba n areas, C-R functions derived from 5 epidemiologic studies, baseline incidence data for specific health e ndpoints, and urban area 6 population estimates to derive estimates of the annual incidence of spec ified health effects 7
attributable to ambient PM concentrations unde r different air quality scenarios. The human 8 health risks were estimated using the risk assessment component of the EPA’s Total Risk 9 Integrated Methodology model (TRIM.Risk). 92 The analyses conducted in the 2010 HREA 10 focused on estimating changes in risks associated w ith air quality adjusted to just meet the then11 existing primary standards, as well as any additi onal risk reductions estimated to occur upon just 12 meeting alternative suites of standards. In the short-term exposure analysis, the 2010 HREA 13 modeled risk down to PRB, while the long-term exposure analysis modeled down to the LML 14 observed in the epidemiologic study. 15

4.2.1 Key Observations in the 2010 HREA 16

Section 5.2 of the 2010 HREA discussed th e key observations from the quantitative 17 analyses (U.S. EPA, 2010a, pp. 5-9 to 5- 10). In summary, the 2010 HREA emphasized 18
cardiovascular-related health eff ects due to the greater degree of confidence in these endpoints 19 stemming from information provided in the 2009 PM ISA relative to ot her health effect 20 outcomes, including respiratory effects (U.S. EPA 2010a, p. 5-9). Thus, for long-term exposure- 21

91 The locally focused rollback ap proach reflected a local patter n of reduction in ambient PM 2.5 concentrations focused exclusively on those monitors within an urban study area that exceeded the 24-hour standard under consideration. As such, this approach was only applied to the subset of urban study ar eas where no adjustment was needed to meet the annual standard. The hybrid approach reflected a combin ation of a more localized pattern of rollback focused on source-oriented monito rs with relatively elevated ambient PM 2.5 levels, followed by a more generalized regional pattern of rollback across all monitors in the study area to just meet the standards. For one urban study area (Pittsburgh), the 2010 HREA also applied a refined rollback approach that used a dual-zone approach to take into account monitor locations and the related topography in that area (U.S. EPA, 2010a, section 3.2.3)

92 Additional information on the risk charact erization module in TRIM can be found at: http://www2.epa.gov/fera/total-risk-integrated-methodology-trim-trimriskApril 2016 4-6 Draft – Do Quote or Cite related risk, the focus of the key observations was on ischemic heart disease (IHD)-related 1 mortality, and for short-term exposures the fo cus was on cardiovascular-r elated mortality and 2 morbidity. The 2010 HREA assessed risks associated with PM 2.5 concentrations adjusted to just 3 meet the then-existing standards and for PM 2.5 levels meeting an alternative suite of annual and 4
24-hour standards. The 2010 HREA also estimated the risks th at remained after attaining 5
alternative annual standard le vels of between 10 to 14 μg/m 3 . This choice accounts both for 6 epidemiologic evidence in the ISA and advice from CASAC. The 2010 HREA recognized that 7 the risks reported at the lower end of the standard levels were subject to greater uncertainty. The 8
2010 HREA evaluated five suites of annual and 24 -hour standard levels to provide a range of 9 combinations across the urban study areas. These air quality analyses found that the annual 10 standard was controlling in some urban study area s, and the 24-hour standard was controlling in 11
others. 93 The analysis reported separate risk estimates for years 2005, 2006 and 2007. However, 12
the 2010 HREA focused on the 2007-based estimate s, as these estimates for 2007 fell in the 13 middle of the risk estimates, in terms of th e magnitude of risk (U.S. EPA, 2010a, p. 4-5). 14 Consequently, 2007-based risk estimates are reflected in the key observations below. 15
16 Magnitude of risk associated with air quality adjusted to ju st meet the then-existing PM 2.5 17 standards (15/35) 18 In considering PM 2.5 -related risks associated with air quality just meeting the then19 existing PM 2.5 standards in the 15 urban study areas, the 2010 HREA focused on the 13 urban 20 study areas that would not meet 15/35 based on air quality from 2005 to 2007. 94 These 13 urban 21 study areas had annual and/or 24-ho ur design values that were a bove the levels of the then22 existing standards. Based on the risk estimat es for these areas, the 2010 HREA made the 23 following key observations regarding the magnitude of risk remaining 95 upon just meeting 15/35 24 (using proportional rollback): 25

93 The controlling standard in a particular area is the one th at, if met, ensures that the other standard would also be met in that area. B ecause the NAAQS for PM 2.5 includes standards using both 24-hour and annual averages, the controlling standard in an area was determined by the annu al or 24-hour average requiring the largest adjustment or “rollback” to meet the existing or potential alternative standa rd(s), if any. In general, only one of the two standards (daily or annual) would be the controlling standard in a particular area and 3-year period.

94 The two urban study areas that did not exceed either the then-existing annual and/or 24-hour design values were Dallas and Phoenix. Thus, the 2010 HREA did not estimate risk reductions in this analysis for these urban study areas. PM 2.5 concentrations in these two areas were not “r olled up” to the then-existing standards.

95 Risk remaining refers to the estimation of total risk fr om the then-existing standard down to the lowest bound for the analysis (eith er PRB or LML).April 2016 4-7 Draft – Do Quote or Cite  Long-term exposure-related mortality risk remaining : The analysis estimated that across the 1 urban study areas, the IHD-related mort ality attributable to long-term PM 2.5 exposure ranged 2 from less than 100 to approximately 2,000 cases per year, with this variability reflecting, to a 3 great extent, differences in the population si ze of each urban study area. These estimates 4 represented from 4 to 17 percent of all IHD-rela ted mortality in a given year across the urban 5 study areas, which is a measure of risk that takes into account differences in population size 6 and baseline mortality rates. 7

 S hort-term exposure-related mortality and morbidity risk remaining : The analysis estimated 8 that across the urban study areas , the cardiovascular-related mort ality attributable to short9 term PM 2.5 exposure ranged from <10 to 500 cases per year. These estimates represented 10 from approximately 1 to 2 percent of total cardiovascular-related mortality in a given year 11 across the urban study areas. In terms of morbid ity risk, cardiovascular-related hospital 12 admissions ranged from approximately 10 to 800 cases per year ac ross the study areas, 13 representing less than one percent of total car diovascular-related hospital admissions in each 14 study area. 15 Magnitude of risk reductions a ssociated with air quality adjust ed to just meet alternative 16
PM 2.5 standards 17 In characterizing PM 2.5 -related risks associated with air quality adjusted to just meet the 18 alternative annual standards (14/35, 13/35 a nd 12/35), the 2010 HREA estimated both the 19 magnitude of risk reductions (relative to risk remaining upon just meeting 15/35) 96 and the 20 magnitude of risk associated with air quality ad justed to just meet th e alternative standards. 97 21 More uniform risk reductions were estimated to result from just meeting the alternative annual 22 standard levels than just meeting alternative 24-hour standard levels. 98 Thus, in discussing these 23 risks, the 2010 HREA focused on the set of urban study areas that would ha ve risk reductions by 24 just meeting each alternative annual standard. 25

 Reductions in long-term expos ure-related mortality risk: Upon just meeting the alternative 26 annual standard levels considered in conjuncti on with the existing 24-hou r standard (denoted 27 as 14/35, 13/35 and 12/35), the analysis estimat ed reductions in long-term exposure-related 28 mortality for 12 99 of the 15 urban study areas, with th e degree of risk reduction increasing 29

96 Risk reductions refers to the difference in risk betw een the then-existing standard (in this case 15/35) and the alternative standard being analyzed.

97 The 2010 HREA also estim ated risks at 10 μg/m 3 for the annual standard; however, the HREA noted the larger degree of uncertainty in these estimates and therefore, these results are not pres ented here (U.S. EPA, 2010a, section 5.2.2).

98 The degree of estimated risk reduction in long-ter m exposure-related IHD mortality risk provided by the alternative 24-hour standards was highly variable across the study areas, in part due to different rollback approaches (U.S. EPA, 2010a, section 4.2.2 and section 5.2.3).

99 For 12/35, three of the urban study areas (i.e., Tacoma, Fresno and Salt Lake City) did not experience any decreases in risk when the annual stan dard was rolled back, as the design values in these urban study areas met the annual standard but exceeded the 24-hour standard, and thus would only experience risk reductions under alternative 24-hour standards.April 2016 4-8 Draft – Do Quote or Cite incrementally across the alternative standard le vels (both in terms of the number of study 1 areas experiencing risk reduction and the magnit ude of those reductions). For the alternative 2 annual standard level of 12.0 μ g/m 3 (in conjunction with the exis ting 24-hour standard), the 3 analysis estimated that these urban study areas ha ve reductions in mortal ity risk (relative to 4 risk remaining upon just meeting then-existing su ite of standards) ranging from about 11 to 5 35 percent. 6

 Reductions in short-term exposure- related mortality and morbidity risk : For the alternative 7 annual standard level of 12.0 μg/m 3 (in conjunction with the ex isting 24-hour standard), the 8 analysis estimated that reductions in both short-term exposure-re lated cardiovascular 9 mortality and morbidity risk ranged from 5 to 23 percent across the urban study areas. 100 10

4.2.2 Key Uncertainties in the 2010 HREA 11
The EPA recognized that both the inputs to th e risk assessment and the risk model used 12 were each subject to uncertainties that affected the magnitude and distribution of the results. The 13
2010 HREA followed the World Health Or ganization (WHO, 2008) framework for 14 characterizing uncertainty in the analyses and incorporated elements intended to increase the 15
EPA’s overall confidence in the risks estimated in the fifteen urban study areas (U.S. EPA, 16 2010a, section 3.5.1 and 4.3), including: 17

 The use of a rigorous, transparen t, and fully documented proce ss subject to peer and public 18 review in developing all key elements of the 2010 HREA (U.S. EPA, 2010a, section 5.1.1); 19

 Integration of key sources of variability in to the design and interpretation of results; 20

 Assessment of the degree to which the urba n study areas included in the 2010 HREA are 21 representative of areas in the U.S. experiencing higher PM 2.5 -related risk; and 22

 Identification and assessment of the impact (i.e., magnitude and direction) of important 23 sources of uncertainty on risk estimates. 24 The 2010 HREA included both qualitative (U.S. EPA, 2010a, section 3.5.3) and 25 quantitative sensitivity analyses (U.S. EPA, 2010a, section 3.5.4 and 4.3) designed to identify 26 sources of uncertainty most influencing the es timated risk. These analyses characterized the 27 sources of uncertainty likely to substantially impact the estimated risk. Since quantitative 28
information was not available to characterize over all levels of confidence in alternative model 29

100 The patterns of risk reduction (as a percentage) were si milar for both sets of endpoints because the rollback was the same for both and the C-R functions were assumed to be linear (U.S. EPA 2010a, section 4.2.2).April 2016 4-9 Draft – Do Quote or Cite inputs, the uncertainty characte rization in the 2010 HREA did not include a full probabilistic 1 assessment of uncertainty and its impact on risk estimates. 2
3 Key observations from analyses of uncertainty 4 The qualitative analysis of uncertainty identi fied the following sources of uncertainty as 5 potentially having a medium to high impact 101 on risk estimates (see Table 3-6, p. 3-72 of the 6 2010 HREA for additional detail, U.S. EPA, 2010a): 7

 Intra-urban variability in PM 2.5 exposure in epidemiologic studies : Use of composite 8 monitors as exposure surrogate s in epidemiologic studies ma y not fully capture spatial 9 variability in PM concentrations within an urban area, and introduces exposure measurement 10 error and uncertainty into the effect estimat es obtained from the epidemiologic studies. 11

 Shape and statistical fit of the C-R functions : There is uncertainty in the shape of the C-R 12 function, particularly at lower ranges of concentrations due to a lack of observations. In 13 addition, we consider the statistical fit of the of the C-R function. The term "statistical fit" as 14 used here indicates the precisi on of a statistical model for cap turing the observations. It can 15 be influenced by a variety of factors, includi ng exposure measurement error, sample size, and 16 control for confounders. 17

 Lag structure (short-term exposure studies) : Different lags may have varying degrees of 18 association with a particular health endpoint, and it may be di fficult to clearly identify the 19 specific lag that produces the majority of a PM-related eff ect. A lack of information 20 regarding the specific lag(s) most associated with a particular health endpoint adds 21 uncertainty into risk es timates for that endpoint. 22

 Transferability of C-R functions from epidem iologic study areas to HREA urban study areas 23 (long-term exposure health endpoints) : The use of effects estima tes based on data collected 24 in a particular location(s) as part of the unde rlying epidemiologic study in different locations 25 (the focus of the risk assessment) introduces uncertainty into the analysis. 26

 Single-city versus multi-city epidemiologic studies : Often both single-city and multi-city 27 epidemiologic studies are available (for a give n health endpoint) for the derivation of C-R 28 functions. Each of these study types has advant ages and disadvantages, and both study types 29 can introduce uncertainty into the analysis. 30

 Historical PM 2.5 exposures: Long-term exposure studies of mo rtality suggest that different 31 time periods of PM exposure can produce s ubstantially different effects estimates, 32 introducing uncertainty in identifying the expos ure window that is most strongly associated 33 with mortality. 34

101 The 2010 HREA classified sources as “medium impact” if they have the potential to change the interpretation of the risk estimates in the context of the PM NAAQS review, and classified so urces as “high impact” if they are likely to influence the interpretation of risk.April 2016 4-10 Draft – Do Quote or Cite  PM compositional differences : The composition of PM can diffe r across urban study areas. If 1 these compositional differences contribute to different effect estimates (i.e., heterogeneity), 2 then substantial uncertainty may be introduced into risk estimates if these compositional 3 differences are not e xplicitly addressed. 4

5 The 2010 HREA included two types of quantitati ve sensitivity analyses: single-factor and 6 multi-factor. The single-factor sensitivity analysis varied one source of uncertainty at a time and 7 identified the following sources of uncertain ty as having a moderate to large impact 102 on risk 8 estimates (U.S. EPA, 2010a, section 4.3.1): 9

 Long-term exposure-related mortality : (a) different C-R functi on model choices (e.g., fixed 10 versus random effects, log-linear versus log-log, singl e- versus co-pollutant), (b) modeling 11 risk down to PRB rather than LML, (c) use of C-R functions from different epidemiologic 12 studies, and (d) nature of the spatial pattern of ambient PM 2.5 reductions (i.e., rollback 13 method). 14

 Short-term exposure-related mortality and morbidity : (a) use of seasonally differentiated 15 versus annual-based C-R functions and (b) diffe rent models, lag structures and single-versus 16 co-pollutant model forms. 17 The multi-factor sensitivity analysis varied mu ltiple sources of uncertainty simultaneously and 18 covered both long-term exposure-related mortality and short-term exposure-related mortality and 19 morbidity. This multi-factor analysis found that a number of sources of uncertainty, identified 20 above, could work in concert to affect risk estimates, and that these combined effects would be 21
more than additive in certain circumst ances (U.S. EPA, 2010a, section 4.3.1.2). 22
23



### 4.3 CONSIDERATION OF POTENTIAL QUANTITATIVE 24


### ASSESSMENTS FOR THIS REVIEW 25

The goal of an HREA is to provide informa tion relevant to answer ing questions regarding 26 the adequacy of the existing PM primary st andards and, if appropriate, the potential 27 improvements in public health from meeting pot ential alternativ e standards. A quantitative 28 HREA for this review, if warranted, would build on the approaches used and lessons learned in 29 the 2010 HREA and would focus on improving th e characterization of PM exposure and 30

102 The 2010 HREA classified factors as “moderate to large impact” if they ha d a 20 percent to greater than a 100 percent difference on risk results.April 2016 4-11 Draft – Do Quote or Cite associated health risks, including relate d uncertainties, by inco rporating a number of 1 enhancements, in terms of newly availa ble models, methods, tools, and data. 2
Characterizing health risks for the current review of the primary PM NAAQS could 3 include conducting air quality an alyses to support quantitative a ssessments of risk and exposure 4 in specific urban study areas as well as putti ng the results into a na tional public health 5 perspective. We anticipate that, consistent with the large body of availa ble scientific and air 6 quality evidence available to support quantitative assessments, the most likely focus of 7 quantitative analyses in an HREA would be PM 2.5 . These assessments would be designed to 8 estimate human exposures and/or to characterize the potential health risks that are associated 9 with recent ambient levels, with ambient PM 2.5 concentrations adjusted to just meet the now10 existing standards (12/35) and, if appropriate, with ambient concentr ations adjusted to just meet 11 alternative standard(s) that may be considered. To the extent that information becomes available 12
in the PM ISA for the current review that could support quantitative analyses of PM 2.5 13 components, PM 10-2.5 , or ultrafine particles, additional quantitative analys es could be considered 14
which focus on these other size fractions or components. Similar to considerations for PM 2.5 risk 15 analyses, we would evaluate whether sufficient in formation is available for other size fractions 16 and/or components, including air quality informat ion, endpoints with causal or likely to be causal 17 determinations in the ISA, availability of concentration-response functions, and baseline 18
incidence data. The considerati ons for all potential qua ntitative epidemiology-based risk analyses 19 are described in greater de tail in section 4.3.1 below. 20

As described further in this section, an HR EA for the current revi ew would consider a 21 variety of health endpoints for which, in staff’ s judgment, there would be adequate information 22 to develop quantitative risk estimates that can me aningfully inform the review of the primary PM 23 NAAQS. We also intend to evalua te the distribution of risks a nd patterns of risk reduction (e.g., 24 among urban case study areas and across ambient PM 2.5 concentrations) and uncertainties in 25 those risk estimates. In presenting the results of any new assessments, we plan to evaluate the 26 influence of various inputs and assumptions on th e exposure and risk esti mates to more clearly 27 differentiate potential alternative standard(s ) that might be consid ered, including potential 28 impacts on various at-risk populations and lifestage s. In addition, we will consider characterizing 29
risk on a national scale. This assessment could also evaluate the distribution of PM-related health 30 risk across the U.S. (and the factor s that influence the distribution of risk) to assess the degree to 31 which risks estimated in each urban study area are representative of national-level risks. 32 An important issue asso ciated with conducting exposur e and human health risk 33 assessments is the treatment of variability and the characterization of uncertainty. Variability 34
refers to the inherent differenc es in a population or variable of interest (e.g., residential air 35April 2016 4-12 Draft – Do Quote or Cite exchange rates); it cannot be redu ced through further research, but it may be better characterized 1 with additional measurement. However, models can account for variability. Uncertainty refers to 2 the lack of knowledge regarding bo th the actual values of model input variables (i.e., parameter 3 uncertainty) and the physical systems or relations hips (i.e., model uncertainty – e.g., the shapes 4 of concentration-response relationships). Unchar acterized spatial and te mporal variability in 5

PM 2.5 mass or species concentrations is often an important source of uncertainty in PM risk 6 assessments. As part of such analyses, variabil ity and uncertainty will be explicitly addressed, 7 where feasible, in any new air quality, exposure, and health risk assessments. 8

Consistent with the 2010 HREA, we ar e considering following the WHO framework 9 (WHO, 2008) to characterize uncertainty and variability, which presents a multi-tiered approach 10 for characterizing uncertainty (and to a lesser ex tent variability) in the context of a risk 11 assessment. This framework provides a method for systematically linking the characterization of 12 uncertainty to the level of complexity of the underlying risk assessment. Ultimately, the decision 13 as to which tier of uncertainty characterization to include in this risk assessment will depend on 14 the availability of information for characterizi ng the various sources of uncertainty. The four 15 WHO tiers range from application of default uncer tainty factors up to probabilistic assessments. 16 Similar to the 2010 HREA, we antic ipate that the uncertainty char acterization in any HREA for 17 the current review would likely ha ve sufficient data to conduct uncertainty assessments in the 18 middle tiers (e.g., qualitative assessm ents of direction/magnitude of the effect on results and 19 sensitivity analyses). 20
Below, we outline the two major compone nts of the quantitative health risk 21 characterization (i.e., epidemiology-based risk asse ssments and exposure assessment) that will be 22
described in more detail in the HREA Pla nning Document. Preparation of this planning 23
document will draw from the assessments of the scie ntific evidence in the first draft PM ISA to 24 facilitate the integration of policy-relevant scie nce into the planning document. In particular, the 25 availability of air quality, exposure-response, co ncentration-response, and baseline incidence and 26 prevalence data as well as consideration of availa ble resources will influence the type of risk and 27 exposure assessments that would be developed. 28

4.3.1 Epidemiology-Based Risk Assessment 29
The goals of an updated epidemiology-based risk assessment for PM would be to: (1) 30 estimate the potential magnitude of mortality and morbidity risks in urban study areas for recent 31
ambient concentrations as well as for PM concentrations adjusted to meet the existing standards 32 and, if appropriate, potential alte rnative standard(s); (2) develop a better understanding of how 33 various inputs and assumptions influence the ri sk estimates, including a characterization of the 34April 2016 4-13 Draft – Do Quote or Cite confidence in the risk estimates ; and (3) gain in sights into the distributi on of risks and patterns 1
of risk reduction across modele d populations (including at-risk populations and lifestages) as 2 well as the spatial distribution of risk within and across modeled study areas. 3 The approach for an epidemiology-based risk assessment for the cu rrent review would 4 build upon the methods developed for and insights gained from the 2010 HREA (section 4.2 5 above). Section 4.3.1.1 below describes the ambient PM concentrations for recent conditions and 6 adjustments to just meet the existing and pot ential alternative sta ndard(s). Section 4.3.1.2 7
discusses factors to be consid ered in designing any new epidem iology-based risk assessment. 8
Section 4.3.1.3 identifies the sources of uncerta inty that had a substantial impact on risk 9 estimates in the 2010 HREA and discusses potenti al strategies for reducing and characterizing 10 those sources of uncertainty in th e current review. Each of these design factors and strategies for 11 reducing uncertainties, including data availabil ity, would be further evaluated in the HREA 12 Planning Document. 13

4.3.1.1 Ambient PM Concentrations 14

Recent Ambient Conditions 15

For an HREA for the current review, we antic ipate relying on data from the national air 16 quality monitoring networks described above (in section 2.3) to characterize ambient PM 17 concentrations for the time period and metric of interest (e.g., size fracti on, form). As described 18 above (in section 4.2), the 2010 HREA used data from these monito ring networks to characterize 19

PM 2.5 concentrations and associated health ri sks during 2005 to 2007 for 15 urban study areas. A 20 similar degree of PM 2.5 monitoring is now available for more recent years that could be 21
considered in the current review. We would sele ct specific urban study areas to assess in this 22 HREA by considering the availabl e monitoring data in conjuncti on with the new epidemiologic 23 studies in the upcoming PM ISA, and this new information may suggest we consider the same 24 study areas in the upcoming HREA that we re assessed in the 2010 HREA. Criteria for 25 identifying urban study areas will be iden tified in the HREA Planning Document. 26 In the 2010 HREA, the air quali ty analyses focused on PM 2.5 . Due to the substantial 27 uncertainties and data gaps that were identi fied, the 2010 HREA did not include quantitative 28 analyses for additional PM size fractions (e.g., PM 10-2.5 or ultrafine particles). For PM 10-2.5 , these 29 uncertainties were related to (1) concerns that the monitoring data for 2005 to 2007 would not be 30 similar to the data used in the epidemiologic studies that provided the effect estimates for the 31 C-R functions; (2) uncertainty in the prediction of ambient concen trations under th e then-existing 32 and alternative standards; (3) concerns that the 15 urban study areas in the 2010 HREA may not 33 be representative of areas experiencing the highest PM 10-2.5 concentrations; and (4) concerns 34April 2016 4-14 Draft – Do Quote or Cite about the much smaller number of re levant epidemiologic studies for PM 10-2.5 compared to the 1 larger number of studies for PM 2.5 . The 2010 HREA also concluded that the available 2 information was too limited to support quantitative assessments for ultrafine particles. A lack of 3 information on the appropriate metric 103 for characterizing ultrafine pa rticles in risk assessments, 4 as well as the lack of a national monitoring network for ultrafine particles, are likely to continue 5 to challenge our ability to conduc t a quantitative assessment for ultr afine particles in the current 6 review. In the current review, we will consider whether new information on these areas of 7 uncertainty has become available since the la st review of the PM NAAQS that would be 8 sufficient to support quantitativ e air quality assessments of recent ambient conditions for PM 10-2.5 9 or ultrafine particles. If so, we will consider in the HREA Planning Document the degree to 10
which these ambient concentrations could be adequately ch aracterized using available data from 11 the national monitoring networks (o r other datasets in the case of ultrafine particles) to support 12
the HREA. 13
The 2010 HREA did not evaluate PM 2.5 composition differences quantitatively because 14 C-R functions for specific PM 2.5 components and sources had not b een identified at that time. 104 15 In the HREA Planning Document, we will consid er whether new information on C-R functions 16 for components and/or sources has become availa ble in the PM ISA for the current review and 17
could necessitate the char acterization of ambient PM 2.5 components and/or sources. If warranted 18 for the HREA for the current review, we would c onsider the degree to which measurements from 19
the CSN and IMPROVE networks described in Chapter 2 could be used to adequately 20
characterize PM 2.5 components or sources. 21

Approach for Adjusting PM Concentrations to Just Meet the Existing and Potential 22 Alternative Standard(s) 23 In order to estimate change s in health risks from just meeting the existing PM 2.5 standards, 24 and potential alternative standard (s) if appropriate, we would firs t need to adjust recent ambient 25
concentrations to reflec t the distribution of PM 2.5 concentrations in an urban area that could 26 correspond to these air quality scenarios. Since there are multiple combinations of emissions 27 profiles that could result in ju st meeting the current standard s or any potentia l alternative 28 standards, there are many possible scenarios of various spatially and te mporally distributed PM 2.5 29

103 For example, total particle number, solid particle num ber, active particle surface area, Brunauer–Emmett–Teller surface area, or mass of partic les in a certain size range.

104 However, the 2010 HREA indirectly considered PM co mposition differences by applying region- or city-specific effect estimates in modeling health risk s for short-term exposure to ambient PM 2.5
.April 2016 4-15 Draft – Do Quote or Cite concentrations that would correspon d to the target air quality scen arios. Given this fact, the 2010 1 HREA used multiple air quality adjustment approaches (i.e ., proportional, local, and hybrid 2 rollback) to estimate the eff ects on the dist ribution of PM 2.5 concentrations at monitors in an 3 urban study area of just meeting the then-existin g and alternative standards. Use of multiple 4 adjustment approaches enabled exploration of the sensitivity of risk resu lts to different spatial 5 patterns of PM 2.5 reduction, with the goal of larg ely bounding potential risks. 6 In the HREA Planning Document, we will cons ider whether it would be appropriate to 7 use additional or different approaches to adjus ting air quality concentrations including methods 8 based on results from chemical transport mode ling of national emission reduction scenarios. 9 These additional or different adju stment approaches would aim to improve the representation of 10

PM 2.5 reduction patterns over an area. If estimates of PRB concentrations are needed for the air 11 quality adjustments in the HREA , we would consider informati on provided in the PM ISA for 12 the current review. In selecting methods for air qu ality adjustment, we woul d consider the ability 13 of the approaches to repr esent the relationship between the annual and 24-hour NAAQS. 14 There is relatively limited information on PM 10-2.5 , specific PM components and sources, 15 or ultrafine particles compared with PM 2.5 to develop approaches for adjusting their 16 concentrations to meet the existing PM 2.5 standards and potential alte rnative standard(s), if 17 appropriate. We will consider in the HREA Planning Document the ability of various adjustment 18 approaches, including those based on statistical and ai r quality modeling rela tionships, to provide 19 reasonable estimates of adjusted concentrations for PM 10-2.5 , specific PM components and 20 sources, and ultrafine part icles, if warranted. 21

4.3.1.2 Factors to Consider in Designing any New Epidemiology-based Risk Assessment 22

 PM size fractions, components, and sources : We anticipate focusing any new quantitative 23 risk assessments primarily on PM 2.5 but will consider, to the exte nt sufficient air quality and 24 epidemiologic data become available in the PM ISA for the current review, characterizing 25 risks associated with PM 10-2.5 and ultrafine particles as well as risks associated with specific 26 PM components and/or sources. 27

 Health endpoints and health input data : For any quantitative risk assessment, we would 28 follow a multi-step process for each health e ndpoint considered. First, we would identify 29 those health endpoints that the PM ISA for the current review determines have either a 30 “causal” or “likely to be cau sal” relationship with PM exposure. Next, we would use 31 information from the PM ISA and the epidemio logic studies to specify C-R functions for 32 those health endpoints, including details on model form and associated effect estimates. Last, 33 we would obtain the necessary baseline incide nce and/or prevalence rate data for each 34 endpoint. These rates originate from a variety of sources and often reflect varying spatial 35 scales. 36April 2016 4-16 Draft – Do Quote or Cite  Exposure metrics: Similar to previous PM HREAs, we anticipate modeling health endpoints 1 associated with both short-term (24-hour aver age) and long-term (annual average) exposure 2 depending on the epidemiologic study data av ailable in the PM ISA for this review. 3 Furthermore, for short-term exposure-related endpoints, we could consider whether to 4 differentiate risk estimates th rough application of seasonally di fferentiated effect estimates 5 paired with seasonal mortality rates, if available. 6

 Spatial scale of the analysis : Based on the epidemiologic studies available in the PM ISA for 7 the current review and the available air quality monitoring data, we would anticipate 8 analyzing a set of study areas in detail and applying effect estimates specific to each study 9 area. We would also antici pate adjusting recent PM 2.5 concentrations to just meet the existing 10 and, if appropriate, potential alternative standard(s), in each urban area, including 11 consideration of various adju stment approaches (e.g., proporti onal rollback). In addition, we 12 will consider whether a national-scale analysis of risk for recent ambient concentrations 13 (such as completed in the 2010 HREA) is useful for evaluating the representativeness of the 14 study areas. We will also consider whether to estimate risk reductions at the national-level 15 from just meeting potential alternative standa rd level(s), if any. However, adjusting air 16 quality can be more challenging at broader regi onal or national scales than at the urban study 17 area scale. We anticipate that any national-level estimates, if generated, would supplement 18 the higher confidence risks esti mated for the study areas. 19

 At-risk populations and lifestages : Based on information from the PM ISA, we would 20 consider whether data would be sufficient to ge nerate more refined risk estimates for these 21 populations groups, including whethe r effect estimates and baseline incidence rates for these 22 at-risk populations and life stages are available. 23

 Risk metrics : The 2010 HREA quantified risks using se veral risk metric s, including (a) 24 PM 2.5 -related incidence (for both morbidity and mort ality endpoints), (b) PM 2.5 -related 25 incidence per 100,000 exposed indivi duals, representing a standardiz ed risk metric that can 26 be readily compared across urban study areas, (c) percent of baseli ne incidence attributable to 27 PM 2.5 exposure, and (d) percent re duction in PM-related risk from just meeting the then28 existing and alternative standard levels. We an ticipate including similar risk metrics in any 29 new risk assessment, and we will consider including some additional risk metrics based on 30 information from the PM ISA to more fully characterize PM-related mortality risk. For 31 example, we may consider metrics that charact erize person-level risk, such as life years 32 gained (from just meeting the existing and potentia l alternative standard(s), if any), life years 33 lost (from exposure to recent PM concentratio ns), and/or estimati on of population-level 34 changes in life expectancy. 35

 Differentiating risk estimates by PM concentration : Based on information from the PM ISA, 36 we would consider whether it would be appr opriate and informative to differentiate the 37 magnitude of risks or overall confidence in risk estimates for different concentration ranges. 38 Such an analysis could reflect, among other factors, reduced confidence in specifying C-R 39 functions at lower PM concentrations where less data exist. For such an analysis, we would 40 explore methods such as (a) bi nning risk estimates into cate gories of confidence based on 41 data available for C-R functions including differences in the size of standard errors at various 42April 2016 4-17 Draft – Do Quote or Cite PM concentrations, and (b) using other types of evidence (clinical and/ or toxicological) to 1 differentiate risk estimates semi-quantitatively within specified PM 2.5 concentration ranges. 2

 BenMAP-CE : Consistent with the HREA conducted for the last ozone NAAQS review (U.S. 3 EPA, 2014), we anticipate using the environmen tal Benefits Mapping and Analysis Program 4 – Community Edition (BenMAP-CE) (U.S. EP A, 2015), the EPA’s GIS-based computer 5 program for the estimation of health impact s associated with changes in air pollution. 105 6 BenMAP-CE draws upon a database of population, baseline incidence and prevalence, and 7 effect estimates to automate th e calculation of health impacts. 106 In addition, BenMAP-CE 8 can utilize standard errors from th e effect estimates to generate 95 th percentile confidence 9 intervals around point estimates . These confidence intervals reflect the statistical fit 10 (precision) of the underlying epidemiologic mode ls, assuming that the form of the model is 11
correct. 12

4.3.1.3 Characterization of Sources of Uncertainty and Consideration of Information Newly 13 Available in this Review 14 As described above, the 2010 HREA primarily us ed sensitivity analys es (including both 15 single and multi-factor) to evaluate the impact of uncertainty in sp ecific input factors on the risk 16 estimates, while a probabilistic analysis (i.e., M onte Carlo) was used to cascade the impact of 17 standard errors in the effect estimates from epidemiologic studies into 95 th percentile confidence 18
intervals around the risk estimat es. Although Monte Carlo analyses could be used to reflect the 19 combined impact of multiple sources of uncertainty affecting the risk estimates, this type of 20 analysis would require informa tion not previously available, including the sp ecification of 21 defensible distributions of values for key i nputs and any potential corr elations between those 22 inputs. For an HREA in the current review, we anticipate relying on single and multi-factor 23 sensitivity analysis as the primary method for ch aracterizing the combined impact of uncertainty 24 from multiple key inputs on the risk estimates, although we will consider additional tools should 25 they become available. Based on information from the PM ISA for the current review, we would 26 anticipate conducting additional sensitivity analyses to better characterize un certainties related to 27 the specification of C-R functi ons (e.g., model specification, tr eatment of copollutants, and 28 treatment of lag for short-term exposure endpoints). 29

105 The BenMAP software and associated docu mentation are available for download at http://www2.epa.gov/benmap

. 106 As noted in section 4.2, the 2010 HREA used the TRIM model to estimate human health risks (U.S. EPA, 2010a). For subsequent NAAQS epidemiology-based risk assessments (U.S. EPA, 2014), we utilize BenMAP-CE, which provides a more efficient and fl exible platform for modeling PM-relatedhealth risk. For example, BenMAPCE allows users to readily conduct sensitivity analyses e xploring the impact of alternative modeling choices (e.g., effect estimates, thresholds, age ranges for target populations , units of spatial aggregation) on risk estimates.April 2016 4-18 Draft – Do Quote or Cite In designing an HREA for the current review , our goal will be to reduce and/or better 1 characterize the impact of the s ources of uncertainty identified in the 2010 HR EA to the extent 2 possible given available information. In addition, we would address any newly identified sources 3 of uncertainty. In Table 4-1 below, we identify several important sour ces of uncertainty and 4
discuss our considerations fo r potentially addressing these sources of uncertainty. These 5 strategies would be further descri bed in the HREA Planning Document. 6April 2016 4-19 Draft – Do Quote or Cite Table 4-1. Areas of Uncertainty Associated wi th Epidemiology-Based Risk Estimates and 1 Potential Strategies for Addressi ng these Sources of Uncertainty 2 Category of Uncertainty/

Limitation Description of Uncertainty/ Limitation in the Last Review Consideration of Information Newly Available in this Review Transferability of C-R functions from epidemiologic study areas to HREA urban study areas At times, the EPA applies effect estimates to urban study areas that were not included in the original epidemiologic study providing those effect estimates. This geographic extrapolation can introduce uncertainty into the risk estimates for those urban study areas. New epidemiologic studies in the PM ISA and other available data may provide additional perspective on which urban areas or regions are likely to have similar population-level responses to PM pollution and which are likely to have different responses. This information may guide decision-making regarding the transferability of effect estimates to broader geographic areas. Transferability of C-R functions from an earlier time period (in the epidemiologic study) to a more recent time period in the HREA Depending on the degree to which conditions associated with PM exposure and risk (e.g., population behavior and mobility, baseline health effects incidence rates, ambient urban PM profiles) changed over time, uncertainty may be associated with the temporal extrapolation of effect estimates. New epidemiologic studies in the PM ISA may provide additional perspective on the degree to which effect estimates vary (for the same geographic location) over time and hence the degree to which uncertainty associated with this type of temporal extrapolation of effect estimates may introduce uncertainty into the risk results. Use of composite monitors as exposure surrogates in the epidemiologic studies The 2010 HREA asserted that the exposure surrogate used in epidemiologic studies (i.e.., a single composite monitor representing an entire urban study area) could impact the magnitude of the effect estimates. New epidemiologic studies in the PM ISA may characterize the degree to which different spatial scales (used in defining exposure surrogates) introduce exposure measurement error, depending on the endpoint, location and pollutant being evaluated. Spatial heterogeneity in effect estimates in the epidemiologic studies In the 2010 HREA, effect estimates for short-term mortality and morbidity endpoints demonstrated considerable spatial heterogeneity. At that time, the EPA noted that this New epidemiologic studies in the PM ISA might provide information regarding which factors drive spatial heterogeneity in effectApril 2016 4-20 Draft – Do Quote or Cite Category of Uncertainty/

Limitation Description of Uncertainty/ Limitation in the Last Review Consideration of Information Newly Available in this Review heterogeneity could reflect a number of factors (e.g., differences in behavior across/within cities, PM compositional/source differences, different degrees of exposure
measurement error ). estimates. This information could help us to differentiate between effect estimates (and hence the risk estimates) in terms of overall confidence.

Shape and statistical fit of the C-R functions 107 There is uncertainty in the shape and statistical fit of the C-R functions, particularly at lower ranges of concentrations. Although the 2010 HREA applied linear C-R functions,these functions could have nonlinearities, thresholds or concentrations with reduced confidence in the effect estimate. New epidemiologic studies in the PM ISA could provide additional information regarding risk across the range of PM concentrations or possible non-linearities in the C-R function, particularly in lower PM concentrations where there tends to be less data. Greater data density at lower concentrations could also result in increased precision (and hence statistical fit) within that range. Lag structure in short-term exposure epidemiologic studies Different lags have varying degrees of association with a particular health endpoint, and it may be difficult to clearly identify the specific lag thatproduces the majority of a PMrelated effect. A lack of information regarding the specific lag(s) most associated with a particular health endpoint adds uncertainty into risk estimates for that endpoint. For short-term mortality, the 2010 HREA used an average of 0 and 1-day lags, and other lags, where available, were considered in sensitivity analyses. New epidemiologic studies in the PM ISA could provide additional information regarding the lag structure most strongly associated with specific health endpoints.

107 The term "statistical fit" as used here indicates the pr ecision of a statistical model for capturing the observations. It can be influenced by a variety of factors, including exposure measurement error, sample size, and control for confounders.April 2016 4-21 Draft – Do Quote or Cite Category of Uncertainty/

Limitation Description of Uncertainty/ Limitation in the Last Review Consideration of Information Newly Available in this Review Single pollutant models versus copollutant models Ozone and other ambient copollutants may confound effect estimates associated with PM. New epidemiologic studies in the PM ISA could provide additional information regarding potential confounding by copollutants. Single-city versus multi-city epidemiologic studies For long-term exposure mortality, the 2010 HREA employed effect estimates from multi-city epidemiologic studies. For short-term exposure mortality, the 2010 HREA used a combination of single and multi-city epidemiologic studies, acknowledging advantages and disadvantages with both types of studies. New epidemiologic studies in the PM ISA could provide additional information regarding whether either type of study (or a combination of both) would be preferred in modeling specific endpoints. New single-city epidemiologic studies in the PM ISA could add confidence to the individual city risk results estimated using multi-city effect estimates. Historical PMexposure in longterm exposure studies Long-term epidemiologic studies suggest that different time periods of PM exposure can produce substantially different effects estimates. This can introduce uncertainty in identifying the exposure window is most strongly associated with an endpoint. New epidemiologic studies in the PM ISA could provide additional information regarding which exposure windows are most strongly associated with long-term exposure endpoints, recognizing potential measurement error linked to population mobility (within and between cities) over time. Differences in PM composition or

sources The composition of PM and overall pollution mixture can differ across urban study areas. If these compositional differences contribute to different effect estimates (i.e., heterogeneity), then substantial uncertainty may be introduced into the risk estimates if these compositional differences are not explicitly addressed. New epidemiologic, toxicological and clinical studies in the PM ISA could provide additional information regarding differences in PM composition, including whether there is sufficient evidence to model risk by applying differential effect estimates.April 2016 4-22 Draft – Do Quote or Cite 4.3.2 Exposure Assessment 1

As noted above, neither the 2010 HREA nor any prior review of the PM NAAQS 2 included a quantitative population-based, micr oenvironmental exposure assessment, largely 3 because of the uncertainties surrounding the pur pose of such an assessment and the insights it 4 could provide in better unders tanding PM-related health risk s beyond those provided using the 5 epidemiology-based approach. In the current revi ew, we will again consider whether to perform 6 an exposure assessment. In doing so, we will consider the extent to which the results of such an 7 assessment could be informative when interpreted in light of important uncertainties. Key factors 8 that we will consider when determining whethe r to perform an exposure assessment include our 9 technical ability to generate estimates of PM e xposure on temporal and spatial scales that would 10 be informative for the review, quantitative and qu alitative characterizations of uncertainties in 11 exposure estimates, and the availability in th is review of PM huma n exposure studies that 12 provide insight into the potenti al public health importance of particular PM exposures. 13
Unlike an epidemiology-based risk assessment that often uses composite ambient monitor 14 concentrations to represent generalized exposur e over an urban area (a s described in section 15 4.3.1), an exposure assessment could estimate th e magnitude, frequency, duration, and pattern of 16 exposures to PM concentrations, considering activity patterns and mi croenvironments. Such 17 quantitative assessments could range from a datasimplified analysis up to a modeled population18 based, microenvironmental exposure assessment. A detailed exposure assessment could provide 19 insight into the populations with the highest PM exposures. In addition, if available human 20 exposure studies provide a basis for identifying ambient-relevant PM exposure concentrations 21 that result in effects of poten tial public health concern, an exposure assessment could also 22 include a comparison of PM exposure estimates to the exposure concentrations shown to cause 23 such effects (i.e., an exposure benchmark analysis). 24

If a quantitative population-based, microenviron mental exposure assessment is warranted, 25 exposure calculations would re ly largely on measurements of ambient PM concentrations 26 potentially supplemented with information from air quality models a nd databases of daily 27 time/location/activity patte rns and personal attributes, as well as information on physical factors 28
that influence microenvironmen tal concentrations, exposures, and internal doses. Important 29 exposure factors include information on atmosphe ric chemistry and components of PM, temporal 30 and spatial distributions of air quality data, time spent in part icular microenvironments and at 31 varying exertion levels, and information on at -risk populations and lifestages. Such an 32 assessment, if warranted, would likely focus primarily on ambient-re lated exposures to PM 2.5 but 33 could consider, to the extent su fficient information becomes available in the PM ISA, exposures 34 associated with other PM size fractions and/or pa rticular PM components. If warranted, such an 35April 2016 4-23 Draft – Do Quote or Cite exposure assessment would build upon the informa tion presented in the PM ISA, could employ a 1 modeling approach recently used for other NAAQS reviews (Nitrogen Dioxide: U.S. EPA, 2008; 2 Sulfur Dioxide: U.S. EPA, 2009b; Carbon Mono xide: U.S. EPA, 2010c; Ozone: U.S. EPA, 3 2014), and would depend upon availa ble data and resources. 4
Section 4.3.2.1 below discusses factors to be considered in designing an exposure 5 assessment. Section 4.3.2.2 presents challenges in conducting such an assessment and sources of 6 uncertainty. These design factor s and strategies for reducing un certainties would be further 7 evaluated in the HREA Planning Document. In the HREA Planning Document, we will consider 8 whether these strategies, includ ing information from the PM ISA for the current review and 9 available air quality monitoring data, would provide sufficient c onfidence to move forward with 10 an exposure assessment and the associated ai r quality analyses in the current review. 11

4.3.2.1 Factors to Consider in De signing an Exposure Assessment 12

 Characterizing ambient PM concentrations . The air quality data used in exposure 13 assessments generally correspond to the finest spatial and temporal scales in ambient 14 concentrations that substantially infl uence important exposure metrics and 15 microenvironments of interest. 108 Developing highly resolved PM 2.5 concentrations from 16 existing monitoring and modeling data to s upport a population-based, microenvironmental 17 exposure would present a number of challenges , including adequately representing temporal 18 and spatial variability in concentrations at fi ne scales over urban ar eas with a variety of 19 microenvironments. The challenges would be greater for PM 2.5 components and/or different 20 PM size fractions, because less monitoring is available, gradients may be sharper, and 21 modeling may be less reliable for PM 2.5 components and different size fractions compared 22 with PM 2.5

. 23

 Exposure model : If a population-based, microenvironm ental exposure is warranted for 24 the current review, we woul d likely use the APEX model 109 to estimate exposures. APEX is a 25 probabilistic human exposure model that simula tes the movement of individuals through time 26 and space within a study area. Exposures ar e calculated in APEX by accounting for the 27 complete time series of exposure concentratio ns and doses as they occur in the simulated 28 individual (minute by minut e), and then typically, they are aggr egated to a metric of interest 29 at the individual level and summarized for the population simulated in the study area. APEX 30 can use any geographic frame of reference (e.g., census tract centroids, 1x1 km grid blocks) 31

108 For example, the temporal and spatial scales used in recent APEX simulations for ozone (U.S. EPA, 2014) were hourly concentrations at the census tract level, due to observed health effects resulting from 6-8 hour ozone exposures in controlled human exposure studies and the availability of comprehensive population demographics.

109 Additional information on APEX can be found at: http://www2.epa.gov/fera/human-exposure-modeling-airpollutants-exposure-model.April 2016 4-24 Draft – Do Quote or Cite and time period (e.g., minute, hourly) to repres ent ambient concentrations for calculating 1
exposures. 2

 Population exposures : An APEX-based exposure assessmen t could be designed to estimate 3 population exposures to ambient PM in urban st udy areas that repres ent a variety of study 4 groups of interest (e.g., at-risk populations). Such an assessment could evaluate the influence 5 of factors that contribu te to temporal/spatial patterns of PM concentrations (e.g., climatic 6 conditions) and variability in activity patterns an d microenvironmental concentrations. 7 Further, because APEX estimates both shor t-term and long-term exposures for each 8 simulated individual, we could determine the importance of short-term exposure variability 9 with respect to long-term cumulative exposur e, which could improve the understanding of 10 the relationship between short-term and long-te rm exposure health e ffects via their linked 11 exposure profiles. 12

 Ambient concentrations and human activity patterns : An APEX-based exposure assessment 13 can use ambient concentrations with a range of time or spatial scales, and we could design an 14 exposure assessment to focus on the scale of other APEX model inpu t data (e.g., population 15 demographics at the census tract level) a nd the exposure output of interest. The human 16 activity data used by APEX are drawn from the EPA’s Consolidated Human Activity 17 Database (CHAD; McCurdy et al., 2000; U.S. EPA, 2002). The CHAD includes data from 18 several surveys sampling at city, state, and na tional levels, including diaries of their daily 19 activities, locations visited, activities perfor med, time-of-day and their durations. We could 20 consider whether it would be info rmative to conduct a child-specific analysis that calculates 21 exposure for various lifestages ut ilizing activity pattern s and exposure parameters specific to 22 these lifestages. However, we note that we ar e currently unaware of exposure parameters for 23 early lifestages (age < 5), and th erefore such an analysis may not be feasible for this review. 24

 Microenvironmental exposure : An APEX-based exposure assessment estimates exposures 25 that individuals experience wh ile in indoor, outdoor, and insi de-vehicle microenvironments 26 using the ambient concen trations and other input variables specific to microenvironments. In 27 addition to drawing on information from the PM ISA for the current review to parameterize 28 these and other input variables, we could c onsider including specific microenvironments and 29 variables in other exposure model analyses (e.g., SHEDS-PM; Burke et al., 2001). Because 30 APEX has a flexible, probabilistic approach to estimating exposure and dose, we could 31 consider developing appropriate distributions representing variability and uncertainty for 32 various inputs (e.g., air exchange rates, d ecay rates, and physiological parameters). 33

 Spatial and temporal scope of exposure assessment : The overall scope of an exposure 34 assessment, if warranted, could focus on a subs et of urban study areas selected for the 35 epidemiology-based assessment. We could evaluate exposures asso ciated with the recent air 36 quality conditions and, if feasible and informativ e, evaluate exposures associated with just 37 meeting the existing and potential alternative stan dard(s), if any. We not e that there are likely 38 to be additional challenges and uncertainties associated with characterizing ambient PM 39 concentrations at high spatial and temporal resolution for just meeting the existing and any 40 potential alternative standard(s). 41

42April 2016 4-25 Draft – Do Quote or Cite 4.3.2.2 Characterization of Sources of Uncertainty and Consideration of Information Newly 1 Available in this Review 2 Conducting an exposure assessment for PM 2.5 using APEX presents a number of 3 challenges in obtaining the inputs for the model. In complete or uncertain model inputs result in 4 uncertainties in the estimated exposures. The pr imary limitations in input data for APEX are 5
listed in Table 4-2. Identification of available model inputs and data limitations is one of the first 6 steps in determining whether an APEX-based expo sure assessment is warranted for this review. 7 These considerations will be discussed, along with possible strategies for addressing the 8 uncertainties and limitations, in the HREA Planning Document. 9

Table 4-2. Uncertainties and Limitations to Input Data used by APEX to Estimate 10 Exposures 11

Category of Uncertainty/

Limitation Description of Uncertainty/ Limitation

Spatial variability of ambient PM 2.5 concentrations APEX requires spatially variable ambient concentrations in order to capture the spatial variation of exposure across the study area, and home/work differential exposures. The spatial resolution of other APEX inputs would be at a census tract level, so ideally tract-to-tract spatial variation of ambient PM 2.5 would be available for input to APEX. PM aerodynamic properties The aerodynamic properties of partic les affect indoor infiltration rates and deposited PM in differe nt lung regions. The breakdown into size fractions and density of the ambient PM 2.5 (which are input to APEX) are likely to be fairly uncertain.Near-road and insidevehicle exposures For some PM size fractions (e.g., PM 10-2.5 , ultrafine particles), the near-road and in-vehicle microe nvironments may be important contributors to high ambient-related exposures. How these concentrations might be characteri zed could have varying degrees of uncertainty depending on the data available or the approach taken. Activity pattern representativeness The extent to which the human ac tivity database (CHAD) provides a balanced representation of the popul ation being modeled will vary across simulated study areas. APEX c onstructs activity sequences to account for the effects of population demographics and local climate, though this adjustment procedure do es not fully capture all of the variability within an urban study ar ea that exists in the people's activities that actually reside in the study area. Also, the extent to which a particular at-risk population or lifestage group is represented by the complete range of CHAD diaries may be uncertain. Approach for developing longitudinal diary profile One limitation of the CHAD activit y pattern data used in our exposure model is that, on average, study participants provided less than two days of diary data. Thus , annual activity sequences of days for each simulated individual in APEX are a combination of diaryApril 2016 4-26 Draft – Do Quote or Cite Category of Uncertainty/

Limitation Description of Uncertainty/ Limitation

days from a single or multiple similarly related subjects (e.g., age, sex), generated using a statistical algorithm and appropriate linking variables (e.g., daily time spent outdoors). Pe rformance evaluations of the APEX algorithms have been limited by the small number of CHAD individuals having multiday diaries. Indoor air exchange rates (AER) Because people generally spend a significant amount of time indoors, AER are important in estimating exposures. APEX uses statistical distributions of AER th at account for regional variability and several temperature ranges and c onsiders separately the presence of mechanical and non-mechanical bu ilding ventilation, to the extent possible. One limitation is that it does not account for spatial differences that may exist in AER within an urban study area (e.g., based on differences in age of re sidence or building). In addition, while the set of existing AER di stributions were developed from measurement studies conducted in specific geographic areas in the U.S., they may not include all sp ecific study areas that could be selected for a population-based exposure assessment. 1



### 4.4 SCIENTIFIC AND PU BLIC REVIEW 2

The HREA Planning Document will be dist ributed to the CASAC for review and 3 provided to the public for review and comment. The document will be the subject of a review 4 with the CASAC at a public meeting or tel econference that will be announced in the Federal 5 Register . The EPA does not produce a final HREA Pl anning Document, but instead considers 6 CASAC recommendations and public comments in the design a nd when conducting the 7 quantitative assessments either in a new HREA or in updating or expanding the last assessment 8 as part of the PA. In either case, staff would prepare at least one draft of the assessment for 9 CASAC review and public comment. CASAC woul d review the document and discuss it at a 10 public meeting that would be announced in the Federal Register . Based on past practice, the 11 EPA expects that CASAC would summarize key a dvice and recommendations for revision of the 12
assessment in a letter to the EPA Administrato r. In revising any draf t HREA, the EPA would 13 take into account any such reco mmendations and also consider comments received from the 14 public, both at the meeting itself and directly in writing. A final assessment would then be made 15 available on an EPA website, with its public availability announced in the Federal Register

. 16April 2016 4-27 Draft – Do Quote or Cite 

### REFERENCES 1

Abt Associates Inc (2008). Environmental Bene fits Mapping and Analysis Program (Version 2 3.0). Bethesda, MD. Prepared for Environm ental Protection Agency, Office of Air 3 Quality Planning and Standards, Air Benef its and Costs Group. Research Triangle Park, 4 NC. 5 Byun, D., and K.L. Schere (2006). Review of the Governing Equations, Computational 6 Algorithms, and Other Components of the Mode ls-3 Community Multiscale Air Quality 7 (CMAQ) Modeling System. Applied Mechanics Reviews, 59, 51-77. 8 Burke, J., Zufall, M., Özkaynak, H. (2001). A popul ation exposure model fo r particulate matter: 9 Case study results for PM 2.5 in Philadelphia, PA. J Expos Anal Environ Epidemiol . 11: 10 470-489. 11 McCurdy, T.; G. Glen; L. Smith and Y. Lakkadi (2000). The National Exposure Research 12 Laboratory's consolidated human activity database. Journal Expos Anal Environ 13 Epidemiol. 10:566-578. 14 Samet (2009a). Letter from Dr. Jonathan M. Samet, Chair Clean Air Scientific Advisory 15 Committee, to Lisa P. Jackson, Administra tor U.S. Environmental Protection Agency 16 regarding “Consultation on EPA’s Particul ate Matter National Ambient Air Quality 17 Standards: Scope and Methods Plan for Hea lth Risk and Exposure Assessment.” May, 18 21, 2009. (letter in docket #EPA-HQ-OAR-2007-0492). 19 U.S. EPA (2002). Consolidated Human Activities Databas e (CHAD) Users Guide: Extracting 20 Human Activity Information from CHAD on the PC . Written for EPA National Exposure 21 Research Laboratory by ManTech Environmenta l Technologies. Modified in June 2002. 22 Available: https://www.epa .gov/sites/production/files/2015- 23 02/documents/chad_manual.pdf. 24 U.S. EPA (2004). Air Quality Criteria fo r Particulate Matter . U.S. EPA, National Center for 25 Environmental Assessment, Office of Resear ch and Development. Research Triangle 26 Park, NC, EPA/600/P-99/002aF and EPA/600/ P-99/002bF. October 2004. Available: 27 http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_cr_cd.html

. 28 U.S. EPA (2009a). Integrated Science Assessment (ISA) for Particulate Matter (Final Report)

. 29 U.S. EPA, National Center for Environmen tal Assessment, Office of Research and 30 Development. Research Triangle Pa rk, NC. December, 2009. EPA/600/R-08/139F. 31 Available at: http://cfpub.epa.gov/ncea/cfm/r ecordisplay.cfm?deid=216546

. 32 U.S. EPA (2011). Policy Assessment for the Review of th e Particulate Matter National Ambient 33 Air Quality Standards . U.S. EPA, Office of Air Qu ality Planning and Standards. 34 Research Triangle Park, NC, EPA 45 2/R-11-003. April, 2011. Available at: 35 http://www.epa.gov/ttn/naaqs/st andards/pm/data/20110419pmpafinal.pdf

. 36 U.S. EPA (2008). Risk and Exposure Assessment to Support the Review of the NO 2 Primary 37 National Ambient Air Quality Standard . U.S. EPA, Office of Air Quality Planning and 38 Standards. Research Triangle Park, NC. EPA 452/R-08-008a/b. November 2008. 39 Available: http://www.epa.gov/ttn/naaqs/st andards/nox/s_nox_cr_rea.html

. 40April 2016 4-28 Draft – Do Quote or Cite U.S. EPA (2009b). Risk and Exposure Assessment to Support the Review of the SO 2 Primary 1 National Ambient Air Quality Standard. U.S. EPA, Office of Air Quality Planning and 2 Standards. Research Triangle Park, NC. July 2009. EPA-452/R-09-007. Available: 3 http://www.epa.gov/ttn/naaqs/standard s/so2/data/200908SO2REAFinalReport.pdf

. 4 U.S. EPA (2010a). Quantitative Risk Assessment for Particulate Matter – Final Rep ort. U.S. 5 EPA, Office of Air Quality Planning and St andards. Research Triangle Park, NC. EPA6 452/R- 10-005. June 2010. Available: 7 http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html 8 U.S. EPA (2010b). Particulate Matter Urban-Focused Vi sibility Assessment – Final Report

. 9 Office of Air Quality Planning and Standard s. Research Triangle Park, NC. EPA-452/R10 10-004. June 2010. Available: 11 http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html

. 12 U.S. EPA (2010c). Q uantitative Risk and Exposure Assessment for Carbon Monoxide – 13 Amended . U.S. EPA, Office of Air Quality Pla nning and Standards. Research Triangle 14 Park, NC EPA-452/R-10-009. July 2010. Available: 15 http://www.epa.gov/ttn/naaqs/standa rds/co/data/CO-REA-Amended-July2010.pdf

. 16 U.S. EPA (2014). Health Risk and Exposure Asse ssment for Ozone, Final Report . U.S. EPA, 17 Office of Air Quality Planning and Standard s. Research Triangle Park, NC. EPA-452/R18 14-004a. August 2014. Available: 19 http://www.epa.gov/ttn/naaqs/standa rds/ozone/data/20140829healthrea.pdf

. 20 U.S. EPA (2015). BenMAP-CE User’s Manual Appendices . U.S. EPA, Office of Air Quality 21 Planning and Standards. Research Triangle Park, NC. Available: 22 http://www2.epa.gov/benmap/manual-and-appendices-benmap-ce 23 World Health Organization (2008). Part 1: Guidance Document on Characterizing and 24 Communicating Uncertainty in Exposure Asse ssment, Harmonization Project Document 25 No. 6. Published under joint sponsorship of the World Health Organization, the 26 International Labour Organization and th e United Nations Environment Programme. 27 WHO Press, World Health Organiza tion, 20 Avenue Appia, 1211 Geneva 27, 28 Switzerland (tel.: +41 22 791 2476). 29April 2016 5-1 Draft – Do Quote or Cite 

## 5 WELFARE-RELATED RISK AND EXPOSURE 1 

## ASSESSMENTS 2



### 5.1 INTRODUCTION 3

Within the context of NAAQS reviews, a quantitative welfare risk and exposure 4 assessment (WREA) is designed to estimat e exposure and risks to public welfare 110 associated 5 with the existing secondary standards and with poten tial alternative secondary standard(s), if any, 6 that might be appropriate to consider. This a ssessment can inform conclusions on the adequacy 7 of the public welfare protection provided by these standards. The purpose of this chapter is to 8 highlight key findings from the quantitative risk assessments conducted in the last review of the 9 PM NAAQS and to identify key issues to be addressed in planni ng for any additional 10 quantitative assessments that might be warrant ed for the current review. The scope of any 11 WREA would be informed by the scientific ev idence in the upcoming PM ISA; existing and 12 historical air quality patterns and trends; the av ailability of improved data, methods, tools, and 13 models that may better characterize important un certainties or provide additional insights beyond 14 those provided by previous assessm ents; and available resources. 15
In the last review of th e PM NAAQS, the quantitative welfare assessments focused 16 primarily on urban visibility and were presente d in the Urban-Focused Visibility Assessment 17 (2010 UFVA, U.S. EPA, 2010b) and the Policy Assessment (2011 PA, U.S. EPA, 2011). The 18 EPA did not conduct quantitative assessments for other welfare-related effects from PM (e.g., 19 ecological effects, climate eff ects, and materials effects). 111 20 In the upcoming WREA Planning Document (discussed in sections 1.2 and 1.5, above), 21 the EPA will evaluate the newly available inform ation within the contex t of the 2010 UFVA and 22 2011 PA analyses from the last review of the PM NAAQS to determine 1) the extent to which 23 important uncertainties may be better character ized by information newly available for the 24 current review and 2) the extent to which ne w information may affect the results of the 25 quantitative analyses from the last review in important ways or may suggest additional 26

110 Welfare effects as defined in CAA 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.”

111 The on-going NO X /SO X review includes consideration of the ecol ogical effects of eco system loading of particulate nitrogen and sulfur compounds. Thus, these endpoints are not discussed in this review.April 2016 5-2 Draft – Do Quote or Cite quantitative analyses that can improve our unde rstanding of the welfar e exposures and risks 1 associated with PM, including consideration of welfare effects beyond visibility impairment. The 2 WREA Planning Document will al so include a preliminary determ ination of whether a distinct 3 WREA document would be needed. CASAC advice and public comments on this draft IRP will 4 be considered in developing the WREA Planni ng Document, which will also be subject to 5 CASAC review and will be made available for p ublic comment. If warranted, one or more drafts 6 of the WREA would then be prepared and rel eased for CASAC review and public comment prior 7 to completion of a final WREA. 8 Section 5.2 below describes the key analyses , findings and uncertainties from the last 9 review of the PM NAAQS. Section 5.3 describes the effect categories to be considered for 10 potential welfare assessments (i.e., visibility impa irment, ecological effects, climate effects, and 11 materials effects) that the EPA will further ev aluate in the WREA Planning Document. Section 12 5.4 describes the process for obtaining scientif ic and public review of the WREA Planning 13 Document and the WREA itself, if warranted. 14



### 5.2 SUMMARY OF WELFARE RISK AND EXPOSURE ASSESSMENT 15


### FROM THE LAST REVIEW 16

In the last review of the PM NAAQS, as summarized below, the EPA conducted 17 quantitative assessments of PM-rela ted visibility impairment in ur ban areas, recognizing that a 18 secondary PM NAAQS developed with an urba n focus would complement the EPA’s Regional 19 Haze Program, which focuses on Class I areas. 112 The purpose of these assessments was to 20 provide information and insights to help inform decisions on the secondary standards. As noted 21 above, these quantitative analyses were provided in two documents for the last review of the PM 22 NAAQS: the 2010 UFVA and the 2011 PA. The 2010 UFVA combined information from urban23 focused public preference studies, urban air qu ality data, and urban visibility protection 24 programs. The 2011 PA incorporated some additiona l air quality analyses and used more recent 25 air quality data. These assessments (described in section 5.2.1) in cluded evaluations of different 26 indicators, levels, averaging times, and forms for their appropriateness in the context of 27 measuring urban visibility impairment and its impacts on public welfare. 28

112 In 1977, Congress established as a national goal ‘‘the prevention of any future, and the remedying of any existing, impairment of visibility in mandatory Federal Class I areas which impairment results from manmade air pollution’’, CAA section 169(a)(1). Currently, 156 national parks and wilderness areas are designated as Class I areas. For more information regarding the EPA’s Regional Haze Program, please see http://www3.epa.gov/visibility/program.html

.April 2016 5-3 Draft – Do Quote or Cite As noted above (in section 5.1), in the last review of the PM NAAQS the EPA did not 1 quantify welfare risks for effects other than visibil ity impairment. At the time of the last review, 2 the Agency determined that any risks estimatedusing the limited data available for other PM3
related welfare effects would have uncertainties too large to provide r easonable and informative 4 results for the review. We discuss below (in secti on 5.2.2) the uncertainties identified in the last 5 review of the PM NAAQS regarding a dditional PM-related welfare effects. 6

5.2.1 Quantitative Assessments of Urban Visib ility Impairment in the Last Review 7

5.2.1.1 Reanalyses of Public Pr eference Survey Studies 8 The 2010 UFVA included a detailed reanalysis of the available urban visibility 9 preference studies. These studies are surveys de signed to elicit informa tion about the public’s 10 preferences regarding visibility impairment by as king participants to rate the acceptability or 11 unacceptability of a haze-obscu red scene from each urban area. Each of these studies 12 investigated the same question, “What level of vi sibility degradation is acceptable?” The studies 13 available for the last review of the PM NAAQS were composed of three completed western 14 urban visibility preference survey studies plus a pair of smaller focus studies designed to explore 15 and further develop urban visibil ity survey methods. The three we stern studies included one in 16 Denver, Colorado (Ely et al., 1991), one in the lower Fraser River valley near Vancouver, British 17 Columbia, Canada (Pryor, 1996), and one in Phoenix, Arizona (BBC Research & Consulting, 18 2003). A pilot focus group with 9 participan ts was conducted in Washington, DC (Abt 19 Associates, Inc., 2001), and a replicate study w ith 26 participants was also conducted for 20 Washington, DC (Smith and Howell, 2009). When taken together, thes e studies included 21 acceptability ratings regardi ng visual air quality (VAQ) 113 from a total of 852 individuals. 22 The approaches in the four studies were a ll derived from the method first developed for 23 the Denver urban visibility study. Although the appro aches used in the four preference studies 24 were similar, the specific mate rials and methods used in each study introduced uncertainties to 25 be considered when interpreting the results of the comparison of the studies. Key differences 26

113 VAQ is defined as the visibility effect caused solely by air quality conditions and excluding those associated with meteorological conditions like fog and precipitation. It is commonly measured as either light extinction (in terms of inverse megameters, Mm -1 ) or the haziness index (in terms of deciview, dv) (Pitchford and Malm, 1993). The deciview scale was developed for use in visibility perception studies because it has a more linear relationship to perceived changes in haze compared with light extinction. A dv is defined as te n times the natural logarithmic of one tenth of the light extinction in Mm -1 (Pitchford and Malm, 1993).April 2016 5-4 Draft – Do Quote or Cite between the studies include the following: 1) scene characteristics; 2) image presentation 1 methods (e.g., projected slides of actual phot os, projected images generated using WinHaze 114 or 2 use of a computer monitoring screen); 3) number of participants in each study; 4) participant 3 representativeness of the general populations of the relevant metropolitan area; and 5) specific 4 wording used to frame the questions used in the group interview process. 5 Given the similarities in the approaches used in the preference studies, the EPA used 6 regression analysis to reanalyze the results of the preferences studies individually and in 7 combination. Specifically, the 2010 UFVA used a l ogit model to develop response curves that 8 depicted the percentage of par ticipants in each study that rated the VAQ (measured in dv) as 9 either “acceptable” or “unacceptabl e”, for each of the visual images presented for a given area. 10 The 2010 UFVA adopted the “50% acceptability” criterion from the Denver preference study 11 (Ely et al., 1991), which identi fies the inflection point along th e response curve above which the 12 visibility impairment of the scenes was found un acceptable by at least 50% of the participants 13 and below which the level of VAQ in the imag es was found acceptable by at least 50% of 14 participants, as a useful index for co mparing the results across studies. 15
These results were used to identify similaritie s in public preferences regarding VAQ and 16 to inform the range of candidate protection levels (CPLs) 115 in the 2010 UFVA and the 2011 PA. 17 Specifically, the 2010 UFVA used the 50 percent accepta nce criteria from each of the four urban 18 preference studies to identify the range of CPLs from 20 dv to 30 dv, with a midpoint of 25 19
dv. 116 These values bracketed the daytime urban li ght extinction conditions that were judged 20 unacceptable by 50 percent of the participants in the preference studies for those urban scenes, 21 and provided low, medium, and high cut-points fo r use in the remaining assessments (U.S. EPA, 22 2010b, pp. 2-28 to 2-29). 23

5.2.1.2 Analyses of Visibility Conditions 24 Building on prior reviews of the PM NAAQS , in the last review the EPA conducted 25 quantitative analyses to further characteri ze ambient PM conditions in terms of PM 26

114 The WinHaze model (Molenar et al., 1994) uses image processing technology to apply user-specified changes in light extinction values to the same base photograph with set scene and lighting characteristics.

115 The term CPL refers to the target le vels of visibility within a range that the EPA staff deemed appropriate for consideration that could, in conjunction with other elements of th e standard, including indi cator, averaging time, and form, potentially provide an appropriate degree of visibility protection.

116 For comparison, 20 dv, 25 dv, and 30 dv are equivalent to 64, 112, and 191 Mm -1 , respectively.April 2016 5-5 Draft – Do Quote or Cite concentrations and light extinction in 15 urban study areas. Analyses of visibility conditions 1 were conducted as a part of the 2010 UFVA and the 2011 PA. Analyses in the 2010 UFVA 2
evaluated calculated PM 10 light extinction and were expa nded in the 2011 PA to evaluate 3
calculated PM 2.5 light extinction. 117 4
The 2010 UFVA focused on calculated PM 10 light extinction as the indicator for the 5 quantitative assessments based on the data colle cted from the IMPROVE network (as described 6 in section 2.3 above) and the requirements of the EPA’s Regional Haze Program (U.S. EPA, 7 2009a, sections 9.2.3.2 and 9.2.3.4). These assessments used a combination of several datasets 118 8 as inputs into the IMPROVE algorithm 119 to estimate the daily maximum 1-hour PM 10 light 9 extinction using data from 2005 to 2007. The goals of these air quality assessments were to: 1) 10 improve understanding of the extent, patterns, and causes of PM-related impairment of urban 11 visibility during daylight hours; 2) create the basis for projections of PM 2.5 mass and PM 10 light 12 extinction under potential alternative standard scenarios; an d 3) examine the correlation between 13

PM 10 light extinction and potential a lternative indicat or(s) based on PM 2.5 mass concentration 14 (U.S. EPA, 2010b, chapters 3, 4, and Appe ndix D; U.S. EPA, 2011, Appendix F). 15 The 2011 PA contained additional air qual ity analyses in order to estimate PM 2.5 light 16
extinction. PM 2.5 is the size fraction of PM responsible for the visibility impairment in most 17 urban areas, and the methods for estimating PM 2.5 light extinction were simpler than the methods 18 used in the 2010 UFVA for estimating PM 10 light extinction. Benefits of moving to a simpler 19 approach included: 1) more transparency in the required calculations; 2) less intensive data 20 processing; 3) an increase in the number of monitoring sites that could meet the data 21 requirements of the approach without adding sampling equipment or additional laboratory 22

117 Analyses in the 2010 UFVA and 2011 PA used the same 15 urban study areas as the 2010 HREA: Tacoma, Fresno, Los Angeles, Phoenix, Salt Lake City, Dallas, Housto n, St. Louis, Birmingham, A tlanta, Detroit, Pittsburgh, Baltimore, Philadelphia, and New York. Collectively, these 15 study areas comprised 31 counties.

118 Several datasets were combined for the 2010 UF VA analysis: 1) continuous hourly averaged PM 2.5 mass concentrations and relative humidity; 2) 24-hour average filter measurements for PM 2.5 composition; 3) hourly daylight PM 2.5 components generated using the Community Multi-s cale Air Quality modeling system (CMAQ); and, 4) estimated/measured hourly PM 10-2.5 concentrations (U.S. EPA, 2010b, section 3). The resulting estimates of hourly averaged PM 2.5 component concentrations, PM 10-2.5 mass concentration, and the measured relative humidity were used in the IMPROVE algorithm to estimate hourly PM 10 light extinction to be calculated for daylight hours with relative humidity no greater than 90 pe rcent (U.S. EPA, 2010b, section 3.2, 3.3).

119 The IMPROVE algorithm is based on data generated at monitoring sites in the IMPROVE network to estimate light extinction as a function of PM concentrations and re lative humidity levels. For more detailed information on the IMPROVE algorithm, see section 9.2.2.2 of the 2009 PM ISA (U.S. EPA, 2009a). As noted above (in section 2.2.2), there is both an original and revised version of the IMPROVE algorithm (Pitchford et al. 2007). The revised version was developed to address observed biases in rural areas under certain light extinction conditions.April 2016 5-6 Draft – Do Quote or Cite analysis; and 4) an increase in the number of days per year for which the calculation of PM light 1 extinction could be conducted (U.S. EPA, 2011, Appendix F). 2 The quantitative analyses of visibility condi tions can be considered as two distinct 3 analyses, covering recent conditions and adjustments to just meet the existing standards. The first 4 analysis presented in both the 2010 UFVA and the 2011 PA characte rized the recent visibility 5 conditions in the 15 urban study areas. However, the 2010 UFVA focused on PM 10 light 6 extinction using monitoring data from 2005 to 2007, whereas the 2011 PA focused on PM 2.5 light 7 extinction using monitoring data from 2007 to 2009. The estimates of the percentage of daily 8 maximum hourly PM 2.5 light extinction values exceeding the CPLs from the 2011 PA were 9
somewhat lower than for the PM 10 light extinction values fr om the 2010 UFVA. However, the 10 patterns of the estimates across the 15 urban stud y areas were similar. Specifically, 13 of the 15 11 urban study areas in the 2011 PA (with the exception of two Texa s and non-California western 12 urban study areas) were estimated to have exceed ed the high CPL (30 dv) from about 10 to 50 13 percent of the days based on the PM 2.5 light extinction analysis, while all 15 urban study areas 14 were estimated to exceed the low CPL (20 dv) from 10 to 90 percent of the days (U.S. EPA, 15 2011, pp. 4-29 to 4-30). 16 The second analysis characterized visibility conditions adjusted to just meet the existing 17 secondary standards. This adjustment applied a proportional rollback approach that uniformly 18
reduced all PM 2.5 components to just meet the target levels (with a lower bound on potential air 19 quality adjustments at PRB). For PM 2.5 light extinction in the 2011 PA, the analysis was 20 designed to assess the likelihood that PM-related visibility impairment would exceed CPLs upon 21 just meeting the suite of secondary PM 2.5 NAAQS (15.0 μg/m 3 annual and 35 μg/m 3 24-hour 22 (98 th percentile form)) (U.S. EPA, 2011, p. 4-33). 120 The PM 2.5 light extinction was estimated in 23 terms of both daily maximum 1-hour average valu es and multi-hour (i.e., 4-hour) average values 24 for daylight hours (U.S. EPA, 2011, p. 4-33). 121 When adjusted to just meet the existing 25 standards, the daily maximum 1-hour average PM 2.5 light extinction values in a majority of the 26 urban study areas were estimated to show im provement across the CPLs (U.S. EPA, 2011, 27 Figures 4-4 and 4-7, Tables 4-3 and 4-6). Similar patterns of vi sibility improvement were also 28

120 The 2010 UFVA included additional analyses characterizing visibility conditions on PM 10 light extinction after adjustments to just meet an al ternative suite of secondary PM 2.5 standards (i.e., 12.0 μg/m 3 annual and 25 μg/m 3 24- hour) (U.S. EPA, 2010b).

121 As mentioned in section 2.2.2, the EPA focused on sub-daily averaging times as the relevant exposure periods for segments of the viewing public due to the short-term natu re of the perception of PM-related visibility impairment.April 2016 5-7 Draft – Do Quote or Cite shown with daily maximum 4-hour average PM 2.5 light extinction values (U.S. EPA, 2011, 1 Figure 4-8, Appendix G, Figure G-3). 2

5.2.1.3 Key Uncertainties in the 2010 UFVA and 2011 PA 3

 Visibility Preferences : In the last review of the PM NA AQS, a number of uncertainties were 4 identified with respect to the public prefer ence studies. There was substantial variability 5 between studies in the range of visibility cond itions that were judged by study participants to 6 be “unacceptable” (U.S. EPA, 2010, Chapter 2). The relative importance of the degree of 7 visibility impairment (e.g., li ght extinction level) versus the frequency and duration of 8 visibility impairment in preference studies was unclear. Additionally, differences in the 9 strength of preference for visi bility conditions across the stud y areas (e.g., why visibility 10 impairment that is acceptable in one area is not acceptable in another area) were not well 11 understood. Moreover, the value of visibility in the preference studies is not distinctly 12 defined beyond acceptable or unacceptable, and consideration of other metrics of valuing 13 visibility may be needed. A better understanding of the reasons for differences in preferences 14 across studies, differences in preference in different urban study ar eas, and alternative 15 measures of acceptable visibility impairments co uld influence the interpretation of the results 16 in defining additional or alternative range of CPLs for visibility impairment. 17

 Calculation of Visibility Conditions : In the last review of the PM NAAQS, a number of 18 uncertainties were identified regarding the es timation of recent visibility conditions and 19 adjustments to just meet alte rnative scenarios. Calculated light extinction estimates have 20 uncertainties compared to directly measured PM light extinction. A nu mber of uncertainties 21 were identified with the inputs for the IMPR OVE algorithm, including the use of measured 22 or estimated PM concentrations and components and the influence of re lative humidity in the 23 IMPROVE calculations. The methods used to temporally apportion 24-hour PM 2.5 24 components to calculate hourly-averaged values relied on monthly-averaged PM 2.5 25 component variations from chemical transpor t modeling. The mass balance method used in 26 this modeling to estimate organic carbon c oncentrations and the loss of nitrate was 27 considered to be a reasonable approach but is not likely to be precise. Moreover, the 28 IMPROVE algorithm was designed for use under th e Regional Haze Program, which applies 29 in rural areas, and the algorithm has not been va lidated for urban areas. Uncertainties remain 30 with respect to the timeframe (e.g., 1-hour , 4-hour, 24-hour) for evaluating visibility 31 conditions, particularly given th at the public preference studies did not provide insight on the 32 frequency or duration of visibility impairment that would be acceptable. In addition, the 33 rollback approach uniformly reduced all non-PRB PM 2.5 components, but emission control 34 programs in practice would not like ly operate in this manner. 35

5.2.2 Consideration of Quantitative Assessmen ts for Additional PM-related Welfare 36
Effects in the Last Review 37

Based on the determination in the 2009 PM ISA (U.S. EPA, 2009a) that there was a 38 “causal” relationship between PM a nd effects on visibility, climate, and materials, as well as a 39 “likely to be causal” determination with ecol ogical effects, the 2009 Scope and Methods Plan 40 (U.S. EPA, 2009c) considered whet her adequate evidence was avai lable to conduct quantitative 41April 2016 5-8 Draft – Do Quote or Cite assessments for each of these categories of effect s. This Plan also noted that the chemical 1 components of PM (to a greater extent than PM mass or size fraction) largely determine the 2 nature, degree, and direction of the non-visibility welfare effects. After a careful evaluation of 3 these categories of effects, the EPA determined in the 2009 PM Scope and Methods Plan that 4 data were not available to conduct quantitative assessments for non-visibili ty welfare effects in 5 the last review, including the following: 6

 Ecological effects from deposition of particulate organics and metals : Data to link PM 7 toxicity to ecosystem function effects were available for only one tree species, and limited 8 data on other species hindered additional analys es. Toxic effects of some PM components on 9 plant leaves and soil were not well-charact erized and it was difficult to isolate these 10 endpoints from other environmental stressors. A lack of data on the site-specific composition 11 of PM and soil-associated biota prevented qua ntitative analysis of population shifts from 12 deposited PM. A lack of data on bioavailabil ity of PM components and uncertainties in 13 cumulative exposure effects prevented quantitative analysis of PM metal toxicity to biota. 14 Data on PM components were only available fo r a few urban areas. Data were unavailable 15 regarding seasonal composition of near roadway PM and trophic transfer to animals that 16 forage on roadsides. 17

 Climate effects : Representation of aerosols in climate models was needed to more accurately 18 predict changes in climate. Complex interact ions of aerosols and li nkages between clouds 19 and the overall climate system limited the feasib ility of conducting a quantitative analysis. 20 Insufficient data on local and regional microclim ate variations for many regions of the U.S. 21 and heterogeneity of cloud formations limite d the feasibility of conducting a quantitative 22 analysis. 23

 Materials effects : New evidence was not sufficient to conduct a quantitative assessment of 24 materials damage or soiling from PM deposition onto surfaces. 25

26


### 5.3 CONSIDERATION OF POTENTIAL QUANTITATIVE 27


### ASSESSMENTS FOR THIS REVIEW 28

The goals of a WREA in the current review w ould be to provide information relevant to 29 answering questions regarding the adequacy of the existing PM seconda ry standards and, if 30 appropriate, the potential improveme nts in public welfare that coul d be achieved from meeting 31 potential alternative standard(s). Any quantitat ive WREA for the current review would build on 32 the approaches used and lessons learned in th e last review and would focus on whether newly 33 available models, methods, tools, and data would substantially reduce the previously identified 34
uncertainties. 35

As described further in this section, any WREA for the current review would consider the 36 main categories of PM-related welfare effects (e. g., visibility effects, eco logical effects, climate 37April 2016 5-9 Draft – Do Quote or Cite effects, and materials) for which, in staff’s j udgment, there would be adequate information to 1 develop quantitative risk estimates that can meaningfully info rm the review of the secondary PM 2 NAAQS. These considerations will be describe d in more detail in the WREA Planning 3 Document. Preparation of the WREA Planning Docu ment will draw from the assessments of the 4 scientific evidence in the first draft PM ISA to facilitate the integration of policy-relevant science 5 into the planning document. In part icular, consideration of the avai lability of new data regarding 6
each of these effects as well as consideration of available resour ces to conduct such assessments 7 will influence whether we develop additional quantitative assessments in a new WREA. We 8 anticipate that any quantitative analys es, if warranted, could focus on PM 2.5 , but we would also 9
consider the extent to which information becomes available in the PM ISA for the current review 10 that could support quantitative analyses of PM components, PM 10-2.5 , or ultrafine particles. 11

5.3.1 Visibility Effects 12
As described above (in section 5.2), th e EPA conducted extensive quantitative 13 assessments of the impact of visibility impair ment on public welfare ba sed on public preferences 14 for VAQ and visibility conditions in 15 urban study areas in the 2010 UFVA and 2011 PA. The 15 goals of any new or additional quantitative assess ment for visibility w ould be to utilize newly 16 available information to address the key uncertaintie s identified in the last review regarding the 17 two key aspects of those analyses: visibility preference studies and air quality analyses. We 18
discuss both of these below. 19

In the last review, the EPA heavily relied on surveys of publ ic preferences regarding the 20 acceptability of various levels of urban VAQ. Quanti tative reanalysis of those survey results in 21 the 2010 UFVA informed the development of the ra nge of visibility CPLs (i.e., 20 to 30 dv). 22 Based on information discussed during the 2015 PM NAAQS kick-off workshop (79 FR 71764), 23 limited new evidence related to visibility preferen ces in urban areas has been identified in the 24
available literature. The WREA Pl anning Document will evaluate any new visibility preference 25
studies identified in the PM ISA for the cu rrent review to determine whether additional 26 quantitative assessments would be warranted. To the extent that additional urban preference 27 studies are identified in the PM ISA, we would consider whether an updated quantitative analysis 28 that considered any new information provided by the new studies would substantially change the 29 range of CPLs identified in the last review. If no additional visibi lity preference studies in urban 30 areas become available in this review, we antic ipate that the upcoming PA would continue to 31 rely upon the quantitative analyses of the preference studies available in the last review. In 32 addition, the PA would consider any additional information be yond preference studies that may 33April 2016 5-10 Draft – Do Quote or Cite become available in the PM ISA relevant to a ssessing adversity to publ ic welfare from urban 1 visibility impairment. 2 In addition, we would consider in the WR EA Planning Document whether providing 3 updated air quality assessments to include more recent PM monitoring data would substantially 4
reduce the uncertainties identified in the la st review of the PM NAAQS regarding the 5 characterization of recent visibility conditions and adjustment approaches to just meet the 6 existing standards. The determination whether to conduct additional quant itative assessments of 7 visibility conditions in the cu rrent review could depend on (1) whether updated information is 8 available in the PM ISA to warrant new air qua lity assessments, such as significantly updated 9 understanding of the variables that affect light ex tinction including relative humidity, PM species 10 composition, PM 10-2.5 data, or the IMPROVE algorithm (Pitc hford et al, 2007), and (2) whether 11 we determine that an updated r eanalysis of the preference studies would be warranted and would 12 substantially change the range of the CPLs identified in the last review (20 to 30 dv). New 13 quantitative air quality assessmen ts, if warranted, could also use more recent air quality 14 monitoring data, including data for PM concentrations and components to determine the extent to 15 which the existing secondary standards are adequate given recent ambient concentrations. For 16 example, such assessments could determine whether exceedances of the range of CPLs would be 17
estimated to occur under more recent ambien t conditions and under the existing secondary 18 standards, if warranted. 19
In the WREA Planning Document, we will consider any new data that have become 20
available in the PM ISA for the current review on preference studies a nd estimating visibility 21
conditions in order to determine whether conducti ng additional quantitative analyses on visibility 22 effects would meaningfully inform the curren t review of the secondary PM NAAQS. The EPA 23 may determine that certain quantitative assessments are more appropriate in a PA rather than in a 24
WREA. 25

5.3.2 Ecological Effects 26
As noted above, the EPA did not include a qua ntitative ecological risk assessment for any 27 prior reviews of the PM NAAQS. For the cu rrent review, we are considering whether 28
information would now be sufficient to conduc t a quantitative ecologi cal risk assessment 29 associated with deposition of PM, primarily part iculate organics and metals, including whether 30
information and data are now available to address the uncertainties identified in the last review 31 of the PM NAAQS that prohibited a quantitative ecological risk a ssessment. As noted above (in 32 section 5.2.2), these uncertainties included limited data to link deposition of PM organics and 33 metals to ecosystem functions and specific ecological receptors (e.g., soils, vegetation, and 34April 2016 5-11 Draft – Do Quote or Cite fauna) effects, and other site-spe cific data. In the WREA Planni ng Document, we would consider 1 whether any new information in the PM ISA for the current review substantially reduces the 2
uncertainties identified in the last review of the PM NAAQS. In particular, we would consider 3 any new information that 1) quantitatively elucid ates pathways of exposure, 2) quantitatively 4 characterizes ecological effects 122 from deposition of PM mass or PM components (e.g., specific 5 organic and metal PM) on ecological receptors, and 3) provides information sufficient to 6 quantify relationships between ambient PM, depos ited PM, specific ecologi cal effects, and, to 7 the extent feasible, associated ecosystem services. 8 The first step in potentially assessing ecol ogical effects associat ed with deposition of 9 organic and metal PM would requ ire the identification and quantification of the pathways of 10 exposure. Pathways of PM exposure for ecologica l receptors can include direct deposition to the 11 receptor surface via wet, dry or o ccult (e.g., fog) deposition, or transfer from one environmental 12 compartment (e.g., aquatic, terrestrial) or organi sm to another. The last review of the PM 13 NAAQS noted that the chemical constituents that make up PM (rather than PM mass) largely 14 determine the nature, degree, and direction of the ecological effects (U.S. EPA, 2009c, Appendix 15 A). The components that make up a given mass con centration of PM can vary substantially both 16 temporally and spatially, which would affect th e nature and magnitude of resulting ecological 17 effects. Uncertainty associated with heterogeneity in deposition of PM components, along with 18 significant data gaps, confounded ef forts to evaluate PM-related ecological effects on ecosystem 19 function at the ecosystem, regional, watershed, or national scale in the last review of the PM 20 NAAQS (U.S. EPA, 2009c, Appendix A). In the WREA Planning Document, we would evaluate 21
whether sufficient data have become available to estimate the spatial heterogeneity in site22 specific PM deposition (across and within ecosystems), partic ularly of organic and metal 23 components, and then to quantitatively link this deposition to ecological e ffects in various types 24 of ecosystems. 25 In the last review of the PM NAAQS, vege tation was shown to be sensitive to heavy 26 metal deposition (U.S. EPA, 2009c, Appendix A). For example, PM dry deposition to leaf 27 surfaces and the inner canopy is well documen ted (U.S. EPA, 2009a, section 3.3.4.3). Impacts on 28 vegetation from PM metal deposition include grow th suppression, toxicity to root colonizing 29 microorganisms, impairment of root developm ent and induction of phyt ochelatins (U.S. EPA, 30

122 As described above, the on-going NO X /SO X review includes consideration of the ecological effects of ecosystem loading of particulate nitrogen and sulfur compounds. Thus, these endpoints are not discussed in this review.April 2016 5-12 Draft – Do Quote or Cite 2009a, section 9.4.5.3). 123 However, the last review of th e PM NAAQS also noted that toxic 1 effects of some components of PM on plants are not well characterized, and it was difficult to 2 isolate these endpoints from other environmenta l stressors (U.S. EPA, 2009c, Appendix A). 3 Similarly, based on information discussed during the 2015 PM NAAQS kick-off workshop, 4
limited new evidence has been identified related to PM effects on vegetation, but most of those 5 plants were not native to the U. S. In addition, workshop participan ts also noted that new studies 6 and models are available to quantify the remova l of ambient PM by plants (e.g., air filtration by 7 dry deposition on leaves), but this is a distinct issue from quantifying how PM deposition affects 8 those plants (e.g., PM deposition on leaf surfaces that inhibits photosynthesis). In the WREA 9 Planning document, we would evaluate whether su fficient data and tools are available to apply 10 environmental modeling techniques to PM concen tration and deposition da ta to quantify the 11 responses in U.S. vegetation and the extent to which such information would provide additional 12 insight regarding how PM toxi city affects ecosystem functi oning considering the inherent 13 uncertainties in such approaches. 14
Information from the last review of the PM NAAQS indicated a variety of potential 15 adverse effects from PM deposition on soils (U .S. EPA, 2009a, section 9.4.5.2). For example, 16
PM effects on soil and soil-associated microfauna from heavy metals (such as zinc, copper, and 17 cadmium) have been shown to be toxic to soil fungi and bacter ia, which could have broader 18 implications at the ecosystem level because many plant species are dependent upon fungal and 19
bacterial associations to obtain nutrients from the rhizosphere (U .S. EPA, 2009a). Shifts in soil 20 microflora populations can also affect nutrient and organic matter cyclin g and carbon utilization. 21 In addition, vegetation can take up heavy metals from the soil, which could lead to effects on 22 wildlife and humans who consume those plants. Th ese effects were not quantified in the last 23 review of the PM NAAQS because of a lack of sufficient data. In the WREA Planning 24 Document, we could evaluate wh ether sufficient data now exist to quantify the site-specific 25 composition of PM deposition and the resulting p opulation shifts in soil-associated biota in 26 response to ecological stressors such as PM deposition. 27 The last review of the PM NAAQS indicat ed that fauna may also be an ecological 28 receptor for deposition of PM organics and meta ls through ingestion, absorption, trophic transfer, 29 transfer between aquatic to te rrestrial compartments, and bioaccumulation and biomagnification 30 of heavy metals across trophic levels (U.S . EPA, 2009a, section 9.4.5.6). However the last 31

123 Phytochelatins are intracellular metal-binding peptides th at act as specific indicators of metal stress (U.S. EPA, 2009a).April 2016 5-13 Draft – Do Quote or Cite review of the PM NAAQS noted that quantitative assessment of particulate metal toxicity to 1 biota was limited due to the heterogeneous compos ition of PM, lack of data on the bioavailability 2 of PM components, and uncertainties in cu mulative exposure effects (U.S. EPA, 2009c, 3 Appendix A). In the WREA Planning Document, we could consider whether new data and 4
information from the PM ISA in the current re view would provide sufficient information on the 5 effects of PM on aquatic and terrestrial inverteb rates, amphibians, birds and mammals to conduct 6 quantitative analyses of these ecological e ffects and associated ecosystem services. 7 In the WREA Planning Document, we coul d consider whether sufficient data have 8
become available in the PM ISA for the current review to conduct quant itative analyses on the 9 PM-related ecological risks to vege tation, soils, and fauna associated with PM deposition in light 10
of inherent uncertainties. A lthough we do not anticipate that sufficient information would 11 become available to reduce these uncertainties, if it did, we would give co nsideration to whether 12 conducting such quantitative analyses of PM-rela ted ecological risks and associated ecosystem 13 services would be practicable and would meaningf ully inform this review. If uncertainties and 14 data gaps prevent the EPA from conducting a quantitative ecological risk assessment for this 15 review, we anticipate that the upcoming PA would rely on information from the PM ISA 16 regarding PM-related ecological effects. 17

5.3.3 Climate Effects 18
As noted above, the EPA did not include a qua ntitative climate risk assessment for any 19 prior reviews of the PM NAAQS. The last review of the PM NAAQS noted that the addition of 20 anthropogenic aerosols 124 to the atmosphere perturbs the Earth’s energy balance and constitutes 21 an aerosol climate forcing (U.S. EPA, 2009c, A ppendix A). The influence of this forcing on 22 various climate metrics across a wide range of scal es is an active area of research, and studies 23
have identified both direct and in direct aerosol forcing pathways that can lead to effects on 24 climate (U.S. EPA, 2009a, section 9.3.1). Aeroso l direct effects on climate can occur when 25 changes in ambient aerosol pr operties (e.g., concentration, composition, and size distribution) 26 alter atmospheric radiative budgets by modifying the scattering and abso rption of radiation by 27 particles. Aerosol indirect effects on climate can occur when changes in aerosol properties alter 28 radiative budgets by modifying cloud amount, lifetime, and microphysical and radiative 29 properties. Aerosol indirect effects include the effects on clouds resul ting from the role of 30

124 As noted above (in section 2.2.1), the term aerosol is used in this document when discussing suspended ambient particles in the context of climate impacts.April 2016 5-14 Draft – Do Quote or Cite particles in the formation of cloud droplets and ice. An aerosol semi-direct effect can occur when 1 clouds are affected by changes in atmospheric pr operties (e.g., relative humidity and vertical 2 temperature structure) resulting from th e absorption of radiation by particles. 3
Recent climate assessments ch aracterize the current scientif ic understanding of aerosol 4 effects on climate (Bond et al., 2013; IPCC, 2014; National Climate Assessment, 2014), and we 5 anticipate that the evalua tion of climate evidence in the PM ISA for the current review would be 6 informed largely by findings of these major a ssessments. Improvements in measurements and 7 modeling of atmospheric aerosol properties are continually occurring and will contribute to the 8 understanding of aerosol effect s on climate in this review. For example, remote sensing 9 measurements from satellite systems a nd surface-based networks (e.g., AERONET 125 ) can 10 facilitate more advanced analys is of variables relevant to aerosol-climate interactions. We 11 anticipate that atmospheric models with improved algorithms will be available in this review to 12 better represent the inter actions of atmospheric particles w ith radiation and clouds and improve 13 the understanding of the role of aeros ols in global climate change. 14 However, our current understanding is that considerable uncertainty in the effects of 15 aerosols on climate still exists (Bond et al., 2013; IPCC, 2014). Large spatial and temporal 16 heterogeneities in direct and indi rect aerosol climate forcings occu r due to the variety of aerosol 17 sources, the intermittency of these sources, the shor t atmospheric lifetime of aerosols relative to 18 the major greenhouse gases, and the chemical a nd microphysical processing that occurs in the 19 atmosphere. These features lead to greater uncerta inty in quantitative estimates of the effect of 20 aerosols on climate relative to that of the major greenhouse gases. This uncertainty is especially 21 large at the local and regional scales in the U. S. that would likely be most relevant to a 22 quantitative assessment of the potential effects of a national PM standard on climate in this 23 review. In the WREA Planning Document, we will consider the extent to which information in 24 the PM ISA for the current review substantially reduces this uncertainty and whether information 25 and tools would be sufficient to quantify the loca l and regional effects from aerosols in this 26 review. Specifically, the WREA Planning Do cument will consider the extent to which 27 conducting a quantitative climate assessment woul d provide meaningful information for this 28 review beyond the information available in the PM ISA and the other major scientific 29 assessments and considering the inherent uncertain ties in such an assessment. For example, we 30 would consider whether a quantit ative assessment in the current review (1) could quantify how 31 the PM NAAQS alone would affect climate and (2 ) how changes in PM (via changes in the 32

125 See http://aeronet.gsfc.nasa.gov/April 2016 5-15 Draft – Do Quote or Cite standards) would result in change s to climate. If uncertainties suggest that it would not be of 1
value to the current review for the EPA to conduc t a quantitative climate risk assessment for this 2 review, we anticipate that the upcoming PA would rely on information from the PM ISA 3 regarding PM-related climate effects. 4

5.3.4 Materials Effects 5
As noted above, the EPA did not include a qua ntitative risk assessment on materials for 6 any prior reviews of the PM NA AQS due to a lack of data. PM -related materials effects are 7 generally classified into two categor ies: materials damage and soiling. 8 Materials damage associated with deposited PM, particularly sulfates and nitrates, 126 9 include the corrosion of metals, degradation of painted surfaces, deterioration of building 10 materials, and weakening of material components. Because of their electrolytic, hygroscopic, and 11 acidic properties and their ability to sorb corrosive gases, particles contribute to materials 12 damage by adding to the effect s of natural weathering proces ses. Deposited pollutants often 13 undergo chemical transformations and are commonl y oxidized to acids, leading to materials 14 damage particularly from reactions between materials and NOx and SO 2 . Wet and dry deposition 15
contribute to PM accumulation and surface dama ge, although the presence of moisture can 16 accelerate some materials damage (e.g., corrosion of metals). Generally, SO 2 is more corrosive 17 than NOx, but mixtures of SO 2 , NOx, and other PM components and species can corrode certain 18
metals at a faster rate than individual pollutants alone. In th e last review of the PM NAAQS, 19
sufficient evidence was not avai lable to conduct a quantitative assessment of PM-attributable 20 materials damage (U.S. EPA, 2004, 2009a, b). While ambient particles play a role in the 21 corrosion of metals and in the weathering of ma terials, no quantitative relationships between 22 ambient particle concentrations and rates of da mages had been established (U.S. EPA, 2009a). If 23
this information becomes available in the PM IS A, we would consider whether this information 24 would be sufficient to support a quantitative assessment for PM-a ttributable materials damage. 25 Deposition of PM onto surfaces, such as metal, paint, and stone, can lead to soiling. 26 Soiling is the result of PM accumulation on an ob ject that alters the optical characteristics 27 (appearance). The presence of PM may alter light transmission or change the reflectivity of a 28 surface. These soiling effects can impact the aesthe tic value of a structure or result in reversible 29

126 In the case of materials effects, it is difficult to is olate the effects of gaseous and particulate N and S wet deposition so both will be considered along with other PM-r elated deposition effects on materials in this review of the PM NAAQS.April 2016 5-16 Draft – Do Quote or Cite or irreversible damage to the surface. The pres ence of air pollution can increase the frequency 1 and duration of cleaning and can enhance biodeterioration processe s on the surface of materials. 2 For example, deposition of carbonaceous components of PM can lead to the formation of black 3 crusts on surfaces, and the bu ildup of microbial biofilms 127 can discolor surfaces by trapping PM 4 more efficiently (U.S. EPA, 2009a, p. 9-195). Add itionally, the organic or nutrient content of 5 deposited PM may enhance microbial growth on surfaces. However, in the last review of the PM 6 NAAQS, sufficient evidence was not available to conduct a quantitative assessment of PM7 attributable soiling effects (U.S. EPA, 2004, 2009a,b) . While soiling associated with fine and 8 coarse particles can result in increased cleaning frequency and repainting of surfaces, no 9 quantitative relationships between particle characteristics and the frequency of cleaning or 10 repainting had been established (U.S. EPA, 2011). Additionally, despite the limited new data in 11 the last review of the PM NAAQS on the role of microbial colonizers in biodeterioration 12 processes and contributions of black crust to soiling, these data were not sufficient for 13 quantitative analyses (U.S. EP A, 2011). Should new informati on about cleaning frequency and 14 repainting of surfaces and the role of microbial co lonizers in soiling effects become available in 15 this review, we would consider whether th is information would support a quantitative 16

assessment. 17 In the WREA Planning Document, we will consider whether sufficient data have become 18
available in the PM ISA for the current revi ew to conduct quantitativ e analyses on either 19 category of PM-related materials effects. If data gaps and uncertainties prevent the EPA from 20 conducting a quantitative materials effects assessment for this re view, we anticipate that the 21 upcoming PA would rely on information from the PM ISA regarding PM-related materials 22
effects. 23

5.3.5 Characterization of Sources of Uncertaint y and Consideration of Information Newly 24
Available in this Review 25
Table 5-1 summarizes the potentially important uncertainties related to the quantification 26
of PM-related welfare effects wh ere additional information, if available, could improve our 27 understanding of PM-related welfar e risks and/or reduce uncertain ties identified in the last 28 review of the PM NAAQS. To the extent that we would not be able to reduce these uncertainties 29 in the current review, the utility of conducting additional quantitative welfare assessments would 30

127 Microbial biofilms, primarily composed of fungi, can stain exposed rock surfaces with yellow, orange, brown, gray, or black colors.April 2016 5-17 Draft – Do Quote or Cite be limited. We will further discuss these issues , including whether additional information has 1 come available in the PM ISA for this review, in the WREA Planning Document. 2
Table 5-1 Areas of Uncertainty in the Welfar e Assessments and Potential Strategies to 3 Address Them 4

Major Uncertainty or Limitation Uncertainty/Limitation Remaining from Last Review Consideration of Information Newly Available in this Review

Variability in “acceptable” VAQ levels

across preference studies and urban areas There was substantial variability in the range of VAQ judged to be “acceptable” by the preference study participants across the urban areas studied. Limited studies and data were available to better inform our understanding of the factors leading to this variability. In addition, differences in the strength of preferences across urban areas were not well understood. If new preference studies are available in the PM ISA and include additional explanatory variables regarding this issue, we would consider whether in corporating these studies into another quantitative assessment of the preference studies would be warranted for this review.

Degree of visibility impairment

versus frequency and duration The relative importance of the degree of visibility impairment (e.g., light extinction level) compared to the frequency and duration of visibility impairment in the preference studies was unclear. If new preference studies are available in the PM ISA and include additional explanatory variables regarding this issue, we would consider whether in corporating these studies into another quantitative assessment of the preference studies would be warranted for this review. Recent visibility conditions Calculated estimates of PM light extinction have inherent uncertainties. For example, the IMPROVE algorithm uses measured or estimated PM concentrations and components, is influenced by relative humidity, and had not been validated for urban areas at the time of the last review. Limited hourly PM 10-2.5 monitoring, continuous PM 2.5 speciation monitoring, and direct measurement of PM 10 light extinction contributed to uncertainties in estimating the light extinction. In addition, the time frame for assessing visibility conditions was uncertain because the If a new quantitative analysis of visibility conditions is warranted for this review (i.e., based on the availability of new preference studies), we would evaluate whether new or different methods are available to reduce this uncertainty in characterizing PM 2.5 light extinction for recent conditions.April 2016 5-18 Draft – Do Quote or Cite Major Uncertainty or Limitation Uncertainty/Limitation Remaining from Last Review Consideration of Information Newly Available in this Review

preference studies did not provide insights on frequency or duration. Visibility conditions under existing and alternative standards The proportional rollback approach used to just meet the existing (and alternative) sta ndards uniformly reduced all PM 2.5 components, but emission control programs in practice would not likely operate in this manner. If a new quantitative analysis of visibility conditions under alternative scenario s is warranted for this review, we would evaluate whether new or different methods are available to reduce this uncertainty in estimating PM 2.5 light extinction upon just meeting the existing standards and, if appropriate, potential alternative standards under evaluation. Heterogeneity and data gaps in quantifying ecological effects Ecological effects from PM deposition on soils, flora, and fauna vary greatly depending on the specific PM component, theecosystem affected, and other sitespecific information. However, data were limited on PM components outside of urban areas (other than near specific point sources) and the associated ecosystem responses from deposition of metals and organics. If studies and data become available in the PM ISA to sufficiently reduce the uncertainties associated with quantifying the ecological effects, we would consider whether this new information would be sufficient to warrant a quantitative ecological assessment for this review.

Aerosols in climate models and local/regional variability Improved representation of aerosols in climate models is essential to more accurate predictions of the role of PM in climate forcing. Most climate model simulations available did not consider lo cal variations in climate forcing due to emissions sources and local meteorological patterns. If the PM ISA provides an improved understanding of the local and regional effects of aerosols on climate, we would evaluate whether this new information would be sufficient to warrant a quantitative climate assessment for this review.

Materials damage and soiling effects No quantitative relationships were available between ambient particle concentrations and rates of corrosion of metals and in the weathering of materials. In addition, no quantitative relationships were available between particles and the frequency of cleaning or repainting of surfaces. Data on the role of If additional studies become available in the PM ISA to substantially reduce the uncertainty in quantifying materials damage and soiling effects, we would consider whether this new information would be sufficient to warrant a quantitative materials assessment for this review.April 2016 5-19 Draft – Do Quote or Cite Major Uncertainty or Limitation Uncertainty/Limitation Remaining from Last Review Consideration of Information Newly Available in this Review

microbial colonizers in biodeterioration processes and contributions of black crust to soiling were not sufficient for quantitative analyses. 1



### 5.4 SCIENTIFIC AND PUBLIC REVIEW 2

The WREA Planning Document will be distribu ted to the CASAC for review and provided 3 to the public for review and comment. The documen t will be the subject of a review with the 4 CASAC at a public meeting or teleconference that will be announced in the Federal Register

. 5 The EPA does not produce a final WREA Pla nning Document but inst ead considers CASAC 6 recommendations and public comments in th e design and when conducting the quantitative 7 assessments either in a new WREA or in updating or expanding the last assessment as part of the 8 PA. In either case, staff would prepare at leas t one draft of the asse ssment for CASAC review 9 and public comment. CASAC would review the document and discuss it at a public meeting that 10
would be announced in the Federal Register . Based on past practice, the EPA expects that 11 CASAC would summarize key advice and recommenda tions for revision of the assessment in a 12
letter to the EPA Administrato r. In revising any draft WREA, the EPA would take into account 13 any such recommendations and al so consider comments received from the public, both at the 14 meeting itself and directly in writing. A final assessment would then be made available on an 15 EPA website, with its public av ailability announced in the Federal Register

. 16April 2016 5-20 Draft – Do Quote or Cite 

### REFERENCES 1

Abt Associates, Inc. (2001). Assessing Public Opinions on Visi bility Impairment due to Air 2 Pollution: Summary Report . Prepared for EPA Office of Air Quality Planning and 3 Standards; funded under EPA Contract No. 68-D-98-001. Abt Associates Inc., Bethesda, 4 MD. January 2001. Available: http://www.epa.gov /ttncaaa1/t1/reports/vis_rpt_final.pdf 5 BBC Research & Consulting (2003). Phoenix Area Visibility Surv ey. Draft Report. Available: 6 http://www.azdeq.gov/environ/air/download/vis_021903f.pdf

. 7 Bond, T. C., et al. (2013), Bounding the role of bl ack carbon in the climate system: A scientific 8 assessment, J. Geophys. Res. Atmos. , 118, 5380–5552. 9 Ely, D.W., J.T. Leary, T.R. Stewart, and D.M. Ross (1991). The Establishment of the Denver 10 Visibility Standard. Presented at the 84th Annual Meeting & Exhibition of the Air and 11 Waste Management Association. June 16-21. 12 Intergovernmental Panel on Climate Change (IPCC). (2013) Climate Change 2013: The Physical 13 Science Basis. Contribution of Working Gr oup I to the Fifth Assessment Report of the 14 Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. 15 Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. 16 Cambridge University Press, Cambridge , United Kingdom and New York, NY, USA, 17 1535 pp, doi:10.1017/CBO9781107415324. 18 Molenar, J.V., W.C. Malm, and C.E. Johnson ( 1994). Visual air quality simulation techniques. 19 Atmospheric Environment 28(5):1055-1063. 20 Pitchford, M. and W. Malm (1993). Development a nd applications of a standard visual index. 21 Atmospheric Environment 28(5):1049-1054. 22 Pitchford M; Malm W; Schich tel B; Kumar N; Lowenthal D; Hand J (2007). Revised algorithm 23 for estimating light extinction from IMPROVE particle speciation data. J Air Waste 24 Manag Assoc 57: 1326–36. 25 Pryor, S.C. (1996). Assessing public perception of visibility for standard setting exercises. 26 Atmospheric Environment 30(15):2705-2716. 27 Smith, A.E. and S. Howell. (2009). An Assessment of the Robustn ess of Visual Air Quality 28 Preference Study Results . CRA International, Washington, DC. March 30. Prepared for 29 the Utility Air Regulatory Group. Submitted as supplemental material to presentation by 30 Anne Smith to the public mee ting of the EPA Clean Air Scie nce Advisory Council. April 31 2. 32 U.S. EPA (2004). Air Quality Criteria fo r Particulate Matter . U.S. EPA, National Center for 33 Environmental Assessment, Office of Resear ch and Development. Research Triangle 34 Park, NC, EPA/600/P-99/002aF and EPA/600/ P-99/002bF. October 2004. Available: 35 http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_cr_cd.html

. 36 U.S. EPA (2009a). Integrated Science Assessment (ISA) for Particulate Matter (Final Report)

. 37 U.S. EPA, National Center for Environmen tal Assessment, Office of Research and 38 Development. Research Triangle Pa rk, NC. December, 2009. EPA/600/R-08/139F. 39 Available at: http://cfpub.epa.gov/ncea/cfm/r ecordisplay.cfm?deid=216546

. 40April 2016 5-21 Draft – Do Quote or Cite U.S. EPA (2011). Policy Assessment for the Review of th e Particulate Matter National Ambient 1 Air Quality Standards . U.S. EPA, Office of Air Qu ality Planning and Standards. 2 Research Triangle Park, NC, EPA 45 2/R-11-003. April, 2011. Available at: 3 http://www.epa.gov/ttn/naaqs/st andards/pm/data/20110419pmpafinal.pdf

. 4 U.S. EPA (2009c). Particulate Matter National Ambien t Air Quality Standards: Scope and 5 Methods Plan for Urban Visibility Impact Assessment . U.S. EPA, Office of Air Quality 6 Planning and Standards, Research Tria ngle Park, NC. EPA- 452/P-09-001. February 7 2009. Available: 8 http://www3.epa.gov/ttn/naaqs/standa rds/pm/data/20090227PMNAAQSWelfare.pdf

. 9 U.S. EPA (2010b). Particulate Matter Urban-Focused Vi sibility Assessment – Final Report

. 10 Office of Air Quality Planning and Standard s, U.S. Environmental Protection Agency, 11 Research Triangle Park, NC. EP A-452/R-10-004. June 2010. Available: 12 http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html

. 13 U.S. Global Change Research Program (2014 ). Climate Change Impacts in the United States: 14 The Third National Climate Assessment . May. Available: 15 http://nca2014.globalchange.gov/

. 16

17
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## 6 POLICY ASSESSMENT AND RULEMAKING 1

As outlined in section 1.2 above, the PA and rulemaking comprise the final phases of the 2 review. These phases are describe d briefly in sections 6.1 (PA) and 6.2 (rulemaking) below. 3



### 6.1 POLICY ASSESSMENT 4

The PA will provide a transparent analysis and presentation of staff conclusions 5 regarding the adequacy of the existing PM standa rds and the potential alte rnatives, if any, that 6 are appropriate to consider in the current re view. The PA will integr ate and interpret the 7 information from the ISA and, if available, REA( s) to frame policy options for consideration by 8
the Administrator. The PA is also intended to facilitate CASAC’s advice to the Agency, and 9 recommendations to the Administrator, on th e adequacy of the ex isting standards and on 10 revisions that may be appropriate to consider, as provided for in the CAA. Staff conclusions will 11
be based on the assessment of the scientific evidence in the PM ISA; the results of exposure and 12 risk assessments in the REA(s), as available; a nd any additional staff ev aluations and analyses 13
that are included in the PA. 14 The discussion in the PA will be framed by consideration of a series of policy-relevant 15 questions drawn from those presented in se ctions 2.1.3 and 2.2.3 above. These will include 16 questions on the adequacy of the current PM st andards and, as appropriate, on the elements of 17 potential alternative standards (i.e., indicator, av eraging time, form, level). The PA will identify 18 evidence-based and exposure-/risk-based appr oaches for addressing these policy-relevant 19 questions and for reaching public health and welfare policy judgments. 20 The PA will identify the range of policy options that the staff concludes could be 21 supported by the available scient ific evidence and the informati on from available quantitative 22 assessments. In so doing, the PA will describe the interpretations of this evidence and 23 information that could support various policy options, as appropriate, and that could be 24 considered by the Administrator in making decisions on the PM NAAQS. This will include the 25 identification of key uncertainties and limitations in the underlying scientific evidence and in the 26 information available from quantitative assessments. 128 27 In identifying ranges of primary and secondary standard options for consideration, the PA 28 will recognize that the Administrator’s final de cisions will reflect publ ic health and public 29

128 In addition to presenting staff conclusions on the NAAQS, the PA will also highlight areas for future health- and welfare-related research, model development, and data collection.April 2016 6-2 Draft – Do Not Quote or Cite welfare policy judgments. It will further recognize that the Administrator’s final decisions will 1 draw upon scientific information and analyses of h ealth or welfare effects and risks, as well as 2 judgments about how to deal with the range of un certainties that are inhe rent in the scientific 3 evidence and analyses. 4 Our approach in the PA to informing the Administrator’s judgments on the primary PM 5 standards will recognize that the available health effects evidence reflects a continuum consisting 6 of PM exposure concentrations at which scientists genera lly agree that health effects are likely to 7 occur, through lower exposure concentrations at which the likelihood and magnitude of the 8 response become increasingly uncertain. This approach is consistent with th e requirements of the 9 NAAQS provisions of the CAA and with how the EPA and the courts have historically 10 interpreted the CAA. These provisions require th e Administrator to establish primary standards 11 that are requisite to protect public health and that are neither more nor less stringent than 12 necessary for this purpose. As discussed in se ction 1.1 above, the provisio ns do not require that 13 primary standards be set at a zero-risk level, but rather at a level that a voids unacceptable risks to 14 public health, including the he alth of at-risk populations. 15 Similarly, our approach in the PA to in forming the Administrator’s judgments on the 16 secondary PM standards will recognize that a fina l decision must draw upon scientific evidence 17 and analyses about effects on public welfare, as well as judgment s about how to deal with the 18 range of uncertainties that are i nherent in the relevant information. As is the case for the primary 19 standards discussed above, this approach is consistent with the re quirements of the NAAQS 20 provisions of the CAA and with how the EPA and the courts have historically interpreted the 21 CAA. These provisions require the Administrato r to establish secondary standards that are 22 requisite to protect public welfar e from any known or anticipated a dverse effects associated with 23 the presence of the pollu tant in the ambient air. In so doing, the Administrator seeks to establish 24
standards that are neither more nor less stringent than necessary for this purpose. The provisions 25 do not require that secondary standa rds be set to eliminate all welfar e effects, but rather at a level 26 that protects public welfare from those effects that are judge d to be adverse. 27 Staff will prepare at least one draft of th e PA for CASAC review and public comment. 28 CASAC will review the draft PA at a public meeting that will be announced in the Federal 29 Register . Based on past practice by CASAC, the EP A expects that CASAC will summarize key 30
advice and recommendations for revision of the docu ment in a letter to the EPA Administrator. 31 In revising the draft PA, we will take into account such recommendations, comments received 32 from CASAC and from the public at the meeting itself, and any written comments received. The 33
final document will be made available on the EPA website, with its public availability 34
announced in the Federal Register

. 35April 2016 6-3 Draft – Do Not Quote or Cite 

### 6.2 RULEMAKING 1

Following the issuance of the final PA and the EPA management consideration of staff 2 analyses and conclusions presented therein, a nd taking into consider ation CASAC advice and 3 recommendations, the Agency will develop a notice of proposed rulemaking. The notice of 4 proposed rulemaking will convey the Administrator’s proposed conclusions regarding the 5 adequacy of the current standard (s) and any revision that may be appropriate. A draft notice of 6 proposed rulemaking will be submitted to the Office of Management and Budget (OMB) for 7 interagency review, in which OMB and other fede ral agencies are provid ed the opportunity for 8 review and comment. After the completion of interagency review, the EPA will publish the 9
notice in the Federal Register seeking comment on the proposed agency action – namely 10 whether or not to revise the current standard, a nd if so, how. Monitoring rule changes associated 11
with review of the PM standards will be deve loped and proposed, as appropriate, in conjunction 12 with the NAAQS rulemaking. 13 At the time of publication of the notice of proposed rulemaking, all materials on which the 14 proposal is based will be made available in the public docket of the rulemaking. 129 Publication of 15 the proposal notice is followed by a public comme nt period, generally lasting 60 to 90 days, 16 during which the public is invite d to submit comments on the propos al to the rulemaking docket. 17 Taking into account comments received on th e proposed rule, the Agency will then 18 develop a notice of final rulemaking, which again undergoes OMB-coordinated interagency 19 review prior to issuance by the EP A of the final rule. At the ti me of the final rulemaking, the 20 Agency responds to all significan t comments on the proposed rule. 130 Publication of the final rule 21
in the Federal Register completes the rulemaking process. 22
23

129 The rulemaking docket for the current PM NAAQS review is identified as the EPA-HQ-OAR-2015-0072. This docket has incorporated the ISA docket (EPA-HQ-ORD-2014-0859) by reference. Both dockets are publicly accessible at www.regulations.gov.

130 For example, Agency responses to all significant comments on the 2009 notice of proposed rulemaking in the last review were provided in the preamble to the final rule and in a document titled Responses to Significant Comments on the 2012 Proposed Rule on the National Ambient Air Quality Standards for Particulate Matter (June 29, 2012; 77 FR 28890) (U.S. EPA, 2012).April 2016 4 Draft – Do Not Quote or Cite 

### REFERENCES

U.S. EPA (2012). Responses to Significan t Comments on the 2012 Proposed Rule on the National Ambient Air Quality Standards for Particulate Matter. U.S. Environmental Protection Agency, Research Tr iangle Park, NC. Available at: http://www.epa.gov/ttn/naaqs/standards/pm/data/20121214rtc.pdf