Document ID: EPA-HQ-OAR-2007-0492-0394
Agency: epa
Document Type: Supporting & Related Material
Title: 
Posted Date: 2012-06-28T04:00Z

From:	Lydia Wegman/RTP/USEPA/US
To:	nfrey@omb.eop.gov
Cc:	Beth Hassett-Sipple/RTP/USEPA/US@EPA, martin.karen@epa.gov, Scott Jenkins/RTP/USEPA/US@EPA, wegman.Lydia@epa.gov
Date:	06/05/2012 09:52 AM
Subject:	Fw: Final PM Policy Assessment - transmittal to CASAC PM Panel

Nathan, 

Here are the documents that were sent to CASAC when we issued the final Policy Assessment.  They include the final policy assessment and my transmittal memo to CASAC.  Please let me know if you have any questions. 

                                April 20, 2011
MEMORANDUM

SUBJECT:  Transmittal of Policy Assessment for the Review of the Particulate Matter National Ambient Air Quality 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 Scientific Advisory Committee
               EPA Science Advisory Board Staff Office

      Attached is the final document, Policy Assessment for the Review of the Particulate Matter National Ambient Air Quality Standards  (Policy Assessment, April 2011), prepared by the Environmental Protection Agency's (EPA) Office 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 Policy Assessment presents considerations and conclusions relevant for EPA's review of the current primary (health-based) standards and secondary (welfare-based) standards for both fine and coarse particles.  This final document draws upon the evidence and information assessed and presented in the Integrated Science Assessment for Particulate Matter (ISA) prepared by EPA's National Center for Environmental Assessment and two risk and exposure assessment documents (REAs) prepared by OAQPS, the Quantitative Health Risk Assessment for Particulate Matter (Risk Assessment) and the Urban-Focused Visibility Assessment for Particulate Matter (Visibility Assessment).  These three final documents reflect consideration of comments from the Clean Air Scientific Advisory Committee (CASAC) Particular Matter Review 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 September 10, 2010 letter (Samet, 2010a).  These comments, and the 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 Matter NAAQS.  I look forward to continuing our productive relationship.
Should you have any questions regarding the final Policy Assessment, please contact Ms. Beth Hassett-Sipple (919-541-4605; email - 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/AQAD
                                  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 supported the following:  
            *          The general approach for translating the available epidemiological evidence, risk information, and air quality information into the basis for reaching conclusions on the adequacy of the current standards and on alternative standards that are appropriate for consideration;
            *          Considering revisions to the current PM2.5 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 PM2.5 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 ug/m[3] in conjunction with retaining or revising the level of the 24-hour standard within a range of 35 to 30 ug/m[3].  The Panel stated that these ranges were "supported by the epidemiological and toxicological evidence, as well as by the risk and air quality information..."  However, the Panel requested further clarification on the rationale for the combinations of annual and 24-hour standards most strongly supported 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 information related to the concentrations that were most influential in generating the health effect estimates in individual studies to inform alternative annual standard levels (Samet, 2010a, p. 2).  
            *          The Panel also commented that the approach presented in the second draft Policy Assessment to identify alternative 24-hour standard levels which focused on peak-to-mean ratios was not relevant for informing the actual level (Samet 2010a, p. 4)
Changes made in chapter 2 in the 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 levels 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 number of figures that summarize the available epidemiological evidence, air quality information, and risk-based considerations (Figures 2-4 to 2-12).  

In our discussion of evidence-based considerations to inform alternative annual standard levels (section 2.3.4.1), we expanded and clarified the different approaches for characterizing the range of PM2.5 concentrations over which we have the most confidence 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 most influential in generating the health effect estimates in individual studies to inform staff conclusions on alternative annual standard levels that would provide appropriate protection for both long- and short-term exposures, we contacted several study investigators to obtain additional information on population-level data (i.e., health events, number of study participants).  In new analyses using distributional statistics, we considered these data in conjunction with air quality data to identify the broader range of PM2.5 concentrations that were most influential in generating health effect estimates in epidemiological studies, and, specifically, the range of PM2.5 concentrations below the long-term means over which we continue to have confidence in the associations observed in these epidemiological studies (Figures 2-7 and 2-8 and associated text).  

In our discussion of evidence-based considerations to inform potential alternative 24-hour standards, consistent with the Panel's comments we focused on the epidemiological evidence from multi- and single-city short-term exposure studies to inform staff conclusions on alternative 24-hour standard levels appropriate to consider (section 2.3.4.1, Figures 2-6 and 2-9).  In addition to the epidemiological evidence, we also considered air quality information to understand the implications of different combinations of alternative 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 supplementation protection (Figure 2-10).  

In the second draft Policy Assessment, staff reached the preliminary conclusion that consideration should be given to alternative annual PM2.5 standard levels in the range of 13 to 11 ug/m[3], in conjunction with retaining the current 24-hour PM2.5 standard level of 35 ug/m[3], and that consideration could also be given to an alternative 24-hour PM2.5 standard level of 30 ug/m[3] particularly in conjunction with an annual standard of 11 ug/m[3].  As noted in section 2.3.4.3, staff conclusions in the final Policy Assessment regarding 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 PM2.5 standard level to a level within the range of 13 to 11 ug/m[3].  Staff further concludes that the evidence most strongly supports consideration of an alternative annual standard level in the range of 12 to 11 ug/m[3].  In conjunction with consideration of an annual standard in the range of 12 to 11 ug/m[3], staff concludes it is appropriate to consider retaining the current 24-hour PM2.5 standard level at 35 ug/m[3].  In conjunction with consideration of an annual standard level of 13 ug/m[3], staff concludes there is limited support to consider revising the 24-hour PM2.5 standard level to somewhat below 35 ug/m[3], such as down to 30 ug/m[3]. 
These final staff conclusions reflect consideration of the Panel's comments as well as public comments on the second draft Policy Assessment and additional analyses, as described above.  
Chapter 3 (Primary Standard for Coarse Particles)
In their review of the second draft Policy Assessment, the Panel recommended the following:  
            *          Revising the current PM10 primary standard to provide increased public health protection against effects associated with exposures to PM10-2.5;
            *          Retaining PM10 as the indicator for thoracic coarse particles, while also encouraging research to provide information for future NAAQS reviews to inform consideration of alternative sizes (e.g., PM10-2.5) 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 potential 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 draft 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 PM10 standard.  Specifically, section 3.3.3 discusses a new analysis of PM10 and PM10-2.5 air quality concentrations in U.S. locations and section 3.3.4 now includes an expanded discussion of PM10 air quality concentrations in U.S. study locations.  Section 3.3.4 also includes an expanded discussion of the relationship between the current standard level and 98[th] percentile PM10 concentrations.  Figure 3-8 presents a regional breakdown of this relationship, and the integration discussion in section 3.3.4 now includes more extensive consideration of different approaches to characterizing this relationship.  In addition, section 3.3.4 includes an expanded discussion of potential alternative standard levels, more clearly articulating the basis for staff's conclusions related 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 PM2.5 standards to provide increased protection against PM-related visibility impairment;
         *          Considering a PM2.5 light extinction indicator in preference to a PM2.5 mass indicator; and
         *          Considering secondary standards for a PM2.5 light extinction indicator in a range of 20 to 30 deciviews.
The Panel expressed its strong preference for directly measuring light extinction over using estimates based on mass measurements and recommended a fuller discussion of the reasons EPA staff believes this is not a feasible approach for this review.  We have expanded the discussion of this issue and added a citation to the recommendations of the advice we received from the Panel's Ambient Air Monitoring and Methods Subcommittee (Russell and Samet, 2010).  

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 rapidly over the course of a day and such changes are almost instantaneously perceptible to human observers.  Based in part on this consideration, the Panel agreed that a 1-hour averaging time would be appropriate to consider in conjunction with a directly measured PM light extinction indicator, noting that a 1-hour averaging time is well within the instrument response times of the various currently available and developing optical monitoring methods that directly measure light extinction.  At that time, the Panel also advised that if a PM2.5 mass indicator were to be used, it would be appropriate to consider "somewhat longer averaging times  -  2 to 4 hours  -  to assure a more stable instrumental response" (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 monitoring methods that were available for the alternative indicators discussed in the draft PA.  We have interpreted the Panel's views on a multi-hour averaging time as extending to a sub-daily calculated PM2.5 light extinction indicator since PM2.5 mass measurements are also required for this indicator.

In preparing the final Policy Assessment, EPA staff conducted analyses to better understand data quality issues associated with the use of continuous Federal Equivalent Methods (FEMs) that were considered as the basis for hourly PM2.5 mass measurements (section 4.3.1.1).  Based in part on these analyses, EPA staff concludes that it is appropriate to consider a 24-hour averaging time, in conjunction with a calculated PM2.5 light extinction indicator and appropriately specified standard level (sections 4.3.2.2 and 4.3.2.4).  This conclusion reflects the judgment that PM2.5 light extinction calculated on a 24-hour basis is a reasonable and appropriate surrogate for sub-daily PM2.5 light extinction calculated on a 4-hour average basis.  This conclusion is also predicated on consideration of a 24-hour average standard level which we have interpreted as providing information on the acceptability of daytime visual air quality over an hourly or multi-hour exposure period (section 4.3.4).

Other changes included in the final Policy Assessment include an analysis of the performance of two somewhat differently defined calculated PM2.5 light extinction indicators using 2007-2009 data (revised Appendix F), removal of detailed material from Chapter 4 regarding a PM2.5 mass indicator (this material is still provided in Appendix E and several technical memos), and the addition of two new appendices, Appendix G and Appendix H.  Appendix G discusses the use of calculated 24-hour average PM2.5 light extinction as the indicator and averaging period for a secondary PM2.5 NAAQS that would be aimed at controlling 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, similar to Appendices C and D which provides information related to the current and alternative primary standards.

We note that since earlier drafts of this Policy Assessment did not include discussion of a calculated PM2.5 indicator based on a 24-hour averaging time, CASAC did not have a basis to express any views regarding a 24-hour averaging time.