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From: Lydia Wegman/RTP/USEPA/US To: nfrey@omb.eop.gov Cc: Janet McCabe/DC/USEPA/US@EPA, martin.karen@epa.gov, Joseph - J

Dougherty/DC/USEPA/US@EPA, hannon.john@epa.gov, Beth Hassett Sipple/RTP/USEPA/US@EPA Date: 06/07/2012 04:35 PM Subject: Revisions to the secondary standard level section Nathan, Please find attached some revisions to the level section for the secondary standard for visibility. We can discuss when I call you, which I will do shortly. Thanks
. Lydia2

4. Level (p. 295) In considering alternative levels for a new standard that would provide requisite protection against PM

- related visibility impairment primarily in urban areas, the Policy Assessment has taken into account the evidence

- and impact

- based considerations discussed above and in section 4.2.1 of the Policy Assessment, with a focus on the results of public perception and attitude surveys related to the acceptability of various levels of visual air quality and on the important limitations in the design and scope of such available studies. The Policy Assessment considered this information in the context of a standard defined in terms of a calculated PM 2.5 light extinction indicator, discussed above and in the Policy Assessment section 4.3.1; with alternative averaging times of 24

- hours or multi

- hour, sub

- daily periods (e.g., 4

- hours), discussed above and in Policy Assessment section 4.3.2; and a 90 th percentile

- based form, discussed above and in section 4.3.3 of the Policy Assessment. As part of th e Policy Assessment’s assessment of the adequacy of the current standards, summarized in section VI.B. above and in Policy Assessment section 4.2.1, it interpreted the results from the visibility preferences studies conducted in four urban areas to define a range of low, middle, and high CPLs for a sub

- daily standard (e.g., 1

- to 4

- hour averaging time) of 20, 25, and 30 dv, which are approximately equivalent to PM 2.5 light extinction of values of 65, 110, and 190 Mm - 1 . The Policy Assessment notes that CASAC agreed that this was an appropriate range of levels to consider for such a standard (Samet, 2010d, p. 11). 1 The Policy Assessment also

1 In 2009, the D.C. Circuit remanded the secondary PM 2.5 standards to the EPA in part because the Agency failed to identify a target level of protection, even though EPA staff and CASAC had identified a range of target levels of protection that were appropriate for consideration. The court determined that the A gency’s failure to identify a target level of protection as part of its final decision was contrary to the statute and therefore unlawful, and that it deprived EPA’s decision

making of a reasoned basis . See 559f. 3d at 528

- 31; see also section VI.A.2 above and the Policy Assessment , section 4.1.2.3

recognizes that to define a range of alternative levels that would be appropriate to consider for a 24

- hour calculated P M 2.5 light extinction standard, it is appropriate to consider whether some adjustment to these CPLs is warranted since these preference studies cannot be directly interpreted as applying to a 24

- hour exposure period (as noted above and in Policy Assessment section 4.3.1). Considerations related to s uch adjustments are more specifically discussed below. As an initial matter, in considering alternative levels for a sub

- daily standard based directly on the four preference study results, the Policy Assessment n otes that the individual low and high CPLs are in fact generally reflective of the results from the Denver and Washington, DC studies respectively, and the middle CPL is very near to the 50 th percentile criteria result from the Phoenix study. As discussed above and in section 4.2.1 of the Policy Assessment, the Phoenix study was by far the best of the studies, providing somewhat more support for the middle CPL. In considering the results from these studies, the Policy Assessment recognizes that the availabl e studies are limited in that they were conducted in only four areas, three in the U.S. and one in Canada. Further, the Policy Assessment recognizes that available studies provide no information on how the duration and variation of time a person spends out doors during the daytime may impact their judgment of the acceptability of different degrees of visibility impairment. As such, there is a relatively high degree of uncertainty associated with using the results of these studies to inform consideration of a national standard for any specific averaging time . Nonetheless, the Policy Assessment concludes, as did CASAC, that these studies are appropriate to use for this purpose (US EPA, 2011a, p. 4

- 61). In considering potential alternative levels for a 24

- hour s tandard, the Policy Assessment explores various approaches to adjusting the CPLs derived directly from the preference studies, as presented and discussed in Appendix G of the Policy Assessment, especially section G

- 5.4

These various approaches, based on ana lyses of 2007

– 2009 data from the 15 urban areas assessed in the Visibility Assessment, focused on estimating CPLs for a 24

- hour standard that would provide generally equivalent protection as that provided by a 4

- hour standard with CPLs of 20, 25, and 30 dv. In so doing, staff recognized that there are multiple approaches for estimating generally equivalent levels on a city

- specific or national basis, and that the inherent spatial and temporal variability in relative humidity and fine particle composition across cities leads to a set of alternative estimates of levels that may be construed as being generally equivalent on a national basis. In conducting these analyses , staff initially expected that the values of 24

- hour average PM 2.5 light extinction and daily maximum daylight 4

- hour average PM 2.5 light extinction would differ on any given day, with the shorter term peak value generally being larger. This would mean that, in concept, the level of a 24

- hour standard should include a d ownward adjustment compared to the level of a 4

- hour standard to provide generally equivalent protection . As discussed more fully in section G.5 of Appendix G and summarized below , this initial expectation was not found to be the case across the range of CPLs considered. In fact, as shown in Table G

- 6 of Appendix G, 2 in considering estimates aggregated or averaged over all 15 cities as well as the range of city

- specific estimates for the various approaches considered, the generally equivalent 24

- hour leve ls ranged from somewhat below the 4

- hour level to just above

2 Note that the city

- specific ranges shown in Table G

- 6, Appendix G of the Policy Assessment are incorrectly stated for Approaches C and E. Drawing from the more detailed and correct results for Approaches C and E presented in Tables G

- 7 and G

- 8, respectively, the city

- specific ranges in Table G

- 6 for Approach C should be 17

– 21 dv for the CPL of 20 dv; 21

– 25 dv for the CPL of 25 dv; and 24

– 30 dv for the CPL of 30 dv; the city

- specific ranges in Table G

- 6 for A pproach E should be 17

– 21 dv for the CPL of 20 dv; 21

– 26 dv for the CPL of 25 dv; and 25

– 31 dv for the CPL of 30 dv5

the 4

- hour level for each of the CPLs. 3 Some of the approaches used in these analyses focused on comparing 24

- hour and 4

- hour light extinction values in each of the 15 urban areas, whereas other approaches focused on comparisons based on using aggregated data across the urban areas. Two of these approaches, which used regressions of city

- specific annual 90 th percentile light extinction values or 3

- year light extinction design values, gave nearly identical results and were considered by staff to be most appropriate for further consideration . These approaches (shown in US EPA, 2011a, Appendix G, Figures G

- 7 and G

- 8 , referred to as Approaches A and B ) were preferred by staff based on the high R 2 values of the regressions and because the regressions were determined by data from days with PM 2.5 light extinction conditions in the range of 20 to 40 dv. This contraste d with the other approaches that were influenced by PM 2.5 light extinction conditions well below this range. Based on these analyses (presented in Appendix G of the Policy Assessment), the Policy Assessment notes that the single approach thought by staff t o be more appropriate for further consideration (referred to as Approach B in Appendix G) yielded adjusted 24

- hour CPLs of 21, 25, and 28 dv as being levels that are generally equivalent in an aggregate or central tendency sense to 4

- hour CPLs of 20, 25, a nd 30 dv. 4 Two of the approaches yielded not only estimates of generally equivalent levels on an

3 As discussed in more detail in Appendix G of the Policy Assessment, some days have higher values for 24

- hour average light extinction than for daily maximum 4

- hour daylight light extinction, and consequently an adjusted "equivalent" 24

- hour CPL can be greater than the original 4

- hour CPL. This can happen for two reasons. First, the use of monthly average historical RH data will lead to cases in which the f (RH) values used for the calculation of 24

- hour average light extinction are higher than all or some of the four hourly values of f (RH) used to determine daily maximum 4

- hour daylight light extinction on the same day. Second, PM 2.5 conc entrations may be greater during non

- daylight periods than during daylight hours. 4 To provide some perspective in considering these results (US EPA, 2011a, Appendix G, Table G

- 6), the Policy Assessment notes that 1 dv is about the amount that persons can distinguish when viewing scenic vistas, and that a difference of 1 dv is equivalent to about a 10 percent difference in light extinction expressed in Mm - 1

.6

aggregated basis but also city

- specific estimates (referred to as Approaches C and E in Appendix G) that showed greater variability than the aggregated estimat es. In all cases, the range of city

specific estimates of generally equivalent 24

- hour levels included the 4

- hour level for each of the CPLs of 20, 25, and 30 dv (as shown in Tables G

- 7 and G

- 8, Appendix G of the Policy Assessment, for Approaches C and E, respectively). Looking more broadly at these results could support consideration of using the same CPL for a 24

- hour standard as for a 4

- hour standard, recognizing that there is no one approach that can most closely identify a generally equivalent 24

- hour standard level in each urban area for each CPL. The use of such an unadjusted CPL for a 24

- hour standard would place more emphasis on the relatively high degree of spatial and temporal variability in relative humidity and fine particle composition observed in urban areas across the country, so as to reduce the potential of setting a 24

- hour standard level that would require more than the intended degree of protection in some areas. In more broadly considering alternative standard levels that would be approp riate for a nationally applicable secondary standard focused on protection from PM

- related urban visibility impairment based on either a 24

- hour or multi

- hour, sub

- daily (e.g., 4

- hour) averaging time, the Policy Assessment was mindful of the important limi tations in the available evidence from public preference studies. The Policy Assessment was also mindful that the scenic vistas available on a daily basis in many urban areas across the country generally do not have the inherent visual interest or the dist ance between viewer and object of greatest intrinsic value as in the Denver and Phoenix preference studies. As in past reviews, the EPA is considering a national visibility standard in conjunction with the Regional Haze Program as a means of achieving appr opriate levels of protection against PM
- related visibility impairment in urban, non

- urban, and Federal Class I areas across the7

country. The EPA recognizes that programs implemented to meet a national standard focused primarily on the visibility problems i n urban areas can be expected to improve visual air quality in surrounding non

- urban areas as well, as would programs now being developed to address the requirements of the Regional Haze Program established for protection of visual air quality in Federal C lass I areas. The EPA also believes that the development of local programs, such as those in Denver and Phoenix, can continue to be an effective and appropriate approach to provide additional protection, beyond that afforded by a national standard, for uni que scenic resources in and around certain urban areas that are particularly highly valued by people living in those areas. Based on the above considerations, the Policy Assessment concludes that it is appropriate to give primary consideration to alternati ve standard levels toward the upper end of the ranges identified above for 24

- hour and sub

- daily standards, respectively (US EPA, 2011a, p. 4

- 63). Thus, the Policy Assessment concludes it is appropriate to consider the following alternative levels: a level of 28 dv or somewhat below, down to 25 dv, for a standard defined in terms of a calculated PM 2.5 light extinction indicator, a 90 th percentile form, and a 24

- hour averaging time; and a standard level of 30 dv or somewhat below, down to 25 dv, for a similar standard but with a 4

- hour averaging time (US EPA, 2011a, p. 4

- 63). The Policy Assessment judges that such standards would provide appropriate protection against PM

- related visibility impairment primarily in urban areas. The Policy Assessment notes that CASAC generally supported consideration of the 20

– 30 dv range as CPLs and, more specifically, that support for consideration of th e upper part of the range of the CPLs derived from the public preference studies was expressed by some CASAC Panel members during the public meeting on the second draft Policy Assessment. The Policy Assessment concludes that such a standard would be8

approp riate in conjunction with the Regional Haze Program to achieve appropriate levels of protection against PM

- related visibility impairment in areas across the country (US EPA, 2011a, p. 4

- 63). Based on the above considerations, taking into account the conclu sions in the Policy Assessment and the extent to which those conclusions reflected consideration of CASAC advice during the development of the Policy Assessment, as an initial matter, the Administrator provisionally concludes that it is appropriate to esta blish a target level of protection

– for a standard defined in terms of a PM 2.5 visibility index; a 90 th percentile form averaged over 3 years; and a 24

- hour averaging time

-- equivalent to the protection afforded by such a sub

- daily (i.e., 4

- hour) standar d at a level of 30 dv, which is the upper end of the range of CPLs identified in the Policy Assessment and generally supported by CASAC. More specifically, the Administrator provisionally concludes that a 24

- hour level of either 30 dv or 28 dv could be
con strued as providing such a degree of protection, and that either level is supported by the available information and is generally consistent with the advice of CASAC. The option of setting such a 24

- hour standard at a level of 30 dv would reflect recogniti on that there is considerable spatial and temporal variability in the key factors that determine the value of the PM 2.5 visibility index in any given urban area, such that there is a relatively high degree of uncertainty as to the most appropriate approach to use in selecting a 24

- hour standard level that would be generally equivalent to a specific 4

- hour standard level. Selecting a 24

- hour standard level of 30 dv would reflect a judgment that such substantial degrees of variability and uncertainty should b e reflected in a higher standard level than would be appropriate if the underlying information were more consistent and certain. Alternatively, the option of setting such a 24

- hour standard at a level of 28 dv would reflect placing more weight on statistic al9

analyses of aggregated data from across the study cities and not placing as much emphasis on the city

- to
- city variability as a basis for determining an appropriate degree of protection on a national scale. In light of these provisional conclusions, the Administrator proposes to set a new 24

- hour standard ( defined in terms of a PM 2.5 visibility index and a 90 th percentile form, averaged over 3 years ) to provide appropriate protection from PM

- related visibility impairment based on one of two options. One option is to set the level of such a standard at 30 dv and the other option is to set the level at 28 dv. In so doing, the Administrator solicits comment on each of these levels and on the various approaches to identifying generally equivalent levels discussed above upon which the alternative proposed levels are based. Recognizing that there was some support for consideration of a broader range of levels, the Administrator also solicits comment on a range of levels down to 25 dv in conjunction with a 24

- hour averaging time. Further, having solicited comment on a sub

- daily (e.g., 4

- hour) averaging time, the Administrator also solicits comment on a range of alternative levels from 30 to 25 dv in conjunction with such a sub

- dai ly averaging time. Finally, as we have indicated, the information available for the Administrator to consider when setting the secondary PM standard raises a number of uncertainties. While CASAC supported moving forward with a new standard on the basis of the available information,, CASAC also recognized these uncertainties, referencing the discussion of key uncertainties and areas for future research in the second draft of the Policy Assessment. In discussing areas of future research, CASAC stated that: “T he range of 50% acceptability values discussed as possible standards are based on just four studies (Figure 4

- 2), which, given the large spread in values, provide only limited confidence that the benchmark candidate protection levels cover the10

appropriate range of preference values. Studies using a range of urban scenes (including, but not limited to, iconic scenes

– “valued scenic elements” such as those in the Washington DC study), should also be considered.” (Samet, 2010d, p. 12). We invite comment on ho w the Administrator should weigh those uncertainties as well as any additional comments and information to inform her consideration of these uncertainties.

F. Administrator’s Proposed Decisions on Secondary PM Standards (p. 324) With regard to the second ary PM standards, the Administrator proposes to set a new standard for PM 2.5 to address PM

- related visibility impairment, focused primarily on visibility in urban areas. The new secondary standard is defined in terms of a calculated PM 2.5 light extinction indicator, translated into the deciview scale, which is referred to as a PM 2.5 visibility index; a 24

- hour averaging time; a 90 th percentile form, averaged over 3 years; and a level set at one of two options

– either 30 dv or 28 dv. The Administrator solic its comment on a range of levels for such a standard down to 25 dv, as well as on alternative standards to address PM

related visibility impairment, including a sub

- daily averaging time (e.g., 4 hours) and associated alternative levels in the range of 30 t o 25 dv. To address other non

- visibility welfare effects, the Administrator proposes to revise the form of the secondary annual PM 2.5 standard to remove the option for spatial averaging and to retain all other elements of the current suite of secondary PM standards.