September 23, 2010

MEMORANDUM

SUBJECT: Transmittal of Final Assessment Documents: Quantitative Health Risk Assessment for Particulate Matter and Particulate Matter Urban-Focused Visibility Assessment

FROM: Lydia N. Wegman, Director Health and Environmental Impacts Division (C504-02) Office of Air Quality Planning and Standards United States Environmental Protection Agency

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

Attached are the final assessment documents: Quantitative Health Risk Assessment for

Particulate Matter (Risk Assessment or RA, June 2010) and Particulate Matter Urban-Focused Visibility Assessment (Visibility Assessment or UFVA, July 2010), prepared by the Environmental Protection Agency’s (EPA) Offi ce of Air Quality Planning and Standards (OAQPS) staff as part of EP A’s ongoing review of the primary (health-based) and secondary (welfare-based) national ambien t air quality standards (NAAQS) for particulate matter (PM). These final documents draw upon information presented in the final Integrated Science Assessment for Particulate Matter (ISA, December 2009) prepared by EPA’s National Center for Environmental Assessment, Research Triangle Park, NC (NCEA-RTP). They also reflect

consideration of comments from the CASAC PM Panel, as well as public comments, on the second draft assessment documents, which were re viewed by the Panel at a meeting on March 10-11, 2010.

Risk Assessment

The main comments from the CASAC PM Pa nel on the second draft Risk Assessment, provided to us in an April 15, 2010 letter (Samet, 2010a) 1 , are briefly summarized below together with a brief description of how we have considered the comments in preparing the final

Risk Assessment.

1 Samet, J. (2010a). Letter from Clean Air Scientific Advisory Committee to the Honorable Lisa P. Jackson, Administrator, US EPA. CASAC Review of Quantitative Health Risk Assessment for Particulate Matter – Second External Review Draft (February 2010). April 15, 2010. Available: http://yosemite.epa.gov/sab/sabproduct.nsf/BC4F6E77B6385155852577070002F09F/$File/EPA-CASAC-10-008- unsigned.pdf2  Regarding methods used to simulate just meetin g current and alternative standards, the Panel recommended that EPA: (a) include a graphica l/mathematical description of each rollback method, (b) give more emphasis to the hybrid rollback method, using th e other two rollback methods to represent bounding estimates, and (c ) rename the “peak shaving” method to more clearly describe the actual methods used.

RESPONSE: In the final Risk Assessment, EPA included an example calculation of the three rollback methods illustrating mathemati cally the application of the three rollback methods as applied to the Detroit urban study area in simulating just meeting current standard levels (Appendix B, section B.3). In presenti ng estimated risk results generated using the

three rollback methods for simu lating alternative standard leve ls, we noted the potential for the hybrid method to reflect a more repres entative approach bounded by the other two rollback methods considered in Chapters 4 a nd 5. In addition, we renamed the “peak shaving” approach the “locally focu sed rollback method" (section 3.2.3).

 Regarding the national-scale assessment, the Pa nel concluded that the key findings of this work presented in Chapter 5 of the second draf t RA related to the representativeness of the 15 urban study areas. The Panel recommended moving the overall discussion of this analysis to an appendix while re taining the key findings.

RESPONSE: For the final Risk Assessment, we moved discussion of the methods used in the national-scale risk assessment into Appe ndix G. In the main body of the document, (Chapters 4 and 5), we focused the discussion of that analysis to the representativeness of the 15 urban study areas.

 Regarding the confidence in the risk estimat es, the Panel recommended that EPA develop and apply specific criteria for determining the lower-bound exposure co ncentrations to be considered in the risk assessment. Specificall y, the Panel suggested consideration should be given to the range of concentrations evalua ted in the epidemiology studies providing the concentration-response functions for the quantitative risk assessm ent as well as the degree of protection afforded to susceptible po pulations under various scenarios.

RESPONSE: For the final Risk Assessment, we expanded our discus sion of the confidence

associated with the core risk estimates by more fully considering how the simulated composite monitor values underlying the risk estimates compared to ambient measurements used to support concentration -response functions in the ep idemiological studies (section 5.1.6. The consideration of the protection afford ed by the current and a lternative suites of standards, including protection afforded to susceptible populations, is discussed in the Policy Assessment for the Review of the Particulate Matter National Ambient Air Quality Standards.

 The Panel recommended that EPA provide addi tional clarification on the selection of exposure scenarios used in the risk assessment.3 RESPONSE: For the final Risk Assessment, we expanded the discussion related to selection

of alternative suites of standards evaluated to more fully discuss the iterative nature of the process we used to identify alternative st andard levels to model (section 2.4) .

 The Panel recommended additional rewriting and clarification of content presented in the integrative discussion (Chapter 6 of the second draft RA).

RESPONSE: For the final Risk Assessment, we made extensive edits in the integrative

discussion to streamline the text and focu s on critical observations (Chapter 5).

 The Panel recommended including a very brief description of how the design values were calculated in the analyses and expressed con cern about the method used in the second draft Risk Assessment to impute missing measurem ent data. The Panel further suggested EPA

consider alternative methods for interpolating missing data.

RESPONSE: In the final Risk Assessment, we included a more rigorous description of how design values are calculated (s ection 3.2.3.1). We also considere d, as part of a sensitivity analysis, an alternative method fo r generating design values that used a different approach for interpolating missing data (A ppendix B, section B1).

 Regarding characterization of uncertainties, the Panel recommended that EPA clarify the approach used to assign high, medium or low cl assifiers to potential sources of uncertainty. The Panel also suggested EPA mo re directly incorporate the results from the qualitative analysis of uncertainty presented in Chapter 4 into the integrative discussion chapter. Furthermore, the Panel suggested that interpreta tion of the sensitivity analysis results include

consideration of the absolute ma gnitude of the change in risk results in addition to focusing on the direction and percent change.

RESPONSE: For the final Risk Assessment, we clarified the approach used to assign descriptors to potential sources of uncertainty (section 3.5.3). We also more fully integrated the results of the qualitative di scussion of uncertainty into the integrative discussion (Chapter 5). In addition, we expanded the presentation of the results of the sensitivity analysis to include information on the magnitude of the core risk estimates as presented in Table 4-4.

 The Panel recommended that the scatter diag rams depicting 24-hour and annual design values be enhanced by including info rmation on geographical regions.

RESPONSE: For the final Risk Assessment, in considering the relationships between annual and 24-hour design values for specific areas, we color coded these areas by geographic region to facilitate our ab ility to observe regional differences (Figure 4-21).

 The Panel recommended that the term "peaky" as used to describe PM patterns be more clearly defined and a pplied consistently.4 RESPONSE: In the final Risk Assessment, we clarified the definition of the term “peaky” and used it consistently in the discussion and interpretation of the risk estimates (Chapters 4 and 5).

Visibility Assessment

The main comments from the CASAC PM Pa nel on the second draft Risk Assessment, provided to us in an April 20, 2010 letter (Samet, 2010b) 2 , are briefly summarized below together with a brief description of how we have considered the comments in preparing the final Visibility Assessment.

 The Panel recommended that it would be important to see a more detailed comparison of the

affected PM 2.5 concentrations, species compositions and levels of visibilit y protection that

would result from the use of alternative PM 10 light extinction, PM 2.5 light extinction or PM 2.5 mass indicators.

RESPONSE: In the final Visibility Assessmen t, the effectiveness for reducing visibility effects of PM by the use of various 1-hour PM 10 light extinction and 24-hour and annual

PM 2.5 mass concentration indicators are compared based on the current design values and the results of a rollback exercise to just meet each NAAQS scenario for 15 urban areas. These comparisons are presented principally by using ta bles and box plots to show the magnitude of current and projected ro llback levels of PM 10 light extinction. To improve the comparisons of the species compositions for highest 1-hour PM 10 light extinction values as selected by the two forms (i.e. maximum daylight daily 1-hour and all daylight1-hour forms), stacked bar plots in Figure 3-13 were changed in the final version of the Visibility Assessment so that both forms included hourly contributions to PM 10 light extinction. These figures showed similar composition for hours selected by the two forms as described in section 3.4.5. Additional analysis utilizing similar plots to characterize the compos ition of hours selected by PM 2.5 mass concentration indicators were included in Appendix 4-C of the Policy Assessment for the Review of Particulate Ma tter National Ambient Air Quality Standards, Second External Review Draft

.

 The Panel recommended the addition of an integrative summary chapter.

RESPONSE: An integrative summary chapter wa s added to the final document (Chapter 5).

 The Panel recommended the addition of a section on further research needs, including future urban visibility preference studies.

RESPONSE: The final Visibility Assessment in cluded brief descriptions of the potential benefits from future research as part of th e Technical Issues subsections in Chapter 5,

2 Samet, J. (2010b). Letter from Clean Air Scientific Advisory Committee to the Honorable Lisa P. Jackson, Administrator, US EPA. CASAC Review of Particul ate Matter Urban-Focused Visibility Assessment – Second External Review Draft (January 2010). April 20, 2010. Available: http://yosemite.epa.gov/sab/sabproduct.nsf/0D5CB 76AFE7FA77C8525770D004EED55/$File/EPA-CASAC-10- 009-unsigned.pdf5 including a discussion of the benefits of addition urban visibility preference studies (section 5.1). A more comprehensive discussion of future research needs is incl uded in section 4.5 of the second draft Policy Assessment.

 The Panel recommended reduction of the level of detail in the desc ription of the logit analysis in Chapter 2.

RESPONSE: As recommended, we streamlined the description of th e logit analysis in chapter 2 and included a complete technical description of th e analysis in a newly added Appendix J.

 The Panel requested a more direct “apples to apples” comparison of the composition between different forms for the plots of hourly PM composition for the various urban areas.

RESPONSE: Stacked bar plots in Figure 3-13 we re modified and a summary plot of urban area averaged composition in Figure 3-14 was added. These plots compare the PM composition selected by the two alternative forms more directly than was done in the second

review draft of the UFVA.

 The Panel expressed concern for the high PM 10-2.5 mass contributions for St. Louis and Los Angeles and recommended closer scrutiny of the data used.

RESPONSE: The final Visibility Assessmen t acknowledged the concerns raised by CASAC with respect to the credibility of unrealistically high PM 10-2.5 mass measurement data for St. Louis (section 3.2.1 including footnote 10 on page 3- 13). Since this concern was raised late in the development of the Visibility Assessmen t (i.e. beyond the point when alternative data could be use as input to a reassessment), th e final document was modified to caution the reader with respect to the St. Louis results wherever they are discussed. The second draft Policy Assessment excluded results from St. Louis. With regard to Los Angeles PM 10-2.5 mass contributions, we acknowledge that the data may be of gr eater uncertainty than other

urban areas with collocated PM 2.5 and PM 10 monitors, however unlike for St. Louis, PM 10-2.5 mass rarely contributes signifi cantly in the periods of time featured in the assessments conducted for Los Angeles, so no change or ad ditional cautionary warnings to the reader

were included in the final UFVA.

Availability of Final Documents

The final assessment documents are available to the CASAC PM Panel in the form of the

attached electronic files. These documents are also available from the EPA website at http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html . Should you have any questions regarding the final PM Risk Assessm ent, please contact Dr. Zach Pekar (919 541- 3704; email pekar.zachary@epa.gov ). Should you have any ques tions regarding the final Visibility Assessment, please contact Ms. Vicki Sandiford (919 541-2629; email sandiford.vicki@epa.gov ).

Attachments6 cc: Vanessa Vu, SAB, OA Karen Martin, OAQPS/HEID Beth Hassett-Sipple, OAQPS/HEID Zach Pekar, OAQPS/HEID Marc Pitchford, NOAA Pradeep Rajan, OAQPS/HEID Mary Ross, ORD/NCEA-RTP Vicki Sandiford, OAQPS/HEID Lindsay Stanek, ORD/NCEA-RTP Jason Sacks, ORD/NCEA-RTP John Vandenberg, ORD/NCEA-RTP