UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON D.C. 20460

OFFICE OF THE ADMINISTRATOR
SCIENCE ADVISORY BOARD May 17, 2010

EPA-CASAC-10-011

The Honorable Lisa P. Jackson
Administrator U.S. Environmental Protection Agency 1200 Pennsylvania Avenue, N.W. Washington, D.C. 20460

Subject: CASAC Review of Policy Assessment for the Revi ew of the PM NAAQS - First External Review Draft (March 2010)

Dear Administrator Jackson,

The Clean Air Scientific A dvisory Committee (CASAC) Par ticulate Matter (PM) Review Panel teleconferenced on April 8, 201 0 and April 9, 2010 to review the Policy Assessment for the Review of the Particulate Matter National Am bient Air Quality Stan dards (NAAQS) - First External Review Draft (March 2010). The Policy Assessment is intended to help “bridge the gap”
between the relevant scientific information and assessments and the judgment required of the EPA Administrator in determining whether and how to revise the Nationa l Ambient Air Quality Standards (NAAQS) for Particulate Matter (PM). This letter highlights CA SAC’s main comments
on the Policy Assessment, followed by our consensus responses to the charge questions and
comments from individual Panel members. Before addressing sp ecific issues associated with the Policy Assessment , we offer some general thoughts below for your co nsideration.

General Comments

In 2006, EPA revised the primary and seco ndary NAAQS for PM to provide increased protection of public health an d welfare, setting the 24-h PM 2.5 standard at 35 μg/m 3 and retaining the annual standard at 15 μg/m 3

. In the Policy Assessment released earlier this year, EPA is considering revisions to thes e primary standards, using PM 2.5 as the indicator for fine particles, and
either PM 10-2.5 (as measured), or the comb ination (difference) of PM 2.5 and PM 10 as the indicator for thoracic coarse particles. EPA has also, for the first time, proposed consideration of a secondary PM standard that would be based on a different indicator – PM light extinction – than the mass-based indicators which have long been us ed for the primary PM standards. The CASAC applauds this initiative and encourages the Ag ency to move aggressively forward toward developing the next generation of indicator s for primary PM standards as well.

1EPA has a history of continuously improving indicators for primary PM NAAQS as new
evidence becomes available. Since the first sta ndard for airborne PM, Total Suspended Particles (TSP), was promulgated in 1971, the EPA has implemented PM NAAQS with progressively more specific indicators from both the pollution source and biological perspec tives. In 1987, EPA changed the indicator from TSP to PM 10 (thoracic fraction penetrating into the thorax) and in 1997, fine PM (PM 2.5 ), which differs substantia lly in chemical composition from the coarse particle
fraction within PM 10 and which penetrates to the gas excha nge region of the l ung, was adopted to supplement the protection provided by the PM 10 standard.

PM 2.5 has been a useful surrogate index si nce it was adopted in the 1997 PM NAAQS promulgation, but may become an increasingly inadequate index of health risk as the mass
concentration limits are reduced to the le vels being contemplated in the current Policy Assessment

. PM 10 is a non-specific indicator of the resp iratory system risks associated with PM 10-2.5 , as widely acknowledged in the Panel's discussions of the Integrated Science Assessment (ISA), Quantitative
Health Risk Assessment , and Policy Assessment documents. Neither index is directly related to health risks associated with ultra-fine particle s (UFP). The Panel also notes the challenge posed by the promulgation of a PM NAAQS directed at coarse particles, which vary widely in mass and composition across the country and between urban and rural areas.

While research evidence on PM and health ha s evolved, we urge the Agency to undertake additional efforts to leverage the gains made thus far. Now is the time to look ahead to future review cycles and reinvigorate support for the de velopment of evidence th at might lead to newer indicators that may correlate be tter with the health effects associated with ambient air concentrations of particulate matter (PM) and for more comprehensive PM monitoring data, including expanding the range of sizes, and adding measurements of numbers, chemistry, species,
and related emissions characteristics of particles. There is an inhe rent feedback in the cycle from research to policy formulation whereby research ers use the monitoring data that are gathered primarily for regulatory purposes with available indicators, and, in turn, expand the scientific basis for regulation. If EPA initiates efforts with air pollution research an d monitoring communities
now to create a more robust m onitoring platform for research, th e Agency will be better positioned
to make an evidence-based trans ition to the “next generation” of indicators of PM-related health
risks.

Draft Policy Assessment (March 2010)

Overall, the first draft Policy Assessment provides a solid start as EPA completes further analyses and deliberations related to thoracic coarse particles and visibility-related effects. As the first instance of moving th rough the sequence from an Integrated Science Assessment (ISA) through a Policy Assessment , the documents and the underlying flow of evidence and analytic findings provide an ordered and transparent basi s for decision-making. CASAC was unanimous in recommending that the docum ent be condensed and carefully edited to remove redundancy.
While the document needs to be self-containe d, the text should quote only the most critical evidence and rely more extensiv ely on citations to the ISA and Risk Assessment. CASAC also suggests that the underlying decision-making algo rithm that flows throug h the major questions posed in the text be made more explicit. (Text, and perhaps a figure, could be provided in Chapter 1, or at the start of Chapters 2-5.)

2Primary Standards

The Policy Assessment recommends consideration of NAAQS that cover both fine particles, using PM 2.5 as the indicator, and thoracic coarse particles, using either PM 10-2.5 or the
combination of PM 2.5 and PM 10 . At the present time, CASAC agrees that these indicators are the best available given scientific knowledge to date. The eviden ce presented in the Integrated Science Assessment, Quantitati ve Health Risk Assessment and Policy Assessment shows that health
effects have been observed in areas that meet current standards for PM 2.5 . Thus, CASAC supports EPA’s conclusion that consideration should be given to revising the current PM 2.5 primary standards to provide increased public health pr otection. Since the last NAAQS review, findings from additional epidemiol ogical studies support the association between PM 10-2.5 and cardiovascular and respiratory morbidity and morta lity. While the certaint y of the associations
between health effects fo r the association with PM 10-2.5 exposure does not match that for PM 2.5 , CASAC also agrees with EPA’s c onclusion that there is sufficie nt evidence to consider an adjustment of the PM 10 standard.

The choice of indicator is driv en by findings of epidemiologi cal studies that have drawn on monitoring data for PM 10 and PM 2.5 as exposure measures, as well as biological and source-related considerations. For the fine particle standard, the Policy Assessment draws heavily on the analyses
in the Quantitative Health Risk Assessment for Particulate Matter , which are based on the assumption of a linear no-thr eshold model for risk. The Risk Assessment covers the evidence supporting this model, drawing on the findings of th e ISA, particularly the finding of associations of PM indicators with morbidity and mortality at concentrations me asured in the United States. In commenting on the Second External Review Draft of the Quantitative Health Risk Assessment, CASAC recommended that EPA develop criteria fo r setting the lower bound for the scenarios considered in the risk analysis. That same issue emerges with the Policy Assessment as lower
bounds are considered for the ra nge for the annual and 24-hr PM 2.5 standards. The approach could be statistically based, using, for example, interquartile range, standard deviation, 10 th percentile level, or lower-bound confidence interval, but also based on broader consideration of uncertainty and of the level of health protec tion to be achieved. In fact, sel ection of the lower bound of the inter-quartile range may not be su fficiently health protective. Specifying the criterion by which a
lower bound concentration is ch osen becomes central in decisi on-making under a no-threshold model, since any suite of NAAQS above policy-relevant background leaves residual morbidity and premature mortality.

Secondary Standard

With respect to EPA’s consideration of a secondary PM standard, CASAC supports the recommendations for secondary PM st andards to protect public welf are as presented in the first
draft Policy Assessment . The focus on protecting visibility is appropriate given the advanced scientific understanding of the direct effects of PM on visual air qua lity, as set out in the Integrated
Science Assessment . The Policy Assessment establishes that the current secondary PM standards are inadequate to protect visibilit y, as their levels are too high, th eir averaging time s are too long, and their (dried) mass-based indicat ors do not fully represent PM effe cts on visual air quality in the ambient atmosphere.

3CASAC supports the proposed “PM light extinct ion” indicator, as it represents an actual and measurable consequence of particles in th e ambient air and it relates directly to the
demonstrated harmful welfare effect of ambi ent PM on human visual perception. PM light extinction also captures the physical and chemical properties of ambient aerosols and associated meteorological conditions. The Policy Assessment also proposes an optional PM 2.5 mass indicator,
which the Panel finds to be a less direct measure of light extinction, but an adequate indicator for a secondary PM standard, especially if the mass sc attering/absorption efficiencies are adjusted on seasonal, site-specific and/or regional basis to reflect differences in aerosol composition and relative humidity. Moreover, a mass-based standard could be considered on an interim basis while methods to measure the preferred PM light extin ction indicator are being developed, tested and deployed.

At most locations, a ma jority of PM light extinction is ca used by fine particles. Coarse particles are less of a contributing factor for lig ht extinction, while posing measurement problems for instruments measuring light s cattering or adsorption. For thes e reasons, an initial focus on

PM 2.5 light extinction may be appropri ate. However, coarse particle visibility effects can be very important at some locations, and a variety of appro aches could be employed to measure or estimate coarse particle effects, rega rdless of whether light extinctio n or mass-based indicators are employed (see responses to questions 14, 17 and individual panelist comments for more detail).

CASAC supports the use of a one-hour averag ing time for a secondary visibility standard, as this time span approximates th e nearly instantaneous nature of human perception of visual air quality, which itself can change rapidly over the cour se of a day. An hourly averaging time would also be well within the instrumental response capabilities of currently available light extinction monitoring instrument s, although if a PM 2.5 mass indicator were us ed, a somewhat longer averaging time may be necessary to accommoda te the larger response variability of some
continuous PM 2.5 monitors. The current focu s on daytime visibility is also appropriate, given the fact that nighttime visibility, while important, has a complex relationship with PM and other factors such as light pollution, for which scientific understanding is less advanced than for daylight
conditions.

The Policy Assessment presents a large number of optio nal combinations of levels and forms, including levels for PM light extinction in the range of 20 to 30 deciviews, with forms ranging between the 90 th and 98 th percentiles, which would be calcula ted based on either the single worst hour in a day (with 90 th or 95 th percentile) or based on all daylight hours (with 95 th or 98 th percentile). These many options are furt her complicated by consideration of PM 2.5 mass as a possible alternative indicator. While the range of options propo sed appears reasonable, CASAC
recommends that the next draft of the Policy Assessment provide more detailed illustrations of the
similarities and differences in th e many optional combinations, to pr ovide a more info rmed view of the policy implications of these options. Specificall y, it would be useful to describe the levels of visibility protection and/or PM 2.5 mass concentration, the PM speci es, the sources and event types that would be most affected, and the temporal a nd spatial variations in these factors that would
result from different combinations of optional indicators, levels and forms.

In addition to its principal focus on visibility protection, the Policy Assessment also includes very brief discussions of effects of PM on climate, ecosystems and materials. CASAC

4concurs with the Policy Assessment’s conclusions that while these effects are important, and should be the focus of future research efforts, there is not currently a strong technical basis to support revisions of the current standards to protect agains t these other welfare effects. Because different PM components that affect visib ility can have differential (cooling or warming) effects on climate, CASAC recommends revising the discussion of climat e effects to better info rm policy makers that reducing certain aerosol components could lead to increased radiative forcing and regional climate warming while having a beneficial effect on visi bility. However, the causal relationship between PM and climate is established, and the risk of aer osol impact on climate is high; therefore further research on a regional basis is urgently required.

Finally, CASAC reiterates its expectation that the revised Policy Assessment will be accompanied by a delineation of key changes from the first draft. This will enhance the efficiency and targeting of our review, and w ill provide a transparent record of the basis for these changes. As always, we appreciate the opportunity to provi de advice on this important subject and look forward to continuing our dial ogue with the Agency on PM.

Sincerely,

/Signed/

Dr. Jonathan M. Samet
Chair
Clean Air Scientific Advisory Committee

Enclosures A: CASAC Particul ate Matter Review Panel Roster B: CASAC Respons es to Charge Questions

C: Individual Panelists’ Re sponses to Charge Questions

5NOTICE

This report has been written as part of the activ ities of the EPA's Clean Ai r Scientific Advisory Committee (CASAC), a federal advi sory committee independently chartered to provide extramural
scientific information and advice to the Administrator and othe r 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 ap proval by the Agency and, he nce, the contents of this report do not necessarily re present the views and policies of the EPA, nor of other agencies within the Executive Branch of the federal govern ment. In addition, any men tion of trade names or commercial products does not constitute a recommend ation for use. CASAC reports are posted on the EPA Web site at: http://www.epa.gov/casac.

6Enclosure A Clean Air Scientific Advisory Committee
Particulate Matter Review Panel

CHAIR Dr. Jonathan M. Samet, Professo r and Chair, Department of Prev entive 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, Nort h Carolina State University, Raleigh, NC

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

IL

Dr. Armistead (Ted) Russell, Prof essor, Department of Civil a nd Environmental Engineering, Georgia Institute of T echnology, Atlanta, GA

Dr. Helen Suh, Associate Professor, Harvard School of Public Hea lth, Harvard University, Boston,

MA

Dr. Kathy Weathers, Senior Scientist, Cary In stitute of Ecosystem Studies, Millbrook, NY

CONSULTANTS Dr. Lowell Ashbaugh, Associate Research Ecol ogist, Crocker Nuclear Lab, University of California, Davis, Davis, CA

Prof. Ed Avol, Professor, Preventive Medicine, K eck School of Medicine, Un iversity of Southern California, Los Angeles, CA

Dr. Wayne Cascio, Professor, Medicine, Cardiolo gy, Brody School of Medici ne at East Carolina University, Greenville, NC

Dr. David Grantz, Director, Botany and Plant Sciences and Air Pollution Research Center, Riverside Campus and K earney Agricultural Center, Univers ity of California, Parlier, CA

Dr. Joseph Helble, Dean and Pr ofessor, Thayer School of Engineering, Dartmouth College, Hanover, NH

7Dr. Rogene Henderson, Senior Scientist Emer itus, Lovelace Respiratory Research Institute, Albuquerque, NM

Dr. Philip Hopke, Bayard D. Cl arkson Distinguished Professo r, Department of Chemical Engineering, Clarkson University, Potsdam, NY

Dr. Morton Lippmann, Professo r, Nelson Institute of Enviro nmental Medicine, New York University School of Medicine, Tuxedo, NY

Dr. William Malm, Research Physicist, Nati onal Park Service Air Resources Division, Cooperative Institute for Research in the Atmosphere, Colorado St ate University, Fort Collins, CO

Mr. Charles Thomas (Tom) Moore, Jr., Air Qu ality 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 & E nvironmental Medicine; Director, Air Pollution Health Effects Laboratory; Profes sor of Occupational & Environmental Health, Center for Occupation & Environm ent Health, College of Medicine , University of California Irvine, Irvine, CA

Dr. Kent Pinkerton, Professor, Regents of the Univ ersity of California, Ce nter for Health and the Environment, University of California, Davis, CA

Mr. Richard L. Poirot, Environm ental Analyst, Air Pollution Cont rol 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 Occupa tional Health Sciences,
School of Public Health a nd Community Medicine, Univers ity of Washington, Seattle, WA

SCIENCE ADVISORY BOARD STAFF Dr. Holly Stallworth, Designated Federal Offi cer, EPA Science Adviso ry Board Staff Office

8Enclosure B

CASAC Responses to EPA Charge Questions on the First Draft Policy Assessment for the Review of the Particulate Matter NAAQS

1. Organizational Structure

a. Does the Panel find the in troductory and background material, including that pertaining to previous reviews of the PM standards and the cu rrent review, to be clearly communicated and appr opriately characterized?

The introductory and background material in the Policy Assessment for the Review of the Particulate Matter NAAQS (PA), including the summary of previous reviews, is appropriate and clearly communi cated; however, the discussion could be condensed or summarized, thereby improving clarity.

b. To what extent does the Panel find that the questions posed appropriately reflect the important policy-relevant issues for this revi ew? Are there additional policy-relevant questions that should be addressed?

The questions posed in the Policy Assessment reflect important policy-relevant issues
relevant to this consideration of the PM NAAQS. As discussed in our letter to the Administrator, we recommend the Agency be gin to consider the evidence needed to
continue the refinement of th e PM indicator for such vari ables as chemical composition and optimal size ranges.

c. What are the Panel’s views regarding the level of detail used to address these policyrelevant questions? Please comment on th e extent to which the discussions are appropriately focused in addressing the questions.

The level of detail is excessive. It should be cut back to pr ovide succinct summaries of the
information extracted from the Integrated Science Assessment (ISA) and Quantitative
Health Risk Assessment (RA) documents. An Executive Su mmary would be very helpful,
and could be based on the su mmaries offered throughout the Policy Assessment.

2. Technical Content

a. Do the discussions accurately reflect and clearly communicate the currently available
health and welfare effect s evidence, including important uncertainties, as
characterized in the final ISA?

Yes, the Policy Assessment captures the currently available health and welfare evidence, as well as important uncertainties as characterized in the final ISA; however, much of the
evidence could be summarized and re ferenced to the ISA, making the Policy Assessment a more "reader friendl y" document. The Policy Assessment satisfactorily captures the range of proven and possible health effects litera ture that has expanded since previous PM
reviews.

The discussion of the welfare ef fects on visibility accurately re flects the currently available
scientific evidence. The rationale for selecti ng the 1-hour averaging time is particularly clear and convincing. The summ ary of the differences betw een nighttime visibility and

9daytime visibility, and the basis for considering the human impa ct of short-term visibility vs. all daylight hours, is clearly stated.

b. Do the discussions accurately reflect and clearly communicate policy-relevant
information from the human health risk and visibility assessments, including important uncertainties, as charact erized in the second draft REAs?

Yes, the Policy Assessment captures the policy-relevant information and important
uncertainties as characterized in the second dr aft RA. However, more of the evidence could
be summarized and refe renced to the RA. The policy-rele vant information for the visibility assessment is clearly communicated, particular ly the discussion of the nighttime visibility
effects and the rationale for se lecting the 1-hour averaging ti me over all daylight hours.

3. Approach (section 2.1.3): Vari ous approaches are described fo r translating different air quality metrics from epidemiological studies in to the basis for reaching preliminary staff conclusions on the adeq uacy of the current PM 2.5 standards and on alternative
standards for consideration. What are th e Panel’s views regardi ng the appropriate weight to place on these various approaches; should specific appr oaches be afforded more or less weight? Are th ere additional approaches that should be considered?

The selection of both evidence- and risk-based a pproaches is sound, as is the consideration of the utility of both annual and 24-hour concentratio n limits, and of variou s pairings of the two in exploring the degree of public health protection offered under possible NAAQS. The
balance between evidence- and risk-b ased approaches is appropriate.

Charge question #3 also pertains to approaches used to tr anslate different air quality metrics from epidemiological studies into the basis for identifying concentration ranges (levels) relevant to assessing the adequacy of the current PM 2.5 standards and to suggesting alternative standards for consideration. These approaches included using c oncentrations somewhat below the aggregate mean, at one standard deviation be low the mean, and at the lowest quartile of the interquartile range. A more direct appr oach would use confid ence bounds on the concentration-response relationships, such as those found in time-seri es studies. Attention could then be focused on the region where th ese bounds and other sources of uncertainty indicate an unacceptable degree of uncertainty a bout the concentration-response relationship. The less direct approaches used in the Policy Assessment instead make use of the
concentrations observed in the epidemiological studies without consideration of the estimates
of effect. The confidence bounds along a concentration-response relationship and
distributional measures of concentrations ar e intrinsically relate d, since the estimated exposure-response relationship is most certain in a concentration range where most of the data reside. We recommend that EPA consider expl oring the use of confidence bounds on the concentration-response relationships, where they are available, rather than the distributional
measures of concentrations.

4. Adequacy of current suite of PM 2.5 standards (section 2.2):

What are the Panel’s views on the following:

a. The appropriateness and characterization of the sets of long- and short-term PM 2.5 exposure studies highlighted? (section 2.2.1)

10• Are there specific studies that should be given more or le ss emphasis?

The Policy Assessment features appropriate studies and they are given appropriate emphasis. The discussion would be enhanced if there were an added indicator in Figure 2.1 to specify which of the studies were multicity vs. single-city studies. This would visually emphasize that more confiden ce should be given to the multicity studies (since the confidence intervals would be tighter) and provi de justification for preferentially relying on multi-city studies. The Krewski et al. (2009) study receives greater emphasis in comparison to the other highlighted studies of annual mortality, however, beca use the study population was a relatively high SES group of vol unteers, the estimate s from the study may
underestimate the risk for the US population in general. The Policy Assessment should acknowledge this potential underestimation, a nd present the findings of this study in the
context of the other US cohort studies.

• Are there additional studies th at should be focused on?

Yes, the section concludes that older adults an d children along with those with pre-existing cardiopulmonary diseases should be considered as part of the suscep tible population. In addition, CASAC suggests that additional gro ups (as identified in the ISA) should be mentioned, including diabetics, and people with specific genetic polymorphisms that were reported in the ISA.

• Does the Panel generally support placing gr eater weight on multi-city vs. singlecity short-term exposure studies?

Yes, see above in response to the first bullet.

• Does the Panel agree with th e characterizations of PM 2.5 air quality at which
associations have been observed?

Yes, the presentation of results indicating PM 2.5 effects below the current 24 hour and annual standard is appropriately summari zed from multiple studies, adds to the observations previously made, and supports th e conclusion about the inadequacy of the current two primary PM standards, However, the selection of the lo wer bound of the interquartile range may not be sufficiently health protective. Further consideration should be given to using the 10th percentile as a level fo r assessing various scenarios of levels for the PM NAAQS.

b. The focus on persons with lo wer socioeconomic status as a susceptible population in addition to consideration of newly availa ble evidence for susceptible populations identified in previous review s (e.g., children, older adults , persons with pre-existing cardiac and respiratory disease)? (section 2.2.1)

The data presented fully justif ies consideration of lower socioeconomic status (SES) people as a susceptible group. This consideration would build from the in tegration of recent findings in the ISA that expand the identification of susceptible groups.

c. The preliminary staff conclusion that the estimated risks remaining upon simulation of just meeting the current suite of stan dards can reasonably be judged to be important from a public health perspective? (section 2.2.2)

11A substantial body of empirical evidence is su mmarized indicating that significant health effects are reported at or just below the curre nt 24 hour and annual stan dards, justifying the
conclusion in the Policy Assessment that the observed effects are important from a public health perspective. Thus, the discussion of estimated public health risks remaining if ambient air quality levels were to just meet the current standard is valuable and should contribute to the deliberations made by th e Administrator in se tting a PM NAAQS to protect the public with an ad equate margin of safety.

d. The relative roles of the annu al and 24-hour standards in providing public health protection as informed by the quantitative ri sk assessment, specific ally in focusing on simulation of estimated risks remaining upon just meeting the current suite of standards? (section 2.2.2)

The approach used to characterize the rela tive contributions of the annual and 24-hour concentrations is clearly presented. The Policy Assessment clearly explains why greater confidence can be placed on the roll-back estimates when the annual standard estimates are controlling, as compared to when the 24-ho ur values are contro lling. The link to the
characteristics of the data available is made clear. As CASAC wrote in discussing the RA, we would have preferred that EPA use Total Cardiovascular Mortality for both comparisons, although the conc lusions would not likely change substantially. The RA and Policy Assessment do explain their use of ischemic heart disease (IHD) mortality.

e. The integration of evidence-based and risk -based considerations to inform the preliminary staff conclusion that the availabl e information clearly calls into question the adequacy of the current suite of PM 2.5 standards and provides strong support for giving consideration to revis ing the current standards to provide increased public health protection? (section 2.2.3)

With regard to the integrati on of evidence-based and risk-based considerations, CASAC
concurs with EPA’s conclusion that the new data strengthens the evidence available on associations previously considered in th e last round of the assessment of the PM 2.5 standard. CASAC also agrees that there are significan t public health consequences at the current levels of the standard that justify consideration of lowering the PM 2.5 NAAQS further. More text might be provided to describe sp ecifically the uncertainties that have been addressed by the new evidence since the last review.

5. Indicator (section 2.3.1):

What are the Panel’s views on the following:

a. The preliminary staff conclusion that it is reasonable to retain PM 2.5 as an indicator for fine particles?

This conclusion is reasonable for this round of the PM NAAQS review. There was insufficient peer-reviewed literature to support any other indicator at this time. However, it is essential that EPA continue to develop the ambient air quality database so that the suite of PM indicators considered in epidemiologi cal studies can be expanded. Population-based studies will be needed to begi n to assess more refined PM in dicators, including chemical speciation of fine particles and measurements of ultrafine particles (UFP) that may more directly reflect the risk of PM 2.5 to human health.

12b. The preliminary staff conclusion that the currently available information is too limited to support a distinct PM st andard for ultrafine particles?

This conclusion was unavoidable in that there was insufficient peer-reviewed literature on ultrafine particle (UFP) exposures and expo sure-response relationships to support a UFP indicator at this time. As for fine PM (above ), EPA needs to implem ent a network of UFP monitors to support broader research on associ ations between UFP exposures and health.

c. The preliminary staff conclusion that th e currently available information is not sufficient to support consid eration of a separate indicator for a specific PM 2.5 component or for the mix of fine particles fr om any specific source category, and that
data are too limited to cons ider eliminating any component or source category from the mix of fine partic les included in the PM 2.5 mass-based indicator?

See answer to 5.a. above.

6. Averaging Times (section 2.3.2):

What are the Panel’s vi ews on the following:

a. The preliminary staff conclusion that it is reasonable to retain annual and 24-hour averaging times?

This conclusion is reasonable in view of the current limited evidence pointing towards other averaging times.

b. The preliminary staff conclusions that the cu rrently available evidence is too limited to support additional averaging times to address sub-daily exposures or seasonal exposures?

This conclusion is reasonable. To the extent that EPA supplements or replaces 24-hour fine PM samplers with continuous monitors, it may become possi ble to conduct studies that demonstrate that other averaging times for ac ute responses may be more appropriate than 24-hour averages, for at least some effects.

7. Forms (section 2.3.3):
What are the Panel’s views on the utility of additional analys es to inform consideration of eliminating provisions includ ed in the current form of th e annual standard that allow for spatial averaging across monitors, specif ically with regard to the potential for disproportionate impacts on susceptible popu lations with lower so cioeconomic status?

Given mounting evidence showing that persons with lower SES le vels are a susceptible group for PM-related health risks, CA SAC recommends that the provis ions that allow for spatial averaging across monitors be elimin ated for the reasons cited in the Policy Assessment. Moreover, it should be recognized that monitors are located specifically to reflect exposures to surrounding populations, which may vary spatially.

13Given this recommendation and its basis, additional analyses are not needed to inform a decision about spatial averaging. Should EPA decide that add itional analyses are warranted, however, a description of the aims, methods, and the decision criteria to apply these analyses
are needed to assess their u tility. CASAC notes the need for additional analyses and models to assess local heterogeneity in PM concen trations, both in terms of assessing population exposure, especially for low SES populations, and as a guide in future monitor siting
decisions.

8. Levels (sections 2.3 .4, 2.3.5, and 2.3.6):

What are the Panel’s views on the following:

a. The preliminary staff conclusions regarding alternative standard levels that are appropriate for consideration, and the ra tionale upon which those conclusions are
based?

CASAC believes that the document provides a clear and appropriate rationale for using the
annual PM 2.5 standard as the controlling standard and the 24-h standard to provide additional protection. As disc ussed in more detail in our re sponse to Charge Question 3, the text could be clarified substantially, specif ically with regard to the rationale used to
select the two sets of alternat e standards considered in the Policy Assessment. This explanation should include the rationale behi nd the use of a par ticular lower bound to
define annual PM 2.5 standards and the relation of the alte rnative standards to policy-relevant background levels.

b. The insights that can be gained from the qu antitative risk assessment to inform our understanding of the roles that the annual and 24-hour standards play in providing public health protection, specifically in focusing on simulations of estimated risks remaining upon just meeting alternative su ites of standards? (sections 2.3.4.2 and 2.3.5.2)

CASAC supports the use of the quantitative risk assessment to illustrate the impact of
alternative standards on health risk. The valu e of the risk assessment to this process would be increased substantially if the disc ussion was clarified and condensed.

c. The policy implications of the uncertainties associated wi th estimating risks, including potential underestimation of risk, in reach ing conclusions regardi ng standards that would provide public health protection with an adequate margin of safety?

CASAC recommends that the impacts of mode l choices on long- an d short-term risk estimates should be expanded to assess whether and how estimated risk s would differ if: (1) comparisons were made to the LML (as compared to the PRB); and (2) alternative concentration-response (C-R) functions were se lected. The selection of C-R functions is relevant to margin of safety considerations . For example, use of C-R functions from Krewski et al. (2009) may undere stimate risks for lower SES groups.

d. A policy approach for identifying a suite of standard levels in which the annual standard would be the “genera lly controlling” standard to pr ovide protection for both long- and short-term PM 2.5 exposures, in conjunction with a 24-hour standard set to provide supplemental protection against days with high peak concentrations

14associated with localized “hotspots” and ri sk arising from seasonal emission that might not be controlled by a national annual standard? (section 2.3.6)

The policy approach for identifyi ng the suite of standard levels was clearly described.

e. Additional considerations that could inform our conclusions related to alternative suites of fine particle standards?

CASAC identified a few areas for further cons ideration, including potential alternative lower bounds for estimating risk, margin of safety issues (as described above) with regard to the impacts on estimated risks of model choi ces, particle speciation and size (e.g., coarse and ultra-fine).

9. Adequacy of the current 24-hour PM 10 standard (Sect. 3.2):

What are the Panel’s vi ews on the following:

a. The preliminary staff conclusion that th e available scientific evidence supports maintaining a standard that provides protectio n against health effects associated with exposure to thoracic coarse particles?

CASAC concurs that the evidence since the last review is stronger in linking adverse health
effects to the thoracic course fraction. One complexity is the findi ng that after taking into account the component of the PM 10 that is made up of PM 2.5 , urban thoracic coarse particles appear to be more toxic than rural PM 10 . Thus, no single measure of thoracic coarse fraction can be applied uniformly across all sites.

b. The various approaches described for translating the evidence and related
uncertainties into the basis for conclusi ons on the adequacy of the current PM 10 standard?

The Policy Assessment describes the uncertainty comi ng from having insufficient PM 10-2.5 monitors and limited geographic coverage, par ticularly for the purpose of comparing the
thoracic coarse fraction in rural and urban ar eas. See the answer to question 13. Further insight could be gained by using the data from all locations with co-located PM samplers
so that PM 10-2.5 could be calculated as PM 10 concentration minus PM 2.5 concentration.

c. The adequacy of the public health protection afforded by the current PM 10 standard against exposures to thoracic coarse particles?

The relatively toxicity of the total PM 10 fraction depends on several factors. The proportion of the PM 10 that is in fact PM 2.5 is different between urban and rural sites. In addition, although the limited evidence is only suggestive, there are independent differential potential health effects of the PM 10-2.5 portion of PM 10 in both urban and rural areas that can be separated from the health impact of PM 2.5 . Since such effects have been reported in both urban and rural areas at concentrations below the current standard, it is
clear that the current PM 10 standard is not adequate to prot ect the public health. It is also
the case that there is no eviden ce to guide the choice between PM 10 or PM 10-2.5 that would be appropriate as a standard fo r both urban and rural regions as a single national standard. Since there are insufficient spatial PM 10-2.5 measurements at this time, CASAC suggests
that we continue with the PM 10 measure as the indicator, bu t encourage EPA to work on a

15national monitoring scheme for a range of particles including both smaller and larger
fractions.

10. Indicator (sections 3.3 .1, 3.3.2, and 3.3.3):

What are the Panel’ s views on the following:

a. The preliminary staff conclusion that it is appropriate to mainta in a standard that provides protection against all thoracic coarse particles, regardless of their source of origin or composition?

This conclusion is justifiable at this time, in view of the evid ence from the PM ISA showing that coarse thoracic PM exposures ar e associated with acute respiratory system responses that are not accounted for by fine PM. However, it is important to recognize that
there is a lack of data on the influence of coarse thoraci c PM composition. While it is reasonable to not consider chemical composition in the current round of review of a coarse thoracic NAAQS, it is essential th at a suitable database for PM 10-2.5 concentrations and composition be developed over th e next several years so that a more satisfactory judgment on the need for composition-speci fic indicators can be made in the next review cycle.

b. The appropriateness of maintaining an indicato r that allows lower PM 10-2.5 concentrations in urban areas than non-urban areas?

Because PM 2.5 concentrations are generally higher in urban areas than rural areas, particles in this size range constitute a greater proportion of PM 10 in such areas.. In view of the evidence that there is a greater proportion of road dust, incinerator effluents, and other
coarse PM that contain known toxicants in urban areas than in windblown soil dusts in rural areas, it is appropriate to maintain a co arse thoracic PM indicator that requires lower
concentrations in urban areas than non- urban areas. In this review cycle, PM 10 can serve as a prudent index of coarse thoracic PM. Ho wever, as noted (in 10.a. above) chemical speciation of PM 10-2.5 may provide a more robust basis for future coarse thoracic PM NAAQS.

c. The appropriateness of either a PM 10 or PM 10-2.5 indicator for a standard meant to protect against exposures to thoracic coarse particles?

While a PM 10-2.5 indicator for a standard meant to pr otect against exposures to thoracic coarse particles would be preferable, a PM 10 indicator is an acceptable substitute in this round of review. However, in lig ht of the implications of di fferent source profiles leading
to differences in the current PM 10 nonattainment areas in the U.S., CASAC notes potential problems with use of either the PM 10 or PM 10-2.5 fractions as the indicator of coarse PM. In the short term, information from the ISA on PM 10-2.5 health effects and regional differences (in particular, section 6.5.2.3) c ould be brought forward into the Policy Assessment to motivate consideration of alternative coarse PM indicators that could allow for a more
focused and health relevant coarse PM st andard. Further analyses based on this information might also be considered. In the long term, inform ation on chemically speciated coarse PM health eff ects would allow consideration of a coarse PM standard that
reflects differential toxici ty related to composition.

11. Averaging Time (section 3.3.4):

16What are the Panel’s views on the prelimin ary staff conclusions that the currently available evidence supports maintaining a 24- hour standard to protect against health
effects associated with short-t erm exposures to thoracic coarse particles, and does not support consideration of a long-term thoracic coarse particle standard?

This conclusion is reasonable.

12. Form (section 3.3.6): What are the Panel’s views on the preliminary staff conclusion that it is appropriate to
consider a 98 th percentile form for a revised 24-hour standard meant to protect against short-term exposures to thoracic coarse particles?

CASAC finds the 98th percentile approach to be appropriate , but some members questioned the approach used to calculate the 98th percentile, noting that in the absence of additional information, a 98th-percentile cal culation from the multi-year dist ribution of values was more defensible than a year-by-year calcu lation over three successive years.

13. Level (section 3.3.7):
What are the Panel’s views on the appropriateness of considering 98 th percentile, 24-
hour PM 10 or PM 10-2.5 concentrations in epidemiologica l study locations for identifying a range of potential alternative standard leve ls for consideration, recognizing the more limited air quality information available for PM 10-2.5 ?

This portion of the Policy Assessment provided only a promissory note that additional analyses would be done, dependent upon th e conclusions as to whether CASAC would recommend staying with PM 10 or moving to PM 10-2.5 as the indicator for coarse thoracic particles. The proposal to use PM 10 for alternative levels para llels what was done with PM 2.5 and seems appropriate. Because of the potential lack of sufficie nt spatial data available for

PM 10-2.5 , it is not clear that similar analyses ca n be accomplished. Ho wever, there may be sufficient data coming from locations with co-located PM 2.5 and PM 10 monitors, so that by
subtraction an estimate of PM 10-2.5 could be made. It would be valuable to conduct some additional analyses if there is a smaller subset with sufficie nt data to carry out such estimates
of PM 10-2.5 . In addition there may be da ta to make direct comparis ons of the estimated levels with directly measured PM 10-2.5 in selected sites for purposes of testing the sensitivity of the
subtraction estimates. This comparison would serve the purpose of demonstrating relative differences (or lack thereof) of the different indicators.

14. Adequacy (section 4.2): What are the Panel’s view s on the preliminary staff conclusion that the currently available information clearl y calls into question the adequacy of the
current suite of PM 2.5 standards to provide public welfar e protection from unacceptable levels of visibility impairment, primarily in urban areas, and suppor ts consideration of alternative standards to provi de appropriate protection?

CASAC agrees that the Policy Assessment clearly describes how th e form and level of the current PM standard are inadequate to prot ect the public from unacceptable levels of visibility impairment. Specifically , the levels of the current PM 2.5 and PM 10 standards are too

17high, and their averaging times are too long, to guard against levels of visual air quality considered adverse over the short (hour or less) time periods during which changes in visual air quality are perceptible. The current mass-based indicators are also not ideal, and could be made much more directly resp onsive to visibility effects by using a PM light extinction indicator. Although an alternative PM 2.5 mass indicator applied over shorter daylight hourly averaging times and at lower levels is not id eal to protect visibility, it would represent a substantial improvement over the current 24-hour and annual means.

The relationship between the maximum daily 1-hour 90 th percentile and the all daylight hours
98 th percentile is clearly and convincingly pres ented. The reasoning for excluding hours with relative humidity above 90% is also readily understood. The box-and-whisker plots of PM light extinction clearly show that rolling back the PM 2.5 concentrations to meet the current standards would not protect vi sibility in most locations, re gardless of which candidate protection level (CPL) or percentile form is co nsidered. It appears from Figure 4-3 that Phoenix (along with Tacoma) would also not exce ed the least restrictive CPL more than 2% of the time. If so, Phoenix should also be mentioned on line 17 of page 4-26.

The summary in section 4.2.2 is very clear in describing why the current PM standards are not protective of visibility. An addition that could strengthen the chapter in future drafts
would be to show – with data examples – how high a 1-hour PM 2.5 mass concentration or a 1- hour PM light extinction level could be on (a) day(s) when the 24-hour PM 2.5 mass concentration does not exceed the current 35 μg/m 3 standard. In addition, some photographic illustrations using actual photos or Winhaze images would be helpful to show what visual air quality looks like at levels of the current standa rds (and at the higher 1-hour levels that are possible without exceeding the 24-hour average standards).

15. Indicator (section 4.3.1): What are th e Panel’s views on the following:

a. The appropriateness of consideri ng PM light extinction and PM 2.5 mass as indicators for a distinct secondary PM standard for visibility protection, and the relative advantages and disadvantages asso ciated with each indicator?
b. The appropriateness of consid ering the contribution of co arse particles with respect to a potential PM light extinction indicator?

CASAC agrees it would be preferable to use PM light extinction as the indicator since it is directly related to visibili ty and can be directly meas ured. Light extinction is a fundamental physical property of the ambient aerosol and thus, it represents a very appropriate indicator for a secondary visibility standard. While PM light extinction is much preferred, PM 2.5 mass (with appropriate averaging time, level and form) could also be an adequate indicator for PM visibility ef fects, and may be more reflective of other possible welfare outcomes.

Since a continuous PM 2.5 mass monitoring network is al ready in operation and robust methods for widespread PM light extinction measurements will take several years to develop, evaluate and deploy, the Agency mi ght consider a phased approach in which a standard is set based on PM light extincti on, with compliance measur ements initially made using Federal Equivalent Method PM 2.5 mass as a surrogate for light extinction, until such

18time as a more direct PM light extinction ne twork is in place. To facilitate a better agreement between mass and ex tinction some consideration should be given to adjusting the mass scattering efficiencies that relate ma ss to extinction in such a way as to reflect spatial and seasonal variability in the relative composition of am bient aerosols and regional differences in relative humidity. Setting a standard to any specific level of PM 2.5 mass concentration would still allow a wide range of visibility effects at different times and locations and would provide much less efficient protection than could be attained with a light extinction indicator. CASAC still encourag es the Agency to develop suitable methods for measuring PM light extincti on, and to evaluate these me thods in a small pilot field
network.

The bulk of the light extinction at a majority of locations is driven by fine particles (PM 2.5 ). There are significant problems with the meas urement of both light scattering and light absorption from larger particle sizes. Consequently, it is a ppropriate to focus initially on
measurement of PM 2.5 light extinction or its components. Another approach that would improve the quality of measurem ents of extinction from both fine and coarse particles would be to deploy a system that periodically switches between PM 2.5 and PM 10 inlets for the same measurement device (nephelometer or aethalometer). A thir d approach would be to limit light extinc tion measurements to instruments with PM 2.5 inlets (which would also
reduce instrumental maintenan ce requirements), and estimate coarse particle extinction
from continuous PM 10-2.5 mass measurements, based on the difference method.

16. Averaging times (section 4.3.2): What are the Panel’s views on the following:

a. The preliminary staff conclusion that cons ideration should be given to a 1-hour averaging time?

CASAC concurs that a one-hour averaging ti me is most appropriate for a secondary standard to protect visibility, since PM effects on visibility can vary widely and rapidly over the course of a day, and such changes ar e almost instantaneously perceptible to human observers. An hourly averaging time is also we ll within the instrumental response times of the various currently available and devel oping optical monitoring methods. If a PM 2.5 mass indicator is used, the Agency may wish to c onsider somewhat longer averaging times - 2 to
4 hours - to assure a more st able instrumental response, although obtaining reliable hourly data from currently available continuous PM 2.5 monitors should be both feasible and a highly desirable objective for a variety of other applications.

b. The advantages and disa dvantages of focusing on a 1- hour daily maximum or each 1- hour average concentration during all daylight hours?

As noted in the second draf t Urban-Focused Visi bility Assessment (UFVA), there is relatively little difference in the levels of visi bility protection that wo uld be provided by a PM light extinction standard based on considering the single worst daylight hour in a day
combined with a relatively low 90 th percentile form and one based on considering all daylight hours combined with a higher 98 th percentile form. It is likely that these two approaches may tend to emphasize differen t kinds of visibility events and source influences, and in its recent review of the UFVA, CASAC requested that the Agency prepare additional analyses to be tter illustrate and evaluate wh at these differences may be.

19We expect that the results of these analyses will be helpful to St aff in recommending the best approach and to CASAC in commenting on it more objectively.

While it may be that the single worst daylight hour is judged to be a better approach,
CASAC did not think that the stated rationa le of protecting the most “sensitive” or “susceptible” individuals who may only have a short period of outdoor time each day to view scenery was an especially strong basis fo r this selection. We su ggest that a different justification needs to be provided if this appro ach is considered superior to one based on all daylight hours. In addition, CA SAC recognizes that there are other complexities associated with evaluating and protecting ni ghttime visibility – such as th e combined influence of PM and light pollution. The Policy Assessment should make clear that the current focus on daytime visibility is not because nighttime visi bility is unimportant, but rather because the scientific understanding of PM visibility ef fects under daylight conditions is currently much more advanced than for nighttime effects.

17. Levels and Forms (section 4 .3.3): What are the Panel’ s views on the following:

a. The preliminary staff conclusions regarding ra nges of options with varying levels and
forms in combination with different indicators ( light extinction and PM 2.5 mass-based indicators) and averaging times (1-hour daily maximum or each 1-hour average concentration during all daylight hours)?

There is general agreement that the standard should be based on 1-hour averaging time. Furthermore, CASAC found that a standard base d on extinction is preferable to a massbased standard. However, because of potential issues in implementing monitoring for light extinction, a mass-based indicator may be acceptable, at least on an interim basis, given the right averaging time and percentile level. However, the consensu s of the committee was that not enough information is provided in the first draft Policy Assessment to clearly evaluate the differences in protection associat ed with the various combinations of levels, percentiles, and 1 hr worst visib ility vs. all daylight hours. The Policy Assessment more specifically does not address how the protectio n afforded by these various combinations would be further modified by the choice of an extinction vs. a mass indicator. For the limited comparisons illustrated in the Policy Assessment , CASAC agreed that 20 to 30 deciviews was an appropriate range of leve ls for a PM light extinction indicator, but concludes that the uppe r bound of 40 – 60 μg/m 3 was unreasonably high for a PM 2.5 mass indicator and that a range more along the lines of 15-35 μg/m 3 should be evaluated in
future drafts.

In considering the implications of using a mass vs. an extinction indicator, it is critical to understand what level of average or median mass concentration corresponds to a given level of extinction as a function of atmospheri c characteristics in representative eastern and western cities. A given level of visibility protection will corres pond to differing mass concentrations around the country, while a given level of PM 2.5 mass will correspond to differences in associated visibility protec tion. More detailed comparisons should be
included in the Policy Assessment to better illustrate the differ ences in visibility protection as the degree of protection varies with ma ss concentration and species composition. Regional and seasonal variation in protec tion should also be explored.

20While it has been demonstrated that a 90 th percentile form comb ined with the worst daylight hour each day would generally result in similar average levels of visibility protection as the 98 th percentile based on all daylight hours, these two options may tend to focus on different kinds of visibility impairing events, PM specie s compositions and
emissions sources. The Policy Assessment should provide clearer illustrations of the differences (or similarities) between these approaches, and how they might be further
modified if a PM 2.5 mass indicator is selected rather than the preferred light extinction
indicator.

b. Additional approaches that could help inform our consideration of alternative levels
and forms?

The 90% RH screen may not be needed if a PM 2.5 indicator is used. Some consideration should be given to using a nephel ometer that cycles between a PM 2.5 and a PM 10 inlet. This approach would allow for the very accurate measurement of PM 2.5 scattering with a reasonable estimate of coarse particle scatte ring. The same approach could be used for a continuous mass or light absorption monitoring system.

As indicated in previ ous comments on the UFVA , a “progress-based” attainment test rather
than the traditional “threshold-based” attainment test would be preferable from a scientific perspective. While the Agency has indicated this is not an option in the standard-setting process, this approach could and should be considered in the implementation phase (where, for example, the Agency could provide guidan ce on what would be considered reasonable rates of progress). Possibly an example of how this approach might work could be provided in the next draft Policy Assessment

.

It would be helpful if the next draft of the Policy Assessment included a section identifying and prioritizing key near-term monitoring and research needs to support refinements and revisions to secondary PM standards in the fu ture. This could include establishing a small pilot urban visibility network to field-test and evaluate alternative PM light extinction measurement methods, a dditional visibility preference st udies to better define levels (and/or frequencies) of visual air quality considered acceptable over a wider range of locations and viewing conditions, and chemically speciated measurements of fine particles to support the linkage between PM mass and visib ility impairment.

18. Climate (section 5.2): What are the Panel’ s views on the preliminary staff conclusion
that there is insufficient information to base a standard on climat e impacts associated
with current ambient PM concentrations?

CASAC agrees that the prelimin ary staff conclusions on the climate impact of aerosols are
correct – there is insufficient evidence on wh ich to base a national standard. However, the causal relationship is established, and the risk of aerosol impact on climate is high so further research on a regional basis is urgently require d. This need should be strongly voiced in the Policy Assessment , and research should be undertaken s ooner rather than later. If possible, research should be designed and begun now to be included in future assessments of the NAAQS.

21While there may be insufficient information to base a secondary standard on potential climate change, CASAC emphasizes that policy makers s hould be better informed that reducing certain aerosol components could lead to increased ra diative forcing and regional climate warming while having a beneficial effect on visibility. There is abundant information demonstrating that
aerosols that scatter visible light (e.g., nitrates and su lfates) are cooling, and can lead to increased/longer lived/more refl ective cloud formation. The Integrated Science Assessment (based largely on other assessments) demonstrates that light scattering aerosols lead to a net decrease in radiative forcing, and while the uncertai nty is significant, it suggests that the effect may be quite large. Further, ther e is sufficient evidence that light absorbing aerosols (e.g., black carbon) can lead to warming. To go forward with a secondary standard based on reducing light extinction, the Policy Assessment needs to more directly weigh the potential that regional warming could accompan y improved visibility if light scattering aerosols are preferentially targeted. There al so may be significant regional heterogeneity to controls that would address a visibility -based secondary standard which sh ould be addressed. For example, the areas that currently have lower PM concentr ations may benefit most from maintaining or improving visibility, but the areas with regionally high sulfate le vels (and reduced visibility) would likely benefit most from the reduced radi ative forcing. At a minimum, EPA needs to address how a secondary standard might impact regional radiative forcing and climate, assess the uncertainties, and provide a reasoned analysis weighing the two issues. Also, on Page 5-11, lines 10-11 and lines 31-32, it is noted that “aerosols that ar e warming are co-emitted with aerosols that are cooling.” While this statem ent is correct in some instances, it does not accurately represent the aerosols with these competing effects. Most of the warming aerosols in the US are emitted by biom ass burning and intern al engine combustion. Much of the cooling aerosol is formed in the atmosphere by oxidation of SO 2 or VOCs. Thus, a set of controls to control warming PM would not neces sarily have that much impact on cooling PM
and vice versa. These statements should be modified accordingly.

Finally putative difficulti es in relating PM to climate effects are laid out in sections 5.2.3 and 5.2.4 (pages 5-11 to 5-13) and again in section 5 .3.4 (page 5-24). However, these apply to all other potential effects of PM, and it is not approp riate to emphasize them here, as if they were uniquely related to climate. For example, othe r PM-effects relationships would be improved by using chemically-speciated mass measurements; other relationships are expected to vary locally and regionally; others have offsetting positive and ne gative effects (warming vs. cooling, radiation attenuation vs. radiation scatte ring); others are confounded by effects at a distance from sources, by the difficulty of distinguishing anthropogenic from natural constituents (PRB issues should be explicitly mentioned here - section 5.2.4); by spatial and temporal heterogeneity; etc. In addition, many of the caveats in section 5.3.4 are equally true of nitrogen oxides, sulfur oxides, and ozone, but ha ve not presented insurmountable obstacles to revising NAAQS for those contaminants.

19. Ecological effects (section 5.3): What are the Panel’s views on the preliminary staff
conclusion that data are insufficient to su pport establishing a distinct standard for ambient PM based on ecosystem effects not addressed in the ongoing NOx/SOx secondary NAAQS review?

2223 CASAC agrees with the conclusions of the Policy Assessment that the published literature is insufficient to support a national standard fo r PM effects on ecosystem services. The best established effects are related to particles c ontaining nitrogen and sulfur, which are no longer considered in this assessment of particulat e matter. CASAC consider s that some causal relationships are known, but that sensitivities are not well characterized. Further research should be advocated, including progress toward a monitoring network that will yield time
resolved information on chemically speciated particulate mass that is likely to be most closely related to ecosystem endpoints.

The references in the Policy Assessment to welfare valuation associated with end use, taken from the ozone assessment documents, and to ecosystem services as specific and individual endpoints, taken from the Millennium Ecological Assessment, may prove useful in structuring
this research.

CASAC recommends incorporation of text into Secti on 5.3 that is similar to that in the current draft of Section 5.4, regarding the importance of maintaining an appropriate degree of control of both fine and coarse particles to address ecos ystem effects attributed to them, even in the
current absence of suff icient information to develop a standard.

20. Material effects (section 5.4): What are th e Panel’s views on the preliminary staff
conclusion that no new evidence calls into question the adequacy of the protection afforded by the current suite of PM standards, and that there continues to be support for retaining an appropriate de gree of control for both fine and coarse particles to provide protection against mat erials damage and soiling?

CASAC agrees with the conclusions of the Policy Assessment that the published literature, including literature published since the last review, is insufficient either to call into question the current level of the standard or to support an y specific national standard for PM effects on materials. However, causal relati onships are well estab lished, particularly w ith regard to soiling of buildings and monuments. CASAC believes th is end point is particularly amenable to demonstration of relationships between PM mass (particularly chemically speciated mass) and levels of soiling, because the non- linear effe cts that characterize ecosystem endpoints may be less significant. Soiling effects of PM on mate rials may be linked to atmospheric burdens simply through an appropriate depositi on velocity for specific components.

We believe it is important to retain the text in the current draft of Section 5.4 regarding the importance of maintaining an appropriate degree of control of both fine a nd coarse particles to address materials damage and soiling attributed to them, ev en in the absence of sufficient information to develop a new standard.Enclosure C

Compendium of Individual Comments on Particulate Matter Policy Assessment (March 2010)

Comments from Dr. Lowell Ashbaugh ....................................................................................... 2
Comments from Mr. Ed Avol ...................................................................................................... 6
Comments from Dr. Joe Brain .................................................................................................. 12 Comments from Dr. Wayne Cascio ........................................................................................... 14 Comments from Dr. Chris Frey ................................................................................................ 17
Comments from Dr. David Grantz ............................................................................................ 18 Comments from Dr. Joseph Helble ........................................................................................... 21 Comments from Dr. Rogene Henderson ................................................................................... 22 Comments from Dr. Mort Lippmann ....................................................................................... 23 Comments from Dr. Phil Hopke ................................................................................................ 31
Comments from Dr. Robert Phalen .......................................................................................... 37
Comments from Mr. Rich Poirot .............................................................................................. 38
Comments from Dr. Armistead Russell .................................................................................... 46 Comments from Dr. Frank Speizer ........................................................................................... 48
Comments from Dr. Helen Suh ................................................................................................. 53
Comments from Dr. Sverre Vedal ............................................................................................. 55

1Comments from Dr. Lowell Ashbaugh

Question 2a: Do the discussions accurately reflect and clearly communicate the currently
available health and welfare e ffects evidence, including important uncertainties, as
characterized in the final ISA?

I believe the discussions of the health effects evidence accurately reflect the currently available evidence, but I’ll focus more on the welfare effects and leave it to the other reviewers to provide
more detail on the health effects evidence.

The discussion of the welfare eff ects on visibility is quite complete and it accurately reflects the currently available science. The rationale for sele cting the 1-hour averaging time is particularly clear and convincing. The summary of the differences between nighttime visibility and daytime visibility, and the reasoning for huma n impact of short-term visib ility vs. all daylight hours is clearly stated.

The term ‘deciview’ is introduced on page 4-18, but it is not defined. A simple description of its relationship to extinction, along with guidance on how to understand it, would be useful. For example, it would help to explain that a one deci view change is just noticeable, and that higher values correspond to reduced visibility.

The discussion of the CPL values a nd how they were arrived at is very good. It is particularly useful to point out that the greater uncertainty, represented by the more scattered data points, for the Denver and British Columbia results may aris e from the use of actu al photos taken under varying conditions, while the better fit of the Phoenix results could be due to the use of WinHaze to alter the same photograph to disp lay different visibility conditions.

The distinction between the Washington, DC resu lts and the results from western cities is accurately and clearly described. The results presented by Smit h (2009) on a new study at Washington, DC are not discussed here, though , and probably should receive some attention. Although I believe there are good reasons to discard the results for the Policy Assessment , they
should be mentioned.

Question 2b: Do the discussion s accurately reflect and clea rly communicate policy-relevant information from the human health risk and visibility assessments, including important uncertainties, as characterized in the second draft REAs?

The policy-relevant information for the visib ility assessment is clearly communicated. I particularly like the discussion of the nighttime visibility effects a nd the rationale for selecting the 1-hour standard over all daylight hours. The se lection of CPLs is described well and the justification for selectin g them is consistent w ith the evidence presented. The only caveat I would make is that the results of the Smith (2009) st udy presented at the April 2009 CASAC meeting should be discussed. The results of that study provide an opportunity to explain uncertainties in visibility studies and why these results should not be included in the final assessment.

2Question 14: Adequacy (section 4.2): What are the Panel’s views on the preliminary staff conclusion that the currently available informat ion clearly calls into que stion the adequacy of the current suite of PM2.5 standards to provide p ublic welfare protection from unacceptable levels of visibility impairment, primarily in urban areas, and suppor ts consideration of alternative standards to pr ovide appropriate protection?

The Policy Assessment clearly describes how the form and level of the current PM standard is not adequate to provide public welf are protection from unacceptable le vels of visibility impairment. The relationship between the maximum daily 1-hour 90 th percentile and the all daylight hours 98 th percentile is clear and convincin g. The reasoning for excluding hours with relative humidity above 90% is also clear. The box-and-whisker plots of PM light extinction are clear evidence that the current levels of PM standards are not protectiv e of visibility, particularly combined with the estimated light extinction if PM levels are rolled b ack to just meet the current standard. It appears from Figure 4-3 that Phoenix (a long with Tacoma) would also not exceed the least restrictive CPL more than 2% of the time. If so, it shoul d be included in lin e 17 of page 4-26.

The summary in section 4.2.2 is very clear in describing why the current PM standards are not protective of visibility.

Question 15: Indica tor (section 4.3.1) : What are the Panel’s views on the following:

a. The appropriateness of consideri ng PM light extinction and PM 2.5 mass as indicators for a distinct s econdary PM standard for visibility protection, and the relative advantages and disadvantages associated with each indicator?
b. The appropriateness of consid ering the contribution of co arse particles with respect to a potential PM light extinction indicator?

The issues associated with selecting PM light extinction as a standard are described well. The limitations of using 24-hour PM 2.5 mass to predict 1-hour visibility impacts could be better described. In particular, the discussion of visi bility impacts clearly point s out that short-term visibility is most clearly represen tative of the welfare effects of vi sibility. PM mass, though, is not currently measured on a 1-hour time scale, so it is not able to adequately represent visibility impacts. Figure 4.3-1 shows the relationship between 24-hour visibility and 1-hour light extinction. The uncertainty associated with this relationship could be discussed in more detail to illustrate the shortcomings of PM 2.5 mass as an indicator of short-term visibility.

It’s appropriate to consider the contribution of coarse particles w ith respect to a potential light extinction indicator. Although coarse particles are not a significant contributor in some parts of the country, they are significant in ot her parts – notably the southwestern U.S. It’s important that EPA acknowledge these differences by includi ng coarse particles in the indicator.

Question 16: Averaging times (s ection 4.3.2): What are the Pa nel’s views on the following:

a. The preliminary staff conclusion that cons ideration should be given to a 1-hour averaging time?
b. The advantages and disadvanta ges of focusing on a 1-ho ur daily maximum or each 1-hour average concentration during all daylight hours?

The discussion of visibility effects on welfare pres ents clear and convincing evidence that a 1-hour averaging time is appropriate for a visibility indicator. The assessme nt points out that a significant fraction of the population is exposed to visibility conditions for only brief periods during the day, and their welfare is affected by these brief expo sures. The relationship between the 1-hour daily

3maximum and 1-hour average daylig ht visibility indicators is clear ly explained and the protective benefits of using the 1-hour maximu m indicator is justified in the Policy Assessment

. Question 17: Levels and Forms (section 4.3.3): What are the Panel’s views on the following:

a. The preliminary staff conclusions regarding ranges of options with varying levels
and forms in combination with different i ndicators (light extinction and PM2.5 mass-based indicators) and averaging times (1-hour daily maximum or each 1-hour average concentration during all daylight hours)?
b. Additional approaches that could help in form our consideration of alternative
levels and forms?

The staff conclusions regarding the levels and fo rms of the light extincti on indicator are related well to the evidence presented earlier in the Policy Assessment . The difficulty in relating PM levels to light extinction is also described we ll, and the selection of alternative PM 2.5 mass concentration levels is well justified. In the discussion on page 4- 34 it is not clear why the 98 th percentile form is
not considered. A brief comment on why it is not included would be helpful. I infer from the
discussion that EPA staff consider s it too restrictive, but this could be explained more explicitly.

The discussion of the maxi mum daily 1-hour indicator versus th e average daylight 1-hour visibility is well done. I like the characterization of people wh o have infrequent access to daytime visibility as a susceptible population, and the explanation th at the 1-hour daily maximum indicator would be also protective of people who have access to visibility throughout th e day is effective.

The box-and-whisker plots and the tables showing the effect of “just meeting” the alternative standards are very effective in conveying the anti cipated results. The use of color-coding in Figure 4.3-2 is very helpful in comparing the alternative standards. The blue shading in the table of Appendix A is too light; it should be darker to more effectively highlight those conditions.

Question 18: Climate (section 5.2): What are the Panel’s vi ews on the preliminary staff
conclusion that there is insufficient informat ion to base a standard on climate impacts
associated with current am bient PM concentrations?

The preliminary staff conclusions on the climat e impact of aerosols are accurate – there is
insufficient evidence on which to base a national standard. The risk of aerosol impact on climate is high, though, so this issue needs further development. It’s important to state that research into the
effects of aerosols on climate is needed and shoul d be undertaken sooner rather than later. If possible, research should be designed and begun no w to be included in future assessments of the NAAQS.

Question 19: Ecological effects (section 5.3): What are the Pa nel’s views on the preliminary
staff conclusion that data are insufficient to support establis hing a distinct standard for ambient PM based on ecosystem effects not addressed in the ongoing NOx/SOx secondary NAAQS review?

The preliminary staff conclusion is appropriate for ecological effects. Wh ile acknowledging that ecological effects occur, it is not possible at th is time to establish a PM level that would be protective of ecosystems.

Question 20: Material effects (section 5.4): What are the Panel’s views on the preliminary
staff conclusion that no new evidence calls in to question the adequacy of the protection afforded by the current suite of PM standards, and that there contin ues to be support for

4retaining an appropriate degree of control for both fine and coarse particles to provide protection against materials damage and soiling?

This preliminary staff conclusion is also appropr iate. The wording of this conclusion could be applied to the climate effects and the ecological ef fects sections. In partic ular, a version of the following sentence from the materi als effects section could be app lied to the other two sections: “However, in the absence of inform ation that provides a basis for establishing a different level of control, observations continue to support retaining an appropriate degree of control on both fine and coarse particles to help address materials damage and soiling associated with PM.”

5Comments from Mr. Ed Avol

General Comments: The objectives of the Policy Assessment (PA) document are laudatory – to provide the Administrator with a review of the policy implications arisin g from the conclusions
drawn from the ISA and RA. The Policy Assessment has all of the elements to make a persuasive and compelling presentation of the assembled data. However, in my opinion, the current Policy
Assessment is too repetitive, too word y, and devotes too many pages to re-visiting previous discussions presented in the IS A and RA documents, rather th an summarizing the findings and moving on to the policy implications.

An inordinate amount of space is afforded to the 2004 AQCD, with regular di scussion of what was presented and/or concluded in the 2004 review do cument. The ISA and RA presented the relevant
science and evaluated it in the context of risk estimates and levels of uncertainty; what are the policy implications of these findings? The cu rrent document should focus on what the cumulative information, through the current review, tells us now about PM exposure, effects, levels, and susceptibility, so that an informed judgment can be made at this point in time. It may be interesting to compare what was known several year s ago with what is known now, but that is not
the central issue at hand . As a result of this approach, this Policy Assessment document is much too long, making it frustrating to re ad. This style of presentation resu lts in weakening the impact of the document, and masking its key messages. I personally found it very difficult to wade through, even though I realize it contains important information that will be critical to the Administrator’s
determinations. This needs to dr amatically improve in the next draft, in order to make this
document accessible and worthwhile.

Specific Comments: P2-2, line 19 to P2-9, line 8 (sections 2.1.1 and 2.1.2) – This is histor ically interesting, helps to lay the groundwork for how EP A got to where it is with the fine particle standard...and is arguably completely irrelevant to the current document and discussion. The issue for the current policy document is interpretation of the currently available information for re-examining the current standard. Details about previous cycles of review and their outcomes could be placed in an appendix, but do not centrally address the focused th eme of this document – th e basis for review of
the current standard.

P2-9, lines24 & 25 – “...the annual and 24-hour sta ndards taken together, rather than to consider each standard separately...” But didn’t the RA cl early demonstrate that the annual standard was “controlling” (i.e., set at a given annual level, it effectively achieved a number of 24-hour standards being considered in conjunction with it?

P2-10 through2-13 – all this preparatory introduc tion about what is going to be discussed is unnecessary meandering (in my opin ion); the document should be a fo cused application of the data presented in the ISA and RA, presented clearly and then clearly summar ized; these pages could (and should) be distilled down to a paragraph or two. The Poli cy document should be brief, focused, and clear; this docume nt has the potential to become that, but isn’t there yet.

6P2-10, line 9 – Declaring a focus on US and Canadian studies si de-steps the issue that careful and well-performed science (or poorly-performed scien ce, for that matter) can be performed in other countries, just as they can be performed in the US and Canada.

P2-10, lines 26 & 27 – This conclu sion line is not needed here; fi rst present the information and then summarize the document’s position in a su ccinct integrative final chapter or section.

P2-13, lines 30 to 35 – not necessary, can be deleted without impacting presentation.

P2-14, lines 11 to 18 – not necessary, can be deleted without impacting presentation.

P2-17, lines 25 to 34 – The text is slipping into a lis ting and re-discussion of studies and findings, which was done quite well in the IS A and re-visited in the RA. This document should be a crafted, directed summary, rather than a re-listing of the studies...so I think this section could be edited to a line or two. The policy-relevant comment is in li nes 25 through 27 (“...loc ations with the largest reductions in PM2.5 saw the larges t improvements in redu ced mortality rates, while those with the
smallest decreases in PM2.5 concentrations saw th e smallest improvements in reduced mortality rates...”); the rest is repetitive carryover from th e ISA. Figure 2.1 (which is on an un-numbered page that might be P2-23) could be refered to and used as the basis for comments about what was reported in the ISA...without going through and talk ing about several of the studies in the text.

P2-19, lines 9-17 – Here, again, I think the point has been made an d re-listing ISA references does not add to the presentation; I th ink these can be deleted. The current presentation seems to have slipped back into a review and listing of the bo dy of evidence that supports a given conclusion (which was already done in the ISA), rather than presenting the conclusions brought forward from the ISA and RA and presenting a di scussion that begins with thos e ISA and RA conclusions being
carried forward.

P2-24, lines 33 to 35 – The noti on of a summary is great and mu ch-appreciated, but this is too wordy and meandering. Delete lines 33 to 35 and get to the point!

P2-25, lines 1 and 2 – same as previous co mment, delete this and get to the point.

P2-25, line 26 to p2-26, line 2 – this is yet an other example of unnecessary meandering and reopening an issue that does not need to be re-visited in this document. Earlier versions of ISAs, and the PM ISA, discussed a nd evolved towards a functional and us eful definition of susceptibility, and this document should begin from that poi nt, not re-visit what the evolution was.

P2-26, line 29 – change the word “factors” to “observations”.

P2-27, lines 8 to 11 – Is this co nsistent with the previous comm ent (P2-10, line9) that the focus would be on US and Canadian studies (a fo cus with which I resp ectfully disagree)?

P2-43, line 4 – replace the phrase “peak shaving” with a more accurate one that describes the approach.

7P2-44, lines 3 to 7 – This statement about the importance of annual average PM 2.5 concentrations on interpreting risk results for both short and long- term exposures is a key observation that should be highlighted, bolded, underlines, or otherwise clearly identified.

P2-45, line 9 and line 21 – The comments about lung cancer here (when the argument was previously made about basing the presentation on “cau sal” levels of determination) raises the issue
of staff confidence and belief in th e strength of association between PM 2.5 long-term exposure and lung cancer. What is the determ ination on this matter that St aff wants to transmit to the
Administrator?

P2-45, line 11 to 14 – Does th is comment about 10 of the 15 study areas having “...design values
which result in the current 24-hour standard c ontrolling...” contradict the previous one (p2-44, lines 3-7), which asserted that annual averages were controlling for both short and long-term exposures? Together with a la ter comment (p2-49, lines 27 to 29, “...This pattern is generally characteristic of the larger set of urban areas across the US that do not meet the current suite of standards...”), this leaves the read er somewhat confused –which st andard is controlling? What is the policy implication?

P2-51, line 27 on to P2-52, line 33 – This discussion of the repr esentativeness of the study areas seems out of place here, 50+ pages into the discus sion...Shouldn’t this be es tablished early in the presentation so that the credibility of all that follows is increased?

P2-52, line 34 to p2-55, line 3 – This seem s like an obvious and unnecessary comment – Does Staff really think that someone might conclude that these 15 areas in the presentation are the ONLY 15 areas in the country for wh ich this discussion is relevant?

P2-52, line 4 to p2-55, line10 – This question and response seems unnecessary and out of place here. The purpose of the NAAQS review is to periodically assess the current information relevant to the current standard and make a judgment about the adequacy of the standard to protect the public health. The determination as to whether there are “risks remaining upon simulation of the
current suite of standards...” will be addressed when th e body of information is presented and the
Administrator makes that determination.

P2-54, lines 24 to 28 – This is yet another ex ample of meandering monolo gue – rephrase this to present the conclusion clearly and succinctly – the data suggest that level of the current PM 2.5 standard needs to be re-considered.

P2-57, lines 6 & 7 – Change this line to read, “These techniques , while widely used in aerosol research, have not yet been widely used in health effects studies , or systematically deployed for extensive time periods in local or regional air monitoring networks .”

P2-57, lines 23 to 28 – Unnecessary and can be deleted...

P2-58, lines 25 to 29 – This is certainly true and potentially a se lf-fulfilling prophecy (in that there
will never be national-level ultra-fine data until an d unless there is directed interest to support the

8collection of such data). Coul d an appendix of “Research Needs To Advance Future Reviews” be
added?

P2-62 – The presentation has slid b ack to a review of data, which has already been done in the ISA (where it rightfully belongs, not here).

P2-64, lines 24 to 34 – This is a useful summary comment. Based on the history of PM research (from mass-based assessments to particle size, constituent, and biological toxicity) and the PM NAAQS (gradually moving to sma ller size fractions), it seems re asonable to anticipate that a component of PM might be the bi ological actor of interest. With the STN network and large-scale chemical characterization studies, we are on the cusp of perhaps collecting the information needed to identify the important chemic al constituents of biological signi ficance. This could and should
be added to the “Research Needs” list.

(The same generic comments apply for most of the next 50+ page s– too wordy, unnecessary detail, substantial editing needed!)

P2-107, section 2.4 – This is a well-constructe d, focused presentation and should serve as the template for the previous 100 pages. These comme nts could be supported by references to the ISA or RA, but the specific supporting materials do no t need to be here to make a convincing presentation (and to the authors’ credit, th e supporting materials do not appear here).

P2-109, Section 2.5 – Key Uncertain ties – This section can and sh ould be a focused, terse, and brief presentation...a few pages at most, possibly only a pa ge or less. It is somewhat surprising that in this first draft, given th e excellent discussion in the RA, th ere is only a title and placeholder
here...

Chapter 3, Thoracic Particles – Th e presentation scheme is analogous to the previous chapter, and in doing so, suffers from the same generic shortfalls (too much detail, too much repetition, only a placeholder for the uncertainty discussion, etc).

Chapters 4 and 5 – defer to my visi bility colleagues on these sections...

Specific Charge Question Assignments:

Question 4: Adequacy of current suite of PM 2.5 standards (section 2.2):
What are the Panel’s vi ews on the following:

a. The appropriateness and characterization of the sets of long- and short-term PM 2.5 exposure studies highlighted? (Section 2.2.1). Too-long-winded a discussion but studies are the appropriate ones.

• Are there specific studies that should be given more or less emphasis ? No, and the studies’ discussion should be referenced to ISA and RA, not re-visited in the manner
and extent here.

• Are there additional studies th at should be focused on? No.

9• Does the Panel generally support placing g reater weight on multi-city vs. singlecity short-term exposure studies? Favor multi-city studies to better substantiate findings and make findings that much more representative.

• Does the Panel agree with th e characterizations of PM 2.5 air quality at which
associations have been observed? Yes.

b. The focus on persons with lo wer socioeconomic status as a susceptible population in addition to consideration of newly availa ble evidence for susceptible populations identified in previous review s (e.g., children, older adults , persons with pre-existing cardiac and respiratory disease)? (section 2.2.1). This is appropriate and could arguably be included in those with compromised health , because lower SES carries with it a host of related increased risks (access to health care, poor diet, increased smoking rates, increased exposure (roadway proximity of residences and occupational exposures), increased violence and stress, etc).

c. The preliminary staff conclusion that the estimated risks remaining upon simulation of just meeting the current suite of stan dards can reasonably be judged to be important from a public health perspective? (section 2.2.2). Based on the referenced health risk estimates, this is a logical conclusion.

d. The relative roles of the annu al and 24-hour standards in providing public health protection as informed by the quantitative ri sk assessment, specific ally in focusing on simulation of estimated risks remaining upon just meeting the current suite of standards? (section 2.2.2). Agreed and acceptable.

e. The integration of evidence-based and risk -based considerations to inform the preliminary staff conclusion that the availabl e information clearly calls into question the adequacy of the current suite of PM 2.5 standards and provides strong support for giving consideration to revis ing the current standards to provide increased public health protection? (section 2.2.3). Agreed and acceptable, but raises a policy issue as to whether PM speciation is potentially more informative rather than total mass.

Question 8: Levels (sectio ns 2.3.4, 2.3.5, and 2.3.6):
What are the Panel’s vi ews on the following:

a. The preliminary staff conclusions regarding alternative standard levels that are appropriate for consideration, and the ra tionale upon which those conclusions are
based? The conclusions are fine – appropriate for the foundational arguments made. The presentation, however, is too wordy, too long, too repetitious, and in need of substantial editing.

b. The insights that can be gained from the qu antitative risk assessment to inform our understanding of the roles that the annual and 24-hour standards play in providing public health protection, specifically in focusing on simulations of estimated risks remaining upon just meeting alternative su ites of standards? (sections 2.3.4.2 and 2.3.5.2) Useful and warranted. Presentation-wise, the figures and th e summaries, with reference to the RA, would have been sufficient to make the point.

c. The policy implications of the uncertainties associated wi th estimating risks, including potential underestimation of risk, in reach ing conclusions regardi ng standards that

10would provide public health protection with an adequate margin of safety? My preference would have been for a clearer and concise section directly discussing uncertainty here, rather than comments about “increased variability” scattered throughout.

d. A policy approach for identifying a suite of standard levels in which the annual standard would be the “gene rally controlling” standard to provide protection for both long- and short-term PM 2.5 exposures, in conjunction with a 24-hour standard set to provide supplemental protection agai nst days with high peak concentrations associated with localized “hotspots” and ri sk arising from seasonal emission that might not be controlled by a national annual standard? (section 2.3.6) The question itself is indicative of the systematic problem permeating the document – lack of clear, succinct and focused presentation.

e. Additional considerations that could inform our conclusions related to alternative suites of fine particle standards? Clarity, focus, and brevity....

Question 12: Form (section 3.3. 6): What are the Panel’s views on the preliminary staff conclusion that it is appropriate to consider a 98 th percentile form for a revised 24-hour standard meant to protect against short-term exposures to thoracic coarse particles? The argument for utilizing a concentration-based approach rather than an exceedance-based approach is compelling, and the presentation is terse but clear.

Typos: P2-1, line 16 – missing a period.

P2-43, line32 – change “ref erences” to “reference’.

P2-51, line 23 – insert the word “to” af ter “...24-hour standard is controlling due...”

11Comments from Dr. Joe Brain

1. Organizational Structure

a. Does the Panel find the in troductory and background material, including that pertaining to previous reviews of the PM standards and the cu rrent review, to be clearly communicated and appr opriately characterized?

The panel views the Policy Assessment (PA) document as critically important to the overall process of standard setting. It is th e culmination of a deliberate process leading from the ISA to the REA, and u ltimately to an informed decisi on by the Administrator. In toto, the panel approves of the current versions of the ISA and the REA, and feels that key ideas from them now appear in the Policy Asse ssment. In particular, the panel feels that the discussion of previous reviews of the PM standards is adequate, appropriate, and clearly communicated.

b. To what extent does the Panel find that the questions posed appropriately reflect the important policy-relevant issues for this revi ew? Are there additional policy-relevant questions that should be addressed?

The panel feels that the questions posed (questions 2-20) are pertinent to an overall
assessment of the evidence fo r the regulation of PM. The questions – and the answers – focus on policy-relevant issues. Other than minor aspects addressed by answers to other charge questions, the panel feels that there ar e no major additional ques tions that should be
addressed.

c. What are the Panel’s views regarding the le vel of detail used to address these policyrelevant questions? Please comment on th e extent to which the discussions are appropriately focused in addressing the questions.

The panel was divided regarding the level of detail present in the current Policy Assessment. Some thought the scope of the present Policy Assessment was appropriate. It may be necessary to include the considerab le detail which charac terizes the current document. However, a substantial minority fe lt that an ideal policy assessment should be
far shorter and more focused. Key staff and the administrato r can turn to the REA and the ISA as necessary. The Policy Assessment could be one thir d its current length and be a brief summary of the evidence and how that relates to alternative PM levels. Moreover, a concise description of how the form of the st andard is important would also be useful.

2. Technical Content

a. Do the discussions accurately reflect and clearly communicate the currently available
health and welfare effect s evidence, including important uncertainties, as
characterized in the final ISA?

The panel welcomes the expansion of material rela ting to health and welfare effects. The range of proven and possible health effects has been expanded since previous PM reviews. We
welcome a discussion of how PM affects visibility and is invo lved in climate change. We

12believe these topics are important, and we applau d the authors’ attempt to concisely inform the Administrator regarding the importance of these relevant outcomes.

b. Do the discussions accurately reflect and clearly communicate policy-relevant
information from the human health risk and visibility assessments, including important uncertainties, as charact erized in the second draft REAs?

The panel believes that the current Policy A ssessment discussion does clearly communicate information relating to human h ealth risks and visibility. Th ere is a good discussion of
uncertainties and how these uncertainties impact quantitative ri sk assessments. As noted earlier, some panel members thought that the Polic y Assessment would be more
effective if it were shorter. More of the evidence contained in it could be summarized and
references to the REA or ISA – as appropriate – could be include d to compensate for some of the missing or truncated detail.

13Comments from Dr. Wayne Cascio

Question 4: Adequacy of current suite of PM 2.5 standards (section 2.2): What are the Panel’s views on the following?

a. The appropriateness and characterization of the sets of long- and short-term PM 2.5 exposure studies highlighted? (Section 2.2.1). Are there specific studies that should be given more or less emphasis? Are there addition al studies that should be focused on? Does the Panel generally support placing grea ter weight on multi- city vs. single-city short-term exposure studies? Does the Pane l agree with the characterizations of PM2.5 air quality at which associations have been observed?

Comment: EPA staff in authoring the Policy Assessment has achieved an appropriate and balanced emphasis between the strengths and weaknesse s of the studies, and weighing their relative
contribution to the assessment. There are no additiona l studies that need to be introduced from the ISA in support of the Policy As sessment. Multi-city st udies do merit greater emphasis (or weight) for the purpose of establishing the association between PM 2.5 exposure and health effects. Table 2- 1 provides an informative overview summary of the causality de terminations for PM 2.5 . While the present ISA does not specifically addre ss long-term neurocognitive effects of PM 2.5 , it is likely to
be a factor to be evaluated in the next ISA. As such it might be wort hwhile placing such an
outcome in the Table. One could use “Central Ner vous System Effects” as is already present in the Short-term category and indicating that the causa l determination is “inadequate”. Figure 2-1 provides an informative summary of the effect es timates and air quality distributions for long-term exposure studies. An added designation that would be useful would be to identify each study as single- or multi-city study and not e the number of cities included in the multi-city studies. The value of multi-city studies is emphasized in the ISA, RA and Policy Assessment therefore it would be useful to see the specific nu mber. Have the region of the country present in the table as has already been done is useful.

b. The focus on persons with lo wer socioeconomic status as a susceptible population in addition to consideration of newly availa ble evidence for susceptible populations identified in previous review s (e.g., children, older adults , persons with pre-existing cardiac and respiratory disease)? (Section 2.2.1)

Comment: The identification of individuals having a lower socioeconomic status as a susceptible population is appropriate. Two noticeable omissi ons are the absence of a description of the association with certain gene polymorphisms associated with enzymes modula ting oxidant stress,
and diabetes. While more data needs to be obtaine d to better establish the magnitude of these risks and define the mechanism accounting for the increased risks, there appears to sufficient evidence (Chapters 4, 6 and 8) in the ISA to comment in the Policy Assessment

.

c. The preliminary staff conclusion that th e estimated risks remaining upon simulation of just meeting the current suite of stan dards can reasonably be judged to be important from a public health perspective? (Section 2.2.2)

Comment: The conclusion that simulations of just meeting the current suite of standards demonstrates persist risk to the h ealth of the public is justified a nd important. Yet, it must be noted

14that these estimates of excess risk are extrapolated to PM 2.5 levels for which ther e are only limited real world data and higher degrees of uncertainly. Consequently, the rationale for further adjusting the PM standard rests with assuring a margin of safety.

d. The relative roles of the annual and 24 -hour standards in providing public health protection as informed by the quantitative ri sk assessment, specific ally in focusing on simulation of estimated risks remaining upon just meeting the current suite of standards? (Section 2.2.2)

Comment: Comparisons of short- term and long-term cardiovascular risk based are challenging
based on Tables 2-2 and 2-3 that describe different health effects end-points, incidence of ischemic heart disease mortality in Table 2- 2 and total cardiovascular mortality in Table 2-3. Providing total cardiovascular mortality in both tables or in the text would a llow a more direct comparison of the
relative roles of the annual and 24-hour standard.

e. Does the current suite of PM 2.5 standards provide adequate protection of public health? (Section 2.2.3) EPA staff in the Policy Assessment has provided a logical approach and justification of the conclusion that the current PM 2.5 standard is insufficient to protect health and should be revised.

Comment: Taken in total the data presented in the ISA and summarized in the Policy Assessment provide strong justification fo r reconsidering the current PM 2.5 standard. Convincing evidence continues to be present indicating that serious cardiovascular and respiratory health effects and
adverse heath outcomes occur at the level of the current standard, and that a lower standard will result in greater protection of health.

Question 9: Adequacy of th e current 24-hour PM standard (section 3.2): What are the Panel’s views on the following?

a. The preliminary staff conclusion that th e available scientific evidence supports maintaining a standard that provides protectio n against health effects associated with exposure to thoracic coarse particles?

Comment: While data from epidem iological studies are suggestive of short-term cardiovascular, respiratory and mortality effects, at the present time significant uncertaintie s exist with respect to the health impact of coarse PM (PM 10-2.5 ). Limitations exist with re spect to exposure assessment, and non-human studies addressing biological plau sibility. Since the last review new information has generally supported an asso ciation but an important multi-c ity Canadian study did not find
association between PM 10-2.5 statistically significant, thus emphasizing the persistent uncertainty of the impact of this PM fraction. On page 3-12 (L. 26-28) it is stated that “Considered as a whole, the ISA notes that epidemiologic studies that have ev aluated thoracic coarse particles have reported consistent, positive associations between PM 10-2.5 and mortality (US EPA, 2009a, section 6.5.2.3)”. It should further be stated, “..., yet, in many cas es the associations did not achieve statistical significance.”

b. The various approaches described for translating the evidence and related
uncertainties into the basis for conclusi ons on the adequacy of the current PM 10

15standard?

Comment: Evidence appeari ng since the last review shows that mortality is increased even in some
cities where the current PM 10 standard is met. This suggests that the PM 10 standard should be reconsidered. Issues related to the uncertainty of air quality estimates in the epidemiological studies reporting the health effects of PM 10-2.5 remain, as does the limitation of few studies addressing confounding by co-pollutants. For these reasons in contrast to PM 2.5 significant uncertainties persist regard ing association between PM 10-2.5 and overall mortality as well as cause specific mortality.

c. The adequacy of the public health protectio n afforded by the current PM10 standard against exposures to thoracic coarse particles?

Comment: Since the last review additional epidemiological studies support the association between

PM 10-2.5 and cardiovascular and respiratory morbidity and mortality. While the precision of the
associations between health eff ects for the association with PM 10-2.5 exposure does not match that
for PM 2.5 there is sufficient evidence to co nsider an adjustment of the PM 10 standard. Because evidence is presented in the ISA that shows that health effects have been observed in areas that meet current standards there is reason to expect that a downward adjustment of the standard will benefit the health of the public. Importantly, these associations at lower than the current standard levels are preserved even in two-pollutant mode ls. And there is limited but supportive evidence from human exposure studies and non-human toxicological studies. While the available evidence
continues to be less robust than the PM 2.5 by the limitations noted, one can argue that the standard should be lowered to provide a greater margin of protection.

16Comments from Dr. Chris Frey

Initial comments on the draft Policy Assessment

‐ It is unusual that C-R estimates based on the low end of a plausible range of values would be used. In public health applications, it is more typical to user upper bound estimates of dose-response relationships in order to be pr otective of public health. Thus, one could argue that EPA has biased the risk characteri zation to be very low and, therefore, is on a path that will not be adequately protective of public health.

‐ P 2-73: The draft Policy Assessment seems to say that the form of the standard will not

be assessed until the 2 nd draft of the Policy Assessment . This would seem to effectively disengage CASAC from being able to comment on a fully specified alternative standard

that takes into account indicator , level, averaging time, and fo rm. All of these must be considered jointly in order to assess a regulatory alternative.

‐ The Policy Assessment is very very long. While it may be useful to provide background for people who have not read the ISA or the RE A, the text is simply too verbose. Avoid being so tentative with statements. Avoid pa ssive phrases such as “we note that...”. The text will have more impact over all if things are said just once and not repeated. While it

is useful to summarize material from the ISA and REA, there does not need to be an

extensive verbose discussion of these. The interested reader can access these documents

for more detail.

‐ the summary paragraphs at the end of each major section are very useful. These summary paragraphs should be the basis of creating an executive summary or synthesis chapter, that would enable a reader to get the main points without having to labor through hundreds of pages of material.

‐ The objective in evaluating alte rnative standards should not be risk reduction but rather seeking a standard that is protective of public health with an adequate margin of safety. (e.g., page 2-87)

‐ P 2-97 – should also take into account that sensitivity analysis of the C-R functions generally lead to higher eff ects estimates that the core estimates. Furthermore, the assessment does not adequately take into account that the C-R functions are likely to be underestimated for reasons not quantified, such as exposure error.

‐ Section 2 does not seem to deal with the num ber of adverse effects cases associated with each alternative standard. This is necessary to consider in order to satisfy the legal objective/statutory mandate for the NAAQS.

17Comments from Dr. David Grantz

Overall, this Policy Assessment is well laid out and presented. It moves smoothly and clearly through the relevant issues and provides abunda nt information on each. There is some repetitive introductory text which might be condensed. The amount of information presented is large, and may be excessive since it has been already carri ed through the ISA and one or both of the Risk Assessments. What needs to be highlighted in th e Policy Assessment are staff conclusions, their implications, and the type of info rmation on which they are based.

Question 14. Adequacy . The Policy Assessment does a nice job of demonstrating that, for a visibility endpoint, the current standard is not prot ective of public welfare. In the text describing Fig. 4-3 it should be noted that Ph eonix as well as Tacoma would me et the candidate level 98% of
the time.

Question 15. Indicator . The Policy Assessmentadequately presents the advantages of a visibilitybased indicator. It also, however, demonstrates that a mass-based PM 2. 5 indicator would work almost as well (subject to modest additional spatial vari ability in achieved visibility).

There are advantages to retaining a mass-ba sed indicator for the Secondary Standard:

1. Choosing a visibility-based indicator would be analogous to choosing one of the several health endpoints as the indicator for the Primary Standard. In either case, this inappropriately diminishes the importance of other endpoints, whet her or not there is sufficient evidence to use them in the current review cycle.
2. Mass is more conducive to future development of concentration-eff ects relationships for other endpoints. Research s hould be advocated in the Policy Assessment to develop appropriate deposition velocities for PM to li nk atmospheric concentrations to loads on ecosystems and materials, and to develop relationships between loading and diverse effects. A similar advantage of the mass a pproach holds for eff ects on cloud nucleation (climate) and radiation scattering (p enetration into plant canopies).
3. Nothing is sacrificed with respect to visibi lity protection if the level of the mass-based
standard is derived from know n physical relationships betw een visibility and PM2.5 mass (accepting some variability) and the human pr eference data (also with considerable regional variability).

A goal to be advocated in the Policy Assessment is movement towards a chemically speciated, mass-based standard. This appears to be equally tr ue for the Primary and Secondary standards. The Policy Assessment should endorse further research on re lationships between chemically speciated mass and various endpoints, and further prolifera tion of monitoring networ ks to support such a
standard in the future. There is insufficient info rmation to consider such an indicator during this review cycle.

Because the coarse PM fraction co ntributes significantly to visibility impairment in some locations, it is appropriate to consider a visibilit y-based standard fo r coarse PM mass.

18Question 16. Averaging time . A visibility-based criterion is reasonably based on a worst one hour averaging time, since the Policy Assessment demonstrates that vi sibility is essentially instantaneously perceived.

It is not appropriate to apply th e concept of a “sensitive sub-popul ation” to individuals who only go outside occasionally (page 4-15; line 22). It is e qually reasonable to postulate that people who spend their whole day outside ar e exposed to repeated instan taneous updates regarding poor visibility, and that they are th e true “sensitive sub-population”.

Any standard based on a one hour averaging ti me will require a new m onitoring protocol. This could be for visibility, or it could be used to push towards a real -time (continuous) mass measurement network. The latter would be useful for more purposes, has been advocated previously by CASAC, and therefore should be given serious consideration at this time.

While visibility and corresponding mass levels co uld be assessed during daylight hours, the standard could apply at all hours if a mass indi cator were selected. This could have potential benefits, for example in control of “dumping” of PM emissions at night when visibility is not
monitored.

Question 17. Levels and Forms . The options are well laid out, in the Policy Assessment and Appendix A. These are presented relative to the Candidate Protection Levels, based on the visibility preference studies. The underlying data regarding visibility preferences are somewhat weak, as appropriately noted in the Policy Assessment , and further research will be required to determine whether there is real regional variability or these relationships ca n be collapsed into a population mean.

It is appropriate to consider a <100% form, allo wing some hours of exceedance. This is more to stabilize the statistic than, as stated in the current draft Policy Assessment , because this is appropriate for an aesthetic standard. A relativ ely high percentile form, with a correspondingly lower level, would support the significance of the chosen level by seeking to minimize its
exceedance.

It is appropriate to consider a screen at 90% RH, to remove non-PM associated visibility impairments.

Question 18. Climate . The Policy Assessment appropriately concludes th at there is insufficient information to proceed toward a national standard for PM effects on climate. However, the causal relationship is established, and further research on a regional basis is urgently required. This should
be advocated in the Policy Assessment

.

A number of putative difficulties in relating PM to cl imate effects are laid ou t in sections 5.2.3 and 5.2.4 (pages 5-11 to 5-13) and again in section 5.3 .4 (page 5-24). However, these apply to all other potential effects of PM, and it is not appropriate to emphasize them here as if they were uniquely related to climate. For example, other PM-effec ts relationships would be improved by using chemically-speciated mass measurements; other relationships are expected to vary locally and regionally; others have offsetting positive and ne gative effects (warming vs.cooling, radiation

19attenuation vs. radiation scattering); others are conf ounded by effects at a dist ance from sources, by the difficulty of distinguishing anthropogenic from natural const ituents (PRB issues should be explicitly mentioned here (section 5.2.4); by spatia l and temporal heterogeneity; etc. In addition, many of the caveats in section 5.3.4 are equally true of N, S a nd ozone, but have not prevented those effects from being used in evalua tion of the NAAQS for those contaminants.

Question 19. Ecological Effects . The Policy Assessment appropriately concludes that there is insufficient information to proceed toward a national standard for PM effects on ecosystem services. However, causal relati onships are known, and further re search should be an Agency priority. This should be advocated in the Policy Assessment , incorporating the desirability of chemically speciated mass determinations.

The framing of the discussion (section 5.3.1) in term s of the end use of the product, taken from the ozone documents, and in terms of ecosystem services , following the Millenni um Assessment, is very good. Structuring future re search in terms of effects on individual ecosystem services may lead to these effects becoming useful in development of a NAAQS for PM.

Question 20. Materials . The Policy Assessment appropriately concludes th at there is insufficient information to proceed toward a national standard for PM effects on materi als. However, causal relationships are well established. Further research should be advocated in the Policy Assessment

, though other potential welfare effects may be mo re significant. Soiling effects on materials may, however, be the most straightforward to relate to atmospheric PM, since the linkage is only through deposition velocity for specific components.

Two editorial comments
1. On page 5-16, line 36, it should be added that plant genotype also determines uptake of metals and organics.
2. On page 5-19, line 32, I assume this is “p eroxisomal” rather than “peroxidomal”.?

20Comments from Dr. Joseph Helble

Charge Question 3: Ap proach (section 2.1.3)

The discussion in section 2.1.3 is very general, and not particularly well-addressed by charge question 3. The text in this section, while clear ly written, is longer than necessary for making the general points that 24 hour and annual standard s should be considered together, since controls
directed towards one will affect th e other, but that the Agency feels that “more consistent risk reductions are likely to be accomplished through strategies aimed at meeting an annual standard” (p 2-11). This is clear. The balance of the section (p. 2-12 and 2-13) is an overview of the approach taken in the rest of the document to de veloping potential standards. My recollection is that this was addressed adequate ly in the RA; a one paragraph su mmary with a reference back to
the RA would be better here.

Small point, but one that arose earlier and persists: the scientific rationale for focusing on studies conducted primarily in the U.S. and Canada (p 2-1 0, line 9) is not clear, and not addressed in the Policy Assessment

.

Charge Question 7: Forms (section 2.3.3)

The question addresses the appropriateness of allowing spatial aver aging in determining compliance with the annual standa rd. The discussion both in this section and elsewhere in the Policy Assessment indicates that EPA is moving away from the use of spatial averaging in this

context.

The utility of spatial averagi ng depends upon the heterogeneity or “spikiness” of the PM concentration distribution relative to the local pop ulation distribution. It will therefore strongly depend upon monitor placement, with respect to population density, source location, and local airflow patterns. EPA notes in the Policy Assessment that it will address th ese questions through “additional analysis” (section 2.3.4.1) that will be addressed in the 2 nd draft Policy Assessment

. Some description and discussion of the planned “additional analysis” would be helpful, as it was not addressed here, nor in the RA.

Further, this is one area where detailed modeli ng of PM concentration distributions could be helpful in assessing local heterogeneity of PM concentrations, both in terms of assessing population exposure and as a guide in future monitor siting decisions.

Additional Comment

In the footnote on p 1-5, is this backwards? The wording is not cl ear, but particles with dp > d 50 are those captured with higher efficiency than those at d 50

. Smaller particles (particles with dp <
d 50 ) are collected with lower efficiency.

21Comments from Dr. Rogene Henderson

Charge Questions 1 and 2, Organizational st ructure and technical content: I found the organizational structure to be help ful in following the logic of the conclusions of the staff. The technical content was excellent. I especially liked the summary paragraphs. It would be helpful to reduce the amount of verbiage by referring back to the ISA or the RA mo re often, rather than repeating the content of those documents.

Charge Question 8. Levels : Based on the lack of ability to de tect a threshold level for adverse health effects in epidemiology studies, and the need to protect sensitive sub populations with a margin of safety, we are beginning to arrive at risk estimates that drive our estimates of healthprotective levels down almost to background le vels. I think this must be discussed in the Policy
Assessment document. As a science advisory bo dy, it is not our place to make policy
recommendations as to where to dr aw the line. However, the Agen cy should discuss the criteria they will use to dete rmine where to draw the line. This is their policy c hoice, but it would be wise
to have their choice informed by discussions from CASAC..

Charge Question 9. Coarse Particles a. I agree with the staff conclusion that the available scientific evidence supports maintaining standard for coarse particles. b. I agree with the staff approaches to consideri ng the adequacy of the current PM 10 standard.

Charge Question 8: Levels fo r Coarse Particle Standards I agree with the described approach.

22Comments from Dr. Mort Lippmann

Major Comment and Concern:
On the basis of the scientific evidence and ri sk assessment, the OAQP S Staff has recommended
that a revised PM 2.5 annual NAAQS in the range of 13 – 12 u g/m 3 is needed to provide better public health protection, and furthermore that consideration should also be given to a PM 2.5 annual NAAQS in the range of 11 – 10 u g/m 3 . I find that these options were well considered, and scientifically justifiable on the ba sis of the analyses cited in the PM Policy Assessment draft. Their implementation would be consistent with the Ad ministrator’s obligations under the Clean Air Act with respect to setting NAAQS that would protec t the public health. However, I also believe that 2 nd draft of the PM Policy Assessment needs to more explicitly address the policy implications of the selection of a concentration li mit that, even at 13 u g/m 3 is considerably more stringent th an the current limit of 15 u g/m 3 . Promulgation of this concentration limit would require: a broad array of new controls on emissions of PM 2.5 and its precursors; would result in much more non-attainment over long peri ods of time; and would only be achievable in a time frame measured in years in most urban areas in the eastern and Midwestern States and
California. For the even lower alte rnate concentration limits (12 -10 u g/m 3 ), the requisite controls
on emissions of fossil fuel combustion effluents would require huge capital investments in new power plants and/or in alternate energy sources. Th ese considerations lead me to conclude it is now time to begin the transition to alte rnate indicators that better target the health-risks that have been
associated with PM 2.5 mass concentration. I come to this conclusion on the basis that: 1. There is a rapidly growing body of scientific evidence, much of it cited in the PM ISA, that
indicates that PM 2.5 -associated cardiovascular mortality and morbidity risk coefficients vary widely across th e US, as does the PM 2.5 chemical composition.
2. The establishment and mainte nance of a chemical speciation network (CSN) over the past decade has made it possible for well-targeted epidemiological studies to demonstrate that the urban areas with the highest health-based risks are those most heavily exposed to PM 2.5 components originating from the combustion of coal and residual oil, as well as the pollutants associated with motor vehicle tr affic. Thus, emission controls focused on
reductions of effluents from these sour ce categories are highly likely to reduce PM 2.5 - associated health risks more than emission re ductions from other source categories or for

PM 2.5 as a whole. 3. Unfortunately, the current limitations of the CSN, in terms of temporal and spatial coverage, have greatly limited the opport unities for epidemiologists to establish
associations between PM 2.5 -components and source categories and health effects. Having data for only every third or sixth day severely limits the ability to st udy acute responses and their lag structure, while having only one or a few sampling sites in an urban area severely
limits studies of both the acute and chr onic effects of components and source-related mixtures that are not uniformly distributed an urban area. 4. Moving toward the designation of better-t argeted indicators for primary PM NAAQS is not a new strategy. In 1987, PM pe netrating into the thorax (PM10) replaced total suspended particulate matter (TSP), an d in 1997, fine PM (PM 2.5 ), which differs subs tantially from the coarse particle fraction within PM 10 , and which penetrates in the gas exchange region of the lung, was adopted to supplement the protection provided by PM 10

. 5. While the scientific evidence to support a designation of one or more new indicators of

PM 2.5 –related health risks is inadequate for this PM NAAQS review round, EPA needs to

23initiate actions to ensure that an adequate scie ntific basis will exist w ithin the next 4 to 5 years for the designation of better and more efficient indices of PM 2.5 –related health risks
for the next round of PM NAAQS review. 6. The most urgent need for data to support new indicators of health risks is to enhance the temporal and spatial coverage of the CSN network for PM 2.5 , and if possible, for PM 10 or PM 10-2.5 , and ultrafine PM as well. An expanded CSN network can be supplemented by arranging for the creation and ma intenance of an archive for da ily FRN Teflon filters that can be made available for epidemiological studi es focused on the health effects of inhaled
trace metals and black carbon. The archived f ilters could support retrospective as well as prospective studies.

General Comments: 1. The OAQPS Staff have done an excellent j ob in summarizing the most relevant findings reported in the PM ISA and REA, and translating them into a suitable policy framework to facilitate and enable rational and defensible decisions by the Administrator on the promulgation of the next suite of primary PM NAAQS. 2. The OAQPS Staff warrants commendation fo r its straightforward and well-reasoned interpretations of the health effect s evidence and risk estimates for PM 2.5 , and their implications to the choice of the most suitable indicators , forms, levels for further consideration, and monitoring s ite data, as well as the optim al combinations of 24h and annual limits for public health protection. They point to the need for selection of a much more stringent annual limit, which will result in exceedance s in most US urban areas. 3. Chapter 2 of the Policy Assessment document, while comprehensiv e in terms of the issues that needed to be addressed, has not yet been sufficiently ed ited to remove the redundancies. In too many places, there are re petitions of the same words, phrases, and whole sentences (e.g., in the introductory pa ragraphs, discussion of the long-term exposurerelated evidence and risk estimates, the di scussion of the short-term exposure-related evidence and risk estimates, and the options for suites of long- and short-term exposure limits). These common issues and themes should be pres ented only once in full, and cited or summarized briefly, where th ey apply, in the later sections.
4. The content of this first dr aft of Chapter 3 on a NAAQS for PM 10 or PM 10-2.5 , represents a place holder, and contains only boiler-plate wording adapted from the more complete Chapter 2 that deals with PM 2.5 NAAQS. Critical comments on Ch apter 3 will have to wait
until we have a chance to see the second draft.

Specific Comments: Page Line Comment 2-33 Fig. 2-1 Separate listings of mortality effects from those of other effects 2-25 17 change “fine particles at least as” to “PM 2.5 NAAQS as, or more”
2-25 23 insert “the extensive” before “interindividual” 2-25 24 insert “likely to be” before “at” 2-26 25 change “to” to “for” 2-26 29 insert “of outdoor origin” after “PM” 2-27 18 change “which” to “that” 2-31 14 insert “chemical compositio n, which varies” after “along” 2-36 17 change “This reduction was” to “ Reductions were”

242-37 19 The ACS and 6-cities based risk estimates were not similar to and 6-cities or those of the
other cited studies 2-41 16 The entry for the brackets is missing 2-43 32 change “references” to “reference” 2-48 23 change “effected” to “affected” 2-59 7 change “larger particle sizes” to “PM 2.5 particle mass” 2-60 33 insert “metals,” before “sulfate” for consistency with other text entries
2-74 32 “MCAPS” has not been defined in the text 2-76 30 change “which” to “that” 2-85 35 What city, other than New Yor k, should be cited within the bracket? 2-86 3 correct the 3.2% entry

Question 1: Organizational Structure

a. Does the Panel find the in troductory and background material, including that pertaining to previous reviews of the PM standards and the cu rrent review, to be clearly communicated and appr opriately characterized?

Yes

b. To what extent does the Panel find that the questions posed appropriately reflect the important policy-relevant is sues for this review?

Yes, but not all of the policy-relevant issues.

Are there additional policy- relevant questions that should be addressed?

Yes. Specifically, the mismatch between associations between PM 2.5 mass concentrations and adverse hea lth effects, and the public hea lth need to control exposures

to PM 2.5 components that account for the effects. As the PM 2.5 level approaches background concentrations, the PM 2.5 indicator becomes much less defensible

.

c. What are the Panel’s views regarding the level of detail used to address these policyrelevant questions? Please comment on th e extent to which the discussions are appropriately focused in addressing the questions.

The level of detail is excessive. It should be cut back to provide succinct summaries
of the information extracted fr om the ISA and REA documents.

Question 2: Technical Content

a. Do the discussions accurately reflect and clearly communicate the currently
available health and we lfare effects evidence, including important uncertainties, as characteri zed in the final ISA?

Yes.

b. Do the discussions accurately reflect and clearly communicate policy-relevant
information from the human health risk and visibility assessments, including important uncertainties, as charact erized in the second draft REAs?

Yes.

25Question 3: Approach (sectio n 2.1.3): Various approaches ar e described for translating different air quality metrics from epidemiological studies into the basis for reaching preliminary staff conclusions on the adequacy of the current PM 2.5 standards and on
alternative standards for consideration. What are the Panel’s views regarding the appropriate weight to place on these various approaches; shou ld specific approaches be afforded more or less weight? Are there additi onal approaches that should be considered?

The selection of both evidence- and risk-based a pproaches is sound, as is the consideration of the utility of both annual and 24 hour concentr ation limits, and of th eir combinations in providing public health protection.

Question 4: Adequacy of current suite of PM 2.5 standards (section 2.2): What are the Panel’s views on the following:

a. The appropriateness and characterization of the sets of long- and short-term

PM 2.5 exposure studies highlighted? (section 2.2.1) The highlighted data sets are appropriate selections.

• Are there specific studies that should be given more or less emphasis?

The Krewski et al. (2009) study is ov eremphasized in relation to the other highlighted studies of annual mortality in th at it relies on a high er SES population than the others and thereby underestimates respon ses for the US population as a whole.

• Are there additional studies that should be focused on?

The 6-cities study, having a more represen tative population, should be given greater emphasis, at least for Easter n and Midwestern populations, where the coefficients of response are greater than for Western populatio ns. If the question refers to additional studies to be highlighted, the answer is no.

• Does the Panel generally support placing gr eater weight on multi-city vs. singlecity short-term exposure studies?

Yes.

• Does the Panel agree with th e characterizations of PM 2.5 air quality at which
associations have been observed?

Yes, but the selection of the lower bo und of the inter-quartile range may not be sufficiently health protectiv e. Further consideration shou ld be given to using the 10 th percentile as a level at which as sociations have been observed.

b. The focus on persons with lower socioeconomic status as a susceptible population in addition to consideration of newly available evidence for susceptible populations iden tified in previous review s (e.g., children, older adults, persons with pre-existing card iac and respiratory disease)? (section 2.2.1)

This was appropriate.

26c. The preliminary staff conclusion that the estimated risks remaining upon simulation of just meeting the current suite of standards can reasonably be judged to be important from a public health perspective? (section 2.2.2)

This was appropriate.

d. The relative roles of the annual and 24- hour standards in providing public health protection as informed by the qu antitative risk assessment, specifically in focusing on simulation of estimated risks remain ing upon just meeting the current suite of standards? (section 2.2.2)

This was appropriate.

e. The integration of evidence-based and risk -based considerations to inform the preliminary staff conclusion that the available information clearly calls into question the adequacy of the current suite of PM 2.5 standards and provides strong support for giving consideration to revising the current standards to provide increased public health protection? (section 2.2.3)

This was appropriate.

Question 5: Indicator (sect ion 2.3.1): What are the Pane l’s views on the following:

a. The preliminary staff conclusion that it is reasonable to retain PM 2.5 as an indicator for fine particles? It was reasonable only because there was insufficient peer-reviewed literature to support any other indicator at this time. Howe ver, it is essential that EPA develop the database, over the next four years, to support the identification of one or more
indicators that are better suited to re present the risks of exposure to PM 2.5 , especially of its components that, based on emerging evidence, represent the greatest risks to public health

.
b. The preliminary staff conclusion that th e currently available information is too limited to support a distinct PM st andard for ultrafine particles?

This conclusion was unavoidable in that there was insufficient peer-reviewed literature to support a UFP indicator at this time.

c. The preliminary staff conclusion that th e currently available information is not sufficient to support consid eration of a separate indicator for a specific PM 2.5 component or for the mix of fine particle s from any specific so urce category, and
that data are too limited to consider eliminating any component or source category from the mix of fine particles included in the PM 2.5 mass-based
indicator?

See answer to 5.a. above.

Question 6: Averaging Times (section 2.3.2):

What are the Panel’s vi ews on the following:

a. The preliminary staff conclusion that it is reasonable to retain annual and 24- hour averaging times?

27It was appropriate.

b. The preliminary staff conclusions that the cu rrently available evidence is too limited to support additional averaging times to address sub-daily exposures or seasonal exposures?

It was appropriate.

Question 7: Forms (section 2.3.3):
What are the Panel’s views on th e utility of additional analyses to inform consideration of eliminating provisions included in the current form of the annu al standard that allow for spatial averaging across monitors, specifi cally with regard to the potential for disproportionate impacts on susceptible popu lations with lower so cioeconomic status? Such analyses are warranted.

Question 8: Levels (sect ions 2.3.4, 2.3.5, and 2.3.6):

What are the Panel’s vi ews on the following:

a. The preliminary staff conclusions regarding alternative standard levels that are appropriate for consideration, and the ra tionale upon which those conclusions are
based? They were appropriate.

b. The insights that can be gained from the qu antitative risk assessment to inform our understanding of the roles that the annual and 24-hour standards play in providing public health protection, specifically in focusing on simulations of estimated risks remaining upon just meeting alternative su ites of standards? (sections 2.3.4.2 and 2.3.5.2)

The insights gained were useful and informative.

c. The policy implications of the uncertainties associated wi th estimating risks, including potential underestimation of risk, in reach ing conclusions regardi ng standards that would provide public health protection with an adequate margin of safety?

Uncertainties need to be defined as well as current information allows. On the other hand, using uncertainty as an excuse for ch oosing a minimally stringent level is not consistent with having an adequate margin of safety.

d. A policy approach for identifying a suite of standard levels in which the annual standard would be the “gene rally controlling” standard to provide protection for both long- and short-term PM 2.5 exposures, in conjunction with a 24-hour standard set to provide supplemental protection agai nst days with high peak concentrations associated with localized “hotspots” and ri sk arising from seasonal emission that might not be controlled by a national annual standard? (section 2.3.6)

This approach is most appropriate.

e. Additional considerations that coul d inform our conclusions related to alternative suites of fine particle standards?

The alternatives that were select ed were very reasonable choices.

28Question 9: Adequacy of the current 24-hour PM 10 standard (Sect. 3.2):

What are the Panel’s vi ews on the following:

a. The preliminary staff conclusion that th e available scientific evidence supports maintaining a standard that provides protectio n against health effects associated with exposure to thoracic coarse particles? This preliminary conclusion was warranted.
b. The various approaches described for translating the evidence and related
uncertainties into the basis for conclusi ons on the adequacy of the current PM 10 standard?

The various approaches that were described were appropriate.

c. The adequacy of the public health protection afforded by the current PM 10 standard against exposures to thoracic coarse particles?

The adequacy is uncertain in view of the very limited database. While it is
reasonable to maintain the current PM 10 NAAQS in this round, it is essential that a suitable
database for PM 10-2.5 concentrations be developed over th e next four years so that a more satisfactory judgment can be made in the next review cycle,

Question 10: Indicator (sect ions 3.3.1, 3.3.2, and 3.3.3):

What are the Panel’s vi ews on the following:

a. The preliminary staff conclusion that it is appropriate to mainta in a standard that provides protection against all thoracic coarse particles, regardless of their source of origin or composition? This conclusion is justifiable at this tim e in view of the absence of data on the influence of coarse thoracic PM composition. While it is reasonable to not consider chemical composition in the current round of review of a coarse thoracic NAAQS, it is
essential that a suitable database for PM 10-2.5 concentrations and composition be developed over the next four years so that a more sa tisfactory judgment can be made in the next review cycle.

b. The appropriateness of maintaining an indicato r that allows lower PM 10-2.5 concentrations in urban areas than non-urban areas?

On the basis that PM 2.5 is higher in urban areas than ru ral areas, it will constitute a greater proportion of PM 10 in urban areas. Therefore, one can expect that for the same PM 10 concentration, that the concentration of PM 10-2.5 will be lower in urban areas. Thus, it is appropriate to maintain an i ndicator that allows lower PM 10-2.5 concentrations in urban areas
than non-urban areas.

c. The appropriateness of either a PM 10 or PM 10-2.5 indicator for a standard meant to protect against exposures to thoracic coarse particles?

While a PM 10-2.5 indicator for a standard meant to protect against exposures to thoracic coarse particles would be preferable, a PM 10 indicator would be an acceptable
substitute in this round of review.

29Question 11: Averaging Time (section 3.3.4): What are the Panel’s views on the prelimin ary staff conclusions that the currently available evidence supports maintaining a 24- hour standard to protect against health effects associated with short-term exposures to thoracic coarse particles, and does not support consideration of a long-term thoracic coarse particle standard? We agree.

Question 12: Form (section 3.3.6): What are the Panel’s views on the preliminary staff conclusion that it is appropriate to
consider a 98 th percentile form for a revised 24-hour standard meant to protect against short-term exposures to thoracic coarse particles? We agree.

Question 13: Level (section 3.3.7): What are the Panel’s views on the appropriateness of considering 98 th percentile, 24-hour PM 10 or PM 10-2.5 concentrations in epidemiological study locations for identifyin g a range of potential alternative standard levels for consideration, recognizing the more limited air quality information available for PM 10-2.5 ? We consider it to be appropriate.

30Comments from Dr. Phil Hopke

Question 5: Indicator (sect ion 2.3.1): What are the Pane l’s views on the following:

a. The preliminary staff conclusion that it is reasonable to retain PM 2.5 as an indicator for fine particles?

b. The preliminary staff conclusion that the currently available information is too limited to support a distinct PM st andard for ultrafine particles?

c. The preliminary staff conclusion that th e currently available information is not sufficient to support consid eration of a separate indicator for a specific PM 2.5 component or for the mix of fine particles fr om any specific source category, and that
data are too limited to consider eliminat ing any component or source category from the mix of fine partic les included in the PM 2.5 mass-based indicator?

These all represent self-fulfilling prophecies. Given the very limited number of measurements of PM1 or UFP, there is clearly no basis for ex tensive epidemiology and thus, no basis for an indicator. If we drop PM 10 and move to a coarse particle indi cator as the companion standard to PM2.5, it would really make more sense based on the nature of the atmospheric aerosol and the sources that would need to be controlled to provi de attainment of one or both sized standards to
switch from 2.5 μ m to 1 μ m (or possibly 1.5 μ m) as a better separation point and eliminate most of the tail from coarse particle sources penetrating into the fine particle indicator.

In spite of significant toxicological evidence of the role of UFP through the work of two PM centers, the Agency has been un willing to deploy adeq uate UFP monitors to provide the data needed for epidemiology. Thus, although it seems reasonable to assume some level of toxicity associated with these particles bey ond that which is directly relate d to their mass, there is no basis for setting an effective number based standard. At th e moment, there seems to be no indication that monitoring will be initiated in time for the data a nd epidemiological results to be available in the
next round of review. There is clearly a major disconnect be tween the laboratory results and
activities in the field that would permit an informed ba sis for deciding if an UFP standard were
needed.

We measure limited composition data, but with varyi ng relationships to observed health effects. There may be some “toxic” metals (Ni) in the PM, but we have no significant data on organic components and particularly on reactive organic com ponents. There will need to be an expanded, but targeted monitoring based on clearly defined hypotheses to develop initial composition – health effects links to begin to serious consider component specific

A bigger issue with respect to the indicator is the measurement me thod since PM mass is operationally defined. PM mass is defined by the sampling system, filter, and post-sample treatment process. This results in a precise re sult with totally unknown ac curacy. We now have continuous monitors that can provide a better measur e of the actual airborne particle mass. These measurements are almost uniformly higher than th e corresponding FRM mass. It would be useful to consider changing the FRM to a more direct, tim e resolved system that be tter reflects the actual
airborne mass concentrations.

31Question 6: Averaging Times (section 2.3.2): What are the Panel’s views on the following:

a. The preliminary staff conclusion that it is reasonable to retain annual and 24- hour averaging times?

b. The preliminary staff conclusions that the curr ently available evidence is too limited to support additional averaging times to address sub-daily exposures or seasonal exposures?

Again, we have only started to collect a reasonab le amount of more highly time resolved particle mass data. However, there may not be sufficiently well time marked health data to begin to look at whether shorter, higher exposures (peaks) are more important than the 24 hour average value that
are now available for health effects models. There are a few hints of short, high exposures inducing acute cardiac effects, but clearly we need far more data and analyses to permit the exploration of time intervals less than 24 hours. Thus, for the moment, we are stuck, but there should be more emphasis on using continuous mon itors and not forcing them to reproduce the known negative bias in mass measurem ents inherent in the FRM values.

Question 7: Forms (section 2.3.3): What are the Panel’s views on the utility of additional analyses to inform consideration of eliminating provisions included in the current form of the annual standard that allow for spatial averaging across monitors, specif ically with regard to the potential for disproportionate impact s on susceptible populations with lower
socioeconomic status?

Monitors are to be placed to provide population ex posure rather than exploring “hot spots.” Thus, it does not make sense to average values across an area since that provides an uneven level of protection to the populations that liv e in high versus low areas.

There should be consideration of looking at three y ears data together rather than on a year by year basis. The idea of averaging the 98 th percentile values determined fo r each of the three year period
does not make a lot of statistical sense. We sh ould be looking at the complete distribution of values measured in that three year period (ass uming an adequate number of samples in each period) to determine the 98 th percentile value.

Question 8: Levels (sect ions 2.3.4, 2.3.5, and 2.3.6):

What are the Panel’s vi ews on the following:

a. The preliminary staff conclusions regarding alternative standard levels that are appropriate for consideration, and the rational e upon which those conclusions are based?

b. The insights that can be gained from the qu antitative risk assessment to inform our understanding of the roles that the annual and 24-hour standards play in providing public health protection, specifically in focusing on simulations of estimated risks remaining upon just meeting alternative suit es of standards? (sect ions 2.3.4.2 and 2.3.5.2)

c. The policy implications of the uncertainties associated wi th estimating risks, including potential underestimation of risk, in reachi ng conclusions regardi ng standards that would provide public health protection with an adequate margin of safety?

d. A policy approach for identifying a suite of sta ndard levels in which the annual standard would be the “generally contro lling” standard to provide protection for both long- and

32e. Additional considerations that could inform ou r conclusions related to alternative suites of fine particle standards?

As noted above, the level cannot be separated from the measurem ent scheme since PM mass is NOT a fundamental property of the aerosol as de fined by the standard. The PM mass would be a fundamental property IF it included the particle -bound water. Thus, we have an operational
definition of “mass” that is known to have a significant negative bias resulting from the loss of semivolatile species (nitrate and SVOC ). It would be better to make it clear that there is such an interdependency and move toward mo re accurate measurement technologies. I find the evidence adequate to lowe r the levels somewhat (13 to 12 μ g/m 3 and 35 to 30 μ g/m 3 ) but I do not believe there is a strong basis from going below these values . Again an additional measure of protection would be af forded by moving to monitoring methods that do not have the known negative bias inherent in the current FRM approach.

Question 9: Adequacy of the current 24-hour PM 10 standard (Sect. 3.2):

What are the Panel’s vi ews on the following:

a. The preliminary staff conclusion that th e available scientific evidence supports maintaining a standard that provides protectio n against health effects associated with exposure to thoracic coarse particles?
b. The various approaches described for transl ating the evidence and related uncertainties
into the basis for conclusions on the adequacy of the current PM 10 standard?

c. The adequacy of the public health protection afforded by the current PM 10 standard against exposures to thoracic coarse particles?

There is certainly adequate evidence to suggest th e need for a standard to protect health against coarse particles. However, it is clear that PM10 is not adequate given the wide variation in the
PM2.5 to PM10 ratio.

Question 10: Indicator (sect ions 3.3.1, 3.3.2, and 3.3.3):

What are the Panel’s vi ews on the following:

a. The preliminary staff conclusion that it is appropriate to mainta in a standard that provides protection against all thoracic coarse particles, regardless of their source of origin or composition?

b. The appropriateness of maintaining an indicato r that allows lower PM 10-2.5 concentrations in urban areas than non-urban areas?

c. The appropriateness of either a PM 10 or PM 10-2.5 indicator for a standard meant to protect against exposures to thoracic coarse particles?

33The arguments in favor of retainin g PM10 as the indicator are unper suasive. It makes much more sense to measure coarse particles directly. There is currently a disparity in the level of protection afforded by the present standard depending on the na ture of the fine to coarse ratio in any given location. It does not appear to me that there is significantly less information on PM coarse now as
there was on PM2.5 in 1996 when we moved ahead with the new indicator. Thus, it is time to
move to a direct indicator of coarse PM. We have as much basis to set a PM coarse standard as we
did to set the initial PM2.5 standard and it is ti me to move away from a corrupted measure like
PM10.

Question 11: Averaging Time (section 3.3.4): What are the Panel’s views on the preliminary
staff conclusions that the cu rrently available evid ence supports maintaining a 24-hour standard to protect against health effects asso ciated with short-term exposures to thoracic coarse particles, and does not support consideration of a long-t erm thoracic coarse particle
standard?

Same arguments as made above regarding short term averaging periods can be made for the coarse particle indicator. We have no basis for looking at anything else and we need to initiate adequate
measurements of PM coarse on a continuous basis so that we can actually have the data to ascertain the adequacy of the va rious possible averaging times.

Question 12: Form (section 3.3.6): What are the Panel’s views on the preliminary staff conclusion that it is appropriate to consider a 98 th percentile form for a revised 24-hour standard meant to protect against short-term ex posures to thoracic coarse particles?

I suggest the same approach as noted above with respect to the form of the PM2.5 standard.

Question 13: Level (section 3.3.7): What are the Panel’s views on the appropriateness of considering 98 th percentile, 24-hour PM 10 or PM 10-2.5 concentrations in epidemiological study locations for identifying a range of potential alternative standard levels for consideration, recognizing the more limited air qu ality information available for PM 10-2.5 ?

There are no specific ranges discussed. At this point, it would make sense to do what was done
with PM2.5 and set a standard based on the smalle r end of the range of PM 10-PM2.5 differences to provide a first estimate on the st andard. Such a value will be similar to the protection offered by the PM10 standard, but will apply uniformly.

Question 14: Adequacy (section 4.2): What are the Panel’s views on the preliminary staff conclusion that the currently available informat ion clearly calls into que stion the adequacy of
the current suite of PM 2.5 standards to provide public welfa re protection from unacceptable levels of visibility impairment, primarily in urban areas, and suppor ts consideration of alternative standards to pr ovide appropriate protection?

I thought there was adequate justification for a vi sibility secondary standard in the last round and there remains a strong justification for setting such a standard particularly one based directly on measured light extinction. There is strong pub lic perception that environmental quality has degraded rather than improved as the data clearly demonstrate. Thus, visibility provides a graphic illustration of improved air quality and is a useful part of the improvem ent of the public welfare.

34Question 15: Indi cator (section 4.3.1) :

What are the Panel’s vi ews on the following:

a. The appropriateness of consideri ng PM light extinction and PM 2.5 mass as indicators for a distinct secondary PM standard for visibility protection, and the relative advantages and disadvantages asso ciated with each indicator?
b. The appropriateness of consid ering the contribution of co arse particles with respect to a potential PM light extinction indicator?

As indicated in the discu ssion of PM coarse, it is best to have an indicator that can be directly measured. Light extinction is a fundamental physical property of the ambient aerosol and thus, it represents a very appropriate indicator for a secondary visibility stan dard. The bulk of the extinction in the vast majority of locations is driven by fine particles (PM2.5). There are significant problems with the measurem ent of the light extinction from all particle sizes. Thus, the initial secondary standard should us e light extinction by PM2.5 particle s as the indicator. It could be possible to extend the size up to 4 to 5 μ m without extensive incr easing the measurement difficulty and that could provide some additional measure of protec tion to those locations that are more prone to high coarse particle mass concentrations.

Question 16: Averaging times (section 4.3.2): What are the Panel’s vi ews on the following:

a. The preliminary staff conclusion that consider ation should be given to a 1-hour averaging
time?

b. The advantages and disa dvantages of focusing on a 1- hour daily maximum or each 1- hour average concentration during all daylight hours?

At this point, there is no really sound scientific basis for picking an averag ing time. An hour is a reasonable starting point.

Question 17: Levels and Forms (section 4.3.3): What are the Panel’s views on the following:

a. The preliminary staff conclusions regarding ra nges of options with varying levels and
forms in combination with different indicators ( light extinction and PM 2.5 mass-based indicators) and averaging times (1-hour daily maximum or each 1-hour average concentration during all daylight hours)?
b. Additional approaches that could help inform our consideration of alternative levels and
forms?

The range of proposed levels is overly large. Ther e is no point in an alternative standard unless it is going to be significantly diff erent from the primary standard. Thus, the level should be set
within the lower third of the proposed range.

Question 18: Climate (section 5.2): What are the Panel’s views on the preliminary staff
conclusion that there is insufficient informat ion to base a standard on climate impacts
associated with current am bient PM concentrations?

35There are both cooling and warming effects of part icles as well as the indi rect effects related to cloud formation and brightening. At this point there are far too great uncertainties in the climate system and the role of particles to propose a standard with a strong scientific foundation.

Question 19: Ecological effects (section 5.3): What are the Panel’s views on the preliminary
staff conclusion that data are insufficient to support establis hing a distinct standard for ambient PM based on ecosystem effects not addressed in the ongoing NOx/SOx secondary NAAQS review?

In reviewing the Policy Assessment and the ISA, there does not seem to be adequate information
available to conclude that there is need for a separate standard to provide ecosystem protection. Thus, the staff conclusion appears justified.

Question 20: Material effects (section 5.4): What are the Panel’s vi ews on the preliminary
staff conclusion that no new evidence calls in to question the adequacy of the protection afforded by the current suite of PM standards, and that there contin ues to be support for retaining an appropriate degree of control for both fine and coarse particles to provide protection against materials damage and soiling?

Neither the ISA nor the Policy Assessment provides evidence to support the consideration of an alternative or new secondary standard to protect against materials degradation.

Other Comments On page 4-11, it says “The amount of light extin ction contributed by PM depends on the particle size distribution and composition, as well as its concentration.” However, particle shape also matters. Not all particles are spherical.

Please do not use “particulate” when you mean “particle”

36Comments from Dr. Robert Phalen

Regarding sections 2.3.1 (Indicator) and 2.3. 2 (Averaging Times), I have a few comments.

1. Both sections are well-written and ade quately thorough in describing the many
uncertainties in relation to the indi cator and averaging times for PM2.5.

2. It is clear that additional research is require d before specific components, and/or specific co-pollutant interactions, can be targeted for health-related policy assessments. For the present time, PM2.5 is the only feasible defau lt indicator for health-effect considerations. Sadly, this will place some U.S. regions at a disadvantage in protecting public health using a mass-based indicator (PM2.5).

3. Similarly, as the available health-associa ted data are robust for 24 hour and annual averaging times, the conclusion to retain these averaging times is appropriate.

4. The lucid discussions of the limitations and uncertainties associated with the indicator and averaging times, will be very helpful for stimulating the need ed research. The EPA staff has provided useful guidance in this respect.

5. As a minor editing suggestion, I would consider eliminating the word “strong” on line 6, pg. 2-70, as it conflicts with the lucid discussion of the limitations and uncertainties previously presented. This is not a st rong suggestion, but it should be considered.

37Comments from Mr. Rich Poirot

Overall, Chapter 4 of the Policy Assessment represents an excellent first draft presentation of justifications and policy options for setting seconda ry PM standards to protect visual air quality. While there are advantages to using an optical indicator (PM light extinc tion) and to using the single worst daylight hour for a regulatory metric, I think there are also certain advantages to using

a PM 2.5 mass indicator, and/or to considering effects in all daylight hours, and that plusses and
minuses associated with these various alternatives could be presented in a somewhat more balanced way.

14. Adequacy (section 4.2): What are the Panel’ s views on the preliminary staff conclusion that the currently available information clearl y calls into question the adequacy of the
current suite of PM 2.5 standards to provide public welf are protection from unacceptable levels of visibility impairment, primarily in urban areas, and suppor ts consideration of alternative standards to provi de appropriate protection?

The Policy Assessment does a good job of demons trating that current PM standards (for which 24-
hour PM 2.5 is most relevant) are not adequate for protec ting visibility in most, if not all sections of the country. Specifically, the levels of current PM 2.5 and PM 10 standards are too high and their averaging times are too long to guard against levels of visual air quality considered adverse, over the short (hour or less) time peri ods over which changes in visual air quality are perceptible. The
current mass-based indicators are also not ideal and could be made much more directly responsive to visibility effects by using a PM lig ht extinction indicator. An optional PM 2.5 mass indicator, applied over shorter daylight hourly averaging ti mes and at lower levels would be adequate, and would represent a substantial improvement over the current 24-hour and annual means.

A possible addition which might strengthen the chapte r in future drafts woul d be to show – with data examples – how extreme a 1-hour PM 2.5 mass concentration or 1-hour PM light extinction level could be on (a) day(s) when the 24-hour PM 2.5 mass concentration does not exceed the current 35 μg/m 3 standard. In addition, y ou might include some photographic illustrations – using actual haze cam photos or Winhaze images showing what visual air quality looks like at levels of the current standards (and at the higher 1-hour le vels that are possible w ithout exceeding the 24- hour average standards).

15. Indicator (section 4.3.1): What are the Panel’s views on the following:

a. The appropriateness of consideri ng PM light extinction and PM 2.5 mass as indicators for a distinct secondary PM standard for visib ility protection, and the relative advantages and disadvantages associated with each indicator?

The Policy Assessment does a good job of demons trating the appropriateness and benefits of a PM light extinction indicator, while show ing that a (daylight only, hourly) PM 2.5 mass-based indicator would also be adequate, and a substantial improve ment over the status quo. To a certain extent, arguments for use of a light extinction indicator can be st rengthened by emphasizing the shortcomings of a PM 2.5 mass-based indicator. However, I think the Policy Assessment could provide a somewhat more balanced view of some of the advant ages and disadvantages of both
alternative indicators.

38A PM light extinction indicator has the major obvious advantage that the indicator would essentially be the effect. PM light extinction is an actua l and measurable characteristic of particles in the atmosphere, which can be directly rela ted on the one hand to the size and composition (including aerosol water) of airbor ne particles which cause it, and on the other hand to the levels of visual air quality considered unacceptable by human observers. There are however also disadvantages to a PM light extinctio n indicator (and advantages to a PM 2.5 mass indicator) that could be presented more clearly in the Policy Assessment

.

A disadvantage of a PM light extinction indicator is that there is currently no monitoring network in place to assess compliance, nor have standard methods been developed which have been deployed in anything other than research-grade ap plications. At a minimu m, at least 2 separate instruments (nephelometer and aethalometer) would be required using currently available technology, and these will functio n best if coarse particles are excluded. Thus the measured indicator would actually be PM 2.5 light extinction, although this could be enhanced where need be
with measurements of and estimates of extinc tion from continuous PM 10-2.5 mass (requiring two additional instruments). Accurate RH measurements will also be more important for this indicator.

Conversely, there is already a large network of continuous PM 2.5 instruments in place that could be used immediately to assess compliance with an hourly PM 2.5 mass indicator, and the quality of that data – and its utility for assessi ng human health or other publ ic welfare effects – could be substantially enhanced by forcing cl oser scrutiny of the accuracy and precision on an hourly basis.

A PM 2.5 mass indicator would allow somewhat higher extinction in the more humid (and generally less scenic) East, and provide relatively better pr otection in the less humi d (and generally more scenic) West – which is not necessarily a disadvantag e. It would also tend to place relatively more emphasis on organic carbon and elemental carbon aerosols, which are more negatively associated with other public welfare (so iling and climate) effects, and which are also generally more influenced by local emissions than are the sulf ate and nitrate compounds which are emphasized by the PM light extinction indicator.

b. The appropriateness of consideri ng the contribution of coarse particles with respect to a potential PM light extinction indicator?

Since coarse particles make relatively minor contri butions to light extinction at most locations, and also present both measurement uncertainties as we ll as increased measurem ent maintenance needs, it may be reasonable to either:

• Exclude coarse particles from the regulatory metric (either re-name it “PM 2.5 light extinction” or keep the same name but exclude coarse particles from monitoring requirements) or,

• Add (either on an all-site ba sis, or at sites where PM 10 :PM 2.5 > X) continuous mass
measurements of PM 10-2.5 by the difference method, estimating the associated PM light extinction increment by multiplying by 0.6 m 2 /g as in the IMPROVE formula.

• Conceptually a similar treatment of PM 10-2.5 effects could be added to a PM 2.5 mass indicator, where the revised mass indicator might be something like PM 2.5 + 0.1 x PM 10-2.5

.

16. Averaging times (section 4.3.2): What are the Panel’s views on the following:

39a. The preliminary staff conclusion that consider ation should be given to a 1-hour averaging
time?

The one-hour averaging time (during daylight hours) is appropriate, given the nearly instantaneous nature of perceived impairment of visual air qu ality. At the same time , I think somewhat longer averaging times (of say 4 daylight hours) could also be justifie d for several reasons, including:

• To minimize the influence of measurement e rrors – which could be important if multiple monitors are used for an optical indicator, and also because some of the continuous PM 2.5 monitors produce “noisy” data over short 1-hour averaging times.

• To minimize the influence of short-term, loca lized meteorological extremes – such as the concurrence of high RH, low wind speed and low mixing heights on cold, clear winter mornings.

• To intentionally focus on visibility-impairing events which last for more than a few hours, and are arguably more objectionable, and effect more people, than events of short duration.

• To follow the reasoning used and precedents se t in locations like Denver and Phoenix where visibility standards have been established, and based on 4-hour averages in both cases.

b. The advantages and disa dvantages of focusing on a 1- hour daily maximum or each 1- hour average concentration during all daylight hours?

I much prefer a metric based on using all available daylight hours (combined with a higher percentile like 98 th ) over one based on only the single wors t daylight hour (combined with a low percentile like 90 th ) for several reasons:

• I think “sensitive” or “susceptible” are poor c hoices of terms for those who care so much about viewing scenery that they chose to work in windowless indoor environments, stay inside during lunch, and (returning home from their 8-hour shifts) fu rther choose not to go
outside or look out their window s during the other 2 to 6 hours of daylight that would be available, during 10 to 14-hour days in different seasons at a mid-latitude location in the US. Do they also stay inside and away from windows on weekends, holidays and vacations? I doubt these are the folks who indicate that only the very clearest leve ls are acceptable in the urban visibility preference studies.

• There’s an implied, but illogical assumption that the single worst hour will coincide with the one hour when the poor “shut-ins” ar e let outside, but th at often won’t occur. At best, you’re disregarding their views on either the to-work or from-work halves of their commutes. What if they work “9 to 5” (as many do), but the wo rst hour comes at 6 to 7 AM (or PM) or 7 to 8 AM or PM (as it often will), or in mid morni ng or mid afternoon, or what if they work the second or third shift? By considering only th e single worst hour, you are specifically not affording protection to all the non-shut-ins for most of the day, and providing no protection at
all for that fraction of the shut-ins whose hour outside doesn’t coincide with the worst hour of the day.

• It puts the maximum possible emphasis on uncontr ollable natural meteorological influences, including the convergence of maximum RH, minimum wind speed and lowest mixing height (along with whatever weather in fluences a 90% RH screen might miss) in the hour just after
sunrise.

• This early morning met effect will be most ex treme in mountain valley locations in winter, but these coldest, calmest winter days often offe r the best visibility later in the day when the

40inversion burns off (or at slightly higher elevat ions just above the inve rsion), so benefits of the extreme pollution controls needed to reduce pollutant concentrations at winter dawn, are likely to be spatially and temporally limited.

• There are not really any viable 1-hour control strategies – es pecially for the hygroscopic SO 4 and NO 3 species which are emphasized by the PM extinction indicator. Conversely, when only the single worst hour B ext is considered, there will be the most minimal knowledge of the pollutants and sources responsible.

• By emphasizing early morning RH and hygroscopi c species, it tends to emphasize East/West differences and deemphasize the importanc e of organic carbon and elemental carbon aerosols, which have other welfare effects such as on soiling and climate.

• For a PM light extinction indicator, m easurements might include nephelometer and aethalometer (preferably with PM 2.5 heads), plus an RH sensor , and could conceivably also
include continuous PM 10 and PM 2.5 mass at some locations to estimate coarse mass
extinction. That’s a lot of th ings that can potentially go wrong, for which a single worst hour/day measurement will be much more sensitive to measurement errors or failures in any
of the above than if a more robust metric based on all daylight hours were considered.

• It seems especially illogical when combined with a low percentile: “even a single bad hour will ruin my day, but I don’t mind a bit until it happens more than 37 days a year.”

17. Levels and Forms (section 4 .3.3): What are the Panel’ s views on the following:

a. The preliminary staff conclusions regarding ra nges of options with varying levels and
forms in combination with different indicators ( light extinction and PM 2.5 mass-based indicators) and averaging times (1-hour daily maximum or each 1-hour average concentration during all daylight hours)?

I think the ranges of options combining various le vels, forms, indicators and averaging times are reasonable, with focus on mid-range combina tions while considering modest upper and lower
bounds. For the PM 2.5 mass indicator, I think th e upper bound concentration levels considered (40 μg/m 3 and 60 μg/m 3 ) are rather unreasonably high and could be replaced in future drafts with smaller 5 μg/m 3 increment calculations within the range of 15 to 35 μg/m 3 . As indicated previously, I much prefer consid eration of all daylight hours, rather than focusing on the single worst hour, and would like to see a full set of calcu lations based on that metric for both the optical
and fine mass indicators included in th e next draft. Along similar lines, the Policy Assessment indicates (p. 4-44, lines 18, 19) an intended focu s on the more lenient 90 th and 95 th percentiles – which I think should specifica lly pertain only to the single wo rst hour/day indicator. Higher percentiles (95 to 98 th ) would be appropriate if all dayli ght hours are consid ered. I suggest rewording this to “... 90 th or 95 th percentile forms is appropriat e if based on the single worst daylight hour, while consideration of the 95 th or 98 th percentiles is more appr opriate if based on all daylight hours.”

Would it be possible to show estimates of what attaining the various hourly optical or PM 2.5 -based secondary standards would do to (or mean in te rms of) changes in annu al and 24-hour average

PM 2.5 levels in the test cities? Along similar lines, woul d it be possible to s how the “incremental
% reductions” in PM 2.5 that would be needed to, or associat ed with efforts to meet the various optical or PM 2.5 -based secondary standards after the current and proposed new primary PM 2.5 standards were first attained?

41I’ve become confused about the differences that would result if PM light extinction levels or PM 2.5 concentrations were rolled back to just meet standards based on single worst hour compared to using all hours (and a higher percentile). At any given level of PM light extinction or PM 2.5 mass, it would seem like rollback to attainment would produce similar results, since once the worst hour is “fixed”, the second worst hour takes precedence , and then the third, etc. until all hours above threshold are reduced – in which case, the single wo rst hour approach become s very similar to the all hours approach. Can this be explored/explained in more detail?

b. Additional approaches that could help inform our consideration of alternative levels and
forms?

As indicated above under Q 16a, I think a 4-hour averaging co uld be considered and justified, especially if the occasionally noisy PM 2.5 indicator is used. I think th e need for a 90 % RH screen becomes less urgent, and might possibly be dropped if a PM 2.5 indicator is used (see other comments on p. 4-44 below). It is definitely needed if an optical indicator is used, and consideration needs to be given to whether an hour would be eliminated if the average RH exceeds 90%, or if any or many (1-m inute) RH levels within the hour exceed 90%.

Because of measurement i ssues with coarse particle extinctio n, consideration might be given to using (and measuring) PM 2.5 light extinction as an indicator . Alternatively, measurements of
continuous PM 10-2.5 mass (by the difference method), combined with an assumed extinction efficiency of say 0.6 m 2 /g could be used to supplement PM 2.5 light extinction measurements – either at all sites or at sites with relatively hi gh coarse particle concentrations. Conceptually, coarse mass by difference could also be used to enhance a PM 2.5 mass indicator, using a relationship of something like PM 2.5 + 0.1 x PM 10-2.5 (assumes a generic PM 2.5 extinction efficiency
of about 6 m 2 /gram – which would represent ammonium sulf ate or nitrate at 66% RH – or a mix of these and organic matter at somewhat higher RH).

PM light extinction is an actual and measurable ch aracteristic of particles in the atmosphere, which can be directly related to the levels of visual air quality c onsidered unacceptable by human observers and to the size and composition (inclu ding aerosol water) of airborne particles which cause it. Given this, a level of a secondary standard could be selected, even in the absence of – or in advance of a monitoring netw ork to determine compliance. Along similar lines, a PM (or PM 2.5 ) light extinction standard could be set, and PM 2.5 mass measurements specified as an FEM to determine compliance – until such time as an appropriate PM light extinction measurement
network can be established.

As indicated in previous comments on the UFVA, a “progress-ba sed” attainment test rather than
the traditional “threshold-based” attainment test woul d be preferable from a sc ientific perspective. While the Agency has indicated this is not an option in the standard -setting process, it is something that could and should be considered in the impl ementation phase (where, for example, the Agency could provide guidance on what would be considered reasonable rates of progress). Possibly an illustrative example of how th is might work could be pr ovided in the next draft Policy Assessment

. I think it would be appropriat e if the next draft of the Policy Assessment included a section identifying and prioritiz ing key near-term monitoring and research need s. This could include things like establishing a small pilot urban visibility network to field-test and evaluate alternative PM light extinction measurement methods, an d should also include recommendations for

42additional visibility preference stud ies to better define levels (and/ or frequencies) of visual air quality considered acceptable over a wider range of locations and viewing conditions, to support
refinements and revisions to seconda ry PM standards in the future.

Other Comments on Chapter 4

P 4-5 line 23: You could add “m ost” at the end of the line.

P 4-5 lines 34-35: You could add “(all but one)” after “most CA SAC Panel members”.

P 4-15 lines 15-31: As indicated above, I’m not a fan of the single worst hour approach, and think
it’s a stretch to claim its needed to protect the most “sensitive” i ndividuals...since they are neither sensitive, nor does it protect them most of the time.

P 4-16, lines 15-23: This is generally true, but especially during the wint er. In warmer months (when people spend more ti me outdoors), RH still peaks at da wn, but morning rush hour occurs several hours later, nocturnal inversions are weaker, SO 2 plumes aloft don’t mix down until mid morning, and secondary fo rmation rates for sulfates and organi cs typically peak in mid-afternoon.

P 4-20 line 17: The “24.3 dv” level cited for the 50 th percentile acceptability response in Phoenix is
different from the “24.15 dv” 50% level for Phoenix in Table 4-1.

P 4-21 lines 16-31: You might al so add something like “It should also be noted that the current
version of the Winhaze model does not include clouds in the base photos. The visi bility of clouds and their contrast with the background sky would be sensitive to changes in light extinction, even in urban city scenes which otherwise lack distant objects in the background.”

P 4-22 line 13: You could add “and Eastern urban scenes with more distant vistas or with background clouds” after “...Western urban scenes.”

P 4-29 lines 9-13: As previously indicated, I think the argument to protect the “sensitive” shut-ins is not the strongest. Better arguments are the inst antaneous nature of the perceived visibility effect, and you might also add an illustration, based on data, showing how high a one-hour PM light extinction (or PM 2.5 mass concentration) could be on a day when the current 35 μg/m 3 secondary

PM 2.5 standard is not exceeded.

P 4-30 lines 21-32: Maybe you coul d set this point up a b it by zooming in from the concept of light extinction to PM light extinc tion (excluding Rayleigh and NO 2 ) – which I assume would be the preferred indicator. Then you mi ght consider but exclude the very small fraction of PM extinction from ultra-coarse particles (> 10 μm) – not be cause they contribute nothing, but because their
contribution is so minor. Then make the point that PM 10-2.5 particles also usually contribute very little (and their extinction effect is more difficult to measure), but can occa sionally be important. This might lead to an optional approach in wh ich “PM light extinction” could be the indicator,
measured as “PM 2.5 light extinction” in most areas, but with supplemental methods to estimate

PM 10-2.5 extinction in areas where coarse particles are important.

P 4-30 line 23: Change “many” to “may”.

43P 4-30 line 34: I think “one to two years” may be optimistic, and would co nstitute “rushing” with all of its various associated pitfalls.

P 4-31 line 2: Use of the term “promulgation/impl ementation” implies that the two things need to be concurrent, but I don’t think th ey need to be so. Conceivabl y, a PM light extinction standard could be promulgated, with an implementation period delayed until a future time period (perhaps to allow a reasonable time frame to develop, te st and deploy appropriate monitoring methods).

P 4-31 line 14: No space n eeded in “widespread”.

P 4-31 line 17: Add something like: “24-hour chemical composition data and” between “produce” and “hourly”, or otherwise correct this sentence.

P 4-31 line 19: Delete “produces”.

P 4-33 lines 1-4: Presumably the frequency of visibility-impairing “w eather” is very small, but not zero, when RH is less than 90%.. It might be informative to kno w that there may still be some
weather influence and that 90% RH is a reasona ble compromise, which e liminates most of the
weather events.

P 4-33, line 28: I think 60 μg/m 3 is a very extreme upper bound, a nd that its nearly impossible to
have PM extinction < 191 Mm -1 with PM 2.5 as high as 60 μg/m 3 (and extinction of 191 Mm -1 with

PM 2.5 of 40 μg/m 3 would be relatively rare as well) . In the entire IMPROVE network for the 5- year period from 2000 th rough 2004, there were 73,410 samples with reconstructed PM extinction
of less than 191 Mm -1 . None of these had PM 2.5 mass concentrations as high as 60 μg/m 3 , and only 2 samples and 9 samples (of 73,410) w ith reconstructed extinction < 191 Mm -1 had fine mass concentrations above 50 and 40 μg/m 3 respectively.

P 4-35, lines 8-9: As indicated before, I don’t bu y the logic that a focus on the worst one hour is needed to protect the “susceptible” shut-ins. For th is to be true, the single hour of poorest visibility would need to correspond to all the shut-ins’ hour outside.

P 4-36 line 4: Remove “could” or the “s” from “affords”. Also , I’m not sure that providing a uniform degree of visibility protection nationwide is such a great advantage. You could add to the end of this sentence “, although efforts to attain it would require substantially greater pollution control efforts in the humid East, where scenic vistas are typically more limited. By comparison, an “equally stringent” nationally uniform PM 2.5 mass indicator would allow somewhat higher levels of visibility impairment in the East, but would provide somewhat better visibility protection in dryer, and typically more scenic, Western urban areas.”

P 4-38: I don’t understand why, for Tacoma and Phoenix, there ar e changes from column a to b (90 th to 95 th percentiles) when both are below the 191 Mm -1 threshold?

P 4-41: This table - with the colo r-coding - is very helpful! Poss ibly future vers ions might focus on a more realistic range of say 35 to 15 μg/m 3 , with smaller (5 μg/m 3 ) increments between bins.

44Would there be a way to estimate the changes in and remaining concentrations of in 24-hr average

PM 2.5 mass that would result if these hourly levels (or the hourly B ext levels in Table 4.3-1) were
obtained? It will be a lot more work, but you shou ld include all the same calculations based on the
98 th percentile using all daylight h ours. Without these y ou will be stuck with illustrations that only apply to your (questionably ju stified) worst 1 hour metric.

P 4-42, lines 11-13: Although presumably there would be substantial overlap between the worst 10% fine mass days (hours) and the worst 10% B ext days (hours). Could this be explored?

P 4-43, line 21: Is there an intent to specifi cally emphasize “urban areas”, or could this be rephrased to “primarily in those rural, suburba n and urban areas which are not protected by the 1999 Regional Haze Rule”.

P 4-44 lines 18, 19: By focusing on the 90 th or 95 th percentile, it sounds like you’ve already made the (questionable) decision to use the single worst daylight hour. Otherwise, you could change this
to “... 90 th or 95 th percentile forms is appropriate if based on the single worst da ylight hour, while
consideration of the 95 th or 98 th percentiles is more appropriate if based on all daylight hours.”

P 4-44, line 19: Conceptually, a 90% RH screen could be used for the same weather-screening
reasons if a PM 2.5 mass, rather than a PM light extinction indicator was use d. As a practical matter, it may be less critical for a mass indicator for se veral reasons. Higher RH will tend to “push” hours into the high percentile light extinction bins, but not so for high PM mass hours. In fact any weather (rain, fog) concurrent with high RH is likely to push high PM hours toward lower PM percentiles. Also, with a PM 2.5 mass indicator, there’s no chance of requiring reductions in very low pollution concentrations that happen to concur with ex tremely high RH conditions, or of having any public perception, howe ver misguided, that EPA is tryi ng to regulate the weather.
There is also no benefit from or need to specifically exclude higher RH conditions from (dried)

PM 2.5 mass measurements, nor would errors in the RH sensor measurements have large influences on whether the “right” or “wrong” hours were excluded or include d from the regulatory metrics.

P 4-44 lines 29-30: I assume this is a typo an d that you meant to say “focus on a level of 20 μg/m 3 as well as levels down to 10 μg/m 3 and up to 30 μg/m 3 ”.

45Comments from Dr. Armistead Russell

Question 7: Forms (section 2.3.3): What are the Panel’s views on the utility of additional analyses to inform consideration of eliminating provisions included in the current form of the annual standard that allow for spatial averaging across monitors, specif ically with regard to the potential for disproportionate impact s on susceptible populations with lower
socioeconomic status?

I am not sure that there was suffic ient justification for spatial aver aging in the past, and do not see
that there is much reason to conti nue the practice. It is likely that a monitor with elev ated levels is being impacted with fresh emissions, and unless that monitor is directly adjacent to the source(s), there are areas with even higher levels. Further, those elevated levels may be due to a source whose emissions are more harmful than the regi onal background PM more evenly distributed across a city. Allowing spatial averaging could lead to a specific area being significantly and consistently adversely impacted beyo nd the region as a whole.

Question 10: Indicator (sect ions 3.3.1, 3.3.2, and 3.3.3):

What are the Panel’s vi ews on the following:

a. The preliminary staff conclusion that it is appropriate to mainta in a standard that provides protection against all thoracic coarse particles, regardless of their source of origin or composition? Agree.

b. The appropriateness of maintaining an indicato r that allows lower PM 10-2.5 concentrations in urban areas than non-urban areas? See below.

c. The appropriateness of either a PM 10 or PM 10-2.5 indicator for a standard meant to protect against exposures to thoracic coarse particles?

While the association of the obse rved health effects with larger particles is viewed as being only suggestive of a causal relationship, sufficient information is available to continue to have a standard that includes particles above 2.5 um. While certain sources may primarily emit particles that are found in the coarse size range (2.5-10 um), the tail of the size
distribution of those emissions contains PM in the sub-2.5 um range, and those particles presumably contribute to the observed h ealth effects in studies using either PM 10 or PM 10-

2.5 . Using a PM 10-2.5 indicator would allow dismissing how this tail contributes. Further, as
discussed in the Policy Assessment , using a PM 10 standard would address the (rather small amount of) evidence that urban coarse particle s appear to have greater health impacts than wind blown dust. The epidem iology can support either range, and controls aimed at controlling PM 10 (beyond those used to reduce PM 2.5 ) would reduce levels of PM 10-2.5 and vice versa. Given the above, a PM 10 standard would appear to be preferred. Question (b) should be rephrased as to allowing higher PM concentrations in non-urban areas.

Question 11: Averaging Time (section 3.3.4): What are the Panel’s views on the preliminary staff conclusions that the current ly available evidence su pports maintaining a 24-hour standard to pr otect against health effects associ ated with short-te rm exposures to thoracic coarse particles, and does not support consideration of a long-term thoracic coarse particle standard? Agree.

46Question 18: Climate (section 5.2): What are the Panel’s views on the preliminary staff
conclusion that there is insufficient informat ion to base a standard on climate impacts
associated with current am bient PM concentrations?

While there may be insufficient information to base a secondary standard on potential climate change, the current discussion does not adequately inform policy makers as to the potential that a standard limiting light extinction would do more ha rm than good. Th ere is sufficient information demonstrating that some aerosols lead to cooling, in particular aerosols that scatter visible light and can lead to increased/longer lived/more reflec tive cloud formation. The REA (based largely on other assessments) demonstrates that light scatte ring aerosols lead to a net decrease in radiative forcing, and while the uncertainty is significant, it suggests that the effect may be quite large. Further, there is sufficient evid ence that light absorbing aerosols can lead to warming. To go forward with a secondary standard based on reducing light extinction, the Policy Assessment needs to more directly weigh the potential dis- benefits of regional warming with improved visibility unless light absorbing aerosols are preferentially target ed. There may be significant regional heterogeneity to controls that would address a visibility-based seco ndary standard which should be addressed. For example, it is the areas that have the lo wer PM concentrations that may benefit most from maintaining/improving visib ility, but the areas with regionally high sulfate levels likely benefit most from th e reduced radiative forcing. At a minimum, EPA staff needs to address how a secondary standard might impact regional radiative forcing and climate, assess the uncertainties, and provide a reasoned analysis weighing the two issu es. Also, on Page 5-11, lines 10-11 and lines 31-31, it is noted that “aerosols that are warming are co-emitted with aerosols that are cooling.” While this is true to some degree in some cases, it skews one’s perception of the
actual case. Most of the warmin g aerosols in the US are emitted by biomass burning and internal engine combustion. Much of th e cooling aerosol is formed in the atmosphere by oxidation of SO2 or VOCs. Thus, a set of co ntrols to control warming PM w ould not necessarily have that much impact on cooling PM and vice versa. These statements should be modified.

Question 20: Material effects (section 5.4): What are the Panel’s views on the preliminary
staff conclusion that no new evidence calls in to question the adequacy of the protection afforded by the current suite of PM standards, and that there continues to be support for retaining an appropriate degree of control for both fine and coarse particles to provide protection against materials damage and soiling? Agree.

Minor:

P 5-22, l 13. Replace “imp ossible” with “difficult”

47Comments from Dr. Frank Speizer

Charge Question 3: A pproach (Section 2.1.3) Page 2.10-2.12: With regard to the weight given to the various approaches Staff appears to indicate that the lower level of the interquartile range for both the long term and short term empirical evidence should be considered, in spite of indicating no threshold. This may be absolutely the correct approach, but some furthe r discussion as to why this decision was made might be warranted. Indicate why not the 90 th or 95 th %tile level. What does “notably wider” mean in discussing confidence in tervals? How much wider? At what point do they cross zero? Page 2.12-13: In discussing the use of the risk es timates Staff indicates that the uncertainties are taken into account by considering the sensitivity of the “core” risk. May need to define “core” risk more explicitly. In addition it is not clear how th e two separate approaches are to be combined and whether the weighting of one over th e other will dominate or be the de termining factor. If I read it one way I might conclude that th e evidence based values will be used and th e risk assessment is simply a test of the sensitivity of reaching a conc lusion. Alternatively (a nd most likely) somehow
the use of the total info rmation will be used to reach a judgment.

Charge Question 4: Adeq uacy of current suite of PM 2.5 standards (Section 2.2)

a. Appropriateness and characterization of sets of studies. It would appe ar that the specific studies chosen are appropriate and there are n one other that need to be added. However, Figure 3.1 seems not to be adeq uately discussed in terms of the presentation of differences in weights to be put on any given set of studi es. (There are also some specific questions about the way the figure is presented). Clear ly the nature of the confidence intervals indicated in the figure provide as estimate of both the nature and size of each study. A more explicit indication on the figure as to which were single city vs multicity studies would be helpful. This w ould provide further evidence of why relying on the multicity studies seems justified. Specifically with re gard to the figure and characterizing the PM exposure there are some questions raised by what is in the figure. For example for a
number of the studies the Lo wer IQR value matches the lowe r bound of the Range. How
does this occur?
b. Page 2.34 The question of suscep tible groups seems to conclude with the standard group of older adults and children along with pre existin g cardiopulmonary diseases. The paragraph justifying lower SES is appropriate. However, no mention is made of diabetics (perhaps much of the data is post ISA, but not all). This is an important group, the data are at least as firm as some other groups, and it is a growin g issue in the face of the obesity epidemic. I would therefore suggest a brief discussion of the risk data and it be added to the list.

c. Use of risk assessment, judge correct. Page 2 .34, line 14: Minor point—top of page 2.37,
line 1: Not sure where the conclusion th at the WHI represented a “healthier cohort population” comes from. If I had noted it in the ISA I would have objected. These women were selected as post menopausal and thus we re aged ~45+. In th e ACS cohort I believe the lower bound age was 35 and th e cohort was probably of a generally higher social class, and in Six Cities it was a random sample of households and generally younger (and probably healthier). Before getting to the question of risk based consideration the several pages leading up to page 2.42 provide subs tantial evidence that the various studies considered demonstrate empirically that signifi cant and substantial health effects have been reported by multiple investigators at or just belo w the current standards. It would seem that

48the conclusion that the current standards are inadequate to protect the public and should be so stated before making the obvious concludi ng sentence on page 2.42, starting on line 5. In fact, it is an interesting c ontrast that one could take the position that since the current standards fail to protect the public and since th ere are not a lot of studies that show effects below the current standard levels, the very reas on for doing the risk assessment is to help the administrator find an appropriate level that includes a margin of safety (rather than simply trying to add the risk assessment inform ation to the empirical data to come to some “combined judgment” I admit this may just be semantics but because risk assessment carries the implication of uncertainty it would seem better to put it in to this context.
d. The argument used for justifying the relative contributions of the annual and 24 hour concentrations is logically presented and clearly stated by summarizing the results of table 2.2. and text on page 2.45. As we indicated in discussing the RA, although the conclusions would not have changed, we understood wh y IHD mortality was us ed but would have preferred Staff using Total Cardiovascular mo rtality. The problem is further complicated by trying to compare directly the results as presented in table 2.3 w ith table 2.2 where the
contrast is between the annual and the 24 hour. Since table 2.2 is IHD results and table 2.3 is cardiovascular and the magnitudes of effect are ~3-10 times larger for IHD the tables do not appear to be directly comparable. The ar gument as to why there is greater confidence
in the roll back estimates from where the annual standard is controlling than where the 24 hour is controlling is straight forward and clearly related to the differences in the volume of
data for each scenario from wh ich to make the estimates. (The argument presented on page
2.52 for the use of the 15 urba n study areas for estimating th e contrast between annual and 24 hour values is persuasive and provides the relative limitations of the sites as a fair assessment.)

e. With regard to the integration of the evidence presented in se ction 2.2.3, Staff is correct in asserting that “newly available information st rengthens the associations between ...” We also agree that there are significant public hea lth consequences at the current levels of the standard that justify consideration of lower sta ndards in the further. However, what is not
is this section is the fact that this is not different from the conclusions of the previous review, but only strengthened by additional data obt ained in the last five years. Remember
it was the Administrator that when outside the recommenda tion of both CASAC and Staff the during the last review. Fu rther without specifying the nature of the uncertainties that were reduced since the last review (page 2.54, line 30) the text does a disservice to the previous conlusions that the standards should have been lowered. What are the specific
uncertainties that have been lowered? What are the mechanisms th at were not known 5 years ago that are better articulated now? It is true that there are a greater suite of health effects, however, they do not meet a higher degree of certai nty and thus add little to the quantitative argument available at the last round. (One canno t avoid the obvious
conclusion that the Administrator in the last round simply ignored the available scientific data.)

Charge Question 5—Indicator

a. With regard to maintaining PM 2.5 Staff’s argument that the data have expanded over the last several years is correct. They are also correct in indicating th at in spite of there being significant advance in being able to be tter characterize both in terms of size, number (and perhaps chemistry) these latte r measures have generally not be applied

49sufficiently in health based research to be able to change the indicator (at least for the
fine fraction from the current one. Of PM 2.5

. b. With regard to Ultrafines (UFP) the data ar e certainly suggestive of health effects. Staff rightfully points out (Page 2.58, Paragrap h beginning line 25) there is currently no network of UFP samplers and thus only lim ited site-specific data sets. These data, however, are compelling and poin t to the need for the esta blishment of a network of samplers under some federal guidelines to po sition EPA to be more effective in making judgments on future particle standards.

c. With regard to speciation and sources perh aps the most important summary statement is that on Page 2.64, sentence beginning line 17, “...evidence not sufficient to support eliminating any component or source from the mix...” However, the suggestion that could find a specific component that might be eliminated is probably a wrong way to conceive of the problem. PM is obviou sly a summary measure of a mixture of both complex air chemistry and source components. The lik elihood of being able to identify or eliminate one of those components is small. More important is the use of this complex chemistry to more accurately id entify and label source s that need to be better controlled. Thus far the data point most specifically to oil burning and traffic pollution sources, and less conclusively to wood burning. This obvi ously is important information for considerations beyond the Standard to the im plementation phase. Rather than simply indicating that the wo rk to date does not justify expanding the Indicator to be more specific in terms of speciation, a more positive statement of the
sources could be made.

Charge Question 6--Averaging times

a. Agree with Staff’s position that the annua l and 24 hour average need to both be
retained as the standards.
b. Also agree that that there is insufficient in formation to consider a shorter than 24 hour average or a seasonal average at this time . However, there is mounting clinical evidence that short term exposures (substantia lly less than 24 hours) are associated with reversible cardiovascular changes. The degree that these changes either from acute or repeated exposures trigger significant advers e events or result in more sustained adverse effects is as present highly sugges tive, They certainly poi nt to the need to consider from a policy pers pective related to susceptib le groups how the 24 hours standard should be modeled to protect the population with a margin of safety. Are there additional analyses that could be done to inform the Administrator on the distributions of the frequencies at which any specific level of expos ure for , say up to 2 hours, would occur at specific le vels of the 24 hour standard?

Charge Question 7—Form The argument that there may be difference in the protective effects of a given standard based upon spatial averaging vs ‘community-wide air quality” recording the highest value only is sufficiently well presented to justify further analyses.

Charge Question 8—Level a-c. The rationale presented regarding alte rnative standard levels is well presented, although it is not clear ho w Staff intends will eventually focus of the which of the two very logical

50alternatives (range 13-10ug/m3, 30-35ug/m3 vs . 11-10ug/m3, 30-25ug/m3) will become the focus
of discussion in the second draft. Perhaps it would be useful for CASAC to weigh in more heavily on these alternatives. (Obviously, the latter provi des a greater degree of safety and is more consistent with an “adequate margin of safety” d. Clearly the idea that the alternative annual standard will shift the distribution of 24 hour measures is well presented. However, it is also we ll presented that “hot spots” would remain and it may be these very hot spots that put the most vulne rable parts of the population at greatest risk. Thus, it becomes appropriate to co ntinue to also regulate 24 hour levels, and thus logical to
consider and maintain an a lternative 24 hour standard.
e. Other considerations. B ecause one national standard may not deal effectively with the seasonal or spatial variations that might occur ( nor the potential localization of susceptible subpopulations at greater risk) it would seem more logical to consider more conservative levels for the standards. Are there additional analyses that could be undertaken to provide more quantitative estimates of the magnitude of the populations that would be left at risk for any given suite of standards? This might be one of the topics to be covered in the second draft of the Policy
Assessment

.

Charge Question 9 –Adequ acy of current 24 hour PM 10 standard.

a. Maintaining a Course Fraction particle standar d. If anything the evidence since the last review is stronger, although still only sugg estive that there are significant adverse
health effects associated with the thoracic course fraction. It would appear that uncertainty issues remaining relate mostly to either lack or sufficient numbers of
monitors from which to make appropriate statistical asso ciations and adequacy of spatial estimates of exposure, potential for co-pollutant effects (mostly separating the effects of fine particles from course particles) or difficulties in technically being able to carry out toxicological studies of eno ugh variety to provide a foundation for the potential mechanisms (differe nt from those that have already been confirmed for PM2.5). Clearly the public health concern re mains high (potentially related more to morbidity effects rather than mortality as evidenced by the relation to hospitalization and emergency room associations). Thus, in spite of the uncer tainties maintaining a thoracic course particle standard is warranted. Further to the degree that the associations reported are at least as significa nt as in the last round of review, and I believe they are even more suggestive, strengt hening the standard can also be defended.

Charge Question 10 Indicator. a-b. Appropriateness of maintaining a standard that protects against particles regardless of source of origin and composition. The answer to this question seems obvious. The issue is that the potential fraction of total course fraction that is combustion generated vs. dust generated may or may not be important. The wind blown dust stud ies that show impacts at far distances are suggestive that irrespective of source and thus po tential toxicity (from wh at we currently know) may not make as much difference. Therefore accepting that so me fraction of the PM10 may be related to the amount of combustion source (read PM 2.5) and thus a portion of the toxicity noted does not negate the importance of reducing total par ticles. Staff seems to be arguing that being
able to reduce PM10 from any source will work to the benefit of both urba n and rural sources. I think I agree with this, but it still would be worth while a full di scussion at CASAC.

51c. With regard to which measure (PM10 or PM10-2.5) is appropriate, I believe we will
need to discuss this fu lly. We cannot leave the question open to the Administrator to decide.
Therefore what we need is some estimates of e xposure fractions with wh ich to make a tentative judgment of what the altern atives would predict.

Charge Question 11—Averaging time

. Staff concludes that the 24 hour average provid es the best estimate of exposure to course fraction and is the exposure value with the most data suggesting an association. I would agree. It probably make the most biological sense and the suggestion that c ontrol of accumulated repeated 24 hour exposures would reduce the potential for longer term averaging time effects is reasonable.

Charge Question 12. Form.
Concur with the use of the 98 th percentile form averag ed over 3 years.

Charge Question 13—Level We currently have a promissory note that St aff will conduct some analyses of alternative
levels of the 24 hour standard for PM10 and PM10-2.5. More sp ecific criteria of a “stopping point” are needed. Will the lower bound be at 140,120, 100ug/m3 for PM 10, and if so on what
basis? For PM10-2.5 will it be at 75%, 60%, 50%, 40%, lower(?) of PM10 and on what basis? (If it were at all possible to see some of these analyses before the Draft 2 it would be useful to include in our discussion.) by in dicating that the focus will be on the upper end of the distributions of daily
PM will Staff will need to take into consideration the differen ces between total PM urban and rural and may have to run two sets of analyses to compare differences.

52Comments from Dr. Helen Suh

The first draft Policy Assessment is a good st art at presenting and discussing the policyrelevant issues in the review of the PM NAAQS. It is comprehens ive in its inclusion of relevant
evidence and risk based informat ion. The summaries (e.g., sec tions 2.3.6, 2.4, 3.2.2, 3.4) were particularly notable, as they were generally succinct and thoughtful, clearly and cogently presenting the staff conclusions. Other sections of the Assessment, howe ver, suffered from too much detail, seemingly recountin g much of information presente d in the ISA and REA. This rehashing of information obscured the key policy related issues a nd brought a lack of focus and clarity to the document. Further distillation and ti ghtening of the document is needed. While not yet written, the sections on “K ey Uncertainties and Needs for Further Research” (for both PM 2.5 and PM 10-2.5 ) are welcomed and important. These secti ons should certainly include discussions of PM composition, with respect to whether particulat e mass is the appropriate indicator. Finally, at its current length, the document would benefit from a chapter either at the beginning or end of the
Assessment that summarizes staf f conclusions for both the primar y and secondary standards.

Question 7: Forms (section 2.3.3): What are the Panel’s views on the utility of additional analyses to inform consideration of eliminating provisions included in the current form of the annual standard that allow for spatial averaging across monitors, specif ically with regard to the potential for disproportionate impact s on susceptible populations with lower
socioeconomic status?

The rationale to conduct additiona l analyses to assess whether sp atial averaging provisions should be eliminated is sensible and appropriate. Furt her, the consideration of alternate forms for the
annual PM 2.5 standard, specifically the highest community monitor level, is appropriate. However, the process by which such consid erations (and from this the appropriate st andard form) will be made is unclear and should be clearly set forth in the second Policy Assessment . In particular, the
second Policy Assessment should describe how likely regional and temporal variation in the comparisons and the relationship between highes t monitor levels and lo w SES populations was
considered.

c. Levels (sections 2.3 .4, 2.3.5, and 2.3.6): What are the Panel’s views on the following:

d. The preliminary staff conclusions regarding alte rnative standard levels that are appropriate for consideration, and the rationale upon which those conclusions are based?

The alternate standard levels to be consid ered and their rationale are appropriate.

e. The insights that can be gained from the qu antitative risk assessment to inform our understanding of the roles that the annual and 24-hour standards play in providing public health protection, specifically in focusing on simulations of estimated risks remaining upon just meeting alternative su ites of standards? (sections 2.3.4.2 and 2.3.5.2)

The quantitative risk asse ssment is a useful and illustrative tool to illustrate the impact of
alternative standards on health risk. The useful ness of the risk assessment to this process

53would be increased if the discussion of the risk assessment results were condensed even
further to focus on the major points.

f. The policy implications of the uncertainties associated wi th estimating risks, including potential underestimation of risk, in reach ing conclusions regardi ng standards that would provide public health protection with an adequate margin of safety?

As noted in discussions and comments from th e March 2010 meeting, the impacts of model choices on long- and short-term risk estimates should be expanded (perhaps on page 2-43, paragraph beginning on line 9), as this informa tion is central to determ inations of margin of safety. As an example, the potential under- (and/or over-) estimation of long-term mortality risks from reliance on C-R functi ons from Krewski et al. (2009) should be
discussed.

g. A policy approach for identifying a suite of standard levels in which the annual standard would be the “genera lly controlling” standard to pr ovide protection for both long- and short-term PM 2.5 exposures, in conjunction with a 24-hour standard set to provide supplemental protection against days with high peak concentrations associated with localized “hotspots” and ri sk arising from seasonal emission that might not be controlled by a national annual standard? (section 2.3.6)

The policy approach for identifying the suite of standard levels was well written and clear.

h. Additional considerations that could inform our conclusions related to alternative suites of fine particle standards? With regard to a margin of sa fety, it may be important to in clude a statement in the risk assessment consideration of results (page 2- 104) regarding the potential implications of model choices regarding under- or over-estimation of risks.

Review of the Primary Standard for Thoracic Coarse Particles (Chapter 3)

[As a general note, the chapter on thoracic coarse particle seems to be less formed and more preliminary than corresp onding sections for PM 2.5 .]

6. Form (section 3.3.6): What are the Panel’s view s on the preliminary staff conclusion that it is appropriate to consider a 98 th percentile form for a revised 24-hour standard meant to protect against short-term exposures to thoracic coarse particles?

This conclusion seems appropriate for practical reasons. However, it is not clear that the logic used to support a 98 th percentile form for NO 2 and PM 2.5 pertains to thoracic coarse particles given that the high end of the PM 10 concentration distribution may reflect higher
contributions of PM 2.5 and not PM 10-2.5 in many parts of the US . Although perhaps this issue can not be addressed, this uncer tainty should probably be mentioned.

54Comments from Dr . Sverre Vedal

Charge Question 1: Organizational structure.

a. Intro and Background

. These are well-organized and informative for both naïve and informed readers.

b. Questions posed

. All questions are appropriate - I can’t think of additional ones that would be useful.

c. Level of detail and focus

. The balance between too little and too much detail is good, in general. There is repetitiveness as parallel arguments are followed through in dealing with long-te rm and short-term exposure risks, but I think this is largely unavoida ble. The historical review in the coarse PM section (3-26 through 3-30) is perhaps too extensive.

Charge Question 2: Technical content.

a. ISA evidence and uncertainties

. The Policy Assessment adequately and faithfu lly summarizes the relevant points from the
ISA. I still maintain a mi nority opinion that the link be tween long-term exposure and cardiovascular disease is appropriately classified as causal but that with total mortality should be classified as likely causal (p. 2- 16, table 2-1). Regardless, the Policy Assessment is faithful to the last version of the ISA, which ha s the links with both car diovascular and total mortality classified
as causal. The section on susceptibility is somewhat poorly focused, incl uding a discussion of lung
function deficits in adu lthood (p. 2-27) of limited relevance. Also, studies of a single stratum of the population (e.g., post-menopa usal women, p. 2-28) that are unable to compare risk across different strata provide little evidence of e nhanced subgroup susceptib ility. The bottom line, however, is appropriate (p.2-29).

b. Risk assessment policy relevan t information and uncertainties

. As in by review of the RA, I take issue with the statement that the magnitude of both longterm and short-term risk depends primarily on annual-average PM 2.5 concentrations (p. 2-44, line 4 and p. 2-48). I know this is intended to refer to short-term effects being driven by concentrations in the middle part of the distribution, but th e statement as stands is not strictly correct.

Charge Question 3: Fine PM primary standard approaches (Section 2.1.3). Approach

.

EPA staff is using evidence- and risk-based a pproaches, as before, to guide consideration of the adequacy of the current standards and the c hoice of alternative standards. Both have their roles and are appropriate to use for these purposes. There is asymmetry in the way EPA staff us es evidence from long-term and short-term exposure studies in assessing protection afforded by the annual and 25-hour standards: evidence from long-term exposure studies is used only in assessing protection afforded by the annual standard (p. 2-10, line 18), whereas evidence from s hort-term exposure studies is used in assessing protection afforded by both the annua l and 24-hour standards (p. 2-11, line 10). Is there a rationale for also considering the evidence from long-term studies in assessing the 24-hour standard? It has

55been argued that it is the cumulativ e effect of repeated daily PM concentration increases that is responsible for the chronic effect of PM exposu re observed in long-term exposure studies (Brook RD, Rajagopalan S. Air pollution and cardiovascula r events. N Engl J Med 2007;356:2104-5). It is therefore possible that chronic eff ects could be better controlled th rough the 24-hour standard than
the annual standard.

The relative weighting

. I agree with using both the an nual and 24-hr standard together in providing protection against PM effects. The balance between ev idence- and risk-based approaches is fine.

Additional approaches ? None to suggest at this time.

Charge Question 8: PM 2.5 level.

a. Conclusions on alternative st andard levels and rationale

. I find the use of the 1SD below the mean or at the lower IQR to define annual mean concentrations of concern to be less appealin g that the use of “somewhat below the long-term mean” concentrations, although either is somewhat arbitrary. I know that we are to limit ourselves here to scientific considerations and ignore issues of feasibility and cost-ben efit, but as ever lower standards are being considered, this becomes more difficult.

b. Insights from the quantitative RA on annual and 24- hour standards, especially simulations of remaining risks with a lternative standards (sections 2.3.4.2 and 2.3.5.2)

. The quantitative RA results are very important. Th e information presented is very dense, for example, in detailing and contrasting effects in individual cities – but, I think this is preferable to being vague. The two scenarios used for a lternative 24-hour standards (13/30 and 12/25) may provide most of the information needed, but ad ditional options may be helpful unless it can be justified that they aren’t.

c. Policy implications of the unc ertainties in estimating risks

. Use of the LML rather than PRB as the lower level for estimati ng risk is appropriate, in my opinion.

d. Approach with annual standard “generally cont rolling” standard for both long- and short-term

PM 2.5 exposures (section 2.3.6)

. I believe the arguments made in favor of the annual standard as the controlling standard are well laid out and ultimately persuasive.

e. Additional considerations rela ted to alternative standards ?
It isn’t clear how the selected studies were chos en to be included in Fig. 2-4 (p. 2-91).

Charge Question 13: PM 10-2.5 level. Appropriateness of 98th %ile, 24-hour PM 10 or PM 10-2.5 in epi study locations fo r identifying range of standards, in light of limited monitoring data
for PM 10-2.5 (Section 3.37)? I am disposed to emphasizing the specific PM 10-2.5 indicator/measure in assessing level
rather than PM 10 . I find that the extent to which PM 10 reflects PM 2.5 (ie, more so in urban areas)

5657 may make it insurmountably problematic in using it for reviewing evidence and deliberating on the level of a standard to pr otect against effects of PM 10-2.5 . I remain open to attempts to accomplish that, however.