September 8, 2009

MEMORANDUM

SUBJECT: CASAC Review of Risk Assessment to Support the Review of the PM Primary National Ambient Air Quality Standa rds - External Review Draft and Particulate Matter Urban-Focused Visibility Assessment – 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 are two draft assessment documents: (1) Risk Assessment to Support the Review of the PM Primary National Ambient Air Q uality Standards - External Review Draft (September 2009) and (2) Particulate Matter Urban-Focused Visibili ty Assessment – External Review Draft (September 2009), prepared by the Environmenta l Protection Agency’s (EPA) Office of Air Quality Planning and Standards (OAQPS) staff as part of EPA’s ongoing re view of the primary (health-based) and secondary (welfare-based) na tional ambient air qual ity standards (NAAQS) for particulate matter (PM). These documents will be the focus of a review by the Clean Air Scientific Advisory Committee (CASAC) PM NAAQS Review Pane l (the CASAC PM Panel) at a public meeting to be held in Chapel Hill, NC on October 5–6, 2009. In addition, on or about September 15, 2009, we plan to release a very preliminary draft of another document, Policy Assessment for the Review of the Particulate Matter National Ambient Air Quality Standards: Preliminary Draft (Policy Assessment), to facilitate di scussion with the CASAC PM Panel on our ongoing efforts to prepare an ex ternal review draft Policy Asse ssment. I am requesting that you forward these draft documents to the CASAC PM Panel to prepare for the October meeting.

As part of EPA’s review of the PM NAA QS, the Agency is conducting quantitative assessments characterizing (1) the health ri sks associated with exposure to ambient PM and (2) urban visibility impairment associated with ambient PM. The two attached draft assessment documents convey the approaches taken to asse ss and characterize PM-associated health risks and urban visibility impairment. These documen ts include descriptions of the scope of the assessments and the methodologies used as well as the initial key resu lts, observations, and

related uncertainties associated with the quantitative analyses conducted.2 The EPA’s plans for conducting the health risk and urban-focused visibility assessments, including the proposed scope and methods of th e analyses, were presented in two planning documents, Particulate Matter National Ambient Ai r Quality Standards: Scope and Methods Plan for Health Risk and Exposure Assessment (February 2009) and Particulate Matter National Ambient Air Quality Standards: Scope and Methods Plan for Urban Visibility Impact

Assessment (February 2009), henceforth, Scope and Methods Plans, see http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_pd.html . These planning documents were the subject of a consultation with CASA C on April 2, 2009. Comments from the CASAC PM Panel as well as public comments were c onsidered in developi ng the draft assessment documents being released at this time.

These draft documents draw upon information presented in the Integrated Science Assessment for Particulate Matter: Second External Review Draft (ISA, July 2009) prepared by

EPA’s National Center for Environmental Asse ssment, Research Triangle Park, NC (NCEARTP), which the CASAC PM Panel will review at the same meeting. The CASAC and public comments on the draft assessment documents will be taken into consideration in making

revisions to the draft assessment documents and in the preparation of an external review draft Policy Assessment.

Draft documents are being made available to the CASAC PM Panel in the form of

attached electronic files. The documents are also available from the EPA website at http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_pd.html . Printed copies of these

documents will be sent to CASAC PM Panel member s via Federal Express. With regard to the Risk Assessment document, we will mail a printe d copy of the main body of the document only. The appendices can be accessed electronically as noted above and printed copies of the appendices will be made availabl e 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 two draft assessment documents, but we would appreciate comments on any other topics as well.

 Risk Assessment: Risk Assessment to Support the Revi ew of the PM Primary National Ambient Air Quality Standards - External Review Draft (September 2009)

Following an introductory chapter, this document discusses the scope of the risk assessment, including modifications based on CASAC c onsultation and public comment on the Scope and Methods Plan; the methods used to estimate risks associated with recent air quality and with air quality concentrations simulated to ju st meet current and alternative standards; the results including core analyses and alterna tive estimates based on a number of sensitivity analyses, as well as an evaluation of the re presentativeness of the urban study areas in a national context; and a national-scale assessment of premature mortality associated with long-term PM 2.5 exposures based on recent air quality. Throughout these chapters, key issues

and uncertainties are discussed.3 Chapters 2 and 3 – Scope of the assessment and Methods used for the urban case studies

1) After careful consideration of evidence provide d in the second draft ISA and of the views expressed by the Panel in consulting on the Scope and Methods Plan, we have decided to quantitatively assess risk associated with both short- and long-term exposure to PM 2.5 only.

Based on our consideration of the evidence for health effects potential ly associated with short-term exposure to PM 10-2.5 , as well as to ultrafine partic les and specific components, and in recognition of the limited available air qua lity data, we decided not to assess risk quantitatively for PM 10-2.5 , ultrafine particles, or specifi c PM components as part of the current assessment. Is the Panel generally suppo rtive of this scope? To what extent is the rationale for this decision clear and appropriate?

2) The final set of health effect categories included in the risk assessment for PM 2.5 are consistent with those outlined in the Scope and Methods Plan (i.e., thos e classified as having

a causal o r likely causal a ssociation with PM 2.5 exposure, as presented in the second draft ISA). We decided not to in clude any of the health eff ect categories classified as suggestive

of a casual association in the second draft ISA, based on a number of considerations as

described in section 3.3.1. Please comment on th e approach taken and on the clarity of the rationale for selecting health effect categories for inclusion in the quantitative risk

assessment.

3) Based on consideration of evidence presented in the second draft ISA, we have identified

four combinations of 24-hour and annual alternative sta ndard levels for analysis in the risk

assessment. Please comment on the extent to which the rationale provided in section 2.5 appropriately supports these combin ations of alternative standard levels for this assessment.

4) General approach

a) For this assessment, we have developed a primary set of risk results based on the application of modeling element choices (e .g., concentration-res ponse (C-R) functions, lag periods) that we believe ha ve the greatest overall support in the literature (referred to as the “core” results). As discussed in s ections 2.4.1, 3.1 and 4.0, while it is not possible at this time to assign quantitative levels of confidence to these core risk estimates, staff believes that these estimates are generally ba sed on inputs having highe r overall levels of confidence, relative to risk estimates that could have been generated using other inputs identified in the literature. Consequently, the core risk estimates receive greater focus when we present, summarize and discuss risk estimates. What is the Panel’s view on the approach used and does the Pane l consider it to be described appropriately and clearly?

b) Based on consideration of uncertainties asso ciated with specifyi ng C-R functions below the lowest measured level (LML) from a pa rticular epidemiological study, we have decided to model risk for long-term PM 2.5 exposures down to the LML, but not to extrapolate down to policy-relevant background (PRB). In contrast, when estimating risk

associated with short-term PM 2.5 exposures, because the LML is generally below the range of PRB values on some days during th e study periods evaluated, we decided to model short-term risk down to PRB (see sec tion 3.1). Is the Panel generally supportive of these approaches?4 5) Air quality inputs

For this assessment, we have included an al ternative approach for simulating air quality levels that just meet either current or alte rnative suites of standards in addition to the proportional analysis that has been used in previous analyses. Specifically, we have employed a hybrid (non-proportional) air quality adjustment procedure which simulates a combination of regional and local controls. The non-propor tional rollback approach was used as part of a sensitivity analysis to examin e uncertainty associated with this aspect of the risk assessment, while the hist orical proportional approach was used for the core analysis. To what extent does the Panel support the us e of the alternative non- proportional rollback approach in the context of the sensitivity analyses? Please provide comments on the alternative approach as presente d in section 3.2.3 and Appendix B.

6) Selection of urban study areas

We have included 15 urban study areas in the ri sk assessment, with the selection of these areas being based on a number of criteria as presented in s ection 3.3.2. To what extent does the Panel support the rationale provided for selection of the urban study areas and the specific locations considered?

7) Selection of epidemiological studies and C-R functions within those studies:

In estimating risks associated with PM 2.5 exposures, we focused on selecting C-R functions from large multi-city studies based on staff’s conclusion that these studies provided more defensible effect estimates (see section 3.3.1) . Concentration-response functions from several single-city studie s evaluating short-term PM 2.5 exposures were also included to provide coverage for additional health effect endpoints (e.g., emergency department visits). To what extent is the Panel supportive of th is approach for selecting C-R functions for modeling risk related to s hort-term and long-term PM 2.5 exposures?

a) Specifically with regard to short-term e xposure-related mortality, focusing on a study of 112 US cities by Zanobetti and Schwartz (2009), we obtained Empirical Bayes “shrunken” city-specific estimat es from the study authors that provided a distinct C-R function for each urban study area location. For short-term exposure-related morbidity, focusing on a study of 202 U.S. counties by Be ll et al. (2008), we used regionallydifferentiated effect estimates provided by the study authors. Please comment on the selection of C-R functions for evaluating shor t-term morbidity and mortality effects. To

what extent do the Panel members consider th e rationales supporting the selection of C-R functions to be clearly an d appropriately presented?

b) Specifically with regard to long-term expos ure-related mortality, we identified a number of effect estimates using the extended follo w-up of the American Cancer Society (ACS) study to use in the core analys is (Krewski et al., 2009). Th ese effect estimates include standard Cox proportional hazards models, w ith 44 individual and 7 ecologic covariates, derived using two separate PM 2.5 monitoring data sets (i.e., 1979-1983 and 1999-2000) (see section 3.3.3 of the RA). To what extent is the rationale for these choices clear and sufficiently justified as the basis for th e core analysis involving long-term PM 2.5 -related mortality?5 8) Addressing uncertainty and variability

a) The treatment of uncertainty and variability in the analysis is based on the multi-tiered approach presented in a recent WHO documen t (WHO, 2008). Specifically, as outlined in section 3.5, we have incl uded qualitative analysis of bot h variability a nd uncertainty (WHO Tier 1), as well as single-factor and multi-factor sensitivity analyses aimed at identifying which potential sources of uncerta inty have the greatest impact on the core risk estimates (WHO Tier 2). In addition, th e sensitivity analyses have been designed to provide a reasonable set of alte rnate risk estimates to supplement the core risk estimates and inform consideration of uncertainty associat ed with the core analysis. To what extent does the Panel support the overall approach fo r addressing uncertainty and variability? To what extent does the Panel agree that the overall approach is appropriate and consistent with the goals of the risk assessment as outlined in chapter 1? Does the Panel have any recommendations for improving th e characterization of variability and/or uncertainty?

b) The qualitative discussion of key sources of variability, and the degree to which the analysis design captures those sources of variability, are presen ted in section 3.5.2. Please provide comments on the approach used. Specifically, do the analyses sufficiently address the issue of variability ? Are there key sources of vari ability that have not been addressed within the qualitative analysis but which could have an important impact on modeling population-level risk associated with PM 2.5 exposure?

c) Table 3-13 provides a qualitative characterizat ion of uncertainties including the potential direction, magnitude, and degr ee of confidence associated with our understanding of the sources of uncertainty. To what extent does the Panel support the ch aracterizations of the key sources of uncertainties identified and the relative ra nkings of the importance of those sources of uncertainty? Are there additional uncertainties that should be

considered?

d) The results of the sensitivity analyses have b een used to gain insi ghts into which sources of uncertainty significantly imp act the core risk estimates and to provide a reasonable set of alternate risk estimates to supplement the core analysis. We are mindful that these estimates do not represent a true uncertainty distribution. With regard to the single- and multi-factor sensitivity analyses, to what ex tent is the Panel supportive of the approach

used to conduct and characterize the results of the sensitivity analyses? Please provide comments on the extent to which the presentation of the results of the sensitivity analyses are clearly and reasonably described? Does the Panel have any recommendations for how the results of the sensitivity analyses could be used more effectively or appropriately in characterizing uncertainty associat ed with the core risk estimates?

Chapter 4 – Results

9) A number of risk metrics as well as different approaches for presenting these metrics are included in tabular and graphical format for bot h the core analysis and sensitivity analyses.

Please comment on the extent to which the ri sk estimates are clearly and appropriately characterized and presented.6 10) Evaluation of the representativeness of the urban study areas in the national context

We completed a comparison of the 15 urban stud y areas against national distributions for key PM risk-related attributes. The goal of this analysis was to determine whether the urban study areas are more nationally-representative of these attributes, or are more focused on a particular portion of the distri bution for a given parameter. In particular, given that one of the goals of the risk analysis is to provid e estimates of risks for those areas likely to experience high levels of PM exposure and ris k, this assessment provides insights as to the extent to which the assessment represents high PM 2.5 risk locations. The results of this analysis were then used to evaluate, in part , whether the set of 15 urban study areas is likely to reflect the broader U.S. population with regard to PM 2.5 –related risk, including coverage for those locations that represent specific at -risk populations. To what extent does the Panel support the approaches used? Please provide comments on th e clarity with which the methods, results, and insights gained from this analysis are described.

Chapter 5 – National-Scale Assessment of Long-Term Mortality Related to PM 2.5 Exposures

11) We completed a national scale assessment focu sed on long-term mortal ity associated with recent air quality conditions. To what extent does the Panel support the approach used? Please comment on the clarity and appropriate ness with which the methods, results, and insights gained from this analysis are described.

12) The national-scale long-term mortality risk as sessment provides perspective for where the 31 counties associated with our 15 urban study area analysis fall along th e national distribution of mortality risk. We note that this analysis is distinct from the representativeness analysis referenced above (and described in section 4.4) in that this analysis focuses on coverage of the 15 urban study areas for long-term mortality risk, while the earlie r representativeness analysis focuses on coverage for PM risk-relat ed factors. To what extent is the Panel supportive of this specific analys is and its intended use to provid e insights into the extent to which the urban study area analysis broadly represents urban PM 2.5 -related risk in the U.S?

 Visibility Assessment Particulate Matter Urban-Focused Vi sibility Assessment – External Review Draft (Visibility Assessment, September 2009)

Following an introductory chapter, this documen t discusses the current scope of the urban focused visibility assessment, including m odifications based on CA SAC consultation and information provided through public comment; the re sults of a reanalysis of urban visibility preference studies; the methods used to evaluate recent PM 2.5 air quality and light extinction

levels with PM 2.5 air quality concentrations simulated to just meet current and alternative

PM 2.5 and PM light extinction stan dards; and results of the evaluations. Throughout these chapters, key issues and un certainties are discussed.

Chapter 1 – Scope of Visibility Assessment

1) After careful consideration of the evidence provided in the second draft ISA, and in particular the significant body of work that has been conducted by the Regional Planning Organizations under the Regional Haze Rule, (i.e. information on urban and rural PM concentrations and compositions), we have decided to continue to focus this assessment on7 the PM induced visibility impairment that is occurring in urban areas. What is the Panel’s view on this approach? Is the rationale supporting the se lected approach clear and appropriate?

2) After further considering the nature of urban ve rsus more remote area PM, and in light of discussions with CASAC at the April 2, 2009 m eeting, we have decided not to develop an urban optimized algorithm at this time, but instead to rely on the original IMPROVE algorithm to relate urban PM to local haze (PM light extinction). Is the Panel generally supportive of this approach? Is the rationale suppor ting this decision appr opriate and clearly presented?

3) In a change from the planned approach presen ted in the Scope and Methods Plan, we have decided to conduct a reanalysis of the urban visi bility preference studie s available at the time of the 2006 PM NAAQS review, rather than co nducting new public preference studies since it is highly unlikely that the results of new studies could be completed in time to inform this review. This reanalysis was designed to explore the similarities and differences (comparability) between the curr ent studies and to assess what information could be drawn

from these results to inform the selection of visual air quality ( VAQ) candidate protection levels (CPLs) to be used in subsequent impact assessments. This reanalysis also includes a recent study by Smith and Howell (2009) for Washington, D.C. which was presented to the CASAC during the public comment phase of the April 2, 2009 meeting a nd later provided to EPA staff. Does the Panel agree that the inform ation provided by this reanalysis is useful to inform the selection of CPLs? Does the Panel agree that inclusion of the Smith and Howell (2009) is appropriate in both th e ISA and Visibility Assessment? To what extent does the Panel consider that the reanalys is of the urban visibility pr eference studies is clearly and appropriately characterized?

4) We have chosen to use the range that represents the 50 th acceptability criteria across the four cites studied (i.e., the VAQ level that best divides the photographs shown into two groups: those with a VAQ rated as acceptable by the major ity of the participants , and those rated not acceptable by the majority of participants) as CP Ls to characterize the nature of the impact on urban VAQ associated with current PM le vels. Please comment on the clarity and appropriateness of the rationale supporting this decision. Does the Panel have suggestions for alternative ranges to consider?

5) A new indicator relating ambient PM to urba n VAQ (i.e., PM light extinction) has been evaluated to improve our characterization of the relationship between ambient PM and visibility impairment. Is the Panel generally supportive of this approa ch? To what extent have we provided an adequate justif ication for the new indicator used?

6) An averaging time of one hour as a practical minimum time period was used in this assessment in recognition that, while the visi bility impacts are near ly instantaneous, the urban VAQ does not generally chan ge significantly from minute to minute, but does vary

from hour to hour. To what extent does the Panel support this appro ach? Does the Panel consider the rationale supporting this approach to be clearly and appr opriately presented?

7) We have chosen to use the 90 th and 95 th percentile forms in our assessment of alternative secondary (welfare-based) standa rds. Please comment on the use of these alternative forms.8 Chapter 2 – Urban Visib ility Preference Studies

8) To what extent does the Panel support the graphi cal displays presented in this chapter? As currently presented, do these figures clearly summarize the assessment results? We have combined data from multiple studies for two locations - British Columbia and Washington, D.C. - (Abt Associates, 2001; Smith and Howell, 2009 test 1) as presented in Figure 2-14. Does the Panel agree with developing a compos ite dataset for each of these two urban areas?

9) Despite significant differences in study charac teristics (e.g., size, location), to what extent does the Panel support combining and comparing the results from the four cities, as shown in Figure 2-14? What is the Panel’s view on the cl arity and adequacy of th e descriptions of the

uncertainties and limitations associated with such a combined assessment and the conclusions that can be drawn from the assessments? Please provide comments on additional insights, uncertainties, or caveat s that should be considered.

10) We have used the combined results presented in this chapter to develop a range of CPLs that are used in subsequent steps of the assessment. To what extent does the Panel support the range of CPLs used and the justification provi ded for selecting this range? Does the Panel

recommend consideration of a ny alternative approaches or criteria for selecting CPLs?

11) Overall, we consider this assessment useful fo r providing information for the design of future urban visibility preference studies. Does the Panel support this conclusion and does the Panel have any recommendations for changes that could be made in the discussions of this

information to enhance its usefulness for this purpose?

Chapter 3 – Estimation of Current PM Concentrations and Light Extinction

12) Are the goals articulated in the first paragraph of this chapter achieved in the remainder of the assessment? If not, does the Panel have suggestions for additional assessments that

should be done?

13) Are the methods and approaches taken in these assessments, including those for monitor site selection, incomplete data adjustments, and the use of the CMAQ model to augment speciation data, appropriate and is the rationa le for their selection clearly articulated?

14) Is the approach used to estimate PRB as desc ribed in chapter 3 and Appendix C appropriate?

15) We consider the results ge nerated by these analyses to be reasonable based on PM composition and relative humidity data. Does the Panel agree? Are there other tests of reasonableness that could be applied?

16) In addition to a qualitative discussion of possi ble sources of uncertain ty and variability, are there quantitative methods for addressing uncerta inty and variability as sociated with these

assessments that the Panel would recommend?

17) A number of appendices are provid ed at the end of this document. Does the Panel agree that

this information is useful to retain? Does the Panel agree with the level of detail provided in the body of the report and its organization and distribution throughout the document?9 Chapter 4 – Total Light Extinct ion Under “What If” Conditions of Just Meeting Specific Alternative Secondary NAAQS

18) Does the Panel agree with the approaches used to simulate just meeting air quality conditions

for the current and alternative PM standards? In particular, is use of the proportional rollback approach appropriate in th e context of the urban PM visibility assessment?

19) To what extent does the Panel consider the pres entation of "what if" scen arios for retention of the current secondary PM 2.5 NAAQS and consideration of al ternative, more protective secondary NAAQS in sections 4.2 and 4.3 to be cl early written with an appropriate level of detail? Do the correlation analyses presente d in Appendix D provide sufficient insight into the suitability of alternative indicators based on sub-24 hour averaging periods for PM 2.5 ?

Are there additional alternative standard scenarios that should be evaluated?

We look forward to discussing these issues with the CASAC PM Panel at our upcoming meeting. Should you have any questions regard ing these draft documents, please contact Dr. Zach Pekar regarding the draft ri sk assessment (919-541-3704; email pekar.zachary@epa.gov ) or Ms. Vicki Sandiford regarding the draft visibility assessmen t (919-541-2629; email sandiford.vicki@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 Meredith Lassiter, OAQPS/HEID Phil Lorang, OAQPS/AQAD Zach Pekar, OAQPS/HEID Marc Pitchford, OAQPS/HEID Pradeep Rajan, OAQPS/HEID Harvey Richmond, OAQPS/HEID Mary Ross, ORD/NCEA-RTP Vicki Sandiford, OAQPS/HEID Lindsay Stanek, ORD/NCEA-RTP Susan Stone, OAQPS/HEID John Vandenberg, ORD/NCEA-RTP