From: Lydia Wegman/RTP/USEPA/US

To: nfrey@omb.eop.gov Cc: martin.karen@epa.gov, hannon.john@epa.gov, Joseph
- J Dougherty/DC/USEPA/US@EPA, Scott

Jenkins/RTP/USEPA/US@EPA, Beth Hassett
- Sipple/RTP/USEPA/US@EPA, Steven Silverman/DC/USEPA/US@EPA Date: 06/08/2012 04:39 PM Subject: Revisions to the PM2.5 level section of the PM NAAQS preamble Nathan, Please find attached a redline file showing revisions to the Administrator's proposed conclusions on the primary PM2.5 standard levels (subsection III.E.4.e). This file includes the entire section on the PM2.5 levels. T he Administrator's proposed conclusions subsection is the last third of this section. We are continuing to edit the earlier subsections of the level section to address the interagency comments we received on June 6 related to the health effects evidence a nd specific comments regarding the primary standard. The attached file does not include any of our responses to those comments. We anticipate sending those additional edits to you on Tuesday morning. Please let me know if you have any questions. Thanks

. In a moment, I will send you our edits to the AQI section of the preamble. Lydia***E.O. 12866 Review

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Page 2 of 52 1. Level 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 princ ipal basis for selecting the level of the annual PM 2.5 standard that would protect against effects associated with long

- term exposures. The EPA relied upon evidence from the short

- term exposures 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 summarized 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 1 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. Approach Used in the Policy Assessment Building upon the lessons learned i n the previous PM NAAQS reviews, in considering alternative standard levels supported by the currently available scientific information, the Policy Assessment uses an approach that integrates evidence

- based and risk

- based considerations, takes into account CASAC advice, and considers 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, for the reasons discussed below, the Policy Assessment concludes it is appropriate to co nsider the protection afforded by the annual and 24

- hour standards taken together against mortality and morbidity effects associated with both long

- and short

- term PM 2.5 exposures. This is consistent with the approach taken in the review completed in 1997 rather than considering each standard separately, as was done in the review

1 Throughout this section, the annual standard level is denoted as an integer value for simplicity, although, as noted above in section I I .B .1 , Table 1, footnote 7, the standard level is defined to one decimal place, such that the current standard level is 15.0 μg/m 3

. Alternative standard levels discussed in this section are similarly defined to one decimal place.***E.O. 12866 Review

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Page 3 of 52 completed in 2006. Beyond looking directly at the relevant epidemiologic evidence, the Policy Assessment considers the extent to which specific alternative PM 2.5 standard levels a re likely to reduce the nature and magnitude of both long

- term exposure
- related mortality risk and short

- term exposure
- related mortality and morbidity risk (US 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 are generally observed as either the annual or 24

- hour standard, or both, are reduced below the level of the current standards (US 2011a, Figures 2

- 11 and 2

- 12; US EPA, 2010a, sections 4.2.2, 5.2.2, and 5.2. 3). Based on the quantitative risk assessment, the Policy Assessment observes, as discussed in section III.A.3, that analyses conducted for this and previous reviews demonstrate that much, if not most, of the aggregate risk associated with short

- term expo sures 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 (US EPA, 2011a, p. 2

- 9). Furthermore, as discussed in section III.C.3, the Risk Assessment observ es that alternative annual standard levels, when controlling, resulted in more consistent risk reductions across urban study areas, thereby potentially providing a more consistent degree of public health protection (US EPA, 2010a, pp. 5

- 15 to 5

- 16). In con trast, the Risk Assessment notes that while the results of simulating alternative suites of PM 2.5 standards including different combinations of alternative annual and 24

- hour standard levels suggest that an alternative 24

- hour standard level can produce ad ditional estimated risk reductions beyond that provided by an alternative annual standard alone. However, the degree of estimated risk reduction provided by alternative 24

- hour standard levels is highly variable, in part due to the choice of rollback appro ached used (US EPA, 2010a, p. 5

- 17). Therefore, the Policy Assessment concludes, consistent with CASAC advice (Samet 2010c, p. 1), that it is appropriate to set a “generally controlling” annual standard that will lower a wide range of***E.O. 12866 Review

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Page 4 of 52 ambient 24

- hour conc entrations. The Policy Assessment concludes 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 effective and effici ent way to reduce total PM 2

- 5 - related population risk and so provide appropriate protection. The staff believes this approach, in contrast to one focusing on a generally controlling 24

- hour standard, would likely reduce aggregate risks associated 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 are either more or less stringent than necessary in d ifferent geographical areas. The Policy Assessment recognizes 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 expected 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 concludes it is appropriate to consider setting a 24

- hour standard to provide s upplemental 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. Based on the above considerati ons, the approach used in the Policy Assessment to identify alternative standard levels that are appropriate for consideration focuses on translating information from epidemiological studies into the basis for staff conclusions on levels. This approach is broader and more integrative than the general approach used by the EPA in previous reviews (see summary in section III.A.3 above; US EPA, 2011a, sections 2.1.3 and 2.3.4.1) and reflects the more extensive and stronger body of scientific evidence now availa ble on health effects related to long

- and short

- term PM 2.5 exposures, a more comprehensive quantitative risk assessment, and more extensive PM 2.5 air quality data. In considering the currently available information, the Policy Assessment focuses on identi fying***E.O. 12866 Review

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Page 5 of 52 levels for an annual standard and a 24

- hour standard that, in combination, provide protection against health effects associated with both long

- and short

- term PM 2.5 exposures. The Policy Assessment also considers the extent to which various combinati ons of annual and 24

- hour standards reflect setting a generally controlling annual standard with a 24

- hour standard providing supplemental protection (US EPA, 2011a, sections 2.1.3, 2.3.4.1). As discussed in the Policy Assessment, EPA staff recognizes that there is no single factor or criterion that comprises the “correct” approach for reaching conclusions on alternative standard levels for consideration, but rather there are various approaches that are reasonable to consider (US EPA, 2011a, section 2.3 .4.1). In reaching conclusions in the Policy Assessment on the ranges of standard levels that are appropriate to consider, staff considered the relative weight to place on different evidence. The Policy Assessment initially focuses on long

- and short

- term PM 2.5 exposure studies conducted in the U.S. and Canada and places the greatest weight on health outcomes judged in the Integrated Science Assessment as having evidence to support a causal or likely causal relationship. The Policy Assessment also considers the evidence for a broader range of health outcomes judged in the Integrated Science Assessment to have evidence suggestive of a causal relationship, specifically studies that focus on effects in susceptible populations, to evaluate whether this evidence provides support for considering lower alternative standard levels. Several factors were taken into account in placing relative weight on the body of available epidemiological studies, for example, study characteristics, including study design (e.g., time period of air quality monitoring, control for potential confounders); strength of the study (in terms of statistical significance and precision of results); and availability of population

- level and air quality distribution data. As noted above in section III.A.3, the Policy Assessment places greatest weight on information from multi

- city epidemiological studies to inform staff conclusions regarding alternative annual standard***E.O. 12866 Review

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Page 6 of 52 levels. These studies have a number of advantages compared to single

- city studies 2 that include providing representation of ambient PM 2.5 concentrations and potential health impacts across a range of diverse locations providing spatial coverage for different regions across the country, reflecting differences in PM 2.5 sources, compositi on, and potentially other exposure

- related factors which might impact PM 2.5 - related risks; lack of ‘publication bias’ (US EPA, 2004, p. 8

- 30); and consideration of larger study populations that afford the possibility of generalizing to the broader national population and provide higher statistical power than single

- city studies to detect potentially statistically significant associations with relatively more precise effect estimates. In reaching conclusions in the Policy Assessment regarding alternative 24

- hour standard levels that are appropriate to consider, staff also considers relevant information from single

- city short

- term PM 2.5 exposure studies. Although, as discussed above, multi

- city studies have greater power to detect associations and provide bro ader geographic coverage in comparison to single

- city studies, the extent to which effects reported in multi

- city short

- term PM 2.5 exposure studies are associated with the specific short

- term air quality in any particular location is unclear, especially wh en considering short

- term concentrations at the upper end of the air quality distribution (i.e., at the 98 th percentile value) for a given study area. In contrast, single

- city studies are more limited in terms of power and geographic coverage but the link between reported health effects and the air quality in a given study area is more straightforward. Therefore, the Policy Assessment considers the results of both multi

- city and single

- city short

- term exposure studies to inform staff conclusions regarding a lternative levels that are appropriate to consider for a 24

- hour standard that is intended to provide supplemental protection in areas where the

2 As discussed in section II I .B.1 above, the Policy Assessment recognizes that single

- city studies provide ancillary evidence to multi

- city stu dies in support of calling into question the adequacy of the current suite of standards
. However, in light of the mixed findings reported in single

- city short

- term PM 2.5 exposure studies, and the likelihood that these results are influenced by localized ev ents and not representative of air quality across the country, the Policy Assessment places comparatively greater weight on the results from multi

- city studies in considering alternative annual and 24

- hour standard levels (US EPA, 2011a, p. 2

- 64)
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Page 7 of 52 annual standard may not offer appropriate protection against the effects of all short

- term exposures (US EPA, 2 011a, pp. 2

- 62 to 2

- 65). b. Consideration of the Annual Standard 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 alternati ve annual standard levels that are appropriate to consider focuses on characterizing the range of PM 2.5 concentrations over which we have the most confidence in the associations reported in the epidemiological studies, and conversely where our confidence i n the association becomes appreciably lower. The most direct approach to address this issue, consistent with CASAC advise (Samet, 2010c, p.10), is to consider epidemiological studies reporting confidence intervals around concentration

- response relationship s (US EPA, 2011a, p. 2

- 63). Based on a thorough search of the available evidence, the Policy Assessment identified three long

- term PM 2.5 exposure studies reporting confidence intervals around concentration

- response functions (i.e., Schwartz et al., 2008; P ope et al., 2002; Miller et al., 2007; US EPA, 2011a, pp. 2

- 65 to 2

- 70 and Figure 2

- 3). 3 In its assessment of these studies, the Policy Assessment places greater weight on analyses that averaged across multiple concentration

- response models since this appr oach represents a more robust examination of the underlying concentration

- response relationship than analyses considering a single concentration

- response model. Although these analyses of long

- term exposure to PM 2.5 provide information on the lack of any d iscernible population threshold, only Schwartz et al. (2008) conducted a multi

- model analysis to characterize confidence intervals around the estimated concentration

- response relationship that can help inform at what PM 2.5 concentrations we have appreciabl y less confidence in the nature of the underlying concentration

- response relationship. Although analyses of confidence intervals associated with concentration

- response relationships can help

3 The E PA carefully analyzed the published evidence, but was unable to identify any short

- term PM 2.5 exposure studies that characterized confidence intervals around concentration

- response relationships
. Nor did CASAC or public comments on this issue, as addressed in their comments on the second draft Policy Assessment, identify any additional analyses.***E.O. 12866 Review

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Page 8 of 52 inform consideration of alternative standard levels, the Policy A ssessment concludes that the single relevant analysis now available is too limited to serve as the principal basis for identifying alternative standard levels in this review (US EPA, 2011a, p. 2

- 70). The Policy Assessment explores other approaches that con sidered different statistical metrics to identify ranges of long

- term mean PM 2.5 concentrations that were most influential in generating health effect estimates in long

- and short

- term epidemiological studies, placing greatest weight on those studies that reported positive and statistically significant associations (US 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 recognizes that the stronge st evidence 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 stu dies. The long

- term mean concentrations represent air quality data typically used in epidemiological analyses and provide a direct link between PM 2.5 concentrations and the observed health effects. Further, these data are available for all long

- and short

- term exposure studies analyzed and, therefore, represent the data set available for the broadest set of epidemiological studies. However, consistent with CASAC’s comments on the second draft Policy Assessment 4 (Samet, 2010d, p. 2), in preparing the final Policy Assessment, 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 concentr ation, to characterize the range of PM 2.5 concentrations down through which staff continued to have confidence in the associations observed in epidemiological studies and below which there is a comparative lack of data such that the staff’s confidence in t he relationship was appreciably less. This would also be the

4 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 9 of 52 range of PM 2.5 concentrations which has the most influence on generating the health effect estimates reported in epidemiological studies. As discussed in section III.A.3 above, the Policy Assessm ent recognizes there is no one percentile value within a given distribution that is the most appropriate or “correct” way to characterize where our confidence in the associations becomes appreciably lower. The Policy Assessment concludes that focusing on c oncentrations within the lower quartile of a distribution, such as the range from the 25 th to the 10 th percentile, is reasonable to consider as a region within which we begin to have appreciably less confidence in the associations observed in epidemiologic al studies. 5 In 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. As outlined in section III.A.3 above, the Policy Assess ment recognizes that there are 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 health effect estimates reported in epidemiological studies. The most rele vant information to consider is the number of health events (e.g., deaths, hospitalizations) occurring within a study population in relation to the distribution of PM 2.5 concentrations likely experienced by study participants. Although not as directly rele vant, the number of participants within each study area can be used as a surrogate for health event data in relation to the distribution of PM 2.5 concentrations. In applying this approach, the Policy Assessment focuses on identifying the broader range of

5 In the last review, staff believed it was appropriate to consider a level for an annu al 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 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 and a range within one standard deviation around the study mean were considered reasonable approaches fo r characterizing the range over which the evidence of association is strongest (US 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 around 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 (US EPA, 2011a, p. 2

- 71)
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Page 10 of 52 PM 2.5 concentrations which had the most influence on generating health effect estimates in epidemiological studies. As discussed below, in working with study investigators, EPA staff was able to obtain health event data for three large multi

- city studies (Krews ki 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 memorandum (Rajan et al., 2011). Figures 1 through 3 summarize multi

- city, long

- and short

- term exposure studies that evaluated endpoints classified in the Integrated Science Assessment as having evidence of a causal or likely causal relationship or suggestive of a causal relationship, showing the studies with long

- term mean PM 2.5 concentrations below 17 μg/m 3

. 6 Figures 1 and 3 provide summaries of long

- and short

- term exposure studies that evaluated mortality (evidence of a causal relationship); cardiovascular effects (evidence of a causal relationship); a nd respiratory effects (evidence of a likely causal relationship) in the general population, as well as in older adults (a susceptible population). Figure 2 provides a summary of studies that evaluated respiratory effects (evidence of a likely causal relat ionship) in children, a susceptible population, as well as long

- term exposure studies of children that evaluated developmental effects (evidence suggestive of a causal relationship). As outlined above in section III.A.3, epidemiological studies typically report concentrations based upon a composite monitor distribution; that is, concentrations averaged across ambient monitors within each area included in a given study are averaged across study areas to calculate an overall study mean concentration. As note d above in section III.A.3 and discussed in the Policy Assessment, a policy approach that uses data based on composite monitor distributions to identify alternative standard levels, and then compares those levels to concentrations at appropriate maximum mo nitors to determine if an area meets a given standard, inherently has the potential to build in some margin of safety (US EPA, 2011a, p. 2

- 14).

6 Additional studies presented and assessed in the Integrate d Science Assessment report effects at higher long

- term mean PM 2.5 concentrations (e.g., US EP A, 2009a, Figures 2

- 1, 2

- 2, 7

- 6, and 7

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

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Page 11 of 52 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

Source: US EPA, 2011a, Figure 2

- 4***E.O. 12866 Review

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Page 12 of 52 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: US EPA, 2011a, Figure 2

- 5***E.O. 12866 Review

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Page 13 of 52 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: US EPA, 2011a, Figure 2

- 6***E.O. 12866 Review

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Page 14 of 52 In analyses conducted by EPA staff based on selected long

- and short

- term exposure studies, the Policy Assessment notes that the differences between the maximum and composite distributions were greater for studies with fewer years of air quality data (i.e. , 1 to 3 years) and smaller numbers of study areas (i.e., 36 to 51 study areas). The differences in the maximum and composite monitor distribution were much smaller for studies with more years of air quality data (i.e., up to 6 years) and larger numbers of study areas (i.e., 112 to 204 study areas) (Hassett

- Sipple et al., 2010; US EPA, 2010f, section 2.3.4.1). Therefore, any margin of safety that may be provided by a policy approach that uses data based on composite monitor distributions to identify alterna tive standard levels, and then compares those levels to concentrations at appropriate maximum monitors to determine if an area meets a given standard, will vary depending upon the number of monitors and air quality distributions within a given area. See al so, footnote 27 in section III.A.3 above and associated text. The Policy Assessment initially considers distributional statistics for both long

- and short

- term exposure studies that evaluated mortality (causal relationship), cardiovascular effects (causal relationship) or respiratory effects (likely causal relationship). In looking first at the long

- term mean concentrations in the long

- term exposure studies, the Policy Assessment observes positive and often statistically significant associations at long

- ter m mean PM 2.5 concentrations ranging from 16.4 to 12.9 μg/m 3 7 (Laden et al., 2006; Lipfert et al., 2006; Krewski et al., 2009; Goss et al., 2004; Miller et al.; 2007; Zeger et al., 2008; Eftim et al., 2008; Dockery et al., 1996; McConnell et al., 2003; see Figures 1 and 2). In considering the one long

- term PM 2.5 exposure study for which health event data are available (Krewski et al., 2009), the Policy Assessment observes that the long

- term mean PM 2.5 concentrations corresponding with study areas contributi ng to the 25 th and 10 th percentiles of the distribution of

7 As discussed in footnote 5 8 above, the lowest long

- term mean PM 2.5 concentration reported in the long

- term exposure studies was based on updated air quality data for Miller et al. (2007)
. As noted in the Policy Assessment, these air quality data were based on only one year of ambient measurements (2000) and in comparison to other long

- term exposure studies that considered multiple years of air quality data, were much more limited (US EPA, 2011a, pp. 2

- 81 to 2

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

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Page 15 of 52 mortality data are 12.0 μg/m 3 and 10.2 μg/m 3 , respectively (US EPA, 2011a, Figure 2

- 7; Rajan et al., 2011, Table 1). As identified above, although less directly relevant than event data, the number of participants within each study area can be used as a surrogate for health event data in relation to the distribution of PM 2.5 concentrations. 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 study participants for Miller et al. (2007) were 11.2 μg/m 3 and 9.7 μg/m 3 , respectively (US EPA, 2011a, Figure 2

- 7; Rajan et al., 2011, Table 1). In then considering information from multi

- city, short

- term exposure studies re porting positive and statistically significant associations with these same broad health effect categories, the Policy Assessment observes positive and statistically significant associations at long

- term mean PM 2.5 concentrations in a similar range of 15.6 to 12.8 μg/m 3 (Franklin et al., 2007, 2008; Klemm and Mason, 2003; Burnett and Goldberg, 2003; Zanobetti and Schwartz, 2009; Burnett et al., 2004; Bell et al., 2008; Dominici et al., 2006a; see Figure 3). In considering the two multi

- city, short

- term PM 2. 5 exposure studies for which health event data are available, the Policy Assessment observes that the long

- term mean PM 2.5 concentrations corresponding with study areas contributing to the 25 th and 10 th percentiles of the distribution of deaths and cardiov ascular

- related hospitalizations are 12.5 μg/m 3 and 10.3 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) (US EPA, 2011a, Figure 2

- 7; Rajan et al., 2011, Table 1). Taking into consi deration additional studies of specific susceptible lifestages (i.e., childhood), the Policy Assessment expands its evaluation of the long

- term exposure studies to include a broader range of health outcomes judged in the Integrated Science Assessment to ha ve evidence suggestive of a causal relationship. This evidence was taken into account to evaluate whether it provides support for considering lower alternative levels than if weight were only placed on studies for which health effects have been judged in t he Integrated Science Assessment to have evidence supporting a causal or likely***E.O. 12866 Review

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Page 16 of 52 causal relationship. The Policy Assessment makes note of a limited number of studies that provide emerging evidence for PM 2.5 - related low birth weight and infant mortality, especially related to respiratory causes during the post

- neonatal period. This more limited body of evidence indicates positive and often statistically significant effects associated with long

- term PM 2.5 mean concentrations in the range of 14.9 to 11.9 μg/ m 3 (Woodruff et al., 2008; Liu et al., 2007; Bell et al., 2007; see Figure 2). As illustrated in Figure 2, although Parker and Woodruff (2008) did not observe an association between quarterly estimates of exposure to PM 2.5 and low birth weight in a multi

- c ity U.S. study, other U.S. and Canadian studies did report positive and statistically significant associations between PM 2.5 and low birth weight at lower ambient concentrations (Bell et al., 2007; Liu et al., 2007). 8 There remain significant limitations ( e.g., identifying the etiologically relevant time period) in the evaluation of evidence on the relationship between PM 2.5 exposures and birth outcomes (US EPA, 2009a, pp. 7

- 48 and 7

- 56) which should be taken into consideration in reaching judgments about h ow to weigh these studies of potential impacts on specific susceptible populations in considering alternative standard levels that provide protection with an appropriate margin of safety. With respect to carcinogenicity, mutagenicity, and genotoxicity (evi dence suggestive of a causal relationship), the strongest evidence currently available is from long

- term prospective cohort studies that report positive associations between PM 2.5 and lung cancer mortality. At this time, the PM 2.5 concentrations reported i n studies evaluating these 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 (US EPA, 2009a, section 7.5). There fore, in selecting alternative standard levels appropriate to consider, the Policy Assessment noted that, in providing protection against mortality and cardiovascular and respiratory effects it is reasonable to anticipate that protection will also

8 As noted in section 7.4 of the Integrated Science Assessment, Parker et al. (2005) reported that over a 9

- m onth exposure period (mean PM 2.5 concentration of 15.4 μg/m 3 ) a significant decrease in birth weight was associated with infants in the highest quartile of PM 2.5 exposure as compared to infants exposed in the lowest quartile.***E.O. 12866 Review

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Page 17 of 52 be provi ded for carcinogenicity, mutagenicity, and genotoxicity effects (US EPA, 2011a, p. 2

- 78). In summarizing the currently available evidence and air quality information within the context of identifying potential alternative annual standard levels for consid eration, the Policy Assessment first notes that the Integrated Science Assessment concludes there is no evidence of a discernible population threshold below which effects would not occur. Thus, health effects may occur over the full range of concentrations observed in the epidemiological studies. In the absence of any discernible thresholds, the general approach used in the Policy Assessment for identifying alternative standard levels that would provide appropriate protection against effects observed in epi demiological studies has focused on the central question of identifying the range of PM 2.5 concentrations below the long

- term mean concentrations where we continue to have confidence in the associations observed in epidemiological studies. In considering the evidence, the Policy Assessment recognizes 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, ultimately 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, considerations of different alternative standard levels could be supported. As discussed in section III.A.3 above, the Policy Assessment recognizes that by applying the general policy approach used in previous reviews, one could focus on identifying alternative standard le vels for the annual standard that are somewhat below the long

- term mean PM 2.5 concentrations reported in the long

- and short

- term exposure studies. By expanding this approach to consider additional population

- level information from epidemiological studies, one could also focus on the range of PM 2.5 concentrations below the long

- term mean concentrations over which we continue to have confidence in the associations observed in epidemiological studies, as well as the extent to which our confidence in the***E.O. 12866 Review

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Page 18 of 52 assoc iations is appreciably less at lower concentrations, to identify alternative annual standard levels. Figure 4 provides a summary of the long

- term mean PM 2.5 concentrations for the long

- and short

- term exposure studies presented in Figures 1 through 3 as we ll as the range of PM 2.5 concentrations corresponding with the 25 th to 10 th percentiles of health event or number of study participants data from the four multi

- city studies, for which distributional statistics are available 9 (US EPA, 2011a, Figure 2

- 7; Ra jan et al., 2011, Table 1). 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 effect estimates in those studies. The EPA anticipates that, in characterizing where the bulk of the data exist, patterns similar to those presented in Figure 4 would occur for the additional long

- and short

- term PM 2.5 exposure studies. Given the currently avail able evidence and considering the various approaches discussed above, the Policy Assessment concludes it is appropriate to focus on an annual standard level within a range of about 12 to 11 μg/m 3 (US EPA, 2011a, pp. 2

- 82, 2

- 101, and 2

- 106). As illustrated in Figure 4, a standard level of 12 μg/m 3 , at the upper end of this range, is somewhat below the long

- term mean PM 2.5 concentrations reported in all the multi

- city long

- and short

- term exposure studies that provide evidence of positive and statistically si gnificant 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 res piratory 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 corresponds with approximately the 25 th percentile of the available dis tributions of health events data in the studies for which population

- level information

9 Health event data (e.g., num ber of deaths, hospitalizations) occurring in a study population were obtained 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 a dditional study (Miller et al., 2007) (US EPA, 2011a, p.2

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

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Page 19 of 52 was available. 10 In addition, a level of 12 μg/m 3 would reflect some consideration of studies that provide more limited evidence of reproductive and developmental effects, which are suggestive of a causal relationship, in that it is about at the same level as the lowest long

- term mean PM 2.5 concentration s reported in such studies (see Figure 4). Alternatively, an annual standard level of 11 μg/m 3 , at the lower end of this range, is well below the lowest long

- term mean PM 2.5 concentrations reported in all multi

- city long

- and short

- term expo sure studies that provide evidence of positive and statistically significant associations with health effects classified as having evidence of a causal or likely causal relationship. A level of 11 μg/m 3 would reflect placing more weight on the distribution s of health event and population data, in that this level is 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. 11 In addition, a level of 11 μg/m 3 is somewhat below the lo west 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 relative ly more emphasis on margin of safety considerations 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 he alth. Further, recognizing the uncertainties inherent in identifying any particular point at which our confidence in reported associations becomes appreciably less, the Policy Assessment concludes that the available evidence does not provide a sufficient b asis to consider alternative annual standard levels below 11 μg/m 3 (US EPA, 2011a, p. 2

- 81).

10 As outlined in section II I .A.3, the Policy Assessment considers the 25 th percentile to be the start of the range of PM 2.5 concentrations below the mean within which the data become appreciabl y more sparse and, thus, where our confidence in the associations observed in epidemiological studies begins to become appreciably less
. 11 As discussed in section II I .A.3, the Policy Assessment identifies the range from the 25 th to the 10 th percentiles as a reasonable range to consider, in that it is a range where we have appreciably less confidence in the associations observed in epidemiological studies (US EPA, 2011a, p. 2

- 12)
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Page 20 of 52 Figure 4. Translating Epidemiological Evidence from Multi - City Exposure Studies into an Annual PM 2.5 Standard 1

2 Source: US EPA, 2011a, Figure 2

- 8 3***E.O. 12866 Review

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Page 21 of 52 The Policy Assessment also considers the extent to which the available evidence provides a basis for considering alternative annual standard levels above 12 μg/m 3 . As discussed below, the Policy Assessment concludes that it could be reasonable t o consider a standard level up to 13 μg/m 3 based on a policy approach that tends to weigh uncertainties in the evidence in such a way as to avoid potentially overestimating PM 2.5 - related risks to public health, especially to the extent that primary emphasi s is placed on long

- term exposure studies as a basis for an annual standard level. A level of 13 μg/m 3 is somewhat below the long

- term mean PM 2.5 concentrations reported in all but one of the long

- term exposure studies providing evidence of positive and st atistically 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 long

- term exposure study with a long

- term mean PM 2.5 concentration just below 13 μg/m 3 is the WHI study (Miller et al., 2007). As noted in section III.D.1.a above, including footnote 58, the Policy Assessment observes that in comparison to other long

- term exposure studies, the WHI study was more limited in that it was based on only one year of air quality data (US EPA, 2011a, pp. 2

- 81 to 2

- 82). Thus, to the extent that less weight is placed on the WHI 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 related effects classified as having a causal or likely causal relationship. In also considering short

- term exposure studies, the Policy Assessment notes that a level of 13 μg/m 3 is below the long

- term mean PM 2.5 concentrations reported in mo st such studies, but is above the long

- term means of 12.8 and 12.9 μg/m 3 reported in Burnett et al. (2004) and Bell et al. (2008), respectively. In considering these studies, the Policy Assessment finds no basis to conclude that these two studies are any m ore limited or uncertain than the other short

- term exposure studies shown in Figures 3 and 4 (US EPA, 2011a, p. 2

- 82). On this basis, as discussed below, the Policy Assessment concludes 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, such that taken together the suite of***E.O. 12866 Review

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Page 22 of 52 PM 2.5 standards would provide appropriate protection from effects on public health related to short

- term exposure to PM 2 .5 (US EPA, 2011a, p. 2

- 82). The Policy Assessment also notes that a standard level of 13 μg/m 3 would reflect a judgment that the uncertainties in the epidemiological evidence as summarized in section III.B.2 above, including uncertainties related to the h eterogeneity 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, are too great to warrant placing any weight on the distributions of he alth event and population data that extend down below the mean 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 i s too uncertain to support consideration of any lower level. Taken together, the Policy Assessment concludes that consideration of alternative annual standard levels in the range of 13 to 11 μg/m 3 may be appropriate. Furthermore, the Policy Assessment
conc ludes that the currently available evidence most strongly supports consideration of an alternative annual standard level in the range of 12 to 11 μg/m 3 (US EPA, 2011a, p. 2

- 82). The Policy Assessment concludes 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 susceptible populations, than would a higher level. This range would also reflect placing weight on information from studies that help to characterize the range of PM 2.5 concentrations over which we continue to have confidence in the associations observed in epidemiological studies, as well as the extent to which our confidence in the associations is ap preciably less at lower concentrations.
c. Consideration of the 24

- Hour Standard in the Policy Assessment As recognized in section III.A.3 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***E.O. 12866 Review

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Page 23 of 52 (unless established at a level so low as to undoubtedly provide more protection than necessary for long

term e xposures). Of particular concern are 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. As a result, the Administrator believes Policy Assessment concludes that it is 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 considers 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 expected to reduce the estimated risks attributed to short

- term fine particle exposures. In considering the available epidemiological evidence, the Policy Assessment takes into account information from multi

- city studies as well as single

- city studies. The Policy Assessment considers 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 recognizing that the annual and 24

- hour standards wo rk together to provide protection from effects associated with short

- term PM 2.5 exposures, the Policy Assessment also considers information on the long

- term mean PM 2.5 concentrations from these studies. In addition to considering the epidemiological evide nce, the Policy Assessment also considers 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 associated with strong local or seasonal
sources . These patterns help 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 with a 24

- hour standard that provides supplemental protection especially for areas with high peak

- to
- mean ratios (US EPA, 2011a, p. 2

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

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Page 24 of 52 In considering the information provided by the short

- term exposure studies, the Policy Assessment recognizes that to the extent these studies were conducted in areas that likely did not meet one or both of the current standards, such studies do 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 places greatest weight on studies conducted in areas that likely met both the current annual and 24

- hour standards. With re gard to multi

- city studies that evaluated effects associated with short

- term PM 2.5 exposures, as summarized in Figure 3, the Policy Assessment observes an overall pattern of positive and statistically significant associations in studies with 98 th percentil e values averaged across study areas in the range of 45.8 to 34.2 μg/m 3 (Burnett et al., 2004; Zanobetti and Schwartz, 2009; Bell et al., 2008; Dominici et al., 2006a, Burnett and Goldberg, 2003; Franklin et al., 2008). The Policy Assessment notes 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 Policy Assessment notes tha t 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 is given to revising the level of the annua l standard, as discussed above in section III.E.4.b, the Policy Assessment recognizes that potential changes associated with meeting such an alternative annual standard would result in lowering risks associated with both long

- and short

- term PM 2.5 exposure s. Consequently, in considering a 24

- hour standard that would work in conjunction with an annual standard to provide appropriate public health protection, the Policy Assessment notes that to***E.O. 12866 Review

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Page 25 of 52 the extent that the level of the annual standard is revised to wi thin 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 effects observed in these multi

- city studies (US EPA, 2011a, p. 2

- 84). In summary, the Policy Assessment concludes that the multi

- city, short

- term exposure studies generally provide support for retaining the 24

- hour standard level at 35 μg/m 3 in conjunction with an annual standard level revised to within a range of 12 to 11 μg/m 3 (US EPA, 2011a, p. 2

- 84). Alternatively, in conjuncti on with an annual standard level of 13 μg/m 3 , the Policy Assessment concludes that the multi

- city studies provide limited support for revising the 24

- hour standard 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 in conjunction with an overall long

- term mean concentration slightly less than 13 μg/m 3 (Figure 3; US E PA, 2011a, p. 2

- 84). In reaching staff conclusions regarding alternative 24

- hour standard levels that are appropriate to consider, the Policy Assessment also takes into account relevant information from single

- city studies that evaluated effects associate d with short

- term PM 2.5 exposures. The Policy Assessment recognizes that these studies may provide additional insights regarding impacts on susceptible populations and/or on areas with isolated peak concentrations. Although, as discussed in section III.E.4 .a above, multi

- city studies have advantages over single

- city studies in terms of statistical power to detect associations and broader geographic coverage as well as other factors such as less likelihood of publication bias, reflecting differences in PM 2.5 sources, composition, and potentially other factors that could impact PM 2.5 - related effects, multi

- city studies often present overall effect estimates rather than single

- city effect estimates. Since short

- term air quality can vary considerably across citi es, the extent to which effects reported in multi

- city studies are associated with short

- term air quality in any particular location is uncertain, especially when considering short

- term concentrations at the upper end of the distribution***E.O. 12866 Review

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Page 26 of 52 of daily PM 2.5 con centrations (i.e., at the 98 th percentile value). In contrast, single

- city studies are more limited in terms of power and geographic coverage but the link between reported health effects and the air quality in a given study area is more straightforward to establish. Therefore, the Policy Assessment also considers evidence from single

- city, short

- term exposure studies to inform staff conclusions regarding alternative levels that are appropriate to consider for a 24

- hour standard that is intended to provide s upplemental protection in areas where the annual standard may not provide an adequate margin of safety against the effects of all short

- term PM 2.5 exposures. As discussed above for the multi

- city studies, the Policy Assessment takes into account both the 2 4

- hour PM 2.5 concentrations in the single

- city studies, focusing on the 98 th percentile air quality values, as well as the long

- term mean PM 2.5 concentrations. The Policy Assessment considers single

- city studies conducted in areas that would likely have me t the current suite of PM 2.5 standards as most useful for informing staff conclusions related to the level of the 24

- hour standard (US EPA, 2011a, Figure 2

- 9). The Policy Assessment notes that additional single

- city studies summarized in that Figure 2

- 9 we re conducted in areas that would likely have met one but not both of the current PM 2.5 standards. To the extent changes in air quality designed to just meet the current suite of PM 2.5 standards are undertaken, one could reasonably anticipate additional pub lic health protection will occur in these study areas. Therefore, the Policy Assessment concludes that these studies are not helpful to inform staff conclusions regarding alternative standard levels that are appropriate to consider (US EPA, 2011a, p. 2

- 87)
. With regard to single

- city studies that were conducted in areas that would likely have met both the current 24

- hour and annual standards, the Policy Assessment first considers studies that reported positive and statistically significant associations. In considering this group of studies, the Policy Assessment notes Mar et al. (2003) reported a positive and statistically significant association for premature mortality in Phoenix with a long

- term mean concentration of 13.5 μg/m 3 in conjunction with a 98 th p ercentile value of 32.2 μg/m 3 (US EPA, 2011a, Figure 2

- 9). To the extent that consideration is***E.O. 12866 Review

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Page 27 of 52 given to revising the level of the annual standard, within a range of 13 to 11 μg/m 3 , as discussed above, additional protection would be provided for the effects observed in this study (US EPA, 2011a, p. 2

- 87). Four additional studies reported positive and statistically significant associations with 98 th percentile values within a range of 31.2 to 25.8 μg/m 3 and long

- term mean concentrations within a range of 12. 1 to 8.5 μg/m 3 (Delfino et al., 1997; Peters et al., 2001; Stieb et al., 2000; and Mar et al., 2004; US EPA, 2011a, Figure 2

- 9). Delfino et al. (1997) reported statistically significant associations between PM 2.5 and respiratory emergency department visits for older adults (greater than 64 years old) but not young children (less than 2 years old), in one part of the study period (summer 1993) but not the other (summer 1992). Peters et al. (2001) reported a positive and statistically significant association between short

- term exposure to PM 2.5 (2

- hour and 24

- hour averaging times) and onset of acute myocardial infarction in Boston. Stieb et al. (2000) reported positive and statistically significant associations with cardiovascular

- and respiratory

- related emer gency department visits in Saint John, Canada, in single pollutant models but not in multi

- pollutant models (US EPA, 2004, pp. 8

- 154 and 8

- 252 to 8

- 253). Mar et al. (2004) reported a positive and statistically significant association for short

- term PM 2.5 e xposures in relation to respiratory symptoms among children but not adults in Spokane, however, this study had very limited statistical power because of the small number of children and adults evaluated. The Policy Assessment also considers short

- term sin gle

- city PM 2.5 exposure studies that reported positive but nonstatistically significant associations for cardiovascular and respiratory endpoints in areas that would likely have met both the current 24

- hour and annual standards. The 98 th percentile values reported in these studies ranged from 31.6 to 17.2 μg/m 3 and the long

- term mean concentrations ranged from 13.0 to 7.0 μg/m 3 (US EPA, 2011a, Figure 2

- 9). These studies included consideration of cardiovascular

- related mortality effects in Phoenix (Wilson et al., 2007), asthma medication use in children in Denver (Rabinovitch et al., 2006), hospital admissions for hemorrhagic and ischemic stroke in Edmonton, Canada (Villeneuve et al., 2006), and hospital admissions for ischemic stroke/transient***E.O. 12866 Review

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Page 28 of 52 ischemic attac k in Nueces County, TX (Lisabeth et al., 2008). Lastly, the Policy Assessment considers single

- city studies conducted in areas that would likely have met both the current 24

- hour and annual standards that reported null findings. The 98 th percentile values reported in these studies ranged from 29.6 to 24.0 μg/m 3 and the long

- term mean concentrations ranged from 10.8 to 8.5 μg/m 3 (US EPA, 2011a, Figure 2

- 9). These studies reported no associations with short

- term PM 2.5 exposures and cardiovascular

- related hospital admissions and respiratory

- related emergency department visits (Slaughter et al., 2005) and cardiovascular

- related emergency department visits (Schreuder et al., 2006) in Spokane; asthma exacerbation in childr en in Denver (Rabinovitch et al., 2004); and hospital admissions for transient ischemic attack in Edmonton, Canada (Villeneuve et al., 2006). Viewing the evidence as a whole, the Policy Assessment observes a limited number of single

city studies that repo rted positive and statistically significant associations 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. Many of these studies had significant limitations (e.g., limited statistical power, limited exposure data) or equivocal results (i.e., mixed results within the same study area) as briefly identified above and discussed in more detail in the Policy Assessment (US EPA, 2011a, p. 2

- 88). Other studies reporte d positive but not statistically significant results or null associations also in areas that would likely have met the current suite of PM 2.5 standards. Overall, the entire body of results from these single

city studies is mixed, particularly as 24

- hour 98 th percentile concentrations go below 35 μg/m 3

. Although a number of single

- city studies report effects at appreciably lower PM 2.5 concentrations than multi

- city short

- term exposure studies, the uncertainties and limitations associated with the single

cit y studies were greater and, thus, the Policy Assessment concludes there is less confidence in using these studies as a basis for setting the level of a standard. Therefore, the Policy Assessment concludes that the multi

- city short

- term exposure studies pro vide the strongest evidence to inform decisions on the***E.O. 12866 Review

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Page 29 of 52 level of the 24

- hour standard, and the single

- city studies do not warrant consideration of 24

- hour standard levels different from those supported by the multi

- city studies (US EPA, 2011a, p. 2

- 88). In addition to considering the epidemiological evidence, the Policy Assessment takes into account air quality information based on county

- level 24

- hour and annual design values to understand the implications of the alternative standard levels supported by th e currently available scientific evidence, as discussed in section III.E.4.b above. As discussed in section III.A.3 above, the Policy Assessment concludes that a policy goal which includes setting the annual standard to be the “generally controlling” stand ard in conjunction with setting the 24

- hour standard to provide supplemental protection, to the extent that additional protection is warranted, is the most effective and efficient way to reduce total population risk associated with both long

- and short

- ter m 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. Therefore, the Policy Assessment considers the extent to which different combinations of alternative annual and 24

- hour standard levels based on the evidence would support this policy goal (US 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 examines the impli cations of three alternative suites of PM 2.5 standards identified as appropriate to consider based on the currently available scientific evidence, as discussed above. The Policy Assessment concludes that an alternative suite of PM 2.5 standards that would i nclude 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 (US EPA, 2011a, pp. 2

- 89 to 2

- 91 and Figure 2

- 10). These Northwest counties generally represent 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 wood smoke emissions. Alternatively, combining an***E.O. 12866 Review

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Page 30 of 52 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 s tandard would likely become the controlling standard 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 concludes that consideration of retaining the 24

- hour 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 conjunction with lowering the annual standard level, especially within a range of 12 to 11 μg/m 3 , this alternative would recognize additional public health protection against effects associated with short

- term PM 2.5 exposures which would be provided by lowering the annual standard such that revision to the 24

- hour standard would not be warranted (US EPA, 2011a, p. 2

- 91). The Policy Assessment also recognizes an alternative approach to considering the evidence that provides some support for revising the level below 35 μg/m 3 , perhaps as low as 30 μg/m 3 (US EPA, 2011a, p. 2

- 92). This alternative 24

- hour standard level would be more compatible with an alternative annual standard of 13 μg/m 3 based on placing greater weight on one multi

- city short

- term exposur e study (Bell et al., 2008) that reported positive and statistically significant effects at a 98 th percentile value less than 35 μg/m 3 (i.e., 34.2 μg/m 3 ) in conjunction with a long

- term mean concentration less than 13 μg/m 3 (i.e., 12.9 μg/m 3 ). Taken toget her, the Policy Assessment concludes that while it is 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 supports consideration for retaining the current 24

- hour st andard 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 (US EPA, 2011a, p. 2

- 92). d. CASAC Advice***E.O. 12866 Review

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Page 31 of 52 Based on its review of the second draft Policy Assessment , CASAC agreed with the general approach for translating the available epidemiological evidence, risk information, and air quality information into the basis for reaching conclusions on alternative standards for consideration. Furthermore, CASAC agreed “th at 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 annu al 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 ep idemiological and toxicological evidence, as well as by the risk and air quality information compiled” in the Integrated Science Assessment , Risk Assessment, and second draft Policy Assessment . CASAC further noted that “[a]lthough there is increasing uncer tainty at lower levels, there is no evidence of a threshold (i.e., a level below which 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 standards. 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 a re appropriate to consider, including consideration of the combination of these standards supported by the available information (Samet, 2010d, p. ii). Specifically, CASAC encouraged staff to focus on information related to the concentrations that were mos t influential in generating the health effect estimates in individual studies to inform alternative standard levels (Samet, 2010d, p. 2). CASAC also commented that the approach***E.O. 12866 Review

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Page 32 of 52 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 retaining 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 annua l standard level of 11 μg/m 3 ) “may not be adequately inclusive” and “[i]t was not clear why, for example 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 appropriate for consideration (Samet 2010d, p. ii). In considering CASAC’s advice as well as public comment on the second draft Policy Assessment, EPA staff co nducted additional analyses and modified their conclusions regarding alternative standard levels that are appropriate to consider. The staff conclusions in the final Policy Assessment (US EPA, 2011a, section 2.3.4.4) differ somewhat from the alternative st andard levels discussed in the second draft Policy Assessment (US 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 t he epidemiological evidence into a basis for staff conclusions on the broadest range of alternative 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). In commenting on draft staff conclusions in the second draft Policy Assessment, CASAC did not have an opportunity to review the analyses of distributional statistics conducted by staff to identify the broader range of PM 2.5 concentrations that we re most influential in generating health effect estimates in epidemiological studies (Rajan et al., 2011). In addition, CASAC was not aware of the revised long

- term mean PM 2.5 concentration in the WHI study as discussed in section III.D.1.a above, specific ally footnote***E.O. 12866 Review

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Page 33 of 52 58, or the staff’s inclusion of that value in its evaluation of the evidence (i.e., in Figure 4 above and related discussion). The WHI study is the only long

- term cohort study that provides information regarding effects classified as having e vidence of a causal or likely causal relationship associated with a long

- term PM 2.5 concentration below 13 μg/m 3 . However, as noted in section III.D.1.a above, this study was based on only one year of air quality data and linked to effects that occurred in earlier years. Furthermore, CASAC did not have an opportunity to review the staff’s revised rationale for the combinations of alternative standards suggested in the final Policy Assessment.
e. Administrator’s Proposed Conclusions on the Primary PM 2.5 Standa rd Levels In reaching her conclusions regarding appropriate alternative standard levels to consider, the Administrator has considered the epidemiological and other scientific evidence, estimates of risk reductions associated with just meeting alternative a nnual and/or 24

- hour standards, air quality analyses, related limitations and uncertainties and the advice of CASAC. As an initial matter, the Administrator agrees with the approach discussed in the Policy Assessment as summarized in sections III.A.3 and I II.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 . This is consistent with the approach taken in the review completed in 1997, in contrast to considering each standard separately, as was done in the review completed in 2006. Furthermore, based on the evidence and quantitative risk assessment, the Administrator provisionally concludes 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 supplemental protection, particularly for areas with high peak

- to
- mean ratios p ossibly 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 concludes this approach would likely reduce aggregate risks associated with both long

- and short

- term exposures more consistently than a generally controlling***E.O. 12866 Review

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Page 34 of 52 24

- hour standard and would be the most effective and efficient way to reduce total PM 2

- 5 - related population risk and so provide appropriate protection. In reaching decisions on alternative standard levels to propose, the Administrator judges that it is appropriate to examine where the evidence of associations observed in the epidemiological studies is strongest and, conversely, where she has 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 the Policy Assessment, the Administrator recognize s 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 studies) as well as important new long

- term exposur e studies (as summarized in Figures 1 and 2). Collectively, the Administrator takes note that these studies, along with evidence available in the last review, provide consistent and stronger evidence of an association with premature mortality, with the str ongest evidence related to cardiovascular

- related mortality, at lower ambient concentrations than previously observed. The Administrator also recognizes the availability of stronger evidence of morbidity effects associated with long

- term PM 2.5 exposures, i ncluding 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. Furthermore, the Administrator recognizes new U.S. multi

- city studies that greatly expand and reinforce our understanding of mortality and morbidity effects associated with short

- term PM 2.5 exposures, providing stronger evidence of associations at ambient concentrations similar to those previously observed (as summarized in Figure 3). The newly available scientific evidence builds upon the previous scientific data base to provide evidence o f generally robust associations and to provide a basis for greater confidence in the reported associations than in the last review. The Administrator recognizes that the strength weight of the scientific evidence for evaluating potential health effects asso ciated with fine particles and notes , as***E.O. 12866 Review

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Page 35 of 52 evaluated in the Integrated Science Assessment concludes that this body of , is strongest for health endpoints classified as having evidence supports of a causal relationship . These relationships include those betwee n long

- and short

- term PM 2.5 exposures and mortality and cardiovascular effects and . She recognizes that the weight of evidence is also strong for health endpoints classified as having evidence of a likely causal relationship , which include those between long

- and short

- term PM 2.5 exposures and respiratory effects. In addition, the Administrator makes note of additional, but the much more limited evidence for a broader range of health endpoints including classified as having evidence suggestive of a causal relationship for , including developmental and , reproductive effects as well as for and 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 long

- and short

- term epidemiological studies and that no discernible threshold for any effects can be identified based on the currently available evidence (US EPA, 2009a, section 2.4.3). She also recognizes, in taking note of CASAC advice and the distributional statistics analysis discussed in the Policy Assessment, that there is significantly greater confidence in observed associations over certain parts of the air quality distribution distributio n s in the studies , and conversely, that there is significantly diminished confidence in ascribing effects to concentrations from toward the lowest low er part of the range distributions
. Consistent with the general approach summarized in section III.A.3 above, and supported by CASAC as discussed in section III.E.4.d above, the Administrator generally agrees that it is appropriate to consider a level for an annual standard that is somewhat below the long

- term mean PM 2.5 concentrations reported in long

- and short

- term exposure studies, recognizing that the evidence of an association in any such study is strongest at and around the long

- term average where the data in the study are most concentrated. The Administrator notes that long

- term mean PM 2.5 concentrations a re***E.O. 12866 Review

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Page 36 of 52 available for each study considered and, therefore, represent the most robust data set to inform her decisions on appropriate annual standard levels. In considering such long

- term mean concentrations, the Administrator understands that it is appropriate to consider the weight of evidence for the health endpoints evaluated in such studies in giving weight to this information. Based on the information summarized in Figure 4 and presented in more detail in the Policy Assessment (US 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 observes an overall pattern of statistically significant 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 ) and ) . She observes 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 ) for ). With regard to effects classified in the Integrated Science Assessment as having a causal or likely causal relationship with PM 2.5 exposures. In looking at information for a broader range of health endpoints, the Administrator also notes more limited evidence of serious effects in susceptible populations as providi ng evidence suggestive of a causal relationship (e.g., developmental and reproductive effects, cancer). With regard to developmental and reproductive effects , the Administrator observes a small number of studies related to developmental and reproductive ef

fects that reported statistically significant associations for long

- term PM 2.5 concentrations with long

- term means down to 11.9 μg/m 3 (in Bell et al., 2007). With respect to cancer, mutagenic, and genotoxic effects, the Administrator observes that the PM 2. 5 concentrations reported in studies evaluating these 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 (US EPA, 2009a, section 7.5). Therefore, the Administrator provisionally concludes***E.O. 12866 Review

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Page 37 of 52 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. 12 The Administrator also considers additional information from epidemiological studies, consistent with CASAC advice, to take into account the broader distribution of PM 2.5 concentrations and the degree of confide nce in the observed associations over the broader air quality distribution. In considering this additional information, she considers the range from the 25 th to the 10 th percentiles, consistent with the Policy Assessment analyses. More specifically, the Ad ministrator recognizes the 25 th percentile as the start of the range of PM 2.5 concentrations below the mean within which the data become appreciably more sparse and, thus, where her confidence in the associations observed in epidemiological studies begins to become appreciably less. As discussed in section III.E.4.b above and summarized in Figure 4, the Administrator takes note of additional population

- level data that are available for four studies (Krewski et al., 2009; Miller et al., 2007; Bell et al., 20 08; Zanobetti and Schwartz, 2009 ). ) , each of which report statistically significant associations with health endpoints classified as having evidence of a causal relationship
. In considering the long

- term mean PM 2.5 concentrations associated with the 25 th percentile values for these four studies, she observes that these values range from somewhat above to somewhat below 12 μg/m 3 (Figure 4). The Administrator recognizes that these four studies represent some of the strongest evidence available within the ov erall body of scientific evidence and notes that three of these studies (Krewski et al., 2009; Bell et al., 2008; Zanobetti and Schwartz, 2009) were used as the basis for concentration

- response functions used in the quantitative risk assessment (US EPA, 20 10a, section 3.3.3). However, t he Administrator also recognizes that additional population

- level data

12 With respect to suggestive evidence related to cancer, mutagenic, and geno toxic 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 (US EPA, 2009a, section 7.5), such 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 38 of 52 are available for only these four studies and, therefore, she believes that these studies comprise a more limited data set than one based on long

- term mea n PM 2.5 concentrations for which data are available for all studies considered, as discussed above. Nonetheless, consistent with CASAC advice In considering this information , the Administrator considers notes that CASAC advi sed that information about the long

term PM 2.5 concentrations that were most influential in generating the health effect estimates in epidemiological studies as helping can help to inform selection of an appropriate annual standard level. The Administrator recogni zes, 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 toxic ity 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 and , magnitude of , and confidence in estimated risks related to increasingly lower ambient PM 2.5 concentrations. Furthermore, the Administrator notes that epidemiological studies have reported heterogeneity in responses both within and between cities and geogr aphic regions across the U.S. She recognizes that this heterogeneity may be attributed, in part, to differences in fine particle composition in different regions and cities. With regard to T he Administrator also recognizes that t here are additional limita tions associated with 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 the mode of action(s) or b iological 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***E.O. 12866 Review

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Page 39 of 52 for considering that serious effects may be occurr ing 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). The Administra tor 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 approp riate 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
. F or the purpose of determining what standard levels are appropriate to propose, the Administrator recognizes, as did EPA staff in the Policy Assessment, that there is no single factor or criterion that comprises the “correct” approach to weighing the variou s types of available evidence and information , but rather there are various approaches t hat are appropriate to consider. The Administrator further recognizes that different evaluations of the evidence and other information before the Administrator could re flect 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 level s. T his recog nition leads the Administrator to consider various approaches to weighing the evidence so as to identify an appropriate range of alternative standard levels , rather than a single level, to propose. In so doing, the Administrator encourage s extensive public comment on alter n ative approaches to weighing the evidence so as to inform her public health policy judgments before reaching final decisions on appropriate standard levels. In considering this th e available information, the Administrator n otes the advice of CASAC that the currently available scientific information provides 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***E.O. 12866 Review

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Page 40 of 52 addition, the Administ rator recognizes that the Policy Assessment concludes that the evidence most strongly supports 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 appropriat e public health protection, the Administrator observes that the Policy Assessment concludes it is appropriate to consider retaining the current 24

- hour standard level at 35 μg/m 3 in conjunction with an annual standard in the range of 12 to 11 μg/m 3 , as well as to consider an alternative 24

- hour standard level of 30 μg/m 3 , particularly in conjunction with an annual standard level of 13 μg/m 3

. As noted in section III.E.4.d above, the Administrator observes that CASAC did not express support for any specifi c levels or combinations of standards within in these ranges , although she recognizes that CASAC did not have an opportunity to review additional information and analyses presented in the final Policy Assessment prepared in response to CASAC’s recommendati ons on the second draft Policy Assessment. Nor did CASAC have an opportunity to review the EPA staff’s revised rationale for the combinations of alternative standards presented in the final document. In considering the extent to which the currently available evidence , as summarized in Figure 4 and discussed more broadly above, the and information on risk, provide support for specific standard levels within the ranges identified by CASAC advice, and the conclusions of the Policy Assessment , the Admini strator provisionally concludes that an annual standard level of 12 μg/m 3 would provide as appropriate protection against effects associated with long

- and short

- term PM 2.5 exposures. In the Administrator’s judgment, an annual standard of 12 μg/m 3 reflects placing greatest weight on evidence of effects for which the Integrated Science Assessment has 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 would be bel ow the for consideration , the Administrator initially considers standard levels within the range of 13 to 11 μg/m 3 for the annual standard. In so doing, the Administrator first considers the long

- term mean PM 2.5 concentrations reported in these studies. Fu rthermore, an annual standard level of 12 μg/m 3***E.O. 12866 Review

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Page 41 of 52 reflects placing some weight on additional population

- level information studies of effects classified as having evidence of a causal or likely causal relationship , as summarized in Figure 4 and discussed more broadly above
. She notes that a level of 13 would be below most but not all the mean concentrations from a limited number of epidemiological studies providing the multi

- city studies of long

- and short

- term exposures, whereas a somewhat lower level , such as 12 μg/m 3 or lower , would be below all such mean concentrations. In considering the appropriate weight to place on this information, the Administrator again notes that the evidence of an association in any such study is strongest at and around the long

- ter m average where the data in the study are most concentrated , and that long

- term mean PM 2.5 concentrations are available for each study considered and, therefore, represent the most robust data set to inform her decisions on appropriate annual standard levels. 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 developmental effects, the Administrator notes that a level of 13 would be below the mean concentration in one of the three studies, while low er levels such as 12 or 11 μg/m 3 would be below the mean concentration in two or three of these studies, respectively
. In considering the appropriate weight to place on this information, the Administrator notes the very limited nature of this evidence of such effects and the additional uncertainties in these epidemiological studies relative to the studies that provide evi dence of causal or likely causal relationships. In considering additional distributional statistics of population

- level information that were available from four of the epidemiological studies that provi de evidence of effects identified as having a causal relationship with long

- or short

- term PM 2.5 concentrations . More specifically, , the Administrator notes that a level of 12 μg/m 3 is the PM 2.5 concentration that generally corresponds with approximately the 25 th percentile of the available distributions of health events data available in the three of the se studies for which population

- level information was available . The Administrator also recogn izes a level***E.O. 12866 Review

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Page 42 of 52 of 12 notes that higher standard levels up to 13 μg/m 3 would reflect placing significantly less weight on this statistical information, whereas lower standard levels down to 11 μg/m 3 would reflect some consideration for studies that provide more limited evidence of reproductive and developmental effects (e.g., infant mortality, low birth weight) identified as having evidence suggestive of a causal relationship with long

- term placing significantly more weight on this information. In considering this information, the Administrator notes that there is no bright line that delineates the start of the r ange of PM 2.5 concentrations . A level of 12 μg/m 3 is approximately at the same level as the lowest long

- term mean concentration reported in such studi es (Figures 2 and 4; 11.9 μg/m 3 for Bell et al., 2007). below the mean within which the data become appreciably more sparse and, thus, where her confidence in the associations observed in epidemiological studies begins to become appreciably less
. The Administrator also recognizes that an In considering mean PM 2.5 concentrations and dist r ibutional statistics from the various sets of epidemiological studies noted above, the Administrator recognizes that such studies typically report concentration s based o n composite monitor distributions , in which concentrations may be averaged across multiple ambient monitors that may be present within each area included in a given study
. Thus, as noted above, a policy approach that uses data based on composite monitor distributions monitors to identify potential alternative standard levels , and then compares those levels to would inherently build in a margin of safety of some degree relative to an alternative standard level based on information from maximum monitors in a n area, since once a standard is set, concentrations at appropriate maximum monitors within an area are generally used to determine if an area meets a given standard , inherently builds in some margin of safety. Using such an approach, an annual standard se t at a level of 12 μg/m 3 would thus provide some
. The Administrator also recognizes that judgments about the appropriate weight to place on any of the factors considered above should reflect consideration not only of the relative strength of the evidence b ut also on the important uncertainties that remain in the evidence and information being***E.O. 12866 Review

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Page 43 of 52 considered in this review
. The Administrator notes that the extent to which t hese uncertainties influence judgments about appropriate annual and daily standard levels within the range of 11 to 13 μg/m 3 would likely be greater for standard levels in the lower part of the range which would necessarily be based on fewer available studies than would higher levels within the range. Based on the above consider ations, the Administrator concludes that it is 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 concludes that a standard set within this range would reflect alternative approaches to appropriately plac ing the most weight on the strongest available evidence, while placing less weight on much more limited evidence and on more uncertain analyses of information available from a relatively small number of s tudies. Further, she provisionally concludes that a standard level within this range would reflect alternative approaches to appropriately providing a n adequate margin of safety for this reason. An the populations at risk 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 recognizes that setting a n annual standard level at the lower end of this range would re flect an approach that places more emphasis on the strength of the evidence, including the analysis of the distribution of air quality concentrations in the studies, and more emphasis
on margin of safety considerations , than would setting a level at the up per end. Conversely, an approach that would support a level at the upper end of this range would place greater weight on the remaining uncertainties in the evidence to avoid potentially overestimating public health improvements , and w ould generally support a view that the uncertainties remaining in the evidence are too great to warrant setting a lower annual standard level of 12
. While the Administrator recognizes that CASAC advised , and the Policy Assessment concluded, that the available scientific informa tion provides support for considering a range that extended down to 11 μg/m 3 , she concludes that proposing such an extended range would reflect a public health policy***E.O. 12866 Review

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Page 44 of 52 approach that places more weight on relatively limited evidence and more uncertain inform ation and analyses than she considers appropriate at this time
. Nonetheless, the Administrator solicits comment on a level down to 11 μg/m 3 would also provide some margin of safety since it is somewhat lower than the long

- term mean concentrations of the studies noted immediately above 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 wa rrant a highly precautionary public health policy response that would incorporate a large margin of safety
. The Administrator recognizes 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 recognizes that such 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 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 considering proposing an annual standard level in the range of 12 to 13 μg/m 3 , the Administrator provisionally concludes that it is 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 ratios 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, the Administrator h as 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 for the standard, the Administrator agrees with the focus in the Policy Assessment of looking at the 98 th percentile values, as well as at the long

- term mean PM 2.5 concentrations in these studies.***E.O. 12866 Review

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Page 45 of 52 In considering the information provided by the short

- term exposure studies, the Administrator recognizes that to the extent these studies were conducted in areas that likely did not meet one or both of the current standards, such studies do not help inform the characterization of the potential public health impro vements 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 anticipates that additional public health protection will occur. Therefore, the Administrator has focused on studies that reported positive and statistically significant associations in areas that would likely have met both the current 24

- hour and annual standards. She has also considered whether or not these studies were conducted in areas that would likely have 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, the Administrator concludes that multi

- city, short

- term exposure studies provide the stro ngest data set for informing her decisions on appropriate 24

- hour standard levels. The Administrator views the single

- city, short

- term exposure studies as a much more limited data set providing mixed results and, therefore, she has less confidence in using these 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 endpoints related to short

- term PM 2.5 co ncentrations 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 statistical 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 associated 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 values averaged across study areas in the range of 45.8 to 34.2 μg/m 3 (Burnett et al., 2004; Zanobetti and Schwartz, 2009; Bell et al., 2008; Dominici et al., 2006a,***E.O. 12866 Review

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Page 46 of 52 Burnett and Goldberg, 2003; Franklin et al., 2008). The Administrator notes that, to the extent air quality distributions are reduced to reflect just meeting t he 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 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 considering revising proposing to revis e the level of the annual standard to 12 within the range of 12 to 13 μg/m 3 , as discussed above, the Administrator r ecognizes that additional 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. Therefore, based on in conjuncti o n 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

. Based on this, it would be reasonable to conclude that revision to the 24

- hour standard would not be warranted in either case
. However , the Administrator has less confidence in judging that a level of 35 μg/m 3 would be appropriate in conjunction with an annual level at the upper end of the r a nge . B ased on the above considerations related to the epidemiological evidence, the Administrator provisionally concludes that it is 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 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 in conjunction with an annual standard level within the proposed range of 12 to 13 μg/m 3

. She has considered whether this suite of standards would meet a public health***E.O. 12866 Review

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Page 47 of 52 policy goal which includes setting the annual standard to be the “generally controlling” standard in conjunction with setting the 24

- hour standard to provide supplemental protec tion to the extent that additional protection is warranted. As discussed above, the Administrator provisionally concludes that this approach is the most effective and efficient way to reduce total population risk associated with both long

- and short

- term P M 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 observes that a suite of PM 2.5 standard s that includes an annual standard level of 12 μg/m 3 and a 24

- hour standard level of 35 μg/m 3 (i.e., 12/35) would result in the annual standard as the generally controlling standard in most regions across the country, except for certain areas in the Northw est, 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 (US EPA, 2011a, pp. 2

- 89 to 2

- 91, Figure 2

- 10). Although not explicitly deline ated on Figure 2

- 10 in 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 considerations into account, the Administrator proposes to revise the level of the primary annual PM 2.5 standard from 15.0 μg/m 3 to 12 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, this such a suite of primary PM 2.5 standards and the rationale supporting these such levels appropriately reflects could reasonably be judged to reflect alternative approaches to the appropriate consideration of the strength of the available evidence and other information and their associated uncertainties and the advice of CASAC. She judges that this suite of standards addresses The Administrator recognizes 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***E.O. 12866 Review

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Page 48 of 52 is solicited, must be clearly responsive to the issues raised by the D.C. Circuit’s remand o f the 2006 primary annual PM 2.5 standard. Furthermore, in the the final suite of standards will reflect the Administrator’s ultimate judgment , this in the final rulemaking as to the suite of primary PM 2.5 standards that would be requisite to protect the pu blic health with an adequate margin of safety from effects associated with fine particle exposures. It would provide significant 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 would also provide an appropriately more limited degree of protection against other health effects for which there is more limited evidence of effects and caus ality, such as reproductive and developmental effects. This Th e final judgment to be made by the Administrator will appropriately considers consider the requirement for a standard that is neither more nor less stringent than necessary and recognizes 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 sufficiently so as to protect public health with an adequate margin of safety. Having reached her decision provisional judgment to propose revising the annual standard level from 15.0 to 12 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 recognizes that different evaluations of solicits public comment on this range of levels and on approaches to considering the available evidence and other information before the Administrator could reflect placing different weight on the relative strengths and limitations of the scientific information and different judgments could be made as to how such information could be used in making public health policy decisions on proposed standards. In particular, the Administrator observes that the Policy Assessment concludes that the currently available information could provide that would support for an annual standard level as high as 13 μg/m 3 and as low as 11 μg/m 3 , but tha t the evidence most strongly supports consideration the choice of an alternative annual standard level within a range of 12 to 11 μg/m 3 (US EPA, 2011a, p. 2

- 101). With regard to the 24

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

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Page 49 of 52 Administrator observes that the Policy Assessment con cludes that there is limited support to consider revising the level to somewhat below 35 μg/m 3 , such as down to 30 μg/m 3 , in conjunction with revising the annual standard level to 13 μg/m 3 and to consider retaining the level at 35 μg/m 3 in conjunction with revising the annual standard level to 11 μg/m 3

. T he Administrator also recognizes that CASAC endorsed annual standard levels within a range of 13 to 11 μg/m 3 and alternative 24

- hour standard levels within a this range of 35 to 30 μg/m 3 , consistent with the general ranges identified in the Policy Assessment (Samet, 2010d, p. ii). As noted in section III.E.4.d above, the Administrator observes that CASAC, in offering its advice on alternative standard levels, did not express support for a ny specific levels or combinations of standards within in these ranges. However, she also observes, as noted in section III.E.4.d above, that CASAC did not have an opportunity to review additional information and analyses presented in the final Policy Asse ssment nor did it have an opportunity to review the EPA staff’s revised rationale for the combinations of alternative standards presented in the final document. The Administrator recognizes that consideration for setting a higher annual standard level, e.g ., up to 13 μg/m 3 , would reflect an approach that places significantly less emphasis on margin of safety considerations than a standard set at 12 μg/m 3 . It would also reflect placing essentially no weight on more limited evidence of serious effects in susc eptible populations (e.g., infant mortality, low birth weight) and would likewise place essentially no weight on additional population

- level data from a limited number of epidemiological studies. In addition, this approach would require the Administrator t o explain why a standard established above the level of the long

- term mean PM 2.5 concentrations reported in several robust well

- conducted studies, notably the Burnett et al. (2004) and Bell et al. (2008) studies, would provide requisite protection with an adequate margin of safety. 13 The Administrator is not

13 In this regard, the Administr ator is less influenced by the reported long

- term mean PM 2.5 concentration from the WHI study (12.9 μg/m 3 ) because that value is extrapolated from a single year of air quality data to the whole study, and the data year (2000) comes from a later year than t he years of***E.O. 12866 Review

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Page 50 of 52 presently aware of any such explanations. This approach would place greater weight on the remaining uncertainties in the evidence to avoid potentially overestimating public health improvements. Such an
a pproach could generally support a view that the uncertainties remaining in the evidence 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 c omponents within the fine particle mixtures 14 and the potential role of co

- pollutants (i.e., distinguishing the effects of PM 2.5 from the effects of other pollutants within the ambient mixture) are too great to warrant setting a lower annual standard level. The Administrator recognizes that consideration for setting a lower annual standard level, e.g., down to 11 μg/m 3 , would reflect an approach that places relatively more emphasis on margin of safety considerations than a standard set at 12 μg/m 3 . It would also reflect placing greater weight on more limited evidence of serious effects in susceptible populations (e.g., infant mortality, low birth weight), as well as assuming associations exist for effects for which at present there is only suggestive evidence of causality. This approach would place less weight on the uncertainties remaining in the evidence including understanding the heterogeneity in responses observed in the epidemiological studies, to avoid potentially underestimating public health improveme nts. Such an approach could generally support a view that the uncertainties associated with the available scientific information warrant a highly precautionary public health policy response that would incorporate a large margin of safety, particularly in l ight of the serious nature of some of the health effects at issue. The Administrator solicits public comment on these approaches and on related standard levels such as alternative annual standard levels up to 13 μg/m 3 and down to 11 μg/m 3 or 24

- hour standa rd health events considered (1994 to 1998) so that air quality concentrations could have been higher in the study’s earlier years. 14 As explained in section II I .E.1, however, the currently available evidence is not sufficient to support replacing or supplementing the PM 2.5 indicator with any other indicator 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 elim inating 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
.***E.O. 12866 Review

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Page 51 of 52 levels down to 30 μg/m 3

. . The Administrator also solicits public comments 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 are is appropriate, along with the approaches and rationales used to support such levels. In addition, given the importance the evidence from epidemiologic studies plays in considering the appropriate annual and 24

- hour levels, the Administrator solicits comment s public comment on issues related to translating epidemiological evidence into standards, including approaches for addressing the uncertainties and limitations associated with this evidence and quantitative risk assessment . C. Administrator’s Proposed 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, a nd public comments to date, the Administrator proposes to revise the current primary PM 2.5 standards. Specifically, the Administrator proposes to revise: (1) the level of the primary annual PM 2.5 standard to 12 a level within the range of 12.0 to 13 .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 allowance for spatial averaging. In 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 proposes to retain the level and form of the primary 24

- hour PM 2.5 standard to provide supplemental protection for areas with high peak PM 2.5 concentrations. The Administrator provisionally concludes that such a revised suite of standards, including a revised annual standard together with the current 24

- hour standard, would c ould provide requisite protection against health effects potentially associated with long

- and short

- term PM 2.5 exposures. The Administrator is not proposing any revisions to the current PM 2.5 indicator and the annual and 24

- hour averaging times for the primary PM 2.5 standards. Data handling conventions are specified in proposed revisions to appendix N, as dis cussed in***E.O. 12866 Review

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Page 52 of 52 section VII below. The Administrator solicits comment on all aspects of this proposed decision. In particular, the Administrator solicits comments on alternative combinations of standards including: (1) an annual standard level up to 13.0 μg/m 3 i n conjunction with an alternative 24

- hour standard level down to 30 μg/m 3 , (2) an annual standard level down to 11.0 μg/m 3 in conjunction with retaining the 24

- hour standard level at 35 μg/m 3 , or (3) other combinations of annual and 24

- hour standards.