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July 1, 2010 

MEMORANDUM

SUBJECT: CASAC Review of the Policy Assessment for the Review of the Particulate Matter 

National Ambient Air Quality Standards – Second External Review Draft 

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 draft document, Policy Assessment for the Review of the Particulate Matter 

National Ambient Air Quality Standards - Second External Review Draft (Policy Assessment), 

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). This document will be the focus of a review by 

the Clean Air Scientific Advisory Committee (CASAC) Particular Matter Review Panel (the 

Panel) on July 26-27, 2010. 

The second draft 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 draft document draws upon the evidence and 

information assessed and presented in the final Integrated Science Assessment for Particulate 

Matter (ISA) prepared by EPA’s National Center for Environmental Assessment and two final 

assessment documents 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 Panel and the public on earlier drafts. 

The second draft Policy Assessment reflects consideration of comments from the Panel, 

as well as public comments, on the first draft Policy Assessment, which was reviewed by the 

Panel during teleconferences on April 8-9 and May 7, 2010. The main comments from the Panel 

on the first draft Policy Assessment were provided to us in a May 17, 2010 letter (Samet, 2010).1

These comments, and the changes made in the second draft Policy Assessment in response to 

them, are summarized in Attachment 1. 

 

1

Samet, J. (2010). Letter from Clean Air Scientific Advisory Committee to the Honorable Lisa P. Jackson, 

Administrator, US EPA. CASAC Review of Policy Assessment for the Review of the PM NAAQS – First External 

Review Draft (March 2010). May 17, 2010. 
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We will take comments from the Panel and the public on the second draft Policy 

Assessment into consideration in preparing a final Policy Assessment, which we plan to release 

in September, 2010. Our review of the PM NAAQS will conclude with Agency rulemaking. 

Our current schedule anticipates that proposed and final rules will be signed in February 2011 

and October 2011, respectively. 

Document Availability 

The second draft 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. Printed copies of this 

document will be sent to members of the Panel via Federal Express. 

Charge to the Panel 

 In their review, we ask the Panel members to focus on the charge questions listed in 

Attachment 2, though we would appreciate comments on other topics as well. 

 We look forward to discussing this second draft Policy Assessment with the Panel at our 

upcoming meeting in July. Should you have any questions regarding this draft document, please 

contact Ms. Beth Hassett-Sipple (919-541-4605; email hassett-sipple.beth@epa.gov). 

cc: Vanessa Vu, SAB, OA 

Holly Stallworth, SAB, OA 

John Vandenberg, ORD/NCEA-RTP 

Debra Walsh, ORD/NCEA-RTP 

Mary Ross, ORD/NCEA-RTP 

Lindsay Stanek, ORD/NCEA-RTP 

Jason Sacks, ORD/NCEA-RTP 

Beth Hassett-Sipple, OAQPS/HEID 

Zachary Pekar, OAQPS/HEID 

Pradeep Rajan, OAQPS/HEID 

Susan Lyon Stone, OAQPS/HEID 

Scott Jenkins, OAQPS/HEID 

Vicki Sandiford, OAQPS/HEID 

Meredith Lassiter, OAQPS/HEID 

Marc Pitchford, OAQPS/HEID 

Karen Martin, OAQPS/HEID 

Rosalina Rodriguez, OAQPS/HEID 
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Attachment 1 

CASAC comments on first draft PM Policy Assessment and responses to those comments 

The CASAC Panel’s comments and recommendations on the first draft of the PM Policy 

Assessment, as well as changes made in the second draft in response to those comments, are 

summarized below. Overarching comments and recommendations are summarized below, 

followed by comments and recommendations on chapters 2 through 4. 

Overarching comments and recommendations

The Panel made several overarching comments and recommendations, including: 

 The document should be streamlined by relying more on the underlying scientific and 

technical documents and editing to reduce redundancy. 

 The staff’s approach to reaching conclusions on policy options should be more explicit. 

In response to these comments, we have made extensive edits throughout the second draft Policy 

Assessment to streamline the document by reducing redundancy and by relying more extensively 

on references to the underlying scientific and technical documents. We have clarified the 

approaches to reviewing the standards (sections 2.1.3, 3.1.4, 4.1.3) and have added figures framing 

these approaches (Figures 2-1, 3-1, 4-1). Throughout the document we have more explicitly 

articulated the application of these approaches in reaching staff conclusions on the current and 

potential alternative standards. We have also added an executive summary and added sections 

discussing areas for future research and data collection (sections 2.5, 3.5, 4.5). 

Chapter 2 (Primary Standards for Fine Particles)

The Panel expressed agreement with a number of preliminary staff conclusions in the first draft 

Policy Assessment, expressing support for the following: 

 Considering revisions to the current PM2.5 primary standard to provide increased public 

health protection; 

 Retaining PM2.5 as the indicator for fine particles, while also encouraging research to 

provide information for future NAAQS reviews to inform our consideration of 

alternative size fractions as well as PM2.5 components and sources; 

 Retaining annual and 24-hour averaging times; 

 Revising the form of the annual standard to eliminate spatial averaging; and 

 Considering a suite of standard levels in which the annual standard would be the 

“generally controlling” standard to provide primary protection for both long- and shortterm PM2.5 exposures, in conjunction with a 24-hour standard set to provide 

supplemental protection. 

Changes made in chapter 2 in the second draft Policy Assessment were primarily focused on 

streamlining the chapter as well as on improving and clarifying the approach for translating the 

epidemiological evidence into a basis for staff conclusions on the current and potential alternative 

standards. We have added a number of figures that summarize the available epidemiological 

evidence and air quality information (Figures 2-2 to 2-9). We have also conducted air quality 

analyses to inform our discussion of form and level. For the annual standard, we conducted 

analyses that focused on understanding potential impacts on susceptible populations, including low 

income populations and minorities (section 2.3.3.1). For the 24-hour standard, we conducted air 
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quality analyses to understand the differences in 98th versus 99th percentile forms (section 2.3.3.2) 

and to inform staff conclusions on level of the 24-hour standard (section 2.3.4.1). 

Chapter 3 (Primary Standard for Coarse Particles)

In reviewing the first draft PM Policy Assessment, the Panel expressed support for the following: 

 Considering revisions to 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 24-hour averaging time; and 

 Considering revising the form to a 98th percentile form. 

We have made important revisions in the second draft Policy Assessment to the discussions of the 

current and potential alternative standards. We have added figures summarizing the available 

epidemiological evidence and air quality data to the discussion on adequacy of the current 

standard (Figures 3-2 and 3-3). We included a new discussion of potential alternative standard 

levels and staff conclusions. To facilitate this discussion, we added figures summarizing the 

available epidemiological evidence and air quality data (Figures 3-5 and 3-6) and we have 

conducted additional PM10 air quality analyses (Figure 3-7, Table 3-2). In addition, we have 

expanded the discussion of considerations related to the standard indicator (section 3.3.1), 

including an analysis of PM10 and PM10-2.5 air quality (Figure 3-4), and we have expanded the 

discussion of standard form (section 3.3.3). 

Chapter 4 (Secondary Standard for PM-related Visibility)

The Panel expressed agreement with a number of staff conclusions included in the first draft Policy 

Assessment, including: 

 Considering revisions to the current PM2.5 standards to provide increased protection 

against PM-related visibility impairment; 

 A one-hour averaging time, including daylight hours only, and excluding hours with 

relative humidity above 90%; and 

 Considering a PM2.5 light extinction indicator. 

In addition to the edits made to address the Panel’s overarching comments, we have addressed 

specific comments on chapter 4. The Panel recognized potential benefits in moving to a PM light 

extinction indicator as well as the lack of monitoring capabilities to support direct PM light 

extinction measurements at this time, and supported consideration of an alternative approach. In 

response, we have developed and evaluated an approach that uses an indicator based on using 

speciated PM2.5 mass to calculate light extinction that allows the coupling of the PM light 

extinction indicator with PM air quality measurements based on the currently available PM mass 

monitoring infrastructure (Appendix B and section 4.3.1). In addition, in response to the Panel’s 

interest in additional analyses to better illustrate and evaluate the similarities and differences 

between the wide range of alternative indices and forms of the standard (e.g., 1-hour daily 

maximum versus all daylight hours) being considered, and the policy implications of these options, 

we have incorporated an assessment of the PM species components that contribute to the high 

value days selected by different combinations of indices/forms (Appendix C). 
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Attachment 2 

Charge to the Panel in Reviewing the Second Draft PM Policy Assessment 

Our charge to the Panel in reviewing the second draft Policy Assessment focuses on chapters 2 

through 4. We ask the Panel to focus on the following charge questions, though we would 

appreciate comments on other topics as well. 

Chapter 2 (Primary Standards for Fine Particles)

1. Current Approach (section 2.1.3): 

a. What are the Panel’s views on the staff’s approach to 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 for consideration? 

b. Has staff appropriately applied this approach in reviewing the adequacy of the current 

standards (section 2.2) and potential alternative standards (section 2.3)? 

2. Form of the Annual Standard (section 2.3.3.1): 

a. What are the Panel’s views on the additional analyses conducted to characterize the 

potential for disproportionate impacts on susceptible populations, including low income 

groups and minorities associated with spatial averaging allowed by the current annual 

standard? 

b. In light of these analyses, what are the Panel’s views on staff’s conclusion that the form 

of the annual standard should be revised to eliminate spatial averaging? 

3. Alternative Levels (section 2.3.4): What are the Panel’s views on the following: 

a. The insights that can be gained into potential alternative standard levels by considering: 

i. Confidence bounds on concentration-response relationships? 

ii. Different statistical metrics that characterize air quality distributions from multicity epidemiological studies? 

b. Potential alternative annual standard levels based on composite monitor distributions 

versus maximum monitor distributions? 

c. Use of risk information in informing staff conclusions on alternative annual and 24-

hour standard levels, including approaches used to assess overall confidence and 

potential bias in the risk estimates? 

d. Staff’s conclusion that alternative annual standard levels in the range of 13 to 11 μg/m3

are most strongly supported by the available evidence and risk-based information? 

e. Staff’s approach of focusing on peak-to-mean ratios to inform the level of a 24-hour 

standard that would provide supplemental protection to a generally controlling annual 

standard? 

f. Staff’s conclusion that consideration should be given to retaining the current 24-hour 

standard level of 35 μg/m3 in conjunction with annual standard levels in the range of 13 

to 11 μg/m3

, and that consideration could also be given to an alternative 24-hour 

standard level of 30 μg/m3 particularly in conjunction with an annual standard level of 

11 μg/m3? 

4. Key Uncertainties and Areas for Future Research and Data Collection (section 2.5): 

What are the Panel’s views on the areas for future research and data collection outlined in this 

section, on relative priorities for research in these areas, and on any other areas that ought to be 

identified? 
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Chapter 3 (Primary Standard for Coarse Particles)

5. Current Approach (sections 3.1.4, 3.2, 3.3): 

a. What are the Panel’s views on the approach to translating the available evidence and air 

quality information into the basis for reviewing the coarse particle standard? 

b. Has staff appropriately applied this approach in reviewing the adequacy of the current 

standard (section 3.2) and potential alternative standards (section 3.3)? 

6. Adequacy of the Current PM10 Standard (section 3.2): What are the Panel’s views on the 

alternative approaches presented for considering the evidence and its uncertainties as they 

relate to the adequacy of the current standard? 

7. Indicator (section 3.3.1): What are the Panel’s views on the approach taken to considering 

standard indicator and on staff’s conclusion that PM10 remains an appropriate indicator in this 

review? 

8. Form (section 3.3.3): What are the Panel’s views on the approach taken to considering the 

form of the standard and on staff’s conclusion that revising the form to a 98th percentile form 

would be appropriate for a 24-hour PM10 standard meant to protect against exposures to 

thoracic coarse particles?

9. Level (section 3.3.4): What are the Panel’s views on the following: 

a. The approach taken by staff to identify potential alternative PM10 standard levels, in 

conjunction with a 98th percentile form, including the weight placed on different 

studies? 

b. Staff’s conclusion that the evidence most strongly supports standard levels around 85 

μg/m3? 

c. The alternative approach to considering the evidence that could support standard levels 

as low as 65 μg/m3? 

10. Key Uncertainties and Areas for Future Research and Data Collection (section 3.5): 

What are the Panel’s views on the areas for future research and data collection outlined in this 

section, on relative priorities for research in these areas, and on any other areas that ought to be 

identified? 

Chapter 4 (Secondary Standard for PM-related Visibility)

11. Current Approach (section 4.1.3): 

a. What are the Panel’s views regarding our approach for translating technical evidence 

and assessment results into the basis for assessing current fine particle standards and 

considering alternative standards to provide protection against PM-related visibility 

impairment? 

b. Has staff appropriately applied this approach in reviewing the adequacy of the current 

standard (section 4.2) and potential alternative standards (section 4.3)? 

12. Nature of the Indicator (section 4.3. 1): What are the Panel’s views on the following: 

a. Staff’s consideration of the three indicators identified in this section and our 

conclusions on the appropriateness of these indicators for consideration in this review? 

b. The development and evaluation of a new approach that is based on using speciated 

PM2.5 mass and relative humidity to calculate PM2.5 light extinction by means of the 

IMPROVE algorithm? 

c. The assessment approach and results comparing the PM components that contribute to 

the hours selected in the top percentiles for PM2.5 mass and PM10 light extinction? 
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13. Alternative Levels and Forms (section 4.3.3): What are Panel views on the following: 

a. The performance assessment which focused on the Candidate Protection Levels of 64, 

112, 191 Mm-1 for PM2.5 light extinction and speciated PM2.5 mass-calculated light 

extinction, and alternative levels of 10, 20, and 30 μg/m3

 for PM2.5 mass concentration? 

b. Use of three-year averaged 90th and 95th percentiles in conjunction with a 1-hour daily 

maximum form and use of three-year averaged 98th percentile in conjunction with the 

all daylight hours form? 

c. Insights to be drawn by comparing the PM components for hours included among the 

10% highest for a 1-hour daily maximum form with the hours included among the 2% 

highest for an all daylight hours form, for the various indicators considered (Appendix 

C)? 

14. Key Uncertainties and Areas for Future Research and Data Collection (section 4.5): 

What are the Panel’s views on the areas for future research and data collection outlined in this 

section, on relative priorities for research in these areas, and on any other areas that ought to be 

identified?