From: Lydia Wegman/RTP/USEPA/US To: "Frey, Nathan J." <Nathan_J._Frey@omb.eop.gov>, Margo_Schwab@omb.eop.gov Cc: Karen Martin/RTP/USEPA/US@EPA, Beth Hassett
- Sipple/RTP/USEPA/US@EPA,

Joseph - J Dougherty/DC/USEPA/US@EPA, John Hannon/DC/USEPA/US@EPA, David Orlin/DC/USEPA/US@EPA Date: 12/13/2012 12:26 PM Subject: Revisions to section III of the PM NAAQS NFR to address you r comments on the annual

standard Nathan and Margo, The attached redline file shows changes made to the Nov. 20 OMB review draft of section III. These changes primarily address your comments as discussed on our 11 AM call yesterday. They begin around p. 88, then mostly appear on pp. 175 - 191 and 207 - 239. In addition, you will see redline in other parts of the section, including our response to comments regarding the Janes et al. and Greven et al. studies (around pp. 72
- 78) which we have previously se nt to you. There are also edits to our response to comments regarding spatial averaging and near - road monitoring related to the form of the annual standard, which are unrelated to your comments of yesterday, but which we have incorporated into the section to strengthen it. You will also see other minor edits throughout this section. Please let us know as soon as possible if you have any questions. We would like to incorporate these revisions into the package later this afternoon. Thanks.***E.O. 12866 Review

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Page 2 of 253 I. Rationale for Final Decisions on the Primary PM 2.5 Standards This section presents the Administrator’s final decision regarding the need to revise the current primary PM 2.5 standards and, more specifically, regarding revisions to the level and form of the existing primary annual PM 2.5 standard in conjunction with retaining the existing primary 24

- hour PM 2.5 standard. As discussed more fully below, the rationale for the final decision is based on a thorough review, in the Integrated Science Assessment, of the latest scientific information, published through mid

- 2009, on human health effects associated with long

- and short

- term exposures to fine particles in the ambient air. Th e final decisions also take into account: (1) staff assessments of the most policy

- relevant information presented and assessed in the Integrated Science Assessment and staff analyses of air quality and human risks presented in the Risk Assessment and the P olicy Assessment, upon which staff conclusions regarding appropriate considerations in this review are based; (2) CASAC advice and recommendations, as reflected in discussions of drafts of the Integrated Science Assessment, Risk Assessment, and Policy Asse ssment at public meetings, in separate written comments, and in CASAC’s letters to the Administrator; (3) the multiple rounds of public comments received during the development of these documents, both in connection with CASAC meetings and separately; and (4) extensive public comments received on the proposal. In developing this final rule, the Administrator recognizes that the CAA requires her to reach a public health policy judgment as to what standards would be requisite

-- neither more nor less stringe nt than necessary

-- to protect public health with an adequate margin of safety, based on scientific evidence and technical assessments that have inherent uncertainties and limitations. This judgment requires making reasoned decisions***E.O. 12866 Review

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Page 3 of 253 as to what weight to place on various types of evidence and assessments, and on the related uncertainties and limitations. Thus, in selecting the final standards, the Administrator is seeking not only to prevent fine particle concentrations that have been demonstrated to be ha

rmful but also to prevent lower fine particle concentrations that may pose an unacceptable risk of harm, even if the risk is not precisely identified as to nature or degree. As discussed below, as well as in more detail in the proposal, a substantial amou nt of new research has been conducted since the close of the science assessment in the last review of the PM 2.5 NAAQS ( U.S. EPA, 2004), with important new information coming from epidemiological studies, in particular. This body of evidence includes hundre ds of new epidemiological studies conducted in many countries around the world. In its assessment of the evidence judged to be most relevant to making decisions on elements of the primary PM 2.5 standards, the EPA has placed greater weight on U.S. and Canad ian studies using PM 2.5 measurements, since studies conducted in other countries may reflect different demographic and air pollution characteristics. 1 The newly available research studies as well as the earlier body of scientific evidence presented and as sessed in the Integrated Science Assessment have undergone intensive scrutiny through multiple layers of peer review and opportunities for public review and comment. In developing this final rule, the EPA has drawn upon an integrative synthesis of the enti re body of evidence concerning exposure to ambient fine particles and a broad range of health endpoints ( U.S. EPA, 2009a, Chapters 2, 4, 5, 6, 7, and 8) focusing on those health endpoints for which the Integrated Science Assessment
1 Nonetheless, the Administrator recognizes the importance of all studies, including international studies, in the Integrated Science Assessment’s considerations of the weight of the evidence that informs causality determinations.***E.O. 12866 Review

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Page 4 of 253 concludes that there is a causal or likely causal relationship with long

- or short

- term PM 2.5 exposures. The EPA has also considered health endpoints for which the Integrated Science Assessment concludes there is evidence suggestive of a causal relationship with long

- term PM 2.5 e xposures. The EPA has also drawn upon a quantitative risk assessment based upon the scientific evidence described and assessed in the Integrated Science Assessment. These analyses, discussed in the Risk Assessment ( U.S. EPA, 2010a) and Policy Assessment ( U.S. EPA, 2011a, chapter 2), have also undergone intensive scrutiny through multiple layers of peer review and multiple opportunities for public review and comment. Although important uncertainties remain in the qualitative and quantitative characterizati ons of health effects attributable to ambient fine particles, progress has been made in addressing these uncertainties in this review . The EPA ’s review of this information has been extensive and deliberate. This intensive evaluation of the scientific evide nce and quantitative assessments has provided a comprehensive and adequate basis for regulatory decision making at this time. This section describes the integrative synthesis of the evidence and technical information contained in the Integrated Science As sessment , the Risk Assessment , and the Policy Assessment with regard to the current and alternative standards. The EPA notes that the final decision for retaining or revising the current primary PM 2.5 standards is a public health policy judgment made by th e Administrator. The Administrator’s final decision draws upon scientific information and analyses related to health effects and risks; judgments about uncertainties that are inherent in the scientific evidence and analyses; CASAC advice; and comments rece ived in response to the proposal.***E.O. 12866 Review

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Page 5 of 253 In presenting the rationale for the final decisions on the primary PM 2.5 standards, this section begins with a summary of the approaches used in setting the initial primary PM 2.5 NAAQS in 1997 and in reviewing and revising those standards in 2006 (section III.A.1). The D.C. Circuit Court of Appeals remand of the primary annual PM 2.5 standard in 2009 is discussed in section III.A.2. Taking into consideration this history, section II I II .A.3 describes the EPA’s general approac h used in the current review for considering the need to retain or revise the current suite of fine particle standards, taking into account public comment on the proposed approach. The scientific evidence and quantitative risk assessment were presented in sections III.B and III.C of the proposal, respectively (77 FR 38906 to 38917, June 29, 2012) and are outlined in sections III.B and III.C below. Subsequent sections of this preamble provide a more complete discussion of the Administrator’s rationale, in l ight of key issues raised in public comments, for concluding that it is appropriate to revise the suite of current primary PM 2.5 standards (section III.D), as well as a more complete discussion of the Administrator’s rationale for retaining or revising the specific elements of the primary PM 2.5 standards, namely the indicator (section III.E.1); averaging time (section III.E.2); form (section III.E.3); and level (section III.E.4). A summary of the final decisions to revise the suite of primary PM 2.5 standards is presented in section III.F. A. Background There are currently two primary PM 2.5 standards providing public health protection from effects associated with fine particle exposures. The annual standard is set at a level of 15.0 μg/m 3 , based on the 3

- year average of annual arithmetic mean PM 2.5 concentrations from single or multiple monitors sited to represent community

- wide air quality. The 24

- hour standard is set at a level of 35 μg/m 3 , based on the 3

- year average of***E.O. 12866 Review

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Page 6 of 253 the 98 th percentile of 24

- hour PM 2.5 concentrations at each population

- oriented monitor within an area. The past and current approaches for reviewing the primary PM 2.5 standards described below are all based most fundamentally on using information from epidemiological studies to infor m the selection of PM 2.5 standards that, in the Administrator’s judgment, protect public health with an adequate margin of safety. Such information can be in the form of air quality distributions over which health effect associations have been observed in scientific studies or in the form of concentration

response functions that support quantitative risk assessment. However, evidence

- and risk

- based approaches using information from epidemiological studies to inform decisions on PM 2.5 standards are complica ted by the recognition that no population threshold, below which it can be concluded with confidence that PM 2.5 - related effects do not occur, can be discerned from the available evidence. 2 As a result, any general approach to reaching decisions on what sta ndards are appropriate necessarily requires judgments about how to translate the information available from the epidemiological studies into a basis for appropriate standards. This includes consideration of how to weigh the uncertainties in the reported as sociations across the distributions of PM 2.5 concentrations in the studies and the uncertainties in quantitative estimates of risk, in the context of the entire body of evidence before the Agency. Such approaches are consistent with setting standards that are neither more nor less stringent than necessary, recognizing that a zero

- risk standard is not required by the CAA.

2 The term "evidence

- based " approach or consideration generally refers to using the information in the scientific evidence to inform judgments on the need to retain or revise the NAAQS. The term "risk

- based" generally refers to using the quantitative information in the Risk Assessm ent to inform such judgments.***E.O. 12866 Review

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Page 7 of 253 1. General Approach Used in Previous Reviews The general approach used to translate scientific information into standards in the previous PM NAAQS reviews focused on consideration of alternative standard levels that were somewhat below the long

- term mean PM 2.5 concentrations reported in key epidemiological studies ( U.S. EPA, 2011a, section 2.1.1). This approach recognized that the strongest ev idence of PM 2.5 - related associations occurs where the bulk of the data exists, which is over a range of concentrations around the long

- term (i.e., annual) mean. In setting primary PM 2.5 annual and 24

- hour standards for the first time in 1997, the Agency r elied primarily on an evidence

- based approach that focused on epidemiological evidence, especially from short

- term exposure studies of fine particles judged to be the strongest evidence at that time ( U.S. EPA, 2011a, section 2.1.1.1). The EPA selected a le vel for the annual standard that was at or below the long

- term mean PM 2.5 concentrations in studies providing evidence of associations with short

- term PM 2.5 exposures, placing greatest weight on those short

- term exposure studies that reported clearly stati stically significant associations with mortality and morbidity effects. Further consideration of long

- term mean PM 2.5 concentrations associated with mortality and respiratory effects in children did not provide a basis for establishing a lower annual stand ard level. The EPA did not place much weight on quantitative risk estimates from the very limited risk assessment conducted, but did conclude that the risk assessment results confirmed the general conclusions drawn from the epidemiological evidence that a serious public health problem was associated with ambient PM levels allowed under the then current PM 10 standards (62 FR 38665/1, July 18, 1997).***E.O. 12866 Review

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Page 8 of 253 The EPA considered the epidemiological evidence and data on air quality relationships to set an annual PM 2.5 standard that was intended to be the “generally controlling” standard; i.e., the primary means of lowering both long

- and short

- term ambient concentrations of PM 2.5 . 3 In conjunction with the annual standard, the EPA also established a 24

- hour PM 2.5 standa rd to provide supplemental protection against days with high peak concentrations, localized “hotspots,” and risks arising from seasonal emissions that might not be well controlled by an annual standard (62 FR 38669/3). In 2006, the EPA used a different ev idence

- based approach to assess the appropriateness of the levels of the 24

- hour and annual PM 2.5 standards ( U.S. EPA, 2011a, section 2.1.1.2). Based on an expanded body of epidemiological evidence that was stronger and more robust than that available in the 1997 review, including additional studies of both short

- and long

- term exposures, the EPA decided that using e vidence of effects associated with periods of exposure that were most closely matched to the averaging time of each standard was the most appropriate public health policy approach for evaluating the scientific evidence to inform selecting the level of each standard. Thus, the EPA relied upon evidence from the short

- term exposure studies as the principal basis for revising the level of the 24

- hour PM 2.5 standard from 65 to 35 μg/m 3 to protect

3 In so doing, the EPA noted that because an annual standard would focus control programs on annual average PM 2.5 concentrations, it would not only control long

- term exposure levels, but would also generally control the overal l distribution of 24

- hour exposure levels, resulting in fewer and lower 24

- hour peak concentrations. Alternatively, a 24

- hour standard that focused controls on peak concentrations could also result in lower annual average concentrations. Thus, the EPA reco gnized that either standard could provide some degree of protection from both short

- and long

- term exposures, with the other standard serving to address situations where the daily peaks and annual averages are not consistently correlated (62 FR 38669, July 18, 1997). In the circumstances presented in that review, the EPA determined that it was appropriate to focus on the annual standard as the standard based best suited to control both annual and daily air quality distributions [ ( 62 FR 38670 ]. ).***E.O. 12866 Review

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Page 9 of 253 against effects associated with short

- term exposures. The EPA reli ed upon evidence from long

- term exposure studies as the principal basis for retaining the level of the annual PM 2.5 standard at 15 μg/m 3 to protect against effects associated with long

- term exposures. This approach essentially took the view that short

- term studies were not appropriate to inform decisions relating to the level of the annual standard, and long

- term studies were not appropriate to inform decisions relating to the level of the 24

- hour standard. With respect to quantitative risk

- based considerat ions, the EPA determined that the estimates of risks likely to remain upon attainment of the 1997 suite of PM 2.5 standards were indicative of risks that could be reasonably judged important from a public health perspective and, thus, supported revision of the standards. However, the EPA judged that the quantitative risk assessment had important limitations and did not provide an appropriate basis for selecting the levels of the revised standards in 2006 (71 FR 61174/1

- 2, October 17, 2006). 2. Remand of Primar y Annual PM 2.5 Standard As noted above in section II.B.2, several parties filed petitions for review in the U.S. Court of Appeals for the District of Columbia Circuit following promulgation of the revised PM NAAQS in 2006. These petitions challenged severa l aspects of the final rule including the level of the primary PM 2.5 annual standard. The primary 24

- hour PM 2.5 standard was not challenged by any of the litigants and, thus, was not considered in the court’s review and decision. On judicial review, the D .C. Circuit remanded the primary annual PM 2.5 NAAQS to the EPA on grounds that the Agency failed to adequately explain why the annual standard provided the requisite protection from both short

- and long

- term exposures to***E.O. 12866 Review

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Page 10 of 253 fine particles including protection for at

- risk populations. American Farm Bureau Federation v. EPA , 559 F. 3d 512 (D.C. Cir. 2009). With respect to human health protection from short

- term PM 2.5 exposures, the court considered the different approaches used by the EPA in the 1997 and 2006 PM NAAQS decisions, as summarized in section III.A.1 above. The court found that the EPA failed to adequately explain why a primary 24

- hour PM 2.5 standard by itself would provide the protection needed from short

- term exposures and remanded the primary annual PM 2.5 standard to the EPA “for further consideration of whether it is set at a level requisite to protect the public health while providing an adequate margin of safety from the risk of short

- term exposures to PM 2.5 .” American Farm Bureau Federation v. EP A , 559 F. 3d at 520

- 24. With respect to protection from long

- term exposure to fine particles, the court found that the EPA failed to adequately explain how the primary annual PM 2.5 standard provided an adequate margin of safety for children and other at

- r isk populations. The court found that the EPA did not provide a reasonable explanation of why certain morbidity studies, including a study of children in Southern California showing lung damage associated with long

- term PM 2.5 exposure (Gauderman et.al, 200 0) and a multi

city study (24

- Cities Study) evaluating decreased lung function in children associated with long

- term PM 2.5 exposures (Raizenne et al., 1996), did not warrant a more stringent annual PM 2.5 standard. Id. at 522

- 23. Specifically, the court fou nd that: EPA was unreasonably confident that, even though it relied solely upon long

- term mortality studies, the revised standard would provide an adequate margin of safety with respect to morbidity among children. Notably absent from the final rule, moreo ver, is any indication of how the standard will adequately reduce risk to the elderly or to those with certain heart or lung diseases despite (a) the EPA’s determination in its proposed rule that those subpopulations are at greater risk from exposure to fi ne particles and (b) the evidence in the record supporting that determination. Id. at 525.***E.O. 12866 Review

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Page 11 of 253 In addition, the court held that the EPA had not adequately explained its decision to base the level of the annual standard essentially exclusively on the results of long

- term studies and the 24

- hour standard level essentially exclusively on the results of short

- term studies. See 559 F. 3d at 522 (“[e]ven if the long

- term studies available today are useful for setting an annual standard,..., it is not clear why the EPA no longer believes it useful to look as well to short

- term studies in order to design the suite of standards that will most effectively reduce the risks associated with short

- term exposure”); see also I d. at 523

- 24 (holding that the EPA had not adequately explained why a standard based on levels in short

- term exposure studies alone provided appropriate protection from health effects associated with short

- term PM 2.5 exposures given the stated need to lower the entire air quality distribution, and not just peak concentrations, in order to control against short

- term effects). In remanding the primary annual PM 2.5 standard for reconsideration, the court did not vacate the standard, Id
. at 530, so the standard remains in effect and is therefore the standard considered by the EPA in this review. 3. General Approach Used in the Policy Assessment for the Current Review This review is based on an assessment of a much expanded body of scientific evidence, more extensive air quality data and analyses, and a more comprehensive quantitative risk assessment relative to the information available in past reviews, as presented and assessed in the Integrated Science Assessment and Risk Assessment and discussed in the Policy Asse ssment . As a result, the EPA’s general approach to reaching conclusions about the adequacy of the current suite of PM 2.5 standards and potential alternative standards that are appropriate to consider was broader and more integrative***E.O. 12866 Review

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Page 12 of 253 than in past reviews. O ur general approach also reflected consideration of the issues raised by the court in its remand of the primary annual PM 2.5 standard as discussed in section III.A.2 above , since decisions made in this review, and the rationales for those decisions, will c omprise the Agency’s response to the remand. The EPA’s general approach took into account both evidence

- based and risk

based considerations and the uncertainties related to both types of information, as well as advice from CASAC (Samet, 2010c,d) and public comments on the first and second draft Policy Assessments ( U.S. EPA, 2010c,f). In so doing, the EPA staff developed a final Policy Assessment ( U.S. EPA, 2011a) which provided as broad an array of policy options as was supported by the available informatio n, recognizing that the selection of a specific approach to reaching final decisions on the primary PM 2.5 standards will reflect the judgments of the Administrator as to what weight to place on the various approaches and types of information available in t he current review. The Policy Assessment concluded it was most appropriate to consider the protection against PM 2.5 - related mortality and morbidity effects, associated with both long

- and short

- term exposures, afforded by the annual and 24

- hour standards t aken together, as was done in the 1997 review, rather than to consider each standard separately, as was done in the 2006 review ( U.S. EPA, 2011a, section 2.1.3). 4 As the EPA recognized in 1997, there are various ways to combine two standards to achieve an

4 By utilizi ng this approach, the Agency also is responsive to the remand of the 2006 standard. As noted in section III.A.2, the D.C. Circuit, in remanding the 2006 primary annual PM 2.5 standard, concluded that the Administrator had failed to adequately explain why an annual standard was sufficiently protective in the absence of consideration of the long

- term mean PM 2.5 concentrations in short

- term exposure studies as well, and likewise had failed to explain why a 24

- hour standard was sufficiently protective in the abs ence of consideration of the effect of an annual standard on reducing the overall distribution of 24

- hour average PM 2.5 concentrations. 559 F. 3d at 520

- 24.***E.O. 12866 Review

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Page 13 of 25 3 appropriate degree of public health protection. The extent to which these two standards are interrelated in any given area depends in large part on the relative levels of the standards, the peak

- to
- mean ratios that characterize air quality patterns in an a rea, and whether changes in air quality designed to meet a given suite of standards are likely to be of a more regional or more localized nature. In considering the combined effect of annual and 24

- hour standards, the Policy Assessment recognized that cha nges in PM 2.5 air quality designed to meet an annual standard would likely result not only in lower annual average PM 2.5 concentrations but also in fewer and lower peak 24

- hour PM 2.5 concentrations. The Policy Assessment also recognized that changes design ed to meet a 24

- hour standard would result not only in fewer and lower peak 24

- hour PM 2.5 concentrations but also in lower annual average PM 2.5 concentrations. Thus, either standard could be viewed as providing protection from effects associated with both short

- and long

- term exposures, with the other standard serving to address situations where the daily peak and annual average concentrations are not consistently correlated. In considering the currently available evidence, the Policy Assessment recognized that the short

- term exposure studies were primarily drawn from epidemiological studies that associated variations in area

- wide health effects with monitor(s) that measured the variation in daily PM 2.5 concentrations over the course of several years. The s trength of the associations in these data was demonstrably in the numerous “typical” days within the air quality distribution, not in the peak days. See also 71 FR 61168, October 17, 2006 and American Farm Bureau Federation v EPA , 559 F. 3d at 523, 524 (ma king the same point). The quantitative risk assessments conducted for this and previous reviews***E.O. 12866 Review

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Page 14 of 253 demonstrated the same point ; that is, much, if not most of the aggregate risk associated with short

- term exposures results from the large number of days during which the 24

- hour average concentrations are in the low

- to mid

- range, below the peak 24

- hour concentrations ( U.S. EPA, 2011a, section 2.2.2; U.S. EPA, 2010a, section 3.1.2.2). In addition, there was no evidence suggesting that risks associated with long

- te rm exposures were likely to be disproportionately driven by peak 24

- hour concentrations. 5 For these reasons, the Policy Assessment concluded that strategies that focused primarily on reducing peak days were less likely to achieve reductions in the PM 2.5
c oncentrations that were most strongly associated with the observed health effects. Furthermore, the Policy Assessment concluded that a policy approach that focused on reducing peak exposures would most likely result in more uneven public health protection across the U.S. by either providing inadequate protection in some areas or overprotecting in other areas ( U.S. EPA, 2011a, p. 2

- 9; U.S. EPA, 2010a, section 5.2.3). This is because, as discussed above, reductions based on control of peak days are less likel y to control the bulk of the air quality distribution. The Policy Assessment concluded that a policy goal of setting a “generally controlling” annual standard that will lower a wide range of ambient 24

- hour PM 2.5 concentrations, as opposed to focusing on control of peak 24

- hour PM 2.5 concentrations, was the most effective and efficient way to reduce total population risk and so provide appropriate protection. This approach, in contrast to one focusing on a generally controlling 24

- hour standard, would like ly reduce aggregate risks associated with both

5 In confirmation, a number of studies have presented analyses excluding higher PM concentration d ays and reported a limited effect on the magnitude of the effect estimates or statistical significance of the association (e.g., Dominici, 2006b; Schwartz et al, 1996; Pope and Dockery, 1992).***E.O. 12866 Review

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Page 15 of 253 long

- and short

- term exposures with more consistency and would likely avoid setting national standards that could result in relatively uneven protection across the country, due to setting standards that are ei ther more or less stringent than necessary in different geographical areas (U.S. EPA, 2011a, p. 2

- 9)
. The Policy Assessment also concluded that an annual standard intended to serve as the primary means for providing protection from effects associated with both long

- and short

- term PM 2.5 exposures cannot be expected to offer sufficient protection against the effects of all short

- term PM 2.5 exposures. As a result, in conjunction with a generally controlling annual standard, the Policy Assessment concluded it was appropriate to consider setting a 24

- hour standard to provide supplemental protection, particularly for areas with high peak

- to
- mean ratios possibly associated with strong local or seasonal sources, or PM 2.5 - related effects that may be associated with shorter

- than

- daily exposure periods ( U.S. EPA, 2011a, p. 2

- 10). The Policy Assessment ’s consideration of the protection afforded by the current and alternative suites of standards focused on PM 2.5 - related health effects associated with long

- term exposures for which the magnitude of quantitative estimates of risks to public health generated in the risk assessment was appreciably larger in terms of overall incidence and percent of total mortality or morbidity effects than for short

- term PM 2.5 - related effects. Nonetheless, the EPA also considered health effects and estimated risks associated with short

- term exposures. In both cases, the Policy Assessment placed greatest weight on health effects that had been judged in the Integrated Science Assessment to have a causal or likely causal relationship with PM 2.5 exposures, while also considering health effects judged to be suggestive of a causal relationship or***E.O. 12866 Review

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Page 16 of 253 evidence that focused on specific at

- risk populations. The Policy Assessment placed relatively greater wei ght on statistically significant associations that yielded relatively more precise effect estimates and that were judged to be robust to confounding by other air pollutants. In the case of short

- term exposure studies, the Policy Assessment placed greatest weight on evidence from large multi

- city studies, while also considering associations in single

- city studies. In translating information from epidemiological studies into the basis for reaching staff conclusions on the adequacy of the current suite of sta ndards, the Policy Assessment considered a number of factors. As an initial matter, the Policy Assessment considered the extent to which the currently available evidence and related uncertainties strengthens or calls into question conclusions from the last review regarding associations between fine particle exposures and health effects. The Policy Assessment also considered evidence of health effects in at

- risk populations and the potential impacts on such populations. Further, the Policy Assessment explore d the extent to which PM 2.5 - related health effects had been observed in areas where air quality distributions extend to lower concentrations than previously reported or in areas that would likely have met the current suite of standards. In translating inf

ormation from epidemiological studies into the basis for reaching staff conclusions on standard levels for consideration ( U.S. EPA, 2011a, sections 2.1.3 and 2.3.4), the Policy Assessment first recognized the absence of discernible thresholds in the concentration

- response functions from long

- and short

- term PM 2.5 exposure studies ( U.S. EPA, 2011a, section 2.4.3). 6 In the absence of any discernible thresholds, the

6 The epidemiological studies evaluated in the Integrated Scien ce Assessment that examined the shape of concentration

- response relationships and the potential presence of***E.O. 12866 Review

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Page 17 of 253 Agency’s general approach for identifying appropriate standard levels for consideration involved characterizing the range of PM 2.5 concentrations over which we have the most confidence in the associations reported in epidemiological studies. In so doing, the Policy Assessment recog nized that there is no single factor or criterion that comprises the “correct” approach, but rather there are various approaches that are reasonable to consider for characterizing the confidence in the associations and the limitations and uncertainties in the evidence. Identifying the implications of various approaches for reaching conclusions on the range of alternative standard levels that is appropriate to consider can help inform the final decisions to either retain or revise the standards. Today’s fina l decisions also take into account public health policy judgments as to the degree of health protection that is to be achieved. In reaching staff conclusions on the range of annual standard levels that was appropriate to consider, the Policy Assessment fo cused on identifying an annual standard that provided requisite protection from effects associated with both long

- and short

- term exposures. In so doing, the Policy Assessment explored different approaches for characterizing the range of PM 2.5 concentratio ns over which our confidence in the nature of the associations for both long

- and short

- term exposures is greatest, as well as the extent to which our confidence is reduced at lower PM 2.5 concentrations. First, the Policy Assessment recognized that the approach that most directly
a threshold focused on cardiovascular

- related hospital admissions and emergency department visits associated with short

- term PM 10 exposures and prem ature mortality associated with long

- term PM 2.5 exposure (U.S. EPA, 2009a, sections 6.5, 6.2.10.10 and 7.6). Overall, the Integrated Science Assessment concluded that the studies evaluated support the use of a no

- threshold, log

- linear model but recognized that “additional issues such as the influence of heterogeneity in estimates between cities, and the effect of seasonal and regional differences in PM on the concentration

- response relationship still require further investigation” (U.S. EPA, 2009a, section 2.4.3).***E.O. 12866 Review

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Page 18 of 253 addressed this issue considered studies that analyzed confidence intervals around concentration

- response relationships and in particular, analyses that averaged across multiple co ncentration

- response models rather than considering a single concentration

response model. 7 The Policy Assessment explored the extent to which such analyses had been published for studies of health effects associated with long

- or short

- term PM 2.5 exposure s. Such analyses could potentially be used to characterize a concentration below which uncertainty in a concentration

- response relationship substantially increases or is judged to be indicative of an unacceptable degree of uncertainty about the existence o f a continuing concentration

- response relationship. The Policy Assessment concluded that identifying this area of uncertainty in the concentration

- response relationship could be used to inform identification of alternative standard levels that are appropri ate to consider. Further, the Policy Assessment explored other approaches that considered different statistical metrics from epidemiological studies. The Policy Assessment first took into account the general approach used in previous PM reviews which focu sed on consideration of alternative standard levels that were somewhat below the long

- term mean PM 2.5 concentrations reported in epidemiological studies using air quality distributions based on composite monitor concentrations. 8 This approach recognized th at

7 This is distinct from confidence intervals around concentration

- response relationships that are related to the magnitude of effect estimates generated at specific PM 2.5 concentrations (i.e., point

- wise confidence intervals) and that are relevant to the precision of the effect estimate across the air quality distribution, rather than to our confidence in the existence of a continuing concentration

- response relationship across the entire air quality distribution on which a reported association was b ased. 8 Using the term “composite monitor” does not imply that the EPA can identify one monitor that represents the air quality evaluated in a specific study area. Rather, the composite monitor concentration represents the average concentration across mon itors within each area with more than one monitor included in a given study as typically***E.O. 12866 Review

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Page 19 of 253 the strongest evidence of PM 2.5 - related associations occurs at concentrations around the long

- term (i.e., annual) mean. In using this approach, the Policy Assessment placed greatest weight on those long

- and short

- term exposure studies that reported sta tistically significant associations with mortality and morbidity effects. In extending this approach, the Policy Assessment also considered information beyond a single statistical metric of PM 2.5 concentrations (i.e., the mean) to the extent such informat ion was available. Pursuant to an express comment from CASAC (Samet 2010d, p. 2), the Policy Assessment utilized distributional statistics (i.e., statistical characterization of an entire distribution of data) to identify the broader range of PM 2.5 concent rations that had the most influence on the calculation of relative risk estimates in both long

- and short

- term exposure epidemiological studies. Thus, the Policy Assessment considered the part of the distribution of PM 2.5 concentrations in which the data a nalyzed in the study (i.e., air quality and population

- level data, as discussed below) w ere most concentrated, specifically, the range of PM 2.5 concentrations around the long

- term mean over which our confidence in the magnitude and significance of associat ions observed in the epidemiological studies was greatest. The Policy Assessment then focused on the lower part of th e distribution to characterize where the data became appreciably more sparse and, thus, where our understanding of the magnitude and signif icance of the associations correspondingly became more uncertain. The Policy Assessment recognized there was no single percentile value within a given distribution that was most appropriate or “correct” to use to characterize where our confidence in the as sociations becomes reported in epidemiological studies. For multi

- city studies, this metric reflects concentrations averaged across multiple monitors or from single monitors within each area and then averaged across study areas for an overall study mean PM 2.5 concentration. This is consistent with the epidemiological evidence considered in other NAAQS reviews.***E.O. 12866 Review

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Page 20 of 253 appreciably lower. The Policy Assessment concluded that the range from the 25 th to 10 th percentiles is a reasonable range to consider as a region where we had appreciably less confidence in the associations observed in epidemiological studies. 9 In considering distributional statistics from epidemiological studies, the final Policy Assessmen t focused on two types of population

- level metrics that CASAC advised were most useful to consider in identifying the PM 2.5 concentrations most influential in generating the health effect estimates reported in the epidemiological studies. 10 Consistent with CASAC advice, the most relevant information was the distribution of health events (e.g., deaths, hospitalizations) occurring within a study population in relation to the distribution of PM 2.5 concentrations. However, in recognizing that access to health ev ent data can be restricted, the Policy Assessment also considered the number of study participants within each study area as an appropriate surrogate for health event data. 9 In the PM NAAQS review completed in 2006, the Staff Paper similarly recognize d that the evidence of an association in any epidemiological study is “strongest at and around the long

- term average where the data in the study are most concentrated. For example, the interquartile range of long

- term average concentrations within a study [with a lower bound of the 25 th percentile] or a range within one standard deviation around the study mean, may reasonably be used to characterize the range over which the evidence of association is strongest” (U.S. EPA, 2005, p. 5

- 22). A range of one stan dard deviation around the mean represents approximately 68 percent of normally distributed data, and below the mean falls between the 25 th and 10 th percentiles. 10 The second draft Policy Assessment focused on the distributions of ambient PM 2.5 concentrations and associated population data across areas included in several multi

- city studies for which such data were available in seeking to identify the most influential range of concentrations (U.S. EPA, 2010f, section 2.3.4.1). In its review of t he second draft Policy Assessment, CASAC advised that it “would be preferable to have information on the concentrations that were most influential in generating the health effect estimates in individual studies” (Samet, 2010d, p.2). Therefore, in the final Policy Assessment, the EPA considered population

- level data (i.e., area

- specific health event data and study area population data) along with corresponding PM 2.5 concentrations to generate a cumulative distribution of the population

- level data relative to long

- term mean PM 2.5 concentrations to determine the most influential part of the air quality distribution (U.S. EPA, 2011a, Figure 2

- 7 and associated text).***E.O. 12866 Review

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Page 21 of 253 The Policy Assessment recognize d that an approach considering analyses of confide nce intervals around concentration

- response functions wa s intrinsically related to an approach that consider ed different distributional statistics. Both of these approaches could be employed to understand the broader distribution of PM 2.5 concentrations wh ich correspond to the health events reported in epidemiological studies. In applying these approaches, the Policy Assessment, consistent with CASAC advice (Samet, 2010d, p.3), considered PM 2.5 concentrations from long

- and short

- term PM 2.5 exposure studies using composite monitor distributions. In reaching staff conclusions on alternative standard levels that were appropriate to consider, the Policy Assessment also included a broader consideration of the uncertainties and limitations of the current scienti fic evidence. Most notably, these uncertainties are related to the heterogeneity observed in the epidemiological studies in the eastern versus western parts of the U.S., the relative toxicity of PM 2.5 components, and the potential role of co

- pollutants ( U. S. EPA, 2011a, pp. 2

- 25 to 2

- 26). The limitations and uncertainties associated with the currently available scientific evidence, including the availability of fewer studies toward the lower range of alternative annual standard levels being considered in th is proposal, are summarized in section III.B below and further discussed in section III.B.2 of the preamble to the proposed rule propos al
. The Policy Assessment recognized that the level of protection afforded by the NAAQS relies both on the level and the form of the standard. The Policy Assessment concluded that a policy approach that used data based on composite monitor distributions to identify alternative sta ndard levels, and then compared those levels to concentrations at maximum monitors to determine whether an area meets a given standard, inherently has***E.O. 12866 Review

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Page 22 of 253 the potential to build in some margin of safety ( U.S. EPA, 2011a, p. 2

- 14). 11 This conclusion was consiste nt with CASAC’s comments on the second draft Policy Assessment , in which CASAC expressed its preference for focusing on an approach using composite monitor distributions “because of its stability, and for the additional margin of safety it provides” when “ compared to the maximum monitor perspective” (Samet, et al., 2010d, pp. 2 to 3). In reaching staff conclusions on alternative 24

- hour standard levels that are appropriate to consider for setting a 24

- hour standard intended to supplement the protection aff

orded by a generally controlling annual standard, the Policy Assessment considered currently available short

- term PM 2.5 exposure studies. The evidence from these studies informed our understanding of the protection afforded by the suite of standards agains t effects associated with short

- term exposures. In considering the short

term exposure studies, the Policy Assessment evaluated both the distributions of 24

- hour PM 2.5 concentrations, with a focus on the 98 th percentile concentrations (to the extent such d ata were available) to match the form of the current 24

- hour PM 2.5 standard, as well as the long

- term mean PM 2.5 concentrations reported in these studies. In addition to considering the epidemiological evidence, the Policy Assessment also considered air

11 Statistical metrics (e.g., means) based on composite monitor distributions may be identical to or below the same statistical metrics based on maximum monitor distributions. For example, some areas may have only one monitor, in which case the composite and maximum monitor distributions will be identical in those areas. Other areas may have multiple m onitors that may be very close to the monitor measuring the highest concentrations, in which case the composite and maximum monitor distributions could be similar in those areas. As noted in Hassett

- Sipple et al. (2010), for studies involving a large numbe r of areas, the composite and maximum concentrations are generally within 5 percent of each other (77 FR 38905, fn. 30). Still other areas may have multiple monitors that may be separately impacted by local sources in which case the composite and maximum m onitor distributions could be quite different (U.S. EPA, 2011a, p. 2

- 14). See further discussion of this issue in section III.E.4.c.i below.***E.O. 12866 Review

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Page 23 of 253 qu ality information based on county

- level 24

- hour and annual design values 12 to understand the policy implications of the alternative standard levels supported by the underlying science. In particular, the Policy Assessment considered the extent to which diff erent combinations of alternative annual and 24

- hour standards would support the policy goal of focusing on a generally controlling annual standard in conjunction with a 24

- hour standard that would provide supplemental protection. In so doing, the Policy A ssessment discussed the roles that each standard might be expected to play in the protection afforded by alternative suites of standards. Beyond these evidence

- based considerations, the Policy Assessment also considered the quantitative risk estimates and the key observations presented in the Risk Assessment. This assessment included an evaluation of 15 urban case study areas and estimated risk associated with a number of health endpoints associated with long

- and short

- term PM 2.5 exposures ( U.S. EPA, 2010a ). As part of the risk

- based considerations, the Policy Assessment considered estimates of the magnitude of PM 2.5 - related risks associated with recent air quality levels and air quality simulated to just meet the current and alternative suites of standards using alternative simulation approaches. The Policy Assessment also characterized the risk reductions, relative to the risks remaining upon just meeting the current standards, associated with just meeting alternative suites of standards. In so doing, the Policy Assessment recognized the uncertainties inherent in such risk estimates, and took such uncertainties into account by considering the sensitivity of the “core” risk estimates to alternative assumptions and methods likely to have substantial impact on the estimates. In addition, the Policy Assessment considered

12 Design values are the metrics (i.e., statistics) that are compared to the NAAQS levels to determine compliance.***E.O. 12866 Review

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Page 24 of 253 additional analyses characterizing the representativeness of the urban study areas within a broader national context to understand the roles that the annual and 24

- hour standards may play in aff

ording protection against effects related to both long

- and short

- term PM 2.5 exposures. Based on the approach discussed above, the Policy Assessment reached conclusions related to the primary PM 2.5 standards that reflected an understanding of both evidence

- based and risk

- based considerations to inform two overarching questions related to: (1) the adequacy of the current suite of PM 2.5 standards and (2) revisions to the standards that were appropriate to consider in this review to protect against health effects associated with both long

- and short

- term exposures to fine particles. When evaluating the health protection afforded by the cu rrent or any alternative suites of standards considered, the Policy Assessment took into account the four basic elements of the NAAQS: the indicator, averaging time, form, and level. The general approach for reviewing the primary PM 2.5 standards described above provided a comprehensive basis that helped to inform the Administrator’s judgments in reaching her proposed and final decisions to revise the current suite of primary fine particle NAAQS and in responding to the remand of the 2006 primary annual PM 2. 5 standard. B. Overview of Health Effects Evidence This section outlines the key information presented in section III.B of the proposal (77 FR 38906 to 38911, June 29, 2012) and discussed more fully in the Integrated Science Assessment (Chapters 2, 4, 5, 6, 7 , and 8) and the Policy Assessment (Chapter 2) related to health effects associated with fine particle exposures. Section III.B.***E.O. 12866 Review

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Page 25 of 253 of the proposal discusses available information on the health effects associated with exposures to PM 2.5 , including the nature of such health effects (section III.B.1) and associated limitations and uncertainties (section III.B.2), at

- risk populations (section III.B.3), and potential PM 2.5 - related impacts on public health (section III.B.4). As was true in the last two reviews, evi dence from epidemiologic al , controlled human exposure and animal toxicological studies played a key role in the Integrated Science Assessment ’s evaluation of the scientific evidence. The 2006 PM NAAQS review concluded that there was “strong epidemiologica l evidence” for linking long

- term PM 2.5 exposures with cardiovascular

- related and lung cancer mortality and respiratory

- related morbidity and for linking short

- term PM 2.5 exposures with cardiovascular

- related and respiratory

- related mortality and morbidity ( U.S. EPA, 2004, p. 9

- 46; U.S. EPA, 2005, p. 5

- 4). Overall, the evidence from epidemiological, toxicological, and controlled human exposure studies supported “likely causal associations” between PM 2.5 and both mortality and morbidity from cardiovascular
a nd respiratory diseases, based on “an assessment of strength, robustness, and consistency in results” ( U.S. EPA, 2004, p. 9

- 48). 13 In this review, based on the expanded body of evidence, the EPA finds that: (1) In looking across the extensive new scientific ev idence available in this review, our overall understanding of health effects associated with fine particle exposures has been greatly expanded. The currently available evidence is largely consistent with evidence available in the last review and substantia lly strengthens what is known about the effects associated with fine particle exposures.

13 The term “likely causal association” was used in the 2004 Criteria Document to summarize the strength of the available evidence available in the last review for PM 2.5 . However, this terminology was not based on a formal framework for evaluating evidence f or inferring causation. Since the last review, the EPA has developed a more formal framework for reaching causal determinations with standardized language to express evaluation of the evidence (U.S. EPA, 2009a, section 1.5).***E.O. 12866 Review

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Page 26 of 253 (2) A number of large multi

- city epidemiological studies have been conducted throughout the U.S., including extended analyses of long

- term exposure studies that were impo rtant to inform decision

- making in the last review. The body of currently available scientific evidence has also been expanded greatly by the publication of a number of new multi

- city, time

- series studies that have used uniform methodologies to investigate the effects of short

- term PM 2.5 exposures on public health. This body of evidence provides a more expansive data base and considers multiple locations representing varying regions and seasons that provide evidence of the influence of different air polluti on mixes on PM 2.5 - associated health effects. These studies provide more precise estimates of the magnitude of effects associated with short

- term PM 2.5 exposure than most smaller

- scale single

city studies that were more commonly available in the last review . These studies have reported consistent increases in morbidity and/or premature mortality related to ambient PM 2.5 concentrations, with the strongest evidence reported for cardiovascular

- related effects. (3) In addition, the findings of new toxicological and controlled human exposure studies greatly expand and provide stronger support for a number of potential biologic al mechanisms or pathways for cardiovascular and respiratory effects associated with long

- and short

- term PM exposures. These studies provide co herence and biological plausibility for the effects observed in epidemiological studies. (4) Using a more formal framework for reaching causal determinations than used in prior reviews 14 , , 15 the EPA concludes that a causal relationship exists between
14 The causal framework draws up on the assessment and integration of evidence from across epidemiological, controlled human exposure, and toxicological studies, and the related uncertainties that ultimately influence our understanding of the evidence. This framework employs a five

- level hierarchy that classifies the overall weight of evidence and causality using the following categorizations: causal relationship, likely to be causal relationship, suggestive of a causal relationship, inadequate to infer a causal relationship, and not likel y to be a causal relationship ( U.S. EPA, 2009a, Table 1

- 3). Th e development of the causal framework reflects considerable input from CASAC and the public, with CASAC concluding that , “ T he five

- level classification of strength of evidence for causal inferen ce has been systemically applied [for PM] ; this approach has provided transparency and a clear statement of the level of confidence with regard to causation, and we recommend its continued use in future ISAs” (Samet, 2009f, p. 1). 15 The causal framework dr aws upon the assessment and integration of evidence from across epidemiological, controlled human exposure, and toxicological studies, and the related uncertainties that ultimately influence our understanding of the evidence. This framework employs a five

- level hierarchy that classifies the overall weight of evidence and causality using the following categorizations: causal relationship, likely to be causal relationship, suggestive of a causal relationship, inadequate to infer a causal relationship, and not likely to be a causal relationship (U.S. EPA, 2009a, Table 1

- 3). The development of the causal framework reflects considerable input from CASAC and the public, with CASAC concluding that, “The five

- level classification of strength of evidence for causal***E.O. 12866 Review

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Page 27 of 253 both long

- and short

- term exposures to PM 2.5 and premature mortality and cardiovascular effects and a likely causal relationship exists between long

- and short

- term PM 2.5 exposures and respirator y effects. Further, there is evidence suggestive of a causal relationship between long

- term PM 2.5 exposures and other health effects, including developmental and reproductive effects (e.g., low birth weight, infant mortality) and carcinogenic, mutagenic, a nd genotoxic effects (e.g., lung cancer mortality). 16 (5) The newly available evidence significantly strengthens the link between long

- and short

- term exposure to PM 2.5 and premature mortality, while providing indications that the magnitude of the PM 2.5 - mortal ity association with long

- term exposures may be larger than previously estimated. The strongest evidence comes from recent studies investigating long

- term exposure to PM 2.5 and cardiovascular

related mortality. The evidence supporting a causal relationship between long

term PM 2.5 exposure and mortality also includes consideration of new studies that demonstrated an improvement in community health following reductions in ambient fine particles. (6) Several new studies have examined the association between cardio vascular effects and long

- term PM 2.5 exposures in multi

- city studies conducted in the U.S. and Europe. While studies were not available in the last review with regard to long

term exposure and cardiovascular

- related morbidity, recent studies have provided new evidence linking long

- term exposure to PM 2.5 with an array of cardiovascular effects such as heart attacks, congestive heart failure, stroke, and mortality. This evidence is coherent with studies of short

- term exposure to PM 2.5 that have observed assoc iations with a continuum of effects ranging from subtle changes in indicators of cardiovascular health to serious clinical events, such as increased hospitalizations and emergency department visits due to cardiovascular disease and cardiovascular mortality
. (7) Extended analyses of studies available in the last review as well as new epidemiological studies conducted in the U.S. and abroad provide stronger evidence of respiratory

- related morbidity effects associated with long

- term PM 2.5 exposure. The strongest e vidence for respiratory

- related effects is from studies that evaluated decrements in lung function growth, increased respiratory symptoms, and asthma development. The strongest evidence from short

- term PM 2.5 exposure studies has been observed for increased respiratory

- related

i nference has been systemically applied [for PM]; this approach has provided transparency and a clear statement of the level of confidence with regard to causation, and we recommend its continued use in future ISAs” (Samet, 2009f, p. 1). 16 These causal infe rences are based not only on the more expansive epidemiological evidence available in this review but also reflect consideration of important progress that has been made to advance our understanding of a number of potential biologic modes of action or path ways for PM

- related cardiovascular and respiratory effects (U.S. EPA, 2009a, chapter 5).***E.O. 12866 Review

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Page 28 of 253 emergency department visits and hospital admissions for chronic obstructive pulmonary disease (COPD) and respiratory infections. (8) The body of scientific evidence is somewhat expanded from the 2006 review but is still limited with respect to associations between long

- term PM 2.5 exposures and developmental and reproductive effects as well as cancer, mutagenic, and genotoxic effects. The strongest evidence for an association between PM 2.5 and developmental and reproductive effects com es from epidemiological studies of low birth weight and infant mortality, especially due to respiratory causes during the post

- neonatal period (i.e., 1 month

- 12 months of age). With regard to cancer effects, “[m]ultiple epidemiologic studies have shown a consistent positive association between PM 2.5 and lung cancer mortality, but studies have generally not reported associations between PM 2.5 and lung cancer incidence” (U.S. EPA 2009a p. 2

- 13 )
. (9) Efforts to evaluate the relationships between PM composition and health effects continue to evolve. While many constituents of PM 2.5 can be linked with differing health effects, the evidence is not yet sufficient to allow differentiation of those constituents or sources that may be more closely related to specific health outcomes nor to exclude any individual component or group of components associated with any source categories from the fine particle mixture of concern. (10) Specific groups within the general population are at increa sed risk for experiencing adverse health effects related to PM exposures . The currently available evidence expands our understanding of previously identified at

- risk populations (i.e., children, older adults, and individuals with pre

- existing heart and lun g disease) and supports the identification of additional at

- risk populations (e.g., persons with lower socioeconomic status, genetic differences). Evidence for PM

- related effects in these at

- risk populations has expanded and is stronger than previously obs erved. There is emerging, though still limited, evidence for additional potentially at

- risk populations, such as those with diabetes, people who are obese, pregnant women, and the developing fetus. (11) The population potentially affected by PM 2.5 is large. In addition, large subgroups of the U.S. population have been identified as at

- risk populations. While individual effect estimates from epidemiological studies may be small in size, the public health impact of the mortality and morbidity associations can be q uite large given the extent of exposure. Taken together, this suggests that exposure to ambient PM 2.5 concentrations can have substantial public health impacts. (12) While the currently available scientific evidence is stronger and more consistent than in prev ious reviews, providing a strong basis for decision making in this review, the EPA recognizes that important uncertainties and limitations in the health effects evidence remain. Epidemiological studies evaluating health effects associated with long

- and sh ort
- term PM 2.5 exposures have reported heterogeneity in responses between cities and geographic regions within the U.S. This heterogeneity may be attributed, in part, to differences in the fine particle***E.O. 12866 Review

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Page 29 of 253 composition or related to exposure measurement error, which can introduce bias and increased uncertainty in associated health effect estimates. Variability in the associations observed across PM 2.5 epidemiological studies may be due in part to exposure error related to measurement

- related issues, the use of central fixed

- site monitors to represent population exposure to PM 2.5 , models used in lieu of or to supplement ambient measurements, and our limited understanding of factors that may influence exposures (e.g., topography, the built environment, weather, so urce characteristics, ventilation usage, personal activity patterns, photochemistry). In addition, where PM 2.5 and other pollutants (e.g., ozone, nitrogen dioxide, and carbon monoxide) are correlated, it can be difficult to distinguish the effects of the v arious pollutants in the ambient mixture (i.e., co

- pollutant confounding). 17 While uncertainties and limitations still remain in the available health effects evidence, the Administrator judges the currently available scientific data base to be stronger and more consistent than in previous reviews providing a strong basis for decision making in this review. C. Overview of Quantitative Characterization of Health Risks In addition to a comprehensive evaluation of the health effects evidence available in this rev iew, the EPA conducted an expanded quantitative risk assessment for selected health endpoints to provide additional information and insights to inform decisions on the primary PM 2.5 NAAQS. 18 As discussed in section III.C of the proposal, the approach used t o develop quantitative risk estimates associated with PM 2.5 exposures was built on the approach used and lessons learned in the last review and focused on improving the characterization of the overall confidence in the risk estimates, including related

17 A copollutant meets the criteria for potential confounding in PM

- health associations if: (1) it is a potential risk factor for the health effect under study; (2) it is correlated with PM; and (3) it does not act as an intermediate step in the pathway between PM exposure and the health effect under study (U.S. EPA, 2004, p. 8

- 10). 18 The quantitative risk assessment conducted for this review is more fully described and presented in the Risk Assessment (U.S. EPA, 2010a) and summarized in detail in the Policy Assessment (U.S. EPA, 2011a, sections 2.2.2. and 2.3.4.2). The scope and methodology for this risk assessment were developed over the last few years with considerabl e input from CASAC and the public as described in section I. C.2 of the proposal
. II.B.3 above
.***E.O. 12866 Review

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Page 30 of 253 unc ertainties, by incorporating a number of enhancements, in terms of both the methods and data used in the analyses. The goals of this quantitative risk assessment were largely the same as those articulated in the risk assessment conducted for the last revi ew. These goals included: (1) to provide estimates of the potential magnitude of premature mortality and/or selected morbidity effects in the population associated with recent ambient levels of PM 2.5 and with simulating just meeting the current and alterna tive suites of PM 2.5 standards in 15 selected urban study areas 19 , , 20 including, where data were available, consideration of impacts on at

- risk populations; (2) to develop a better understanding of the influence of various inputs and assumptions on the risk estimates to more clearly differentiate among alternative suites of standards; and (3) to gain insights into the distribution of risks and patterns of risk reductions and the variability and uncertainties in those risk estimates. In

19 T he Risk Assessment conclude d that these 15 urban study areas we re generally representative of urban areas in the U.S. likely to experience relatively elevated levels of risk related to ambient PM 2.5 exposure with the potential for better characterization at the higher end of that distribution ( U.S. EPA, 2011a, p. 2

- 42; U.S. EPA, 2010a, section 4.4, Figure 4

- 17). The representativeness analysis also show ed that the 15 urban study areas do not capture areas with the highest baseline morality risks or the oldest populations (both of which can result in higher PM 2.5 - related mortality estimates)
. However, some of the areas with the highest values for these at tributes ha d relatively low PM 2.5 concentrations (e.g., urban areas in Florida) and, consequently, the Risk Assessment conclude d failure to include these areas i n the set of urban study areas wa s unlikely to exclude high PM 2.5 - risk locations ( U.S. EPA, 2010a, section 4.4.1). 20 The Risk Assessment concluded that these 15 urban study areas were generally representative of urban areas in the U.S. likely to experience relatively elevated levels of risk related to ambient PM 2.5 exposure with the potenti al for better characterization at the higher end of that distribution (U.S. EPA, 2011a, p. 2

- 42; U.S. EPA, 2010a, section 4.4, Figure 4

- 17). The representativeness analysis also showed that the 15 urban study areas do not capture areas with the highest bas eline morality risks or the oldest populations (both of which can result in higher PM 2.5 - related mortality estimates). However, some of the areas with the highest values for these attributes had relatively low PM 2.5 concentrations (e.g., urban areas in Flo rida) and, consequently, the Risk Assessment concluded failure to include these areas in the set of urban study areas was unlikely to exclude high PM 2.5 - risk locations (U.S. EPA, 2010a, section 4.4.1).***E.O. 12866 Review

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Page 31 of 253 addition, the quantitative risk assessment included nationwide estimates of the potential magnitude of premature mortality associated with long

- term exposure to recent ambient PM 2.5 concentrations to more broadly characterize this risk on a national scale and to support the interpretation of the more detailed risk estimates generated for select ed urban study areas. The expanded and updated risk assessment conducted in this review included estimates of risk for: (1) all

- cause, ischemic heart disease

- related, cardiopulmonary

related, and lung cancer

- related mortality associated with long

- term PM 2 .5 exposure; (2)
non - accidental, cardiovascular

- related, and respiratory

- related mortality associated with short

- term PM 2.5 exposure; and (3) cardiovascular

- related and respiratory

- related hospital admissions and asthma

- related emergency department visits associated with short

- term PM 2.5 exposure. 21 The Risk Assessment included a core set of risk estimates supplemented by an alternative set of risk results generated using single

- factor and multi

- factor sensitivity analyses. The core set of risk estimates wa s developed using the combination of modeling elements and input data sets identified in the Risk Assessment as having higher confidence relative to inputs used in the sensitivity analyses. The results of the sensitivity analyses provided information to ev aluate and rank the potential impacts of key sources of uncertainty on the core risk estimates. In addition, the sensitivity analyses represented a set of reasonable alternatives to the core set of risk estimates that fell within an overall set of plausibl e risk estimates surrounding the core estimates.

21 The evidence available for these selected health eff ect endpoints generally focused on the entire population, although some information was available to support analyses that considered differences in estimated risk for at

- risk populations including older adults and persons with pre

- existing cardiovascular and respiratory diseases.***E.O. 12866 Review

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Page 32 of 253 The EPA recognized that there were many sources of variability and uncertainty inherent in the inputs to its quantitative risk assessment. 22 The design of the risk assessment included a number of elements to address these issues in order to increase the overall confidence in the risk estimates generated for the 15 urban study areas, including using guidance from the World Health Organization (WHO, 2008) as a framework for characterizing uncertainty in the ana lyses. 23 With respect to the sources of variability, the Risk Assessment considered those that contributed to differences in risk across urban study areas, but did not directly affect the degree of risk reduction associated with the simulation of just meet ing current or alternative standard levels (e.g., differences in baseline incidence rates, demographics and population behavior). The Risk Assessment also focused on factors that not only introduced variability into risk estimates across study areas, but a lso played an important role in determining the magnitude of risk reductions upon simulation of just meeting current or alternative standard levels (e.g., peak

- to
- mean ratios of ambient PM 2.5 concentrations within individual urban study areas and the natur e of the rollback approach used to simulate just meeting the current or alternative standards). Key sources of potential variability that were likely to affect population risks included the following : (1) intra

- urban variability in ambient PM 2.5 concentrat ions, including PM 2.5 composition; (2) variability in the patterns of reductions in PM 2.5 concentrations associated with different rollback approaches when simulating just meeting the current or alternative

22 Variability refers to the heterogeneity of a variable of interest within a population or across different populations. Uncertainty refers to the lack of knowledge regarding the actual values of inputs to an analysis (U.S. EPA, 2 010a, p. 3

- 63). 23 The extent to which key sources of potential variability were (or were not) fully captured in the design of the risk assessment are discussed in section 3.5.2 of the Risk Assessment (U.S. EPA, 2010a, pp. 3

- 67 to 3

- 69).***E.O. 12866 Review

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Page 33 of 253 standards; co

- pollutant exposures; (3) factors related to demographic and socioeconomic status; (4) behavioral differences across urban study areas (e.g., time spent outdoors); (5) baseline incidence rates; and (6) longer

- term temporal variability in ambient PM 2.5 concentrations reflecting meteorologic al trends as well as future changes in the mix of PM 2.5 sources, including changes in air quality related to future regulatory actions. With regard to uncertainties, single and multi

- factor sensitivity analyses were combined with a qualitative analysis to assess the impact of potential sources of uncertainty on the core risk estimates. Key sources of uncertainty included: (1) characterizing intra

- urban population exposure in the context of epidemiolog y ical studies linking PM 2.5 to specific health effects; (2) statistical fit of the concentration

- response functions for short

- term exposure
- related health endpoints; (3) shape of the concentration

- response functions; (4) specifying the appropriate lag structure for short

term exposure studies; (5) transferabili ty of concentration

- response functions from study locations to urban study area locations for long

- term exposure
- related health endpoints; (6) use of single

- city versus multi

- city studies in the derivation of concentration

- response functions; (7) impact of historical air quality on estimates of health risk associate with long

- term PM 2.5 exposures; and (8) potential variation in effect estimates reflecting compositional differences in PM 2.5 . Beyond characterizing uncertainty and variability, a number of desi gn elements were included in the risk assessment to increase the overall confidence in the risk estimates generated for the 15 urban study areas ( U.S. EPA, 2011a, pp. 2

- 38 to 2

- 41). These elements included: (1) use of a deliberative process for specifying components of the risk model that reflects consideration of the latest research on PM 2.5 exposure and risk***E.O. 12866 Review

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Page 34 of 253 ( U.S. EPA, 2010a, section 5.1.1); (2) integration of key sources of variability into the design as well as the interpretation of risk estimates (U.S. EPA, 2010a, section 5.1.2); (3) assessment of the degree to which the urban study areas are representative of areas in the U.S. experiencing higher PM 2.5 - related risk (U.S.EPA, 2010a, section 5.1.3); and (4) identification and assessment of important sourc es of uncertainty and the impact of these uncertainties on the core risk estimates (U.S.EPA, 2010a, section 5.1.4). Further, additional analyses examined potential bias and overall confidence in the risk estimates. Greater confidence is associated with ris k estimates based on simulated annual mean PM 2.5 concentrations that are within the region of the air quality distribution used in deriving the concentration

- response functions where the bulk of the data reside (e.g., within one standard deviation around t he long

- term mean PM 2.5 concentration) ( U.S. EPA, 2011a, p. 2

- 38). Key observations and insights from the PM 2.5 risk assessment, together with important caveats and limitations , were discussed in section III.C.3 of the proposal. In general, in considering the set of quantitative risk estimates and related uncertainties and limitations related to long

- and short

- term PM 2.5 exposure together with consideration of the health endpoints which could not be quantified, the Policy Assessment concluded this informat ion provided strong evidence that risks estimated to remain upon simulating just meeting the current suite of PM 2.5 standards are important from a public health perspective, both in terms of severity and magnitude of effects. Patterns of increasing estimat ed risk reductions were generally observed as either the annual or 24

- hour standard level, or both, were reduced over the ranges considered in the Risk Assessment. The magnitude of both long

- and short

- term exposure
- related risk estimated to***E.O. 12866 Review

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Page 35 of 253 remain upon ju st meeting the current suite of standards as well as alternative standard levels w as strongly associated with the simulated change in annual mean PM 2.5 concentrations. Although long

- and short

- term exposure
- related mortality rates have similar patterns in terms of the subset of urban study areas experiencing risk reductions for the current suite of standard levels, the magnitude of risk remaining is high er for long

term exposure
- related mortality and substantially lower for short

- term exposure
- related mortality. Short

- term exposure
- related morbidity risk estimates w ere greater for cardiovascular

- related than respiratory

- related events and emergency depart ment visits for asthma

- related events were significant: Furthermore, most of the aggregate risk associated with short

- term exposures was not primarily driven by the small number of days with PM 2.5 concentrations in the upper tail of the air quality distrib ution, but rather by the large number of days with PM 2.5 concentrations at and around the mean of the distribution, that is, the 24

- hour average concentrations that are in the low

- to mid

- range, well below the peak 24

- hour concentrations (U.S. EPA, 2011a, p . 2

- 3)
. With regard to characterizing estimates of PM 2.5 - related risk associated with simulation of alternative standards, the Policy Assessment recognized that greater overall confidence was associated with estimates of risk reduction than for estimates o f absolute risk remaining ( U.S. EPA, 2011a, p. 2

- 94). Furthermore, the Policy Assessment recognized that estimates of absolute risk remaining for each of the alternative standard levels considered, particularly in the context of long

- term exposure
- related mortality,***E.O. 12866 Review

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Page 36 of 253 may be underestimated 24 . In addition, the Policy Assessment observed that in considering the overall confidence associated with the quantitative analyses, the Risk Assessment recognized that: (1) substantial variability existed in the magnitude o f risk remaining across urban study areas and (2) in general, higher confidence was associated with risk estimates based on PM 2.5 concentrations near the mean PM 2.5 concentrations in the underlying epidemiological studies providing the concentration

- respon se functions ( i. e . g . , within one standard deviation of the mean PM 2.5 concentration reported). Furthermore, although the Risk Assessment estimated that the alternative 24

- hour standard levels considered (when controlling) would result in additional estimat ed risk reductions beyond those estimated for alternative annual standard levels alone, these additional estimated reductions were highly variable. Conversely, the Risk Assessment recognized that alternative annual standard levels, when controlling, result ed in more consistent risk reductions across urban study areas, thereby potentially providing a more consistent degree of public health protection ( U.S. EPA, 2010a, p. 5

- 17). D. Conclusions on the Adequacy of the Current Primary PM 2.5 Standards 1. Introduction The initial issue to be addressed in the current review of the primary PM 2.5

24 Based on the con sideration of both the qualitative and quantitative assessments of uncertainty, the Risk Assessment concluded that it is unlikely that the estimated risks are over - stated, particularly for premature mortality related to long

- term PM 2.5 exposures. In fact, the Policy Assessment and the Risk Assessment concluded that the core risk estimates for this category of health effects may well be biased low based on consideration of alternative model specifications evaluated in the sensitivity ana lyses (U.S. EPA, 2011a, p. 2

- 41; U.S. EPA, 2010a, p. 5

- 16; Figures 4

- 7 and 4

- 8). In addition, the Policy Assessment recognized that the currently available scientific information included evidence for a broader range of health endpoints and at

- risk populat ions beyond those included in the quantitative risk assessment, including decrements in lung function growth and respiratory symptoms in children as well as reproductive and developmental effects (U.S. EPA, 2011a, section 2.2.1).***E.O. 12866 Review

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Page 37 of 253 standards is whether, in view of the advances in scientific knowledge and other information reflected in the Integrated Science Assessment, the Risk Assessment, and the Policy Ass essment, the existing standards should be retained or revised. In considering the adequacy of the current suite of PM 2.5 standards, the Administrator has considered the large body of evidence presented and assessed in the Integrated Science Assessment ( U.S
. EPA, 2009a), the quantitative assessment of risks, staff conclusions and associated rationales presented in the Policy Assessment , views expressed by CASAC, and public comments. The Administrator has taken into account both evidence

- and risk

- based consi derations 25 in developing final conclusions on the adequacy of the current primary PM 2.5 standards.
a. Evidence

- and Risk

- based Considerations in the Policy Assessment In considering the available epidemiologic al evidence in this review, the Policy Assessm ent took a broader approach than was used in the last review. This approach reflected the more extensive and stronger body of evidence available since the last review on health effects related to both long

- and short

- term exposure to PM 2.5 . As discussed in section III.A.3 above, this broader approach focused on setting the annual standard as the “generally controlling” standard for lowering both short

- and long

- term PM 2.5 concentrations and so providing requisite protection to public health . In conjunction with

25 Evidence

- based considera tions include the assessment of epidemiological, toxicological, and controlled human exposure studies evaluating long

- or short

- term exposures to PM 2.5 , with supporting evidence related to dosimetry and potential pathways/modes of action, as well as the in tegration of evidence across each of these disciplines, as assessed in the Integrated Science Assessment (U.S. EPA, 2009a) and focus on the policy

- relevant considerations as discussed in section III.B above and in the Policy Assessment (U.S. EPA, 2011a, se ction 2.2.1). Risk

- based considerations draw from the results of the quantitative analyses presented in the Risk Assessment (U.S. EPA, 2010a) and focus on the policy

- relevant considerations as discussed in section III.C above and in the Policy Assessment ( U.S. EPA, 2011a, section 2.2.2).***E.O. 12866 Review

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Page 38 of 253 such an annual standard, this approach focused on setting the 24

- hour standard to provide supplemental protection against days with high peak PM 2.5 concentrations. In addressing the question whether the evidence now available in this review supports c onsideration of standards that are more protective than the current PM 2.5 standards, the Policy Assessment considered whether : (1) statistically significant health effects associations with long

- or short

- term exposures to fine particles occur in areas tha t would likely have met the current PM 2.5 standards ( [ see American Trucking Ass’ns Ass ociatio n , 283 F. 3d at 369, 376 (revision of level of PM NAAQS justified when health effects are observed in areas meeting the existing standard )), ) ] , and (2) associations with long

- term exposures to fine particles extend down to lower air quality concentrations than had previously been observed. With regard to associations observed in long

- term PM 2.5 exposure studies, the Policy Assessment recognized t hat extended follow

- up analyses of the ACS and Harvard Six Cities studies provided consistent and stronger evidence of an association with mortality at lower air quality distributions than had previously been observed ( U.S. EPA, 2011a, pp. 2

- 31 to 2

- 32). T he original and reanalysis of the ACS study reported positive and statistically significant effects associated with a long

- term mean PM 2.5 concentration of 18.2 μg/m 3 across 50 metropolitan areas for 1979 to 1983 (Pope et al., 1995; Krewski et al., 2000). 26 In extended analyses, positive and statistically significant effects of approximately similar magnitude were associated with declining PM 2.5 concentrations, from an aggregate long

term mean in 58 metropolitan areas of 21.2 μg/m 3 in the original monitoring period (1979

26 The study periods referred to in the Policy Assessment (U.S. EPA, 2011a) and in this final rule reflect the years of air quality data that were included in the analyses, whereas the study periods identified in the Integra ted Science Assessment (U.S. EPA, 2009a) reflect the years of health status event data that were included.***E.O. 12866 Review

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Page 39 of 253 to 1983) to 14.0 μg/m 3 for 116 metropolitan areas in the most recent years evaluated (1999

- 2000), with an overall average across the two study periods in 51 metropolitan areas of 17.7 μg/m 3 (Pope et al., 2002; Krewski et al., 2009). With rega rd to the Harvard Six Cities Study, the original and reanalysis reported positive and statistically significant effects associated with a long

- term mean PM 2.5 concentration of 18.0 μg/m 3 for 1980 to 1985 (Dockery et al., 1993; Krewski et al., 2000). In an extended follow

- up of this study, the aggregate long

- term mean concentration across all years evaluated was 16.4 μg/m 3 for 1980 to 1988 27 (Laden et al., 2006). In an additional analysis of the extended follow

up of the Harvard Six Cities study, investigators reported that the concentration

- response relationship was linear and “clearly continuing below the level” of the current annual standa rd ( U.S. EPA, 2009a, p. 7

- 92; Schwartz et al., 2008). Cohort studies conducted since the last review provided additional evidence of mortality associated with air quality distributions that are generally lower than those reported in the ACS and Harvard Si x Cities studies, with effect estimates that were similar or, in some studies, significantly greater in magnitude than in the ACS and Harvard Six Cities studies (see also, section III.D.1.a of the proposal, 77 FR 38918 to 28919; U.S. EPA, 2011a, pp. 2

- 32 t o 2

- 33). The Women’s Health Initiative (WHI) study reported positive and most often statistically significant associations between long

- term PM 2.5 exposure and cardiovascular

- related mortality as well as morbidity effects, with much larger relative risk es timates for mortality than in the ACS and Harvard Six Cities studies, at an aggregate long

- term mean PM 2.5 concentration of 12.9 μg/m 3 for 2000

27 Aggregate mean concentration provided by study author (personal communication from Dr. Francine Laden, 2009).***E.O. 12866 Review

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Page 40 of 253 (Miller et al., 2007). 28 Using the Medicare cohort, Eftim et al. (2008) reported somewhat higher effect estimate s than in the ACS and Harvard Six Cities studies with aggregate long

- term mean concentrations of 13.6 μg/m 3 and 14.1 μg/m 3 , respectively, for 2000

- to 2002. Zeger et al. (2008) reported associations between long

- term PM 2.5 exposure and mortality for the
ea stern region of the U.S. at an aggregated long

- term PM 2.5 median concentration of 14.0 μg/m 3 , although no association was reported for the western region with an aggregate long

- term PM 2.5 median concentration of 13.1 μg/m 3 ( U.S. EPA, 2009a, p. 7

- 88). 29 Pre mature mortality in children reported in a national infant mortality study as well as mortality in a cystic fibrosis cohort including both children and adults reported positive but statistically nonsignificant effects associated with long

- term aggregate me an concentrations of 14.8 μg/m 3 and 13.7 μg/m 3 , respectively (Woodruff et al., 2008; Goss et al., 2004). With respect to respiratory morbidity effects associated with long

- term PM 2.5 exposure, the across

- city mean of 2

- week average PM 2.5 concentrations rep orted in the initial Southern California Children’s Health Study was approximately 15.1 μg/m 3

28 The Policy Assessment noted that in comparison to other long

- term exposure studies, the Miller et al. (2007) study was more limited in that it was based on only one year of air quality data (U.S. EPA, 2011a, p. 2

- 82). The proposal further noted that the air quality data considered were extra polated from that one single year of air quality data (2000) to the whole study, and that the air quality data post

- dated the years of health events considered (i.e., 1994 to 1998) (77 FR 38918, fn 62). 29 Zeger et al. (2008) also reported positive and stat istically significant effects for the central region, with an aggregate long

- term mean PM 2.5 concentration of 10.7 μg/m 3

. However, in contrast to the eastern and western risk estimates, the central risk estimate increased with adjustment for COPD (used as a proxy for smoking status). Due to the potential for confounding bias influencing the risk estimate for the central region, the Policy Assessment did not focus on the results reported in the central region to inform the adequacy of the current suite of st andards or alternative annual standard levels (U.S. EPA, 2011a, p. 2

- 32).***E.O. 12866 Review

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Page 41 of 253 (Peters et al., 1999). These results were found to be consistent with results of cross

sectional analyses of the 24

- Cities Study (Dockery et al., 1996; Raizenne e t al., 1996), which reported a long

- term cross
- city mean PM 2.5 concentration of 14.5 μg/m 3

. 30 In this review, extended analyses o f the Southern California Children’s Health Study provide stronger evidence of PM 2.5 - related respiratory effects, at lower air quality concentrations than had previously been reported, with a four

- year aggregate mean concentration of 13.8 μg/m 3 across the 12 study communities (McConnell et al., 2003; Gauderman et al., 2004, U.S. EPA, 2009a, Figure 7

- 4). In also considering health effects for which the Integrated Science Assessment concluded evidence was suggestive of a causal relationship, the Policy Assessment noted a limited number of birth outcome studies that reported positive and statistically significant effects related to a ggregate long

- term mean PM 2.5 concentrations down to approximately 12 μg/m 3 ( U.S. EPA, 2011a, p. 2

- 33). Collectively, the Policy Assessment concluded that currently available evidence provided support for associations between long

- term PM 2.5 exposure and m ortality and morbidity effects that extend to distributions of PM 2.5 concentrations that are lower than those that had previously been associated with such effects, with aggregate long

- term mean PM 2.5 concentrations extending to well below the level of the current annual standard. The Policy Assessment also considered the long

- term mean PM 2.5 concentrations in short

- term exposure studies in assessing the appropriateness of the level of the current annual standard. See American Farm Bureau Federation v. EPA , 559 F. 3d at 522, 523

-

30 See American Farm Bureau Federation v. EPA , 559 F. 3d at 525 (noting the importance of these studies, as well as EPA’s failure to properly take them into account).***E.O. 12866 Review

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Page 42 of 253 24 (remanding 2006 standard because the EPA had not adequately explained its choice not to consider long

- term means of short

- term exposure studies in assessing adequacy of primary annual PM 2.5 standard). In light of the mixed finding s reported in single

- city, short

- term exposure studies, the Policy Assessment placed comparatively greater weight on the results from multi

- city studies in considering the adequacy of the current suite of standards ( U.S. EPA, 2011a, pp. 2

- 34 to 2

- 35). Wit h regard to associations reported in short

- term PM 2.5 exposure studies, the Policy Assessment recognized that long

- term mean concentrations reported in new multi

city U.S. and Canadian studies provided evidence of associations between short

- term PM 2.5 expo sure and mortality at similar air quality distributions t o those that had previously been observed in an 8

- cities Canadian study (Burnett and Goldberg, 2003; aggregate long

- term mean PM 2.5 concentration of 13.3 μg/m 3 ). In a multi

- city time

- series analysis of 112 U.S. cities, Zanobetti and Schwartz (2009) reported a positive and statistically significant association with all

- cause, cardiovascular

- related (e.g., heart attacks, stroke), and respiratory

- related mortality and short

- term PM 2.5 exposure, in which the aggregate long

- term mean PM 2.5 concentration was 13.2 μg/m 3 ( U.S. EPA, 2009a, Figure 6

- 24). Furthermore, city

- specific effect estimates indicated the association between short

- term exposure to PM 2.5 and total mortality and cardiovascular

- and respirato ry - related mortality was consistently positive for an overwhelming majority (99 percent) of the 112 cities across a wide range of air quality concentrations (long

- term mean concentrations ranging from 6.6 μg/m 3 to 24.7 μg/m 3 ; U.S. EPA, 2009a, Figure 6

- 24, p. 6

- 178 to 179). The EPA staff noted that for all

- cause mortality, city

- specific effect estimates were statistically significant for 55 percent of the 112 cities, with long

- term***E.O. 12866 Review

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Page 43 of 253 city

- mean PM 2.5 concentrations ranging from 7.8 μg/m 3 to 18.7 μg/m 3 and 24

- ho ur PM 2.5 city

- mean 98 th percentile concentrations ranging from 18.4 to 64.9 μg/m 3 (personal communication with Dr. Antonella Zanobetti, 2009). 31 With regard to cardiovascular and respiratory morbidity effects, in the first analysis of the Medicare cohort c onducted by Dominici et al. (2006a) across 204 U.S. counties, investigators reported a statistically significant association with hospitalizations for cardiovascular and respiratory diseases and short

- term PM 2.5 exposure, in which the aggregate long

- term m ean PM 2.5 concentration was 13.4 μg/m 3 . Furthermore, a sub

analysis restricted to days with 24

- hour average concentrations of PM 2.5 at or below 35 μg/m 3 indicated that, in spite of a reduced statistical power from a smaller number of study days, statistica lly significant associations were still observed between short

- term exposure to PM 2.5 and hospital admissions for cardiovascular and respiratory diseases (Dominici, 2006b). 32 In an extended analysis of this cohort, Bell et al (2008) reported a positive and statistically significant increase in cardiovascular hospitalizations associated with short

- term PM 2.5 exposure, in which the aggregate long

- term mean PM 2.5 concentration was 12.9 μg/m 3 . These results, along with the observation that approximately 50 perce nt of the 204 county

- specific mean 98 th percentile PM 2.5 concentrations in the study aggregated across all years were below the 24

- hour standard

31 Single

- city Ba yes - adjusted effect estimates for the 112 cities analyzed in Zanobetti and Schwartz (2009) were provided by the study authors (personal communication with Dr. Antonella Zanobetti, 2009; see also U.S. EPA, 2009a, Figure 6

- 24). 32 This sub

- analysis was not included in the original publication (Dominici et al., 2006a). The study authors provided sub

- analysis results for the Administrator’s consideration as a letter to the docket following publication of the proposed rule in January 2006 (personal communication with Dr. Francesca Dominici, 2006b). As noted in section III.A.3, this study is part of the basis for the conclusion that there is no evidence suggesting that risks associated with long

- term exposures are likely to be dispropor tionately driven by peak 24

- hour concentrations.***E.O. 12866 Review

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Page 44 of 253 of 35 μg/m 3 , not only indicated that effects are occurring in areas that would meet the current standards but a lso suggested that the overall health effects observed across the U.S. are not primarily driven by the higher end of the PM 2.5 air quality distribution (Bell, 2009a, personal communication from Dr. Michelle Bell regarding air quality data for Bell et al., 2008 and Dominici et al., 2006a). Collectively, the Policy Assessment concluded that the findings from short

- term PM 2.5 exposure studies provided evidence of PM 2.5 - associated health effects occurring in areas that would likely have met the current suite of PM 2.5 standards ( U.S. EPA, 2011a, p. 2

- 35). These findings were further bolstered by evidence of statistically significant PM 2.5 - related health effects occurring in analyses restricted to days in which 24

- hour average PM 2.5 concentrations were below 35 μg/m 3 (Dominici, 2006b). In evaluating the currently available scientific evidence, as summarized in section III.B of the proposal, the Policy Assessment first concluded that there was stronger and more consistent and coherent support for associations bet ween long

- and short

- term PM 2.5 exposures and a broad range of health outcomes than was available in the last review, providing the basis for fine particle standards at least as protective as the current PM 2.5 standards ( U.S. EPA, 2011a, p. 2

- 26). Having r eached this initial conclusion, the Policy Assessment addressed the question of whether the available evidence supported consideration of standards that were more protective than the current standards. In so doing, the Policy Assessment considered whether there was now evidence that health effect associations have been observed in areas that likely met the current suite of PM 2.5 standards. As discussed above, long

- and short

- term PM 2.5 exposure studies provided evidence of associations with mortality and ca rdiovascular and respiratory effects both at***E.O. 12866 Review

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Page 45 of 253 lower ambient PM 2.5 concentrations than had been observed in the previous review and at concentrations allowed by the current standards ( U.S. EPA, 2011a, p. 2

- 35). In reviewing this information, the Policy Asse ssment recognized that important limitations and uncertainties associated with this expanded body of scientific evidence, as discussed in section III.B.2 of the proposal, needed to be carefully considered in determining the weight to be placed on the body of studies available in this review. Taking these limitations and uncertainties into consideration, the Policy Assessment concluded that the currently available evidence clearly calls into question whether the current suite of primary PM 2.5 standards prote cts public health with an adequate margin of safety from effects associated with long

- and short

- term exposures. Furthermore, the Policy Assessment concluded this evidence provides strong support for considering fine particle standards that would afford in creased protection beyond that afforded by the current standards ( U.S. EPA, 2011a, p. 2

- 35). In addition to evidence

- based consideration, the Policy Assessment also considered the extent to which health risks estimated to occur upon simulating just meeting the current PM 2.5 standards may be judged to be important from a public health perspective, taking into account key uncertainties associated with the quantitative health risk estimates. In so doing, the Policy Assessment first noted that the quantitative risk assessment addresses: (1) the core PM 2.5 - related risk estimates; (2) the related uncertainty and sensitivity analyses, including additional sets of reasonable risk estimates generated to supplement the core analysis; (3) an assessment of the represent ativeness of the urban study areas within a national context; 33 and (4) consideration of patterns in design values

33 Based on analyses of the representativeness of the 15 urban study areas in the broader national context, the Policy Assessment concludes that these study areas are generally***E.O. 12866 Review

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Page 46 of 253 and air quality monitoring data to inform interpretation of the risk estimates, as discussed in section III.C above. In considering the healt

h risks estimated to remain upon simulation of just meeting the current suite of standards and considering both the qualitative and quantitative assessment of uncertainty completed as part of the assessment, the Policy Assessment concluded these risks are important from a public health standpoint and provided strong support for consideration of alternative standards that would provide increased protection beyond that afforded by the current PM 2.5 ( U.S. EPA, 2011a, pp. 2

- 47 to 2

- 48). This conclusion reflecte d consideration of both the severity and the magnitude of the effects. For example, the Risk Assessment indicated the possibility that premature deaths related to ischemic heart disease associated with long

- term PM 2.5 exposure alone would likely be on the order of thousands of deaths per year in the 15 urban study areas upon simulating just meeting the current standards 34 ( U.S. EPA, 2011a, pp. 2

- 46 to 2

- 47). Moreover, additional risks were anticipated for premature mortality related to cardiopulmonary effect s and lung cancer associated with long

- term PM 2.5 exposure as well as mortality and cardiovascular

- and respiratory

- related morbidity effects (e.g., hospital admissions, emergency department visits) associated with short

term PM 2.5 exposures. Based on the consideration of both qualitative and quantitative assessments of uncertainty completed as part of the quantitative risk assessment, the Risk Assessment concluded that it was unlikely that the estimated risks are over

- stated, particularly for mortality rel ated to long

- term PM 2.5 exposure, and may well be biased representative of urban areas i n the U.S. likely to experience relatively elevated levels of risk related to ambient PM 2.5 exposures (U.S. EPA, 2011a, p. 2

- 42). 34 Premature mortality for all causes attributed to PM 2.5 exposure was estimated to be on the order of tens of thousands of de aths per year on a national scale based on 2005 air quality data (U.S. EPA, 2010a, Appendix G, Table G

- 1).***E.O. 12866 Review

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Page 47 of 253 low based on consideration of alternative model specifications evaluated in the sensitivity analyses ( U.S. EPA, 2010a, p. 5

- 16; U.S. EPA, 2011a, p. 2

- 41). Furthermore, the currently available scienti fic information summarized in section III.B of the proposal provided evidence for a broader range of health endpoints and at

- risk populations beyond those included in the quantitative risk assessment ( U.S. EPA, 2011a, p. 2

- 47). b. CASAC Advice The CASAC, b ased on their its review of drafts of the Integrated Science Assessment, the Risk Assessment, and the Policy Assessment, provided an array of advice both with regard to interpreting the scientific evidence and quantitative risk assessment, as well as with regard to conside ration of the adequacy of the current PM 2.5 standards (Samet, 2009a b,c,d,e,f; Samet 2010a,b,c,d). With regard to the adequacy of the current standards, CASAC concluded that the “currently available information clearly calls into question the adequacy of t he current standards” (Samet, 2010d, p. i) and that the current standards are “not protective” (Samet, 2010d, p. 1). Further, in commenting on the first draft Policy Assessment, CASAC noted: With regard to the integration of evidence

- based and risk

- based c onsiderations, CASAC concurs with EPA’s conclusion that the new data strengthens the evidence available on associations previously considered in the last round of the assessment of the PM 2.5 standard. CASAC also agrees that there are significant public hea lth consequences at the current levels of the standard that justify consideration of lowering the PM 2.5 NAAQS further (Samet, 2010c, p.12).
c. Administrator's Proposed Conclusions Concerning the Adequacy of the Current Primary PM 2.5 Standards At the time of the proposal, in considering the body of scientific evidence, the Administrator concluded there was stronger and more consistent and coherent support for associations between long

- and short

- term PM 2.5 exposure and a broader range of health outcomes th an was available in the last review, providing the basis for fine particle***E.O. 12866 Review

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Page 48 of 253 standards at least as protective as th e current PM 2.5 standards. In particular, the Administrator recognized in section III.D.4 of the proposal that the Integrated Science Assessmen t concluded that the results of epidemiological and experimental studies form a plausible and coherent data set that supports a causal relationship between long

- and short

- term PM 2.5 exposures and mortality and cardiovascular effects and a likely causal
re lationship between long

- and short

- term PM 2.5 exposures and respiratory effects. Furthermore, the Administrator reflected that effects had been observed at lower ambient PM 2.5 concentrations than what had been observed in the last review, including at ambi ent PM 2.5 concentrations in areas that likely met the current PM 2.5 NAAQS. With regard to the results of the quantitative risk assessment, the Administrator note d that the Risk Assessment conclude s d that the risks estimated to remain upon simulation of jus t meeting the current standards are we re important from a public health standpoint in terms of both the severity and magnitude of the effects. At the time of the proposal, in considering whether the current suite of PM 2.5 standards should be revised to pro vide requisite public health protection, the Administrator carefully considered the staff conclusions and rationales presented in the Policy Assessment, the advice and recommendations from CASAC, and public comments to date on this issue. In so doing, the Administrator placed primary consideration on the evidence obtained from the epidemiological studies and provisionally found the evidence of serious health effects reported in long

- and short

- term exposure studies conducted in areas that would have met the current standards to be compelling, especially in light of the extent to which such studies are part of an overall pattern of positive and frequently statistically significant associations across a broad range of studies that collectively***E.O. 12866 Review

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Page 49 of 253 represent a stro ng and robust body of evidence. As discussed in the Integrated Science Assessment and Policy Assessment, the Administrator recognized that much progress has been made since the last review in addressing some of the key uncertainties that were important co nsiderations in establishing the current suite of PM 2.5 standards. For example, progress made since the last review provides increased confidence in the long

- and short

- term exposure studies as a basis for considering whether any revision of the annual sta ndard is appropriate and increased confidence in the short

- term exposure studies as a basis for considering whether any revision of the 24

- hour standard is appropriate. 35 Based on her consideration of these conclusions, as well as consideration of CASAC’s conclusion that the evidence and risk assessment clearly call ed into question the adequacy of the public health protection provided by the current PM 2.5 NAAQS and public comments on the proposal, the Administrator provisionally concluded that the current p rimary PM 2.5 standards, taken together, are we re not requisite to protect public health with an adequate margin of safety and that revision is wa s needed to provide increased public health protection. The Administrator provisionally concluded that the scient ific evidence and information on risk provide d strong support for consideration of alternative standards that would provide increased public health protection beyond that afforded by the current PM 2.5 standards. 2. Comments on the Need for Revision

35 The EPA notes that this increased confidence in the long

- and short

- term associations generally reflects less uncertainty as to the likely causal n ature of such associations, but does not address directly the question of the extent to which such associations remain toward the lower end of the range of ambient PM 2.5 concentrations. This question is central to the Agency’s evaluation of the relevant ev idence to determine appropriate standards levels, as discussed below in section III.E.4.***E.O. 12866 Review

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Page 50 of 253 This secti on addresses general comments based on relevant facts that either support or oppose any change to the current suite of primary PM 2.5 standards. Comments on specific long

- and short

- term exposure studies that relate to consideration of the appropriate level s of the annual and 24

- hour standards are addressed in section III.E.4 below. Many public comments asserted that the current PM 2.5 standards are insufficient to protect public health with an adequate margin of safety and that revisions to the standards are therefore appropriate, indeed necessitated. Among those calling for revisions to the current standards were the Children’s Health Protection Advisory Committee (CHPAC); major medical and public health groups including the American Heart Association (AHA) , American Lung Association (ALA), American Public Health Association (APHA), American Thoracic Society (ATS); the Physicians for Social Responsibility (PSR); major environmental groups such as the Clean Air Council, Clean Air Task Force, Earthjustice, Env ironmental Defense Fund (EDF), National Resources Defense Council (NRDC), and Sierra Club; many environmental justice organizations as well as medical doctors, academic researchers, health professionals, and many private citizens. For example, the American Heart Association and other major national public health and medical organizations stated that, “[o]ur organizations are keenly aware of the public health and medical threats from particulate matter” and called on the EPA to “significantly strengthen” bot h the annual and 24

- hour PM 2.5 standards “to help us protect the health of our patients and our nation” (AHA et al., 2012, pp 1 and 13). AHA et al. and ALA et al., as well as a group of more than 350 physicians, environmental health researchers, and public health and medical professionals articulated similar comments on the available evidence:***E.O. 12866 Review

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Page 51 of 253 Ample scientific evidence supports adopting tighter standards to protect the health of people who are most susceptible to the serious health effects of these pollutan ts. More than 10,000 peer

- reviewed scientific studies have been published since 1997 when EPA adopted the current annual standard. These studies validate and extend earlier epidemiologic research linking both acute and chronic fine particle pollution with serious morbidity and mortality. The newer research has also expanded our understanding of the range of health outcomes associated with PM and has identified adverse respiratory and cardiovascular health effects at lower exposure levels than previously rep orted. As discussed and interpreted in the EPA’s 2009 Integrated Science Assessment for Particulate Matter, the new evidence reinforces already strong existing studies and supports the conclusion that PM 2.5 is causally associated with numerous adverse heal th effects in humans at exposure levels far below the current standard. Such a conclusion demands prompt action to protect human health. (AHA et al., 2012, pp. 1 to 2; ALA et al., pp. 4 to 5; similar comment submitted by Rom et al., 2012, p. 1). All of the se medical and public health commenters stated that the current PM 2.5 standards need to be revised, and that even more protective standards than those proposed by the EPA are needed to adequately protect public health, particularly for at

- risk populations. Many environmental justice organizations and individual commenters also expressed such views. The National Association of Clean Air Agencies (NACAA), the Northeast States for Coordinated Air Use Management (NESCAUM), and many State and local air agencies and health departments who commented on the PM 2.5 standards supported revision of the suite of current PM 2.5 standards, as did five s tate a ttorneys g eneral (Schneiderman et al., 2012) and the National Tribal Air Association (NTAA). These commenters based their views chiefly on the body of evidence and technical analyses presented and discussed in the Integrated Science Assessment, the Risk Assessment, and the Policy Assessment finding the available scientific information to be strong er and more compelling than in the last review. These commenters generally placed much weight on CASAC’s recommendation to revise the PM 2.5 standards to provide increased public health protection and on the EPA staff conclusions presented in***E.O. 12866 Review

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Page 52 of 253 the final Poli cy Assessment. Some of these commenters specifically mentioned extended analyses of seminal long

- term exposure studies

- the ACS (Krewski et al., 2009), Harvard Six Cities (Laden et al., 2006), and Southern California Children’s Health (Gauderman et al., 2 004) studies. These commenters also highlighted the availability of additional long

- term exposure studies in this review, specifically a study of premature mortality in older adults (Eftim et al., 2008) and the WHI study of cardiovascular morbidity and mor tality effects in women (Miller et al., 2007) providing stronger evidence of mortality and morbidity effects associated with long

- term PM 2.5 exposures at lower concentrations than had previously been observed, including studies of effects in at

- risk popula tions. For example, some commenters asserted: Evidence during the last review showed clearly that the annual average standard needed to be much lower than the standard of 15 μg/m 3 that was first set in 1997. The evidence has only grown since then. Multiple , multi

- city studies over long periods of time have shown clear evidence of premature death, cardiovascular and respiratory harm as well as reproductive and developmental harm at contemporary concentrations far below the level of the current (annual) stand ard (ALA et al., 2012, p. 39; AHA et al., 2012, p. 10). These commenters also highlighted the availability of a number of short

- term PM 2.5 exposure studies as providing evidence of mortality and morbidity effects at levels concentration s below the level of the current 24

- hour PM 2.5 standard. Specifically, these commenters made note of multi

- city studies of premature mortality (Zanobetti and Schwartz, 2009) and increased hospitalizations for cardiovascular and respiratory

- related effects in older adults (Bel l et al., 2008). These commenters also asserted the importance of many of the single

- city studies, arguing that these studies “provide valuable information regarding impacts on susceptible populations and on health risk in areas with high peak to mean conc entration ratios” (ALA, et al., 2012, p. 65). Collectively,***E.O. 12866 Review

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Page 53 of 253 considering the multi

- and single

- city short

- term exposure studies, these commenters asserted “the record clearly supports a more stringent 24

- hour standard of 25 μg/m 3 to provide uniform protecti on in all regions of the country particularly from short

- term spikes in pollution and from the sub

- daily exposures that trigger heart attacks and strokes” (ALA et al., 2012, p. 62). A group of more than 350 physicians, environmental health researchers, and public health and medical professionals argued, “[s]tudies of short

- term exposure demonstrate that PM 2.5 air pollution increases the risk of hospital admissions for heart and lung problems even when you exclude days with pollution concentrations at or abo ve the current daily standard of 35 μg/m 3 . Daily concentrations must be capped at lower levels to protect against peak exposure days that occur due to local and seasonal sources of emissions” (Rom et al., 2012, p. 2). In addition, many of these commenters generally concluded that progress had been made in reducing many of the uncertainties identified in the last review, in better understanding mechanisms by which PM 2.5 may be causing the observed health effects, and in improving our understanding of at

- risk populations. 36 Further, these Further, a number of commenters argued that by making the standards more protective, the PM 2.5 NAAQS would be more consistent with other existing standards (e.g., California's annual average standard of 12 μg/m 3 ) (CARB, 2012; CA OEHHA, 2012). Other commenters argued that revising the primary PM 2.5 standards would be more consistent with the recommendations of the World Health Organization (WHO) and/or Canada (e.g., ALA et al., 2012, p. 62; ISEE, 2012, p. 2 ; MOE

- Ontario, 2012, p . 1 ; ISEE, 2012, p. 2 ).

36 In addition, the EPA notes that CASAC found that the Integrated Science Assessment clearly presented and discussed the current scientific information related to potential modes of action (Chapter 5) and at

- risk populations (Chapter 8) (Samet, 2009e, pp. 7 to 8; Samet, 2009f, pp. 2 and 11 to 12).***E.O. 12866 Review

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Page 54 of 253 With regard to the scope of the literature reviewed for PM 2.5 - related health effects, some commenters asserted that the EPA inappropriately narrowed the scope of the review by excluding a number of categories of relevant studies, s pecifically related to studies of diesel pollution and traffic

- related pollution (ALA, et al., 2012, p. 17). These commenters argued that, based upon the exclusion of these types of studies, the Integrated Science Assessment “came to the erroneous conclusi on that the causal relationship between PM and cancer is merely suggestive. This conclusion does not square with the International Agency Research on Cancer (IARC) finding that diesel emissions are a known human carcinogen nor with the conclusions of the e xtended analyses of the [Harvard] Six Cities and ACS cohort studies that report positive and statistically significant associations between PM 2.5 and lung cancer.” Id. Some of these commenters also noted the results of the EPA’s quantitative risk assessment, concluding that it showed that the risks estimated to remain when the current standards are met are large and important from a public health perspective and warrant increased protection. For example, ALA et al., noted that the Risk Assessment i ndicated the quantitative risk analyses likely underestimated PM 2.5 - related mortality ( U.S. EPA, 2010a, p. 5

- 16) and argued that “the measurements of risk should be treated conservatively” (ALA, et al., 2012, p. 73). These commenters also summarized an exp anded analysis of alternative PM 2.5 standard levels that they argued documented the need for more protective standards (McCubbin, 2011). In general, all of these commenters agreed on the importance of results from the large body of scientific studies revi ewed in the Integrated Science Assessment and on the need to revise the suite of PM 2.5 standards as articulated in the EPA’s proposal, while***E.O. 12866 Review

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Page 55 of 253 generally differing with the EPA’s proposed judgments about the extent to which the standards should be revised bas ed on this evidence, specifically for providing protection for at

- risk populations. The EPA generally agrees with these commenters’ conclusion regarding the need to revise the current suite of PM 2.5 standards. The scientific evidence noted by these
commen ters was generally the same as that assessed in the Integrated Science Assessment and the Policy Assessment, and the EPA agrees that this evidence provides a strong basis for concluding that the current PM 2.5 standards, taken together, are not requisite to protect public health with an adequate margin of safety, and they need to be revised to provide increased protection. For reasons discussed in section III.E.4.c below, however, the EPA disagrees with aspects of these commenters’ views on the level of prot ection that is appropriate
. T he EPA disagrees with these commenters’ views that diesel exhaust studies were excluded from the Integrated Science Assessment and were not considered when making the causality determination for cancer, mutagenicity, and genotoxicity. As discussed in
s ecti on 7.5 of the Integrated Science Assessment, diesel exhaust studies were integrated within the broader body of scientific evidence that was considered in reaching the causality determination for these health endpoints. Additionally, as discussed in section 1.5.3 of the Integrated Science Assessment, the evidence from diesel exhaust studies was also considered as part of the collective evidence evaluated when making determinations for other, noncancer health outcomes (e.g., cardiovascular and respiratory eff ects). 37

37 In developing the second draft Integrated Science Assessment, the EPA reexamined the controlled human exposure and to xicological studies of fresh diesel and gasoline exhaust and considered This information, in addition to other considerations , supported a change in the causal determinations for ultrafine particles. Specifically, in reevaluating the causal***E.O. 12866 Review

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Page 56 of 253 Specifically, when evaluating this evidence , the focus was on understanding the effects of diesel exhaust particles. It is important to recognize that the Integrated Science Assessment focused on experimental studies of diesel exhaust that evaluat ed exposures that were relevant to ambient concentrations, i.e., “within one or two orders of magnitude of ambient PM concentrations” ( U.S. EPA, 2009a, section 1.3). The causal determination for cancer, mutagenicity, and genotoxicity presented in the Integ rated Science Assessment represents an integration of experimental and observational evidence of exposures to ambient PM concentrations. T he EPA fully considered the findings of studies that assessed the se and other health effects associated with exposure to diesel particles in reaching causality determinations regarding health outcomes associated with PM 2.5 exposures. Furthermore, CASAC supported the EPA’s change to the causal determination for cancer and long

term PM 2.5 concentrations from “inadequate” to “suggestive” (Samet, 2009f, p. 2). With regard to traffic studies, the EPA disagrees with the commenters’ views that traffic studies that focused on exposure indicators such as distance to roadways should have been included in the Integrated Science Asses sment. These studies were excluded from consideration because they did not measure ambient concentrations of specific air pollutants, including PM 2.5 , but instead we re studies evaluating exposure to the undifferentiated “traffic related air pollution” mixture (ALA et al., 2012, p.17) ( U.S. EPA, 2009a, section 1.3). As a result, these studies do not add to the collective body of evidence on the relationship between long

- or short

- term exposure to ambient
determinations for short

- term ultrafine particle exposures and cardiovascular and respiratory effects, the EPA changed the classification from “inadequate” to “suggestive ” for both categories of health outcomes (Vandenberg, 2009, p. 3). CASAC agreed with the EPA’s ration ale for revising these causal determinations (Samet, 2009f, p. 10).***E.O. 12866 Review

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Page 57 of 253 concentrations of PM 2.5 and health effects. Some o f these commenters also identified “new” studies that were not included in the Integrated Science Assessment as providing further support for the need to revise the primary PM 2.5 standards. As discussed above in section II.B.3 above , the EPA notes that,
as in past NAAQS reviews, the Agency is basing the final decisions in this review on the studies and related information included in the PM air quality criteria that have undergone CASAC and public review and will consider the “new” studies for purposes of d ecision making in the next PM NAAQS review. Nonetheless, in provisionally evaluating commenters’ arguments (see Response to Comments document), the EPA notes that its provisional assessment of “new” science found that such studies did not materially change the conclusions in the Integrated Science Assessment (U.S. EPA, 2012b)
. Another group of commenters opposed revising the current PM 2.5 standards. These views were most extensively presented in comments from the Utility Air Regulatory Group (UARG), represe nting a group of electric generating companies and organizations and several national trade associations; the American Petroleum Institute (API) representing more than 500 oil and natural gas companies; the National Association of Manufacturers (NAM), the American Chemistry Council (ACC), the American Fuel & Petroleum Manufacturers (AFPM), the Alliance of Automobile Manufacturers , (AAM) , and other manufacturing associations; the Electric Power Research Institute (EPRI); and the Texas Commission on Environme ntal Quality (T exas CEQ). These commenters generally mentioned many of the same studies that were cited by the commenters who supported revising the standards, as well as other studies, but***E.O. 12866 Review

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Page 58 of 253 highlighted different aspects of these studies in reaching substan tially different conclusions about their strength and the extent to which progress has been made in reducing uncertainties in the evidence since the last review. Furthermore, they asserted that the evidence that has become available since the last review d oes not establish a more certain risk or a risk of effects that are significantly different in character to those that provided a basis for the current standards, nor does the evidence demonstrate that the risk to public health upon attainment of the curre nt standards would be greater than was understood when the EPA established the current standards in 2006. These commenters generally expressed the view that the current standards provide the requisite degree of public health protection. In supporting thei r view, these commenters generally argued that the EPA’s conclusions are inconsistent with the current state of the science and questioned the underlying scientific evidence including the causal determinations reached in the Integrated Science Assessment. More specifically, this group of commenters argued that: (1) the EPA did not apply its framework for causal determination consistently across studies or health outcomes and, in the process, the EPA relied on a selective group of long

- and short

- term exposu re studies to reach conclusions regarding causality; (2) toxicological and controlled human exposure studies do not provide supportive evidence that the health effects observed in epidemiological studies are biologically plausible; (3) uncertainties in the underlying health science are as great or greater than in 2006; ( 4 ) there is no evidence of greater risk since the last review to justify tightening the current annual PM 2.5 standard; and ( 5 ) “new” studies not included in the Integrated Science Assessment continue to increase uncertainty about possible health risks associated with exposure to PM 2.5 . These comments are discussed in turn below.***E.O. 12866 Review

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Page 59 of 253 (l) Some of these commenters asserted that the EPA did not apply its framework for causal determinations consistent ly across studies or health outcomes ( ACC, 2012, Attachment A, pp. 1 to 2; API, 2012, Attachment 1, p. 30; NAM et al., 2012, pp. 22 to 25; Texas CEQ, 2012, pp 2 to 3 ). 38 These commenters argued that the EPA downplayed epidemiological studies with null or in consistent results, inappropriately used the Hill criteria when evaluating the epidemiologic al evidence, and used the same study and the same underlying database to conclude that there was a causal association between mortality and multiple criteria pollut ants . The EPA disagrees with these commenters’ views. First, the EPA recognizes that the evaluation of the scientific evidence and its application of the causal framework used in the current PM NAAQS review was the subject of exhaustive and detailed review by CASAC and the public. As summarized in section II.B.3 above, p rior to finalizing the Integrated Science Assessment, two drafts were released for CASAC and public review to evaluate the scientific integrity of the documents. Evidence related to the substantive issues raised by CASAC and public commenters with regard t o the content of the first and second draft Integrated Science Assessments were discussed at length during these public CASAC meetings and considered in developing the final Integrated Science Assessment. CASAC supported the development of the EPA’s causal ity framework and its use in the current PM NAAQS review and concluded: The five

- level classification of strength of evidence for causal inference has been systematically applied; this approach has provided transparency and a clear statement of the level o f confidence with regard to causation, and we recommend 38 The EPA notes that the same concerns about the causal determinations presented in the Integrated Science Assessment were raised in comments to CASAC on the draft Integrated Science Asses sments (e.g., UARG, 2009; API, 2009; ACC, 2012, Appendix B). CASAC, therefore, had the opportunity to consider these comments in reaching consensus conclusions on this issue.***E.O. 12866 Review

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Page 60 of 253 its continued use in future Integrated Science Assessments (Samet 2009f, p. 1). These commenters asserted that during the application of the causal framework the EPA inappropriately relied on a selec tive group of long

- and short

- term exposure studies in reaching causal inferences (API, 2012, pp 12 to 17; ACC, 2012, Attachment A, pp 1 to 2; NAM et al., 2012, pp. 22 to 25; Texas CEQ, 2012, pp 2 to 3). Additionally, these commenters expressed the view th at the EPA focused on a subset of epidemiological studies that reported positive and statistically significan t results while ignoring other studies, especially those that reported no statistically significan t associations, those that reported potential thr esholds, or those that highlighted uncertainties and limitations in study design or results. Furthermore, some of these commenters argued that epidemiological studies are observational in nature and cannot provide evidence of a causal association. The EPA disagrees with these commenters’ views on assessing the health effects evidence and on the conclusions regarding the causal ity determinations reached in the Integrated Science Assessment
. In conducting a comprehensive evaluation of the evidence in the Inte grated Science Assessment, the EPA recognized the distinction between the evaluation of the relative scientific quality of individual study results and the evaluation of the pattern of results within the broader body of scientific evidence and considered b oth in reaching causality determinations. The more detailed characterizations of individual studies included an assessment of the quality of the study based on specific criteria as described in the Integrated Science Assessment ( U.S. EPA, 2009a, section 1. 5.3). In developing an integrated assessment of the health effects evidence for PM, the EPA emphasized the importance of examining the pattern of results across various***E.O. 12866 Review

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Page 61 of 253 studies and did not focus solely on statistical significance 39 as a criterion of study strength. This approach is consistent with views clearly articulated throughout the epidemiological and causal inference literature, specifically, that it is important not to focus on results of statistical tests to the exclusion of other information. 40 The concepts underlying the EPA’s approach to evaluating statistical associations have been discussed in numerous publications, including a report by the U.S. Surgeon General on the health consequences of smoking (Centers for Disease Control and Prevention, 2 004). This report cautions against over

- reliance on statistical significance in evaluating the overall evidence for an exposure

- response relationship. Criteria characterized by Hill (1965) also addressed the value, or lack thereof, of statistical tests in the determination of cause: No formal tests of significance can answer those [causal] questions. Such tests can, and should, remind us of the effects the play of chance can create, and they will instruct us in the likely magnitude of those effects. Beyond that, they contribute nothing to the ‘proof’ of our hypothesis (Hill, 1965, p. 299). The statistical significance of individual study findings has played an important role in the EPA’s evaluation of the study’s results and the EPA has placed greater emph asis on studies reporting statistically significant results. However, in the broader evaluation of the evidence from many epidemiological studies, and subsequently during

39 Statistical significance is an indicator of the precision of a study’s results , which is influenced by a variety of factors including, but not limited to, the size of the study, exposure and measurement error, and statistical model specifications. Studies typically calculate “p

- values” to determine whether the study results are stat istically significant or whether the study results are likely to occur simply by chance. In general practice, effects are considered statistically significant if p values are less than 0.05. 40 For example, Rothman (1998) stated, “Many data analysts appear to remain oblivious to the qualitative nature of significance testing [and that]... statistical significance is itself only a dichotomous indicator. As it has only two values, significant or not significant ....Nevertheless, p

- values still confound effect size with study size, the two components of estimation that we believe need to be reported separately.” As a result, Rothman recommended that p

- values be omitted as long as point and interval estimates are available.***E.O. 12866 Review

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Page 62 of 253 the process of forming causality determinations in integrating evidence across epidem iological, controlled human exposure, and toxicological studies, the EPA has emphasized the pattern of results across epidemiological studies, and whether the effects observed were coherent across the scientific disciplines for drawing conclusions on the relationship between PM 2.5 and different health outcomes. Thus, the EPA did not limit its focus or consideration to just studies that reported positive associations or where the results were statistically significant. In addition, some commenters asserted that the EPA inappropriately used the Hill criteria by failing to consider the limitations of studies with weak associations, thereby overstating the consistency of the observed association s (API, 2012, Attachment 1, pp
. 30 to 35). These commenters argued that risk estimates greater than 3 to 4 reflect strong associations supportive of a causal link, while smaller risk estimates (i.e., 1.5 to 3) are considered to be weak and require other li nes of evidence to demonstrate causality. As discussed in section 1.5.3 of the Integrated Science Assessment, the EPA thoroughly considered the limitations of all studies during its evaluation of the scientific literature (U.S. EPA,, 2009a, p. 1

- 14). This collective body of evidence, including known uncertainties and limitations of the studies evaluated, were considered during the process of forming causality determinations as discussed in chapters 6 and 7 of the Integrated Science Assessment. For example, the EPA concluded that “a causal relationship exists between short

- term PM 2.5 exposure and cardiovascular effects , ” however, in reaching this conclusion, the Agency recognized and considered limitations of the current evidence that still requires further examination (U.S. EPA, 2009a
. , in s ection 6.2.12.1 ). Therefore, t he EPA disagrees with these commenters’ views that the Hill criteria were***E.O. 12866 Review

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Page 63 of 253 inappropriately used in that the limitations of studies were not considered. The EPA also disagrees with the comment ers commenters ’ assertion that the magnitude of the association must be large to support a determination of causality. As discussed in the Integrated Science Assessment, the strength of the observed association is an important aspect to aid in judging causa lity and “while large effects support causality, modest effects therefore do not preclude it” ( U.S. EPA, 2009a, Table 1

- 2, section 1.5.4). The weight of evidence approach used by the EPA encompasses a multitude of factors of which the magnitude of the asso ciation is only one component ( U.S. EPA, 2009a, Table 1

- 3). An evaluation of the association across multiple investigators and locations supports the “reproducibility of findings [which] constitutes one of the strongest arguments for causality” ( U.S. EPA, 2009a, Table 1

- 2). Even though the risk estimates for air pollution studies may be modest, the associations are consistent across hundreds of studies as demonstrated in the Integrated Science Assessment. Furthermore, the causality determinations rely on di fferent lines of evidence, by integrating evidence across disciplines, including animal toxicological studies and controlled human exposure studies. Furthermore, as summarized in section III.B above and discussed more fully in section III.B.3 of the propos al , the EPA recognizes that the population potentially affected by PM 2.5 is considerable, including large subgroups of the U.S. population that have been identified as at

- risk populations (e.g., children, older adults, persons with underlying cardiovascula r or respiratory disease). While individual effect estimates from epidemiological studies may be modest in size, the public health impact of the mortality and morbidity associations can be quite large given that air pollution is ubiquitous.***E.O. 12866 Review

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Page 64 of 253 Indeed, with th e large population exposed, exposure to a pollutant causally associated at a population level with mortality and serious illness has significant public health consequences, virtually regardless of the relative risk. Taken together, th is information indicat es that exposure to ambient PM 2.5 concentrations has substantial public health impacts. In addition, these commenters believed that the EPA downplayed null or inconsistent findings in numerous long

- term mortality studies with reported PM 2.5 concentrations above and below the level of the current annual standard. The EPA disagrees that studies with null or inconsistent findings were not accurately presented and considered in the Integrated Science Assessment. For example, as discussed through out section 7.6 and depicted in Figures 7

- 6 and 7

- 7 of the Integrated Science Assessment, the EPA presented the collective evidence from all studies that examined the association between long

- term PM 2.5 exposure and mortality. Overall, across these studies there was evidence of consistent positive associations in different cohorts. That evidence, in combination with the biological plausibility provided by experimental and toxicological studies evaluated in sections 7.1 and 7.2 of the Integrated Science Asse ssment, supported a causal relationship exists between long

- term PM 2.5 exposure and mortality
. Lastly, some of these commenters argued that in some cases, the EPA used the same study and the same underlying database to conclude that there is a causal
asso ciation between mortality and multiple criteria pollutants. These commenter s argued, “[i]n doing so, EPA attributes the cause of the mortality effects observed to whichever criteria pollutant it is reviewing at the time” (API, 2012, pp. 14 to 16). The EPA strongly disagrees that the Agency “attributes the cause of mortality***E.O. 12866 Review

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Page 65 of 253 effects observed to whichever criteria pollutant it is reviewing at the time.” The EPA consistently recognizes that other pollutants are also associated with health outcomes, as is refl ected in the fact that the EPA has established regulations to limit emissions of the particulate criteria pollutants as well as other gaseous criteria pollutants. Epidemiologic al studies often examine the association between short

- and long

- term exposures to multiple air pollutants and mortality within a common dataset in an attempt to identify the air pollutant(s) of the complex mixture most strongly associated with mortality. In evaluating these studies , the EPA employs specific study selection criteria t o identify those studies most relevant to the review of the NAAQS. In its assessment of the health evidence regarding PM 2.5 , the EPA has carefully evaluated the potential for confounding, effect measure modification , and the role of PM PM 2.5 as a component of a complex mixture of air pollutants ( U.S. EPA, 2009, p. 1

- 9). The EPA use d a rigorous weight of evidence approach to inform causality that evaluate d consistency across studies within a discipline, evidence for coherence across disciplines, and biologica l plausibility. Additionally, during this process, the EPA assesse d the limitations of each study in the context of the collective body of evidence. It wa s the collective evidence, not one individual study that ultimately determine d whether a causal relati onship exists between a pollutant and health outcome. In the Integrated Science Assessment , the combination of epidemiologic al and experimental evidence formed the basis for the Agency concluding for the first time that a causal relationship exists between short

- or long

- term exposure to a criteria pollutant and mortality ( U.S. EPA, 2009, s ection s 2.3.1.1 and 2.3.1.2). Additionally, while the EPA has evaluated some of the studies used to inform the causality determination for PM in the Integrated Science Assessments for the other***E.O. 12866 Review

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Page 66 of 253 criteria air pollutants, the Agency has done so in the context of examining the collective body of evidence for each of the respective criteria air pollutants. As such, the body of evidence to inform causality has varied from poll utant to pollutant resulting in the association between each criteria air pollutant and mortality being classified at a different level of the five

- level hierarchy used to inform causation ( See e.g., U.S. EPA, 2008 e , U.S. EPA, 2008 f , U.S. EPA, 2010 k ). The EPA notes that the final causality determinations presented in the Integrated Science Assessment reflected CASAC’s recommendations on the second draft Integrated Science Assessment (Samet, 2009f, pp. 2 to 3). Specifically, CASAC supported the EPA’s changes (in the second versus first draft Integrated Science Assessment) from “likely causal” to “causal” for long

- term exposure to PM 2.5 and cardiovascular effects and for cancer and PM 2.5 (from “inadequate” to “suggestive”)
. Id . Furthermore, CASAC recommended “ upgrading” the causal classification for PM 2.5 and total mortality to “causal” for both the short

- and long

- term timeframes. Id. W i th regard to mortality, the “EPA carefully reevaluated the body of evidence, including the collective evidence for biological plausibility for mortality effects, and determined that a causal relationship exists for short

- and long

- term exposure to PM 2.5 and mortality, consistent with the CASAC comments” (Jackson, 2012). (2) With regard to toxicological and controlled human expo sure studies, these commenters argued that the available evidence does not provide coherence or biological plausibility for health effects observed in epidemiological studies (API, 2012, pp. 21 to 22, Attachment 1, pp. 25 to 29; AAM, 2012, pp. 15 to 16; T e xas CEQ, 2012, p. 3). With regard to the issue of mechanisms, these commenters noted that although the EPA***E.O. 12866 Review

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Page 67 of 253 recognizes that new evidence is now available on potential mechanisms and plausible biological pathways, the evidence provided by toxicological and c ontrolled human exposure studies still does not resolve all questions about how PM 2.5 at ambient concentrations could produce the mortality and morbidity effects observed in epidemiological studies. More specifically, for example, some of these commenters argued that: A review of the Integrated Science Assessment, however, suggests that the experimental evidence is inconsistent and not coherent with findings in epidemiology studies. Specifically, the findings of mild and reversible effects in most experimen tal studies conducted at elevated exposures are not consistent with the more serious associations described in epidemiology studies (e.g., hospital admissions and mortality). Also, both animal studies and controlled human exposure studies have identified n o effect levels for acute and chronic exposure to PM and PM constituents at concentrations considerably above ambient levels. EPA should consider the experimental findings in light of these higher exposure levels and what the relevance may be for ambient e xposures (API, 2012, Attachment 1, p. 25). The EPA notes that in the review completed in 1997 , the Agency considered the lack of demonstrated biologic al mechanisms for the varying effects observed in epidemiological studies to be an important caution in it s integrated assessment of the health evidence upon which the standards were based ( 71 FR 61157, October 17, 2006 ). In the review completed in 2006, the EPA recognized the findings from additional research that indicated that different health responses wer e linked with different particle characteristics and that both individual components and complex particle mixtures appeared to be responsible for many biologic responses relevant to fine particle exposures. Id. Since that review, there has been a great dea l of research directed toward advancing our understanding of biologic mechanisms. While this research has not resolved all questions, and further research is warranted ( U.S. EPA, 2011a, section 2.5), it has provided important insights as discussed in secti on III.B.1 of the proposal (77 FR at***E.O. 12866 Review

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Page 68 of 253 38906 to 38909) and discussed more fully in the Integrated Science Assessment ( U.S. EPA, 2009a, C hapter 5). As noted in the proposal, toxicological studies provide evidence to support the biologic al plausibility of car diovascular and respiratory effects associated with long

- and short

- term PM exposures observed in epidemiological studies (77 FR 38906) and provide supportive mechanistic evidence that the cardiovascular morbidity effects observed in long

- term exposure epi demiological studies are coherent with studies of cardiovascular

related mortality (77 FR 38907). The Integrated Science Assessment concluded that t he new evidence available in this review “greatly expands” upon the evidence available in the last review “p articularly in providing greater understanding of the underlying mechanisms for PM 2.5 induced cardiovascular and respiratory effects for both short

- and long

- term exposures ” ( U.S. EPA, 2009a, p. 2

- 17). The mechanistic evidence now available, taken together with newly available epidemiological evidence, increases the Agency’s confidence that a causal relationship exists between long

- and short

- term exposure to PM 2.5 and cardiovascular effects and mortality. 41 In addition, CASAC supported the Integrated Scienc e Assessment approach and characterization of potential mechanisms or modes of action (Samet, 2009e, pp. 7 to 8; Samet, 2009f, p. 11), as well
41 See American Trucking Assn’s Ass ociation v. EPA, 175 F. 3d 1027, 1055

- 56 (D.C. Cir. 1999) rev ’ erse d in part and affirmed in part sub nom , Whitman v. American Trucking Assn’s, 531 U.S. 457 (2001) holding that the EPA could establish NAAQS without identifying a biological mechanism (“ To begin wit h, the statute itself requires no such proof. The Administrator may regulate air pollutants "emissions of which, in his judgment, cause or contribute to air pollution which may reasonably be anticipated to endanger public health or welfare ." ( emphasis adde d by the court). Moreover, this court has never required the type of explanation petitioners seek from EPA. In fact, we have expressly held that EPA's decision to adopt and set air quality standards need only be based on ‘reasonable extrapolations from som e reliable evidence’.... Indeed, were we to accept petitioners' view, EPA (or any agency for that matter) would be powerless to act whenever it first recognizes clear trends of mortality or morbidity in areas dominated by a particular pathogen.”).***E.O. 12866 Review

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Page 69 of 253 as the findings of a causal relationship at the population level between exposure to PM 2.5 and mortality and card iovascular effects (Samet, 2009f, pp. 2 to 3). 42 Additionally, the EPA disagrees with commenters that the mild and reversible effects observed in controlled human exposure studies are inconsistent with the more serious effects observed in epidemiologic al studies. Ethical considerations regarding the types of studies that can be performed with human subjects generally limit the effects that can be evaluated to those that are transient, reversible, and of limited short

- term consequence. The relatively small number of subjects recruited for controlled exposure studies should also be expected to have less variability in health status and risk factors than occurring in the general population. 43 Consequently, the severity of health effects observed in controlled human exposure studies evaluating the effects of PM should be expected to be less than observed in epidemiologic studies. Nonetheless, that effects are observed in relatively healthy individuals participating in controlled exposure studies serves as an ind icator that PM is initiating health responses and that more severe responses may reasonably be expected in a more diverse population.

43 For example, the EPA excludes from its controlled human exposure studies involving exposure to PM 2.5 any individual with a significant risk factor for experiencing adverse effects from such exposure. Thus, the EPA excludes a priori the following categorie s of persons: those with a history of angina, cardiac arrhythmias, and ischemic myocardial infarction or coronary bypass surgery; those with a cardiac pacemaker; those with uncontrolled hypertension (greater than 150 systolic and 90 diastolic); those with neurogenetive diseases; those with a history of bleeding diathesis; those taking beta

blockers; those using oral anticoagulants; those who are pregnant, attempting to become pregnant, or breastfeeding; those who have experienced a respiratory infection wit hin four weeks of exposure; those experiencing eye or abdominal surgery within six weeks of exposure; those with active allergies; those with a history of chronic illnesses such as diabetes, cancer, rheumatologic diseases, immunodeficiency state, known car diovascular disease, or chronic respiratory diseases; smokers. The EPA “Application for Independent Review Board Approval of Human Subjects Research: Cardiopulmonary Effects of healthy Older GSTM1 Null and Sufficient individuals to Concentrated Ambient Air Particles (CAPTAIN)”, Nov. 9, 2011, p. 9.***E.O. 12866 Review

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Page 70 of 253 It should also be noted that there is a small body of toxicological evidence demonstrating mortality in rodents exposed t o PM (e.g., Killingsworth et al. 1997; Godleski et al. 1996). Overall it is not surprising that lethality is not induced in more toxicological research, as these types of studies do not readily lend themselves to this endpoint. Epidemiologic al studies have observed associations between PM and mortality in communities with populations in the range of many thousands to millions of people. Clearly, it is not feasible to expose hundreds (if not thousands) of animals to ambient PM (potentially over many years) i n a laboratory setting to induce enough lethalities to distinguish between natural deaths and those attributable to PM. Furthermore, the heterogeneous human populations sampled in epidemiological studies are comprised of individuals with different physical , genetic, health, and socioeconomic backgrounds which may impact the outcome. However, in toxicological studies, the rodent groups are typically inbred, such that inter

- individual variability is minimized. Thus, if the rodent strain used is quite robust, PM

- induced effects may not be observed at low exposure concentrations. (3) In asserting that the uncertainties in the underlying health science are as great or greater than in the last review and therefore do not support revision to the standards at this t ime, commenters in this group variously discussed a number of issues related to: (a) confounding, (b) heterogeneity in risk estimates, (c) exposure measurement error, (d) model specification , (e) the concentration

- response relationship, and ( f ) understandi ng the relative toxicity of components within the mixture of fine particles. Each of these issues is addressed below and some are discussed in more detail in the Response to Comments document
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Page 71 of 253 In summary, these commenters concluded that the substantial un certainties present in the last review have not been resolved and/or that the uncertainty about the possible health risks associated with PM 2.5 exposure has not diminished. As discussed below, the EPA believes that the overall uncertainty about possible he alth risks associated with both long

- and short

- term PM 2.5 exposure has diminished to an important degree since the last review. While the EPA agrees that important uncertainties remain, and that future research directed toward addressing these uncertainti es is warranted, the EPA disagrees with commenters’ views that the remaining uncertainties in the scientific evidence are too great to warrant revising the current PM 2.5 NAAQS. ( a ) Confounding Some commenters have criticized the EPA for not adequately ad dressing the issue of confounding in both long

- and short

- term exposure studies of mortality and morbidity. This includes confounding due to copollutants, as well as unmeasured confounding. 44 With regard to copollutant confounding, these commenters asserte d that the EPA has not adequately interpreted the results from studies that examined the effect of copollutants on the relationship between long

- and short

- term PM 2.5 exposures and mortality and morbidity outcomes. These commenters contend that the EPA has inappropriately concluded that PM 2.5 - related mortality and morbidity associations are

44 The Integrated Science Assessment defines confounding as “a confusion of effects. Specifically, the apparent effect of the exposure of interest is distorted because the effect of an extraneous factor is mistaken for or mixed with the actual exposure effect (which may be null) (Rothman and Greenland, 1998)” (U.S. EPA, 2009a, p. 1

- 16). Epidemiological analyses attempt to adjust or control for these characteristics (i.e., potential confounders) that differ between e xposed and non

- exposed individuals (U.S. EPA, 2009a, section 1.5.3). Not all risk factors can be controlled for within a study design/model and are termed “unmeasured confounders.” An unmeasured confounder is a confounder that has not previously been measu red and therefore is not included in the study design/model.***E.O. 12866 Review

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Page 72 of 253 generally robust to confounding. The commenters stated that statistically significant PM 2.5 associations in single

- pollutant models in epidemiologic al studies do not rem ain statistically significant in copollutant models. The loss of statistical significance or the reduction in the magnitude of the effect estimate when a co

- pollutant model is used may be the result of factors other than confounding. These changes do not prove either the existence or absence of confounding. These impacts must be evaluated in a broader context that considers the entire body of evidence. The broader examination of this issue in the Integrated Science Assessment included a focus on evaluating the stability of the size of the effect estimates in epidemiological studies conducted by a number of research groups using single

- and copollutant models ( U.S. EPA, 2009a, sections 6.2.10.9, 6.3.8.5, and 6.5, Figures 6

- 5, 6

- 9, and 6

- 15). This examination found that, for most epidemiological studies, there was little change in effect estimates based on single

- and copollutant models, although the Integrated Scien ce Assessment recognized that in some cases, the PM 2.5 effect estimates were markedly reduced in size and lost statistical significance. Additionally, the EPA notes that these comments do not adequately reflect the complexities inherent in assessing the is sue of copollutant confounding. As discussed in the proposal (77 FR 38907, 38909, and 38910) and more fully in the Integrated Science Assessment ( U.S. EPA, 2009a, sections 6.2, 6.3, and 6.5), although copollutant models may be useful tools for assessing whe ther gaseous copollutants may be potential confounders, such models alone cannot determine whether copollutants are in fact confounders. Interpretation of the results of copollutant models is complicated by correlations that often exist among air pollutant s, by the fact that some pollutants play a role in the***E.O. 12866 Review

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Page 73 of 253 atmospheric reactions that form other pollutants such as secondary fine particles, and by the statistical power of the studies in question inherent in the study methodology. For example, the every

- thir d or sixth

- day sampling schedule often employed for PM 2.5 measurements compared to daily measurements of gaseous copollutants drastically reduces the overall sample size to assess the effect of copollutants on the PM 2.5 - morbidity or mortality relationship, such that the reduced sample size can lead to less precise effect estimates (e.g., wider confidence intervals). The EPA recognizes that when PM 2.5 is correlated with gaseous pollutants it can be difficult to identify the effect of individual pollutants in the ambient mixture (77 FR 38910). However, based on the available evidence, the EPA concludes epidemiological studies continue to support the conclusion that PM 2.5 associations with mortality and morbidity outcomes are robust to the inclusion of gaseous copollutants in statistical models. The EPA evaluated the potential confounding effects of gaseous copollutants and, although it is recognized that uncertainties and limitations still remain, the Agency concluded the collective body of scientific evidence is “stronger and more consistent than in previous reviews providing a strong basis for decision making in this review" (77 FR 38910/1). Several commenters offered detailed comments on the long

- term PM 2.5 exposure studies arguing that associations from mor tality studies are subjected to unmeasured confounding and as a result are not appropriately characterized as being cau s al ( providing evidence of a causal relationship between long

- term PM 2.5 exposure and mortality (e.g., UARG, 2012, pp. 10 to 11, Attachme nt A, pp. 17 to 23; API, 2012, pp. 13 to 14, Attachment 1, pp. 11 to 14 , Attachment 7, pp. 2

- 10 ; ACC, 2012, p. 18 to 21; AFPM,***E.O. 12866 Review

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Page 74 of 253 2012, p. 8; TCEQ Texas CEQ , 2012, p. 4). Specifically, these commenters cited two studies (i.e., Janes et al. , 2007 and Greven et al. , 2011) that used a new type of statistical analysis , in which the study authors to examine associations between annual (long

- term) and monthly (sub

- chronic) PM 2.5 exposure and mortality. The commenters interpreted the results of the analysis these analyses as evidence of unmeasured confounding in the long

term PM 2.5 exposure - mortality relationship. These commenters interpreted these studies as raising fundamental questions regarding the EPA’s determination that a causal relationship e xists between long

- term PM 2.5 exposure and mortality. The first study, Janes et al., 2007, In addition to the commenters mentioned above, all of the authors of the publications by Janes et al. (2007) and Greven et al. (2011) (i.e., Francesca Dominici, Scot t Zeger, Holly Janes, and Sonja Greven) submitted a joint comment to the public docket in order to clarify specific points regarding these two studies (Dominici et al., 2012). The first study, Janes et al. ( 2007 ) , was evaluated in the Integrated Science As sessment (U.S. EPA, 2009a, p. 7

- 88). The second study, Greven et al ., . ( 2011 , ), an extension of the Janes et al. (2007) study adding three more years of data, is a “new” study discussed in the Provisional Science Assessment (U.S. EPA, 2012 ) and the Respon se to Comments document. ). Both studies used nationwide Medicare mortality data to examine the association between monthly average PM 2.5 concentrations over the preceding 12 months and monthly mortality rates in 113 U.S. counties
. and examined whether comm

unity

- specific trends in monthly PM 2.5 concentrations and mortality declined at the same rate as the national rate. The investigators decomposed examined this by decomposing the association between PM 2.5 and mortality into two components: (1)***E.O. 12866 Review

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Page 75 of 253 “national tren ds” national trends , defined as the association between the national average trend in monthly PM 2.5 concentrations averaged over the previous 12 months and the national average trend in monthly mortality rates , and (2) “ local trends ,” , defined as county
- specific deviations in monthly PM 2.5 concentrations and monthly mortality rates from national trends. The EPA does not question the results of the national trends analyses conducted by Janes et al. (2007) and Greven et al. (2011). These analyses demonstrated associations similar in magnitude and precision to other studies of long

- term PM 2.5 exposure and mortality. However, the authors hypothesized that the results from the “local” and “national” analyses should be similar in magnitude, a nd that any difference between the two results would be due to unmeasured confounding. 45 The authors provide d no references to support their assumptions that associations between PM 2.5 and mortality should be similar across temporal and spatial scales nor why any differences in effect estimate size would be due to unmeasured confounding. 46 Both Janes et al. (2007) and Greven et al. (2011) observed positive and statistically significant associations between long

- term exposure to PM 2.5 and mortality in their n ational analyses. However, Janes et al. (2007) and Greven et al. (2011) eliminated all of the spatial variation in air pollution and mortality in their data set when estimating the national effect, focusing instead on both chronic (yearly) and sub

- chronic (monthly) temporal differences in the data

45 Unmeasured confound ers need to be factors that are associated with both the exposure and outcome of interest, but in the case of the Janes and Greven stud ies this would also need to hold true over multiple dimensions of time and space as stated by Pope and Burnett , 2007
. 46 In its evaluation of Janes et al. (2007) in the I ntegrated S cience A ssessment , the EPA did not identify limitations in the statistical methods used per se (U.S. EPA, 2009a, p. 7

- 88) and included the results of the national

- scale analyses in that study in the body of evidence that supported the determination that there is a causal relationship between long

- term PM 2.5 exposure and mortality
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Page 76 of 253 (Dominici et al. 2012). Janes et al. (2007) (Table 1) highlight ed that over 90 percent of the variance in the data set used for the analyses conducted by both Janes et al. (2007) and Greven et al. (2011) was attri butable to spatial variability, which the authors chose to discard. As noted above, the focus of the analyses by Janes et al. (2007) and Greven et al. (2011) was on two components: (1) a temporal or time component, i.e., the “national” trends analysis, whi ch examined the association between the national average trend in monthly PM 2.5 concentrations averaged over the previous 12 months and the national average trend in monthly mortality rates and (2) a space

- by

- time component, i.e., the “local” trends analys is, which examined county
- specific deviations in monthly PM 2.5 concentrations and monthly mortality rates from national trends. These two components combined comprised less than 10 percent of the variance in the data set. The authors included a focus on th e space - by

- time component, which represented approximately 5 percent of the variance in the data set, in an attempt to identify, absent confounding, if PM 2.5 was associated with mortality at this unique exposure window. Thus, these studies are not directly comparable to other cohort studies investigating the relationship between long

- term exposure to PM 2.5 and mortality, which make use of spatial variability i n air pollution and mortality data. 47 This point was highlighted by the study authors who stated that “when one considers that this wealth of information is not accounted for in [Janes 2007], it is not as surprising that... vastly different estimates of the P M 2.5 /mortality

47 Though not dire ctly comparable, the national effect estimates for mortality reported by Janes et al. (2007) and Greven et al. (2011) are coincidentally similar in magnitude to those previously reported. It is important to note that previous cohort studies have focused on identifying spatial differences in PM 2.5 concentrations between cities, while Janes et al. (2007) and Greven et al. (2011) focus primarily on temporal differences in PM 2.5 concentrations. In fact, Greven et al. (2011) state “We do not focus here on a thir d type [of statistical approach] used in cohort studies, measuring the association between average PM 2.5 levels and average age

- adjusted mortality rates across cities (purely spatial or cross - sectional association).”***E.O. 12866 Review

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Page 77 of 253 relationship [were observed] than in other studies that do exploit that variability” (Dominici et al., 2012, p. 2 ). The EPA notes that the results of the local trends analyses conducted by Janes et al. (2007) and Greven et al. (2011) are li mited by the monthly timescale used in these analyses. This view is consistent with comments on the Janes et al. (2007) study articulated in Pope and Burnett (2007), the EPA notes 48 which noted that an important limitation of the local scale analysis conduc ted by Janes et al. (2007) and subsequently by Greven et al. (2011) is was the subchronic exposure window considered in these analyses. Both studies used annual average PM 2.5 concentrations to characterize long

- term national trends which is was consistent wi th exposure windows considered in other studies of long

term exposure to PM 2.5 and mortality studies.
. 49 However, the local scale analyses used monthly average PM 2.5 concentrations to characterize county

- specific deviations from national trends (the “ local ” scale). The use of monthly average data likely does not provide enough exposure contrast to observe temporal changes in mortality at the local scale. It also represents a different exposure window than considered in the large body of evidence of health ef

fects related to short

- term (from less than one day to up to several days) and chronic (one or more years) measures of PM 2.5 . As discussed by Pope and Burnett (2007) and highlighted in the I ntegrated S cience A ssessment , the conclusions of Janes et al
. Furt hermore, the EPA disagrees with commenters that studies by Janes et al. (2007) and Greven et al. (2011) provide evidence

48 S ome commenters argued that there were flaws in the criticisms offered by Pope and Burnett (2007) on the paper by Janes et al. (2007) (UARG, 2012, Attachment A, pp. 19 to 23). The EPA responds to each of these specific comments in the Response to Comments document. 49 As noted above, howeve r, Janes et al. (2007) and Greven et al. (2011) focus ed on temporal variability and other studies of long

- term exposure to PM 2.5 and mortality focus on spatial variability
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Page 78 of 253 that other studies of long

- term exposure to PM 2.5 and mortality are affected by unmeasured confounding. As noted above, the design of t he studies conducted by Janes et al (2007) and Greven et al (2011) are fundamentally different than those used in other studies of long

- term exposure to PM 2.5 and mortality, including the ACS cohort and the Harvard Six Cities study. Studies, such as the AC S and Harvard Six Cities studies, used the spatial variation between cities to measure the effect of long

- term (annual) exposures to PM 2.5 on mortality risk, and did not conduct any analyses relying on the temporal variation in PM 2.5 . The opposite is true of the Janes et al. (2007) and Greven et al. (2011) studies which first removed the spatial variability in PM 2.5 and then examined the temporal variation at both the national and local scale to measure the effects of temporal differences in PM 2.5 on mortal ity risk. Janes et al. (2007) and Greven et al. (2011) focus on changes in PM 2.5 concentrations over time and , therefore , control for confounders would be based on including variables that vary over time rather than over space. As a result, any evidence of potential confounding of the PM 2.5 - mortality risk relationship derived from Janes et al. (2007) and Greven et al. (2011) cannot be extrapolated to draw conclusions related to potential spatial confounding in studies based on the spatial variation in PM 2.5 concentrations. As detailed in the Integrated Science Assessment (U.S. EPA, 2009a, section 7.6) , and recognized by the authors of Janes et al. (2007) and Greven et al. (2011), the cohort studies that informed the causality determination for long

- term PM 2.5 exposure and mortality “have developed approaches to adjust for measured and unmeasured confounders” (Dominici et al., 2012, p. 2). These approaches were specifically designed to adjust for spatial confounding. The hypothesis that the authors of Janes et al. (2007)***E.O. 12866 Review

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Page 79 of 253 and Greven et al. (2011) chose to examine was that differences in the local and national effects indicated u nmeasured temporal confounding in either the local or national effect estimate. This hypothesis was specific to these two studies that examined temporal variability in exposure to air pollution and did not include known potential confounders at either the national or local scale as time

- varying covariates in the statistical model. The authors acknowledge d that the interpretation of either the national or local estimates needs to occur with an appreciation of the potential confounding effects of national and local scale covariates that were omitted from the model ( Dominici et al., 2012 ). It is important to recognize that because Janes et al. (2007) and Greven et al. (2011) focus ed on variations in PM 2.5 over time and not space, the results from these two stud ies do not provide any indication that other studies of long

- term exposure to PM 2.5 and mortality exhibit spatial confounding, or that PM 2.5 does not cause mortality. 50 The authors of Janes et al. (2007) and Greven et al. (2011) recognized that “it is entirely possible that these papers are looking for an association at a timescale for which no association truly exists” (Dominici et al.,. 2012, p. 3). Furthermore, as highlighted in the Integrated Science Assessment and discussed by Pope and Burnett (200 7), the conclusions of Janes et al. (2007) “are overstated. . . [T]heir analysis tells us little or nothing about unmeasured confounding in those and related studies because the methodology of Janes et al
. largely excludes the sources of variability that a re exploited in those other studies. By using monthly mortality counts and lagged 12

- month average pollution concentrations, the authors eliminate the opportunity to exploit short

- term or day

- to
- day variability.” Some commenters argued that there were flaw s in the criticisms

50 Further, the EPA notes that Janes et al. (2007) and Greve n et al. (2011) provide no information relevant to examining confounding in studies of short

- term exposure to PM 2.5 .***E.O. 12866 Review

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Page 80 of 253 offered by Pope and Burnett (2007) on the paper by Janes et al. (2007) (UARG, 2012, Attachment A, pp. 19 to 23). The EPA responds to each of these specific comments in the Response to Comments document. In its evaluation of Janes et al. (2007), the EPA did not identify limitations in the statistical methods used per se ( U.S. EPA, 2009a, p. 7

- 88) and the results of the national

- scale analyses were included in the body of evidence that supported the determination that there is a causal rel ationship between long

- term PM 2.5 exposure and mortality In conclusion, the EPA believes interprets the results of the analyses conducted by Janes et al. (2007) and Greven et al. (2011) are as being consistent with prior knowledge of examining associations with long

- term exposure to PM 2.5 at the national scale using long

- term average PM 2.5 concentrations. However, For the reasons presented above and discussed in more detail in the Response to Comments document, the Agency disagrees with the commenters’ assum ption that their “national” and “local” scale analyses should produce similar the results and their conclusion that differing results is evidence of Janes et al. (2007) and Greven et al. (2011) indicate unmeasured confounding
. in the results of other coho rt studies of long

- term exposure to PM 2.5 and mortality
. Therefore, the EPA concludes that these studies do not bring into question invalidate the large body of epidemiological evidence indicating that supports the EPA’s determination that a causal associati on relationship exists between long

- term PM 2.5 exposure and mortality. 51 ( b ) Heterogeneity in Risk Estimates Industry Some commenters argued that the heterogeneity in risk estimates

51 The EPA notes that the EPA’s conclusion with regard to interpretation of the results from Janes et al. (2007) and Greven et al. (2012) is supported by the study authors ’ conclusion that “[ o]ur results do not invalidate previous epidemiologic al studies ” (Dominici, 2012, p. 1 (emphasis original)).***E.O. 12866 Review

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Page 81 of 253 observed in multicity multi

- city epidemiological studies and the lack of statistical significance in many regional or seasonal estimates highlights a potential bias associated with combined multi

- city epidemiological study results (e.g., API, 2012, Attachment 1, pp. 15 to 19). These comm enters further argued that more refined intra

- urban exposure estimates conducted for two of the largest cities included in the ACS study, Los Angeles and New York City, based on land

- use regression models and/or kriging methods (Krewski et al., 2009) “unde rscore the importance of considering city

- specific health estimates, which may account for heterogeneity in PM 2.5 concentrations or other differences among cities, rather than relying on pooled nationwide results from multi

- city studies” (API, 2012, Attach ment 1, p. 17). With respect to understanding the nature and magnitude of PM 2.5 - related risks, the EPA agrees that epidemiological studies evaluating health effects associated with long

and short

- term PM 2.5 exposures have reported heterogeneity in respons es between cities and effect estimates across geographic regions of the U.S. ( U.S. EPA, 2009a, sections 6.2.12.1, 6.3.8.1, 6.5.2, and 7.6.1; U.S. EPA, 2011a, p. 2

- 25). For example, when focusing on short

- term PM 2.5 exposure, the Integrated Science Assessme nt found that multi

- city studies that examined associations with mortality and cardiovascular and respiratory hospital admissions and emergency department visits demonstrated greater cardiovascular effects in the eastern versus the western U.S. (Dominici, et al., 2006; Bell et al., 2008; Franklin et al. (2007, 2008)). In addition, the Integrated Science Assessment evaluated studies that provided some evidence for seasonal differences in PM 2.5 risk estimates, specifically in the northeast. The PM ISA I ntegra ted S cience A ssessment found evidence indicating that***E.O. 12866 Review

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Page 82 of 253 individuals may be at greater risk of dying from higher exposures to PM 2.5 in the warmer months, and at greater risk of PM 2.5 associated hospitalization for cardiovascular and respiratory diseases durin g colder months of the year. The limited influence of seasonality on PM risk estimates in other regions of the U.S. may be due to a number of factors including varying PM composition by season, exposure misclassification due to regional tendencies to spend more or less time outdoors and air conditioning usage, and the prevalen ce of infectious diseases during the winter months ( U.S. EPA, 2009a, p. 3

- 182). Overall, the EPA took note in the proposal that uncertainties still remain regarding various factors that contribute to heterogeneity observed in epidemiological studies (77 F R 38909/3). Nonetheless, the EPA recognizes that this heterogeneity could be attributed, at least in part, to differences in PM 2.5 composition across the U.S., as well as to exposure differences that vary regionally such as personal activity patterns, micr oenvironmental characteristics, and the spatial variability of PM 2.5 concentrations in urban areas ( U.S. EPA, 2009a, section 2.3.2; 77 FR 38910). As recognized in the Policy Assessment, the current epidemiological evidence and the limited amount of city

- s pecific speciated PM 2.5 data do not allow conclusions to be drawn that specifically differentiate effects of PM 2.5 in different locations ( U.S. EPA, 2011a, p. 2

- 25). Furthermore, the Integrated Science Assessment concluded “that many constituents of PM 2.5 can be linked with multiple health effects, and the evidence is not yet sufficient to allow differentiation of those constituents or sources that are more closely related to specific health outcomes ” ( U.S. EPA, 2009a, p. 2

- 17). CASAC thoroughly reviewed th e EPA’s presentation of the scientific evidence indicating***E.O. 12866 Review

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Page 83 of 253 heterogeneity in PM 2.5 effect estimates in epidemiological studies and concurred with the overall conclusions presented in the Integrated Science Assessment. (c) Exposure Measurement Error Industr y Some commenters argued that the EPA did not adequately consider exposure measurement error, which they asserted is an important source of bias in epidemiological studies that can bias effect estimates in either direction (e.g., API, 2012, Attachment 1, pp . 19 to 20). The EPA agrees that exposure measurement error is an important source of uncertainty and that the variability in risk estimates observed in multi

- city studies could be attributed, in part, to exposure error due to measurement

- related issues ( 77 FR 38910). However, the Agency disagrees with the commenters’ assertion that exposure measurement error was not adequately considered in this review. The Integrated Science Assessment included an extensive discussion that addresses issues of exposure
me asurement error ( U.S. EPA, 2009a, sections 2.3.2
. and 3.8.6). Exposure measurement error may lead to bias in effect estimates in epidemiological studies. A number of studies evaluated in the last review ( U.S. EPA, 2004, section 8.4.5) and in the current re view ( U.S. EPA, 2009a, section 3.8.6) have discussed the direction and magnitude of bias resulting from specified patterns of exposure measurement error (Armstrong 1998; Thomas et al. 1993; Carroll et al. 1995) and have generally concluded “classical” (i.e ., random, within

- person) exposure measurement error can bias effect estimates towards the null. Therefore, consistent with conclusions reached in the last review, the Integrated Science Assessment concluded “in most circumstances, exposure error tends to bias a health effect estimate downward ” ( U.S. EPA, 2009a, sections 2.3.2 and 3.8.6) (emphasis***E.O. 12866 Review

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Page 84 of 253 added). Thus, the EPA has both considered and accounted for the possibility of exposure measurement error, and the possible bias would make it more difficult to d etect true associations, not less difficult. ( d ) Model Specification Commenters contend contend ed that the EPA did not account for the fact that “selecting an appropriate statistical model for epidemiologic studies of air pollution involves several choices that involve much ambiguity, scant biological evidence, and a profound impact on analytic results, gi ven that many estimated associations are weak” (ACC, 2012, p. 5) For short

- term exposure studies , the EPA recognizes, as summarized in the HEI review panel commentary that selecting a level of control to adjust for time

varying factors, such as temperature , in time

- series epidemiologic al studies involves a trade

- off (HEI, 2003). For example, if the model does not sufficiently adjust for the relationship between the health outcome and temperature, some effects of temperature could be falsely ascribed to the pollution variable. Conversely, if an overly aggressive approach is used to control for temperature, the result would possibly underestimate the pollution

- related effect and compromise the ability to detect a small but true pollution effect ( U.S. EPA, 2004 , p. 8

- - 236; HEI, 2003, p. 266). The selection of approaches to address such variables depends in part on prior knowledge and judgments made by the investigators, for example, about weather patterns in the study area and expected relationships between weat her and other time

- varying factors and health outcomes considered in the study. As demonstrated in s ection 6.5 of the Integrated Science Assessment, the EPA thoroughly considered each of these issues and the overall effect of different model specifications on the association between short

- term PM 2.5 exposure and mortality. Regardless of the model employed, consistent positive associations were***E.O. 12866 Review

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Page 85 of 253 observed across studies that controlled for the potential confounding effects of time and weather using different a

pproaches ( US U
. S
. EPA 2009, Figure 6

- 27). The EPA also considered the influence of model specification in the examination of long

- term PM 2.5 exposure studies. For example, in s ection 7.6 of the Integrated Science Assessment , Figures 7

- 6 and 7

- 7 summarize t he collective evidence that evaluated the association between long

- term PM 2.5 exposure and mortality. Regardless of the model used, these studies collectively found evidence of consistent positive associations between long

- term PM 2.5 exposure and mortality
. The EPA, therefore, disagrees with commenters that model specification was not considered when evaluating the epidemiologic al evidence used to form causality determinations. The EPA specifically points out that the process of assessing the scientific qu ality and relevance of epidemiologic al studies includes examining “important methodological issues (e.g., lag or time period between exposure and effects, model specifications, thresholds, mortality displacement) related to interpretation of the health evi dence ( US U
. S
. EPA, 2009, p. 1

- 9).” Consistent with the conclusions of the 2004 PM AQCD A ir Q uality C riteria D ocument , the EPA recognizes that there is still no clear consensus at this time as to what constitutes appropriate control of weather and temporal trends in short

- term exposure studies, and that no single statistical modeling approach is likely to be most appropriate in all cases ( U.S. EPA, 2004, p. 8

- 238). However, the EPA believes that the available evidence interpreted in light of these remaining uncertainties does provide increased confidence relative to the last review in the reported associations between short

- and long

- term PM 2.5 exposures and mortality and morbidity effects, alone and in combination with other pollutants.***E.O. 12866 Review

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Page 86 of 253 ( e ) Concentration

- res ponse Relationship Additionally, commenters questioned the interpretation of the shape of the concentration

- response relationship, specifically stat ing that multiple studies have demonstrated that there is a threshold in the PM

- health effect relationship a nd that the log

- linear model is not biologically plausible (API, 2012, Attachment 9; ACC, 2012, Appendix A, pp. 7 to 8). The EPA disagrees with this assertion due to the number of studies evaluated in the Integrated Science Assessment that continue to supp ort the use of
a no - threshold, log

- linear model to most appropriately represent the PM concentration

response relationship ( U.S. EPA, 2009a, section 2.4.3). W hile recognizing that uncertainties remain, the EPA believes that our understanding of this issue for both long

and short

- term exposure studies has advanced since the last review. As discussed in the Integrated Science Assessment, both long

- and short

- term exposure studies have employed a variety of statistical approaches to examine the shape of the co ncentration

response function and whether a threshold exists. While the EPA recognizes that there likely are individual biologic al thresholds for specific health responses, the Integrated Science Assessment concluded the overall evidence from existing epid emiological studies do es not support the existence of thresholds at the population level, for effects associated with either long

- term or short

- term PM exposures within the ranges of air quality observed in these studies (U.S. EPA, 2009a, section 2.4.3)
. 52 The Integrated Science Assessment concluded that this evidence collectively supported the conclusion that a no

- threshold, log

- linear model is most appropriate ( U.S. EPA, 2009a, sections

52 While epidemiological analyses have not identified a population threshold in the range of air quality concentrations e valuated in these studies, the EPA recognizes that it is possible that such thresholds exist towards the lower end of these ranges (or below these ranges).***E.O. 12866 Review

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Page 87 of 253 6.2.10.10, 6.5.2.7, and 7.6.4). CASAC likewise advised that “[a]lthoug h there is increasing uncertainty at lower levels, there is no evidence of a threshold (Samet, 2010d, p. ii). The EPA recognizes that some short

- term exposure studies have examined the PM PM 2.5 concentration

- response relationship in individual cities or on a city

- to
- city basis and observed heterogeneity in the shape of the concentration

- response curve across cities. As discussed in (b) above, these findings are a source of uncertainty that the EP A agrees requires further investigation. Nonetheless, the Integrated Science Assessment concluded that “the studies evaluated further support the use of a no

- threshold, log

- linear model, but additional issues such as the influence of heterogeneity in estim ates between cities and the effects of seasonal and regional differences in PM on the concentration

- response relationship still require further investigation” ( U.S. EPA, 2009a, p. 2

- 25). (f) Relative Toxicity of PM 2.5 Components Some commenters highligh ted uncertainties in understanding the role of individual constituents with in the mix of fine particles. These commenters asserted that a
mass - based standard may not be appropriate due to the growing body of evidence indicating that certain PM 2.5 component s may be more closely related to specific health outcomes (e.g., EC and OC) (EPRI, 2012, p. 2). With regard to questions about the role of individual constituents within the mix of fine particle s , as a general matter, the EPA recognizes that although new research directed toward this question has been conducted since the last review, important questions remain and the issue remains an important element in the Agency’s ongoing research program. At the time of the last review, the Agency determined that it w as***E.O. 12866 Review

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Page 88 of 253 appropriate to continue to control fine particles as a group, as opposed to singling out any particular component or class of fine particles (71 FR 61162 to 61164, October 17, 2006). This distinction was based largely on epidemiological evidence of heal th effects using various indicators of fine particles in a large number of areas that had significant contributions of differing components or sources of fine particles, together with some limited experimental studies that provided some evidence suggestive of health effects associated with high concentrations of numerous fine particle components. In this review, as discussed in the proposal (77 FR 38922 to 38923) and in section III.E.1 below, while most epidemiological studies continue to be indexed by PM 2.5 mass, several recent epidemiological studies included in the Integrated Science Assessment have used PM 2.5 speciation data to evaluate health effects associated with fine particle exposures. In the Integrated Science Assessment, the EPA thoroughly eval uated the scientific evidence that examined the effect of different PM 2.5 components and sources on a variety of health outcomes ( U.S. EPA, 2009a, section 6.6) and observed that the available information continues to suggest that many different chemical co mponents of fine particles and a variety of different types of source categories are all associated with, and probably contribute to, effects associated with PM 2.5 . The Integrated Science Assessment concluded that the current body of scientific evidence in dicated that “many constituents of PM can be linked with differing health effects and the evidence is not yet sufficient to allow differentiation of those constituents or sources that are more closely related to specific health outcomes” ( U.S. EPA, 2009a, p. 2

- 26 and 6

- 212). Furthermore, the Policy Assessment concluded that the evidence is not sufficient to support eliminating any component or group of components associated with any specific source categories***E.O. 12866 Review

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Page 89 of 253 from the mix of fine particles included in the P M 2.5 indicator ( U.S. EPA, 2009a, p. 2

- 56). CASAC agreed that it was reasonable to retain PM 2.5 as an indicator for fine particles in this review as “[t]here was insufficient peer

- reviewed literature to support any other indicator at this time” (Samet, 2010 c, p. 12). This information is relevant to the Agency’s decision to retain PM 2.5 as the indicator for fine particles as discussed in section III.E.1 below. The EPA also believes that it is relevant to the Agency’s conclusion as to whether revision of the s uite of primary PM 2.5 standards is appropriate. While there remain uncertainties about the role and relative toxicity of various components of fine PM, the current evidence continues to support the view that fine particles should be addressed as a group fo r purposes of public health protection. In summary, in considering the above issues related to uncertainties in the underlying health science, on balance, the EPA believes that the available evidence interpreted in light of these remaining uncertainties d oes provide increased confidence relative to the last review in the reported associations between long

- and short

- term PM 2.5 exposures and mortality and morbidity effects, alone and in combination with other pollutants, and supports stronger inferences as to the causal nature of the associations. The EPA also believes that this increased confidence, when taken in context of the entire body of available health effects evidence and in light of the evidence from epidemiological studies of associations observe d in areas meeting the current primary PM 2.5 standards, specifically in areas meeting the current primary annual PM 2.5 standard, adds support to its conclusion that the current suite of PM 2.5 standards needs to be revised to provide increased public health protection.***E.O. 12866 Review

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Page 90 of 253 (4) In asserting that there is no evidence of greater risk since the 2006 review to justify lowering the current annual PM 2.5 standard, some commenters argued that, “if the current primary PM 2.5 annual standard of 15 μg/m 3 was considered to be adequately protective of public health in 2006, given relative risk estimates that EPA was using at that time, then that standard would surely still be adequately protective of the public health if relative risk estimates remain at th e same level (or lower)” (UARG, 2012, Attachment 1, p. 24). These commenters compared risk coefficients used for mortality in the EPA’s risk assessment done in the last review with those from the Agency’s core risk assessment done as part of this review, a nd they concluded that “the entire range of the core relative risk for long

- term mortality is lower now than it was in the prior review” (UARG, 2012, Attachment 1, p. 24). These commenters used this conclusion as the basis for a claim that there is no reas on to revise the current annual PM 2.5 standard. The EPA believes that this claim is fundamentally flawed as it fails to take into account that exposure to a pollutant causally associated at a population

- level with premature mortality and serious illness ha s significant public health consequences, virtually regardless of the relative risk.
. In comparing the scientific understanding of the risk presented by exposure to PM 2.5 between the last and current reviews, one must examine not only the quantitative esti mate of risk from those exposures (e.g., the numbers of premature deaths or increased hospital admissions at various concentrations), but also the degree of confidence that the Agency has that the observed health effects are causally linked to PM 2.5 exposu re at those concentrations. As documented in the Integrated Science Assessment and in the recommendations and conclusions of CASAC, the EPA recognizes significant advances in our understanding of the health effects of***E.O. 12866 Review

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Page 91 of 253 PM 2.5 , based on evidence that is stron ger than in the last review because of its breadth and the substantiation of previously observed health effects.
. As a result of these advances, the EPA is now more certain that fine particles, alone or in combination with other pollutants, present a signi ficant risk to public health at concentrations allowed by the current primary PM 2.5 standards. From this more comprehensive perspective, since the risks presented by PM 2.5 are more certain, similar or even somewhat lower relative risk estimates would not b e a basis to conclude that no revision to the suite of PM 2.5 standards is “requisite” to protect public health with an adequate margin of safety. This also ignores that the relative risk estimate is only one factor considered by the Administrator, e.g. it ignores that epidemiological studies since the last review indicate associations between PM 2.5 and mor t ality and morbidity in areas meeting the current annual standard. In any case, the commenters’ reliance on the flawed 2006 review is misplaced. As discus sed in section III.A.2 above, the D.C. Circuit remanded Administrator Johnson’s 2006 decision to retain the primary annual PM 2.5 standard because the Agency failed to adequately explain why the annual standard provided the requisite protection from both sh ort
- and long

- term exposure to fine particles including protection for at

- risk populations. The 2006 standard was also at sharp odds with CASAC advice and recommendations as to the requisite level of protection (Henderson, 2006a,b). In other words, the jud gment of the then

- Administrator that the 2006 primary annual PM 2.5 standard was requisite to protect public health with an adequate margin of safety is not an appropriate benchmark for comparison. (5) Some of these commenters also identified “new” as well as older studies that***E.O. 12866 Review

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Page 92 of 253 had been included in prior reviews as providing additional evidence that the causality determinations presented in the Integrated Science Assessment did not consider the totality of the scientific literature , further supporting the ir view that a revision of the PM 2.5 is unwarranted. As discussed in section II.B.3 above, the EPA notes that, as in past NAAQS reviews, the Agency is basing the final decisions in this review on the studies and related information included in the PM ISA I ntegrated S cience A ssessment that have undergone CASAC and public review, and will consider newly published studies for purposes of decision making in the next PM NAAQS review. In provisionally evaluating commenters’ arguments (see Response to Comments doc ument), the EPA notes that its provisional assessment of “new” science found that such studies did not materially change the conclusions reached in the Integrated S cience Assessment (U.S. EPA, 2012b)
. 3. Administrator’s Final Conclusions Concerning the Adequ acy of the Current Primary PM 2.5 Standards Having carefully considered the public comments, as discussed above, the Administrator believes the fundamental scientific conclusions on the effects of PM 2.5 reached in the Integrated Science Assessment, and disc ussed in the Policy Assessment, are valid. In considering whether the suite of primary PM 2.5 standards should be revised, the Administrator places primary consideration on the evidence obtained from the epidemiological studies. The Administrator believes t hat this literature, combined with the other scientific evidence discussed in the ISA I ntegrated S cience A ssessment , collectively represents a strong and generally robust body of evidence of serious health effects associated with both long

- and short

- term e xposures to PM 2.5 . As discussed in the Integrated Science Assessment and Policy Assessment, the EPA believes that much progress has been made since the last review in reducing some of the major uncertainties***E.O. 12866 Review

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Page 93 of 253 that were important considerations in establishi ng the current suite of PM 2.5 standards. In that context, the Administrator finds the evidence of serious health effects reported in exposure studies conducted in areas with long

- term means mean concentration s ranging from approximately at or above the leve l of the annual standard to long

- term means mean concentration s significantly below the level of the annual standard to be compelling, especially in light of the extent to which such studies are part of an overall pattern of positive and frequently statisti cally significant associations across a broad range of studies. The information in the quantitative risk assessment lends support to this conclusion. There has been extensive critical review of this body of evidence, the quantitative risk assessment, and r elated uncertainties, including review by CASAC and the public. The public comments on the basis for the EPA’s proposed decision to revise the suite of primary PM 2.5 standards have identified a number of issues about which different parties disagree includ ing issues for which additional research is warranted. Having weighed all comments and the advice of CASAC, the Administrator believes that since the last review the overall uncertainty about the public health risks associated with both long

- and short

- ter m exposure to PM 2.5 has been diminished to an important degree. The remaining uncertainties in the available evidence do not diminish confidence in the associations between exposure to fine particles and mortality and serious morbidity effects. Based on her increased confide nce in the association between exposure to PM 2.5 and serious public health effects, combined with evidence of such an association in areas that would meet the current standards, the Administrator agrees with CASAC that revision of the current suite of PM 2. 5 standards to provide increased public health protection is necessary. Based***E.O. 12866 Review

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Page 94 of 253 on these considerations, the Administrator concludes that the current suite of primary PM 2.5 standards is not sufficient, and thus not requisite, to protect public health with an adequate margin of safety, and that revision is needed to increase public health protection. It is important to note that this conclusion, and the reasoning on which it is based, do not resolve the question of what specific revisions are appropriate. Tha t requires looking specifically at the current 24

- hour and annual PM 2.5 standards, including their indicator, averaging times, forms, and levels, and evaluating the scientific evidence and other information relevant to determining the appropriate revision of the suite of standards. E. Conclusions on the Elements of the Primary Fine Particle Standards 1. Indicator In initially setting standards for fine particles in 1997, the EPA concluded it was appropriate to control fine particles as a group, rather than singli ng out any particular component or class of fine particles. The EPA noted that community health studies had found significant associations between various indicators of fine particles, and that health effects in a large number of areas had significant mass contributions of differing components or sources of fine particles. In addition, a number of toxicological and controlled human exposure studies had reported health effects associations with high concentrations of numerous fine particle components. It was also not possible to rule out any component within the mix of fine particles as not contributing to the fine particle effects found in the epidemiologic studies (62 FR 38667, July 18, 1977). In establishing a size

- based indicator in 1977 to distinguish fi ne particles from particles in the coarse***E.O. 12866 Review

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Page 95 of 253 mode, the EPA noted that the available epidemiological studies of fine particles were based largely on PM 2.5 and also considered monitoring technology that was generally available. The selection of a 2.5 μm size cu t reflected the regulatory importance of defining an indicator that would more completely capture fine particles under all conditions likely to be encountered across the U.S., especially when fine particle concentrations and humidity are likely to be high, while recognizing that some small coarse particles would also be captured by current methods to monitor PM 2.5 (62 FR 38666 to 38668, July 18, 1997). In the last review, based on the same considerations, the EPA again recognized that the available informat ion supported retaining the PM 2.5 indicator and remained too limited to support a distinct standard for any specific PM 2.5 component or group of components associated with any source categories of fine particles (71 FR 61162 to 61164, October 17, 2006). In this current review, the same considerations continue to apply for selection of an appropriate indicator for fine particles. As an initial matter, the Policy Assessment recognizes that the available epidemiological studies linking mortality and morbidity effects with long

- and short

- term exposures to fine particles continue to be largely indexed by PM 2.5 . For the same reasons discussed in the last two reviews, the Policy Assessment concluded that it was appropriate to consider retaining a PM 2.5 indicator t o provide protection from effects associated with long

- and short

- term fine particle exposures ( U.S. EPA, 2011, p. 2

- 50). The Policy Assessment also considered the expanded body of evidence available in this review to consider whether there was sufficient evidence to support a separate***E.O. 12866 Review

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Page 96 of 253 standard for ultrafine particles 53 or whether there was sufficient evidence to establish distinct standards focused on regulating specific PM 2.5 components or a group of components associated with any source categories of fine particles ( U.S. EPA, 2011a, section 2.3.1). A number of studies available in this review have evaluated potential health effects associated with short

- term exposures to ultrafine particles. As noted in the Integrated Science Assessment, the enormous numbe r and larger, collective surface area of ultrafine particles are important considerations for focusing on this particle size fraction in assessing potential public health impacts ( U.S. EPA, 2009a, p. 6

- 83). Per unit mass, ultrafine particles may have more opportunity to interact with cell surfaces due to their greater surface area and their greater particle number compared with larger particles ( U.S. EPA, 2009a, p. 5

- 3). Greater surface area also increases the potential for soluble components (e.g., transit ion metals, organics) to adsorb to ultrafine particles and potentially cross cell membranes and epithelial barriers ( U.S. EPA, 2009a, p. 6

- 83). In addition, evidence available in this review suggests that the ability of particles to enhance allergic sensit ization is associated more strongly with particle number and surface area than with particle mass ( U.S. EPA, 2009a, p. 6

- 127). New evidence, primarily from controlled human exposure and toxicological studies, expands our understanding of cardiovascular an d respiratory effects related to short

- term ultrafine particle exposures. However, the Policy Assessment concluded that this evidence was still very limited and largely focused on exposure to diesel exhaust, for which the Integrated Science Assessment conc luded it was unclear whether the effects 53 Ultrafine particles, generally including particles with a mobility diameter less than or equal to 0.1 μm, are emitted directly to the atmosphere or are formed by nucleation of gaseous constituents in the atmosphere (U.S. EPA, 2009a, p. 3

- 3).***E.O. 12866 Review

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Page 97 of 253 observed are due to ultrafine particles, larger particles within the PM 2.5 mixture, or the gaseous components of diesel exhaust ( U.S. EPA, 2009a, p. 2

- 22). In addition, the Integrated Science Assessment noted uncert ainties associated with the controlled human exposure studies using concentrated ambient particle systems which have been shown to modify the composition of ultrafine particles ( U.S. EPA, 2009a, p. 2

- 22, see also section 1.5.3). The Policy Assessment reco gnized that there are relatively few epidemiological studies that have examined potential cardiovascular and respiratory effects associated with short

- term exposures to ultrafine particles ( U.S. EPA, 2011a, p. 2

- 51). These studies have reported inconsisten t and mixed results ( U.S. EPA, 2009a, section 2.3.5). Collectively, in considering the body of scientific evidence available in this review, the Integrated Science Assessment concluded that the currently available evidence was suggestive of a causal relati onship between short

- term exposures to ultrafine particles and cardiovascular and respiratory effects. Furthermore, the Integrated Science Assessment concluded that evidence was inadequate to infer a causal relationship between short

- term exposure to ultra fine particles and mortality as well as long

- term exposure to ultrafine particles and all outcomes evaluated ( U.S. EPA, 2009a, sections 2.3.5, 6.2.12.3, 6.3.10.3, 6.5.3.3, 7.2.11.3, 7.3.9, 7.4.3.3, 7.5.4.3, and 7.6.5.3; Table 2

- 6). With respect to our understanding of ambient ultrafine particle concentrations, at present, there is no national network of ultrafine particle samplers; thus, only episodic and/or site

- specific data sets exist ( U.S. EPA, 2009a, p. 2

- 2). Therefore, the Policy Assessment recogn ized a national characterization of concentrations, temporal and spatial patterns, and trends was not possible at this time, and the availability of ambient ultrafine***E.O. 12866 Review

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Page 98 of 253 measurements to support health studies was extremely limited ( U.S. EPA, 2011a, p. 2

- 51). In general, measurements of ultrafine particles are highly dependent on monitor location and, therefore, more subject to exposure error than accumulation mode particles ( U.S. EPA, 2009a, p. 2

- 22). Furthermore, the number of ultrafine particles generally de creases sharply downwind from sources, as ultrafine particles may grow into the accumulation mode by coagulation or condensation ( U.S. EPA, 2009a, p. 3

- 89). Limited studies of ambient ultrafine particle measurements have suggested that these particles exhi bit a high degree of spatial and temporal heterogeneity driven primarily by differences in nearby source characteristics ( U.S. EPA, 2009a, p. 3

- 84). Internal combustion engines and, therefore, roadways are a notable source of ultrafine particles,
so concen trations of these particles near roadways are generally expected to be elevated ( U.S. EPA, 2009a, p. 2

- 3). Concentrations of ultrafine particles have been reported to drop off much more quickly with distance from roadways than fine particles ( U.S. EPA, 200 9a, p. 3

- 84). In considering both the currently available health effects evidence and the air quality data, the Policy Assessment concluded that this information was still too limited to provide support for consideration of a distinct PM standard for ultra fine particles ( U.S. EPA, 2011a, p. 2

- 52). In addressing the issue of particle composition, the Integrated Science Assessment concluded that, “[f]rom a mechanistic perspective, it is highly plausible that the chemical composition of PM would be a better pr edictor of health effects than particle size” ( U.S. EPA, 2009a, p. 6

- 202). Heterogeneity of ambient concentrations of PM 2.5 constituents (e.g., elemental carbon, organic carbon, sulfates, nitrates) observed in different***E.O. 12866 Review

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Page 99 of 253 geographical regions as well as regi onal heterogeneity in PM 2.5 - related health effects reported in a number of epidemiological studies are consistent with this hypothesis ( U.S. EPA, 2009a, section 6.6). With respect to the availability of ambient measurement data for fine particle component s in this review, the Policy Assessment noted that there were now more extensive ambient PM 2.5 speciation measurement data available through the Chemical Speciation Network (CSN) than in previous reviews ( U.S. EPA, 2011a, section 1.3.2 and Appendix B, sect

ion B.1.3). The Integrated Science Assessment observed that data from the CSN provided further evidence of spatial and seasonal variation in both PM 2.5 mass and composition among cities and geographic regions ( U.S. EPA, 2009a, pp. 3

- 50 to 3

- 60; Figures 3

- 1 2 to 3

- 18; Figure 3

- 47). Some of this variation may be related to regional differences in meteorology, sources, and topography ( U.S. EPA, 2009a, p. 2

- 3). The currently available epidemiological, toxicological, and controlled human exposure studies evaluat

ed in the Integrated Science Assessment on the health effects associated with ambient PM 2.5 constituents and categories of fine particle sources used a variety of quantitative methods applied to a broad set of PM 2.5 constituents, rather than selecting a fe w constituents a priori ( U.S. EPA, 2009a, p. 2

- 26). Epidemiological studies have used measured ambient PM 2.5 speciation data, including monitoring data from the CSN, while all of the controlled human exposure and most of the toxicological studies have used concentrated ambient particles and analyzed the constituents therein ( U.S. EPA, 2009a, p. 6

- 203). 54 The CSN provides PM 2.5 speciation measurements generally on

54 Most studies considered between 7 to 20 ambient PM 2.5 constituents, with elemental carbon, organic carbon, sul fates, nitrates, and metals most commonly measured. Many of the studies grouped the constituents with various factorization or source apportionment techniques to examine the relationship between the grouped constituents and various***E.O. 12866 Review

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Page 100 of 253 a one - in

- three or one

- in

- six day sampling schedule and, thus, do es not capture data every day at most sites. 55 The Policy Assessment recognized that several new multi

- city studies evaluating short

- term exposures to fine particle constituents are now available. These studies continued to show an association between mortality and cardiovascular and/or respiratory morbidity effects and short

- term exposures to various PM 2.5 components including nickel, vanadium, elemental carbon, organic carbon, nitrates, and sulfates ( U.S. EPA, 2011a, section 2.3.1; U.S. EPA, 2009a, sections 6.5.2.5 and 6.6). Limited ev idence is available to evaluate the health effects associated with long

term exposures to PM 2.5 components ( U.S. EPA, 2009a, section 7.6.2). The Policy Assessment noted the most significant new evidence was provided by a study that evaluated multiple PM 2.5 components and an indicator of traffic density in an assessment of health effects related to long

- term exposure to PM 2.5 (Lipfert et al., 2006). Using health data from a cohort of U.S. military veterans and PM 2.5 measurement data from the CSN, Lipfert et al. (2006) reported positive associations between mortality and long

- term exposures to nitrates, elemental carbon, nickel, and vanadium as well as traffic density and peak ozone concentrations ( U.S. EPA, 2011a, p. 2

- 54; U.S. EPA, 2009a, pp. 7

- 89 to 7

- 90). With respect to source categories of fine particles associated with a range of health effects. However, not all studies labeled the constituent groupings according to their presumed source and a small number of controlled human exposure and toxicological studies did not use any constituent grouping. These differences across studies substantially limit any i ntegrative interpretation of these studies (U.S. EPA, 2009a, p. 6

- 203). 55 To expand our understanding of the role of specific PM 2.5 components and sources with respect to the observed health effects, researchers have expressed a strong interest in having access to PM 2.5 speciation measurements collected more frequently (U.S. EPA, 2011a, p. 2

- 53, including footnote 47).***E.O. 12866 Review

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Page 101 of 253 health endpoints, the Integrated Science Assessment reported that the currently available evidence suggests associations between cardiovascular effects and a number of specific PM 2.5 – related source categories, specifically oil combustion, wood or biomass burning, motor vehicle emissions, and crustal or road dust sources ( U.S. EPA, 2009a, section 6.6; Table 6

- 18). In addition, a few studies have evaluated associations between PM 2 .5 - related source categories and mortality. One stud y reported an association between mortality and a PM 2.5 coal combustion factor (Laden et al., 2000), while other studies linked mortality to a secondary sulfate long

- range transport PM 2.5 source (Ito et al., 2006; Mar et al., 2006) ( U.S. EPA, 2009a, section 6.6.2.1). There was less consistency in associations observed between sources of fine particles and respiratory health effects, which may be partially due to the fact that fewer studies have evaluated respiratory

- related outcomes and measures. However, there was some evidence for PM 2.5 - related associations with secondary sulfate and decrements in lung function in asthmatic and healthy adults ( U.S. EPA, 2009a, p. 6

- 211; Gong et al., 2005; Lanki et al., 2006). Respiratory effects relating to the crustal/soil/road dust and traffic sources of PM have been observed in asthmatic children and adults ( U.S. EPA, 2009a, p. 6

- 205; Gent et al., 2009; Penttinen et al., 2006). Recent studies have show n that source apportionment methods have the potential to add useful insights into which sources and/or PM constituents may contribute to different health effects. Of particular interest are several epidemiological studies that compared source apportionmen t methods and reported consistent results across research groups ( U.S. EPA, 2009a, p. 6

- 211; Hopke et al., 2006; Ito et al., 2006; Mar et al., 2006; Thurston et al., 2005). These studies reported associations between total mortality and secondary sulfate i n two cities for two different lag times. The sulfate effect was stronger***E.O. 12866 Review

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Page 102 of 253 for total mortality in Washington D.C. and for cardiovascular

- related mor t ality in Phoenix ( U.S. EPA, 2009a, p. 6

- 204). These studies also found some evidence for associations with m ortality and a number of source categories (e.g., biomass/wood combustion, traffic, copper smelter, coal combustion, sea salt) at various lag times ( U.S. EPA, 2009a, p. 6

- 204). Sarnat et al. (2008) compared three different source apportionment methods and reported consistent associations between emergency department visits for cardiovascular diseases with mobile sources and biomass combustion as well as increased respiratory

- related emergency department visits associated with secondary sulfate ( U.S. EPA, 20 09a, pp. 6

- 204 and 6

- 211). Collectively, in considering the currently available evidence for health effects associated with specific PM 2.5 components or groups of components associated with any source categories of fine particles as presented in the Integr ated Science Assessment, the Policy Assessment concluded that additional information available in this review continues to provide evidence that many different constituents of the fine particle mixture as well as groups of components associated with specif ic source categories of fine particles are linked to adverse health effects ( U.S. EPA, 2011a, p. 2

- 55). However, as noted in the Integrated Science Assessment, while “[t]here is some evidence for trends and patterns that link particular ambient PM constitu ents or sources with specific health outcomes...there is insufficient evidence to determine whether these patterns are consistent or robust” ( U.S. EPA, 2009a, p. 6

- 210). Assessing this information, the Integrated Science Assessment concluded that “the eviden ce is not yet sufficient to allow differentiation of those constituents or sources that are more closely related to specific health outcomes” ( U.S. EPA, 2009a, pp. 2

- 26 and 6

- 212). Therefore, the Policy***E.O. 12866 Review

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Page 103 of 253 Assessment concluded that the currently available evi dence is not sufficient to support consideration of a separate indicator for a specific PM 2.5 component or group of components associated with any source category of fine particles. Furthermore, the Policy Assessment concluded that the evidence is not suff icient to support eliminating any component or group of components associated with any source categories of fine particles from the mix of fine particles included in the PM 2.5 indicator ( U.S. EPA, 2011a, p. 2

- 56). The CASAC agreed with the EPA staff concl usions presented in the Policy Assessmen t and concluded that it is appropriate to consider retaining PM 2.5 as the indicator for fine particles and further asserted, “There [is] insufficient peer

- reviewed literature to support any other indicator at this ti me” (Samet, 2010c, p. 12). CASAC expressed a strong desire for the EPA to “look ahead to future review cycles and reinvigorate support for the development of evidence that might lead to newer indicators that may correlate better with the health effects ass ociated with ambient air concentrations of PM ...” (Samet, 2010c, p 2). Consistent with the staff conclusions presented in the Policy Assessment and CASAC advice, the Administrator proposed to retain PM 2.5 as the indicator for fine particles. Further, the A dministrator provisionally concluded that currently available scientific information does not provide a sufficient basis for supplementing mass

- based, primary fine particle standards with standards using a separate indicator for ultrafine particles or a se parate indicator for a specific PM 2.5 component or group of components associated with any source categories of fine particles. In addition, the Administrator also provisionally concluded that the currently available scientific information did not provide***E.O. 12866 Review

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Page 104 of 253 a sufficient basis for eliminating any individual component or group of components associated with any source categories from the mix of fine particles included in the PM 2.5
mass - based indicator. The EPA received comparatively few public comments on issue s related to the indicator for fine particles. 56 Some commenters emphasized the need to conduct additional research to more fully understand the effect of specific PM 2.5 components and/or sources on public health. These commenters expressed views about the importance of evaluating health effect associations with various fine particle components and types of source categories as a basis for focusing ongoing and future research to reduce uncertainties in this area and for considering whether alternative indica tor(s) may be appropriate to consider in future PM NAAQS reviews for standards intended to protect against the array of health effects that have been associated with fine particles as indexed by PM 2.5 . For example, the PSR encouraged more research and moni toring related to PM 2.5 components and noted the importance of components associated with coal combustion (PSR, 2012, pp. 5 to 6). EPRI asserted that “new” studies support focusing on EC and OC and encouraged the EPA to seriously consider the mass

- based ap proach (EPRI, 2012, p. 2). Likewise, Georgia Mining Association supported additional monitoring and research efforts related to PM 2.5 composition and specifically encouraged the evaluation of using particle number (e.g., particle count) (GMA, 2012, pp. 2 t o 3). The Administrator agrees with CASAC as well as these commenters that the results of additional research and monitoring efforts will be helpful for informing future PM NAAQS reviews. Information from such studies could also help inform the

56 No public co mments were submitted regarding the use of a different size cut for fine particles.***E.O. 12866 Review

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Page 105 of 253 developmen t of strategies that emphasize control of specific types of emission sources so as to address particles of greatest concern to public health. However, based upon the scientific information considered in the Integrated Science Assessment as well as the publ ic comments summarized above, the Administrator continues to take note there is evidence that many different constituents of the fine particle mixture as well as groups of components associated with specific sources of fine particles are linked to adverse health effects. Furthermore, she recognizes that the evidence is not yet sufficient to differentiate those constituents or sources that are most closely related to specific health outcomes nor to exclude any PM 2.5 components or sources of fine particles fr om the mix of particles included in the PM 2.5 indicator. Having considered the public comments on this issue, the Administrator concurs with the Policy Assessment conclusions and CASAC recommendations and concludes that it is appropriate to retain PM 2.5 a s the indicator for fine particles. 2. Averaging Time In 1997, the EPA initially set both an annual standard, to provide protection from health effects associated with both long

- and short

- term exposures to PM 2.5 , and a 24

- hour standard to supplement the protection afforded by the annual standard (62 FR 38667 to 38668, July, 18, 1997). In the last review, the EPA retained both annual and 24

- hour averaging times (71 FR 61164, October 17, 2006). These decisions were based, in part, on evidence of health effe cts related to both long

- term (from a year to several years) and short

- term (from less than one day to up to several days) measures of PM 2.5 . The overwhelming majority of studies conducted since the last review continue to utilize annual (or multi

- year) an d 24

- hour averaging times, reflecting the averaging times***E.O. 12866 Review

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Page 106 of 253 of the current PM 2.5 standards. These studies continue to provide evidence that health effects are associated with annual and 24

- hour averaging times. Therefore, the Policy Assessment concluded it is appropriate to retain the current annual and 24

- hour averaging times to prov ide protection from effects associated with both long

- and short

- term PM 2.5 exposures ( U.S. EPA, 2011a, p. 2

- 57). In considering whether the information available in this review supports consideration of different averaging times for PM 2.5 standards specif ically with regard to considering a standard with an averaging time less than 24 hours to address health effects associated with sub

- daily PM 2.5 exposures, the Policy Assessment noted there continues to be a growing body of studies that provide additional evidence of effects associated with exposure periods less than 24

- hours ( U.S. EPA, 2011a, p. 2

- 57). Relative to information available in the last review, recent studies provide additional evidence for cardiovascular effects associated with sub

- daily (e.g., one to several hours) exposure to PM, especially effects related to cardiac ischemia, vasomotor function, and more subtle changes in markers of systemic inflammation, hemostasis, thrombosis and coagulation ( U.S. EPA, 2009a, section 6.2). Because these stu dies have used different indicators (e.g., PM 2.5 , PM 10 , PM 10

- 2.5 , ultrafine particles), averaging times (e.g., 1, 2, and 4 hours), and health outcomes, it is difficult to draw conclusions about cardiovascular effects associated specifically with sub

- daily exposures to PM 2.5 . With regard to respiratory effects associated with sub

- daily PM 2.5 exposures, the currently available evidence was much sparser than for cardiovascular effects and continues to be very limited. The Integrated Science Assessment conclud ed that for several studies of hospital admissions or medical visits for respiratory diseases, the***E.O. 12866 Review

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Page 107 of 253 strongest associations were observed with 24

- hour average or longer exposures, not with less than 24

- hour exposures ( U.S. EPA, 2009a, section 6.3). Collecti vely, the Policy Assessment concluded that this information, when viewed as a whole, is too unclear, with respect to the indicator, averaging time and health outcome, to serve as a basis for consideration of establishing a primary PM 2.5 standard with an av eraging time shorter than 24

- hours at this time ( U.S. EPA, 2011a, p. 2

- 57). With regard to health effects associated with PM 2.5 exposure across varying seasons in this review, Bell et al. (2008) reported higher PM 2.5 risk estimates for hospitalization for cardiovascular and respiratory diseases in the winter compared to other seasons. In comparison to the winter season, smaller statistically significant associations were also reported between PM 2.5 and cardiovascular morbidity for spring and autumn, and a positive, but statistically non

- significant association was observed for the summer months. In the case of mortality, Zanobetti and Schwartz (2009) reported a 4

- fold higher effect estimate for PM 2.5 - associated mortality for the spring as compared to the wi nter. Taken together, these results provided emerging but limited evidence that individuals may be at greater risk of dying from higher exposures to PM 2.5 in the warmer months and may be at greater risk of PM 2.5 - associated hospitalization for cardiovascula r and respiratory diseases during colder months of the year ( U.S. EPA, 2011a, p. 2

- 58). Overall, the Policy Assessment observed that there are few studies presently available to deduce a general pattern in PM 2.5 - related risk across seasons. In addition, t hese studies utilized 24

- hour exposure periods within each season to assess the PM 2.5 - associated health effects and do not provide information on health effects associated with a season

- long exposure to PM 2.5 . Due to these limitations in the currently***E.O. 12866 Review

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Page 108 of 253 avai lable evidence, the Policy Assessment concluded that there was no basis to consider a seasonal averaging time separate from a 24

- hour averaging time. Based on the above considerations, the Policy Assessment concluded that the currently available informatio n provided strong support for consideration of retaining the current annual and 24

- hour averaging times but does not provide support for considering alternative averaging times ( U.S. EPA, 2011a, p. 2

- 58). In addition, CASAC considered it appropriate to ret ain the current annual and 24

- hour averaging times for the primary PM 2.5 standards (Samet, 2010c, pp. 2 to 3). At the time of the proposal, the Administrator concurred with the staff conclusions and CASAC advice and proposed that the averaging times for th e primary PM 2.5 standards should continue to include annual and 24

- hour averages to protect against health effects associated with long

- and short

- term exposures. Furthermore, the Administrator provisionally concluded, consistent with conclusions reached i n the Policy Assessment and by CASAC, that the currently available information was too limited to support consideration of alternative averaging times to establish a national standard with a shorter

- than 24

- hour averaging time or with a seasonal averaging time. The EPA received no significant public comments on the issue of averaging time for the PM 2.5 primary standards. The Administrator concurs with recommendations made by CASAC and the staff conclusions presented in the Policy Assessment and concludes, as proposed, that it is appropriate to retain the current annual and 24

- hour averaging times for the primary PM 2.5 standards to protect against health effects associated with long

- and short

- term exposure periods. 3. Form***E.O. 12866 Review

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Page 109 of 253 The “form” of a standard defines the air quality statistic that is to be compared to the level of the standard in determining whether an area attains the standard. In this review, the EPA considers whether currently available information supports retaining or revising the forms for the annual or 24

- hour PM 2.5 standards.
a. Annual Standard In 1997, the EPA established the form of the annual PM 2.5 standard as an annual arithmetic mean, averaged over 3 years, from single or multiple community

- oriented monitors. This form was intended to represent a relatively stable measure of air quality and to characterize longer

- term area
- wide PM 2.5 concentrations, in conjunction with a 24

- hour standard designed to provide adequate protection against localized peak or seasonal PM 2.5 concentrations. The level of the standard was to be compared to measurements made at each community

- oriented monitoring site, or, if specific criteria were met, measurements from multiple community

- oriented monitoring sites could be averaged (i.e., spatia l averaging) 57 (62 FR 38671 to 38672, July 18, 1997). The constraints were intended to ensure that spatial averaging would not result in inequities in the level of protection provided by the standard (62 FR 38672, July 18, 1997). This approach was consisten t with the epidemiological studies on which the PM 2.5 standard was primarily based, in which air quality data were generally averaged across multiple monitors in an area or were taken from a single monitor that was selected to represent community

- wide expo sures. In the last review, the EPA tightened the criteria for use of spatial averaging to pr ovide increased protection for vulnerable populations exposed to PM 2.5 . This change

57 Spatial averaging as part of the form of the annual PM 2.5 standard is unique to this standard and is not used with other PM standards nor with other NAAQS.***E.O. 12866 Review

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Page 110 of 253 was based in part on an analysis of the potential for disproportionate impacts on potentially at

- risk populations, which found that the highest concentrations in an area tend to be measured at monitors located in areas where the surrounding population is more likely to have lower education and income levels and higher percentages of minority populations (71 FR 61166/2, October 17, 2006; U.S. EPA, 2005, section 5.3.6.1). In this review, as outlined in section III.B above and discussed more fully in section III.B.3 of the proposal, there now exist more health data such that the Integrat ed Science Assessment has identified persons from lower socioeconomic strata as an at

- risk population ( U.S. EPA, 2009a, section 8.1.7; U.S. EPA, 2011a, section 2.2.1). Moreover, there now exist more years of PM 2.5 air quality data than were available in th e last review. Consideration in the Policy Assessment of the spatial variability across urban areas that was revealed by this expanded data base has raised questions as to whether an annual standard that allows for spatial averaging, even within specified constraints as narrowed in 2006 (71 FR 61165 to 61167, October 17, 2006) , would provide appropriate public health protection. In considering the potential for disproportionate impacts on at

- risk populations, the Policy Assessment considered an update of a n air quality analysis conducted for the last review ( U.S. EPA, 2011a, pp. 2

- 59 to 60; Schmidt, 2011 a , Analysis A). This analysis focused on determining whether the spatial averaging provisions, as modified in 2006, could introduce inequities in protection for at

- risk populations exposed to PM 2.5 . Specifically, the Policy Assessment considered whether persons of lower socioeconomic status , minority groups, or different age groups (i.e., children or older adults) are more***E.O. 12866 Review

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Page 111 of 253 likely than the general population t o live in areas in which the monitors recording the highest air quality values in an area are located. Data used in this analysis included demographic parameters measured at the Census Block or Census Block Group level, including percent minority populatio n, percent minority subgroup population, percent of persons living below the poverty level, percent of persons 18 years of age or older, and percent of persons 65 years of age and older. In each candidate geographic area, data from the Census Block(s) or C ensus Block Group(s) surrounding the location of the monitoring site (as delineated by radii buffers of 0.5, 1.0, 2.0, and 3.0 miles) in which the highest air quality value was monitored were compared to the average of monitored values in the area. This an alysis looked beyond areas that would meet the current spatial averaging criteria and considered all urban areas (i.e., Core Based Statistical Areas or CBSAs) with at least two valid annual desig n value monitors (Schmidt, 2011 a , Analysis A). Recognizing th e limitations of such cross

- sectional analyses, the Policy Assessment observed that the highest concentrations in an area tend to be measured at monitors located in areas where the surrounding populations are more likely to live below the poverty line and to have higher percentage of minorities ( U.S. EPA, 2011a, p. 2

- 60). Based upon the analysis described above, the Policy Assessment concluded that the existing constraints on spatial averaging, as modified in 2006, may be inadequate to avoid substantially greater exposures in some areas, potentially resulting in disproportionate impacts on at

- risk populations of persons with lower SES levels as well as minorities. Therefore, the Policy Assessment concluded that it was appropriate to consider revising the fo rm of the annual PM 2.5 standard such that it did not allow for the use of spatial averaging across monitors. In doing so, the level of the annual PM 2.5***E.O. 12866 Review

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Page 112 of 253 standard would be compared to measurements made at the monitoring site that represents
area - wide air qua lity recording the highest PM 2.5 concentrations 58 ( U.S. EPA, 2011a, p. 2

- 60). The CASAC agreed with staff conclusions that it was “reasonable” for the EPA to eliminate the spatial averaging provisions (Samet, 2010d, p. 2). Further, in CASAC’s comments on the first draft Policy Assessment, it noted, “Given mounting evidence showing that persons with lower SES levels are a susceptible group for PM

- related health risks, CASAC recommends that the provisions that allow for spatial averaging across monitors be e liminated for the reasons cited in the (first draft) Policy Assessment” (Samet, 2010c, p. 13). In its review of the second draft Policy Assessment, CASAC recognized “although much of the epidemiological research has been conducted using community

- wide aver ages, several key studies reference the nearest measurement site, so that some risk estimates are not necessarily biased by the averaging process. Further, the number of such studies is likely to expand in the future” (Samet, 2010d, pp. 1 to 2). Only two a reas in the country used the initial spatial averaging provisions for demonstrating attainment with the primary annual PM 2.5 standard set in 1997 ( 70 FR 19847, April 14, 2005; U.S. EPA, 2006c ). Since these provisions were tightened in 2006 , no area has used spatial averaging to demonstrate attainment. No areas in the country are currently using the spatial averaging provisions to demonstrate attainment with the current primary annual PM 2.5 standard. In considering the Policy Assessment’s con clusions based on the results of the analysis discussed above and concern over the evidence of potential disproportionate 58 As discussed in section VIII.B.1 below, the EPA is revising several terms associated with PM 2.5 monitor placement. Specifically, the EPA is revoking the term “community

oriented” and replacing it with the term “area

- wide” monitoring.***E.O. 12866 Review

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Page 113 of 253 impacts on at

- risk populations as well as CASAC advice, the Administrator proposed to revise the form of the annual PM 2.5 standard to eliminate the use of spatial averaging. Thus, the Administrator proposed revising the form of the annual PM 2.5 standard to compare the level of the standard with measurements from each “appropriate” monitor in
an area 59 with no allowance for spatial averagi ng. Thus, for an area with multiple monitors, the appropriate reporting monitor with the highest design value would determine the attainment status for that area. Of the commenters noted in section III.D.2 above who supported a more stringent annual PM 2.5 standard, those who commented on the form of the annual PM 2.5 standard supported the EPA’s proposal to eliminat e the spatial averaging provisions. These commenters contended that the EPA ’s analyses of the potential impacts of spatial averaging, discussed a

bove and in the proposal , (77 FR 38924) , demonstrate d that the current form results in uneven public health protection leading to disproportionate impacts on at

- risk populations. Specifically, the ALA and other environmental and public health commenters co ntended that “ spatial averaging allows exposure of people to unhealthy levels of pollution at specific locales even within an area meeting the standard” (ALA et al., 2012, p. 23 ). These commenters particularly focused on the importance for low

- income and m inority populations of eliminating the spatial averaging provisions. They concluded that spatial averaging “is an environmental justice concern because poor people are more likely to live near roads, depots, factories, ports, and other pollution sources.” Id. p. 24.

59 As discussed in section VIII.B. 2.b below, the EPA concludes that PM 2.5 monitoring sites at micro

- and middle

- scale locations should be comparable to the annual standard unless the monitoring site has been approved by the Regional Administrator as a “relatively unique micro

- scale, or loc alized hot

- spot, or unique middle

- scale site.”***E.O. 12866 Review

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Page 114 of 253 Other commenters (e.g., AAM , 2012 ; Dow , 2012 ) also supported the elimination of spatial averaging in order to “avoid potential disproportionate impacts on at

- risk populations” and to maximize “the benefits to public health of reducing the annual PM 2.5 standard.” However, these groups expressed conc ern that the elimination of spatial averaging, in combination with the requirement for near road monitors (as discussed in section VIII.B.3.b.i of the proposal) , would effectively and inappropriately in crease the stringency of the annual PM 2.5 standard. This concern was also shared by other commenters who disagreed with the elimination of spatial averaging. For example, the Class of ’85 RRG emphasized concerns about increasing the stringency of the stan dard while providing few health benefits if spatial averaging is eliminated, particularly in combination with the requirement for near

- road monitors. These commenters contended that “[b]ecause EPA proposes to use the readings from the highest single worst case monitor (rather than the average of all community area monitors), and since roadway monitoring locations will likely be worst case monitors, the proposed NAAQS will become more stringent without targeting the PM 2.5 species most harmful to human health ” (Class of ’85 RRG, 2012, p. 6). Several commenters also ma intained that because spatial averaging is consistent with how air quality data are considered in the underlying epidemiological studies, such averaging should not be eliminated. Specifically, com menters including NAM et al. , AFPM, and ACC pointed out that PM 2.5 epidemiological studies use spatially averaged multi

- monitor concentrations, rather than the single highest monitor, when evaluating health effects. Therefore, these commenters contended th at allowing spatial averaging***E.O. 12866 Review

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Page 115 of 253 would make the PM 2.5 standard more consistent with the approaches used in the epidemiological studies upon which the standard is based. In addition, some commenters also contended that the EPA failed to consider whether modify ing, rather than eliminating, the constraints on spatial averaging would have been sufficient to protect the public health. If so, th ese commenter s argued that “elimination of spatial averaging would go beyond what is requisite to protect the public health ” (NAM et al., 2012, p. 20 ) )
. In considering the public comments on the form of the annual standard, the EPA recognizes a number of commenters agreed with the basis for the EPA’s proposal to eliminate spatial averaging. While other commenters expressed disagreement or concern with the proposed decision to eliminate the spatial averaging provisions, the A gency notes that these comment er s did not challenge the analyses or considerations that provided the fundamental basis for the Administrator’s propos ed d ecision
. Rather, these commenters generally raised concerns that eliminating the option for spatial averaging would increase the stringency of the standard, especially in light of additional monitoring sites in near

- road environments (as discussed in secti on VIII.B.3.b.1 below). In The EPA does not agree with the comment that siting some monitors in near roadway environments makes the standard more stringent or impermissibly more stringent . As discussed in section VIII.B.3.b.i below, a significant fraction of the population lives in proximity to major roads , and t hese exposures occur in locations that represent ambient air. M onitoring in such areas does not make the standard more stringent than warranted , but rather affords the intended protection to the exposed populations, among them at

- risk populations, exposed to fine particl es in these areas.***E.O. 12866 Review

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Page 116 of 253 Thus, the EPA has made a determination that monitors re presentative of area - wide air quality may be compared to the annual standard. The 24

- hour and annual NAAQS are designed to protect the public with an adequate margin of safety, and this siting provision is fully consistent with providing the protection the standard is designed to provide and does not make the standard more stringent or more stringent than nece ssary. Monitors that are representative of area

- wide air quality may be compared to the annual standard . T his is consistent with the use of monitoring data in the epidemiological studies that provide the primary basis for determining the level of the ann ual standard
. In addition, the EPA notes that the annual standard is designed to protect against b oth long

and short

- term exposures through controlling the broad distribution of air quality across an area over time. 60 It is fully consistent with the protection the standard is designed to provide for near road monitors to be compared to the annual standard if the monitor is representative of area

- wide air quality. This does not make the standard either more stringent or impermissibly more stringent
. In further considering these comments, the EPA notes that the stringency or level of protection provided by each NAAQS is not based solely on the form of the standard; rather, the four elements of the standard that together s erve to define each standard (i.e., indicator, averaging time, form, and level) must be considered collectively in evaluating the protection afforded by each standard. Therefore, the EPA considers these comments
are more also appropriate to discuss collecti vely with other issues related to the appropriate level for annual standard, and are discussed below in section s III.E.4.c

- d.

60 This is in contrast to the 24

- hour standard which is designed to provide supplemental protection, addressing peak exposures that might not otherwise be addressed by the annual standard. Consistent with this, monitors are not required to be representative of area

- wide air quality to be compared to the 24

- hour standard.***E.O. 12866 Review

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Page 117 of 253 In reaching a final decision on the form of the annual standard, the Administrator considers the available analyses, CASAC advice , and public comments on form as discussed above . She also considers related issues in the public comments on the level of the annual standard as discussed in section III.E.4.c below . She notes that even when the annual PM 2.5 standard was first set in 1997 , the spatial averaging provisions included constraints intended to ensure that inequities in the level of protection would not result. These constraints on spatial averaging were tightened in the last review, based on an analysis showing the potential for spatial averaging to allow higher PM 2.5 concentrations in locations where subgroups within the general population we re potentially disproportionately exposed and hence, at disproportionate risk (e.g., low income and minority communities). The Administrato r notes that in proposing to eliminate spatial averaging altogether in this review, she has relied on further analyses in the current review (Schmidt, 2011 a , Analysis A ). As discussed above and in the proposal (77 FR 38924) , these analyses showed that the current constraints on spatial averaging may be inadequate in some areas to avoid substantially greater exposures for people living near monitors recording the highest PM 2.5 concentrations. Such exposures could result in disproportionate impacts to at
- risk populations, including low

- income populations as well
as minority groups. On this basis, t

he Administrator concludes that public health would not be protected with an adequate margin of safety in all locations , as required by law, if disproportionately higher exposure concentrations in at
- risk populations such as low income communities as well as minority communities were averaged together with lower concentrations measured at other sites in a large urban area. See ALA v. EPA , 134 F. 3d***E.O. 12866 Review

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Page 118 of 253 388, 389 (D.C. Cir., 1998) (“this court has held that ‘NAAQS must protect not only average healthy individuals, but also sensitive citizens such as children,’ and ‘if a pollutant adversely affects the health of these sensitive individuals, EPA must s trengthen the entire national standard’”) and Coalition of Battery Recyclers Association v. EPA, 604 F 3d. 613, 617 (D.C. Cir., 2010) (“Petitioners’ assertion that the revised lead NAAQS is overprotective because it is more stringent than necessary to prot ect the entire population of young U.S. children ignores that the Clean Air Act allows protection of sensitive subpopulations.”) In reaching this conclusion, the Administrator further notes that her concern over possible disproportionate PM 2.5 - related heal th impacts in at

- risk populations extends to populations living near important sources of PM 2.5 , including the large populations that live near major roadways. 61 In light of all of the above considerations, including consideration of available analyses, CA SAC advice, and public comments, the Administrator concludes that the current form of the annual PM 2.5 standard should be revised to eliminate spatial averaging provisions. Thus, the level of the revised annual PM 2.5 standard established with this notice w ill be compared with measurements from each appropriate monitor in an area, with no allowance for spatial averaging. The Administrator’s conclusions with regard to the appropriate level of the annual PM 2.5 standard to set in conjunction with this form are discussed below in section III.E.4.d. b. 24

- Hour Standard In 1997, the EPA established the form of the 24

- hour PM 2.5 standard as the 98 th percentile of 24

- hour concentrations at each population

- oriented monitor within an area,

61 Section VIII.B.3.b.i below discusses public comments specifically related to the proposed requirement for near

- road monitors.***E.O. 12866 Review

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Page 119 of 253 averaged over three years (62 FR at 38671 to 38674, July 18, 1997). The Agency selected the 98 th percentile as an appropriate balance between adequately limiting the occurrence of peak concentrations and providing increased stability which, when averaged over 3 years, facilitated effecti ve health protection through the development of more stable implementation programs. By basing the form of the standard on concentrations measured at population

- oriented monitoring sites, the EPA intended to provide protection for people residing in or nea r localized areas of elevated concentrations. In the last review, in conjunction with lowering the level of the 24

- hour standard, the EPA retained this form based in part on a comparison with the 99 th percentile form. 62 In revisiting the stability of a 98 t h versus 99 th percentile form for a 24

- hour standard intended to provide supplemental protection for a generally controlling annual standard, an analysis presented in the Policy Assessment considered air quality data reported in 2000 to 2008 to update our understanding of the ratio between peak

- to
- mean PM 2.5 concentrations. This analysis provided evidence that the 98 th percentile value was a more stable metric than the 99 th percentile ( U.S. EPA, 2011a, Figure 2

- 2, p. 2

- 62). At the time of the proposal, the Agency recognized that the selection of the appropriate form of the 24

- hour standard includes maintaining adequate protection against peak 24

- hour concentrations while also providing a stable target for risk management programs, which serves to provide fo r the most effective public health

62 In reaching t

his final decision, the EPA recognized a technical problem associated with a potential bias in the method used to calculate the 98 th percentile concentration for this form. The EPA adjusted the sampling frequency requirement in order to reduce this bias. A ccordingly, the Agency modified the final monitoring requirements such that areas that are within 5 percent of the standards are required to increase the sampling frequency to every day (71 FR 61164 to 61165, October 17, 2006).***E.O. 12866 Review

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Page 120 of 253 protection in the long run. 63 As in previous reviews, the EPA recognized that a concentration

- based form, compared to an exceedance

- based form, was more reflective of the health risks posed by elevated pollutant concentrat ions because such a form gives proportionally greater weight to days when concentrations are well above the level of the standard than to days when the concentrations are just above the level of the standard. Further, the Agency provisionally concluded tha t a concentration

- based form, when averaged over three years, provided an appropriate balance between limiting peak pollutant concentrations and providing a stable regulatory target, thus facilitating the development of more stable implementation programs. In considering the information provided in the Policy Assessment and recognizing that the degree of public health protection likely to be afforded by a standard is a result of the combination of the form and the level of the standard, the Administrator proposed to retain the 98 th percentile form of the 24

- hour standard. The Administrator provisionally concluded that the 98 th percentile form represents an appropriate balance between adequately limiting the occurrence of peak concentrations and providing increased stability relative to an alternative 99 th percentile form. Few public commenters commented specifically on the for m of the 24

- hour standard. None of the public commenters raised objections to continuing the use of a concentration

- based form for the 24

- hour standard. Many of the individuals and groups who supported a more stringent 24

- hour PM 2.5 standard noted in secti on III.D.2 above, however, recommended a more restrictive concentration

- based percentile form,

63 See ATA III , 283 F.3d at 3 74

- 376 which concludes that it is legitimate for the EPA to consider overall stability of the standard and its resulting promotion of overall effectiveness of NAAQS control programs in setting a standard that is requisite to protect the public health.***E.O. 12866 Review

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Page 121 of 253 specifically a 99 th percentile form. The limited number of these commenters who provided a specific rationale for this recommendation generally expressed their c oncern that the 98 th percentile form could allow too many days where concentrations exceeded the level of the standard, and thus fail to adequately protect public health. Other public commenters representing s tate and local air agencies and industry groups generally supported retaining the current 98 th percentile form. In most cases, these groups expressed the overall view that the current 24

- hour PM 2.5 standard, including the form of the current standard, should be retained. The EPA notes that the viewpoi nts represented in this review are similar to comments submitted in the last review and through various NAAQS reviews. The EPA recognizes that the selection of the appropriate form includes maintaining adequate protection against peak 24

- hour values while also providing a stable target for risk management programs, which serves to provide for the most effective public health protection in the long run. 64 Nothing in the commenters’ views has provided a reason to change the Administrator’s previous conclusion regarding the appropriate balance represented in the proposed form of the 24

- hour PM 2.5 standard. Therefore, the Administrator concurs with staff conclusions presented in the Policy Assessment and CASAC recommendations and concludes that it is appropriate to retain the 98 th percentile form for the 24

- hour PM 2.5 standard. 4. Level

64 A s just noted above, it is legitimate for the EPA to consider promotion of overall effectiveness of risk management programs designed to attain the NAAQS, including their overall stability, in setting a standard that is requisite to protect the public healt h. The context for the court’s discussion in ATA III is identical to that here; whether to adopt a 98 th percentile form for a 24

- hour standard intended to provide supplemental protection for a generally controlling annual standard.***E.O. 12866 Review

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Page 122 of 253 In the last review, the EPA selected levels for the annual and the 24

- hour PM 2.5 standards using evidence of effects associated with periods of exposure that were most closely matched to the averaging time of each standard. Thus, as discussed in section III.A.1, the EPA relied upon evidence from long

- term exposure studies as the principal basis for selecting the level of the annual PM 2.5 standard that would protect against effects asso ciated with long

- term exposures. The EPA relied upon evidence from the short

- term exposure studies as the principal basis for selecting the level of the 24

- hour PM 2.5 standard that would protect against effects associated with short

- term exposures. As summ arized in section III.A.2 above, the 2006 decision to retain the level of the annual PM 2.5 standard at 15 μg/m 3 65 was challenged and on judicial review, the D.C. Circuit remanded the primary annual PM 2.5 standard to the EPA, finding that EPA’s explanation for its approach to setting the level of the annual standard was inadequate.
a. General Approach for Considering Standard Levels Building upon the lessons learned in the previous PM NAAQS reviews, in considering alternative standard levels supported by the c urrently available scientific information, the Policy Assessment used an approach that integrated evidence

- based and risk

- based considerations, took into account CASAC advice, and considered the issues raised by the court in remanding the primary annual PM 2.5 standard. Following the general approach outlined in section III.A.3 above, for the reasons discussed below, the Policy Assessment concluded it was appropriate to consider the protection afforded by the annual and 24

- hour standards taken together again st mortality and morbidity effects 65 Throughout this sectio n, the annual standard levels are denoted as integer values for simplicity, although, as noted above in section II.B.1, Table 1, the annual standard level is defined to one decimal place, such that the current annual standard level is 15.0 μg/m 3

. Alternati ve annual standard levels discussed in this section are similarly defined to one decimal place.***E.O. 12866 Review

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Page 123 of 253 associated with both long

- and short

- term PM 2.5 exposures. This was consistent with the approach taken in the review completed in 1997 rather than considering each standard separately, as was done in the review completed in 2006. Beyond looking directly at the relevant epidemiologic evidence, the Policy Assessment considered the extent to which specific alternative PM 2.5 standard levels were likely to reduce the nature and magnitude of both long

- term exposure
- related mort ality risk and short

- term exposure
- related mortality and morbidity risk ( U.S. EPA, 2011a, section 2.3.4.2; U.S.EPA, 2010a, section 4.2.2). As noted in section III.C.3 above, patterns of increasing estimated risk reductions were generally observed as either the annual or 24

- hour standard, or both, were reduced below the level of the current standards ( U.S. 2011a, Figures 2

- 11 and 2

- 12; U.S. EPA, 2010a, sections 4.2.2, 5.2.2, and 5.2.3). Based on the quantitative risk assessment, the Policy Assessment observ ed, as discussed in section III.A.3, that analyses conducted for this and previous reviews demonstrated that much, if not most, of the aggregate risk associated with short

- term exposures results from the large number of days during which the 24

- hour averag e concentrations are in the low

- to mid

- range, below the peak 24

- hour concentrations ( U.S. EPA, 2011a, p. 2

- 9). Furthermore, as discussed in section III.C above and in section III.C.3 of the proposal, the Risk Assessment observed that alternative annual sta ndard levels, when controlling, resulted in more consistent risk reductions across urban study areas, thereby potentially providing a more consistent degree of public health protection ( U.S. EPA, 2010a, pp. 5

- 15 to 5

- 16). In contrast, the Risk Assessment n oted that the results of simulating alternative suites of PM 2.5 standards including different***E.O. 12866 Review

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Page 124 of 253 combinations of alternative annual and 24

- hour standard levels suggested that an alternative 24

- hour standard level can produce additional estimated risk reductio ns beyond that provided by an alternative annual standard alone. However, the degree of estimated risk reduction provided by alternative 24

- hour standard levels was highly variable, in part due to the choice of rollback approached used ( U.S. EPA, 2010a, p. 5

- 17). Based on its review of the second draft Policy Assessment, CASAC agreed with the EPA staff’s general approach for translating the available epidemiological evidence, risk information, and air quality information into the basis for reaching conclus ions on alternative standards for consideration. Furthermore, CASAC agreed “that it is appropriate to return to the strategy used in 1997 that considers the annual and the short

term standards together, with the annual standard as the controlling standard, and the short

- term standard supplementing the protection afforded by the annual standard” and “considers it appropriate to place the greatest emphasis” on health effects judged to have evidence supportive of a causal or likely causal relationship as prese nted in the Integrated Science Assessment (Samet, 2010d, p. 1). Therefore, the Policy Assessment concluded, consistent with specific CASAC advice, that it was appropriate to set a “generally controlling” annual standard that will lower a wide range of amb ient 24

- hour concentrations. The Policy Assessment concluded this approach would likely reduce aggregate risks associated with both long

- and short

term exposures with more consistency than a generally controlling 24

- hour standard and would be the most eff

ective and efficient way to reduce total PM 2.5 - related population risk and so provide appropriate protection. The staff believed this approach, in contrast to***E.O. 12866 Review

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Page 125 of 253 one focusing on a generally controlling 24

- hour standard, would likely reduce aggregate risks ass ociated with both long

- and short

- term exposures with more consistency and would likely avoid setting national standards that could result in relatively uneven protection across the country due to setting standards that were either more or less stringent t han necessary in different geographical areas. The Policy Assessment recognized that an annual standard intended to serve as the primary means for providing protection against effects associated with both long

- and short

- term PM 2.5 exposures cannot be exp ected to offer an adequate margin of safety against the effects of all short

- term PM 2.5 exposures. As a result, in conjunction with a generally controlling annual standard, the Policy Assessment concluded it was appropriate to consider setting a 24

- hour st andard to provide supplemental protection, particularly for areas with high peak

- to
- mean ratios possibly associated with strong local or seasonal sources, or PM 2.5 - related effects that may be associated with shorter

- than

daily exposure periods. At the time of the proposal, the Administrator agreed with the approach discussed in the Policy Assessment as summarized in section III.A.3 above, and supported by CASAC, of considering the protection afforded by the annual and 24

- hour standards taken together for mo rtality and morbidity effects associated with both long

- and short

term exposures to PM 2.5 . Furthermore, based on the evidence and quantitative risk assessment, the Administrator provisionally concluded it was appropriate to set a “generally controlling” annual standard that will lower a wide range of ambient 24

- hour concentrations, with a 24

- hour standard focused on providing supplemental protection, particularly for areas with high peak

- to
- mean ratios possibly associated with strong local***E.O. 12866 Review

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Page 126 of 253 or seasonal sou rces, or PM 2.5 - related effects that may be associated with shorter

- than daily exposure periods. The Administrator provisionally concluded this approach would likely reduce aggregate risks associated with both long

- and short

- term exposures more consistentl y than a generally controlling 24

- hour standard and would be the most effective and efficient way to reduce total PM 2

- 5 - related population risk. The Administrator is mindful that considering what standards are requisite to protect public health with an ade quate margin of safety requires pub lic health policy judgments that neither overstate nor understate the strength and limitations of the evidence or the appropriate inferences to be drawn from the evidence. At the time of the proposal, in considering how t o translate the available information into appropriate standard levels, the Administrator weighed the available scientific information and associated uncertainties and limitations. For the purpose of determining what standard levels were appropriate to pro pose, the Administrator recognized, as did the EPA staff in the Policy Assessment, that there was no single factor or criterion that comprised the “correct” approach to weighing the various types of available evidence and information, but rather there were various approaches that were appropriate to consider. The Administrator further recognized that different evaluations of the evidence and other information before the Administrator could reflect placing different weight on the relative strengths and limit ations of the scientific information, and different judgments could be made as to how such information should appropriately be used in making public health policy decisions on standard levels. This recognition led the Administrator to consider various appr oaches to weighing the evidence so as to identify appropriate standard levels to propose. In so doing, the Administrator encouraged extensive public comment on***E.O. 12866 Review

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Page 127 of 253 alternative approaches to weighing the evidence and other information so as to inform her public health policy judgments before reaching final decisions on appropriate standard levels. b. Proposed Decisions on Standard Levels i. Consideration of the Alternative Standard Levels in the Policy Assessment In recognizing the absence of a discernible population threshold below which effects would not occur, the Policy Assessment’s general approach for identifying alternative annual standard levels that were appropriate to consider focused on characterizing th e part of the distribution of PM 2.5 concentrations in which we had the most confidence in the associations reported in the epidemiological studies and conversely where our confidence in the association became appreciably lower. The most direct approach to address this issue, consistent with CASAC advice (Samet, 2010c, p.10), was to consider epidemiological studies reporting confidence intervals around concentration

- response relationships ( U.S. EPA, 2011a, p. 2

- 63). Based on a thorough search of the availabl e evidence, the Policy Assessment identified only one study (Schwartz et al., 2008) that conducted a multi

- model analysis to characterize confidence intervals around the estimated concentration

- response relationship. The Policy Assessment concluded that th is single relevant analysis was too limited to serve as the principal basis for identifying alternative standard levels in this review ( U.S. EPA, 2011a, p. 2

- 70). The Policy Assessment explored other approaches that considered different statistical metrics to identify the part of the distributions of long

- term mean PM 2.5 concentrations that were most influential in generating health effect estimates in long

-***E.O. 12866 Review

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Page 128 of 253 and short

- term epidemiological studies, and placed greatest weight on those studies that reported po sitive and statistically significant associations ( U.S. EPA, 2011a, p. 2

- 63). First, as discussed in section III.A.3 above, the Policy Assessment considered the statistical metric used in previous reviews. This approach recognized that the strongest eviden ce of associations occurs at concentrations around the long

- term mean concentration. Thus, in earlier reviews, the EPA focused on identifying standard levels that were somewhat below the long

- term mean concentrations reported in PM 2.5 exposure studies. The long

- term mean concentrations represented air quality data typically used in epidemiological analyses and provided a direct link between PM 2.5 concentrations and the observed health effects. Further, these data were available for all long

- and short

- term exposure studies analyzed and, therefore, represented the data set available for the broadest set of epidemiological studies. However, consistent with CASAC’s comments on the second draft Policy Assessment 66 (Samet, 2010d, p. 2), in preparing the final Pol icy Assessment, the EPA staff explored ways to take into account additional information from epidemiological studies, when available (Rajan et al., 2011). These analyses focused on evaluating different statistical metrics, beyond the long

- term mean concent ration, to characterize the part of the distribution of PM 2.5 concentrations in which staff continued to have confidence in the associations observed in epidemiological studies and below which there was a comparative lack of data such that the staff’s conf idence in the relationship was appreciably less. This would also be the part of the distribution of PM 2.5 concentrations

66 While CASAC expressed the view that it would be most desirable to have information on concentration

- response relationships, they recognized that it would also be “preferable to have information on the concentrations that were most influential in generating the health effect estimates in individual studies” (Samet, 2010d, p. 2).***E.O. 12866 Review

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Page 129 of 253 which had the most influence on generating the health effect estimates reported in epidemiological studies. As discussed in section III .A.3 above, the Policy Assessment recognized there was no one percentile value within a given distribution that was the most appropriate or “correct” way to characterize where our confidence in the associations becomes appreciably lower. The Policy Assessm ent concluded that focusing on concentrations within the lower quartile of a distribution, such as the range from the 25 th to the 10 th percentile, was reasonable to consider as a region within which we begin to have appreciably less confidence in the assoc iations observed in epidemiological studies. 67 In the EPA staff’s view, considering lower PM 2.5 concentrations, down to the lowest concentration observed in a study, would be a highly uncertain basis for selecting alternative standard levels ( U.S. EPA, 2009 a, p. 2

- 71). As outlined in section III.A.3 above, the Policy Assessment recognized that there were two types of population

- level information to consider in identifying the range of PM 2.5 concentrations which have the most influence on generating the healt h effect estimates reported in epidemiological studies. The most relevant information to consider was the number of health events (e.g., deaths, hospitalizations) occurring within a study population in relation to the distribution of PM 2.5 concentrations l ikely experienced by
67 In the last review, staff believed it was appropriate to consider a level for an annual PM 2.5 standard that was somewhat below the averages of the long

- term concentrations across the cities in each of the key long

- term exposures studies, recognizing that the evidence of an association in any such study was strongest at and around the l ong - term average where the data in the study are most concentrated. For example, the interquartile range of long

- term average concentrations within a study and a range within one standard deviation around the study mean were considered reasonable approache s for characterizing the range over which the evidence of association is strongest (U.S. EPA, 2005, pp. 5

- 22 to 5

- 23). In this review, the Policy Assessment noted the interrelatedness of the distributional statistics and a range of one standard deviation a round the mean which contains approximately 68 percent of normally distributed data, in that one standard deviation below the mean falls between the 25 th and 10 th percentiles (U.S. EPA, 2011a, p. 2

- 71).***E.O. 12866 Review

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Page 130 of 253 study participants. However, in recognizing that access to health event data may be restricted, and consistent with advice from CASAC (Samet 2010d, p.2), EPA staff also considered the number of participants within each study area, in r elation to the distribution of PM 2.5 concentrations (i.e., study population data), as a surrogate for health event data. In applying this approach, the Policy Assessment focused on identifying the part of the distribution of PM 2.5 concentrations which had the most influence on generating health effect estimates in epidemiological studies, as discussed in section III.A.3 above. As discussed below, in working with study investigators, the EPA staff was able to obtain health event dat a for three large multi

- city studies (Krewski et al., 2009; Zanobetti and Schwartz, 2009; Bell et al., 2008) and population data for the same three studies and one additional long

- term exposure study (Miller et al., 2007) , as documented in a staff memorand um (Rajan et al., 2011). 68 For the three studies for which both health event and study population data were available, the EPA staff analyzed the reliability of using study population data as a surrogate for health event data. Based on these analyses, the E PA staff recognized that the 10 th and 25 th percentiles of the health event and study population distributions are nearly identical and concluded that the distribution of population data can be a useful surrogate for event data, providing support for consid eration of the study population data for Miller et al. (2007), for which health event data were not available (Rajan et al., 2011, Analysis 1 and Analysis 2, in particular, Table 1 and Figures 1 and 2). With regard to the long

- term mean PM 2.5 concentration s which are relevant to the

68 The distributional statistical analysis of populat ion

- level data built upon an earlier analysis that evaluated the distributions of air quality and associated population data for three long

- term exposure studies and three short

- term exposure studies (Schmidt et al., 2010, Analysis 2).***E.O. 12866 Review

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Page 131 of 253 first approach, Figures 1 through 3 ( U.S. EPA, 2011a, Figures 2

- 4, 2

- 5, 2

- 6, and 2

- 8) summarize data available for multi

- city, long

- and short

- term exposure studies that evaluated endpoints classified in the Integrated Science A ssessment as having evidence of a causal or likely causal relationship or evidence suggestive of a causal relationship, showing the studies with long

- term mean PM 2.5 concentrations below 17 μg/m 3

. 69 As discussed in more detail in section III.E.4.b of the pr oposal, Figures 1 and 3 summarize the health outcomes evaluated, relative risk estimates, air quality data, and geographic scope for long

- and short

- term exposure studies, respectively, that evaluated mortality (evidence of a causal relationship); cardiova scular effects (evidence of a causal relationship); and respiratory effects (evidence of a likely causal relationship) in the general population, as well as in older adults, an at

- risk population. Figure 2 provides this same summary information for long

- te rm exposure studies that evaluated respiratory effects (evidence of a likely causal relationship) in children, an at

- risk population, as well as developmental effects (evidence suggestive of a causal relationship).

69 Additional studie s presented and assessed in the Integrated Science Assessment report effects at higher long

- term mean PM 2.5 concentrations (e.g., U.S. EPA, 2009a, Figures 2

- 1, 2

- 2, 7

- 6, and 7

- 7).***E.O. 12866 Review

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Page 132 of 253 

### Figure 1. Summary of Effect Estimates (per 10 μg/m 3 

### ) and Air Quality Distributions for Multi - City, Long - term PM 2.5 

### Exposure Studies of the General Population and Older Adults 70 , 71 , 72

70 

### The air quality data for the Miller et al. (2007) study is discussed more fully in the Response to Comments document. 71 

### The Goss et al. (2004) study patients over the age of 6 years enrolled in the Cystic Fibrosis Foundation National Patient Reg istry in 1999 and 2000. The average age of the study participants was 18.4 (SD 10). 72 The air quality data reported in Figure 1 of the proposal incorrectly identified the long

- term mean PM 2.5 concentration for this study as 14.3 μg/m 3 , which was the long

term mean PM 2.5 concentration for Lipfert et al. (2006b). This mistake was also made in the Figure 2

- 2 of the ISA (U.S. EPA, 2009a, p. 2

- 15). The EPA notes that footnote a for Figure 4 of Lipfert et al. (2006a) identifies that the mortality risks for PM 2.5 are based on o ne year of air quality data (1999). However, this study does not report the long

- term mean PM 2.5 concentration for 1999. Rather, in Table 1 of Lipfert et al. (2006a), the study authors reported long

- term mean PM 2 .5 concentrations of 14.3 μg/m 3 f

or the year s 1989 to 1996 and 14.6 μg/m 3 for the years 1997 to 2001.***E.O. 12866 Review

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Page 133 of 253 Formatted: Font: 12 pt***E.O. 12866 Review

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Page 134 of 253 

### Source: U.S. EPA, 2011a, Figure 2

- 4 Formatted: Font: 12 pt***E.O. 12866 Review

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Page 135 of 253 

### Figure 2. Summary of Effect Estimates (per 10 μg/m 3 

### ) and Air Quality Distributions for Multi - City, Long - term PM 2.5 

### Exposure Studies of Children

Source: U.S. EPA, 2011a, Figure 2

- 5***E.O. 12866 Review

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Page 136 of 253 

### Figure 3. Summary of Effect Estimates (per 10 μg/m 3 

### ) and Air Quality Distributions for Multi - City, Short - term PM 2.5 

### Exposure Studies of the General Population and Older Adults

Source: U.S. EPA, 2011 a, Figure 2

- 6***E.O. 12866 Review

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Page 137 of 253 With regard to consideration of additional information from epidemiological studies which was relevant to the second approach, the EPA staff compiled a summary of the range of PM 2.5 concentrations corresponding with the 25 th to 10 th percentiles of health event or study population data from the four multi

- city studies, for which distributional statistics are available 73 ( U.S. EPA, 2011a, Figure 2

- 7; Rajan et al., 2011, Table 1). By considering this approach, one could focus on the rang e of PM 2.5 concentrations below the long

- term mean ambient concentrations over which we continue to have confidence in the associations observed in epidemiological studies (e.g., above the 25 th percentile) where commensurate public health protection could be obtained for PM 2.5 - related effects and, conversely, identify the range in the distribution below which our confidence in the associations is appreciably less, to identify alternative annual standard levels. The mean PM 2.5 concentrations associated with the studies summarized in Figures 1, 2, and 3 and with the distributional statistics analyses (Rajan et al., 2011) are based on concentrations averaged across ambient monitors within each area included in a given study and then averaged across study areas to calculate an overall study mean concentration, as discussed above. Figure 4, discussed in more detail in section III.E.4.a of the proposal, summarizes statistical metrics for those key studies 74 included in

73 The EPA staff obtained health event data (e.g., number of deaths, hospitalizations) occurring in a study population for three multi

- city studies (Krewski et al., 2009; Zanobetti and Schwartz, 2009 ; Bell et al., 2008) and study population data were obtained for the same three studies and one additional study (Miller et al., 2007) (U.S. EPA, 2011a, p.2

- 71). If health event or study population data were available for additional studies, the EPA could employ distributional statistics to identify the broader range of PM 2.5 concentrations that were most influential in generating health effect estimates in those studies. 74 Long

- and short

- term exposure studies considered “key” studies for consideration ar e summarized in Figure 4 and include those studies observing effects for which the evidence supported a causal or likely causal association. This figure represents the subset of multi

- city studies included in Figures 1 through 3 that provided evidence of p ositive and generally statistically significant effects associated in whole or in part with more recent air quality data, generally representing health effects associated with lower PM 2.5 concentrations than had previously been considered in the last revie w. The EPA notes that many of these studies evaluated multiple health endpoints, and not all of the effects evaluated provided evidence of positive and statistically significant effects. For purposes of informing the Administrator’s decision on the appropr iate standard levels, the Agency considers the full body of scientific evidence and focuses on those aspects of the key studies that provided evidence of positive and generally statistically significant effects.***E.O. 12866 Review

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Page 138 of 253 

### Figure 4. Translating Epidemiol ogical Evidence from Multi - City Exposure Studies into an Annual PM 2.5 

### Standard 75



### Source: U.S. EPA, 2011a, Figure 2

-
75 

### The air quality data for the Miller et a l. (2007) study is discussed more fully in the Response to Comments document.***E.O. 12866 Review

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Page 139 of 253 Figures 1, 2, and 3 that provide evidence of positive and generally statistically significant PM 2.5 - related effects, whi ch are relevant to the two approaches for translating epidemiological evidence into potential standard levels as discussed above. The top of Figure 4 includes information for long

- term exposure studies evaluating health outcomes classified as having eviden ce of a cau s al or likely cau s al relationship with PM 2.5 exposures (long

- term mean PM 2.5 concentrations indicated by diamond symbols). The middle of Figure 4 includes information for short

- term exposure studies evaluating health outcomes classified as having evidence of a cau s al or likely cau s al relationship with PM 2.5 exposures (long

- term mean PM 2.5 concentrations indicated by triangle symbols). The bottom of Figure 4 includes information for l ong - term exposures studies evaluating health outcomes classified as having evidence suggestive of a causal relationship (long

term mean PM 2.5 concentrations indicated by square symbols). Figure 4 also summarizes the range of PM 2.5 concentrations correspond ing with the 25 th (indicated by solid circles) to 10 th (indicated by open circles) percentiles of the health event or study population data from the four multi

- city studies (highlighted in bold text) for which distributional statistics are available. In co nsidering the evidence, the Policy Assessment recognized that NAAQS are standards set so as to provide requisite protection, neither more nor less stringent than necessary to protect public health, with an adequate margin of safety. This judgment, ultimate ly made by the Administrator, involves weighing the strength of the evidence and the inherent uncertainties and limitations of that evidence. Therefore, depending on the weight placed on different aspects of the evidence and inherent uncertainties, conside ration of different alternative standard levels could be supported.***E.O. 12866 Review

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Page 140 of 253 Given the currently available evidence discussed in more detail in section III.E.4.b of the proposal and considering the various approaches discussed above, the Policy Assessment conclude d it was appropriate to focus on an annual standard level within a range of about 12 to 11 μg/m 3 ( U.S. EPA, 2011a, pp. 2

- 82, 2

- 101, and 2

- 106). As illustrated in Figure 4, the Policy Assessment recognized that a standard level of 12 μg/m 3 , at the upper end of this range, was somewhat below the long

- term mean PM 2.5 concentrations reported in all the multi

- city, long

- and short

- term exposure studies that provided evidence of positive and statistically significant associations with health effects classified as having evidence of a causal or likely causal relationship, including premature mortality and hospitalizations and emergency department visits for cardiovascular and respiratory effects as well as respiratory effects in children. Further, a level of 12 μg/ m 3 would reflect consideration of additional population

- level information from such epidemiological studies in that it generally corresponded with approximately the 25 th percentile of the available distributions of health events data in the studies for whi ch population

- level information was available. In addition, a level of 12 μg/m 3 would reflect some consideration of studies that provided more limited evidence of reproductive and developmental effects, which were suggestive of a causal relationship, in th at it was about at the same level as the lowest long

- term mean PM 2.5 concentrations reported in such studies (see Figure 4). Alternatively the Policy Assessment recognized that an annual standard level of 11 μg/m 3 , at the lower end of this range, was well below the lowest long

- term mean PM 2.5 concentrations reported in all multi

- city long

- and short

- term exposure studies that provide evidence of positive and statistically significant associations with health effects***E.O. 12866 Review

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Page 141 of 253 classified as having evidence of a causa l or likely causal relationship. A level of 11 μg/m 3 would reflect placing more weight on the distributions of health event and population data, in that this level was within the range of PM 2.5 concentrations corresponding to the 25 th and 10 th percentiles of all the available distributions of such data. In addition, a level of 11 μg/m 3 was somewhat below the lowest long

- term mean PM 2.5 concentrations reported in reproductive and developmental effects studies that are suggestive of a causal relationship. Thus, a level of 11 μg/m 3 would reflect an approach to translating the available evidence that places relatively more emphasis on margi n of safety considerations and less certain causal relationships than would a standard set at a higher level. Such a policy approach would tend to weigh uncertainties in the evidence in such a way as to avoid potentially underestimating PM 2.5 - related risks to public health. Further, recognizing the uncertainties inherent in identifying any particular point at which our confidence in reported associations becomes appreciably less, the Policy Assessment concluded that the available evidence did not provide a sufficient basis to consider alternative annual standard levels below 11 μg/m 3 ( U.S. EPA, 2011a, p. 2

- 81). The Policy Assessment also considered the extent to which the available evidence provided a basis for considering alternative annual standard levels above 12 μg/m 3 . As discussed below, the Policy Assessment concluded that it could be reasonable to consider a standard level up to 13 μg/m 3 based on a policy approach that weighed uncertainties in the evidence in such a way as to avoid potentially overest imating PM 2.5 - related risks to public health, especially to the extent that primary emphasis was placed on long

- term exposure studies as a basis for an annual standard level. A level of 13 μg/m 3 was somewhat below the long

- term mean PM 2.5 concentrations re ported in all but one of the***E.O. 12866 Review

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Page 142 of 253 long

- term exposure studies providing evidence of positive and statistically significant associations with PM 2.5 - related health effects classified as having a causal or likely causal relationship. As shown in Figure 4, the one l ong - term exposure study with a long

- term mean PM 2.5 concentration just below 13 μg/m 3 was the Miller et al ., ( ., ( 2007) study
. However, as noted in section III.D.1.a of the proposal and discussed in more detail in the Response to Comments document , the Poli cy Assessment observed that in comparison to other long

- term exposure studies, the Miller et al. study was more limited in that it was based on only one year of air quality data and the one year was after the health outcomes were reported ( U.S. EPA, 2011a, pp. 2

- 81 to 2

- 82). Thus, to the extent that less weight was placed on the Miller et al. study than on other long

- term exposure studies with more robust air quality data, a level of 13 μg/m 3 could be considered as being protective of long

- term exposure rel ated effects classified as having a causal or likely causal relationship. In also considering short

- term exposure studies, however, the Policy Assessment noted that a level of 13 μg/m 3 was below the long

- term mean PM 2.5 concentrations reported in most but not all such studies . In particular , two studies

-- Burnett et al. (2004) and Bell et al. (2008)

-- reported long

- term mean PM 2.5 concentration s of 12.8 and 12.9 μg/m 3 , respectively. In considering these studies, the Policy Assessment found no basis to conclude that these two studies were any more limited or uncertain than the other short

- term exposure studies shown in Figures 3 and 4 ( U.S. EPA, 2011a, p. 2

- 82). On this basis, as discussed below, the Policy Assessment concluded that consideration of an annual standard level of 13 μg/m 3 would have implications for the degree of protection that would need to be provided by the 24

- hour standard, in order that the suite of PM 2.5 standards, taken together, would provide***E.O. 12866 Review

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Page 143 of 253 appropriate protection from effects on public health related to short

- term exposure to PM 2.5 ( U.S. EPA, 2011a, p. 2

- 82). The Policy Assessment also noted that a standard level of 13 μg/m 3 would reflect a judgment that the uncertainties in the epidemiological evidence as summarized in section II I.B above and discussed in more detail in section III.B.2 of the proposal, including uncertainties related to the heterogeneity observed in the epidemiological studies in the eastern versus western parts of the U.S., the relative toxicity of PM 2.5 componen ts, and the potential role of co

- pollutants, are too great to warrant placing any weight on the distributions of health event and population data that extend down below the long

- term mean concentrations into the lower quartile of the data. This level would also reflect a judgment that the evidence from reproductive and developmental effects studies that is suggestive of a causal relationship was too uncertain to support consideration of any lower level. Beyond evidence

- based considerations, the Policy Asses sment also considered the extent to which the quantitative risk assessment supported consideration of these alternative standard levels or provided support for lower levels. In considering simulations of just meeting alternative annual standard levels with in the range of 13 to 11 μg/m 3 (in conjunction with the current 24

- hour standard level of 35 μg/m 3 ), the Policy Assessment concluded that important public health improvements are associated with risk reductions estimated for standard levels of 13 and 12 μg /m 3 and noted that the level of 11 μg/m 3 was not included in the quantitative risk assessment. The Policy Assessment noted that the overall confidence in the quantitative risk estimates varied for the different alternative standard levels evaluated and was stronger for the higher levels and***E.O. 12866 Review

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Page 144 of 253 substantially lower for the lowest level evaluated (i.e., 10 μg/m 3 ). Based on the above considerations, the Policy Assessment concluded that the quantitative risk assessment provided support for considering alternative a nnual standard levels within a range of 13 to 11 μg/m 3 , but did not provide strong support for considering lower alternative standard levels ( U.S. EPA, 2011a, pp. 2

- 102 to 2

- 103). Taken together, the Policy Assessment concluded that consideration of altern ative annual standard levels in the range of 13 to 11 μg/m 3 may be appropriate. Furthermore, the Policy Assessment concluded that the currently available evidence most strongly supported consideration of an alternative annual standard level in the range of 12 to 11 μg/m 3 ( U.S. EPA, 2011a, p. 2

- 82). The Policy Assessment concluded that an alternative level within the range of 12 to 11 μg/m 3 would more fully take into consideration the available information from all long

- and short

- term PM 2.5 exposure studies , including studies of at

- risk populations, than would a higher level. This range also reflected placing weight on information from studies that helped to characterize the range of PM 2.5 concentrations over which we continue to have confidence in the assoc iations observed in epidemiological studies, as well as the extent to which our confidence in the associations was appreciably less at lower concentrations. As recognized in sections III.A.3 and III.E.4.a above, an annual standard intended to serve as the primary means for providing protection from effects associated with both long

- and short

- term PM 2.5 exposures is not expected to provide appropriate protection against the effects of all short

- term PM 2.5 exposures (unless established at a level so low
as to undoubtedly provide more protection than necessary for long

- term exposures). Of particular concern are areas with high peak

- to
- mean ratios possibly associated with***E.O. 12866 Review

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Page 145 of 253 strong local or seasonal sources, or PM 2.5 - related effects that may be associated with sh orter
- than

- daily exposure periods. As a result, the Policy Assessment concluded that it was appropriate to consider alternative 24

- hour PM 2.5 standard levels that would supplement the protection provided by an annual standard. As outlined in section III.A .3 above, the Policy Assessment considered the available evidence from short

- term PM 2.5 exposure studies, as well as the uncertainties and limitations in that evidence, to assess the degree to which alternative annual and 24

- hour PM 2.5 standards can be exp ected to reduce the estimated risks attributed to short

term fine particle exposures. In considering the available epidemiological evidence, the Policy Assessment took into account information from multi

- city studies as well as single

- city studies. The Pol icy Assessment considered the distributions of 24

- hour PM 2.5 concentrations reported in short

- term exposure studies, focusing on the 98 th percentile concentrations to match the form of the 24

- hour standard as discussed in section III.E.3.b above. In recogn izing that the annual and 24

- hour standards work together to provide protection from effects associated with short

- term PM 2.5 exposures, the Policy Assessment also considered information on the long

- term mean PM 2.5 concentrations from these studies. In addition to considering the epidemiological evidence, the Policy Assessment considered air quality information, specifically peak

- to
- mean ratios using county

- level 24

- hour and annual design values, to characterize air quality patterns in areas possibly
ass ociated with strong local or seasonal sources. These patterns helped in understanding the extent to which different combinations of annual and 24

- hour standards would be consistent with the policy goal of setting a generally controlling annual standard wit h a***E.O. 12866 Review

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Page 146 of 253 24

- hour standard that provides supplemental protection especially for areas with high peak

- to
- mean ratios ( U.S. EPA, 2011a, p. 2

- 14). In considering the information provided by the short

- term exposure studies, the Policy Assessment recognized that to the extent these studies were conducted in areas that likely did not meet one or both of the current standards, such studies did not help inform the characterization of the potential public health improvements of alternative standards set at lower levels. Therefore, in considering the short

- term exposure studies to inform staff conclusions regarding levels of the 24

- hour standard that are appropriate to consider, the Policy Assessment placed greatest weight on studies conducted in areas that likely met both the current annual and 24

- hour standards. With regard to multi

- city studies that evaluated effects associated with short

- term PM 2.5 exposures, as summarized in Figure 3 above and discussed in more detail in section III.E.4.c of the proposal, the Policy As sessment noted that, to the extent air quality distributions were reduced to reflect just meeting the current 24

- hour standard, additional protection would be anticipated for the effects observed in the three multi

- city studies with 98 th percentile values greater than 35 μg/m 3 (Burnett et al., 2004; Burnett and Goldberg, 2003; Franklin et al., 2008). In the three additional studies with 98 th percentile values below 35 μg/m 3 , specifically 98 th percentile concentrations of 34.2, 34.3, and 34.8 μg/m 3 , the Poli cy Assessment noted that these studies reported long

- term mean PM 2.5 concentrations of 12.9, 13.2, and 13.4 μg/m 3 , respectively (Bell et al., 2008; Zanobetti and Schwartz, 2009; Dominici et al., 2006a). To the extent that consideration was given to revisin g the level of the annual standard, as discussed in section III.E.4.b of the proposal, the Policy Assessment recognized that potential changes associated with***E.O. 12866 Review

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Page 147 of 253 meeting such an alternative annual standard would result in lowering risks associated with both l ong - and short

- term PM 2.5 exposures. Consequently, in considering a 24

- hour standard that would operate in conjunction with an annual standard to provide appropriate public health protection, the Policy Assessment noted that to the extent that the level of the annual standard was revised to within a range of 13 to 11 μg/m 3 , in particular in the range of 12 to 11 μg/ m 3 , additional protection would be provided for the long

- term effects observed in these multi

- city studies ( U.S. EPA, 2011a, p. 2

- 84). Based on this information, the Policy Assessment concluded that the multi

- city, short

- term exposure studies generally provided support for retaining the 24

- hour standard level at 35 μg/m 3 so long as the standard is in conjunction with an annual standard level revi sed to within a range of 12 to 11 μg/m 3 ( U.S. EPA, 2011a, p. 2

- 84). Alternatively, in conjunction with an annual standard level of 13 μg/m 3 , the Policy Assessment concluded that the multi

- city studies provided limited support for revising the 24

- hour stand ard level somewhat below 35 μg/m 3 , such as down to 30 μg/m 3 , based on one study (Bell et al., 2008) that reported positive and statistically significant effects with an overall 98 th percentile value below the level of the current 24

- hour standard and an o verall long

- term mean concentration slightly less than 13 μg/m 3 (Figure 3; U.S. EPA, 2011a, p. 2

- 84). In reaching staff conclusions regarding alternative 24

- hour standard levels that were appropriate to consider, the Policy Assessment also took into accou nt relevant information from single

- city studies that evaluated effects associated with short

- term PM 2.5 exposures. The Policy Assessment recognized that these studies may provide additional insights regarding impacts on at

- risk populations and/or on areas with isolated peak concentrations.***E.O. 12866 Review

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Page 148 of 253 As discussed in more detail in section III.E.4.c of the proposal, although a number of single

- city studies reported effects at appreciably lower PM 2.5 concentrations than multi

- city short

- term exposure studies, the unce rtainties and limitations associated with the single

- city studies were considerably greater than those associated with the multi

- city studies and, thus, the Policy Assessment concluded there was less confidence in using these studies as a basis for setting the level of a standard. Therefore, the Policy Assessment concluded that the multi

- city short

- term exposure studies provided the strongest evidence to inform decisions on the level of the 24

- hour standard, and the single

- city studies did not warrant consi deration of 24

- hour standard levels different from those supported by the multi

- city studies ( U.S. EPA, 2011a, p. 2

- 88). In addition to considering the epidemiological evidence, the Policy Assessment took into account air quality information based on coun ty
- level 24

- hour and annual design values to understand the public health implications of the alternative standard levels supported by the currently available scientific evidence, as discussed in section III.E.4.b above. Consistent with the general approac h discussed in section III.A.3 above, the Policy Assessment considered the extent to which different combinations of alternative annual and 24

- hour standard levels based on the evidence would support the policy goal of lowering annual and 24

- hour air quali ty distributions by using the annual standard to be the “generally controlling” standard in conjunction with setting the 24

- hour standard to provide supplemental protection ( U.S. EPA, 2011a, pp 2

- 88 to 2

- 91, Figure 2

- 10). Using information on the relationship of the 24

- hour and annual design values, the Policy Assessment examined the implications of three alternative suites of PM 2.5***E.O. 12866 Review

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Page 1 49 of 253 standards identified as appropriate to consider based on the currently available scientific evidence, as discussed ab ove. The Policy Assessment concluded that an alternative suite of PM 2.5 standards that would include an annual standard level of 11 or 12 μg/m 3 and a 24

- hour standard with a level of 35 μg/m 3 (i.e., 11/35 or 12/35) would result in the annual standard being the generally controlling standard in most areas although the 24

- hour standard would continue to be the generally controlling standard in the Northwest ( U.S. EPA, 2011a, pp. 2

- 89 to 2

- 91 and Figure 2

- 10). These Northwest counties generally represented areas where the annual mean PM 2.5 concentrations have historically been low but where relatively high 24

- hour concentrations occur, often related to seasonal woo d smoke emissions. Alternatively, combining an alternative annual standard of 13 μg/m 3 with a 24

- hour standard of 30 μg/m 3 would result in many more areas across the country in which the 24

- hour standard would likely become the controlling standard (the st andard driving air quality distributions lower) than if an alternative annual standard of 12 or 11 μg/m 3 were paired with the current level of the 24

- hour standard (i.e., 35 μg/m 3 ). The Policy Assessment concluded that consideration of retaining the 24

- ho ur standard level at 35 μg/m 3 would reflect placing greatest weight on evidence from multi

city studies that reported positive and statistically significant associations with health effects classified as having a causal or likely causal relationship. In co njunction with lowering the annual standard level, especially within a range of 12 to 11 μg/m 3 , this alternative recognized additional public health protection against effects associated with short

- term PM 2.5 exposures which would be provided by lowering t he annual standard such that revision to the 24

- hour standard would not be warranted ( U.S. EPA, 2011a, p. 2

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Page 150 of 253 Beyond evidence

- based considerations, the Policy Assessment also considered the extent to which the quantitative risk assessment supported con sideration of retaining the current 24

- hour standard level or provided support for lower standard levels. In considering simulations of just meeting the current 24

- hour standard level of 35 μg/m 3 or alternative levels of 30 or 25 μg/m 3 (in conjunction with alternative annual standard levels within a range of 13 to 11 μg/m 3 ), the Policy Assessment noted that the overall confidence in the quantitative risk estimates varied for the different standard levels evaluated and was stronger for the higher levels and substantially lower for the lowest level evaluated (i.e., 25 μg/m 3 ). Based on this information, the Policy Assessment concluded that the quantitative risk assessment provided support for considering a 24

- hour standard level of 35 or 30 μg/m 3 (in conjunctio n with an alternative standard level within a range of 13 to 11 μg/m 3 ) but did not provide strong support for considering lower alternative 24

- hour standard levels ( U.S. EPA, 2011a, pp. 2

- 102 to 2

- 103). Taken together, the Policy Assessment concluded that while it was appropriate to consider an alternative 24

- hour standard level within a range of 35 to 30 μg/m 3 , the currently available evidence most strongly supported consideration for retaining the current 24

- hour standard level at 35 μg/m 3 in conjunction with lowering the level of the annual standard within a range of 12 to 11 μg/m 3 ( U.S. EPA, 2011a, p. 2

- 92). ii. CASAC Advice Based on its review of the second draft Policy Assessment, CASAC agreed with the general approach for translating the available epidemi ological evidence, risk information, and air quality information into the basis for reaching conclusions on alternative standards for consideration. Furthermore, CASAC agreed “that it is***E.O. 12866 Review

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Page 151 of 253 appropriate to return to the strategy used in 1997 that considers the annual and the short

term standards together, with the annual standard as the controlling standard, and the short

- term standard supplementing the protection afforded by the annual standard” and “considers it appropriate to place the greatest emphasis” on health effects judged to have evidence supportive of a causal or likely causal relationship as presented in the Integrated Science Assessment (Samet, 2010d, p. 1). CASAC concluded that the range of levels presented in the second draft Policy Assessment (i .e., alternative annual standard levels within a range of 13 to 11 μg/m 3 and alternative 24

- hour standard levels within a range of 35 to 30 μg/m 3 ) “are supported by the epidemiological and toxicological evidence, as well as by the risk and air quality info rmation compiled” in the Integrated Science Assessment, Risk Assessment, and second draft Policy Assessment. CASAC further noted that “[a]lthough there is increasing uncertainty at lower levels, there is no evidence of a threshold (i.e., a level below whic h there is no risk for adverse health effects)” (Samet, 2010d, p. ii). Although CASAC supported the alternative standard level ranges presented in the second draft Policy Assessment, it did not express support for any specific levels or combinations of st andards. Rather, CASAC encouraged the EPA to develop a clearer rationale in the final Policy Assessment for staff conclusions regarding annual and 24

- hour standards that were appropriate to consider, including consideration of the combination of these stan dards supported by the available information (Samet, 2010d, p. ii). Specifically, in commenting on a distributional statistical analysis of air quality and associated population data presented in the second draft Policy Assessment, CASAC encouraged staff t o focus on information related to the concentrations that were most***E.O. 12866 Review

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Page 152 of 253 influential in generating the health effect estimates in individual studies to inform alternative standard levels. CASAC urged that the EPA redo that analysis using health event or study p opulation data (Samet, 2010d, p. 2). CASAC also commented that the approach presented in the second draft Policy Assessment to identify alternative 24

- hour standard levels which focused on peak

- to
- mean ratios was not relevant for informing the actual level (Samet 2010d, p. 4). Further, they expressed the concern that the combinations of annual and 24

- hour standard levels discussed in the second draft Policy Assessment (i.e., in the range of 13 to 11 μg/m 3 for the annual standard, in conjunction with retaini ng the current 24

- hour PM 2.5 standard level of 35 μg/m 3 ; alternatively, revising the level of the 24

- hour standard to 30 μg/m 3 in conjunction with an annual standard level of 11 μg/m 3 ) “may not be adequately inclusive” and “[i]t was not clear why, for exam

ple a daily standard of 30 μg/m 3 should only be considered in combination with an annual level of 11 μg/m 3 ” (Samet, 2010d, p. ii). CASAC encouraged the EPA to more clearly explain its rationale for identifying the 24

- hour/annual combinations that are appro priate for consideration (Samet 2010d, p. ii). In considering CASAC’s advice as well as public comment on the second draft Policy Assessment, the EPA staff conducted additional analyses and modified their conclusions regarding alternative standard levels that were appropriate to consider. The staff conclusions in the final Policy Assessment ( U.S. EPA, 2011a, section 2.3.4.4) differed somewhat from the alternative standard levels discussed in the second draft Policy Assessment ( U.S. EPA, 2010f, section 2.3. 4.3), upon which CASAC based its advice. Changes made in the final Policy Assessment were primarily focused on improving and clarifying the approach for translating the epidemiological evidence into a***E.O. 12866 Review

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Page 153 of 253 basis for staff conclusions on the broadest range of al ternative standard levels supported by the available scientific information and more clearly articulating the rationale for the staff’s conclusions (Wegman, 2011, pp. 1 to 2). Consistent with CASAC’s advice to consider more information from epidemiological studies, as discussed in section III.E.4.b.1 above, the EPA analyzed additional population

- level data obtained from several study authors (Rajan et al., 2011). In transmitting the final Policy Assessment to CASAC, the Agency notified CASAC that the final staff conclusions reflected consideration of CASAC’s advice and that those staff conclusions were based, in part, on the specific distributional analysis that CASAC had urged the EPA to conduct (Wegman, 2011, p.2). Thus, CASAC had an opportunity to comment on the final Policy Assessment, but chose not to provide any additional comments or advice after receiving it. iii. Administrator’s Proposed Decisions on the Primary PM 2.5 Standard Levels In reaching her conclusions regarding appropriate alternative standard levels to consider, the Administrator considered the epidemiological and other scientific evidence, estimates of risk reductions associated with just meeting alternative annual and/or 24

- hour standards, air quality analyses, related limitations and uncerta inties, staff conclusions as presented in the Policy Assessment, and the advice of CASAC. As an initial matter, the Administrator agreed with the general approach discussed in the Policy Assessment as summarized in sections III.A.3 and III.E.4.a above, and supported by CASAC, of considering the protection afforded by the annual and 24

- hour standards taken together for mortality and morbidity effects associated with both long

- and short

term exposures to PM 2.5 ( 77 FR 38939 ) . Furthermore, based on the evidenc e and***E.O. 12866 Review

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Page 154 of 253 quantitative risk assessment, the Administrator provisionally concluded it is appropriate to set a “generally controlling” annual standard that will lower a wide range of ambient 24

- hour concentrations, with a 24

- hour standard focused on providing su pplemental protection, particularly for areas with high peak

- to
- mean ratios possibly associated with strong local or seasonal sources, or PM 2.5 - related effects that may be associated with shorter

- than daily exposure periods. The Administrator provisionally concluded this approach would likely reduce aggregate risks associated with both long

- and short

- term exposures more consistently than a generally controlling 24

- hour standard and would be the most effective and efficient way to reduce total PM 2

- 5 - related population risk. Id. In reaching decisions on alternative standard levels to propose, the Administrator judged that it was most appropriate to examine where the evidence of associations observed in the epidemiological studies was strongest and, conversely , where she had appreciably less confidence in the associations observed in the epidemiological studies. Based on the characterization and assessment of the epidemiological and other studies presented and assessed in the Integrated Science Assessment and t he Policy Assessment, the Administrator recognized the substantial increase in the number and diversity of studies available in this review including extended analyses of the seminal studies of long

- term PM 2.5 exposures (i.e., ACS and Harvard Six Cities st udies) as well as important new long

- term exposure studies (as summarized in Figures 1 and 2). Collectively, the Administrator noted that these studies, along with evidence available in the last review, provided consistent and stronger evidence of an assoc iation with premature mortality, with the strongest evidence related to cardiovascular

- related mortality, at lower ambient concentrations than previously observed. The Administrator also recognized the***E.O. 12866 Review

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Page 155 of 253 availability of stronger evidence of morbidity effects associated with long

- term PM 2.5 exposures, including evidence of cardiovascular effects from the WHI study and respiratory effects, including decreased lung function growth, from the extended analyses for the Southern California Children’s Health Study. F urthermore, the Administrator recognized new U.S. multi

- city studies that greatly expanded and reinforced our understanding of mortality and morbidity effects associated with short

- term PM 2.5 exposures, providing stronger evidence of associations at ambien t concentrations similar to those previously observed (as summarized in Figure 3). Id. at 38939

- 40. The newly available scientific evidence built upon the previous scientific data base to provide evidence of generally robust associations and to provide a b asis for greater confidence in the reported associations than in the last review. The Administrator recognized that the weight of evidence, as evaluated in the Integrated Science Assessment, was strongest for health endpoints classified as having evidence of a causal relationship. These relationships included those between long

- and short

- term PM 2.5 exposures and mortality and cardiovascular effects. She recognized that the weight of evidence was also strong for health endpoints classified as having evidenc e of a likely causal relationship, which included those between long

- and short

- term PM 2.5 exposures and respiratory effects. In addition, the Administrator made note of the much more limited evidence for health endpoints classified as having evidence sugg estive of a causal relationship, including developmental, reproductive and carcinogenic effects. Id . at 38940. Based on information discussed and presented in the Integrated Science Assessment, the Administrator recognized that health effects may occur ove r the full***E.O. 12866 Review

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Page 156 of 253 range of concentrations observed in the long

- and short

- term epidemiological studies and that no discernible threshold for any effects can be identified based on the currently available evidence ( U.S. EPA, 2009a, section 2.4.3). She also recogni zed, in taking note of CASAC advice and the distributional statistics analysis discussed in section III.E.4.b.i above and in the Policy Assessment, that there was significantly greater confidence in observed associations over certain parts of the air quali ty distributions in the studies, and conversely, that there was significantly diminished confidence in ascribing effects to concentrations toward the lower part of the distributions. Consistent with the general approach summarized in section III.A.3 above, and supported by CASAC as discussed in section III.E.4.a above, the Administrator generally agreed that it was appropriate to consider a level for an annual standard that was somewhat below the long

- term mean PM 2.5 concentrations reported in long

- and sho rt
term exposure studies. In recognizing that the evidence of an association in any such study was strongest at and around the long

- term average where the data in the study are most concentrated, she understood that this approach did not provide a bright l ine for reaching decisions about appropriate standard levels. The Administrator noted that long

term mean PM 2.5 concentrations were available for each study considered and, therefore, represented the most robust data set to inform her decisions on appropri ate annual standard levels. She also noted that the overall study mean PM 2.5 concentrations were generally calculated based on monitored concentrations averaged across monitors in each study area with multiple monitors, referred to as a composite monitor c oncentration, in contrast to the highest concentration monitored in each study area, referred to as a maximum monitor concentration, which are used to determine whether an area meets a***E.O. 12866 Review

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Page 157 of 253 given standard. In considering such long

- term mean concentrations, the Administrator understood that it was appropriate to consider the weight of evidence for the health endpoints evaluated in such studies in giving weight to this information. Id
. Based on the information summarized in Figure 4 above and presented in more det ail in the Policy Assessment ( U.S. EPA, 2011a, chapter 2) for effects classified in the Integrated Science Assessment as having a causal or likely causal relationship with PM 2.5 exposures, the Administrator observed an overall pattern of statistically sign ificant associations reported in studies of long

- term PM 2.5 exposures with long

- term mean concentrations ranging from somewhat above the current standard level of 15 μg/m 3 down to the lowest mean concentration in such studies of 12.9 μg/m 3 (in Miller et al ., 2007). 76 She observed a similar pattern of statistically significant associations in studies of short

- term PM 2.5 exposures with long

- term mean concentrations ranging from around 15 μg/m 3 down to 12.8 μg/m 3 (in Burnett et al., 2004). With regard to effects classified as providing evidence suggestive of a causal relationship, the Administrator observed a small number of long

- term exposure studies related to developmental and reproductive effects that reported statistically significant associations with overall study mean PM 2.5

76 The EPA notes that the Miller et al., (2007) study provides strong evidence of cardiovascular related effects associated with long

- term PM 2.5 exposures. At the time of the proposal, the EPA recognized the limited nature of the air quality data considered in this study (77 FR 38918, fn. 62). The EPA has reviewed those limitations, in conjunction with consideration of public comments received on the proposal as discussed in section III.E.4.c, in conjunction with reaching a final decision on the level of the annual standard.***E.O. 12866 Review

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Page 158 of 253 concentrations down to 11.9 μg/m 3 (in Bell et al., 2007). 77 Id. The Administrator also considered additional information from epidemiological studies, consistent with CASAC advice, to tak e into account the broader distribution of PM 2.5 concentrations and the degree of confidence in the observed associations over the broader air quality distribution. In considering this additional information, she understood that the Policy Assessment prese nted information on the 25 th and 10 th percentiles of the distributions of PM 2.5 concentrations available from four multi

- city studies to provide a general frame of reference as to the part of the distribution in which the data become appreciably more spars e and, thus, where her confidence in the associations observed in epidemiological studies would become appreciably less. As summarized in Figure 4 above, the Administrator took note of additional population

- level data that were available for four studies (Krewski et al., 2009; Miller et al., 2007; Bell et al., 2008; Zanobetti and Schwartz, 2009), each of which reported statistically significant associations with health endpoints classified as having evidence of a causal relationship. In considering the lon g - term PM 2.5 concentrations associated with the 25 th percentile values of the population

- level data for these four studies, she observed that these values ranged from somewhat above to somewhat below 12 μg/m 3 . The Administrator recognized that these four s tudies represented some of the strongest evidence available within the overall body of scientific evidence and noted that three of these studies (Krewski et al., 2009; Bell et al., 2008; Zanobetti and Schwartz, 2009) were
77 With respect to suggestive evidence related to cancer, mutagenic, and genotoxic effects, the PM 2.5 concentrations reported in studies 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, 2009a, section 7.5), such that in selecting alt ernative standard levels that provide protection from mortality and cardiovascular and respiratory effects, it is reasonable to anticipate that protection will also be provided for carcinogenic effects.***E.O. 12866 Review

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Page 159 of 253 used as the basis for concentratio n - response functions used in the quantitative risk assessment ( U.S. EPA, 2010a, section 3.3.3). In considering this information, the Administrator noted that CASAC advised that information about the long

- term PM 2.5 concentrations that were most influentia l in generating the health effect estimates in epidemiological studies can help to inform selection of an appropriate annual standard level. However, t he Administrator also recognized that additional population

- level data were available for only these four studies and, therefore, she believed that these studies comprised a more limited data set than one based on long

- term mean PM 2.5 concentrations for which data were available for all studies considered, as discussed above. The Administrator recognized, as summarized in section III.B.2 above, that important uncertainties remain in the evidence and information considered in this review of the primary fine particle standards. These uncertainties are generally related to understanding the relative toxicity of the different components in the fine particle mixture, the role of PM 2.5 in the complex ambient mixture, exposure measurement errors inherent in epidemiological studies based on concentrations measured at fixed monitor sites, and the nature, magnitude, and confidence in estimated risks related to increasingly lower ambient PM 2.5 concentrations. Furthermore, the Administrator noted that epidemiological studies have reported heterogeneity in responses both within and between cities and geographic regions acro ss the U.S. She recognized that this heterogeneity may be attributed, in part, to differences in fine particle composition in different regions and cities. The Administrator also recognized that t here are additional limitations associated with evidence for reproductive and developmental effects,***E.O. 12866 Review

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Page 160 of 253 identified as being suggestive of a causal relationship with long

- term PM 2.5 exposures, including: the limited number of studies evaluating such effects; uncertainties related to identifying the relevant exposure ti me periods of concern; and limited toxicological evidence providing little information on the mode of action(s) or biological plausibility for an association between long

- term PM 2.5 exposures and adverse birth outcomes. Id . at 38941. The Administrator was mindful that considering what standards were requisite to protect public health with an adequate margin of safety required public health policy judgments that neither overstated nor understated the strength and limitations of the evidence or the appr opriat e inferences to be drawn from the evidence. In considering how to translate the available information into appropriate standard levels, the Administrator weighed the available scientific information and associated uncertainties and limitations. For the pur

pose of determining what standard levels were appropriate to propose, the Administrator recognized, as did EPA staff in the Policy Assessment, that there was no single factor or criterion that comprised the sole “correct” approach to weighing the various t ypes of available evidence and information, but rather there were various approaches that are appropriate to consider. The Administrator further recognized that different evaluations of the evidence and other information before the Administrator could refl ect placing different weight on the relative strengths and limitations of the scientific information, and different judgments could be made as to how such information should appropriately be used in making public health policy decisions on standard levels. This recognition led the Administrator to consider various approaches to weighing the evidence so as to identify appropriate standard levels to propose. In so doing, the***E.O. 12866 Review

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Page 161 of 253 Administrator encouraged extensive public comment on alternative approaches to weigh ing the evidence and other information so as to inform her public health policy judgments before reaching final decisions on appropriate standard levels. In considering the available information, the Administrator noted the advice of CASAC that the current ly available scientific information, including epidemiological and toxicological evidence as well as risk and air quality information, provided support for considering an annual standard level within a range of 13 to 11 μg/m 3 and a 24

- hour standard level w ithin a range of 35 to 30 μg/m 3 . In addition, the Administrator recognized that the Policy Assessment concluded that the available evidence and risk

- based information support consideration of annual standard levels in the range of 13 to 11 μg/m 3 , and that the Policy Assessment also concluded that the evidence most strongly supported consideration of an annual standard level in the range of 12 to 11 μg/m 3 . In considering how the annual and 24

- hour standards work together to provide appropriate public health protection, the Administrator observed that CASAC did not express support for any specific levels or combinations of standards within these ranges . Nor did CASAC choose to comment on additional information and analyses presented in the final Policy Assessm ent prepared in response to CASAC’s recommendations on the second draft Policy Assessment (Wegman, 2011)
. In considering the extent to which the currently available evidence and information provided support for specific standard levels within the ranges i dentified by CASAC and the Policy Assessment as appropriate for consideration, the Administrator initially considered standard levels within the range of 13 to 11 μg/m 3 for the annual standard. In so doing, the Administrator first considered the long

- term mean PM 2.5***E.O. 12866 Review

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Page 162 of 253 concentrations reported in studies of effects classified as having evidence of a causal or likely causal relationship, as summarized in Figure 4 above and discussed more broadly above. She noted that a level at the upper end of this range would be below m ost but not all the overall study mean concentrations from the multi

- city studies of long

- and short

term exposures, whereas somewhat lower levels within this range would be below all such overall study mean concentrations. In considering the appropriate w eight to place on this information, the Administrator again noted that the evidence of an association in any such study was strongest at and around the long

- term average where the data in the study are most concentrated, and that long

- term mean PM 2.5 conce ntrations were available for each study considered and, therefore, represented the most robust data set to inform her decisions on appropriate annual standard levels. Further, she was mindful that this approach did not provide a bright line for reaching de cisions about appropriate standard levels. Id. In considering the long

- term mean PM 2.5 concentrations reported in studies of effects classified as having evidence suggestive of a causal relationship, as summarized in Figure 4 for reproductive and developme ntal effects, the Administrator noted that a level at the upper end of this range would be below the overall study mean concentration in one of the three studies, while levels in the mid

- to lower part of this range would be below the overall study mean co ncentrations in two or three of these studies. In considering the appropriate weight to place on this information, the Administrator noted the very limited nature of this evidence of such effects and the additional uncertainties in these epidemiological st

udies relative to the studies that provide evidence of causal or likely causal relationships.***E.O. 12866 Review

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Page 163 of 253 The Administrator also considered the distributional analyses of population

- level information that were available from four of the epidemiological studies that provide evidence of effects identified as having a causal relationship with long

- or short

- term PM 2.5 concentrations for annual standard levels within the same range of 13 to 11 μg/m 3

. In so doing, the Administrator first noted that a level in the mid

- part of this range generally corresponds with approximately the 25 th percentile of the distributions of health events data available in three of these studies. The Administrator also noted that standard levels toward the upper part of this range would reflect placing substantially less weight on this information, whereas standard levels toward the lower part of this range would reflect placing substantially more weight on this information. In considering this information, the Administrator noted that there was no bright line that delineates the part of the distribution of PM 2.5 concentrations within which the data become appreciably more sparse and, thus, where her confidence in the associations observed in epidemiological studies became appreciably less. In con sidering mean PM 2.5 concentrations and distributional analyses from the various sets of epidemiological studies noted above, the Administrator was mindful, as noted above, that such studies typically report concentrations based on composite monitor distrib utions, in which concentrations may be averaged across multiple ambient monitors that may be present within each area included in a given study. Thus, a policy approach that used data based on composite monitors to identify potential alternative standard l evels would inherently build in a margin of safety of some degree relative to an alternative standard level based on measurements at the monitor within an area that records the highest concentration, or the maximum monitor, since once a standard was***E.O. 12866 Review

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Page 164 of 253 set, c oncentrations at appropriate maximum monitors within an area were generally used to determine whether an area meets a given standard. The Administrator also recognized that judgments about the appropriate weight to place on any of the factors discussed abo ve should reflect consideration not only of the relative strength of the evidence but also on the important uncertainties that remained in the evidence and information being considered in this review. The Administrator noted that the extent to which these uncertainties influenced judgments about appropriate annual standard levels within the range of 13 to 11 μg/m 3 would likely be greater for standard levels in the lower part of this range which would necessarily be based on fewer available studies than woul d higher levels within this range. Based on the above considerations, the Administrator concluded that it was appropriate to propose to set a level for the primary annual PM 2.5 standard within the range of 12 to 13 μg/m 3 . The Administrator provisionally co ncluded that a standard set within this range would reflect alternative approaches to appropriately placing the most weight on the strongest available evidence, while placing less weight on much more limited evidence and on more uncertain analyses of infor mation available from a relatively small number of studies. Further, she provisionally concluded that a standard level within this range would reflect alternative approaches to appropriately providing an adequate margin of safety for the populations at ris k for the serious health effects classified as having evidence of a causal or likely causal relationship, depending in part on the emphasis placed on margin of safety considerations. The Administrator recognized that setting an annual standard level at the lower end of this range would reflect an approach that placed more emphasis on the entire body of the evidence, including the***E.O. 12866 Review

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Page 165 of 253 analysis of the distribution of air quality concentrations most influential in generating health effect estimates in the studies, and on margin of safety considerations, than would setting a level at the upper end of the range. Conversely, an approach that would support a level at the upper end of this range would place more emphasis on the remaining uncertainties in the evidence to avoid potentially overestimating public health improvements, and would generally support a view that the uncertainties remaining in the evidence are too great to warrant setting a lower annual standard level. Id . at 38942
. At the time of the proposal, whi le the Administrator recognized that CASAC advised, and the Policy Assessment concluded, that the available scientific information provided support for considering a range that extended down to 11 μg/m 3 , she concluded that proposing such an extended range would reflect a public health policy approach that placed more weight on relatively limited evidence and more uncertain information and analyses than she considered appropriate at this time. Nonetheless, the Administrator solicited comment on a level down to 11 μg/m 3 as well as on approaches for translating scientific evidence and rationales that would support such a level. Such an approach might reflect a view that the uncertainties associated with the available scientific information warrant a highly prec autionary public health policy response that would incorporate a large margin of safety. The Administrator recognized that potential air quality changes associated with meeting an annual standard set at a level within the range of 12 to 13 μg/m 3 will result in lowering risks associated with both long

- and short

- term PM 2.5 exposures. However, the Administrator recognized that such an annual standard intended to serve as the primary means for providing protection from effects associated with both l ong - and short

- term***E.O. 12866 Review

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Page 166 of 253 PM 2.5 exposures would not by itself be expected to offer requisite protection with an adequate margin of safety against the effects of all short

- term PM 2.5 exposures. As a result, in conjunction with proposing an annual standard level i n the range of 12 to 13 μg/m 3 , the Administrator provisionally concluded that it was appropriate to continue to provide supplemental protection by means of a 24

- hour standard set at the appropriate level, particularly for areas with high peak

- to
- mean ratio s possibly associated with strong local or seasonal sources, or for PM 2.5 - related effects that may be associated with shorter

than

- daily exposure periods. Based on the approach discussed in section III.A.3 above, at the time of the proposal the Administra tor relied upon evidence from the short

- term exposure studies as the principal basis for selecting the level of the 24

- hour standard. In considering these studies as a basis for the level of a 24

- hour standard, and having selected a 98 th percentile form fo r the standard, the Administrator agreed with the focus in the Polic y Assessment of looking at the 98 th percentile values, as well as at the long

- term mean PM 2.5 concentrations in these studies. In considering the information provided by the short

- term exp osure studies, the Administrator recognized that to the extent these studies were conducted in areas that likely did not meet one or both of the current standards, such studies did not help inform the characterization of the potential public health improve ments of alternative standards set at lower levels. By reducing the PM 2.5 concentrations in such areas to just meet the current standards, the Administrator anticipated that additional public health protection would occur. Therefore, the Administrator focu sed on studies that reported positive and statistically significant associations in areas that would likely have met both the current***E.O. 12866 Review

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Page 167 of 253 24

- hour and annual standards. She also considered whether or not these studies were conducted in areas that would likely h ave met an annual standard level of 12 to 13 μg/m 3 to inform her decision regarding an appropriate 24

- hour standard level. As discussed in section III.E.4.a, consistent with the Policy Assessment, the Administrator concluded that multi

- city, short

- term exp osure studies provided the strongest data set for informing her decisions on appropriate 24

- hour standard levels. The Administrator viewed the single

city, short

- term exposure studies as a much more limited data set providing mixed results and, therefore, she had less confidence in using those studies as a basis for setting the level of a 24

- hour standard. With regard to the limited number of single

- city studies that reported positive and statistically significant associations for a range of health endpoint s related to short

- term PM 2.5 concentrations in areas that would likely have met the current suite of PM 2.5 standards, the Administrator recognized that many of those studies had significant limitations (e.g., limited statistical power, limited exposure da ta) or equivocal results (mixed results within the same study area) that made them unsuitable to form the basis for setting the level of a 24

- hour standard. With regard to multi

- city studies that evaluated effects associated with short

- term PM 2.5 exposure s, the Administrator observed an overall pattern of positive and statistically significant associations in studies with 98 th percentile values averaged across study areas in the range of 45.8 to 34.2 μg/m 3 (Burnett et al., 2004; Zanobetti and Schwartz, 200 9; Bell et al., 2008; Dominici et al., 2006a, Burnett and Goldberg, 2003; Franklin et al., 2008). The Administrator noted that, to the extent air quality distributions were reduced to reflect just meeting the current 24

- hour standard, additional protection would be anticipated for the effects observed in the three multi

- city studies with 98 th***E.O. 12866 Review

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Page 168 of 253 percentile values greater than 35 μg/m 3 (Burnett et al., 2004; Burnett and Goldberg, 2003; Franklin et al., 2008). In the three additional studies with 98 th percentile values below 35 μg/m 3 , specifically 98 th percentile concentrations of 34.2, 34.3, and 34.8 μg/m 3 , the Administrator noted that these studies reported long

- term mean PM 2.5 concentrations of 12.9, 13.2, and 13.4 μg/m 3 , respectively (Bell et al., 2008; Zanobetti and Schwartz, 2009; Dominici et al., 2006a). In proposing to revise the level of the annual standard to within the range of 12 to 13 μg/m 3 , as discussed above, the Administrator recognized that additional protection would be provided for the shor t
- term effects observed in these multi

- city studies in conjunction with an annual standard level of 12 μg/m 3 , and in two of these three studies in conjunction with an annual standard level of 13 μg/m 3 . She noted that the study

- wide mean concentrations were based on averaging across monitors within study areas and that compliance with the standard would be based on concentrations measured at the monitor reporting the highest concentration within each area. The Administrator believed it would be reasonable to conclude that revision to the 24

- hour standard would not be appropriate in conjunction with an annual standard within this range. Based on the above considerations related to the epidemiological evidence, the Administrator provisionally concluded that it was appropriate to retain the level of the 24

- hour standard at 35 μg/m 3 , in conjunction with a revised annual standard level in the proposed range of 12 to 13 μg/m 3

. In addition to considering the epidemiological evidence, the Administrator also took into account air quality information based on county

- level 24

- hour and annual design values to understand the public health implications of retaining the 24

- hour***E.O. 12866 Review

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Page 169 of 253 standard level at 35 μg/m 3 in conjunction with an annual standard level within the proposed range o f 12 to 13 μg/m 3 . She considered whether these suites of standards would meet a public health policy goal which included setting the annual standard to be the “generally controlling” standard in conjunction with setting the 24

- hour standard to provide supp lemental protection to the extent that additional protection is warranted. As discussed above, the Administrator provisionally concluded that this approach was the most effective and efficient way to reduce total population risk associated with both long

and short

- term PM 2.5 exposures, resulting in more uniform protection across the U.S. than the alternative of setting the 24

- hour standard to be the controlling standard. In considering the air quality information, the Administrator first recognized that t here was no annual standard within the proposed range of levels, when combined with a 24

- hour standard at the proposed level of 35 μg/m 3 , for which the annual standard would be the generally controlling standard in all areas of the country. She further obs erved that such a suite of PM 2.5 standards with an annual standard level of 12 μg/m 3 would result in the annual standard as the generally controlling standard in most regions across the country, except for certain areas in the Northwest, where the annual m ean PM 2.5 concentrations have historically been low but where relatively high 24

- hour concentrations occur, often related to seasonal wood smoke emissions ( U.S. EPA, 2011a, pp. 2

- 89 to 2

- 91, Figure 2

- 10). Although not explicitly delineated on Figure 2

- 10 i n the Policy Assessment, an annual standard of 13 μg/m 3 would be somewhat less likely to be the generally controlling standard in some regions of the U.S. outside the Northwest in conjunction with a 24

- hour standard level of 35 μg/m 3

. Taking the above cons iderations into account, the Administrator proposed to***E.O. 12866 Review

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Page 170 of 253 revise the level of the primary annual PM 2.5 standard from 15.0 μg/m 3 to within the range of 12.0 to 13.0 μg/m 3 and to retain the 24

- hour standard level at 35 μg/m 3 . In the Administrator’s judgment, su ch a suite of primary PM 2.5 standards and the rationale supporting such levels could reasonably be judged to reflect alternative approaches to the appropriate consideration of the strength of the available evidence and other information and their associate d uncertainties and the advice of CASAC. The Administrator recognized that the final suite of standards selected from within the proposed range of annual standard levels, or the broader range of annual standard levels on which public comment was solicited, must be clearly responsive to the issues raised by the D.C. Circuit’s remand of the 2006 primary annual PM 2.5 standard. Furthermore, at the time of the proposal, she recognized that the final suite of standards will reflect her ultimate judgment in the fi nal rulemaking as to the suite of primary PM 2.5 standards that would be requisite to protect the public health with an adequate margin of safety from effects associated with fine particle exposures. The final judgment to be made by the Administrator will a ppropriately consider the requirement for a standard that is neither more nor less stringent than necessary and will recognize that the CAA does not require that primary standards be set at a zero

- risk level, but rather at a level that reduces risk suffici ently so as to protect public health with an adequate margin of safety. At the time of the proposal, having reached her provisional judgment to propose revising the annual standard level from 15.0 to within a range of 12.0 to 13.0 μg/m 3 and to propose retaining the 24

- hour standard level at 35 μg/m 3 , the Administrator solicited public comment on this range of levels and on approaches to considering the available evidence and information that would support the choice of levels within this range. The***E.O. 12866 Review

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Page 171 of 253 Administrator also solicited public comment on alternative annual standard levels down to 11 μg/m 3 and on the combination of annual and 24

- hour standards that commenters may believe is appropriate, along with the approaches and rationales used to support such levels. In addition, given the importance the evidence from epidemiologic studies played in considering the appropriate annual and 24

- hour levels, the Administrator solicited public comment on issues related to translating epidemiological e vidence into standards, including approaches for addressing the uncertainties and limitations associated with this evidence.
c. Comments on Standard Levels This section addresses comments that relate to consideration of the appropriate levels of the primary a nnual and 24

- hour PM 2.5 standards , including c omments on the general approach used by the EPA to translate the available scientific information into standard levels and how specific PM 2.5 exposure studies should be considered as a basis for the standard le vel s. These comments on standard levels expand upon the more general comments that either support ed or oppose d any change to the current suite of primary PM 2.5 standards , which are addressed above in section III.D.2. 78 As explained there, one group of comme nters generally opposed any change to the current primary PM 2.5 standards and more specifically disagreed with the basis for the EPA’s proposal to revise the annual standard level. Another group of commenters supported revising the current suite of primary PM 2.5 standards to provide increased public health protection. Some commenters in this second group argued that both the annual and 24

- hour standard levels should be lowered while other commenters in this group agreed with the EPA’s proposal

78 Specific comments on the forms of the annual and 24

- hour standards are addressed in section III.E.3.a and III.E.3.b, respectively.***E.O. 12866 Review

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Page 172 of 253 to retain the level of the 24

- hour standard in conjunction with revising the level of the annual standard. While generally supporting the EPA’s proposal to lower the level of the annual standard, many commenters in this group disagreed that a level within the EPA’s pro posed range was adequately protective and supported a level of 11 μg/m 3 or below. i. Annual Standard Level The group of commenters opposed to any change to the current suite of primary PM 2.5 standards generally raised questions regarding the underlying scientific evidence, including the causal determinations reached in the Integrated Science Assessment, and focused strongly on the uncertainties they saw in the scientific evidence as a basis f or their conclusion that no changes to the current standard levels were warranted. In commenting on the proposed standard levels, these commenters typically relied on the arguments summarized and addressed above in section III.D.2 as to why they believed i t was inappropriate for the EPA to make any revisions to the suite of primary PM 2.5 standards. That is, they asserted that the EPA’s causal determinations were not adequately supported by the underlying scientific information; the biological plausibility of health effects observed in epidemiologic al studi es has not been demonstrated in
c ontrolled human exposure and toxicological studies ; uncertainties in the underlying health science are as great or greater than in 2006; there is no evidence of greater risk since the last review to justify tightening the current annual PM 2.5 standard; and “new” studies not included in the Integrated Science Assessment continue to increase uncertainty about possible health risks associated with exposure to PM 2.5 . With regard to the level of the annual standard, these commenters strongly disagreed with the A gency’s proposed decision to revise the level to within a range of 12***E.O. 12866 Review

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Page 173 of 253 to 13 μg/m 3 and argued that the current standard level of 15 μg/m 3 should be retained
. For example, UARG, API, and other commenters in this group raised a number of issues that they asse rted called into question the EPA’s interpretation of the epidemiological evidence to support revising the annual standard level. These commenters raised specific questions related to the general approach used by the EPA to translate the air quality and ot her information from specific epidemiological studies into standard levels, including : (1) the EPA’s approach for using composite monitor air quality distributions reported in epidemiological studies to select a standard level that would be compared to
mea surements at the monitor recording the highest value in an area to determine compliance with the standard; (2) the appropriate exposure period for effects observed in long

- term exposure mortality studies; and (3) the use of the EPA’s analysis of distributi on s of underlying population

- level data (i.e., health event and study population data) for those epidemiological studies for which such information was available. These commenters also raised questions regarding the EPA’s consideration of specific scientific evidence as a basis for setting a standard level, including : (4) evidence of respiratory morbidity effects in long

- term exposure studies and (5) more limited evidence of health effects which have been categorized in the Integrated Science Assess ment as suggestive of a causal relationship (i.e., developmental and reproductive outcomes ). These comments are discussed in turn below. (1) Some commenters in this group argued that one reason why they believe there is no basis for setting a standard leve l below 15 μg/m 3 is that the air quality metric from epidemiological studies that the EPA relied on in the proposal is not the same metric that will be compared to the level of the standard to determine compliance with the standard.***E.O. 12866 Review

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Page 174 of 253 That is, commenters not ed that the long

- term mean PM 2.5 concentrations that the EPA considered, shown in Figure 4 above, are composite monitor mean concentrations (i.e., concentrations averaged across multiple monitors within areas with more than one monitor), whereas the PM 2.5 concentrations that will be compared to the level of the standard are maximum monitor concentrations (i.e., the concentration measured by the monitor within an area reporting the highest concentration). This comment was presented most specifically in UARG’ s comments (UARG, 2012, Attachment 1, pp. 2 to 6), which raised two overarching issues as discussed below. First, the commenter noted that the EPA’s approach of considering composite monitor mean PM 2.5 concentrations in selecting a standard level, and then comparing the maximum monitor mean PM 2.5 concentration in each area to the standard level when the standard is implemented, was characterized in the proposal as inherently having the potential to build in a margin of safety (UARG, 2012, Attachment 1, p. 4 , citing 77 FR 38905). The commenter asserted that the Administrator is ignoring this distinction between composite and maximum monitor concentrations, and that this approach creates an unwarranted case for lowering the standard level, since in the comment er’s view, it would result in a margin of safety that would be arbitrary, not based on evidence, and unquantified (UARG, 2012, Attachment 1, p. 4). In support of this view, the commenter asserted that there is a significant difference between composite mon itor mean PM 2.5 concentrations and maximum monitor mean PM 2.5 concentrations. The commenter asserted that the maximum monitor value will always be higher than the composite monitor value (except in areas that contain only a single monitor), such that when an area just attains the NAAQS, that area’s composite monitor long

- term mean PM 2.5***E.O. 12866 Review

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Page 175 of 253 concentration will be lower than the level of the standard (UARG, 2012, Attachment 1, p. 3). Second, the commenter asserted that a more “reasoned and consistent approach
wou ld be to decide on a mean composite monitor PM 2.5 level that should be achieved and then identify the maximum monitor level that would result in that composite value” (UARG, 2012, Attachment 1, p. 4). The commenter conducted an analysis of maximum monitor versus composite monitor annual mean PM 2.5 concentrations using monitoring data 79 from 2006 to 2008 and presented results averaged across areas within two groups (i.e., those with design values 80 above the current standard level and those with design values just below the current standard level) to illustrate their suggested alternative approach. The commenter interpreted this analysis as showing that the composite monitor long

- term mean PM 2.5 concentrations from the subset of the epidemiological studies show n in Figure 4 (of the proposal and above) that the commenter considered to be an appropriate focus for this analysis would be achieved across the U.S. if the current annual NAAQS of 15 μg/m 3 is retained and attained
. The commenter considered the subset of epidemiological studies that included only long

- term exposures studies of effects for which the evidence is categorized as causal or likely causal, but did not consider short

term exposure studies. On this basis, the commenter asserted that attaining the current annual PM 2.5 standard would result in composite monitor long

- term mean concentrations in all areas that would be generally within or below the range of the composite monitor long

- term mean concentrations from such studies and, as a result, there is no reason to

79 The commenter indicated that this analysis was based on monitoring data for every core based statistical area (CBSA) in th e EPA’s Air Quality System (AQS) database. 80 The design value is the air quality statistic that is compared to the level of the NAAQS to determine the attainment status of a given area.***E.O. 12866 Review

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Page 176 of 253 lower the level of the current annual NAAQS. In considering the first issue related to the EPA’s approach, the EPA notes that in proposing to revise both the form and level of the annual standard, the Ad ministrator clearly took into account the distinction between the composite monitor long

- term mean PM 2.5 concentrations from the epidemiological studies, considered as a basis for selecting an annual standard level, and maximum monitor long

- term mean PM 2.5 concentrations. In deciding to focus on the composite monitor long

- term mean concentrations in selecting the standard level, and on the maximum monitor concentrations in selecting the form of the standard (i.e., consistent with proposing to eliminate the option for spatial averaging across monitors within an area when implementing the standard 81 ), the Administrator reasonably considered the distinction between these metrics in a manner that was consistent with advice from CASAC (Samet et al., 2010d, pp. 2 t o 3). As noted above in section III.A.3, the EPA recognizes that a statistical metric (e.g., the mean of a distribution) based on maximum monitor concentrations may be identical to or above the same statistical metric based on composite monitor concentrati ons. More specifically, many areas have only one monitor, in which case the composite and maximum monitor concentrations are identical. Based on the most recent data from the EPA’s AQS from 2009 to 2011 in the 331 CBSAs in which valid PM 2.5 data are availa

ble, as discussed in Frank (2012a, Table 5), there were 20 8 such areas (with design values ranging up to about 15 μg/m 3 ). Frank (2012a) also observed that other areas have multiple monitors with composite and maximum monitor mean PM 2.5 concentrations that were the same or relatively close, with 5 7 areas in which the maximum monitor mean concentration was no more than 0.5 μg/m 3 higher than the 81 As discussed above in section III.E.3.a.***E.O. 12866 Review

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Page 177 of 253 composite monitor mean concentration and 56 areas in which the difference was between 0.6 and 2 μg/m 3 . Further, ther e were only a few other areas in which the maximum monitor mean concentration was appreciably higher than the composite monitor mean concentration, such as areas in which some monitors may be separately impacted by local sources. There were only 10 such ar eas in the country in which the maximum monitor mean concentration was between 2 to 6 μg/m 3 higher than the composite monitor concentration (Frank, 2012a, Table 4). 82 Thus, the EPA does not agree that there is a significant difference between composite moni tor mean PM 2.5 concentrations and maximum monitor mean PM 2.5 concentrations in the large majority of areas across the country. In proposing to revise the form of the annual PM 2.5 standard, as discussed above in section III.E.3.a, the EPA noted that when an annual PM 2.5 standard was first set in 1997, the form of the standard included the option for averaging across measurements at appropriate monitoring sites within an area, generally consistent with the composite monitor approach used in epidemiological st udies, with some constraints intended to ensure that spatial averaging would not result in inequities in the level of protection for communities within large metropolitan areas. In the last review the EPA tightened the constraints on spatial averaging, and in this review has eliminated the option altogether, on the basis of analyses in each review that showed that such constraints may be inadequate to avoid substantially greater exposures for people living in locations around the monitors recording the high est PM 2.5 concentrations in some areas, potentially

82 The average difference be tween the maximum and composite design value among the 123 CBSAs with two or more monitors is 0.8 μg/m 3 and the median difference is 0.6 μg/m 3 . The 25 th and 75 th percentiles are 0.3 and 1.0 μg/m 3 , respectively (Frank, 2012a, p. 4).***E.O. 12866 Review

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Page 178 of 253 resulting in disproportionate impacts on at

- risk populations of persons with lower SES levels as well as minorities . In light of these analyses, and consistent with the Administrator’s decision to revise the form of the annual PM 2.5 standard by eliminating the option for spatial averaging, the EPA continues to conclude that a standard level based on consideration of long

- term mean concentrations from composite monitors, and applied at each monitor within a n area including the monitor measuring the highest concentration, is the appropriate approach to use in setting a standard that will protect public health, including the health of at

- risk populations, with an adequate margin of safety, as required by the C AA. The EPA acknowledges that at proposal, the Agency characterized the approach of using maximum monitor concentrations to determine compliance with the standard, while selecting the standard level based on consideration of composite monitor concentration s, as one that inherently had the potential to build in a margin of safety (77 FR 38905), and CASAC reiterated that view in supporting the EPA’s approach (Samet, 2010d, p. 3). Nonetheless, in light of the discussion above, the EPA more specifically recogni zes that this approach does not build in any margin of safety in the large number of areas across the country with only one monitor. Further, based on the analyses done to inform consideration of the form of the standard (Schmidt, 2011, Analysis A), the EP A concludes that this approach does not provide a margin of safety for the at

- risk populations that live around the monitor measuring the highest concentration, such as in those few areas in which the maximum monitor concentration is appreciably higher tha n the composite monitor concentration. Rather, this approach properly treats those at

- risk populations the same way it does the broader populations that live in areas with only one***E.O. 12866 Review

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Page 179 of 253 monitor, by providing the same degree of protection for those at

- risk popul ations that would otherwise be disproportionately impacted as it does for the broader populations in other areas, While the EPA recognizes that this approach can result in some additional margin of safety for the subset of areas with multiple monitors in w hich at

- risk populations may not be disproportionately represented in areas around the maximum monitor, which may be the case in areas with relatively small differences between the maximum and composite monitor concentrations, the EPA notes that this margi n would be relatively small in such areas. Based on the above considerations, the EPA does not agree that the Agency’s approach of using maximum monitor concentrations to determine compliance with the standard, while selecting the standard level based on c onsideration of composite monitor concentrations creates an unwarranted case for lowering the standard level based on a margin of safety that would be arbitrary, not based on evidence, or lack quantification. The EPA recognizes that setting a standard to p rotect public health, including the health of at

- risk populations, with an adequate margin of safety, depends upon selecting a standard level sufficiently below where there is clear the EPA has found the strongest evidence of health effects so as to provide such protection, and that the EPA’s approach regarding consideration of composite and maximum monitor concentrations is intended to, and does, serve to address this requirement as part of and not separate from t he selection of an appropriate standard level based on the health effects evidence. In considering the second issue related to the commenter’s suggested alternative approach, the EPA strongly disagrees with the commenter’s view that a more “reasoned and co nsistent approach would be to decide on a mean composite monitor PM 2.5 level***E.O. 12866 Review

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Page 180 of 253 that should be achieved and then identify the maximum monitor level that would result in that composite value” (UARG, 2012, Attachment 1, p. 4). As discussed above, the EPA notes that for areas with only one monitor, or with multiple monitors that measure concentrations that are very close in magnitude, the maximum monitor level that would limit the composite monitor PM 2.5 level to be no greater than the level that should be achiev ed to protect public health with an adequate margin of safety, would essentially be the same as that composite monitor level. Further, as discussed above, even for areas in which the maximum monitor concentration is appreciably higher than other monitor
co ncentrations within the same area, public health would not be protected with an adequate margin of safety if the disproportionately higher exposures of at

- risk, susceptible populations around the monitor measuring the highest concentration were in
essence averaged away with measurements from monitors in other locations within large urban areas. Further, the commenter’s suggested approach would be based on annual average PM 2.5 concentrations that have been measured over some past time period. Such an approac h would reflect the air quality that existed in the past, but it would not necessarily provide appropriate constraints on the range of concentrations that would be allowed by such a standard in the future, when relationships between maximum and composite m onitor concentrations in areas across the country may be different. For these reasons, the EPA fundamentally rejects the commenter’s suggested approach because it results in a standard that demonstrably would not protect public health, including providing protection for at

- risk populations, with an adequate margin of safety in areas across the country. More specifically, in further considering the commenter’s analysis of design***E.O. 12866 Review

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Page 181 of 253 values based on maximum versus composite monitor annual mean PM 2.5 concentration s using monitoring data from 2006 to 2008 which they assert supports retaining the current standard level of 15 μg/m 3 , the EPA finds flaws with the numerical results and the scope of the analysis, as well as flaws in the commenter’s translation of the anal ysis results into the basis for selecting an annual standard level. In considering the commenter’s analysis, the EPA notes that the analysis compared maximum versus composite monitor annual mean PM 2.5 concentrations, averaged over 3 years, for two groups o f areas: (1) areas with design values that exceed the current annual standard level (i.e., greater than 15.0 μg/m 3 ) and (2) areas with design values that are just attaining the current annual standard (i.e., between 14.5 and 15.0 μg/m 3 ). 83 The commenter ind icated that they used the full body of PM 2.5 monitoring data from the EPA’s AQS database (UARG, 2012, Attachment 1, p. 4), In attempting to reproduce the commenter’s results, the EPA repeated the calculations using only valid air quality data (i.e., data t

hat meet data completeness and monitor siting criteria) from the AQS database for the same time period (Frank, 2012a). 84 Based on this corrected analysis, the EPA finds that the composite monitor concentrations averaged across the areas within each group ar e somewhat higher than those calculated by the commenter, and the average differences between the maximum and composite monitor concentrations 83 For the first group of areas (which included 33 areas), this analysis calculated an average across the areas of maximum monitor annual mean PM 2.5 concentrations, averaged over 3 years, of 17.2 μg/m 3 compared to an average of composite monitor concentrations of 14.3 μg/m 3 . For t he second group of areas (which included 11 areas), this analysis calculated an average across the areas of maximum monitor annual mean concentrations, averaged over 3 years, of 14.8 μg/m 3 compared to an average of composite monitor concentrations of 13.6 μg/m 3 (UARG, 2012, Attachment 1, Table 1). 84 The EPA notes that the Frank (2012a) analysis is similar to an earlier EPA staff analysis (Hassett

- Sipple et al., 2010), which used air quality data from EPA’s AQS database to compare maximum versus composite mo nitor long

- term mean PM 2.5 concentrations across the study areas in six selected multi

- city epidemiological studies.***E.O. 12866 Review

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Page 182 of 253 are somewhat smaller (Frank, 2012a, Table 3). 85 Notably, the difference between the maximum and composite monitor average concentrations for the second group of areas is substantially reduced in the corrected analysis, such that the difference (averaged across the 10 areas with valid data in the second group) is approximately 0.5 μg/m 3 , not 1.2 μg/m 3 as in the comment er’s analysis. In addition, the commenter’s analysis compared the average of the composite monitors to the average of the maximum monitors for each subset of areas. This comparison of averages across all the areas in each subset masks the fact that the lar ge majority of areas across the country have only one monitor, with the composite monitor and maximum monitor values the same for such areas, and many other areas have a maximum monitor value that is close to the composite monitor value. As discussed above , these circumstances have a major impact on the protection that would be achieved by the approach suggested by the commenter. With regard to the scope of the commenter’s analysis, the EPA finds that by limiting the scope to a small subset of areas with de sign values above or just below the current annual standard level of 15 μg/m 3 , the analysis ignores the large number of areas across the country with lower design values that are relevant to consider in light of the epidemiological evidence of serious heal th effects at lower concentrations, well below the level of the current standard. In translating the analysis results into the basis for selecting an annual standard 85 The EPA’s analysis was intended to repeat the commenter’s analysis, but using only valid air quality data (from 2006 to 2008). For the fi rst group of areas (which included 21 areas with valid data), the EPA’s analysis calculated an average across the areas of maximum monitor annual mean concentrations, averaged of 3 years, of 16.8 μg/m 3 compared to an average of composite monitor concentrat ions of 14.8 μg/m 3 . For the second group of areas (which included 10 areas with valid data), the EPA’s analysis calculated an average across the areas of maximum monitor annual mean concentrations, averaged over 3 years, of 14.8 μg/m 3 compared to an averag e of composite monitor concentrations of 14.2 μg/m 3 (Frank, 2012a, Table 3).***E.O. 12866 Review

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Page 183 of 253 level, the commenter’s translation is premised on the view that the “natural focal point” for setting an annual PM 2.5 standard level should be somewhere within the range of the long

- term mean PM 2.5 concentrations from the subset of epidemiological studies that included only long

- term exposure studies of effects for which the evidence is categor ized as causal or likely causal, but not for effects categorized as suggestive of causality, nor did it include short

- term exposure studies (which are included in Figure 4 of the proposal notice and above). Such a view is not consistent with setting a stan dard that would provide sufficient protection from the serious health effects reported even in the limited subset of studies considered by the commenter, including protecting public health with an adequate margin of safety. As discussed below, the EPA does not agree with the commenter’s view as to the appropriate focal point for selecting the level of an annual PM 2.5 standard, or with the limited set of studies considered by the commenter as a basis for selecting the level of the annual PM 2.5 standard. Rega rding an appropriate focal point for selecting the level of the annual standard, as discussed in the proposal and as advised by CASAC, the EPA has focused on PM 2.5 concentrations somewhat below the lowest long

- term mean concentrations from each of the key studies of both long

- and short

- term exposures of effects for which the evidence is causal or likely causal, as considered by the EPA (i.e., the first two sets of studies shown in Figure 4). If the level of the annual standard was set just some where within the range of the long

- term mean concentrations from the various long

- term exposure studies, then one or more of the stud ie s would have a long

- term mean concentration below the selec ted level of the standard. Absent some reason to ignore or dis count these studies, which the commenter does not provide (and of which the EPA is unaware) , setting such a***E.O. 12866 Review

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Page 184 of 253 standard would allow that level of air quality , where the evidence of health effects is strongest, and its associated risk of PM 2.5 - related mortalit y and /or morbidity effects to continue. Selecting such a standard level that would explicitly allow such projected PM 2.5 - related mortality and morbidity effects to continue to occur could not be considered sufficient to protect the public health with an adequate margin of safety. Further, focusing on just the long

- term mean PM 2.5 concentrations in the key epidemiological studies

– even the lowest long

- term mean concentration from the set of key studies

-- is not appropriate. Concentrations at and aro und the long

- term mean concentration s represent the part of the air quality distribution where the data in any given study are most concentrated and, thus, where the confidence in the magnitude and significance of an associati on in such study is strongest. However , the evidence of an association with adverse health effects in the studies is not limited to the PM 2.5 concentrations just at and around the long

- term mean, but rather extends more broadly to a lower part of the distribution, recognizing that no d iscernible population

- level threshold for any such effects can be identified based on the available evidence . This broader region of the distribution of PM 2.5 concentrations should be considered to the extent relevant information is available , recognizing that the degree of confidence in the association identified in a study would change become lower as one moves away from below concentrations at and around the long

- term mean concentration in any given study. The commenter’s approach ignores this fundamental consideration. Regarding the set of studies that is appropriate to inform the selection of the level of the annual PM 2.5 standard, the EPA finds that limiting consideration only to the long

term exposure studies, as this commenter suggests, would be tantam ount to ignoring the***E.O. 12866 Review

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Page 185 of 253 short

- term exposure studies , 86 which provide some of the strongest evidence from the entire body of ep idemiological studies. Thus, s e lecting a n annual standard level using the limited set of studies suggested by the commenter would fail to provide a degree of protection that would be sufficient to protect public health with an adequate margin of safety. For all the reasons discussed above, the EPA finds the commenter’s concerns with the EPA’s approach to considering composite and maximum monitor PM 2.5 concentrations in selecting the level of the annual PM 2.5 standard to be without merit. Further, the EPA finds no support in the commenter’s analysis for their suggested alternative approach. (2) With respect to the appropriate exposure peri od for mortality effects observed in long

- term exposure studies, some commenters in this group generally expressed views consistent with comments from UARG that argued that these studies “are most likely detecting health risk from earlier, higher PM 2.5 lev els and misattributing those risks to more recent, lower PM 2.5 levels” (UARG, 2012, Attachment 1, p 7). Further, this commenter asserted that “there is no knowledge or evidence indicating whether premature deaths are the result of PM 2.5 exposures in the mo st recent year; or due to 86 The commenter suggests that the EPA should not place significant reliance on the long

term mean concentrations from short

- term exposure studies because “[T]he short
‐ term studies did not use the annual average of PM 2.5 to develop their associations; they used the daily 24
‐ hour averages of PM 2.5 . Thus, short
‐ term studies do not provide a natural indicator for the appropriate level of an annual standard....” (UARG, 2012, Attachment 1, p. 3). The EPA finds this argument unpersuasive. Quite simply, effects were observed in these studies with an air quality distribution that can meaningfully be characterized by these long

- term mean concentrations. Indeed, in remanding the 2006 standard, t he D.C. Circuit discussed at length the interrelationship of the long

- and short

- term standards and studies, and remanded the 2006 standard to the EPA, in part, for ignoring those relationships without adequate explanation. American Farm Bureau Federation v. EPA. 559 F. 3d at 522

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Page 186 of 253 physical damages incurred from PM 2.5 exposures much earlier in life (with the impact on lifespan only emerging later in life); or due to total accumulated PM 2.5 exposure over many years.” Id . Further, the commenter asserted that t he long

- term exposure studies of mortality are central to the EPA’s basis for proposing to set a lower annual standard level, since most of the estimated benefits associated with a lower annual PM 2.5 standard are based on reductions in mortality related to long

- term exposures to PM 2.5 . As an initial matter, the EPA has recognized t he challenge in distinguishing between PM 2.5 - associated effects due to past and recent long

- term exposures , and in identif ying the relevant latency period for long

- term exposure to PM and resultant health effects (U.S. EPA, 2009a, section 7.6.4 ; 77 FR 38941/1). While the EPA has acknowledged that there remain important uncertainties related to characterizing the most relevant exposure periods in long

- term exposure studies, the assertion that there is “no knowledge or evidence” that helps to inform this issue is not correct, as discussed below. Both in the last review and in the current review , the EPA has assessed studies that used different a ir quality periods for estimating long

- term exposure and tested associations with mortality for the different exposure periods ( U.S. EPA, 2004, section 8 .2.3.5; U.S. EPA 2009a, section 7.6.4)
. In this review, the Integrate d Science Assessment discussed stu dies available since the last review that have assessed the relationship between long

- term exposure to PM 2.5 and mortality to explore the issue of the latency period between exposure to PM 2.5 and death ( U.S. EPA, 2009 a , s ection 7.6.4 ). Notably, i n a recent analys i s of the extended Harvard Six Cities Study, Schwartz et al. (2008) used model averaging (i.e., multiple models were averaged and weighted by probability of accuracy) to assess exposure periods prospectively (77 FR 38907/1

- 2) . The***E.O. 12866 Review

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Page 187 of 253 exposure periods w ere estimated across a range of unconstrained distributed lag models (i.e., same ye ar, one year prior, two years prior to death ). In comparing lags , the authors reported that the effects of changes in exposure to PM 2.5 on mortality we re strongest within a 2

- year period prior to death ( U.S. EPA, 2009a, p. 7

- 92, Figure 7

- 9 )
. Similarly, a large multi

- city study of the elderly found that the mortality risk associated with long

term exposure to PM 10 reported cumulative effect s that extended over the year s that deaths were observed in the study population (i.e., the follow

- up period) and for the 3

- year period prior to death (Zanobetti et al., 2008). Further, i n a study of two locations that experienced an abrupt decline in PM 2.5 concentrations (i.e. , Utah Steel Strike, coal ban in Ireland), Röösli et al. (2005) reported that approximately 75 percent of health benefits were observed in the first 5 years ( U.S. EPA, 2009a , Table 7

- 9). Schwartz et al. (2008) and Puett et al. (2008) found, in a comparison of exposure periods ranging from 1 month to 48 months prior to death , that exposure to PM 10 24 months prior to death exhibited the strongest association, and the weakest association was reported for exposure in the time period of 1 month prior to death. Overall, the EPA notes that the available evidence for determining the exposure period that is causally related to the mortality effects of long

- term PM 2.5 exposures , as discussed above, cannot specifically disentangle the effects observed in long

- term exposure stu dies associated with more recent air quality measurements from effects that may have been associated with earlier, and most likely higher, PM 2.5 exposures. While the evidence suggests that a latency period of up to five years would account for the majority of deaths , it does not provide a basis for concluding that it is solely recent PM 2.5***E.O. 12866 Review

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Page 188 of 253 concentrations that account for the mortality risk observed in such studies. Nonetheless, the more recent air quality data does well at explaining the relationships observed between long

- term exposures to PM 2.5 and mortality , with the strongest association observed in the two years prior to death. Further, the EPA recognizes that there is no discernible population

- level threshold below which effects would not occur, s uch that it is reasonable to consider that health effects may occur over the full range of concentrations observed in the epidemiological studies, including the lower concentrations in the latter years. In light of this evidence and these considerations, t he EPA concludes that it is appropriate to consider air quality concentrations that are generally contemporaneous with the collection of health event data (i.e., collected over the same time period) as being causally associated with at least some proportio n of the deaths assessed in a long

- term exposure study. This would include long

- term mean PM 2.5 concentrations from most of the key long

- term exposure studies of effects with causal or likely causal evidence shown in Figure 4 above, which reported long

- ter m mean PM 2.5 concentrations ranging from 13.6 μg/m 3 to 14.3 μg/m 3

. These studies include studies of mortality by Eftim et al. (2008), which separately analyzed the ACS and Harvard Six City sites, Zeger et al. (2008), and Lipfert et al. (2006), as well as s tudies of morbidity endpoints by Goss et al. (2004), McConnell et al. (2003) and Gauderman et al. (2004), and Dockery et al. (1996) and Razienne et al. (1996). The EPA acknowledges that uncertainty in the relevant exposure period is most notable in two oth er long

- term exposure studies of mortality. The Miller et al. (2007) reported a long

- term mean PM 2.5 concentration for a 1

- year exposure period that post

- dated the follow

- up period in which health event data were collected by***E.O. 12866 Review

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Page 189 of 253 two years. Also, the Krewski e t al. (2009) study reported a long

- term mean PM 2.5 concentration for an exposure period that included only the last two years of the 18

- year follow

- up period. Based on these considerations, the EPA does not now consider it appropriate to put weight on the reported long

- term mean concentrations from these two studies for the purpose of translating the information from the long

- term mortality studies into a basis for selecting the level of the annual PM 2.5 standard. 87 In addition, the EPA acknowledges that exp osure periods that extend at least a couple years prior to the follow

- up period in which health event data were collected would likely more fully capture the PM

- related deaths in such studies. To explore how much higher the long

- term mean PM 2.5 concentrati ons would likely have been had air quality data prior to the follow

- up years of the studies been included, the EPA conducted a sensitivity analysis of long

- term mean PM 2.5 concentrations (Schmidt, 2012 a ) particularly considering studies that only included deaths from a relatively recent follow

up period. As examples of such studies, this analysis considered the Eftim et al. (2008) study of mortality in 51 the ACS sites and the Harvard Six Cities sites, as well as sites in the eastern region in the Zeger et al. (2008) study. Using data from the EPA’s AQS database, the analysis added the two years of air quality data just prior to the follow

- up period in each study, which was 2000 to 2002 in Eftim et al. (20 08) and 2000 to 2005 in Zeger et al. (2008). The analysis then calculated the extended long

- term mean PM 2.5 concentration for each study. As discussed in Schmidt (2012 a ), in each case the long

term mean PM 2.5 concentration averaged over the extended exposu re period was less than

87 Nonetheless, the EPA notes that the Krewski et al. (2009) and Miller et al. (2007) studies provide strong evidence of mortality and cardiovascular

- related effects associated with long

- term PM 2.5 exposures to inform causality determinations reached in the Integrated Science Assessment (U.S. EPA, 2009a, sections 7.2.11 and 7.6).***E.O. 12866 Review

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Page 190 of 253 0. 3 4 μg/m 3 higher than the long

- term mean PM 2.5 concentration averaged over the follow

- up period. The EPA finds it reasonable to conclude that such a relatively small difference in long

- term mean PM 2.5 concentrations would likely ap ply for other long

- term exposure studies that used similarly recent follow

- up periods as well (e.g., Goss et al., 2004; Lipfert et al., 2006). Based on the above considerations, the EPA concludes that it is appropriate to consider the available air quality information from the long

- term exposure studies, while taking into account the uncertainties in the relevant long

- term exposure periods in weighing the information from these studies. The EPA recognizes that considering such information in selecting an ap propriate annual standard level has the potential to build in some margin of safety. The EPA further concludes that it is appropriate to consider the air quality information from the set of long

- term exposure studies discussed above in the context of the b roader array of epidemiological studies that inform the EPA’s consideration of the level of the annual PM 2.5 standard. The EPA also notes that while the long

- term exposure studies are an important component of the epidemiological evidence that informs the Agency’s consideration of the level of the annual standard, they do not provide the only relevant information, nor are they the set of studies for which the relevant long

- term mean PM 2.5 concentrations are the lowest. As discussed in the proposal, the EPA also considers the long

- term mean PM 2.5 concentrations from the short

- term mortality and morbidity studies as providing important information in considering the level of the annual standard. As discussed above, a large proportion of the aggregate risk asso ciated with short

- term exposures results from the large number of days during which the 24

- hour average concentrations***E.O. 12866 Review

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Page 191 of 25 3 are in the low

- to mid

- range of the concentrations observed in the studies. Thus, setting the level of the annual standard based on long

- term mean concentrations, as well as the distribution of concentrations below the mean, in the short

- term exposure studies is the most effective and efficient way to reduce total PM 2.5 - related risk from the broad array of mortality and morbidity effects as sociated with short

- term exposures. Further, the EPA notes that the relevant exposure period for the short

- term exposure studies is the period contemporaneous with the collection of health event data, and that this exposure period is not subject to the unc ertainties discussed above related to the long

- term exposure studies. Recognizing that the long

- term mean PM 2.5 concentrations from several of the multi

- city short

- term exposure studies shown in Figure 4 are below the long

- term mean PM 2.5 concentrations fr om the long

- term exposure studies (with the exception of Miller et al., 2007). 88 it is reasonable that in selecting the level of the annual standard primary consideration should be given to the information from this set of short

- term exposure studies. There is no reasonable basis to discount the long

- term mean concentrations of the short

- term exposure studies for purposes of setting the level of the annual standard. Thus, the commenter is incorrect in asserting that the long

- term exposure studies, not the short

- term exposure studies, would be central in the Administrator’s decision on the level of the annual standard. The standard is ultimately intended to protect no t just against the single type of effect that contributes the most to quantitative estimates of risk to public health, but rather to the broad array of effects, including mortality and morbidity effects from long

- and short

- term exposures across the 88 As noted above, the EPA is not placing weight on the reported long

- term mean concentrations from the Miller et al. (2007) study for the purpose of tr anslating the information from the long

- term mortality studies into a basis for selecting the level of the annual PM 2.5 standard.***E.O. 12866 Review

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Page 192 of 253 range of at

- risk populations impacted by PM 2.5 - related effects. (3) With regard to the EPA’s analysis of distribution s of underlying population

level data (i.e., health event and study population data) and corresponding air quality data from each study area in certain key multi

- city epidemiological studies (Rajan et al., 2011), some commenters in this group raised a number of issues related to this analysis
. (API, 2012, Attachment 1 pp. 5 to 6; McClennan, 2012, p p.2 to 4 )
. Some commenters noted the limited numbe r of studies for which health event and study population data were available, and questioned whether these distributions would apply to other studies. Commenters expressed concerns that this analysis had not been formally reviewed by CASAC and was not publ ished in the peer

- review literature. Based on such concerns, some commenters asserted that the EPA should not consider this information as a basis for selecting a standard level. As an initial matter, as discussed in section III.E.4.b above, the EPA agrees with CASAC’s advice that it is appropriate to consider additional data beyond the mean PM 2.5 concentrations in key multi

- city studies to help inform selection of the level of the annual PM 2.5 standard. As both the EPA and CASAC recognize, in the absence o f a discernible threshold, health effects may occur over the full range of concentrations observed in the epidemiological studies , . Nonetheless , the EPA recognizes that confidence in the magnitude and there significance of an association is a high degree of confidence that the observed effects are associated with concentrations that extend below highest at and around the long

- term mean PM 2.5 concentrations reported in the studies and the degree of confidence becomes lower at lower concentrations within any gi ven study . Following CASAC’s advice (Samet, 2010d, p.2), the EPA used additional population

- level and air***E.O. 12866 Review

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Page 193 of 253 quality data made available by study authors to conduct an analysis of the distributions of such data, to help provide information on inform considerat ion of how the degree of confidence in the magnitude and significance of observed associations varies across the range of long

- term mean PM 2.5 concentrations in study areas within key multi

- city epidemiological studies. In the EPA’s view, such consideration is important in selecting a level for an annual standard that will protect public health with an adequate margin of safety. With regard to the number of multi

- city studies for which an analysis of the distributions of population

- level data ac ross the study areas and the corresponding annual mean PM 2.5 concentrations was done, the EPA noted at proposal that data for such an analysis were made available from study authors for four studies, including two long

term exposure studies and two short

- t erm exposure studies. 89 The EPA recognized that access to health event data can be restricted due to confidentiality issues, such that it is not reasonable to expect that such information could be made available from all studies. In considering the informat ion from these four studies, the EPA has further taken into consideration uncertainties discussed in response to the above comment related to the appropriate exposure period for long

- term exposure studies. Based on these considerations, as noted above, the EPA concludes that such uncertainties are an important factor in evaluating the usefulness of the air quality information from the two long

- term exposure studies in this analysis (Krewski et al., 2009; Miller et al., 2007) and that it would not be appropr iate to place weight on the distributional analysis of health

89 Health event data and study population data were available from two short

- term exposure studies (Bell et al. 2008; Zanobett i and Schwartz, 2009) and one long

- term exposure study (Krewski et al., 2009). Only study population data were available from another long

- term exposure study (Miller et al., 2007).***E.O. 12866 Review

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Page 194 of 253 event and air quality data from these two studies specifically for the purpose of translating the information from the long

- term mortality studies into a basis for selecting the level of the ann ual PM 2.5 standard. Such uncertainties are not relevant to the short

term exposure studies, and thus, the Agency focuses on the two short

- term exposure studies in this analysis (Bell et al., 2008; Zanobetti and Schwartz, (2009). In focusing on these two sh ort
- term exposure studies, the EPA first notes that these studies are key multi

- city studies that reported positive and statistically significant associations between mortality and cardiovascular

- related hospital admissions across a large number of areas t

hroughout the U.S. (112 U.S. cities in Zanobetti and Schwartz, 2009; 202 U.S. counties in Bell et al., 2008) using relatively recent air quality and health event data (i.e., 1999 through 2005 in both studies). The EPA considers this to be a modest but impo rtant data set to use for this distributional analysis to help inform consideration of how much below the long

- term mean PM 2.5 concentrations in key multi

city long

- and short

- term exposure studies the annual PM 2.5 standard level should be set. While the E PA acknowledges that having such data available from more studies would have been useful, the Agency finds the information from this limited set of studies to be an important consideration in selecting an annual standard level, consistent with CASAC advice to consider such information. The results of this distributional analysis are shown below in Figure 5 (adapted from Figure 3 in Rajan et al., 2011). For each study, this figure shows the cumulative frequency of the number of health events in each study ar ea and the corresponding long

term mean PM 2.5 concentrations in each area. Consistent with CASAC advice (Samet, 2010d, p.2), such an analysis helps to inform the EPA’s understanding of the long

- term***E.O. 12866 Review

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Page 195 of 253 mean PM 2.5 concentrations that were most influential in g enerating the health effect estimates in individual studies. In particular, the EPA recognizes that there is significantly greater confidence in the magnitude and significance of observed associations in that part of the air quality distribution correspond ing to where the bulk of the health events evaluated in each study have been observed. With regard to the part of the distribution in which confidence in the magnitude and significance of associations observed may become appreciably lower In considering t he results of this distributional analysis , as discussed more fully in the Response to Comments document , the EPA considers PM 2.5 concentrations between the 25 th and 10 th percentiles of the distribution of health events to be a reasonable range for providing a general frame of reference for that part of the distribution in which confidence may become in the magnitude and significance of the association may be appreciably lower . As highlighted in Figure 5, than confidence at and around the long

- ter m mean PM 2.5 concentrations corresponding with study areas contributing to the 25 th and 10 th percentiles of the distribution of deaths and cardiovascular

- related hospitalizations in concentration
. For the two short

- term exposure studies included in this analysis, the EPA notes that the PM 2.5 concentrations corresponding to the 25 th percentiles of the distributions of health events were 12.5 μg/m 3 and 10.3 11.5 μg/m 3 , respectively, for Zanobetti and Schwartz (2009 ), ) and 11.5 μg/m 3 and 9.8 μg/m 3 , respectively, for Bell et al. (2008 ) . The EPA also ) , with the 10 th percentiles being lower by approximately 2 μg/m 3 in each study (Rajan et al., 2011, Table 1)
. In considering this information, t he EPA recognizes, however, that there is no clear dividing line or single percentile within a given distribution (including both above and below the 25 th percentile ) provided by the scientific evidence that is most appropriate or***E.O. 12866 Review

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Page 196 of 253 ‘correct’ to use to characterize where the degree of confidence in the associations warrants setting the annual standard level. The decision as to the appropriate standard level below the long

- term mean concentrations of the key studies is largely a public health policy judgment to be made by the Administrator, taking into account all of the evidence and its related uncertainties, as discussed in section III.E.4.d below.

In response to concerns that this analysis was not reviewed by CASAC nor Formatted: Font: 12 pt***E.O. 12866 Review

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Page 197 of 253 published in the peer

- reviewed literature, the EPA notes that this analysis was conducted to directly respond to advice from CASA C , as discussed in section III.E.4.b.1 above, in conjunction with their review of the Policy Assessment. The EPA notes that the same type of distributional analysis was presented in the second draft Policy Assessment bas ed on air quality data, as well as population

- weighted air quality data, rather than health event or study population data. In considering that distributional information, CASAC urged that the EPA redo the analysis using health event or study population da ta, which is exactly what the EPA did and presented in the final Policy Assessment. The EPA provided CASAC with the final Policy Assessment and communicated how the final staff conclusions reflected consideration of its advice and that those staff conclusi ons were based in part on the specific distributional analysis that CASAC had urged the EPA to conduct (Wegman, 2011, Attachment p. 2). CASAC did not choose to provide any additional comments or advice after receiving the final Policy Assessment. The EPA
c onsiders this distributional analysis to be the product of the peer review conducted by CASAC of the Policy Assessment, and thus does not agree with commenters’ characterization that the analysis lacked appropriate peer review. The EPA’s final analysis was based on the comments provided by CASAC, the pe e r review committee established pursuant to the CAA , on the draft analysis, such that the final analysis stems directly from CASAC’s advice and the EPA’s response to its comments. Based on the above considera tions, the EPA continues to conclude that its analysis of distributions of health event and air quality data from two key multi

- city epidemiological studies provides important information related to understanding the associations between health events obse rved in each city (e.g., deaths, hospitalizations)***E.O. 12866 Review

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Page 198 of 253 and the corresponding long

- term mean PM 2.5 concentrations observed in the studies. While recognizing that this is a relatively modest data set, the EPA further concludes that such information can appropria tely help to inform the selection of the level of an annual standard that will protect public health with an adequate margin of safety from these types of health effects which are causally related to long

- and short

- term exposures to PM 2.5 . (4) Some commen ters in this group asserted there were limitations in the long

term exposure studies of morbidity, including studies evaluating respiratory effects in children. For example, one commenter (UARG, 2012, p. 12, Attachment 1, pp. 14 to 16) asserted there were serious limitations in the long

- term exposure studies of respiratory morbidity in each of the studies considered by the EPA (including McConnell et al., 2003; Gauderman et al., 2004; Dockery et al., 1996; Raizenne et al., 1996; and Goss et al., 2004) and a

rgued that this evidence provides only a “weak association” with PM 2.5 exposures. This commenter asserted that many of these long

- term exposure studies evaluating respiratory effects were considered at the time the EPA reaffirmed the current annual standard level of 15 μg/m 3 in 2006, that the Administrator in the last review determined that the information they provided “was too limited to serve as the basis for setting a level of a national standard,” and that they should be given little weight in
s etting the level of the annual standard in this review (UARG, 2012, Attachment 1, p. 14). More specifically, this commenter asserted that the McConnell et al. (2003) and Gauderman et al. (2004) stud ies reported mixed results for associations with PM 2.5 an d stronger associations with NO 2 (API, 2012, Attachment 1, pp. 14 to 15). Similarly, this***E.O. 12866 Review

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Page 199 of 253 commenter argued that the Dockery et al. (1 996) and Raizenne et al. (1996) studies show ed stronger associations with acidity than with fine particles (measured as PM 2 .1 ). Id. pp. 15 to 16. With regard to the cystic fibrosis study, this commenter noted that the association between pulmonary exacerbations and PM 2.5 in this study was no longer statistically significant when the model adjusted for each individual’s baseli ne lung function. The commenters referred to the data on lung function as an “important explanatory variable,” and suggested that the EPA should rely on results from the model that included individual baseline lung function information. Id . p. 16. For the reasons discussed below and in more detail in the Response to Comments document, t he EPA disagrees with the commenters’ interpretation of these studies
. As an initial matter, the EPA notes that three of these studies (McConnell et al., 2003; Dockery et al ., 1996; Raizenne et al., 1996) as well as the initial studies from the Southern California Children’s Health Study ( Peters et al., 1999; McConnell et al., 1999’ Gauderman et al., 2000, 2002 ; Avol et al., 2001 ) were discussed and considered in the 2004 Air Quality Criteria Document ( U.S. EPA, 2004) and , thus, considered within the air quality criteria supporting the EPA’s final decisions in the review completed in 2006. Two additional studies (Gauderman et al., 2004; Goss et al., 2004) were discussed and
co nsidered in the provisional science assessment conducted for the last review ( U.S. EPA, 2006a). The EPA concluded that “new” studies considered in the provisional assessment completed in 2006 did not materially change any of the broad scientific conclusion s regarding the health effects of PM exposure made in the Criteria Document (71 FR 61148 to 61149, October 17, 2006). All of these studies were considered in the Integrated Science Assessment that informs the current review ( U.S. EPA, 2009a).***E.O. 12866 Review

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Page 200 of 253 With regard to the Southern California Children’s Health Study, extended analyses considered in the Integrated Science Assessment provided evidence that clinically important deficits in lung function 90 associated with long

- term exposure to PM 2.5 persist into early adulthood (U.S. EPA, 2009a, p. 7

- 27; Gauderman et al., 2004). These effects remained positive in copollutant models. 91 Additional analyses of the Southern California Children’s Health Study cohort reported an association between long

- ter m PM 2.5 exposure and bronchitic symptoms ( U.S. EPA, 2009a, p. 7

- 23 to 7

- 24; McConnell et al., 2003, long

- term mean concentration of 13.8 μg/m 3 ) that remained positive in co

- pollutant models, with the PM 2.5 effect estimates increasing in magnitude in some m odels and decreasing in others, and a strong modifying effect of PM 2.5 on the association between lung function and asthma incidence ( U.S. EPA, 2009 a , 7

- 24; Islam et al., 2007). T he outcomes observed in the more recent reports from the Southern California Children’s Health Study, including evaluation of a broader range of endpoints and longer follow

- up periods, were larger in magnitude and more precise than reported in the initial version of the study . Supporting these results were new longitudinal cohort
s tudies conducted by other researchers in varying locations using different methods ( U.S. EPA, 2009a, section 7.3.9.1). The EPA, therefore, disagrees with the commenters that the studies by McConnell et al. (2003) and Gauderman et al. (2004) are flawed and should

90 Clinical significance was defined as an FEV 1 below 80 percent of the pre dicted value, a criterion commonly used in clinical settings to identify persons at increased risk for adverse respiratory conditions (U.S. EPA, 2009a, p. 7

- 29 to 7

- 30). The primary NAAQS for sulfur dioxide (SO 2 ) also included this interpretation for FEV 1 (75 FR 35525, June 22, 2010). 91 Gauderman et al. (2004) clearly stated throughout their analysis that NO 2 was one component of a highly correlated mixture that contains PM 2.5 . Gauderman et al. (2004) did not present the results from copollutants models but stated “two

- pollutant models for any pair of pollutants did not provide a significantly better fit to the data than the corresponding single

- pollutant models.”***E.O. 12866 Review

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Page 201 of 253 not be used in the PM NAAQS review process. The 24

- City study 92 by Dockery et al. (1996) (long

- term mean concentration of 14.5 μg/m 3 ) was considered in the current as well as two previous reviews ( U.S. EPA, 2009a; U.S. EPA, 2004; U.S. EPA, 1996). Thi s study observed that PM, specifically “particle strong acidity” and sulfate particles (indicators of fine particles), were associated with reports of bronchitis in the previous year. Similarly, the magnitude of the associations between bronchitis and PM 10 and PM 2.1 were similar to those for acidi c aerosols and sulfate particles, though the confidence intervals for the PM 10 and PM 2.1 associations were slightly wider and the associations were not statistically significant. Acid aerosols , sulfate, and fine pa rticles are formed in secondary reactions of the emissions from incomplete combustion and these pollutants have similar regional and temporal distributions . As noted by the study authors, “the strong correlations of several pollutants in this study, especi ally particle strong acidity with sulfate (r=0.90) and PM 2.1 (r=0.82), make it difficult to di stinguish the agent of interest ” (Dockery et al., 1996, p. 505). Overall, Dockery et al. (1996) (and, similarly, Raizenne et al., 1996) observed similar associati ons between respiratory health effects and acid aerosols , sulfate, PM 10 and PM 2.1 concentrations. The commenters noted that the associations with particle acidity were sensitive to the inclusion of the six Canadian sites. The EPA notes that none of these Canadian cities were in the “sulfate belt” where particle strong acidity was highe st. Thus, the change in the effect estimate when the six Canadian cities were excluded from the analysis is likely due to the lower prevalence of bronchitis and the lower concentrations of acid aerosols in these cities, and not due to some difference in 92 The 24

- City study conducted by Dockery et al. (1996) included 18 sites in the U.S. and 6 site s in Canada. The Raizenne et al. (1996) study considered 22 of these 24 study areas. Athens, OH and South Brunswick, NJ were not included in this study.***E.O. 12866 Review

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Page 202 of 253 su sceptibility to bronchitis between the U.S. and Canadian populations that is not due to air pollution, as suggested by the commenters (UARG, 2012, Attachment 1, p. 15). In fact, contrary to the statements made by the commenters, the authors did not observe any subgroups that appeared to be markedly more susceptible to the risk of bronchitis. The Goss et al. (2004) study considered a U.S. cohort of cystic fibrosis patients and provided evidence of association between long

- term PM 2.5 exposures and exacerbati ons of respiratory symptoms resulting in hospital admissions or use of home intravenous antibiotics ( U.S. EPA, 2009a, p. 7

- 25; long

- term mean concentration of 13.7 μg/m 3 ). The commenters noted that the association between pulmonary exacerbations and PM 2.5 in this study was no longer statistically significant when the model adjusted for each individual’s baseline lung function. The commenters referred to the data on lung function as an “important explanatory variable,” and suggested that the EPA should rely on results from the model that included individual baseline lung function information. The EPA disagrees with the commenters’ interpretation of this study. The Agency concludes it is unlikely that lung function is a potential confounder or an important exp lanatory variable in this study. In fact, the authors noted that “it is more likely that lung function decline may be intimately associated with chronic exposure to air pollutants and may be part of the causal pathway in worsening prognosis in CF [cystic f ibrosis]; in support of this explanation, we found both cross

- sectional and longitudinal strong inverse relationships between FEV 1 and PM levels” (Goss et al., 2004, p. 819). The EPA notes that adjusting for a variable that is on the causal pathway can lea d to overadjustment bias, which is likely to attenuate the association (Schisterman et al. 2009); this is likely what was observed by the authors. Thus, the EPA continues to believe it is appropriate to focus***E.O. 12866 Review

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Page 203 of 253 on the results reported in Goss et al. (2004) t hat did not include individual baseline lung function in the model. In addition, the EPA disagrees with commenters’ reliance solely on statistical significance when interpreting the study results from individual study results and the collective evidence ac ross studies. As discussed in section III.D.2 above, statistical significance of individual study findings has played an important role in the EPA’s evaluation of the study’s results and the EPA has placed greater emphasis on studies reporting statisticall y significant results. However, in the broader evaluation of the evidence from many epidemiological studies, and subsequently during the process of forming causality determinations in the Integrated Science Assessment by integrating evidence from across ep idemiological, controlled human exposure, and toxicological studies, the EPA has emphasized the pattern of results across epidemiological studies and whether the effects observed were coherent across the scientific disciplines for drawing conclusions on th e relationship between PM 2.5 and different health outcomes. As noted in section III.B.1.a of the proposal, with regard to respiratory effects, the Integrated Science Assessment concluded that extended analyses of studies available in the last review as we ll as new epidemiological studies conducted in the U.S. and abroad provided stronger evidence of respiratory

- related morbidity associated with long

- term PM 2.5 exposure (77 FR 38918). The strongest evidence for respiratory

- related effects available in this review was from epidemiological studies that evaluated decrements in lung function growth in children and increased respiratory symptoms and disease***E.O. 12866 Review

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Page 204 of 253 incidence in adults (U.S. EPA, 2009a, sections 2.3.1.2, 7.3.1.1, and 7.3.2.1). 93 In considering the collecti ve evidence from epidemiological, toxicological, and controlled human exposure studies, including the studies discussed above, the EPA recognizes that the Integrated Science Assessment concluded that a causal relationship is likely to exist between long

- te rm PM 2.5 exposures and respiratory effects ( U.S. EPA, 2009a, p. 2

- 12, pp. 7

- 42 to 7

- 43). CASAC concurred with this causality determination (Samet, 2009f, p.9). The commenter’s assertion that the EPA should adhere to its assessment of these studies as it di d in the review completed in 2006 is significantly mistaken. Most obviously, the EPA’s final decision in the last review was held to be deficient by the D.C. Circuit in remanding the 2006 primary annual PM 2.5 standard. As discussed in section III.A.2 above , the D.C. Circuit specifically held that the EPA did not provide a reasonable explanation of why certain morbidity studies, including an earlier study from the Southern California Children’s Health Study (Gauderman et al., 2000 , long

- term mean PM 2.5 conce ntration approximately 15 μg/m 3 ) and the 24

- Cities Study (Raizenne et al., 1996 , long

- term mean concentrations approximately 14.5 μg/m 3 ) did not warrant a more stringent annual PM 2.5 standard when the long

- term mean PM 2.5 concentrations reported in those studies were at or lower than the level of the annual standard. American Farm Bureau Federation v. EPA . 559 F. 3d at 525. Indeed, the court found that, viewed together, the Gauderman et al. (2000) and Raizenne et al., (1996) studies “are related and together indicate a significant public health risk...On this record, therefore, it appears the EPA too hastily discounted the Gauderman and 24

- Cities studies as lacking in 93 Supporting evidence comes from studies “that observed associations between long

term exposure to PM 10 and an increase in respiratory symptoms and reductions in lung function growth in areas where PM 10 is dominated by PM 2.5 ” ( U.S. EPA, 2009a, p. 2

- 12)
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Page 205 of 253 significance.” Id. In this review, the EPA recognizes a significant amou nt of evidence beyond these two studies that expands our understanding of respiratory effects associated with long

term PM 2.5 exposures. This body of scientific evidence includes an extended and new analyses from the Southern California Children’s Health S tudy (Gauderman et al., 2004; Islam et al., 2007; Stanojevic et al., 2008) as well as additional studies that examined these health effects (Kim et al., 2004; Goss et al., 2004). Thus, even more so than in the last review, the evidence indicates a “signifi cant public health risk” to children from long

- term PM 2.5 exposures at concentrations below the level of the current annual standard. A standard that does not reflect appropriate consideration of this evidence would not be requisite to protect public healt h with an adequate margin of safety. (5) With regard to the use of studies of health effects for which the EPA finds the evidence to be “suggestive” of a causal relationship, some commenters argued that such studies “do not merit any weight in the setting of the annual NAAQS” (e.g., UARG, 2012, Appendix 1, p. 3). The EPA disagrees with the commenter’s view that studies of health effects for which the evidence is suggestive of a causal relationship, rather than studies of health effects for which the evidenc e supports a causal or likely causal relationship, merit no weight at all in setting the NAAQS. To place no weight at all on such evidence would in essence treat such evidence as though it had been categorized as “not likely to be a causal relationship.” T o do so would ignore the important distinctions in the nature of the evidence supporting these different causality determinations in the Integrated Science Assessment. It would also ignore the CAA requirement that primary standards are to be***E.O. 12866 Review

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Page 206 of 253 set to provide protection with an adequate margin of safety, including providing protection for at

- risk populations. Thus, ignoring this information in making decisions on the appropriate standard level would not be appropriate. 94 Nonetheless, in considering studies of h ealth effects for which the evidence is suggestive of a causal relationship, the EPA does believe that it is appropriate to place less weight on such studies than on studies of health effects for which there is evidence of a causal or likely causal relatio nship. A second group of commenters supported revising the suite of primary PM 2.5 standards to provide increased public health protection. These commenters found the available scientific information and technical analyses to be stronger and more compelling than in the last review. These commenters generally placed substantial weight on CASAC advice and on the EPA staff analyses presented in the final Policy Assessment, which concluded that the evidence most strongly supported an annual standard level within a range of 11 to 12 μg/m 3 ( U.S. EPA, 2011a, p. 2

- 206). While some of these commenters felt that the level should be set within the proposed range (12 to 13 μg/m 3 ), most of these commenters advocated a level of 11 μg/m 3

. 95 For example, ALA et al., asserted: The EPA’s proposed PM 2.5 standards, while a step in the right direction are insufficient to protect public health, including the health of susceptible populations, with an adequate margin of safety as required by the Clean Air Act...we will discuss the en ormous gap in public health protection afforded by an 94 As discussed in section II.A above, the requirement that primary standards provide an adequate margi n of safety was intended to address uncertainties associated with inconclusive scientific and technical information available at the time of standard setting. I was also intended to provide a reasonable degree of protection against hazards that research ha s not yet identified. This certainly encompasses consideration of effects for which there is evidence suggestive of a causal relationship. 95 As discussed in section III.E.4.c.ii, many of these commenters also supported lowering the level of the primary 24

- hour PM 2.5 standard.***E.O. 12866 Review

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Page 207 of 253 annual standard of 13 μg/m 3 , at the upper end of the proposed range, compared to the more protective 11 μg/m 3 , as advocated by our organizations (ALA et al., 2012, p. 6). In general, these commenters e xpressed the view that given the strength of the available scientific evidence, the serious nature of the health effects associated with PM 2.5 exposures, the large size of the at

- risk populations, the risks associated with long

- and short

- term PM 2.5 exposu res, and the important uncertainties inherently present in the evidence, the EPA should follow a highly precautionary policy response by selecting an annual standard level that incorporates a large margin of safety. More specifically, these commenters off ered a range of comments related to the general approach used by the EPA to select standard levels, including: (1) the EPA’s approach for setting a generally controlling annual standard; (2) the importance of the greatly expanded and stronger overall scien tific data base; (3) consideration of the distributional statistical analysis conducted by the EPA and other approaches for translating the air quality information from specific epidemiological studies into standard levels; and (4) the significance of the PM 2.5 - related public health impacts, especially potential impacts on at

- risk populations, including children, in reaching judgments on setting standards that provide protection with an adequate margin of safety. These comments are discussed in turn below. (1) Some of these commenters disagreed with the EPA’s approach for setting a “generally controlling” annual standard in conjunction with a 24

- hour standard providing supplemental protection particularly for areas with high peak

- to
- mean ratios. These
commen ters argued this approach would lead to “regional inequities” as demonstrated in the EPA’s analyses contained in Appendix C of the Policy Assessment (ALA et al., pp. 26 to 27). Specifically, these commenters argued:***E.O. 12866 Review

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Page 208 of 253 There is no basis in the Clean Air Act f or such a determination. The Clean Air Act requires only that the NAAQS achieve public health protection with an adequate margin of safety. It is well

- documented that both long

- and short

- term exposures to PM 2.5 have serious and sometimes irreversible heal th impacts. There is no health protection reason to argue tha t one standard should be “controlling” as a matter of policy without regard to the health consequences of such a policy. To adopt such a policy ignores the obligation to provide equal protection under the law to all Americans because it would result in uneven protection from air pollution in different localities and regions of the country (ALA et al., 2012, p. 26). The EPA believes these commenters misunderstood the basis for the EPA’s policy goal of setting a “generally controlling” annual standard. This approach relates exclusively to setting standards that will provide requisite protection against effects associated with both long

- and short

- term PM 2.5 exposures. It does so by lowering the
overa ll air quality distributions across an area, recognizing that changes in PM 2.5 air quality designed to meet an annual standard would likely result not only in lower annual mean PM 2.5 concentrations but also in fewer and lower peak 24

- hour PM 2.5 concentrati ons. As discussed in section III.A.3 in the proposal and above, the EPA recognizes that there are various ways to combine the two primary PM 2.5 standards to achieve an appropriate degree of public health protection. Furthermore, the extent to which these t wo standards are interrelated in any given area depends in large part on the relative levels of the standards, the peak

- to
- mean ratios that characterize air quality patterns in an area, and whether changes in air quality designed to meet a given suite of
s tandards are likely to be of a more regional or more localized nature. In focusing on a

n approach of setting a generally controlling annual standard, the EPA’s intent is in fact to avoid the potential “regional inequities” that are of concern to the commenters. The EPA judges that the most appropriate way to set standards that provide more consistent public health protection is by using the approach of setting a***E.O. 12866 Review

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Page 209 of 253 generally controlling annual standard. This judgment builds upon information presented in the Policy Assessment as discussed in section III.A.3 above. More specifically, the Policy Assessment recognized that the short

- term exposure studies primarily evaluated daily variations in health effects with monitor(s) that measured the variation in dail y PM 2.5 concentrations over the course of several years. The strength of the associations observed in these epidemiological studies was demonstrably in the numerous “typical” days within the air quality distribution, not in the peak days ( U.S. EPA, 2011a, p. 2

- 9). In addition, the quantitative risk assessments conducted for this and previous reviews demonstrated the same point, that is, much, if not most , of the aggregate risk associated with short

- term PM 2.5 exposures results from the large number of days during which the 24

- hour average concentrations are in the low

- to mid

- range, below the peak 24

- hour concentrations ( U.S. EPA, 2011a, section 2.2.2; U.S. EPA, 2010a, section 3.1.2.2). In addition, there was no evidence suggesting that risks associated with long

- term exposures were likely to be disproportionately driven by peak 24

- hour concentrations. 96 For these reasons, the Policy Assessment concluded that strategies that focused primarily on reducing peak days were less likely to achieve reductions in the PM 2.5 concentrations that were most strongly associated with the observed health effects. Furthermore, the Policy Assessment concluded that a n approach that focused on reducing peak exposures would most likely result in more uneven public health protection across the U.S. by either providing inadequate protection in some areas or overprotecting in other areas ( U.S. EPA, 2011a, p. 2

- 9; U.S. EPA, 2010a, section 5.2.3). This is because

96 In confirmation, a number of studies have presented analyses excluding higher PM concentration days and reported a limited effect on the magnitude of the effect estimates or statistical significance of the association (e.g., Dominici , 2006b; Schwartz et al., 1996; Pope and Dockery, 1992).***E.O. 12866 Review

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Page 210 of 253 reductions based on control of peak days are less likely to control the bul k of the air quality distribution. As a result, the EPA believes a n approach that focuses on a generally controlling annual standard would likely reduce aggregate risks associated with both long

- and short

term exposures more consistently than a generally controlling 24

- hour standard and, therefore, would be the most effective and efficient way to reduce total PM 2

- 5 - related population risk. The CASAC agreed with this approach and considered it was “appropriate to return to the strategy used in 1997 that co nsiders the annual and the short

term standards together, with the annual standard as the controlling standard, and the short

- term standard supplementing the protection afforded by the annual standard” (Samet, 2010d, p. 1). For the reasons discussed above, the EPA disagrees with the comments that this approach will result in the concerns raised by the commenters; rather the EPA concludes that this approach will help to address these concerns. (2) Many of these commenters asserted that the currently availabl e scientific information is greatly expanded and stronger compared to the last review. Some of these commenters highlighted the availability of multiple, multi

- city long

- and short

- term exposure studies providing “repeated, consistent evidence of effects b elow the current annual standard level” (ALA et al., 2012, pp. 39 to 49) and, more specifically, “significant evidence of harm with strong confidence well below EPA’s proposed annual standard range of 12

- 13 μg/m 3 ” (AHA et al., 2012, pp. 10 to 12). The EPA recognizes that in setting standards that are requisite to protect public health with an adequate margin of safety, the Administrator must weigh the various types of available scientific information in reaching public health policy judgments that neither***E.O. 12866 Review

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Page 211 of 253 overstate nor understate the strength and limitations of this information or the appropriate inferences to be drawn from the available science. In general, the EPA agrees with these commenters’ views that the currently available scientific evidence is str onger “because of its breadth and the substantiation of previously observed health effects” (77 FR 38906/2) and provides “greater confidence in the reported associations than in the last review” (77 FR 38940/1). The EPA also agrees with the commenters’ pos ition that it is appropriate to consider the regions within the broader air quality distributions where we have the strongest confidence in the associations reported in epidemiological studies in setting the level of the annual standard. However, as discussed in section III.E.4.d below, in weigh ing the available evidence and technical analyses, as well as the associated uncertainties and limitations in that information, the EPA disagrees with the commenters’ views regarding the extent to which the available scientific information provides support for considering an annual standard level below the proposed range (i.e., below 12 to 13 μg/m 3 ). In particular, the EPA disagrees with the degree to which these commenters place more weight on the relatively more uncertain evidence that is suggestive of a causal relationship (e.g., low birth weight). Consistent with CASAC advice (Samet, 2010d, p. 1), the Agency concludes it is appropriate and reasonable to place the greatest emphasis on health effects for which the Integrated Science Assessment concluded th ere is evidence of a causal or likely causal relationship and to place less weight on the health effects that provide evidence that is only suggestive of a causal relationship.
. (3) With regard to us ing the air quality information from epidemiological stu dies to inform decisions on standard levels, commenters in this group generally supported the***E.O. 12866 Review

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Page 212 of 253 EPA’s efforts to explore different statistical metrics from epidemiological studies to inform the Administrator’s decisions. These commenters argued that by consi dering different analytic measures

-- either concentrations one standard deviation below the long

- term means reported in the epidemiological studies or the EPA’s d istributional statistical analysis of population

- level data that extends the approach used in previous PM NAAQS reviews to consider information beyond a single statistical metric

-- “the annual standard must be significantly lower than EPA has proposed” (ALA et al., 2012, pp. 50 to 61). Furthermore, with regard to characterizing the PM 2.5 air qual ity at which associations have been observed, some of these commenters highlighted CASAC’s recommendation that “[f]urther consideration should be given to using the 10 th percentile as a level for assessing various scenarios of levels for the PM NAAQS” (Sam et, 2010c, p. 11) (ALA et al., 2012, p. 55). Other commenters urged that the EPA extend the distributional analysis to include additional studies. For example, CHPAC urged the EPA to also conduct distributional analysis for children’s health studies to bet ter inform standards that would protect both children and adults from adverse health outcomes (CHPAC, 2012, p. 3) The EPA agrees with these commenters’ views that it is appropriate to take into account different statistical metrics from epidemiological stu dies to inform the decisions on standard levels that are appropriate to consider
. in setting a standard that will protect public health with an adequate margin of safety
. In the development of the Policy Assessment, the EPA staff explored various approache s for us ing information from epidemiological studies in setting the standards. The general approach used in the final Policy Assessment, discussed in sections III.A.3 and III.E.4.a above, reflects consideration of CASAC advice (Samet, 2010c, d) and public comments on multiple***E.O. 12866 Review

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Page 213 of 253 drafts of the Policy Assessment
. With regard to using the distributional statistical analysis to characterize the confidence in the associations , the EPA emphasizes that there is no clear dividing line provided by the scientific eviden ce, and that choosing how far below the long

- term mean concentrations from the epidemiological studies is appropriate to identify a standard level that will provide protection for the public health with an adequate margin of safety is largely a public heal th policy judgment. The EPA considers the region from approximately the 25 th to 10 th percentiles to be a reasonable range for providing a general frame of reference as to the part of the distribution over which our confidence in the magnitude and significa

nce of the associations observed in epidemiological studies becomes is appreciably lower. However Based on these considerations, t he EPA concludes that it is not appropriate to place as much confidence in the magnitude and significance of the assoc i ation s over the lower percentiles of the distributions in each study as at and around the long

- term mean concentrations. Thus , the EPA disagrees with the commenters’ views that the available information this analysis compels placing more emphasis on the lower part of this range in selecting a level for an annual standard that will protect public health with an adequate margin of safety
. The EPA recognizes that this information comes primarily from two short

- term exposure studies, a relatively modest data set. In li ght of the limited nature of this information, and in recognition of more general uncertainties inherent in the epidemiological evidence, the Administrator deems it reasonable not to place more emphasis on concentrations in the lower part of this range, as discussed below in section III.E.4.d. With regard to the scope of the distributional statistical analysis, the EPA***E.O. 12866 Review

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Page 214 of 253 requested additional population

- level data from the study authors for a group of six multi

city studies for which previous air quality analy ses had been conducted (Hassett

- Sipple et al., 2010; Schmidt et al., 2010, Analysis 2). These six studies were originally selected because they considered multiple locations representing varying geographic regions across multiple years. Thus, these studies provided evidence on the influence of different particle mixtures on health effects associated with long

- and short

- term PM 2.5 exposures. In addition, these multi

- city studies considered relatively more recent health events and air quality conditions (199 9 to 2005). As discussed in section III.E.4.b.i above, the EPA received and analyzed population

- level data for four of the six studies (Rajan et al., 2011). T hree of these four studies (Krewski et al., 2009; Bell et al., 2008; Zanobetti and Schwartz, 2009) served as the basis for the concentration

- response functions used to develop the core risk estimates ( U.S. EPA, 2010a, section 3.3.3). While, the EPA agrees that it would be useful to have such data from more studies, the Agency believes that the addition al data that was requested and received from study authors provide useful information to help inform the Administrator’s selection of the annual standard level. (4) Many commenters in this group highlighted PM 2.5 - related impacts on at

- risk populations, in cluding potential impacts on children, older adults, persons with pre

existing heart and lung disease, and low

- income populations, to support their views that the annual standard should be revised to a level of 11 μg/m 3 or lower (CHPAC, 2012; AHA et al., 2 012; ALA, 2012, pp. 29 to 38; Rom et al., 2012; Air Alliance Houston, et al, 2012). These commenters urged the EPA to adopt a policy approach that placed less weight on the remaining uncertainties and limitations in the evidence and placed more emphasis on margin of safety considerations, including providing protection against***E.O. 12866 Review

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Page 215 of 253 effects for which there is more limited scientific evidence. For example, CHPAC urged the EPA “to place the same weight on studies examining impacts on children’s health as that of ad ult studies. ... The fact that there may be stronger evidence from adult studies does not mean that standards based on adult studies will be protective for children and consequently will meet the standard requisite to protect public health with an adequate
m argin of safety” (CHPAC, 2012 p. 3). Furthermore, with regard to the EPA’s approach for weighing uncertainties, some of these commenters stated that “we find no justification in the preamble for an annual standard level as high as 13 μg/m 3 , other than the vague assertion that uncertainties increase at lower concentrations. Further, the final proposal completely failed to address the Policy Assessment recommendations that if 13 μg/m 3 was proposed, the 24

- hour standard should be strengthened as well” (ALA et al., p. 7). The EPA has carefully evaluated and considered evidence of effects in at

- risk populations. With regard to effects classified as having evidence of a causal or likely causal relationship with long

- or short

- term PM 2.5 exposures (i.e., premature mortality, cardiovascular effects, and respiratory effects), the Agency takes note that it considered the full range of studies evaluating these effects, including studies of at

- risk populations, to inform its review of the primary PM 2.5 standards. Specifi c multi

- city studies summarized in Figures 1, 2, and 3 above highlight evidence of effects observed in two different lifestages

– children and older adults

– that have been identified as at

- risk populations. Thus, the EPA places as much weight on studies t hat explored effects in children for which the evidence is causal or likely causal in nature as on studies of such effects in adults, including older adults
. . As discussed above in responses to commenters supporting the retention of the current standards, in setting the standard, the EPA has***E.O. 12866 Review

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Page 216 of 253 focused on considering PM 2.5 concentrations somewhat below the lowest long

- term mean concentrations from each of the key studies of both long

- and short

- term exposures of effects for which the evidence supports a causal or likely causal relationship (i.e., the first two sets of studies shown in Figure 4). Absent some reason to ignore or discount these studies, which the commenter does not provide (and of which the EPA is unaware) , the EPA considers the available evidence of effects in children as well as other at

- risk populations. With respect to the EPA’s consideration of more limited studies providing evidence suggestive of a causal relationship (e.g., developmental and reproductive effects), as noted above in respondin g to comments from the first group of commenters, the Agency agrees that it is important to place some weight on this body of evidence in setting standards that provide protection for at

- risk populations, as required by the CAA. However, the Agency does no t agree that the same weight must be placed on this information as on the body of scientific information for which there is evidence of a causal or likely causal relationship. To do so would ignore the difference in the breadth and strength of the evidence supporting the different causality determinations reached in the Integrated Science Assessment. With regard to weighing the uncertainties and limitations remaining in the evidence and technical analyses, as discussed in section II.A above, the EPA recogn izes that in setting a primary NAAQS that provides an adequate margin of safety, the Administrator must consider a number of factors including the nature and severity of the health effects involved, the size of sensitive population(s) at risk, and the kind and degree of the uncertainties that remain. As discussed in section III.E.4.d below, the Agency***E.O. 12866 Review

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Page 217 of 253 agrees with these commenters that, in weighing the available evidence and technical analyses including the uncertainties and limitations in this scientific in formation, there is no justification for setting a primary PM 2.5 annual standard level as high as 13 μg/m 3

. Finally, some commenters in both groups also identified “new” studies that were not included in the Integrated Science Assessment as providing furth er support for their views on the level of the annual standard. As discussed in section II.B.3 above, the EPA completed a provisional review and assessment of “new” studies published since the close of the Integrated Science Assessment, including “new” stu dies submitted by commenters (U.S. EPA, 2012a). The provisional assessment found that the “new” studies expand the scientific information considered in the Integrated Science Assessment and provide important insights on the relationship between PM 2.5 expos ure and health effects of PM (U.S. EPA, 2012b) . However, the EPA notes that the provisional assessment found that the “new” science did not materially change the conclusions reached in the Integrated Science Assessment. The EPA notes that, as in past NAAQS reviews, the Agency is basing the final decisions in this review on the studies and related information included in the Integrated Science Assessment that have undergone CASAC and public review, and will consider newly published studies for purposes of de cision making in the next PM NAAQS review. ii. 24

- Hour Standard Level With respect to the level of the 24

- hour standard, the EPA received comments on the proposal from two distinct groups of commenters. One group that included virtually all commenters repr esenting industry associations , businesses , and many States agreed with the Agency’s proposed decision to retain the level of the 24

- hour PM 2.5 standard.***E.O. 12866 Review

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Page 218 of 253 The other group of commenters included many medical groups, numerous physicians and academic researche rs, many public health organizations, some State and local agencies, five State Attorneys General, and a large number of individual commenters. These commenters disagreed with the Agency’s proposed decision and argued that EPA should lower the level of the 24

- hour standard to 30 or 25 μg/m 3 . Comments from these groups
on the level of the 24

- hour PM 2.5 standard are a ddressed below and in the Response to Comments Document
. As noted above, o f the public commenters who addressed the level of the 24

- hour PM 2.5 standard, all industry commenters and most State and l ocal commenters supported the proposed decision to retain the current level of 35 g/m 3 . In many cases, these groups agreed with the rationale supporting the Administrator’s proposed decision to retain the current 24

- hour PM 2.5 standard, including her emphasis on the annual standard as the generally controlling standard with the 24

- hour standard providing supplementary protection, and her conclusion that multi

- city, short

- term exposure studies provide t he strongest data set for informing decisions on the appropriate 24

- hour standard level. Many of these commenters agreed with the Administrator’s view that the single

- city, short

- term studies provided a much more limited data set (e.g., limited statistical power, limited exposure data) and more equivocal results (e.g., mixed results within the same study area), making them an unsuitable basis for setting the level of the 24

- hour standard. While these commenters agreed with the EPA’s proposed decision to re tain the current 24

- hour PM 2.5 standard, some did not agree with the EPA’s approach to considering the evidence from short

- term multi

- city studies. For example, a commenter representing UARG pointed out that the 98 th percentile concentrations reported in t he***E.O. 12866 Review

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Page 219 of 253 proposal for multi

- city studies reflect the averages of 98 th percentile concentrations across the cities included in those studies (UARG, 2012; Attachment 1; p. 25). This commenter contended that such averaged 98 th percentile PM 2.5 concentrations do not provide information that can appropriately inform a decision on the adequacy of the public health protection provided by the current or alternative 24

- hour standards. While the EPA agrees that there is uncertainty in linking effects reported in multi

ci ty studies to specific air quality concentrations (U.S. EPA, 2011, section 2.3.4.1), the EPA disagrees with this commenter’s view that such uncertainty precludes the use of averaged 98 th percentile PM 2.5 concentrations to inform a decision on the appropria teness of the protection provided by the 24

- hour PM 2.5 standard. In particular, the EPA notes that averaged 98 th percentile concentrations do provide information on the extent to which study cities contributing to reported associations would likely have me t or violated the current 24

- hour PM 2.5 standard during the study period. As evidence of this, the EPA notes the three multi

- city studies specifically highlighted by this commenter as having averaged 98 th percentile 24

- hour PM 2.5 concentrations below 35 g/m 3 (Dominici et al., 2006; Bell et al., 2008; Zanobetti and Schwartz, 2009). Based on the 98 th percentiles of 24

- hour PM 2.5 concentrations in the individual cities evaluated in these studies, the EPA notes that the majority of these study cities would li kely have met the current standard during the study periods (Hassett

- Sipple et al., 2010). Therefore, regardless of whether the averaged 98 th percentile concentrations or the 98 th percentile concentrations in each city are considered, these studies provide evidence for associations between short

- term PM 2.5 and mortality or morbidity across a large number of U.S. cities, the majority of which would likely have met the current 24

- hour PM 2.5 standard during study periods. In***E.O. 12866 Review

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Page 220 of 253 their review of the PM Policy Asses sment, CASAC endorsed the conclusions drawn from analyses of averaged 98 th percentile 24

- hour PM 2.5 concentrations, and the EPA continues to conclude that this type of information can appropriately inform the Administrator’s decision on the current 24

- hour PM 2.5 standard. 97 A nother group of commenters argued that the 24

- hour standard level should be lowered . Many of these commenters supported setting the level of the 24

- hour PM 2.5 standard at either 25 or 30 g/m 3 . In support of their position, the ALA et. al. , AHA et al., five state Attorneys General, and a number of additional groups pointed to 98 th percentile PM 2.5 concentrations in locations of multi

- city and single

- city epidemiological studies. For example, the ALA and others pointed to multi

- city studies by Dominici et al. (2006), Zanobetti and Schwartz (2009), Burnett et al. (2000), and Bell et al. (2008) as providing evidence for associations with mortality and morbidity in study locations with averaged (i.e., averaged across cities) 98 th percent ile 24

- hour PM 2.5 concentrations below 35 g/m 3 . These commenters also pointed to several single

- city and panel studies reporting associations between short

- term PM 2.5 and mortality or morbidity in locations with relatively low 24

- hour PM 2.5 concentrations
. Because some of these multi

- and single

- city studies have reported associations with health effects in locations with 98 th percentile PM 2.5 concentrations below 35 g/m 3 , commenters maintained that the current 24

- hour PM 2.5 standard (i.e., with its level of 35 g/m 3 ) does not provide an appropriate degree of

97 This is not to say that the EPA’s decision on whether to revise the 24

- hour PM 2.5 standard should be based on or only be informed by considerations of whether studies reported associations with mort ality or morbidity in areas with averaged 98 th percentile PM 2.5 concentrations less than 35 mg/m 3 . As discussed below, in reaching a decision in this final notice on the most appropriate approach to strengthen the suite of PM 2.5 standards, the Administrato r considers the degree of public health protection provided by the combination of the annual and 24

- hour standards together.***E.O. 12866 Review

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Page 221 of 253 protection in all areas. In further support of their position that the level of the current 24

- hour standard should be lowered , these commenters pointed out the variability across the U.S. in ratios
o f 24

- hour to annual PM 2.5 concentrations. They noted that some locations, including parts of the northwestern U.S., experience relatively low annual PM 2.5 concentrations but can experience relatively high 24

- hour concentrations at certain times of the year . In order to provide protection against effects associated with short

- term PM 2.5 exposures, especially in locations with high ratios of 24

- hour to annual PM 2.5 concentrations, these commenters advocated setting a lower level for the 24

- hour standard. The EPA agrees with these commenters that it is appropriate to maintain a 24

- hour PM 2.5 standard in order to supplement the protection provided by the revised annual standard, particularly in locations with relatively high ratios of 24

- hour to annual PM 2.5
co ncentrations. However, in highlighting 98 th percentile PM 2.5 concentrations in study locations without also considering the impact of a revised annual standard on short

- term concentrations, these commenters ignore the fact that many areas would be expected to experience decreasing short

- and long

- term PM 2.5 concentrations in response to a revised annual standard. In considering the specific multi

- city studies highlighted by public commenters who advocated a more stringen t 24

- hour standard, the EPA notes that such studies have reported consistently positive and statistically significant associations with short

- term PM 2.5 exposures in locations with averaged 98 th percentile PM 2.5 concentrations ranging from 45.8 to 34.2 μg/m 3 and long

- term m ean PM 2.5 concentrations rang ing from 13.4 to 12.9 (Burnett and Goldberg, 2003; Burnett et al., 2004; Dominici et al., 2006 a ; Bell et al.,***E.O. 12866 Review

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Page 222 of 253 2008; Franklin et al., 2008; Zanobetti and Schwartz, 2009). 98 The EPA notes that to the extent air quality distributio ns are reduced to meet the current 24

- hour standard with its level of 35 g/m 3 and/or the revised annual standard with its level of 12 g/m 3 , additional protection would be anticipated against the effects reported in these short

- term , multi

- city studies. P ut another way, to attain an annual standard with a level below the long

- term means in the locations of these short

- term studies (as EPA is adopting here), the overall air quality distributions in the majority of study cities will necessarily be reduced,
r esulting in lower daily PM 2.5 ambient concentrations. We therefore expect that the revised annual standard will result in 98 th percentile PM 2.5 concentrations in these cities that are lower than those measured in the studies, and that the overall distribut ions of PM 2.5 concentrations will be lower than those reported to be associated with health effects. Thus, even for effects reported in multi

- city studies with averaged 98 th percentile concentrations below 35 μ g/m 3 , additional protection from the risks associated with short

- term exposures is anticipated from the revised annual standard, without revising the 24

- hour standard, because long

- term average PM 2.5 concentrations in multi

- city study

98 Commenters also highlighted associations with short

- term PM 2.5 concentrations reported in sub

- analyses restricted to days with 24

- hour concentrations at or below 35 3 (Dominici, 2006b). These sub

- analyses were not included in the original publication by Dominici et al. (2006a). Authors provided results of sub

- analyses for the Administrator’s consideration in a letter to the dock et following publication of the proposed rule in January 2006 (personal communication with Dr. Francesca Dominici, 2006b). As noted in section III.A.3, these sub

- analyses are part of the basis for the conclusion that there is no evidence suggesting that ri sks associated with long

- term exposures are likely to be disproportionately driven by peak 24

- hour concentrations. Because the sub

- analyses did not present long

- term average PM 2.5 concentrations, it is not clear whether they reflected PM 2.5 air quality tha t would have been allowed by the revised annual PM 2.5 standard being established in this notice.***E.O. 12866 Review

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Page 223 of 253 locations were above the level of the revised annual standard (i .e., 12 μ g/m 3 ). 99 As discussed above, reducing the annual standard is the most efficient way to reduce the risks from short

- term exposures identified in these studies, as the bulk of the risk comes from the large number of days across the bulk of the air qu ality distribution, not the relatively small number of days with peak concentrations. In considering the single

- city studies highlighted by public commenters who advocated a more stringen t 24

- hour standard, the EPA first notes that, overall, these single

- city studies reported mixed results. Specifically, some studies reported positive and statistically significant associations with PM 2.5 , some studies reported positive but
non - significant associations, and several studies reported negative associations or a mix of positive and negative associations with PM 2.5 . In light of these inconsistent results, the proposal noted that the overall body of evidence from single

- city studies is mixed, particularly in locations with 98 th percentile s of 24

- hour concentration s below 35 μg/m 3

. Therefore, a lthough some single

- city studies report ed effects at appreciably lower PM 2.5 concentrations than short

- term multi

- city studies, the uncertainties and limitations associated with the single

- city studies were noted to be greater . In light of these greater uncertainties and limitations, the Administrator concluded in the proposal that she had less confidence in using these studies as a basis for setting the level of the standard (77 FR 38943). Given the considerations and conclus ions noted above, in the proposal the

99 It is also the case that additional protection is anticipated in locations with 98 th percentile 24

- hour PM 2.5 concentrations above 35 μg/m 3 , even if long

- term concentrations are below 12 μg/m 3 . As noted in the proposal and in the Policy Assessment (U.S. EPA, 2011, Figure 2

- 10), parts of the northwestern U.S. are more likely than other parts of the country to violate the 24

- hour standard and meet the re vised annual standard.***E.O. 12866 Review

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Page 224 of 253 Administrator concluded that the short

- term multi

- city studies provide the strongest evidence to inform decisions on the level of the 24

- hour stan dard. F urther , she viewed single

- city, short

- term exposure studies as a much more limited data set providing mixed results, and she had less confidence in using these studies as a basis for setting the level of a 24

- hour standard (77 FR 38942)
. . In highlighting specific single

- city studies, public health, environmental, and St ate and local commenters appear to have selectively focused on studies reporting associations with PM 2.5 and to have overlooked studies that reported more equivocal results (e.g., Ostro et al., 2003; Rabinovitch et al., 2004; Slaughter et al., 2005; Villen euve et al., 2006) (U.S. EPA, 2011, Figure 2

- 9). As such, these commenters have not presented new information that causes the EPA to reconsider its decision to emphasize multi

- city studies over single

- city studies when identifying the appropriate level of the 24

- hour PM 2.5 standard. In further considering the single

- city studies highlighted by public commenters, the EPA notes that some commenters advocating for a lower level for the 24

- hour PM 2.5 standard also discussed short

- term studies that have been pub lished since the close of the Integrated Science Assessment. These recent studies were conducted in single cities or in small panels of volunteers. As in prior NAAQS reviews and as discussed above in more detail (section II.B.3) , the EPA is basing its deci sions in this review on studies and related information assessed in the Integrated Science Assessment. The studies assessed in the Integrated Science Assessment, and the conclusions based on those studies, have undergone extensive critical review by the EP A, CASAC, and the public. The rigor of that review makes the studies assessed in the Integrated Science Assessment, and the conclusions based on those studies, the most reliable source of scientific information on***E.O. 12866 Review

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Page 225 of 253 which to base decisions on the NAAQS. How ever, as discussed above (section II.B.3) , the EPA recognizes that ‘‘new studies” may sometimes be of such significance that it is appropriate to delay a decision on revision of a NAAQS and to supplement the pertinent air quality criteria so the studies
ca n be taken into account. In the present case, the EPA’s provisional consideration of ‘‘new studies” concludes that, taken in context, the “new” information and findings do not materially change any of the broad scientific conclusions made in the air qualit y criteria regarding the health effects of PM 2.5 ( U.S. EPA , 2012a). For this reason, reopening the air quality criteria review would not be warranted , even if there were time to do so under the court order governing the schedule for completing this review . Accordingly, the EPA is basing its final decisions in this review on the studies and related information included in the PM Integrated Science Assessment (i.e., the air quality criteria) that has undergone CASAC and public review. The EPA will consider t he “new studies” in the next periodic review of the PM NAAQS, which will provide an opportunity to fully assess these studies through a more rigorous review process involving the EPA, CASAC, and the public. Some p ublic health, medical , and env ironmental c ommenters also criticized the EPA’s interpretation of PM 2.5 risk results. These commenters presented risk estimates for combinations of annual and 24

- hour standards using more recent air quality data than that used in the EPA’s Risk Assessment (U.S. EPA, 2 010a). Based on these additional risk analyses, the ALA and other commenters contended that public health benefits could continue to increase as annual and 24

- hour standard levels decrease below 13 g/m 3 and 35 g/m 3 , respectively
.***E.O. 12866 Review

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Page 226 of 253 The EPA agrees with com menters that important public health benefits are expected as a result of revising the level of the annual standard to 12 g/m 3 , as is done in this notice, rather than 13 g/m 3 . The Agency also acknowledges that estimated PM 2.5 - associated health risks continue to decrease with annual standard levels below 12 g/m 3 and/or with 24

- hour standard levels below 35 g/m 3 . However, the EPA disagrees with the commenters’ views regarding the extent to which risk estimates support setting standard levels below 12 μg/m 3 (annual standard) and 35 g/m 3 (24

- hour standard). 100 The CAA charges the Administrator with setting NAAQS that are “requisite” (i.e., neither more nor less stringent than necessary) to protect public health with an adequate m argin of safety . In setting such standards the Administrator must weigh the available scientific evidence and information, including associated uncertainties and limitations . As described above, in reaching her proposed decisions on the PM 2.5 standards that would provide “requisite” protection , the Administrator carefully considered the available scientific evidence and risk information , making public health policy judgments that , in her view, neither overstate d nor understate d the strengths a nd limitations of that evidence and information. In contrast, a s discussed more fully above , public health, medical, and environmental commenters who recommended levels below 35 g/m 3 for the 24

- hour PM 2.5 standard have not provided new information or anal yses to suggest that such standard levels are appropriate, given the uncertainties and limitations in the available health evidence , particularly uncertainties in studies conducted in locations with 98 th percentile 24

- hour PM 2.5 concentrations below 35 g/ m 3 and long

- term average concentrations below 12 g/m 3

. 100 This section focuses on the 24

- hour standard. Section III.E.4.c.i above also discusses these commenters’ recommendations within the context of the annual PM 2.5 standard.***E.O. 12866 Review

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Page 227 of 253 d. Administrator’s Final Conclusions on the Primary PM 2.5 Standard Levels In reaching her conclusions regarding appropriate standard levels, the Administrator has considered the epidemiological and othe r scientific evidence, estimates of risk reductions associated with just meeting alternative annual and/or 24

- hour standards, air quality analyses, related limitations and uncertainties, the advice of CASAC, and extensive public comments on the proposal. A fter careful consideration of all of these, the Administrator has decided to revise the level of the primary annual PM 2.5 standard from 15.0 μg/m 3 to 12.0 μg/m 3 and to retain the level of the primary 24

- hour standard at 35 μg/m 3

. As an initial matter, the Administrator agrees with the approach supported by CASAC and discussed in the Policy Assessment as summarized in sections III.A.3 and III.E.4.a above, of considering the annual and 24

- hour standards together in determining the protection afforded against mortality and morbidity effects associated with both long

and short

- term exposures to PM 2.5 . This approach is consistent with the approach taken in the review completed in 1997, in contrast to the approach used in the review completed in 2006 where each s tandard was considered independently of the other (i.e., only data from long

- term exposure studies were used to inform the level of the annual standard and only data from short

- term exposure studies were used to inform the level of the 24

- hour standard). 101 Based on the evidence and quantitative risk assessment, the Administrator concludes that it is appropriate to set an annual standard that is generally controlling, which will lower the broad distribution of 24

- hour average concentrations in an area as wel l as the annual average concentration, so as to provide protection from both long

- and 101 See 71 FR 61148 and 61168, October 17, 2006.***E.O. 12866 Review

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Page 228 of 253 short

- term PM 2.5 exposures. In conjunction with this, it is appropriate to set a 24

- hour standard focused on providing supplemental protection, particularly for areas wi th high peak

- to
- mean ratios of 24

- hour concentrations, possibly associated with strong local or seasonal sources, and for PM 2.5 - related effects that may be associated with shorter

- than daily exposure periods. The Administrator concludes this approach will reduce aggregate risks associated with both long

- and short

- term exposures more consistently than a generally controlling 24

- hour standard and is the most effective and efficient way to reduce total PM 2

- 5 - related population risk and so provide appropriate protection to protect public health with an adequate margin of safety
. In selecting the level of the annual PM 2.5 standard, b ased on the characterization and assessment of the epidemiological and other studies presented and assessed in the Integrated Scien ce Assessment and the Policy Assessment, the Administrator recognizes the substantial increase in the number and diversity of studies available in this review , including . This expanded body of evidence includes extended analyses of the seminal studies of l ong - term PM 2.5 exposures (i.e., ACS and Harvard Six Cities studies) as well as important new long

- term exposure studies (as summarized in Figures 1 and 2). Collectively, the Administrator notes that these studies, along with evidence available in the last review, provide consistent and stronger evidence than previously observed of an association between long

- term PM 2.5 exposures and premature mortality in areas with lower long

- term ambient concentrations than previously observed, with the strongest evidence related to cardiovascular

- related mortality. The Administrator also recognizes the availability of stronger evidence of morbidity effects associated with long

- term PM 2.5 exposures, including evidence of respiratory effects such as decreased lung function***E.O. 12866 Review

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Page 229 of 253 growth, from the extended analyses for the Southern California Children’s Health Study and evidence of cardiovascular effects from the WHI study. Furthermore, the Administrator recognizes new U.S. multi

- city studies that greatly expand and reinforce
our un derstanding of mortality and morbidity effects associated with short

- term PM 2.5 exposures, providing stronger evidence of associations in areas with ambient concentrations similar to those previously observed in short

- term exposure studies considered in th e previous review (as summarized in Figure 3). The Administrator recognizes the strength of the scientific evidence for evaluating health effects associated with fine particles, noting that the newly available scientific evidence builds upon the previous scientific data base to provide evidence of generally robust associations and a basis for greater confidence in the reported associations than in the last review. She notes the conclusion of the Integrated Science Assessment that this body of evidence supp orts a causal relationship between long

- and short

- term PM 2.5 exposures and mortality and cardiovascular effects and a likely causal relationship between long

- and short

- term PM 2.5 exposures and respiratory effects. In addition, the Administrator notes add itional, but more limited evidence, for a broader range of health endpoints including evidence suggestive of a causal relationship for developmental and reproductive effects as well as for carcinogenic effects. Based on information discussed and presented in the Integrated Science Assessment, the Administrator recognizes that health effects may occur over the full range of concentrations observed in the epidemiological studies of both long

- term and short

- term exposures, since no discernible population

- level threshold for any such effects can be identified based on the currently available evidence (U.S. EPA, 2009a, section***E.O. 12866 Review

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Page 230 of 253 2.4.3). To inform her decisions on an appropriate level for the annual standard levels that will protect public health with an adequate mar gin of safety, in the absence of any discernible population

- level thresholds, the Administrator judges that it is appropriate to consider the relative degree to which the evidence of an association confidence in the magnitude and significance of the associa tions observed in an epidemiological study is supported stud ies across the range of long

- term PM 2.5 concentrations in the study, and therefore the degree to which the study provides confidence in the effects across this range of concentrations such studies . Further, she recognizes, in taking note of CASAC advice and the distributional statistics analysis discussed in the Policy Assessment and in section III.E.4.a above, that there is significantly greater confidence in the magnitude and significance of obse rved associations for certain parts the part of the air quality distribution corresponding to where the bulk of the health events evaluated in each study have been observed
. , generally at and around the long

- term mean concentrations
. Conversely, she also re cognizes that there is significantly diminished confidence in the magnitude and significance of observed associations in the low e st r part of the air quality distribution corresponding to where a relatively small proportion of the health events were observe d. Based on the above considerations, the Administrator takes into account information that characterizes the part of the air quality distributions that corresponds to the large proportion of health event data that was most influential in defining the
asso ciation between PM 2.5 and the health endpoints evaluated in each study. In so doing F urther , the Administrator recognizes that the long

- term mean concentrations, or any other specific point in the air quality distribution of each study, do not represent a “bright line” at and above which effects have been observed and below***E.O. 12866 Review

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Page 231 of 253 which effects have not been observed. As just noted, no discernible population

- level threshold for any such effects can be identified based on the currently available evidence. The Adm inistrator notes that the concentrations at and around the long

- term mean concentrations, for both the long

- and short

- term exposure studies, represents a part of the air quality distribution in which the health event data in any given study are generally most concentrated and, thus, where these data have the most influence on the magnitude and significance of the association observed in such study. The Administrator notes that long

- term mean PM 2.5 concentrations are generally available for each published s tudy and, therefore, represent the most comprehensive data set to inform her decisions on the appropriate annual standard level. Nonetheless, I n considering the long

- term mean concentrations reported in epidemiological studies, the Administrator recognizes that in setting an selecting a level of the annual standard level that will protect public health with an adequate margin of safety , it is not sufficient to focus on a concentration generally somewhere within the range of long

- term mean concentrations from the key long

- term and short

- term exposure studies that reported lower concentrations than had been observed in earlier reviews. These key stud ies provide information for various types of serious health endpoints (including mortality and morbidity effects), different study populations (which may include at

- risk populations such as children and older adults), and different air quality distribution s that are specific to each study. A level somewhere within the range of long

term mean concentrations of the full set of key studies would be higher than the long

term mean of at least one of the studies being considered and therefore would fail to protec t not provide a sufficient degree of protection against the health effects associated***E.O. 12866 Review

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Page 232 of 253 with the air quality distribution observed in that study. Absent some reasoned basis to place less weight on the evidence in the epidemiological study with the lowest long

- term mean concentration among these key studies, this approach would fail to provide sufficient protection not be consistent with the requirement to set a standard that will protect public health with an adequate margin of safety. 102 Thus, the Administrator
r ecognizes it is important to protect against the serious effects observed in each of these studies
. so as to protect public health with an adequate margin of safety
. In so doing, she looks to identify the study with the lowest long

- term mean concentration within the full set of key studies to help inform her decision of the appropriate standard level which will provide protection for the broad array of health outcomes observed in all of the studies, including effects observed in at

- risk populations. Further , consistent with the general approach summarized in section III.E.4.a above and supported by CASAC as discussed in section III.E.4.b.ii above, the Administrator recognizes that it is appropriate to consider a level for an annual standard that is not just at but rather is somewhat below the long

- term mean PM 2.5 concentrations reported in each of the key long

- and short

- term exposure studies. In so doing, she focuses especially on multi

- city studies that evaluated health endpoints for which the associations are causal or likely causal (i.e., mortality and cardiovascular and respiratory effects associated with both long

- and short

- term PM 2.5 exposures). As discussed above, the importance of considering a level somewhat below the lowest long

- term mean concentra tions in this set of key studies is to establish a standard that would be protective against the observed effects in all of the studies, and that takes into account the relative

102 See American Farm Bureau Federation v. EPA , 559 F. 3d 512, 525

- 26 (D.C. Cir. 2009).***E.O. 12866 Review

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Page 233 of 253 degree of confidence in the magnitude and significance of observed association s across the air quality distributions in these studies. The Administrator recognizes that there is no clear way to identify how much below the long

- term mean concentrations of key studies to set a standard that would provide requisite protection with an adequate margin of safety. She therefore must use her judgment to weigh the available scientific and technical information, and associated uncertainties, to reach a final decision on the appropriate standard level. In considering the information in Figures 1

- 4 for effects classified as having evidence of a causal or likely causal relationship with long

- or short

- term PM 2.5 exposures, she observes a cluster of short

- term exposure studies with long

- term mean concentrations within a range of 13.4 μg/m 3 down t o 12.8 μg/m 3 (Dominici et al., 2006; Burnett and Goldberg, 2003; Zanobetti and Schwartz, 2009; Bell et al., 2008; Burnett et al., 2004). She also observes a cluster of long

- term exposure studies with long

- term mean concentrations within a range of 14.5 μg/ m 3 to 13.6 μg/m 3 (Dockery et al., 1996; Lipfert et al., 2006; Zeger et al., 2008; McConnell et al., 2003; Goss et al., 2004; Eftim et al., 2008). For the reasons discussed in response to public comments in section III.E.4.c above, the Administrator is less influenced by the long

- term mean PM 2.5 concentrations from the Miller et al. (2007) and Krewski et al. (2009) studies with reported long

- term mean PM 2.5 concentrations of 12.9 and 14.0 μg/m 3 , respectively. In each case, the most relevant exposure periods would likely have had higher mean PM 2.5 concentrations than those reported in the studies. 103 Thus, the Administrator considers the long

- term mean PM 2.5 concentrations from these

103 In the case of Miller et al. (2007), the mean concentration is based on a single year of air quality data which post

- dated by two years the period for which the health events data were collected. In the case of Krewski et al. (2009),the air quality data were based on the last two years of the 18

- year period for which the health event data were collected.***E.O. 12866 Review

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Page 234 of 253 two studies to be a highly uncertain basis for informing her selection of the a nnual standard level. 104 To help guide her judgment of the appropriate level below the long

- term mean concentrations in the epidemiological studies at which to set the standard, the Administrator considered additional information from epidemiological studie s concerning the broader distribution of PM 2.5 concentrations which correspond to the health events observed in these studies (e.g., deaths, hospitalizations). The Administrator observes that the development and use of this information in considering stand ard levels is consistent with CASAC’s advice, as discussed in section III.E.4.b.ii above, to focus on understanding the concentrations that were most influential in generating the health effect estimates in individual studies (Samet, 2010d, p. 2). In considering this additional population

- level information, the Administrator recognizes that, in general, the confidence in the magnitude and significance of an association identified in a study is strongest at and around the long

- term mean concentration for the air quality distribution, as this represents the part of the distribution in which the data in any given study are generally most concentrated. She also recognizes that the degree of confidence decreases as one moves towards the lower part of the distribution. Consistent with the approach used in the Policy Assessment, the Administrator believes that the range from approximately the 25 th to 10 th percentiles is a reasonable range for providing a general frame of reference as to the part of the distr ibution in which her confidence in the associations observed in epidemiological

104 Nonetheless, as noted above, the EPA notes that the Krewski et al. (20 09) and Miller et al. (2007) studies provide strong evidence of mortality and cardiovascular

- related effects associated with long

- term PM 2.5 exposures to inform causality determinations reached in the Integrated Science Assessment (U.S. EPA, 2009a, section s 7.2.11 and 7.6).***E.O. 12866 Review

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Page 235 of 253 studies becomes is appreciably lower. However , as noted above , it is important to emphasize that there is no clear dividing line or single percentile within a given distribution provided by the scientific evidence that is most appropriate or ‘correct’ to use to characterize where the degree of confidence in the associations warrants setting the annual standard level. The decision of the appropriate standard level below the long

- t erm mean concentrations of the key studies , which in conjunction with the other elements of the standard would protect public health with an adequate margin of safety, is largely a public health policy judgment, taking into account all of the evidence and its related uncertainties. As discussed in section III.E.4.b, the Administrator takes note of additional population

- level data that were made available to the EPA by study authors. 105 In considering this information, the Administrator particularly focuses on the analysis of the distributions of the health event data for each area within these studies and the corresponding air quality data for the two short

- term exposure studies (Zanobe tti and Schwartz, 2009; Bell et al., 2008). These short

- term exposure studies evaluate the relationship between daily changes (one or more days) in PM 2.5 concentrations and daily changes in health events (e.g., deaths, hospitalizations), such that the air quality concentrations that comprise the most relevant exposure periods in these studies are

105 As summarized in section III.E.4.a, population

- level data were provided to the EPA for four studies. These four studies represent some of the strongest evidence showing associations between health effects and PM 2.5 within the overall body of scientific evidence and include three studies (Krewski et al., 2009; Bell et al., 2008; and Zanobetti and Schwartz, 2009) that were used as the basis for concentration

- response functions in the quantitative risk assessment (U.S. EPA, 2010a, section 3.3.3). T he Administrator recognizes that the additional population

- level data available for these four multi

- city studies represents a more limited data set compared to the set of long

- term mean PM 2.5 concentrations which were available in the published literature for all studies considered in the Integrated Science Assessment.***E.O. 12866 Review

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Page 236 of 253 contemporaneous with the health event data. In addition, these studies considered more recent air quality data, representing generally lower PM 2.5 concentrations, in a large number of study areas across the U.S. Thus, such studies provide the most useful evidence for an analysis evaluating the distribution of health event data and the corresponding long

- term mean PM 2.5 concentrations across the areas included in eac h multi

- city study. The Administrator also considered the additional population

- level data that were made available to EPA for two long

- term exposure studies (Krewski et al., 2009; Miller et al., 2007). She re cognizes that in long

- term exposure studies in vestigators follow a specific group of study participants (i.e., cohort) over time and across urban study areas, and evaluate how PM 2.5 concentrations averaged over a period of years are associated with specific health endpoints (e.g., deaths) across citie s. As discussed in response to public comments in section III.E.4.c, disentangling the effects observed in long

- term exposure studies associated with more recent air quality measurements from effects that may have been associated with earlier, and most lik ely higher, PM 2.5 exposures introduces some uncertainty with regard to understanding the appropriate exposure window associated with the observed effects. This is in contrast to the short

- term exposure studies where the relevant exposure period is contempo raneous to the period for which the health data were collected. In light of these considerations, as noted above, the Administrator considers the analysis of air quality concentrations that correspond to the distribution of population

- level data in these t wo studies to be a highly uncertain basis for informing her selection of the annual standard level. Based on the above considerations, the Administrator views the additional***E.O. 12866 Review

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Page 237 of 253 population

- level data for the two short

- term exposure studies as appropriate to h elp inform her judgment of how much below the long

- term mean concentrations to set the level of the annual standard. The Administrator notes that the long

- term mean PM 2.5 concentrations corresponding with study areas contributing to the 25 th and 10 th perce ntiles of the distribution of deaths and cardiovascular

- related hospitalizations in these two short

- term exposure studies were 12.5 μg/m 3 and 10.3 11.5 μg/m 3 , respectively, for Zanobetti and Schwartz (2009 ), ) and 11.5 μg/m 3 and 9.8 μg/m 3 , respectively, for Bell et al. (2008 ) (Figure 5 above; Rajan et al., 2011, Table 1). ) , with the 10 th percentiles being lower by approximately 2 μg/m 3 in each study.
. The Administrator recognizes, as summarized in section III.B above and discussed more fully in section III.B. 2 of the proposal, that important uncertainties remain in the evidence and information considered in this review of the primary fine particle standards. These uncertainties are generally related to understanding the relative toxicity of the different compo nents in the fine particle mixture, the role of PM 2.5 in the complex ambient mixture, exposure measurement errors, and the nature and magnitude of estimated risks related to increasingly lower ambient PM 2.5 concentrations. Furthermore, the Administrator no tes that epidemiological studies have reported heterogeneity in responses both within and between cities and geographic regions across the U.S. She recognizes that this heterogeneity may be attributed, in part, to differences in fine particle composition i n different regions and cities. 106

106 Nonetheless, as explained in section III.E.1, the currently available evidence is not sufficient to support replacing or supplementing the PM 2.5 indicator with any other indicat or defined in terms of a specific fine particle component or group of components associated with any source categories of fine particles. Furthermore, the evidence is not sufficient to support eliminating any component or group of components associated wit h any source categories of fine particles from the mix of fine particles included in the PM 2.5***E.O. 12866 Review

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Page 238 of 253 With regard to evidence for reproductive and developmental effects identified as being suggestive of a causal relationship with long

- term PM 2.5 exposures, the Administrator recognizes that t here are a number of limitations associated with this body of evidence including: the limited number of studies evaluating such effects; uncertainties related to identifying the relevant exposure time periods of concern; and limited toxicological evidence providing little information on t he mode of action(s) or biological plausibility for an association between long

- term PM 2.5 exposures and adverse birth outcomes. Nonetheless, the Administrator believes that this more limited body of evidence provides some support for considering that seri ous effects may be occurring in a susceptible population at concentrations lower than those associated with effects classified as having a causal or likely causal relationship with long

- term PM 2.5 exposures (i.e., mortality, cardiovascular, and respiratory effects). Overall, the Administrator believes that the available evidence interpreted in light of the remaining uncertainties, as summarized above and discussed more fully in the Integrated Science Assessment and the Policy Assessment, provides increased confidence relative to information available in the last review and provides a strong basis for informing her final decisions in the current review. The Administrator is mindful that considering what standards are requisite to protect public health with an adequate margin of safety requires public health policy judgments that neither overstate nor understate the strength and limitations of the evidence or the appropriate inferences to be drawn from the evidence. In considering how to translate the available information into appropriate standard levels, the Administrator weighs the available scientific information and associated uncertainties and limitations. For the purpose of determining what annual indicator.***E.O. 12866 Review

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Page 239 of 253 standard level is appropriate the Administrator recognizes that there is no single factor or criterion that comprises the ‘‘correct’’ approach to weighing the various types of available evidence and information. In considering this information, the Administrator notes the advice of CASAC that “there are significa nt public health consequences at the current levels of the standards that justify consideration of lowering the PM 2.5 NAAQS further” (Samet, 2010c, p. 12). In addition, she recognizes that CASAC concluded, “although there is increasing uncertainty at lower levels, there is no evidence of a threshold (i.e., a level below which there is no risk for adverse effects)” (Samet, 2010, p.ii) and that the final decisions on standard levels must reflect a judgment of the available scientific information with respect to her interpretation of the CAA’s requirement to set primary standards that provide requisite protection to public health with an adequate margin of safety (Samet, 2010d, p. 4). The Administrator recognizes CASAC’s advice that the currently available scie ntific information provided support for considering an annual standard level within a range of 13 to 11 μg/m 3 and a 24

- hour standard level within a range of 35 to 30 μg/m 3 . In considering how the annual and 24

- hour standards work together to provide approp riate public health protection, the Administrator observes that CASAC did not express support for any specific levels or combinations of standards within these ranges. She also notes that CASAC encouraged the EPA staff to consider additional data from epid emiological studies to help quantify the characterization of the PM 2.5 concentrations that were most influential in generating the health effect estimates in these studies (Samet, 2010d, p. 2). In response to CASAC’s advice, the Administrator recognizes t hat the EPA staff***E.O. 12866 Review

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Page 240 of 253 acquired additional data from authors of key epidemiological studies and analyzed these data to characterize the distribution of PM 2.5 concentrations in relation to health events data to better understand the degree of confidence in the a ssociations observed in the studies as discussed above. The Administrator recognizes that the final Policy Assessment included consideration of these additional analyses in reaching final staff conclusions with regard to the broadest range of alternative s tandard levels supported by the science. She takes note that the final Policy Assessment concluded that while alternative standard levels within the range of 13 to 11 μg/m 3 were appropriate to consider, the evidence most strongly supported consideration of an annual standard level in the range of 12 to 11 μg/m 3 . The Administrator is aware that, in transmitting the final Policy Assessment to CASAC, the Agency notified CASAC that the final staff conclusions reflected consideration of CASAC’s advice and that t hose staff conclusions were based, in part, on the specific distributional analysis that CASAC had urged the EPA to conduct (Wegman, 2011). Thus, CASAC had an opportunity to comment on the final Policy Assessment, but chose not to provide any additional co mments or advice after receiving it. In selecting the annual standard level, the Administrator has considered many factors including the nature and severity of the health effects involved, the strength of the overall body of scientific evidence as conside red in reaching causality determinations, the size of the at

- risk populations, and the estimated public health impacts. She has also considered the kind and degree of the uncertainties that remain in the available scientific information. She recognizes tha t the association between PM 2.5 and serious health effects is well established, including at concentrations below those allowed by the current***E.O. 12866 Review

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Page 241 of 253 standard. Further, she recognizes the CAA requirement that requires primary standards to provide an adequate marg in of safety was intended to address uncertainties associated with inconclusive scientific and technical information as well as to provide a reasonable degree of protection against hazards that research has not yet identified. In considering the currently available evidence, as summarized and discussed more broadly above, the information on risk, CASAC advice, the conclusions of the Policy Assessment, and public comments on the proposal, the Administrator strongly believes that a lower annual standard level is needed to protect public health with an adequate margin of safety. In this instance, the association between PM 2.5 and serious health effects is well established, including at concentrations below those allowed by the current standard. In reaching her final decision on the appropriate annual standard level to set, the Administrator is mindful that the CAA does not require that primary standards be set at a
zero - risk level, but rather at a level that reduces risk sufficiently so as to protect public hea lth, including the health of at

- risk populations, with an adequate margin of safety. On balance, the Administrator concludes that an annual standard level of 12 μg/m 3 would be requisite to protect the public health with an adequate margin of safety from ef fects associated with long

- and short

- term PM 2.5 exposures, while still recognizing that uncertainties remain in the scientific information. In the Administrator’s judgment, an annual standard of 12 μg/m 3 appropriately reflects placing greatest weight on evidence of effects for which the Integrated Science Assessment determined there is a causal or likely causal relationship with long

- and short

- term PM 2.5 exposures. An annual standard level of 12 μg/m 3 is below the long

- term mean PM 2.5 concentrations reported in each of the key multi

- city, long

- and short

- term***E.O. 12866 Review

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Page 242 of 253 exposures studies providing evidence of an array of serious health effects (e.g., premature mortality, increased hospitalization for cardiovascular and respiratory effects). As noted above, the importance of considering a level somewhat below the lowest long

- term mean concentration in the full set of studies considered is to set a standard that would be protective provide appropriate protecti on against the observed effects in all such studies. In reaching her decision, the Administrator has taken into account that at and around the mean PM 2.5 concentration in any given study represents a part of the air quality distribution in which the health event da ta in that study are generally most concentrated. Furthermore, in identifying an appropriate annual standard level below the long

- term mean concentrations, she recognizes that there is no evidence to support the existence of any discernible threshold, and, therefore, she has a high degree of confidence that the observed effects are associated with concentrations not just at but extending somewhat below the long

- term mean concentration. To further inform her judgment in setting the annual standard level so a s to protect public health with an adequate margin of safety , the Administrator has placed weight on additional population

- level information available from a subset of these epidemiological studies, consistent with CASAC advice. In particular, she has draw n from two short

- term exposure studies, which provide the most relevant information for evaluating the distribution of health events and corresponding long

- term PM 2.5 concentrations. As explained above, this provides information on helps inform her judgment as to the degree of confidence in the observed associations in the epidemiological studies. In this regard, the Administrator generally judges the region around the 25 th percentile as a reasonable part of the distribution to help guide her decision on the appropriate standard level. Since this evidence comes primarily***E.O. 12866 Review

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Page 243 of 253 from two studies, a relatively modest data set, the Administrator deems it reasonable not to draw further inferences from air quality and health event data in the lower part of the distributi on for the purpose of setting a standard level. The Administrator notes that the long

- term mean PM 2.5 concentrations around the 25 th percentile of the distributions of deaths and cardiovascular

- related hospitalizations were approximately around 12 .5 μg/m 3 and 11.5 μg/m 3 in Zanobetti and Schwartz (2009) and in Bell et al. (2008), respectively (Figure 5; Rajan et al., 2011, Table 1). these two studies
. The Administrator views this information as helpful in guiding her determination as to where she continues to have sufficient her confidence in the magnitude and significance of the associations to warrant setting an annual is reduced to such a degree that a standard set at a lower level would not be warrant ed to provide requisite protection that is neither more no r less than needed to provide an adequate margin of safety
. The Administrator also recognizes that a level of 12 μg/m 3 places some weight on studies which provide evidence of reproductive and developmental effects (e.g., infant mortality, low birth weight) . These studies were identified in the Integrated Science Assessment as having evidence suggestive of a causal relationship with long

- term PM 2.5 concentrations. A level of 12 μg/m 3 is approximately the same level as the lowest long

term mean concentration reported in such studies (Figures 2 and 4; 11.9 μg/m 3 for Bell et al., 2007). 107 While the Administrator acknowledges that this evidence is limited, she

107 With respect to cancer, mutagenic, and genotoxic effects, the Administrator observes that the PM 2.5 concentrations reported in studies evaluating t hese effects 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, 2009a, section 7.5). Therefore, the Administra tor concludes that in selecting alternative standard levels that provide protection from mortality and cardiovascular and respiratory effects, it is reasonable to anticipate that protection will also be provided for carcinogenic effects.***E.O. 12866 Review

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Page 244 of 253 believes it is appropriate to place some weight on these studies in order to set a standard that provides protection with an adequate margin of safety, including providing protection for at

- risk populations, as required by the CAA. Due to the limited nature of this evidence, she has determined it is not necessary to set a standard below the lowest long

- term m ean concentration in these studies. In reflecting on extensive public comments received on the proposal as discussed in section III.E.4.c above, the Administrator recognizes that some commenters have offered different evaluations of the evidence and other information available in this review and would make different judgments about the weight to place on the relative strengths and limitations of the scientific information and about how such information could be used in making public health policy decisions on the annual standard level. One group of such commenters who supported a higher annual standard level (e.g., above 13 μg/m 3 ) would place greater weight on the remaining uncertainties in the evidence as a basis for discounting the overall strength of the evidence than the Administrator judges to be appropriate. Such an approach is based on these commenters’ judgment that the uncertainties remaining in the evidence are too great to warrant setting a lower annual standard level. The Administrator does not a gree. As an initial matter, an annual standard level of 13 μg/m 3 or higher would be above the long

- term mean concentrations reported in two well

- conducted, multi

- city short

- term exposure studies reporting positive and statistically significant association s of serious effects (Burnett et al., 2004 and Bell et al., 2008). These important studies are fully consistent with the pattern of evidence presented by the large body of evidence in this review. As the Administrator recognized in the proposal, and as adv ised by CASAC,***E.O. 12866 Review

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Page 245 of 253 the appropriate focus for selecting the level of the annual PM 2.5 standard is on concentrations somewhat below the lowest long

- term mean concentrations from the set of key studies of both long

- term and short

- term PM 2.5 exposures considered by the EPA (i.e., as shown in Figure 4). Thus, a standard level set at 13 μg/m 3 or higher would clearly not provide protection for the effects observed in the full set epidemiological studies and, therefore, this standard level could not be judged to be requisite with an adequate margin of safety. 108 In addition, as noted above, in recognizing that there is no evidence to support the existence of a discernible threshold below which an effect would not occur, the Administrator is mindful that effects occur around and below the long

- term mean concentrations reported in both the short

- term and long

- term the epidemiological studies. A standard level of 13 μg/m 3 or higher would place essentially no weight on not appropriately take into account evidence from the two well

- conducted, multi

- city, short

term exposure studies reporting serious effects with long

- term mean concentrations below 13 μg/m 3 noted above (Burnett et al, 2004; Bell et al., 2008). Such a standard level would also place essentia lly no weight on not appropriately take into account additional population

- level data from a limited number of epidemiological studies. This approach would ignore CASAC’s advice to consider such information in order to better understand the concentrations t hat were most influential in generating over which there is a high

108 The Administrato r is mindful that, in reviewing the 2006 final PM NAAQS decisions, the D.C. Circuit Court of Appeals concluded that the EPA failed to adequately explain why that annual standard provided requisite protection from effects associated with both long

- and shor t
- term exposures or from morbidity effects in children and other at

- risk populations when long

- term means of important short

- term studies were below the level the Administrator selected for the annual standard. See American Farm Bureau v. EPA. 559 F. 3d 51 2, 524

- 26. There is no reasonable basis to discount these two studies for purposes of setting the level of the annual standard.***E.O. 12866 Review

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Page 246 of 253 degree of confidence regarding the health effect estimates magnitude and significance of the associations observed in individual epidemiological studies and where there is appreciably less co nfidence
. Furthermore, a standard level of 13 μg/m 3 or higher would place no weight on not appropriately take into account the more limited evidence of effects in some at

- risk populations (e.g., low birth weight). In the Administrator’s view, placing no we ight on a standard set at this information level would fail to not provide protection with an adequate margin of safety, including providing protection for at

- risk populations. The Administrator is mindful that the CAA requirement that primary standards provi de an adequate margin of safety, discussed in section II.A above, was intended to address uncertainties associated with inconclusive scientific and technical information available at the time of standard setting as well as to provide a reasonable degree of protection against hazards that research has not yet identified. In light of the entire body of evidence as discussed above, the Administrator judges that an annual standard level set above 12 μg/m 3 would not be sufficient to protect public health with a n adequate margin of safety from the serious health effects associated with long

- and short

- term exposure to PM 2.5. The Administrator also recognizes that a second group of commenters supported a lower annual standard level (e.g., no higher than 11 μg/m 3 ). Such a standard level would reflect placing essentially as much weight on the relatively more limited data providing evidence suggestive of a causal relationship for effects observed in some at

- risk populations (e.g., low birth weight) as on more certai n evidence of effects classified as having a causal or likely causal relationship with PM 2.5 exposures. In the Administrator’s***E.O. 12866 Review

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Page 247 of 253 view, while it is important to place some weight on such suggestive evidence, it would not be appropriate to place as much weight on it as the commenters would do. An annual standard level of 11 μg/m 3 would also reflect these commenters’ judgment that it is appropriate to focus on a lower part of the distributions of health event data from the small number of epidemiological studie s for which this information was made available than the Administrator believes is warranted. In the Administrator’s view, using this type of information to set a standard level of 11 μg/m 3 or below would assume too high a degree of confidence in the magni tude and significance of the associations observed in the lower part of the distributions of health events observed in these studies. Given the uncertainties in the evidence and the limited set of studies for which the EPA has information on the distributi on of health event data and corresponding air quality data, the Administrator believes it is not appropriate to focus on the lower part of the distributions of health events data. On balance, the Administrator finds that the available evidence interpreted in light of the remaining uncertainties does not justify a standard level set below 12 μg/m 3 as necessary to protect public health with an adequate margin of safety. After carefully considering the above considerations and the public comments summarized in section III.E.4.c above, the Administrator has decided to set the level of the primary annual PM 2.5 standard at 12 μg/m 3 . In her judgment, a standard set at this level provides the requisite degree of public health protection, including the health of at

risk populations, with an adequate margin of safety and is neither more nor less stringent than necessary for this purpose. As discussed above, the Administrator concludes that an approach that focuses on***E.O. 12866 Review

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Page 248 of 253 setting a generally controlling annual standard is the most effective and efficient way to reduce total population risk associated with both long

- and short

- term PM 2.5 exposures. Such an approach would result in more uniform protection across the U.S. than the alternative of setting the levels of the 24

- h our and annual standard such that the 24

- hour standard would generally be the controlling standard in areas across the country (see section III.A.3). The Administrator recognizes that potential air quality changes associated with meeting an annual standar d level of 12.μg/m 3 will result in lowering risks associated with both long

- and short

- term PM 2.5 exposures by lowering the overall air quality distribution. However, the Administrator recognizes that such an annual standard alone would not be expected to offer sufficient protection with an adequate margin of safety against the effects of all short

- term PM 2.5 exposures. As a result, in conjunction with an annual standard level of 12 μg/m 3 , the Administrator concludes that it is appropriate to continue to pr ovide supplemental protection by means of a 24

- hour standard set at the appropriate level, particularly for areas with high peak

- to
- mean ratios possibly associated with strong local or seasonal sources and for areas with PM 2.5 - related effects that may be
a ssociated with shorter

- than

- daily exposure periods. In selecting the level of a 24

- hour standard meant to provide such supplemental protection, the Administrator relies upon evidence and air quality information from key short

- term exposure studies. In con sidering these studies, the Administrator notes that to the extent air quality distributions in the study areas considered are reduced to meet the current 24

- hour standard (at a level of 35 μg/m 3 ) or to meet the revised annual standard discussed above (at a level of 12 μg/m 3 ), additional protection would be anticipated***E.O. 12866 Review

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Page 249 of 253 against the effects observed in these studies. In light of this, when selecting the appropriate level for the 24

- hour standard, the Administrator considers both the 98 th percentiles of 24

- hou r PM 2.5 concentrations and the long

- term mean PM 2.5 concentrations in the locations of the short

- term exposure studies. She notes that such consideration of both short

- and long

- term PM 2.5 concentrations can inform her decision on the extent to which a giv en 24

- hour standard, in combination with the revised annual standard established in this notice, would provide protection against the health effects reported in short

- term studies. As discussed in section III.E.4.a above, the Administrator concludes that multi

city short

- term exposure studies provide the strongest data set for informing her decisions on appropriate 24

- hour standard levels. With regard to the limited number of single

- city studies that reported positive and statistically significant associat ions for a range of health endpoints related to short

- term PM 2.5 concentrations in areas that would likely have met the current suite of PM 2.5 standards, the Administrator recognizes that many of these studies had significant limitations (e.g., limited sta tistical power, limited exposure data) or equivocal results (mixed results within the same study area) that make them unsuitable to form the basis for setting the level of a 24

- hour standard. With regard to multi

- city studies that evaluated effects associ ated with short

- term PM 2.5 exposures, the Administrator observes an overall pattern of positive and statistically significant associations in studies with 98 th percentile 24

- hour values averaged across study areas within the range of 45.8 to 34.2 μg/m 3 (Bu rnett et al., 2004; Zanobetti and Schwartz, 2009; Bell et al., 2008; Dominici et al., 2006a, Burnett and Goldberg, 2003; Franklin et al., 2008). The Administrator notes that, to the extent air***E.O. 12866 Review

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Page 250 of 253 quality distributions are reduced to reflect just meeting the c urrent 24

- hour standard, additional protection would be provided for the effects observed in the three multi

- city studies with 98 th percentile values greater than 35 μg/m 3 (Burnett et al., 2004; Burnett and Goldberg, 2003; Franklin et al., 2008). In the th ree additional multi

- city studies with 98 th percentile values below 35 μg/m 3 , specifically 98 th percentile concentrations of 34.2, 34.3, and 34.8 μg/m 3 , the Administrator notes that these studies reported long

- term mean PM 2.5 concentrations of 12.9, 13.2, and 13.4 μg/m 3 , respectively (Bell et al., 2008; Zanobetti and Schwartz, 2009; Dominici et al., 2006a). In revising the level of the annual standard to 12 μg/m 3 , as discussed above, the Administrator recognizes that additiona l protection would be provided for the short

- term effects observed in these multi

- city studies such that revision to the 24

- hour standard would not be warranted. That is, by lowering the level of the annual standard to 12 μg/m 3 , the 98 th percentile of the distribution would be lowered as well such that additional protection from effects associated with short

- term exposures would be afforded. Therefore, the epidemiological evidence supports a conclusion that it is appropriate to retain the level of the 24

- ho ur standard at 35 μg/m 3 , in conjunction with a revised annual standard level of 12 μg/m 3

. In addition to considering the epidemiological evidence, the Administrator also has taken into account air quality information based on county

- level 24

- hour and annual design values to understand the implications of revising the annual standard level from 15 to 12 μg/m 3 in conjunction with retaining the 24

- hour standard level at 35 μg/m 3 . She has considered this information to evaluate the public health protection provided by the two standards in combination and to evaluate the most appropriate means of developing a suite of standards providing requisite public health protection with an adequate margin of***E.O. 12866 Review

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Page 251 of 253 safety. In considering the air quality information, the Adm inistrator observes that a suite of PM 2.5 standards that includes an annual standard level of 12 μg/m 3 and a 24

- hour standard level of 35 μg/m 3 would result in the annual standard as the generally controlling standard in most regions across the country, ex cept for certain areas in the Northwest, where the annual mean PM 2.5 concentrations have historically been low but where relatively high 24

- hour concentrations occur, often related to seasonal wood smoke emissions (U.S. EPA, 2011a, pp. 2

- 89 to 2

- 91, Figure 2

- 10). In fact, these are the type of areas for which the supplemental protection afforded by the 24

- hour standard is intended, such that the two standards together provide the requisite degree of protection. The Administrator concludes the current 24

- hou r standard at a level of 35 μg/m 3 , in conjunction with a revised annual standard level of 12 μg/m 3 , will provide appropriate protection from effects observed in studies in such areas in which the long

- term mean concentrations were below 12 μg/m 3 and the 98 th percentile 24

- hour concentrations were above 35 μg/m 3 (e.g., areas in the Northwest U.S.). After carefully taking the public comments and above considerations into account, the Administrator has decided to retain the current level of the primary PM 2.5 24

- hour standard at 35 μg/m 3 in conjunction with revising the annual standard level from 15.0 μg/m 3 to 12.0 μg/m 3

. 109 In the Administrator’s judgment, this suite of primary PM 2.5 standards and the rationale supporting these levels appropriately reflects cons ideration of the strength of the available evidence and other information and its associated uncertainties as well as the advice of CASAC and consideration of public comments. In 109 As noted in section II.B.1, Table 1 and section III.E.4.a above, the annual standard level is defined to one decimal place. Thr oughout this section, the annual standard levels discussed have been denoted as integer values (e.g., 12 μg/m 3 ) for simplicity.***E.O. 12866 Review

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Page 252 of 253 the Administrator’s judgment, this suite of primary PM 2.5 standards is suffic ient but not more protective than necessary to protect the public health, including at

- risk populations, with an adequate margin of safety from effects associated with long

- and short

- term exposures to fine particles. This suite of standards will provide s ignificant protection from serious health effects including premature mortality and cardiovascular and respiratory morbidity effects that are causally or likely causally related to long

- and short

term PM 2.5 exposures. These standards will also provide an appropriate degree of protection against other health effects for which there is more limited evidence of effects and causality, such as reproductive and developmental effects. This judgment by the Administrator appropriately considers the requirement for a standard that is requisite to protect public health but is neither more nor less stringent than necessary. 110 D. Administrator’s Final Decisions on Primary PM 2.5 Standards For the reasons discussed above, and taking into account the information and assessments presented in the Integrated Science Assessment, Risk Assessment, and Policy Assessment, the advice and recommendations of CASAC, and public comments to date, the Administrator revises the current suite of primary PM 2.5 standards. Specifically, the Administrator revises: (1) the level of the primary annual PM 2.5 standard to 12.0 μg/m 3 and (2) the form of the primary annual PM 2.5 standard to one based on the highest appropriate area

- wide monitor in an area, with no option for spatial averaging. I n conjunction with revising the primary annual PM 2.5 standard to provide protection from effects associated with long

- and short

- term PM 2.5 exposures, the Administrator retains the level of 35 μg/m 3 and the 98 th percentile form of the primary 24

- hour PM 2.5 standard 110 The Administrator also judges that this suite of standards addresses the issues raised by the D.C. Circuit’s remand of the 200 6 primary annual PM 2.5 standard by appropriately revising that standard.***E.O. 12866 Review

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Page 253 of 253 to continue to provide supplemental protection for areas with high peak PM 2.5 concentrations. The Administrator is not revising the current PM 2.5 indicator or the annual and 24

- hour averaging times for the primary PM 2.5 standards. The Administrat or concludes that this suite of standards would be requisite to protect public health with an adequate margin of safety against health effects potentially associated with long

- and short

- term PM 2.5 exposures.