# National Ambient Air Quality Standards for Ozone

> Briefs, arguments, decisions, and more.

URL: https://www.frixlaw.com/law-library/documents/fr%3A97-18580

## Record

- **Collection:** Federal Register
- **Document type:** Rule
- **Published:** July 18, 1997
- **Citation:** 62 FR 38856

## Text

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).
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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).
---------------------------------------------------------------------------

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).
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

(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:
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

(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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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

18 The EPA anticipates that additional people would be protected
through regional measures adopted for purposes of an 8-hour, 0.08
ppm standard.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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.
---------------------------------------------------------------------------

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

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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.
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Source: Frix Law Library, https://www.frixlaw.com/law-library/documents/fr%3A97-18580. Public record. Not legal advice.