UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

WASHINGTON D.C. 20460

OFFICE OF THE ADMINISTRATOR

SCIENCE ADVISORY BOARD

June 26, 2014

EPA-CASAC-14-004

The Honorable Gina McCarthy

Administrator

U.S. Environmental Protection Agency

1200 Pennsylvania Avenue, N.W.

Washington, D.C. 20460

Subject: CASAC Review of the EPA’s Second Draft Policy Assessment for the Review of the 

Ozone National Ambient Air Quality Standards

Dear Administrator McCarthy:

The Clean Air Scientific Advisory Committee (CASAC) Ozone Review Panel met on March 25 - 27, 

2014, to review the EPA’s Second Draft Policy Assessment for the Review of the Ozone National 

Ambient Air Quality Standards, hereafter referred to as the Second Draft PA. This letter highlights the 

chartered CASAC’s consensus advice, followed by consensus responses to the charge questions from 

the Agency. Individual review comments from the CASAC Ozone Review Panel are also attached. 

Overall, the Second Draft PA is an excellent summary of information needed to judge the adequacy of 

the current National Ambient Air Quality Standards (NAAQS) for ozone and to consider alternative 

standards. The information on emissions, atmospheric chemistry and common patterns of ozone 

concentration is presented clearly and is appropriately characterized. “Background” ozone (i.e., ozone 

that originates from precursors from natural sources or anthropogenic international emissions) is 

extensively and appropriately characterized, although in our consensus responses to charge questions, 

we have some technical comments that should be addressed to improve the coverage of this issue. The 

Second Draft PA is not clear as to how background estimates might impact the primary and secondary

standards and whether these impacts may differ regionally. The Second Draft PA cites a 2002 court 

decision (American Trucking Associations, Inc. v. EPA, 283 F.3d at 379) that allows the EPA to 

consider relative proximity to peak background levels when evaluating alternative standards but it also 

cites a case where the court said “attainability and technological feasibility are not relevant 

considerations in the promulgation of the NAAQS” (American Petroleum Institute v. Costle, 665 F. 2d 

at 1185). The Second Draft PA was silent as to how the EPA intends to navigate between these two legal 

guidelines when considering background ozone in a policy and standard-setting context. This question 

became an important issue in the CASAC deliberations as we listened to public comments regarding 
high background levels in the intermountain Western United States.

In addressing the adequacy of the primary standard, the Second Draft PA presents scientifically sound 

information on the health effects evidence for each major effect category: lung function decrements, 

pulmonary inflammation, respiratory symptoms, respiratory morbidity and respiratory mortality. The 

CASAC finds scientific justification that current evidence and the results of the exposure and risk 

assessment call into question the adequacy of the current standard. Furthermore, there is clear scientific 

support for the need to revise the standard. The CASAC supports the scientific rationale presented in 

the Second Draft PA on these points. 

The CASAC concurs with the staff’s justifications in the Second Draft PA for retaining the current 

indicator (ozone), averaging time (maximum daily 8-hour average) and form (annual 4th highest 

maximum daily 8-hour average, averaged over three years) for the primary standard. The indicator of 

ozone is appropriate based on its causal or likely causal associations with multiple adverse health 

outcomes and its representation of a class of pollutants known as photochemical oxidants. The current 

8-hour averaging time is justified by the combined evidence from epidemiologic and clinical studies 

referenced in Chapter 4. The CASAC concurs that the ozone standard should be based on the fourth 

highest, daily maximum 8-hour average value (averaged over three years). This averaging time provides 

programmatic stability by allowing for atypical meteorological conditions that can lead to abnormally 

high ambient ozone concentrations while providing health protection. 

The CASAC further concludes that there is adequate scientific evidence to recommend a range of 

levels for a revised primary ozone standard from 70 ppb to 60 ppb. The CASAC reached this 

conclusion based on the scientific evidence from clinical studies, epidemiologic studies, and animal 

toxicology studies, as summarized in the Integrated Science Assessment (ISA), the findings from the 

exposure and risk assessments as summarized in the HREA, and the interpretation of the implications 

of these sources of information as given in the Second Draft PA. However, as noted below, we believe 

there is an important distinction in our finding and advice regarding the upper bound level of 70 ppb as 

compared to that of EPA staff as given in the Second Draft PA.

In reaching its scientific judgment regarding a recommended range of levels for a revised ozone 

primary standard, the CASAC focused on the scientific evidence that identifies the type and extent of 

adverse effects on public health. The CASAC acknowledges that the choice of a level within the range 

recommended based on scientific evidence is a policy judgment under the statutory mandate of the 

Clean Air Act. The CASAC advises that, based on the scientific evidence, a level of 70 ppb provides 

little margin of safety for the protection of public health, particularly for sensitive subpopulations. In 

this regard, our advice differs from that offered by EPA staff in the Second Draft PA. At 70 ppb, there 

is substantial scientific evidence of adverse effects as detailed in the charge question responses, 

including decrease in lung function, increase in respiratory symptoms, and increase in airway 

inflammation. Although a level of 70 ppb is more protective of public health than the current standard, 

it may not meet the statutory requirement to protect public health with an adequate margin of safety. 

In this regard, the CASAC deliberated at length regarding advice on other levels that might be 

considered to be protective of public health with an adequate margin of safety. For example, the 

recommended lower bound of 60 ppb would certainly offer more public health protection than levels of 

70 ppb or 65 ppb and would provide an adequate margin of safety. Thus, our policy advice is to set the 

level of the standard lower than 70 ppb within a range down to 60 ppb, taking into account your 

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judgment regarding the desired margin of safety to protect public health, and taking into account that 

lower levels will provide incrementally greater margins of safety.

With respect to the secondary standard, the CASAC concurs with EPA’s identification of adverse 

welfare effects related to ecosystem services, food and fiber products from crops, and damage to 

resource use from foliar injury. The CASAC concurs that tree species relative biomass loss, foliar

injury, and crop yield loss are appropriate surrogates of adverse welfare effects. The CASAC further 

supports the causality determinations of the ISA between exposure to ozone and adverse welfare

effects. The CASAC supports the scientific conclusion in the Second Draft PA that the current 

secondary standard is not adequate to protect against current and anticipated welfare effects of ozone 

on vegetation. We recommend retaining the current indicator (ozone) but establishing a revised form of 

the secondary standard to be the biologically-relevant W126 index accumulated over a 12-hour period

(8 a.m. – 8 p.m.) over the 3-month summation period of a single year resulting in the maximum value 

of W126 (henceforth W126). The CASAC recommends that the level associated with this form be 

within the range of 7 ppm-hrs to 15 ppm-hrs to protect against current and anticipated welfare effects 

of ozone. The CASAC does not support a level higher than 15 ppm-hrs. For example, at 17 ppm-hrs, 

the median tree species has 6% relative biomass loss, and the median crop species has over 5% yield 

loss. These levels are unacceptably high. These combinations of indicator, form, averaging time, and 

level are scientifically justifiable given evidence of current and anticipated welfare effects as captured 

in the Second Draft PA, and supported by the ISA and the second draft of the WREA. 

In reaching its scientific judgment regarding the indicator, form, summation time, and range of levels 

for a revised secondary standard, the CASAC has focused on the scientific evidence for the 

identification of the kind and extent of adverse effects on public welfare. The CASAC acknowledges 

that the choice of a level within the range recommended based on scientific evidence is a policy 

judgment under the statutory mandate of the Clean Air Act. Specifically, the Clean Air Act grants

discretion to the Administrator to specify a standard that is “requisite to protect the public welfare from 

any known or anticipated adverse effects associated with the presence of [the] pollutant in the ambient 

air” (Section 302(h), 42 U.S.C., §7602(h)). As a policy recommendation, separate from its advice 

above regarding scientific findings, the CASAC advises that a level of 15 ppm-hrs for the highest 3-

month sum in a single year is requisite to protect crop yield loss, but that lower levels provide 

additional protection against crop yield loss. Furthermore, there are specific economically significant 

crops, such as soybeans, that may not be protected at 15 ppm-hrs but would be protected at lower 

levels. A level below 10 ppm-hrs is required to reduce foliar injury. A level of 7 ppm-hrs is protective 

of relative biomass loss for trees and offers additional protection against crop yield loss and foliar 

injury. Therefore, 7 ppm-hrs is protective of ecosystem services. Thus, lower levels within the 

recommended range offer a greater degree of protection of more endpoints than do higher levels within

the range.

The CASAC does not recommend the use of a three-year averaging period for the secondary standard. 

We favor a single-year period for determining the highest three-month summation which will provide 

more protection for annual crops and for the anticipated cumulative effects on perennial species. The 

scientific analyses considered in this review, and the evidence upon which they are based, are from 

single-year results. If, as a policy matter, the Administrator prefers to base the secondary standard on a 

three-year averaging period for the purpose of program stability, then the level of the standard should 

be revised downward such that the level for the highest three-month summation in any given year of 

the three-year period would not exceed the scientifically recommended range of 7 ppm-hrs to 15 ppmiii
hrs. For example, if in a three-year period the highest three-month summation during a one year period

is 15 ppm-hrs, and the corresponding lowest value associated with a three-year average of the highest 

three-month summations in each year is 13 ppm-hrs, then the appropriate level for the three-year 

average would be 13 ppm-hrs to protect against a peak one year level of 15 ppm-hrs. The final Policy 

Assessment should quantify the ratio of the three-year average of the highest three-month summations 

in each year to the highest three-month summation in the highest year. This ratio should be used to 

determine what downward adjustment from the three-month summation in one year recommended here 

is needed if a three-year form is selected.

The CASAC recommends that EPA facilitate research needed for the next review of the ozone NAAQS. 

For the health-based standard, we note that the Second Draft PA outlines key uncertainties and research 

that needs to be addressed for future reviews of the health-based standards. Specifically, we underscore 

the need for research to address the characterization of the exposure-response function; the identification 

of population thresholds; the role of co-pollutants and temperature in modifying or contributing to ozone 

effects; alternative modeling specifications; population-based information on human exposure for at-risk 

populations; time-activity data to improve population-based exposure and risk assessment; and the 

characterization of background levels. 

For the secondary standard, the Second Draft PA also identifies uncertainties and needed research to 

develop data and better methods for extrapolating results to plant species for which exposure-response 

functions have not been developed; assessing the effects of ozone on climate (and the effects of climate 

on ozone); characterizing the effects of ozone on whole ecosystem structure and function; and 

evaluating how the public judges the adversity of various kinds of ecological effects including foliar 

injury and estimated reduced tree biomass growth. This policy-relevant research could be conducted in 

collaboration with other federal and non-governmental organizations to improve our understanding of 

ozone effects in support of the next review of the ozone NAAQS. 

While these scientific research priorities will enhance future scientific reviews of the ozone primary and 

secondary standards, we also make clear that there is sufficient scientific evidence, and sufficient 

confidence in the available research results, to support the advice we have given above for this review 

cycle of the primary and secondary standards.

Although CASAC was not asked to comment about international transport of ozone, we would like to 

call your attention to this issue as a matter separate from our advice regarding the standard. North 

American background ozone is defined by the EPA as the ozone that would be present in U.S. surface 

air in the absence of North American anthropogenic emissions. North American background ozone can 

be estimated using global models by conducting simulations with North American anthropogenic 

emissions set to zero. Results indicate that background is only partly natural (lightning, biosphere, fires, 

stratospheric influence) and is enhanced by anthropogenic sources outside North America. Estimates of 

this external anthropogenic enhancement are fairly consistent across models [Fiore et al., 2009]. Zhang 

et al. [2011] estimated that during spring-summer 2006-2008 the mean enhancement from 

intercontinental pollution and anthropogenic methane is 9 ppb at low-altitude sites and 13 ppb at highaltitude sites (>1,500 m elevation), both roughly one third of the North American background ozone in 

the respective areas. The authors also indicated that the background ozone is higher than average when 

ozone concentrations exceed 60 ppb, particularly in the intermountain West. There is currently no 

international legal agreement on ozone or its precursors that would effectively deal with long-range 

transport, despite the recommendations by the National Academy of Sciences (2009) and the Task Force 

iv
on Hemispheric Transport of Air Pollution (2010) that such an agreement be sought. Given the 

significant portion of ozone coming from anthropogenic sources outside North America, the CASAC 

recommends that EPA seek opportunities for international cooperation to reduce long-range transport of 

ozone. 

During the course of the review of the Second Draft PA, the CASAC received public comments focused 

on costs and implementation issues associated with a possible revised ozone standard, mainly focused 

on the primary standard. Whitman vs. American Trucking Associations, Inc. (2001) decreed that the EPA 

cannot consider implementation costs in setting the NAAQS. Furthermore, “[a]ttainability and 

technological feasibility are not relevant considerations in the promulgation of national ambient air 

quality standards” (American Petroleum Institute vs. Costle, 665 F. 2d at 1185) and EPA need not tailor 

the NAAQS to fit each region or locale. Thus, cost and implementation issues are not relevant or 

allowable considerations in setting or revising a NAAQS. Therefore, CASAC did not consider such 

issues in its scientific review of the current standards or in developing its advice regarding revising the 

standards. However, the CASAC acknowledges that the Clean Air Act, section 109(d), states that the 

CASAC shall “advise the Administrator of any adverse public health, welfare, social, economic, or 

energy effects which may result from various strategies for attainment and maintenance of such national 

ambient air quality standards.” Separate from the standard-setting process, the CASAC would be 

receptive to a request from EPA to review EPA analyses of “adverse public health, welfare, social, 

economic, or energy effects which may result from various strategies for attainment and maintenance of 

such national ambient air quality standards” (42 U.S. Code § 7409). It should be noted, however, that 

not all of these effects will be “adverse” and any comprehensive assessment would include both adverse 

and beneficial effects. For example, positive economic effects accrue from implementation of national 

ambient air quality standards, such as the economic benefit of avoided morbidity and mortality. In 

response to such a request, the SAB Staff Office would form an ad hoc CASAC panel to obtain the full 

expertise necessary to conduct such a review.

The current approach to review and revision of the primary NAAQS is based on a one-pollutant-at-atime approach. As the state of science regarding the joint effects of human exposure to multiple 

pollutants improves, the EPA should consider how review and revision of the NAAQS can be done 

synergistically for logical, scientifically relevant groupings of criteria pollutants. For example, O3 and 

NO2 are both criteria pollutants that are inter-related via atmospheric chemistry, and human exposure to 

these pollutants is often in the form of a mixture that includes both, and other pollutants such as 

particulate matter. The National Research Council and the North American Research Strategy for 

Tropospheric Ozone have both made detailed recommendations for multipollutant approaches to air 

quality management, and EPA has been exploring a multipollutant approach for the secondary standards 

for SOx and NOx. CASAC encourages EPA to explore multipollutant approaches for review of the 

primary standards, and would be receptive to a request by EPA to review planning or methods 

documents for such approaches.

Overall, we find the Second Draft PA to be adequate for its intended purpose of providing a strong 

scientific basis for findings regarding the inadequacy of current primary and secondary ozone air quality 

standards; for scientifically justifiable indicators, averaging times, and forms for alternative revised 

primary and secondary standards; and for our advice regarding scientifically justifiable ranges of levels 

for each of the primary and secondary standards. The CASAC appreciates the opportunity to provide 

advice on the Second Draft PA and looks forward to receiving the agency’s response.

v
Sincerely,

/signed/

Dr. H. Christopher Frey, Chair

Clean Air Scientific Advisory Committee

Enclosures

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NOTICE

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

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

scientific information and advice to the Administrator and other officials of the EPA. The CASAC 

provides balanced, expert assessment of scientific matters related to issues and problems facing the 

agency. This report has not been reviewed for approval by the agency and, hence, the contents of this 

report do not necessarily represent the views and policies of the EPA, nor of other agencies within the 

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

products does not constitute a recommendation for use. The CASAC reports are posted on the EPA 

website at: http://www.epa.gov/casac.

vii
U.S. Environmental Protection Agency

Clean Air Scientific Advisory Committee (CASAC)

CHAIR

Dr. H. Christopher Frey, Distinguished University Professor, Department of Civil, Construction 

and Environmental Engineering, College of Engineering, North Carolina State University, Raleigh, 

NC and Visiting Professor, Department of Civil and Environmental Engineering, Adjunct 

Professor, Division of Environment, Hong Kong University of Science and Technology

MEMBERS

Mr. George A. Allen, Senior Scientist, Northeast States for Coordinated Air Use Management 

(NESCAUM), Boston, MA

Dr. Ana Diez-Roux, Dean, School of Public Health, Drexel University, Philadelphia, PA

Dr. Jack Harkema, Professor, Department of Pathobiology, College of Veterinary Medicine, 

Michigan State University, East Lansing, MI

Dr. Helen Suh, Interim Chair, Director of Population Health Doctoral Program, Department of 

Health Sciences, Northeastern University, Boston, MA

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

Dr. Ronald Wyzga, Technical Executive, Air Quality Health and Risk, Electric Power Research 

Institute, Palo Alto, CA

SCIENCE ADVISORY BOARD STAFF

Mr. Aaron Yeow, Designated Federal Officer, U.S. Environmental Protection Agency, Science 

Advisory Board (1400R), 1200 Pennsylvania Avenue, NW, Washington, DC 20460

viii
U.S. Environmental Protection Agency

Clean Air Scientific Advisory Committee

Ozone Review Panel

CHAIR

Dr. H. Christopher Frey, Distinguished University Professor, Department of Civil, Construction 

and Environmental Engineering, College of Engineering, North Carolina State University, Raleigh, 

NC and Visiting Professor, Department of Civil and Environmental Engineering, Adjunct 

Professor, Division of Environment, Hong Kong University of Science and Technology

CASAC MEMBERS

Mr. George A. Allen, Senior Scientist, Northeast States for Coordinated Air Use Management 

(NESCAUM), Boston, MA

Dr. Ana Diez-Roux, Dean, School of Public Health, Drexel University, Philadelphia, PA

Dr. Jack Harkema, Professor, Department of Pathobiology, College of Veterinary Medicine, 

Michigan State University, East Lansing, MI

Dr. Helen Suh, Interim Chair, Director of Population Health Doctoral Program, Department of 

Health Sciences, Northeastern University, Boston, MA

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

Dr. Ronald Wyzga, Technical Executive, Air Quality Health and Risk, Electric Power Research 

Institute, Palo Alto, CA

CONSULTANTS

Mr. Ed Avol, Professor, Preventive Medicine, Keck School of Medicine, University of Southern 

California, Los Angeles, CA

Dr. Michelle Bell, Professor, School of Forestry and Environmental Studies, Yale University, New 

Haven, CT

Dr. Joseph D. Brain, Cecil K. and Philip Drinker Professor of Environmental Physiology, 

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

Boston, MA

Dr. David Chock, Independent Consultant, Bloomfield Hills, MI

Dr. David A. Grantz, Department of Botany and Plant Sciences, University of California at 

Riverside, Kearney Agricultural Center, Parlier, CA

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Dr. Daniel Jacob, Professor, Atmospheric Sciences, School of Engineering and Applied Sciences, 

Harvard University, Cambridge, MA

Dr. Steven Kleeberger, Professor and Lab Chief, Laboratory of Respiratory Biology, National 

Institute of Environmental Health Sciences, National Institutes of Health, Research Triangle Park, 

NC

Dr. Frederick J. Miller, Independent Consultant, Cary, NC

Dr. Howard Neufeld, Professor, Department of Biology, Appalachian State University, Boone, 

NC

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

Georgia Institute of Technology, Atlanta, GA

Dr. James Ultman, Professor, Chemical Engineering, Bioengineering Program, Pennsylvania 

State University, University Park, PA

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

School of Public Health, University of Washington, Seattle, WA

Dr. Peter Woodbury, Senior Research Associate, Department of Crop and Soil Sciences, College 

of Agriculture and Life Sciences, Cornell University, Ithaca, NY, U.S.A.

SCIENCE ADVISORY BOARD STAFF

Dr. Holly Stallworth, Designated Federal Officer, U.S. Environmental Protection Agency, 

Science Advisory Board (1400R), 1200 Pennsylvania Avenue, NW, Washington, DC 20460

x
CASAC Consensus Responses 

to Charge Questions

On the Second Draft Policy Assessment

for the Review of the National Ambient Air Quality Standards for Ozone

Introduction (Chapter 1)

1. Does the Panel find the introductory and background material (sections 1.1 and 1.2) to be 

appropriately characterized and clearly communicated?

This chapter is an excellent introduction to the legislative requirements of the Clean Air Act as they 

apply to ozone. It also provides an excellent history of the standard-setting process; Table 1-1 does a 

good job summarizing the different NAAQS that have been set historically. The historical review of 

legal challenges to previous decisions and their eventual outcomes is well done. The chapter clearly 

delineates the scope and approach for the Second Draft PA. This review is especially informative about 

the ruling by the U.S. Court of Appeals for the District of Columbia concerning the failure of the 

CASAC to be clear in its recommendations on “whether it was providing scientific or policy 

recommendations....” which led to retention of the 75 ppb standard instead of a standard between 60 

and 70 ppb. 

2. In section 1.3, we describe the general approach for the review. This includes the key aspects of the

approach employed in the last review in judging the adequacy of the then-existing standards and in

selecting revised standards. Does the Panel find this description of the approach in the previous

review adequate and clear? Does the summary of the approach in the current review appropriately

describe important considerations in this review?

Sections 1.3.1 through 1.3.1.2 clearly delineate the Administrator’s stated rationale for lowering the 

NAAQS in 2008 based on the weight of the evidence at that time. The process by which this decision 

was made is explained in a clear and lucid manner. Figure 1-1 is an excellent flow diagram that 

establishes the basis for the Second Draft PA on the primary standard. The description of the five-point 

hierarchical weight of evidence classifications and how they are used in the Second Draft PA (e.g., 

greatest weight placed on those effects deemed to be caused, or likely to be caused, by ozone) is clearly 

explained. The fact that the Second Draft PA focuses on at-risk populations for which the evidence is 

“adequate” is also made clear (see page 1-21). Stressed throughout is the EPA’s concern about the 

uncertainty and likelihood of ozone effects at lower exposures, which is important for setting a lower 

end to the recommended range for the NAAQS. How the EPA deals with this type of uncertainty is very 

well explained throughout this chapter and the rest of the Second Draft PA.

How the EPA deals with controlled human exposure studies and epidemiologic studies is well 

delineated. There is considerable discussion about the possible existence of threshold effects, with the 

EPA concluding that there is no evidence for a sharp break point between exposures of 80 and 60 ppb. 

There is an extensive discussion of how the welfare risks were evaluated in previous reviews (section

1.3.2.1) and why in the last review the secondary standard was set equal to the primary standard, even 

though the CASAC had recommended a different form and level from the primary standard (i.e., a 

cumulative exposure index, the W126; pg 1-30). The discussion of the weight of the evidence and how 

it was considered in the Second Draft PA is quite understandable and well written.

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In several places (e.g., page 1-27, lines 7-10; page 1-36, lines 24-27) the document states that at low 

W126 exposures, the “magnitude of the response becomes increasingly uncertain.” This statement is

misleading; the exposure-response functions for seedlings of some tree species definitely show growth 

losses (decrements) at chronically low exposure levels, whereas other species show decrements only at 

higher exposures. Crop species show a similar range of responses. For both crop and tree species, there 

is strong evidence of adverse effects on common, ecologically and economically important species at 

exposure levels at and below 7 ppm-hrs (W126).

Overall, this is a well written introduction which sets the stage for the rest of the Second Draft PA.

Ozone Monitoring and Air Quality (Chapter 2)

1. To what extent does the Panel agree that the most relevant information on monitoring (section

2.1), emissions and atmospheric chemistry (section 2.2), and common patterns of O3 

concentrations (section 2.3) is presented, and to what extent is the information presented 

appropriately characterized and clearly communicated?

Chapter 2 is concise and well written. In sections 2.1 to 2.3, the discussions of monitoring, atmospheric 

chemistry and ozone patterns are well done. The chapter focuses primarily on the issues involving 

background ozone, which is an appropriate discussion, but it should further discuss the response of 

lower level ozone to controls (e.g., as an extension of the section on atmospheric chemistry or as a 

stand-alone section). As shown in the Second Draft HREA, this is a very important consideration. The

Second Draft PA should be clear that controls designed to reduce the peak levels of ozone (e.g., the 4th 

highest annual MDA8) may not be effective at reducing lower levels of ozone on more typical days and 

may actually increase ozone levels on days where ozone concentrations are low. The EPA should 

consider showing the meteorologically adjusted ozone levels in the figures. 

2. With regard to information on estimating O3 concentrations associated with nonanthropogenic sources or “background O3” (section 2.4), to what extent is this information 

appropriately characterized and clearly communicated?

The discussion of background ozone is extensive and generally clear though some pieces are missing. 

First, the method by which the various backgrounds are calculated or taken into account (e.g., models 

used) should be further described, and the uncertainties discussed. This section should discuss how the 

background might impact various standards (both health and welfare-based) and how that might differ 

regionally. The discussion of the source apportionment model estimates is too minimal to really 

understand what is being done and its importance is not evident; consequently, it should be moved to the 

appendix. The issues of using monitoring to estimate background should be discussed. 

There appears to be confusion in the proper use of the zero-out approach. On p. 2-12, lines 23-26, and 

again on p. 2A-7, lines 231-241, the Second Draft PA indicates that removing NOx emissions completely 

and unrealistically could lead to inflated estimates of background ozone in urban areas where NOx

titration of ozone is significant. The authors consider this a paradoxical result of the zero-out approach. 

It is not apparent what is meant by paradoxical in this case as the behavior is well known, and is part of 

the non-linearity in ozone chemistry (see above suggesting a further discussion of the increase in lower 

ozone levels from controls). Furthermore, the authors ran separate Community Multi-scale Air Quality

(CMAQ) model runs for base case (designated as total), natural background (NB), North American 

Background (NAB) and United States Background (USB), and then took the ratios of one of the 

2
background runs to the base case runs as the percent contribution of the background to the base case. 

This is inappropriate because it assumes ozone additivity; however, ozone chemistry is nonlinear. The 

zero-out approach is not intended for use in assigning relative contributions, and relative contribution is 

not a meaningful concept unless the perturbation due to some source emissions is small enough that 

linearity can be approximated. Based on the above discussion, in the case of the zero-out approach, it is 

best to change the text in the chapter from “percent contribution” (like in Fig. 2-11 on p. 2-18) to “ratio” 

when the background ozone is compared to the base case ozone. 

Adequacy of the Primary Standard (Chapter 3)

1. To what extent does section 3.1 (Evidence-based Considerations) capture and appropriately 

characterize the key aspects of the evidence assessed and integrated in the ISA? To what extent is

staff’s consideration of the health effects evidence, including the adversity of reported respiratory

effects and public health implications technically sound and clearly communicated at an

appropriate level of detail? In the Panel’s view has the information been appropriately interpreted

for the purpose of assessing the adequacy of the current standard?

Section 3.1 captures the important studies discussed in the ISA and integrates them into a logical 

narrative to summarize the important findings in each of the major effect categories: lung function 

decrements, pulmonary inflammation, respiratory symptoms, respiratory morbidity, and respiratory 

mortality. The adversity of the effects and their implications for public health are discussed in a 

straightforward and clear manner that leads the reader through the body of data. 

The CASAC notes that Figure 3.1, which is intended to illustrate mode-of-action, does not present a 

logical sequence of steps leading to specific endpoints. The discussion of mode-of-action could be 

more clearly communicated as it has been in the Appendix. Various specific technical comments 

are included in individual panel member comments. In some cases, individual panelists suggest 

changes in the wording or thrust of some of the sentences and paragraphs. One such example is the 

discrepancy between epidemiological studies supporting anti-oxidants being partially protective of 

ozone-induced lung function decrements and controlled human studies showing no such protection. 

The CASAC concurs with the findings of the Integrated Science Assessment, as summarized in the 

Second Draft PA, pertaining to the scientific evidence of the kinds of identifiable effects on public 

health that are expected from the presence of ozone in the ambient air. 

For public health, these effects are health outcomes from short-term exposure to ozone that include 

respiratory effects, cardiovascular effects, central nervous system effects, and total mortality. Of 

these, the scientific weight of evidence of a causal relationship between short-term exposure and 

adverse effect is “causal” for respiratory effects, “likely to be causal” for cardiovascular effects and 

total mortality, and “suggestive of a causal relationship” for central nervous system effects. Given 

the stronger weight of evidence for several of these endpoints, EPA has appropriately focused its 

assessments of short-term exposure levels of concern to those most related to respiratory and 

cardiovascular effects, and its assessments of risk based on epidemiologic studies to mortality from 

short-term exposures. In the context of exposure and risk assessment, the CASAC concurs that 

estimation of FEV1 decrements of ≥15% is appropriate as a scientifically relevant surrogate for 

adverse health outcomes in active healthy adults, whereas an FEV1 decrement of ≥10% is a 

scientifically relevant surrogate for adverse health outcomes for people with asthma and lung 

disease.

3
For long-term exposures, the CASAC concurs with the findings of the ISA that the scientific weight 

of evidence for long-term exposure to ozone and adverse health effects is “likely to be causal” for 

respiratory effects and “suggestive of a causal relationship” for cardiovascular effects, reproductive 

and developmental effects, central nervous system effects, and total mortality. In terms of 

quantitative risk assessment, the most relevant scientific evidence available is with respect to 

epidemiologic estimates of the relationship between ambient concentration and mortality. Thus, 

EPA’s risk assessment appropriately focuses on this particular heath end point for long-term 

exposure.

Furthermore, with regard to the exposure assessments, the CASAC concurs that children are an 

important at-risk group. In particular, school-age children spend an increased amount of time outdoors 

in relatively high levels of activity, which increases air intake, and include asthmatic children. Outdoor 

workers and other adults who engage in moderate exertion for prolonged periods or heavy exertion for 

shorter periods during the day also comprise at-risk groups. Therefore, the focus on estimation of FEV1

decrements for asthmatic school age children and adult populations is appropriate. Asthmatic subjects 

appear to be at least as sensitive, if not more sensitive, than non-asthmatic subjects in manifesting 

ozone-induced pulmonary function decrements.

At the level of the current standard, 11% to 22% of school age children are predicted to experience at 

least one day with an FEV1 decrement ≥10%, which is not protective of public health. The range of 

values represents variability among the analyzed cities. The proportion of school age children predicted 

to experience at least one day with an FEV1 decrement ≥10% is 8% to 20% at a level of 70 ppb; 2% to 

18% at a level of 65 ppb; and 4% to 13% at a level of 60 ppb. Concurrently, the proportion of school 

age children experiencing ≥ 6 days with FEV1 decrements ≥10% decreases with level, at 1% to 6% for a 

level of 75 ppb; 1% to 5% at a level of 70 ppb; 0% to 4% at a level of 65 ppb; and 0% to 3% at a level of 

60 ppb. 

2. With regard to the presentation of the exposure and risk information for the purpose of 

assessing the adequacy of the current standard, to what extent is the information, including 

associated limitations and uncertainties, sufficiently characterized, appropriately interpreted 

and clearly communicated?

The major exposure and risk information requisite to assess the adequacy of the current standard is 

well presented for the adjusted air quality data, exposure-based considerations, and risk-based 

considerations. Overall, the salient points are clearly presented with enough detail to allow the 

reader to make judgments on how much weight to assign to any limitations or uncertainties. 

Individual panelist comments are provided that, if addressed, will strengthen these points. Major 

points are supported by reference to studies or data presented either earlier in the Second Draft PA

or in the Second Draft ISA or Second Draft HREA, which leads to the conclusion that the points 

have been appropriately interpreted.

3. In the Panel’s view, does the discussion in section 3.4 provide an appropriate and sufficient 

rationale to support staff’s preliminary conclusion that the current evidence and exposure/risk 

information call into question the adequacy of the current standard and that it is appropriate to 

consider revising the standard to achieve additional public health protection?

Section 3.4 clearly articulates the findings and points that underpin the EPA staff’s preliminary 

conclusion to call into question the adequacy of the current standard and the appropriateness of revising 

4
it. The CASAC finds scientific justification that current evidence and exposure/risk information call 

into question the adequacy of the current standard. Furthermore, there is scientific support for the need 

to revise the standard to achieve additional public health protection.

The CASAC finds that the current NAAQS for ozone is not protective of human health. The HREA 

emphasizes the conclusion reached in the ISA that there is a causal relationship between short-term 

ozone exposure and a range of respiratory effects, including lung function decrements, respiratory 

symptoms, and inflammation—all of which are observed below the level of the current ozone NAAQS. 

As summarized in our advice on the HREA, the HREA presents ample scientific evidence from human 

controlled exposure and epidemiology studies that adverse health effects in young healthy adults occur 

with exposures to 72 ppb of ozone for 6.6 hours. For example, the combination of decrements in FEV1

together with the statistically significant alterations in symptoms in human subjects exposed to 72 ppb 

ozone meets the American Thoracic Society’s definition of an adverse health effect (American Thoracic 

Society, 2000). It is the judgment of CASAC that if subjects had been exposed to ozone using the 8-

hour averaging period used in the standard, adverse effects could have occurred at lower concentration. 

Further, in our judgment, the level at which adverse effects might be observed would likely be lower for 

more sensitive subgroups, such as those with asthma.

While the scientific evidence supporting the finding that the current standard is inadequate to protect 

public health is strongest based on the controlled human exposure studies of respiratory effects, the 

CASAC also finds sufficient scientific evidence based on epidemiologic studies for mortality and 

morbidity associated with short-term exposure to ozone at the level of the current standard. Recent 

animal toxicological studies support identification of modes of action and, therefore, the biological 

plausibility associated with the epidemiological findings. The scientific evidence from multiple 

approaches including toxicology, clinical studies, and epidemiologic studies support an overall finding 

that the current standard is not adequate to protect public health. The Second Draft PA provides more 

detailed discussion on these and related points in the section on pages 3-118 to 3-123 in supporting the 

staff conclusion, which the CASAC supports, that the current standard is not adequate to protect public 

health. In particular, the scientific evidence provides strong support for the occurrence of a range of 

adverse respiratory effects and mortality under air quality conditions that would meet the current 

standard. Therefore, the CASAC unanimously recommends that the Administrator revise the current 

primary ozone standard to protect public health.

Consideration of Potential Alternative Primary Standards (Chapter 4)

1. In the Panel’s view, has the evidence and exposure/risk information, including associated 

limitations and uncertainties, been appropriately characterized and interpreted for the purpose of

considering potential alternative standards?

This chapter provides a comprehensive, clear, and carefully documented assessment of potential 

alternative primary standards for ozone. As discussed in some individual comments, it could be 

improved to minimize repetition within the chapter and with earlier chapters. The discussion could be 

more focused on the salient points such as in the discussion of studies conducted in locations that meet 

possible alternative standards (p. 4-12 to 4-13) and the cut-point analysis (p. 4-14 to 4-15). Figures 4.1 –

4.8 could use some cosmetic improvements. 

2. In the Panel’s view, does the discussion in section 4.6 provide an appropriate and sufficient 

rationale, supported by the discussions in sections 4.1 through 4.4, to support staff’s preliminary

5
conclusions regarding alternative primary standards (including the indicator, level, averaging time

and form) that it is appropriate to consider?

Section 4.6 is well written with a clear rationale presented for each of the possible alternative 

standards. Scientific justification for retaining the current indicator (ozone), averaging time (maximum 

daily 8-hour average), and form (annual 4th highest maximum daily 8-hour average, averaged over 

three years) is provided, as well as the scientific basis for consideration of alternative levels. 

The CASAC concurs with staff conclusions in the Second Draft PA that the current indicator, 

averaging time, and form be retained. The indicator of ozone is appropriate based on its causal or likely 

causal associations with multiple adverse health outcomes and its representation of a class of pollutants 

known as photochemical oxidants. 

The current 8-hour averaging time is justified by the combined evidence from epidemiologic and 

clinical studies referenced in Chapter 4. Results from clinical studies, for example, show a wide range 

of respiratory effects in healthy adults following 6.6 hours of exposure to ozone, including pulmonary 

function decrements, increases in respiratory symptoms, lung inflammation, lung permeability, 

decreased lung host defense, and airway hyperresponsiveness. These findings are supported by 

evidence from epidemiological studies that show causal associations between short-term exposures of 

1, 8 and 24-hours and respiratory effects and “likely to be causal” associations for cardiovascular 

effects and premature mortality. The 8-hour averaging window also provides protection against the 

adverse impacts of long-term ozone exposures, which were found to be “likely causal” for respiratory 

effects and premature mortality. 

Regarding the form of the standard, the CASAC concurs that the ozone standard should be based on 

the fourth highest, daily maximum 8-hour average value (averaged over three years). This provides 

health protection while allowing for atypical meteorological conditions that can lead to abnormally 

high ambient ozone concentrations which, in turn, provides programmatic stability. 

In considering the upper and lower bound of the range of levels that CASAC recommends for 

consideration by the Administrator, CASAC took into account the scientific knowledge of the kind and 

extent of identifiable effects on public health from exposure to ambient ozone, including scientific 

information on the nature and severity of the health effects, size of the sensitive populations at risk, and 

the kind and degree of uncertainties. While uncertainty is inherent in assessments of this type, the 

CASAC finds that there is sufficient weight of evidence and degree of confidence to reach the 

following scientific conclusions.

CASAC concurs with the summary of the public health significance of exposure benchmarks levels of 

concern as described in the Second Draft PA on Page 5-18, lines 15-21. The 80 ppb-8hr benchmark 

level represents an exposure level for which there is substantial clinical evidence demonstrating a 

range of ozone-related effects including lung inflammation and airway responsiveness in healthy 

individuals. The 70 ppb-8hr benchmark level reflects the fact that in healthy subjects, decreases in 

lung function and respiratory symptoms occur at concentrations as low as 72 ppb and that these effects 

almost certainly occur in some people, including asthmatics and others with low lung function who are 

less tolerant of such effects, at levels of 70 ppb and below. The 60 ppb-8hr benchmark level represents 

the lowest exposure level at which ozone-related effects have been observed in clinical studies of 

healthy individuals. Based on its scientific judgment, the CASAC finds that the 60 ppb-8hr exposure 

benchmark is relevant for consideration with respect to adverse effects on asthmatics.

6
The CASAC concurs with EPA staff regarding the finding based on scientific evidence that a level of 

60 ppb corresponds to the lowest exposure concentration demonstrated to result in lung function 

decrements large enough to be judged an abnormal response by ATS and that could be adverse in 

individuals with lung disease. The CASAC further finds, as does EPA staff, that a level of 60 ppb also 

corresponds to the lowest exposure concentration at which pulmonary inflammation has been reported. 

Based on the exposure assessments conducted by EPA, a standard with a level of 60 ppb would reduce 

children exposures of concern of 60 ppb or higher over 8-hours by 96% and would allow virtually no 

children to experience two or more exposures in a year at this exposure of concern. Such a standard 

would allow 2% or fewer of children to have lung function FEV1 decrements ≥15% one or more times 

per year, although it would allow 5 to 11% of children, including asthmatic children, to have ozoneinduced lung function decrements ≥10%. A standard with a level of 60 ppb would be expected to 

reduce epidemiology-based mortality and morbidity risk for short-term exposures to ozone.

The Second Draft PA concludes that the scientific evidence and available information support 

consideration of a new primary ozone standard within the 60 ppb to 70 ppb range based on ozone as 

the indicator, an 8-hour averaging time, and annual 4th highest daily form of the standard (averaged 

over three years). The CASAC concurs that 60 ppb is an appropriate and justifiable scientifically

based lower bound for a revised primary standard. This is based upon findings of adverse effects, 

including clinically significant lung function decrements and airway inflammation, after exposures to 

60 ppb ozone in healthy adults with moderate exertion (Adams 2006; Schelegle et al., 2009; Brown et 

al. 2008; Kim et al., 2011), with limited evidence of adverse effects below 60 ppb. The CASAC 

further notes that clinical studies do not address sensitive subgroups, such as children with asthma, and 

that there is a scientific basis to anticipate that the adverse effects for such subgroups are likely to be 

more significant at 60 ppb than for healthy adults.

At a level of 70 ppb for the averaging time and form of the current standard, clinical and 

epidemiological studies show adverse effects to human health. As discussed in the Second Draft 

HREA and the Second Draft PA, approximately 1% of children are estimated to experience exposures 

of 70 ppb or more (daily maximum 8-hour exposures) in an ozone season, with 3% to 10% of children 

(depending on urban area) estimated to experience one or more exposures of concern at or above 60 

ppb. Up to 5% of children are expected to experience ozone-induced lung function decrements greater 

than or equal to 15% in a “worst case” year with respect to meteorological conditions. Exposures of 

these magnitudes have been shown to result in significant adverse effects. For example, controlled 

human exposure studies show respiratory symptoms combined with clinically significant lung function 

decrements following ozone exposures to 60 ppb to 70 ppb in healthy individuals. On average over the 

years 2006 to 2010, a standard set at 70 ppb is estimated to allow about 11 to 17% of children to 

experience one or more moderate O3-induced lung function decrements (i.e., ≥ 10%), which could be 

adverse for people with lung disease. This reflects an average reduction of about 15%, compared to 

current standard. A standard with a level of 70 ppb is also estimated to allow about 6 to 11% of 

children to experience two or more such decrements (17% reduction, compared to current standard). 

With regard to epidemiologic studies the CASAC concurs with the EPA staff finding in the Second 

Draft PA that, compared to the current standard, a revised standard with a level of 70 ppb would be 

more effective in maintaining short-term ambient O3 concentrations below those present in locations 

that provided the basis for positive and statistically significant health effect associations. However, a 

level of 70 ppb offers only modest incremental reductions in short-term mortality risk compared to the 

current standard. Taken as a whole, these findings indicate that ozone exposures of 70 ppb pose 

reduced risk compared to the current standard but, nonetheless, are of significant concern, especially 

for children, asthmatics, the elderly and other at risk populations.

7
We also considered the adverse health implications of a level of 65 ppb. An alternative standard level 

of 65 ppb would reduce the frequency of occurrence of lung function decrements of 15% or higher, as 

compared to a level of 70 ppb, but does not eliminate such occurrences. Further, an alternative 

standard level of 65 ppb would lead to lower frequency of short-term premature mortality than the 

current standard or a level of 70 ppb. The frequency of lung function decrements and premature 

mortality from short-term exposure to ozone decreases even further when the alternative standard is 

lowered to 60 ppb. As noted earlier, based on results for clinical studies of healthy adults, and 

scientific considerations of differences in responsiveness of asthmatic children compared to healthy 

adults, there is scientific support that 60 ppb is an appropriate exposure of concern for asthmatic 

children. 

In summary, based on the scientific evidence from clinical studies, epidemiologic studies, animal 

toxicology studies, as summarized in the ISA, the findings from the exposure and risk assessments as 

summarized in the HREA, and the interpretation of the implications of all of these sources of 

information as given in the Second Draft PA, the CASAC concludes that there is adequate scientific 

evidence to recommend a range of levels for a revised primary ozone standard from 70 ppb to 60 ppb. 

However, as noted below, we believe that there is an important distinction in our finding regarding the 

level of 70 ppb in contrast to that of EPA staff as given in the Second Draft PA.

In reaching its scientific judgment regarding a recommended range of levels for a revised ozone 

primary standard, the CASAC has focused on the scientific evidence for the identification of the kind 

and extent of adverse effects on public health. The CASAC acknowledges that the choice of a level 

within the range recommended based on scientific evidence is a policy judgment under the statutory 

mandate of the Clean Air Act. The CASAC advises that, based on the scientific evidence, at a level of 

70 ppb, there is little margin of safety for the protection of public health, particularly for sensitive 

subpopulations. In this regard, our advice differs from that offered by EPA staff in the Second Draft 

PA. At 70 ppb, there is substantial scientific certainty of a variety of adverse effects, including 

decrease in lung function, increase in respiratory symptoms, and increase in airway inflammation. 

Although a level of 70 ppb is more protective of public health than the current standard, it may not 

meet the statutory requirement to protect public health with an adequate margin of safety. In this 

regard, the CASAC deliberated at length regarding advice on other levels that might be considered to 

be protective of public health with an adequate margin of safety. For example, the recommended 

lower bound of 60 ppb would certainly offer more public health protection than levels of 70 ppb or 65 

ppb and would provide an adequate margin of safety. Thus, our policy advice is to set the level of the 

standard lower than 70 ppb within a range down to 60 ppb, taking into account your judgment 

regarding the desired margin of safety to protect public health.

Other suggestions for improving the section were relatively minor, including better labeling, annotation, 

and discussion of tables and figures, such as Figure 4-13, and adding sub-headings for the consideration 

of 70, 65, and 60 ppb standard levels.

3. Does the Panel have any recommendations regarding additional interpretations and conclusions 

based on the available information that would be appropriate for consideration beyond those 

discussed in this chapter?

The chapter provides a cogent presentation of the rationale behind the Second Draft PA’s conclusions 

and the key uncertainties and areas for future research (Section 4.7). The CASAC recommends future 

research to address key uncertainties related to ozone health effects. This research, which could be 

8
conducted in collaboration with other federal and non-governmental organizations, will help to improve 

our understanding of ozone health effects in support of the next review of the ozone NAAQS. 

The current approach to review and revision of the primary National Ambient Air Quality Standards 

(NAAQS) is based on a one-pollutant-at-a-time approach. As the state of science regarding the joint 

effects of human exposure to multiple pollutants improves, the EPA should consider how review and 

revision of the NAAQS can be done synergistically for logical, scientifically relevant groupings of 

criteria pollutants. For example, O3 and NO2 are both criteria pollutants that are inter-related via 

atmospheric chemistry, and human exposure to these pollutants is often in the form of a mixture that 

includes both, and other pollutants such as particulate matter. The National Research Council (NRC, 

2004) and the North American Research Strategy for Tropospheric Ozone (Hidy et al., 2011) have both 

made detailed recommendations for multipollutant approaches to air quality management, and EPA has 

been exploring a multipollutant approach for the secondary standards for SOx and NOx. CASAC 

encourages EPA to explore multipollutant approaches for review of the primary standards, and would be 

receptive to a request by EPA to review planning or methods documents for such approaches.

Adequacy of the Secondary Standard (Chapter 5)

1. To what extent does the information in sections 5.1 through 5.5 capture and appropriately 

characterize the key aspects of the evidence for ozone welfare effects assessed and integrated in

the ISA? To what extent does the information in section 5.1 (Nature of Effects and Biologically

Relevant Exposure Metric) appropriately summarize the nature of ozone welfare effects and to

what extent does it appropriately characterize the evidence with regard to biologically relevant

exposures?

This chapter does a nice job summarizing evidence for welfare effects of ozone exposure and for linking 

ecological effects to welfare effects. We support EPA’s continued emphasis on Class I and other 

protected areas. The discussion of flux-based metrics is useful and appropriate, concluding that potential 

benefit may eventually derive from such metrics but that excessive uncertainty remains at this time. We 

note that when discussing the W126 metric, the phrase “Exposure-Response” (E-R) should be used in 

place of “Concentration-Response”. The discussion regarding the reduction of uncertainty associated 

with Open Top Chamber (OTC) derived E-R relationships since the last review (page 5-10; page 5-31) 

is appropriate and clearly presented. It should be further emphasized in the revised chapter that the 

National Crop Loss Assessment Network (NCLAN) studies covered multiple locations in the U.S. and 

multiple crops, along with multiple ozone exposure levels, using consistent methods. All of these 

factors are important because they enhance the reliability of the results. 

The secondary standard should be protective against known or anticipated ozone effects that are 

adverse to the public welfare. The CASAC concurs with EPA staff that adverse effects of interest are 

characterized as “damage,” which are injury effects that reach sufficient magnitude as to reduce or 

impair the intended use or value of the plant to the public, and thus are adverse to public welfare. 

The CASAC supports the concept of ecosystem services, which are the benefits that individuals and 

organizations obtain from ecosystems, as part of the scope of characterizing damage that is adverse to 

public welfare. For example, CASAC concurs that trees are important from a public welfare 

perspective because they provide valued services to humans, including aesthetic value, food, fiber, 

timber, other forest products, habitat, recreational opportunities, climate regulation, erosion control, 

air pollution removal, and hydrologic and fire regime stabilization. Damage effects to trees that are 

9
adverse to public welfare occur in such locations as national parks, national refuges, and other 

protected areas, as well as to timber for commercial use. The CASAC concurs that biomass loss in 

trees is a relevant surrogate for damage to tree growth that affects ecosystem services such as habitat 

provision for wildlife, carbon storage, provision of food and fiber, and pollution removal. Biomass 

loss may also have indirect process-related effects such as on nutrient and hydrologic cycles. 

Therefore, biomass loss is a scientifically valid surrogate of a variety of adverse effects to public 

welfare.

The CASAC concurs that another important surrogate for damage that is adverse to public welfare is 

crop loss. Crops provide food and fiber services to humans. Evaluation of market-based welfare 

effects of ozone exposure in forestry and agricultural sectors is an appropriate approach to take into 

account damage that is adverse to public welfare.

The CASAC concurs that visible foliar injury can impact public welfare by damaging or impairing the 

intended use or service of a resource. Visible foliar injury that is adverse to public welfare can 

include: visible damage to ornamental or leafy crops that affects their economic value, yield, or 

usability; visible damage to plants with special cultural significance; and visible damage to species 

occurring in natural settings valued for scenic beauty or recreational appeal. 

In summary, CASAC concurs that relative biomass loss for tree species, crop yield loss, and visible 

foliar injury are appropriate surrogates of a wide range of damage that is adverse to public welfare.

2. To what extent is staff’s consideration of the welfare effects evidence, including the implications

of reported vegetation effects with regard to adversity to public welfare technically sound and

clearly communicated at an appropriate level of detail? In the Panel’s view has the information

been appropriately interpreted for the purpose of assessing the adequacy of the current

standard?

The linkage of ecological effects of ozone to welfare effects is effective in this draft. The effort to 

monetize welfare impacts and benefits is appropriate although techniques for this monetization are not 

yet fully developed. Specifically, calculation of consumer and producer surpluses is a useful 

contribution to quantification of welfare effects. However, this national-level approach does not 

adequately account for negative effects on individual farmers and forest owners in high-ozone areas.

Tabulating and discussing the number of counties in which yield loss is predicted to exceed a 

threshold of 5% for individual sensitive crops for alternative candidate standards should be added to 

Table 6-4 to help address this issue.

The interaction of agriculture and forestry as modeled by the Forest and Agricultural Sector

Optimization Model with Greenhouse Gases (FASOM-GHG) is mentioned in both the Second Draft 

WREA and the Second Draft PA but not adequately explained.

The cottonwood data (Figures 5-1 and 5-3) receive too much emphasis. These results are from a 

gradient study that did not control for ozone and climatic conditions and show extreme sensitivity to 

ozone compared to other studies, as already noted in the text (page 5-14, line 5). Although they are 

important results, they are not as strong as those from other experiments that developed E-R functions 

based on controlled ozone exposure. 

E-R functions for individual tree seedling species, supported by results from other methods such as 

10
Free Air Carbon Dioxide/Ozone Enrichment (FACE) and naturally occurring gradients, demonstrate 

that some species are very sensitive to ozone and show decreased growth at very low chronic 

exposure levels, while other species show little response even at much higher levels. A similar result 

is found for crop species. Thus there is strong evidence of decreased growth and yield of sensitive tree 

and crop species at very low ozone levels. 

The method used with FASOM for forest growth is based on individual species’ E-R functions, but 

this is strictly accurate only for forest stands comprised of single species. For mixed-species forest 

stands, competition among species with different sensitivity will reduce overall stand growth losses, 

but also exacerbate effects on sensitive species. Some panel members were concerned about the 

difficulty of interpreting “median” response for both ozone-sensitive and relatively insensitive species. 

It should not be assumed that species of unknown sensitivity are tolerant to ozone. It is more 

appropriate to assume that the sensitivity of species without E-R functions might be similar to the 

range of sensitivity for those species with E-R functions. 

The spatial extent and degree of impact on sensitive species expected at current ozone exposures, the 

current standard, and at alternate standards should be better quantified for different regions of the 

country. A county-level analysis will provide insights regarding the spatial extent and degree of 

impact. For example, rather than focusing solely on the median relative biomass loss (RBL), the 

number of counties containing sensitive tree species that are expected to have growth loss of greater 

than 2% should be quantified. 

In addition, the Second Draft PA should clarify whether the denominator basal area in the calculation 

includes only the 12 species with available E-R functions, or rather includes all species. If it is all 

species, then there is a bias introduced by implicitly assuming that species without E-R functions are 

insensitive to ozone. If it only includes the species with E-R functions, then the interpretation will 

vary depending on what fraction of the basal area is represented by species without known E-R 

functions. In either case this requires explicit consideration.

3. With regard to the presentation of the exposure and risk information for the purpose of assessing

the adequacy of the current standard, to what extent is the information, including associated

limitations and uncertainties, sufficiently characterized, appropriately interpreted and clearly

communicated?

This chapter makes a strong case that the current secondary standard fails to protect vegetation and 

ecosystem services from adverse effects. The form of the current standard is inadequate to provide such 

protection. From correlation analysis based on the Higher Order Direct Decoupled Method (HDDM), 

the EPA suggests that a W126 level of 15 ppm-hrs may in many cases be similar to the current standard.

However, as noted in the CASAC’s review of the Second Draft WREA (EPA-CASAC-14-003), the 

CASAC finds that a W126 level of 15 ppm-hrs may not be similar to the current standard, since the 

actual approaches that would be used to achieve such a level are likely to be different than those 

assumed in the HREA air quality scenarios for just meeting the current standard. Specifically, and 

quoting from our review of the Second Draft WREA: 

“The currently reported finding of only small differences in risk between just meeting 

the current standard and a W126-based level of 15 ppm-hrs must not be interpreted to 

mean that just meeting the current standard will be as protective as meeting a W126-

based standard at 15 ppm-hrs. There are two key factors that must be considered when 

11
making this comparison. First, air quality was simulated in the Second Draft WREA 

based on the magnitude of across-the-board reductions in NOx emissions required to 

bring the highest monitor down to the target level. Meeting a target level at the highest 

monitor requires substantial reductions below the targeted level through the rest of the 

region. This artificial simulation does not represent an actual control strategy and may 

conflate differences in control strategies required to meet different standards and 

different targets. As a result, there may be a number of monitors that meet the current 

standard but would not meet an alternative W126 standard. Second, and equally 

important, the current form of the standard is much less biologically relevant for 

protecting vegetation than is a seasonal, peak weighted index such as the W126, which 

was designed to measure the cumulative effects of ozone exposure”

Because injury is clearly observed at and below 15 ppm-hrs, the chapter demonstrates that the current 

standard is inadequate to protect against welfare effects due to ozone. Despite the paucity of data in 

certain areas, the Second Draft PA makes appropriate statements about causality and risk with which to 

evaluate the adequacy of the current welfare standard.

The uncertainties are well described and appropriately interpreted. As mentioned previously, there is 

some confusion that should be clarified regarding increasing uncertainty of responses at lower ozone 

levels versus smaller magnitudes of response. There is adequate evidence for effects in sensitive species 

at levels of W126 well below 15 ppm-hrs. In Figure 5-5 some information is needed about the 

referenced sites. Uncertainties do not weaken the case for a more stringent standard. The paucity of data 

on ozone sensitivity of most U.S. plant species should not prevent the Second Draft PA from discussing

“anticipated” effects on a number of unidentified sensitive species. As in the Second Draft WREA, the 

consideration of uncertainty is repetitive to the point of detracting from the considerable strength of the 

analyses and the evidence on which they are based. 

The discussion of economic losses due to bark beetles and fire perpetuates the confounding of spatial 

association with causation in the Second Draft PA. As stated, this does not contribute much to the 

assessment of risk nor evaluation of the adequacy of the current or alternative standards.

4. In the Panel’s view, does the discussion in section 5.7 provide an appropriate and sufficient 

rationale to support staff’s preliminary conclusion that the current evidence and exposure/risk 

information call into question the adequacy of the current standard and that it is appropriate to 

consider revising the standard to achieve additional public welfare protection?

The CASAC concurs with the justification in this section that the form of the standard should be 

changed from the current 8-hr form to the cumulative W126 index and finds that the discussion provides 

an appropriate and sufficient rationale.

This section clearly demonstrates that ozone-induced injury may occur in areas that meet the current 

standard. As noted above, the correlative similarity between the current standard and a level of the 

W126 index of 15 ppm-hrs must not be interpreted to mean that just meeting the current standard is 

equivalent to just meeting a W126 level of 15 ppm-hrs. Most of the analyses found effects below 15 

ppm-hrs (many at 10 or even 7 ppm-hrs). Based on review of relevant science, the CASAC concludes 

that the upper bound of the range that should be considered for the W126 standard should not exceed 15

ppm-hrs. The CASAC does not support a level higher than 15 ppm-hrs. Levels above 15 ppm-hrs

should not be included in the revised PA as options for an alternate secondary standard. For example, at 

12
17 ppm-hrs, the median tree species has 6% relative biomass loss, and the median crop species has over 

5% loss. These levels are unacceptably high. 

The CASAC does not recommend the use of a three-year averaging period. We favor a single-year 

averaging period, which will provide more protection for annual crops and for the anticipated 

cumulative effects on perennial species. The scientific analyses considered in this review, and the 

evidence upon which they are based, are from single-year results. If a 3-year averaging period is 

established, then the upper limit will need to be reduced to protect against one-year ozone peaks. We

consider this further in the response to charge questions for Chapter 6. 

In summary, the CASAC concurs with the Second Draft PA that the current secondary standard is 

inadequate with respect to form, level and averaging time. Only the current indicator (ozone) should be 

retained. The potential revised standard is considered further in the response to the charge questions for

Chapter 6 below. 

Consideration of Potential Alternative Secondary Standards (Chapter 6)

1. In the Panel’s view, has the evidence and exposure/risk information, including associated 

limitations and uncertainties, been appropriately characterized and interpreted for the purpose of

considering levels of protection and potential alternative standards?

2. In the Panel’s view, does the discussion in section 6.5 provide an appropriate and sufficient 

rationale, supported by the discussions in sections 6.1 through 6.4, to support staff’s preliminary

conclusions regarding alternative secondary standards (including the indicator, level, averaging

time and form) that it is appropriate to consider?

3. Does the Panel have any recommendations regarding additional interpretations and conclusions 

based on the available information that would be appropriate for consideration beyond those 

discussed in this chapter?

Charge Questions 1, 2, and 3 are all closely related and are being addressed together in this summary 

response.

The Second Draft PA makes a very strong case, consistent with previous CASAC judgment, for changing 

the secondary metric to the W126 averaged over the highest three-month interval. Accumulation over the 

08:00 a.m. – 08:00 p. m. daytime 12-hour period is a scientifically acceptable and recommended means of 

generalizing across latitudes and seasons. 

The suggestion in Section 6.2 to use a 3-year averaging period is not supported by the available data. We 

have not supported it in the past nor do we support it here. The primary justification for a 3-year 

averaging period is to improve the program stability of the classification of regions as being in or out of 

compliance. The proposed form includes a 3-month period, so it is not nearly as sensitive to extreme 

events as an hourly or 8-hour averaging period. The case has not been made that welfare benefits from the 

stability of a 3-year average are greater than those from using the biologically relevant 1-year value. If a 

3-year averaging period is implemented, it should be at a lower level than a single-year standard to protect 

against single unusually damaging years that will be obscured in the average.

13
The key issue in the Second Draft PA with respect to welfare effects is the level of the standard. If 

protection of the most sensitive members of the community is extended to components of ecosystems that 

impact public welfare, then several potential levels of the standard should be considered. A 2% biomass 

loss is an appropriate scientifically based value to consider as a benchmark of adverse impact for longlived perennial species such as trees, because effects are cumulative over multiple years. For example, a 

2% annual RBL fully explains the observed the biomass loss of 21% over 7 years in the study of pure 

stands of aspen at the Rhinelander, WI FACE site (Wittig et al. 2009). The CASAC considers it 

significant that a similar value of 1% to 2% for tree seedling biomass loss was recommended previously 

by a consensus meeting of experts on ecological effects of ozone (Heck and Cowling 1997). In our 

scientific judgment, it is appropriate to identify a range of levels of alternative W126-based standards that 

includes levels that aim for not greater than 2% RBL for the median tree species. 

The CASAC considered carefully the data presented in Figure 5-2 and Table 6-1 of the Second Draft 

PA. The Monte Carlo analysis (red dots, Fig. 5-2) should not be used in evaluating the effect of ozone 

on RBL of tree seedlings. This analysis overemphasizes the species for which relatively few E-R 

functions are available, is biased toward the few less sensitive response functions available for some 

individual species, makes unsupported assumptions regarding the representativeness of available 

response functions, and confounds intra- and inter-species variability in unquantifiable ways. We favor

using a measure of central tendency of the data, specifically the median across species (the green line in 

Fig. 5-2). This analysis provides the median of best available estimates within each species, and the 

median across species with all species treated equally. Table 6-1 presents the RBL results for individual 

species for different levels of W126. This table demonstrates that a range of 7 ppm-hrs to 15 ppm-hrs

will protect against RBL of 2% for at least 5 of the 12 species. We do not consider a value of 17 ppmhrs from Table 6-1 because even though only 5 of 12 tree species are estimated to have relative biomass 

loss of 2 percent or less at this level, the median species has relative biomass loss of 6.0 percent, which 

is unacceptably high. With compounding over the harvest cycle or life span of these species, this will 

result in considerably greater cumulative RBL as discussed above. For the more sensitive tree seedlings,

a value closer to the lower end of the range (7 ppm-hrs) would be more appropriate. The level of 7 ppmhrs is the only level analyzed for which the relative biomass loss for the median tree species is less than or 

equal to 2 percent. At 7 ppm-hrs, 7 of the 12 analyzed species have relative biomass loss of less than 2%. 

Visible foliar injury is even more sensitive than RBL of 2%, with W126 values below 10 ppm-hr required 

to reduce the number of sites showing visible foliar symptoms. 

The range of 7 ppm-hrs to 15 ppm-hrs is protective of median crop loss of 5% or less, with lower values 

within the range offering more protection than higher values. Crop loss appears to be less sensitive than 

these other indicators, largely because of the CASAC judgment that a 5% yield loss represents an adverse 

impact, and in part due to more opportunities to alter management of annual crops. At a W126 level of 15 

ppm-hrs, the median species crop yield loss is less than 5%, with 6 of the 10 analyzed species having crop 

yield loss less than 5%. At a level of 7 ppm-hrs, all analyzed crop species are estimated to have crop yield 

losses less than 5%. 

This discussion, like that in the Second Draft WREA and Second Draft PA, focuses on annual values for 

W126, and lower values should be considered for a multi-year average. 

The spatial region for which a standard is intended to be protective should be specified. Some analyses are 

done for large regions of the country, some for counties, etc. A county scale is appropriate for assessing 

crop yield loss. Calculating producer and consumer surpluses at national or large region scales does not 

14
provide adequate protection. Farmers growing sensitive crops in high ozone locations can be considered a 

“sensitive population” for welfare impacts, and crop yields under these conditions should be protected.

Care should be taken not to overstate uncertainties. For example, there is quite a lot of certainty in 

estimates of biomass loss for forest tree seedling species and crop species for which E-R functions have 

been developed. Because several dominant crop species have E-R functions, there is a quite a lot of 

certainty about impacts of ozone on crop yield across most annual cropland in the U.S.. 

There is considerable uncertainty in extrapolating from the 12 forest tree species to all forest tree species 

in the U.S. It should be anticipated that there are species of vegetation that are highly sensitive to ozone 

that do not have E-R functions, and others that are insensitive. It is scientifically justifiable to extrapolate 

from the known E-R curves, assuming that they are representative of the un-sampled population.

Thus, based on identification of known or anticipated ozone effects that are adverse to public welfare, 

taking into account the weight of evidence for causality of exposure to ozone and adverse welfare effects 

as given in Table 2-4 of the Integrated Science Assessment; results of the Second Draft WREA with regard 

to assessment of relative biomass loss for tree species, foliar injury, and crop yield loss; and the breadth of 

adverse welfare effects for ecosystem services, foliar injury, and crop loss, the CASAC recommends that 

the secondary standard for ozone be revised as follows: (1) ozone should be the indicator; (2) the form 

and summation time of the standard should be the W126 index summed over the highest three-month

interval during a year, based on accumulation over the 08:00 a.m. – 08:00 p.m. daytime 12-hour period; 

and (3) the level of the standard should be between 7 ppm-hrs and 15 ppm-hrs. These recommendations 

are based on scientific evidence of adverse effect associated with the presence of ozone in ambient air. 

Note that these levels are based on an annual form of the standard. 

In reaching its scientific judgment regarding the indicator, form, averaging time, and range of levels for 

a revised secondary standard, the CASAC has focused on the scientific evidence for the identification of 

the kind and extent of adverse effects on public welfare. The CASAC acknowledges that the choice of a 

level within the range recommended based on scientific evidence is a policy judgment under the 

statutory mandate of the Clean Air Act. Specifically, the Clean Air Act grants discretion to the 

Administrator to specify a standard that is “requisite to protect the public welfare from any known or 

anticipated adverse effects associated with the presence of [the] pollutant in the ambient air” (Section 

302(h), 42 U.S.C., §7602(h)). As a policy recommendation, separate from its advice above regarding 

scientific findings, the CASAC advises that a level of 15 ppm-hrs is requisite to protect crop yield loss, 

but that lower levels provide additional protection of crop yield loss. Furthermore, there are specific 

economically significant crops that may not be protected at 15 ppm-hrs but that would be protected at 

lower levels. Based on scientific judgment of CASAC, a level of 10 ppm-hrs is required to reduce foliar 

injury. A level of 7 ppm-hours is protective of relative biomass loss for trees. Furthermore, 7 ppmhours offers additional protection against crop yield loss and foliar injury. Therefore, 7 ppm hours is 

protective of ecosystem services. Thus, lower levels from the recommended range offer a greater degree 

of protection of more endpoints than do higher levels from the range.

If, as a policy matter, the Administrator prefers to base the secondary standard on a three year averaging 

period for the purpose of program stability, then the level of the standard should be revised downward 

such that the annual level in any given year of the three year period would not exceed the scientifically 

recommended range of annual levels of 7 ppm-hrs to 15 ppm-hrs. For example, if in a three year period 

the highest annual W126 value is 15 ppm-hrs, and the lowest W126 value associated with a three year 

average is 13 ppm-hrs, then the appropriate level for the three year average would be 13 ppm-hrs to 

15
protect against a peak annual level of 15 ppm-hrs. The final Policy Assessment should quantify the ratio 

of the annual to three year average W126 values to determine what downward adjustment from the 

annual levels recommended here is needed if a three year form is selected.

16
References

Adams, W.C. 2006. Comparison of chamber 6.6 hour exposures to 0.04 – 0.08 ppm ozone via square 

wave triangular profiles on pulmonary responses. Inhalation Toxicology. 18:127-136. 

http://dx.doi.org/10.1080/08958370500306107

American Thoracic Society. 2000. What constitutes an adverse health effect of air pollution? Am. J. 

Respir. Crit. Care Med. 161: 665-673.

Brown, J.S.; T.F. Bateson, and W.F. McDonnell, W.F. 2008. Effects of exposure to 0.06 ppm ozone on 

FEV1 in humans: A secondary analysis of existing data. Environ Health Perspect 116: 1023-1026. 

http://dx.doi.org/10.1289/ehp.11396

Fiore, A.M., and 47 others. 2009. Multi-model Estimates of Intercontinental Source-Receptor 

Relationships for Ozone Pollution, J. Geophys. Res., 114, D04301.

Heck, W. W. and E. B. Cowling. 1997. The need for a long term cumulative secondary ozone standard -

an ecological perspective. Environmental Manager. (1): 23-33.

Hidy G.M., et al. (Eds). 2011. Technical Challenges of Risk- and Results-Based Multipollutant Air 

Quality Management, Springer.

Kim, C.S., N.E. Alexis, A.G. Rappold, H. Kehrl, M.J. Hazucha, J.C. Lay, M.T. Schmitt, M. Case, R. B. 

Devlin, D.B. Peden, D. Diaz-Sanchez. 2011. Lung function and inflammatory responses in healthy young 

adults exposed to 0.06 ppm ozone for 6.6 hours. Am J Respir Crit Care Med. 183: 1215-1221. 

http://dx.doi.org/10.1164/rccm.201011-1813OC

National Research Council. 2004. Air Quality Management in the United States. National Academies 

Press, Washington, DC.

National Research Council. 2009. Global Sources of Local Pollution: An Assessment of Long-Range 

Transport of Key Air Pollutants to and from the United States. Washington, DC: The National Academies 

Press.

Schelegle, E.S.; Morales, C.A.; Walby, W.F.; Marion, S; Allen, R.P. 2009. 6.6-hour inhalation of ozone 

concentrations from 60 to 87 parts per billion in healthy humans. Am J Respir Crit Care Med. 180: 265-

272. http://dx.doi.org/10.1164/rccm.200809-1484OC

Task Force on Hemispheric Transport of air Pollution. 2010. Hemispheric Transport of Air Pollution, Part 

D: Answers to Policy-Relevant Science Questions, Air Pollution Studies No. 20. 

Prepared by the Task Force on Hemispheric Transport of Air Pollution acting within the framework of the

Convention on Long-range Transboundary Air Pollution. United Nations, New York and Geneva. 

http://www.htap.org/publications/2010_report/2010_Final_Report/HTAP%202010%20Part%20D%2011

0407.pdf

17
Wittig, V. E., E. A. Ainsworth, S. L. Naidu, D. F. Karnosky, and S. P. Long. 2009. Quantifying the impact 

of current and future tropospheric ozone on tree biomass, growth, physiology and biochemistry: a 

quantitative meta-analysis. Global Change Biology. 15:396-424.

Zhang, L., D.J. Jacob, N.V. Smith-Downey, D.A. Wood, D. Blewitt, C.C. Carouge, A. van Donkelaar, 

D.B.A. Jones, L.T. Murray, and Y. Wang. 2011. Improved estimate of the policy-relevant background 

ozone in the United States using the GEOS-Chem global model with 1/2ox2/3o horizontal resolution over 

North America, Atmos. Environ., 45, 6769-6776.

18
Appendix A

Individual Comments on the Policy Assessment

For the Review of the Ozone NAAQS (Second Draft)

CASAC Ozone Review Panel

Contents

George Allen ..............................................................................................................................A-2

Joe Brain ....................................................................................................................................A-9

David Chock.............................................................................................................................A-11

Ana Diez Roux .........................................................................................................................A-13

David Grantz ...........................................................................................................................A-17

Daniel J. Jacob.........................................................................................................................A-20

Steven Kleeberger ...................................................................................................................A-21

Fred Miller ...............................................................................................................................A-22

Howard S. Neufeld ..................................................................................................................A-25

Armistead (Ted) Russell .........................................................................................................A-28

Helen Suh .................................................................................................................................A-30

James Ultman ..........................................................................................................................A-33

Sverre Vedal.............................................................................................................................A-35

Peter Woodbury ......................................................................................................................A-37

Ronald E. Wyzga.....................................................................................................................A-46

A-1
George Allen

Charge Questions on O3 Monitoring and Air Quality (Chapter 2).

Ch. 2, Q #1. To what extent does the Panel agree that the most relevant information on monitoring 

(section 2.1), emissions and atmospheric chemistry (section 2.2), and common patterns of O3 

concentrations (section 2.3) is presented, and to what extent is the information presented

appropriately characterized and clearly communicated?

Section 2.1, Monitoring. National trends of annual 4th highest max 8-hour values are plotted in 

Figure 2-2, page 2-4. Section 2.1 appropriately notes the distinct drop between 2002 and 2004, 

consistent with the drop in summer NOx emissions due to the “NOx SIP call”, and notes the 

decreasing trend between 2000 and 2009. While that time period does appear to have a distinct 

downward trend, it is also informative to look at this same plot constrained to the period from 2004 

through 2012:

This 9-year time period starting after the NOx SIP call drop in O3 shows no indication of a trend, 

and leads to a very different conclusion. While both this time window and EPA’s interpretation of 

O3 trends over 2000 through 2009 are valid, the latter is totally driven by a one-time intervention; 

since then there does not appear to be any progress in reducing O3 concentrations. Year to year 

variations in summer meteorological conditions can play a large role in “raw” trends of less than 15 

to 20 years duration. In the past EPA has presented trend estimates that include adjustments for 

meteorology; see: http://www.epa.gov/airtrends/weather.html and references therein. It may be 

helpful to present such “adjusted trend” data to better assess progress since the NOx SIP call; these 

adjustments tend to pull “high” years down and “low” years up in concentration. 2013 O3-season 

data is now in AQS; even though those data will not be “certified” for another 3 months, it would 

be informative to add that data for 2013 to this trend plot.

Section 2.2, Emissions and Atmospheric Chemistry. This section is a clearly written and concise 

summary of this topic. It makes the interesting point regarding the co-benefit from NOx emission 

reductions for O3, NO2, and PM2.5.

Section 2.3, Air Quality Concentrations. This section is a clearly written and concise summary of 

this topic. Footnote 7, page 2-10, makes the sometimes overlooked point that since O3 is measured 

seasonally in most areas, the 4th highest day’s value is similar to the 98th percentile annual metric 

form used for some other criteria pollutants.

A-2
Section 2.4, Background O3. 

Ch. 2, Q #2. With regard to information on estimating O3 concentrations associated with 

nonanthropogenic sources or “background O3” (section 2.4), to what extent is this information

appropriately characterized and clearly communicated?

This section is the core of this chapter. Estimates of background O3 now play a minimal role in the 

REA document given the new approach to estimating risk under various emission reduction 

scenarios using the HDDM rollback method and total O3 concentrations.

Background O3 is still a factor in the Policy Assessment however, since a 2002 court decision 

allows EPA to consider background levels when evaluating risk for alternative (lower) standards 

(section 1.3.1, page 1-26, lines 17-19). But case law also states that “that attainability and technical 

feasibility are not relevant considerations in the setting of a NAAQS” (section 1.2.1, page 1-4 lines 

19-21, API v. Costle, 1981). It is unclear how EPA might navigate between these two legal 

guidelines in terms of how background O3 would be used in a policy and standard-setting context.

EPA performed new 2007 base “year” (7-months) zero-out and CAMx source apportionment 

modeling that is presented in this section. Section 2.4.2 (page 2-16, lines 6-14) introduces the 

concept of “apportionment-based US background” O3 (AB-USB?) as the most relevant metric for 

estimation of a “fractional background” metric. Overall this chapter is difficult to follow. It seems 

the new modeling’s utility is to confirm earlier outcomes using these improved modeling 

approaches. It would be helpful if the chapter could better focus on these specific issues.

Section 2.4.3: The discussion on page 2-17, lines 1-12, is helpful in understanding the fractional 

contribution of background O3 on days with elevated O3.

Figures 2-13 and 2-14 on page 2-19 could benefit from the addition of “N” (# of site-days) to each 

bin. Figure 2-13 is difficult to interpret without this information.

Section 2.4.4 presents background O3 in the context of the 12 urban case study areas. Table 2-2 

(page 2-21) seems to be the most relevant presentation, but is only for site-days > 60 ppb; it would 

be helpful to also include this information for site-days >65 and > 70.

Section 2.4.5 presents background O3 in the context of a W126 secondary standard form for four 

locations (2 are large urban areas). Page 2-22 lines 10-12 refer to figure 2-7 (page 2-7) as showing 

high observed 2010-2012 W126 values for these four sites. These sites can not readily be 

identified on this map, so these values also need to be provided in a text form.

Other Comments.

Chapter 1, Section 1.2.2. (History of O3 NAAQS reviews)

This section is a useful summary of recent actions and court rulings regarding the O3 NAAQS 

review process. There are two topics regarding the 2008 NAAQS revision and subsequent 

reconsideration process that I would like to expand on that may be relevant to the current review.

First is the “Reconsideration” of the 2008 O3 primary NAAQS, discussed on page 1-9. It is not 

widely known that in the summer of 2011, EPA sent a final rule to OMB/ORIA with 65 ppb as the 

standard. This and the role that ORIA played in the process was detailed in a New York Times 

A-3
article on Nov. 17, 2011:

www.nytimes.com/2011/11/17/science/earth/policy-and-politics-collide-as-obama-enterscampaign-mode.html

It is worth noting that EPA proposed this standard (in the middle of the CASAC range of 60 to 70 

ppb) based on the scientific literature used for the 2008 rule – e.g., new studies since 2006 could 

not be considered in this reconsidered rulemaking. EPA subsequently posted the full preamble of 

what was to be the final Summer 2011 rule, as well as the draft impact analysis 

at:http://www.epa.gov/glo/actions.html

While this background material is not directly relevant to the current review process, it provides 

some useful context for the decisions the agency made in 2011 during the reconsideration process, 

and may be of interest to the current O3 panel.

Second, this section is a useful summary of the court’s 7/23/2013 decision (reissued 12/11/13) 

regarding the 2008 O3 NAAQS rule. While this ruling upheld the 2008 primary NAAQS of 75 

ppb, it did so based on an unusual interpretation of CASAC’s intent in saying a range of 60 to 70 

ppb was appropriate to consider. This may have implications on how future CASAC advisory 

reviews are written. Although this issue is not part of the PA review, it would be helpful if EPA 

staff could provide some guidance to CASAC on how to avoid future perceived ambiguity in its 

recommendations.

On page 1-10 lines 10-14, the court’s rationale for the 0.075 ppm not being inconsistent with 

CASAC advice is correctly explained. However it is informative to look more closely at the 

detailed wording of this argument, especially since it may require the CASAC to be more explicit 

in future letters regarding this issue.

The court decision is summarized at:

http://www.lawandenvironment.com/2013/07/mississippi-v-epa-support-of-the-clean-air-scienceadvisory-committee-is-not-necessary-to-affirm-epas-naaqs/

The decision itself:

http://www.lawandenvironment.com/wp-content/uploads/2013/07/08-1200-1447980.pdf

The essence of the decision, on page 41:

“...in order for EPA to explain adequately its reasons for disagreeing with CASAC, CASAC itself 

must be precise about the basis for its recommendations. Because in this case CASAC failed to 

specify whether the 0.070 ppm level it recommended as a maximum rested on a scientific 

conclusion about the existence of adverse health effects at that level, EPA’s invocation of scientific 

uncertainty and more general public health policy considerations satisfies its obligations under the 

statute.”

Additional excerpts from the decision relevant to CASAC follow.

Pages 38-39:

EPA did not make such a specific scientific determination about the 0.070 ppm level that served as 

A-4
the ceiling of CASAC’s recommendation; instead, EPA referred generally to declining certainty 

below 0.075 ppm. Had CASAC reached a scientific conclusion that adverse health effects were 

likely to occur at the 0.070 ppm level, EPA’s failure to justify its uncertainty regarding the 

existence of adverse health effects at this level would be unacceptable. Indeed, it is a familiar 

principle that agencies may not “merely recite the terms ‘substantial uncertainty’ as a justification 

for [their] actions”; instead, they “must explain the evidence which is available, and must offer a 

rational connection between the facts found and the choice made.” State Farm, 463 U.S. at 52 

(internal quotation marks omitted). In other words, EPA must explain why the evidence on which 

CASAC relied cannot support the degree of confidence CASAC placed in it. This is especially true 

given the added layer of stringency imposed by EPA’s obligations under section 307(d)(6).

But we are unable to determine whether CASAC reached any such scientific conclusion. Although 

CASAC stated that “overwhelming scientific evidence” supported its recommendation that the 

standard be set no higher than 0.070 ppm, Mar. 2007 CASAC Letter, at 2, it never explained 

whether this proposal was based on its scientific judgment that adverse health effects would occur 

at that level or instead based on its more qualitative judgment that the range it proposed would be 

appropriately protective of human health with an adequate margin of safety. Indeed, although 

CASAC concluded that “there is no longer significant scientific uncertainty regarding [its] 

conclusion that the current 8-hr primary NAAQS must be lowered,” given the “large body of data 

clearly demonstrat[ing] adverse human health effects at the current level,” CASAC recognized that 

“[s]cientific uncertainty does exist with regard to the lower level of ozone exposure that would be 

fully-protective of human health.” Oct. 2006 CASAC Letter, at 5.

To be sure, EPA’s statutory obligation to respond to CASAC does not evaporate whenever CASAC 

exercises judgment amidst scientific uncertainty. Quite to the contrary, had CASAC acknowledged 

uncertainty in the scientific evidence but explained that, based on its expert scientific judgment, it 

nonetheless believed adverse health effects were likely to occur at the 0.070 ppm level, then section 

307(d)(6) would have required EPA to explain why it disagreed with this scientific conclusion. Put 

differently, to the extent that CASAC has exercised scientific judgment, EPA must respond in kind. 

But because CASAC never made clear the precise basis for its recommendation, all we know for 

certain is this: both CASAC and EPA believed the existence of adverse health effects to be certain 

at the 0.08 ppm level and reached differing conclusions about what level below 0.08 ppm was 

requisite to protect the public health with an adequate margin of safety. [end quote]

Page 41:

Absent a definitive scientific conclusion from CASAC that adverse health effects would occur at 

the 0.070 ppm level, we must assume that it too took these same considerations into account and 

simply exercised its judgment to recommend a standard set at a lower level. Although both 

CASAC and EPA must exercise public health policy judgment when confronted with scientific 

evidence that does not direct it to a specific outcome, it is to EPA’s judgment that we must defer.

And (as noted earlier):

But in order for EPA to explain adequately its reasons for disagreeing with CASAC, CASAC itself 

must be precise about the basis for its recommendations. Because in this case CASAC failed to 

specify whether the 0.070 ppm level it recommended as a maximum rested on a scientific 

conclusion about the existence of adverse health effects at that level, EPA’s invocation of scientific 

uncertainty and more general public health policy considerations satisfies its obligations under the 

statute.

A-5
Consideration of Potential Alternative Primary Standards (Chapter 4). These are general comments 

regarding this chapter.

Section 4 of the draft Policy Assessment is a concise summary of the science presented in the ISA 

and the health REA with regard to evaluating the health impacts of the current and alternative 

ozone NAAQS. I agree that all aspects of the form of the current ozone NAAQS are appropriate to 

retain. It is worth noting that in much of the country, ozone is monitored for 6 or 7 months of the 

year; this makes the 4th-highest 8-h daily mean form similar to the 98th percentile form used in 

other NAAQS with a daily form.

When choosing ozone concentrations to consider for alternative (lower) values of a standard, there 

is a continuum of decreased risk along with increased uncertainty of the quantitative assessment of 

that risk as ozone exposures decrease. Thus there are no “bright risk lines” at any one ozone 

concentration when considering values for a revised standard. However, the risk and exposure 

assessment process creates bright lines at intervals of 5 ppb, ranging from 80 to 60 ppb, focusing 

on health risks at standards of 70, 65, and 60 ppb in this review. This approach is appropriate since 

there is no meaningful value in attempting to characterize differences in risk between standards of 

70 and 69 ppb for example; the supporting science simply isn’t that precise, and we are working 

from a starting point of 75 ppb (the current ozone NAAQS).

Section 4.6 of the draft Policy Assessment summarizes the reduction in risk for various health 

endpoints associated with alternative standards of 70, 65, and 60 ppb. 70 ppb is the upper end of 

the range recommended in this assessment. I agree with the many panel members who expressed 

concern during the March 27, 2014 CASAC meeting that 70 ppb was not sufficiently protective of 

vulnerable populations. In that context, EPA’s discussion of risks and the science supporting those 

risks for 65 ppb (starting on page 4-52) is informative to this process. Lines 3-13 on that page 

provide a framework for this value, noting 65 ppb is “somewhat below” the 70 ppb level where 

health effects “judged adverse” by the ATS were reported, and higher than the level where lung 

function decrements “that could be adverse in individuals with lung disease.” 65 ppb is also above 

the 60 ppb level where “pulmonary inflammation has been reported.”

Risk is not eliminated at 65 ppb, but this is a concentration where the science behind the reported 

health effects of concern can be considered to be sufficiently robust for the NAAQS process. Thus 

I recommend that EPA consider setting a revised ozone standard that is no higher than 65 ppb. 

This is consistent with the CASAC letter of March 30, 2011 regarding the ozone “reconsideration” 

review process, which says that 70 ppb “would provide little margin of safety”. This review was 

based on the science available to the panel in the 2008 NAAQS revision, and thus does not reflect 

new research since 2006. It is also consistent with the “first version” of EPA’s final rule for the 

reconsideration process, which went to OMB in 2011 with a standard of 65 ppb (see my comments 

on Chapter 1 of this document).

Finally, although not directly relevant to this process, it is worth noting that a new Canadian 

Ambient Air Quality Standard (CAAQS) for ozone was approved in 2012; this replaces the 

existing Canada Wide Standard of 65 ppb. The ozone CAAQS of 63 ppb (same form as the current 

ozone NAAQS) goes into effect in 2015, followed by a standard of 62 ppb in 2020. More 

information on the ozone CAAQS can be found at:

http://gazette.gc.ca/rp-pr/p1/2013/2013-05-25/html/notice-avis-eng.html#d106

A-6
Ed Avol

CHAPTER 1 INTRODUCTION

1. P1-2, line 16 and Footnote 5: not clear that this footnote or caveat are needed; there could 

be other reasons, including substantive technical as well as basic grammatical or textual, 

reasons that might lead to a request for a 2nd draft document.

2. P1-14, line 4: With all due respect, there was considerable controversy over the 

Administrator’s recommendation of a 0.075 ppm ozone standard. One cannot “know” 

what the Administrator “relied” on to make his determination. It would be more 

appropriate (and accurate) to say that “...the Administrator was provided the available 

scientific evidence...He subsequently revised the level of the 8-hour primary O3 

standard...”

3. P1-14, line 21: We cannot know what “The Administrator believed...” This should be 

changed to something like “In the opinion of the Administrator...”

4. P1-19, Figure 1-1: A more accurate presentation of the review of the primary standard 

would suggest that the Averaging Time box in the figure be re-worded to allow for the 

possibility of either a longer or shorter -term averaging time.

5. P1-21, lines 8-12: This is a pretty convoluted and wordy sentence, almost obscuring the 

message. The point here is that based on available research, there is no evidence of a 

biological threshold for ozone health effects (...and that’s a lot shorter and more 

understandable sentence!).

6. P1-27, lines 21 forward: Why is so much time and effort spent in this document 

discussing what a former Administrator did or did not do with regard to the last review? 

While it’s appropriate to refer to this, it seems like there is an inordinate amount of text 

devoted to revisiting (or arguably, attempting to re-formulate) the historical record with 

regard to what a former Administrator did or did not rely on to make his prior 

determination. The issue before the current CASAC is NOT what the prior review did or 

did not decide; the issue before the current CASAC is the strength of the cumulative 

current evidence regarding ozone exposure and protection of the public’s health, and the 

clarity and appropriateness of proposed staff recommendations to the current 

Administrator.

7. P1-27, line29: We do not and cannot know to what extent the Administrator carefully 

considered the public comments...or to what degree he further recognized that several 

additional lines of evidence had progressed sufficiently since the 1997 review to provide a 

more complete and coherent picture... (p1-28, lines 1-3); this phrasing should be 

removed. The comments and information were provided, the Administrator had access to 

them, and he made a determination. (This PA is not the place to justify or re-interpret 

previous Administrator’s actions, but rather to present current data and judgments).

8. (typographical error; p1-35, line 35, “evidence”)

9. P1-40, lines 25 to 34: this is a useful paragraph describing the organization of the overall 

document, but it is completely out of place at the end of Chapter 1. This should be moved 

to the first few pages of Chapter 1, prior to the Background section, and an overview 

sentence could be added describing the presentation in Chapter 1.

A-7
CHAPTER 2 OZONE MONITORING AND AIR QUALITY

10. P2-8, line 13: This is an important point but is awkwardly phrased. Recommend rewording to say, “...contributes to subsequent O3 formation further downwind.”

11. P2-9, line 7: replace “high” with “elevated”, so that sentence reads “...result in a higher 

frequency and duration of days with elevated O3 conditions.”

12. P2-9, line16: replace “high” with “higher” and “low” with “lower”

13. P2-10, lines 26 to 27: The lower rates of chemical scavenging in downwind rural areas 

can often result in characteristically broader, more gradual hourly ambient O3

concentrations, rather than the more”peaky” O3 spikes often seen in urban areas with 

substantive rush-hour-type combustion NO contributions. This observation helps to 

clarify why locations such as Lake Arrowhead downwind of Los Angeles can exhibit 

elevated eight-hour levels compared to surrounding reporting locations.

14. P2-11 forward, Section 2.4Background O3: Although I appreciate the figures, depth, and 

discussion regarding background ozone levels, this presentation seems to conflict with 

the prior determination that background levels are less important, since total ozone 

concentrations are being used in the current document to assess risk. This section might 

be valuable as a supplement or Appendix, but if total ozone is the perspective and 

approach being used, this whole section seems overly detailed, out of scope, and a 

diversion from keeping the presentation focused and crisp. If staff were to consider every 

possible question that might be asked of them and seek to develop and provide as 

complete an answer to every other possible question, the resulting document would be 

several times larger than it already is and considerably less accessible to the Reader. In 

my opinion, this document should focus on the approach, implications, and process put 

into place by the related ISA and HREA, and not delve off into addressing every possible 

corollary or potential derivative consideration.

CHAPTER 4 CONSIDERATION OF ALTERNATIVE PRIMARY STANDARDS

(No specific comments on specific sections)

This chapter provides a useful and carefully documented assessment of alternative 

primary standards for ozone. Although I personally found it wordy and a bit indirect, it 

does provide a comprehensive evaluation of the anticipated health implications of 

alternative ozone standards in the 60 to 70ppb range. The figures and tabular summaries 

regarding assorted health indices should be of particular utility to the Administrator in her 

assessment.

A-8
Joe Brain

O3 Monitoring and Air Quality (Chapter 2): This chapter provides a description of the current 

O3 monitoring network and recent concentrations, information on emissions and atmospheric 

chemistry, common patterns and variability in O3 concentrations, as well as, discussion of current 

information on estimating O3 concentrations associated with non-anthropogenic sources.

1. To what extent does the Panel agree that the most relevant information on monitoring 

(section 2.1), emissions and atmospheric chemistry (section 2.2), and common patterns of O3 

concentrations (section 2.3) is presented, and to what extent is the information presented 

appropriately characterized and clearly communicated?

I believe that to a great extent, the most relevant information on monitoring, emissions, 

atmospheric chemistry, and resulting patterns of ozone concentration are presented in Chapter 2. A 

great deal of information is presented concisely. Especially the figures are helpful in understanding 

the geographic distribution of the network and the ozone concentrations that have been measured.

A key question is not answered. How does the information collected – the geographic distribution 

of monitoring stations – correlate with the distribution of humans throughout the United States. It’s 

clear that information is more densely collected in the northeast and in coastal California. We know 

that that makes sense. But overall, if one simply designed a system of monitoring sites that was 

solely based on accurately measuring exposure of as many inhabitants as possible, would it be the 

same or would it be different?

For example, one can imagine that the monitoring sites were selected decades ago. To what extent 

does the current network operating today represent recent changes in population, such as dramatic 

declines in Detroit and growth in Las Vegas. There should be a paragraph or so defending the 

network or at least explaining the extent to which it resembles an ideal, unbiased network. This 

same discussion should be made not only in relation to all people, but in relation to more 

responsive populations. What’s the distribution of children? What’s the distribution of people with 

preexisting disease and/or the elderly? To what extent do these distributions resemble the current 

ozone monitoring network?

Ozone, as we all know, is not a primary emission from cars, trucks, factories, or other 

anthropogenic sources. As we know, ozone comes from two primary precursors, oxides of nitrogen 

and volatile organic compounds. When they combine in the presence of sunlight, ozone is 

produced. Carbon monoxide and methane may modulate these chemical reactions.

Shouldn’t we also have a map showing the distribution of sites that monitor these precursors or 

perhaps a map showing the relative quantitative importance of these precursor emissions? Should 

we then comment on the extent to which ozone creation is produced from local sources to ones that 

contribute because of long distance transport mechanisms? Of course, these issues are perhaps 

more related to control strategies than to the focused mandate of this report.

A-9
2. With regard to information on estimating O3 concentrations associated with 

nonanthropogenic sources or “background O3” (section 2.4), to what extent is this 

information appropriately characterized and clearly communicated?

I am delighted at the well-developed Section 2.4, which deals with background levels of ozone and 

their contributions from natural sources, as well as from anthropogenic emissions outside our 

borders. The PRB or the NAB (North American background) is important. (There is also the USB, 

US background.) The text and the figures are extremely useful, and clearly demonstrate that these

background levels are appreciable. 

Figures 2-8 through 2-10 include the phrase “zero-out modeling.” The text, especially 2-12, has a 

thorough discussion of the limitations of this strategy. But what approaches to dealing with this 

background are rational and how have they been incorporated into this document? This clearly 

affects the magnitude of attributable outcomes to ozone and to the nature of the dose-response 

curves at low and realistic levels. It also calls into question pivotal clinical studies. For example, 

when examining the responses of exercising human chamber subjects to 60, 70, 80, or 100 ppb 

ozone, should their measurements be compared to 0 ppb or is it more relevant and appropriate to 

compare that to background ozone levels? That has rarely been done, but would clearly diminish 

the magnitude of the changes reported. Again, I would be interested in variability in ozone levels in 

these geographic areas. The hypothesis that greater variability is associated with heightened 

responses, even if the average values are the same, is a hypothesis worth exploring. I also think 

there should be more discussion of co-exposures such as ozone and PM or ozone and heat stress.

A-10
David Chock

CHAPTER 2: OZONE MONITORING AND AIR QUALITY

Charge questions:

1. To what extent does the Panel agree that the most relevant information on monitoring (section 

2.1), emissions and atmospheric chemistry (section 2.2), and common patterns of ozone 

concentrations (section 2.3) is presented, and to what extent is the information presented 

appropriately characterized and clearly communicated?

2. With regard to information on estimating ozone concentrations associated with nonanthropogenic sources or “background ozone” (section 2.4), to what extent is this information 

appropriately characterized and clearly communicated?

This Chapter provides a very clear and concise picture of the monitoring network, the recent 

observed ozone concentration trends, both spatially and temporally, and a very brief but relevant 

and credible description of the emissions and atmospheric chemistry. It also provides a clear 

description of the different definitions of background ozone concentrations.

There appears to be a confusion in the proper use of the zero-out approach. On p. 2-12, lines 23-

24, and again on p. 2A-7, lines 231-241, the authors indicate that removing NOx emissions 

completely and unrealistically could lead to inflated estimates of background ozone in urban areas 

where NOx titration of ozone is significant. The authors consider this result as a paradoxical result 

of the zero-out approach. The implication is that background ozone should not be higher than 

when anthropogenic precursor emissions are involved. This is erroneous, and in fact contradictory 

to the acknowledged notion that ozone chemistry is nonlinear. Furthermore, the authors ran 

separate CMAQ runs for base case (designated as total), NB, NAB and USB, and then took the 

ratios of one of the background runs to the base case runs as the percent contribution of the 

background to the base case. This is again erroneous, because it assumes ozone additivity, which 

violates chemistry’s nonlinearity. The zero out approach is not intended for use to assign relative 

contributions, and relative contribution is not a meaningful concept unless the perturbation due to 

some source emissions is so small that linearity can be approximated. The source-apportionment 

method can be used to assign relative background contributions when base case (total) emissions 

are run, but the resulting relative background contributions are valid only for these particular base 

case conditions, and the contributions cannot be converted to absolute concentrations to represent 

background ozone for other emission scenarios including the background emissions alone. Note 

also that the source apportionment methodology used in CAMx is an approximate tool taking some 

ozone nonlinearity (local identifications of NOx-limited and VOC-limited environments) into 

consideration. Its general applicability to a wide range of conditions remains to be established.

Based on the above discussion, in the case of the zero out approach, it is best to change the text in 

the Chapter from “percent contribution” (like in Fig. 2-11 on p. 2-18) to “ratio” when the 

background ozone is compared to the base case ozone. Here two model results are compared, and 

the ratios need not be less than 100%. In the case of source apportionment, “percent contribution” 

can be used, but is applicable only to the base case run. A separate model run still has to be made to 

determine the background-only ozone concentrations. So if the authors are willing to replace 

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“percent contribution” by “ratio”, the zero-out approach is actually more straightforward and does 

not involve the additional assumptions in the source-apportionment methodology.

In the case of W126, the EPA uses a counterfactual assumption by determining the ozone 

concentrations by separately zeroing out different background emissions based on the definitions of 

NB, NAB and USB. The procedures are more complicated but are presented in the Appendix. The 

resulting estimates of background fractions for different definitions of background are generally 

consistent with but slightly lower than those for the MDA8. This is partly due to the definition of 

W126 which has a higher weighting for higher ozone concentrations.

One very minor comment: Since seasonal means have been used quite extensively, it is better to 

incorporate the definition of season in the text rather than leaving it in the footnote (footnote 8 on 

p. 2-13).

Overall, other than the misstatements about the zero out approach and the erroneous implications 

that background ozone cannot become greater than when anthropogenic emissions are involved, 

this is an outstanding chapter in terms of clarity, conciseness, and scientific credibility. The 

authors should be congratulated for a job well done.

A-12
Ana Diez Roux

Chapter 3. Adequacy of the Primary Standard

1. To what extent does section 3.1 (Evidence-based Considerations) capture and appropriately 

characterize the key aspects of the evidence assessed and integrated in the ISA? To what extent is 

staff’s consideration of the health effects evidence, including the adversity of reported respiratory 

effects and public health implications technically sound and clearly communicated at an 

appropriate level of detail? In the Panel’s view has the information been appropriately interpreted 

for the purpose of assessing the adequacy of the current standard?

Overall section 3.1 appropriately describes key aspects of the evidence. I found the consideration if 

the evidence to be technically sound, and the information appropriately interpreted for the purpose 

of assessing the adequacy of the current standard. My main comment is that the section would 

benefit from synthesis and emphasis of the most important facts relevant to assessing the adequacy 

of the current standard. There is also some repetition within sections (for example the section on at 

risks populations repeats the key message several times).

2. With regard to the presentation of the exposure and risk information for the purpose of

assessing the adequacy of the current standard, to what extent is the information, including 

associated limitations and uncertainties, sufficiently characterized, appropriately interpreted and 

clearly communicated?

Section 3.2 also contains abundant repetitions from the REA and could be synthesized.

The section refers to two important issues in estimating the health impact of alternative standards:

1. It is noted that the simulations used to estimate Ozone levels under alternative standards 

result in spatial patterns different than those observed in the epidemiologic studies on which 

the health effects measures are based. This would result in different health impacts than 

those predicted from the epidemiologic studies if one or both of the following conditions 

are met (a) factors associated with space modify the effects of ozone on heath or (b) spatial 

mobility of persons within the area is a key driver of individual-level exposures. If we are 

confident that the impact of these two conditions is absent or negligible then we can be 

confident in the expected health benefits as predicted despite the change in the spatial 

pattern.

2. It is noted that based on the approach used to model ozone reductions under alternative 

standards, ozone levels may actually rise in some areas when meeting lower overall 

standards. This is because of the dynamics used to model ozone reductions. It should be 

noted that as a consequence the estimates of the health effects are not precisely the health 

impacts of reducing ozone to a certain level, but rather the health impact of meeting an 

alternative standard through a postulated set of changes to precursors (some of which 

results in reductions and some of which result in increases in ozone). This is a subtle but 

important difference I think. It may be useful to at least note this. Also, is the approach used 

to model meeting alternative standards (which results in increases in some locations but 

decreases in others) realistic?

A-13
Pg 3-106 lines 23-28 suggest that since approximately 30-60% of the average daytime O3 is 

attributable to US anthropogenic sources, then 30-60% of total 03- associated health risks in the 

urban case studies is attributable to US anthropogenic sources. I don't think this statement is 

accurate: if the reductions in ozone exposure necessary to eliminate or sharply reduce ozone 

associated health effects can be achieved through redctions in US anthropogenic sources alone, 

then much more than 30-60% in health effects can be attributed to anthropogenic sources.

3. In the Panel’s view, does the discussion in section 3.4 provide an appropriate and sufficient 

rationale to support staff’s preliminary conclusion that the current evidence and exposure/risk 

information call into question the adequacy of the current standard and that it is appropriate to 

consider revising the standard to achieve additional public health protection?

Overall I though this section was adequate but could benefit from synthesis and emphasis.

Chapter 4. Consideration of Potential Alternative Primary Standards 

1. In the Panel’s view, has the evidence and exposure/risk information, including associated 

limitations and uncertainties, been appropriately characterized and interpreted for the 

purpose of considering potential alternative standards?

Overall I found the chapter to be very well written and to the point. The point regarding 

ozone serving as an indicator for a standard meant to provide protection against 

photochemical oxidants is well taken. The discussion regarding averaging times is focused 

and supported by appropriate evidence. The discussion regarding the form was also very 

well written. The points supporting he use of an nth highest daily maximum (as opposed to 

an expected excedance or percentile-based form) were well stated, however I found the 

justification of the 4th highest daily max (as opposed to the nth highest) incomplete.

The section on controlled human exposures studies is an excellent summary although it 

loses focus in the latter part (pg 4-10 line 19 through pg 4-11 line 6 ). For example it is not 

clear why panel studies are discussed here as they are not controlled human exposures 

studies. The section on page 4-11 lines 6-20 should be consistent with and avid repetitions 

with pg 4-10 lines 1-18.

The approach of summarizing associations in cities meeting various alternative standards 

may be informative but the point of this analysis is not stated clearly and the overall 

conclusion is not well stated (pg 4-13 ). What can we conclude then from table 4-1? If 

studies conducted in areas that have met lower standards do not show an effect do we 

conclude then that the standard produces appropriate health protection? But if they do does 

this suggest that an even lower standard is necessary? The logic of this analysis needs to be 

clarified. 

The subsequent section (on associations below various cutpoints) is clearer but the 

conclusion could also be summarized more clearly. Is the key point that a standard of 60

ppb is protective whereas a standard of 65 or 70 is not because studies for which all 

exposures were below 65-70 still reported associations whereas those at levels below 60 did 

not? I also found Table 4-2 confusing. The main point needs to be summarized. The 

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reference to the table in the text was confusing.

The section on protection from long term exposures is well done and convincing.

Section 4.4.2.1 would benefit from a final statement of the key conclusions derived from 

figure 4-1 to 4-4. The same applies to section 4.4.2.2. the bullets are useful but an overall 

summary statement of what we can conclude from these bullets taken together would be 

very helpful.

Section 4.4.2.3. The reason for the large difference in the % reduction in mortality 

associated with meeting a standard of 70 ppb for areas with area wide concentrations > 

40ppb and >60ppb is not clear (the footnote does not help clarify). This also applies to other 

health outcomes. Also the rationale for reporting these two particular estimates is not 

presented. These types of estimates are repeated later in the chapter so their meaning needs 

to be clarified.

I’m not sure I would characterize a 9% reduction in ozone associated mortality as a “small “ 

change (pg 4-41 , top of page). In any case it is larger than the effect observed with a 

standard f 70 ppb so it is not clear why it is considered small.

The chapter also does a reasonable job of grappling and acknowledging the complex issue 

of uncertainties.

Minor comment: avid using the word mortality ( a rate) when you mean total number of 

deaths (as in Figure 4-10).

2. In the Panel’s view, does the discussion in section 4.6 provide an appropriate and sufficient 

rationale, supported by the discussions in sections 4.1 through 4.4, to support staff’s

preliminary conclusions regarding alternative primary standards (including the indicator, 

level, averaging time and form) that it is appropriate to consider?

The section provides an appropriate and sufficient rationale. Overall he section is very well 

organized and the arguments are laid out n a clear and compelling way. A few 

clarifications, particularly of the data presented, would make this an outstanding chapter.

Tables 4-4 and 4-5 are clear but I found figure 4-13 cryptic. It is not clear exactly what is 

shown on the Y axis. Is it the ratio of deaths attributable to ozone for alternative standards 

compared to the 75 ppb standard ? Maybe label the x axis : total ozone attributable deaths, 

ozone attributable deaths at ozone levels > 20, >40 and >60. 

It is difficult to follow the calculations reported on page 4-51 lines 14-21. “For days with 

area wide concentrations at or above 20ppb a standard with a level of 70....”. Is this derived 

from figure 4-13? But if so isn’t this the reduction in deaths attributable to ozone above 

20ppb (not on days with area wide concentrations at or above 20 ppb??)

A-15
3. Does the Panel have any recommendations regarding additional interpretations and 

conclusions based on the available information that would be appropriate for consideration 

beyond those discussed in this chapter?

No additional recommendations. Overall this is an excellent chapter. The final section in 

particular is very well done.

A-16
David Grantz

Chapter 5. Adequacy of the Secondary Standard.

1. To what extent does the information in sections 5.1 through 5.5 capture and appropriately 

characterize the key aspects of the evidence for ozone welfare effects assessed and integrated in the 

ISA? To what extent does the information in section 5.1 (Nature of Effects and Biologically 

Relevant Exposure Metric) appropriately summarize the nature of ozone welfare effects and to 

what extent does it appropriately characterize the evidence with regard to biologically relevant 

exposures?

This chapter does a nice job off summarizing evidence for welfare effects of ozone exposure. The 

paragraph (page 1-37, lines 4-14) provides an excellent rationale for considering the range of 

available studies, and how they might be assessed. Similarly, lines 30-36 on page 1-37 provide an 

excellent rationale for emphasis on Class I and other protected areas. 

The discussion of flux based metrics is useful and appropriate, concluding that potential benefit 

may eventually derive from such metrics but that excessive uncertainty remains at this time. The 

discussion regarding reduced uncertainty associated with OTC derived C-R relationships (page 5-

10; page 5-31) is appropriate and clearly presented. 

The reference to EPA 2013 (page 5-13, line 5) is curious. Meta-analysis has demonstrated that 

reduced carbon transport to roots is a generally observed phenomenon, though exceptions exist. 

This sentence needs to be reviewed, for accuracy and for syntax.

2. To what extent is staff’s consideration of the welfare effects evidence, including the implications 

of reported vegetation effects with regard to adversity to public welfare technically sound and 

clearly communicated at an appropriate level of detail? In the Panel’s view has the information 

been appropriately interpreted for the purpose of assessing the adequacy of the current standard?

The linkage of ecological effects to welfare effects is clearly and appropriately explained, and in 

sufficient detail.

The cottonwood data (Figures 5-1 and 5-3) receive too much emphasis. These data are clearly 

outliers, as already noted in the text (page 5-14, line 5) and require further confirmation.

The effort to monetize welfare impacts and benefits is appropriate, though techniques for this are 

not yet fully developed. Specifically, calculation of consumer and producer surplus data is a useful 

contribution to quantification of welfare effects. The interaction of agriculture and forestry as 

modeled by the Forestry and Agricultural Sector Optimization Model with Greenhouse Gases 

(FASOM-GHG) is mentioned in both the WREA and the PA but not adequately explained.

3. With regard to the presentation of the exposure and risk information for the purpose of assessing 

the adequacy of the current standard, to what extent is the information, including associated 

limitations and uncertainties, sufficiently characterized, appropriately interpreted and clearly 

communicated?

Given that a W126 of 15 ppm hr is in many cases approximately equivalent to the current standard, 

and that injury is clearly observed below 15 ppm hr, the chapter demonstrates that the current 

standard is inadequate to protect against welfare effects due to ozone. The consideration of 

uncertainty (page 5-22, line 23 on) represents an appropriate level of concern and level of 

A-17
interpretation. A similar tone should be adopted in the WREA. However, as in the WREA, the 

periodic consideration of uncertainty is again accumulated and repeated later (e.g. Page 5-27). 

Consolidation near the end of the chapter would enhance the impact of the evidence, reduce 

redundancy, and substantially shorten the document.

It is unclear why the information on foliar injury in four National Wildlife Refuges (Table 5-6) did 

not appear in the Risk Assessment.

The discussion at the top of page 5-55, related to economic losses due to bark beetles and to fire, 

perpetuates the questionable discussion in the WREA, confounding association with any evidence 

of causation. As stated these effects do not contribute much to the assessment of risk due to ozone 

nor to the adequacy of the current or alternative standards.

In Table 5-8 the ranges for Normal and Dry Palmer Z indices overlap. Is this intentional?

4. In the Panel’s view, does the discussion in section 5.7 provide an appropriate and sufficient 

rationale to support staff’s preliminary conclusion that the current evidence and exposure/risk 

information call into question the adequacy of the current standard and that it is appropriate to 

consider revising the standard to achieve additional public welfare protection?

This section can be made more concise and impactful. It clearly demonstrates that ozone induced 

injury may occur in areas that meet the current standard. It systematically justifies the conclusion 

that the form of the standard should be reconsidered, and begins to build the case for levels that 

should be considered. 

There is a wrong word/typographical error at page 5-62, line 2, which alters the meaning.

Chapter 6. Consideration of Potential Alternative Secondary Standards.

1. In the Panel’s view, has the evidence and exposure/risk information, including associated 

limitations and uncertainties, been appropriately characterized and interpreted for the purpose of 

considering levels of protection and potential alternative standards?

It is well justified and consistent with previous CASAC judgment, that a cumulative, non-threshold 

metric, such as W126 is an appropriate form for the standard. Accumulation over the 08:00 – 20:00 

daytime 12 hour period is an acceptable means of generalizing across latitudes and seasons. The 

compromises involved in this selection are clearly explained. 

It is not convincing to argue that a multi-year averaging period is superior to a single year standard. 

Many cultivated and un-managed species are annuals, or cultivated as annuals. Perennials 

including trees may compound annual effects, but the effects are inherently single year impacts. 

Potential differences in soil moisture do not really bear on this question, as there are many factors 

that vary between years. The only significant reason provided in the chapter to consider a three 

year average is for increased statistical stability (page 6-11, lines 14-27). This may be sufficient 

reason, but this should be clearly stated. If a three year averaging period is implemented, it should 

be at a lower level than a single year standard to protect against single unusually damaging years 

that will be obscured in the average.

The key issue in the PA with respect to Welfare Effects is the level of the standard. It is surprising 

to find the statement at page 2-20, line 17-18, that “we are not able to identify a range of 

appropriate W126 index values”. If protection of the most sensitive members of the community is 

extended to components of ecosystems that impact public welfare, then several potential levels of 

the standard suggest themselves. Both visibility and seedling biomass exhibit identifiable 

A-18
thresholds at around 10 ppm hr (though visibility is more of a slope change than a decline to low 

injury level) and for relative biomass loss it is closer to 7 ppm hr. Crop loss appears to be less 

sensitive than these other indicators from the current analysis.

There is substantial redundancy in this chapter that could be consolidated for clarity and brevity.

2. In the Panel’s view, does the discussion in section 6.5 provide an appropriate and sufficient 

rationale, supported by the discussions in sections 6.1 through 6.4, to support staff’s preliminary 

conclusions regarding alternative secondary standards (including the indicator, level, averaging 

time and form) that it is appropriate to consider?

Given the apparent break points around 7-10 ppm hr for various endpoints, it is difficult to 

understand how staff comes to suggest a standard as high as 17 ppm hr. In many cases, 15 ppm hr 

is nearly equivalent to the current standard, which is considered here to be inadequate to protect 

against ozone induced welfare effects. If uncertainty is invoked to prevent over-protection, then 15 

ppm hr is the highest justifiable level for the revised standard based on the internal logic of the 

WREA and PA. If, as seems more likely given patchy species and spatial data coverage, the 

uncertainty results in potential underestimation of risk, then a lower level should be considered.

3. Does the Panel have any recommendations regarding additional interpretations and conclusions 

based on the available information that would be appropriate for consideration beyond those 

discussed in this chapter? 

None.

A-19
Daniel J. Jacob

Introduction (Chapter 1):

1. Does the Panel find the introductory and background material (sections 1.1 and 1.2) to be

appropriately characterized and clearly communicated?

Yes. My only confusion is in the use of “We” at various points in the text. It isn’t clear to me who 

“We” refers to.

On page 1-9 lines 3-4, “a causal relationship between O3 and 8-hour exposures” doesn’t seem to 

make sense. Probably a typo.

2. In section 1.3, we describe the general approach for the review. This includes the key aspects

of the approach employed in the last review in judging the adequacy of the then-existing

standards and in selecting revised standards. Does the Panel find this description of the

approach in the previous review adequate and clear? Does the summary of the approach in the

current review appropriately describe important considerations in this review?

It is generally fine. I only have a few concerns:

1. Page 1-38: The choice of the W126 index as metric for the secondary standard is not 

revisited as part of the current review. Why is it not? 

2. Page 1-40: It’s not clear if the analysis of the background contribution to ozone is to have 

solely a scientific purpose or also a policy purpose.

3. Page 1-40, lines 22-24: the notion that background ozone does not significantly impact the 

W126 index has been challenged by recent work, particularly for the Intermountain West 

where the background is high.

A-20
Steven Kleeberger

Chapter 4: Consideration of Potential Alternative Primary Standards

1. In Panel's view, has the evidence and exposure/risk information, including associated limitations 

and uncertainties, been appropriately characterized and interpreted for the purpose of considering 

potential alternative standards?

I believe the information has been appropriated characterized and interpreted. 

2. In the Panel's view, does the discussion in section 4.6 provide an appropriate and sufficient 

rationale, supported by the discussions in sections 4.1 through 4.4, to support staff's preliminary 

conclusions regarding alternative primary standards (including the indicator, level, averaging time 

and form) that it is appropriate to consider?

In my opinion, the rationale and discussion that lead to preliminary conclusions are appropriate. 

For more clear presentation, staff may wish to consider sub-headings for the consideration of 70, 

65, and 60 ppb standard levels. Conclusions (p 4-57) are clearly stated, and the rationale for not 

considering levels below 60 ppb is appropriate. However, in general, the table and figure legends 

should provide more detail to enable the reader to understand better what is presented. 

Specifically, legends for Figures 4.1 – 4.4 and 4.5 – 4.8 are good examples where more detail in the 

figure legends would help the reader understand all of the included information. 

3. Does the Panel have any recommendations regarding additional interpretations and conclusions 

based on the available information that would be appropriate for consideration beyond those 

discussed in this chapter?

I do not have additional interpretations or conclusions to add to the chapter. However, I would like 

to commend the staff for including the key uncertainties and areas for future research (4.7). This is 

very helpful for the reader to understand that the ‘ozone field’ still requires much additional 

effort/studies to fully understand all of the consequences of exposure to this pollutant. 

A-21
Fred Miller

Introduction (Chapter 1):

1. Does the Panel find the introductory and background material (sections 1.1 and 1.2) to be 

appropriately characterized and clearly communicated?

2. In section 1.3, we describe the general approach for the review. This includes the key aspects of 

the approach employed in the last review in judging the adequacy of the then-existing standards 

and in selecting revised standards. Does the Panel find this description of the approach in the 

previous review adequate and clear? Does the summary of the approach in the current review 

appropriately describe important considerations in this review?

Response: The introductory and background material provides the reader with a synopsis of the 

evolution of the NAAQS review process for photochemical oxidants together with insights into 

major litigation actions that have occurred over the last 30 years. The description of the approach in 

the previous review is clearly presented, and the summary of the current review approach captures 

the salient features of the review process.

O3 Monitoring and Air Quality (Chapter 2):

1. To what extent does the Panel agree that the most relevant information on monitoring (section 

2.1), emissions and atmospheric chemistry (section 2.2), and common patterns of O3 

concentrations (section 2.3) is presented, and to what extent is the information presented 

appropriately characterized and clearly communicated?

2. With regard to information on estimating O3 concentrations associated with nonanthropogenic 

sources or “background O3” (section 2.4), to what extent is this information appropriately 

characterized and clearly communicated?

Response: My comments address the layout of the figures and tables in this chapter and do not 

address the charge questions. The authors should consider a different color scheme for some of the 

figures -- it is hard for the reader to sometimes discern differences (e. g., Figure 2-1). Since figures 

and tables should stand alone, the legends sometimes need to be expanded so the reader does not 

have to refer to the text to interpret the table or figure (e. g., Figure 2-2).

Adequacy of the Primary Standard (Chapter 3):

1. To what extent does section 3.1 (Evidence-based Considerations) capture and appropriately 

characterize the key aspects of the evidence assessed and integrated in the ISA? To what extent is 

staff’s consideration of the health effects evidence, including the adversity of reported respiratory 

effects and public health implications technically sound and clearly communicated at an 

appropriate level of detail? In the Panel’s view has the information been appropriately interpreted 

for the purpose of assessing the adequacy of the current standard?

Response: This section captures the important studies discussed in the ISA and integrates them into 

a logical narrative of what the important findings were in each category of effect such as lung 

function decrements, pulmonary inflammation, respiratory symptoms, and respiratory mortality. 

A-22
The adversity of the effects and their implications for public health is discussed in a straightforward 

and clear manner that leads the reader through the body of data that has been amassed for this 

ubiquitous pollutant. The level of detail used is appropriate for the task at hand. Most importantly, 

the studies have been appropriately interpreted and discussed in Section 3.1.3 in the context of 

assessing the adequacy of the current standard. Section 3.1.3 presents the discussion of adversity in 

a manner that one might find in a legal briefing document, which speaks to the clarity of the points 

raised and supported by facts brought forward from the ISA and the HREA. 

On page 3-15, the statement is made that the group mean decrements in various controlled human 

exposure studies at 60 ppb O3 are not consistently statistically significant. While a correct 

statement, the authors should add that this is due to a lack of consistency in statistical power among 

the studies reflecting an inadequate number of subjects in some of the studies. There are places 

where paragraphs are duplicated almost verbatim on the same page, such as on page 72 for the first 

2 paragraphs. On page 3-81, there is a reference to Table 3-12 but no such table appears in the 

chapter.

2. With regard to the presentation of the exposure and risk information for the purpose of

assessing the adequacy of the current standard, to what extent is the information, including 

associated limitations and uncertainties, sufficiently characterized, appropriately interpreted and 

clearly communicated?

Response: The exposure and risk information pertinent to assessing the adequacy of the current 

standard is presented for 3 main categories: the adjusted air quality data, exposure-based 

considerations, and risk-based considerations. The salient points are clearly presented, and enough 

detail is provided so the reader can ascertain how much weight to assign to any limitations or 

uncertainties. Major points being made are always supported by reference to studies or data 

presented either earlier in this draft of the PA or in the ISA or HREA, which leads one to conclude 

that the points have been appropriately interpreted.

Consideration might be given to having the Y-axis on each of Figures 3-7 to 3-10 all be from 0 to 

30 percent. This would allow the reader to better understand the importance of the different points 

that are being made in this body of figures.

3. In the Panel’s view, does the discussion in section 3.4 provide an appropriate and sufficient 

rationale to support staff’s preliminary conclusion that the current evidence and exposure/risk 

information call into question the adequacy of the current standard and that it is appropriate to 

consider revising the standard to achieve additional public health protection?

Response: Absolutely! – Section 3.4 is a “slam dunk”. This section, which is just slightly over 5 

pages in length, clearly articulates the findings and points that underpin Staff’s preliminary 

conclusion to call into question the adequacy of the current standard and the appropriateness of 

revising it.

Consideration of Potential Alternative Primary Standards (Chapter 4):

1. In the Panel’s view, has the evidence and exposure/risk information, including associated 

limitations and uncertainties, been appropriately characterized and interpreted for the purpose of 

A-23
considering potential alternative standards?

2. In the Panel’s view, does the discussion in section 4.6 provide an appropriate and sufficient 

rationale, supported by the discussions in sections 4.1 through 4.4, to support staff’s preliminary 

conclusions regarding alternative primary standards (including the indicator, level, averaging time 

and form) that it is appropriate to consider?

3. Does the Panel have any recommendations regarding additional interpretations and conclusions 

based on the available information that would be appropriate for consideration beyond those 

discussed in this chapter?

Response: The evidence and exposure/risk information together with an acknowledgement of the 

inherent limitations and uncertainties is presented in a logical manner and the data have been 

appropriately interpreted. The discussion in section 4.6 is well constructed and the case for 

considering alternative standards is articulated clearly. However, the CASAC O3 Panel should 

discussion meeting the summary paragraphs for the 3 alternative levels considered by staff as the 

arguments/discussions presented in the PA have this reviewer inclined to want to revisit the upper 

level of 70 ppb based upon scientific body of evidence considerations and not on any policy 

recommendations.

A-24
Howard S. Neufeld

Chapter 1: Introduction

1. This chapter is an excellent introduction to the history of the standard setting process and 

the legal challenges to previous decisions and their outcomes. It also clearly outlines the 

goals of the PA. This was a well-written and well organized chapter.

2. Yes and yes. I have no other substantive comments.

Chapter 2: Monitoring and Air Quality

First item here deleted as it was incorrect – the 8 hr standard should be expressed in units 

of concentration. I had previously confused it with an exposure index that has hours of ppb*hrs.

1. The discussion on background ozone is satisfactory and clearly explains how staff is 

dealing with this concept.

Chapter 3: Adequacy of the Primary Standard

1. The analysis of the ISA conclusions is well done. The particular emphasis placed on 

studies on the low end of ozone concentrations is commendable. Staff has done a careful 

and thorough analysis of respiratory effects purportedly caused by ozone. The writing is 

clear and understandable to the general public.

2. I thought staff did an excellent job of translating the ISA and Risk Assessment results into a 

statement of adequacy with regards to the current standard. Their analysis of the 

uncertainty and variability is both thorough and complete and serves to strengthen their 

conclusions reached about the adequacy of the current standard.

3. As noted above, staff has properly interpreted the new scientific studies and reached a 

logical conclusion that the current standard is not adequately protecting human health. This 

chapter was one of the strongest of all in the document: well synthesized, well justified, and 

with appropriate conclusions drawn from the analyses. I feel, therefore, that they are 

justified in proposing that the current standard should be revised.

Chapter 4: Consideration of Potential Alternative Primary Standards

1. The analyses of the various standard attributes (indicator, averaging time, form, and level) 

are well done. The conclusions that follow are appropriately stated and thoroughly 

justified.

2. I agree in all respects with the conclusions in section 4.6. I think the analyses preceding 

this section clearly justify the proposals in this section. I found nothing with which to 

disagree. In particular, staff’s analysis of the difficulties in setting the standard too low are 

much appreciated and their detailed consideration of alternative metrics are to be 

commended. They clearly justify why the current indicator, averaging time and form of the 

standard should be retained, but that the level should be lowered. 

3. I have no additional recommendations here.

A-25
Chapter 5: Adequacy of the Secondary Standard

1. Staff make a strong case (perhaps stronger than in any previous reviews) both that the 

current secondary standard fails to protect vegetation and ecosystem services from adverse 

effects, and that the form of the standard is inadequate to provide such protection. Sections 

5.1 through 5.5 clearly lay out the argument for the impacts of ozone on ecological 

processes and ecosystem services. Their descriptions and analyses of the uncertainties are 

refreshingly clear and unbiased. Despite the paucity of data in certain areas, staff is still 

able to make statements of causality and risk with which to evaluate the adequacy of the 

current welfare standard.

2. Staff did an excellent job regarding technical soundness and providing clarity to the public. 

I might note that during the risk analysis, and also here, staff compares changes in seedling 

growth under ozone exposure to adult tree changes in circumference, expressed as percent 

losses. However, circumference as a surrogate for growth is somewhat questionable since 

growth in diameter would imply an increase in area, which is related to changes in 

circumference by the square (and total growth, i.e. volume, would increase by the cube). A 

10% reduction in circumference would translate into a 19% reduction in trunk area. How 

this might affect the conclusions drawn I don’t know, but it suggests that using 

circumference underestimates the effects.

With regard to adequately interpreting the data for the purpose of assessing the adequacy of 

the current standard, I am satisfied with the analyses presented and agree with staff’s 

interpretations.

3. The uncertainties are well laid out and explained and place the interpretations into proper 

perspective. It appears both in this section, and in the previous chapter, that staff has gone 

to great lengths to justify the conclusions reached from their analyses of the ISA and REA 

documents as well as making sure to follow the requirements of the Clean Air Act. I was 

very impressed with this aspect of the current PA.

4. I agree with most of the conclusions in section 5.7. I support moving from the 8-hr 

standard form to the cumulative W126 index, and I agree with using the maximum 3 month 

interval. I think a strong case can still be made that the timing should be for an individual 

year, rather than averaged over three years. I am concerned about the level and at what 

upper limit it should be set. Most of the analyses seemed to find effects below 15 ppm*hrs 

(many at 10 or even 7), so it would seem reasonable to set it lower than 15 ppm*hrs, and 

not as high as 17 ppm*hrs. Also, in many cases 15 ppm*hrs is approximately equivalent to 

the current standard, so keeping it that high would engender little benefit.

Chapter 6: Consideration of Alternative Secondary Standards

1. Staff make a very strong case for switching the secondary form to the W126 and for 

averaging it over three months and using the highest three month interval as the metric that 

is evaluated. The lack of an arbitrary threshold and the higher weightings for higher ozone 

concentrations are the appealing aspects of this ozone metric. I also support the use of 

daylight hours for this metric, from 8 am to 8 pm. There could be some quibbling about 

whether this time interval is shifted too late in the day, and misses some uptake early in the 

morning, but as staff notes, ozone at low elevations rarely rises to high values before 8 am. 

A-26
However, in mountain regions, ozone is high over a 24 hour period, and as such, starting 

the metric at 8 am instead of 7 am or even 6 am, may miss some aspects of the exposure 

impacts. However, given that only one time interval can be selected, and that most areas 

across the country are not at high elevations, I can support using the 8 am to 8 pm interval.

2. I am less convinced that the three year average form is better than a single year form. I 

fully understand staff’s arguments about stability but remain to be convinced that this 

would provide superior protection (requisite protection) given the comments from CASAC 

on this topic from earlier reviews. And if the increased statistical stability is that important, 

then the level should be reduced in order to protect the most sensitive vegetation. 

There seems little justification for allowing the increased flexibility of setting the level of 

the W126 above 15 ppm*hrs. See comments above in the Chapter 5 section. Most of the 

tree data show 2% annual growth losses at up to 14 ppm*hrs. It would seem prudent to take 

out the statement that the Administrator could consider exposure values above 15 ppm*hrs.

3. I have no further recommendations except one: the PA document contains many 

redundancies, which take away from its ability to clearly transmit its message to the public. 

This is especially so for Chapters 5 and 6. If there is any prudent way to shorten these 

chapters some, I think that would improve this document.

In conclusion, I would like to commend EPA Staff for their due diligence and hard work in putting 

these documents together. I was much impressed by the analyses and conclusions. They represent 

a real step forward from the first drafts.

A-27
Armistead (Ted) Russell 

Overall, I found the PA informative and providing much of the information needed to inform the 

Administrator in regards to potentially modifying the ozone NAAQS. It generally has a good 

discussion on the adequacy of the current health and welfare standards, and potential revisions. 

Further, the preliminary revisions are in line with the evidence provided in the ISA and the 

analyses in the two REAs. The current presentation, for the most part, picks a reasonable balance 

between the desire to make the PA readable, concise and to the point, and providing sufficient 

information. The greatest need has to deal with issues involving the increases in lower levels of 

ozone in response to controls designed to reduce higher ozone levels. This issue impacts the risk 

and exposure assessments and the form of the standard.

Chapter 2: O3 Monitoring and Air Quality

1. To what extent is the most relevant information on monitoring, emissions and chemistry, 

and common patters of ozone concentrations is presented, etc.:

The current Chapter 2 is very streamlined; too much so. At present, it focuses primarily on the 

issues involving background ozone, which is an appropriate discussion, but there is at least one 

larger issue that needs to be addressed here in some detail, that being the response of lower level 

ozone levels to controls. As shown in the Health REA this is a very important consideration, and 

should be discussed in more detail in Chapter 2 as it is an important consideration in the potential 

form of a standard, and the possible limitations of the current form. As such, the PA should 

provide a discussion of how the observed ozone levels at various percentiles have been found to be 

evolving, e.g., the decreases in higher levels and increases in lower levels. This should be 

augmented with results from the modeling. The PA should provide the Administrator with a firm 

understanding that controls oriented at reducing the peak levels of ozone (e.g., the 4th highest 

annual MDA8) may not be that effective at reducing more typical levels and may actually increase 

ozone levels on lower ozone levels and also increase 24 hour levels on a broader range of days.

Chapter 2 needs an overall summary. What are the major take-home points for the Administrator 

(and others) from Chapter 2? 

2. Is the discussion of Background Ozone appropriately characterized and adequately 

communicated?

The discussion of background ozone is much more extensive than any other part of the air quality 

characterization. None-the-less, there are some missing pieces. First, the method by which the NB 

is calculated (e.g., models used) should be further described. The discussion of the source 

apportionment model estimates is much too minimal to really understand what is being done. 

Provide an extra sentence or two. The sentences beginning on 2-16, line 9 going to line 14 are not 

clear. The potential use of monitoring to estimate background should be discussed. I would also 

include a bit more on the range of controversy surrounding this issue. This should be recapped 

later on as well. In general, however, the discussion does provide a good and reasonably thorough 

assessment of the “background ozone” issue on setting a standard.

In the PA, I would also bring forward more of the results on the levels of controls needed to just 

meet various levels of the standards being assessed, both for the health and welfare standards. One 

A-28
could use the two tables from the Appendices for the H-REA (Table 2 of Appendix 4) and the WREA (Table 4A-2). This could be part of a synthesis as well. 

Page 2-16, line 16: It is not apparent that the difference between 66 and 59 is due to the 

definitional approach versus the difference in model .

2-17, l21-23: What exactly does this mean? In particular, does “but for” mean if background 

sources were not present, there would not be an exceedance, or does it mean, if only background 

sources were present, there would be an exceedance?

2-9, l34: When discussing specific metrics, be very careful as to what is being said as to not be 

ambiguous.

2-9 l 14. I think you mean “intrusions” not “inversions”

Chapter 4: Form of the health based standard. Given the potential for controls to increase lower 

levels of ozone, one might consider a different form of the standard that would be protective at 

lowering high levels of ozone and also decreasing mid and lower levels. This should at least be 

discussed at a level that could lead the Administrator/reader to confidently say that the current form 

is appropriate. Indeed, one might come to the conclusion that another form would be better.

Chapter 6. One of the conclusions of the W-REA was that just meeting the current standard (75 

ppb) leads to very similar ozone levels as a W126 of 15. This should be brought out more. Indeed, 

I am not sure that the difference is beyond the uncertainties in the approaches used. Given that a 

W126 of 15 roughly corresponds to a 75 ppb standard, the rationale for considering a W126 of 17 

should be further discussed. 

The PA could use a synthesis as well. The Synthesis should include how the health and welfare 

standards might work together. Further, it could identify the critical findings that would likely 

drive the decision to keep or revise the standards, including the characterization of the likely 

benefits of various choices of the standards and the uncertainties that are key. Maybe this will be 

included as part of the Executive Summary in the next draft. At present, the Executive Summary is 

a bit too short and weak. For example, it currently uses the phrase “call in to question”, which 

might be stated as finds that the current standard is inadequate to protect health, and provide the 

specific evidence to suggest so. One thing that the synthesis could provide is the similarities in 

ozone fields at different levels of the health and welfare standards under consideration. It could 

also include tables showing the levels of control to meet those levels. 

Executive Summary:

As noted above, the ES is rather short, and appears to be a work in progress. Compared to the ES’s 

for the two REAs, this one does not stand up. It really does not do the PA justice. An important 

point from the W-REA should be made here, that being that a W126 of 15 ppm-hrs is very similar 

to just meeting the current standard. The ES could also use a synthesis. 

A-29
Helen Suh

Adequacy of the Primary Standard (Chapter 3)

1. To what extent does section 3.1 (Evidence-based Considerations) capture and appropriately 

characterize the key aspects of the evidence assessed and integrated in the ISA? To what extent 

is staff’s consideration of the health effects evidence, including the adversity of reported 

respiratory effects and public health implications technically sound and clearly communicated 

at an appropriate level of detail? In the Panel’s view has the information been appropriately 

interpreted for the purpose of assessing the adequacy of the current standard?

The section is comprehensive. While this comprehensive summary is accurate and clear, it does 

appear in other documents. Further, its volume is overwhelming. As a result, the Chapter is 

somewhat unfocused, and evidence supporting its conclusions regarding the adequacy of the 

primary standard are not sufficiently targeted. As one suggestion to increase the clarity of the 

Chapter, Section 3.4 could be moved to the beginning of the Chapter, with the summaries of 

findings and other sections used to support the conclusions of Section 3.4. Other comments and 

suggestions are discussed briefly below:

• Figures need additional annotation, better titles and a better color scheme (for example Figures 

3-7 to 3-10).

• The discussion of the policy-relevant background risks should be removed or moved to the 

discussion of the history. 

• Subsection 3.1.2

o The subsection 3.1.2, which addresses the nature and strength of conclusions, could be 

more targeted, focused less on a summary of all findings but instead on findings 

contributing to the adequacy determination. In this way, it can provide an introduction to 

the topics discussed in later subsections, including adversity of effects and concentrations 

associated with observed impacts, with these later subsections being at the heart of Section 

3.1. 

o While causal determinations were stated at relevant places in the text, it would be helpful to 

include at the beginning of Section 3.1.2 a table that lists the causal determinations made 

in the 2006 and current ISA. This table should be accompanied by a brief discussion that 

explains how health outcomes were selected for further discussion in Section 3.1.2.

o Summary figures and/or tables should be added to Subsection 3.1.2 in place of text for the 

major outcomes. While summary figures of epidemiological studies were included (such 

as Figure 3-2), a preferable model for summarizing findings may be to include tables, such 

as Tables 4-23 and 5-19 from the NOx ISA, which summarize information succinctly 

across evidence and study types to support causality determinations. It may also be helpful 

to note in these summary figures and tables studies or findings that show ozone impacts at 

standard-relevant ozone levels.

o The summary of ozone-attributed health outcomes in epidemiological studies should 

include a brief discussion of the potential for confounding of the observed effects, since is 

it is relevant to causal determinations.

o Page 3-53, line 29-33 The statement beginning “Generally, the epidemiologic studies used 

nearest air monitors to assess ozone concentrations...explained by the different exposure 

assignment methods used...” relates not only to this subsection but also to previous 

A-30
subsections. It should be mentioned in earlier subsections, if only to say that significant 

associations were found despite the presence of exposure error resulting from the use of 

ambient ozone concentrations to assess exposures. 

• Section 3.1.3: It seems that much of this section is a repeat of earlier discussions, although 

with a different focus. To reduce repetition, it may make sense for this discussion to be 

incorporated into section 3.1.2, possibly using the following outline 

o Health outcome 1

 Summary of findings (including causality determination and whether 

it has changed)

 Adversity of impacts 

 Ozone concentrations associated with health effects

o Health outcome 2 (etc.)

• Section 3.1.4: Important discussion that summarizes information across health effects. The 

summary tables 3-1 and 3-2 were very helpful. This subsection would be improved with 

further organization and integration of the findings across health effects, as this would help to 

demonstrate coherence with regard to the lowest ozone concentration at which key health 

impacts have been observed. The discussion of coherence doesn’t begin for many pages (page 

3-71) and is consequently buried. It would be better to summarize the earlier discussion more 

concisely to highlight the key points of the section. 

2. With regard to the presentation of the exposure and risk information for the purpose of assessing 

the adequacy of the current standard, to what extent is the information, including associated 

limitations and uncertainties, sufficiently characterized, appropriately interpreted and clearly 

communicated?

Again, this section is comprehensive and accurate. The discussion on page 3-94 was clear, to the 

point, and clearly related to standard-setting considerations. Similarly, the discussion of 

uncertainties was well written and concise. However, in other areas, the section was overly 

repetitive and should be summarized more concisely to highlight discussions that focus more 

specifically on standard-relevant issues. 

3. In the Panel’s view, does the discussion in section 3.4 provide an appropriate and sufficient 

rationale to support staff’s preliminary conclusion that the current evidence and exposure/risk 

information call into question the adequacy of the current standard and that it is appropriate to 

consider revising the standard to achieve additional public health protection.

Section 3.4 was a terrific synthesis of the current health and exposure/risk information. In some 

ways, the chapter should lead with this section, as it captures the key points, summarizes the 

evidence clearly and concisely in a manner that keeps the focus on standard-setting considerations.

Consideration of Potential Alternative Primary Standards (Chapter 4)

1. In the Panel’s view, has the evidence and exposure/risk information, including associated 

limitations and uncertainties, been appropriately characterized and interpreted for the purpose 

of considering potential alternative standards?

A-31
This Chapter was well written, comprehensive, clear, and focused. It was a pleasure to read. 

Suggestions to improve the chapter are rather minor. They include: 

• In general, the figures and tables need further descriptions, better titles and better 

annotation. For example, several figures, such as Figures 4-1 and 4-2 and Figures 4-3 and 

4-4, seem extremely similar (with the same title) and it is not clear what the graphs are 

depicting.

• The question on page 4-8 (and following text) should be reworded to focus on lung function 

decrements and airway hyperresponsiveness rather than controlled human studies given the 

inclusion of panel study results in this section. Correspondingly, the title of the subsection 

“epidemiological evidence” to hospital admissions and mortality should be reworded to 

focus on health outcomes rather than study type.

• The discussion on page 4-14 of the cut-point analysis is a repeat of that in Chapter 3. 

Rather than repeat the discussion, instead reference it and draw conclusions relative to the 

level of the standard.

• The interpretation of Figure 4-10 is unclear from the text and the figure. 

• Figure 4-9 (and other figures), the y axis should be labeled as “deaths” and not “mortality”. 

In the text, it may be helpful to explain reasons for the observed between-city variability in 

figures such as Figure 4-9. Is this between-city variability important?

2. In the Panel’s view, does the discussion in section 4.6 provide an appropriate and sufficient 

rationale, supported by the discussions in sections 4.1 through 4.4, to support staff’s 

preliminary conclusions regarding alternative primary standards (including the indicator, 

level, averaging time and form) that it is appropriate to consider?

Yes. The section was clear, well-written, and effective.

3. Does the Panel have any recommendations regarding additional interpretations and 

conclusions based on the available information that would be appropriate for consideration 

beyond those discussed in this chapter?

The chapter was a cogent presentation of the rationale behind the report’s conclusions.

A-32
James Ultman

To what extent does section 3.1 (Evidence-based Considerations) capture and appropriately

characterize the key aspects of the evidence assessed and integrated in the ISA? To what extent

is staff’s consideration of the health effects evidence, including the adversity of reported

respiratory effects and public health implications technically sound and clearly communicated 

at an appropriate level of detail? In the Panel’s view has the information been appropriately

interpreted for the purpose of assessing the adequacy of the current standard?

The chapter does an excellent job of summarizing the current evidence-based considerations of 

short-term and long-term O3 health effects and placing them in the contexts of adversity to the 

individual as well as public health implications.

Section 3.1.1

I believe that appendix 3A describes specific modes of action much better than current text in 

section 3.1.3. I would go so far as to replace the latter by the former.

Regarding figure 3-1 (copied from figure 5-8 in the ISA), the mode-of-action pathways for specific 

adverse effects do not necessarily follow from the hierarchy in the figure. For example, 

inflammation and cell remodeling are both placed on the second level while epithelial metaplasia 

appears on the third level. I would argue that a more accurate sequence for the metaplastic changes 

that have been observed in toxicological studies might be: inflammation (second level)cell repair 

and remodeling (third level) metaplasia (fourth level not currently on figure). 

The mode-of-action discussion implies that secondary oxidation products rather than ozone itself 

drive the respiratory responses. This point of view is based on well-accepted dosimetry analyses 

indicating that ozone is almost completely reacted during its transit through the mucous layer in 

conducting airways. However, these analyses are not directly supported by experimental 

observations. Furthermore, it is still quite possible that ozone quantitatively penetrates the thin 

surfactant layer in alveoli distal to the conducting airways. 

The first step in the respiratory response is described as oxidant stress, but this catch-all term does 

not tell the whole story. While ozone and some of its reaction products are oxidants that can be 

detoxified by endogenous antioxidants, other reaction products (e.g., aldehydes) cause cell damage 

by non-oxidative processes.

Page 3-13 (line 6) gives a literal interpretation of the McDonnell and the Schelegle models in 

terms of a specific mechanism (i.e., oxidant stress). Although this is a reasonable hypothesis, 

one should recognize that both models are simply two-stage mathematical constructs that 

include a build-up of inhaled ozone dose by continuous inhalation in competition of a reduction 

in biologically-effective dose by some clearance or metabolic process. It is also possible that 

such a reduction is the result of absorption of ozone in airways regions (such as the nose and 

mouth) that are proximal to the airway sites where dysfunction actually occurs.

A-33
Section 3.1.2.2

Entry is missing from the table of contents.

With regard to the presentation of the exposure and risk information for the purpose of

assessing the adequacy of the current standard, to what extent is the information, including

associated limitations and uncertainties, sufficiently characterized, appropriately interpreted

and clearly communicated?

I think that the document is quite effective in presenting risk reduction information between recent 

conditions and just meeting the current standard. 

In the Panel’s view, does the discussion in section 3.4 provide an appropriate and sufficient

rationale to support staff’s preliminary conclusion that the current evidence and exposure/risk

information call into question the adequacy of the current standard and that it is appropriate to 

consider revising the standard to achieve additional public health protection?

This section provides a sufficient rationale for staff’s conclusion the current standard does not 

provide adequate health protection. 

A-34
Sverre Vedal

Ch. 3. Adequacy of the current standard

Adequacy of the Primary Standard (Chapter 3)

1. To what extent does section 3.1 (Evidence-based Considerations) capture and appropriately 

characterize the key aspects of the evidence assessed and integrated in the ISA? To what extent is 

staff’s consideration of the health effects evidence, including the adversity of reported respiratory 

effects and public health implications technically sound and clearly communicated at an 

appropriate level of detail? In the Panel’s view has the information been appropriately interpreted 

for the purpose of assessing the adequacy of the current standard?

• Although there is some evidence from epi studies that anti-oxidants partially protect from lung 

function declines due to ozone exposure (3-15), the more direct evidence from human clinical 

studies does not support this.

• Toxicologic morphologic changes do not provide evidence of bronchial hyperresponsiveness –

these changes occur at the level of the respiratory bronchiole and alveoli, which probably does 

not influence larger airways effects such as those in asthma. Perhaps there is some problem 

with the wording or intent here (3-40, lines 28-32).

• Observations on three endpoints (and conclusions on 3-119): 

oLong-term exposure effects on lung-function: valiant attempts are made to provide 

evidence for this using relatively weaker studies, whereas the best study (CHS) showed 

no effects.

o Short-term exposure effects on symptoms in asthmatic children: arguments to justify not 

considering the two multi-city (multi-site, actually) studies that find no evidence of 

associations. I wonder if this same effort would have been made if these were the only 

two studies in which evidence for associations was found?

o New onset asthma: argument is presented as to why the lack of a confirming main effect of 

long-term ozone exposure in the CHS is ok in light of the interesting gene polymorphism 

interaction analysis.

• In “Pulmonary Structure and Function” (3-44) there is no mention of the CHS study that 

provides the strongest evidence against long-term exposure effects of ozone on lung function.

• Does Section 3.1.3, Adversity of Effects, really require so much exposition? It’s very 

repetitious of earlier material.

• Is compression of the ozone distribution due to model-based air quality adjustments realistic, 

i.e., decreases in high ozone concentrations and increases in low concentrations? (3-86)

• It is difficult to accept, if I’m understanding this correctly, that the percentage of children 

experiencing lung function declines is approximately the same as the percentage of children 

exposed (Figures 3-7 through 3-14). For example, in Atlanta, 14% of children are estimated to 

experience at least one exposure of concern at or above 60 ppb (Fig. 3-7) and 17% of children 

are estimated to experience at least one day of >10% decline in FEV1 (Fig. 3-11). 

• In addition to the sensitivity of epidemiologic-based risk on C-R functions due to choice of 

study region, e.g., large vs. small (3-114), there was also seeming substantial sensitivity to 

choice of regional vs. national C-R functions.

• Missing references detected: Rojas-Martinez 2007 (3-44, line 11), Joad 2006 (3-45, line 16), 

NRC 2008 (3-85), US EPA 2007 (3-98).

A-35
• [Refs to check: Kim 2011 AJRCCM re: inflamm at 60 ppb, Lin EHP 2008 on first asthma 

admission; Fanucchi 2006 infant rhesus]

2. With regard to the presentation of the exposure and risk information for the purpose of

assessing the adequacy of the current standard, to what extent is the information, including 

associated limitations and uncertainties, sufficiently characterized, appropriately interpreted and 

clearly communicated?

I found this section to be among the best sections of Chapter 3.

3. In the Panel’s view, does the discussion in section 3.4 provide an appropriate and sufficient 

rationale to support staff’s preliminary conclusion that the current evidence and exposure/risk 

information call into question the adequacy of the current standard and that it is appropriate to 

consider revising the standard to achieve additional public health protection?

Most definitely. It’s well done.

A-36
Peter Woodbury

Executive Summary

Page ES-2, line 26. I don’t think suggesting that values “somewhat above” 15 ppm-hrs is 

appropriate. If the EPA staff judge that a value above 15 ppm-hrs for W126 should be considered, 

then the analysis throughout the WREA and the PA should include a specific value above 15 ppmhrs so that this suggestion can be reviewed by CASAC and others.

Introduction (Chapter 1): This chapter provides context for the review, including the background 

of past reviews, as well as the scope and approach for the current review. This includes discussion 

of the basis for the current standard.

1. Does the Panel find the introductory and background material (sections 1.1 and 1.2) to be 

appropriately characterized and clearly communicated?

Yes, this material is important and the coverage is appropriate.

2. In section 1.3, we describe the general approach for the review. This includes the key aspects of 

the approach employed in the last review in judging the adequacy of the then-existing standards 

and in selecting revised standards. 

Does the Panel find this description of the approach in the previous review adequate and clear? 

Yes, this material is important and the coverage is appropriate.

Does the summary of the approach in the current review appropriately describe important 

considerations in this review?

Overall, this summary is cogent and useful. However, regarding the secondary standard, 

certain important conclusions are misleading and require revision. For example, on page 1-27, lines 

7-10 states that the “magnitude of the response becomes increasingly uncertain”. A similar 

statement is made on page 1-36, lines 24-27. This is somewhat misleading. Data such as the 

concentration-response functions for individual tree seedling species, supported by results from 

other methods such as FACE and naturally occurring gradients demonstrate that some species are 

very sensitive to ozone and show decreased growth at very low chronic exposure levels, while 

other species show little response to much higher levels. A similar result is found for crop species. 

Thus there is strong evidence of decreased growth and yield of some common tree and crop species 

at very low ozone levels. The more important source of uncertainty at these low levels is 

determining what degree of growth decrement should be considered unacceptable to protect public 

welfare. This issue extends throughout the PA, and the PA could be strengthened by more 

specifically quantifying the spatial extent and degree of impact expected at current ozone 

exposures, the current standard, and at the alternate standards. For example, rather than focusing on 

the “median RBL”, quantify the number of counties containing sensitive tree species that are 

expected to have growth loss of greater than 1%, 2%, etc.

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O3 Monitoring and Air Quality (Chapter 2): This chapter provides a description of the current

O3 monitoring network and recent concentrations, information on emissions and atmospheric 

chemistry, common patterns and variability in O3 concentrations, as well as, discussion of current 

information on estimating O3 concentrations associated with non-anthropogenic sources.

1. To what extent does the Panel agree that the most relevant information on monitoring (section

2.1), emissions and atmospheric chemistry (section 2.2), and common patterns of O3 

concentrations (section 2.3) is presented, and to what extent is the information presented 

appropriately characterized and clearly communicated?

2. With regard to information on estimating O3 concentrations associated with non-anthropogenic 

sources or “background O3” (section 2.4), to what extent is this information appropriately 

characterized and clearly communicated?

The large difference in “counterfactual” vs “source apportionment” methods for estimating 

backgrounds, is important for W126 (p. 2-23 and elsewhere). This issue is challenging to describe, 

but is done reasonably well. In particular, the summary on Page 2-26 and 2-27 is helpful..

“Anthropogenic” emissions of VOCs are distinguished from “natural” sources. However, 

as mentioned on Page 2-7 (lines 19-20) and 2-8 (lines 1-4), “natural” emissions can include humaninfluenced emissions from fire, agriculture, forestry, and other land management practices. This 

issue of definitions should be further clarified (see my further comment below). Even more 

importantly, the extent to which such human-influenced emissions are included in “natural 

background” or other “background” ozone scenarios, should be clarified, and preferably quantified 

since it could affect interpretation of what portion of ozone is potentially controllable.

On a more minor but related point, the terms “anthropogenic”, “man-made” and 

“manmade” all seem to be used to mean the same thing, with “anthropogenic” being the most 

commonly used term. Perhaps the term “man-made” should be used throughout for emissions 

directly from human activity, with the term “anthropogenic” used more broadly to include indirect 

human-influenced emissions such as from agriculture, forestry, and other land management 

practices. Or if the term “anthropogenic” is used throughout then, make it clear that this narrower 

and I believe non-standard definition is being used.

Adequacy of the Secondary Standard (Chapter 5): This chapter discusses key aspects of the 

welfare effects evidence and exposure/risk information, particularly relevant to consideration of 

adequacy of the current secondary standard and specifically describes staff’s consideration of this 

information in reaching preliminary conclusions about the adequacy of the current standard.

1. To what extent does the information in sections 5.1 through 5.5 capture and appropriately 

characterize the key aspects of the evidence for ozone welfare effects assessed and integrated in the 

ISA? 

In general, the information from the ISI is presented appropriately. The brief quotes are 

particularly helpful, as are the references to specific portions of the ISI.

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To what extent does the information in section 5.1 (Nature of Effects and Biologically Relevant 

Exposure Metric) appropriately summarize the nature of ozone welfare effects and to what extent 

does it appropriately characterize the evidence with regard to biologically relevant exposures?

In general, Section 5.1 is useful and appropriate, and the use of questions and answers is a good 

format. However, I suggest rearranging the order of material within each subsection such that the 

question is answered at the end of the section discussing each question. For example, the current 

section on page 5-1, lines 21-33 should be placed just before Page 5-3, line 9. Furthermore, each 

question should be clearly answered. For example, Page 5-7, before Line 1, there should be a short 

paragraph that directly answers the question about appropriate paradigm posed on Page 5-5, lines 

29-30.

Page 5-2, line 25. Replace “vegetative species” with “many species of vegetation”.

Page 5-13, line 5. Delete “although”

2. To what extent is staff’s consideration of the welfare effects evidence, including the implications 

of reported vegetation effects with regard to adversity to public welfare technically sound and 

clearly communicated at an appropriate level of detail? 

In general, the draft is appropriate and substantially improved from the previous draft, with 

some caveats. First, it is important to appropriately address the fact that the sensitivity of most tree 

species and many crop species has not been quantified in terms of a C-R function. It should not be 

assumed that species of unknown sensitivity are not sensitive to ozone. For example, on page 5-18, 

lines 28-29, discusses “if present in these specially protected areas”, referring to 7 of the 12 tree 

species for which C-R functions are available. More appropriately, it should state that “if ozonesensitive species are present”. This may sound like a minor point about language, but I believe it is 

actually an important point about how to apply the available scientific data to ecosystems, and it 

has large implications. For example, stating that “Half (6/12) of species with known C-R functions 

would have growth decreases greater than 5%, and of these species are representative of responses 

of unmeasured species, this degree of impact would occur in [state percentage of studied locations 

with this level of response]. In brief, it is important not to assume that unmeasured species are not 

sensitive to ozone, it is much more appropriate to assume that the sensitivity of species without CR functions might be similar to the range of sensitivity for those species with C-R functions.

In the Panel’s view has the information been appropriately interpreted for the purpose of assessing 

the adequacy of the current standard?

Please see comments above.

3. With regard to the presentation of the exposure and risk information for the purpose of assessing 

the adequacy of the current standard, to what extent is the information, including associated 

limitations and uncertainties, sufficiently characterized, appropriately interpreted and clearly 

communicated?

The choice of the word “paradigm” seems odd in question on p. 5-5, but I don’t have a 

suggestion of a better term.

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Make sure not to define “adverse” effects too narrowly (p. 5-6), loss of biomass growth 

could be important even if the species is not harvested for timber or fiber. This topic is mentioned 

elsewhere, and on Page 5-12 this issue is appropriately broadened, but perhaps on p. 5-6 some 

mention of other effects could be made, or a reference to other locations that address these broader 

impacts.

p. 5-13, line 5 delete “although”

Figure 5-1 should be improved by moving the legend to the right of the main figure panel 

and arranging the legend species in the same order (top to bottom) as in the main figure panel.

p. 5-14, line 16 and elsewhere. As I mentioned in comments on the previous drafts, it is 

difficult to interpret a “median” response for both ozone-sensitive and relatively insensitive 

species. Instead, it makes sense to characterize the expected impacts on the sensitive species, and 

quantify the spatial extent and effect on biomass growth for (1) known sensitive species (i.e., those 

that are shown be particularly sensitive with their C-R functions, and (2) the same result assuming 

that the 12 species with known C-R functions represent all tree species. A more complex scheme 

could be developed to try to extrapolate known species to unknown species based on physiological 

characteristics, as was done for crops in the FASOM analysis, but there would be substantial 

uncertainty in such extrapolation.

p. 5-21. I think that the “modeling regions” in Table 5-4, are the 9 large US climate regions 

shown in Fig. 4-6, but this should be made explicit (the term “modeling region” doesn’t seem to be 

defined in the text currently).

p. 5-24. As in my comments on the first draft WREA and PA, and second draft WREA 

(Section 6.8) I still have a question about the RBL values weighted by basal area. Does the 

denominator basal area in the calculation include only the 12 species with C-R functions or does it 

include all species? If the latter, it is biased. If the former, the interpretation will vary depending on 

what fraction of the basal area is for species without C-R functions. Furthermore, if the goal is to 

assess ozone effects on total biomass growth of a mixed-species forest, then this value is not very 

informative because it will overestimate impacts in mixed species forests because of not including 

competition between sensitive and insensitive species (see previous comments on competition). If 

the purpose is to assess ozone impacts on sensitive species, this value is also not informative 

because it underestimates impacts on sensitive species for the same reason. A comparatively small 

growth decline in a sensitive species (e.g. 2%) based on a seedling study may translate into a larger 

effect at the stand scale. 

Page 5-25. The method used with FASOM for forest growth is based on individual species 

C-R functions, but that is only appropriate for mono-specific stands. For mixed-species stands, 

overall forest growth will not be affected as much as would be implied by a weighted average of 

the growth rates (or yield losses) from individual C-R functions. This is because of competition 

among species with different sensitivity to ozone. This is a serious limitation in the approach for 

mixed-species forests that are common in many parts of the USA. 

A-40
I still don’t agree about ignoring impacts on farmers and forest owners in high ozone areas 

just because national assessments include winners and losers. An example of such a calculation is 

presented on page 5-32, line 9-12 for soybean for 2 counties in Kansas. The number of counties in 

which yield loss is predicted to exceed 1, 2% or 5% could be tabulated for alternative standards. 

See comment for Chapter 6 of the WREA related to this topic. Summaries of county-scale 

information could be added to Table 6-4. 

p. 5-30 line 31 etc. Clarify that NCLAN covered multiple locations in the USA and multiple 

crops, with multiple O3 exposure levels using consistent methods – all of these factors are very 

important because they mean that the results are highly valuable for national risk assessments.

Check for occurrences of “PSDI”, should be “PDSI” throughout.

p. 5-41, line 6. Change “by of” to “by”. 

Figure 5-5 (page 5-48). In figure legend, provide some information about the sites.

EPA should assure that uncertainties are not suggested or implied to always weaken the 

case for a more stringent standard. For example, the paucity of data on ozone sensitivity of most 

US plant species should be considered as “anticipated” that there are a large number of unidentified 

sensitive species, as well as of course many less sensitive species.

Page 5-62, replace “commiserate” with “commensurate”.

Page 5-63, beginning line 31. Rephrase the sentence on line 31 to be more definite (replace 

“might be” with “are”).

Page 5-65, lines 20-23. Replace “likelihood and magnitude of a response become 

increasingly uncertain” with “magnitude of effects become smaller”. As discussed above, the 

evidence is very strong for tree biomass loss and crop yield loss for sensitive species at W126 

values of 5-10. It is the magnitude of the effect that is smaller. And for less sensitive species, there 

will be little or no biomass loss at low ozone exposure values. Again the important uncertainty is 

determining what magnitude of an effect is important for welfare, not whether there are any effects 

at lower ozone exposure levels. This is an important distinction.

4. In the Panel’s view, does the discussion in section 5.7 provide an appropriate and sufficient 

rationale to support staff’s preliminary conclusion that the current evidence and exposure/risk 

information call into question the adequacy of the current standard and that it is appropriate to 

consider revising the standard to achieve additional public welfare protection?

In general, this section is appropriate. However, because it is a summary section, many comments 

on other sections of this chapter should also be applied to this section. Also, note my specific 

comments above for this section (i.e. Pages 5-59 through 5-65).

Consideration of Potential Alternative Secondary Standards (Chapter 6): This chapter discusses 

key aspects of the welfare effects evidence and exposure/risk information particularly relevant to 

consideration of potential alternative secondary standards and specifically describes staff’s 

A-41
consideration of this information in reaching preliminary conclusions on alternative standards 

appropriate to consider.

1. In the Panel’s view, has the evidence and exposure/risk information, including associated 

limitations and uncertainties, been appropriately characterized and interpreted for the purpose of 

considering levels of protection and potential alternative standards?

In general, yes, except for a few points. First, I don’t understand the suggestion of values 

“somewhat above” 15 ppm-hrs. If the EPA staff judge that a value above 15 ppm-hrs for W126 

should be considered, then the analysis throughout the WREA and the PA should include a specific 

value above 15 ppm-hrs so that this suggestion can be reviewed by CASAC and others. Second, 

there needs to be greater attention paid to sensitive species. While there is analysis of both sensitive 

crop and tree species, much of the focus is on a median response, for example for tree species. And 

even when sensitive species are discussed, it is with statements such as 7 of 12 species had a 

relative yield loss of X below an ozone exposure value of y. However, with trees, the two most 

sensitive species had a substantial yield loss well below this value. Thus more attention should be 

paid to including information about commonly occurring sensitive species. Third, more attention 

should be paid to crop yield loss and tree biomass growth losses at smaller spatial scales such as 

counties. If yield of a sensitive crop such as soybean is greater than 5% in a county, it affects the 

farmers in that county, even if at larger regional or national scales there are smaller impacts on 

yield or on producer surpluses. Fourth, the suggestion to use a 3 year averaging period is not 

supported by the available data, nor has it been supported by CASAC. The only justification for a 

3-year averaging period is to improve the stability of the classification of regions as being in or out 

of compliance. Greater attention should be paid to accounting for cumulative impacts of a 1% or 

2% loss in growth of tree species and other impacts if a 3-year averaging period is to be used. 

Specifically, a lower value of the standard would be appropriate for a longer averaging period than 

1 year. See also detailed comments below.

Additionally it seems to me that there is likely to be a strong bias effect of using across-the-board 

NOx reductions (see comments for Chapter 4 of WREA). For the large climate regions used, there 

is a wide variation in ozone exposure values throughout the region. If “across-the-board” cuts are 

used to reduce ozone exposure in the highest locations, then ozone exposure in locations where it is 

lower to start with will tend to become very low. But an actual targeted control strategy would 

likely only reduce NOx in the locations necessary to bring the high ozone-exposure locations into 

compliance, thus having much less effect on other locations than would across-the-board cuts. If 

this bias is large, then it strongly affects all of the risk analyses based on the alternate standards, 

because impacts of ozone under the alternate standards would be underestimated because ozone 

exposure values are underestimated for much of each region. If this bias is substantial it could 

mean that the ozone exposure is underestimated and thus the benefit of the alternate standards 

might all be underestimated. This could mean that the benefits of any of the alternate standards 

compared to “just meeting” the current standard and are underestimated as well.

Page 6-8, line 4-5. Change to “extremely highly correlated metrics, with Pearson correlation 

coefficients of 0.99”.

Page 6-9, line 16-17. I don’t find that this conclusion is warranted – the data support an 

annual time frame. There should be some compelling reason to use a multi-year time frame. Note 

A-42
that the proposed form already includes a 3-month period, so it is not as sensitive as an hourly or 8-

hour period to extreme events.

Page 6-9, lines 18-36. As in my comments in the previous 1st draft PA, it is not appropriate 

to assume that the only welfare effect of crop yield loss is total producer and consumer surpluses. I 

think that a goal of avoiding yield losses of sensitive crops of 5% or greater for each county would 

be appropriate to protect welfare. Farmers growing sensitive crops in high ozone locations can be 

considered a “sensitive population” for welfare impacts, and their crop yields should be protected. 

Furthermore, I do not find any support herein for the idea that the data do not support an annual 

time period for yield losses in annual crops.

Page 6-12. The argument that stability of compliance is of value is stated on this page. I 

agree with the previous CASAC statement (lines 26-29) that if a multi-year period is chosen for 

stability purposes, the level of the standard should be lowered to prevent exceedences of a 

threshold of impact. This is a very important point as it affects the choice of a level depending on 

the averaging time (1 versus 3 years).

Page 6-17 and 6-18. This discussion of individual species responses to different W126 

levels is very helpful and informative, as is Table 6-1. However, I think Table 6-1 could be 

reformatted to make it easier to read by moving much of the text into column headings, and 

increasing the number of columns. For example “ppm-hrs” should appear at the top of the first 

column, under the column heading rather than be repeated on every row. And “median species” 

could be a column heading for both tree seedlings and crops, as could “loss”. These changes would 

make it easier to see the actual values in the table. Also, it is not clear to me what “varying lower” 

means in the table.

Page 6-24, lines 10-24. See previous comments herein and for the first draft PA regarding a 

question with the weighted RBL scheme. 

Page 6-25, line 14. Change “great” to “greater”.

Page 6-30, lines 14-18. It would be helpful to include here and elsewhere the fraction of US 

forests represented by the species with C-R functions (probably using basal area) as well as the 

fraction of US crop area covered by the crop species with C-R functions. This helps quantify the 

uncertainty, which is quite different for crops and forest tree species. This information is available 

in the REA and could be summarized here as well.

Beginning page 6-30 line 6 and onward. While it is useful to list the various uncertainties, it 

would be more helpful to give some idea of how the uncertainty might affect the interpretation. I 

realize that this is challenging, but my concern that it is important to communicate what is known 

with reasonable certainty versus what is really unknown. I commend the staff for accomplishing 

this challenging task well in the REA in Table 7-23. There is quite a lot of certainty in estimates of 

biomass loss for forest tree seedling species and crop species for which C-R functions have been 

developed. Because several dominant crop species have C-R functions, there is a quite a lot of 

certainty about impacts of ozone on crop yield across most annual cropland in the USA. But it is 

much more uncertain to extrapolate from the 12 forest tree species to all forest tree species in the 

US. For uncertainty in ozone exposure, while it is true that the sparseness of rural monitors means 

A-43
that in many regions there is uncertainty, there are large portions of the US where monitors are 

dense enough, and where there are not large mountains or other features that make interpolation 

more difficult, such that regional estimates of ozone exposure are pretty certain, even if there are 

somewhat larger uncertainties for individual locations.

Page 6-39, lines 29-31. This is a non-sequitur. The difficulty in determining the degree of 

impact that is important for welfare is not related to the question of averaging the standard across 1 

or 3 years. Also, as quoted in the PA (page 6-36, line 19), the CASAC said “averaging across years 

in not recommended”. 

Page 6-43, line 13-14. As for the tree species, crop results should focus on both a group 

(such as median) response and also individual species response. This is important because sensitive 

species such as soybean are very widespread and important crops. Also, there is little attention 

given in the PA and WREA to non-crop annual species. The results for annual crops can be 

considered as also surrogates for a very large number of annual non-crop species that may have 

many welfare values. While I appreciate the much greater attention to effects on crop yield in this 

second draft compared to the first draft, I still think a bit more attention to crops is warranted given 

the strength of the database on crop yield response to ozone.

Page 6-43, line 35 and elsewhere. While the EPA chose to focus on 2% biomass loss for 

forest species, greater acknowledgement should be made that CASAC recommended 1 to 2%. This 

is particularly important in conjunction with the decision by EPA to focus on a 3-year rather than 

annual averaging time as recommended by CASAC.

Page 6-44, line 21. I think it is worth discussing the implications of focusing on sensitive 

tree species in addition to the existing focus on median and majority species. I think it is 

misleading for example on line 14-15 to say “less than 9 or 10” without including that the 2 

remaining species have much higher predicted biomass losses. I am not suggesting that these 

sensitive species should be the primary focus, but rather including them for consideration rather 

than not including them, as happens with the current emphasis. As for sensitive crop species, these 

sensitive tree species are ecologically important and widespread. Furthermore, they may also serve 

as surrogates for the high likelihood that there are other sensitive tree species for which C-R 

functions have not been developed. As an example of how information on sensitive species might 

be included, the human health section of this PA includes estimates of the number of not just all 

children, but also asthmatics for example in Table 4-45, to better represent sensitive populations.

Page 6-45, lines 21-23. I don’t understand why these lines are here. The EPA has selected a 

range of appropriate alternate values for the standard, and it is in accord with many previous 

CASAC recommendations. But this sentence says that the Administrator can reasonably choose a 

value beyond this range. This is a very open ended statement, and I don’t understand what it is 

based on. If the EPA staff judge that a value above 15 ppm-hrs for W126 should be considered, 

then the analysis throughout the WREA and the PA should include a specific value above 15 ppmhrs so that this suggestion can be reviewed by CASAC and others.

Page 6-45 lines 24-35. This is very helpful, pointing out the implications of choosing 

different values for the standard among the values put forward by EPA and by CASAC.

A-44
Page 6-46, lines 3-5 and 13-14. As mentioned above for the previous page, I don’t 

understand the suggestion of values “somewhat above”. If the EPA staff judge that a value above 

15 ppm-hrs for W126 should be considered, then the analysis throughout the WREA and the PA 

should include a specific value above 15 ppm-hrs so that this suggestion can be reviewed by 

CASAC and others.

Page 6-48, lines 12-13. The only support that I find in the PA for a 3-consecutive-year time 

frame is stability of compliance among years. As discussed in the PA and in my prior comments, 

CASAC specifically recommends NOT averaging across years, so I think this recommendation 

should be reconsidered or at least further qualified.

Page 6-48, line 18, Again I find the usage of “somewhat above” to be vague and misleading 

and impossible to evaluate, see comments above.

2. In the Panel’s view, does the discussion in section 6.5 provide an appropriate and sufficient 

rationale, supported by the discussions in sections 6.1 through 6.4, to support staff’s preliminary 

conclusions regarding alternative secondary standards (including the indicator, level, averaging 

time and form) that it is appropriate to consider?

For the most part yes, except for the issue of mentioning values “somewhat above 15 ppmhrs (see comments above). Also, I think more attention needs to be paid to suggesting a lower value 

for the standard if using a 3-year rather than a 1-year averaging time.

3. Does the Panel have any recommendations regarding additional interpretations and conclusions 

based on the available information that would be appropriate for consideration beyond those 

discussed in this chapter?

Please see comments above.

A-45
Ronald E. Wyzga

Introduction (Chapter 1):

Charge questions:

1. Does the Panel find the introductory and background material (sections 1.1 and 1.2) to be 

appropriately characterized and clearly communicated?

I believe that these sections are extremely well-written. I especially commend the Agency’s 

intent to provide a document “written to be understandable to a broad audience”. With respect 

to the latter, there are a few places where jargon and/or technical terms have crept in that could 

be clarified for a more naïve audience. For example, p. 1-7, l. 19: “certoriori”, p. 1-21: 

“Controlled Human Exposure Studies”; p. 1-36: “OTC”, which I believe refers to open-topped 

chambers.

In other places legal references could be placed in a footnote as they are distracting from the 

text; e..g, p. 1-3, ll. 24-28. 

2. In section 1.3, we describe the general approach for the review. This includes the key 

aspects of the approach employed in the last review in judging the adequacy of the thenexisting standards and in selecting revised standards. Does the Panel find this description 

of the approach in the previous review adequate and clear? Does the summary of the 

approach in the current review appropriately describe important considerations in this 

review?

This is well-written and provides an important introduction. 

A minor comment is that some of the material in section 1.3.1.2.3 is repetitious of material in 

section 1.2.2.

Some comments on Chapters 3 and 4:

Does the currently available scientific evidence and exposure/risk information ...support 

or call into question the adequacy of the current O3 primary standard?

The studies of Schelegle et al. (2009) clearly demonstrate that there are adverse health effects 

among a subpopulation of healthy young subjects after a 6.6 hour expsoure of 72ppb, a level 

below the current standard; hence there is clear scientific evidence that exposures at the current 

standard could lead to adverse effects and alternative standards are appropriate for 

consideration. It should be noted that lung function results from clinical studies at exposure 

levels at or below 72ppb also demonstrate a clear response. Whether these are “adverse” 

depends upon the definition of “adverse”; the Schelegle et al study clearly statisfies the 

definition of “adverse” as defined by the American Thoracic Society, which defines adversity 

as a combination of lung functions changes accompanied by symptoms. If an alternative 

definition of “adverse” is used, it should be clearly defined. There is also epidemiological 

support that finds adverse health responses at contemporary ozone levels in the US. 

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What is the range of potential alternative standards that are supported by the currently 

available scientific evidence....?

Clearly, from the above, the upper end must be at or below 72ppb. The Schelegle et al. (2009) 

study was conducted using healthy volunteers 18-25 years of age for an exposure of 6.6 hours. 

At issue is how to compensate for the shorter exposure time and the possible impacts among a 

more sensitive or less healthy population. Figure 2 from the Schelegle et al. (2009) study 

shows that at higher exposure levels lung function and symptom scores tend to increase with 

longer exposures. This increase is less apparent for the 70 and 80 ppb protocol exposures; 

nevertheless prudence suggests that some compensation could be made to adjust for the 6.6 

hour exposure period. Panel studies also suggest that more sensitive individuals can respond to 

levels at or below 70ppb. There is no easy way to extrapolate from exposure levels at which 

healthy adults respond to comparable levels among sensitive populations, such as asthmatics 

and children; hence there is uncertainty associated with the lower end of the proposed range. 

A-47