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November 30, 1995

EPA-SAB-CASAC-LTR-96-002

Honorable Carol M. Browner

Administrator

U.S. Environmental Protection Agency

401 M Street, S.W.

Washington, DC 20460

RE: CASAC Closure on the Primary Standard Portion of the Staff

Paper for Ozone

Dear Ms. Browner:

A Panel of the Clean Air Scientific Advisory Committee (CASAC) of EPA’s

Science Advisory Board (SAB) met on March 22, 1995, to review a draft of the primary

standard part of the document entitled Review of National Ambient Air Quality

Standards for Ozone Assessment of Scientific and Technical Information OAQPS Staff

Paper. At that time, a draft of the secondary standard portion of the document was not

completed. At the March meeting, the Panel made extensive recommendations for

strengthening the document. In August 1995, a revised Staff Paper, which included a

first draft of the secondary standard portion was sent to CASAC panel members for

review. On September 19 and 20, 1995, the Panel met to compete this review. The

Panel members’ comments reflect their satisfaction with the improvements made in the

scientific quality and completeness of the primary standard portion of the Staff Paper. 

The changes made in that portion of the document are consistent with CASAC’s

recommendations. However, the Panel Members provided additional comments to your

staff at the meeting and subsequently in writing. Although the Panel would like to have

these comments considered for incorporation in the Staff Paper, the Panel did not feel

that it was necessary to review another revised version and came to closure on the

primary standard portion. It was the consensus of the Panel that although our

understanding of the health effects of ozone is far from complete, the document

provides an adequate scientific basis for making regulatory decisions concerning a

primary ozone standard.

The Panel could not come to closure, however, on the secondary standard
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portion of the Staff Paper which was a first draft. To facilitate further development of

this part of the Staff Paper, the Panel members have provided detailed comments to

your staff. The Panel felt that the suggested revisions were extensive enough to

warrant a review of the next draft.

I would like to summarize for you the Panel’s recommendations concerning the

primary standard. It was the consensus of the Panel that EPA’s selection of ozone as

the surrogate for controlling photochemical oxidants is correct. It was also the

consensus of the Panel that an 8-hour standard was more appropriate for a human

health-based standard than a 1-hour standard. The Panel was in unanimous

agreement that the present 1-hour standard be eliminated and replaced with an 8-hour

standard.

The Panel felt that the weight of the health effects evidence indicates that there

is no threshold concentration for the onset of biological responses due to exposure to

ozone above background concentrations. Based on information now available, it

appears that ozone may elicit a continuum of biological responses down to background

concentrations. This means that the paradigm of selecting a standard at the lowestobservable-effects-level and then providing an “adequate margin of safety” is no longer

possible. It further means that EPA’s risk assessments must play a central role in

identifying an appropriate level.

To conduct the risk assessments, the Agency had to identify the population at

risk and the physiological responses of concern, develop a model to estimate the

exposure of this population to ozone, and develop a model to estimate the probability of

an adverse physiological response to the exposure. The Panel agrees with EPA that

the selection of “outdoor children” and “outdoor workers,” particularly those with

preexisting respiratory disease are the appropriate populations with the highest risks. 

After considerable debate, it was the consensus of the Panel that the Agency’s criteria

for the determination of an adverse physiological response was reasonable. 

Nevertheless, there was considerable concern that the criteria for grading physiological

and clinical responses to ozone was confusing if not misleading. The Panel concurs,

with the Agency that the models selected to estimate exposure and risk are appropriate

models. However, because of the myriad of assumptions that are made to estimate

population exposure and risk, large uncertainties exist in these estimates.

The results of two of the risk analyses are presented in Tables VI-1 and VI-2 in

the Staff Paper and are reproduced in the attached tables. The ranges of the risk

estimates across nine cities for outdoor children are presented in Table VI-1. Because

of the large number of stochastic variables used in the exposure models, the exposure
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estimates vary from run to run. However, the ranges are not reflective of all of the

uncertainties associated with the numerous assumptions that were made to develop the

estimates.

The single estimates presented in Table VI-2 do not reflect any of the

uncertainties associated with these estimates. (Table VI-2 contains only the estimated

hospital admissions due to asthma which account for over 85% of the estimated total

hospital admissions due to ozone exposure). These uncertainties need to be explicitly

articulated in order to put the estimates in proper perspective. Nevertheless, based on

the results presented in these and other similar tables presented in the Staff Paper, the

Panel concluded that there is no “bright line” which distinguishes any of the proposed

standards (either the level or the number of allowable exceedences) as being

significantly more protective of public health. For example, the differences in the

percent of outdoor children (Table VI-1) responding between the present standard and

the most stringent proposal (8H1EX at 0.07 ppm) are small and their ranges overlap for

all health endpoints. In Table VI-2, the estimates in row 1, which appeared in the draft

Staff Paper, suggest considerable differences between the several options. However,

when ozone-aggravated asthma admissions are compared to total asthma admissions

(rows 5 and 6), the differences between the various options are small. Consequently,

the selection of a specific level and number of allowable exceedences is a policy

judgment. Although it was the consensus of the Panel that the ranges of

concentrations and allowable exceedences proposed by the Agency were appropriate, 

a number of Panel members expressed “personal” preferences for the level and

number of allowable exceedences. Of the ten panel members who expressed their

opinions, all ten favored multiple allowable exceedences, three favored a level of 0.08

ppm, one favored the mid to upper range (0.08 - 0.09 ppm), three favored the upper

range (0.09 ppm), one favored a 0.009 - 0.10 ppm range with health advisories issued

when the 8-hour ozone concentration was forecasted to exceed 0.007 ppm, and two

just endorsed the range presented by the Agency as appropriate and stated that the

selection should be a policy decision. The members who favored the lower numbers

expressed concern over the evidence for chronic deep lung inflammation from the

controlled human and animal exposure studies and the observations of pain on deep

inspiration in some subjects.

Because there is no apparent threshold for responses and no “bright line” in the

risk assessment, a number of panel members recommended that an expanded air

pollution warning system be initiated so that sensitive individuals can take appropriate

“exposure avoidance” behavior. Since many areas of the country already have an

infrastructure in place to designate “ozone action days” when voluntary emission
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reduction measures are put in place, this idea may be fairly easy to implement.

It was also the consensus of the Panel that the form of the 8-hr standard be

more robust than the present 1-hour standard. The present standard is based on an

extreme value statistic which is significantly dependent on stochastic processes such

as extreme meteorological conditions. The result is that areas which are near

attainment will randomly flip in and out of compliance. A more robust, concentrationbased form will minimize the “flip-flops,” and provide some insulation from the impacts

of extreme meteorological events. The Panel also endorses the staff recommendation

for creating a “too close to call” category.

Since the last ozone NAAQS review, the scientific community has made great

strides in their understanding of the health effects of ozone exposure because of

ongoing research programs. Panel members were very impressed with how much

more we understand now as compared to the prior round. Nevertheless, there are still

many gaps in our knowledge and large uncertainties in many of the assessments. For

example, there is little information available on the frequency of human activity patterns

involving outdoor physical exercise. Little is also known about the possible chronic

health impacts of ozone exposure over a period of many years. In addition, there is no

clear understanding of the significance of the inflammatory response inferred from the

broncholavage data. Panel members stated, however, that the scientific community is

now in a position to frame the questions that need to be better resolved so the

uncertainties can be reduced before the next ozone review in 5 years. For this reason,

it is important that research efforts on the health and ecological effects of ozone not be

reduced because we have come to closure on this review.

CASAC would appreciate being kept informed of progress on establishing a

revised or new ozone standard, and plans for research on ozone effects. Please do

not hesitate to contact me if CASAC can be of further assistance in this matter. We

look forward to receiving the revisions of the secondary standard portion of the Staff

Paper.

Sincerely,

 /signed/

Dr. George T. Wolff, Chair

Clean Air Scientific Advisory Committee
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Page left blank to accomodate insert table - see meeting file or report file for a copy of

this page.
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Table VI-2 (revised)

ESTIMATED HOSPITAL ADMISSIONS FOR ASTHMATICS IN THE NEW YORK CITY AREA

1H1EX 1H1EX 8H1EX 8H1EX 8H1EX 8H1EX 8H5EX 8H5EX AS IS

0.12 0.10 0.10 0.09 0.08 0.07 0.09 0.08

Excess Admissions 210 130 240 180 110 60 180 120 =385 a d

% ^ from present std 0% -38% +14% -14% -48% -71% -14% -42% +83%Excess + background 890 810 920 860 790 740 860 800 1065 b e% ^ from present std 0% -9% +3% -3% -11% -17% -3% -10% +20%All asthma admissions 28,295 28,215 28,325 28,265 28,195 28,145 28,265 28,205 28,470 c f% ^ from present std 0% -0.3% +0.1% -0.1% -0.4% -0.5% -0.1% -0.3% +0.6%

a - excess asthma admissions attributed to ozone levels exceeding a background concentration of 0.04 ppm; from Table VI-2, page 155 in the

August 1995 OAQPS Draft Staff Paper

b - asthma admissions included in (a) plus those due to background ozone concentrations; admissions due to background = 1065 - 385 = 680 e d

c - asthma admissions due to all causes = 28,470 - 385 - Excess Admissions from row 1 f dd - estimated from Figure V-15, page 125 in the August 1995 OAQPS Draft Staff Papere - from page 127, line 13 in the August 1995 OAQPS Draft Staff Paperf - total admissions from asthma = total asthmatics (365,000 - from page 126, line 24) x hospitalization rate (78/1000 asthmatics - from page 126,

line 29)
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SCIENCE ADVISORY BOARD

CLEAN AIR SCIENTIFIC ADVISORY COMMITTEE

OZONE PANEL ROSTER

Chair

Dr. George T. Wolff, General Motors Environmental & Energy Staff, Detroit, MI

Members

Dr. Stephen M. Ayres, Office of International Health Programs, Virginia Commonwealth University, Medical

College of Virginia, Richmond, VA

Dr. Jay S. Jacobson, Boyce Thompson Institute, Cornell University, Ithaca, NY

Dr. Joe L. Mauderly, Inhalation Toxicology Research Institute, Lovelace Biomedical & Environmental Research

Institute, Albuquerque, NM

Dr. Paulette Middleton, Science & Policy Associates, Inc.,Boulder, CO (did not participate)

Dr. James H. Price, Jr., Texas Natural Resource Conservation Commission, Austin, TX 

Consultants to CASAC

Dr. Stephen D. Colome, Integrated Environmental Services, University Tower, Irvine, CA

Dr. A. Myrick Freeman, Department of Economics, Bowdoin College,, Brunswick, ME

Dr. Allan Legge, Biosphere Solutions,Calgary, Alberta, CANADA

Dr. Morton Lippmann, Institute of Environmental Medicine, New York University Medical Center, Tuxedo, NY

Dr. William Manning, Department of Plant Pathology, University of Massachusetts, Amherst, MA 

Dr. Roger O. McClellan, Chemical Industry Institute of Toxicology, Research Triangle Park, NC 

Dr. D. Warner North, Decision Focus, Inc., Mountain View, CA

Dr. Frank E. Speizer, Harvard Medical School, Channing Lab, Boston, MA 

Dr. George Taylor, Biological Services Center, Desert Research Institute, University of Nevada, Reno, NV 

Dr. Mark J. Utell, Pulmonary Disease Unit, University of Rochester Medical Center, Rochester, NY 

Science Advisory Board Staff

Mr. A. Robert Flaak, Designated Federal Official, U. S. Environmental Protection Agency, Science Advisory

Board (1400F), 401 M Street, SW, Washington, DC 20460 

Ms. Connie Valentine, Staff Secretary, U. S. Environmental Protection Agency, Science Advisory Board

(1400F), 401 M Street, SW, Washington, DC 20460 
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NOTICE

This report has been written as part of the activities of the Science Advisory Board, a public advisory

group providing extramural scientific information and advice to the Administrator and other officials of the

Environmental Protection Agency. The Board is structured to provide balanced, expert assessment of scientific

matters related to 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 Environmental

Protection Agency, nor of other agencies in the Executive Branch of the Federal government, nor does mention

of trade names or commercial products constitute a recommendation for use.
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