2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

Page -1-

Contents

George Allen ........................................................................................................................................2

John Balmes.........................................................................................................................................6

James Gauderman ..........................................................................................................................10

Rogene Henderson ............................................................................................................................12

Philip K. Hopke .................................................................................................................................15

Lianne Sheppard ...............................................................................................................................18

Frank Speizer.....................................................................................................................................19

Helen Suh ...........................................................................................................................................22
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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George Allen

Caveat: With regard to the range of ozone concentrations under consideration, these comments 

assume the form of the NAAQS will remain unchanged from what was promulgated in the 2008 

rule. Any change in the form (daily average duration, percentile, multi-year averaging) will 

change the effects of a standard even if the numerical value (e.g., .060 to .070 ppm) remains the 

same.

Q 1. What is your advice on the overall strengths and limitations of the evidence from controlled 

human exposure and epidemiological studies and the results of the exposure and risk assessments, 

in the context of EPA's selection of a standard level within the proposed range that would be 

requisite to protect public health with an adequate margin of safety, including the need to protect 

susceptible populations, such as children and people with asthma?

As with nearly all other pollutants, the exposure-response relationship is stronger and more 

scientifically robust as you go to higher concentrations. This holds for both controlled human 

exposures and epidemiological studies. Both approaches have their limitations, especially toward 

the lower end of the proposed range. The controlled exposure studies usually do not include 

sensitive and vulnerable populations (SVP) as subjects; this makes it more difficult to extrapolate 

results to the SVP that the NAAQS is intended to protect. The bias here is to underestimate the 

effects of a given concentration on SVP. These types of studies do allow detailed assessment of 

physiological markers such as FEV1 and inflammatory markers that epidemiological studies can 

not (usually) assess. Epidemiological studies do include SVP, although they are usually not 

constrained to this group. These studies have much greater exposure mis-classification than 

controlled exposure studies, and potential confounding from other pollutants and uncontrolled 

variables; these factors would usually bias effect results toward the null. However, since the 

ambient ozone measurements used in epidemiological studies are reasonably specific to ozone, 

they are actually an indicator of strong oxidants in the air, and thus the health effects may be larger 

than if the exposure were only to ozone. This is different than the ozone concentrations used in 

controlled exposure studies where other strong oxidants are presumably not present; thus these 

studies may underestimate the reported ozone health effects relative to epidemiological studies. 

Another potential difference between controlled exposure and epidemiological studies is the 

reaction products from ozone once it gets indoors (Weschler, Atmospheric Environment 38 (2004) 

5715B5716); these include a wide range of gas-phase respiratory irritants and ultra-fine particles.

Q2. Recognizing that controlled human exposure studies at 0.080 ppm O3 and above have 

provided evidence of other health effects, including inflammation and increased airway 

responsiveness which may occur through different physiological mechanisms than the reduction in 

FEV1, how should the results of these studies inform our understanding the health effects to 

healthy adults at exposures levels from 0.060 to 0.070 ppm? 

As noted in the background material included in these charge questions, the available data suggest 

that there probably is a reasonably Asmooth exposure-response curve@ going from .080 to .060 
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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ppm. This does not imply that this holds at even lower levels, since that gets into the issue of 

thresholds. And as with all other aspects of the science, this assumption is weaker at .060 than at 

.070 ppm.

Q3. How should the results of the controlled human exposure studies at 0.060 ppm O3, showing 

effects on FEV1 and respiratory symptoms, in the context of the larger body of evidence from 

controlled human exposure studies, mentioned above, inform our understanding of the health 

effects to healthy adults at exposure levels from 0.060 to 0.070 ppm? 

These studies support the concept of a reasonably smooth exposure-response curve down to these 

levels as opposed to a health effect threshold near .060 ppm.

Q4. With respect to the information from controlled human exposure studies at 0.060 ppm O3, 

what is the scientific importance of the small, group mean FEV1 decrements relative to the 

findings that 7 to 20% of the subjects experienced FEV1 decrements ∃ 10%? Please consider this 

question from both a public health and a clinical perspective.

For healthy adult subjects in controlled human exposure studies, these FEV1 decrements indicate 

some biological response, but the clinical significance of this is unclear especially in light of some 

studies showing inflammatory responses without FEV1 decrements. From a public health 

perspective, where SVP would be expected to have an enhanced response to exposures to these 

concentrations, these results may have more importance. Ideally, controlled human exposure 

studies would be conducted at these levels using SVP, but that has risks of adverse outcomes in the 

study subjects, making such studies difficult to do.

Q5. The evidence, including that summarized above, indicates that susceptible populations may 

have greater responses than healthy people. In light of this evidence, how can we appropriately 

use the results of controlled human exposure studies conducted on healthy adults, as well as the 

epidemiological studies of susceptible groups, to inform a judgment on the effects of ozone 

exposure on susceptible populations?

The results of controlled human exposure studies conducted on healthy adults provide a Abest 

case@ (least health effect) scenario relative to SVP. Epidemiological studies that focus on SVP 

would be expected to show greater health effects for a given concentration, but are subject to the 

confounding factors noted above. The best approach may be a Aweight of evidence@ scenario that 

assesses the consistency (or lack thereof) across these very different approaches to quantifying 

ozone health effects.
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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Q6. To what extent does your confidence that the effects observed in epidemiological studies are 

attributable specifically to O3 lessen or otherwise change, if at all, at the lower levels in the 

proposed range as compared to the higher levels?

As noted previously, the uncertainty (or confidence if you wish) of any exposure study decreases 

as the exposure concentrations decrease. For epidemiological studies, the effects of confounders is 

likely to be larger at .060 than .070 ppm. However, it=s a reasonable assumption that this factor 

would bias observed health effects toward the null, not strengthen them.

Q7. EPA's exposure assessment quantified the number of all children and asthmatic children 

likely to be exposed to specific benchmark levels of ozone, including in particular 0.060 and 0.070 

ppm. Considering the patterns of change in the estimates of exposures of concern at and above the 

0.060 and 0.070 ppm benchmark levels, and the uncertainties and limitations in the estimates, what 

is the relative importance from a public health perspective of the estimated reductions in 

exposures of concern, as well as the exposures remaining, for alternative standards across the 

proposed range?

There is little doubt that reduced exposure, both in size of SVP exposed and the concentrations 

they are exposed to, has some public health benefit as you go from .070 to .060 ppm. However, it 

is difficult to quantify the changes in public health benefits across this range of concentrations. 

There will always be some remaining exposures with health effects across the proposed range in 

SVP.

Q8. EPA's quantitative risk assessment estimated the numbers of occurrences of various ozone 

related health effects associated with just meeting alternative standard levels down to a standard 

level of 0.064 ppm. Considering the patterns of change in the estimates of health effects in the risk 

assessment at the alternative standard levels, and the uncertainties and limitations in the estimates, 

what is the relative importance from a public health perspective of the estimated reductions in risk, 

as well as the risk remaining, for alternative standards across the proposed range? Please consider 

this question in light of the scientific evidence as a whole.
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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This is really a policy question, not a science question. There is likely some risk (i.e., not 0) for 

SVP even at the low end of the proposed range. This is not unique to ozone; some residual risk is 

present for every NAAQS pollutant, since none of them (except maybe CO) have a clear effect 

threshold. The quantitative risk assessment does not provide a bright line; it only provides 

guidance to the best estimate of risk at the various ranges considered. The science can only take 

the process so far, and after that it becomes a policy judgment that weighs the estimated (and more 

uncertain at the lower end of the range) health benefits against the difficulty of implementing 

effective control strategies to meet any given NAAQS.

Additional Comments.

Although the reconsideration of the 2008 ozone NAAQS is constrained to the literature available 

during that NAAQS review process, it is worth noting that more recent studies over the last 4-5 

years support and perhaps strengthen the scientific justification for an ozone NAAQS in the range 

of .060 to .070 ppm.

Some interested parties have raised the question of the quality of the ozone data used in the 

epidemiologic studies, saying that there are common situations where the UV absorption 

measurement method normally used in the ozone monitoring network can significantly over-report 

ozone concentrations. There is evidence that this can happen, but it is unclear if this a significant 

factor in the overall ozone exposure-health effect relationship. Additionally, the difference 

between chamber studies and ambient air exposures with the additional load of strong oxidants not 

being included in the measurement further reduces the implications of a modest issue with the UV 

method. It should also be noted that nearly all ambient air measurements of NAAQS pollutants 

have various biases associated with them, sometimes positive (NO2, non-trace CO, SO2 when NO 

is elevated, sometimes negative (the PM2.5 FRM, depending how it is run), sometimes biases 

between different FRMs for PM10 (the SSI Hi-Vol Awar@ in the 1980's), and sometimes just very 

goofy (the Hi-Vol FRM for lead). Some of these biases are as large or larger than the likely 

positive bias from the UV ozone method. In this context, I am not concerned with the reported 

biases in the UV method. However, since there may be effective ways to reduce the biases in this 

method, EPA may want to consider additional specifications for the testing of UV ozone analyzers 

in the Federal Equivalent Method (FEM) regulations to assess this issue.
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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John Balmes

1. What is your advice on the overall strengths and limitations of the evidence from 

controlled human exposure and epidemiological studies and the results of the exposure 

and risk assessments, in the context of EPA's selection of a standard level within the 

proposed range that would be requisite to protect public health with an adequate margin 

of safety, including the need to protect susceptible populations, such as children and 

people with asthma?

Taken together, the evidence from controlled human and epidemiological studies strongly 

supports the selection of a new primary ozone standard that is well below the 1997 standard 

of 0.08 ppm over an 8-hour averaging time. There is scientific certainty that 6.6-hour 

exposures to concentrations ≥0.08 ppmwith intermittent exercise cause clinically relevant 

decrements of lung function in young, healthy volunteers. The results of multiple 

epidemiological studies also show that children and adults with asthma are at increased risk 

of acute exacerbations of this disease on or shortly after days when ozone concentrations are 

elevated above background but remain below 0.08 ppm. Given the need to protect public 

health with an adequate margin of safety and the results of EPA’s exposure and risk 

assessments, setting a new NAAQS in the range of 0.060 to 0.070 is appropriate.

 

2. Recognizing that controlled human exposure studies at 0.080 ppm O3 and above have 

provided evidence of other health effects, including inflammation and increased airway 

responsiveness which may occur through different physiological mechanisms than the 

reduction in FEV1, how should the results of these studies inform our understanding the 

health effects to healthy adults at exposures levels from 0.060 to 0.070 ppm?

The results of studies that show that exposure to ozone at 0.080 ppm and above causes 

airway inflammation, increased permeability, and increased responsiveness provide 

mechanistic support for the observed epidemiological associations with regard to 

exacerbations of asthma at concentrations below 0.080 ppm. The mechanism of ozoneinduced decrements in lung function may not be related to airway inflammation. 

3. How should the results of the controlled human exposure studies at 0.060 ppm O3, 

showing effects on FEV1 and respiratory symptoms, in the context of the larger body of 

evidence from controlled human exposure studies, mentioned above, inform our 

understanding of the health effects to healthy adults at exposure levels from 0.060 to 

0.070 ppm?

At the time of the last EPA review of the evidence on the health effects of ozone, only the 

study of Adams et al. (2006) provided data on exposures at concentrations ≤0.080 ppm. 

Although that study as published reported a non-significant group decrease (~3%) in FEV1, 

several subjects experienced decreases ≥10%, which have been previously determined to be 

of clinical relevance. These results fit well with those from multiple other studies of ozone’s 

effect on lung function at concentrations ≥0.080 ppm, which have consistently shown that 

some individuals are more sensitive to this effect of ozone than others. The selection of a 
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

Page -7-

NAAQS for ozone needs to consider an adequate margin of safety to protect the most 

sensitive subgroup of individuals. Since the scientific evidence was reviewed for the

preparation of the 2006 Criteria Document for Ozone, the results of the Adams et al. (2006) 

study have been carefully reanalyzed (Brown et al., 2008) and actually show a statistically 

significant group effect. In addition, two other studies have shown statistically significant 

decrements in FEV1 after 6.6-hour exposures to 0.070 ppm (Schelgele et al., 2009) and 0.060 

ppm (Kim et al., 2011), respectively.

4. With respect to the information from controlled human exposure studies at 0.060 ppm O3, 

what is the scientific importance of the small, group mean FEV1 decrements relative to 

the findings that 7 to 20% of the subjects experienced FEV1 decrements ≥ 10%? Please 

consider this question from both a public health and a clinical perspective.

From a clinical perspective, a 10% decrement in FEV1 is often associated with respiratory 

symptoms, especially in individuals with pre-existing pulmonary or cardiac disease. For 

example, people with chronic obstructive pulmonary disease have decreased ventilatory 

reserve (i.e., decreased baseline FEV1) such that a ≥10% decrement could be associated with 

moderate to severe respiratory symptoms. From a public health perspective, the exposure 

and risk assessment conducted for the last review of the ozone NAAQS clearly document that 

a substantial proportion of the U.S. population is exposed to levels of ozone at the various 

alternative standards considered. This means that even if a NAAQS of 0.060 ppm were to be 

selected, some sensitive individuals could still be exposed to concentrations that could cause 

them to have a clinically relevant decrement in lung function.

5. The evidence, including that summarized above, indicates that susceptible populations 

may have greater responses than healthy people. In light of this evidence, how can we 

appropriately use the results of controlled human exposure studies conducted on healthy 

adults, as well as the epidemiological studies of susceptible groups, to inform a judgment 

on the effects of ozone exposure on susceptible populations?

Controlled human exposure studies have shown that individuals with asthma have enhanced 

responses to ozone, in terms of both airway inflammation and lung function decrements with 

exercise. Epidemiological studies have shown that such individuals are at increased risk of 

exacerbations of their disease on or shortly after days with elevated ambient ozone 

concentrations. Taken together, the results of these studies provide strong evidence that 

people with asthma are a subgroup of the population with increased susceptibility to ozone. 

Given the effects on lung function that have been documented in healthy adults exposed to 

ozone at concentrations ≤0.080 ppm, a NAAQS with a margin of safety is necessary to 

protect the susceptible population of children and adults with asthma. Older individuals 

with pre-existing lung and heart disease, who have not been adequately investigated in 

controlled human exposure studies, as well as young children who cannot participate in such 

studies, may also be more susceptible than the healthy young adults who have been studied to 

date.

6. To what extent does your confidence that the effects observed in epidemiological studies 
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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are attributable specifically to O3 lessen or otherwise change, if at all, at the lower levels 

in the proposed range as compared to the higher levels?

While the effects of ozone cannot be easily isolated from the effects of other pollutants in 

epidemiological studies, health care utilization for asthma has been shown to decrease when 

ozone concentrations are decreased. For example, when traffic density was decreased during 

the Summer Olympic Games in Atlanta in 1996, there was significantly decreased use of 

pediatric care for asthma that correlated best with a reduction in peak ozone concentrations 

(Friedman et al., 2001). In this study, the relative risk of asthma events increased stepwise at 

cumulative ozone concentrations 0.060 to 0.089 ppm and 0.090 ppm or more compared with 

ozone concentrations of less than 0.060 ppm. The reduction of the adverse effects on asthma 

in this study was dependent on reduction of ozone exposures to levels below 60 ppb.

7. EPA’s exposure assessment quantified the number of all children and asthmatic children 

likely to be exposed to specific benchmark levels of ozone, including in particular 0.060 

and 0.070 ppm. Considering the patterns of change in the estimates of exposures of 

concern at and above the 0.060 and 0.070 ppm benchmark levels, and the uncertainties 

and limitations in the estimates, what is the relative importance from a public health 

perspective of the estimated reductions in exposures of concern, as well as the exposures 

remaining, for alternative standards across the proposed range?

The cumulative evidence to date on the ozone exposure-lung function response relationship 

strongly suggests that it is linear with no threshold, at least through 0.060 ppm. Therefore, it 

is reasonable to assume a similar exposure-response relationship for exacerbations of 

asthma. Considering the patterns of change in the estimates of exposures at alternative 

standards, as well as the uncertainties and limitations of the estimates, it is likely that 

susceptible individuals would still be adversely affected at a NAAQS of 0.060 ppm, although 

the number of such individuals would be substantially lower than at higher alternate 

standards.

8. EPA’s quantitative risk assessment estimated the numbers of occurrences of various 

ozone related health effects associated with just meeting alternative standard levels down 

to a standard level of 0.064 ppm. Considering the patterns of change in the estimates of 

health effects in the risk assessment at the alternative standard levels, and the 

uncertainties and limitations in the estimates, what is the relative importance from a 

public health perspective of the estimated reductions in risk, as well as the risk 

remaining, for alternative standards across the proposed range? Please consider this 

question in light of the scientific evidence as a whole.

In addition to what I have stated in my responses to the previous seven questions, it is also 

important to consider the effect of reductions in exposures to ozone on mortality with the 

alternate standards. Although the evidence from epidemiological studies of ozone-related 

mortality published prior to 2006 was not considered sufficiently robust by CASAC to serve 

as the basis for a new NAAQS, EPA estimated effects on mortality in the exposure and risk 

assessment components of the 2007 Staff Paper. The evidence regarding the ozone exposure-
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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mortality relationship has grown stronger since the publication of the Staff Paper (e.g., 

Jerrett et al., 2009) and a mortality effect was seen at concentrations below the current 

standard.

References Cited:

Brown JS, Bateson TF, McDonnell WF. 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.

Friedman MS, Powell KE, Hutwagner L, Graham LM, Teague WG. 2001. Impact of changes in 

transportation and commuting behaviors during the 1996 Summer Olympic Games in Atlanta on 

air quality and childhood asthma. JAMA 285:897-905.

Jerrett M, Burnett RT, Pope CA 3rd, Ito K, Thurston G, Krewski D, Shi Y, Calle E, Thun M. 2009. 

Long-term ozone exposure and mortality. N Engl J Med 360:1085-1095.

Kim CS, Alexis NE, Rappold AG, Kehrl H, Hazucha Mj, Lay JC, Schmitt MT, Case M, Devlin 

RB, Peden DB, Diez-Sanchez D. 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 Jan 7 [Epub 

ahead of print].

Schelegle ES, Morales CA, Walby WF, Marion S, Allen RP. 6.6-hour inhalation of ozone 

concentration from 60 to 87 parts per million in healthy humans. 2009. Am J Respir Crit Care Med

180:265-272.
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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James Gauderman

Charge Question #4. With respect to the information from controlled human exposure 

studies at 0.060 ppm O3, what is the scientific importance of the small, group mean FEV1 

decrements relative to the findings that 7 to 20% of the subjects experienced FEV1 

decrements ≥ 10%? Please considerthis question from both a public health and a clinical 

perspective.

In the re-analysis of Adams (2006) study of 30 subjects by EPA (Brown, 2007), a small 

but statistically significant decline in FEV1 was observed. Specifically, a 2.85% mean O3-

induced decline in FEV1 was observed following 6.6 hr square wave exposure to 0.060 

ppm O3 compared to 6.6 hr filtered air (FA) exposure. The statistical analysis by EPA 

was based on a straightforward paired comparison, and they conservatively used a 

nonparametric sign test to obtain a p-value of 0.002 for the 0.06 ppm vs. FA comparison. 

Alternative, more powerful analytic methods using either a Wilcoxon signed-rank test or a 

paired t-test yielded even lower p-values in the EPA analysis. The EPA comparison 

remained significant after a Bonferroni correction for multiple comparisons. The original 

analysis of the data by Adams did not find a significant difference in FEV1 between the 

0.06 and FA exposure conditions. However, that analysis was based on a Scheffe 

correction for multiple comparisons, which is known to have very low power for the type of 

pairwise comparisons conducted by Adams compared to other well-known methods for 

multiple-testing correction (Kirk, 1982). Thus, from my understanding of the statistical 

analyses that have been conducted, I would argue that the analysis by EPA should be 

preferred to that of Adams for the specific comparison of the FEV1 effects of 0.06 ppm 

exposure relative to FA exposure. 

Of the 30 study subjects in Adams, 24 showed some evidence for an O3-induced decline 

in FEV1, and 2 of the 30 (7%) experienced a decline greater than 10%. Although the 

sample size is relatively small, the consistency of effects across O3 exposure levels, as 

well as the consistency with effects observed by an earlier independent study 

(McDonnell, 2002), indicates that the observed deficits in FEV1 at the 0.060 ppm from the 

Adams study are not spurious. In other words, it is likely that prolonged exposure to 0.06 

ppm O3 causes a general shift in the distribution of FEV1 towards lower values. The 

following plot of the Adams data, derived from Figure 8-2 of Volume I of the “Air Quality 

Criteria for Ozone and Related Photochemical Oxidants, 2006” document, shows an 

approximate normal distribution in the O3-induced changes in FEV1 with exposure to 

0.06 ppm. 
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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Although the mean decrement is less than 3% and would not be considered clinically 

important, the shift to the right in this distribution pushes a fraction of subjects into the 

region that becomes clinically interesting (>10%). All of the Adams study subjects were 

healthy volunteers. From a public health standpoint, these results suggest that a large 

number of individuals in the general population (that are otherwise healthy), are likely to 

experience FEV1 deficits greater than 10% with prolonged exposure to 0.06 ppm O3. 

Although most healthy individuals can probably sustain a short-term 10-15% decline in 

FEV1 with little or no noticeable effect, it is not clear how they might be affected in the 

longer term if they experience repeated lung function deficits due to 0.06 ppm or greater 

O3 exposures over multiple days or weeks. Based on several other controlled exposure 

studies, we might expect that O3-induced FEV1 deficits in subjects with an existing 

respiratory condition (e.g. asthma) would be shifted even further to the right compared to 

the above figure. A 10-15% (or greater) pollution-related deficit in FEV1 in an individual 

with an existing respiratory condition is large enough that it could cause a clinically 

observable response. 
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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Rogene Henderson

February 9, 2011

1. What is your advice on the overall strengths and limitations of the evidence from controlled 

human exposure and epidemiological studies and the results of the exposure and risk assessments, 

in the context of EPA's selection of a standard level within the proposed range that would be 

requisite to protect public health with an adequate margin of safety, including the need to protect 

susceptible populations, such as children and people with asthma?

I reviewed the previous correspondence between CASAC and the Agency as well as the 

Federal Register notice of the reconsideration of the 2008 primary NAAQS for ozone and 

found that the evidence from controlled human exposures and epidemiological studies, as 

well as the results of the exposure and risk assessments, fully supported the selection of the 

primary ozone standard in the range of 0.060 to 0.070 ppm to protect public health with a 

margin of safety. Human exposure studies provide the most direct evidence of the health 

effects on humans and the studies clearly show that adverse effects occur in some healthy 

adults after exposure for 6.6 hr to 0.060 ppm ozone. This finding has recently been 

confirmed in clinical studies in 59 healthy young adults exposed to 0.060 ppm ozone for 6.6 

hours (Kim et al., dol:10.1164/rccm.201011-18130C, Lung function and inflammatory 

responses in healthy young adults exposed to 0.060 ppm ozone for 6.6 hours.) Asthmatic 

persons are known to be more sensitive to ozone than are healthy persons. Therefore, to 

provide some margin of safety, the standard must take into consideration these sensitive 

subpopulations.

2.. Recognizing that controlled human exposure studies at 0.080 ppm O3 and above have

provided evidence of other health effects, including inflammation and increased airway

responsiveness which may occur through different physiological mechanisms than the reduction in 

FEV1, how should the results of these studies inform our understanding the health effects to 

healthy adults at exposures levels from 0.060 to 0.070 ppm?

These additional health-effect endpoints should definitely be taken into account in setting the 

standards to the extent that information is available. The recent publication by Kim et al. 

(2011) provides information on both types of endpoints endpoints.

3. How should the results of the controlled human exposure studies at 0.060 ppm O3, showing 

effects on FEV1 and respiratory symptoms, in the context of the larger body of evidence from

controlled human exposure studies, mentioned above, inform our understanding of the health 

effects to healthy adults at exposure levels from 0.060 to 0.070 ppm?

The results of human controlled exposures to 0.080. 0.070. and 0.060 form a continuum of 

levels of effect that must all be considered in setting a standard with a margin of safety. The 

results of the 0.06 ppm exposures provide increased confidence and decreased uncertainty 

about the health effects of ozone exposure at that concentration. Thus it essential that the 
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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results of the controlled human exposure studies at 0.060 ppm be taken into consideration for 

the understanding of the health effects of ozone in the range of 0.070-0.060 ppm.

4. With respect to the information from controlled human exposure studies at 0.060 ppm O3, what 

is the scientific importance of the small, group mean FEV1 decrements relative to the findings that 

7 to 20% of the subjects experienced FEV1 decrements ≥ 10%? Please consider this question from 

both a public health and a clinical perspective.

I am not a clinician, so will not comment on that aspect. From a public health viewpoint, I 

think the effect is significant. The Clean Air Act requires that a margin of safety be taken 

into account, and from a public health viewpoint, the 0.060 level does induce adverse health 

effects in a portion of the healthy community and those effects are likely to be greater in the 

asthmatic population.

5. The evidence, including that summarized above, indicates that susceptible populations may have 

greater responses than healthy people. In light of this evidence, how can we appropriately use the 

results of controlled human exposure studies conducted on healthy adults, as well as the 

epidemiological studies of susceptible groups, to inform a judgment on the effects of ozone 

exposure on susceptible populations.

The epidemiology data showing increased use of medication, school absences, and hospital 

admissions is one way to evaluate the response of sensitive populations to ozone. The 

controlled human exposures gives you a ceiling level which is higher than the level that 

would be protective of sensitive populations.

6. To what extent does your confidence that the effects observed in epidemiological studies are 

attributable specifically to O3 lessen or otherwise change, if at all, at the lower levels in the 

proposed range as compared to the higher levels?

For any pollutant, as one goes down the dose-response curve to lower levels of exposure, 

confidence in the effects seen decrease and uncertainties increase. However, the effects of 

ozone exposure can best be considered as a continuum, with decreasing incidence or severity 

with decreasing exposure. However, the endpoints of concern remain the same, providing 

some confidence that the effects are due mainly to ozone.

7. . EPA’s exposure assessment quantified the number of all children and asthmatic children likely 

to be exposed to specific benchmark levels of ozone, including in particular 0.060 and 0.070 ppm. 

Considering the patterns of change in the estimates of exposures of concern at and above the 0.060 

and 0.070 ppm benchmark levels, and the uncertainties and limitations in the estimates, what is the 

relative importance from a public health perspective of the estimated reductions in exposures of 

concern, as well as the exposures remaining, for alternative standards across the proposed range?

The exposure assessments were reasonable and made with the best data available. The 

assessments indicate that the number of children and asthmatic children exposed to ozone 

levels of concern is significant from a public health viewpoint.
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

Page -14-

8. . EPA’s quantitative risk assessment estimated the numbers of occurrences of various ozone 

related health effects associated with just meeting alternative standard levels down to a standard 

level of 0.064 ppm. Considering the patterns of change in the estimates of health effects in the risk 

assessment at the alternative standard levels, and the uncertainties and limitations in the estimates, 

what is the relative importance from a public health perspective of the estimated reductions in risk, 

as well as the risk remaining, for alternative standards across the proposed range? Please consider 

this question in light of the scientific evidence as a whole.

The CASAC took into account the uncertainties associated with assessing the risks to low 

levels of ozone and concluded that in a range of 0.060 to 0.070 ppm exposures, one could have 

confidence in the observed effects. I am still in agreement with that conclusion. 
2-14-11 Preliminary Individual Comments on the Ozone Reconsideration

These comments are preliminary and do not represent consensus CASAC advice or EPA 

policy. Do not cite or quote.

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Philip K. Hopke

The charge questions provided to the ozone panel revolve primarily around the toxicological and 

epidemiological evidence for the adverse health effects of exposure to ozone and other oxidants. 

One critical aspect that I believe is generally lost in the discussion is the presence of other 

photochemical oxidants. Thus, if we are looking at controlled exposures to ozone alone, we will 

be underestimating the effects of the total collection of oxidants in the ambient atmosphere. 

Epidemiology would take these other oxidants into account to some greater or lesser extent with 

respect to the covariance of the other ambient oxidants with ozone. However, central monitors 

particularly monitors typically placed in downwind locations in urban areas to avoid significant 

titration effects of motor vehicle emissions, may not be an adequate measure of population 

exposure across that urban area. 

We also have to recognize the full extent of the change made with the promulgation of the 2008 

ozone NAAQS. By changing the reported precision of the measurements, we have effectively 

lowered the standard from 84 ppb to 75.4 ppm and not from 80 to 75 ppb. This difference is a 

relatively large reduction whose effects have not yet been fully felt. Given that there is another 

review underway and this review is not supposed to take new literature into account, my 

recommendation would be that the standard not be lowered any further than 70.0 ppb, the upper 

end of the range judged as likely to be protective of public health, and reexamine all of the body of 

information available as part of the current round of review. Then a better informed judgment can 

be rendered.

Charge Question #4. With respect to the information from controlled human exposure 

studies at 0.060 ppm O3, what is the scientific importance of the small, group mean FEV1 

decrements relative to the findings that 7 to 20% of the subjects experienced FEV1 

decrements ≥ 10%? Please considerthis question from both a public health and a clinical 

perspective.

In the re-analysis of Adams (2006) study of 30 subjects by EPA (Brown, 2007), a small 

but statistically significant decline in FEV1 was observed. Specifically, a 2.85% mean O3-

induced decline in FEV1 was observed following 6.6 hr square wave exposure to 0.060 

ppm O3 compared to 6.6 hr filtered air (FA) exposure. The statistical analysis by EPA 

was based on a straightforward paired comparison, and they conservatively used a 

nonparametric sign test to obtain a p-value of 0.002 for the 0.06 ppm vs. FA comparison. 

Alternative, more powerful analytic methods using either a Wilcoxon signed-rank test or a 

paired t-test yielded even lower p-values in the EPA analysis. The EPA comparison 

remained significant after a Bonferroni correction for multiple comparisons. The original 

analysis of the data by Adams did not find a significant difference in FEV1 between the 

0.06 and FA exposure conditions. However, that analysis was based on a Scheffe 

correction for multiple comparisons, which is known to have very low power for the type of 

pairwise comparisons conducted by Adams compared to other well-known methods for 

multiple-testing correction (Kirk, 1982). Thus, from my understanding of the statistical 

analyses that have been conducted, I would argue that the analysis by EPA should be 
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policy. Do not cite or quote.

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preferred to that of Adams for the specific comparison of the FEV1 effects of 0.06 ppm 

exposure relative to FA exposure. 

Of the 30 study subjects in Adams, 24 showed some evidence for an O3-induced decline 

in FEV1, and 2 of the 30 (7%) experienced a decline greater than 10%. Although the 

sample size is relatively small, the consistency of effects across O3 exposure levels, as 

well as the consistency with effects observed by an earlier independent study 

(McDonnell, 2002), indicates that the observed deficits in FEV1 at the 0.060 ppm from the 

Adams study are not spurious. In other words, it is likely that prolonged exposure to 0.06 

ppm O3 causes a general shift in the distribution of FEV1 towards lower values. The 

following plot of the Adams data, derived from Figure 8-2 of Volume I of the “Air Quality 

Criteria for Ozone and Related Photochemical Oxidants, 2006” document, shows an 

approximate normal distribution in the O3-induced changes in FEV1 with exposure to 

0.06 ppm. 

Although the mean decrement is less than 3% and would not be considered clinically 

important, the shift to the right in this distribution pushes a fraction of subjects into the 

region that becomes clinically interesting (>10%). All of the Adams study subjects were 

healthy volunteers. From a public health standpoint, these results suggest that a large 

number of individuals in the general population (that are otherwise healthy), are likely to 

experience FEV1 deficits greater than 10% with prolonged exposure to 0.06 ppm O3. 

Although most healthy individuals can probably sustain a short-term 10-15% decline in 

FEV1 with little or no noticeable effect, it is not clear how they might be affected in the 

longer term if they experience repeated lung function deficits due to 0.06 ppm or greater 

O3 exposures over multiple days or weeks. Based on several other controlled exposure 

studies, we might expect that O3-induced FEV1 deficits in subjects with an existing 

respiratory condition (e.g. asthma) would be shifted even further to the right compared to 

the above figure. A 10-15% (or greater) pollution-related deficit in FEV1 in an individual 

with an existing respiratory condition is large enough that it could cause a clinically 

observable response. 
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policy. Do not cite or quote.

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Charge Question 5. The evidence, including that summarized above, indicates that susceptible 

populations may have greater responses than healthy people. In light of this evidence, how can we 

appropriately use the results of controlled human exposure studies conducted on healthy adults, as 

well as the epidemiological studies of susceptible groups, to inform a judgment on the effects of 

ozone exposure on susceptible populations? 

Response -- In many ways, the lowest exposure level of 0.06 ppm showing some symptom 

changes and statistically significant lung function changes in healthy subjects in an EPA analysis 

conducted for the last O3 NAAQS review represented a greatest lower bound on the ozone 

concentration of public health concern. In all of the controlled human exposure studies at 0.08-ppm 

ozone and below, a reasonable percentage of healthy subjects have lung function changes much 

higher than the average response (e.g., FEV1 changes > 10 %). While FEV1 changes > 10% may 

still allow healthy individuals to go about their normal daily activities, individuals with 

compromised lungs, such as asthmatics, incur significant health impacts with such lung function 

changes. As CASAC has noted in the past to the Agency, evidence is accumulating that persons 

with asthma, and particularly children, are more sensitive and experience larger decrements in lung 

function due to O3 exposure than do healthy volunteers. 

This, coupled with the fact that a number of epidemiology studies discussed in the last review were 

showing O3-related effects on various health endpoints (e.g., emergency department visits, 

increased hospital emissions, and mortality increases) at relatively low exposure levels leads one to 

conclude that O3 may cause effects even below 0.06 ppm. Since strengthening such a conclusion 

would need additional data from new studies, the CASAC concluded at the last review that the 

lower range of consideration for revision of the NAAQS should be 0.060 ppm O3. By doing so, the 

CASAC felt that margin of safety considerations would better be met than at 0.070 ppm O3. 

Moreover, since the relative strength of the science is weaker as one lowers the O3 concentration 

under consideration, a range of 0.060 to 0.070 ppm O3 allows the Administrator to place her 

judgment on the weight that any uncertainties and limitations in the science play in selecting an 

exposure level protective of public health.
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policy. Do not cite or quote.

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Lianne Sheppard

February 11, 2011

Individual comments

I still fully agree with the advice provided by CASAC in its letters of October 24, 2006 (EPACASAC-07-001), March 26, 2007 (EPA-CASAC-07-002), and February 10, 2010 (EPA-CASAC10-007). My opinion has been strengthened by the experience I have gained since 2008 through 

my continued involvement in air pollution and health research; this has contributed to my updated 

understanding of the evidence available in the 2008 review.

:

Preliminary thoughts on a draft response to Charge Question 6 (for CASAC discussion)

6. To what extent does your confidence that the effects observed in epidemiological studies are 

attributable specifically to O3 lessen or otherwise change, if at all, at the lower levels in the 

proposed range as compared to the higher levels?

:

Possible points for CASAC’s response:

• The endpoints of concern do not change at the lower levels of the proposed range.

• Many of the epidemiological studies had mean exposures well below the proposed range of 

0.070 ppm to 0.060 ppm and found ozone-related health effects. These include time series 

studies, field studies, and panel studies. The strengths and weaknesses of these studies do not 

differ appreciably in the proposed range.

• The epidemiological evidence does not suggest a threshold exists for mean concentrations 

within or above the proposed range. 

• While it is always difficult to tease out the effects of a single pollutant in epidemiological 

studies, there is evidence regarding ozone-related health effects from epidemiological studies 

that is consistent with the evidence from controlled exposure studies. This holds for the entire 

proposed range.

• While the effects attributed to ozone in epidemiological studies may not be specific to ozone, it 

is likely that reductions in population exposures to ozone will result in fewer adverse health 

effects. Our confidence in this statement does not change at the lower levels in the proposed 

range.
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policy. Do not cite or quote.

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Frank Speizer

Feb 8, 2011

Charge Question 1. What is your advice on the overall strengths and limitations of the evidence 

from controlled human exposure and epidemiological studies and the results of the exposure and 

risk assessments, in the context of EPA's selection of a standard level within the proposed range 

that would be requisite to protect public health with an adequate margin of safety, including the 

need to protect susceptible populations, such as children and people with asthma?

Although the two Adams studies represent the only reported work at levels of exposure below 

0.080 ppm of Ozone what has been pointed out and what is highly significant is that first the 

studies were done in normals and second that some 7-20% of the subjects experienced what I 

would consider very significant lung function decreases (> 10%) and or moderate respiratory 

symptoms. These findings essential preclude, because of the ethics of carrying out clinical studies 

in diseased individuals, from extending these studies to what are likely to be an even more 

sensitive groups. Thus, without having specific studies among asthmatics and children at these 

levels of exposure it is most prudent that, in spite of the uncertainty—more later on this issue—that 

EPA is justified to select an exposure level below the 0.080pppm (and I would say closer to the 

0.060 ppm level) to “protect public health with an adequate margin of safety, including the need to 

protect susceptible populations...”

Charge Question 2. Recognizing that controlled human exposure studies at 0.080 ppm O3 and 

above have provided evidence of other health effects, including inflammation and increased airway 

responsiveness which may occur through different physiological mechanisms than the reduction in 

FEV1, how should the results of these studies inform our understanding the health effects to healthy 

adults at exposures levels from 0.060 to 0.070 ppm?

Given the evidence of pathophysiologic changes in smaller airways with exposures at 0.08 ppm as 

well as the occurrence of pulmonary function changes in a substantial number of normal subjects, 

the only mechanism that would change these finding in diseased subjects if there were some way 

that the diseased airways, perhaps because of the presence of excess mucus, would be “protected” 

from the potential oxidative effects of ozone. This seems highly unlikely in that disease subjects 

studied at 0.08 ppm and higher seem to respond more than normals and thus would not likely be 

protected more at the lower levels to which normals have responded. Clearly, these experiments 

have not been done and one might argue that thus there is uncertainty; however, as indicated above 

such experiments might be considered unethical. 

Charge Question 3. How should the results of the controlled human exposure studies at 0.060 ppm 

O3, showing effects on FEV1 and respiratory symptoms, in the context of the larger body of 
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policy. Do not cite or quote.

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evidence from controlled human exposure studies, mentioned above, inform our understanding of 

the health effects to healthy adults at exposure levels from 0.060 to 0.070 ppm?

Because these results represent a continuum of effects and it is unlikely that there is a threshold I 

would argue that the results are informative and suggest that EPA in carrying out its obligation 

must suggest a standard in the range indicated. I would argue that because there is no threshold 

that the data are consistent with the lower end of the range being more protective than the upper 

end. 

Charge Question 4. With respect to the information from controlled human exposure studies at 

0.060 ppm O3, what is the scientific importance of the small, group mean FEV1 decrements relative 

to the findings that 7 to 20% of the subjects experienced FEV1 decrements ≥ 10%? Please consider 

this question from both a public health and a clinical perspective.

Please see answer to Charge Question 1 and 3. These small numbers of up to one-fifth of normals 

of the studied populations having changes in lung function or symptoms of this magnitude strongly 

suggests that the susceptible population would respond even greater and could reach clinically 

significant responses that might result in emergency room visits and or hospitalizations. 

Charge Question 5. The evidence, including that summarized above, indicates that susceptible 

populations may have greater responses than healthy people. In light of this evidence, how can we 

appropriately use the results of controlled human exposure studies conducted on healthy adults, as 

well as the epidemiological studies of susceptible groups, to inform a judgment on the effects of 

ozone exposure on susceptible populations?

It would be difficult to make an actual estimate of the difference in impact that might occur 

between 7-20% of normals responding and even a similar if not greater number of diseased 

subjects who might have similar size responses. It would be reasonable to assume that the 

responses certainly would not be less frequent and are likely to be of greater magnitude or at least 

large enough to increase the likelihood that symptomatic responses would need to be treated. 

Given the substantial number of potentially at risk adults in the population and the distributions of 

possible exposures even at the lower level of the bounded exposures

it would be prudent to argue that there will be some individuals remaining at risk. The judgment is 

how large a population is the Administrator willing to tolerate as being still at risk, not whether she 

can protect the entire population of potentially susceptible individuals. 

Charge Question 6. To what extent does your confidence that the effects observed in 

epidemiological studies are attributable specifically to O3 lessen or otherwise change, if at all, at 

the lower levels in the proposed range as compared to the higher levels?

Clearly there is greater uncertainty at the lower bound of the range of exposure; however, whether 

this is due to the mixture of addition pollutants coming into play rather than simply more 

variability in response cannot be determined. The few cities in which there are essentially no 

alternative pollutants to consider or where seasonal selection has been used to minimize alternative 

pollutants still show similar effects, and thus the likely cause of the uncertainly relates to greater 
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variability rather than confounding by additional pollutants and thus the effects noted seem 

attributable to ozone pollution. 

Charge Question 7. EPA’s exposure assessment quantified the number of all children and 

asthmatic children likely to be exposed to specific benchmark levels of ozone, including in 

particular 0.060 and 0.070 ppm. Considering the patterns of change in the estimates of exposures 

of concern at and above the 0.060 and 0.070 ppm benchmark levels, and the uncertainties and 

limitations in the estimates, what is the relative importance from a public health perspective of the 

estimated reductions in exposures of concern, as well as the exposures remaining, for alternative 

standards across the proposed range?

As indicated in the discussion across the 12 urban areas the assessment are considerably larger for 

the benchmark level of 0.60 ppm compared to the 0.070 ppm benchmark. However, they also note 

that the pattern of exposure is similar for all children and asthmatic school age children. The 

Administrator also stated that she must consider the public health impact in cities receiving 

considerably less protection associated with air quality just meeting the same standard. This is a 

difficult criteria to meet with a single standard. Thus it becomes prudent to weigh the impact of the 

exposure against the cost of meeting that standard. The science is clear that there will be children 

as risk at any reasonable standard chosen. Thus the public health consideration is how big a 

population the Administrator is willing to leave at risk. 

Charge Question 8. EPA’s quantitative risk assessment estimated the numbers of occurrences of 

various ozone related health effects associated with just meeting alternative standard levels down 

to a standard level of 0.064 ppm. Considering the patterns of change in the estimates of health 

effects in the risk assessment at the alternative standard levels, and the uncertainties and 

limitations in the estimates, what is the relative importance from a public health perspective of the 

estimated reductions in risk, as well as the risk remaining, for alternative standards across the 

proposed range? Please consider this question in light of the scientific evidence as a whole.

From the Fed Reg TABLE 3—NUMBER AND PERCENT OF ALL AND ASTHMATIC SCHOOL AGE CHILDREN IN 12 

URBAN AREAS ESTIMATED TO EXPERIENCE 8-HOUR OZONE EXPOSURES ABOVE 0.060 AND 0.070 PPM WHILE AT 

MODERATE OR GREATER EXERTION,ONE OR MORE TIMES PER SEASON ASSOCIATED WITH JUST MEETING 

ALTERNATIVE 8-HOUR STANDARDS BASED ON ADJUSTING 2002 AND 2004 AIR QUALITY DATA1 2

This table not reproduced here suggests a wide range of at risk children dependent upon the choice 

of levels of exposure. Unfortunately, it is not clear that 2002 is the “worse case” or 2004 is the 

“best case”. Nevertheless, with regard to protecting the public health the range of all children aged 

5-18 between 0.064-0.074 is between 4.5 million and 950, 000 in the worse case vs 350,000 and 

10,000 in the best case, with proportionately lower numbers for asthmatic children. Clearly truth 

must lay somewhere in between. Even these lower numbers represent a substantial fraction of at 

risk children. Given the evidence of the pathophysiology, the clinical studies data in normals and 

the likelihood that symptomatic subjects will respond to a greater degree, and the fact that there is 

no evidence for a threshold of effects, the prudent decision is to set a standard that is as protective 

of the public health with a margin of safety as mandated by law.
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Helen Suh

1. What is your advice on the overall strengths and limitations of the evidence from controlled 

human exposure and epidemiological studies and the results of the exposure and risk 

assessments, in the context of EPA's selection of a standard level within the proposed range 

that would be requisite to protect public health with an adequate margin of safety, including 

the need to protect susceptible populations, such as children and people with asthma?

The scientific evidence from controlled human exposure and epidemiological studies and from 

the exposure and risk assessments supports a primary ozone standard (with a margin of safety) 

between 0.060 to 0.070 ppm. The controlled human exposure studies by Adams (2002, 2006) 

show statistically significant changes in lung function from a 6.6 hour exposure to 0.060 ppm 

ozone. While these studies were limited in number, they were well designed and results were 

consistent with those from previous studies, thus lending credibility to their findings. Of 

particular interest is the fact that a small but important fraction of the study subjects 

experienced lung function decrements greater than 10% at exposures to 0.060 ppm ozone. 

These findings suggest that the impacts of ozone exposures at these levels may be significant 

for individuals with pre-existing respiratory conditions and must be considered to ensure 

adequate margin of safety for sensitive subpopulations.

2. Recognizing that controlled human exposure studies at 0.080 ppm O3 and above have provided 

evidence of other health effects, including inflammation and increased airway responsiveness 

which may occur through different physiological mechanisms than the reduction in FEV1, how 

should the results of these studies inform our understanding the health effects to healthy adults 

at exposures levels from 0.060 to 0.070 ppm?

It is reasonable to consider findings of sub-clinical adverse impacts, such as increased 

inflammation and airway responsiveness, when considering adverse health impacts to healthy 

adults at exposures levels from 0.060 to 0.070 ppm. These findings are certainly pertinent to 

margin of safety considerations. 

3. How should the results of the controlled human exposure studies at 0.060 ppm O3, showing 

effects on FEV1 and respiratory symptoms, in the context of the larger body of evidence from 

controlled human exposure studies, mentioned above, inform our understanding of the health 

effects to healthy adults at exposure levels from 0.060 to 0.070 ppm?

These results provide important evidence that exposures to 0.060 ppm of ozone are harmful 

and are consistent with previous observations of no safe level for ozone exposures. Findings 

from Adams studies (2002, 2006) must be considered, at the least as being central to margin of 

safety determinations. 

4. With respect to the information from controlled human exposure studies at 0.060 ppm O3, 

what is the scientific importance of the small, group mean FEV1 decrements relative to the 
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policy. Do not cite or quote.

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findings that 7 to 20% of the subjects experienced FEV1 decrements ≥ 10%? Please consider 

this question from both a public health and a clinical perspective.

For individuals with pre-existing respiratory disease, a 10% decrement in FEV1 is significant. 

5. The evidence, including that summarized above, indicates that susceptible populations may 

have greater responses than healthy people. In light of this evidence, how can we 

appropriately use the results of controlled human exposure studies conducted on healthy 

adults, as well as the epidemiological studies of susceptible groups, to inform a judgment on 

the effects of ozone exposure on susceptible populations.

Although the sample sizes are small, the variability in the response observed for healthy adults 

in the controlled human studies can inform judgments on the effects of ozone in susceptible 

populations. For example, the 7-20% of healthy adults who were found to have large ozonemediated responses in controlled exposure studies may provide an indication of the fraction of 

individuals in the general population who may also be large responders. Ozone-mediated 

response may comprise an even greater percentage of the susceptible population. 

6. To what extent does your confidence that the effects observed in epidemiological studies are 

attributable specifically to O3 lessen or otherwise change, if at all, at the lower levels in the 

proposed range as compared to the higher levels?

The uncertainty in the epidemiological findings at low ozone levels is certainly greater than 

that at high ozone levels, with greater confidence about the existence of health effects at the 

upper end and less confidence at lower O3 levels. Confounding by other pollutants is certainly 

of concern. However, ozone mediated impacts have been observed for a variety of endpoints, 

including those such as school absences that have not been related to particulate matter (PM), 

perhaps the most important potential confounder. Further, ozone-mediated impacts have been 

demonstrated in a number of locations, with varying correlations between ozone and PM. 

Finally, additional support for epidemiological findings is provided by results from controlled 

exposure studies. 

7 . EPA’s exposure assessment quantified the number of all children and asthmatic children 

likely to be exposed to specific benchmark levels of ozone, including in particular 0.060 and 

0.070 ppm. Considering the patterns of change in the estimates of exposures of concern at and 

above the 0.060 and 0.070 ppm benchmark levels, and the uncertainties and limitations in the 

estimates, what is the relative importance from a public health perspective of the estimated 

reductions in exposures of concern, as well as the exposures remaining, for alternative 

standards across the proposed range?

The exposure assessment shows considerable temporal and spatial variability in exposure 

estimates, which is expected and which has important implications in determinations about

adequate margin of safety. Given results from health studies, it is reasonable to assume no 

threshold in ozone-mediated impacts. As a result, even with uncertainty in the benchmark 
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policy. Do not cite or quote.

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exposures, it is likely that a significant fraction of asthmatic children will remain exposed to 

ozone exposures above the benchmark level.

8 . EPA’s quantitative risk assessment estimated the numbers of occurrences of various ozone 

related health effects associated with just meeting alternative standard levels down to a 

standard level of 0.064 ppm. Considering the patterns of change in the estimates of health 

effects in the risk assessment at the alternative standard levels, and the uncertainties and 

limitations in the estimates, what is the relative importance from a public health perspective of 

the estimated reductions in risk, as well as the risk remaining, for alternative standards across 

the proposed range? Please consider this question in light of the scientific evidence as a 

whole.

The quantitative risk assessment showed public health significant reductions in risk in going 

from a 0.074 ppm to a 0.064 ppm standard. As acknowledged by the Administrator, 

reductions in risk may be even greater, as the risk assessment examined only a fraction of the 

observed health outcomes, with many unexamined health outcomes posing greater risks for 

sensitive subgroups. These limitations may outweigh, or at the least counteract, any concerns 

regarding uncertainty in the risk estimates.