February 9, 2010

MEMORANDUM

SUBJECT: CASAC Review of Quantitative Health Risk Assessment for Particulate Matter -- Second External Review Draft

FROM: Lydia N. Wegman, Director /s/ 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 is the second draft assessment document: Quantitative Health Risk Assessment for Particulate Matter (February 2010), prepared by the En vironmental Protection Agency’s (EPA) Office of Air Quality Planning and Stan dards (OAQPS) staff as part of EPA’s ongoing review of the primary (hea lth-based) national ambient ai r quality standards (NAAQS) for particulate matter (PM). This document will be one of the documents to be reviewed by the Clean Air Scientific Advisory Committee (C ASAC) PM NAAQS Review Panel (the CASAC PM Panel) at a public meeting to be held in Chapel Hill, NC on March 10-11, 2010. I am requesting that you forward this draft document to the CASAC PM Panel to prepare for the March meeting.

The other document to be reviewed at the March meeting, Particulate Matter UrbanFocused Visibility Assessment – Second External Review Draft , was sent to you on January 20, 2010. As I noted at that time, we are also preparing anot her draft document, Policy Assessment for the Review of the Particulate Matter Na tional Ambient Air Quality Standards – First External Review Draft, to be reviewed by the CASAC PM Panel by teleconference on April 8-9, 2010. I expect to send the draft Policy Asse ssment to you around the beginning of March, in advance of the March meeting.

This draft document draws upon information presented in the final Integrated Science Assessment for Particulate Matter (ISA, December 2010) prepared by EPA’s National Center for Environmental Assessment, Research Triangle Park, NC (NCEA-RTP). It also reflects

consideration of comments from the CASAC PM Panel, as well as public comments, on the first draft PM Risk Assessment, which was reviewed by the Panel at a meeting on October 5-6, 2009.2 The CASAC and public comments on this second draft Risk Assessment will be taken into consideration in preparing th e final PM Risk Assessment.

The main comments from the CASAC PM Pa nel on the first draft Risk Assessment, provided to us in a November 24, 2009 letter (Samet, 2009), are briefly summarized below together with a brief description of how we ha ve considered the comments in preparing this

second draft PM Risk Assessment.

 The Panel recommended that we include an integrated discussion that draws on the uncertainty and variability analyses as well as the various national-scale analyses completed as part of this assessment, to interpret the core risk estimates.

RESPONSE: We have added a new chapter 6 to provide an integrative discussion of the risk-related analyses presented throughout this second draft Risk Assessment, including the

PM 2.5 -related risk estimates gene rated for the set of urban study areas and the related uncertainty and sensitivity analyses, the repr esentativeness analyses, and the national-scale long-term exposure PM 2.5 mortality assessment. The goal of this integrative discussion is to inform our understanding of important policy-relevant risk-based questions.

 Regarding EPA staff’s decision to focu s the first draft risk assessment on PM 2.5 and not to estimate risk for coarse-fraction PM, the Pa nel generally agreed that the focus on PM 2.5 was appropriate, although the Panel sugge sted that consideration be given to ways to carry out some form of exploratory analys es related specifically to PM 10-2.5 . While acknowledging the uncertainty that would be i nvolved, the Panel also recommen ded that we generate semiquantitative risk estimates for both reproductive effects and lung cancer.

RESPONSE: We have not included a quantitat ive assessment of risk associated with PM 10-

2.5 due to continued concerns th at the uncertainty in any such estimates that we could generate would be so great that they would not serve the purpos e of informing our review of the PM NAAQS. We discuss the basis for th is decision briefly in section 2.3 of the document with additional discussion provided in Appendix H. We also note that the evidence-based considerations to be pres ented in the upcoming draft Policy Assessment

document will address PM 10-2.5 exposure and risk. Regarding reproductive and developmental effects and lung cancer, we note that the risk assessment does include estimates of lung-cancer mortalit y as part of modeling long-ter m exposure-related mortality. However, in the case of reproductive and developm ental effects, we continue to believe that there are insufficient data at this time (particularly with regard to identifying appropriate exposure windows) to support quantitative risk assessment. Nonetheless, these endpoints will be covered as part of the evidence-based considerations to be presented in the draft Policy Assessment.

 The Panel expressed the view th at stronger justificat ion was needed for designating some of

the risk estimates as core estimates. The Panel also recommended that we provide further explanation for how specific long-term and short-term multi-city epidemiological studies

were selected for inclusion in the risk assessm ent and why other studie s of potential interest were not included. For long-term exposure-relate d risk, the Panel suggest ed that we provide additional rationale for the speci fic set of C-R functi ons and effect estimates selected from the Krewski et al. (2009) study for modeling long-term exposur e-related mortality for the core and sensitivity analyses.3 RESPONSE: We have expanded the discussi on (in section 3.3.3) of our rationale for identifying modeling choices comprising the core risk model, including both the selection of specific epidemiological studies for use in deri ving C-R functions as well as specific choices made in specifying those functions. In a ddition, we have added clarification for why alternative candidate epidemiological studies and alternative C-R function specifications

were not included in the core risk assessment.

 Regarding the characterization of variability, th e Panel recommended that additional detail be provided on how different sources of variability were compared and prioritized. In addition, the Panel suggested that the sour ces of variability cons idered in the analysis be augmented to include differences in PM copollutant concen trations and discussion of land use, source locations, housing stock, and SES.

RESPONSE: We have added clarification for the process used to evaluate sources of variability as part of section 3.5.2 of the docum ent. In addition, we added coverage for the specific sources of variability referenced in the Panel’s comments.

 With regard to the qualitative assessment of uncertainty, the Panel recommended that additional detail be provided on the met hod used to rank and categorize sources of uncertainty, and that we discuss implications for interpreting the urban study area risk estimates. The Panel encouraged us to comment on the degree to which dependencies exist between pair-wise combinations of sources of uncertainty. The Panel also recommended that we address more directly the potential for e xposure misclassification (in the epidemiological studies providing the C-R functions) to intr oduce uncertainty into the risk assessment.

RESPONSE: We have expanded our discussion of the qualitative analysis of uncertainty (in section 3.5.3) to more explicitly describe the pr ocess used. The integrative discussion in the new chapter 6 includes consideration for how the qualitative analysis of uncertainty impacts the interpretation of core risk estimates. We have also include d comparisons of selected pairwise interactions of sources of uncertainty that have the potential to impact risk estimates.

 Regarding the sensitivity analysis, the Pa nel made two specific recommendations for additional analyses: consider alternative lags for short-te rm morbidity endpoints based on Bell et al. (2008) and consider risk for short-te rm mortality using regional effect estimates from Zanobetti and Schwartz (2009). More generally, the Panel recommended that we compare the impact of uncertainty in the statistica l fit of the effect estim ates used in the core analysis with the impact of other sources of uncer tainty considered in the sensitivity analysis. The Panel also suggested that we do the follo wing: 1) provide a dditional rationale for focusing on long-term exposure-related mortalit y in using the result s of the sensitivity analysis to inform consideration of uncertainty in the core risk estimates; 2) discuss whether the lower and upper bounds of the sensitivity an alysis represent plausible upper and lower bounds on the core risk estimates; and 3) consid er the results of the sensitivity analysis together with the results of the qualitative uncertainty analysis to inform interpretation of the

core risk estimates.

RESPONSE: We have expanded the sensitivit y analysis to include consideration for alternative lag periods in modeling risk for s hort-term morbidity using Bell et al., 2008 (see section 3.5.4). However, we concluded that ex panding the sensitivity analysis to include coverage for regional effect estimat es (in addition to the city-specific effect estimates used in the core risk assessment) was not warranted in light of the resources and time that would4 have been required. We have expanded our discussion of uncertainty (in section 3.5.3) to include explicit consideration for uncertainty in the statistical fit of the C-R functions and specifically how this compares to other factors assessed as part of the sensitivity analysis. The discussion of the sensitivity analysis has be en expanded to address the use of the results

as an alternative set of reasona ble risk estimates for informing consideration of uncertainty in the core risk estimates (incl uding the degree to which we belie ve the sensitivity analysis captured plausible high- and low-bound risk esti mates – see section 4.3.2). The integrated discussion in the new chapter 6 integrates consideration of the sensitivity analysis results with other analyses completed for the risk a ssessment, including the qualitative uncertainty analysis as noted above, to inform consider ation of overall confiden ce in the core risk

estimates.

 With regard to the national-sc ale long-term exposure-related mortality analysis, the Panel recommended that risk estimates be generated fo r the full set of air quality scenarios included in the risk assessment (i.e., curr ent and alternative suites of st andards, in addition to a recent conditions analysis) and that ad ditional health effect endpoints matching those modeled for the 15 urban study areas be included in the national-scale analysis.

RESPONSE: Following deliberative review of available data and methods, combined with consideration for the policy goals of the nationa l-scale mortality analysis (as differentiated from the health benefits assessment that the Ag ency conducts as part of a Regulatory Impact Analysis), and taking into consideration the re sources and time needed for such an expanded assessment, we have decided not to expand the national-scale mortality analysis to include

consideration of either alterna tive suites of standards or addi tional health endpoints. We have

included our rationale for th is decision in section 5.1.

Document Availability

The draft document is being made available to the CASAC PM Panel in the form of the

attached electronic file. The document is also available from the EPA website at http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_risk.html . Printed copies of this

document will be sent to CASAC PM Panel me mbers via Federal Express. We will mail a printed copy of the main body of the docum ent only. The appendi ces can be accessed electronically as noted above and printed copies of the appendices will be made available to Panel members upon request.

Charge to the CASAC PM Review Panel

We ask the CASAC PM Panel to focus on th e charge questions lis ted below in their

review of the Quantitative Health Risk Asse ssment for Particulate Matter , but we would appreciate comments on a ny other topics as well.

Chapter 3 – Urban Case Study Analysis Methods

1) Air quality inputs (section 3.2): We have expanded the consider ation of alternative approaches to simulating just meeting th e current and alternative suites of PM 2.5 standards5 (i.e., rollback approaches) to in clude a peak shaving approach, in addition to the hybrid and proportional approaches considered in the first dr aft assessment. This peak shaving approach is intended to represent more localize d, rather than regi onal, patterns of PM 2.5 reductions (discussed in section 3.2.3.3).

a) To what extent does the Panel believe that the use of the pe ak shaving approach provides useful additional exploration of variab ility associated with how ambient PM 2.5 concentrations are simulated to change upon just meeting the current and alternative

suites of standards?

b) We have used comparisons of composite monitor annual averages generated using the different rollback approaches as a surrogate for differences in long-term exposure-related mortality in looking across all three rollback approaches. To what extent does the Panel believe that this is a reasonable approach for assessing the impact of variability associated with simulating changes in air quality patterns on estim ates of long-term exposure-related mortality?

2) Selection of model inputs (secti on 3.3): We have expanded a nd clarified the discussion of our rationale for identifying modeling choices co mprising the core risk model, focusing in particular on selection of C-R functions (sec tion 3.3.3). To what extent does the Panel

consider this discussion to be clear and the model selec tions appropriate?

3) Addressing uncertainty and variab ility (section 3.5): We have clarified the process used to evaluate sources of variability and added covera ge for specific sources of variability (section 3.5.2); expanded our discussion of the qualitative analysis of uncertainty (section 3.5.3); and included analyses of pair-wise in teractions of sources of uncertainty (section 3.5.4). To what

extent does the Panel consider these di scussions to be clear and appropriate?

Chapter 4 – Urban Case Study Results

4) Sensitivity analysis results (section 4.3): We ha ve included a discussion of how the results of the sensitivity analysis can be us ed as an additional set of reason able risk estimates to inform consideration of uncertainty in the core risk estimates (s ee section 4.3.2). What are the

Panel’s views on how we have used the sensitiv ity analysis results to support consideration of uncertainty in the core risk estimates?

5) Consideration of design va lues and patterns of PM 2.5 monitoring data in interpreting core risk estimates (section 4.5): To enhance our interpre tation of the patterns of core risk estimates generated for both the current and alternative suites of standards, we have included analyses of 24-hour and annual design values together with patterns of PM 2.5 monitoring data for the 15 urban study areas. This reflects the fact that these two factors play a key role in determining the degree of risk reduction es timated upon just meeting the current and

alternative suites of standard s under alternative rollback a pproaches. As part of the consideration of design values, we have also contrasted the 15 urban study areas with patterns of design values seen for the broader set of urban areas in the U.S. in order to help place the urban study area in a broader national context

a) To what extent is the Panel supporti ve of these additional assessments?6 b) Does the Panel have any recommendations for additional insights based on consideration of patterns in design values and PM 2.5 monitoring data across the 15 urban study areas

and at the national level?

Chapter 6 – Integrative Discussion of PM 2.5 -related Risks

6) We have developed an inte grated discussion of the PM 2.5 -related risk estimates which considers the results of the qualitative a nd quantitative treatment of uncertainty and variability together with the va rious national-scale assessments completed for the analysis to support interpretation of the core risk estimates. As part of the integrative discussion, we also provide key observations that bear on policy-relevant risk-based questions.

a) To what extent does the Panel believe that we have captured the key policy-relevant questions that can be addre ssed by this risk assessment?

b) We provide a set of key obser vations related to estimates of risk associated with simulations of just meeting the current and alternative suites of standards. These observations are based not only on considera tion of trends in risk reduction across

alternative suites of standards and residual risk remaining afte r simulation of just meeting specific suites of standards, but also on addi tional factors that can impact risk (e.g., the

role of annual and 24-hour de sign values, the peakiness of PM 2.5 distributions within a study area, and application of different rollb ack approaches). To what extent do the

Panel members believe that the observations presented in section 6.2 are well supported by the results of the analyses? Are there ot her observations that might be made that would help to address the polic y-relevant ques tions identified at the beginning of the chapter?

c) Part of our interpretation of the core risk estimates presented in section 6.2 is our

characterization of confidence in the core risk estimates a nd in observations made based

on those estimates. These assessments of confidence are based on consideration of the results of the sensitivity analysis as well as on the qualitative asse ssment of uncertainty and variability. To what extent does the Panel believe that the characterizations of

confidence in the core risk estimates and associated policy-related observations are reasonable given available information?

d) As part of the integrative discussion, we use the results of several national-scale analyses (i.e., the national scale PM 2.5 mortality analysis, the representativeness analysis, and the new exploration of design values and patterns of PM 2.5 monitoring data presented in section 4.5) to place the result s of the risk assessment in a broader national-context. What are the Panel members’ views on appropria teness of this effort to place results of the analysis in a national context?

e) We conclude chapter 6 with a list of key observations. Does the Panel believe that we have appropriately highlighted key findings of the risk asse ssment in these observations? Of particular note is the obser vation that, while alternative 24 -hour standard levels can be used to reduce annual-average PM 2.5 concentrations and thus to reduce estimated risk, the results are likely to be highly variable across urban areas. More c onsistent lowering of annual-average PM 2.5 concentrations across study ar eas, and thus more consistent reductions in estimated risk, may result from application of altern ative annual standard

levels. We also note that simulation of th e alternative 24-hour standard level of 25 μ g/m 37 resulted in reductions in annual-average PM 2.5 levels for some study areas that were well

below the lowest annual standard level assessed (i.e., below 12 μ g/m 3 ). As a consequence, we observed risk reductions re flecting these changes in annual-average

PM 2.5 levels below 12 μ g/m 3 . Given these results, does the Panel believe that there is utility in estimating risks for altern ative annual standard levels below 12 μ g/m 3 ?

We look forward to discussing these issues with the CASAC PM Panel at our upcoming meeting. Should you have any questions regarding this draft document, pl ease contact Dr. Zach Pekar (919-541-3704; email pekar.zachary@epa.gov ).

Attachments

cc: Vanessa Vu, SAB, OA Karen Martin, OAQPS/HEID Neal Fann, OAQPS/HEID Beth Hassett-Sipple, OAQPS/HEID Bryan Hubbell, OAQPS/HEID Phil Lorang, OAQPS/AQAD Zach Pekar, OAQPS/HEID Pradeep Rajan, OAQPS/HEID Mary Ross, ORD/NCEA-RTP Lindsay Stanek, ORD/NCEA-RTP Susan Stone, OAQPS/HEID John Vandenberg, ORD/NCEA-RTP Jason Sacks, ORD/NCEA-RTP