February 27, 2009 

MEMORANDUM

SUBJECT: CASAC Consultation on Particulate Matter National Ambient Air Quality 

Standards: Scope and Methods Plan for Health Risk and Exposure Assessment 

and Particulate Matter National Ambient Air Quality Standards: Scope and 

Methods Plan for Urban Visibility Impact 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 two planning documents, (1) Particulate Matter National Ambient Air 

Quality Standards: Scope and Methods Plan for Health Risk and Exposure Assessment (Health 

Assessment Plan), and (2) Particulate Matter National Ambient Air Quality Standards: Scope 

and Methods Plan for Urban Visibility Impact Assessment (Welfare Assessment Plan), 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 primary (health-based) and secondary 

(welfare-based) national ambient air quality standards (NAAQS) for particulate matter (PM). 

These plans will be the focus of a consultation by the Clean Air Scientific Advisory Committee 

(CASAC) PM NAAQS Review Panel (the CASAC PM Panel), scheduled for a public meeting to 

be held in Chapel Hill, NC, on April 2, 2009. I am requesting that you forward these planning 

documents to the CASAC PM Panel to prepare for that consultation. 

The purpose of the Health Assessment Plan is to outline the scope and approaches that 

staff is planning or considering to use to conduct a human health risk assessment and an 

exposure assessment for fine particles and a health risk assessment for thoracic coarse particles. 

The purpose of the Welfare Assessment Plan is to outline the scope and approaches that staff is 

planning to use to conduct a quantitative assessment of urban visibility impairment and 

qualitative assessments of other welfare-related effects. In addition, the plans highlight key 

issues involved in these assessments. These plans are intended to provide enough specificity to 

facilitate consultation with CASAC, as well as for public review, in order to obtain advice on the 

overall scope, approaches, and key issues in advance of the conduct of the risk and exposure 
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analyses and presentation of results in the first draft Risk and Exposure Assessment (REA). The 

plans draw upon information presented in Integrated Science Assessment for Particulate Matter: 

First External Review Draft (PM ISA, December 2008) prepared by EPA’s National Center for 

Environmental Assessment, Research Triangle Park, NC (NCEA-RTP). CASAC consultation on 

these plans coincides with their review of the first draft PM ISA. CASAC and public comments 

on the plans will be taken into consideration in the development of the first draft REA, the 

preparation of which will coincide with and draw from the second draft ISA. The second draft 

REA will draw on the final ISA and will reflect consideration of CASAC and public comments 

on the first draft REA. The final REA will reflect consideration of CASAC and public 

comments on the second draft REA. 

EPA’s overall plan and schedule for this PM NAAQS review was presented in the 

Integrated Review for the National Ambient Air Quality Standards for Particulate Matter, which 

was the subject of a consultation by the CASAC PM Panel on November 30, 2007 (see 

http://www.epa.gov/ttn/naaqs/standards/pm/s_pm_2007_pd.html). That plan outlines the Clean 

Air Act (CAA) requirements related to the establishment and reviews of the NAAQS, the 

process and schedule for conducting the current PM NAAQS review, and plans for the key 

components in the NAAQS review process including the ISA, REA, and policy assessment and 

rulemaking documents. It also lays out key policy-relevant issues to be addressed in this review 

as a series of policy-relevant questions that frame our approach to determining whether the 

current primary and secondary NAAQS for PM should be retained or revised. An updated 

schedule for completing the REA is outlined in the attached plans. Currently, our schedule calls 

for completion of the PM ISA by December 2009, completion of the REA by July 2010, and 

proposed and final rules to be issued in 2011. 

Documents for Consultation 

The following documents are being made available to the CASAC PM Panel in the form 

of an attached electronic file. 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 this 

document will be sent to Panel members via Federal Express. 

 Attachment: Particulate Matter National Ambient Air Quality Standards: Scope and 

Methods Plan for Health Risk and Exposure Assessment (Health Assessment Plan, 

February 2009) 

Following an introductory section, this document discusses air quality considerations that 

are relevant to both the planned human health risk and exposure assessments. The next two 

sections present the planned scope and approach for the health risk assessment and exposure 

analysis, respectively. Throughout these sections, key issues are discussed and staff’s plans for 

addressing these issues are noted. The final section summarizes the schedule and interim 

milestones related to these assessments. 

 Attachment: Particulate Matter National Ambient Air Quality Standards: Scope and 

Methods Plan for Urban Visibility Impact Assessment (Welfare Assessment Plan, 

February 2009) 
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Following an introductory section, two sections of this document discuss the planned 

scope and approach for assessing visibility impairments in urban areas. The final section 

summarizes the schedule and interim milestones related to these assessments. Attachment A 

outlines issues related to planned qualitative assessments of other welfare effects. 

Charge to the CASAC PM Review Panel 

We ask the CASAC PM Panel to focus on the charge questions listed below in their 

consultation on these planning documents. 

A. Health Assessment Plan 

Chapter 1 – Introduction/Overarching Questions

The introductory section presents an overview of the goals and planned approaches for 

conducting the health risk and exposure assessments. 

1. What are the Panel members’ views on the general structure and overall design of the 

planned analyses? 

2. Is the plan clear and transparent in its description of the proposed approaches? Are the 

various assumptions and judgments that must be made in carrying out the planned risk 

analyses clear and transparent? 

3. What are the Panel members’ views on the goals identified for the risk and exposure 

assessments? 

4. Given the goals set forth for the planned analyses, has the plan appropriately drawn from 

the existing scientific and technical information in developing the overall approach? Are 

there relevant features that should be added or modified in the planned approach? 

Chapter 2 - Air Quality Considerations: 

1. Do Panel members generally agree with the planned approach for obtaining and 

analyzing the air quality data that will be used in the risk and assessments? 

2. With regard to approaches for simulating air quality that just meets the current or 

alternative standards under consideration: 

a. What are the Panel members’ views on the planned use of a proportional (i.e., 

linear) approach to adjusting air quality (proportional rollback)? 

b. What are the Panel member's views on also considering the alternative rollback 

approach being considered for PM2.5 (model-based rollback)? 
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3. What are the Panel members’ views on the planned approach for estimating and using 

policy-relevant background concentrations? 

Chapter 3 – Scope and Approach for the Health Risk Assessment

1. Regarding selection of health effects endpoints to model in the risk assessment: 

a. To what extent are the Panel members supportive of EPA’s planned approach to 

focus on selected health effects endpoints (e.g, emergency department visits and 

hospitalizations for ischemic heart disease) within broader health effect categories 

(e.g, cardiovascular morbidity) initially classified in the first draft ISA as having a 

causal or likely-causal association with ambient PM2.5? 

b. What are the Panel members’ views regarding EPA’s plans to consider for 

inclusion additional health effects endpoints (e.g, birth outcomes) for PM2.5 that 

are within broader health effect categories (e.g, reproductive, developmental, 

prenatal and neonatal outcomes) that have been initially classified in the first draft 

ISA as having suggestive evidence of a causal association? What are the Panel 

members’ views with respect to addressing the challenges in designing a 

quantitative risk assessment to appropriately consider birth outcome endpoints? 

c. Are the Panel members generally supportive of EPA's planned approach to 

conduct a risk assessment for PM10-2.5 considering health effect endpoints within 

broader health effect categories that have been initially classified in the first draft 

ISA as having suggestive evidence of a causal association? 

2. Regarding specification of concentration-response functions for use in the risk 

assessment: 

a. In modeling health impacts associated with short-term ambient PM, to what 

extent are Panel members supportive of EPA’s planned approach to place 

emphasis on distributed lags, where they are available, with additional lags (e.g., 

0, 1 day lags) being included as part of sensitivity analyses, based on 

consideration of the degree of biological support for these lags? 

b. What are the Panel members' views on EPA’s planned approach to place 

emphasis on multi-city studies which provide city-specific effect estimates, 

particularly Empirical Bayes adjusted effect estimates which consider both the 

regional signal as well as the local (city-specific) signal in deriving adjusted cityspecific effect estimates? 

c. What are the Panel members’ views regarding EPA's planned approach to place 

equal weight on single and multi-pollutant models in recognition of the competing 

advantages and disadvantages provided by both types of models? 
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d. Based on information provided in the first draft ISA regarding potential 

population thresholds, EPA is planning to place primary emphasis on modeling 

risk down to policy-relevant background or the lowest reported measured level in 

the epidemiological studies. In contrast to the prior review, EPA is planning to 

place less emphasis on consideration of hypothetical population thresholds. 

What are the Panel members’ views on this approach or alternative approaches 

that could be considered? 

3. Regarding selection of urban study areas: 

a. EPA plans to include 15 to 20 urban study areas in the PM2.5 health risk 

assessment, with areas selected based on application of the criteria presented in 

the plan. What are the Panel members’ views on the planned criteria for selecting 

urban study areas? 

b. The scope of the planned assessment for PM10-2.5 is much more limited. What are 

the Panel members’ views regarding the overall approach and, specifically, on the 

criteria for selecting study areas for evaluating the health impacts associated with 

ambient thoracic coarse particles? 

4. Regarding the approach for addressing uncertainty and variability: 

a. In the plan, EPA describes an uncertainty analysis approach based on the 

application of single and multi-element sensitivity analysis. What are the Panel 

members' views on this planned approach for addressing uncertainty in the risk 

assessment? 

b. Do Panel members generally agree that the planned approach sufficiently captures 

key sources of variability related to PM-related risk? Are there any important 

sources of variability which are not captured by the proposed risk assessment 

approach and, if so, what are the Panel members’ views regarding how these 

sources of variability could be incorporated into the analyses? 

5. Regarding analyses being considered to place the urban study area risk results in a 

broader context with regard to national patterns of risk and risk-related indices: 

a. EPA is considering conducting a national-scale health impact assessment of the 

mortality impacts in the U.S. population associated with long-term exposure to 

ambient PM2.5 under recent air quality conditions to support interpretation of the

risk estimates generated for the urban study areas. What are the Panel members’ 

views related to including such a national-sale analysis in the risk assessment? 

What are the Panel members’ views regarding the general structure and overall 

design of this analysis? 

b. EPA’s planned approach also includes analyses to compare the information for 

the selected urban study areas with national statistics for a set of key PM risk-
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related indices (e.g., baseline incidence rates for health effects modeled in the risk 

assessment, rates of air conditioner use, housing stock). What are the Panel 

members’ views on this planned comparison? 

Chapter 4 – Scope and Approach for Population Exposure Analysis

1. What are the Panel members’ views on the general structure and overall design of the 

exposure assessment to provide insight on population exposures with respect to 

informing the interpretation of available epidemiologic studies? 

2. What are the Panel members’ views regarding the planned measures of exposure? 

3. EPA is planning to focus the exposure assessment on a subset of the urban study areas 

evaluated in the risk assessment. What are the Panel members’ views regarding the 

selection of these study areas and the planned time periods to be modeled? 

4. Regarding the approach for addressing uncertainty and variability, are Panel members 

generally supportive of the planned approach? 

B. Welfare Assessment Plan 

Chapter 1 – Introduction

The introductory section presents an overview of the goals and planned approaches for 

conducting urban visibility assessments. 

1. What are the Panel members’ views on the general structure and overall design of the 

planned analyses? 

2. Is the plan clear and transparent in its description of the planned approaches? Are the 

various assumptions and judgments that must be made in carrying out the planned 

assessments clear and transparent? 

3. Given the goals set forth for the planned analyses, has the plan appropriately drawn from 

the existing scientific and technical information in developing the overall approach? Are 

there relevant features that should be added or modified in the planned approach? 

4. In addition to the sub-daily PM2.5 alternative standard considered in the last PM NAAQS 

review and summarized in this chapter, an alternative standard structure is being 

considered in this review. This alternative structure would use daylight hourly PM light 

extinction, which can be measured either by a combination of instruments (nephelometer 

– PM light scattering and aethalometer – PM light absorption) or calculated from PM 

speciation and concurrent relative humidity data using a linear algorithm. 

 
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a. What are the Panel members’ views regarding this alternative structure and its 

utility in the context of this PM NAAQS review? 

b. What are the Panel members’ views regarding advantages and disadvantages of 

this alternate structure compared to the sub-daily PM mass concentration 

approach? 

5. The public’s preferences for urban visual air quality (VAQ) levels were assessed in the 

last review in part by considering results from past western U.S. urban preference studies 

that used scenes with distant mountain backdrops. 

a. What are the Panel members’ views on the usefulness of the planned approach to 

conduct a focus group study in different regions of the country with different 

scene types to enhance our understanding of the applicability of this earlier body 

of work to U.S. urban areas in general? 

b. What are the Panel members’ views regarding the scope and approach envisioned 

for this effort, given the time available in this review? 

Chapter 2 – Assessment of Urban Visibility Conditions

1. Visibility impairment is caused by both PM2.5 and PM10-2.5, though the latter is less 

effective on a per unit concentration basis and there is less available PM10-2.5 data 

available in urban areas with which to conduct an assessment. PM in the atmosphere 

includes liquid water which contributes to light extinction but is removed when filter 

samples are desiccated prior to mass and composition analysis. 

 

c. What are the Panel members’ views regarding to what degree and using what 

approaches EPA should assess the role of PM10-2.5 in urban light extinction? 

d. What are the Panel members’ views regarding the advantages and disadvantages 

of using direct measurements of ambient PM light extinction (e.g., nephelometer 

plus aethalometer, or transmissometer) compared to using a linear algorithm that 

includes particle composition and concurrent relative humidity to calculate 

(reconstitute) PM light extinction? 

e. What are the Panel members’ views regarding the importance of refining the 

IMPROVE algorithm so that it is optimized for urban areas in order to estimate 

PM light extinction for use in this assessment? 

2. This plan anticipates using the same approach to estimate policy-relevant background PM 

levels as in the health risk assessment. What are the Panel members’ views on this 

planned approach and its use in the context of the urban visibility conditions assessment? 

3. The planned approach includes consideration of high time resolution PM mass and 

component concentrations as well as PM light extinction data, together with relative 
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humidity values, to assess recent air quality as well as air quality simulated to just meet 

current and alternative standards under consideration. However, such high time 

resolution data are not broadly available. 

a. What are the Panel members’ views on this planned approach or on other 

approaches or data sources that might be explored? 

b. What are the Panel members’ views regarding useful approaches for 

characterizing the uncertainties associated with the urban visibility conditions 

assessment? 

Chapter 3 – Quantitative Visual Air Quality Impact Assessment

1. EPA plans to conduct public preference studies to supplement the information from past 

studies concerning VAQ levels that impact public welfare. The planned approach is to 

conduct an investigative focus group in one location to develop the approach that will 

then be used in group interviews in four urban areas. The proposed approach would ask 

participants to view an urban-specific iconic scene and a generic scene in each study 

location, all selected to be sensitive to changes in PM light extinction using WinHaze 

superimposed haze levels. 

a. What are the Panel members’ views regarding the appropriateness of EPA’s 

preference study approach and its adequacy to accomplish the goals outlined in 

the plan? 

b. What are the Panel members’ views with respect to alternative approaches that 

could be considered in this review to acquire this and/or additional relevant 

information? 

2. EPA is not planning to include monetary valuation study questions (e.g. willingness to 

pay, conjoint analysis) in the studies conducted for this review. 

a. What are the Panel members’ views regarding the usefulness of adding valuation 

questions to the proposed four urban-areas group interview surveys and the 

adequacy of such limited information to inform estimate of the value of improved 

visibility in the broader nationwide context? 

b. What are the Panel members’ views with respect to possible approaches for 

estimating monetary values associated with improved visibility that should be 

considered? 

We look forward to discussing these issues with the CASAC PM Panel at our upcoming 

meeting. Should you have any questions regarding these planning documents, please contact Dr. 

Karen Martin (919-541-5274; email martin.karen@epa.gov) or Ms. Beth Hassett-Sipple (919 

541-4605; email hassett-sipple.beth@epa.gov) regarding the Health Assessment Plan or Ms. 
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Vicki Sandiford (919-541-2629; email sandiford.vicki@epa.gov) regarding the Welfare 

Assessment Plan. 

Attachments 

cc: Vanessa Vu, SAB, OA 

Karen Martin, OAQPS/HEID 

John Vandenberg, ORD/NCEA-RTP 

Mary Ross, ORD/NCEA-RTP 

Lindsay Stanek, ORD/NCEA-rTP 

Beth Hassett-Sipple, OAQPS/HEID 

Vicki Sandiford, OAQPS/HEID 

Harvey Richmond, OAQPS/HEID 

Zach Pekar, OAQPS/HEID 

John Langstaff, OAQPS/HEID 

Pradeep Rajan, OAQPS/HEID 

Susan Stone, OAQPS/HEID 

Meredith Lassiter, OAQPS/HEID 

Bryan Hubbell, OAQPS/HEID 

 Marc Pitchford, OAQPS/HEID