National Ambient Air Quality Standards for Ozone

SUMMARY: This document describes EPA's decision to revise the national

ambient air quality standards (NAAQS) for ozone (O3) based

on its review of the available scientific evidence linking exposures to

ambient O3 to adverse health and welfare effects at levels

allowed by the current O3 standards. The current 1-hour

primary standard is replaced by an 8-hour standard at a level of 0.08

parts per million (ppm) with a form based on the 3-year average of the

annual fourth-highest daily maximum 8-hour average O3

concentrations measured at each monitor within an area. The new primary

standard will provide increased protection to the public, especially

children and other at-risk populations, against a wide range of

O3-induced health effects, including decreased lung

function, primarily in children active outdoors; increased respiratory

symptoms, particularly in highly sensitive individuals; hospital

admissions and emergency room visits for respiratory causes, among

children and adults with pre-existing respiratory disease such as

asthma; inflammation of the lung, and possible long-term damage to the

lungs. The current 1-hour secondary standard is replaced by an 8-hour

standard identical to the new primary standard. The new secondary

standard will provide increased protection to the public welfare

against O3-induced effects on vegetation, such as

agricultural crop loss, damage to forests and ecosystems, and visible

foliar injury to sensitive species.

EFFECTIVE DATE: This rule is effective September 16, 1997.

ADDRESSES: A docket containing information relating to the EPA's review

of the O3 primary and secondary standards (Docket No. A-95-

58) is available for public inspection in the Central Docket Section of

the U.S. Environmental Protection Agency, South Conference Center, Room

4, 401 M St., SW., Washington, DC. This docket incorporates the docket

from the previous review of the O3 standards (Docket No. A-

92-17) and the docket established for the air quality criteria document

(Docket No. ECAO-CD-92-0786). The docket may be inspected between 8

a.m. and 3 p.m. on weekdays, and a reasonable fee may be charged for

copying. The information in the docket constitutes the complete basis

for the decision announced in this final rule. For the availability of

related information, see ``SUPPLEMENTARY INFORMATION.''

FOR FURTHER INFORMATION CONTACT: David McKee, MD-15, Air Quality

Standards and Strategies Division, Office of Air Quality Planning and

Standards, U.S. Environmental Protection Agency, Research Triangle

Park, NC 27711; telephone: (919) 541-5288; e-mail:

[email protected].

SUPPLEMENTARY INFORMATION:

Availability of Related Information

Certain documents are available from the U.S. Department of

Commerce, National Technical Information Service, 5285 Port Royal Road,

Springfield, VA 22161. Available documents include:

(1) Air Quality Criteria for O3 and Other Photochemical

Oxidants (``Criteria Document'') (three volumes, EPA/600/P-93-004aF

through EPA/600/P-93-004cF, July 1996, NTIS # PB-96-185574, $169.50

paper copy, $58.00 microfiche).

(2) The Review of the National Ambient Air Quality Standards for

O3: Assessment of Scientific and Technical Information

(``Staff Paper'')(EPA-452/R-96-007, June 1996, NTIS # PB-96-203435,

$67.00 paper copy and $21.50 microfiche). (Add a $3.00 handling charge

per order.)

A limited number of copies of other documents generated in

connection with this standard review, such as documents pertaining to

human exposure and health risk assessments, and vegetation exposure,

risk, and benefits analyses can be obtained from: U.S. Environmental

Protection Agency Library (MD-35), Research Triangle Park, NC 27711,

telephone (919) 541-2777. These and other related documents are also

available for inspection and copying in the EPA docket identified under

``ADDRESSES''.

Electronic Availability

The Staff Paper and human exposure and health risk assessment

support documents are now available on the Agency's Office of Air

Quality Planning and Standards (OAQPS) Technology Transfer Network

(TTN) Bulletin Board System (BBS) in the Clean Air Act Amendments area,

under Title I, Policy/Guidance Documents. To access the bulletin board,

a modem and communications software are necessary. To dial up, set your

communications software to 8 data bits, no parity and one stop bit.

Dial (919) 541-5742 and follow the on-screen instructions to register

for access. After registering, proceed to choice `` Gateway to TTN

Technical Areas'', then choose `` CAAA BBS''. From the main menu,

choose `` Title I: Attain/Maint of NAAQS'', then `` Policy

Guidance Documents.'' To access these documents through the World Wide

Web, click on ``TTN BBSWeb'', then proceed to the Gateway to TTN

Technical areas, as above. If assistance is needed in accessing the

system, call the help desk at (919) 541-5384 in Research Triangle Park,

NC.

Implementation Strategy for Revised Air Quality Standards

On Wednesday, July 16, 1997, President Clinton signed a memorandum

to the Administrator specifying his goals for the implementation of the

O3 and PM standards. Attached to the President's memorandum

is a strategy prepared by an interagency Administration group outlining

the next steps that would be necessary for implementing these

standards. The EPA will prepare guidance and proposed rules consistent

with the President's memorandum. Copies of the Presidential document

are available in paper copy by contacting the U.S. Environmental

Protection Agency Library at the address under ``Availability of

Related Information'' and in electronic form as discussed above in

``Electronic Availability.''

The following topics are discussed in this preamble:

I. Background

A. Legislative Requirements

B. Related Control Requirements

C. Review of Air Quality Criteria and Standards for

O3

D. Summary of Proposed Revisions to the O3 Standards

II. Rationale for the Primary O3 Standard

A. Introduction

B. Elements of the Primary Standard

C. Communication of Public Health Information

III. Rationale for the Secondary O3 Standard

A. Introduction

B. Need for Revision of Current Secondary Standard

C. Final Decision on the Secondary Standard

IV. Other Issues

A. Cost Considerations

B. Margin of Safety

C. Comment Period

D. 1990 Act Amendments

V. Technical Changes to Part 50

VI. Revisions to Appendices D, E, and H

VII. Regulatory and Environmental Impact Analyses

[[Page 38857]]

A. Executive Order 12866

B. Regulatory Flexibility Analysis

C. Impact of Reporting Requirements

D. Unfunded Mandates Reform Act

E. Environmental Justice

F. Submission to Congress and Comptroller General

VIII. Response to Petition for Administrator Browner's Recusal

IX. References

I. Background

A. Legislative Requirements

Two sections of the Act govern the establishment, review, and

revision of NAAQS. Section 108 (42 U.S.C. 7408) directs the

Administrator to identify certain pollutants which ``may reasonably be

anticipated to endanger public health or welfare'' and to issue air

quality criteria for them. These air quality criteria are to

``accurately reflect the latest scientific knowledge useful in

indicating the kind and extent of all identifiable effects on public

health or welfare which may be expected from the presence of [a]

pollutant in the ambient air ***.''

Section 109 (42 U.S.C. 7409) directs the Administrator to propose

and promulgate ``primary'' and ``secondary'' NAAQS for pollutants

identified under section 108. Section 109(b)(1) defines a primary

standard as one ``the attainment and maintenance of which in the

judgment of the Administrator, based on [the] criteria and allowing an

adequate margin of safety, are requisite to protect the public

health.'' The margin of safety requirement was intended to address

uncertainties associated with inconclusive scientific and technical

information available at the time of standard setting, as well as to

provide a reasonable degree of protection against hazards that research

has not yet identified. Both kinds of uncertainties are components of

the risk associated with pollution at levels below those at which human

health effects can be said to occur with reasonable scientific

certainty. Thus, by selecting primary standards that provide an

adequate margin of safety, the Administrator is seeking not only to

prevent pollution levels that have been demonstrated to be harmful but

also to prevent lower pollutant levels that she finds may pose an

unacceptable risk of harm, even if the risk is not precisely identified

as to nature or degree. The Act does not require the Administrator to

establish a primary NAAQS at a zero-risk level but rather at a level

that reduces risk sufficiently so as to protect public health with an

adequate margin of safety. The selection of any particular approach to

providing an adequate margin of safety is a policy choice left

specifically to the Administrator's judgment. Lead Industries

Association v. EPA. (647 F.2d 1130, 1161-62 (D.C. Cir. 1980)).

A secondary standard, as defined in section 109(b)(2), must

``specify a level of air quality the attainment and maintenance of

which in the judgment of the Administrator, based on [the] criteria,

[are] requisite to protect the public welfare from any known or

anticipated adverse effects associated with the presence of [the]

pollutant in the ambient air.'' Welfare effects as defined in section

302(h) (42 U.S.C. 7602(h)) include, but are not limited to, ``effects

on soils, water, crops, vegetation, manmade materials, animals,

wildlife, weather, visibility, and climate, damage to and deterioration

of property, and hazards to transportation, as well as effects on

economic values and on personal comfort and well-being.''

Section 109(d)(1) of the Act requires periodic review and, if

appropriate, revision of existing air quality criteria and NAAQS.

Section 109(d)(2) requires appointment of an independent scientific

review committee to review criteria and standards and recommend new

standards or revisions of existing criteria and standards, as

appropriate. The committee established under section 109(d)(2) is known

as the Clean Air Scientific Advisory Committee (CASAC), a standing

committee of EPA's Science Advisory Board.

B. Related Control Requirements

States are primarily responsible for ensuring attainment and

maintenance of ambient air quality standards once EPA has established

them. Under section 110 of the Act (42 U.S.C. 7410) and related

provisions, States are to submit, for EPA approval, State

implementation plans (SIP's) that provide for the attainment and

maintenance of such standards through control programs directed to

sources of the pollutants involved. The States, in conjunction with

EPA, also administer the prevention of significant deterioration

programs (42 U.S.C. 7470-7479) for these pollutants. In addition,

Federal programs provide for nationwide reductions in emissions of

these and other air pollutants under Title II of the Act (42 U.S.C.

7521-7574), which involves controls for automobile, truck, bus,

motorcycle, nonroad engine, and aircraft emissions; the new source

performance standards under section 111 (42 U.S.C. 7411); and the

national emission standards for hazardous air pollutants under section

112 (42 U.S.C. 7412).

C. Review of Air Quality Criteria and Standards for O3

The last review of O3 air quality criteria and standards

was completed in March 1993 with notice of a final decision not to

revise the existing primary and secondary standards (58 FR 13008). The

current primary and secondary standards are each set at a level of 0.12

ppm, with a 1-hour averaging time and a 1-expected-exceedance form,

such that the standards are attained when the expected number of days

per calendar year with maximum hourly average concentrations above 0.12

ppm is equal to or less than 1, averaged over 3 years (as determined by

40 CFR part 50, Appendix H).1

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1 A more complete history of the O3 NAAQS is

presented in section II.B. of the Office of Air Quality Planning and

Standards Staff Paper, Review of National Ambient Air Quality

Standards for O3: Assessment of Scientific and Technical

Information (U.S. EPA, 1996b).

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The EPA initiated this current review of the air quality criteria

and standards in August 1992 with the development of a revised Air

Quality Criteria Document for O3 and Other Photochemical

Oxidants, henceforth the ``Criteria Document.'' Several workshops were

held by EPA's National Center for Environmental Assessment (NCEA) to

discuss health and welfare effects information during the summer and

fall of 1993. An external review draft of the Criteria Document made

available to the public and to the CASAC in the spring of 1994 was

reviewed at a public CASAC meeting held on July 20-21, 1994. Based on

comments made at the meeting, NCEA staff prepared a second external

review draft, which was reviewed at a public CASAC meeting on March 21-

22, 1995. At the same meeting, the CASAC also reviewed draft portions

of a staff paper prepared by the OAQPS, Review of National Ambient Air

Quality Standards for O3: Assessment of Scientific and

Technical Information (henceforth, the ``Staff Paper''), focusing on

health effects and the primary NAAQS.2 Taking into account

CASAC and public comments, staff revised both documents and made new

drafts available for public and CASAC review during the summer of 1995.

The OAQPS staff also prepared and made available draft portions of the

Staff Paper focusing on welfare effects and the secondary standard.

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2 The Staff Paper evaluates policy implications of the key

studies and scientific information in the Criteria Document,

identifies critical elements that EPA staff believes should be

considered, and presents staff conclusions and recommendations of

suggested options for the Administrator's consideration.

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[[Page 38858]]

A public CASAC meeting was held on September 19-20, 1995, at which

time CASAC came to closure in its review of the draft Criteria Document

and the primary standard sections of the draft Staff Paper. In a

November 28, 1995 letter from the CASAC chair to the Administrator,

CASAC advised that the final draft Criteria Document ``provides an

adequate review of the available scientific data and relevant studies

of O3 and related photochemical oxidants'' (Wolff, 1995a).

Further, in a November 30, 1995 letter, CASAC advised the Administrator

that the primary standard portion of the draft Staff Paper ``provides

an adequate scientific basis for making regulatory decisions concerning

a primary O3 standard'' (Wolff, 1995b). The final Criteria

Document (U.S. EPA, 1996a) reflects CASAC and public comments received

at and subsequent to the September 1995 CASAC meeting.

Based on comments on the Staff Paper from the September 1995 CASAC

meeting, revisions were made to the secondary standard sections of the

Staff Paper, which were reviewed at a public CASAC meeting held on

March 21, 1996. At that meeting and in a subsequent letter to the

Administrator, CASAC concluded that the secondary standard sections of

the draft Staff Paper ``provide an appropriate scientific basis for

making regulatory decisions concerning a secondary O3

standard'' (Wolff, 1996). The final Staff Paper (U.S. EPA, 1996b)

reflects CASAC and public comments received at and subsequent to the

September 1995 and March 1996 meetings on the primary standard and

secondary standard sections, respectively.

On November 27, 1996 EPA announced its proposed decision to revise

the NAAQS for O3 (61 FR 65716, December 13, 1996,

hereinafter ``proposal'') as well as its proposed decision to revise

the NAAQS for particulate matter (PM). In the proposal, EPA identified

proposed revisions, based on the air quality criteria for

O3, and solicited public comments on alternative primary and

secondary standards and on the proposed forms of the standards.

To ensure the broadest possible public input on the O3

and PM proposals, EPA took extensive and unprecedented steps to

facilitate the public comment process beyond the normal process of

providing an opportunity to request a hearing and receiving written

comments submitted to the rulemaking docket. The EPA established a

national toll-free telephone hotline to facilitate public comments on

the proposed revisions to the O3 and PM NAAQS, and on

related notices dealing with the implementation of revised

O3 and PM standards, as well as a system for the public to

submit comments on the proposals electronically via the Internet. Over

14,000 calls and over 4,000 electronic mail messages were received

through these channels. The public could also access key supporting

documents (including the Criteria Document, Staff Paper, related

technical documents and fact sheets) via the Internet.

The EPA also held several public hearings and meetings across the

country to provide direct opportunities for public comment on the

proposed revisions to the O3 and PM NAAQS and to disseminate

information to the public about the proposed standard revisions. On

January 14 and 15, 1997, EPA held concurrent, 2-day public hearings in

Boston, MA, Chicago, IL, and Salt Lake City, UT. A fourth public

hearing, which focused primarily on PM monitoring issues, was held in

Durham, NC on January 14, 1997. Over 400 citizens and organizations

testified during these public hearings. EPA also held two national

satellite telecasts to answer questions on the standards and

participated in meetings sponsored by the Air and Waste Management

Association on the proposed revisions to the standards at more than 10

locations across the country. Beyond that, several EPA regional offices

held public meetings and workshops and participated in hearings that

States and cities held around the country.

As a result of this intensive effort to solicit public input, over

50,000 written and verbal comments were received on the proposed

revisions to the O3 NAAQS by the close of the public comment

period on March 12, 1997. The major issues raised in the comments are

discussed throughout the preamble of this final rule. A comprehensive

summary of all significant comments, along with EPA's response to such

comments (hereafter ``Response to Comments''), can be found in the

docket for this rulemaking (Docket No. A-95-58).

The focus of this current review of the air quality criteria and

standards for O3 and related photochemical oxidants is on

public health and welfare effects associated with exposure to ambient

levels of tropospheric O3. Tropospheric O3 is

chemically identical to stratospheric O3, which is produced

miles above the earth's surface and provides a protective shield from

excess ultraviolet radiation. In contrast, tropospheric O3

at sufficient concentrations has been associated with harmful effects

due to its oxidative properties and its presence in the air that people

and plants take up during respiratory processes. Ozone is not emitted

directly from mobile or stationary sources but, like other

photochemical oxidants, commonly exists in the ambient air as an

atmospheric transformation product. Ozone formation is the result of

chemical reactions of volatile organic compounds (VOC), nitrogen oxides

(NOx), and oxygen in the presence of sunlight and generally

at elevated temperatures. A detailed discussion of atmospheric

formation, ambient concentrations, and health and welfare effects

associated with exposure to O3 can be found in the Criteria

Document and in the Staff Paper.

D. Summary of Proposed Revisions to the O3 Standards

For reasons discussed in the proposal, the Administrator proposed

to replace the current 1-hour primary standard for O3 with

an 8-hour standard set at 0.08 ppm, which would be met at an ambient

air quality monitoring site when the 3-year average of the annual

third-highest daily maximum 8-hour average O3 concentration

is less than or equal to 0.08 ppm. The proposal solicited comments on

alternative 8-hour standards set at 0.09 ppm, which generally

represents the continuation of the present level of protection, and

0.07 ppm, which would be highly precautionary in nature, as well as on

retaining the current primary standard. The proposal also solicited

comments on alternative forms of the standard, specific data handling

and rounding conventions used in determining attainment with the

standard, and issues related to the communication of public health

information.

With regard to the secondary standard, the Administrator proposed

to replace the current 1-hour secondary standard with one of two

alternative standards: either one set identical to the proposed primary

standard or a new seasonal standard expressed as a sum of hourly

O3 concentrations greater than or equal to 0.06 ppm,

cumulated over 12 hours per day during the consecutive 3-month period

of maximum concentrations during the O3 monitoring season,

set at a level of 25 ppm-hour. The proposal solicited comments on these

two alternatives, as well as on specific issues related to the form of

a seasonal standard and on an enhanced rural air quality monitoring

network.

[[Page 38859]]

II. Rationale for the Primary Standard

A. Introduction

1. Overview . This notice presents the Administrator's final

decision regarding the need to revise the current primary O3

standard, and, more specifically, regarding the averaging time, level,

and form of a new primary standard to replace the current 1-hour

standard. This decision is based on a thorough review, in the Criteria

Document, of the scientific information on human health effects

associated with exposure to ambient levels of O3, including

evaluation of key studies published through 1995. This decision also

takes into account:

(1) Staff Paper assessments of the most policy-relevant information

in the Criteria Document and analyses of human exposure and risk,

presented in the Staff Paper and supporting technical reports.

(2) CASAC advice and recommendations, as reflected in discussions

of drafts of the Criteria Document and Staff Paper at public meetings,

in separate written comments, and in CASAC's letters to the

Administrator.

(3) Public comments received during the development of these

documents, either in connection with CASAC meetings or separately.

(4) Extensive public comments received on the proposal regarding

the primary O3 standard.

After taking this information and comments into account and for the

reasons discussed below in this unit, the Administrator concludes that

revisions to the current primary standard to provide increased public

health protection are appropriate at this time to protect public health

with an adequate margin of safety. Further, the Administrator

determines that it is appropriate to establish a revised 8-hour, 0.08

ppm primary standard with a form based on the 3-year average of the

annual fourth-highest daily maximum 8-hour average O3

concentrations measured at each monitor within an area.

As discussed more fully below in this unit, the rationale for the

final decision regarding the O3 primary NAAQS includes

consideration of:

(1) Health effects information to inform judgments as to the

likelihood that exposures to ambient O3 result in adverse

health effects for exposed individuals.

(2) Insights gained from human exposure and risk assessments to

provide a broader perspective for judgments about protecting public

health from the risks associated with O3 exposure.

(3) Specific conclusions with regard to the elements of a standard

(i.e., averaging time, level, and form) that, taken together, would be

appropriate to protect public health with an adequate margin of safety.

(4) Alternative views of the significance of the effects and

factors to be considered in policy judgments about the appropriate

elements of the standard.

The health effects information and human exposure and risk

assessments were summarized in the proposal and are only briefly

outlined below. More fully discussed in the following units of this

preamble is the Administrator's rationale, in light of key issues

raised in public comments, for concluding that it is appropriate to

revise the specific elements of the current standard including

averaging time (Unit II.B.1.), level (Unit II.B.2.), and form (Unit

II.B.3.). Finally, the related subject of the communication of public

health information, and the public comments received on this subject,

are summarized in Unit II.C.

2. Health effects information. The last review of the air quality

criteria for O3 included an evaluation of key studies

published through early 1989 and was the basis for EPA's 1993 decision

not to revise the primary standard at that time. However, in

recognition of the large number of new studies, particularly on 6- to

8-hour exposures to O3, that had become available since

early 1989 but had not undergone rigorous assessment and review by

CASAC, the EPA made clear in the 1993 final decision notice that it

would proceed with the next review as rapidly as possible to consider

this new information. Thus, the current review of health effects

information focused on a large body of information published since 1989

that would lead to a more informed decision than was possible in 1993

as to whether an O3 primary standard with a longer averaging

time was appropriate to protect public health.

The proposal reviewed the human health effects associated with

exposure to ambient levels of O3 based on an integrative

assessment of human clinical, epidemiological, and animal toxicological

studies available through 1995, as assessed in the Criteria Document

and Staff Paper. Based on this information, an array of health effects

has been attributed to short-term (1 to 3 hours), prolonged (6 to 8

hours), and long-term (months to years) exposures to O3.

Acute health effects3 are induced by short-term

exposures to O3 (observed at concentrations as low as 0.12

ppm), generally while individuals are engaged in moderate or heavy

exertion, and by prolonged exposures to O3 (observed at

concentrations as low as 0.08 ppm), typically while individuals are

engaged in moderate exertion. Moderate exertion levels are more

frequently experienced by individuals than heavy exertion levels. The

acute health effects include transient pulmonary function responses,

transient respiratory symptoms, effects on exercise performance,

increased airway responsiveness, increased susceptibility to

respiratory infection, increased hospital admissions and emergency room

visits, and transient pulmonary inflammation. Based in particular on

new information available since the last review of the air quality

criteria for O3 was completed, such acute health effects

have been observed following prolonged exposures at moderate levels of

exertion at concentrations of O3 as low as 0.08 ppm. Groups

at increased risk of experiencing such effects include active children

and outdoor workers who regularly engage in outdoor activities and

individuals with preexisting respiratory disease (e.g., asthma, chronic

obstructive lung disease). Further, it is recognized that some

individuals are unusually responsive to O3 and may

experience much greater functional and symptomatic effects from

exposure to O3 than the average individual.

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3 ``Acute health effects'' of O3 are defined as those

effects induced by short-term and prolonged exposures to

O3. Examples of these effects are functional,

symptomatic, biochemical, and physiologic changes.

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With regard to chronic health effects4, the collective

data from studies of laboratory animals and human populations have many

ambiguities, but provide suggestive evidence of such effects in humans.

It is clear from toxicological data that O3-induced lung

injury is roughly similar across species (including monkeys, rats, and

mice) with responses that are concentration dependent. The currently

available information provides at least a biologically plausible basis

for considering the possibility that repeated inflammation associated

with exposure to O3 over a lifetime may result in sufficient

damage to respiratory tissue such that individuals later in life may

experience a reduced quality of life,

[[Page 38860]]

although such relationships remain highly uncertain.

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4 ``Chronic health effects'' of O3 are defined as

those effects induced by long-term exposures to O2.

Examples of these effects are structural damage to lung tissue and

accelerated decline in baseline lung function.

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EPA's consideration of this health effects information necessarily

included judgments with respect to when these physiological effects

become so significant that they should be regarded as adverse to the

health of individuals experiencing the effects. In making these

judgments, the Administrator looked to guidelines published by the

American Thoracic Society (1985) and the advice of CASAC. The proposal

summarized the criteria and reasoning for EPA's judgments on this

issue, upon which the CASAC panel expressed a consensus view that these

``criteria for the determination of an adverse physiological response

was reasonable'' (Wolff, 1995b). The criteria take into account the

degree of severity of the effects; the likelihood that the effects

would interfere with normal activity for individuals with impaired

respiratory systems or active healthy individuals; the likelihood that

the effects would result in additional or more frequent use of

medication, medical treatment, or emergency room visits for individuals

with impaired respiratory systems; and the implications of single or

repeated occurrences of the effects for an individual.

Some commenters raised concerns regarding the criteria used by EPA

to make determinations as to when effects become adverse, citing

CASAC's closure letter (Wolff, 1995b) stating that ``there was

considerable concern that the criteria for grading physiological and

clinical responses to O3 was confusing if not misleading.''

These concerns with the draft criteria were discussed at length during

a public CASAC meeting, resulting in very specific agreements as to how

to revise the draft criteria so as to be consistent with CASAC's advice

(Transcript of CASAC meeting, September 19-20, 1995, pp. 242-248).

Having reached such specific agreement, CASAC advised that further

review of the final version of these criteria, subsequently

incorporated in both the final Criteria Document and Staff Paper, was

unnecessary.

Other commenters have questioned whether judgments made in this

review are consistent with those made in the last review with regard to

when physiological and clinical effects become adverse to individuals

experiencing such effects. Specifically, the commenters focused on the

judgment stated in the 1993 final decision notice (58 FR 13008, March

9, 1993) that ``lesser effects associated with [1- to 3-hour] exposure

to O3 in the range of 0.12 ppm to 0.15 ppm observed in the

controlled human studies did not constitute adverse effects for

purposes of section 109 of the Act.'' The ``lesser effects'' referred

to in that notice involved responses of a maximum decrease in lung

function [as measured by forced expiratory volume in 1 second

(FEV1)] of from 9 percent to 16 percent for the most

sensitive individuals exposed in this range, with few, if any,

symptoms. The EPA notes that this judgment is, in fact, consistent with

judgments presented in the 1996 proposal, which identify moderate and

large lung function decrements (as reflected in EPA's risk assessment

by FEV1 decreases of 15 percent and

20 percent, respectively, with the most sensitive individuals

experiencing FEV1 decreases as large as 40 percent to 50

percent at 6- to 8-hour exposures in the range of 0.08 ppm to 0.10 ppm

in controlled human studies), and moderate to severe symptoms as being

adverse.

3. Exposure and risk assessments. To put judgments about health

effects that are adverse for individuals into a broader public health

context, EPA conducted quantitative assessments to estimate

O3 exposures and related risks for the general population

and two at-risk groups, ``outdoor children'' and ``outdoor workers,''

living in nine representative U.S. urban areas. This broader context

included consideration, to the extent possible, of the size of the

particular population groups identified as at risk for various effects,

the estimated number of people within at-risk groups likely to

experience O3-related adverse effects, the estimated number

of occurrences of such effects, and the estimated number of people who

would experience exposures of concern5 associated with

various air quality scenarios representing attainment of the current

and alternative 8-hour standards. Consideration was also given to the

kind and degree of uncertainties inherent in assessing such exposures

and risks. Such considerations provided a basis for judgments discussed

in the proposal about the levels of exposure and risk associated with

the current and alternative standards, which helped inform judgments

about the adequacy of public health protection afforded by the current

and alternative standards.

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5 ``Exposures of concern'' refer throughout to exposures at and

above 0.08 ppm, 8-hour average, at which a range of health effects

have been observed in controlled human studies, but for which data

were too limited to allow for quantitative risk assessment.

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Risk estimates were developed for those effects for which

sufficient concentration-response information was available from

studies evaluated in the Criteria Document, including adverse lung

function and respiratory symptom responses. In a separate analysis,

excess respiratory hospital admissions for individuals with asthma

associated with attainment of alternative standards were also

estimated, using a risk model for this health endpoint based on the

results of an epidemiological study in New York City (Thurston et al.,

1992) for which adequate air quality information was available to

assess population risk6. These quantitative risk estimates

(for that subset of O3-related effects for which information

is sufficient to conduct such quantitative analyses) add to our

understanding of the broader array of health effects that are

associated with exposure to O3 but for which quantitative

risk estimates could not be developed.

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6 This study is one of several studies, mainly conducted in the

northeastern portion of the United States and southeastern Canada,

reporting excess daily respiratory-related hospital admissions

associated with elevated O3 levels within the general

population and, more specifically, for individuals with asthma.

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The methodology, results, and key observations from these

assessments were presented in the proposal. The EPA believes, and CASAC

concurred, that the models selected to estimate exposure and risk were

appropriate and that the methods used to conduct the health risk

assessment for adverse lung function and respiratory symptom responses

represent the state of the art. Nevertheless, the Administrator and

CASAC recognized that there are many uncertainties inherent in such

analyses, and that not all uncertainties inherent in such analyses

could be quantified and reflected in ranges of risk estimates (Wolff,

1995b), as discussed in the proposal and the referenced technical

support documents.

The exposure and risk assessments available at the time of proposal

had been conducted to evaluate the O3 exposures and risks

associated with attainment of the current 1-hour standard and various

alternative 8-hour standards under consideration early in the standards

review process when the assessments were initiated. The EPA and CASAC

recognized at that time that additional alternative standards might

need to be analyzed later in the review process. Upon deciding to

propose a standard with a concentration-based form in the Fall of 1996,

EPA staff initiated supplemental analyses to estimate exposures and

risks7 for the

[[Page 38861]]

specific standard to be proposed and alternative standards on which the

proposal solicited comment. In conducting these supplemental analyses,

several technical changes were made based on insights gained from the

initial analyses.8 The supplemental assessment (Richmond,

1997) was placed in the docket and on the TTN on February 12, 1997, and

its availability was announced in the Federal Register notice extending

the public comment period on the proposal, providing the public the

opportunity to comment on the supplemental assessment (61 FR 7743,

February 20, 1997).

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7 The analyses were conducted for the at-risk population of

outdoor children, the group with the highest exposures and risks.

Outdoor children are the subset of children between the ages of 6

and 18 years old who tend to be active outdoors, and include

approximately over 30 percent to 45 percent of all children in this

age group in the nine urban areas analyzed.

8 These changes primarily focused on the air quality data used

in the exposure analysis and on the air quality adjustment

procedures used to simulate ambient O3 concentrations

upon attainment of alternative standards.

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Key observations and results from the initial and supplemental

exposure and risk assessments that are most pertinent to the decision

to revise the current primary standard are highlighted in the following

unit, together with discussion of the key issues raised in public

comments on the methodology and public health implications of these

assessments.

B. Elements of the Primary Standard

In selecting a primary standard for O3, the

Administrator must specify: Averaging time, O3 concentration

(i.e., level), and form (i.e., the air quality statistic to be used as

a basis for determining compliance with the standard).9 All

three of these elements are necessary to define a standard and to

determine the degree of public health protection afforded by the

standard. The proposal outlined the key factors considered in selecting

each of these elements for the proposed standard, as well as the range

of options for each element on which the EPA solicited comment. The

factors reflect an integration of information on acute and chronic

health effects associated with exposure to ambient O3;

expert judgments on the adversity of such effects for individuals; and

policy judgments, informed by air quality and exposure analyses and

quantitative risk assessment when possible, as to the point at which

risks would be reduced sufficiently to achieve protection of public

health with an adequate margin of safety.

---------------------------------------------------------------------------

9 This review focused only on a standard for O3, as

the most appropriate surrogate for photochemical oxidants.

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This approach to selecting a primary standard was endorsed by CASAC

(Wolff, 1995b), particularly through its advice to the Administrator

that ``EPA's risk assessments must play a central role in identifying

an appropriate level'' and its recognition that ``the selection of a

specific level and [form] is a policy judgment.'' Further, it was the

consensus view of CASAC that the ranges of 8-hour average levels (0.07

to 0.09 ppm) and forms (concentration-based forms that generally allow

for 1 to 5 exceedances) on which the proposal solicited comment were

appropriate.

The following discussion focuses primarily on those considerations

that were most influential in the Administrator's final decisions on

these elements, taking into account the comments received on the range

of options identified in the proposal.

1. Averaging time. In proposing to change the averaging time of the

primary standard from 1 to 8 hours, the Administrator was concurring

with the unanimous recommendation of CASAC (Wolff, 1995b) ``that the

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

standard,'' and that more research is needed to resolve uncertainties

about potential chronic effects before appropriate consideration can be

given to establishing a long-term (e.g., seasonal or annual) primary

standard. The Administrator's proposed decision was supported by the

following key observations and conclusions:

(1) The 1-hour averaging time specified in the current NAAQS was

originally selected primarily on the basis of health effects associated

with short-term (i.e., 1- to 3-hour) exposures, with qualitative

consideration given to preliminary information on potential

associations with longer exposure periods.

(2) Substantial new health effects information available for

consideration in this review demonstrates associations between a wide

range of health effects and prolonged (i.e., 6- to 8-hour) exposures

below the level of the current 1-hour NAAQS.

(3) Results from the quantitative risk analyses show that attaining

a standard with a 1-hour averaging time reduces the risk of

experiencing health effects associated with both 1-hour and 8-hour

exposures. Likewise, attaining an 8-hour standard reduces the risk of

experiencing health effects associated with both 8-hour and 1-hour

exposures. Thus, reductions in risks from both short-term and prolonged

exposures can be achieved through a primary standard with an averaging

time of either 1 or 8 hours. As a result, establishment of both 1-hour

and 8-hour standards would not be necessary to reduce risks associated

with the full range of observed acute health effects.

(4) The 8-hour averaging time is more directly associated with

health effects of concern at lower O3 concentrations than is

the 1-hour averaging time. It was thus the consensus of CASAC ``that an

8-hour standard was more appropriate for a human health-based standard

than a 1-hour standard.'' (Wolff, 1995b)

(5) While there is a large animal toxicology database providing

clear evidence of associations between long-term (e.g., from several

months to years) exposures and lung tissue damage, with additional

evidence of reduced lung elasticity and accelerated loss of lung

function, there is no corresponding evidence for humans. Moreover, the

state of the science has not progressed sufficiently to permit

quantitative extrapolation of the animal-study findings to humans.

Thus, the Administrator concluded that consideration of a separate

long-term primary O3 standard is not appropriate at this

time. As discussed below, however, the Administrator considered the

possibility of long-term effects in selecting the level of an 8-hour

standard, which will provide protection against such effects to the

extent they may occur in humans, by lowering overall air quality

distributions and, thus, reducing cumulative long-term exposures.

The public comments reflect broad support for a standard with an 8-

hour averaging time, either alone or in conjunction with a 1-hour

standard. This support was typically based on references to:

(1) Evidence of health effects from 6- to 8-hour exposures to

O3 concentrations down to 0.08 ppm, which are lower than

those concentrations that have induced such effects after 1- to 3-hour

exposures, and which are lower than the 0.12 ppm level of the current

standard.

(2) Analyses indicating that an 8-hour standard would limit both 1-

and 8-hour exposures.

(3) CASAC's unanimous agreement that the current 1-hour standard

should be replaced by an 8-hour standard. In considering the adequacy

of the current 1-hour standard alone in light of the health effects

evidence, some commenters have highlighted the statement in the

Criteria Document that there is ``strong evidence that ambient

exposures to O3 can cause significant exacerbations of

preexisting respiratory disease in the general public at concentrations

below 0.12 ppm.'' (U.S. EPA, 1996a, p. 7-171)

Commenters expressing support for an 8-hour averaging time included

not only those who supported a level of public health protection

consistent with

[[Page 38862]]

or greater than that reflected by EPA's proposed standard, but also

many who disagreed for various reasons with the need for increased

public health protection beyond that provided by the current standard.

Of those supporting an 8-hour averaging time but not supporting the

need for increased protection, some expressed the view that the

averaging time of a health-based standard should be consistent with the

exposures of most concern, while others were simply neutral between the

choices of retaining the current 1-hour standard and replacing it with

an ``equivalent'' 8-hour standard.

The EPA agrees with the considerations raised by those commenters

who favor an 8-hour standard. Further, in considering the

appropriateness of an 8-hour standard as compared to a 1-hour standard,

EPA also notes the results of its exposure and risk assessments which

show variability across the nine urban areas analyzed with regard to

the extent to which the current 1-hour standard, and alternative 8-hour

standards, limit 8-hour exposures of concern and associated risks of

adverse health effects. As noted in the proposal and in the

supplemental risk assessment, there is much greater variability across

urban areas, particularly in looking at the seven current nonattainment

areas examined, in the extent to which the current 1-hour standard

limits such exposures of concern and risks than for the alternative 8-

hour standards. For example, the updated assessment estimates that the

current 1-hour standard results in 8-hour exposures of concern at and

above 0.08 ppm10 that vary by almost two orders of magnitude

across these areas. In contrast, alternative 8-hour standards at the

proposed level of 0.08 ppm result in estimated 8-hour exposures of

concern and risks that are much more consistent.11 In EPA's

view, the fact that an averaging time of 8 hours results in a

significantly more uniformly protective national standard than the

current 1-hour standard is an important public health policy

consideration that supports the selection of an 8-hour averaging time.

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10 More precisely, exposures at and above 0.08 ppm refers to

estimates of exposures to O3 concentrations

0.081 ppm from the exposure assessment.

11 In terms of the percent of outdoor children estimated to be

exposed to O3 concentrations at and above 0.08 ppm while

engaged in moderate exertion, the current 1-hour standard results in

a range across the seven nonattainment areas of approximately 0.3

percent to 24 percent of such children, whereas alternative 8-hour

standards, at the proposed level of 0.08 ppm, result in a

significantly more uniform degree of protection, with ranges of

approximately 2 percent to 9 percent, third-highest concentration

form, and 3 percent to 11 percent, fifth-highest concentration form,

across the areas.

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Those commenters who did not support EPA's proposal for an 8-hour

averaging time generally did not support any revision to the current

standard. These commenters predominantly focused on two basic points:

The generally improving trends in air quality under the current

standard and associated air quality management programs, which,

commenters argued, suggest that there is no need for EPA to adopt any

more stringent standard; and observations made in CASAC's closure

letter (Wolff, 1995b) with regard to EPA's risk assessment not

demonstrating any ``bright line'' threshold of effects or acceptable

risk. With regard to the first issue, EPA agrees that air quality

trends are improving as a consequence of ongoing control programs

designed to attain the current NAAQS. The EPA does not, however,

believe that these trends relieve the Agency of its statutory mandate

to review and, if appropriate, revise the NAAQS on the basis of the

best available scientific evidence to establish standards that protect

public health with an adequate margin of safety. The fact that current

control programs are resulting in progress toward improving air quality

does suggest that it is important to ensure that such progress is

maintained during any transition to a revised standard.

With regard to the second issue, commenters very frequently quoted

from the CASAC closure letter (Wolff, 1995b) stating ``that there is no

bright line' which distinguishes any of the proposed standards (either

the level or the number of allowable exceedances) as being

significantly more protective of public health'' and that ``the

selection of a specific level and number of allowable exceedances is a

policy judgment.'' These commenters have variously interpreted these

statements as a CASAC consensus that the differences in the public

health protection afforded by any of the alternative standards were too

small to be important from a public health perspective, not

statistically significantly different, or simply not different at all.

Based on these interpretations, the commenters argued that it is not

appropriate to revise the standard in any way, because a revised

standard would result in disruption to ongoing programs, additional

planning requirements, and increased implementation costs, but would

provide no or only very little improvement in public health protection.

The EPA believes that these commenters have misconstrued or too

narrowly interpreted CASAC's advice to the Administrator by not

considering the entire range of views and recommendations included in

its closure letter. Specifically, CASAC began its summary of

recommendations to the Administrator (Wolff, 1995b) by stating that

``[t]he Panel was in unanimous agreement that the present 1-hour

standard be eliminated and replaced with an 8-hour standard.'' This

agreement was based on ``the consensus of the Panel that an 8-hour

standard was more appropriate for a human health-based standard than a

1-hour standard.'' Thus, CASAC was unequivocal in its advice to the

Administrator with regard to which averaging time the health effects

evidence more strongly supports. While some commenters have also quoted

statements by individual Panel members at CASAC meetings suggesting

that choosing between a 1- or 8-hour averaging time is a ``policy''

choice, these individual statements during the course of CASAC's review

do not contradict nor supersede the clear and unanimous agreement of

CASAC on averaging time as conveyed to the Administrator in its closure

letter.

In considering these comments, EPA also believes it is important to

put into a public health perspective CASAC's observations about the

differences among alternative standards in protecting the public from

the health effects that were quantitatively estimated in EPA's risk

assessment. In the closure letter (Wolff, 1995b), CASAC observed that

``the differences in the percent of outdoor children *** responding

between the present standard and the most stringent proposal *** are

small and their ranges overlap for all health endpoints.'' Most

importantly, EPA notes that the primary standard would provide

protection from a broader array of health effects than it was possible

to consider in its quantitative risk assessment. This perspective is

clearly shared in particular by those CASAC panel members who

personally favored a level or range of levels that included the

proposed level of 0.08 ppm, in that the closure letter characterizes

their views as reflecting, in part, their ``concern over the evidence

for chronic deep lung inflammation from the controlled human and animal

exposure studies.'' While the risk of this effect, as well as other

effects related to 6- to 8-hour exposures in the Criteria Document and

Staff Paper (including increased airway responsiveness, impairment of

host

[[Page 38863]]

defenses suggesting an increased susceptibility to respiratory

infection, and increased emergency room visits, doctor visits, and

frequency of medication use by individuals with impaired respiratory

systems) could not be quantitatively estimated in EPA's risk

assessment, EPA believes that consideration of these effects is

nevertheless important in making public health policy judgments.

Further, in interpreting CASAC's statements on EPA's risk

assessment report (Whitfield et al., 1996) that there is no ``bright

line'' which distinguishes any of the standards as being

``significantly'' more protective, and that the ``ranges overlap,'' EPA

notes that there are statistically significant differences in the

estimated risks for the standards analyzed with 1- and 5-exceedance

forms. This information was presented to CASAC at its September 1995

meeting (CASAC meeting transcript, September 19-20, 1995, pp. 108-109).

Further, EPA again notes that whether one judges the differences to be

significant or small can depend on whether one focuses on percentages,

as CASAC's letter did, or on total numbers of times that children or

other at-risk individuals experience such effects. The overlap in the

ranges of risk referred to in the CASAC letter reflect differences

among urban areas used in EPA's risk analysis (e.g., air quality,

exposure patterns, environmental factors), not random uncertainties in

risk estimates within any given urban area. Thus, the fact that the

ranges overlap does not mean that there are no real or statistically

significant differences in protection among alternative standards. To

the extent that the quoted statements from CASAC's closure letter are

read as implying that CASAC considered the differences not to be

statistically significant (or that there are no differences at all in

the protection afforded by the alternative standards), EPA disagrees

with that reading.

Another group of commenters, while supporting an 8-hour standard,

specifically opposed replacing the current 1-hour standard with an 8-

hour standard, but favored instead both 8-hour and 1-hour standards.

These commenters generally felt that a greater degree of public health

protection than that provided by the proposed standard was warranted,

and that standards based on both averaging times were necessary to

provide the requisite protection from 1- and 8-hour exposures of

concern. These commenters generally argued that an 8-hour standard

alone could still allow for high 1-hour exposures of concern, or that

the retention of the current 1-hour standard was critical to

maintaining current pollution control measures. As an initial matter,

EPA is delaying revocation of the 1-hour standard to ensure an

effective transition to the 8-hour standard, as discussed in Unit

II.B.4 of this preamble. While EPA agrees that it is possible that an

8-hour standard alone could allow for high 1-hour exposures of concern,

at and above 0.12 ppm,12 EPA's exposure assessments estimate

that alternative 8-hour standards, at the proposed level of 0.08 ppm

but with different forms, would be very effective in limiting 1-hour

exposures, and generally even more effective in limiting 1-hour

exposures of concern than is the current 1-hour standard. More

specifically, the updated assessment estimates that upon attainment of

alternative 8-hour, 0.08 ppm standards, with forms ranging up to the

fifth-highest concentration form, less than 0.1 percent of outdoor

children are likely to experience any 1-hour exposures greater than

0.12 ppm while at heavy exertion levels in four to seven of the nine

urban areas analyzed, whereas this is true for only two of the nine

areas upon attainment of the current 1-hour standard. In all nine areas

both the current and alternative 8-hour, 0.08 ppm standards are

estimated to limit such exposures to less than 1 percent of the outdoor

children. Thus, EPA concludes that an 8-hour averaging time does

effectively limit both 1- and 8-hour exposures of concern.

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12 The EPA recognizes this possibility exists especially in the

very few areas with unusually ``peaky'' air quality patterns (i.e.,

in which the ratio of the 1- and 8-hour average design values for

the current and proposed standards is greater than 1.5).

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For the reasons discussed above in this unit, and after taking into

account the range of views expressed in the public comments, the

Administrator finds that replacing the current 1-hour standard with an

8-hour standard, in combination with the decisions on level and form

described below, is appropriate to provide adequate and more uniform

protection of public health from both short-term (1 to 3 hours) and

prolonged (6 to 8 hours) exposures to O3 in the ambient air.

2. Level. Taken together, the level and form of the standard, for a

given averaging time, determine the degree of public health protection

afforded by the standard. Consideration of the level of the standard

discussed in this unit of the preamble reflects a recognition of this

linkage between level and form (discussed separately below in Unit

II.B.3).

The Administrator's decision to propose the level of an 8-hour

primary O3 standard at 0.08 ppm, and to solicit comment on

alternative levels, necessarily reflected a recognition, as emphasized

by CASAC, that it is likely that ``O3 may elicit a continuum

of biological responses down to background concentrations'' (Wolff,

1995b). Thus, in the absence of any discernible threshold, it is not

possible to select a level below which absolutely no effects are likely

to occur. Nor does it seem possible, in the Administrator's judgment,

to identify a level at which it can be concluded with confidence that

no ``adverse'' effects are likely to occur. In such a case, as CASAC

has advised, the traditional paradigm for standard-setting cannot be

applied in the usual way, and assessments of risk ``must play a central

role in identifying an appropriate level'' (Wolff, 1995b). Thus, the

Administrator's task became one of attempting to select a standard

level that would reduce risks sufficiently to protect public health

with an adequate margin of safety, since a zero-risk standard is

neither possible nor required by the Act. In this and other NAAQS

reviews the CASAC has generally recognized that the selection of

specific standards requires that the Administrator make public health

policy judgments in addition to determinations of a strictly scientific

nature. The Administrator's public health policy judgment on the level

of the proposed standard was framed by the considerations discussed

above in this unit and informed by the following key observations and

conclusions:

(1) During the last review of the O3 criteria and

standards, CASAC concluded that the existing 1-hour standard set at

0.12 ppm O3 provided ``little, if any, margin of safety,''

and that the upper end of the range of consideration for a 1-hour

standard should be 0.12 ppm (McClellan, 1989). In addition, several

members of the CASAC panel recommended that consideration should be

given to a lower 1-hour level of 0.10 ppm to offer some protection

against effects for which there was preliminary information at that

time of associations with 8-hour exposures to O3.

Regarding currently available evidence of O3-related

effects:

(2) Based on a significant body of information available since the

last review, there is now clear evidence from human clinical studies

that O3 effects of concern are associated with the 6- to 8-

hour exposures tested. Studies were done at 6- to 8-hour exposure

levels of 0.12, 0.10, and 0.08 ppm. This includes evidence of the

following statistically significant responses at 6- to 8-hour exposures

to the lowest concentration evaluated, 0.08 ppm O3, at

moderate

[[Page 38864]]

exertion: lung function decrements, respiratory symptoms (e.g., cough,

pain on deep inspiration), nonspecific bronchial responsiveness, and

biochemical indicators of pulmonary inflammation. Field studies provide

evidence of similar functional and symptomatic effects at ambient

O3 exposures that are consistent with the clinical findings.

Laboratory animal studies provide supporting evidence of O3-

induced biochemical indicators of inflammation and functional changes.

(3) Numerous epidemiological studies have reported excess hospital

admissions and emergency department visits for respiratory causes (for

asthmatic individuals and the general population) attributed primarily

to ambient O3 exposures, including O3

concentrations below the level of the current standard, with no

discernible threshold at or below this level. The biological

plausibility of attributing such effects to ambient O3

exposures is supported by human studies showing increased nonspecific

bronchial responsiveness, laboratory animal studies showing pulmonary

changes that decrease the effectiveness of the lung's defenses against

bacterial respiratory infections, and the reasonable anticipation that

O3 exposures also increase the risk of respiratory

infections in humans, based on the many similarities between animal and

human defense mechanisms.

(4) Long-term laboratory animal studies suggest that changes in

lung biochemistry and structure may, under certain circumstances,

become irreversible, although it is unclear whether long-term exposures

to ambient O3 levels result in similar chronic health

effects in humans.

Regarding the types and severity of O3-induced

physiological effects that are considered to be adverse to the health

status of individuals experiencing such effects:

(5) With regard to lung function decrements and respiratory

symptoms, the Administrator recognized that these O3-induced

effects are transient and reversible, and concluded that the extent to

which such effects are adverse to the health status of an individual

depends upon the severity, duration, and frequency with which an

individual experiences such effects throughout the O3

season. While group mean responses in clinical studies at the lowest

exposure level tested of 0.08 ppm are typically small or mild in

nature, responses of some sensitive individuals are sufficiently severe

and extended in duration to be considered adverse. This would

especially be true to the extent that those individuals likely to

experience such effects would, on average, experience them several

times a year.

(6) With regard to increased hospital admissions and emergency room

visits, the Administrator judged that such effects are clearly adverse

to individuals.

(7) With regard to pulmonary inflammation, the Administrator

recognized that singular occurrences of inflammation are likely

reversible and potentially of little health significance. On the other

hand, based on laboratory animal studies, repeated inflammatory

responses associated with exposure to O3 over a lifetime

have the potential to result in damage to respiratory tissue such that

individuals later in life may experience a reduced quality of life.

Furthermore, there is the possibility that repeated pulmonary

inflammatory responses could adversely affect asthmatic individuals by

resulting in increased medication use, medical treatment, and/or

emergency room visits and hospital admission. Such effects in

asthmatics are of special concern particularly in light of the growing

asthma problem in the United States and the increasing rates of asthma-

related mortality and hospitalizations, especially among children in

general and black children in particular. While O3 has not

been shown to cause asthma, the available evidence suggests that

O3 may exacerbate asthma. Accordingly, the Administrator

judged that repeated exposures to O3 levels that produce

inflammation of the lungs are adverse to individuals likely to

experience such exposures over long periods of time.

The Administrator considered the results of the exposure and risk

analyses and the following key observations and conclusions from these

analyses in putting effects considered to be adverse to individuals

into a broader public health perspective and in making judgments about

the level of a standard that would reduce risk sufficiently to protect

public health with an adequate margin of safety:

(8) The median risk estimates for respiratory functional and

symptomatic effects, as well as for excess hospital admissions of

asthmatics for respiratory causes, are approximately the same or only

marginally smaller for some of the 8-hour, 0.09 ppm standard options

evaluated (including those with forms ranging from 1- to 3-expected-

exceedances13) as compared to the current 1-hour, 0.12 ppm

NAAQS (risk estimates are somewhat larger for an 8-hour, 0.09 ppm, 5-

expected-exceedance standard as compared to those for the current

NAAQS).

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13 The upper end of this range, 3-expected-exceedances, was

based on air quality comparisons, since risk estimates were only

available at the time of proposal for the 1- and 5-expected-

exceedance forms of a 0.09 ppm standard. This range is consistent

with the results of the updated risk assessment.

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(9) Within any given urban area, statistically significant

reductions in exposure and risk associated with respiratory functional

and symptomatic effects result from alternative 8-hour standards as the

level changes from 0.09 ppm to 0.08 ppm to 0.07 ppm. These reductions

represent differences of hundreds of thousands of times that children

in the nine urban areas included in the analysis would likely

experience such effects under the range of alternative standards

considered relative to the current standard. There are significant

uncertainties in such quantitative estimates, however, and there is no

break point or bright line that differentiates between acceptable and

unacceptable risks within this range.

(10) Similarly, reductions in hospital admissions for respiratory

causes for asthmatic individuals and the general population are

estimated to occur with each change in the level of the standard from

0.09 ppm to 0.08 ppm to 0.07 ppm. However, hospital admissions for

asthmatic individuals associated with ambient O3 exposures

within the range of standard levels under consideration represent a

relatively small fraction of the total respiratory-related hospital

admissions for asthmatics over the O3 season.

(11) Estimated exposures to O3 concentrations at and

above 0.08 ppm (at which increased nonspecific bronchial

responsiveness, decreased pulmonary defense mechanisms, and indicators

of pulmonary inflammation have been observed in humans) while engaged

in moderate exertion are essentially zero at the 0.07 ppm standard

level (with a 1-expected-exceedance form) for the seven nonattainment

areas evaluated in the exposure analyses for the at-risk population of

outdoor children. Such exposures of outdoor children increase to

approximately 0 to 1 percent at the 0.08 ppm standard level, while the

estimated range at the 0.09 ppm standard level increases to

approximately 3 to 7 percent of outdoor children for these areas.

(12) While recognizing that sensitive individuals may experience

adverse but transient effects with a standard set at 0.08 ppm, no CASAC

panel member supported selection of 0.07 ppm as the level of a primary

standard. Of the

[[Page 38865]]

members who expressed their personal views, three indicated a

preference for a level of 0.08 ppm, one for a range of 0.08 to 0.09

ppm, three for a level of 0.09 ppm (with one of the three expressing a

preference for selecting a form that would result in equivalent

protection to the current standard), and one for a range of 0.09 to

0.10 ppm, associated with public advisories for O3 levels at

and above 0.07 ppm. Other CASAC panel members also expressed support

for such public notices or advisories reflecting potential effects for

extremely sensitive individuals associated with O3 levels as

low as 0.07 ppm.

These observations and conclusions resulted in the Administrator

focusing in particular on the alternative levels of 0.08 ppm and 0.09

ppm, having placed great weight on the fact that none of the CASAC

panel members expressed support for a standard set below 0.08 ppm. In

deciding between these two levels, the Administrator took into account

quantitative estimates of the risks associated with attaining standards

set at these levels for those effects for which such quantitative risk

estimates could be developed. Other factors that were important in the

Administrator's proposed decision include:

(1) Quantitative estimates of 8-hour exposures of concern (i.e., at

and above 0.08 ppm) associated with these standard levels.

(2) The consistency of the clinical, field, and epidemiological

studies, in which effects were seen not only from controlled exposures

to 0.08 ppm, but also in ambient environments in which 8-hour average

O3 concentrations ranged from above to below the 0.08 ppm

level.

(3) The importance of increased protection for those sensitive

individuals who may experience respiratory symptomatic and functional

effects at lower O3 concentrations than the population as a

whole.

(4) The uncertainties in considering the potentially more serious

but as yet uncertain chronic effects.

As discussed above in Unit II.A.3., EPA completed and made

available for public comment supplemental exposure and risk assessments

subsequent to the proposal. For any of the alternative standards

considered in the assessment, the new estimates of exposures at and

above 0.08 ppm are somewhat higher than those available at the time of

proposal, while the new estimates of risks, for adverse effects

including moderate and large decreases in lung function, moderate to

severe respiratory symptoms, and hospital admissions for asthmatics,

are lower. However, the relative differences in estimated exposures and

risks between alternative standard levels remain about the same as at

the time of proposal. Thus, while the Administrator's final decision

takes into account the more recent assessments, the differences in the

quantitative results between the initial and supplemental assessments

do not fundamentally alter the basis for the judgments expressed at the

time of proposal.

To aid in comparing the public health protection associated with 8-

hour standards at the 0.08 ppm and 0.09 ppm levels, observations from

the updated exposure and risk assessments for all nine urban areas

evaluated are summarized below (assuming the third-highest

concentration form, which was the upper end of the range of

consideration for forms for the 0.09 ppm level).

(1) The percentages of outdoor children exposed to O3

concentrations at and above 0.08 ppm (at which increased nonspecific

bronchial responsiveness, decreased pulmonary defense mechanisms, and

indicators of pulmonary inflammation have been observed in humans)

while engaged in moderate exertion are estimated to be approximately 3

percent at the 0.08 ppm standard level, ranging from approximately 2

percent to 10 percent in the nine areas, increasing to approximately 11

percent at a standard level of 0.09 ppm, ranging from approximately 7

percent to 29 percent in the nine areas.

Updated risk estimates in terms of the percentages14 and

numbers of outdoor children estimated to experience various health

effects, and the total numbers of occurrences of these effects in

outdoor children, upon attainment of these two alternative standards

for all nine urban areas combined15 are as follows:

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14 These updated risk estimates in terms of the percentage of

outdoor children in the nine urban areas are roughly comparable to

the range of original estimates presented in Table 1 of the proposal

for 1- and 5-expected-exceedance forms of the standards.

15 Approximately 3.1 million outdoor children reside in these

nine urban areas.

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(2) For moderate lung function (FEV1) decreases

15 percent, approximately 6 percent of outdoor children

(180,000 children) would experience this effect one or more times per

year (650,000 occurrences) at the 0.08 ppm standard level, increasing

to approximately 8 percent of outdoor children (250,000 children and

1,100,000 occurrences) at the 0.09 ppm standard level.

(3) For large lung function (FEV1) decreases

20 percent, approximately 2 percent of outdoor children (58,000

children) would experience this effect one or more times per year

(100,000 occurrences) at the 0.08 ppm standard level, increasing to

approximately 3 percent of outdoor children (97,000 children and

220,000 occurrences) at the 0.09 ppm standard level.

(4) For moderate or severe pain on deep inspiration, approximately

0.9 percent of outdoor children (27,000 children) would experience this

effect one or more times per year (120,000 occurrences) at the 0.08 ppm

standard level, increasing to over 1 percent of outdoor children

(41,000 children and 220,000 occurrences) at the 0.09 ppm standard

level.

Many public commenters supported EPA's proposed level of 0.08 ppm

for an 8-hour standard, including most public health associations and

groups of medical professionals, many citizens, and some States and

regional associations. There were also large numbers of commenters who

expressed strong views in opposition to the proposed level. Of those

who did not support the proposed 8-hour level, almost all commenters

representing businesses and industry associations, many local

governmental groups and private citizens, and some States either

supported no change to the current standard or, if EPA were to replace

the current 1-hour standard with an 8-hour standard, supported a level

of 0.09 ppm directly or simply one that would be ``equivalent'' to the

current standard. On the other hand, environmental groups, many

citizens, and some medical professionals and researchers supported a

level of 0.07 ppm for an 8-hour standard.

In general, the issues raised by these groups of commenters can be

addressed in three categories: Comments on the strength and adequacy of

the health effects evidence upon which the proposed decision was based,

comments on the quantitative exposure and risk assessments and the

extent to which the assessments either over- or under-predict exposures

and risks among sensitive populations, and judgments as to whether the

differences in public health protection provided by alternative

standards are significant from a public health perspective. Each of

these categories of key issues is discussed separately below.

With regard to the first category of comments, on the strength and

adequacy of the health effects evidence, commenters who did not support

the need for any increased protection beyond that provided by the

current standard questioned the adequacy or highlighted the limitations

of the

[[Page 38866]]

various types of health effects studies that have related O3

exposures to adverse effects. For example, some commenters questioned

the controlled human exposure studies, arguing that: Many such studies

used patterns of exposures and exercise levels that are not

representative of normal population exposures to ambient O3;

some exposure chambers using artificially generated O3 may

have been contaminated with other pollutants that could have accounted

for some of the observed effects; and responses to elevated

O3 levels were compared to responses to air with essentially

no O3 rather than to background levels typical of ambient

air. Some commenters argued that these flaws in the study designs would

result in overestimating responses to non-background levels of ambient

O3 or in erroneous findings of statistical significance. In

contrast, others commented that because the chambers did not contain

other pollutants and natural pulmonary irritants (e.g., pollens, dust)

or a full range of environmental conditions (e.g., high temperatures

and humidity) typical of ambient air, the results may underestimate the

true impact of O3 in the ambient air.

Some commenters also questioned the summer camp and other field

studies and epidemiological studies reporting increased hospital

admissions and emergency room visits, arguing that: The responses in

these studies were inherently confounded by exposures to other

pollutants, the camp studies did not differentiate activity levels of

the participants, and linear regression down to or below background

levels was unjustifiably used to analyze the results of the hospital

admission studies. These commenters expressed the view that these and

other flaws call into question any conclusions about whether the

reported associations are causal. In contrast, other commenters argued

that the hospital admissions reported in these studies are indicative

of a pyramid of adverse health effects, including increased mortality,

increased visits to emergency and outpatient departments and

physicians, increased numbers of asthma attacks resulting in increased

medication use, and increased numbers of restricted activity days and

acute respiratory symptom days, that EPA has not adequately taken into

account. The EPA notes that these comments are consistent with

statistics published by the U.S. Department of Health and Human

Services, which indicate that for every hospital admission of an

individual with asthma for respiratory causes, there are more than five

emergency and outpatient department visits and more than 20 office-

based physician visits (U.S. DHHS, 1996).

With regard to studies related to pulmonary inflammation and

chronic respiratory damage, some commenters argued that the linkage

between repeated inflammatory responses and chronic respiratory damage

was merely speculation, and, therefore, should not be considered as

part of the basis for decisions on the primary standard. In contrast,

others commented that animal studies had demonstrated that repeated

pulmonary inflammation leads to degenerative or irreversible lung

damage, that these studies are consistent with observations in human

exposure studies, and, therefore, that they should be considered in

decisions on the standard.

The EPA notes that many of these comments did not reflect an

integrative assessment of the evidence--the approach CASAC has

historically urged EPA to follow--but rather a piecemeal look at each

individual study or type of study, which tends to miss the strength of

the entire body of evidence taken together. Other commenters did

consider the body of evidence in a more integrative manner, and many of

these commenters expressed the view that the body of evidence as a

whole provided clear evidence of O3-related effects at and

below O3 concentrations allowed by the current standard.

Some commenters highlighted the large number of studies that

demonstrate evidence of effects for prolonged exposures at and below

0.08 ppm, and criticized EPA for giving too little weight to those

studies which reported serious effects, but for which the data were not

sufficient to do quantitative risk assessments.

With regard to the second category of comments, on the exposure and

risk assessments, a number of commenters raised concerns about key

aspects of the assessments, including the exposure model, the

development of concentration-response functions, the application of the

risk model, and the measures of risk used to characterize the results

of the assessments. With regard to the exposure model, a number of

commenters claimed that: The model overestimates the exertion level

that can be achieved by most children and outdoor workers and the

fraction of time that these groups spend in moderate or heavy exertion;

the model overestimates outdoor ambient exposures because fixed-site

monitors overestimate outdoor personal exposures; and the air quality

adjustment procedures used to simulate attainment of the standards are

inappropriate or highly uncertain. Other commenters expressed concern

that the exposure model may be significantly underestimating exposures

for children and outdoor workers who repeatedly exercise due to

limitations in the available human activity pattern data.

As discussed in the proposal, EPA recognizes that the exposure

model necessarily contains many sources of uncertainty, although every

effort has been made to account for such uncertainties to the extent

possible. In particular, the model incorporates and is sensitive to

analytical procedures used to simulate spatial and temporal

distributions of O3 concentrations that would occur as a

result of an area just attaining any of the alternative standards

addressed in the exposure assessment. These air quality adjustment

procedures are based on generalized models intended to reflect the

patterns of changes in distributions of O3 concentrations

that have historically been observed in areas implementing control

programs designed to attain the O3 NAAQS. The EPA recognizes

that future changes in air quality distributions are area-specific, and

will be affected by whatever specific control strategies are

implemented in the future to attain the revised NAAQS. Thus,

generalized models are expected to be more uncertain for any given area

than when exposure results are aggregated across many areas (as was

done across the nine urban areas analyzed in EPA's exposure

assessment).

Some commenters questioned the specific air quality adjustment

procedure used in the initial and supplemental assessment16,

and a few of these commenters recommended revisions or alternative

procedures that they believed would be more representative of

historical or projected future air quality patterns. As discussed in

more detail in the Response to Comments, EPA acknowledges that both

procedures used in the assessments result in projections of air quality

that deviate to some degree from historical patterns of air quality

changes observed in specific urban areas, and that other procedures may

be more representative of air quality patterns in specific areas. While

EPA will take these comments into account as future refinements are

made to the air quality adjustment

[[Page 38867]]

procedures used in the exposure model, EPA believes, and CASAC

concurred, that the procedures used in the assessments conducted as

part of this review are reasonable given the uncertainties inherent in

projecting future changes in air quality patterns.

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16 The initial risk assessment used both ``Weibull'' and

``proportional'' air quality adjustment procedures, whereas the

supplemental risk assessment used a ``proportional'' air quality

adjustment procedure for all nine urban areas. In responding to

comments on the air quality adjustment procedures, EPA also

evaluated an alternative ``quadratic'' procedure (as discussed in

the Response to Comments), which generally resulted in risk

estimates between those from the Weibull and proportional

procedures.

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In commenting on the air quality adjustment procedure used in the

supplemental assessment, some commenters particularly focused on the

results for two of the nine areas analyzed in which, contrary to

results from the initial assessment, lower risks were estimated for the

current standard as compared to the proposed standard. As discussed

more fully in the Response to Comments, EPA believes that these results

for each area cannot be distinguished within the sensitivity of the

alternative air quality adjustment procedures used in the initial and

supplemental assessments. Further, EPA notes that these two areas have

much higher ratios of peak 1-hour to 8-hour O3

concentrations than the vast majority of areas in which O3

is monitored17, and it is thus reasonable to expect that

generalized air quality adjustment procedures would be particularly

uncertain for such areas.

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17 The two areas are Houston and parts of Los Angeles county,

which are two of only six areas nationwide with peak 1- to 8-hour

design value ratios greater than 1.5.

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Comments focusing on the development of concentration- response

functions for use in the risk model have included a number of claims.

Some commenters claimed that EPA inappropriately selected studies for

developing the functions by excluding studies that reported lower

response rates and by using only studies conducted by EPA scientists.

Some commenters asserted that contaminants in the controlled exposure

chambers may be responsible for some of the effects incorporated into

the concentration-response functions for O3. Further, some

commenters asserted that it was inappropriate to extrapolate the

concentration-response functions to background levels or to develop

concentration-response functions for symptomatic responses in children

based on studies of such responses in adults.

Of the comments focusing on the application of the risk model, some

commenters claimed that the aggregate risk results were overstated

because of: Many of the methodological problems noted in the above

summary of comments, the failure to take into account the known

attenuation of effects, and the assumption of an inappropriately low

background concentration in calculating risks attributable to non-

background sources of O3. On the other hand, other

commenters claimed that aggregate risk results were understated because

of: Methodological problems, noted above, that underestimate exposures,

limiting the analyses to only a subset of adverse health effects rather

than estimating the full range of effects that have been attributed to

O3, and by focusing only on nine urban areas rather than

projecting risk reductions from alternative standards nationally.

While EPA has included comprehensive responses to these comments in

the Response to Comments, most of the issues and concerns raised by

commenters concerning the health effects evidence and the methods used

in the exposure and risk assessments are essentially restatements of

concerns raised during the review of the Criteria Document and the

development and review of these quantitative assessments as part of the

preparation and review of the Staff Paper. EPA presented and the CASAC

reviewed in detail the approaches used to assess exposure and health

risk, the studies and health effect categories selected for which

concentration-response functions were estimated, and the presentation

of the exposure and risk results summarized in the Staff Paper. As

stated in the proposal, EPA believes and CASAC concurred, that the

general models selected to estimate exposure and risk are appropriate

and that the methods used to conduct the exposure and risk assessments

represent the state of the art. EPA does not believe that the exposure

or risk assessments are fundamentally biased in one direction or the

other as claimed in some of the comments.

The Administrator and CASAC have recognized, however, that there

are many uncertainties inherent in such assessments and that the

resulting ranges of quantitative risk estimates do not reflect all of

the uncertainties associated with the numerous assumptions inherent in

such analyses (Wolff, 1995b). EPA summarized some of the most important

caveats and limitations concerning both the exposure analyses and the

risk assessments for lung function changes, respiratory symptoms, and

hospital admissions in the proposal. A more complete discussion of

assumptions and uncertainties is contained in the Staff Paper and

technical support documents (Johnson et al., 1996 a,b; Whitfield et

al., 1996; Richmond, 1997).

With regard to the third category of comments, reflecting

commenters' judgments as to whether the differences in public health

protection of alternative standards are significant from a public

health perspective, EPA notes that highly divergent judgments were

expressed by different groups of commenters. A large number of

commenters who expressed the view that the differences in public health

protection were not significant or important enough to warrant any

standard more stringent than the current standard used CASAC as the

basis for their position, as discussed above in Unit II.B.1. on

averaging time. Others cited small percentages of outdoor children and

other sensitive groups likely to be affected based on EPA's assessment,

or even smaller percentages as modified by analyses conducted by the

commenter to correct perceived errors in the analyses. In contrast,

other commenters cited large total numbers of children likely to be

affected, not only for the subset of O3-related effects and

the nine areas analyzed in EPA's assessments, but also for a broader

array of related effects projected nationally.

The core issue in this review of the primary O3

standard, as stated by the Administrator at the time of proposal, is

who is to be protected, and from what. Clearly, for pollutants, such as

O3, that have no discernible thresholds for health effects,

no standard can be risk-free. The Administrator's task is to select a

standard level that will reduce risks sufficiently to protect public

health with an adequate margin of safety since a zero-risk standard is

neither possible nor required by the Act. As CASAC and the

Administrator recognize, the selection of a specific standard level for

such pollutants requires public health policy judgments in addition to

determinations of a strictly scientific nature.

In making such judgments, the Administrator rejects the notion that

because standards cannot be risk-free they should not be revised to

provide increased protection for sensitive populations, particularly

including children in this case, when available evidence points to

greater impacts on public health than had previously been demonstrated.

In carefully reassessing both those risks to public health that can be

quantified as well as those for which quantitative risk information is

more limited, the Administrator has focused on the following

comparisons between the degree of public health protection likely to be

afforded by an 8-hour standard at the proposed level of 0.08 ppm and an

alternative standard set at a level of 0.09 ppm (assuming the same

third-highest concentration form):

(1) Based on EPA's updated analyses of estimated moderate or large

decreases

[[Page 38868]]

in lung function and moderate to severe pain on deep inspiration in

outdoor children in nine urban areas (Richmond, 1997), a standard set

at 0.09 ppm would allow approximately 40 percent to 65 percent more

outdoor children to experience such effects than would a 0.08 ppm

standard, and approximately 70 percent to 120 percent more occurrences

of such effects in outdoor children per year.

(2) While only relatively small percentages of outdoor children are

estimated to experience such effects, the differences in these

percentages between the two standard levels represent tens of thousands

more children, and hundreds of thousands more occurrences of adverse

effects in these children, in these nine urban areas alone, for a 0.09

ppm standard as compared to a 0.08 ppm standard.

(3) Based on EPA's updated risk assessment of increased hospital

admissions in New York City (Richmond, 1997), a standard set at 0.09

ppm would allow approximately 40 more excess hospital admissions of

asthmatics within an O3 season in New York City for

respiratory causes as compared to a 0.08 ppm standard, which represents

approximately a 40 percent increase in excess O3-related

admissions, but only approximately a 0.3 percent increase in total

admissions of asthmatics. The EPA believes that while these numbers of

hospital admissions are relatively small from a public health

perspective, they are indicative of a pyramid of much larger numbers of

related O3-induced effects, including respiratory-related

hospital admissions among the general population, emergency and

outpatient department visits, doctors visits, and asthma attacks and

related increased use of medication that are important public health

considerations.

(4) Based on EPA's exposure analyses in the nine urban areas, a

standard set at 0.09 ppm would allow more than three times as many

children to experience 8-hour average exposures of concern as would a

0.08 ppm standard, with the number of outdoor children likely to

experience such exposures increasing from approximately 100,000 to more

than 300,000 in the nine urban areas alone, representing an increase

from approximately 3 percent to approximately 11 percent of the outdoor

children likely to experience such exposures.

(5) These exposures of concern are judged by EPA to be an important

indicator of the public health impacts of those O3-related

effects for which information is too limited to develop quantitative

estimates of risk, but which have been observed in humans at a level of

0.08 ppm for 6- to 8-hour exposures. Such effects include the

following: increased nonspecific bronchial responsiveness (related, for

example, to aggravation of asthma), decreased pulmonary defense

mechanisms (suggestive of increased susceptibility to respiratory

infection), and indicators of pulmonary inflammation (related to

potential aggravation of chronic bronchitis or long-term damage to the

lungs).

(6) To put these risks and exposures into broader perspective, EPA

notes that approximately 46 million more people, including

approximately 13 million more children and 3 million more individuals

with asthma, live in areas that would not attain a 0.08 ppm standard

compared to a 0.09 ppm standard. The general population as well as

children and asthmatics would breathe cleaner air as a direct result of

control measures designed to bring areas into attainment with the

proposed standard.18

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18 The EPA anticipates that additional people would be protected

through regional measures adopted for purposes of an 8-hour, 0.08

ppm standard.

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While recognizing the inherent uncertainties in these estimates,

and after taking into account the range of views and judgments

expressed in the public comments, the Administrator finds the public

health impacts described in the proposal, as updated above, to be

important and sufficiently large as to warrant a standard set at a

level of 0.08 ppm, as proposed.

The Administrator recognizes the views of those who argue that

similarly large improvements in public health protection would result

from a standard set at 0.07 ppm as compared to the proposed standard,

such that, based on the same reasoning, the evidence warrants a

standard set at 0.07 ppm. In considering these views, the Administrator

gives significant weight to the following considerations:

(1) No member of the CASAC panel of experts supported a standard

set lower than 0.08 ppm, specifically after considering a range of

alternative standards that included 0.07 ppm.

(2) The most certain O3-related effects, while judged to

be adverse, are transient and reversible (particularly at O3

exposures below 0.08 ppm), and the more serious effects with greater

immediate and potential long-term impacts on health are less certain,

both as to the percentage of individuals exposed to various

concentrations who are likely to experience such effects and as to the

long-term medical significance of these effects.

(3) As many commenters have noted, based on information in the

Criteria Document with regard to ambient concentrations of

O3 from background sources, an 8-hour standard set at a 0.07

ppm level would be closer to peak background levels that infrequently

occur in some areas due to nonanthropogenic sources of O3

precursors, and thus more likely to be inappropriately targeted in some

areas on such sources.

After taking into account the public comments, and for the reasons

outlined above, the Administrator finds that a standard set at a level

of 0.07 ppm is not requisite to protect public health with an adequate

margin of safety.

3. Form. The form of the current 1-hour, 0.12 ppm standard is a

``1-expected-exceedance'' form. That is, the current standard is based

on the expected19 number of days per year, on average over 3

years, on which the level of the standard is exceeded, and limits that

number of expected exceedances to be less than or equal to 1.0.

---------------------------------------------------------------------------

19 The term ``expected'' means that the numbers of exceedances

per year are averaged over 3 years and may be calculated using

specific adjustments to account for missing data.

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In evaluating alternative forms for the primary standard, the

adequacy of the public health protection provided was the

Administrator's foremost consideration. The Administrator also

recognized, however, that concerns have been raised with the current

form since it was promulgated in 1979 due to the inherent lack of year-

to-year stability in the measure of air quality on which the 1-

expected-exceedance form is based.20 The CASAC specifically

took such concerns into account in recommending that the current form

be revised and in noting that a more robust, concentration-based form

would minimize such instability and provide some insulation from the

impacts of extreme meteorological events that are conducive to

O3 formation (Wolff, 1995b). Such instability can have the

effect of reducing public health protection by disrupting ongoing

implementation plans and associated control programs.

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20 The 1-expected-exceedance form essentially requires the

fourth-highest air quality value in 3 years, based on adjustments

for missing data, to be less than or equal to the level of the

standard for the standard to be met at an air quality monitoring

site.

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As discussed in the proposal, based on information presented in

sections IV. and V.I of the Staff Paper and the advice of CASAC, the

Administrator focused her consideration on the following alternatives:

(1) Revising the current 1-expected-exceedance form of the standard

to

[[Page 38869]]

allow for multiple (up to five) expected exceedances per year, averaged

over 3 years. A multiple-exceedance form would be based on a less

extreme air quality statistic and, thus, would increase the stability

of the expected-exceedance form.

(2) Adopting a concentration-based statistic, such as the 3-year

average of the nth-highest daily maximum 8-hour average O3

concentration, as an alternative to an expected exceedance statistic.

Air quality analyses presented in the Staff Paper indicate that the 3-

year averages of the annual third-, fourth-, and fifth-highest daily

maximum 8-hour concentrations would provide approximately the same

health protection as the 3-, 4-, and 5-expected-exceedance forms

averaged over the same period, respectively.

It was the consensus of the CASAC Panel that this range of

allowable exceedances (i.e., up to 5 exceedances), and the

consideration of comparable concentration-based forms, was appropriate.

Further, CASAC acknowledged that selecting from within this range of

alternative forms is a policy judgment, especially given the nature of

the health effects and the absence of a ``bright line'' that clearly

differentiates between acceptable and unacceptable risks within this

range. All 10 CASAC Panel members who expressed specific opinions on

the form of the standard favored one that would allow for multiple

exceedances (Wolff, 1995b).

In reaching her proposed decision on the form of an 8-hour standard

set at 0.08 ppm, the Administrator had to choose a specific form within

the range of up to 5 allowable exceedances or up to the comparable

fifth-highest concentration, and either an exceedance-based or a

concentration-based form. As discussed in the proposal, in considering

possible forms within the range of 1 to 5 exceedances (or their

concentration-based counterparts) the Administrator took into

consideration aggregate risk estimates for those health effects for

which quantitative risk analyses have been done; estimated exposures

associated with those effects for which no quantitative risk estimates

could be developed; and the magnitude of peak measurements of 8-hour

average O3 concentrations, and the number of days on which

the level of the standard would likely be exceeded, based on an

analysis of historical air quality data (Freas, 1996). In considering

exposure and risk estimates available at the time of proposal for 1-

and 5-expected-exceedance forms, the Administrator noted that the level

of the standard is a more dominant factor in determining the degree of

exposure and risk reductions achieved, with the form being associated

with smaller differences in risk estimates within a continuum of risk.

In considering air quality comparisons for standards across the range

of forms considered, the Administrator focused in particular on the

extent to which alternative forms would limit the number of days in

which the level of the standard would be exceeded in areas that just

attain the standard21, and the magnitude of peak 8-hour

average O3 concentrations22 that would occur in

such areas.23 More specifically, the Administrator took into

consideration the percentage of monitoring sites just attaining an 8-

hour, 0.08 ppm standard that would have 8-hour peak O3

concentrations above a benchmark level of 0.09 ppm. This benchmark

level is the upper end of the range of levels endorsed by CASAC for an

8-hour O3 standard. The Administrator believes, given the

uncertainties associated with this kind of complex health decision,

that it is an appropriate goal to limit the percentages of areas

experiencing such daily peaks.

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21 Areas that ``just attain the standard'' are defined as those

whose design value falls between 0.075 and 0.084 ppm.

22 Peak 8-hour average concentrations are defined in terms of

the fourth-highest daily maximum concentration in 3 years (i.e., the

design value for the current 1-expected-exceedance form of the

standard).

23 The results of these air quality analyses are presented in

Freas (1996) and summarized in the proposal for the third- and

fifth-highest concentration forms and the 3- and 5-expected-

exceedance forms. Based on these considerations, and the air quality

comparisons in particular, the Administrator judged that the middle

of the range of exceedances considered, three expected exceedances,

or the comparable third-highest concentration, represented a

reasonable policy choice, and proposed the 3-year average of the

annual third-highest daily maximum 8-hour average O3

concentrations as the form of the standard. In recognition of a

range of views on the degree of health protection that would be

appropriate, she also solicited comment on other concentration-based

forms, including the second-, fourth-, and fifth-highest

concentration forms.

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In choosing to propose a concentration-based form, the

Administrator recognized the advantages of a concentration-based form

over an exceedance-based form. As discussed in the proposal, the

principal advantage of a concentration-based form is that it is more

directly related to the ambient O3 concentrations that are

associated with health effects. That is, given that there is a

continuum of effects associated with exposures to varying levels of

O3, the extent to which public health is affected by

exposure to ambient O3 is related to the actual magnitude of

the O3 concentration, not just whether the concentration is

above a specified level. With an exceedance-based form, days on which

the ambient O3 concentration is well above the level of the

standard are given equal weight to those days on which the

O3 concentration is just above the standard (i.e., each day

is counted as 1 exceedance), even though the public health impact on

the two days is significantly different. With a concentration-based

form, days on which higher O3 concentrations occur would

weigh proportionally more than days with lower O3

concentrations, since the actual concentrations are used directly in

determining whether the standard is attained. A concentration-based

form also has greater temporal stability than the expected-exceedance

form and, thus, would facilitate the development of more stable

implementation programs by the States.

As discussed above in Units II.A.3. and II.B.2., EPA completed and

made available for public comment supplemental exposure and risk

assessments subsequent to the proposal. These updated assessments,

which specifically analyzed the third- and fifth-highest concentration-

based forms, aid in comparing the differences in public health

protection among alternative concentration-based forms within the range

considered in the proposal for 8-hour, 0.08 ppm standards. Based on

these updated assessments, the Administrator again notes that the level

of the standard is the more dominant factor in determining the degree

of risk reduction achieved, with these alternative forms being

associated with much smaller differences in risk estimates within a

continuum of risk. For example, within the nine urban areas included in

the risk assessment, approximately 180,000 outdoor children would

experience moderate lung function (FEV1) decreases

15 percent upon attainment of an 8-hour, 0.08 ppm standard

with a third-highest concentration form, compared to approximately

200,000 outdoor children with a fourth-highest concentration form and

220,000 outdoor children with a fifth-highest concentration form.

The public comments include a large number that specifically

addressed the form of the standard. Those commenters who expressed

views on the form of the standard can be divided into three groups,

according to the level of 8-hour standard and the relative degree of

public health protection that the commenter supported. These groups

include: Commenters who supported an 8-hour, 0.08 ppm standard to

provide increased public health protection relative to the current

standard;

[[Page 38870]]

commenters who supported either an 8-hour, 0.09 ppm standard, or simply

an 8-hour standard ``equivalent'' to the current standard; and

commenters who supported an 8-hour, 0.07 ppm standard to provide a

greater margin of safety than that afforded by the proposed standard.

The first group included many private citizens, some medical

professionals and researchers, and some States and local governmental

groups. While a number of commenters in the first group specifically

supported the proposed third-highest concentration form, generally for

the reasons presented in the proposal, others supported either a 1-

expected-exceedance form or a concentration-based form in the upper

part of the range (i.e., the fourth- or fifth-highest forms). The

second group of commenters, which included many local governmental

groups and private citizens, some States, and most commenters

representing businesses and industry associations, almost exclusively

supported a concentration-based form in general, and a form in the

upper part of the range (or above the range) in particular. In sharp

contrast, the third group of commenters, which included environmental

groups, many private citizens, and some medical professionals and

researchers, almost exclusively supported a 1-expected-exceedance form

in conjunction with an 8-hour, 0.07 ppm standard to provide the largest

margin of safety within the range of alternative standards considered.

To the extent that the second and third groups of commenters argued

for a different level than the Agency adopts today, the Administrator

disagrees with their comments for the reasons set forth in the

discussion of the standard level above in Unit II.B.2. To the extent

that they argued for more than 5 exceedances (or the concentration-

based equivalent), the Administrator disagrees with their views because

such forms fall outside the range recommended by CASAC and would

provide less public health protection than she deems appropriate. To

the extent that the second and third groups of commenters addressed the

merits of particular forms within the range of forms considered in the

proposal, they raised points similar to those raised by commenters in

the first group. These points are discussed below.

Among the commenters in the first group (i.e., those supporting an

8-hour, 0.08 ppm standard to provide increased public health

protection), many felt that there was no compelling basis for selecting

the third-highest rather than the fourth- or fifth-highest

concentration-based form. These commenters frequently quoted CASAC's

closure letter (Wolff, 1995b) as stating ``that there is no bright

line' which distinguishes any of the proposed standards (either the

level or the number of exceedances) as being significantly more

protective of public health,'' and that ``the selection of a specific

level and number of allowable exceedances is a policy judgment.'' In

general, these commenters did not give weight to the air quality

comparisons that were a major consideration in the Administrator's

decision to propose the third-highest concentration form. Some

commenters seem to view such air quality comparisons, particularly with

regard to pollutants such as O3 that have no discernible

threshold of effects, as relating more to people's perceptions of how

well air pollution is controlled than to any objective measure of

actual risks to public health.

These commenters made a number of points in questioning the need to

specify an 8-hour, 0.08 ppm standard in terms of the third-highest

rather than the fourth- or fifth-highest concentration form. Many noted

that a change to an 8-hour averaging time in and of itself would

appropriately focus air quality management programs on prolonged

exposures of most concern. Further, many noted that a level of 0.08

ppm, regardless of the form within the range of forms considered in the

proposal, would provide significantly increased protection from

O3-related risks to public health associated with acute

effects (i.e., those resulting from short-term and prolonged exposures)

for which they believe there is sufficient evidence to be used as a

basis for a standard at this time. Some of these commenters expressed

the view that the potential for chronic effects (i.e., those resulting

from long-term exposures) would be better addressed through continued

research, rather than by adding a greater margin of safety to a revised

standard based primarily on effects of short-term and prolonged

exposures. Many of these commenters recognized, as did EPA in the

proposal, that there is a continuum of risks associated with

O3 exposures, that no standard can therefore be risk-free,

and that there are large uncertainties in any estimates of the degree

of protection associated with alternative forms. In general, these

commenters also noted that, for the same reasons, CASAC advised that

the selection of a form from within the range considered in the

proposal was a policy judgment, not one that could be decided on the

basis of science alone. In essence, these commenters argued that a more

restrictive form than the upper part of the range endorsed by CASAC is

not requisite to protect public health.

In contrast, other commenters in the first group (i.e., those

supporting an 8-hour, 0.08 ppm standard) supported either the proposed

third-highest or second-highest concentration form or a 1-expected-

exceedance form. These commenters generally gave greater weight to

limiting the magnitude of peak O3 concentrations and the

number of days on which the standard level would be exceeded in areas

meeting such a standard, and, in some cases, to providing a greater

margin of safety to account for potential chronic effects. Such views

suggest that limiting the number of days on which the standard level

would be exceeded, for example, is an important factor in risk

communication and in the public's understanding of the degree to which

a standard protects people from exposures to O3 that may

interfere with their ability to engage in normal activities or may

result in the need for increased medication or medical treatment,

especially for those individuals with asthma or other respiratory

diseases. As discussed above in this unit, although some of these

commenters felt that the third-highest concentration form would protect

public health while also providing increased stability, others

expressed concern that public health could be compromised by any form

that allowed for multiple exceedances of the standard. The advantages

of forms that allow for multiple exceedances, thus providing increased

stability as discussed in the proposal, and the views of the CASAC

panel members who expressed opinions, all of whom favored such forms,

were not given weight by commenters within this group who supported a

1-expected-exceedance form.

The Administrator has carefully reassessed the relative risks to

public health of specific forms within the range of the second- to

fifth-highest concentration forms or their exceedance-based

equivalents, taking into account the public comments summarized above,

and the advice from CASAC Panel members that the current form be

replaced by a form that allows multiple exceedances. In doing so, the

Administrator focused on the following considerations:

(1) The CASAC advised that concentration-based forms, within the

range considered up to the fifth-highest concentration form, are

appropriate for a health-based primary O3 standard, and that

selection from within this range is a policy judgment that cannot be

based

[[Page 38871]]

on science alone. This advice reflects CASAC's recognition that

O3 exhibits a continuum of effects, such that there is no

discernible threshold above which public health protection requires

that no exposures be allowed or below which all risks to public health

can be avoided. The CASAC also recognized that a concentration-based

form would increase the stability of the standard by providing some

insulation from the impacts of extreme meteorological events (Wolff,

1995b).

(2) Estimates of the differences in risk to public health, for

those effects that could be considered quantitatively, within a range

of alternative forms from the second- to fifth-highest concentrations

(for an 8-hour, 0.08 ppm standard) are relatively small compared to the

differences between alternative levels. In other words, the choice of

level is substantially more important to the degree of public health

protection afforded by the standard than the choice of form from within

this range of forms.

(3) Measures that distinguish between the alternatives within the

range of the second- to fifth-highest forms, based on air quality

analyses, reflect considerations related to how some individuals

understand the degree to which an air quality standard protects public

health. These considerations are a distinct aspect of risk

communication to individual citizens even though the days on which

exceedances occur are accounted for in EPA's quantitative assessments

of risks to public health.

(4) To assess the comparative effect of all forms within the range

of the second- to fifth-highest concentration forms, EPA considered air

quality comparisons for all such forms (Freas, 1996). These comparisons

(based on 1993 to 1995 data) show that 8-hour, 0.08 ppm second- and

third-highest concentration standards are very similar in that each

standard limits the percent of monitoring sites that would experience

peak days above the benchmark level of 0.09 ppm to 1 percent of such

sites, and the number of days on which the standards would likely be

exceeded in the worst of 3 years would be no more than 6 and 7,

respectively. While less restrictive than either of these standards, an

8-hour, 0.08 ppm fourth-highest concentration standard would be

significantly more restrictive than a fifth-highest standard. For

example, the 8-hour, 0.08 ppm fourth-highest concentration standard

would limit the percent of monitoring sites that would experience peak

days about the benchmark level of 0.09 ppm to 8 percent of such sites,

and the number of days on which the standards would likely be exceeded

in the worst of 3 years would be no more than nine. In comparison, the

fifth-highest concentration standard would limit the percent of

monitoring sites that would experience peak days about the benchmark

level of 0.09 ppm to 17 percent of such sites, and the number of days

on which the standards would likely be exceeded in the worst of 3 years

would be no more than 11.

(5) The extent to which the alternatives within the range of the

second- to fifth-highest concentration forms provide protection against

the more serious, but less certain effects that have been associated

with exposure to O3, including potential chronic effects,

cannot be quantitatively assessed at this time. Given that all such

forms would result in significant reductions in exposures to

O3 at and above 0.08 ppm (the level where suggestive

evidence of such effects is available), any form within this range

would provide some margin of safety against these effects.

Based on these considerations, the available health effects

evidence, the quantitative assessments contained in the Criteria

Document, Staff Paper, and supplemental analyses and supporting

documents, and the range of views and judgments expressed in the public

comments on the appropriate form, the Administrator has reconsidered

the form of the standard that is requisite to protect public health

with an adequate margin of safety. As an initial matter, the

Administrator has decided to adopt a concentration-based form which

allows for more than one exceedance. While the Adminstrator understands

the views of the many citizens who are concerned about a standard that

would allow for multiple days on which the level of the standard may be

exceeded, the Administrator concludes that such concerns are more

relevant for pollutants that exhibit a clear threshold of effects than

for pollutants such as O3 that exhibit a continuum of

effects. The Administrator believes that the public health risks

associated with such pollutants can be appropriately addressed through

a standard that allows for multiple exceedances to provide increased

stability, but that also significantly limits both the number of days

on which the level may be exceeded and the magnitude of such

exceedances. This approach recognizes that exposures associated with

such exceedances are already reflected in the exposure and risk

assessments that were an important consideration in selecting a 0.08

ppm level for the primary O3 standard, and that increased

stability in the standard is important to avoid disruption to ongoing

control programs, and thus to maintain ongoing public health

protection.

Having again concluded that a concentration-based O3

standard that allows for multiple exceedances is appropriate, the

Administrator considered the extent to which the form of an 8-hour

standard should be selected so as to provide a margin of safety against

possible, but uncertain chronic effects. The Administrator carefully

considered the views of the many commenters who emphasized the

uncertainties in the evidence, primarily from laboratory animal

studies, that was available in this review of the criteria and

standards to relate long-term exposures to ambient levels of

O3 to possible chronic effects in humans. These commenters,

as did CASAC, advised that further research into potential chronic

effects in humans should be continued, and the results considered in

the next review of the O3 standard. The Administrator is

persuaded that the difference between the margins of safety for these

potential chronic effects afforded by the alternatives within the range

of the second- to fifth-highest concentration forms is not well enough

understood at this time to use as the basis for choosing the most

restrictive forms (i.e., the second- or third-highest concentration

form). On the other hand, the Administrator also judges that the

relatively large percentage of sites that would experience

O3 peaks above a benchmark level of 0.09 ppm even when

attaining a fifth-highest concentration standard and the number of days

on which the level of a fifth-highest concentration standard may be

exceeded argue against choosing that form, which is the least

restrictive within the range considered.

For the reasons outlined above, and taking into account the range

of views in the public comments, the Administrator concludes that an

intermediate form, the fourth-highest concentration form, would serve

to appropriately balance these public health considerations in

conjunction with the 8-hour averaging time and 0.08 ppm level selected,

as discussed above in Units II.B.1. and II.B.2., that are of primary

importance in determining the degree of public health protection

afforded by the standard. In addition, the Administrator notes that

based on an analysis of air quality in counties that would attain an 8-

hour, 0.08 ppm fourth-highest concentration standard (based on 1993-

1995 data), over 99 percent of such counties would be expected to have

four or fewer days on which the level of the standard is exceeded in an

average year (Freas,

[[Page 38872]]

1997). This number of exceedances is clearly within the range of

multiple exceedances that CASAC judged to be appropriate for a health-

based primary O3 standard. Thus, in the Administrator's

judgment, based on the information currently available, an 8-hour, 0.08

ppm standard with a fourth-highest concentration form will protect

public health with an adequate margin of safety.

In the proposal, which maintained the current approach of using air

quality data from the monitor measuring the highest O3

concentrations in an area to determine whether the primary standard for

O3 is attained, the Administrator solicited comment on the

alternative of using some form of averaging across monitors. As

discussed in the proposal, EPA recognized that during the review of the

Staff Paper, a number of commenters suggested that averaging across

monitors might be appropriate to increase the degree to which

monitoring data used in determining attainment of the standard reflects

population exposure and aggregate population health risk. Further,

these commenters suggested that averaging data from multiple monitors

in an area would produce a more stable measure of air quality and would

take into account broader population exposure patterns across an area

than would the current approach of considering data from each monitor

independently.

The Administrator did not propose the use of spatial averaging

because of concerns outlined in the proposal including: The difficulty

in determining an appropriate level for a spatially averaged primary

standard given that the bulk of the human health effects evidence

supporting a decision on an appropriate O3 standard is based

on controlled human exposure studies that relate known O3

exposures directly to responses in individuals; and questions as to

whether adequate health protection would be provided to individuals

within the populations that live or work in communities that routinely

experience higher O3 concentrations within a broad

metropolitan area.

To address these two concerns, it would be necessary to define

criteria for geographic locations or communities (e.g., spatial

averaging zones) within which the use of spatially averaged

O3 data would be acceptable. Such criteria would be

important since O3 air quality concentrations can vary

significantly across most urban areas. The lowest concentrations

typically occur in the urban center and in locations near O3

precursor sources, mid-range concentrations in neighborhoods and

locations surrounding the urban center, and peak concentrations are

typically measured downwind along the outermost suburban regions of the

urban area. Also, the location of residences, schools, parks, and other

places where individuals might be exposed more frequently to ambient

O3 concentrations of concern would be an important

consideration. Unless the O3 concentration gradients within

each spatial averaging zone were relatively homogeneous, there may be

significant numbers of sensitive individuals exposed to high

O3 concentrations in areas where the spatial average

indicates that the overall air quality is acceptable.

In the proposal, EPA also noted the need to help State and local

governments devise different O3 monitoring networks by

revising relevant regulations and guidance, should spatial averaging be

adopted. This would likely involve defining general criteria for

monitoring network design, siting, and spatial averaging zones in

nationally implementable terms, with case-by-case evaluation of each

monitoring network. The EPA recognized that this activity would place

additional burdens on State and local air quality management districts.

In soliciting comment on whether it would be desirable to adopt

some form of spatial air quality averaging for O3, the

Administrator also solicited comment on specific alternative approaches

that could be used to address the issues of concern. In particular, the

Administrator was interested in analyses that inform questions about

monitoring network design, siting requirements, and approaches for

specification of spatial averaging zones; the distribution of public

health protection that would result from such alternative approaches;

and the extent to which the level of the standard would need to be

adjusted, if any, to provide public health protection consistent with

the level of protection contemplated in the proposal.

The EPA received many comments on the subject of using spatially

averaged data to determine when the primary standard for O3

is attained. Commenters from business and industry associations

frequently supported the use of spatially averaged data, as did many

local governments and a small number of States, principally because it

would provide a more stable air quality indicator and would better

represent population exposure and risk. Some of these commenters felt

that the use of spatial averaging would be consistent with the use of

risk assessment as a policy tool for standard setting. Many of these

commenters agreed that the heterogeneity of O3

concentrations across geographic areas would need to be addressed by

network design, with a few expressing the opinion that this would not

be an insurmountable problem given that there is continual movement of

monitors within existing networks. Some commenters suggested averaging

approaches that included the use of population weighting of monitored

data, and some supported the use of a public health information system

to allow individuals residing in ``hot spot'' areas to reduce their

exposures to O3 concentrations of concern.

In contrast, environmental associations, public health

professionals, most States, and many individuals voiced strong concerns

that the use of spatially averaged data would routinely allow

individuals who live or work in communities with consistently higher

O3 levels than those occurring across the broader urban area

to be exposed to concentrations of concern. Many of these commenters

raised the issue of environmental equity, expressing the view that

communities with consistently higher O3 concentrations

typically are composed predominantly of individuals of lower

socioeconomic status, or are composed of a predominantly minority

population. The EPA notes that this view is not consistent with the air

quality data discussed earlier in this unit, in that O3

concentrations are typically lower in urban centers than in locations

surrounding or downwind of urban centers. Some commenters also raised

concerns about the complexity and burdens associated with redesigning

existing monitoring networks.

Taking into account the comments received, the Administrator does

not find that the issues of concern, as outlined in the proposal and

above, have been adequately addressed in this review of the

O3 standard. In particular, while EPA strongly agrees with

the importance of public health advisories in addition to adequately

protective standards, relying on the use of public health advisories to

provide information for at-risk populations who may consistently be

exposed to localized O3 concentrations of concern is

considered by the Administrator to be an insufficient approach to

protecting public health with an adequate margin of safety. Further,

the suggested use of population weighting of monitored data may, in

many cases, be insufficiently sensitive to local O3

variations to ensure adequate protection of these populations from

localized O3 concentrations. Thus, the revised O3

standard will maintain the current

[[Page 38873]]

approach of using air quality data from the monitor measuring the

highest O3 concentrations in an area to determine whether

the standard is attained within an area.

The EPA has also considered spatial averaging in the context of the

decision to revise the PM NAAQS, in part, by adopting a form of an

annual standard for fine particles (i.e., PM2.5) that allows

for spatial averaging within appropriate criteria. It is important to

note that different considerations apply in these two cases. One

principal difference is the nature of the health effects evidence for

O3 and PM2.5. When considering averaging

approaches for O3, it should be recognized that much of the

human health effects evidence supporting the O3 standard is

based on controlled human exposure studies that relate individual

O3 exposures directly to responses in individuals, whereas

the health effects evidence supporting the PM2.5 standards

is from epidemiological studies relating community measures of

PM2.5 concentrations to population-wide responses. Thus,

information available for determining an appropriate level of a

standard in these two cases is predominantly individual-oriented in the

case of O3 and community-oriented in the case of

PM2.5. As a consequence, additional research and exposure

and risk assessments beyond those available in this review would be

necessary to provide a basis for further consideration of a spatially

averaged standard for O3. The EPA will continue to explore

this approach.

Another important difference between the O3 and PM

standards is that the suite of annual and 24-hour PM2.5

standards permits the use of the 24-hour PM2.5 standard,

which would not be spatially averaged, as a backstop to control

localized ``hot spots,'' whereas a single O3 standard does

not allow for such a dual approach. Also, EPA notes that the existence

of an established, extensive O3 monitoring network would

require substantial redesigning and relocation of monitors for the

purpose of spatial averaging, in contrast to the current absence of

such a network for PM2.5 which can be newly designed to

address community-oriented monitoring from the outset.

As discussed in the proposal, the Administrator recognizes that no

standard within the range of levels and forms considered in this

review, including the selected standard, is risk free, due to the

continuum of risk likely posed by exposures to ambient O3

potentially down to background levels. Accordingly, consistent with

CASAC advice, the Administrator solicited comment in the proposal on

elements of an enhanced public health advisory system. The

Administrator believes that the information that could be made

available through such a public health advisory system would be

particularly useful to extremely sensitive individuals in making

personal decisions about avoiding exposures with the potential to cause

transient adverse effects on days when 8-hour average O3

concentrations are predicted to be at or near the level of the

standard. Approaches to developing an enhanced system, and comments

received on such approaches, are discussed in Unit II.C. of this

preamble.

4. Final decision on the primary standard. After carefully

considering the information presented in the Criteria Document and the

Staff Paper, the advice and recommendations of CASAC, public comments

received on the proposal, and for the reasons discussed above, the

Administrator is replacing the existing 1-hour, 0.12 ppm primary

standard with a new 8-hour, 0.08 ppm primary standard. The new 8-hour

standard will become effective September 16, 1997.

The 8-hour, 0.08 ppm primary standard will be met at an ambient air

quality monitoring site when the 3-year average of the annual fourth-

highest daily maximum 8-hour average O3 concentration is

less than or equal to 0.08 ppm. Data handling conventions are specified

in a new Appendix I to 40 CFR part 50 as discussed in Unit VI below.

In the proposal, EPA proposed that the revocation of the existing

1-hour O3 standard be delayed for certain purposes until EPA

had approved State Implementation Plans to implement the new 8-hour

O3 standard. EPA had proposed continuing the applicability

of the 1-hour standard in this way in order to facilitate continuity in

public health protection during the transition to a new standard. (See

Memorandum from John S. Seitz to Mary D. Nichols, November 20, 1996;

Docket No. A-95-58, item II-B-3.) Also, at the time of the proposal of

the new O3 standard, EPA had proposed an interpretation of

the Act in the proposed Interim Implementation Policy (61 FR 65764,

December 13, 1996) under which the provisions of subpart 2 of part D of

Title I of the Act would not apply to existing O3

nonattainment areas once a new O3 standard becomes

effective.

In light of comments received regarding the interpretation proposed

in the Interim Implementation Policy, EPA has reconsidered that

interpretation and now believes that the Act should be interpreted such

that the provisions of subpart 2 continue to apply to O3

nonattainment areas for purposes of achieving attainment of the current

1-hour standard. As a consequence, the provisions of subpart 2, which

govern implementation of the 1-hour O3 standard in

O3 nonattainment areas, will continue to apply as a matter

of law for so long as an area is not attaining the 1-hour standard.

Once an area attains that standard, however, the purpose of the

provisions of subpart 2 will have been achieved and those provisions

will no longer apply. However, the provisions of subpart 1 of part D of

Title I of the Act would apply to the implementation of the new 8-hour

O3 standards.

To facilitate the implementation of those provisions and to ensure

a smooth transition to the implementation of the new 8-hour standard,

the 1-hour standard should remain applicable to areas that are not

attaining the 1-hour standard. Therefore, the 1-hour standard will

remain applicable to an area until EPA determines that it has attained

the 1-hour standard, at which point the 1-hour standard will no longer

apply to that area.

C. Communication of Public Health Information

Information on the public health implications of ambient

concentrations of criteria pollutants is currently made available

primarily through two EPA programs. The first program is designed to

prevent ambient pollutant concentrations from reaching the significant

harm level (i.e., an exposure level that constitutes an imminent and

substantial endangerment to public health). The second program is the

Pollutant Standards Index (PSI),24 which is a health

advisory system. The proposal focused on the potentially expanded use

of the PSI in regard to allowing sensitive individuals to reduce their

risk of exposure. Currently, EPA and local officials use the PSI as a

public information tool to advise the public about the general health

effects associated with different pollution levels and to describe

whatever precautionary steps may need to be taken if air pollution

levels rise into the unhealthful range. By notifying the public when a

PSI value exceeds 100 (which corresponds to the NAAQS for each criteria

pollutant)25, citizens are given the opportunity to take

appropriate steps to avoid exposures of concern. This use of the PSI

could be expanded to provide more specific health information for

O3 concentrations

[[Page 38874]]

close to the level of the primary standard. Given the continuum of

risks associated with exposure to O3, this information,

while perhaps of interest to all citizens, would be particularly useful

to those individuals who are extremely sensitive to relatively low

O3 concentrations. As an example, the proposal mentioned the

possibility of expanding the PSI to include two new descriptive

categories in the Index, one including concentrations within a range

somewhat below the level of the new primary standard (with a possible

descriptor of ``moderately good''), the other including concentrations

within a range somewhat above the level of the standard (with a

possible descriptor of ``moderately unhealthful''). Such an approach

could better reflect the increased understanding of health effects

associated with O3 exposure developed during this review,

and would be consistent with the recommendation of a number of CASAC

panel members ``that an expanded air pollution warning system be

initiated so that sensitive individuals can take appropriate 'exposure

avoidance' behavior'' (Wolff, 1995b).

---------------------------------------------------------------------------

24 For a discussion of these programs, see the proposal.

25 Currently, a PSI value of 100 for O3 corresponds

to an ambient concentration of 0.12 ppm, averaged over 1 hour.

---------------------------------------------------------------------------

The proposal also discussed the use of forecasting in combination

with this expanded use of the PSI. For a health advisory system to be

effective, citizens need to be notified as early as possible to be able

to avoid exposures of concern. The notice indicated that if the current

1-hour primary NAAQS for O3 is replaced with an 8-hour

standard, there would clearly be increased value in using forecasted

O3 concentrations in providing cautionary statements to the

public. Currently, when a health advisory indicates that the 1-hour

O3 PSI value of 100 has been exceeded, citizens generally

have time to avoid exposures of concern because O3 levels

tend to remain elevated for several hours during the day. With the new

8-hour standard, however, this would likely not be the case, since by

the time a PSI value is reported, the potential for prolonged exposures

of concern would likely have passed for that day. Forecasting 8-hour

maximum O3 concentrations would facilitate the risk-

reduction function of the PSI by giving citizens more time to limit or

avoid exposures of concern.

The EPA did not formally propose revisions to the PSI in the

proposal. Instead, the Administrator requested comment, and indicated

that the Agency might propose revisions to the PSI in conjunction with

future proposals associated with the implementation of a revised NAAQS.

The EPA received a large number of comments from a wide variety of

commenters on the usefulness of both an expanded health advisory system

and the forecasting of 8-hour ambient O3 concentrations.

Commenters representing State and local agencies, business and industry

associations, as well as environmental associations overwhelmingly

endorsed the use of an expanded public health advisory system and many

noted the importance of forecasting 8-hour O3 concentrations

in conjunction with the PSI, while recognizing a number of issues that

would need to be addressed.

Comments from environmental associations endorsed increasing the

specificity of warnings with regard to the health effects that could

occur as a result of exposure, and noted that citizens are capable of

dealing with complex information. These commenters also took exception

to describing O3 levels around the level of the standard

that have been shown to result in decreased lung function and increased

respiratory symptoms, as ``moderately good,'' stating that this

descriptor is misleading and might not be heeded by people who could,

if they fully understood the nature of the health risk, take action to

minimize their exposures. Other commenters felt that the descriptors

``moderately good'' and ``moderately unhealthful'' were unnecessarily

confusing.

Industry commenters were uniformly supportive of enhancing the risk

reduction function of the PSI by issuing health advisories with

specific health information at and above the level of the standard.

Several industry commenters also recommended that the function of the

PSI be combined with the function of an O3 action system,

which would recommend voluntary actions to reduce ambient O3

concentrations when the level of the standard is forecasted to be

exceeded. This would result in a system that not only could provide

accurate health effects information specific to the members of the

population likely to experience effects, but also could help prevent

exposures to levels of O3 at or above the level of the

standard.

Commenters from State and local air pollution control authorities

strongly endorsed expanding the use of the PSI and the utilization of

forecasted 8-hour O3 concentrations. These commenters

encouraged EPA to develop any such approaches to revise the PSI in

consultation with State and local agencies, specifically in the areas

of sharing real-time O3 monitoring data among neighboring

States, risk communication with the public, and coordination of a

national program. States also expressed the need for flexibility in the

implementation of such approaches and for guidance from EPA on

technical aspects such as forecasting.

The EPA will take all of these comments into consideration when

developing a proposal to revise the PSI (40 CFR 58.50) for

O3. The EPA plans to propose these revisions, as well as

revisions to the significant harm level program (40 CFR 51.16), at a

later date.

III. Rationale for the Secondary O3 Standard

A. Introduction

1. Overview. This notice presents the Administrator's final

decision regarding the need to revise the current secondary

O3 standard, and more specifically, to replace the existing

1-hour, 0.12 ppm O3 secondary NAAQS with a secondary

standard equal in form, level, and averaging time to the new 8-hour,

0.08 ppm primary standard. This decision is based on a thorough review

of the scientific information on vegetation effects associated with

exposure to ambient levels of O3 as assessed in the Criteria

Document. This decision also takes into account:

(1) Staff Paper assessments of the most policy-relevant information

in the Criteria Document and staff analyses of air quality, vegetation

exposure and risk, and economic values presented in the Staff Paper,

upon which staff recommendations for a new O3 secondary

standard were based.

(2) Consideration of the degree of protection to vegetation

potentially afforded by the new 8-hour, 0.08 ppm primary standard

compared to alternative secondary standards.

(3) CASAC advice and recommendations as reflected in discussion of

drafts of the Criteria Document and Staff Paper at public meetings, in

separate written comments, and in CASAC's letter to the Administrator

(Wolff, 1996).

(4) Public comments received during development of these documents

either in conjunction with CASAC meetings or separately.

(5) Extensive public comments received on the proposed decision

regarding the secondary O3 standard.

After taking this information into account and for the reasons

discussed in this Unit, the Administrator concludes that revisions to

the current secondary standard are appropriate at this time to provide

increased protection against adverse effects to public welfare, and

that it is appropriate to set the new secondary standard identical to

the new primary standard.

This review has focused on O3 effects on vegetation

since these public welfare effects are of most concern at O3

[[Page 38875]]

concentrations typically occurring in the United States. By affecting

commercial crops and natural vegetation, O3 may also

indirectly affect natural ecosystem components such as soils, water,

animals, and wildlife. Based on the scientific literature assessed in

the Criteria Document, the Administrator believes it is reasonable to

conclude that a secondary standard that protects the public welfare

categories of commercial crops and natural vegetation from known or

anticipated adverse effects would also afford increased protection to

these other related public welfare categories. With regard to

O3 effects on manmade materials and deterioration of

property, the scientific literature assessed in the Criteria Document

contains little new information since the last review. Accordingly, EPA

again concludes for the reasons set forth in 1993 (58 FR 13008, March

9, 1993) that O3-related effects on materials do not provide

a basis for selecting an averaging time and level for a secondary

standard. In addition, since the effects of O3 on personal

comfort and well-being (e.g., nose and throat irritation, chest

discomfort, and cough) have been accounted for in the review of the

primary standard, these effects are not considered in this review of

the secondary standard.

The vegetation effects information, exposure and risk assessment,

and economic analyses presented in the Staff Paper and proposal are

briefly outlined in the remainder of Unit III.A. of this preamble. The

key issues raised in public comments with regard to: Whether revisions

to the current secondary standard are requisite to protect public

welfare from adverse effects and the specific elements of a revised

secondary standard are discussed in Unit III.B. along with the

Administrator's rationale for concluding that it is appropriate to

revise the current secondary standard to be identical to the new

primary standard.

2. Vegetation effects information. Exposures to O3 have

been associated quantitatively and qualitatively with a wide range of

vegetation effects such as visible foliar injury, growth reductions and

yield loss in annual crops, growth reductions in tree seedlings and

mature trees, and effects that can have impacts at the forest stand and

ecosystem level. Summarized below are key findings for each of the

above effects categories that are discussed in more detail in the

Criteria Document, Staff Paper, and proposal.

Visible foliar injury can represent a direct loss of the intended

use of the plant, ranging from reduced yield and/or marketability for

some agricultural species to impairment of the aesthetic value of urban

ornamental species. On a larger scale, foliar injury is occurring on

native vegetation in national parks, forests, and wilderness areas, and

may be degrading the aesthetic quality of the natural landscape, a

resource important to public welfare.

Ozone can interfere with carbon gain (photosynthesis) and

allocation of carbon with or without the presence of visible foliar

injury. As a result of decreased carbohydrate availability, remaining

carbohydrates may be allocated to sites of injured tissue or employed

in other repair or compensatory processes, thus reducing the

carbohydrates available for plant growth and/or yield. Growth and yield

effects of O3 have been well documented for numerous

species, including commodity crops, fruits and vegetables, and

seedlings of both coniferous and deciduous tree species.

Due to a number of differences between seedlings and mature trees

in their responses to O3 exposures, data from tree seedling

studies cannot, at this time, be extrapolated to quantify responses to

O3 in mature trees. However, long-term observational studies

of mature trees have shown growth reductions in the presence of

elevated O3 concentrations. Where these growth reductions

are not attributed to O3 alone, due to the presence of many

other environmental variables, it has been reported that O3

is a significant contributor that potentially exacerbates the effects

of other environmental stresses (e.g., pests). In addition, studies

show that sensitivity to O3 with respect to visible foliar

injury and growth and yield effects can vary significantly within and

between species for both crops and trees.

Growth reductions can indicate that plant vigor is being

compromised such that the plant can no longer compete effectively for

essential nutrients, water, light, and space. When many O3-

sensitive individuals make up a population, the whole population may be

affected. Changes occurring within sensitive populations, or stands, if

they are severe enough, ultimately can change community and ecosystem

structure. Structural changes that alter the ecosystem functions of

energy flow and nutrient cycling can alter ecosystem succession.

In the CASAC closure letter, all CASAC panel members agreed that

``damage is occurring to vegetation and natural resources at

concentrations below the present 1-hour national ambient air quality

standard (NAAQS) of 0.12 ppm,'' and the vegetation experts agreed that

``plants appear to be more sensitive to O3 than humans''

(Wolff, 1996). Further, the CASAC panel agreed ``that a secondary

NAAQS, more stringent than the present primary standard, was necessary

to protect vegetation from O3'' (Wolff, 1996). The

Administrator concurred in the proposal with the unanimous view of

CASAC that the current standard of 0.12 ppm, 1-hour average, does not

provide adequate protection to vegetation from the adverse effects of

O3, based on the following specific observations that were

taken from key studies and other biological effects information

reported in the O3 Criteria Document and Staff Paper:

(1) O3 concentrations 0.10 ppm can be

phytotoxic to a large number of plant species, and can produce acute

foliar injury responses and reduced crop yield and biomass production.

(2) O3 concentrations within the range of 0.05 to 0.10

ppm have the potential over a longer duration of creating chronic

stress on vegetation that can result in reduced plant growth and yield,

shifts in competitive advantages in mixed populations, decreased vigor

leading to diminished resistance to pest and pathogens, and injury from

other environmental stresses. Some sensitive species can experience

foliar injury and growth and yield effects even when concentrations

never exceed 0.08 ppm.

The Administrator further concluded that the available scientific

information supports the conclusion that a cumulative seasonal exposure

index, such as the proposed SUM06 index,26 is more

biologically relevant than a single event or mean index.

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26 The SUM06 exposure index cumulates over a given time period

and diurnal window all hourly O3 concentrations greater

than or equal to 0.06 ppm.

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3. Vegetation exposure and risk analyses. In reaching a judgment in

the proposal as to a standard requisite to protect crops and vegetation

against the adverse effects of O3, the Administrator took

into account several additional considerations including the extent of

exposure of O3-sensitive species, potential risks of adverse

effects to such species, and monetized and nonmonetized categories of

increased vegetation protection associated with reductions in

O3 exposures. In so doing, the Administrator recognized that

markedly improved air quality, and thus significant reductions in

O3 exposures would result from attainment of the alternative

0.08 ppm, 8-hour primary standards within the range of 1- and 5-

expected exceedance forms. Thus, as a matter of policy, the Agency

estimated the increased protection from O3-related

[[Page 38876]]

effects on vegetation associated with attainment of alternative 8-hour,

0.08 ppm primary standards, and then considered the incremental

protection associated with attainment of a seasonal secondary standard.

The ability of EPA to characterize O3 air quality in

rural and remote sites was limited by the available rural O3

monitoring network. Therefore, EPA conducted national analyses using

geographic information systems (GIS) and data from existing air quality

monitoring sites to estimate seasonal O3 air quality for the

year 1990, in terms of the 3-month, 12-hour, SUM06 exposure index. The

year 1990 was selected because it was a fairly typical year in terms of

O3 air quality. The estimated 1990 air quality was then used

as a baseline from which to roll back O3 concentrations to

project O3 air quality that would be expected to occur when

alternative standards were just attained.

The regulatory scenarios examined included just attaining the

existing 1-hour secondary standard, alternative 8-hour primary

standards in the range of 0.07 to 0.09 ppm, including standards set at

0.08 ppm, with 1- and 5-expected-exceedance forms, and a range of

seasonal standards using the SUM06 index, based on a single year of

data. Estimates of air quality associated with alternative 8-hour

primary standards with 1- and 5-expected-exceedance forms were used to

roughly bound air quality estimates for 8-hour standards with

concentration-based forms ranging from the annual second- to the fifth-

highest concentration-based forms, and including the proposed third-

highest concentration-based form.

By comparing these projected air quality scenarios for alternative

standards with maps showing the growing regions for O3-

sensitive crops and tree seedling species, estimates of exposures of

concern and risks of adverse effects for various species were developed

for alternative standards. Taking into account the body of information

concerning O3 effects on vegetation, as presented in the

Criteria Document and Staff Paper and summarized in the proposal, EPA

considered both quantifiable risks (when exposure-response functions

were available) as well as those risks that could only be qualitatively

characterized.

The Administrator concluded in the proposal that attaining a 8-

hour, 0.08 ppm primary standard within the range of forms under

consideration would provide substantially improved protection of

vegetation from seasonal O3 exposures of concern. The

Administrator recognized, however, that some areas may continue to have

elevated seasonal exposures, including forested park lands and other

natural areas and Class I areas that are federally mandated to preserve

certain air quality related values.

In its discussions of uncertainties, described in the proposal, the

CASAC Panel members expressed concerns about the use of the GIS

methodology to project national O3 air quality and exposures

of O3-sensitive species. As is the case with other analytic

methods (e.g., Krieging, inverse distance weighting), the GIS

methodology contains numerous assumptions and uncertainties, and

incorporates various databases each with their own set of

uncertainties. As noted in the Staff Paper and proposal, the EPA and

CASAC recognized that the uncertainties in exposure and risk estimates

derived from the GIS methodology are large and unquantifiable, but that

the method provides useful information that is appropriate to consider

in comparing the relative protection afforded by alternative standards.

Further, EPA noted in the Staff Paper and proposal that the GIS-

generated air quality estimates compare reasonably well with the

limited available O3 monitoring data. In taking the results

from these analyses into account, the Administrator recognized these

inherent limitations and primarily considered the comparative results

in assessing the degree of protection afforded by alternative

standards.

While the analyses discussed above indicated that an 8-hour, 0.08

ppm primary standard within the range of alternatives considered, would

provide increased protection for commercial and natural vegetation, it

remained uncertain as to the extent to which air quality improvements

designed to reduce 8-hour O3 concentrations would reduce

O3 exposures measured by a seasonal SUM06 index. To further

explore this question, EPA also examined the design values for

alternative 8-hour, 0.08 ppm standards, within the range of 1- and 5-

expected exceedances, averaged over 3 years, and a 3-month, 12-hour

SUM06 standard for 581 counties (those having sufficient monitoring

data for the period 1991 - 1993). As discussed in the Staff Paper and

proposal, this analysis revealed that almost all areas that are within

or above a SUM06 range of 25-38 ppm-hours would also have an 8-hour

daily maximum design value of greater than 0.08 ppm. Thus, in those

areas in which air quality monitoring is being conducted, areas that

would likely be of most concern for effects on vegetation, as measured

by the SUM06 exposure index, would also be addressed by an 8-hour

primary standard set at a 0.08 ppm level.

4. Monetized estimates of vegetation protection. As discussed in

section VII.F. of the Staff Paper and in the proposal, EPA developed

monetized estimates of increased protection associated with several

alternative standards for economically important commodity crops

nation-wide27 and for fruit and vegetable crops in

California.28 These analyses were based on the GIS-generated

projections of O3 air quality for various alternative

standards. Monetized estimates of increased protection could not be

developed for other important categories of vegetation, such as urban

ornamentals, Class I areas, and commercial and other forests because of

a lack of available concentration-response functions and appropriate

economic valuation models. The available data suggested, however, that

reductions in ambient O3 concentrations resulting from

attainment of alternative standards would confer increased protection

for these categories as well by reducing biomass loss, protecting

functional, aesthetic, and existing values, and by preserving

biodiversity and native habitats.

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