1 April 20, 2011
MEMORANDUM

SUBJECT: Transmittal of Policy Assessment for the Review of the Pa rticulate Matter National Ambient Air Qua lity Standards – Final Document

FROM: Lydia N. Wegman, Director /s/ Health and Environmental Impacts Division Office of Air Quality Planning and Standards

TO: Holly Stallworth Designated Federal Officer
Clean Air Sc ientific Advisory Committee EPA Science Advisory Board Staff Office

Attached is the final document, Policy Assessment for the Revi ew of the Particulate Matter
National Ambient Air Quality Standards (Policy Assessment, April 2011), prepared by the Environmental Protection Agency’s (EPA) Offi ce of Air Quality Planning and Standards (OAQPS) staff as part of EPA’ s ongoing review of the national ambient air quality standards (NAAQS) for particulate matter (PM). The Poli cy Assessment presents considerations and
conclusions relevant for EPA’s review of the current primar y (health-based) standards and secondary (welfare-based) standa rds for both fine and coarse pa rticles. This final document draws upon the evidence and informa tion assessed and presented in the Integrated Science Assessment for Particulate Matter (ISA) prepared by EPA’s Nati onal Center for Environmental Assessment and two risk and exposure assessment documents (REAs) prepared by OAQPS, the Quantitative Health Risk Assess ment for Particulate Matter (Risk Assessment) and the UrbanFocused Visibility Assessmen t for Particulate Matter (Visibility Assessment). 1 These three final
documents reflect consideration of comments from the Clean Air Scientific Advisory Committee (CASAC) Particular Matter Revi ew Panel (the Panel) and the public on earlier drafts.

The Policy Assessment reflects consideration of comments from the Panel, as well as public comments, on the second draft Policy Assessment, which was reviewed by the Panel at a meeting on July 26-27, 2010. Comments from the Panel on the second draft Policy Assessment were provided to us in a Sept ember 10, 2010 letter (Samet, 2010a). 2 These comments, and the

1 All documents related to the current PM NAAQS review are available at: http://www.epa.gov/ttn/naaqs/st andards/pm/s_pm_index.html

. 2 Samet, J (2010a). Letter from Dr, Jonathan M. Samet, Chair, Clean Air Scientific Advisory Committee to the Honorable Lisa P. Jackson, Administrator, US EPA. CASAC Review of Policy Assessment for the Review of the PM NAAQS – Second External Review Draft (June 2010). September 10, 2010. Available at: http://yosemite.epa.gov/sab/sabproduct.nsf/264c b1227d55e02c85257402007446a4/CCF9F4C0500C500F8525779D00 73C593/$File/EPA-CASAC-10-015-unsigned.pdf2 changes made in the final Policy Assessment in response to them, are summarized in the
Attachment.

Availability of Final Document

The Policy Assessment is being made available to the Panel in the form of the attached electronic file, which we request that you forward to members of the Panel. This document is
also available on the EPA website: http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_pa.html

.

Please accept my gratitude for the advice the Panel has provided throughout our review
of the Particulate Matt er NAAQS. I look forward to cont inuing our productive relationship. Should you have any questions regarding the fina l Policy Assessment, please contact Ms. Beth Hassett-Sipple (919-541-4605; ema il - hassett-sipple.beth@epa.gov).

cc: Vanessa Vu, SAB, OA Rosalina Rodriguez, OAQPS/HEID Karen Martin, OAQPS/HEID John Vandenberg, ORD/NCEA-RTP Debra Walsh, ORD/NCEA-RTP Mary Ross, ORD/NCEA-RTP Doug Johns, ORD/NCEA-RTP Lindsay Stanek, ORD/NCEA-RTP Beth Hassett-Sipple, OAQPS/HEID Zachary Pekar, OAQPS/HEID Pradeep Rajan, OAQPS/HEID Scott Jenkins, OAQPS/HEID Vicki Sandiford, OAQPS/HEID Meredith Lassiter, OAQPS/HEID Marc Pitchford, NOAA Chet Wayland, OAQPS/AQAD Phil Lorang, OAQPS/AQPD Lewis Weinstock, OAQPS/AQAD Patrick Dolwick, OAQPS/AQAD James Hemby, OAQPS/AQAD1 Attachment CASAC Comments on Second Draft PM Policy Assessment and Responses to those
Comments

The CASAC PM Panel’s comments and recommendations on the second draft of the PM Policy Assessment, as well as changes made in the final document in response to those comments for chapters 2 through 4, are summarized below.

Chapter 2 (Primary Standards for Fine Particles)

The Panel expressed agreement with a number of staff conclusions in the second draft Policy Assessment, and suppor ted the following:

 The general approach for translating the available epidemiologi cal evidence, risk information, and air quality information into the basis for reaching conclusions on the adequacy of the current standards and on alte rnative standards that are appropriate for consideration;

 Considering revisions to the current PM 2.5 primary standard to provide increased public health protection;

 Returning to the strategy used in 1997 that considers a suite of standard levels in which the annual standard would be the “generally controlling” standard to provide primary protection for health effects associated with both long- and short-term PM 2.5 exposures, in conjunction with a 24-hour standard set to provide supplemental protection;

 Revising the form of the annual standard to eliminate spatial averaging; and

 Revising the annual standard level within the range of 13 to 11 μg/m 3 in conjunction with retaining or revising the level of the 24-hour standard within a range of 35 to 30 μg/m 3 . The Panel stated that these ranges we re “supported by the epidemiological and toxicological evidence, as well as by the ri sk and air quality inform ation...” However, the Panel requested further clar ification on the rationale for the combinations of annual and 24-hour standards most strongly supporte d by the currently available information, as well the rationale for excluding other combinations within the ranges considered.

 In addition, the Panel encouraged staff to focus on informa tion related to the
concentrations that were most influential in generating the health effect estimates in
individual studies to inform alternative annu al standard levels (Samet, 2010a, p. 2).

 The Panel also commented that the appro ach presented in the second draft Policy Assessment to identify alternative 24-hour standard levels which focused on peak-tomean ratios was not relevant for inform ing the actual level (Samet 2010a, p. 4)

Changes made in chapter 2 in th e final Policy Assessment were primarily focused on improving and clarifying the approach for translating the epidemiological evidence into a basis for staff conclusions on potential alternative standard leve ls and more clearly articulating the basis for
staff’s conclusions related to alternative standard levels that are appropriate for consideration. Specifically, we have updated and streamlined the discussion of the general approach used in the current review (section 2.1.3). We have modified or added a numbe r of figures that summarize the available epidemiological evidence, air quality info rmation, and risk-based c onsiderations (Figures 2-4 to 2-12).2 In our discussion of evidence-based considerations to inform alternative a nnual standard levels (section 2.3.4.1), we expanded and clarified the diff erent approaches for characterizing the range of

PM 2.5 concentrations over which we have the most co nfidence in the associations observed in the epidemiological studies. Consistent with the Panel’s comments to consider more information from epidemiological studies related to the concentrations that were mo st influential in generating the
health effect estimates in individual studies to inform staff conclusions on alternative annual standard levels that would provide appropriate pr otection for both long- and short-term exposures, we contacted several study inves tigators to obtain additional inform ation on population-level data (i.e., health events, number of st udy participants). In new analyses using distributional statistics, we considered these data in conj unction with air quality data to identify th e broader range of PM 2.5 concentrations that were most in fluential in generating health effe ct estimates in epidemiological studies, and, specifically, the range of PM 2.5 concentrations below the long-term means over which
we continue to have confidence in the associ ations observed in these epidemiological studies (Figures 2-7 and 2-8 and associated text).

In our discussion of evidence-based considera tions to inform poten tial alternative 24-hour standards, consistent with the Panel’s comments we focused on the epidemiological evidence from multi- and single-city short-term exposure studie s to inform staff conc lusions on alternative 24- hour standard levels appropriate to consider (sec tion 2.3.4.1, Figures 2-6 an d 2-9). In addition to the epidemiological evidence, we also consid ered air quality information to understand the implications of different combinations of alte rnative annual and 24-hour standards that would support the policy goal of focusing on a generally controlling annual standard in conjunction with a 24-hour standard that would provide s upplementation protection (Figure 2-10).

In the second draft Policy Assess ment, staff reached the preliminar y conclusion that consideration should be given to alternative annual PM 2.5 standard levels in th e range of 13 to 11 μg/m 3 , in conjunction with retaining the current 24-hour PM 2.5 standard level of 35 μg/m 3 , and that consideration could also be give n to an alternative 24-hour PM 2.5 standard level of 30 μg/m 3
particularly in conjunction with an annual standard of 11 μg/m 3 . As noted in section 2.3.4.3, staff conclusions in the final Policy Assessment regard ing alternative pairings of annual and 24-hour standards that are appropriate to consider differ somewhat from the pairings of annual and 24-hour standards discussed in the second draft Policy Assessment upon which the Panel based its advice. In the final Policy Assessment, staff again concludes that consideration should be given to revising
the current annual PM 2.5 standard level to a level with in the range of 13 to 11 μg/m 3 . Staff further
concludes that the evidence most st rongly supports consideration of an alternative annual standard level in the range of 12 to 11 μg/m 3 . In conjunction with considerati on of an annual standard in the range of 12 to 11 μg/m 3 , staff concludes it is appropriate to consider retaining the current 24-hour

PM 2.5 standard level at 35 μg/m 3 . In conjunction with considerati on of an annual standard level of 13 μg/m 3 , staff concludes there is limited sup port to consider revising the 24-hour PM 2.5 standard level to somewhat below 35 μg/m 3 , such as down to 30 μg/m 3

.
These final staff conclusions reflect consideratio n of the Panel’s commen ts as well as public comments on the second draft Policy Assessment a nd additional analyses, as described above.3 Chapter 3 (Primary Standa rd for Coarse Particles)

In their review of the second draft Policy Asse ssment, the Panel recommended the following:

 Revising the current PM 10 primary standard to provide increased public health protection against effects associated with exposures to PM 10-2.5 ;

 Retaining PM 10 as the indicator for thoracic coarse particles, while also encouraging research to provide informa tion for future NAAQS reviews to inform consideration of alternative sizes (e.g., PM 10-2.5 ) as well as components and sources;

 Retaining the 24-hour averaging time;

 Revising the form to the 98 th percentile, while also noting that additional characterization is needed regarding the pot ential implications of such a change in form; and

 Setting the level of the revised standard within the range of 75 to 65  g/m 3

. Changes made to chapter 3 since the second draf t Policy Assessment have been focused largely on improving and expanding the discussion of potential alternative standards in section 3.3. In sections 3.3.3 and 3.3.4, we have included additional analysis and discussion of the potential public health impacts of revising the form and level of the current PM 10 standard. Specifically, section 3.3.3 discusses a new analysis of PM 10 and PM 10-2.5 air quality concentrations in U.S. locations and
section 3.3.4 now includes an expanded discussion of PM 10 air quality concentra tions in U.S. study locations. Section 3.3.4 also includes an expa nded discussion of the relationship between the
current standard level and 98 th percentile PM 10 concentrations. Figure 3-8 presents a regional breakdown of this relationship, and the integratio n discussion in section 3.3.4 now includes more
extensive consideration of different approaches to characterizi ng this relationship. In addition, section 3.3.4 includes an expanded discussion of potential alternativ e standard levels, more clearly articulating the basis for staff’s conclusions relate d to alternative levels that are appropriate for
consideration.

Chapter 4 (Secondary Standard for PM-related Visibility)

The Panel expressed agreement with a number of staff conclusions included in the second draft Policy Assessment, including:

 Considering revisions to the current PM 2.5 standards to provide increased protection against PM-related visibility impairment;

 Considering a PM 2.5 light extinction indicator in preference to a PM 2.5 mass indicator;
and

 Considering secondary standards for a PM 2.5 light extinction indicator in a range of 20
to 30 deciviews.

The Panel expressed its strong preference for di rectly measuring light extinction over using
estimates based on mass measurements and reco mmended a fuller discussi on of the reasons EPA
staff believes this is not a feasib le approach for this review. We have expanded the discussion of
this issue and added a citation to the recommendati ons of the advice we received from the Panel’s Ambient Air Monitoring and Methods Su bcommittee (Russell and Samet, 2010). 3

3 Russell A, Samet JM (2010). Letter from the Clean Air Science Advisory Committee (CASAC) Ambient Air Monitoring and Methods Subcommittee (AAMMS) to the Honorable Lisa P, Jackson, Administrator, US EPA. Review of the White Paper on Particulate Matter (PM) Light Extinction Measurements. April 29, 2010, Available at:4 In its review of the first draft Policy Assessment , the Panel agreed with the staff conclusion that PM effects on visibility can vary widely and rapi dly over the course of a day and such changes are almost instantaneously perceptible to human observers. 4 Based in part on this consideration, the Panel agreed that a 1-hour aver aging time would be appropriate to consider in conjunction with a directly measured PM light extinction indicator, no ting that a 1-hour averaging time is well within the instrument response times of the various cu rrently available and developing optical monitoring methods that directly measure light extinction. At that time, the Panel also advised that if a PM 2.5 mass indicator were to be used , it would be appropriate to cons ider “somewhat longer averaging
times – 2 to 4 hours – to assure a more stable instrumental resp onse” (Samet, 2010b, p. 19). Thus, the Panel’s views on averaging times that would be appropriate for consideration were predicated in part on the capabilities of mon itoring methods that were availabl e for the alternative indicators discussed in the draft PA. We have interprete d the Panel’s views on a mu lti-hour averaging time as extending to a sub-daily calculated PM 2.5 light extinction indicator since PM 2.5 mass measurements are also re quired for this indicator.

In preparing the final Policy Assessment, EPA st aff conducted analyses to better understand data quality issues associated with the use of continuou s Federal Equivalent Methods (FEMs) that were considered as the basis for hourly PM 2.5 mass measurements (section 4 .3.1.1). Based in part on these analyses, EPA staff concludes that it is appr opriate to consider a 24- hour averaging time, in conjunction with a calculated PM 2.5 light extinction indicator and appropriately specified standard level (sections 4.3.2.2 and 4. 3.2.4). This conclusion reflects the judgment that PM 2.5 light
extinction calculated on a 24-hour basis is a r easonable and appropriate surrogate for sub-daily

PM 2.5 light extinction calculated on a 4-hour average ba sis. This conclusion is also predicated on consideration of a 24-hour average standard le vel which we have interpreted as providing information on the acceptability of daytime visu al air quality over an hourly or multi-hour exposure period (section 4.3.4).

Other changes included in the fi nal Policy Assessment include an analysis of the performance of two somewhat differently defined calculated PM 2.5 light extinction indicators using 2007-2009 data (revised Appendix F), removal of detailed material from Chapter 4 regarding a PM 2.5 mass indicator (this material is s till provided in Appendix E and several techni cal memos), and the addition of two new appendices, Appendix G and A ppendix H. Appendix G discusses the use of calculated 24-hour average PM 2.5 light extinction as the indica tor and averaging period for a secondary PM 2.5 NAAQS that would be aimed at cont rolling daily maximum daylight 4-hour average light extinction conditions. Appendix H provides information on the number and percentage of counties that likely would not meet the current and alternative secondary standards,

http://yosemite.epa.gov/sab/sabproduct.nsf/264c b1227d55e02c85257402007446a4/92C9F5AA09A76A938525771500 04A782/$File/EPA-CASAC-10-010-unsigned.pdf

. 4 Samet J (2010b). Letter from Dr. Jonathan M. Samet, Chair, Clean Air Scientific Advisory Committee to the Honorable Lisa P. Jackson, Administrator, US EPA. CASAC Review of Policy Assessment for the Review of the PM NAAQS – First External Review Draft (March 2010). May 17, 2010. Available at: http://yosemite.epa.gov/sab/sabproduct.nsf/264cb1227d55e02c85257402007446a4/E504EE3276D87A9E85257727 00647AFB/$File/EPA-CASAC-10-011-unsigned.pdf/

.5 similar to Appendices C and D wh ich provides information related to the current and alternative primary standards.

We note that since earlier drafts of this Polic y Assessment did not include discussion of a
calculated PM 2.5 indicator based on a 24-hour averagi ng time, CASAC did not have a basis to express any views regarding a 24-hour averaging time.