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From: Lydia Wegman/RTP/USEPA/US To: nfrey@omb.eop.gov, dmancini@omb.eop.gov Cc: martin.karen@epa.gov, hannon.john@epa.gov, Beth Hassett
- Sipple/RTP/USEPA/US@EPA, Joseph
- J

Dougherty/DC/USEPA/US@EPA, Janet McCabe/DC /USEPA/US@EPA, Gina McCarthy/DC/USEPA/US@EPA Date: 06/14/2012 04:10 PM Subject: Edits to the secondary standard section Nathan and Dom, Attached are edits to the secondary standard section addressing interagency comments received last night. Please le t us know if you have any questions.Page 2 of 10

Revisions to section VI.D.4 in draft PM NAAQS NPR

VI. Rationale for Proposed Decisions on the Secondary Standards D. Consideration of Alternative Standards for Visibility Impairment 4. Level 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
sc ope 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 av eraging 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 the Policy Asses sment’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 t his was an appropriate range of levels to consider for such aPage 3 of 10

standard (Samet, 2010d, p. 11). 1 The Policy Assessment also recognizes that to define a range of alternative levels that would be appropriate to consider for a 24

- hour calculated PM 2.5 light ext inction 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 notes 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 s ection 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 available 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 outdoors during t he 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 stan dard 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 standard, the P olicy Assessment explores

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.Page 4 of 10

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. These various approaches, based on analyses 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 doin g, 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 da ylight 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 downward 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 a cross 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 equi valent 24

- hour levels ranged from somewhat below the 4

- hour level to just above the 4

- hour level for each of the CPLs. 3

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 dv 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 inPage 5 of 10

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 ar eas, 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 va lues, 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 o n 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 contrasted with the other approaches that were influenced by PM 2.5 light extincti on 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 to 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, and 30 dv. 4 Two of the approaches yielded not only estimates of generally equivalent levels on an aggregated basis but also city

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

- specific estimates of generally equi valent 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 consi deration of using the same CPL
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

.Page 6 of 10

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 unadj usted 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 set ting 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 appropriate for a nationally applicable secondary standard focused on protecti on 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 limitations in the available evidence from public preference studies. While the P olicy A ssessment concluded , consistent with CASAC advice, that it is appropriate to consider a distinct secondary PM 2.5 standard to address PM

- related visibility impairment focused primarily in urban areas based on the evidence from public preference studies , it also recognize d that there are a number of uncertainties and limitations associated with the preference studies that have served as a basis for selecting an appropriate range of levels to consider , as discussed above in section VI.B.2
. The se uncertainties and limitations are due in part to the small number of stated preference studies available for this review , ; the relatively small number of study participants and the extent to which the study participants may not be representative of the broader study area population in some of the studies , ; and the variations in the specific materials and methods used in each study such as scene characteristics, the range of VAQ levels presented to study parti cipants, image presentation methods and specific wording used to frame the questions used in the group interview s . In addition t he Policy Assessment was mindful that the scenic vistas available on a daily basis in many urban areas across the country gener ally do not have the inherent visual interest or the distance between viewer and object of greatest intrinsic value as in the Denver and Phoenix preference studies , and that there is the possibility that there could be regional differences in individual pr eferences for VAQ.Page 7 of 10

Given the se uncertainties and limita tions noted a bove , the EPA broadly solicit s comment on the strengths and limitations associated with these preference studies and the use of these stu dies to inform the selection of a range of levels that could be used to provide an appropriate degree of public welfare protection when combined with the other elements of the standard (i.e. indicator, form and averaging time). In particular , the EPA solicits comment on the following specific aspe cts of the public preference studies and on how these studies should appropriately be considered in this review. Recognizing that all of these studies evaluated a 50 percent acceptabili ty criterion as the basis for reaching judgments in the context of each study , the EPA requests comment on the extent to which this criterion is an appropriate basis for establishing target protecti o n levels in the context of establishing a distinct secondary NAAQS t o address PM

- related visibility impairment in urban areas. Rec ognizing that these studies vary in the extent to which the study participants may be representative of the broader study area population, the EPA requests comment on how this aspect of the study design s should appropriately be weighed in the context of co nsidering these studies in reaching proposed c onclusions on a distinct
secon dary NAAQS. The EPA also solicits comment on the extent to which the range s of VAQ levels presented to participants in each of the studies may have influenced study results and on how this aspect of the study designs should appropriately be weighed in the context of considering these st udies in the context of this review. As in past reviews, the EPA is considering a national visibility standard in conjunction with the Region al Haze Program as a means of achieving appropriate levels of protection against PM

- related visibility impairment in urban, non

- urban, and Federal Class I areas across the country. The EPA recognizes that programs implemented to meet a national standard fo cused primarily on the visibility problems in 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 p rotection of visual air quality in Federal Class I areas. The EPA also believes that the development of local programs, such as those in Denver and Phoenix, can continue to be anPage 8 of 10

effective and appropriate approach to provide additional protection, beyond t hat afforded by a national standard, for unique 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 appropriat e to give primary consideration to alternative 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 consid er 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 be 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.Page 9 of 10

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 al 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 discu ssed 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

- hou r 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

- daily averaging time. Finally, as we have indicated, the information available for the Administrator to consider whenPage 10 of 10

setting the secondary PM standard raises a number of uncertainties. While CASAC supported moving forward with a new standard on the basi s of the available information, CASAC a lso 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: “The range of 50% acceptability value s 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 the 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 how the Administrator should weigh th ose uncertainties as well as any additional comments and information to inform her consideration of these uncertainties.