From: Lydia Wegman/RTP/USEPA/US

To: dmancini@omb.eop.gov, nfrey@omb.eop.gov Cc: Janet McCabe/DC/USEPA/US@EPA, Gina McCarthy/DC/USEPA/US@EPA, hannon.john@epa.gov, Karen

Wesson/RTP/USEPA/US@EPA, Joseph
- J Dougherty/DC/USEPA/US@EPA, Beth Hassett
Sipple/RTP/USEPA/US@EPA Date: 06/14/2012 11:16 AM Subject: Further edits to Administrator conc lusion section on PM2.5 levels (section III.D.4.e) In response to the comments we received last night, please find attached further edits to the Administrator's conclusion section on the PM2.5 levels. We look forward to talking at 11:30.***E.O. 12866 Review

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Page 2 of 16 e. Administrator’s Proposed Conclusions on the Primary PM 2.5 Standard 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 annual 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 dis cussed in the Policy Assessment as summarized in sections III.A.3 and III.E.4.a above, and supported by CASAC, of considering the protection afforded by the annual and 24

- hour standards taken together for mortality and morbidity effects associated with bot h 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 suppleme ntal protection, particularly for areas with high peak

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

- than daily exposure periods. The Administrator provisionally concl udes this approach would likely reduce aggregate risks associated with both long

- and short

- term exposures more consistently than a generally controlling 24

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

- 5 - related popul ation risk and so provide appropriate protection.
. In reaching decisions on alternative standard levels to propose, the Administrator judges that it is most 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 Integra ted Science Assessment and the Policy Assessment,***E.O. 12866 Review

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Page 3 of 16 the Administrator recognizes 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., A CS and Harvard Six Cities studies) as well as important new long

- term exposure 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 a nd stronger evidence of an association with premature mortality, with the strongest evidence related to cardiovascular

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

- term PM 2.5 exposures, including evidence of cardiovascular effects from the WHI study and respiratory effects, including decreased lung function growth, from the extended analyses for the Southern Calif ornia 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 evide nce 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 of 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 weight of evidence, as evaluated in the Integrated Science Assessment, is strongest for health endpoints classified as hav ing evidence of a causal relationship . These relationships include those between long

- and short

- term PM 2.5 exposures and mortality and cardiovascular effects . She recognizes that the weight of evidence is also strong for health endpoints classified as hav ing 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 the much more limited evidence for health endpoints classified as having evidence suggestive of a causal relationship, including developmental , reproductive and carcinogenic***E.O. 12866 Review

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Page 4 of 16 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 section III.E.4.b above and in the Policy Assessment, that there is significantly greater confidence in observed associations over certain parts of the air quality dis tribution s in the studies , and conversely, that there is significantly diminished confidence in ascribing effects to concentrations toward the low er part of the distributions
. Consistent with the general approach summarized in section III.A.3 above, and su pported 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 e xposure studies , . In 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
. , she understands that this approach does not provide a bright line fo r reaching decisions about appropriate standard levels
. The Administrator notes 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. She also notes that the overall study mean PM 2.5 concentrations are generally calculat ed based on monitored concentrations averaged across monitors in each study area with multiple monitors, referred to as a composite monitor concentration, in contrast to the highest concentration monitored in study area, referred to as a maximum monitor co ncentration , which are used to determine whether an area meets a given standard
. In considering such long

- term mean concentrations, the Administrator understands that it is appropriate to***E.O. 12866 Review

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Page 5 of 16 consider the weight of evidence for the health endpoints evaluated i n 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 ca usal 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) . She observes a similar pattern of statistically significant associations in studies of short

- term PM 2.5 exposures with lon g - term mean concentrations ranging from around 15 μg/m 3 down to 12.8 μg/m 3 (in Burnett et al., 2004). With regard to effects classified as providing evidence suggestive of a causal relationship , the Administrator observes a small number of long

- term exposure studies related to developmental and reproductive effects that reported statistically significant associations for long

- term
w ith overall study mean PM 2.5 concentrations with long

- term mean concentrations down to 11.9 μg/m 3 (in Bell et a l., 2007). 1 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 confidence in the observed associations over the broader air quality distribution. In considering this additional information, she considers the range from understands that the Policy Assessment presented information on th e 25 th to the and 10 th percentiles , consistent with the Policy Assessment analyses. More specifically, the Administrator recognizes the 25 th percentile as the start of the range distribution s of

1 With respect to suggestive evidence related to cancer, mutagenic, and genotoxic effects, the PM 2.5 concentrations reported in studies generally included ambient concentrations that are equal to or greater than ambient concentrations observed in studies that reported mortality and cardiovascular and respiratory effects (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 6 of 16 PM 2.5 concentrations below the mean available from four multi

- ci ty studies to provide a general frame of reference as to the part of the distribution within which the data become appreciably more sparse and, thus, where her confidence in the associations observed in epidemiological studies begins to would be come 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., 2008; Zanob etti 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 P M 2.5 concentrations associated with the 25 th percentile
v alues of the population

- level data 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 overall 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, 2010a, section 3.3.3). However, t he Administrator also recognizes that additional population

- level data 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 mean PM 2.5 concentrations for which data are available for all studies considered, as discussed above. In considering this information, the Administrator 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 can help to inform selection of an appropriate annual standard level. The Administrator recognizes, as summarized in section III.B.2 above, that important
unc ertainties remain in the evidence and information considered in this review of the primary fine particle standards. These uncertainties are generally related to understanding the relative toxicity of the different components in the fine particle mixture, t he role of PM 2.5 in the complex ambient mixture,***E.O. 12866 Review

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Page 7 of 16 exposure measurement errors inherent in epidemiological studies based on concentrations measured at fixed monitor sites , and the nature , magnitude , and confidence in estimated risks related to increasingly lower ambient PM 2.5 concentrations. Furthermore, the Administrator notes that epidemiological studies have reported heterogeneity in responses both within and between cities and geographic regions across the U.S. Sh e recognizes that this heterogeneity may be attributed, in part, to differences in fine particle composition in different regions and cities. T he Administrator also recognizes that t here are additional limitations associated with evidence for reproductive and developmental effects , identified as being suggestive of a causal relationship with long

- term PM 2.5 exposures , including: the limited number of studies evaluating such effects; uncertainties related to identifying the relevant exposure time periods of concern; and limited toxicological evidence providing little information on the mode of action(s) or biological plausibility for an association between long

- term PM 2.5 exposures and adverse birth outcomes. The Administrator is mindful that considering what standards are requisite to protect public health with an adequate margin of safety requires public health policy judgments that neither overstate nor understate the strength and limitations of the evidence or the appropriate inferences to be drawn from th e 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 various types of available evidence and informati on , 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 reflect placing different weight on the relat ive strengths and limitations of the scientific information , and different judgments could be made as to how such information should***E.O. 12866 Review

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Page 8 of 16 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 and other information so as to inform her public health policy judgments before reaching final decisions on appropriate standard levels. In considering th e available information, the Administrator notes the advice of CAS AC that the currently available scientific information , including epidemiological and toxicological evidence , as well
as the risk and air quality 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 addition, the Administrator recognizes that the Policy Assessment concludes that the available evidence and risk

based information supports support consideration of alternative annual standard leve ls in the range of 13 to 11 μg/m 3 , and further 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 appropriate 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 specific 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 recommendations 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.***E.O. 12866 Review

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Page 9 of 16 In considering the extent to which the currently available evidence and information provide support for specific standard levels within the ranges identified by CASAC and the Policy Assessment as appropriate 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 Administra tor first considers the long

- term mean PM 2.5 concentrations reported in 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 μg/ m 3 would be below most but not all the overall study mean concentrations from 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 overall study 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

- term 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 overall st udy mean concentration in one of the three studies, while lower levels such as 12 or 11 μg/m 3 would be below the overall study mean concentration concentration s 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 , the Administrator notes that a level of***E.O. 12866 Review

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Page 10 of 16 12 μg/m 3 is the PM 2.5 concentration that generally corresponds with approximately the 25 th percentile of the distributions of health events data available i n three of the se studies . The Administrator 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 placing significantly more weight on this information. In considering this information, the Administrator notes that there is no bright line that delineates the start part of the range distribution 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 become s appreciably less
. In considering mean PM 2.5 concentrations and dist r ibutional statistics from the various sets of epidemiological studies noted above, the Administrator recognizes is mindful, as noted above, that such studies typically report concentration s based on 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 monitors to identify potential alternative standard levels would inherently build in a margin of safety of some degree relative to an alternative standard level based on measurements at the monitor within an area that re cords the highest concentration, or the “ maximum monitor ”, , since , once a standard is set, concentrations at appropriate maximum monitors wi thin an area are generally used to determine if an area meets a given standard. The Administrator also recognizes that judgments about the appropriate weight to place on any of the factors discussed above should reflect consideration not only of the relative strength of the evidence but also on the important uncertainties that remain in the evidence and information being considered in this review
. The Administrator notes that the extent to which t hes e uncertainties influence judgments about appropriate annual 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***E.O. 12866 Review

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Page 11 of 16 available studies than would higher levels within the range. Based on the above considerations, 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 inf ormation available from a relatively small number of studies. 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 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 reflect an approach that places more emphasis on the strength of the evidence, including the analysis of the distribution of air quality concentrations most influential for in gener ating health effect estimates in the studies, and more emphasis on margin of safety considerations , than would setting a level at the upper end of this the range . 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. While the Administrator recognizes that CASAC advised , and the Policy Assessment concluded, that the available scientific information 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 approach that places more weight on relatively limited evidence and more uncertain information and analyses than she considers appropriate at this time
. Nonetheless, the Administrator s olicits comment on a level down to 11 μg/m 3 as well as on approaches for translating scientific evidence and rationales that***E.O. 12866 Review

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Page 12 of 16 would support such a level
. Such an approach might reflect 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
. The Administrator recognizes that potential air quality changes associated with meeting an annual standard set at a level within the r ange 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 proposing an a nnual 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 hi gh 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 has 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 t he 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. In considering the information provided by the short

- term exposu re 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 improvement s of alternative standards set at lower levels. By reducing the PM 2.5 concentrations in such***E.O. 12866 Review

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Page 13 of 16 areas to just meet the current standards, the Administrator anticipates that additional public health protection will occur. Therefore, the Administrator has focus ed 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 likel y 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 strongest 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 concentr ations 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 result s 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 overa ll 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, Burnett and Goldberg, 2003; Franklin et al., 2008). The Administrator notes that, to the extent air quality distributions are reduced to reflect just meeting the current 24

- hour standard, additional protection would be anticipated for the effects o bserved 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***E.O. 12866 Review

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Page 14 of 16 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 proposing to revis e the level of the annual standard to within the range of 12 to 13 μg/m 3 , as discussed above, the Administrator recognizes that additional protection would be provided for the short

- term effects observed in these multi

- city studies 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, She notes that the study

- wide mean concentrations are based on averaging across moni tors within study areas and that compliance with the standard would be based on concentrations measured at the monitor reporting the highest concentration within each area. The Administrator believes it would be reasonable to conclude that revision to the 24

- hour standard would not be warranted in either case
. However , the Administrator she 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 p roposed 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 retaini ng 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 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 protection to the extent that additional protection is warranted. As discussed above, the***E.O. 12866 Review

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Page 15 of 16 Administrator provisionally concludes tha t this approach is the most effective and efficient way to reduce total population risk associated with both long

- and short

- term PM 2.5 exposures, resulting in more uniform protection across the U.S. than the alternative of setting the 24

- hour standard to be the controlling standard. In considering the air quality information, the Administrator observes that a suite of PM 2.5 standards that includes an annual standard level of 12 μg/m 3 and a 24

- hour standard level of 35 μg/m 3 (i.e., 12/35) would result in t he annual standard as the generally controlling standard in most regions across the country, except for certain areas in the Northwest, where the annual mean PM 2.5 concentrations have historically been low but where relatively high 24

- hour concentrations occur, often related to seasonal wood smoke emissions (US EPA, 2011a, pp. 2

- 89 to 2

- 91, Figure 2

- 10). Although not explicitly delineated on Figure 2

- 10 in the Polic y 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 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, such a suite of primary PM 2.5 standards and the rationale supporting such levels could reasonably be judged to reflect alternative approaches to the appropriate consideration of the strength of the available evidence and other information and their associated uncertainties and the advice of CASAC. The Administrator recognizes that the final suite of standards selected from within the proposed range of annual stan dard levels , or the broader range of annual standard levels on which public comment is solicited, must be clearly responsive to the issues raised by the D.C. Circuit’s remand of the 2006 primary annual PM 2.5 standard. Furthermore, the final suite of standa rds will reflect the Administrator’s ultimate judgment in the final rulemaking as to the suite of primary PM 2.5 standards that would be***E.O. 12866 Review

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Page 16 of 16 requisite to protect the public health with an adequate margin of safety from effects associated with fine particle expo sures. Th e final judgment to be made by the Administrator will appropriately consider the requirement for a standard that is neither more nor less stringent than necessary and will recognize that the CAA does not require that primary standards be set at a zero - risk level, but rather at a level that reduces risk sufficiently so as to protect public health with an adequate margin of safety. Having reached her provisional judgment to propose revising the annual standard level from 15.0 to within a range of 12.0 to 13.0 μg/m 3 and to propose retaining the 24

- hour standard level at 35 μg/m 3 , the Administrator solicits public comment on this range of levels and on approaches to considering the available evidence and information that would support the choice of l evels within this range. The Administrator also solicits public comment on alternative annual standard levels down to 11 μg/m 3 and on the combination of annual and 24

- hour standards that commenters may believe is appropriate, along with the approaches and rationales used to support such levels. In addition, given the importance the evidence from epidemiologic studies plays in considering the appropriate annual and 24

- hour levels, the Administrator solicits public comment on issues related to translating epi demiological evidence into standards, including approaches for addressing the uncertainties and limitations associated with this evidence.