UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

WASHINGTON D.C. 20460 

 

OFFICE OF THE ADMINISTRATOR 

 SCIENCE ADVISORY BOARD 

April 15, 2010 

EPA-CASAC-10-008 

The Honorable Lisa P. Jackson 

Administrator 

U.S. Environmental Protection Agency 

1200 Pennsylvania Avenue, N.W. 

Washington, D.C. 20460 

Subject: CASAC Review of Quantitative Health Risk Assessment for Particulate 

Matter – Second External Review Draft (February 2010) 

Dear Administrator Jackson, 

The Clean Air Scientific Advisory Committee (CASAC) Particulate Matter (PM) 

Review Panel met on March 10–11, 2010 to review the Quantitative Health Risk 

Assessment for Particulate Matter – Second External Review Draft (February 2010) and 

Particulate Matter Urban-Focused Visibility Assessment – Second External Review Draft

(January 2010). This letter provides our main comments concerning the Quantitative 

Health Risk Assessment for Particulate Matter (RA). CASAC’s responses to the charge 

questions, along with comments from individual Panel members follow. 

The Second Draft RA presents quantitative assessments of PM-associated risks to 

support judgments that will be made in the Policy Assessment (PA) with regard to 

recommendations for the PM National Ambient Air Quality Standard (NAAQS). The 

RA provides estimates of the degree and nature of risk reductions associated with various 

population exposure scenarios, corresponding to alternative suites of annual and 24-hour 

PM2.5 standards for the 15 selected urban case study areas. Toward that end, the Second 

Draft has largely accomplished its objective of providing input to the PA. The Second 

Draft has been substantially improved in response to comments provided by CASAC 

following our review of the first draft. The rationale, methods and results for the 

assessment are well described. The discussion and clarifications regarding uncertainty 

and variability and the characterization of confidence in the core risk estimates markedly 

enhance the document. The enhanced discussion of the interplay of annual and 24-hour 

design values together with patterns in PM2.5 monitoring helps to interpret patterns of risk 

reduction in study areas. With some additional changes recommended here, the RA will 

be a solid foundation for the PA. 

While the Second Draft has appropriately justified EPA’s decision not to estimate 

risks for thoracic coarse PM (PM10-2.5) based on limitations in the health effects data and 

the PM10-2.5 monitoring network, we encourage EPA to remain focused on pursuing the 

1
research needed for a quantitative risk assessment of thoracic coarse PM. As mentioned 

in our letter of November 24, 2009 reviewing the first draft RA, we also encourage the 

Agency to develop the capacity to conduct a formal quantitative exposure assessment for 

future revisions of the NAAQS. 

As part of simulating air quality standards in the chapter on Urban Case Study 

Analysis Methods (Chapter 3), EPA uses three different approaches for simulating just 

meeting the current and alternative suites of PM2.5 standards: the proportional approach, 

the hybrid approach, and the peak-shaving approach. CASAC recommends sharpening 

the descriptions of these three alternatives. We suggest a graphical and/or mathematical 

approach, along with the inclusion of examples based on the 15 urban study areas. EPA 

might also consider discussing how these three approaches relate to potential control 

scenarios. The hybrid approach merits the greatest emphasis, while the proportional and 

peak-shaving approaches represent bounding scenarios. As a suggestion on 

nomenclature, an alternative label for the "peak shaving" approach would be preferable, 

since this term does not adequately describe the actual method. 

The Second Draft RA includes a new chapter which provides a national scale 

assessment of long-term mortality related to PM2.5 exposure (Chapter 5). In addition to 

providing a national estimate, this chapter identifies where the urban case study areas fall 

along the distribution of national risk. While this chapter is useful for assessing the 

generalizability of the findings in the 15 urban study areas, its findings are otherwise not 

central to the risk assessment. Consequently, CASAC recommends that the chapter be 

moved to an appendix and that discussion of the key findings, summarized in Figure 5-4, 

be placed at the appropriate points in Chapter 4 (Urban Case Study Results) and in the 

current Chapter 6 (Integrative Discussion of Urban Case Study Analysis of PM2.5-related 

Risks). 

The Second Draft estimates risk reductions for different air quality scenarios 

involving specified values of 24-hr and annual standards. Five alternative sets of 

standards are considered, with the lowest scenario being an annual standard of 12 μg/m3

combined with a 24-hour standard of 25 μg/m3

. Two additional scenarios were presented 

at the March 2010 CASAC meeting with pairings of 10/35 and 10/25 μg/m3

. The 

reduction of the annual standard to10 μg/m3

 showed additional benefits beyond those 

estimated for the scenarios in the RA. However, it was not clear whether these additional 

scenarios represented potential revisions to the NAAQS and will be added to the final 

RA. With the assumption of a linear, no-threshold risk model, further reductions would 

be anticipated as the annual standard is progressively lowered. We recommend that EPA 

develop and apply specific criteria for determining the lower-bound exposure 

concentrations to be considered in the risk assessment. Mounting uncertainty at lower 

concentrations would be one such reasonable basis. Other relevant considerations 

include the range of concentrations at which the epidemiological studies have been 

carried out and the need for consideration of the degree of protection afforded to 

susceptible populations under various scenarios. The interpretation of the findings should 

also acknowledge the controlling influence of the annual average concentration as the 

proposed scenario values are progressively lowered. 

2
On a related matter, CASAC recommends greater clarity as to the basis for 

selecting the exposure scenarios included in the RA. Are the potential suites of standards 

or exposure concentration scenarios intended to guide selection among alternative 

revisions to the NAAQS? As the new overall approach to NAAQS revision is 

implemented, CASAC and the EPA need to address the extent to which the RA and the 

PA should be linked. 

In response to CASAC’s previous advice, EPA provided an integrated discussion 

of risk-related analyses that draws on uncertainty and variability analyses as well as the 

national-scale analyses completed as part of this assessment. This integrated discussion 

is presented in Chapter 6, arguably the most critical chapter of the document. EPA has 

captured the key policy-relevant questions and appropriately characterized the 

uncertainty and variability associated with its core risk estimates. While we are in 

general agreement with EPA’s interpretations of urban study area results as well as its 

observations on the degree of risk reduction likely to be associated with alternative suites 

of standards, given its importance, we recommend a careful rewriting and editing of 

Chapter 6 to ensure that its findings are clearly presented and that unneeded detail is 

removed. 

CASAC thanks the Agency for the opportunity to provide advice on the Risk 

Assessment. We look forward to continued discussions with the Agency as we review 

the Policy Assessment for the Review of the PM NAAQS - First External Review Draft

(March 2010). 

Sincerely, 

 /Signed/ 

Dr. Jonathan M. Samet 

Chair 

Clean Air Scientific Advisory Committee 

Enclosures A: CASAC Particulate Matter Review Panel Roster 

 B: CASAC Responses to EPA’s Charge Questions 

 C: Individual Panelists’ Responses to Charge Questions 

3
NOTICE 

This report has been written as part of the activities of the EPA's Clean Air Scientific 

Advisory Committee (CASAC), a federal advisory committee independently chartered to 

provide extramural scientific information and advice to the Administrator and other 

officials of the EPA. CASAC provides balanced, expert assessment of scientific matters 

related to issues and problems facing the Agency. This report has not been reviewed for 

approval by the Agency and, hence, the contents of this report do not necessarily 

represent the views and policies of the EPA, nor of other agencies within the Executive 

Branch of the federal government. In addition, any mention of trade names or 

commercial products does not constitute a recommendation for use. CASAC reports are 

posted on the EPA Web site at: http://www.epa.gov/casac. 

4
Enclosure A

Clean Air Scientific Advisory Committee 

Particulate Matter Review Panel 

CHAIR 

Dr. Jonathan M. Samet, Professor and Chair, Department of Preventive Medicine, 

University of Southern California, Los Angeles, CA 

CASAC MEMBERS 

Dr. Joseph Brain, Philip Drinker Professor of Environmental Physiology, Department of 

Environmental Health, Harvard School of Public Health, Harvard University, Boston, 

MA 

Dr. H. Christopher Frey, Professor, Department of Civil, Construction and Environmental 

Engineering, College of Engineering, North Carolina State University, Raleigh, NC 

Dr. Donna Kenski, Data Analysis Director, Lake Michigan Air Directors Consortium, 

Rosemont, IL 

Dr. Armistead (Ted) Russell, Professor, Department of Civil and Environmental 

Engineering, Georgia Institute of Technology, Atlanta, GA 

Dr. Helen Suh, Associate Professor, Harvard School of Public Health, Harvard 

University, Boston, MA 

Dr. Kathy Weathers, Senior Scientist, Cary Institute of Ecosystem Studies, Millbrook, 

NY 

CONSULTANTS 

Dr. Lowell Ashbaugh, Associate Research Ecologist, Crocker Nuclear Lab, University of 

California, Davis, Davis, CA 

Prof. Ed Avol, Professor, Preventive Medicine, Keck School of Medicine, University of 

Southern California, Los Angeles, CA 

Dr. Wayne Cascio, Professor, Medicine, Cardiology, Brody School of Medicine at East 

Carolina University, Greenville, NC 

Dr. David Grantz, Director, Botany and Plant Sciences and Air Pollution Research 

Center, Riverside Campus and Kearney Agricultural Center, University of California, 

Parlier, CA 

Dr. Joseph Helble, Dean and Professor, Thayer School of Engineering, Dartmouth 

College, Hanover, NH 

5
Dr. Rogene Henderson, Senior Scientist Emeritus, Lovelace Respiratory Research 

Institute, Albuquerque, NM 

Dr. Philip Hopke, Bayard D. Clarkson Distinguished Professor, Department of Chemical 

Engineering, Clarkson University, Potsdam, NY 

Dr. Morton Lippmann, Professor, Nelson Institute of Environmental Medicine, New 

York University School of Medicine, Tuxedo, NY 

Dr. William Malm, Research Physicist, National Park Service Air Resources Division, 

Cooperative Institute for Research in the Atmosphere, Colorado State University, Fort 

Collins, CO 

Mr. Charles Thomas (Tom) Moore, Jr., Air Quality Program Manager, Western 

Governors' Association, Cooperative Institute for Research in the Atmosphere, Colorado 

State University, Fort Collins, CO 

Dr. Robert F. Phalen, Professor, Department of Community & Environmental Medicine; 

Director, Air Pollution Health Effects Laboratory; Professor of Occupational & 

Environmental Health, Center for Occupation & Environment Health, College of 

Medicine, University of California Irvine, Irvine, CA 

Dr. Kent Pinkerton, Professor, Regents of the University of California, Center for Health 

and the Environment, University of California, Davis, CA 

Mr. Richard L. Poirot, Environmental Analyst, Air Pollution Control Division, 

Department of Environmental Conservation, Vermont Agency of Natural Resources, 

Waterbury, VT 

Dr. Frank Speizer, Edward Kass Professor of Medicine, Channing Laboratory, Harvard 

Medical School, Boston, MA 

Dr. Sverre Vedal, Professor, Department of Environmental and Occupational Health 

Sciences, School of Public Health and Community Medicine, University of Washington, 

Seattle, WA 

SCIENCE ADVISORY BOARD STAFF 

Dr. Holly Stallworth, Designated Federal Officer, EPA Science Advisory Board Staff 

Office 

6
Enclosure B 

CASAC Responses to EPA’s Charge Questions 

Chapter 3 – Urban Case Study Analysis Methods 

 

Charge Question 1: Air quality inputs (section 3.2): We have expanded the 

consideration of alternative approaches to simulating just meeting the current and 

alternative suites of PM2.5 standards (i.e., rollback approaches) to include a peak 

shaving approach, in addition to the hybrid and proportional approaches 

considered in the first draft assessment. This peak shaving approach is intended to 

represent more localized, rather than regional, patterns of PM2.5 reductions 

(discussed in section 3.2.3.3). 

a) To what extent does the Panel believe that the use of the peak shaving approach 

provides useful additional exploration of variability associated with how ambient 

PM2.5 concentrations are simulated to change upon just meeting the current and 

alternative suites of standards? 

As noted in our overall comments, CASAC recommends that the "peak shaving" 

approach be more clearly defined in a graphical and/or mathematical fashion. We also 

recommend that it be renamed, given the potential to misinterpret its actual application. 

The “peak shaving” approach does provide useful information, but specific examples are 

needed as to the situation(s) and potential control approach(es) it is meant to simulate. 

Appendix B should also provide the specific mathematical formulation. It would be 

instructive to provide an example of the three rollback approaches as applied to data for 

several cities in section 3.2, or in Appendix B. 

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 

estimates of long-term exposure-related mortality? 

A very brief description of how annual design values are currently calculated should be 

provided to help motivate the procedure developed here. CASAC is uncomfortable with 

the approach used for imputing missing values, and has discussed alternatives in the 

members' individual comments. Whatever method is chosen, the impact of the approach 

taken can be characterized using data from monitors where there is little missing data, 

then removing some data, applying the imputation approach, and testing to see how 

closely the method reproduces the original annual average. The approaches to 

compositing and imputing missing values would be more easily followed if equations 

were provided. 

7
Charge Question 2: Selection of model inputs (section 3.3): We have expanded and 

clarified the discussion of our rationale for identifying modeling choices comprising 

the core risk model, focusing in particular on selection of C-R functions (section 

3.3.3). To what extent does the Panel consider this discussion to be clear and the 

model selections appropriate? 

CASAC commends the authors for expanding and clarifying the rationale for identifying 

modeling choices comprising the core risk model in a logical and satisfactory manner. 

Their model selections were appropriate for this review cycle, which is focused on PM2.5 

exposure and cardiovascular responses. The stated rationale provides a solid foundation 

for the selection of the epidemiological studies that were utilized to establish C-R 

functions. The expansion of the discussion and integration of the ISA was useful in 

reinforcing gaps in knowledge, as in the text on p. 3-20 stating that there were no multicity studies for the category of short-term exposure to PM2.5 and emergency department 

visits for cardiovascular and/or respiratory illnesses. The summary tables (Tables 3-5 

through 3-8) provide a useful synopsis of the model inputs for the core risk models and 

sensitivity analyses. 

Charge Question 3: Addressing uncertainty and variability (section 3.5): We have 

clarified the process used to evaluate sources of variability and added coverage 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 

interactions of sources of uncertainty (section 3.5.4). To what extent does the Panel 

consider these discussions to be clear and appropriate? 

In general, the second draft RA appropriately identifies and discusses key sources of 

variability and uncertainty, and includes sensitivity analyses that provide insight 

regarding the impact of some sources of uncertainty on the core risk estimates. The 

authors have provided a footnote explaining the rationale for identifying “key” sources of 

variability. The document should indicate if the same process was used to identify “key” 

sources of uncertainty. We note that EPA added material regarding co-pollutant 

concentrations and demographic and socioeconomic status, as requested in CASAC 

comments on the first draft of the RA. 

EPA did not address CASAC's recommendation on the first draft RA suggesting that 

“exposure modeling should be included in the REA. A probabilistic Tier 3 approach 

should be used for the exposure assessment.” While we understand that timing may have 

precluded adequate treatment of this topic, we urge EPA to develop the capacity to do so 

for future revisions of the NAAQS. CASAC made the same recommendation at the time 

of the last review of the PM NAAQS. With regard to uncertainties, in response to 

CASAC comments on the first draft of the REA, EPA has included uncertainty in the CR function itself, which was developed from single studies. EPA has appropriately taken 

into account differences in C-R functional form associated with studies that addressed 

long-term or short-term effects for single or multi-city studies even if they were not the 

basis for the final set of C-R functions used in the RA. 

8
The RA now provides adequate explanation of the uncertainty categories of “low”, 

“medium”, and “high.” However, there is a confusing statement to the effect that “high” 

sources of uncertainty “are likely to influence the interpretation of risk...” “if those 

sources of uncertainty are reduced or more fully characterized.” The parenthetical “if” 

clause seems to confuse the issue and should be deleted. The RA needs to describe the 

process by which "staff consensus" was achieved (see lines 6-20 of p. 3-63). If staff 

consensus is an element of decision-making in carrying out the RA, then this aspect of 

the process needs to be described. 

EPA has adequately commented on the extent to which there are dependencies among 

pairwise combinations of sources of uncertainty, and whether these dependencies would 

tend to offset or to increase the overall range and direction of uncertainty in the 

assessment results. For example, the statistical fit of the C-R functions, and the shape of 

the functions, are inter-related. 

Based on quantifiable sensitivity analysis, the report generally clearly conveys that the 

“core” estimates appear to be at the low end of alternative “plausible” estimates. 

However, particularly in Chapter 6, the role of sources of uncertainty treated qualitatively 

should also be addressed. In particular, given exposure misclassification, it is likely that 

the core estimates are biased low and hence conservative, an important point to convey 

consistently. 

Chapter 4 – Urban Case Study Results

Charge Question 4: Sensitivity analysis results (section 4.3): We have included a 

discussion of how the results of the sensitivity analysis can be used as an additional 

set of reasonable risk estimates to inform consideration of uncertainty in the core 

risk estimates (see section 4.3.2). What are the Panel’s views on how we have used 

the sensitivity analysis results to support consideration of uncertainty in the core 

risk estimates? 

Overall, the sensitivity analysis section 4.3 is very good and nicely covers a complex 

topic. Table 4-3 is a useful summary. The classification of descriptive categories for 

small, moderate, moderate-large, and large contributions is useful. However, it would be 

more appropriate to refer to these as contributions to “sensitivity” rather than 

“uncertainty.” As noted in several place, the sensitivity analyses represent plausible 

alternatives to the core estimate, but are not probabilistic. The language of the RA is 

appropriate on this point and has clearly articulated that the sensitivity analyses results 

represent plausible and scientifically defensible estimates. The range of these estimates 

provides an indication of the implications of uncertainty. 

The evaluation of alternative model structure is critically important, because model 

structure can potentially be a larger source of uncertainty than the range of values for an 

input to a given model. The results in Table 4-3 indicate, for example, that the random 

effects log-log model provides larger risk estimates than the fixed effects log-linear 

9
model used for the core estimates. This information is very useful and is an excellent 

addition to the RA. The more thorough treatment of model choices and alternative C-R 

functions provides plausible alternative estimates to the core estimate. 

Per CASAC’s comments on the first draft RA, EPA indicates the direction of the percent 

changes in risk. In addition to the percent difference, the actual difference in risk should 

be reported to provide further context. The second draft RA seems to put emphasis on 

relative changes in risk. However, the NAAQS are intended to be protective of public 

health, and therefore the magnitude of the risk estimates is ultimately a more useful 

policy-relevant metric. 

The sensitivity analysis related to peak shaving and “peakiness” was not very clear in its 

interpretation. What are the main points to take away from these analyses? 

Charge Question 5: Consideration of design values and patterns of PM2.5 

monitoring data in interpreting core risk estimates (section 4.5): To enhance our 

interpretation 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 PM2.5 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 estimated upon just meeting the current 

and alternative suites of standards under alternative rollback approaches. 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 supportive of these additional assessments? 

b) Does the Panel have any recommendations for additional insights based on 

consideration of patterns in design values and PM2.5 monitoring data across the 15 

urban study areas and at the national level? 

The graphical presentations depicting the 24-hour and annual average design values for 

US urban areas and the 15 urban study areas used in the RA were very helpful for 

understanding the concept of the controlling standard, the implications of reducing either 

the annual or the 24-hour standard, or both, and the representativeness of the 15 urban 

study areas. To further enhance the value of these graphical presentations, more complex 

color coding could be used to provide information on the US region of each urban study 

area. In these plots, unsupported conclusions were drawn for cities lying on the border 

between zones. Graphical presentation of the design values by monitoring site for the 15 

urban study areas provides valuable insights into the role of patterns of PM monitoring 

data in different cities in determining consequences of various control strategies. We 

recommend that the term “peaky” as used to describe PM patterns be better defined and 

applied consistently. The main observations from both sets of plots should be 

summarized, especially as regards impacts of the alternative rollback procedures. 

10
Chapter 5 of the revised RA provides estimates of the numbers of deaths attributable to 

long-term PM2.5 exposure, based on air quality estimates from the Community Model for 

Air Quality (CMAQ) and the environmental Benefits Mapping and Analysis Program 

(BenMap), and uses the risk estimates derived for the Krewski, 2009 assessment of the 

ACS data with a LML of 5.8 ug/m3

. A principal purpose for inclusion of this chapter is 

to place the PM2.5-associated risks for the 15 urban study areas within the distribution of 

risks nationally. Figure 5-4 provides the key findings in regard to this purpose and 

indicates that the selected urban study areas in large part fall in the highest 20% of the 

distribution of sites. . 

We recommend that Chapter 5 be moved to an Appendix with inclusion of Figure 5-4 at 

appropriate points within Chapter 4 and the current Chapter 6. The figure provides 

information relevant to the generalizability of findings from the 15 areas to the entire 

United States. However, the estimates themselves are not directly relevant to the overall 

purpose of the RA; the estimation approach differs from that used for the 15 urban study 

areas; and the chapter is brief and does not adequately set out sources of uncertainty and 

variability. By placing the chapter's contents into an appendix and specifically 

acknowledging its purpose, it will not distract from the flow of the RA and the major 

objective of the analysis will be met by inclusion of Figure 5-4 in Chapter 4 and the 

revised Chapter 5. 

Chapter 6 – Integrative Discussion of PM2.5-related Risks 

Charge Question 6: We have developed an integrated discussion of the PM2.5-

related risk estimates which considers the results of the qualitative and quantitative 

treatment of uncertainty and variability together with the various 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. 

CASAC was unanimously pleased by the addition of this chapter to the document. The 

chapter summarizes the many detailed analyses carried out in Chapter 4 and extended in 

the Appendices. However, the results presented could be summarized more effectively 

and rather than being presented in great detail, there should be a more integrative 

discussion. The choice of the 15 urban study areas was previously discussed in Chapter 4. 

Similarly, the choices of endpoints were already documented. Clearly, the use of IHD 

mortality (as opposed to all- causes of cardiovascular mortality) represents an upper 

bound of effects. This outcome was apparently selected because of its availability in the 

Krewski et al. 2009 analysis. 

CASAC discussed the selection of alternative scenarios under the assumption of a linear, 

no-threshold C-R function. In the current draft RA, the lowest levels assessed were 12/25 

μg/m3

; however, preliminary analyses at 10/25 μg/m3 were presented, indicating a 

variable effect across the 15 urban study areas, resulting from different characteristics of 

some of the areas. As mentioned previously, specific criteria need to be developed and 

applied in selecting the lower bound scenarios. These scenarios will be particularly 

11
informative for considering protection of susceptible populations as uncertainty increases 

at lower bound concentrations. There are a number of potential bases for the specification 

of these scenarios including the concentrations at which observations have been made, 

the level of uncertainty, and the extent of protection to be achieved. 

a) To what extent does the Panel believe that we have captured the key policyrelevant questions that can be addressed by this risk assessment? 

EPA has presented and captured the key-policy relevant questions. However, CASAC 

continues to recommend a qualitative discussion on PM10-2.5 and on those effects of PM2.5 

for which the evidence was found to be “suggestive.” 

b) We provide a set of key observations 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 consideration of trends in risk reduction across 

alternative suites of standards and residual risk remaining after simulation of just 

meeting specific suites of standards, but also on additional factors that can impact 

risk (e.g., the role of annual and 24-hour design values, the peakiness of PM2.5

distributions within a study area, and application of different rollback 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 other 

observations that might be made that would help to address the policy-relevant 

questions identified at the beginning of the chapter? 

Section 6.2 summarizes the findings of key analyses. The sensitivity analyses presented 

explore multiple factors including the roll back approach, concentration scenarios, and 

location, the latter influencing findings through the the PM2.5 concentration profile and 

mortality rate. The text describing these key observations is too long and not sufficiently 

structured. While the analyses do support the observations made, the text does not make 

these linkages with sufficient clarity. In fact, much of the discussion becomes too 

anecdotal as individual cities and scenarios are reviewed. 

Key observations are presented and adequately discussed with regard to the roles of 

annual and 24-hour design values in determining population risk and of the role of 

“peakiness” of distributions. The text should more sharply characterize the critical 

finding of the cross-area variation in the extent of risk reduction under the various 

scenarios. This variation needs emphasis as extension of the findings from the 15 urban 

study areas to the entire country is considered. 

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 and 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 

assessment 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? 

12
13

See above. The RA reasonably and appropriately describes the level of confidence that 

can be given to its analyses, given sources of uncertainty and variability. 

d) As part of the integrative discussion, we use the results of several national-scale 

analyses (i.e., the national scale PM2.5 mortality analysis, the representativeness 

analysis, and the new exploration of design values and patterns of PM2.5 

monitoring data presented in section 4.5) to place the results of the risk assessment 

in a broader national-context. What are the Panel members’ views on 

appropriateness of this effort to place results of the analysis in a national context? 

The RA presents multiple analyses that explore issues related to the extension of the 

findings from the 15 urban study areas to a national-scale. These areas were admittedly 

not chosen as a representative sample per se, but to be illustrative of locations with 

different patterns of PM2.5 concentrations. The analyses presented in sections 4.4 and 4.5 

and in Chapter 5 satisfactorily set out a basis for placing the RA results in a national 

context. Figure 5.4 is also valuable, and should be included in the revised Chapter 6. 

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 assessment in these 

observations? Of particular note is the observation that, while alternative 24-hour 

standard levels can be used to reduce annual-average PM2.5 concentrations and 

thus to reduce estimated risk, the results are likely to be highly variable across 

urban areas. More consistent lowering of annual-average PM2.5 concentrations 

across study areas, and thus more consistent reductions in estimated risk, may 

result from application of alternative annual standard levels. We also note that 

simulation of the alternative 24-hour standard level of 25 μg/m3 resulted in 

reductions in annual-average PM2.5 levels for some study areas that were well 

below the lowest annual standard level assessed (i.e., below 12 μg/m3). As a 

consequence, we observed risk reductions reflecting these changes in annualaverage PM2.5 levels below 12 μg/m3. Given these results, does the Panel believe 

that there is utility in estimating risks for alternative annual standard levels below 

12 μg/m3?

Key observations are presented in a balanced and fair way. Staff acknowledges that the 

ranges of effects are in two categories: 3-9% and 0-3% in two halves of the country. 

This may be less precise than what the data indicate in that it would appear from their 

own estimates that the bulk of the effect comes from the upper end of the exposure in the 

counties (pg 5.8, line 12-15). 
Enclosure C 

Compendium of Individual Preliminary Panelists Comments 

Quantitative Health Risk Assessment for Particulate Matter (February 2010) 

Comments from Mr. Ed Avol .......................................................................................... 2 

Comments from Dr. Joe Brain ........................................................................................ 9 

Comments from Dr. Wayne Cascio............................................................................... 12 

Comments from Dr. Christopher Frey ......................................................................... 13 

Comments from Dr. Joseph Helble ............................................................................... 16 

Comments from Dr. Rogene Henderson....................................................................... 18 

Comments from Dr. Philip Hopke ................................................................................ 21 

Comments from Dr. Morton Lippmann....................................................................... 23 

Comments from Dr. Robert Phalen .............................................................................. 28 

Comments from Dr. Ted Russell................................................................................... 29 

Comments from Dr. Frank E. Speizer.......................................................................... 32 

Comments from Dr. Helen Suh ..................................................................................... 36 

Comments from Dr. Sverre Vedal................................................................................. 37 

1
Comments from Mr. Ed Avol 

General: 

The second external review draft of the Quantitative Health Risk Assessment for 

Particulate Matter is a dramatic and substantial improvement over previous versions, and 

sets a new thoughtful foundation and prototype for subsequent risk assessments to 

generally follow. Improved presentations, superior figures, and useful tables and 

footnotes are present to guide the reader through the process by which EPA staff and 

consultants have reviewed available data, performed additional analyses, and interpreted 

the results of those analyses. The NAAQS health risk assessment process is becoming 

increasingly transparent and trackable (to the benefit of the reader and the public), but 

some convolutions and meanderings still persist to prevent complete clarity of 

presentation and focused presentations of conclusions, decisions, and positions. Chapter 

4 provided a detailed step-by-step examination of the approach, the analyses, and the 

results in appropriate depth. Chapter 5 seemed minimal and uncertain as to whether the 

authors wanted to present it in the main body of the risk assessment or in an appendix. 

The addition of Chapter 6 as an opportunity to present an integrated view of the work 

performed is much-appreciated and was generally well-presented. 

Charge Questions to CASAC: 

1a) Utility of the peak-shaving approach: 

The peak shaving approach seems useful and warranted, and aids in understanding the 

impact and effects of various reduction approaches for a range of possible 24hr/annual 

standards. 

1b) Use of the composite monitor approach: 

This may well be the appropriate approach to take, but it would be more convincing if 

some supporting data for this approach were provided in the appendix or main body of 

the document. This could readily be done using sites in several of the urban study areas 

with complete or near-complete data, and dropping out one or more data points, creating 

the “need” for fill-in strategies and a ready comparison with the actual (observed) data. 

2) Selection of model inputs: 

This seemed generally clear and supported. The justified emphasis on PM2.5 and 

cardiovascular endpoints may be appropriate at this point in the NAAQS review cycle, 

but ongoing concern about other particle sizes and constituents, as well other health 

endpoints, makes the current specific approach time-limited and in need of likely review 

in successive cycles. 

3) Addressing uncertainty and variability: 

 The discussion and clarifications regarding uncertainty and variability are muchimproved, much-appreciated, and markedly enhance the credibility and stature of the 

entire document. The presentations are definitely appropriate and mostly clear. 

4) In general, the approach seemed appropriate and well-documented. Some assumptions 

appear to have been made (or at least, not justified in the main body of the presentation), 

2
such as the consideration of Philadelphia and Los Angeles as “representative” East and 

West Coast urban areas, respectively, for sensitivity analyses. 

5a) The approach to include both 24hr and annual design values in assessing core risk 

estimates is a reasonable one that helps to clarify differences between reduction strategies 

that may not otherwise have been apparent. Expansion of the discussion to 15 urban 

study areas is a worthwhile endeavor that yields a number of insights and benefits (not 

the least of which is added credibility to the calim of national representativeness). The 

approach was generally well-done, added to the discussion, and enhanced the validity of 

the presentation. Several specific questions remain (see detailed queries below) but in 

general, I am wholly supportive of the presented approach and applaud the staff and 

consultants for their work. 

5b) (No additional insights or recommendations at this time) 

6a) The key policy-relevant questions have been captured in the presentation. 

6b) The observations in Section 6.2 are well-supported but not always clearly articulated. 

6c) The characterization of confidence in the core risk estimates is a marked 

improvement over previous versions of the document, and helps to establish the 

credibility of the overall approach. Given the available information, the presentation 

appears appropriate. 

6d) The presentation of the placement of the risk assessment results in to a national 

context appeared a bit tentative and unsure. A more forceful presentation and assertion 

about representativeness could and should be made. 

6e) The key observations listed at the end of Chapter 6 are generally present, but not 

presented in as clear or concise a manner as could be done. I believe it is useful to 

present estimated risks for a range of standards and levels, so that the Administrator has a 

more complete perspective of the possible implications of the various reduction 

strategies. However, I don’t think it is worth a great deal of effort or time to estimate risk 

reduction at 6 or 8 or 10 ug/m3

 annual average. Practically speaking, there are US urban 

areas unlikely to ever get those low levels, so with a uniform national standard, it seems 

more of an academic exercise. 

Questions: 

P3-11, lines 30 on (the composite monitor approach) – The procedure is described for 

filling in missing data, but there is not presentation or reference to any validation of how 

precise, accurate, or appropriate the fill-in approach is, based on more complete data at 

sites within the respective urban study areas. Was any assessment of the efficacy of this 

approach done? The comment in the text (p3-13, lines 7-11 that in New York, for 

example, 2/3 of the data was interpolated may raise some cause for concern that could be 

allayed by providing some sample analyses with existing and retrievable data. 

3
 

P4-28, line 18, sensitivity analysis modeling using Philadelphia and Los Angeles as 

“representative” East and West Coast urban areas...how was this decision made? On 

what basis or comparison criteria? How ”representative” are either of these urban areas of 

their respective coastal counterparts? Some explanation or justification should be 

provided for these selections, even if it is only to refer to an Appendix or footnote. 

P4-49, line2 – the explanation behind this discussion of determinants of PM2.5 health 

estimates is confusing. On p4-48, lines 21-24, the estimates of risk in the risk assessment 

framework are claimed to be based on four elements: “...population, baseline incidence 

rates, air quality, and the coefficient rating air quality and the health outcome (i.e, the 

PM2.5 effect estimates)”. On the next page, the determinants of the PM2.5 effect estimates 

are claimed to”... be grouped into three areas: demographics, baseline health conditions, 

and climate and air quality” (which are actually four areas). However, it would appear 

that these statements argue that the fourth element of the basis for the risk estimates is 

composed of the first three elements (if population = demographics, baseline incidence 

rates = baseline health conditions, and air quality = air quality), which seems a bit 

circular in description and confusing. 

P4-49, line 14 bullet – It is not clear why climate and air quality are included in the same 

bullet, since the references and variables listed seem to cover each of the climate and air 

quality categories separately and without overlap. 

P4-51, Table 4-5, Co-Pollutant Levels row – in the text discussion of PM2.5 and relevant 

risk estimates, SO2 is specifically identified and included in the figures and tables, yet in 

the table presented national-level data for use in developing risk determinants, ozone is 

the only co-pollutant presented. It would therefore seem appropriate to note why Ozone 

is listed (cardiovascular mortality reference?) and why SO2 is not. 

P4-54, line27 – It is a bit confusing for the reader to follow the discussion from text to 

table to figures, since the number of urban case study areas plotted vary in the table (4-6) 

by category, are not presented in any key with the appropriate figures, and don’t appear 

to be consistent between the table listing and the related figure. 

P4-57, Figure 4-9 through 4-16: (a) It would make it easier for the reader to follow the 

discussion and the illustrated material in the figures if some additional information were 

provided in a key or caption with the figures, such as the number (n) for each of the three 

data categories plotted (all counties CDF, Case study counties CDF, case study counties) 

and some comment about the splines or plots and inflection points displayed; (b) there is 

an inconsistency in the presentation of these figures, since some specifically comment on 

the number of urban case study areas above or below a given percentile (Figures 4-9, 4-

11,4-14, 4-15, 4-16), while others have no comment (Figure 4-10, 4-12, 4-13); A 

summary comment for these three figures would help guide the reader as to the key 

implications of the provided figure; (c) Would there be additional clarity or power of 

argument gained by somehow highlighting or identifying the plotted values of the 15 

urban study areas from amongst the larger number shown? 

4
P4-66, lines 10-12 and P4-67 (Figure 4-17) – The text and figure are inconsistent, since 

the text says (with respect to the 35/15 plot in Figure 4-17) “...Atlanta, Birmingham, and 

Houston fall into this zone...” (Zone C), but Figure 4-17 shows Birmingham in Zone B2, 

Atlanta arguably on the cusp between C and D, and Houston well into Zone D...and in 

fact, the next bullet in the text (P4-66, lines 13-16) discusses Houston’s presence in Zone 

D. 

Chapter 5 (National-Scale Assessment of Long-Term Mortality) – This chapter seems a 

bit tentative. The data presented is critical to the overall discussion, but the manner in 

which it is presented doesn’t fit with the previous chapter or document flow. The 

introductory sections are fine and lay the ground for presentation of the results, but the 

methods section seemed spotty and uncertain in tone as to whether this should be better 

placed entirely in Appendix G with more details, or presented more conceptually here, 

with reference to the appropriate appendix for details. The two figures presented are the 

key information for the chapter. The text provides a description of what is literally 

presented in the figures, but provides little in the way of interpretation (see text related to 

Figure 5-3, for example). What is the intended message associated with Figure 5-3? A 

sentence or two would help to direct readers’ interpretation or consideration of this. 

P5-2, lines14 thru 21 (interplay between regional-scale reductions in adjacent urban 

areas) – the issue under discussion and the key problem being identified still is not 

clear... 

P5-5, line 15 - The reference to “...7 Health Effects Institute PM regions...” seems 

unnecessary and distracting; this discussion of health impacts relates to geographic 

regions of the country (southwest, southeast, etc, as presented in Table 3.2, p3-14), and 

how the Health Effects Institute identifies these areas does not seem germane to the 

central argument. 

Chapter 6 (Integrative Discussion) offers the promise of pulling together the previous 

chapters’ presentations into one focused summary for reader review, but up through 

Section 6.3, too often self-destructs by using meandering phrasing and including 

extraneous comments in conclusionary statements. The net result of the writing approach 

employed is to obscure the message and frustrate the reader. There are some excellent, 

insightful, and important points to be made in this presentation, but they are often hidden 

in multiple qualifying commentaries when the main point is being presented. Use of 

bullets in the commentary can be an effective way of focusing the reader on the main 

persuasive points of the presentation, but in this chapter, their use suffers from a lack of 

clarity. With each bullet, make the statement, and then provide a terse justification in the 

ensuing paragraph. For example, the bullet might be “Dramatically different rates of 

mortality risk reduction are observed in areas with peaky PM2.5 distributions, when peakshaving, compared to proportional rollback , approaches are used.” A brief supporting 

paragraph could use Salt Lake City or Los Angeles data as an example to make the point. 

5
P6-7, line 21-22 – This comment is self-obvious and not necessary; of course the 

variability in incidence estimates is driven by differences in the study population (if the 

analyses are correctly performed and identifiable confounders are adjusted for). Remove 

this opening sentence and begin this paragraph with something like, “Substantial 

variability in incidence estimates was observed for the 15 urban study cases. 

Substantially less variability would be expected in estimates...” 

P6-17, lines 26 thru 29 – This seems like a very odd disclosure comment to make as a 

closing comment. Under what set of circumstances does EPA believe someone reading 

this document would interpret the 15 urban areas under discussion being the ONLY 15 

areas in the country having health risks associated with PM2.5? This last sentence in the 

paragraph seems entirely unnecessary, but if there is a sense that this point is worthy of a 

comment, I would suggest that the last two sentences in this section of the text (lines 24-

29) be deleted and replaced with something like the following: “The results of the 

national-scale mortality analysis suggests that the 15 urban study areas selected for 

presentation in this document are representative of a continuum of urban area results 

towards the upper end of the cumulative mortality distribution.” 

P6-19, lines 16 thru 23 (the final bullet on the page) – This comment, which establishes 

the credibility for evaluating the 15 urban study areas chosen, does not directly address 

the policy –relevant question posed under which it is listed, but does go to a central issue 

in the considering the relevance of the risk assessments undertaken. Accordingly, this 

bullet should be moved up to become the first bullet in Section 6.4, establishing the 

credibility of the study areas used in the analyses, before the results of those analyses and 

their relevance to policy are presented. 

Editing Details: 

P2-6, line 28 – delete one of the periods at the end of the sentence 

P2-8, line 27 – something is missing where the “(chapter 5)” placeholder is in the 

sentence; perhaps “long-term mortality”? 

P3-7, line 34 – need hyphen between “empirically estimated” 

P3-13, line 6 – “synced” is mis-spelled; shouldn’t this be “synched” or “synchronized”? 

P4-17, line 22 – remove underline for “of total incidence” 

P4-17, line 28 – change “these head negative point estimates” to “these had negative...” 

P.4-23, line 13 – change “...2-4hour average risk...” to “24-hour average risk” 

P4-27, line 26 – capitalize “eleven” to become “Eleven” 

P4-38, line 2 – “...morality...” should be “....mortality...” 

P4-40, line 26 - “...at the same urban study are...” should be “...at the same urban study 

area...” 

P4-41, line 25 - This first sentence anticipates a listing of several factors that are then 

never presented, so the sentence should be re-structured, perhaps as, “There are several 

observations regarding key sources of ... that can be made.” 

P4-41, line 28 – change “factor” to “factors” 

P4-42, line 1 – what does “...the highest sensitivity analysis results...” mean? Does it 

mean the biggest changes, or the best outcome? A little re-phrasing would help. 

6
P4-42, line 25 – for consistency with previous line, probably better to say “...log-linear 

model with fixed effects...” 

P4-42, line 28 – remove hyphen from local-sources 

P4-42, line 34 – should be re-phrased to read “...in the area of the curve between the 

LML and the PRB” rather than “...as you move below the LML” 

P4-42, lines 36 to 38 – this is an important comment that, as written, is difficult to 

understand. I would offer the following: “ Due to large uncertainties associated with C-R 

functions in the range between the LML and PRB, such estimates should be excluded 

when considering reasonable alternative risks associated with core risk estimates.” 

P4-45, footnote refers to open circles in Figures 4-6 and 4-7, but neither has open circles 

nor displays SO2 risk estimates; I believe Figure 4-8 is the correct reference. 

P4-46, Figure 4-8 key – add a “g” to “modelin” 

P4-47, line 13 – change phrasing from “...attributable to secondarily formed PM2.5” to 

“...partially attributable to secondary formation of PM2.5” 

P4-47, line 18 – this statement can be more definitive, based on Figure 4-8; Instead of 

“Most if not all”, change to read “Virtually all of the alternative model specifications...” 

P4-47, lines 29, 31, and 32 – Figure references should be to Figures 4-7 and 4-8, not 4-6 

and 4-7. 

P4-49, line2 – shouldn’t this be four areas, not three (demographics, baseline health, 

climate, and air quality)? 

P4-49, line3 – change “..., and climate and air quality...” to “..., climate, and air 

quality...” 

P4-49, line31 – Incorrect table referenced; should be Table 4-5 in current draft version. 

P4-54, line 5 –Kolmogorov- Smirnov test results appear in Table 4-7, not in Table 4-4. 

P4-54, line21 – Figure numbers are incorrect in text. 

P4-70, Table 4-8 – the entry for Urban study area Pittsburgh PA has a superscript “5” 

following it, but no footnote or key to what this refers to. 

P4-71, line 5 – should be Figure 4-19, not F-19. 

P4-75, footnote 61 – second line should read “...related mortality – see section...” 

P4-75, lines 22 thru 27 – this sentence can and should be divided into several shorter 

sentences. 

P5-5, lines 27 thru 29 – this looks like the title of a table or figure, not part of the 

text...??? 

P5-6, footnote, second-to-last line – should read “...are subject to greater uncertainty...” 

P6-1, line 31 – remove one of the two periods at the end of the sentence. 

P6-4, line 23 – “INTERPRETATION” is mis-spelled (missing a T). 

P6-6, line 2 – it would be clearer to re-phrase this to read: “...relatively high 24-hr design 

values compared to the respective area’s corresponding annual average design values...” 

P6-6, line 6 – the term “composite monitor” should be defined or explained in a 

parenthetical comment or footnote in this integrative summary chapter, to avoid having 

readers backtrack to previous chapters to try and find the intended meaning. 

P6-6, line 18 – the correct figure reference (for the current standard values) is Figure 4-

17. 

P6-7, lines 17 & 18 – Actual IHD mortality values in Table 4-1 are 15-19 for Salt Lake 

City and 1755-2222 for New York City. 

P6-7, line 25 – should read “...current suite of standards...”, not “...if standards...” 

7
P6-9, line 27 – change “that” to “than” 

P6-11, line 1 – change “...just meeting the a given...” to “...just meeting a given...” 

P6-14, footnotes 78 and 79 – references to Figure 4-20 should be 4-19 

P6-15, lines 7-9 – This sentence is garbled and confusing, and needs re-writing and 

clarification. 

P6-15, footnote 81 – reference Figure 4-18, not 4-20. 

P6-18, lines 11-12 – delete the rest of the sentence and end after “...2,000 cases per 

year.” (This is repetitive and not needed in this summary statement). 

P6-18, lines 14-15 – delete the rest of the sentence after “...in a given year for the urban 

study areas.” 

P6-18, line 17 – Delete “Generally comparable” and begin the sentence “Estimates of 

CV-related mortality...” 

P6-18, lines 24-25 – Correct first sentence to read, “A broader array of health effects has 

also been associated with PM2.5 exposures, including reproductive effects and 

developmental effects in children.” 

P6-18, lines 29-32 – Change first sentence to read:”Given the quantitative and qualitative 

assessments of uncertainty and variability performed as part of the risk assessment, it is 

unlikely that the degree of risk remaining upon the simulated meeting of the current 

(15/35) suite of standards has been over-stated.” 

P6-18, line 41- Re-write to read: “This variability in annual-average PM2.5 concentrations 

is most prominent in study areas where the 24-hour standard is “controlling”.” 

P6-19, line 14 – Delete the word “well”; not clear what the definition of “well below a 

value” is, if some of the values are said to be approximately equal to it). In this context, 

it seems sufficient to state that the annual average concentrations under discussion are 

below the level of the current annual standard. 

P6-19, line 19 – delete the phrase “in most such areas”; it is redundant, given the 

beginning of the sentence and the sentence structure. 

P6-19, line 21 – replace “reflective of” with “as do” 

P6-19, line 36 – add “%’ after “11” 

P6-21, line 2 – delete comma after “... with a” 

P6-21, line 3 – insert “U.S.” before “...counties” 

P6-21, line 5 – replace the phrase “...likely capture well...” with “do represent” 

P6-21, lines 7-9 – why is this comment here? Isn’t it self-evident in selecting a 

representative sub-sample? As I have commented previously, this is unnecessary and can 

be deleted. 

8
Comments from Dr. Joe Brain 

Charge Question #6a-e 

6) We have developed an integrated discussion of the PM2.5-related risk estimates which 

considers the results of the qualitative and quantitative treatment of uncertainty and 

variability together with the various 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 addressed by this risk assessment? 

Response: Chapter 6 is the culmination a rationale developed throughout the document. 

It needs to pull all the pieces together and clearly integrate them in a form that provides 

the basis for decisions. The panel responds positively to Question 6a. We believe that 

this second draft does effectively capture the key policy-relevant questions that can be 

addressed by the preceeding risk assessment. 

b) We provide a set of key observations 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 consideration of trends in risk reduction across 

alternative suites of standards and residual risk remaining after simulation of just 

meeting specific suites of standards, but also on additional factors that can impact risk 

(e.g., the role of annual and 24-hour design values, the peakiness of PM2.5 distributions 

within a study area, and application of different rollback 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 other observations that might be made 

that would help to address the policy-relevant questions identified at the beginning of the 

chapter? 

Response: The panel believes that Section 6.2, Interpretation of Urban Study Area 

Results, is well supported by the results of the previous analyses. We are not aware of 

other observations that might affect the answers to the policy-relevant questions 

identified at the beginning of Chapter 6. 

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 and 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 assessment 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? 

9
Response: The authors have done an appropriate sensitivity analysis and have adequately 

characterized both uncertainly and variability. The panel believes that the degree of 

confidence expressed in the core risk estimates is appropriate. We believe that the 

adjacent policy-related observations are reasonable given the information available to the 

EPA and summarized in the final version of the PM ISA. 

d) As part of the integrative discussion, we use the results of several national-scale 

analyses (i.e., the national scale PM2.5 mortality analysis, the representativeness analysis, 

and the new exploration of design values and patterns of PM2.5 monitoring data presented 

in section 4.5) to place the results of the risk assessment in a broader national-context. 

What are the Panel members’ views on appropriateness of this effort to place results of 

the analysis in a national context? 

Response: One could always suggest additional cities or parts of the country where PM 

data could be applied. The panel believes that the national-scale analyses which were 

carried out are appropriate and are reasonably varied and thus they do provide the context 

for placing the results of the policy analysis in a reasonably representative 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 assessment in these observations? 

Of particular note is the observation that, while alternative 24-hour standard levels can 

be used to reduce annual-average PM2.5 concentrations and thus to reduce estimated risk, 

the results are likely to be highly variable across urban areas. More consistent lowering 

of annual-average PM2.5 concentrations across study areas, and thus more consistent 

reductions in estimated risk, may result from application of alternative annual standard 

levels. We also note that simulation of the alternative 24-hour standard level of 25 μg/m3 

resulted in reductions in annual-average PM2.5 levels for some study areas that were well 

below the lowest annual standard level assessed (i.e., below 12 μg/m3). As a 

consequence, we observed risk reductions reflecting these changes in annual-average 

PM2.5 levels below 12 μg/m3. Given these results, does the Panel believe that there is 

utility in estimating risks for alternative annual standard levels below 12 μg/m3? 

Response: Section 6.4, Key Observations, is a valuable part of this chapter and of the 

document as a whole. The three questions asked are important and the answers provided 

are well founded and useful. They get to the heart of the matter. What are the 

consequences of maintaining the current standard? What are the likely benefits of 

lowering the standards? To what extent are policies about PM2.5 applicable throughout 

the country? The bullets following the three questions succinctly address these questions, 

and will be useful to the administrator in forming the basis for her decision. 

Consistent with discussions at the last meeting of the PM advisory committee, we are 

comfortable with not estimating risks for alternative annual standard levels below 12 

μg/meter3

. At these concentrations, data is increasingly less common and less reliable. 

Therefore, estimates of risk will be subject to greater and greater uncertainty. We believe 

10
that the risk estimates at levels higher than this provide an adequate basis for decision 

making. 

11
Comments from Dr. Wayne Cascio 

General Comments: 

With the second draft assessment document the staff of the EPA’s Office of Air Quality 

Planning and Standards (OAQPS) has produces an excellent document that largely 

addresses concerns raised by members of CASAC and the public. Specifically, the 

second external review draft now contains a more comprehensive discussion of the core 

risk estimate through the integration of uncertainty and variability analyses from 15 urban 

centers, and national-scale long-term exposure PM2.5 mortality assessment. The rationale 

for not including a quantitative assessment of risk associated with PM10-2.5 presented in 

section 2.3 and appendix H is justified based on the limitations in the data available for 

characterizing PM10-2.5 exposure and risk. The overall presentation and discussion of 

the consideration of variability and uncertainty is much improved. 

Charge Question 2. Selection of model inputs (section 3.3): We have expanded and 

clarified the discussion of our rationale for identifying modeling choices comprising the 

core risk model, focusing in particular on selection of C-R functions (section 3.3.3). To 

what extent does the Panel consider this discussion to be clear and the model selections 

appropriate? 

Response. The expanded discussion provided in Section 3.3.3 Selection of 

Epidemiological Studies and Concentration-response (C-R) Function within those Studies

conveys the rationale for identifying modeling choices and adequately justifies the 

selection of specific epidemiological studies utilized to establish the C-R functions. The 

rules employed for study selection as described on 3.27 and 3.28 provided a strong 

foundation to identify studies that provide the most accurate data to derive the C-R 

relationship. The expansion of the discussion and integration of the ISA was also very 

useful in that it provides an opportunity to reinforce the gaps in knowledge, for example 

on 3-30 where it is stated that, “There were no multi-city studies for this [short-term 

exposure to PM2.5 and emergency department visits for cardiovascular and/or respiratory 

illnesses] category of health endpoint.” 

12
Comments from Dr. Christopher Frey 

Charge Question 3: 

In general, the second draft REA appropriately identifies and discusses key sources of 

variability and uncertainty, and includes sensitivity analysis that provides insight 

regarding the impact of some sources of uncertainty on the core risk estimates. 

EPA provided a footnote explaining the rationale for identifying “key” sources of 

variability. The document should indicate if the same process was used to identify “key” 

sources of uncertainty. 

In the discussion of key sources of variability, EPA added material regarding copollutant 

concentrations and on demographic and socioeconomic status, as requested in CASAC 

comments on the first draft of the REA. As a minor comment, it is not entirely clear that 

age of housing only affects air exchange rate because of air conditioning use. Newer 

homes are typically “tighter” than older homes, and thus have lower infiltration rates. 

Climate zones are another factor in infiltration. For example, northeastern homes do not 

have as high a proportion of central air conditioning as southeastern homes. Given its 

effect on particle composition, concentrations, ventilation and activity patterns, it would 

make sense to also include seasonality in the list of variability sources. 

We note that EPA did not address a comment on the first draft REA to the effect that 

“exposure modeling should be included in the REA. A probabilistic Tier 3 approach 

should be used for the exposure assessment.” While we understand that timing may have 

precluded adequate treatment of this topic, we expect that EPA will develop this capacity 

for future revisions of the standard. CASAC asked for this five years ago, and would 

like to see this in the next revision. 

With regard to uncertainties, in response to CASAC comments on the first draft of the 

REA, EPA has included uncertainty in the C-R function itself, which was developed from 

single studies. EPA has appropriately taken into account differences in C-R functional 

form associated with studies that addressed long-term or short-term effects for single or 

multi-city studies even if they were not the basis for the final set of C-R functions used in 

the REA. 

EPA has provide some explanation of the meaning of uncertainty categories of “low”, 

“medium”, and “high.” This discussion is adequate. However, there is a confusing 

statement to the effect that “high” sources of uncertainty “are likely to influence the 

interpretation of risk...” “if those sources of uncertainty are reduced or more fully 

characterized.” The parenthetical “if” clause seems to confuse the issue, and should be 

deleted. A reader of the paragraph on lines 6-20 of p. 3-63 might wonder how “staff 

consensus” was achieved, and whether consensus is an appropriate goal when 

characterizing uncertainty. A potential concern is that achievement of “consensus” might 

mean that some opinions over-ride others and that the resulting characterization of 

13
uncertainty might be biased. There are short-comings of group-based elicitation 

processes, such as dominance by strong personalities or a tendency to provide opinions 

about goals rather than state of knowledge. It would be useful to explain the process by 

which “consensus” was achieved. 

EPA has done a nice job on commenting on the extent to which there are dependencies 

among pairwise combinations of sources of uncertainty, and whether these dependencies 

would tend to offset or to increase the overall range and direction of uncertainty in the 

assessment results. For example, the statistical fit of the C-R functions, and the shape of 

the functions, are inter-related. EPA has provided a nice treatment of this on page 3-71. 

Based on quantifiable sensitivity analysis, the report generally clearly conveys that the 

“core” estimates appear to be at the low end of alternative “plausible” estimates. 

However, particularly in Chapter 6, the role of sources of uncertainty treated qualitatively 

should also be addressed. In particular, given exposure misclassification, it is likely that 

the core estimates are biased low. This is an important point to convey consistently. The 

core estimates seem to be conservative in the sense of being underestimated, which is not 

typical practice for public health endpoints, given that virtually all of the sensitivity 

analyses result in higher risk estimates as compared to the core. 

Charge Question 4: 

Overall, the sensitivity analysis section 4.3 is very good and nicely covers a complex 

topic. Table 4-3 is a useful summary. The classification of descriptive categories for 

small, moderate, moderate-large, and large contributions is useful. However, it would be 

more appropriate to refer to these as contributions to “sensitivity” rather than 

“uncertainty.” As noted in several place, the sensitivity analyses represent plausible 

alternatives to the core estimate, but are not a probability sample. Thus, there is not a 

probabilistic interpretation to the sensitivity analysis results. EPA has appropriately 

addressed this point and has clearly articulated, quite reasonably, that the sensitivity 

analysis results represent plausible and scientifically defensible estimates. The range of 

these estimates provides an indication of the implications of uncertainty. 

The evaluation of alternative model structure is critically important, because model 

structure can potentially be a larger source of uncertainty than the range of values for an 

input to a given model. The results in Table 4-3 indicate, for example, that the random 

effects log-log model provides larger risk estimates than the fixed effects log-liner model 

used for the core estimates. This information is very useful and is an excellent addition 

to the REA. The more thorough treatment of model choices and alternative C-R 

functions provides plausible alternative estimates to the core estimate. 

It was not apparent that EPA responded to this comment on the first draft REA: “The 

range of uncertainty associated with confidence intervals for a given C-R function (which 

is an example of a Tier 3 assessment, which should be mentioned) should be compared to 

the range of estimates obtained by comparing alternative functional forms. This would 

provide insight as to whether model structure, or random error for a given model, is a 

14
more important source of uncertainty.” It would be useful to make this comparison, 

which can be discussed qualitatively. 

Per CASAC’s comments on the first draft REA, EPA indicates the direction of the 

percent changes in risk. In addition to the percent difference, the actual difference in risk 

should be reported to provide further context. The second draft REA seems to put 

emphasis on relative changes in risk. However, the NAAQS are intended to be protective 

of public health, and therefore the magnitude of the risk estimates is ultimately a more 

useful policy-relevant metric. 

The sensitivity analysis related to peak shaving and “peakiness” was not very clear. 

What are the main points to take away from these analysis could be clarified. Is there an 

implication of some sort of risk trade-off between the cities with and without 

“peakiness”, as shown in the comparison of results for the different roll-back approaches? 

What is the premise of the overarching conclusions – e.g., that there are strong regional 

or inter-city effects? Would this carry forth to the policy analysis in some way? 

15
Comments from Dr. Joseph Helble 

1) Air quality inputs (section 3.2): We have expanded the consideration of alternative 

approaches to simulating just meeting the current and alternative suites of PM2.5 

standards (i.e., rollback approaches) to include a peak shaving approach, in addition to 

the hybrid and proportional approaches considered in the first draft assessment. This 

peak shaving approach is intended to represent more localized, rather than regional, 

patterns of PM2.5 reductions (discussed in section 3.2.3.3). 

a) To what extent does the Panel believe that the use of the peak shaving approach 

provides useful additional exploration of variability associated with how ambient PM2.5 

concentrations are simulated to change upon just meeting the current and alternative 

suites of standards? 

It is certainly reasonable to explore alternative approaches to just-meeting standards. The 

traditional proportional rollback approach was augmented in an earlier draft of the current 

PM risk assessment by including “hybrid rollback,” in which localized monitor-specific 

reductions are imposed and then allowed to propagate through an air quality study area 

through imposition of a distance-decay function. Area-wide proportional rollback is then 

applied as needed. As noted previously, this seems a reasonable approach to estimating 

the potential effect of local controls on PM levels for comparison with the region-wide 

effects approximated by proportional rollback. 

The current question regards the benefits of adding a third approach that involves peakshaving of concentrations at specific monitors within an air quality study area in an effort 

to assess the potential effects of highly localized controls. In this approach, only those 

monitors exceeding the 24 hour standard are rolled back. The use of this alternative to 

examine hypothetical “what-if”scenarios seems reasonable if the goal is to understand 

whether reducing concentrations at only the peak monitoring locations would be 

sufficient to meet overall air quality targets in a given study area. Beyond this, however, 

the value of the exercise is not clear. It is difficult to imagine a scenario in which such 

targeted localized controls could be effectively deployed for PM2.5. Given this, the 

hybrid approach seems more appropriate. 

b) We have used comparisons of composite monitor annual averages generated using the 

different rollback approaches as a surrogate for differences in long-term exposurerelated 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 estimates of long-term 

exposure-related mortality? 

Given the uncertainty in the data, particularly due to incomplete monitoring datasets or 

differences in data collection patterns from region to region, this approach is reasonable. 

Related to this, regarding the approach to generating composite data sets in locations 

where there are gaps in individual monitor datasets, was the accuracy of the interpolation 

16
routines tested? If at least one urban study area has a complete data set, the accuracy of 

the interpolation approach could be assessed by artificially (randomly) deleting specific 

values from the monitoring dataset, interpolating as before, and then comparing the 

estimated values with actual. 

17
Comments from Dr. Rogene Henderson 

Comments on Assigned Charge Questions for 2nd Draft of PM-RA 

Charge Question 5: Consideration of design values and patterns of PM2.5 monitoring 

data in interpreting core risk estimates (section 4.5): To enhance our interpretation 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 PM2.5 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 estimated 

upon just meeting the current and alternative suites of standards under alternative 

rollback approaches. 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 supportive of these additional assessments? 

I found Figures 17-21 quite helpful in putting the 15 urban areas into context with the 

monitoring values from other cities in the US. The figures also helped me to visualize 

what the overall picture looked like and what the controlling values are. 

 I would like to have more discussion about how the peak shaving rollback method 

was used. When the short-term values are controlling, it does not make sense to me to 

use the same percentage rollback for the annual values as is required by the short-term 

values. This results in non-feasible annual values (e.g., 7 ug/m3) for some cities such as 

SLC. Do we have actual evidence to indicate that if the short-term value were reduced 

55% that the annual value would also be reduced 55%? I do not see the logic to that 

assumption. 

Why not consider the risk of mortality from short-term exposures separately from the risk 

of mortality from the average annual exposures. It is stated in the beginning of Chapter 

6 (page 6-1) that the primary focus will be based on risk associated with long-term 

exposure to PM, because long-term exposure to PM2.5 has been shown to produce 

substantially larger mortality risk compared to short-term PM2.5 exposure. Based on 

that, one might expect the calculated risks from the annual exposures to be the most 

critical consideration to protect public health. I do not think it is appropriate to mix the 

two design values in the rollback procedures. 

 But perhaps I do not understand how the peak shaving rollback method was used. 

It states on page 3-15, lines 20-23, that the proportional rollback method was the only one 

used to generate core risk estimates and the other two rollback methods were only used 

for sensitivity analysis. I would appreciate more discussion of this at our meeting. 

 I suggest adding the term "design value" to the list of terms on page viii, with a 

reference to page 3-16 for a definition. 

b) Does the Panel have any recommendations for additional insights based on 

consideration of patterns in design values and PM2.5 monitoring data across the 15 urban 

study areas and at the national level? 

18
It would be nice to have Figures 17-19 in three dimensions with some measure of health 

effects for the 15 cities on the third axis. Can that be done? It stated that the C-R 

functions are fairly linear and it would be nice to see that. 

Chapter 6 – Integrative Discussion of PM2.5-related Risks 

6) We have developed an integrated discussion of the PM2.5-related risk estimates which 

considers the results of the qualitative and quantitative treatment of uncertainty and 

variability together with the various 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 addressed by this risk assessment? 

I thought the policy-relevant questions were well stated. 

b) We provide a set of key observations 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 consideration of trends in risk reduction across 

alternative suites of standards and residual risk remaining after simulation of just meeting 

specific suites of standards, but also on additional factors that can impact risk (e.g., the 

role of annual and 24-hour design values, the peakiness of PM2.5 distributions within a 

study area, and application of different rollback 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 other observations that might be made that would help 

to address the policy-relevant questions identified at the beginning of the chapter? 

 I thought the list of observations was appropriate. 

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 and 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 assessment 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? 

 The confidence statements were well presented. 

d) As part of the integrative discussion, we use the results of several national-scale 

analyses (i.e., the national scale PM2.5 mortality analysis, the representativeness analysis, 

and the new exploration of design values and patterns of PM2.5 monitoring data 

presented in 

section 4.5) to place the results of the risk assessment in a broader national-context. What 

are the Panel members’ views on appropriateness of this effort to place results of the 

analysis in a national context? 

 I thought it was a good idea. 

19
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 assessment in these observations? 

Of particular note is the observation that, while alternative 24-hour standard levels can be 

used to reduce annual-average PM2.5 concentrations and thus to reduce estimated risk, 

the results are likely to be highly variable across urban areas. More consistent lowering of 

annual-average PM2.5 concentrations across study areas, and thus more consistent 

reductions in estimated risk, may result from application of alternative annual standard 

levels. We also note that simulation of the alternative 24-hour standard level of 25 μg/m3 

resulted in reductions in annual-average PM2.5 levels for some study areas that were well 

below the lowest annual standard level assessed (i.e., below 12 μg/m3). As a 

consequence, we observed risk reductions reflecting these changes in annual-average 

PM2.5 levels below 12 μg/m3. Given these results, does the Panel believe that there is 

utility in estimating risks for alternative annual standard levels below 12 μg/m3? 

 Definitely not. I think there is too much uncertainty to do that with much 

confidence.

20
Comments from Dr. Philip Hopke 

In general, there are no major problems with this assessment. It is generally following 

the approaches that we have now seen in multiple rounds of review. 

1) Air quality inputs (section 3.2): We have expanded the consideration of alternative 

approaches to simulating just meeting the current and alternative suites of PM2.5 standards 

(i.e., rollback approaches) to include a peak shaving approach, in addition to the hybrid 

and proportional approaches considered in the first draft assessment. This peak shaving 

approach is intended to represent more localized, rather than regional, patterns of PM2.5 

reductions (discussed in section 3.2.3.3). 

a) To what extent does the Panel believe that the use of the peak shaving approach 

provides useful additional exploration of variability associated with how ambient PM2.5 

concentrations are simulated to change upon just meeting the current and alternative 

suites of standards? 

It does not seem useful to me since it is unlikely that there are obvious sources that could 

be controlled that would let one shave peaks in practice. Thus, it provides unrealistic 

scenarios that really do not contribute useful information to the assessment. The other 

rollback approaches seem fine and it is hard to see a role for the peak shaving approach. 

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 estimates of long-term 

exposure-related mortality? 

It would make the compositing easier to follow if equations were provided. If you do not 

wish to put them into the main chapter, then an appendix can be added to guide the 

interested reader through exactly how all of the calculations were performed. 

I agree with the approach to removing quarters in which too few values are reported to 

provide a reliable estimate of the average concentration during that period. However, it 

makes little sense to replace missing values with a mean value. If you are going to 

attempt to impute missing values, then a much more sophisticated approach should be 

employed using other monitors in the area as well as historic data for similar 

meteorological conditions. I would suggest that for those quarters where there are 

missing values, but a sufficient number of values to provide a valid mean value, then that 

should be the value used in the health analyses. 

2) Selection of model inputs (section 3.3): We have expanded and clarified the discussion 

of our rationale for identifying modeling choices comprising the core risk model, 

focusing in particular on selection of C-R functions (section 3.3.3). To what extent does 

the Panel consider this discussion to be clear and the model selections appropriate? 

21
3) Addressing uncertainty and variability (section 3.5): We have clarified the process 

used to evaluate sources of variability and added coverage 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 interactions of sources of 

uncertainty (section 3.5.4). To what extent does the Panel consider these discussions to be 

clear and appropriate? 

It is time to move toward stochastic uncertainty analysis. Every time we get a risk 

assessment, we continue to get the qualitative review of uncertainties and some hand 

waving. If there are insufficient resources available to do the full stochastic risk 

assessment, then the Agency should state this clearly so that it can be made clear why 

they have chosen not to move to a more complete analysis. Otherwise, we should not see 

them continue to duck this approach. 

22
Comments from Dr. Morton Lippmann 

Overall Comments:

The authors have been very responsive to the prior CASAC PM Panel comments and 

suggestions, and the 2nd draft provides a thorough and well-prepared presentation of 

realistic quantitative estimates of the effects of long-term ambient air PM2.5 exposures on 

premature mortality in 15 US urban areas, their variability and uncertainties, and their 

representativeness of the US population as a whole. The alternate risk assessments (RAs) 

for recent years’ concentrations, meeting the current suite of PM2.5 NAAQS, and alternate 

NAAQS (14, 13, and 12 ug/m3

 annual and 30 and 25 ug/m3 daily, and combinations 

thereof) is an appropriate way to tee up the selection options for the Policy Assessment 

(PA). 

Having offered a strong endorsement of the overall work of the OAQPS in preparing the 

RA document, I need to raise two issues that I have raised before that have not been 

properly addressed. These are: 

1) The fact that the ACS cohort is not a representative US population, but rather is of 

higher SES. Within this cohort, the mortality risk is lower for those of higher 

SES. Thus, the risk coefficient for a representative population would be higher, as 

it is for the 6-cities cohort that was selected to be more representative (at least for 

cities in the eastern half of the US). 

2) The description and use of the data from the Ito et al. (2007) study has not been 

corrected. As noted below, this was a study covering all of New York City 

(Kings, Queens, New York, Bronx, and Richmond Counties), not just New York 

County (Borough of Manhattan). 

Specific Comments on Text Entries: 

Page Line Comment

3-13 Table 3.1. The entry for New York City is incorrect. Change New York City 

(Manhattan)” to “New York County (Manhattan)”. 

3-13 6 Change “New York (Manhattan)” to “New York City ”. 

3-30 11 Delete “(Manhattan)”. 

3-31 7 The number of members of the ACS cohort in the 156 MSAs with air 

quality data is much smaller than 1.2 million. 

3-40 Counties Column for “New York”. Change New York City (Manhattan)” to “New 

York County (Manhattan)”, and delete “New York City (Manhattan)” where it precedes 

“Ito et al. (2007)”. The Ito et al. (2007) study covered all of NYC, not just Manhattan! 

23
3-50 Table 3-10. There should not be two entries for New York, NY. As noted above, 

the Ito et al. (2007) study covered all of NYC, not just Manhattan! The second New 

York entry, which shows only the population of New York County (Manhattan), should 

be deleted, and the calculations for the Ito et al. study need to be revised to reflect the 

whole NYC population and all of the NYC PM2.5 monitors. 

3-77 Section 3.54.3. This section refers to single- and multiple-elements, as well as to 

single- and multiple-factors, in terms of sensitivity analyses. There is no definition 

provided as to what constitutes an element or a factor. I suggest that element is a poor 

choice in terms of terminology, since it implies, at least to me, a chemical element. This 

will become important in the next round of PM NAAQS review. [On page 4-42, there is a 

clarification indicating that elements refers to “modeling elements”] 

4-19 10 Change “fig” to “fit”. 

4-19 11 Change “greater” to “great”. 

4-36 12 Change “CPD” to “CVD”. 

4-45 Note at bottom of the page: Change “Figures 4-6 and 4-7” to “Figure 4-8”. 

4-47 29 Change “Figures 4-6 and 4-7” to “Figures 4-7 and 4-8”. 

4-48 para. 2 : Once again, there are elements and factors with no definitions. Here the 

elements are not modeling elements, but something else. [On page 4-54, line 21, I learned 

that these were “critical risk function elements”]. Please reword to avoid confusion! 

4-55 23 Change “population” to “populated”. 

6-1 31 Delete extra period at the end. 

6-14 25 Change “Pitts” to “Pittsburgh”. 

6-18 15,16 Where can we find these estimates? 

6-18 21-23 Where can we find these estimates? 

6-21 8 Change “PM2.5” to “PM2.5”. 

Charge Questions to the CASAC PM Review Panel - focus on the charge questions 

listed below in review of the Quantitative Health Risk Assessment for Particulate Matter

Chapter 3 – Urban Case Study Analysis Methods 

24
Charge Question #2: Selection of model inputs (section 3.3): 

We have expanded and clarified the discussion of our rationale for identifying modeling 

choices comprising the core risk model, focusing in particular on selection of C-R 

functions (section 3.3.3). To what extent does the Panel consider this discussion to be 

clear and the model selections appropriate? 

Response: 

The Panel commends the authors for expanding and clarifying their rationale for 

identifying modeling choices comprising the core risk model in a logical and satisfactory 

manner. Their model selections were appropriate 

Chapter 6 – Integrative Discussion of PM2.5-related Risks 

Charge Questions #6a-e: 

We have developed an integrated discussion of the PM2.5-related risk estimates which 

considers the results of the qualitative and quantitative treatment of uncertainty and 

variability together with the various 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. 

Charge Questions #6a: To what extent does the Panel believe that we have captured the 

key policy-relevant questions that can be addressed by this risk assessment? 

Response: 

The Panel considers that the authors have captured the key policy-relevant questions that 

can be addressed by this risk assessment that is focused solely on PM2.5. 

Charge Questions #6b: 

We provide a set of key observations 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 consideration of trends in risk reduction across 

alternative suites of standards and residual risk remaining after simulation of just meeting 

specific suites of standards, but also on additional factors that can impact risk (e.g., the 

role of annual and 24-hour design values, the peakiness of PM2.5 distributions within a 

study area, and application of different rollback 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 other observations that 

might be made that would help to address the policy-relevant questions identified at the 

beginning of the chapter? 

Response: 

The Panel considers that the observations presented in section 6.2 are consistent with the 

analytical results, and provide all of the information needed in the development of the PA 

document. 

25
Charge Questions #6c: Part of our interpretation of the core risk estimates presented in 

section 6.2 is our characterization of confidence in the core risk estimates and 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 

assessment 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? 

Response: 

The Panel considers that the characterizations of confidence in the core risk estimates and 

associated policy-related observations are reasonable. 

Charge Questions #6d: As part of the integrative discussion, we use the results of 

several national-scale analyses (i.e., the national scale PM2.5 mortality analysis, the 

representativeness analysis, and the new exploration of design values and patterns of 

PM2.5 monitoring data presented in section 4.5) to place the results of the risk assessment 

in a broader national-context. 

What are the Panel members’ views on appropriateness of this effort to place results of 

the analysis in a national context? 

Response: 

The Panel considers that the effort to place results of the analysis in a national context 

was appropriate. 

Charge Questions #6e: We conclude chapter 6 with a list of key observations. 

Does the Panel believe that we have appropriately highlighted key findings of the risk 

assessment in these observations? 

Response: 

The Panel considers that Staff has appropriately highlighted key findings of the risk 

assessment in these observations 

Of particular note is the observation that, while alternative 24-hour standard levels can be 

used to reduce annual-average PM2.5 concentrations and thus to reduce estimated risk, the 

results are likely to be highly variable across urban areas. More consistent lowering of 

annual-average PM2.5 concentrations across study areas, and thus more consistent 

reductions in estimated risk, may result from application of alternative annual standard 

levels. We also note that simulation of the alternative 24-hour standard level of 25 μg/m3

resulted in reductions in annual-average PM2.5 levels for some study areas that were well 

below the lowest annual standard level assessed (i.e., below 12 μg/m3

). As a 

consequence, we observed risk reductions reflecting these changes in annual-average 

PM2.5 levels below 12 μg/m3. 

26
Given these results, does the Panel believe that there is utility in estimating risks for 

alternative annual standard levels below 12 μg/m3

? 

Response: 

The Panel does not consider that estimating risks for alternative annual standard levels 

below 12 μg/m3 is a worthwhile endeavor on several grounds. One, the extrapolation of 

the risk coefficients at such concentrations becomes increasingly uncertain; and two, the 

prospects of achieving compliance with such levels in the foreseeable future is 

vanishingly small. 

27
Comments from Dr. Robert Phalen 

General Comments: 

The second draft of “Quantitative Health Risk Assessment for Particulate Matter” is 

clearly-written and the logical development is well-described. The staff has done an 

excellent job. My enthusiasm for the entire document is diminished by factors that are 

apparently outside of policy-driven limitations imposed on EPA staff. These limitations 

include: 

• PM2.5 is a mass-based metric (indicator) for assessing health-effects. It is likely 

that specific components, such as vanadium, nickel, and elemental carbon, are actually 

driving the health effects. The use of a mass-based indicator can lead to air-quality 

standards that do not permit appropriate abatements. 

• Secondary health effects, e.g. as generated by abatements that adversely affect the 

economy (and the many associated health effects), are not considered. Such indirect 

adverse health effects are real, and the affected populations must face them along with 

the direct effects. 

• The current risk assessment does not conform to the recommendations made by 

the National Research Council of the National Academies (Science and Decisions: 

Advancing Risk Assessment, the National Academies Press, Washington D.C., 2008). 

Specifically, ... “that risk assessment should be viewed as a method for evaluating the 

relative merits of various options for managing risk rather than as an end in itself.” The 

concept of managing risk must include all of the significant risks associated with a 

particular decision, not just some selected direct effects associated with the decision. 

• National air quality standards have the disadvantage of forcing abatements on 

regions of the U.S. for which the abatements may harm health to a greater extent than 

they improve health. As an example consider restrictions on diesel-emissions to try to 

meet standards in areas where a significant portion of PM2.5 can be found in soil fineparticle mass. Control of soil aerosols is not practical, so the diesels must be targeted. 

Specific Comments on Section 3.3 

This reviewer found only minor errors. 

Table 3-4, pg. 3-24: Replace “LA” with “Los Angeles”, as LA is also the designator for 

Louisiana. 

Line 34, pg. 3-31: Drop either “the” or “our” for clarity.

28
Comments from Dr. Ted Russell 

Overall, I continue to be pleased with the amount of analysis conducted in this PM Risk 

Assessment (RA), though I am still disappointed that a more comprehensive exposure 

modeling effort was not made. The document provides the type of information needed to 

inform the review of the primary NAAQS, and does s good job of providing a 

quantitative assessment of the potential risks, and has done a commendable sensitivity 

analysis. 

While I appreciate the addition of Chapter 6, it was not as effective as it might be. First, I 

was looking for Chapter 6 to be more integrative of the results from Chapter 4 and 5 as it 

is now more focused on Chapter 4. Second, I was looking for it to also integrate 

uncertainties in to the discussion to a greater degree. This is the point that they could 

bring in the issue of using the LML as the zero risk level, and how that might influence 

the overall interpretation of the results. Third, it was a bit repetitive, bringing up the 

issue of “peaky nature” and explaining it more often than necessary. It is an important 

concept, but it was overdone in Chapter 6. Still, Chapter 6 is a good addition, but it could 

be made stronger in response to the above comments. 

Chapter 3 Charge Questions: 

1) Air quality inputs (section 3.2): We have expanded the consideration of alternative 

approaches to simulating just meeting the current and alternative suites of PM2.5 

standards 5 (i.e., rollback approaches) to include a peak shaving approach, in addition 

to the hybrid and proportional approaches considered in the first draft assessment. This 

peak shaving approach is intended to represent more localized, rather than regional, 

patterns of PM2.5 reductions (discussed in section 3.2.3.3). 

a) To what extent does the Panel believe that the use of the peak shaving approach 

provides useful additional exploration of variability associated with how ambient PM2.5 

concentrations are simulated to change upon just meeting the current and alternative 

suites of standards? 

Response: This approach, along with the hybrid approach, provide a reasonable method 

to get an estimate of the lower bound impact of what would happen when an urban area 

attains a specific standard. This approach is specifically of interest in areas where the 24-

hour standard will be the driving standard, and the proportional roll-back would lead to 

reductions in the annual level beyond that which might be viewed as likely. The method, 

either in the report or in the appendices, should be specified mathematically, as well as in 

words. They might present a specific set of example applications of the approaches, e.g., 

for three different cities, at this point. 

b) We have used comparisons of composite monitor annual averages generated using the 

different rollback approaches as a surrogate for differences in long-term exposure29
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 estimates of long-term 

exposure-related mortality? 

Response: First, the approach to compositing should be better explained. A critical 

question is how well it aligns with what is actually done in reporting for the calculation of 

design values. Indeed, the approach they used should be motivated by first explaining 

how the annual average PM is found (provide specific equations as needed), and then 

showing that the approach taken is in line with how the annual average PM is now found. 

Also, they need to explain how and when compositing is used in calculating design 

values. This will explain why quarterly averages are first calculated, and may impact my 

thoughts on how the current approach to compositing should be altered. 

I do not like how they replace missing values, i.e., using the average value to replace 

missing values when a certain number of samples are missing. It seems to be a bit 

arbitrary, and could lead to a bias. Is this what is done in practice (i.e., specified)? In 

terms of compositing, the values could each be adjusted using a centering approach. In 

this case, the annual average from each monitor being used in the composite is subtracted 

from the daily value from that monitor, leading to a string of values that have a mean of 

zero. These annual averages are also used to calculate the composite annual average of 

the stations being used in the composite. The daily values for each monitor (after 

subtracting the mean of that station) are then averaged as available. This leads to the 

average variation from the mean for that day. The annual average composite value is 

then added back to get the daily composite value. This is relatively insensitive to stations 

dropping out. Further, it should exactly give the observed annual mean at each station, 

and well as the composite mean. The current approach for imputing missing days can 

lead to an average that would not agree with the reported value. The same approach for 

calculating quarterly averages, that are then used to calculate the annual average and 

design value, can be used. 

Like my response to part (a), the mathematical equations should be provided here or in 

the appendix. 

5) Consideration of design values and patterns of PM2.5 monitoring data in interpreting 

core risk estimates (section 4.5): To enhance our interpretation 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 PM2.5 

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 estimated upon just meeting 

the current and alternative suites of standards under alternative rollback approaches. 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 supportive of these additional assessments? 

30
Response: These are beneficial. Figures 4-17 to 4-19, and Table 4-8 do a good job of 

identifying which are the controlling standards for each of the 15 cities, and also show 

that the cities examined do a good job of spanning the space of conditions for cities 

around the US. It might have been good to also identify some of the major outliers on 

Fig. 4-17 (there really is only one to identify). Also, you could consider color coding the 

dots on the figure, such that each portion of the US is assigned a color, so it would be 

apparent if there were specific areas where an issue might identified. This would also 

help address why no Upper Midwest city is targeted. Without this, I don’t think this 

section really does as good job of contrasting the 15 urban study areas with other areas, 

that they are supposed to represent, particularly at a regional level. Section 4.4 presents 

additional information putting other areas in to perspective, but what would be valuable is 

to show that all regions and sizes of cities are addressed adequately. 

b) Does the Panel have any recommendations for additional insights based on 

consideration of patterns in design values and PM2.5 monitoring data across the 15 urban 

study areas and at the national level? 

Response: See above. I think this section could be strengthened by being able to have a 

concluding statement somewhat along the lines of “We have captured the range of 

conditions found for cities that would be in non-attainment of the various combinations 

of standards in each of the six of the seven (I would have preferred all seven) regions of 

the country, and the 15 cities capture X% of the population. The analysis has identified 

cities that span the range of non-attainment levels, and which standard would require the 

greatest level of control based on this analysis.” It is close to being able to say this. 

Other details: 

Page 3-8, Footnote: This footnote is not needed and I find it confusing. Also, while it 

need not be added at this point, unless βΔx is above about 0.2, the error in linearizing (3) 

and (4) is rather small. This might simplify interpretation of later analyses since it 

makes the response to concentration changes linear. 

In Chapter 3, no city in the Upper Midwest was identified. Might this be alleviated? 

31
Comments from Dr. Frank E. Speizer 

Pre-meeting Comments: 3/5/2010 

General Comment: 

Staff has done an excellent job of using the available literature and assessments from the 

ISA to generate a series of outcome assessments over an appropriate range of alternative 

levels of both 24 hour and annual averages of PM2.5 that are justified by the available 

data. They appear to have been response to our previous comments on the first draft, and 

where they have not followed our suggestions have presented evidence that they 

considered our requests and accepted or rejected or modified with appropriate 

justification. The one area where I would have like to have seen more analyses is with 

regard to PM10-2.5, simply to have demonstrated the “:inappropriateness” of trying to 

rely on such an analysis would have emphasized the need for more data related to the 

course fraction effects. 

Specific Comments and Charge Questions 

Chapter 2 

Page2.4, line 14. Typo: PM2.5 

Page 2.6, line 2-4 Query the continuing developmental work on population exposure 

analysis methodology. It would have been useful to read or hear further what this plan 

would be. One would have thought that over the years much of this would have already 

been worked out. 

Page 2.6, line 22-24. Appendix H provides a well reasoned argument for Staff concluding 

that they could not do a quantitative risk assessment for PM10-2.5. From my perspective 

it would seem to me that some estimate of risk should be made if for no other reason than 

to document wide confidence intervals and thus reason for not including it in the 

quantitative assessment. 

Page 2.7, line 10-11. Perhaps at the end of this process a note could be sent to CASAC to 

indicate what the plan might be for the future to prepare for the next round by carrying 

out the methods development necessary to use “specialized analysis of risk...” Is this 

important enough for CASAC to include such a request in our letter to the administrator? 

Page 2.12, line 13-20. The full set of model choices offered seems appropriate, given the 

plan is to maintain an annual as well as a 24 hour standard.. 

Chapter 3 

Page 3.19-3.20 and Charge Question 1a and 1b. Use of peak shaving rollback approach 

as discussed is confusing. Staff indicates (at top of page 3.20) that because of time 

constraints they did not calculate health risks using this method. They go on to indicate 

what the method does. The appendix that discusses the method more fully refers to 

Tables F-49 and F-50. These tables present the curious finding that except for Fresno 

(where there is virtually no change) and Tacoma, all of the other cities show a 

progressive increase in maximum values going from the “proportional” to “hybrid” to 

32
“shaving”. This certainly does not seem to indicate that the shaving analyses were not 

done. I t also raises for me concern that more effort is needed to understand which is a 

better technique or more representative of “truth”. Thus I am worried that “time 

constraints may be once again getting in the way of what the proper analysis should be. 

Section 3.3., Charge Question 2 asks about the discussion of rationale for modeling 

choices and selection of CR function. The section follows a logical rationale and 

provides appropriate documentation of both model and site selection. 

Page 3.49, Section 3.4.1.3. It might be worth adding a sentence that approximately 52 x 

106 people are represented in the 15 cities or about 20% of the total population of US 

(even if not a representative sample). 

Page 3.53-54, Table 3.11. there is far too much missingness in this table to make it at all 

useful. It raises more questions about the quality of the health input than would be 

justified. The lack of COPD for all sites but LA just doesn’t compute for the 4th major 

cause of death in the US. Why are there not values for All Ages for All Causes? The data 

are presented for some but not all categories of disease. Someone needs to take the time 

to get all these cells filled in. These data all exist at the Federal level in one book o(or on 

one web site)! 

Charge Question 3, Uncertainty and Variability. The discussion is quite complete dealing 

with a number of issues. What is not fully considered is the role of the potential for nonrandom missingness in both site selection within the 15 cities and thus the selection of the 

cities themselves. 

Chapter 4 

Charge Question 4-Sensitivity Analysis 

Section 4.3, Table 4.1, page 4.6. This table needs to define denominators for Incidence 

(in title). Assuming both are the same then in general hospitalization considerably more 

frequent than mortality. (My concern is mortality may be x/100,000 and morbidity might 

be y/10,000 and if this is the case there are strikingly different numbers that need to be 

discussed more fully). 

Page 4.17, line 6. Need to indicate denominators for these incidence rates. 

Page4.46 Figures 4.7 &4.8. I have difficulty in interpreting these figures. For HD total 

incidence for LA go from 5-10% to as high as 19%. For Philadelphia from10-15% 

to14-15% with outlier at 23%. For total mortality the variation are separately 2-6% and 

3-4 to 8%. For both these cases the core analysis seems too high and the delta seems too 

big, as tests of sensitivity. Is this the wrong interpretation? 

Page 4.47, line 29. Should this be figures 4.7 and 4.8 rather than 4.6 and 4.7? 

Page 4.54, line 5. This should be changed to Table 4.7 (page 4.56). 

 Line 21. Figure numbers seem not to match up with text being discussed. Please 

check. 

33
Page 4.67-4.69, Figures 4.17-4.19. These are very effective presentations of design 

values. I suggest either change titles or text numbers so that 24 hour/annual are presented 

consistently in both. 

Charge Question 5a. Design values analysis and assessments. These analyses are quite 

useful, as they are described. They provide visual interpretations directly of the range of 

effects related to the alternative standards. Notably in Chapter 3 the suggestion is made 

tht the use of peak rollback shaving is not to be considered; however, it looks like it is 

being used here. 

Charge Question 5b. Additional suggestions. I think the ranges of outcomes are well 

demonstrated in figures 4.20 and 4.21. Rather than simply ending with the description of 

how they were constructed it might be worth adding a paragraph or two that summarize 

the degree to which the various alternative would provide changes in some fraction or all 

of the cities, rather than just ending with selected examples (maybe this will happen in 

Chapter 6). 

Chapter 5 

 This chapter leaves me uneasy and I would like to suggest we spend some time 

discussing it. It look to me that it is a straight forward extrapolation of results from the 

two large cohort studies (ACS and 6 Cities). The level of exposure are extracted from the 

15 urban areas and then scaled up to the US. This leads to ~88,000 (4-8% of total 

mortality—a figure repeated in Chapter 6). However, this seems too high. At one point 

there is a suggestion that the figures come from upper end of urban mortality risk, but 

isn’t the calculation for the whole nation where exposure levels must be a lot lower? Lets 

discuss! 

Chapter 6 

Page 6;.7, line 25. Typo change “if “to “of” 

General Comment: The integrated discussion pulls together and highlights some of the 

specific details presented in Chapter 4 and the Appendices. It reflects the obvious and 

not so obvious conclusions that results from manipulating the various alternative 

scenarios between current existing exposure, estimates to current NAAQS levels and the 

various alternatives proposed. In spite of the evidence that there does not appear to be a 

threshold the lowest level assessed 12/25 seems appropriate in that the evidence of an 

effect below those levels is simply too uncertain to evaluate. On the other hand the 

question of margin of safety remains and it will need to be argued that any level chosen 

(above that level) will need to be defended as to whether there is adequate margin of 

safety. 

With regard to the Charge Questions: 

a. Staff has done an excellent job in presenting and capturing the key-policy relevant 

questions. However, as indicated early on in this document there was to be a 

qualitative discussion on PM10-2.5 and on those effects that were deemed only 

34
“suggestive” but might have important public health implications (e.g. lung 

cancer, reproductive effects), but for which quantitative risk assessment was not 

thought warranted but that would appear in the PA (page 2.6). I would have 

thought that some remarks in this chapter would be necessary to assure that the 

PA would discuss the issues. 

b. Key observations are presented and discussed with adequate discussion of the 

relevant contribution of the role of annual and 24 hour design values and the role 

of “peakiness” of distributions. One observation that appears to be focused upon 

and may be a driving force is the uneven distribution among the 15 urban sites on 

the impact of the various scenarios and whether this fact is sufficiently taken into 

account in scaling up for the national estimates. More discussion and or analyses 

on this point may be warranted. For example what role does the actual estimates 

from these 15 sites play is coming to the estimates of 3-9% excess mortality? It 

may be too much to expect (in spite of the statistics) that 63,000-88,000 

premature deaths would be prevented. Part of the country is already well below 

the proposed alternative levels and thus would not contribute to lives saved. Are 

there additional alternative sensitivity analyses that would provide either 

alternative estimates or put more confidence in these estimates by taking into 

account better population weighted C-R analyses? 

c. See above. In spite of the last comment, the uncertainties and variability of the 

core assessments seems to be as good as it can be. 

d. Evaluation of the several national scale analyses, as indicated above is of some 

concern. If I read the Tables in Appendix E correctly, the effect of moving to the 

lowest alternative (25/12) in some cases within the 15 urban sites produces a 

range of 32-67% (with one outlier at 11% and one at 100%) reduction in the IHD 

compared to the current standard. The question is, is this the best baseline for the 

comparison or should it be the current recent measurements, which would drop 

the percent changes considerably (and perhaps provide a more realistic estimated 

of the potential benefits from implementing changes). Obviously, the 

proportional ranking and changes would be the same, but the impact on “lives 

saved” on a national scale might be considerably less and more realistic. 

e. Key observations seem to be presented in a balanced and fair way. Although the 

national assessment suggests a range of 63,000-88,000 premature deaths per year 

attributable to PM2.5 does not jive with a fairly often quoted figure from 2006 

that moving the annual standard from 15 to 14 ppm would result is “more lives 

than perished in 9/11”. (That figure translated into about 3000 lives.) Staff 

acknowledges that the rage of effects are in two categories: 3-9% and 0-3% in 

two halves of the country. This may be less precise than what the data indicate in 

that it would appear from their own estimates that the bulk of the effect comes fro 

the upper end of the exposure in the counties (pg 5.8, line 12-15). 

35
Comments from Dr. Helen Suh 

The Second Draft of the Risk Assessment is a clear and comprehensive presentation of 

the rationale, methods and results for the assessment the acute and chronic PM-mediated 

health risks. In this draft, the authors have thoughtfully considered and incorporated the 

comments and suggestions from the CASAC panel. As an overall comment, the rationale 

that was used in the decision to forego a risk assessment for PM10-2.5 made logical sense. 

Further, inclusion of a discussion of PM10-2.5 exposure and risk in the upcoming draft 

Policy Assessment document is welcomed. However, it still seems that a qualitative and 

indirect assessment of PM10-2.5 risks could be made based on PM10 monitoring and health data 

for metropolitan areas where PM10-2.5 concentrations comprise a large fraction of PM10. 

While certainly not ideal, this qualitative assessment may provide valuable information about 

PM10-2.5 risks. 

Charge Question 2: Selection of model inputs (section 3.3): We have expanded and 

clarified the discussion of our rationale for identifying modeling choices comprising the 

core risk model, focusing in particular on selection of C-R functions (section 3.3.3). To 

what extent does the Panel consider this discussion to be clear and the model selections 

appropriate? 

The revisions to section 3.3 represent a significant improvement over the previous draft, 

with the selection rationale for the core risk model clearly and cogently presented and 

previous concerns addressed. The rationale provided is a thoughtful and sensible 

approach to assess particle-mediated health risks. Further, the summary tables (Table 3.5 

- 3.8) provide a useful and nice synopsis of the model inputs for the core risk models and 

sensitivity analyses. As a very minor comment, it might be possible to condense Table 

3.7 somewhat by replacing certain columns with check boxes instead of text (for example 

to indicate short-term or long-term). 

Charge Question 3: Addressing uncertainty and variability (section 3.5): We have 

clarified the process used to evaluate sources of variability and added coverage 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 interactions of 

sources of uncertainty (section 3.5.4). To what extent does the Panel consider these 

discussions to be clear and appropriate? 

The discussions of uncertainty and variability were clear and thoughtful, representing a 

substantial improvement over the previous draft. The sources of variability and 

uncertainty were well represented, although some explicit discussion of the impact of 

seasonality on risks should be included given its effects on each of the other discussed 

sources. 

36
Comments from Dr. Sverre Vedal 

PM Risk Assessment, Charge Question 6. 

General: 

1. There is a too much formulaic and detailed presentation of results, for example when 

presenting findings of just meeting the current standards and just meeting alternative 

standards. This seems out of place in an integrative discussion. 

2. While there is some opinion that effects of long-term exposure on IHD mortality (as 

opposed to all-cause cardiovascular mortality) are especially strong, this is based on 

relatively weak evidence from the ACS cohort (Pope 2004), in my opinion. It is 

therefore not clear why it was elected to present risk assessment results largely for IHD in 

this discussion (p. 6-6) and in chapter 4 of the RA. On second thought, it is clear because 

all-cause CVD mortality effects were not presented in Krewski 2009, unfortunately, and 

Krewski 2009 was chosen to provide the most defensible effect estimates. 

3. The remaining percent PM-attributable effect of long-term exposure on total mortality 

is presented (p. 6-7, line 18; p. 6-8, line 8 and lines 14 & 15). These are ridiculously 

high. Presumably this should be on IHD mortality. The first bullet under the first Key 

Observation (p. 6-18) gets it right, I believe. 

4. I question whether short-term exposure-related risk (p. 6-5, line 3) is also driven by 

changes in long-term average PM concentrations. Short-term effects are observed 

independent of long-term PM concentration, ie, down to the lowest baseline 

concentrations. Therefore the argument in this paragraph for motivating attention to the 

annual average is not sound. 

 

6.a. Key questions captured? 

Yes 

6.b. Role of additional factors? 

Observations in 6.2 are well-supported. No other observations are apparent. 

6.c. Characterization of confidence. 

Again (see above), the emphasis on IHD mortality as opposed to all-cause cardiovascular 

mortality reduces our confidence in effect estimates; unfortunately, all-cause 

cardiovascular effect estimates are not provided in Krewski 2009. IHD effect estimates 

are highest in the ACS cohort. Otherwise, estimates are conservative. 

6.d. National context. 

I’m not sure I agree that the 15 cities capture “the overall distribution of risk for the 

nation,” (p.6-16, line 36) given the fact that these are the more polluted cities in the 

nation. More correct is the contention that these cities reflect the experience of cities 

with relatively elevated levels of PM-related risk and attributable mortality. Both can’t 

be true. 

37
38

6.e. Key observations. 

These observations are fine. I see little utility in estimating risk below an annual standard 

of 12 mcg/m3

.